Apelin Controls Fetal and Neonatal Glucose Homeostasis and Is Altered by Maternal Undernutrition

Immunohistochemistry and molecular biology studies of apelin and apelin receptor in queen placenta

Placenta is a tissue where vasculogenesis, blood pressure and blood flow are dramatically important to allow normal embryonic and foetal growth and requires the production of numerous growth factors, hormones and transcription factors. Apelin is a pleiotropic peptide, and its major action relates to energy metabolism, cardiovascular function, body fluid homeostasis via its receptor. The involvement of the apelinergic system during pregnancy in veterinary medicine has been investigated only in bitches. Thereafter, the aim of our study was to investigate, for the first time, presence and distribution of this system in the queen placenta at mid- and end-gestation. Ten pregnant mixed-breed queens were used. The animals were equally divided into two groups based on the stage of pregnancy (mid and end gestation) and, with the written consent of their owners, were subjected to ovariohysterectomy or non-conservative caesarean section. The Real-Time PCR (RT-PCR) analysis showed the presence of transcripts for apelin and its receptor in all the foetal and maternal placenta samples processed. The immunohistochemical (IHC) study evidenced the presence and the distribution of positive immunoreactions for apelin and its receptor in all the samples observed. In particular, in the placental labyrinthic portion, apelin and apelin receptor immunopositivity was evident in the cytoplasm of trophoblasts and endothelial cells. The uterine glands also exhibited a positive immune reaction for apelin and corresponding receptor. Based on our results, apelin and its receptor, also in the queen placenta, could be an important system involved in the physiological development of placenta, embryo and foetal growth.

Decoding Apelin: Its Role in Metabolic Programming, Fetal Growth, and Gestational Complications

Placental insufficiency and gestational diabetes, which are both serious pregnancy complications, are linked to altered fetal growth, whether restricted or excessive, and result in metabolic dysfunction, hypoxic/oxidative injury, and adverse perinatal outcomes. Although much research has been carried out in this field, the underlying pathogenetic mechanisms have not as yet been fully elucidated. Particularly because of the role it plays in cardiovascular performance, glucose metabolism, inflammation, and oxidative stress, the adipokine apelin was recently shown to be a potential regulator of fetal growth and metabolic programming. This review investigated the numerous biological actions of apelin in utero and aimed to shed more light on its role in fetal growth and metabolic programming. The expression of the apelinergic system in a number of tissues indicates its involvement in many physiological mechanisms, including angiogenesis, cell proliferation, energy metabolism, inflammation, and oxidative stress. Moreover, it appears that apelin has a major function in disorders such as diabetes mellitus, fetal growth abnormalities, fetal hypoxia, and preeclampsia. We herein describe in detail the regulatory effects exerted by the adipokine apelin on fetal growth and metabolic programming while stressing the necessity for additional research into the therapeutic potential of apelin and its mechanisms of action in pregnancy-related disorders.

Immunodetection of selected pancreatic hormones under intragastric administration of apelin-13, a novel endogenous ligand for an angiotensin-like orphan G-protein coupled receptor, in unweaned rats

Introduction

This study investigated the effects of intragastric administration of apelin-13 on the secretion of critical pancreatic hormones in a cohort of three-week-old Wistar rats. The research aimed to uncover apelin's modulatory roles in endocrine interactions dictating metabolic homeostasis during early life.

Material and Methods

Rats were randomly assigned to control or experimental groups, receiving apelin-13 or saline for 14 days. The study population consisted of three-week-old Wistar rats of both sexes, weighing between 20 and 25 grams. Histological examination, analysis of variance and t-tests were employed to assess significant differences.

Results

Distinctive alterations in large islet morphology were observed, indicating a notable reduction in size. Additionally, an increase in alpha- and beta-cell density within specific islet sizes was noted, suggesting significant changes in cell populations. The study found a substantial increase in mitotic activity and a decrease in apoptosis in small and medium-sized islets post apelin-13 administration, indicating its potential role in regulating cell survival and proliferation.

Conclusion

The notable reduction in large islet size coupled with increased alpha and beta cell density implies a targeted impact of apelin-13 on pancreatic cell dynamics. Also, the observed increase in mitotic activity and decrease in apoptosis in small and medium-sized islets suggest its potential regulatory role in cell survival and proliferation within the pancreatic microenvironment.

Adipokines in pregnancy

Reproductive success consists of a sequential events chronology, starting with the ovum fertilization, implantation of the embryo, placentation, and cellular processes like proliferation, apoptosis, angiogenesis, endocrinology, or metabolic changes, which taken together finally conduct the birth of healthy offspring. Currently, many factors are known that affect the regulation and proper maintenance of pregnancy in humans, domestic animals, or rodents. Among the determinants of reproductive success should be distinguished: the maternal microenvironment, genes, and proteins as well as numerous pregnancy hormones that regulate the most important processes and ensure organism homeostasis. It is well known that white adipose tissue, as the largest endocrine gland in our body, participates in the synthesis and secretion of numerous hormones belonging to the adipokine family, which also may regulate the course of pregnancy. Unfortunately, overweight and obesity lead to the expansion of adipose tissue in the body, and its excess in both women and animals contributes to changes in the synthesis and release of adipokines, which in turn translates into dramatic changes during pregnancy, including those taking place in the organ that is crucial for the proper progress of pregnancy, i.e. the placenta. In this chapter, we are summarizing the current knowledge about levels of adipokines and their role in the placenta, taking into account the physiological and pathological conditions of pregnancy, e.g. gestational diabetes mellitus, preeclampsia, or intrauterine growth restriction in humans, domestic animals, and rodents.

