Predominance of interaction among wild-type alleles of CYP11B2 in Himalayan natives associates with high-altitude adaptation

Association of combined -344T/C and K173R polymorphisms in aldosterone synthase gene with type 2 diabetes mellitus in the Moroccan population

Background: Aldosterone synthase (CYP11B2) is crucial for aldosterone production, and variations in its gene may influence type 2 diabetes mellitus (T2DM) development. This study explores the link between two single nucleotide polymorphisms (SNPs) in the CYP11B2 gene - -344T/C and K173R and T2DM in the Moroccan population . Methods: The research involved 86 individuals with T2DM and 75 control subjects. Genotyping for the -344T/C and K173R SNPs was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis . Result: Results indicated significant differences in the genotype and allelic distribution of the CYP11B2 K173R polymorphism between T2DM patients and control subjects, with P-values of 0.02 and 0.04, respectively. The -344T/C polymorphism showed no significant genomic level differences, but its allelic variations were statistically significant (P=0.01), indicating a notable association between the C allele and T2DM. Furthermore, the K173R polymorphism was found to significantly increase T2DM risk, with a 2.34-fold higher risk in individuals carrying the KR genotype. The study also examined the combined effect of these SNPs. The dominant model analysis (TT vs. TC+CC and KK vs. KR+RR) showed significant differences between T2DM patients and controls for both SNPs. Additionally, a haplotype-based analysis revealed that the C-R haplotype was associated with an increased risk of T2DM. Conclusion: Our study suggests a significant association between the CYP11B2-K173R polymorphism and T2DM in the Moroccan population. Conversely, while the CYP11B2 -344T/C polymorphism exhibits a significant difference in allelic distribution, no significant difference is observed at the genomic level.

Vascular homeostasis at high-altitude: role of genetic variants and transcription factors

High-altitude pulmonary edema occurs most frequently in non-acclimatized low landers on exposure to altitude ≥2500 m. High-altitude pulmonary edema is a complex condition that involves perturbation of signaling pathways in vasoconstrictors, vasodilators, anti-diuretics, and vascular growth factors. Genetic variations are instrumental in regulating these pathways and evidence is accumulating for a role of epigenetic modification in hypoxic responses. This review focuses on the crosstalk between high-altitude pulmonary edema-associated genetic variants and transcription factors, comparing high-altitude adapted and high-altitude pulmonary edema-afflicted subjects. This approach might ultimately yield biomarker information both to understand and to design therapies for high-altitude adaptation.

An overview of the classical and tissue-derived renin-angiotensin-aldosterone system and its genetic polymorphisms in essential hypertension

The renin-angiotensin-aldosterone system (RAAS) is a specific hormonal cascade implicated in the blood pressure control and sodium balance regulation. Several components of this pathway have been identified including renin, angiotensinogen, angiotensin-converting enzyme, angiotensins with a wide range of distinct subtypes and receptors, and aldosterone. The RAAS is not only confined to the systemic circulation but also exists locally in specific tissues such as the heart, brain, and blood vessels with a particular paracrine action. Alteration of RAAS function can contribute to the development of hypertension and the emergence of its associated end-organ damage. Genotypic variations of the different genes of RAAS cascade have been linked to the susceptibility to essential hypertension. Accordingly, to understand the pathogenesis of essential hypertension and its related complications, deep insight into the physiological and genetic aspects of RAAS with its different components and pathways is necessary. In this review, we aimed to illustrate the physiological and genetic aspects of RAAS and the underlying mechanisms which link this system to the predisposition to essential hypertension.

The association of angiotensin-converting enzyme gene insertion/deletion polymorphisms with adaptation to high altitude: A meta-analysis

Background:

Fluid retention is linked to the physiology and pathophysiology of humans at high altitude (HA). The angiotensin-converting enzyme (ACE) gene plays a role in the regulation of plasma volume and vascular tone.

Materials and methods:

In this meta-analysis, eligible studies published before 1 September 2015 that focused on the association between the ACE insertion/deletion (I/D) polymorphism and HA adaption were identified by searching the PubMed, Web of Science, Embase and Medline online databases. We used a fixed-effects model and assessed the study qualities multiple times.

Results:

The seven selected studies included a total of 582 HA-native individuals and 497 low-altitude controls, and these subjects were analyzed for the ACE I/D gene polymorphism. A significant association was found between the ACE DD genotype and HA maladaptation. The results for genotype DD versus ID + II were as follows: Odds ratio (OR) = 0.46; 95% CI 0.31–0.70; p = 0.0002. The results for genotype ID versus DD were as follows: OR = 1.97; 95% CI 1.27–3.06; p = 0.002.

