The sperm chemoattractant secreted from human cumulus cells is progesterone

BACKGROUND: Human spermatozoa appear to be guided by chemotaxis to the oocyte in the female genital tract. While one of the sources of sperm chemoattractants is the cumulus cells that surround the oocyte, the identity of the chemoattractant secreted from them is unknown. Progesterone, recognized to be secreted from cumulus cells, was demonstrated, at the pM concentration range, to be a chemoattractant for human spermatozoa. Here, we examined whether this steroid is the cumulus-originated chemoattractant for human spermatozoa. METHODS: Human cumulus cells were cultured, and the cultured medium was demonstrated to be chemotactically active. Progesterone was then eliminated from the medium by a specific anti-progesterone antibody, and the residual chemotactic activity was assessed. RESULTS: The rate of progesterone secretion from the cells decreased with time. Removal of progesterone from the cumulus-cultured medium resulted in total loss of the chemotactic activity of the medium. Furthermore, the cumulus-cultured medium could substitute for progesterone in stimulating changes in the intracellular Ca²⁺ concentration in the spermatozoa, and the changes were very similar to those caused by measured progesterone concentrations in the medium. CONCLUSIONS: Taken together, the results suggest that progesterone is the main, if not the sole, chemoattractant secreted by human cumulus cells.