Combination of high-fat diet and cadmium impairs testicular spermatogenesis in an m6A-YTHDF2-dependent manner

Emerging roles of RNA methylation modifications in environmental metalloid or metal pollutants toxicity

The common environmental metalloid or metal pollutants such as arsenic, cadmium, chromium, lead, aluminum, cobalt and manganese have increasingly significant impacts on public health. They have been confirmed to be enriched step by step through the food chain to display serious toxic effects on multiple organs and tissues. Recently, emerging studies have indicated that RNA methylation modification plays essential roles in various organs and tissue toxicity under the treatment of environmental metalloid or metal pollutants. In this review, the roles and mechanisms of major RNA methylation modifications such as N6-methyladenosine (m6A), 5-methylcytosine (m5C), N1-methyladenosine (m1A) and 7-methylguanine (m7G) in the regulation of multiple organs and tissues toxic damage caused by environmental metalloid or metal pollutants are summarized. Additionally, we explore potential avenues for future investigation within the realm of RNA methylation as it pertains to the toxicity of environmental metalloid or metal pollutants. The insights presented herein are intended to offer critical research leads and a scientific foundation for the mitigation and advancement of strategies addressing the toxicity of environmental metalloid or metal pollutants.

Melatonin Mitigates Cd-Induced Growth Repression and RNA m6A Hypermethylation by Triggering MMR-Mediated DNA Damage Response

Melatonin (MT) has been found to mitigate cadmium (Cd) toxicity with negligible environmental risks. It remains poorly understood as to how MT mitigates Cd-induced growth repression and regulates RNA m6A methylation. We aimed to elucidate the effect of MT on growth repression and RNA m6A methylation in Arabidopsis (Arabidopsis thaliana) exposed to Cd stress. MT mitigated, on average, 13.96% and 8.42% of growth repression resulting from Cd and mismatch repair (MMR) deficiency. The ameliorative effect on Cd stress was reduced by 70.56% and 34.23% in msh2 and msh6 mutants, respectively. With distinct dose-effect relationships, m6A hypermethylation responded to Cd stress rather than Cu stress, which was further elevated in MMR-deficient seedlings. MT reduced m6A levels by 22.98% even without stress induction, whereas the depressed m6A levels in MMR-deficient seedlings, greatly exceeding those in the WT. The "writer" and "eraser" gene expression responsible for m6A methylation was reduced with the concentration of stresses due to MT, but VIR and ALKBH9B no longer responded to Cd stress in msh2 and msh6. Despite the remarkable repression, MMR gene expression was regularly promoted by MT under Cd and Cu stress. Our study provides novel insights into the molecular mechanisms underlying the restorative effects of MT on growth repression and m6A methylation regulation, which shed light on Cd phytoremediation.

Changes of N6-methyladenosine and ferroptosis in cadmium-induced reproductive toxicity of male mice fed a high fat and high sugar diet

Cadmium (Cd) and high-fat and high-sugar diet (HFHS) are risk factors contributing to the decline in male sperm quality. N6-methyladenosine (m6A) is essential in the processes of testicular development and spermatogenesis. Ferroptosis, a form of cell death that depends on iron, is prone to causing testicular dysfunction. However, the changes in m6A modification regulatory proteins and ferroptosis signaling molecules in male mice with sperm abnormalities resulting from combined exposure to Cd and HFHS remain incompletely elucidate. Our present data indicate that the combined treatment of Cd and HFHS significantly reduced sperm quality in comparison to those in single Cd or HFHS treatment. In addition, indicators related to ferroptosis in the combined treatment of Cd and HFHS group have also undergone significant changes. In detail, the contents of malondialdehyde (MDA) and Fe2+ as well as Slc7a11 expression were increased while Gclc expressions were reduced in the testicular tissue of Cd and HFHS combined treatment mice. Further detect results showed that the combined exposure to Cd and HFHS synergistically elevated the m6A modification levels alongside a downregulation of the Mettl3, Fto, Alkbh5 and Ythdc2 at the protein level when compared with those in single Cd or HFHS treatment. Altogether, it can be inferred that Cd and HFHS combined treatment may alter the levels of m6A modification regulatory proteins in testicular tissue, leading to increased Fe2+ and MDA production, thus activating the Slc7a11/Gpx4 signaling pathway, ultimately decreasing the sperm quality in mice, providing preliminary evidence for the occurrence of ferroptosis in testicular cells. Our findings may provide direction for the study of reproductive toxicity of cadmium and offer reference for the selection of molecular targets.

Sperm RNA code in spermatogenesis and male infertility

Spermatozoa are traditionally thought to be transcriptionally inert, but recent studies have revealed the presence of sperm RNA, some of which is derived from the residues of spermatocyte transcription and some from epididymosomes. Paternal sperm RNA can be affected by external factors and further modified at the post-transcriptional level, for example N6-methyladenosine (m6A), thus shaping spermatogenesis and reproductive outcome. This review briefly introduces the origin of sperm RNA and, on this basis, summarizes the current knowledge on RNA modifications and their functional role in spermatogenesis and male infertility. The bottlenecks and knowledge gaps in the current research on RNA modification in male reproduction have also been indicated. Further investigations are needed to elucidate the functional consequences of these modifications, providing new therapeutic and preventive strategies for reproductive health and genetic inheritance.

