Environmental epigenetics and effects on male fertility

Ti3C2 (MXene) nanosheets disrupt spermatogenesis in male mice mediated by the ATM/p53 signaling pathway

BACKGROUND

Two-dimensional ultrathin Ti₃C₂ nanosheets are increasingly being used in biomedical applications owing to their special physicochemical properties. But, the biological effects of its exposure on the reproductive system is still unclear. This study evaluated the reproductive toxicity of Ti₃C₂ nanosheets in the testes.

RESULTS

Ti₃C₂ nanosheets at doses of 2.5 mg/kg bw and 5 mg/kg bw in mice caused defects in spermatogenic function, and we also clarified an underlying molecular mechanism of it in vivo and in vitro model. Ti₃C₂ nanosheets induced an increase of reactive oxygen species (ROS) in testicular and GC-1 cells, which in turn led to the imbalance in oxidative and antioxidant systems (also known as oxidative stress). Additionally, oxidative stress often induces cellular DNA strand damages via the oxidative DNA damages, which triggered cell cycle arrest in the G1/G0 phase, leading to cell proliferation inhibition and irreversible apoptosis. ATM/p53 signaling manifest key role in DNA damage repair (DDR), and we demonstrate that ATM/p53 signaling was activated, and mediated the toxic damage process caused by Ti₃C₂ nanosheet exposure.

CONCLUSION

Ti₃C₂ nanosheet-induced disruption of proliferation and apoptosis of spermatogonia perturbed normal spermatogenic function that was mediated by ATM/p53 signaling pathway. Our findings shed more light on the mechanisms of male reproductive toxicity induced by Ti₃C₂ nanosheets.

Single-cell transcriptomics allows novel insights into the endocrine-disrupting chemicals induced mammalian reproductive disorder

Increasing environmental pollution has led to the spread of many endocrine-disrupting chemicals (EDCs) around the world, which are toxic substances in the form of compounds that pose a great threat to the reproductive health of mammals and become a potential cause of many reproductive function-related diseases. In the past decade, the rapid development of single-cell RNA sequencing (scRNA-seq) technology has greatly promoted the study of the toxic mechanisms of EDCs in the mammalian reproductive system, including DEHP, ZEN, BPA, and BDE47. These studies aim to resolve the interference of EDCs in critical stages of reproductive development, including prepubertal and pubertal in males, meiosis I and early follicle formation in females. This paper introduces the sequencing process and analysis methods of current mainstream scRNA-seq technology, systematically reviews the outstanding contributions and specific research ideas of this technology in the study of reproductive system toxicity, lists representative cases of using this technology to explore reproductive damage caused by EDCs, and summarizes in detail the connection between environmental pollution and reproductive development disorders. It provides an important theoretical basis and direction for further exploring the mechanism of damage to the physiological functions of toxic substances on the reproductive system and the prevention and treatment of reproductive diseases.

Transcriptomic and epigenomic profiling of young and aged spermatogonial stem cells reveals molecular targets regulating differentiation

Spermatogonial stem cells (SSC), the foundation of spermatogenesis and male fertility, possess lifelong self-renewal activity. Aging leads to the decline in stem cell function and increased risk of paternal age-related genetic diseases. In the present study, we performed a comparative genomic analysis of mouse SSC-enriched undifferentiated spermatogonia (Oct4-GFP+/KIT-) and differentiating progenitors (Oct4-GFP+/KIT+) isolated from young and aged testes. Our transcriptome data revealed enormous complexity of expressed coding and non-coding RNAs and alternative splicing regulation during SSC differentiation. Further comparison between young and aged undifferentiated spermatogonia suggested these differentiation programs were affected by aging. We identified aberrant expression of genes associated with meiosis and TGF-β signaling, alteration in alternative splicing regulation and differential expression of specific lncRNAs such as Fendrr. Epigenetic profiling revealed reduced H3K27me3 deposition at numerous pro-differentiation genes during SSC differentiation as well as aberrant H3K27me3 distribution at genes in Wnt and TGF-β signaling upon aging. Finally, aged undifferentiated spermatogonia exhibited gene body hypomethylation, which is accompanied by an elevated 5hmC level. We believe this in-depth molecular analysis will serve as a reference for future analysis of SSC aging.

