APLN Gene Research Articles

Apelin regulates mitochondrial dynamics by inhibiting Mst1-JNK-Drp1 signaling pathway to reduce neuronal apoptosis after spinal cord injury

In the secondary injury stage of spinal cord injury, mitochondrial dysfunction leads to decreased ATP production, increased ROS production, and activation of the mitochondria-mediated apoptosis signaling pathway. This ultimately intensifies neuronal death and promotes the progression of the injury. Apelin, a peptide produced by the APLN gene, has demonstrated promise in the treatment of spinal cord injury. The aim of this study was to investigate how Apelin protects neurons after spinal cord injury by influencing the mitochondrial dynamics. The results showed that Apelin has the ability to reduce mitochondrial fission, enhance the mitochondrial membrane potential, improve antioxidant capacity, facilitate the clearance of excess ROS, and ultimately decrease apoptosis in PC12 cells. Moreover, Apelin is overexpressed in neurons in the damaged part of the spinal cord, contributing to reduce mitochondrial fission, improve antioxidant capacity, increase ATP production, decrease apoptosis, promote spinal cord morphological repair, maintain the number of nissl bodies, and enhance signal transduction in the descending spinal cord pathway. Apelin exerts its protective effect by inhibiting the Mst1-JNK-Drp1 signaling pathway. In summary, our study further improved the effect of Apelin in the treatment of spinal cord injury, revealed the mechanism of Apelin in protecting damaged neurons after spinal cord injury by maintaining mitochondrial homeostasis, and provided a new therapeutic mechanism for Apelin in spinal cord injury.

Beneficial effects of Apelin-13 on metabolic diseases and exercise.

Apelin, a novel endogenous ligand of the G-protein-coupled receptor APJ, is encoded by the APLN gene and can be hydrolyzed into multiple subtypes, with Apelin-13 being one of the most active subtypes of the Apelin family. Recent studies have revealed that Apelin-13 functions as an adipokine that participates in the regulation of different biological processes, such as oxidative stress, inflammation, apoptosis, and energy metabolism, thereby playing an important role in the prevention and treatment of various metabolic diseases. However, the results of recent studies on the association between Apelin-13 and various metabolic states remain controversial. Furthermore, Apelin-13 is regulated or influenced by various forms of exercise and could therefore be categorized as a new type of exercise-sensitive factor that attenuates metabolic diseases. Thus, in this review, our purpose was to focus on the relationship between Apelin-13 and related metabolic diseases and the regulation of response movements, with particular reference to the establishment of a theoretical basis for improving and treating metabolic diseases.

APELIN IN HEART FAILURE.

Apelin is a biologically active protein encoded by the APLN gene. It was first isolated in 1998 as a ligand for the APJ receptor. It exists in several isoforms differing in polypeptide chain length and biological activity. It is secreted by white adipose tissue, and its expression has been identified in many body tissues, including the cardiovascular system, kidneys, lungs, CNS (especially the hypothalamus, suprachiasmatic and ventricular nuclei), skeletal muscle, mammary glands, adrenal glands, ovaries, stomach, liver cells, placenta, and breast milk. However, the highest concentrations were observed in the endocardium and endothelium of vascular smooth muscle cells. In myocardial tissue, apelin has a positive inotropic effect and exerts an opposing effect to the RAA (renin-angiotensin-aldosterone) system, lowering blood pressure. Therefore, its positive role in early stages of heart failure, in patients with hypertension and ischemic heart disease is emphasized. The synthesis and secretion of apelin by adipocytes makes it possible to classify this peptide as an adipokine. Therefore, its production in adipose tissue is enhanced in obesity. Furthermore, apelin has been shown to increase cellular sensitivity to insulin and improve glucose tolerance in the onset of type 2 diabetes, and therefore appears to play a significant role in the pathogenesis of metabolic disease. An accurate assessment of the importance of apelin in cardiovascular disease requires further studies, which may contribute to the use of apelin in the treatment of heart failure.

