Direct Effects of Leptin on Mouse Reproductive Function: Regulation of Follicular, Oocyte, and Embryo Development

Leptin- and cytokine-like unpaired signaling in Drosophila

Animals have evolved a multitude of signaling pathways that enable them to orchestrate diverse physiological processes to tightly regulate systemic homeostasis. This signaling is mediated by various families of peptide hormones and cytokines that are conserved across the animal kingdom. In this review, we primarily focus on the unpaired (Upd) family of proteins in Drosophila which are evolutionarily related to mammalian leptin and the cytokine interleukin 6. We summarize expression patterns of Upd in Drosophila and discuss the parallels in structure, signaling pathway, and functions between Upd and their mammalian counterparts. In particular, we focus on the roles of Upd in governing metabolic homeostasis, growth and development, and immune responses. We aim to stimulate future studies on leptin-like signaling in other phyla which can help bridge the evolutionary gap between insect Upd and vertebrate leptin and cytokines like interleukin 6.

Metabolic hormones are integral regulators of female reproductive health and function

The female reproductive system is strongly influenced by nutrition and energy balance. It is well known that food restriction or energy depletion can induce suppression of reproductive processes, while overnutrition is associated with reproductive dysfunction. However, the intricate mechanisms through which nutritional inputs and metabolic health are integrated into the coordination of reproduction are still being defined. In this review, we describe evidence for essential contributions by hormones that are responsive to food intake or fuel stores. Key metabolic hormones-including insulin, the incretins (glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1), growth hormone, ghrelin, leptin, and adiponectin-signal throughout the hypothalamic-pituitary-gonadal axis to support or suppress reproduction. We synthesize current knowledge on how these multifaceted hormones interact with the brain, pituitary, and ovaries to regulate functioning of the female reproductive system, incorporating in vitro and in vivo data from animal models and humans. Metabolic hormones are involved in orchestrating reproductive processes in healthy states, but some also play a significant role in the pathophysiology or treatment strategies of female reproductive disorders. Further understanding of the complex interrelationships between metabolic health and female reproductive function has important implications for improving women's health overall.

The intrafollicular concentration of leptin as a potential biomarker to predict oocyte maturity in in-vitro fertilization

Oocyte maturity is critical to the development potential of the embryo and pregnancy outcomes in natural and in-vitro fertilization (IVF). In IVF, oocyte maturity is typically evaluated using morphological criteria, although such assessment remains highly subjective. To identify reliable biomarkers of oocyte maturity, this study investigates the relationship between follicular cytokine concentrations and oocyte maturity in IVF patients with different ovarian reserves. In this prospective study, follicular fluid was collected during oocyte retrieval and the concentrations of cytokines involved in ovarian folliculogenesis were determined. Follicular fluid cytokine concentrations were compared between participants in three groups according to serum anti-Mullerian hormone (AMH) concentration, as follows: low AMH, < 2 ng/mL; normal AMH, 2-5 ng/mL; and high AMH, > 5 ng/mL. Pearson's correlation coefficient analysis showed that the number of mature oocytes correlated positively and strongly with serum AMH level (r = 0.719; p < 0.01). The leptin concentration in follicular fluid was significantly higher in women with normal AMH level than in those with low or high levels. ROC curve analysis showed that the follicular fluid levels of leptin (area under ROC curve, 0.829; 95% confidence interval, 0.659-0.998; p < 0.01) and SCF (area under ROC curve, 0.706; 95% confidence interval, 0.491-0.921; p = 0.087) were the best predictors of oocyte maturity. At an optimal cut-off value of 16 ng/mL, leptin had positive predictive value (sensitivity) up to 70% and negative predictive value (specificity) of 91% for indicating oocyte maturity. The concentration of leptin in follicular fluid is closely related to ovarian reserve and may serve as a biomarker to predict oocyte maturity.

Deficiency of C1QL1 Reduced Murine Ovarian Follicle Reserve Through Intraovarian and Endocrine Control

Ovarian aging is associated with depletion of the ovarian follicle reserve, which is the key determinant of fertility potential in females. In this study, we found that the small, secreted protein complement 1Q-like (C1QL1) is involved in the regulation of follicle depletion through intraovarian and endocrine control in a multidimensional collaborative manner. C1ql1 was detected to be conserved in the ovary and showed high transcript levels during folliculogenesis. Blockade of C1QL1 by IP and ovarian intrabursal injection of C1QL1 antiserum into prepubertal mice impaired folliculogenesis accompanied by reductions in body weight, fat mass, and intraovarian lipid accumulation. An elevation of circulating estradiol levels, reduction of hypothalamic KISS1 and GnRH expression, and a decrease in serum FSH levels were found in C1QL1-deficient mice. In C1QL1-deficient ovaries, many primordial follicles were recruited and developed into medium follicles but underwent atresia at the large follicle stages, which resulted in depletion of follicle reserve. Depletion of C1QL1 alleviated the inhibitory effect of C1QL1 on granulosa cell apoptosis and the stimulatory effect of C1QL1 on granulosa cell autophagy, which resulted in accumulation in the preantral and early antral follicles and an increase in the atretic follicles. The abnormal profile of endocrine hormones accelerated the intraovarian effect of C1QL1 deficiency and further led to depletion of ovarian reserve. Altogether, this study revealed the expression patterns and the mechanism of action of C1QL1 during folliculogenesis and demonstrated that deficiency of C1QL1 caused ovarian follicular depletion.

The effects of high intensity-interval training on vaspin, adiponectin and leptin levels in women with polycystic ovary syndrome

AIM

We aimed to investigate the metabolic effects of HIIT exercise on PCOS patients and how it affects adiponectin, vaspin and leptin.

MATERIAL AND METHODS

Twenty women with PCOS were included in the study and were divided into two groups. HIIT program was applied for 10 PCOS and Medium Intensity Continuous Training (MICT) program was applied for other 10 PCOS. At the beginning and at the end of the study, total cholesterol, low-density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), triglyceride(TG), insulin, Adiponectin, Leptin, Vaspin levels of both PCOS groups were evaluated.

RESULTS

When PCOS patients by performed HIIT exercise for 12 weeks, we found that the levels of leptin and vaspin did not change while adiponectin levels increased. Moreover serum levels of insulin, TG, total cholesterol, LDL-C decreased but levels of HDL-C increased.

