Irisin stimulates gonadotropins gene expression in tilapia (Oreochromis niloticus) pituitary cells

Exercise-induced muscle hormone "irisin" controls luteinizing hormone and follicle-stimulating hormone secretion by bovine gonadotrophs

Irisin is a hormone secreted by muscle in response to exercise. The irisin receptor (IrisinR) is a heterodimer of integrin alpha V (ITGAV) and integrin beta 5 (ITGB5) subunits. Since irisin may mediate some beneficial effects of exercise on animal reproduction, we tested the hypothesis that bovine gonadotrophs express IrisinR and irisin stimulates luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion by gonadotrophs. Reverse transcription polymerase chain reaction was used to detect the mRNA expression of both ITGAV and ITGB5 in the anterior pituitary glands (APs) of post pubertal heifers and mouse gonadotroph cell line "LβT2." Western blotting was used to detect protein expression in bovine APs. Immunofluorescence microscopy, utilizing the same antibody, visualized IrisinR on the plasma membrane of majority of gonadotrophs. We prepared AP cells from healthy postpubertal heifers, cultured them for 3.5 d, and treated them with increasing concentrations (0, 0.01, 0.1, 1, or 10 nM) of irisin for 5 min before either no treatment or gonadotropin-releasing hormone (GnRH) stimulation. After 2 h, media were harvested for LH and FSH assays. Irisin (0.1-10 nM) stimulated basal LH and FSH secretion, and these stimulatory effects were inhibited by the extracellular signal-regulated kinase or SMAD pathway inhibitors. In the presence of GnRH, irisin at 0.01-1 nM stimulated LH and FSH secretion. A higher dose of irisin (10 nM), however, suppressed the GnRH-induced LH and FSH levels. In conclusion, bovine gonadotrophs expressed IrisinR, and irisin controlled LH and FSH secretion from bovine gonadotrophs.

Irisin as an emerging target in the regulation of reproductive functions in health and disease

Germ cells are highly conserved in the gonads, nurtured to either develop into a gamete or self-renew into a stem cell reserve. Preserving the germ cell pool and protecting the reproductive organs is essential for maintaining an individual's fertility. Several factors, including a sedentary lifestyle, pollutants, hormonal disruption, drugs, and a disease condition, have been shown to impair normal reproductive function. Irisin has recently been identified as an adipomyokine involved in modulating physiological functions based on the body's metabolic status. It is being studied for its role in various functions, including fertility. Findings show the localization of irisin in various parts of the reproductive axis, with the highest levels observed during puberty and pregnancy. This raises questions about its role and function in reproduction. Studies support irisin's role in protecting against disease-induced reproductive abnormalities and infertility. Therefore, the current review focuses on how irisin influences spermatogenesis and ovarian follicular development and plays a significant role in indirectly preserving the germ cell pool by protecting the gonads against oxidative stress and inflammation.

Irisin combined index to diagnose central precocious puberty in girls: a cross-sectional study

BACKGROUND

To investigate serum irisin levels in girls at different developmental status and explore the significance of irisin for the diagnosis of central precocious puberty (CPP) in girls.

METHODS

In this cross-sectional study 111 girls were enrolled, including 43 cases of CPP, 44 cases of peripheral precocious puberty (PPP) and 24 cases of girls with normal sexual development as controls. The data on age, weight and height, measured blood levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol, and irisin were collected. Pelvic Doppler ultrasound was performed to evaluate uterine length, transverse diameter, anteroposterior diameter. The girls were divided into non-CPP group and CPP group according to gonadotropin-releasing hormone (GnRH) stimulation test.

RESULTS

Serum irisin levels were significantly higher in CPP group than in PPP group and normal control group. Serum irisin level was positively correlated with basal LH level, basal FSH level, peak LH level, peak LH /FSH ratio, uterine volume, bone age, and bone age index. The area under the curve, cut-off value, sensitivity and specificity of serum irisin were 0.958, 219.255 pg/ml, 100% and 80.6%. The combined diagnosis of CPP in girls by serum irisin and serum basal LH combined with uterine volume had an AUC, sensitivity, and specificity of 0.994, 97.6%, and 100%, superior to that of the single index.

