Adiponectin and its receptors are expressed in the chicken testis: influence of sexual maturation on testicular ADIPOR1 and ADIPOR2 mRNA abundance

Cardiac-derived CTRP9 mediates the protection of empagliflozin against diabetes-induced male subfertility in mice

Previous studies have shown beneficial effects of empagliflozin (Empa), a selective inhibitor of the sodium-glucose cotransporter 2 (SGLT2), on diabetes and cardiovascular outcomes in patients with diabetes. However, whether Empa could ameliorate diabetes mellitus (DM)-induced male spermatogenesis dysfunction remains unclear. Our study aimed to investigate the effect of Empa in the development of DM-induced male spermatogenesis dysfunction and to reveal the molecular mechanisms. DM mice were orally treated with Empa to investigate the effects of Empa on DM-induced male mice spermatogenesis dysfunction. We employed a cardiac-specific C1q/tumor necrosis factor-related protein 9 (CTRP9)-deficient mouse model and a cardiac-specific CTRP9 overexpression mouse model to investigate its role in the protection of Empa against diabetes-induced male subfertility. We found that Empa treatment could improve DM-induced male mice subfertility. Interestingly, we discovered that cardiac-derived CTRP9 was decreased in DM mice and this decrease was prevented by Empa treatment. A CTRP9 blocking antibody or cardiac-specific depletion of CTRP9 abolished the protection of Empa on DM-induced male subfertility. Cardiac-specific CTRP9 overexpression ameliorated DM-induced male subfertility. Mechanistically, we identified that cardiac-derived CTRP9 increased steroidogenesis in mice with diabetes in a PKA-dependent manner. We also provided direct evidence that activation of AMP activated protein kinase α (AMPKα)/nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signalling pathway by CTRP9 was responsible for the attenuation of ferroptosis in Leydig cells. In conclusions, we supposed that Empa was a potential therapeutic agent against DM-induced male mice spermatogenesis dysfunction.

Obesity and male fertility disorders

Often associated with obesity, male infertility represents a widespread condition that challenges the wellbeing of the couple. In this article, we provide a comprehensive and critical analysis of studies exploring the association between obesity and male reproductive function, to evaluate the frequency of this association, and establish the effects of increased body weight on conventional and biofunctional sperm parameters and infertility. In an attempt to find possible molecular markers of infertility in obese male patients, the numerous mechanisms responsible for infertility in overweight/obese patients are reviewed in depth. These include obesity-related functional hypogonadism, insulin resistance, hyperinsulinemia, chronic inflammation, adipokines, irisin, gut hormones, gut microbiome, and sperm transcriptome. According to meta-analytic evidence, excessive body weight negatively influences male reproductive health. This can occurr through a broad array of molecular mechanisms. Some of these are not yet fully understood and need to be further elucidated in the future. A better understanding of the effects of metabolic disorders on spermatogenesis and sperm fertilizing capacity is very useful for identifying new diagnostic markers and designing therapeutic strategies for better clinical management of male infertility.

The Role of Adipokines in the Control of Pituitary Functions

The pituitary gland is a key endocrine gland in all classes of vertebrates, including mammals. The pituitary gland is an important component of hypothalamus-pituitary-target organ hormonal regulatory axes and forms a functional link between the nervous system and the endocrine system. In response to hypothalamic stimuli, the pituitary gland secretes a number of hormones involved in the regulation of metabolism, stress reactions and environmental adaptation, growth and development, as well as reproductive processes and lactation. In turn, hormones secreted by target organs at the lowest levels of the hormonal regulatory axes regulate the functions of the pituitary gland in the process of hormonal feedback. The pituitary also responds to other peripheral signals, including adipose-tissue-derived factors. These substances are a broad group of peptides known as adipocytokines or adipokines that act as endocrine hormones mainly involved in energy homeostasis. Adipokines, including adiponectin, resistin, apelin, chemerin, visfatin, and irisin, are also expressed in the pituitary gland, and they influence the secretory functions of this gland. This review is an overview of the existing knowledge of the relationship between chosen adipose-derived factors and endocrine functions of the pituitary gland, with an emphasis on the pituitary control of reproductive processes.

Partial Lipectomy of the Epididymal Fat Alters Expression of the Steroidogenic Enzymes in the Mouse Testis at Different Postnatal Ages

The epididymal fat is a type of gonadal adipose tissue, which is localized closely to the testis. Even though it has been suggested that the epididymal fat is necessary for maintenance of spermatogenesis in the testis, the influence of epididymal fat on expression of testicular steroidogenic enzymes has not been examined. In the present research, expressional changes of steroidogenic enzymes in the mouse testis after 2 weeks of the surgical partial lipectomy of epididymal fat at different postnatal ages were determined by real-time polymerase chain reaction analysis. The transcript levels of all molecules at 2 months of postnatal age were significantly increased by the lipectomy of epididymal fat. However, the lipectomy at 5 months of postnatal age resulted in decreases of expression levels of all molecules examined in the testis. Except a reduced transcript level of hydroxysteroid 17-beta dehydrogenase 3, there were no significant changes of expression levels of other steroidogenic enzymes by the lipectomy at 8 months of postnatal age. At 12 months of postnatal age, the lipectomy caused a significant increase of transcript level of steroidogenic acute regulatory protein and a significant decrease of transcript level of hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1, without any expressional change of cytochrome P450 side chain cleavage, hydroxysteroid 17-beta dehydrogenase 3, and hydroxysteroid 17-beta dehydrogenase 3 in the testis. These findings suggest that the substances derived from epididymal fat could differentially influence on expression of steroidogenic enzymes in the testis during postnatal period.

Adiponectin inhibits GnRH secretion via activating AMPK and PI3K signaling pathways in chicken hypothalamic neuron cells

It has been reported that adiponectin (AdipoQ), an adipokine secreted by white adipose tissue, plays an important role in the control of animal reproduction in addition to its function in energy homeostasis by binding to its receptors AdipoR1/2. However, the molecular mechanisms of AdipoQ in the regulation of animal reproduction remain elusive. In this study, we investigated the effects of AdipoQ on hypothalamic reproductive hormone (GnRH) secretion and reproduction-related receptor gene (estrogen receptor [ER] and progesterone receptor [PR]) expression in hypothalamic neuronal cells (HNCs) of chickens by using real-time fluorescent quantitative PCR (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), Western blot (WB) and cell counting kit-8 (CCK-8) assays and found that overexpression of AdipoQ could increase the expression levels of AdipoR1/2 and reproduction-related receptor genes (P < 0.05) while decreasing the expression level of GnRH. In contrast, interference with AdipoQ mRNA showed the opposite results in HNCs. Furthermore, we demonstrated that AdipoQ exerts its functions through the AMPK and PI3K signaling pathways. Finally, our in vitro experiments found that AdipoRon (a synthetic substitute for AdipoQ) treatment and AdipoR1/2 RNAi interference co-treatment resulted in no effect on GnRH secretion, suggesting that the inhibition of GnRH secretion by AdipoQ is mediated by the AdipoR1/2 signaling axis. In summary, we uncovered, for the first time, the molecular mechanism of AdipoQ in the regulation of reproductive hormone secretion in hypothalamic neurons in chickens.

