Cytokine and catabolic enzyme expression in synovium, synovial fluid and articular cartilage of naturally osteoarthritic equine carpi

Reasons for performing study: Understanding the expression of catabolic and anabolic genes during osteoarthritis progression should help to identify the major mediators of the disease.

Objective: To compare the cytokine and anabolic marker concentrations in synovium, synovial fluid and cartilage between normal and osteoarthritic joints.

Methods: Carpi from horses age 2-11 years were used. Tissues were harvested at the time of surgery or euthanasia, and RNA was isolated for RT-PCR analysis. Tumour necrosis factor alpha (TNFα), interleukin-1beta (IL-1β), aggrecanase 1 (ADAMTS-4), aggrecanase 2 (ADAMTS-5), matrix metalloproteinase-13 (MMP-13), interleukin 17 (IL-17) and collagen type I alpha 1(Col-1) expression were determined in synovium. TNFα, IL-1β, ADAMTS-4, ADAMTS-5, MMP-13, IL-17, collagen type IIB (Col-2B), and aggrecan expression were determined in cartilage. TNFα concentration in the synovial fluid was determined by enzyme-linked immunosorbent assay (ELISA).

Results: Expression of TNFα, ADAMTS-5 and MMP-13 was significantly increased in synovial tissue from OA joints. Synovial membrane IL-1β abundance showed only moderate elevations in OA, without reaching significant levels. Cytokine expression was increased significantly in OA cartilage samples, particularly TNFα, IL-1β, ADAMTS-4 and MMP-13; and collagen type I expression was significantly increased in synovial tissues from OA groups. Collagen type II message was diminished in mild and moderate stages of OA, but rebounded to significant elevations in severely degenerate joints. Conversely, aggrecan levels significantly declined in cartilage from all OA groups. Synovial fluid TNFα peptide concentration was significantly increased in severe OA cases.

Conclusion: TNFα was increased in all degrees of equine OA, and was abundantly expressed in synovial membrane and cartilage. IL-1β was overexpressed in OA cartilage, but not to a significant extent in synovium.

Potential relevance: Control of TNFα should be considered further as a target in the treatment of OA. ADAMTS-4 may be the primary aggrecanase causing cartilage breakdown in OA.