Naturally occurring human genetic variation in the 3'-untranslated region of the secretory protein chromogranin A is associated with autonomic blood pressure regulation and hypertension in a sex-dependent fashion

Catestatin induces glycogenesis by stimulating the phosphoinositide 3-kinase-AKT pathway

AIM

Defects in hepatic glycogen synthesis contribute to post-prandial hyperglycaemia in type 2 diabetic patients. Chromogranin A (CgA) peptide Catestatin (CST: hCgA352-372 ) improves glucose tolerance in insulin-resistant mice. Here, we seek to determine whether CST induces hepatic glycogen synthesis.

METHODS

We determined liver glycogen, glucose-6-phosphate (G6P), uridine diphosphate glucose (UDPG) and glycogen synthase (GYS2) activities; plasma insulin, glucagon, noradrenaline and adrenaline levels in wild-type (WT) as well as in CST knockout (CST-KO) mice; glycogen synthesis and glycogenolysis in primary hepatocytes. We also analysed phosphorylation signals of insulin receptor (IR), insulin receptor substrate-1 (IRS-1), phosphatidylinositol-dependent kinase-1 (PDK-1), GYS2, glycogen synthase kinase-3β (GSK-3β), AKT (a kinase in AKR mouse that produces Thymoma)/PKB (protein kinase B) and mammalian/mechanistic target of rapamycin (mTOR) by immunoblotting.

RESULTS

CST stimulated glycogen accumulation in fed and fasted liver and in primary hepatocytes. CST reduced plasma noradrenaline and adrenaline levels. CST also directly stimulated glycogenesis and inhibited noradrenaline and adrenaline-induced glycogenolysis in hepatocytes. In addition, CST elevated the levels of UDPG and increased GYS2 activity. CST-KO mice had decreased liver glycogen that was restored by treatment with CST, reinforcing the crucial role of CST in hepatic glycogenesis. CST improved insulin signals downstream of IR and IRS-1 by enhancing phospho-AKT signals through the stimulation of PDK-1 and mTORC2 (mTOR Complex 2, rapamycin-insensitive complex) activities.

CONCLUSIONS

CST directly promotes the glycogenic pathway by (a) reducing glucose production, (b) increasing glycogen synthesis from UDPG, (c) reducing glycogenolysis and (d) enhancing downstream insulin signalling.

Gut microbial DNA and immune checkpoint gene Vsig4/CRIg are key antagonistic players in healthy aging and age-associated development of hypertension and diabetes

AIMS

Aging is associated with the development of insulin resistance and hypertension which may stem from inflammation induced by accumulation of toxic bacterial DNA crossing the gut barrier. The aim of this study was to identify factors counter-regulating these processes. Taking advantage of the Chromogranin A (CgA) knockout (CgA-KO) mouse as a model for healthy aging, we have identified Vsig4 (V-set and immunoglobulin domain containing 4) as the critical checkpoint gene in offsetting age-associated hypertension and diabetes.

METHODS AND RESULTS

The CgA-KO mice display two opposite aging phenotypes: hypertension but heightened insulin sensitivity at young age, whereas the blood pressure normalizes at older age and insulin sensitivity further improves. In comparison, aging WT mice gradually lost glucose tolerance and insulin sensitivity and developed hypertension. The gut barrier, compromised in aging WT mice, was preserved in CgA KO mice leading to major 35-fold protection against bacterial DNA-induced inflammation. Similarly, RNA sequencing showed increased expression of the Vsig4 gene (which removes bacterial DNA) in the liver of 2-yr-old CgA-KO mice, which may account for the very low accumulation of microbial DNA in the heart. The reversal of hypertension in aging CgA-KO mice likely stems from (i) low accumulation of microbial DNA, (ii) decreased spillover of norepinephrine in the heart and kidneys, and (iii) reduced inflammation.

CONCLUSION

We conclude that healthy aging relies on protection from bacterial DNA and the consequent low inflammation afforded by CgA-KO. Vsig4 also plays a crucial role in "healthy aging" by counteracting age-associated insulin resistance and hypertension.

Neuropeptide Y gene variants in obesity, dietary intake, blood pressure, lipid and glucose metabolism: A longitudinal birth cohort study

OBJECTIVE

Neuropeptide Y affects several physiological functions, notably appetite regulation. We analysed the association between four single nucleotide polymorphisms (SNP) in the NPY gene (rs5574, rs16147, rs16139, rs17149106) and measures of obesity, dietary intake, physical activity, blood pressure, glucose and lipid metabolism from adolescence to young adulthood.

METHODS

The sample included both birth cohorts of the Estonian Children Personality Behaviour and Health Study at ages 15 (n = 1075 with available complete data), 18 (n = 913) and 25 (n = 926) years. Linear mixed-effects regression models were used for longitudinal association between NPY SNP-s and variables of interest. Associations at ages 15, 18 and 25 were analysed by ANOVA.

RESULTS

Rs5574 CC-homozygotes had a greater increase per year in waist-to-hip ratio (WHR) and a smaller decrease in daily energy intake and carbohydrate intake from age 15-25 years; fasting glucose and cholesterol were higher in rs5574 CC-homozygotes. Rs16147 TT-homozygotes had higher body weight and a greater increase in sum of 5 skinfolds, waist circumference, WHR and waist-to-height ratio; however, they had lower carbohydrate intake throughout the observation period. Rs16147 TT-homozygotes and both rs16139 and rs17149106 heterozygotes had higher triglyceride levels. All NPY SNP-s were associated with blood pressure: rs5574 TT-and rs16147 CC-homozygotes had a smaller increase in diastolic blood pressure, while rs16139 and rs17149106 heterozygous had lower blood pressure throughout the study.

