Male obesity impacts DNA methylation reprogramming in sperm

Isoform-resolution single-cell RNA sequencing reveals the transcriptional panorama of adult Baoshan pig testis cells

BACKGROUND

As the primary organ of the male reproductive system, the testis facilitates spermatogenesis and androgen secretion. Due to the complexity of spermatogenesis, elucidating cellular heterogeneity and gene expression dynamics within the porcine testis is critical for advancing reproductive biology. Nevertheless, the cellular composition and regulatory mechanisms of porcine testes remain insufficiently characterized. In this study, we applied integrated long-read (Nanopore) and short-read (Illumina) scRNA-seq to Baoshan pig testes, establishing a comprehensive transcriptional profile to delineate cellular heterogeneity and molecular regulation.

RESULTS

Through systematic analysis of testicular architecture and the temporal progression of spermatogenesis, we characterized 11,520 single cells and 23,402 genes, delineating germ cell developmental stages: proliferative-phase spermatogonia (SPG), early-stage spermatocytes (Early SPC) and late-stage spermatocytes (Late SPC) during meiosis, and spermiogenic-phase round spermatids (RS) followed by elongating/elongated spermatids (ES), culminating in mature spermatozoa (Sperm). We further identified nine distinct testicular cell types, with germ cells spanning all developmental stages and somatic components comprising Sertoli cells, macrophages, and peritubular myoid cells as microenvironmental constituents, revealing the cellular heterogeneity of testicular tissue and dynamic characteristics of spermatogenesis. We obtained the dynamic expression changes of 16 vital marker genes during spermatogenesis and performed immunofluorescence validation on 7 marker genes. Gene ontology analysis revealed that germ cells at various stages were involved in specific biological processes, while cell communication networks highlighted eight pivotal signaling pathways, including MIF, NRG, WNT, VEGF, BMP, CCL, PARs, and ENHO pathways. Long-read sequencing further captured the full integrity and diversity of RNA transcripts, identifying 60% of the novel annotated isoforms and revealing that FSM isoforms exhibited longer transcript lengths, longer coding sequences, longer open reading frames, and a great number of exons, suggesting the complexity of isoforms within the testicular microenvironment.

CONCLUSIONS

Our results provide insight into the cellular heterogeneity, intercellular communication, and gene expression/transcript diversity in porcine testes, and offer a valuable resource for understanding the molecular mechanisms of porcine spermatogenesis.

In vitro fertilization induces reproductive changes in male mouse offspring and has multigenerational effects

In vitro fertilization (IVF) is a noncoital method of conception used to treat human infertility. Although IVF is viewed as largely safe, it is associated with adverse outcomes in the fetus, placenta, and adult offspring. Because studies focusing on the effect of IVF on the male reproductive system are limited, we used a mouse model to assess the morphological and molecular effects of IVF on male offspring. We evaluated 3 developmental stages: 18.5-day fetuses and 12- and 39-week-old adults. Regardless of age, we observed changes in testicular-to-body weight ratios, serum testosterone levels, testicular morphology, gene expression, and DNA methylation. Also, sperm showed changes in morphology and DNA methylation. To assess multigenerational phenotypes, we mated IVF-conceived and naturally conceived males with wild-type females. Offspring from IVF males exhibited decreased fetal-to-placental weight ratios and changes in placenta gene expression and morphology regardless of sex. At 12 weeks of age, offspring showed higher body weights and differences in glucose, triglyceride, insulin, total cholesterol, HDL-C, and LDL/VLDL-C levels. Both sexes showed changes in gene expression in liver, testes, and ovaries and decreased global DNA methylation. Collectively, our findings demonstrate that male IVF offspring exhibit abnormal testicular and sperm morphology and molecular alterations with a multigenerational impact.

Integrative Molecular and Functional Analysis of Human Sperm Subpopulations to Identify New Biomarkers of Fertilization Potential

BACKGROUND

Human ejaculates are composed of sperm subsets with heterogeneous characteristics. Comparative studies of sperm subpopulations with differences in motility may serve to investigate the functional and molecular features that are crucial for reaching the oocyte and fertilizing.

OBJECTIVE

To identify functional and molecular markers that characterize sperm subpopulations with high and low motility.

MATERIALS AND METHODS

Semen samples from 11 donors with proven fertility were processed by density gradient centrifugation to isolate high (F1) and low (F2) motility sperm subpopulations. Besides motility, we evaluated viability, chromatin integrity, mitochondrial membrane potential, capacitation, and acrosomal status. F1 and F2 were subjected to comparative methylome and transcriptome analyses by whole-genome bisulfite sequencing and RNA sequencing, respectively. Further validation of candidate biomarkers at the RNA and protein levels was performed with semen samples from six normozoospermic volunteers using quantitative PCR and Western blotting.

RESULTS

Spermatozoa from the F1 fractions exhibited higher mitochondrial membrane potential and viability than F2. Comparative methylome and transcriptome analyses of F1 and F2 identified 271 differentially methylated genes and 82 differentially expressed genes. Notably, CEP128 and CSTPP1 were downregulated and differentially methylated in the F2 fraction. Quantitative PCR confirmed the downregulation of these two genes in F2, and the downregulation of CEP128 was further validated at the protein level by Western blotting.

CONCLUSION

F1 spermatozoa are characterized by elevated mitochondrial membrane potential, viability, and higher expression of CEP128 and CSTPP1. Future studies should evaluate the potential of these functional variables and genes as biomarkers of fertility, either individually or in combination.

Lifestyle and Environmental Factors Affecting Male Fertility, Individual Predisposition, Prevention, and Intervention

Current lifestyles bring about an increasing prevalence of unhealthy habits that can negatively affect male fertility. Cigarette smoking, alcohol intake, stress, inadequate physical activity, an unequilibrated diet leading to obesity, and use of mobile telephones and portable electronic devices can affect the male reproductive system through multiple mechanisms. Moreover, the modern man is often exposed to environmental factors independent of his will, such as air pollution, exposure to heat or toxicants in his workplace, or the presence of harmful chemicals in food, beverages, agricultural and industrial products, etc. The susceptibility to these factors depends on genetic and epigenetic predisposition, potentially present systemic disease and medication, and local affections of the genitourinary system. The multifaceted nature of both the causative factors and the susceptibility background makes the resulting fertility disturbance highly individual and variable among different men exposed to the same conditions. This paper critically reviews the current knowledge of different causative and susceptibility factors with a special attention to the molecular mechanisms of their action. Finally, strategies for the prevention of abnormalities due to lifestyle and environmental factors and available treatment modalities for already-present abnormalities are exposed.

Type 2 diabetes impacts DNA methylation in human sperm

AIMS/HYPOTHESIS

Disorders of the reproductive system, including hypogonadism and reduced fertility, are an under-recognized complication of diabetes. Based on experimental data in mice, hyperglycemia and obesity may modify epigenetic marks in sperm and impact health and development of offspring, but data are more limited in humans. Thus, we sought to study the impact of type 2 diabetes and glycemic control on sperm quality and DNA methylation.

