RNA N6-methyladenosine modification in female reproductive biology and pathophysiology

METTL14 mediates nerve growth factor-stimulated testosterone synthesis in porcine theca cells†

Ovarian theca cells produce testosterone, which acts as a vital precursor substance for synthesizing estrogens during follicular development. Nerve growth factor (NGF) has been shown to participate in reproductive physiology, specifically to follicular development and ovulation. There is currently no available data on the impact of NGF on testosterone synthesis in porcine theca cells. Furthermore, m6A modification is the most common internal modification in eukaryotic mRNAs that are closely associated with female gametogenesis, follicle development, ovulation, and other related processes. It is also uncertain whether the three main enzymes associated with m6A, such as Writers, Erasers, and Readers, play a role in this process. The present study, with an in vitro culture model, investigated the effect of NGF on testosterone synthesis in porcine theca cells and the role of Writers-METTL14 in this process. It was found that NGF activates the PI3K/AKT signaling pathway through METTL14, which regulates testosterone synthesis in porcine theca cells. This study will help to further elucidate the mechanisms by which NGF regulates follicular development and provide new therapeutic targets for ovary-related diseases in female animals. Summary Sentence  The present study investigated the effect of NGF on testosterone synthesis in porcine theca cells. It was found that NGF activates the PI3K/AKT signaling pathway through METTL14, which regulates testosterone synthesis in porcine theca cells.

The role of epigenetics in women's reproductive health: the impact of environmental factors

This paper explores the significant role of epigenetics in women's reproductive health, focusing on the impact of environmental factors. It highlights the crucial link between epigenetic modifications-such as DNA methylation and histones post-translational modifications-and reproductive health issues, including infertility and pregnancy complications. The paper reviews the influence of pollutants like PM2.5, heavy metals, and endocrine disruptors on gene expression through epigenetic mechanisms, emphasizing the need for understanding how dietary, lifestyle choices, and exposure to chemicals affect gene expression and reproductive health. Future research directions include deeper investigation into epigenetics in female reproductive health and leveraging gene editing to mitigate epigenetic changes for improving IVF success rates and managing reproductive disorders.

METTL3 deficiency leads to ovarian insufficiency due to IL-1β overexpression in theca cells

Premature ovarian insufficiency (POI) is a clinical syndrome characterised by a decline in ovarian function in women before 40 years of age and is associated with oestradiol deficiency and a complex pathogenesis. However, the aetiology of POI is still unclear and effective preventative and treatment strategies are still lacking. Methyltransferase like 3 (METTL3) is an RNA methyltransferase that is involved in spermatogenesis, oocyte development and maturation, early embryonic development, and embryonic stem cell differentiation and formation, but its role in POI is unknown. In the present study, METTL3 deficiency in follicular theca cells was found to lead to reduced fertility in female mice, with a POI-like phenotype, and METTL3 knockout promoted ovarian inflammation. Further, a reduction in METTL3 in follicular theca cells led to a decrease in the m6A modification of pri-miR-21, which further reduced pri-miR-21 recognition and binding by DGCR8 proteins, leading to a decrease in the synthesis of mature miR-21-5p. Decrease of miR-21-5p promoted the secretion of interleukin-1β (IL-1β) from follicular theca cells. Acting in a paracrine manner, IL-1β inhibited the cAMP-PKA pathway and activated the NF-κB pathway in follicular granulosa cells. This activation increased the levels of reactive oxygen species in granulosa cells, causing disturbances in the intracellular Ca2+ balance and mitochondrial damage. These cellular events ultimately led to granulosa cell apoptosis and a decrease in oestradiol synthesis, resulting in POI development. Collectively, these findings reveal how METTL3 deficiency promotes the expression and secretion of IL-1β in theca cells, which regulates ovarian functions, and proposes a new theory for the development of POI disease.

The reduction of the m6A methyltransferase METTL3 in granulosa cells is related to the follicular cysts in pigs

Follicular cysts are a common reproductive disorder in domestic animals that cause considerable economic losses to the farming industry. Effective prevention and treatment methods are lacking because neither the pathogenesis nor formation mechanisms of follicular cysts are well-understood. In this study, we first investigated the granulosa cells (GCs) of cystic follicles isolated from pigs. We observed a significant reduction in the expression of methyltransferase-like 3 (METTL3). Subsequent experiments revealed that METTL3 downregulation in GCs caused a decrease in m6A modification of pri-miR-21. This reduction further inhibited DGCR8 recognition and binding to pri-miR-21, dampening the synthesis of mature miR-21-5p. Additionally, the decrease in miR-21-5p promotes IL-1β expression in GCs. Elevated IL-1β activates the NFκB pathway, in turn upregulating apoptotic genes TNFa and BAX/BCL2. The subsequent apoptosis of GCs and inhibition of autophagy causes downregulation of CYP19A1 expression. These processes lower oestrogen secretion and contribute to follicular cyst formation. In conclusion, our findings provide a foundation for understanding and further exploring the mechanisms of follicular-cyst development in farm animals. This work has important implications for treating ovarian disorders in livestock and could potentially be extended to humans.

The Heterogeneity of Post-Menopausal Disease Risk: Could the Basis for Why Only Subsets of Females Are Affected Be Due to a Reversible Epigenetic Modification System Associated with Puberty, Menstrual Cycles, Pregnancy and Lactation, and, Ultimately, Menopause?

