P-13/BO-02 : SIRT6 inhibits cardiac fibrosis by repressing SMAD3 transcription factor

posted Jan 26, 2017, 6:37 AM by sourav ghosh   [ updated Jan 26, 2017, 8:24 AM ]

Jaseer Muhamed1Faiz Ahamed1Mahesh P. Gupta2Nagalingam R. Sundaresan1
(1) Indian Institute of Science, Bangalore India, (2) Cardiothoracic Surgery Research Program, Biological Sciences Division And The Pritzker School of Medicine, University of Chicago, Chicago

Objective: Cardiac fibrosis is a major complication associated with aging and several cardiovascular diseases. Till now, there is no definitive therapy available for treatment of cardiac fibrosis. Our previous study identified the class-III histone deacetylase SIRT6 as a key regulator of cardiomyocyte hypertrophy. Objective of this study is to understand the role of SIRT6 in cardiac fibrosis. 
Methods: Cardiac fibrosis and TGF-β1 signaling was evaluated by histology and western blotting in SIRT6 deficient mice hearts. Gene expression was studied by real time RT-PCR. Neonatal cardiac fibroblasts were used for in vitro genetic experiments. TGF-β/SMAD3 signaling and α-SMA promoter activity was evaluated by luciferase assays. SIRT6 and SMAD3 interaction was probed by co-immunoprecipitation. SMAD3 occupancy in TGF-β1 promoter was investigated by chromatin immunoprecipitation (ChIP) assay. 
Results: Histology and or immunoblot analysis of SIRT6-/- mice heart, and SIRT6-/- fibroblasts showed increased expression of fibrotic markers like fibronectin 1, collagen 1a, and alpha smooth muscle actin (SMA). Interestingly, TGF-β/SMAD3 signaling was found to be spontaneously activated in SIRT6-/- heart and fibroblasts, which is associated with transcriptional up-regulation of TGF-β/SMAD3 signaling genes. Moreover, SIRT6 deficient cells express increased membrane associated TGF-β1 under basal conditions. On the other hand, over expression of SIRT6 in cardiac fibroblasts decreased the expression of fibrotic markers and TGF-β/SMAD3 signaling. Immunoprecipitation and Chromatin immunoprecipitation results suggested that SIRT6 interact with SMAD3 transcription factor and reduces the occupancy of SMAD3 to TGF-β1 promoter resulting in the repression of TGF-β1 promoter. Finally, inhibition of SMAD3 with specific inhibitor rescued the fibrotic phenotype of SIRT6 deficient cardiac fibroblasts.