Joseph K. Folger

Variation in the Ovarian Reserve Is Linked to Alterations in Intrafollicular Estradiol Production and Ovarian Biomarkers of Follicular Differentiation and Oocyte Quality in Cattle

Abstract The mechanisms whereby the high variation in numbers of morphologically healthy oocytes and follicles in ovaries (ovarian reserve) may have an impact onovarian function, oocyte quality, and fertility are poorly understood. The objective was to determine whether previously validated biomarkers for follicular differentiation and function, as well as oocyte quality differed between cattle with low versus a high antral follicle count (AFC). Ovaries were removed (n = 5 per group) near the beginning of the nonovulatory follicular wave, before follicles could be identified via ultrasonography as being dominant, from heifers with high versus a low AFC. The F1, F2, and F3 follicles were dissected and diameters determined. Follicular fluid and thecal, granulosal, and cumulus cells and the oocyte were isolated and subjected to biomarker analyses. Although the size and numerous biomarkers of differentiation, such as mRNAs for the gonadotropin receptors, were similar, intrafollicular concentrations of estradiol and the abundance of mRNAs for CYP19A1 in granulosal cells and ESR1, ESR2, and CTSB in cumulus cells were greater, whereas mRNAs for AMH in granulosal cells and TBC1D1 in thecal cells were lower for animals with low versus a high AFC during follicle waves. Hence, variation in the ovarian reserve may have an impact on follicular function and oocyte quality via alterations in intrafollicular estradiol production and expression of key genes involved in follicle-stimulating hormone action (AMH) and estradiol (CYP19A1) production by granulosal cells, function and survival of thecal cells (TBC1D1), responsiveness of cumulus cells to estradiol (ESR1, ESR2), and cumulus cell determinants of oocyte quality (CTSB).

Evidence That High Variation in Ovarian Reserves of Healthy Young Adults Has a Negative Impact on the Corpus Luteum and Endometrium During Estrous Cycles in Cattle

Abstract Low progesterone concentrations and diminished ovarian reserves (total number of healthy oocytes) during reproductive cycles are linked to infertility in single-ovulating species like cattle. However, the extent and mechanisms whereby the inherently high variation in ovarian reserves may negatively affect progesterone production are unknown. Cattle were chosen to address these questions because the size of their ovarian reserves can be predicted based on an antral follicle count (AFC) during follicular waves. The present study determined if progesterone concentrations, differentiation and function of the corpus luteum (CL), and endometrial thickness differed during reproductive cycles of age-matched healthy young adult cattle with low versus high AFC during follicular waves. The results showed that, despite enhanced LH secretion, progesterone concentrations were lower during estrous cycles for animals with low versus high AFC. Animals with low versus high AFC also had a decreased basal, LH-, and 25-hydroxycholesterol-induced capacity of luteal and granulosal cells to produce progesterone, reduced amounts of STAR and mRNAs for STAR and LH receptor in the CL, and no change in endometrial thickness during estrous cycles. Taken together, these results 1) supported the conclusion that high variation in ovarian reserves of young adults is associated with alterations in differentiation and function of the CL and 2) provided insight into the potential factors that may cause suboptimal luteal function (e.g., heightened LH secretion and desensitization of the LH receptor, diminished LH responsiveness, diminished STAR, inherent deficiency in capacity of granulosal cells to undergo luteinization) and infertility (e.g., low progesterone, poor endometrial growth) in individuals with diminished ovarian reserves.

Regulation of Angiogenesis-Related Prostaglandin F2alpha-Induced Genes in the Bovine Corpus Luteum

