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A6364 - Mitochondrial Uncoupling Protein-2 Regulates Age-Related Lung Fibrosis Via Alterations in Cellular Reactive Oxygen Species, Metabolism and Senescence
Author Block: S. Rangarajan1, M. L. Locy2, D. Chanda2, D. Kurundkar2, A. Kurundkar2, K. Bernard2, J. Deshane2, J. W. Zmijewski1, V. Darley-Usmar3, V. J. Thannickal4; 1Division of Pulmonary and Critical Care, Department of Medicine, Birmingham, AL, United States, 2Division of Pulmonary and Critical Care, Department of Medicine, University of Alabama at Birmingham, Birmingham, AL, United States, 3Pathology, University of Alabama at Birmingham, Birmingham, AL, United States, 4Division of Pulmonary and Critical Care, Department of Medicine, University of Alabama At Birmingham, Birmingham, AL, United States.
Rationale Idiopathic pulmonary fibrosis (IPF) has a strong association with aging. Cellular senescence and mitochondrial dysfunction have been implicated in aging and age-related disease. Excessive generation of reactive oxygen species (ROS), and altered metabolism resulting from mitochondrial dysfunction may contribute to senescence. Mitochondrial uncoupling proteins (UCPs) localized in the inner mitochondrial membrane regulate the mitochondrial membrane potential, with a possible role in thermogenesis and bioenergetic homeostasis. We detected high UCP2 expression in lung fibroblasts of human subjects with progressive IPF, and explored its potential role in pathobiology.
Methods We performed our studies on tissues and fibroblasts isolated from lung explants of IPF patients and murine model of lung fibrosis and resolution following bleomycin-induced lung injury. We utilized siRNA for silencing UCP2 expression in vitro and in vivo. Specific endpoints were analyzed by RT-PCR, SDS-PAGE western blotting, immunofluorescence, flow cytometry and extracellular flux analysis.
Results UCP2 gene expression was increased in lung fibroblasts of IPF patients with rapidly progressive clinical course compared to those with a slower course. Human lung fibroblasts undergoing replicative senescence expressed high levels of UCP2. UCP2 silencing in IPF fibroblasts decreased pro-fibrotic markers such as collagen 1a1 and α-SMA; this was associated with decreased mitochondrial ROS (superoxide and hydrogen peroxide) and decreased aerobic glycolysis. Interestingly, UCP2 silencing induced increase in cell-cycle regulatory genes and increased proliferation of fibroblasts; this was associated with decreased senescence markers and decreased expression of senescence-associated secretory phenotype (SASP) genes. Bleomycin lung injury in mice resulted in increase in UCP2 levels in fibroblasts in the fibrotic phase (3 weeks post-bleomycin). In bleomycin-injured aged mice, intra-tracheal administration of UCP2 siRNA during the fibrotic phase resulted in decreased lung collagen and fibrotic remodeling, indicating enhanced resolution capacity.
Conclusion Our results indicate that mitochondrial UCP2 is highly expressed in lung fibroblasts of human subjects with rapidly progressive IPF; UCP2 promotes myofibroblast senescence and impairs resolution of bleomycin injury-induced fibrosis in aged mice. Further studies are warranted to study the link between cellular aging and UCP2, and the therapeutic potential of targeting UCP2 in age-related fibrotic disorders such as IPF.