CHOP mediates XBP1S-induced renal mesangial cell necrosis following high glucose treatment

Abstract

High glucose (HG)-induced apoptosis in mesangial cells (MCs) is a critical determinant during the pathogenesis of diabetic nephropathy. The signaling cascade inducing MCs apoptosis by HG involves overproduction of reactive oxygen species. Our previous studies have demonstrated that HG-induced oxidative stress is mediated by suppression of spliced/active X-box binding protein 1 (XBP1S), suggesting the importance of XBP1S in HG-induced MCs apoptosis. CHOP, an endoplasmic reticulum stress-associated proapoptotic signal, is involved in downstream of XBP1S. In the present study, we explored the effect of XBP1S in modulating HG-induced apoptosis in renal MCs and then identified the role of CHOP in these processes. Apoptosis and necrosis were quantified by flow cytometry; protein levels of XBP1S, caspase3, Bax, Bcl2, BNIP3, and CHOP were analyzed by Western blotting. The cellular localization of XBP1S was determined by immunofluorescence histochemistry. The binding of XBP1 to CHOP promoter was determined by chromatin immunoprecipitation assays. In addition, adenoviruses harboring XBP1S gene (Ad-XBP1S) were used to overexpress XBP1S, whereas the knockdown of CHOP was achieved by small interference RNA. HG suppressed nuclear distribution of XBP1S and induced apoptosis and necrosis in MCs. Ad-XBP1S infection enhanced the nuclear translocation of XBP1S and reduced MCs apoptosis and necrosis. XBP1S bound to the promoter region of CHOP and upregulated CHOP expression. Conversely, CHOP expression was reduced upon HG exposure and knockdown of CHOP increased necrosis but not apoptosis in MCs. These results suggest that XBP1S protected MCs from HG-induced apoptosis and necrosis, and CHOP participates in XBP1S-regulated necrosis but not apoptosis.