MicroRNAs in Serum Exosomes as Circulating Biomarkers for Postmenopausal Osteoporosis with Fragility Fractures

Background Postmenopausal osteoporosis (PMOP) brings a heavy burden to society and seriously affects the quality of life of elderly people. Circulating biomarkers based on miRNAs, especially exosomal miRNAs, are widely studied. However, miRNAs in serum exosomes have not yet been reported in PMOP. The present study aimed to investigate the differences in miRNA expression profiles in PMOP with fragility fractures to identify the key circulating miRNAs in serum exosomes and to validate these molecules as potential biomarkers. Methods Postmenopausal women with osteoporotic fracture (severe osteoporosis, SOP group) and normal bone mass (Ctrl group) were selected from community. Serum exosomes were isolated by traditional differential ultracentrifugation from participants. Isolated exosomes were identified by electron microscopy, western blotting and nanoparticle-tracking analysis and then examined for exosomal miRNAs sequencing. Target gene pathways enrichment of differently expressed miRNAs were performed by the online bioinformatics tools TargetScan and DAVID. Moreover, the function of miRNAs associating with bone mineral density (BMD) on bone turnover were further confirmed by transfecting these miRNAs into human bone marrow mesenchymal stem cells (hBMSCs) to detect ALP activities. Results Compared to control group, 170 miRNAs were found to be significantly upregulated and 69 miRNAs were downregulated in SOP group. Three miRNAs (miR-324-3p, miR-766-3p and miR-1247-5p) were found to be associated with BMD of L1-L4, FN and TH, while miR-330-5p and miR-3124-5p were associated with BMD of FN and TH. Target gene signaling pathways analysis of these five miRNAs showed that Wnt signaling pathway was the most enrichment pathway relating to bone metabolism. Furthermore, miR-330-5p was found to promote the ALP activity of hBMSCs, while mir-3124-5p showed the opposite result. Conclusion Serum exosomal miRNAs were differentially expressed in postmenopausal osteoporosis patients with fragility fractures. Our study provides the first evidence that exosomal miRNA profiling revealed aberrant circulating miRNA in postmenopausal osteoporosis. MiR-324-3p, miR-766-3p, miR-1247-5p, miR-330-5p and miR-3124-5p, which were associated with BMD, may serve as candidate biomarkers for the diagnosis of PMOP with fragility fractures and provide future research directions.