CC16-TNF-α negative feedback loop formed between Clara cells and normal airway epithelial cells protects against diesel exhaust particles exposure-induced inflammation

We have previously shown that exposure to diesel exhaust particles (DEPs) stimulates human airway epithelial cells to secrete the inflammatory cytokines interleukin-8, interleukin-1β, and granulocyte-macrophage colony-stimulating factor (GM-CSF) involved in allergic diseases. In the present paper, we studied the mechanisms underlying the increase in GM-CSF release elicited by DEPs using the human bronchial epithelial cell line 16HBE14o−. RT-PCR analysis has shown an increase in GM-CSF mRNA levels after DEP treatments. Comparison of the effects of DEPs, extracted DEPs, or extracts of DEPs has shown that the increase in GM-CSF release is mainly due to the adsorbed organic compounds and not to the metals present on the DEP surface because the metal chelator desferrioxamine had no inhibitory effect. Furthermore, radical scavengers inhibited the DEP-induced GM-CSF release, showing involvement of reactive oxygen species in this response. Moreover genistein, a tyrosine kinase inhibitor, abrogated the effects of DEPs on GM-CSF release, whereas protein kinase (PK) C, PKA, cyclooxygenase, or lipoxygenase inhibitors had no effect. PD-98059, an inhibitor of mitogen-activated protein kinase, diminished the effects of DEPs, whereas SB-203580, an inhibitor of p38 mitogen-activated protein kinase, had a lower effect, and DEPs did actually increase the active, phosphorylated form of the extracellular signal-regulated kinase as shown by Western blotting. In addition, cytochalasin D, which inhibits the phagocytosis of DEPs, reduced the increase in GM-CSF release after DEP treatment. Together, these data suggest that the increase in GM-CSF release is mainly due to the adsorbed organic compounds and that the effect of native DEPs requires endocytosis of the particles. Reactive oxygen species and tyrosine kinase(s) may be involved in the DEP-triggered signaling of the GM-CSF response.

Download Full-text

Diesel exhaust particles upregulate eotaxin gene expression in human bronchial epithelial cells via nuclear factor-κB-dependent pathway

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00358.2002 ◽

2003 ◽

Vol 284 (6) ◽

pp. L1055-L1062 ◽

Cited By ~ 37

Author(s):

Hajime Takizawa ◽

Shinji Abe ◽

Hitoshi Okazaki ◽

Tadashi Kohyama ◽

Isamu Sugawara ◽

...

Keyword(s):

Gene Expression ◽

Epithelial Cells ◽

Diesel Exhaust ◽

Airway Epithelial Cells ◽

Diesel Exhaust Particles ◽

Pyrrolidine Dithiocarbamate ◽

Airway Epithelial ◽

Bronchial Epithelial ◽

Exhaust Particles

Fine particles derived from diesel engines, diesel exhaust particles (DEP), have been shown to augment gene expression of several inflammatory cytokines in human airway epithelial cells in vitro. However, it remains unclear whether or not DEP have any effect on the expression and production of eotaxin, an important chemokine involved in eosinophil recruitment into the airways. We studied the effects of DEP by using a conventional suspended DEP and by a recently established in vitro cell exposure system to diesel exhaust (Abe S, Takizawa H, Sugawara I, and Kudoh S, Am J Respir Cell Mol Biol 22: 296–303, 2000). DEP showed a dose-dependent stimulatory effect on eotaxin production by normal human peripheral airway epithelial cells as well as by bronchial epithelial cell line BET-1A as assessed by specific ELISA. mRNA levels increased by DEP were shown by RT-PCR. DEP showed an additive effect on IL-13-stimulated eotaxin expression. DEP induced NF-κB activation by EMSA as previously reported but did not induce signal transducer and activator of transcription (STAT) 6 activation according to Western blot analysis. Finally, antioxidant agents ( N-acetyl cysteine and pyrrolidine dithiocarbamate), which inhibited NF-κB activation but failed to affect STAT6 activation, almost completely attenuated DEP-induced eotaxin production, whereas these agents failed to attenuate IL-13-induced eotaxin production. These findings suggested that DEP stimulated eotaxin gene expression via NF-κB-dependent, but STAT6-independent, pathways.

Download Full-text