Summary: Substantial reductions in brain blood flow are found in patients and mouse models of neurodegenerative diseases, including frontotemporal dementia (FTD). These blood flow reductions likely contribute to disease symptoms and progression, but the mechanism remains unknown. Recently, two new mechanisms contributing to brain blood flow reductions in Alzheimer's disease were proposed. Interestingly, both capillary stalling and pericyte constriction are associated with microvasculature dysfunction. In preliminary experiments, the PI has shown that capillary stalling found in Alzheimer's disease mice, also occurs in Progranulin (PGRN) deficient mice, a model for FTD. Thus, the project proposed here will investigate the contribution of stalled blood flow and pericyte constriction in capillaries to brain blood flow reductions. Further, this project aims to elucidate the mechanism behind these phenomena using transcriptome analyses and cell-surface proteomics of microvessels from PGRN-deficient mice. The pathology and region predicted to suffer from blood flow reductions in the PGRN deficient mice is the prefrontal cortex, which can be readily studied with the two-photon excited fluorescence imaging tools used previously by the PI. Preliminary data suggests that PRGN-deficient mice display increased capillary stalling caused by white blood cells adhered to the endothelium. For Aim 1, we will use high-resolution, multiphoton, in vivo imaging approaches to structurally and functionally determine blood flow rates in individual capillaries, measure capillary stalling and pericyte constriction, and their interplay. This data will identify the cause of brain blood flow reduction associated with FTD. Aim 2 will elucidate the molecular mechanism linking vascular inflammation to brain blood flow reductions in PGRN-deficient mice by using transcriptomic and cell-surface proteomics to profile microvessels. These experiments will generate two datasets that will allow us to pinpoint molecular aberrations in microvessels of PGRN deficient mice. The data will also shed light on the role of vascular inflammation and vascular obstructions contributing to blood flow reductions. Selected genes and proteins identified in these screens will be independently confirmed and later further analyzed by functional in vivo multiphoton imaging, labeling antibodies, inhibiting drugs, and/or cell-type-specific mouse models. We predict that candidate genes and proteins will be involved in vascular inflammation and associated with oxidative stress, blood-brain barrier breakdown, protein degradation, and lysosomal dysfunction. The idea of capillary stalling is new, and - if confirmed -, could represent a mechanism contributing to brain blood flow reductions in neurodegenerative disease in general, and not just specifically to FTD. If correct, novel therapeutic strategies targeting microvascular inflammation could be developed to improve brain blood flow in patients with FTD and pos...