Single cell atlas of enthesitis reveals a mechanical strain responsing and SOX5 programmed SDC1+ sheath fibroblast in ankylosing spondylitis [bulk RNA-seq]

Ankylosing spondylitis (AS) is an osteoimmunology related disease characterized by enthesitis. Previous researches demonstrated that mechanical strain played the evoked role in AS enthesitis, but the detailed cell interaction and molecular mechanism in microenvironment were unclear. Herein, we constructed the hind paw loading/unloading model in SKG mice and revealed the single cell atlas of mechanical strain related enthesitis. Through single cell RNA sequencing, fibroblast was determined as the major mechanotransductive signal converter in AS enthesitis, and a SDC1+ subpopulation was identified to positively relate to both mechanical strain and disease progression. Located at the sheath side of enthesis, SDC1+ fibroblasts converted the physical strain signal into various cytokines signal, forming the interaction network with downstream inflammatory cells in the enthesitis. Furthermore, computational trajectory analysis uncovered a distinct fate branch of mechanical strain responsing SDC1+ sheath fibroblasts under the control of transcriptional factor SOX5 mediated enhancer and super-enhancer. Specifically inhibiting SOX5 expression in enthesis fibroblast using rAAV9.HAP-1 carrying siRNA sequence for Sox5 intercepted mechanical strain responsing SDC1+ sheath fibroblasts generation, and markedly remit AS enthesitis development. This study may not only contribute to the elucidation of AS pathogenesis but also provide insight into clinical therapy for AS.