Abstract 3290: Increased Type 5 Adenylyl Cyclase Expression Mediates Chronic Catecholamine Stress via Increases in Oxidative Stress and Down-regulation of MnSOD
Since knocking out (KO) type 5 adenylyl cyclase (AC5) has been shown to be protective against cardiac stress with chronic high dose of isoproterenol (ISO), we hypothesized that the effects of transgenic cardiac overexpression of AC5 (AC5 Tg) would exacerbate the adverse effects of cardiac stress induced by chronic ISO. Since oxidative stress is protective in AC5 KO, in part by upregulation of Mn-superoxide dismutase (SOD), we hypothesized further that a key mechanism mediating the diametric differences in response to chronic ISO in the AC5 Tg and AC5 KO involved oxidative stress. Accordingly, we compared the effects of chronic ISO (60mg/kg/day), delivered by implanted mini-osmotic pumps, in AC5 Tg, AC5 KO and wild type (WT) mice. Mortality was significantly greater, p<0.01, i.e., 25% AC5 Tg mice died after day-7 with heart failure while none of the WT died. At 1 week after ISO (n=10/group) LV ejection fraction (LVEF) in AC5 Tg was lower (48±3% vs 58±2%, p<0.05) but was higher in AC5 KO (63±1.6%). Cardiac fibrosis was increased in AC5 Tg (8.4±0.2%) vs WT (5.2±0.3%), p<0.05. Apoptosis, measured by TUNEL, was increased more in AC5 Tg (1.4±0.3 positive cells/mm2) vs WT (0.6±0.1 positive cells/mm2), p<0.05. Therefore, adverse effects were observed in AC5 Tg. Oxidative stress induced by ISO was detected by 8-Hydroxy-2′-deoxyguanosine (8-OHdG) staining and AC5 Tg hearts showed 27% more positive staining than WT. The antioxidant MnSOD protein was 40% lower in AC5 Tg than in WT, but 40% higher in AC5 KO. After AC5 KO were mated with MnSOD heterozygous KO mice, the LV ejection fraction with chronic ISO (58±1%) was no longer higher than in WT. We also hypothesized that inhibition of AC5 activates Sirt1 and FoxO3a, key transcription regulators of MnSOD. Sirt1 and FoxO3a were 2.7-fold and 5-fold higher, respectively, in AC5 knockdown myocytes than AC5 overexpressed myocytes. We also found a 3.6-fold increase in MnSOD mRNA in AC5 knock down myocytes compared with LacZ controls, p<0.05. Thus, AC5, when overexpressed, exacerbates the adverse effects of chronic catecholamine stress, whereas AC5 inhibition is protective. These opposite effects are mediated, in part, by oxidative mechanisms.