Role of central Adiponectin and its interactions with NPY and GABAergic systems on food intake in neonatal layer chicken

BACKGROUND & AIM

Adiponectin is a member of the adipokine family and contributes to regulating energy homeostasis, reproduction, and various biological functions, such as insulin receptor signaling pathway sensitivity, mitochondrial biogenesis, oxidative metabolism, neurogenesis, and suppression of inflammation. This study aimed to investigate the effects of intracerebroventricular (ICV) injection of adiponectin and its interaction with the neuropeptide Y (NPY) and GABAergic systems on central appetite regulation in neonatal layer-type chickens.

MATERIALS & METHODS

In this study, 6 experiments were conducted, each of which included 4 experimental groups. In the first experiment, the chickens were injected with saline and adiponectin (20.73, 41.45, and 62.18 nmol). In the second experiment, saline, adiponectin (62.18 nmol), B5063 (NPY1 receptor antagonist, 2.12 nmol), and simultaneous injections of adiponectin and B5063 were performed. Experiments 3 to 6 were done in the same way to experiment 1, but the chickens were injected with SF22 (NPY2 receptor antagonist, 2.66 nmol), SML0891 (NPY5 receptor antagonist, 2.89 nmol), picrotoxin (GABAA receptor antagonist, 0.89 nmol), CGP54626 (GABAB receptor antagonist, 0.047 nmol) instead of B5063. Feed consumption was measured 120 min after the injection.

RESULTS

A dose-dependent increase in appetite was observed after the injection of adiponectin (20.73, 41.45, and 62.18 nmol) (P<0.05). The injection of B5063 + adiponectin attenuated the hyperphagic effect of adiponectin (P< 0.05). In addition, co-injection of picrotoxin and adiponectin significantly decreased adiponectin-induced hyperphagia (P<0.05). In addition, adiponectin significantly increased the number of steps, jumps, exploratory food, pecks, and standing time, while decreasing sitting time and rest time (P<0.05).

CONCLUSION

These results suggest that the hyperphagic effects of adiponectin are probably mediated through NPY1 and GABAA receptors in neonatal layer-type chickens.

Osteocalcin and Its Potential Functions for Preventing Fatty Liver Hemorrhagic Syndrome in Poultry

Osteocalcin (OCN) is synthesized and secreted by differentiating osteoblasts. In addition to its role in bone, OCN acts as a hormone in the pancreas, liver, muscle, fat, and other organs to regulate multiple pathophysiological processes including glucose homeostasis and adipic acid metabolism. Fat metabolic disorder, such as excessive fat buildup, is related to non-alcoholic fatty liver disease (NAFLD) in humans. Similarly, fatty liver hemorrhage syndrome (FLHS) is a metabolic disease in laying hens, resulting from lipid accumulation in hepatocytes. FLHS affects hen health with significant impact on poultry egg production. Many studies have proposed that OCN has protective function in mammalian NAFLD, but its function in chicken FLHS and related mechanism have not been completely clarified. Recently, we have revealed that OCN prevents laying hens from FLHS through regulating the JNK pathway, and some pathways related to the disease progression have been identified through both in vivo and vitro investigations. In this view, we discussed the current findings for predicting the strategy for using OCN to prevent or reduce FLHS impact on poultry production.

Presence, Tissue Localization, and Gene Expression of the Adiponectin Receptor 1 in Testis and Accessory Glands of Male Rams during the Non-Breeding Season

Adiponectin (ADIPOQ) is a member adipocytokines, and its actions are supported by two receptors, ADIPOQ receptor 1 and -2, respectively (ADIPOR1 and -R2). Our study was performed to evaluate the ADIPOR1 presence and location and its gene expression in reproductive tissues of the male ram, during its non-breading season. The different portions of the male ram reproductive system (testis, epididymis, seminal vesicle, ampoule vas deferens, bulb-urethral gland) were collected in a slaughterhouse. Immunohistochemistry showed ADIPOR1 positive signals in the cytoplasm of all the glandular epithelial cells, with a location near the nucleus; in the testes, the positive reaction was evidenced in the cytoplasm in the basal portion of the germinal epithelial cells. The immune reaction intensity was highest (p < 0.001) in the prostate and seminal vesicles glands than that of other parts of the ram reproductive tract. RT-qPCR detected the ADIPOR1 transcript in the testes, epididymis, vas deferens, bulbourethral glands, seminal vesicles, and prostate; the expression levels were high (p < 0.01) in the prostate and low (p < 0.01) in the testis, epididymis, and bulbourethral glands. The present results evidenced the possible ADIPOQ/ADIPOR1 system's role in regulating the testicular activity of male rams during the non-breading season.

The adiponectin receptor agonist, AdipoRon, promotes reproductive hormone secretion and gonadal development via the hypothalamic-pituitary-gonadal axis in chickens

Adiponectin is a key hormone secreted by fat tissues that has multiple biological functions, including regulating the energy balance and reproductive system by binding to its receptors AdipoR1 and AdipoR2. This study investigated the correlation between the levels of adiponectin and reproductive hormones in the hypothalamic-pituitary-ovarian (HPO) axis of laying hens at 4 different developmental stages (15, 20, 30, and 68 wk) and explored the effects of AdipoRon (an activator of adiponectin receptors) on the hypothalamic-pituitary-gonadal (HPG) axis and follicle and testicular Leydig cells in vitro and in vivo. The results demonstrated that the adiponectin level was significantly correlated with that of reproductive hormones in the HPO axis (e.g., GnRH, FSH, LH, and E2) in laying hens at 4 different ages. Moreover, AdipoRon could promote the expression of AdipoR1 and AdipoR2 and the secretion of reproductive hormones in the HPG axis, including GnRH, FSH, LH, P4, and T. AdipoRon could also upregulate the expression of genes related to follicular steroidogenesis (STAR, CYP19A1, CYP17A1, and CYP11A1), hepatic lipid synthesis (OVR, MTP), follicular lipid uptake (PPAR-g), and follicular angiogenesis (VEGFA1, VEGFA2, VEGFR1, ANGPT1, ANGPT2, TEK) in the oviposition period, and all of these findings were consistent with the results obtained from in vitro experiments after the transfection of small white follicles (SWFs) with AdipoRon. Furthermore, the results suggest that AdipoRon increases the diameter of testicular seminiferous tubules, the number of spermatogenic cells and sperm production in vivo and enhances the expression of AdipoR1, AdipoR2 and steroid hormones in vitro. Collectively, the findings suggest that AdipoRon could facilitate the expression and secretion of reproductive hormones in the HPG axis by activating its receptors and then improve the growth and development of follicles and testes in chickens.

