Sympathoadrenal catecholamine secretion is exocytotic (all-or-none), releasing not just catecholamines but also the acidic proteins with which catecholamines are stored: chromogranins/secretogranins, quantitatively major components being chromogranin A (CHGA) and chromogranin B (CHGB). Both CHGA and CHGB seem to be necessary factors (?on/off switches?) in the biogenesis of catecholamine secretory vesicles. CHGA is cleaved to biologically active fragments, including the endogenously formed ?catestatin? that inhibits catecholamine and vesicular co-transmitter release; its specific inhibitory mechanism seems to be nicotinic cholinergic antagonism. Data collected in the initial stages of HL58120 include discovery of substantial and functional human genetic diversity (polymorphism) at the CHGA and CHGB loci, including 3 novel variants of catestatin with differential potency as nicotinic antagonists, and 8 common CHGA proximal promoter SNPs, giving rise to common CHGA promoter haplotypes with different transcriptional activities in chromaffin cells. Common CHGA promoter polymorphisms (especially G-988T) predicted plasma CHGA concentration. Common 3?-UTR polymorphisms in both CHGA (C+87T) and CHGB (C+85A) predicted heritable variation in stress blood pressure responses in human twins. CHGB expression cosegregated (LOD=5.84) with a novel locus on chromosome 11q24-q25, suggesting the presence of a previously uncharacterized major gene regulating human sympathetic outflow. We will therefore emphasize effects of common human genetic variation (polymorphism) at the CHGA and CHGB loci on their biosynthesis, release, cellular targets, and autonomic consequences. We will characterize the inhibitory effects of catestatin variants on nicotinic cholinergic receptors and their signal transduction, as well as vesicular co-transmitter release. We will explore whether polymorphisms at CHGA/catestatin and CHGB influence catecholamine release and autonomic physiology in vivo or in vitro. To explore the significance of such polymorphisms, we propose a series of 5 specific aims, in which questions give rise to testable hypotheses that can be confirmed or refuted by crucial experiments. The studies are designed to shed light upon heritable regulation of nicotinic receptor-mediated release of catecholamines, and their consequences for autonomic control of the circulation and hence genetic risk of hypertension.
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