Year of Publication

2018

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department

Neuroscience

First Advisor

Dr. Gregory J. Bix

Second Advisor

Dr. Justin F. Fraser

Abstract

Stroke is a leading cause of death and disability worldwide. Although rapid recognition and prompt treatment have dropped mortality rates, most stroke survivors are left with permanent disability. Approximately 87% of all strokes result from the thromboembolic occlusion of the cerebrovasculature (ischemic strokes). Potential stroke therapeutics have included anti-inflammatory drugs, as well as many other targets with the goal of mitigating the acute and chronic inflammatory responses typically seen in an ischemic stroke. While these approaches have had great success in preclinical studies, their clinical translation has been less successful. Master inflammatory cytokines, such as IL-1, are of particular interest. IL-1’s isoforms, IL-1α and IL-1β, were long thought to have similar function. While IL-1β has been extensively studied in stroke, the role of IL-1α during post stroke inflammation has been overlooked. Because IL-1 inhibitors have been unsuccessful in clinical application, we reasoned that IL-1α may provide previously unknown benefits to the brain after injury. We hypothesized that IL-1α could be protective or even accelerate reparative processes in the brain such as producing new blood vessels (angiogenesis) or neurons (neurogenesis).

To test that IL-1α is protective after stroke, we tested IL-1α’s protective effects on primary cortical neurons in in vitro models of stroke. We showed that IL-1α was directly protective on primary cortical neurons in a dose-dependent fashion. We then performed mouse middle cerebral artery occlusion stroke studies to determine the safety of giving IL-1α in vivo. These studies showed that administering IL-1α acutely was neuroprotective. However, intravenous (IV) administration of IL-1α resulted in transient, hemodynamic changes following drug delivery. To minimize these systemic effects, we administered IL-1α intra-arterially (IA) directly into the stroke affected brain tissue, allowing us to significantly lower the concentration of administered IL-1α. In comparison to IV, IA IL-1α showed greater histological protection from ischemic injury as well as improved functional recovery following stroke, all without systemic side effects.

To test that IL-1α could aid in neurorepair following stroke, we tested IL-1α’s ability to help damaged blood vessels repair in vitro. We found that IL-1α significantly increased brain endothelial cell activation, proliferation, migration, and capillary formation. We tested IL-1α’s proangiogenic properties in vivo by administering IL-1α three days following stroke. Delayed administration allowed us to separate IL-1α’s acute neuroprotective effects from potential subacute angiogenic effects. We found that mice receiving IL-1α performed significantly better on behavioral tests and also showed greater vascularization within the penumbra two weeks following stroke. We also found that IL-1α treated animals showed more endothelial activation than vehicle treated animals. Finally, our studies showed that IL-1α treated animals showed increased early-phase neurogenesis with evidence of increased proliferation at the subventricular zone suggesting that IL-1α’s beneficial effects are even more far-reaching than previously thought. In conclusion, our experiments suggest that the inflammatory cytokine IL-1α is neuroprotective and neuroreparative in experimental ischemic stroke and worthy of further study as a novel stroke therapy.

Digital Object Identifier (DOI)

https://doi.org/10.13023/ETD.2018.070

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