The Unfolding Role of Microglia in Alcohol Withdrawal

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Abstract Alcohol withdrawal is a medical emergency and a behavioral barrier to reducing alcohol abuse. Unlike withdrawal to other drugs, there is ample evidence that withdrawal to alcohol becomes worse after multiple cycles of alcohol consumption and abstinence, increasing the risks for serious adverse complications including seizures, delirium tremens, and death. Furthermore, the negative reinforcement inherent to cycles of alcohol abstinence and relapse to alcohol consumption complicates any behavioral interventions to reduce alcohol abuse. Many clues suggest that neuroinflammation is involved in both alcohol tolerance as well as withdrawal, but this realization has not led to new treatments for alcohol use disorder. The purpose of this proposal is to develop our hypothesis that chronic, intermittent alcohol exposure alters the way microglia, the innate immune cells that reside in the brain, modulate neuroimmune as well as neuronal synaptic signaling. In pilot experiments using RNA sequencing of ribosome-associated RNA from microglia after multiple cycles of alcohol exposure and abstinence, we found that alcohol withdrawal causes oxidative stress in microglia and activates the “unfolded protein response” (UPR), a mechanism that is involved in cellular stress responses leading to neuroinflammatory signaling and derangements in microglia function that can lead to cell death. We propose to block the full activation of the microglial UPR by knocking out CHOP, a key transcription factor involved in this pathway that was dramatically upregulated in microglia during withdrawal, using a recently developed, selective cre-driver mouse line, Tmem119-2A-Cre-ERT2/TdTomato, crossed with commercially available floxed CHOP mice to investigate this biology. We will examine how blunting UPR signaling alters the signs of alcohol withdrawal by testing if CHOP knockout alters several behavioral manifestations and reduces microglia morphological and gene expression changes associated with withdrawal. Using in vivo two-photon time lapse microscopy, we will examine if CHOP knockout from microglia changes morphology and motility associated during alcohol withdrawal. We will also test whether microglial CHOP impacts the motivation to drink alcohol in a model of voluntary alcohol drinking after multiple cycles of ethanol vapor exposure and withdrawal. Together, these experiments examine the role of neuroinflammation in the mechanisms of alcohol dependence and withdrawal from a new angle that has not been previously considered and is well matched to the R21 mechanism due to its high novelty and potential to develop new treatments.