# Cxcr2 is Required for Osteoclast Regulation, Bone Structure, and Hematological Response During Bone (Re)modeling

## TL;DR

Cxcr2 is essential for bone health and immune balance, and its absence leads to bone loss and immune issues in mice.

## Contribution

This study reveals Cxcr2's role in bone remodeling and immune regulation through a Cxcr2-deficient mouse model.

## Key findings

- Cxcr2 deficiency causes reduced bone volume and strength due to increased osteoclast activity.
- Cxcr2 KO mice show immune dysregulation with elevated cytokines and altered blood cell counts.
- Cxcr2 KO provides a model for studying inflammatory bone loss and osteoimmunological interactions.

## Abstract

Cxcr2 is a chemokine receptor involved in immune cell trafficking, inflammation, and wound healing that has been implicated in multiple diseases and cancers. However, there is a relative lack of knowledge of the in vivo functions of Cxcr2 in bone cell biology. Here we characterized the skeletal and hematological phenotypes of Cxcr2-deficient mice (Cxcr2 KO) backcrossed onto the FVB/N background. Structural and biomechanical testing demonstrated that Cxcr2 KO caused a significant loss of trabecular and cortical bone volume, altered bone geometry, and an associated loss of bone strength relative to controls. Histological analysis suggests that this is a consequence of increased osteoclast activity in Cxcr2 KO mice, while osteoblasts were not affected. Serum analysis revealed elevated levels of the bone resorption marker CTX-1, with no change in the bone formation marker P1NP, suggesting a shift towards increased osteoclast-mediated bone turnover. While both RANKL and OPG were decreased in Cxcr2 KO bones, the RANKL/OPG ratio was not different compared to WT mice. Additionally, Cxcr2 KO mice displayed systemic immune dysregulation, including elevated serum cytokines and altered hematological parameters, fewer megakaryocytes in bone marrow, higher neutrophil counts in blood, and anisocytosis. Our data point to Cxcr2 as a critical and multifunctional regulator of healthy bone homeostasis, linking immune function with skeletal integrity. This work highlights the Cxcr2 KO model as a valuable system for studying inflammatory bone loss and osteoimmunological interactions.