CONCLUSIONS

Serum irisin level in girls with CPP is significantly increased. An irisin combined index could help the diagnosis of CPP in girls.

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.

The Role of Irisin throughout Women's Life Span

Since its discovery, much attention has been drawn to irisin's potential role in metabolic and reproductive diseases. This narrative review summarizes and updates the possible role played by this fascinating molecule in different physiological (puberty and menopause) and pathological (polycystic ovary syndrome (PCOS), functional hypothalamic amenorrhea (FHA), endometriosis, and gestational diabetes) conditions that can affect women throughout their entire lives. Irisin appears to be an important factor for the hypothalamic-pituitary-gonadal axis activation, and appears to play a role in the timing of puberty onset. Serum irisin levels have been proposed as a biomarker for predicting the future development of gestational diabetes (GDM). Its role in PCOS is still controversial, although an "irisin resistance" mechanism has been hypothesized. In addition to its impact on metabolism, irisin also appears to influence bone health. Irisin levels are inversely correlated with the prevalence of fractures in postmenopausal women. Similar mechanisms have also been postulated in young women with FHA. In clinical settings, further controlled, prospective and randomized clinical trials are needed to investigate the casual relationship between irisin levels and the conditions described and, in turn, to establish the role of irisin as a prognostic/diagnostic biomarker or a therapeutic target.

Irisin in domestic animals

Irisin is a 112 amino acid peptide hormone cleaved from the fibronectin type III domain-containing protein. Irisin is highly conserved across vertebrates, suggesting evolutionarily conserved common functions among domestic animals. These functions include the browning of white adipose tissue and increased energy expenditure. Irisin has been detected and studied primarily in plasma, serum, and skeletal muscle, but has also been found in adipose tissue, liver, kidney, lungs, cerebrospinal fluid, breast milk, and saliva. This wider tissue presence of irisin suggests additional functions beyond its role as a myokine in regulating energy use. We are beginning to understand irisin in domestic animals. The goal of this review is to provide an up-to-date commentary on irisin structure, tissue distribution, and functions across vertebrates, especially mammals of importance in veterinary medicine. Irisin could be explored as a potential candidate for developing therapeutic agents and biomarkers in domestic animal endocrinology.

Central Irisin Signaling Is Required for Normal Timing of Puberty in Female Mice

Timing of puberty requires exquisite coordination of genes, hormones, and brain circuitry. An increasing level of body adiposity, signaled to the brain via the fat-derived hormone leptin, is recognized as a major factor controlling puberty onset. However, it is clear that leptin is not the only metabolic cue regulating puberty, and that developmental regulation of this process also involves tissues other than adipose, with muscle development potentially playing a role in the timing of puberty. The proteolytic processing of fibronectin type 3 domain-containing protein 5 (FNDC5) releases a hormone, irisin. Irisin is primarily produced by muscle and is released into circulation, where levels increase dramatically as puberty approaches. We investigated the effects of a global deletion of the Fndc5 gene on pubertal timing. The absence of irisin induced a delay in puberty onset in female knockout mice compared with controls, without affecting body weight or gonadotropin-releasing hormone (GnRH) neuronal density. We next treated pre-pubertal wild-type male and female mice with an irisin receptor antagonist, cilengitide, for 7 days and observed a delay in first estrus occurrence compared to vehicle-treated control mice. Male puberty timing was unaffected. Next, we deleted the irisin receptor (integrin subunit alpha V) in all forebrain neurons and found a delay in the occurrence of first estrus in knockout females compared to controls. Taken together, these data suggest irisin plays a role in the timing of puberty onset in female mice via a centrally mediated mechanism.

