Porcine heart valves produce a protein that induces cell-mediated connective tissue degradation: II. Biochemical properties of the partially purified protein

Interleukin-1 beta promotes matrix metalloproteinase expression and cell proliferation in calcific aortic valve stenosis

Calcific aortic valve stenosis (AS), the main heart valve disease in the elderly, is characterized by extensive remodeling of the extracellular matrix. Matrix metalloproteinases (MMPs) are upregulated in calcific AS and might modulate matrix remodeling. The regulatory mechanisms are unclear. As recent studies have suggested that calcific AS might result from an inflammatory process involving leukocyte invasion and activation, the present study aimed to elucidate the role of the pro-inflammatory cytokine interleukin (IL)-1 beta on MMP expression and cell proliferation in human aortic valves. Immunohistochemistry for leukocytes, IL-1 beta and MMP-1 was performed on aortic valves with (n=6) and without (n=6) calcification obtained at valve replacement or autopsy. Stenotic valves showed marked leukocyte infiltration and associated expression of IL-1 beta and MMP-1. In control valves only scattered leukocytes, low staining for MMP-1 and no staining for IL-1 beta were present. Double-label immunostaining localized IL-1 beta expression mainly to leukocytes and MMP-1 expression to myofibroblasts. Stimulation of cultured human aortic valve myofibroblasts with IL-1 beta lead to a time-dependently increased expression of MMP-1 and MMP-2 by Western blotting and zymography, whereas MMP-9 remained unchanged. Cell proliferation was increased by IL-1 beta as determined by bromodesoxyuridine incorporation. Thus, IL-1 beta may regulate remodeling of the extracellular matrix in calcific AS.

Advances towards understanding heart valve response to injury

BACKGROUND

Composed of endocardial endothelial, valvular interstitial, cardiac muscle, and smooth muscle cells (SMC), heart valves are prone to various pathologic conditions the morphology of which has been well described. The morphology of diseased valves suggest that the "response to injury" process occurs in these valves, and is associated with an accumulation of interstitial cells and matrix, valvular inflammation and calcification, conditions that lead to dysfunction. The purpose of this study is to describe the current knowledge of the regulation of the valvular "response to injury" process, since we feel that this paradigm is essential to understanding valve disease.

METHODS

The pertinent literature relating to the cell and molecular biology of valvular repair, and specifically interstitial cell function in valve repair, is reviewed.

RESULTS

The cell and molecular biology of valve interstitial cells are poorly understood. Molecules regulating some of the aspects of the "response to injury" process have been studied, however, the signal transduction pathways, gene activation, and interactions of bioactive molecules with each other, with cells, and with the matrix have not been characterized. Initial studies identify the cell and molecular biology of interstitial cells to be an important area of research. Agents that have been studied include nitric oxide (NO) and FGF-2 and several matrix-related proteins including osteopontin. The present review suggests several directions for future study and a working model of valvular repair is presented.

DISCUSSION

The regulation of the "response to injury" process in the human heart valve is still largely unknown. The cell and molecular events and processes that occur in heart valve function and repair remain poorly understood. These events and processes are vital to our understanding of the pathobiology of heart valve disease, and to the successful design of tissue engineered replacement valves.