Clinical Science (2014) 127, 423–433 (Printed in Great Britain) doi: 10.1042/CS20140075

Role of the potassium channel KCa3.1 in diabetic nephropathy Chunling HUANG∗ †, Carol A. POLLOCK∗ and Xin-Ming CHEN∗

www.clinsci.org

∗ Kolling Institute of Medical Research, Sydney Medical School, University of Sydney, Royal North Shore Hospital, St Leonards, NSW 2065, Australia †Xiamen Center of Clinical Laboratory, Xiamen Zhongshan Hospital, Medical College of Xiamen University, Xiamen 361004, China

Abstract There is an urgent need to identify novel interventions for mitigating the progression of diabetic nephropathy. Diabetic nephropathy is characterized by progressive renal fibrosis, in which tubulointerstitial fibrosis has been shown to be the final common pathway of all forms of chronic progressive renal disease, including diabetic nephropathy. Therefore targeting the possible mechanisms that drive this process may provide novel therapeutics which allow the prevention and potentially retardation of the functional decline in diabetic nephropathy. Recently, the Ca2 + -activated K + channel KCa 3.1 (KCa3.1) has been suggested as a potential therapeutic target for nephropathy, based on its ability to regulate Ca2 + entry into cells and modulate Ca2 + -signalling processes. In the present review, we focus on the physiological role of KCa 3.1 in those cells involved in the tubulointerstitial fibrosis, including proximal tubular cells, fibroblasts, inflammatory cells (T-cells and macrophages) and endothelial cells. Collectively these studies support further investigation into KCa 3.1 as a therapeutic target in diabetic nephropathy. Key words: diabetic nephropathy, calcium-activated potassium channel, inflammatory cell, KCa 3.1, kidney, renal fibrosis

Clinical Science

INTRODUCTION Diabetic nephropathy is a major cause of ESKD (end-stage kidney disease) and premature mortality, affecting approximately 30 % of patients with diabetes mellitus. Although strategies such as glycaemic control, blood pressure control and inhibition of the renin–angiotensin–aldosterone system have been shown to be effective, the number of patients with diabetes that ultimately develop progressive renal disease remains high [1]. Therefore it is of utmost importance to discover novel therapeutic targets that prevent and retard the progression of diabetic nephropathy [2]. Progressive renal fibrosis is an important characteristic of diabetic nephropathy and is believed to be an important component of the pathogenesis leading to chronic kidney disease and ultimately ESKD. Studies suggest that tubulointerstitial fibrosis is the final common pathway of almost all forms of chronic progressive renal disease, including diabetic nephropathy [3]. Although the glomerulus has been at the centre of attention as the primary site of injury that characterizes diabetic nephropathy [4], tubulointerstitial fibrosis has been shown to be the strongest morphological

predicator of clinical outcome and the best correlate with the progression of diabetic nephropathy [5]. With the realization that the degree of tubulointerstitial fibrosis is the most tightly linked to the rate of progression of renal dysfunction, interest has focused on the possible mechanisms that may drive this process.

OVERVIEW OF K Ca 3.1 (KCa3.1) Ca2 + -activated K + channels link Ca2 + -signalling pathways to changes in membrane potential that are critically required for various cellular processes. Physiological and pharmacological analyses have subdivided Ca2 + -activated K + channels into three groups: small-conductance (SKCa , ∼4–14 pS), intermediateconductance (IKCa , ∼32–39 pS) and large-conductance (BKCa , ∼200–300 pS) channels. The intermediate-conductance Ca2 + activated K + channel KCa 3.1 (also known as IK1, SK4 or KCNN4) has a single-channel conductance which is larger than the conductance of the SKCa channels (KCa 2.1– KCa 2.3)

Abbreviations: AGE, advanced glycation end-product; AP-1, activation protein-1; bFGF, basic fibroblast growth factor; CCL20, CC chemokine ligand 20; CTGF, connective tissue growth factor; CTL, clotrimazole; ECM, extracellular matrix; EDHF, endothelium-derived hyperpolarization factor; EMT, epithelial–mesenchymal transition; EndMT, endothelial–mesenchymal transition; ESKD, end-stage kidney disease; MCP-1, monocyte chemoattractant protein-1; MTMR6, myotubularin-related protein 6; PDGF, platelet-derived growth factor; PKA, protein kinase A; REST, repressor element-1 silencing transcription factor; ROS, reactive oxygen species; α-SMA, α-smooth muscle actin; STZ, streptozotocin; TGF, transforming growth factor; UUO, unilateral ureteral obstruction. Correspondence: Professor Carol A. Pollock (email [email protected]).

 C The Authors Journal compilation  C 2014 Biochemical Society

423

C. Huang, C.A. Pollock and X.-M. Chen

but smaller than the conductance of BKCa channels (KCa 1.1). The channels exhibit 42–44 % sequence identity and 50–55 % similarity with the KCa 2 channels. KCa 3.1 is composed of six transmembrane domains with the pore region (S5–S6) containing the K + -selective amino acid sequence GYG, which is highly selective for K + ions. The S4 domain, containing only two positively charged amino acids, confers voltage sensitivity on the KV channels. Therefore KCa 3.1 is voltage-independent and requires only a small increase in intracellular Ca2 + to open and then maintain a negative membrane potential through K + efflux. At the transcription level, KCa 3.1 can be regulated by the transcription factors AP-1 (activation protein-1) (Fos/Jun), Ikaros-2 [6] and REST (repressor element-1 silencing transcription factor) [7]. Up-regulation of AP-1 and down-regulation of REST are associated with the up-regulation of KCa 3.1 [8–10]. At the protein level, KCa 3.1 can be directly activated by the binding of intracellular Ca2 + to calmodulin, a Ca2 + -binding protein that is constitutively associated with the C-terminus of the channel [11–14]. In addition, KCa 3.1 activity is increased by PKA (protein kinase A) [15] and NDPK-B (nucleoside diphosphate kinase-B) [16] and inhibited by PKC (protein kinase C) [17], arachidonic acid [18], MTMR6 (myotubularin-related protein 6) [16], the histidine phosphatase PHPT1 (phosphohistidine phosphatase 1) [19] and AMPK (AMP-activated protein kinase) [20]. KCa 3.1 was first described by Gardos [21] in erythrocytes in 1958 and has been demonstrated to be a target for sickle cell anaemia by preventing erythrocyte dehydration and regulating red blood cell volume [22,23]. Since KCa 3.1 was cloned by three groups in 1997 [24–26], its tissue distribution has been studied extensively. KCa 3.1 has been found to be widely expressed throughout the body, including placenta, lung, salivary gland, distal colon, prostate, lymphoid organs, endothelial cells and proliferating smooth muscle. In all of these tissues, KCa 3.1 is part of signalling cascades that involve relatively global and prolonged increases in Ca2 + during cell proliferation, secretion and volume regulation [27]. In blood vessels, KCa 3.1 drives not only the proliferation of dedifferentiated smooth muscle cells, but also the proliferation of microvascular and macrovascular endothelial cells [28,29]. Therefore KCa 3.1 has been proposed as a target for the treatment of cardiovascular diseases, such as restenosis of mechanically dilated arteries and atherosclerosis [9,30]. A numbers of reviews have documented its potential therapeutic role in vascular disease [31–33], which is of course a significant co-morbidity in diabetic nephropathy and hence targeting the channel may provide both vascular and renal protection. Furthermore KCa 3.1 has been demonstrated to be involved in the proliferation of several cancer cell lines, including GL-15 glioblastoma [34–36], MiaPaCa-2 and BXPC3 pancreatic carcinomas [37], MCF7 breast carcinoma [38], LNCaP and PC-3 prostate carcinoma [39], IGR1 melanoma [40] and HEC-1-A and KLE endometrial carcinomas [41], suggesting KCa 3.1 as a possible target for cancer therapy [42]. More recently, KCa 3.1 has also been identified within sensory neurons and microglia, leading to the proposal that this channel may constitute a therapeutic target in the central nervous system for acute and chronic neurodegenerative disorders, such as stroke and Alzheimer’s disease [43–46].

424

 C The Authors Journal compilation  C 2014 Biochemical Society

PHYSIOLOGICAL ROLE OF K Ca 3.1 IN DIABETIC NEPHROPATHY On the basis of the finding that KCa 3.1 is present in multiple cells implicated in tubulointerstitial fibrosis, including proximal tubular cells, fibroblasts, inflammatory cells (T-cells and macrophages) and endothelial cells, KCa 3.1 is considered as a potential target for diabetic nephropathy.

