Leptin expression in the fetus and placenta during mouse pregnancy

Both endothelial mineralocorticoid receptor expression and hyperleptinemia are required for clinical characteristics of placental ischemia in mice

One of the initiating events in preeclampsia (PE) is placental ischemia. Rodent models of placental ischemia do not present with vascular endothelial dysfunction, a hallmark of PE. We previously demonstrated a role for leptin in endothelial dysfunction in pregnancy in the absence of placental ischemia. We hypothesized that placental ischemia requires hyperleptinemia and endothelial mineralocorticoid receptor (ECMR) expression to induce PE-associated endothelial dysfunction in pregnant mice. We induced placental ischemia via the reduced uterine perfusion pressure (RUPP) procedure in pregnant ECMR-intact (ECMR+/+) and ECMR deletion (ECMR-/-) mice at gestational day (GD) 13. ECMR+/+ RUPP pregnant mice also received concurrent leptin infusion via miniosmotic pump (0.9 mg/kg/day). RUPP increased blood pressure via radiotelemetry and decreased fetal growth in ECMR+/+ pregnant mice. Both increases in blood pressure and reduced fetal growth were abolished in RUPP ECMR-/- mice. Placental ischemia did not decrease endothelial-dependent relaxation to acetylcholine (ACh) but increased phenylephrine (Phe) contraction in mesenteric arteries of pregnant mice, which was ablated by ECMR deletion. Addition of leptin to RUPP mice significantly reduced ACh relaxation in ECMR+/+ pregnant mice, accompanied by an increase in soluble FMS-like tyrosine kinase-1 (sFlt-1)/placental growth factor (PLGF) ratio. In conclusion, our data indicate that high leptin levels drive endothelial dysfunction in PE and that ECMR is required for clinical characteristics of hypertension and fetal growth restriction in placental ischemia PE. Collectively, we show that both ECMR and leptin play a role to mediate PE.NEW & NOTEWORTHY Leptin is a key feature of preeclampsia that initiates vascular endothelial dysfunction in preeclampsia characterized by placental ischemia. Endothelial mineralocorticoid receptor (ECMR) deletion in placental ischemia protects pregnant mice from elevations in blood pressure and fetal growth restriction in pregnancy. Increases in leptin production mediate the key pathological feature of endothelial dysfunction in preeclampsia in rodents. ECMR activation contributes to the increase in blood pressure and fetal growth restriction in preeclampsia.

Neurodevelopmental Programming of Adiposity: Contributions to Obesity Risk

This review analyzes the published evidence regarding maternal factors that influence the developmental programming of long-term adiposity in humans and animals via the central nervous system (CNS). We describe the physiological outcomes of perinatal underfeeding and overfeeding and explore potential mechanisms that may mediate the impact of such exposures on the development of feeding circuits within the CNS-including the influences of metabolic hormones and epigenetic changes. The perinatal environment, reflective of maternal nutritional status, contributes to the programming of offspring adiposity. The in utero and early postnatal periods represent critically sensitive developmental windows during which the hormonal and metabolic milieu affects the maturation of the hypothalamus. Maternal hyperglycemia is associated with increased transfer of glucose to the fetus driving fetal hyperinsulinemia. Elevated fetal insulin causes increased adiposity and consequently higher fetal circulating leptin concentration. Mechanistic studies in animal models indicate important roles of leptin and insulin in central and peripheral programming of adiposity, and suggest that optimal concentrations of these hormones are critical during early life. Additionally, the environmental milieu during development may be conveyed to progeny through epigenetic marks and these can potentially be vertically transmitted to subsequent generations. Thus, nutritional and metabolic/endocrine signals during perinatal development can have lifelong (and possibly multigenerational) impacts on offspring body weight regulation.

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.

Insulin Elevates ID2 Expression in Trophoblasts and Aggravates Preeclampsia in Obese ASB4-Null Mice

