Hyaluronic acid-induced capacitation involves protein kinase C and tyrosine kinase activity modulation with a lower oxidative metabolism in cryopreserved bull sperm.

Hyaluronic acid is a glycosaminoglycan present in uterine and oviductal fluids in female ruminants, which has been used as a sperm capacitation inducer prior to in vitro fertilization in several species. CD44 is a specific hyaluronic acid receptor, present in the sperm plasma membrane, but its signaling transduction system has not been elucidated yet. Our aim was to study protein kinase C and tyrosine kinase participation in intracellular signaling and oxidative metabolism in hyaluronic acid-induced capacitation of cryopreserved bull spermatozoa. Sperm capacitation was induced with hyaluronic acid or heparin. GF-109203× and genistein were used as protein kinase C and tyrosine kinase inhibitors, respectively. Capacitation, sperm plasma membrane and acrosome integrity were studied using CTC and trypan blue - DIC, while variations in enzymatic activities were determined by spectrophotometry. The inhibition of protein kinase C and tyrosine kinase blocked hyaluronic acid and heparin induced capacitation. Metabolic enzymes such as NADP-dependent isocitrate and malate dehydrogenases participate in hyaluronic acid capacitation, in coincidence with a lower mitochondrial metabolism compared with heparin. On the other hand, NAD-dependent isocitrate and malate dehydrogenase were not modified by hyaluronic acid induction. These dehydrogenases were also modulated by protein kinase C and tyrosine kinase in the capacitation induced by heparin or hyaluronic acid. In conclusion, hyaluronic acid intracellular signal system involves protein kinase C and tyrosine kinase activities, which may modulate capacitation in cryopreserved bull sperm with a lower oxidative metabolism than heparin.