Expression of miR-339-3p and OPRM1 in relation to sperm function in male infertility.

Background: Infertility is the inability of a couple to conceive after 12 months of unprotected intercourse. The µ-opioid receptor involved in mediating opioid effects and may be associated with male fertility. µ-Opioid receptors were expressed in testicular tissues and spermatozoa, where they may influence spermatogenesis and sperm motility. miR-339-3p was thought to suppress OPRM1 mRNA expression in neuronal cells following opioid exposure through post-transcriptional modulation. However, its role in male infertility remains unexplored.

Objectives: To investigate the relationship between miR-339-3p expression, OPRM1 mRNA expression, and µ-opioid receptor protein level in spermatozoa of infertile versus fertile men, and to assess their association with semen parameters, oxidative stress, and hormonal profile.

Materials and methods: This case-controlled study was conducted on 45 infertile men and 45 healthy fertile men recruited from andrology outpatient clinic, Mansoura University Hospital. Semen analysis, acrosin activity, oxidative stress markers, and serum hormones levels were evaluated. Relative quantification of miR-339-3p and OPRM1 mRNA expression was quantified using qRT-PCR. µ-Opioid receptor protein levels were measured by enzyme-linked immunosorbent assay technique. Correlation and receiver-operating characteristic analyses were performed.

Results: Infertile men exhibited significantly elevated levels of µ-opioid receptor protein (median: 6.41 ng/mL) compared to fertile controls (5.45 ng/mL, p < 0.001), alongside a marked upregulation of OPRM1 mRNA expression (relative quantification = 4.05 vs. 0.993, p < 0.001), representing approximately a 4.08-fold increase. In contrast, miR-339-3p expression was significantly reduced in the infertile group (relative quantification = 0.538 vs. 1.01, p < 0.001), indicating an approximate 0.53-fold change, or nearly 2-fold downregulation. A significant negative correlation was observed between miR-339-3p and OPRM1 mRNA levels (r_s = -0.704, p < 0.001). Receiver-operating characteristic analysis indicated excellent diagnostic accuracy for OPRM1 mRNA (AUC = 0.916) and miR-339-3p (AUC = 0.914) in differentiating infertile from fertile men.

Conclusions: Downregulation of miR-339-3p and overexpression of µ-opioid receptor are associated with impaired semen quality and oxidative imbalance in infertile men. These molecular markers may serve as potential diagnostic indicators in male infertility, pending further validation.