siRNA-mediated Eppin testicular silencing causes changes in sperm motility and calcium currents in mice

Epididymal protease inhibitor (EPPIN) is differentially expressed in the reproductive tissues (such as testicles, outlet tubes, epididymis, vas deferens, and seminal vesicles). Its critical role in sperm function and male reproduction has shed light on EPPIN as a candidate target for male contraceptive vaccines. In this study, we endeavored to further reveal the mechanism through which EPPIN exerts its function. We created a mouse model of reduced Eppin expression by microinjecting small interfering RNA targeting Eppin expression into seminiferous tubules of mice. This mouse model was then used to explore the effects of low Eppin expression on sperm function, which was assessed by Computer Assisted Semen Analysis and patch clamp recording of T-type Ca²⁺ current in spermatogenic cells. We found that the sperm motility significantly declined when Eppin was downregulated. Further investigation demonstrated that Eppin downregulation significantly affected T-type Ca²⁺ currents and messenger RNA expression of three subtypes of T-type Ca²⁺ channels in spermatogenic cells. These findings indicate that low Eppin gene expression induces decreased T-type Ca²⁺ currents and mRNA expression, which in turn results in the reduced sperm motility.