The Sphingosine Kinase 1 Inhibitor, PF543, Mitigates Pulmonary Fibrosis by Reducing Lung Epithelial Cell mtDNA Damage and Recruitment of Fibrogenic Monocytes

Our plain-English summary of The Sphingosine Kinase 1 Inhibitor, PF543, Mitigates Pulmonary Fibrosis by Reducing Lung Epithelial Cell mtDNA Damage and Recruitment of Fibrogenic Monocytes, by P. Cheresh, S.J. Kim, L.S. Huang, et al (International Journal of Molecular Sciences, 2020).

The study

• Authors: P. Cheresh, S.J. Kim, L.S. Huang, S. Watanabe, N. Joshi, K.J.N. Williams, M. Chi, Z. Lu, A. Harijith, A. Yeldandi, A.P. Lam, C. Gottardi, A.V. Misharin, G.R.S. Budinger, V. Natarajan, D.W. Kamp
• Journal: International Journal of Molecular Sciences
• Published: 2020;21(16)
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Idiopathic pulmonary fibrosis (IPF) is a chronic disease for which novel approaches are urgently required. We reported increased sphingosine kinase 1 (SPHK1) in IPF lungs and that SPHK1 inhibition using genetic and pharmacologic approaches reduces murine bleomycin-induced pulmonary fibrosis. We determined whether PF543, a specific SPHK1 inhibitor post bleomycin or asbestos challenge mitigates lung fibrosis by reducing mitochondrial (mt) DNA damage and pro-fibrotic monocyte recruitment-both are implicated in the pathobiology of pulmonary fibrosis. Bleomycin (1.5 U/kg), crocidolite asbestos (100 µg/50 µL) or controls was intratracheally instilled in Wild-Type (C57Bl6) mice. PF543 (1 mg/kg) or vehicle was intraperitoneally injected once every two days from day 7-21 following bleomycin and day 14-21 or day 30-60 following asbestos. PF543 reduced bleomycin- and asbestos-induced pulmonary fibrosis at both time points as well as lung expression of profibrotic markers, lung mtDNA damage, and fibrogenic monocyte recruitment. In contrast to human lung fibroblasts, asbestos augmented lung epithelial cell (MLE) mtDNA damage and PF543 was protective. Post-exposure PF543 mitigates pulmonary fibrosis in part by reducing lung epithelial cell mtDNA damage and monocyte recruitment. We reason that SPHK1 signaling may be an innovative therapeutic target for managing patients with IPF and other forms of lung fibrosis.

In plain English

This animal experiment, with accompanying cell-culture work, tested PF543, a specific sphingosine kinase 1 (SPHK1) inhibitor, given to mice after exposure to fibrogenic agents; in vitro, MLE-12 lung epithelial cells were pre-treated with PF543 before asbestos. Wild-type C57Bl/6J and Cx3cr1ER-Cre x ZsGreen mice received a single intratracheal instillation of bleomycin (1.5 U/kg), crocidolite asbestos (100 micrograms in 50 microlitres) or control (PBS/DMSO or TiO2), then intraperitoneal PF543 (1 mg/kg) or vehicle every other day. PF543 reduced bleomycin-induced lung fibrosis at 21 days by histology and Sircol collagen, lowered bronchoalveolar lavage cell counts and protein, and reduced lung fibronectin, Col1A2 and alpha-SMA. Asbestos-induced fibrosis was reduced at 21 and 60 days. Compared with vehicle-treated controls, PF543 lowered plasma S1P at 21 days by about 50%, and lung mtDNA damage in asbestos-exposed mice by about 60%. In MLE-12 cells asbestos caused mtDNA damage that PF543 nearly abolished, whereas asbestos-exposed human lung fibroblasts showed negligible damage. Recruitment of fate-mapped monocyte-derived alveolar macrophages was reduced. The authors concluded SPHK1 signalling may be a therapeutic target.

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: Controlled animal (mouse) experiment with accompanying in vitro cell-culture experiments; mice were treated with PF543 after exposure, whereas MLE-12 cells were pre-treated with PF543 before asbestos
• Who was studied: Male and female 8- to 10-week-old C57Bl/6J wild-type mice and Cx3cr1ER-Cre x ZsGreen reporter mice; plus cultured murine lung epithelial MLE-12 cells and primary human lung fibroblasts
• Exposure: In mice, a single intratracheal instillation of bleomycin (1.5 U/kg) or crocidolite asbestos (100 micrograms in 50 microlitres), with PBS/DMSO or TiO2 (100 micrograms in 50 microlitres) as controls, followed by intraperitoneal PF543 (1 mg/kg) or saline every other day
• Main results:
  • In bleomycin-exposed mice, PF543 started 7 days after exposure reduced lung fibrosis at 21 days and reduced total BAL cells and protein compared with untreated animals
  • In bleomycin-exposed mice, PF543 reduced lung expression of fibronectin, collagen-1A2 and alpha-smooth muscle actin
  • In crocidolite asbestos-exposed mice, PF543 reduced lung fibrosis at 21 days and, when begun 30 days after instillation, at 60 days (histology, fibrosis score, lung collagen)
  • Plasma S1P at 21 days was about 50% lower with PF543 than in vehicle-treated controls: 1153 ± 60 versus 540 ± 240 pmol/mL (p less than 0.05, n = 3); the figure panel is labelled baseline plasma S1P levels
  • Lung mtDNA damage in asbestos-exposed mice was about 60% lower with PF543: 1.13 ± 0.54 versus 2.60 ± 0.23 lesion frequency per mtDNA fragment (p less than 0.05, n = 3 to 4)
  • In cultured MLE cells, asbestos-induced mtDNA damage was 0.94 ± 0.16 versus 0.16 ± 0.07 lesion frequency per mtDNA fragment with PF543; asbestos-exposed human lung fibroblasts showed negligible mtDNA damage
  • At 60 days after asbestos, PF543 begun at 30 days reduced numbers of fate-mapped monocyte-derived alveolar macrophages: 93,782 ± 86,419 (vehicle) versus 17,333 ± 9170 (PF543), n = 5 to 10, p less than 0.05
• The authors' conclusion: The authors concluded that PF543 given after exposure to bleomycin or asbestos substantially mitigated lung fibrosis, in part by reducing lung profibrotic marker expression, lung and epithelial cell mtDNA damage, and monocyte-derived alveolar macrophage recruitment, and they reason that limiting SPHK1 signalling is a therapeutic target for IPF and other lung fibrosis
• Limitations the authors state:
  • The detailed molecular mechanisms by which PF543 reduces mtDNA damage and monocyte-derived alveolar macrophage recruitment were not determined and need further study
  • Other macrophage populations (tissue-resident peribronchial or interstitial macrophages) may also mediate the beneficial effects of PF543
  • mtDNA release was not investigated in this study

Topics

Medical terms in this study, explained in our Lexicon: Pulmonary Fibrosis, Fibrogenic, Idiopathic, Fibrosis, Crocidolite, Fibroblast.

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