title: Axonal Degeneration in Retinal Ganglion Cells Is Associated with a Membrane Polarity-Sensitive Redox Process.
abstract: Axonal degeneration is a pathophysiological mechanism common to several neurodegenerative diseases. The slow Wallerian degeneration (WldS) mutation, which results in reduced axonal degeneration in the central and peripheral nervous systems, has provided insight into a redox-dependent mechanism by which axons undergo self-destruction. We studied early molecular events in axonal degeneration with single-axon laser axotomy and time-lapse imaging, monitoring the initial changes in transected axons of purified retinal ganglion cells (RGCs) from wild-type and WldSrat retinas using a polarity-sensitive annexin-based biosensor (annexin B12-Cys101,Cys260-N,N'-dimethyl-N-(iodoacetyl)-N'-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) ethylenediamine). Transected axons demonstrated a rapid and progressive change in membrane phospholipid polarity, manifested as phosphatidylserine externalization, which was significantly delayed and propagated more slowly in axotomized WldSRGCs compared with wild-type axons. Delivery of bis(3-propionic acid methyl ester)phenylphosphine borane complex, a cell-permeable intracellular disulfide-reducing drug, slowed the onset and velocity of phosphatidylserine externalization in wild-type axons significantly, replicating the WldSphenotype, whereas extracellular redox modulation reversed the WldSphenotype. These findings are consistent with an intra-axonal redox mechanism for axonal degeneration associated with the initiation and propagation of phosphatidylserine externalization after axotomy.SIGNIFICANCE STATEMENTAxonal degeneration is a neuronal process independent of somal apoptosis, the propagation of which is unclear. We combined single-cell laser axotomy with time-lapse imaging to study the dynamics of phosphatidylserine externalization immediately after axonal injury in purified retinal ganglion cells. The extension of phosphatidylserine externalization was slowed and delayed in Wallerian degeneration slow (WldS) axons and this phenotype could be reproduced by intra-axonal disulfide reduction in wild-type axons and reversed by extra-axonal reduction in WldSaxons. These results are consistent with a redox mechanism for propagation of membrane polarity asymmetry in axonal degeneration.
authors.affiliation: Maisonneuve-Rosemont Hospital Research Center and Department of Ophthalmology, University of Montreal, Montreal, Quebec H1T 2M4, Canada.|Departments of Ophthalmology and Neurology, McGill University, Montreal, Quebec H4A 3S5, Canada, and.
authors.forename: Mohammadali
authors.identifier: 0000-0003-1533-6642
authors.initials: M
authors.lastname: Almasieh
authors.affiliation: Maisonneuve-Rosemont Hospital Research Center and Department of Ophthalmology, University of Montreal, Montreal, Quebec H1T 2M4, Canada.
authors.forename: Maria-Magdalena
authors.initials: MM
authors.lastname: Catrinescu
authors.affiliation: Maisonneuve-Rosemont Hospital Research Center and Department of Ophthalmology, University of Montreal, Montreal, Quebec H1T 2M4, Canada.
authors.forename: Loïc
authors.initials: L
authors.lastname: Binan
authors.affiliation: Maisonneuve-Rosemont Hospital Research Center and Department of Ophthalmology, University of Montreal, Montreal, Quebec H1T 2M4, Canada.
authors.forename: Santiago
authors.initials: S
authors.lastname: Costantino
authors.affiliation: Maisonneuve-Rosemont Hospital Research Center and Department of Ophthalmology, University of Montreal, Montreal, Quebec H1T 2M4, Canada, leonard.levin@mcgill.ca.|Departments of Ophthalmology and Neurology, McGill University, Montreal, Quebec H4A 3S5, Canada, and.|Department of Ophthalmology and Visual Science, University of Wisconsin, Madison, Wisconsin 53706.
authors.forename: Leonard A
authors.identifier: 0000-0002-1399-250X
authors.initials: LA
authors.lastname: Levin
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D019771:Axotomy / Q000009:adverse effects; D002462:Cell Membrane / Q000378:metabolism* / Q000473:pathology; D016764:Cell Polarity / Q000502:physiology*; D002478:Cells, Cultured; D005260:Female; D008297:Male; D010084:Oxidation-Reduction; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D055647:Rats, Transgenic; D012165:Retinal Ganglion Cells / Q000378:metabolism* / Q000473:pathology; D014855:Wallerian Degeneration / Q000378:metabolism* / Q000473:pathology
keywords: Wallerian degeneration slow; axon membrane; axonal degeneration; phosphatidylserine; redox