Abstract 13222: Transgenic Mice with Cardiac-Directed Expression of a Catalytically Inactive AC6 have Increased LV Contractile Function Despite Marked Diminution of cAMP Production
Background: Cardiac-directed expression of adenylyl cyclase type 6 (AC6) has favorable effects on the failing heart, which is paradoxical since other agents that increase cAMP are deleterious in heart failure. One possibility is that AC6's beneficial effects on left ventricular (LV) function are independent of cAMP production.
Methods & Results: To test this hypothesis, we made a catalytically inactive AC6 mutant (AC6mut). To preserve structural similarity to normal AC6, we changed only a single amino acid, replacing aspartic acid with alanine at position 426 in the C1 loop. Gene transfer of AC6mut in cultured cardiac myocytes showed markedly impaired cAMP generation in response to isoproterenol (Iso) and forskolin (Fsk). We then generated transgenic (TG) mice with cardiac-directed AC6mut expression. Line 2 was a low expresser (2-fold increase in AC6 protein), but Lines 1 and 3 showed high level expression (6- and 7-fold), had similar results in LV cAMP generation and physiological studies, and were therefore combined in a single group. LV samples showed marked impairment of Iso- (74% reduction; p<0.001) and Fsk-stimulated (54% reduction; p<0.01) cAMP production (Figure, left). Isolated hearts from these animals (vs TG negative sibling mice) showed increased LV dP/dt response to isoproterenol infusion (Figure, right), despite impaired cAMP generation. In contrast, we previously showed that AC6 deleted TG mice have similarly impaired cAMP production, and have impaired LV contractile function.
Conclusion: Increased LV function despite marked impairment of cAMP generating capacity indicates that AC6mut beneficially affects LV function through cAMP-independent effects.
- © 2010 by American Heart Association, Inc.