Background: In a) OVE26 mice with type 1 diabetes, b) C57BI/6 mice with diet induced obesity and insulin resistance, and c) db/db mice with type 2 diabetes mellitus, we have found increased renal expression of the transcriptional factors, i) the sterol regulatory element binding proteins 1 and 2 (SREBP-1 and SREBP-2), and ii) the carbohydrate response element binding protein (ChREBP), which result in increased synthesis and accumulation of triglyceride and cholesterol. The lipid accumulation is associated with development of robust glomerulosclerosis, tubulointerstitial fibrosis, and proteinuria. We have also found that the Farnesoid X Receptor (FXR) is highly expressed in the kidney and the expression of FXR and its target enzymes is decreased in the diabetic kidney. Furthermore we have determined that FXR is an important regulator of SREBP-1 and ChREBP expression as well as oxidative stress, advanced glycation end products (AGEs/RAGE), pro-inflammatory cytokines, and fibrosis inducing growth factors. Hypothesis: Based on these finding we propose that FXR plays an important role on the pathogenesis of diabetic nephropathy. We hypothesize that deletion of FXR will markedly enhance and overexpression of FXR will attenuate diabetic nephropathy in mouse models of type 1 (OVE26) and type 2 (db/db) diabetes. Mouse Model 1: A) We will generate FXR knockout mice, currently on the C57BI/6 genetic background, on Background: In a) OVE26 mice with type 1 diabetes, b) C57BI/6 mice with diet induced obesity and insulin the FVB, and if need be and DBA/2J genetic backgrounds, 2 genetic backgrounds that have been documented to have increased susceptibility to diabetic nephropathy. B) We will then cross breed FXR KO mice on FVB background with i) OVE26 mice (type 1 diabetes) on FVB background or ii) db/db mice (type 2 diabetes) on FVB background to determine if FXR deletion accentuates and accelerates diabetic nephropathy. C) We will generate renal podocyte specific FXR knockout mice on FVB background using the Lox-Cre approach (FXRf/f mice crossed with Nphs2 Cre mice). D) We will then crossbreed podocyte FXR KO mice with i) OVE26 mice or ii) db/db mice. Mouse Model 2: A) We will generate renal podocyte specific conditional and inducible FXR transgenic mice in the FVB Background. B) We will then crossbreed the podocyte specific FXR transgenic mice with OVE26 or db/db mice to determine if increased expression of FXR attenuates or prevents diabetic nephropathy. Phenotyping: In these mice we will determine a) the manifestation of diabetic nephropathy, including glomerular filtration rate, glomerulosclerosis, tubulointerstitial fibrosis, and proteinuria and b) the cellular and biochemical mechanisms that mediate diabetic renal injury including lipid and carbohydrate metabolism, inflammation, fibrosis, oxidative stress, and AGEs/RAGE.
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