Alpha-adrenoceptor gene variants and autonomic nervous system function in a young healthy Japanese population

Adrenergic receptors gene polymorphisms and autonomic nervous control of heart and vascular tone

Adrenergic receptors (ARs) are the primary targets of catecholamines released from the sympathetic nerve endings during their activation. ARs play a central role in autonomic nervous system and serve as important targets of widely used drugs. Several ARs gene polymorphisms were found to be associated with cardiovascular disease in previous clinical studies. Although more precise mechanism of the polymorphisms influence on autonomic control of cardiovascular system was studied in many previous physiological studies, their results are not unequivocal. This paper reviews the results of clinical and physiological studies focused on the impact of selected common single nucleotide polymorphisms of ARs genes involved in sympathetic control on cardiovascular system and its control. In summary, many studies assessed only a very limited range of cardiovascular control related parameters providing only very limited view on the complex cardiovascular control. The overview of partially contradicting results underlines a need to examine wider range of cardiovascular measures including their reactivity under various stress conditions requiring further study. It is expected that an effect of one given polymorphism is not very prominent, but it is suggested that even subtle differences in cardiovascular control could – on a longer time scale – lead to the development of severe pathological consequences.

Role of α2-Adrenoceptors in Hypertension: Focus on Renal Sympathetic Neurotransmitter Release, Inflammation, and Sodium Homeostasis

The kidney is extensively innervated by sympathetic nerves playing an important role in the regulation of blood pressure homeostasis. Sympathetic nerve activity is ultimately controlled by the central nervous system (CNS). Norepinephrine, the main sympathetic neurotransmitter, is released at prejunctional neuroeffector junctions in the kidney and modulates renin release, renal vascular resistance, sodium and water handling, and immune cell response. Under physiological conditions, renal sympathetic nerve activity (RSNA) is modulated by peripheral mechanisms such as the renorenal reflex, a complex interaction between efferent sympathetic nerves, central mechanism, and afferent sensory nerves. RSNA is increased in hypertension and, therefore, critical for the perpetuation of hypertension and the development of hypertensive kidney disease. Renal sympathetic neurotransmission is not only regulated by RSNA but also by prejunctional α2-adrenoceptors. Prejunctional α2-adrenoceptors serve as autoreceptors which, when activated by norepinephrine, inhibit the subsequent release of norepinephrine induced by a sympathetic nerve impulse. Deletion of α2-adrenoceptors aggravates hypertension ultimately by modulating renal pressor response and sodium handling. α2-adrenoceptors are also expressed in the vasculature, renal tubules, and immune cells and exert thereby effects related to vascular tone, sodium excretion, and inflammation. In the present review, we highlight the role of α2-adrenoceptors on renal sympathetic neurotransmission and its impact on hypertension. Moreover, we focus on physiological and pathophysiological functions mediated by non-adrenergic α2-adrenoceptors. In detail, we discuss the effects of sympathetic norepinephrine release and α2-adrenoceptor activation on renal sodium transporters, on renal vascular tone, and on immune cells in the context of hypertension and kidney disease.

The correlation between SNPs within the gene of adrenergic receptor and neuropeptide Y and risk of cervical vertigo

BACKGROUND

The current investigation was aimed to explore the potential associations of SNPs within ADRB2, ADRB1, NPY, and ADRA1A with risk and prognosis of cervical vertigo.

METHODS

Altogether 216 patients with cervical vertigo and 204 healthy controls were gathered, and their DNAs were extracted utilizing the whole-blood DNA extraction kit. Besides, the PCR reactions were conducted using the TaqMan^R single nucleotide polymorphism (SNP) genotyping assays, and the SNPs were detected on the 7900HT real-time fluorogenic quantitative polymerase chain reaction (PCR) instrument. Finally, the severity of cervical vertigo was classified according to the JOA scoring, and the recovery rate (RR) of cervical vertigo was calculated in light of the formula as: [Formula: see text] RESULTS: The SNPs within ADRA1A [rs1048101 (T>C) and rs3802241 (C>T)], NPY [rs16476 (A>C), rs16148 (T>C), and rs5574 (C>T)], ADRB1 [rs28365031 (A>G)] and ADRB2 [rs2053044 (A>G)] were all significantly associated with regulated risk of cervical vertigo (all P < .05). Haplotypes of ADRA1A [CT and TC] and NPY [CCT and ATT] were also suggested as the susceptible factors of cervical vertigo in comparison with other haplotypes. Furthermore, the SNPs within ADRA1A [rs1048101 (T>C)], NPY [rs16476 (A>C), rs16148 (T>C)], as well as ADRB1 [rs28365031 (A>G)] all appeared to predict the prognosis of cervical vertigo in a relatively accurate way (all P < .05). Ultimately, the haplotypes of ADRA1A (CC) and NPY (CCT) tended to decrease the RR.