Beneficial effects of irisin in experimental paroxetine-induced hyperprolactinemia

OBJECTIVE

It is known that selective serotonin reuptake inhibitors (SSRIs), represent an important and effective treatment of depression and other psychological disorders, these medications can increase prolactin levels mainly through activation of the serotonergic pathway. In this study, we aimed to determine the beneficial effects of irisin on paroxetine, a SSRI, induced hyperprolectinemia and in some other reproductive hormonal changes associated with hyperprolactinemia.

METHODS

Thirty two male Spraque-Dawley rats were used and divided into four groups including sham-operated control (vehicle), irisin (100 ng/kg/day for 28 days with mini-osmotic pumps), paroxetine (treated with 20 mg/kg paroxetine by oral gavage), irisin and paroxetine+irisin groups (n = 8). Serum prolactin (PRL), kisspeptin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone and 5-alpha reductase levels were determined with enzyme-linked immunosorbent analysis (ELISA).

RESULTS

In animals treated with paroxetine, PRL level increased and testosterone level decreased significantly (p < 0.05). Serum LH level was significantly increased in the group, but no significant changes were observed in the FSH, kisspeptin and 5-alpha reductase levels. Serum prolactin levels was significantly decreased in the group treated with irisin. While no significant difference was observed in kisspeptin, FSH and 5-alpha reductase levels, an increase in serum LH and testosterone levels with irisin administration (p < 0.05).

CONCLUSION

In conclusion, chronic irisin exposure may reverse paroxetine-induced hyperprolactinemia. These results indicate that irisin may have the potential to be used as a therapeutic agent by primarily affecting paroxetine-induced increased prolactin and decreased testosterone levels.

Irisin: circulating levels in serum and its relation to gonadal axis

Irisin is an exercise-induced myokine/adipokine in mice and humans that plays an important role in 'browning' of white adipose tissue and has shown great potential as a treatment for some metabolic diseases, such as obesity, insulin resistance, and inflammation. The circulating irisin level is reported to be associated with exercise, obesity, diet, diseases, and exposure to different pharmacological agents. Several studies have attempted to characterize the role of irisin in PCOS and other reproductive diseases, but contradictory results have been reported. Our previous study showed that irisin may serve further functions in folliculogenesis and fertility. In this review, we present the current knowledge on the physiology of irisin and its role in gonadal axis. Firstly, we describe irisin circulating levels and speculate on the potential mechanisms involved in irisin secretion and regulation. Then, we focus on the irisin levels in PCOS, and explore the relationships between, BMI, insulin resistance, and hyperandrogenism. Finally, we present the results from animal interventional studies and in vitro experiments to investigate the relationship between irisin and gonadal axis, indicating its novel effects on reproduction and fertility.

Irisin ameliorates male sexual dysfunction in paroxetine-treated male rats

Sexual dysfunction is a common clinical condition due to different causes including the use of selective serotonin reuptake inhibitors (SSRI). Especially, SSRI paroxetine is known to cause numerous types of sexual dysfunction in men. There is growing interest in exercise as a non-pharmacological approach for the treatment of SSRI-induced sexual dysfunction. With these in mind, we investigated the effects of irisin, which is a recently detected exercise-linked hormone, on paroxetine-induced sexual dysfunction in male rats. Our findings showed that circulating irisin levels were lower in paroxetine-induced sexual dysfunction in male rats (20 mg/kg/day for 8 weeks by oral gavage than in vehicle-treated rats). In addition, results from sexual behavioral tests revealed that subcutaneous irisin perfusion (100 ng/kg/day via mini-osmotic pumps for 28 days) ameliorated sexual motivation and copulatory performance in sexually impaired male rats treated with paroxetine. The significantly reduced serum testosterone levels and α1-adrenoceptors (ADRA1A) and tyrosine hydroxylase gene (TH) expression levels in the nucleus accumbens (NAc) in paroxetine-induced sexually dysfunctioning male rats were markedly increased following irisin exposure. Similarly, the expression levels of ADRA1A and TH in the medial preoptic area (mPOA) significantly increased in male rats co-administered with paroxetine and irisin compared to the vehicle-treated male rats. These results demonstrate that irisin may be a therapeutic modality that mimics/supports the beneficial effects of exercise for improving SSRI-associated sexual dysfunction in men through increase in serum testosterone levels and increased expression of α1-adrenoceptors and TH in the NAc and mPOA associated with sexual motivation and copulatory behaviors.

