Impact of cigarette-smoking on sperm DNA methylation and its effect on sperm parameters

Adverse Effects of Nicotine on Human Sperm Nuclear Proteins

The effects of smoking on human health have long been documented. However, only a few studies have highlighted the direct effects of nicotine on sperm function. Nicotine, as a chemical compound found in tobacco, has been shown to modulate different aspects of spermatogenesis and sperm functions. Nicotine can lead to a reduction in the number of sperm, their motility and functionality. It can change the molecular expressions involved in sperm function, including genes encoding sperm nuclear proteins. The most important nuclear proteins that play a critical role in sperm function are known as H2B histone family, member W, testis-specific (H2BFWT), transition protein 1 (TNP1), transition protein 2 (TNP2), protamine-1 (PRM1), and protamine-2 (PRM2). These proteins are involved in sperm chromatin condensation, which in turn affects fertilization and embryonic development. Any alteration in the expression of these genes due to nicotine exposure/usage may lead to adverse implications in couples' fertility and the health of future generations. Since research in this area is still relatively new, it underscores the importance of understanding the potential side effects of environmental factors such as nicotine on reproductive health.

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.

The Impact of Heavy Smoking on Male Infertility and Its Correlation with the Expression Levels of the PTPRN2 and PGAM5 Genes

Smoking has been linked to male infertility by affecting the sperm epigenome and genome. In this study, we aimed to determine possible changes in the transcript levels of PGAM5 (the phosphoglycerate mutase family member 5), PTPRN2 (protein tyrosine phosphatase, N2-type receptor), and TYRO3 (tyrosine protein kinase receptor) in heavy smokers compared to non-smokers, and to investigate their association with the fundamental sperm parameters. In total, 118 sperm samples (63 heavy-smokers (G1) and 55 non-smokers (G2)) were included in this study. A semen analysis was performed according to the WHO guidelines. After a total RNA extraction, RT-PCR was used to quantify the transcript levels of the studied genes. In G1, a significant decrease in the standard semen parameters in comparison to the non-smokers was shown (p < 0.05). Moreover, PGAM5 and PTPRN2 were differentially expressed (p ≤ 0.03 and p ≤ 0.01, respectively) and downregulated in the spermatozoa of G1 compared to G2. In contrast, no difference was observed for TYRO3 (p ≤ 0.3). In G1, the mRNA expression level of the studied genes was correlated negatively with motility, sperm count, normal form, vitality, and sperm membrane integrity (p < 0.05). Therefore, smoking may affect gene expression and male fertility by altering the DNA methylation patterns in the genes associated with fertility and sperm quality, including PGAM5, PTPRN2, and TYRO3.

Inheritance of paternal lifestyles and exposures through sperm DNA methylation

Many different lifestyle factors and chemicals present in the environment are a threat to the reproductive tracts of humans. The potential for parental preconception exposure to alter gametes and for these alterations to be passed on to offspring and negatively affect embryo growth and development is of concern. The connection between maternal exposures and offspring health is a frequent focus in epidemiological studies, but paternal preconception exposures are much less frequently considered and are also very important determinants of offspring health. Several environmental and lifestyle factors in men have been found to alter sperm epigenetics, which can regulate gene expression during early embryonic development. Epigenetic information is thought to be a mechanism that evolved for organisms to pass on information about their lived experiences to offspring. DNA methylation is a well-studied epigenetic regulator that is sensitive to environmental exposures in somatic cells and sperm. The continuous production of sperm from spermatogonial stem cells throughout a man's adult life and the presence of spermatogonial stem cells outside of the blood-testis barrier makes them susceptible to environmental insults. Furthermore, altered sperm DNA methylation patterns can be maintained throughout development and ultimately result in impairments, which could predispose offspring to disease. Innovations in human stem cell-based spermatogenic models can be used to elucidate the paternal origins of health and disease.

Patient with multiple morphological abnormalities of sperm flagella caused by a novel ARMC2 mutation has a favorable pregnancy outcome from intracytoplasmic sperm injection

PURPOSE

To investigate the potential genetic cause in a primary infertility patient with multiple morphological abnormalities of sperm flagella (MMAF).

METHODS

The patient's sperm was observed by light and electron microscopy. Whole-exome sequencing (WES) was carried out to identify candidate genes. Then, the mutation found by WES was verified by Sanger sequencing. The proteins interacting with ARMC2 were revealed by co-immunoprecipitation (co-IP) and mass spectrometry. Intracytoplasmic sperm injection (ICSI) was carried out to achieve successful pregnancy.