Association of Apelin gene rs3115757 variation and expression with metabolic syndrome among female students in King Abdulaziz University

Metabolic syndrome (MetS) is a cluster of medical components that, when occurring together, increase the risk of heart disease, stroke, and type 2 diabetes. This syndrome is widespread around the world, affecting over one billion individuals according to recent reports. Abdominal obesity is a cornerstone of MetS. Apelin is an endogenous peptide and a member of the adipokine family that exhibits a positive correlation with obesity.In this study, we analyzed data on a total of 160 healthy female students aged 18–25 years to estimate the contributions of the apelin gene variant to MetS components in female students at King Abdulaziz University. APLN gene rs3115757 (C < G) was genotyped using TaqMan SNP genotyping assay. ELISA technique was performed on serum to detect; apelin, Insulin Resistance (HOMA-IR), fasting blood glucose (FG), triglycerides (TG) and high-density lipoprotein (HDL), serum triglycerides and glucose concentrations were colorimetric determined. Body mass index (BMI), waist circumference (WC), systolic and diastolic blood pressures (SBP/DBP) were also measured and compared among subjects. The association between the genotype distribution and MetS risk was evaluated using Chi-square test of independence. No significant difference was recorded in apelin levels between MetS and control groups, however, significant differences were recorded in TG, FG, HOMA-IR, WC, and BMI (p < 0.005) between the control and MetS subjects. We also recorded an increase in the frequency of APLN gene rs3115757 variant, however it wasn't significantly associated with an increased risk of MetS.Further investigation on the apelin rs3115757 polymorphism is needed to draw a firm conclusion about its association with the risk of MetS in different ethnicities.

Maternal serum Apelin 13 and APLN gene promoter variant -1860T > C in preeclampsia

Objective To evaluate the apelin (APLN) −1860 T > C (rs56204867) polymorphism and maternal serum apelin 13 levels in preeclampsia and its association with blood pressure. Methods This case-control study was conducted in department of Biochemistry, Sri Devaraj Urs Medical College, Karnataka, India. A total of 181 subjects were enrolled in the study from department of Department of Obstetrics and Gynecology. The recruited women were grouped as: Group–I (n = 91) cases with preeclampsia and Group–II (n = 90) normotensive healthy pregnant women as controls. Under aseptic conditions, the collected 5 mL blood was distributed for serum separation (3 mL) and genetic analysis (2 mL). Serum was stored at −80 °C after centrifugation at 3000 rpm for 10 min. The collected five mL urine sample was used for urinary protein analysis by dipstick method. The APLN gene −1860 T > C polymorphism and Apelin 13 levels were analyzed by molecular methods and ELISA technique respectively. Birth weight and demographic details were recorded. Results In the present study, no significant difference was observed for mean gestational age and maternal age. Systolic (158.7 ± 14.0 mmHg) and diastolic (104.9 ± 10.7 mmHg) blood pressure, and mean arterial pressure (MAP) (123.0 ± 11.1 mmHg) (p-value .001) were significantly increased in preeclamptic women compared with healthy pregnant women. Birth weight (2.4 ± 0.5 kg) (p-value .001) was significantly decreased in babies born to preeclamptic mothers. Birth weights were also expressed in centiles, according to Fenton Chart. Number of small for gestational age (SGA) babies were more in preeclampsia (n = 55) than healthy pregnant women (n = 28). Mean maternal serum apelin 13 (239.4 ± 126.3 pg/mL) (p-value .001) concentrations were significantly lower in preeclampsia compared with healthy controls. Maternal serum apelin 13 concentration in preeclampsia was negatively correlated with systolic blood pressure (r = −0.235), diastolic blood pressure (r= −0.172) and mean arterial pressure (r = –0. 206). However, maternal serum apelin 13 levels showed insignificant positive correlation with age, gestational age and birth weight. The genotype and allele frequencies of APLN gene were found significant between study groups as in preeclampsia (χ2 = 11.69; df = 2; p = .0028 and χ2 = 14.27; df = 1; p = .00013 respectively). CC genotype and C allele of APLN − 1860 T > C site was high in preeclampsia. Conclusion Study concludes that preeclamptic women have low level of serum apelin 13 and −1860 T > C polymorphism at APLN gene promoter site with increased allelic frequency of CC genotype and C allele compared to normotensive pregnant women. And this evidence may link to cardiac complications in preeclamptic women after delivery in later stage.

Association of genetic defects in the apelin-AGTRL1 system with myocardial infarction risk in Han Chinese

