Pathogenesis of Ulcerative Colitis: the role of Claudin-8 in epithelial barrier function and inflammation

Title
Pathogenesis of Ulcerative Colitis: the role of Claudin-8 in epithelial barrier function and inflammation

Importance:
Ulcerative Colitis (UC) is a potentially fatal, chronic inflammatory disease of the bowel. It affects 120,000 people in the UK, triples the risk of developing colon cancer, and costs the NHS £720 million per year to treat. The inflammation in UC is intermittent, causes ulceration and damage of the lining of the large bowel, and can be severe.

The underlying cause of UC is unknown. The cells lining the bowel act as a barrier between the contents of the bowel and the immune system. There is increasing evidence that patients with UC have abnormalities in the structures that hold these cells together. These structures are known as tight-junctions, and abnormalities in them can cause the bowel lining to become leaky. Understanding the role of these abnormalities in UC can potentially help find new treatments.

The tight-junctions are made up of a number of proteins. One of these proteins is called CLDN8 and we have discovered that patients with UC have significantly lower levels of CLDN8 in their colon. However, the role of CLDN8 in the development and progression of UC is not yet fully understood.

In order to study the role of CLDN8, it is important to use mice that are genetically engineered to lack CLDN8. We will use mice because they are the standard mammalian animal model for gene targeting technology and no alternative is available for studying the role that CLDN8 plays during inflammation. In parallel to the animal studies, we will also study colon samples from patients with UC. We plan to follow-up the patients we have already studied, and take further colonic biopsies from these patients when their inflammation flares up and also after it settles. This will allow us to investigate how the composition of the proteins that make up the tight-junctions change over several cycles of UC flare-up.

The human and animal studies together will provide the first insights into the relationship of CLDN8 level in the bowel with UC, a relationship that might have important diagnostic implications. Furthermore, if CLDN8 is shown to be of central importance in the development or progression of UC, it might prove beneficial to treat UC by elevating the levels of CLDN8. This can potentially be done, for example, by local gene therapy that can be easily administered using an enema. Also, abnormalities in the function of the bowel lining may potentially allow environmental cancer-causing chemicals to enter the underlying tissue, thus increasing the risk of colon cancer in patients with UC. The findings of our study may therefore also improve our knowledge of how colon cancer is developed.

Title
Pathogenesis of Ulcerative Colitis: the role of Claudin-8 in epithelial barrier function and inflammation

Background
Ulcerative Colitis (UC) is a chronic Inflammatory Bowel Disease affecting 120,000 people in the UK. There is evidence that abnormal epithelial barrier function could drive aberrant immune responses in genetically susceptible individuals. Studies in humans and animals have shown that the composition of several tight-junction molecules, in particular members of the claudin (CLDN) family, become altered in active colitis. Recent work in our laboratory, the only study investigating UC patients in clinical remission, revealed a significant reduction in CLDN8 expression in colonic samples of UC patients. In contrast, the expression of other CLDN proteins was not altered in our study. Further analysis of our data revealed that reduced expression of CLDN8 mirrored the disease distribution in the colon.

Aims:
1. Determine the functional significance of CLDN8 in bowel homeostasis and inflammation
2. Define the changes in CLDN expression levels in individual UC patients in longitudinal studies

Methodology:
The changes in the structure, epithelial turnover and permeability of the colon will be studied in a CLDN8 knockout mouse model. Several models of inflammation, including acute and chronic colitis, will also be used in the mutant mice to assess the role of CLDN8 in inflammation. In addition, colonic biopsies will be taken during relapse and remission of UC in the same patients. This will be used to determine the changes in CLDN8 expression, and possible compensatory changes in the expression of other CLDNs as the disease reverts or relapses.

Scientific and Medical opportunities
If CLDN8 is shown to be aetiologically implicated in UC, it might prove beneficial to treat the condition by elevating the levels of the molecule in the colonic mucosa, for example by the induction of gene expression, or gene therapy, delivered by enema

My research is designed to study the role that epithelial barrier dysfunction, and more specifically CLDN8, plays in initiation and resolution of inflammation, as well as its role in diarrhoea and abnormal muscular contractility. I will study patients with Ulcerative Colitis (UC), both during inflammation and remission.

The findings from this study will potentially benefit patients across multiple specialities.

First, my research findings will ultimately benefit patients with Inflammatory Bowel Disease (IBD), and in particular UC, which is a chronic disease with frequent flare-ups. UC is prevalent throughout the world, and its incidence is increasing. Many patients suffer from symptoms of diarrhoea and abdominal cramps even they are on optimal medical therapy. My research will provide the first insights into the relationship of CLDN8 expression in the bowel with UC, a relationship that might have important diagnostic and prognostic implications. If CLDN8 is shown to be aetiologically implicated in UC, it might prove beneficial to further investigate treating UC by elevating the levels of the molecule in the colonic mucosa, for example by the induction of gene expression, or gene therapy, delivered by enema. Such treatment may improve patient's overall quality of life and health. It can also potentially be of benefit to the nation's and the world's economy by reducing sick-leave and increasing productivity.

Second, the role of epithelial barrier dysfunction, and more specifically CLDN8, in inflammation and other conditions is not solely limited to the colon. Having a detailed understanding of the function of CLDN8 will potentially benefit patients by advancing research into the pathogenesis and new treatment options in other conditions such as Sjogren syndrome and renal diseases.

Third, UC is known to triple the risk colorectal (CRC) development. The mechanisms behind this are unknown; however, epithelial barrier dysfunction may play a role by allowing entry of environmental carcinogens into the tissue. Therefore the results of this study may elucidate some of the mechanisms involved in the development of CRC.

The research that I will be undertaking has no obvious inherent commercial value. However, should any valuable intellectual property emerge, UCL has an experienced technology transfer mechanism in the form of UCL business. Any unique diagnostic or therapeutic advance would be patented or licensed through this pre-existing system.

Finally, I aim to undertake an academic career in gastroenterology, specifically in IBD. This is an exciting time for IBD research and many laboratory-based discoveries may potentially benefit patients by allowing development of novel treatment options. During this fellowship I will undertake three years of intense scientific training that will include laboratory work, use of animal models in the study of colitis, human studies and learning about administrative and regulatory aspects of clinical research. This fellowship is therefore essential in my aim to establish myself as an independent investigator, apply for funding and run a team to contribute to translating basic scientific research into clinical treatments.