KCa 3.1 in tubular epithelial cells The most prominent cell type in the renal cortex is the proximal tubular epithelial cell, which is responsible for the reabsorption of fluid, glucose, amino acids and ions from the glomerular filtrate [47]. The renal proximal tubular epithelial cells are increasingly implicated in the pathogenesis of diabetic nephropathy [48–50]. Nephrotoxicity studies in animals have suggested that albuminuria is a highly sensitive marker of early tubular toxicity in the absence of glomerular pathology, which may occur as a consequence of decreased tubular reabsortion [51]. Under diabetic conditions, tubular epithelial cells can be activated by multiple pathways, including hyperglycaemia, AGEs (advanced glycation end-products) and ROS (reactive oxygen species), to induce proinflammatory and pro-fibrotic signalling events. The activated tubular cells synthesize inflammatory molecules such as MCP-1 (monocyte chemoattractant protein-1), IL-6 (interleukin-6) and CCL20 (CC chemokine ligand 20), as well as chemokines including TGF (transforming growth factor)-β1, which further lead to tubulointerstitial damage, interstitial inflammation and eventually renal failure [52–54]. In addition, it has been suggested that the activated tubular epithelial cells can undergo marked phenotypic changes, via EMT (epithelial–mesenchymal transition), and contribute to interstitial fibrosis [55]. There are some controversial reports, using genetic labelling techniques, which question whether the EMT process exists in vivo [56,57]. In contrast, Carew et al. [58] have provided convincing evidence that supports type II EMT as a direct contributor to the kidney myofibroblast population in the development of renal fibrosis. Therefore the role of EMT in renal fibrosis warrants further definitive investigation. Nonetheless, it is considered that renal proximal tubular epithelial cells play a critical and primary role in the genesis of diabetic nephropathy [59]. KCa 3.1 has been shown to be typically expressed on the basolateral membrane, providing a polarized pathway for K + flux, which helps to facilitate apical Cl − secretion and consequently water transport across the epithelia [60]. It has been demonstrated that activation of KCa 3.1 by pharmacological modulators results in increased transepithelial Cl − secretion across multiple epithelia (including bronchial and colonic epithelia), leading to the proposal that pharmacological modulation of this channel may be of therapeutic benefit in diseases such as cystic fibrosis and COPD (chronic obstructive pulmonary disease) [61– 64]. In renal epithelia, KCa 3.1 has also been demonstrated to be critical for cAMP-dependent Cl − secretion and cyst growth in autosomal-dominant polycystic kidney disease, which is regulated by cAMP, PKA and MTMR6 [65]. Most recently, our group has found increased expression of KCa 3.1 in kidneys of patients and animal models with diabetic nephropathy (Figure 1) [66].

Role of the potassium channel KCa 3.1 in diabetic nephropathy

Figure 1

Increased KCa 3.1 expression in kidneys of humans and mice with diabetic nephropathy (A) Immunohistochemical analysis demonstrated increased KCa 3.1 expression in kidney biopsies from patients with diabetic nephropathy (DM) compared with non-diabetic control kidneys (Non-DM control) (n = 8). (B) Quantification of KCa 3.1 expression in human biopsies. (C) Immunohistochemical analysis demonstrated that the expression of KCa 3.1 was increased in kidneys of diabetic KCa 3.1 + / + (K + / + DM) mice compared with normal mice (K + / + control). There is no KCa 3.1 expression in KCa 3.1 − / − mice (K − / − ) (n = 8). (E) Immunohistochemical analysis demonstrated increased KCa 3.1 expression in kidneys of diabetic eNOS − / − mice (DM + DMSO) compared with normal mice (Non-DM control) and TRAM34 suppressed KCa 3.1 expression in kidney of diabetic eNOS − / − mice (DM + TRAM34) (n = 6). eNOS, endothelial ∗ NO synthase. (D and F) Quantification of KCa 3.1 expression in mouse kidneys. Results are means + − S.E.M. P < 0.05 and ∗∗ P < 0.01. Original magnification, ×400. This Figure was published previously in Huang et al. Blockade of KCa3.1 ameliorates renal fibrosis through the TGF-β1/Smad pathway in diabetic mice. Diabetes 2013; 62:2923–2934. Copyright 2013 by the American Diabetes Association.

We have also demonstrated that inhibition of KCa 3.1 suppresses inflammatory and fibrotic responses in both in vitro studies of human proximal tubular cells and diabetic mouse models [67,68], indicating an important role of KCa 3.1 in diabetic tubulointerstitial fibrosis.

KCa 3.1 in renal fibroblasts Fibroblasts are localized in the interstitial space between the capillaries and the epithelia in normal kidneys [69]. They spread throughout the renal parenchyma to stabilize and organize the tissue architecture [70]. Morphological analyses have revealed that these fibroblasts are stellate shaped and display a rough endoplasmic reticulum, collagen-containing granules and actin filaments [71]. Under normal conditions, fibroblasts are responsible for homoeostasis of the interstitial matrix against physiological conditions by producing an essential basal level of ECM (extracellular matrix) components. Under diabetic conditions, these interstitial

fibroblasts become activated. Activated fibroblasts are characterized by two key features: proliferation and myofibroblastic activation. This fibroblast proliferation results in the expansion of the fibroblast population and ECM deposition in the interstitial space in damaged kidneys [71]. Following stimulation with pro-fibrotic cytokines including TGF-β, CTGF (connective tissue growth factor), PDGF (platelet-derived growth factor) and FGF2 (fibroblast growth factor 2) [72], these interstitial fibroblasts are activated and undergo phenotypic change into myofibroblasts by expressing α-SMA (α-smooth muscle actin), vimentin and FSP1 (fibroblast-specific protein 1), which were identified as the primary cell type responsible for interstitial matrix accumulation in fibrotic diseases, including the kidney [73,74]. It has been reported that, in addition to activated resident interstitial fibroblasts, myofibroblasts may also derive from tubular epithelial cells via EMT [75] or EndMT (endothelial–mesenchymal transition) [76], bone-marrow-derived fibrocytes [77] and perivascular fibroblasts [78].

 C The Authors Journal compilation  C 2014 Biochemical Society

425

C. Huang, C.A. Pollock and X.-M. Chen

Pena and Rane [79] were the first to clone and characterize KCa 3.1 in fibroblasts and called the channel FIK (fibroblast intermediate-conductance Ca2 + -activated K + channel). They also demonstrated that mitogenic stimulation by bFGF (basic fibroblast growth factor) or TGF-β leads to an increased expression of KCa 3.1 through activation of the Ras/MEK/ERK pathway [MEK is mitogen-activated protein kinase/ERK (extracellularsignal-regulated kinase) kinase], suggesting that KCa 3.1 positively regulates signalling pathways involved in cell proliferation in the fibroblast [80]. Similar to the finding reported by Pena and Rane [79], Grgic et al. [81] observed a robust up-regulation of KCa 3.1 in cultured renal fibroblasts induced by bFGF. Selective pharmacological inhibition of KCa 3.1 by TRAM34 was capable of suppressing mitogen-driven proliferation of renal fibroblasts via cell-cycle arrest in G0 /G1 [81]. Furthermore, genetic disruption of KCa 3.1 or pharmacological blockade of KCa 3.1 with TRAM34 significantly reduced renal fibrosis in mice following UUO (unilateral ureteral obstruction), indicating that induction of KCa 3.1 might constitute an important step for the initiation of renal fibroblast proliferation in response to mitogenic and profibrotic stimuli [81]. Most recently, our group has found that kidney fibroblast activation to myofibroblasts, characterized by acquisition of an α-SMA phenotype and increased ECM production, is regulated through KCa 3.1 [82]. Furthermore, blockade of KCa 3.1 normalizes regulators of matrix production and matrix protein expression induced in the diabetic milieu and thus reduces renal fibrosis. This has been demonstrated in mice with KCa 3.1 genetic deletion, as well as in mice treated with the pharmacological KCa 3.1 inhibitor TRAM34. The importance of KCa 3.1 in renal fibroblast mitogenesis is underpinned by its ability to enhance the driving force for Ca2 + influx via membrane hyperpolarization and thus allow a sustained elevation in intracellular Ca2 + concentration needed for gene transcription, as has been reported in vascular smooth muscle cells [83], T-cells [84] and cancer cells [37,38].

