Molecular mechanisms of leptin action in adult rat testis: potential targets for leptin-induced inhibition of steroidogenesis and pattern of leptin receptor messenger ribonucleic acid expression

Presence of leptin and its receptor in the ram reproductive system and in vitro effect of leptin on sperm quality

Leptin is a 16 kDa hormone encoded by obese (OB) gene in adipocytes. This molecule not only regulates energy metabolism but also plays a role in the reproduction of mammals. Leptin and its receptor (OBR) have been found in male reproductive systems of human, bovine, equine and pig. The effects of leptin on sperm quality vary widely from different research findings. However, the presence of leptin and its receptor in the ram reproductive system and the in vitro effect of leptin on sperm quality have not reported yet. In the present study, we found that the OB was highly expressed in primary and secondary spermatocytes of the testes, OBR was highly expressed in secondary spermatocytes of the testes. The expressions of OB were in stereocilia of epididymis and in columnar cells of epididymal caput and cauda, the expressions of OBR were in columnar cells of epididymis and in stereocilia of epididymal corpus and cauda. The presence of both OB and OBR in testes, epididymis and sperm were confirmed through RT-PCR, immunolocalization and Western blot analyses. The RT-qPCR results indicated OB and OBR had higher expression levels in epididymal sperm than that of the ejaculated sperm in rams. When sperm were treated with 5 ng/mL leptin, the progressive motility (P < 0.01), straight-line velocity (VSL) (P < 0.05), average path velocity (VAP) (P < 0.05), membrane mitochondrial potential (MMP) (P < 0.01) and viability (P < 0.05) significantly increased, while DNA fragmentation index (DFI) and reactive oxygen species (ROS) significantly decreased compared to the control (P < 0.01), and the other semen parameters such as acrosome integrity and acrosome reaction rate had no significant changes between groups (P > 0.05). In conclusion, this is probably the first report describing localization of leptin and its receptors in the reproductive system of rams and their effects on sperm quality parameters. Our findings suggest that 5 ng/mL leptin treatment enhanced sperm motility, viability and MMP, and decrease DFI and ROS without obvious influence on the acrosome reaction in ram sperm. The potential mechanisms may be related to leptin's ability to reduce the oxidative stress and apoptosis of sperms and improve their mitochondrial function and energy supply, therefore, to maintain the physiological homeostasis of the sperm.

The Head-to-Toe Hormone: Leptin as an Extensive Modulator of Physiologic Systems

Leptin is a well-known hunger-sensing peptide hormone. The role of leptin in weight gain and metabolic homeostasis has been explored for the past two decades. In this review, we have tried to shed light upon the impact of leptin signaling on health and diseases. At low or moderate levels, this peptide hormone supports physiological roles, but at chronically higher doses exhibits detrimental effects on various systems. The untoward effects we observe with chronically higher levels of leptin are due to their receptor-mediated effect or due to leptin resistance and are not well studied. This review will help us in understanding the non-anorexic roles of leptin, including their contribution to the metabolism of various systems and inflammation. We will be able to get an alternative perspective regarding the physiological and pathological roles of this mysterious peptide hormone.

Insights into Interactions of Human Cytochrome P450 17A1: Review

Abstract:

Cytochrome P450s are a widespread and vast superfamily of hemeprotein monooxygenases that metabolize physiologically essential chemicals necessary for most species' survival, from protists to plants to humans. They catalyze the synthesis of steroid hormones, cholesterol, bile acids, and arachidonate metabolites and the degradation of endogenous compounds such as steroids, fatty acids, and other catabolizing compounds as an energy source and detoxifying xenobiotics such as drugs, procarcinogens, and carcinogens. The human CYP17A1 is one of the cytochrome P450 genes located at the 10q chromosome. The gene expression occurs in the adrenals and gonads, with minor amounts in the brain, placenta, and heart. This P450c17 cytochrome gene is a critical steroidogenesis regulator which performs two distinct activities: 17 alpha-hydroxylase activity (converting pregnenolone to 17-hydroxypregnenolone and progesterone to 17-hydroxyprogesterone, these precursors are further processed to provide glucocorticoids and sex hormones) and 17, 20-lyase activity (which converts 17-hydroxypregnenolone to DHEA). Dozens of mutations within CYP17A1 are found to cause 17-alpha-hydroxylase and 17, 20-lyase deficiency. This condition affects the function of certain hormone-producing glands, resulting in high blood pressure levels (hypertension), abnormal sexual development, and other deficiency diseases. This review highlights the changes in CYP17A1 associated with gene-gene interaction, drug-gene interaction, chemical-gene interaction, and its biochemical reactions; they have some insights to correlate with the fascinating functional characteristics of this human steroidogenic gene. The findings of our theoretical results will be helpful to further the design of specific inhibitors of CYP17A1.

Leptin secreted from testicular microenvironment modulates hedgehog signaling to augment the endogenous function of Leydig cells

Although testosterone deficiency (TD) may be present in one out of five men 40 years or older, the factors responsible for TD remain largely unknown. Leydig stem cells (LSCs) differentiate into adult Leydig cells (ALC) and produce testosterone in the testes under the pulsatile control of luteinizing hormone (LH) from the pituitary gland. However, recent studies have suggested that the testicular microenvironment (TME), which is comprised of Sertoli and peritubular myoid cells (PMC), plays an instrumental role in LSC differentiation and testosterone production under the regulation of the desert hedgehog signaling pathway (DHH). It was hypothesized that the TME releases paracrine factors to modulate LSC differentiation. For this purpose, cells (Sertoli, PMCs, LSCs, and ALCs) were extracted from men undergoing testis biopsies for sperm retrieval and were evaluated for the paracrine factors in the presence or absence of the TME (Sertoli and PMC). The results demonstrated that TME secretes leptin, which induces LSC differentiation and increases testosterone production. Leptin's effects on LSC differentiation and testosterone production, however, are inversely concentration-dependent: positive at low doses and negative at higher doses. Mechanistically, leptin binds to the leptin receptor on LSCs and induces DHH signaling to modulate LSC differentiation. Leptin-DHH regulation functions unidirectionally insofar as DHH gain or loss of function has no effect on leptin levels. Taken together, these findings identify leptin as a key paracrine factor released by cells within the TME that modulates LSC differentiation and testosterone release from mature Leydig cells, a finding with important clinical implications for TD.

Synthetic leptin c-fragment peptide minimises heat-induced impairment of spermatogenesis in mice via Stat3 signalling

Mammalian spermatogenesis is a temperature-sensitive process, and an increase in testicular temperature impairs spermatogenesis. Leptin modulates testicular activity, but the effect of leptin or its synthetic analogue on heat-induced testicular impairment is unclear. We investigated the effects of synthetic leptin peptide (116-130 amides) on testicular activity in heat-stressed mice model. 15 adult mice (25.54 ± 1.43 g) were selected for the study. Ten mice were subjected to a single heat stress treatment (HS) at 43 °C for 15 min by submerging the lower half of the body in a thermostatic water bath. After heat treatment, mice were divided into two groups, the heat-stressed HS group (n = 5) and the second group as HSL, treated with leptin peptide (116-130 amide) for 14 days. The HS group showed a significant (p < 0.05) decline in the GSI (0.25 ± 0.018), Johnsenscore (4.5 ±.19), seminiferous tubule diameter (160.75 ± 10.18 μm), germinal epithelium height, (GEH) (37.5 ± 1.59 μm) compared to the CN (GSI-0.37 ± 0.015; Johnsen score-7.9 ± 0.20; GEH- 73.25 ± 1.29 μm; tubule diameter-230.25 ± 1.39 μm) and the HSL groups (GSI-0.38 ± 0.014; Johnsen' score-8.0 ± 0.32; GEH- 37.5 ± 1.59 μm; tubule diameter-160.75 ± 10.18 μm) groups. Heat treatment significantly (p < 0.05) increased the intra-testicular levels of leptin (HS-20.11 ± 2.1 pg/mg protein; CN-10.50 ± 0.17 pg/mg protein; HSL-12.99 ± 0.52 pg/mg protein) with a reduced level of pStat3, suggesting leptin resistance during testicular hyperthermia. Furthermore, heat treatment was associated with significantly (p < 0.05) decreased germ cell proliferation and reduced circulating testosterone levels (HS-2.69 ± 2.01 ng/mL; CN-7.69 ± 0.32 ng/mL; HSL-5.36 ± 0.73 ng/mL). However, the circulating androstenedione levels showed a significant (p < 0.05) increase in the HS group (0.75 ± 0.03 ng/mL) compared to the CN (0.51 ± 0.02 ng/mL) and HSL (0.57 ± 0.07 ng/mL) groups. Immunolocalisation of 3β-HSD showed moderate to faint staining in the Leydig cells in the HS group compared to the CN and HSL groups. Treatment with leptin peptide resulted in decrease in the intra-testicular leptin levels with increased phosphorylation of Stat3, suggesting improved leptin resistance, which was positively associated with increased germ cell proliferation, elevated testosterone levels, and improved testicular histoarchitecture. Testicular hyperthermia may cause leptin resistance and impaired leptin signalling, decreased testosterone biosynthesis and suppressed spermatogenesis, which could be a manifestation of leptin resistance. Treatment with leptin peptide improves leptin signalling and testicular activity in heat-stressed mice, but the underlying mechanism is still unclear.

