Activin inhibition of estradiol and progesterone production in porcine granulosa cells

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.

Effects of transforming growth factor β1 on steroidogenesis of feline granulosa cells cultured in vitro

CONTEXT

Little is known about the hormonal regulation of feline ovarian granulosa cell proliferation and steroidogenesis.

AIMS

To determine if transforming growth factor β1 (TGFB1), activin, epidermal growth factor (EGF), follicle stimulating hormone (FSH), luteinizing hormone (LH), melatonin, and insulin-like growth factor 1 (IGF1) regulate granulosa cell steroidogenesis and proliferation in cats, three experiments were conducted in winter season.

METHODS

Granulosa cells were isolated and treated in vitro with various hormones in serum-free medium for 48h after an initial 48h plating in 10% fetal calf serum.

KEY RESULTS

Treatment with IGF1 and FSH increased (P<0.05) estradiol production by 2.3- and 1.33-fold, respectively. In contrast, TGFB1 blocked (P<0.05) IGF1-induced estradiol production and inhibited FSH-induced estradiol production by 60%. Combined with FSH or FSH plus IGF1, TGFB1 inhibited (P<0.05) cell proliferation, whereas TGFB1 increased progesterone production by 2.8-fold in the presence of FSH plus IGF1. EGF decreased (P<0.05) FSH plus IGF1-induced estradiol production by 89% but did not affect progesterone production or cell numbers. Activin did not affect (P>0.10) cell numbers or steroidogenesis in the presence of FSH plus IGF1. Melatonin and LH decreased (P<0.05) estradiol production 53% and 59%, respectively, without affecting progesterone production or cell proliferation.

CONCLUSIONS

The present study has identified TGFB1 as a major regulator of feline ovarian function, in addition to EGF, IGF1, melatonin, LH and FSH.

IMPLICATIONS

These studies will provide useful information for future development of fertility control in feline species.

Activin A attenuates apoptosis of granulosa cells in atretic follicles through ERβ-induced autophagy

It is well known that about 99% of ovarian follicles in mammals suffer from a degenerative process known as atresia, which is a huge waste of genetic resource in female animals. Studies have shown that activin A (ACT-A) is located in ovarian granulosa cells and has different effects in granulosa cell depending on species. Although granulosa cells play a critical role during follicular atresia, the mechanism of action of ACT-A in bovine ovarian granulosa cells (BGC) is poorly understood. In this study, we firstly determined the apoptosis of BGCs isolated from growth follicles and atretic follicles, respectively. Then, BGC isolated from atretic follicles were used as a model to elucidate the role of ACT-A in cattle ovary. The results showed that apoptosis occurred in both growing follicles and atretic follicles, and the percentage of apoptotic cells in atretic follicles was higher than that in growing follicles. The current results indicated that ACT-A can attenuate apoptosis of BGC through maintaining the function of BGC in atretic follicles. Increased ERβ induced by ACT-A promoted BGC autophagy but had no effect on apoptosis. In summary, this study suggests that ACT-A attenuates BGC apoptosis in atretic follicles by ERβ-mediated autophagy signaling.

Expression and characterization of the serum proteome from yak induced into estrus by improved nutrition

Regulation of estrus plays a crucial role in the livestock industry. It is reported that providing better nutrition can induce early estrus in animals. However, little is known about the major endocrine and physiological mechanisms that could enhance estrus in anestrus animals. Hence in the current research two different groups of yaks, non-breeding season (February-June, NBS) estrus yaks as the experiment group and breeding season (July-September, BS) estrus animals as the control group were compared using the isobaric tags for relative and absolute quantitation (iTRAQ) technique. Study displayed that cold season supplementation significantly improved growth performance, serum biochemical indicators and reproductive hormone concentrations in yaks. We also identified 25 differentially expressed proteins in yak serum using iTRAQ proteomics. Go and KEGG analysis indicated that calcium signaling pathway and beta-alanine metabolism may be candidate pathways for seasonal estrus induced by nutrition. Differential protein expression was validated using parallel reaction monitoring (PRM). The results of this study initially identified A2M, IGF2, A1BG and APOA1 as candidate proteins for seasonal estrus induced by nutrition. Altogether, In conclusion, our results show that providing additional nutrients in the cold season can improve yak productivity and reproductive efficiency, and provide a new reference.

Conception Rate and Reproductive Hormone Secretion in Holstein Cows Immunized against Inhibin and Subjected to the Ovsynch Protocol

Simple Summary

In recent decades, conception rates in lactating dairy cows have dramatically decreased, and improving the conception rate has become a major challenge in dairy cow reproduction. Various Ovsynch protocols have been developed to aid in the resumption of ovarian follicular activity for timely breeding in post-partum cows. However, the effect of Ovsynch protocols on improving the conception rate is unsatisfactory. In addition, immunization against inhibin was reported to improve the fertility of domestic animals. Thus, a novel reproductive technique combining immunization against inhibin and the widely used Ovsynch protocol was proposed and tested in this study. Our results showed that immunization against inhibin has the potential to improve conception rates in cows, but also compromised luteal function. According to these results, additional luteal-stimulating treatments are suggested to further improve cow fertility based on immunization and the Ovsynch protocol.

Abstract

This study was conducted to investigate the feasibility of improving fertility in dairy cows via immunization against inhibin. Thirty-two cows were divided into Control (n = 11), Low-dose (n = 10) and High-dose (n = 11) groups. The High-dose and Low-dose cows were treated with 1 and 0.5 mg of the inhibin immunogen, respectively. All the cows were subjected to the Ovsynch protocol from the day of antigen administration and were artificially inseminated. Blood samples were serially collected over a 24-day period from the start of the Ovsynch protocol to 14 days after insemination. The results showed that immunization against inhibin dose-dependently increased the plasma concentrations of follicle-stimulating hormone (FSH), estradiol (E2), and activin A, but decreased progesterone (P4) concentrations in the luteal phase. Immunization also increased the plasma interferon (IFN)-τ concentrations in pregnant cows on day 14 after initial insemination. The conception rates in High-dose (45.5%) and Low-dose (40%) cows marginally increased compared to that in Control cows (27.3%), but the increases were not significant (p > 0.05). In conclusion, a single immunization against inhibin has the potential to improve conception rates, despite impaired luteal development. To further improve the reproductive performance of dairy cows, additional luteal-stimulating treatments are suggested in combination with immunization against inhibin and Ovsynch techniques.

The effects of fibroblast co-culture and activin A on in vitro growth of mouse preantral follicles

BACKGROUND

This study was conducted to evaluate fibroblast co-culture and Activin A on in vitro maturation and fertilization of mouse preantral follicles.

METHODS

The ovaries from 12-14-day-old mice were dissected, and 120-150 μm preantral follicles were cultured individually in α-MEM as based medium for 12 days. A total number of 456 follicles were cultured in four conditions: (i) base medium as control group (n = 113), (ii) base medium supplemented with 30 ng/ml Activin A (n = 115), (iii) base medium co-cultured with mouse embryonic fibroblast (n = 113), and (iv) base medium supplemented with 30 ng/ml Activin A and co-cultured with fibroblast (n = 115). Rate of growth, survivability, antrum formation, ovulation, embryonic development and steroid production were evaluated. Analysis of Variance and Duncan test were applied for analyzing.

RESULTS

Both co-culture and co-culture + Activin A groups showed significant difference (P<0.05) in growth (on days 4, 6, and 8 of culture period) and survival rates. However, there was no significant difference in antrum formation, ovulation rate, and embryonic development of ovulated oocytes. There were significant differences (P<0.05) in the estradiol production on days 8, 10, and 12 between co-culture + Activin A and the control group. Progesterone production also was significant (P<0.05) in co-culture + Activin A group on days 6, 8, 10, and 12 compared to control group.

CONCLUSION

Fibroblast co-culture and Activin A promoted growth and survivability of preantral follicles. However, simultaneous use of them was more efficient.

Transforming growth factor-β1 inhibits luteinization and promotes apoptosis in bovine granulosa cells

We have previously shown that TGFB1 inhibits estradiol (E2) and progesterone (P4) biosynthesis in FSH-stimulated bovine granulosa cells by selective inhibition of steroidogenic enzymes. The objective of this study was to assess the effects of TGFB1 on E2and P4steroidogenesis in bovine granulosa cells cultured in the absence of FSH and to measure the effects of TGFB1 on cell proliferation and apoptosis in the presence and absence of FSH. Bovine granulosa cells from 2 to 5 mm follicles were cultured in serum-free medium for 2–6 days. In the absence of FSH, the secretion of P4increased with time in culture (P<0.05). Addition of TGFB1 for 6 days decreased P4secretion and mRNA levels of the P4synthesis-associated genesSTAR,CYP11A1,HSD3B1, andGSTA(P<0.05). In the absence of FSH, the secretion of E2decreased and addition of TGFB1 for 6 days partially reversed this decline and stimulated E2biosynthesis,CYP19A1andHSD17B1mRNA levels and CYP19A1 activity (P<0.05). Conversely, TGFB1 did not affectHSD17B7expression and HSD17B-reducing activity. TGFB1 decreased the proportion of cells in the G0/G1 and S+G2/M phases in FSH-stimulated and unstimulated granulosa cells (P<0.05). Furthermore, in the presence or absence of FSH, TGFB1 increased the proportion of cells in apoptosis measured by propidium iodide staining and flow cytometry and confirmed by increased levels of cleaved caspase-3 (P<0.05). Our results therefore indicate that TGFB1 inhibits luteinization in cultured bovine granulosa cells while maintaining an estrogenic phenotype, and this effect was associated with increased apoptosis.