Obesity is a risk factor for preeclampsia. We investigated how obesity influences preeclampsia in mice lacking ankyrin-repeat-and-SOCS-box-containing-protein 4 (ASB4), which promotes trophoblast differentiation via degrading the inhibitor of DNA-binding protein 2 (ID2). Asb4^-/- mice on normal chow (NC) develop mild preeclampsia-like phenotypes during pregnancy, including hypertension, proteinuria, and reduced litter size. Wild-type (WT) and Asb4^-/- females were placed on a high-fat diet (HFD) starting at weaning. At the age of 8-9 weeks, they were mated with WT or Asb4^-/- males, and preeclamptic phenotypes were assessed. HFD-WT dams had no obvious adverse outcomes of pregnancy. In contrast, HFD-Asb4^-/- dams had significantly more severe preeclampsia-like phenotypes compared to NC-Asb4^-/- dams. The HFD increased white fat weights and plasma leptin and insulin levels in Asb4^-/- females. In the HFD-Asb4^-/- placenta, ID2 amounts doubled without changing the transcript levels, indicating that insulin likely increases ID2 at a level of post-transcription. In human first-trimester trophoblast HTR8/SVneo cells, exposure to insulin, but not to leptin, led to a significant increase in ID2. HFD-induced obesity markedly worsens the preeclampsia-like phenotypes in the absence of ASB4. Our data indicate that hyperinsulinemia perturbs the timely removal of ID2 and interferes with proper trophoblast differentiation, contributing to enhanced preeclampsia.

Trajectory of leptin and leptin receptor in vertebrates: Structure, function and their regulation

The present review provides a comparative insight into structure, function and control of leptin system in fishes, herptiles, birds and mammals. In general, leptin acts as an anorexigenic hormone since its administration results in decrease of food intake in vertebrates. Nonetheless, functional paradox arises in fishes from contradictory observations on level of leptin during fasting and re-feeding. In addition, leptin is shown to modulate metabolic functions in fishes, reptiles, birds and mammals. Leptin also regulates reproductive and immune functions though more studies are warranted in non-mammalian vertebrates. The expression of leptin and its receptor is influenced by numerous factors including sex steroids, stress and stress-induced catecholamines and glucocorticoids though their effect in non-mammalian vertebrates is hard to be generalized due to limited studies.

Pregnancy-induced changes in β-cell function: what are the key players?

Maternal metabolic adaptations during pregnancy ensure appropriate nutrient supply to the developing fetus. This is facilitated by reductions in maternal peripheral insulin sensitivity, which enables glucose to be available in the maternal circulation for transfer to the fetus for growth. To balance this process and avoid excessive hyperglycaemia and glucose intolerance in the mother during pregnancy, maternal pancreatic β-cells undergo remarkable changes in their function including increasing their proliferation and glucose-stimulated insulin secretion. In this review we examine how placental and maternal hormones work cooperatively to activate several signalling pathways, transcription factors and epigenetic regulators to drive adaptations in β-cell function during pregnancy. We also explore how adverse maternal environmental conditions, including malnutrition, obesity, circadian rhythm disruption and environmental pollutants, may impact the endocrine and molecular mechanisms controlling β-cell adaptations during pregnancy. The available data from human and experimental animal studies highlight the need to better understand how maternal β-cells integrate the various environmental, metabolic and endocrine cues and thereby determine appropriate β-cell adaptation during gestation. In doing so, these studies may identify targetable pathways that could be used to prevent not only the development of pregnancy complications like gestational diabetes that impact maternal and fetal wellbeing, but also more generally the pathogenesis of other metabolic conditions like type 2 diabetes.

Expression of a hypomorphic Pomc allele alters leptin dynamics during late pregnancy

Proopiomelanocortin (POMC) neurons in the hypothalamic arcuate nucleus (ARC) are essential for normal energy homeostasis. Maximal ARC Pomc transcription is dependent on neuronal Pomc enhancer 1 (nPE1), located 12 kb upstream from the promoter. Selective deletion of nPE1 in mice decreases ARC Pomc expression by 70%, sufficient to induce mild obesity. Because nPE1 is located exclusively in the genomes of placental mammals, we questioned whether its hypomorphic mutation would also alter placental Pomc expression and the metabolic adaptations associated with pregnancy and lactation. We assessed placental development, pup growth, circulating leptin and expression of Pomc, Agrp and alternatively spliced leptin receptor (LepR) isoforms in the ARC and placenta of Pomc∆1/∆1 and Pomc+/+ dams. Despite indistinguishable body weights, lean mass, food intake, placental histology and Pomc expression and overall pregnancy outcomes between the genotypes, Pomc ∆1/∆1 females had increased pre-pregnancy fat mass that paradoxically decreased to control levels by parturition. However, Pomc∆1/∆1 dams had exaggerated increases in circulating leptin, up to twice of that of the typically elevated levels in Pomc+/+ mice at the end of pregnancy, despite their equivalent fat mass. Pomc∆1/∆1dams also had increased placental expression of soluble leptin receptor (LepRe), although the protein levels of LEPRE in circulation were the same as Pomc+/+ controls. Together, these data suggest that the hypomorphic Pomc∆1/∆1 allele is responsible for the perinatal super hyperleptinemia of Pomc∆1/∆1 dams, possibly due to upregulated leptin secretion from individual adipocytes.

