PGC-1 alpha in Lung Immune Response

Pseudomonas aeruginosa is a major health challenge that causes recalcitrant multi-drug resistant infections, especially in immunocompromised and hospitalized patients. Multi- and pan-drug resistant strains of P. aeruginosa are increasing threats that contribute to high mortality in these patients (1-3). Hence, there is an urgent need to develop new strategies to combat P. aeruginosa and other resistant pathogens. The pathogenic profile of P. aeruginosa is related to its ability to secrete a variety of virulence factors. Novel therapeutic strategies that strengthen the ability of the host would enhance immune defenses and improve outcomes. Over the previous funding cycle, we elucidated the mechanisms by which lipid mediators regulate the lung’s innate immune responses to P. aeruginosa virulence factors (5-8). We discovered that 15d-PGJ2, stimulates host responses to P. aeruginosa through peroxisome proliferator-activated receptor gamma (PPAR), a ligand- activated transcription factor (9-11). Further, we showed that PPAR agonists inhibit P. aeruginosa biofilm formation and enhance bacterial clearance from the lungs. Studies to determine the mechanisms by with PPAR modulates host response in epithelial cells revealed that P. aeruginosa : 1) inhibit paraoxanase-2, a key mitochondrial enzyme that hydrolyses C12-HSL (12, 13), and 2) inhibit PPAR coactivator 1-alpha (PGC- 1α) and mitochondrial transcription factor A (TFAM), disrupting mitochondrial biogenesis and bioenergetics (14,15). These mitochondrial derangements impaired epithelial ATP production, increased reactive oxygen species (ROS), and enhanced glycolysis to disrupt epithelial barrier integrity and immune function. Most importantly, our new data show that PGC-1α overexpression or activation rescues mitochondrial bioenergetics and epithelial junctional integrity preventing bacterial transmigration in vitro and enhancing clearance of bacteria in lungs of mice infected with P. aeruginosa in vivo. Therefore, we hypothesize that P. aeruginosa evades host defenses by disrupting mitochondrial biogenesis, epithelial barrier integrity, and immune function. Strategies to restore PGC-1α provide a novel therapeutic approach to stimulate mitochondrial biogenesis and enhance immune function in P. aeruginosa lung infections. To test this hypothesis, we propose three specific aims: 1) Investigate the molecular mechanisms by which P. aeruginosa attenuates PGC-1α in host lung epithelial cells.2) Elucidate how attenuation of PGC-1α compromises host epithelial barrier and immune function in response to P. aeruginosa. 3) Define the impact of rescuing PGC-1α activation and mitochondrial biogenesis in P. aeruginosa pneumonia in vivo. The PI’s investigative team provides needed and complementary expertise to advance this paradigm-shifting work focused on enhancing host resistance to invasive pathogens. Successful completion of these integrated studies will provide new insights into the molecular pathogenesis of P. aeruginosa-induced airway epithelial cell dysfunction (Aim 1), define novel pathways perturbing critical host cell functions (Aim 2), and explore new therapeutic paradigms for restoring cell functions involved in host defense (Aim 3). The overarching goal of this proposal is to define novel molecular approaches to rescue host mitochondrial function and immune responses to pathogens such as P. aeruginosa. The impact of these studies is further enhanced by their potential relevance to other pathogens and by the exploration of existing pharmacological tools permitting rapid clinical translation and benefit to veterans infected with virulent pathogens.