Single-cell RNA-Seq reveals a repair pattern in cystic lesions in steroid induced osteonecrosis of the femoral head

Peng Peng^1,2Jia-qing Tian³Kun Lin⁴Weihua Fang⁴Fangming Yao⁴Xiaoqiang Yang⁴Wenyuan Hou⁴Fangjun Xiao⁴Shun Lu⁴Wei He^2,5,6Min-Cong He^2,5,6Huan Xiao^7*Qiu-Shi Wei^2,5,6*

• ¹Guangdong Provincial Second Hospital of Traditional Chinese Medicine, Guangzhou University of Chinese Medicine, Guangzhou, China
• ²National Key Laboratory of Traditional Chinese Medicine Syndrome, Guangzhou, China
• ³The fifth clinical college of Guangzhou university of Chinese medicine, Guangzhou, China
• ⁴Guangzhou university of Chinese medicine, Guangzhou, China
• ⁵Guangdong Research Institute for Orthopedics and Traumatology of Chinese Medicine, Guangzhou, China
• ⁶The Third Affiliated Hospital, Guangzhou University of Chinese Medicine, Guangzhou, China
• ⁷Bijie Traditional Chinese Medicine Hospital, Bijie, China

Background: Studies have indicated that cystic lesions play a crucial role in the repair processes of steroid-induced osteonecrosis of the femoral head and its subsequent collapse. Here, we employed single-cell RNA sequencing (scRNA-seq) technology to investigate the transcriptomic landscape and repair mechanisms of cystic lesions in SIONFH. Methods: We applied scRNA-seq combined with computational approaches to characterize distinct cell subsets and their molecular signatures within cystic lesions from three SIONFH patients. Additionally, histological assays were conducted to observe pathological manifestations of these lesions. Results: Eight cell types were identified in cystic lesions of SIONFH. Among them, chondrocytes were divided into five subgroups. Among them, chondrocytes were divided into five subgroups: homeostatic chondrocytes (HomC), fibrocartilage chondrocytes (FC), prehypertrophic chondrocytes (preHTC), inflammatory chondrocytes (InflamC), and hypertrophic chondrocytes (HTC). Additionally, histological assays showed the presence of chondrocytes and a transition zone from chondrocytes to bone tissue within the cystic lesions. Notably, we report that one of the HTC clusters with CLIC3+ expression exhibited a strong involved in bone mineralization, osteoblast differentiation, and cell differentiation. Conclusion: We have delineated the cellular heterogeneity and molecular signatures of cystic lesions in SIONFH. The results reveal a distinct repair program within these lesions, which might be driven by chondrocyte hypertrophy and might culminate in osteogenic differentiation.