Loss of ANT1 Increases Fibrosis and Epithelial Cell Senescence in Idiopathic Pulmonary Fibrosis

Our plain-English summary of Loss of ANT1 Increases Fibrosis and Epithelial Cell Senescence in Idiopathic Pulmonary Fibrosis, by J. Sui, J.C. Boatz, J. Shi, et al (American Journal of Respiratory Cell and Molecular Biology, 2023).

The study

• Authors: J. Sui, J.C. Boatz, J. Shi, Q. Hu, X. Li, Y. Zhang, M. Königshoff, C.R. Kliment
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 2023;69(5):556-569
• Cited by: 40 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Idiopathic pulmonary fibrosis (IPF) is an interstitial lung disease characterized by progressive lung scarring and remodeling. Although treatments exist that slow disease progression, IPF is irreversible, and there is no cure. Cellular senescence, a major hallmark of aging, has been implicated in IPF pathogenesis, and mitochondrial dysfunction is increasingly recognized as a driver of senescence. Adenine nucleotide translocases (ANTs) are abundant mitochondrial ATP-ADP transporters critical for regulating cell fate and maintaining mitochondrial function. We sought to determine how alterations in ANTs influence cellular senescence in pulmonary fibrosis. We found that SLC25A4 (solute carrier family 25 member 4) (ANT1) and SLC25A5 (ANT2) expression is reduced in the lungs of patients with IPF, particularly within alveolar type II (AT2) cells, by single-cell RNA sequencing and tissue staining. Loss of ANT1 by siRNA in lung epithelial cells resulted in increased senescence markers such as β-galactosidase and p21, with a reduction in the ratio of nicotinamide adenine dinucleotide to reduced nicotinamide adenine dinucleotide. Bleomycin-treated ANT1 knockdown cells also had increased senescence markers compared with bleomycin-treated control cells. Loss of ANT1 in AT2 cells resulted in a reduction in alveolar organoid growth, with an increase in p21 by staining. Global loss of ANT1 resulted in worse lung fibrosis and increased senescence in the bleomycin- and asbestos-induced mouse models of pulmonary fibrosis. In summary, loss of ANT1 contributes to IPF pathogenesis through mitochondrial dysfunction, increased senescence, and decreased regenerative capacity of AT2 cells, resulting in enhanced lung fibrosis. Modulation of ANTs presents a new therapeutic avenue that may alter cellular senescence pathways and limit pulmonary fibrosis.

In plain English

This laboratory study examined ANT1, a mitochondrial transporter of the cell's energy molecules, in idiopathic pulmonary fibrosis (IPF), a scarring lung disease. In one data set, lung tissue from 255 patients with IPF showed lower expression of the ANT1 and ANT2 genes than tissue from 137 healthy control subjects. A second cohort of 40 IPF lungs and 29 control lungs showed the same reduction. Staining found less of both proteins in alveolar type II (AT2) cells. In human lung cell lines, lowering ANT1 raised markers of senescence, an aging-like state in which cells stop dividing. It also lowered the ratio of NAD to its reduced form, NADH. AT2 cells from mice lacking ANT1 formed fewer alveolar organoids. Mice lacking ANT1 showed increased lung fibrosis after bleomycin. They also showed increased fibrosis after crocidolite asbestos placed into the windpipe. In the asbestos model, inflammation scores did not differ significantly between knockout and normal mice. The authors concluded that ANT1-related mitochondrial dysfunction may be a key driver of senescence in AT2 cells. They noted as a limitation that their mice lacked ANT1 in all 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: Laboratory study combining analysis of human lung tissue, experiments in human lung epithelial cell lines, mouse alveolar organoids, and animal experiments in mice lacking Ant1 (bleomycin and asbestos models of lung fibrosis)
• Who was studied: Human lung tissue from patients with IPF and controls: 255 IPF and 137 healthy control subjects in a Lung Genomics Research Consortium data set, and a separate cohort of 40 IPF and 29 control lungs (University of Pittsburgh tissue core). Also three human lung epithelial cell lines (BEAS-2B, HBEC3-KT, A549). Male and female wild-type and Ant1-knockout mice, 10 to 12 weeks old, 6 to 10 per group.
• Exposure: Loss of ANT1 by siRNA knockdown or CRISPR knockout in cells, and global Ant1 knockout in mice. Mice received intratracheal bleomycin or saline control, or crocidolite asbestos or titanium dioxide (an inert control particle) at 0.1mg in saline. Mice were killed 28 days after treatment.
• Main results:
  • Gene expression of SLC25A4 (ANT1) and SLC25A5 (ANT2) was significantly reduced in lungs of patients with IPF (n=255) compared with healthy control subjects (n=137).
  • The reduction was confirmed in a separate cohort of 40 IPF lungs and 29 normal control lungs.
  • ANT1 and ANT2 protein was moderately reduced in alveolar cells in fibrotic alveolar tissue from patients with IPF compared with control tissue.
  • In BEAS-2B lung epithelial cells, ANT1 knockdown was associated with significant increases in the senescence markers p21 (P=0.022) and p53 (P=0.020).
  • ANT1 knockdown in BEAS-2B cells significantly reduced the normalized NAD to NADH ratio (P=0.004).
  • AT2 cells from ANT1 knockout mice formed significantly fewer alveolar organoids.
  • In the bleomycin model, Ant1 knockout mice had a significantly increased fibrosis index (P=0.0255).
  • In the bleomycin model, lung hydroxyproline (a measure of collagen) was significantly higher in Ant1 knockout mice than in bleomycin-treated wild-type mice (P=0.0234).
  • In the bleomycin model, p21 staining was notably higher in Ant1 knockout mice than in wild-type mice.
  • In the crocidolite asbestos model, Ant1 knockout mice had increased fibrosis on tissue staining and an increased fibrosis index on tissue scoring. The data are shown only in supplementary figures; no numbers are given in the article text.
  • In the asbestos model, neutrophil and macrophage inflammation indices did not differ significantly between wild-type and Ant1 knockout asbestos-treated mice.
• The authors' conclusion: The authors concluded that ANT1-related mitochondrial dysfunction may be a key driver of senescence in AT2 cells of the lung through metabolic imbalance. They concluded that it presents a potential therapeutic target for limiting fibrosis development in IPF.
• Limitations the authors state:
  • Ant1 was removed from all cells in the knockout mice, not only lung epithelial cells.
  • The role of ANT1 in other lung cell types, such as immune cells and fibroblasts, remains unclear.
  • It is unclear whether ANT1 or ANT2 plays the larger role in AT2 cell senescence.

Topics

Medical terms in this study, explained in our Lexicon: Fibrosis, Idiopathic, Pulmonary Fibrosis, Interstitial Lung Disease, Disease Progression.

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