Disruption of IP(3)R2-mediated Ca2+ signaling pathway in astrocytes ameliorates neuronal death and brain damage while reducing behavioral deficits after focal ischemic stroke

摘要

Inositol trisphosphate receptor (IP3R)-mediated intracellular Ca2+ increase is the major Ca2+ signaling pathway in astrocytes in the central nervous system (CNS). Ca2+ increases in astrocytes have been found to modulate neuronal function through gliotransmitter release. We previously demonstrated that astrocytes exhibit enhanced Ca2+ signaling in vivo after photothrombosis (PT)-induced ischemia, which is largely due to the activation of G-protein coupled receptors (GPCRs). The aim of this study is to investigate the role of astrocytic IP3R-mediated Ca2+ signaling in neuronal death, brain damage and behavior outcomes after PT. For this purpose, we conducted experiments using homozygous type 2 IP3R (IP(3)R2) knockout (KO) mice. Histological and immunostaining studies showed that IP(3)R2 KO mice were indeed deficient in IP(3)R2 in astrocytes and exhibited normal brain cytoarchitecture. IP(3)R2 KO mice also had the same densities of S100 beta+ astrocytes and NeuN+ neurons in the cortices, and exhibited the same glial fibrillary acidic protein (GFAP) and glial glutamate transporter (GLT-1) levels in the cortices and hippocampi as compared with wild type (WT) mice. Two-photon (2-P) imaging showed that IP(3)R2 KO mice did not exhibit ATP-induced Ca2+ waves in vivo in the astrocytic network, which verified the disruption of IP3R-mediated Ca2+ signaling in astrocytes of these mice. When subject to PT, IP(3)R2 KO mice had smaller infarction than WT mice in acute and chronic phases of ischemia. IP(3)R2 KO mice also exhibited less neuronal apoptosis, reactive astrogliosis, and tissue loss than WT mice. Behavioral tests, including cylinder, hanging wire, pole and adhesive tests, showed that IP(3)R2 KO mice exhibited reduced functional deficits after PT. Collectively, our study demonstrates that disruption of astrocytic Ca2+ signaling by deleting IP(3)R2s has beneficial effects on neuronal and brain protection and functional deficits after stroke. These findings reveal a novel non-cell-autonomous neuronal and brain protective function of astrocytes in ischemic stroke, whereby suggest that the astrocytic IP(3)R2-mediated Ca2+ signaling pathway might be a promising target for stroke therapy. (C) 2015 Elsevier Ltd. All rights reserved.