Expression of PPARγ and Paraoxonase 2 Correlated with Pseudomonas aeruginosa Infection in Cystic Fibrosis

Phoebe E Griffin,Yvonne C Belessis,Roxanne Strachan,Sean Beggs,Adam Jaffe,Louise F Roddam,Margaret A Cooley,Gunnar F Kaufmann

doi:10.1371/journal.pone.0042241

Abstract

The Pseudomonas aeruginosa quorum sensing signal molecule N-3-oxododecanoyl-l-homoserine lactone (3OC12HSL) can inhibit function of the mammalian anti-inflammatory transcription factor peroxisome proliferator activated receptor (PPAR)γ, and can be degraded by human paraoxonase (PON)2. Because 3OC12HSL is detected in lungs of cystic fibrosis (CF) patients infected with P. aeruginosa, we investigated the relationship between P. aeruginosa infection and gene expression of PPARγ and PON2 in bronchoalveolar lavage fluid (BALF) of children with CF. Total RNA was extracted from cell pellets of BALF from 43 children aged 6 months–5 years and analyzed by reverse transcription–quantitative real time PCR for gene expression of PPARγ, PON2, and P. aeruginosa lasI, the 3OC12HSL synthase. Patients with culture-confirmed P. aeruginosa infection had significantly lower gene expression of PPARγ and PON2 than patients without P. aeruginosa infection. All samples that were culture-positive for P. aeruginosa were also positive for lasI expression. There was no significant difference in PPARγ or PON2 expression between patients without culture-detectable infection and those with non-Pseudomonal bacterial infection, so reduced expression was specifically associated with P. aeruginosa infection. Expression of both PPARγ and PON2 was inversely correlated with neutrophil counts in BALF, but showed no correlation with other variables evaluated. Thus, lower PPARγ and PON2 gene expression in the BALF of children with CF is associated specifically with P. aeruginosa infection and neutrophilia. We cannot differentiate whether this is a cause or the effect of P. aeruginosa infection, but propose that the level of expression of these genes may be a marker for susceptibility to early acquisition of P. aeruginosa in children with CF.

Highlights

Individuals with cystic fibrosis (CF) are susceptible to infection with the opportunistic pathogen Pseudomonas aeruginosa, and over 80% of adults with CF patients are infected with this organism [1]
Cells from bronchoalveolar lavage fluid (BALF) samples from all subjects were examined for PPARc gene expression by RT–Quantitative Polymerase Chain Reaction (qPCR), for the presence of P. aeruginosa by culture and RT–qPCR, and for the presence of any other pathogen by culture only. ‘‘Culture positive’’ and airway infection were defined as detection of .105 colony-forming units per mL (cfu/mL) in BALF [29,30]
Previous studies in human cell lines and cftr knockout mice have suggested that expression of PPARc is reduced in CF [10,15,16], this has not been directly demonstrated in individuals with CF, and no previous study has suggested an association of PPARc expression with P. aeruginosa infection

Summary

Introduction

Individuals with cystic fibrosis (CF) are susceptible to infection with the opportunistic pathogen Pseudomonas aeruginosa, and over 80% of adults with CF patients are infected with this organism [1]. The mammalian transcription factor, peroxisome proliferator activated receptor (PPAR)c is a master negative regulator of inflammation, modulating signaling through NFkB and MAP kinases It is expressed in respiratory epithelium [10] and has been reported to be expressed in immune cells such as macrophages and neutrophils [11,12,13,14]. The expression and function of PPARc have been reported to be low in human CF respiratory epithelial cell lines [10] and in cystic fibrosis transmembrane conductance regulator (cftr) knockout mice [15,16]. This deficiency may contribute to the hyperinflammatory response in CF. PPARc agonists have been reported to ameliorate intestinal symptoms in cftr knockout mice, and their potential use as therapy in chronic inflammatory disease has been widely discussed [17]

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Results

Conclusion