Follicle development in pigs: State of the art

Understanding the factors and pathways involved with recruitment, atresia, and selection of follicles in the pig, may provide insight into approaches to limit fertility failures. Antral follicles depend upon FSH to the 2-3 mm stage, become codependent upon LH at 4-5 mm, and rely on LH when >5 mm. Within the follicle, gonadotropin binding, steroids, growth factors, and inhibin interact to determine the fate of the follicle. Continuous recruitment appears likely for follicles, and once >1 mm, they may have a limited period for survival, before selection or atresia. If true, then the number of healthy follicles that can respond to a hormone signal for selection, could vary by size and development stage. Which follicles are selected may depend upon their age, numbers of capillaries, granulosa and thecal cells, and FSH and LH receptors. This might also suggest that factors such as management, nutrition, and stress in prior weeks, could affect different cohorts of follicles to determine which of those from the ovarian population will be selected.

Paradoxical effects of kisspeptin: it enhances oocyte in vitro maturation but has an adverse impact on hatched blastocysts during in vitro culture

Kisspeptin (Kp) is best known as a multifunctional peptide with roles in reproduction, the cardiovascular system and cancer. In the present study the expression of kisspeptin hierarchy elements (KISS1, GNRH1 and LHB) and their receptors (KISS1R, GNRHR and LHCGR, respectively) in porcine ovary and in cumulus-oocyte complexes (COCs) were investigated, as were its effects on the in vitro maturation (IVM) of oocytes and their subsequent ability to sustain preimplantation embryo competence after parthenogenetic electrical activation. Kp system elements were expressed and affected IVM of oocytes when maturation medium was supplemented with 10(-6)M Kp. Oocyte maturation, maternal gene expression (MOS, GDF9 and BMP15), blastocyst formation rate, blastocyst hatching and blastocyst total cell count were all significantly increased when oocytes were matured in medium containing Kp compared with the control group (without Kp). A Kp antagonist (p234) at 4×10(-6)M interfered with this hierarchy but did not influence the threshold effect of gonadotrophins on oocyte maturation. FSH was critical and permissive to Kp action on COCs by increasing the relative expression of KISS1R. In contrast, Kp significantly increased apoptosis, the expression of pro-apoptotic gene, BAK1, and suppressed trophoblast outgrowths from hatched blastocysts cultured on feeder cells. The present study provides the first functional evidence of the Kp hierarchy in porcine COCs and its role in enhancing oocyte maturation and subsequent developmental competence in an autocrine-paracrine manner. However, Kp supplementation may have a harmful impact on cultured hatched blastocysts reflecting systemic or local regulation during the critical early period of embryonic development.

Expression profiles of key candidate genes involved in steroidogenesis during follicular atresia in the pig ovary

More than 99 % of follicles in mammalian ovaries undergo a degenerative process known as atresia, and thus only a limited number of ovarian follicles actually ovulate after full growth and development. The endocrinological regulatory mechanisms involved in follicular development have been studied extensively, but the precise and systematic molecular mechanisms of steroidogenesis enzymes involved in atresia are unclear. In the present study, we examined whether and how the steroidogenesis enzymes are involved in porcine ovary follicular atresia. Expression of steroidogenic acute regulatory protein, CYP11, CYP17, 3β-hydroxysteroid dehydrogenase (3β-HSD), CYP19, as well as related pituitary and ovarian hormone receptors were quantified in ovaries. During porcine follicular atresia, expressions of P450 cholesterol side chain cleavage enzyme, progesterone and androgen receptors increased significantly during the late atretic stage, while the expression of aromatase and follicle-stimulating hormone receptors decreased significantly in the early stage. These data suggested that the regulation of aromatase by follicle-stimulating hormone might induce follicular atresia, and that progesterone and androgen production further promoted follicular atresia. Additionally, a correlation analysis indicated a large and complex interactive network among these genes and the endocrinological microenvironment of the follicles. Significant correlations were observed between expression of steroidogenic enzymes and their receptors, and also between progesterone and 17β-estradiol (E2) levels in follicular fluid. Taken together, these results suggest that CYP19 plays a role during early atresia by regulating the production of E2, whereas CYP11 and 3β-HSD increase atresia progression by increasing progesterone levels.

Elevated level of 17β-estradiol is associated with overexpression of FSHR, CYP19A1, and CTNNB1 genes in porcine ovarian follicles after prenatal and neonatal flutamide exposure

Recent studies suggest that disturbed androgen action during gestational and neonatal periods leads to reprogramming of the trajectory of ovarian development, manifested by altered follicular functioning in adulthood. In this study, we tested whether prenatal and neonatal exposure to antiandrogen flutamide affected ovarian 17β-estradiol (E(2)) synthesis and the associated gene expression in large antral follicles of adult pigs. Flutamide was injected into pregnant gilts between Days 80 and 88 of gestation and into female piglets between Days 2 and 10 postnatally. After animals reached sexual maturity, the ovaries were collected from treated and nontreated (control) pigs. The analysis of E(2) concentration in follicular tissues, as well as FSH and LH levels in plasma of control and flutamide-treated animals were conducted. In addition, the expression of mRNAs and proteins for FSH receptor (FSHR), cytochrome P450 aromatase (CYP19A1) and β-catenin (CTNNB1) was examined in large antral follicles of adult pigs. The E(2) concentration was greater in response to flutamide administered prenatally (P < 0.05) and neonatally (P < 0.01), whereas there was no changes in plasma gonadotropin concentration. Real-time polymerase chain reaction analysis revealed significant upregulation of FSHR, CYP19A1, and CTNNB1 at the mRNA level after maternal (P < 0.001, P < 0.01, P < 0.05, respectively) and neonatal (P < 0.001, P < 0.001, P < 0.01, respectively) flutamide exposure. The expression of FSHR protein was higher (P < 0.01) only after neonatal exposure to flutamide, whereas CYP19A1 and CTNNB1 proteins were upregulated in response to both prenatal (P < 0.01) and neonatal (P < 0.001) flutamide administration. Furthermore, membranous CTNNB1 immunolocalization indicates that it is not involved in regulation of FSH-mediated CYP19A1 activity as a transcription factor, but rather contributes to the intercellular adhesion. Concluding, it appears that the higher E(2) level in response to flutamide treatments is a result of the intensified aromatization and local E(2) action at the ovary level. The observed changes might influence the normal follicle development and pig fertility as a consequence.