17β-estradiol rescues the damage of thiazolidinedione on chicken Sertoli cell proliferation via adiponectin

Thiazolidinedione (TZD) is an oral anti-diabetic drug that exhibits some side effects on the male reproductive system by interfering with the steroidogenesis and androgenic activity and also shows anti-proliferative effect on several cell types. This study investigated the effect of TZD on immature chicken Sertoli cell (SC) proliferation and the potential mechanism by which 17β-estradiol regulated this process. Chicken SC viability was investigated under different treatment concentration and time of TZD. 17β-estradiol (0.001 μM, 24 h) was added to analyze its effects on TZD-mediated cell viability, cell metabolic activity, cell growth, cell cycle progression, reactive oxygen species (ROS) level, antioxidant enzyme activity, mitochondria activity, oxygen consumption rate, adenosine triphosphate (ATP) level, and mitochondrial respiratory chain enzyme activity, adiponectin expression and several cell proliferation-related genes mRNA and protein levels. We performed the microRNA (miRNA) array to find TZD-induced differentially expressed miRNAs and validated whether miR-1577 can target on adiponectin via the dual luciferase reporter assay, as well as verified the effect of adiponectin addition with different concentrations on the SC viability. Further, SCs were transfected with miR-1577 agomir (a double-stranded synthetic miRNA mimic) in the presence or absence of TZD and antagomir (a single-stranded synthetic miRNA inhibitor) in the presence or absence of 17β-estradiol to analyze whether miR-1577 was involved in TZD-mediated SC proliferation and whether 17β-estradiol regulated this process. Results showed that TZD significantly inhibited SC viability, cell metabolic activity, cell growth, and cell cycle progression, while increased adiponectin level and ROS generation. TZD-treated SCs presented decreases of antioxidant enzyme activity, mitochondria activity, basal and maximal respiration, ATP production and level, mitochondrial respiratory chain enzyme activity, and mRNA and protein expressions of several cell proliferation-related genes, as well as the significant alteration of miRNA expressions (a total number of 55 miRNAs were up-regulated whereas 53 miRNAs down-regulated). Whereas, 17β-estradiol played a positive role in chicken SC proliferation and rescued the damage of TZD on SC proliferation by up-regulating miR-1577 expression whose target gene was validated to be the adiponectin. In addition, exogenous adiponectin (more than 1 μg/ml) treatment exhibited a significant inhibition on the SC viability. Transfection of miR-1577 agomir promoted the SC proliferation via down-expressed adiponectin, and increased the mitochondrial function and cell proliferation-related gene expression, while TZD weakened the positive effect of miR-1577 agomir on SCs. On the other hand, transfection of miR-1577 antagomir inhibited SC proliferation by producing the opposite effects on above parameters, while 17β-estradiol attenuated the negative effect of miR-1577 antagomir on SCs. These findings suggest down-expressed miR-1577 is involved in the regulation of TZD-inhibited SC proliferation through increasing adiponectin level, and this damage of TZD on the immature chicken SC proliferation can be ameliorated by appropriate dose of exogenous 17β-estradiol treatment. This study provides an insight into the cytoprotective effect of 17β-estradiol on TZD-damaged SC proliferation and may suggest a potential strategy for reducing the risk of SC dysfunction caused by the abuse of TZD.

Adipokines in metabolic and reproductive functions in birds: An overview of current knowns and unknowns

Adipose tissue is now recognized as an active endocrine organ, which synthesizes and secretes numerous peptides factors called adipokines. In mammals, they exert pleiotropic effects affecting energy metabolism but also fertility. In mammals, secretion of adipokines is altered in adipose tissue dysfunctions and may participate to obesity-associated disorders. Thus, adipokines are promising candidates both for novel pharmacological treatment strategies and as diagnostic tools. As compared to mammals, birds exhibit several unique physiological features, which make them an interesting model for comparative studies on endocrine control of metabolism and adiposity and reproductive functions. Some adipokines such as leptin and visfatin may have different roles in avian species as compared to mammals. In addition, some of them found in mammals such as CCL2 (chemokine ligand 2), resistin, omentin and FGF21 (Fibroblast Growth factor 21) have not yet been mapped to the chicken genome model and among its annotated gene models. This brief review aims to summarize data (structure, metabolic and reproductive roles and molecular mechanisms involved) related to main avian adipokines (leptin, adiponectin, visfatin, and chemerin) and we will briefly discuss the adipokines that are still lacking in avian species.

Expression and localization of apelin and its receptor in the testes of diabetic mice and its possible role in steroidogenesis

Type 1 diabetes mellitus (T1DM) is a metabolic disorder with severe hyperglycemia, one of the complications of which is testicular dysfunctions, androgen deficiency and decreased male fertility. In the diabetic testes, the expression and signaling pathways of leptin and a number of other adipokines are significantly changed. However, there is no information on the localization and expression of adipokine, apelin and its receptor (APJ) in the diabetic testes, although there is information on the involvement of apelin in the regulation of reproductive functions. The aim of this study was to investigate the expression and localization of apelin and APJ in the testes of mice with streptozotocin-induced T1DM and to estimate the effects of agonist (apelin-13) and antagonist (ML221) of APJ on the testosterone production by diabetic testis explants in the in vitro conditions. We first detected the expression of apelin and its receptor in the mouse testes, and showed an increased intratesticular expression of apelin and APJ along with the reduced testosterone secretion in T1DM. Using imunohistochemical approach, we showed that apelin and APJ are localized in the Leydig and germ cells, and in diabetes, the amount of these proteins was significantly higher than in the control mice. The diabetic testes had a decrease in germ cell proliferation (the reduced PCNA and GCNA levels) and an increase in apoptosis (the increased active caspase-3 and decreased BCL2 levels). These results suggest an involvement of apelin and APJ in T1DM-induced testicular pathogenesis. Treatment of the cultured testis explants with ML221 significantly increased the testosterone secretion, whereas apelin-13 was ineffective. Thus, hyperapelinemia in the testes can significantly contribute to testicular pathogenesis in T1DM, and pharmacological inhibition of apelin receptors can improve testicular steroidogenesis.

Effect of exercise training on gene expression of adiponectin and its receptors in testicles and sex hormones in diabetic rats

Adiponectin and its receptors are expressed in the male reproductive system, which play a role in regulating male sex hormones and fertility. Diabetes was induced by Streptozotocin-Nicotinamide (STZ-NA i.p) in rats and after performing the trainings, adiponectin gene expression and its receptors in the testis were evaluated using real time PCR, and blood serum was then used in order to assess FSH, LH and testosterone. The STZ-NA significantly increased the fasting blood glucose, gene expression of adiponectin AdipoR1 in the testicles of diabetic rats. A significant reduction in serum testosterone and LH levels were observed in the diabetic group. Resistance and endurance training decreased blood glucose, adiponectin and AdipoR1 gene, and also increased the serum testosterone and LH levels in diabetic rats. Overall, our data suggest the role played by training in improve expression of adiponectin and AdipoR1 gene by increasing the serum testosterone and LH levels in type 2 diabetic rats.

