Emerging role of myostatin and its inhibition in the setting of chronic kidney disease

The past two decades have witnessed tremendous progress in our understanding of the mechanisms underlying wasting and cachexia in chronic kidney disease (CKD) and in other chronic illnesses, such as cancer and heart failure. In all these conditions wasting is an effect of the activation of protein degradation in muscle, a response that increases the risk of morbidity and mortality. Major recent advances in our knowledge on how CKD and inflammation affect cellular signaling include the identification of the myostatin (MSTN)/activin system, and its related transcriptional program that promotes protein degradation. In addition, the identification of the role of MSTN/activin in the vascular wall shows premise that its inhibition can better control or prevent some effects of CKD on vessels, such as accelerated atherosclerosis and vascular calcifications. In this review, we summarize the expanding role of MSTN activation in promoting muscle atrophy and the recent clinical studies that investigated the efficacy of MSTN/activin pathway antagonism in sarcopenic patients. Moreover, we also review the utility of MSTN inhibition in the experimental models of CKD and its potential advantages in CKD patients. Lessons learned from clinical studies on MSTN antagonism in sarcopenic patients tell us that the anabolic intervention is likely better if we use a block of the two ActRII receptors. At the same time, however, it is becoming clear that MSTN-targeted therapies should not be seen as a substitute for physical activity and nutritional supplementation which are mandatory to successfully manage patients with wasting. The past two decades have witnessed tremendous progress in our understanding of the mechanisms underlying wasting and cachexia in chronic kidney disease (CKD) and in other chronic illnesses, such as cancer and heart failure. In all these conditions wasting is an effect of the activation of protein degradation in muscle, a response that increases the risk of morbidity and mortality. Major recent advances in our knowledge on how CKD and inflammation affect cellular signaling include the identification of the myostatin (MSTN)/activin system, and its related transcriptional program that promotes protein degradation. In addition, the identification of the role of MSTN/activin in the vascular wall shows premise that its inhibition can better control or prevent some effects of CKD on vessels, such as accelerated atherosclerosis and vascular calcifications. In this review, we summarize the expanding role of MSTN activation in promoting muscle atrophy and the recent clinical studies that investigated the efficacy of MSTN/activin pathway antagonism in sarcopenic patients. Moreover, we also review the utility of MSTN inhibition in the experimental models of CKD and its potential advantages in CKD patients. Lessons learned from clinical studies on MSTN antagonism in sarcopenic patients tell us that the anabolic intervention is likely better if we use a block of the two ActRII receptors. At the same time, however, it is becoming clear that MSTN-targeted therapies should not be seen as a substitute for physical activity and nutritional supplementation which are mandatory to successfully manage patients with wasting. Myostatin (MSTN) is a member of the transforming growth factor–β (TGF-β) super family that is predominantly produced in skeletal muscle in response to diverse stimuli, including oxidative stress,1Sriram S. Subramanian S. Sathiakumar D. et al.Modulation of reactive oxygen species in skeletal muscle by myostatin is mediated through NF-κB.Aging Cell. 2011; 10: 931-948Crossref PubMed Scopus (0) Google Scholar inflammation,2Zhang L. Pan J. Dong Y. et al.Stat3 activation links a C/EBPδ to myostatin pathway to stimulate loss of muscle mass.Cell Metab. 2013; 18: 368-379Abstract Full Text Full Text PDF PubMed Google Scholar hyperammoniemia,3Qiu J. Thapaliya S. Runkana A. et al.Hyperammonemia in cirrhosis induces transcriptional regulation of myostatin by an NF-κB-mediated mechanism.Proc Natl Acad Sci U S A. 2013; 110: 18162-18167Crossref PubMed Scopus (0) Google Scholar angiotensin II,4Wang B.W. Chang H. Kuan P. Shyu K.G. Angiotensin II activates myostatin expression in cultured rat neonatal cardiomyocytes via p38 MAP kinase and myocyte enhance factor 2 pathway.J Endocrinol. 