COVID-19 and varicocele: the possible overlap factors and the common therapeutic approaches

Varicocele is recognized as one of the main attributable causes of male infertility which can affect spermatogenesis by various pathophysiological mechanisms. Recent studies have identified oxidative stress and reduction in antioxidant, hyperthermia, hypoxia, hormonal dysfunction, and inflammatory conditions as major factors in the pathophysiology of varicocele, all of which have known direct associations with the coronavirus disease 2019 (COVID-19) and can significantly increase the risk of detrimental COVID-19-related outcomes. Emerging data have shown an association between COVID-19 and inflammation, overproduction of cytokine, and other pathophysiological processes. The present review, summarizes the current understanding of the pathophysiology of varicocele and investigates the potential correlation between the severity of COVID-19 and the varicocele disease. In addition, various possible treatments which can be effective in both diseases were examined. Despite numerous challenges associated with the prevalence of COVID-19 in healthcare systems in infected countries, special attention should be given to maintaining a high level of care for complex patients with a pre-existing disease such as varicocele and providing appropriate practical advice for optimal control of the COVID-19 disease. This article is protected by copyright. All rights reserved.

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.

Impairment of testes development in Yangzhou ganders by augmentation of leptin receptor signaling

The aim of this study was to determine the cellular and molecular mechanisms of leptin (LEP) and the leptin receptor (LEPR) in testicular development of prepubertal ganders. In an in vivo animal experiment, active immunization against LEPR severely depressed prepubertal testicular development by significantly reducing testicular weights at 200 and 227 days of age. The number of elongated spermatids in the seminiferous tubules was also significantly decreased by immunization with LEPR at ages of 200 and 227 days. Inhibition of testicular development by LEPR immunization was associated with decreases in LHR, StAR, 3β-HSD, CYP11A1, CYP17A1, and PRLR mRNA expression levels in testicular tissue, which resulted in a significant decrease in testosterone synthesis. In the in vitro experiments, the addition of LEP combined with anti-LEPR antibodies strengthened LEPR signal transduction, and inhibited significantly testosterone production in cultured Leydig cells isolated from prepubertal gander testes. The mRNA expression of LHR, StAR, 3β-HSD, CYP11A1, CYP17A1 also decreased significantly after treatment with LEP combined with anti-LEPR antibodies in cultured Leydig cells. These results suggest that anti-LEPR antibodies strengthen LEPR signaling transduction in the presence of LEP, and immunization against LEPR inhibited testes development and testosterone secretion in prepubertal ganders.

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.

Exploratory Analysis in the Differences in Blood Serum and Seminal Plasma of Adipose-Tissue Related Peptides in Obese and Non-Obese Men and Their Correlations With Semen Parameters

OBJECTIVES

Evaluating the relationship between circulating metabolic biomarkers and semen parameters in obese, overweight and normal-weight patients.

METHODS

Patients were recruited at the "Andrology and Pathophysiology of Reproduction Unit", in Santa Maria Goretti Hospital. Divided into three groups were 98 participants (obese, overweight and normal-weight patients) according to BMI and were analyzed for three adipokines and six hormone peptides in blood serum and seminal plasma using Luminex assay. Standard semen analysis was performed for ejaculate volume, sperm concentration, total sperm count, motility, morphology and leukocytes.

RESULTS

In all groups of subjects, we observed a higher concentration of blood serum c-peptide, GIP, PAI-1, leptin, ghrelin and GLP-1 in comparison to seminal plasma; differently, higher levels in seminal plasma were observed for insulin and visfatin. In comparison to the non-obese subjects, obese subjects showed a higher blood serum concentration of c-peptide, GLP-1, GIP and leptin and a higher concentration of seminal plasma of GIP and insulin. Total sperm count, progressive motility, motility, and atypical forms directly correlated with PAI-1 and visfatin, whereas GLP-1 directly correlated only with total progressive motility.

CONCLUSION

Obese men showed a different pattern of blood serum and seminal plasma adipokines and hormone peptides concentrations in comparison to normal-weight men. Furthermore, these molecules correlated with functional seminal parameters. Our findings support the option to consider these molecules as new biomarkers and pharmacological targets for a new therapeutic approach in male infertility. However, further studies identifying other potential biomarkers of male infertility with important clinical implication and characterizing their mechanisms of action are mandatory.

Elevated CCL2 causes Leydig cell malfunction in metabolic syndrome

Metabolic syndrome (MetS), which is associated with chronic inflammation, predisposes males to hypogonadism and subfertility. The underlying mechanism of these pathologies remains poorly understood. Homozygous leptin-resistant obese db/db mice are characterized by small testes, low testicular testosterone, and a reduced number of Leydig cells. Here we report that IL-1β, CCL2 (also known as MCP-1), and corticosterone concentrations were increased in the testes of db/db mice relative to those in WT controls. Cultured murine and human Leydig cells responded to cytokine stress with increased CCL2 release and apoptotic signals. Chemical inhibition of CCL2 rescued Leydig cell function in vitro and in db/db mice. Consistently, we found that Ccl2-deficient mice fed with a high-energy diet were protected from testicular dysfunction compared with similarly fed WT mice. Finally, a cohort of infertile men with a history of MetS showed that reduction of CCL2 plasma levels could be achieved by weight loss and was clearly associated with recovery from hypogonadism. Taken together, we conclude that CCL2-mediated chronic inflammation is, to a large extent, responsible for the subfertility in MetS by causing damage to Leydig cells.

MCP-1/CCL2 upregulation associates with metabolic syndrome–induced male subfertility in both mice and men.

The effect of metformin treatment on the basal and gonadotropin-stimulated steroidogenesis in male rats with type 2 diabetes mellitus

Type 2 diabetes mellitus impairs reproductive functions in men, and important tasks are deciphering the mechanisms of testicular dysfunctions in diabetes and the search of effective approaches to their correction. The purpose was to study the effect of four-week metformin treatment (120 mg kg^-1  day^-1 ) of male Wistar rats with high-fat diet/low-dose streptozotocin-induced type 2 diabetes on basal and gonadotropin-stimulated steroidogenesis, intratesticular content of leptin and the leptin and luteinising hormone receptors and on spermatogenesis. Diabetic rats had hyperleptinaemia, androgen deficiency and reduced sperm count and quality, and in the testes, they had the increased leptin level and the decreased content of the leptin and luteinising hormone receptors and 17-hydroxyprogesterone. The stimulating effects of chorionic gonadotropin on testosterone production and expression of steroidogenic genes (Star, Cyp11a1) were decreased. Metformin restored basal and gonadotropin-stimulated blood testosterone levels. In the testes, it restored gonadotropin-stimulated 17-hydroxyprogesterone, androstenedione and testosterone levels, Star expression and the content of leptin and the leptin and luteinising hormone receptors. Metformin also improved epididymal sperm count and morphology. We concluded that metformin treatment normalises the testicular steroidogenesis in diabetic rats, which is due to restoration of the gonadotropin and leptin systems in the testes and is associated with an improvement in spermatogenesis.