Hormonal Determinants of Growth and Weight Gain in the Human Fetus and Preterm Infant

The factors controlling linear growth and weight gain in the human fetus and newborn infant are poorly understood. We review here the changes in linear growth, weight gain, lean body mass, and fat mass during mid- and late gestation and the early postnatal period in the context of changes in the secretion and action of maternal, placental, fetal, and neonatal hormones, growth factors, and adipocytokines. We assess the effects of hormonal determinants on placental nutrient delivery and the impact of preterm delivery on hormone expression and postnatal growth and metabolic function. We then discuss the effects of various maternal disorders and nutritional and pharmacologic interventions on fetal and perinatal hormone and growth factor production, growth, and fat deposition and consider important unresolved questions in the field.

The role of apelinergic system in metabolism and reproductive system in normal and pathological conditions: an overview

Lifestyle changes have made metabolic disorders as one of the major threats to life. Growing evidence demonstrates that obesity and diabetes disrupt the reproductive system by affecting the gonads and the hypothalamus-pituitary-gonadal (HPG) axis. Apelin, an adipocytokine, and its receptor (APJ) are broadly expressed in the hypothalamus nuclei, such as paraventricular and supraoptic, where gonadotropin-releasing hormone (GnRH) is released, and all three lobes of the pituitary, indicating that apelin is involved in the control of reproductive function. Moreover, apelin affects food intake, insulin sensitivity, fluid homeostasis, and glucose and lipid metabolisms. This review outlined the physiological effects of the apelinergic system, the relationship between apelin and metabolic disorders such as diabetes and obesity, as well as the effect of apelin on the reproductive system in both gender. The apelin-APJ system can be considered a potential therapeutic target in the management of obesity-associated metabolic dysfunction and reproductive disorders.

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.

Programming of metabolism by adipokines during development

The intrauterine and early postnatal periods represent key developmental stages in which an organism is highly susceptible to being permanently influenced by maternal factors and nutritional status. Strong evidence indicates that either undernutrition or overnutrition during development can predispose individuals to disease later in life, especially type 2 diabetes mellitus and obesity, a concept known as metabolic programming. Adipose tissue produces important signalling molecules that control energy and glucose homeostasis, including leptin and adiponectin. In addition to their well-characterized metabolic effects in adults, adipokines have been associated with metabolic programming by affecting different aspects of development. Therefore, alterations in the secretion or signalling of adipokines, caused by nutritional insults in early life, might lead to metabolic diseases in adulthood. This Review summarizes and discusses the potential role of several adipokines in inducing metabolic programming through their effects during development. The identification of the endocrine factors that act in early life to permanently influence metabolism represents a key step in understanding the mechanisms behind metabolic programming. Thus, future strategies aiming to prevent and treat these metabolic diseases can be designed, taking into consideration the relationship between adipokines and the developmental origins of health and disease.

Maternal obesity reduces apelin level in cord blood without altering the placental apelin/elabela-APJ system

The APJ receptor and its two endogenous ligands, apelin and elabela, exert key roles in fetoplacental development. In adult, this system is altered by obesity but no data are available during pregnancy. We measured apelin and elabela levels in maternal plasma and cord blood and quantified placental gene expression of apelin, elabela and APJ in obese and non-obese mothers. We found that obesity reduced apelin level in cord blood without affecting maternal and cord blood elabela levels as well as placental gene expression of this system. Our data suggest that obesity alters fetal apelinemia in humans.

Possible roles of exercise and apelin against pregnancy complications

The prevalence of maternal obesity during pregnancy is associated with the risk of gestational diabetes, preeclampsia, and cardiomyopathy. Environmental factors such as active lifestyles and apelin may lead to beneficial changes. In rats, apelin and exercise (45 to 65% VO2max for 6 to 9 weeks) during pregnancy increase brown adipose tissue (BAT) proteins such as Cidea, Elovl3, UCP1, PRDM16, and PGC-1α in males and females fetuses, while white adipose tissue (WAT) is reduced. In humans and animals, apelin and exercise stimulate the expression of the glucose transporters (GLUT1/2/4) in the muscle and adipose tissue through the PI3K/Akt and AMPK pathways. Hence, exercise and apelin may are known as regulators of energy metabolism and be anti-obesity and anti-diabetic properties. In mice, exercise also creates a short-term hypoxic environment in the pregnant mother, activating HIF-1, VEGF, and VEGFR, and increasing angiogenesis. Exercise and apelin also increase vasodilation, angiogenesis, and suppression of inflammation through the L-arginine/eNOS/NO pathway in humans. Exercise can stimulate the ACE2-Ang-(1-7)-Mas axis in parallel with inhibiting the ACE-Ang II-AT1 pathway. Exercise and apelin seem to prevent preeclampsia through these processes. In rats, moderate-intensity exercise (60 to 70% VO2max for 8 weeks) and apelin/APJ also may prevent pathological hypertrophy in pregnancy by activating the PI3K/Akt/mTOR/p70S6K pathway, PI3k-Akt-ERK1/2-p70S6K pathway, and the anti-inflammatory cytokine IL-10. Since pre-clinical studies have been more on animal models, future research with scientific guidelines should pay more attention to human specimens. In future research, time factors such as the first, second, and third trimesters of pregnancy and the intensity and duration of exercise are important variables that should be considered to determine the optimal intensity and duration of exercise.

