title: ATP and glutamate released via astroglial connexin 43 hemichannels mediate neuronal death through activation of pannexin 1 hemichannels.
abstract: Inflammation contributes to neurodegeneration in post-ischemic brain, diabetes, and Alzheimer's disease. Participants in this inflammatory response include activation of microglia and astrocytes. We studied the role of microglia treated with amyloid-β peptide (Aβ) on hemichannel activity of astrocytes subjected to hypoxia in high glucose. Reoxygenation after 3 h hypoxia in high glucose induced transient astroglial permeabilization via Cx43 hemichannels and reduction in intercellular communication via Cx43 cell-cell channels. Both responses were greater and longer lasting in astrocytes previously exposed for 24 h to conditioned medium from Aβ-treated microglia (CM-Aβ). The effects of CM-Aβ were mimicked by TNF-α and IL-1β and were abrogated by neutralizing TNF-α with soluble receptor and IL-1β with a receptor antagonist. Astrocytes under basal conditions protected neurons against hypoxia, but exposure to CM-Aβ made them toxic to neurons subjected to a sub-lethal hypoxia/reoxygenation episode, revealing the additive nature of the insults. Astrocytes exposed to CM-Aβ induced permeabilization of cortical neurons through activation of neuronal pannexin 1 (Panx1) hemichannels by ATP and glutamate released through astroglial Cx43 hemichannels. In agreement, inhibition of NMDA or P2X receptors only partially reduced the activation of neuronal Panx1 hemichannels and neuronal mortality, but simultaneous inhibition of both receptors completely prevented the neurotoxic response. Therefore, we suggest that responses to ATP and glutamate converge in activation of neuronal Panx1 hemichannels. Thus, we propose that blocking hemichannels expressed by astrocytes and/or neurons in the inflamed nervous system could represent a novel and alternative strategy to reduce neuronal loss in various pathological states including Alzheimer's disease, diabetes and ischemia.
authors.affiliation: Departamento de Fisiología, Pontificia Universidad Católica de Chile, Santiago, Chile. jaorella@uc.cl
authors.forename: Juan A
authors.initials: JA
authors.lastname: Orellana
authors.forename: Nicolas
authors.initials: N
authors.lastname: Froger
authors.forename: Pascal
authors.initials: P
authors.lastname: Ezan
authors.forename: Jean X
authors.initials: JX
authors.lastname: Jiang
authors.forename: Michael V L
authors.initials: MV
authors.lastname: Bennett
authors.forename: Christian C
authors.initials: CC
authors.lastname: Naus
authors.forename: Christian
authors.initials: C
authors.lastname: Giaume
authors.forename: Juan C
authors.initials: JC
authors.lastname: Sáez
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D016229:Amyloid beta-Peptides / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D019921:Biotinylation / Q000379:methods; D016923:Cell Death / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D018920:Coculture Techniques / Q000379:methods; D018031:Connexin 43 / Q000172:deficiency / Q000378:metabolism*; D017630:Connexins / Q000378:metabolism* / Q000494:pharmacology; D017077:Culture Media, Conditioned / Q000494:pharmacology; D005260:Female; D005452:Fluoresceins; D018698:Glutamic Acid / Q000378:metabolism* / Q000494:pharmacology; D053583:Interleukin-1beta / Q000378:metabolism; D007811:Lanthanum / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D008869:Microtubule-Associated Proteins / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000378:metabolism* / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009479:Neuropeptides / Q000494:pharmacology; D010100:Oxygen / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D018031:Connexin 43; D017630:Connexins; D017077:Culture Media, Conditioned; D005452:Fluoresceins; D053583:Interleukin-1beta; D008869:Microtubule-Associated Proteins; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; C503631:Panx1 protein, mouse; D010446:Peptide Fragments; D014409:Tumor Necrosis Factor-alpha; C074636:amyloid beta-protein (25-35); C534582:fluoro-jade C; C028521:lanthanum chloride; D018698:Glutamic Acid; D007811:Lanthanum; D000255:Adenosine Triphosphate; D010100:Oxygen