KCa 3.1 in inflammatory cells Diabetic nephropathy is increasingly considered as an inflammatory disease characterized by leucocyte and macrophage infiltration [85–87]. Leucocytes and macrophages are key inflammatory cells mediating kidney inflammation in experimental and human diabetes [52]. Activated T-cells and macrophages elaborate a host of pro-inflammatory, pro-fibrotic, and pro-angiogenic factors that contribute to the development and progression of diabetic nephropathy [52]. Nikolic-Paterson [88] has proposed three potential mechanisms by which CD4 + T-cells may promote renal fibrosis: “(i) T-cells may act directly on renal fibroblasts and pericytes (possibly via TGF-β1) to promote their migration, proliferation and differentiation, resulting in the accumulation of α-SMA + myofibroblasts, which synthesize and deposit interstitial matrix; (ii) T-cells may induce a pro-fibrotic phenotype in the infiltrating macrophage population, which, in turn, secrete proproliferative and pro-fibrotic cytokines and growth factors (for example, PDGF, TGF-β1 and CTGF) that induce fibroblast migration, proliferation and differentiation; and (iii) T-cells may act directly on tubular epithelial cells to induce the secretion of cytokines and growth factors that, in turn, act on fibroblasts.” Mac-

426

 C The Authors Journal compilation  C 2014 Biochemical Society

rophage accumulation in diabetic kidneys has been shown to predict declining renal function and macrophage-derived products can induce inflammation in the diabetic kidney [87,89]. Under diabetic conditions, high glucose and AGEs will increase the recruitment of macrophages and leucocytes to the kidney and stimulate them to produce ROS, cytokines and proteases, which lead to tissue injury and ultimately to fibrosis [90–92]. As mentioned above, KCa 3.1 is also expressed in T-cells and macrophages [93,94]. In T-cells, KCa 3.1 is believed to play an important role in the volume regulation, as they traverse the hyperosmolar environment of the renal medulla [95]. In addition, KCa 3.1 has been reported to be involved in lymphocyte apoptosis by mediating cell shrinkage in Ca2 + -induced apoptosis or P2X7-receptor stimulated cell death in lymphocytes [96,97]. Furthermore, KCa 3.1 also plays a key role in T-cell function during the immune response as it traffics to the immunological synapse to regulate cell potential and thus Ca2 + entry. On the basis of this, KCa 3.1 has become a significant target for immunosuppression, as has been extensively reviewed by Lam and Wulff [98]. KCa 3.1-mediated elevation of intracellular Ca2 + is necessary for the production of inflammatory chemokines and cytokines by T-cells, macrophages and mast cells [6,99]. Activation of KCa 3.1 is believed to contribute to migration, activation and proliferation of immunologically active cells [100], and the channel has therefore been proposed as a target for the treatment of autoimmune diseases [98,101]. The combination of TRAM34 with the KV 1.3-blocking peptide ShK was further shown to reduce T-cell and macrophage infiltration in the early stages of chronic kidney transplant rejection in rats [102], suggesting that KCa 3.1 blockers may represent a novel alternative therapy for prevention of kidney allograft rejection.

KCa 3.1 in endothelial cells Endothelial cells play an important role in maintaining renal function. Studies have also demonstrated that endothelial cells act as a source of renal fibroblasts via EndMT and hence contribute to diabetic interstitial fibrosis [76,103,104]. In the mouse model of STZ (streptozotocin)-induced diabetic nephropathy, Zeisberg et al. [103] found that 40–50 % of myofibroblasts co-expressed the endothelial cell marker CD31 and the (myo)fibroblast marker α-SMA, suggesting that these fibroblasts are probably of endothelial origin. Similarly, using an endothelial-lineage traceable mouse, Li et al. [76] also revealed the existence and contribution of EndMT in the early development of interstitial fibrosis in STZ-induced diabetic nephropathy. A recent report further confirmed that 10 % of myofibroblasts were derived through differentiation from EndMT in a mouse model of UUO [105]. Although the exact role of EndMT in renal fibrosis is unclear, these studies all indicate that endothelial cells might be an important contributor to renal fibrosis. KCa 3.1 has long been known to play a significant role in endothelial cell hyperpolarization and vasodilation [106–112], since KCa 3.1 was first identified and characterized in endothelial cells by Cai et al. [113] in 1998. KCa 3.1 has been shown to be expressed in the vascular endothelium of rodents, humans and pigs [114,115]. In the vascular endothelium, KCa 3.1 mediates the socalled ‘EDHF (endothelium-derived hyperpolarization factor)’

Role of the potassium channel KCa 3.1 in diabetic nephropathy

response, which has been recognized as an important vasodilator system along with NO and prostacyclin [31,114,116,117]. The activation of KCa 3.1 initiates hyperpolarization and subsequent EDHF responses, which leads to smooth muscle relaxation by closing voltage-gated Ca2 + channels, thus decreasing intracellular Ca2 + influx and finally producing relaxation and vasodilation [33]. Dysfunction of KCa 3.1 has therefore been implicated in endothelial dysfunction in many experimental models of vascular diseases, such as hypertension [109,118], and models of hypercholesterolaemia [119] and diabetes [120,121]. In vivo mice studies have confirmed that genetic deficiency of KCa 3.1 resulted in an increase in blood pressure [109,118]. Furthermore, EDHFmediated relaxation has been demonstrated to be impaired in small mesenteric arteries in animal models of diabetes which involve endothelial KCa 3.1 and/or KCa 2.3 channels [120,122–124]. Most recently, Zhao et al. [125] have demonstrated that AGEs impaired KCa 3.1- and KCa 2.3-mediated vasodilatation in rat mesenteric arteries via down-regulation of both KCa 3.1 and KCa 2.3 expression, which is associated with increased oxidative stress. It has been known that the EDHF-mediated vasodilatory pathways mediate endothelial dysfunction and abnormal arterial tone observed in human and experimental models of chronic renal failure [126,127]. Kohler et al. [128], using a 5/6-nephrectomized rat model, demonstrated that EDHF-dependent vasodilation is impaired in chronic renal failure in parallel with reduced endothelial mRNA expression of endothelial KCa 3.1 and/or KCa 2.3. In addition, several studies have suggested a role for KCa 3.1 in the regulation of the renal vasculature by influencing renal salt and water excretion, fluid homoeostasis and blood pressure [129]. In addition to its role in endothelium-dependent vasodilation and EDHF signalling, KCa 3.1 has also been implicated in endothelial cell proliferation. Grgic et al. [28] observed an upregulation KCa 3.1 mRNA expression in cultured endothelial cells following stimulation with VEGF (vascular endothelial growth factor) and bFGF. Blockade of KCa 3.1 suppressed in vitro endothelial cell proliferation and vascularization of MatrigelTM plugs in vivo, indicating that KCa 3.1 plays a direct role in endothelial cell proliferation associated with angiogenesis [28]. To date, the regulation of KCa 3.1 in endothelial dysfunction under diabetic conditions has not been reported. However, it is well accepted that diabetic nephropathy is a long-term major microvascular complication of uncontrolled hyperglycaemia, and endothelial dysfunction has been implicated as a potential major mechanism for renal chronic microvascular complications both in diabetic and non-diabetic patients with albuminuria [130,131]. Therefore it is proposed that KCa 3.1 also mediates the development of diabetic nephropathy through regulating endothelial dysfunction. However, further investigations are required in this regard.

PHARMACOLOGICAL BLOCKERS OF K Ca 3.1 The pharmacology of KCa 3.1 has been relatively well developed compared with other ion channels. Numerous blockers of KCa 3.1 have been developed, which include peptidic and non-peptidic inhibitors, providing an impressive toolbox for the identification of

the role of KCa 3.1 in complex tissues. Although the peptide blockers maurotoxin and charybdotoxin display the strongest potency, both of them are not selective for KCa 3.1 [132–134]. Several nonpeptidic molecules have been found to block KCa 3.1, such as the antimycotic triarylmethane CTL (clotrimazole) [135]. The poorly selective CTL has led to the production of several more effective KCa 3.1 blockers, including TRAM34 [84] and ICA-17043 (Senicapoc) [136]. TRAM34, synthesized by Wulff et al. [137] in 2000, is currently the most widely used pharmacological tool compound for investigating the biology of KCa 3.1 based on its high selectivity for KCa 3.1 and its availability to academic researchers. To date, TRAM34 has been tested in various animal models, including ischaemia/reperfusion in stroke [138] and restenosis [83] in rats, traumatic spinal cord injury [139], atherosclerosis [30] and inflammatory bowel disease [140] in mice, and angioplasty in pigs [9]. In vivo treatments with TRAM34 do not indicate any general toxicity of this compound. Daily administration of TRAM34 in a 28-day toxicity study in mice did not cause any discernible change in blood chemistry, haematology or necropsy of any of the major organs [30]. A subsequent 28-day or 6-month toxicity study with TRAM34 in rats also did not report any changes in these parameters [138]. ICA-17043, which is structurally similar to TRAM34, has proven to be safe and well-tolerated in a Phase I clinical trial in healthy volunteers [141] and was subsequently found to be both effective and safe in Phase II clinical trials in patients with sickle cell anaemia [23]. However, the Phase III trials of ICA-17 043 in sickle cell anaemia were halted due to a lack of efficacy in reducing sickling crises, despite no excess of significant adverse events [142]. Long-term pharmacological KCa 3.1 blockade with TRAM34 in mice and in dose-escalating studies with ICA-17 043 in 28 otherwise healthy patients with sickle cell disease did not increase blood pressure or lead to ECG changes [23,30,143].