We aimed to test the hypothesis that apelin (APLN) and its receptor AGTRL1 (APLNR) genes may contribute to the pathogenesis of myocardial infarction in Han Chinese. This is a hospital-based, case-control association study, involving 1067 patients with myocardial infarction and 942 healthy controls. Myocardial infarction is diagnosed by electrocardiogram or anatomopathological examination. Eight polymorphisms in APLN gene and 5 in APLNR gene were genotyped using the TaqMan assay. Risk was summarized as odds ratio (OR) and 95% confidence interval (CI). In males, rs56204867-G allele (adjusted OR, 95% CI, p: 0.21, 0.08–0.55, 0.002) and rs2235309-T allele (0.60, 0.42–0.84, 0.004) was associated with a significantly reduced risk of myocardial infarction, and the mutations of rs2235310 was associated with an increased risk (1.41, 1.06–2.52, 0.021), as well as for rs948847-GG genotype (1.85, 1.23–2.91, 0.007). In females, the presence of rs56204867-AG and -GG genotypes was significantly associated with 44% and 50% reduced risk (0.56 and 0.50, 0.40–8.04 and 0.29–0.86, 0.007 and 0.036), respectively; for rs2235310, CC genotype was associated with 72% increased risk (1.72, 1.09–3.22, 0.016), and the odds of myocardial infarction was 3.47 for rs9943582-TT genotype (95% CI: 1.53–7.57, 0.009). The gender-specific association of APLN and APLNR genes with myocardial infarction was reinforced by further linkage and haplotype analyses. Finally, nomograms based on significant polymorphisms are satisfactory, with the C-indexes over 80% for both genders. Taken together, our findings indicate that APLN and APLNR genes are potential candidates in the pathogenesis of myocardial infarction in Han Chinese, and importantly their contribution is gender-dependent.

Intrathecally Administered Apelin-13 Alleviated Complete Freund’s Adjuvant-Induced Inflammatory Pain in Mice

Apelin is the endogenous ligand for APJ, a G-protein-coupled receptor. Apelin gene and protein are widely distributed in the central nervous system and peripheral tissues. The role of apelin in chronic inflammatory pain is still unclear. In the present study, a mouse model of complete Freund’s adjuvant (CFA)-induced inflammatory pain was utilized, and the paw withdrawal latency/threshold in response to thermal stimulation and Von Frey filament stimulation were recorded after intrathecal (i.t.) injection of apelin-13 (0.1, 1, and 10 nmol/mouse). The mRNA and protein expression, concentration of glutamic acid (Glu), and number of c-Fos immunol staining in lumbar spinal cord (L4/5) were determined. The results demonstrated that Apln gene expression in the lumbar spinal cord was down-regulated in the CFA pain model. Apelin-13 (10 nmol/mouse, i.t.) alleviated CFA-induced inflammatory pain, and it exhibited a more potent antinociceptive effect than apelin-36 and (pyr)apelin-13. The antinociception of apelin-13 could be blocked by APJ antagonist apelin-13(F13A). I.T. apelin-13 attenuated the increased levels of Aplnr, Grin2b, Camk2d, and c-Fos genes expression, Glu concentration, and NMDA receptor 2B (GluN2B) protein expression caused by CFA. Apelin-13 significantly reduced the number of Fos-positive cells in laminae III and IV/V of the dorsal horn. This study indicated that i.t. apelin-13 exerted an analgesic effect against inflammatory pain, which was mediated by activation of APJ, and inhibition of Glu/GluN2B function and neural activity of the spinal dorsal horn.

Resequencing Study Identifies Rare Renin-Angiotensin-Aldosterone System Variants Associated With Blood Pressure Salt-Sensitivity: The GenSalt Study.

The role of rare variants in blood pressure (BP) salt-sensitivity is unknown. We conducted a resequencing study of the renin-angiotensin-aldosterone system (RAAS) to identify rare variants associated with BP salt-sensitivity among participants of the Genetic Epidemiology Network of Salt-Sensitivity (GenSalt) study. The GenSalt study was conducted among 1,906 participants who underwent a 7-day low-sodium (51.3 mmol sodium/day) followed by a 7-day high-sodium feeding study (307.8 mmol sodium/day). The 300 most salt-sensitive and 300 most salt-resistant GenSalt participants were selected for the resequencing study. Seven RAAS genes were resequenced using capillary-based sequencing methods. Rare variants were tested for association with BP salt-sensitivity using traditional burden tests. Single-marker analyses were employed to test associations of low-frequency and common variants. Aggregate rare variant analysis revealed an association of the RAAS pathway with BP salt-sensitivity. Carriers of rare RAAS variants had a 1.55-fold [95% confidence interval (CI): 1.15, 2.10] higher odds of salt-sensitivity compared to noncarriers (P = 0.004), a finding which was significant after Bonferroni correction. A nominal association of the APLN gene with salt-sensitivity was also identified, with rare APLN variants conferring a 2.22-fold (95% CI: 1.05, 6.58) higher odds of salt-sensitivity (P = 0.03). Single-marker analyses did not identify variant-BP salt-sensitivity associations after Bonferroni adjustment. A nominal association of a low-frequency, missense RENBP variant was identified. Each minor allele of rs78377269 conferred a 2.21-fold (95% CI: 1.10, 4.42) increased odds of salt-sensitivity (P = 0.03). This study presents of the first evidence of a contribution of rare RAAS variants to BP salt-sensitivity. Clinical Trial RegistryTrial Number: NCT00721721.

