Project Grant F30AI197371

INNATE IMMUNE SENSING OF BACTERIAL PHENAZINE TOXINS - PROJECT SUMMARY THE GOAL OF THIS PROJECT IS TO ENHANCE OUR UNDERSTANDING OF HOW HOST GENETIC VARIATION INFLUENCES INFECTION OUTCOMES. THROUGHOUT HUMAN HISTORY, INFECTIOUS OUTBREAKS HAVE DEMONSTRATED THAT IDENTICAL PATHOGENS CAUSE DRAMATICALLY DIFFERENT OUTCOMES IN INDIVIDUAL PATIENTS, FROM ASYMPTOMATIC TO FATAL. HOWEVER, THE IMPACT OF HOST GENETIC FACTORS UNDERLYING THIS VARIATION REMAINS LARGELY UNCHARACTERIZED. UNDERSTANDING HOW NATURALLY OCCURRING GENETIC POLYMORPHISMS INFLUENCE INFECTION OUTCOMES IS CRITICAL FOR PREDICTING DISEASE SUSCEPTIBILITY AND DEVELOPING TARGETED INTERVENTIONS. THE NEMATODE CAENORHABDITIS ELEGANS PROVIDES A POWERFUL MODEL TO CHARACTERIZE THE EVOLUTIONARY FORCES THAT SHAPE HOST-PATHOGEN INTERACTIONS. THE CRITICALLY IMPORTANT HUMAN PATHOGEN PSEUDOMONAS AERUGINOSA CAUSES LETHAL INFECTION IN C. ELEGANS, PROVIDING AN EXPERIMENTAL PLATFORM TO STUDY BACTERIAL PATHOGENESIS. THE KEY VIRULENCE DETERMINANT OF P. AERUGINOSA IS THE PRODUCTION OF PHENAZINE TOXINS-PYOCYANIN (PYO), PHENAZINE-1- CARBOXAMIDE (PCN), PHENAZINE-1-CARBOXYLIC ACID (PCA), AND 1-HYDROXYPHENAZINE (1-HP). THESE TOXINS GENERATE REACTIVE OXYGEN SPECIES AND KILL HOST CELLS ACROSS MULTIPLE SPECIES. UNLIKE MAMMALS, C. ELEGANS LACKS CANONICAL PATTERN RECOGNITION RECEPTORS (TLRS, NLRS) AND INSTEAD EMPLOYS PATTERNS OF PATHOGENESIS. THIS MEANS C. ELEGANS SURVEYS FOR PATHOGEN-INDUCED DISTURBANCES IN HOST PHYSIOLOGY TO MOUNT SPECIFIC IMMUNE RESPONSES. PREVIOUS WORK FROM OUR LABORATORY DEMONSTRATED THAT THE NUCLEAR HORMONE RECEPTOR NHR-86 FUNCTIONS AS A NON-CANONICAL PHENAZINE RECEPTOR, DIRECTLY BINDING PCN TO ACTIVATE PROTECTIVE IMMUNE RESPONSES. THIS ESTABLISHED THAT C. ELEGANS CAN CO-OPT METABOLIC RECEPTORS AS PATHOGEN SENSORS. THE CENTRAL HYPOTHESIS OF THIS PROPOSAL IS THAT PHENAZINES SHAPED THE EVOLUTION OF C. ELEGANS IMMUNE SURVEILLANCE MECHANISMS. I PROPOSE THAT ENVIRONMENTAL EXPOSURE TO PHENAZINE TOXINS FUELED THE EVOLUTION OF MECHANISMS TO DETECT THEIR PRESENCE AND IDENTIFY BACTERIAL INFECTION. MY PRELIMINARY RESEARCH SUPPORTS THIS HYPOTHESIS. FIRST, I IDENTIFIED NATURAL VARIATIONS IN SUSCEPTIBILITY TO BACTERIAL PHENAZINE TOXINS AMONG WILD-CAUGHT POPULATIONS OF C. ELEGANS. SECOND, IN A GENOME-WIDE ASSOCIATION STUDY (GWAS) OF 130 NATURAL ISOLATES, I MAPPED THIS VARIATION TO A MAJOR QUANTITATIVE TRAIT LOCUS (QTL) ON CHROMOSOME V (~1.7 MB REGION) AND FOUR SECONDARY LOCI. THIRD, I DEMONSTRATED THAT THE CHROMOSOME V QTL INDEPENDENTLY CONTRIBUTES ~16% TO RESISTANCE THROUGH RECIPROCAL EFFECTS USING NEAR-ISOGENIC LINES. THE TOP CANDIDATE GENE, NHR-243, ENCODES A NUCLEAR HORMONE RECEPTOR WITH A LEUCINE-TO-VALINE SUBSTITUTION IN ITS LIGAND-BINDING DOMAIN. THIS SUGGESTS CONVERGENT EVOLUTION WHERE MULTIPLE NUCLEAR HORMONE RECEPTORS MAY HAVE BEEN CO-OPTED AS PHENAZINE SENSORS. THIS PROPOSAL SEEKS TO IDENTIFY AND CHARACTERIZE THE GENETIC DETERMINANTS OF NATURAL VARIATION IN RESISTANCE TO BACTERIAL TOXINS (AIM 1) AND DEFINE THE GENETIC ARCHITECTURE OF PHENAZINE RESISTANCE (AIM 2).