SIRT3 Overexpression Ameliorates Asbestos-Induced Pulmonary Fibrosis, mt-DNA Damage, and Lung Fibrogenic Monocyte Recruitment

Our plain-English summary of SIRT3 Overexpression Ameliorates Asbestos-Induced Pulmonary Fibrosis, mt-DNA Damage, and Lung Fibrogenic Monocyte Recruitment, by P. Cheresh, S.J. Kim, R. Jablonski, et al (International Journal of Molecular Sciences, 2021).

The study

• Authors: P. Cheresh, S.J. Kim, R. Jablonski, S. Watanabe, Z. Lu, M. Chi, K.A. Helmin, D. Gius, G.R.S. Budinger, D.W. Kamp
• Journal: International Journal of Molecular Sciences
• Published: 2021;22(13)
• Cited by: 43 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Alveolar epithelial cell (AEC) mitochondrial (mt) DNA damage and fibrotic monocyte-derived alveolar macrophages (Mo-AMs) are implicated in the pathobiology of pulmonary fibrosis. We showed that sirtuin 3 (SIRT3), a mitochondrial protein regulating cell fate and aging, is deficient in the AECs of idiopathic pulmonary fibrosis (IPF) patients and that asbestos- and bleomycin-induced lung fibrosis is augmented in Sirt3 knockout (Sirt3-/-) mice associated with AEC mtDNA damage and intrinsic apoptosis. We determined whether whole body transgenic SIRT3 overexpression (Sirt3Tg) protects mice from asbestos-induced pulmonary fibrosis by mitigating lung mtDNA damage and Mo-AM recruitment. Crocidolite asbestos (100 µg/50 µL) or control was instilled intratracheally in C57Bl6 (Wild-Type) mice or Sirt3Tg mice, and at 21 d lung fibrosis (histology, fibrosis score, Sircol assay) and lung Mo-AMs (flow cytometry) were assessed. Compared to controls, Sirt3Tg mice were protected from asbestos-induced pulmonary fibrosis and had diminished lung mtDNA damage and Mo-AM recruitment. Further, pharmacologic SIRT3 inducers (i.e., resveratrol, viniferin, and honokiol) each diminish oxidant-induced AEC mtDNA damage in vitro and, in the case of honokiol, protection occurs in a SIRT3-dependent manner. We reason that SIRT3 preservation of AEC mtDNA is a novel therapeutic focus for managing patients with IPF and other types of pulmonary fibrosis.

In plain English

This study used mice and cultured cells, not people. The authors tested whether mice engineered to make extra SIRT3, a mitochondrial protein, were protected from asbestos-caused lung scarring (fibrosis). Normal (wild-type) and SIRT3 mice got one dose of crocidolite asbestos or titanium dioxide (control) into the windpipe. At 21 days, asbestos increased fibrosis in normal mice; asbestos-exposed SIRT3 mice had less fibrosis than asbestos-exposed normal mice by tissue staining, fibrosis score and collagen (4 to 13 mice per group). Lung mitochondrial DNA damage from asbestos was abolished in SIRT3 mice; this and the immune-cell work used 3 to 4 mice per group. In separate SIRT3 mice, a scar-promoting immune cell differed negligibly after asbestos versus control. The normal-mouse comparison came from the authors' earlier study. In cells exposed to amosite asbestos or hydrogen peroxide, resveratrol and viniferin reduced mitochondrial DNA damage. Honokiol reduced it by about 50% (p = 0.07, described as a trend), and blocking SIRT3 removed this effect. The authors concluded that raising lung SIRT3 is an innovative treatment target for lung fibrosis.

