The Role of Perilipin 2 in Macrophages after Experimental Spinal Cord Injury

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PROJECT SUMMARY/ABSTRACT Spinal cord injury (SCI) leads to permanent motor and sensory loss that is exacerbated by persistent inflammation months after the injury. After SCI, monocyte-derived macrophages (MDMs) infiltrate the lesion to aid in cellular debris clearance. However, this response is emerging as a double- edged sword. Lingering debris inhibits repair and plasticity while clearance of the debris by infiltrating MDMs induces a proinflammatory and damaging phenotype. Clearance of cholesterol-rich myelin debris causes MDMs to resemble proinflammatory foam cells both phenotypically and morphologically. Foam cells are lipid- laden macrophages with numerous lipid droplets (LDs) that form when excessive cholesterol uptake overwhelms cholesterol metabolism. Foam cells also drive chronic inflammation in atherosclerosis and non- alcoholic steatohepatitis (NASH). Foam cells persist chronically in the injured cord and may contribute to the sustained proinflammatory lesion environment. However, their role in the chronic inflammatory state is poorly understood. Therefore, elucidating the effect of foam cell formation after SCI is integral to understanding the contribution of MDMs to injury pathology. Preliminary and published data identify Perilipin 2 (Plin2) as a key differentially upregulated gene in both infiltrating MDMs after SCI and foam cells in atherosclerosis. Plin2 is essential in regulating the formation and storage of cholesterol (i.e., lipid droplets (LDs)) in macrophages as lipid metabolites are either exported from these cells or stored in LDs. Plin2 coats LDs, sequesters them in the cytosol and prevents lipolytic enzymes from accessing their cargo. Reducing Plin2, may, therefore, reduce LD accumulation and mitigate foam cell formation after SCI. In models of atherosclerosis and NASH, Plin2 deficient mice produced fewer foam cells and were protected from atherosclerotic plaque formation and cirrhosis, respectively. To understand the effects of Plin2 upregulation in MDMs after SCI a novel targeted deletion of Plin2 using a LysMCre/lox system will be employed. Using this mouse model, this project will determine (1) the role of Plin2 in myelin-induced foam cell formation using an in vitro approach and (2) the effects of targeted Plin2 deletion in MDMs on foam cell formation, inflammation, and locomotor recovery after experimental. These experiments will test the hypothesis that cell-specific Plin2 ablation in MDMs suppresses foam cell formation after SCI, inhibits inflammation, and promotes functional recovery. If successful, this project will provide novel insight into how CNS macrophages metabolize myelin and may provide new therapeutic targets to improve SCI recovery by resolving chronic intraspinal inflammation. Through the completion of this training grant, the PI will receive ample training regarding the implementation of project management, responsible conduct of research, and the dissemination of findings. This training will provide the PI with the skillset necessary to carry out the specific aims and lay the foundation for the PI to become an independent physician-scientist with an extramurally supported research portfolio in the field of neurotrauma.