Joint disease biomarkers - discovery and application

Abstract: Dysregulated cartilage homeostasis, articular cartilage degradation and abnormal bone remodeling are common denominators in joint disease and can lead to severe disability for the patients. The molecular pathways behind the disease pathology can overlap across different joint diseases. For example, pro-inflammatory cytokines are involved in the pathogenesis of both osteoarthritis and psoriatic arthritis. The aim of this thesis is to investigate how the turnover (synthesis/breakdown) of cartilage extracellular matrix proteins responds to selected pro–inflammatory cytokines, thereby, gaining knowledge about cartilage biology, function and pathology. The second aim is to develop novel biomarkers of joint tissue turnover. In Paper I we investigated the effect of pro-inflammatory cytokine interleukin-17 on articular cartilage in a bovine explant model system. We observed induction of matrix metalloproteinase (MMP)-mediated collagen and A Disintegrin And Metalloproteinase with Thrombospondin Motifs-mediated aggrecan degradation markers, and the upregulation of proteases was confirmed by gelatin zymography and/or mass spectrometry. We also found that interleukin-17A can upregulate other pro-inflammatory cytokine release from chondrocytes and a release of both proteins and protein metabolism fragments into conditioned media. In Paper II we developed a novel biomarker ELISA assay for MMP-cleaved prolargin (PROM), that was elevated in psoriatic arthritis patients compared to healthy controls, indicating that this is a marker that is associated with disease. In Paper III, we developed and validated a robust and specific ELISA assay measuring a MMP-1 and MMP-13 cleaved type II collagen fragment (T2CM) that we identified in the study for Paper I. It was elevated in response to pro-inflammatory cytokine treatment of bovine articular cartilage, and in osteoarthritis patients referred for a total knee joint replacement surgery compared to patients with moderate or severe disease. Additionally, T2CM levels were decreased in osteoarthritis patients treated with oral salmon calcitonin compared to the placebo group. Either alone or in a biomarker panel T2CM could be useful for assessing cartilage degradation in osteoarthritis. Finally, in Paper IV we investigated the levels of extracellular matrix turnover markers in healthy individuals throughout life. There is a need to investigate the age characteristics and natural history of collagen turnover biomarkers to maximize their potential use in osteoarthritis. Collagen turnover is an essential part of growth and can vary as a function of age and disease. We found that formation of type I, II and type V collagens, measured by PRO-C1, PRO-C2, and PRO-C5 biomarkers was age dependent. This needs to be accounted for when measuring collagen turnover across different age groups.