CONCLUSION

Variants of the NPY gene were associated with measures of obesity, dietary intake, glucose and lipid metabolism and blood pressure from adolescence to young adulthood.

Immunosuppression of Macrophages Underlies the Cardioprotective Effects of CST (Catestatin)

[Figure: see text].

Chromogranin A pathway: from pathogenic molecule to renal disease

BACKGROUND

Chromogranin A (CHGA) is an index granin protein critical for biogenesis and exocytotic release of catecholamine storage granules. It is elevated in plasma of patients with sympathetic over-activity and kidney dysfunction. Several CHGA polymorphisms are associated with hypertensive kidney disease. Previously, we unraveled the molecular mechanism by which CHGA expression is regulated in African Americans carrying a genetic variation associated with hypertensive chronic kidney disease (CKD).

METHOD

Experimental CKD mouse model were created by 5/6th nephrectomy (Npx) using wild-type and Chga-/- knockout mouse strains to delineate the role of CHGA in CKD.

RESULT

Wild-type-Npx mice expressing Chga developed exacerbated azotemia and fibrosis as compared with their knockout-Npx counterparts. Gene expression profiling revealed downregulation of mitochondrial respiratory complexes genes consistent with maladaptive mitochondria in wild-type-Npx mice, contrasted to knockout-Npx. In healthy individuals, an inverse relationship between circulating CHGA levels and glomerular function was observed. In vitro, mesangial cells treated with CHGA-triggered nitric oxide release by a signaling mechanism involving scavenger receptor SR-A. The CHGA-treated and untreated mesangial cells displayed differential expression of cytokine, chemokine, complement, acute phase inflammatory and apoptotic pathway genes. Thus, build-up of plasma CHGA because of kidney injury served as an insult to the mesangial cells resulting in expression of genes promoting inflammation, fibrosis, and progression of CKD.

CONCLUSION

These findings improve understanding of the role of elevated CHGA in the progression of CKD and reveal novel pathways that could be exploited for therapeutic strategies in hypertensive kidney disease.

Mice overexpressing chromogranin A display hypergranulogenic adrenal glands with attenuated ATP levels contributing to the hypertensive phenotype

OBJECTIVE

Elevated circulating chromogranin A (CHGA) is observed in human hypertension. CHGA is critical for granulogenesis and exocytosis of catecholamine stores from secretory large dense core vesicles (LDCV). This study aims to understand the morphological, molecular and phenotypic changes because of excess CHGA and the mechanistic link eventuating in hyper-adrenergic hypertension.

METHODS

Blood pressure and heart rate was monitored in mouse models expressing normal and elevated level of CHGA by telemetry. Catecholamine and oxidative stress radicals were measured. Adrenal ultrastructure, LDCV content and mitochondrial abundance were compared and respiration analyzed by Seahorse assay. Effect of CHGA dosage on adrenal ATP content, electron transport chain components and uncoupling protein 2 (UCP-2) were compared in vivo and in vitro.

RESULTS

Mice with excess-CHGA displayed hypertensive phenotype, higher heart rate and increased sympathetic tone. They had elevated plasma catecholamine and adrenal ROS levels. Excess-CHGA caused an increase in size and abundance of LDCV and adrenal mitochondria. Nonetheless, they had attenuated levels of ATP. Isolated adrenal mitochondria from mice with elevated CHGA showed higher maximal respiration rates in the presence of protonophore, which uncouples oxidative phosphorylation. Elevated CHGA resulted in overexpression of UCP2 and diminished ATP. In vitro in chromaffin cells overexpressing CHGA, concomitant increase in UCP2 protein and decreased ATP was detected.

CONCLUSION

Elevated CHGA expression resulted in underlying bioenergetic dysfunction in ATP production despite higher mitochondrial mass. The outcome was unregulated negative feedback of LDCV exocytosis and secretion, resulting in elevated levels of circulating catecholamine and consequently the hypertensive phenotype.

Report: NIA workshop on translating genetic variants associated with longevity into drug targets

To date, candidate gene and genome-wide association studies (GWAS) have led to the discovery of longevity-associated variants (LAVs) in genes such as FOXO3A and APOE. Unfortunately, translating variants into drug targets is challenging for any trait, and longevity is no exception. Interdisciplinary and integrative multi-omics approaches are needed to understand how LAVs affect longevity-related phenotypes at the molecular physiologic level in order to leverage their discovery to identify new drug targets. The NIA convened a workshop in August 2017 on emerging and novel in silico (i.e., bioinformatics and computational) approaches to the translation of LAVs into drug targets. The goal of the workshop was to identify ways of enabling, enhancing, and facilitating interactions among researchers from different disciplines whose research considers either the identification of LAVs or the mechanistic or causal pathway(s) and protective factors they influence for discovering drug targets. Discussions among the workshop participants resulted in the identification of critical needs for enabling the translation of LAVs into drug targets in several areas. These included (1) the initiation and better use of cohorts with multi-omics profiling on the participants; (2) the generation of longitudinal information on multiple individuals; (3) the collection of data from non-human species (both long and short-lived) for comparative biology studies; (4) the refinement of computational tools for integrative analyses; (5) the development of novel computational and statistical inference techniques for assessing the potential of a drug target; (6) the identification of available drugs that could modulate a target in a way that could potentially provide protection against age-related diseases and/or enhance longevity; and (7) the development or enhancement of databases and repositories of relevant information, such as the Longevity Genomics website ( https://www.longevitygenomics.org ), to enhance and help motivate future interdisciplinary studies. Integrative approaches that examine the influence of LAVs on molecular physiologic phenotypes that might be amenable to pharmacological modulation are necessary for translating LAVs into drugs to enhance health and life span.