METHODS

In this prospective cohort study, we recruited 40 men with BMI greater than 25 kg/m2 including 18 with type 2 diabetes, 6 with prediabetes, and 16 normoglycemic controls. Assessments were repeated after 3 months in 9 men with type 2 diabetes and 7 controls. We analyzed reproductive hormones, sperm concentration and motility, and sperm DNA methylation (MethylationEPIC BeadChip).

RESULTS

Men with type 2 diabetes had higher levels of follicle-stimulating hormone (FSH), but similar testosterone levels and sperm quality as controls. Sperm DNA methylation was stable with repeat sampling at 3 months in men with and without type 2 diabetes. We identified differential methylation at 655 of 745,804 CpG sites in men with type 2 diabetes versus controls (FDR < 0.05). Of these, 96.5% showed higher methylation in type 2 diabetes, with a mean difference in DNA methylation (beta value, β) of 0.16 ± 0.004 (16 ± 0.4%). Ontology analysis of differentially methylated loci revealed annotation to genes regulating synaptic signaling, actin, cAMP-dependent pathways, and G protein-coupled receptor pathways. 24% of probes differentially regulated in men with type 2 diabetes versus control overlapped with probes associated with HbA1c, suggesting additional factors beyond glycemic control contributed to diabetes-associated differences in DNA methylation.

CONCLUSIONS/INTERPRETATION

Men with type 2 diabetes showed higher DNA methylation levels in sperm relative to normoglycemic controls with similar BMI. Whether these differences are reversible with glucose-lowering treatment or may contribute to post-fertilization transcriptional regulation warrants further investigation.

TRIAL REGISTRATION

NCT03860558.

Introducing artificial intelligence and sperm epigenetics in the fertility clinic: a novel foundation for diagnostics and prediction modelling

Worldwide, infertility is a rising problem. A couple's lifestyle, age and environmental exposures can interfere with reproductive health. The scientific field tries to understand the various processes how male and female factors may affect fertility, but translation to the clinic is limited. I here emphasize potential reasons for failure in optimal treatment planning and especially why current prediction modelling falls short. First, Assisted Reproductive Technology (ART) has become a mainstream solution for couples experiencing infertility, while potential causes of infertility remain unexplored or undetermined. For instance, the role of men is generally left out of preconceptional testing and care. Second, regularly used statistical or computational methods to estimate pregnancy outcomes miss important biological and environmental factors, including features from the male side (e.g., age, smoking, obesity status, alcohol use and occupation), as well as genetic and epigenetic characteristics. I suggest using an integrated approach of biostatistics and machine learning methods to improve diagnostics and prediction modelling in the fertility clinic. The novelty of this concept includes the use of empirically collected information on the sperm epigenome combined with readily available data from medical records from both partners and lifestyle factors. As the reproductive field needs well-designed models at different levels, derivatives are needed. The objectives of patients, clinicians, and embryologists differ slightly, and mathematical models need to be adapted accordingly. A multidisciplinary approach where patients are seen by both, clinicians and biomedically skilled counsellors, could help provide evidence-based assistance to improve pregnancy success. Next, when it concerns factors that may change the ability to produce optimal embryos in ART, the embryologist would benefit from a personalized prediction model, including medical history of the patient as well as genetic and epigenetic data from easily accessible germ cells, such as sperm.

Embryonic heat conditioning induces paternal heredity of immunological cross- tolerance: coordinative role of CpG DNA methylation and miR-200a regulation

Background

Enhancing an organism's survival hinges on the development of balanced and adaptable stress response systems. While the initial stress-response set-points in the hypothalamus may be genetically determined, they are further influenced by epigenetic factors during embryonic development. A debate persists regarding the heritability of such behavioral traits. The chick in ovo heat conditioning model offers a unique insight into this fundamental question, where manipulation during embryonic development can induce heat resilience and even cross-tolerance to promote immunological resilience. In this study, we conducted an analysis of thermal manipulation during embryogenesis to demonstrate paternal heredity and investigate its transmission through sperm DNA methylation in coordination with miR-200a action.

Result

First-generation embryos underwent in ovo heat conditioning (EHC), creating a cohort of embryonic EHC and control chicks. These chicks were then subjected to an intracranial lipopolysaccharide (LPS) challenge. Conditioning rendered the chicks immune resilient, as evidenced by their fibril effect. Male offspring were raised to maturity, and their sperm was analyzed for methylome patterns, revealing significant differences between treatments, particularly in immune and development related genes. Additionally, sperm from EHC males was used for artificial insemination of naïve Cobb hens, resulting in untreated offspring that displayed immune resilience upon LPS challenge, indicating transgenerational effects. Overlap analysis of sperm methylome and differentially methylated sites (DMS) of offspring hypothalamus revealed inheritance of altered methylation associated with specific genes. Several of these genes are potential effectors of miR-200a, whose expression profile in the hypothalamus during LPS challenge was conserved across both generations. To evaluate the role of miR-200a in cross-tolerance acquisition, miR-200a was intracranially injected, and RNA-seq analysis of the hypothalamus revealed genes involved in the regulation of developmental and metabolic processes, stress, and immune response.

Conclusion

This study demonstrates paternal trait heredity by revealing that EHC induces cross-tolerance with the immunological system, rendering chicks resilient to LPS that transgenerationally transmit this to untreated offspring. Additionally, analysis of sperm methylation patterns in EHC mature chicks led to identification of genes associated with neuronal development and immune response, indicating potential neural network reorganization. Finally, miR-200a emerges as a regulator potentially involved in mediating the cross-tolerance effect.

Estrogen Receptor Signaling Alters Sperm DNA Methylation Landscape in Adult Male Rats

Estrogen through its receptors, ERα and ERβ, regulate various aspects of spermatogenesis and male fertility. Because the sperm epigenome is an important contributing factor to male fertility, we evaluated the effects of estrogen signaling activation through the ERs on sperm DNA methylome in adult rats. Whole genome-bisulfite sequencing in caudal sperm DNA was performed. The differentially methylated CpG (DMC) sites were validated by pyrosequencing, and the expression of differentially methylated genes (DMGs) was evaluated in testis by quantitative RT-PCR. Activation of ERα signaling brought about large-scale changes in the sperm DNA methylome compared to ERβ. There were 28074 DMCs and 5189 DMGs obtained after ERα agonist 4,4',4''-(4-Propyl-[1H] pyrazole-1,3,5-triyl) (PPT) treatment, whereas 1492 DMCs and 336 DMGs for ERβ agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN). In genic regions, most of the DMCs were intronic, followed by promoter and upstream regions. DMCs were distributed around the transcription start site and in transcription factor-binding regions, implicating their plausible role in gene expression regulation. Genes important for spermatogenesis were identified and validated which showed a similar trend of differential methylation as obtained by whole genome-bisulfite sequencing. The expression of the DMGs was also found to be altered in the testis. There was a considerable overlap (14% to 50%) of PPT DMGs with the DMGs reported to be affected in clinical conditions of male infertility. This study highlights the role of ERs in shaping the sperm epigenome and that aberrant estrogen signaling could be a contributing factor in clinical conditions of male infertility.

