Treatment of stroke is limited to only a few approved therapeutic options that have to be administered within rigid short timeframes resulting in the exclusion of many patients. The overarching goal of this proposal is to further our understanding of different microglia (Mg) and macrophage (M) phenotypes to drive the development of new personalized therapies for stroke. Activated Mg and M are the dominant inflammatory cells in stroke, peaking early and persisting into the chronic stage. These cells are highly dynamic and modulate both damage and repair. Human stroke trials using broad nonspecific anti-inflammatory therapies have failed, likely in part because human stroke is heterogeneous and reparative cells may have been inadvertently blocked in many patients. However, current knowledge on these cells and their functions had been derived mostly from in vitro assays that prevent longitudinal tracking in living animals and patients. How different Mg/M subtypes function in vivo, especially in response to interventions, is poorly understood. To enable in vivo investigations of Mg and M functions, we propose to thoroughly define the transcriptomes and proteomes and of Mg and M subsets in stroke to identify potential imaging targets for damaging and reparative Mg/M phenotypes. Oxidative stress and phagocytosis are two key functional manifestations of Mg/ M activity that can be manipulated for stroke therapy, and can be used to functionally differentiate between damaging and reparative Mg/M. Mg/M-derived reactive oxygen species (ROS) increase damage after stroke, and are mostly produced by M1-type cells. Phagocytosis is important in repair, but can be seen in both M1- and M2-type Mg/M. Our previous transcriptome profiling identified myeloperoxidase (MPO) as a major product secreted by M1-type cells. MPO plays key roles in increasing oxidative stress and tissue damage after stroke, and remains elevated in the ischemic brain for weeks. Moreover, MPO can modulate the inflammatory response toward damage by interacting with the mannose receptor, though a key role of the mannose receptor is repair. Interestingly, mannose receptors are abundantly expressed on M2-type Mg and M, and can be increased by D-mannose administration even in M1-type cells. However, how D-mannose treatment will change Mg and M phenotypes in vivo in stroke is unknown. The proposed experiments will deepen our fundamental understanding of the functional diversity and plasticity of Mg and M in stroke, identify Mg/M based on their functional phenotypes, and lead to new imaging targets urgently needed for stroke.
The specific aims are 1A) perform transcriptome-proteomics analysis to profile damaging and reparative Mg and M phenotypes and discover potential targets for these phenotypes, 1B) validate imaging agents to report on the phenotypes of Mg and M in stroke, 3) perform in vivo imaging to map damaging and reparative Mg and M activity after stroke, and 4) investigate changes in Mg and M phenotypes after D-mannose administration in stroke.
The heterogeneity of human stroke and the dynamic roles different microglia (Mg) and macrophage (M) subsets play at different stages of stroke evolution underscore the need for imaging tools to noninvasively map and track the evolution of different Mg and macrophage M functions, especially in response to potential therapies. Our approach will rationally identify imaging targets and validate current imaging agents for damaging and reparative Mg and M phenotypes and spur the development of new imaging agents from the community.