Adiponectin/AdipoRs signaling as a key player in testicular aging and associated metabolic disorders

Aging undergoes serious worsening of peripheral organs and vital physiological processes including reproductive performances. Altered white adipose tissue and adipocyte functioning during aging results in ectopic lipid storage/obesity or metabolic derangements, leading to insulin resistance state. Eventually, accelerating cellular senescence thereby enhancing the high risk of age-associated metabolic alterations. Such alterations may cause derangement of numerous physiologically active obesity hormones, known as "adipokines." Specifically, adiponectin exhibits insulin sensitizing action causing anti-aging and anti-obesity effects via activation of adiponectin receptors (AdipoRs). The male reproductive physiology from reproductive mature stage to advanced senescent stage undergoes insidious detrimental changes. The mechanisms by which testicular functions decline with aging remain largely speculative. Adiponectin has also recently been shown to regulate metabolism and longevity signaling thus prolonging lifespan. Therefore, the strategy for activating adiponectin/AdipoRs signaling pathways are expected to provide a solid basis for the prevention and treatment of aging and obesity-associated reproductive dysfunctions, as well as for ensuring healthy reproductive longevity in humans.

Adverse effects of metabolic disorders in childhood on adult reproductive function and fertility in the male

Over the last 50 years, there has been a steady decline in fertility rates in humans, which has occurred in parallel with an increasing incidence of obesity and metabolic disorders. The potential impact of these disorders and plausible mechanisms by which they negatively influence male reproduction are only partly understood and published data are often controversial. Obesity is one of the most important health challenges worldwide and is becoming more prevalent in children and adolescents. Obesity, the metabolic syndrome and related co-morbidities can lead to impaired male reproductive function, including adverse effects on spermatogenesis and steroidogenesis as illustrated by reduced sperm number and quality, decreased testosterone levels and elevated inflammatory markers. The incidence of diabetes mellitus type I is also dramatically increasing and may negatively impact spermatogenesis and testicular function, resulting in decreased serum testosterone and epididymal weight. In this review, we summarize and discuss the effects of metabolic diseases that typically develop during childhood and adolescence on later reproductive function and fertility. While impact on reproductive health is likely observed in both sexes, we have chosen to focus on the male in the current review. Specifically, we illustrate adverse effects of obesity, type 1 diabetes, the metabolic syndrome and insulin resistance on sperm function and testosterone metabolism. Identification of pathophysiological mechanisms during childhood may open up new avenues for early prevention and treatment resulting in better reproductive outcomes and improved fertility rates during adulthood.

Adiponectin and its receptor genes' expression in response to Marek's disease virus infection of White Leghorns

Marek’s disease virus (MDV) causes T-cell lymphoma in susceptible chicken and is also related to an imbalance of the lipid metabolism. Adiponectin is a circulatory cytokine secreted from adipose tissue and exerts critical metabolic functions. Although the associations between adiponectin and diseases, including lipid disorder and noncardiac vascular diseases, have been reported, little is known about the relationship between MDV infection and adiponectin. Here, we challenged white Leghorns from Marek’s disease (MD)-susceptible and MD-resistant lines with MDV at 7 D of age and then explored the body weight and plasma lipoprotein levels at 21 D after MDV infection. Meanwhile, adiponectin and the expression of its receptors were detected using quantitative real-time PCR and Western blot. The results showed that MDV infection induced body weight loss in all the experimental birds. Meanwhile, the concentrations of total cholesterol and high-density lipoprotein were lower after the infection, although there was no significant difference (P > 0.05). However, the infection did not affect adiponectin circulating levels in plasma. MD-susceptible birds had much lower plasma adiponectin than MD-resistant birds (P < 0.01). In abdominal fat, there was no significant difference in adiponectin mRNA level. Still, we observed a significant decrease in adiponectin protein concentration, as well as adipoR1 and adipoR2, at both mRNA and protein levels in the infected compared with the noninfected MD-susceptible chickens. In the spleen, MDV infection significantly reduced the adiponectin mRNA expression but increased the protein in MD-susceptible chickens, which decreased both adipoR1 mRNA expression and protein levels. Also interestingly, the adipoR1 mRNA expression level was significantly increased in MD-susceptible chickens in the liver after MDV infection. All findings in the present study provided interesting insights into adiponectin metabolism in chickens after MDV infection, which helps to advance the understanding of lipid metabolism in response to herpesvirus infection.

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.

An integrated analysis of testis miRNA and mRNA transcriptome reveals important functional miRNA-targets in reproduction traits of roosters

The reproductive efficiency of roosters is an important trait in poultry production; however, the molecular mechanisms underlying this trait are not clearly understood. Here, we compared the mRNA and microRNA (miRNA) transcriptomes of testis from roosters with divergent sperm motility. A total of 302 differentially expressed genes (DEGs), including 182 upregulated genes and 120 downregulated genes, were identified in high sperm motility groups compared with low sperm motility groups. A subset of these DEGs related to steroid hormone biosynthesis and thus could be important for spermatogenesis. Additionally, we detected 13 differentially expressed miRNAs (DEMs) between two groups, and target gene prediction indicated seven of these could be associated with spermatogenesis. Based on a comprehensive analysis of these transcriptomes, miRNA-mRNA interaction networks were constructed. Six DEGs were predicted to be regulated by DEMs. Subsequently, we validated the negative regulation of family with sequence similarity 84, member A (FAM84A) by miR-215 using a dual-luciferase reporter system. These results provide new insights into the molecular profile of the testis and identify genes that may determine sperm motility in chickens.

Direct actions of adiponectin on changes in reproductive, metabolic, and anti-oxidative enzymes status in the testis of adult mice

Obesity is a major health problem that is linked to decreased sperm count. It is hypothesized that an obesity-associated reduction in adiponectin secretion may be responsible for impairment of spermatogenesis. Therefore, the aim of the study was to evaluate the direct role of adiponectin in spermatogenesis and steroid synthesis in adult mice. This study showed that adiponectin receptors (AdipoR1 and AdipoR2) were localized in Leydig cells and seminiferous tubules in the testis of adult mice. The result of the in vitro study showed the direct action of adiponectin on spermatogenesis by stimulating cell proliferation (PCNA) and survival (Bcl2) and by suppressing cell apoptosis. Treatment of testis with adiponectin also enhanced transport of the energetic substrates glucose and lactate to protect cells from undergoing apoptosis. Adiponectin treatment further showed a significant reduction in oxidative stress and nitric oxide. Our findings suggest that adiponectin effectively facilitates cell survival and proliferation, as well as protects from apoptosis. Thus, adiponectin treatment may be responsible for enhancing sperm counts. Interestingly, this study showed the stimulatory effect of adiponectin in spermatogenesis but showed an inhibitory effect on testosterone and estradiol synthesis in the testes. Based on the present study, it is hypothesized that systemic adiponectin treatment may be a promising therapeutic strategy for the improvement of spermatogenesis and sperm count.

