Role of RNA N6-Methyladenosine Modification in Male Infertility and Genital System Tumors

The epigenetic approach of varicocele: a focus on sperm DNA and m6A-RNA methylation

BACKGROUND

Varicocele is an abnormal dilation and torsion of the pampiniform venous plexus in the scrotum due to venous reflux, primarily affecting the left side. It affects 15% of men and is a prevalent contributor to male infertility. Varicocele is a complex disorder influenced by genetic, epigenetic, and environmental factors. Epigenetic modifications, which regulate genome activity independently of DNA or RNA sequences, may contribute to the development and severity of varicocele. These include DNA methylation, histone modifications, and RNA modifications like N6-methyladenosine (m6A). Irregularities in DNA and m6A-RNA methylation during spermatogenesis can cause gene expression abnormalities, DNA damage, and decreased fertility in varicocele patients.

OBJECTIVE AND RATIONALE

The review aims to comprehensively understand the underlying mechanisms of varicocele, a condition that can significantly impact male fertility. By exploring the role of methylation modifications, specifically DNA and m6A-RNA methylation, the review aims to synthesize evidence from basic, preclinical, and clinical research to expand the existing knowledge on this subject. The ultimate goal is to identify potential avenues for developing targeted treatments that can effectively improve varicocele and ultimately increase sperm quality in affected individuals.

SEARCH METHODS

A thorough investigation of the scientific literature was conducted through searches in PubMed, Google Scholar, and Science Direct databases until May 2024. All studies investigating the relationship between DNA and m6A-RNA methylation and male infertility, particularly varicocele were reviewed, and the most pertinent reports were included. Keywords such as varicocele, epigenetics, DNA methylation, m6A-RNA methylation, hypermethylation, hypomethylation, spermatozoa, semen parameters, spermatogenesis, and male infertility were used during the literature search, either individually or in combination.

OUTCOMES

The sperm has a specialized morphology essential for successful fertilization, and its epigenome is unique, potentially playing a key role in embryogenesis. Sperm DNA and RNA methylation, major epigenetic marks, regulate the expression of testicular genes crucial for normal spermatogenesis. This review explores the role of DNA and m6A-RNA methylation, in responding to oxidative stress and how various nutrients influence their function in varicocele condition. Evidence suggests a potential link between varicocele and aberrant DNA/m6A-RNA methylation patterns, especially hypomethylation, but the body of evidence is still limited. Further studies are needed to understand how abnormal expression of DNA/m6A-RNA methylation regulators affects testicular gene expression. Thus, analyzing sperm DNA 5mC/5hmC levels and m6A-RNA methylation regulators may reveal spermatogenesis defects and predict reproductive outcomes.

WIDER IMPLICATIONS

Nutri-epigenomics is an emerging field that could enhance the knowledge and management of diseases with unpredictable risks and consequences, even among individuals with similar lifestyles, by elucidating the influence of nutrition on DNA/m6A-RNA methylation through one-carbon metabolism. However, the importance of one-carbon metabolism to varicocele is not well-recognized. Health status and diet influence one-carbon metabolism and its associated DNA/m6A-RNA methylation modification. Future research should identify optimal methylation patterns that promote health and investigate modulating one-carbon metabolism to achieve this. Furthermore, additional studies are necessary to develop personalized dietary strategies through clinical and longitudinal research. However, a research gap exists on dietary interventions utilizing epigenetics as a therapeutic method for treating varicocele.

REGISTRATION NUMBER

Not applicable.

Alterations Expression of Key RNA Methylation (m6A) Enzymes in Testicular Tissue of Rats with Induced Varicocele

