Background Autophagy is a basic cellular homeostatic process important to cell fate decisions under conditions of stress. Dysregulation of autophagy impacts numerous human diseases including cancer and chronic obstructive lung disease. This study investigates the role of autophagy in idiopathic pulmonary fibrosis. Methods Human lung tissues from patients with IPF were analyzed for autophagy markers and modulating proteins using western blotting, confocal microscopy and transmission electron microscopy. To study the effects of TGF-β1 on autophagy, human lung fibroblasts were monitored by fluorescence microscopy and western blotting. In vivo experiments were done using the bleomycin-induced fibrosis mouse model. Results Lung tissues from IPF patients demonstrate evidence of decreased autophagic activity as assessed by LC3, p62 protein expression and immunofluorescence, and numbers of autophagosomes. TGF-β1 inhibits autophagy in fibroblasts in vitro at least in part via activation of mTORC1; expression of TIGAR is also increased in response to TGF-β1. In the bleomycin model of pulmonary fibrosis, rapamycin treatment is antifibrotic, and rapamycin also decreases expression of á-smooth muscle actin and fibronectin by fibroblasts in vitro. Inhibition of key regulators of autophagy, LC3 and beclin-1, leads to the opposite effect on fibroblast expression of á-smooth muscle actin and fibronectin. Conclusion Autophagy is not induced in pulmonary fibrosis despite activation of pathways known to promote autophagy. Impairment of autophagy by TGF-β1 may represent a mechanism for the promotion of fibrogenesis in IPF.
Parkhitko A, Myachina F, Morrison TA, Hindi KM, Auricchio N, et al. (2011) Tumorigenesis in tuberous sclerosis complex is autophagy and p62/sequestosome 1 (SQSTM1)-dependent. Proc Natl Acad Sci U S A 108: 12455–12460.
Mi S, Li Z, Yang HZ, Liu H, Wang JP, et al. (2011) Blocking IL-17A promotes the resolution of pulmonary inflammation and fibrosis via TGF-beta1-dependent and -independent mechanisms. J Immunol 187: 3003–3014.
Korfei M, Ruppert C, Mahavadi P, Henneke I, Markart P, et al. (2008) Epithelial endoplasmic reticulum stress and apoptosis in sporadic idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 178: 838–846.
Tzouvelekis A, Harokopos V, Paparountas T, Oikonomou N, Chatziioannou A, et al. (2007) Comparative expression profiling in pulmonary fibrosis suggests a role of hypoxia-inducible factor-1alpha in disease pathogenesis. Am J Respir Crit Care Med 176: 1108–1119.
Lu Y, Azad N, Wang L, Iyer AK, Castranova V, et al. (2010) Phosphatidylinositol-3-kinase/akt regulates bleomycin-induced fibroblast proliferation and collagen production. Am J Respir Cell Mol Biol 42: 432–441.
Lee M, Hwang JT, Lee HJ, Jung SN, Kang I, et al. (2003) AMP-activated protein kinase activity is critical for hypoxia-inducible factor-1 transcriptional activity and its target gene expression under hypoxic conditions in DU145 cells. J Biol Chem 278: 39653–39661.
Mizushima N, Yamamoto A, Matsui M, Yoshimori T, Ohsumi Y (2004) In vivo analysis of autophagy in response to nutrient starvation using transgenic mice expressing a fluorescent autophagosome marker. Mol Biol Cell 15: 1101–1111.
Poulalhon N, Farge D, Roos N, Tacheau C, Neuzillet C, et al. (2006) Modulation of collagen and MMP-1 gene expression in fibroblasts by the immunosuppressive drug rapamycin. A direct role as an antifibrotic agent? J Biol Chem 281: 33045–33052.
Rahimi RA, Andrianifahanana M, Wilkes MC, Edens M, Kottom TJ, et al. (2009) Distinct roles for mammalian target of rapamycin complexes in the fibroblast response to transforming growth factor-beta. Cancer Res 69: 84–93.
Goc A, Choudhary M, Byzova TV, Somanath PR (2011) TGFbeta- and bleomycin-induced extracellular matrix synthesis is mediated through Akt and mammalian target of rapamycin (mTOR). J Cell Physiol 226: 3004–3013.
Lin L, Zhou Z, Zheng L, Alber S, Watkins S, et al. (2008) Cross talk between Id1 and its interactive protein Dril1 mediate fibroblast responses to transforming growth factor-beta in pulmonary fibrosis. Am J Pathol 173: 337–346.
Yoshizaki A, Yanaba K, Iwata Y, Komura K, Ogawa F, et al. (2010) Treatment with rapamycin prevents fibrosis in tight-skin and bleomycin-induced mouse models of systemic sclerosis. Arthritis Rheum 62: 2476–2487.
Lawson WE, Crossno PF, Polosukhin VV, Roldan J, Cheng DS, et al. (2008) Endoplasmic reticulum stress in alveolar epithelial cells is prominent in IPF: association with altered surfactant protein processing and herpesvirus infection. Am J Physiol Lung Cell Mol Physiol 294: L1119–1126.