In vitro effect of leptin on growth hormone (GH)- and insulin-like growth factor-I (IGF-I)-stimulated progesterone secretion and apoptosis in developing and mature corpora lutea of pig ovaries

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.

Growth hormone in fertility and infertility: Mechanisms of action and clinical applications

Secreted by the anterior pituitary gland, growth hormone (GH) is a peptide that plays a critical role in regulating cell growth, development, and metabolism in multiple targeted tissues. Studies have shown that GH and its functional receptor are also expressed in the female reproductive system, including the ovaries and uterus. The experimental data suggest putative roles for GH and insulin-like growth factor 1 (IGF-1, induced by GH activity) signaling in the direct control of multiple reproductive functions, including activation of primordial follicles, folliculogenesis, ovarian steroidogenesis, oocyte maturation, and embryo implantation. In addition, GH enhances granulosa cell responsiveness to gonadotropin by upregulating the expression of gonadotropin receptors (follicle-stimulating hormone receptor and luteinizing hormone receptor), indicating crosstalk between this ovarian regulator and the endocrine signaling system. Notably, natural gene mutation of GH and the age-related decline in GH levels may have a detrimental effect on female reproductive function, leading to several reproductive pathologies, such as diminished ovarian reserve, poor ovarian response during assisted reproductive technology (ART), and implantation failure. Association studies using clinical samples showed that mature GH peptide is present in human follicular fluid, and the concentration of GH in this fluid is positively correlated with oocyte quality and the subsequent embryo morphology and cleavage rate. Furthermore, the results obtained from animal experiments and human samples indicate that supplementation with GH in the in vitro culture system increases steroid hormone production, prevents cell apoptosis, and enhances oocyte maturation and embryo quality. The uterine endometrium is another GH target site, as GH promotes endometrial receptivity and pregnancy by facilitating the implantation process, and the targeted depletion of GH receptors in mice results in fewer uterine implantation sites. Although still controversial, the administration of GH during ovarian stimulation alleviates age-related decreases in ART efficiency, including the number of oocytes retrieved, fertilization rate, embryo quality, implantation rate, pregnancy rate, and live birth rate, especially in patients with poor ovarian response and recurrent implantation failure.

Adipokines change the balance of proliferation/apoptosis in the ovarian cells of human and domestic animals: A comparative review

Adipose tissue secretes multiple hormones termed adipokines, which are important regulators of many processes. There are four types of evidence supporting an association between adipokines and female fertility which are effects that occur: centrally at the pituitary; peripherally and locally at the ovary and reproductive tract; directly on the oocyte/embryo and during pregnancy. In this review, there was a focus on the description of adipokines (leptin, apelin, resistin, chemerin, adiponectin, vaspin and visfatin) on ovarian cell proliferation, cell cycle progression and apoptosis in comparison to effects on human and domestic animal ovaries including pigs, cattle and chickens. Knowledge about molecules which regulate the balance between proliferation and apoptosis so that these processes are optimal for ovarian function is essential for understanding the physiology and reducing the incidence of infertility. Furthermore, oogenesis, folliculogenesis, oocyte loss/selection and atresia are important processes for optimal ovarian physiological functions. There, however, is ovulation from only a few follicles, while the majority undergo atresia that is induced by apoptosis.

Novel Insights on the Corpus Luteum Function: Role of Vaspin on Porcine Luteal Cell Angiogenesis, Proliferation and Apoptosis by Activation of GRP78 Receptor and MAP3/1 Kinase Pathways

