Knee pain is a common complaint among older Americans, nearly half of whom have developed or will develop painful osteoarthritis. Osteoarthritis is primarily a disease of articular cartilage, the low‐friction, shock‐absorbing connective tissue that lines long bones at their articulating surfaces. Within these joint tissues and within arthritis, the protein collagen VI plays an uncertain role, although it has been implicated in several muscle and ligament disorders. Determination of the collagen VI role in bone and cartilage of the knee is the focus of this dissertation.
Within articular cartilage, collagen VI exclusively localizes to and delimits the pericellular matrix (PCM), which differs from the extracellular matrix (ECM) in composition and structure. To interact with the cell, a molecule must first pass through the PCM. Fluorescent dextran diffusivities were quantified in the cartilage PCM using a newly developed model of scanning microphotolysis (SCAMP), a line photobleaching technique. Diffusion was slower in the PCM than in the ECM, although not in early‐ stage arthritic tissue. These results support the hypothesis that diffusivity is lower in the PCM than in the ECM of healthy articular cartilage, presumably due to differences in proteoglycan content.
Arthritic degradation is partly mediated by interleukin‐1 (IL‐1), a catabolic cytokine that affects the mechanical properties of articular cartilage and preferentially binds to cell‐surface receptors in the surface zone. Since cells are the cartilage metabolic units, matrix degradation is hypothesized to influence molecular transport in the PCM before the ECM. Cartilage was cultured with or without IL‐1, soaked in FITC‐ ovalbumin, and photobleached using SCAMP to measure diffusivity. Over 7 days of culture, IL‐1 doubled the diffusivity in both zones (surface, middle) and matrices (PCM, ECM) of the cartilage. Diffusivity within the PCM was slightly lower than within the ECM. No increase in PCM diffusivity relative to ECM diffusivity was detected within either zone, suggesting that PCM‐localized degradation either cannot be distinguished at these time points or cannot be detected by measures of ovalbumin diffusion.
To determine the effects of collagen VI absence on the morphometry and physical properties of the joint, knees of 2‐, 9‐, and 15‐month‐old Col6a1+/+ and Col6a1‐/‐ mice were studied. Bone morphometry was evaluated using micro‐computed tomography (microCT). Subchondral bone thickness, joint‐capsule thickness, and cartilage degradation were assessed by histology. Cartilage elastic modulus, roughness, and coefficient of friction were measured by atomic force microscopy (AFM). Diffusion through the cartilage ECM was determined by SCAMP. Overall, collagen VI absence had profound effects on the morphometry of the proximal tibia and the overall histological structures of the mouse knee, yet minimal effects on the friction, roughness, elastic modulus, and diffusional properties of the articular cartilage. Musculoskeletal abnormalities at the knee do result from collagen VI absence.
|1993||Chipman SD, Sweet HO, McBride DJ Jr, Davisson MT, Marks SC Jr, Shuldiner AR, Wenstrup RJ, Rowe DW, Shapiro JR. Defective proα2(I) collagen synthesis in a recessive mutation in mice: a model of human osteogenesis imperfecta. Proc Natl Acad Sci USA. March 1993;90(5):1701-1705.|
|2000||Guilak F, Mow VC. The mechanical environment of the chondrocyte: a biphasic finite element model of cell–matrix interactions in articular cartilage. J Biomech. December 2000;33(12):1663-1673.|
|1995||Buschmann MD, Gluzband YA, Grodzinsky AJ, Hunziker EB. Mechanical compression modulates matrix biosynthesis in chondrocyte/agarose culture. J Cell Sci. April 1995;108(4):1497-1508.|
|1991||Lai WM, Hou JS, Mow VC. A triphasic theory for the swelling and deformation behaviors of articular cartilage. J Biomech Eng. August 1991;113(3):245-258.|
|2003||Amblard D, Lafage-Proust M-H, Laib A, Thomas T, Rüegsegger P, Alexandre C, Vico L. Tail suspension induces bone loss in skeletally mature mice in the C57BL/6J strain but not in the C3H/HeJ strain. J Bone Miner Res. March 2003;18(3):561-569.|
|1971||Hayes WC, Mockros LF. Viscoelastic properties of human articular cartilage. J Appl Physiol. October 1971;31(4):562-568.|
|2006||Darling EM, Zauscher S, Guilak F. Viscoelastic properties of zonal articular chondrocytes measured by atomic force microscopy. Osteoarthritis Cartilage. June 2006;14(6):571-579.|
|2007||Leddy HA. Diffusional Properties of Articular Cartilage [PhD thesis]. Duke University; 2007.|
|2006||Fritton JC. Mechanical Loading Induced Adaptation of the Mouse Tibia [PhD thesis]. Ithaca, NY: Cornell University; January 2006.|
|2005||Fritton JC, Myers ER, Wright TM, van der Meulen MCH. Loading induces site-specific increases in mineral content assessed by microcomputed tomography of the mouse tibia. Bone. June 2005;36(6):1030-1038.|
|2003||Mauck RL, Hung CT, Ateshian GA. Modeling of neutral solute transport in a dynamically loaded porous permeable gel: implications for articular cartilage biosynthesis and tissue engineering. J Biomech Eng. October 2003;125(5):602-614.|
|1996||Beamer WG, Donahue LR, Rosen CJ, Baylink DJ. Genetic variability in adult bone density among inbred strains of mice. Bone. May 1996;18(5):397-403.|
|2000||Laib A, Barou O, Vico L, Lafage-Proust MH, Alexandre C, Rügsegger P. 3D micro-computed tomography of trabecular and cortical bone architecture with application to a rat model of immobilisation osteoporosis. Med Biol Eng Comput. May 2000;38(3):326-332.|
|1997||Hildebrand T, Rüegsegger P. Quantification of bone microarchitecture with the structure model index. Comput Methods Prog Biomed. 1997;1(1):15-23.|
|1980||Mow VC, Kuei SC, Lai WM, Armstrong CG. Biphasic creep and stress relaxation of articular cartilage in compression: theory and experiments. J Biomech Eng. February 1980;102(1):73-84.|
|1971||Mankin HJ, Dorfman H, Lippiello L, Zarins A. Biochemical and metabolic abnormalities in articular cartilage from osteo-arthritic human hips, II: correlation of morphology with biochemical and metabolic data. J Bone Joint Surg. April 1971;51A(3):523-537.|
|1984||Mow VC, Holmes MH, Lai WM. Fluid transport and mechanical properties of articular cartilage: a review. J Biomech. 1984;17(5):377-394.|
|1992||Mow VC, Ratcliffe A, Robin Poole A. Cartilage and diarthrodial joints as paradigms for hierarchical materials and structures. Biomaterials. 1992;13(22):67-97.|
|1970||Muir H, Bullough P, Maroudas A. The distribution of collagen in human articular cartilage with some of its physiological implications. J Bone Joint Surg. August 1970;52B(3):554-563.|
|2005||Alexopoulos LG, Williams GM, Upton ML, Setton LA, Guilak F. Osteoarthritic changes in the biphasic mechanical properties of the chondrocyte pericellular matrix in articular cartilage. J Biomech. March 2005;38(3):509-517.|
|2003||Alexopoulos LG, Haider MA, Vail TP, Guilak F. Alterations in the mechanical properties of the human chondrocyte pericellular matrix with osteoarthritis. J Biomech Eng. June 2003;125(3):323-333.|