CeO2 nanoparticles induce pulmonary fibrosis via activating S1P pathway as revealed by metabolomics

摘要

CeO2 nanoparticles (NPs) have been shown to cause lung fibrosis, however, the underlying molecular mechanisms are not well understood. In this study, we have conducted a mass spectrometry-based global metabolomic analysis of human bronchial epithelial BEAS-2B cells treated by CeO2 NPs with different aspect ratios and assessed their toxicity on the bronchial epithelial cells by various cell-based functional assays. Although CeO2 NPs at doses ranging from 12.5 mu g/mL to 25 mu g/mL displayed low cytotoxicity on the bronchial epithelial cells, the metabolomic analysis revealed a number of metabolites in the cellular me-tabolic pathways of sphingosine-1-phosphate, fatty acid oxidation, inflammation, etc. were significantly altered by CeO2 NPs, especially those with high aspect ratios. The robustness of metabolomics findings was further validated in mouse models upon acute and chronic exposures to CeO2 NPs. Mechanistically, CeO2 NPs upregulated transforming growth factor beta-1 (TGF-beta 1) levels in BEAS-2B cells in an aspect ratio-dependent manner through enhancing the expression of early growth response protein 1 (EGR-1). In ad-dition, both in vitro and in vivo studies demonstrated that CeO(2 )NPs significantly induced the expression of sphingosine kinase 1 (SHPK1), phosphorylated Smad2/3 and lung fibrosis markers. Moreover, targeting SPHK1, TGF beta receptor or Smad3 phosphorylation significantly attenuated the fibrosis-promoting effects of CeO2 NPs, and SPHK1-S1P pathway exerted a greater effect on the TGF-beta 1-mediated lung fibrosis compared to the conventional Smad2/3 pathway. Collectively, our studies have identified the metabolomic changes in BEAS-2B cells exposed to CeO2 NPs with different aspect ratios and revealed the subtle changes in metabolic activities that traditional functional assays might have missed. More importantly, we have discovered a previously unknown molecular mechanism underlying CeO2 NP-induced lung fibrosis with different aspect ratios, shedding new insights on the environmental hazard potential of CeO2 NPs.

关键词