Damage to the endothelium is an important contributor to the initiation and progression of atherosclerosis. GRP78 is an endoplasmic reticulum (ER)-resident molecular chaperone in normal healthy endothelium that functions to assist in the correct folding of newly synthesized proteins and to prevent the aggregation of folding intermediates. In addition, GRP78 is present as a transmembrane protein on the surface of lesion-resident endothelial cells. Surface GRP78 is known to act as a surface signaling receptor in cancer cells and is activated by anti-GRP78 autoantibodies (GRP78a-Abs) isolated from the serum of cancer patients. However, the role of cell surface GRP78 on endothelial cells and the influence of GRP78a-Abs in atherosclerosis is unknown. The objectives of this study were to investigate the effects of GRP78a-Abs on lesion development, examine whether engagement of cell surface GRP78 by GRP78a-Abs modulates endothelial cell function, and determine whether GRP78a-Abs were associated with cardiovascular disease (CVD) in humans. This research showed that ApoE-/- mice with advanced atherosclerotic lesions have elevated serum levels of GRP78a-Abs and ApoE-/- mice immunized against recombinant GRP78 demonstrated a significant increase in GRP78a-Abs titers as well as accelerated lesion growth. Furthermore, this work demonstrated that activation of surface GRP78 on endothelial cells by GRP78a-Abs significantly increases gene expression of adhesion molecules ICAM-1 and VCAM-1 as well as leukocyte adhesion through the NFκB pathway. Additionally, middle-aged to elderly adults at risk for CVD showed a tendency toward elevated circulating GRP78a-Ab levels. Our results suggest that signaling through cell surface GRP78 can activate intracellular pathways that contribute to endothelial cell activation and augment atherosclerotic lesion development. These findings demonstrate a novel role for GRP78a-Abs and surface GRP78 receptor activity in endothelial cell function and the early stages of lesion development, as well as establish an initial framework for future work involving circulating GRP78a-Abs and atherosclerotic disease in humans. Furthermore, this work indicates inhibiting the interaction of GRP78a-Abs with cell surface GRP78 could present a novel therapeutic strategy to modulate lesion growth, thereby reducing the risk for atherosclerosis and cardiovascular disease. / Thesis / Doctor of Philosophy (PhD)

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Stroke is a leading cause of morbidity and long-term neurological disability in the U.S. Ischemic stroke, which accounts for approximately 90% of all strokes, is the result of an occlusion in the arteriole cerebrovascular network. No effective treatment options exist to provide neuroprotection from occlusion, and limited success has been seen clinically when attempting to restore blood flow to vulnerable neural tissue regions. Enhancement of pial collateral remodeling (Arteriogenesis) has recently been shown to improve blood flow and mitigate neural tissue damage following stroke (1-3). Arteriogenesis is the remodeling of pre-existing arteriole vessel which are able to re-route blood to blood-deprived regions of tissue. Arteriogenesis requires endothelial cell (EC) and smooth muscle cell proliferation, extracellular matrix degradation and recruitment of circulating bone marrow-derived cells (4-6). Unlike spouting angiogenesis, which requires weeks following occlusion to develop, arteriogenesis begins as early as 24-48hrs post-stroke (7, 8) and can expeditiously enhance blood flow to ischemic regions, making it an attractive target for therapeutic intervention. Our preliminary studies, in an EphA4 global knockout mouse model, indicated that EphA4 receptor tyrosine kinase severely limits pial arteriole collateral formation. The preliminary work also showed that activation of EC EphA4 receptor in vitro inhibited vascular formation. Additionally, ECs lining the collateral vessel have been shown to play a role in collateral remodeling (9). Taken together, the objective of this dissertation was to elucidate the cell autonomous role of the EphA4 receptor and given the central role of the EC in collateral remodeling, we postulated that EphA4 receptor on ECs the limits pial collateral formations. Using a cell-specific loss-of-function approach, we tested the hypothesis that EC-specific EphA4 plays an important role in pial collateral development and remodeling after induced stroke. The results from this dissertation show that (1) EphA4 expression on ECs suppress the formation of pial collaterals during development and limits EC growth via suppression of p-Akt in vitro (2) EC-specific EphA4 ablation leads to increased collateral remodeling, enhanced blood flow recovery, tissue protection and improved neurological behavioral outcomes after stroke and (3) Mechanistically, EphA4 limits pial collateral remodeling via attenuation of the Tie2/Angiopoietin-2 signaling pathway. The work presented in this dissertation demonstrate that EphA4 can be targeted therapeutically to increase pial collateral remodeling to alleviate neurological deficits after ischemic stroke. / Doctor of Philosophy / Stroke is the fifth leading cause of death in the United States. Ischemic stroke is the most common type of stroke and occurs when blood flow to part of the brain is impeded. Lack of blood results in cell death and tissue damage in the brain. In an effort to restore blood flow, specialized blood vessels in the brain called collaterals remodel and become larger to allow re-routed blood to the blood-deprived region of the brain. The duration it takes to remodel these remarkable blood vessels and re-route blood varies in humans, and sometimes is not able to prevent adequate tissue damage. The current work explores novel therapeutic targets to accelerate collateral remodeling in an effort to reduce tissue loss after stroke. We present studies which show that a protein called EphA4, found on endothelial cells restricts remodeling, and when inhibited in the brain can increase collateral remodeling and reduced adverse effects after ischemic stroke.

