Modulation of mitochondrial gene expression in pulmonary epithelial cells exposed to oxidants

Our plain-English summary of Modulation of mitochondrial gene expression in pulmonary epithelial cells exposed to oxidants, by Y.M. Janssen, K.E. Driscoll, C.R. Timblin, et al (Environmental Health Perspectives, 1998).

The study

• Authors: Y.M. Janssen, K.E. Driscoll, C.R. Timblin, D. Hassenbein, B.T. Mossman
• Journal: Environmental Health Perspectives
• Published: 1998;106 Suppl 5(Suppl 5):1191-5
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Oxidants are important in the regulation of signal transduction and gene expression. Multiple classes of genes are transcriptionally activated by oxidants and are implicated in different phenotypic responses. In the present study, we performed differential mRNA display to elucidate genes that are induced or repressed after exposure of rat lung epithelial (RLE) cells to H2O2 or crocidolite asbestos, a pathogenic mineral that generates oxidants. After 8 or 24 hr of exposure, RNA was extracted, reverse transcribed, and amplified by polymerase chain reaction with degenerate primers to visualize alterations in gene expression. The seven clones obtained were sequenced and encoded the mitochondrial genes, NADH dehydrogenase subunits ND5 and ND6, and 16S ribosomal RNA. Evaluation of their expression by Northern blot analysis revealed increased expression of 16S rRNA after 1 or 2 hr of exposure to H2O2. At later time periods (4 and 24 hr), mRNA levels of 16S rRNA and NADH dehydrogenase were decreased in H2O2-treated RLE cells when compared to sham controls. Crocidolite asbestos caused increases in 16S rRNA levels after 8 hr of exposure, whereas after 24 hr of exposure to asbestos, 16S rRNA levels were decreased in comparison to sham controls. In addition to these oxidants, the nitric oxide generator spermine NONOate caused similar decreases in NADH dehydrogenase mRNA levels after 4 hr of exposure. The present data and previous studies demonstrated that all oxidants examined resulted in apoptosis in RLE cells during the time frame where alterations of mitochondrial gene expression were observed. As the mitochondrion is a major organelle that controls apoptosis, alterations in expression of mitochondrial genes may be involved in the regulation of apoptosis.

In plain English

This laboratory study used rat cells, not people. The authors exposed rat lung epithelial cells (RLE-6TN) to hydrogen peroxide (H2O2), crocidolite asbestos, or spermine NONOate, which releases nitric oxide. Of seven gene fragments sequenced, five were 16S rRNA and the others NADH dehydrogenase subunits ND5 and ND6, both mitochondrial genes. With 300 micromolar H2O2, 16S rRNA rose 130% at 1 hour and 30% at 2 hours, then fell 35% at 4 hours and 70% at 24 hours versus controls. NADH dehydrogenase mRNA fell at every time point (90%, 33%, 46% and 65%). Crocidolite raised 16S rRNA at 8 hours and lowered it at 24 hours. Rat pleural mesothelial cells also showed a 24-hour decrease. Spermine NONOate lowered NADH dehydrogenase mRNA, and 16S rRNA was unchanged at the 2 and 4 hours tested. Groups had one or two samples (H2O2 time course) or two (asbestos and spermine NONOate). Apoptosis (cell death) results were shown only for H2O2, which increased it from 4 hours. The authors concluded that mitochondrial gene changes may be involved in regulating apoptosis, and said the mechanism was unclear.

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: Laboratory cell-culture experiment (differential mRNA display, then Northern blot analysis)
• Who was studied: Rat alveolar epithelial cell line RLE-6TN, which has characteristics of alveolar type II cells. Rat pleural mesothelial (RPM) cells were also tested with asbestos. No humans or animals were studied directly.
• Exposure: Hydrogen peroxide (200 micromolar for differential display, 300 micromolar for the time-course, 100 micromolar for apoptosis), crocidolite asbestos (5 micrograms per square centimetre for differential display), and the nitric oxide donor spermine NONOate (300 micromolar or 1 mM), for periods from 1 to 24 hours
• Main results:
  • Of the seven clones sequenced, five encoded 16S rRNA and the others encoded NADH dehydrogenase subunits ND5 and ND6, both mitochondrial genes
  • In RLE cells given 300 micromolar H2O2 (n=1-2 per group), NADH dehydrogenase mRNA changed by -90% at 1 hr, -33% at 2 hr, -46% at 4 hr and -65% at 24 hr compared with controls
  • In RLE cells given 300 micromolar H2O2, 16S rRNA changed by +130% at 1 hr, +30% at 2 hr, -35% at 4 hr and -70% at 24 hr compared with controls
  • In RLE cells, crocidolite asbestos increased 16S rRNA after 8 hr and decreased it after 24 hr compared with sham controls (n=2 per group)
  • In rat pleural mesothelial cells, 24 hr of asbestos exposure also decreased 16S rRNA
  • In RLE cells (n=2 per group), spermine NONOate at 300 micromolar and 1 mM produced relative decreases in NADH dehydrogenase mRNA of 29% and 13% after 2 hr, and of 45% and 60% after 4 hr, compared with sham controls. No change in 16S rRNA was observed at these time points.
  • In RLE cells given 100 micromolar H2O2, the percentage of cells undergoing apoptosis increased as early as 4 hr after exposure. The Methods say apoptosis was also evaluated after spermine NONOate, but only H2O2 results are shown. For asbestos, the authors cite an earlier study.
• The authors' conclusion: The authors concluded that, because the mitochondrion is a major organelle controlling apoptosis, the changes they saw in mitochondrial gene expression may be involved in the regulation of apoptosis
• Limitations the authors state:
  • About 80% of the bands picked up by differential display were false positives on Northern blotting
  • Because separate blots were used, changes in control cultures over time could not be evaluated
  • It is unknown whether the gene-expression changes affect protein levels or mitochondrial function
  • The mechanism by which oxidants alter mitochondrial gene expression remains unclear

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Apoptosis.

Related studies

• Crocidolite activates NF-kappa B and MIP-2 gene expression in rat alveolar epithelial cells. Role of mitochondrial-derived oxidants — K.E. Driscoll, J.M. Carter, et al. (1998)
• Mitochondria-targeted Ogg1 and aconitase-2 prevent oxidant-induced mitochondrial DNA damage in alveolar epithelial cells — S.J. Kim, P. Cheresh, et al. (2014)
• Mitochondrial-targeted nitroxides disrupt mitochondrial architecture and inhibit expression of peroxiredoxin 3 and FOXM1 in malignant mesothelioma cells — B. Cunniff, K. Benson, et al. (2013)
• Different accumulation of activated extracellular signal-regulated kinases (ERK 1/2) and role in cell-cycle alterations by epidermal growth factor, hydrogen peroxide, or asbestos in pulmonary epithelial cells — S. Buder-Hoffmann, C. Palmer, et al. (2001)
• 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)
• Negative modulation of mitochondrial oxidative phosphorylation by epigallocatechin-3 gallate leads to growth arrest and apoptosis in human malignant pleural mesothelioma cells — D. Valenti, L. de Bari, et al. (2013)

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