Expression of steroidogenic enzymes and synthesis of steroid hormones during development of ovarian follicles in prepubertal goats

The mechanisms that control the preantral to early antral follicle transition and the strategies to have efficient culture systems to promote their growth in vitro

Preantral to early antral follicles transition is a complex process regulated by endocrine and paracrine factors, as well as by a precise interaction among oocyte, granulosa cells and theca cells. Understanding the mechanisms that regulate this step of folliculogenesis is important to improve in vitro culture systems, and opens new perspectives to use oocytes from preantral follicles for assisted reproductive technologies. Therefore, this review aims to discuss the endocrine and paracrine mechanisms that control granulosa cell proliferation and differentiation, formation of the antral cavity, estradiol production, atresia, and follicular fluid production during the transition from preantral to early antral follicles. The strategies that promote in vitro growth of preantral follicles are also discussed.

Modulation of granulosa cell function via CRISPR-Cas fuelled editing of BMPR-IB gene in goats (Capra hircus)

BMPs are multifunctional growth factors implicated in regulating the ovarian function as key intra-ovarian factors. Biological effects of BMPs are mediated through binding with membrane bound receptors like BMPR-IB and initiating downstream Smad signaling pathway. FecB mutation, regarded as a loss of function mutation in the BMPR-IB gene was identified in certain sheep breeds having high fecundity. Similar type of fecundity genes in goats have not been discovered so far. Hence, the current study was designed to investigate the effects of BMPR-IB gene modulation on granulosa cell function in goats. The BMPR-IB gene was knocked out using CRISPR-Cas technology in granulosa cells and cultured in vitro with BMP-4 stimulation for three different durations In addition, the FecB mutation was introduced in the BMPR-IB gene applying Easi-CRISPR followed by BMP-4/7 stimulation for 72 h. Steroidogenesis and cell viability were studied to explore the granulosa cell function on BMPR-IB gene modulation. BMPRs were found to be expressed stage specifically in granulosa cells of goats. Higher transcriptional abundance of R-Smads, LHR and FSHR indicating sensitisation of Smad signaling and increased gonadotropin sensitivity along with a significant reduction in the cell proliferation and viability was observed in granulosa cells upon BMPR-IB modulation. The inhibitory action of BMP-4/7 on P4 secretion was abolished in both KO and KI cells. Altogether, the study has revealed an altered Smad signaling, steroidogenesis and cell viability upon modulation of BMPR-IB gene in granulosa cells similar to that are documented in sheep breeds carrying the FecB mutation.

Leptin induced in vitro development of ovarian follicles in sheep is related to the expression of P450 aromatase and steroidogenesis

The objective of this study was to test the hypothesis that Leptin induced in vitro growth in preantral follicles in sheep involves modulation of P450 aromatase expression and steroidogenesis. Accordingly, the expression of P450 aromatase gene was studied in the cumulus cells and oocytes isolated from different stages of preantral follicles (PFs') grown in vivo, cultured in TCM 199B, TCM 199B + Leptin (10 ng/ml) (TCM199BL) or a standard PF culture medium supplemented with Leptin (10 ng/ml) (SML). Ovarian follicles grown in vivo or in SML expressed P450 aromatase both in cumulus cells and oocytes at all the development stages. In the oocytes from PFs' grown in vitro, P450 expression was consistently lower than in those from in vivo grown follicles at all except the preantral stage. The patterns of expression of aromatase gene in the cumulus cells from in vivo grown and the PFs' cultured in TCM 199BL were similar. Significantly higher levels of progesterone production were supported by SML at all the development stages than the other two media. Oestradiol concentration in the spent TCM 199B and SML showed a significant increase as the development progressed from preantral to large antral stage. However, such increase was not sustained beyond early antral stage in the PFs' cultured in TCM199BL. It is concluded that Leptin modulates the expression P450 aromatase while supporting the in vitro development of the ovarian follicles in sheep.

