PROJECT 1 ABSTRACT/SUMMARY Vascular contributions to cognitive impairment and dementia (VCID) are a major cause of dementia, both alone and co-morbid with Alzheimer’s disease (AD) and AD Related Dementias (ADRD). Astrocytic end-feet are physically anchored to the vascular basement membranes via dystroglycan complexes. At the end-feet are potassium and water channels Kir4.1 and aquaporin 4 (AQP4), as well as monocarboxylic acid transporters (MCTs). AQP4 and Kir4.1 channels are polarized at the end-foot and are co-anchored via a -syntrophin- dystrophin 1 complex. We have found that cerebral small vessel disease (cSVD) induced by hyperhomocysteinemia (HHcy) resulted in degeneration and dissociation of the astrocytic end-feet and an associated loss of AQP4 and Kir4.1 from the end-feet. This suggests that the end-feet are particularly susceptible to vascular injury and as such may mediate neuronal dysfunction and neurodegeneration associated with dementia. We have observed increased activity of matrix metalloproteinases (MMPs), in particular MMP9, coincident with astrocytic end-foot degeneration. We therefore hypothesize that MMP9 is necessary and sufficient for astrocytic end-foot degeneration and associated neurovascular coupling, and metabolic and ionic dyshomeostasis. We will test our hypothesis in mice by manipulating MMP9 in our well-characterized HHcy mouse model of VCID and our multi-modal, multi-faceted outcome measures leverage the specific expertise of our Cores including intravital, MRI/MRS, and electrophysiological measures provided by Core B, and human tissue, images, and biospecimens from Core C. We collaborate extensively with Projects 2-4 to determine relationships between end-foot disruption and glutamate transporters, K+ATP channels, and insulin transporters. All data will flow through Core D to quantitatively assess relationships between MMP9 and astrocytic and neuronal function within this Project and across all Projects in our P01—Strategies for Targeting Astrocyte Reactivity in ADRD P01. To test our hypothesis, we propose three distinct aims. Specific Aim 1: MMP9 mediated astrocytic end-foot degeneration will result in cerebrovascular dysfunction impaired neurovascular coupling. Specific Aim 2: MMP9 mediated astrocytic end-foot degeneration will result in metabolic and ionic dyshomeostasis. Specific Aim 3: Astrocytic end-foot degeneration results in profound changes in gene and protein expression and end-foot proteins can be used as biomarkers of end-foot degeneration.