Yenidoğan hipoglisemisine güncel yaklaşım

Neonatal hipoglisemi yenidoğan döneminde sık görülen, yaşamın ilerleyen dönemlerini de etkileyen bir sağlık sorunudur. Hipoglisemi akut ve kronik komplikasyonlara neden olarak yenidoğan bebeğin büyümesi ve gelişmesinde kalıcı ve geri dönüşümsüz nörolojik sorunlara yol açabilmektedir. Hipoglisemiyi saptamak için en duyarlı test halen plazma glukozu ile ölçümü olsa da, yıllardır kullanılan geleneksel glukoz ölçüm yöntemleri ile birlikte son yıllarda noninvaziv glukoz ölçüm yöntemlerindeki gelişmeler ile riskli bebeklerde hipogliseminin tanı ve tedavisinde bu teknolojik ölçüm yöntemleri yaygın kullanılmaya başlamıştır. Glukometre, kan gazı analizatörleri, laboratuvarda enzimatik ölçüm geleneksel ölçüm yöntemleri iken, sürekli glukoz ölçüm sistemleri yeni nesil glukoz ölçümünde yer almaya başlayan yeni bir tekniktir. Hipoglisemi gelişimini engellemek için koruyucu önlemler alırken erken dönemde anne sütü ile emzirme desteği sağlanmalı ve teşvik edilmelidir. Hangi durumların hipoglisemi için risk oluşturduğu, hangi glukoz eşik değerinde tedavi vermek gerektiği ve son kullanılan yeni nesil glukoz ölçüm yöntemlerinin etkileri ve güncel tedaviler bu derlemede tartışılmıştır. Riskli bebeklerde kan şekeri ölçümleri ve klinik bulguların gözlenmesi yanında hipoglisemide ayırıcı tanı yapılarak tedavinin yönetilmesi de prognozda önemli bir yer tutar.

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.

Acetone Ingestion Mimics a Fasting State to Improve Glucose Tolerance in a Mouse Model of Gestational Hyperglycemia

Gestational diabetes mellitus results, in part, from a sub-optimal β-cell mass (BCM) during pregnancy. Artemisinins were reported to increase BCM in models of diabetes by α- to β-cell conversion leading to enhanced glucose tolerance. We used a mouse model of gestational glucose intolerance to compare the effects of an artemisinin (artesunate) on glycemia of pregnant mice with vehicle treatment (acetone) or no treatment. Animals were treated daily from gestational days (GD) 0.5 to 6.5. An intraperitoneal glucose tolerance test was performed prior to euthanasia at GD18.5 or post-partum. Glucose tolerance was significantly improved in both pregnant and non-pregnant mice with both artesunate and vehicle-alone treatment, suggesting the outcome was primarily due to the acetone vehicle. In non-pregnant, acetone-treated animals, improved glucose tolerance was associated with a higher BCM and a significant increase in bihormonal insulin and glucagon-containing pancreatic islet cells, suggesting α- to β-cell conversion. BCM did not differ with treatment during pregnancy or post-partum. However, placental weight was higher in acetone-treated animals and was associated with an upregulation of apelinergic genes. Acetone-treated animals had reduced weight gain during treatment despite comparable food consumption to non-treated mice, suggesting transient effects on nutrient uptake. The mean duodenal and ileum villus height was reduced following exposure to acetone. We conclude that acetone treatment may mimic transient fasting, resulting in a subsequent improvement in glucose tolerance during pregnancy.

Maternal Undernutrition during Pregnancy Alters Amino Acid Metabolism and Gene Expression Associated with Energy Metabolism and Angiogenesis in Fetal Calf Muscle

To elucidate the mechanisms underlying maternal undernutrition (MUN)-induced fetal skeletal muscle growth impairment in cattle, the longissimus thoracis muscle of Japanese Black fetal calves at 8.5 months in utero was analyzed by an integrative approach with metabolomics and transcriptomics. The pregnant cows were fed on 60% (low-nutrition, LN) or 120% (high-nutrition, HN) of their overall nutritional requirement during gestation. MUN markedly decreased the bodyweight and muscle weight of the fetus. The levels of amino acids (AAs) and arginine-related metabolites including glutamine, gamma-aminobutyric acid (GABA), and putrescine were higher in the LN group than those in the HN group. Metabolite set enrichment analysis revealed that the highly different metabolites were associated with the metabolic pathways of pyrimidine, glutathione, and AAs such as arginine and glutamate, suggesting that MUN resulted in AA accumulation rather than protein accumulation. The mRNA expression levels of energy metabolism-associated genes, such as PRKAA1, ANGPTL4, APLNR, CPT1B, NOS2, NOS3, UCP2, and glycolytic genes were lower in the LN group than in the HN group. The gene ontology/pathway analysis revealed that the downregulated genes in the LN group were associated with glucose metabolism, angiogenesis, HIF-1 signaling, PI3K-Akt signaling, pentose phosphate, and insulin signaling pathways. Thus, MUN altered the levels of AAs and expression of genes associated with energy expenditure, glucose homeostasis, and angiogenesis in the fetal muscle.

