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A6208 - ATF3 Plays a Role in AECII ER Stress-Mediated Mitochondrial Dysfunction and the Susceptibility to Lung Fibrosis
Author Block: M. Bueno, K. Fiedler, B. G. Mays, A. Nasser, S. J. Shulkowski, A. Potkonjak, J. Pogue, J. T. Carter, M. Rojas, A. L. Mora; University of Pittsburgh, Pittsburgh, PA, United States.
Rationale: ATF3 (activating transcription factor 3) is a hub of the cellular adaptive-response network. We recently found that ATF3 is highly expressed in aging human lungs and AECII lining honeycomb areas of IPF lungs. In addition, we demonstrated that ER stress, via ATF3, can regulate mitochondrial homeostasis by repression of PINK1 (PTEN-induced putative kinase 1) gene transcription. PINK1 is a key regulator of mitochondrial homeostasis and impaired PINK1 expression leads to accumulation of damaged mitochondria in lung epithelial cells and increased susceptibility to lung fibrosis. These data might implicate that ATF3 modulates mitochondrial function and have a role in the pathobiology of lung fibrosis. Methods: A549 human lung alveolar epithelial cells were transfected to obtain ATF3 overexpression. Mice with ATF3 exon 2 coding region flanked with LoxP recombination sites (ATF3 fl/fl) and mice carrying a doxycycline-inducible Cre-recombinase under the control of a regulatory sequence of the SP-C gene were bred. To promote recombination and generate a homozygous conditional type II lung epithelial cells ATF3 knockout mice (ATF3 spc-KO), mice were fed doxycycline chow (625 mg/kg, Envigo) for 2 weeks before injury induction. A dose of 1.5U/kg of intra-tracheal bleomycin was used in 3 month old ATF3 WT, ATF3 fl/fl and ATF3 spc-KO mice. Results: ATF3 overexpression resulted mitochondrial alterations characterized by low mitochondrial membrane potential, increase of mitochondrial mass, and higher levels of mitochondrial ROS. ATF3 spc-KO mice show reduced lung pathology and decreased collagen deposition at day 15 post bleomycin treatment. ATF3 spc-KO mice also preserve a higher expression of PINK1 even after injury. Additionally, collagen and fibronectin expression was reduced in the ATF3 spc-KO mice at day 15 post bleomycin treatment. Moreover, ATF3 WT and ATF3 fl/fl lung showed higher levels of the profibrotic mediators TGFβ and FGF2. Inflammatory responses were also more severe in the control mice than in the ATF3 spc-KO littermates, as determined by BAL cell counts and the changes in mRNA levels of the cytokines TNFα, and IL6. Conclusion: Upregulation of ATF3 leads to mitochondrial dysfunction. Conditional deletion of ATF3 in type II lung epithelial cells protected from lung fibrosis induced by bleomycin showing a better outcome measured by pro-fibrotic, and pro-inflammatory markers while preserving PINK1 expression in the lung. These data strongly suggest that ATF3, via regulation of PINK1, has a key role in the AECIIs susceptibility to lung injury, and development of lung fibrosis. Funding: HL131789-01