Transcriptional and translational abundance of visfatin (NAMPT) in buffalo ovary during estrous cycle and its in vitro effect on steroidogenesis

The role of asprosin in regulating ovarian granulosa- and theca-cell steroidogenesis: a review with comparisons to other adipokines

Adipose tissues produce a variety of biologically active compounds, including cytokines, growth factors and adipokines. Adipokines are important as they function as endocrine hormones that are related to various metabolic and reproductive diseases. The goal of this review was to summarise the role of asprosin, a recently discovered adipokine, and compare its role in ovarian steroidogenesis with that of other adipokines including adiponectin, leptin, resistin, apelin, visfatin, chemerin, irisin, and gremlin 1. The summary of concentrations of these adipokines in humans, rats and other animals will help researchers identify appropriate doses to test in future studies. Review of the literature indicated that asprosin increases androstenedione production in theca cells (Tc), and when cotreated with FSH increases oestradiol production in granulosa cells (Gc). In comparison, other adipokines (1) stimulate Gc oestradiol production but inhibit Tc androgen production (adiponectin), (2) inhibit Gc oestradiol production and Tc androstenedione production (leptin and chemerin), (3) inhibit Gc steroidogenesis with no effect on Tc (resistin), (4) inhibit Gc oestradiol production but stimulate Tc androgen production (gremlin 1), and (5) increase steroid secretion by Gc, with unknown effects on Tc steroidogenesis (apelin and visfatin). Irisin has direct effects on Gc but its precise role (inhibitory or stimulatory) may be species dependent and its effects on Tc will require additional research. Thus, most adipokines have direct effects (either positive or negative) on steroid production in ovarian cells, but how they all work together to create a cumulative effect or disease will require further research.

In vitro effect of visfatin on endocrine functions of the porcine corpus luteum

Previously, we demonstrated the expression of visfatin in porcine reproductive tissues and its effect on pituitary endocrinology. The objective of this study was to examine the visfatin effect on the secretion of steroid (P4, E2) and prostaglandin (PGE2, PGF2α), the mRNA and protein abundance of steroidogenic markers (STAR, CYP11A1, HSD3B, CYP19A1), prostaglandin receptors (PTGER2, PTGFR), insulin receptor (INSR), and activity of kinases (MAPK/ERK1/2, AKT, AMPK) in the porcine corpus luteum. We noted that the visfatin effect strongly depends on the phase of the estrous cycle: on days 2-3 and 14-16 it reduced P4, while on days 10-12 it stimulated P4. Visfatin increased secretion of E2 on days 2-3, PGE2 on days 2-3 and 10-12, reduced PGF2α release on days 14-16, as well as stimulated the expression of steroidogenic markers on days 10-12 of the estrous cycle. Moreover, visfatin elevated PTGER mRNA expression and decreased its protein level, while we noted the opposite changes for PTGFR. Additionally, visfatin activated ERK1/2, AKT, and AMPK, while reduced INSR phosphorylation. Interestingly, after inhibition of INSR and signalling pathways visfatin action was abolished. These findings suggest a regulatory role of visfatin in the porcine corpus luteum.

Visfatin impact on the proteome of porcine luteal cells during implantation

Visfatin (VIS) is a hormone belonging to the adipokines' group secreted mainly by the adipose tissue. VIS plays a crucial role in the control of energy homeostasis, inflammation, cell differentiation, and angiogenesis. VIS expression was confirmed in the hypothalamic-pituitary-gonadal (HPG) axis structures, as well as in the uterus, placenta, and conceptuses. We hypothesised that VIS may affect the abundance of proteins involved in the regulation of key processes occurring in the corpus luteum (CL) during the implantation process in pigs. In the present study, we performed the high-throughput proteomic analysis (liquid chromatography with tandem mass spectrometry, LC-MS/MS) to examine the in vitro influence of VIS (100 ng/mL) on differentially regulated proteins (DRPs) in the porcine luteal cells (LCs) on days 15-16 of pregnancy (implantation period). We have identified 511 DRPs, 276 of them were up-regulated, and 235 down-regulated in the presence of VIS. Revealed DRPs were assigned to 162 gene ontology terms. Western blot analysis of five chosen DRPs, ADAM metallopeptidase with thrombospondin type 1 motif 1 (ADAMTS1), lanosterol 14-α demethylase (CYP51A1), inhibin subunit beta A (INHBA), notch receptor 3 (NOTCH3), and prostaglandin E synthase 2 (mPGES2) confirmed the veracity and accuracy of LC-MS/MS method. We indicated that VIS modulates the expression of proteins connected with the regulation of lipogenesis and cholesterologenesis, and, in consequence, may be involved in the synthesis of steroid hormones, as well as prostaglandins' metabolism. Moreover, we revealed that VIS affects the abundance of protein associated with ovarian cell proliferation, differentiation, and apoptosis, as well as CL new vessel formation and tissue remodelling. Our results suggest important roles for VIS in the regulation of ovarian functions during the peri-implantation period.