Formation and limited lifespan of corpus luteum (CL) are important for proper ovarian periodicity and fertility. Failed vascularization, imbalance between proliferation and apoptosis leads to luteal phase deficiency and infertility. The aim of this study was to examine the effect of vaspin on angiogenesis, apoptosis and proliferation as well as the involvement of 78-kDa glucose-regulated protein receptor (GRP78) and mitogen-activated kinase (MAP3/1) in these processes. Porcine luteal cells were incubated with vaspin (0.1-10 ng/mL) for 24 h to 72 h and then mRNA and protein expression of angiogenesis: vascular endothelial growth factor (VEGFA), fibroblast growth factor 2 (FGF2), angiopoietin 1 (ANGPT1), VEGFA receptors (VEGFR1, VEGFR2), apoptosis: caspase 3, bcl-2-like protein 4 (BAX), B-cell lymphoma (BCL2), and proliferation: proliferating cells nuclear antigen (PCNA), cyclin A factors as well as secretion of VEGFA, FGF2, ANGT1 were measured by real-time polymerase chain reaction (PCR), immunoblotting and enzyme-linked immunosorbent assay (ELISA), respectively. Moreover, apoptosis was assessed by caspase activity using the Caspase-Glo 3/7 assay, while proliferation was by alamarBlue. We found that vaspin enhanced luteal cell angiogenesis, proliferation, and significantly decreased apoptosis. Additionally, using GRP78 siRNA and the pharmacological inhibitor of MAP3/1 (PD98059), we observed that the effect of vaspin was reversed to the control level in all investigated processes. Taken together, our results suggest that vaspin is a new regulator of female fertility by direct regulation of CL formation and maintenance of luteal cell function.

Expression of insulin-like growth factor 1 and its receptor in preovulatory follicles and in the corpus luteum in the bitch

In the bitch, ovarian follicular and corpus luteum (CL) development and function are regulated by gonadotropins as well as local factors, the role of which is especially important during the early CL phase of relative gonadotrophic independence. We assumed that insulin-like growth factor 1 (IGF1) has a paracrine/autocrine regulatory role in ovarian follicular and luteal function in the dog. To address our hypothesis, we studied gene and protein expression of IGF1 and its receptor (IGF1R) in preovulatory follicles and in the CL of pregnant and non-pregnant dogs, and following antigestagen (aglepristone, progesterone receptor blocker) treatment in mid-gestation. Ovaries in the follicular phase were collected from five bitches. CL were collected on pregnancy Days 8-12 (pre-implantation), 18-25 (post-implantation), 35-40 (mid-gestation), at prepartum luteolysis, and 24 h and 72 h after aglepristone treatment in mid-gestation (n = 3-5 per group). From non-pregnant bitches, CL were collected on Days 5, 15, 25, 35, 45, 65 after ovulation (n = 4-5 per group). Semi-quantitative real-time (TaqMan) PCR and immunohistochemistry were applied. IGF1 immunostaining in preovulatory follicles seemed stronger in theca interna than granulosa cells. IGF1R signals appeared more intense in granulosa cells at the apical part of mural folds. In pregnant dogs, luteal IGF1 mRNA expression decreased significantly from pre-implantation to prepartum luteolysis, while IGF1R expression increased at prepartum luteolysis. Aglepristone treatment in mid-gestation had no effect on IGF1 and IGF1R mRNA levels. In non-pregnant bitches, highest IGF1 mRNA concentrations were found in the early CL and decreased by Days 45 and 65, while IGF1R expression did not change. In the CL of pregnant bitches, signals for IGF1 and IGF1R in luteal cells were strongest at pre- and post-implantation and weakest at prepartum luteolysis. IGF1 and IGF1R immunostaining was also detected in macrophages and in blood vessels. In conclusion, IGF1 may have a paracrine or autocrine role in granulosa and theca interna cells in preovulatory follicles. As IGF1 was highest represented in early luteal stages in pregnant and non-pregnant bitches, this may support a role for IGF1 in steroid synthesis, angiogenesis and cell proliferation as well as in immune function in the early canine CL. The unaffected mRNA levels after aglepristone treatment may support that IGF1 is not directly regulated by local progesterone in an auto- or paracrine manner.

Multiple Effects of Growth Hormone in the Body: Is it Really the Hormone for Growth?

