NDT Advance Access originally published online on January 12, 2005
Nephrology Dialysis Transplantation 2005 20(3):524-531; doi:10.1093/ndt/gfh642
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P-Cadherin is decreased in diabetic glomeruli and in glucose-stimulated podocytes in vivo and in vitro studies
1 Department of Internal Medicine, College of Medicine, Institute of Kidney Disease, Brain Korea 21, Yonsei University, Seoul, Korea, 2 Division of Nephrology and Hypertension, Department of Internal Medicine, Harbor–UCLA Research and Education Institute, Torrance, CA, USA and 3 Department of Diabetes, Beckman Research Institute of the City of Hope, Duarte, CA, USA
Correspondence and offprint requests to: Shin-Wook Kang, MD, PhD, Yonsei University College of Medicine, Department of Internal Medicine, 134 Shinchon-Dong, Seodaemoon-Gu, Seoul 120-752, Korea. Email: kswkidney{at}yumc.yonsei.ac.kr.
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.
Keywords: P-cadherin; diabetic nephropathy; high glucose; podocyte; proteinuria
The authors wish it to be known that, in their opinion, the first four authors contributed equally to this work.