RT Journal Article
SR Electronic
T1 Taxonomy of fibroblasts and progenitors in the synovial joint at single-cell resolution
JF Annals of the Rheumatic Diseases
JO Ann Rheum Dis
FD BMJ Publishing Group Ltd and European League Against Rheumatism
SP annrheumdis-2021-221682
DO 10.1136/ard-2021-221682
A1 Fraser L Collins
A1 Anke J Roelofs
A1 Rebecca A Symons
A1 Karolina Kania
A1 Ewan Campbell
A1 Elaina S R Collie-duguid
A1 Anna H K Riemen
A1 Susan M Clark
A1 Cosimo De Bari
YR 2022
UL http://ard.bmj.com/content/early/2022/11/22/ard-2021-221682.abstract
AB Objectives Fibroblasts in synovium include fibroblast-like synoviocytes (FLS) in the lining and Thy1+ connective-tissue fibroblasts in the sublining. We aimed to investigate their developmental origin and relationship with adult progenitors.Methods To discriminate between Gdf5-lineage cells deriving from the embryonic joint interzone and other Pdgfrα-expressing fibroblasts and progenitors, adult Gdf5-Cre;Tom;Pdgfrα-H2BGFP mice were used and cartilage injury was induced to activate progenitors. Cells were isolated from knees, fibroblasts and progenitors were sorted by fluorescence-activated cell-sorting based on developmental origin, and analysed by single-cell RNA-sequencing. Flow cytometry and immunohistochemistry were used for validation. Clonal-lineage mapping was performed using Gdf5-Cre;Confetti mice.Results In steady state, Thy1+ sublining fibroblasts were of mixed ontogeny. In contrast, Thy1-Prg4+ lining fibroblasts predominantly derived from the embryonic joint interzone and included Prg4-expressing progenitors distinct from molecularly defined FLS. Clonal-lineage tracing revealed compartmentalisation of Gdf5-lineage fibroblasts between lining and sublining. Following injury, lining hyperplasia resulted from proliferation and differentiation of Prg4-expressing progenitors, with additional recruitment of non-Gdf5-lineage cells, into FLS. Consistent with this, a second population of proliferating cells, enriched near blood vessels in the sublining, supplied activated multipotent cells predicted to give rise to Thy1+ fibroblasts, and to feed into the FLS differentiation trajectory. Transcriptional programmes regulating fibroblast differentiation trajectories were uncovered, identifying Sox5 and Foxo1 as key FLS transcription factors in mice and humans.Conclusions Our findings blueprint a cell atlas of mouse synovial fibroblasts and progenitors in healthy and injured knees, and provide novel insights into the cellular and molecular principles governing the organisation and maintenance of adult synovial joints.Data are available in a public, open access repository. Data are available on reasonable request. Single-cell RNA sequencing data that support the findings of this study have been deposited in Gene Expression Omnibus (GEO) with the accession code GSE214500. All data relevant to the study are included in the article or uploaded as online supplemental information.