RESULTS

Typical MMAF phenotype (absent, short, coiled, bent irregular flagella) was shown in the patient's sperm. A novel homozygous mutation in ARMC2 (c.1264C > T) was identified. The proteins interacting with ARMC2 we found were CEP78, PGAM5, RHOA, FXR1, and SKIV2L2. The ICSI therapy was successful, and boy-girl twins were given birth.

CONCLUSION

We found a novel mutation in ARMC2 which led to MMAF and male infertility. This is the first report of ICSI outcome of patient harboring ARMC2 mutation. The interacting proteins indicated that ARMC2 might be involved in multiple processes of spermatogenesis.

Cigarette heavy smoking alters DNA methylation patterns and gene transcription levels in humans spermatozoa

Tobacco smoking is considered the most common reason of death and infertility around the world. This study was designed to assess the impact of tobacco heavy smoking on sperm DNA methylation patterns and to determine whether the transcription level of ALDH3B2, PTGIR, PRICKLE2, and ALS2CR12 genes is different in heavy smokers compared to non-smokers. As a screening study, the 450 K array was used to assess the alteration in DNA methylation patterns between heavy smokers (n = 15) and non-smokers (n = 15). Then, four CpGs that have the highest difference in methylation level (cg16338278, cg08408433, cg05799088, and cg07227024) were selected for validation using deep bisulfite sequencing in an independent cohort of heavy smokers (n = 200) and non-smokers (n = 100). A significant variation was found between heavy smokers and non-smokers in the methylation level at all CpGs within the PRICKLE2 and ALS2CR12 gene amplicon (P < 0.001). Similarly, a significant variation was found in the methylation level at nine out of thirteen CpGs within the ALDH3B2 gene amplicon (P < 0.01). Additionally, eighteen CpGs out of the twenty-six within the PTGIR gene amplicon have a significant difference in the methylation level between heavy smokers and non-smokers (P < 0.01). The study showed a significant difference in sperm global DNA methylation, chromatin non-condensation, and DNA fragmentation (P < 0.001) between heavy smokers and non-smokers. A significant decline was shown in the transcription level of ALDH3B2, PTGIR, PRICKLE2, and ALS2CR12 genes (P < 0.001) in heavy smokers. In conclusion, heavy smoking influences DNA methylation at several CpGs, sperm global DNA methylation, and transcription level of the PRICKLE2, ALS2CR12, ALDH3B2, and PTGIR genes, which affects negatively the semen parameters of heavy smokers.

Effects of the air pollution dynamics on semen quality and sperm DNA methylation in men living in urban industrial agglomeration

Human populations living in urban industrial regions of developed countries are exposed to high levels of environmental pollutants. The reproductive consequences of the exposure to air pollution can be monitored through semen analysis and molecular methods. In this study, we tested the possible impact of seasonal changes in the level of air pollution on the semen quality and sperm DNA methylation of 24 men living and working in the industrial agglomeration of Ostrava (Czech Republic). The study participants were healthy non-smokers. The study group was homogeneous regarding their profession, moderate alcohol consumption, no drug abuse and no additional exposure to chemical toxicants. We performed targeted methylation next generation sequencing (NGS) using Agilent SureSelect Human Methyl-Seq and Illumina NextSeq 500 platform to analyze semen samples collected repeatedly from the same men following the season of high (winter) and low (summer) air pollution exposure. We did not detect any adverse effects of the increased exposure on the semen quality; neither we found any difference in average sperm DNA methylation between the two sampling periods. Our search for differentially methylated CpG sites did not reveal any specific CpG methylation change. Our data indicate that the seasonal changes in the level of the air pollution probably do not have any substantial effect on sperm DNA methylation of men living in the highly polluted industrial agglomeration for a long period of time.

