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Yi Lin Department of Physiology, College of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA

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Zhongjie Sun Department of Physiology, College of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA

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Conventional therapies for diabetic patients, such as strict glycemic control, do not completely stop the progression of diabetic nephropathy. Serum-free tri-iodothyronine (T3) levels were lower in patients with type II diabetes. The purpose of this study was to test a hypothesis that treatment with T3 would improve diabetic nephropathy in db/db mice, a model of type II diabetes. Male db/db mice (16 weeks) were treated with T3 for 4 weeks. Urinary excretions of albumin and blood glucose levels were measured. Kidneys were collected for histological examination and molecular assays of transforming growth factor-β1 (TGF-β1) expression and phosphatidylinositol 3-kinase (PI3K). T3 attenuated albuminuria in db/db mice, suggesting an improved kidney function. T3 significantly decreased accumulation of collagenous components in cortical interstitium (interstitial fibrosis) and expansion of mesangial matrix in glomeruli (glomerulosclerosis) and prevented the loss of glomeruli in db/db mice. Therefore, T3 improved the renal structural damage seen in diabetic mice. Notably, diabetic nephropathy was accompanied by a significant decrease in PI3K activity and an increase in TGF-β1 expression in kidneys. T3 restored renal PI3K activity, attenuated hyperglycemia, and decreased renal TGF-β1 expression in db/db mice. These effects of T3 were abolished by simultaneous treatment with PI3K inhibitor (LY294002). These data suggest that T3 prevented progressive kidney damage and remodeling in db/db mice by improving insulin signaling (e.g. PI3K activity).

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Yi Lin Department of Physiology, College of Medicine, University of Oklahoma Health Sciences Center (OUHSC), BMSB 662A, PO Box 26901, 940 SL Young Boulevard, Oklahoma City, Oklahoma 73104, USA

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Zhongjie Sun Department of Physiology, College of Medicine, University of Oklahoma Health Sciences Center (OUHSC), BMSB 662A, PO Box 26901, 940 SL Young Boulevard, Oklahoma City, Oklahoma 73104, USA

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Type 2 diabetes mellitus (T2DM) affects a large population worldwide. T2DM is a complex heterogeneous group of metabolic disorders including hyperglycemia and impaired insulin action and/or insulin secretion. T2DM causes dysfunctions in multiple organs or tissues. Current theories of T2DM include a defect in insulin-mediated glucose uptake in muscle, a dysfunction of the pancreatic β-cells, a disruption of secretory function of adipocytes, and an impaired insulin action in liver. The etiology of human T2DM is multifactorial, with genetic background and physical inactivity as two critical components. The pathogenesis of T2DM is not fully understood. Animal models of T2DM have been proved to be useful to study the pathogenesis of, and to find a new therapy for, the disease. Although different animal models share similar characteristics, each mimics a specific aspect of genetic, endocrine, metabolic, and morphologic changes that occur in human T2DM. The purpose of this review is to provide the recent progress and current theories in T2DM and to summarize animal models for studying the pathogenesis of the disease.

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