Mechanism underlying the stimulation by IGF-1 of LHCGR expression in porcine granulosa cells

Roles of GDF9 and BMP15 in equine follicular development: in vivo content and in vitro effects of IGF1 and cortisol on granulosa cells

BACKGROUND

In horses, the mechanisms behind ovarian follicle growth and oocyte maturation remain largely unknown. In other species, oocyte-secreted factors growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) have been related to the acquisition of developmental competence and to interaction with granulosa cells for the regulation of follicle development. This study assessed the expression and localization of GDF9 in the equine ovary, and its possible relationship with granulosa cell function.

RESULTS

Using custom-made antibodies, GDF9 protein was localized in oocytes from the primary follicle stage onwards. Together with BMP15, its intrafollicular concentration was higher in small antral follicles compared to larger ones (P < 0.05). Negative correlations were observed between intrafollicular BMP15 concentration and estradiol sulfate (E2S) (r = -0.36, P = 0.048), as well as between BMP15 and E2S/P4 ratio (r = -0.37, P = 0.046). In vivo, equine granulosa cells showed increasing mRNA expression of genes involved in steroidogenesis (STAR and HSD3B2) and cell proliferation (KI67) with increasing follicle size, while expression of GDF9 and of apoptosis-related genes (BCL2 and CASP3) were not affected by follicle size. Simultaneous stimulation of granulosa cells in vitro with IGF1 and cortisol significantly increased HSD3B2 and CYP19A1 transcriptional levels, as well as E2 concentration in culture media, while IGF1-induced P4 secretion was suppressed in the presence of cortisol. Blocking the stimulatory effect of IGF1 on E2, E2S and P4 by H89 was associated with increased GDF9 mRNA levels and reduced STAR, PCNA, KI67 and BCL2 mRNA expression. Significant negative correlations of GDF9 with STAR and PCNA mRNA, respectively, were seen in vivo and in vitro.

CONCLUSIONS

Together, our results show GDF9 localization and expression in the equine ovary and a temporal relationship with steroidogenesis and cell proliferation within the surrounding granulosa cells. Moreover, results of the in vitro study suggest a supporting role of cortisol during follicle maturation. Our study sheds light on possible mechanisms for the regulation of ovarian function in horses using GDF9.

Acute heat stress regulates estradiol synthesis in ovine ovarian granulosa cells through the SREBPs/MVK-LHR pathway

The adverse effects of heat stress on reproductive performance of sheep are becoming increasingly severe. Previous research has revealed that heat stress decreases both cholesterol and estradiol content; however, regulation of estradiol by cholesterol and its regulatory mechanism under heat stress are unclear. Mevalonate kinase (MVK), a key cholesterol synthesis pathway enzyme, binds to the luteinizing hormone receptor (LHR; a key gene regulating hormone synthesis) mRNA. In this study, ovine ovarian granulosa cells (GCs) were used in an in vitro model. To elucidate the underlying molecular mechanism, immunofluorescence, quantitative reverse transcription polymerase chain reaction, western blotting, enzyme-linked immunosorbent assay, and an RNA electrophoretic mobility shift assay (REMSA) were used to investigate whether the decrease in cholesterol caused by acute heat stress resulted in a decrease in estradiol synthesis. Acute heat stress reduced the cholesterol content in ovine ovarian GCs, which transactivated the cholesterol synthesis pathway corresponding to the gene expression of sterol regulatory element-binding protein (SREBP-1A), SREBP-2, and MVK. Upregulated MVK increased the MVK-LHR mRNA complex, which caused LHR mRNA decay and downregulation, further leading to the downregulation of CYP19A1 and a decrease in estradiol. The cholesterol synthesis inhibitor, PF-429242, alleviated the decrease in estradiol synthesis caused by acute heat stress. Overall, acute heat stress caused a decrease in total cholesterol, which transactivated the expression of cholesterol synthesis genes, such as SREBP-1A, SREBP2, and MVK, increasing the MVK-LHR complex, downregulating LHR expression, and further decreasing estradiol.

