The −318 C>G Single-Nucleotide Polymorphism in GNAI2 Gene Promoter Region Impairs Transcriptional Activity through Specific Binding of Sp1 Transcription Factor and Is Associated with High Blood Pressure in Caucasians from Italy

Central Gαi2 Protein Mediated Neuro-Hormonal Control of Blood Pressure and Salt Sensitivity

Hypertension, a major public health issue, is estimated to contribute to 10% of all deaths worldwide. Further, the salt sensitivity of blood pressure is a critical risk factor for the development of hypertension. The hypothalamic paraventricular nucleus (PVN) coordinates neuro-hormonal responses to alterations in plasma sodium and osmolality and multiple G Protein-Coupled Receptors (GPCRs) are involved in fluid and electrolyte homeostasis. In acute animal studies, our laboratory has shown that central Gαi/o subunit protein signal transduction mediates hypotensive and bradycardic responses and that Gz/q, proteins mediate the release of arginine vasopressin (AVP) and subsequent aquaretic responses to acute pharmacological stimuli. Extending these studies, our laboratory has shown that central Gαi2 proteins selectively mediate the hypotensive, sympathoinhibitory and natriuretic responses to acute pharmacological activation of GPCRs and in response to acute physiological challenges to fluid and electrolyte balance. In addition, following chronically elevated dietary sodium intake, salt resistant rats demonstrate site-specific and subunit-specific upregulation of Gαi2 proteins in the PVN, resulting in sympathoinhibition and normotension. In contrast, chronic dietary sodium intake in salt sensitive animals, which fail to upregulate PVN Gαi2 proteins, results in the absence of dietary sodium-evoked sympathoinhibition and salt sensitive hypertension. Using in situ hybridization, we observed that Gαi2 expressing neurons in parvocellular division of the PVN strongly (85%) colocalize with GABAergic neurons. Our data suggest that central Gαi2 protein-dependent responses to an acute isotonic volume expansion (VE) and elevated dietary sodium intake are mediated by the peripheral sensory afferent renal nerves and do not depend on the anteroventral third ventricle (AV3V) sodium sensitive region or the actions of central angiotensin II type 1 receptors. Our translational human genomic studies have identified three G protein subunit alpha I2 (GNAI2) single nucleotide polymorphisms (SNPs) as potential biomarkers in individuals with salt sensitivity and essential hypertension. Collectively, PVN Gαi2 proteins-gated pathways appear to be highly conserved in salt resistance to counter the effects of acute and chronic challenges to fluid and electrolyte homeostasis on blood pressure via a renal sympathetic nerve-dependent mechanism.

Genetic Variants in Transcription Factor Binding Sites in Humans: Triggered by Natural Selection and Triggers of Diseases

Variants of transcription factor binding sites (TFBSs) constitute an important part of the human genome. Current evidence demonstrates close links between nucleotides within TFBSs and gene expression. There are multiple pathways through which genomic sequences located in TFBSs regulate gene expression, and recent genome-wide association studies have shown the biological significance of TFBS variation in human phenotypes. However, numerous challenges remain in the study of TFBS polymorphisms. This article aims to cover the current state of understanding as regards the genomic features of TFBSs and TFBS variants; the mechanisms through which TFBS variants regulate gene expression; the approaches to studying the effects of nucleotide changes that create or disrupt TFBSs; the challenges faced in studies of TFBS sequence variations; the effects of natural selection on collections of TFBSs; in addition to the insights gained from the study of TFBS alleles related to gout, its associated comorbidities (increased body mass index, chronic kidney disease, diabetes, dyslipidemia, coronary artery disease, ischemic heart disease, hypertension, hyperuricemia, osteoporosis, and prostate cancer), and the treatment responses of patients.

