Aquaporin-6 May Increase the Resistance to Oxidative Stress of Malignant Pleural Mesothelioma Cells

Our plain-English summary of Aquaporin-6 May Increase the Resistance to Oxidative Stress of Malignant Pleural Mesothelioma Cells, by G. Pellavio, S. Martinotti, M. Patrone, et al (Cells, 2022).

The study

• Authors: G. Pellavio, S. Martinotti, M. Patrone, E. Ranzato, U. Laforenza
• Journal: Cells
• Published: 2022;11(12)
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive cancer of the pleural surface and is associated with previous asbestos exposure. The chemotherapy drug is one of the main treatments, but the median survival ranges from 8 to 14 months from diagnosis. The redox homeostasis of tumor cells should be carefully considered since elevated levels of ROS favor cancer cell progression (proliferation and migration), while a further elevation leads to ferroptosis. This study aims to analyze the functioning/role of aquaporins (AQPs) as a hydrogen peroxide (H2O2) channel in epithelial and biphasic MPM cell lines, as well as their possible involvement in chemotherapy drug resistance. Results show that AQP-3, -5, -6, -9, and -11 were expressed at mRNA and protein levels. AQP-6 was localized in the plasma membrane and intracellular structures. Compared to normal mesothelial cells, the water permeability of mesothelioma cells is not reduced by exogenous oxidative stress, but it is considerably increased by heat stress, making these cells resistant to ferroptosis. Functional experiments performed in mesothelioma cells silenced for aquaporin-6 revealed that it is responsible, at least in part, for the increase in H2O2 efflux caused by heat stress. Moreover, mesothelioma cells knocked down for AQP-6 showed a reduced proliferation compared to mock cells. Current findings suggest the major role of AQP-6 in providing mesothelioma cells with the ability to resist oxidative stress that underlies their resistance to chemotherapy drugs.

In plain English

This laboratory study used cells grown in dishes, not patients, and did not study asbestos exposure. The authors used three human cell lines: non-malignant mesothelial MeT-5A cells, and epithelioid (REN) and biphasic (MSTO-211H) malignant pleural mesothelioma cells. They examined aquaporins, which are membrane water-channel proteins, and whether they carry hydrogen peroxide, a chemical involved in oxidative stress. Aquaporin-6 (AQP6) was found in discrete areas of the outer membrane of the mesothelioma cells. Hydrogen peroxide reduced water movement through MeT-5A cells but not through the mesothelioma cells. Heating cells to 42 degrees Celsius increased water movement. Gene silencing partly reduced AQP6, by about 44% to 70% depending on the cell line. When hydrogen peroxide was added, a sensor inside silenced cells peaked about 84% lower than in control cells. Separately, silenced cells grew less. Under added oxidative stress, AQP6-silenced REN and MSTO-211H cells grew to about 15% and 19% of controls. The authors concluded that AQP6 could explain this tumor's resistance to conventional chemotherapy and radiotherapy and is a promising treatment target. They noted that much more experimental work is needed.

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) experiments on human cell lines, including gene silencing of aquaporin-6
• Who was studied: Three human cell lines: MeT-5A (non-malignant mesothelial cells), REN (epithelioid malignant pleural mesothelioma cells) and MSTO-211H (biphasic malignant pleural mesothelioma cells). No patients were studied.
• Exposure: No asbestos or fiber exposure was studied. Cells were exposed to oxidative stress, either 50 µM hydrogen peroxide for 45 minutes or heat (3 hours at 42 °C), and to mercury chloride. Aquaporins (mainly AQP6, also AQP3 and AQP5) were silenced with siRNA.
• Main results:
  • All aquaporins tested (AQP3, 5, 6, 8, 9 and 11) were expressed at mRNA and protein level in the three cell lines. The exception was AQP8, which was found only at the mRNA level.
  • In the mesothelioma cell lines, AQP6 showed strong labeling in discrete areas of the plasma membrane, in addition to intracellular staining.
  • Normal mesothelial MeT-5A cells had significantly higher osmotic water permeability than the mesothelioma cells: 4.88 × 10^-2 cm/s (n = 24), versus 2.87 × 10^-2 cm/s for REN (n = 25) and 3.23 × 10^-2 cm/s for MSTO-211H (n = 24).
  • Hydrogen peroxide treatment significantly reduced water permeability in MeT-5A cells. It increased water permeability in REN cells and did not change it in MSTO-211H cells.
  • Heat stress increased water permeability by about 55% in MeT-5A cells, about 20% in REN cells and about 60% in MSTO-211H cells.
  • Mercury chloride increased hydrogen peroxide permeability rather than reducing it: by about 66% in MeT-5A, 53% in REN and 90% in MSTO-211H cells.
  • Silencing reduced AQP6 protein by approximately 70% in MeT-5A, 62% in REN and 44% in MSTO-211H cells. It reduced water permeability in REN cells only; MeT-5A and MSTO-211H cells were unaffected.
  • After 50 µM hydrogen peroxide was added to the cells, the maximal fluorescence of the HyPer7 hydrogen peroxide sensor in AQP6-silenced cells was reduced by about 84% compared with mock-transfected control cells.
  • AQP6 silencing reduced proliferation of mesothelioma cells by about 50%.
  • Under oxidative stress, AQP6-silenced REN and MSTO-211H cells proliferated at about 15% and 19% of controls, respectively.
• The authors' conclusion: The authors concluded that AQP6's role in moving hydrogen peroxide out of mesothelioma cells could explain the tumor's resistance to conventional chemotherapy and radiotherapy. They called AQP6 a promising target for novel treatments.
• Limitations the authors state:
  • The authors state that a great deal of further experimental work will be needed to fully understand the mechanisms.
  • The authors state that the Pearson's correlation coefficients from the colocalization analysis fell in a range from which no conclusions can be drawn.

Topics

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

Medical terms in this study, explained in our Lexicon: Oxidative Stress, Pleural Mesothelioma, Asbestos Exposure, Chemotherapy, Median Overall Survival, Biphasic Mesothelioma, Mesothelial Cells, Mesothelioma.

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• Chronic Inflammation, Oxidative Stress and Metabolic Plasticity: Three Players Driving the Pro-Tumorigenic Microenvironment in Malignant Mesothelioma — I. Fiorilla, S. Martinotti, et al. (2023)
• Augmentation of chrysotile-induced oxidative stress by BHA in mice lungs — I. Ahmad, K. Krishnamurthi, et al. (1995)
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