2008; 197: 85-93Crossref PubMed Scopus (0) Google Scholar and glucocorticoids5Wang R. Jiao H. Zhao J. et al.Glucocorticoids enhance muscle proteolysis through a myostatin-dependent pathway at the early stage.PLoS One. 2016; 11: e0156225PubMed Google Scholar (Figure 1). MSTN expression is not only restricted to skeletal muscle; low levels of mRNA are reported in smooth muscle,6Verzola D. Milanesi S. Bertolotto M. et al.Myostatin mediates abdominal aortic atherosclerosis progression by inducing vascular smooth muscle cell dysfunction and monocyte recruitment.Sci Rep. 2017; 7: 46362Crossref PubMed Scopus (3) Google Scholar synovia,7Hu S.L. Chang A.C. Huang C.C. et al.Myostatin promotes interleukin-1β expression in rheumatoid arthritis synovial fibroblasts through inhibition of miR-21-5p.Front Immunol. 2017; 8: 1747Crossref PubMed Scopus (12) Google Scholar adipose tissue, cardiac muscle,8Breitbart A. Auger-Messier M. Molkentin J.D. Heineke J. Myostatin from the heart: local and systemic actions in cardiac failure and muscle wasting.Am J Physiol Heart Circ Physiol. 2011; 300: H1973-H1982Crossref PubMed Scopus (0) Google Scholar and brain.9McPherron A.C. Lawler A.M. Lee S.J. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member.Nature. 1997; 387: 83-90Crossref PubMed Google Scholar MSTN is synthesized as a 375-amino acid propeptide that becomes cleaved into an amino-terminal propeptide and carboxy terminal mature region to give rise to a 26-kDa active processed peptide.9McPherron A.C. Lawler A.M. Lee S.J. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member.Nature. 1997; 387: 83-90Crossref PubMed Google Scholar, 10Carnac G. Vernus B. Bonnieu A. Myostatin in the pathophysiology of skeletal muscle.Curr Genomics. 2007; 8: 415-422Crossref PubMed Google Scholar The TGF-β superfamily of genes encode secreted factors that regulate embryonic development and tissue homeostasis in adults. MSTN binds to the activin receptor type II B (ActRIIB) and with a weaker affinity to the activin receptor type II A (ActRIIA), which recruits either of the activin type I receptors (activin-receptor–like kinase [ALK]4 or ALK5).9McPherron A.C. Lawler A.M. Lee S.J. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member.Nature. 1997; 387: 83-90Crossref PubMed Google Scholar, 10Carnac G. Vernus B. Bonnieu A. Myostatin in the pathophysiology of skeletal muscle.Curr Genomics. 2007; 8: 415-422Crossref PubMed Google Scholar, 11Trendelenburg A.U. Meyer A. Rohner D. et al.Myostatin reduces Akt/TORC1/p70S6K signaling, inhibiting myoblast differentiation and myotube size.Am J Physiol Cell Physiol. 2009; 296: C1258-C1270Crossref PubMed Scopus (409) Google Scholar Activin A, a major form of the activins, binds to ActRIIA receptor and mediates a number of actions, including cell proliferation and differentiation, immune response and angiogenesis, and wound healing. Several activities of other members of the TGF-β family, such as growth differentiation factor 11 and activin A, are redundant with those of MSTN. The activation of the ALKs induces the phosphorylation and activation of the transcription factors Sma- and Mad-related protein (SMAD) 2 and SMAD3, which translocate to the nucleus upon phosphorylation, repressing genes required for muscle differentiation11Trendelenburg A.U. Meyer A. Rohner D. et al.Myostatin reduces Akt/TORC1/p70S6K signaling, inhibiting myoblast differentiation and myotube size.Am J Physiol Cell Physiol. 2009; 296: C1258-C1270Crossref PubMed Scopus (409) Google Scholar and activating signaling pathways that decrease protein synthesis and stimulate protein breakdown.9McPherron A.C. Lawler A.M. Lee S.J. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member.Nature. 1997; 387: 83-90Crossref PubMed Google Scholar, 12Wang X.H. Mitch W.E. Mechanisms of muscle wasting in chronic kidney disease.Nat Rev Nephrol. 