CONCLUSION

HIIT increased in the adiponectin levels in women with PCOS and provided more weight loss.

Leptin improves in-vitro maturation of goat oocytes through MAPK and JAK2/STAT3 pathways and affects gene expression of cumulus cells

We investigated whether the recombinant leptin (1, 10, 100 ng/mL) influences the meiotic maturation of goat oocytes, whether the MAPK and JAK2/STAT3 pathways mediate the effects of leptin during in-vitro maturation, and whether leptin differently affects the abundance of mRNAs relevant to leptin signal transduction and apoptosis in oocytes and cumulus cells. The addition of leptin to the maturation medium positively affected the number of oocytes that completed nuclear maturation. Nuclear oocyte maturation stimulated by leptin was significantly impaired when we added the specific inhibitors of MAPK (U0126) and JAK2/STAT3 (AG490) to the maturation medium. The addition of leptin (10 ng/mL) during maturation did not affect the expression of AMPKα1, PPARα, Caspase 3, and BCL2 genes in oocytes or cumulus cells. The PPARγ and BAX mRNA abundances were significantly reduced in cumulus cells in the leptin group compared to the control group. Our results demonstrate that supplementation of the in-vitro maturation medium with leptin significantly improves nuclear maturation and reveal the important role of the MAPK and JAK2/STAT3 signaling pathways in establishing the leptin-mediated nuclear maturation of goat oocytes. Moreover, leptin treatment affects PPARγ and BAX gene expression in cumulus cells.

Effect of reproductive and lifestyle factors on anti-mullerian hormone levels in women of Indian origin

Background:

Infertility is a world-wide problem and one third females. Over the years, anti-mullerian hormone (AMH) has emerged as a major marker of ovarian reserve. There is also increasing interest in determining the factors which can impact AMH levels.

Aims:

To correlate the association of reproductive and lifestyle factors on AMH levels in women of Indian origin.

Settings and Design:

Multicentric cross sectional study.

Materials and Methods:

The study was conducted using data extracted from the patient records of seven private fertility practices located in North India. Women who were attending these clinics for fertility treatment were requested to fill the questionnaire related to reproductive and lifestyle factors.

Statistical Analysis used:

Our outcome variable was level of AMH measured in the past 3 months, and was assessed as normal or low. All analyses were conducted using STATA 17.

Results:

We found a direct association of low AMH with increasing age, short cycles, amenorrhea and women with family history of premature menopause. We found a direct correlation of high AMH and women with polycystic ovary syndrome and those whose partners had Oligoasthenoteratozoospermia (OATS) or azoospermia. There was no correlation with smoking, sleep, diet, body mass index, cell phone or laptop use in our study.

Conclusion:

Reproductive and lifestyle factors may affect ovarian reserve and but there was a dearth of human studies in this area. To the best of our knowledge this is the first human study on the effect of AMH on Laptop and Cell phone use. We urgently need more studies to confirm or refute our findings so that we can counsel our patients well.

Metabolic Syndrome in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common endocrinopathy in women of reproductive age. Although its essential clinical manifestation includes a plethora of symptoms and signs, which largely reflects the underlying hyperandrogenism, oligo/anovulation, and polycystic ovarian morphology, PCOS may also be associated with many metabolic derangements. These metabolic derangements happen to overlap with many of the core constituents of the metabolic syndrome (MBS)—increased insulin resistance, central obesity, and dyslipidemia. The two disorders also display similarly increased risks for certain metabolic and vascular diseases, such as type 2 diabetes mellitus, hypertension, and cardiovascular diseases. Due to the many similarities between metabolic syndrome and PCOS, this review aims to examine the evidence concerning the overlapping features, the risks for comorbidities, possible shared mechanisms, and treatment strategies in patients with coexisting PCOS and MBS.

Fibroinflammatory Signatures Increase with Age in the Human Ovary and Follicular Fluid

The female reproductive system ages before any other organ system in the body. This phenomenon can have tangible clinical implications leading to infertility, miscarriages, birth defects and systemic deterioration due to estrogen loss. “Fibroinflammation” is a hallmark of aging tissues; there is an increase in inflammatory cytokines and fibrotic tissue in the aging ovarian stroma. We systematically evaluated immunomodulatory factors in human follicular fluid, which, like the stroma, is a critical ovarian microenvironment directly influencing the oocyte. Using a cytokine antibody array, we identified a unique fibroinflammatory cytokine signature in follicular fluid across an aging series of women (27.7–44.8 years). This signature (IL-3, IL-7, IL-15, TGFβ1, TGFβ3 and MIP-1) increased with chronologic age, was inversely correlated to anti-Müllerian hormone (AMH) levels, and was independent of body mass index (BMI). We focused on one specific protein, TGFβ3, for further validation. By investigating this cytokine in human cumulus cells and ovarian tissue, we found that the age-dependent increase in TGFβ3 expression was unique to the ovarian stroma but not other ovarian sub-compartments. This study broadens our understanding of inflammaging in the female reproductive system and provides a defined fibroinflammatory aging signature in follicular fluid and molecular targets in the ovary with potential clinical utility.

Revisiting the Impact of Local Leptin Signaling in Folliculogenesis and Oocyte Maturation in Obese Mothers

The complex nature of folliculogenesis regulation accounts for its susceptibility to maternal physiological fitness. In obese mothers, progressive expansion of adipose tissue culminates with severe hyperestrogenism and hyperleptinemia with detrimental effects for ovarian performance. Indeed, maternal obesity is associated with the establishment of ovarian leptin resistance. This review summarizes current knowledge on potential effects of impaired leptin signaling throughout folliculogenesis and oocyte developmental competence in mice and women.