Epigenetics impacts male fertility and reproductive disorders. RNA modifications, like m6A, influence RNA metabolism. Varicocele contributes to male infertility, and oxidative stress affects sperm function. This study investigates the expression of key RNA modification enzymes in a rat varicocele model, aiming to elucidate the relationship between varicocele, oxidative stress, and fertility. Fifteen male Wistar rats were divided into Control, Sham, and Varicocele induction groups. Varicocele was induced in the rats surgically. After 8 weeks, testicular tissues and sperm were collected for analysis, including histopathological assessment and evaluation of sperm parameters, functional tests, and gene expression of key RNA modification enzymes: METTL3 as a writer, ALKBH5 and FTO as erasers, and YTHDF2 as a reader involved in recognizing m6A-modified RNA using qRT-PCR. One-way ANOVA with post-hoc Tukey HSD was used for comparing tests within groups. Varicocele induction resulted in histological changes in testicular tissues, including irregularly variable-sized seminiferous tubules. Sperm parameters were significantly affected, with lower concentration, motility, and higher percentage of abnormal sperm in the varicocele group. Increased levels of oxidative stress markers (Sperm lipid peroxidation, and intracytoplasmic ROS) and sperm DNA damage were observed, indicating the presence of oxidative stress in varicocele. Moreover, the expression of key enzymes involved in RNA metabolism was downregulated in the varicocele group. These findings highlight the detrimental impact of varicocele on testicular health, sperm quality, and gene expression, providing insights into the underlying mechanisms of male infertility associated with varicocele.

Shenqi Qiangjing Granules Ameliorate Asthenozoospermia in Mice by Regulating Ferroptosis through the METTL3/GPX4 Signaling Axis

Asthenozoospermia is a leading cause of male infertility, yet current pharmacotherapies yield suboptimal outcomes, underscoring the urgent need for novel treatment modalities. Herein, we induced asthenozoospermic mouse models using busulfan and investigated the therapeutic effects of Shenqi Qiangjing Granules (SQ) on testicular pathology, serum sex hormone and steroidogenic enzyme levels, and ferroptosis. Furthermore, utilizing GC-1 spg cell lines, we elucidated the role of the METTL3-mediated m6A modification in GPX4 mRNA stability. Treatment with SQ or Fer-1 (an inhibitor of ferroptosis) significantly ameliorated testicular pathological injury, restored abnormal serum sex hormone levels, and enhanced testicular steroidogenic enzyme expression, highlighting the therapeutic potential of targeting ferroptosis in asthenozoospermia. In elucidating the molecular mechanism of METTL3 in ferroptosis, we found that METTL3 regulates GPX4 mRNA stability, subsequently impacting ferroptosis and sperm quality. Knockdown of METTL3 mimicked the effects of SQ treatment, while overexpression of METTL3 partially reversed SQ-mediated effects on ferroptosis and asthenozoospermia, underscoring the pivotal role of METTL3 in SQ therapy. In conclusion, the METTL3-GPX4-ferroptosis axis emerges as a novel regulatory pathway in the pathogenesis of asthenozoospermia. Targeting this axis, particularly through interventions such as SQ treatment, holds promise for the management of male infertility.

RNA methylation: A potential therapeutic target in autoimmune disease

Autoimmune diseases such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and inflammatory bowel disease (IBD) are caused by the body's immune response to autoantigens. The pathogenesis of autoimmune diseases is unclear. Numerous studies have demonstrated that RNA methylation plays a key role in disease progression, which is essential for post-transcriptional regulation and has gradually become a broad regulatory mechanism that controls gene expression in various physiological processes, including RNA nuclear output, translation, splicing, and noncoding RNA processing. Here, we outline the writers, erasers, and readers of RNA methylation, including N6-methyladenosine (m6A), 2'-O-methylation (Nm), 2'-O-dimethyladenosine (m6Am), N1-methyladenosine (m1A), 5-methylcytidine (m5C) and N7-methylguanosine (m7G). As the role of RNA methylation modifications in the immune system and diseases is explained, the potential treatment value of these modifications has also been demonstrated. This review reports the relationship between RNA methylation and autoimmune diseases, highlighting the need for future research into the therapeutic potential of RNA modifications.

