Simultaneous inhibition of ID1 and ID3 mitigates fibroblast activation via cell cycle and MEK/ERK pathways in pulmonary fibrosis.

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease for which novel therapeutic approaches are urgently needed. Transforming Growth Factor-β (TGF-β) plays a central role in IPF pathogenesis by activating lung fibroblasts. Inhibitor of DNA binding (ID) proteins are regulated by TGF-β; however, their role in IPF remains poorly understood. We aimed to evaluate the regulation of ID proteins in IPF and to determine their functional role in human lung fibroblasts (HLF) in vitro and pulmonary fibrosis in vivo.

METHODS

ID protein expression was assessed in lungs and lung fibroblasts from mice and patients with pulmonary fibrosis. In vitro, the effects of ID1/ID3 inhibition and overexpression on HLF proliferation, migration and differentiation into myofibroblasts were evaluated. Genetic and pharmacological approaches were used in vivo to determine the role of ID1/ID3 in pulmonary fibrosis.

RESULTS

ID1/ID3 levels were elevated in lungs and lung fibroblasts from mice and patients with pulmonary fibrosis, as well as in HLFs treated with TGF-β. ID1/ID3 knockdown reduced proliferation, migration and differentiation of healthy and IPF-derived HLFs. Bleomycin-exposed ID1/ID3 double KO mice exhibited improved lung function and reduced fibrosis compared with WT mice. Pharmacological inhibition of ID1/ID3 decreased HLF proliferation, migration and differentiation in vitro and attenuated pulmonary fibrosis in vivo. Lung-specific inhibition of ID1/ID3 using adeno-associated viruses expressing short hairpins targeting ID1 and ID3 also reversed pulmonary fibrosis in mice. Mechanistically, ID1/ID3 inhibition reduced fibroblast proliferation through regulation of cell cycle genes and attenuated fibroblast differentiation via the MEK/ERK pathway.

CONCLUSIONS

Simultaneous inhibition of ID1 and ID3 attenuates pulmonary fibrosis. Targeting ID1/ID3 represents a potential novel therapeutic strategy for IPF.