Matrix metalloproteinase expression by endothelial cells in collagen lattices changes during co-culture with fibroblasts and upon induction of decorin expression

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Abstract
EA.hy 926 cells, a derivative of human umbilical vein endothelial cells, in the presence of fibroblasts show the phenomena of angiogenesis, express the proteoglycan decorin and escape apoptosis, when they are maintained in collagen lattices, while fibroblast‐free cultures do not show these changes. Virus‐mediated decorin expression can substitute for the presence of fibroblasts. Since the expression of matrix metalloproteinases (MMPs) is an essential step in the formation of capillaries, several MMPs and tissue inhibitors of metalloproteinases (TIMPs) were investigated. MMP‐1, MMP‐2, MMP‐9, and the cell‐associated MMP‐14 were augmented on the protein level in the presence of fibroblasts. No effect was seen with respect to MMP‐3, TIMP‐1, and TIMP‐2. Semiquantitative RT‐PCRs of endothelial cells in co‐culture revealed a 7‐, 19‐, and 11‐fold increase for mRNAs of MMP‐1, MMP‐2, and MMP‐14 after six days, respectively. Virus‐mediated decorin expression also was accompanied by an up‐regulation of these MMPs. The expression of MMP‐1 mRNAs increased 5‐fold after 2 days and gradually declined thereafter. In contrast, MMP‐2 and MMP‐14 showed a 7‐fold and a 14‐fold increase on day two which returned to basal levels within 24 h, indicating that the expression of MMP‐1 is differentially regulated from MMP‐2 and MMP‐14. In spite of the upregulation of the proteases, an enhanced degradation of decorin was not observed. These results indicate that the expression of decorin is a sufficient signal in EA.hy 926 cells for a finely tuned induction of selected MMPs which are involved in angiogenesis whereas the up‐regulation of MMPs does not lead to the degradation of the responsible proteoglycan.