Mecanismos reguladores y acciones de la proteasa MT4-MMP en monocitos patrulleros y macrófagos de ratón

Abstract

There are two main subsets of monocytes in mice with different roles in the innate immune system. On the one hand, the classical monocytes or pro-inflammatory monocytes (Ly6C+), which act as reservoir of cells that can be recruited in response to inflammation or tissue damage and cross the vasculature to differentiate onto macrophages or dendritic cells, allowing the reposition of resident cells and promoting the clearance of pathogenic particles. On the other hand, the non-classical or patrolling monocytes (Ly6C-), a less-characterized population, which remain mainly intravascular helping to maintain the homeostasis of the endothelium through the clearance of damaged endothelial cells and the engulfment of circulating particles. Although the patrolling monocytes can also extravasate and differentiate onto a different subset of macrophages and dendritic cells in certain pathophysiological contexts. The patrolling monocytes are able to perform a movement of crawling over the endothelium independent of the flow direction, allowing them to examine large areas of the vasculature and finally to perform the phagocytosis of different particles such as modified-LDLs, apoptotic cells and even tumour cells particles. This crawling movement is regulated by monocyte adhesion via different integrins such as integrin CD11a/CD18 and CD11b/CD18 to their ligands on the resting and inflamed endothelium respectively. In this project, we studied the role of the GPI-anchored membrane-type matrix metalloproteinase 4 (MT4-MMP), also known as MMP17, as a regulator of patrolling monocyte crawling and of phagocytosis of melanoma cells in vitro and in vivo and the influence on these processes of fibrinogen, a ligand of the integrin CD11b/CD18 given that MT4-MMP can process CD11b. We present the validation of the first fusion protein of MT4-MMP with the red fluorescent protein mCherry that will help to understand the role of MT4-MMP in the future. Our results indicate that the matrix, in particular fibrinogen, influences the subcellular localization of MT4-MMP in peritoneal lavage macrophages and the crawling of patrolling monocytes. In addition, we have seen that MT4-MMP-deficient macrophages are able to engulf more apoptotic melanoma particles in vitro compared to the wild types and that mice deficient in MT4-MMP show enhanced clearance of melanoma metastatic particles in vivo in spite of no significant differences in the uptake of these particles by patrolling monocytes after 24 hours of i.v. injection of melanoma cells