Abdominal aortic aneurysms (AAAs) are a common degenerative disease with life-threatening implications. While the pathophysiologic events underlying the development of AAA are still poorly understood, they clearly involve degenerative remodeling of aortic wall connective tissue. Recent studies have implicated three processes in this pathologic pattern of remodeling: (1) impaired repair of fibrillar extracellular matrix proteins, (2) chronic mononuclear inflammation, and (3) excessive local production of matrix-degrading proteinases. The purpose of this collaborative research program is to gain better understanding of the molecular mechanisms regulating these three processes. First, Drs. William C. Parks and J. Michael Shipley will examine the molecular factors that appear to limit the effective production of elastic fibers in the aneurysm wall environment. Using tissues obtained from human and experimental AAA and aneurysm-derived vascular smooth muscle cells in culture, they will specifically evaluate the molecular pathways controlling tropoelastin gene expression and tropoelastin mRNA stability, as well as the regulation of additional gene products involved in elastic fiber assembly, such as fibrillin-1 and latent TGF-beta binding protein-2. Second, Dr. Jay Heinecke will examine protein oxidation associated with chronic inflammation as an important pathway of tissue destruction. Using novel methods to detect and measure the contributions of different oxidative pathways to protein modification, he will determine the dominant oxidative pathways in human and experimental AAA, elucidate how protein oxidation serves to promote matrix metalloproteinase activity in aneurysm tissue, and examine how genetic manipulation affecting specific oxidative pathways might alter aneurysm development in a mouse model. Third, Dr. Robert W. Thompson will examine the regulated expression of three different interstitial collagenases, both in human AAA tissues from various stages of disease and in cultured SMC exposed to proinflammatory cytokines, phorbol ester and doxycycline. These studies will have a particular focus on collagenase-3 (MMP-13), providing new insight into the regulation of MMP-13 expression in vascular wall cells. Knowledge gained through these three closely-linked studies will help advance our understanding of the molecular pathophysiology of aortic aneurysms, potentially leading to new treatment strategies.
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