Objective: Osteoarthritis (OA) is a disease with multiple endotypes. A hallmark of OA is loss of cartilage; however, it is evident that the rate of cartilage loss differs among patients, which may partly be attributed to differential capacity for cartilage repair. We hypothesize that a low cartilage repair endotype exists and that such endotypes are more likely to progress radiographically. The aim of this study was to examine the associations of level of cartilage formation with OA severity and radiographic OA progression. We used the blood-based marker PRO-C2, reflecting type II collagen formation, to assess levels of cartilage formation. Methods: The type II collagen propeptide PRO-C2 was measured in the serum/plasma of knee OA subjects from New York University (NYU, n=106) and a subcohort of the phase III oral salmon calcitonin (sCT) trial SMC021-2301 (SMC, n=147). The risk of radiographic medial joint space narrowing (JSN) over 24 months was compared between quartiles (very low, low, moderate, and high) of PRO-C2. Progression was defined as two-year JSN > 0.35 mm. Associations were adjusted for age, gender, BMI, race, baseline pain levels, and baseline joint space width.Results: In both the NYU and SMC cohorts, subjects with low PRO-C2 levels had greater JSN compared to subjects with high PRO-C2. The mean difference in JSN between subjects with very low and high levels of PRO-C2 was 0.65 mm (p = 0.002), corresponding to a 3.4 [1.4 – 8.6]-fold higher risk of progression. There was no significant effect of sCT treatment, compared to placebo, on JSN over two years before stratification based on baseline PRO-C2. However, there were proportionately fewer progressors in the sCT arm of the very low/low PRO-C2 group compared to the moderate/high group (chi-squared = 6.5, p = 0.011). Conclusions: Serum/plasma level of type II collagen formation, PRO-C2, may be an objective indicator of a low cartilage repair endotype, displaying radiographic progression and superior response to a proanabolic drug.
Background Osteoarthritis (OA) is a progressive, chronic disease characterized by articular cartilage destruction. The pro-inflammatory cytokine IL-17 levels have been reported elevated in serum and synovial fluid of OA patients and correlated with increased cartilage defects and bone remodeling. The aim of this study was to characterize an IL-17-mediated articular cartilage degradation ex-vivo model and to investigate IL-17 effect on cartilage extracellular matrix protein turnover. Methods Full-depth bovine femoral condyle articular cartilage explants were cultured in serum-free medium for three weeks in the absence, or presence of cytokines: IL-17A (100 ng/ml or 25 ng/ml), or 10 ng OSM combined with 20 ng/ml TNFα (O+T). RNA isolation and PCR analysis were performed on tissue lysates to confirm IL-17 receptor expression. GAG and ECM-turnover biomarker release into conditioned media was assessed with dimethyl methylene blue and ELISA assays, respectively. Gelatin zymography was used for matrix metalloproteinase (MMP) 2 and MMP9 activity assessment in conditioned media, and shotgun LC-MS/MS for identification and label-free quantification of proteins and protein fragments in conditioned media. Results IL-17RA mRNA was expressed in bovine full-depth articular cartilage and the treatment with IL-17A did not interfere with metabolic activity of the model. IL-17A induced cartilage breakdown; conditioned media GAG levels were 3.6-fold-elevated compared to untreated. IL-17A [100 ng/ml] induced ADAMTS-mediated aggrecan degradation fragment release (14-fold increase compared to untreated) and MMP-mediated type II collagen fragment release (6-fold-change compared to untreated). MS data analysis revealed 16 differentially expressed proteins in IL-17A conditioned media compared to untreated. Conclusions We showed that IL-17A has cartilage modulating potential. It induces collagen and aggrecan degradation indicating an upregulation of MMPs. This was confirmed by zymography and mass spectrometry data. We also showed that the expression of other cytokines is induced by IL-17A, which provide further insight to the pathways that are active in response to IL-17A. This exploratory study confirms that IL-17A may play a role in cartilage pathology and that the applied model may be a good tool to further investigate it.
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