Enterovirus 71 induces autophagy in mice via mTOR inhibition and ERK pathway activation

Enterovirus 71 (EV71) is one of the main viruses that cause hand-foot-mouth disease; however, its pathogenic mechanism remains unclear. This study characterized the relationship between EV71 infection and autophagy in vivo and explored the molecular mechanism underlying EV71-induced autophagy. A mouse model of EV71 infection was prepared by intraperitoneally injecting one-day-old BALB/c suckling mice with 30 μL/g of EV71 virus stock solution for 3 days. The behavior, fur condition, weight, and mice mortality were monitored, and disease scores were calculated. The pathological damage to the brain, lung, and muscle tissues after the viral infection was assessed by hematoxylin and eosin staining. Western blot and immunofluorescence analyses were used to detect the expression levels of viral protein 1, Beclin-1, microtubule-associated protein light chain 3B, mammalian target of rapamycin (mTOR), phosphorylated (p)-mTOR, extracellular signal-regulated protein kinase (ERK) 1/2, and p-ERK. EV71 infection can trigger autophagy in the brains, lungs, and muscles of infected mice. The autophagy response triggered by EV71 is achieved by the simultaneous mTOR inhibition and the ERK pathway activation. Blocking the mTOR pathway may aggravate autophagy, whereas ERK inhibition alleviates autophagy but cannot completely prevent it. EV71 infection can induce autophagy in mice, involving mTOR and ERK signaling pathways. These two signaling pathways are independent and do not interfere with each other.