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+/-0.20x10(-2) attm/ng RNA) than in C rats (2.61+/-0.33x10(-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.