Obesity restricts oligodendrocyte maturation and impedes repair after white matter stroke

Abstract

Obesity is a growing public health problem that increases rates of white matter atrophy and increases the likelihood of ischemic lesions within white matter. However, the cellular and molecular mechanisms that regulate these changes are unknown. We hypothesized that obesity may alter oligodendrocytes and myelin priming white matter for worsening injury and repair responses after ischemia. C57Bl/6 mice fed a high fat diet (60% kcal from fat) show increased numbers of oligodendrocyte precursor cells (OPCs), decreased myelin thickness with elevated g-ratios, and shorter paranodal axonal segments, indicating accelerated myelin turnover. Fate mapping of OPCs in PDGFR-CreERT;Rpl22tm1.1Psam mice demonstrated that OPC differentiation rates are enhanced by obesity. Gene expression analyses using a novel oligodendrocyte staging assay demonstrated OPC differentiation is blocked by obesity in between the pre-myelinating and myelinating stage. Using a model of subcortical white matter stroke, the number of stroke-responsive OPCs in obese mice was increased after stroke. At early time points after ischemic white matter stroke, spatial mapping of stroke-responsive OPCs indicates that obesity leads to increased OPCs at the edge of ischemic white matter lesions. At later time points, obesity results in increased OPCs within the ischemic lesion while reducing the number of GST-{pi}-positive mature oligodendrocytes in the lesion core. These data indicate that obesity disrupts normal white matter biology by blocking oligodendrocyte differentiation, leads to an exaggerated response of OPCs to white matter ischemia, and limits remyelination after stroke.\n\nSignificance StatementObesity is a growing public health crisis that specifically increases the development of white matter lesions and silent brain infarcts. This relationship implies a direct cellular effect on white matter yet direct evidence is limited. We modeled diet-induced obesity in mice and studied the effect on oligodendrocyte biology and the response to focal white matter stroke. Adult-onset obesity results in thinner myelin, compromised axonal microdomain structure, and blocks the differentiation of OPCs, leaving the white matter with increased numbers of OPCs. After focal white matter stroke in obese mice, the early OPC response to stroke is exaggerated while late reparative OPC differentiation is blocked. These results suggest that obesity specifically blocks OPC differentiation with consequence on brain repair after stroke.