Macropinocytosis inhibition attenuates pro-fibrotic responses in lung fibroblasts and pulmonary fibrosis models

Idiopathic pulmonary fibrosis (IPF) is a devastating chronic lung disorder with limited treatment options. Macropinocytosis is one of the key cellular processes involved in nutrient consumption from the extracellular environment under stress conditions. Here, we studied the role of macropinocytosis in experimental pulmonary fibrosis models. We found that macropinocytosis is increased in human lung fibroblasts (HLFs) derived from IPF patients. The inhibition of macropinocytosis with 5-(n-ethyl-n-isopropyl)-amiloride (EIPA) inhibited profibrotic responses in IPF-derived and TGF-1-stimulated HLFs and reduced pulmonary fibrosis in bleomycin (Bleo)-injured mice. EIPA exerted its antifibrotic effects by regulating amino acid (AA) uptake, mammalian target of rapamycin complex 1 (mTORC1) activation and mesenchyme homeobox1 (MEOX1) expression in activated HLFs. Fittngly, genetic inhibition of macropinocytosis also ameliorated lung fibroblast activation and pulmonary fibrosis in mice. Using IPF-derived precision cut lung slices (PCLS), we observed robust repression of profibrotic gene expression programs in EIPA-treated PCLS across different fibroblast subpopulations. Finally, we found that imipramine (Imi), a tricyclic antidepressant approved by the Food and Drug Administration (FDA), effectively inhibited macropinocytosis and ameliorated profibrotic responses in lung fibroblasts, Bleo-injured mice and IPF-derived PCLS. Taken together, our results suggest macropinocytosis inhibition can be considered as a potential therapeutic strategy to treat pulmonary fibrosis.