The role of miRNAs in male human reproduction: a systematic review.

BACKGROUND: The presence of miRNAs in human reproductive tissue is intriguing and suggests the possibility that these important regulatory molecules play a role in reproductive function. However, the regulatory role of miRNAs in reproductive tissue remains poorly understood with a significant amount of controversial and contradicting data. OBJECTIVES: To systematically review the high-quality studies published to date investigating miRNAs associated with male human reproduction in order to describe their roles and relations with infertility and update the knowledge in the field. MATERIALS AND METHODS: A comprehensive systematic review of the published literature in MEDLINE-PubMed and EMBASE databases from the earliest available online indexing year until June 2018 (complimentary search until July 2019) was performed, in accordance with the PRISMA guidelines. We have included descriptive, case-control, cross-sectional, and observational prospective and retrospective studies in which fertile/infertile men were well-defined. The primary outcome was the miRNA expression in testis, epididymis, sperm cells, seminal plasma, and extracellular vesicles (i.e., exosomes and microvesicles). RESULTS: We identified 25,204 articles, of which 42 were selected for qualitative analysis. Of the 42 articles included, 15 evaluated the miRNAs in testis, five in epididymis, 13 in spermatozoa, and 11 in seminal plasma and/or extracellular vesicles. Two studies tackled more than one sub-group. As far as miRNA presence and content, the results of this systematic review indicated that every tissue/cell contains a well-defined and stable population of miRNAs that could be potentially related to spermatogenesis and embryogenesis. DISCUSSION AND CONCLUSION: Our systematic review of descriptive and observational studies shows a consistent relationship between aberrant miRNA expression and infertility. Therefore, it seems reasonable that measuring the expression of particular miRNAs might be useful not only as infertility biomarkers, but also for developing therapeutic strategies.

Semen parameters are unaffected by statin use in men evaluated for infertility.

The effects of statin use on conventional semen parameters in humans are largely unknown and have not been previously studied in subfertile men. We retrospectively reviewed data from 10,140 patients seen at our fertility clinic between 2002 and 2013 to assess the effects of statin use on semen parameters. Men who used any statins for >3 months before semen sample collection were included as cases. Data were gathered on patient age, medication use and conventional semen parameters. A total of 118 patients (126 samples) used statins for at least 3 months before semen sample collection. Data from 7698 patients (8,760 samples), who were not using any medications, were used as controls. In age-adjusted regression models, statin use was not associated with statistically significant changes in semen parameters. When used in combination with other nonspermatotoxic medications, it was associated with 0.3 ml decrease in semen volume (95% confidence interval: 0.02 to 0.58 ml, p-value = .04). In conclusion, statin use was not adversely associated with semen parameters other than semen volume in subfertile patients. These findings from our large-scale retrospective study suggest that there are no clinically relevant deleterious effects from statin use on conventional semen parameters.

Cigarette smoking significantly alters sperm DNA methylation patterns.

Numerous health consequences of tobacco smoke exposure have been characterized, and the effects of smoking on traditional measures of male fertility are well described. However, a growing body of data indicates that pre-conception paternal smoking also confers increased risk for a number of morbidities on offspring. The mechanism for this increased risk has not been elucidated, but it is likely mediated, at least in part, through epigenetic modifications transmitted through spermatozoa. In this study, we investigated the impact of cigarette smoke exposure on sperm DNA methylation patterns in 78 men who smoke and 78 never-smokers using the Infinium Human Methylation 450 beadchip. We investigated two models of DNA methylation alterations: (i) consistently altered methylation at specific CpGs or within specific genomic regions and (ii) stochastic DNA methylation alterations manifest as increased variability in genome-wide methylation patterns in men who smoke. We identified 141 significantly differentially methylated CpGs associated with smoking. In addition, we identified a trend toward increased variance in methylation patterns genome-wide in sperm DNA from men who smoke compared with never-smokers. These findings of widespread DNA methylation alterations are consistent with the broad range of offspring heath disparities associated with pre-conception paternal smoke exposure and warrant further investigation to identify the specific mechanism by which sperm DNA methylation perturbation confers risk to offspring health and whether these changes can be transmitted to offspring and transgenerationally.

Sperm DNA damage output parameters measured by the alkaline Comet assay and their importance.