CONCLUSIONS

The SNPs within ADRB2, ADRB1, NPY, and ADRA1A might act as the diagnostic biomarkers and treatment targets for cervical vertigo.

Genetic variation in alpha2-adrenoreceptors and heart rate recovery after exercise

Heart rate recovery (HRR) after exercise is an independent predictor of adverse cardiovascular outcomes. HRR is mediated by both parasympathetic reactivation and sympathetic withdrawal and is highly heritable. We examined whether common genetic variants in adrenergic and cholinergic receptors and transporters affect HRR. In our study 126 healthy subjects (66 Caucasians, 56 African Americans) performed an 8 min step-wise bicycle exercise test with continuous computerized ECG recordings. We fitted an exponential curve to the postexercise R-R intervals for each subject to calculate the recovery constant (kr) as primary outcome. Secondary outcome was the root mean square residuals averaged over 1 min (RMS1min), a marker of parasympathetic tone. We used multiple linear regressions to determine the effect of functional candidate genetic variants in autonomic pathways (6 ADRA2A, 1 ADRA2B, 4 ADRA2C, 2 ADRB1, 3 ADRB2, 2 NET, 2 CHT, and 1 GRK5) on the outcomes before and after adjustment for potential confounders. Recovery constant was lower (indicating slower HRR) in ADRA2B 301-303 deletion carriers (n = 54, P = 0.01), explaining 3.6% of the interindividual variability in HRR. ADRA2A Asn251Lys, ADRA2C rs13118771, and ADRB1 Ser49Gly genotypes were associated with RMS1min. Genetic variability in adrenergic receptors may be associated with HRR after exercise. However, most of the interindividual variability in HRR remained unexplained by the variants examined. Noncandidate gene-driven approaches to study genetic contributions to HRR in larger cohorts will be of interest.

Gender-related associations of genetic polymorphisms of α-adrenergic receptors, endothelial nitric oxide synthase and bradykinin B2 receptor with treadmill exercise test responses

BACKGROUND

Treadmill exercise test responses have been associated with cardiovascular prognosis in individuals without overt heart disease. Neurohumoral and nitric oxide responses may influence cardiovascular performance during exercise testing. Therefore, we evaluated associations between functional genetic polymorphisms of α-adrenergic receptors, endothelial nitric oxide synthase, bradykinin receptor B2 and treadmill exercise test responses in men and women without overt heart disease.

METHODS

We enrolled 766 (417 women; 349 men) individuals without established heart disease from a check-up programme at the Heart Institute, University of São Paulo Medical School. Exercise capacity, chronotropic reserve, maximum heart-rate achieved, heart-rate recovery, exercise systolic blood pressure (SBP), exercise diastolic blood pressure (DBP) and SBP recovery were assessed during exercise testing. Genotypes for the α-adrenergic receptors ADRA1A Arg347Cys (rs1048101), ADRA2A 1780 C>T (rs553668), ADRA2B Del 301-303 (rs28365031), endothelial nitric synthase (eNOS) 786 T>C (rs2070744), eNOS Glu298Asp (rs1799983) and BK2R (rs5810761) polymorphisms were assessed by PCR and high-resolution melting analysis.

RESULTS

Maximum SBP was associated with ADRA1A rs1048101 (p=0.008) and BK2R rs5810761 (p=0.008) polymorphisms in men and ADRA2A rs553668 (p=0.008) and ADRA2B rs28365031 (p=0.022) in women. Maximum DBP pressure was associated with ADRA2A rs553668 (p=0.002) and eNOS rs1799983 (p=0.015) polymorphisms in women. Exercise capacity was associated with eNOS rs2070744 polymorphisms in women (p=0.01) and with eNOS rs1799983 in men and women (p=0.038 and p=0.024).

CONCLUSIONS

The findings suggest that genetic variants of α-adrenergic receptors and bradykinin B2 receptor may be involved with blood pressure responses during exercise tests. Genetic variants of endothelial nitric oxide synthase may be involved with exercise capacity and blood pressure responses during exercise tests. These responses may be gender-related.

Association of alpha 2A adrenergic receptor gene (ADRAlpha2A) polymorphism with irritable bowel syndrome, microscopic and ulcerative colitis

BACKGROUND

Alpha 2 adrenergic receptors (alpha2 ARs) play a central role in the regulation of systemic sympathetic activity. Prejunctional alpha 2A adrenoceptor regulates through negative feedback at presynaptic nerve ending. A-1291 C>G polymorphism located in alpha2-adrenergic receptor gene (ADRAlpha2A) has been identified. We investigated the possible association between 1291 C>G polymorphism in the promoter region of ADRAlpha2A in clinical subtypes of IBS, ulcerative and microscopic colitis patients.