Identification of novel loci affecting circulating chromogranins and related peptides

Chromogranins are pro-hormone secretory proteins released from neuroendocrine cells, with effects on control of blood pressure. We conducted a genome-wide association study for plasma catestatin, the catecholamine release inhibitory peptide derived from chromogranin A (CHGA), and other CHGA- or chromogranin B (CHGB)-related peptides, in 545 US and 1252 Australian subjects. This identified loci on chromosomes 4q35 and 5q34 affecting catestatin concentration (P = 3.40 × 10-30 for rs4253311 and 1.85 × 10-19 for rs2731672, respectively). Genes in these regions include the proteolytic enzymes kallikrein (KLKB1) and Factor XII (F12). In chromaffin cells, CHGA and KLKB1 proteins co-localized in catecholamine storage granules. In vitro, kallikrein cleaved recombinant human CHGA to catestatin, verified by mass spectrometry. The peptide identified from this digestion (CHGA360-373) selectively inhibited nicotinic cholinergic stimulated catecholamine release from chromaffin cells. A proteolytic cascade involving kallikrein and Factor XII cleaves chromogranins to active compounds both in vivo and in vitro.

Correlation study on chromogranin A genetic polymorphism and prognosis of critically ill patients

OBJECTIVE

The objective was to investigate the correlation between single nucleotide polymorphism (SNP) of chromogranin A (CHGA) and prognosis of critically ill patients.

METHODS

We screened 357 critically ill patients consecutively admitted to our intensive care unit. The -89/-415/-462 SNP locus in the promoter region and the +9559/+9578/+9590/+9611 SNP locus in exon 7 coding of CHGA were genotyped by polymerase chain reaction and DNA sequencing technology. Subsequently, the correlation between genotype and prognosis of patients was analyzed.

RESULTS

(1) Three hundred critically ill Chinese Han patients were enrolled in the study. CHGA-415/-462/+9559/+9611 SNPs were polymorphically distributed. Phenotypes of the 4 SNPs were shown not to be in linkage disequilibrium, and there were no significant differences in the minor allele frequencies (MAFs) of the 4 SNPs between participants of this study and healthy people in Asia. (2) The CHGA-415 T/C MAF of the nonsurvival group was significantly higher than that of the survival group (MAF 0.3813 and 0.2864, respectively; P=.026). Survival analysis showed that there were significant differences between the CHGA-415 T/C mutation group (including TC and CC genotypes) and the wild-type group (TT genotype) (log rank=8.887, P=.003). The mortality in the mutant group was significantly higher than that in the wild-type group (0.3333 and 0.1852, respectively; P=.004). (3) Binary logistic analysis showed that CHGA-415 T/C polymorphism was an independent risk factor for the mortality of critically ill patients (odds ratio, 2.286; 95% confidence interval, 1.165-4.484; P=.016).

CONCLUSIONS

Critically ill patients with CHGA-415 T/C mutant genotype display higher 30-day mortality than those with the wild-type group. CHGA-415 T/C polymorphism is an independent risk factor of poor prognosis in critically ill Chinese Han patients.

Analysis and validation of traits associated with a single nucleotide polymorphism Gly364Ser in catestatin using humanized chromogranin A mouse models

OBJECTIVE

The human prohormone chromogranin A (CHGA), an index member of the granin family is processed to generate catestatin, a peptide that is hypotensive in action and modulates catecholamine release within the sympathoadrenal system. Hypertensive patients with excess sympathetic activity have diminished catestatin. Often the study of physiological consequences of human genetic variation is confounded by elements such as other variations in obligatory linkage disequilibrium with the variant being studied. Also the phenotype of the variant may be influenced by genetic background that varies amongst individuals. This study addresses the effects of a human catestatin polymorphism (rs9658667) using humanized CHGA mouse models.

METHODS

We created pertinent humanized mouse models wherein the mouse Chga gene locus was replaced by the human ortholog wild-type and the variant versions. This allowed for probing of the effects of catestatin variation in vivo with controls for other variations and global genetic background.

RESULTS

Both the wild-type and variant human catestatin expressing mouse models were normotensive. The variant catestatin mouse model recapitulated physiological influence of the polymorphism on autonomic traits. These mice had diminished catecholamine, attenuated stress response and increased baroreceptor slopes that would suggest reduced risk of developing hypertension. Elevated plasma glucose, a trait observed in humans was not observed in mice expressing the variant catestatin.

CONCLUSION

This functional genomics approach of creating humanized mouse models to study rs9658667 polymorphism recapitulated and validated many of the human trait associations. This approach can also be applied in the study of other human gene polymorphisms.

Roles of catecholamine related polymorphisms in hypertension

The objective of this review is to summarize current data obtained so far in catecholamine-essential hypertension (EH) relationships on a genetic basis. As the major elements driving the sympathetic system’s actions, catecholamines modulate a variety of physiological processes and mutations related to the system. This could generate serious disorders, such as severe mental illnesses, stress-induced disorders, or impaired control of blood pressure or motor pathways. EH is idiopathic, and the genetic basis of its causes and substantial interindividual discrepancies in response to different types of treatments are the focus of interest. Susceptibility to disease or efficacy of treatments are thought to reflect genomic variabilities among individuals. Therefore, outlining the available knowledge in functional genetic polymorphisms linked to EH will make the picture clearer and will help to establish future prospects in the field.

