Essential Role of the ELABELA-APJ Signaling Pathway in Cardiovascular System Development and Diseases:

Elabela is a reliable biomarker for predicting early onset preeclampsia: A comparative study

BACKGROUND

Preeclampsia (PE) is a multisystemic metabolic disease with an undetermined etiology. PE is a worldwide cause of maternal and perinatal morbidity, subdivided into early (EoPE) and late-onset (LoPE) according to 34 wk of gestation as a divider. Many researchers investigated biomarkers for predicting PE to halt its consequences on the feto-maternal outcome. Elabela (Ela) is a newly discovered peptide hormone that was implicated in PE pathogenesis. Earlier rodent studies discussed Ela’s role in controlling blood pressure. Moreover, Ela deficiency was associated with PE development.

AIM

To test whether plasma Ela could serve as a reliable marker for predicting PE based on the time of onset (EoPE vs LoPE) compared to age and body mass matched healthy controls since no definitive treatment exists for PE but to terminate a pregnancy.

METHODS

This case-control study recruited (n = 90) pregnant who fulfilled inclusion criteria; they were allocated into three groups: EoPE (30/90) (< 34 wk of gestation); LoPE (30/90) (≥ 34 wk of gestation); and healthy pregnant (30/90). Demographic criteria; biochemical, hematological, and maternal plasma Ela levels were recorded for comparison.

RESULTS

Serum Ela was significantly reduced in EoPE compared to LoPE and healthy controls (P = 0.0023). The correlation confirmed a strong inverse relationship with mean atrial blood pressure (r = -0.7, P < 0.001), while gestational age and platelets count showed a moderate correlation with (r = 0.4 with P < 0.0001). No correlation was confirmed between the body mass index (BMI) and urine albumin. The predictive ability of 25 centile serum Ela had an Odds ratio of 5.21, 95% confidence interval (1.28, 21.24), P = 0.02 for predicting EoPE. The receiver operator characteristic curve defined the Ela cutoff value at > 9.156 with 96.7% and 93.3% sensitivity and specificity, P < 0.0001 in predicting EoPE.

CONCLUSION

A strong correlation of serum Ela with PE parameters with excellent sensitivity and specificity in distinguishing EoPE independent of the BMI, age, and blood pressure which makes Ela a recommendable marker in screening. Further research is warranted to explore prognostic and therapeutic applications for Ela in PE.

Elabela-APJ axis mediates angiogenesis via YAP/TAZ pathway in cerebral ischemia/reperfusion injury

Angiogenesis helps to improve neurological recovery by repairing damaged brain tissue and restoring cerebral blood flow (CBF). The role of the Elabela (ELA)-Apelin receptor (APJ) system in angiogenesis has gained much attention. We aimed to investigate the function of endothelial ELA on postischemic cerebral angiogenesis. Here, we demonstrated that the endothelial ELA expression was upregulated in the ischemic brain and treatment with ELA-32 mitigated brain injury and enhanced the restoration of CBF and newly formed functional vessels following cerebral ischemia/reperfusion (I/R) injury. Furthermore, ELA-32 incubation potentiated proliferation, migration, and tube formation abilities of the mouse brain endothelial cells (bEnd.3 cells) under oxygen-glucose deprivation/reoxygenation (OGD/R) condition. RNA sequencing analysis indicated that ELA-32 incubation had a role in the Hippo signaling pathway, and improved angiogenesis-related gene expression in OGD/R-exposed bEnd.3 cells. Mechanistically, we depicted that ELA could bind to APJ and subsequently activate YAP/TAZ signaling pathway. Silence of APJ or pharmacological blockade of YAP abolished the pro-angiogenesis effects of ELA-32. Together, these findings highlight the ELA-APJ axis as a potential therapeutic strategy for ischemic stroke by showing how activation of this pathway promotes poststroke angiogenesis.