Role of Placental Glucose Transporters in Determining Fetal Growth

Maternal nutrient availability and its transport through the placenta are crucial for fetal development. Nutrients are transported to the fetus via specific transporters present on the microvillous (MVM) and basal membrane (BM) of the placenta. Glucose is the most abundant nutrient transferred to the fetus and plays a key role in the fetal growth and development. The transfer of glucose across the human placenta is directly proportional to maternal glucose concentrations, and is mediated by glucose transporter family proteins (GLUTs). Maternal glucose concentration influences expression and activity of GLUTs in the MVM (glucose uptake) and BM (glucose delivery). Alteration in the number and function of these transporters may affect the growth and body composition of the fetus. The thin-fat phenotype of the Indian baby (low ponderal index, high adiposity) is proposed as a harbinger of future metabolic risk. We propose that placental function mediated through nutrient transporters contributes to the phenotype of the baby, specifically that glucose transporters will influence neonatal fat. This review discusses the role of various glucose transporters in the placenta in determining fetal growth and body composition, in light of the above hypothesis.

Ontology of the apelinergic system in mouse pancreas during pregnancy and relationship with β-cell mass

The apelin receptor (Aplnr) and its ligands, Apelin and Apela, contribute to metabolic control. The insulin resistance associated with pregnancy is accommodated by an expansion of pancreatic β-cell mass (BCM) and increased insulin secretion, involving the proliferation of insulin-expressing, glucose transporter 2-low (Ins+Glut2LO) progenitor cells. We examined changes in the apelinergic system during normal mouse pregnancy and in pregnancies complicated by glucose intolerance with reduced BCM. Expression of Aplnr, Apelin and Apela was quantified in Ins+Glut2LO cells isolated from mouse pancreata and found to be significantly higher than in mature β-cells by DNA microarray and qPCR. Apelin was localized to most β-cells by immunohistochemistry although Aplnr was predominantly associated with Ins+Glut2LO cells. Aplnr-staining cells increased three- to four-fold during pregnancy being maximal at gestational days (GD) 9-12 but were significantly reduced in glucose intolerant mice. Apelin-13 increased β-cell proliferation in isolated mouse islets and INS1E cells, but not glucose-stimulated insulin secretion. Glucose intolerant pregnant mice had significantly elevated serum Apelin levels at GD 9 associated with an increased presence of placental IL-6. Placental expression of the apelinergic axis remained unaltered, however. Results show that the apelinergic system is highly expressed in pancreatic β-cell progenitors and may contribute to β-cell proliferation in pregnancy.

Reproductive roles of novel adipokines apelin, visfatin, and irisin in farm animals

The adipose tissue has a substantial impact on reproduction in mammals, specifically in females. As an energy depository organ, it is precisely associated with the reproductive success of mammals. Adipose tissue secretes many single molecules that are called 'adipokines' which mainly act as endocrine hormones. Adipokines homeostasis is fundamental to energy regulation, metabolic and cardiovascular diseases. The endocrine function of adipokines is influential for the long-term control of energy metabolism and performs an important function in metabolic state and fertility modulation. During the last years, new roles for adipokines have been appearing in the field of fertility. The adipokines have functions in reproduction at levels of the hypothalamus, the pituitary, and the gonads in humans, rodents, and other animals. Normal levels of adipokines are indispensable to protect the integrity of the hypothalamus-hypophysis-gonadal axis, regular ovulatory processes, and successful embryo implantation. Leptin and adiponectin are the most studied adipokines, but also the novel adipokines; apelin, visfatin, and irisin are important adipokines having several functions within the reproductive tract. Due to the known and unknown effects of these novel adipokines in the reproduction of farm animals, in this review, we will highlight the reproductive functions of apelin, visfatin, and irisin and summarize the known reproductive effects in farm animals to introduce the gaps for future studies in farm animals.