CONCLUSIONS Given the current evidence, we propose that KCa 3.1 is a promising therapeutic target for diabetic nephropathy based on its expression and demonstrated role in fibrosis and inflammation in tubular epithelia, fibroblasts, inflammatory cells and endothelial cells, which are mechanically involved in the development of diabetic nephropathy. Our group has provided multiple lines of evidence that KCa 3.1 is implicated in diabetic nephropathy as summarized in Figure 2 [66–68,82]. First, we have demonstrated that KCa 3.1 expression is increased in both humans and in mice models with diabetic nephropathy. Subsequently, blockade of KCa 3.1 attenuated inflammation, regulators of matrix production and matrix protein expression, and thus reduces renal fibrosis in diabetic mice. Furthermore, we have demonstrated that KCa 3.1 plays an important role in the activation of renal fibroblasts in diabetic nephropathy. Blockade of KCa 3.1 suppressed the activation of myofibroblasts, as well as ECM production, in diabetic mice. Collectively, given that blockade of KCa 3.1 prevents the development of diabetic nephropathy through limiting inflammatory

 C The Authors Journal compilation  C 2014 Biochemical Society

427

C. Huang, C.A. Pollock and X.-M. Chen

Figure 2

Simplistic overview illustrating the role of KCa 3.1 in diabetic nephropathy ERK1/2, extracellular-signal-regulated kinase 1/2; NF-κB, nuclear factor κB.

and fibrotic responses in both proximal tubular cells and fibroblasts, future studies focusing on arresting or reversing established nephropathy, which more closely reflects clinical settings, are necessary. Since vascular endothelial dysfunction contributes to the progression of diabetic nephropathy, the role of KCa 3.1 in endothelial dysfunction under diabetic conditions needs to be defined. Thus targeting of KCa 3.1 in early but established diabetic nephropathy deserves further exploration. To date, KCa 3.1 appears to be safe as a therapeutic target. Two independently generated KCa 3.1 − / − mice [95,109] were both viable, of normal appearance, produced normal litter sizes, did not show any gross abnormalities in any of their major organs and exhibited rather mild phenotypes (impaired volume regulation in erythrocytes and lymphocytes and impaired EDHF response, together with a small increase in blood pressure) [27]. The selective KCa 3.1 blockers ICA-17043 and TRAM34 have also been found to be non-toxic, as discussed above. In our laboratory, we have administered TRAM34 at high doses to mice for up to 24 weeks without observing any adverse effects or any organ changes (C. Huang, J. Chen, C. A. Pollock and X.-M. Chen, unpublished work). Although the efficacy results from the sickle cell disease clinical trials were disappointing, it was clear that ICA-17043 is safe and well-tolerated in humans, and that it was biologically active at the doses given. Therefore additional development of these compounds to improve their specificity and bioavailability is desirable and would further validate these channels as novel drug targets in diabetic nephropathy.

FUNDING

Our own work was supported by Australian National Health and Medical Research Council [project grant number APP1025918] and a University of Sydney Postgraduate Award (to C.H.).

428

 C The Authors Journal compilation  C 2014 Biochemical Society

REFERENCES 1

2

3

4 5

6

7

8

9

Rosolowsky, E. T., Skupien, J., Smiles, A. M., Niewczas, M., Roshan, B., Stanton, R., Eckfeldt, J. H., Warram, J. H. and Krolewski, A. S. (2011) Risk for ESRD in type 1 diabetes remains high despite renoprotection. J. Am. Soc. Nephrol. 22, 545–553 CrossRef PubMed Wolf, G. and Ritz, E. (2003) Diabetic nephropathy in type 2 diabetes prevention and patient management. J. Am. Soc. Nephrol. 14, 1396–1405 CrossRef PubMed Zeisberg, M. and Neilson, E. G. (2010) Mechanisms of tubulointerstitial fibrosis. J. Am. Soc. Nephrol. 21, 1819–1834 CrossRef PubMed Fioretto, P. and Mauer, M. (2007) Histopathology of diabetic nephropathy. Semin. Nephrol. 27, 195–207 CrossRef PubMed Rodriguez-Iturbe, B., Johnson, R. J. and Herrera-Acosta, J. (2005) Tubulointerstitial damage and progression of renal failure. Kidney Int. Suppl., S82–S86 CrossRef Ghanshani, S., Wulff, H., Miller, M. J., Rohm, H., Neben, A., Gutman, G. A., Cahalan, M. D. and Chandy, K. G. (2000) Up-regulation of the IKCa1 potassium channel during T-cell activation. Molecular mechanism and functional consequences. J. Biol. Chem. 275, 37137–37149 CrossRef PubMed Cheong, A., Bingham, A. J., Li, J., Kumar, B., Sukumar, P., Munsch, C., Buckley, N. J., Neylon, C. B., Porter, K. E., Beech, D. J. and Wood, I. C. (2005) Downregulated REST transcription factor is a switch enabling critical potassium channel expression and cell proliferation. Mol. Cell 20, 45–52 CrossRef PubMed Park, S., Kim, J. A., Joo, K. Y., Choi, S., Choi, E. N., Shin, J. A., Han, K. H., Jung, S. C. and Suh, S. H. (2011) Globotriaosylceramide leads to KCa3.1 channel dysfunction: a new insight into endothelial dysfunction in Fabry disease. Cardiovasc. Res. 89, 290–299 CrossRef PubMed Tharp, D. L., Wamhoff, B. R., Wulff, H., Raman, G., Cheong, A. and Bowles, D. K. (2008) Local delivery of the KCa3.1 blocker, TRAM-34, prevents acute angioplasty-induced coronary smooth muscle phenotypic modulation and limits stenosis. Arterioscler. Thromb. Vasc. Biol. 28, 1084–1089 CrossRef PubMed

Role of the potassium channel KCa 3.1 in diabetic nephropathy

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

Ohya, S., Niwa, S., Kojima, Y., Sasaki, S., Sakuragi, M., Kohri, K. and Imaizumi, Y. (2011) Intermediate-conductance Ca2 + -activated K + channel, KCa3.1, as a novel therapeutic target for benign prostatic hyperplasia. J. Pharmacol. Exp. Ther. 338, 528–536 CrossRef PubMed Xia, X. M., Fakler, B., Rivard, A., Wayman, G., Johnson-Pais, T., Keen, J. E., Ishii, T., Hirschberg, B., Bond, C. T., Lutsenko, S. et al. (1998) Mechanism of calcium gating in smallconductance calcium-activated potassium channels. Nature 395, 503–507 CrossRef PubMed Fanger, C. M., Ghanshani, S., Logsdon, N. J., Rauer, H., Kalman, K., Zhou, J., Beckingham, K., Chandy, K. G., Cahalan, M. D. and Aiyar, J. (1999) Calmodulin mediates calciumdependent activation of the intermediate conductance KCa channel, IKCa1. J. Biol. Chem. 274, 5746–5754 CrossRef PubMed Keen, J. E., Khawaled, R., Farrens, D. L., Neelands, T., Rivard, A., Bond, C. T., Janowsky, A., Fakler, B., Adelman, J. P. and Maylie, J. (1999) Domains responsible for constitutive and Ca2 + -dependent interactions between calmodulin and small conductance Ca2 + -activated potassium channels. J. Neurosci. 19, 8830–8838 PubMed Li, W., Halling, D. B., Hall, A. W. and Aldrich, R. W. (2009) EF hands at the N-lobe of calmodulin are required for both SK channel gating and stable SK-calmodulin interaction. J. Gen. Physiol. 134, 281–293 CrossRef PubMed Gerlach, A. C., Gangopadhyay, N. N. and Devor, D. C. (2000) Kinase-dependent regulation of the intermediate conductance, calcium-dependent potassium channel, hIK1. J. Biol. Chem. 275, 585–598 CrossRef PubMed Srivastava, S., Li, Z., Ko, K., Choudhury, P., Albaqumi, M., Johnson, A. K., Yan, Y., Backer, J. M., Unutmaz, D., Coetzee, W. A. and Skolnik, E. Y. (2006) Histidine phosphorylation of the potassium channel KCa3.1 by nucleoside diphosphate kinase B is required for activation of KCa3.1 and CD4 T cells. Mol. Cell 24, 665–675 CrossRef PubMed Wulf, A. and Schwab, A. (2002) Regulation of a calciumsensitive K + channel (cIK1) by protein kinase C. J. Membr. Biol. 187, 71–79 CrossRef PubMed Hamilton, K. L., Syme, C. A. and Devor, D. C. (2003) Molecular localization of the inhibitory arachidonic acid binding site to the pore of hIK1. J. Biol. Chem. 278, 16690–16697 CrossRef PubMed Srivastava, S., Zhdanova, O., Di, L., Li, Z., Albaqumi, M., Wulff, H. and Skolnik, E. Y. (2008) Protein histidine phosphatase 1 negatively regulates CD4 T cells by inhibiting the K + channel KCa3.1. Proc. Natl. Acad. Sci. U.S.A. 105, 14442–14446 CrossRef PubMed Klein, H., Garneau, L., Trinh, N. T., Prive, A., Dionne, F., Goupil, E., Thuringer, D., Parent, L., Brochiero, E. and Sauve, R. (2009) Inhibition of the KCa3.1 channels by AMP-activated protein kinase in human airway epithelial cells. Am. J. Physiol. Cell Physiol. 296, C285–C295 CrossRef PubMed Gardos, G. (1958) The function of calcium in the potassium permeability of human erythrocytes. Biochim. Biophys. Acta 30, 653–654 CrossRef PubMed Nagalla, S. and Ballas, S. K. (2012) Drugs for preventing red blood cell dehydration in people with sickle cell disease. Cochrane Database Syst. Rev. 7, CD003426 PubMed Ataga, K. I., Smith, W. R., De Castro, L. M., Swerdlow, P., Saunthararajah, Y., Castro, O., Vichinsky, E., Kutlar, A., Orringer, E. P., Rigdon, G. C. et al. (2008) Efficacy and safety of the Gardos channel blocker, senicapoc (ICA-17043), in patients with sickle cell anemia. Blood 111, 3991–3997 CrossRef PubMed Joiner, W. J., Wang, L. Y., Tang, M. D. and Kaczmarek, L. K. (1997) hSK4, a member of a novel subfamily of calciumactivated potassium channels. Proc. Natl. Acad. Sci. U.S.A. 94, 11013–11018 CrossRef PubMed

