Chondrocyte Adhesion to RGD-bonded Alginate: Effect on Mechanotransduction and Matrix Metabolism: a Dissertation

Abstract

The mechanism of mechanotransduction in chondrocyte matrix metabolism is not well understood, in part because of the density of cartilage and in part because of limitations in in vitroculture systems. Using alginate covalently modified to include the integrin adhesion ligand R-G-D (arginine-glycine-aspartate) represents a unique approach to studying mechanotransduction in that it allows for exploration of the role of integrin adhesion in mediating changes to chondrocyte behavior. The hypothesis of this research was that chondrocytes will form a cytoskeletal adhesion to RGD-alginate mediated integrins, that this attachment will enable chondrocyte sensation of mechanical signals, and this signaling will alter chondrocyte matrix metabolism. The first aim of this research was to characterize chondrocyte attachment to RGD-alginate, and assess the role of substrate mechanics on chondrocyte attachment kinetics and morphology. Secondly, the effect of chondrocyte attachment to RGD-alginate in 3D culture on matrix biosynthesis was assessed, as were changes in substrate mechanics. Finally, this research aimed to determine the metabolic response of chondrocytes to changes in intrinsic and extrinsic mechanics. It was found that the RGD ligand functionalized the alginate scaffold, enabling chondrocytes to sense the mechanical environment. Attachment kinetics, morphology, and proteoglycan metabolism were found to adapt to hydrogel matrix stiffness when an integrin adhesion was present. Externally applied compression was transmitted through this integrin attachment, causing changes in proteoglycan synthesis. Components of media serum were found to modulate the effects of integrin mechanotransduction. These results were obtained by analyzing a novel approach with established techniques, such as the DMB dye assay for sulfated GAG content. The conclusions conform to diverse data from cartilage explant loading and monolayer culture studies, yet were accomplished using one versatile system in a straightforward manner. The potential of this system extends further, into identification of intracellular signaling pathways and extracellular modulation of matrix components. Seeded RGD-alginate is well suited for studying consequences of integrin attachment.