Fibroblast-derived TGFb1 regulates skin repair and fibrosis

Activation of fibroblasts and formation of myofibroblasts are essential for granulation tissue formation following injury. In fibrotic reactions, excessive deposition of ECM by the activated fibroblasts determines scar formation and functional failure. Although these events critically depend on the activity of a plethora of growth factors and cytokines, TGFß1 is a unique player controlling the immune response and proliferation of many cell types. Different cell types contribute to its release and activation, which is also regulated by the interaction with the ECM and by mechanical forces. The aim of this study was to elaborate whether fibroblast-derived TGFß1 plays a critical role during these processes. The data demonstrate a dynamic expression of TGFß1 during tissue repair. Cell-specific ablation of Tgfb1 in fibroblasts revealed that deletion of TGFß1 attenuates bleomycin-induced skin fibrosis and delays maturation of granulation tissue in skin wounds. Absence of fibroblast-derived TGFß1 induced vascular alterations (less vascular density and branching, hemorrhage) in early wound healing, potentially influenced by coincident alterations in the formation of stable ECM structure. This can be explained by paracrine regulation of endothelial cells or pericytes by fibroblast-released TGFß1 and by impaired expression of pro-angiogenic factors in TGFß1-deficient fibroblasts. Our findings provide novel mechanistic insights into the central role of fibroblast-derived TGFß1 for early stages of tissue repair and fibrosis in the skin. Overall design: To elucidate the effect the molecular mechanisms of cell-specific ablation of Tgfb1 in fibroblasts, fibroblasts were isolated from tamoxifen-fed Tgfb1fl/fl:Col1a2-CreERT (termed TGFß1FKO) mice and controls, mice expressing the floxed Tgfb1 alleles, but no Cre recombinase. RNA was extracted from isolated fibroblast cultured in serum replacement medium for 72h on fibronectin and then submitted to Novogene (Cambridge, U.K.) for bulk RNA-sequencing.