Single-cell analysis reveals heterogeneity of juvenile idiopathic arthritis fibroblast-like synoviocytes with implications for disease subtype

Background Fibroblast-like synoviocytes (FLS) play a crucial role in JIA pathogenesis; however, the mechanisms by which they contribute to disease progression are not well described. Previous studies demonstrated that rheumatoid arthritis FLS are heterogeneous, and subpopulations with transformed, aggressive phenotypes cause invasive and destructive disease activity. We employ single-cell RNA-sequencing (scRNA-seq) to investigate JIA FLS heterogeneity and gene expression that distinguishes JIA subtypes. Methods JIA FLS cell lines from three persistent oligoarticular, three pre-extension oligoarticular, and three polyarticular subtypes were cultured. scRNA-seq was performed by Genewiz according to 10 × Genomics Chromium protocols. SeuratR package was used for QC, analysis, and exploration of data. Results FLS are heterogeneous and have characteristics of fibroblasts, chondrocytes, and smooth muscle cells. The chondrocyte-like subpopulation is the predominant cell type and percentages of this subpopulation increase with disease severity. Despite overlapping subpopulations, the chondrocyte-like cells have unique genetic fingerprints that distinguish between JIA subtypes. LRRC15, GREM1, and GREM2 are overexpressed in chondrocyte-like cells from persistent oligoarticular JIA FLS compared to pre-extension oligoarticular JIA FLS. S100A4, TIMP3, and NBL1 are overexpressed in pre-extension oligoarticular JIA FLS compared to polyarticular JIA FLS. CRLF1, MFAP5, and TNXB are overexpressed in persistent oligoarticular JIA FLS compared to polyarticular JIA FLS. Conclusions We found biologically relevant differences in gene expression between JIA subtypes that support a critical role for FLS in pathogenesis. We also demonstrate that gene expression within the chondrocyte-like subpopulation can be used to distinguish between these subtypes.