Antagonism Of Histamine H3 Receptor Promotes Angiogenesis Following Focal Cerebral Ischemia

The neurological recovery following ischemic stroke is limited.Promoting angiogenesis might be significant to the neurogenesis and neurological recovery for ischemic stroke.It has been reported that histamine can promote angiogenesis in vitro,but histamine cannot pass the blood-brain barrier,which in turn limits its clinical applications.Nevertheless,antagonism of histamine H3 receptor can promote the synthesis and release of histamine within histaminergic neurons.The aim of this study is to explore the effect of blocking histamine H3 receptor on angiogenesis after ischemic stroke.The focal cerebral ischemic mice model was prepared by photothrombosis,and H3 receptor antagonist,H3 receptor agonist,H1 receptor antagonist,H2 receptor antagonist or histidine decarboxylase inhibitor ?-FMH was continuously administrated one dayafter surgery.Meanwhile,grid test and cylinder test were used to evaluate the motorfunctions of mice.The level of angiogenesis was determined by staining of Lectin orCD31.In addition,the angiogenesis level after cerebral ischemia in histidinedecarboxylase gene knockout mice(HDC-/-),H3 receptor knockout mice(Hrh3-/-)and mice with specifically histamine H3 receptor knockout on the vascular endothelial cells(Hrh3fl/fl;Tie2CreERT2)was examined.The results showed that histamine H3 receptor antagonist thioperamide significantly increased the Lectin-labeled blood vessels and CD31-labeled neo-vascularization in the penumbra area at 14 days following cerebral ischemia,but had no effect on the blood vessels in the penumbra area at 3 days after cerebral ischemia.Meanwhile,thioperamide also reduced infarction volume and improved the motor function evaluated by grid test and cylinder test at 28 d after cerebral ischemia.The effect of thioperamide on promoting angiogenesis was reversed by the histamine H3 receptor agonist immepip.Moreover,we found angiogenesis level in Hrh3-/-mice was significantly higher compared to wild type mice after cerebral ischemia,and thioperamide did not further promote angiogenesis in In addition,the promotion of angiogenesis conferred by thioperamide was not reversed by histidine decarboxylase inhibitor a-FMH or in histidine decarboxylase gene knockout(HDC-/-)mice.Neither pyrilamine nor cimetidine could reverse the effect of thioperamide on promoting angiogenesis.It indicates that the action of histamine H3 receptor antagonist on promoting angiogenesis is independent of histaminergic neurons.Furthermore,we generated mice that specifically knockout histamine H3 receptor on the vascular endothelial cells(Hrh3fl/fl;Tie2CreERT2),and found that Hrh3fl/fl;Tie2CreERT2 mice had a higher angiogenesis level compared with control mice.In conclusion,this study shows that antagonism of histamine H3 promotes angiogenesis after focal cerebral ischemia,which is independent of histaminergic neurons,but related to the H3 receptors on vascular endothelial cells.Histamine H3 receptors can serve as a new target for the treatment of ischemic stroke.Histamine H3 receptor antagonists might be good drug candidates to improve the neurological recovery after ischemic stroke.