Spermatozoa acquire fertilization ability through post-translational modifications. These membrane surface alterations occur in various segments of the epididymis. Quiescin sulfhydryl
oxidases, which catalyze
thiol-oxidation reactions, are involved in
disulfide bond formation, which is essential for sperm maturation, upon transition and migration in the epididymis. Using
castration and
azoospermia transgenic mouse models, in the present study, we showed that quiescin
sulfhydryl oxidase 1 (QSOX1)
protein expression and secretion are positively correlated with the presence of
testosterone and sperm cells. A two-dimensional in vitro epithelium-sperm co-culture system provided further evidence in support of the notion that both
testosterone and its dominant metabolite, 5α-dihydrotestosterone, promote epididymal QSOX1 secretion. We also demonstrated that immature caput spermatozoa, but not mature cauda sperm cells, exhibited great potential to stimulate QSOX1 secretion in vitro, suggesting that sperm maturation is a key regulatory factor for mouse epididymal QSOX1 secretion. Proteomic analysis identified 582 secretory
proteins from the co-culture supernatant, of which 258 were sperm-specific and 154 were of epididymal epithelium-origin. Gene Ontology analysis indicated that these secreted
proteins exhibit functions known to facilitate sperm membrane organization, cellular activity, and sperm-egg recognition. Taken together, our data demonstrated that
testosterone and sperm maturation status are key regulators of mouse epididymal QSOX1
protein expression and secretion.