The Association Between Apelin Gene Polymorphism and Coronary Artery Disease in Young Patients with Acute Obstructive Coronary Syndrome

The purpose of this study was to evaluate the association between V103V, 6140AG, TGA-Stop-TAA Stop, and 6016CA polymorphisms of the apelin (APLN) gene detected for the first time among young patients with acute coronary syndrome (ACS) and coronary artery disease (CAD). This was a prospective cross-sectional study. The study population was divided into 2 groups. The first group included 132 patients who were found to have critical lesions in their coronary arteries, while the control group consisted of 41 patients who were found to have normal coronary arteries or non-critical atherosclerotic lesions. Among the gene polymorphisms, V103V was found to be more common in the critical CAD patients with the GG genotype compared with the control group (67.4% vs. 46.3%). On the other hand, the GT genotype was more common in the control group (53.7% vs. 32.6%). Univariate and multivariate logistic regression analysis revealed that the GG genotype of V103V was an independent predictor for the presence of critical CAD (odds ratio: 2.397; 95% confidence interval, 1.174-4.892; p=0.016). In cases of V103V polymorphism of the APLN gene, patients with the GG genotype were at a greater risk for the presence of atherosclerotic critical lesions compared with the control group.

Polymorphisms of APLN-APLNR system are associated with essential hypertension in Mexican-Mestizo individuals

The aim of this study was to evaluate if polymorphisms of APLN and APLNR genes may play a role as susceptibility markers for hypertension in a group of Mexican-Mestizo patients. A case-control study was carried out including normotensive and hypertensive individuals. For these, two polymorphisms of APLN (rs3761581 and rs56204867) and two of APLNR () genes were genotyped by 5′ exonuclease TaqMan assay in 400 normotensive individuals and 383 patients. The results showed that, under an additive model adjusted by BMI, HDL, triglycerides, glucose and family history of essential hypertension, the rs7119375 and rs10501367 polymorphisms of APLNR gene were associated significantly with a decreased risk of essential hypertension (P=0.039 and P=0.029, respectively). Besides, the haplotypes analysis of these polymorphisms showed that H1 haplotype was associated with an increased risk of essential hypertension (P=0.026), while the H2 haplotype was associated with a decreased risk (P=0.032). Contrary, the rs3761581 and rs56204867 polymorphisms of APLN gene were not associated with essential hypertension (P=0.1707 and P=0.0769, respectively). The data suggest that APLNR rs7119375 and rs10501367 are associated with a decreased risk of essential hypertension in our Mexican-Mestizo studied group, but further studies are warranted.

OP9-Lhx2 stromal cells facilitate derivation of hematopoietic progenitors both in vitro and in vivo

Generating engraftable hematopoietic stem cells (HSCs) from pluripotent stem cells (PSCs) is an ideal approach for obtaining induced HSCs for cell therapy. However, the path from PSCs to robustly induced HSCs (iHSCs) in vitro remains elusive. We hypothesize that the modification of hematopoietic niche cells by transcription factors facilitates the derivation of induced HSCs from PSCs. The Lhx2 transcription factor is expressed in fetal liver stromal cells but not in fetal blood cells. Knocking out Lhx2 leads to a fetal hematopoietic defect in a cell non-autonomous role. In this study, we demonstrate that the ectopic expression of Lhx2 in OP9 cells (OP9-Lhx2) accelerates the hematopoietic differentiation of PSCs. OP9-Lhx2 significantly increased the yields of hematopoietic progenitor cells via co-culture with PSCs in vitro. Interestingly, the co-injection of OP9-Lhx2 and PSCs into immune deficient mice also increased the proportion of hematopoietic progenitors via the formation of teratomas. The transplantation of phenotypic HSCs from OP9-Lhx2 teratomas but not from the OP9 control supported a transient repopulating capability. The upregulation of Apln gene by Lhx2 is correlated to the hematopoietic commitment property of OP9-Lhx2. Furthermore, the enforced expression of Apln in OP9 cells significantly increased the hematopoietic differentiation of PSCs. These results indicate that OP9-Lhx2 is a good cell line for regeneration of hematopoietic progenitors both in vitro and in vivo.

Sirt3 is essential for apelin-induced angiogenesis in post-myocardial infarction of diabetes.

