Antagonism of histamine H3 receptor promotes angiogenesis following focal cerebral ischemia

Our previous study showed that H₃ receptor antagonists reduced neuronal apoptosis and cerebral infarction in the acute stage after cerebral ischemia, but through an action independent of activation of histaminergic neurons. Because enhanced angiogenesis facilitates neurogenesis and neurological recovery after ischemic stroke, we herein investigated whether antagonism of H₃R promoted angiogenesis after brain ischemia. Photothrombotic stroke was induced in mice. We showed that administration of H₃R antagonist thioperamide (THIO, 10 mg·kg⁻¹·d⁻¹, i.p., from D1 after cerebral ischemia) significantly improved angiogenesis assessed on D14, and attenuated neurological defects on D28 after cerebral ischemia. Compared with wild-type mice, Hrh3^−/− mice displayed more blood vessels in the ischemic boundary zone on D14, and THIO administration did not promote angiogenesis in these knockout mice. THIO-promoted angiogenesis in mice was reversed by i.c.v. injection of H₃R agonist immepip, but not by H₁ and H₂ receptor antagonists, histidine decarboxylase inhibitor α-fluoromethylhistidine, or histidine decarboxylase gene knockout (HDC^−/−), suggesting that THIO-promoted angiogenesis was independent of activation of histaminergic neurons. In vascular endothelial cells (bEnd.3), THIO (10⁻⁹−10⁻⁷M) dose-dependently facilitated cell migration and tube formation after oxygen glucose deprivation (OGD), and H₃R knockdown caused similar effects. We further revealed that H₃R antagonism reduced the interaction between H₃R and Annexin A2, while knockdown of Annexin A2 abrogated THIO-promoted angiogenesis in bEnd.3 cells after OGD. Annexin A2-overexpressing mice displayed more blood vessels in the ischemic boundary zone, which was reversed by i.c.v. injection of immepip. In conclusion, this study demonstrates that H₃R antagonism promotes angiogenesis after cerebral ischemia, which is independent of activation of histaminergic neurons, but related to the H₃R on vascular endothelial cells and its interaction with Annexin A2. Thus, H₃R antagonists might be promising drug candidates to improve angiogenesis and neurological recovery after ischemic stroke.