25

26

27

28

29

30

31

32

33

34

35

36

37

38

Ishii, T. M., Silvia, C., Hirschberg, B., Bond, C. T., Adelman, J. P. and Maylie, J. (1997) A human intermediate conductance calcium-activated potassium channel. Proc. Natl. Acad. Sci. U.S.A. 94, 11651–11656 CrossRef PubMed Logsdon, N. J., Kang, J., Togo, J. A., Christian, E. P. and Aiyar, J. (1997) A novel gene, hKCa4, encodes the calcium-activated potassium channel in human T lymphocytes. J. Biol. Chem. 272, 32723–32726 CrossRef PubMed Wulff, H., Kolski-Andreaco, A., Sankaranarayanan, A., Sabatier, J. M. and Shakkottai, V. (2007) Modulators of small- and intermediate-conductance calcium-activated potassium channels and their therapeutic indications. Curr. Med. Chem. 14, 1437–1457 CrossRef PubMed Grgic, I., Eichler, I., Heinau, P., Si, H., Brakemeier, S., Hoyer, J. and Kohler, R. (2005) Selective blockade of the intermediateconductance Ca2 + -activated K + channel suppresses proliferation of microvascular and macrovascular endothelial cells and angiogenesis in vivo. Arterioscler. Thromb. Vasc. Biol. 25, 704–709 CrossRef PubMed Su, X. L., Zhang, H., Yu, W., Wang, S. and Zhu, W. J. (2013) Role of KCa3.1 channels in proliferation and migration of vascular smooth muscle cells by diabetic rat serum. Chin. J. Physiol. 56, 155–162 PubMed Toyama, K., Wulff, H., Chandy, K. G., Azam, P., Raman, G., Saito, T., Fujiwara, Y., Mattson, D. L., Das, S., Melvin, J. E. et al. (2008) The intermediate-conductance calcium-activated potassium channel KCa3.1 contributes to atherogenesis in mice and humans. J. Clin. Invest. 118, 3025–3037 CrossRef PubMed Kohler, R., Kaistha, B. P. and Wulff, H. (2010) Vascular KCa-channels as therapeutic targets in hypertension and restenosis disease. Expert Opin. Ther. Targets. 14, 143–155 CrossRef PubMed Tharp, D. L. and Bowles, D. K. (2009) The intermediateconductance Ca2 + -activated K + channel (KCa3.1) in vascular disease. Cardiovasc. Hematol. Agents Med. Chem. 7, 1–11 CrossRef PubMed Wulff, H. and Kohler, R. (2013) Endothelial small-conductance and intermediate-conductance KCa channels: an update on their pharmacology and usefulness as cardiovascular targets. J. Cardiovasc. Pharmacol. 61, 102–112 CrossRef PubMed Fioretti, B., Castigli, E., Micheli, M. R., Bova, R., Sciaccaluga, M., Harper, A., Franciolini, F. and Catacuzzeno, L. (2006) Expression and modulation of the intermediate- conductance Ca2 + -activated K + channel in glioblastoma GL-15 cells. Cell. Physiol. Biochem. 18, 47–56 CrossRef PubMed Ruggieri, P., Mangino, G., Fioretti, B., Catacuzzeno, L., Puca, R., Ponti, D., Miscusi, M., Franciolini, F., Ragona, G. and Calogero, A. (2012) The inhibition of KCa3.1 channels activity reduces cell motility in glioblastoma derived cancer stem cells. PLoS ONE 7, e47825 CrossRef PubMed Catacuzzeno, L., Fioretti, B. and Franciolini, F. (2012) Expression and role of the intermediate-conductance calcium-activated potassium channel KCa 3.1 in glioblastoma. J. Signal Transduct. 2012, 421564 CrossRef PubMed Jager, H., Dreker, T., Buck, A., Giehl, K., Gress, T. and Grissmer, S. (2004) Blockage of intermediate-conductance Ca2 + activated K + channels inhibit human pancreatic cancer cell growth in vitro. Mol. Pharmacol. 65, 630–638 CrossRef PubMed Ouadid-Ahidouch, H., Roudbaraki, M., Delcourt, P., Ahidouch, A., Joury, N. and Prevarskaya, N. (2004) Functional and molecular identification of intermediate-conductance Ca2 + -activated K + channels in breast cancer cells: association with cell cycle progression. Am. J. Physiol. Cell Physiol. 287, C125–C134 CrossRef PubMed

 C The Authors Journal compilation  C 2014 Biochemical Society

429

C. Huang, C.A. Pollock and X.-M. Chen

39

40

41

42

43

44

45

46

47

48

49

50

51

52 53

54

55

56

430

Parihar, A. S., Coghlan, M. J., Gopalakrishnan, M. and Shieh, C. C. (2003) Effects of intermediate-conductance Ca2 + activated K + channel modulators on human prostate cancer cell proliferation. Eur. J. Pharmacol. 471, 157–164 CrossRef PubMed Tajima, N., Schonherr, K., Niedling, S., Kaatz, M., Kanno, H., Schonherr, R. and Heinemann, S. H. (2006) Ca2 + -activated K + channels in human melanoma cells are up-regulated by hypoxia involving hypoxia-inducible factor-1α and the von Hippel-Lindau protein. J. Physiol. 571, 349–359 CrossRef PubMed Wang, Z. H., Shen, B., Yao, H. L., Jia, Y. C., Ren, J., Feng, Y. J. and Wang, Y. Z. (2007) Blockage of intermediate-conductanceCa2 + -activated K + channels inhibits progression of human endometrial cancer. Oncogene 26, 5107–5114 CrossRef PubMed Chou, C. C., Lunn, C. A. and Murgolo, N. J. (2008) KCa 3.1: target and marker for cancer, autoimmune disorder and vascular inflammation? Expert Rev. Mol. Diagn. 8, 179–187 CrossRef PubMed Maezawa, I., Jenkins, D. P., Jin, B. E. and Wulff, H. (2012) Microglial KCa 3.1 channels as a potential therapeutic target for Alzheimer’s disease. Int. J. Alzheimers Dis. 2012, 868972 PubMed Kuiper, E. F., Nelemans, A., Luiten, P., Nijholt, I., Dolga, A. and Eisel, U. (2012) KCa2 and KCa3 channels in learning and memory processes, and neurodegeneration. Front. Pharmacol. 3, 107 CrossRef PubMed Wulff, H. and Zhorov, B. S. (2008) K + channel modulators for the treatment of neurological disorders and autoimmune diseases. Chem. Rev. 108, 1744–1773 CrossRef PubMed Maljevic, S. and Lerche, H. (2013) Potassium channels: a review of broadening therapeutic possibilities for neurological diseases. J. Neurol. 260, 2201–2211 CrossRef PubMed Jenkin, K. A., Verty, A. N., McAinch, A. J. and Hryciw, D. H. (2012) Endocannabinoids and the renal proximal tubule: an emerging role in diabetic nephropathy. Int. J. Biochem. Cell Biol. 44, 2028–2031 CrossRef PubMed Tang, S. C. and Lai, K. N. (2012) The pathogenic role of the renal proximal tubular cell in diabetic nephropathy. Nephrol. Dial. Transplant. 27, 3049–3056 CrossRef PubMed Vallon, V. (2011) The proximal tubule in the pathophysiology of the diabetic kidney. Am. J. Physiol. Regul. Integr. Comp. Physiol. 300, R1009–R1022 CrossRef PubMed Kaissling, B., Lehir, M. and Kriz, W. (2013) Renal epithelial injury and fibrosis. Biochim. Biophys. Acta 1832, 931–939 CrossRef PubMed Yu, Y., Jin, H., Holder, D., Ozer, J. S., Villarreal, S., Shughrue, P., Shi, S., Figueroa, D. J., Clouse, H., Su, M. et al. (2010) Urinary biomarkers trefoil factor 3 and albumin enable early detection of kidney tubular injury. Nat. Biotechnol. 28, 470–477 CrossRef PubMed Lim, A. K. and Tesch, G. H. (2012) Inflammation in diabetic nephropathy. Mediators Inflamm. 2012, 146154 PubMed Wada, J. and Makino, H. (2013) Inflammation and the pathogenesis of diabetic nephropathy. Clin. Sci. 124, 139–152 CrossRef PubMed Qi, W., Chen, X., Zhang, Y., Holian, J., Mreich, E., Gilbert, R. E., Kelly, D. J. and Pollock, C. A. (2007) High glucose induces macrophage inflammatory protein-3α in renal proximal tubule cells via a transforming growth factor-β1 dependent mechanism. Nephrol. Dial. Transplant. 22, 3147–3153 CrossRef PubMed Liu, Y. (2004) Epithelial to mesenchymal transition in renal fibrogenesis: pathologic significance, molecular mechanism, and therapeutic intervention. J. Am. Soc. Nephrol. 15, 1–12 CrossRef PubMed Kriz, W., Kaissling, B. and Le Hir, M. (2011) Epithelial-mesenchymal transition (EMT) in kidney fibrosis: fact or fantasy? J. Clin. Invest. 121, 468–474 CrossRef PubMed

