Single-cell transcriptomic profiling identifies YY1 as a key regulator of fibroblast plasticity in hypertrophic scar formation

Abstract Background Hypertrophic scars (HS) are characterised by excessive extracellular matrix deposition and impaired scar remodelling. Fibroblasts are central to HS pathogenesis, yet clinical strategies remain limited by an incomplete understanding of fibroblast heterogeneity and transcriptional regulation. This study aimed to identify a key fibroblast subpopulation and its regulatory transcription factors to address this translational gap. Methods Single-cell RNA sequencing was performed on dermal cells from freshly excised human HS and normal skin (NS) tissues. Fibroblast subsets and transcriptional regulators were identified using Seurat, pseudotime, transcription factor prediction, and cell-cell communication analyses. Functional validation involved lentiviral overexpression of Yin Yang 1 (YY1) in fibroblasts derived from patients with hypertrophic scars, followed by bulk RNA sequencing, western blotting, CUT&Tag and immunofluorescence assays. Results Clinical HS specimens showed characteristic collagen overproduction and vascular hyperplasia. Single-cell analysis of 43,303 cells revealed disease-specific shifts in cellular composition, including pronounced pericyte expansion and reduced fibroblast abundance. Notably, fibroblast subcluster Fib_5 (ADAM12+ COMP+ POSTNhi) increased despite the overall fibroblast decline in HS and exhibited upregulated fibrotic gene expression. Cross-validation using combined public datasets comprising 21 samples indicated that the Fib_5-like subcluster is conserved across fibrotic conditions. Pseudotime analyses placed Fib_5 within a HS-dominant branch, state 6; transcription factor prediction from branch-dependent differentially expressed genes identified YY1 as the only predicted transcription factor also differentially expressed in state 6. Functional validation showed that YY1overexpression in fibroblasts derived from patients with HS reversed fibrotic gene expression profiles, with Fib_5 identified as a primary responder by Scissor. CUT&Tag analysis validated these findings at the epigenomic level. Cell-cell communication analyses further revealed marked reprogramming of fibroblast-pericyte signalling across multiple fibrosis-related pathways in HS. Conclusion This work establishes the Fib_5-YY1 axis as a central hub in HS pathogenesis, with YY1-mediated fibroblast plasticity as a key transcriptional mechanism underlying skin fibrogenesis.