Calpastatin prevents Angiotensin II–mediated podocyte injury through maintenance of autophagy

Abstract

The strong predictive value of proteinuria in chronic glomerulopathies is firmly established as well as the pathogenic role of angiotensin II promoting progression of glomerular disease with an altered glomerular filtration barrier, podocyte injury and scarring of glomeruli. Here we found that chronic angiotensin II-induced hypertension inhibited autophagy flux in mouse glomeruli. Deletion of Atg5 (a gene encoding a protein involved autophagy) specifically in the podocyte resulted in accelerated angiotensin II-induced podocytopathy, accentuated albuminuria and glomerulosclerosis. This indicates that autophagy is a key protective mechanism in the podocyte in this condition. Angiotensin-II induced calpain activity in podocytes inhibits autophagy flux. Podocytes from mice with transgenic expression of the endogenous calpain inhibitor calpastatin displayed higher podocyte autophagy at baseline that was resistant to angiotensin II-dependent inhibition. Also, sustained autophagy with calpastatin limited podocyte damage and albuminuria. These findings suggest that hypertension has pathogenic effects on the glomerular structure and function, in part through activation of calpains leading to blockade of podocyte autophagy. These findings uncover an original mechanism whereby angiotensin II-mediated hypertension inhibits autophagy via calcium-induced recruitment of calpain with pathogenic consequences in case of imbalance by calpastatin activity. Thus, preventing a calpain-mediated decrease in autophagy may be a promising new therapeutic strategy for nephropathies associated with high renin-angiotensin system activity. The strong predictive value of proteinuria in chronic glomerulopathies is firmly established as well as the pathogenic role of angiotensin II promoting progression of glomerular disease with an altered glomerular filtration barrier, podocyte injury and scarring of glomeruli. Here we found that chronic angiotensin II-induced hypertension inhibited autophagy flux in mouse glomeruli. Deletion of Atg5 (a gene encoding a protein involved autophagy) specifically in the podocyte resulted in accelerated angiotensin II-induced podocytopathy, accentuated albuminuria and glomerulosclerosis. This indicates that autophagy is a key protective mechanism in the podocyte in this condition. Angiotensin-II induced calpain activity in podocytes inhibits autophagy flux. Podocytes from mice with transgenic expression of the endogenous calpain inhibitor calpastatin displayed higher podocyte autophagy at baseline that was resistant to angiotensin II-dependent inhibition. Also, sustained autophagy with calpastatin limited podocyte damage and albuminuria. These findings suggest that hypertension has pathogenic effects on the glomerular structure and function, in part through activation of calpains leading to blockade of podocyte autophagy. These findings uncover an original mechanism whereby angiotensin II-mediated hypertension inhibits autophagy via calcium-induced recruitment of calpain with pathogenic consequences in case of imbalance by calpastatin activity. Thus, preventing a calpain-mediated decrease in autophagy may be a promising new therapeutic strategy for nephropathies associated with high renin-angiotensin system activity. Translational StatementGiven the crucial role of autophagy in the development of kidney diseases, pharmacological modulation of autophagy might be a promising strategy for the prevention and treatment of several kidney diseases. In parallel, overactivation of calpain activity in podocytes was found to play detrimental effects on podocyte function whereas its deleterious mechanisms of action were not identified. Here, we provide evidence that calpain links the deleterious action of angiotensin II to the detrimental blockade of autophagy in podocytes and suggest that calpain inhibition could be a promising therapeutic target for podocyte diseases partially through maintenance of podocyte autophagy. Given the crucial role of autophagy in the development of kidney diseases, pharmacological modulation of autophagy might be a promising strategy for the prevention and treatment of several kidney diseases. In parallel, overactivation of calpain activity in podocytes was found to play detrimental effects on podocyte function whereas its deleterious mechanisms of action were not identified. Here, we provide evidence that calpain links the deleterious action of angiotensin II to the detrimental blockade of autophagy in podocytes and suggest that calpain inhibition could be a promising therapeutic target for podocyte diseases partially through maintenance of podocyte autophagy. 