Introduction: Ischemic stroke negatively affects the proteome of the brain, causing protein misfolding and aggregation, a pathological event that can lead to cell death and neuroinflammation. Heat shock proteins (HSPs) are chaperone proteins that maintain proteostasis by folding client proteins into active conformations and aiding in the degradation of misfolded proteins. Recent studies in cancer, Alzheimer’s disease, Parkinson’s disease, and traumatic brain injury have defined the epichaperome , a large, tightly bound protein complex composed of heat shock protein 90 (HSP90), heat shock cognate 70 (HSC70), and HSC70/HSP90 organizing protein (HOP) that forms following injury. When bound in the epichaperome, HSPs cannot perform their functions of maintaining proteostasis within the cell, thereby prolonging the negative effects on the proteome. Hypothesis: We hypothesize that the epichaperome forms following ischemic stroke and extends proteomic disturbances, leading to additional tissue death and neurological deficits. Our goal is to characterize, for the first time, the epichaperome formation and its role in ischemic stroke. Methods: C57/BL6J mice underwent 45 minutes of transient middle cerebral artery occlusion (tMCAO). Mice were euthanized at 1, 2, 5, and 7 days after tMCAO. Brains were separated into ipsilateral and contralateral hemispheres and homogenized to isolate protein for SDS-PAGE and native-PAGE analysis of epichaperome components. Results: Beginning at one day after tMCAO, there was a significant increase in epichaperome-associated high molecular weight HSP90α and HSP90β in the ipsilateral hemisphere compared to the contralateral hemisphere ( p =0.0491 and p =0.0467, respectively). Additionally, HOP levels were increased in the ipsilateral hemisphere ( p =0.0151). Levels of high molecular weight HSP90β peaked at 5 days post-MCAO, illustrating a potential therapeutic window for delivery of epichaperome inhibitors prior to 5 days post-stroke. Conclusions: These results support our hypothesis, and shows for the first time, that the high molecular weight epichaperome complex forms following ischemic stroke and may contribute to the pathological events of the ischemic cascade. Understanding epichaperome formation may reveal a novel therapeutic target for ischemic stroke. Studies are ongoing to further delineate the timing of epichaperome formation post-stroke, its cellular origin, and how blocking the epichaperome complex impacts stroke outcomes.
Howell et al. (Thu,) studied this question.