Elabela, a new endogenous ligand of APJ, functions in embryos and adults organisms

A promising therapeutic peptide and preventive/diagnostic biomarker for age-related diseases: The Elabela/Apela/Toddler peptide

Elabela (ELA), Apela or Toddler peptide is a hormone peptide belonging to the adipokine group and a component of apelinergic system, discovered in 2013-2014. Given its high homology with apelin, the first ligand of APJ receptor, ELA likely mediates similar effects. Increasing evidence shows that ELA has a critical function not only in embryonic development, but also in adulthood, contributing to physiological and pathological conditions, such as the onset of age-related diseases (ARD). However, still little is known about the mechanisms and molecular pathways of ELA, as well as its precise functions in ARD pathophysiology. Here, we report the mechanisms by which ELA/APJ signaling acts in a very complex network of pathways for the maintenance of physiological functions of human tissue and organs, as well as in the onset of some ARD, where it appears to play a central role. Therefore, we describe the possibility to use the ELA/APJ pathway, as novel biomarker (predictive and diagnostic) and target for personalized treatments of ARD. Its potentiality as an optimal peptide candidate for therapeutic ARD treatments is largely described, also detailing potential current limitations.

ELABELA-APJ-Akt/YAP Signaling Axis: A Novel Mechanism of Aerobic Exercise in Cardioprotection of Myocardial Infarction Rats

PURPOSE

The aim of this study was to investigate the function and mechanisms of ELABELA (ELA) in the aerobic exercise-induced antiapoptosis and angiogenesis of ischemic heart.

METHODS

The myocardial infarction (MI) model of Sprague-Dawley rat was established by the ligation of the left anterior descending coronary artery. MI rats underwent 5 wk of Fc-ELA-21 subcutaneous injection and aerobic exercise training using a motorized rodent treadmill. Heart function was evaluated by hemodynamic measures. Cardiac pathological remodeling was evaluated by Masson's staining and the calculation of left ventricular weight index. Cell proliferation, angiogenesis, and Yes-associated protein (YAP) translocation were observed by immunofluorescence staining. Cell apoptosis was analyzed by TUNEL. Cell culture and treatment were used to elucidate the molecular mechanism of ELA. Protein expression was detected by Western blotting. Angiogenesis was observed by tubule formation test. One-way or two-way ANOVA and Student's t -test were used for statistical analysis.

RESULTS

Aerobic exercise stimulated the endogenous ELA expression. Exercise and Fc-ELA-21 intervention significantly activated APJ-Akt-mTOR-P70S6K signaling pathway, kept more cardiomyocytes alive, and increased angiogenesis, so as to inhibit the cardiac pathological remodeling and improved the heart function of MI rats. Fc-ELA-32 also had the cellular and functional cardioprotective activities in vivo . In vitro , ELA-14 peptide regulated the phosphorylation and nucleoplasmic translocation of YAP and activated the APJ-Akt signaling pathway so as to increase the proliferation of H9C2 cells. Moreover, the antiapoptosis and the tubule formation of HUVECs were also enhanced by ELA-14, whereas the inhibition of Akt activity weakened such effects.

CONCLUSIONS

ELA is a potential therapeutic member that plays a key role through APJ-Akt/YAP signaling axis in aerobic exercise-induced cardioprotection of MI rats.

The Apelinergic System in Pregnancy

The apelinergic system is a highly conserved pleiotropic system. It comprises the apelin receptor apelin peptide jejunum (APJ) and its two peptide ligands, Elabela/Toddler (ELA) and apelin, which have different spatiotemporal localizations. This system has been implicated in the regulation of the adipoinsular axis, in cardiovascular and central nervous systems, in carcinogenesis, and in pregnancy in humans. During pregnancy, the apelinergic system is essential for embryo cardiogenesis and vasculogenesis and for placental development and function. It may also play a role in the initiation of labor. The apelinergic system seems to be involved in the development of placenta-related pregnancy complications, such as preeclampsia (PE) and intrauterine growth restriction, but an improvement in PE-like symptoms and birth weight has been described in murine models after the exogenous administration of apelin or ELA. Although the expression of ELA, apelin, and APJ is altered in human PE placenta, data related to their circulating levels are inconsistent. This article reviews current knowledge about the roles of the apelinergic system in pregnancy and its pathophysiological roles in placenta-related complications in pregnancy. We also discuss the challenges in translating the actors of the apelinergic system into a marker or target for therapeutic interventions in obstetrics.