Hypothalamic Paraventricular Nucleus Gαi2 (Guanine Nucleotide-Binding Protein Alpha Inhibiting Activity Polypeptide 2) Protein-Mediated Neural Control of the Kidney and the Salt Sensitivity of Blood Pressure

We have previously reported that in salt-resistant rat phenotypes brain, Gαi2 (guanine nucleotide-binding protein alpha inhibiting activity polypeptide 2) proteins are required to maintain blood pressure and sodium balance. However, the impact of hypothalamic paraventricular nucleus (PVN) Gαi2 proteins on the salt sensitivity of blood pressure is unknown. Here, by the bilateral PVN administration of a targeted Gαi2 oligodeoxynucleotide, we show that PVN-specific Gαi2 proteins are required to facilitate the full natriuretic response to an acute volume expansion (peak natriuresis [μeq/min] scrambled (SCR) oligodeoxynucleotide 41±3 versus Gαi2 oligodeoxynucleotide 18±4; P<0.05) via a renal nerve-dependent mechanism. Furthermore, in response to chronically elevated dietary sodium intake, PVN-specific Gαi2 proteins are essential to counter renal nerve-dependent salt-sensitive hypertension (mean arterial pressure [mm Hg] 8% NaCl; SCR oligodeoxynucleotide 128±2 versus Gαi2 oligodeoxynucleotide 147±3; P<0.05). This protective pathway involves activation of PVN Gαi2 signaling pathways, which mediate sympathoinhibition to the blood vessels and kidneys (renal norepinephrine [pg/mg] 8% NaCl; SCR oligodeoxynucleotide 375±39 versus Gαi2 oligodeoxynucleotide 850±27; P<0.05) and suppression of the activity of the sodium chloride cotransporter assessed as peak natriuresis to hydrochlorothiazide. Additionally, central oligodeoxynucleotide-mediated Gαi2 protein downregulation prevented PVN parvocellular neuron activation, assessed by FosB immunohistochemistry, in response to increased dietary salt intake. In our analysis of the UK BioBank data set, it was observed that 2 GNAI2 single nucleotide polymorphism (SNP) (rs2298952, P=0.041; rs4547694, P=0.017) significantly correlate with essential hypertension. Collectively, our data suggest that selective targeting and activation of PVN Gαi2 proteins is a novel therapeutic approach for the treatment of salt-sensitive hypertension.

GNAI2 polymorphic variance associates with salt sensitivity of blood pressure in the Genetic Epidemiology Network of Salt Sensitivity study

Salt sensitivity of blood pressure (BP) increases hypertension risk and associated adverse cardiovascular outcomes. At present, there are no validated rapid tests or diagnostic markers to identify salt sensitivity of BP in clinical practice. Based on our prior animal studies that report a role for brain Gαi₂ proteins in the salt sensitivity of BP and evidence that GNAI2 single nucleotide polymorphisms (SNPs) associate with hypertension risk, we investigated the hypothesis that GNAI2 SNPs associate with salt sensitivity of BP in humans. Our data provide the first evidence that a GNAI2 SNP ( rs10510755 ) positively associates with salt sensitivity of BP in the Genetic Epidemiology of Salt Sensitivity data set (continuous phenotype P = 0.049, case-control phenotype P = 0.039; n = 968), independently of subject sex or age. These observations suggest that genotyping at GNAI2 may be a useful biomarker in identifying individuals at risk for developing salt-sensitive BP and related complications or in identifying salt sensitivity within the hypertensive population.

Molecular genetics of essential hypertension

Hypertension is a major public health problem in the developing as well as in developed countries due to its high prevalence and its association with coronary heart disease, renal disease, stroke, peripheral vascular disease, and related disorders. Essential hypertension (EH) is the most common diagnosis in this disease, suggesting that a monocausal etiology has not been identified. However, a number of risk factors associated with EH have also been identified such as age, sex, demographic, environmental, genetic, and vascular factors. Recent advances in molecular biological research had achieved clarifying the molecular basis of Mendelian hypertensive disorders. Molecular genetic studies have now identified mutations in several genes that cause Mendelian forms of hypertension in humans. However, none of the single genetic variants has emerged from linkage or association analyses as consistently related to the blood pressure level in every sample and in all populations. Besides, a number of polymorphisms in candidate genes have been associated with differences in blood pressure. The most prominent candidate has been the polymorphisms in the renin-angiotensin-aldosterone system. In total, EH is likely to be a polygenic disorder that results from inheritance of a number of susceptibility genes and involves multiple environmental determinants. These determinants complicate the study of blood pressure variations in the general population. The complex nature of the hypertension phenotype makes large-scale studies indispensable, when screening of familial and genetic factors was intended. In this review, recent genetic studies exploring the molecular basis of EH, including different molecular pathways, are highlighted.

