Autonomic function in hypertension; role of genetic variation at the catecholamine storage vesicle protein chromogranin B.

Overview

abstract

RATIONALE: Hypertension is a complex trait with deranged autonomic control of the circulation. Chromogranin B (CHGB) is the most abundant core protein in human catecholamine secretory vesicles, playing an important role in their biogenesis. Does common inter-individual variation at the CHGB locus contribute to phenotypic variation in CHGB and catecholamine secretion, autonomic stability of the circulation, or blood pressure in the population? METHODS AND RESULTS: To probe inter-individual variability in CHGB, we systematically studied polymorphism across the locus by re-sequencing CHGB (~6 kbp footprint spanning the promoter, 5 exons, exon/intron borders, UTRs) in n=160 subjects (2n=320 chromosomes) of diverse biogeographic ancestries. We identified 53 SNPs, of which 22 were common. We then studied n=1182 subjects drawn from the most extreme BP values in the population (highest and lowest 5^th %iles), typing 4 common polymorphisms spanning the ~14 kbp locus. Sliding-window haplotype analysis indicated BP associations peaking in the 5′/promoter region, and most prominent in men, and a peak effect in the proximal promoter at variant A-261T (A>T), accounting for ~8/~6 mmHg SBP/DBP in males. The promoter allele (A-261) that was a predictor of higher DBP and SBP was also associated with lower circulating/plasma CHGB concentration (CHGB_439-451 epitope) in twin pairs. In twins, the same CHGB variants that were predictors of lower basal CHGB secretion were also associated with exaggerated catecholamine secretion and BP response to environmental (cold) stress; likewise, women displayed increased plasma CHGB_439–451, but decreased catecholamine secretion as well as BP response to environmental stress. The effect of A-261T on CHGB expression was confirmed in chromaffin cells by site-directed mutagenesis on transfected CHGB promoter/luciferase reporter activity, and the allelic effects of A-261T on gene expression were directionally coordinate in cella and in vivo. To confirm these clinical associations experimentally, we undertook targeted homozygous (−/−) ablation of the mouse Chgb gene; knockout mice displayed substantially increased BP, by ~20/~18 mmHg SBP/DBP, confirming the mechanistic basis of our findings in humans. CONCLUSIONS: We conclude that common genetic variation at the CHGB locus, especially in the proximal promoter, influences CHGB expression, and later catecholamine secretion and the early heritable responses to environmental stress, eventuating in changes in resting/basal BP in the population. Both the early (gene expression) and late (population BP) consequences of CHGB variation are sex-dependent. The results point to new molecular strategies for probing autonomic control of the circulation, and ultimately the susceptibility to and pathogenesis of cardiovascular disease states such as hypertension.