Critical Review Processing, Signaling, and Physiological Function of Chemerin
Faculty of Biosciences, Pharmacy and Psychology, Biochemistry, Universita€t Leipzig, Leipzig, Germany
Institute
Andreas Mattern* Tristan Zellmann* Annette G. Beck-Sickinger
of
Abstract Chemerin is an immunomodulating factor secreted predominantly by adipose tissue and skin. Processed by a variety of proteases linked to inflammation, it activates the G-protein coupled receptor chemokine-like receptor 1 (CMKLR1) and induces chemotaxis in natural killer cells, macrophages, and immature dendritic cells. Recent developments revealed the role of the nonsignaling chemerin receptor C-C chemokine receptor-like 2
(CCRL2) in inflammation. Besides further research establishing its link to inflammatory skin conditions such as psoriasis, functions in healthy skin have also been reported. Here, the current understanding of chemerin processing, signaling and physiological function has been summarized, focusing on the regulation of its activity, its different receptors and its controversially discussed C 2014 IUBMB Life, 66(1):19–26, 2014 role in diseases. V
Keywords: chemerin; CMKLR1; inflammation; skin; psoriasis; obesity
Introduction Studying the links between obesity and associated diseases has identified adipose tissue as an active endocrine organ (1). Endocrine compounds secreted by adipocytes include proteins like leptin, a protein implied in regulating food intake and insulin sensitivity (2), or adiponectin, which regulates gluconeogenesis and lipid metabolism (3). In addition to molecules involved in energy homeostasis, adipocytes also secrete cytokines that play a role in cell-cell-signaling as well as in cell differentiation (1). Adipocytokines such as tumor necrosis factor alpha (TNFa; 4) or interleukin-6 (IL-6; 5) have been suggested as links between obesity, type 2 diabetes and chronic inflammatory states. Chemerin (6) was first termed tazarotene-induced gene 2 protein (TIG2), reflecting the discovery of its mRNA in skin cell raft cultures after tazarotene application (7). Chemerin is
C 2014 International Union of Biochemistry and Molecular Biology V
Volume 66, Number 1, January 2014, Pages 19–26 *Address correspondence to: Prof. Dr. Annette G. Beck-Sickinger, Uni€ r Biochemie, Bru € derstraße 34, D-04103 Leipzig, versita€t Leipzig, Institut fu Germany. Tel.: 1493419736901; Fax: 1493419736909. E-mail: [email protected] *Both authors contributed equally to this work. Received 27 October 2013; Accepted 22 December 2013 DOI 10.1002/iub.1242 Published online in Wiley Online Library (wileyonlinelibrary.com)
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expressed as preprochemerin that consists of 163 amino acids. Several isoforms of chemerin have been identified that are dependent on the processing by various serine and cysteine proteases. Recent data demonstrated that chemerin and its receptors CMKLR1 (8), G protein-coupled receptor 1 (GPR1) (9) and C-C chemokine receptor-like 2 (CCRL2) (10) are involved in adipogenesis (11), osteoclastogenesis (12), angiogenesis (13), and inflammatory processes in skin (14) and adipose tissue (15).
Postsecretory Processing of Chemerin and Functional Consequences After truncation of the 20 amino acid N-terminal signal peptide, chemerin is secreted as 143 residue prochemerin (8). In different tissues, various isoforms of chemerin have been detected (Fig. 1). Of these, chemerinS157 (8) and chemerinF156 (16) demonstrate the highest affinity to CMKLR1, while other isoforms such as prochemerin (8), chemerinK158 (17), or chemerinF154 (18), exhibit a much lower affinity. The different chemerin isoforms are suggested to regulate a biochemical cascade by competition binding to the corresponding receptors. By comparing different chemerin isoforms Yamaguchi et al. found that chemerinA155 competed the binding of chemerinS157 as a weak antagonist (19). Although this only occurred when chemerinA155 was added in a large excess, it might indicate a complex regulatory interaction of all chemerin variants.
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Fig 1
A: Processing of chemerin with different proteases related to inflammation. B: Amino acid sequence of chemerin. The signal peptide (underlined) is cleaved prior to secretion. Cleavage of the C-terminus (bold) results in active chemerinS157 as well as other isoforms. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Using specific antibodies for the prochemerin, chemerinK , and chemerinS157, Zhao et al. have examined the amount of these forms in different body fluids (20). While prochemerin was the dominant isoform in plasma from healthy subjects constituting 80% of the total chemerin, chemerinS157 was almost not detectable. The situation was opposite in synovial fluid from arthritis patients, where total chemerin levels were 2-fold increased and prochemerin only made up about 25%. Though chemerinS157 was only present in small concentrations, the high level of chemerinK158 clearly demonstrates the physiological relevance of chemerin processing in vivo. So far, eight proteases have been shown to C-terminally process prochemerin or chemerin in vitro including cathepsin G, plasmin, and elastase (21). As chemerinS157 and chemer158
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inF156 show the highest affinity to CMKLR1, simple cleavage by cathepsin G or elastase may be important for in vivo activation of chemerin, although sequential processing with different proteases like elastase and carboxypeptidase has also been suggested (17, 21; Fig. 1). Testing peptides of different length derived from the C-terminus, Wittamer et al. reported chemerin149–157 (YFPGQFAFS) as the most active fragment (22). This peptide was shown to reach nearly full length properties with respect to both binding affinity and receptor activation. Shorter fragments did not show any detectable binding, longer ones had progressively lower activity. An alanine scan of the nonapeptide chemerin149–157 revealed the residues P151, Q153, and S157 to have only a low impact on binding affinity, while mutating
Processing, Signaling, and Physiological Function of Chemerin
Fig 2
Superposition of homology models of prochemerin (dark green) and chemerinF156 (light yellow) as described recently by Schultz et al. (14) with a magnification of the C-terminus. The structural change of the C-terminus accompanying processing to chemerinF156 is suggested to enable receptor binding. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
the positions G152, F154, and F156 resulted in a peptide with no detectable affinity. Schultz et al. postulated that the structural function of Cterminal processing of chemerin lies in removing the positively charged residues K158 and R162, changing the C-terminal structure as to increase the affinity to CMKLR1. Based on homology modeling, these residues are supposed to form a salt bridge with a glutamic acid cluster consisting of E126, E128, E129, and E132. This is supported by the prochemerin mutants K158A and R162A, which exhibit higher potency in CMKLR1 signal transduction assays. A mutant deficient of the glutamic acid cluster achieved a potency almost on par with chemerinS157 and chemerinF156, demonstrating that the actual length of the C-terminus does not impede CMKLR1 binding (Fig. 2).
Chemerin and its Receptors Chemerin has been reported to bind to three G-protein coupled receptors (GPCR) named CMKLR1, GPR1, and CCRL2. CMKLR1 was first reported in 1996 as orphan GPCR (23; Table 1). As receptors with closer similarity include the chemoattractant receptors complement component 3a receptor 1, complement component 5a receptor 1, and formyl Met-Leu-Phe receptors (fMLPR), a similar role was postulated for CMKLR1 (24). Chemerin was shown to specifically bind and activate CMKLR1, which leads to Ca21-mobilization and chemotaxis in dendritic cells (DC) (8, 16). Furthermore, CMKLR1 shows a specific expression profile in cells of the adaptive immune system with high levels of mRNA found in macrophages (24), myeloid, plasmacytoid, and immature DC (8, 25). In the case of myeloid and plasmacytoid DC, chemerin expression is reduced during maturation. Langerhans cells do not express CMKLR1. In lymphocyte cells, CMKLR1 is
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found in natural killer cells but not in B- or T-cells (15). Platelet cells (26) and adipocytes also express CMKLR1 (11). Heteromerization of GPCRs is known to affect signaling pathways, ligand binding affinity, as well as internalization behavior (27). De Poorter et al. (28) have demonstrated CMKLR1 heteromerization with C-X-C chemokine receptor type 4 and CC chemokine receptor type 7 (CCR7) in stably transfected Chinese hamster ovary (CHO) cells with bioluminescence resonance energy transfer-assays. Coexpression of CMKLR1 with either CXCR4 or CCR7 led to heteromerization and cross-competition of the latter’s native ligands C-X-C motif chemokine 12 (CXCL12) and C-C motif chemokine 19 (CCL19), increasing their respective IC50 values. Cross-competition of chemerinS157 binding to CMKLR1 had a comparably lower magnitude. Interestingly, there was no cross-competition between the bicyclamic AMD3100, a CXCR4 specific antagonist, and chemerin (28). Previous work showed that heteromerization of CXCR4 and C-C chemokine receptor type 2 (CCR2) as well as C-C chemokine receptor type 5 (CCR5) led to a competition of their native ligands CXCL12 and CCL19 with AMD3100 (29). Missing competition in case of CMKLR1 indicates that the interaction between CMKLR1 and CXCR4 is only indirect and possibly related to signaling events or includes a different binding site. Investigating the effect of heteromerization on receptor internalization with fluorescence-activated cell sorting, the number of cell surface CMKLR1 after stimulation with chemerinS157 was found to be decreased while those of CXCR4 and CCR7 did not (28). In the same way, stimulation with either C-XC motif chemokine 2 or CCL19 led to internalization of their respective receptors, but not to the cointernalization of CMKLR1. Cross-inhibition was also investigated by comparing mouse bone marrow DC (BMDC), which naturally express CXCR4 and CMKLR1, with BMDC prepared from CMKLR1knockout mice (28). In experiments measuring specific CXCL12 binding, coincubation with chemerin lowered the specific binding of CXCL12 (28). This effect was absent in knockout mouse derived BMDCs. As these effects could also be caused by downstream signaling effects, the authors summarize that the existence of heterodimers of either CXCR4 or CCR7 to CMKLR1 cannot be sufficiently proven under physiological conditions (28). A second receptor shown to bind chemerin is GPR1, which is closely related to CMKLR1 (9, 30). GPR1 was initially reported presumably not to be activated by chemerinS157 in Ca21 mobilization bioassays (8). The interaction was demonstrated using the TangoTM GPCR assay (Life Technologies), which relies on arrestin recruitment following ligand binding instead of the release of second messengers. In this assay, an EC50 value of 0.24 nM was determined for GPR1 compared to 3 nM for CMKLR1 (Table 1). This higher affinity also extended to the chemerin nonapeptide 149YFPGQFAFS157 with 1 nM at GPR1 and 24 nM at CMKLR1. In Ca21-mobilization assays, GPR1 showed only a third of the Ca21-flux in comparison to CMKLR1. Radioligand saturation binding assays showed a KD value of 5.3 nM for GPR1 and 4.9 nM for CMKLR1 (9; Table 1). The very low Ca21-mobilization detectable on chemerin binding is most
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Summary of the three known chemerin receptors
TABLE 1
Related receptors
Associated tissues
KD (nM)
EC50 (nM), EC50 (nM) apoaequorin TangoTM assay GPCR assay
Signaling/ internalization
Function
CMKLR1 C3aR, c5aR, Adipose fMLPR (30) tissue (28), leukocytes (8, 25, 27)
4.9 (9)
4.5 (7)
3 (9)
Strong Ca21, internalization (8)
Chemotaxis (8), energy metabolism (15), cell differentiation (11–13)
GPR1
C3aR, c5aR, CNS-related fMLPR (30) (32–34)
5.3 (9)
n.d.