In this review, we analyze the effects of growth hormone on a number of tissues and organs and its putative role in the longitudinal growth of an organism. We conclude that the hormone plays a very important role in maintaining the homogeneity of tissues and organs during the normal development of the human body or after an injury. Its effects on growth do not seem to take place during the fetal period or during the early infancy and are mediated by insulin-like growth factor I (IGF-I) during childhood and puberty. In turn, IGF-I transcription is dependent on an adequate GH secretion, and in many tissues, it occurs independent of GH. We propose that GH may be a prohormone, rather than a hormone, since in many tissues and organs, it is proteolytically cleaved in a tissue-specific manner giving origin to shorter GH forms whose activity is still unknown.

Modulatory role of leptin on ovarian functions in water buffalo (Bubalus bubalis)

The aim of the present study was to demonstrate the modulatory role of leptin on bubaline granulosa cells (GCs) and luteal cells (LCs) functions using an in vitro cell culture system and to establish a cross talk between leptin and insulin-like growth factor-1 (IGF-1). GCs were collected from group IV follicles (>13 mm size) and LCs from mid-luteal phase corpus luteum and were grown in serum-containing media supplemented with leptin at three different dose rates (0.1, 1, and 10 ng/mL) and time durations (24, 48, and 72 hours). We evaluated the production and secretion of estradiol (E2) and progesterone (P4) using RIA and the mRNA expression of steroidogenic acute regulatory protein (STARD1), cytochrome P450 cholesterol side-chain cleavage (CYP11A1), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 aromatase (CYP19A1), sterol regulatory element-binding protein 1 (SREBP1), steroidogenic factor-1 (SF1), anti-apoptotic gene PCNA, pro-apoptotic gene caspase 3 and endothelial cell marker, Von Willebrand factor (vWF), using quantitative real-time polymerase chain reaction. The results depicted a direct inhibitory action of leptin on GCs steroidogenesis in a time-dependent manner (P < 0.05), whereas in the presence of IGF-1 the inhibitory effect was reverted. Furthermore, leptin augmented both cellular proliferation (PCNA) and apoptosis (caspase 3). On the other hand, in LCs, leptin alone showed an apparent stimulatory effect on steroidogenesis (P < 0.05); however, in the presence of IGF-1, an antagonistic effect was witnessed. Moreover, leptin had an inhibitory effect on apoptosis while promoted cellular proliferation and angiogenesis. These findings were further strengthened by immunocytochemistry. To conclude, these observations for the first time reported that in buffaloes leptin has a direct dose-, time-, and tissue-dependent effect on ovarian steroidogenesis, angiogenesis, and cytoprotection, and furthermore, it can regulate the effect of systemic factors like IGF-1. Hence, this in vitro study provides an insight into the putative roles of leptin alone and its interactions in vivo.

Growth hormone and reproduction: a review of endocrine and autocrine/paracrine interactions

The somatotropic axis, consisting of growth hormone (GH), hepatic insulin-like growth factor I (IGF-I), and assorted releasing factors, regulates growth and body composition. Axiomatically, since optimal body composition enhances reproductive function, general somatic actions of GH modulate reproductive function. A growing body of evidence supports the hypothesis that GH also modulates reproduction directly, exerting both gonadotropin-dependent and gonadotropin-independent actions in both males and females. Moreover, recent studies indicate GH produced within reproductive tissues differs from pituitary GH in terms of secretion and action. Accordingly, GH is increasingly used as a fertility adjunct in males and females, both humans and nonhumans. This review reconsiders reproductive actions of GH in vertebrates in respect to these new conceptual developments.

Leptin stimulation of cell cycle and inhibition of apoptosis gene and protein expression in OVCAR-3 ovarian cancer cells

