Magnesium-containing intramedullary nails promote fracture healing in type 2 diabetic animal model via recruiting regulatory T cells into the fracture callus

Magnesium-containing intramedullary nails (Mg-IMN) have been shown to promote fracture healing across various types of fractures, including osteoporotic and atypical femoral fractures. However, their role in the challenging chronic inflammatory type 2 diabetes (T2D) fracture healing remains unclear. In this study, we investigated the effect of Mg-IMN on fracture healing in a T2D mouse model and explored the involvement of regulatory T cells (Tregs) in this process. Our results demonstrated that Mg-IMN promotes fracture healing in Lepr db/db T2D mice. At 5 days post-fracture, flow cytometry showed an increased number of Tregs in the fracture callus. Notably, depletion of Tregs via injection of PC61 neutralizing antibody abolished the promotive effect of Mg-IMN, indicating the critical role of Tregs in this process. Bulk RNA sequencing of the bone callus at 5 days post-fracture revealed significant enrichment of pathways related to chemokine signaling and CCR chemokine receptor interactions, suggesting a mechanism of Treg recruitment. Transwell migration assays in vitro preliminarily indicated the chemotactic effect of CCL19 and CCL21 in recruiting Tregs. Furthermore, Mg 2+ treatment enhanced the mRNA expression levels of amphiregulin ( Areg ) and granulin ( Grn ) in Tregs, as indicated by qRT-PCR analysis. These findings may pave the way for new applications of Mg-IMN in fracture repair and provide unique insights into osteoimmunology during the complex process of T2D fracture healing.