Obesity and recurrent spontaneous abortion: the crucial role of weight management in pregnancy

Recurrent spontaneous abortion (RSA), characterized by the loss of two or more pregnancies, impacts approximately 1-2% of couples and poses a significant challenge for individuals of childbearing age. The precise mechanisms underlying RSA remain incompletely understood. Concurrently, the global prevalence of obesity is on the rise, with obesity being closely associated with female reproductive disorders and infertility. This study initially examines the pathways through which obesity contributes to RSA, encompassing factors such as embryonic euploid miscarriage, endometrial development, immune function, among others. Furthermore, adipokines and the fat mass and obesity-related (FTO) are identified as potential contributors to RSA. The study also explores the enhancement of pregnancy outcomes through various weight management strategies, with a particular focus on the roles of dietary interventions, physical activity, and weight control during pregnancy. Obesity is closely related to RSA in multiple aspects. Additional clinical prospective and experimental studies are required to explore its precise pathogenesis. Through this review, we aim to provide strategies for improvement and treatment approaches for RSA related to obesity. Through this review, we suggest potential clinical management strategies and research avenues aimed at offering enhancements and therapeutic insights for miscarriages linked to obesity and its associated risk factors.

Diet-Induced Obesity in the Rat Impairs Sphingolipid Metabolism in the Brain and This Metabolic Dysfunction Is Transmitted to the Offspring via Both the Maternal and the Paternal Lineage

Obesity leads to a number of health problems, including learning and memory deficits that can be passed on to the offspring via a developmental programming process. However, the mechanisms involved in the deleterious effects of obesity on cognition remain largely unknown. This study aimed to assess the impact of obesity on the production of sphingolipids (ceramides and sphingomyelins) in the brain and its relationship with the learning deficits displayed by obese individuals. We also sought to determine whether the effects of obesity on brain sphingolipid synthesis could be passed on to the offspring. Learning abilities and brain concentration of sphingolipids in male and female control and obese founder rats (F0) and their offspring (F1) were evaluated, respectively, by the novel object recognition test and by ultra-performance liquid chromatography tandem mass spectrometry. In addition, a global lipidome profiling of the cerebral cortex and hippocampus was performed. Both male and female F0 rats showed impaired learning and increased concentrations of ceramides and sphingomyelins in the hippocampus and frontal cortex compared to their control counterparts. However, the overall lipidome profile of these brain regions did not change with obesity. Remarkably, the alterations in brain sphingolipid synthesis, as well as the cognitive impairment induced by obesity, were also present in adult F1 male rats born to obese mothers or sired by obese fathers and were associated with enhanced expression of mRNAs coding for enzymes involved in the de novo synthesis of ceramides. These results show that the cognitive deficits and impaired sphingolipid metabolism induced by obesity can be transmitted to the offspring through both the maternal and paternal lineages and suggest that an increase in the brain concentration of sphingolipids could play a causal role in the cognitive deficits associated with obesity.

Prepregnancy and Gestational Interventions to Prevent Childhood Obesity

Childhood obesity is a significant global health issue with complex and multifactorial origins, often beginning before conception and influenced by both maternal and paternal health. The increased prevalence of prepregnancy obesity and gestational diabetes mellitus in women of reproductive age contributes to a heightened risk of metabolic dysfunction in offspring. Current clinical practices often implement lifestyle interventions after the first trimester and have limited success, implying that they miss a critical window for effective metabolic adjustments. This review examines the limitations of lifestyle interventions during pregnancy in improving perinatal outcomes and highlights the importance of initiating such interventions before conception to positively impact parental health and fetal development. A re-evaluation of strategies is needed to enhance the metabolic health of prospective parents as a preventive measure against childhood obesity.

Paternal Contributions to Recurrent Pregnancy Loss: Mechanisms, Biomarkers, and Therapeutic Approaches

Background and Objectives: Recurrent pregnancy loss (RPL) affects numerous couples worldwide and has traditionally been attributed mainly to maternal factors. However, recent evidence highlights significant paternal influences on pregnancy viability and outcomes. This review aims to comprehensively examine male contributions to pregnancy loss, focusing on underlying mechanisms, novel biomarkers, and integrated strategies for improved reproductive success. Materials and Methods: A comprehensive narrative review was conducted by searching databases including PubMed and Embase for the literature published from January 2004 to October 2024. Studies focusing on paternal influences in RPL-encompassing oxidative stress, genetic and epigenetic mechanisms, health conditions, lifestyle factors, environmental exposures, and advancements in sperm proteomics-were included. Inclusion criteria were peer-reviewed articles in English that directly addressed paternal factors in RPL; studies not meeting these criteria were excluded. Results: The review identified that paternal factors such as advanced age, metabolic and cardiovascular health issues, chronic diseases, lifestyle habits (e.g., smoking, alcohol consumption, poor diet), and environmental exposures significantly affect sperm integrity through mechanisms like oxidative stress, DNA fragmentation, and epigenetic alterations. Advanced paternal age and poor health conditions are associated with increased risks of miscarriage and adverse pregnancy outcomes. Novel sperm proteomic biomarkers have been identified, offering potential for enhanced diagnostics and personalized interventions. Integrated approaches involving multidisciplinary assessments, preventive strategies, and genetic counseling are essential for effectively addressing RPL. Conclusions: Integrating paternal factors into clinical evaluations is crucial for effectively addressing recurrent pregnancy loss. Recognizing and modifying paternal risk factors through lifestyle changes, medical interventions, and environmental management can improve pregnancy outcomes. The findings underscore the need for incorporating paternal assessments into standard care and highlight the importance of future research focusing on standardizing diagnostic protocols, expanding studies on paternal contributions, and integrating proteomic biomarkers into clinical practice to facilitate personalized treatment strategies.