ABSTRACT We recently compared prostaglandin F2alpha (PG)-induced global gene expression profiles in PG-refractory, bovine corpus luteum (CL) collected on Day 4 of the estrous cycle, versus PG-responsive, Day 11 CL. Transcriptome analyses led us to study the regulation of angiogenesis-related genes by PG and their functions in luteal endothelial cells (ECs). We found that PG regulated angiogenesis-modulating factors in a luteal stage-dependent way. A robust increase in FGF2 expression (mRNA and protein) occurred in the PG-refractory Day 4 CL promoting CL survival and function. Inhibitors of FGF2 action, thrombospondin 1 and 2, their receptor (CD36), and PTX3 were upregulated by PG specifically in Day 11 CL undergoing luteolysis. VEGF mRNA decreased 4 h post-PG in both Day 4 and Day 11 CL. The resulting destabilization of blood vessels in Day 11 CL is expected to weaken the gland and reduce its hormonal output. These genes were expressed in dispersed luteal ECs and steroidogenic cells; however, thrombospondin 1 and FGF2 were more abundant in luteal ECs. Expression of such genes and their ability to modulate FGF2 actions were investigated. Similar to its in vivo effect, PG, in vitro, stimulated the expression of thrombospondins and PTX3 genes in several luteal cell models. Importantly, these factors influenced the angiogenic properties of luteal ECs. FGF2 dose-dependently enhanced cell migration and proliferation, whereas thrombospondin 1 and PTX3 inhibited FGF2 actions in luteal ECs. Collectively, the data presented here suggest that, by tilting the balance between pro- and antiangiogenic factors, PG can potentially control the ability of the CL to resist or advance toward luteolysis.

Granulosa cells are refractory to FSH action in individuals with a low antral follicle count

The reason ovarian function and fertility are diminished in women with a low antral follicle count (AFC), despite significant numbers of follicles remaining in ovaries, is unknown. The bovine model is unique to address this question because cattle and women with a low AFC exhibit similar phenotypic characteristics including a diminished ovarian reserve, reduced circulating concentrations of anti-Müllerian hormone (AMH) but heightened FSH secretion during reproductive cycles. Because women and cattle with a low AFC respond minimally to gonadotropin stimulation during IVF cycles or superovulation, granulosa cells in individuals with a low AFC are hypothesised to be refractory to FSH. The present study evaluates this hypothesis by testing whether capacity of granulosa cells to respond to FSH differs between cattle with a low and a high AFC. Granulosa cells from cattle with a low (≤15 follicles ≥3 mm in diameter) or a high (≥25 follicles) AFC were cultured with different doses of FSH. Treatments were evaluated by measurement of oestradiol (E), progesterone (P) and AMH in media and abundance of mRNAs for aromatase (CYP19A1), AMH, FSH receptor (FSHR) and oxytocin (OXT). Progesterone and OXT mRNA are well-established markers of granulosa cell luteinisation. Although high doses of FSH induced granulosa cell luteinisation, basal and FSH-induced increases in E and AMH production and expression of mRNAs for CYP19A1, FSHR and AMH in granulosa cells were much lower, while P production and OXT mRNA expression were higher in non-luteinised and luteinised granulosa cells from the low than the high AFC group. Granulosa cells in cattle with a low AFC are refractory to FSH action, which could explain why ovarian function, responsiveness to gonadotropin stimulation and fertility are diminished in individuals with a low versus a high AFC.

Evidence that high variation in antral follicle count during follicular waves is linked to alterations in ovarian androgen production in cattle

Androgens have an important role in ovarian follicular growth and function, but circulating androgen concentrations are also associated with ovarian dysfunction, cardiovascular disease, and metabolic disorders in women. The extent and causes of the variation in androgen production in individuals, however, are unknown. Because thecal cells of follicles synthesize androstenedione and testosterone, variation in production of these androgens is hypothesized to be directly related to the inherently high variation in number of healthy growing follicles in ovaries of individuals. To test this hypothesis, we determined whether thecal CYP17A1 mRNA (codes for a cytochrome P450 enzyme involved in androgen synthesis), LH-induced thecal androstenedione production, androstenedione concentrations in follicular fluid, and circulating testosterone concentrations were lower in cattle with relatively low versus high number of follicles growing during follicular waves and whether ovariectomy reduced serum testosterone concentrations. Results demonstrated that cattle with a low follicle number had lower (P<0.05) abundance of CYP17A1 mRNA in thecal cells, reduced (P<0.01) capacity of thecal cells to produce androstenedione in response to LH, lower (P<0.01) androstenedione concentrations in ovulatory follicles, and lower (P<0.02) circulating testosterone concentrations during estrous cycles compared with animals with high follicle number. Also, serum testosterone in cattle with low or high follicle number was reduced by 63 and 70%, respectively, following ovariectomy. In conclusion, circulating androgen concentrations are lower in cattle with low versus high number of follicles growing during follicular waves, possibly because of a reduced responsiveness of thecal cells to LH.

