Background and Objectives Osteoblasts are derived from bone marrow mesenchymal stem cells (BMMSCs) and play important role in bone remodeling. While our previous studies have investigated the cell subtypes and heterogeneity in osteoblasts and BMMSCs separately, cell-to-cell communications between osteoblasts and BMMSCs in vivo in humans have not been characterized. The aim of this study was to investigate the cellular communication between human primary osteoblasts and bone marrow mesenchymal stem cells. Methods and Results To investigate the cell-to-cell communications between osteoblasts and BMMSCs and identify new cell subtypes, we performed a systematic integration analysis with our single-cell RNA sequencing (scRNA-seq) transcriptomes data from BMMSCs and osteoblasts. We successfully identified a novel preosteoblasts subtype which highly expressed ATF3, CCL2, CXCL2 and IRF1. Biological functional annotations of the transcriptomes suggested that the novel preosteoblasts subtype may inhibit osteoblasts differentiation, maintain cells to a less differentiated status and recruit osteoclasts. Ligand-receptor interaction analysis showed strong interaction between mature osteoblasts and BMMSCs. Meanwhile, we found FZD1 was highly expressed in BMMSCs of osteogenic differentiation direction. WIF1 and SFRP4, which were highly expressed in mature osteoblasts were reported to inhibit osteogenic differentiation. We speculated that WIF1 and sFRP4 expressed in mature osteoblasts inhibited the binding of FZD1 to Wnt ligand in BMMSCs, thereby further inhibiting osteogenic differentiation of BMMSCs. Conclusions Our study provided a more systematic and comprehensive understanding of the heterogeneity of osteogenic cells. At the single cell level, this study provided insights into the cell-to-cell communications between BMMSCs and osteoblasts and mature osteoblasts may mediate negative feedback regulation of osteogenesis process.

中文翻译：

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以单细胞分辨率解析骨关节炎中人原代成骨细胞和骨髓间充质干细胞之间的细胞通讯。

背景和目的成骨细胞来源于骨髓间充质干细胞（BMMSC），在骨重塑中发挥重要作用。虽然我们之前的研究分别研究了成骨细胞和 BMMSC 的细胞亚型和异质性，但人类体内成骨细胞和 BMMSC 之间的细胞间通讯尚未得到表征。本研究的目的是研究人类原代成骨细胞和骨髓间充质干细胞之间的细胞通讯。方法和结果为了研究成骨细胞和 BMMSC 之间的细胞间通讯并鉴定新的细胞亚型，我们利用来自 BMMSC 和成骨细胞的单细胞 RNA 测序 (scRNA-seq) 转录组数据进行了系统整合分析。我们成功鉴定了一种高表达 ATF3、CCL2、CXCL2 和 IRF1 的新型前成骨细胞亚型。转录组的生物学功能注释表明，新的前成骨细胞亚型可能抑制成骨细胞分化，维持细胞分化程度较低的状态并招募破骨细胞。配体-受体相互作用分析显示成熟成骨细胞和 BMMSC 之间存在很强的相互作用。同时我们发现FZD1在成骨分化方向的BMMSCs中高表达。据报道，在成熟成骨细胞中高表达的 WIF1 和 SFRP4 可抑制成骨分化。我们推测成熟成骨细胞中表达的WIF1和sFRP4抑制了BMMSC中FZD1与Wnt配体的结合，从而进一步抑制了BMMSC的成骨分化。结论我们的研究为成骨细胞的异质性提供了更系统、更全面的理解。在单细胞水平上，这项研究提供了对 BMMSC 和成骨细胞之间细胞间通讯的见解，成熟的成骨细胞可能介导成骨过程的负反馈调节。