SIRT6 attenuates angiotensin II-induced podocyte cholesterol accumulation and injury via negative modulation of SREBP2

Introduction: Angiotensin (Ang) II can cause podocyte injury and leads to chronic kidney disease (CKD), but the specific mechanism is not clear. In our previous study, we found that Ang II reduced the expression of cholesterol efflux associated molecule by regulating Sirtuin 6 (SIRT6), thereby inducing podocyte cholesterol accumulation and injury. However, the effect of SIRT6 on podocyte cholesterol synthesis is unclear. In this study, we evaluated the role of SIRT6 in the expression of cholesterol synthesis associated molecular sterol regulatory element-binding protein 2 (SREBP2), cholesterol content, and apoptosis levels in podocytes. Methods: Ang II-infused rat model was constructed. Cholesterol quantification was examined using a cholesterol quantitation kit. The expression of SIRT6 and SREBP2 were examined by western blot and immunofluorescence assay. The podocyte apoptotic level was detected by flow cytometry. Transfection of podocytes with pcDNA 3.1 SIRT6 plasmid and the deacetylase-inactive SIRT6 mutant plasmid (pcDNA 3.1 SIRT6 H133Y) was performed to investigate whether SIRT6 regulates SREBP2 expression and to further determine if this regulatory effect is dependent on SIRT6’s deacetylase activity. Results: Ang II promoted lipid droplet and cholesterol accumulation in rat glomeruli, suppressed SIRT6 expression, and enhanced SREBP2 activation, evidenced by increased SREBP2 levels and nuclear translocation. Transfection of pcDNA3.1SIRT6 into podocytes attenuated SREBP2 activation, reducing Ang II-induced cholesterol accumulation and apoptosis. Experiments using pcDNA3.1 SIRT6 and pcDNA3.1 SIRT6 H133Y plasmids indicate that SIRT6-mediated suppression of SREBP2 requires its histone deacetylase activity. Conclusion: We conclude that SIRT6 serves as a key protective regulator of podocytes against RAS activation, at least in part by suppressing SREBP2 expression and thereby alleviating cholesterol accumulation and associated podocyte injury. It provides a new target for clinical treatment of CKD.