PON2 mediates mitochondrial dysfunction in tracheal epithelial cells in response to a quorum sensing molecule...

The opportunistic bacterium Pseudomonas aeruginosa secretes the quorum-sensing molecule N-(3-oxododecanoyl)-l-homoserine lactone (C12) to co-ordinate gene expression profiles favorable for infection. Recent studies have demonstrated that high concentrations of C12 impair many aspects of host cell physiology, including mitochondrial function and cell viability. The cytotoxic effects of C12 are mediated by the lactonase enzyme, Paraoxonase 2 (PON2), which hydrolyzes C12 to a reactive metabolite. However, the influence of C12 on host cell physiology at concentrations observed in patients infected with P. aeruginosa is largely unknown. Since the primary site of P. aeruginosa infections is the mammalian airway, we sought to investigate how PON2 modulates the effects of C12 at subtoxic concentrations using immortalized murine tracheal epithelial cells (TECs) isolated from wild-type (WT) or PON2-knockout (PON2-KO) mice. Our data reveal that C12 at subtoxic concentrations disrupts mitochondrial bioenergetics to hinder cellular proliferation in TECs expressing PON2. Subtoxic concentrations of C12 disrupt normal mitochondrial network morphology in a PON2-dependent manner without affecting mitochondrial membrane potential. In contrast, higher concentrations of C12 depolarize mitochondrial membrane potential and subsequently trigger caspase signaling and apoptotic cell death. These findings demonstrate that different concentrations of C12 impact distinct aspects of host airway epithelial cell physiology through PON2 activity in mitochondria.