Flutamide Alters the Expression of Chemerin, Apelin, and Vaspin and Their Respective Receptors in the Testes of Adult Rats

Adipokines influence energy metabolism and have effects on male reproduction, including spermatogenesis and/or Sertoli cell maturation; however, the relationship between these active proteins and androgens in testicular cells is limited. Here, we studied the impact of short-term exposure to flutamide (an anti-androgen that blocks androgen receptors) on the expression of chemerin, apelin, vaspin and their receptors (CCRL2, CMKLR1, GPR1, APLNR, GRP78, respectively) in adult rat testes. Moreover, the levels of expression of lipid metabolism-modulating proteins (PLIN1, perilipin1; TSPO, translocator protein) and intercellular adherens junction proteins (nectin-2 and afadin) were determined in testicular cells. Plasma levels of adipokines, testosterone and cholesterol were also evaluated. Gene expression techniques used included the quantitative real-time polymerase chain reaction (qRT-PCR), Western blot (WB) and immunohistochemistry (IHC). The androgen-mediated effects observed post-flutamide treatment were found at the gonadal level as chemerin, apelin, and vaspin gene expression alterations at mRNA and protein levels were detected, whereas the cellular targets for these adipokines were recognised by localisation of respective receptors in testicular cells. Plasma concentrations of all adipokines were unchanged, whereas plasma cholesterol content and testosterone level increased after flutamide exposure. Differential distribution of adipokine receptors indicates potential para- or autocrine action of the adipokines within the rat testes. Additionally, changes in the expression of PLIN1 and TSPO, involved in the initial step of testosterone synthesis in Leydig cells, suggest that testicular cells represent a target of flutamide action. Increase in the gene expression of PLIN1 and TSPO and higher total plasma cholesterol content indicates enhanced availability of cholesterol in Leydig cells as a result of androgen-mediated effects of flutamide. Alterations in adherens junction protein expression in the testis confirm the flutamide efficacy in disruption of androgen signalling and presumably lead to impaired para- and autocrine communication, important for proper functioning of adipokines.

Interstitial Leydig Cell Tumorigenesis-Leptin and Adiponectin Signaling in Relation to Aromatase Expression in the Human Testis

Although epidemiological studies from the last years report an increase in the incidences of Leydig cell tumors (previously thought to be a rare disease), the biochemical characteristics of that tumor important for understanding its etiology, diagnosis, and therapy still remains not completely characterized. Our prior studies reported G-protein coupled estrogen receptor signaling and estrogen level disturbances in Leydig cell tumors. In addition, we found that expressions of multi-level-acting lipid balance- and steroidogenesis–controlling proteins including peroxisome proliferator-activated receptor are altered in this tumor. In order to get deeper into the other molecular mechanisms that regulate lipid homeostasis in the Leydig cell tumor, here we investigate the presence and expression of newly-described hormones responsible for lipid homeostasis balancing (leptin and adiponectin), together with expression of estrogen synthase (aromatase). Samples of Leydig cell tumors (n = 20) were obtained from patients (31–45 years old) and used for light and transmission electron microscopic, western blotting, and immunohistochemical analyses. In addition, body mass index (BMI) was calculated. In tumor mass, abundant lipid accumulation in Leydig cells and various alterations of Leydig cell shape, as well as the presence of adipocyte-like cells, were observed. Marked lipid content and various lipid droplet size, especially in obese patients, may indicate alterations in lipid homeostasis, lipid processing, and steroidogenic organelle function in response to interstitial tissue pathological changes. We revealed significantly increased expression of leptin, adiponectin and their receptors, as well as aromatase in Leydig cell tumors in comparison to control. The majority of patients (n = 13) were overweight as indicated by their BMI. Moreover, a significant increase in expression of phospholipase C (PLC), and kinases Raf, ERK which are part of adipokine transductional pathways, was demonstrated. These data expand our previous findings suggesting that in human Leydig cell tumors, estrogen level and signaling, together with lipid status, are related to each other. Increased BMI may contribute to certain biochemical characteristics and function of the Leydig cell in infertile patients with a tumor. In addition, altered adipokine-estrogen microenvironment can have an effect on proliferation, growth, and metastasis of tumor cells. We report here various targets (receptors, enzymes, hormones) controlling lipid balance and estrogen action in Leydig cell tumors indicating their possible usefulness for diagnostics and therapy.

Acid sphingomyelinase downregulation alleviates vascular endothelial leptin resistance in rats

Leptin resistance in endothelial cells leads to vascular endothelial dysfunction, which is the beginning and crucial link of atherosclerosis. However, the mechanism of leptin resistance remains obscure. Acid sphingomyelinase (ASM) catalyzes the hydrolysis of sphingomyelin to produce ceramide, which plays an important role in the progression of metabolic and cardiovascular diseases. In this study, we investigated whether ASM could regulate leptin resistance in vascular endothelial cells. We induced endothelial leptin resistance in rat aortic endothelial cells through treatment with palmitic acid (0.3 mM) or knockdown of leptin receptor (Ob-Rb), which resulted in the increase of suppressor of cytokine signaling 3 expression, the decrease of Ob-Rb expression, and signal transducer and activator of transcription 3 (STAT3) phosphorylation at Tyr705. We found that these indicators of leptin resistance were reversed by knockdown of ASM or by the selective ASM inhibitors amitriptyline (AMI) and imipramine (IMI). Supplementation of ceramide inhibited Ob-Rb expression and STAT3 phosphorylation by inhibiting extracellular signal-regulated kinase 1/2 activation. Furthermore, we found that knockdown of ASM enhanced endothelial nitric oxide (NO) synthase activity and NO production, as well as the Akt phosphorylation at ser473, which was regulated by STAT3. High-fat diet (HFD) feeding-induced leptin resistance in rats in vivo; administration of AMI and IMI (10 mg· kg⁻¹ per day, intraperitoneally, for 2 weeks) increased the release of endothelial NO to relieve the vasodilatory response and improved the endothelial leptin resistance in the aorta of HFD-fed rats. These results suggest that ASM downregulation reverses endothelial leptin resistance, and consequently improves vascular endothelial dysfunction. This study highlighted ASM as a potential therapeutic target for endothelial leptin resistance.

Leptin Receptor as a Potential Target to Inhibit Human Testicular Seminoma Growth

Although in past decades the adipokine leptin and its own receptor have been considered as significant cancer biomarkers, their potential involvement in human testicular seminoma growth and progression remains unexplored. Here, we showed that the expression of leptin and its receptor was significantly higher in human testicular seminoma compared with normal adult testis. Human seminoma cell line TCam-2 also expressed leptin along with the long and short isoforms of leptin receptor, and in response to leptin treatment showed enhanced activation of its downstream effectors. In line with these results, leptin stimulation significantly increased the proliferation and migration of TCam-2 cells. Treatment of TCam-2 cells with the peptide Leu-Asp-Phe-Ile (LDFI), a full leptin-receptor antagonist, completely reversed the leptin-mediated effects on cell growth and motility as well as reduced the expression of several leptin-induced target genes. More importantly, the in vivo xenograft experiments showed that LDFI treatment markedly decreased seminoma tumor growth. Interestingly, LDFI-treated tumors showed reduced levels of the proliferation marker Ki-67 as well as decreased expression of leptin-regulated genes. Taken together, these data identify, for the first time, leptin as a key factor able to affect testicular seminoma behavior, highlighting leptin receptor as a potential target for novel potential treatments in this type of cancer.

