Epsilon Open Archive

Abstract

Osteoarthritis (OA) is a disease involving inflammation and subsequent degeneration of joint tissues. The disease progresses with time-dependent stages of degeneration, loss and remodelling of the extracellular matrix (ECM) of articular cartilage, and phenotypical changes in the chondrocytes. Currently, OA is diagnosed clinically late in the disease process when irreversible damages to the cartilage are already evident. An understanding of the disease mechanism in the early stage of the inflammatory process is therefore crucial if early stage diagnostic biomarkers are to be identified.

The aim of this thesis was to follow cartilage changes during normal development and interleukin (IL)-1β-induced inflammation. Biomarkers of early OA are needed and a prerequisite for finding unique molecular markers is an understanding of the cellular, genetic and molecular events that occur in chondrogenic development and inflammation. The hypothesis was that inflammation-related events occur at specific time points which can be used to differentiate stages of OA from each other.

The localisation of proteins in developing equine cartilage was studied using immunohistochemistry with the aim of characterising different phenotypes of chondrocytes and their surrounding ECM. The expression of matrix molecules, Notch signalling components, and the stem cell-indicating factor Stro-1 showed spatial changes in expression and localisation during maturation.

Equine articular cartilage explants stimulated with IL-1β were used as an in vitro model mimicking the IL-1β-induced inflammation that occurs during the progression of equine OA. The longitudinal release induced by IL-1β of molecules from the explants into the media was studied using quantitative proteomics and the gene expression in the cartilage explants was evaluated using microarray. The secretion of ECM components and inflammatory mediators followed a time-dependent pattern. Microarray analysis also revealed time-dependent differences in gene expression related to inflammation, ECM, and phenotype.

The data from this thesis contribute to the understanding of cellular, genetic and molecular events in the progression of OA. Stimulation of equine articular cartilage explants with IL-1β induces release of proteins and altered gene expression in a time-dependent pattern. This in vitro model has the potential to aid in testing medical treatments of equine OA, prior to testing in live animals, thereby minimising the use of research animals.