Molecular Mechanism for Hypertensive Renal Disease: Differential Regulation of Chromogranin A Expression at 3'-Untranslated Region Polymorphism C+87T by MicroRNA-107

Chromogranin A (CHGA) is coreleased with catecholamines from secretory vesicles in adrenal medulla and sympathetic axons. Genetic variation in the CHGA 3'-region has been associated with autonomic control of circulation, hypertension, and hypertensive nephropathy, and the CHGA 3'-untranslated region (3'-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 3'-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 3'-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.

Adrenergic genetic mechanisms in hypertension and hypertensive kidney disease

Catecholamine secretory traits were significantly heritable, as were stress-induced blood pressure changes. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine biosynthesis. In the tyrosine hyroxylase promoter, significant associations were found for urinary catecholamine excretion and for blood pressure response to stress. TH promoter haplotype 2 (TGGG) showed pleiotropy, increasing both norepinephrine excretion and blood pressure during stress. In hypertension, 2 independent case-control studies (1,266 subjects with 53% women and 927 subjects with 24% women) replicated the effect of C-824T in the determination of blood pressure. Chromogranin A (CHGA) plays a fundamental role in the biogenesis of catecholamine secretory granules. Changes in the storage and release of CHGA in clinical and experimental hypertension prompted us to study whether genetic variation at the CHGA locus might contribute to alterations in autonomic function, and hence hypertension and its target organ consequences such as hypertensive kidney disease (nephrosclerosis). Systematic polymorphism discovery across the human CHGA locus revealed such regulatory regions as the proximal promoter and 3'-UTR. In chromaffin cell-transfected CHGA 3'-UTR and promoter/luciferase reporter plasmids, the functional consequences of the regulatory/non-coding allelic variants were documented. Variants in both the proximal promoter and the 3'-UTR displayed statistical associations with hypertension and hypertensive end stage renal disease. Therefore, I would like to review the common genetic variation in TH and CHGA as a cause of inter-individual variation in sympathetic activity, and ultimately blood pressure and hypertensive kidney disease.

MicroRNA-22 and promoter motif polymorphisms at the Chga locus in genetic hypertension: functional and therapeutic implications for gene expression and the pathogenesis of hypertension

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.

Common genetic variants of the human uromodulin gene regulate transcription and predict plasma uric acid levels

Uromodulin (UMOD) genetic variants cause familial juvenile hyperuricemic nephropathy, characterized by hyperuricemia with decreased renal excretion of UMOD and uric acid, suggesting a role for UMOD in the regulation of plasma uric acid. To determine this, we screened common variants across the UMOD locus in one community-based Chinese population of 1000 individuals and the other population from 642 American twins and siblings of European and Hispanic ancestry. Transcriptional activity of promoter variants was estimated in luciferase reporter plasmids transfected into HEK-293 cells and mIMCD3 cells. In the primary Chinese population, we found that carriers of the GCC haplotype had higher plasma uric acid, and three promoter variants were associated with plasma uric acid. UMOD promoter variants displayed reciprocal effects on urine uric acid excretion and plasma uric acid concentration, suggesting a primary effect on renal tubular handling of urate. These UMOD genetic marker-on-trait associations for uric acid were replicated in the independent American cohort. Site-directed mutagenesis at trait-associated UMOD promoter variants altered promoter activity in transfected luciferase reporter plasmids. Thus, UMOD promoter variants seem to initiate a cascade of transcriptional and biochemical changes influencing UMOD secretion, leading to altered plasma uric acid levels.

The regulated secretory pathway and human disease: insights from gene variants and single nucleotide polymorphisms

The regulated secretory pathway provides critical control of peptide, growth factor, and hormone release from neuroendocrine and endocrine cells, and neurons, maintaining physiological homeostasis. Propeptides and prohormones are packaged into dense core granules (DCGs), where they frequently undergo tissue-specific processing as the DCG matures. Proteins of the granin family are DCG components, and although their function is not fully understood, data suggest they are involved in DCG formation and regulated protein/peptide secretion, in addition to their role as precursors of bioactive peptides. Association of gene variation, including single nucleotide polymorphisms (SNPs), with neuropsychiatric, endocrine, and metabolic diseases, has implicated specific secreted proteins and peptides in disease pathogenesis. For example, a SNP at position 196 (G/A) of the human brain-derived neurotrophic factor gene dysregulates protein processing and secretion and leads to cognitive impairment. This suggests more generally that variants identified in genes encoding secreted growth factors, peptides, hormones, and proteins involved in DCG biogenesis, protein processing, and the secretory apparatus, could provide insight into the process of regulated secretion as well as disorders that result when it is impaired.

The USC Adult Twin Cohorts: International Twin Study and California Twin Program

The study of twin subjects permits the documentation of crude heritability and may promote the identification of specific causal alleles. We believe that at the current time, the chief research advantage of twins as subjects, especially monozygotic twins, is that the commonality of their genetic and cultural identity simplifies the interpretation of biological associations. In order to study genetic and environmental determinants of cancer and chronic diseases, we developed two twin registries, maintained at the University of Southern California: The International Twin Study (ITS) and the California Twin Program (CTP). The ITS is a volunteer registry of twins with cancer and chronic disease consisting of 17,245 twin pairs affected by cancer and chronic disease, respectively, ascertained by advertising in periodicals from 1980-1991. The CTP is a population-based registry of California-born twin pairs ascertained by linking the California birth records to the State Department of Motor Vehicles. Over 51,000 individual California twins representing 36,965 pairs completed and returned 16-page questionnaires. Cancer diagnoses in the California twins are updated by regular linkage to the California Cancer Registry. Over 5,000 cancer patients are represented in the CTP. Twins from both registries have participated extensively in studies of breast cancer, melanoma, lymphoma, multiple sclerosis, systemic lupus erythematosus, diabetes mellitus type 1, mammographic density, smoking, and other traits and conditions.

Disorders of blood pressure regulation-role of catecholamine biosynthesis, release, and metabolism

Catecholamines (epinephrine and norepinephrine) are synthesised and produced by the adrenal medulla and postganglionic nerve fibres of the sympathetic nervous system. It is known that essential hypertension has a significant neurogenic component, with the rise in blood pressure mediated at least in part by overactivity of the sympathetic nervous system. Moreover, novel therapeutic strategies aimed at reducing sympathetic activity show promise in the treatment of hypertension. This article reviews recent advances within this rapidly changing field, particularly focusing on the role of genetic polymorphisms within key catecholamine biosynthetic enzymes, cofactors, and storage molecules. In addition, mechanisms linking the sympathetic nervous system and other adverse cardiovascular states (obesity, insulin resistance, dyslipidaemia) are discussed, along with speculation as to how recent scientific advances may lead to the emergence of novel antihypertensive treatments.

Chromogranin A and derived peptides in health and disease

Chromogranin A (CgA) is a member of the granins, a family of acidic proteins found in abundance in (neuro)endocrine cells (e.g., in chromaffin cells) and in some tumors. Like other granins, CgA has a granulogenic role in secretory granule biogenesis and is stored in these organelles. CgA is partially processed differentially in various cell types to yield biologically active peptides, such as vasostatin, pancreastatin, catestatin, and serpinins. In this review, we describe the roles of CgA and several of its derived peptides. CgA, which is elevated in the blood of cancer patients, inhibits angiogenesis and exerts protective effects on the endothelial barrier function in tumors, thus affecting response to chemotherapy. Recent studies indicate that the serpinins promote cell survival and myocardial contractility and relaxation. Other peptides such as pancreastatin were found to have significant effects on inhibition of glucose-stimulated insulin secretion and glucose up-take, induction of glycogenolysis in hepatocytes, and inhibition of lipogenesis. In contrast, catestatin has opposite effects to that of pancreastatin in glucose metabolism and lipogenesis. Catestatin appears to also play a significant role in cardiac function, blood pressure regulation, and mutations in the catestatin domain of the CgA gene are associated with hypertension in humans.

The extended granin family: structure, function, and biomedical implications

The chromogranins (chromogranin A and chromogranin B), secretogranins (secretogranin II and secretogranin III), and additional related proteins (7B2, NESP55, proSAAS, and VGF) that together comprise the granin family subserve essential roles in the regulated secretory pathway that is responsible for controlled delivery of peptides, hormones, neurotransmitters, and growth factors. Here we review the structure and function of granins and granin-derived peptides and expansive new genetic evidence, including recent single-nucleotide polymorphism mapping, genomic sequence comparisons, and analysis of transgenic and knockout mice, which together support an important and evolutionarily conserved role for these proteins in large dense-core vesicle biogenesis and regulated secretion. Recent data further indicate that their processed peptides function prominently in metabolic and glucose homeostasis, emotional behavior, pain pathways, and blood pressure modulation, suggesting future utility of granins and granin-derived peptides as novel disease biomarkers.

Chromogranin A: a novel factor acting at the cross road between the neuroendocrine and the cardiovascular systems

Chromogranin A (CHGA) is a secretory protein stored in and released from neurons and cells of the diffuse neuroendocrine system. Cells of the adrenal medulla and adrenergic terminals are a main source of CHGA but also myocardial cells produce it under stress conditions. After secretion, CHGA is cleaved into several biologically active fragments, including vasostatins and catestatin. CHGA and its proteolytic peptides exert a broad spectrum of activities on the cardiovascular system. They act on blood pressure by controlling the vascular tone and the cardiac inotropic and chronotropic function. CHGA revealed to be a sensitive marker of myocardial dysfunction, with a high predictive power of morbidity and mortality in heart failure and ischemic heart disease. In addition, CHGA has been involved in the control of sustained endothelial inflammation and has been shown to be a good marker of persistent vascular inflammation in rheumatologic disorders affecting vessels.

Contemporary approaches to genetic influences on hypertension

PURPOSE OF REVIEW

Essential hypertension has long been considered to be primarily 'genetic,' though recent studies have only revealed minor contributions to blood pressure. Technology has advanced tremendously in the recent years, with much focus on DNA studies utilizing both candidate gene and genome-wide association studies. However, many new areas that need continued investigation have arisen.

RECENT FINDINGS

In addition to DNA studies, genetic studies are actively pursuing previously unexplored areas of potential variation, such as that which occurs posttranscriptionally in RNA and posttranslationally in protein structure. Advances have also been made in animal models and systems biology for large-scale integrative approaches. However, many other areas need continued investigation in the genetics of hypertension, including improved phenotyping and trait definition, gene-by-gene interactions (epistasis), and gene-by-environment interactions. 'Next generation' sequencing will assist researchers in performing more extensive genetic studies even more quickly, especially on unusual (rare) genetic variants.