Dysfunction in Sertoli cells participates in glucocorticoid-induced impairment of spermatogenesis

The effect of stress on male fertility is a widespread public health issue, but less is known about the related signaling pathway. To investigate this, we established a hypercortisolism mouse model by supplementing the drinking water with corticosterone for four weeks. In the hypercortisolism mice, the serum corticosterone was much higher than in the control, and serum testosterone was significantly decreased. Moreover, corticosterone treatment induced decrease of sperm counts and increase of teratozoospermia. Increased numbers of multinucleated giant cells and apoptotic germ cells as well as downregulated meiotic markers suggested that corticosterone induced impaired spermatogenesis. Further, upregulation of macrophage-specific marker antigen F4/80 as well as inflammation-related genes suggested that corticosterone induced inflammation in the testis. Lactate content was found to be decreased in the testis and Sertoli cells after corticosterone treatment, and lactate metabolism-related genes were downregulated. In vitro phagocytosis assays showed that the phagocytic activity in corticosterone-treated Sertoli cells was downregulated and accompanied by decreased mitochondrial membrane potential, while pyruvate dehydrogenase kinase-4 inhibitor supplementation restored this process. Taken together, our results demonstrated that dysfunctional phagocytosis capacity and lactate metabolism in Sertoli cells participates in corticosterone-induced impairment of spermatogenesis.

Environmental pollutants exposure and male reproductive toxicity: The role of epigenetic modifications

Male fertility rates have shown a progressive decrease in recent decades. There is a growing concern about the male reproductive dysfunction caused by environmental pollutants exposure, however the underlying molecular mechanisms are still not well understood. Epigenetic modifications play a key role in the biological responses to external stressors. Therefore, this review discusses the roles of epigenetic modifications in male reproductive toxicity induced by environmental pollutants, with a particular emphasis on DNA methylation, histone modifications and miRNAs. The available literature proposed that environmental pollutants can directly or cause oxidative stress and DNA damage to induce a variety of epigenetic changes, which lead to gene dysregulation, mitochondrial dysfunction and consequent male reproductive toxicity. However, future studies focusing on more kinds of epigenetic modifications and their crosstalk as well as epidemiological data are still required to fill in the current research gaps. In addition, the intrinsic links between pollutants-mediated epigenetic regulations and male reproduction-related physiological responses deserve to be further explored.

Improvement of Qilin pills on male reproductive function in tripterygium glycoside-induced oligoasthenospermia in rats

This study established an oligoasthenospermic rat model using tripterygium glycosides (TGs) and investigated the mechanism by which Qilin pills (QLPs) ameliorate reproductive hypofunction. Thirty-two male Sprague Dawley rats were allocated to four equal-sized groups: (1) the control group received continuous physiological levels of saline; (2) the oligoasthenospermia model group was induced with TGs by daily intragastric administration for 28 days; (3 and 4) oligoasthenospermic rats were treated intragastrically with low dose (1.62 g kg^-1  d^-1 ) and high dose (3.24 g kg^-1  d^-1 ) of QLPs once daily for 60 days. The QLP-treated rats showed a marked increase (p < .05) in testicular mass, testicular index and semen parameters compared with the untreated rats. Histopathologically, the QLP-treated groups exhibited restored seminiferous tubules in contrast to the model group. Reactive oxygen species and malondialdehyde levels were dramatically decreased (p < .05) in the testes of the QLP-treated rats. QLP treatment partly reverted (p < .05) the circulatory levels of reproductive hormones (FSH, LH, testosterone, prolactin and SHBG) and hepatic and renal function (AST, Cr and urea). Our results showed that oral QLP treatment had a curative effect on the testicular mass, sperm quality, testicular pathomorphology, antioxidants, plasmatic hormones, and liver and renal function of rats.

Antioxidant-Based Therapies in Male Infertility: Do We Have Sufficient Evidence Supporting Their Effectiveness?