Conclusions:

Our findings suggested that the DD genotype of ACE is a risk factor for HA maladaptation and that the presence of fewer ACE DD allele carriers in a population indicates a greater ability of that population to adapt to HA.

Lungs at high-altitude: genomic insights into hypoxic responses

Hypobaric hypoxia at high altitude (HA) results in reduced blood arterial oxygen saturation, perfusion of organs with hypoxemic blood, and direct hypoxia of lung tissues. The pulmonary complications in the cells of the pulmonary arterioles due to hypobaric hypoxia are the basis of the pathophysiological mechanisms of high-altitude pulmonary edema (HAPE). Some populations that have dwelled at HA for thousands of years have evolutionarily adapted to this environmental stress; unadapted populations may react with excessive physiological responses that impair health. Individual variations in response to hypoxia and the mechanisms of HA adaptation provide insight into physiological responses. Adaptive and maladaptive responses include alterations in pathways such as oxygen sensing, hypoxia signaling, K+- and Ca2+-gated channels, redox balance, and the renin-angiotensin-aldosterone system. Physiological imbalances are linked with genetic susceptibilities, and nonhomeostatic responses in gene regulation that occur by small RNAs, histone modification, and DNA methylation predispose susceptible humans to these HA illnesses. Elucidation of the interaction of these factors will lead to a more comprehensive understanding of HA adaptations and maladaptations and will lead to new therapeutics for HA disorders related to hypoxic lungs.

Association of CYP11B2 polymorphisms with metabolic syndrome patients

Aldosterone synthase is a key enzyme in aldosterone production. Polymorphisms of the aldosterone synthase gene, CYP11B2, have been suggested to be involved in the pathogenesis of diabetes mellitus (DM), hypertension and cardiovascular diseases. In the light of these findings, we hypothesized that CYP11B2 genetic polymorphisms play a role in metabolic syndrome (MetS). Therefore, we investigated the associations of three CYP11B2 polymorphisms [-344T>C, K173R and intron 2 conversion (IC)] with Korean MetS patients. In total, 640 subjects comprising 320 cases and 320 control individuals) were included in the present study. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) techniques were used to assess CYP11B2 polymorphisms. The CYP11B2 -344T>C, K173R and IC polymorphisms did not exhibit a significant difference in the genotype and allele frequencies between the MetS and control groups. However, the -344T>C polymorphism in males and haplotypes comprising the three polymorphisms were associated with susceptibility to MetS. Thus, the pattern of haplotype associations was gender-specific. Based on these results, the -344T>C polymorphism in males and haplotypes of the CYP11B2 gene potentially affect MetS susceptibility. These findings remain to be confirmed in various ethnic populations with a larger sample size.

Association of polymorphisms in angiotensin and aldosterone synthase genes of the renin–angiotensin–aldosterone system with high-altitude pulmonary edema

Studies on different populations have suggested variability in individual susceptibility to altitude sickness depending on genetic makeup. The renin–angiotensin–aldosterone system (RAAS) pathway plays a key role in regulation of vascular tone and circulatory homeostasis. The present study was undertaken to investigate the possible association of the RAAS in the development of high-altitude pulmonary edema (HAPE) in lowlanders exposed to high altitude. Three categories of subjects were selected: individuals who developed HAPE on acute induction to high altitude ( HAPE); individuals tolerant to high-altitude exposure who showed no symptoms of HAPE (resistant controls; rCON); and natives of high altitude ( HAN). Genetic variants in the genes of the RAAS such as renin ( REN), angiotensin ( AGT), angiotensin-converting enzyme ( ACE), aldosterone synthase ( CYP11B2) and angiotensin II receptor type 1 ( AGTR1) have been investigated. The T174M polymorphism in AGT showed a significant difference in HAPE and HAN and also HAN and controls. Also, genotyping in the CYP11B2 T-344C promoter region resulted in a significant difference between HAPE and HAN both at genotypic and allelic levels. The genotypic difference was statistically insignificant for the AGTR1 A1166C 3’ UTR. The present investigation demonstrates a possible association between the polymorphisms existing in the RAAS pathway T174M and CYP11B2 C-344T and sensitivity of an individual to develop HAPE. The results also indicate the existence of ethnic variation between the HAN and the other two groups comprising lowlanders.

