Genes and Environment in Diabetes Mellitus : A multi-species approach

Type 1 diabetes (T1D) affects more than 400,000 people in the UK including up to 30,000 children. Treatment involves lifelong daily insulin injections and the disease arises as the result of genetic and environmental factors, which cause the immune system to destroy the cells in the pancreas which normally produce insulin.

This project is aimed at understanding more about the risk factors involved in type 1 diabetes (T1D) and in particular whether it might be possible to reduce the risk of T1D by making environmental changes.

The incidence of T1D has been rising year on year since the 1950s, coinciding with more frequent use of antibiotics for childhood infections.

One theory is that antibiotics disrupt the balance of micro-organism in the gut (known as the microbiome). The microbiome is known to be involved in the development of the immune system and a healthy microbiome is thought to be involved in protecting against the development of T1D. Studies of the microbiome in children affected with T1D demonstrate many differences in the type, frequency and diversity of micro-organisms compared to the microbiome of children without T1D. Mouse models of T1D such as the NOD (non-obese diabetic) mouse have also demonstrated a relationship between antibiotic use and T1D risk.

In addition, recent evidence has suggested that a gene called DEXI may be involved in microbiome development, as well as T1D risk. This proposal will examine the relationship between the microbiome, the DEXI gene and T1D risk.

In the NOD model, the microbiome will be examine by looking at the genetic material from micro-organisms in the faeces, throughout the life course. The effect on the microbiome of of having an functional or non-functional Dexi gene will also be explored. In addition, the impact of measures to improve microbiome health on the development of T1D on this model will also be explored.

In addition, a new model for studying the microbiome and diabetes development will be explored. Pet dogs can develop spontaneous insulin-dependent diabetes mellitus just like young humans and importantly they have the advantage over the NOD model that they share our environment. This study will also use a large veterinary database to assess the impact of antibiotic use on the risk of diabetes development in pet dogs. In addition, samples of faeces will be collected from pet dogs undergoing treatment for newly diagnosed diabetes in a veterinary hospital, as well as non-diabetic dogs to determine if the same relationship between microbiome and diabetes exists in dogs as in children.

Finally, the role of DEXI in the human immune system will be explored. New methods of detection of the DEXI protein in blood samples and the immune system will be developed, to allow the relationship between DEXI, the microbiome and the development of the human immune system to be explored in future.

Aims: The aim of this project is to understand the biology of the DEXI gene which has been associated with susceptiblity to multiple autoimmune diseases including type 1 diabetes (T1D), multiple sclerosis and primary biliary cirrhosis. The specific questions of the functional impact of this gene in the context of the immune system and the microbiome will be addressed.

Objectives: The first objectives of this study are to evaluate the impact of DEXI knockout on diabetes suceptibility, the microbiome and the function of the immune system. Additionally, this project will generate novel monoclonal antibodies to facilitate study of DEXI protein across species, including humans. This project will also endeavour to evaluate the client-owned domestic pet dog, which also suffers from spontaneous diabetes, as a potential spontaneous model for study of the microbiome in T1D.

Methodology: Gene knockdown has already been achieved using CRISPR-Cas9 technology in the non-obese diabetic (NOD) model. Immunological and phenotypic studies will include evaluation of cytokine production and activation status in response to a range of stimuli and single cell RNA-Seq of selected cell types. Microbiome analysis will be undertaken on DNA extracted from faeces in the NOD and in spontaneously diabetic pet dogs undergoing veterinary treatment. Microbiome transfer experiments will also be undertaken in the NOD model in the presence and absence of Dexi.

Scientific and medical opportunities: Discovery of novel pathways in autoimmune disease susceptibility offers new opportunities for therapeutic or preventative intervention.

The proposed project aims to understand how natural resistance to type 1 diabetes (T1D) breaks down, and to determine how this natural resistance may be exploited for new interventions to prevent T1D. This research has the potential to confirm DEXI as a potential therapeutic candidate for microbiome manipulation in prevention of autoimmune disease, leading to the use of DEXI itself (or a pathway which it affects) to prevent the development of autoimmunity in susceptible individuals.The project's results will also further the MRC's aim of understanding the role of the microbiome in development and function of the immune system over the life course. In addition, this work will also make a contribution to the One Health agenda, by examining the role of the microbiome in a companion animal species and identifying links between canine and human health.

There are therefore several stakeholders who may benefit from this research:
1. Patients at genetic risk of autoimmune diseases in which the genetic region encoding DEXI has been implicated (e.g. type 1 diabetes, multiple sclerosis, primary biliary sclerosis). The results of this work may have exciting positive implications for those families with a genetic pre-disposition to autoimmune disease. Disease prevention is preferable to the disease management options available at present, which focus mainly on control of clinical signs of disease and are associated with complications and side-effects. Such families would be offered hope and potentially involvement in a trial of a future intervention to prevent disease developing, avoiding the burden of treatment of chronic disease and enhancing quality of life.
2. Clinicians managing patients with an increased risk of autoimmune disease and setting budgets for their care. There are more than 3.6 million people diagnosed with T1D in the UK and the incidence is rising, therefore the results of this study have great potential to have a positive clinical and financial impact on the NHS. Type 1 diabetes costs the NHS in excess of £1.8 billion per year (http://www.diabetes.co.uk/cost-of-diabetes.html). In addition, the results of this work may add further evidence to the important discussion regarding rational use of anti-microbial therapies in human and veterinary medicine, which could have a wide-reaching impact.
3. Scientific researchers in T1D and other autoimmune disease in which the DEXI gene has been implicated will benefit from the results of this study, which might open up new research or therapeutic avenues in diseases other than T1D.
4. Pet owners will benefit from the results of this work by engaging with the One Health agenda and gaining improved understanding of the importance of the microbiome in human and animal health, which may inform dietary and breeding strategies.
5. Veterinary surgeons will benefit from the results of this work by learning more about gastrointestinal health in dogs and the relationship between the microbiome, anti-microbial useage and diabetes in certain dog breeds, which may influence their antibiotic prescribing practices.
6. Commercial companies such as those developing probiotic / prebiotic supplements or foods for humans as well as those manufacturing dog food may benefit from this data. The global probiotics market exceeded US$35bn in 2015 and the UK petcare market is worth more than £4bn annually.