Constitutive secretion of MMP9 by early-passage cultured human endothelial cells

Matrix metalloproteinase-9 (MMP9) plays an important role during angiogenesis. It is an inducible enzyme which is known to be secreted from human endothelial cells in response to phorbol myristate acetate (PMA), but thought not to be constitutively expressed. We examined the secretion of MMP9 by primary culture (P0), passage 1 (P1) and passage 2 (P2) human umbilical vein endothelial cells (HUVE). Whereas there was no detectable MMP9 in P2 cells under basal conditions, P0 HUVE secreted MMP9, as detected by zymography and ELISA. RT-PCR and cycloheximide inhibition studies confirmed that MMP was synthesized by P0 HUVE. MMP9 secretion was passage-dependent, decreasing rapidly as the cells were passaged in culture and was not detected at P2. The decrease was largely due to the population doubling of cells as they are cultured. This is the first report to show that cultured HUVE constitutively express MMP9 and that this secretion is restricted to very early-passage cells. These findings may be relevant to the angiogenic potential of human endothelial cells as they age.