Date of Degree
MS (Master of Science)
James A. Martin
While mechanical loading is essential for articular cartilage homeostasis, it also plays a central role in the etiology of osteoarthritis. The mechanotransduction events underlying these dual effects, however, remain unclear. Previously, we have shown that lethal amounts of reactive oxygen species (ROS) were liberated from mitochondrial complex 1 in response to a mechanical insult. The sensitivity of this response to an actin polymerase inhibitor, cytochalasin B, indicated a link between ROS release and cytoskeletal distortion caused by excessive compressive strain. It did not, however, rule out the possibility that ROS may also mediate the beneficial effects of normal stresses that induce lower tissue strains required for proper homeostasis. If this possibility is true, one would expect the amount of ROS released in loaded cartilage to be positively correlated with the level of strain, and ROS should only reach lethal levels under super-physiological deformations. To test this hypothesis, full cartilage tissue strains were measured in cartilage explants subjected to static normal stresses of 0, 0.1, 0.25, 0.5, and1.0 MPa. After compression, the percentage of ROS-producing cells was measured using the oxidation-sensitive fluorescent probe, dihydroethidium, and confocal microscopy. In support of our theory, the percentage of fluorescing cells increased linearly with increasing strains (0-75%, r2 = 0.8, p < 0.05). Additionally, hydrostatic stress, which causes minimal tissue strain, induced minimal ROS release. In terms of cell viability, cartilage explants compressed with strains >40% experienced substantial cell death, while explants with strains
Articular Cartilage, Chondrocytes, Live-cell Imaging, Mechanical Stress, Oxidative Stress, Tissue Strain
viii, 41 pages
Includes bibliographical references (pages 32-41).
Copyright 2012 Marc James Brouillette