Novel quantitative approaches for the assessment of pathological features in murine models of Osteoarthritis

Abstract

Osteoarthritis (OA) is the most prevalent joint pathology, an incurable and painful condition that is a leading cause of reduction in quality of life among the elderly. Originally considered a cartilage disorder due to lesions observed in this tissue, it is now agreed by the scientific community that OA is a complex ‘organ failure’ involving the whole joint. Notwithstanding the dramatic modifications observed radiographically in subchondral bone, their contribution to the pathology is not fully understood and little is known about bone role in the pathogenesis. The aim of this thesis was to characterize the involvement of subchondral bone using a surgical mouse model. Due to their amenability for genetic studies, murine models are increasingly essential tools to identify new therapeutic targets, but their assessment is limited by time-consuming, qualitative histopathology. This work presents novel high-throughput approaches to automatically quantify subchondral bone, articular cartilage, and osteophytes in mouse tibiae. Cartilage was assessed by novel 3D imaging methodologies that overcame the lack of non-destructive imaging previously available for mouse cartilage and constitute a major technological novelty. Changes in bone mechanical properties were further investigated by nanoindentation testing. Microstructural changes in bone were detected by micro-CT before evident cartilage degradation. Nanomechanical properties were altered only at the late stages of the pathology and not associated with alterations in mineral composition. Furthermore, although changes in bone and cartilage were co-localised, correlation analysis showed that they developed independently over time. In conclusion, this thesis presents a 3D quantitative assessment of changes occurring in bone and cartilage within tibiae during OA progression and demonstrates the key involvement of bone in the pathogenesis. The proposed approaches provide an unprecedented high-throughput solution for analysis in the mouse model and might be useful to improve the understanding of murine OA.