Elabela-APJ axis attenuates cerebral ischemia/reperfusion injury by inhibiting neuronal ferroptosis

Ferroptosis is a form of non-apoptotic cell death caused by iron-dependent peroxidation of lipids. It contributes to ischemic stroke-induced neuronal damage. Elabela (ELA), a novel endogenous ligand for Apelin receptor (APJ), regulates oxidative stress and exerts a protective role in cardiovascular disease. However, the effect of ELA-APJ axis on cellular ferroptosis in cerebral ischemia/reperfusion (I/R) remains elusive. The present study showed that ELA and APJ were expressed on neurons and increased after cerebral I/R injury. The I/R insult triggered typical molecular and morphological features of neuronal ferroptosis, including iron and MDA accumulation, mitochondrial shrink and membrane rupture, upregulation of positive ferroptosis regulators and downregulation of negative regulators. ELA-32 treatment reduced brain infarction and ameliorated neurobehavioral deficits and cognitive dysfunction. Moreover, ELA-32 administration alleviated neuronal ferroptosis, accompanied by reduced iron deposition, decreased mitochondrial damage, relived lipid peroxidation and glutathione reduction. Such effects of ELA-32 were abolished by AAV-APJ-RNAi or nuclear factor erythroid 2-related factor 2 (NRF2) inhibitor ML385. Mechanistically, ELA was shown to bind to APJ and activate NRF2/ARE anti-oxidative signaling pathway via Gα13. Together, these findings suggested that ELA-APJ axis mitigates neuronal ferroptosis after ischemic stroke and that the ELA-32 peptide may be a putative therapeutic avenue for ischemic stroke.

Reduced Apela/APJ system expression in patients with pulmonary artery hypertension secondary to chronic obstructive pulmonary disease

BACKGROUND

Pulmonary artery hypertension (PAH) is a common disease that seriously threatens human physical and mental health. Chronic obstructive pulmonary disease (COPD) is the main cause of secondary PAH.

OBJECTIVES

This study observed the differential expression of the endogenous Apela/APJ system in COPD patients with or without PAH.

METHODS

A total of 69 COPD patients were enrolled, including 31 patients with PAH (COPD+PAH). Lung tissue from healthy controls, COPD patients, and COPD patients with PAH was used for RT-PCR and histological examination.

RESULTS

The serum level of endogenous Apela in COPD+PAH patients was significantly lower than those in the control and COPD groups. Correlation analysis showed that systolic pulmonary artery pressure in COPD+PAH patients was negatively correlated with the serum level of endogenous Apela (r = -0.3842, p < 0.05). The percentage of intima thickening and muscularization of pulmonary arterioles was increased in COPD+PAH patients, while the expression of Apela/APJ was decreased. Compared with the healthy controls and COPD patients, the expression of endothelial markers vWF and CD34 mRNA in the pulmonary arterioles in COPD+PAH patients decreased, while the expression of interstitial markers α-SMA and vimentin mRNA was up-regulated.

CONCLUSION

The present study suggests that expression of the Apela/APJ system is decreased in PAH secondary to COPD. The pathological changes involved in PAH secondary to COPD include thickening of the intima and muscularization of the pulmonary arterioles, as well as endothelial-to-mesenchymal transition. Corrective action targeting the diminished Apela/APJ system may be a promising therapeutic strategy for PAH in the future.

The Apelinergic System: Apelin, ELABELA, and APJ Action on Cell Apoptosis: Anti-Apoptotic or Pro-Apoptotic Effect?

The apelinergic system comprises two peptide ligands, apelin and ELABELA, and their cognate G-protein-coupled receptor, the apelin receptor APJ. Apelin is a peptide that was isolated from bovine stomach extracts; the distribution of the four main active forms, apelin-36, -17, -13, and pyr-apelin-13 differs between tissues. The mature form of ELABELA-32 can be transformed into forms called ELABELA-11 or -21. The biological function of the apelinergic system is multifaceted, and includes the regulation of angiogenesis, body fluid homeostasis, energy metabolism, and functioning of the cardiovascular, nervous, respiratory, digestive, and reproductive systems. This review summarises the mechanism of the apelinergic system in cell apoptosis. Depending on the cell/tissue, the apelinergic system modulates cell apoptosis by activating various signalling pathways, including phosphoinositide 3-kinase (PI3K), extracellular signal-regulated protein kinase (ERK1/2), protein kinase B (AKT), 5'AMP-activated protein kinase(AMPK), and protein kinase A (PKA). Apoptosis is critically important during various developmental processes, and any dysfunction leads to pathological conditions such as cancer, autoimmune diseases, and developmental defects. The purpose of this review is to present data that suggest a significant role of the apelinergic system as a potential agent in various therapies.

