Bone Abstracts

Introduction: Cartilage intermediate layer protein (CILP) is a promising marker of osteoarthritis (OA). CILP is an extracellular matrix glycoprotein, which is produced by cartilage chondrocytes. Still, there are data that CILP could be found also in other tissues. We aimed to investigate the expression level of CILP mRNA in the synovial membrane and evaluated the associations of CILP expression with traits of radiographic knee OA (rKOA) and features of histological synovitis.

Methods: The synovial biopsy samples were harvested during arthroscopy from 44 subjects with chronic knee complaints. The rKOA features (the presence of osteophytes, joint space narrowing (JSN)) were evaluated on plain radiographs. Different histological features of synovitis (number of synovial lining cells, lymphocyte infiltration, fibrosis, hyperaemia, fibrin deposits, and perivascular oedema) were graded 0–3 in synovial biopsies. Expression of CILP mRNA in synovial samples was measured by the TaqMan gene expression assay.

Results: The early rKOA (grade I) was found in 29 subjects and late rKOA (grade II–III) in ten subjects. The CILP mRNA expression was observed in 96% of synovial samples. The downregulation of CILP mRNA in synovial membrane was observed in patients with late stage of JSN, than compared to subjects without radiographic changes (P=0.006).The analysis of histological synovitis features revealed that CILP mRNA is overexpressed in fibrotic samples and correlated with severity of synovial fibrosis (P=0.31, P=0.026). Additionally, the negative correlation with thickness of synovial lining (P=−0.4, P=0.003) and CILP mRNA was observed.

Conclusion: • The production of CILP seems to be not restricted to cartilage. The presence of CILP mRNA in synovial tissue suggests its possible production in synovium.

• Upregulation of CILP mRNA in fibrotic synovial tissue could suggest the involvement of CILP in OA-associated remodelling of the synovial membrane.

• Synovial production of CIlLP mRNA seems to be downregulated in late radiographic stage of knee OA.