In Vitro Fertilization induces reproductive changes in male mouse offspring and has multigenerational effects

In vitro fertilization (IVF) is a non-coital method of conception used to treat human infertility. Although IVF is viewed as largely safe, it is associated with adverse outcomes in the fetus, placenta, and adult offspring life. Because studies focusing on the effect of IVF on the male reproductive system are limited, we used a mouse model to assess the morphological and molecular effects of IVF on male offspring. We evaluated three developmental stages: 18.5-day fetuses and 12- and 39-week-old adults. Regardless of age, we observed changes in testicular-to-body weight ratios, serum testosterone levels, testicular morphology, gene expression, and DNA methylation. Also, sperm showed changes in morphology and DNA methylation. To assess multigenerational phenotypes, we mated IVF and naturally conceived males with wild-type females. Offspring from IVF males exhibited decreased fetal weight-to-placental weight ratios and changes in placenta morphology regardless of sex. At 12-weeks-of-age, offspring showed higher body weights and differences in glucose, triglycerides, insulin, total cholesterol, HDL and LDL/VLDL levels. Both sexes showed changes in gene expression in liver, testes and ovaries, and decreased global DNA methylation. Collectively, our findings demonstrate that male IVF offspring exhibit abnormal testicular and sperm morphology and molecular alterations and transmit defects multigenerationally.

Multifaceted paternal exposures before conception and their epigenetic impact on offspring

As scientific research progresses, there is an increasing understanding of the importance of paternal epigenetics in influencing the health and developmental path of offspring. Prior to conception, the environmental exposures and lifestyle choices of fathers can significantly influence the epigenetic state of sperm, including DNA methylation and histone changes, among other factors. These alterations in epigenetic patterns have the potential for transgenerational transmission potential and may exert profound effects on the biological characteristics of descendants. Paternal epigenetic changes not only affect the regulation of gene expression patterns in offspring but also increase the risk to certain diseases. It is crucial to comprehend the conditions that fathers are exposed to before conception and the potential outcomes of these conditions. This understanding is essential for assessing personal reproductive decisions and anticipating health risks for future generations. This review article systematically summarizes and analyzes current research findings regarding how paternal pre-pregnancy exposures influence offspring as well as elucidates underlying mechanisms, aiming to provide a comprehensive perspective for an enhanced understanding of the impact that paternal factors have on offspring health.

A Mendelian randomization study on causal relationship between metabolic factors and abnormal spermatozoa

Background

Male infertility is a global health problem. There is an increasing attention on the association of metabolic status with spermatogenesis. However, the impacts of metabolic factors on semen parameters are still unclear. To provide evidence for developing appropriate interventions on disease screening and prevention, we performed a Mendelian randomization (MR) analysis to assess causality between various metabolic factors and abnormal spermatozoa.

Methods

We conducted a two-sample MR study to appraise the causal effects of 16 metabolic factors (including indexes of metabolic traits, glucose metabolism, lipid profile, adipokines, uric acid and metabolic diseases) on abnormal spermatozoa from genome-wide association studies (GWASs). Filtering with strict criteria, eligible genetic instruments closely associated with each of the factors were extracted. We employed inverse variance weighted for major analysis, with supplement MR methods including MR-Egger and weighted median. Heterogeneity and pleiotropy tests were further used to detect the reliability of analysis.

Results

After rigorous quality control in this MR framework, we identified that body fat percentage [odds ratio (OR) =1.49, 95% confidence interval (CI): 1.01-2.20, P=0.046] and resistin (OR =1.55, 95% CI: 1.11-2.19, P=0.01) were causally associated with a higher risk of abnormal spermatozoa. In terms of other indexes of metabolic traits, glucose metabolism, serum lipid profile and uric acid and metabolic diseases including type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD), no causal effects were observed (P>0.05).

Conclusions

Our MR analysis provides robust evidence that body fat percentage and resistin are risk factors for abnormal spermatozoa, suggesting implications of identifying them for potential interventions and clinical therapies in male infertility. Further investigation in larger-scale GWASs on subgroups of abnormal spermatozoa will verify impacts of metabolic factors on spermatogenesis.

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.

Effect of body mass index on semen quality, sperm chromatin integrity and sperm DNA methylation

Obesity represents a growing problem due to its impacts on human health and reproduction. In this study, we analysed semen quality, sperm DNA integrity and gene-specific CpG methylation in 116 healthy men from normal population. The men were divided into three groups according to their body mass index (BMI), and their ejaculates were analysed using standard methods, sperm chromatin structure assay (SCSA), methylation next generation sequencing (NGS) and amplicon sequencing. The sperm methylation NGS revealed six significantly differentially methylated regions (DMRs). Using subsequent targeted amplicon sequencing in 116 men, two of the DMRs were proved as differentially methylated in sperm of men with normal BMI vs. BMI ≥ 25. The DMRs were located in the EPHA8 and ANKRD11 gene. Also, we detected a significant decline in the EPHA8, ANKRD11 and CFAP46 gene methylation in association with increasing BMI values. The genes EPHA8 and ANKRD11 are involved in the nervous system and brain development; the CFAP46 gene plays a role in a flagellar assembly and is associated with sperm motility. Significantly lower rates of motile and progressive motile sperm were observed in men with BMI ≥ 30. Our results show that excess body weight can modify CpG methylation of specific genes, affect sperm motility, and compromise sperm chromatin integrity. These factors can stand behind the observed reduced fertility in men with obesity. The methylation changes might be transmitted to their offspring through sperm, and become a basis for possible developmental and reproductive issues in the next generation.

Current Updates on the Understanding of the Role of DNA Methylation on Obesity

Obesity is a condition in which there is an accumulation of excess body fat leading to a weight far above the normal range that poses significant health risks. According to WHO, 8 billion people in the world were obese in 2022. Consequently, obesity has become a pandemic with negative impacts on both global health and economies. Obesity is influenced by various factors including environmental influences, lifestyle choices, gut microbiota, genetic factors, and epigenetic mechanisms such as DNA methylation. DNA methylation can affect an individual's phenotype and condition without altering their DNA sequence. It is the most extensively studied epigenetic alteration and it plays an important part in controlling gene activity associated with obesity. Numerous studies have indicated that DNA methylation is implicated in obesity, thus this review aims to elaborate the roles of DNA methylation to inform the development of preventive measures for obesity.

Differential methylation patterns in paternally imprinted gene promoter regions in sperm from hepatitis B virus infected individuals

BACKGROUND

Hepatitis B virus (HBV) infection poses a substantial threat to human health, impacting not only infected individuals but also potentially exerting adverse effects on the health of their offspring. The underlying mechanisms driving this phenomenon remain elusive. This study aims to shed light on this issue by examining alterations in paternally imprinted genes within sperm.

METHODS

A cohort of 35 individuals with normal semen analysis, comprising 17 hepatitis B surface antigen (HBsAg)-positive and 18 negative individuals, was recruited. Based on the previous research and the Online Mendelian Inheritance in Man database (OMIM, https://www.omim.org/ ), targeted promoter methylation sequencing was employed to investigate 28 paternally imprinted genes associated with various diseases.

RESULTS

Bioinformatic analyses revealed 42 differentially methylated sites across 29 CpG islands within 19 genes and four differentially methylated CpG islands within four genes. At the gene level, an increase in methylation of DNMT1 and a decrease in methylation of CUL7, PRKAG2, and TP53 were observed. DNA methylation haplotype analysis identified 51 differentially methylated haplotypes within 36 CpG islands across 22 genes.

