International Journal of Cardiology 195 (2015) 45–47
Contents lists available at ScienceDirect
International Journal of Cardiology journal homepage: www.elsevier.com/locate/ijcard
Letter to the Editor
Moving with and beyond CANTOS: How to put out the fire of inflammation in atherosclerosis? Zhaohua Cai, Linghong Shen, Ben He ⁎ Department of Cardiology, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200127, China
a r t i c l e
i n f o
Article history: Received 6 May 2015 Accepted 19 May 2015 Available online 21 May 2015 Keywords: CANTOS IL-1β NLRP3 inflammasome Autophagy
Accumulating evidence indicates that inflammation contributes to all phases of atherogenesis from early endothelial dysfunction to advanced plaque rupture. Therefore, lowering inflammation may theoretically and practically reduce cardiovascular event rates. This hypothesis of the pivotal role of inflammation in atherosclerosis has now gained widespread recognition and been translated into clinical practice. Recently, two large-scale, randomized, placebo-controlled trials – CANTOS and CIRT – have been initiated. CANTOS strives to use canakiumab, a monoclonal antibody that selectively neutralizes interleukin-1 beta (IL-1β), to evaluate whether IL-1β inhibition can reduce rates of recurrent myocardial infarction, stroke, and cardiovascular death, based on the particularly substantive role of IL-1β in atherosclerosis [1]. It is the first large-scale clinical trial to test the inflammatory hypothesis of atherosclerosis and will provide insight into whether IL1β-mediated inflammation is a potential effective therapeutic target for atherosclerosis. Moving forward with CANTOS, however, there's still a clear and urgent need for reevaluating the anti-inflammatory strategies in atherosclerosis. Although the inflammatory nature of atherosclerosis is now firmly established, the origin/cause of inflammatory responses and the mechanism by which inflammation leads to atherosclerosis have presented a long-standing puzzle. Indeed, solving this puzzle may help put out the fire of inflammation in atherosclerosis. Recently, it's noted that cholesterol crystals might be the predominant endogenous danger signals that incite inflammation in atherosclerotic plaques via stimulating the caspase-1-activating NLRP3 inflammasome, which results in cleavage ⁎ Corresponding author. E-mail address: [email protected] (B. He).
http://dx.doi.org/10.1016/j.ijcard.2015.05.123 0167-5273/© 2015 Elsevier Ireland Ltd. All rights reserved.
and secretion of IL-1β and IL-18 and ultimately leads to increased production of other inflammatory cytokines [2,3]. Moreover, several lines of evidence revealed that autophagy regulates NLRP3 inflammasome activation and serves as a regulatory node of inflammation and lipid metabolism in atherosclerosis [4,5]. These findings have raised the possibility and led to efforts to develop novel anti-inflammatory strategies for prevention and treatment of atherosclerotic cardiovascular disease. The inflammasome is a multiprotein platform composed of NRLP3, ASC and procaspase-1, which cleaves the precursor forms of IL-1β and IL-18 into mature secreted forms when activated. The NRLP3 inflammasome has strongly been implicated in the pathogenesis of atherosclerosis during which it is abnormally activated. Cholesterol crystals are the predominant danger signal in atherosclerosis development to activate the NRLP3 inflammasome, mainly in lesional macrophages [2,3]. NLRP3 inflammasome has now emerged as a critical link between inflammation and cholesterol metabolism. Moreover, it's recently been demonstrated that low and oscillatory shear stress triggers NLRP3 inflammasome activation and incites inflammation in endothelial cells, resulting in endothelial dysfunction, which leads to subsequent genesis of atherosclerosis. This finding even links atheroprone flow induced-NLRP3 inflammasome activation between disturbed flow patterns and inflammation [6]. Therefore, the inflammasome NLRP3 has been regarded as a central regulator for inflammation in atherosclerosis. It has been well demonstrated that hypercholesterolemic Ldlr−/− mice reconstituted with bone marrow from NLRP3 −/− or ASC −/− mice exhibits smaller and more stable atherosclerotic lesions compared to those reconstituted with wild-type bone marrow. Moreover, recent researches demonstrated that the NLRP3 inflammasome inhibitor, Arglbin, exerts markedly anti-inflammatory and anti-atherosclerotic effects in atherosclerotic mice [7]. Meanwhile, various small-molecule inhibitors of the NLRP3 inflammasome have now been regarded as potential target for the treatment of inflammatory diseases, including atherosclerosis [8]. Obviously, modulating NLRP3 inflammasome presents certain advantages over the use of specific cytokine inhibitors, such as neutralizing IL-1β antibody Canakiumab, one just aiming at blocking the outcomes of inflammasome activation. Therefore, directly targeting NLRP3 inflammasome might represent a potential therapeutic target to treat atherosclerosis. Autophagy is an evolutionarily conserved process by which cytoplasmic components are sequestered by autophagosomes and subsequently degraded on fusion with lysosomes for recycling. Growing evidence reveals that basic autophagy is atheroprotective during the development of atherosclerosis [4,5,9]. However, macrophage autophagy
46
Z. Cai et al. / International Journal of Cardiology 195 (2015) 45–47
Fig. 1. Schematic depiction of the links between cholesterol metabolism, autophagy dysfunction, NLRP3 inflammasome hyperactivation and inflammatory boosts within atherosclerotic plaques.