The Role of Circular RNAs in Male Infertility and Reproductive Cancers: A Narrative Review

Infertility is a global health problem affecting about 15% of all couples, of which 50% are due to male infertility. Although the etiology of infertility is known in most infertile men, idiopathic male infertility remains a challenge. Therefore, there is a need for novel diagnostic methods to detect the underlying mechanisms and develop appropriate therapies. Recent studies have focused on the role of non-coding RNAs (ncRNAs) in male infertility. Circular RNAs (CircRNAs), a type of ncRNAs, are found to play a key role in the development of some pathological conditions, including cardiovascular diseases, diabetes, cancers, autoimmune diseases, etc. Several studies have reported the presence of CircRNAs and their target genes in the human reproductive system. In addition, their expression in testicular tissues, sperm cells, and seminal fluid has been identified. Abnormal expression of CircRNAs has been associated with azoospermia and asthenozoospermia in infertile men. The present narrative review provides a brief description of the role of CircRNAs in spermatogenic cells, male infertility, and reproductive cancers. In addition, some CircRNAs have been identified as potential biomarkers for disease detection and treatment.

Comprehensive Analysis of the Transcriptome-Wide m6A Methylome in Shaziling Pig Testicular Development

RNA N6-methyladenosine (m6A) modification is one of the principal post-transcriptional modifications and plays a dynamic role in testicular development and spermatogenesis. However, the role of m6A in porcine testis is understudied. Here, we performed a comprehensive analysis of the m6A transcriptome-wide profile in Shaziling pig testes at birth, puberty, and maturity. We analyzed the total transcriptome m6A profile and found that the m6A patterns were highly distinct in terms of the modification of the transcriptomes during porcine testis development. We found that key m6A methylated genes (AURKC, OVOL, SOX8, ACVR2A, and SPATA46) were highly enriched during spermatogenesis and identified in spermatogenesis-related KEGG pathways, including Wnt, cAMP, mTOR, AMPK, PI3K-Akt, and spliceosome. Our findings indicated that m6A methylations are involved in the complex yet well-organized post-transcriptional regulation of porcine testicular development and spermatogenesis. We found that the m6A eraser ALKBH5 negatively regulated the proliferation of immature porcine Sertoli cells. Furthermore, we proposed a novel mechanism of m6A modification during testicular development: ALKBH5 regulated the RNA methylation level and gene expression of SOX9 mRNA. In addition to serving as a potential target for improving boar reproduction, our findings contributed to the further understanding of the regulation of m6A modifications in male reproduction.

Transcriptome Studies Reveal the N6-Methyladenosine Differences in Testis of Yaks at Juvenile and Sexual Maturity Stages

Studying the mechanism of spermatogenesis is key to exploring the reproductive characteristics of male yaks. Although N6-methyladenosine (m6A) RNA modification has been reported to regulate spermatogenesis and reproductive function in mammals, the molecular mechanism of m6A in yak testis development and spermatogenesis remains largely unknown. Therefore, we collected testicular tissue from juvenile and adult yaks and found that the m6A level significantly increased after sexual maturity in yaks. In MeRIP-seq, 1702 hypermethylated peaks and 724 hypomethylated peaks were identified. The hypermethylated differentially methylated RNAs (DMRs) (CIB2, AK1, FOXJ2, PKDREJ, SLC9A3, and TOPAZ1) mainly regulated spermatogenesis. Functional enrichment analysis showed that DMRs were significantly enriched in the adherens junction, gap junction, and Wnt, PI3K, and mTOR signaling pathways, regulating cell development, spermatogenesis, and testicular endocrine function. The functional analysis of differentially expressed genes showed that they were involved in the biological processes of mitosis, meiosis, and flagellated sperm motility during the sexual maturity of yak testis. We also screened the key regulatory factors of testis development and spermatogenesis by combined analysis, which included BRCA1, CREBBP, STAT3, and SMAD4. This study indexed the m6A characteristics of yak testicles at different developmental stages, providing basic data for further research of m6A modification regulating yak testicular development.

Modulation of translational decoding by m6A modification of mRNA

N6-methyladenosine (m6A) is an abundant, dynamic mRNA modification that regulates key steps of cellular mRNA metabolism. m6A in the mRNA coding regions inhibits translation elongation. Here, we show how m6A modulates decoding in the bacterial translation system using a combination of rapid kinetics, smFRET and single-particle cryo-EM. We show that, while the modification does not impair the initial binding of aminoacyl-tRNA to the ribosome, in the presence of m6A fewer ribosomes complete the decoding process due to the lower stability of the complexes and enhanced tRNA drop-off. The mRNA codon adopts a π-stacked codon conformation that is remodeled upon aminoacyl-tRNA binding. m6A does not exclude canonical codon-anticodon geometry, but favors alternative more dynamic conformations that are rejected by the ribosome. These results highlight how modifications outside the Watson-Crick edge can still interfere with codon-anticodon base pairing and complex recognition by the ribosome, thereby modulating the translational efficiency of modified mRNAs.

