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.
Xia Zhou, Lucy X. Fan, William E. Sweeney Jr., John M. Denu, Ellis D. Avner, Xiaogang Li
(A) qRT-PCR analysis of relative Sirt1 mRNA expression in WT MEK (WT), Pkd1-null MEK (Null), PH2, and PN24 cells. (B) Top: Western blot analysis of SIRT1 and c-MYC expression from whole cell lysates. Bottom: Relative SIRT1 expression, quantified from 3 independent immunoblots and standardized to actin. (C) Top: Western blot analysis of SIRT1 expression in mouse IMCD3 cells with Pkd1 knockdown by 2 different lentivector-mediated Pkd1 shRNAs, VIRHD/P/siPkd13297 (siPKD13297) and pGIPZ-siPkd1, compared with that in the cells transduced with the respective control vectors, VIRHD/P/siLuc and pGIPZ-NS. Bottom: Relative Pkd1 knockdown efficiency, evaluated by qRT-PCR, indicated that Pkd1 expression was reduced by more than 90% and 70% in VIRHD/P/siPKD13297– and pGIPZ-siPkd1–transduced mouse IMCD3 cells, respectively, compared with that in control vector–transduced cells. (D) Top: Western blot analysis of SIRT1 expression in kidneys from WT and Pkd1nl/nl mice collected at P7, P14, P21, and P28. Bottom: Relative SIRT1 expression in the kidneys, standardized to tubulin. (E and F) qRT-PCR analysis of Sirt1 mRNA expression (E) and Western blot analysis of SIRT1 and c-MYC expression (F) in P7 kidneys from Pkd1+/+:Ksp-Cre (WT) and Pkd1flox/flox:Ksp-Cre (Flox) neonates. (G) Western blot analysis of SIRT1 expression in primary human ADPKD and NHK cells. **P < 0.01.