CONCLUSIONS

This is the first study to explore the effects of HBV infection on sperm DNA methylation and the potential underlying mechanisms of intergenerational influence of paternal HBV infection.

Behind the Genetics: The Role of Epigenetics in Infertility-Related Testicular Dysfunction

In recent decades, we have witnessed a progressive decline in male fertility. This is partly related to the increased prevalence of chronic diseases (e.g., obesity and diabetes mellitus) and risky lifestyle behaviors. These conditions alter male fertility through various non-genetic mechanisms. However, there is increasing evidence that they are also capable of causing sperm epigenetic alterations, which, in turn, can cause infertility. Furthermore, these modifications could be transmitted to offspring, altering their general and reproductive health. Therefore, these epigenetic modifications could represent one of the causes of the progressive decline in sperm count recorded in recent decades. This review focuses on highlighting epigenetic modifications at the sperm level induced by non-genetic causes of infertility. In detail, the effects on DNA methylation, histone modifications, and the expression profiles of non-coding RNAs are evaluated. Finally, a focus on the risk of transgenerational inheritance is presented. Our narrative review aims to demonstrate how certain conditions can alter gene expression, potentially leading to the transmission of anomalies to future generations. It emphasizes the importance of the early detection and treatment of reversible conditions (such as obesity and varicocele) and the modification of risky lifestyle behaviors. Addressing these issues is crucial for individual health, in preserving fertility, and in ensuring the well-being of future generations.

Cold exposure impacts DNA methylation patterns in cattle sperm

DNA methylation is influenced by various exogenous factors such as nutrition, temperature, toxicants, and stress. Bulls from the Pacific Northwest region of the United States and other northern areas are exposed to extreme cold temperatures during winter. However, the effects of cold exposure on the methylation patterns of bovine sperm remain unclear. To address, DNA methylation profiles of sperm collected during late spring and winter from the same bulls were analyzed using whole genome bisulfite sequencing (WGBS). Bismark (0.22.3) were used for mapping the WGBS reads and R Bioconductor package DSS was used for differential methylation analysis. Cold exposure induced 3,163 differentially methylated cytosines (DMCs) with methylation difference ≥10% and a q-value < 0.05. We identified 438 differentially methylated regions (DMRs) with q-value < 0.05, which overlapped with 186 unique genes. We also identified eight unique differentially methylated genes (DMGs) (Pax6, Macf1, Mest, Ubqln1, Smg9, Ctnnb1, Lsm4, and Peg10) involved in embryonic development, and nine unique DMGs (Prmt6, Nipal1, C21h15orf40, Slc37a3, Fam210a, Raly, Rgs3, Lmbr1, and Gan) involved in osteogenesis. Peg10 and Mest, two paternally expressed imprinted genes, exhibited >50% higher methylation. The differential methylation patterns of six distinct DMRs: Peg10, Smg9 and Mest related to embryonic development and Lmbr1, C21h15orf40 and Prtm6 related to osteogenesis, were assessed by methylation-specific PCR (MS-PCR), which confirmed the existence of variable methylation patterns in those locations across the two seasons. In summary, cold exposure induces differential DNA methylation patterns in genes that appear to affect embryonic development and osteogenesis in the offspring. Our findings suggest the importance of replicating the results of the current study with a larger sample size and exploring the potential of these changes in affecting offspring development.

Exposure to air pollution is associated with DNA methylation changes in sperm

Exposure to air pollutants has been associated with adverse health outcomes in adults and children who were prenatally exposed. In addition to reducing exposure to air pollutants, it is important to identify their biologic targets in order to mitigate the health consequences of exposure. One molecular change associated with prenatal exposure to air pollutants is DNA methylation (DNAm), which has been associated with changes in placenta and cord blood tissues at birth. However, little is known about how air pollution exposure impacts the sperm epigenome, which could provide important insights into the mechanism of transmission to offspring. In the present study, we explored whether exposure to particulate matter less than 2.5 microns in diameter, particulate matter less than 10 microns in diameter, nitrogen dioxide (NO2), or ozone (O3) was associated with DNAm in sperm contributed by participants in the Early Autism Risk Longitudinal Investigation prospective pregnancy cohort. Air pollution exposure measurements were calculated as the average exposure for each pollutant measured within 4 weeks prior to the date of sample collection. Using array-based genome-scale methylation analyses, we identified 80, 96, 35, and 67 differentially methylated regions (DMRs) significantly associated with particulate matter less than 2.5 microns in diameter, particulate matter less than 10 microns in diameter, NO2, and O3, respectively. While no DMRs were associated with exposure to all four pollutants, we found that genes overlapping exposure-related DMRs had a shared enrichment for gene ontology biological processes related to neurodevelopment. Together, these data provide compelling support for the hypothesis that paternal exposure to air pollution impacts DNAm in sperm, particularly in regions implicated in neurodevelopment.

Frequency, morbidity and equity - the case for increased research on male fertility

Currently, most men with infertility cannot be given an aetiology, which reflects a lack of knowledge around gamete production and how it is affected by genetics and the environment. A failure to recognize the burden of male infertility and its potential as a biomarker for systemic illness exists. The absence of such knowledge results in patients generally being treated as a uniform group, for whom the strategy is to bypass the causality using medically assisted reproduction (MAR) techniques. In doing so, opportunities to prevent co-morbidity are missed and the burden of MAR is shifted to the woman. To advance understanding of men's reproductive health, longitudinal and multi-national centres for data and sample collection are essential. Such programmes must enable an integrated view of the consequences of genetics, epigenetics and environmental factors on fertility and offspring health. Definition and possible amelioration of the consequences of MAR for conceived children are needed. Inherent in this statement is the necessity to promote fertility restoration and/or use the least invasive MAR strategy available. To achieve this aim, protocols must be rigorously tested and the move towards personalized medicine encouraged. Equally, education of the public, governments and clinicians on the frequency and consequences of infertility is needed. Health options, including male contraceptives, must be expanded, and the opportunities encompassed in such investment understood. The pressing questions related to male reproductive health, spanning the spectrum of andrology are identified in the Expert Recommendation.

