Maternal obesity alters the apelinergic system at the feto-maternal interface

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.

The investigation of apelin and apelin receptor expressions in mouse endometrium during peri-implantation period

BACKGROUND

Fertilization, pre-implantation embryo development, implantation, and decidualization are critical for a healthy pregnancy. Successful implantation requires a competent blastocyst and a receptive uterus. Apelin was purified from the bovine stomach in 1998. Apelin receptor (APJ) is a member of G protein-coupled receptors. Apelin/APJ system's physiological role was shown in cardiovascular system, immune response, stress response, fluid regulation, nutrient uptake, angiogenesis, and adipoinsular axis; however, whether apelin/APJ system plays a role in implantation is unknown. In our study, we aimed to evaluate the localization and expressions of the apelin/APJ system in the peri-implantation period mouse uterus.

METHODS

Uteri and implantation sites were collected from mice on the estrous phase and the 1st, 4th, 5th, 6th, and 8th days of pregnancy. Also, inter-implantation sites were collected from the 5th day of the pregnancy group. Localization and expressions of apelin and APJ were determined by immunohistochemistry and Western blot, respectively.

RESULTS

Apelin and APJ were expressed in the luminal and gland epithelium, the stroma of all experimental groups. Two isoforms of apelin-8 and 16 kDa were detected by Western blot. While apelin expression increased from the estrous to the 8th day of pregnancy, APJ expression increased from the estrous to the 4th day of pregnancy, reached the highest expression level, then decreased.

CONCLUSIONS

Our findings suggest that the apelin/APJ system might be involved in implantation and decidualization. Our findings will guide further studies and may help elucidate the underlying causes of implantation failure and pregnancy loss.

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% VO_2max 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% VO_2max 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.

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.

Breast milk apelin level increases with maternal obesity and high-fat feeding during lactation

OBJECTIVE

Recent evidence indicates that levels of breast milk (BM) hormones such as leptin can fluctuate with maternal adiposity, suggesting that BM hormones may signal maternal metabolic and nutritional environments to offspring during postnatal development. The hormone apelin is highly abundant in BM but its regulation during lactation is completely unknown. Here, we evaluated whether maternal obesity and overnutrition impacted BM apelin and leptin levels in clinical cohorts and lactating rats.

METHODS

BM and plasma samples were collected from normal-weight and obese breastfeeding women, and from lactating rats fed a control or a high fat (HF) diet during lactation. Apelin and leptin levels were assayed by ELISA. Mammary gland (MG) apelin expression and its cellular localization in lactating rats was measured by quantitative RT-PCR and immunofluorescence, respectively.

RESULTS

BM apelin levels increased with maternal BMI, whereas plasma apelin levels decreased. BM apelin was also positively correlated with maternal insulin and C-peptide levels. In rats, maternal HF feeding exclusively during lactation was sufficient to increase BM apelin levels and decrease its plasma concentration without changing body weight. In contrast, BM leptin levels increased with maternal BMI in humans, but did not change with maternal HF feeding during lactation in rats. Apelin is highly expressed in the rat MG during lactation and was mainly localized to mammary myoepithelial cells. We found that MG apelin gene expression was up-regulated by maternal HF diet and positively correlated with BM apelin content and maternal insulinemia.

CONCLUSIONS

Our study indicates that BM apelin levels increase with long- and short-term overnutrition, possibly via maternal hyperinsulinemia and transcriptional upregulation of MG apelin expression in myoepithelial cells. Apelin regulates many physiological processes, including energy metabolism, digestive function, and development. Further studies are needed to unravel the consequences of such changes in offspring development.

Circulating levels of Elabela and Apelin in the second and third trimesters of pregnancies with gestational diabetes mellitus

We design this study to detect levels of Elabela (ELA) and Apelin (APLN) in women with and without gestational diabetes mellitus (GDM) in the second and third trimesters, and to identify whether there is any association between ELA, APLN, and metabolic parameters. Seventy-nine GDM and 80 control subjects in the second trimester and 87 GDM and 88 healthy subjects in the third trimester were included. In the second trimester, lower ELA levels [(14.1 versus 16.9) ng/ml, p = .025] and higher APLN levels [(1021.8 versus 923.5) pg/ml, p = .046] were observed in GDM patients compared to controls. ELA levels were positively correlated with fasting plasma glucose (FPG) (r = 0.423, p < .001) in the control group, and APLN levels were negatively correlated with triglycerides (TG) (r = -0.251, p = .025) in the control group and total cholesterol (TC) (r = -0.227, p = .044) in the GDM group. ELA appeared to be related to glucose metabolism and APLN is involved in lipid metabolism during pregnancy. The expression of ELA is significantly downregulated from the second trimester to the third trimester.

Apelin and apelin receptor in human placenta: Expression, signalling pathway and regulation of trophoblast JEG‑3 and BeWo cells proliferation and cell cycle

Placentation requires the production of numerous growth factors, hormones and transcription factors. Many of them, like the adipose tissue-derived leptin or adiponectin, have been identified in the placenta and their role has been established in the proliferation and subsequent development of the placenta. Apelin is another adipokine known for proliferative effects in different cell types. PCR, immunoblotting and immunocytochemistry were used to study mRNA and protein expression of apelin and its receptor (APJ) in syncytiotrophoblast (BeWo) and cytotrophoblast (JEG-3) cells as well in immunohistochemistry in human normal placenta slides. The effect of apelin on cell proliferation study was investigated by alamarBlue^® and Cell Counting Kit-8 assays, the cell cycle by the flow cytometry method and the protein expression of cyclins and phosphorylation level of extracellular signal-regulated kinases (ERK)1/2, phosphatidylinositol 3′-kinase/protein kinase B (Akt), signal transducer and activator of transcription 3 (Stat3) and 5′-monophosphate-activated protein kinase (AMPKα) were studied by western blotting. Apelin was increased in JEG-3 compared with in BeWo cells, while APJ was the same in both placenta cell lines. Immunocytochemical analyses revealed high cytoplasmic and/or membrane apelin localisation in JEG-3, while BeWo cells exhibited markedly weaker apelin signal in the cytoplasm. Apelin increased cell proliferation as well as the percentage of cells in the G2/M phase of the cell cycle, cyclin proteins and the expression of all kinases mentioned above. In conclusion, apelin by promotion of trophoblast cell proliferation by APJ and ERK1/2, Stat3 and AMPKα signalling could be a new important adipokine in the regulation of early placental development.

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.

[Sport: A key element for myometrial contractility and regulation of adipokines in obese pregnant women?]

Obesity is a major public health problem. Pregnant women are also affected by this epidemic. In pregnant women, obesity increases obstetric and neonatal complications, and is associated with alterations in the quality of labor that could be explained by reduced myometrial contractility. This leads to an increase in the rate of caesarean sections and postpartum haemorrhages in this population at risk. Adipokines, hormones secreted by adipose tissue, may have a role in altering the myometrial contractility. Weight loss in these patients is based on dietary management and on physical activity, which could be a way to improve adipokines action and uterine contractility. The objective of this literature review was to review current knowledge about the role of adipokines on uterine contractility in obese pregnant women and to assess the interest of sport in improving contractility and in reducing obstetric complications in these women.