Influence of tobacco cigarette heavy smoking on DNA methylation patterns and transcription levels of MAPK8IP3, GAA, ANXA2, PRRC2A, and PDE11A genes in human spermatozoa

Background

Tobacco smoking is considered as one of the lifestyles factors that influence the sperm DNA methylation and global sperm DNA methylation and that may affect the sperm phenotype. This study was performed to investigate whether tobacco cigarette heavy smoking influences sperm DNA methylation patterns and semen parameters and to determine whether there is an alteration in the transcription level of MAPK8IP3, GAA, ANXA2, PRRC2A, and PDE11A genes in heavy smokers compared to non-smokers. Thirty samples were subjected to 450K arrays as a screening study to assess the variation in sperm DNA methylation levels between heavy smokers and non-smokers. Five CpG sites have the highest difference in methylation levels (cg07869343, cg05813498, cg09785377, cg06833981, and cg02745784), which are located in the MAPK8IP3, GAA, ANXA2, PRRC2A, and PDE11A genes, respectively, and were selected for further analysis using deep bisulfite sequencing in 280 independent samples (120 proven non-smokers and 160 heavy smokers) with a mean age of 33.8 ± 8.4 years. The global sperm DNA methylation, sperm DNA fragmentation, and chromatin non-condensation were evaluated also.

Results

A significant increase was found in the methylation level at seven, three, and seventeen CpGs within the GAA, ANXA2, and MAPK8IP3 genes amplicon, respectively (P< 0.01) in heavy smokers compared to non-smokers. Additionally, a significant increase was found in the methylation levels at all CpGs within PRRC2A and PDE11A gene amplicon (P< 0.01). A significant increase was found in the level of sperm chromatin non-condensation, DNA fragmentation, and global DNA methylation (P < 0.001) in heavy smokers compared to non-smokers.

Conclusion

These results indicate that tobacco cigarette smoking can alter the DNA methylation level at several CpGs, the status of global DNA methylation, and transcription level of the following genes “MAPK8IP3, GAA, ANXA2, PRRC2A, and PDE11A” in human spermatozoa. These findings may affect negatively semen parameters and men’s fertility.

The effects of thirdhand smoke on reproductive health

Tobacco smoke is an environmental pollutant that can cause follicle destruction and oocyte dysfunction. Thirdhand smoke (THS) is residual tobacco smoke existing in the environment long after cigarettes have been extinguished, which can react with other environmental compounds to produce secondary pollutants. THS contains a variety of toxic and harmful chemicals, such as nicotine and 1-(N-methyl-N-nitrosamino)-1-(3-pyridinyl)-4-butanal (NNA), a logical biomarker of THS exposure. The health hazards of THS exposure and its components have been researched in recent years. In this review, we have summarized research progress on the effects of THS exposure on organs in mice and humans especially on the reproductive system. This review may help evaluate the health risks of THS, in particular reproduction and offspring health. We hope this review will guide public health education on the dangers of THS exposure and promotion of healthy living habits.

Simulated Wildfire Smoke Significantly Alters Sperm DNA Methylation Patterns in a Murine Model

Wildfires are now a common feature of the western US, increasing in both intensity and number of acres burned over the last three decades. The effects of this changing wildfire and smoke landscape are a critical public and occupational health issue. While respiratory morbidity due to smoke exposure is a priority, evaluating the molecular underpinnings that explain recent extrapulmonary observations is necessary. Here, we use an Apoe-/- mouse model to investigate the epigenetic impact of paternal exposure to simulated wildfire smoke. We demonstrate that 40 days of exposure to smoke from Douglas fir needles induces sperm DNA methylation changes in adult mice. DNA methylation was measured by reduced representation bisulfite sequencing and varied significantly in 3353 differentially methylated regions, which were subsequently annotated to 2117 genes. The differentially methylated regions were broadly distributed across the mouse genome, but the vast majority (nearly 80%) were hypermethylated. Pathway analyses, using gene-derived and differentially methylated region-derived gene ontology terms, point to a number of developmental processes that may warrant future investigation. Overall, this study of simulated wildfire smoke exposure suggests paternal reproductive risks are possible with prolonged exposure.

Potential effect of tobacco cigarettes smoking on global DNA methylation status and protamines transcripts in human spermatozoa

Background

Epigenetics refers to an alteration in gene expression without alteration in the sequence of DNA and this process may be affected by environmental factors and lifestyle like cigarette smoking. This study was designed to evaluate the potential effect of cigarette smoking on the global DNA methylation status and the transcription level of protamine 1 and protamine 2 in human spermatozoa. A total of 188 semen samples were collected from men with a mean age of 34.9 ± 5.8 years old (98 heavy smokers and 90 non-smokers). The DNA and RNA were isolated from purified spermatozoa, then the status of global DNA methylation and the transcription level of protamine 1 and protamine 2 were evaluated using ELISA and qPCR, respectively. The chromatin non-condensation and DNA fragmentation in human spermatozoa were evaluated using chromomycin A3 staining and TUNEL assay, respectively.

