Endothelial mesenchymal transition promotes pannus formation in ankylosing spondylitis by activation of TGF-β/SMAD signalling pathway.

Objectives: To explore the role of endothelial-mesenchymal transition (EndMT) mediated by the TGF-β/SMAD signalling pathway in the pathogenesis of ankylosing spondylitis (AS).
Methods: Serum levels of TGF-β1 were measured by enzyme-linked immunosorbent assay (ELISA) in 48 patients with AS and 15 healthy subjects. The expression levels of TGF-β1, SMAD7, CTGF, CD34 and EndMT-related markers (α-SMA, vimentin, FSP-1, VE-cadherin) in the sacroiliac joint (SIJ) of three AS patients were detected by immunohistochemistry, and three non-spondyloarthritis (SpA) autopsy samples were used as controls.
Results: Serum TGF-β1 level of AS patients was significantly higher than that of healthy controls (22971 ± 7667 pg/ml vs. 14837±4653 pg/ml, p<0.01). Compared with the non-SpA control group, the microvascular density (MVD) at the pannus formation site of SIJ in AS patients was significantly increased, accompanied by respectively increased expressions of TGF-β1, CTGF, α-SMA, vimentin, and FSP-1 (all p<0.05), whereas respectively decreased expressions of VE-cadherin and SMAD7 (p<0.01). The expression level of FSP-1 was positively correlated with levels of TGF-β1 and MVD, and negatively correlated with SMAD7.
Conclusions: Our findings show that EndMT is involved in the promotion of pannus formation by TGF-β/SMAD signalling pathway activation in AS.