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S. et al.Angiotensin II increases the calcium activity in podocytes of the Int. 2000; Full Text Full Text PDF PubMed Scopus Google J. A. Fischer K.G. et al.Angiotensin II of Full Text Full Text PDF PubMed Scopus Google Scholar and type receptor D. E. et expression via an angiotensin mechanism in human of J 2010; 298: PubMed Scopus Google Scholar, and mechanisms of the in J 2006; PubMed Scopus Google Scholar, et of a angiotensin system in podocytes by Int. 2004; 65: Full Text Full Text PDF PubMed Scopus Google Scholar, P. C. et in rat J Pathol. Google Scholar, M. damage is a in the development of in the hypertensive PubMed Scopus Google Scholar These mechanisms in the leading to glomerulosclerosis. for blood pressure and and enzyme and blockers for the treatment of hypertension and in blockers also a protective on kidney was to be for the maintenance of in J. et of autophagy and function with Full Text Full Text PDF PubMed Scopus Google C. T. 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A. et of and autophagy injury in Dis. 2011; PubMed Scopus Google Scholar In of the on the that calpain could autophagy through the of autophagy and by in glomeruli treatment we did not in expression of in glomeruli from and mice of hypertension, glomeruli from mice different of of the and with expression of and as with that autophagy in podocytes and glomeruli from mice of several of the and as well as expression of protein factor factor protein protein apoptosis of protein receptor in a new results that calpastatin could glomerular injury by and In the we that in hypertension, podocyte autophagy is Furthermore, mice with of Atg5 were to and podocyte that autophagy in podocytes the development of hypertensive the role of autophagy in podocyte injury. is the that and results on the of podocyte autophagy by In human podocyte is a of glomerular injury leading to is to play an role in podocyte function high of autophagy even in the of that autophagy through the of in a podocyte A. S. S. et II autophagy in J 2010; PubMed Scopus Google Scholar is a of autophagy in and the for with findings this we podocytes and expression and in and not that podocytes an high of autophagy. of the of in the or of is to flux is or studies have this A. S. S. et II autophagy in J 2010; PubMed Scopus Google Scholar Here, we a hypertensive model on and Podocytes receptor and to as T. Sloan A.J. Hoenderop J.G. et al.Angiotensin II contributes to podocyte injury by increasing TRPC6 expression via an NFAT-mediated positive feedback signaling pathway.Am J Pathol. 2011; 179: 1719-1732Abstract Full Text Full Text PDF PubMed Scopus (153) Google A. Gagliardini E. Remuzzi G. Changes in glomerular perm-selectivity induced by angiotensin II imply podocyte dysfunction and slit diaphragm protein rearrangement.Semin Nephrol. 2004; 24: 131-140Abstract Full Text Full Text PDF PubMed Scopus (42) Google et of a angiotensin system in podocytes by Int. 2004; 65: Full Text Full Text PDF PubMed Scopus Google P.J. Spurney R.F. of the factor receptor by angiotensin II in glomerular Nephrol. 2006; PubMed Scopus Google Scholar, et of II receptor in rat kidney a J 1997; Google Scholar, D. J. et expression of the renin-angiotensin system in human J 2006; PubMed Scopus (109) Google Scholar, angiotensin II in the 2000; 23: PubMed Scopus Google Scholar, H.H. The system in Nephrol. 2012; Full Text Full Text PDF PubMed Scopus Google Scholar is that the effects of inhibition could to a blockade of this in studies the of on podocyte injury and gene of that activation of in the in experimental is to kidney injury in the of J. G. J. et al.Angiotensin II expression and podocyte J Nephrol. PubMed Scopus Google M.P. P. et type angiotensin kidney injury and in Clin 2009; Google Scholar autophagy in model could be to a signaling on podocyte or to be a of may provide an early to this in the we also found in podocytes from hypertensive mice This that autophagy blockade in podocytes in this is to be independent of D. et not hypertension or renal Google Scholar studies podocyte injury to calpain activity and flux in mice for in podocytes be to of podocyte autophagy on or effects of and activity is by specific calpastatin inhibits calpains and to activation has to kidney injury in several J. D. et role of endothelial calpain in kidney injury via of the and Med. 52: PubMed Scopus Google M. R.G. activity underlies angiotensin II-induced aldosterone in an PubMed Scopus Google Scholar The calcium receptor was found to in podocytes via of patients with and had receptor calpain and and expression of the calpain target is for podocyte M. et links TRPC6 activity to podocyte Nephrol. PubMed Scopus Google Scholar receptor also to and This is crucial for the of and of D.J. et to and independent of its and podocyte and Nephrol. PubMed Scopus Google Scholar mice calpastatin and E. J. A. et the system as a new strategy to cardiovascular in angiotensin II-induced PubMed Scopus Google in of J. A. J. et activation and glomerular injury in experimental evidence from Nephrol. 2006; PubMed Scopus Google Scholar L. G. C. et by J Med. 2012; PubMed Scopus Google Scholar or E. M. et role of the in J 2011; PubMed Scopus Google and G. L. S. et calpain inhibition kidney PubMed Scopus Google Scholar injury in mice has not et that of calpastatin in J. A. 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