Serum miR-519d-3p and BMP2: potential early diagnostic markers and their mechanism in delayed fracture healing.

Background: Delayed fracture healing (DFH) affects patients' quality of life, and there are limitations in diagnosis by CT scan. The purpose of the study is to evaluate the potential and mechanism of clinical application of miRNAs in DFH for early diagnosis and intervention.

Methods: Serum samples were obtained from delayed and normal fracture healing patients and the levels of miR-519d-3p and BMP2 were measured by RT-qPCR, and the value of both in the diagnosis of DFH was assessed by ROC curve. Cell viability and apoptosis were monitored using CCK8 kit and flow cytometry, respectively, and mRNA expression of osteogenesis and apoptosis-related genes were detected by RT-qPCR. The molecular interactions were verified using luciferase reporter gene system and RIP technique.

Results: Up-regulation of miR-519d-3p expression and down-regulation of BMP2 in the serum of fracture patients four weeks after surgery can be used as an early warning marker of DFH and a risk factor for poor fracture healing. Further studies showed that overexpression of miR-519d-3p markedly inhibited the expression of RUNX2, OCN and ALP and prevented osteoblast differentiation. Meanwhile, it inhibited cell viability, promoted apoptosis, upregulated Bax and Cleaved-caspase-3 mRNA expression, and downregulated Bcl-2 expression. BMP2, targeted by miR-519d-3p, enhanced osteogenesis and reversed the inhibitory of action miR-519d-3p.

Conclusions: Serum miR-519d-3p and BMP2 can be used as early diagnostic markers for DFH. miR-519d-3p inhibited osteogenesis by targeting BMP2, which may slow down fracture healing.