Epigenetic modifications of gonadotropin receptors can regulate follicular development

The spatiotemporal transcription of follicle-stimulating hormone receptor (FSHR) and luteinizing hormone/human chorionic gonadotropin receptor (LHCGR) are crucial events for follicular development. However, their regulatory mechanisms are unclear. DNA methylation and histone acetylation are the main epigenetic modifications, and play important roles in transcriptional expression, which regulate cell responses including cell proliferation, senescence and apoptosis. This review will discuss the dynamic epigenetic modifications of FSHR and LHCGR that occur during the process of follicular development and their response to gonadotropins. In addition, some alteration patterns that occur during these epigenetic modifications, as well as their retrospect retrotransposons, which regulate the gene expression levels of FSHR and LHCGR will be discussed.

Multiomics Analyses Provide New Insight into Genetic Variation of Reproductive Adaptability in Tibetan Sheep

Domestication and artificial selection during production-oriented breeding have greatly shaped the level of genomic variability in sheep. However, the genetic variation associated with increased reproduction remains elusive. Here, two groups of samples from consecutively monotocous and polytocous sheep were collected for genome-wide association, transcriptomic, proteomic, and metabolomic analyses to explore the genetic variation in fecundity in Tibetan sheep. Genome-wide association study revealed strong associations between BMPR1B (p.Q249R) and litter size, as well as between PAPPA and lambing interval; these findings were validated in 1,130 individuals. Furthermore, we constructed the first single-cell atlas of Tibetan sheep ovary tissues and identified a specific mural granulosa cell subtype with PAPPA-specific expression and differential expression of BMPR1B between the two groups. Bulk RNA-seq indicated that BMPR1B and PAPPA expressions were similar between the two groups of sheep. 3D protein structure prediction and coimmunoprecipitation analysis indicated that mutation and mutually exclusive exons of BMPR1B are the main mechanisms for prolific Tibetan sheep. We propose that PAPPA is a key gene for stimulating ovarian follicular growth and development, and steroidogenesis. Our work reveals the genetic variation in reproductive performance in Tibetan sheep, providing insights and valuable genetic resources for the discovery of genes and regulatory mechanisms that improve reproductive success.

Effects of flaxseed oil supplementation on metaphase II oocyte rates in IVF cycles with decreased ovarian reserve: a randomized controlled trial

Background

This study was designed to explore the effects of flaxseed oil on the metaphase II (MII) oocyte rates in women with decreased ovarian reserve (DOR).

Methods

The women with DOR were divided into a study group (n = 108, flaxseed oil treatment) and a control group (n = 110, no treatment). All patients were treated with assisted reproductive technology (ART). Subsequently, the ART stimulation cycle parameters, embryo transfer (ET) results, and clinical reproductive outcomes were recorded. The influencing factors affecting the MII oocyte rate were analyzed using univariate analysis and multivariate analysis.

Results

Flaxseed oil reduced the recombinant human follicle-stimulating hormone (r-hFSH) dosage and stimulation time and increased the peak estradiol (E2) concentration in DOR women during ART treatment. The MII oocyte rate, fertilization rate, cleavage rate, high-quality embryo rate, and blastocyst formation rate were increased after flaxseed oil intervention. The embryo implantation rate of the study group was higher than that of the control group (p = 0.05). Additionally, the female age [odds ratio (OR): 0.609, 95% confidence interval (CI): 0.52-0.72, p < 0.01] was the hindering factor of MII oocyte rate, while anti-Müllerian hormone (AMH; OR: 100, 95% CI: 20.31-495, p < 0.01), peak E2 concentration (OR: 1.00, 95% CI: 1.00-1.00, p = 0.01), and the intake of flaxseed oil (OR: 2.51, 95% CI: 1.06-5.93, p = 0.04) were the promoting factors for MII oocyte rate.

