Halofuginone Ameliorates Autoimmune Arthritis in Mice by Regulating the Balance Between Th17 and Treg Cells and Inhibiting Osteoclastogenesis

Objective The small molecule halofuginone has been shown to inhibit fibrosis, angiogenesis, and tumor progression. This study was undertaken to evaluate the effects of halofuginone in preventing autoimmune arthritis in mice. Methods The effects of halofuginone on joint diseases were assessed by clinical scoring and histologic analysis. Protein expression levels were confirmed by immunohistochemistry, enzyme‐linked immunosorbent assay, flow cytometry, and/or Western blotting. The expression levels of messenger RNA (mRNA) for various molecules were determined by real‐time polymerase chain reaction (PCR). Proliferation of osteoclast precursors was assessed by bromodeoxyuridine uptake. Osteoclast differentiation and activity were determined by quantifying tartrate‐resistant acid phosphatase (TRAP)–positive multinucleated cells and area of resorbed bone. Results Treatment with halofuginone suppressed the development of autoimmune arthritis and reciprocally regulated Th17 cells and FoxP3+ Treg cells. These effects of halofuginone on Th17 differentiation involved increased signaling of ERK and reduction of STAT‐3 and NF‐ATc1 expression. Furthermore, halofuginone induced the expression of indoleamine 2,3‐dioxygenase (IDO) in dendritic cells, leading to reduced production of Th17 cells. In addition, halofuginone prevented the formation and activity of osteoclasts through suppression of transcription factors, such as activator protein 1 and NF‐ATc1, and inhibited cell cycle arrest by the committed osteoclast precursors via expression of Ccnd1 encoding cyclin D1. Conclusion Taken together, our results suggest that halofuginone is a promising therapeutic agent for the treatment of Th17 cell–mediated inflammatory diseases and bone diseases.