Post-ischemic protection of white matter following an ischemic attack

Oregon Health & Science University, Portland OR

Investigators

Abstract

Project Summary Stroke is the leading cause of disability in the United States and around the world. The improved stroke care has increased the number of stroke survivors. White matter injury (WMI) underlies the majority of clinical deficits observed in stroke patients. Investigating the mechanisms of WMI is challenging in rodent brains due to the smaller volume of WM compared to human brains. Because conventional animal stroke models mainly affect gray matter, sparing the corpus callosum, WM protection has not been a primary target in many proposed studies. A scientific gap therefore remains in the research into preserving WM function, which requires a combination of an in vivo WMI rodent model with a clinically relevant approach to preserve WM integrity after stroke. To address this scientific gap, we employed a consistent and reliable in vivo selective subcortical WMI model that can be quantified histologically and with behavioral tests, and longitudinal imaging studies using MRI. We previously showed that ischemia upregulates Casein Kinase 2 (CK2) causing WMI via Cdk5 and AKT/GSK3β pathways. CX-4945, an FDA-approved selective and specific CK2 inhibitor that crosses the blood-brain barrier, promotes axon function recovery by conserving mitochondria in WM when applied after ischemia. Since ischemia activates NADPH oxidase (NOX) in neurons to increase oxidative stress causing mitochondrial dysfunction, we propose a novel mechanism whereby CK2 activates NOX causing mitochondrial dysfunction during ischemia in WM. WM mitochondrial dynamics and axon function show a sexually dimorphic age-dependent recovery after an ischemic episode, because young female axons have better functional recovery with less interruption in mitochondrial motility than young male axons, yet this difference is not observed within aging populations. These findings warrant further investigation of post-ischemic benefits of CK2 inhibition in WM. Our preliminary data show that the selective focal WM injury causes behavioral impairments indicated by loss of bilateral paw use in the cylinder test and paw dexterity in the pasta-eating test. These deficits correspond with persistent edema formation in scans obtained by using MRI modalities. Administration of CX-4945 at 6 hours after stroke preserves WM integrity, alleviates behavioral deficits, and improves MRI modalities. Furthermore, impaired mitochondrial motility following oxygen and glucose deprivation correlates with lower mitochondrial respiratory function in live isolated mitochondria from WM. Because ischemia upregulates NOX enzyme activity in in vitro WM injury and post-ischemic CX-4945 application attenuates NOX activity, we propose that CK2 inhibition after stroke confers WM protection and improves behavioral outcomes by regulating NOX activity to conserve mitochondrial dynamics. We will test our hypothesis in both young and aging male and female WM in an animal model of selective focal WMI.