Metabolic Adaptations to Pregnancy in Healthy and Gestational Diabetic Pregnancies: The Pancreas - Placenta Axis

Normal pregnancy is associated with increased insulin resistance as a metabolic adaptation to the nutritional demands of the placenta and fetus, and this is amplified in obese mothers. Insulin resistance is normally compensated for by an adaptive increase in pancreatic β-cell mass together with enhanced glucose-stimulated insulin release. Placentally-derived hormones and growth factors are central to the altered pancreatic morphology and function. A failure of β-cells to undergo adaptive change after the first trimester has been linked with gestational diabetes. In the pregnant mouse, an increase in β-cell replication contributes to a 2-3-fold increase in mass peaking in late gestation, depending on the proliferation of existing β-cells, the differentiation of resident progenitor β-cells, or islet cell transdifferentiation. Using mouse models and human studies placenta- and islet of Langerhans-derived molecules have been identified that are likely to contribute to the metabolic adaptations to pregnancy and whose physiology is altered in the obese, glucose-intolerant mother. Maternal obesity during pregnancy can create a pro-inflammatory environment that can disrupt the response of the β-cells to the endocrine signals of pregnancy and limit the adaptive changes in β-cell mass and function, resulting in an increased risk of gestational diabetes.

Liver Proteome Profile of Growth Restricted and Appropriately Grown Newborn Wistar Rats Associated With Maternal Undernutrition

Background

Fetal growth restriction (FGR) has been associated with adverse perinatal outcomes and epigenetic modifications that impact gene expression leading to permanent changes of fetal metabolic pathways and thereby influence development of disease in childhood and adult life. In this study, we investigated the result of maternal food restriction on liver protein expression in Wistar male newborn pups.

Materials & Methods

Ten (n = 10) timed pregnant Wistar rats on their 14th day of gestation were randomly assigned to either control (n = 4) or food restricted group (n = 6). The control group had ad libitum access to food. In the food restricted group, maternal diet was limited in a moderate fashion (50%) from day 15 of pregnancy until delivery. All rats delivered spontaneously on day 21 and newborn pups were immediately weighed. Pups born to normally nourished mothers were considered as controls, while pups born to food restricted mothers were subdivided into two groups, based on their birth weight: growth restricted (FGR) and appropriately grown (non-FGR). Rats were euthanized immediately after birth and liver tissues of 11 randomly selected male offspring (FGR n = 4, non-FGR n = 4, control n = 3) were collected and analyzed using quantitative proteomics.

Results

In total 6,665 proteins were profiled. Of these, 451 and 751 were differentially expressed in FGR and non-FGR vs. control, respectively, whereas 229 proteins were commonly expressed. Bioinformatics analysis of the differentially expressed proteins (DEPs) in FGR vs. control revealed induction of the super-pathway of cholesterol biosynthesis and inhibition of thyroid hormone metabolism, fatty acid beta oxidation and apelin liver signaling pathway. Analysis of DEPs in non-FGR vs. control groups showed inhibition of thyroid hormone metabolism, fatty acid beta oxidation, and apelin liver signaling pathway.

Conclusion

This study demonstrates the impact of prenatal food restriction on the proteomic liver profile of FGR and non-FGR offspring underlying the importance of both prenatal adversities and birth weight on liver-dependent postnatal disease.

Anti-Apoptotic Effect of Apelin in Human Placenta: Studies on BeWo Cells and Villous Explants from Third-Trimester Human Pregnancy

Previously, we demonstrated the expression of apelin and G-protein-coupled receptor APJ in human placenta cell lines as well as its direct action on placenta cell proliferation and endocrinology. The objective of this study was to examine the effect of apelin on placenta apoptosis in BeWo cells and villous explants from the human third trimester of pregnancy. The BeWo cells and villous explants were incubated with apelin (2 and 20 ng/mL) alone or with staurosporine for 24 to 72 h. First, we analysed the dose- and time-dependent effect of apelin on the expression of apoptotic factors on the mRNA level by real-time PCR and on the protein level using Western blot. Next, we checked caspase 3 and 7 activity by Caspase-Glo 3/7, DNA fragmentation by the Cell Death Detection ELISA kit and oxygen consumption by the MitoXpress-Xtra Oxygen Consumption assay. We found that apelin increased the expression of pro-survival and decreased proapoptotic factors on mRNA and protein levels in both BeWo cells and villous explants. Additionally, apelin inhibited caspase 3 and 7 activity and DNA fragmentation in staurosporine-induced apoptosis as also attenuated oxidative stress by increasing extracellular oxygen consumption. The antiapoptotic effect of apelin in BeWo cells was mediated by the APJ receptor and mitogen-activated protein kinase (ERK1/2/MAP3/1) and protein kinase B (AKT). The obtained results showed the antiapoptotic effect of apelin on trophoblast cells, suggesting its participation in the development of the placenta.

Potential pathophysiological role of microRNA 193b-5p in human placentae from pregnancies complicated by preeclampsia and intrauterine growth restriction