 C The Authors Journal compilation  C 2014 Biochemical Society

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72 73

74

75

Fragiadaki, M. and Mason, R. M. (2011) Epithelialmesenchymal transition in renal fibrosis: evidence for and against. Int. J. Exp. Pathol. 92, 143–150 CrossRef PubMed Carew, R. M., Wang, B. and Kantharidis, P. (2012) The role of EMT in renal fibrosis. Cell Tissue Res. 347, 103–116 CrossRef PubMed Bonventre, J. V. (2012) Can we target tubular damage to prevent renal function decline in diabetes? Semin. Nephrol. 32, 452–462 Halm, S. T., Liao, T. and Halm, D. R. (2006) Distinct K + conductive pathways are required for Cl- and K + secretion across distal colonic epithelium. Am. J. Physiol. Cell Physiol. 291, C636–C648 CrossRef PubMed Mall, M., Gonska, T., Thomas, J., Schreiber, R., Seydewitz, H. H., Kuehr, J., Brandis, M. and Kunzelmann, K. (2003) Modulation of Ca2 + -activated Cl − secretion by basolateral K + channels in human normal and cystic fibrosis airway epithelia. Pediatr. Res. 53, 608–618 CrossRef PubMed Singh, S., Syme, C. A., Singh, A. K., Devor, D. C. and Bridges, R. J. (2001) Benzimidazolone activators of chloride secretion: potential therapeutics for cystic fibrosis and chronic obstructive pulmonary disease. J. Pharmacol. Exp. Ther. 296, 600–611 PubMed Wang, J., Haanes, K. A. and Novak, I. (2013) Purinergic regulation of CFTR and Ca2 + -activated Cl − channels and K + channels in human pancreatic duct epithelium. Am. J. Physiol. Cell Physiol. 304, C673–C684 CrossRef PubMed Nanda Kumar, N. S., Singh, S. K. and Rajendran, V. M. (2010) Mucosal potassium efflux mediated via Kcnn4 channels provides the driving force for electrogenic anion secretion in colon. Am. J. Physiol. Gastrointest. Liver Physiol. 299, G707–G714 CrossRef PubMed Albaqumi, M., Srivastava, S., Li, Z., Zhdnova, O., Wulff, H., Itani, O., Wallace, D. P. and Skolnik, E. Y. (2008) KCa3.1 potassium channels are critical for cAMP-dependent chloride secretion and cyst growth in autosomal-dominant polycystic kidney disease. Kidney Int. 74, 740–749 CrossRef PubMed Huang, C., Shen, S., Ma, Q., Chen, J., Gill, A., Pollock, C. A. and Chen, X. M. (2013) Blockade of KCa3.1 ameliorates renal fibrosis through the TGF-β1/Smad pathway in diabetic mice. Diabetes. 62, 2923–2934 CrossRef PubMed Huang, C., Day, M. L., Poronnik, P., Pollock, C. A. and Chen, X. M. (2014) Inhibition of KCa3.1 suppresses TGF-β1 induced MCP-1 expression in human proximal tubular cells through Smad3, p38 and ERK1/2 signaling pathways. Int. J. Biochem. Cell Biol. 47, 1–10 CrossRef PubMed Huang, C., Pollock, C. A. and Chen, X. M. (2014) High glucose induces CCL20 in proximal tubular cells via activation of the KCa3.1 channel. PLoS ONE 9, e95173 CrossRef PubMed Kanasaki, K., Taduri, G. and Koya, D. (2013) Diabetic nephropathy: the role of inflammation in fibroblast activation and kidney fibrosis. Front. Endocrinol. (Lausanne) 4, 7 PubMed Kaissling, B. and Le Hir, M. (2008) The renal cortical interstitium: morphological and functional aspects. Histochem. Cell Biol. 130, 247–262 CrossRef PubMed Strutz, F. and Zeisberg, M. (2006) Renal fibroblasts and myofibroblasts in chronic kidney disease. J. Am. Soc. Nephrol. 17, 2992–2998 CrossRef PubMed Liu, Y. (2011) Cellular and molecular mechanisms of renal fibrosis. Nat. Rev. Nephrol. 7, 684–696 CrossRef PubMed Hinz, B. (2007) Formation and function of the myofibroblast during tissue repair. J. Invest. Dermatol. 127, 526–537 CrossRef PubMed Barnes, J. L. and Gorin, Y. (2011) Myofibroblast differentiation during fibrosis: role of NAD(P)H oxidases. Kidney Int. 79, 944–956 CrossRef PubMed Yamashita, S., Maeshima, A. and Nojima, Y. (2005) Involvement of renal progenitor tubular cells in epithelial-to-mesenchymal transition in fibrotic rat kidneys. J. Am. Soc. Nephrol. 16, 2044–2051 CrossRef PubMed

Role of the potassium channel KCa 3.1 in diabetic nephropathy

76

77

78

79

80

81

82

83

84

85

86

87

88 89

90

91

92

Li, J., Qu, X. and Bertram, J. F. (2009) Endothelial-myofibroblast transition contributes to the early development of diabetic renal interstitial fibrosis in streptozotocin-induced diabetic mice. Am. J. Pathol. 175, 1380–1388 CrossRef PubMed Li, J., Deane, J. A., Campanale, N. V., Bertram, J. F. and Ricardo, S. D. (2007) The contribution of bone marrow-derived cells to the development of renal interstitial fibrosis. Stem Cells. 25, 697–706 CrossRef PubMed Lin, S. L., Kisseleva, T., Brenner, D. A. and Duffield, J. S. (2008) Pericytes and perivascular fibroblasts are the primary source of collagen-producing cells in obstructive fibrosis of the kidney. Am. J. Pathol. 173, 1617–1627 CrossRef PubMed Pena, T. L. and Rane, S. G. (1999) The fibroblast intermediate conductance KCa channel, FIK, as a prototype for the cell growth regulatory function of the IK channel family. J. Membr. Biol. 172, 249–257 CrossRef PubMed Pena, T. L., Chen, S. H., Konieczny, S. F. and Rane, S. G. (2000) Ras/MEK/ERK Up-regulation of the fibroblast KCa channel FIK is a common mechanism for basic fibroblast growth factor and transforming growth factor-β suppression of myogenesis. J. Biol. Chem. 275, 13677–13682 CrossRef PubMed Grgic, I., Kiss, E., Kaistha, B. P., Busch, C., Kloss, M., Sautter, J., Muller, A., Kaistha, A., Schmidt, C., Raman, G. et al. (2009) Renal fibrosis is attenuated by targeted disruption of KCa3.1 potassium channels. Proc. Natl. Acad. Sci. U.S.A. 106, 14518–14523 CrossRef PubMed Huang, C., Shen, S., Ma, Q., Gill, A., Pollock, C. A. and Chen, X. M. (2014) KCa3.1 mediates activation of fibroblasts in diabetic renal interstitial fibrosis. Nephrol. Dial. Transplant. 29, 313–324 CrossRef PubMed Kohler, R., Wulff, H., Eichler, I., Kneifel, M., Neumann, D., Knorr, A., Grgic, I., Kampfe, D., Si, H., Wibawa, J. et al. (2003) Blockade of the intermediate-conductance calcium-activated potassium channel as a new therapeutic strategy for restenosis. Circulation 108, 1119–1125 CrossRef PubMed Wulff, H., Miller, M. J., Hansel, W., Grissmer, S., Cahalan, M. D. and Chandy, K. G. (2000) Design of a potent and selective inhibitor of the intermediate-conductance Ca2 + -activated K + channel, IKCa1: a potential immunosuppressant. Proc. Natl. Acad. Sci. U.S.A. 97, 8151–8156 CrossRef PubMed Ruster, C. and Wolf, G. (2008) The role of chemokines and chemokine receptors in diabetic nephropathy. Front. Biosci. 13, 944–955 CrossRef PubMed Galkina, E. and Ley, K. (2006) Leukocyte recruitment and vascular injury in diabetic nephropathy. J. Am. Soc. Nephrol. 17, 368–377 CrossRef PubMed Nguyen, D., Ping, F., Mu, W., Hill, P., Atkins, R. C. and Chadban, S. J. (2006) Macrophage accumulation in human progressive diabetic nephropathy. Nephrology 11, 226–231 CrossRef PubMed Nikolic-Paterson, D. J. (2010) CD4 + T cells: a potential player in renal fibrosis. Kidney Int. 78, 333–335 CrossRef PubMed Chow, F., Ozols, E., Nikolic-Paterson, D. J., Atkins, R. C. and Tesch, G. H. (2004) Macrophages in mouse type 2 diabetic nephropathy: correlation with diabetic state and progressive renal injury. Kidney Int. 65, 116–128 CrossRef PubMed Hickey, F. B. and Martin, F. (2013) Diabetic kidney disease and immune modulation. Curr. Opin. Pharmacol. 13, 602–612 CrossRef PubMed Tesch, G. H. (2007) Role of macrophages in complications of type 2 diabetes. Clin. Exp. Pharmacol. Physiol. 34, 1016–1019 CrossRef PubMed Wu, C. C., Sytwu, H. K., Lu, K. C. and Lin, Y. F. (2011) Role of T cells in type 2 diabetic nephropathy. Exp. Diabetes Res. 2011, 514738 CrossRef PubMed

