Peptide hormone ELABELA enhances extravillous trophoblast differentiation, but placenta is not the major source of circulating ELABELA in pregnancy

Targeting the apelin system for the treatment of cardiovascular diseases

Cardiovascular disease is the leading cause of death worldwide. Its prevalence is rising due to ageing populations and the increasing incidence of diseases such as chronic kidney disease, obesity, and diabetes that are associated with elevated cardiovascular risk. Despite currently available treatments, there remains a huge burden of cardiovascular disease-associated morbidity for patients and healthcare systems, and newer treatments are needed. The apelin system, comprising the apelin receptor and its two endogenous ligands apelin and elabela, is a broad regulator of physiology that opposes the actions of the renin-angiotensin and vasopressin systems. Activation of the apelin receptor promotes endothelium-dependent vasodilatation and inotropy, lowers blood pressure, and promotes angiogenesis. The apelin system appears to protect against arrhythmias, inhibits thrombosis, and has broad anti-inflammatory and anti-fibrotic actions. It also promotes aqueous diuresis through direct and indirect (central) effects in the kidney. Thus, the apelin system offers therapeutic promise for a range of cardiovascular, kidney, and metabolic diseases. This review will discuss current cardiovascular disease targets of the apelin system and future clinical utility of apelin receptor agonism.

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.

Cardiovascular aspects of ELABELA: A potential diagnostic biomarker and therapeutic target

ELABELA, an early endogenous ligand for the G protein-coupled receptor APJ (apelin peptide jejunum, apelin receptor), has been known as an important regulator in cardiovascular homeostasis and may be a novel therapeutic target for multiple cardiovascular diseases (CVDs). At the physiological level, ELABELA exhibits angiogenic and vasorelaxant effects and is essential for heart development. At the pathological level, circulating ELABELA levels may be a novel diagnostic biomarker for various CVDs. ELABELA peripherally displays antihypertensive, vascular-protective, and cardioprotective effects, whereas central administration of ELABELA elevated BP and caused cardiovascular remodeling. This review highlights the physiological and pathological roles of ELABELA in the cardiovascular system. Enhancement of the peripheral ELABELA may be a promising pharmacological therapeutic strategy for CVDs.

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.

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.

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.

Animal models of preeclampsia: investigating pathophysiology and therapeutic targets

Animal models have been critical in investigating the pathogenesis, mediators, and even therapeutic options for a number of diseases, including preeclampsia. Preeclampsia is the leading cause of maternal and fetal morbidity and mortality worldwide. The placenta is thought to play a central role in the pathogenesis of this disease because it releases antiangiogenic and proinflammatory factors into the maternal circulation, resulting in the maternal syndrome. Despite the deleterious effects preeclampsia has been shown to have on the mother and baby during pregnancy and postpartum, there is still no effective treatment for this disease. Although clinical studies in patients are crucial to identify the involvement of pathogenic factors in preeclampsia, there are obvious limitations that prevent detailed investigation of the quantitative importance of time-dependent mechanisms involved in this syndrome. Animal models allow investigators to perform proof-of-concept studies and examine whether certain factors found in women with preeclampsia mediate hypertension and other manifestations of this disease. In this brief review, we summarize some of the more widely studied models used to investigate pathophysiological mechanisms that are thought to be involved in preeclampsia. These include models of placental ischemia, angiogenic imbalance, and maternal immune activation. Infusion of preeclampsia-related factors into animals has been widely studied to understand the specific mediators of this disease. These models have been included, in addition to a number of genetic models involved in overexpression of the renin-angiotensin system, complement activation, and trophoblast differentiation. Together, these models cover multiple mechanisms of preeclampsia from trophoblast dysfunction and impaired placental vascularization to the excess circulating placental factors and clinical manifestation of this disease. Most animal studies have been performed in rats and mice; however, we have also incorporated nonhuman primate models in this review. Preclinical animal models not only have been instrumental in understanding the pathophysiology of preeclampsia but also continue to be important tools in the search for novel therapeutic options for the treatment of this disease.

