Exposure of endothelial cells (ECs) to hypoxia has separately been shown to induce their angiogenesis or death. Matrix Metalloproteinase (MMP)-2 is associated with ECs angiogenesis, though recent studies also implicate this molecule in ECs death. We studied the effect of hypoxia, in the absence or presence of TNF-a (characteristic of the inflammatory microenvironment accompanying hypoxia), on MMP-2 expression and its role in angiogenesis (proliferation, migration and tube formation) and death of primary human umbilical vein endothelial cells (HUVEC). Hypoxia (24-48h; 3% oxygen), furthermore when combined with TNF-a, significantly enhanced MMP-2 expression and activity. Hypoxia also led to a reduction of MT1-MMP and TIMP-2 mRNA and protein while enhancing the expression of aVb3 integrin, and the cytoskeletal protein, phosphopaxillin. Moreover hypoxia led to co-localization of aVb3 and MMP-2, but not MT1-MMP, with phosphopaxillin in ECs. These results suggest MT1-MMP-independent activation of MMP-2 during hypoxia and support interactions between the ECM, integrins and cytoskeleton in hypoxia-induced MMP-2-related functions.

Hypoxia enhanced ECs migration in an MMP-2-dependent manner, while leading to a reduction of cell number via their apoptotsis, also dependent on MMP-2. In addition hypoxia caused aberrant tube-like formation on Matrigel that appeared to be unaffected by MMP-2. The hypoxia-induced MMP-2-dependent migration of ECs is in accordance with the pro-angiogenic role ascribed to MMP-2, while the involvement of this protease in the hypoxia-related death of ECs, supports an additional apoptotic role for this protease. Hence MMP-2, in the hypoxic microenvironment, appears to have a dual autocrine role in determining the fate of ECs.