Extensive temporal transcriptome and microRNA analyses identify molecular mechanisms underlying mitochondrial dysfunction induced by multi-walled carbon nanotubes in human lung cells

Our plain-English summary of Extensive temporal transcriptome and microRNA analyses identify molecular mechanisms underlying mitochondrial dysfunction induced by multi-walled carbon nanotubes in human lung cells, by P. Nymark, P. Wijshoff, R. Cavill, et al (Nanotoxicology, 2015).

The study

• Authors: P. Nymark, P. Wijshoff, R. Cavill, M. van Herwijnen, M.L. Coonen, S. Claessen, J. Catalán, H. Norppa, J.C. Kleinjans, J.J. Briedé
• Journal: Nanotoxicology
• Published: 2015;9(5):624-35
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Understanding toxicity pathways of engineered nanomaterials (ENM) has recently been brought forward as a key step in twenty-first century ENM risk assessment. Molecular mechanisms linked to phenotypic end points is a step towards the development of toxicity tests based on key events, which may allow for grouping of ENM according to their modes of action. This study identified molecular mechanisms underlying mitochondrial dysfunction in human bronchial epithelial BEAS 2B cells following exposure to one of the most studied multi-walled carbon nanotubes (Mitsui MWCNT-7). Asbestos was used as a positive control and a non-carcinogenic glass wool material was included as a negative fibre control. Decreased mitochondrial membrane potential (MMP↓) was observed for MWCNTs at a biologically relevant dose (0.25 μg/cm(2)) and for asbestos at 2 μg/cm(2), but not for glass wool. Extensive temporal transcriptomic and microRNA expression analyses identified a 330-gene signature (including 26 genes with known mitochondrial function) related to MWCNT- and asbestos-induced MMP↓. Forty-nine of the MMP↓-associated genes showed highly similar expression patterns over time (six time points) and the majority was found to be regulated by two transcription factors strongly involved in mitochondrial homeostasis, APP and NRF1. In addition, four miRNAs were correlated with MMP↓ and one of them, miR-1275, was found to negatively correlate with a large part of the MMP↓-associated genes. Cellular processes such as gluconeogenesis, mitochondrial LC-fatty acid β-oxidation and spindle microtubule function were enriched among the MMP↓-associated genes and miRNAs. These results are expected to be useful in the identification of key events in ENM-related toxicity pathways for the development of molecular screening techniques.

In plain English

This was a laboratory (in vitro) study in human bronchial epithelial BEAS 2B cells exposed to Mitsui MWCNT-7 multi-walled carbon nanotubes, with UICC crocidolite asbestos as a positive fibre control and MMVF10 glass wool as a negative fibre control, at 0.25, 2 and 10 micrograms per square centimetre. After 24 hours, the nanotubes caused a statistically significant fall in mitochondrial membrane potential at all three doses in a dose-dependent way; asbestos did so only at 2 and 10, not at 0.25; glass wool did not at any dose. Persistence was tested at 48 hours only for the two lower doses: the decrease persisted at 2 for nanotubes and asbestos, but not at 0.25. No significant change in mitochondrial radical formation was found for any material. Gene and microRNA expression measured at six time points yielded a 330-gene signature shared by the conditions with decreased membrane potential, including 26 mitochondria-related genes, plus four microRNAs; 49 genes with similar time patterns were largely linked to the transcription factors NRF1 and APP. The authors concluded these genes and microRNAs were associated with decreased membrane potential after low-dose nanotube and asbestos exposure.

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 toxicogenomics experiment in a human lung cell line, with temporal transcriptome and microRNA microarray analysis
• Who was studied: Immortalised human bronchial epithelial BEAS 2B cells (passages 49-50), grown in serum-free medium; three biological replicates per condition
• Exposure: Mitsui MWCNT-7 multi-walled carbon nanotubes, UICC standard reference crocidolite asbestos (positive control) and MMVF10 glass wool (negative fibre control), at 0.25, 2 and 10 micrograms per square centimetre
• Main results:
  • At 24 hours MWCNTs significantly decreased mitochondrial membrane potential at all three doses, dose-dependently
  • Asbestos caused significant depolarisation only at 2 and 10 micrograms per square centimetre; glass wool at no dose
  • Persistence at 48 hours was tested only for 0.25 and 2 micrograms per square centimetre; the decrease persisted at 2 for MWCNT and asbestos, not at 0.25
  • At 48 hours no material decreased membrane potential at the lowest dose, while MWCNT2 and ASB2 showed a persisting decrease
  • No significant change in mitochondrial radical formation was detected for any of the three materials
  • 330 genes, 26 of them mitochondria-related, were shared by the three conditions that decreased membrane potential (asbestos 2, MWCNT 0.25 and MWCNT 2)
  • Comparison conditions with unchanged membrane potential (asbestos 0.25, glass wool 0.25 and 2) shared 333 genes, 19 mitochondria-related
  • 49 of the signature genes shared highly similar time profiles and largely formed a network with transcription factors NRF1 and APP
  • Four microRNAs correlated with decreased membrane potential; 51 of the 330 genes anti-correlated with at least one of them in all three conditions, with miR-1275 most prominent
• The authors' conclusion: The authors concluded that a set of 330 genes, two transcription factors (NRF1 and APP) and four microRNAs were associated with decreased mitochondrial membrane potential after low-dose exposure to MWCNTs and asbestos, while glass wool did not affect membrane potential
• Limitations the authors state:
  • Some genes in the signature may be only correlative, with no direct relation to the decrease in membrane potential
  • A liberal statistical approach with unadjusted p values and low fold changes was used
  • Target genes of miR-1275 have not been verified
  • Genes anti-correlating with a microRNA may not be its direct targets

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic.

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• Acute effects of multi-walled carbon nanotubes on primary bronchial epithelial cells from COPD patients — S. Beyeler, S. Chortarea, et al. (2018)
• Toxicogenomic comparison of multi-wall carbon nanotubes (MWCNTs) and asbestos — J.S. Kim, K.S. Song, et al. (2012)

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