Project Summary/Abstract Aging is associated with a striking increase in the incidence of stroke, which is a major cause of disability among those aged 65 years and older. Effective therapeutics for stroke remain a pressing need for elderly Americans. Ischemic stroke is caused by an occlusion of a cerebral artery leading to neuronal cell death and blood-brain barrier (BBB) disruption while inducing a systemic signaling cascade of reactions in the blood, “stroke-induced blood dyscrasia (SIBD)” and causing long-term disability in elderly stroke patients. BBB disruption and SIBD exacerbate brain injury and neurological outcomes, and SIBD is more severe in elderly patients. We have shown that blood substitution (BS) reduces neutrophils and matrix metalloproteinase-9 (MMP-9) in the blood, protects BBB integrity, ameliorates SIBD, decreases infarct volume and mortality, and improves neurological deficits in the acute phase after stroke. Increased BBB permeability assessed using MRI persists in the acute phase after stroke in patients and focal stroke mice. We have discovered that mitochondrial oxidative phosphorylation (OxPhos) in cerebrovascular endothelial cells (CECs) plays a critical role in the maintenance of BBB integrity. Dysfunctional mitochondria in CECs cause BBB dysfunction and induce SIBD, which results in leukocytes infiltrating through the BBB leading to exacerbation of the brain injury after stroke and contributing to long-term functional disability. We have found a mitochondrial membrane protein is nearly absent in the CECs of brains from stroke patients and focal ischemic stroke mice. MMP-9, a proteinase mainly secreted by activated neutrophils, is associated with BBB leakage, extracellular matrix degradation, and infarct evolution after stroke. During the acute phase after stroke, neutrophils adhere to the CECs where they release MMP-9. Aging correlates with MMP-9 levels in both stroke patients and animal studies. We have found that MMP-9 degrades the mitochondrial membrane protein in cultured CECs. Further, we have designed peptides (stable binding models shown with MMP-9 crystal 3D structure) to block MMP-9 activity in CECs. As we have recently developed an aptamer targeting CECs specifically, we have further designed the conjugates of CEC-specific aptamer with peptides to preserve mitochondrial membrane protein specifically in CECs in vivo. The central hypothesis is that BS therapy reduces stroke severity by removing neutrophils and MMP-9 in the blood thereby preserving mitochondrial membrane protein from degradation in CECs after stroke. To test the hypothesis, we will employ two strains of aged mice and use two in vivo murine focal cerebral ischemia models (a transient stroke model and a permanent stroke model) and in vitro human and murine CEC culture models. We have devised two independent aims: Aim 1: To investigate the ability of BS to improve outcomes after stroke in both male and female aged mice. Aim 2: To test the hypothe...