The role of the immune cell transcription factor T-bet in metabolic physiology and pathophysiology.

Obesity and diabetes are getting more common. In the UK, there were1.4 million people with diabetes in 1996. This number has now risen to 2.9 million and is predicted to rise to over 4 million by 2025. Most of these cases are what is known as Type 2 diabetes. This kind of diabetes used to only affect people in later life but, as people are getting fatter, it now seems to affect younger adults, even some children. Indeed, in 2009 almost a quarter of all adults in the UK were classified as being obese. This increase is a major worry as these conditions are associated with high blood pressure, heart attacks and strokes. Obesity is usually accompanied by the resistance to the sugar-lowering hormone insulin, meaning that insulin cannot work effectively. This 'insulin resistance' is a major factor in the development of Type 2 diabetes and its complications. However, it is unclear exactly how getting fatter leads to insulin resistance and progression to Type 2 diabetes.
Recent work has found that that both Type 2 diabetes and obesity are characterised by low levels of inflammation in the body, particularly in abdominal fat. It seems that, as people get fatter, unknown to them, white blood cells (cells of the immune system that normally protect against infections) infiltrate fat. Here, they silently cause inflammation by releasing chemicals ('cytokines') which can stop insulin working effectively. In terms of inflammation, there seem to be some types of white cells that are 'bad' for metabolism and others that are 'good' or 'protective'. Changing from thin to fat seems to alter the numbers and types of different white cells in fat, with fewer 'good 'cells and more 'bad' white cells with increasing obesity. Interestingly, replacing a type of white cell (T cells) in mice that lacked them improved their insulin resistance and brought down their high sugar (glucose) levels. However, the genes and molecules that control this process are still unknown.
We aim to build on this research by investigating the role of a gene, known as 'T-bet', which is critical in the development of a certain type of white cell (known as a Th1 cell).This cell type particularly accumulates in fat in obesity and may be metabolically 'bad'.We think that T-bet, the molecule that controls the development of these cells, could be important in causing certain white cells to accumulate in fat in obesity.These calls may then cause inflammation in the fat, resulting in resistance to insulin (and so risking Type 2 diabetes and cardiovascular disease). An improved understanding of the molecules responsible for causing these changes leading to inflammation in fat, particularly in obesity, and how they alter the action of insulin could lead to the development of new therapies in the prevention and treatment of obesity, diabetes and its complications.
Our preliminary work shows that that amount and type of white cells in fat depend on the action of the T-bet gene. T-bet may also subsequently influence glucose levels. We want to investigate this further. Specifically, using a model lacking the T-bet gene, we will look at the effect of diet on the development of obesity and correlate this with measurements of metabolism (such as glucose and insulin levels).We will also analyse the type of white cells and their inflammation-causing chemicals. We will perform further studies to elucidate which white cell type is important for the effects we see. Additional studies will address what other molecules may be important for the action of T-bet. This work will identify the role of the immune cell molecule T-bet in inflammation in fat and and metabolism and could lead to the development of new types of drugs to be used in the prevention and treatment obesity and Type 2 diabetes.

Building on our own substantial preliminary data which suggests a role for the immune system in obesity-associated inflammation, this proposal aims to investigate the role for the immune cell transcription factor T-bet in adipose tissue inflammation, metabolic physiology and pathophysiology. To date, no immune specific transcription factor has been described to have a role in this process. We will determine impact of T-bet on energy homeostasis and adipose tissue inflammation by undertaking a series of in vivo and ex vivo studies involving manipulation of the T-bet axis. We will examine the effect of high fat diet on the susceptibility to obesity and its metabolic complications and correlate the findings with adipose immune infiltration/inflammation in various models of T-bet deficiency. The metabolic response to low and high fat diet will involve weekly measurements of food intake and body weight, together with periodic evaluation of hormonal profiles (by ELISA) and evaluation of glucose homeostasis by glucose and insulin tolerance testing. Such in vivo measures will be correlated with other measurements ex vivo. Body fat levels and distribution will be quantified by measuring the weight of the different adipose tissue depots. A variety of immune cell populations within the different adipose depots will be phenotyped using multiparameter flow cytometry. Further measurements of immune and adipose gene expression and production of anti-inflammatory and pro-inflammatory cytokines and other molecules involved in immune cell trafficking will also be evaluated using quantitative PCR, organ culture and ELISAs. Additional in vivo models, including adoptive T cell transfer studies, will enable us to map the beneficial effect of T bet deficiency found in our preliminary work to the adaptive or innate immune system and explore potential downstream molecular pathways.

Academic Impact
This aspect of impact is covered under 'Academic beneficiaries' as suggested.

Economic and Societal Impact
The long term aim of this research is for improved patient health. Obesity and diabetes are already major public health problems and their prevalence continues to increase at an alarming rate. In 2009, almost a quarter of adults (22 per cent of men and 24 per cent of women aged 16 or over) in England were classified as obese (BMI 30kg/m2 or over). Since 1996, the number of people with diabetes in the UK has risen from 1.4 million to 2.9 million (4.5% UK population). Diabetes prevalence is estimated to rise to 4 million by 2025. Thus, it is the public at risk of obesity and diabetes and their long term complications, together with their carers and relatives, who would be the long term beneficiaries of this work.

Obesity and Type 2 diabetes are associated with significant morbidity and mortality. These are accompanied by significant personal costs in terms of altered quality of life due to poor health. Healthcare costs, estimated at nine billion per year (10% of the annual NHS budget) for the treatment of diabetes and its complications, and the unquantified additional economic costs incurred due to loss of ability to work are considerable. Our work may identify potentially novel targets for the prevention and treatment of obesity and its metabolic complications which could have longer term societal and economic benefits.

Exactly how obesity leads to insulin resistance and progression to Type 2 diabetes is unclear, but low grade inflammation in fat is recognised to play a significant role. We believe that the immune cell transcription factor, T-bet, is critical in this process. Many of the drugs used in Type 2 diabetes (eg metformin/glitazones) work by improving insulin sensitivity; others serve to promote insulin secretion to in order to overcome insulin resistance. Targeting T-bet and its genomic targets involved in the inflammatory process causing insulin resistance would offer a new, alternative therapeutic approach in the prevention and treatment of Type 2 diabetes and other conditions associated with insulin resistance (metabolic syndrome together with its inherent risk of cardiovascular disease). Our preliminary data also suggest a novel role for T-bet in the regulation of body weight. The work in this proposal is at the discovery science end of the translational spectrum but will provide novel mechanistic insight in the role of the immune system in metabolism relating to an area of considerable disease burden. In this regard the proposal has potential for commercial application in the future for patient benefit, perhaps within 5 to 10 years.