2014; 10: 504-516Crossref PubMed Scopus (172) Google Scholar, 13Han H.Q. Zhou X. Mitch W.E. Goldberg A.L. Myostatin/activin pathway antagonism: molecular basis and therapeutic potential.Int J Biochem Cell Biol. 2013; 45: 2333-2347Crossref PubMed Scopus (127) Google Scholar On one hand MSTN and activin A can suppress phosphorylated Akt downward signaling, with subsequent phosphorylation of the transcription factors Forkhead box O (FoxO) and increased expression of the ubiquitin E3 ligases atrogin-1 and muscle RING-finger protein–1 (MuRF1), thus driving ubiquitin-proteasome–mediated protein degradation.9McPherron A.C. Lawler A.M. Lee S.J. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member.Nature. 1997; 387: 83-90Crossref PubMed Google Scholar, 13Han H.Q. Zhou X. Mitch W.E. Goldberg A.L. Myostatin/activin pathway antagonism: molecular basis and therapeutic potential.Int J Biochem Cell Biol. 2013; 45: 2333-2347Crossref PubMed Scopus (127) Google Scholar On the other hand, MSTN inhibits the Akt/mammalian target of rapamycin pathway in response to progrowth signals (e.g., insulin and insulin-like growth factor 1 [IGF-I]) and therefore suppresses protein synthesis.9McPherron A.C. Lawler A.M. Lee S.J. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member.Nature. 1997; 387: 83-90Crossref PubMed Google Scholar, 13Han H.Q. Zhou X. Mitch W.E. Goldberg A.L. Myostatin/activin pathway antagonism: molecular basis and therapeutic potential.Int J Biochem Cell Biol. 2013; 45: 2333-2347Crossref PubMed Scopus (127) Google Scholar MSTN suppresses growth in skeletal muscle. As observed in the Belgian Blue and Piedmontese cattle, the inhibition of MSTN leads to approximately a 2-fold increase in muscle mass, leading to the “double-muscled phenotype.”14Grobet L. Martin L.J. Poncelet D. et al.A deletion in the bovine myostatin gene causes the double-muscled phenotype in cattle.Nat Genet. 1997; 17: 71-74Crossref PubMed Scopus (0) Google Scholar, 15Kambadur R. Sharma M. Smith T.P. et al.Mutations in myostatin (GDF8) in double-muscled Belgian Blue and Piedmontese cattle.Genome Res. 1997; 7: 910-916Crossref PubMed Scopus (194) Google Scholar In 2004, Schuelke et al.16Schuelke M. Wagner K.R. Stolz L.E. et al.Myostatin mutation associated with gross muscle hypertrophy in a child.N Engl J Med. 2004; 350: 2682-2688Crossref PubMed Scopus (925) Google Scholar described the first case of an MSTN mutation in an extremely muscular child, thus providing evidence that MSTN also plays an important role in regulating muscle mass in humans. One mechanism by which MSTN negatively regulates muscle growth is through inhibiting myogenesis during development. In vitro, MSTN suppresses myoblast growth and also inhibits myogenic differentiation in part by downregulation of myogenic differentiation.17Langley B. Thomas M. Bishop A. et al.Myostatin inhibits myoblast differentiation by down-regulating MyoD expression.J Biol Chem. 2002; 277: 49831-49840Crossref PubMed Scopus (570) Google Scholar Moreover, in adult muscle, MSTN negatively regulates satellite cell activation and self-renewal.18McCroskery S. Thomas M. Maxwell L. et al.Myostatin negatively regulates satellite cell activation and self-renewal.J Cell Biol. 2003; 162: 1135-1147Crossref PubMed Scopus (507) Google Scholar MSTN-null mice show a dramatic gain in skeletal muscle mass because of an increase in the number and thickness of fibers (hyperplasia + hypertrophy).8Breitbart A. Auger-Messier M. Molkentin J.D. Heineke J. Myostatin from the heart: local and systemic actions in cardiac failure and muscle wasting.Am J Physiol Heart Circ Physiol. 2011; 300: H1973-H1982Crossref PubMed Scopus (0) Google Scholar Of great interest is the opposing role of IGF-1 and MSTN in regulating muscle growth and size, with IGF-1 stimulating growth and MSTN inhibiting growth.19Hennebry A. Oldham J. Shavlakadze T. et al.IGF1 stimulates greater muscle hypertrophy in the absence of myostatin in male mice.J Endocrinol. 2017; 23: 187-200Crossref Scopus (2) Google Scholar, 20Williams N.G. Interlichia J.P. Jackson M.F. et al.Endocrine actions of myostatin: systemic regulation of the IGF and IGF binding protein axis.Endocrinology. 2011; 152: 172-180Crossref PubMed Scopus (0) Google Scholar A greater effect on the growth of skeletal muscle is observed when MSTN is absent and IGF-1 is in excess. Of note, MSTN and IGF-1 regulate skeletal muscle size and myofiber type through mechanisms that involve increasing the total abundance and phosphorylation status of Akt.10Carnac G. Vernus B. Bonnieu A. Myostatin in the pathophysiology of skeletal muscle.Curr Genomics. 