Sirtuin‐1‐dependent COX2 Induction is an Essential Survival Mechanism in Renal Medullary Interstitial Cells against Oxidative Stress

Abstract

The present studies examined the role of NAD+‐dependant deacetylase sirtuin‐1 (SIRT1) in protecting the cells in renal medulla against oxidative stress. High levels of nitrosylated tyrosine were detected in renal medulla compared with renal cortex of C57BL6/j mice by immunohistochemistry, consistence with the presence of oxidative stress in renal medulla. Immunoblot and immunohistochemistry also showed abundant SIRT1 in renal medulla, mainly co‐localizing with COX2 in renal medullary interstitial cells (RMICs) by immunofluorescence. Selective knock‐down of SIRT1 in cultured mouse RMICs by shRNA significantly increased H2O2 (500 μM) induced cell death (from 48±5% to 78±4%, P<0.0001), accompanied with increased activated‐caspase‐3 levels. SIRT1 knock‐down also almost abolished H2O2‐induced COX2 expression (P<0.0001). ChIP showed physical association of SIRT1 with mouse COX2 gene promoter, supporting a role of SIRT1 in modulating COX2 transcription. Pre‐treatment with PGE2 (0.1, 1 μM) dose dependently protected cultured SIRT1‐deleted RMICs from H2O2 induced cell death (from 57±5% to 31±6% and 18±9% respectively, P<0.0001), suggesting COX2 derived PGE2 contributes to the protective effect of SIRT1. These data are consistent with an important role for SIRT1 in regulating COX2 expression and promoting cell adaptation to oxidative stress in renal medulla. Research supported by NIH.