Interleukin-1 is not involved in synovial inflammation and cartilage destruction in collagenase-induced osteoarthritis

OBJECTIVE: Interleukin-1 (IL-1) is an alleged important cytokine in osteoarthritis (OA), although the exact contribution of IL-1 to joint destruction remains unclear. Here we investigated the involvement of IL-1alpha and IL-1beta in joint pathology during collagenase-induced OA (CiOA). METHODS: CiOA was induced in wild type (WT) and IL-1alphabeta-/- mice. Additionally, IL-1 signaling was inhibited in WT mice with CiOA using osmotic pumps containing IL-1RA. Joint pathology was assessed using histology. Activity of cartilage-degrading enzymes was determined using antibodies against aggrecan neo-epitopes VDIPEN and NITEGE. Synovial gene expression was analyzed using quantitative real-time polymerase chain reaction (qRT-PCR). Serum protein levels were measured with Luminex or enzyme-linked immunosorbent assay (ELISA). RESULTS: Synovial IL-1beta expression was strongly elevated 7 days after induction of CiOA in WT mice but decreased afterwards, whereas S100A8/A9, previously described to aggravate OA, remained elevated for 21 days. Remarkably, synovial inflammation was comparable between WT and IL-1alphabeta-/- mice on day 7 of CiOA. In line, synovial mRNA expression of genes involved in IL-1 signaling and inflammatory mediators was comparable between WT and IL-1alphabeta-/- mice, and serum levels for Keratinocyte Chemoattractant (KC)/IL-6/S100A8/S100A9/IL-10 were equal. Synovial matrix metalloproteinase (MMP)/aggrecanase expression and activity in cartilage was not different in WT and IL-1alphabeta-/- mice on day 7 of CiOA. Cartilage destruction on day 42 was not different between WT and IL-1alphabeta-/- mice, which was supported by our finding that IL-1RA treatment in WT mice with CiOA did not alter joint destruction. CONCLUSIONS: IL-1alpha and IL-1beta are not involved in synovial inflammation and cartilage destruction during CiOA, implicating that other mediators are responsible for the joint damage