Lrsam1 deficiency suppresses osteoclastogenesis and attenuates bone loss through the JNK2-NFATc1 axis

Excessive osteoclast-mediated bone resorption is a major contributor to osteoporosis and other osteolytic diseases. Here, we investigated the role of the E3 ubiquitin ligase Lrsam1 in osteoclastogenesis and bone metabolism using myeloid-specific Lrsam1-deficient mice. Lrsam1 deletion increased trabecular bone mass in vivo, reduced osteoclast numbers in the distal femur, and attenuated ovariectomy-induced bone loss without significantly affecting bone formation parameters. In vitro, Lrsam1-deficient bone marrow-derived macrophages exhibited impaired RANKL-induced osteoclast differentiation, as indicated by fewer TRAP-positive multinucleated cells, impaired F-actin ring formation, and reduced expression of osteoclast-related genes and proteins. Proteomic analysis identified JNK2 as a candidate mediator of Lrsam1 deficiency. Consistently, JNK2 protein levels were elevated in Lrsam1-deficient cells, whereas inhibition of JNK signaling partially rescued osteoclast differentiation and restored NFATc1 nuclear translocation. Taken together, these findings identify Lrsam1 as a positive regulator of osteoclastogenesis and suggest that its effects on osteoclast differentiation are associated, at least in part, with JNK2-dependent regulation of NFATc1 nuclear translocation.