Insights into leptin signaling and male reproductive health: the missing link between overweight and subfertility?

Obesity stands as one of the greatest healthcare challenges of the 21st century. Obesity in reproductive-age men is ever more frequent and is reaching upsetting levels. At the same time, fertility has taken an inverse direction and is decreasing, leading to an increased demand for fertility treatments. In half of infertile couples, there is a male factor alone or combined with a female factor. Furthermore, male fertility parameters such as sperm count and concentration went on a downward spiral during the last few decades and are now approaching the minimum levels established to achieve successful fertilization. Hence, the hypothesis that obesity and deleterious effects in male reproductive health, as reflected in deterioration of sperm parameters, are somehow related is tempting. Most often, overweight and obese individuals present leptin levels directly proportional to the increased fat mass. Leptin, besides the well-described central hypothalamic effects, also acts in several peripheral organs, including the testes, thus highlighting a possible regulatory role in male reproductive function. In the last years, research focusing on leptin effects in male reproductive function has unveiled additional roles and molecular mechanisms of action for this hormone at the testicular level. Herein, we summarize the novel molecular signals linking metabolism and male reproductive function with a focus on leptin signaling, mitochondria and relevant pathways for the nutritional support of spermatogenesis.

Adipokines in Semen: Physiopathology and Effects on Spermatozoas

Adipokines are secreted by adipose tissue and could be the link between obesity and infertility. Different studies investigated the involvement of adipokines in reproductive functions but only a few have looked into the male part. This review assesses adipokine functions on male reproductive parameters. Adiponectin seems to have a positive effect on sperm parameters, whereas other adipokines such as resistin or chemerin would have a rather deleterious effect on spermatogenesis. Semen parameters seem to be impacted when resistin and chemerin are increased: indeed, there is a decrease of sperm motility. Sperm morphology is improved when adiponectin is increased. The most studied adipokine, leptin, has a dual effect with a positive effect on sperm at physiological levels and a negative one for high seminal concentrations. Many semen parameters and fertility itself are disturbed according to semen adipokine levels, even if it is not the only interfering element. Taken together, adipokines are found in human and animal semen and most of them or their receptors are expressed in male genital tract. Although the pathophysiological role of adipokines in semen is not clearly elucidated, the adipokines could influence sperm functionality and could be potential biomarkers of male fertility.

Exogenous leptin affects sperm parameters and impairs blood testis barrier integrity in adult male mice

BACKGROUND

Serum leptin levels are augmented in obese infertile men and in men with azoospermia. They also correlate inversely with sperm concentration, motility and normal forms. The mechanisms underlying the adverse effects of excess leptin on male reproductive function remain unclear. The present study aimed to evaluate the effects of exogenous leptin on sperm parameters in mice and to explore the underlying mechanisms.

METHODS

We treated normal adult male mice with saline, 0.1, 0.5 or 3 mg/kg leptin daily for 2 weeks. After treatment, serum leptin levels, serum testosterone levels, sperm parameters and testicular cell apoptosis were evaluated. Blood testis barrier integrity and the expression of tight junction-associated proteins in testes were also assessed. We further verified the direct effects of leptin on tight junction-associated proteins in Sertoli cells and the possible leptin signaling pathways involved in this process.

RESULTS

After treatment, there were no significant differences in body weights, reproductive organ weights, serum leptin levels and serum testosterone levels between leptin-treated mice and control mice. Administration of 3 mg/kg leptin reduced sperm concentration, motility and progressive motility while increasing the percentage of abnormal sperm and testicular cell apoptosis. Mice treated with 3 mg/kg leptin also had impaired blood testis barrier integrity, which was related to decreased tight junction-associated proteins in testes. Leptin directly reduced tight junction-associated proteins in Sertoli cells, JAK2/STAT, PI3K and ERK pathways were suggested to be involved in this process.

CONCLUSIONS

Exogenous leptin negatively affects sperm parameters and impairs blood testis barrier integrity in mice. Leptin reduced tight junction-associated proteins in Sertoli cells, indicating that leptin has a direct role in impairing blood testis barrier integrity. Given the function of blood testis barrier in maintaining normal spermatogenesis, leptin-induced blood testis barrier impairment may be one of the mechanisms contributing to male subfertility and infertility.

Role of leptin and the leptin receptor in the pathogenesis of varicocele-induced testicular dysfunction

The present study investigated the expression of leptin and its receptor in the left testis and hypothalamus of rats with varicocele and clarified their roles in the pathogenesis of varicocele-induced testicular dysfunction. A total of 40 male rats were divided randomly into four groups. Groups 1 (G1) and 3 (G3) underwent a sham operation. Groups 2 (G2) and 4 (G4) underwent operations to form a varicocele created by partial ligation of the left renal vein. G1 and G2 rats were euthanized 4 weeks after the operation while G3 and G4 rats were euthanized at 8 weeks. The expression of leptin and its receptor was analyzed by immunohistochemistry. The mRNA levels of leptin, its receptor, kisspeptin (KiSS-1), G-protein coupled receptor 54 (GPR54), gonadotropin releasing hormone (GnRH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were measured by reverse transcription-quantitative polymerase chain reaction. Testicular spermatogenesis function and gonadal hormone levels were measured. Compared with G1 and G3, the expression of leptin and its receptor in rat testis was significantly higher in G2 and G4, respectively. Leptin expression was inversely associated with the number of sperm in the left epididymis, thickness of the seminiferous epithelium and the diameter of seminiferous tubules. The expression of leptin receptors in the hypothalamus of G2 and G4 was significantly increased compared with that in G1 and G3, respectively. The mRNA levels of KiSS-1, GPR54, GnRH, LH and FSH in G2 and G4 were significantly increased compared with that in G1 and G3, respectively. Serum testosterone levels in G2 and G4 rats were significantly lower than those in G1 and G3 rats, respectively. There was no significant difference between the serum levels of FSH, LH and leptin. These results suggest that leptin and its receptor may serve significant roles in the pathogenesis of varicocele-induced testicular dysfunction.

Review of the role of leptin in the regulation of male reproductive function

Since discovered in 1994, leptin has been thought to be a pleiotropic hormone that regulates food intake, controls energy balance in the body and influences multiple tissues in the body. Leptin plays an important mediating role in the regulation of neuroendocrine and can transmit the nutritional status signals to the reproductive-related central nervous system. Many studies have shown that leptin may play an important role in the control of reproductive function. Leptin can act on all levels of the hypothalamus-pituitary-gonadal (HPG) axis and may have local effects on the function of testis and spermatogenesis. Leptin is critical for puberty initiation and can also modulate testosterone synthesis by downregulating cAMP-dependent activation of steroidogenic genes expressions. Leptin is found to be higher in infertile men than in normal subjects. Yet, the exact role of leptin in the regulation of male reproductive function remains incomplete. The purpose of this review was to summarise the recent research about the biological effects of leptin on male reproductive system. In-depth study of leptin in reproductive system will help to reveal the pathogenesis of infertility and provide new treatment ideas for human assisted reproductive technology.

Effects of androgens on the leptin system in immature male Atlantic salmon parr

Leptin modulates all levels of the reproductive endocrine axis in mammals, and in turn, both leptin and the leptin receptor are regulated by sex steroids. The aim of this study was to investigate if sex steroids regulate the leptin system also in fish. Immature one-year old male Atlantic salmon parr were implanted with Silclear capsules that were either empty or filled with 11-ketoandrostenedione (11KA) or testosterone (T) and the effects of 35-days treatment were investigated on measures of maturation, gene expression of leptin (lepa1, lepa2), leptin receptor (lepra1) and circulating plasma leptin. Both 11-KA and T stimulated the reproductive axis by increasing testes weight and up-regulated pituitary lh-β mRNA levels and for T also fsh-β. T up-regulated transcription levels of lepa1 and lepra1 in the pituitary, while 11-KA had no effect. Leptin receptor expression in the testis was unaltered by either androgen. T up-regulated lepa1 mRNA levels significantly also in the liver, but had no effect on lepa2, and 11KA did not affect hepatic gene expression of either lepa1 or lepa2. Plasma leptin levels did not differ significantly between treatments. The results indicate that androgens regulate gene expression of leptin and the leptin receptor in different tissues in fish and that the effects of leptin might be tissue specific considering plasma levels remained unaltered. Overall, the results suggest a role for leptin in fish reproduction, where sex steroids are able to regulate components of the leptin system differentially in liver and important tissues of the reproductive axis.

