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 (10-7M 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 × 10-2 attm/ng RNA) than in C rats (2.61±0.33 × 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.
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Acknowledgements. The authors are thankful to Dr Peter Mundel (Albert Einstein College of Medicine, Bronx, NY, USA) for kindly providing us with the immortalized mouse podocyte cell line. This work was supported by a Korea Research Foundation grant (KRF-2002-042-E00045) and grants from the Juvenile Diabetes Research Foundation (to S.G.A. and R.N.) and the National Institutes of Health (RO1-DK58191) (to R.N.).
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