15 February 2020 by Martina Korfei

Increased susceptibility to gammaherpesvirus-induced lung fibrosis of transgenic mice with conditional overexpression of the ER stress-factor Chop in alveolar epithelium

Idiopathic pulmonary fibrosis (IPF) is an age-related interstitial lung disease with fatal outcome. The main characteristic of IPF is ER-stress and apoptosis in type-II alveolar epithelial cells (AECII), which in consequence cause chronic epithelial injury and progressive lung fibrosis. We developed double-transgenic mice expressing the proapoptotic ER-stress-factor Chop exclusively in AECII by using the Tetracycline-On-system (SP-C rtTA/tetO7-Chop).

In response to 28 days doxycycline-feeding (Dox+), nuclear Chop-overexpression in AECII resulted in AECII-apoptosis, but not in development of lung fibrosis. We thus suggested that the extent of AECII apoptosis in the ′Chop-mice′ was not sufficient to cause lung fibrosis, and that ′second hits′ such as age, (herpes)virus-infection, ROS-exposure etc. may be required for ′full-blown′ AECII-ER-stress and ′high-level′ AECII apoptosis. Indeed, several studies have suggested that herpesviruses may play a role in IPF-pathogenesis. We therefore infected Chop transgenic mice after 28 days transgene-induction (Dox+), as well as without transgene induction (Dox-), intranasally with murine gammaherpesvirus-68 (MHV68). At 15 days post infection, mice were sacrificed and analysed. Lungs of MHV68-infected (Dox+) Chop-mice, but not of infected (Dox-) Chop-mice or uninfected (Dox+) and (Dox-) Chop-mice, evidently showed thickening of alveolar septae and fibrotic remodelling. In addition, ER-stress and strong apoptosis-induction (caspase-9/-3-activation, PARP1-cleavage) was observed in lungs of both MHV68-infected (Dox+) and (Dox-) Chop-mice versus controls, presumably due to virus-induced lung injury, but was more pronounced in the infected (Dox+) Chop-mice. Interestingly, Chop was not (endogenously) induced in (Dox-) Chop-mice in response to MHV68-infection, despite evident virus-induced ER-stress! Further, MHV68-infected (Dox+) and (Dox-) Chop-mice indicated upregulation of profibrotic protein-expression (Mmp2, Pai-1, p-Smad3) versus controls, but was “biggest” in the infected (Dox+) Chop-mice.

We conclude that our transgenic Chop-mouse-model resembles human IPF, since IPF-patients have been defined as (genetically) susceptible individuals prone to develop disease with second hits.

Idiopathic pulmonary fibrosis (IPF) is an age-related interstitial lung disease with fatal outcome. The main characteristic of IPF is ER-stress and apoptosis in type-II alveolar epithelial cells (AECII), which in consequence cause chronic epithelial injury and progressive lung fibrosis. We developed double-transgenic mice expressing the proapoptotic ER-stress-factor Chop exclusively in AECII by using the Tetracycline-On-system (SP-C rtTA/tetO7-Chop). In response to 28 days doxycycline-feeding (Dox+), nuclear Chop-overexpression in AECII resulted in AECII-apoptosis, but not in development of lung fibrosis. We thus suggested that the extent of AECII apoptosis in the ′Chop-mice′ was not sufficient to cause lung fibrosis, and that ′second hits′ such as age, (herpes)virus-infection, ROS-exposure etc. may be required for ′full-blown′ AECII-ER-stress and ′high-level′ AECII apoptosis. Indeed, several studies have suggested that herpesviruses may play a role in IPF-pathogenesis. We therefore infected Chop transgenic mice after 28 days transgene-induction (Dox+), as well as without transgene induction (Dox-), intranasally with murine gammaherpesvirus-68 (MHV68). At 15 days post infection, mice were sacrificed and analysed. Lungs of MHV68-infected (Dox+) Chop-mice, but not of infected (Dox-) Chop-mice or uninfected (Dox+) and (Dox-) Chop-mice, evidently showed thickening of alveolar septae and fibrotic remodelling. In addition, ER-stress and strong apoptosis-induction (caspase-9/-3-activation, PARP1-cleavage) was observed in lungs of both MHV68-infected (Dox+) and (Dox-) Chop-mice versus controls, presumably due to virus-induced lung injury, but was more pronounced in the infected (Dox+) Chop-mice. Interestingly, Chop was not (endogenously) induced in (Dox-) Chop-mice in response to MHV68-infection, despite evident virus-induced ER-stress! Further, MHV68-infected (Dox+) and (Dox-) Chop-mice indicated upregulation of profibrotic protein-expression (Mmp2, Pai-1, p-Smad3) versus controls, but was “biggest” in the infected (Dox+) Chop-mice. We conclude that our transgenic Chop-mouse-model resembles human IPF, since IPF-patients have been defined as (genetically) susceptible individuals prone to develop disease with second hits.

About the author


profile picture of Martina Korfei

Martina Korfei

Post-doctoral research fellow, lab leader

Justus-Liebig-University Giessen, Universities of Giessen and Marburg Lung Center (UGMLC)

Germany

Key Contributors

Martina Korfei, Mohamed Smaida, Oleksiy Klymenko, Clemens Ruppert, Ingrid Henneke, Martin Huehn, Poornima Mahavadi, Susanne Herold, Werner Seeger, Heiko Adler and Andreas Guenther Universities of Giessen and Marburg Lung Center (UGMLC), Biomedical Research Center Seltersberg (BFS), Justus-Liebig-University Giessen, D-35392 Giessen, Germany. UGMLC, Department of Internal Medicine, Medical Clinic II, D-35392 Giessen, Germany. German Center for Lung Research (DZL). Max-Planck-Institute for Heart and Lung Research, Department of Lung Development and Remodeling, D-61231 Bad Nauheim, Germany. Research Unit Lung Repair and Regeneration, Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH), D-81377, Munich, Germany. Agaplesion Lung Clinic Waldhof Elgershausen, D-35753 Greifenstein, Germany. European IPF Network and European IPF Registry.


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