PI3Kα inactivation in leptin receptor cells increases leptin sensitivity but disrupts growth and reproduction

The role of PI3K in leptin physiology has been difficult to determine due to its actions downstream of several metabolic cues, including insulin. Here, we used a series of mouse models to dissociate the roles of specific PI3K catalytic subunits and of insulin receptor (InsR) downstream of leptin signaling. We show that disruption of p110α and p110β subunits in leptin receptor cells (LRΔα+β) produces a lean phenotype associated with increased energy expenditure, locomotor activity, and thermogenesis. LRΔα+β mice have deficient growth and delayed puberty. Single subunit deletion (i.e., p110α in LRΔα) resulted in similarly increased energy expenditure, deficient growth, and pubertal development, but LRΔα mice have normal locomotor activity and thermogenesis. Blunted PI3K in leptin receptor (LR) cells enhanced leptin sensitivity in metabolic regulation due to increased basal hypothalamic pAKT, leptin-induced pSTAT3, and decreased PTEN levels. However, these mice are unresponsive to leptin's effects on growth and puberty. We further assessed if these phenotypes were associated with disruption of insulin signaling. LRΔInsR mice have no metabolic or growth deficit and show only mild delay in pubertal completion. Our findings demonstrate that PI3K in LR cells plays an essential role in energy expenditure, growth, and reproduction. These actions are independent from insulin signaling.

Obesity-Induced Infertility in Male Mice Is Associated With Disruption of Crisp4 Expression and Sperm Fertilization Capacity

Approximately 15% of human couples of reproductive age have impaired fertility, and the male component accounts for about half of these cases. The etiology is usually unknown, but high correlation with the increase in obesity rates is documented. In this study, we show that diet-induced and genetically obese mice display copulatory behavior comparable to controls, but the number of females impregnated by obese males is remarkably low. Screening for changes in gene expression in the male reproductive tract showed decreased Crisp4 expression in testis and epididymis of obese mice. Lack of CRISP4 in the luminal membrane of epididymal cells indicated inadequate secretion. Consistent with CRISP4 action in acrosome reaction, sperm from mice fed a high-fat diet (HFD) had decreased fertilization capacity. CRISP4 treatment of sperm from HFD mice prior to in vitro fertilization improved fertilization rate. In leptin-deficient obese and infertile mice, leptin's effect to restore CRISP4 expression and function required gonadal hormones. Our findings indicate that the obesity-induced decline in sperm motility and fertilization capacity results in part from the disruption of epididymal CRISP4 expression and secretion.

Obesity, energy balance and spermatogenesis

Obesity has grown to pandemic proportions. It affects an increasing number of children, adolescents and young adults exposed to the silent comorbidities of this disorder for a longer period. Infertility has arisen as one important comorbidity associated with the energy dysfunction promoted by obesity. Spermatogenesis is a highly regulated process that is determined by specific energetic requirements. The reproductive potential of males relies on hormonal-dependent and -independent stimuli that control sperm quality. There are conflicting data concerning the impact of male overweight and obesity on sperm quality, as well as on the possible paternal-induced epigenetic trait inheritance of obesity. In addition, it remains a matter of debate whether massive weight loss induced by lifestyle interventions, drugs or bariatric surgery may or may not benefit obese men seeking fatherhood. Herein, we propose to discuss how energy balance may modulate hormonal signalling and sperm quality in overweight and obese men. We also discuss some molecular mechanisms that mediate obesity-related dysfunction in male reproductive system and how paternal obesity may lead to trait inheritance. Finally, we will discuss how lifestyle modifications and sustained weight loss, particularly the loss achieved by bariatric surgery, may revert some of the deleterious effects of obesity in men and their offspring.

Steroidogenic genes expressions are repressed by high levels of leptin and the JAK/STAT signaling pathway in MA-10 Leydig cells

The adipose tissue is an important endocrine organ secreting numerous peptide hormones, including leptin. Increased circulating levels of leptin, as a result of hormonal resistance in obese individuals, may contribute to lower androgen production in obese males. However, the molecular mechanisms involved need to be better defined. Androgens are mainly produced by Leydig cells within the testis. In male rodents, activation of the leptin receptor modulates a cascade of intracellular signal transduction pathways which may lead to regulation of transcription factors having influences on steroidogenesis in Leydig cells. Thus, as a result of high leptin levels interacting with its receptor and modulating the activity of the JAK/STAT signaling pathway, the activity of transcription factors important for steroidogenic genes expressions may be inhibited in Leydig cells. Here we show that Lepr is increasingly expressed within Leydig cells according to postnatal development. Although high levels of leptin (corresponding to obesity condition) alone had no effect on Leydig cells' steroidogenic genes expression, it downregulated cAMP-dependent activations of the cholesterol transporter Star and of the rate-limiting steroidogenic enzyme Cyp11a1. Our results suggest that STAT transcriptional activity is downregulated by high levels of leptin, leading to reduced cAMP-dependent steroidogenic genes (Star and Cyp11a1) expressions in MA-10 Leydig cells. However, other transcription factors such as members of the SMAD and NFAT families may be involved and need further investigation to better define how leptin regulates their activities and their relevance for Leydig cells function.

Loss of PI3K p110α in the Adipose Tissue Results in Infertility and Delayed Puberty Onset in Male Mice

Deletion of PI3K catalytic subunit p110α in adipose tissue (aP2-Cre/p110α^flx/flx, α−/− hereafter) results in increased adiposity, glucose intolerance, and liver steatosis. Because this endocrine organ releases hormones like leptin, which are important in reproductive physiology, we investigated the reproductive phenotype of α−/− males. Compared to controls, α−/− males displayed delayed onset of puberty accompanied by a reduction in plasma LH levels and testicular weight. At postnatal day 30, α−/− mice exhibited normal body weight but elevated fasted plasma leptin levels. Testicular leptin gene expression was increased, whereas expression of the cholesterol transporter StAR and of P450 cholesterol side chain cleavage enzyme was decreased. Adult α−/− males were infertile and exhibited hyperandrogenemia with normal basal LH, FSH, and estradiol levels. However, neither sperm counts nor sperm motility was different between genotypes. The mRNA levels of leptin and of 17-beta-dehydrogenase 3, and enzyme important for testosterone production, were significantly higher in the testis of adult α−/− males. The mRNA levels of ERα, an important regulator of intratesticular steroidogenesis, were lower in the testis of adult and peripubertal α−/− males. We propose that chronic hyperleptinemia contributes to the negative impact that disrupting PI3K signaling in adipocytes has on puberty onset, steroidogenesis, and fertility in males.

