Background/Aims: ATP is essential for mammalian sperm to survive and maintain fertilizing capacity. AMP-activated protein kinase (AMPK) is a sensor of cellular energy status. The aims of the present study were to explore the localization of AMPK in goat sperm and to investigate whether and how AMPK regulates sperm functions in vitro. Methods: Sperm were treated with AMPK modulators (AICAR, metformin and Compound C) during incubation. Sperm motility was assessed with a computer-assisted spermatozoa analysis system (CASA). Membrane integrity, acrosome reaction and mitochondrial membrane potentials were detected by SYBR-14/PI, FITC-PNA and JC-1 staining, respectively. And the lactate content, ATP content, AMPK activity, activity of pyruvate kinase (PK) and lactate dehydrogenase (LDH) were also measured with the commercial assay kits. Immunofluorescence staining was used to analyze the distribution of PK, LDH, AMPK and phospho-Thr172-AMPK in sperm. The role of AMPK was further studied during induction of capacitation and acrosome reaction. Results: We found that AMPKα was localized in the entire acrosomal region, the midpiece and the flagellum, while the phospho-Thr172-AMPK was distributed in the head, the midpiece and flagellum. Activation of AMPK by AICAR and metformin significantly improved sperm motility, membrane integrity and acrosome reaction, largely maintained sperm mitochondrial membrane potentials, lactate content and ATP content, and enhanced the activity of AMPK, PK and LDH, whereas inhibition by Compound C triggered the converse effects. Moreover, PK was localized in the acrosomal area and the midpiece, while LDH was distributed in the tail. Induction of capacitation and acrosome reaction led to AMPK phosphorylation. AMPK phosphorylation regulated the activity of energetic enzymes. Conclusion: This study for the first time provides evidence that AMPK governs goat sperm functions through energy metabolism in vitro. This finding will help to improve assisted reproductive techniques in goats and the other species.

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.

Mammalian sperm is highly susceptible to the reactive oxygen species (ROS) stress caused by biochemical and physical modifications during the cryopreservation process. 5′AMP-activated protein kinase (AMPK) is involved in regulating both cell metabolism and cellular redox status. The aim of the present study was to investigate whether the resveratrol protects boar sperm against ROS stress via activation of AMPK during cryopreservation. Boar sperm was diluted with the freezing medium supplemented with resveratrol at different concentrations (0, 25, 50, 75, 100, and 125 μM). It was observed that the addition of 50 μM resveratrol significantly improved the postthaw sperm progressive motility, membrane integrity, acrosome integrity, mitochondrial activity, glutathione (GSH) level, activities of enzymatic antioxidants (glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase), and the phosphorylation of AMPK. Meanwhile, the lipid peroxidation, ROS levels, and apoptosis of postthaw sperm were reduced in the presence of 50 μM resveratrol. Furthermore, when fresh boar sperm was incubated with the medium in the presence of 50 μM resveratrol and 30 μM Compound C (an AMPK inhibitor), the effects of the resveratrol were partly counteracted by the Compound C. These observations suggest that the resveratrol protects boar sperm via promoting AMPK phosphorylation. In conclusion, the addition of resveratrol to the freezing extenders protects boar sperm against ROS damage via promoting AMPK phosphorylation for decreasing the ROS production and improving the antioxidative defense system of postthaw sperm. These findings provide novel insights into understanding the mechanisms of resveratrol on how to protect boar sperm quality contrary to the ROS production during cryopreservation.

No abstract

Proline was reported to improve sperm quality in rams, stallions, cynomolgus monkeys, donkeys, and canines during cryopreservation. However, the underlying mechanism remains unclear. The aim of this study was to investigate the effect of proline on boar semen during liquid storage at 17 °C and explore the underlying mechanism. Freshly ejaculated boar semen was supplemented with different concentrations of proline (0, 25, 50, 75, 100, 125 mM) and stored at 17 °C for nine days. Sperm motility patterns, membrane integrity, ATP (adenosine triphosphate), reactive oxygen species (ROS), and GSH (glutathione) levels, and the activities of catalase (CAT) and superoxide dismutase (SOD) were evaluated after storage for up to five days. It was observed that boar sperm quality gradually decreased with the extension of storage time, while the ROS levels increased. Addition of 75 mM proline not only significantly improved sperm membrane integrity, motility, and ATP levels but also maintained the redox homeostasis via increasing the GSH levels and activities of CAT and SOD. When hydrogen peroxide (H2O2) was used to induce oxidative stress, addition of proline significantly improved sperm quality and reduced ROS levels. Moreover, addition of proline also improved sperm quality during the rapid cooling process. Notably, addition of DL-PCA (DL-pipecolinic acid) rescued the reduction of progressive motility and total motility caused by H2O2, and THFA (tetrahydro-2-furoic acid) failed to provide protection. Furthermore, addition of proline at 75 mM increased the activity of proline dehydrogenase (PRODH) and attenuated the H2O2-induced reduction in progressive motility. These data demonstrate that proline protects sperm against oxidative stress through the secondary amine structure and proline dehydrogenase-mediated metabolism.