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

Effects of cigarette smoking on semen quality, reproductive hormone levels, metabolic profile, zinc and sperm DNA fragmentation in men: results from a population-based study

Background

Cigarette smoking seems to have a negative impact on men's reproductive health, but our knowledge of its effects on the reproductive function of Russian men is still very limited. The purpose of this study was to evaluate the effect of cigarette smoking on semen quality, including sperm DNA fragmentation, hormonal, zinc and metabolic status in young men from the general multi-ethnic Russian population (n=1,222, median age 23 years) and to find out the ethno-specific effects of smoking by comparing male groups of different ethnicity.

Methods

Each participant filled out a standardized questionnaire, provided one blood and semen sample. Semen parameters, serum reproductive hormones, lipids, glucose, uric acid and seminal zinc were analyzed. Participants were classified as smokers (n=450) and non-smokers (n=772), and smokers were stratified into moderate (≤10 cigarettes/day) and heavy (>10 cigarettes/day) smokers.

Results

In the entire study population, heavy smokers were characterized by a decrease in semen volume, total sperm count, sperm concentration and motility, and an increase in sperm DNA fragmentation and teratozoospermia compared with non-smokers (p<0.05). There was also a reduction in the serum and seminal zinc level as well as an impairment in metabolic health in smokers compared with non-smokers (p<0.05). No significant differences between smokers and non-smokers were found for serum levels of LH, FSH, inhibin B, testosterone and estradiol. In the second part of our study, the most numerous ethnic groups of Slavs (n=654), Buryats (n=191), and Yakuts (n=125) were selected from the entire study population. Among three ethnic groups, the smoking intensity was higher in Slavs than in Buryats or Yakuts suggesting a greater tobacco addiction in Slavs than in Asians. A decrease in semen parameters and seminal zinc levels, and an increase in sperm DNA fragmentation and teratozoospermia was observed only in smoking Slavs (p<0.05); moderate decrease in testosterone and increase in triglyceride levels were revealed in smoking Yakuts (p<0.05), but no significant changes were detected in smoking Buryats.

Conclusion

We concluded that cigarette smoking has an ethno-specific effect on male reproductive function, probably due to the different activity of the seminal antioxidant system, which is yet to be elucidated.

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.

Sperm epigenetics landscape: correlation with embryo quality, reproductive outcomes and offspring's health

Epigenetics refers to how gene expression and function are modulated without modifying the DNA sequence but through subtle molecular changes or interactions with it. As spermatogenesis progresses, male germ cells suffer plenty of epigenetic modifications, resulting in the definitive epigenome of spermatozoa conditioning its functionality, and this process can be altered by several internal and external factors. The paternal epigenome is crucial for sperm function, fertilization, embryo development, and offspring's health, and altered epigenetic states are associated with male infertility with or without altered semen parameters, embryo quality impairment, and worse ART outcomes together with the future offspring's health risks mainly through intergenerational transmission of epigenetic marks. Identifying epigenetic biomarkers may improve male factor diagnosis and the development of targeted therapies, not only to improve fertility but also to allow an early detection of risk and disease prevention in the progeny. While still there is much research to be done, hopefully in the near future, improvements in high-throughput technologies applied to epigenomes will permit our understanding of the underlying epigenetic mechanisms and the development of diagnostics and therapies leading to improved reproductive outcomes. In this review, we discuss the mechanisms of epigenetics in sperm and how epigenetics behave during spermatogenesis. Additionally, we elaborate on the relationship of sperm epigenetics with sperm parameters and male infertility, and highlight the impact of sperm epigenetic alterations on sperm parameters, embryo quality, ART outcomes, miscarriage rates and offspring's health. Furthermore, we provide insights into the future research of epigenetic alterations in male infertility.

Impact of waterpipe and tobacco cigarette smoking on global DNA methylation and nuclear proteins genes transcription in spermatozoa: a comparative investigation

BACKGROUND

Waterpipe smoking is harmful and dangerous, and it is a growing threat to public health.

OBJECTIVES

This study was performed to evaluate the influence of waterpipe smoking on global DNA methylation, DNA fragmentation, and protamine deficiency in spermatozoa compared to cigarette heavy smokers and nonsmokers, and to determine whether the transcription levels of spermatozoa nuclear proteins genes 'PRM1, PRM2, and H2BFWT' in waterpipe smokers are different compared to cigarette heavy smokers and nonsmokers.

METHODS

A total of 900 semen samples were collected from males with a mean age of 32.5 ± 6.3 years (300 waterpipe smokers, 300 cigarette heavy smokers, and 300 nonsmokers). The nucleic acids were isolated from purified spermatozoa, and then the global DNA methylation and transcription levels of the PRM1, PRM2, and H2BFWT genes were assessed using ELISA and qPCR, respectively.