Differential effect of visfatin inhibition on the testicular androgen and estrogen receptors expression in early pubertal mice

BACKGROUND

It is now well known that visfatin is expressed in the testis and ovary of various animals. Visfatin is known to regulate gonadal functions such as steroidogenesis, proliferation, and apoptosis in the ovary and testis of mice. Recently, we have shown that visfatin has an inhibitory role in the infantile mice testis. It has also been shown that visfatin stimulates testicular steroidogenesis in adult rats. However, the role of visfatin during puberty has not been investigated in relation to the above-mentioned process.

OBJECTIVE

The objective of the present study was to examine the effect of visfatin inhibition by FK866 from PND25 to PND35 (pre-pubertal to early pubertal) in male Swiss albino mice on steroidogenesis, proliferation, and apoptosis.

METHODS

Sixteen mice (25 days old) were divided into two groups, one group was given normal saline and the other group was administered with an inhibitor of visfatin (FK866) at the dose of 1.5 mg/kg by intraperitoneal injection for 10 days. Histopathological and immunohistochemical analysis, western blot analysis and hormonal assay were done.

RESULTS

Visfatin inhibition resulted in increased estrogen secretion, body weight, seminiferous tubule diameter, germinal epithelium height, and proliferation along with increased expression of BCl2, casapse3, ERs and aromatase expression in the mice testis. Visfatin inhibition down-regulated the testicular visfatin expression and also decreased abundance in the adipose tissues.

CONCLUSION

In conclusion, decreased AR expression and increased ERs expression by FK866, suggest that visfatin might have a stimulatory effect on AR signaling than ERs in the early pubertal stage of mice.

Expression of visfatin in the ovarian follicles of prepubertal and mature gilts and in vitro effect of gonadotropins, insulin, steroids, and prostaglandins on visfatin levels

Recent studies have demonstrated that visfatin participates in the regulation of female reproduction. Due to the lack of data concerning the level of visfatin in the ovarian follicles of pigs, one of the most economically important livestock species, the aim of this study was to investigate the expression and localisation of visfatin and the follicular fluid concentration in the ovarian follicles of prepubertal and mature gilts. We also aimed to examine the in vitro effects of gonadotropins (LH, FSH), insulin, progesterone (P4), oestradiol (E2), prostaglandin E2 (PGE2) and F2α (PGF2α) on visfatin levels. In the present study, we have demonstrated that visfatin expression is dependent on the maturity of the animals and the stage of ovarian follicle development. Visfatin signal was detected in individual follicular compartments from primordial to antral follicles and even in atretic follicles. We have shown that the expression of visfatin in granulosa cells was higher than in theca cells. The level of visfatin is upregulated by LH, FSH, E2, and P4 and downregulated by insulin, while prostaglandins have modulatory effects, dependent on the dose and type of ovarian follicular cells. To summarise, our research has shown that visfatin is widely expressed in the ovarian follicles of prepubertal and mature pigs, and its expression is regulated by gonadotropins, insulin, steroids, and prostaglandins, suggesting that visfatin appears to be an important intra-ovarian factor that could regulate porcine ovarian follicular function.

