Delineating the regulation and function of gamma-synuclein in adipocyte lipid metabolism

Obesity represents one of the biggest current medical challenges worldwide and so there is a clear need to find new potential therapies to combat this increasingly prevalent condition. Fat tissue is comprised of adipocytes which are cells specialised to allow the safe storage of fat in one large lipid droplet occupying most of the cell. The bigger the lipid droplet is the larger the fat cell becomes and the greater the overall mass of fat tissue. In obesity, it appears that the safe lipid storage capacity of fat tissue may be exceeded and lipids then instead go to other tissues causing harmful effects. Many prevalent diseases are linked to the negative effects of these lipids including diabetes, heart disease and some forms of dementia.
We have recently found that inhibiting a protein called gamma-synuclein might prevent the development of obesity. The gamma-synuclein protein is particularly highly expressed in fat cells. In fat cells lacking gamma-synuclein the breakdown of the lipid droplet is increased. However, this does not cause a problematic rise in lipids going to other tissues because it seems that the lipid that comes from the lipid droplet in the fat cell can be preferentially burnt as a fuel to provide energy in a way that lipids from the diet are not.
This burning of lipids particularly occurs in specialised brown fat cells which are capable of doing this and then dissipating the energy generated as heat. Activating this process is seen a potential way to treat obesity by effectively burning excess lipids and wasting energy. We have found that inhibiting gamma-synuclein may help brown fat cells to do this more efficiently. Therefore, overall the effect of gamma-synuclein inhibition may be both to break down fat stores and then to burn the lipid in the brown fat cells.
In this study we aim to understand 1) how the gamma-synuclein gene is switched on and off in fat cells, 2) how precisely gamma-synuclein controls the breakdown of the lipid droplet and 3) how losing gamma-synuclein makes brown fat cells burn more lipids. All of these may suggest ways to change levels of gamma-synuclein or alter the way it works to reduce body weight and/or treat the diseases associated with obesity.

The incidence of obesity has increased dramatically and is linked to the development of conditions such as diabetes and cardiovascular disease. Altered lipid homeostasis due to adipocyte dysfunction in obesity is believed to significantly contribute to the development of these conditions. We recently found that knockout of gamma-synuclein can increase energy expenditure and prevent the development of high fat diet induced obesity. This appears to involve increased lipolysis in white adipose tissue (WAT) and increased lipid oxidation in brown adipose tissue (BAT), both significant sites of gamma-synuclein expression. This proposal will investigate the molecular mechanisms underlying these effects and determine how gamma-synuclein expression is regulated. Specifically:
1) We will interrogate prexisting genome wide ChIP-seq and DHS-seq data sets from adipocytes, to identify putative transcriptional regulators of gamma-synuclein expression in these cells. Their importance will then be examined in both white and brown adipocyte cell lines using targeted promoter/reporter assays, ChIP assays and transcription factor knockdown.
2) We will determine the molecular mechanisms via which gamma-synuclein regulates lipolysis in adipocytes. We will investigate the interaction of gamma-synuclein with regulators of lipolysis including ATGL, for which we have already demonstrated binding. These studies will employ co-IPs and immunofluorescent cell imaging techniques to reveal the subcellular localisation and dynamic regulation of any interactions.
3) We will elucidate the molecular mechanisms via which gamma-synuclein may increase lipid oxidation and energy expenditure in BAT. We hypothesize that gamma-synuclein loss in BAT cells increases lipolysis providing lipid species that may be preferred for oxidation in this tissue. In addition, lipids from the increased lipolysis caused by gamma-synuclein loss may selectively activate an oxidative gene expression profile.

Academic impact:
Research into metabolic health and disease is continually expanding and the UK has major strength and expertise in this field. This field involves multidisciplinary research from fundamental molecular and cellular biology to whole organism physiology, multi-tissue crosstalk, systems biology, genetics, epigenetics, pharmacology, nutrition and public health.
The work proposed spans several of these areas and would be of significant interest to a wide range of investigators from basic to clinical scientists. By increasing the UK's research output, skills training and profile in the area of metabolic disease the work will contribute to the building of new capacity on this area. The research will also apply new techniques and generate new reagents that will be of significant benefit to other academic researchers. These will be made available to other academic researchers to accelerate the pace of discovery in this field.

Economic and societal impacts:
Obesity is a major health problem in the UK, leading to increased risk of disease and a health service burden in excess of a half billion pounds a year in direct costs. Current pharmacological therapies are extremely limited and so the identification of new potential therapeutic avenues is essential. The work proposed aims to uncover novel pathways via which adipocyte function and lipid metabolism might be regulated. This has the power to reveal new targets for the development of molecular or pharmacological therapies for the treatment of insulin resistance, dyslipidaemia, obesity and metabolic disease.
The majority of the work addresses the fundamental questions regarding the molecular mechanisms controlling adipocyte lipolysis and lipid oxidation. When amenable and relevant pathways are identified through these studies, therapeutic drugs are likely to be 10 years or more from clinical use. However, the novel findings of this research may be of significant value to pharmaceutical companies with an interest in this area. The insights gained into novel regulators of these processes may reveal new candidates to be screened in individuals with unsolved lipodystrophy or who appear likely to have severe monogenic forms of insulin resistance, dyslipidaemia or obesity. As such it may be valuable in genetic diagnosis of these individuals, aiding their appropriate treatment. This could provide a significant benefit in the short-term to the health of affected individuals. In addition we aim to determine how gamma-synuclein is nutritionally regulated in adipose tissue. If, as our preliminary data suggests, altering gamma-synuclein levels could have some beneficial effects on metabolic health this might also provide insights into how this might be achieved by altered nutrition.
Intellectual property arising from the proposed research will be exploited through the University of Cambridge's technology transfer company Cambridge Enterprise and the BBSRC. The proposed research may inform and benefit the bioscience sector through access to new knowledge, technology development and data. Thus it may enhance the knowledge economy and economic competitiveness of the UK. The research is also readily accessible to the public, given its clear relevance to the well-publicised problem of obesity. Advances in this area have the potential to improve health, lifespan and quality of life.