Oxidative stress-induced vascular pathology and dysfunction in Alzheimer’s disease

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PROJECT SUMMARY/ ABSTRACT Vascular contributions to cognitive impairment and dementia (VCID) is highly comorbid with Alzheimer's disease (AD) where it exacerbates and hastens functional deficits. Mechanistic studies of vascular pathology formation and its effects on brain function, especially in AD, is limited. Developing translational imaging for application to mixed pathology models is necessary to understand the complex pathophysiological processes that link VCID and AD. Recently, we modified and optimized the oxidative stress-induced photothrombosis protocol (I.e. photoactivation of IV-injected Rose Bengal dye) for targeting individual capillaries in rodents. The major advantage of this novel vascular oxidative stress model is that vessel stalls, occlusion, and microhemorrhage can be followed in single capillaries in living mice, in real time, using multiphoton imaging. In this R21, we aim to apply this technique to 5xFAD mice to generate and characterize a novel AD/VCID mouse model en route to determining fibronectin— a matrix protein that supports vascular structure and integrity—as an indicator for the oxidative stress that arises from both cerebrovascular disease and AD. Our ongoing work on postmortem human brain specimens has revealed that astrocyte-derived fibronectin strongly colocalizes with the oxidative stress marker, nitrotyrosine (NT) especially around cerebrovessels and Aβ deposits. Photothrombosis of small cerebral arterioles revealed accumulation of fibronectin/NT colocalization at intravascular and nearby perivascular regions, similar to what we observe in human AD brain tissue. Here, we propose to use cutting edge physiology approaches combined with human postmortem brain specimens from our world class brain bank at the Sanders-Brown Center on Aging, to test the hypothesis that oxidative stress—indicated by NT incorporation into fibronectin— exacerbates cerebrovascular and synaptic dysfunction in the context of AD. In Aim 1, we will determine the effect of microvascular oxidative stress on neurovascular function in WT and 5xFAD mice. Multiphoton imaging techniques will be used to apply and to observe, in real-time, the development of microvascular pathologies including blood vessel stalls, vessel occlusion (infarct), and microhemorrhage as well as their effects on neurovascular coupling. Mouse brain tissues and postmortem samples from humans with confirmed vascular pathology and AD pathology will also be used to assess fibronectin/NT interactions with blood vessels, and to cross-validate our novel photothrombotic mouse model of mixed AD/VCID pathology. In Aim2, we will test the hypothesis that oxidative stress-induced microvascular pathology in 5xFAD mice leads to the global exacerbation of cognition and synaptic function in the context of AD-like pathology. The proposed studies will fill a critical knowledge gap surrounding the convergence of pathologic sequelae in cerebrovascular disease and AD. Moreover, establishment of a novel mouse model for mixed AD/VCID pathology will help inform new strategies for treating individuals with both AD and vascular pathology.