Pdk1 Is A Key Regulator Of Podocyte Viability And Maintenance Of Glomerular Function

In diabetic states, altered activity of insulin signaling pathway is likely to play key roles in insulin resistance and in kidney dysfunction. Since the 3-phosphoinositide-dependent protein kinase 1 (PDK1) serves as a major signaling molecule in the regulation of cellular responses in multiple organs by mediating the phosphoinositide 3-kinase signaling pathway, we tested the hypothesis that podocyte-specific deletion of PDK1 leads to podocyte injury and proteinuric kidney disease. PDK1 was selectively silenced in podocytes using Cre-mediated recombination controlled by the podocin promoter. Mice with a podocyte-specific deletion of PDK1 (PDK1 KO) developed proteinuria, and died due to end-stage renal disease by 5 weeks after birth. Histologically, features characteristic of glomerulosclerosis, including podocyte foot process effacement, mesangial sclerosis, and protein casts, were observed in PDK1 KO at 3 weeks of age. We also examined podocyte distribution in glomeruli using the podocyte markers synaptopodin and WT-1, and found that their expressions were lost in some glomeruli of PDK1 KO at 3 weeks of age although their expression patterns at 1 weeks of age PDK1 KO were almost comparable with control mice. We next examined a possible role of forkhead transcription factor, forkhead box O1 (FoxO1) in linking PDK1 of podocytes to kidney function. For this, we generated podocyte-specific PDK1 and FoxO1 double knockout mice (DKO) by introducing Foxo1-flox gene into PDK1 KO mice. DKO exhibited a reduced level of proteinuria compared with age-matched PDK1 KO, and the maximal survival time of DKO had extended to 6.6 weeks after birth. Taken together, PDK1-FoxO1 pathway may be one of the critical signal transduction pathways that links podocyte injury and kidney dysfunction in diabetic states. Disclosure W. Iwata: None. H. Unoki-Kubota: None. H. Kato: None. M. Matsumoto: None. M. Nangaku: Consultant; Self; Akebia Therapeutics, Astellas Pharma Inc., Bayer AG, Boehringer Ingelheim International GmbH, Daiichi Sankyo, GlaxoSmithKline plc., Japan Tobacco Inc., Kyowa Hakko Kirin Co., Ltd., Mitsubishi Tanabe Pharma Corporation, Novo Nordisk Inc., Otsuka Pharmaceutical Co., Ltd., Scohia Pharma Inc. Research Support; Self; Takeda Pharmaceutical Company Limited. Speaker’s Bureau; Self; AstraZeneca, Torii Pharmaceutical Co. Ltd. Y. Kaburagi: None.