Irisin Improves High-Fat Diet-Induced Sexual Dysfunction in Obese Male Rats

INTRODUCTION

Obesity is known to cause sexual dysfunction including erectile dysfunction and poor semen quality. Lifestyle modifications such as exercise have increasingly been more recognized to lower the likelihood of having sexual dysfunction or infertility in obese men. In this context, as an exercise-mimetic hormone, irisin has a potential to improve obesity-related reproductive dysfunctions. We aimed to elucidate possible effects of irisin on high-fat diet (HFD)-induced reproductive dysfunction in obese male rats.

METHODS

Rats were divided into four groups: vehicle, irisin, obese, and obese + irisin. The rats in obese and obese+irisin groups were fed with HFD (60% kcal fat) pellets for 12 weeks to induce obesity, and then obesity-induced sexual dysfunction was confirmed by the sexual behavior test (SBT). Irisin and obese+irisin groups received irisin (100 ng/kg/day) infusion by an s.c. osmotic minipump for 4 weeks after HFD-induced obesity was formed.

RESULTS

Irisin did improve a number of measures of copulation, including penile erection, ejaculation, and sexual performance, and also improved sperm morphology and motility and decreased fat-induced testicular damage. It decreased serum leptin levels. On the other hand, irisin did not affect serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone. It also increased gene expression of tyrosine hydroxylase (TH) and adrenoceptor alpha 1A (ADRA1A) in the medial preoptic area (mPOA) and nucleus accumbens (NAc).

CONCLUSION

Irisin provided a marked enhancement of HFD-induced decrease in libido, potency, sexual performance, and erection in SBT. Taken together, our results emphasize that irisin has a restorative and improver role in HFD-induced reproductive dysfunctions in obese male rats.

Irisin, Energy Homeostasis and Male Reproduction

Irisin is a novel skeletal muscle- and adipose tissue-secreted peptide. It is conventionally regarded as an adipomyokine and is a cleaved fragment of Fibronectin type III domain-containing protein 5 (FNDC5). It is involved in the browning of white adipose tissue, glucose tolerance, and reversing of metabolic disruptions. Fertility is closely linked to energy metabolism and the endocrine function of the adipose tissue. Moreover, there is established association between obesity and male infertility. Irisin bears strong therapeutic promise in obesity and its associated disorders, as well as shown to improve male reproductive functions. Thus, irisin is a molecule of great interest in exploring the amelioration of metabolic syndrome or obesity-induced male infertility. In this review we aim to enumerate the most significant aspects of irisin actions and discuss its involvement in energy homeostasis and male reproduction. Though current and future research on irisin is very promiscuous, a number of clarifications are still needed to reveal its full potential as a significant medicinal target in several human diseases including male infertility.

Reproductive roles of novel adipokines apelin, visfatin, and irisin in farm animals

The adipose tissue has a substantial impact on reproduction in mammals, specifically in females. As an energy depository organ, it is precisely associated with the reproductive success of mammals. Adipose tissue secretes many single molecules that are called 'adipokines' which mainly act as endocrine hormones. Adipokines homeostasis is fundamental to energy regulation, metabolic and cardiovascular diseases. The endocrine function of adipokines is influential for the long-term control of energy metabolism and performs an important function in metabolic state and fertility modulation. During the last years, new roles for adipokines have been appearing in the field of fertility. The adipokines have functions in reproduction at levels of the hypothalamus, the pituitary, and the gonads in humans, rodents, and other animals. Normal levels of adipokines are indispensable to protect the integrity of the hypothalamus-hypophysis-gonadal axis, regular ovulatory processes, and successful embryo implantation. Leptin and adiponectin are the most studied adipokines, but also the novel adipokines; apelin, visfatin, and irisin are important adipokines having several functions within the reproductive tract. Due to the known and unknown effects of these novel adipokines in the reproduction of farm animals, in this review, we will highlight the reproductive functions of apelin, visfatin, and irisin and summarize the known reproductive effects in farm animals to introduce the gaps for future studies in farm animals.

