Autosomal-dominant polycystic kidney disease (ADPKD) is caused by mutations in either PKD1 or PKD2 and is characterized by the development of multiple bilateral renal cysts that replace normal kidney tissue. Here, we used Pkd1 mutant mouse models to demonstrate that the nicotinamide adenine dinucleotide–dependent (NAD-dependent) protein deacetylase sirtuin 1 (SIRT1) is involved in the pathophysiology of ADPKD. SIRT1 was upregulated through c-MYC in embryonic and postnatal Pkd1-mutant mouse renal epithelial cells and tissues and could be induced by TNF-α, which is present in cyst fluid during cyst development. Double conditional knockouts of Pkd1 and Sirt1 demonstrated delayed renal cyst formation in postnatal mouse kidneys compared with mice with single conditional knockout of Pkd1. Furthermore, treatment with a pan-sirtuin inhibitor (nicotinamide) or a SIRT1-specific inhibitor (EX-527) delayed cyst growth in Pkd1 knockout mouse embryonic kidneys, Pkd1 conditional knockout postnatal kidneys, and Pkd1 hypomorphic kidneys. Increased SIRT1 expression in Pkd1 mutant renal epithelial cells regulated cystic epithelial cell proliferation through deacetylation and phosphorylation of Rb and regulated cystic epithelial cell death through deacetylation of p53. This newly identified role of SIRT1 signaling in cystic renal epithelial cells provides the opportunity to develop unique therapeutic strategies for ADPKD.
Authors
Xia Zhou, Lucy X. Fan, William E. Sweeney Jr., John M. Denu, Ellis D. Avner, Xiaogang Li
(A) Western blot analysis of p53 and active caspase-3 expression in Pkd1-null MEK cells transfected or not with p53 siRNA for 24 hours and then treated or not with 10 mM nicotinamide for another 24 hours. (B) Knockdown of p53 with siRNA prevented nicotinamide-induced apoptosis, as detected by TUNEL assay, in Pkd1-null MEK cells that were transfected or not with p53 siRNA for 24 hours and then treated or not with 10 mM nicotinamide for 24 hours. (C) Overexpression of WT p53, but not mutant p53-8KR (which is mutated at 8 acetylation sites), increased apoptosis in Pkd1-null MEK cells treated with nicotinamide. Pkd1-null MEK cells were transfected with WT p53, mutant p53-8KR, or empty vector together with or without nicotinamide for 24 hours, then analyzed by TUNEL assay. (D) SIRT1-mediated pathways in Pkd1-mutant renal epithelial cells. Pkd1 knockout or mutation upregulates SIRT1 through c-MYC. Upregulated SIRT1 in Pkd1-mutant renal epithelial cells (i) is a target of nicotinamide, which decreases proliferation and induces apoptosis of cystic epithelial cells to delay cyst growth in Pkd1-null mouse kidneys; (ii) regulates the acetylation and phosphorylation of Rb and further affects Rb-E2F–mediated S-phase entry; (iii) regulates the p53 acetylation and p53-dependent apoptosis in response to nicotinamide; and (iv) can be regulated by c-MYC and induced by TNF-α. Scale bars: 50 μm. **P 0.01.