New insights into the expression profile and function of micro-ribonucleic acid in human spermatozoa

Objective: To characterize the microRNA (miRNA) expression profile in spermatozoa from human fertile individuals and their implications in human fertility.

Design: The expression levels of 736 miRNAs were evaluated using TaqMan arrays. Ontologic analyses were performed to determine the presence of enriched biological processes among their targets.

Setting: University research and clinical institutes.

Patient(s): Ten individuals with normal seminogram, standard karyotype, and proven fertility.

Intervention(s): None.

Main outcome measure(s): Expression levels of 736 miRNAs, presence of enriched metabolic routes among their targets, homogeneity of the population, influence of demographic features in the results, presence of miRNA stable pairs, and best miRNA normalizing candidates.

Result(s): A total of 221 miRNAs were consistently present in all individuals, 452 were only detected in some individuals, and 63 did not appear in any sample. The ontologic analysis of the 2,356 potential targets of the ubiquitous miRNAs showed an enrichment of processes related to cell differentiation, development, morphogenesis, and embryogenesis. None of the miRNAs were significantly correlated with age, semen volume, sperm concentration, motility, or morphology. Correlations between samples were statistically significant, indicating a high homogeneity of the population. A set of 48 miRNA pairs displayed a stable expression, a particular behavior that is discussed in relationship to their usefulness as fertility biomarkers. Hsa-miR-532-5p, hsa-miR-374b-5p, and hsa-miR-564 seemed to be the best normalizing miRNA candidates.

Conclusion(s): Human sperm contain a stable population of miRNAs potentially related to embryogenesis and spermatogenesis.