Abstract 14687: Activation of Sirt1 Suppresses Hypertrophic Response of Cardiomyocytes by Inhibition of H3K9 Acetylation via Proteasome-mediated p300 Degradation.
Background: Histone acetylation promotes gene transcription and plays a role in cardiac hypertrophy. Although activation of the histone/protein deacetylase Sirt1 has been shown to afford cardiomyocyte protection against various types of injury, significance of histone deacetylation by Sirt1 is still unclear. In this study, we hypothesized that activation of Sirt1 suppresses cardiomyocyte hypertrophy by inhibiting histone acetylation at the gene promoter.
Methods and Results: Neonatal rat cardiomyocytes were exposed to phenylephrine (PE, 50 μM) to induce hypertrophic responses. Overexpression of wild-type Sirt1, but not that of a catalytically inactive mutant, significantly suppressed myocyte enlargement induced by PE. Likewise, pretreatment with a Sirt1 activator resveratrol (RSV) inhibited PE-induced increases in myocyte size and atrial natriuretic peptide (ANP) expression. Immunoblotting showed that the level of acetylated histone H3 at lysine 9 (H3K9) was significantly increased after PE treatment, which was completely suppressed by RSV pretreatment. H3K9 deacetylation by RSV was abolished by knockdown of Sirt1 by siRNA. The protein level of a transcription cofactor p300, which possesses histone acetyltransferase activity and is reported to be activated upon PE stimulation, was significantly decreased by RSV. In contrast, the p300 mRNA level was not changed by RSV. Blocking Sirt1 activity using nicotinamide or knockdown of Sirt1 caused an increase in p300 protein level. A proteasome inhibitor, MG132, not only increased the p300 protein level but also blocked the RSV-induced reduction in p300 protein, suggesting that Sirt1 promotes p300 protein degradation via the ubiquitin-proteasome pathway. Chromatin immunoprecipitation assay demonstrated that the levels of acetyl-H3K9 at the promoters of ANP and beta-myosin heavy chain (MHC), but not that of alpha-MHC, were reduced by RSV in the presence of PE, indicating that Sirt1 activation inhibited hypertrophic response by H3K9 deacetylation at the promoters.
Conclusion: The findings suggest that activation of Sirt1 suppresses hypertrophic response by inhibiting H3K9 acetylation via proteasome-mediated p300 degradation besides direct histone deacetylation by Sirt1.
- © 2010 by American Heart Association, Inc.