The discovery of receptor activator of nuclear factor-ĸB 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.
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.
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.
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.

© 2021 The Authors. Clinical and Translational Medicine published by John Wiley & Sons Australia, Ltd on behalf of Shanghai Institute of Clinical Bioinformatics.