The Role of Dysfunctional Na+/H+ Exchange in the Development of Dysbiosis and Subsequent Colitis

Abstract

The last half-century has seen a dramatic and alarming rise in the incidence of autoimmune disease in industrialized nations too rapid to be accounted for by genetics alone. Among those, Inflammatory Bowel Disease (IBD) has risen from a western disease affecting industrialized populations to an emerging global threat affecting diverse populations around the world. IBD is a complex disease that combines genetic susceptibility and environmental exposure, but one aspect appears to be clear: the involvement of the gut microbiome. Current thought holds that IBD is an autoimmune attack on commensal microbiota, causing extensive collateral damage to the host intestinal tissues in the process. However, it has remained unclear in the field whether the changes observed in the IBD microbiome are causative in nature or whether the microbiome is responding to already-underway inflammatory processes within the host. This dissertation investigates one host factor in particular with regard to the microbiome and the development of inflammation: sodium-hydrogen exchange at the brush border, mediated by sodium hydrogen exchanger 3 (NHE3). NHE3 is inhibited during active IBD, but its loss in knockout animals is also enough to promote spontaneous colitis in a microbiome-dependent fashion. This dissertation investigates the specific contribution of the microbiome in NHE3 knockout animals to determine whether loss of NHE3 may be mediating the onset of colitis through pro-inflammatory changes in the microbiome. Our results suggest that the microbiome fostered in an NHE3-deficient environment may accelerate the onset and severity of experimental colitis, though likely in concert with additional host factors.