Circulating levels of Elabela in pregnant women with missed abortion

ObjectiveThis study aimed to detect Elabela concentrations in the serum of Missed abortion (MA) and compare them with the healthy pregnancies.Materials and methodsThis retrospective case-control study was performed in the second affiliated hospital, Xi'an Jiaotong University March 2019 to September 2019. A total of 108 healthy (35 early, 36 middle and 37 late) pregnant women and 25 (early gestational stage) MA patients were involved. Demographic and clinical characteristics were recorded. The concentration of plasma Elabela was examined using ELISA.ResultsThe level of plasma Elabela was increased in early and middle stages and decreased in late stage of healthy pregnant women. Maternal serum Elabela levels were significantly lower in MA patients (4.59 ± 1.23 ng/mL) compared to healthy pregnant women (5.77 ± 1.21 ng/mL, p < 0.01).ConclusionMaternal circulating levels of Elabela were significantly lower in MA patients than in healthy pregnant women. We consider that Elabela might be a crucial biomarker of the pathophysiologic process in MA.

Vascular Functional Effect Mechanisms of Elabela in Rat Thoracic Aorta

BACKGROUND

Elabela is a recently discovered peptide hormone. The present study aims to investigate the vasorelaxant effect mechanisms of elabela in the rat thoracic aorta.

METHODS

The vascular rings obtained from the thoracic aortas of the male Wistar Albino rats were placed in the isolated tissue bath system. Resting tension was set to 1 gram. After the equilibration period, the vessel rings were contracted with phenylephrine or potassium chloride. Once a stable contraction was achieved, elabela-32 was applied cumulatively (10^-9 - 10^-6 molar) to the vascular rings. The experimental protocol was repeated in the presence of specific signaling pathway inhibitors or potassium channel blockers to determine the effect mechanisms of elabela.

RESULTS

Elabela showed a significant vasorelaxant effect in a concentration-dependent manner (p < 0.001). The vasorelaxant effect level of elabela was significantly reduced by the apelin receptor antagonist F13A, cyclooxygenase inhibitor indomethacin, adenosine monophosphate-activated protein kinase inhibitor dorsomorphin, protein kinase C inhibitor bisindolmaleimide, large-conductance calcium-activated potassium channel blocker iberiotoxin, and intermediate-conductance calcium-activated potassium channel blocker TRAM-34 (p < 0.001). However, the vasorelaxant effect level of elabela was not significantly affected by the endothelial nitric oxide synthase inhibitor nitro-L-arginine methyl ester and mitogen-activated protein kinase inhibitor U0126.

CONCLUSIONS

Elabela exhibits a prominent vasodilator effect in rat thoracic aorta. Apelin receptor, prostanoids, adenosine monophosphate-activated protein kinase, protein kinase C, and calcium-activated potassium channels are involved in the vasorelaxant effect mechanisms of elabela.

The first report on predictive comparative ligand-based multi-QSAR modeling analysis of 4-pyrimidinone and 2-pyridinone based APJ inhibitors

The APJ system participates in several major disorders including cancer. A multi-QSAR modeling study on some APJ inhibitors was performed for the first time. Some potential molecules were also designed based on the QSAR study conducted.

The Role of Apelin-APJ System in Diabetes and Obesity

Nowadays, diabetes and obesity are two main health-threatening metabolic disorders in the world, which increase the risk for many chronic diseases. Apelin, a peptide hormone, exerts its effect by binding with angiotensin II protein J receptor (APJ) and is considered to be linked with diabetes and obesity. Apelin and its receptor are widely present in the body and are involved in many physiological processes, such as glucose and lipid metabolism, homeostasis, endocrine response to stress, and angiogenesis. In this review, we summarize the literatures on the role of the Apelin-APJ system in diabetes and obesity for a better understanding of the mechanism and function of apelin and its receptor in the pathophysiology of diseases that may contribute to the development of new therapies.

Elabela Protects Spontaneously Hypertensive Rats From Hypertension and Cardiorenal Dysfunctions Exacerbated by Dietary High-Salt Intake

Objectives: Arterial hypertension, when exacerbated by excessive dietary salt intake, worsens the morbidity and mortality rates associated with cardiovascular and renal diseases. Stimulation of the apelinergic system appears to protect against several circulatory system diseases, but it remains unknown if such beneficial effects are conserved in severe hypertension. Therefore, we aimed at determining whether continuous infusion of apelinergic ligands (i.e., Apelin-13 and Elabela) exerted cardiorenal protective effects in spontaneously hypertensive (SHR) rats receiving high-salt diet.