Perinatal depression: Heterogeneity of disease and in animal models

Perinatal depression (PND) can have either an antepartum or postpartum onset. Although the greatest risk factor for PND is previous depression history,de novoPND occurs with the majority of cases occurring in the postpartum. Timing of depression can impact etiology, prognosis, and response to treatment. Thus, it is crucial to study the impact of the heterogeneity of PND for better health outcomes. In this review, we outline the differences between antepartum and postpartum depression onset of PND. We discuss maternal physiological changes that differ between pregnancy and postpartum and how these may differentially impact depression susceptibility. We highlight changes in the maternal steroid and peptide hormone levels, immune signalling, serotonergic tone, metabolic factors, brain morphology, and the gut microbiome. Finally, we argue that studying the heterogeneity of PND in clinical and preclinical models can lead to improved knowledge of disease etiopathology and treatment outcomes.

Genetics of recurrent pregnancy loss among Iranian population

Background

Recurrent pregnancy loss (RPL) is one of the most common reproductive disorders which is defined as the occurrence of recurrent miscarriage before 24 weeks of gestation and is observed among 1%–5% of women.

Methods

Various factors are associated with RPL such as immunological disorders, maternal age, obesity, alcohol, chromosomal abnormality, endocrine disorders, and uterine abnormalities. About half of the RPL cases are related with chromosomal abnormalities. Therefore, RPL genetic tests are mainly limited to karyotyping. However, there is a significant proportion of RPL cases without any chromosomal abnormalities that can be related to the single‐gene aberrations. Therefore, it is required to prepare a diagnostic panel of genetic markers besides karyotyping.

Results

In the present review, we have summarized all the significant reported genes until now which are associated with RPL among Iranian women. We categorized all the reported genes based on their cellular and molecular functions in order to determine the molecular bases of RPL in this population.

Conclusion

This review paves the way of introducing a population‐based diagnostic panel of genetic markers for the first time among Iranian RPL cases. Moreover, this review clarifies the genetic and molecular bases of RPL in this population.

The Role of Placental Hormones in Mediating Maternal Adaptations to Support Pregnancy and Lactation

During pregnancy, the mother must adapt her body systems to support nutrient and oxygen supply for growth of the baby in utero and during the subsequent lactation. These include changes in the cardiovascular, pulmonary, immune and metabolic systems of the mother. Failure to appropriately adjust maternal physiology to the pregnant state may result in pregnancy complications, including gestational diabetes and abnormal birth weight, which can further lead to a range of medically significant complications for the mother and baby. The placenta, which forms the functional interface separating the maternal and fetal circulations, is important for mediating adaptations in maternal physiology. It secretes a plethora of hormones into the maternal circulation which modulate her physiology and transfers the oxygen and nutrients available to the fetus for growth. Among these placental hormones, the prolactin-growth hormone family, steroids and neuropeptides play critical roles in driving maternal physiological adaptations during pregnancy. This review examines the changes that occur in maternal physiology in response to pregnancy and the significance of placental hormone production in mediating such changes.

Exercise during pregnancy and its impact on mothers and offspring in humans and mice

Exercise during pregnancy has beneficial effects on maternal and offspring’s health in humans and mice. The underlying mechanisms remain unclear. This comparative study aimed to determine the long-term effects of an exercise program on metabolism, weight gain, body composition and changes in hormones [insulin, leptin, brain-derived neurotrophic factor (BDNF)]. Pregnant women (n=34) and mouse dams (n=44) were subjected to an exercise program compared with matched controls (period I). Follow-up in the offspring was performed over 6 months in humans, corresponding to postnatal day (P) 21 in mice (period II). Half of the mouse offspring was challenged with a high-fat diet (HFD) for 6 weeks between P70 and P112 (period III). In period I, exercise during pregnancy led to 6% lower fat content, 40% lower leptin levels and an increase of 50% BDNF levels in humans compared with controls, which was not observed in mice. After period II in humans and mice, offspring body weight did not differ from that of the controls. Further differences were observed in period III. Offspring of exercising mouse dams had significantly lower fat mass and leptin levels compared with controls. In addition, at P112, BDNF levels in offspring were significantly higher from exercising mothers while this effect was completely blunted by HFD feeding. In this study, we found comparable effects on maternal and offspring’s weight gain in humans and mice but different effects in insulin, leptin and BDNF. The long-term potential protective effects of exercise on biomarkers should be examined in human studies.