Visfatin in the porcine pituitary gland: expression and regulation of secretion during the oestrous cycle and early pregnancy

Visfatin is a multifunctional protein which, besides the control of energy homeostasis, seems to be also involved in the regulation of female fertility through the influence on the endocrine hypothalamus-pituitary-gonadal axis, including the pituitary. The aim of this study was to investigate the expression of visfatin mRNA and protein in the anterior (AP) and posterior pituitary lobes of the pig during the oestrous cycle and early pregnancy. In AP, we also examined colocalisation of visfatin with pituitary tropic hormones. Moreover, we aimed to evaluate the in vitro effects of GnRH, FSH, LH, and insulin on visfatin protein concentration and secretion in AP cells during the cycle. The study showed that visfatin is present in all types of porcine pituitary endocrine cells and its expression is reliant on stage of the cycle or pregnancy. GnRH, FSH, LH and insulin stimulated visfatin secretion by AP cells on days 17 to 19 of the cycle, while on days 2 to 3 visfatin release was enhanced only by LH. Summarising, visfatin is locally produced in the pituitary in a way dependent on hormonal milieu typical for reproductive status of pigs. Further research is required to clarify the role of visfatin in the pituitary gland.

Evidence of the inhibitory role of visfatin in the testicular activity of mice during the infantile stage

Adipokines have emerged as regulators of gonadal function in many mammalian and non-mammalian species. In the present study, we have investigated the developmental expression of testicular and ovarian visfatin along with its possible role in the testicular activity infantile stages. Previously, our group has the extensive role of ovarian visfatin in relation to steroidogenesis, proliferation, and apoptosis in female mice. To the best of our knowledge, no study has shown the role of visfatin in mice testis. Our results from the previous study and present study showed that visfatin in the testis and ovaries are developmentally regulated. To unravel the role of visfatin, we have used FK866, as visfatin inhibitor. FK866 was used as a visfatin inhibitor, to decipher the role of visfatin in the testis of mice. Our results showed that visfatin expression in the testis was developmentally regulated in the testis. Leydig cells as well as germ have shown the presence of visfatin in mice testis, which suggest its role in testicular steroidogenesis and spermatogenesis. Furthermore, visfatin inhibition by FK866 significantly increased the testosterone secretion, and expression of AR, Bcl2, and ERα. The expression of GCNA was upregulated by FK866 treatment. These results suggest that visfatin has an inhibitory role in testicular steroidogenesis and germ cell proliferation in the infantile stage. Further research is required to define the precise role of visfatin in infantile mice testis.

Orexin system in buffalo ovarian follicles and effect of orexin on oestradiol production

Orexin is a ligand for orexin receptors OX1R and OX2R; it is a neuropeptide with pleiotropic functions, including regulation of reproduction. The current study was carried out to investigate the mRNA expression of the prepro-orexin gene (PPO) and orexin receptors (OX1R and OX2R) in ovarian follicles during different stages of their development in the ovary of water buffalo (Bubalus bubalis) and to determine the role of orexin on oestradiol production. Ovarian follicles were classified into four groups based on size and oestradiol (E₂ ) level in the follicular fluid (FF) as follows: (i) small or F1, (ii) medium or F2, (iii) large or F3, and (iv) dominant/pre-ovulatory follicle or F4. In follicles, the mRNA expression of PPO and OX1R was greater in F3 and F4 follicles in granulosa cells (GC) and theca interna (TI) cells. OX2R expression did not vary among the different follicular stages in GC. Orexin-A and orexin receptors were localized in the cytoplasm of GC and TI, and intensity was higher in F3 and F4 follicles. In addition, we cultured GC and treated them at 0.1, 1.0, and 10 ng/mL orexin-A alone or in the presence of FSH (30 ng/mL) or IGF-I (10 ng/mL) for 48 h. There was a significant (p < .05) increase in oestradiol (E₂ ) secretion and cytochrome P0450 family 19 subfamily A member 1 (CYP19A1) expression from GC at 1.0 and 10.0 ng/mL orexin-A in the presence of 30 ng/mL follicle-stimulating hormone (FSH) or 10 ng/mL insulin-like growth factor-I (IGF-I). In conclusion, the present study provided evidence that the orexin system is expressed in buffalo ovarian follicles, and orexin-A in the presence of FSH and IGF-I has a stimulatory effect on oestradiol secretion from the GC of water buffalo.