Adipocytokines may delay pubertal maturation of human Sertoli cells

Reproduction is an important target of obesity complications, including adverse effects on spermatogenesis and steroidogenesis. Adipocytokines are key mediators in various complications of obesity. Our aim was to study the potential of adipocytokines to affect Sertoli cell function, which is crucial for spermatogenesis, and possibly link these findings to the observed attenuation of spermatogenesis in obese males. Testicular biopsies were obtained from healthy donors. Highly purified adult human Sertoli cells (HSCs) were isolated by fluorescence-activated cell sorting. Cells were cultured and exposed to different concentrations of adipocytokines (10-1000ngmL-1 ) for 2-7 days. Expression of selected Sertoli cell genes was quantified by quantitative polymerase chain reaction. Long-term treatment (7 days) of HSCs with higher concentrations of chemerin, irisin, nicotinamide phosphoribosyltransferase (Nampt), resistin and progranulin significantly suppressed FSH receptor expression (by 79%, 83%, 64%, 71% and 26% respectively; P P invitro , may negatively affect Sertoli cell maturation and retain these cells in a more prepubertal stage. This could negatively affect testis function and add to fertility problems in obese adults.

Estrogenic Compounds or Adiponectin Inhibit Cyclic AMP Response to Human Luteinizing Hormone in Mouse Leydig Tumor Cells

Mouse Leydig Tumor cells (mLTC), transiently expressing cAMP-dependent luciferase, were used to study the influence of sexual steroids and of adiponectin (ADPN) on the cAMP response to luteinizing hormones (LH). While testosterone and progesterone had no significant effect, several molecules with estrogenic activity (17β-estradiol, ethynylestradiol, and bisphenol A) provoked a decrease in intracellular cyclic AMP accumulation under 0.7 nM human LH stimulation. Adiponectin exhibited a bimodal dose-effect on LH response: synergistic between 2–125 ng/mL and inhibitory between 0.5–5 µg/mL. In brief, our data indicate that estrogens and ADPN separately exert rapid (<1 h) inhibitory and/or synergistic effects on cAMP response to LH in mLTC-1 cells. As the inhibitory effect of each estrogenic molecule was observed after only 1-h preincubation, it might be mediated through the G protein-coupled estrogen receptor (GPER) membrane receptor, but this remains to be demonstrated. The synergistic effect with low concentrations of ADPN with human Luteinizing Hormone (hLH) was observed with both fresh and frozen/thawed ADPN. In contrast, the inhibitory effect with high concentrations of ADPN was lost with frozen/thawed ADPN, suggesting deterioration of its polymeric structure.

Mechanisms of Adiponectin Action in Fertility: An Overview from Gametogenesis to Gestation in Humans and Animal Models in Normal and Pathological Conditions

Adiponectin is the most abundant plasma adipokine. It mainly derives from white adipose tissue and plays a key role in the control of energy metabolism thanks to its insulin-sensitising, anti-inflammatory, and antiatherogenic properties. In vitro and in vivo evidence shows that adiponectin could also be one of the hormones controlling the interaction between energy balance and fertility in several species, including humans. Indeed, its two receptors—AdipoR1 and AdipoR2—are expressed in hypothalamic–pituitary–gonadal axis and their activation regulates Kiss, GnRH and gonadotropin expression and/or secretion. In male gonads, adiponectin modulates several functions of both somatic and germ cells, such as steroidogenesis, proliferation, apoptosis, and oxidative stress. In females, it controls steroidogenesis of ovarian granulosa and theca cells, oocyte maturation, and embryo development. Adiponectin receptors were also found in placental and endometrial cells, suggesting that this adipokine might play a crucial role in embryo implantation, trophoblast invasion and foetal growth. The aim of this review is to characterise adiponectin expression and its mechanism of action in male and female reproductive tract. Further, since features of metabolic syndrome are associated with some reproductive diseases, such as polycystic ovary syndrome, gestational diabetes mellitus, preeclampsia, endometriosis, foetal growth restriction and ovarian and endometrial cancers, evidence regarding the emerging role of adiponectin in these disorders is also discussed.

Adipose tissue and reproductive health

The understanding of adipose tissue role has evolved from that of a depot energy storage organ to a dynamic endocrine organ. While genetics, sexual phenotype and sex steroids can impact the mass and distribution of adipose tissue, there is a counter-influence of white adipocytes on reproduction. This primarily occurs via the secretion of adipokines, the most studied of which- leptin and adiponectin- are highlighted in this article. Leptin, the "satiety hormone" primarily acts on the hypothalamus via pro-opiomelanocortin (POMC), neuropeptide Y (NPY), and agouti-related peptide (AgRP) neurons to translate acute changes in nutrition and energy expenditure, as well as chronic adipose accumulation into changes in appetite and potentially mediate insulin resistance via shared pathway and notably impacting reproductive health via influence on GnRH secreting neurons. Meanwhile, adiponectin is notable for its action in mediating insulin sensitivity, with receptors found at every level of the reproductive axis. Both have been examined in the context of physiologic and pathologic reproductive conditions. Leptin has been shown to influence puberty, pregnancy, hypothalamic amenorrhea, and lipodystrophy, and with a potential therapeutic role for both metabolic and reproductive health. Adiponectin mediates the relative state of insulin resistance in pregnancy, and has been implicated in conditions such as polycystic ovary syndrome and reproductive malignancies. There are numerous other adipokines, including resistin, visfatin, chemerin and retinol binding protein-4, which may also play roles in reproductive health and disease states. The continued examination of these and other adipokines in both normal reproduction and reproductive pathologies represents an important avenue for continued study. Here, we seek to provide a broad, yet comprehensive overview of many facets of these relationships and highlight areas of consideration for clinicians and future study.

The complex association between metabolic syndrome and male hypogonadism

BACKGROUND

The complex association between metabolic syndrome (MetS) and male hypogonadism is well established. A number of observational studies show that low testosterone is associated with insulin resistance and an increased risk for diabetes mellitus and MetS in men.

AIMS

To elucidate the association between MetS and male hypogonadism, present epidemiological data on the co-existence of the two comorbidities, enlighten the underlying pathophysiology and appraise the effects of testosterone supplementation therapy (TTh) and lifestyle modifications on MetS and body composition in men.

