Background: Low back pain (LBP) is one of the most prevalent diseases affecting quality of life [1, 2], with no disease-modifying therapy [3]. During abnormal mechanical stressand, inflammation or spinal degeneration, the balance between the normal endplate (EP) bilayers of cartilage and bone shifts to more bone [4]. Furthermore, the remodeling bony EP, with increased porosity caused by osteoclastic activity, may be a source of LBP due to aberrant neurovascular ingrowth within the endplate [5]. However, little is known about why osteoclasts exhibit abnormal activity and cause an imbalance in the bone homeostasis of the EB.

Objectives: This study aims to identify the key cell cluster that maintain bone metabolic homeostasis in the EP and to explore potential methods for alleviating endplate remodeling and pain.

Methods: We established sham, 2-week, 6-week, and 12-week spinal instability mouse models to simulate EP remodeling and performed single-cell sequencing on their EP to identify EP-specific stem cell populations. Subsequently, we generated Zic1-Cre; EGFP ^CAG mice and Zic1-CreERT; MFGE8 ^fl/fl mice to observe the spatiotemporal changes of specific stem cells during EP remodeling and their impact on osteoclasts. Finally, we validated our findings in human endplate specimens.

Results: We identified a trilineage-differentiable zinc finger in cerebellum+ (Zic1+) vertebral mesenchymal stem cells (Zic1+vSSCs) [Lin (CD31/CD45/Ter119)- THY- 6C3- CD105- CD200+] specifically expressed in the EP (Figure1). Under abnormal mechanical stress or inflammatory conditions, these cells highly expressed MFGE8 and Angptl2 proteins. In vivo and in vitro experiments showed that MFGE8/Angptl2 proteins promoted the migration/differentiation of Mincle+ osteoclast precursor cells (OPCs), a process inhibited by the specific inhibitor of the potential MFGE8 receptor avß3avß5, Cyclo(-RGDfK). Mincle+ osteoclasts recognized and phagocytized differentiated/senescent Zic1+ vSSCs through DAMPs. EP remodeling was significantly inhibited in spinal instability model mice with MFGE8 knockout in Zic1+ vSSCs, resulting in significant pain relief (Figure1).

Conclusion: This study refines and proves the theoretical hypothesis that endplate remodeling induces spine pain. Under mechanical stress or inflammation, endplate-specific Zic1+ vSSCs activate and produce MFGE8 and Angptl2. MFGE8 induces Mincle+ OPCs to migrate to the endplate, and Angptl2 induces Mincle+ OPCs differentiation, resulting in increased endplate pore formation. Zic1+ vSSCs differentiate into osteogenic cells, maintaining bone homeostasis, which leads to increased endplate calcification. Mincle+ osteoclasts phagocytize differentiated/senescent Zic1+ vSSCs, disrupting bone homeostasis. CGRP+ C fibers and TH+ sympathetic nerve fibers grow in, ultimately causing spine pain (Figure2).

REFERENCES: [1] JAMA. 2008 Feb 13;299(6):656-64.

[2] Lancet. 2018 Jun 9;391(10137):2302.

[3] Lancet. 2017 Feb 18;389(10070):736-747.

[4] Nat Commun. 2024 Apr 5;15(1):2939.

[5] Sci Transl Med. 2023 Nov 15;15(722):eadg8982.

Figure 1.

the upper yellow box), Scale bar: 200 µm, 200 µm, and 20 µm. (H-J) Quantitative analysis of endplate porosity, endplate trabecular separation and endplate cartilage area from (G). (K-N) Analysis of mechanical withdrawal threshold, maximum active distance, active time, and maximum running speed in mice. (O-P) MRI analysis of mouse spine (yellow arrows indicate intervertebral disc signal), Scale bar: 1 mm. BM(S): spinal bone marrow, BM(F): femoral bone marrow, EP: endplate, MT: neural tube, S: spinal lamina, AR: Alizarin red, AB: Alcian blue, ORO: Oil Red O, LSI: spinal instability model.

bone resorption while also secreting TGF-β1 to promote the osteogenic differentiation of stem cells, thereby maintaining bone homeostasis. Conversely, differentiated Mincle+ osteoclasts recognize damage or differentiated Zic1+ vSSCs through DAMPs/PAMPs generated by TLR and PRR, leading osteoclasts to release a large amount of active mediators through the inflammasome, promoting the destruction and phagocytosis of damaged or differentiated Zic1+ vSSCs. This results in an imbalance between Zic1+ vSSCs and Mincle+ OPCs, leading to an imbalance in bony EP homeostasis.

Acknowledgements: NIL.

Disclosure of Interests: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.