The Importance of Leptin to Reproduction

A healthy nutritional state is required for all aspects of reproduction and is signaled by the adipokine leptin. Leptin acts in a relatively narrow concentration range: too much or too little will compromise fertility. The leptin signal timing is important to prepubertal development in both sexes. In the brain, leptin acts on ventral premammillary neurons which signal kisspeptin (Kiss1) neurons to stimulate gonadotropin releasing hormone (GnRH) neurons. Suppression of Kiss1 neurons occurs when agouti-related peptide neurons are activated by reduced leptin, because leptin normally suppresses these orexigenic neurons. In the pituitary, leptin stimulates production of GnRH receptors (GnRHRs) and follicle-stimulating hormone at midcycle, by activating pathways that derepress actions of the messenger ribonucleic acid translational regulatory protein Musashi. In females, rising estrogen stimulates a rise in serum leptin, which peaks at midcycle, synchronizing with nocturnal luteinizing hormone pulses. The normal range of serum leptin levels (10-20 ng/mL) along with gonadotropins and growth factors promote ovarian granulosa and theca cell functions and oocyte maturation. In males, the prepubertal rise in leptin promotes testicular development. However, a decline in leptin levels in prepubertal boys reflects inhibition of leptin secretion by rising androgens. In adult males, leptin levels are 10% to 50% of those in females, and high leptin inhibits testicular function. The obesity epidemic has elucidated leptin resistance pathways, with too much leptin in either sex leading to infertility. Under conditions of balanced nutrition, however, the secretion of leptin is timed and regulated within a narrow level range that optimizes its trophic effects.

Functional Analysis of Steroidogenic Factor 1 (sf-1) and 17α-Hydroxylase/Lyase (cyp17α) Promoters in Yellow Catfish Pelteobagrus fulvidraco

The present study was performed to clone and characterize the structures and functions of steroidogenic factor 1 (sf-1) and 17α-hydroxylase/lyase (cyp17α) promoters in yellow catfish Pelteobagrus fulvidraco, a widely distributed freshwater teleost. We successfully obtained 1981 and 2034 bp sequences of sf-1 and cyp17α promoters, and predicted the putative binding sites of several transcription factors, such as Peroxisome proliferator-activated receptor alpha (PPARα), Peroxisome proliferator-activated receptor gamma (PPARγ) and Signal transducer and activator of transcription 3 (STAT3), on sf-1 and cyp17α promoter regions, respectively. Overexpression of PPARγ significantly increased the activities of sf-1 and cyp17α promoters, but overexpression of PPARα significantly decreased the promoter activities of sf-1 and cyp17α. Overexpression of STAT3 reduced the activity of the sf-1 promoter but increased the activity of the cyp17α promoter. The analysis of site-mutation and electrophoretic mobility shift assay suggested that the sf-1 promoter possessed the STAT3 binding site, but did not the PPARα or PPARγ binding sites. In contrast, only the PPARγ site, not PPARα or STAT3 sites, was functional with the cyp17α promoter. Leptin significantly increased sf-1 promoter activity, but the mutation of STAT3 and PPARγ sites decreased leptin-induced activation of sf-1 promoter. Our findings offered the novel insights into the transcriptional regulation of sf-1 and cyp17α and suggested leptin regulated sf-1 promoter activity through STAT3 site in yellow catfish.

Overaccumulation of Fat Caused Rapid Reproductive Senescence but not Loss of Ovarian Reserve in ob/ob Mice

Ovarian reserve and fertility are reduced by aging and a poor energy balance. To date, the relationships of high energy accumulation and aging with the ovarian reserve have not been elucidated. Here, the effects of obesity on the aging ovarian reserve were evaluated in a leptin-deficient (ob/ob) mouse model. Abnormal estrous cyclicity appeared as early as 6 weeks and worsened with aging. The blood level patterns of 17β-estradiol (E2), testosterone (T), and progesterone (P4) with aging were similar between lean and ob/ob mice. The blood level of E2 but not P4 or T was similar at 24 weeks. Many more atretic follicles but fewer corpora lutea were observed in ob/ob mice than in lean mice within all age groups. Anti-Müllerian hormone (Amh) mRNA levels were similar between genotypes. Dazl, Stra8, and ZP3 mRNAs were highly expressed in ob/ob mice after 12 weeks. Sohlh1 and Ybx2 mRNAs were highly expressed at 24 weeks in ob/ob compared with lean mice. In addition, SOHLH1-positive primordial follicle counts were significantly increased in ob/ob mice at 24 weeks. The proportions of AMH-positive secondary and small antral follicles were similar between genotypes. Together, these results show that the ovarian reserve lasts longer in ob/ob mice than in lean mice, suggesting that the loss of normal physiological or physical status causes decreased fertility at a young age in ob/ob mice and that an increase in adipocytes without leptin, as in ob/ob mice, can improve the ovarian reserve. Such knowledge can be applied to understanding reproductive dysfunction.

Neuroanatomical Framework of the Metabolic Control of Reproduction

A minimum amount of energy is required for basic physiological processes, such as protein biosynthesis, thermoregulation, locomotion, cardiovascular function, and digestion. However, for reproductive function and survival of the species, extra energy stores are necessary. Production of sex hormones and gametes, pubertal development, pregnancy, lactation, and parental care all require energy reserves. Thus the physiological systems that control energy homeostasis and reproductive function coevolved in mammals to support both individual health and species subsistence. In this review, we aim to gather scientific knowledge produced by laboratories around the world on the role of the brain in integrating metabolism and reproduction. We describe essential neuronal networks, highlighting key nodes and potential downstream targets. Novel animal models and genetic tools have produced substantial advances, but critical gaps remain. In times of soaring worldwide obesity and metabolic dysfunction, understanding the mechanisms by which metabolic stress alters reproductive physiology has become crucial for human health.

Association between parental anthropometric measures and the outcomes of intracytoplasmic sperm injection cycles

PURPOSE

To study the association between body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR), and waist-to-height ratio (WHtR), and response to controlled ovarian stimulation, semen quality, and intracytoplasmic sperm injection (ICSI) outcomes.

METHODS

This prospective observational study included data from 402 couples undergoing ICSI between January/2010-September/2016. Participants had their weight, height, waist, and hip measured before ICSI treatment.

RESULTS

Gonadotropin dose was positively associated with maternal WHR. Maternal WC and WHR negatively influenced the estradiol level, number of follicles, oocytes, and mature oocytes. Maternal BMI negatively influenced oocyte yield. Semen volume was negatively influenced by male BMI. Sperm concentration was negatively associated with WHR and WHtR. Progressive sperm motility was negatively influenced by all anthropometric measures (AMs). The TMSC was negatively affected by all AM but WC. Significant differences were observed in all ICSI outcomes except pregnancy and miscarriage rates, favoring women with AM below the cut off values compared to women above the cut off. It was observed that men with AM below the cut off values showed significantly higher rates of fertilization, embryo and blastocyst development, implantation, and pregnancy than men above the cut off. When combined maternal and paternal AM were analyzed, significant differences were observed in fertilization, embryo and blastocyst development and implantation rates, favoring couples with normal BMI, WC, and WHR.

