Decoding Endoplasmic Reticulum Stress on Chondrocyte Driving Osteoarthritis Development through Integrating Single-Cell and Transcriptomic Profiling

<b>Background:</b> Endoplasmic reticulum stress (ERS) as a potent disease regulator has been proven to be engaged in the pathogenesis and progression of numerous disorders. Osteoarthritis (OA) is a widespread degenerative disease of the joints with chondrocyte damage as the main pathologic mechanism. However, the specific role of ERS in chondrocytes during OA development remains poorly understood. <b>Methods:</b> Integration of single-cell RNA sequencing (scRNA-seq) and bulk RNA-seq analyses to thoroughly assess the landscape of ERS in chondrocytes from OA samples. The WGCNA and unsupervised cluster analysis were integrated to identify ERS patterns. Furthermore, we screened ERS key regulators for diagnosis and prediction of OA development by three algorithms (LASSO, Random Forest, and PPI analysis). Finally, we constructed <i>in vitro</i> OA models for validating the biological roles of the identified ERS key regulators. <b>Result:</b> scRNA-seq analysis revealed a robust association between ERS and OA progression. Unfolded protein responses, TNFA signaling via NF-κB, and apoptosis were significantly activated in the high ERS risk subpopulation. Cellular communication analysis demonstrated markedly enhanced cell-cell interactions and signaling pathways in high ERS risk subpopulations compared to low ERS risk subpopulations. Unsupervised cluster analysis identified two ERS patterns exhibiting distinct metabolic and inflammation signaling sceneries. Additionally, we identified two key ERS regulators, IGFBP3 and S100A4, and developed a novel nomogram based on these markers, which demonstrated excellent clinical predictive and guiding capabilities. Finally, we found that suppressing IGFBP3 expression <i>in vitro</i> could maintain chondrocyte metabolic homeostasis and inhibit PERK/ATF4/CHOP cascade-mediated ERS to reduce chondrocyte apoptosis. <b>Conclusion:</b> The present study integrated scRNA-seq and bulk RNA-seq to delve into the pathogenesis of ERS driving the progression of OA and identify ERS key regulators for OA diagnosis and therapeutic intervention.