Augmenting MNK1/2 activation by c-FMS proteolysis promotes osteoclastogenesis and arthritic bone erosion

摘要

Osteoclasts are bone-resorbing cells that play an essential role in homeostatic bone remodeling and pathological bone erosion.Macrophage colony stimulating factor(M-CSF)is abundant in rheumatoid arthritis(RA).However,the role of M-CSF in arthritic bone erosion is not completely understood.Here,we show that M-CSF can promote osteoclastogenesis by triggering the proteolysis of c-FMS,a receptor for M-CSF,leading to the generation of FMS intracellular domain(FICD)fragments.Increased levels of FICD fragments positively regulated osteoclastogenesis but had no effect on inflammatory responses.Moreover,myeloid cell-specific FICD expression in mice resulted in significantly increased osteoclast-mediated bone resorption in an inflammatory arthritis model.The FICD formed a complex with DAP5,and the FICD/DAP5 axis promoted osteoclast differentiation by activating the MNK1/2/EIF4E pathway and enhancing NFATcl protein expression.Moreover,targeting the MNK1/2 pathway diminished arthritic bone erosion.These results identified a novel role of c-FMS proteolysis in osteoclastogenesis and the pathogenesis of arthritic bone erosion.