0.24 (9)
Weak Ca21, internalization (9)
Decoy receptor (9)
CCRL2
CCR1, CCR2, CCR3, CCR5 (10)
n.d.
n.d.
a
1.6a (10) leukocytes, mast cells (37), EC (36)
No signaling, no Natural killer cell internalization (10) recruitment (36)
MurineCCRL2.
probably caused by a mutation of the DRY receptor motif to DHY. Reviewing DRY mutants of more than 20 receptors, Rovati et al. concluded that nonconservative arginine mutation led to decreased agonist-induced activity while not affecting arrestindependant internalization (31). In contrast to CMKLR1, GPR1 is not expressed in monocytes, macrophages, or peripheral blood lymphocytes, but instead in cells related to the central nervous system. The glioblastoma cell line U87 (32), brain-derived fibroblast-like cell lines such as BT3 and BT-20/N (33) and hippocampus tissue (34) have been described to express GPR1. While the biological role of GPR1 is poorly understood at this point, the markedly different expression pattern suggests a different role compared with CMKLR1. The third receptor reported to bind chemerin is CCLR2 (10), also a GPCR belonging to the chemokine receptor family, sharing 40% sequence identity with CCR1, CCR2, CCR3, and CCR5 (35). It is not directly related to CMKLR1, sharing only 20% sequence identity. CCLR2 mRNA as well as protein level expression was found in neutrophils, DC, T cells, and macrophages (36). In contrast to CMKLR1 and GPR1, neither Ca21-mobilization nor internalization could be detected after chemerin incubation (37). This apparent lack of signaling is possibly caused by some deviations within its sequence, most obvious in the DRYLAIV motif, which is conserved in chemokine receptors and important for G-protein binding (38). In CCRL2, this motif is mutated to QRYLVFL. The same motif is changed in the nonsignaling chemokine receptors duffy antigen receptor for chemokines and CXCR7, which are thought to act as ligand scavengers, locally regulating chemokine concentrations (39). Concerning ligand-binding affinity, a C-terminal His8-tag at chemerin did not impede chemerin binding. CCRL2-bound chemerin was still able to be bound by an anti-His antibody (10). Furthermore, mCCRL2-transfected cells loaded with chem-
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erin were able to induce Ca21-mobilization in CMKLR1transfected cells, suggesting the possibility that CCRL2 serves to increase local chemerin concentrations and present it to CMKLR1 expressed on neighboring cells in vivo (10). Finally, CCRL2 was shown to bind CCL19, a chemokine also bound by C-C chemokine receptor type 8. Interestingly, radioligand binding assays could not show competition between these two ligands, possibly owing to different binding sites (10). Concerning intracellular signaling of chemerin, only CMKLR1 has been characterized to some extent. In transiently transfected CHO cells, chemerin has been demonstrated to lead to Ca21-mobilization, inhibition of cAMP accumulation, phosphorylation of p42 and p44 mitogen-activated protein kinase (MAPK), all being dependant on Gi signaling (8). In human endothelial cells (EC), chemerin induces activation of p38 MAPK, extracellular signal-regulated kinases and phosphoinositid-3-kinase/protein kinase B pathways in a dosedependent manner (13). Besides p38 MAPK and ERK-1/2, the nuclear factor “kappa-light-chain-enhancer” (NF-jB) pathway is also activated by chemerin administration in skeletal muscle cells (40).
Biological Role of Chemerin Obesity Chemerin was first reported to belong to the adipokine family when Goralski et al. (11) could demonstrate expression of both chemerin and CMKLR1 in white adipose tissue as well as chemerin secretion by adipocytes (11). Expression and secretion depend on maturation of these cells. CMKLR1 or chemerin knockdown with small hairpin RNA (shRNA) impaired differentiation of 3T3-L1 preadipocytes (11). Serum chemerin levels
Processing, Signaling, and Physiological Function of Chemerin
Fig 3
Chemerin is involved in a variety of functions in inflammation, skin, obesity, and cell differentiation. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
have been correlated to multiple obesity-related parameters such as body mass index (BMI; 41), blood pressure, serum lipid, insulin, and cholesterol level (42). Weight-loss owing to exercise, bariatric surgery, or reduction of caloric intake reduces serum chemerin levels and might correlate with improved insulin resistance (43). Chemerin regulates insulin secretion of beta cells in mice while chemerin knockdown mice exhibit glucose intolerance (44). In CMKLR1 knockdown mice, Ernst et al. could show a reduction in caloric intake, body weight, percentage of body fat and glucose tolerance compared to wild type mice regardless of diet (45). As other investigators could not show any correlation between chemerin and insulin resistance (46), the actual role of chemerin as a mediator of obesity and type 2 diabetes remains to be clarified. Chemerin seems to play a major role in the placenta as shown by Garces et al. who studied the expression pattern of chemerin in pregnant rats by real time PCR and ELISA. While serum chemerin levels were initially the same in all animals, they decreased following the first trimester of gestation compared to virgin rats (47). Fitting the proinflammatory role thought to be exerted by chemerin, the second and third trimesters are associated with antiinflammatory conditions. The
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authors concluded that the expression profile of chemerin during pregnancy seems similar to adiponectin in that both adipokines show inverse correlation with increased insulin resistance (48).
Inflammation The earliest findings linking chemerin to inflammation were reported by Wittamer et al. who found high concentrations in synovial fluid from arthritis patient as well as ascitic fluid from ovary carcinoma (8). The authors also presented CMKLR1 as a receptor expressed on macrophages and immature DC along with a chemotactic effect on those cells (8; Fig. 3). Various proteases associated with inflammation such as cathepsin G, elastase, or tryptase have been shown to be able to activate chemerin (21). Taken together, the proinflammatory function of chemerin is firmly established. Apart from CMKLR1, these functions seem to be supported by CCRL2. As reported by Monnier et al. (37) CCRL2 expression is upregulated in EC following activation with TNFa in conjunction with lipopolysaccharide (LPS) and interferon gamma (IFN-c). In CCRL2 knockdown mice, serum chemerin levels were increased after systemic LPS treatment while
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natural killer cells trafficking into lung tissue with LPSinduced inflammation was selectively impaired. Using a static endothelial adhesion assay, the authors demonstrated strong adhesion of CMKLR11 L1.2 cells to activated, chemerinS157 loaded ECs. This effect was absent when using, wild type L1.2 cells, not activating the ECs or in the absence of chemerin. Ha et al. correlated increased plasma levels of chemerin with the disease activity score of rheumatoid arthritis and suggested chemerin to be used as a biomarker in rheumatoid arthritis. Interestingly, the authors also reported a negative correlation of chemerin concentration and BMI, hypothesizing obesity-related systemic inflammation as cause of elevated chemerin levels as opposed to the increased adipose tissue itself (49). While Herenius et al. (50) found no correlation between serum chemerin concentration and BMI at all, a correlation between disease activity levels and chemerin levels was reported in agreement with Ha et al. (49). In addition to serum levels of other inflammatory markers, such as Creactive protein (CRP) and Il-6, both disease activity levels and chemerin levels were reduced after 16 weeks of treatment with adalimumab, a TNFa antibody (50). While most reports suggest a proinflammatory role of chemerin, the situation has become more complex with reports of antiinflammatory effects by Cash et al. in 2008 (51). In a mouse model of inflammation, intraperitoneal administration of chemerin140–154 protected the mice against zymosaninduced peritonitis by reducing neutrophil and monocyte recruitment in a CMKLR1-dependent manner. It has been reported that pretreating macrophages with the same peptide led to decreased production of inflammatory mediators such as TNFa and IL6 after macrophage activation with LPS/IFNy. As these latter effects could not be reproduced by Bondue et al. (52), they suggested nonleukocytic cells as the probable cause of the reported antiinflammatory effects.