Heart failure following myocardial infarction (MI) is the leading cause of death in diabetic patients. Angiogenesis contributes to cardiac repair and functional recovery in post-MI. Our previous study shows that apelin (APLN) increases Sirtuin 3 (Sirt3) expression and ameliorates diabetic cardiomyopathy. In this study, we further investigated the direct role of Sirt3 in APLN-induced angiogenesis in post-MI model of diabetes. Wild-type (WT) and Sirt3 knockout (Sirt3KO) mice were induced into diabetes by i.p. streptozotocin (STZ). STZ mice were then subjected to MI followed by immediate intramyocardial injection with adenovirus-apelin (Ad-APLN). Our studies showed that Sirt3 expression was significantly reduced in the hearts of STZ mice. Ad-APLN treatment resulted in up-regulation of Sirt3, angiopoietins/Tie-2 and VEGF/VEGFR2 expression together with increased myocardial vascular densities in WT-STZ+MI mice, but these alterations were not observed in Sirt3KO-STZ+MI mice. In vitro, overexpression of APLN increased Sirt3 expression and angiogenesis in endothelial progenitor cells (EPC) from WT mice, but not in EPC from Sirt3KO mice. APLN gene therapy increases angiogenesis and improves cardiac functional recovery in diabetic hearts via up-regulation of Sirt3 pathway.

Apelin Is Required for Non-Neovascular Remodeling in the Retina

Retinal pathologies are frequently accompanied by retinal vascular responses, including the formation of new vessels by angiogenesis (neovascularization). Pathological vascular changes may also include less well characterized traits of vascular remodeling that are non-neovascular, such as vessel pruning and the emergence of dilated and tortuous vessel phenotypes (telangiectasis). The molecular mechanisms underlying neovascular growth versus non-neovascular remodeling are poorly understood. We therefore undertook to identify novel regulators of non-neovascular remodeling in the retina by using the dystrophic Royal College of Surgeons (RCS) rat and the retinal dystrophy 1 (RD1) mouse, both of which display pronounced non-neovascular remodeling. Gene expression profiling of isolated retinal vessels from these mutant rodent models and wild-type controls revealed 60 differentially expressed genes. These included the genes for apelin (Apln) and for its receptor (Aplnr), both of which were strongly up-regulated in the mutants. Crossing RD1 mice into an Apln-null background substantially reduced vascular telangiectasia. In contrast, Apln gene deletion had no effect in two models of neovascular pathology [laser-induced choroidal neovascularization and the very low density lipoprotein receptor (Vldlr)-knockout mouse]. These findings suggest that in these models apelin has minimal effect on sprouting retinal angiogenesis, but contributes significantly to pathogenic non-neovascular remodeling.

Association of Genetic Variants in the Apelin-APJ System and ACE2 With Blood Pressure Responses to Potassium Supplementation: The GenSalt Study

Genetic factors may influence blood pressure (BP) responses to dietary potassium intake. We examined the association of genetic variants in the apelin-APJ system and angiotensin-converting enzyme 2 (ACE2) with BP responses to potassium supplementation. We conducted a 7-day potassium supplementation (60 mmol/day) intervention among 1,906 Chinese adults who participated in the Genetic Epidemiology Network of Salt-Sensitivity (GenSalt) study. Tag single-nucleotide polymorphisms (SNPs) based on HapMap data and potential functional SNPs were selected in the APLN, APLNR, and ACE2 genes. Because the ACE2 and APLN genes are located on the X chromosome, men and women were analyzed separately. In women, SNP rs2235306 in the APLN gene was significantly associated with diastolic BP (DBP) response to potassium supplementation (P = 0.0009). The DBP responses (95% confidence interval (CI)) among those with genotypes T/T, T/C, and C/C were -2.22 (-2.74, -1.70), -1.69 (-2.20, -1.19), and -0.81 (-1.54, -0.09) mm Hg, respectively. In men, SNP rs4646174 of the ACE2 gene was significantly associated with systolic BP (SBP), DBP, and mean arterial pressure (MAP) responses to potassium supplementation (P = 0.0001, P = 0.001, and P = 3.0 x 10(-6), respectively). The SBP, DBP, and MAP responses (95% CI) were -0.79 (-2.27, 0.69) vs. -3.53 (-3.94, -3.12), 1.07 (-0.34, 2.49) vs. -1.06 (-1.43, -0.69), and 0.44 (-0.60, 1.48) vs. -1.89 (-2.22, -1.55) mm Hg among men with minor G allele compared to those with major C allele of rs4646174, respectively. Our study indicates that genetic variation of APLN and ACE2 may influence BP response to potassium intake.