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A5772 - Decreased Autophagy and Endoplasmic Reticulum (ER) Stress Induction During Aging, Is Associated with Aberrant Macrophage Recruitment and Lung Remodeling in Mouse
Author Block: M. Maciel1, A. C. McQuattie-Pimentel2, R. Piseaux-Aillon2, D. Hernandez-Barrientos1, M. Selman3, A. Pardo1, G. Budinger2, S. Cabrera1; 1Universidad Nacional Autonoma de Mexico, UNAM. Facultad de Ciencias, Mexico, Mexico, 2Northwestern University Feinberg School of Medicine, Chicago, IL, United States, 3Instituto Nacional de Enfermedades Respiratorias, Ismael Cosio Villegas, Mexico, Mexico.
RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a lethal disease of unknown etiology. Advanced age is one of the most important risk factors for IPF, however, the molecular mechanisms underlying the increased susceptibility to IPF in aging are still unclear. Recent evidence suggests that lung epithelial cells lungs show impaired proteostasis characterized by reduced autophagy and increased endoplasmic reticulum (ER) stress during aging. As the lung microenvironment plays a key role in determining the function of alveolar macrophages, we sought to test the hypothesis that the induction of lung proteostatic stress would alter the function of alveolar macrophages during fibrosis. METHODS: In order to define the interplay between aging, ER stress and autophagy in the development of lung fibrosis, we instilled the N-linked glycosylation inhibitor, tunicamycin (10µg/ml) intratracheally into young (2 months) and old (24 months) WT mice. Tunicamycin causes the accumulation of misfolded proteins and is widely used to induce ER stress. 21 days after tunicamycin treatment, ER stress and autophagy biomarkers, apoptosis, inflammation and fibrosis were evaluated in lungs from young and old mice. RESULTS: When compared with young mice, aged mice showed a dramatically enhanced susceptibility to tunicamycin induced lung injury as measured by reduced survival, worsened parenchymal destruction, increased epithelial staining for cleaved caspase-3, and increased infiltration of inflammatory cells, especially macrophages which were characterized by crystalline cytoplasmic content and collagen accumulation. Under basal conditions, we found accumulation of both LC3-I/II as well as p62, in lungs from old WT mice compared to young mice, reflecting decreased autophagic activity. Moreover, the level of ER stress markers, CHOP, BiP and XBP1 were upregulated in lungs from old mice. Flow cytometry of lung homogenates showed that treatment with tunicamycin resulted in expansion of interstitial and alveolar macrophages at 7, 14 and 21 days.Conclusion: Our results demonstrate that alterations in proteostasis during aging, such autophagy impairment, sensitize the lung to tunicamycin-induced ER stress. Older mice show marked susceptibility to tunicamycin induced injury and inflammatory cell infiltration. Strategies that improve proteostatic function may prove promising for the amelioration of pulmonary fibrosis.