METTL14 promotes doxorubicin-induced cardiomyocyte ferroptosis by regulating the KCNQ1OT1-miR-7-5p-TFRC axis

Doxorubicin (DOX) has toxic effects on the heart, causing cardiomyopathy and heart injury, but the underlying mechanisms of these effects require further investigation. This study investigated the role of DOX in promoting ferroptosis to induce myocardial injury. AC16 cardiomyocyte and neonatal rat ventricle cardiomyocytes were used as an in vitro model to study the molecules involved in myocardial injury using gene silencing, ectopic expression, and RNA immunoprecipitation. Messenger RNA and protein level analyses showed that DOX treatment resulted in the upregulation of methyltransferase-like 14 (METTL14), which catalyzes the m6A modification of the long non-coding RNA KCNQ1OT1, a miR-7-5p sponge. The RNA-binding protein IGF2BP1 is associated with KCNQ1OT1 to increase its stability and robustly inhibit miR-7-5p activity. Furthermore, a lack of miR-7-5p expression led to increased levels of transferrin receptor, promoting the uptake of iron and production of lipid reactive oxygen species and demonstrating that DOX-induced ferroptosis occurs in AC16 cells. Additionally, we found that miR-7-5p targets METTL14 in AC16 cells. Meanwhile, the role of METTL14/KCNQ1OT1/miR-7-5p axis in regulating ferroptosis in neonatal rat ventricle cardiomyocytes was also confirmed. Our results indicate that selectively inhibiting ferroptosis mediated by a METTL14/KCNQ1OT1/miR-7-5p positive feedback loop in cardiomyocytes could provide a new therapeutic approach to control DOX-induced cardiac injury.

Effects of Moderate-Intensity Continuous Training and High-Intensity Interval Training on Testicular Oxidative Stress, Apoptosis and m6A Methylation in Obese Male Mice

Exercise is an effective way to improve reproductive function in obese males. Oxidative stress and apoptosis are important pathological factors of obesity-related male infertility. Accumulating studies have demonstrated that N6-methyladenosine (m6A) methylation is associated with obesity and testicular reproductive function. Our study aimed to investigate and compare the effect of 8 weeks of moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) on testicular oxidative stress, apoptosis and m6A methylation in obese male mice. Male C57BL/6 mice were randomly allocated into the four groups: normal diet (ND) group, high-fat diet (HFD) group, high-fat diet with moderate-intensity continuous training (HFD-MICT) group and high-fat diet with high-intensity interval training (HFD-HIIT) group. Mice in the HFD-MICT and HFD-HIIT groups were subjected to 8 weeks of MICT or HIIT treadmill protocols after 12 weeks of HFD feeding. We found that MICT and HIIT increased the protein expression of Nrf2, HO-1 and NQO-1 in the testes of obese mice, and HIIT increased it more than MICT. The Bax/Bcl-2 ratio, Cleaved Caspase-3 protein expression and TUNEL-positive cells were consistently up-regulated in the testes of obese mice, but MICT and HIIT restrained these HFD-induced effects. In addition, HFDs increased m6A levels and the gene expression of METTL3, YTHDF2 and FTO in the testes, but these effects were reversed by MICT and HIIT. However, HIIT was more effective than MICT in reducing m6A methylation in the testes of obese mice. These results demonstrate that both MICT and HIIT protected against HFD-induced oxidative stress, apoptosis and m6A methylation in testicular tissues; as a result, testicular morphological and functional impairment improved. In particular, HIIT was more beneficial than MICT in increasing the mRNA expression of steroidogenic enzymes and testicular antioxidant capacity and decreasing m6A methylation in the testes of HFD-fed mice.