CONCLUSIONS

Lower AMs have a protective effect on fertility. Awareness and counseling on how to minimize its impact in both partners could improve ICSI outcomes.

The Responses of Mouse Preimplantation Embryos to Leptin In Vitro in a Transgenerational Model for Obesity

The aim of the present study was to test the hypothesis that leptin can directly mediate the negative effect of maternal obesity on preimplantation embryos. As previously shown, maternal obesity retards early embryonic development in vivo and increases the incidence of apoptosis in blastocysts. When two-cell embryos isolated from control and obese mice were transferred to identical (leptin free) conditions in vitro, no differences in any growth or quality parameters were recorded, including apoptosis incidence in blastocysts. Embryos isolated from control mice responded to transfer to environments with a high concentration of leptin (10 ng/mL) with a significant increase in arrest at the first or subsequent cell cycle. However, the majority of non-arrested embryos developed into blastocysts, showing morphology comparable to those cultured in the leptin-free group. On the other hand, the exposure of embryos isolated from obese mice to high leptin concentration in vitro did not retard their development. Furthermore, these embryos developed into blastocysts, showing a lower incidence of apoptosis. In vivo-developed blastocysts recovered from obese mice showed elevated expression levels of the proapoptotic gene BAX and the insulin-responsive glucose transporter gene SLC2A4. In conclusion, elevated leptin levels have both positive and negative effects on preimplantation embryo development in vitro, a response that likely depends on the body condition of the embryo donor. Moreover, these results suggest that leptin acts as a survival factor rather than an apoptotic inductor in embryonic cells. Since no elevations in the expression of the leptin receptor gene (LEPR) or fat metabolism-associated genes (PLIN2, SLC27A4) were recorded in blastocysts recovered from obese mice, the role of leptin in mediating the effects of obesity on embryos at the peripheral level is likely lower than expected.

Effect of obesity and its related metabolic factors on serum anti-Müllerian hormone concentrations in women with and without polycystic ovaries

The relationship between serum anti-Müllerian hormone (AMH) levels, body mass index (BMI) and related metabolic factors were investigated in women with polycystic ovary syndrome (PCOS). A total of 691 women aged between 18 and 35 years, referred to the Department of Gynaecological Endocrinology at the University Hospital of Lille between 2009 and 2014 were included: 137 controls and 554 women with PCOS. Mean serum AMH levels were slightly but significantly lower in women with PCOS who were overweight or obese (BMI ≥25) compared with women of normal weight (BMI <25) (P < 0.05). No such difference was found in the control group. After bivariate analysis, no significant correlation was found between BMI and AMH in controls. In the PCOS group, this relationship was significant (P = 0.0001) but weak (r = -0.177). Stepwise multiple regression analysis yielded a significant model, including five variables (follicle count, serum androstenedione, BMI, serum LH and FSH) explaining 38.6%, 3.4%, 1.4%, 0.7% and 1.4% of the total serum AMH variance, respectively. No effect of metabolic status was found on serum AMH levels in controls, but a significant, albeit weak, negative independent correlation was found between AMH and BMI in women with PCOS.

Expression of leptin receptor in the oviduct of Chinese brown frog (Rana dybowskii)

The oviduct of Chinese brown frog ( Rana dybowskii) expands specifically during prehibernation instead of in the breeding period. In this study, we investigated the expression of leptin receptor (Ob-Rb) in Rana dybowskii oviduct during the breeding period and prehibernation. Histologically, the oviduct of Rana dybowskii consists of glandular cells, tubule lumen, and epithelial cells. The oviductal weight and pipe diameter also revealed significant differences, which were higher in prehibernation than that of the breeding period. Ob-Rb was observed in stromal cells of oviductal tissue in both the breeding period and prehibernation. The mean protein and mRNA levels of the Ob-Rb were significantly higher in prehibernation as compared with the breeding period. In addition, oviductal content of leptin was also higher in prehibernation than that of the breeding period. These results suggested that oviduct of Rana dybowskii might be a target organ of leptin, and leptin may play an autocrine/paracrine role mediated by Ob-Rb in regulating the oviductal hypertrophy during prehibernation.

The Influence of LepR Tyrosine Site Mutations on Mouse Ovary Development and Related Gene Expression Changes

Leptin exerts many biological functions, such as in metabolism and reproduction, through binding to and activating the leptin receptor, LepRb, which is expressed in many regions of the brain. To better understand the roles of LepR downstream signaling pathways, Y123F mice, which expressed mutant leptin receptors with phenylalanine (F) substituted for three tyrosines (Y) (Tyr985, Tyr1077 and Tyr1138), were generated. The body weight and abdominal fat deposits of Y123F homozygous mice (HOM) were higher than those of wild-type mice (WT). HOM ovaries were atrophic and the follicles developed abnormally; however, the HOM ovaries did not exhibit polycystic phenotypes. Moreover, Y123F HOM adults had no estrous cycle and the blood estrogen concentration remained stable at a low level below detection limit of 5 pg/ml. LepR expression in HOM ovaries was higher than in WT ovaries. Using cDNA Microarrays, the mRNA expressions of 41 genes were increased, and 100 were decreased in HOM vs. WT ovaries, and many signaling pathways were evaluated to be involved significantly. The expressions of 19 genes were validated by real-time quantitative PCR, most of which were consistent with the microarray results. Thus, Y123F HOM mice were suggested as a new animal model of PCOS for research that mainly emphasizes metabolic disorders and anovulation, but not the polycystic phenotype. Meanwhile, using the model, we found that JAK-STAT and hormone biosynthesis pathways were involved in the follicular development and ovulation disorders caused by LepR deficiency in ovaries, although we could not exclude indirect actions from the brain.

