miR-21 mediates nickel nanoparticle-induced pulmonary injury and fibrosis

Abstract

We and other groups have demonstrated that exposure to nickel nanoparticles (Nano-Ni) results in severe and persistent lung inflammation and fibrosis, but the underlying mechanisms remain unclear. Here, we propose that miR-21 may play an important role in Nano-Ni-induced lung inflammation, injury, and fibrosis. Our dose- and time-response studies demonstrated that exposure of C57BL/6J (WT) mice to Nano-Ni resulted in upregulation of miR-21, proinflammatory cytokines, and profibrotic mediators. Histologically, exposure to Nano-Ni caused severe pulmonary inflammation and fibrosis. Based on the dose- and time-response studies, we chose a dose of 50 µg of Nano-Ni per mouse to compare the effects of Nano-Ni on WT with those on miR-21 KO mouse lungs. At day 3 post-exposure, Nano-Ni caused severe acute lung inflammation and injury that were reflected by increased neutrophil count, CXCL1/KC level, LDH activity, total protein concentration, MMP-2/9 protein levels and activities, and proinflammatory cytokines in the BALF or lung tissues from WT mice, which were confirmed histologically. Although Nano-Ni had similar effects on miR-21 KO mice, the above-mentioned levels were significantly lower than those in WT mice. Histologically, lungs from WT mice exposed to Nano-Ni had infiltration of a large number of polymorphonuclear (PMN) cells and macrophages in the alveolar space and interstitial tissues. However, exposure of miR-21 KO mice to Nano-Ni only caused mild acute lung inflammation and injury. At day 42 post-exposure, Nano-Ni caused extensive pulmonary fibrosis and chronic inflammation in the WT mouse lungs. However, exposure of miR-21 KO mice to Nano-Ni only caused mild lung fibrosis and chronic lung inflammation. Our results also showed that exposure to Nano-Ni caused upregulation of TGF-β1, phospho-Smad2, COL1A1, and COL3A1 in both WT and miR-21 KO mouse lungs. However, levels were significantly lower in miR-21 KO mice than in WT mice, except TGF-β1, which was similar in both kinds of mice. Decreased expression of Smad7 was observed in WT mouse lungs, but not in miR-21 KO mice. Our results demonstrated that knocking out miR-21 ameliorated Nano-Ni-induced pulmonary inflammation, injury, and fibrosis, suggesting the important role of miR-21 in Nano-Ni-induced pulmonary toxicity.

Keywords:

• Nickel nanoparticles (Nano-Ni)
• miR-21
• lung injury
• lung fibrosis
• Smad7

Acknowledgements

The results were presented in part at 2019 Society of Toxicology (SOT) Annual Conference; March 10-14, 2019; Baltimore, Maryland, USA.

Ethics approval and consent to participate

The protocols and the use of animals were approved by and in accordance with the University of Louisville Animal Care and Use Committee.

Consent for publication

Not applicable.

Author contributions

YM and YZ designed and performed the experiments, analyzed the data, and interpreted the results of experiments. Pulmonary histopathological evaluations were done by YM, RW, MJ, and YX. QZ conceived and supervised the study. The manuscript was written by YM and YZ and revised critically by QZ. All authors read and approved the final manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Availability of data and materials

All data and materials are included in the manuscript.

Additional information

Funding

This work was partly supported by NIH [ES023693, ES028911 and HL147856], KSEF-148-RED-502-16-381, and Kentucky Lung Cancer Research Program to Dr. Qunwei Zhang.