Irisin deletion induces a decrease in growth and fertility in mice

BACKGROUND

Irisin, which is cleaved from fibronectin type III domain-containing protein 5 (Fndc5), plays an important role in energy homeostasis. The link between energy metabolism and reproduction is well known. However, the biological actions of irisin in reproduction remain largely unexplored.

METHODS

In this study, we generated Fndc5 gene mutation to create irisin deficient mice. Female wild-type (WT) and Fndc5 mutant mice were fed with standard chow for 48 weeks. Firstly, the survival rate, body weight and fertility were described in mice. Secondly, the levels of steroid hormones in serum were measured by ELISA, and the estrus cycle and the appearance of follicles were determined by vaginal smears and ovarian continuous sections. Thirdly, mRNA-sequencing analysis was used to compare gene expression between the ovaries of Fndc5 mutant mice and those of WT mice. Finally, the effects of exogenous irisin on steroid hormone production was investigated in KGN cells.

RESULTS

The mice lacking irisin presented increased mortality, reduced body weight and poor fertility. Analysis of sex hormones showed decreased levels of estradiol, follicle-stimulating hormone and luteinizing hormone, and elevated progesterone levels in Fndc5 mutant mice. Irisin deficiency in mice was associated with irregular estrus, reduced ratio of antral follicles. The expressions of Akr1c18, Mamld1, and Cyp19a1, which are involved in the synthesis of steroid hormones, were reduced in the ovaries of mutant mice. Exogenous irisin could promote the expression of Akr1c18, Mamld1, and Cyp19a1 in KGN cells, stimulating estradiol production and inhibiting progesterone secretion.

CONCLUSIONS

Irisin deficiency was related to disordered endocrinology metabolism in mice. The irisin deficient mice showed poor growth and development, and decreased fertility. Irisin likely have effects on the expressions of Akr1c18, Mamld1 and Cyp19a1 in ovary, regulating the steroid hormone production. This study provides novel insights into the potential role of irisin in mammalian growth and reproduction.

The myokine irisin: localization and effects in swine late medium and large antral ovarian follicle

Irisin is mainly synthesized by skeletal muscle tissue, where it is believed to be responsible for the benefits of exercise on metabolism and cardiovascular system. In adipose tissue, its best-known effect is the browning of white adipocytes, resulting in the increase of thermogenesis and energy expenditure. As it has been largely documented that metabolic dysfunctions can frequently be associated with reductions in fertility, the possible involvement of this molecule in the regulation of reproductive processes represents an issue to be addressed. On this basis, the first aim of this work was the evaluation of the presence of irisin in the swine ovary; then, we investigated the expression of the associated molecules FNDC5, PGC-1α, and PPAR-γ. To verify a potential modulatory role both on ovarian function and on redox status, cell growth, steroidogenesis, production of superoxide anion and nitric oxide, the nonenzymatic antioxidant scavengers, were assessed in vitro on granulosa cells treated with increasing concentrations of irisin (50, 100, and 150 ng/mL). The data collected demonstrate the presence of irisin in swine ovarian follicle. Moreover, the highest concentrations tested stimulated metabolic activity and inhibited cell proliferation (P < 0.05); the peptide exerted a biphasic effect on progesterone (P < 0.01) production and, at the highest concentrations, inhibited nitric oxide while stimulated the nonenzymatic antioxidant power (P < 0.05). Superoxide anion and estradiol 17β were unaffected. The demonstration of the local presence of irisin at the ovarian level and the highlighted effects allow us to qualify this molecule as a potential physiological regulator of follicular function.