DataSheet_1_Single-Cell RNA Sequencing Reveals B Cells Are Important Regulators in Fracture Healing.docx

The bone marrow microenvironment is composed primarily of immune and stromal cells that play important roles in fracture healing. Although immune cells have been identified in mouse bone marrow, variations in their numbers and type during the fracture healing process remain poorly defined. In this study, single-cell RNA sequencing was used to identify immune cells in fracture tissues, including neutrophils, monocytes, T cells, B cells, and plasma cells. The number of B cells decreased significantly in the early stage of fracture healing. Furthermore, B cells in mice fracture models decreased significantly during the epiphyseal phase and then gradually returned to normal during the epiphyseal transformation phase of fracture healing. The B-cell pattern was opposite to that of bone formation and resorption activities. Notably, B-cell–derived exosomes inhibited bone homeostasis in fracture healing. In humans, a decrease in the number of B cells during the epiphyseal phase stimulated fracture healing. Then, as the numbers of osteoblasts increased during the callus reconstruction stage, the number of B cells gradually recovered, which reduced additional bone regeneration. Thus, B cells are key regulators of fracture healing and inhibit excessive bone regeneration by producing multiple osteoblast inhibitors.

骨髓微环境主要由免疫和基质细胞构成，这些细胞在骨折愈合过程中发挥着至关重要的作用。尽管已在小鼠骨髓中识别出免疫细胞，但它们在骨折愈合过程中的数量和类型变化尚不明确。在本研究中，通过单细胞RNA测序技术，对骨折组织中的免疫细胞进行了鉴定，包括中性粒细胞、单核细胞、T细胞、B细胞和浆细胞。在骨折愈合的早期阶段，B细胞数量显著减少。此外，在骨折模型的干骺端阶段，B细胞数量显著下降，随后在骨折愈合的干骺端转换阶段逐渐恢复正常。B细胞的模式与骨形成和吸收活动相反。值得注意的是，由B细胞衍生的外泌体抑制了骨折愈合过程中的骨稳态。在人类中，干骺端阶段B细胞数量的减少刺激了骨折愈合。随后，在骨痂重建阶段，成骨细胞数量增加，B细胞数量逐渐恢复，从而减少了额外的骨再生。因此，B细胞是骨折愈合的关键调节因子，通过产生多种成骨细胞抑制剂来抑制过度骨再生。