Invited Paper BI1-WeM6
Using Thin Films of Fibrillar Type I Collagen to Investigate a Signaling Mechanism that Mediates Growth Arrest in Smooth Muscle Cells
Smooth muscle cells (SMC) on fibrillar collagen activate different signaling pathways, have a minimally spread morphology and appear growth arrested compared to SMC cultured on non-fibrillar native collagen. Because studies suggest that SMC interact with both matrices through the same integrin receptors, it appears that it is the supramolecular fibrils that are responsible for the phenotypic response. We used thin films of fibrillar collagen assembled on hexadecanethiol monolayers to investigate which properties of the collagen fibrils control the proliferation signaling. The films are on average 30 nm thick and composed of collagen fibrils that are microns long and as large as several hundred nanometers in diameter. They also have optical properties that are ideal for both phase and fluorescence microscopy. When the fibrillar films are kept hydrated, they induce a growth arrest response in SMC that is similar to the response that is observed on fibrillar collagen gels. If the thin films are dried for several hours before rehydration, the SMC exhibit a well-spread proliferative phenotype and begin to proliferate. Atomic force microscopy (AFM) analysis of these fibrillar films indicates that they are nearly identical in topography, density of fibrils and size of fibrillar structures. These data suggest that the presence of collagen fibrils alone is not sufficient to induce the growth-arrested phenotype. AFM imaging of the fibrillar films under aqueous conditions suggest that the flexibility of the collagen fibrils is reduced during the drying process. We hypothesize that the mechanical properties of the fibrils are an essential determinant of the SMC growth-arrest response. We are currently using live-cell microscopy to understand how these cells interrogate the mechanical properties of collagen fibrils when deciding their phenotypic state.