MATERIALS AND METHODS

Systematic search to PubMed and Medline databases for publications reporting data on association between MetS and male hypogonadism.

RESULTS

Both MetS and male hypogonadism have a high prevalence in the general population and are frequently co-existing e.g. in males with diabetes. Accumulating evidence from animal and human studies suggests that MetS is involved in the pathogenesis of hypogonadism in males as well as the other way around. On the other hand, there is evidence for a favorable effect of testosterone supplementation in testosterone deficient men with MetS and/or diabetes mellitus.

CONCLUSIONS

Studies with superior methodological characteristics are needed in order to establish a role for testosterone supplementation in men with MetS and/or diabetes mellitus.

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.

Chicken Is a Useful Model to Investigate the Role of Adipokines in Metabolic and Reproductive Diseases

Reproduction is a complex and essential physiological process required by all species to produce a new generation. This process involves strict hormonal regulation, depending on a connection between the hypothalamus-pituitary-gonadal axis and peripheral organs. Metabolic homeostasis influences the reproductive functions, and its alteration leads to disturbances in the reproductive functions of humans as well as animals. For a long time, adipose tissue has been recognised as an endocrine organ but its ability to secrete and release hormones called adipokines is now emerging. Adipokines have been found to play a major role in the regulation of metabolic and reproductive processes at both central and peripheral levels. Leptin was initially the first adipokine that has been described to be the most involved in the metabolism/reproduction interrelation in mammals. In avian species, the role of leptin is still under debate. Recently, three novel adipokines have been discovered: adiponectin (ADIPOQ, ACRP30), visfatin (NAMPT, PBEF), and chemerin (RARRES2, TIG2). However, their mode of action between mammalian and nonmammalian species is different due to the different reproductive and metabolic systems. Herein, we will provide an overview of the structure and function related to metabolic and reproductive mechanisms of the latter three adipokines with emphasis on avian species.

Differential Susceptibility of Germ and Leydig Cells to Cadmium-Mediated Toxicity: Impact on Testis Structure, Adiponectin Levels, and Steroidogenesis

This study investigated the relationship between germ and Leydig cell death, testosterone, and adiponectin levels in cadmium-mediated acute toxicity. Cadmium chloride was administered in a single dose to five groups of rats: G1 (0.9% NaCl) and G2 to G5 (0.67, 0.74, 0.86, and 1.1 mg Cd/kg). After 7 days, the animals were euthanized, and the testosterone and testes were analyzed. Dose-dependent Cd accumulation in the testes was identified. At 0.86 and 1.1 mg/kg, animals exhibited marked inflammatory infiltrate and disorganization of the seminiferous epithelium. While Leydig cells were morphologically resistant to Cd toxicity, massive germ cell death and DNA oxidation and fragmentation were observed. Although numerical density of Leydig cells was unchanged, testosterone levels were significantly impaired in animals exposed to 0.86 and 1.1 mg Cd/kg, occurring in parallel with the reduction in total adiponectins and the increase in high-molecular weight adiponectin levels. Our findings indicated that Leydig and germ cells exhibit differential microstructural resistance to Cd toxicity. While germ cells are a primary target of Cd-induced toxicity, Leydig cells remain resistant to death even when exposed to high doses of Cd. Despite morphological resistance, steroidogenesis was drastically impaired by Cd exposure, an event potentially related to the imbalance in adiponectin production.

Adiponectin and resistin: potential metabolic signals affecting hypothalamo-pituitary gonadal axis in females and males of different species

Adipokines, including adiponectin and resistin, are cytokines produced mainly by the adipose tissue. They play a significant role in metabolic functions that regulate the insulin sensitivity and inflammation. Alterations in adiponectin and resistin plasma levels, or their expression in metabolic and gonadal tissues, are observed in some metabolic pathologies, such as obesity. Several studies have shown that these two hormones and the receptors for adiponectin, AdipoR1 and AdipoR2 are present in various reproductive tissues in both sexes of different species. Thus, these adipokines could be metabolic signals that partially explain infertility related to obesity, such as polycystic ovary syndrome (PCOS). Species and gender differences in plasma levels, tissue or cell distribution and hormonal regulation have been reported for resistin and adiponectin. Furthermore, until now, it has been unclear whether adiponectin and resistin act directly or indirectly on the hypothalamo–pituitary–gonadal axis. The objective of this review was to summarise the latest findings and particularly the species and gender differences of adiponectin and resistin on female and male reproduction known to date, based on the hypothalamo–pituitary–gonadal axis.

Ghrelin affects stopover decisions and food intake in a long-distance migrant

Billions of birds migrate long distances to either reach breeding areas or to spend the winter at more benign places. On migration, most passerines frequently stop over to rest and replenish their fuel reserves. To date, we know little regarding how they decide that they are ready to continue their journey. What physiological signals tell a bird's brain that its fuel reserves are sufficient to resume migration? A network of hormones regulates food intake and body mass in vertebrates, including the recently discovered peptide hormone, ghrelin. Here, we show that ghrelin reflects body condition and influences migratory behavior of wild birds. We measured ghrelin levels of wild garden warblers (Sylvia borin) captured at a stopover site. Further, we manipulated blood concentrations of ghrelin to test its effects on food intake and migratory restlessness. We found that acylated ghrelin concentrations of garden warblers with larger fat scores were higher than those of birds without fat stores. Further, injections of unacylated ghrelin decreased food intake and increased migratory restlessness. These results represent experimental evidence that appetite-regulating hormones control migratory behavior. Our study lays a milestone in migration physiology because it provides the missing link between ecologically dependent factors such as condition and timing of migration. In addition, it offers insights in the regulation of the hormonal system controlling food intake and energy stores in vertebrates, whose disruption causes eating disorders and obesity.

Correlation of Adiponectin mRNA Abundance and Its Receptors with Quantitative Parameters of Sperm Motility in Rams

Background

Adiponectin and its receptors (AdipoR1 and AdipoR2), known as adiponectin system, have some proven roles in the fat and glucose metabolisms. Several studies have shown that adiponectin can be considered as a candidate in linking metabolism to testicular function. In this regard, we evaluated the correlation between sperm mRNA abundance of adiponectin and its receptors, with sperm motility indices in the present study.

Materials and Methods

In this completely randomized design study, semen samples from 6 adult rams were fractionated on a two layer discontinuous percoll gradient into high and low motile sperm cells, then quantitative parameters of sperm motility were determined by computer-assisted sperm analyzer (CASA). The mRNA abundance levels of Adiponectin, AdipoR1 and AdipoR2 were measured quantitatively using real-time reverse transcriptase polymerase chain reaction (qRT-PCR) in the high and low motile groups.

