Interdependency of cell adhesion, force generation and extracellular proteolysis in matrix remodeling.

It is becoming increasingly evident that the micromechanics of cells and their environment determine cell fate and function as much as soluble molecular factors do. We hypothesized that extracellular matrix proteolysis by membrane type 1 matrix metalloproteinase (MT1-MMP) depends on adhesion, force generation and rigidity sensing of the cell. Melanoma cells (MV3 clone) stably transfected with MT1-MMP, or the empty vector as a control, served as the model system. α2ß1 integrins (cell adhesion), actin and myosin II (force generation and rigidity sensing) were blocked by their corresponding inhibitors (α2ß1 integrin antibodies, Cytochalasin D, blebbistatin). A novel, anisotropic matrix array of parallel, fluorescently labeled collagen-I fibrils was used. Cleavage and bundling of the collagen-I fibrils, and spreading and durotaxis of the cells on this matrix array could be readily discerned and quantified by a combined set-up for fluorescence and atomic force microscopy. In short, expression of the protease resulted in the generation of structural matrix defects, clearly indicated by gaps in the collagen lattice and loose fiber bundles. This key feature of matrix remodeling depended essentially on the functionality of α2ß1 integrin, the actin filament network and myosin II motor activity. Interference with any of these negatively impacted matrix cleavage and three-dimensional matrix entanglement of cells.

Experimental hypertension triggers varicosis-like maladaptive venous remodeling through activator protein-1.

An increase in circumferential wall tension (CWT) is an important determinant of vascular remodeling during hypertension or arteriosclerosis but also arteriogenesis. Although pivotal for such processes, the effect of this biomechanical force on venous remodeling has not yet been delineated. To this end, we raised the filling pressure in veins of the mouse auricle, which led to a 2.5-fold enlargement of these blood vessels within 4 d along with an increase in smooth muscle cell proliferation, matrix metalloproteinase 2 (MMP-2) expression and gelatinase activity. These changes were likewise observed in tissue samples of human varicose veins. Topical treatment of the auricles with a decoy oligonucleotide-neutralizing activator protein 1 (AP-1) inhibited these effects. Likewise, proliferation, MMP-2 expression, and gelatinase activity in both native and cultured venous smooth muscle cells exposed to enhanced stretch was decreased by up to 80% through inhibiting AP-1. In contrast, mutant control oligonucleotides had no effect on smooth muscle cell activation. These findings indicate that an increase in venous filling pressure and thus CWT is sufficient to activate AP-1, which, in turn, triggers varicose remodeling through fuelling MMP-2 activity and smooth muscle cell hyperplasia in the venous vessel wall.

The extracellular matrix remodeled: Interdependency of matrix proteolysis, cell adhesion, and force sensing.

Membrane Type-1 Matrix Metalloproteinase (MT1-MMP, MMP-14) is regarded as the prototype of a membrane- tethered protease. It drives fundamental biological processes ranging from embryogenesis to cancer metastasis. The proteolytic cleavage of proteins by MT1-MMP can rapidly alter the biophysical properties of a cell's microenvironment. Cell's must thus be able to sense and react to these alterations and transduce these effectively in biochemical signals and cell responses. Although many cells react as acutely to such physical stimuli as they do to chemical ones, the regulatory effects of these have been less extensively explored. In order to investigate a possible interdependency of proteolytic matrix cleavage by MT1-MMP and the generation and sensing of force by cells, a model system was established which exploits the properties of a matrix array of parallel collagen-I fibers. The resulting an-isotropy of the matrix with high tensile strength along the fibers and high mobility perpendicular to it allows the convenient detection of bundling and cleavage of the collagen fibers, as well as spreading and durotaxis of the cells. In summary, we have demonstrated that cell adhesion, force generation, and force sensing are vital for the regulation of MT1-MMP for efficient cleavage of collagen-I.