Impaired sodium-evoked paraventricular nucleus neuronal activation and blood pressure regulation in conscious Sprague-Dawley rats lacking central Gαi2 proteins

AIM

We determined the role of brain Gαi2 proteins in mediating the neural and humoral responses of conscious male Sprague-Dawley rats to acute peripheral sodium challenge.

METHODS

Rats pre-treated (24-h) intracerebroventricularly with a targeted oligodeoxynucleotide (ODN) (25 μg per 5 μL) to downregulate brain Gαi2 protein expression or a scrambled (SCR) control ODN were challenged with an acute sodium load (intravenous bolus 3 m NaCl; 0.14 mL per 100 g), and cardiovascular parameters were monitored for 120 min. In additional groups, hypothalamic paraventricular nucleus (PVN) Fos immunoreactivity was examined at baseline, 40, and 100 min post-sodium challenge.

RESULTS

In response to intravenous hypertonic saline (HS), no difference was observed in peak change in mean arterial pressure between groups. In SCR ODN pre-treated rats, arterial pressure returned to baseline by 100 min, while it remained elevated in Gαi2 ODN pre-treated rats (P < 0.05). No difference between groups was observed in sodium-evoked increases in Fos-positive magnocellular neurons or vasopressin release. V1a receptor antagonism failed to block the prolonged elevation of arterial pressure in Gαi2 ODN pre-treated rats. A significantly greater number of Fos-positive ventrolateral parvocellular, lateral parvocellular, and medial parvocellular neurons were observed in SCR vs. Gαi2 ODN pre-treated rats at 40 and 100 min post-HS challenge (P < 0.05). In SCR, but not Gαi2 ODN pre-treated rats, HS evoked suppression of plasma norepinephrine (P < 0.05).

CONCLUSION

This highlights Gαi2 protein signal transduction as a novel central mechanism acting to differentially influence PVN parvocellular neuronal activation, sympathetic outflow, and arterial pressure in response to acute HS, independently of actions on magnocellular neurons and vasopressin release.

Evidence of a causal relationship between high serum adiponectin levels and increased cardiovascular mortality rate in patients with type 2 diabetes

BACKGROUND

Despite its beneficial role on insulin resistance and atherosclerosis, adiponectin has been repeatedly reported as an independent positive predictor of cardiovascular mortality.

METHODS

A Mendelian randomization approach was used, in order to evaluate whether such counterintuitive association recognizes a cause-effect relationship. To this purpose, single nucleotide polymorphism rs822354 in the ADIPOQ locus which has been previously associated with serum adiponectin at genome-wide level, was used as an instrument variable. Our investigation was carried out in the Gargano Heart Study-prospective design, comprising 356 patients with type 2 diabetes, in whom both total and high molecular weight (HMW) adiponectin were measured and cardiovascular mortality was recorded (mean follow-up = 5.4 ± 2.5 years; 58 events/1922 person-year).

RESULTS

The A allele of rs822354 was associated with both total and HMW adiponectin [β (SE) = 0.10 (0.042), p = 0.014 and 0.17 (0.06), p = 0.003; respectively]. In a Poisson model comprising age, sex, smoking habits, BMI, HbA1c, total cholesterol, HDL-cholesterol, triglycerides, insulin therapy and hypertension, both rs822354 (IRR = 1.94, 95 % CI 1.23-3.07; p = 0.005), as well as the genetic equivalent of total adiponectin change (IRR = 1.07, 95 % CI 1.02-1.12; p = 0.003) were significantly associated with cardiovascular mortality. The observed genetic effect was significantly greater than that exerted by the genetic equivalent change of serum adiponectin (p for IRR heterogeneity = 0.012). In the above-mentioned adjusted model, very similar results were obtained when HMW, rather than total, adiponectin was used as the exposure variable of interest.

CONCLUSIONS

Our data suggest that the paradoxical association between high serum adiponectin levels and increased cardiovascular mortality rate is based on a cause-effect relationship, thus pointing to an unexpected deleterious role of adiponectin action/metabolism on atherosclerotic processes.

