Cysteine-rich secretory
protein 2 (CRISP2) is an important sperm
protein and plays roles in spermatogenesis, modulation of flagellar motility, acrosome reaction, and gamete fusion. Clinical evidence shows a reduced CRISP2 expression in spermatozoa from asthenozoospermic patients, but the molecular mechanism underlying its reduction remains unknown. Herein, we carried out a study focusing on the CRISP2 reduction and its roles in
asthenozoospermia. Initially, through analyzing CRISP2 expression and methylation on CRISP2 promoter activity in sperm, we observed a decreased expression of CRISP2
protein rather than its
mRNA in the ejaculated spermatozoa from asthenozoospermic patients and no methylation in the CRISP2 promoter, suggesting CRISP2 expression may be regulated in the sperm at the posttranscriptional level. Subsequently, we found that
microRNA 27b (miR-27b), predicted as a candidate regulator of CRISP2 using bioinformatics, was highly expressed in the ejaculated spermatozoa from asthenozoospermic patients.
Luciferase reporter assay and transfection experiments disclosed that this
microRNA could target CRISP2 by specifically binding its
3' untranslated region, suppressing CRISP2 expression. Extended clinical observation further confirmed a highly expressed miR-27b and its obviously negative correlation with CRISP2
protein expression in ejaculated spermatozoa samples from asthenozoospermic patients. Finally, we conducted a retrospective follow-up study to support that either high miR-27b expression or low CRISP2
protein expression was significantly associated with low sperm progressive motility, abnormal morphology, and
infertility. Thus, this study provides the first preliminary insight into the mechanism leading to the reduced CRISP2 expression in
asthenozoospermia, offering a potential therapeutic target for treating
male infertility or for
male contraception.