Unveiling Epigenetic Molecular Mechanisms in Bone Fracture Risk: Insights From 731 Immune Cells, 1400 Metabolites,...

The aging population and advancements in medical science have heightened the focus on fractures, which affect over 150 million individuals annually, with substantial health and economic consequences.

This study investigated the potential causal relationships between 731 immune cells, 1400 metabolites, and nine fracture types using Mendelian randomization (MR).

A combination of bidirectional MR, two-sample MR, and mediation MR was employed to assess potential causal links. Sensitivity analysis was performed using MR-PRESSO. Bioinformatics analyses, including functional enrichment and protein-protein interaction (PPI) network analysis, were conducted. Colocalization analysis was used to examine associations between key genes and fractures.

Bidirectional MR identified 7 immune cell subtypes (e.g., B cells, Tregs, and monocytes) and 11 metabolite classes (e.g., lipids, amino acids) with significant MR-supported associations with fracture risk, with effects varying by skeletal site. Mediation analysis revealed that the increased wrist fracture risk associated with CD28+CD45RA-CD8br T cells was mediated by 5-methylthioadenosine (19.6%), while the reduced foot fracture risk linked to CD28-CD8dim T cells was mediated via the taurine-to-cysteine ratio (20.9%). SNP nearest gene integration highlighted enriched pathways related to immune response, cell adhesion, and metabolism. PPI network analysis pinpointed 9 hub genes, six of which (CD8A, PRKACA, IL-6, ITGB1, ITPR1, and STAT3) showed strong colocalization evidence with fractures. Moreover, DNA methylation at cg09664550 (ITGB1) showed the most significant negative impact on thoracic spine fractures (OR = 1.986), whereas cg18112163 (STAT3) conferred the strongest protective effect against foot fractures (OR = 0.602; all p  < 0.05).

The findings suggest that immune cells and metabolites may have genetically predicted effects on fracture risk, with metabolites potentially serving as key mediators. Critical pathways, hub genes, and fracture-associated SNPs were identified, along with potential epigenetic regulation via methylation sites. These preliminary insights offer novel directions for future research into the underlying mechanisms of fracture risk and intervention.