Skin Psoriasis is a complex condition of the skin, which has been considered to be an immune-mediated disease. The initial discovery of chemerin mRNA in skin was complemented when Schultz et al. demonstrated the in vitro cleavage of recombinant prochemerin by the protease KLK7 in skin (14; Fig. 3). Immunohistochemical colocalization studies showed that chemerin and its processing protease KLK7 are not colocalized in skin of healthy subjects or nonlesional skin of psoriasis patients, but are colocalized in lesional psoriatic skin. Expression of the KLK7 inhibitor vaspin and colocalization with KLK7 were strongly reduced in psoriatic skin compared to healthy skin. Accordingly, this suggests a possible regulatory role of chemerin in psoriasis (14). The relationship between psoriasis and high serum chemerin levels, along with other cytokines, was further explored by Lora et al. (53). Treatment of 27 psoriasis patients with the TNFaantibody infliximab led to a decrease in serum chemerin after 12 months, which was comparable to the healthy control patients. As chemerin levels in patients expressing autoantibodies (ANA1)
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declined faster than in ANA2 patients, they speculated that lower chemerin levels led to a reduced clearance of nuclear debris suggested to induce autoantibody expression (53). Another interesting skin related chemerin paper was recently published by Banas et al. reporting that chemerin has antimicrobiological functions in skin (54; Fig. 3). As described by the authors, chemerin was abundant in epidermis samples from multiple anatomic positions and primarily expressed in basal and suprabasal layers. Chemerin was also abundant in 3D keratinocyte cell culture medium at a concentration of 20 ng/mL and inhibited growth of the E. coli strain H101, a phenomenon absent in anti-chemerin antibody treated medium. Synthesis of 14 overlapping chemerin-derived peptides covering the entire sequence allowed the authors to narrow down the chemerin sequence, which is responsible for these observed effects. While several peptides partly inhibited E. coli growth, chemerin66–85 led to almost full inhibition after 24 h treatment. The antimicrobial activity of this peptide was also demonstrated against the bacteria S. aureus, S. epidermis, P. aeruginosa, and the fungus C. albicans. The authors hypothesized that the positively charged peptide directly interacts with negatively charged bacterial surface to disrupt membrane integrity. Using a mouse model of melanoma, Pachinsky et al. reported the CMKLR1 dependent function of chemerin as a tumorsuppressor in skin (55). Injection of chemerinS157 increased natural killer cell recruitment and inhibited tumor growth. In human melanoma and other solid cell neoplasms, chemerin gene expression was downregulated, suggesting this downregulation as a method of evading the host immune system (55).
Conclusion Chemerin is an immunomodulating factor secreted predominantly by adipose tissue (11) and skin (7). Activation of its primary receptor CMKLR1 necessitates proteolytic C-terminal truncation of its secreted progenitor prochemerin while Proteases such as cathepsin G and KLK7 have shown to exhibit this cleavage. They are expressed by different tissues and have been associated with inflammatory conditions. In addition, chemerin serves as a chemoattractant for different leukocyte populations that express CMKLR1 (7). While antiinflammatory functions have been reported in isolated models (51, 52), both clinical studies in humans and in vitro experiments have served to firmly establish its role in inflammation and suggested its use as biomarker for diseases like arthritis (49, 50), a chronic inflammation of the joints. The role of chemerin in obesity and accompanying diseases is discussed controversially as there is a multitude of contradictory reports concerning correlations with typical obesity parameters like BMI, blood lipids and glucose tolerance (41, 46). As obesity is a systemic condition often accompanied by chronic inflammation states, these inconsistent results are likely complicated by the established proinflammatory properties of chemerin. While first discovered as gene with upregulation in psoriatic skin (7) recent developments have expanded especially on
Processing, Signaling, and Physiological Function of Chemerin
the role of chemerin in psoriatic skin lesions (14). Chemerin as well as the activating protease KLK7 are also found in healthy skin, but they are only colocalized in psoriatic skin. Psoriasis also contributes to heightened serum chemerin levels, which are decreased after treatment with the TNFa antibody infliximab (53). Another chemerin receptor, CCRL2 was shown to be expressed by EC in inflamed tissue, increasing recruitment of natural killer cells (37). While these results suggest chemerin as a cause of the inflammation in psoriatic skin, they are contrasted by evidence highlighting its possible role in healthy skin. Chemerin was demonstrated to inhibit tumor growth in melanoma (55) and to provide antimicrobial properties against skin pathogens such as E. coli or C. albicans (54). Concluding these developments, chemerin is an important regulator in skin and should be considered a highly attractive target for future investigations in skin-related diseases. Various proteases have been shown to C-terminally process chemerin, which results in chemerin isoforms with different affinity to CMKLR1. These proteases have been suggested to regulate chemerin function with respect to the tissue they are expressed in. This research is complicated by the lack of commercially available antibodies able to distinguish between the different isoforms. First, progress has been achieved by the use of antibodies specific for prochemerin, chemerinS157, and chemerinK158 (20). While arthritic synovial fluids were among those first reported to exhibit high chemerin levels (8), the application of these specific antibodies could only show very low concentrations of the active isoform chemerinS157, with the bulk being present as chemerinK158, an isoform with considerably lower affinity at CMKLR1. Unfortunately, an antibody for the other active isoform chemerinF156, which is produced by cleavage by cathepsin G as well as by KLK7, has not been reported so far. Any future effort to elucidate the function of chemerin should include antibodies able to distinguish all isoforms in order to achieve a precise overall pattern of the tissue specific formation of the different isoforms.
Acknowledgements The financial contribution of the Deutsche Forschungsgemeinschaft (TRR67/A4 and SFB 1052/C2) is kindly acknowledged.
References [1] Trayhurn, P., and Beattie, J. H. (2001) Physiological role of adipose tissue: white adipose tissue as an endocrine and secretory organ. Proc. Nutr. Soc. 60, 329–339. [2] Rosen, E. D., and Spiegelman, B. M. (2006) Adipocytes as regulators of energy balance and glucose homeostasis. Nature 444, 847–853. [3] Nedvidkova, J., Smitka, K., Kopsky, V., and Hainer, V. (2005) Adiponectin, an adipocyte-derived protein. Physiol Res 54, 133–140. [4] Hotamisligil, G. S. (1999) The role of TNF alpha and TNF receptors in obesity and insulin resistance. J. Intern. Med. 245, 621–625. [5] Rotter, V., Nagaev, I., and Smith, U. (2003) Interleukin-6 (IL-6) induces insulin resistance in 3T3-L1 adipocytes and is, like IL-8 and tumor necrosis factoralpha, overexpressed in human fat cells from insulin-resistant subjects. J. Biol. Chem. 278, 45777–45784.
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[6] Bozaoglu, K., Bolton, K., McMillan, J., Zimmet, P., Jowett, J., et al. (2007) Chemerin is a novel adipokine associated with obesity and metabolic syndrome. Endocrinology 148, 4687–4694. [7] Nagpal, S., Patel, S., Jacobe, H., DiSepio, D., Ghosn, C., et al. (1997) Tazarotene-induced gene 2 (TIG2), a novel retinoid-responsive gene in skin. J. Invest. Dermatol. 109, 91–95. [8] Wittamer, V., Franssen, J. D., Vulcano, M., Mirjolet, J. F., Le Poul, E., et al. (2003) Specific recruitment of antigen-presenting cells by chemerin, a novel processed ligand from human inflammatory fluids. J. Exp. Med. 198, 977–985. [9] Barnea, G., Strapps, W., Herrada, G., Berman, Y., Ong, J., et al. (2008) The genetic design of signaling cascades to record receptor activation. Proc. Natl. Acad. Sci. USA 105, 64–69. [10] Zabel, B. A., Nakae, S., Zuniga, L., Kim, J. Y., Ohyama, T., et al. (2008) Mast cell-expressed orphan receptor CCRL2 binds chemerin and is required for optimal induction of IgE-mediated passive cutaneous anaphylaxis. J. Exp. Med. 205, 2207–2220. [11] Goralski, K. B., McCarthy, T. C., Hanniman, E. A., Zabel, B. A., Butcher, E. C., et al. (2007) Chemerin, a novel adipokine that regulates adipogenesis and adipocyte metabolism. J. Biol. Chem. 282, 28175–28188. [12] Muruganandan, S., Roman, A. A., and Sinal, C. J. (2010) Role of chemerin/ CMKLR1 signaling in adipogenesis and osteoblastogenesis of bone marrow stem cells. J. Bone Miner. Res. 25, 222–234. [13] Kaur, J., Adya, R., Tan, B. K., Chen, J., and Randeva, H. S. (2010) Identification of chemerin receptor (ChemR23) in human endothelial cells: chemerininduced endothelial angiogenesis. Biochem. Biophys. Res. Commun. 391, 1762–1768. [14] Schultz, S., Saalbach, A., Heiker, J. T., Meier, R., Zellmann, T., et al. (2013) Proteolytic activation of prochemerin by kallikrein 7 breaks an ionic linkage and results in C-terminal rearrangement. Biochem. J. 452, 271–280. [15] Parolini, S., Santoro, A., Marcenaro, E., Luini, W., Massardi, L., et al. (2007) The role of chemerin in the colocalization of NK and dendritic cell subsets into inflamed tissues. Blood 109, 3625–3632. [16] Meder, W., Wendland, M., Busmann, A., Kutzleb, C., Spodsberg, N., et al. (2003) Characterization of human circulating TIG2 as a ligand for the orphan receptor ChemR23. FEBS Lett. 555, 495–499. [17] Du, X. Y., Zabel, B. A., Myles, T., Allen, S. J., Handel, T. M., et al. (2009) Regulation of chemerin bioactivity by plasma carboxypeptidase n, carboxypeptidase b (activated thrombin-activable fibrinolysis inhibitor), and platelets. J. Biol. Chem. 284, 751–758. [18] Guillabert, A., Wittamer, V., Bondue, B., Godot, V., Imbault, V., et al. (2008) Role of neutrophil proteinase 3 and mast cell chymase in chemerin proteolytic regulation. J. Leukoc. Biol. 84, 1530–1539. [19] Yamaguchi, Y., Du, X. Y., Zhao, L., Morser, J., and Leung, L. L. K. (2011) Proteolytic cleavage of chemerin protein is necessary for activation to the active form, Chem157S, which functions as a signaling molecule in glioblastoma. J. Biol. Chem. 286, 39510–39519. [20] Zhao, L., Yamaguchi, Y., Sharif, S., Du, X. Y., Song, J. J., et al. (2011) Chemerin158K protein is the dominant chemerin isoform in synovial and cerebrospinal fluids but not in plasma. J. Biol. Chem. 286, 39520–39527. [21] Zabel, B. A., Allen, S. J., Kulig, P., Allen, J. A., Cichy, J., et al. (2005) Chemerin activation by serine proteases of the coagulation, fibrinolytic, and inflammatory cascades. J. Biol. Chem. 280, 34661–34666. [22] Wittamer, V., Gregoire, F., Robberecht, P., Vassart, G., Communi, D., et al. (2004) The C-terminal nonapeptide of mature chemerin activates the chemerin receptor with low nanomolar potency. J. Biol. Chem. 279, 9956–9962. [23] Gantz, I., Konda, Y., Yang, Y. K., Miller, D. E., Dierick, H. A., et al. (1996) Molecular cloning of a novel receptor (CMKLR1) with homology to the chemotactic factor receptors. Cytogenet. Cell Genet. 74, 286–290. [24] Samson, M., Edinger, A. L., Stordeur, P., Rucker, J., Verhasselt, V., et al. (1998) ChemR23, a putative chemoattractant receptor, is expressed in monocyte-derived dendritic cells and macrophages and is a coreceptor for SIV and some primary HIV-1 strains. Eur. J. Immunol. 28, 1689–1700. [25] Vermi, W., Riboldi, E., Wittamer, V., Gentili, F., Luini, W., et al. (2005) Role of ChemR23 in directing the migration of myeloid and plasmacytoid dendritic cells to lymphoid organs and inflamed skin. J. Exp. Med. 201, 509–515.
