Cellular response of Fusarium oxysporum to crocidolite asbestos as revealed by a combined proteomic approach

Our plain-English summary of Cellular response of Fusarium oxysporum to crocidolite asbestos as revealed by a combined proteomic approach, by M. Chiapello, S. Daghino, E. Martino, et al (Journal of Proteome Research, 2010).

The study

• Authors: M. Chiapello, S. Daghino, E. Martino, S. Perotto
• Journal: Journal of Proteome Research
• Published: 2010;9(8):3923-31
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Cellular mechanisms of asbestos toxicity rely, at least in part, on the chemical composition of these minerals. Iron ions are directly involved in the accepted mechanism of fiber toxicity because they constitute active centers where release of free radicals and reactive oxygen species takes place. Although no current technology is available for the remediation of asbestos polluted sites, the soil fungus Fusarium oxysporum was found to be very effective in iron extraction from crocidolite asbestos in vitro, and to cause a significant reduction in asbestos surface reactivity and oxidative damage to naked DNA. As little information is available on the molecular mechanisms of the fungus-asbestos interactions, a combined proteomic approach that used 2-DE, shotgun and quantitative iTRAQ proteomics was used to investigate the fungal metabolic activities in the presence of crocidolite, an iron-rich type of asbestos. Although global proteomic analyses did not show significant changes in the protein expression pattern of F. oxysporum when exposed to asbestos fibers, some proteins specifically regulated by asbestos suggest up-regulation of metabolic pathways involved in protection from oxidative stress. When compared with the response to crocidolite observed by other authors in human lung epithelial cells, that unlike fungi can internalize the asbestos fibres, a significant difference was the regulation of the pentose phosphate pathway.

In plain English

This was a laboratory experiment on a soil fungus, Fusarium oxysporum, not on people. The authors added crocidolite asbestos fibres (2.3 g in 100 mL of water) to liquid fungal cultures; controls received water only. Three protein-analysis methods tracked the fungus's proteins over 8 days. At the reproducible later sampling times (1, 2 and 8 days), protein patterns differed most from controls at 2 days and were closest at 8 days. Grouping proteins by function showed no significant alterations, and most protein changes were modest. A membrane proton pump rose 4.7-fold after 8 days, and antioxidant enzymes called catalase-peroxidases increased. Iron in the medium reached 16.90 plus or minus 1.34 ppm (2 days) and 23.58 plus or minus 1.74 ppm (8 days) in asbestos-treated cultures, versus 0.95 plus or minus 0.17 and 1.09 plus or minus 0.17 ppm in controls. The authors concluded that their results suggest the fungus's iron release increased oxidative stress, and that it may shift its sugar metabolism early as a defence. Both points were inferred from protein amounts, which the authors noted do not necessarily reflect enzyme activity.

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 (in vitro) experiment on fungal cultures, comparing asbestos-exposed and control cultures with three protein-analysis (proteomic) methods: 2-DE gels, shotgun proteomics and quantitative iTRAQ
• Who was studied: Cultures of the soil fungus Fusarium oxysporum grown in liquid medium in the laboratory (University of Torino, Italy). The 2-DE analysis used 3 biological replicates per condition, each run 3 times. The shotgun analysis used 2 biological replicates at 2 and 8 days, each run 3 times. No humans or animals were studied.
• Exposure: UICC crocidolite asbestos fibres, added as a suspension (2.3 g of fibres in 100 mL of distilled water) after 14 days of fungal growth. Controls received an equal volume of sterile water. Fungus was collected 1 hour, 5 hours, 1 day, 2 days and 8 days after the fibres were added.
• Main results:
  • Among the three later sampling times (1, 2 and 8 days), which were reproducible, similarity between treated and control protein patterns was lowest at 2 days and highest at 8 days.
  • The authors interpreted the gel results as showing that protein expression was significantly affected 2 days after crocidolite was added. They also took them to suggest that metabolic activity returned close to that of controls by 8 days.
  • 328 proteins were identified by shotgun proteomics and 554 by iTRAQ.
  • Analysis of protein functions at the two time points did not reveal significant alterations in the fungus caused by crocidolite.
  • With some exceptions, changes in protein levels in the iTRAQ analysis were usually modest.
  • Iron in the culture medium of asbestos-treated cultures (supplemented iron plus iron released from the fibres by the fungus) reached 16.90 plus or minus 1.34 ppm after 2 days and 23.58 plus or minus 1.74 ppm after 8 days. Control cultures had 0.95 plus or minus 0.17 ppm and 1.09 plus or minus 0.17 ppm. The authors reported both treated values as significantly higher. The article does not say what the plus-or-minus figures measure.
  • In asbestos-exposed fungus, the plasma membrane proton pump (H+-ATPase) was among the most strongly increased proteins: 4.7-fold after 8 days.
  • Two proteins similar to FKBP proteins increased up to 2.8-fold and 4.9-fold in asbestos-exposed fungus 8 days after exposure.
  • In asbestos-exposed fungus, catalase-peroxidases (antioxidant enzymes) increased after 8 days of exposure.
  • In asbestos-exposed fungus, most forms of the glycolysis enzyme GAPDH decreased, most strongly 2 days after the fibres were added.
  • 6-phosphogluconate dehydrogenase, an enzyme of the pentose phosphate pathway, increased by up to 2.3-fold in asbestos-exposed fungus.
  • The authors interpreted the drop in glycolysis enzymes and the rise in pentose phosphate pathway enzymes at 2 days as suggesting that the fungus may reroute its metabolism early to resist oxidants.
  • Subunits of mitochondrial ATP synthase increased by up to 2.6-fold in asbestos-exposed fungus. The authors suggested this may be another marker of oxidative stress.
• The authors' conclusion: The authors concluded that their results suggest the fungus's ability to release iron from asbestos fibres results in increased oxidative stress. They proposed that the fungus appears to counter this with antioxidant enzymes and, as an early response, by rerouting its sugar metabolism.
• Limitations the authors state:
  • Protein amounts do not necessarily reflect enzyme activity.
  • Shotgun proteomics is not a quantitative method.
  • Most peptides matching translation elongation factors could not be measured by iTRAQ because protein identification confidence was low.
  • Gel patterns from control cultures at 1 and 5 hours were poorly reproducible.

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, Reactive Oxygen Species (ROS), Surface Reactivity, Oxidative Stress.

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