Mitochondria-targeted Ogg1 and aconitase-2 prevent oxidant-induced mitochondrial DNA damage in alveolar epithelial cells

Our plain-English summary of Mitochondria-targeted Ogg1 and aconitase-2 prevent oxidant-induced mitochondrial DNA damage in alveolar epithelial cells, by S.J. Kim, P. Cheresh, D. Williams, et al (The Journal of Biological Chemistry, 2014).

The study

• Authors: S.J. Kim, P. Cheresh, D. Williams, Y. Cheng, K. Ridge, P.T. Schumacker, S. Weitzman, V.A. Bohr, D.W. Kamp
• Journal: The Journal of Biological Chemistry
• Published: 2014;289(9):6165-76
• Cited by: 87 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Mitochondria-targeted human 8-oxoguanine DNA glycosylase (mt-hOgg1) and aconitase-2 (Aco-2) each reduce oxidant-induced alveolar epithelial cell (AEC) apoptosis, but it is unclear whether protection occurs by preventing AEC mitochondrial DNA (mtDNA) damage. Using quantitative PCR-based measurements of mitochondrial and nuclear DNA damage, mtDNA damage was preferentially noted in AEC after exposure to oxidative stress (e.g. amosite asbestos (5-25 μg/cm(2)) or H2O2 (100-250 μM)) for 24 h. Overexpression of wild-type mt-hOgg1 or mt-long α/β 317-323 hOgg1 mutant incapable of DNA repair (mt-hOgg1-Mut) each blocked A549 cell oxidant-induced mtDNA damage, mitochondrial p53 translocation, and intrinsic apoptosis as assessed by DNA fragmentation and cleaved caspase-9. In contrast, compared with controls, knockdown of Ogg1 (using Ogg1 shRNA in A549 cells or primary alveolar type 2 cells from ogg1(-/-) mice) augmented mtDNA lesions and intrinsic apoptosis at base line, and these effects were increased further after exposure to oxidative stress. Notably, overexpression of Aco-2 reduced oxidant-induced mtDNA lesions, mitochondrial p53 translocation, and apoptosis, whereas siRNA for Aco-2 (siAco-2) enhanced mtDNA damage, mitochondrial p53 translocation, and apoptosis. Finally, siAco-2 attenuated the protective effects of mt-hOgg1-Mut but not wild-type mt-hOgg1 against oxidant-induced mtDNA damage and apoptosis. Collectively, these data demonstrate a novel role for mt-hOgg1 and Aco-2 in preserving AEC mtDNA integrity, thereby preventing oxidant-induced mitochondrial dysfunction, p53 mitochondrial translocation, and intrinsic apoptosis. Furthermore, mt-hOgg1 chaperoning of Aco-2 in preventing oxidant-mediated mtDNA damage and apoptosis may afford an innovative target for the molecular events underlying oxidant-induced toxicity.