Results

A significant increase has been found in the status of global DNA methylation in spermatozoa of heavy smokers compared to non-smokers (7.69 ± 0.69 ng/μl vs. 4.90 ± 0.40 ng/μl, P < 0.001). Additionally, a significant reduction has been found in transcription level of protamine 1 (25.49 ± 0.31 vs. 23.94 ± 0.40, P < 0.001) and protamine 2 (28.27 ± 0.39 vs. 23.45 ± 0.30, P < 0.001) in heavy smokers. A downregulation has been found in the transcription level of protamine 1 and protamine 2 with a fold change of 0.497 and 0.047, respectively. A significant increase has been shown in the level of DNA fragmentation and chromatin non-condensation in heavy smokers compared to non-smokers (P < 0.001). On the other hand, a significant positive correlation has been found between sperm chromatin non-condensation, sperm DNA fragmentation, transcription level of protamine 1, transcription level of protamine 2, and global DNA methylation status (r = 0.304, P < 0.001; r = 0.399, P < 0.001; r = 0.216, P = 0.003; r = 0.494, P < 0.001, respectively).

Conclusion

Tobacco cigarette smoking has a potential influence on the global DNA methylation and the transcription level of protamine genes in human spermatozoa, and consequently, affect negatively on the semen parameters.

DNA methylation in human sperm: a systematic review

BACKGROUND

Studies in non-human mammals suggest that environmental factors can influence spermatozoal DNA methylation, and some research suggests that spermatozoal DNA methylation is also implicated in conditions such as subfertility and imprinting disorders in the offspring. Together with an increased availability of cost-effective methods of interrogating DNA methylation, this premise has led to an increasing number of studies investigating the DNA methylation landscape of human spermatozoa. However, how the human spermatozoal DNA methylome is influenced by environmental factors is still unclear, as is the role of human spermatozoal DNA methylation in subfertility and in influencing offspring health.

OBJECTIVE AND RATIONALE

The aim of this systematic review was to critically appraise the quality of the current body of literature on DNA methylation in human spermatozoa, summarize current knowledge and generate recommendations for future research.

SEARCH METHODS

A comprehensive literature search of the PubMed, Web of Science and Cochrane Library databases was conducted using the search terms 'semen' OR 'sperm' AND 'DNA methylation'. Publications from 1 January 2003 to 2 March 2020 that studied human sperm and were written in English were included. Studies that used sperm DNA methylation to develop methodologies or forensically identify semen were excluded, as were reviews, commentaries, meta-analyses or editorial texts. The Grading of Recommendations, Assessment, Development and Evaluations (GRADE) criteria were used to objectively evaluate quality of evidence in each included publication.

OUTCOMES

The search identified 446 records, of which 135 were included in the systematic review. These 135 studies were divided into three groups according to area of research; 56 studies investigated the influence of spermatozoal DNA methylation on male fertility and abnormal semen parameters, 20 studies investigated spermatozoal DNA methylation in pregnancy outcomes including offspring health and 59 studies assessed the influence of environmental factors on spermatozoal DNA methylation. Findings from studies that scored as 'high' and 'moderate' quality of evidence according to GRADE criteria were summarized. We found that male subfertility and abnormal semen parameters, in particular oligozoospermia, appear to be associated with abnormal spermatozoal DNA methylation of imprinted regions. However, no specific DNA methylation signature of either subfertility or abnormal semen parameters has been convincingly replicated in genome-scale, unbiased analyses. Furthermore, although findings require independent replication, current evidence suggests that the spermatozoal DNA methylome is influenced by cigarette smoking, advanced age and environmental pollutants. Importantly however, from a clinical point of view, there is no convincing evidence that changes in spermatozoal DNA methylation influence pregnancy outcomes or offspring health.

WIDER IMPLICATIONS

Although it appears that the human sperm DNA methylome can be influenced by certain environmental and physiological traits, no findings have been robustly replicated between studies. We have generated a set of recommendations that would enhance the reliability and robustness of findings of future analyses of the human sperm methylome. Such studies will likely require multicentre collaborations to reach appropriate sample sizes, and should incorporate phenotype data in more complex statistical models.