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

Hanley, P. J., Musset, B., Renigunta, V., Limberg, S. H., Dalpke, A. H., Sus, R., Heeg, K. M., Preisig-Muller, R. and Daut, J. (2004) Extracellular ATP induces oscillations of intracellular Ca2 + and membrane potential and promotes transcription of IL-6 in macrophages. Proc. Natl. Acad. Sci. U.S.A. 101, 9479–9484 CrossRef PubMed Ghanshani, S., Wulff, H., Miller, M. J., Rohm, H., Neben, A., Gutman, G. A., Cahalan, M. D. and Chandy, K. G. (2000) Up-regulation of the IKCa1 potassium channel during T-cell activation. Molecular mechanism and functional consequences. J. Biol. Chem. 275, 37137–37149 CrossRef PubMed Begenisich, T., Nakamoto, T., Ovitt, C. E., Nehrke, K., Brugnara, C., Alper, S. L. and Melvin, J. E. (2004) Physiological roles of the intermediate conductance, Ca2 + -activated potassium channel Kcnn4. J. Biol. Chem. 279, 47681–47687 CrossRef PubMed Elliott, J. I. and Higgins, C. F. (2003) IKCa1 activity is required for cell shrinkage, phosphatidylserine translocation and death in T lymphocyte apoptosis. EMBO Rep. 4, 189–194 CrossRef PubMed Taylor, S. R., Gonzalez-Begne, M., Dewhurst, S., Chimini, G., Higgins, C. F., Melvin, J. E. and Elliott, J. I. (2008) Sequential shrinkage and swelling underlie P2×7-stimulated lymphocyte phosphatidylserine exposure and death. J. Immunol. 180, 300–308 CrossRef PubMed Lam, J. and Wulff, H. (2011) The lymphocyte potassium channels Kv1.3 and KCa3.1 as targets for immunosuppression. Drug Dev. Res. 72, 573–584 CrossRef PubMed Cruse, G., Duffy, S. M., Brightling, C. E. and Bradding, P. (2006) Functional KCa3.1 K + channels are required for human lung mast cell migration. Thorax 61, 880–885 CrossRef PubMed Chung, I., Zelivyanskaya, M. and Gendelman, H. E. (2002) Mononuclear phagocyte biophysiology influences brain transendothelial and tissue migration: implication for HIV-1-associated dementia. J. Neuroimmunol. 122, 40–54 CrossRef PubMed Chandy, K. G., Wulff, H., Beeton, C., Pennington, M., Gutman, G. A. and Cahalan, M. D. (2004) K + channels as targets for specific immunomodulation. Trends Pharmacol. Sci. 25, 280–289 CrossRef PubMed Grgic, I., Wulff, H., Eichler, I., Flothmann, C., Kohler, R. and Hoyer, J. (2009) Blockade of T-lymphocyte KCa3.1 and Kv1.3 channels as novel immunosuppression strategy to prevent kidney allograft rejection. Transplant. Proc. 41, 2601–2606 CrossRef PubMed Zeisberg, E. M., Potenta, S. E., Sugimoto, H., Zeisberg, M. and Kalluri, R. (2008) Fibroblasts in kidney fibrosis emerge via endothelial-to-mesenchymal transition. J. Am. Soc. Nephrol. 19, 2282–2287 CrossRef PubMed Li, J. and Bertram, J. F. (2010) Endothelial-myofibroblast transition, a new player in diabetic renal fibrosis. Nephrology 15, 507–512 CrossRef PubMed LeBleu, V. S., Taduri, G., O’Connell, J., Teng, Y., Cooke, V. G., Woda, C., Sugimoto, H. and Kalluri, R. (2013) Origin and function of myofibroblasts in kidney fibrosis. Nat. Med. 19, 1047–1053 CrossRef PubMed Jiang, Z. G., Shi, X. R., Guan, B. C., Zhao, H. and Yang, Y. Q. (2007) Dihydropyridines inhibit acetylcholine-induced hyperpolarization in cochlear artery via blockade of intermediate-conductance calcium-activated potassium channels. J. Pharmacol. Exp. Ther. 320, 544–551 CrossRef PubMed Sheng, J. Z. and Braun, A. P. (2007) Small- and intermediateconductance Ca2 + -activated K + channels directly control agonist-evoked nitric oxide synthesis in human vascular endothelial cells. Am. J. Physiol. Cell Physiol. 293, C458–C467 CrossRef PubMed Gillham, J. C., Myers, J. E., Baker, P. N. and Taggart, M. J. (2007) Regulation of endothelial-dependent relaxation in human systemic arteries by SKCa and IKCa channels. Reprod. Sci. 14, 43–50 CrossRef PubMed

 C The Authors Journal compilation  C 2014 Biochemical Society

431

C. Huang, C.A. Pollock and X.-M. Chen

109

110

111

112

113

114

115

116

117

118

119

120

121

122

432

Si, H., Heyken, W. T., Wolfle, S. E., Tysiac, M., Schubert, R., Grgic, I., Vilianovich, L., Giebing, G., Maier, T., Gross, V. et al. (2006) Impaired endothelium-derived hyperpolarizing factor-mediated dilations and increased blood pressure in mice deficient of the intermediate-conductance Ca2 + -activated K + channel. Circ. Res. 99, 537–544 CrossRef PubMed Absi, M., Burnham, M. P., Weston, A. H., Harno, E., Rogers, M. and Edwards, G. (2007) Effects of methyl β-cyclodextrin on EDHF responses in pig and rat arteries; association between SKCa channels and caveolin-rich domains. Br. J. Pharmacol. 151, 332–340 CrossRef PubMed Sainsbury, C. A., Coleman, J., Brady, A. J., Connell, J. M., Hillier, C. and Petrie, J. R. (2007) Endothelium-dependent relaxation is resistant to inhibition of nitric oxide synthesis, but sensitive to blockade of calcium-activated potassium channels in essential hypertension. J. Hum. Hypertens. 21, 808–814 CrossRef PubMed Ceroni, L., Ellis, A., Wiehler, W. B., Jiang, Y. F., Ding, H. and Triggle, C. R. (2007) Calcium-activated potassium channel and connexin expression in small mesenteric arteries from eNOS-deficient (eNOS − / − ) and eNOS-expressing (eNOS + / + ) mice. Eur. J. Pharmacol. 560, 193–200 CrossRef PubMed Cai, S., Garneau, L. and Sauve, R. (1998) Single-channel characterization of the pharmacological properties of the K(Ca2 + ) channel of intermediate conductance in bovine aortic endothelial cells. J. Membr. Biol. 163, 147–158 CrossRef PubMed Grgic, I., Kaistha, B. P., Hoyer, J. and Kohler, R. (2009) Endothelial Ca2 + -activated K + channels in normal and impaired EDHF-dilator responses–relevance to cardiovascular pathologies and drug discovery. Br. J. Pharmacol. 157, 509–526 CrossRef PubMed Feletou, M. (2009) Calcium-activated potassium channels and endothelial dysfunction: therapeutic options? Br. J. Pharmacol. 156, 545–562 CrossRef PubMed Edwards, G., Feletou, M. and Weston, A. H. (2010) Endothelium-derived hyperpolarising factors and associated pathways: a synopsis. Pflugers Arch. 459, 863–879 CrossRef PubMed Dalsgaard, T., Kroigaard, C. and Simonsen, U. (2010) Calcium-activated potassium channels – a therapeutic target for modulating nitric oxide in cardiovascular disease? Expert Opin. Ther. Targets. 14, 825–837 CrossRef PubMed Brahler, S., Kaistha, A., Schmidt, V. J., Wolfle, S. E., Busch, C., Kaistha, B. P., Kacik, M., Hasenau, A. L., Grgic, I., Si, H. et al. (2009) Genetic deficit of SK3 and IK1 channels disrupts the endothelium-derived hyperpolarizing factor vasodilator pathway and causes hypertension. Circulation 119, 2323–2332 CrossRef PubMed Wolfle, S. E. and de Wit, C. (2005) Intact endotheliumdependent dilation and conducted responses in resistance vessels of hypercholesterolemic mice in vivo. J. Vasc. Res. 42, 475–482 CrossRef PubMed Brondum, E., Kold-Petersen, H., Simonsen, U. and Aalkjaer, C. (2010) NS309 restores EDHF-type relaxation in mesenteric small arteries from type 2 diabetic ZDF rats. Br. J. Pharmacol. 159, 154–165 CrossRef PubMed Matsumoto, T., Ishida, K., Taguchi, K., Kobayashi, T. and Kamata, K. (2010) Losartan normalizes endothelium-derived hyperpolarizing factor-mediated relaxation by activating Ca2 + -activated K + channels in mesenteric artery from type 2 diabetic GK rat. J. Pharmacol. Sci. 112, 299–309 CrossRef PubMed Ding, H., Hashem, M., Wiehler, W. B., Lau, W., Martin, J., Reid, J. and Triggle, C. (2005) Endothelial dysfunction in the streptozotocin-induced diabetic apoE-deficient mouse. Br. J. Pharmacol. 146, 1110–1118 CrossRef PubMed

