title: Motor neuron impairment mediated by a sumoylated fragment of the glial glutamate transporter EAAT2.
abstract: Dysregulation of glutamate handling ensuing downregulation of expression and activity levels of the astroglial glutamate transporter EAAT2 is implicated in excitotoxic degeneration of motor neurons in amyotrophic lateral sclerosis (ALS). We previously reported that EAAT2 (a.k.a. GLT-1) is cleaved by caspase-3 at its cytosolic carboxy-terminus domain. This cleavage results in impaired glutamate transport activity and generates a proteolytic fragment (CTE) that we found to be post-translationally conjugated by SUMO1. We show here that this sumoylated CTE fragment accumulates in the nucleus of spinal cord astrocytes of the SOD1-G93A mouse model of ALS at symptomatic stages of disease. Astrocytic expression of CTE, artificially tagged with SUMO1 (CTE-SUMO1) to mimic the native sumoylated fragment, recapitulates the nuclear accumulation pattern of the endogenous EAAT2-derived proteolytic fragment. Moreover, in a co-culture binary system, expression of CTE-SUMO1 in spinal cord astrocytes initiates extrinsic toxicity by inducing caspase-3 activation in motor neuron-derived NSC-34 cells or axonal growth impairment in primary motor neurons. Interestingly, prolonged nuclear accumulation of CTE-SUMO1 is intrinsically toxic to spinal cord astrocytes, although this gliotoxic effect of CTE-SUMO1 occurs later than the indirect, noncell autonomous toxic effect on motor neurons. As more evidence on the implication of SUMO substrates in neurodegenerative diseases emerges, our observations strongly suggest that the nuclear accumulation in spinal cord astrocytes of a sumoylated proteolytic fragment of the astroglial glutamate transporter EAAT2 could participate to the pathogenesis of ALS and suggest a novel, unconventional role for EAAT2 in motor neuron degeneration.
authors.affiliation: Weinberg Unit for ALS Research, Department of Neuroscience, Farber Institute for Neuroscience, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Emily
authors.initials: E
authors.lastname: Foran
authors.forename: Alexey
authors.initials: A
authors.lastname: Bogush
authors.forename: Michael
authors.initials: M
authors.lastname: Goffredo
authors.forename: Paola
authors.initials: P
authors.lastname: Roncaglia
authors.forename: Stefano
authors.initials: S
authors.lastname: Gustincich
authors.forename: Piera
authors.initials: P
authors.lastname: Pasinelli
authors.forename: Davide
authors.initials: D
authors.lastname: Trotti
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D053148:Caspase 3 / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D018920:Coculture Techniques; D027342:Excitatory Amino Acid Transporter 2 / Q000737:chemistry / Q000633:toxicity*; D005455:Fluorescent Antibody Technique; D007150:Immunohistochemistry; D051379:Mice; D008822:Mice, Transgenic; D046228:Microarray Analysis; D009046:Motor Neurons / Q000187:drug effects*; D010446:Peptide Fragments / Q000737:chemistry / Q000633:toxicity; D060888:Real-Time Polymerase Chain Reaction; D025842:SUMO-1 Protein / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000235:genetics; D000072105:Superoxide Dismutase-1
chemical_list: D027342:Excitatory Amino Acid Transporter 2; D010446:Peptide Fragments; D025842:SUMO-1 Protein; C493396:Slc1a2 protein, mouse; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D053148:Caspase 3