title: Disruption of IP₃R2-mediated Ca²⁺ signaling pathway in astrocytes ameliorates neuronal death and brain damage while reducing behavioral deficits after focal ischemic stroke.
abstract: Inositol trisphosphate receptor (IP3R)-mediated intracellular Ca(2+) increase is the major Ca(2+) signaling pathway in astrocytes in the central nervous system (CNS). Ca(2+) increases in astrocytes have been found to modulate neuronal function through gliotransmitter release. We previously demonstrated that astrocytes exhibit enhanced Ca(2+) 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 Ca(2+) signaling in neuronal death, brain damage and behavior outcomes after PT. For this purpose, we conducted experiments using homozygous type 2 IP3R (IP3R2) knockout (KO) mice. Histological and immunostaining studies showed that IP3R2 KO mice were indeed deficient in IP3R2 in astrocytes and exhibited normal brain cytoarchitecture. IP3R2 KO mice also had the same densities of S100β+ 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 IP3R2 KO mice did not exhibit ATP-induced Ca(2+) waves in vivo in the astrocytic network, which verified the disruption of IP3R-mediated Ca(2+) signaling in astrocytes of these mice. When subject to PT, IP3R2 KO mice had smaller infarction than WT mice in acute and chronic phases of ischemia. IP3R2 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 IP3R2 KO mice exhibited reduced functional deficits after PT. Collectively, our study demonstrates that disruption of astrocytic Ca(2+) signaling by deleting IP3R2s 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 IP3R2-mediated Ca(2+) signaling pathway might be a promising target for stroke therapy.
authors.affiliation: Dalton Cardiovascular Research Center, University of Missouri-Columbia, MO 65211, United States; Department of Bioengineering, University of Missouri-Columbia, MO 65211, United States.
authors.forename: Hailong
authors.initials: H
authors.lastname: Li
authors.affiliation: Dalton Cardiovascular Research Center, University of Missouri-Columbia, MO 65211, United States; Department of Bioengineering, University of Missouri-Columbia, MO 65211, United States.
authors.forename: Yicheng
authors.initials: Y
authors.lastname: Xie
authors.affiliation: Dalton Cardiovascular Research Center, University of Missouri-Columbia, MO 65211, United States.
authors.forename: Nannan
authors.initials: N
authors.lastname: Zhang
authors.affiliation: Department of Bioengineering, University of Missouri-Columbia, MO 65211, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yu
authors.affiliation: Department of Bioengineering, University of Missouri-Columbia, MO 65211, United States.
authors.forename: Qiao
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Dalton Cardiovascular Research Center, University of Missouri-Columbia, MO 65211, United States; Department of Bioengineering, University of Missouri-Columbia, MO 65211, United States. Electronic address: dings@missouri.edu.
authors.forename: Shinghua
authors.initials: S
authors.lastname: Ding
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D001522:Behavior, Animal / Q000502:physiology*; D001921:Brain / Q000378:metabolism; D001930:Brain Injuries / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D016923:Cell Death; D004195:Disease Models, Animal; D005260:Female; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000172:deficiency / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D020521:Stroke / Q000235:genetics / Q000378:metabolism*
chemical_list: D053496:Inositol 1,4,5-Trisphosphate Receptors; C580990:Ip3r2 protein, mouse; D002118:Calcium
keywords: Astrocytic Ca(2+) signaling; Behavioral tests; Infarction; Ischemic stroke; Neuronal death; Photothrombosis; Reactive astrogliosis; Two-photon imaging