SUMMARY

Hypertension appears to have many genetic contributions from each regulatory area ranging from DNA to RNA to protein to postprotein to interactive influences of the environment on genes. New technologies have enabled such research to advance in the recent years. However, for this complex trait of hypertension, continued efforts must progress in all of these areas as well as in increased modeling and sequencing, so that the knowledge may be united for a comprehensive understanding of this common disease, such that diagnosis and treatment options in hypertensive patients and those at risk are facilitated.

Proteomic analysis yields an unexpected trans-acting point in control of the human sympathochromaffin phenotype

BACKGROUND

The secretory protein chromogranin A (CHGA) plays a necessary role in formation of catecholamine storage vesicles and gives rise to a catecholamine release-inhibitory fragment. Because genetic variation in the proximal human CHGA promoter predicts autonomic function and blood pressure, we explored how a common genetic variant alters transcription of the gene.

METHODS AND RESULTS

Bioinformatic analysis suggested that the common G-462A promoter variant (rs9658634) may disrupt as many as 3 transcriptional control motifs: LEF1, COUP-TF, and PPARγ-RXRα. During electrophoretic mobility shifts, chromaffin cell nuclear proteins bound specifically to the A (though not G) allele of CHGA promoter G-462A. On oligonucleotide affinity chromatography followed by electrospray ionization followed by 2-dimensional (tandem) mass spectrometry analysis of A allele eluates, the transcription factor LEF1 (lymphoid enhancer-binding factor-1) was identified. Interaction of LEF1 with the A allele at G-462A was confirmed by supershift. On cotransfection, LEF1 discriminated between the allelic variants, especially in chromaffin cells. Allele specificity of trans-activation by LEF1 was transferable to an isolated G-462A element fused to a heterologous (SV40) promoter. Because β-catenin (CTNNB1) can heterodimerize with LEF1, we tested the effect of cotransfection of this factor and again found A allele-specific perturbation of CHGA transcription.

CONCLUSIONS

Common genetic variation within the human CHGA promoter alters the interaction of specific factors in trans with the promoter, with LEF1 identified by proteomic analysis and confirmed by supershift. Coexpression experiments show functional effects of LEF1 and CTNNB1 on CHGA promoter. The findings document a novel role for components of the immune and WNT pathways in control of human sympathochromaffin phenotypes.

Naturally occurring genetic variants in human chromogranin A (CHGA) associated with hypertension as well as hypertensive renal disease

Chromogranin A (CHGA) plays a fundamental role in the biogenesis of catecholamine secretory granules. Changes in storage and release of CHGA in clinical and experimental hypertension prompted us to study whether genetic variation at the CHGA locus might contribute to alterations in autonomic function, and hence hypertension and its target organ consequences such as hypertensive renal disease (nephrosclerosis). Systematic polymorphism discovery across the human CHGA locus revealed both common and unusual variants in both the open reading frame and such regulatory regions as the proximal promoter and 30-UTR. In chromaffin cell-transfected CHGA 30-UTR and promoter/luciferase reporter plasmids, the functional consequences of the regulatory/non-coding allelic variants were documented. Variants in both the proximal promoter and the 30-UTR displayed statistical associations with hypertension. Genetic variation in the proximal CHGA promoter predicted glomerular filtration rate in healthy twins. However, for hypertensive renal damage, both end-stage renal disease and rate of progression of earlier disease were best predicted by variants in the 30-UTR. Finally, mechanistic studies were undertaken initiated by the clue that CHGA promoter variation predicted circulating endothelin-1. In cultured endothelial cells, CHGA triggered co-release of not only the vasoconstrictor and pro-fibrotic endothelin-1, but also the pro-coagulant von Willebrand Factor and the pro-angiogenic angiopoietin-2. These findings, coupled with stimulation of endothelin-1 release from glomerular capillary endothelial cells by CHGA, suggest a plausible mechanism whereby genetic variation at the CHGA locus eventuates in alterations in human renal function. These results document the consequences of genetic variation at the CHGA locus for cardiorenal disease and suggest mechanisms whereby such variation achieves functional effects.

Catecholamine storage vesicles: role of core protein genetic polymorphisms in hypertension

Hypertension is a complex trait with deranged autonomic control of the circulation. The sympathoadrenal system exerts minute-to-minute control over cardiac output and vascular tone. Catecholamine storage vesicles (or chromaffin granules) of the adrenal medulla contain remarkably high concentrations of chromogranins/secretogranins (or "granins"), catecholamines, neuropeptide Y, adenosine triphosphate (ATP), and Ca(2+). Within secretory granules, granins are co-stored with catecholamine neurotransmitters and co-released upon stimulation of the regulated secretory pathway. The principal granin family members, chromogranin A (CHGA), chromogranin B (CHGB), and secretogranin II (SCG2), may have evolved from shared ancestral exons by gene duplication. This article reviews human genetic variation at loci encoding the major granins and probes the effects of such polymorphisms on blood pressure, using twin pairs to probe heritability and individuals with the most extreme blood pressure values in the population to study hypertension.

Effects of chromogranin A deficiency and excess in vivo: biphasic blood pressure and catecholamine responses

OBJECTIVE

The phenotype of the chromogranin A (Chga) null (knockout) mouse is hypertensive. However, hypertensive humans and spontaneously hypertensive rats display elevated CHGA expression. This study addresses the paradox that both ablation and elevation of CHGA result in hypertension.

