Suppression of Development of Ankylosing Spondylitis Through Soluble Flt-1.

BACKGROUND/AIMS Circulating monocytes/macrophages are origins of osteoclasts that mediate the development of ankylosing spondylitis (AS). Moreover, infiltrated macrophages facilitate the AS progression through production and secretion of pro-inflammatory cytokines. Thus, suppression of the recruitment of circulating monocytes/macrophages may be an effective AS treatment, which is, however, not available so far in clinic. Soluble fms-like tyrosine kinase-1 (sFlt-1) is a decoy receptor for vascular endothelial growth factor (VEGF) to compete with VEGF receptor (VEGFR2) for VEGF binding in endothelial cells, while its application in treating AS and effects on the recruitment of circulating monocytes/macrophages has not been reported before. METHODS We used a proteoglycan-induced arthritis (PGIA) mouse model for human AS. We injected sFlt-1 into the articular cavity and evaluated its effects on PGIA by incidence of arthritis, and clinical and pathological arthritis severity. We isolated and analyzed macrophages and endothelial cells in the articular cavity before and after treatment. RESULTS Injection of sFlt-1 significantly decreased the incidence and severity of PGIA in mice, and significantly reduced the number of infiltrated macrophages, possibly through reduction of vessel permeability, in a VEGFR2-dependent manner. CONCLUSION Our data suggest that sFlt-1 may have a therapeutic effect on AS, resulting from suppression of VEGF signaling-mediated recruitment of circulating monocytes/macrophages.