# C-X-C motif chemokine ligand 13 suppresses osteoclast differentiation via interference with RANKL–RANK interaction

## TL;DR

CXCL13 suppresses osteoclast formation by blocking RANKL-RANK signaling, offering a new target for treating bone loss disorders.

## Contribution

CXCL13 is newly identified as a suppressor of osteoclast differentiation via interference with RANKL-RANK interaction.

## Key findings

- CXCL13 inhibits RANKL-induced osteoclast formation and disrupts F-actin ring assembly.
- CXCL13 promotes apoptosis in mature osteoclasts and suppresses MAPK and NF-κB signaling.
- CXCL13 competitively interferes with RANKL-RANK binding and downstream TRAF6 signaling.

## Abstract

Osteoclastogenesis, the differentiation of osteoclasts from monocyte/macrophage precursors, is essential for physiological bone remodeling but contributes to pathological bone loss in arthritis, osteoporosis, and bone metastasis when dysregulated. CXCL13 is a CXC chemokine well recognized for its role in immune regulation; however, its function in osteoclast biology remains undefined. This study aimed to investigate the effects of CXCL13 on RANKL-induced osteoclastogenesis.

RAW264.7 cells were stimulated with RANKL to induce osteoclastogenesis. Osteoclast formation was evaluated by TRAP and F-actin ring staining, and quantitative real-time PCR (qPCR). GEO bioinformatic analysis revealed gene expression changes during RANKL-induced osteoclastogenesis. Mature osteoclast apoptosis was analyzed by cleaved caspase-3 immunofluorescence staining. MAPK and NF-κB signaling activation was examined by Western blotting and NF-κB luciferase reporter assays. Molecular docking and co-immunoprecipitation were performed to evaluate the interaction between CXCL13 and RANK.

CXCL13 inhibited RANKL-induced osteoclast formation, suppressed osteoclast marker expression, disrupted F-actin ring assembly, and promoted apoptosis in mature osteoclasts. Mechanistically, CXCL13 attenuated MAPK and NF-κB activation and blocked p65 nuclear translocation in a CXCR5-independent manner by competitively interfering with RANKL–RANK binding and downstream RANK–TRAF6 signaling.

These findings identify CXCL13 as a novel suppressor of osteoclastogenesis by interfering with RANKL–RANK signaling, unveiling an unrecognized regulatory role in osteoclast biology and suggesting potential therapeutic relevance for bone loss disorders.