Articular cartilage is a connective tissue that distributes mechanical loads within the knee. When injured, cartilage has a limited ability to heal. If left untreated, cartilage injuries can lead to chondrocyte death, which leads to cartilage deterioration (osteoarthritis), pain, and disability. Mechanical factors, such as impact injuries, are considered a major cause of the resulting cartilage degeneration. However, therapies that focus on early intervention have not been developed. Furthermore, high and low weight bearing regions exist within the knee. Differences in cartilage mechanical conditioning in these regions result in regional properties differences such as thickness, proteoglycan content, metabolism, and chondrocyte behavior. These differences could play an important role in regional injury development. Therefore, this dissertation focuses on creating an injury model for studying early injury development.
Cartilage samples were harvested using a bone-side extruding method, and cultured in a 37°C, humidity regulated incubator at 20% oxygen in high glucose (4.5g/L) serum-free media. To create an in-vitro injury model, reproducible single-impact injuries were created by releasing a 500 gram weight from a height of 15 cm.
A force-controlled compression bioreactor system was developed to investigate the effects of mechanical loading on cell viability and apoptotic activities. This study determined that 0.5MPa of mechanical loading following acute impact injury decreases apoptosis, helping to counteract the damage that occurs during injuries. Furthermore, the study identified a positive result threshold, above which the application of mechanical loading has detrimental rather than beneficial effects on viability. Taken in combination, the early intervention window, and therapeutic threshold can be used to design injury rehabilitation guidelines for maintaining cartilage health and promoting osteoarthritis disease deterrence.
This dissertation uses microarray analysis to evaluate differences in baseline regional gene expression and regional injury response in human articular knee cartilage. Our study shows that baseline differences in regional gene expression exist and effect injury response within those regions is different. These finding suggest that mechanical preconditioning may occur which could cause regional genetic changes that might result in different phenotypic expression.
The findings of this dissertation contribute to the growing body of evidence that supports genetics as a potential metric to evaluate cartilage health and the effects of respective treatments. As medicine moves towards a more personalized predictive and preventive approach, understanding early injury developments will be critical in clinical care.
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