Evidence for a genetic basis for altitude illness: 2010 update

Altitude illness refers to a group of environmentally mediated pathophysiologies. Many people will suffer acute mountain sickness shortly after rapidly ascending to a moderately hypoxic environment, and an unfortunate few will develop potentially fatal conditions such as high altitude pulmonary edema or high altitude cerebral edema. Some individuals seem to be predisposed to developing altitude illness, suggesting an innate contribution to susceptibility. The implication that there are altitude-sensitive and altitude-tolerant individuals has stimulated much research into the contribution of a genetic background to the efficacy of altitude acclimatization. Although the effect of altitude attained and rate of ascent on the etiology of altitude illness is well known, there are only tantalizing, but rapidly accumulating, clues to the genes that may be involved. In 2006, we reviewed what was then known about the genetics of altitude illness. This article updates that review and attempts to tabulate all the available genetic data pertaining to these conditions. To date, 58 genes have been investigated for a role in altitude illness. Of these, 17 have shown some association with the susceptibility to, or the severity of, these conditions, although in many cases the effect size is small or variable. Caution is recommended when evaluating the genes for which no association was detected, because a number of the investigations reviewed in this article were insufficiently powered to detect small effects. No study has demonstrated a clear-cut altitude illness gene, but the accumulating data are consistent with a polygenic condition with a strong environmental component. The genes that have shown an association affect a variety of biological pathways, suggesting that either multiple systems are involved in altitude pathophysiology or that gene-gene interactions play a role. Although numerous studies have been performed to investigate specific genes, few have looked for evidence of heritability or familial transmission, or for epidemiological patterns that would be consistent with genetically influenced conditions. Future trends, such as genome-wide association studies and epigenetic analysis, should lead to enhanced understanding of the complex interactions within the genome and between the genome and hypoxic environments that contribute to an individual's capacity to acclimatize rapidly and effectively to altitude.

Association of the human CYP11B2 gene and essential hypertension in southwest Han Chinese population: a haplotype-based case-control study

Aldosterone synthase produces aldosterone, which regulates electrolytes and thereby blood pressure (BP). The aldosterone-synthase gene (CYP11B2) has been regarded as a candidate gene for essential hypertension. To address this issue, we carried out a haplotype-based, case-control study to explore the association between a human CYP11B2 gene and essential hypertension (EH) in the southwest Han population of China (n = 1020 individuals). Four tag single-nucleotide polymorphisms (SNPs) (rs4536, rs4545, rs3097, and rs3802230) and the C-344T polymorphism, as well as the K173R polymorphism in the CYP11B2 gene, were genotyped using the PCR-RFLP method. Single-locus analysis showed that the C allele of rs3802230 was significantly more prevalent in the EH subjects as compared to control subjects, adjusted for covariates. Haplotype analysis showed that the haplotype AAGC constructed by the tag SNPs (rs4536, rs4545, rs3097, and rs3802230), which carried the susceptible rs3802230 C allele, significantly increased the risk of essential hypertension with an odds ratios equal to 3.56 (P = 0.0001). The present results indicated that the rs3802230 C allele might be a risk marker for essential hypertension and haplotype AAGC might confer high genetic susceptibility to essential hypertension in a southwest Han Chinese population.

Haplotype-based case-control study of the human CYP11B2 gene and essential hypertension in Yi and Hani minorities of China

This haplotype-based case-control study investigated whether the aldosterone synthase gene (CYP11B2) might be implicated in the pathogenesis of essential hypertension in Yi (226 individuals) and Hani (296 individuals) minorities of China. Four tag SNPs (rs4536, rs4545, rs3097, and rs3802230) and the K173R polymorphism were genotyped using the PCR-RFLP method. In the Hani minority, rs4536 was significantly associated with hypertension, after Bonferroni correction. H9 AGGC constructed by tag SNPs was significantly higher in hypertensives than in controls (P = 0.001). Further, we observed that haplotype AGGC remained significantly associated with male hypertension after adjustment for covariates (OR = 3.76, P = 0.002). In the Yi minority, it was found that the CYP11B2 gene was not significantly associated with hypertension. These results indicated that haplotype AGGC conferred an increased risk for hypertension in the Hani minority male. In addition, CYP11B2 may not be associated with hypertension in the Yi minority of China.

The cerebral effects of ascent to high altitudes

Cellular hypoxia is the common final pathway of brain injury that occurs not just after asphyxia, but also when cerebral perfusion is impaired directly (eg, embolic stroke) or indirectly (eg, raised intracranial pressure after head injury). We Review recent advances in the understanding of neurological clinical syndromes that occur on exposure to high altitudes, including high altitude headache (HAH), acute mountain sickness (AMS), and high altitude cerebral oedema (HACE), and the genetics, molecular mechanisms, and physiology that underpin them. We also present the vasogenic and cytotoxic bases for HACE and explore venous hypertension as a possible contributory factor. Although the factors that control susceptibility to HACE are poorly understood, the effects of exposure to altitude (and thus hypobaric hypoxia) might provide a reproducible model for the study of cerebral cellular hypoxia in healthy individuals. The effects of hypobaric hypoxia might also provide new insights into the understanding of hypoxia in the clinical setting.