Trichomonas vaginalis excretory secretory proteins reduce semen quality and male fertility.

Trichomonas vaginalis (T. vaginalis) infection is the most common non-viral sexually transmitted disease (STD) in the world. It can cause male reproductive dysfunction and infertility. However, the pathogenic mechanism is not clear. In this study, the excretory secretory proteins of T. vaginalis (TvESPs) were collected, concentrated, and sterilized. After sperm co-cultured with TvESPs, the survival rate and motility of sperms were analyzed by seminal routine examination, and the results showed that the TvESPs could significantly reduce the survival rate and motility of sperms. Fluorescence staining displayed that TvESPs could destroy the integrity of sperm acrosomes. Flow cytometry indicated that TvESPs induced sperm apoptosis. By mouse in vitro fertilization, we confirmed that TvESPs could significantly reduce the fertilization ability of sperms and negatively affect the development of the fertilized ovum. Via semi-quantitative analysis, we found that the apoptosis-related p27, SMAC, p53, BAX, BCL-2, XIAP, and BCL-W molecules were down-regulated in mouse sperm cells after interaction between the sperms and TvESPs, which played an important role in regulating sperm apoptosis. In conclusion, our study showed that T. vaginalis degraded semen quality and negatively affected male fertility by TvESPs. TvESPs may damage sperms by breaking the balance between sperm pro-apoptotic and anti-apoptotic molecules. This study proves that T. vaginalis infection is a risk factor for infertility.