A possible role of Fas antigen in ejaculated spermatozoa of fertile bulls: an immunocytochemical quantitative approach

The Fas/Fas L system is a widely recognized apoptosis signal transduction pathway in which transmembrane receptor protein (Fas) triggers a programmed cell death when bound by the Fas ligand (Fas L). This system in the testis is believed to be a paracrine signaling system by which Sertoli cells expressing Fas L can initiate killing of Fas-expressing germ cells during spermatogenesis. So far, the presence of Fas antigen in ejaculated spermatozoa was related only to subfertility or infertility conditions. We demonstrated for the first time that normal ejaculated spermatozoa also express Fas antigen. Our data showed that a large percentage of normal ejaculated spermatozoa of fertile bulls are immunocytochemically positive for Fas. Our observations provide further evidence of the “regionalization” of sperm membrane antigens. Furthermore, we suggest that in mature fertile ejaculated spermatozoa the Fas antigen may also provide resistance to programmed cell death, like in some other cells expressing molecules that inhibit the signals induced by Fas or the death program itself. In addition, we suggest that Fas antigen can partly protect the spermatozoa against apoptosis induced by lipoperoxidative damage that can occur spontaneously in the male gamete at various stages in its lifetime.