Role of transforming growth factor-β1 in gene expression and activity of estradiol and progesterone-generating enzymes in FSH-stimulated bovine granulosa cells

Survival and inhibitory factors regulate steroidogenesis and determine the fate of developing follicles. The objective of this study was to determine the role of transforming growth factor-β1 (TGFB1) in the regulation of estradiol-17β (E2) and progesterone (P4) secretion in FSH-stimulated bovine granulosa cells. Granulosa cells were obtained from 2 to 5 mm follicles and cultured in serum-free medium. FSH dose (1 and 10 ng/ml for 6 days) and time in culture (2, 4, and 6 days with 1 ng/ml FSH) increased E2secretion and mRNA expression of E2-related enzymes cytochrome P450 aromatase (CYP19A1) and 17β-hydroxysteroid dehydrogenase type 1 (HSD17B1), but notHSD17B7. TGFB1 in the presence of FSH (1 ng/ml) inhibited E2secretion, and decreased mRNA expression of FSH receptor(FSHR),CYP19A1, andHSD17B1, but notHSD17B7. FSH dose did not affect P4secretion and mRNA expression of 3β-hydroxysteroid dehydrogenase (HSD3B) and α-glutathioneS-transferase (GSTA), but inhibited the amount of steroidogenic acute regulatory protein(STAR)mRNA. Conversely, P4and mRNA expression ofSTAR, cytochrome P450 side-chain cleavage(CYP11A1),HSD3B, andGSTAincreased with time in culture. TGFB1 inhibited P4secretion and decreased mRNA expression ofSTAR,CYP11A1,HSD3B, andGSTA. TGFB1 modified the formation of granulosa cell clumps and reduced total cell protein. Finally, TGFB1 decreased conversion of androgens to E2, but did not decrease the conversion of estrone (E1) to E2and pregnenolone to P4. Overall, these results indicate that TGFB1 counteracts stimulation of E2and P4synthesis in granulosa cells by inhibiting key enzymes involved in the conversion of androgens to E2and cholesterol to P4without shutting down HSD17B reducing activity and HSD3B activity.

Evidence of a local negative role for cocaine and amphetamine regulated transcript (CART), inhibins and low molecular weight insulin like growth factor binding proteins in regulation of granulosa cell estradiol production during follicular waves in cattle

The ability of ovarian follicles to produce large amounts of estradiol is a hallmark of follicle health status. Estradiol producing capacity is lost in ovarian follicles before morphological signs of atresia. A prominent wave like pattern of growth of antral follicles is characteristic of monotocous species such as cattle, horses and humans. While our knowledge of the role of pituitary gonadotropins in support of antral follicle growth and development is well established, the intrinsic factors that suppress estradiol production and may help promote atresia during follicular waves are not well understood. Numerous growth factors and cytokines have been reported to suppress granulosa cell estradiol production in vitro, but the association of expression of many such factors in vivo with follicle health status and their physiological significance are not clear. The purpose of this review is to discuss the in vivo and in vitro evidence supporting a local physiological role for cocaine and amphetamine regulated transcript, inhibins and low molecular weight insulin like growth factor binding proteins in negative regulation of granulosa cell estradiol production, with emphasis on evidence from the bovine model system.

