Inflammatory regulation of extracellular matrix remodeling in calcific aortic valve stenosis

Abstract

Background: Calcific aortic stenosis (AS), the most frequent heart valve disorder in developed countries, leads to the calcification and fibrous thickening of the valve. While several studies have addressed the process of valvular calcification, the molecular pathomechanisms of the extensive matrix remodeling remain unclear. Because inflammation is present in stenotic valves, we hypothesized that the proinflammatory cytokine tumor necrosis factor alpha (TNFα) might influence cell proliferation and regulate the expression and activation of matrix metalloproteinases (MMPs)-enzymes that are thought to be involved in calcific AS. Methods: Immunohistochemistry for leukocytes, TNFα, MMP-1, and the endogenous MMP inhibitor tissue inhibitor of metalloproteinase (TIMP)-1 was performed on human stenotic (n=19) and control (n=8) valves. Primary cultures of human aortic valve myofibroblasts were incubated with and without TNFα, and cell proliferation was assessed. The expression and activation of MMP-1 were detected by Western blotting and a specific MMP-1 activity assay. Results: Control valves showed scattered macrophages and low expression of TNFα, MMP-1, and TIMP-1. In stenotic valves, leukocyte infiltration and a strong, colocalized expression of TNFα and MMP-1 were present, while TIMP-1 remained unchanged. Double-label immunofluorescence localized TNFα mainly to macrophages. In cultured human aortic valve myofibroblasts, TNFα stimulated proliferation and induced a time-dependent increase in MMP-1 expression and activation, while TIMP-1 remained unchanged. Conclusion: The results indicate that matrix remodeling in calcific AS involves the expression and activation of MMPs. Activated leukocytes, by the secretion of TNFα, may stimulate valvular myofibroblasts to proliferate and express MMPs, thus regulating actively the matrix remodeling in calcific AS. © 2005 Elsevier Inc. All rights reserved.