ERK/HIF-1α/VEGF pathway: a molecular target of ELABELA (ELA) peptide for attenuating cardiac ischemia-reperfusion injury in rats by promoting angiogenesis

BACKGROUND

Myocardial ischemia-reperfusion (I/R) injury is caused by a chain of events such as endothelial dysfunction. This study was conducted to investigate protective effects of ELABELA against myocardial I/R in Wistar rats and clarify its possible mechanisms. METHODS AND RESULTS: MI model was established based on the left anterior descending coronary artery ligation for 30 min. Then, 5 µg/kg of ELA peptide was intraperitoneally infused in rats once per day for 4 days. Western blot assay was used to assay the expression of t-ERK1/2, and p-ERK1/2 in different groups. The amount of myocardial capillary density, the expression levels of VEGF and HIF-1α were evaluated using immunohistochemistry assay. Masson's trichrome staining was utilized to assay cardiac interstitial fibrosis. The results showed that establishment of MI significantly enhanced cardiac interstitial fibrosis and changed p-ERK1/2/ t-ERK1/2 ratio. Likewise, ELA post-treatment markedly increased myocardial capillary density, the expression of several angiogenic factors (VEGF-A, HIF-1α), and reduced cardiac interstitial fibrosis by activation of ERK1/2 signaling pathways.

CONCLUSION

Collectively, ELA peptide has ability to reduce myocardial I/R injury by promoting angiogenesis and reducing cardiac interstitial fibrosis through activating ERK/HIF-1α/VEGF pathway.

Plasma Levels of Apelinergic System Components in Patients with Chronic and Acute Coronary Syndromes-A Pilot Study

The effects of the apelinergic system components apelin (AP) and elabela (ELA) in the regulation of human cardiovascular homeostasis, and data concerning the relationship between ELA and AP and coronary artery disease (CAD) are yet unknown. The aim of the study was the evaluation of AP, ELA and APJ-receptor levels in the plasma of patients with chronic coronary syndromes (CCS) and acute coronary syndromes (ACS). The study group consisted of 114 patients with CAD and 33 healthy controls. Patients were divided into two groups: with CCS (n = 30) and ACS (n = 84). Routine laboratory tests and plasma ELA, AP-17, AP-13 and APJ receptor levels were measured. Echocardiographic data were analyzed in all patients. Levels of AP-17 and ELA were significantly lower in CCS than in healthy controls and ACS patients. We demonstrated significant increase of levels of plasma apelinergic system peptides, especially ELA and AP-17 in ACS patients compared with healthy controls and CCS, suggestive of compensating up-regulation mechanisms. There is a relationship between circulating ELA and AP-17 levels and classical, biochemical markers of ischemia and left ventricular ejection faction as well.

The role of Elabela in kidney disease

Elabela, also known as Toddler or Apela, is a recently discovered hormonal peptide containing 32 amino acids. Elabela is a ligand of the apelin receptor (APJ). APJ is a G protein-coupled receptor widely expressed throughout body, and together with its cognate ligand, apelin, it plays an important role in various physiological processes including cardiovascular functions, angiogenesis and fluid homeostasis. Elabela also participates in embryonic development and pathophysiological processes in adulthood. Elabela is highly expressed in undifferentiated embryonic stem cells and regulates endoderm differentiation and cardiovascular system development. During differentiation, Elabela is highly expressed in pluripotent stem cells and in adult renal collecting ducts and loops, where it functions to maintain water and sodium homeostasis. Other studies have also shown that Elabela plays a crucial role in the pathogenesis of kidney diseases. This review addresses the role of Elabela in kidney diseases including renal ischemia/reperfusion injury, hypertensive nephropathy, diabetic nephropathy, and cardiorenal syndrome.

Association between ELABELA Serum Concentrations in First Trimester and Pregnancy-Induced Hypertension

ELABELA (ELA) is considered to be implicated in the pathophysiology of preeclampsia (PE), since ELA-deficient mice exhibited PE-like symptoms and infusion of exogenous ELA normalized the gestational hypertension (GH) and proteinuria. However, no evidence show that circulating ELA is deficient in early placental development among women who destined to develop GH/PE. This nested case-control study was conducted to investigate the association between serum ELA concentration in early pregnancy and the risk of later GH/PE. Participants were recruited and sampled in 10-14⁺⁶ weeks of gestation. Definite GH/PE cases were matched 1 : 3 to controls with respect to age and gestational age. Serum concentration of ELA was measured using enzyme immunoassay. Women with later GH (N = 28) had a slightly lower median concentration of ELA (46.72 ng/mL versus 53.54 ng/mL), while those with later PE (N = 16) had a slightly higher median concentration of ELA (74.8 ng/mL versus 66.30 ng/mL) compared to the controls. Yet, both the increments did not reach statistically significant difference (GH: P = 0.380, PE: P = 0.799). ELA serum concentrations were unchanged in first trimester in women with GH/PE. Further studies are still needed to identify the dynamic changes in serum ELA concentrations during the whole pregnancy, especially in those with pregnancy-induced hypertensive disorders.

Interaction of apelin, elabela and nitric oxide in schizophrenia patients

Background

Apelin (APLN), elabela (ELA), and nitric oxide (NO) have effects on physiological and behavioural properties in biological systems. This study was designed to determine APLN, ELA and NO levels in schizophrenia patients and assess whether these molecules are of diagnostic value.

Methods

A total of 33 schizophrenic patients and 32 ageand sex-adjusted healthy participants were included in the study. ELA, APLN and NO levels were measured using ELISA methods.