RESULTS

A significant increase was found in the level of global DNA methylation (8.6 ± 0.6 ng/μl vs. 7.1 ± 0.6 ng/μl and 4.7 ± 0.6 ng/μl, p < 0.001), protamine deficiency (72.8 ± 15.3 vs. 51.7 ± 19.2 and 15.3 ± 5.9%, p < 0.001), and DNA fragmentation (73.4 ± 13.4 vs. 50.5 ± 18.9 and 9.3 ± 4.3%, p < 0.001) in waterpipe smokers compared to cigarette heavy smokers and nonsmokers. A significant increase was shown in the transcription levels of PRM1, PRM2, and H2BFWT genes in waterpipe smokers compared to cigarette heavy smokers and nonsmokers (p < 0.001). A down-regulation was found in the transcription level of these genes in different smoker groups compared to nonsmokers (<0.001).

CONCLUSION

This study suggests that waterpipe smoking is more harmful than cigarette smoking on semen parameters, global DNA methylation, and transcription of nuclear protein genes.

Targeted DNA methylation analysis and prediction of smoking habits in blood based on massively parallel sequencing

Tobacco smoking is a frequent habit sustained by > 1.3 billion people in 2020 and the leading preventable factor for health risk and premature mortality worldwide. In the forensic context, predicting smoking habits from biological samples may allow broadening DNA phenotyping. In this study, we aimed to implement previously published smoking habit classification models based on blood DNA methylation at 13 CpGs. First, we developed a matching lab tool based on bisulfite conversion and multiplex PCR followed by amplification-free library preparation and targeted paired-end massively parallel sequencing (MPS). Analysis of six technical duplicates revealed high reproducibility of methylation measurements (Pearson correlation of 0.983). Artificially methylated standards uncovered marker-specific amplification bias, which we corrected via bi-exponential models. We then applied our MPS tool to 232 blood samples from Europeans of a wide age range, of which 90 were current, 71 former and 71 never smokers. On average, we obtained 189,000 reads/sample and 15,000 reads/CpG, without marker drop-out. Methylation distributions per smoking category roughly corresponded to previous microarray analysis, showcasing large inter-individual variation but with technology-driven bias. Methylation at 11 out of 13 smoking-CpGs correlated with daily cigarettes in current smokers, while solely one was weakly correlated with time since cessation in former smokers. Interestingly, eight smoking-CpGs correlated with age, and one displayed weak but significant sex-associated methylation differences. Using bias-uncorrected MPS data, smoking habits were relatively accurately predicted using both two- (current/non-current) and three- (never/former/current) category model, but bias correction resulted in worse prediction performance for both models. Finally, to account for technology-driven variation, we built new, joint models with inter-technology corrections, which resulted in improved prediction results for both models, with or without PCR bias correction (e.g. MPS cross-validation F₁-score > 0.8; 2-categories). Overall, our novel assay takes us one step closer towards the forensic application of viable smoking habit prediction from blood traces. However, future research is needed towards forensically validating the assay, especially in terms of sensitivity. We also need to further shed light on the employed biomarkers, particularly on the mechanistics, tissue specificity and putative confounders of smoking epigenetic signatures.

An epigenetic synopsis of parental substance use

The rate of substance use is rising, especially among reproductive-age individuals. Emerging evidence suggests that paternal pre-conception and maternal prenatal substance use may alter offspring epigenetic regulation (changes to gene expression without modifying DNA) and outcomes later in life, including neurodevelopment and mental health. However, relatively little is known due to the complexities and limitations of existing studies, making causal interpretations challenging. This review examines the contributions and influence of parental substance use on the gametes and potential transmissibility to the offspring's epigenome as possible areas to target public health warnings and healthcare provider counseling of individuals or couples in the pre-conception and prenatal periods to ultimately mitigate short- and long-term offspring morbidity and mortality.

Effect of hubble-bubble smoking on global DNA methylation and transcription levels of protamine and histone genes in human spermatozoa

This study was conducted to assess the impact of hubble-bubble smoking on global DNA methylation, DNA fragmentation; protamine deficiency of spermatozoa, and to determine whether the transcription levels of the protamine and histone genes are different in hubble-bubble smokers compared to nonsmokers. Five hundred semen samples were collected from males with an average age of 32.2 ± 6.1 years (300 hubble-bubble smokers "60%" and 200 nonsmokers "40%"). The nucleic acid was isolated from purified sperm, then ELISA and qPCR were used to evaluate the global DNA methylation and transcription level of protamine and histone, respectively. A significant elevation in global DNA methylation, protamine deficiency, and DNA fragmentation was found in hubble-bubble smokers compared to nonsmokers (P < 0.0001). A significant decline was shown in transcription levels of protamine and histone genes in hubble-bubble compared to nonsmokers (P < 0.0001). Additionally, a down-regulation in the transcription levels of protamine and histone was revealed in hubble-bubble compared to nonsmokers with fold change (0.0001 and 0.007, respectively). In conclusion, this study provided proof that hubble-bubble smoking has a negative impact on global DNA methylation, DNA fragmentation, protamine deficiency, and the transcription of protamine and histone genes in spermatozoa, and these findings influence negatively males' fecundity.