FSH receptor in vitro modulation by testosterone and hCG in human luteinized granulosa cells

OBJECTIVE

To investigate the effect of testosterone and hCG on FSH receptor (FSHR) protein and mRNA expression in human granulosa cells (GC) in vitro.

STUDY DESIGN

Experimental in vitro cell culture obtained from healthy women undergoing IVF/ICSI due to male factor infertility. Human follicular fluid samples were obtained and after cumulus-oocyte complexes were identified, fluids were pipetted onto Ficoll gradients and centrifuged for 15 min at 400 × g at room temperature. Cells at the interface were removed and plated in 24-well plates for 3 days in M-199 with 10% FBS. Cells were treated with different concentrations of testosterone and hCG. After purification, cells were labeled with specific antibodies and the protein expression of the FSHR was evaluated by flow cytometry in the GC population. Also, total RNA was extracted from confluent GC and the FSHR gene expression was evaluated by RT-PCR.

RESULTS

FSHR expression was modulated by treating GC in vitro at different testosterone/hCG concentrations. When compared with untreated GC, we observed a significant effect of testosterone and hCG on the expression of the FSHR at the protein level. Time course experiments confirmed that the gene expression of the FSHR peaked at 12-24h when testosterone or hCG was used as a stimulus.

CONCLUSIONS

Both testosterone and hCG are able to positively modulate FSHR expression at gene and protein level in human GC in vitro.

Prenatal and neonatal exposure to flutamide affects function of Leydig cells in adult boar

In this study, flutamide, an androgen receptor antagonist, was used as a tool to better understand the role of androgen receptor signaling and androgen signaling disruption during fetal and neonatal periods on porcine Leydig cell development and function. Flutamide, 50 mg kg(-1) d(-1) was administered into pregnant gilts during gestational days 20 to 28 and days 80 to 88 and into male piglets on postnatal days 2 to 10 (PD2). Leydig cells of flutamide-exposed boars, especially those of PD2 males, displayed morphologic alterations, increased size, and occupied increased area (P < 0.001) of the testes when compared with the control. Despite this, testosterone concentrations were reduced significantly in comparison with those of controls (P < 0.05, P < 0.001). Reduced testosterone production in response to flutamide exposure appeared to be related to changes in testosterone metabolism, as shown by increased aromatase mRNA (P < 0.05, P < 0.01), protein expression (P < 0.01, P < 0.001), and elevated estradiol concentrations (P < 0.001). Moreover, impaired Leydig cell responsiveness to LH was indicated by the decreased expression of LH receptor (P < 0.05, P < 0.001). No significant effect of flutamide was found on LH and FSH concentrations. Taken together, our data indicate that flutamide when administered during prenatal or neonatal period have a long-term effect on Leydig cell structure and function, leading to androgen-estrogen imbalance. Leydig cell failure was most evident in adult boars neonatally exposed to flutamide, suggesting that androgen action during neonatal development is of pivotal importance for the differentiation and function of porcine adult Leydig cell population.

Effects of androgens on serum concentrations of gonadotropins and ovarian steroids in gilts

To examine how androgens affect endocrine events associated with increased ovulation rate, gilts were injected with androgen receptor agonists, an antagonist, or a combination of both. Blood samples were collected hourly from Day 13 to estrus (Day 0 = onset of estrus) coincident with gilts (n = 6 per treatment) receiving daily treatments of vehicle (corn oil), 10 mg of testosterone, 10 mg of 5 alpha-dihydrotestosterone (dihydrotestosterone), 1.5 g of flutamide (an androgen receptor antagonist), testosterone plus flutamide, or dihydrotestosterone plus flutamide. Treatment of gilts with testosterone or dihydrotestosterone alone increased (P < 0.05) concentrations of FSH in serum, and these effects were blocked by cotreatment with flutamide. Estradiol-17beta and androstenedione concentrations in serum were increased (P < 0.05) at 2 h after injection of testosterone or testosterone plus flutamide but not after dihydrotestosterone treatment, probably because of the role of testosterone as a substrate for estradiol-17beta and androstenedione synthesis. There were no effects of the six treatments on serum concentrations of progesterone during luteolysis, but treating gilts with testosterone shortened (P < 0.05) the proestrous period. Total embryonic loss by Day 11 in gilts treated with dihydrotestosterone was reversed when gilts were cotreated with dihydrotestosterone plus flutamide. Results of this experiment indicated that androgen actions both increased FSH secretion and reduced embryonic survival by a mechanism(s) dependent on the androgen receptor.