Abstract
Ischemic stroke is the second leading cause of death worldwide and the leading cause of adult long-term disability in the United States. Despite its prevalence, there are few therapeutic interventions available. The neuroprotective compound P7C3-A20 (A20) has been shown to reduce mature neuronal cell death while also increasing the net magnitude of postnatal neurogenesis in models of neurodegeneration and acute brain injury. A20 compounds demonstrate protection by enhancing the flux of nicotinamide adenine dinucleotide (NAD) in mammalian cells, a proposed therapeutic approach to treating cerebral ischemia. The studies carried out in this dissertation sought to investigate the effectiveness of A20 treatment after focal cerebral ischemia by assessing subacute and chronic histopathological and behavioral outcomes, as well as ischemia-induced neurogenesis. In the first series of experiments, rats underwent a weeklong course of A20 or vehicle treatment, beginning immediately after a 90 minute unilateral transient middle cerebral artery occlusion (tMCAO). A20-treated rats performed significantly better than vehicle-treated controls in sensorimotor cylinder and grid-walk tasks, and in a chronic test of spatial learning and memory. These behavioral improvements with A20 treatment were correlated with significantly decreased cortical and hippocampal atrophy as well as increased neurogenesis in the subventricular zone and hippocampal dentate gyrus subgranular zone. Furthermore, cerebral ischemia significantly depleted NAD in the cortex, but treating with A20 restored cortical NAD levels. After demonstrating efficacy of A20 treatment at an early, post-ischemic timepoint, we then sought to examine A20’s treatment window of opportunity. Due to a limited therapeutic window, current stroke pharmacological treatment is rarely administered to ischemic patients. Therefore, we investigated a more clinically relevant time point and again treated tMCAO rats for one week with A20, beginning either immediately (iA20) or at a delayed point (dA20) 6 hours post-reperfusion. dA20 treatment significantly reduced ischemia-induced sensorimotor deficits in motor coordination and limb-use asymmetry as well as cognitive deficits in hippocampal-dependent spatial learning, memory retention, and working memory. In the cerebral cortex, dA20 treatment significantly increased tissue sparing 7 weeks after stroke and reduced infarct volumes 48 hours after reperfusion compared to vehicle-treated animals. At 48 hours after injury, there was no change in striatal infarct volumes between tMCAO groups. However, when tissue volume was reassessed at 7 weeks, A20-treated animals had a significant increase in striatal tissue volume, suggesting that A20’s protection in the ischemic striatum requires an extended treatment regimen. In the hippocampus, only iA20-treated animals had a significant increase in tissue sparing compared to vehicle-treated stroke animals. This translated into minimal hippocampal-dependent behavioral improvements with dA20 treatment. However, all rats treated with dA20 did demonstrate a significant improvement in both sensorimotor tasks compared to vehicle controls, suggesting a somatosensory driven recovery. Overall, our studies show that A20 treatment is an effective strategy against focal cerebral ischemia by mitigating chronic neurodegeneration, enhancing repair, and rescuing stroke-induced behavioral deficits when treated at a clinically relevant time point. Therefore, treatment with A20 compounds represent a novel therapeutic approach to safely augment NAD tissue levels, promoting two independent processes critical to protecting the brain from ischemic stroke; mature neuron survival and postnatal hippocampal neurogenesis throughout the post-ischemic brain.