Sevoflurane post-conditioning alleviated hypoxic-ischemic brain injury in neonatal rats by inhibiting endoplasmic reticulum stress-mediated autophagy via IRE1 signalings

Abstract

Post-conditioning with sevoflurane, a volatile anesthetic, has been proved to be neuroprotective against hypoxic-ischemic brain injury (HIBI). Our previous research showed that autophagy is over-activated in a neonatal HIBI rat model, and inhibition of autophagy confers neuroprotection. There is increasing recognition that autophagy can be stimulated by activating endoplasmic reticulum (ER) stress. Herein, we purposed to explore: i) the association of ER stress with autophagy in the setting of neonatal HIBI; and ii) the possible roles of ER stress-triggered autophagy, as well as IRE1 signaling in the neuroprotection of sevoflurane post-conditioning against neonatal HIBI. Seven-day-old rats underwent ligation of the left common artery, and a subsequent 2 h hypoxia (8% O2/92% N2). The association of ER stress with autophagy was examined by ER stress inducer (tunicamycin), 4-PBA (ER stress inhibitor), or 3-MA (autophagy inhibitor). Rats in the sevoflurane post-conditioning groups were treated with 2.4% sevoflurane for 30 min after HIBI stimulation. The roles of ER stress-mediated autophagy, as well as the IRE1-JNK-beclin1 signaling cascade in the neuroprotection afforded by sevoflurane were explored by ER stress inducer (tunicamycin) and the IRE1 inhibitor (STF-083010). HIBI over-activated ER stress and autophagy in neonatal rats. HIBI-induced autophagy was significantly aggravated by tunicamycin but blocked by 4-PBA; however, HIBI-induced ER stress was not affected by 3-MA. Sevoflurane post-conditioning significantly alleviated ER stress, autophagy, cell apoptosis, and cognitive impairments, which were remarkably abolished by tunicamycin. Also, tunicamycin blocked sevoflurane-induced downregulation of IRE1-JNK-beclin1 signaling pathway. Whereas, IRE1 inhibitor could reverse the effects of tunicamycin. ER stress contributes to autophagy induced by HIBI. Furthermore, sevoflurane post-conditioning significantly protects against HIBI in neonatal rats by inhibiting ER stress-mediated autophagy via IRE1-JNK-beclin1 signaling cascade.

Keywords: Autophagy; Endoplasmic reticulum stress; Hypoxic-ischemic brain injury; IRE1; Sevoflurane post-conditioning.