P-Cadherin is decreased in diabetic glomeruli and in glucose-stimulated podocytes in vivo and in vitro studies

Background. Proteinuria is a cardinal feature of glomerular disease, including diabetic nephropathy, and the glomerular filtration barrier acts as a filter, restricting protein excretion in urine. We tested whether the expression of P-cadherin, a molecule known to be located at the slit diaphragm, was altered by diabetes in vivo and by high glucose in vitro. Methods. In vivo, 24 Sprague-Dawley rats were injected with diluent [control (C), n = 8] or streptozotocin intraperitoneally and the latter were left untreated (DM, n = 8) or treated with insulin (DM+I, n = 8) for 6 weeks. In vitro, immortalized mouse podocytes were cultured in media with 5.6 mM glucose (LG), LG + 19.4 mM mannitol (LG + M) or 25 mM glucose (HG) with or without protein kinase C (PKC) inhibitor (10(-7) M calphostin C or 10(-6) M GF 109203X). Reverse transcription-polymerase chain reaction, western blotting for P-cadherin mRNA and protein expression, respectively, were performed with sieved glomeruli and cell lysates, and immunofluorescence staining was undertaken with renal tissue. Results. Twenty-four hour urinary albumin excretion was significantly higher in DM compared with C and DM+I rats (P < 0.05). Glomerular P-cadherin mRNA expression was significantly lower in DM (1.36 +/- 0.20 x 10(-2) attm/ng RNA) than in C rats (2.61 +/- 0.33 x 10(-2) attm/ng RNA) (P < 0.05). P-Cadherin protein expression, assessed by western blot and immunofluorescence staining, was also decreased in DM compared with C and DM+I glomeruli. HG significantly reduced P-cadherin mRNA and protein expression in cultured podocytes by 42% and 62%, respectively (P < 0.05), and these decrements were ameliorated by PKC inhibitor. Conclusions. Diabetes in vivo and exposure of podocytes to HG in vitro reduced P-cadherin mRNA and protein expression, and PKC was involved in the regulation of HG-induced down-regulation of P-cadherin. These findings suggest that the decrease in P-cadherin expression is connected with the early changes of diabetic nephropathy and, thus, may contribute to the development of proteinuria.