Transforming growth factor β induces fibroblast fibrillin‐1 matrix formation

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Abstract
Objective: Fibrillin, an extracellular matrix protein implicated in dermal fibrosis, is increased in the reticular dermis of systemic sclerosis (SSc) skin. We undertook this study to investigate the hypothesis that transforming growth factor β (TGFβ) or other cytokines regulate fibrillin matrix formation by normal and SSc fibroblasts. We further investigated the mechanism of TGFβ‐induced fibrillin fibrillogenesis and its relationship to myofibroblasts.Methods: Fibrillin and fibronectin matrix deposition and α‐smooth muscle actin expression by fibroblast cultures from normal and SSc skin treated with TGFβ or other cytokines were analyzed by immunofluorescence. Supernatant and extracellular matrix from normal and SSc fibroblasts treated with or without TGFβ were evaluated by Western blot and Northern blot for fibrillin protein and messenger RNA (mRNA) expression, respectively.Results: Immunofluorescence demonstrated increased fibrillin matrix formation by normal and scleroderma fibroblasts after TGFβ treatment. Other cytokines, including tumor necrosis factor α, interleukin‐1β (IL‐1β), IL‐4, granulocyte–macrophage colony‐stimulating factor, and platelet‐derived growth factor, did not affect fibrillin fibrillogenesis. Fibrillin matrix formed in proximity to myofibroblasts and independently of up‐regulation of fibronectin matrix or cell number. Western blot analysis of extracellular matrix confirmed increased fibrillin after TGFβ stimulation of normal or scleroderma fibroblasts. However, TGFβ did not alter the expression of either soluble fibrillin protein or fibrillin mRNA.Conclusion: Our data show that TGFβ induces fibrillin protein incorporation into the extracellular matrix without affecting fibrillin gene expression or protein synthesis, suggesting that fibrillin matrix assembly is regulated extracellularly. TGFβ might increase fibrillin matrix by activating myofibroblasts. Such TGFβ‐mediated effects could account for the increased fibrillin matrix observed in SSc skin.