Roles of leptin in reproduction, pregnancy and polycystic ovary syndrome: consensus knowledge and recent developments

As an essential function for perpetuation of species, reproduction, including puberty onset, is sensitive to the size of body energy stores and the metabolic state of the organism. Accordingly, impaired energy homeostasis, ranging from extreme leanness, such as in anorexia or cachexia, to morbid obesity has an impact on the timing of puberty and is often associated to fertility problems. The neuroendocrine basis for such phenomenon is the close connection between numerous metabolic hormones and nutritional cues with the various elements of the so-called hypothalamic-pituitary-gonadal (HPG) axis. Yet, despite previous fragmentary knowledge, it was only the discovery of the adipose-hormone, leptin, in 1994 what revolutionized our understanding on how metabolic and reproductive systems closely interplay and allowed the definition of the neurohormonal causes of perturbations of puberty and fertility in conditions of impaired body energy homeostasis. In this article, we aim to provide a synoptic view of the mechanisms whereby leptin engages in the regulation of different elements of the HPG axis, with special attention to its effects and mechanisms of action on the different elements of the reproductive brain and its proven direct effects in the gonads. In addition, we will summarize the state-of-the-art regarding the putative roles of leptin during gestation, including its potential function as placental hormone. Finally, comments will be made on the eventual leptin alterations in reproductive disorders, with special attention to the polycystic ovary syndrome (PCOS), a disease in which reproductive, metabolic and neuroendocrine alterations are commonly observed. All in all, we intend to provide an updated account of our knowledge on the physiological roles of leptin in the metabolic regulation of the reproductive axis and its eventual pathophysiological implications in prevalent reproductive disorders, such as PCOS.

Progressive obesity alters the steroidogenic response to ovulatory stimulation and increases the abundance of mRNAs stored in the ovulated oocyte

Obese women who are able to attain pregnancy are at increased risk for early-pregnancy loss due, in part, to reduced oocyte quality. We and others have demonstrated that female Lethal Yellow (LY) mice and female C57BL/6 mice fed a high fat diet (B6-HFD) exhibit phenotypes consistent with human obesity. These studies also showed that zygotes collected from LY and B6-HFD females have reduced developmental competence. The current hypothesis is that LY and B6-HFD females exhibit an abnormal response to gonadotropin stimulation compared to C57BL/6 controls fed normal rodent chow (B6-ND), resulting in the ovulation of oocytes with an altered molecular phenotype which may contribute to its reduced developmental competence. To test this hypothesis, age-matched B6-ND, B6-HFD, and LY females were stimulated with exogenous gonadotropins, then circulating hormone levels and the phenotypes of ovulated oocytes were analyzed. There was no difference in ovulation rate or in the percentage of morphologically abnormal oocytes collected from the oviduct of any females. Progesterone and progesterone/estradiol ratios, however, were increased in B6-HFD and LY compared to B6-ND females 16 hr post-human chorionic gonadotropin treatment. The transcript abundance of several candidate oocyte genes was also increased in B6-HFD- and LY-derived oocytes compared to B6-ND-derived oocytes. These data suggest that increased insulin and leptin levels of obese females elevated circulating progesterone concentrations, altered transcriptional activity during oocyte growth, and/or impaired mechanisms of RNA translation and degradation during oocyte maturation. These changes in mRNA abundance likely contribute to reduced oocyte quality and the subsequent poor embryogenesis associated with obesity.

Minireview: Metabolism of female reproduction: regulatory mechanisms and clinical implications

Female fertility is highly dependent on successful regulation of energy metabolism. Central processes in the hypothalamus monitor the metabolic state of the organism and, together with metabolic hormones, drive the peripheral availability of energy for cellular functions. In the ovary, the oocyte and neighboring somatic cells of the follicle work in unison to achieve successful metabolism of carbohydrates, amino acids, and lipids. Metabolic disturbances such as anorexia nervosa, obesity, and diabetes mellitus have clinically important consequences on human reproduction. In this article, we review the metabolic determinants of female reproduction and their role in infertility.

Management of reproduction and pregnancy complications in maternal obesity: which role for dietary polyphenols?

Obesity is a global and dramatic public health problem; maternal obesity represents one of the main risk factors of infertility and pregnancy complications as it is associated with adverse maternal and offspring outcomes. In the last few years, adipose tissue dysfunction associated with altered adipocytokine secretion has been suggested to play a critical role in all the phases of reproductive process. Obesity is a nutrition-related disorder. In this regard, dietary intervention strategies, such as high intake of fruit and vegetables, have shown significant effects in both preserving health and counteracting obesity-associated diseases. Evidence has been provided that polyphenols, important constituents of plant-derived food, can influence developmental program of oocyte and embryo, as well as pregnancy progression by modulating several cellular pathways. This review will examine the controversial results so far obtained on adipocytokine involvement in fertility impairment and pregnancy complications. Furthermore, the different effects exerted by polyphenols on oocyte, embryo, and pregnancy development will be also taken in account.

Different levels of leptin regulate different target enzymes involved in progesterone synthesis

OBJECTIVE

To study the effects of different doses of leptin on the expression of proteins involved in P synthesis, such as steroidogenic acute regulatory protein (StAR), cytochrome P450 side chain cleavage (P450scc), and 3β-hydroxysteroid dehydrogenase (3βHSD).

DESIGN

Experimental studies.

SETTING

Research laboratory.

ANIMAL(S)

Immature rats primed with gonadotropins to induce ovulation.

INTERVENTION(S)

In vivo studies: rats received either an acute or daily treatment with leptin. In vitro studies: ovarian explants were cultured in the absence or presence of leptin (0.3-500 ng/mL).

MAIN OUTCOME MEASURE(S)

The expression of both messenger RNA and protein of StAR, P450scc, and 3βHSD were measured by reverse transcription-polymerase chain reaction (PCR) and Western blot, respectively.

RESULT(S)

The acute treatment with leptin, which inhibits the ovulatory process, caused a significant reduction in the ovarian expression of P450scc without changes in StAR or 3βHSD. In contrast, the daily treatment, which induces the ovulatory process, showed an increased expression of the ovarian 3βHSD protein, without differences in the other proteins measured. We also found that leptin increased the protein of both P450scc and 3βHSD at physiological levels and inhibited both messenger RNA and protein of 3βHSD at higher concentrations.

CONCLUSION(S)

The results indicate that 1) leptin is able to regulate the expression of the 3βHSD protein in a dose-dependent manner; and 2) leptin seems to exert its dual effects on P synthesis on different targets in a dose-dependent manner.

