Transcriptional up-regulation of MMP12 and MMP13 by asbestos occurs via a PKCdelta-dependent pathway in murine lung

Our plain-English summary of Transcriptional up-regulation of MMP12 and MMP13 by asbestos occurs via a PKCdelta-dependent pathway in murine lung, by A. Shukla, T.F. Barrett, K.I. Nakayama, et al (FASEB Journal, 2006).

The study

• Authors: A. Shukla, T.F. Barrett, K.I. Nakayama, K. Nakayama, B.T. Mossman, K.M. Lounsbury
• Journal: FASEB Journal
• Published: 2006;20(7):997-9
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos is a known inflammatory, carcinogenic, and fibrotic agent, but the mechanisms leading to asbestos-induced lung diseases are unclear. Using a murine inhalation model of fibrogenesis, we show that asbestos causes significant increases in mRNA levels of lung matrix metalloproteinases (MMPs 12 and 13) and tissue inhibitor of metalloproteinases (TIMP1), as well as increased activities of MMP 2, 9, and 12 in bronchoalveolar lavage fluids (BALF). Asbestos-exposed PKCdelta knockout (PKCdelta-/-) mice exhibited decreased expression of lung MMP12 and MMP13 compared with asbestos-exposed wild-type mice. Studies using small molecule inhibitors in murine alveolar epithelial type II cells (C10) and primary lung fibroblasts confirmed that asbestos transcriptionally up-regulates MMPs via an EGFR (or other growth factor receptors)/PI3K/PKCdelta/ERK1/2 pathway. Moreover, use of a broad-spectrum MMP inhibitor showed that MMPs play an important role in further enhancing asbestos-induced signaling events by activating EGFR. These data reveal a potentially important link between asbestos signaling and integrity of the extracellular matrix (ECM) that likely contributes to asbestos-induced lung remodeling and diseases.

In plain English

This was an experimental study in mice and in cultured mouse lung cells. C57Bl/6 wild-type and PKCdelta knockout mice inhaled NIEHS reference chrysotile asbestos (7 mg/m3 air, 6 h/day, 5 days/week for 3, 9 or 40 days); lung RNA was analysed by microarray (3 mice per group) and ribonuclease protection assay (6 mice per group), and bronchoalveolar lavage fluid (BALF) by gelatin zymography. Murine alveolar epithelial type II cells (C10) and primary lung fibroblasts were exposed to NIEHS crocidolite (5 micrograms per square centimetre) with small-molecule inhibitors. In wild-type mice asbestos increased lung MMP12 mRNA at 3, 9 and 40 days, and MMP13 and TIMP1 at 9 days, while MMP3, 7, 8, 9 and TIMP2 and 3 were unchanged; the MMP12 and MMP13 increases were attenuated in PKCdelta knockout mice. BALF showed increased proMMP2, proMMP9 and MMP12 activity at 9 days, with only MMP12 still elevated at 40 days. In C10 epithelial cells, pretreatment with actinomycin D completely blocked the asbestos-induced increases in MMP13 and TIMP1 mRNA, and the MMP inhibitor GM6001 inhibited asbestos-induced EGFR activation and ERK1/2 phosphorylation.

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: Experimental laboratory study: mouse asbestos inhalation model (wild-type and PKCdelta knockout mice) plus in vitro experiments in a lung epithelial cell line and primary lung fibroblasts
• Who was studied: C57Bl/6 wild-type mice (8-12 weeks old) and PKCdelta knockout littermates (3 per group for microarray, 6 per group for ribonuclease protection assay); murine alveolar epithelial type II cells (C10 line) and primary lung fibroblasts from 10-week-old C57Bl/6 mice; University of Vermont
• Exposure: Inhaled NIEHS reference chrysotile asbestos, 7 mg/m3 air, 6 h/day, 5 days/week, for 3, 9 or 40 days in mice; NIEHS reference crocidolite asbestos at 5 micrograms per square centimetre added to cultured cells
• Main results:
  • In wild-type mice, asbestos inhalation significantly increased lung MMP12 mRNA at 3, 9 and 40 days (microarray)
  • Ribonuclease protection assay: MMP12, MMP13 and TIMP1 were increased in wild-type lungs at 9 days, while MMP3, 7, 8, 9 and TIMP2 and 3 were unchanged from sham mice
  • PKCdelta knockout mice exposed to asbestos showed attenuated lung MMP12 and MMP13 mRNA compared with wild-type mice
  • BALF zymography in asbestos-exposed mice: proMMP9, proMMP2 and MMP12 activities increased at 9 days; at 40 days MMP2 and MMP9 returned to control levels while MMP12 stayed elevated
  • Asbestos-exposed PKCdelta knockout mice still showed increased MMP2, MMP9 and MMP12 activities in BALF
  • In C10 epithelial cells, actinomycin D pretreatment completely blocked the asbestos-induced rise in MMP13 and TIMP1 mRNA
  • Inhibitor experiments in cells indicated EGFR, PI3K and PKCdelta involvement; the EGFR inhibitor reduced MMP13 but not MMP12 mRNA
  • In C10 epithelial cells, the broad-spectrum MMP inhibitor GM6001 inhibited asbestos-induced EGFR activation and ERK1/2 phosphorylation
• The authors' conclusion: The authors concluded that asbestos-induced MMP up-regulation depends on signalling by growth factor receptors and on the PI3K, PKCdelta and ERK1/2 pathways
• Limitations the authors state:
  • The authors noted that antibodies to detect most non-gelatinase mouse MMPs, including MMP12 and MMP13, are rudimentary and of suspect specificity, so protein expression was not determined
  • The authors stated they could not readily explain the increased MMP12 activity seen in sham-exposed PKCdelta knockout mice
  • The authors stated the precise role of individual MMPs in asbestos-induced lung pathology remained to be explored with MMP12 and MMP13 knockout models
  • Crocidolite rather than chrysotile had to be used in the cell experiments because reference crocidolite was insufficient in quantity for inhalation studies

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic, Bronchoalveolar Lavage (BAL), Fibroblast, EGFR.

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