Conclusion

Flaxseed oil improved ovarian response and the quality of oocytes and embryos, thereby increasing the fertilization rate and high-quality embryo rate in DOR patients. The use of flaxseed oil was positively correlated with MII oocyte rate in women with DOR.

Clinical trial number

https://www.chictr.org.cn/, identifier ChiCTR2300073785.

Insulin-like growth factor (IGF) performance in ovarian function and applications in reproductive biotechnologies

The role of the insulin-like growth factor (IGF) system has attracted close attention. The activity of IGF binding proteins (IGFBPs) within the ovary has not been fully elucidated to date. These proteins bind to IGF with an equal, or greater, affinity than to the IGF1 receptor, thus being in the main position to regulate IGF signalling, in addition to extending the half-life of IGFs within the bloodstream and promoting IGF storage in specific tissue niches. IGF1 has an important part in cell proliferation, differentiation and apoptosis. Considering the importance of IGFs in oocyte maturation, this review sought to elucidate aspects including: IGF production mechanisms; constituent members of their family and their respective functions; the role that these factors play during folliculogenesis, together with their functions during oocyte maturation and apoptosis, and their performance during luteal development. This review also explores the role of IGFs in biotechnological applications, focusing specifically on animal genetic gain.

In missed abortion the decrease of IGF-1 down-regulates PI3K/AKT signaling pathway reducing the secretion of progesterone and β-hCG

OBJECTIVE

To explore whether the reduction of IGF-1 in missed abortion down-regulates PI3K/AKT signaling pathway, thereby causing trophoblast cell apoptosis and reducing the secretion of β-hCG and progesterone.

DESIGN

12 pairs of serum and villous tissues were selected from missed abortion patients and normal early pregnant women who had terminated pregnancy by artificial abortion. The subjects in two groups had same age and gestational week. Wes Simple Western system and qRT-PCR were used to detect the expression of IGF-1, IGF-1R, PI3K/AKT signaling pathway and apoptosis-related factors in villous tissues. Radioimmunoassay and Enzyme-linked immunosorbent assay were used to detect β-hCG, progesterone and IGF-1 in serum.

RESULTS

The serum levels of β-hCG, progesterone and IGF-1 were decreased in missed abortion group than those in normal early pregnant women. In addition, compared with normal early pregnant women, the genes and proteins levels of IGF-1 and PI3K/AKT signaling pathway and anti-apoptosis related factors were significantly decreased.

CONCLUSIONS

Our results suggested that the reduction of IGF-1 in missed abortion patients could down-regulate the expression of PI3K/AKT signaling pathway, thereby increasing the apoptosis of trophoblast cells, leading to decreased secretion of β-hCG and progesterone, which may be one of the important mechanisms of missed abortion.

Chronic superphysiologic AMH promotes premature luteinization of antral follicles in human ovarian xenografts

Anti-Müllerian hormone (AMH) is produced by growing ovarian follicles and provides a diagnostic measure of reproductive reserve in women; however, the impact of AMH on folliculogenesis is poorly understood. We cotransplanted human ovarian cortex with control or AMH-expressing endothelial cells in immunocompromised mice and recovered antral follicles for purification and downstream single-cell RNA sequencing of granulosa and theca/stroma cell fractions. A total of 38 antral follicles were observed (19 control and 19 AMH) at long-term intervals (>10 weeks). In the context of exogenous AMH, follicles exhibited a decreased ratio of primordial to growing follicles and antral follicles of increased diameter. Transcriptomic analysis and immunolabeling revealed a marked increase in factors typically noted at more advanced stages of follicle maturation, with granulosa and theca/stroma cells also displaying molecular hallmarks of luteinization. These results suggest that superphysiologic AMH alone may contribute to ovulatory dysfunction by accelerating maturation and/or luteinization of antral-stage follicles.