Melatonin protects human spermatozoa from apoptosis via melatonin receptor– and extracellular signal–regulated kinase-mediated pathways

ObjectiveTo evaluate whether the protective effect of melatonin on H2O2-induced caspase activation and DNA fragmentation depends on the interaction between melatonin and its surface receptors.DesignLaboratory study.SettingCenter for assisted human reproduction at a Spanish hospital.Patient(s)Twenty-one healthy donors.Intervention(s)Human spermatozoa were treated with increasing concentrations of hydrogen peroxide (H2O2; 1μM, 10 μM, 100 μM, 1mM) and preincubated with 1 mM melatonin.Main Outcomes Measure(s)Activation of caspase-3 and -9 as well as DNA fragmentation were examined by fluorescence methods.Result(s)Our findings showed that H2O2 induced a significant increase in caspase-9 and caspase-3, which was dose independent. Conversely, pretreatment with melatonin reduced H2O2-mediated caspase activation in a dose-dependent way. Moreover, the antiapoptotic effects of melatonin in ejaculated human spermatozoa may involve membrane melatonin receptor MT1. In addition, we found that the survival-promoting pathway extracellular signal–regulated kinase (ERK) is likely to have a role in the protective actions of melatonin in ejaculated human spermatozoa. Finally, we confirmed these results further by demonstrating that melatonin prevention of H2O2-induced DNA fragmentation is dependent on both MT1 receptor and ERK signaling.Conclusion(s)These results indicate that the stimulation with melatonin triggers a set of events culminating in cell death prevention in ejaculated human spermatozoa.