RNA reading protein YTHDF2 mediates Benzo(k)fluoranthene induced male reproductive injury by regulating the stability of BCL2

Benzo (k) fluoranthene (BkF) has adverse effects on male reproduction, but its specific mechanism of action is still unclear. This study focused on the role of RNA reading protein YTHDF2 and its mechanism in BkF induced male reproductive injury. Mouse GC-2 spermatocytes were exposed to 0, 40, 80, 160 μM BkF. It was found that BkF significantly increased the apoptosis of GC-2 cell and decreased its survival rate. BCL2 in spermatocytes decreased significantly, while the expression of P53 and BAX exhibited a notable increase. Interestingly, the expression of RNA reading protein YTHDF2 progressively rose in tandem with the escalating BkF exposure dosage. Overexpression of YTHDF2 significantly reduced the viability of cells and increased the apoptosis rate. Meanwhile, there was a substantial increase in the expression of P53 and BAX, BCL2 was significantly down-regulated. On the contrary, interfering with YTHDF2 increased cell proliferation and reduced cell apoptosis. Furthermore, YTHDF2 overexpression exacerbated the decrease in cell viability under BkF exposure, while YTHDF2 knockdown was the opposite. The results from the RIP assay demonstrated a significant enhancement in the interaction of YTHDF2 protein with BCL2 mRNA following the overexpression of YTHDF2. In addition, animal experiments showed that there was an increase in apoptosis and a decrease in proliferation of testicular cells in mice in the high-dose (30 mg/kg) BkF group by TUNEL staining and Ki67 staining. Immunohistochemical analysis showed that BCL2 levels were significantly lower in the high-dose group than in the control group, while YTHDF2, P53 and BAX were dramatically increased. In summary, our study suggests that YTHDF2 has been implicated in BkF-induced male reproductive injury by promoting the degradation of BCL2.

Role of reactive oxygen species in regulating epigenetic modifications

Reactive oxygen species (ROS) originate from diverse sources and regulate multiple signaling pathways within the cellular environment. Their generation is intricately controlled, and disruptions in their signaling or atypical levels can precipitate pathological conditions. Epigenetics, the examination of heritable alterations in gene expression independent of changes in the genetic code, has been implicated in the pathogenesis of various diseases through aberrant epigenetic modifications. The significant contribution of epigenetic modifications to disease progression underscores their potential as crucial therapeutic targets for a wide array of medical conditions. This study begins by providing an overview of ROS and epigenetics, followed by a discussion on the mechanisms of epigenetic modifications such as DNA methylation, histone modification, and RNA modification-mediated regulation. Subsequently, a detailed examination of the interaction between ROS and epigenetic modifications is presented, offering new perspectives and avenues for exploring the mechanisms underlying specific epigenetic diseases and the development of novel therapeutics.

The Role of Oxidative Stress and DNA Hydroxymethylation in the Pathogenesis of Benzo[a]pyrene-Impaired Reproductive Function in Male Mice

Benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon, is known to cause teratogenesis. Environmental exposure of BaP has led to wide public concerns due to their potential risk of reproductive toxicity. However, the exact mechanism is still not clear. We aimed to explore the alterations of oxidative stress and DNA hydroxymethylation during BaP-impaired reproductive function. BALB/c mice were intragastrically administered with different doses of BaP (0.01, 0.1, and 1 mg/kg/day, once a day), while control mice were administered with corn coil. Then, the reproductive function, alterations of oxidative stress, DNA methylation, and DNA hydroxymethylation of testis tissues were evaluated. We found that BaP caused obvious histopathological damages of testis tissues. As for sperm parameters after BaP administration, testis weight and the rate of teratosperm were increased, as well as sperm count and motility were decreased. In mechanism, BaP upregulated HO-1 and MDA levels and downregulated SOD and CAT activity and GSH content in testis tissues, indicating that oxidative stress was induced by BaP. Furthermore, a significant induction of hydroxymethylation and inhibition of methylation were observed in testis tissues after BaP exposure. Collectively, BaP-induced oxidative stress and hydroxymethylation were involved in impairing reproductive function, which may be the mechanism of the male infertility.

FTO mediates bisphenol F-induced blood-testis barrier impairment through regulating ferroptosis via YTHDF1/TfRc and YTHDF2/SLC7A11 signal axis

Bisphenol F (BPF) has been extensively utilized in daily life, which brings new hazards to male reproductive health. However, the specific functional mechanism is still unclear. Both cell and animal models were utilized for exploring the role of RNA methylation and ferroptosis and its underlying mechanisms in male reproductive injury induced by BPF. In animal model, BPF severely destroyed the integrity of the blood-testis barrier (BTB) and induced ferroptosis. Furthermore, BPF significantly affected the barrier function of TM4 cells and promoted ferroptosis. Importantly, ChIP assays revealed that BPF inhibited AR transcriptional regulation of FTO and FTO expression was downregulated in TM4 cells. Overexpression of FTO prevented the impairment of BTB by inhibiting ferroptosis in TM4 cells. Mechanistically, FTO could significantly down-regulate the m6A modification level of TfRc and SLC7A11 mRNA through MeRIP experiment. RIP experiments showed that YTHDF1 can bind to TfRc mRNA and promote its translation while YTHDF2 could bind to SLC7A11 mRNA and reduce its mRNA stability. Therefore, our results suggest that FTO plays a key role in BPF induced male reproductive toxicity through YTHDF1-TfRc axis and YTHDF2-SLC7A11 axis and may provide new ideas and methods for the prevention and treatment of male reproductive diseases associated with environmental pollutants.