2007; 8: 415-422Crossref PubMed Google Scholar, 20Williams N.G. Interlichia J.P. Jackson M.F. et al.Endocrine actions of myostatin: systemic regulation of the IGF and IGF binding protein axis.Endocrinology. 2011; 152: 172-180Crossref PubMed Scopus (0) Google Scholar In addition, MSTN influences the synthesis and secretion of IGF-1 in the liver, thereby regulating the amount of circulating IGF-1.20Williams N.G. Interlichia J.P. Jackson M.F. et al.Endocrine actions of myostatin: systemic regulation of the IGF and IGF binding protein axis.Endocrinology. 2011; 152: 172-180Crossref PubMed Scopus (0) Google Scholar Since its isolation and characterization almost 20 years ago, investigators have perceived MSTN as acting primarily in skeletal muscle. The cachexia-inducing effects of MSTN have led to strong interest in its inhibition as a new treatment strategy for wasting and frailty in several cachexia-associated states. However, in past years we have witnessed a paradigm shift with respect to our understanding of the effects of MSTN/activin signaling in organs distant from muscle. Consequently, these myriad “off-target” actions of MSTN mandate an expansion and revision of the traditional concept of MSTN. Ever-increasing evidence shows that the MSTN/activin pathway affects the heart8Breitbart A. Auger-Messier M. Molkentin J.D. Heineke J. Myostatin from the heart: local and systemic actions in cardiac failure and muscle wasting.Am J Physiol Heart Circ Physiol. 2011; 300: H1973-H1982Crossref PubMed Scopus (0) Google Scholar and the vasculature6Verzola D. Milanesi S. Bertolotto M. et al.Myostatin mediates abdominal aortic atherosclerosis progression by inducing vascular smooth muscle cell dysfunction and monocyte recruitment.Sci Rep. 2017; 7: 46362Crossref PubMed Scopus (3) Google Scholar and that MSTN influences insulin sensitivity,21Zhang C. McFarlane C. Lokireddy S. et al.Myostatin-deficient mice exhibit reduced insulin resistance through activating the AMP-activated protein kinase signalling pathway.Diabetologia. 2011; 54: 1491-1501Crossref PubMed Scopus (81) Google Scholar, 22Guo T. Jou W. Chanturiya T. et al.Myostatin inhibition in muscle, but not adipose tissue, decreases fat mass and improves insulin sensitivity.PLoS One. 2009; 4: e4937Crossref PubMed Scopus (213) Google Scholar vascular remodeling,6Verzola D. Milanesi S. Bertolotto M. et al.Myostatin mediates abdominal aortic atherosclerosis progression by inducing vascular smooth muscle cell dysfunction and monocyte recruitment.Sci Rep. 2017; 7: 46362Crossref PubMed Scopus (3) Google Scholar cell senescence, and fibrosis. These actions might contribute substantively to the pathophysiology of wasting, inflammation, vascular damage, and possibly progressive renal dysfunction in persons with chronic kidney disease (CKD). Besides its autocrine and paracrine effects, MSTN also can act as an endocrine factor. Several in vitro and in vivo data support the concept that MSTN affects glucose and fat metabolism and increases energy expenditure. Loss of MSTN or reduction in active MSTN levels leads to increased insulin sensitivity.21Zhang C. McFarlane C. Lokireddy S. et al.Myostatin-deficient mice exhibit reduced insulin resistance through activating the AMP-activated protein kinase signalling pathway.Diabetologia. 2011; 54: 1491-1501Crossref PubMed Scopus (81) Google Scholar, 22Guo T. Jou W. Chanturiya T. et al.Myostatin inhibition in muscle, but not adipose tissue, decreases fat mass and improves insulin sensitivity.PLoS One. 2009; 4: e4937Crossref PubMed Scopus (213) Google Scholar, 23Brandt C. Hansen R.H. Hansen J.B. et al.Over-expression of Follistatin-like 3 attenuates fat accumulation and improves insulin sensitivity in mice.Metabolism. 2015; 64: 283-295Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar MSTN-null mice, in association with increased muscle mass and reduced body fat, also exhibit increased insulin sensitivity because of an adenosine monophosphate–activated protein kinase.21Zhang C. McFarlane C. Lokireddy S. et al.Myostatin-deficient mice exhibit reduced insulin resistance through activating the AMP-activated protein kinase signalling pathway.Diabetologia. 