Semen quality and sperm DNA integrity in city policemen exposed to polluted air in an urban industrial agglomeration

Sperm chromatin: Evaluation, epigenetic signatures and relevance for embryo development and assisted reproductive technology outcomes

Sperm chromatin is distinct from somatic cell chromatin, as a result of extensive remodeling during the final stages of spermatogenesis. In this process, the majority of histones is replaced with protamines. The chromatin is consequently highly condensed and inert, which facilitates protection of the DNA. The sperm epigenomic landscape is shaped by histone retention, histone and protamine modification, DNA methylation, and RNAs. In recent years, sperm chromatin integrity and its epigenetic marks have been increasingly studied, and the constitution of sperm chromatin is steadily being uncovered. This growing body of research prompts assessment of the frequently overlooked involvement of sperm in fertility and embryonic development. Moreover, numerous endogenous and exogenous factors are known to affect sperm chromatin, which may in turn impact the reproductive success. Concerns have been raised about the effects of assisted reproductive technology (ART) on the sperm epigenome, embryonic development and offspring health. This review examines the structure and epigenetic signatures of sperm chromatin in the context of fertility and early embryonic development. Additionally, sperm chromatin evaluation and causes of aberrant integrity are outlined. Building on the knowledge discussed in the current review, future research should aim to elucidate the intricate relationship between all aspects of sperm chromatin and embryo development. This could lead to the uncovering of new targets for treating infertility, as well as the acquisition of much needed insights into the possible reciprocal association between ART and sperm chromatin integrity.

Episodic ozone exposure in Long-Evans rats has limited effects on cauda sperm motility and non-coding RNA populations

Epidemiological evidence suggests the potential for air pollutants to induce male reproductive toxicity. In experimental studies, exposure to ozone during sensitive windows in the sperm lifecycle has been associated with impaired sperm motility. Subsequently, we sought to investigate the effects of episodic exposure to ozone during sperm maturation in the rat. Long-Evans rats were exposed to either filtered air or ozone (0.4 or 0.8 ppm) for five non-consecutive days over two weeks. Ozone exposure did not impact male reproductive organ weights or sperm motility ∼24 hours following the final exposure. Furthermore, circulating sex hormones remained unchanged despite increased T3 and T4 in the 0.8 ppm group. While there was indication of altered adrenergic signaling attributable to ozone exposure in the testis, there were minimal impacts on small non-coding RNAs detected in cauda sperm. Only two piwi-interacting RNAs (piRNAs) were altered in the mature sperm of ozone-exposed rats (piR-rno-346434 and piR-rno-227431). Data across all rats were next analyzed to identify any non-coding RNAs that may be correlated with reduced sperm motility. A total of 7 microRNAs (miRNAs), 8 RNA fragments, and 1682 piRNAs correlated well with sperm motility. Utilizing our exposure paradigm herein, we were unable to substantiate the relationship between ozone exposure during maturation with sperm motility. However, these approaches served to identify a suite of non-coding RNAs that were associated with sperm motility in rats. With additional investigation, these RNAs may prove to have functional roles in the acquisition of motility or be unique biomarkers for male reproductive toxicity.

Impact of air pollution from different sources on sperm DNA methylation

Environmental exposure is associated with increased incidence of respiratory and cardiovascular diseases and reduced fertility. Exposure to air pollution can influence gene expression through epigenetic mechanisms. In this study, we analysed gene-specific CpG methylation in spermatozoa of city policemen occupationally exposed to air pollution in two Czech cities differing by sources and composition of the air pollution. In Prague, the pollution is mainly formed by NO2 from heavy traffic. Ostrava is a hotspot of industrial air pollution with high concentrations of particular matter (PM) and benzo[a]pyrene (B[a]P). We performed genome-wide methylation sequencing using the SureSelectXT Human Methyl-Seq system (Agilent Technologies) and next-generation sequencing to reveal differentially methylated CpG sites and regions. We identified differential methylation in the region chr5:662169 - 663376 annotated to genes CEP72 and TPPP. The region was then analysed in sperm DNA from 117 policemen using targeted methylation sequencing, which proved its hypermethylation in sperm of Ostrava policemen.

Implications of Exposure to Air Pollution on Male Reproduction: The Role of Oxidative Stress

Air pollution, either from indoor (household) or outdoor (ambient) sources, occurs when there is presence of respirable particles in the form of chemical, physical, or biological agents that modify the natural features of the atmosphere or environment. Today, almost 2.4 billion people are exposed to hazardous levels of indoor pollution, while 99% of the global population breathes air pollutants that exceed the World Health Organization guideline limits. It is not surprising that air pollution is the world's leading environmental cause of diseases and contributes greatly to the global burden of diseases. Upon entry, air pollutants can cause an increase in reactive oxygen species (ROS) production by undergoing oxidation to generate quinones, which further act as oxidizing agents to yield more ROS. Excessive production of ROS can cause oxidative stress, induce lipid peroxidation, enhance the binding of polycyclic aromatic hydrocarbons (PAHs) to their receptors, or bind to PAH to cause DNA strand breaks. The continuous and prolonged exposure to air pollutants is associated with the development or exacerbation of pathologies such as acute or chronic respiratory and cardiovascular diseases, neurodegenerative and skin diseases, and even reduced fertility potential. Males and females contribute to infertility equally, and exposure to air pollutants can negatively affect reproduction. In this review, emphasis will be placed on the implications of exposure to air pollutants on male fertility potential, bringing to light its effects on semen parameters (basic and advanced) and male sexual health. This study will also touch on the clinical implications of air pollution on male reproduction while highlighting the role of oxidative stress.