Results

Although the ELA and NO levels of the patients were lower than the control group, APLN levels were higher (p = 0.039, p = 0.019, p = 0.048, respectively). There was a significant negative correlation between APLN levels and triglyceride (TG) and body mass index (BMI) levels (r = -0.426, p = < 0.001 and r = -0.330, p = 0.007, respectively). Respectively, the areas under the receiver-operating characteristic (ROC) curves of the ELA/APLN, ELA/NO and APLN/NO ratios were 0.628, 0.590 and 0.709, 95% confident intervals (CI): 0.491-0.764, 0.450-0.730 and 0.579-0.840.

Conclusions

Decreased levels of ELA and NO and increased APLN levels in schizophrenia suggest that these molecules may be involved in its etiopathology. The APLN/NO ratio also seems to show promise in the diagnosis of the disease and may be used in future.

Apela/Elabela/Toddler: New perspectives in molecular mechanism of heart failure

Background. Despite significant therapeutic advances, heart failure (HF) remains unacceptably high in morbidity and mortality. Additionally, its high-care and costs make HF a deadly and costly disease. First reported independently by two group of researchers, Apela/Elabela/Toddler (ELA) is the second endogenous apelin-receptor ligand discovered which is encoded from a previously classified non-coding gene, and has emerged as a key signalling-pathway in the cardiovascular system.

Aims. To explore and summarise the biological effects and diagnostic potential of ELA as a new biomarker for heart failure.

Results. ELA (prepro-ELA 54 AA) is a molecule with three isoforms (ELA 11,16 and 32), recently identified as the second endogenous ligand to APJ-receptor and functions to mediate early cardiac development during zebrafish embryogenesis by inducing cardiogenesis, vasculogenesis and bone formation. In adults, it enhances cardiac contractility, promotes vasodilatory effects, mediates fluid homeostasis, reduces food intake, limits kidney dysfunction and exerts anti-atherosclerotic as well as anti-oxidative properties.

Conclusion. These results show that ELA, an endogenous agonist of the APJ-receptor exerts cardiovascular effects comparable and potentially more potent than apelin and is found to be downregulated in experimental models and humans with heart failure.

Loss of Apelin Augments Angiotensin II-Induced Cardiac Dysfunction and Pathological Remodeling

Apelin is an inotropic and cardioprotective peptide that exhibits beneficial effects through activation of the APJ receptor in the pathology of cardiovascular diseases. Apelin induces the expression of angiotensin-converting enzyme 2 (ACE2) in failing hearts, thereby improving heart function in an angiotensin 1⁻7-dependent manner. Whether apelin antagonizes the over-activation of the renin⁻angiotensin system in the heart remains elusive. In this study we show that the detrimental effects of angiotensin II (Ang II) were exacerbated in the hearts of aged apelin-gene-deficient mice. Ang II-mediated cardiac dysfunction and hypertrophy were augmented in apelin knockout mice. The loss of apelin increased the ratio of angiotensin-converting enzyme (ACE) to ACE2 expression in the Ang II-stressed hearts, and Ang II-induced cardiac fibrosis was markedly enhanced in apelin knockout mice. mRNA expression of pro-fibrotic genes, such as transforming growth-factor beta (TGF-β) signaling, were significantly upregulated in apelin knockout hearts. Consistently, treatment with the ACE-inhibitor Captopril decreased cardiac contractility in apelin knockout mice. In vitro, apelin ameliorated Ang II-induced TGF-β expression in primary cardiomyocytes, accompanied with reduced hypertrophy. These results provide direct evidence that endogenous apelin plays a crucial role in suppressing Ang II-induced cardiac dysfunction and pathological remodeling.

Apelin/APJ system: A novel promising target for anti-aging intervention

Apelin, an endogenous ligand for the G protein-coupled receptor APJ, is widely expressed in various organs. Recent research has indicated that the Apelin/APJ system plays an important role in aging. Apelin and APJ receptor expression are down-regulated with increasing age. In murine models, Apelin and APJ knockouts exhibit accelerated senescence whereas Apelin-restoration results in enhanced vigor and rejuvenated behavioral and circadian phenotypes. Furthermore, aged Apelin knockout mice develop progressive impairment of cardiac contractility associated with systolic dysfunction. Apelin is crucial to maintain cardiac contractility in aging. Moreover, the Apelin/APJ system appears to be involved in regulation of renin-angiotensin-aldosterone system (RAAS), apoptosis, inflammation and oxidative stress which promotes aging. Likewise, the Apelin/APJ system regulates autophagy, stem cells and the sirtuin family thus contributing to anti-aging. In this review, we describe the relationship between Apelin/APJ system and aging. We elaborate on the role of the Apelin/APJ system in aging stimulators, aging inhibitors and age-related diseases such as obesity, diabetes and cardiovascular disease. We conclude that Apelin/APJ system might become a novel promising therapeutic target for anti-aging.