Follicular fluid concentration of transforming growth factor-beta1 is negatively correlated with estradiol and follicle size at the early stage of development of the first-wave cohort of bovine ovarian follicles

The objectives of this study were to characterize the relationship between estradiol and transforming growth factor-beta1(TGF-beta1) concentrations in follicular fluid of growing bovine ovarian follicles, and to examine the effect of TGF-beta1 on FSH-stimulated estradiol secretion in cultured bovine granulosa cells. Follicular fluid was collected from individual follicles >5 mm in diameter by ultrasound-guided transvaginal puncture (n = 12 heifers). Follicles were sampled at four different stages of development of the first post-ovulatory wave during selection of the single dominant follicle. Estradiol, progesterone and total TGF-beta1 were measured in follicular fluid of the three or four largest follicles sampled when the largest follicle (F1) had reached either 6.5, 7.5, 8.5 or 9.5+/-0.5 mm stage of development. There was a significant negative relationship between follicular fluid TGF-beta1 and estradiol concentrations (R2 = 0.44; p < 0.002), and between TGF-beta1 concentrations and follicle diameter (R2 = 0.23; p < 0.01) in cohort follicles at the 6.5 mm stage, but not at any later stage of development of the follicle wave. There was no correlation between progesterone and TGF-beta1 concentrations at any stage. To assess the causal relationship between TGF-beta1 and estradiol, granulosa cells from follicles measuring 2-5 mm at dissection were placed in serum-free culture. TGF-beta1 caused a dose-dependent decrease in FSH-stimulated estradiol secretion (P < 0.001). These findings suggest that TGF-beta1 has an inhibitory effect on estradiol secretion in FSH-stimulated follicles and that a reduction in TGF-beta1 inhibition may be part of the mechanism of selection of a single dominant follicle.

Evidence for autocrine or paracrine roles of alpha2-macroglobulin in regulation of estradiol production by granulosa cells and development of dominant follicles

alpha(2)-Macroglobulin (alpha(2)-M) inhibits proteinases and modulates the actions of growth factors and cytokines. Despite the key roles proteinases, growth factors, and cytokines have in folliculogenesis, the role of alpha(2)-M in follicular development is unknown. Our objectives were to: 1) determine whether granulosa cells produce alpha(2)-M and have alpha(2)-M receptors, 2) examine the effect of alpha(2)-M on estradiol production by granulosa cells, 3) establish whether amounts of alpha(2)-M and alpha(2)-M receptors were altered during dominant nonovulatory follicle development, and 4) examine alpha(2)-M's mechanism of action. The results demonstrated that bovine granulosa cells contain 5.2- and 15-kb mRNAs and 720- and 500-kDa proteins that correspond, respectively, to sizes of mRNAs and proteins for alpha(2)-M and the alpha(2)-M receptor. Treatment of granulosa cells with alpha(2)-M resulted in a specific dose-responsive increase in estradiol production. Cell viability, cell number, and the amount of aromatase in granulosa cells were not altered by alpha(2)-M. Treatment of granulosa cells with factors that bind alpha(2)-M or its receptor did not mimic alpha(2)-M action. Although intrafollicular amounts of alpha(2)-M remained unchanged, amounts of alpha(2)-M receptor in granulosa cells were strongly inversely associated with concentrations of estradiol in dominant and subordinate follicles. Based on these results, we concluded that alpha(2)-M may have autocrine or paracrine roles in granulosa cells potentially important for regulation of estradiol production and development of dominant follicles.

Activin and transforming growth factor-beta as local regulators of ovarian steroidogenesis in the goldfish

This study explores the hypothesis that activin and TGFbeta(1) serve as local regulators of ovarian function in the goldfish. Initial studies demonstrated the presence of TGFbeta in the ovary through the use RT-PCR, which amplified a 225 bp product from early vitellogenic (EVIT) and prematurational full-grown (PFG) follicles. This transcript showed high homology to TGFbeta in other teleosts. Both goldfish recombinant activin B and human recombinant TGFbeta(1) suppressed basal testosterone production by EVIT follicles incubated in vitro. Activin B also inhibited hCG-stimulated testosterone production by EVIT follicles. Our experiments suggest that activin B mediates these effects through actions at sites upstream of cholesterol formation and/or mobilization in the steroidogenic pathway, and through mechanisms that were independent of effects on cAMP formation. In experiments with PFG follicles, TGFbeta(1) decreased basal testosterone production. Activin B did not affect T production by PFG follicles, suggesting that this hormone has differential effects on steroidogenesis in the goldfish ovary depending on the stage of ovarian maturity. In other tests with PFG follicles, TGFbeta(1) and activin B, to a limited extent, inhibited the conversion of 17 alpha-OHP to the maturation-inducing hormone, 17 alpha,20 beta-dihydroxy-4-pregnen-3-one. In conclusion, this study shows that TGF is expressed in the goldfish ovary, and that both activin and TGFbeta affect steroid production, which provides evidence that these members of the TGFbeta superfamily may act as local regulators of ovarian function in a teleost.

