Halofuginone ameliorates autoimmune arthritis by regulating the balance between Th17 and regulatory T cells and inhibiting osteoclastogenesis.

Objective. The small molecule halofuginone (HF) has been shown to inhibit fibrosis, angiogenesis, and tumor progression. The objective of this study was to evaluate the effects of HF in preventing autoimmune arthritis in mice. Methods. The effects of HF on joint diseases were assessed by clinical scoring and histological analysis. Protein expression levels were confirmed by immunohistochemistry, ELISA, flow cytometry, and/or Western blotting. The mRNA expression levels of various molecules were determined by real-time PCR. Proliferation of osteoclast precursors was assessed by bromodeoxyuridine uptake. Osteoclast differentiation and activity were determined by quantifying tartrate-resistant acid phosphatase (TRAP)+ multinucleated cells and area of resorbed bone. Results. Treatment with HF suppressed the development of autoimmune arthritis and reciprocally regulated Th17 cell and Foxp3+ regulatory T (Treg) cells. These effects of HF on Th17 differentiation involved increased signaling of extracellular signal-regulated kinase (ERK), and reduction of signal transducer and activator of transcription 3 (STAT3) and nuclear factor of activated T cells cytoplasmic 1 (NFATc1) expression. Furthermore, HF induced expression of indoleamine 2, 3-dioxygenase (IDO) in dendritic cells, leading to reduced production of Th17 cells. In addition, HF prevented the formation and activity of osteoclasts through suppression of transcription factors, such as activator protein-1 (AP-1) and NFATc1, and inhibited cell cycle arrest by the committed osteoclast precursors via expression of ccnd1 encoding cyclin D1. Conclusion. Taken together, our results suggest that HF is a promising therapeutic agent for the treatment of Th17 cell-mediated inflammatory diseases and bone diseases. © 2013 American College of Rheumatology.