Epigenetic changes in sperm are associated with paternal and child quantitative autistic traits in an autism-enriched cohort

There is a need to consider paternal contributions to autism spectrum disorder (ASD) more strongly. Autism etiology is complex, and heritability is not explained by genetics alone. Understanding paternal gametic epigenetic contributions to autism could help fill this knowledge gap. In the present study, we explored whether paternal autistic traits, and the sperm epigenome, were associated with autistic traits in children at 36 months enrolled in the Early Autism Risk Longitudinal Investigation (EARLI) cohort. EARLI is a pregnancy cohort that recruited and enrolled pregnant women in the first half of pregnancy who already had a child with ASD. After maternal enrollment, EARLI fathers were approached and asked to provide a semen specimen. Participants were included in the present study if they had genotyping, sperm methylation data, and Social Responsiveness Scale (SRS) score data available. Using the CHARM array, we performed genome-scale methylation analyses on DNA from semen samples contributed by EARLI fathers. The SRS-a 65-item questionnaire measuring social communication deficits on a quantitative scale-was used to evaluate autistic traits in EARLI fathers (n = 45) and children (n = 31). We identified 94 significant child SRS-associated differentially methylated regions (DMRs), and 14 significant paternal SRS-associated DMRs (fwer p < 0.05). Many child SRS-associated DMRs were annotated to genes implicated in ASD and neurodevelopment. Six DMRs overlapped across the two outcomes (fwer p < 0.1), and, 16 DMRs overlapped with previous child autistic trait findings at 12 months of age (fwer p < 0.05). Child SRS-associated DMRs contained CpG sites independently found to be differentially methylated in postmortem brains of individuals with and without autism. These findings suggest paternal germline methylation is associated with autistic traits in 3-year-old offspring. These prospective results for autism-associated traits, in a cohort with a family history of ASD, highlight the potential importance of sperm epigenetic mechanisms in autism.

Higher incidence of embryonic defects in mouse offspring conceived with assisted reproduction from fathers with sperm epimutations

Assisted reproductive technologies (ART) account for 1-6% of births in developed countries. While most children conceived are healthy, increases in birth and genomic imprinting defects have been reported; such abnormal outcomes have been attributed to underlying parental infertility and/or the ART used. Here, we assessed whether paternal genetic and lifestyle factors, that are associated with male infertility and affect the sperm epigenome, can influence ART outcomes. We examined how paternal factors, haploinsufficiency for Dnmt3L, an important co-factor for DNA methylation reactions, and/or diet-induced obesity, in combination with ART (superovulation, in vitro fertilization, embryo culture and embryo transfer), could adversely influence embryo development and DNA methylation patterning in mice. While male mice fed high-fat diets (HFD) gained weight and showed perturbed metabolic health, their sperm DNA methylation was minimally affected by the diet. In contrast, Dnmt3L haploinsufficiency induced a marked loss of DNA methylation in sperm; notably, regions affected were associated with neurodevelopmental pathways and enriched in young retrotransposons, sequences that can have functional consequences in the next generation. Following ART, placental imprinted gene methylation and growth parameters were impacted by one or both paternal factors. For embryos conceived by natural conception, abnormality rates were similar for WT and Dnmt3L+/- fathers. In contrast, paternal Dnmt3L+/- genotype, as compared to WT fathers, resulted in a 3-fold increase in the incidence of morphological abnormalities in embryos generated by ART. Together, the results indicate that embryonic morphological and epigenetic defects associated with ART may be exacerbated in offspring conceived by fathers with sperm epimutations.

The impact of obesity and metabolic health on male fertility: a systematic review

The impact of paternal obesity and metabolic disease on semen quality and fertility outcomes is not fully appreciated. With increasing obesity rates, researchers have studied the intricate relationship between paternal body mass index, metabolic health, and male fertility. This systematic review identified 112 articles in the MEDLINE database between 2013 and 2023 that investigated the effects of body mass index, diabetes, metabolic syndrome, exercise, weight loss medication, or bariatric surgery on semen parameters, sperm quality, or fertility outcomes. This review suggests that obesity, diabetes, and metabolic syndrome have a negative impact on various parameters of male fertility, from semen quality to sperm deoxyribonucleic acid integrity. There is also mounting evidence that male obesity is correlated negatively with live births via both natural conception and assisted reproductive technologies. Lifestyle interventions, such as physical exercise, generally appear to improve male fertility markers; however, the type and intensity of exercise may play a crucial role. Pharmacologic treatments for weight loss, such as metformin and glucagon-like peptide 1 agonists, present a more complex picture, with studies suggesting both beneficial and detrimental effects on male reproductive health. Similarly, surgical interventions, such as gastric bypass surgery, show promise in improving hormonal imbalances but have mixed effects on semen parameters. Future research is needed to clarify these associations and inform clinical guidelines. In the interim, health practitioners should incorporate these insights into clinical practices, encouraging proactive lifestyle changes and providing targeted treatments to improve male reproductive health.

Paternal high-fat diet altered SETD2 gene methylation in sperm of F0 and F1 mice

Paternal high-fat diet (HFD) can alter the epigenetics of sperm DNA, resulting in the transmission of obesity-related traits to the offspring. Previous studies have mainly focused on the HFD-induced changes in DNA methylation of imprinted genes, overlooking the potential involvement of non-imprinted genes in this process. SETD2, an important epigenetically-regulated gene known for its response to environmental stress, remains poorly understood in the context of high-fat diet-induced epigenetic changes. Here we examined the effect of obesity from a HFD on paternal SETD2 expression and methylation in sperm, and embryos at the blastocyst stage and during subsequent development, to determine the alteration of SETD2 in paternal intergenerational and transgenerational inheritance. The result showed that mice fed with HFD for two months had significantly increased SETD2 expression in testis and sperm. The paternal HFD significantly altered the DNA methylation level with 20 of the 26 CpG sites being changed in sperm from F0 mice. Paternal high-fat diet increased apoptotic index and decreased total cell number of blastocysts, which were closely correlated with DNA methylation level of sperm. Out of the 26 CpG sites, we also found three CpG sites that were significantly changed in the sperm from F1 mice, which meant that the methylation changes at these three CpG sites were maintained.In conclusion, we found that paternal exposure to an HFD disrupted the methylation pattern of SETD2 in the sperm of F0 mice and resulted in perturbed SETD2 expression. Furthermore, the paternal high-fat diet influenced embryo apoptosis and development, possibly through the SETD2 pathway. The altered methylation of SETD2 in sperm induced by paternal HFD partially persisted in the sperm of the F1 generation, highlighting the role of SETD2 as an epigenetic carrier for paternal intergenerational and transgenerational inheritance.

Preconception origins of asthma, allergies and lung function: The influence of previous generations on the respiratory health of our children

Emerging research suggests that exposures occurring years before conception are important determinants of the health of future offspring and subsequent generations. Environmental exposures of both the father and mother, or exposure to disease processes such as obesity or infections, may influence germline cells and thereby cause a cascade of health outcomes in multiple subsequent generations. There is now increasing evidence that respiratory health is influenced by parental exposures that occur long before conception. The strongest evidence relates adolescent tobacco smoking and overweight in future fathers to increased asthma and lower lung function in their offspring, supported by evidence on parental preconception occupational exposures and air pollution. Although this literature is still sparse, the epidemiological analyses reveal strong effects that are consistent across studies with different designs and methodologies. The results are strengthened by mechanistic research from animal models and (scarce) human studies that have identified molecular mechanisms that can explain the epidemiological findings, suggesting transfer of epigenetic signals through germline cells, with susceptibility windows in utero (both male and female line) and prepuberty (male line). The concept that our lifestyles and behaviours may influence the health of our future children represents a new paradigm. This raises concerns for future health in decades to come with respect to harmful exposures but may also open for radical rethinking of preventive strategies that may improve health in multiple generations, reverse the imprint of our parents and forefathers, and underpin strategies that can break the vicious circle of propagation of health inequalities across generations.

