Pathogenesis of Early- Versus Late-Stage Alcohol-Mediated White Matter Degeneration - Chronic heavy or binge alcohol consumption damages the structural and functional integrity of the brain. Ethanol’s neurotoxic and degenerative effects target white matter (WM) across the lifespan, resulting in loss of myelin, impaired myelin maintenance, and degeneration of axons. Since WM integrity is critical to many CNS functions, better understanding of how ethanol exerts its adverse effects on WM is needed to prevent or remediate the associated neurobehavioral and cognitive deficits. Oligodendrocyte dysfunction is at the core of WM degeneration since oligodendroglia are responsible for synthesizing and maintaining myelin. Myelin is needed to support and protect axons and ensure efficient neuronal conductivity. We hypothesize that alcohol- related brain degeneration (ARBD) involving WM could be divided into: 1) an early, reversible stage that is mainly associated with myelin loss and mediated by oxidative stress, inflammation, and neurotoxic ceramide accumulation via myelin breakdown and dysregulation of lipid metabolism; and 2) a later stage marked by impaired insulin/IGF-1 signaling through PI3K-Akt-mTOR-mTORC. Consequences of the latter include loss of mature oligodendrocytes and compact myelin, impaired maturation of oligodendroglia, axonal damage, and further progressive dysregulated sphingolipid metabolism with ceramide accumulation and sulfatide depletion. We anticipate that abstinence will be sufficient to remediate early stages of WM ARBD, whereas active interventions, such as insulin sensitizer treatments, will be required to reverse WM damage sustained by long periods of heavy alcohol exposure. However, both early and late stages of ARBD will likely respond to ceramide inhibitors such as myriocin. Aim 1 will characterize the structural, biochemical and molecular pathologies of early-stage WM ARBD in an established rat model of chronic ethanol exposure. Aim 2 will utilize a rat model and human postmortem brains to assess the roles of impaired insulin/IGF-1 signaling through PI3K-Akt-mTOR and mTORC1 versus mTORC2 as drivers of oligodendrocyte dysfunction and altered sphingolipid metabolism in the later stages of WM ARBD. Aim 3 will evaluate the effectiveness of abstinence, ceramide inhibitor, and insulin sensitizer treatments in remediating oligodendrocyte dysfunction and associated alterations in myelin sphingolipid composition in early versus late stages of WM ARBD. In addition, a novel sub-aim will determine the degree to which ethanol-induced CNS WM myelin sphingolipid abnormalities and their responses to treatment can be detected in peripheral blood mononuclear cells (PBMCs). Our underlying hypotheses are addressed through the use of quantitative immunohistochemistry, electron microscopy, multiplex ELISAs, mRNA studies, and Matrix-assisted laser desorption/ionization-imaging mass spectrometry. The research plan is novel, mechanistic, robust, transparent, and inclusive of both sexes, human validation studies, prospects for stratifying treatment according to ARBD stage, and approaches for potentially monitoring ARBD-associated WM biochemical pathology and responses to treatment with non-invasive PBMC assays.