becomes dysfunctional with atherosclerotic plaque progression. Mechanistically, lysosomal dysfunction is increasingly regarded as the major reason for defective autophagic flux and dysfunctional autophagy in atherosclerosis [10]. And these deficiencies contribute to hyperinflammatory states, abnormalities in cholesterol efflux, increased apoptosis and defective efferocytosis in lesional macrophages, leading to dramatic exacerbations of atherosclerosis [4,5,9]. Mounting evidence now supports the notion that macrophage autophagy might be the nexus between inflammatory signaling and lipid metabolism in atherosclerosis. Recently, it's demonstrated that macrophage autophagy plays a critical role in regulating activation of the NLRP3 inflammasome. Macrophage-specific deletion of ATG5 resulted in inflammasome hyperactivation and a dramatically increased burden of cholesterol crystal within atherosclerotic lesions [4]. These data suggest that defective autophagy may result in aberrant cholesterol crystal-induced NLRP3 inflammasome activation and IL-1β release and subsequent exacerbation of atherosclerosis. Autophagy can directly limit NLRP3 inflammasome activation by targeting ubiquitinated inflammasomes for destruction [11]. Moreover, autophagy can indirectly suppress the inflammasome activation by promoting cholesterol efflux and thus to oppose cholesterol crystal formation [5]. Lipophagy, a special kind of autophagy, regulates cholesterol efflux from foam cells via sequestering lipid droplets in autophagosomes that fuse with lysosomes for breakdown by lysosomal acid lipase [5]. Dysfunctional autophagy reduces cholesterol efflux and reverse cholesterol transport from lesional macrophages. As accumulating cholesterol in atherosclerotic plaques may give rise to cholesterol crystal formation, this will further indirectly results in inflammasome hyperactivation. Based on the emerging evidences strongly supporting the substantive role of autophagy in atherosclerosis, restoring or enhancing the autophagy function might help stabilize and reverse atherosclerotic plaque via inhibiting inflammasome activation and promoting cholesterol efflux. It has been demonstrated that overexpression of transcription factor EB, the only known transcription factor that drives the expression of lysosomal and autophagy genes, can rescue lysosome function and exert atheroprotective effects via reducing IL-1β secretion, enhancing cholesterol efflux, and decreasing polyubiquitinated protein aggregation [10]. Thus, this might have important implications for
future therapeutic interventions targeting lysosomal and autophagy function to treat atherosclerosis. In conclusion, this review highlights the huge potential for directly targeting NLRP3 inflammasome and autophagy for anti-inflammatory and anti-atherosclerotic treatment. Mounting evidence strongly reveals that during the development of atherosclerosis, cholesterol crystals lead to lysosomal dysfunction, which incites NLRP3 inflammasome hyperactivation and autophagy dysfunction, causing inflammatory boosts and abnormalities of cholesterol metabolism in lesional macrophages and creating a vicious cycle in atherosclerosis (Fig. 1). Therefore, interference with NLRP3 inflammasome and autophagy may ultimately put out the fire of inflammation in atherosclerosis. Conflict of interest The authors report no relationships that could be construed as a conflict of interest. References [1] P.M. Ridker, T. Thuren, A. Zalewski, P. Libby, Interleukin-1beta inhibition and the prevention of recurrent cardiovascular events: rationale and design of the Canakinumab Anti-inflammatory Thrombosis Outcomes Study (CANTOS), Am. Heart J. 162 (2011) 597–605. [2] P. Duewell, H. Kono, K.J. Rayner, C.M. Sirois, G. Vladimer, et al., NLRP3 inflammasomes are required for atherogenesis and activated by cholesterol crystals, Nature 464 (2010) 1357–1361. [3] K. Rajamaki, J. Lappalainen, K. Oorni, E. Valimaki, S. Matikainen, et al., Cholesterol crystals activate the NLRP3 inflammasome in human macrophages: a novel link between cholesterol metabolism and inflammation, PLos One 5 (2010) e11765. [4] B. Razani, C. Feng, T. Coleman, R. Emanuel, H. Wen, et al., Autophagy links inflammasomes to atherosclerotic progression, Cell Metab. 15 (2012) 534–544. [5] M. Ouimet, V. Franklin, E. Mak, X. Liao, I. Tabas, et al., Autophagy regulates cholesterol efflux from macrophage foam cells via lysosomal acid lipase, Cell Metab. 13 (2011) 655–667. [6] H. Xiao, M. Lu, T.Y. Lin, Z. Chen, G. Chen, et al., Sterol regulatory element binding protein 2 activation of NLRP3 inflammasome in endothelium mediates hemodynamicinduced atherosclerosis susceptibility, Circulation 128 (2013) 632–642. [7] A. Abderrazak, D. Couchie, D.F. Mahmood, R. Elhage, C. Vindis, et al., Antiinflammatory and antiatherogenic effects of the NLRP3 inflammasome inhibitor arglabin in ApoE2.Ki mice fed a high-fat diet, Circulation 131 (2015) 1061–1070.