ZBED1 Regulates Genes Important for Multiple Biological Processes of the Placenta

The transcription factor ZBED1 is highly expressed in trophoblast cells, but its functions in the processes of trophoblast and placental biology remain elusive. Here, we characterized the role of ZBED1 in trophoblast cell differentiation using an in vitro BeWo cell model. We demonstrate that ZBED1 is enhanced in its expression early after forskolin-induced differentiation of BeWo cells and regulates many of the genes that are differentially expressed as an effect of forskolin treatment. Specifically, genes encoding markers for the differentiation of cytotrophoblast into syncytiotrophoblast and factors essential for trophoblast cell fusion and invasion were negatively regulated by ZBED1, indicating that ZBED1 might be important for maintaining a steady pool of cytotrophoblast cells. In addition, ZBED1 affected genes involved in the regulation of trophoblast cell survival and apoptosis, in agreement with the observed increase in apoptosis upon knockdown of ZBED1 in forskolin-treated BeWo cells. In addition, genes implicated in the differentiation, recruitment, and function of innate immune cells by the placenta were affected by ZBED1, further suggesting a role for this protein in the regulation of maternal immune tolerance. In conclusion, our study implicates ZBED1 in major biological processes of placental biology.

Apelin, APJ, and ELABELA: Role in Placental Function, Pregnancy, and Foetal Development-An Overview

The apelinergic system, which includes the apelin receptor (APJ) as well as its two specific ligands, namely apelin and ELABELA (ELA/APELA/Toddler), have been the subject of many recent studies due to their pleiotropic effects in humans and other animals. Expression of these factors has been investigated in numerous tissues and organs—for example, the lungs, heart, uterus, and ovary. Moreover, a number of studies have been devoted to understanding the role of apelin and the entire apelinergic system in the most important processes in the body, starting from early stages of human life with regulation of placental function and the proper course of pregnancy. Disturbances in the balance of placental processes such as proliferation, apoptosis, angiogenesis, or hormone secretion may lead to specific pregnancy pathologies; therefore, there is a great need to search for substances that would help in their early diagnosis or treatment. A number of studies have indicated that compounds of the apelinergic system could serve this purpose. Hence, in this review, we summarized the most important reports about the role of apelin and the entire apelinergic system in the regulation of placental physiology and pregnancy.

Circulating levels of Elabela in pregnant women complicated with intrauterine growth restriction

OBJECTIVE

This study aimed to detect Elabela concentrations in the serum of normotensive pregnant women complicated with intrauterine growth restriction (IUGR) and compare them with the uncomplicated healthy pregnancies.

MATERIAL AND METHODS

This prospective case-control study was performed from May 1, 2020 to September 30, 2020. Of the 92 pregnant patients included in the study, we enrolled 49 normotensive patients complicated with IUGR as the study group, and 43 normotensive healthy gestational age-matched and body mass index (BMI)-matched patients without IUGR or additional pregnancy complication as the control group. Demographic and clinical characteristics, and maternal serum Elabela concentrations were recorded.

RESULTS

Maternal serum Elabela levels were significantly lower in IUGR pregnancies (4.02±3.42 ng/mL) compared to healthy pregnant women (14.01±18.38 ng/mL, p<0.001). There was a positive intermediate correlation between maternal serum Elabela levels and the birth weight (r = 0.308, p = 0.004).

CONCLUSION

Maternal circulating levels of Elabela were significantly lower in IUGR pregnancies than in healthy pregnant women. Also, birth weight was positively correlated with maternal serum Elabela levels. We consider that Elabela might be a crucial biomarker of the pathophysiologic process in pregnancies complicated by IUGR.

ELABELA alleviates syncytiotrophoblast hypoxia/reoxygenation injury and preeclampsia-like symptoms in mice by reducing apoptosis

INTRODUCTION

Preeclampsia (PE) is associated with increased syncytiotrophoblast apoptosis. ELABELA (ELA) is a circulating hormone secreted by the placenta. Here, we investigated the involvement of ELA in the pathogenesis of PE.

