Collective epithelial cell invasion overcomes mechanical barriers of collagenous extracellular matrix by a narrow tube-like geometry and MMP14-dependent local softening

Abstract

Collective cell invasion (CCI) through interstitial collagenous extracellular matrix (ECM) is crucial to the initial stages of branching morphogenesis, and a hallmark of tissue repair and dissemination of certain tumors. The collagenous ECM acts as a mechanical barrier against CCI. However, the physical nature of this barrier and how it is overcome by cells remains incompletely understood. To address these questions, we performed theoretical and experimental analysis of mammary epithelial branching morphogenesis in 3D type I collagen (collagen-I) gels. We found that the mechanical resistance of collagen-I is largely due to its elastic rather than its viscous properties. We also identified two strategies utilized by mammary epithelial cells that can independently minimize ECM mechanical resistance during CCI. First, cells adopt a narrow tube-like geometry during invasion, which minimizes the elastic opposition from the ECM as revealed by theoretical modeling of the most frequent invasive shapes and sizes. Second, the stiffness of the collagenous ECM is reduced at invasive fronts due to its degradation by matrix metalloproteinases (MMPs), as indicated by direct measurements of collagen-I microelasticity by atomic force microscopy. Molecular techniques further specified that the membrane-bound MMP14 mediates degradation of collagen-I at invasive fronts. Thus, our findings reveal that MMP14 is necessary to efficiently reduce the physical restraints imposed by collagen-I during branching morphogenesis, and help our overall understanding of how forces are balanced between cells and their surrounding ECM to maintain collective geometry and mechanical stability during CCI.

SPRY1 regulates mammary epithelial morphogenesis by modulating EGFR-dependent stromal paracrine signaling and ECM remodeling

“…Our data showing up-regulation of Mmp2, Mmp11, Mmp14, Lox, and Lox3 are consistent with a previous report on regulation of Mmp expression and collagen contraction by EGFR-ERK signaling in mouse embryonic fibroblasts (48). Importantly, several Mmps, including Mmp2, Mmp3, and Mmp14, have been shown to regulate mammary epithelial branching in vivo (49,50). Consistent with increased Mmp and Lox gene expression, we found that organized collagen deposition was higher in Spry1KO mammary glands than in Spry1het glands during development.…”

Matrix Stiffening and β1 Integrin Drive Subtype-Specific Fibroblast Accumulation in Lung Cancer

“…All these findings strongly support that matrix stiffening alone may be as important as soluble growth factors in driving fibroblast accumulation in vivo, thereby challenging the current view of stromagenesis as driven by paracrine signaling only (3,(8)(9)(10). Moreover, they extend previous evidence of a positive feedback loop in which activated fibroblasts lay out increased amounts of fibrotic ECM components that render a stiffer ECM, which in turn may drive fibroblast activation and accumulation further (11,14).…”

“…First, increasing the rigidity of culture substrata enhances the effects of exogenous growth factors on the survival and/or proliferation of fibroblasts from nonmalignant tissues (11)(12)(13). Second, a marked increase in matrix rigidity is expected in the stroma of NSCLC, because two hallmarks of desmoplastic tumors-abundant collagen-I fibers and a-SMA þ fibroblastshave been associated with dramatic tissue hardening (14)(15)(16)(17).…”

A spectrophotometer-based diffusivity assay reveals that diffusion hindrance of small molecules in extracellular matrix gels used in 3D cultures is dominated by viscous effects

“…The recognition of the important ECM regulatory role in vivo has extended the use of three-dimensional (3D) cultures based on growing cells embedded in gels of native ECM components [1,2]. Thus, the availability of ECM macromolecules from major tissue types including type I collagen (COLI) and reconstituted basement membrane (rBM, also known as Matrigel or EHS matrix) has enabled using 3D cultures to study different cell types in a variety of physiopathological processes such as differentiation, morphogenesis and invasion [3][4][5][6].…”