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

Objective To evaluate whether the protective effect of melatonin on H 2 O 2 -induced caspase activation and DNA fragmentation depends on the interaction between melatonin and its surface receptors. Design Laboratory study. Setting Center 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 (H 2 O 2 ; 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 H 2 O 2 induced a significant increase in caspase-9 and caspase-3, which was dose independent. Conversely, pretreatment with melatonin reduced H 2 O 2 -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 H 2 O 2 -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.