miR-342-3p as a Candidate Biomarker and Potential Regulator of Osteogenic Dysfunction in Experimental Radiation-Combined Bone Injury

Radiation-combined bone injury (RCBI) is commonly caused by nuclear incidents, yet its healing mechanisms are poorly understood and therapeutic options remain limited. This study explores the expression and regulatory role of miR-342-3p in experimental RCBI using human radiation-exposure and fracture cohorts, a murine RCBI model, and irradiated mouse bone marrow stromal cell (mBMSC) assays.

Differentially expressed miRNAs linked to radiation exposure and fracture healing were identified from GEO datasets and cross-analyzed to prioritize candidates. Target genes were predicted by TargetScan 8.0 and validated by dual-luciferase assays. Plasma miR-342-3p was measured in glioma patients undergoing radiotherapy, long-bone fracture patients, and healthy volunteers. Murine RCBI and irradiated mBMSC models were established to characterize pathophysiology; the effect of a miR-342-3p inhibitor on osteogenic function was assessed in vitro.

Circulating miR-342-3p is context-dependently regulated: its change during early fracture healing was normalization-dependent (upregulated with the miR-16-based two-step normalization but reversed with spike-in-only normalization) and could not be reliably established, whereas it was downregulated post-radiotherapy. Dual-luciferase assays confirmed RUNX2 as a direct target. In murine RCBI, radiation and bone injury exerted interactive (radiation-dominant) effects on hematopoiesis and synergistic suppression of osteogenic protein expression; histological evaluation at day 7 revealed reduced collagen deposition and impaired early callus formation. Intracellular miR-342-3p was upregulated in irradiated mBMSCs, with exploratory correlation analysis (n=3 per group) suggesting altered association patterns between miR-342-3p and osteogenic gene expression under irradiation; these descriptive correlations do not establish a mechanistic switch. The miR-342-3p inhibitor reduced radiation-induced apoptosis and restored osteogenic differentiation in vitro.

This exploratory study demonstrates that circulating miR-342-3p is differentially regulated by radiation and fracture healing in separate human cohorts, although the fracture-associated direction was normalization-dependent and could not be reliably established, and its intracellular expression is associated with altered osteogenic gene regulation in irradiated mBMSCs. These findings identify miR-342-3p as a preliminary candidate biomarker and regulator of osteogenic dysfunction in experimental RCBI.