Intergenerational Inheritance of Hepatic Steatosis in a Mouse Model of Childhood Obesity: Potential Involvement of Germ-Line microRNAs

Childhood obesity increases the risk of developing metabolic syndrome later in life. Moreover, metabolic dysfunction may be inherited into the following generation through non-genomic mechanisms, with epigenetics as a plausible candidate. The pathways involved in the development of metabolic dysfunction across generations in the context of childhood obesity remain largely unexplored. We have developed a mouse model of early adiposity by reducing litter size at birth (small litter group, SL: 4 pups/dam; control group, C: 8 pups/dam). Mice raised in small litters (SL) developed obesity, insulin resistance and hepatic steatosis with aging. Strikingly, the offspring of SL males (SL-F1) also developed hepatic steatosis. Paternal transmission of an environmentally induced phenotype strongly suggests epigenetic inheritance. We analyzed the hepatic transcriptome in C-F1 and SL-F1 mice to identify pathways involved in the development of hepatic steatosis. We found that the circadian rhythm and lipid metabolic process were the ontologies with highest significance in the liver of SL-F1 mice. We explored whether DNA methylation and small non-coding RNAs might be involved in mediating intergenerational effects. Sperm DNA methylation was largely altered in SL mice. However, these changes did not correlate with the hepatic transcriptome. Next, we analyzed small non-coding RNA content in the testes of mice from the parental generation. Two miRNAs (miR-457 and miR-201) appeared differentially expressed in the testes of SL-F0 mice. They are known to be expressed in mature spermatozoa, but not in oocytes nor early embryos, and they may regulate the transcription of lipogenic genes, but not clock genes, in hepatocytes. Hence, they are strong candidates to mediate the inheritance of adult hepatic steatosis in our murine model. In conclusion, litter size reduction leads to intergenerational effects through non-genomic mechanisms. In our model, DNA methylation does not seem to play a role on the circadian rhythm nor lipid genes. However, at least two paternal miRNAs might influence the expression of a few lipid-related genes in the first-generation offspring, F1.

Effect of Dietetic Obesity on Testicular Transcriptome in Cynomolgus Monkeys

Obesity is a metabolic disorder resulting from behavioral, environmental and heritable causes, and can have a negative impact on male reproduction. There have been few experiments in mice, rats, and rabbits on the effects of obesity on reproduction, which has inhibited the development of better treatments for male subfertility caused by obesity. Nonhuman primates are most similar to human beings in anatomy, physiology, metabolism, and biochemistry and are appropriate subjects for obesity studies. In this investigation, we conducted a transcriptome analysis of the testes of cynomolgus monkeys on high-fat, high-fructose, and cholesterol-rich diets to determine the effect of obesity on gene expression in testes. The results showed that the testes of obese monkeys had abnormal morphology, and their testes transcriptome was significantly different from that of non-obese animals. We identified 507 differentially abundant genes (adjusted p value < 0.01, log2 [FC] > 2) including 163 up-regulated and 344 down-regulated genes. Among the differentially abundant genes were ten regulatory genes, including IRF1, IRF6, HERC5, HERC6, IFIH1, IFIT2, IFIT5, IFI35, RSAD2, and UBQLNL. Gene ontology (GO) and KEGG pathway analysis was conducted, and we found that processes and pathways associated with the blood testes barrier (BTB), immunity, inflammation, and DNA methylation in gametes were preferentially enriched. We also found abnormal expression of genes related to infertility (TDRD5, CLCN2, MORC1, RFX8, SOHLH1, IL2RB, MCIDAS, ZPBP, NFIA, PTPN11, TSC22D3, MAPK6, PLCB1, DCUN1D1, LPIN1, and GATM) and down-regulation of testosterone in monkeys with dietetic obesity. This work not only provides an important reference for research and treatment on male infertility caused by obesity, but also valuable insights into the effects of diet on gene expression in testes.

Obesity: A Doorway to a Molecular Path Leading to Infertility

The dramatic rise in obesity has recently made it a global health issue. About 1.9 billion were overweight, and 650 million global populations were obese in 2016. Obese women suffer longer conception time, lowered fertility rates, and greater rates of miscarriage. Obesity alters hormones such as adiponectin and leptin, affecting all levels within the hypothalamic-pituitary-gonadal axis. Advanced glycation end products (AGEs) and monocyte chemotactic protein-1 (MCP-1) are inflammatory cytokines that may play an important role in the pathophysiology of ovarian dysfunction in obesity. In obese males, there are altered sperm parameters, reduced testosterone, increased estradiol, hypogonadism, and epigenetic modifications transmitted to offspring. The focus of this article is on the possible adverse effects on reproductive health resulting from obesity and sheds light on different molecular pathways linking obesity with infertility in both female and male subjects. Electronic databases such as Google Scholar, Embase, Science Direct, PubMed, and Google Search Engine were utilized to find obesity and infertility-related papers. The search strategy is detailed in the method section. Even though multiple research work has shown that obesity impacts fertility in both male and female negatively, it is significant to perform extensive research on the molecular mechanisms that link obesity to infertility. This is to find therapeutics that may be developed aiming at these mechanisms to manage and prevent the negative effects of obesity on the reproductive system.

The Legacy of Parental Obesity: Mechanisms of Non-Genetic Transmission and Reversibility

While a dramatic increase in obesity and related comorbidities is being witnessed, the underlying mechanisms of their spread remain unresolved. Epigenetic and other non-genetic mechanisms tend to be prominent candidates involved in the establishment and transmission of obesity and associated metabolic disorders to offspring. Here, we review recent findings addressing those candidates, in the context of maternal and paternal influences, and discuss the effectiveness of preventive measures.

Reprotoxic Impact of Environment, Diet, and Behavior

Reproductive health is progressively declining due to multiples endogenous and exogenous factors, such as environmental contaminants, diet and behavior. Accumulated evidences confirm that fertility and reproductive function have been adversely affected by exposure to chemical contaminants released in the environment. Today, the impact of diet and behavior on reproductive processes is also receiving special attention from the scientific community. Indeed, a close relationship between diet and fertility has been proven. Furthermore, a combination of unhealthy behavior, such as exposure to hazardous compounds and stress factors, poses living organisms at higher risk of reprotoxic effects. In particular, it has been described that poor life behaviors are associated with reduced male and female fertility due to decreased gamete quality and function. Most of the erroneous behaviors are, furthermore, a source of oxidative stress that, leading to epigenetic alterations, results in an impaired reproductive fitness. This review reports the detrimental impact of the most common environmental chemical stressors, diet, and behavior on reproductive functionality and success. Although clear evidences are still scarce, reassuring data are provided that a healthy diet and reverting unhealthy lifestyles may be of help to recover physiological reproductive conditions.