METHODS

Mice with varying copy number of the CHGA gene were generated. In these mice CHGA, catecholamine and blood pressure (BP) were measured. Also a cohort of healthy human individuals was stratified into tertiles based on plasma CHGA expression and phenotyped for characteristics including their BP response to environmental (cold) stress.

RESULTS

The mice displayed a direct CHGA gene dose-dependent (0-4 copies/genome) activation of CHGA expression in both plasma and adrenal gland, yet the BP dependence of CHGA gene dose was U-shaped, maximal at 0 and four copies of the gene, whereas minimal at two copies (i.e., the wild-type gene dosage). Plasma catecholamine showed a parallel U-shaped dose/response in mice, whereas adrenal epinephrine exhibited a reciprocal (inverted) U-shaped response, suggesting dysregulated neurotransmission at both extremes of CHGA expression. The human individuals also showed a nonlinear relationship between CHGA expression and pressor responses to environmental (cold) stress, that were maximal in the highest and lowest tertiles, though basal BPs did not differ among the groups. The human CHGA tertiles also differed in epinephrine secretion as well as degree of CHGA processing to catestatin (catecholamine release-inhibitory peptide derived from CHGA processing).

CONCLUSION

Thus, across mammalian species, an optimal amount of CHGA may be required to establish appropriate catecholamine storage and release, and hence BP homeostasis.

Role of reactive oxygen species in hyperadrenergic hypertension: biochemical, physiological, and pharmacological evidence from targeted ablation of the chromogranin a (Chga) gene

BACKGROUND

Oxidative stress, an excessive production of reactive oxygen species (ROS) outstripping antioxidant defense mechanisms, occurs in cardiovascular pathologies, including hypertension. In the present study, we used biochemical, physiological, and pharmacological approaches to explore the role of derangements of catecholamines, ROS, and the endothelium-derived relaxing factor nitric oxide (NO(•)) in the development of a hyperadrenergic model of hereditary hypertension: targeted ablation (knockout [KO]) of chromogranin A (Chga) in the mouse.

METHODS AND RESULTS

Homozygous ⁻(/)⁻ Chga gene knockout (KO) mice were compared with wild-type (WT, +/+) control mice. In the KO mouse, elevations of systolic and diastolic blood pressure were accompanied by not only elevated catecholamine (norepinephrine and epinephrine) concentrations but also increased ROS (H₂O₂) and isoprostane (an index of lipid peroxidation), as well as depletion of NO(•). Renal transcript analyses implicated changes in Nox1/2, Xo/Xdh, and Sod1,2 mRNAs in ROS elevation by the KO state. KO alterations in blood pressure, catecholamines, H₂O₂, isoprostane, and NO(•) could be abrogated or even normalized (rescued) by either sympathetic outflow inhibition (with clonidine) or NADPH oxidase inhibition (with apocynin). In cultured renal podocytes, H₂O₂ production was substantially augmented by epinephrine (probably through β₂-adrenergic receptors) and modestly diminished by norepinephrine (probably through α₁-adrenergic receptors).

CONCLUSIONS

ROS appear to play a necessary role in the development of hyperadrenergic hypertension in this model, in a process mechanistically linking elevated blood pressure with catecholamine excess, renal transcriptional responses, ROS elevation, lipid peroxidation, and NO(•) depletion. Some of the changes appear to be dependent on transcription, whereas others are immediate. The cycle could be disrupted by inhibition of either sympathetic outflow or NADPH oxidase. Because common genetic variation at the human CHGA locus alters BP, the results have implications for antihypertensive treatment as well as prevention of target-organ consequences of the disease. The results document novel pathophysiological links between the adrenergic system and oxidative stress and suggest new strategies to probe the role and actions of ROS within this setting.

Pro-hormone secretogranin II regulates dense core secretory granule biogenesis in catecholaminergic cells

Processes underlying the formation of dense core secretory granules (DCGs) of neuroendocrine cells are poorly understood. Here, we present evidence that DCG biogenesis is dependent on the secretory protein secretogranin (Sg) II, a member of the granin family of pro-hormone cargo of DCGs in neuroendocrine cells. Depletion of SgII expression in PC12 cells leads to a decrease in both the number and size of DCGs and impairs DCG trafficking of other regulated hormones. Expression of SgII fusion proteins in a secretory-deficient PC12 variant rescues a regulated secretory pathway. SgII-containing dense core vesicles share morphological and physical properties with bona fide DCGs, are competent for regulated exocytosis, and maintain an acidic luminal pH through the V-type H(+)-translocating ATPase. The granulogenic activity of SgII requires a pH gradient along this secretory pathway. We conclude that SgII is a critical factor for the regulation of DCG biogenesis in neuroendocrine cells, mediating the formation of functional DCGs via its pH-dependent aggregation at the trans-Golgi network.

Chromogranin A: a novel susceptibility gene for essential hypertension

Chromogranin A (CHGA) is ubiquitously expressed in secretory cells of the endocrine, neuroendocrine, and neuronal tissues. Although this protein has long been known as a marker for neuroendocrine tumors, its role in cardiovascular disease states including essential hypertension (EH) has only recently been recognized. It acts as a prohormone giving rise to bioactive peptides such as vasostatin-I (human CHGA(1-76)) and catestatin (human CHGA(352-372)) that exhibit several cardiovascular regulatory functions. CHGA is over-expressed but catestatin is diminished in EH. Moreover, genetic variants in the promoter, catestatin, and 3'-untranslated regions of the human CHGA gene alter autonomic activity and blood pressure. Consistent with these findings, targeted ablation of this gene causes severe arterial hypertension and ventricular hypertrophy in mice. Transgenic expression of the human CHGA gene or exogenous administration of catestatin restores blood pressure in these mice. Thus, the accumulated evidence establishes CHGA as a novel susceptibility gene for EH.

