Interleukin‐17A Inhibition Diminishes Inflammation and New Bone Formation in Experimental Spondyloarthritis

Abstract

Objective. It remains unclear if and how inflammation and new bone formation in spondyloarthritis (SpA) are coupled. We undertook this study to assess the hypothesis that interleukin-17A (IL-17A) is a pivotal driver of both processes.Methods. The effect of tumor necrosis factor (TNF) and IL-17A on osteogenesis was tested in an osteoblastic differentiation assay using SpA fibroblast-like synoviocytes (FLS) differentiated with dexamethasone, β-glycophosphatase, and ascorbic acid. IL-17A blockade was performed in HLA-B27/human β 2 -microglobulin (hβ 2 m)-transgenic rats, which served as a model for SpA in both prophylactic and therapeutic settings. Inflammation and new bone formation were evaluated by micro-computed tomography imaging, histologic analysis, and gene expression profiling.Results. TNF and IL-17A significantly increased in vitro osteoblastic differentiation. In vivo, prophylactic blockade of IL-17A significantly delayed spondylitis and arthritis development and decreased arthritis severity. Anti-IL-17A treatment was also associated with prevention of bone loss and periosteal new bone formation. Therapeutic targeting of IL-17A after the initial inflammatory insult also significantly reduced axial and peripheral joint inflammation. This treatment was again associated with a marked reduction in spinal and peripheral structural damage, including new bone formation. RNA sequencing of target tissue confirmed that IL-17A is a key driver of the molecular signature of disease in this model and that therapeutic anti-IL-17A treatment reversed the inflammatory signature and the selected gene expression related to bone damage.Conclusion. Both prophylactic and therapeutic inhibition of IL-17A diminished inflammation and new bone formation in HLA-B27/hβ 2 m-transgenic rats. Taken together with the ability of IL-17A to promote osteoblastic differentiation of human SpA FLS, these data suggest a direct link between IL-17A-driven inflammation and pathologic new bone formation in SpA.

mTOR Blockade by Rapamycin in Spondyloarthritis: Impact on Inflammation and New Bone Formation in vitro and in vivo

“…Primary human SpA FLS (n = 11) were obtained from synovial tissue biopsies according to standardized protocol (9,25). FLS viability was assessed in the presence of vehicle (0.00005%DMSO) or rapamycin (5 nM) with WST-1 assay (Roche) and Trypan Blue 0.4% solution (Gibco) (26).…”

“…Alkaline phosphatase (ALP) staining was performed at days 7 and 14. Alizarin red (2%) staining was performed at day 21 for the osteogenic conditions without cytokines and at day 14 for conditions supplemented with cytokines, consistent with prior published protocols (9). The percentage of ALP staining and alizarin red staining in the wells were scored semi-quantitively by 2 observers, as described previously (9).…”

“…Pictures were taken on an epifluorescence imaging microscope (Leica) and analyzed using ImageJ (1.50i) software. The quantity of pS6 staining was scored on a 3point semiquantitative scale by two independent observers, who were blinded for the diagnosis of the patients, according to standardized methods (9,(27)(28)(29).…”

“…The etiology of the new bone formation in SpA remains unclear (1,10). We and others (9,11,12) have previously demonstrated that fibroblast-like synoviocytes (FLS) isolated from the synovial tissue may act as bone precursor cells and differentiate in vitro to osteoblast-like-cells. Osteoblasts are the bone-forming cells responsible for bone matrix and bone mineralization (10).…”

“…Osteoblasts are the bone-forming cells responsible for bone matrix and bone mineralization (10). It has also been demonstrated that TNFα and IL-17A can accelerate osteogenic differentiation of FLS cells in vitro (9,12).…”