Effects of obesity and exercise on testicular leptin signal transduction and testosterone biosynthesis in male mice

To explore the role of the testicular leptin and JAK-STAT[leptin (LEP)-JAK-STAT] pathway in testosterone biosynthesis during juvenile stages and exercise for weight loss, male C57BL/6J mice were randomly divided into normal-diet and high-fat diet groups. After 10 wk, mice in the high-fat diet-fed group were further divided randomly into obese control, obese moderate-volume exercise, and obese high-volume exercise groups. Mice in the obese moderate-volume exercise group were provided with 2 h/day, 6 days/wk swimming exercise for 8 wk, and mice in the obese high-volume exercise group underwent twice the amount of daily exercise intervention as the obese moderate-volume exercise group. The results showed that a high-fat diet causes obesity, leptin resistance, inhibition of the testicular LEP-JAK-STAT pathway, decreased mRNA and protein expression of steroidogenic factor-1, steroidogenic acute regulatory protein, and the P-450 side-chain cleavage enzyme, a decrease in the serum testosterone-to-estradiol ratio, and declines in sperm quality parameters. Both moderate and high-volume exercise were able to reduce body fat and increase the mRNA and protein expression of LEP-JAK-STAT, but only moderate exercise significantly increased the mRNA and protein expression of steroidogenic factor-1, steroidogenic acute regulatory protein, and P-450 side-chain cleavage enzyme and significantly reversed the serum testosterone-to-estradiol ratio and sperm quality parameters. These findings suggest that by impairing the testicular LEP-JAK-STAT pathway, early-stage obesity inhibits the biosynthesis of testosterone and sexual development and reduces male reproductive potential. Long-term moderate and high-volume exercise can effectively reduce body fat and improve obesity-induced abnormalities in testicular leptin signal transduction, whereas only moderate-volume exercise can reverse the negative impacts of obesity on male reproductive function.

Hormonal and testicular changes in rats submitted to congenital hypothyroidism in early life

The goal of this study was to evaluate the influence of hypothyroidism induced by MMI, during gestation (G) or gestation plus lactation (GL) on testis and its relation with leptin in rats. Six to eight pups were killed at 90 days of age. For statistical analysis One-way ANOVA followed by the Holm-Sìdak post hoc test was used. Hypothyroidism resulted in a significant reduction in LH, FSH and testosterone and an increase in leptin serum levels (p < 0.04). There was a significant decrease in StAR, AR, FSHR, LHR, pSTAT3 and SOCS3 (p < 0.04) protein expression and in the fertility parameters (p < 0.04). We can conclude that hypothyroidism is associated with reduction of steroidogenesis and spermatogenesis leading to a low fertility potential in these animals. This outcome could be a consequence of low pituitary stimulus and testicular response and probably are not related with leptin hormone since its signaling pathway is down-regulated in the testis.

Leptin Suppresses Human Chorionic Gonadotropin-Induced Cyclooxygenase-2 Expression and Prostaglandin Production in Cultured Human Granulose Luteal Cells

OBJECTIVE

In a previous study, we demonstrated that high leptin levels at the time of human chorionic gonadotropin (hCG) injection impaired the pregnancy rate for women undergoing in vitro fertilization. In this study we examine leptin's effect on prostaglandin formation and cyclooxygenase (COX) expression induced by hCG in human granulose luteal (GL) cells.

METHODS

Human GL cells were obtained from women undergoing ovarian hyperstimulation. COX expression and microsomal prostaglandin E synthase (mPGES) expression, as well as prostaglandin E(2) (PGE(2)) and prostaglandin F(2alpha) (PGF(2alpha)) production were studied. This was done in both the presence and absence of leptin following hCG stimulation. PGE(2) and PGF(2alpha) were determined by enzyme-linked immunosorbent assay (ELISA). The expressions of COX and mPGES were investigated by using immunocytochemical techniques in addition to Western blotting and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis.

RESULTS

HCG and leptin do not affect COX-1 expression. However, leptin blocked COX-2 and mPGES expression induced by hCG. Moreover, while leptin, in various concentrations, did not affect PGE(2) and PGF(2alpha) levels, it inhibited the elevation of PGE(2) and PGF(2alpha) concentrations in response to hCG.

CONCLUSIONS

The study confirms that the expression of COX-2 is up-regulated by hCG in human GL cells. Leptin suppresses hCG-induced PGE(2) formation through the inhibition of COX-2 and mPGES expression. The preliminary results suggest a potential inhibiting effect of leptin on human GL cells induced by hCG.

Neonatal overfeeding induces early decline of the ovarian reserve: Implications for the role of leptin

Early life nutrition is crucial for reproduction. Overweight and obese girls are more likely to experience early menarche, increasing the risk of adult disease. We have previously demonstrated neonatal overfeeding in the rat leads to accelerated growth, early puberty and increased circulating levels of leptin, an adipocyte-derived hormone that regulates puberty. However, the long-term consequences of accelerated puberty and metabolic dysfunction on ovarian reserve are unknown. Here we show that neonatal overfeeding reduced the number of ovarian follicles in adult rats; specifically, the primordial follicle pool was reduced compared to controls. The reduction of ovarian reserve coincided with a diminished release of pituitary gonadotropins at ovulation and altered expression of ovarian markers important for follicular recruitment and survival. These changes were associated with increased levels of ovarian leptin and its receptor. Postnatal administration of leptin antagonist did not reverse the weight gain induced by early life overfeeding, but rescued the decline in the primordial follicle pool and abolished the differences in circulating leptin and gonadotropins. Our findings suggest that the acute effects of elevated circulating leptin may be responsible for the long-term reproductive outcomes after neonatal overfeeding, leading to premature ovarian ageing and changes in reproductive efficiency.

Leptin Within the Subphysiological to Physiological Range Dose Dependently Improves Male Reproductive Function in an Obesity Mouse Model

Obesity has recently been linked with reduced fertility, and the mechanisms underpinning this effect are currently unknown. The adipokine leptin is dysregulated in obesity and affects reproductive tracts; therefore, we investigated the dose-dependent effects of leptin on Leydig cell function and spermatogenesis. Eight-week-old leptin-deficient obese (ob/ob) male mice were treated with subphysiological (0.1- or 0.5-mg/kg body weight [BW]/d) or physiological (3.0-mg/kg BW/d) doses of leptin or saline for 12 weeks (chronic treatment) or 72 hours (acute treatment). We then evaluated male reproductive function markers. Mean testis weight increased significantly in the 0.1- and 3.0-mg/kg BW/d groups compared with saline controls (both P < .05). Intratesticular testosterone levels relative to testis weight significantly increased in the 0.5-mg/kg BW/d group compared with saline controls (P < .05). FSH levels increased in a dose-dependent manner with leptin treatment, whereas LH levels did not change. Leptin treatment significantly up-regulated both mRNA and protein expression of the steroidogenic enzyme cytochrome P450 17A1. Spermatogenesis improved in leptin-treated animals. Significantly more seminiferous tubules were observed in stages I-VIII (P < .01), and there were fewer abnormal seminiferous tubule structures (P < .01). Acute treatment with physiological leptin doses partially improved male reproductive markers without changing BW. Administration of subphysiological to physiological doses of leptin improves Leydig cell function and spermatogenesis.

Anti-estrogenic effect of semicarbazide in female zebrafish (Danio rerio) and its potential mechanisms

Semicarbazide (SMC), a member of the hydrazine family, has various toxic effects and has been detected in organisms, aquatic environments, and food. SMC exposure inhibited the transcription of hepatic vitellogenin and estrogen receptors in female zebrafish (Danio rerio), suggesting that it had anti-estrogenic properties. In order to elucidate the mechanisms underlying these, we exposed female zebrafish to SMC and used enzyme-linked immunosorbent assays to examine plasma 17β-estradiol (E2) and testosterone (T) levels. Gonad histology was analyzed and the mRNA expression of genes involved in the reproductive axis, the gamma-aminobutyric acid (GABA) shunt, and leptin was quantified by real-time PCR. Zebrafish were exposed to 1, 10, 100, or 1000μg/L SMC in a semi-static system for 96hours or 28 days. Plasma E2 levels were significantly decreased and ovarian maturation was inhibited by SMC, suggesting that its anti-estrogenic effect was exerted by reducing endogenous E2 levels. This was likely due to the SMC-mediated inhibition of cytochrome P450 (CYP) 19A mRNA levels, because this enzyme catalyzes the conversion of T to E2 in the gonads. In addition, down-regulation of the mRNA expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase, steroidogenic acute regulatory protein, CYP17, and 17beta-hydroxysteroid dehydrogenase was observed; this was predicted to reduce T concentrations and further contribute to the reduced E2 levels. SMC-induced changes in the expression of these steroidogenic genes correlated with decreased transcription of gonadotropic hormones (follicle-stimulating hormone and luteinizing hormone) and significantly elevated leptin expression. Furthermore, SMC also altered expression of the key enzyme in gamma-aminobutyric acid (GABA) synthesis, GABA receptors, and salmon gonadotropin-releasing hormone, thus affecting gonadotropin expression. Overall, SMC acted at multiple sites related to reproduction to reduce plasma E2 levels, consequently exerting an anti-estrogenic effect in female zebrafish. These effects were observed at environmentally relevant concentrations and highlight the importance of controlling SMC contamination.

