Resetting proteostasis with ISRIB promotes epithelial differentiation to attenuate pulmonary fibrosis

Our plain-English summary of Resetting proteostasis with ISRIB promotes epithelial differentiation to attenuate pulmonary fibrosis, by S. Watanabe, N.S. Markov, Z. Lu, et al (Proceedings of the National Academy of Sciences of the United States of America, 2021).

The study

• Authors: S. Watanabe, N.S. Markov, Z. Lu, R. Piseaux Aillon, S. Soberanes, C.E. Runyan, Z. Ren, R.A. Grant, M. Maciel, H. Abdala-Valencia, Y. Politanska, K. Nam, L. Sichizya, H.G. Kihshen, N. Joshi, A.C. McQuattie-Pimentel, K.A. Gruner, M. Jain, J.I. Sznajder, R.I. Morimoto, P.A. Reyfman, C.J. Gottardi, G.R.S. Budinger, A.V. Misharin
• Journal: Proceedings of the National Academy of Sciences of the United States of America
• Published: 2021;118(20)
• Cited by: 84 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Pulmonary fibrosis is a relentlessly progressive and often fatal disease with a paucity of available therapies. Genetic evidence implicates disordered epithelial repair, which is normally achieved by the differentiation of small cuboidal alveolar type 2 (AT2) cells into large, flattened alveolar type 1 (AT1) cells as an initiating event in pulmonary fibrosis pathogenesis. Using models of pulmonary fibrosis in young adult and old mice and a model of adult alveologenesis after pneumonectomy, we show that administration of ISRIB, a small molecule that restores protein translation by EIF2B during activation of the integrated stress response (ISR), accelerated the differentiation of AT2 into AT1 cells. Accelerated epithelial repair reduced the recruitment of profibrotic monocyte-derived alveolar macrophages and ameliorated lung fibrosis. These findings suggest a dysfunctional role for the ISR in regeneration of the alveolar epithelium after injury with implications for therapy.

Copyright © 2021 the Author(s). Published by PNAS.

In plain English

This was an experimental study in mice. The authors gave young adult mice (3 to 5 mo) and old mice (18 to 24 mo) intratracheal bleomycin (0.025 unit/50 microlitres) or crocidolite asbestos (100 micrograms/50 microlitres) and reported that old mice developed more severe and more prolonged fibrosis than young adult mice, with decreased lung compliance, elevated collagen, worse histologic scores, and more monocyte-derived alveolar macrophages measured by flow cytometry. In the bleomycin model, ISRIB (2.5 mg/kg intraperitoneally daily, starting 7 d after instillation) was associated with higher lung compliance, lower collagen, reduced blinded Masson's trichrome fibrosis scores and fewer monocyte-derived alveolar macrophages in both young adult and old mice; in the asbestos model ISRIB was associated with reduced fibrosis scores and less collagen. Using lineage-labelled mice, ISRIB increased the number of GFP-positive AT1 cells after bleomycin and after pneumonectomy and reduced GFP-positive KRT8-positive transitional cells; in a separate assay using surfactant protein C and TUNEL staining, ISRIB reduced apoptotic AT2 cells. The authors concluded that ISRIB removes a barrier to AT2 to AT1 differentiation imposed by the integrated stress response, and state their findings support but do not prove their model.

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 (mouse) experimental study using bleomycin- and crocidolite asbestos-induced pulmonary fibrosis models, genetic lineage tracing, flow cytometry, bulk RNA sequencing and a pneumonectomy model
• Who was studied: Young adult mice (8 to 12 wk old according to the Methods; described as 3 to 5 mo in the results and figure legends) and old mice (over 18 mo; 18 to 24 mo in the results); only male mice were used
• Exposure: Intratracheal bleomycin (0.025 unit/50 microlitres) or crocidolite asbestos (100 micrograms/50 microlitres)
• Main results:
  • Treatment schedule: after bleomycin, mice received ISRIB 2.5 mg/kg or vehicle intraperitoneally daily beginning at day 7
  • Old mice developed more severe fibrosis than young adult mice 28 d after bleomycin, and collagen stayed raised in old mice up to 56 d
  • After crocidolite asbestos, young adult mice had only mild peribronchial fibrosis with unchanged body weight and lung compliance, while old mice lost weight and had reduced compliance, increased collagen and increased fibrosis at 28 d
  • Interstitial macrophages and monocyte-derived alveolar macrophages were increased in old compared with young adult mice 28 d after either bleomycin or asbestos
  • ISRIB from day 7 after bleomycin improved lung compliance, collagen, histologic fibrosis score and weight loss in both young adult and old mice compared with vehicle
  • In the asbestos model, ISRIB was associated with reduced fibrosis scores in both young adult and old mice
  • In the asbestos model, ISRIB-treated young adult and old mice had less lung collagen (by second harmonic generation microscopy) than vehicle-treated mice
  • In young adult mice at day 21 after bleomycin, ISRIB did not change tissue-resident alveolar macrophage numbers but reduced monocyte-derived alveolar macrophages, interstitial macrophages and classical monocytes; in old mice classical monocytes were unaffected
  • In lineage-labelled SftpcCreER x zsGreen mice after bleomycin, ISRIB increased GFP-positive AT1 cells measured by flow cytometry
  • By immunofluorescent microscopy in the same lineage-labelled mice, GFP-positive KRT8-positive transitional cells were reduced and GFP-positive PDPN-positive AT1 cells increased with ISRIB
  • Apoptosis was measured in a separate experiment: ISRIB given 6 d after bleomycin, with apoptotic cells counted 24 h later by dual surfactant protein C and TUNEL staining
  • In that apoptosis assay, ISRIB reduced the number of TUNEL-positive AT2 cells
  • After pneumonectomy, GFP-positive AT2 cells were similar with vehicle or ISRIB, but GFP-positive AT1 cells were increased with ISRIB
  • RNA sequencing showed no evidence of integrated stress response activation in lung monocytes or alveolar macrophages during bleomycin-induced fibrosis
• The authors' conclusion: The authors concluded that ISRIB attenuated bleomycin-induced resolving fibrosis and asbestos-induced nonresolving fibrosis in young adult and old mice, partly by promoting epithelial repair
• Limitations the authors state:
  • Effects of ISRIB on other lung or extrapulmonary cells cannot be excluded, and the fall in monocyte-derived alveolar macrophages cannot be attributed to effects on epithelial proteostasis
  • It is not known whether relief of translational inhibition, inhibition of ATF4-mediated gene expression, or both are required for the effects
  • Some assays relied on marker quantification in lung tissue without stereology, so they cannot be considered definitive
  • Only male mice were used, so sex differences could not be evaluated
  • The authors state their findings support but do not prove their proposed multicellular model

Topics

Medical terms in this study, explained in our Lexicon: Pulmonary Fibrosis, Pneumonectomy, Alveolar Macrophage, Fibrosis, Epithelium.

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