Abstract TP98: Aging-Related Impairment in Post-Ischemic O-GlcNAcylation Activation Critically Contributes to Stroke Outcome

Abstract

Introduction: Activity of the unfolded protein response (UPR) declines with age. The most conserved UPR branch is mediated by inositol- requiring enzyme-1 (IRE1). Once activated, IRE1 is converted to an endonuclease that splices X-box binding protein-1 (Xbp1) mRNA, leading to production of a new 54-kDa protein, XBP1s. XBP1s was recently shown to be capable of up-regulating expression of all major hexosamine biosynthetic pathway (HBP) enzymes. HBP generates UDP-GlcNAc, the sugar donor for O-GlcNAc modification (O-GlcNAcylation). These pathways together form the IRE1/XBP1s/HBP/O-GlcNAc axis. Our previous data demonstrated a pivotal role of this axis in stroke outcome, especially in the aged brain. Here, we expanded on our previous findings and further elucidated that aging-related impairment in post-ischemic O-GlcNAcylation activation critically contributes to stroke outcome. Methods: Permanent and transient middle cerebral artery occlusion (MCAO) surgeries were performed on young and aged animals. Conditional XBP1 transgenic (XBP1s-TG) and knockout (Xbp1-cKO) mice were used to determine the role of the XBP1 branch in stroke outcome. Thiamet-G was used to increase O-GlcNAcylation. Short- and long-term stroke studies were conducted. Functional outcome was evaluated by various behavioral tests. Results and Conclusions: In line with our previous data, XBP1s-TG mice exhibited improved stroke outcome, and boosting O-GlcNAcylation with thiamet-G rescued worse stroke outcome observed in Xbp1-cKO mice. Moreover, intervention with thiamet-G to enhance O-GlcNAcylation in the brain improved not only long-term outcome after transient MCAO in young mice, but also long-term functional recovery after permanent MCAO in aged rats, likely due to its rescue effect on impaired O-GlcNAcylation activation in the aged brain. Finally, we discovered that UDP-GlcNAc production under the physiologic state and after ischemia was compromised in the aged brain, which constitutes a potential mechanism responsible for impaired O-GlcNAcylation activation after stroke. Together, the findings strengthen our notion that targeting pro-survival pathways that are activated in the young, but not the aged, ischemic brain is a new promising therapeutic strategy in stroke.