HLA-B27–mediated activation of TNAP phosphatase promotes pathogenic syndesmophyte formation in ankylosing spondylitis
Chin-Hsiu Liu, … , Shih-Chieh Hung, Kuo-I Lin
Chin-Hsiu Liu, … , Shih-Chieh Hung, Kuo-I Lin
Published November 4, 2019
Citation Information: J Clin Invest. 2019;129(12):5357-5373. https://doi.org/10.1172/JCI125212.
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Research Article Autoimmunity Bone biology

HLA-B27–mediated activation of TNAP phosphatase promotes pathogenic syndesmophyte formation in ankylosing spondylitis

Abstract

Ankylosing spondylitis (AS) is a type of axial inflammation. Over time, some patients develop spinal ankylosis and permanent disability; however, current treatment strategies cannot arrest syndesmophyte formation completely. Here, we used mesenchymal stem cells (MSCs) from AS patients (AS MSCs) within the enthesis involved in spinal ankylosis to delineate that the HLA-B27–mediated spliced X-box–binding protein 1 (sXBP1)/retinoic acid receptor-β (RARB)/tissue-nonspecific alkaline phosphatase (TNAP) axis accelerated the mineralization of AS MSCs, which was independent of Runt-related transcription factor 2 (Runx2). An animal model mimicking AS pathological bony appositions was established by implantation of AS MSCs into the lumbar spine of NOD-SCID mice. We found that TNAP inhibitors, including levamisole and pamidronate, inhibited AS MSC mineralization in vitro and blocked bony appositions in vivo. Furthermore, we demonstrated that the serum bone-specific TNAP (BAP) level was a potential prognostic biomarker to predict AS patients with a high risk for radiographic progression. Our study highlights the importance of the HLA-B27–mediated activation of the sXBP1/RARB/TNAP axis in AS syndesmophyte pathogenesis and provides a new strategy for the diagnosis and prevention of radiographic progression of AS.

Authors

Chin-Hsiu Liu, Sengupta Raj, Chun-Hsiung Chen, Kuo-Hsuan Hung, Chung-Tei Chou, Ing-Ho Chen, Jui-Teng Chien, I-Ying Lin, Shii-Yi Yang, Takashi Angata, Wen-Chan Tsai, James Cheng-Chung Wei, I-Shiang Tzeng, Shih-Chieh Hung, Kuo-I Lin

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Figure 1

Runx2-independent accelerated mineralization in AS MSCs.

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Runx2-independent accelerated mineralization in AS MSCs. (A) ARS stainin...
(A) ARS staining of enhanced mineralization in AS MSCs cultured under osteogenic conditions at the indicated days compared with control MSCs. (B) Quantification of ARS staining showing the differential rate in mineralization between AS MSCs and control MSCs at the indicated days. (C) RT-qPCR of Runx2 mRNA levels in AS MSCs and control MSCs at days 0 and 7 under osteogenic induction. (D–F) MSCs were transduced with lentiviral vectors carrying 2 independent shRNAs against Runx2 (shRunx2) or control shRNA (shCtrl) under osteogenic conditions. (D) RT-qPCR showing the knockdown efficiency by shRunx2 in AS MSCs and control MSCs at day 7 under osteogenic induction, normalized to the value of control MSCs expressing shCtrl. (E) ARS staining showing the effects of Runx2 knockdown on the mineralization of AS MSCs and control MSCs with quantification (F) at day 18 under osteogenic induction. (G) Immunofluorescence staining of AS MSCs and control MSCs at day 14 under osteogenic induction with DAPI (blue) and osteoadherin-specific antibody (green). (H and I) RT-qPCR of collagen 1A1 (H) and osteocalcin (I) mRNA levels in AS MSCs and control MSCs at days 0 and 7 under osteogenic induction. All experiments were done in the AS patient group using AS MSCs (derived from A1, A2, and A3 with experimental triplicates) and in the control group using control MSCs (derived from C1, C2, and C3 with experimental triplicates). Data are shown as the mean ± SEM. *P < 0.05; **P < 0.01; ****P < 0.0001 by 1-way ANOVA, followed by Tukey’s honestly significant difference (HSD) test. Representative images from AS (A1) MSCs and control (C3) MSCs are shown in E and G. Scale bars: 200 μm (A and E); 20 μm (G).