2011; 54: 1491-1501Crossref PubMed Scopus (81) Google Scholar In addition, both inhibition of MSTN by dominant-negative MSTN receptor and the overexpression of follistatin-like 3 improve insulin sensitivity in mice.23Brandt C. Hansen R.H. Hansen J.B. et al.Over-expression of Follistatin-like 3 attenuates fat accumulation and improves insulin sensitivity in mice.Metabolism. 2015; 64: 283-295Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar In a genetic type 1 diabetes mellitus mouse model, a decreased skeletal muscle expression of MSTN mRNA prevented the loss of muscle mass and increased muscle Glut1 and Glut4 and glucose uptake in response to insulin.23Brandt C. Hansen R.H. Hansen J.B. et al.Over-expression of Follistatin-like 3 attenuates fat accumulation and improves insulin sensitivity in mice.Metabolism. 2015; 64: 283-295Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar Of note, both serum and muscle MSTN are increased in insulin-resistant extremely obese women24Hittel D.S. Berggren J.R. Shearer J. et al.Increased secretion and expression of myostatin in skeletal muscle from extremely obese women.Diabetes. 2009; 58: 30-38Crossref PubMed Scopus (168) Google Scholar; serum MSTN is also elevated in patients with type 2 diabetes mellitus.25Allen D.L. Hittel D.S. McPherron A.C. Expression and function of myostatin in obesity, diabetes, and exercise adaptation.Med Sci Sports Exerc. 2011; 4: 1828-1835Crossref Scopus (75) Google Scholar It is interesting that in type 2 diabetes mellitus, MSTN is positively associated with fasting plasma glucose and indexes of insulin resistance (HOMA-IR).25Allen D.L. Hittel D.S. McPherron A.C. Expression and function of myostatin in obesity, diabetes, and exercise adaptation.Med Sci Sports Exerc. 2011; 4: 1828-1835Crossref Scopus (75) Google Scholar, 26Guo T. Bond N.D. Jou W. et al.Myostatin inhibition prevents diabetes and hyperphagia in a mouse model of lipodystrophy.Diabetes. 2012; 61: 2414-2423Crossref PubMed Scopus (38) Google Scholar These data suggest the involvement of MSTN in the pathogenesis of insulin resistance and type 2 diabetes. For all these reasons, MSTN antagonism has been proposed not only for anticatabolic purposes but also as an adjuvant treatment of type 1 diabetes mellitus, type 2 diabetes mellitus, and related metabolic syndrome.27Coleman S.K. Rebalka I.A. D’Souza D.M. et al.Myostatin inhibition therapy for insulin-deficient type 1 diabetes.Sci Rep. 2016; 6: 32495Crossref PubMed Scopus (5) Google Scholar, 28Assyov Y.S. Velikova T.V. Kamenov Z.A. Myostatin and carbohydrate disturbances.Endocr Res. 2017; 42: 102-109Crossref PubMed Scopus (1) Google Scholar Recently, Dong et al.29Dong J. Dong Y. Dong Y. et al.Inhibition of myostatin in mice improves insulin sensitivity via irisin-mediated cross talk between muscle and adipose tissues.Int J Obes. 2016; 40: 434-442Crossref PubMed Google Scholar demonstrated that MSTN inhibition in mice improves insulin sensitivity via an irisin-mediated mechanism that stimulates white adipose tissue browning and suppresses inflammation. No information on MSTN inhibition in patients with diabetes is available. The association between malnutrition, inflammation, and atherosclerosis, described for the first time by Stenvinkel et al.,30Stenvinkel P. Heimbürger O. Paultre F. et al.Strong association between malnutrition, inflammation, and atherosclerosis in chronic renal failure.Kidney Int. 1999; 55: 1899-1911Abstract Full Text Full Text PDF PubMed Scopus (1346) Google Scholar remains puzzling. Accumulating evidence shows that MSTN has a role in vascular inflammation, aging, and atherosclerotic damage. The atherosclerotic process is a chronic inflammatory condition that occurs principally in large- and medium-sized elastic and muscular arteries. Its development is sustained by a multifactorial ensemble of stimuli that may act synergistically. The natural history of progressive aortic atherosclerosis has been described recently in humans.31van Dijk R.A. Virmani R. von der Thüsen J.H. et al.The natural history of aortic atherosclerosis: a systematic histopathological evaluation of the peri-renal region.Atherosclerosis. 