Non-invasive assessment of cartilaginous tissues in small animal models of injury and disease
Mangano Drenkard, Lauren Michelle
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Cartilage is a tissue that is critical for skeletal function, yet its study has been limited by a lack of quantitative, non-destructive, three-dimensional imaging techniques that enable simultaneous interrogation of both bone and cartilage. Recently, methods of contrast-enhanced micro-computed tomography (CECT) have been developed that exploit the electrostatic interactions between ionic contrast agents and negatively charged glycosaminoglycans (GAGs) in cartilage, thus providing information about the composition and morphology of cartilage that was previously only available via destructive methods. The goal of this dissertation project was to apply CECT, a non-destructive, three-dimensional imaging method, to understand the how the morphology and composition of cartilage changes in response to injury and disease. First, CECT was applied to a model of growth plate injury to quantify changes to the cartilaginous tissue of the growth plate and formation of bone bridges within this tissue in response to injury. Using CECT, it was possible to identify increased thickness and CECT attenuation at the injury site. This result, paired with histological evidence of localized dysregulation of cellular activity, suggests that treatment designed to reduce bone bridge formation at the injury site should also consider the effects of the treatment on the adjacent cartilage. Second, CECT was applied to a collagen antibody-induced arthritis (CAIA) model to determine the role of the A2B adenosine receptor (A2BAR) in the arthritic deterioration of bone and cartilage. CECT scans demonstrated that loss of GAG in the cartilage preceded degeneration, but that ablation of the A2BAR in mice had little effect on the degenerative changes in bone and cartilage associated with CAIA. These results suggest that the A2BAR does not independently mediate these changes and that it may be necessary to target multiple adenosine receptors. Third, the ability of CECT to monitor the fracture healing and predict the stiffness of the cartilaginous fracture callus was assessed both at the level of the whole callus and at the level of the cartilage tissue. Callus stiffness was negatively correlated with the size of the callus and the amount of cartilage, while neither stiffness nor indentation modulus were correlated with CECT attenuation, suggesting that the stiffness of the cartilaginous fracture callus depends on the amount, rather than GAG content of cartilage. The work presented in this dissertation provides outlines changes in both bone and cartilage that occur in pathological conditions and provides new insights for both the treatment and assessment of these conditions.