The arthritis severity locusCia5dis a novel genetic regulator of the invasive properties of synovial fibroblasts

Abstract

Objective The synovial fibroblast, or fibroblast‐like synoviocyte (FLS), has a central role in pannus invasion and destruction of cartilage and bone in rheumatoid arthritis (RA). However, regulation of the FLS remains incompletely understood. The aim of this study was to determine whether the invasive properties of FLS are genetically regulated by arthritis severity loci. Methods DA rats (arthritis susceptible) and rat strains congenic for arthritis‐protective intervals were studied. Primary FLS cell lines were generated from each strain and used in a well‐established FLS invasion model through a collagen‐rich barrier. Cells or culture supernatants were analyzed for gene expression, activity of different matrix metalloproteinases (MMPs), cytoskeleton integrity, and cell proliferation. Results The median number of FLS from DA.F344(Cia5d) rats that invaded through the collagen‐rich barrier was reduced 86.5% compared with the median number of invading FLS from DA rats. Histologic examination showed that DA.F344(Cia5d) rats preserved a normal joint without pannus, hyperplasia, or erosions. FLS from DA.F344(Cia5d) rats produced significantly lower levels of active MMP‐2 compared with FLS from DA rats, but the levels of proMMP‐2 and MMP‐2 messenger RNA in DA.F344(Cia5d) rats were similar to those in DA rats. Treatment of FLS from DA rats with an MMP‐2 inhibitor reduced cell invasion to a level similar to that in DA.F344(Cia5d) rats, demonstrating that MMP‐2 activity accounted for the difference between FLS from these 2 strains. Analysis of MMP‐2–activating pathways revealed increased levels of soluble membrane type 1 (MT1)–MMP in DA rats compared with DA.F344(Cia5d) rats. Conclusion These data represent the first evidence for a genetic component in the regulation of FLS invasion. A gene located within the Cia5d interval accounts for this effect and operates via the regulation of soluble MT1‐MMP production and MMP‐2 activation. These observations suggest novel potential pathways for prognostication and therapy.