Cardiac-Directed Expression of Adenylyl Cyclase Catalytic Domain () Attenuates Deleterious Effects of Pressure Overload.

A fusion protein (C1C2) constructed by fusing the intracellular C1 and C2 segments of adenylyl cyclase type 6 (AC6) retains beneficial effects of AC6 expression, without increasing cyclic adenosine monophosphate generation. The effects of cardiac-directed expression in pressure overload is unknown. Left ventricular (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 function 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 4 weeks after TAC ( = 0.02), despite similar and substantial cardiac hypertrophy. In addition to higher LV peak +dP/dt , cardiac myocytes from C1C2 mice showed shorter time-to-peak Ca2+ transient amplitude ( = 0.002) and a reduced time constant of cytosolic Ca2+ decline (Tau;  = 0.003). Sarcomere shortening fraction ( < 0.03) and the rate of sarcomere shortening ( < 0.02) increased in C1C2 cardiac myocytes. Myofilament sensitivity to Ca2+ was increased in systole ( = 0.02) and diastole ( = 0.04) in C1C2 myocytes. These findings indicate enhanced Ca2+ handling associated with expression. Favorable effects on Ca2+ handling and LV function were associated with increased LV SERCA2a protein content ( = 0.015) and reduced LV fibrosis ( = 0.008). Cardiac-directed 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.