Bisphenol H exposure disrupts Leydig cell function in adult rats via oxidative stress-mediated m6A modifications: Implications for reproductive toxicity

Bisphenol H (BPH) has emerged as a potential alternative to bisphenol A (BPA), which has been curtailed for use due to concerns over its reproductive and endocrine toxicity. This study investigates whether BPH exerts antiandrogenic effects by impairing Leydig cell function, a critical component in testosterone production. We administered orally BPH to adult male rats at doses of 0, 1, 10, and 100 mg/kg/day for 7 days. Notably, BPH treatment resulted in a dose-dependent reduction in testicular testosterone levels, with significant decreases observed at ≥ 1 mg/kg/day. Additionally, BPH affected the expression of key genes involved in steroidogenesis and cholesterol metabolism, including Nr5a1, Nr3c4, Lhcgr, Scarb1, and Star, at higher doses (10 and/or 100 mg/kg/day). The study also revealed alterations in antioxidant gene expression (Sod2 and Cat) and modulation of m6A-related genes (Ythdf1-3 and Foxo3) and their proteins. Through MeRIP-qPCR analysis, we identified increased m6A modifications in Scarb1 and Star genes following BPH exposure. In vitro experiments with primary Leydig cells confirmed that BPH enhanced oxidative stress and diminished testosterone production, which were partially mitigated by antioxidant vitamin E supplementation and Ythdf3 knockdown. Meanwhile, simultaneous administration of BPH and vitamin E to primary Leydig cells partially counteracted BPH-induced alterations in the Ythdf3 expression. Our findings underscore a novel mechanism by which BPH disrupts Leydig cell function through the oxidative stress-m6A modification-autophagy pathway, raising concerns about its potential reproductive toxicity.

Plin4 exacerbates cadmium-decreased testosterone level via inducing ferroptosis in testicular Leydig cells

Strong evidence indicates that environmental stressors are the risk factors for male testosterone deficiency (TD). However, the mechanisms of environmental stress-induced TD remain unclear. Based on our all-cause male reproductive cohort, we found that serum ferrous iron (Fe2⁺) levels were elevated in TD donors. Then, we explored the role and mechanism of ferroptosis in environmental stress-reduced testosterone levels through in vivo and in vitro models. Data demonstrated that ferroptosis and lipid droplet deposition were observed in environmental stress-exposed testicular Leydig cells. Pretreatment with ferrostatin-1 (Fer-1), a specific ferroptosis inhibitor, markedly mitigated environmental stress-reduced testosterone levels. Through screening of core genes involved in lipid droplets formation, it was found that environmental stress significantly increased the levels of perilipins 4 (PLIN4) protein and mRNA in testicular Leydig cells. Further experiments showed that Plin4 siRNA reversed environmental stress-induced lipid droplet deposition and ferroptosis in Leydig cells. Additionally, environmental stress increased the levels of METTL3, METTL14, and total RNA m6A in testicular Leydig cells. Mechanistically, S-adenosylhomocysteine, an inhibitor of METTL3 and METTL14 heterodimer activity, restored the abnormal levels of Plin4, Fe2⁺ and testosterone in environmental stress-treated Leydig cells. Collectively, these results suggest that Plin4 exacerbates environmental stress-decreased testosterone level via inducing ferroptosis in testicular Leydig cells.

Sirt1 m6A modification-evoked Leydig cell senescence promotes Cd-induced testosterone decline

Diminished testosterone levels have been documented as a key factor in numerous male health disorders. Both human and animal studies have consistently demonstrated that cadmium (Cd), a pervasive environmental heavy metal, results in decreased testosterone levels. However, the exact mechanism through which Cd interferes with testosterone synthesis remains incompletely elucidated. This research sought to examine the impact of cellular senescence on Cd-suppressed testosterone synthesis. We also investigated the related m6A modification mechanism. The results demonstrated that Cd (100 mg/L) led to a decrease in testosterone levels, along with downregulated expression of testosterone synthase in C57BL/6 N male mice. Furthermore, Cd significantly increased β-galactosidase staining intensity, senescence-related proteins, and senescence-related secretory phenotypes in mouse testicular Leydig cells. Subsequent investigations revealed that Cd decreased the mRNA and protein levels of NAD-dependent deacetylase Sirtuin-1 (SIRT1) in Leydig cells. Mechanistically, mice treated with resveratrol (50 mg/kg), a specific SIRT1 activator, mitigated Leydig cell senescence and reversed Cd-reduced testosterone levels in mouse testes. These effects were also restored by SIRT1 overexpression in Leydig cells. Additionally, we found that Cd increased the level of methyltransferase enzyme METTL3 and Sirt1 m6A modification in Leydig cells. Mettl3 siRNA effectively restored Cd-enhanced Sirt1 m6A level and reversed Cd-downregulated Sirt1 mRNA expression in Leydig cells. Overall, our findings suggest that Cd exposure inhibits testosterone synthesis via Sirt1 m6A modification-mediated senescence in mouse testes. These results offer an experimental basis for investigating the causes and potential treatments of hypotestosteronemia induced by environmental factors.

