Systematic Comparison of the TGF-β Isoforms in Normal Dermal and Lung Fibroblasts Identifies TGF-β2 and TGF-β3 as Priority Targets in Tissue Fibrosis

Systemic sclerosis (SSc) is a multi-organ autoimmune disease characterized by fibrosis of the skin and internal organs. Interstitial lung disease (ILD) is a major complication and leading cause of mortality in SSc. Transforming growth factor-β (TGF-β) has been implicated as a central mediator of fibrosis; however, while TGF-β1 has been extensively studied, the roles of TGF-β2 and TGF-β3 remain incompletely defined. Here, we systematically compared the effects of TGF-β1, TGF-β2, and TGF-β3 in dermal and lung fibroblasts, evaluating extracellular matrix synthesis and contraction, cytokine secretion, proliferation, and myofibroblast differentiation. TGF-β2 and TGF-β3 induced greater profibrotic cytokine release of Interleukin (IL)-6 and IL-11 and increased collagen-I and fibronectin synthesis compared with TGF-β1 in dermal and lung fibroblasts (all p < 0.05). TGF-β2 and TGF-β3 stimulated greater collagen-I contraction in dermal fibroblasts (p < 0.05), but greater myofibroblast differentiation in lung fibroblasts (p < 0.05). The TGF-β isoforms did not affect proliferation. All TGF-β isoforms activated SMAD2/3 signalling; however, TGF-β2 and TGF-β3 reduced expression of TGF-β Receptor II and the inhibitory regulator, SMAD7. In summary, TGF-β2 and TGF-β3 have a more pronounced profibrotic effect than TGF-β1 on dermal and lung fibroblast functions, making them potential targets for treatment for skin and lung fibrosis in diseases such as SSc.