Melatonin mediates via melatonin receptor 1 in a temperature-dependent manner regulating ATP metabolism and antioxidative enzyme activity of boar spermatozoa in vitro

Abstract

Researches indicated that melatonin (MLT) could ameliorate oxidative damage and increase sperm motility for conservation sperms, whereas the underlying mechanism remains unknown. And elucidating this, present study was designed to investigate the energy metabolism of sperm throughout preservation at 17 °C and activating with 37 °C. Herein, semen of ten Landrace boars (16∼18 months of age) were diluted and treated with gradient concentrations of MLT (0 nM, 1 nM, 10 nM, 1 μM, 1 mM and 5 mM), and kept away from light in the incubator of 17 °C for 5 days (preservation), and the sperm motility was evaluated after 37 °C incubation for 10 min (activating). The results showed that 1.0 μM MLT treated-sperms had higher motility than other treatments from the 2nd onward. On the 3rd day 17 °C storage, 1.0 μM MLT significantly decreased the ATP content and the mRNA abundance of mitochondrial DNA encoding genes, including NADH dehydrogenase subunits (NDs) 1–4 and 4L, cytochrome b (CYTB), cytochrome c oxidases (COXs) 1 and 3, ATP synthase 6, but increased the hexokinase activity (HK) and the malondialdehyde (MDA) content compared to that of the control. Whereas after 10 min 37 °C incubation, 1.0 μM MLT increased the ATP content, and the mRNA expressions of ND2 and 4L, CYTB, COX1, ATP6, and the activities of mitochondrial respiratory chain complex I and superoxide dismutase (SOD), but depressed the pyruvate kinase (PK) activity in contrast to that at 17 °C. Furthermore, 1.0 μM MLT treated sperms had a higher MLT receptor 1 (MT1) protein level at 17 °C storage than that after 10 min 37 °C incubation, no changes of the MT2 expression were observed at different temperature. This study suggests that MLT might mediate via MT1 in a temperature-dependent manner regulating sperm ATP generation and antioxidative enzyme activity in vitro.