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[26] Dona, M., Fredman, G., Schwab, J. M., Chiang, N., Arita, M., et al. (2008) Resolvin E1, an EPA-derived mediator in whole blood, selectively counterregulates leukocytes and platelets. Blood 112, 848–855. [27] Haack, K. K. V., and McCarty, N. A. (2011) Functional consequences of GPCR heterodimerization: GPCRs as allosteric modulators. Pharmaceuticals 4, 509–523. [28] de Poorter, C., Baertsoen, K., Lannoy, V., Parmentier, M., and Springael, J. Y. (2013) Consequences of ChemR23 heteromerization with the chemokine receptors CXCR4 and CCR7. PLoS One 8, e58075. [29] Sohy, D., Yano, H., de Nadai, P., Urizar, E., Guillabert, A., et al. (2009) Hetero-oligomerization of CCR2, CCR5, and CXCR4 and the Protean Effects of "Selective" Antagonists. J. Biol. Chem. 284, 31270–31279. [30] Joost, P., and Methner, A. (2002) Phylogenetic analysis of 277 human Gprotein-coupled receptors as a tool for the prediction of orphan receptor ligands. Genome Biol. 3. [31] Rovati, G. E., Capra, V., and Neubig, R. R. (2007) The highly conserved DRY motif of class A G protein-coupled receptors: Beyond the ground state. Mol. Pharmacol. 71, 959–964. [32] Marchese, A., Docherty, J. M., Nguyen, T., Heiber, M., Cheng, R., et al. (1994) Cloning of human genes encoding novel G-protein-coupled receptors. Genomics 23, 609–618. [33] Shimizu, N., Soda, Y., Kanbe, K., Liu, H. Y., Jinno, A., et al. (1999) An orphan G protein-coupled receptor, GPR1, acts as a coreceptor to allow replication of human immunodeficiency virus types 1 and 2 in brain-derived cells. J. Virol. 73, 5231–5239. [34] Edinger, A. L., Hoffman, T. L., Sharron, M., Lee, B., O’Dowd, B., et al. (1998) Use of GPR1, GPR15, and STRL33 as coreceptors by diverse human immunodeficiency virus type 1 and simian immunodeficiency virus envelope proteins. Virology 249, 367–378. [35] Fan, P., Kyaw, H., Su, K., Zeng, Z. Z., Augustus, M., et al. (1998) Cloning and characterization of a novel human chemokine receptor. Biochem. Biophys. Res. Commun. 243, 264–268. [36] Migeotte, I., Franssen, J. D., Goriely, S., Willems, F., and Parmentier, M. (2002) Distribution and regulation of expression of the putative human chemokine receptor HCR in leukocyte populations. Eur. J. Immunol. 32, 494–501. [37] Monnier, J., Lewen, S., O’Hara, E., Huang, K., Tu, H., et al. (2012) Expression, regulation, and function of atypical chemerin receptor CCRL2 on endothelial cells. J. Immunol. 189, 956–967. [38] Damaj, B. B., McColl, S. R., Neote, K., Na, S. Q., Ogborn, K. T., et al. (1996) Identification of G-protein binding sites of the human interleukin-8 receptors by functional mapping of the intracellular loops. FASEB J. 10, 1426–1434. [39] Yoshimura, T., and Oppenheim, J. J. (2011) Chemokine-like receptor 1 (CMKLR1) and chemokine (C-C motif) receptor-like 2 (CCRL2); Two multifunctional receptors with unusual properties. Exp. Cell Res. 317, 674–684. [40] Becker, M., Rabe, K., Lebherz, C., Zugwurst, J., Goke, B., et al. (2010) Expression of human chemerin induces insulin resistance in the skeletal muscle but does not affect weight, lipid levels, and atherosclerosis in LDL receptor knockout mice on high-fat diet. Diabetes 59, 2898–2903.
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[41] Landgraf, K., Friebe, D., Ullrich, T., Kratzsch, J., Dittrich, K., et al. (2012) Chemerin as a mediator between obesity and vascular inflammation in children. J. Clin. Endocrinol. Metab. 97, E556–564. [42] Bozaoglu, K., Segal, D., Shields, K. A., Cummings, N., Curran, J. E., et al. (2009) Chemerin is associated with metabolic syndrome phenotypes in a Mexican-American population. J. Clin. Endocrinol. Metab. 94, 3085–3088. [43] Chakaroun, R., Raschpichler, M., Kloting, N., Oberbach, A., Flehmig, G., et al. (2012) Effects of weight loss and exercise on chemerin serum concentrations and adipose tissue expression in human obesity. Metabolism 61, 706–714. [44] Takahashi, M., Takahashi, Y., Takahashi, K., Zolotaryov, F. N., Hong, K. S., et al. (2008) Chemerin enhances insulin signaling and potentiates insulinstimulated glucose uptake in 3T3-L1 adipocytes. FEBS Lett. 582, 573–578. [45] Ernst, M. C., Haidl, I. D., Zuniga, L. A., Dranse, H. J., Rourke, J. L., et al. (2012) Disruption of the chemokine-like receptor-1 (CMKLR1) gene is associated with reduced adiposity and glucose intolerance. Endocrinology 153, 672–682. [46] Rouger, L., Denis, R., Luangsay, S., and Parmentier, M. (2013) ChemR23 knockout mice display mild obesity but no deficit in adipocyte differentiation. J Endocrinol 219, 279–289. [47] Garces, M. F., Sanchez, E., Acosta, B. J., Angel, E., Ruiz, A. I., et al. (2012) Expression and regulation of chemerin during rat pregnancy. Placenta 33, 373–378. [48] Ritterath, C., Rad, N. T., Siegmund, T., Heinze, T., Siebert, G., et al. (2010) Adiponectin during pregnancy: correlation with fat metabolism, but not with carbohydrate metabolism. Arch. Gynecol. Obstet. 281, 91–96. [49] Ha, Y. J., Kang, E. J., Song, J. S., Park, Y. B., Lee, S. K., et al. Plasma chemerin levels in rheumatoid arthritis are correlated with disease activity rather than obesity. Joint Bone Spine, in press. [50] Herenius, M. M., Oliveira, A. S., Wijbrandts, C. A., Gerlag, D. M., Tak, P. P., et al. (2013) Anti-TNF therapy reduces serum levels of chemerin in rheumatoid arthritis: a new mechanism by which anti-TNF might reduce inflammation. PLoS One 8, e57802. [51] Cash, J. L., Hart, R., Russ, A., Dixon, J. P. C., Colledge, W. H., et al. (2008) Synthetic chemerin-derived peptides suppress inflammation through ChemR23. J. Exp. Med. 205, 767–775. [52] Bondue, B., De Henau, O., Luangsay, S., Devosse, T., de Nadai, P., et al. (2012) The chemerin/ChemR23 system does not affect the pro-inflammatory response of mouse and human macrophages ex vivo. PLoS One 7, e40043. [53] Lora, V., Bonaguri, C., Gisondi, P., Sandei, F., Battistelli, L., et al. (2013) Autoantibody induction and adipokine levels in patients with psoriasis treated with infliximab. Immunol. Res. 56, 382–389. [54] Banas, M., Zabieglo, K., Kasetty, G., Kapinska-Mrowiecka, M., Borowczyk, J., et al. (2013) Chemerin is an antimicrobial agent in human epidermis. PLoS One 8, e58709. [55] Pachynski, R. K., Zabel, B. A., Kohrt, H. E., Tejeda, N. M., Monnier, J., et al. (2012) The chemoattractant chemerin suppresses melanoma by recruiting natural killer cell antitumor defenses. J. Exp. Med. 209, 1427–1435.
