Regulation of sperm function by protein tyrosine phosphorylation in diverse wild felid species.

Abstract

Protein tyrosine phosphorylation is associated with sperm capacitation and the acrosome reaction in several mammalian species. Changes in phosphorylation of a 95-kDa protein in human, mouse, and domestic cat spermatozoa are known to be influenced by capacitation and exposure to zona pellucida (ZP) proteins. We previously reported diminished phosphorylation of 95- and 160-kDa proteins in spermatozoa from teratospermic cats, compared with normospermic domestic cats. To determine if these proteins and mechanisms are present in other species in the phenotypically diverse Felidae family, we examined the relationship between tyrosine-phosphorylated sperm proteins and sperm morphology in the leopard cat (approximately 65% normal sperm/ejaculate), tiger (approximately 65%), clouded leopard (approximately 15%), and cheetah (approximately 30%). Furthermore, we investigated the involvement of cyclic adenosine monophosphate (cAMP) in the regulation of sperm protein tyrosine phosphorylation. Specifically, we assessed the following: 1) presence of tyrosine-phosphorylated proteins in sperm extracts; 2) changes in protein tyrosine phosphorylation after sperm capacitation and swim-up separation; 3) impact of tyrosine kinase inhibition on leopard cat sperm protein phosphorylation and ZP penetration; and 4) involvement of a cAMP-dependent pathway in the regulation of protein tyrosine phosphorylation. Immunoblotting analysis with anti-phosphotyrosine antibody (PY20) indicated that a 95-kDa protein was present in all four species. Additional phosphorylated proteins were detected in the leopard cat (145- and 175-kDa proteins), tiger (185-kDa protein), clouded leopard (160- and 190-kDa proteins), and cheetah (115- and 155-kDa proteins). Sperm capacitation in vitro increased phosphorylation of one or more proteins in the leopard cat, tiger and clouded leopard, but not in the cheetah. Although swim-up separation increased the proportion of morphologically normal spermatozoa in the clouded leopard and cheetah, no changes were observed in phosphorylation of the 95-kDa sperm protein. Thus, phosphorylation of the 95-kDa protein appeared to be related to the condition of teratospermia. Exposing leopard cat spermatozoa to the tyrosine kinase inhibitor, tyrphostin, reduced (P < 0.05) phosphorylation of the 95- and 145-kDa proteins, as well as ZP penetration, without affecting sperm motility. Similarly, when spermatozoa were incubated in the presence of cAMP analogs or active and inactive stereoisomers of cAMP, phosphorylation of sperm proteins was either stimulated or inhibited. Together, these data suggest that protein tyrosine kinase mechanisms appear conserved within the family Felidae and are regulated by a cAMP/protein kinase A pathway.