Role of material-driven fibronectin fibrillogenesis in protein remodeling

Protein remodeling at the cell-material interface is an important phenomenon that should be incorporated into the design of advanced biomaterials for tissue engineering. In this work, we address the relationship between fibronectin (FN) activity at the material interface and remodeling, including proteolytic cascades. To do so, we studied FN adsorption on two chemically similar substrates, poly(ethyl acrylate) (PEA) and poly(methyl acrylate) (PMA), which resulted in different distribution and conformation of the protein at the material interface: FN organized spontaneously upon adsorption on PEA into physiological-like fibrils, through a process called material-driven FN fibrillogenesis. The amount of adsorbed FN and its conformation were investigated in two different coating concentrations (2 and 20 μg/mL). Since FN activity at the material interface determines the initial cellular response, we followed the formation of focal adhesions (vinculin) and subsequent cell signaling by focal adhesion kinase (FAK) expression and its phosphorylation (pFAK). More detailed studies were performed to get further insights into integrin binding by crosslinking and extraction followed by immunofluorescence, as well as protein and gene expression for α5 and αv. To correlate cell adhesion with matrix degradation, gene expression and activity (zymography) of matrix metalloproteinases (MMPs) were measured. Overall, we demonstrated that the material-driven FN fibrillogenesis triggers proteolytic activity: MMP activity was higher on the material-driven FN fibrils, as a compensatory mechanism to the inability of cells to reorganize this FN network.