GTS-21 alleviates murine collagen-induced arthritis through inhibition of peripheral monocyte trafficking into the synovium

Emerging preclinical and clinical evidence reveals a critical role for the cholinergic anti-inflammatory pathway (CAP) in mediating rheumatoid arthritis (RA). Activation of CAP via vagus nerve stimulation or alpha 7 nicotinic acetylcholine receptor (α7nAChR) agonists has previously been shown to significantly reduce inflammation and improve outcomes in animal models of experimental arthritis. In this study, we sought to determine the protective mechanism of CAP on inflammatory arthritis, specifically RA, by using a selective α7nAChR agonist, GTS-21, to examine the role of CAP in the recruitment of monocytes/macrophages into the synovium in a collagen-induced arthritis (CIA) mouse model. We found that GTS-21 ameliorated systemic and local synovial inflammation, thereby reducing synovial macrophage infiltration in CIA mice. Using in vivo imaging, we further demonstrated that GTS-21 suppressed the trafficking of monocytes into inflamed joints, while our in vitro Transwell assay data confirmed that GTS-21 reduced the migratory ability of monocytes. In addition, we found that GTS-21 reduced the number of peripheral inflammatory monocytes and down-regulated expression of the chemokines CCR2 and CCR5 on monocytes and CCL2 in the paw tissue. GTS-21 also mediated the expression levels of the adhesion molecules LFA-1 and VLA-4 on monocytes and VCAM-1 in the paw tissue, thereby blocking monocyte adhesion to the extracellular matrix. Together, our data demonstrate that GTS-21 alleviates arthritis by inhibiting peripheral monocyte trafficking into the synovium. Our findings describe a novel mechanism through which the cholinergic signaling pathway can reduce synovial inflammation in RA patients.