Key words: recurrent UTI, young women, TGF-β1 YASUDA MAKO, TAGAWA ATSUKO, KUME SHINJI, YAMAHARA KOSUKE, ARAKI HISAZUMI, ISSHIKI KEIJI, ARAKI SHIN-ICHI, UZU TAKASHI, MAEGAWA HIROSHI Deparment of Medicine, Shiga University of Medical Science,
Japan Introduction: Diabetic nephropathy is a leading cause of end-stage renal disease worldwide. Methods for reducing proteinuria in check details the patients with diabetic nephropathy are still required. Since podocytes are terminally differentiated and are unable to proliferate, disruption of cell homeostasis in podocytes results in impairment to glomerular filtration barrier function, leading to proteinuria in diabetic nephropathy. Intracellular degradation systems are essential for maintaining cell homeostasis. One of these systems, autophagy, is evolutionary buy MLN0128 conserved machinery for bulk degradation of cytoplasmic components. Alterations in autophagy
have recently been found to be the pathogenesis for some metabolic diseases. Therefore, this study examined the role of podocyte autophagy in diabetic nephropathy. Methods: We first examined the relationship between activity of podocyte autophagy and the progression of diabetic nephropathy by using human renal biopsy samples. We next generated podocyte-specific autophagy-deficient (Podo-Atg5−/−) mice by podocyte-specific Atg5 gene deletion. Eight-week-old control (Atg5f/f) and Podo-Atg5−/− mice were fed with either a standard diet or a high-fat diet for 32 weeks to induce type 2 diabetes. Results: Massive accumulation of p62 protein, a marker of autophagy insufficiency, was observed in the podocytes of the diabetic patients with overt proteinuria. To reveal the relationship between autophagy insufficiency and the progression of diabetic
nephropathy, we next conducted an animal study using Podo-Atg5−/− mice. At the end of the experimental period of a HFD feeding for 32 weeks, both Atg5f/f and Podo-Atg5−/− mice developed obesity and hyperinsulinemic hyperglycemia resembling type 2 diabetes mellitus. In Podo-Atg5−/− mice, high-fat Farnesyltransferase diet-induced increases in urinary albumin excretion were significantly higher compared with those of Atg5−/−, although high-fat diet-induced glomerular histological changes were almost the same in both groups. Fibrosis and infiltration of inflammatory cells in tubulointerstitial lesions were significantly exacerbated in Podo-Atg5−/− mice fed a high-fat diet. Conclusion: The results suggest that autophagy is essential to protect podocytes from diabetes-related cellular toxicity. Although further study is required, autophagy appears to be a possible new therapeutic target for reducing proteinuria in diabetic nephropathy.