Epigenome-wide association study on asthma and chronic obstructive pulmonary disease overlap reveals aberrant DNA methylations related to clinical phenotypes

We hypothesized that epigenetics is a link between smoking/allergen exposures and the development of Asthma and chronic obstructive pulmonary disease (ACO). A total of 75 of 228 COPD patients were identified as ACO, which was independently associated with increased exacerbations. Microarray analysis identified 404 differentially methylated loci (DML) in ACO patients, and 6575 DML in those with rapid lung function decline in a discovery cohort. In the validation cohort, ACO patients had hypermethylated PDE9A (+ 30,088)/ZNF323 (− 296), and hypomethylated SEPT8 (− 47) genes as compared with either pure COPD patients or healthy non-smokers. Hypermethylated TIGIT (− 173) gene and hypomethylated CYSLTR1 (+ 348)/CCDC88C (+ 125,722)/ADORA2B (+ 1339) were associated with severe airflow limitation, while hypomethylated IFRD1 (− 515) gene with frequent exacerbation in all the COPD patients. Hypermethylated ZNF323 (− 296) / MPV17L (+ 194) and hypomethylated PTPRN2 (+ 10,000) genes were associated with rapid lung function decline. In vitro cigarette smoke extract and ovalbumin concurrent exposure resulted in specific DNA methylation changes of the MPV17L / ZNF323 genes, while 5-aza-2′-deoxycytidine treatment reversed promoter hypermethylation-mediated MPV17L under-expression accompanied with reduced apoptosis and decreased generation of reactive oxygen species. Aberrant DNA methylations may constitute a determinant for ACO, and provide a biomarker of airflow limitation, exacerbation, and lung function decline.

Exposure to drugs of abuse induce effects that persist across generations

Substance use disorders are highly prevalent and continue to be one of the leading causes of disability in the world. Notably, not all people who use addictive drugs develop a substance use disorder. Although substance use disorders are highly heritable, patterns of inheritance cannot be explained purely by Mendelian genetic mechanisms. Vulnerability to developing drug addiction depends on the interplay between genetics and environment. Additionally, evidence from the past decade has pointed to the role of epigenetic inheritance in drug addiction. This emerging field focuses on how environmental perturbations, including exposure to addictive drugs, induce epigenetic modifications that are transmitted to the embryo at fertilization and modify developmental gene expression programs to ultimately impact subsequent generations. This chapter highlights intergenerational and transgenerational phenotypes in offspring following a history of parental drug exposure. Special attention is paid to parental preconception exposure studies of five drugs of abuse (alcohol, cocaine, nicotine, cannabinoids, and opiates) and associated behavioral and physiological outcomes in offspring. The highlighted studies demonstrate that parental exposure to drugs of abuse has enduring effects that persist into subsequent generations. Understanding the contribution of epigenetic inheritance in drug addiction may provide clues for better treatments and therapies for substance use disorders.

The preconception environment and sperm epigenetics

BACKGROUND

Infertility is a common reproductive disorder, with male factor infertility accounting for approximately half of all cases. Taking a paternal perceptive, recent research has shown that sperm epigenetics, such as changes in DNA methylation, histone modification, chromatin structure, and noncoding RNA expression, can impact reproductive and offspring health. Importantly, environmental conditions during the preconception period has been demonstrated to shape sperm epigenetics.

OBJECTIVES

To provide an overview on epigenetic modifications that regulate normal gene expression and epigenetic remodeling that occurs during spermatogenesis, and to discuss the epigenetic alterations that may occur to the paternal germline as a consequence of preconception environmental conditions and exposures.

MATERIALS AND METHODS

We examined published literature available on databases (PubMed, Google Scholar, ScienceDirect) focusing on adult male preconception environmental exposures and sperm epigenetics in epidemiologic studies and animal models.

RESULTS

The preconception period is a sensitive developmental window in which a variety of exposures such as toxicants, nutrition, drugs, stress, and exercise, affects sperm epigenetics.

DISCUSSION AND CONCLUSION

Understanding the environmental legacy of the sperm epigenome during spermatogenesis will enhance our understanding of reproductive health and improve reproductive success and offspring well-being.

Understanding the correlation between artificial insemination and offspring health outcomes

Although numerous articles have shown intracytoplasmic sperm injection and in vitro fertilization to be correlated with increased risk of disease, a few works have been published on the risks associated with artificial insemination. Meanwhile, questions about the possible causes underlying these correlations have remained in the background. The main objective of this work is not to review the risks associated with artificial insemination, but rather to describe how developmental processes may be affected by these techniques. Thus, we offer a theoretical framework for understanding the possible causes that underlie the correlation between low-complexity or milder techniques and offspring health outcomes.