Processing, Signaling, and Physiological Function of Chemerin
Faculty of Biosciences, Pharmacy and Psychology, Biochemistry, Universita€t Leipzig, Leipzig, Germany
Institute
Andreas Mattern* Tristan Zellmann* Annette G. Beck-Sickinger
of
Abstract Chemerin is an immunomodulating factor secreted predominantly by adipose tissue and skin. Processed by a variety of proteases linked to inflammation, it activates the G-protein coupled receptor chemokine-like receptor 1 (CMKLR1) and induces chemotaxis in natural killer cells, macrophages, and immature dendritic cells. Recent developments revealed the role of the nonsignaling chemerin receptor C-C chemokine receptor-like 2
(CCRL2) in inflammation. Besides further research establishing its link to inflammatory skin conditions such as psoriasis, functions in healthy skin have also been reported. Here, the current understanding of chemerin processing, signaling and physiological function has been summarized, focusing on the regulation of its activity, its different receptors and its controversially discussed C 2014 IUBMB Life, 66(1):19–26, 2014 role in diseases. V
Keywords: chemerin; CMKLR1; inflammation; skin; psoriasis; obesity
Introduction Studying the links between obesity and associated diseases has identified adipose tissue as an active endocrine organ (1). Endocrine compounds secreted by adipocytes include proteins like leptin, a protein implied in regulating food intake and insulin sensitivity (2), or adiponectin, which regulates gluconeogenesis and lipid metabolism (3). In addition to molecules involved in energy homeostasis, adipocytes also secrete cytokines that play a role in cell-cell-signaling as well as in cell differentiation (1). Adipocytokines such as tumor necrosis factor alpha (TNFa; 4) or interleukin-6 (IL-6; 5) have been suggested as links between obesity, type 2 diabetes and chronic inflammatory states. Chemerin (6) was first termed tazarotene-induced gene 2 protein (TIG2), reflecting the discovery of its mRNA in skin cell raft cultures after tazarotene application (7). Chemerin is
C 2014 International Union of Biochemistry and Molecular Biology V
Volume 66, Number 1, January 2014, Pages 19–26 *Address correspondence to: Prof. Dr. Annette G. Beck-Sickinger, Uni€ r Biochemie, Bru € derstraße 34, D-04103 Leipzig, versita€t Leipzig, Institut fu Germany. Tel.: 1493419736901; Fax: 1493419736909. E-mail: [email protected] *Both authors contributed equally to this work. Received 27 October 2013; Accepted 22 December 2013 DOI 10.1002/iub.1242 Published online in Wiley Online Library (wileyonlinelibrary.com)
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expressed as preprochemerin that consists of 163 amino acids. Several isoforms of chemerin have been identified that are dependent on the processing by various serine and cysteine proteases. Recent data demonstrated that chemerin and its receptors CMKLR1 (8), G protein-coupled receptor 1 (GPR1) (9) and C-C chemokine receptor-like 2 (CCRL2) (10) are involved in adipogenesis (11), osteoclastogenesis (12), angiogenesis (13), and inflammatory processes in skin (14) and adipose tissue (15).
Postsecretory Processing of Chemerin and Functional Consequences After truncation of the 20 amino acid N-terminal signal peptide, chemerin is secreted as 143 residue prochemerin (8). In different tissues, various isoforms of chemerin have been detected (Fig. 1). Of these, chemerinS157 (8) and chemerinF156 (16) demonstrate the highest affinity to CMKLR1, while other isoforms such as prochemerin (8), chemerinK158 (17), or chemerinF154 (18), exhibit a much lower affinity. The different chemerin isoforms are suggested to regulate a biochemical cascade by competition binding to the corresponding receptors. By comparing different chemerin isoforms Yamaguchi et al. found that chemerinA155 competed the binding of chemerinS157 as a weak antagonist (19). Although this only occurred when chemerinA155 was added in a large excess, it might indicate a complex regulatory interaction of all chemerin variants.
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Fig 1
A: Processing of chemerin with different proteases related to inflammation. B: Amino acid sequence of chemerin. The signal peptide (underlined) is cleaved prior to secretion. Cleavage of the C-terminus (bold) results in active chemerinS157 as well as other isoforms. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Using specific antibodies for the prochemerin, chemerinK , and chemerinS157, Zhao et al. have examined the amount of these forms in different body fluids (20). While prochemerin was the dominant isoform in plasma from healthy subjects constituting 80% of the total chemerin, chemerinS157 was almost not detectable. The situation was opposite in synovial fluid from arthritis patients, where total chemerin levels were 2-fold increased and prochemerin only made up about 25%. Though chemerinS157 was only present in small concentrations, the high level of chemerinK158 clearly demonstrates the physiological relevance of chemerin processing in vivo. So far, eight proteases have been shown to C-terminally process prochemerin or chemerin in vitro including cathepsin G, plasmin, and elastase (21). As chemerinS157 and chemer158
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inF156 show the highest affinity to CMKLR1, simple cleavage by cathepsin G or elastase may be important for in vivo activation of chemerin, although sequential processing with different proteases like elastase and carboxypeptidase has also been suggested (17, 21; Fig. 1). Testing peptides of different length derived from the C-terminus, Wittamer et al. reported chemerin149–157 (YFPGQFAFS) as the most active fragment (22). This peptide was shown to reach nearly full length properties with respect to both binding affinity and receptor activation. Shorter fragments did not show any detectable binding, longer ones had progressively lower activity. An alanine scan of the nonapeptide chemerin149–157 revealed the residues P151, Q153, and S157 to have only a low impact on binding affinity, while mutating
Processing, Signaling, and Physiological Function of Chemerin
Fig 2
Superposition of homology models of prochemerin (dark green) and chemerinF156 (light yellow) as described recently by Schultz et al. (14) with a magnification of the C-terminus. The structural change of the C-terminus accompanying processing to chemerinF156 is suggested to enable receptor binding. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
the positions G152, F154, and F156 resulted in a peptide with no detectable affinity. Schultz et al. postulated that the structural function of Cterminal processing of chemerin lies in removing the positively charged residues K158 and R162, changing the C-terminal structure as to increase the affinity to CMKLR1. Based on homology modeling, these residues are supposed to form a salt bridge with a glutamic acid cluster consisting of E126, E128, E129, and E132. This is supported by the prochemerin mutants K158A and R162A, which exhibit higher potency in CMKLR1 signal transduction assays. A mutant deficient of the glutamic acid cluster achieved a potency almost on par with chemerinS157 and chemerinF156, demonstrating that the actual length of the C-terminus does not impede CMKLR1 binding (Fig. 2).
Chemerin and its Receptors Chemerin has been reported to bind to three G-protein coupled receptors (GPCR) named CMKLR1, GPR1, and CCRL2. CMKLR1 was first reported in 1996 as orphan GPCR (23; Table 1). As receptors with closer similarity include the chemoattractant receptors complement component 3a receptor 1, complement component 5a receptor 1, and formyl Met-Leu-Phe receptors (fMLPR), a similar role was postulated for CMKLR1 (24). Chemerin was shown to specifically bind and activate CMKLR1, which leads to Ca21-mobilization and chemotaxis in dendritic cells (DC) (8, 16). Furthermore, CMKLR1 shows a specific expression profile in cells of the adaptive immune system with high levels of mRNA found in macrophages (24), myeloid, plasmacytoid, and immature DC (8, 25). In the case of myeloid and plasmacytoid DC, chemerin expression is reduced during maturation. Langerhans cells do not express CMKLR1. In lymphocyte cells, CMKLR1 is
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found in natural killer cells but not in B- or T-cells (15). Platelet cells (26) and adipocytes also express CMKLR1 (11). Heteromerization of GPCRs is known to affect signaling pathways, ligand binding affinity, as well as internalization behavior (27). De Poorter et al. (28) have demonstrated CMKLR1 heteromerization with C-X-C chemokine receptor type 4 and CC chemokine receptor type 7 (CCR7) in stably transfected Chinese hamster ovary (CHO) cells with bioluminescence resonance energy transfer-assays. Coexpression of CMKLR1 with either CXCR4 or CCR7 led to heteromerization and cross-competition of the latter’s native ligands C-X-C motif chemokine 12 (CXCL12) and C-C motif chemokine 19 (CCL19), increasing their respective IC50 values. Cross-competition of chemerinS157 binding to CMKLR1 had a comparably lower magnitude. Interestingly, there was no cross-competition between the bicyclamic AMD3100, a CXCR4 specific antagonist, and chemerin (28). Previous work showed that heteromerization of CXCR4 and C-C chemokine receptor type 2 (CCR2) as well as C-C chemokine receptor type 5 (CCR5) led to a competition of their native ligands CXCL12 and CCL19 with AMD3100 (29). Missing competition in case of CMKLR1 indicates that the interaction between CMKLR1 and CXCR4 is only indirect and possibly related to signaling events or includes a different binding site. Investigating the effect of heteromerization on receptor internalization with fluorescence-activated cell sorting, the number of cell surface CMKLR1 after stimulation with chemerinS157 was found to be decreased while those of CXCR4 and CCR7 did not (28). In the same way, stimulation with either C-XC motif chemokine 2 or CCL19 led to internalization of their respective receptors, but not to the cointernalization of CMKLR1. Cross-inhibition was also investigated by comparing mouse bone marrow DC (BMDC), which naturally express CXCR4 and CMKLR1, with BMDC prepared from CMKLR1knockout mice (28). In experiments measuring specific CXCL12 binding, coincubation with chemerin lowered the specific binding of CXCL12 (28). This effect was absent in knockout mouse derived BMDCs. As these effects could also be caused by downstream signaling effects, the authors summarize that the existence of heterodimers of either CXCR4 or CCR7 to CMKLR1 cannot be sufficiently proven under physiological conditions (28). A second receptor shown to bind chemerin is GPR1, which is closely related to CMKLR1 (9, 30). GPR1 was initially reported presumably not to be activated by chemerinS157 in Ca21 mobilization bioassays (8). The interaction was demonstrated using the TangoTM GPCR assay (Life Technologies), which relies on arrestin recruitment following ligand binding instead of the release of second messengers. In this assay, an EC50 value of 0.24 nM was determined for GPR1 compared to 3 nM for CMKLR1 (Table 1). This higher affinity also extended to the chemerin nonapeptide 149YFPGQFAFS157 with 1 nM at GPR1 and 24 nM at CMKLR1. In Ca21-mobilization assays, GPR1 showed only a third of the Ca21-flux in comparison to CMKLR1. Radioligand saturation binding assays showed a KD value of 5.3 nM for GPR1 and 4.9 nM for CMKLR1 (9; Table 1). The very low Ca21-mobilization detectable on chemerin binding is most
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Summary of the three known chemerin receptors
TABLE 1
Related receptors
Associated tissues
KD (nM)
EC50 (nM), EC50 (nM) apoaequorin TangoTM assay GPCR assay
Signaling/ internalization
Function
CMKLR1 C3aR, c5aR, Adipose fMLPR (30) tissue (28), leukocytes (8, 25, 27)
4.9 (9)
4.5 (7)
3 (9)
Strong Ca21, internalization (8)
Chemotaxis (8), energy metabolism (15), cell differentiation (11–13)
GPR1
C3aR, c5aR, CNS-related fMLPR (30) (32–34)
5.3 (9)
n.d.
