Background
Currently, the precise mechanisms that underline male infertility are still unclear. Accumulating data implicate non-coding RNA cargo of seminal plasma extracellular vesicles due to their association with poor semen quality and higher expression levels relative to vesicle-free seminal plasma. Method: We assessed sperm-free seminal plasma extracellular vesicle non-coding RNA profiles from 91 semen samples collected from male participants of couples seeking infertility treatment. Men were classified into two groups (poor, n = 32; normal, n = 59) based on World Health Organization semen cutoffs. Small RNA sequencing reads were mapped to standard biotype-specific transcriptomes in the order micro RNA > transfer RNA > piwi-interacting RNA > ribosomal RNA > ribosomal RNA > circular RNA > long non-coding RNA using STAR. Differential expression of normalized non-coding RNA read counts between the two groups was conducted by EdgeR (Fold change ≥1.5 and (false discovery rate [FDR] < 0.05). Result: Small RNA sequencing identified a wide variety of seminal plasma extracellular vesicle non-coding RNA biotypes including micro RNA, ribosomal RNAs, piwi-interacting RNAs, transfer RNA, long non-coding RNAs as well as circular RNAs, and fragments associated with pseudogenes, and nonsense-mediated decay. The expression levels of 57 seminal plasma extracellular vesicle non-coding RNAs (micro RNA: 6, piwi-interacting RNA: 4, ribosomal RNA: 6, circular RNA: 34, and long non-coding RNA: 7) were altered in men with poor semen quality relative to normal semen parameters, many (60%) of which were circular RNA species. Ontology analysis of differentially expressed micro RNAs and circular RNAs showed enrichment in functional terms related to cellular communication and early development.
Conclusion
This is the first study to generate comprehensive seminal plasma extracellular vesicle non-coding RNA profiles in a clinical setting and to determine the differences between men with normal and abnormal semen parameters. Thus, our study suggests that seminal plasma extracellular vesicle non-coding RNAs may represent novel biomarkers of male reproductive phenotypes.