title: Ubiquitin proteasome-mediated synaptic reorganization: a novel mechanism underlying rapid ischemic tolerance.
abstract: Ischemic tolerance is an endogenous neuroprotective mechanism in brain and other organs, whereby prior exposure to brief ischemia produces resilience to subsequent normally injurious ischemia. Although many molecular mechanisms mediate delayed (gene-mediated) ischemic tolerance, the mechanisms underlying rapid (protein synthesis-independent) ischemic tolerance are relatively unknown. Here we describe a novel mechanism for the induction of rapid ischemic tolerance mediated by the ubiquitin-proteasome system. Rapid ischemic tolerance is blocked by multiple proteasome inhibitors [carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG132), MG115 (carbobenzoxy-L-leucyl-L-leucyl-L-norvalinal), and clasto-lactacystin-beta-lactone]. A proteomics strategy was used to identify ubiquitinated proteins after preconditioning ischemia. We focused our studies on two actin-binding proteins of the postsynaptic density that were ubiquitinated after rapid preconditioning: myristoylated, alanine-rich C-kinase substrate (MARCKS) and fascin. Immunoblots confirm the degradation of MARCKS and fascin after preconditioning ischemia. The loss of actin-binding proteins promoted actin reorganization in the postsynaptic density and transient retraction of dendritic spines. This rapid and reversible synaptic remodeling reduced NMDA-mediated electrophysiological responses and renders the cells refractory to NMDA receptor-mediated toxicity. The dendritic spine retraction and NMDA neuroprotection after preconditioning ischemia are blocked by actin stabilization with jasplakinolide, as well as proteasome inhibition with MG132. Together these data suggest that rapid tolerance results from changes to the postsynaptic density mediated by the ubiquitin-proteasome system, rendering neurons resistant to excitotoxicity.
authors.affiliation: Robert S. Dow Neurobiology Laboratories, Legacy Research, Portland, Oregon 97232, USA. rmeller@downeurobiology.org
authors.forename: Robert
authors.initials: R
authors.lastname: Meller
authors.forename: Simon John
authors.initials: SJ
authors.lastname: Thompson
authors.forename: Theresa Ann
authors.initials: TA
authors.lastname: Lusardi
authors.forename: Andrea Nicole
authors.initials: AN
authors.lastname: Ordonez
authors.forename: Michelle Dawn
authors.initials: MD
authors.lastname: Ashley
authors.forename: Veronica
authors.initials: V
authors.lastname: Jessick
authors.forename: Weihzen
authors.initials: W
authors.lastname: Wang
authors.forename: Daniel John
authors.initials: DJ
authors.lastname: Torrey
authors.forename: David Clifford
authors.initials: DC
authors.lastname: Henshall
authors.forename: Philip R
authors.initials: PR
authors.lastname: Gafken
authors.forename: Julie Anne
authors.initials: JA
authors.lastname: Saugstad
authors.forename: Zhi-Gang
authors.initials: ZG
authors.lastname: Xiong
authors.forename: Roger Pancoast
authors.initials: RP
authors.lastname: Simon
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D002232:Carbocyanines; D002352:Carrier Proteins / Q000378:metabolism; D016923:Cell Death; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000172:deficiency; D000860:Hypoxia / Q000150:complications; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D007511:Ischemia / Q000209:etiology / Q000378:metabolism*; D019194:Ischemic Preconditioning; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D008565:Membrane Proteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D009474:Neurons / Q000166:cytology / Q000187:drug effects; D018408:Patch-Clamp Techniques; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000502:physiology*; D013997:Time Factors; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D002232:Carbocyanines; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; C000619712:Marcks protein, rat; D008565:Membrane Proteins; D008840:Microfilament Proteins; D025801:Ubiquitin; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; C020324:fascin; C098044:3,3'-dioctadecyloxacarbocyanine; D046988:Proteasome Endopeptidase Complex; D005947:Glucose