Traumatic brain injury (TBI) can cause a number of deleterious effects to the neurovascular system, including reduced cerebral blood flow (CBF), vascular regression, and ischemia, resulting in cognitive decline. Research into therapeutic targets to restore neurovascular function following injury has identified endothelial EphA4 receptor tyrosine kinase as a major regulator of vascular regrowth. The research outlined herein utilizes an endothelial-specific EphA4 knockout mouse model (KO-EphA4flf/Tie2-Cre) to determine the extent to which this receptor may influence vascular regrowth following TBI. Analysis of the colocalization and proximity of endothelial and mural cell markers (i.e. PECAM-1 and PDGFRβ, respectively) in immunohistochemically-stained brain sections demonstrates that EphA4 silencing does not seem to affect the physical association between, nor total amounts of, endothelial cells and pericytes, between genotypes by 4 days post-injury (dpi). Nevertheless, these measures demonstrate that these cell types may preferentially proliferate and/or expand into peri-lesion tissue in both KO-EphA4flf/Tie2-Cre) and WT-EphA4fl/fl mice. These data further suggest that both genotypes experience homogeneity of PECAM-1 and PDGFRβ expression between regions of the injury cavity. Gene expression analysis using mRNA samples from both genotypes reveals that KO-EphA4flf/Tie2-Cre CCI-injured mice experience increased expression of Vegfa, Flt1, and Fn (Fibronectin) compared to sham-injured condition knockouts. These results demonstrate changes in expression of angiogenic factors in the absence of early differences in patterns of vessel formation, which may underlie improved vascular regrowth, as well as outline a potential mechanism wherein the interplay between these factors and EphA4 silencing may lead to improved cognitive outcomes following TBI. / Master of Science / Every day in the United States, an average of 155 people die due to the consequences of traumatic brain injury (TBI), with many survivors suffering life-long debilitating effects, including deficits in behavior, mobility, and cognitive ability. Because of this, there is a need for researchers to identify therapeutic strategies to stimulate recovery and improve patient outcomes. Recent advancements in the field of vascular biology have identified the regrowth of the blood vessels in the brain following TBI-induced damage as an important step in the recovery process, since the resulting increases in blood flow to damaged tissue will provide oxygen and nutrients necessary to fuel recovery. The work presented in this Masters thesis follows in this vein by examining a protein receptor known as EphA4, which is found on cells within blood vessels and has been implicated in reducing the rate of vessel growth under injury conditions. By blocking the activity of EphA4, we hoped to find increased vascular regrowth following brain injury in mice. During the experiments outlined herein, it was found that there were no statistically significant differences in vessel-associated cell densities between mice with or without EphA4 activity 4 days after injury, but there were differences in the levels of proteins and/or signals associated with vessel growth. Based on these results, we conclude that removing EphA4 activity increases expression of these pro-vessel growth proteins in mouse brains following injury at these early time points, potentially leading to increased vessel growth and improved recovery over subsequent weeks following injury.