Disrupted sperm mirna expression profiles revealed a fingerprint of impaired spermatogenesis in oligozoospermia males

Abstract

MicroRNAs (miRNAs) are short, single stranded noncoding RNA molecules that function as post-transcriptional regulators inhibiting mRNA translation. Sperm microRNAs have been recognized as playing a key role in testicular function. However, there are limited studies investigating the importance of miRNAs in male factor infertility. The aim of this study was to correlate specific sperm miRNA expression in association with male factor infertility diagnoses to further the understanding of miRNAs in impaired spermatogenesis. Research study. Sperm samples were donated with patient consent: oligozoospermia (<10 million/ml; n=7; mean paternal age = 37.7 years), 0% normal morphology (Kruger strict criteria; n=6; mean paternal age = 41.7 years), and normozoospermic controls (n=7; mean paternal age = 38.1 years). miRNA was isolated from individual sperm samples (n=19) to determine the expression profiles of 10 specific miRNAs using qPCR with Taqman® miRNA assays (Thermo Scientific). Statistical analysis was performed with REST© software (Qiagen), significance at P<0.05. There were no significant differences observed between the groups for paternal age. None of the 10 specific miRNAs displayed significant differences in expression levels for the 0% normal morphology group compared to normozoospermic controls or oligozoospermia males. Conversely, oligozoospermia males displayed altered sperm miRNA expression profiles compared to normozoospermic controls, specifically, 3 miRNAs (122, 449 and 15b) exhibited decreased expression (P<0.05), while 2 miRNAs (141 and 200a) showed increased expression (P<0.05). Target gene analysis of these altered miRNAs identified several important spermatogenesis genes including, among others BCL2 (a regulator of spermatogonial apoptosis) and NOTCH1 (differentiation and survival of germ cells). Interestingly, both upregulated miRNAs, miR-141 (6.02 fold; P<0.05) and 200a (3.05 fold; P<0.05), are known suppressors of sperm associated antigen 9 (SPAG9), which is a critical gene located in the acrosomal compartment that has been implicated in capacitation and the sperm-oocyte interaction. Significant suppression of SPAG9 expression could represent one molecular mechanism contributing to compromised spermatogenesis in oligozoospermic males. MiRNAs function post-transcriptionally to regulate downstream target gene expression typically by inhibiting or repressing mRNA translation. Oligozoospermia displayed significant disruptions to specific sperm miRNA expression profiles revealing a fingerprint of impaired spermatogenesis resulting in low sperm concentration. In contrast, it would appear that for these specific miRNAs there was no association with abnormal sperm morphology. Determining the underlying mechanisms associated with male factor infertility will assist in improving clinical diagnosis and patient management during infertility treatment.