AUTHOR=Zhang Chi , Xiao Dan , Shu Li , Gong Maoqi , Liu Xinghua , Jiang Xieyuan 

TITLE=Single-cell RNA sequencing uncovers cellular heterogeneity and the progression of heterotopic ossification of the elbow

JOURNAL=Frontiers in Pharmacology

VOLUME=Volume 15 - 2024

YEAR=2024

URL=https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2024.1434146

DOI=10.3389/fphar.2024.1434146

ISSN=1663-9812

ABSTRACT=Heterotopic ossification of the elbow (HOE) is a complicated pathologic process with extra bone formation in the elbow. Bone formation is a complex developmental process involving the differentiation of mesenchymal stem cells to osteoblasts. The aim of this study is to explore cellular origin and the progression of HOE by single-cell RNA sequencing. We identified thirteen clusters of cells in HOE, and further analyzed the subclusters for four of the main cell types. Six subclusters of osteoblasts, nine subclusters of chondrocytes, six subclusters of fibroblasts and five subclusters of MPs were identified and analyzed. The new findings of OSX and SOX9 expression in osteoblast subclusters and chondrocyte subclusters indicate that HOE is medicated through endochondral ossification. Further identification of the corresponding signature gene sets of distinct subclusters indicated that subclusters of osteoblasts_3, osteoblasts_4, osteoblasts_5 and osteoblasts_6 are relative more mature during the osteoblastic progression of HOE. The trajectory analysis of the osteoblasts demonstrated that some genes were gradually down-regulated such as CRYAB, CCL3, SFRP4, WIF1 and IGFBP3 while other critical genes were upregulated such as VCAN, IGFBP4, FSTL1, POSTN, MDK, THBS2 and ALPL, suggesting these factors may participate in HOE progression. Cell-cell communication networks revealed extensive molecular interactions among HOE 13 clusters. Ligand-receptor pairs for IL6, COL24A1, COL22A1, VWF, FZD6, FGF2 and NOTCH1 were identified, suggesting that multiple signaling pathways may be involved in HOE. In conclusion, this study provided the cellular atlas for HOE. We have established a greater extent of the heterogeneity of HOE cells than previously known through transcriptomic analysis at the single-cell level. We have observed gradual patterns of signature gene expression during the differentiation and maturation progression of osteoblasts from stem cells in HOE with higher resolution. The cell heterogeneity of HOE deserves further investigation to pave a way for the identification of potential targets for HOE early diagnosis and therapeutic treatment.