Salmonellae cause an estimated 150 million cases of gastroenteritis and 25 million cases of invasive disease (enteric fever and non-typhoidal bacteremia), leading to 300,000 deaths per year. Findings based on inbred mouse strains and rare human mutations indicate that the clinical presentations and outcomes of salmonellosis are influenced by the host?s genetic makeup. However, we do not understand the impact of common, naturally occurring human genetic differences on Salmonella infections. Our long-term goal is to leverage high- throughput cellular phenotyping of infection and natural genetic diversity to define molecular parameters of susceptibility to human infectious diseases. While genome-wide association studies (GWAS) of enteric fever and bacteremia identified genetic differences regulating susceptibility, such studies are limited by high variability in patient exposure, pathogen genetic diversity, and a limited understanding of the pathophysiology of identified variants. We developed a complementary cellular GWAS approach (Hi-HOST: High-throughput Human in vitrO Susceptibility Testing; http://h2p2.oit.duke.edu) to perform high resolution analysis of human genetic differences that impact host-pathogen traits while enabling experimental dissection of these traits. In the previous funding period, we focused on human genetic variants that regulate Salmonella invasion of host cells. We identified a regulatory variant in VAC14 that modulates levels of plasma membrane cholesterol and thus limits the docking of the Salmonella SPI-1 type III secretion system to host cells. Humans with the high-invasion allele of VAC14 have increased risk of typhoid fever and bacteremia. The objectives of this application are to define and characterize human genetic differences that alter the full spectrum of Salmonella host-pathogen interactions and assess their impact on disease. Building from our unique resource of Hi-HOST cellular GWAS of Salmonella invasion, replication, and host cytokine levels, we have identified SNPs mediating susceptibility to infection phenotypes that will undergo experimental validation and mechanistic studies. We will determine how regulatory SNPs affecting ARHGEF26 and MCOLN2 expression impact Salmonella invasion and replication and the role these genes play during infection in mice. For ARHGEF26, a Rho GEF that stimulates Salmonella-induced membrane ruffling, our association data and experimental evidence indicate SNPs regulate ARHGEF26 expression to increase invasion dependent on the Salmonella effector sopB. For MCOLN2, we hypothesize that this divalent cation channel is a novel factor that regulates intracellular replication by modulating nutrient access, metal toxicity, and/or immune cell polarization. Using Arhgef26 and Mcoln2 mice, we will elucidate how altered expression of these genes regulates bacterial burden and immune response during infection. Finally, we will test whether SNPs identified by Hi-HOST are associated with enteric fever and bacteremia in humans. Revealing these mechanisms could lead to new therapeutic strategies for salmonellosis and other diseases impacted by the same genetic variants.
Salmonellae are a leading cause of gastroenteritis and systemic disease worldwide, with widespread multi-drug resistance and a high global burden of morbidity and mortality. This proposal uses identification and mechanistic studies of natural human genetic variation regulating Salmonella invasion, replication, and host cytokine production, along with studies of human populations and mouse models, to improve our understanding of how Salmonella interacts with host cells and how this affects risk of typhoid fever and bacteremia. This study will reveal why certain genetic differences predispose individuals to Salmonella infections and may also reveal new targets for host-directed therapeutic intervention.