Detection of quinone oxidoreductase 1 (NQO1) single-nucleotide polymorphisms (SNP) related to benzene metabolism in immortalized B lymphocytes from a Chinese Han population

Single-nucleotide polymorphisms (SNP) in genes coding metabolizing enzymes modulate gene functions and cellular toxicity in response to chemicals. Quinone oxidoreductase 1 (NQO1) is an important detoxification enzyme involved in the catabolism of 1,4-benzoquinone (1,4-BQ), a benzene metabolite believed to be associated with bone-marrow toxicity and leukemia. Gene function was evaluated in immortalized human B lymphocytes derived from a Chinese Han population with independent genotypes at 2 NQO1 SNP sites. 1,4-Benzoquinone was incubated with these immortalized lymphocytes of differing genotypes. Among the genotypes of 2 SNP examined, cell lines with rs1800566CC showed a higher NQO1 enzymic activity after a 48 h of treatment with 10 muM 1,4-BQ, and a lower comet rate compared with cells of CT/TT genotypes. Data suggested that NQO1 rs1800566 might serve as a functional genetic marker for benzene toxicity in the Chinese Han population. The immortalized B lymphocytes derived from different populations might thus be used as a biomarker to detect functional genetic markers related to exposure to environmental chemicals.

Long human CHGA flanking chromosome 14 sequence required for optimal BAC transgenic "rescue" of disease phenotypes in the mouse Chga knockout

Chromogranin A (CHGA) plays a catalytic role in formation of catecholamine storage vesicles and also serves as precursor to the peptide fragment catestatin, a catecholamine secretory inhibitor whose expression is diminished in the hypertensive individuals. We previously reported the hypertensive, hyperadrenergic phenotype of Chga-/- knockout (KO) mice and rescue by the human ortholog. In the present study, we compare two humanized CHGA mouse models. Into the Chga null background, by bacterial artificial chromosome transgenesis human CHGA transgene has been introduced. Both lines have the complete approximately 12 kbp CHGA gene integrated stably in the genome but have substantial differences in CHGA expression, as well as consequent sympathochromaffin biochemistry and physiology. A mouse model with longer-insert HumCHGA31 displays integration encompassing not only CHGA but also long human flanking sequences. This is in contrast to mouse model HumCHGA19 with limited flanking human sequence co-integrated. As a consequence, HumCHGA19 mice have normal though diminished pattern of spatial expression of CHGA, and 14-fold lower circulating CHGA, with failure to rescue KO phenotypes to normalcy. In the longer-insert HumCHGA31 mice, catecholamine secretion, exaggerated responses to environmental stress, and hypertension were all alleviated. Promoter regions of the transgenes in both HumCHGA19 and HumCHGA31 display minimal CpG methylation, weighing against differential "position effects" of integration, and thus suggesting that lack of cis elements required for optimal CHGA expression occurs in HumCHGA19 mice. Such "humanized" CHGA mouse models may be useful in probing the physiological consequences of variation in CHGA expression found in humans, with consequences for susceptibility to hypertension and cardiovascular disease.

Global metabolic consequences of the chromogranin A-null model of hypertension: transcriptomic detection, pathway identification, and experimental verification

Chromogranin A (CHGA) has a crucial role in formation of regulated secretory granules in neuroendocrine tissues and is also a prohormone that is proteolytically processed into peptides with diverse and complex actions. CHGA and several of its peptide products, including catestatin and pancreastatin, are implicated in pathogenesis of essential hypertension, insulin resistance, and the metabolic syndrome. The Chga knockout mouse (Chga KO) displays severe hypertension coupled with reduction in size, number, and density of regulated secretory granules. We performed genome-wide transcriptome profiling in Chga KO adrenal gland and liver for insight into biochemical and physiological systems altered in this monogenic mouse model of hypertension. Adrenal gene expression pathway prediction of enhanced insulin sensitivity (P = 0.03) in Chga KO was confirmed with glucose, insulin, and homeostasis model assessment of insulin resistance (HOMA-IR) measurements: blood glucose was normal in Chga KO, blood insulin was reduced 4.5-fold (P < 0.0001), and HOMA-IR was decreased 3.8-fold (P < 0.002). Remarkably, such observations conclusively dissociate fundamental features of the metabolic syndrome in this monogenic hypertension model. Exogenous pancreastatin treatment restored insulin sensitivity in the Chga KO to near-normal levels. Gene expression predictions of decreased adrenal cholesterol biosynthesis (P < 0.001) and increased hepatic cholesterol biosynthesis (P < 0.001) were verified with tissue total cholesterol assays: Chga KO adrenal cholesterol decreased 1.8-fold (P = 0.039) and hepatic cholesterol increased 1.8-fold (P = 0.018). Transcriptional regulatory network prediction identified sets of transcription factors that may provide insight into the unclear mechanistic links among CHGA, cholesterol, insulin sensitivity, and the metabolic syndrome. These experiments demonstrate, for the first time, that genetic variation at the CHGA locus impacts insulin sensitivity and tissue cholesterol levels in an intact, living organism. The Chga KO may constitute a unique model for studying the relationship between the CHGA locus and disease phenotypes of the metabolic syndrome.