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 (genemediated) 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-␤-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.

Calcium signalling-dependent mitochondrial dysfunction and bioenergetics regulation in respiratory chain Complex II deficiency

“…29,30 Proteasome-dependent degradation of SERCA2a isoform was reported in an earlier work by Ihara et al 31 Ubiquitination of PMCA1 isoform has also been detected after preconditioning ischaemia in rat cortical neuronal cultures. 32 As polyubiquitylated proteins are the preferred proteasome 26S substrates, we postulate that SERCA2b and PMCA2 undergo proteasome-dependent degradation after their ubiquitination.…”

Role of the ubiquitin–proteasome system in brain ischemia: Friend or foe?

“…These results suggest a rapid degradation of cell death promoting proteins and rapid neuroprotection by the UPS. Moreover, the UPS was found to increase neuronal resistance to excitotoxicity through rapid modulation of postsynaptic densities after preconditioning ischemia (Meller et al, 2008). Ubiquitination and degradation of proteins involved in the structure and function of PSD, namely MARCKS (myristoylated, alanine-rich C-kinase substrate) and fascin (actin binding proteins), result in the reorganization of actin cytoskeleton after preconditioning ischemia.…”

“…Ubiquitination and degradation of proteins involved in the structure and function of PSD, namely MARCKS (myristoylated, alanine-rich C-kinase substrate) and fascin (actin binding proteins), result in the reorganization of actin cytoskeleton after preconditioning ischemia. These alterations result in the loss of NMDAR from the PSD and a concomitant selective attenuation of toxic NMDAR-mediated signaling at the time when tolerance to ischemia is acquired (Meller et al, 2008). Accordingly, inhibition of proteasome activity was found to block the rapid ischemic tolerance-induced neuroprotection (Meller et al, 2008).…”

“…These alterations result in the loss of NMDAR from the PSD and a concomitant selective attenuation of toxic NMDAR-mediated signaling at the time when tolerance to ischemia is acquired (Meller et al, 2008). Accordingly, inhibition of proteasome activity was found to block the rapid ischemic tolerance-induced neuroprotection (Meller et al, 2008). Accordingly, activation of NMDA receptors was shown to induce PSD-95 degradation by the UPS, together with a loss of dendritic spines, in cultured cerebrocortical neurons (Waataja et al, 2008).…”

Extracellular Signal-regulated Kinase (ERK) Regulates Cortactin Ubiquitination and Degradation in Lung Epithelial Cells

“…Actin-binding proteins are not stable under certain biological conditions. Alanine-rich kinase substrate (MARCKS) and fascin, two actin-binding proteins, are ubiquitinated, displaying a rapid turnover rate after preconditioning ischemia (46). Here, cortactin displayed extended in vivo stability consistent with half-lives of structural and regulatory proteins, but destabilized in the presence of LPS.…”