# Lactate-Driven Reprogramming of Monocyte Bridges Bone Loss in Inflammatory Comorbidities

## TL;DR

This study reveals how lactate affects monocytes to cause bone loss in inflammatory diseases like periodontitis and rheumatoid arthritis.

## Contribution

The study identifies a lactate-driven immunometabolic axis linking immune activation and bone resorption in comorbid inflammatory diseases.

## Key findings

- Elevated lactate levels correlate with disease severity in periodontitis and rheumatoid arthritis models.
- Lactate metabolism genes are upregulated in specific monocyte subsets, promoting inflammation and bone loss.
- SAT1, TET2, and HIF1A are core lactate-related genes with diagnostic potential for inflammation-related bone loss.

## Abstract

Inflammatory bone loss is a shared pathological feature of chronic diseases such as periodontitis (PD) and rheumatoid arthritis (RA). Despite affecting distinct tissues, these diseases exhibit a bidirectional association and converge on common immune-mediated mechanisms of bone resorption. To uncover the molecular drivers underlying bone destruction across inflammatory comorbidities, we combined bioinformatic analyses with experimental validation, using PD and RA as clinically relevant models of inflammatory disease comorbidities. Elevated blood lactate levels were observed in murine models of PD and RA and correlated positively with disease severity. Single-cell RNA sequencing data from PD and RA cohorts revealed upregulation of lactate metabolism-related genes in specific monocyte subsets, accompanied by enhanced pro-inflammatory signaling and osteoclastogenic programs. Using multiple machine learning approaches, SAT1, TET2 and HIF1A were identified as core lactate-related genes with strong diagnostic potential for both diseases. In vivo and in vitro experiments further validated that lactate-driven reprogramming of monocytes, marked by activation of core lactate-related genes in circulating monocytes and local macrophages, functionally connects immune activation with exacerbated bone resorption in comorbid PD and RA. Together, these findings define a lactate-driven immunometabolic axis connecting immune responses and bone remodeling and identify SAT1, TET2 and HIF1A as potential biomarkers for inflammation-related bone loss.