Secretory mouse quiescin sulfhydryl oxidase 1 aggregates defected human and mouse spermatozoa in vitro and in vivo

A flavin-dependent enzyme quiescin Q6 sulfhydryl oxidase 1 (QSOX1) catalyzes the oxidation of thiol groups into disulfide bonds. QSOX1 is prominently expressed in the seminal plasma. However, its role in male reproduction is elusive. Here, we purified the secreted form of QSOX1, i.e., QSOX1c, from mouse seminal vesicle secretions and revealed for the first time its function involved in sperm physiology. Exogenous addition of QSOX1c time-dependently promoted the in vitro aggregation of thiol-rich, oxidative stressed, and apoptotic mouse and human sperm cells. Also, in vivo aggregated sperm cells collected from mouse uterine and human ejaculates also showed high levels of QSOX1c, intracellular reactive oxygen species, annexin V, and free thiols. In summary, our studies demonstrated that QSOX1c could agglutinate spermatozoa susceptible to free radical attack and apoptosis. This characteristic may provide an opportunity to separate defective sperm cells and improve sperm quality before artificial insemination in humans and animals.