Cardiovascular diseases associated with tissue ischemia continue to be a leading cause of death worldwide. The incidence of ischemic tissue disease is significantly increased by the presence of certain risk factors, such as hypertension (HTN), diabetes, obesity, and hypercholesterolemia (HCh), with combinations of risk factors exerting a synergistic effect on disease incidence. Despite the widespread recognition that one or more cardiovascular risk factors generally accompany ischemic tissue disease, much of the literature on ischemia and ischemia-reperfusion (I/R) induced tissue injury is based on studies on animals that are otherwise normal. The long-term objective of the work outlined in this proposal is determine if/how two well established risk factors (HTN and HCh), either alone or in combination, lead to enhanced I/R-induced tissue injury and the accompanying microvascular dysfunction, inflammation and oxidative stress. We provide preliminary evidence suggesting that the presence of either HTN or HCh induces an inflammatory and pro-oxidative phenotype, which renders the microvasculature more vulnerable to the deleterious effects of I/R. Evidence from our laboratory and in the recent literature implicate immune cells, cytokines and the renin-angiotensin system in the microvascular dysfunction associated with both HTN and HCh. Intravital videomicroscopy, the dual radiolabeled antibody technique and other measures of microvascular inflammation and dysfunction will be employed to test the central hypothesis that the severity of the microvascular dysfunction, inflammation and tissue injury resulting from ischemia-reperfusion is increased in the presence of cardiovascular risk factors (HCh and/or HTN) due to angiotensin II type 1 receptor (AT1r)-mediated release of cytokines from circulating immune cells. Different components of the central hypothesis will be addressed by experiments outlined under 3 specific aims: 1) to define the influence of HTN and/or HCh on the microvascular dysfunction, inflammation, and tissue injury elicited in the normal and post-ischemic brain, 2) to determine whether AT1r expressed on circulating blood cells account for the inflammation and injury responses elicited in post-ischemic tissue of HTN and/or HCh mice, and 3) to define the contribution of immune cells and immune cell-derived cytokines to the AT1r-induced inflammatory and injury responses in post-ischemic brain of HTN and/or HCh mice. Mutant mice, bone marrow chimeras, and adoptive transfer strategies will be employed to assess the contribution of blood cell vs vessel wall AT1r to the injury responses. The proposed work should significantly extend our understanding of the mechanisms by which cardiovascular risk factors influence the microvascular, inflammatory and injury responses to ischemic tissue disease.
It is well known that risk factors for cardiovascular disease (CVD) render tissues, such as heart and brain, more vulnerable to an ischemic episode, through enhanced formation of atherosclerotic plaques and/or thrombi that occlude major arterial vessels. This project will examine whether risk factors, such as hypertension and hypercholesterolemia, can also lead to enhanced microvascular dysfunction, inflammation and tissue injury following exposure of tissues to a defined ischemic insult that is followed by reperfusion. We propose that the CVD risk factors, either alone or in combination, enhance ischemia-reperfusion induced tissue injury via mechanisms that involve angiotensin II type-1 receptors, circulating immune cells and their products of activation.
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