Hypertension is a common hereditary syndrome with unclear pathogenesis. Chromogranin A (Chga), which catalyzes formation and cargo storage of regulated secretory granules in neuroendocrine cells, contributes to blood pressure homeostasis centrally and peripherally. Elevated Chga occurs in spontaneously hypertensive rat (SHR) adrenal glands and plasma, but central expression is unexplored. In this report, we measured SHR and Wistar-Kyoto rat (control) Chga expression in central and peripheral nervous systems, and found Chga protein to be decreased in the SHR brainstem, yet increased in the adrenal and the plasma. By re-sequencing, we systematically identified five promoter, two coding and one 3'-untranslated region (3'-UTR) polymorphism at the SHR (versus WKY or BN) Chga locus. Using HXB/BXH recombinant inbred (RI) strain linkage and correlations, we demonstrated genetic determination of Chga expression in SHR, including a cis-quantitative trait loci (QTLs) (i.e. at the Chga locus), and such expression influenced biochemical determinants of blood pressure, including a cascade of catecholamine biosynthetic enzymes, catecholamines themselves and steroids. Luciferase reporter assays demonstrated that the 3'-UTR polymorphism (which disrupts a microRNA miR-22 motif) and promoter polymorphisms altered gene expression consistent with the decline in SHR central Chga expression. Coding region polymorphisms did not account for changes in Chga expression or function. Thus, we hypothesized that the 3'-UTR and promoter mutations lead to dysregulation (diminution) of Chga in brainstem cardiovascular control nuclei, ultimately contributing to the pathogenesis of hypertension in SHR. Accordingly, we demonstrated that in vivo administration of miR-22 antagomir to SHR causes substantial (∼18 mmHg) reductions in blood pressure, opening a novel therapeutic avenue for hypertension.

Objectives We coupled two strategies – trait extremes and genome-wide pooling – to discover a novel BP locus that encodes a previously uncharacterized thiamine transporter. Background Hypertension is a heritable trait that remains the most potent and widespread cardiovascular risk factor, though details of its genetic determination are poorly understood. Methods Representative genomic DNA pools were created from male and female subjects in the highest and lowest 5th %iles of BP in a primary care population of >50,000 individuals. The peak associated SNPs were typed in individual DNA samples, as well as twins/siblings phenotyped for cardiovascular and autonomic traits. Biochemical properties of the associated transporter were evaluated in cellular assays. Results After chip hybridization and calculation of relative allele scores, the peak associations were typed in individual samples, revealing association of hypertension, SBP, and DBP to the previously uncharacterized solute carrier SLC35F3. The BP genetic association at SLC35F3 was validated by meta-analysis in an independent sample from the original source population, as well as the ICBP (across North America and Western Europe). Sequence homology to a putative yeast thiamine (vitamin B1) transporter prompted us to express human SLC35F3 in E. coli, which catalyzed [3H]-thiamine uptake. SLC35F3 risk allele (T/T) homozygotes displayed decreased erythrocyte thiamine content on microbiological assay. In twin pairs, the SLC35F3 risk allele predicted heritable cardiovascular traits previously associated with thiamine deficiency, including elevated cardiac stroke volume with decreased vascular resistance, and elevated pressor responses to environmental (cold) stress. Allelic expression imbalance (AEI) confirmed that cis-variation at the human SLC35F3 locus influenced expression of that gene, and the AEI peak coincided with the hypertension peak. Conclusions Novel strategies were coupled to position a new hypertension susceptibility locus, uncovering a previously unsuspected thiamine transporter whose genetic variants predicted several disturbances in cardiac and autonomic function. The results have implications for the pathogenesis and treatment of systemic hypertension.

Chromogranin A (CHGA) is coreleased with catecholamines from secretory vesicles in adrenal medulla and sympathetic axons. Genetic variation in the CHGA 39-region has been associated with autonomic control of circulation, hypertension, and hypertensive nephropathy, and the CHGA 39-untranslated region (39-UTR) variant C+87T (rs7610) displayed peak associations with these traits in humans. Here, we explored the molecular mechanisms underlying these associations. C+87T occurred in a microRNA-107 (miR-107) motif (match: T.C), and CHGA mRNA expression varied inversely with miR-107 abundance. In cells transfected with chimeric luciferase/ CHGA 39-UTR reporters encoding either the T allele or the C allele, changes in miR-107 expression levels had much greater effects on expression of the T allele. Cotransfection experiments with hsa-miR-107 oligonucleotides and eukaryotic CHGA plasmids produced similar results. Notably, an in vitro CHGA transcription/translation experiment revealed that changes in hsa-miR-107 expression altered expression of the T allele variant only. Mice with targeted ablation of Chga exhibited greater eGFR. Using BAC transgenesis, we created a mouse model with a humanized CHGA locus (T/T genotype at C+87T), in which treatment with a hsa-miR-107 inhibitor yielded prolonged falls in SBP/DBP compared with wild-type mice. We conclude that the CHGA 39-UTR C+87T disrupts an miR-107 motif, with differential effects on CHGA expression, and that a cis:trans (mRNA:miR) interaction regulates the association of CHGA with BP and hypertensive nephropathy. These results indicate new strategies for probing autonomic circulatory control and ultimately, susceptibility to hypertensive renal sequelae.

CHGB is the major matrix protein in human catecholamine storage vesicles. CHGB genetic variation alters catecholamine secretion and blood pressure. Here effective Chgb protein under-expression was achieved by siRNA in PC12 cells, resulting in ~48% fewer secretory granules on EM, diminished capacity for catecholamine uptake (by ~79%), and a ~73% decline in stores available for nicotinic cholinergic-stimulated secretion. In vivo, loss of Chgb in knockout mice resulted in a ~35% decline in chromaffin granule abundance and ~44% decline in granule diameter, accompanied by unregulated catecholamine release into plasma. Over-expression of CHGB was achieved by transduction of a CHGB-expressing lentivirus, resulting in ~127% elevation in CHGB protein, with ~122% greater abundance of secretory granules, but only ~14% increased uptake of catecholamines, and no effect on nicotinic-triggered secretion. Human CHGB protein and its proteolytic fragments inhibited nicotinic-stimulated catecholamine release by ~72%. One conserved-region CHGB peptide inhibited nicotinic-triggered secretion by up to ~41%, with partial blockade of cationic signal transduction. We conclude that bi-directional quantitative derangements in CHGB abundance result in profound changes in vesicular storage and release of catecholamines. When processed and released extra-cellularly, CHGB proteolytic fragments exert a feedback effect to inhibit catecholamine secretion, especially during nicotinic cholinergic stimulation.

The use of continuous-mode diagnostic frequency ultrasound is beneficial in preventing long-term ischemia-reperfusion effects in the microcirculation as shown by the return of microvascular parameters to baseline values, an effect not attained in the absence of ultrasound treatment. The effects may be in part due to the production of nitric oxide consequent to locally induced shear stress effects by ultrasound exposure.