Methods: A combination of echocardiography, binding assay, histology, and biochemical approaches were used to investigate the cardiovascular and renal effects of Apelin-13 or Elabela infusion over 6 weeks in SHR fed with normal-salt or high-salt chow.

Results: High-salt intake upregulated the cardiac and renal expression of APJ receptor in SHR. Importantly, Elabela was more effective than Apelin-13 in reducing high blood pressure, cardiovascular and renal dysfunctions, fibrosis and hypertrophy in high-salt fed SHR. Unlike Apelin-13, the beneficial effects of Elabela were associated with a counter-regulatory role of the ACE/ACE2/neprilysin axis of the renin-angiotensin-aldosterone system (RAAS) in heart and kidneys of salt-loaded SHR. Interestingly, Elabela also displayed higher affinity for APJ in the presence of high salt concentration and better resistance to RAAS enzymes known to cleave Apelin-13.

Conclusion: These findings highlight the protective action of the apelinergic system against salt-induced severe hypertension and cardiorenal failure. As compared with Apelin-13, Elabela displays superior pharmacodynamic and pharmacokinetic properties that warrant further investigation of its therapeutic use in cardiovascular and kidney diseases.

ELABELA ameliorates hypoxic/ischemic-induced bone mesenchymal stem cell apoptosis via alleviation of mitochondrial dysfunction and activation of PI3K/AKT and ERK1/2 pathways

Background

Mesenchymal stem cells (MSCs) have exerted their brilliant potential to promote heart repair following myocardial infarction. However, low survival rate of MSCs after transplantation due to harsh conditions with hypoxic and ischemic stress limits their therapeutic efficiency in treating cardiac dysfunction. ELABELA (ELA) serves as a peptide hormone which has been proved to facilitate cell growth, survival, and pluripotency in human embryonic stem cells. Although ELA works as an endogenous ligand of a G protein-coupled receptor APJ (Apelin receptor, APLNR), whether APJ is an essential signal for the function of ELA remains elusive. The effect of ELA on apoptosis of MSCs is still vague.

Objective

We studied the role of ELABELA (ELA) treatment on the anti-apoptosis of MSCs in hypoxic/ischemic (H/I) conditions which mimic the impaired myocardial microenvironment and explored the possible mechanisms in vitro.

Methods

MSCs were obtained from donated rats weighing between 80~120 g. MSCs were exposed to serum-free and hypoxic (1% O₂) environments for 24 h, which mimics hypoxic/ischemic damage in vivo, using serum-containing normoxic conditions (20% O₂) as a negative control. MSCs that were exposed to H/I injury with ELA processing were treated by 5 μM of ELA. Cell viability and apoptosis of MSCs were evaluated by CCK8 and flow cytometry, respectively. Mitochondrial function of MSCs was also assessed according to mitochondrial membrane potential (MMP) and ATP content. The protein expression of key kinases of the PI3K/AKT and ERK1/2 signaling pathways involving t-AKT, p-AKT, t-ERK1/2, and p-ERK1/2, as well as apoptosis-related protein expression of Bcl-2, Bax, and cleaved Caspase 3, were monitored by Western blot.

Results

We found that ELA treatment of H/I-induced MSCs improved overall cell viability, enhanced Bcl/Bax expression, and decreased Caspase 3 activity. ELA inhibited H/I-induced mitochondrial dysfunction by increasing ATP concentration and suppressing the loss of mitochondrial transmembrane potential. However, this anti-apoptotic property of ELA was restrained in APJ-silenced MSCs. Additionally, ELA treatment induced the phosphorylation of AKT and ERK, while the blockade of PI3K/AKT and ERK1/2 pathways with respective inhibitors, LY294002 and U0126, suppressed the action of ELA.

Conclusion

ELA positively affected on the survival of MSCs and exhibited anti-apoptotic characteristics when exposed to hypoxic/ischemic condition in vitro. Also, the function of ELA was correlated with the APJ receptor, reduced mitochondrial damage, and activation of the PI3K/AKT and ERK1/2 signal axes.