Genetics, epigenetics and transgenerational transmission of obesity in children

Sedentary lifestyle and consumption of high-calorie foods have caused a relentless increase of overweight and obesity prevalence at all ages. Its presently epidemic proportion is disquieting due to the tight relationship of obesity with metabolic syndrome and several other comorbidities which do call for urgent workarounds. The usual ineffectiveness of present therapies and failure of prevention campaigns triggered overtime a number of research studies which have unveiled some relevant aspects of obesity genetic and epigenetic inheritable profiles. These findings are revealing extremely precious mainly to serve as a likely extra arrow to allow the clinician's bow to achieve still hitherto unmet preventive goals. Evidence now exists that maternal obesity/overnutrition during pregnancy and lactation convincingly appears associated with several disorders in the offspring independently of the transmission of a purely genetic predisposition. Even the pre-conception direct exposure of either father or mother gametes to environmental factors can reprogram the epigenetic architecture of cells. Such phenomena lie behind the transfer of the obesity susceptibility to future generations through a mechanism of epigenetic inheritance. Moreover, a growing number of studies suggests that several environmental factors such as maternal malnutrition, hypoxia, and exposure to excess hormones and endocrine disruptors during pregnancy and the early postnatal period may play critical roles in programming childhood adipose tissue and obesity. A deeper understanding of how inherited genetics and epigenetics may generate an obesogenic environment at pediatric age might strengthen our knowledge about pathogenetic mechanisms and improve the clinical management of patients. Therefore, in this narrative review, we attempt to provide a general overview of the contribution of heritable genetic and epigenetic patterns to the obesity susceptibility in children, placing a particular emphasis on the mother-child dyad.

Molecular Mechanisms Underlying the Relationship between Obesity and Male Infertility

In recent decades, the worldwide prevalence of obesity has risen dramatically and is currently estimated to be around 20%. Obesity is linked to an increased risk of comorbidities and premature mortality. Several studies have shown that obesity negatively impacts male fertility through various mechanisms. This review aims to investigate the molecular mechanisms through which obesity impairs male reproduction, including obesity-associated hypogonadism and its effects on spermatogenesis, chronic inflammation, and oxidative stress. Obesity negatively impacts both conventional and biofunctional sperm parameters, and it also induces epigenetic changes that can be transferred to offspring. Moreover, obesity-related diseases are linked to a dysregulation of adipocyte function and micro-environmental inflammatory processes. The dysregulated adipokines significantly influence insulin signaling, and they may also have a detrimental effect on testicular function. Sirtuins can also play an important role in inflammatory and metabolic responses in obese patients. Understanding the molecular mechanisms that are involved in obesity-induced male infertility could increase our ability to identify novel targets for the prevention and treatment of obesity and its related consequences.

A Review on Epigenetic Inheritance of Experiences in Humans

If genetics defines the inheritance of DNA, epigenetics aims to regulate and make it adaptable. Epigenetic alterations include DNA methylation, chromatin remodelling, post-translational modifications of histone proteins and activity of non-coding RNAs. Several studies, especially in animal models, have reported transgenerational inheritance of epigenetic marks. However, evidence of transgenerational inheritance in humans via germline in the absence of any direct exposure to the driving external stimulus remains controversial. Most of the epimutations exist in relation with genetic variants. The present review looks at intergenerational and transgenerational inheritance in humans, (both father and mother) in response to diet, exposure to chemicals, stress, exercise, and disease status. If not transgenerational, at least intergenerational human studies could help to understand early processes of inheritance. In humans, female and male germline development follow separate paths of epigenetic events and both oocyte and sperm possess their own unique epigenomes. While DNA methylation alterations are reset during epigenetic reprogramming, non-coding RNAs via human sperm provide evidence of being reliable carriers for transgenerational inheritance. Human studies reveal that one mechanism of epigenetic inheritance cannot be applied to the complete human genome. Multiple factors including time, type, and tissue of exposure determine if the modified epigenetic mark could be transmissible and till which generation. Population-specific differences should also be taken into consideration while associating inheritance to an environmental exposure. A longitudinal study targeting one environmental factor, but different population groups should be conducted at a specific geographical location to pinpoint heritable epigenetic changes.

Exposures during the prepuberty period and future offspring's health: evidence from human cohort studies†

Emerging evidence suggests that exposures in prepuberty, particularly in fathers-to-be, may impact the phenotype of future offspring. Analyses of the RHINESSA cohort find that offspring of father’s exposed to tobacco smoking or overweight that started in prepuberty demonstrate poorer respiratory health in terms of more asthma and lower lung function. A role of prepuberty onset smoking for offspring fat mass is suggested in the RHINESSA and ALSPAC cohorts, and historic studies suggest that ancestral nutrition during prepuberty plays a role for grand-offspring’s health and morbidity. Support for causal relationships between ancestral exposures and (grand-)offspring’s health in humans has been enhanced by advancements in statistical analyses that optimize the gain while accounting for the many complexities and deficiencies in human multigeneration data. The biological mechanisms underlying such observations have been explored in experimental models. A role of sperm small RNA in the transmission of paternal exposures to offspring phenotypes has been established, and chemical exposures and overweight have been shown to influence epigenetic programming in germ cells. For example, exposure of adolescent male mice to smoking led to differences in offspring weight and alterations in small RNAs in the spermatozoa of the exposed fathers. It is plausible that male prepuberty may be a time window of particular susceptibility, given the extensive epigenetic reprogramming taking place in the spermatocyte precursors at this age. In conclusion, epidemiological studies in humans, mechanistic research, and biological plausibility, all support the notion that exposures in the prepuberty of males may influence the phenotype of future offspring.

Epigenetics of Male Infertility: The Role of DNA Methylation

In recent years, a number of studies focused on the role of epigenetics, including DNA methylation, in spermatogenesis and male infertility. We aimed to provide an overview of the knowledge concerning the gene and genome methylation and its regulation during spermatogenesis, specifically in the context of male infertility etiopathogenesis. Overall, the findings support the hypothesis that sperm DNA methylation is associated with sperm alterations and infertility. Several genes have been found to be differentially methylated in relation to impaired spermatogenesis and/or reproductive dysfunction. Particularly, DNA methylation defects of MEST and H19 within imprinted genes and MTHFR within non-imprinted genes have been repeatedly linked with male infertility. A deep knowledge of sperm DNA methylation status in association with reduced reproductive potential could improve the development of novel diagnostic tools for this disease. Further studies are needed to better elucidate the mechanisms affecting methylation in sperm and their impact on male infertility.