Abstract 1336: Increased Enzyme Activity and Increased Beta-adrenergic-mediated Vasodilation in Subjects Expressing a Single Nucleotide Variant of Human Adenylyl Cyclase 6
Cyclic AMP is a critical regulator of metabolic and cardiovascular function. Alterations in adenylyl cyclase (AC) regulation have been implicated in the pathogenesis and/or maintenance of insulin resistance, obesity, hypertension and heart failure. However, the role of genetic variability in the regulation of cyclic AMP-mediated effects is unclear. Therefore, we examined the role of a recently identified missense genetic variant of human AC isoform 6 (AC6 S674) in a sample of Caucasian subjects. We assessed the effect of AC6 S674 expression on AC-mediated function in adherent mononuclear leukocyte fractions and on beta-adrenergic-mediated vasodilation in human subjects. In addition, we examined the role of AC6 S674 on AC activity and cytoskeletal reorganization of rat vascular smooth muscle cells (VSMCs) following AC6 S674 gene transfer. In adherent mononuclear leukocytes isolated from AC6 S674-expressing individuals, forskolin-stimulated AC activity was significantly increased as compared to wild-type AC6 (WT AC6)-expressing subjects (WT AC6: 104±19 vs. AC6 S674: 193±33 pmol/min/mg protein, n=12, p<0.05). Similarly, forskolin-mediated cytoskeletal reorganization of adherent mononuclear leukocytes from AC6 S674 expressing subjects was significantly increased as compared to WT AC6 control subjects (154±18% of WT AC6, p<0.05). In dorsal hand vein vascular reactivity studies, subjects expressing the AC6 S674 variant had significantly greater vascular sensitivity to the beta-adrenergic agonist isoproterenol as assessed by both a greater potency and greater maximal effect than in subjects expressing WT AC6. In rat VSMCs, gene transfer of AC6 S674 increased forskolin-stimulated AC activity as compared to WT AC6-infected rat VSMCs (141±18% of AC6 WT, n=8, p<0.05). Similarly, forskolin-induced cytoskeletal reorganization was significantly greater in AC6 S674 expressing VSMCs than in WT AC6 expressing VSMCs (139±15% of WT AC6, n=6, p<0.05). In summary, these data indicate that the expression of a novel, relatively common variant of human AC6 parallels an increase in adenylyl cyclase activity and AC-mediated function both in humans.