Abstract 17474: Type 5 Adenylyl Cyclase Increases Oxidative Stress by Transcriptional Regulation of MnSOD via the Sirt1/FoxO3a Pathway
We previously reported that increased type 5 adenylyl cyclase (AC5) expression in AC5 transgenic (Tg) mice enhances chronic catecholamine stress via increases in oxidative stress and down-regulation of Mn superoxide dismutase (SOD). The first goal of the current study was to determine if the cardiomyopathy induced by chronic catecholamine stress in AC5 Tg mice can be rescued by increasing MnSOD by mating them with MnSOD Tg mice. The second goal was to determine the signaling pathway involved in the rescue. The cardiomyopathy was induced by chronic isoproterenol (ISO)(60mg/kg/day, delivered by osmotic pump for 7 days). The severity of the cardiomyopathy was significantly less, p<0.05, after chronic ISO stimulation in the bigenic mice, as reflected by attenuated decreases in left ventricular (LV) ejection fraction (EF) (-13±1% from 84±1%) than in AC5 Tg mice (-45±1% from 81±1%), but similar to that in the wild type mice, indicating that MnSOD played a key role in mediating the enhanced cardiomyopathy in AC5 Tg mice. Next, we investigated the pathway that regulated MnSOD by AC5. Since we found previously that AC5 regulated MnSOD in a transcriptional manner, potential candidates were screened. In the nuclear fraction of AC5 knockdown (KD) myocytes, 2 fold elevation of FoxO3a was detected by western blotting along with 3 fold more transcriptional activity of FoxO3a. Chromatin immunoprecipitation (ChIP) assay showed 3 fold more FoxO3a binding to the MnSOD promoter in AC5 KD H9C2 cells. Since transcriptional activity of FoxO3a was activated by de-acetylation and less acetyl-FoxO3a was detected in AC5 KO heart, we investigated whether deacetylase, such as Sirt1, was involved in the regulation of MnSOD in AC5 KD myocytes. Co-immunoprecipitation (co-IP) showed that more Sirt1 binds directly to FoxO3a in AC5 KD myocytes. Inhibition of Sirt1 activity by nicotinamide eliminated the elevation of transcriptional activity of FoxO3a and MnSOD expression in AC5 KD myocytes. In conclusion, AC5 inhibits Sirt1 activity, which consequently decreases the interaction between Sirt1 and FoxO3a, thus decreasing MnSOD expression, which is the mechanism for the exacerbation of catecholamine cardiomyopathy in AC5 Tg mice.
- © 2012 by American Heart Association, Inc.