Association of Sperm Methylation at LINE-1, Four Candidate Genes, and Nicotine/Alcohol Exposure With the Risk of Infertility

In this study, we examined whether smoking and drinking affect sperm quality and the DNA methylation of the repetitive element LINE-1, MEST, P16, H19, and GNAS in sperm. Semen samples were obtained from 143 male residents in a minority-inhabited district of Guizhou province in southwest China. Quantitative DNA methylation analysis of the samples was performed using MassARRAY EpiTYPER assays. Sperm motility was significantly lower in both the nicotine-exposed (P = 0.0064) and the nicotine- and alcohol-exposed (P = 0.0008) groups. Follicle-stimulating hormone (FSH) levels were higher in the nicotine-exposed group (P = 0.0026). The repetitive element LINE-1 was hypermethylated in the three exposed groups, while P16 was hypomethylated in the alcohol and both the alcohol and nicotine exposure groups. Our results also show that alcohol and nicotine exposure altered sperm cell quality, which may be related to the methylation levels of MEST and GNAS. In addition, MEST, GNAS, and the repetitive element LINE1 methylation was significantly associated with the concentration of sperm as well as FSH and luteinizing hormone levels.

A systematic review of smoking-related epigenetic alterations

The aim of this study is to provide a systematic review of the known epigenetic alterations caused by cigarette smoke; establish an evidence-based perspective of their clinical value for screening, diagnosis, and treatment of smoke-related disorders; and discuss the challenges and ethical concerns associated with epigenetic studies. A well-defined, reproducible search strategy was employed to identify relevant literature (clinical, cellular, and animal-based) between 2000 and 2019 based on AMSTAR guidelines. A total of 80 studies were identified that reported alterations in DNA methylation, histone modifications, and miRNA expression following exposure to cigarette smoke. Changes in DNA methylation were most extensively documented for genes including AHRR, F2RL3, DAPK, and p16 after exposure to cigarette smoke. Likewise, miR16, miR21, miR146, and miR222 were identified to be differentially expressed in smokers and exhibit potential as biomarkers for determining susceptibility to COPD. We also identified 22 studies highlighting the transgenerational effects of maternal and paternal smoking on offspring. This systematic review lists the epigenetic events/alterations known to occur in response to cigarette smoke exposure and identifies the major genes and miRNAs that are potential targets for translational research in associated pathologies. Importantly, the limitations and ethical concerns related to epigenetic studies are also highlighted, as are the effects on the ability to address specific questions associated with exposure to tobacco/cigarette smoke. In the future, improved interpretation of epigenetic signatures will lead to their increased use as biomarkers and/or in drug development.

Customized MethylC-Capture Sequencing to Evaluate Variation in the Human Sperm DNA Methylome Representative of Altered Folate Metabolism

BACKGROUND

The sperm DNA methylation landscape is unique and critical for offspring health. If gamete-derived DNA methylation escapes reprograming in early embryos, epigenetic defects in sperm may be transmitted to the next generation. Current techniques to assess sperm DNA methylation show bias toward CpG-dense regions and do not target areas of dynamic methylation, those predicted to be environmentally sensitive and tunable regulatory elements.

OBJECTIVES

Our goal was to assess variation in human sperm DNA methylation and design a targeted capture panel to interrogate the human sperm methylome.

METHODS

To characterize variation in sperm DNA methylation, we performed whole genome bisulfite sequencing (WGBS) on an equimolar pool of sperm DNA from a wide cross section of 30 men varying in age, fertility status, methylenetetrahydrofolate reductase (MTHFR) genotype, and exposures. With our targeted capture panel, in individual samples, we examined the effect of MTHFR genotype ([Formula: see text] 677CC, [Formula: see text] 677TT), as well as high-dose folic acid supplementation ([Formula: see text], per genotype, before and after supplementation).

RESULTS

Through WGBS we discovered nearly 1 million CpGs possessing intermediate methylation levels (20-80%), termed dynamic sperm CpGs. These dynamic CpGs, along with 2 million commonly assessed CpGs, were used to customize a capture panel for targeted interrogation of the human sperm methylome and test its ability to detect effects of altered folate metabolism. As compared with MTHFR 677CC men, those with the 677TT genotype (50% decreased MTHFR activity) had both hyper- and hypomethylation in their sperm. High-dose folic acid supplement treatment exacerbated hypomethylation in MTHFR 677TT men compared with 677CC. In both cases, [Formula: see text] of altered methylation was found in dynamic sperm CpGs, uniquely measured by our assay.

