Endothelial Enhancer of Zeste Homolog 2 in Cerebral Amyloid Angiopathy and Alzheimer's disease

About This Grant

ABSTRACT Vascular dysfunction is central to the pathology of Cerebral Amyloid Angiopathy (CAA) and Alzheimer’s Disease (AD). Nitric oxide (NO) (produced via nitric oxide synthase), is a vasodilator and signaling molecule essential for the regulation of cerebral blood flow (CBF). Low expression/activity of endothelial NOS (eNOS) contributes to reduced cerebrovascular reactivity, impaired clearance of β-amyloid along the intramural periarterial drainage pathways, and contributes blood-brain barrier (BBB) impairment. Interestingly, cerebral vessels of AD patients have reduced eNOS expression, also known to be controlled by a master epigenetic modifier, enhancer of zeste homolog 2 (EZH2). EHZ2 is a key component of the polycomb repressive complex 2 (PRC2), which catalyzes the trimethylation of lysine 27 in histone 3 (H3K27me3). EZH2 causes transcriptional repression of eNOS and claudin-5, the most enriched tight-junction protein in blood-brain barrier. Our studies revealed significant increase in EZH2 levels and H3K27 trimethylation, its direct target, in the vasculature of Tg-SWDI (CAA model) mice. Importantly, pharmacological inhibition of EZH2 in aged models of CAA and AD (Tg-2576 mice) not only enhances eNOS, but also improves claudin-5, (tight-junction protein). EZH2's role in autoregulation of CBF, BBB integrity and cognition is unknown. The proposal will also reveal new insights into how epigenetic modifications by EZH2 contribute to the sex differences in dementia. We hypothesized that EZH2 is enhanced in models of dementia (CAA model and AD model), leading to decreased eNOS, and reductions in important BBB tight junction proteins(Claudin 5). Enhanced EZH2 contributes to CBF dysregulation, neuroinflammation, and BBB impairment in our established CAA and AD models. Given the increasing incidence of dementia with age, our study will also employ aged transgenic mice of BOTH sexes. Our Specific Aim 1 will determine the role of EZH2 in blood flow autoregulation and its interaction with eNOS in Tg-SwDI and Tg-2576 mice in both sexes. We will test the effect of endothelial EZH2 knockdown (AAV) and pharmacological inhibition in CBF autoregulation in both models. We also hypothesize that EZH2 produces CBF dysregulation by increasing trimethylation at eNOS gene promoter. Our Specific Aim 2 will determine the role of EZH2 in Aβ pathology and BBB integrity in Tg- SwDI and Tg-2576 mice in both sexes. Our Specific Aim 3 will determine if pharmacological EZH2 inhibition and EZH2 KD improve behavioral function in Tg-SwDI and Tg-2576 mice in both sexes. Given EZH2's contribution in key pathological aspects in AD and CAA, we will conduct a series of longitudinal cognitive function tests on aged mice treated with EZH2 inhibitor or endothelial EZH2 KD AAV across both dementia models.