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: Animal experiment in mice (wild-type versus mice genetically engineered to overexpress SIRT3), plus laboratory (in vitro) experiments in cultured lung cell lines
• Who was studied: Male and female 8- to 10-week-old C57Bl/6J wild-type mice and Sirt3Tg (SIRT3-overexpressing) mice, studied at Northwestern University and Jesse Brown VA Medical Center, Chicago. There were 4 to 13 mice per group for fibrosis measures and 3 to 4 per group for mitochondrial DNA and immune-cell studies. Human (A549) and mouse (MLE-12) lung epithelial cell lines were used for the cell experiments.
• Exposure: Mice: a single intratracheal instillation of crocidolite asbestos (100 µg in 50 µL), with titanium dioxide (100 µg in 50 µL) as the non-fibrogenic control. Cells: amosite asbestos (25 µg/cm2) or hydrogen peroxide (250 µM) for 24 hours, after pretreatment with resveratrol, viniferin or honokiol. The asbestos was UICC reference standard material.
• Main results:
  • In wild-type mice, crocidolite asbestos increased lung fibrosis at 21 days compared with titanium dioxide controls
  • Asbestos-induced lung fibrosis was reduced in SIRT3-overexpressing mice compared with wild-type mice, by histology, fibrosis score and lung collagen. The difference was p less than 0.05 versus wild-type, with n = 4 to 13; values are shown only in figures.
  • The fibrosis measurements used 4 to 13 mice per group
  • Asbestos-associated lung mitochondrial DNA damage seen in wild-type mice was abolished in SIRT3-overexpressing mice (N = 3)
  • In a separate group of SIRT3-overexpressing mice, numbers of lung monocyte-derived alveolar macrophages (scar-promoting immune cells), total alveolar macrophages and tissue-resident macrophages differed negligibly between asbestos and titanium dioxide exposure
  • The wild-type comparison for these immune cells (about a 3-fold increase after asbestos versus titanium dioxide) came from the authors' previously published study, not from new wild-type mice in this experiment
  • In human A549 cells, resveratrol and viniferin each reduced mitochondrial DNA damage caused by amosite asbestos or hydrogen peroxide
  • The benefit of viniferin was associated with increased SIRT3 levels and less programmed cell death (apoptosis) in A549 cells
  • In mouse MLE-12 cells, honokiol reduced mitochondrial DNA damage caused by amosite asbestos or hydrogen peroxide by about 50%. This was not statistically significant (p = 0.07); the authors described it as trending toward significance.
  • When SIRT3 was blocked with siRNA in MLE-12 cells, the protective effect of honokiol disappeared (p less than 0.05; n = 3)
• The authors' conclusion: The authors concluded that strategies to increase lung SIRT3 levels are an innovative therapeutic target for managing patients with idiopathic pulmonary fibrosis and other forms of lung fibrosis
• Limitations the authors state:
  • The precise molecular mechanisms, including how SIRT3 prevents lung mitochondrial DNA damage and immune-cell recruitment, were not established
  • The study focused on alveolar epithelial cells rather than other lung cell types such as fibroblasts
  • The cell experiments used transformed cell lines rather than primary lung cells; the authors stated they believe this does not alter the main conclusions

Topics

Medical terms in this study, explained in our Lexicon: Pulmonary Fibrosis, Fibrogenic, Alveolar Macrophage, Idiopathic, Fibrosis, Apoptosis, Crocidolite, Histology.

Related studies

• The Sphingosine Kinase 1 Inhibitor, PF543, Mitigates Pulmonary Fibrosis by Reducing Lung Epithelial Cell mtDNA Damage and Recruitment of Fibrogenic Monocytes — P. Cheresh, S.J. Kim, et al. (2020)
• SIRT3 deficiency promotes lung fibrosis by augmenting alveolar epithelial cell mitochondrial DNA damage and apoptosis — R.P. Jablonski, S.J. Kim, et al. (2017)
• 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 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)
• The Role of Mitochondrial DNA in Mediating Alveolar Epithelial Cell Apoptosis and Pulmonary Fibrosis — S.J. Kim, P. Cheresh, et al. (2015)
• Asbestos-induced pulmonary toxicity: role of DNA damage and apoptosis — D. Upadhyay, D.W. Kamp (2003)

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