The OVCAR-3 cell line expressing the long (ObRb) and short (ObRt) isoforms of leptin receptor mRNA was used to analyze the effect of leptin on the expression of selected genes and proteins involved in the cell cycle and apoptosis. OVCAR-3 cells were exposed to 2, 20, 40, and 100 ng/ml of leptin. Cell proliferation was determined using the alamarBlue cell viability test and flow cytometry. Apoptosis was measured using a cellular DNA fragmentation ELISA kit. The expression of selected cell cycle and apoptosis genes was evaluated by real-time PCR and confirmed by western blot. The stimulatory action of leptin on cell proliferation was observed as an increase in cells in the S and G2/M phases. Up-regulation of genes responsible for inducing cell proliferation and suppression of genes responsible for inhibition of proliferation were noted. Western blots revealed increased expression of cyclins D and A and inhibition of p21WAF1/CIP1 protein expression by leptin. Inhibition of DNA fragmentation was observed under all leptin doses. Suppression of genes involved in the extrinsic and intrinsic apoptotic pathway was observed. Western blots illustrated decreased Bad, TNFR1, and caspase 6 protein expression in response to leptin treatment. Leptin promotes ovarian cancer cell line growth by up-regulating genes and proteins responsible for inducing cell proliferation as well as down-regulating pro-apoptotic genes and proteins in apoptotic pathways. Results of this study warrant examining the relationship between the risk of ovarian cancer and elevated leptin levels in obese women.

Leptin directly controls proliferation, apoptosis and secretory activity of cultured chicken ovarian cells

The aim of our in-vitro experiments was to examine, whether leptin can directly control functions of avian ovarian cells and to outline potential intracellular mediators of its effects. Granulosa cells or fragments of ovarian follicular wall were cultured with leptin (0, 1, 10 or 100 ng/mL medium). The expression of peptides involved in apoptosis (TdT, bax, its binding protein, bcl-2, ASK-1 and p53), cell cycle-related peptides (PCNA and cyclin B1), release of hormones (progesterone, testosterone, estradiol, arginine-vasotocin), as well as the expression of protein kinases (PKA, MAPK/ERK1,2 and CDK/p34) in the ovarian cells were examined by using immunocytochemistry, TUNEL, SDS-PAGE-Western immunoblotting, EIA and RIA. It was found that leptin inhibited expression of all markers of cytoplasmic apoptosis (bax, ASK-1 and p53), stimulated expression of anti-apoptotic peptide bcl-2, but did not affect nuclear DNA fragmentation (TdT). Furthermore, leptin inhibited expression of PCNA (marker of S-phase of mitosis), but not of cyclin B1 (marker of G phase of cell cycle). Moreover, it promoted release of progesterone and estradiol, suppressed release of testosterone, but did not affect arginine-vasotocin. Finally, leptin inhibited expression of MAPK/ERK1,2 and CDK/p34 and stimulated expression of PKA. The present observations demonstrate that leptin can directly control basic chicken ovarian functions - inhibit cytoplasmic apoptosis and proliferation (S-phase, but not G-phases of mitosis), regulate secretory activity (release of steroids, but not nonapeptide hormone) and expression of MAPK, PKA and CDC2, which might be potential intracellular mediators of leptin action.

Action of IGF-I on Expression of the Long Form of the Leptin Receptor (ObRb) in the Prepubertal Period and Throughout the Estrous Cycle in the Mature Pig Ovary

Leptin is an important satiety hormone and reproductive regulator found, along with its receptors, throughout the ovary. To date, the changes in ovarian expression of leptin receptor during the prepubertal period and throughout the estrous cycle in the pig have not been studied. In this study, the long form of the leptin receptor was a detectable level in immature pig ovarian follicles when assayed using semiquantitative reverse transcription-polimerase chain reaction (RT-PCR). Moreover, its level was increased in growing follicles during follicular phase of the estrous cycle (6-fold in early antral [EAF] and antral [AF] follicles) and was highest in newly formed corpora lutea. Its changes paralleled those in steroid secretion and especially progesterone (P(4)) secretion. Additionally, we showed that insulin-like growth factor (IGF)-I had stimulatory effect on leptin receptor expression using a tissue culture model of follicular and luteal cells, with a 12-fold increase in prepubertal ovaries and a 1.5- to 2-fold increase in growing follicles and newly formed corpora lutea (CL). These results suggest that ovarian expression of leptin receptor is regulated throughout the estrous cycle by ovarian steroids, with peak expression at ovulation, indicating a possible involvement in follicular development and corpus luteum formation. Moreover, this data points to an important role of IGF-I in leptin receptor expression during the entire estrous cycle, with a special role during the prepubertal period.