Background The discovery of receptor activator of nuclear factor‐?B ligand (RANKL) as the final effector in the pathogenesis of osteoporosis has led to a better understanding of bone remodeling. When RANKL binds to its receptor (RANK), osteoclastic differentiation and activation are initiated. Herein, we propose a strategy using a novel RANKL variant as a competitive inhibitor for RANKL. The RANKL variant activates LGR4 signaling, which competitively regulates RANK and acts as an immunogen that induces anti‐RANKL antibody production. Methods We modified the RANK‐binding site on RANKL using minimal amino acid changes in the RANKL complex and its counterpart receptor RANK and tried to evaluate the inhibitory effects on osteoclastogenesis. Results The novel RANKL variant did not bind RANK in osteoclast progenitor cells, but activated LGR4 through the GSK3‐β signaling pathway, thereby suppressing activated T cell cytoplasmic nuclear factor calcineurin‐dependent 1 (NFATc1) expression and activity during osteoclastogenesis. Our RANKL variant generated high levels of RANKL‐specific antibodies, blocked osteoclastogenesis, and inhibited osteoporosis in ovariectomized mouse models. Generated anti‐RANKL antibodies showed a high inhibitory effect on osteoclastogenesis in vivo and in vitro . Conclusions We observed that the novel RANKL indeed blocks RANKL via LGR4 signaling and generates anti‐RANKL antibodies, demonstrating an innovative strategy in the development of general immunotherapy. Schematic diagram of mRANKL‐MT3 in dual inhibitory effect against RANKL during osteoclastogenesis. The first effect of mRANKL‐MT3 is induced to RANKL‐LGR4 modulation of the RANKL–NFATc1 signaling cascade by a negative‐feedback mechanism, which controls osteoclast activity. The second effect is induced to anti‐RANKL generation by mutant RANKL, which inhibits osteoclastogenesis and bone erosion.
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