ABSTRACT
Spinal supraspinous ligament (SL) osteogenesis is the key risk of ankylosing spondylitis (AS), with an unclear pathogenesis. We previously found that transforming growth factor ß1 (TGF-ß1), bone morphogenetic proteins (eg BMP2) and type III TGF-ß1 receptor (TßRIII) expression were markedly up-regulated in AS-SLs. However, the roles of these closely related molecules in AS are unknown. Here, we showed that BMP2, TGF-ß1, TßRIII and S100A4 (a fibroblast marker) were abundant in active osteogenic AS-SL tissues. In vitro, AS-SL fibroblasts (AS-SLFs) showed high BMP2, TGF-ß1 and TßRIII expression and auto-osteogenic capacity. We further evaluated the role of TßRIII in the osteogenesis of normal SLFs. BMP2 combined with TGF-ß1 induced the osteogenesis of TßRIII-overexpressing SLFs, but the activity was lost in SLFs upon TßRIII knockdown. Moreover, our data suggested that BMP2 combined with TGF-ß1 significantly activated both TGF-ß1/Smad signalling and BMP2/Smad/RUNX2 signalling to induce osteogenesis of SLFs with TßRIII up-regulation. Furthermore, our multi-strategy molecular interaction analysis approach indicated that TGF-ß1 presented BMP2 to TßRIII, sequentially facilitating BMP2 recognition by BMPR1A and promoting the osteogenesis of TßRIII-overexpressing SLFs. Collectively, our results indicate that TGF-ß1 combined with BMP2 may participate in the osteogenic differentiation of AS-SLF by acting on up-regulated TßRIII, resulting in excessive activation of both TGF-ß1/Smad and BMP2/BMPR1A/Smad/RUNX2 signalling.
