MATRIX METALLOPROTEINASE-9 (92-KD GELATINASE TYPE-IV COLLAGENASE EQUALS GELATINASE-B) CAN DEGRADE ARTERIAL ELASTIN

Degradation of elastic fibers in the arterial walls is an important st ep in the development of atherosclerosis. To identify the enzyme(s) re sponsible for the elastinolysis, we have designed an ex vivo model of aortic explants cultured with or without THP-1 cells (human monocyte/m acrophage-like cells). After culturing with THP-1 cells for 5 days, el astic fibers of the aortic explants were fragmented and lost. With ins oluble [H-3] elastin as a substrate, elastin-degrading activity could be detected in the culture medium. Zymography in sodium dodecyl sulfat e-polyacrylamide gel electrophoresis containing alpha-elastin showed t he presence of elastinolytic activity with 92 kd in the medium from th e aortic tissue with THP-1 cell cultures, whereas the medium from the aortic tissue without THP-1 cells contained negligible elastinolytic a ctivity. The activity was inhibited by ethylenediamine tetraacetic aci d but not by phenylmethane sulfonyl fluoride, N-ethylmaleimide, or pep statin A, indicating that the enzyme belongs to a class of metalloprot einases. In addition, destruction of the elastic fibers of the aortic explants cultured with THP-1 cells was completely inhibited only by me talloproteinase inhibitors. Immunoblot analyses demonstrated that the proteinase responsible for the elastinolytic activity is matrix metall oproteinase-9 (92-kd gelatinase/type IV collagenase = gelatinase B). U sing immunocytochemistry, the metalloproteinase was localized in the T HP-1 cells but not in the medial smooth muscle cells. These results su ggest that matrix metalloproteinase-3 produced by THP-1 cells is of im portance to degradation of elastic fibers in the aortic explants. The role of macrophages in the atherosclerosis is discussed with reference to elastinolysis of the arterial walls.