Characterization of a distinctive pattern of periovulatory leptin secretion and its relationship with ovulation rate and luteal function in swine with obesity/leptin resistance

Patterns of leptin secretion during the estrous cycle and the possible relationship of changes in circulating leptin during the periovulatory period with ovarian function in sows of obese (Iberian breed) and lean genotype (Large White x Landrace) were evaluated in two consecutive experiments. Plasma leptin concentrations throughout the estrous cycle in lean sows remain unchanged, but Iberian females showed a periovulatory increase in circulating leptin levels without associated changes in body condition and fatness. In these sows, plasma leptin concentrations at Days -1 and 0 of the cycle were found to be positively correlated with the ovulation rate (r=0.943 and r=0.987, respectively; P<0.05 for both), but the levels of leptin at Day 0 were negatively correlated with the progesterone release from Day 3 (r=-0.557; P<0.05) and, became more evident at Day 5 of the estrous cycle (r=-0.924; P<0.005). Such relationships were not observed in the females of the lean genotype. In conclusion, the present study indicates the existence of a distinctive pattern in the periovulatory leptin secretion in swine with obesity and leptin resistance, which is associated with the number and functionality of the corpora lutea present in the subsequent cycle.

Effect of passive immunization against leptin on ovarian follicular development in prepubertal mice

Leptin has been demonstrated to be essential for reproduction. However, all the relevant studies reported to date have investigated either the effect of a complete absence of leptin both centrally and peripherally, or excess leptin administration. The aim of this present study was to investigate the effect of reducing peripheral leptin concentrations on ovarian follicular development in prepubertal animals via administration of an anti-leptin antibody. Pre-pubertal female mice were administered anti-leptin antibody under the skin behind the head for four days, with or without gonadotropins, and ovaries were weighed and collected for follicle counting. Control animals were treated with non-immune serum. Passive immunization against leptin, with or without gonadotropins, resulted in a significant increase in ovarian weight compared with control ovaries. Furthermore, the ovaries from the anti-leptin group had significantly greater numbers of primary follicles per ovarian section than the control group, thus suggesting an increase in the transition of primordial to primary follicles after treatment. Interestingly, animals treated with anti-leptin plus gonadotropins had a significantly higher number of Graafian follicles in their ovaries compared with the other groups. Collectively, the results of the present study indicate that reduction of leptin in the circulation promotes ovarian follicle development in female mice, suggesting that peripheral leptin acts as an inhibitor of ovarian follicle development.

The association between severe obesity and characteristics of failed fertilized oocytes

STUDY QUESTION

Is the cytoskeletal and chromosomal organization of failed fertilized oocytes from severely obese patients (BMI ≥ 35 kg/m²) altered compared with that in patients with normal BMI (BMI 18.5-24.9 kg/m²)?

SUMMARY ANSWER

Compared with normal BMI patients, severe obesity was associated with a greater prevalence of spindle anomalies and non-aligned chromosomes in failed fertilized oocytes.

WHAT IS KNOWN AND WHAT THIS PAPER ADDS

Obesity is associated with poor reproductive outcomes, but little is known regarding the underlying mechanisms. To address potential mechanisms, our study compared the cytoskeletal and chromosome organization in failed fertilized oocytes from severely obese and normal BMI patients.

DESIGN

The study population was drawn from IVF patients treated in a hospital-based infertility clinic between February 2010 and July 2011. The prevalence of meiotic spindle and chromosome alignment anomalies in failed fertilized oocytes from patients with severe obesity (i.e. Class II and III; BMI 35.0-50.1 kg/m²) was compared with those from patients with normal BMI (BMI 18.5-24.9 kg/m²). Oocytes were fixed and then labeled for tubulin, actin and chromatin. Spindle number and integrity, as well as chromosome alignment, were assessed using immunofluorescence microscopy and, in some cases, confocal microscopy. Generalized estimating equations were applied, which account for the correlation among oocytes from the same patient to estimate odds ratio (OR), 95% confidence intervals (CIs) and two-sided Wald P-values. Models were adjusted for continuous age at cycle start, cycle type (IVF or ICSI) and polycystic ovarian syndrome (PCOS) a priori.

PARTICIPANTS AND SETTING

University-affiliated infertility clinic. A total of 276 oocytes that failed to fertilize from 137 patients were evaluated: 105 oocytes from severely obese women (n = 47) and 171 oocytes from normal BMI patients (n = 90).

MAIN RESULTS AND THE ROLE OF CHANCE

(i) Significantly more oocytes from the severely obese group exhibited two spindles compared with those from the normal BMI group (58.9 versus 35.1%; OR = 2.68, CI = 1.39-5.15, P-value = 0.003). (ii) Among oocytes with a single spindle, those from severely obese patients showed a significantly higher prevalence of disarranged spindles with non-aligned chromosomes compared with those from normal BMI patients (28.6 versus 8.6%; OR = 4.58, CI = 1.05-19.86, P-value = 0.04).

BIAS, CONFOUNDING AND OTHER REASONS FOR CAUTION

Inclusion of only failed fertilized oocytes, small sample size, unknown factors such as non-PCOS comorbidity.

GENERALIZABILITY TO OTHER POPULATIONS

For this study, by design, it is unclear whether the findings are generalizable to successfully fertilized oocytes, and whether this oocyte-level influence of obesity is generalizable to infertile women who do not undergo stimulation or, more broadly, to spontaneous conceptions in fertile women.

STUDY FUNDING/COMPETING INTEREST(S)

none.

TRIAL REGISTRATION NUMBER

n/a.

Leptin signaling and circuits in puberty and fertility

Leptin is an adipocyte-derived hormone involved in a myriad of physiological process, including the control of energy balance and several neuroendocrine axes. Leptin-deficient mice and humans are obese, diabetic, and display a series of neuroendocrine and autonomic abnormalities. These individuals are infertile due to a lack of appropriate pubertal development and inadequate synthesis and secretion of gonadotropins and gonadal steroids. Leptin receptors are expressed in many organs and tissues, including those related to the control of reproductive physiology (e.g., the hypothalamus, pituitary gland, and gonads). In the last decade, it has become clear that leptin receptors located in the brain are major players in most leptin actions, including reproduction. Moreover, the recent development of molecular techniques for brain mapping and the use of genetically modified mouse models have generated crucial new findings for understanding leptin physiology and the metabolic influences on reproductive health. In the present review, we will highlight the new advances in the field, discuss the apparent contradictions, and underline the relevance of this complex physiological system to human health. We will focus our review on the hypothalamic circuitry and potential signaling pathways relevant to leptin’s effects in reproductive control, which have been identified with the use of cutting-edge technologies of molecular mapping and conditional knockouts.

