Metabolism of exogenous fatty acids, fatty acid‐mediated cholesterol efflux, PKA and PKC pathways in boar sperm acrosome reaction

Abstract

Abstract Purpose For understanding the roles of fatty acids on the induction of acrosome reaction which occurs under association of cholesterol efflux and PKA or PKC pathways in boar spermatozoa, metabolic fate of alone and combined radiolabeled 14 C‐oleic acid and 3 H‐linoleic acid incorporated in the sperm was compared, and behavior of cholesterol and effects of PKA and PKC inhibitors upon fatty acid‐induced acrosome reaction were examined. Methods Semen was collected from a Duroc boar, and the metabolic activities of fatty acids in the spermatozoa were measured using radioactive compounds and thin layer chromatography. Cholesterol efflux was measured with a cholesterol determination assay kit. Participation of fatty acids on the AR through PKA and PKC pathways was evaluated using a specific inhibitor of these enzymes. Results Incorporation rate of 14 C‐oleic acid into the sperm lipids was significantly higher than that of 3 H‐linoleic acid ( P < 0.05). The oxidation of 14 C‐oleic acid was higher in combined radiolabeling rather than in one. The highest amounts of 3 H‐linoleic acid and 14 C‐oleic acid were recovered mainly in the triglycerides and phospholipids fraction, and 14 C‐oleic acid distribution was higher than the 3 H‐linoleic acid in both labeled ( P < 0.05) sperm lipids. In the 3 H‐linoleic and 14 C‐oleic acid combined radiolabeling, the incorporation rate of the radioactive fatty acids in all the lipid fractions increased 15 times more than the alone radiolabeling. Boar sperm utilize oleic acid to generate energy for hyperactivation ( P < 0.05). Supplementation of arachidonic acid significantly increased ( P < 0.05) cholesterol efflux in sperm. When spermatozoa were incubated with PKA or PKC inhibitors, there was a significant reduction of arachidonic acid‐induced acrosome reaction (AR) ( P < 0.05), and inhibition by PKA inhibitor is stronger than that by PKC inhibitor. Conclusions Incorporation of unsaturated fatty acids, especially oleic acid, into triglycerides and phospholipids provides prerequisite energy for AR. Cholesterol efflux by arachidonic acid triggers AR. Arachidonic acid activated PKA and PKC pathway participate in induction of the AR.