Recipient Organization
IOWA STATE UNIVERSITY
S. AND 16TH ELWOOD
AMES,IA 50011
Performing Department
Veterinary Medicine
Non Technical Summary
Even though IBD affects approximately one in every 300 individuals in the U.S., this long-term disorder of the gastrointestinal tract is still poorly understood. In fact, an overarching question is: How much of IBD arises from our DNA, or genes, and how much comes from external factors such as microbes in our intestinal tract or ones acquired from the environment Studies of identical twins, and the fact that IBD often occurs later in life, point the way to both factors, and perhaps a complex interaction between the two, as being important. However, only a very small percentage of the overall risk of disease development can be attributed to variations in genes. These findings indicate that external factors are important in disease onset, too. My research focuses on the microbial causes of IBD. It specifically targets the microbiota already present in the gut and seeks to define their role in exacerbating inflammation of the gut after a low-grade, external trigger. I anticipate that understanding the role of the microbiota already present in the gut will help us identify biomarkers and develop bioassays to help predict who is susceptible to IBD and to test and identify new treatments. Until now, defining the role of the resident microbiota in the inflammation of IBD would seem daunting. This is because the gut contains more than 10 billion organisms per gram of contents representing over 400 bacterial species. This comprises a highly complex system. To reduce complexity, I will employ a highly simplified mouse model called the ASF, short for altered Schaedler flora. The gut of an ASF mouse contains only eight microbes, and this simplicity provides an ideal system for understanding IBD from the perspective of the host interacting with its GI microbial community. Even though an ASF mouse is highly simplified, it exhibits all the normal immune and GI functions of normal mice. Moreover, members of the ASF represent the types of resident microbes found in the human GI tract, making this model relevant to IBD patients. My basic experimental approach is as follows, and will be repeated and expanded, as needed, for various triggers of IBD. A third of the mice will serve as controls. The rest will be colonized with Escherichia coli, an apparently harmless and ubiquitous bacteria. Symptoms of IBD will be triggered in half of the colonized mice. The inflammatory response induced will be evaluated by looking for the presence of disease, measuring the response of cells that promote inflammation and assessing changes in the microbiota. Anticipated outcomes include defining the role of microbes resident in the gut in the onset of IBD. Specifically, I will uncover how E. coli alters these resident microbiota and causes them to "turn" on the gut and produce an inflammatory response triggered by an external stimulus. I will also detect changes in the numbers and locations of the resident microbiota following colonization with E. coli. My future work will build on these results to seek biomarkers for disease susceptibility, onset of symptoms, and understanding of responses that might lead to new therapies for IBD.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
While it is clear that aberrant mucosal immune responses to microbial antigens significantly contribute to inflammatory bowel diseases (IBD), as do genetic and environmental factors, the mechanisms by which resident enteric bacteria elicit pathogenic responses are not fully understood. Lack of such knowledge is a significant problem because it severely limits both the identification of biomarkers for disease susceptibility and the development of new therapeutic targets. My long-term goal is to systematically define how and why the composition of the resident enteric microbiota contributes to or triggers an immunologically mediated predisposition to the onset of IBD. Data from our laboratory indicate that prior colonization with an otherwise non-pathogenic bacterial provocateur, such as Escherichia coli SWW33, perturbs mucosal homeostasis and predisposes to disease following an inflammatory trigger. My central hypothesis is that E. coli colonization reshapes the spatial and temporal function of the gut's resident microbial community, thereby inducing immune responses pathogenic to the host. Successful completion of the proposed research will delineate how susceptibility to an inflammatory insult is increased by the influence of an opportunistic organism on the resident microbiota and the host immune system. These results will ultimately lead to the development of biomarkers and improved therapeutic interventions for IBD patients.
Project Methods
I will test this hypothesis by using a highly simplified mouse model, the altered Schaedler flora (ASF) model, which contains only eight defined microbial species. First, I will use effector CD4+ T cell responses to define the functional alterations in microbial density and spatial distribution after colonization with E. coli SWW33. I hypothesize that colonization of defined microbiota mice with E. coli SWW33 alters the distribution and colonization levels of the model bacterial community to favor the activation of antigen-specific CD4+ T cells following a mild, inflammatory insult. CD4+ T cell responses against the individual ASF organisms will be evaluated. The density and spatial distribution of the resident microbiota following the introduction of E. coli SWW33 and the induction of inflammation will be defined. These aims will be accomplished using a combination of cell culture techniques, quantitative PCR, fluorescent in situ hybridization and in vivo/ex vivo imaging. Second, I will demonstrate that pathogenic CD4+ T cells capable of perpetuating chronic inflammation mediate the disease observed in E. coli-colonized mice exposed to an inflammatory insult. I hypothesize that eliminating CD4+ T cells from mice colonized with E. coli and exposed to a mild, inflammatory insult will ameliorate histological and immune-mediated disease severity. A series of experiments will be performed in which CD4+ T cells are depleted in vivo using an anti-CD4 antibody. The timing of the anti-CD4 antibody and inflammatory insult administration will be modified in each experiment to address specific questions about the initiation and perpetuation of pathogenic CD4+ T cell responses.