Transcriptomic integration and ligand-receptor crosstalk reveal the underlying molecular mechanisms between hip cartilage and subchondral bone in osteonecrosis of femoral head.

Osteonecrosis of femoral head (ONFH) is characterized not only by ischemic bone tissue necrosis but also by cartilage degeneration, which plays an essential role in the pathogenesis of ONFH. The molecular communication between tissues contributes to disease progression, however the communication between cartilage and subchondral bone in the progression of ONFH remains unclear. In this study, we integrated transcriptomic data from ONFH cartilage and subchondral bone, exploring common differentially expressed genes (DEGs), pathway and function enrichment analyses, the protein-protein interaction (PPI) network, and hub genes to comprehensively study molecular integration. Additionally, we explored the molecular crosstalk between and within cartilage and subchondral bone using ligand-receptor pairs and ONFH cartilage proteomic data. Finally, key genes and ligand-receptor pairs were validated by quantitative real-time PCR (qRT-PCR). There were 27 common DEGs and five hub genes in cartilage and subchondral bone. The defined hub genes included COL1A1, COLIA2, CTSK, SPARC, and MXRA5. Notably, pathways related to ossification, extracellular matrix, and collagen formation were significantly altered in ONFH. Ligand-receptor data combined with DEGs revealed 60 differentially expressed ligands and 51 differentially expressed receptors in cartilage and four ligands and three receptors in subchondral bone. In inter-tissue comparisons, ligands from chondrocytes predominantly paired with receptors on osteoblasts in the subchondral bone, such as FN1, MMP2, and FGF1. Conversely, ligands from osteoblasts and osteocytes in the subchondral bone frequently paired with chondrocyte receptors, including FN1, COL1A1, and SEMA7A. At the protein level, we identified thirteen ligands and one receptor, with COL3A1 being the most highly expressed ligand and CD82 the only differentially expressed receptor in ONFH. This study highlights common molecular mechanisms and ligand-receptor crosstalk between and within cartilage and subchondral bone in ONFH, offering new insights into the disease's pathophysiology and potential molecular targets for therapeutic intervention.