0.24 (9)
Weak Ca21, internalization (9)
Decoy receptor (9)
CCRL2
CCR1, CCR2, CCR3, CCR5 (10)
n.d.
n.d.
a
1.6a (10) leukocytes, mast cells (37), EC (36)
No signaling, no Natural killer cell internalization (10) recruitment (36)
MurineCCRL2.
probably caused by a mutation of the DRY receptor motif to DHY. Reviewing DRY mutants of more than 20 receptors, Rovati et al. concluded that nonconservative arginine mutation led to decreased agonist-induced activity while not affecting arrestindependant internalization (31). In contrast to CMKLR1, GPR1 is not expressed in monocytes, macrophages, or peripheral blood lymphocytes, but instead in cells related to the central nervous system. The glioblastoma cell line U87 (32), brain-derived fibroblast-like cell lines such as BT3 and BT-20/N (33) and hippocampus tissue (34) have been described to express GPR1. While the biological role of GPR1 is poorly understood at this point, the markedly different expression pattern suggests a different role compared with CMKLR1. The third receptor reported to bind chemerin is CCLR2 (10), also a GPCR belonging to the chemokine receptor family, sharing 40% sequence identity with CCR1, CCR2, CCR3, and CCR5 (35). It is not directly related to CMKLR1, sharing only 20% sequence identity. CCLR2 mRNA as well as protein level expression was found in neutrophils, DC, T cells, and macrophages (36). In contrast to CMKLR1 and GPR1, neither Ca21-mobilization nor internalization could be detected after chemerin incubation (37). This apparent lack of signaling is possibly caused by some deviations within its sequence, most obvious in the DRYLAIV motif, which is conserved in chemokine receptors and important for G-protein binding (38). In CCRL2, this motif is mutated to QRYLVFL. The same motif is changed in the nonsignaling chemokine receptors duffy antigen receptor for chemokines and CXCR7, which are thought to act as ligand scavengers, locally regulating chemokine concentrations (39). Concerning ligand-binding affinity, a C-terminal His8-tag at chemerin did not impede chemerin binding. CCRL2-bound chemerin was still able to be bound by an anti-His antibody (10). Furthermore, mCCRL2-transfected cells loaded with chem-
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erin were able to induce Ca21-mobilization in CMKLR1transfected cells, suggesting the possibility that CCRL2 serves to increase local chemerin concentrations and present it to CMKLR1 expressed on neighboring cells in vivo (10). Finally, CCRL2 was shown to bind CCL19, a chemokine also bound by C-C chemokine receptor type 8. Interestingly, radioligand binding assays could not show competition between these two ligands, possibly owing to different binding sites (10). Concerning intracellular signaling of chemerin, only CMKLR1 has been characterized to some extent. In transiently transfected CHO cells, chemerin has been demonstrated to lead to Ca21-mobilization, inhibition of cAMP accumulation, phosphorylation of p42 and p44 mitogen-activated protein kinase (MAPK), all being dependant on Gi signaling (8). In human endothelial cells (EC), chemerin induces activation of p38 MAPK, extracellular signal-regulated kinases and phosphoinositid-3-kinase/protein kinase B pathways in a dosedependent manner (13). Besides p38 MAPK and ERK-1/2, the nuclear factor “kappa-light-chain-enhancer” (NF-jB) pathway is also activated by chemerin administration in skeletal muscle cells (40).
Biological Role of Chemerin Obesity Chemerin was first reported to belong to the adipokine family when Goralski et al. (11) could demonstrate expression of both chemerin and CMKLR1 in white adipose tissue as well as chemerin secretion by adipocytes (11). Expression and secretion depend on maturation of these cells. CMKLR1 or chemerin knockdown with small hairpin RNA (shRNA) impaired differentiation of 3T3-L1 preadipocytes (11). Serum chemerin levels
Processing, Signaling, and Physiological Function of Chemerin
Fig 3
Chemerin is involved in a variety of functions in inflammation, skin, obesity, and cell differentiation. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
have been correlated to multiple obesity-related parameters such as body mass index (BMI; 41), blood pressure, serum lipid, insulin, and cholesterol level (42). Weight-loss owing to exercise, bariatric surgery, or reduction of caloric intake reduces serum chemerin levels and might correlate with improved insulin resistance (43). Chemerin regulates insulin secretion of beta cells in mice while chemerin knockdown mice exhibit glucose intolerance (44). In CMKLR1 knockdown mice, Ernst et al. could show a reduction in caloric intake, body weight, percentage of body fat and glucose tolerance compared to wild type mice regardless of diet (45). As other investigators could not show any correlation between chemerin and insulin resistance (46), the actual role of chemerin as a mediator of obesity and type 2 diabetes remains to be clarified. Chemerin seems to play a major role in the placenta as shown by Garces et al. who studied the expression pattern of chemerin in pregnant rats by real time PCR and ELISA. While serum chemerin levels were initially the same in all animals, they decreased following the first trimester of gestation compared to virgin rats (47). Fitting the proinflammatory role thought to be exerted by chemerin, the second and third trimesters are associated with antiinflammatory conditions. The
Mattern et al.
authors concluded that the expression profile of chemerin during pregnancy seems similar to adiponectin in that both adipokines show inverse correlation with increased insulin resistance (48).
Inflammation The earliest findings linking chemerin to inflammation were reported by Wittamer et al. who found high concentrations in synovial fluid from arthritis patient as well as ascitic fluid from ovary carcinoma (8). The authors also presented CMKLR1 as a receptor expressed on macrophages and immature DC along with a chemotactic effect on those cells (8; Fig. 3). Various proteases associated with inflammation such as cathepsin G, elastase, or tryptase have been shown to be able to activate chemerin (21). Taken together, the proinflammatory function of chemerin is firmly established. Apart from CMKLR1, these functions seem to be supported by CCRL2. As reported by Monnier et al. (37) CCRL2 expression is upregulated in EC following activation with TNFa in conjunction with lipopolysaccharide (LPS) and interferon gamma (IFN-c). In CCRL2 knockdown mice, serum chemerin levels were increased after systemic LPS treatment while
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natural killer cells trafficking into lung tissue with LPSinduced inflammation was selectively impaired. Using a static endothelial adhesion assay, the authors demonstrated strong adhesion of CMKLR11 L1.2 cells to activated, chemerinS157 loaded ECs. This effect was absent when using, wild type L1.2 cells, not activating the ECs or in the absence of chemerin. Ha et al. correlated increased plasma levels of chemerin with the disease activity score of rheumatoid arthritis and suggested chemerin to be used as a biomarker in rheumatoid arthritis. Interestingly, the authors also reported a negative correlation of chemerin concentration and BMI, hypothesizing obesity-related systemic inflammation as cause of elevated chemerin levels as opposed to the increased adipose tissue itself (49). While Herenius et al. (50) found no correlation between serum chemerin concentration and BMI at all, a correlation between disease activity levels and chemerin levels was reported in agreement with Ha et al. (49). In addition to serum levels of other inflammatory markers, such as Creactive protein (CRP) and Il-6, both disease activity levels and chemerin levels were reduced after 16 weeks of treatment with adalimumab, a TNFa antibody (50). While most reports suggest a proinflammatory role of chemerin, the situation has become more complex with reports of antiinflammatory effects by Cash et al. in 2008 (51). In a mouse model of inflammation, intraperitoneal administration of chemerin140–154 protected the mice against zymosaninduced peritonitis by reducing neutrophil and monocyte recruitment in a CMKLR1-dependent manner. It has been reported that pretreating macrophages with the same peptide led to decreased production of inflammatory mediators such as TNFa and IL6 after macrophage activation with LPS/IFNy. As these latter effects could not be reproduced by Bondue et al. (52), they suggested nonleukocytic cells as the probable cause of the reported antiinflammatory effects.