NAT10-mediated N4-acetylcytidine modification is required for meiosis entry and progression in male germ cells

Post-transcriptional RNA modifications critically regulate various biological processes. N⁴-acetylcytidine (ac⁴C) is an epi-transcriptome, which is highly conserved in all species. However, the in vivo physiological functions and regulatory mechanisms of ac⁴C remain poorly understood, particularly in mammals. In this study, we demonstrate that the only known ac⁴C writer, N-acetyltransferase 10 (NAT10), plays an essential role in male reproduction. We identified the occurrence of ac⁴C in the mRNAs of mouse tissues and showed that ac⁴C undergoes dynamic changes during spermatogenesis. Germ cell-specific ablation of Nat10 severely inhibits meiotic entry and leads to defects in homologous chromosome synapsis, meiotic recombination and repair of DNA double-strand breaks during meiosis. Transcriptomic profiling revealed dysregulation of functional genes in meiotic prophase I after Nat10 deletion. These findings highlight the crucial physiological functions of ac⁴C modifications in male spermatogenesis and expand our understanding of its role in the regulation of specific physiological processes in vivo.

The analysis of N6-methyladenosine regulators impacting the immune infiltration in clear cell renal cell carcinoma

The tumor immune microenvironment (TIME) and N6-methyladenosine (m6A) are related to the progression of several types of cancer. Nevertheless, the impact of m6A on the TIME of clear cell renal cell carcinoma (ccRCC) remains unclear. This study used an unsupervised clustering algorithm to divide the samples into distinct subgroups. The single sample gene set enrichment analysis (ssGSEA) algorithm to estimate the TIME. The correlation between m6A regulators and immune cells in different subgroups was calculated using Spearman analysis. At last, the relationship between IGF2BP2 and HMGA2 was validated in several datasets, including TCGA-KIRC, GEO, and HPA datasets. We found that m6A regulators were differently expressed in several clinical groups. Based on the expression of m6A regulators, we divided the samples into three subgroups. Then, the survival analysis for these three subgroups showed that the cluster 2 subgroup had poor overall survival (OS). Further, we found that IGF2BP2 and IGF2BP3 were essential components in the cluster 2 subgroup using the principal component analysis (PCA) algorithm. In addition, the expression of these two genes was significantly correlated with survival time. At last, we found that HMGA2 was significantly correlated with IGF2BP2 in several datasets, which indicated that HMGA2 is an essential role in affecting IGF2BP2 regulating the TIME. There is a close correlation between m6A regulators and TIME. Moreover, IGF2BP2 is related to the progression of ccRCC and plays an essential role in affecting the TIME.

Melatonin: Regulation of Biomolecular Condensates in Neurodegenerative Disorders

Biomolecular condensates are membraneless organelles (MLOs) that form dynamic, chemically distinct subcellular compartments organizing macromolecules such as proteins, RNA, and DNA in unicellular prokaryotic bacteria and complex eukaryotic cells. Separated from surrounding environments, MLOs in the nucleoplasm, cytoplasm, and mitochondria assemble by liquid-liquid phase separation (LLPS) into transient, non-static, liquid-like droplets that regulate essential molecular functions. LLPS is primarily controlled by post-translational modifications (PTMs) that fine-tune the balance between attractive and repulsive charge states and/or binding motifs of proteins. Aberrant phase separation due to dysregulated membrane lipid rafts and/or PTMs, as well as the absence of adequate hydrotropic small molecules such as ATP, or the presence of specific RNA proteins can cause pathological protein aggregation in neurodegenerative disorders. Melatonin may exert a dominant influence over phase separation in biomolecular condensates by optimizing membrane and MLO interdependent reactions through stabilizing lipid raft domains, reducing line tension, and maintaining negative membrane curvature and fluidity. As a potent antioxidant, melatonin protects cardiolipin and other membrane lipids from peroxidation cascades, supporting protein trafficking, signaling, ion channel activities, and ATPase functionality during condensate coacervation or dissolution. Melatonin may even control condensate LLPS through PTM and balance mRNA- and RNA-binding protein composition by regulating N6-methyladenosine (m6A) modifications. There is currently a lack of pharmaceuticals targeting neurodegenerative disorders via the regulation of phase separation. The potential of melatonin in the modulation of biomolecular condensate in the attenuation of aberrant condensate aggregation in neurodegenerative disorders is discussed in this review.