SIRT3 Blocks Aging-Associated Tissue Fibrosis in Mice by Deacetylating and Activating Glycogen Synthase Kinase 3β.

Tissue fibrosis is a major cause of organ dysfunction during chronic diseases and aging. A critical step in this process is transforming growth factor beta 1 (TGF-beta 1)-mediated transformation of fibroblasts into myofibroblasts, cells capable of synthesizing extracellular matrix. Here, we show that SIRT3 controls transformation of fibroblasts into myofibroblasts via suppressing the profibrotic TGF-beta 1 signaling. We found that Sirt3 knockout (KO) mice with age develop tissue fibrosis of multiple organs, including heart, liver, kidney, and lungs but not whole-body SIRT3-overexpressing mice. SIRT3 deficiency caused induction of TGF-beta 1 expression and hyperacetylation of glycogen synthase kinase 3 beta(GSK3 beta) at residue K15, which negatively regulated GSK3 beta activity to phosphorylate the substrates Smad3 and beta-catenin. Reduced phosphorylation led to stabilization and activation of these transcription factors regulating expression of the profibrotic genes. SIRT3 deacetylated and activated GSK3 beta and thereby blocked TGF-beta 1 signaling and tissue fibrosis. These data reveal a new role of SIRT3 to negatively regulate aging-associated tissue fibrosis and discloses a novel phosphorylation-independent mechanism controlling the catalytic activity of GSK3 beta.