Melatonin facilitates the anti-EV71 activity by inhibiting apoptosis through the regulation of the Caspase-7 signaling pathway

To investigate the impacts and potential underlying mechanisms of melatonin on enterovirus 71(EV71). Three-day-old ICR mice were randomly divided into seven groups: control group, vehicle group, melatonin 10, 50, and 100 mg/kg group, ribavirin 50 mg/kg group, and melatonin 50 mg/kg combined ribavirin 50 mg/kg group. The mice were intracranial injected with 50 μL EV71 (5 ×10³ TCID₅₀) and treated with different medications once a day for four days. Clinical scores, body weights of mice were recorded, and the expression of VP1 protein in the hindlimb muscles and brainstem was analyzed using western blot. In vitro, CCK-8 assays were employed to assess cell proliferation, Reed-Muench method was used to calculate viral titers, western blot was conducted to evaluate the expression of VP1 and caspase-7 proteins, flow cytometry and TMRE staining were utilized to assess cell apoptosis, molecular docking was performed to calculate binding activity. Melatonin significantly alleviated the clinical symptoms induced by EV71 and effectively suppressed the expression of VP1 protein in the hindlimb muscles and brainstem of mice. In vitro, Melatonin effectively reduced the TCID₅₀ and the expression of VP1 protein and rescued the apoptosis induced by EV71; Melatonin enhanced the fluorescence intensity of TMRE compared to the infected group; the binding energy between melatonin and caspase-7 was calculated to be -7.2 kcal/mol, and melatonin inhibited the expression of caspase-7 protein after EV71 infection. Melatonin inhibited EV71 replication both in vivo and vitro, and its mechanism may involve preventing EV71-induced apoptosis by inhibiting the expression of cleaved caspase-7.