METHODS

We measured ELA expression in the placental villi of patients with severe PE and healthy controls. A cellular model of hypoxia and reoxygenation was used to simulate PE hypoxia, and changes in the proliferation and apoptosis of trophoblasts in response to different ELA concentrations were measured. In addition, we used NG-nitro-l-arginine methyl ester (l-NAME) to generate a mouse model of pregnancy-induced hypertension and explore whether ELA can improve the symptoms of PE.

RESULTS

ELA expression was decreased in severe PE. ELA promoted the proliferation of BeWo cells and improved the decreased cell proliferation rate after hypoxia/reoxygenation injury. ELA reversed the phenotypes of l-NAME-induced PE mice and regulated the expression of mouse placental apoptosis factors.

DISCUSSION

ELA reduced apoptosis in BeWo cells and improved PE-like symptoms in mice, suggesting its value as a potential novel treatment for PE.

The Role of the Adipokines in the Most Common Gestational Complications

Adipocytokines are hormonally active molecules that are believed to play a key role in the regulation of crucial biological processes in the human body. Numerous experimental studies established significant alterations in the adipokine secretion patterns throughout pregnancy. The exact etiology of various gestational complications, such as gestational diabetes, preeclampsia, and fetal growth abnormalities, needs to be fully elucidated. The discovery of adipokines raised questions about their potential contribution to the molecular pathophysiology of those diseases. Multiple studies analyzed their local mRNA expression and circulating protein levels. However, most studies report conflicting results. Several adipokines such as leptin, resistin, irisin, apelin, chemerin, and omentin were proposed as potential novel early markers of heterogeneous gestational complications. The inclusion of the adipokines in the standard predictive multifactorial models could improve their prognostic values. Nonetheless, their independent diagnostic value is mostly insufficient to be implemented into standard clinical practice. Routine assessments of adipokine levels during pregnancy are not recommended in the management of both normal and complicated pregnancies. Based on the animal models (e.g., apelin and its receptors in the rodent preeclampsia models), future implementation of adipokines and their receptors as new therapeutic targets appears promising but requires further validation in humans.

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.

The Elabela in hypertension, cardiovascular disease, renal disease, and preeclampsia: an update

: Although considerable success has been shown for antihypertensive medications, the resistant hypertension and hypertension-related organ damages are still the important clinical issues and pose as high health and economic pressure. Therefore, novel therapeutic techniques and antihypertensive drugs are needed to advance more effective therapy of hypertension and hypertension-related disease to ameliorate mortality and healthcare costs worldwide. In this review, we highlight the latest progress in supporting the therapeutic potential of Elabela (ELA), a recently discovered early endogenous ligand for G-protein-coupled receptor apelin peptide jejunum, apelin receptor. Systemic administration of ELA exerts vasodilatory, antihypertensive, cardioprotective, and renoprotective effects, whereas central application of ELA increases blood pressure and causes cardiovascular remodeling primarily secondary to the hypertension. In addition, ELA drives extravillous trophoblast differentiation and prevents the pathogenesis of preeclampsia (a gestational hypertensive syndrome) by promoting placental angiogenesis. These findings strongly suggest peripheral ELA's therapeutic potential in preventing and treating hypertension and hypertension-related diseases including cardiovascular disease, kidney disease, and preeclampsia. Since therapeutic use of ELA is mainly limited by its short half-life and parenteral administration, it may be a clinical application candidate for the therapy of hypertension and its complications when fused with a large inert chemicals (e.g. polyethylene glycol, termed polyethylene glycol-ELA-21) or other proteins (e.g. the Fc fragment of IgG and albumin, termed Fc-ELA-21 or albumin-ELA-21), and new delivery methods are encouraged to develop to improve the efficacy of ELA fragments on apelin peptide jejunum or alternative unknown receptors.