A Simultaneous Inhibition of ID1 and ID3 Protects Against Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease for which novel therapeutic approaches are desperately needed. Inhibitor of DNA binding (ID) proteins are regulated by Transforming Growth Factor-b. However, the regulation and the effects of ID proteins in IPF remain poorly understood. We aimed to assess the expression of ID proteins in IPF and determine the effects of ID proteins on human lung fibroblasts (HLF) in vitro and pulmonary fibrosis in vivo.

The expression of ID proteins in lungs and lung fibroblasts from mice and human patients with pulmonary fibrosis was evaluated. The effects of ID1/ID3 inhibition and overexpression on HLF were assessed. Genetic and pharmacological approaches were used in vivo to determine the role of ID1/ID3 in pulmonary fibrosis.

ID1/ID3 levels were elevated in HLFs isolated from pulmonary fibrosis-diseased patients and mice. ID1/ID3 knockdown decreased IPF-diseased HLF proliferation and differentiation into myofibroblasts. Bleomycin-exposed ID1/ID3 KO mice displayed improved lung function and presented with decreased lung fibrosis when compared to WT mice. A pharmacological inhibitor of ID1/ID3 decreased IPF-diseased HLF proliferation and differentiation in vitro and attenuated pulmonary fibrosis in vivo. A lung specific inhibition of ID1/ID3, using adeno-associated viruses expressing short hairpins targeting ID1 and ID3, reversed pulmonary fibrosis in mice. Mechanistically, ID1/ID3 inhibition decreased fibroblast proliferation through cell cycle genes and inhibited fibroblast differentiation through the MEK/ERK pathway.

Our data indicate that a simultaneous inhibition of ID1 and ID3 attenuates pulmonary fibrosis. ID1/ID3 inhibition holds potential as a novel therapeutic treatment for IPF.