AGEs-rage system down-regulates sirt1 through the ubiquitin-proteasome pathway to promote fn and tgf-ß1 expression in male rat glomerular mesangial cells

Abstract

We previously demonstrated that advanced glycation-end products (AGEs) promote the pathological progression of diabetic nephropathy by decreasing silent information regulator 2-related protein 1 (Sirt1) expression in glomerular mesangial cells (GMCs). Here, we investigated whether AGEs-receptor for AGEs (RAGE) system down-regulated Sirt1 expression through ubiquitin-proteasome pathway and whether Sirt1 ubiquitination affected fibronectin (FN) and TGF-ß1, 2 fibrotic indicators in GMCs. Sirt1 was polyubiquitinated and subsequently degraded by proteasome. AGEs increased Sirt1 ubiquitination and proteasome-mediated degradation, shortened Sirt1 half-life, and promoted FN and TGF-ß1 expression. Ubiquitin-specific protease 22 (USP22) reduced Sirt1 ubiquitinationanddegradationanddecreasedFNandTGF-ß1 expression inGMCsunder both basal and AGEs-treated conditions. USP22 depletion enhanced Sirt1 degradation and displayed combined effects with AGEs to further promote FN and TGF-ß1 expression. RAGE functioned crucial mediating roles in these processes via its C-terminal cytosolic domain. Inhibiting Sirt1 by EX-527 substantially suppressed the down-regulation of FN and TGF-ß1 resulting from USP22 overexpression under both normal and AGEs-treated conditions, eventually leading to their up-regulation in GMCs. These results indicated that the AGEs-RAGE system increased the ubiquitination and subsequent proteasome-mediated degradation of Sirt1 by reducing USP22 level, and AGEs-RAGEUSP22-Sirt1 formed a cascade pathway that regulated FN and TGF-ß1 level, which participated in the pathological progression of diabetic nephropathy.