Abstract 111: Myeloid Specific Deletion of CD36 Increases Microglia-Like CD45 Low Subset and Exacerbates Stroke-Induced Brain Injury

Abstract

Objective: CD36 regulates biological and pathological processes including inflammation, resolution, phagocytosis, and angiogenesis. Highly expressed in monocytes/macrophages (MM), MM CD36 has been implicated in both detrimental and beneficial effects in acute stroke outcome and recovery. Using myeloid specific deficiency of CD36 (CD36KO MM ) mice, the present study addresses the role of MM CD36 on subset composition of MM in the acute and recovery phases of stroke. Methods: WT (CD36 fl/fl ) and CD36KO MM (M/F, 12w old) mice were subjected to transient focal ischemia. Brain immune cells were collected at 3d, 7d and 2m (n=8-12/timepoint). Infarct volume and hemispheric swelling were measured at 3d (n=13/genotype). In the isolated brain immune cells, CD11b+ cells were further distinguished by CD45 Hi and CD45 Low subsets. The extent of MM trafficking was determined by an intravenous infusion of control GFP+ splenocytes into the stroked WT and CD36KO MM mice 1d prior to sacrifice and MM subset analyses. Results: Compared to WT mice, CD36KO MM mice showed no difference in CD45 Low subset at 3d, 7d and 2m after stroke. However, CD36KO MM mice displayed a significant reduction of CD45 Hi subset, presumably infiltrating cells, at these time points (n=4-8 /group, P<0.01). Adoptive transfer of control GFP+ splenocytes to stroked CD36KO MM mice resulted in an increase of GFP+ cells in CD45 Low but a profound reduction in CD45 Hi subset. Despite the near absence of CD45 Hi and increased CD45 Low population in the post-ischemic brain, CD36KO MM mice displayed exacerbation of brain injury (15.1±13.7 vs 25.8±17.5 mm 3 , p<0.05) and brain swelling (12.1±10.3 vs 18.4±12.7 %, p=0.1). Conclusion: The observed reduction of CD45 Hi subset and exacerbation of brain injury in CD36KO MM mice suggests a beneficial role of infiltrated CD45 Hi MMs in limiting stroke injury. The sustained trafficking at 2m indicates potential involvement of MM CD36 in the recovery process. Further studies to assess long-term outcomes of CD36KO MM mice will provide critical insights on the role of macrophage CD36 in stroke recovery.