Klinefelter syndrome: etiology and clinical considerations in male infertility†

Klinefelter syndrome (KS) is the most prevalent chromosomal disorder occurring in males. It is defined by an additional X chromosome, 47,XXY, resulting from errors in chromosomal segregation during parental gametogenesis. A major phenotype is impaired reproductive function, in the form of low testosterone and infertility. This review comprehensively examines the genetic and physiological factors contributing to infertility in KS, in addition to emergent assisted reproductive technologies, and the unique ethical challenges KS patients face when seeking infertility treatment. The pathology underlying KS is increased susceptibility for meiotic errors during spermatogenesis, resulting in aneuploid or even polyploid gametes. Specific genetic elements potentiating this susceptibility include polymorphisms in checkpoint genes regulating chromosomal synapsis and segregation. Physiologically, the additional sex chromosome also alters testicular endocrinology and metabolism by dysregulating interstitial and Sertoli cell function, collectively impairing normal sperm development. Additionally, epigenetic modifications like aberrant DNA methylation are being increasingly implicated in these disruptions. We also discuss assisted reproductive approaches leveraged in infertility management for KS patients. Application of assisted reproductive approaches, along with deep comprehension of the meiotic and endocrine disturbances precipitated by supernumerary X chromosomes, shows promise in enabling biological parenthood for KS individuals. This will require continued multidisciplinary collaboration between experts with background of genetics, physiology, ethics, and clinical reproductive medicine.

Adolescent co-exposure to environmental cadmium and high-fat diet induces cognitive decline via Larp7 m6A-mediated SIRT6 inhibition

The effects and underlying mechanisms of adolescent exposure to combined environmental hazards on cognitive function remain unclear. Here, using a combined exposure model, we found significant cognitive decline, hippocampal neuronal damage, and neuronal senescence in mice exposed to cadmium (Cd) and high-fat diet (HFD) during adolescence. Furthermore, we observed a significant downregulation of Sirtuin 6 (SIRT6) expression in the hippocampi of co-exposed mice. UBCS039, a specific SIRT6 activator, markedly reversed the above adverse effects. Further investigation revealed that co-exposure obviously reduced the levels of La ribonucleoprotein 7 (LARP7), disrupted the interaction between LARP7 and SIRT6, ultimately decreasing SIRT6 expression in mouse hippocampal neuronal cells. Overexpression of Larp7 reversed the combined exposure-induced SIRT6 decrease and senescence in mouse hippocampal neuronal cells. Additionally, the results showed notably elevated levels of Larp7 m6A and YTH domain family protein 2 (YTHDF2) in mouse hippocampal neuronal cells treated with the combined hazards. Ythdf2 short interfering RNA, RNA immunoprecipitation, and RNA stability assays further demonstrated that YTHDF2 mediated the degradation of Larp7 mRNA under combined exposure. Collectively, adolescent co-exposure to Cd and HFD causes hippocampal senescence and cognitive decline in mice by inhibiting LARP7-mediated SIRT6 expression in an m6A-dependent manner.

Cadmium exposure elicited dynamic RNA m6A modification and epi-transcriptomic regulation in the Pacific whiteleg shrimp Litopenaeus vannamei

N6-methyladenosine (m6A) methylation is the most prevalent post-transcriptional RNA modification in eukaryotic organisms, but its roles in the regulation of physiological resistance of marine crustaceans to heavy metal pollutants are poorly understood. In this study, the transcriptome-wide m6A RNA methylation profiles and dynamic m6A changes induced by acute Cd2+ exposure in the the pacific whiteleg shrimp Litopenaeus vannamei were comprehensively analyzed. Cd2+ toxicity caused a significant reduction in global RNA m6A methylation level, with major m6A regulators including the m6A methyltransferase METTL3 and the m6A binding protein YTHDF2 showing declined expression. Totally, 11,467 m6A methylation peaks from 6415 genes and 17,291 peaks within 7855 genes were identified from the Cd2+ exposure group and the control group, respectively. These m6A peaks were predominantly enriched in the 3' untranslated region (UTR) and around the start codon region of the transcripts. 7132 differentially expressed genes (DEGs) and 7382 differentially m6A-methylated genes (DMGs) were identified. 3186 genes showed significant changes in both gene expression and m6A methylation levels upon cadmium exposure, and they were related to a variety of biological processes and gene pathways. Notably, an array of genes associated with antioxidation homeostasis, transmembrane transporter activity and intracellular detoxification processes were significantly enriched, demonstrating that m6A modification may mediate the physiological responses of shrimp to cadmium toxicity via regulating ROS balance, Cd2+ transport and toxicity mitigation. The study would contribute to a deeper understanding of the evolutionary and functional significance of m6A methylation to the physiological resilience of decapod crustaceans to heavy metal toxicants.

