Circ_0018814 promotes the osteogenic differentiation of mesenchymal stem cells in ankylosing spondylitis by regulating the miR-944/KLF4 axis

Ankylosing spondylitis (AS) is a chronic inflammatory disease primarily affecting the spine and sacroiliac joints. This study investigated the impact of circ_0018814 on the osteogenic differentiation of mesenchymal stem cells (MSCs) in AS through the regulation of the miR-944/KLF4 axis and to evaluate its potential role in the progression of AS. GSE203155 was used as an exploratory screening dataset to identify candidate circRNAs associated with osteogenic differentiation in AS-MSCs. Circ_0018814 expression was further evaluated in bone marrow samples and primary MSCs. The effects of circ_0018814 on osteogenic differentiation markers (ALP, RUNX2, COL1A1) in MSCs from AS patients were assessed using western blot, ALP assay, and alizarin red S staining. The targeting relationship between circ_0018814, KLF4, and miR-944 was confirmed through luciferase reporter and RNA immunoprecipitation assays. Fluorescence in situ hybridization was used for cellular localization. Further experiments in a murine AS model evaluated the impact of circ_0018814 on AS lesions and MSC differentiation. The results showed that overexpression of circ_0018814 significantly enhanced the expression of osteogenic markers ALP, RUNX2, and COL1A1, and promoted the osteogenic differentiation of MSCs. Additionally, circ_0018814 regulated KLF4 expression by targeting miR-944. Inhibition of miR-944 upregulated KLF4 expression and promoted osteogenic differentiation. In the AS mouse model, downregulation of circ_0018814 significantly alleviated spinal lesions, restored normal expression levels of miR-944 and KLF4, and reduced disease-related osteogenic changes. This study demonstrates that circ_0018814 plays an important role in the pathological progression of AS by regulating the miR-944/KLF4 axis. circ_0018814 may serve as a novel potential therapeutic target for AS, providing new insights for future treatment strategies. However, the in vivo findings should be interpreted cautiously because tail vein delivery of lentiviral constructs is not MSC-specific.