Reduced glutathione alleviates tunicamycin-induced endoplasmic reticulum stress in mouse preimplantation embryos

Endoplasmic reticulum (ER) stress, a dysfunction in protein-folding capacity, is involved in many pathological and physiological responses, including embryonic development. This study aims to determine the developmental competence, apoptosis, and stress-induced gene expression in mouse preimplantation embryos grown in an in vitro culture medium supplemented with different concentrations of the ER stress inducer tunicamycin (TM) and the antioxidant glutathione (GSH). Treatment of zygotes with 0.5 µg/ml TM significantly decreased (P < 0.05) the rate of blastocyst formation, whereas 1 mM GSH supplementation improved the developmental rate of blastocysts. Furthermore, TM treatment significantly increased (P < 0.05) the apoptotic index and reduced the total number of cells, whereas GSH significantly increased the total number of cells and decreased the apoptotic index. The expression levels of ER chaperones, including immunoglobulin-binding protein, activating transcription factor 6, double-stranded activated protein kinase-like ER kinase, activating transcription factor 4, and C/EBP homologous protein were significantly increased (P < 0.05) by TM, but significantly decreased (P < 0.05) by GSH treatment. A similar pattern was observed in the case of the pro-apoptotic gene, B cell lymphoma-associated X protein. The expression level of the anti-apoptotic gene B cell lymphoma 2, was decreased by TM, but significantly increased after co-treatment with GSH. In conclusion, GSH improves the developmental potential of mouse embryos and significantly alleviates ER stress.

Hypothyroidism Reduces the Size of Ovarian Follicles and Promotes Hypertrophy of Periovarian Fat with Infiltration of Macrophages in Adult Rabbits

Ovarian failure is related to dyslipidemias and inflammation, as well as to hypertrophy and dysfunction of the visceral adipose tissue (VAT). Although hypothyroidism has been associated with obesity, dyslipidemias, and inflammation in humans and animals, its influence on the characteristics of ovarian follicles in adulthood is scarcely known. Control and hypothyroid rabbits were used to analyze the ovarian follicles, expression of aromatase in the ovary, serum concentration of lipids, leptin, and uric acid, size of adipocytes, and infiltration of macrophages in the periovarian VAT. Hypothyroidism did not affect the percentage of functional or atretic follicles. However, it reduced the size of primary, secondary, and tertiary follicles considered as large and the expression of aromatase in the ovary. This effect was associated with high serum concentrations of total cholesterol and low-density lipoprotein cholesterol (LDL-C). In addition, hypothyroidism induced hypertrophy of adipocytes and a major infiltration of CD68+ macrophages into the periovarian VAT. Our results suggest that the reduced size of ovarian follicles promoted by hypothyroidism could be associated with dyslipidemias, hypertrophy, and inflammation of the periovarian VAT. Present findings may be useful to understand the influence of hypothyroidism in the ovary function in adulthood.

An immortalized steroidogenic goat granulosa cell line as a model system to study the effect of the endoplasmic reticulum (ER)-stress response on steroidogenesis

With granulosa and theca cells, the ovaries are responsible for producing oocytes and secreting sex steroids such as estrogen and progesterone. Endoplasmic reticulum stress (ERS) plays an important role in follicle atresia and embryo implantation. In this study, goat granulosa cells were isolated from medium-sized (4-6 mm) healthy follicles. Primary granulosa cells were immortalized by transfection with human telomerase reverse transcriptase (hTERT) to establish a goat granulosa cell line (hTERT-GGCs). These hTERT-GGCs expressed hTERT and had relatively long telomeres at passage 50. Furthermore, hTERT-GGCs expressed the gonadotropin receptor genes CYP11A1, StAR, and CYP19A1, which are involved in steroidogenesis. Additionally, progesterone was detectable in hTERT-GGCs. Although the proliferation potential of hTERT-GGCs significantly improved, there was no evidence to suggest that the hTERT-GGCs are tumorigenic. In addition, thapsigargin (Tg) treatment led to a significant dose-dependent decrease in progesterone concentration and steroidogenic enzyme expression. In summary, we successfully generated a stable goat granulosa cell line. We found that Tg induced ERS in hTERT-GGCs, which reduced progesterone production and steroidogenic enzyme expression. Future studies may benefit from using this cell line as a model to explore the molecular mechanisms regulating steroidogenesis and apoptosis in goat granulosa cells.

