Project Summary: While mechanical thrombectomy has advanced the treatment of large vessel occlusion
(LVO) stroke, over 50% of patients still suffer from significant disability or death. Ischemia/reperfusion injury
(I/RI), the result of restoring blood flow to deeply ischemic tissue, accelerates recruitment of polymorphonuclear
neutrophils (PMNs). PMNs exert poor outcomes in two ways. First, PMNs physically obstruct
cerebral microvessels in the stroke bed despite macrovascular reperfusion – a condition known as microvascular
‘no-reflow’. Second, PMNs exert toxic effects regionally once recruited at postcapillary venules and extravasated
into the infarcted brain. Accordingly, preclinical studies that block PMN recruitment have had success in reducing
stroke burden and improving neurologic outcome. Unfortunately, these preclinical studies have not been
successful in human trials. These translational roadblocks may be addressed by investigating the spatiotemporal
determinants of PMN recruitment as it relates to the in vivo cerebrovasculature during stroke. Using a mouse
stroke model to simulate the LVO population and novel histopathological and imaging techniques, my preliminary
data have found that PMN recruitment throughout I/RI is non-uniform up to 72 hours after infarction. PMNs were
also found to progress cortically to subcortically throughout I/RI over the course of 72 hours, with partial restriction
to the cortical surface by administration of an antibody that blocks transendothelial migration (TEM). These
results support the concept of stroke microenvironments – highly regionalized areas within an infarct where
inflammation and impaired microcirculation interface with each other. I hypothesize that these stroke
microenvironments within an infarct are due to feedback loops between 1) microvascular flow and oxygenation;
and 2) PMN recruitment. To test this hypothesis, I will investigate two aims: 1) Defining and physiologically
manipulating the stroke microenvironment 2) Determine how PMN infiltration and position regulates I/RI over
time. I will test these aims using techniques of multimodal in vivo animal imaging, advanced microscopy, and
targeted manipulation of both leukocyte biology and stroke physiology. These studies will ultimately be used to
identify molecular similarities of PMNs in particularly toxic stroke microenvironments, facilitating the investigation
and creation of novel leukocyte-based therapies. To complete these long-term goals, I will incorporate a
multidisciplinary mentorship team and short-term goals of developing expertise in live-animal imaging, advanced
microscopy, and leukocyte biology. With this K08 proposal, I will build a unique translational stroke program that
defines the interplay of stroke physiology and pathology to develop more precise and translatable therapies for
stroke patients.