Inherent capacity of the pituitary gland to produce gonadotropins is not influenced by the number of ovarian follicles >= 3 mm in diameter in cattle

We hypothesised that higher serum FSH concentrations in cattle with low v. high follicle numbers during follicular waves are caused by a different capacity of the pituitary gland to produce gonadotropins. Dairy cows with high (> or = 30; n = 5) and low (< or = 15; n = 5) follicle numbers were selected and serum concentrations of oestradiol and FSH during an oestrous cycle were measured. Cows were ovariectomised at oestrus and bled frequently up to 8 days after ovariectomy. After 33 days, cows were injected with gonadotropin-releasing hormone (GnRH) and bled intensively up to 8 h after GnRH injection. One day later, animals were injected with follicular fluid (FF) from bovine follicles and were bled intensively up to 2 days after the first injection. Serum concentrations of FSH and LH were measured. After 2 days, cows were killed and their pituitary glands collected. Prior to ovariectomy, serum oestradiol concentrations were similar between groups, whereas FSH concentrations were higher in cattle with low v. high numbers of follicles. No differences were detected in serum gonadotropin concentrations after ovariectomy, GnRH injection or FF challenge between groups. The results indicate that the inherent capacity of the pituitary gland to secrete gonadotropins does not differ between cattle with high v. low numbers of follicles during follicular waves.

Evidence Supporting a Role for Cocaine- and Amphetamine-Regulated Transcript (CARTPT) in Control of Granulosa Cell Estradiol Production Associated with Dominant Follicle Selection in Cattle

We demonstrated previously a negative association of granulosa cell cocaine- and amphetamine-regulated transcript (CARTPT) expression with follicle health status and inhibitory effects of the mature CARTPT peptide (CART) on follicle-stimulating hormone (FSH) signal transduction in vitro, resulting in reduced bovine granulosa cell CYP19A1 mRNA and estradiol production. The objectives of this study were to investigate temporal regulation of granulosa cell CARTPT expression (granulosa cell mRNA and follicular fluid CART peptide concentrations) during follicular waves, CART regulation of androstenedione production (precursor for estradiol biosynthesis) by thecal tissue collected at specific stages of a follicular wave, FSH regulation of granulosa cell CARTPT mRNA expression, and the ability of CART to inhibit granulosa cell estradiol production and CYP19A1 mRNA expression when administered in vivo. CART concentrations in healthy, estrogen-active follicles (estradiol greater than progesterone in follicular fluid) decreased after dominant follicle selection, and CARTPT mRNA was lower in healthy, estrogen-active versus estrogen-inactive atretic follicles (progesterone greater than estradiol) collected at the predeviation and early dominance stages. CART treatment reduced luteinizing hormone-induced androstenedione production by thecal tissue collected at predeviation and early dominance stages but not at later stages of a follicular wave. The FSH or insulin-like growth factor 1 treatment in vitro reduced granulosa cell CARTPT mRNA in a dose-dependent fashion. Administration of CART in vivo into follicles at the early dominance stage reduced follicular fluid estradiol concentrations and granulosa cell CYP19A1 mRNA. Collectively, results support a potential stage-specific regulatory role for CART in negative regulation of estradiol production associated with selection of the dominant follicle.

Evidence Supporting a Role for SMAD2/3 in Bovine Early Embryonic Development: Potential Implications for Embryotropic Actions of Follistatin

ABSTRACT The TGF-beta-SMAD signaling pathway is involved in regulation of various aspects of female reproduction. However, the intrinsic functional role of SMADs in early embryogenesis remains poorly understood. Previously, we demonstrated that treatment with follistatin, an activin (TGF-beta superfamily ligand)-binding protein, is beneficial for bovine early embryogenesis and specific embryotropic actions of follistatin are dependent on SMAD4. Because SMAD4 is a common SMAD that can bind both SMAD2/3 and SMAD1/5, the objective of this study was to further determine the intrinsic role of SMAD2/3 in the control of early embryogenesis and delineate if embryotropic actions of follistatin in early embryos are SMAD2/3 dependent. By using a combination of pharmacological and small interfering RNA-mediated inhibition of SMAD2/3 signaling in the presence or absence of follistatin treatment, our results indicate that SMAD2 and SMAD3 are both required for bovine early embryonic development and stimulatory actions of follistatin on 8- to 16-cell and that blastocyst rates, but not early cleavage, are muted when SMAD2/3 signaling is inhibited. SMAD2 deficiency also results in reduced expression of the bovine trophectoderm cell-specific gene CTGF. In conclusion, the present work provides evidence supporting a functional role of SMAD2/3 in bovine early embryogenesis and that specific stimulatory actions of follistatin are not observed in the absence of SMAD2/3 signaling.

