Abstract 179: Activation of the Longevity Factor, SIRT1 Deacetylase Blocks the Phenylephrine-induced Cardiomyocyte Hypertrophy
Background: SIRT1 is a member of class-III histone deacetylases. It has been shown to participate in a wide array of cellular functions including, gene silencing, cell-growth, apoptosis and aging. Since histone acetylases (p300/CBP) have been shown to participate in the development of cardiomyocyte hypertrophy, we hypothesized that SIRT1 deacetylase may function as a negative regulator of cardiac hypertrophy.
Methods and Results: Primary cultures of neonatal rat heart myocytes, maintained in serum-free media, were stimulated with phenylephrine (PE, 20μM) to induce hypertrophy. Seventy two hours following PE-stimulation, cells were harvested and hypertrophy was determined by monitoring protein-synthesis, sarcomere organization and induction of fetal genes (ANF, βMHC and sk-α-actin) expression. To examine the effect of SIRT1 on myocyte growth, cells were infected with adenovirus vectors expressing either wild-type or mutant SIRT1, having H355Y mutation that destroys the catalytic activity of the deacetylase. PE-stimulation enhanced the myocyte protein content by almost two folds and resulted into highly organized structures of sarcomeres with increased myocyte size. This PE-mediated hypertrophy response of myocytes was completely blocked by over expression of the SIRT1 deacetylase, but not the mutant vector. Similarly, SIRT1 activation prevented the PE-mediated induction of fetal gene transcripts of ANF, βMHC and sk-α-actin, thus, indicating a negative hypertrophy role of SIRT1 activation. To understand the mechanism behind this anti-hypertrophy effect of SIRT1, we analyzed its effect on the ANF promoter/ luciferase reporter gene activity by the transient transfection analysis. PE-treatment induced the ANF promoter activity by almost 4 folds in control cells; however, in cells where SIRT1 was over expressed no reporter gene induction could be observed. Also a shorter fragment of the ANF promoter that was insensitive to PE-treatment was unresponsive to SIRT1 activation, suggesting that SIRT1 interferes with the activity of a PE-responsive transcription factor that regulates the ANF promoter activity during hypertrophy.
Conclusion: SIRT1 deacetylase is a negative regulator of agonist-mediated cardiomyocyte hypertrophy.