Regulation of human lung epithelial cell numbers by diesel exhaust particles

¹ Thoracic Medicine, National Heart & Lung Institute, Imperial College, London, UK; and Dept of Respiratory Medicine, School of Medicine, Dicle University, Diyarbakir, Turkey
² Thoracic Medicine, National Heart & Lung Institute, Imperial College, London, UK

^* To whom correspondence should be addressed. E-mail: f.chung{at}imperial.ac.uk.

	Abstract

Particulate air pollution is associated with respiratory morbidity and has cytotoxic and proinflammatory effects. We examined the effects of diesel exhaust particles (DEP) on proliferation and apoptosis of A549 lung epithelial cells.

When deprived of serum (serum starvation), epithelial cell numbers fell, but DEP (5-200 µg·ml^-1) prevented this. Using flow cytometric analysis of propidium iodide (PI) staining, DEP (10 µg·ml^-1) increased cells in S phase of cell cycle from 12.85% to 18.75% (p<0.0001) after 48hrs, reversing serum starvation-induced G_0/1 arrest. DEP also reduced the increase in apoptotic cells, as defined by double-expression of annexinV/PI, observed after serum starvation (from 28.35 to 15.46%; p<0.05). The anti-oxidants, N-acetylcysteine (NAC, 33 mM) and AEOL10113 (10-100 µM), the N-terminal c-jun kinase (JNK) inhibitor, SP600125 (33 µM), and NF-B inhibitor, SN50 (33µM), inhibited DEP-induced cell number increase. NAC inhibited DEP-induced reduction of G_0/1 and increase in cells in the S and G₂/M phases. Expression of p21^CIP1/WAF1 mRNA and protein seen with serum-starvation was reduced by DEP.

DEP prevented serum-starvation-led decreases in A549 epithelial cells by inducing cell cycle progression and preventing apoptosis, processes involving oxidative stress, inhibition of p21^CIP1/WAF1 expression and stimulation of JNK and NF-B. Therefore, low-dose DEP exposure may lead to lung epithelial cell hyperplasia.

Keywords:  Anti-oxidants, apoptosis, cell proliferation, diesel exhaust particles, nuclear factor-B

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