The protective effects of rapamycin on cell autophagy in the renal tissues of rats with diabetic nephropathy via mTOR-S6K1-LC3II signaling pathway

Background: Previous studies have shown that podocyte autophagy is an important trigger for proteinuria and glomerulosclerosis. The mammalian rapamycin target protein (mTOR) occupies a pivotal position in the autophagy pathway. In this study, we planned to clarify the mechanism of mTOR regulation of podocyte autophagy and the effect of rapamycin (RAPA). Methods: All rats were randomly divided into normal control group (n = 8), DN group (n = 8), and RAPA group (n = 8). Blood and urine samples were collected at the 4th, 8th, and 12th weeks of the experiment. The serum creatinine (Scr), urine volume levels, and the 24 h urine protein (UP) levels were examined. The nephrin, podocin, mTOR, ribosomal S6 kinase 1 (S6K1), and autophagy marker light chain 3 (LC3II) expression levels were evaluated by immunohistochemistry, quantitative PCR, and immunoblotting. Results: The urine volume, 24 h UP, and Scr of the DN and RAPA groups increased significantly compared with the NC group (p < .05). Nephrin and podocin expression was decreased in the kidney tissues of the DN and RAPA groups compared with the NC group (p < .05). The expression levels of mTOR and S6K1 increased and LC3II expression decreased in the renal tissues of the DN and RAPA groups compared with the NC group (p < .05). After RAPA treatment, all the above indexes were improved compared with the DN group (p < .05), but were significantly abnormal compared with the NC group (p < .05). Conclusion: The proteinuria and kidney function had improved after RAPA treatment. These results confirmed that RAPA specifically binds to mTOR kinase, and inhibits mTOR activity, thereby regulating the pathological autophagic process.