Skin Psoriasis is a complex condition of the skin, which has been considered to be an immune-mediated disease. The initial discovery of chemerin mRNA in skin was complemented when Schultz et al. demonstrated the in vitro cleavage of recombinant prochemerin by the protease KLK7 in skin (14; Fig. 3). Immunohistochemical colocalization studies showed that chemerin and its processing protease KLK7 are not colocalized in skin of healthy subjects or nonlesional skin of psoriasis patients, but are colocalized in lesional psoriatic skin. Expression of the KLK7 inhibitor vaspin and colocalization with KLK7 were strongly reduced in psoriatic skin compared to healthy skin. Accordingly, this suggests a possible regulatory role of chemerin in psoriasis (14). The relationship between psoriasis and high serum chemerin levels, along with other cytokines, was further explored by Lora et al. (53). Treatment of 27 psoriasis patients with the TNFaantibody infliximab led to a decrease in serum chemerin after 12 months, which was comparable to the healthy control patients. As chemerin levels in patients expressing autoantibodies (ANA1)
24
declined faster than in ANA2 patients, they speculated that lower chemerin levels led to a reduced clearance of nuclear debris suggested to induce autoantibody expression (53). Another interesting skin related chemerin paper was recently published by Banas et al. reporting that chemerin has antimicrobiological functions in skin (54; Fig. 3). As described by the authors, chemerin was abundant in epidermis samples from multiple anatomic positions and primarily expressed in basal and suprabasal layers. Chemerin was also abundant in 3D keratinocyte cell culture medium at a concentration of 20 ng/mL and inhibited growth of the E. coli strain H101, a phenomenon absent in anti-chemerin antibody treated medium. Synthesis of 14 overlapping chemerin-derived peptides covering the entire sequence allowed the authors to narrow down the chemerin sequence, which is responsible for these observed effects. While several peptides partly inhibited E. coli growth, chemerin66–85 led to almost full inhibition after 24 h treatment. The antimicrobial activity of this peptide was also demonstrated against the bacteria S. aureus, S. epidermis, P. aeruginosa, and the fungus C. albicans. The authors hypothesized that the positively charged peptide directly interacts with negatively charged bacterial surface to disrupt membrane integrity. Using a mouse model of melanoma, Pachinsky et al. reported the CMKLR1 dependent function of chemerin as a tumorsuppressor in skin (55). Injection of chemerinS157 increased natural killer cell recruitment and inhibited tumor growth. In human melanoma and other solid cell neoplasms, chemerin gene expression was downregulated, suggesting this downregulation as a method of evading the host immune system (55).
Conclusion Chemerin is an immunomodulating factor secreted predominantly by adipose tissue (11) and skin (7). Activation of its primary receptor CMKLR1 necessitates proteolytic C-terminal truncation of its secreted progenitor prochemerin while Proteases such as cathepsin G and KLK7 have shown to exhibit this cleavage. They are expressed by different tissues and have been associated with inflammatory conditions. In addition, chemerin serves as a chemoattractant for different leukocyte populations that express CMKLR1 (7). While antiinflammatory functions have been reported in isolated models (51, 52), both clinical studies in humans and in vitro experiments have served to firmly establish its role in inflammation and suggested its use as biomarker for diseases like arthritis (49, 50), a chronic inflammation of the joints. The role of chemerin in obesity and accompanying diseases is discussed controversially as there is a multitude of contradictory reports concerning correlations with typical obesity parameters like BMI, blood lipids and glucose tolerance (41, 46). As obesity is a systemic condition often accompanied by chronic inflammation states, these inconsistent results are likely complicated by the established proinflammatory properties of chemerin. While first discovered as gene with upregulation in psoriatic skin (7) recent developments have expanded especially on
Processing, Signaling, and Physiological Function of Chemerin
the role of chemerin in psoriatic skin lesions (14). Chemerin as well as the activating protease KLK7 are also found in healthy skin, but they are only colocalized in psoriatic skin. Psoriasis also contributes to heightened serum chemerin levels, which are decreased after treatment with the TNFa antibody infliximab (53). Another chemerin receptor, CCRL2 was shown to be expressed by EC in inflamed tissue, increasing recruitment of natural killer cells (37). While these results suggest chemerin as a cause of the inflammation in psoriatic skin, they are contrasted by evidence highlighting its possible role in healthy skin. Chemerin was demonstrated to inhibit tumor growth in melanoma (55) and to provide antimicrobial properties against skin pathogens such as E. coli or C. albicans (54). Concluding these developments, chemerin is an important regulator in skin and should be considered a highly attractive target for future investigations in skin-related diseases. Various proteases have been shown to C-terminally process chemerin, which results in chemerin isoforms with different affinity to CMKLR1. These proteases have been suggested to regulate chemerin function with respect to the tissue they are expressed in. This research is complicated by the lack of commercially available antibodies able to distinguish between the different isoforms. First, progress has been achieved by the use of antibodies specific for prochemerin, chemerinS157, and chemerinK158 (20). While arthritic synovial fluids were among those first reported to exhibit high chemerin levels (8), the application of these specific antibodies could only show very low concentrations of the active isoform chemerinS157, with the bulk being present as chemerinK158, an isoform with considerably lower affinity at CMKLR1. Unfortunately, an antibody for the other active isoform chemerinF156, which is produced by cleavage by cathepsin G as well as by KLK7, has not been reported so far. Any future effort to elucidate the function of chemerin should include antibodies able to distinguish all isoforms in order to achieve a precise overall pattern of the tissue specific formation of the different isoforms.
Acknowledgements The financial contribution of the Deutsche Forschungsgemeinschaft (TRR67/A4 and SFB 1052/C2) is kindly acknowledged.
References [1] Trayhurn, P., and Beattie, J. H. (2001) Physiological role of adipose tissue: white adipose tissue as an endocrine and secretory organ. Proc. Nutr. Soc. 60, 329–339. [2] Rosen, E. D., and Spiegelman, B. M. (2006) Adipocytes as regulators of energy balance and glucose homeostasis. Nature 444, 847–853. [3] Nedvidkova, J., Smitka, K., Kopsky, V., and Hainer, V. (2005) Adiponectin, an adipocyte-derived protein. Physiol Res 54, 133–140. [4] Hotamisligil, G. S. (1999) The role of TNF alpha and TNF receptors in obesity and insulin resistance. J. Intern. Med. 245, 621–625. [5] Rotter, V., Nagaev, I., and Smith, U. (2003) Interleukin-6 (IL-6) induces insulin resistance in 3T3-L1 adipocytes and is, like IL-8 and tumor necrosis factoralpha, overexpressed in human fat cells from insulin-resistant subjects. J. Biol. Chem. 278, 45777–45784.
Mattern et al.
[6] Bozaoglu, K., Bolton, K., McMillan, J., Zimmet, P., Jowett, J., et al. (2007) Chemerin is a novel adipokine associated with obesity and metabolic syndrome. Endocrinology 148, 4687–4694. [7] Nagpal, S., Patel, S., Jacobe, H., DiSepio, D., Ghosn, C., et al. (1997) Tazarotene-induced gene 2 (TIG2), a novel retinoid-responsive gene in skin. J. Invest. Dermatol. 109, 91–95. [8] Wittamer, V., Franssen, J. D., Vulcano, M., Mirjolet, J. F., Le Poul, E., et al. (2003) Specific recruitment of antigen-presenting cells by chemerin, a novel processed ligand from human inflammatory fluids. J. Exp. Med. 198, 977–985. [9] Barnea, G., Strapps, W., Herrada, G., Berman, Y., Ong, J., et al. (2008) The genetic design of signaling cascades to record receptor activation. Proc. Natl. Acad. Sci. USA 105, 64–69. [10] Zabel, B. A., Nakae, S., Zuniga, L., Kim, J. Y., Ohyama, T., et al. (2008) Mast cell-expressed orphan receptor CCRL2 binds chemerin and is required for optimal induction of IgE-mediated passive cutaneous anaphylaxis. J. Exp. Med. 205, 2207–2220. [11] Goralski, K. B., McCarthy, T. C., Hanniman, E. A., Zabel, B. A., Butcher, E. C., et al. (2007) Chemerin, a novel adipokine that regulates adipogenesis and adipocyte metabolism. J. Biol. Chem. 282, 28175–28188. [12] Muruganandan, S., Roman, A. A., and Sinal, C. J. (2010) Role of chemerin/ CMKLR1 signaling in adipogenesis and osteoblastogenesis of bone marrow stem cells. J. Bone Miner. Res. 25, 222–234. [13] Kaur, J., Adya, R., Tan, B. K., Chen, J., and Randeva, H. S. (2010) Identification of chemerin receptor (ChemR23) in human endothelial cells: chemerininduced endothelial angiogenesis. Biochem. Biophys. Res. Commun. 391, 1762–1768. [14] Schultz, S., Saalbach, A., Heiker, J. T., Meier, R., Zellmann, T., et al. (2013) Proteolytic activation of prochemerin by kallikrein 7 breaks an ionic linkage and results in C-terminal rearrangement. Biochem. J. 452, 271–280. [15] Parolini, S., Santoro, A., Marcenaro, E., Luini, W., Massardi, L., et al. (2007) The role of chemerin in the colocalization of NK and dendritic cell subsets into inflamed tissues. Blood 109, 3625–3632. [16] Meder, W., Wendland, M., Busmann, A., Kutzleb, C., Spodsberg, N., et al. (2003) Characterization of human circulating TIG2 as a ligand for the orphan receptor ChemR23. FEBS Lett. 555, 495–499. [17] Du, X. Y., Zabel, B. A., Myles, T., Allen, S. J., Handel, T. M., et al. (2009) Regulation of chemerin bioactivity by plasma carboxypeptidase n, carboxypeptidase b (activated thrombin-activable fibrinolysis inhibitor), and platelets. J. Biol. Chem. 284, 751–758. [18] Guillabert, A., Wittamer, V., Bondue, B., Godot, V., Imbault, V., et al. (2008) Role of neutrophil proteinase 3 and mast cell chymase in chemerin proteolytic regulation. J. Leukoc. Biol. 84, 1530–1539. [19] Yamaguchi, Y., Du, X. Y., Zhao, L., Morser, J., and Leung, L. L. K. (2011) Proteolytic cleavage of chemerin protein is necessary for activation to the active form, Chem157S, which functions as a signaling molecule in glioblastoma. J. Biol. Chem. 286, 39510–39519. [20] Zhao, L., Yamaguchi, Y., Sharif, S., Du, X. Y., Song, J. J., et al. (2011) Chemerin158K protein is the dominant chemerin isoform in synovial and cerebrospinal fluids but not in plasma. J. Biol. Chem. 286, 39520–39527. [21] Zabel, B. A., Allen, S. J., Kulig, P., Allen, J. A., Cichy, J., et al. (2005) Chemerin activation by serine proteases of the coagulation, fibrinolytic, and inflammatory cascades. J. Biol. Chem. 280, 34661–34666. [22] Wittamer, V., Gregoire, F., Robberecht, P., Vassart, G., Communi, D., et al. (2004) The C-terminal nonapeptide of mature chemerin activates the chemerin receptor with low nanomolar potency. J. Biol. Chem. 279, 9956–9962. [23] Gantz, I., Konda, Y., Yang, Y. K., Miller, D. E., Dierick, H. A., et al. (1996) Molecular cloning of a novel receptor (CMKLR1) with homology to the chemotactic factor receptors. Cytogenet. Cell Genet. 74, 286–290. [24] Samson, M., Edinger, A. L., Stordeur, P., Rucker, J., Verhasselt, V., et al. (1998) ChemR23, a putative chemoattractant receptor, is expressed in monocyte-derived dendritic cells and macrophages and is a coreceptor for SIV and some primary HIV-1 strains. Eur. J. Immunol. 28, 1689–1700. [25] Vermi, W., Riboldi, E., Wittamer, V., Gentili, F., Luini, W., et al. (2005) Role of ChemR23 in directing the migration of myeloid and plasmacytoid dendritic cells to lymphoid organs and inflamed skin. J. Exp. Med. 201, 509–515.
