VCAM1 in brain endothelial cell activation in aging and Alzheimer's disease

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Aging leads to the decline of brain structure and function which increases the susceptibility to neurodegenerative disorders. Work from the Wyss-Coray lab support a cell non-autonomous and reversible mechanism of brain aging regulated by the systemic milieu. Aged plasma drives brain aging in young mice as shown by the reduction in hippocampal neurogenesis, increase in microglia reactivity, and decline in cognitive functions. While young plasma reverses these hallmarks in aged mice. As the identity of the pro-youthful and pro-aging factors is being revealed, it remains unclear how they signal into the brain across the highly impermeable blood brain barrier. Recent work from our lab revealed that aged plasma upregulates on brain endothelial cells (BEC) the expression of an adhesion protein VCAM1 (Vascular Cell Adhesion Molecule 1), which also increases during normal aging. The genetic ablation of VCAM1 from BECs or its neutralization with a systemic antibody abolishes the effects of aged plasma and reverses hallmarks of brain aging. This supports a crucial role for VCAM1 as a mediator of age-related circulatory cues. Yet it remains unclear how VCAM1 alters BECs to drive brain aging. At a single cell level, VCAM1 expressing BECs exhibit a high inflammatory profile compared to VCAM1 negative BECs and blocking VCAM1 reduces brain inflammation suggesting that it may induce the inflammatory signaling in BECs. In addition to aging, VCAM1 increases in the cerebral vessels of Alzheimer’s disease (AD) mice and colocalizes with amyloid plaques and reactive microglia. Soluble VCAM1 also increases in AD patient plasma and highly correlates with dementia severity and pathological hallmarks of AD. Based on these combined observations, this proposal will test the hypothesis that increased VCAM1 disrupts brain endothelial cell signaling during aging and promotes AD-like disease in mice. Aim 1 will determine whether VCAM1 induces the expression of inflammatory genes in aged BEC using single cell transcriptomic analysis of hippocampal BECs and proteomic analysis of microvessels. Experiments will be performed using aged mice where VCAM1 is genetically ablated from BECs or neutralized with an antibody and using young mice where VCAM1 is overexpressed in BEC using the AAV2- BR1 virus. Aim 2 will identify the mechanism behind which VCAM1 signals to induce BEC activation. Primary BECs overexpressing wild-type or mutant VCAM1 will be cultured in the presence or absence of the VCAM1 ligand VLA-4 (very late antigen-4) to determine its effect on the expression of inflammatory genes in BEC. Mutant VCAM1 that shows the highest reduction in BEC activation will be introduced in vivo using the AAV2-BR1 virus to assess microglia reactivity and neural stem cell activity. Aim 3 will determine the role of VCAM1 in a mouse model of AD. VCAM1 neutralizing antibody will be systemically introduced to determine its effect on amyloid plaques, reactive microglia, cognitive deficits, and the activation of BECs as measured by transcriptomic analysis of inflammatory genes. This project will identify aging-induced inflammatory pathways altered by VCAM1 in BECs along with its mechanism of signaling, and determine the potential of VCAM1 as a therapeutic target for AD.