Preeclampsia (PE) and intrauterine growth restriction (IUGR) are pregnancy complications resulting from abnormal placental development. MicroRNAs can regulate placental development and contribute to disease, by influencing gene expression. Our previous study revealed an increase in miR-193b-5p expression in placentae from patients with early-onset pregnancy complications and identified candidate gene targets for miR-193b-5p. The purpose of this study is two-fold, first to validate candidate gene targets predicted for miR-193b-5p from microRNA-RNA expression data. Second, to overexpress miR-193b-5p in a trophoblast cell line (HTR-8/SVneo) to assess impact on trophoblast cell proliferation and migration. Integration of the miRNA and RNA sequencing expression data revealed 10 candidate gene targets for miR-193b-5p across all patient groups (PE only, IUGR only, PE + IUGR). Luciferase experiments identified two gene targets for miR-193b-5p, APLN and FGF13. Real-time PCR confirmed a median 45% decrease of FGF13 expression across 3 patient groups, and 50% decrease of APLN expression in patients with PE + IUGR. Following transfection of HTR-8/SVneo cells with miR-193b-5p mimics, APLN and FGF13 mRNA expression in HTR-8/SVneo was reduced by a median percentage of 30% and 45%, respectively. Concomitantly, HTR-8/SVneo cells demonstrate 40% reduction in cell migration. APLN and FGF13 immunoreactivity was identified strongly in the cytotrophoblast cells of the human placentae. These findings suggest that miR-193b-5p may contribute to trophoblast dysfunction observed in pregnancy complications such as PE and IUGR.

Under-carboxylated osteocalcin regulates glucose and lipid metabolism during pregnancy and lactation in rats

PURPOSE

Under-carboxylated osteocalcin (UcOC), a bone-released hormone is suggested to regulate energy metabolism. Pregnancy and lactation physiological conditions that require high levels of energy. The current study attempts to examine whether UcOC is involved in regulating energy metabolism during these conditions using adult Wistar rats.

METHODS AND RESULTS

Insulin tolerance tests indicated insulin resistance during late pregnancy (day 19 of pregnancy; P19) and insulin sensitivity during early lactation (day 6 of lactation; L6). Gene expression analyses suggested that muscle glucose metabolism was downregulated during P19 and enhanced during L6. Concomitantly, circulatory UcOC levels were lower during pregnancy but higher during early lactation; the rise in UcOC levels was tightly linked to the lactation process. Altering endogenous UcOC levels pharmacologically with warfarin and alendronate in P19 and L6 rats changed whole-body insulin response and muscle glucose transporter (Glut4) expression. Glut4 expression can be increased by either UcOC or estrogen receptors (ERs), both of which act independent of each other. A high fat diet decreased UcOC levels and insulin sensitivity in lactating rats, suggesting that diet can compromise UcOC-established energy homeostasis. Gene expression of lipid metabolism markers and triglyceride levels suggested that UcOC suppression during early pregnancy is an essential step in maternal lipid storage.

CONCLUSION

Taken together, we found that UcOC plays an important role in energy homeostasis via regulation of glucose and lipid metabolism during pregnancy and lactation.

Maternal exercise via exerkine apelin enhances brown adipogenesis and prevents metabolic dysfunction in offspring mice

The obesity rate is rapidly increasing, which has been attributed to lack of exercise and excessive energy intake. Here, we found a previously unidentified explanation, due to lack of maternal exercise. In this study, healthy maternal mice were assigned either to a sedentary lifestyle or to exercise daily, and fetal brown adipose tissue (BAT) development and offspring metabolic health were analyzed. Compared to the sedentary group, maternal exercise enhanced DNA demethylation of Prdm16 promoter and BAT development and prevented obesity of offspring when challenged with a high-energy diet. Apelin, an exerkine, was elevated in both maternal and fetal circulations due to exercise, and maternal administration of apelin mimicked the beneficial effects of exercise on fetal BAT development and offspring metabolic health. Together, maternal exercise enhances thermogenesis and the metabolic health of offspring mice, suggesting that the sedentary lifestyle during pregnancy contributes to the obesity epidemic in modern societies.

Apelin/Elabela-APJ: a novel therapeutic target in the cardiovascular system

Apelin and Elabela (ELA) are endogenous ligands of angiotensin domain type 1 receptor-associated proteins (APJ). Apelin/ELA-APJ signal is widely distributed in the cardiovascular system of fetuse and adult. The signal is involved in the development of the fetal heart and blood vessels and regulating vascular tension in adults. This review described the effects of apelin/ELA-APJ on fetal (vasculogenesis and angiogenesis) and adult cardiovascular function [vascular smooth muscle cell (VSMC) proliferation, vasodilation, positive myodynamia], and relative diseases [eclampsia, hypertension, pulmonary hypertension, heart failure (HF), myocardial infarction (MI), atherosclerosis, etc.] in detail. The pathways of apelin/ELA-APJ regulating cardiovascular function and cardiovascular-related diseases are summarized. The drugs developed based on apelin and ELA suggests APJ is a prospective strategy for cardiovascular disease therapy.

