Abstract 392: Increased Oxidative Stress and Apoptosis as Mechanisms for Adverse Effects of Chronic Pressure Overload and Catecholamine Stress in Mice with Cardiac Overexpression of Type 5 Adenylyl Cyclase

Abstract

Studies with cardiac overexpression of type 6 adenylyl cyclase (AC6) suggest it protects against cardiac stress. Less is known about cardiac overexpression of AC5. We generated transgenic (Tg) mice with cardiac specific overexpression of AC5 and examined both the effects of pressure overload induced by 1 wk of transverse aortic banding (TAC) and 1 wk of chronic isoproterenol (ISO) delivered by osmotic mini-pump (n=8/group). TAC induced greater, p<0.05, left ventricular (LV) hypertrophy, as assessed by LV/body weight, in AC5 Tg (4.9±0.2) compared with wild type (WT) (4.0±0.1) and exhibited a significant decrease, p<0.05, in LV ejection fraction (LVEF) (58±4%) where LVEF was maintained in WT (75±1%). TUNEL analysis shows that apoptosis in AC5 Tg was twice that in WT, p<0.05. This was confirmed by a 2-fold increase in activity of caspase 3 in AC5 Tg compared to WT mice, p<0.05. The AC5 Tg began to develop heart failure as reflected by increased, p<0.05, lung/body weight (10.2±1.6) vs WT (6.4±0.2). In the heart, the antioxidant manganese superoxide dismutase (MnSOD), quantified by western blotting, was decreased by 40% in AC5 Tg compared to WT mice, p<0.05, after 1 wk of aortic banding. Chronic ISO also induced a greater, p<0.05, decrease in LVEF (48±4%) compared to WT (60±2%). 100 microM of ISO stimulation increased cell viability by 36% and decreased apoptosis by 34% (p<0.05 vs LacZ control). MnSOD was upregulated by 2.9-fold in AC5 knockdown myocytes after treatment with ISO for 48 hrs. These results demonstrate that cardiac overexpression of AC5 exerts adverse effects on oxidative stress and apoptosis in response to both chronic pressure overload and catecholamine stress.