Peroxisome proliferator-activated receptor-γ agonists attenuate biofilm formation by Pseudomonas aeruginosa

Pseudomonas aeruginosa is a significant contributor to recalcitrant multidrug-resistant infections, especially in immunocompromised and hospitalized patients. The pathogenic profile of P. aeruginosa is related to its ability to secrete a variety of virulence factors and to promote biofilm formation. Quorum sensing (QS) is a mechanism where in P. aeruginosa secretes small diffusible molecules, specifically acyl homo serine lactones, such as N-(3-oxo-dodecanoyl)l-homoserine lactone (3O-C12-HSL), that promote biofilm formation and virulence via interbacterial communication. Strategies that strengthen the host's ability to inhibit bacterial virulence would enhance host defenses and improve the treatment of resistant infections. We have recently shown that peroxisome proliferator-activated receptor gamma (PPAR gamma) agonists are potent immunostimulators that play a pivotal role in host response to virulent P. aeruginosa. Here, we show that QS genes in P. aeruginosa (strain PAO1) and 3O-C12-HSL attenuate PPAR gamma expression in bronchial epithelial cells. PAO1 and 3O-C12-HSL induce barrier derangements in bronchial epithelial cells by lowering the expression of junctional proteins, such as zonula occludens-1, occludin, and claudin-4. Expression of these proteins was restored in cells that were treated with pioglitazone, a PPAR gamma agonist, before infection with PAO1 and 3O-C12-HSL. Barrier function and bacterial permeation studies that have been performed in primary human epithelial cells showed that PPAR gamma agonists are able to restore barrier integrity and function that are disrupted by PAO1 and 3O-C12-HSL. Mechanistically, we show that these effects are dependent on the induction of paraoxonase-2, a QS hydrolyzing enzyme, that mitigates the effects of QS molecules. Importantly, our data show that pioglitazone, a PPAR gamma agonist, significantly inhibits biofilm formation on epithelial cells by a mechanism that is mediated via paraoxonase-2. These findings elucidate a novel role for PPAR gamma in host defense against P. aeruginosa. Strategies that activate PPAR gamma can provide a therapeutic complement for treatment of resistant P. aeruginosa infections.