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); 1 mu M, 10 mu M, 100 mu M, 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. (Fertil Steril (R) 2011; 95: 2290-6. (C) 2011 by American Society for Reproductive Medicine.)