Activin A and gonadotropin regulation of follicle-stimulating hormone and luteinizing hormone receptor messenger RNA in avian granulosa cells

Activin A regulation of the expression of mRNA for the LH receptor, FSH receptor, and the inhibin alpha subunit as well as the effect of activin A on the secretion of progesterone were investigated in chicken granulosa cell cultures. Granulosa layers were isolated from the F(1) and F(3) + F(4) follicles from five hens, pooled according to size, dispersed, and cultured for 48 h. In experiment 1 (n = 3 replications), granulosa cells were cultured with or without highly purified ovine (o) FSH at 50 ng/ml and in the presence of 0, 10, or 50 ng/ml of recombinant chicken activin A. Experiment 2 (n = 4 replications) followed the same protocol as experiment 1, except that oFSH was replaced with oLH. Results from these experiments showed that addition of activin A to the granulosa cell cultures had no effect on the expression of mRNA for the inhibin alpha subunit or the FSH receptor, but it did affect the expression of mRNA for the LH receptor. Treatment of F(3) + F(4) granulosa cells with LH stimulated the expression of mRNA for the LH receptor; however, when LH was combined with either dose of activin A, this induction was prevented. The highest dose of activin A with or without LH resulted in decreased expression of the LH receptor compared to the untreated controls in the F(3) + F(4) cell cultures. Progesterone secretion by the granulosa cells from both follicle sizes was not altered by activin A. In experiment 3 (n = 3 replications), the effect of activin A on the growth of granulosa cells was examined with the following treatments: 0, 10, or 50 ng/ml of activin A; 50 ng/ml of either oLH or oFSH; and oLH or oFSH combined with 10 ng/ml of activin A. The highest dose of activin reduced the rate of granulosa cell proliferation in both follicle types. Growth of F(1) and F(3) + F(4) granulosa cells was stimulated by the addition of either gonadotropin, and the presence of 10 ng/ml of activin A with either gonadotropin did not alter this proliferation, except for the LH-treated F(3) + F(4) granulosa cells, in which the increase in proliferation was prevented. The results suggest that activin A could act as a local factor that regulates follicular maturation by preventing excessive or untimely LH receptor expression.

Role of tumor necrosis factor in preovulatory follicles of swine

The effects of tumor necrosis factor (TNF) on cultured porcine granulosa cells that were obtained from preovulatory follicles were studied with regard to following parameters: 1) TNF receptor type I expression, 2) progesterone receptor and transforming growth factor beta receptor type II (TbetaR II) as markers of luteinization, 3) proliferation, and 4) apoptosis. For comparative purposes the effects of TNF were also studied on insulin/forskolin-treated cells, as this treatment is well established to induce luteinization. Cytochemical methods followed by semiquantitative analysis were used. Our data show that TNF treatment upregulates TNF receptor type I expression in granulosa cells. TNF downregulates the expression of TbetaR II of insulin/forskolin-stimulated and of unstimulated cells. The progesterone receptor is also downregulated by the cytokine after insulin/forskolin-induced luteinization. Supplementation of the medium with TNF leads to increased proliferation and at the same time it induces apoptosis. Our results indicate that TNF exerts an inhibitory influence on luteinization and that TNF influences the balance between follicular growth (proliferation) and atresia (apoptosis).

Angiogenesis and vascular regression in the ovary

Angiogenesis is prominent during development and downregulated in the adult. Strictly controlled angiogenesis in the healthy adult occurs cyclically in the ovary and corpus luteum, which therefore make an excellent model with which to study vascular growth. Dysfunctional or uncontrolled angiogenesis is involved in a number of diseases and is responsible for growth and dissemination of tumours. This review focuses on the following aspects of the ovary: the gross and microscopical anatomy of the blood vessels, described mainly--but not exclusively--in the bovine; vascularization of the follicle before and after ovulation; angiogenesis in the developing and the mature corpus luteum as well as in the corpus luteum of pregnancy. The potential mechanisms of vascular regression during luteolysis and the potential role of vascular growth in dominance and atresia of follicles will be described. Furthermore, recent research on ovarian angiogenic and potential anti-angiogenic factors including fibroblast growth factor (FGF), vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF), angiopoietin and metalloproteinase inhibitor will be presented. Finally, the role of hormones including FSH, LH, sexual steroids, prostaglandins, prolactin, oxytocin and activin/inhibin in ovarian angiogenesis will be summarized. Future research is likely to yield valuable information that can contribute to the development of novel therapeutic strategies for the treatment of diseases characterized by disregulated angiogenesis and vascular regression.