Association of living environmental and occupational factors with semen quality in chinese men: a cross-sectional study

Sperm quality can be easily influenced by living environmental and occupational factors. This study aimed to discover potential semen quality related living environmental and occupational factors, expand knowledge of risk factors for semen quality, strengthen men's awareness of protecting their own fertility and assist the clinicians to judge the patient's fertility. 465 men without obese or underweight (18.5 < BMI < 28.5 kg/m2), long-term medical history and history of drug use, were recruited between June 2020 to July 2021, they are in reproductive age (25 < age < 45 years). We have collected their semen analysis results and clinical information. Logistic regression was applied to evaluate the association of semen quality with different factors. We found that living environment close to high voltage line (283.4 × 106/ml vs 219.8 × 106/ml, Cohen d = 0.116, P = 0.030) and substation (309.1 × 106/ml vs 222.4 × 106/ml, Cohen d = 0.085, P = 0.015) will influence sperm count. Experienced decoration in the past 6 months was a significant factor to sperm count (194.2 × 106/ml vs 261.0 × 106/ml, Cohen d = 0.120, P = 0.025). Living close to chemical plant will affect semen PH (7.5 vs 7.2, Cohen d = 0.181, P = 0.001). Domicile close to a power distribution room will affect progressive sperm motility (37.0% vs 34.0%, F = 4.773, Cohen d = 0.033, P = 0.030). Using computers will affect both progressive motility sperm (36.0% vs 28.1%, t = 2.762, Cohen d = 0.033, P = 0.006) and sperm total motility (57.0% vs 41.0%, Cohen d = 0.178, P = 0.009). After adjust for potential confounding factors (age and BMI), our regression model reveals that living close to high voltage line is a risk factor for sperm concentration (Adjusted OR 4.03, 95% CI 1.15-14.18, R2 = 0.048, P = 0.030), living close to Chemical plants is a protective factor for sperm concentration (Adjusted OR 0.15, 95% CI 0.05-0.46, R2 = 0.048, P = 0.001) and total sperm count (Adjusted OR 0.36, 95% CI 0.13-0.99, R2 = 0.026, P = 0.049). Time spends on computer will affect sperm total motility (Adjusted OR 2.29, 95% CI 1.11-4.73, R2 = 0.041, P = 0.025). Sum up, our results suggested that computer using, living and working surroundings (voltage line, substation and chemical plants, transformer room), and housing decoration may association with low semen quality. Suggesting that some easily ignored factors may affect male reproductive ability. Couples trying to become pregnant should try to avoid exposure to associated risk factors. The specific mechanism of risk factors affecting male reproductive ability remains to be elucidated.

Effects of various environments on epigenetic settings and chromosomal damage

Air pollution is a dominant environmental exposure factor with significant health consequences. Unexpectedly, research in a heavily polluted region of the Czech Republic, with traditional heavy industry, revealed repeatedly the lowest frequency of micronuclei in the season with the highest concentrations of air pollutants including carcinogenic benzo[a]pyrene (B[a]P). Molecular findings have been collected for more than 10 years from various locations of the Czech Republic, with differing quality of ambient air. Preliminary conclusions have suggested adaptation of the population from the polluted locality (Ostrava, Moravian-Silesian Region (MSR)) to chronic air pollution exposure. In this study we utilize the previous findings and, for the first time, investigate micronuclei (MN) frequency by type: (i) centromere positive (CEN+) MN, representing chromosomal losses, and (ii) centromere negative (CEN-) MN representing chromosomal breaks. As previous results indicated differences between populations in the expression of XRCC5, a gene involved in the non-homologous end-joining (NHEJ) repair pathway, possible variations in epigenetic settings in this gene were also investigated. This new research was conducted in two seasons in the groups from two localities with different air quality levels (Ostrava (OS) and Prague (PG)). The obtained new results show significantly lower frequencies of chromosomal breaks in the OS subjects, related to the highest air pollution levels (p < 0.001). In contrast, chromosomal losses were comparable between both groups. In addition, significantly lower DNA methylation was found in 14.3% of the analyzed CpG loci of XRCC5 in the population from OS. In conclusion, the epigenetic adaptation (hypomethylation) in XRCC5 involved in the NHEJ repair pathway in the population from the polluted region, was suggested as a reason for the reduced level of chromosomal breaks. Further research is needed to explore the additional mechanisms, including genetic adaptation.

Decrease of air pollution during lockdown in Tuscany (Italy): An effect on sperm DNA fragmentation?

