Serum miR-539-5p decreases in ankylosing spondylitis and regulates osteogenic and osteoclastogenic phenotypes in vitro via SPP1

Reliable biomarkers for the early diagnosis of ankylosing spondylitis (AS) and for monitoring its pathological bone remodeling imbalance remain insufficient. This study aimed to determine whether miR-539-5p can serve as a diagnostic biomarker and whether it modulates osteogenic and osteoclast differentiation in vitro by targeting SPP1 . Serum samples were collected from AS patients, a Lumbar Muscle Strain (LMS) group, and Healthy Controls (HC). Induced MC3T3-E1 and RAW264.7 cells were transfected with miR-539-5p mimics/inhibitors. Biological functions and mechanisms were evaluated using CCK-8, ALP/TRAP activity assays, qRT-PCR, Western blot, and dual-luciferase reporter assays. Rescue experiments were performed using an SPP1 overexpression plasmid. Serum miR-539-5p was significantly downregulated in AS patients and showed high diagnostic accuracy in distinguishing AS from LMS (AUC = 0.881). It was also identified as an independent protective factor. In vitro, miR-539-5p overexpression suppressed the DEX-induced increase in osteoblast viability, as well as osteoclastogenesis and abnormal ALP/TRAP activities. miR-539-5p directly targeted SPP1 , whose mRNA expression was negatively correlated with miR-539-5p in patient sera. Furthermore, SPP1 overexpression substantially attenuated the regulatory effects of the miR-539-5p mimic. Our study suggests that serum miR-539-5p may serve as a promising diagnostic biomarker for AS. It may also influence cellular phenotypes in in vitro bone remodeling cell models by targeting SPP1 and partially modulating osteogenic and osteoclast differentiation.