Functional effects of differentially expressed microRNAs in A549 cells exposed to MWCNT-7 or crocidolite

Our plain-English summary of Functional effects of differentially expressed microRNAs in A549 cells exposed to MWCNT-7 or crocidolite, by C. Ventura, L. Vieira, C. Silva, et al (Toxicology Letters, 2020).

The study

• Authors: C. Ventura, L. Vieira, C. Silva, A. Sousa-Uva, M.J. Silva
• Journal: Toxicology Letters
• Published: 2020;328:7-18
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Multi-walled carbon nanotubes (MWCNT) are engineered nanomaterials widely used in industrial and biomedical applications. Yet, MWCNT inhalation may induce pulmonary adverse effects, and the MWCNT-7 (Mitsui-7) has been classified as possibly carcinogenic to humans. However, its molecular mechanisms of action are poorly understood and there are no biomarkers of exposure for occupational monitoring. Several pulmonary diseases, including lung cancer, have been associated with alterations in microRNA expression that are used as biomarkers of disease progression, and differentially-expressed microRNAs (DE miRNAs) can also allow understanding the molecular effects induced by a toxicant. In this study, we identify DE miRNAs in A549 alveolar epithelial cells following 24 h exposure to MWCNT-7 or crocidolite, as well as their enriched cellular functional pathways. These indicate that both materials change cell survival, differentiation and proliferative properties under the influence of AMPK, FoxO, TGF-β and Hippo pathways, and their metabolic activity and cell-to-cell communication. In addition, MWCNT-7 affects the actin cytoskeleton, ubiquitin mediated proteolysis, and ECM-receptor interactions; crocidolite the PI3K-Akt and mTOR pathways, endocytosis, and central carbon metabolism. Since deregulation of these pathways may be related to carcinogenesis, an interaction network of DE miRNAs and corresponding target cancer-related genes was constructed, highlighting the carcinogenic potential of Mitsui-7.

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In plain English

This laboratory study looked at human lung cells grown in dishes, not at people or animals. The authors exposed A549 cells, a human alveolar epithelial cell line, for 24 hours to 0.25 micrograms per square centimetre of either the multi-walled carbon nanotube MWCNT-7 (Mitsui-7) or crocidolite asbestos. They compared these with unexposed cells. They sequenced microRNAs, small molecules that help control gene activity, and used computer tools to predict which genes and cell pathways the changes might affect. After filtering, 17 microRNAs were differently expressed in MWCNT-7-exposed cells and 21 in crocidolite-exposed cells. Most predicted pathways were shared by both materials and related to cell metabolism, cell growth and death, cell-to-cell communication and signalling. Some differed. Actin cytoskeleton, ubiquitin mediated proteolysis and ECM-receptor interaction appeared only for MWCNT-7. Endocytosis and the PI3K-Akt and mTOR pathways, among others, appeared only for crocidolite. The authors concluded that comparing networks of cancer-related target genes suggested crocidolite had a higher impact than MWCNT-7 on cancer-related pathways in these A549 cells. They noted that results from this cell line may not match normal lung cells.

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 laboratory experiment: microRNA sequencing (next generation sequencing) of cultured human lung cells, with computer-based pathway and gene network analysis
• Who was studied: A549 human alveolar epithelial cell line (from the American Type Culture Collection), with non-exposed cells as controls; no humans or animals were studied
• Exposure: 0.25 micrograms per square centimetre of MWCNT-7 (Mitsui-7, sample NRCWE-006) or of UICC standard reference crocidolite fibres for 24 hours. The authors describe the MWCNT-7 dose as having been considered occupationally relevant.
• Main results:
  • After filtering, 17 microRNAs were differentially expressed in MWCNT-7-exposed cells and 21 in crocidolite-exposed cells, compared with non-exposed cells
  • Most enriched pathways were shared by both exposures and related to cell metabolism, cell growth and death, cell-to-cell communication, protein processing and signal transduction
  • Pathways enriched only in MWCNT-7-exposed cells were regulation of actin cytoskeleton, ubiquitin mediated proteolysis and ECM-receptor interaction
  • Pathways enriched only in crocidolite-exposed cells included endocytosis, central carbon metabolism in cancer, microRNAs in cancer, non-small cell lung cancer, PI3K-Akt signalling and mTOR signalling
  • Target genes in the cancer pathway set were found for 14 of 17 microRNAs in MWCNT-7-exposed cells (56 target genes) and 17 of 21 in crocidolite-exposed cells (60 target genes)
  • The gene networks included oncogenes (such as CCND1, EGFR, MDM2, MYC) and tumour suppressor genes (such as PTEN, RUNX1, SMAD2). Comparing the networks suggested crocidolite had a higher impact than MWCNT-7 on cancer-related pathways in A549 cells.
• The authors' conclusion: The authors concluded that both materials appeared to change cell survival, differentiation and proliferation through pathways including AMPK, FoxO, TGF-beta and Hippo. They also concluded that crocidolite had a greater impact than MWCNT-7 on cell survival, differentiation and proliferation in these cells. They called for repeating the work in primary cells before the microRNAs could be used as exposure biomarkers.
• Limitations the authors state:
  • Results come from an established cell line; other pathways might be affected in normal primary lung epithelial cells
  • The protein-rich culture medium could form a protein layer on the materials that may change their toxic effects
  • The gene networks showed only part of the possible microRNA-target gene interactions, because some interactions are not described in the database used

Topics

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

Medical terms in this study, explained in our Lexicon: A549 Cells, Crocidolite, Carcinogenic, Biomarker, Lung Cancer, Disease Progression, Carcinogenesis.

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