Metformin Effectively Treats <i>Tsc1</i> Deletion-Caused Kidney Pathology by Upregulating AMPK Phosphorylation

Abstract

Tuberous sclerosis complex (TSC) is characterized by hamartomatous lesions in multiple organs, with most patients developing polycystic kidney disease and leading to a decline of renal function. TSC is caused by loss-of-function mutations in either Tsc1 or Tsc2 gene, but currently there is no effective treatment for aberrant kidney growth in TSC patients. By generating a renal proximal tubule-specific Tsc1 gene knockout (Tsc1 ptKO) mouse model, we observed that Tsc1ptKO mice developed aberrantly enlarged kidneys primarily due to hypertrophy and proliferation of proximal tubule cells, along with some cystogenesis, interstitial inflammation and fibrosis. Mechanistic studies revealed inhibition of AMP-activated protein kinase (AMPK) phosphorylation at Thr-172 and activation of Akt phosphorylation at Ser-473 and Thr-308. We therefore treated Tsc1 ptKO mice with the AMPK activator, metformin, by daily intraperitoneal injection. Our results indicated that metformin increased the AMPK phosphorylation but decreased the Akt phosphorylation. These signaling modulations resulted in inhibition of proliferation and induction of apoptosis in the renal proximal tubule cells of Tsc1ptKO mice. Importantly, metformin treatment effectively prevented aberrant kidney enlargement and cyst growth, inhibited inflammatory response, attenuated interstitial fibrosis, and protected renal function. The effects of metformin were further confirmed by in vitro experiments. In conclusion, this study indicates a potential therapeutic effect of metformin on Tsc1 deletion-induced kidney pathology, although currently metformin is primarily prescribed to treat patients with type 2 diabetes. Funding Statement: This work was supported by grants from the Science and Technology Commission of Shanghai Municipality (No. 15140902900). Declaration of Interests: The authors have no conflict of interest to report. Ethics Approval Statement: Animal care and all experimental procedures were approved by Fudan University Basic Medical School’s Experimental Animal Ethical Committee (No.20150119-056), and complied with the guidelines of National Institutes of Health.