Phagocytosis and remodeling of collagen matrices.

The biodegradation of collagen and the deposition of new collagen-based extracellular matrices are of central importance in tissue remodeling and function. Similarly, for collagen-based biomaterials used in tissue engineering, the degradation of collagen scaffolds with accompanying cellular infiltration and generation of new extracellular matrix is critical for the integration of in vitro grown tissues in vivo. In earlier studies we observed significant impact of collagen structure on primary lung fibroblast behavior in vitro in terms of collagen uptake and matrix remodeling. Therefore, in the present work, the response of human fibroblasts (IMR-90) to the structural state of collagen was studied with respect to phagocytosis in the presence and absence of inhibitors. Protein content and transcript levels for collagen I (Col-1), matrix metalloproteinase 1 (MMP-1), matrix metalloproteinase 2 (MMP-2), tissue inhibitor of matrix metalloproteinase 1 (TIMP-1), tissue inhibitor of matrix metalloproteinase 2 (TIMP-2), and heat shock protein 70 (HSP-70) were characterized as a function of collagen matrix concentration, structure and cell culture time to assess effects on cellular collagen matrix remodeling processes. Phagocytosis of collagen was assessed quantitatively by the uptake of collagen-coated fluorescent beads incorporated into the collagen matrices. Significantly higher levels of collagen phagocytosis were observed for the cells grown on the denatured collagen versus native collagen matrices. Significant reduction in collagen phagocytosis was observed by blocking several phagocytosis pathways when the cells were grown on denatured collagen versus non-denatured collagen. Collagen phagocytosis inhibition effects were significantly greater for PDL57 IMR-90 cells versus PDL48 cells, reflecting a reduced number of collagen processing pathways available to the older cells. Transcript levels related to the deposition of new extracellular matrix proteins varied as a function of the structure of the collagen matrix presented to the cells. A four-fold increase in transcript level of Col-1 and a higher level of collagen matrix incorporation were observed for cells grown on denatured collagen versus cells grown on non-denatured collagen. The data suggest that biomaterial matrices incorporating denatured collagen may promote more active remodeling toward new extracellular matrices in comparison to cells grown on non-denatured collagen. A similar effect of cellular action toward denatured (wound-related) collagen in the remodeling of tissues in vivo may have significant impact on tissue regeneration as well as the progression of collagen-related diseases.