Circulating MicroRNAs as Biomarkers of Osteoporosis and Fragility Fractures

Context: Measurement of circulating microRNAs (miRNAs) as potential biomarkers of fragility fracture risk has recently become a subject of investigation. Objective: Measure by next-generation sequencing (NGS), global miRNA expression in serum samples of osteoporotic subjects vs individuals with normal bone mineral density (BMD). Design: Samples were collected from patients with different bone phenotypes and/or fragility fractures who did not receive any antiresorptive and/or bone-forming drug at the time of blood collection. Setting: Samples and data were collected at 7 medical centers in Italy. Patients: NGS prescreening: 50 osteoporotic patients vs 30 individuals with normal BMD. Droplet digital polymerase chain reaction (ddPCR) validation: 213 patients with different bone phenotypes, including the NGS-analyzed cohort. Results: NGS identified 5 miRNAs (miR-8085, miR-320a-3p, miR-23a-3p, miR-4497, miR-145-5p) differentially expressed in osteoporosis cases without fractures vs controls. ddPCR validation confirmed lower c-miR-23a-3p expression in osteoporotic patients, with or without fracture, than in osteopenic and normal subjects and increased c-miR-320a-3p expression in osteoporotic patients with fracture and lower expression in osteoporotic patients without fracture. ddPCR analysis showed a significantly increased expression of miR-21-5p in osteoporotic patients, with or without fracture, than in osteopenic and normal subjects, not evidenced by the NGS prescreening. Discussion: Our study confirmed levels of c-miR-23a-3p and c-miR-21-5p as able to distinguish osteoporotic patients and subjects with normal BMD. Increased levels of c-miR-320a-3p specifically associated with fractures, independently by BMD, suggesting c-miR-320a-3p as a prognostic indicator of fracture risk in osteoporotic patients, to be confirmed in prospective studies on incident fractures.