Expression and regulation of visfatin/NAMPT in the porcine corpus luteum during the estrous cycle and early pregnancy

Visfatin/NAMPT creates a hormonal link between energy metabolism and female reproduction. A recent study documented visfatin expression in the ovary and its action on follicular cells; however, the expression of visfatin in luteal cells is still unknown. The aim of this study, therefore, was to investigate the transcript and protein expression of visfatin as well as its immunolocalization in the corpus luteum (CL) and to examine the involvement of extracellular signal-regulated kinases (ERK1/2) in the regulation of visfatin level in response to LH, insulin, progesterone (P₄), prostaglandin E₂ (PGE₂) and F_2α (PGF_2α). Corpora lutea were harvested from gilts on days 2-3, 10-12 and 14-16 of the estrous cycle and on days 10-11, 12-13, 15-16 and 27-28 of pregnancy. The current study demonstrated that visfatin expression depends on hormonal status related to the phase of the estrous cycle or early pregnancy. Visfatin was immunolocalized to the cytoplasm of small and large luteal cells. Moreover, visfatin protein abundance was increased by P₄, and decreased by both prostaglandins, while LH and insulin have modulatory effects, depending on the phase of the cycle. Interestingly, LH, P₄ and PGE₂ effects were abolished in response to the inhibition of ERK1/2 kinase. Thus, this study demonstrated that expression of visfatin in the porcine CL is determined by the endocrine status related to the estrous cycle and early pregnancy and by the action of LH, insulin, P₄ and prostaglandins via activation of the ERK1/2 pathway.

Expression and localization of apelin and apelin receptor (APJ) in buffalo ovarian follicles and corpus luteum and the in-vitro effect of apelin on steroidogenesis and survival of granulosa cells

Apelin is an adipose tissue-derived hormone with many physiological functions, including the regulation of female reproduction. It acts through an orphan G protein-coupled receptor APJ/APLNR. The present study aimed to investigate the expression of apelin and its receptor APJ in the ovarian follicles and corpus luteum (CL) and the role of apelin on steroidogenesis and cell survival. Ovarian follicles were classified into four groups based on size and estradiol (E₂) level in the follicular fluid as follows: (i) F1 (4-6 mm; <0.5 ng/mL) (ii) F2 (7-9 mm; 0.5-5 ng/mL) (iii) F3 (10-13 mm; 5-40 ng/mL) and (iv) F4 (dominant/pre-ovulatory follicle) (>13 mm; >180 ng/mL). The corpora lutea (CL) were categorized into early (CL1), mid (CL2), late luteal (CL3), and regressing (CL4) CL stages. Expression of apelin increased with follicle size, with significantly greatest in the dominant or pre-ovulatory follicle (P < 0.05). Expression of APJ was greater in large and dominant follicles than in small and medium follicles (P < 0.05). In CL, the mRNA and protein abundance of apelin and apelin receptor was greater during mid (CL2) and late luteal (CL3) stages as compared to early (CL1) and regressing (CL4) stages (P < 0.05). Both the factors were localized in granulosa and theca cells of follicles and small and large luteal cells of CL. The pattern of the intensity of immunofluorescence was similar to mRNA and protein expression. Granulosa cells were cultured in vitro and treated at 1, 10, and 10 ng/mL apelin-13 either alone or in the presence of the follicle-stimulating hormone (FSH) (30 ng/mL) or insulin-like growth factor-I (IGF-I) (10 ng/mL) for 48 h. The luteal cells were treated with apelin-13 at 1, 10, and 100 ng/mL doses for 48 h. Apelin treatment at 10 and 100 ng/ml significantly (P < 0.05) increased E₂ secretion, cytochrome P450 aromatase or CYP19A1 expression in GC. In luteal cells, apelin at 10 ng/mL and 100 ng/mL significantly (P < 0.05) increased progesterone (P₄) secretion and HSD3B1 expression. In GCs, apelin, either alone or in combination, increased PCNA expression and inhibited CASPASE3 expression suggesting its role in cell survival. In conclusion, this study provides novel evidence for the presence of apelin and receptor APJ in ovarian follicles and corpora lutea and the stimulatory effect on E₂ and P₄ production and promotes GC survival in buffalo, suggesting the role of apelin in follicular and luteal functions in buffalo.