25
IUBMB LIFE
[26] Dona, M., Fredman, G., Schwab, J. M., Chiang, N., Arita, M., et al. (2008) Resolvin E1, an EPA-derived mediator in whole blood, selectively counterregulates leukocytes and platelets. Blood 112, 848–855. [27] Haack, K. K. V., and McCarty, N. A. (2011) Functional consequences of GPCR heterodimerization: GPCRs as allosteric modulators. Pharmaceuticals 4, 509–523. [28] de Poorter, C., Baertsoen, K., Lannoy, V., Parmentier, M., and Springael, J. Y. (2013) Consequences of ChemR23 heteromerization with the chemokine receptors CXCR4 and CCR7. PLoS One 8, e58075. [29] Sohy, D., Yano, H., de Nadai, P., Urizar, E., Guillabert, A., et al. (2009) Hetero-oligomerization of CCR2, CCR5, and CXCR4 and the Protean Effects of "Selective" Antagonists. J. Biol. Chem. 284, 31270–31279. [30] Joost, P., and Methner, A. (2002) Phylogenetic analysis of 277 human Gprotein-coupled receptors as a tool for the prediction of orphan receptor ligands. Genome Biol. 3. [31] Rovati, G. E., Capra, V., and Neubig, R. R. (2007) The highly conserved DRY motif of class A G protein-coupled receptors: Beyond the ground state. Mol. Pharmacol. 71, 959–964. [32] Marchese, A., Docherty, J. M., Nguyen, T., Heiber, M., Cheng, R., et al. (1994) Cloning of human genes encoding novel G-protein-coupled receptors. Genomics 23, 609–618. [33] Shimizu, N., Soda, Y., Kanbe, K., Liu, H. Y., Jinno, A., et al. (1999) An orphan G protein-coupled receptor, GPR1, acts as a coreceptor to allow replication of human immunodeficiency virus types 1 and 2 in brain-derived cells. J. Virol. 73, 5231–5239. [34] Edinger, A. L., Hoffman, T. L., Sharron, M., Lee, B., O’Dowd, B., et al. (1998) Use of GPR1, GPR15, and STRL33 as coreceptors by diverse human immunodeficiency virus type 1 and simian immunodeficiency virus envelope proteins. Virology 249, 367–378. [35] Fan, P., Kyaw, H., Su, K., Zeng, Z. Z., Augustus, M., et al. (1998) Cloning and characterization of a novel human chemokine receptor. Biochem. Biophys. Res. Commun. 243, 264–268. [36] Migeotte, I., Franssen, J. D., Goriely, S., Willems, F., and Parmentier, M. (2002) Distribution and regulation of expression of the putative human chemokine receptor HCR in leukocyte populations. Eur. J. Immunol. 32, 494–501. [37] Monnier, J., Lewen, S., O’Hara, E., Huang, K., Tu, H., et al. (2012) Expression, regulation, and function of atypical chemerin receptor CCRL2 on endothelial cells. J. Immunol. 189, 956–967. [38] Damaj, B. B., McColl, S. R., Neote, K., Na, S. Q., Ogborn, K. T., et al. (1996) Identification of G-protein binding sites of the human interleukin-8 receptors by functional mapping of the intracellular loops. FASEB J. 10, 1426–1434. [39] Yoshimura, T., and Oppenheim, J. J. (2011) Chemokine-like receptor 1 (CMKLR1) and chemokine (C-C motif) receptor-like 2 (CCRL2); Two multifunctional receptors with unusual properties. Exp. Cell Res. 317, 674–684. [40] Becker, M., Rabe, K., Lebherz, C., Zugwurst, J., Goke, B., et al. (2010) Expression of human chemerin induces insulin resistance in the skeletal muscle but does not affect weight, lipid levels, and atherosclerosis in LDL receptor knockout mice on high-fat diet. Diabetes 59, 2898–2903.
26
[41] Landgraf, K., Friebe, D., Ullrich, T., Kratzsch, J., Dittrich, K., et al. (2012) Chemerin as a mediator between obesity and vascular inflammation in children. J. Clin. Endocrinol. Metab. 97, E556–564. [42] Bozaoglu, K., Segal, D., Shields, K. A., Cummings, N., Curran, J. E., et al. (2009) Chemerin is associated with metabolic syndrome phenotypes in a Mexican-American population. J. Clin. Endocrinol. Metab. 94, 3085–3088. [43] Chakaroun, R., Raschpichler, M., Kloting, N., Oberbach, A., Flehmig, G., et al. (2012) Effects of weight loss and exercise on chemerin serum concentrations and adipose tissue expression in human obesity. Metabolism 61, 706–714. [44] Takahashi, M., Takahashi, Y., Takahashi, K., Zolotaryov, F. N., Hong, K. S., et al. (2008) Chemerin enhances insulin signaling and potentiates insulinstimulated glucose uptake in 3T3-L1 adipocytes. FEBS Lett. 582, 573–578. [45] Ernst, M. C., Haidl, I. D., Zuniga, L. A., Dranse, H. J., Rourke, J. L., et al. (2012) Disruption of the chemokine-like receptor-1 (CMKLR1) gene is associated with reduced adiposity and glucose intolerance. Endocrinology 153, 672–682. [46] Rouger, L., Denis, R., Luangsay, S., and Parmentier, M. (2013) ChemR23 knockout mice display mild obesity but no deficit in adipocyte differentiation. J Endocrinol 219, 279–289. [47] Garces, M. F., Sanchez, E., Acosta, B. J., Angel, E., Ruiz, A. I., et al. (2012) Expression and regulation of chemerin during rat pregnancy. Placenta 33, 373–378. [48] Ritterath, C., Rad, N. T., Siegmund, T., Heinze, T., Siebert, G., et al. (2010) Adiponectin during pregnancy: correlation with fat metabolism, but not with carbohydrate metabolism. Arch. Gynecol. Obstet. 281, 91–96. [49] Ha, Y. J., Kang, E. J., Song, J. S., Park, Y. B., Lee, S. K., et al. Plasma chemerin levels in rheumatoid arthritis are correlated with disease activity rather than obesity. Joint Bone Spine, in press. [50] Herenius, M. M., Oliveira, A. S., Wijbrandts, C. A., Gerlag, D. M., Tak, P. P., et al. (2013) Anti-TNF therapy reduces serum levels of chemerin in rheumatoid arthritis: a new mechanism by which anti-TNF might reduce inflammation. PLoS One 8, e57802. [51] Cash, J. L., Hart, R., Russ, A., Dixon, J. P. C., Colledge, W. H., et al. (2008) Synthetic chemerin-derived peptides suppress inflammation through ChemR23. J. Exp. Med. 205, 767–775. [52] Bondue, B., De Henau, O., Luangsay, S., Devosse, T., de Nadai, P., et al. (2012) The chemerin/ChemR23 system does not affect the pro-inflammatory response of mouse and human macrophages ex vivo. PLoS One 7, e40043. [53] Lora, V., Bonaguri, C., Gisondi, P., Sandei, F., Battistelli, L., et al. (2013) Autoantibody induction and adipokine levels in patients with psoriasis treated with infliximab. Immunol. Res. 56, 382–389. [54] Banas, M., Zabieglo, K., Kasetty, G., Kapinska-Mrowiecka, M., Borowczyk, J., et al. (2013) Chemerin is an antimicrobial agent in human epidermis. PLoS One 8, e58709. [55] Pachynski, R. K., Zabel, B. A., Kohrt, H. E., Tejeda, N. M., Monnier, J., et al. (2012) The chemoattractant chemerin suppresses melanoma by recruiting natural killer cell antitumor defenses. J. Exp. Med. 209, 1427–1435.
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