For decades, NRAMP1 (for natural resistance-associated macrophage protein 1, renamed SLC11A1 for solute carrier protein family 11, member 1) has been characterized as a divalent cation/H+ antiporter in the phagosomal membrane of macrophages that pumps iron and manganese out of the vacuole. This mechanism contributes to nutritional immunity against intracellular pathogens by depleting the phagosomal environment of essential metal cofactors. Mouse macrophages expressing mutant Slc11a1 are functionally compromised in control of several intracellular pathogens, including Salmonella enterica serovar Typhimurium (S. Typhimurium). Further, human polymorphisms in SLC11A1 are associated with susceptibility to both autoimmune and infectious disease. However, until now the role of SLC11A1 has been assumed to be macrophage-specific. Remarkably, during studies on vitamin A deficiency, our lab has uncovered an unsuspected role for SLC11A1 in control of systemic S. Typhimurium infection by neutrophils. Our preliminary results show that increased susceptibility of vitamin A-deficient mice to disseminated S. Typhimurium infection is dependent on synthesis of SLC11A1 by neutrophils, which challenges conventional wisdom that SLC11A1-dependent host defenses are associated exclusively with macrophages. However, strong evidence for a role of SLC11A1 as essential in neutrophil antimicrobial response is needed to establish this novel concept. Our central hypothesis is that SLC11A1 function promotes the bactericidal activity of neutrophils. The objective of this application is to investigate the role of SLC11A1 in neutrophil control of S. Typhimurium infection. To test our hypothesis, we will use a triangulated approach assessing neutrophil function and response to infection by utilizing human neutrophils in cell culture, mouse neutrophils ex vivo and a systemic S. Typhimurium infection in vivo mouse model. We are drawing on collaborative expertise to employ CRISPR for generation of a SLC11A1-/- cell line and utilize the Cre-lox system to create a mouse strain that has a conditional knockout of Slc11a1 only in neutrophils. Our rigorous studies of SLC11A1 in neutrophil response to infection will provide fundamental knowledge in the fields of microbiology and immunology, thereby advancing biomedical research. Further, this project will have broad implications for translation to improve human health, as polymorphisms in SLC11A1 make certain patients more susceptible to disease. The integrated training plan outlined in this application will provide an in-depth research experience, training in cutting-edge technologies like CRISPR, expertise from core facilities, and education from faculty in the School of Veterinary Medicine, the School of Medicine, the College of Agricultural and Environmental Sciences, and the College of Biological Sciences. Importantly, this plan embodies the structured dual-degree mentorship at UC Davis with a supportive sponsor and lab that addresses clinically relevant microbiological questions, a clinical mentor, a graduate school adviser, medical school advisers and an MD/PhD adviser.
NRAMP1 (for natural resistance-associated macrophage protein 1, renamed SLC11A1 for solute carrier protein family 11, member 1) is a divalent cation/H+ antiporter in the phagosomal membrane of macrophages that contributes to defense from intracellular pathogens and has been genetically linked to susceptibility to both infection and autoimmune disease. Our lab has discovered preliminary evidence suggesting a novel role for SLC11A1 in neutrophil-mediated control of Salmonella infection. In this application, we propose to assess the role of SLC11A1 in human and mouse neutrophil antimicrobial response, which will provide new insights into the function of neutrophils in immune defense against pathogens and inform translational studies in infectious disease.
