Associations between gene polymorphisms of the apelin–APJ system and the risk of hypertension

Serum Elabela expression is decreased in hypertensive patients and could be associated with the progression of hypertensive renal damage

BACKGROUND

Elabela, a recently discovered hormonal peptide containing 32 amino acids, is a ligand for the apelin receptor. It can lower blood pressure and attenuate renal fibrosis. However, the clinicopathological relationship between Elabela level and renal damage caused by benign hypertension (BHT) and malignant hypertension (MHT) has not been elucidated. Therefore, we investigated the clinicopathological correlation between serum Elabela level and renal damage caused by BHT and MHT.

METHODS

The participants comprised 50 patients and 25 age-matched healthy adults. The 50 patients were separated into two groups: MHT (n = 25) and BHT groups (n = 25). We analyzed their medical histories, demographics, and clinical examinations, including physical and laboratory tests.

RESULTS

The results showed that serum Elabela level decreased gradually with a continuous increase in blood pressure from the healthy control group, BHT, to MHT. Moreover, Elabela levels negatively correlated with BMI (R =  - 0.27, P = 0.02), SBP (r =  - 0.64, P < 0.01), DBP (r =  - 0.58, P < 0.01), uric acid (r =  - 0.39, P < 0.01), bun (r =  - 0.53, P < 0.01), and Scr (r =  - 0.53 P < 0.01) but positively correlated with eGFR (r = 0.54, P < 0.01). Stepwise multivariate linear regression analysis showed that SBP was the variable most related to Elabela (t =  - 5.592, P < 0.01).

CONCLUSIONS

Serum Elabela levels decreased in patients with hypertension, especially malignant hypertension, and has the potential to be a marker of hypertension-related kidney damage.

The apelin/APJ system in the regulation of vascular tone: friend or foe?

The apelin (APJ) receptor was originally cloned as a gene encoding a putative G protein-coupled receptor related to angiotensin receptor type I. To date, two endogenous peptide ligands for APJ have been identified: apelin and elabela/Toddler. The apelin/APJ system regulates blood pressure and vascular tone. The endothelial and smooth muscle apelin/APJ systems exert opposite actions in the regulation of vascular tone. Binding of apelin to endothelial APJ promotes the release of vasodilators, such as nitric oxide and prostacyclin, leading to vasodilation. Alternatively, binding of apelin to smooth muscle APJ induces vasoconstriction, although the molecular mechanisms of the apelin-induced vasoconstriction are poorly understood. Recently, a critical role for interaction of APJ with α1-adrenergic receptor in the apelin-induced vasoconstriction was reported. The action of apelin on vascular tone may depend upon blood vessel type or pathological condition. Although the apelin/APJ system could serve as a potential therapeutic target for hypertension and cardiovascular disease, the role of this system in various cell types appears to be complicated.

The APLNR gene polymorphism rs7119375 is associated with an increased risk of development of essential hypertension in the Chinese population: A meta-analysis

Hypertension (HT) has recently been defined as a systolic blood pressure (BP) of ≥130 mm Hg and/or a diastolic BP of ≥80 mm Hg. It is important to further understand the pathophysiology of essential HT as its proportion is larger among most of the diagnosed HT cases. The apelin and apelin receptor (APLNR) are known to play roles in regulating BP, but the putative associations of single nucleotide polymorphisms in the APLNR gene with the risk of development of essential HT have not yet been fully investigated. Herein, we conducted a meta-analysis to investigate the relationship between single nucleotide polymorphisms in the APLNR gene and the risk of essential HT.We conducted a search in the PubMed and Web of Science databases for eligible studies. The pooled odds ratios (ORs) with their 95% confidence intervals (CI) were calculated using random-effects models when heterogeneity was expected across the studies. Otherwise, fixed-effect models were used.Regarding the SNP rs7119375, 5 studies were analyzed, which included a total of 3567 essential HT patients and 3256 healthy controls. Four of the 5 studies were from China and 1 was from Mexico. The meta-analysis showed the existence of a significant association between the AA genotype of rs7119375 and the risk of developing essential HT in the Chinese population, as determined using additive and recessive models (OR, 2.11; 95% CI, 1.12-3.96; I = 86% for AA vs GG. OR, 1.53; 95% CI, 1.21-1.94; I = 28% for AA vs AG. OR, 1.88; 95% CI, 1.13-3.12; I = 79% for AA vs AG + GG).Our study showed, for the first time, the existence of an association between rs7119375 and the risk of development of essential HT in the Chinese population, although the sample size was small and there was considerable population heterogeneity. The apelin/APLNR system could be a novel therapeutic target for the treatment of essential HT, and more studies are warranted to further investigate the association.

