OBJECTIVE Histamine H3 receptor(H3R) was reported important in regulation of central nervous system diseases.But less study was carried on cerebral ischemia.Here we demonstrated that inhibition of H3R was protective against ischemia reperfusion injury through reinforcement of protective autophagy.METHODS Transient focal cerebral ischemia model(MCAO) in mice and OGD /reperfusion injury on cultured rat cortical neurons were carried out.RESULTS Histamine H3R was upregulated after ischemia reperfusion injury,and eitherinhibition of H3R by three antagonists(thioperamide,clobenpropit and A331440) or H3R knock out attenuated ischemia reperfusion induced injury in mice,evidenced by lower cell injury and anti-apoptosis in vivo and in vitro,which was reversed by H3R agonist immepip in WT mice.Given that autophagy may inhibit cell apoptosis,we surprisingly found that autophagy was further activated by both H3R knock out and inhibition after ischemia,and the neuroprotective effects were significantly reversed by administration of 3-MA which is an autophagy inhibitor.Both siRNA of Atg7 gene on neurons and knock out of Atg5 gene on MEF cell lines were carried out to make sure again the importance of autophagy in protection of H3R inhibition.To explore the mechanism of regulation of H3R induced neuroprotection,interestingly,we found that histamine was not involved in H3R action.Further studies indicated that CLIC4 which was reported that lower expression led to up-regulated autophagy level interacted with H3R C-terminal tail consisting of amino acid 414-436(H3RCT) was involved in the protection of H3R inhibition through suppressing Akt/GSK3/mTOR signaling.Because inhibiting of H3R and CLIC4 interaction presented neuroprotection in cultured neurons against OGD reperfusion injury.CONCLUSION Taken together,the study demonstrated that upregulated H3R expression during ischemia reperfusion was autophagy inhibitory through activating Akt/GSK3/mTOR signaling.Inhibiting H3R inactivated the signaling by suppressing H3R and CLIC4 interaction,and then led to autophagy upregulated to protect cells against ischemia reperfusion injury,suggesting that H3R may be an attractive clinical therapeutic target. OBJECTIVE Histamine H3 receptor (H3R) was reported important in regulation of central nervous system diseases.Here we demonstrated that inhibition of H3R was protective against ischemia reperfusion injury through reinforcement of protective autophagy. METHODS Transient focal cerebral ischemia model (MCAO) in mice and OGD / reperfusion injury on cultured rat cortical neurons were carried out .RESULTS Histamine H3R was upregulated after ischemia reperfusion injury, and either inhibitor of H3R by three antagonists (thioperamide, clobenpropit and A331440) or H3R knockout attenuated ischemia reperfusion induced injury in mice, evidenced by lower cell injury and anti-apoptosis in vivo and in vitro, which has reversed by H3R agonist immepip in WT mice. Given that autophagy may inhibit cell apoptosis, we surprisingly found that autophagy was further activated by both H3R knock out and inhibition after ischemia, and the neuroprotective effects were significan tly by by administration of 3-MA which is an autophagy inhibitor. Both siRNA of Atg7 gene on neurons and knock out of Atg5 gene on MEF cell lines were carried out to make sure the the of autophagy in protection of H3R inhibition. explore the mechanism of regulation of H3R induced neuroprotection, interestingly, we found that histamine was not involved in H3R action. Facilitations studies that that CLIC4 which was reported that lower expression led to up-regulated autophagy level interacted with H3R C-terminal tail consisting of amino acid 414-436 (H3RCT) was involved in the protection of H3R inhibition through suppressing Akt / GSK3 / mTOR signaling. Inhibit of H3R and CLIC4 interaction presented neuroprotection in cultured neurons against OGD reperfusion injury. CONCLUSION Taken together, the study of that upregulated H3R expression during ischemia reperfusion was autophagy inhibitory through activating Akt / GSK3 / mTOR signaling. Inhibition of H3R inactivated the signaling by suppressing H3R and CLIC4 interaction, and then led to autophagy upregulated to protect cells against ischemia reperfusion injury, suggesting that H3R may be an attractive clinical therapeutic target.