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

RATIONALE

Hypertension is a complex trait with deranged autonomic control of the circulation. Chromogranin B () 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 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 , we systematically studied polymorphism across the locus by re-sequencing (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 %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 DBP and SBP was also associated with circulating/plasma CHGB concentration (CHGB epitope) in twin pairs. In twins, the same variants that were predictors of basal CHGB secretion were also associated with catecholamine secretion and BP response to environmental (cold) stress; likewise, women displayed plasma CHGB, but 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 promoter/luciferase reporter activity, and the allelic effects of A-261T on gene expression were directionally coordinate and . To confirm these clinical associations experimentally, we undertook targeted homozygous (−/−) ablation of the mouse gene; knockout mice displayed substantially 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 locus, especially in the proximal promoter, influences 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 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.