Gamete Biology

Seminal Plasma Proteins Regulate the Association of Lipids and Proteins Within Detergent-Resistant Membrane Domains of Bovine Spermatozoa

Abstract
Maturing spermatozoa acquire full fertilization competence by undergoing major changes in membrane fluidity and protein composition and localization. In epididymal spermatozoa, several proteins are associated with cholesterol- and sphingolipid-enriched detergent-resistant membranes (DRM) domains. These proteins dissociate from DRM in capacitated sperm cells, suggesting that DRM may play a role in the redistribution of integral and peripheral proteins in response to cholesterol removal. Since seminal plasma regulates sperm cell membrane fluidity, we hypothesized that seminal plasma factors could be involved in DRM disruption and redistribution of DRM-associated proteins. Our results indicated that (a) the sperm-associated proteins P25b and AK1 are linked to DRM of epididymal spermatozoa, but were exclusively associated with detergent-soluble material in ejaculated spermatozoa; (b) seminal plasma treatment of cauda epididymal spermatozoa significantly lowered the content of cholesterol and the ganglioside GM1 in DRM; and (c), seminal plasma dissociates P25b from DRM in epididymal spermatozoa. We found that the seminal plasma protein Niemann-Pick C2 protein (NPC2) is involved in cholesterol and GM1 depletion within DRM, and then leading to membrane redistribution of P25b that occurs in a very rapid and capacitation-independent manner. Together, these data suggest that DRM of ejaculated spermatozoa are reorganized by specific seminal plasma proteins which induce lipid efflux as well as dissociation of DRM-anchored proteins. This process could be physiologically relevant in vivo to allow sperm survival and attachment within the female reproductive tract and to potentiate recognition, binding and penetration of the oocyte.

Key words: Gamete Biology • Male Reproductive Tract • Epididymis • Sperm maturation