UBC Theses and Dissertations
Metabolic reprogramming supports microglial survival and immune function York, Elisa
In addition to energy production, metabolic pathways, such as glycolysis and mitochondrial metabolism, are important in regulating peripheral immune cell activity. This thesis examines whether cellular metabolism also regulates the immunological functions of microglia, the brain’s resident immune cells. The metabolic and anatomical complexity of the brain provides unique challenges for these studies, which required the development of two new methodological approaches. The first, 3DMorph, allows automatic and unbiased quantification of microglial morphology in three dimensions, improving the efficiency, accuracy, and reproducibility of microglial morphology analyses. The second establishes the use of fluorescence lifetime imaging of endogenous nicotinamide adenine dinucleotide (NADH-FLIM) within single microglia of acute hippocampal slices. This work demonstrates that GFP exhibits blue emission with short fluorescence lifetimes, which contaminates the metabolic signal, and alternatively validates microglial identification using tomato lectin to allow metabolic measurements by NADH-FLIM in situ. Using these techniques, microglial metabolism was investigated at baseline, as was their metabolic flexibility following nutrient depletion. Relative to the surrounding neuropil, microglia are highly glycolytic in control conditions. However, upon removal of glucose, microglial glutaminolysis is sufficient to support mitochondrial metabolism, cell viability, and immune surveillance. This flexibility may permit microglial survival and function during metabolic perturbations, such as stroke or hypoglycemia. Changes in cellular metabolism also regulated microglial immune activity. Lipopolysaccharide (LPS) application to acute hippocampal slices triggered an increase in microglial glycolysis, which was inhibited by co-incubation with 2-deoxy-D-glucose (2DG), a glycolysis inhibitor. LPS stimulation also increased production of the pro-inflammatory cytokines IL-1β and TNFα. LPS-induced production of these cytokines was decreased in the presence of 2DG, confirming a role for glycolysis in regulating microglial immune function. These data indicate that microglia exhibit remarkable metabolic flexibility that exceeds the ability of neurons. In addition, the activity of metabolic pathways impacts microglial immune function by altering IL-1β and TNFα production. The microglial morphology and metabolism tools presented here will continue to provide insights into metabolic signals regulating brain immune function. Both microglial and metabolic dysregulation are implicated in neurodegeneration following trauma or disease, making metabolic manipulations for therapeutic intervention or disease prevention a promising area of study.
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