Abstract 17154: G Protein-Coupled Receptor Kinase-2 Regulates Alpha2a-Adrenergic Receptor Function and Catecholamine Release in Human Adrenal Chromaffin Cells
We recently reported that adrenal G protein-coupled receptor kinase-2 (GRK2) up-regulation causes enhanced catecholamine (CA) secretion via desensitization of sympatho-inhibitory alpha2-adrenergic receptors (α2ARs) of chromaffin cells of the adrenal medulla, aggravating heart failure. In the present study, we sought to investigate whether manipulation of adrenal GRK2 levels/activity regulates physiological CA secretion in isolated primary human chromaffin cells. Chromaffin cells extracted from human adrenal glands were cultured and infected in vitro with adenovirus (Ad) encoding for full length GRK2 for overexpression or Green Fluorescent Protein (GFP) as control Ad. After 24 hours, we performed in vitro CA secretion assays using nicotine to activate nicotinic cholinergic receptors (the physiological stimulus for CA secretion from these cells) and the α2AR-selective full agonist UK14304 to activate these negative feedback receptors. Nicotine stimulated Epinephrine and Norepinephrine secretion to an equal extent from the chromaffin cells from both experimental groups. Interestingly, in control AdGFP chromaffin cells, UK14304 abolishes CA secretion in response to nicotine as expected, but this effect of UK14304 is lost in chromaffin cells from AdGRK2-treated rats. Moreover, to mimic a condition of elevated adrenergic tone, we exposed human chromaffin cells to isoproterenol stimulation. Importantly, human chromaffin cells exposed to isoproterenol showed a 2.5-fold increase in GRK2 protein expression compared to non-treated cells and UK14307 failed to inhibit CA release in these cells, indicating GRK2-dependent α2AR dysfunction (desensitization). Finally, when cells stimulated with isoproterenol were pre-infected with βARKct (a potent GRK2 inhibitor), isoproterenol-induced α2AR dysfunction was prevented; in fact, UK14307 retrieved its ability to inhibit CA release from these cells.
Conclusion: Taken together, these data clearly show that adrenal GRK2 activity is an important physiological regulator of CA secretion in humans and suggest that its inhibition might be a useful therapeutic strategy in diseases that are precipitated or confounded by sympathetic overactivity, such as chronic heart failure.
- © 2012 by American Heart Association, Inc.