Results

Firstly, we showed that adiponectin and its receptors (AdipoR1 and AdipoR2) were transcriptionally expressed in the ram sperm cells. Using Pfaff based method qRT- PCR, these levels of transcription were significantly higher in the high motile rather than low motile samples. This increase was 3.5, 3.6 and 2.5 fold change rate for Adiponectin, AdipoR1 and AdipoR2, respectively. Some of sperm motility indices [curvilinear velocity (VCL), straight-line velocity (VSL), average path velocity (VAP), linearity (LIN), wobble (WOB) and straightness (STR)] were also significantly correlated with Adiponectin and AdipoR1 relative expression. The correlation of AdipoR2 was also significant with the mentioned parameters, although this correlation was not comparable with adiponectin and AdipoR1.

Conclusion

This study revealed the novel association of adiponectin system with sperm motility. The results of our study suggested that adiponectin is one of the possible factors which can be evaluated and studied in male infertility disorders.

Expression of adiponectin, chemerin and visfatin in plasma and different tissues during a laying season in turkeys

BACKGROUND

In mammals, adipose tissue is able to secrete various hormones called adipokines including adiponectin (ADP), chemerin (Chem) and visfatin (Visf) which are involved in controlling energy metabolism as well as reproductive functions. Visf receptor is still unknown whereas ADP and Chem mainly act through AdipoR1, AdipoR2 and CMKLR1 and GPR1 receptors, respectively. No studies have yet demonstrated the presence of these three adipokines in peripheral tissues, ovarian cells or turkey plasma. Here, we investigated the expression (mRNA and protein) of ADP, Chem, Visf and their receptors in peripheral tissues and ovarian cells (granulosa and theca cells) from hierarchical follicles. Furthermore, we determined the plasma profile of ADP, Visf and Chem at different physiological stages: start, peak and end of the laying period in Meleagris gallopavo turkeys. This data was correlated with the metabolic data (plasma glucose, triglycerides, cholesterol and phospholipids).

METHODS

Tissue and ovarian cells mRNA and protein expression levels were determined by RT-qPCR and immunoblot, respectively. Plasma adipokines were measured by chicken ELISA and immunoblotting.

RESULTS

In turkeys, Chem is mainly expressed in the liver while ADP and Visf are mainly expressed in the abdominal adipose tissue and pectoral muscles,respectively. As in mammals, AdipoR1 and AdipoR2 expression levels (mRNA and protein) are highly present in muscle and liver, respectively, whereas the mRNA expression of CMKLR1 and GPR1 is ubiquitous. In ovarian cells, ADP, Visf, Chem and their receptors are more highly expressed in theca cells than in granulosa cells excepted for AdipoR1. Furthermore, we found that plasma levels of ADP, Chem and Visf were reduced at the end of the laying period compared to the start of this period. At the plasma levels, the levels of these adipokines are strongly negatively correlated with glucose and only plasma Chem is negatively correlated with cholesterol, triglycerides and phospholipids.

CONCLUSIONS

In turkeys, ADP, Visf and Chem and their receptors are expressed in peripheral tissues and ovarian cells. Plasma concentration of ADP, Visf and Chem decrease at the end of laying period and only plasma Chem is negatively correlated with levels of cholesterol, triglycerides and phospholipids levels during the entire laying period.

Characterization of adiponectin concentrations and molecular weight forms in serum, seminal plasma, and ovarian follicular fluid from cattle

Adiponectin (AdipoQ), an adipocyte-derived hormone, is one of the most abundant adipokines in the blood circulation. Adiponectin has various metabolic functions, such as improving insulin sensitivity in humans and rodents. The role of AdipoQ in reproduction is not yet fully understood, but the expression of AdipoQ in reproductive tissues has been observed in various animals and humans, including chicken testis, bovine ovary, and human placenta. The objective of this study was to characterize AdipoQ in the bovine body fluids related to reproduction. Therefore, we evaluated the seminal plasma (SP) from breeding bulls (n = 29) and follicular fluid (FF) from heifers (n = 14), and we also collected blood samples from these animals. In addition, blood samples from other bulls (n = 30) and heifers (n = 14) were assayed for AdipoQ. The concentrations were assessed using a bovine-specific ELISA, and the molecular weight (MW) pattern of the AdipoQ protein was estimated by the Western blot analysis. The SP AdipoQ concentrations were approximately 180-fold lower compared with that in the serum concentrations. Furthermore, the AdipoQ concentrations in the serum and SP were positively correlated. The MW patterns of AdipoQ in the serum and SP were different such that the high MW form of AdipoQ was more abundant in the SP than serum. The AdipoQ concentrations in the serum and SP also increased with age: old bulls (>6 years) had higher AdipoQ concentrations in the serum and SP than bulls aged 24 months or lesser (P < 0.05). In the FF, the AdipoQ concentrations were 1.6-fold lower than those in the corresponding serum samples, and the concentrations in the serum and FF were not correlated (P > 0.1). In the FF, only the middle MW forms of AdipoQ were detectable by Western blotting. The MW pattern in the serum did not differ between the sexes. Our data provide both the AdipoQ concentration and the MW patterns for bovine body fluids related to reproduction.

Effect of perches on liver health of hens

Fatty liver is a common energy metabolic disorder in caged laying hens. Considering that the egg industry is shifting from conventional cages to alternative housing systems such as enriched cages, the objective of this study was to determine the effects of perches on fat deposition and liver health in laying hens. Three hundred twenty-four 17-wk-old White Leghorn hens were housed in 1 of 4 treatments with 9 hens per cage. Treatment 1 hens never had access to perches during their life cycle. Treatment 2 hens had access to perches during the pullet phase only. Treatment 3 hens had access to perches during the laying phase only. Treatment 4 hens always had access to perches. Liver weight, abdominal fat pad weight, BW, liver fat, and circulating alanine transaminase, aspartate transaminase, and adiponectin were determined. Provision of perches during either the rearing or laying phase did not affect liver health in 71-wk-old hens. However, perch access compared with no perch access during the egg laying phase reduced relative fat pad weight. These results suggest that providing perches as a means of stimulating activity reduced abdominal fat deposition in caged hens during the laying period. However, perch access in caged hens was ineffective in reducing fat deposition in the liver and altering enzyme activities related to improved liver function.

Implications of adiponectin in linking metabolism to testicular function

Obesity is a major health problem, contributing to the development of various diseases with aging. In humans, obesity has been associated with reduced testosterone production and subfertility. Adipose tissue is an important source of hormones having influences on both metabolism and reproduction. Among them, the production and secretion of adiponectin is inversely correlated to the severity of obesity. The purpose of this review of literature is to present the current state of knowledge on adiponectin research to determine whether this hormone affects reproduction in men. Surprisingly, evidences show negative influences of adiponectin on GnRH secretion from the hypothalamus, LH and FSH secretion from the pituitary and testosterone at the testicular level. Thus far, the involvement of adiponectin in the influence of metabolism on reproduction in men is limited. However, adiponectin and its receptors are expressed by different cell types of the male gonad, including Leydig cells, spermatozoa, and epididymis. In addition, actions of adiponectin at the testicular level have been shown to promote spermatogenesis and sperm maturation. Therefore, autocrine/paracrine actions of adiponectin in the testis may contribute to support male reproductive function.