Evidence Supporting a Functional Requirement of SMAD4 for Bovine Preimplantation Embryonic Development: A Potential Link to Embryotrophic Actions of Follistatin

ABSTRACT Transforming growth factor beta (TGFbeta) superfamily signaling controls various aspects of female fertility. However, the functional roles of the TGFbeta-superfamily cognate signal transduction pathway components (e.g., SMAD2/3, SMAD4, SMAD1/5/8) in early embryonic development are not completely understood. We have previously demonstrated pronounced embryotrophic actions of the TGFbeta superfamily member-binding protein, follistatin, on oocyte competence in cattle. Given that SMAD4 is a common SMAD required for both SMAD2/3- and SMAD1/5/8-signaling pathways, the objectives of the present studies were to determine the temporal expression and functional role of SMAD4 in bovine early embryogenesis and whether embryotrophic actions of follistatin are SMAD4 dependent. SMAD4 mRNA is increased in bovine oocytes during meiotic maturation, is maximal in 2-cell stage embryos, remains elevated through the 8-cell stage, and is decreased and remains low through the blastocyst stage. Ablation of SMAD4 via small interfering RNA microinjection of zygotes reduced proportions of embryos cleaving early and development to the 8- to 16-cell and blastocyst stages. Stimulatory effects of follistatin on early cleavage, but not on development to 8- to 16-cell and blastocyst stages, were observed in SMAD4-depleted embryos. Therefore, results suggest SMAD4 is obligatory for early embryonic development in cattle, and embryotrophic actions of follistatin on development to 8- to 16-cell and blastocyst stages are SMAD4 dependent.

Expression of TGFβ superfamily components and other markers of oocyte quality in oocytes selected by brilliant cresyl blue staining: relevance to early embryonic development.

Brilliant cresyl blue (BCB) is a super‐vital stain that has been used to select competent oocytes in different species. One objective of the present study was to assess the relationship between BCB staining, which correlates with an oocytes developmental potential, and the transcript abundance for select TGFβ‐superfamily components, SMAD2/3 and SMAD1/5 phosphorylation levels, and oocyte (JY1) and cumulus‐cell (CTSB, CTSK, CTSS, and CTSZ) transcript markers in bovine oocytes and/or adjacent cumulus cells. The capacity of exogenous follistatin or JY1 supplementation or cathepsin inhibitor treatment to enhance development of embryos derived from low‐quality oocytes, based on BCB staining, was also determined. Cumulus‐oocyte complexes (COCs) from abattoir‐derived ovaries were subjected to BCB staining, and germinal‐vesicle‐stage oocytes and cumulus cells were harvested from control, BCB+, and BCB− (low‐quality oocyte) groups for real‐time PCR or Western‐blot analysis. Remaining COCs underwent in vitro maturation, in vitro fertilization, and embryo culture in the presence or absence of the above exogenous supplements. Levels of FST, JY1, BMP15, and SMAD1, 2, 3, and 5 transcripts were higher in BCB+ oocytes whereas CTSB, CTSK, CTSS, and CTSZ mRNA abundance was higher in cumulus cells surrounding BCB− oocytes. Western‐blot analysis revealed higher SMAD1/5 and SMAD2/3 phosphorylation in BCB+ than BCB− oocytes. Embryo‐culture studies demonstrated that follistatin and cathepsin inhibitor treatment, but not JY‐1 treatment, improve the developmental competence of BCB− oocytes. These results contribute to a better understanding of molecular indices of oocyte competence. Mol. Reprod. Dev. 82: 251–264, 2015.