Advances in immunology of male reproductive toxicity induced by common environmental pollutants

Humans are exposed to an ever-increasing number of environmental toxicants, some of which have gradually been identified as major risk factors for male reproductive health, even associated with male infertility. Male infertility is usually due to the reproductive system damage, which may be influenced by the exposure to contaminants such as heavy metals, plasticizers, along with genetics and lifestyle. Testicular immune microenvironment (TIM) is important in maintaining normal physiological functions of the testis, whether disturbed TIM after exposure to environmental toxicants could induce reproductive toxicity remains to be explored. Therefore, the current review aims to contribute to the further understanding of exposure and male infertility by characterizing environmental exposures and the effect on TIM. We first summarized the male reproductive toxicity phenotypes induced by common environmental pollutants. Contaminants including heavy metals and plastic additives and fine particulate matter (PM2.5), have been repetitively associated with male infertility, whereas emerging contaminants such as perfluoroalkyl substances and micro(nano)plastics have also been found to disrupt TIM and lead to male reproductive toxicity. We further reviewed the importance of TIM and its homeostasis in maintaining the normal physiological functions of the testis. Most importantly, we discussed the advances in immunology of male reproductive toxicity induced by metals and metalloids, plastic additives, persistent organic pollutants (POPs), micro(nano)plastic and PM2.5 to suggest the importance of reproductive immunotoxicology in the future study of environmental toxicants, but also contribute to the development of effective prevention and treatment strategies for mitigating adverse effects of environmental pollutants on human health.

m6A-methylated Lonp1 drives mitochondrial proteostasis stress to induce testicular pyroptosis upon environmental cadmium exposure

Cadmium (Cd) is a widely distributed typical environmental pollutant and one of the most toxic heavy metals. It is well-known that environmental Cd causes testicular damage by inducing classic types of cell death such as cell apoptosis and necrosis. However, as a new type of cell death, the role and mechanism of pyroptosis in Cd-induced testicular injury remain unclear. In the current study, we used environmental Cd to generate a murine model with testicular injury and AIM2-dependent pyroptosis. Based on the model, we found that increased cytoplasmic mitochondrial DNA (mtDNA), activated mitochondrial proteostasis stress occurred in Cd-exposed testes. We used ethidium bromide to generate mtDNA-deficient testicular germ cells and further confirmed that increased cytoplasmic mtDNA promoted AIM2-dependent pyroptosis in Cd-exposed cells. Uracil-DNA glycosylase UNG1 overexpression indicated that environmental Cd blocked UNG-dependent repairment of damaged mtDNA to drive the process in which mtDNA releases to cytoplasm in the cells. Interestingly, we found that environmental Cd activated mitochondrial proteostasis stress by up-regulating protein expression of LONP1 in testes. Testicular specific LONP1-knockdown significantly reversed Cd-induced UNG1 protein degradation and AIM2-dependent pyroptosis in mouse testes. In addition, environmental Cd significantly enhanced the m6A modification of Lonp1 mRNA and its stability in testicular germ cells. Knockdown of IGF2BP1, a reader of m6A modification, reversed Cd-induced upregulation of LONP1 protein expression and pyroptosis activation in testicular germ cells. Collectively, environmental Cd induces m6A modification of Lonp1 mRNA to activate mitochondrial proteostasis stress, increase cytoplasmic mtDNA content, and trigger AIM2-dependent pyroptosis in mouse testes. These findings suggest that mitochondrial proteostasis stress is a potential target for the prevention of testicular injury.

Arsenic exposure causes decline in sperm motility accompanied by energy metabolism disorders in mouse testes

Arsenic (As) is a notorious environmental toxicant widely present in various natural environments. As exposure has been correlated with the decline in sperm motility. Yet, the mechanism has not been fully elucidated. Adult male C57 mice were given 0, 1, or 15 mg/L NaAsO2 for 10 weeks. The mature seminiferous tubules and sperm count were decreased in As-exposed mice. Sperm motility and several sperm motility parameters, including average path velocity (VAP), straight-line velocity (VSL), curvilinear velocity (VCL), beat-cross frequency (BCF), linearity (LIN), straightness (STR), and amplitude of lateral head displacement (ALH), were declined in As-exposed mice. RNA sequencing and transcriptomics analyses revealed that differentially expressed genes (DEGs) were mainly enriched in metabolic pathways. Untargeted metabolomics analyses indicated that energy metabolism was disrupted in As-exposed mouse testes. Gene set enrichment analysis showed that glycolysis and oxidative phosphorylation were disturbed in As-exposed mouse testes. As-induced disruption of testicular glucose metabolism and oxidative phosphorylation was further validated by RT-PCR and Western blotting. In conclusion, As exposure causes decline in sperm motility accompanied by energy metabolism disorders in mouse testes.