Under physiological conditions, reactive oxygen species (ROS) play pivotal roles in various processes of human spermatozoa. Indeed, semen requires the intervention of ROS to accomplish different stages of its maturation. However, ROS overproduction is a well-documented phenomenon occurring in the semen of infertile males, potentially causing permanent oxidative damages to a vast number of biological molecules (proteins, nucleic acids, polyunsaturated fatty acids of biological membrane lipids), negatively affecting the functionality and vitality of spermatozoa. ROS overproduction may concomitantly occur to the excess generation of reactive nitrogen species (RNS), leading to oxidative/nitrosative stress and frequently encountered in various human pathologies. Under different conditions of male infertility, very frequently accompanied by morpho-functional anomalies in the sperm analysis, several studies have provided evidence for clear biochemical signs of damages to biomolecules caused by oxidative/nitrosative stress. In the last decades, various studies aimed to verify whether antioxidant-based therapies may be beneficial to treat male infertility have been carried out. This review analyzed the results of the studies published during the last ten years on the administration of low-molecular-weight antioxidants to treat male infertility in order to establish whether there is a sufficient number of data to justify antioxidant administration to infertile males. An analysis of the literature showed that only 30 clinical studies tested the effects of the administration of low-molecular-weight antioxidants (administered as a single antioxidant or as a combination of different antioxidants with the addition of vitamins and/or micronutrients) to infertile males. Of these studies, only 33.3% included pregnancy and/or live birth rates as an outcome measure to determine the effects of the therapy. Of these studies, only 4 were case–control studies, and only 2 of them found improvement of the pregnancy rate in the group of antioxidant-treated patients. Additionally, of the 30 studies considered in this review, only 43.3% were case–control studies, 66.7% enrolled a number of patients higher than 40, and 40% carried out the administration of a single antioxidant. Therefore, it appears that further studies are needed to clearly define the usefulness of antioxidant-based therapies to treat male infertility.

"It's Never Too Early": Preconception Care and Postgenomic Models of Life

In this article, we are concerned with the expanded public health interest in the "preconception period" as a window of opportunity for intervention to improve long-term population health outcomes. While definitions of the "preconception period" remain vague, new classifications and categories of life are becoming formalized as biomedicine begins to conduct research on, and suggest intervention in, this undefined and potentially unlimited time before conception. In particular, we focus on the burgeoning epidemiological interest in epigenetics and Developmental Origins of Health and Disease (DOHaD) research as simultaneously a theoretical spyglass into postgenomic biology and a catalyst toward a public health focus on preconception care. We historicize the notion that there are long-term implications of parental behaviors before conception, illustrating how, as Han and Das have noted, "newness comes to be embedded in older forms even as it transforms them" (Han and Das, 2015, p. 2). We then consider how DOHaD frameworks justify a number of fragmented claims about preconception by making novel evidentiary assertions. Engaging with the philosophy of Georges Canguilhem, we examine the relationship between reproductive risk and revised understandings of biological permeability, and discuss some of the epistemic and political implications of emerging claims in postgenomics.

Histone Post-Translational Modifications and CircRNAs in Mouse and Human Spermatozoa: Potential Epigenetic Marks to Assess Human Sperm Quality

Spermatozoa (SPZ) are motile cells, characterized by a cargo of epigenetic information including histone post-translational modifications (histone PTMs) and non-coding RNAs. Specific histone PTMs are present in developing germ cells, with a key role in spermatogenic events such as self-renewal and commitment of spermatogonia (SPG), meiotic recombination, nuclear condensation in spermatids (SPT). Nuclear condensation is related to chromatin remodeling events and requires a massive histone-to-protamine exchange. After this event a small percentage of chromatin is condensed by histones and SPZ contain nucleoprotamines and a small fraction of nucleohistone chromatin carrying a landascape of histone PTMs. Circular RNAs (circRNAs), a new class of non-coding RNAs, characterized by a nonlinear back-spliced junction, able to play as microRNA (miRNA) sponges, protein scaffolds and translation templates, have been recently characterized in both human and mouse SPZ. Since their abundance in eukaryote tissues, it is challenging to deepen their biological function, especially in the field of reproduction. Here we review the critical role of histone PTMs in male germ cells and the profile of circRNAs in mouse and human SPZ. Furthermore, we discuss their suggested role as novel epigenetic biomarkers to assess sperm quality and improve artificial insemination procedure.

