White matter (WM) occupies 50% of the total brain volume in human and has a metabolic rate similar to that of gray matter. Yet, WM has a disproportionally small blood supply and less collateral circulation, making it highly susceptible to hypoxic-ischemic insults. However, due to the difficulty in detection by conventional MRI or CT methods, WM injury has not been an integral part of clinical assessment in acute ischemic stroke. Similarly, the search for strategies of WM protection was not at the forefront of pre- clinical studies of stroke in the past. Thus, it remains uncertain whether thrombolytic therapy is sufficient, or additional cytoprotective agents are needed, to salvage WM in acute ischemic stroke. The present project is based on our recent results showing that diffusion tensor imaging (DTI) can be used to detect distinct histopathologies of WM injury in a rodent model of thrombotic stroke. Specifically, we found that rapid reduction of radial/transverse diffusivity correlates with oligodendrocyte swelling and compression of the axoplasma, while the late-onset, large reduction of fractional anisotropy (FA) signifies severe structural breakdown of the axons. Moreover, WM injury was associated with reactive oxidative stress in oligodendrocytes, which may play a causal role. Together, these results not only re-capitulate the signature pattern of DTI alterations in stroke patients (i.e. rapid reduction of radial diffusivity and little initial change of fractional anisotropy), but also provide an experimental system to study the strategies of WHITE MATTER PROTECTION IN ACUTE ISHCMEIC STROKE. Based on these preliminary results, we will test two strategies of WM protection in the present project.
In Aim 1, we will test the hypothesis that the combination of tPA and Edaravone, an anti-oxidant, is needed for the maximal protection of WM in stroke. This is because reperfusion following cerebral hypoxia-ischemia may paradoxically increase the oxidative stress in WM. Edarovone is a potent blood- brain-barrier-permeable free radical scavenger already approved for treating acute ischemic stroke in Japan, but its effects on WM protection are yet to be examined.
In Aim 2, we will test the targets of anti-oxidant supplement for WM protection in ischemic stroke. We hypothesize that boosting Cu/Zn superoxide dismutase (SOD1) and the cell membrane-associated phospholipids hydroperoxidase (GPx4) can reduce oligodendrocyte and WM injury in ischemic stroke. This is because sequential actions of SOD1 and GPx are needed to detoxify superoxide and hydroxyl radicals. Further, GPx4 is particularly potent in limiting the membrane-bound lipid peroxidation. In this project, a total of eight groups of adult mice will be subjected to a thrombotic model of stroke with various genetic and pharmacological therapies, and examined by a panel of histological, biochemical, and DTI evaluations. By quantitative analysis and outcome comparison among various treatment-groups, these experiments will suggest strategies of WM protection and shed new insights into the mechanisms of WM injury in acute ischemic stroke.
Stroke is the second leading cause of death in the Western world, ranking after heart disease but before all types of cancer combined. Past research of stroke focuses on salvaging the grey matter, but recent studies suggest that damage to the white matter (WM), which connects and integrates different parts of the nervous system, is a critical, if not more important cause of functional disability in stroke. However, there are no sensitive and validated imaging methods to detect WM injury in acute stroke, and very few studies specifically designed to develop WM protection in animal models of acute ischemic stroke. This project applies diffusion tensor imaging (DTI), biochemical, and histological assays in a thrombotic model of stroke to investigate the causes and therapies of ischemic WM injury. Positive outcomes of this project will validate the use of DTI to assess WM injury in acute ischemic stroke and suggest novel strategies of WM protection.
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