Peroxisome proliferator-activated receptor gamma signaling in human sperm physiology

Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of the PPARs, which are transcription factors of the steroid receptor superfamily. PPARγ acts as an important molecule for regulating energy homeostasis, modulates the hypothalamic-pituitary-gonadal (HPG) axis, and is reciprocally regulated by HPG. In the human, PPARγ protein is highly expressed in ejaculated spermatozoa, implying a possible role of PPARγ signaling in regulating sperm energy dissipation. PPARγ protein is also expressed in Sertoli cells and germ cells (spermatocytes). Its activation can be induced during capacitation and the acrosome reaction. This mini-review will focus on how PPARγ signaling may affect fertility and sperm quality and the potential reversibility of these adverse effects.

Leptin modulates human Sertoli cells acetate production and glycolytic profile: a novel mechanism of obesity-induced male infertility?

Human feeding behavior and lifestyle are gradually being altered, favoring the development of metabolic diseases, particularly type 2 diabetes and obesity. Leptin is produced by the adipose tissue acting as a satiety signal. Its levels have been positively correlated with fat mass and hyperleptinemia has been proposed to negatively affect male reproductive function. Nevertheless, the molecular mechanisms by which this hormone affects male fertility remain unknown. Herein, we hypothesize that leptin acts on human Sertoli cells (hSCs), the "nurse cells" of spermatogenesis, altering their metabolism. To test our hypothesis, hSCs were cultured without or with leptin (5, 25 and 50ng/mL). Leptin receptor was identified by qPCR and Western blot. Protein levels of glucose transporters (GLUT1, GLUT2 and GLUT3), phosphofructokinase, lactate dehydrogenase (LDH) and monocarboxylate transporter 4 (MCT4) were determined by Western Blot. LDH activity was assessed and metabolite production/consumption determined by proton nuclear magnetic resonance. Oxidative damage was evaluated by assessing lipid peroxidation, protein carbonilation and nitration. Our data shows that leptin receptor is expressed in hSCs. The concentration of leptin found in lean, healthy patients, upregulated GLUT2 protein levels and concentrations of leptin found in lean and obese patients increased LDH activity. Of note, all leptin concentrations decreased hSCs acetate production illustrating a novel mechanism for this hormone action. Moreover, our data shows that leptin does not induce or protect hSCs from oxidative damage. We report that this hormone modulates the nutritional support of spermatogenesis, illustrating a novel mechanism that may be linked to obesity-induced male infertility.

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.

Regulation of the seasonal leptin and leptin receptor expression profile during early sexual maturation and feed restriction in male Atlantic salmon, Salmo salar L., parr

In mammals, leptin acts as an adiposity signal and is a crucial link between nutritional status and the reproductive axis. So far the link between leptin and energy balance during sexual maturation in teleosts has been poorly investigated. In this study, seasonal gene expression changes in two leptin genes (lepa1 and lepa2) and the leptin receptor were investigated during early sexual maturation in male Atlantic salmon parr under fully fed (control) and feed restricted conditions from April through September. Both Atlantic salmon lepa1 and lepa2 in the liver and lepr in the brain were significantly down-regulated in non-maturing control males in early spring, coinciding with the start of the growth and fat accumulation. In maturing control males, hepatic leptin expression increased during mid-spermatogenesis and lepa1 and lepa2 mRNA levels were up-regulated by 7.7 and 49 times respectively during final maturation. For the first time in a fish species, a significant up-regulation of lepr expression was observed in the testis throughout mid to late spermatogenesis. Feed restriction decreased the incidence of sexual maturation by 53% and highly up-regulated both leptin genes in the liver and the leptin receptor in the pituitary. This study shows that hepatic lepa1 and lepa2 expression and lepr expression in the testis is affected by early sexual maturation in male Atlantic salmon parr. Fast growth and high fat stores are associated with low leptin levels while feed restriction has a stimulatory effect on hepatic leptin and leptin receptor gene expression in the pituitary, suggesting a role for leptin other than that as an adiposity signal.

Reproductive function of the male obese Zucker rats: alteration in sperm production and sperm DNA damage

Obesity has been considered a public health issue in many countries and is of increasing concern for authorities over the past 6 years. The Zucker rat is a good experimental model for obesity and diabetes studies due to its metabolic characteristics that are similar to those developed by humans. A total of 12 obese Zucker rats and their lean littermates were killed in pubertal and young adult phases for assessing organ weights (testis and epididymis), testicular histomorphometric and stereological analyses, daily sperm production, and transit time in the epididymis. Sperm integrity was also investigated in the adult animals using the Comet assay. Alterations in organ weights, seminiferous epithelium architecture, sperm production, and transit time were noticed in the pubertal fatty rats. The volume density of the lymphatic space was decreased in both the ages. Adult animals had a significant increase in the extent of damage found in sperm DNA. Our results show for the first time that leptin receptor deficiency compromises sperm production during puberty and that genetic obese Zucker rats have increased sperm DNA fragmentation.

Thyroid hormone and leptin in the testis

Leptin is primarily expressed in white adipose tissue; however, it is expressed in the hypothalamus and reproductive tissues as well. Leptin acts by activating the leptin receptors (Ob-Rs). Additionally, the regulation of several neuroendocrine and reproductive functions, including the inhibition of glucocorticoids and enhancement of thyroxine and sex hormone concentrations in human beings and mice are leptin functions. It has been suggested that thyroid hormones (TH) could directly regulate leptin expression. Additionally, hypothyroidism compromises the intracellular integration of leptin signaling specifically in the arcuate nucleus. Two TH receptor isoforms are expressed in the testis, TRa and TRb, with TRa being the predominant one that is present in all stages of development. The effects of TH involve the proliferation and differentiation of Sertoli and Leydig cells during development, spermatogenesis, and steroidogenesis. In this context, TH disorders are associated with sexual dysfunction. An endocrine and/or direct paracrine effect of leptin on the gonads inhibits testosterone production in Leydig cells. Further studies are necessary to clarify the effects of both hormones in the testis during hypothyroidism. The goal of this review is to highlight the current knowledge regarding leptin and TH in the testis.

Leptin's effect on accelerated fracture healing after traumatic brain injury

OBJECTIVE

To investigate mechanisms behind the faster rehabilitation of limb fractures when associated with traumatic brain injury (TBI).

METHODS

New Zealand rabbits were divided into TBI group and sham-operation group for four studies as follows: (1) blood and cerebrospinal fluid (CSF) were drawn on days 1, 3, and 7 to demonstrate changes in serum leptin, growth hormone (GH), insulin-like growth factor 1 (IGF-1), and CSF leptin; (2) bone defection was created by drilling in the tibial bone and either leptin or normal saline was injected into rabbit's cerebellomedullary cistern. X-ray was taken at 1 days, 2 weeks, and 5 weeks and evaluated by criteria to determine rate of bone healing; (3) FITC-labeled rabbit leptin was injected into TBI and sham-operation groups, and frozen sections of rabbit brain were observed to identify differences in central nervous system (CNS) leptin by fluorescence; (4) polymerase chain reaction (PCR) was used to evaluate the expression of leptin production by brain tissue.