We, the developing rete testis, efferent ducts, and Wolffian duct, all hereby agree that we need to connect

BACKGROUND

The mechanisms by which the rete testis joins the efferent ducts, which joins the Wolffian duct during development, are not known. Mouse and chick models have been helpful in identifying genes that are important for the development of each part, but genes have not been identified as to those that play a role in the joining of each part. Clinical implications of the failure of the male reproductive tract to form a fully functional conduit for spermatozoa are not trivial. Epididymal disjunction, the failure of the efferent ducts to join the testis, is one of several epididymal anomalies that have been observed in some boys who were cryptorchid at birth.

OBJECTIVE

A systematic review of studies focusing on the morphogenesis of the mesonephric duct and mesonephric tubules in different species, and identification of clinical issues should there be failure of these tissues to develop.

DESIGN

PubMed and GUDMAP databases, and review of books on kidney development were searched for studies reporting on the mechanisms of morphogenesis of the kidney and epididymis.

MAIN OUTCOMES MEASURE(S)

Gaps in our knowledge were identified, and hypotheses coupled with suggestions for future experiments were presented.

RESULTS

A total of 64 papers were identified as relevant, of which 53 were original research articles and 11 were book chapters and reviews covering morphogenesis and clinical issues. Investigators utilized multiple species including, human, mouse, chick, Xenopus, bovine, and sheep.

CONCLUSION

Fundamental understanding of the morphogenesis of the male reproductive tract is limited, especially the morphogenesis of the rete testis and efferent ducts. Therefore, it is not surprising that we do not understand how each part unites to form a whole. Only one mechanism of joining of one part of the tract to another was identified: the joining of the Wolffian duct to the cloaca via controlled apoptosis.

Epigenetics in male reproduction: effect of paternal diet on sperm quality and offspring health

Epigenetic inheritance and its underlying molecular mechanisms are among the most intriguing areas of current biological and medical research. To date, studies have shown that both female and male germline development follow distinct paths of epigenetic events and both oocyte and sperm possess their own unique epigenomes. Fertilizing male and female germ cells deliver not only their haploid genomes but also their epigenomes, which contain the code for preimplantation and postimplantation reprogramming and embryonal development. For example, in spermatozoa, DNA methylation profile, DNA-associated proteins, protamine 1:protamine 2 ratio, nucleosome distribution pattern, histone modifications and other properties make up a unique epigenetic landscape. However, epigenetic factors and mechanisms possess certain plasticity and are affected by environmental conditions. Paternal and maternal lifestyle, including physical activity, nutrition and exposure to hazardous substances, can alter the epigenome and, moreover, can affect the health of their children. In male reproductive health, data are emerging on epigenetically mediated effects of a man's diet on sperm quality, for example through phytochemicals, minerals and vitamins, and nutritional support for subfertile men is already being used. In addition, studies in animal models and human epidemiological data point toward a transgenerational effect of the paternally contributed sperm epigenome on offspring health.

Decreased activity of superoxide dismutase in the seminal plasma of infertile men correlates with increased sperm deoxyribonucleic acid fragmentation during the first hours after sperm donation

Sperm DNA fragmentation varies between individuals and is more pronounced with increased patient age and time after sperm donation. The intensification of DNA fragmentation depends on the balance of the oxidoreductive system, which is regulated mainly by two enzymes - superoxide dismutase (SOD) and catalase. The objective of this study was to determine the relationship between sperm DNA fragmentation dynamics, fertility and seminal SOD and catalase activity. The study was conducted in 2013 and 2014 at the Non-Public Health Care Unit 'Ovum Reproduction and Andrology' in Lublin, Lublin, Poland, and covered 218 men aged 25-35 (85 fertile and 133 patients treated for infertility). Percentage of fragmented DNA was measured in a modified chromatin dispersion test at four time points after sperm donation (t = 0, 3, 6, 12 h). SOD and catalase activities were determined spectrophotometrically. We confirmed that the activity of SOD in the seminal plasma of men with reproductive disorders was lower compared with fertile men. Conversely, no significant correlations were found between fertility and catalase activity. Sperm DNA of infertile males was initially more fragmented than fertile male sperm DNA. SOD and catalase activity did not correlate with the degree of DNA fragmentation in fertile men. In men with reproductive disorders, the rate of DNA fragmentation was slow within first 3 h after sperm donation and then increased between 6 and 12 h. In this group of infertile men, those with higher SOD activity had a lower DNA fragmentation index (DFI) after 12 h, and a reduced rate of intensity of fragmentation from 6 to 12 h. Alternatively, higher catalase activity among men treated for infertility was accompanied by higher initial DFI and higher rate of DNA fragmentation from 6 to 12 h. These results highlight the importance of determining a proper time window between sperm donation and procedures of assisted reproductive technology.

