Cardiac-directed Expression of Adenylyl Cyclase Catalytic Domain (C1C2)
 Attenuates Deleterious Effects of Pressure Overload

A fusion protein (C1C2) constructed by fusing the intracellular C1 and C2 segments of 3 adenylyl cyclase type 6 (AC6) retains beneficial effects of AC6 expression, without increasing cAMP generation. The effects of cardiac-directed C1C2 expression in pressure- overload is unknown. LV pressure overload was induced by transverse aortic constriction (TAC) in C1C2 mice and in transgene negative (TG-) mice. Four weeks after TAC, LV systolic and diastolic function were measured, and Ca2+ handling was assessed. Four weeks after TAC, TG- animals showed reduced LV peak +dP/dt. LV peak +dP/dt in C1C2 mice was statistically indistinguishable from that of normal mice and was higher than that seen in TG- mice 4w after TAC (p=.02), despite similar and substantial cardiac hypertrophy. In addition to higher LV peak +dP/dt in vivo, cardiac myocytes from C1C2 mice showed shorter time to peak Ca2+ transient (p=.002) and a reduced time constant of cytosolic Ca2+ decline (Tau; p=.003). Sarcomere shortening fraction (p=.03) and the rate of sarcomere shortening (p<.02) were increased in C1C2 cardiac myocytes. Myofilament sensitivity to Ca2+ was increased in systole (p=.02) and diastole (p=.04) in C1C2 myocytes. These findings indicate enhanced Ca2+ handling associated with C1C2 expression. Favorable effects on Ca2+ handling and LV function were associated with increased LV SERCA2a protein content (p<.017) and reduced LV fibrosis (p=.008). Cardiac-directed C1C2 expression improves Ca2+ handling and increases LV contractile function in pressure- overload. These data provide a rationale for further exploration of C1C2 gene transfer as a potential treatment for heart failure.