Background <p>Rapid and stable regeneration of bone defects remains a pressing clinical challenge. We previously fabricated stem cell aggregates (CA) by mimicking developmental condensation and demonstrated their efficacy in promoting bone defect repair. Endogenous Gli1<sup>+</sup> skeletal stromal/progenitor cells (SSPCs) are a pivotal SSPC subtype known to maintain bone homeostasis and enhance bone regeneration; however, the functional properties and translational potential of CA derived from these cells (Gli1<sup>+</sup> CA) remain largely elusive.</p> Methods <p>Single-cell RNA sequencing was performed to characterize differential gene expression profiles between Gli1<sup>high</sup> and Gli1<sup>low</sup> SSPCs. The spatial relationship among Gli1<sup>+</sup> cells, RUNX2<sup>+</sup> cells, and type H vessels in vivo was further validated. <i>Gli1-CreER</i><sup><i>T2</i></sup>;<i>mT/mG</i> transgenic mice were generated to enable the isolation of Gli1<sup>+</sup> SSPCs and the subsequent fabrication of Gli1<sup>+</sup> CA. The pro-angiogenic potential of Gli1<sup>+</sup> CA was assessed in vitro, and the underlying regulatory mechanisms were further explored. Finally, Gli1<sup>+</sup> CA were implanted into a mouse femoral defect model, and bone regenerative efficacy was evaluated by micro-CT and immunofluorescence staining.</p> Results <p>Single-cell RNA sequencing revealed that, compared with Gli1<sup>low</sup> SSPCs, Gli1<sup>high</sup> SSPCs highly expressed genes associated with osteogenesis, angiogenesis, and extracellular matrix synthesis. In vivo validation demonstrated robust enrichment of Gli1<sup>+</sup> cells in the metaphysis; these cells exhibited a tight spatial correlation with the osteogenic master transcription factor RUNX2 and type H vessels. We subsequently sorted Gli1<sup>+</sup> SSPCs via flow cytometry and fabricated CA, and in vitro analysis confirmed that their expression profiles were consistent with the sequencing data. Functional assays further revealed that Gli1<sup>+</sup> CA promoted endothelial tube formation through paracrine signaling. Ultimately, Gli1<sup>+</sup> CA markedly accelerated bone regeneration in a mouse femoral defect model compared with unsorted CA and Gli1⁻ CA, likely by inducing type H vessel formation.</p> Conclusions <p>This study not only addresses a critical knowledge gap in Gli1<sup>+</sup> CA-mediated bone regeneration, but also proposes a novel strategy termed “precision screening of endogenous SSPC subsets coupled with targeted aggregate fabrication”. This approach offers a more precise therapeutic direction for the regenerative treatment of bone defects.</p>

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Gli1⁺ cell aggregates promote type H vessel formation and orchestrate bone defect regeneration

  • Chao Ma,
  • Yu-Ru Gao,
  • Hao Wang,
  • Bing-Dong Sui,
  • Shan-Shan Huang,
  • Yi Zhang,
  • Lu Liu,
  • Xiao-Hui Zhang,
  • Shu-Juan Xing,
  • Yuan-Yuan Li,
  • Yi-Han Xiao,
  • Ya-Nan Zheng,
  • Li-Heng Ren,
  • Yan Jin,
  • Chen-Xi Zheng,
  • Hao-Kun Xu,
  • Ji Chen

摘要

Background

Rapid and stable regeneration of bone defects remains a pressing clinical challenge. We previously fabricated stem cell aggregates (CA) by mimicking developmental condensation and demonstrated their efficacy in promoting bone defect repair. Endogenous Gli1+ skeletal stromal/progenitor cells (SSPCs) are a pivotal SSPC subtype known to maintain bone homeostasis and enhance bone regeneration; however, the functional properties and translational potential of CA derived from these cells (Gli1+ CA) remain largely elusive.

Methods

Single-cell RNA sequencing was performed to characterize differential gene expression profiles between Gli1high and Gli1low SSPCs. The spatial relationship among Gli1+ cells, RUNX2+ cells, and type H vessels in vivo was further validated. Gli1-CreERT2;mT/mG transgenic mice were generated to enable the isolation of Gli1+ SSPCs and the subsequent fabrication of Gli1+ CA. The pro-angiogenic potential of Gli1+ CA was assessed in vitro, and the underlying regulatory mechanisms were further explored. Finally, Gli1+ CA were implanted into a mouse femoral defect model, and bone regenerative efficacy was evaluated by micro-CT and immunofluorescence staining.

Results

Single-cell RNA sequencing revealed that, compared with Gli1low SSPCs, Gli1high SSPCs highly expressed genes associated with osteogenesis, angiogenesis, and extracellular matrix synthesis. In vivo validation demonstrated robust enrichment of Gli1+ cells in the metaphysis; these cells exhibited a tight spatial correlation with the osteogenic master transcription factor RUNX2 and type H vessels. We subsequently sorted Gli1+ SSPCs via flow cytometry and fabricated CA, and in vitro analysis confirmed that their expression profiles were consistent with the sequencing data. Functional assays further revealed that Gli1+ CA promoted endothelial tube formation through paracrine signaling. Ultimately, Gli1+ CA markedly accelerated bone regeneration in a mouse femoral defect model compared with unsorted CA and Gli1⁻ CA, likely by inducing type H vessel formation.

Conclusions

This study not only addresses a critical knowledge gap in Gli1+ CA-mediated bone regeneration, but also proposes a novel strategy termed “precision screening of endogenous SSPC subsets coupled with targeted aggregate fabrication”. This approach offers a more precise therapeutic direction for the regenerative treatment of bone defects.