Fibroblast-Derived TGFβ1 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, TGFβ1 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 TGFβ1 plays a critical role during these processes. The data demonstrate a dynamic expression of TGFβ1 during tissue repair. Cell-specific ablation of Tgfb1 in fibroblasts revealed that deletion of TGFβ1 attenuates bleomycin-induced skin fibrosis and perturbs maturation of granulation tissue in skin wounds. Absence of fibroblast-derived TGFβ1 induced vascular alterations (less vascular density and branching, haemorrhage) in early wound healing. This was associated with alterations in the formation of stable ECM structure. This can be explained by paracrine regulation of endothelial cells or pericytes by fibroblast-released TGFβ1 and by impaired expression of pro-angiogenic factors in TGFβ1-deficient fibroblasts. Our findings provide novel mechanistic insights into the central role of fibroblast-derived TGFβ1 for early stages of tissue repair and fibrosis in the skin.