Ischemic stroke is characterized by a disruption of blood supply to a part of the brain tissue, which leads to a focal ischemic infarct. The expression and activity of MMP-9 is increased in ischemic stroke and is considered to be one of the main factors responsible for damages to the cerebral vasculature, resulting in compromised blood-brain barrier (BBB) integrity. However, the regulatory mechanisms of MMP-9 expression and activity are not well established in ischemic stroke. Since hypoxia/ischemia and reperfusion generates reactive oxygen species (ROS), I hypothesize that ROS is one of factors involved in up-regulation of MMP-9 expression in brain cells and ROS-mediated effect may occur via MAPK signaling pathway. My study has provided the evidence that ROS is responsible for an increase in MMP-9 expression in astrocytes mediated via MAPK-AP1 signaling pathway. Preliminary studies with an in vitro model of the BBB suggest that inhibition of MMP-9 is a critical component of reducing ROS-induced BBB permeability.

The disruption of the blood-brain barrier (BBB) occurs after ischemic and hemorrhagic stroke and contributes to secondary brain damage. Matrix metalloproteinase-9 (MMP9) has been identified to be the main mediator of post-stroke BBB disruption. It is unknown whether deposition of heme/iron in the brain following stroke would affect MMP9 expression. In this study, I have demonstrated that heme/iron up-regulated MMP9 expression in rat astrocytes and that this upregulation was most likely due to reactive oxygen species (ROS) generated by heme/iron deposition on cells. ROS can activate AP-1 and NFκB signaling pathways which were responsible for increased MMP9 expression. Inhibiting AP-1 and NFκB decreased MMP9 expression. Heme/iron deposition also activated Nrf-2 and increased the expression of neuroprotective heme oxygenase-1. My study suggests that heme and iron deposition generates ROS and increases MMP9 expression through AP-1 and NFκB signaling pathways and that targeting these pathways or clearance of heme and iron may modulate MMP9 expression for reduced damage.

Tim-3 has been linked to several inflammatory diseases by regulation on both adaptive and innate immunities. Here, we assessed the augmented expression of Tim-3 in brain tissue of ischemia-reperfusion mice and PBMCs of ischemic stroke (IS) patients. The augmented expression of Tim-3 significantly correlated with abnormal lipid levels. In vitro studies showed that plasma from ischemic stroke patients induced Tim-3 expression in THP- 1 cells. More importantly, our results revealed a significant correlation of Tim-3 expression on CD4 + T cells with systemic IL-17 in patients with ischemic stroke. Consistently, we also found a positive correlation of Tim-3 expression on CD14 + monocytes and serum TNF-a in IS patients. Collectively, augmented expression of Tim-3 may play an important role in the pathogenesis of ischemic stroke by regulation of proinflammatory cytokines. Further studies will give us new insights on the pathogenesis of ischemic stroke and potentially provide a new target at the medical therapy.

Background: Patients who have suffered an acute ischemic stroke (AIS) and are smokers may have a better outcome following thrombolytic therapy when compared with non-smokers. While this finding is controversial, data on baseline clinical risk factors to predict treatment efficacy of thrombolytic therapy using ambulatory status in patients who suffered AIS and are smokers is not common. Methods: Between 2010 and 2016, retrospective data on patients who have suffered an AIS and received recombinant tissue plasminogen activator (rtPA) were obtained from Greenville health system registry. Assessment of clinical risk factors and the likelihood of an improvement in post-stroke ambulation among smokers and non-smokers was carried out using multivariate logistic regression. Results: Of 1001 patients, 70.8% were smokers and 29.2% non-smokers. Among the smokers and non-smokers, 74.6% and 84.6% improvement in ambulation respectively at discharge. The odds of improved ambulation decrease among smokers as age group increases compared to those below 50 [(60–69 years, aOR, 0.30, 95% C.I, 0.108–0.850, p < 0.05), (70–79 years aOR, 0.27, 95% C.I, 0.096–0.734, p < 0.05), (80+ years aOR, 0.16, 95% C.I, 0.057–0.430, P < 0.01). Patients with National Institute of Health Stroke Scale Score (NIHSS) score > 7 (reference <7) were 91% less likely to have improved ambulation among smokers and non-smokers (aOR, 0.09, 95% C.I, 0.055–0.155, P = 0.01), and (aOR, 0.08, 95% C.I, 0.027–0.214, P = 0.01) respectively. Atrial fibrillation was an independent predictor of decreased improvement in ambulation only among smokers (aOR, 0.58, 95% C.I, 0.356–0.928 P < 0.05). Conclusion: Our findings suggest that elderly smokers with atrial fibrillation would benefit more from aggressive management of atrial fibrillation than non-smokers.