In plain English

This was a laboratory cell-culture study of how oxidative stress damages mitochondrial DNA (mtDNA) in alveolar epithelial cells. The authors exposed A549 human lung adenocarcinoma cells to amosite asbestos (5 to 25 micrograms per square centimetre) or hydrogen peroxide (100 to 250 micromolar) for 24 hours, and exposed primary alveolar type II cells from wild-type and ogg1-deficient mice, the MLE-12 mouse lung epithelial cell line and the RLE-6TN rat alveolar type II cell line to asbestos at 25 micrograms per square centimetre or hydrogen peroxide at 250 micromolar for 24 hours; DNA damage was measured by quantitative PCR. In A549 cells both oxidants produced dose-dependent mtDNA lesions; the other cells also showed mtDNA damage, at lower levels, while nuclear DNA damage was negligible. Overexpressing mitochondria-targeted human Ogg1, either wild-type or a mutant unable to repair DNA, blocked mtDNA damage, mitochondrial p53 accumulation and intrinsic apoptosis; knocking down Ogg1, or using cells from ogg1-deficient mice, increased these effects at baseline and further after oxidant exposure. Overexpressing aconitase-2 was protective, while silencing it increased damage and apoptosis. Silencing aconitase-2 removed the protection given by the repair-deficient Ogg1 mutant but not by wild-type Ogg1. The authors concluded that mt-hOgg1 and Aco-2 preserve mtDNA integrity, preventing p53 translocation and apoptosis.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: in vitro cell culture experiments (cell lines and primary mouse alveolar type II cells) using gene overexpression and knockdown, with quantitative PCR-based DNA damage assays
• Who was studied: Alveolar epithelial cells: A549 human lung adenocarcinoma cells, MLE-12 mouse lung epithelial cells, RLE-6TN rat alveolar type II cells, and primary alveolar type II cells isolated from wild-type C57/BL6 and ogg1-deficient mice
• Exposure: Amosite asbestos fibres (UICC reference standard samples) at 5 to 25 micrograms per square centimetre in A549 cells and 25 micrograms per square centimetre in the other cells, or hydrogen peroxide at 100 to 250 micromolar in A549 cells and 250 micromolar in the other cells, for 24 hours
• Main results:
  • In A549 cells, mtDNA lesions rose dose-dependently with asbestos (5-25 micrograms per square centimetre) or hydrogen peroxide (100-250 micromolar) over 24 hours
  • Oxidative stress also caused mtDNA damage in primary murine AT2, MLE-12 and RLE-6TN cells, at lower levels than in A549 cells
  • Nuclear DNA damage was negligible in all the alveolar epithelial cells tested after asbestos or hydrogen peroxide
  • In A549 cells, overexpression of either wild-type mitochondria-targeted hOgg1 or the repair-incapable mutant prevented asbestos-induced mtDNA damage and intrinsic apoptosis, and reduced mitochondrial p53
  • In A549 cells, hOgg1 shRNA increased mtDNA damage, mitochondrial p53 and apoptosis at baseline, with further increases after asbestos or hydrogen peroxide
  • Untreated primary AT2 cells from ogg1-deficient mice had more mtDNA lesions, less Aco-2, more mitochondrial p53 and more apoptosis than wild-type AT2 cells
  • In A549 cells, Aco-2 overexpression lowered mtDNA lesions after asbestos or hydrogen peroxide compared with empty-vector controls, and also lowered mitochondrial p53 and apoptosis
  • In A549 cells, Aco-2 siRNA increased mtDNA lesions at baseline and further after oxidants, and raised baseline apoptosis by nearly 50% as measured by DNA fragmentation
  • Co-transfection experiments in A549 cells: Aco-2 silencing removed the protection of the repair-incapable mt-hOgg1 mutant but not of wild-type mt-hOgg1
• The authors' conclusion: The authors concluded that mitochondria-targeted hOgg1 and Aco-2 preserve alveolar epithelial cell mtDNA integrity, thereby blocking oxidant-induced mitochondrial dysfunction, p53 mitochondrial translocation and intrinsic apoptosis, and they suggested this may be a target for oxidant-induced toxicity.
• Limitations the authors state:
  • The authors stated the in vivo relevance of these in vitro findings is unclear.
  • The authors stated the precise mechanisms by which mitochondrial p53 and Aco-2 affect AT2 cell mtDNA and apoptosis, and their role in other cell types, await further study.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite.

Medical terms in this study, explained in our Lexicon: Apoptosis, Oxidative Stress, Amosite, Translocation, A549 Cells.

Related studies

• Mitochondrial catalase overexpressed transgenic mice are protected against lung fibrosis in part via preventing alveolar epithelial cell mitochondrial DNA damage — S.J. Kim, P. Cheresh, et al. (2016)
• SIRT3 deficiency promotes lung fibrosis by augmenting alveolar epithelial cell mitochondrial DNA damage and apoptosis — R.P. Jablonski, S.J. Kim, et al. (2017)
• The Role of Mitochondrial DNA in Mediating Alveolar Epithelial Cell Apoptosis and Pulmonary Fibrosis — S.J. Kim, P. Cheresh, et al. (2015)
• P53 mediates amosite asbestos-induced alveolar epithelial cell mitochondria-regulated apoptosis — V. Panduri, S. Surapureddi, et al. (2006)
• Modulation of mitochondrial gene expression in pulmonary epithelial cells exposed to oxidants — Y.M. Janssen, K.E. Driscoll, et al. (1998)
• Asbestos-induced pulmonary fibrosis is augmented in 8-oxoguanine DNA glycosylase knockout mice — P. Cheresh, L. Morales-Nebreda, et al. (2015)

Browse more research in The Journal of Biological Chemistry, or return to medical research.