The source of leptin, but not leptin depletion in response to food restriction, changes during early pregnancy in mice

Maternal food restriction during pregnancy results in adverse consequences for offspring, including obesity and cardiovascular disease. Early pregnancy is a critical period for this programming effect. Leptin is a regulator of energy homeostasis that also affects placental and fetal development. As food restriction results in decreased serum leptin levels, at least in non-pregnant animals, leptin depletion may be one mechanism by which food restriction affects development. The objective of this study was to test whether moderate food restriction affects serum leptin concentrations during the first half of pregnancy. We found that restriction to 50% of ad libitum consumption levels resulted in a significant decrease in serum leptin concentrations in both pregnant and non-pregnant female mice. There was no significant difference in serum leptin concentrations between non-pregnant females and at pregnancy day 11.5 when fed ad libitum. However, there was a difference in the source of leptin during pregnancy, with greater production in visceral fat in pregnant mice, and greater production in subcutaneous fat in non-pregnant mice. Leptin concentrations were dependent on time of day and time of sampling relative to feeding, particularly in restricted mice. There was a significant difference in serum leptin concentrations between fed and restricted mice when they were fed and sampled in afternoon, but not when they were fed and sampled in morning. We conclude that food restriction results in a significant decrease in leptin concentration during the first half of pregnancy in mice, but that detection of this relationship is subject to experimental design considerations.

The prolonged effect of repeated maternal glucocorticoid exposure on the maternal and fetal leptin/insulin-like growth factor axis in Papio species

BACKGROUND

Maternal obesity represents a risk factor for pregnancy-related complications. Glucocorticoids are known to promote obesity in adults.

METHODS

We evaluated maternal and fetal metabolic changes during and after 3 weekly courses of betamethasone administered to pregnant baboons (Papio subspecies) at doses equivalent to those given to pregnant women.

RESULTS

Betamethasone administration during the second half of pregnancy increased maternal weight but neither maternal food intake nor fetal weight, as assessed at the end of gestation. Betamethasone increased maternal serum glucose concentration, the ratio of insulin-like growth factor-I and insulin-like growth factor binding protein-3, and serum leptin during treatment (normalized by 17, 35, and 45 days posttreatment, respectively, for each parameter). Maternal and fetal serum leptin concentrations did not differ between groups at the end of gestation.

CONCLUSION

Prolonged maternal hyperleptinemia caused by betamethasone administration in the second half of gestation did not change fetal metabolic parameters measured and placental leptin distribution at the end of gestation.

Different physiological roles of serum leptin in the regulation of energy intake and thermogenesis between pregnancy and lactation in primiparous Brandt's voles (Lasiopodomys brandtii)

Reproduction, especially lactation, is associated with major metabolic adaptive changes. In this study, we investigated the metabolic changes and the roles of leptin during different periods of reproduction in primiparous Brandt's voles (Lasiopodomys brandtii). Energy intake, thermogenic capacity and serum leptin levels were examined in non-reproductive, mid pregnant, late pregnant, early lactating and peak lactating voles. Voles increased body mass by nearly 70% during late pregnancy compared to the non-breeding controls. The increase in body mass was mainly due to the increase in body fat mass which increased by 56%, and the growth of the reproductive tissues and digestive organs. Lactating voles decreased body fat by nearly 27% at peak lactation compared to the controls, and 53% compared to late pregnant voles. At the same time they increased food intake significantly. Uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT) decreased significantly at peak lactation. Serum leptin increased significantly in the mid pregnancy, at a time when there was no increase in body fat, and remained at this high level in late pregnancy. Leptin levels decreased after parturition and reached a nadir at peak lactation. Serum leptin was negatively correlated with energy intake during lactation, but not during pregnancy. These data suggest that Brandt's voles adjust energy intake, thermogenic capacity and body reserves to match the high energy demands for reproduction. Hyperleptinemia, without decreased energy intake suggests a state of leptin resistance during pregnancy, and hypoleptinemia during lactation might act as a signal to stimulate energy intake.