In March 2020, the Italian government imposed a national lockdown which was almost completely removed in June 2020. Due to the abrupt stop of human activities, emissions of air pollutants decreased. Air pollution is an environmental risk factor for noncommunicable disease and mortality. Emerging evidence also suggests a role in male infertility. In this study, we compared sperm DNA fragmentation (sDF) levels and conventional semen parameters between subjects undergoing sDF determination and routine semen analysis in a single Italian centre, during about 6 months before (N = 119) and after lockdown (N = 105). After lockdown, we found an improvement of sperm progressive motility (48.00[38.50-58.00]% vs. 42.00[33.00-53.00]%) and sDF levels (as total: 24.79[18.33-33.97]% vs. 35.02[25.04-45.73]%, p < .001; brighter: 14.02[10.69-17.93]% vs 18.54[13.58-25.82]%, p < .001 and dimmer sDF: 9.24[5.64-15.78]% vs. 12.24[8.08-19.10]%, p < .01), mirrored by a decrease of leukocyte semen concentration (p < .01). The improvement of sperm motility and DNA quality was maintained after adjusting for leukocyte concentration and several conditions known to affect sperm motility and/or sDF levels. With a significant decrease in air pollution observed in Tuscany during and after lockdown, associated improvement in sperm motility and DNA quality in patients referred to the infertility clinic is suggestive of the potential role of air pollution in male infertility.

Spectrum of sperm mtDNA deletions in men exposed to industrial air pollution

Sperm mtDNA status can serve as a molecular marker of oxidative stress and environmental exposure. High levels of air pollution may be associated with increased mitochondrial DNA (mtDNA) deletion rates in sperm. We compared the length spectra of sperm mtDNA deletions in semen samples collected from city policemen exposed to traffic and industrial air pollution in two seasons with different levels of air pollution. We used long-range PCR to amplify a fragment of mtDNA (8066 bp) frequently affected by deletions, visualized the PCR products by gel electrophoresis, and analysed aberrant bands corresponding to deleted mtDNA, using gel documentation software. The predominance of undeleted sperm mtDNA was accompanied by a variety of shorter PCR product lengths in the vast majority of sperm samples, in both seasons. Sperm mtDNA molecules and bands corresponding to long deletions were more frequently detected than shorter deletions, in both seasons. We did not detect any difference in the total number of electrophoretic bands corresponding to deleted sperm mtDNA and in the number of deleted sperm mtDNA molecules between the two seasons. In our study, air pollution during sperm maturation did not induce formation of large mtDNA deletions detectable by long PCR and gel electrophoresis (>1 kb) in maturing sperm mtDNA.

Association between sperm mitochondrial DNA copy number and deletion rate and industrial air pollution dynamics

The effects of air pollution on men's reproductive health can be monitored by evaluating semen quality and sperm DNA damage. We used real-time PCR to analyse the effects of air pollution on sperm mitochondrial DNA copy number (mtDNAcn) and deletion (mtDNAdel) rates in semen samples collected from 54 men in two seasons with different levels of industrial and traffic air pollution. MtDNAdel rates were significantly higher following the high exposure period and were positively correlated with mtDNAcn. However, we did not find any difference in mtDNAcn between the two seasons. MtDNAcn was positively correlated with the DNA fragmentation index and the rates of sperm with chromatin condensation defects, previously assessed by sperm chromatin structure assay, and negatively correlated with sperm concentration, progressive motility, viability, and normal morphology. This indicates that mtDNAcn is more closely associated with male fertility than mtDNAdel rates. In contrast, mtDNAdel might be a more sensitive biomarker of air pollution exposure in urban industrial environments.

Genome-Wide DNA Methylation in Policemen Working in Cities Differing by Major Sources of Air Pollution

DNA methylation is the most studied epigenetic mechanism that regulates gene expression, and it can serve as a useful biomarker of prior environmental exposure and future health outcomes. This study focused on DNA methylation profiles in a human cohort, comprising 125 nonsmoking city policemen (sampled twice), living and working in three localities (Prague, Ostrava and Ceske Budejovice) of the Czech Republic, who spent the majority of their working time outdoors. The main characterization of the localities, differing by major sources of air pollution, was defined by the stationary air pollution monitoring of PM2.5, B[a]P and NO₂. DNA methylation was analyzed by a genome-wide microarray method. No season-specific DNA methylation pattern was discovered; however, we identified 13,643 differentially methylated CpG loci (DML) for a comparison between the Prague and Ostrava groups. The most significant DML was cg10123377 (log₂FC = −1.92, p = 8.30 × 10⁻⁴) and loci annotated to RPTOR (total 20 CpG loci). We also found two hypomethylated loci annotated to the DNA repair gene XRCC5. Groups of DML annotated to the same gene were linked to diabetes mellitus (KCNQ1), respiratory diseases (PTPRN2), the dopaminergic system of the brain and neurodegenerative diseases (NR4A2). The most significant possibly affected pathway was Axon guidance, with 86 potentially deregulated genes near DML. The cluster of gene sets that could be affected by DNA methylation in the Ostrava groups mainly includes the neuronal functions and biological processes of cell junctions and adhesion assembly. The study demonstrates that the differences in the type of air pollution between localities can affect a unique change in DNA methylation profiles across the human genome.