Z. Cai et al. / International Journal of Cardiology 195 (2015) 45–47 [8] R.C. Coll, A.A. Robertson, J.J. Chae, S.C. Higgins, R. Munoz-Planillo, et al., A smallmolecule inhibitor of the NLRP3 inflammasome for the treatment of inflammatory diseases, Nat. Med. 21 (2015) 248–255. [9] X. Liao, J.C. Sluimer, Y. Wang, M. Subramanian, K. Brown, et al., Macrophage autophagy plays a protective role in advanced atherosclerosis, Cell Metab. 15 (2012) 545–553. [10] R. Emanuel, I. Sergin, S. Bhattacharya, J.N. Turner, S. Epelman, et al., Induction of lysosomal biogenesis in atherosclerotic macrophages can rescue lipid-induced
47
lysosomal dysfunction and downstream sequelae, Arterioscler. Thromb. Vasc. Biol. 34 (2014) 1942–1952. [11] C.S. Shi, K. Shenderov, N.N. Huang, J. Kabat, M. Abu-Asab, et al., Activation of autophagy by inflammatory signals limits IL-1beta production by targeting ubiquitinated inflammasomes for destruction, Nat. Immunol. 13 (2012) 255–263.
Contents lists available at ScienceDirect
International Journal of Cardiology journal homepage: www.elsevier.com/locate/ijcard
Letter to the Editor
Moving with and beyond CANTOS: How to put out the fire of inflammation in atherosclerosis? Zhaohua Cai, Linghong Shen, Ben He ⁎ Department of Cardiology, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200127, China
a r t i c l e
i n f o
Article history: Received 6 May 2015 Accepted 19 May 2015 Available online 21 May 2015 Keywords: CANTOS IL-1β NLRP3 inflammasome Autophagy
Accumulating evidence indicates that inflammation contributes to all phases of atherogenesis from early endothelial dysfunction to advanced plaque rupture. Therefore, lowering inflammation may theoretically and practically reduce cardiovascular event rates. This hypothesis of the pivotal role of inflammation in atherosclerosis has now gained widespread recognition and been translated into clinical practice. Recently, two large-scale, randomized, placebo-controlled trials – CANTOS and CIRT – have been initiated. CANTOS strives to use canakiumab, a monoclonal antibody that selectively neutralizes interleukin-1 beta (IL-1β), to evaluate whether IL-1β inhibition can reduce rates of recurrent myocardial infarction, stroke, and cardiovascular death, based on the particularly substantive role of IL-1β in atherosclerosis [1]. It is the first large-scale clinical trial to test the inflammatory hypothesis of atherosclerosis and will provide insight into whether IL1β-mediated inflammation is a potential effective therapeutic target for atherosclerosis. Moving forward with CANTOS, however, there's still a clear and urgent need for reevaluating the anti-inflammatory strategies in atherosclerosis. Although the inflammatory nature of atherosclerosis is now firmly established, the origin/cause of inflammatory responses and the mechanism by which inflammation leads to atherosclerosis have presented a long-standing puzzle. Indeed, solving this puzzle may help put out the fire of inflammation in atherosclerosis. Recently, it's noted that cholesterol crystals might be the predominant endogenous danger signals that incite inflammation in atherosclerotic plaques via stimulating the caspase-1-activating NLRP3 inflammasome, which results in cleavage ⁎ Corresponding author. E-mail address: [email protected] (B. He).
http://dx.doi.org/10.1016/j.ijcard.2015.05.123 0167-5273/© 2015 Elsevier Ireland Ltd. All rights reserved.
