Integrated Transcriptomic Analysis Suggests a C1Q-Related Macrophage–Fibroblast Signaling Axis in Keloids

Keloids are fibroproliferative scars characterized by immune dysregulation, persistent fibroblast activation, and excessive extracellular matrix deposition. The mechanisms by which macrophage functional states regulate pathological fibroblast activation remain incompletely understood. Bulk RNA-seq and single-cell RNA-seq datasets were integrated to characterize the immune–fibrotic microenvironment of keloids and infer candidate macrophage–fibroblast communication axes. Candidate findings were further assessed by tissue immunofluorescence and preliminary in vitro phenotypic evaluation using C1Q stimulation and RAP intervention in keloid fibroblasts. Bulk transcriptomic analysis revealed coordinated activation of immune-related and fibrotic remodeling programs in keloids. Single-cell analysis identified activated profibrotic fibroblast states and a macrophage population with M2-like features. Ligand–target inference nominated C1QB as a candidate macrophage-associated ligand transcript potentially involved in fibroblast activation, while low-density lipoprotein receptor-related protein 1 (LRP1), a biologically plausible receptor candidate, was enriched in activated fibroblast states. Tissue immunofluorescence showed the coexistence of C1QB+ macrophages and LRP1+ fibroblasts in keloid lesions. In vitro phenotypic assessment using the intact C1Q complex showed that C1Q increased ACTA2 expression in primary keloid fibroblasts, whereas RAP attenuated this effect; COL1A1 and POSTN showed no consistent induction. Together, these findings support a candidate C1Q-related macrophage–fibroblast communication model and provide a preliminary framework for understanding immune-driven fibroblast activation during keloid progression, with implications for future exploration of potential intervention strategies.