Leptin resistance during pregnancy in the rat

The adipose-derived hormone leptin primarily acts in the hypothalamus to decrease appetite and increase energy expenditure, thereby maintaining body fat levels around a set point. Pregnancy is a physiological state where this feedback mechanism is not beneficial. Successful reproductive efforts are highly demanding on the resources of the mother; thus, it is imperative that the maternal body can increase energy stores without restraint. Food intake, fat mass and serum leptin concentrations increase during pregnancy in the rat, suggesting that the feedback loop between adipose tissue and appetite is disrupted and a state of leptin resistance exists. In support of this, there is an attenuation of the satiety response to exogenous leptin administration in pregnant rats. This state of leptin resistance is associated with impaired activation of the leptin-induced Janus activating kinase (JAK)/signal transducer and activator of transcription (STAT) signalling pathway in the ventromedial nucleus of the hypothalamus (VMH) and arcuate nucleus, and reduced expression of leptin receptor mRNA in the VMH. Furthermore, pregnant rats do not show a satiety response to exogenous alpha-melanocyte stimulating hormone. This model offers the possibility of examining how hypothalamic leptin signalling can be modified in response to changes in physiological conditions.

Inhibition of trophoblast invasiveness in vitro by immunoneutralization of leptin in the bat, Myotis lucifugus (Chiroptera)

In addition to effects on metabolism and appetite, leptin is a reproductive hormone produced and secreted by the placenta of many, but not all mammalian species. In mice, in which the placenta does not secrete leptin, exogenously added leptin stimulates invasiveness of early (but not late)-gestation trophoblast cells. We report a similar phenomenon occurs in Myotis lucifugus (little brown myotis), a species in which the placenta synthesizes and secretes leptin. Immunoneutralization of endogenously secreted leptin from cultured M. lucifugus trophoblast cells inhibited the ability of these cells to invade a matrigel matrix. The effect was not due to an inhibitory effect of the antibody on cell proliferation, nor was it a non-specific effect of antibody administration. Cell invasion was significantly reduced in untreated cells obtained from late-gestation placentas, and the antibody had no effect at that time. This occurred despite continued expression throughout gestation of the long (OBRb) and short (OBRa) isoforms of leptin receptor mRNA. This study suggests that an important function of leptin during pregnancy is an effect on trophoblast cell invasiveness, at a time when the placenta is becoming established. That this occurs in two phylogenetically unrelated and distant species, regardless of whether the placenta is a source of secreted leptin, suggests that this is a highly conserved reproductive action of leptin.

The role of the leptin in reproduction

PURPOSE OF REVIEW

Since its discovery in 1994, leptin has appeared to be a pleiotrophic hormone, governing energy homeostasis and affecting many tissues in the body. Numerous pieces of evidence have accumulated showing that leptin potentially plays an important role in the control of the reproductive function.

RECENT FINDINGS

This review presents the major concepts for the role of leptin in the modulation of reproductive function. As a marker of the nutritional status, leptin affects the hypothalamo-pituitary-gonadal axis, regulating gonadotrophin-releasing hormone and luteinising hormone secretion, and appears to be a permissive factor in the onset of the puberty. This protein and its receptor have been found in the reproductive tissues, indicating that this system could be also implicated in several processes such as embryo development, implantation and pregnancy. Moreover, disorders of the leptin system have been related to some reproductive pathologies such as pre-eclampsia and polycystic ovary syndrome. However, controversy surrounds several aspects of the action of leptin in reproduction that require a deeper investigation of this system.

SUMMARY

Results to date suggest that this system could be implicated in important reproductive processes such as embryonic development and implantation. Moreover, understanding the role of leptin might be useful for new treatments in reproductive pathologies.

Leptin in pregnancy: an update

Leptin influences satiety, adiposity, and metabolism and is associated with mechanisms regulating puberty onset, fertility, and pregnancy in various species. Maternal hyperleptinemia is a hallmark of mammalian pregnancy, although both the roles of leptin and the mechanisms regulating its synthesis appear to be taxa specific. In pregnant humans and nonhuman primates, leptin is produced by both maternal and fetal adipose tissues, as well as by the placental trophoblast. Specific receptors in the uterine endometrium, trophoblast, and fetus facilitate direct effects of the polypeptide on implantation, placental endocrine function, and conceptus development. A soluble isoform of the receptor may be responsible for inducing maternal leptin resistance during pregnancy and/or may facilitate the transplacental passage of leptin for the purpose of directly regulating fetal development. The steroid hormones are linked to the regulation of leptin and the leptin receptor and probably interact with other pregnancy-specific, serum-borne factors to regulate leptin dynamics during pregnancy. In addition to its effects on normal conceptus development, leptin is linked to mechanisms affecting a diverse array of pregnancy-specific pathologies that include preeclampsia, gestational diabetes, and intrauterine growth restriction. Association with these anomalies and with mechanisms pointing to a fetal origin for a range of conditions affecting the individual's health in adult life, such as obesity, diabetes mellitus, and cardiovascular disease, reiterate the need for continued research dedicated to elucidating leptin's roles and regulation throughout gestation.