Revisiting the Role of Interleukin-1 Pathway in Osteoarthritis: Interleukin-1α and-1β, and NLRP3 Inflammasome Are Not Involved in the Pathological Features of the Murine Menisectomy Model of Osteoarthritis

Background: Innate immune response components such as toll-like receptors (TLRs) and NLRP3-inflammasome act in concert to increase IL-1 alpha/beta secretion by synovial macrophages. Previous results suggest that IL-1 alpha/beta) could be an important mediator involved in the pathogenesis of osteoarthritis (OA). Objectives: The aim of our study was to evaluate the role of NLRP3, IL-1 beta, and IL-1 alpha in the menisectomy (MNX) model of murine OA. Methods: Murine chondrocytes (CHs) and bone marrow-derived machrophages (BMDM) were stimulated with hydroxyapatite (HA) crystals, a form of calcium containing crystal found in human OA, and IL-1 beta and IL-6 secretion assayed by ELISA.Conversely, the ability of IL-l beta and IL-6 to induce CHs calcification was assessed in vitro by Alizarin red staining. Knees from 8 to 10 weeks old C57BI/6J wild-type (WT) (n = 7), NLRP3(-/-)(n = 9), IL-1 alpha(-/-) (n = 5), and IL-1 beta)(-/-)(n= 5) mice were menisectomized, using the sham-operated contralateral knee as control. 8 weeks later, knee cartilage degradation and synovial inflammation were evaluated by histology. In addition, apoptotic chondrocytes, metalloproteases activity, and collagen-type 2 expression were evaluated in all mice. Joint calcification and subchondral bone parameters were quantified by CT-scan in WT and IL-1 beta(-/-) menisectomized knees. Results: In vitro, HA crystals induced significant increased IL-6 secretion by CHs, while IL-1 beta) remained undetectable.Conversely, both IL-6 and IL-1 beta) were able to increase chondrocytes mineralization. In vivo, operated knees exhibited OA features compared to sham-operated knees as evidenced by increased cartilage degradation and synovial inflammation. In menisectomized KO mice, severity and extent of cartilage lesions were similar (IL-1 alpha(-/-) mice) or exacerbated (IL-1 beta(-/-) and NLRP3(-/-) mice) compared to that of menisectomized WT mice. Metalloproteases activity, collagen-type 2 expression,chondrocytes apoptosis, and synovial inflammation were similar between KO and WT mice menisectomized knees. Moreover, the extent of joint calcification in osteoarthritic knees was comparable between IL-1 beta(-/-) and WT mice. Conclusions: MNX knees recapitulated features of OA, i.e, cartilage destruction, synovial inflammation, cell death, and joint calcification. Deficiency of IL-1 alpha did not impact on the severity of these features, whereas deficiency of IL-1 beta or of NLRP3 led to increased cartilage erosion. Our results suggest that IL1 alpha and IL-1 beta,are not key mediators in this murine OA model and may explain the inefficiency of IL-1 targeted therapies in OA.