DISCUSSION

Our sperm panel allowed the discovery of differential methylation following conditions affecting folate metabolism in novel dynamic sperm CpGs. Improved ability to examine variation in sperm DNA methylation can facilitate comprehensive studies of environment-epigenome interactions. https://doi.org/10.1289/EHP4812.

Epigenetic impacts of maternal tobacco and e-vapour exposure on the offspring lung

In utero exposure to tobacco products, whether maternal or environmental, have harmful effects on first neonatal and later adult respiratory outcomes. These effects have been shown to persist across subsequent generations, regardless of the offsprings' smoking habits. Established epigenetic modifications induced by in utero exposure are postulated as the mechanism underlying the inherited poor respiratory outcomes. As e-cigarette use is on the rise, their potential to induce similar functional respiratory deficits underpinned by an alteration in the foetal epigenome needs to be explored. This review will focus on the functional and epigenetic impact of in utero exposure to maternal cigarette smoke, maternal environmental tobacco smoke, environmental tobacco smoke and e-cigarette vapour on foetal respiratory outcomes.

Cannabinoid exposure and altered DNA methylation in rat and human sperm

Little is known about the reproductive effects of paternal cannabis exposure. We evaluated associations between cannabis or tetrahydrocannabinol (THC) exposure and altered DNA methylation in sperm from humans and rats, respectively. DNA methylation, measured by reduced representation bisulfite sequencing, differed in the sperm of human users from non-users by at least 10% at 3,979 CpG sites. Pathway analyses indicated Hippo Signaling and Pathways in Cancer as enriched with altered genes (Bonferroni p < 0.02). These same two pathways were also enriched with genes having altered methylation in sperm from THC-exposed versus vehicle-exposed rats (p < 0.01). Data validity is supported by significant correlations between THC exposure levels in humans and methylation for 177 genes, and substantial overlap in THC target genes in rat sperm (this study) and genes previously reported as having altered methylation in the brain of rat offspring born to parents both exposed to THC during adolescence. In humans, cannabis use was also associated with significantly lower sperm concentration. Findings point to possible pre-conception paternal reproductive risks associated with cannabis use.

Significantly altered peripheral blood cell DNA methylation profile as a result of immediate effect of metformin use in healthy individuals

BACKGROUND

Metformin is a widely prescribed antihyperglycemic agent that has been also associated with multiple therapeutic effects in various diseases, including several types of malignancies. There is growing evidence regarding the contribution of the epigenetic mechanisms in reaching metformin's therapeutic goals; however, the effect of metformin on human cells in vivo is not comprehensively studied. The aim of our study was to examine metformin-induced alterations of DNA methylation profiles in white blood cells of healthy volunteers, employing a longitudinal study design.

RESULTS

Twelve healthy metformin-naïve individuals where enrolled in the study. Genome-wide DNA methylation pattern was estimated at baseline, 10 h and 7 days after the start of metformin administration. The whole-genome DNA methylation analysis in total revealed 125 differentially methylated CpGs, of which 11 CpGs and their associated genes with the most consistent changes in the DNA methylation profile were selected: POFUT2, CAMKK1, EML3, KIAA1614, UPF1, MUC4, LOC727982, SIX3, ADAM8, SNORD12B, VPS8, and several differentially methylated regions as novel potential epigenetic targets of metformin. The main functions of the majority of top-ranked differentially methylated loci and their representative cell signaling pathways were linked to the well-known metformin therapy targets: regulatory processes of energy homeostasis, inflammatory responses, tumorigenesis, and neurodegenerative diseases.

CONCLUSIONS

Here we demonstrate for the first time the immediate effect of short-term metformin administration at therapeutic doses on epigenetic regulation in human white blood cells. These findings suggest the DNA methylation process as one of the mechanisms involved in the action of metformin, thereby revealing novel targets and directions of the molecular mechanisms underlying the various beneficial effects of metformin.

TRIAL REGISTRATION

EU Clinical Trials Register, 2016-001092-74. Registered 23 March 2017, https://www.clinicaltrialsregister.eu/ctr-search/trial/2016-001092-74/LV .