Macrophage-Dependent Trafficking and Remodeling of the Basement Membrane-Interstitial Matrix Interface

Abstract

Macrophages infiltrate and remodel extracellular matrix barriers during development and disease. Bahr and Weiss demonstrate that human macrophages remodel native basement membrane barriers in an MT1-MMP-dependent fashion while retaining the ability to traverse tissue barriers by actomyosin-dependent forces alone.\n\nAbstractMacrophages dominate inflammatory environments where they modify the extracellular matrix by mobilizing complex repertoires of proteolytic enzymes. Nevertheless, the dominant proteinases used by macrophage as they confront physiologic tissue barriers remain undefined. Herein, we have characterized the molecular mechanisms that define human macrophage-extracellular matrix interactions ex vivo. Resting and immune-polarized macrophages are shown to proteolytically remodel basement membranes while infiltrating the underlying interstitial matrix. In an unbiased screen to identify key proteases, we find that the macrophage metalloproteinase, MT1-MMP, is the dominant effector of basement membrane degradation and invasion. Unexpectedly, macrophages can alternatively use actomyosin-dependent forces to transmigrate native basement membrane pores that provide cells with proteinase-independent access to the interstitial matrix. These studies not only identify MT1-MMP as a key proteolytic effector of extracellular matrix remodeling by human macrophages, but also define the invasive strategies used by macrophages to traverse physiologic tissue barriers.