2010; 210: 100-106Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar The dynamics of progressive lesions occurring in the aortic wall include adaptive intimal thickening, intimal xanthoma, intimal thickening, early and late fibroatheroma, and thin cap fibroatheroma, until plaque rupture and its healing into fibrotic calcified plaque (Figure 2). These lesions progress following the interaction of several factors, among which are age, sex, proliferation and migration of vascular smooth muscle cells (VSMCs), and monocyte/macrophage accumulation, together with intraplaque hemorrhage and plaque neovascularization.31van Dijk R.A. Virmani R. von der Thüsen J.H. et al.The natural history of aortic atherosclerosis: a systematic histopathological evaluation of the peri-renal region.Atherosclerosis. 2010; 210: 100-106Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar Notably, disease progression leads to loss of aortic elasticity and deterioration of the vessel wall. This process may result in the development of life-threatening complications in the form of the fissure and rupture of an abdominal aortic aneurysm, peripheral embolization, and limb ischemia.32Ross R. Atherosclerosis: an inflammatory disease.N Engl J Med. 1999; 340: 115-126Crossref PubMed Scopus (17649) Google Scholar The development of atherosclerosis involves the response to a number of insults and a complex interplay between VSMCs, endothelial cells, and infiltrating cells of the innate and adaptive immune system. An inflammatory, proatherogenic milieu activates endothelial cells and VSMCs, which undergo a morphologic and functional transition from a contractile to a synthetic phenotype, with an increased proliferative and migratory rate and release of a number of chemokines and cytokines that interact with infiltrating cells, thus boosting inflammation, loss of arterial elasticity, and deterioration of the vessel wall.31van Dijk R.A. Virmani R. von der Thüsen J.H. et al.The natural history of aortic atherosclerosis: a systematic histopathological evaluation of the peri-renal region.Atherosclerosis. 2010; 210: 100-106Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar, 32Ross R. Atherosclerosis: an inflammatory disease.N Engl J Med. 1999; 340: 115-126Crossref PubMed Scopus (17649) Google Scholar This phenotypic shift is accompanied by reduced expression of VSMC marker proteins such as smooth muscle α actin, smooth muscle 22-α, smooth muscle myosin heavy chain, and the transcription factors myocardin and smoothelin,33Shankman L.S. Gomez D. Cherepanova O.A. et al.KLF4-dependent phenotypic modulation of smooth muscle cells has a key role in atherosclerotic plaque pathogenesis.Nat Med. 2015; 21: 628-637Crossref PubMed Scopus (305) Google Scholar, 34Chistiakov A. Orekhov A.N. Bobryshev Y.V. Vascular smooth muscle cell in atherosclerosis.Acta Physiol. 2015; 214: 33-50Crossref PubMed Scopus (96) Google Scholar, 35van Eys G.J. Niessen P.M. Rensen S.S. Smoothelin in vascular smooth muscle.Cells Trends Cardiovasc Med. 2007; 17: 26-30Crossref PubMed Scopus (0) Google Scholar which are responsible for the dysfunction of the contractility of VSMCs. In addition, uremia induces a VSMC phenotype switch and contributes to neointimal hyperplasia formation in vivo, decreasing aortic contractility.36Monroy M.A. Fang J. Li S. et al.Chronic kidney disease alters vascular smooth muscle cell phenotype.Front Biosci. 2015; 20: 784-795Crossref PubMed Google Scholar, 37Madsen M. Aarup A. Albinsson S. et al.Uremia modulates the phenotype of aortic smooth muscle cells.Atherosclerosis. 2017; 257: 64-70Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar MSTN and ActRIIs are expressed in mouse aortas.38Guo W. Wong S. Bhasin S. AAV-mediated administration of myostatin pro-peptide mutant in adult Ldlr null mice reduces diet- induced hepatosteatosis and arteriosclerosis.PLoS One. 2013; 8: e71017Crossref PubMed Scopus (8) Google Scholar Genetic inactivation of MSTN in low-density lipoprotein receptor–deficient mice blunts diet-induced atherosclerosis.39Tu P. Bhasin S. Hruz P.W. et al.Genetic disruption of myostatin reduces the development of proatherogenic dyslipidemia and atherogenic lesions in Ldlr null mice.Diabetes. 