Abstract
OBJECTIVE: To further our understanding of the role of tumor necrosis factor (TNF)α on the inflammatory response in chondrocytes. DESIGN: We explored the effects of TNFα on the transcriptome of epiphyseal chondrocytes from newborn C57BL/6 mice at the total and single cell (sc) resolution. RESULTS: Gene set enrichment analysis of total RNA-Seq from TNFα-treated chondrocytes revealed enhanced response to biotic stimulus, defense and immune response and cytokine signaling and suppressed cartilage and skeletal morphogenesis and development. scRNA-Seq analyzed 14,239 cells and 24,320 genes and distinguished 16 cell clusters. The more prevalent ones were constituted by limb bud and chondrogenic cells and fibroblasts comprising ∼73 % of the cell population. Genes expressed by joint fibroblasts were detected in 5 clusters comprising ∼45 % of the cells isolated. Pseudotime trajectory finding revealed an association between fibroblast and chondrogenic clusters which was not modified by TNFα. TNFα decreased the total cells recovered by 18.5 % and the chondrogenic, limb bud and mesenchymal clusters by 32 %, 27 % and 7 %, respectively. TNFα had profound effects on the insulin-like growth factor (IGF) axis decreasing Igf1, Igf2 and Igfbp4 and inducing Igfbp3 and Igfbp5, explaining an inhibition of collagen biosynthesis, cartilage and skeletal morphogenesis. Ingenuity Pathway Analysis of scRNA-Seq data revealed that TNFα enhanced the osteoarthritis, rheumatoid arthritis, pathogen induced cytokine storm and interleukin 6 signaling pathways and suppressed fibroblast growth factor signaling. CONCLUSIONS: Epiphyseal chondrocytes are constituted by diverse cell populations distinctly regulated by TNFα to promote inflammation and suppression of matrix biosynthesis and growth.