Presence and expression of apelin and apelin receptor in bitch placenta

Apelin is a potent inotropic agent causing endothelium-mediated vasodilation and is involved in vessel formation by interacting with a specific receptor. Its cardiovascular profile suggests a role in the regulation of gestational hemodynamic changes. The expression of apelin and its receptor has been reported in some portions of the reproductive tract of different mammalian species. As far as we know, there are no reports describing the expression of apelin and apelin receptor in bitch's placenta. Therefore, the aim of this study was to investigate, for the first time, the presence and distribution of apelin and apelin receptor in bitch placenta by molecular biology and immunohistochemical techniques. Sixteen adult female half-breed bitches were used. The animals were divided into two groups based on the stage of pregnancy: group 1 (mid-gestation n = 8) and group 2 (end gestation n = 8). These bitches were subjected to ovariohysterectomy (group1) or non-conservative caesarean section (group 2). The immunohistochemical technique revealed the presence of positive immune reaction for apelin and apelin receptor in all the samples examined at 30 days and at the end of pregnancy. In particular, apelin and apelin receptor staining was evident in the cytoplasms of cytotrophoblasts and in epithelial cells of the maternal portion. Even if not included into the structure of the placenta, the uterine glands also exhibited a positive immune reaction for apelin and apelin receptor. The RT-PCR analysis showed the presence of transcripts for apelin and apelin receptor in all the placenta samples examined. On the basis of our results it was also possible to hypothesize a potential role of apelin in the control of local placenta blood flow during pregnancy development in bitches.

Involvement of Novel Adipokines, Chemerin, Visfatin, Resistin and Apelin in Reproductive Functions in Normal and Pathological Conditions in Humans and Animal Models

It is well known that adipokines are endocrine factors that are mainly secreted by white adipose tissue. Their central role in energy metabolism is currently accepted. More recently, their involvement in fertility regulation and the development of some reproductive disorders has been suggested. Data concerning the role of leptin and adiponectin, the two most studied adipokines, in the control of the reproductive axis are consistent. In recent years, interest has grown about some novel adipokines, chemerin, visfatin, resistin and apelin, which have been found to be strongly associated with obesity and insulin-resistance. Here, we will review their expression and role in male and female reproduction in humans and animal models. According to accumulating evidence, they could regulate the secretion of GnRH (Gonadotropin-Releasing Hormone), gonadotropins and steroids. Furthermore, their expression and that of their receptors (if known), has been demonstrated in the human and animal hypothalamo-pituitary-gonadal axis. Like leptin and adiponectin, these novel adipokines could thus represent metabolic sensors that are able to regulate reproductive functions according to energy balance changes. Therefore, after investigating their role in normal fertility, we will also discuss their possible involvement in some reproductive troubles known to be associated with features of metabolic syndrome, such as polycystic ovary syndrome, gestational diabetes mellitus, preeclampsia and intra-uterine growth retardation in women, and sperm abnormalities and testicular pathologies in men.

The role of adipokines in developmental programming: evidence from animal models

Alterations in the environment during critical periods of development, including altered maternal nutrition, can increase the risk for the development of a range of metabolic, cardiovascular and reproductive disorders in offspring in adult life. Following the original epidemiological observations of David Barker that linked perturbed fetal growth to adult disease, a wide range of experimental animal models have provided empirical support for the developmental programming hypothesis. Although the mechanisms remain poorly defined, adipose tissue has been highlighted as playing a key role in the development of many disorders that manifest in later life. In particular, adipokines, including leptin and adiponectin, primarily secreted by adipose tissue, have now been shown to be important mediators of processes underpinning several phenotypic features associated with developmental programming including obesity, insulin sensitivity and reproductive disorders. Moreover, manipulation of adipokines in early life has provided for potential strategies to ameliorate or reverse the adverse sequalae that are associated with aberrant programming and provided insight into some of the mechanisms involved in the development of chronic disease across the lifecourse.

Apelin is a novel regulator of human trophoblast amino acid transport

Apelin is an insulin-sensitizing hormone increased in abundance with obesity. Apelin and its receptor, APJ, are expressed in the human placenta, but whether apelin regulates placental function in normal body mass index (BMI) and obese pregnant women remains unknown. We hypothesized that apelin stimulates amino acid transport in cultured primary human trophoblast (PHT) cells and that maternal circulating apelin levels are elevated in obese pregnant women delivering large babies. Treating PHT cells with physiological concentrations of the pyroglutamated form [Pyr¹]apelin-13 (0.1-10.0 ng/ml) for 24 h dose-dependently increased System A amino acid transport (P < 0.05) but did not affect System L transport activity. Mechanistic target of rapamycin (mTOR), extracellular signal-regulated kinase-1/2 (ERK1/2), and AMP-activated protein kinase-α (AMPKα) signaling were unaffected by apelin (P > 0.05). Plasma apelin was not different in obese women (BMI 35.8 ± 0.7, n = 21) with large babies compared with normal-BMI women (23.1 ± 0.5, n = 16) delivering normal birth weight infants. Apelin was highly expressed in placental villous tissue (20-fold higher vs. adipose), and APJ was present in syncytiotrophoblast microvillous membrane, but neither differed in abundance between normal-BMI and obese women. Phosphorylation (Thr¹⁷²) of placental AMPKα strongly correlated with microvillous membrane APJ expression (P < 0.01, R = 0.63) but negatively correlated with placental apelin abundance (P < 0.01, R = -0.62). Neither placental APJ nor apelin abundance correlated with maternal BMI, plasma insulin, birth weight, or mTOR or ERK1/2 signaling (P > 0.05). Hence, apelin stimulates trophoblast amino acid uptake, establishing a novel mechanism regulating placental function. We found no evidence that apelin constitutes an endocrine link between maternal obesity and fetal overgrowth.

