Abstract P198: High Glucose Degrades (PRO) Renin Receptor by Autophagy and Ubiquitin Proteasome System in Inner Medullary Collecting Duct Cells

Abstract

Previously we reported high glucose (HG) regulation of PRR expression in the kidney. However, in contrast to the observed increase in PRR expression in mesangial cells and podocytes, its expression decreased in distal tubules in response to HG. We hypothesize that HG degrades PRR through autophagy and ubiquitin proteasome system in inner medullary collecting duct cells. Mouse inner medullary collecting duct cells (mIMCDs) were cultured for 3 days in normal glucose (NG, 5 mmol/L) or HG (25 mmol/L). The mRNA and protein expressions of PRR were evaluated in response to HG alone and in presence of the proteasome inhibitor, MG-132 (10 mM) during the HG exposure. In addition, we monitored protein expressions of PRR and the autophagy activity markers, LC3-II and p62, in response to the autophagy inhibitor, bafilomycin A1 (160 nM). HG significantly increased PRR mRNA level after HG treatment (28% vs NG, P<0.05). In contrast, PRR protein expression was significantly decreased (31% vs NG, P<0.05). Pretreatment of MG-132 for 4 hours increased PRR expression after 3 days HG exposure (66% vs HG, P<0.05). Similarly, HG decreased LC3-II and p62 at 3 days of HG exposure (66% and 50% respectively, P<0.05). Bafilomycin A1 pretreatment for 2 hours attenuated the HG induced reduction in PRR protein and increased the expression of LC3-II and p62 (250% and 71% respectively, P<0.05). We conclude that HG degrades mIMCDs PRR protein via increased autophagy and ubiquitin-proteasome activity.