Transforming growth factor-β isoforms drive common and distinct signaling pathways in dermal fibroblasts: insights into the signaling diversity in keloid pathogenesis

Objective: Keloids are characterized by excessive fibroblast proliferation and abnormal extracellular matrix deposition, driven by transforming growth factor (TGF)-β signaling partly. However, TGF-β isoforms’ distinct roles remain unclear. This study investigated the common and unique signaling pathways induced by TGF-β1, TGF-β2, and TGF-β3 in dermal fibroblasts and elucidated their contributions to keloid pathogenesis. Methods: Keloid lesion tissues ( n = 24), keloid-surrounding tissues ( n = 19), and normal skin tissues ( n = 6) were obtained from the biobank at Hospital for Skin Diseases (Institute of Dermatology), Chinese Academy of Medical Sciences and Peking Union Medical College. The mRNA expression levels of all TGF-β isoforms were analyzed (TGF-β1, TGF-β2, and TGF-β3), and their distributions were determined by single-cell RNA sequencing. Fibroblasts stimulated with the TGF-β isoforms were subjected to transcriptomic analysis, and key signaling proteins were evaluated by quantitative RT-PCR and immunostaining. Results: TGF-β1 and TGF-β3 were considerably upregulated in keloid lesion tissues, with TGF-β1 exhibiting a 10-fold increase and TGF-β3 exhibiting a 2-fold increase compared with normal skin tissues (TGF-β1: 10.04 ± 7.9 vs. 1.00 ± 0.59, P < 0.001; TGF-β2: 1.26 ± 1.19 vs. 1.00 ± 0.55, P = 0.619; TGF-β3: 2.06 ± 1.00 vs. 1.00 ± 0.76, P < 0.001). The transcriptomic analysis identified upregulation of genes related to extracellular matrix organization and PI3K-Akt signaling by all three isoforms, together with a collective downregulation of genes related to lipid metabolism (all P < 0.001). TGF-β isoform-specific effects were also evident. Specifically, TGF-β1 preferentially activated the adipocytokine signaling pathway, TGF-β2 induced the Wnt signaling pathway, and TGF-β3 upregulated the hypoxia-inducible factor-1 signaling pathway (all P < 0.001). Analysis of key components in these pathways exhibited consistent alterations in keloid lesions at the mRNA and protein levels. Conclusions: TGF-β1 and TGF-β3 play prominent roles in keloid development by regulating fibroblast activity. The specific signaling pathways influenced by the different TGF-β isoforms uncover novel mechanisms driving keloid development and and highlight potential targets for therapeutic intervention.