The effect of leptin on maturing porcine oocytes is dependent on glucose concentration

Increased body weight is often accompanied by increased circulating levels of leptin and glucose, which alters glucose metabolism in various tissues, including perhaps the oocyte. Alteration of glucose metabolism impacts oocyte function and may contribute to the subfertility often associated with obese individuals. The objective of this study was to determine the effect of leptin (0, 10, and 100 ng/ml) on the oocyte and cumulus cells during in vitro maturation under differing glucose concentrations. We examined the effects of leptin on oocyte maturation, blastocyst development, and/or gene expression in oocytes and cumulus cells (IRS1, IGF1, PPARγ, IL6, GLUT1) in a physiological glucose (2 mM) and high glucose (50 mM) environment. We also evaluated the effect of leptin on glucose metabolism via glycolysis and the pentose phosphate pathway. In a physiological glucose environment, leptin did not have an influence on oocyte maturation, blastocyst development, or oocyte gene expression. Expression of GLUT1 in cumulus cells was downregulated with 100 ng/ml leptin treatment, but did not affect oocyte glucose metabolism. In a high glucose environment, oocyte maturation and glycolysis were decreased, but in the presence of 100 ng/ml leptin, these parameters were improved to levels similar to control. This effect is potentially mediated by an upregulation of oocyte IRS1 and a correction of cumulus cell IGF1 expression. The present study demonstrates that in a physiological glucose concentration, leptin plays a negligible role in oocyte function. However, leptin appears to modulate the deleterious impact of a high glucose environment on oocyte function.

Ghrelin and leptin did not improve meiotic maturation of porcine oocytes cultured in vitro

To improve culture system for in vitro maturation (IVM) of porcine oocytes, ghrelin, leptin or growth hormone (GH), at concentration of 0, 0.5, 5, 50 and 500 ng/ml were added to the porcine follicular fluid (pFF)-supplemented medium NCSU23, and their effects on the maturation and cytoskeletal distribution of the oocytes with or without cumulus cells were compared. In the cumulus-denuded oocytes, no significant changes were noted in the maturation rate by different hormone treatments due to a marked decline in the controls. Maturation of the cumulus intact oocytes was moderately interfered by ghrelin (0.5-50 ng/ml, p < 0.01), but not significantly affected by leptin and GH. Distribution density of the cytoplasmic microtubules was decreased significantly by addition of ghrelin (by approximately 30% in 50-500 ng/ml, p < 0.01), whereas no remarkable effect was noted by leptin supplementation. High concentration (500 ng/ml) of ghrelin or leptin decreased significantly the cytoplasmic microfilaments in density (by 43% and 38%, p < 0.01, respectively). GH did not affect cytoskeletal distribution. The results suggest, in the culture system using pFF-supplemented medium that (i) ghrelin may have some inhibitory effect on the organization of microtubules and microfilaments, probably being a factor in lowered maturation rate and (ii) the addition of higher concentration of leptin may decrease microfilaments in density with no effect on meiotic maturation of the porcine oocytes.

PPAR Gamma: Coordinating Metabolic and Immune Contributions to Female Fertility

Peroxisome proliferator-activated receptor gamma (PPARG) regulates cellular functions such as adipogenesis and immune cell activation. However, new information has indicated additional roles of PPARG directing the cyclic changes that occur within ovarian tissue of female mammals, including those that facilitate the release of oocytes each estrous cycle. In addition to ovarian PPARG expression and function, many PPARG actions within adipocytes and macrophages have additional direct and indirect implications for ovarian function and female fertility. This encompasses the regulation of lipid uptake and transport, insulin sensitivity, glucose metabolism, and the regulation of inflammatory mediator synthesis and release. This review discusses the developing links between PPARG activity and female reproductive function, and highlights several mechanisms that may facilitate such a relationship.

The impact of obesity on egg quality

Obesity in women is a concern in many countries. This causes numerous health issues; however, this review focuses on the impact of obesity on women's reproduction, and in particular the oocyte. Data from infertility clinics and experimental animal models that address the effects of obesity are presented. Bidirectional communication and metabolic support from the surrounding cumulus cells are critical for oocyte development, and the impact of obesity on these cells is also addressed. Both oocyte maturation and metabolism are impaired due to obesity, negatively impacting further development. In addition to reproductive hormones, obesity induced elevations in insulin, glucose, or free fatty acids, and changes in adipokines appear to impact the developmental competence of the oocyte. The data indicate that any one of these hormones or metabolites can impair oocyte developmental competence in vivo, and the combination of all of these factors and their interactions are the subject of ongoing investigations.

Role of leptin in delayed embryonic development in the Indian short-nosed fruit bat, Cynopterus sphinx

An adiposity-associated rise in leptin occurs at the time of delayed embryonic development in Cynopterus sphinx. The aim of present study was to examine the mechanism by which leptin may inhibit progesterone, and therefore could be responsible for delayed development. The study showed a significant increase in circulating leptin level during the period of increased fat accumulation, which coincided with significant decrease in serum progesterone level and delayed embryonic development in C. sphinx. The study showed increased Ob-R expression in the corpus luteum and in the utero-embryonic unit during the period of delayed embryonic development. The in vitro study showed suppressive effect of leptin on progesterone synthesis. The effect of high dose of leptin on ovarian steroidogenesis was found to be mediated through decreased expression of StAR and LH-R proteins in the ovary. The treatment with leptin caused increased expression of STAT 3 and iNOS proteins in the ovary, which correlated with decreased expression of StAR protein in the ovary. The inhibitory effects of leptin on progesterone synthesis in the ovary are thus mediated through STAT 3 and iNOS-NO signaling pathways. This study further demonstrated low expression of PCNA coinciding with the increased concentration of the leptin receptor in the utero-embryonic unit and high circulating leptin level during November. In conclusion, adiposity associated increased leptin level during November-December might play role in suppressing progesterone synthesis in the corpus luteum as well as suppressing the rate of cell-proliferation in the utero-embryonic unit thereby causing delayed embryonic development in C. sphinx.