 C The Authors Journal compilation  C 2014 Biochemical Society

123

124

125

126

127

128

129

130

131 132

133

134

135

136

137

138

Morikawa, K., Matoba, T., Kubota, H., Hatanaka, M., Fujiki, T., Takahashi, S., Takeshita, A. and Shimokawa, H. (2005) Influence of diabetes mellitus, hypercholesterolemia, and their combination on EDHF-mediated responses in mice. J. Cardiovasc. Pharmacol. 45, 485–490 CrossRef PubMed Weston, A. H., Absi, M., Harno, E., Geraghty, A. R., Ward, D. T., Ruat, M., Dodd, R. H., Dauban, P. and Edwards, G. (2008) The expression and function of Ca2 + -sensing receptors in rat mesenteric artery; comparative studies using a model of type II diabetes. Br. J. Pharmacol. 154, 652–662 CrossRef PubMed Zhao, L. M., Wang, Y., Ma, X. Z., Wang, N. P. and Deng, X. L. (2013) Advanced glycation end products impair KCa3.1- and KCa2.3-mediated vasodilatation via oxidative stress in rat mesenteric arteries. Pflugers Arch. 466, 307–317 CrossRef PubMed Martinez-Leon, J. B., Segarra, G., Medina, P., Vila, J. M., Lluch, P., Peiro, M., Otero, E. and Lluch, S. (2003) Ca2 + -activated K + channels mediate relaxation of forearm veins in chronic renal failure. J. Hypertens. 21, 1927–1934 CrossRef PubMed Kalliovalkama, J., Jolma, P., Tolvanen, J. P., Kahonen, M., Hutri-Kahonen, N., Saha, H., Tuorila, S., Moilanen, E. and Porsti, I. (1999) Potassium channel-mediated vasorelaxation is impaired in experimental renal failure. Am. J. Physiol. 277, H1622–H1629 PubMed Kohler, R., Eichler, I., Schonfelder, H., Grgic, I., Heinau, P., Si, H. and Hoyer, J. (2005) Impaired EDHF-mediated vasodilation and function of endothelial Ca-activated K channels in uremic rats. Kidney Int. 67, 2280–2287 CrossRef PubMed Sorensen, C. M., Braunstein, T. H., Holstein-Rathlou, N. H. and Salomonsson, M. (2012) Role of vascular potassium channels in the regulation of renal hemodynamics. Am. J. Physiol. Renal Physiol. 302, F505–F518 CrossRef PubMed Karalliedde, J. and Gnudi, L. (2011) Endothelial factors and diabetic nephropathy. Diabetes Care. 34 (Suppl. 2), S291–S296 CrossRef PubMed Forbes, J. M. and Cooper, M. E. (2013) Mechanisms of diabetic complications. Physiol. Rev. 93, 137–188 CrossRef PubMed Castle, N. A., London, D. O., Creech, C., Fajloun, Z., Stocker, J. W. and Sabatier, J. M. (2003) Maurotoxin: a potent inhibitor of intermediate conductance Ca2 + -activated potassium channels. Mol. Pharmacol. 63, 409–418 CrossRef PubMed Rauer, H., Lanigan, M. D., Pennington, M. W., Aiyar, J., Ghanshani, S., Cahalan, M. D., Norton, R. S. and Chandy, K. G. (2000) Structure-guided transformation of charybdotoxin yields an analog that selectively targets Ca2 + -activated over voltagegated K + channels. J. Biol. Chem. 275, 1201–1208 CrossRef PubMed Visan, V., Fajloun, Z., Sabatier, J. M. and Grissmer, S. (2004) Mapping of maurotoxin binding sites on hKv1.2, hKv1.3, and hIKCa1 channels. Mol. Pharmacol. 66, 1103–1112 CrossRef PubMed Alvarez, J., Montero, M. and Garcia-Sancho, J. (1992) High affinity inhibition of Ca2 + -dependent K + channels by cytochrome P-450 inhibitors. J. Biol. Chem. 267, 11789–11793 PubMed Stocker, J. W., De Franceschi, L., McNaughton-Smith, G. A., Corrocher, R., Beuzard, Y. and Brugnara, C. (2003) ICA-17043, a novel Gardos channel blocker, prevents sickled red blood cell dehydration in vitro and in vivo in SAD mice. Blood. 101, 2412–2418 CrossRef PubMed Wulff, H., Gutman, G. A., Cahalan, M. D. and Chandy, K. G. (2001) Delineation of the clotrimazole/TRAM-34 binding site on the intermediate conductance calcium-activated potassium channel, IKCa1. J. Biol. Chem. 276, 32040–32045 CrossRef PubMed Chen, Y. J., Raman, G., Bodendiek, S., O’Donnell, M. E. and Wulff, H. (2011) The KCa3.1 blocker TRAM-34 reduces infarction and neurological deficit in a rat model of ischemia/reperfusion stroke. J. Cereb. Blood Flow Metab. 31, 2363–2374 CrossRef PubMed

Role of the potassium channel KCa 3.1 in diabetic nephropathy

139

140

Bouhy, D., Ghasemlou, N., Lively, S., Redensek, A., Rathore, K. I., Schlichter, L. C. and David, S. (2011) Inhibition of the Ca2 + -dependent K + channel, KCNN4/KCa3.1, improves tissue protection and locomotor recovery after spinal cord injury. J. Neurosci. 31, 16298–16308 CrossRef PubMed Di, L., Srivastava, S., Zhdanova, O., Ding, Y., Li, Z., Wulff, H., Lafaille, M. and Skolnik, E. Y. (2010) Inhibition of the K + channel KCa3.1 ameliorates T cell-mediated colitis. Proc. Natl. Acad. Sci. U.S.A. 107, 1541–1546 CrossRef PubMed

141

142

143

Ataga, K. I., Orringer, E. P., Styles, L., Vichinsky, E. P., Swerdlow, P., Davis, G. A., Desimone, P. A. and Stocker, J. W. (2006) Dose-escalation study of ICA-17043 in patients with sickle cell disease. Pharmacotherapy 26, 1557–1564 CrossRef PubMed Wulff, H. and Castle, N. A. (2010) Therapeutic potential of KCa3.1 blockers: recent advances and promising trends. Expert Rev. Clin. Pharmacol. 3, 385–396 CrossRef PubMed Ataga, K. I. and Stocker, J. (2009) Senicapoc (ICA-17043): a potential therapy for the prevention and treatment of hemolysis-associated complications in sickle cell anemia. Expert Opin. Investig. Drugs 18, 231–239 CrossRef PubMed

Received 29 January 2014/24 March 2014; accepted 16 April 2014 Published on the Internet 17 June 2014, doi: 10.1042/CS20140075

 C The Authors Journal compilation  C 2014 Biochemical Society

433

Copyright of Clinical Science is the property of Portland Press Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.