Adipose tissue and ovarian aging: Potential mechanism and protective strategies

Ovarian aging occurs approximately 10 years prior to the natural age-associated functional decline of other organ systems. With the increase of life expectancy worldwide, ovarian aging has gradually become a key health problem among women. Therefore, understanding the causes and molecular mechanisms of ovarian aging is very essential for the inhibition of age-related diseases and the promotion of health and longevity in women. Recently, studies have revealed an association between adipose tissue (AT) and ovarian aging. Alterations in the function and quantity of AT have profound consequences on ovarian function because AT is central for follicular development, lipid metabolism, and hormonal regulation. Moreover, the interplay between AT and the ovary is bidirectional, with ovary-derived signals directly affecting AT biology. In this review, we summarize the current knowledge of the complex molecular mechanisms controlling the crosstalk between the AT and ovarian aging, and further discuss how therapeutic targeting of the AT can delay ovarian aging.

New Aspects of Corpus Luteum Regulation in Physiological and Pathological Conditions: Involvement of Adipokines and Neuropeptides

The corpus luteum is a small gland of great importance because its proper functioning determines not only the appropriate course of the estrous/menstrual cycle and embryo implantation, but also the subsequent maintenance of pregnancy. Among the well-known regulators of luteal tissue functions, increasing attention is focused on the role of neuropeptides and adipose tissue hormones—adipokines. Growing evidence points to the expression of these factors in the corpus luteum of women and different animal species, and their involvement in corpus luteum formation, endocrine function, angiogenesis, cells proliferation, apoptosis, and finally, regression. In the present review, we summarize the current knowledge about the expression and role of adipokines, such as adiponectin, leptin, apelin, vaspin, visfatin, chemerin, and neuropeptides like ghrelin, orexins, kisspeptin, and phoenixin in the physiological regulation of the corpus luteum function, as well as their potential involvement in pathologies affecting the luteal cells that disrupt the estrous cycle.

Apelin and Apelin Receptor in Follicular Granulosa Cells of Buffalo Ovaries: Expression and Regulation of Steroidogenesis

Apelin (APLN), as a ligand for APJ (an orphan G-protein-coupled receptor), is an adipokine with pleiotropic effects in many physiological processes of the body. It has an important role in the control of reproduction particularly in females (mainly in control of ovarian function). This study was carried out to investigate the mRNA and protein amounts of APLN/APJ in granulose cells (GCs) of ovarian follicles with small (SF), medium (MF), and large (LF) sizes of buffalo (Bubalus bubalis) and the effect of IGF1 and follicle-stimulating hormone (FSH) on the expression levels of APLN/APJ. In addition, we evaluated the effect of various doses of APLN (isoforms -13 and -17) singly or in combination with IGF1 and FSH on estradiol (E2) and progesterone (P4) secretion in GCs. The mRNA and protein abundance of APLN was the highest in GCs of LF while the APJ expression enhanced with follicle enlargement in GCs (p-value <0.01). IGF1 and FSH elevated the mRNA and protein amounts of APLN and FSH, and IGF1 increased the expression of APJ in buffalo GCs (p-value <0.01). Both isoforms of APLN (-13/-17) singly or in the presence of IGF1 or FSH increased the secretion of E2 and P4 with or without preincubation of cells with APJ antagonist (ML221 10 µM), although we had some variation in the effects. Concurrently, APLN-13/-17 significantly increased the mRNA and protein expression of CYP19A1 and StAR (p-value <0.01). ML221 substantially diminished the secretion of E2 and P4 and also the expression of CY19A1 and StAR in buffalo GCs (p-value <0.01). We also revealed that APLN-13/-17 (10^-9 M), singly or in response to IGF1 and FSH, increased the production of E2 and P4 in different times of stimulation. In conclusion, APLN may play a crucial role in steroidogenesis and follicular development in ovarian GCs of buffalo.

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.