2009; 58: 1739-1748Crossref PubMed Scopus (30) Google Scholar Moreover, the exposure of aortic endothelial cells to MSTN leads to activation of TGF-β signaling, decrease of endothelial nitric oxide synthase phosphorylation, and increased expression of the proatherogenic adhesion molecules intercellular adhesion molecule 1 and vascular cell adhesion molecule 1.39Tu P. Bhasin S. Hruz P.W. et al.Genetic disruption of myostatin reduces the development of proatherogenic dyslipidemia and atherogenic lesions in Ldlr null mice.Diabetes. 2009; 58: 1739-1748Crossref PubMed Scopus (30) Google Scholar, 40Burgess K. Xu T. Brown R. et al.Effect of myostatin depletion on weight gain, hyperglycemia, and hepatic steatosis during five months of high-fat feeding in mice.PLoS One. 2011; 6: e17090Crossref PubMed Scopus (0) Google Scholar Recently, to define whether MSTN tissue levels change along with the progression of abdominal aortic atherosclerosis, we studied MSTN expression in a large number of aorta specimens that were comprehensive of the full spectrum of atherosclerotic stages.6Verzola D. Milanesi S. Bertolotto M. et al.Myostatin mediates abdominal aortic atherosclerosis progression by inducing vascular smooth muscle cell dysfunction and monocyte recruitment.Sci Rep. 2017; 7: 46362Crossref PubMed Scopus (3) Google Scholar MSTN was not detectable in normal vessels, but it was overexpressed and mainly localized in resident medial VSMCs during early aortic wall remodeling. In addition, MSTN also was observed in the neointima, in neovessels, and in infiltrating cells at the site of atherosclerotic lesions, and its expression rose with the progression of the aortic vascular damage (Figure 2). An important finding is that MSTN was expressed in infiltrating macrophages in correspondence to the plaque shoulders and in proximity of neovasa. At later stages, when thinning of the fibrotic cap occurred, MSTN accumulated in the media along the border and within the cellular structural and inflammatory component of the plaques. These findings indicate that MSTN participates in inflammation and wall remodeling that propagates from the media to the neointima. Another set of data shows that MSTN plays an active role in VSMC activation, monocyte chemiotaxis, and, ultimately, in vascular wall remodeling. It is interesting that some of MSTN’s effects, such as its chemoattractant and profibrotic roles, also are shared by TGF-β.41Border W.A. Noble N.A. Yamamoto T. et al.Antagonists of transforming growth factor-beta: a novel approach to treatment of glomerulonephritis and prevention of glomerulosclerosis.Kidney Int. 1992; 41: 566-570Abstract Full Text PDF PubMed Google Scholar VSMCs exposed to MSTN in vitro upregulate CCR2 and monocyte chemoattractant protein-1 (MCP1). Moreover, MCP1-treated cells express MSTN, indicating the occurrence of a loop between MCP1 and MSTN.6Verzola D. Milanesi S. Bertolotto M. et al.Myostatin mediates abdominal aortic atherosclerosis progression by inducing vascular smooth muscle cell dysfunction and monocyte recruitment.Sci Rep. 2017; 7: 46362Crossref PubMed Scopus (3) Google Scholar MCP1 is one of the principal mediators of vascular inflammation: MCP1 chemotactically induces the migration of monocytes into the vascular wall, an effect that accelerates atherogenesis.42Schober A. Chemokines in vascular dysfunction and remodeling.Arterioscler Thromb Vasc Biol. 2008; 28: 1950-1959Crossref PubMed Scopus (198) Google Scholar Moreover, in atherosclerotic lesions, we observed that CD45+ cells also expressed MSTN, and MSTN was chemoattractive for monocytes; in turn, MCP1 induced MSTN.6Verzola D. Milanesi S. Bertolotto M. et al.Myostatin mediates abdominal aortic atherosclerosis progression by inducing vascular smooth muscle cell dysfunction and monocyte recruitment.Sci Rep. 2017; 7: 46362Crossref PubMed Scopus (3) Google Scholar These observations suggest that MSTN sets the stage to propagate and perpetuate inflammation throughout the vessel wall, linking the dysfunctional phenotype of VSMCs and interacting with monocytes in a deleterious loop that accelerates the progression of atherosclerosis. Moreover, in both VSMCs and monocytes, MSTN induces c-Jun N-terminal kinase phosphorylation, a critical mediator of inflammatory activation.43Chen L. F