Ubiquitination and endoplasmic reticulum stress of renal intrinsic cells in hyperglycemia / 中华肾脏病杂志

ABSTRACT

Objective To investigate the effects of hyperglycemia on ubiquitination and endoplasmic reticulum stress in renal intrinsic cells (podocytes and proximal tubular epithelial cells)and its role in pathogenesis of diabetic nephropathy.Methods Diabetic mice were induced by streptozotocin injection.After 16 weeks of hyperglycemia,immunofluorescence was used to detect the expressions of ubiquitination and glucose-regulating protein 94 (GRP94) in renal cortex and medulla area of kidney sections.Primary mouse podocyte and proximal tubular epithelial cells were isolated by flow cytometry,and exposed to 30 mmol/L glucose for indicated time (1 d,3 d and 7 d).Their ubiquitination and GRP94 expressions were evaluated by Western blotting.Results Diabetic mice presented microalbuminuria and slightly widened mesangium was found in glomerular area.Ubiquitinated proteins,mainly localized in podocytes and tubular epithelial cells,exhibited an apparently higher expression in diabetic mice than control mice (all P ＜ 0.05).Hyperglycemia promoted the ubiquitination in a time-dependent manner.Compared with their normal cells,primary mouse podocyte and primary tubular epithilial cells treated with high glucose for 3 d and 7 d showed increased ubiquitinated protein (all P ＜ 0.05).GRP94 was interspersed in podocytes and proximal tubular epithelial cells.Expression of GRP94 was significantly increased in glomerular area of diabetic mice and podocyte with 3 and 7 day-high glucose as compared with those in their control groups (all P ＜ 0.05).GRP94 expression had no significant change in tubular area and tubular epithilial cells treated with high glucose.Conclusions Hyperglycemia may lead to accumulation of ubiquitinated proteins in intrinsic kidney cells.The imbalance of protein homeostasis in podocyte may contribute to podocyte injury during the onset of diabetic nephropathy.