Nutritional signals and reproduction

There is extensive evidence that nutrition influences reproductive function in various mammalian species (agricultural animals, rodents and human). However, the mechanisms underlying the relationship between nutrition, energy metabolism and reproductive function are poorly understood. This review considers nutrient sensors as a molecular link between food molecules and consequences for female and male fertility. It focuses on the roles and the molecular mechanisms of some of the relevant hormones, such as insulin and adipokines, and of energy substrates (glucose, fatty acids and amino acids), in the gonadotropic axis (central nervous system and gonads). A greater understanding of the interactions between nutrition and fertility is required for both better management of the physiological processes and the development of new molecules to prevent or cure metabolic diseases and their consequences for fertility.

Adiponectin decreases lipids deposition by p38 MAPK/ATF2 signaling pathway in muscle of broilers

Adiponectin is an adipokine hormone that influences glucose utilization, insulin sensitivity and energy homeostasis. To investigate the effect of adiponectin on lipids deposition in broilers, rosiglitazone and dexamethasone were used to treat broilers. A total of 120 twenty-three-day-old male Cobb broilers were randomly divided into 3 groups for 3 weeks of drug treatment. Serum adiponectin level and fatty acid composition in muscles were measured. Adiponectin, adiponectin receptors (adipoR1, adipoR2) and lipid metabolism-related genes expression levels in muscles were measured using real-time PCR. Western blot was used to measure the expression levels of lipid metabolism-related proteins and the phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK)/activating transcription factor 2 (ATF2) pathway marker proteins. Rosiglitazone increased serum adiponectin concentration and the expression levels of adiponectin and adipoR1 (P < 0.05), while dexamethasone had the opposite effect. Intramuscular fat content, total fatty acid, saturated fatty acid and monounsaturated fatty acid reduced in the rosiglitazone treatment group (P < 0.05). In the rosiglitazone treatment group, the expression levels of lipogenic genes and proteins decreased in the muscles, whereas the expression levels of lipolysis genes increased. Meanwhile, the phosphorylation levels of p38MAPK and ATF2 increased with supplementation of rosiglitazone and decreased in the dexamethasone treatment group (P < 0.01). These results indicated that rosiglitazone and dexamethasone could regulate adiponectin expression in muscle of broilers and adiponectin had an anti-lipogenic effect by p38 MAPK/ATF2 signaling pathway.

Expression of adiponectin and its receptors in avian species

Adipose tissue is a dynamic endocrine organ secreting a variety of hormones that affect physiological functions within the central nervous system, cardiovascular system, reproductive, and immune systems. The endocrine role of avian adipose tissue remains enigmatic as many of the classical hormones found in mammalian adipose tissue have not been found in avians. This mini-review summarizes our current knowledge on avian adiponectin, one of the most abundant adipose tissue hormones, and its receptors. We cloned the genes encoding chicken adiponectin and its receptors, AdipoR1 and AdipoR2. Using anti-chicken adiponectin antibody, we found that chicken adipose tissue and plasma predominantly contain a unique polymer of adiponectin with a mass greater than 669kDa, unlike mammalian adiponectin which is found as three distinct oligomers. Mass spectrometric analyses of chicken adiponectin revealed certain post-translational modifications that are likely to favor the unique multimerization of adiponectin in chickens. Unlike adiponectin, the nucleotide sequences of chicken AdipoR1- and AdipoR2 cDNA are highly similar to that of mammalian adiponectin receptors. Both adiponectin and adiponectin receptors are widely expressed in several tissues in the chicken. Herein, we review the unique biochemistry of adiponectin as well as expression of adiponectin and its receptors in the chicken. Future studies should focus on elucidating the role of adiponectin, AdipoR1, and AdipoR2 on metabolism, steroidogenesis, and adipose tissue remodeling during growth and reproduction in birds.

Differential regulation of adipokines may influence migratory behavior in the white-throated sparrow (Zonotrichia albicollis)

White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat stores to fuel migration. Adipose tissue produces hormones and signaling factors in a rhythmic fashion and may be controlled by a clock in adipose tissue or driven by a master clock in the brain. The master clock may convey photoperiodic information from the environment to adipose tissue to facilitate pre-migratory fattening, and adipose tissue may, in turn, release adipokines to indicate the extent of fat energy stores. Here, we present evidence that a change in signal from the adipokines adiponectin and visfatin may act to indicate body condition, thereby influencing an individual's decision to commence migratory flight, or to delay until adequate fat stores are acquired. We quantified plasma adiponectin and visfatin levels across the day in captive birds held under constant photoperiod. The circadian profiles of plasma adiponectin in non-migrating birds were approximately inverse the profiles from migrating birds. Adiponectin levels were positively correlated to body fat, and body fat was inversely related to the appearance of nocturnal migratory restlessness. Visfatin levels were constant across the day and did not correlate with fat deposits; however, a reduction in plasma visfatin concentration occurred during the migratory period. The data suggest that a significant change in the biological control of adipokine expression exists between the two migratory conditions and we propose a role for adiponectin, visfatin and adipose clocks in the regulation of migratory behaviors.

The complex interaction between obesity, metabolic syndrome and reproductive axis: a narrative review

The aim of this narrative review is to provide current evidence for the interaction between obesity, metabolic syndrome (MS) and reproductive axis. Gonadotropin-releasing hormone (GnRH) pulses and, consequently, normal function of reproductive (hypothalamus-pituitary-gonadal) axis depend on normal energy balance, which presupposes sufficient food intake, reasonable energy consumption and average thermoregulatory costs. In case of an energy imbalance, reproductive dysfunction may occur. In young women, excessive leanness is accompanied by puberty delay, whereas premature puberty might be a manifestation of obesity. In a similar way, obesity in men affects fertility. Excess adipose tissue results in increased conversion of testosterone to estradiol, which may lead to secondary hypogonadism through reproductive axis suppression. Moreover, oxidative stress at the level of the testicular micro-environment may result in decreased spermatogenesis and sperm damage. Products of the adipocyte, such as leptin, adiponectin and resistin, and gut peptides, such as ghrelin, are considered to be crucial in the interaction between energy balance and reproduction. Finally, an indirect evidence for the interplay between MS and reproductive axis is the fact that when treating components of one, parameters of the other can be improved as well. These therapeutic interventions include lifestyle modifications, pharmacological agents, such as sex hormone replacement therapy, and surgical procedures. Although many issues remain unclear, the elucidation of the complex interaction between MS and reproductive axis will have obvious clinical implications in the therapeutic approach of both entities.