Co-treatment with interferon-γ and 1-methyl tryptophan ameliorates cardiac fibrosis through cardiac myofibroblasts apoptosis

Cardiac remodeling characterized by cardiac fibrosis is a pathologic process occurring after acute myocardial infarction. Fibrosis can be ameliorated by interferon-gamma (IFN-γ), which is a soluble cytokine showing various effects such as anti-fibrosis, apoptosis, anti-proliferation, immunomodulation, and anti-viral activities. However, the role of IFN-γ in cardiac myofibroblasts is not well established. Therefore, we investigated the anti-fibrotic effects of IFN-γ in human cardiac myofibroblasts (hCMs) in vitro and whether indoleamine 2,3-dioxygenase (IDO), induced by IFN-γ and resulting in cell cycle arrest, plays an important role in regulating the biological activity of hCMs. After IFN-γ treatment, cell signaling pathways and DNA contents were analyzed to assess the biological activity of IFN-γ in hCMs. In addition, an IDO inhibitor (1-methyl tryptophan; 1-MT) was used to assess whether IDO plays a key role in regulating hCMs. IFN-γ significantly inhibited hCM proliferation, and IFN-γ-induced IDO expression caused cell cycle arrest in G0/G1 through tryptophan depletion. Moreover, IFN-γ treatment gradually suppressed the expression of α-smooth muscle actin. When IDO activity was inhibited by 1-MT, marked apoptosis was observed in hCMs through the induction of interferon regulatory factor, Fas, and Fas ligand. Our results suggest that IFN-γ plays key roles in anti-proliferative and anti-fibrotic activities in hCMs and further induces apoptosis via IDO inhibition. In conclusion, co-treatment with IFN-γ and 1-MT can ameliorate fibrosis in cardiac myofibroblasts through apoptosis.