PROJECT SUMMARY/ABSTRACT Although the pathophysiology of Alzheimer’s Disease (AD) is complex and multifactorial, vascular comorbidities and cerebrovascular insufficiency occur in almost two-thirds of AD patients. However, how cerebrovascular insufficiency interacts with and contributes to AD remains poorly understood. Recently, the brain vasculome (i.e. transcriptome profiles of cerebral endothelial cells and pericytes) has been proposed as a conceptual framework to investigate vascular mechanisms in CNS diseases. In response to RFA-AG-23-014 (Mechanisms of Brain Hypoperfusion in AD/ADRD), we propose to test the hypothesis that cerebrovascular insufficiency perturbs the AD brain vasculome, eventually leading to cognitive impairment. The normal brain compensates for hypoperfusion by inducing endogenous vascular remodeling and angiogenesis. The presence of AD interferes with endogenous angiogenesis and vascular recovery in response to hypoperfusion, and this exacerbates AD progression and worsens the AD brain vasculome. Because circadian rhythms and circadian genes are known to regulate angiogenesis, we further hypothesize that AD disrupts circadian homeostasis in the brain vasculome, thus interfering with the endogenous angiogenic response to hypoperfusion. The importance of investigating these interactions between AD, vascular responses, and circadian rhythms is emphasized by our pilot data. For example, we show a greater difference in transcriptome profiles of cerebral endothelial cells and pericytes of wild-type vs AD mice when tested during the active (awake) phase compared to the inactive (sleep) phase. For testing our hypotheses, we propose three integrated aims. Aim 1 will show that AD brains exhibit a lower capacity of compensatory angiogenesis in response to hypoperfusion, and Aim 2 will show that circadian rhythms are disrupted in AD brains and that disrupted circadian rhythms suppress angiogenic response. And finally, Aim 3 will examine whether re-normalizing circadian rhythms improves the brain vasculome and promotes angiogenesis after hypoperfusion in AD mice. Whether and how AD brains lose compensatory angiogenesis capacity after cerebral hypoperfusion is unknown. Therefore, we have designed a multi-disciplinary multi-lab project to fill this gap of knowledge by examining how perturbations in circadian rhythms disrupt the brain vasculome and worsen hypoperfusion in AD.