and secretion of IL-1β and IL-18 and ultimately leads to increased production of other inflammatory cytokines [2,3]. Moreover, several lines of evidence revealed that autophagy regulates NLRP3 inflammasome activation and serves as a regulatory node of inflammation and lipid metabolism in atherosclerosis [4,5]. These findings have raised the possibility and led to efforts to develop novel anti-inflammatory strategies for prevention and treatment of atherosclerotic cardiovascular disease. The inflammasome is a multiprotein platform composed of NRLP3, ASC and procaspase-1, which cleaves the precursor forms of IL-1β and IL-18 into mature secreted forms when activated. The NRLP3 inflammasome has strongly been implicated in the pathogenesis of atherosclerosis during which it is abnormally activated. Cholesterol crystals are the predominant danger signal in atherosclerosis development to activate the NRLP3 inflammasome, mainly in lesional macrophages [2,3]. NLRP3 inflammasome has now emerged as a critical link between inflammation and cholesterol metabolism. Moreover, it's recently been demonstrated that low and oscillatory shear stress triggers NLRP3 inflammasome activation and incites inflammation in endothelial cells, resulting in endothelial dysfunction, which leads to subsequent genesis of atherosclerosis. This finding even links atheroprone flow induced-NLRP3 inflammasome activation between disturbed flow patterns and inflammation [6]. Therefore, the inflammasome NLRP3 has been regarded as a central regulator for inflammation in atherosclerosis. It has been well demonstrated that hypercholesterolemic Ldlr−/− mice reconstituted with bone marrow from NLRP3 −/− or ASC −/− mice exhibits smaller and more stable atherosclerotic lesions compared to those reconstituted with wild-type bone marrow. Moreover, recent researches demonstrated that the NLRP3 inflammasome inhibitor, Arglbin, exerts markedly anti-inflammatory and anti-atherosclerotic effects in atherosclerotic mice [7]. Meanwhile, various small-molecule inhibitors of the NLRP3 inflammasome have now been regarded as potential target for the treatment of inflammatory diseases, including atherosclerosis [8]. Obviously, modulating NLRP3 inflammasome presents certain advantages over the use of specific cytokine inhibitors, such as neutralizing IL-1β antibody Canakiumab, one just aiming at blocking the outcomes of inflammasome activation. Therefore, directly targeting NLRP3 inflammasome might represent a potential therapeutic target to treat atherosclerosis. Autophagy is an evolutionarily conserved process by which cytoplasmic components are sequestered by autophagosomes and subsequently degraded on fusion with lysosomes for recycling. Growing evidence reveals that basic autophagy is atheroprotective during the development of atherosclerosis [4,5,9]. However, macrophage autophagy
46
Z. Cai et al. / International Journal of Cardiology 195 (2015) 45–47
Fig. 1. Schematic depiction of the links between cholesterol metabolism, autophagy dysfunction, NLRP3 inflammasome hyperactivation and inflammatory boosts within atherosclerotic plaques.
becomes dysfunctional with atherosclerotic plaque progression. Mechanistically, lysosomal dysfunction is increasingly regarded as the major reason for defective autophagic flux and dysfunctional autophagy in atherosclerosis [10]. And these deficiencies contribute to hyperinflammatory states, abnormalities in cholesterol efflux, increased apoptosis and defective efferocytosis in lesional macrophages, leading to dramatic exacerbations of atherosclerosis [4,5,9]. Mounting evidence now supports the notion that macrophage autophagy might be the nexus between inflammatory signaling and lipid metabolism in atherosclerosis. Recently, it's demonstrated that macrophage autophagy plays a critical role in regulating activation of the NLRP3 inflammasome. Macrophage-specific deletion of ATG5 resulted in inflammasome hyperactivation and a dramatically increased burden of cholesterol crystal within atherosclerotic lesions [4]. These data suggest that defective autophagy may result in aberrant cholesterol crystal-induced NLRP3 inflammasome activation and IL-1β release and subsequent exacerbation of atherosclerosis. Autophagy can directly limit NLRP3 inflammasome activation by targeting ubiquitinated inflammasomes for destruction [11]. Moreover, autophagy can indirectly suppress the inflammasome activation by promoting cholesterol efflux and thus to oppose cholesterol crystal formation [5]. Lipophagy, a special kind of autophagy, regulates cholesterol efflux from foam cells via sequestering lipid droplets in autophagosomes that fuse with lysosomes for breakdown by lysosomal acid lipase [5]. Dysfunctional autophagy reduces cholesterol efflux and reverse cholesterol transport from lesional macrophages. As accumulating cholesterol in atherosclerotic plaques may give rise to cholesterol crystal formation, this will further indirectly results in inflammasome hyperactivation. Based on the emerging evidences strongly supporting the substantive role of autophagy in atherosclerosis, restoring or enhancing the autophagy function might help stabilize and reverse atherosclerotic plaque via inhibiting inflammasome activation and promoting cholesterol efflux. It has been demonstrated that overexpression of transcription factor EB, the only known transcription factor that drives the expression of lysosomal and autophagy genes, can rescue lysosome function and exert atheroprotective effects via reducing IL-1β secretion, enhancing cholesterol efflux, and decreasing polyubiquitinated protein aggregation [10]. Thus, this might have important implications for
future therapeutic interventions targeting lysosomal and autophagy function to treat atherosclerosis. In conclusion, this review highlights the huge potential for directly targeting NLRP3 inflammasome and autophagy for anti-inflammatory and anti-atherosclerotic treatment. Mounting evidence strongly reveals that during the development of atherosclerosis, cholesterol crystals lead to lysosomal dysfunction, which incites NLRP3 inflammasome hyperactivation and autophagy dysfunction, causing inflammatory boosts and abnormalities of cholesterol metabolism in lesional macrophages and creating a vicious cycle in atherosclerosis (Fig. 1). Therefore, interference with NLRP3 inflammasome and autophagy may ultimately put out the fire of inflammation in atherosclerosis. Conflict of interest The authors report no relationships that could be construed as a conflict of interest. References [1] P.M. Ridker, T. Thuren, A. Zalewski, P. Libby, Interleukin-1beta inhibition and the prevention of recurrent cardiovascular events: rationale and design of the Canakinumab Anti-inflammatory Thrombosis Outcomes Study (CANTOS), Am. Heart J. 162 (2011) 597–605. [2] P. Duewell, H. Kono, K.J. Rayner, C.M. Sirois, G. Vladimer, et al., NLRP3 inflammasomes are required for atherogenesis and activated by cholesterol crystals, Nature 464 (2010) 1357–1361. [3] K. Rajamaki, J. Lappalainen, K. Oorni, E. Valimaki, S. Matikainen, et al., Cholesterol crystals activate the NLRP3 inflammasome in human macrophages: a novel link between cholesterol metabolism and inflammation, PLos One 5 (2010) e11765. [4] B. Razani, C. Feng, T. Coleman, R. Emanuel, H. Wen, et al., Autophagy links inflammasomes to atherosclerotic progression, Cell Metab. 15 (2012) 534–544. [5] M. Ouimet, V. Franklin, E. Mak, X. Liao, I. Tabas, et al., Autophagy regulates cholesterol efflux from macrophage foam cells via lysosomal acid lipase, Cell Metab. 13 (2011) 655–667. [6] H. Xiao, M. Lu, T.Y. Lin, Z. Chen, G. Chen, et al., Sterol regulatory element binding protein 2 activation of NLRP3 inflammasome in endothelium mediates hemodynamicinduced atherosclerosis susceptibility, Circulation 128 (2013) 632–642. [7] A. Abderrazak, D. Couchie, D.F. Mahmood, R. Elhage, C. Vindis, et al., Antiinflammatory and antiatherogenic effects of the NLRP3 inflammasome inhibitor arglabin in ApoE2.Ki mice fed a high-fat diet, Circulation 131 (2015) 1061–1070.
Z. Cai et al. / International Journal of Cardiology 195 (2015) 45–47 [8] R.C. Coll, A.A. Robertson, J.J. Chae, S.C. Higgins, R. Munoz-Planillo, et al., A smallmolecule inhibitor of the NLRP3 inflammasome for the treatment of inflammatory diseases, Nat. Med. 21 (2015) 248–255. [9] X. Liao, J.C. Sluimer, Y. Wang, M. Subramanian, K. Brown, et al., Macrophage autophagy plays a protective role in advanced atherosclerosis, Cell Metab. 15 (2012) 545–553. [10] R. Emanuel, I. Sergin, S. Bhattacharya, J.N. Turner, S. Epelman, et al., Induction of lysosomal biogenesis in atherosclerotic macrophages can rescue lipid-induced
47
lysosomal dysfunction and downstream sequelae, Arterioscler. Thromb. Vasc. Biol. 34 (2014) 1942–1952. [11] C.S. Shi, K. Shenderov, N.N. Huang, J. Kabat, M. Abu-Asab, et al., Activation of autophagy by inflammatory signals limits IL-1beta production by targeting ubiquitinated inflammasomes for destruction, Nat. Immunol. 13 (2012) 255–263.