The adverse effects of obesity on conception and implantation

Whilst many multiparous women are obese (body mass index >30 kg/m(2)), obesity has been associated with impaired fecundity; however, the mechanism which links obesity to reduced fertility remains to be fully elucidated. Obese women, particularly those with central obesity, are less likely to conceive per cycle. Obese women suffer perturbations to the hypothalamic-pituitary-ovarian axis, menstrual cycle disturbance and are up to three times more likely to suffer oligo-/anovulation. A fine hormonal balance regulates follicular development and oocyte maturation, and it has been observed that obesity can alter the hormonal milieu. Leptin, a hormone produced by adipocytes, is elevated in obese women, and raised leptin has been associated with impaired fecundity. Obesity impairs ovulation but has also been observed to detrimentally affect endometrial development and implantation. The expression of polycystic ovary syndrome (PCOS) is regulated, in part, by weight, and so obese women with PCOS often have a more severe phenotype and experience more subfertility. Obesity also impairs the response of women to assisted conception treatments. Weight loss through lifestyle modification or bariatric surgery has been demonstrated to restore menstrual cyclicity and ovulation and improve the likelihood of conception. In this article, we will discuss the effect of obesity upon key reproductive mechanisms and its relation to fertility treatments.

Influence of leptin on in vitro maturation and steroidogenic secretion of cumulus–oocyte complexes through JAK2/STAT3 and MEK 1/2 pathways in the rabbit model

Extreme body mass indexes may impair reproductive outcome in assisted reproductive technologies. Leptin reflects the amount of body fat and could act as a modulator of oocyte quality through activation of specific transcription factors. The aim of this work was to establish whether: 1) leptin influences meiotic and cytoplasmic oocyte maturation; 2) STAT3 and MAPK mediate the effects of leptin and 3) leptin modulates steroid secretion by cumulus–oocyte complexes (COC) duringin vitromaturation (IVM). We confirmed immunolocalisation of leptin receptor in oocytes, cumulus/granulosa cells during the peri-ovulatory period. The confocal study showed that COC supplemented with 1, 10 and 100 ng/ml leptin had a significantly higher metaphase II (MII) percentage than those IVM without leptin (P<0.05) and a similar MII index compared to the group supplemented with 10% FCS. Leptin did not increase the percentage of cytoplasmically matured oocytes in terms of cortical granule migration rate, whereas a significantly higher index was found in the FCS group (P<0.001). Oestradiol concentrations in spent media were higher in the FCS group compared to other treatments (P<0.001). Leptin-stimulated nuclear oocyte maturation was significantly impaired when leptin-induced JAK2/STAT3 and MEK 1/2 activation was suppressed by the inhibitors (P<0.001). Steroid secretion of COC was not affected by leptin activation of JAK2/STAT3 or MEK 1/2 pathways. In conclusion, JAK2/STAT3 and MEK 1/2 pathways mediate the enhancement of nuclear oocyte maturation by leptin; however, neither cytoplasmic oocyte maturation nor steroidogenic response of COC were improved in the present rabbit model.

Leptin and ObRa/MEK signalling in mouse oocyte maturation and preimplantation embryo development

Recent studies indicate that LH stimulates production of ovarian paracrine factors that induce meiosis of the oocyte. DNA microarray analyses of ovarian transcripts were performed in mice and major increases of a short isoform of leptin receptor, ObRa, were identified by the preovulatory LH/human chorionic gonadotrophin (HCG) surge. In oocytes, the level of ObRa transcripts was increased shortly after HCG stimulation, whereas the level of ObRb transcripts was not changed. Leptin was produced by cumulus, granulosa, theca and interstitial cells of ovaries and its transcript level was not regulated during gonadotrophin treatment. Treatment with leptin promoted germinal vesicle breakdown (GVBD) in oocytes within preovulatory follicles, and enhance first polar body extrusion in both cumulus-oocyte complexes and denuded oocytes. The leptin-promoted GVBD and first polar body extrusion were blocked by a mitogen-activated protein kinase extracellular signal regulated kinase kinases (MEK)1/2 inhibitor, U0126, but not its inactive analogue U0124. Furthermore, leptin promoted fertilization of oocytes and the in-vitro development of zygotes to preimplantation embryos. These findings suggest paracrine roles of leptin in the enhancement of nuclear maturation of oocytes through MEK1/2 signalling, and in the promotion of cytoplasmic maturation essential for successful oocyte development to the preimplantation embryos.

Effects of leptin supplementation in in vitro maturation medium on meiotic maturation of oocytes and preimplantation development of parthenogenetic and cloned embryos in pigs

The objective of the present study was to investigate the effects of leptin addition in in vitro maturation (IVM) medium on meiotic maturation of oocytes and preimplantation development of parthenogenetic and cloned embryos in pigs. In experiment 1, oocytes were matured in North Carolina State University 23 (NCSU-23) medium supplemented with various concentrations of leptin: 0, 1, 10 and 100 ng/ml. IVM medium added with 10 or 100 ng/ml leptin significantly increased the rate of oocytes reaching metaphase II compared to the control (76.8% and 73.8% versus 61.7%). In experiment 2, the influence of the timing of leptin addition in IVM medium on meiotic maturation of porcine oocytes was assessed, and maximum maturation rate of oocytes developing to metaphase II was achieved when supplemented during the first half (0-22 h), the latter half (22-44 h) or the entire maturation period (0-44 h) compared to the control (80.5%, 84.7% and 78.1% versus 70.4%). In experiment 3, leptin strikingly increased the blastocyst rate of parthenogenetic embryos at the concentration of 10 ng/ml (37.5% versus 21.7%) and this increase was independent of the addition timing (0-44, 0-22, 22-44 h) compared to the control (32.5%, 34.6% and 31.5% versus 16.2%). Moreover, total cell number per blastocyst of parthenogenetic embryos was obviously increased in the 10 and 100 ng/ml leptin treatments as compared with the control (36, 38 versus 28). In experiment 4, 10 ng/ml leptin treatment significantly increased the rate of cleavage (72% versus 56%) of cloned embryos. Meanwhile, the rate of blastocyst formation was also improved although no significant difference was found (12.8% versus 7.1%). Collectively, our results indicate that leptin supplementation in IVM medium may be beneficial not only for developmental potential of oocytes but for subsequent developmental competence of embryos produced by parthenogenetic activation and the cleavage of embryos derived by somatic cell nuclear transfer (SCNT).