Association of Apelin and Apelin Receptor Polymorphisms With the Risk of Comorbid Depression and Anxiety in Coronary Heart Disease Patients

The Apelin (APLN)/apelin receptor (APLNR) signaling pathway is a newly identified regulator in various cardiovascular diseases, which is considered as a candidate pathway for the occurrence of coronary heart disease (CHD), depression, and anxiety. The goal of this study was to investigate the association between APLN/APLNR gene polymorphisms and the risk of depression and anxiety in CHD patients. To this end, a case-control study involving 269 CHD patients and 184 healthy control individuals was conducted. The 269 patients with CHD including 122 patients with and 147 patients without depression, and 56 patients with and 213 patients without anxiety Four single nucleotide polymorphisms were selected and successfully genotyped using Sanger sequencing. The APLN rs2235310T allele and APLNR rs9943582C allele were found to be associated with an increased risk of CHD after multiple test correction (P-adjust < 0.05). The patients with CHD who carried the rs9943582C allele had a higher risk of depression, after adjusting for alcohol drinking habits, insomnia, hypertension, and stroke history, with the Bonferroni correction (P-adjust = 0.018). The APLNR rs2282623 T allele was associated with an increased risk of anxiety in CHD patients after adjusting for related disease complications, with the Bonferroni correction (P-adjust = 0.022). We reported for the first time that the APLN rs2235310 and APLNR rs2282623 polymorphisms are associated with the risks of psychiatric disorders in CHD patients and may serve as novel biomarkers for therapy.

International Union of Basic and Clinical Pharmacology. CVII. Structure and Pharmacology of the Apelin Receptor with a Recommendation that Elabela/Toddler Is a Second Endogenous Peptide Ligand

The predicted protein encoded by the APJ gene discovered in 1993 was originally classified as a class A G protein-coupled orphan receptor but was subsequently paired with a novel peptide ligand, apelin-36 in 1998. Substantial research identified a family of shorter peptides activating the apelin receptor, including apelin-17, apelin-13, and [Pyr1]apelin-13, with the latter peptide predominating in human plasma and cardiovascular system. A range of pharmacological tools have been developed, including radiolabeled ligands, analogs with improved plasma stability, peptides, and small molecules including biased agonists and antagonists, leading to the recommendation that the APJ gene be renamed APLNR and encode the apelin receptor protein. Recently, a second endogenous ligand has been identified and called Elabela/Toddler, a 54-amino acid peptide originally identified in the genomes of fish and humans but misclassified as noncoding. This precursor is also able to be cleaved to shorter sequences (32, 21, and 11 amino acids), and all are able to activate the apelin receptor and are blocked by apelin receptor antagonists. This review summarizes the pharmacology of these ligands and the apelin receptor, highlights the emerging physiologic and pathophysiological roles in a number of diseases, and recommends that Elabela/Toddler is a second endogenous peptide ligand of the apelin receptor protein.

The association between apelin polymorphisms and hypertension in China: A meta-analysis

INTRODUCTION:

Apelin plays an important part in regulating blood pressure, metabolism, and the development of cancer. Recent studies have investigated the association of apelin polymorphisms and hypertension risk, but no meta-analysis has been conducted.

MATERIALS AND METHODS:

Five studies were included in this meta-analysis in total. The pooled odds ratio and its corresponding 95% confidence interval were calculated by the random-effect model.

RESULTS:

The overall pooled odds ratio of the distribution of rs3761581 G allelic frequency was 0.90 (95% confidence interval: 0.82-1.00). In female participants, the pooled odds ratio of the frequency of G allele was 1.01 (95% confidence interval: 0.89-1.14). For males, the pooled odds ratio of the frequency of G allele was 0.69 (95% confidence interval: 0.46-1.03). As for rs56204867, the overall pooled odds ratio of the frequency of G allele was 1.09 (95% confidence interval: 0.86-1.37). In females, the pooled odds ratio of the frequencies of the G allele was 1.05 (95% confidence interval: 0.86-1.29). In male participants, the frequency of G allele did not show significant correlation with hypertension (pooled odds ratio=1.21 95% confidence interval: 0.81-1.79).

CONCLUSION:

This meta-analysis revealed that there was no correlation between apelin polymorphisms, rs3761581 and rs56204867, and the prevalence of hypertension.

Association study of apelin-APJ system genetic polymorphisms with incident metabolic syndrome in a Chinese population: a case-control study

Objectives: Apelin-APJ system has been implicated in the regulation of metabolic homeostasis. This study aimed to explore the genetic predisposition of the apelin-APJ system to metabolic syndrome.

Materials And Methods: 1005 subjects were enrolled, including 448 metabolic syndrome patients and 557 controls. Seven single nucleotide polymorphisms, including rs909656, rs5975126, and rs3115757 of the apelin gene and rs7119375, rs10501367, rs9943582 and rs11544374 of the APJ gene, were genotyped.

Results: For males, apelin-36 were higher in metabolic syndrome subjects compared with controls (p < 0.05). Apelin-36 were significantly lower in those with TT genotype of rs10501367 than those with CC and CT genotypes (p < 0.05), and fasting plasma glucose were higher in T allele carriers of rs10501367 and A allele carriers of rs7119375 compared with non-carriers (both p < 0.05). A significant difference in genotype distribution between diabetes mellitus patients and controls existed for both rs10501367 and rs7119375 (both p < 0.05). However, the association between apelin-APJ system genetic polymorphisms and metabolic syndrome was nonsignificant.

For females, apelin-36 were higher in metabolic syndrome subjects compared with controls (p < 0.05). The association between apelin-APJ system genetic polymorphisms and apelin-36, fasting plasma glucose and diabetes mellitus was nonsignificant. However, carrying A allele in rs7119375 was associated with lower metabolic syndrome risk compared with non-carriers of A allele (odds ratio: 0.646, 95% confidence interval: 0.420–0.994, p = 0.043).

Conclusions: The current findings revealed a gender-specific association of apelin-APJ system genetic polymorphisms with metabolic syndrome and glucose homeostasis disorders in a Han Chinese population.