Patients with atrial fibrillation (AF) are at increased risk of stroke. Warfarin anticoagulation therapy reduces the incidence of stroke and increases the incidence of hemorrhagic events. This dissertation further informs the decision to use anticoagulation therapy in AF patients by examining outcomes in patients with major hemorrhages, further examination of stroke risk in diabetic patients with AF, and by evaluating the association between warfarin and stroke while accounting for competing risk events. These studies utilized data from the AnTicoagulation and Risk Factors In Atrial Fibrillation (ATRIA) and ATRIA-CVRN (Cardiovascular Research Network) (Study 1 only) studies which consist of patients from Kaiser Permanente Northern and Southern California. Study 1 examined short and long-term mortality in patients who experienced major gastrointestinal (GI) hemorrhages. In the ATRIA cohort, patients using and not using warfarin at the time of GI hemorrhage were equally likely to die within 30-days, while in ATRIA-CVRN, patients using warfarin were much less likely to die within 30-days (adjusted mortality rate ratio (aMRR): 0.33, 95% CI: 0.16-0.70). For longer-term mortality, both cohorts were consistent with a reduced mortality rate among patients whose GI hemorrhage occurred while using warfarin. Study 2 assessed the association between diabetes characteristics (duration of diabetes and glycemic control) and incidence of ischemic stroke among patients with AF and diabetes. Duration ≥ 3 years was associated with a large increase in rate of stroke (adjusted hazard ratio (aHR): 2.04, 95% CI: 1.27-3.26) compared to patients with duration < 3 years. Patients with the poorest glycemic control (hemoglobin A1c (HbA1c) values ≥ 9.0%) did not have an increased rate of ischemic stroke compared to patients with HbA1c < 7.0%. Study 3 evaluated the association between warfarin and thromboembolism in analyses that did and did not account for competing death events. In analyses not accounting for competing events, the adjusted HR was 0.61 (95% CI: 0.54-0.69), and after accounting for competing death events this association was attenuated (aHR: 0.87, 95% CI: 0.77-0.99). In summary, these studies add to the literature about the benefits of warfarin therapy and risk of stroke in patients with AF, findings that can improve decisions about use of anticoagulants in patients with AF.

No description available.