Co-exposure of microcystin and nitrite enhanced spermatogenic disorders: The role of mtROS-mediated pyroptosis and apoptosis

Microcystins (MCs) and nitrites are coexisted in the environment and have reproductive toxicity. The combined toxic effect and mechanism of MCs and nitrite on spermatogenesis remain largely unclear. In the present study, co-exposure to microcystin-leucine arginine (MC-LR) and sodium nitrite (NaNO2) aggravated testicular damage of Balb/c mice and mitochondrial impairment of spermatogonia, Sertoli cells, and sperm. Furthermore, MC-LR and NaNO2 reduced sperm density with a synergistic effect. In addition, MC-LR and NaNO2 synergistically induced oxidative stress in the reproductive system by decreasing superoxide dismutase (SOD) activity and glutathione (GSH) levels and increasing levels of mitochondrial reactive oxygen species (mtROS) and reactive oxygen species (ROS). More importantly, mitoquidone mesylate (MitoQ), an inhibitor of mtROS, blocked MC-LR and NaNO2-induced spermatogonia and Sertoli cell apoptosis by inhibiting high expression of Bax, Fadd, Caspase-8, and cleaved-Caspase-3. On the other hand, MitoQ suppressed pyroptosis of Sertoli cells by inhibiting the expression of NLRP3, N-GSDMD, and cleaved-Caspase-1. Additionally, MitoQ alleviated co-exposure-induced sperm density reduction and organ index disorders in F1 generation mice. Together, co-exposure of MC-LR and NaNO2 can enhance spermatogenic disorders by mitochondrial oxidative impairment-mediated germ cell death. This study emphasizes the potential risks of MC-LR and NaNO2 on reproduction in realistic environments and highlights new insights into the cause and treatment of spermatogenic disorders.

Environmental cadmium inhibits testicular testosterone synthesis via Parkin-dependent MFN1 degradation

Low testosterone (T) levels are associated with many common diseases, such as obesity, male infertility, depression, and cardiovascular disease. It is well known that environmental cadmium (Cd) exposure can induce T decline, but the exact mechanism remains unclear. We established a murine model in which Cd exposure induced testicular T decline. Based on the model, we found Cd caused mitochondrial fusion disorder and Parkin mitochondrial translocation in mouse testes. MFN1 overexpression confirmed that MFN1-dependent mitochondrial fusion disorder mediated the Cd-induced T synthesis suppression in Leydig cells. Further data confirmed Cd induced the decrease of MFN1 protein by increasing ubiquitin degradation. Testicular specific Parkin knockdown confirmed Cd induced the ubiquitin-dependent degradation of MFN1 protein through promoting Parkin mitochondrial translocation in mouse testes. Expectedly, testicular specific Parkin knockdown also mitigated testicular T decline. Mito-TEMPO, a targeted inhibitor for mitochondrial reactive oxygen species (mtROS), alleviated Cd-caused Parkin mitochondrial translocation and mitochondrial fusion disorder. As above, Parkin mitochondrial translocation induced mitochondrial fusion disorder and the following T synthesis repression in Cd-exposed Leydig cells. Collectively, our study elucidates a novel mechanism through which Cd induces T decline and provides a new treatment strategy for patients with androgen disorders.

Melatonin counteracts cadmium-induced rat testicular toxicity via the mechanistic target rapamycin (mTOR) pathway

The protective action of melatonin (MLT) against the harmful effects of cadmium (Cd) on testicular activity in rats has been documented previously; however, the involved molecular mechanisms have yet to be elucidated. Herein, we investigate the involvement of the mammalian target of rapamycin (mTOR) on the ability of MLT to counteract the damage induced by Cd on the rat testicular activity. Our study confirmed that Cd has harmful effects on the testes of rats and the protective action exerted by MLT. We reported, for the first time, that the addition of rapamycin (Rapa), a specific mTOR inhibitor, to animals co-treated with Cd and MLT completely abolished the beneficial effects exerted by MLT, indicating that the mTOR pathway partially modulates its helpful effects on Cd testicular toxicity. Interestingly, Rapa-alone treatment, provoking mTOR inhibition, produced altered morphological parameters, increased autophagy of germ and somatic cells, and reduced serum testosterone concentration. In addition, mTOR inhibition also reduced protein levels of markers of steroidogenesis (3β-Hydroxysteroid dehydrogenase) and blood-testis barrier integrity (occludin and connexin 43). Finally, Rapa altered sperm parameters as well as the ability of mature spermatozoa to perform a proper acrosome reaction. Although further investigation is needed to better clarify the molecular pathway involved in MLT action, we confirm that MLT alleviating Cd effects can be used as a supplement to enhance testicular function and improve male gamete quality.

Multigenerational paternal obesity enhances the susceptibility to male subfertility in offspring via Wt1 N6-methyladenosine modification

There is strong evidence that obesity is a risk factor for poor semen quality. However, the effects of multigenerational paternal obesity on the susceptibility to cadmium (a reproductive toxicant)-induced spermatogenesis disorders in offspring remain unknown. Here, we show that, in mice, spermatogenesis and retinoic acid levels become progressively lower as the number of generations exposed to a high-fat diet increase. Furthermore, exposing several generations of mice to a high fat diet results in a decrease in the expression of Wt1, a transcription factor upstream of the enzymes that synthesize retinoic acid. These effects can be rescued by injecting adeno-associated virus 9-Wt1 into the mouse testes of the offspring. Additionally, multigenerational paternal high-fat diet progressively increases METTL3 and Wt1 N6-methyladenosine levels in the testes of offspring mice. Mechanistically, treating the fathers with STM2457, a METTL3 inhibitor, restores obesity-reduced sperm count, and decreases Wt1 N6-methyladenosine level in the mouse testes of the offspring. A case-controlled study shows that human donors who are overweight or obese exhibit elevated N6-methyladenosine levels in sperm and decreased sperm concentration. Collectively, these results indicate that multigenerational paternal obesity enhances the susceptibility of the offspring to spermatogenesis disorders by increasing METTL3-mediated Wt1 N6-methyladenosine modification.