For much of human evolution, the average lifespan was <40 years, due in part to disease, infant mortality, predators, food insecurity, and, for females, complications of childbirth. Thus, for much of evolution, many females did not reach the age of menopause (45-50 years of age) and it is mainly in the past several hundred years that the lifespan has been extended to >75 years, primarily due to public health advances, medical interventions, antibiotics, and nutrition. Therefore, the underlying biological mechanisms responsible for disease risk following menopause must have evolved during the complex processes leading to Homo sapiens to serve functions in the pre-menopausal state. Furthermore, as a primary function for the survival of the species is effective reproduction, it is likely that most of the advantages of having such post-menopausal risks relate to reproduction and the ability to address environmental stresses. This opinion/perspective will be discussed in the context of how such post-menopausal risks could enhance reproduction, with improved survival of offspring, and perhaps why such risks are preserved. Not all post-menopausal females exhibit risk for this set of diseases, and those who do develop such diseases do not have all of the conditions. The diseases of the post-menopausal state do not operate as a unified complex, but as independent variables, with the potential for some overlap. The how and why there would be such heterogeneity if the risk factors serve essential functions during the reproductive years is also discussed and the concept of sets of reversible epigenetic changes associated with puberty, pregnancy, and lactation is offered to explain the observations regarding the distribution of post-menopausal conditions and their potential roles in reproduction. While the involvement of an epigenetic system with a dynamic "modification-demodification-remodification" paradigm contributing to disease risk is a hypothesis at this point, validation of it could lead to a better understanding of post-menopausal disease risk in the context of reproduction with commonalities may also lead to future improved interventions to control such risk after menopause.

A review on the role of RNA methylation in aging-related diseases

Senescence is the underlying mechanism of organism aging and is robustly regulated at the post-transcriptional level. This regulation involves the chemical modifications, of which the RNA methylation is the most common. Recently, a rapidly growing number of studies have demonstrated that methylation is relevant to aging and aging-associated diseases. Owing to the rapid development of detection methods, the understanding on RNA methylation has gone deeper. In this review, we summarize the current understanding on the influence of RNA modification on cellular senescence, with a focus on mRNA methylation in aging-related diseases, and discuss the emerging potential of RNA modification in diagnosis and therapy.

Transcriptome-wide m6A methylation profiling of Wuhua yellow-feathered chicken ovary revealed regulatory pathways underlying sexual maturation and low egg-laying performance

RNA N6-melthyladenosine (m6A) can play an important role in regulation of various biological processes. Chicken ovary development is closely related to egg laying performance, which is a process primarily controlled by complex gene regulations. In this study, transcriptome-wide m6A methylation of the Wuhua yellow-feathered chicken ovaries before and after sexual maturation was profiled to identify the potential molecular mechanisms underlying chicken ovary development. The results indicated that m6A levels of mRNAs were altered dramatically during sexual maturity. A total of 1,476 differential m6A peaks were found between these two stages with 662 significantly upregulated methylation peaks and 814 downregulated methylation peaks after sexual maturation. A positive correlation was observed between the m6A peaks and gene expression levels, indicating that m6A may play an important role in regulation of chicken ovary development. Functional enrichment analysis indicated that apoptosis related pathways could be the key molecular regulatory pathway underlying the poor reproductive performance of Wuhua yellow-feathered chicken. Overall, the various pathways and corresponding candidate genes identified here could be useful to facilitate molecular design breeding for improving egg production performance in Chinese local chicken breed, and it might also contribute to the genetic resource protection of valuable avian species.

The bidirectional interplay between ncRNAs and methylation modifications in gastrointestinal tumors

The aberrant expression of methylation and ncRNAs, two crucial regulators of epigenetic modifications, has been widely demonstrated in cancer. The complex interplay between them is essential in promoting malignant phenotype, poor prognosis, and drug resistance in GI tumors (including esophageal, gastric, colorectal, liver, and pancreatic cancers). Therefore, we summarize the interrelation process between ncRNAs and methylation modifications in GI tumors, including the detailed mechanism of methylation enzyme regulation of ncRNAs, the molecular mechanism of ncRNAs regulation of methylation modifications, and the correlation between the interactions between ncRNAs and methylation modifications and clinical features of tumors. Finally, we discuss the potential value of ncRNAs and methylation modifications in clinical diagnosis and therapy.

Short-chain fatty acid-butyric acid ameliorates granulosa cells inflammation through regulating METTL3-mediated N6-methyladenosine modification of FOSL2 in polycystic ovarian syndrome

Polycystic ovary syndrome (PCOS) is an endocrine and metabolic disorder characterized by chronic low-grade inflammation. Previous studies have demonstrated that the gut microbiome can affect the host tissue cells' mRNA N6-methyladenosine (m6A) modifications. This study aimed to understand the role of intestinal flora in ovarian cells inflammation by regulating mRNA m6A modification particularly the inflammatory state in PCOS. The gut microbiome composition of PCOS and Control groups was analyzed by 16S rRNA sequencing, and the short chain fatty acids were detected in patients' serum by mass spectrometry methods. The level of butyric acid was found to be decreased in the serum of the obese PCOS group (FAT) compared to other groups, and this was correlated with increased Streptococcaceae and decreased Rikenellaceae based on the Spearman's rank test. Additionally, we identified FOSL2 as a potential METTL3 target using RNA-seq and MeRIP-seq methodologies. Cellular experiments demonstrated that the addition of butyric acid led to a decrease in FOSL2 m6A methylation levels and mRNA expression by suppressing the expression of METTL3, an m6A methyltransferase. Additionally, NLRP3 protein expression and the expression of inflammatory cytokines (IL-6 and TNF-α) were downregulated in KGN cells. Butyric acid supplementation in obese PCOS mice improved ovarian function and decreased the expression of local inflammatory factors in the ovary. Taken together, the correlation between the gut microbiome and PCOS may unveil crucial mechanisms for the role of specific gut microbiota in the pathogenesis of PCOS. Furthermore, butyric acid may present new prospects for future PCOS treatments.