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Mitochondrial dysfunction contributes to the senescent phenotype of IPF lung fibroblasts.

ABSTRACT: Increasing evidence highlights that senescence plays an important role in idiopathic pulmonary fibrosis (IPF). This study delineates the specific contribution of mitochondria and the superoxide they form to the senescent phenotype of lung fibroblasts from IPF patients (IPF-LFs). Primary cultures of IPF-LFs exhibited an intensified DNA damage response (DDR) and were more senescent than age-matched fibroblasts from control donors (Ctrl-LFs). Furthermore, IPF-LFs exhibited mitochondrial dysfunction, exemplified by increases in mitochondrial superoxide, DNA, stress and activation of mTORC1. The DNA damaging agent etoposide elicited a DDR and augmented senescence in Ctrl-LFs, which were accompanied by disturbances in mitochondrial homoeostasis including heightened superoxide production. However, etoposide had no effect on IPF-LFs. Mitochondrial perturbation by rotenone involving sharp increases in superoxide production also evoked a DDR and senescence in Ctrl-LFs, but not IPF-LFs. Inhibition of mTORC1, antioxidant treatment and a mitochondrial targeting antioxidant decelerated IPF-LF senescence and/or attenuated pharmacologically induced Ctrl-LF senescence. In conclusion, increased superoxide production by dysfunctional mitochondria reinforces lung fibroblast senescence via prolongation of the DDR. As part of an auto-amplifying loop, mTORC1 is activated, altering mitochondrial homoeostasis and increasing superoxide production. Deeper understanding the mechanisms by which mitochondria contribute to fibroblast senescence in IPF has potentially important therapeutic implications.

SUBMITTER: Schuliga M

PROVIDER: S-EPMC6237609 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature

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Project description:The activated fibroblast is the central effector cell for the progressive fibrotic process that characterizes idiopathic pulmonary fibrosis (IPF). An understanding of the genomic phenotype of this cell in isolation is essential to the understanding of disease pathogenesis and is integral to strategizing therapeutic trials. Employing a unique technique that minimizes cellular phenotypic alterations, we characterized the genomic phenotype of non-cultured pulmonary fibroblasts from the lungs of patients with advanced IPF. This approach revealed several novel genes and pathways previously unreported in IPF fibroblasts. Specifically, we demonstrate altered expression in proteasomal constituents, ubiquitination mediators, the Wnt pathway and several cell cycle regulators suggestive of loss of normal cell cycle controls. The pro-inflammatory cytokine CXCL12 was also up-regulated which may provide a mechanism for fibrocytes’ recruitment, while up-regulated oncogenic KIT may promote fibroblast over proliferation. Paradoxically, pro-apoptotic inducers such as death inducing ligand TRAIL (TNFSF10) and pro-apoptotic Bax were also up-regulated. This comprehensive description of altered gene expression within IPF fibroblasts sheds further light on the complex interactions that characterize IPF. Further studies including therapeutic interventions directed at these pathways hold promise for the treatment of this devastating disease. 58 samples of total RNA isolated from 12 lungs of patients with end-stage idiopathic pulmonary fibrosis and 6 donors of normal lungs (controls) who were designated brain dead, non-diseased donors whose lungs failed criteria for transplantation and who were organ donors for research. RNA extraction followed the Qiagen RNeasy Kit using QIshredder columns for shredding of DNA contiminants. Experimental/control samples were amplified amino-allylated RNA labeled with Cy5 and Stratagene Reference RNA was amplified and amino-allylated and labeled with Cy3. Amplification was one round using Ambion MessageAmp II kit with amino-allylated UTP according to the protocol of the Duke University Institute for Genome Sciences and Policy. Amplification and amino-allylation of the Stratagene Reference RNA and Hybridization of Reference with patient samples and controls was done by the Duke Institute for Genomic Sciences and Policy.

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Mitochondrial dysfunction contributes to the senescent phenotype of IPF lung fibroblasts.

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