Methyltransferase-like 3 mediated RNA m6 A modifications in the reproductive system: Potentials for diagnosis and therapy

Several studies have highlighted the functional indispensability of methyltransferase-like 3 (METTL3) in the reproductive system. However, a review that comprehensively interprets these studies and elucidates their relationships is lacking. Therefore, the present work aimed to review studies that have investigated the functions of METTL3 in the reproductive system (including spermatogenesis, follicle development, gametogenesis, reproductive cancer, asthenozoospermia and assisted reproduction failure). This review suggests that METTL3 functions not only essential for normal development, but also detrimental in the occurrence of disorders. In addition, promising applications of METTL3 as a diagnostic or prognostic biomarker and therapeutic target for reproductive disorders have been proposed. Collectively, this review provides comprehensive interpretations, novel insights, potential applications and future perspectives on the role of METTL3 in regulating the reproductive system, which may be a valuable reference for researchers and clinicians.

Like father, like daughter:Paternal cadmium exposure causes hepatic glucose metabolic disorder and phospholipids accumulation in adult female offspring

Cadmium (Cd), is a well-known reproductive toxicant. The impacts of paternal Cd exposure on offspring glucose and lipid metabolism remain unclear, despite the abundance of adverse reports following early exposure from the mother. Here, we assessed paternally acquired metabolic derailment using a mouse model. LC-MS/MS, transcriptomics and molecular experimental techniques were subsequently applied in this study to explore the potential mechanism. We found that paternal Cd exposure caused glucose intolerance, lower insulin sensitivity and abnormal hepatic glycogen storage in adult female offspring, but not in males. LC-MS/MS data showed that hepatic phospholipids accumulation was also only observed in adult female offspring after paternal Cd exposure. Gene expression data showed that the level of insulin signaling and lipid transport-related genes was decreased in Cd-treated adult female offspring livers. Meanwhile, AHR, a transcription factor that combines with phospholipids to promote insulin resistance, was increased in Cd-treated adult female offspring livers. In addition, the escalation of the afore-mentioned lipid metabolites in the liver occurred as early as fetal stages in the female pups following paternal Cd exposure, suggesting the potential for these lipid species to be selected as early markers of disease for metabolic derailment later in life. Altogether, paternal Cd exposure causes offspring glucose metabolism disorder and phospholipids accumulation in a sex-dependent manner. This study provides a theoretical framework for future understanding of paternal-originated metabolic diseases.

Sperm Rhoa m6A modification mediates intergenerational transmission of paternally acquired hippocampal neuronal senescence and cognitive deficits after combined exposure to environmental cadmium and high-fat diet in mice

Little is currently known about the effect and mechanism of combined paternal environmental cadmium (Cd) and high-fat diet (HFD) on offspring cognitive ability. Here, using in vivo model, we found that combined paternal environmental Cd and HFD caused hippocampal neuronal senescence and cognitive deficits in offspring. MeRIP-seq revealed m6A level of Rhoa, a regulatory gene of cellular senescence, was significantly increased in combined environmental Cd and HFD-treated paternal sperm. Interestingly, combined paternal environmental Cd and HFD markedly enhanced Rhoa mRNA, its m6A and reader protein IGF2BP1 in offspring hippocampus. STM2457, the inhibitor of m6A modification, markedly mitigated paternal exposure-caused the elevation of hippocampal Rhoa m6A, neuronal senescence and cognitive deficits in offspring. In vitro experiments, Rhoa siR significantly reversed mouse hippocampal neuronal senescence. Igf2bp1 siR obviously reduced the level and stability of Rhoa in aging mouse hippocampal neuronal cells. In conclusion, combined paternal environmental Cd and HFD induce offspring hippocampal neuronal senescence and cognitive deficits by promoting IGF2BP1-mediated Rhoa stabilization in offspring hippocampus via elevating Rhoa m6A in paternal sperm.

Emerging Roles for DNA 6mA and RNA m6A Methylation in Mammalian Genome

Epigenetic methylation has been shown to play an important role in transcriptional regulation and disease pathogenesis. Recent advancements in detection techniques have identified DNA N6-methyldeoxyadenosine (6mA) and RNA N6-methyladenosine (m6A) as methylation modifications at the sixth position of adenine in DNA and RNA, respectively. While the distributions and functions of 6mA and m6A have been extensively studied in prokaryotes, their roles in the mammalian brain, where they are enriched, are still not fully understood. In this review, we provide a comprehensive summary of the current research progress on 6mA and m6A, as well as their associated writers, erasers, and readers at both DNA and RNA levels. Specifically, we focus on the potential roles of 6mA and m6A in the fundamental biological pathways of the mammalian genome and highlight the significant regulatory functions of 6mA in neurodegenerative diseases.

