Methotrexate inhibits glucocorticoids-induced osteoclastogenesis via activating IFN-γR/STAT1 pathway in the treatment of rheumatoid arthritis.

Objectives: Rheumatoid arthritis (RA) is a chronic autoimmune disease characterised by the synovitis and bone erosion. The combination therapy of glucocorticoids (GCs) and methotrexate (MTX) is recommended in early RA management, although the precise underlying mechanism of action remains unclear. This study is aimed to clarify the mechanism of MTX in combined with GC in treating RA.

Methods: GC-induced osteoporosis (GIOP) mouse model was used to investigate the bone-protective role of MTX. Lipopolysaccharide-induced arthritis mouse model was used to evaluate the anti-inflammatory effects of GCs and MTX. Functional role of MTX on osteoclastogenesis was assessed by trap staining and micro-computer tomography. Western blot, RT-qPCR and coimmunoprecipitation were used to explore the underlying mechanisms.

Results: We demonstrate that GCs, but not MTX, rapidly inhibited synovitis in arthritis model. MTX treatment was observed to inhibit osteoclastogenesis induced by GC in vitro and mitigate bone loss attributed by GIOP. GCs were found to augment the interaction between the membrane GC receptor (mGR) and signal transducer and activator of transcription 1 (STAT1), leading to the suppression of IFN-γR/STAT1 signalling pathways. Interestingly, MTX was found to inhibit osteoclastogenesis induced by GCs through the enhancement of the A2AR and IFN-γR interaction, thereby activating the IFN-γR/STAT1 signalling cascade. Consequently, this process results in a reduction in the mGR and STAT1 interaction.

Conclusions: Our study provides compelling evidence that MTX can make GCs effectively to suppress synovitis and reduce bone loss induced by GCs. This sheds light on the potential mechanistic insights underlying the efficacy of GCs in conjunction with MTX for treating RA.