Swainsonine differentially affects steroidogenesis and viability in caprine luteal cells in vitro

Plants containing swainsonine (SW) have been reported to impair reproductive function and fertility after long-term ingestion by livestock. However, direct effects of SW on luteal cell steroidogenesis remain unclear. In this study, primary and transfected luteal cells were used to investigate the effects of SW on progesterone secretion and cell viability and the mechanisms involved in these processes. After treatment with various concentrations of SW for 24 or 48 hours, progesterone production and the number of living cells were assessed using radioimmunoassay and trypan blue dye exclusion assay, respectively. Lower concentrations of SW enhanced basal, 22R-hydroxycholesterol- or pregnenolone-stimulated progesterone secretion (P < 0.05), whereas higher concentrations of SW inhibited progesterone secretion (P < 0.05). Lower concentrations of SW promoted expression of P450 side-chain cleavage enzyme and 3β-hydroxysteroid dehydrogenase, two key enzymes involved in luteal cell steroidogenesis, at mRNA and protein levels (P < 0.05), but did not affect expression of steroidogenic acute regulatory protein and cell proliferation. In contrast, higher concentrations of SW inhibited luteal cell proliferation by inducing growth phase 1/quiescent state cell cycle arrest and apoptosis (P < 0.05). Taken together, these results demonstrated that lower concentrations of SW induced progesterone production through upregulation of P450 side-chain cleavage enzyme and 3β-hydroxysteroid dehydrogenase without affecting cell viability, whereas higher concentrations of SW induced cell cycle arrest and apoptosis and impaired steroidogenesis. These findings provided new insights into understanding the effect of SW on luteal cell steroidogenesis.

Immunoreactivities of androgen receptor, estrogen receptors, p450arom, p450c17 proteins in wild ground squirrels ovaries during the nonbreeding and breeding seasons

The aim of this study was to elucidate the regulatory role of androgen in the follicular development of wild female ground squirrels. Immunohistochemical staining of FSHR, LHR, P450c17, P450arom, androgen receptor (AR), estrogen receptors (ERa and ERb) were executed in ovaries of female ground squirrels from both breeding and nonbreeding seasons. In addition, total ovarian proteins were extracted from the ovaries of squirrels from breeding and nonbreeding seasons, and Western blot analysis were performed in order to probe for FSHR, LHR, P450c17, P450arom, AR, ERa and ERb. The results of immunohistochemical staining and Western blotting of P450c17 showed that there was no significant difference between the breeding and nonbreeding seasons. It was found that granulosa cells expressed P450arom during the breeding season. In contrast, there was no positive staining of P450arom in the nonbreeding season. There was no significant difference in immunoreactivity of AR between the breeding and nonbreeding seasons. However, the immunoreactivities of ERa and ERb were both significantly reduced in the nonbreeding season compared to the breeding season. The positive stains of FSHR and LHR were found in the granulosa cells and theca cells of the ovaries of the breeding and nonbreeding seasons. In addition, the Western blotting results of FSHR and LHR showed a significant reduction in the nonbreeding season compared with the breeding season. These findings suggested that androgen might be predominantly converted into estrogen in order to regulate the follicular development via binding of estrogen receptors during the breeding season, whereas androgen might predominantly directly bind androgen receptor to regulate the follicular development during the nonbreeding season in the ovaries of wild female ground squirrels.

Immunohistochemical localization of aromatase during the development and atresia of ovarian follicles in prepubertal horses

Ovarian steroidogenesis from the neonatal to pubertal period in horses is poorly understood. This study was designed to immunolocalize cytochrome P450 aromatase in the ovarian follicles of slaughtered fillies ages approximately (I) 6-9 mo (<10MF); (II) 1 y (1YF); and (III) 1.5 y (1.5YF). The ovaries of adult mares were used as controls. In each age group, immunoreactivity for P450arom was observed in the mural granulosa of nonatretic follicles >5 mm in diameter. Staining intensity was dependent on the size and morphology of the follicle. In nonatretic follicles 5-10 mm in diameter, the reaction was weak and heterogeneous, while most intense staining was observed in preovulatory follicles. In follicles (diameter <20 mm) in the groups <10MF and 1YF, the reaction was less intense than in adult mare follicles of similar size. In each age group, several follicles with early or advanced signs of atresia exhibited a heterogeneous staining pattern, which subsequently disappeared in late atretic follicles. No immunoreactivity was detected in the theca interna, preantral follicle, or stroma cells. Our observations reveal that the mural granulosa of viable follicles in fillies about 6-18 mo old contains aromatase, indicating that the ovary is capable of estrogen synthesis. Immunoreactivity for P450arom was dependent on follicle size and disappeared in atretic follicles.