title: Pressure induces loss of gap junction communication and redistribution of connexin 43 in astrocytes.
abstract: Astrocytes, the major glia in the nonmyelinated optic nerve head (ONH), connect via gap junctions built of connexin-43 (Cx43) to form a functional syncytium allowing communication and control of ionic and metabolic homeostasis of retinal ganglion cells (RGCs) axon. We examined gap junction intercellular communication (GJIC) by scrape loading assays in human ONH astrocytes exposed to hydrostatic (HP) or ambient pressure (CP) in vitro. Immunostaining, immunoprecipitation, and immunoblots were used to detect Cx43 distribution and phosphorylation in astrocytes exposed to HP with/without EGF receptor (EGFR) tyrosine kinase inhibitors AG1478 and AG82 and MAPK inhibitors U0126, PD98059, and SB203580. The data indicates that upon exposure to HP, astrocytes decrease GJIC and exhibit altered cellular localization and phosphorylation of Cx43. Inhibition of EGFR blocked the effects of HP on GJIC and HP-induced Cx43 tyrosine phosphorylation. Inhibitors of MAPK- ERK1/2 and -p38 caused partial closure of GJIC under CP and HP, which was maintained for 6 h. Inhibition of Big Mitogen-Activated Kinase 1/ERK5 (BMK1/ERK5) caused partial closure under CP and HP followed by full recovery after 6 h. Inhibition of MAPK did not affect the HP-induced increase in Cx43 serine 279/282 phosphorylation. We conclude that activation of the EGFR pathway in response to HP leads to decrease of GJIC via tyrosine phosphorylation of Cx43 in ONH astrocytes. In glaucoma under conditions of elevated intraocular pressure (IOP), astrocytes may lose GJIC altering the homeostasis of RGC axons, adopting the reactive phenotype, contributing to glaucomatous neuropathy.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, USA.
authors.forename: Paula
authors.initials: P
authors.lastname: Malone
authors.forename: Haixi
authors.initials: H
authors.lastname: Miao
authors.forename: Amy
authors.initials: A
authors.lastname: Parker
authors.forename: Santiago
authors.initials: S
authors.lastname: Juarez
authors.forename: M Rosario
authors.initials: MR
authors.lastname: Hernandez
mesh_terms: D000328:Adult; D000368:Aged; D001253:Astrocytes / Q000378:metabolism* / Q000473:pathology; D002450:Cell Communication / Q000187:drug effects; D002478:Cells, Cultured; D018031:Connexin 43 / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D017629:Gap Junctions / Q000378:metabolism* / Q000473:pathology; D005901:Glaucoma / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D007150:Immunohistochemistry; D007429:Intraocular Pressure; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009898:Optic Disk / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D009901:Optic Nerve Diseases / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D010766:Phosphorylation / Q000187:drug effects; D014443:Tyrosine / Q000378:metabolism
chemical_list: D018031:Connexin 43; D004791:Enzyme Inhibitors; D014443:Tyrosine; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases