Single-cell profiling reveals senescent bone marrow mesenchymal stem cell subpopulations driving pathological ossification in ankylosing spondylitis.

OBJECTIVES

Aberrant new bone formation is a hallmark of ankylosing spondylitis (AS), yet the cellular mechanisms remain unclear. Bone marrow-derived mesenchymal stem cells (BMSCs) are crucial for skeletal homeostasis and may be pathologically reprogrammed under chronic inflammation. We aimed to characterize the cellular heterogeneity and differentiation states of BMSCs in AS, identify BMSC subpopulations associated with structural damage, and explore their molecular features and potential therapeutic targets.

METHODS

Single-cell RNA sequencing was performed on BMSCs from 12 AS patients stratified into severe structural damage (SSD, n = 9) and no structural damage (NSD, n = 3) groups based on mSASSS and SPARCC-SSS assessments. After quality control, 47 628 cells were analysed by unsupervised clustering, trajectory inference, metabolic profiling, pathway enrichment and in silico drug screening to characterize pathogenic subpopulations.

RESULTS

The analysis revealed eight BMSC subpopulations forming a continuum from progenitors to lineage-committed cells. A distinct senescence-related cluster (SRC) was identified as the predominant population in patients with advanced syndesmophytes. The SRC displayed a dual phenotype of cellular senescence and hyperactive metabolism, characterized by elevated glycolysis and oxidative phosphorylation. This state supported the secretion of matrix-remodeling factors (MMP2) and inflammatory cytokines (IL-6). A specific gene signature (CDR1, PLPPR2, CMBL, SRXN1 and PPP1R3C) linked oxidative stress to this aberrant differentiation trajectory. Furthermore, computational prediction highlighted JAK inhibitors (baricitinib and filgotinib) as potential therapeutics to attenuate the SRC phenotype.

CONCLUSION

This study identifies a senescence-associated, hypermetabolic BMSC subpopulation that is closely associated with structural progression in AS, providing a cellular basis for pathological bone formation and suggests that JAK inhibitors may serve as effective agents to reverse this pathogenic BMSC signature.