RESULTS

Serum and CSF leptin, GH, and IGF-1 concentrations were found to be higher in the TBI group than the sham-operation group at days 1, 3, and 7 (P<0·05). CSF leptin of the TBI group was positively correlated with serum leptin on day 1 (P<0·05), and positively correlated with GH and IGF-1 on days 3 and 7 (P<0·05). X-ray criteria demonstrated that leptin administration caused significantly faster healing calluses at 3 and 5 weeks as compared to control animals (P<0·05). FITC-labeled leptin study demonstrated that TBI animals had stronger expression of leptin in the brain than sham-operated animals. However, PCR of brain tissue leptin showed no significant differences between TBI and sham-operated animals in the expression of leptin.

CONCLUSIONS

Our study suggests that increased CSF leptin, likely from blood-brain barrier breakdown, combined with elevated serum GH and IGF-1 after TBI, leads to accelerated fracture healing.

Relationship of leptin administration with production of reactive oxygen species, sperm DNA fragmentation, sperm parameters and hormone profile in the adult rat

PURPOSE

Leptin, an adipose tissue-derived hormone, plays an important role in energy homeostasis and metabolism, and in the neuroendocrine and reproductive systems. The function of leptin in male reproduction is unclear; however, it is known to affect sex hormones, sperm motility and its parameters. Leptin induces mitochondrial superoxide production in aortic endothelia and may increase oxidative stress and abnormal sperm production in leptin-treated rats. This study aims to evaluate whether exogenous leptin affects sperm parameters, hormone profiles, and the production of reactive oxygen species (ROS) in adult rats.

METHODS

A total of 65 Sprague-Dawley rats were divided into three treated groups and a control group. Treated rats received daily intraperitoneal injections of 5, 10 and 30 μg/kg of leptin administered for a duration of 7, 15, and 42 days. Control rats were given 0.1 mL of 0.9 % normal saline for the same period. One day after final drug administration, we evaluated serum specimens for follicle-stimulating hormone (FSH), leutinizing hormone (LH), free testosterone (FT), and total testosterone (TT) levels. Samples from the rat epididymis were also evaluated for sperm parameters and motility characteristics by a Computer-Aided Semen Analysis (CASA) system. Samples were treated with 2',7'-dichlorofluorescein-diacetate (DCFH-DA) and analyzed using flow cytometry and TUNEL to determine the impact of leptin administration on sperm DNA fragmentation.

RESULTS

According to CASA, significant differences in all sperm parameters in leptin-treated rats and their age-matched controls were detected, except for TM, ALH and BCF. Serum FSH and LH levels were significantly higher in rats that received 10 and 30 μg/kg of leptin compared to those treated with 5 μg/kg of leptin in the same group and control rats (P < 0.05). ROS and sperm DNA fragmentation was significantly higher in rats injected with 10 and 30 μg/kg of leptin for 7 and 15 days compared with rats treated with 5 μg/kg of leptin and the control group (P < 0.05) for the same time period. However, at day 42 of treatment, ROS and sperm DNA fragmentation levels significantly decreased in all groups (P < 0.05).

CONCLUSION

According to these results, leptin can possibly affect male infertility by ROS induction or hormone profile modulation.

Inhibition of ghrelin signaling improves the reproductive phenotype of male ob/ob mouse

OBJECTIVE

To investigate whether ghrelin signaling is involved in the pathogenesis of male factor infertility induced by leptin deficiency.

DESIGN

Experimental study.

SETTING

University academic medical center.

ANIMAL(S)

Ten-week-old C57BL/6J mice and ob/ob mice.

INTERVENTION(S)

Western blotting, (quantitative) reverse transcription-polymerase chain reaction (qRT-PCR), immunohistochemistry, and in situ end labeling of fragmented DNA.

MAIN OUTCOME MEASURE(S)

Expression levels of ghrelin and its functional receptor growth hormone (GH) secretagogue receptor 1a (GHS-R1α) were examined by Western blotting and immunohistochemistry. Ob/ob mice were injected IP with specific GHS-R1α antagonist, and thereafter germ cell apoptosis and steroidogenic capability were assessed by TUNEL assay, (q) RT-PCR, and radioimmunoassay.

RESULT(S)

Expression of GHS-R1α and its endogenous ligand ghrelin was both up-regulated in ob/ob testis. Inhibition of the ghrelin pathway restored androgen synthesis, reduced germ cell apoptosis, and thereby resulted in improved sperm production in ob/ob mice.

CONCLUSION(S)

Ghrelin, as an antagonistic partner of leptin in the endocrinic/paracrine circuit, may be involved in the pathogenesis of male factor infertility induced by leptin deficiency.

Leptin-mediated modulation of steroidogenic gene expression in hypoxic zebrafish embryos: implications for the disruption of sex steroids

Hypoxia can impair reproduction of fishes through the disruption of sex steroids. Here, using zebrafish (Danio rerio) embryos, we investigated (i) whether hypoxia can directly affect steroidogenesis independent of pituitary regulation via modulation of steroidogenic gene expression, and (ii) the role of leptin in hypoxia-induced disruption of steroidogenesis. Exposure of fertilized zebrafish embryos to hypoxia (1.0 mg O(2) L(-1)) from 0-72 h postfertilization (hpf), a developmental window when steroidogenesis is unregulated by pituitary influence, resulted in the up-regulation of cyp11a, cyp17, and 3β-hsd and the down-regulation of cyp19a. Similar gene expression patterns were observed for embryos exposed to 10 mM cobalt chloride (CoCl(2), a chemical inducer of hypoxia-inducible factor 1, HIF-1), suggesting a regulatory role of HIF-1 in steroidogenesis. Testosterone (T) and estradiol (E2) concentrations in hypoxic embryos were greater and lesser, respectively, relative to the normoxic control, thus leading to an increased T/E2 ratio. Expression of the leptin-a gene (zlep-a) was up-regulated upon both hypoxia and CoCl(2) treatments. Functional assays suggested that under hypoxia, elevated zlep-a expression might activate cyp11a and 3β-hsd and inhibit cyp19a. Overall, this study indicates that hypoxia, possibly via HIF-1-induced leptin expression, modulates sex steroid synthesis by acting directly on steroidogenic gene expression.

Leptin action in pubertal development: recent advances and unanswered questions

In recent years we have witnessed a considerable advance in the understanding of the processes involved in pubertal development. This is partially due to the discovery of the kisspeptin system and its fundamental role in the control of reproductive physiology. In addition, the suspected relationship between increasing rates of childhood obesity and the apparent reduction in the age of puberty onset in girls has generated a growing interest in identifying the mechanisms by which nutrition may influence reproductive maturation. This review will focus on recent data unveiling the sites of leptin action in pubertal development that were generated using novel molecular techniques and genetically engineered mouse models. It will also emphasize areas of contention and the many relevant questions that remain unanswered.

Endocrine disrupting chemicals: Multiple effects on testicular signaling and spermatogenesis

In the past 200 years, an enormous number of synthetic chemicals with diverse structural features have been produced for industrial, medical and domestic purposes. These chemicals, originally thought to have little or no biological toxicity, are widely used in our daily lives as well as are commonly present in foods. It was not until the first World Wildlife Federation Wingspread Conference held in 1994 were concerns about the endocrine disrupting (ED) effects of these chemicals articulated. The potential hazardous effects of endocrine disrupting chemicals (EDCs) on human health and ecological well-being are one of the global concerns that affect the health and propagation of human beings. Considerable numbers of studies indicated that endocrine disruption is linked to "the developmental basis of adult disease," highlighting the significant effects of EDC exposure on a developing organism, leading to the propensity of an individual to develop a disease or dysfunction in later life. In this review, we intend to provide environmental, epidemiological and experimental data to associate pollutant exposure with reproductive disorders, in particular on the development and function of the male reproductive system. Possible effects of pollutant exposure on the processes of embryonic development, like sex determination and masculinization are described. In addition, the effects of pollutant exposure on hypothalamus-pituitary-gonadal axis, testicular signaling, steroidogenesis and spermatogenesis are also discussed.