Elabela and Apelin actions in healthy and pathological pregnancies

Pregnancy is a dynamic and precisely organized process during which one or more baby develops. Embryonic development relies on the formation of the placenta, allowing nutrient and oxygen exchange between the mother and the fetus. Dysfunction of placental formation lead to pregnancy disorders such as preeclampsia (PE) with serious deleterious consequences for fetal and maternal health. Identifying factors involved in fetoplacental homeostasis could inform better diagnostic and therapeutic strategies for these pathological pregnancies. Here, we summarize actions of elabela, apelin and their common receptor APJ in the fetoplacental unit. Studies indicate that elabela is crucial for embryo cardiovascular system formation and early placental development, while apelin acts in mid/late gestation to modulate fetal angiogenesis and energy homeostasis. Most of these findings, drawn from animal models, indicate a key role of elabela/apelin-APJ system in the fetoplacental unit. This review also provides an overview of clinical studies investigating elabela/apelin-APJ system in pathological complicated pregnancies such as PE and gestational diabetes mellitus (GDM). While elabela-deficient mice display all the features of PE, current clinical studies show no difference in circulating elabela levels between PE and control patients which does not support a role in PE development. Conversely, apelin levels are increased during PE, but the use of apelin as an early PE marker remains to be fully investigated.

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.

Near to One's Heart: The Intimate Relationship Between the Placenta and Fetal Heart

The development of the fetal heart is exquisitely controlled by a multitude of factors, ranging from humoral to mechanical forces. The gatekeeper regulating many of these factors is the placenta, an external fetal organ. As such, resistance within the placental vascular bed has a direct influence on the fetal circulation and therefore, the developing heart. In addition, the placenta serves as the interface between the mother and fetus, controlling substrate exchange and release of hormones into both circulations. The intricate relationship between the placenta and fetal heart is appreciated in instances of clinical placental pathology. Abnormal umbilical cord insertion is associated with congenital heart defects. Likewise, twin-to-twin transfusion syndrome, where monochorionic twins have unequal sharing of their placenta due to inter-twin vascular anastomoses, can result in cardiac remodeling and dysfunction in both fetuses. Moreover, epidemiological studies have suggested a link between placental phenotypic traits and increased risk of cardiovascular disease in adult life. To date, the mechanistic basis of the relationships between the placenta, fetal heart development and later risk of cardiac dysfunction have not been fully elucidated. However, studies using environmental exposures and gene manipulations in experimental animals are providing insights into the pathways involved. Likewise, surgical instrumentation of the maternal and fetal circulations in large animal species has enabled the manipulation of specific humoral and mechanical factors to investigate their roles in fetal cardiac development. This review will focus on such studies and what is known to date about the link between the placenta and heart development.

The Role of Malnutrition during Pregnancy and Its Effects on Brain and Skeletal Muscle Postnatal Development

“Foetal programming” refers to nutritional and hormonal variations during pregnancy. A maternal proper diet has a fundamental role in decreasing pregnancy complications and to prevent possible diseases in postnatal life. In our narrative review, we analyze and discuss the role of malnutrition during pregnancy and its effects on pre- and postnatal development of embryos. Our review proposes a comprehensive and careful analysis of the studies in this field regarding malnutrition and foetal programming. Evidence shows that nutrient imbalance before implantation may result in somatic hypoevolutism at birth, and endocrine and metabolic dysfunctions in postnatal life. In addition, the maternal malnutrition could exert a suppressive effect on the maternal and foetal immune response. It could also affect both the proliferation of myogenic precursors reducing the number of muscle fibres and the future reproductive maturation with possible consequent impaired fertility and quality of gametes. In conclusion, it is necessary to develop dietary strategies to optimize nutrition, not only during pregnancy but already when it is programmed, in order to improve the outcomes of pregnancy, promote growth, healthy child development, reduce the risk of chronic diseases, and slow down the metabolic decline associated with aging.

Apelin/APJ system as a therapeutic target in diabetes and its complications

The G-protein-coupled receptor APJ and its endogenous ligand apelin are widely expressed in many peripheral tissues and central nervous system, including adipose tissue, skeletal muscles and hypothalamus. Apelin/APJ system, involved in numerous physiological functions like angiogenesis, fluid homeostasis and energy metabolism regulation, is notably implicated in the development of different pathologies such as diabetes and its complications. Increasing evidence suggests that apelin regulates insulin sensitivity, stimulates glucose utilization and enhances brown adipogenesis in different tissues associated with diabetes. Moreover, apelin is also involved in the regulation of diabetic complications via binding to APJ receptor. Apelin improves diabetes-induced kidney hypertrophia, normalizes obesity-associated cardiac hypertrophy and negatively promotes retinal angiogenesis in diabetic retinopathy. In this review, we provide a comprehensive overview about the role of apelin/APJ system in different tissues related with diabetes. Furthermore, we describe the pathogenesis of diabetic complications associated with apelin/APJ system. Finally, agonists and antagonists targeted to APJ receptor are described in the literature. Thus, we highlight apelin/APJ system as a novel therapeutic target for pharmacological intervention in treating diabetes and its complications.