Brain Gαi 2 -subunit proteins and the prevention of salt sensitive hypertension

To counter the development of salt-sensitive hypertension, multiple brain G-protein-coupled receptor (GPCR) systems are activated to facilitate sympathoinhibition, sodium homeostasis, and normotension. Currently there is a paucity of knowledge regarding the role of down-stream GPCR-activated Gα-subunit proteins in these critically important physiological regulatory responses required for long-term blood pressure regulation. We have determined that brain Gαi₂-proteins mediate natriuretic and sympathoinhibitory responses produced by acute pharmacological (exogenous central nociceptin/orphanin FQ receptor (NOP) and α₂-adrenoceptor activation) and physiological challenges to sodium homeostasis (intravenous volume expansion and 1 M sodium load) in conscious Sprague–Dawley rats. We have demonstrated that in salt-resistant rat phenotypes, high dietary salt intake evokes site-specific up-regulation of hypothalamic paraventricular nucleus (PVN) Gαi₂-proteins. Further, we established that PVN Gαi₂ protein up-regulation prevents the development of renal nerve-dependent sympathetically mediated salt-sensitive hypertension in Sprague–Dawley and Dahl salt-resistant rats. Additionally, failure to up-regulate PVN Gαi₂ proteins during high salt-intake contributes to the pathophysiology of Dahl salt-sensitive (DSS) hypertension. Collectively, our data demonstrate that brain, and likely PVN specific, Gαi₂ protein pathways represent a central molecular pathway mediating sympathoinhibitory renal-nerve dependent responses evoked to maintain sodium homeostasis and a salt-resistant phenotype. Further, impairment of this endogenous “anti-hypertensive” mechanism contributes to the pathophysiology of salt-sensitive hypertension.

Gαi2-protein-mediated signal transduction: central nervous system molecular mechanism countering the development of sodium-dependent hypertension

Excess dietary salt intake is an established cause of hypertension. At present, our understanding of the neuropathophysiology of salt-sensitive hypertension is limited by a lack of identification of the central nervous system mechanisms that modulate sympathetic outflow and blood pressure in response to dietary salt intake. We hypothesized that impairment of brain Gαi2-protein-gated signal transduction pathways would result in increased sympathetically mediated renal sodium retention, thus promoting the development of salt-sensitive hypertension. To test this hypothesis, naive or renal denervated Dahl salt-resistant and Dahl salt-sensitive (DSS) rats were assigned to receive a continuous intracerebroventricular control scrambled or a targeted Gαi2-oligodeoxynucleotide infusion, and naive Brown Norway and 8-congenic DSS rats were fed a 21-day normal or high-salt diet. High salt intake did not alter blood pressure, suppressed plasma norepinephrine, and evoked a site-specific increase in hypothalamic paraventricular nucleus Gαi2-protein levels in naive Brown Norway, Dahl salt-resistant, and scrambled oligodeoxynucleotide-infused Dahl salt-resistant but not DSS rats. In Dahl salt-resistant rats, Gαi2 downregulation evoked rapid renal nerve-dependent hypertension, sodium retention, and sympathoexcitation. In DSS rats, Gαi2 downregulation exacerbated salt-sensitive hypertension via a renal nerve-dependent mechanism. Congenic-8 DSS rats exhibited sodium-evoked paraventricular nucleus-specific Gαi2-protein upregulation and attenuated hypertension, sodium retention, and global sympathoexcitation compared with DSS rats. These data demonstrate that paraventricular nucleus Gαi2-protein-gated pathways represent a conserved central molecular pathway mediating sympathoinhibitory renal nerve-dependent responses evoked to maintain sodium homeostasis and a salt-resistant phenotype. Impairment of this mechanism contributes to the development of salt-sensitive hypertension.