The alkaline Comet assay has shown high diagnostic value to determine male reproductive health and prognostic ability to predict ART success. Here, spermatozoon was analysed in 47 fertile donors and 238 patients, including 132 couples undergoing ART [semen was collected: Group I - within 3 months of their treatment (n = 79); and Group II - 3 months prior to their treatment (n = 53)]. We introduce four Comet distribution plots (A, B1, B2 and C) by plotting the level of DNA damage (x-axis) and percentage of comets (y-axis). Fertile donors had low mean DNA damage, olive tail moment and per cent of spermatozoa with damage and increased type A plots. Comet parameters were associated with clinical pregnancies in Group I. About 66% of couples with type A distribution plot were successful after ART, whereas couples with type B1, B2 and C distribution plots achieved 56%, 44% and 33% pregnancies respectively. The efficiency of the Comet assay was due to complete decondensation process, where the compact sperm nuclear DNA (28.2 ± 0.2 µm3 ) is decondensed to ~63 µm3 (before lysis) and ~1018 µm3 (after lysis). A combinational analysis of all the Comet output parameters may provide a comprehensive evaluation of patient's reproductive health as these parameters measure different aspects of DNA damage within the spermatozoa.

Teratozoospermia and asthenozoospermia are associated with specific epigenetic signatures.

Semen analysis is commonly used as a tool to assess the fertility potential of a male, despite its relatively low predictive power. In this study, we have assessed associations between semen analysis findings (low count, low motility, low viability, poor sperm penetration assay results, poor morphology, and increased DNA damage) and DNA methylation patterns in mature spermatozoa. DNA methylation patterns in the mature spermatozoa are thought to be indicative of patterns in the adult germline stem cells and may offer insight into potential perturbations to cellular pathways involved in spermatogenesis. In this study, sperm DNA methylation at >480,000 CpGs was assessed in 94 men using the Illumina 450k HumanMethylation Array and compared to standard measures of sperm quality. We did not identify any global changes to methylation profiles that were associated with reduced semen parameters. Similarly, we found no significant difference in methylation variability that was associated with any abnormal semen analysis parameter, although sperm displaying abnormal parameters tended to have an increased coefficient of variability, suggesting that, in some samples, this may be a contributing factor. Analysis of methylation at single CpGs and genomic regions did identify associations for low viability and low motility, and to a smaller extent, low count. Interestingly, based on GO Term analysis, differentially methylated regions associated with low viability were over-represented in regions important in meiosis, spermatogenesis, and genomic imprinting. These results suggest that while there are not global alterations to the sperm methylome associated with semen abnormalites, some viability associated regional alterations do exist that may be indicative of perturbed cellular pathways during spermatogenesis.

Genetic variation among 82 pharmacogenes: The PGRNseq data from the eMERGE network.

Genetic variation can affect drug response in multiple ways, although it remains unclear how rare genetic variants affect drug response. The electronic Medical Records and Genomics (eMERGE) Network, collaborating with the Pharmacogenomics Research Network, began eMERGE-PGx, a targeted sequencing study to assess genetic variation in 82 pharmacogenes critical for implementation of "precision medicine." The February 2015 eMERGE-PGx data release includes sequence-derived data from ∼5,000 clinical subjects. We present the variant frequency spectrum categorized by variant type, ancestry, and predicted function. We found 95.12% of genes have variants with a scaled Combined Annotation-Dependent Depletion score above 20, and 96.19% of all samples had one or more Clinical Pharmacogenetics Implementation Consortium Level A actionable variants. These data highlight the distribution and scope of genetic variation in relevant pharmacogenes, identifying challenges associated with implementing clinical sequencing for drug treatment at a broader level, underscoring the importance for multifaceted research in the execution of precision medicine.

A genome-wide association study identifies variants in KCNIP4 associated with ACE inhibitor-induced cough.

The most common side effect of angiotensin-converting enzyme inhibitor (ACEi) drugs is cough. We conducted a genome-wide association study (GWAS) of ACEi-induced cough among 7080 subjects of diverse ancestries in the Electronic Medical Records and Genomics (eMERGE) network. Cases were subjects diagnosed with ACEi-induced cough. Controls were subjects with at least 6 months of ACEi use and no cough. A GWAS (1595 cases and 5485 controls) identified associations on chromosome 4 in an intron of KCNIP4. The strongest association was at rs145489027 (minor allele frequency=0.33, odds ratio (OR)=1.3 (95% confidence interval (CI): 1.2-1.4), P=1.0 × 10(-8)). Replication for six single-nucleotide polymorphisms (SNPs) in KCNIP4 was tested in a second eMERGE population (n=926) and in the Genetics of Diabetes Audit and Research in Tayside, Scotland (GoDARTS) cohort (n=4309). Replication was observed at rs7675300 (OR=1.32 (1.01-1.70), P=0.04) in eMERGE and at rs16870989 and rs1495509 (OR=1.15 (1.01-1.30), P=0.03 for both) in GoDARTS. The combined association at rs1495509 was significant (OR=1.23 (1.15-1.32), P=1.9 × 10(-9)). These results indicate that SNPs in KCNIP4 may modulate ACEi-induced cough risk.