Year of Publication

2019

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department/School/Program

Neuroscience

First Advisor

Dr. Gregory J. Bix

Second Advisor

Dr. Justin F. Fraser

Abstract

Stroke is the 5th leading cause of death and the leading cause of disability in the United States, but there are only two available therapies, tissue plasminogen activator and endovascular thrombectomy. As both therapies focus on removal of the clot, the subsequent pathologic processes, i.e. inflammation, cerebrovascular breakdown, ATP depletion, etc. are left untreated, contributing to worsened patient outcome. Many clinical trials have unsuccessfully attempted to address these mechanisms. The blood-brain barrier (BBB), a system of non-fenestrated endothelial cells, extracellular matrix, and astrocytic endfeet, is significantly impacted after ischemic stroke in its role of preventing the free movement of proteins from the blood into the brain. In fact, BBB dysfunction is viewed as one of the major facilitators of damage following ischemic stroke, leading to increased infarct volumes and worsened patient outcomes. Interestingly, a family of endothelial integrins, the b1 integrins, have been shown to regulate tight junction proteins preventing the free movement of molecules. When expression of the tight junctions are decreased, this results in increased BBB permeability. To test this concept, our laboratory has previously shown the knockout of the particular β1 integrin, α5β1, is neuroprotective following ischemic stroke through BBB stabilization.

To determine if therapeutically targeting integrin a5b1 was feasible, we first determined if brain integrin a5b1 expression increases after experimental mouse ischemic stroke model, specifically tandem/transient common carotid artery/middle cerebral artery occlusion. We found that integrin a5b1 does increase acutely, by post-stroke day (PSD)2, and continued in an exponential fashion through PSD4. Next, we determined if integrin a5b1 was therapeutically accessible by systemic treatment (i.e. intraperitoneal or intravenous) by being located on the inside (luminal surface) of vasculature. We found that location of integrin a5b1 was dependent on the area relative to the stroke injury. The core, or area of direct impact, demonstrated expression of integrin a5b1 on the outside vasculature (abluminal surface), while per-infarct expression was localized to the lumen. Lastly, to determine the activity of integrin a5b1 following ischemic stroke, we showed that the potential ligands (binding partners), plasma fibronectin, fibrinogen, and amyloid-b, do not bind integrin a5b1 after ischemic stroke.

Next, we determined the therapeutic potential of targeting integrin a5b1 with the small peptide, ATN-161. ATN-161 has undergone clinical trials in solid tumors, with limited side effects reported. First, we determined that intraperitoneal (IP) injection of ATN-161 was safe after ischemic stroke, showing no changes in heart rate, pulse distention (blood pressure), or body temperature. Next, we found that IP administration of ATN-161 after experimental ischemic stroke reduced infarct volumes, edema, and functional deficit. Furthermore, these results were due to reduction of BBB permeability and anti-inflammatory effects. Interestingly, ATN-161 reduced cytokine production, prevented leukocyte infiltration, and leukocyte recruitment. Collectively, these results suggest that targeting integrin a5b1 with ATN-161 is 1) feasible, 2) safe and 3) effective, suggesting that ATN-161 may be a novel therapeutic treatment for ischemic stroke.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2019.051

Funding Information

TL1TR001997, NIH RO1 NS065842-08

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