Refined mapping of a hypertension susceptibility locus on rat chromosome 12

Previously, we found that transferring 6.1 Mb of salt-sensitive (SS) chromosome 12 (13.4-19.5 Mb) onto the consomic SS-12(BN) background significantly elevated mean arterial pressure in response to an 8% NaCl diet (178±7 versus 144±2 mm Hg; P<0.001). Using congenic mapping, we have now narrowed the blood pressure locus by 86% from a 6.1-Mb region containing 133 genes to an 830-kb region (chr12:14.36-15.19 Mb) with 14 genes. Compared with the SS-12(BN) consomic, the 830-kb blood pressure locus was associated with a ∆+15 mm Hg (P<0.01) increase in blood pressure, which coincided with elevated albuminuria (∆+32 mg/d; P<0.001), proteinuria (∆+48 mg/d; P<0.01), protein casting (∆+154%; P<0.05), and renal fibrosis (∆+79%; P<0.05). Of the 14 genes residing in the 830-kb locus, 8 were differentially expressed, and among these, Chst12 (carbohydrate chondroitin 4 sulfotransferase 12) was most consistently downregulated by 2.6- to 4.5-fold (P<0.05) in both the renal medulla and cortex under normotensive and hypertensive conditions. Moreover, whole genome sequence analysis of overlapping blood pressure loci revealed an ≈86-kb region (chr12:14 541 567-14 627 442 bp) containing single-nucleotide variants near Chst12 that are unique to the hypertensive SS strain when compared with the normotensive Brown Norway, Dahl salt-resistant, and Wistar-Kyoto strains. Finally, the 830-kb interval is syntenic to a region on human chromosome 7 that has been genetically linked to blood pressure, suggesting that insight gained from our SS-12(BN) congenic strain may be translated to a better understanding of human hypertension.

Single nucleotide polymorphism in ATM gene, cooking oil fumes and lung adenocarcinoma susceptibility in Chinese female non-smokers: a case-control study

BACKGROUND

The ataxia-telangiectasia mutated (ATM) gene plays an important role in the DNA double-strand breaks repair pathway. Single nucleotide polymorphisms (SNPs) of DNA repair genes are suspected to influence the risk of lung cancer. This study aimed to investigate the association between the ATM -111G>A (rs189037) polymorphism, environmental risk factors and the risk of lung adenocarcinoma in Chinese female non-smokers.

METHODS

A hospital-based case-control study of 487 lung cancer patients and 516 matched cancer-free controls was conducted. Information concerning demographic and environmental risk factors was obtained for each case and control by a trained interviewer. After informed consent was obtained, 10 ml venous blood was collected from each subject for biomarker testing. Single nucleotide polymorphism was determined by using TaqMan method.

RESULTS

This study showed that the individuals with ATM rs189037 AA genotype were at an increased risk for lung adenocarcinoma compared with those carrying the GA or GG genotype (adjusted odds ratios (OR) 1.44, 95% confidence interval (CI) 1.02-2.02, P = 0.039). The stratified analysis suggested that increased risk associated with ATM rs189037 AA genotype in individuals who never or seldom were exposed to cooking oil fumes (adjusted OR 1.89, 95%CI 1.03-3.49, P = 0.040).

CONCLUSIONS

ATM rs189037 might be associated with the risk of lung adenocarcinoma in Chinese non-smoking females. Furthermore, ATM rs189037 AA genotype might be a risk factor of lung adenocarcinoma among female non-smokers without cooking oil fume exposure.

Central nervous system Gαi2-subunit proteins maintain salt resistance via a renal nerve-dependent sympathoinhibitory pathway

In salt-resistant phenotypes, chronic elevated dietary sodium intake evokes suppression of renal sodium-retaining mechanisms to maintain sodium homeostasis and normotension. We have recently shown that brain Gαi(2) protein pathways are required to suppress renal sympathetic nerve activity and facilitate maximal sodium excretion during acute intravenous volume expansion in Sprague-Dawley rats. Here, we studied the role of brain Gαi(2) proteins in the endogenous central neural mechanisms acting to maintain fluid and electrolyte homeostasis and normotension during a chronic elevation in dietary salt intake. Naive or bilaterally renal denervated adult male Sprague-Dawley rats were randomly assigned to receive an intracerebroventricular scrambled or Gαi(2) oligodeoxynucleotide infusion and then subjected to either a normal salt (0.4%) or high-salt (8.0%) diet for 21 days. In scrambled oligodeoxynucleotide-infused rats, salt loading, which did not alter blood pressure, evoked a site-specific increase in hypothalamic paraventricular nucleus Gαi(2) protein levels and suppression of circulating norepinephrine content and plasma renin activity. In salt-loaded rats continuously infused intracerebroventricularly with a Gαi(2) oligodeoxynucleotide, animals exhibited sodium and water retention, elevated plasma norepinephrine levels, and hypertension, despite suppression of plasma renin activity. Furthermore, in salt-loaded bilaterally renal denervated rats, Gαi(2) oligodeoxynucleotide infusion failed to evoke salt-sensitive hypertension. Therefore, in salt-resistant rats subjected to a chronic high-salt diet, brain Gαi(2) proteins are required to inhibit central sympathetic outflow to the kidneys and maintain sodium balance and normotension. In conclusion, these data demonstrate a central role of endogenous brain, likely paraventricular nucleus-specific, Gαi(2)-subunit protein-gated signal transduction pathways in maintaining a salt-resistant phenotype.

