Evidence for presence of hyaluronan binding protein on spermatozoa and its possible involvement in sperm function

Hyaluronic acid, a major component of the extracellular matrix, plays an important role in the regulation of different cellular processes, e.g., locomotion, cell-cell interaction during morphogenesis, and differentiation. Distribution of hyaluronic acid with respect to the role of sperm hyaluronidase in sperm penetration and gamete interaction is well established. In order to elucidate this mechanism, in our current study we have identified and demonstrated, for the first time, the presence of a 68-kDa cell surface hyaluronic acid binding glycoprotein (HABP) in spermatozoa of different species (rat, mice, bull, and human) by immunoblot analysis and indirect immunofluorescence using the polyclonal antibodies raised against purified HABP. Furthermore, we were able to demonstrate a differential distribution of 68-kDa HA binding protein on the sperm head, midpiece, and tail of different species. To identify its role in sperm function, we observed its declining pattern during epididymal maturation and also the inhibition of sperm-oolemmal adherence by pretreatment of the sperms with anti-HABP antibodies. We have further observed its in vivo phosphorylation in motile spermatozoa. All our data clearly indicate that sperm hyaluronan binding protein may have a specific role in sperm maturation, motility, and fertilization processes.