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Stroke is a leading cause of morbidity and long-term neurological disability in the U.S. Ischemic stroke, which accounts for approximately 90% of all strokes, is the result of an occlusion in the arteriole cerebrovascular network. No effective treatment options exist to provide neuroprotection from occlusion, and limited success has been seen clinically when attempting to restore blood flow to vulnerable neural tissue regions. Enhancement of pial collateral remodeling (Arteriogenesis) has recently been shown to improve blood flow and mitigate neural tissue damage following stroke (1-3). Arteriogenesis is the remodeling of pre-existing arteriole vessel which are able to re-route blood to blood-deprived regions of tissue. Arteriogenesis requires endothelial cell (EC) and smooth muscle cell proliferation, extracellular matrix degradation and recruitment of circulating bone marrow-derived cells (4-6). Unlike spouting angiogenesis, which requires weeks following occlusion to develop, arteriogenesis begins as early as 24-48hrs post-stroke (7, 8) and can expeditiously enhance blood flow to ischemic regions, making it an attractive target for therapeutic intervention. Our preliminary studies, in an EphA4 global knockout mouse model, indicated that EphA4 receptor tyrosine kinase severely limits pial arteriole collateral formation. The preliminary work also showed that activation of EC EphA4 receptor in vitro inhibited vascular formation. Additionally, ECs lining the collateral vessel have been shown to play a role in collateral remodeling (9). Taken together, the objective of this dissertation was to elucidate the cell autonomous role of the EphA4 receptor and given the central role of the EC in collateral remodeling, we postulated that EphA4 receptor on ECs the limits pial collateral formations. Using a cell-specific loss-of-function approach, we tested the hypothesis that EC-specific EphA4 plays an important role in pial collateral development and remodeling after induced stroke. The results from this dissertation show that (1) EphA4 expression on ECs suppress the formation of pial collaterals during development and limits EC growth via suppression of p-Akt in vitro (2) EC-specific EphA4 ablation leads to increased collateral remodeling, enhanced blood flow recovery, tissue protection and improved neurological behavioral outcomes after stroke and (3) Mechanistically, EphA4 limits pial collateral remodeling via attenuation of the Tie2/Angiopoietin-2 signaling pathway. The work presented in this dissertation demonstrate that EphA4 can be targeted therapeutically to increase pial collateral remodeling to alleviate neurological deficits after ischemic stroke. / Doctor of Philosophy / Stroke is the fifth leading cause of death in the United States. Ischemic stroke is the most common type of stroke and occurs when blood flow to part of the brain is impeded. Lack of blood results in cell death and tissue damage in the brain. In an effort to restore blood flow, specialized blood vessels in the brain called collaterals remodel and become larger to allow re-routed blood to the blood-deprived region of the brain. The duration it takes to remodel these remarkable blood vessels and re-route blood varies in humans, and sometimes is not able to prevent adequate tissue damage. The current work explores novel therapeutic targets to accelerate collateral remodeling in an effort to reduce tissue loss after stroke. We present studies which show that a protein called EphA4, found on endothelial cells restricts remodeling, and when inhibited in the brain can increase collateral remodeling and reduced adverse effects after ischemic stroke.

The Georgia Department of Public Health has been engaged in a registry-based quality improvement initiative to monitor and improve the quality of stroke care. It is important to evaluate effectiveness of the quality improvement initiative in order to expand the effort to other sites or disease conditions. The studies, included in this dissertation, addressed whether acute ischemic stroke patients cared for by hospitals participating in the Georgia Coverdell Acute Stroke Registry (GCASR) had a better survival than those treated at other facilities, assessed whether quality of care as measured by nationally accepted ten performance measures is associated with improved patient outcome and evaluated the impact of intravenous alteplase treatment on 1-year mortality. Three data sources – GCASR, Georgia Discharge Data System and the death data – were used for analyses. These data sources were linked applying both a hierarchical deterministic and a probabilistic linkage methods. Survival after stroke incident was analyzed using the extended Cox proportional hazard model. Generalized estimating equation (glimmix procedure) and conditional logistic regression were applied, respectively, to assess the association of quality of care and intravenous alteplase use with 1-year mortality. Acute ischemic stroke patients treated at nonparticipating facilities had a hazard ratio for death of 1.14 (95% confidence interval, 1.03–1.26; p-value = .01) after the first week of admission compared with patients cared for by hospitals participating in the registry. Among patients treated in GCASR-participating hospitals, patients who received the lowest and intermediate quality care respectively had a 3.94 (95%CI: 3.27, 4.75; p-value <0.0001) and a 1.38 (95%CI: 1.12, 1.62; p-value=0.002) times higher odds of dying in one year compared to those who got the best quality stroke care. Patients who were eligible but did not receive IV alteplase had a 1.49 (95%CI: 1.09-2.04; p-value=0.01) times higher odds of dying within one year than those who were treated with the thrombolytic agent. The results strongly suggest that registry-based quality improvement effort has brought significant improvements in ischemic stroke patients’ outcomes. Therefore, it is critical that hospitals adopt a quality improvement strategy to change the process of care delivery for a better patient outcome.