Lymphangiogenesis and extracellular matrix remodeling

Lymphangiogenesis, the formation of new lymphatic vessels from preexisting ones, is an important biological process associated with diverse pathologies, such as metastatic dissemination and graft rejection. Our laboratory has previously identified MMP2 as a key regulator of lymphangiogenesis in vitro and in vivo. However, the exact function of MMP2 in this process is yet unknown. The present work aims at elucidating the mechanisms of MMP2 action during lymphangiogenesis. MMP2 could either act as a growth factor activator or as a regulator of matrix remodeling.
To address this question, we studied the effect of MMP2 on lymphangiogenesis in an novel in vitro model of sprouting cells from small aggregates (spheroids) seeded in a collagen gel. In this model, quantification of the lymphangiogenic response is performed through computerized methods allowing the measurement of the distance of migration, but also the evaluation of how the cell are migrating. We evaluated the impact of MMP2 blockage through the use of physiological (TIMP2) or chemical inhibitors or by downregulating its expression with specific siRNA. The importance of extracellular matrix composition is evaluated by embedding these spheroids into different matrices (matrigel versus collagen; pepsinized collagen versus native collagen; different collagen concentrations). Our results reveal a modification of cell migration through collagen gel after MMP2 inhibition. The utilization of DQ collagen and microscopy refractance confirmed the importance of MMP2 collagenoyitic activity for lymphangiogenesis.