Loss of Atg5 in Sertoli cells enhances the susceptibility of cadmium-impaired testicular spermatogenesis in mice

Cadmium (Cd), one of the most common contaminants in diet and drinking water, impairs testicular germ cell development and spermatogenesis. Autophagy is essential for maintaining Sertoli cell function and Sertoli-germ cell communication. However, the role of Sertoli cell autophagy in Cd-caused spermatogenesis disorder remains unclear. Here, the mice of autophagy-related gene 5 (Atg5) knockouts in Sertoli cells were used to investigate the effect of autophagy deficiency on Cd-impaired spermatogenesis and its underlying mechanisms. Results showed that Sertoli cell-specific knockout of Atg5 exacerbated Cd-reduced sperm count and MVH (a specific marker for testicular germ cells) level in mice. Additionally, Sertoli cell Atg5 deficiency reduced the number of spermatocytes and decreased the level of meiosis-related proteins (SYCP3 and STRA8) in Cd-treated mouse testes. Loss of Atg5 in Sertoli cell exacerbated Cd-reduced the level of retinoic acid (RA) and retinal dehydrogenase (ALDH1A1 and ALDH1A) in mouse testes. Meanwhile, we found that the level of transcription factor WT1 was significantly downregulated in Atg5-/- plus Cd-treated testes. Further experiments showed that Wt1 overexpression restored Cd-decreased the levels of ALDH1A1 in Sertoli cells. Collectively, the above data suggest that knockout of Atg5 in Sertoli cell enhances the susceptibility of Cd-impaired testicular spermatogenesis. These findings provide new insights into autophagy of Sertoli cell preventing environmental toxicants-impaired testicular spermatogenesis.

METTL3-mediated m6A mRNA modification was involved in cadmium-induced liver injury

Cadmium is an environmental pollutant that has extensive deleterious effects. However, the mechanisms underlying the hepatotoxicity induced by long-term exposure to cadmium remained undefined. In the present study, we explored the role of m6A methylation in the development of cadmium-induced liver disease. We showed a dynamic change of RNA methylation in liver tissue from mice administrated with cadmium chloride (CdCl2) for 3, 6 and 9 months, respectively. Particularly, the METTL3 expression was declined in a time-dependent manner, associated with the degree of liver injury, indicating the involvement of METTL3 in hepatotoxicity induced by CdCl2. Moreover, we established a mouse model with liver-specific over-expression of Mettl3 and administrated these mice with CdCl2 for 6 months. Notably, METTL3 highly expressed in hepatocytes attenuated CdCl2-induced steatosis and liver fibrosis in mice. In vitro assay also showed METTL3 overexpression ameliorated the CdCl2-induced cytotoxicity and activation of primary hepatic stellate cells. Furthermore, transcriptome analysis identified 268 differentially expressed genes both in mice liver tissue treated with CdCl2 for 3 months and 9 months. Among them, 115 genes were predicted to be regulated by METTL3 determined by m6A2Target database. Further analysis revealed the perturbation of metabolic pathway, glycerophospholipid metabolism, ErbB signaling pathway, Hippo signaling pathway, and choline metabolism in cancer, and circadian rhythm, led to hepatotoxicity induced by CdCl2. Collectively, our findings reveal new insight into the crucial role of epigenetic modifications in hepatic diseases caused by long-term exposure to cadmium.

Evidence of the protective role of D-Aspartate in counteracting/preventing cadmium-induced oxidative stress in the rat testis

Cadmium (Cd), by producing oxidative stress and acting as an endocrine disruptor, is known to cause severe testicular injury, documented by histological and biomolecular alterations, such as decreased serum testosterone (T) level and impairment of spermatogenesis. This is the first report on the potential counteractive/preventive action of D-Aspartate (D-Asp), a well-known stimulator of T biosynthesis and spermatogenesis progression by affecting hypothalamic-pituitary-gonadal axis, in alleviating Cd effects in the rat testis. Our results confirmed that Cd affects testicular activity, as documented by the reduction of serum T concentration and of the protein levels of steroidogenesis (StAR, 3β-HSD, and 17β-HSD) and spermatogenesis (PCNA, p-H3, and SYCP3) markers. Moreover, higher protein levels of cytochrome C and caspase 3, together with the number of cells positive to TUNEL assay, indicated the intensification of the apoptotic process. D-Asp administered either simultaneously to Cd, or for 15 days before the Cd-treatment, reduced the oxidative stress induced by the metal, alleviating the consequent harmful effects. Interestingly, the preventive action of D-Asp was more effective than its counteractive effect. A possible explanation is that giving D-Asp for 15 days induces its significant uptake in the testes, reaching the concentrations necessary for optimum function. In summary, this report highlights, for the first time, the beneficial role played by D-Asp in both counteracting/preventing the adverse Cd effects in the rat testis, strongly encouraging further investigations to consider the potential value of D-Asp also in improving human testicular health and male fertility.