Exogenous Oleic Acid and Palmitic Acid Improve Boar Sperm Motility via Enhancing Mitochondrial Β-Oxidation for ATP Generation

Abstract

It takes several hours for mammalian sperm to migrate from the ejaculation or insemination site to the fertilization site in the female reproductive tract in which glucose, amino acids, and fatty acids are regarded as the primary substrates for ATP generation. The present study was designed to investigate whether oleic acid and palmitic acid were beneficial to boar sperm in vitro; and if yes, to elucidate the mechanism that regulates sperm motility. Therefore, the levels of oleic acid and palmitic acid, motility, membrane integrity, acrosome integrity, and apoptosis of sperm were evaluated. Moreover, the enzymes involved in mitochondrial β-oxidation (CPT1: carnitine palmitoyltransferase 1; ACADVL: long-chain acyl-coenzyme A dehydrogenase) were detected with immunofluorescence and Western blotting. Consequently, the ATP content and the activities of CPT1, ACADVL, malate dehydrogenase (MDH), and succinate dehydrogenase (SDH) were also measured. We observed that CPT1 and ACADVL were expressed in boar sperm and localized in the midpiece. The levels of oleic acid and palmitic acid were decreased during storage at 17 °C. The addition of oleic acid and palmitic acid significantly increased sperm motility, progressive motility, straight-line velocity (VSL), membrane integrity, and acrosome integrity with a simultaneous decrease in sperm apoptosis after seven days during storage. When sperm were incubated with oleic acid and palmitic acid at 37 °C for 3 h, the activities of CPT1 and ACADVL, the ATP level, the mitochondrial membrane potential, the activities of MDH and SDH, as well as sperm motility patterns were significantly increased compared to the control (p < 0.05). Moreover, the addition of etomoxir to the diluted medium in the presence of either oleic acid or palmitic acid and the positive effects of oleic acid and palmitic acid were counteracted. Together, these data suggest that boar sperm might utilize oleic acid and palmitic acid as energy substrates for ATP production via β-oxidation. The addition of these acids could improve sperm quality.