Pharmacogenetics of D2 dopamine receptor gene in prolactin-secreting pituitary adenomas

IMPORTANCE OF THE FIELD

Dopamine-agonists are the treatment of choice of prolactin-secreting pituitary adenomas (PRL-omas). Their actions on D2 dopamine receptor (DRD2) and the clinical outcome may be affected by polymorphisms.

AREAS COVERED IN THIS REVIEW

PRL-omas are well-differentiated endocrine tumors expressing DRD2. The dopamine-agonist cabergoline (CB), normalizes prolactin and reduces tumor size in about 80 - 90% of patients. DRD2 polymorphisms correlate with neuropsychiatric disorders, in particular alcoholism and schizophrenia. This review describes the DRD2 polymorphisms, their functional effects, and their impact on susceptibility and response to dopamine-agonists treatment. Searching PubMed database for pertinent articles we found that some DRD2 polymorphisms, particularly TaqIA, TaqIB and NcoI, are associated with different receptor binding in brain areas. One study carried out in patients with PRL-omas found a correlation between NcoI and TaqIA and resistance to CB. In particular, resistant patients had higher prevalence of NcoI-T allele than the responsive patients, while the commonest haplotype (having TaqIA2 allele) was associated with better response.

WHAT THE READER WILL GAIN

This review deals with the connection between DRD2 polymorphisms and PRL-oma treatment and suggests hypotheses for further studies.

TAKE HOME MESSAGE

Only one study was carried out to analyze the role of DRD2 polymorphisms in PRLomas response to CB. Further studies, including pituitary and hypothalamus in vivo determination of DRD2 binding according to DRD2 genotypes, investigation of possible post-receptorial mechanisms involved, as well as population studies in collaboration with psychiatrists and neurologists, are needed.

Hypertension in mice lacking the CXCR3 chemokine receptor

The CXC chemokine receptor 3 (CXCR3) has been linked to autoimmune and inflammatory disease, allograft rejection, and ischemic nephropathy. CXCR3 is expressed on endothelial and smooth muscle cells. Although a recent study posited that antagonizing of CXCR3 function may reduce atherosclerosis, the role of CXCR3 in controlling physiological vascular functions remains unclear. This study demonstrates that disruption of CXCR3 leads to elevated mean arterial pressures in anesthetized and conscious mice, respectively. Stimulation of isolated resistance vessels with various vasoconstrictors showed increased contractibility in CXCR3-/- mice in response to angiotensin II (ANG II) and a decreased vasodilatation in response to acetylcholine (ACh). The increased contractibility was related to higher ANG II type 1 receptor (AT1R) expression, whereas the decreased vasodilatation was related to lower M3-ACh receptor expression in the mesenteric arteries of CXCR3-/- mice compared with wild-type mice. The vasodilatatory response to ACh could be antagonized by the nonselective ACh receptor antagonist atropine and the selective M3 receptor antagonist 4-DAMP, but not by M1, M2, and M4 receptor antagonists. Additionally, EMSA studies revealed that transcription factors SP-1 and EGR-1 interact as a complex with the murine AT1R promoter region. Furthermore, we could show increased expression of SP-1 in CXCR3-/- mice indicating an imbalanced SP-1 and EGR-1 complex formation which causes increased AT1R expression and hypertension. The data indicate that CXCR3 receptor is important in vascular contractility and hypertension, possibly through upregulated AT1R expression.