Vascular remodeling is an adaptive mechanism for long-term modification of vascular diameter. In hypertension, inward remodeling, that is, the structural reduction of the lumen diameter in resistance vessels, is associated with an increased risk for myocardial infarction and stroke. However, despite its prevalence and clinical importance, the mechanisms that control the inward remodeling process remain largely unknown. Our goal here is to identify mechanisms in the inward remodeling process of the resistance vasculature that may be intervened with novel strategies to prevent, stop or reverse the remodeling process, and consequently diminish the life-threatening cardiovascular events associated with it. Current publications and our own preliminary data indicate that tissue-type transglutaminase (TG2), LIM kinase (LIMK), and matrix metalloproteinase-2 (MMP2) within vascular smooth muscle cells (VSMC) are involved in the remodeling process. Therefore, as we and others have determined that inwardly remodeled resistance vessels have actin cytoskeletal structures that reduce their passive diameters and extracellular matrix (ECM) features characterized by a reduction in the number and size of fenestrae in the internal elastic lamina (IEL): Our hypothesis is that during the early stages of the inward remodeling process in resistance vessels, prolonged vasoconstriction leads to formation of permanent VSMC cytoskeletal structures via the intracellular activity of TG2 and LIM kinase, which in turn stimulate the production of MMP2 and the modification of the ECM, in particular the IEL. We will test our hypothesis in VSMC, isolated resistance arteries and a whole animal model of hypertension. Cells and tissues will come from animals, as well as from normotensive and hypertensive individuals. The expression and activity of the remodeling components tested in our hypotheses will be modulated using pharmacological and molecular means. Experimental outcomes will be measured using traditional and leading-edge techniques in protein and enzymatic activity analyses, as well as, atomic force, multiphoton, and long-term intravital microscopy.
Our specific aims will test the hypotheses that: 1) Intracellular TG2 activates RhoA, Rho kinase and LIMK to phosphorylate and inactivate cofilin to favor formation of actin networks and stress-fibers, with TG2 further crosslinking actin structures to make them more persistent; and 2) that LIMK activates MMP14 and leads to expression/secretion of MMP2 from VSMC. Then MMP2 through its elastolytic actions generates elastin peptides that activate VSMC to produce more elastin. This new elastin is incorporated in the IEL and reduces the size and number of fenestrae in the IEL. We expect this study will provide new insights on how cytoskeletal and IEL structures of resistance arteries are modified in hypertension. This knowledge should have a positive impact on strategies for preventing and treating hypertension, and the management of diseases associated with vascular remodeling.
The proposed research is highly relevant to public health because hypertension and cardiovascular disease constitute the number one cause of death in the United States. Discovery of the mechanisms that reduce the structural diameter of resistance vessels in hypertension, as outlined in this proposal, is expected to increase our understanding of the origins and development of high blood pressure and its life threatening consequences. This understanding is expected will provide new avenues to develop novel strategies for preventing, stopping, and/or reversing the remodeling process and the life threatening events that are associated with it.
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