Effects of the environmental estrogenic contaminants bisphenol A and 17α-ethinyl estradiol on sexual development and adult behaviors in aquatic wildlife species

Endocrine disrupting chemicals (EDCs), including the mass-produced component of plastics, bisphenol A (BPA) are widely prevalent in aquatic and terrestrial habitats. Many aquatic species, such as fish, amphibians, aquatic reptiles and mammals, are exposed daily to high concentrations of BPA and ethinyl estradiol (EE2), estrogen in birth control pills. In this review, we will predominantly focus on BPA and EE2, well-described estrogenic EDCs. First, the evidence that BPA and EE2 are detectable in almost all bodies of water will be discussed. We will consider how BPA affects sexual and neural development in these species, as these effects have been the best characterized across taxa. For instance, such chemicals have been in many cases reported to cause sex-reversal of males to females. Even if these chemicals do not overtly alter the gonadal sex, there are indications that several EDCs might demasculinize male-specific behaviors that are essential for attracting a mate. In so doing, these chemicals may reduce the likelihood that these males reproduce. If exposed males do reproduce, the concern is that they will then be passing on compromised genetic fitness to their offspring and transmitting potential transgenerational effects through their sperm epigenome. We will thus consider how diverse epigenetic changes might be a unifying mechanism of how BPA and EE2 disrupt several processes across species. Such changes might also serve as universal species diagnostic biomarkers of BPA and other EDCs exposure. Lastly, the evidence that estrogenic EDCs-induced effects in aquatic species might translate to humans will be considered.

Transgenerational effects from early developmental exposures to bisphenol A or 17α-ethinylestradiol in medaka, Oryzias latipes

The transgenerational consequences of environmental contaminant exposures of aquatic vertebrates have the potential for broad ecological impacts, yet are largely uninvestigated. Bisphenol A (BPA) and 17α-ethinylestradiol (EE2) are two ubiquitous estrogenic chemicals present in aquatic environments throughout the United States and many other countries. Aquatic organisms, including fish, are exposed to varying concentrations of these chemicals at various stages of their life history. Here, we tested the ability of embryonic exposure to BPA or EE2 to cause adverse health outcomes at later life stages and transgenerational abnormalities in medaka fish. Exposures of F0 medaka to either BPA (100 μg/L) or EE2 (0.05 μg/L) during the first 7 days of embryonic development, when germ cells are differentiating, did not cause any apparent phenotypic abnormalities in F0 or F1 generations, but led to a significant reduction in the fertilization rate in offspring two generations later (F2) as well as a reduction of embryo survival in offspring three generations later (F3). Our present observations suggest that BPA or EE2 exposure during development induces transgenerational phenotypes of reproductive impairment and compromised embryonic survival in fish of subsequent generations. These adverse outcomes may have negative impacts on populations of fish inhabiting contaminated aquatic environments.

Environmentally induced epigenetic transgenerational inheritance of male infertility

Decreasing male fertility has been observed for the past fifty years. Examples of affected reproductive parameters include decreases in sperm count and sperm quality and increases in testicular cancer, cryptorchidism and hypospadias. Exposures to environmental toxicants during fetal development and early postnatal life have been shown to promote infertility. Environmental exposures inducing epigenetic changes related to male infertility range from life style, occupational exposures, environmental toxicants and nutrition. Exposures during fetal gonadal sex determination have been shown to alter the epigenetic programming of the germline that then can transmit this altered epigenetic information to subsequent generations in the absence of any exposures. This environmentally induced epigenetic transgenerational inheritance of disease will be a component of the etiology of male infertility.