METHODS

This prospective case control study included 92 patients with diarrhea predominant IBS (D-IBS), 44 with constipation predominant IBS (C-IBS), 15 with alternating diarrhea and constipation IBS (M-IBS), 75 ulcerative colitis (UC), 41 microscopic colitis (MC) and 100 healthy controls. The subjects were genotyped by using PCR amplification of the promoter region of ADRAlpha2A gene followed by digestion with the restriction enzyme MspI. The study was approved by the institute ethical committee.

RESULTS

A strong genotypic association was observed between alpha2A-1291 C>G polymorphism and D-IBS (chi2=6.38, df=2, p<0.05). There was no significant difference in alpha2A-1291 C>G genotype and allele frequency between C-IBS, M-IBS, UC, MC cases and control subjects.

CONCLUSIONS

A significant association was observed between alpha2A-1291C>G polymorphism and D-IBS. Thus, alpha2 AR gene may be a potential candidate involved in the pathophysiology of D-IBS.

Association of alpha2A-adrenergic receptor gene polymorphism with susceptibility to suicide in Japanese females

OBJECTIVES

It has been suggested that noradrenergic system abnormalities are involved in suicide. Postmortem brain studies have shown that molecular and functional alterations in alpha2A-adrenergic receptor-induced signal transduction are associated with suicide and depression. Recently, a single nucleotide polymorphism (SNP) within a coding region of the alpha2A-adrenergic receptor gene (ADRA2A), which results in an Asn-to-Lys change at amino acid 251 (N251K), has been implicated in susceptibility to suicide in Caucasians. The aim of our study is to determine whether genetic variants of the ADRA2A gene are also associated with suicide in a Japanese population.

METHODS

Three SNPs, C-1291G, N251K and rs3750625C/A, and one insertion/deletion polymorphism in the ADRA2A gene were genotyped in 184 completed suicides and 221 control subjects with the polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

Neither variation of the N251K SNP nor the insertion/deletion polymorphism was found in our Japanese samples. The C-1291G SNP in the promoter region was found to be significantly associated with suicide in females (P=0.043 and 0.013 for genotypic and allelic comparisons, respectively). One of the common haplotypes, CC of C-1291G and rs3750625C/A, was also associated with suicide in females (P=0.015). These associations were also significant in the female violent suicide victims (P=0.009 and 0.009 for allelic and CC haplotypic comparisons, respectively). Although the significance was nominal, it was maintained even after correction for multiple comparisons. By contrast, neither of these two SNPs showed any association with violent and/or non-violent suicide in males.

CONCLUSION

Our results raise the possibility that promoter genetic variation in the ADRA2A gene is associated with either suicide or violent suicide in females.

ADRA2A polymorphism and smoking in a Turkish population

Adrenoceptors (ARs) consist of nine subtypes, which are involved in a wide spectrum of physiological functions and are the site of action for a considerable percentage of currently prescribed therapeutics. All AR subtypes (except α1D) can be polymorphic because of the genetic variations in the coding and non-coding regions. Sixteen sequence variations were identified in α-adrenergic 2A (ADRA2A) gene. Among them, ADRA2A C1291G polymorphism is one of the most important polymorphisms, which plays a major role in regulating neurotransmitter release, blood pressure, lipolysis, insulin secretion, and platelet aggregation. A C–G transversion results in an MspI restriction fragment length polymorphism located at 1291 bp upstream of the origin of transcription. Because Medline search showed no study showing the allelic frequencies, and no information is available on inter-individual variability of ADRA2A C1291G polymorphism in Turkish population, we genotyped 203 healthy Turkish subjects. Because of large genetic variation of the polymorphism, we aimed to find out the distribution of C1291G polymorphism in Turkish population. Furthermore, we evaluated the possible association between the C1291G polymorphism in the ADRA2A receptor gene and smoking. The frequencies for the 1291C and 1291G alleles were 64% and 36%, respectively. The genotype frequencies for C1291C, C1291G, and G1291G were 35.5%, 57.6%, and 6.9%, respectively, in Turkish population. The allelic frequencies (1291C and 1291G) and G1291G homozygous variant genotype were similar to those reported in different Caucasian populations; however, C1291C and C1291G genotypes were different. We also observed that the frequency of the G allele was slightly higher in smoker subjects and lower among controls. The ADRA2A G allele may play a role in the predisposition to smoking. There is a need for expanding genotype and haplotype studies because of its importance in various physiological disorders and to confirm the association of this polymorphism with smoking.