Effects of Atmospheric Particulate Matter on the post-transcriptional control of the pro-inflammatory mediators interleukin-6 and interleukin-8

Epidemiological, clinical, in vivo and in vitro studies have shown consistent associations between particulate matter (PM) exposure and the induction of pro-inflammatory responses. Posttranscriptional control mechanisms are essential in the regulation of pro-inflammatory mediators such as IL-6 and IL-8; however the role of PM exposure in the posttranscriptional control of IL-6 and IL-8 has not been evaluated. Therefore the hypothesis of this study is that exposure to PM2.5 promotes the stabilization of IL-6 and IL-8 mRNAs by the AU-rich elements (AREs) mediated pathway. This hypothesis was addressed through the following specific aims: 1) Evaluate the effects of PM2.5 in the induction of IL-6 and IL-8; 2). Evaluate the role of PM2.5 in the mRNA stability of IL-6 and IL-8; and 3). Determine if PM2.5 promotes the activation of the AU-rich binding proteins HuR and AUF-1. Organic extracts derived from PM2.5 collected in Guaynabo and Fajardo were used to test the hypothesis. In addition a standard reference material for diesel exhaust particles (DEP) was used. In vitro studies with a human bronchial epithelial cell line showed that our extracts were able to induce the production of IL-6 and IL-8 with significant increases in mRNA steady-state levels as early as 15 min of exposure. The mRNA half-lives were significantly increased in exposed cells indicating that the mRNA were being stabilized. To confirm if the mRNA stabilization was due to post-transcriptional control mechanisms, nuclear run-ons assays were conducted to measure the transcription rates of the IL-6 and IL-8 genes. Only the Guaynabo extract and DEP induce de novo synthesis of IL-8 at 15 min, indicating that transcriptional mechanisms were also at play. The involvement of the HuR and AUF-1 in the stabilization of the mRNAs was explored by measuring their levels in the cytoplasm. While AUF-1 was not detected, a cytoplasmic enrichment of HuR was observed in cells exposed to the Guaynabo extract. Overall, this study demonstrated for the first time that PM exerts an effect in the transcriptional and posttranscriptional regulation of IL-6 and IL-8, providing evidence of molecular mechanisms involved in the adverse health effects observed with PM.