PM and PM-Components of Widely Different Characteristics Induce CXCL8 Responses Through Common Mechanisms: Role of EGFR, TGF-alpha and TACE in Bronchial Epithelial Cells

Johan Øvrevik(1) , Annike Totlandsdal (1), Marit Låg (1), Magne Refsnes (1), Jørn Holme (1), Thomas Sandstrøm (2), PER SCHWARZE (1)

(1) Norwegian Institute of Public Health, Oslo, Norway (2) Umeå University, Umeå, Sweden

     Abstract Number: 219
     Last modified: November 9, 2009

Abstract
Airborne particulate matter (PM) has a complex composition, and contains a variety of compounds that may contribute to the detrimental effects of ambient PM on human health.
Clarifying the particle characteristics and associated components responsible for PM-induced effects is pivotal for the understanding of PM toxicity. Here we have studied their effects on pro-inflammatory responses. Inflammation is believed to play a key role in a variety of health effects associated with PM exposure, including development and exacerbation of both lung and cardiovascular diseases.

We have recently shown that increased expression of neutrophil-recruiting CXC-chemokines, in particular CXCL8 (IL-8) is a dominating pro-inflammatory response of bronchial epithelial cells (BEAS-2B) to exposure to both different types of PM with wide differences in physico-chemical characteristics and to pure PM-components. This study explores mechanisms of induced CXCL8 release from BEAS-2B cells after exposure to selected compounds commonly found in ambient PM (zinc and iron salts, 1-nitropyrene [1-NP; a marker of diesel exhaust], lipopolysaccharide [LPS] and crystalline silica [positive control]). Examination of their effects on expression of 84 genes representative of 18 different signaling pathways by real-time PCR, revealed that a predominant role for NF-kappaB-signalling pathways. The mechanisms involved in the regulation of CXCL-8 were further examined using a panel of 15 pharmacological inhibitors. CXCL8 release measured by ELISA revealed that the different compounds induced CXCL8 through activation of many of the same signaling pathways, but that the relative importance of different signaling pathways varied. Most strikingly the EGF-receptor (EGFR) inhibitor AG1478 always markedly reduced CXCL8 release . The importance of EGFR in regulating CXCL8 was further confirmed by using an EGFR-blocking antibody. Preliminary studies suggest that the increased CXCL8-release may be attenuated by targeting the EGFR ligand TGF-alpha. This attenuation may either be achieved directly by using a neutralizing antibody, or indirectly by inhibiting TNF-alpha coverting enzyme (TACE) which cleaves and releases membranebound TGF-alpha. The notion that EGFR potentially may be a central regulator of PM-induced cytokine responses was further strengthened by the observation thatAG1478 also attenuated the effects of diesel exhaust particles (DEP) in BEAS-2B cells. Interestingly, phosphorylation of EGFR has previously been detected in lung epithelium from human volunteers exposed to DEP via inhalation.

In summary, we have investigated the importance of different intracellular signaling pathways in CXCL8 regulation in BEAS-2B cells upon exposure to substances representative of different compound-groups commonly found in ambient PM. Although there were apparent differences in the underlying mechanisms of CXCL8 regulation, the similarities in the effects are striking, given the considerable variation in physico-chemical characteristics of the tested compounds. Most notably, the EGFR appears to play a central role in PM-induced CXCL8 release, possibly through cleavage and release of membrane bound TGF-a. The study also emphasizes the need for further clarification of the potential role of EGFR in other PM-induced effects such as carcinogenesis.