Characterisation of the role of NPAT in metformin regulation of body weight and glycaemic control; moving GWAS data to biological function

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There is no cure for diabetes. The main drug prescribed for diabetes (taken by millions world-wide) is metformin, which improves insulin action to reduce blood glucose levels. However metformin does not reduce blood glucose in all patients, it can take 3-6 months of treatment to establish whether the drug is effective and its efficacy reduces with time. Our previous work identified genetic variations in people with diabetes, which were linked to the ability of metformin to improve glucose control. This implies that these gene sequences directly influence an aspect of the drug action in the diabetes population. The most significant genetic polymorphism focused to a region of the genome, which encodes 7 genes including the cell growth regulating genes ATM and NPAT. Further work, funded by the MRC, confirmed ATM and NPAT as the genes responsible for the variation in metformin action in human patients. The ultimate purpose of doing these very expensive genetic studies is to identify 'markers' that could help predict which patient will respond to which drug, without having to wait for months of treatment. The reality is that very few of these markers are strong or common enough to be used in this way. However the second big hope is that understanding how the 'hits' we identify (like ATM and NPAT) influence drug action may illuminate how the drug works and why it doesn't work in some people. This will help improve our ability to treat or prevent the disease. Our data argues that changing NPAT amount modifies the body response to metformin. We now propose to gain detailed biological and molecular insight into how NPAT influences metformin action. We will perform investigations to elucidate the physiological, cellular and molecular connections between metformin action and the NPAT gene: Firstly we will characterize glucose metabolism and hormone action in a mouse lacking NPAT and in a mouse lacking NPAT only in the liver (this is because metformin is thought to work mostly on the liver). We will use state of the art techniques to compare how the liver, muscle, fat tissue, pancreas and brain work together to control body weight and blood glucose and the response to hormones and metformin in these models with defective NPAT. This will tell us if NPAT is necessary (and if liver NPAT specifically is necessary) for basic regulation of glucose physiology, and in the clinical response to metformin.Secondly we will perform studies on isolated liver cells lacking NPAT to learn how NPAT contributes to biology inside the cells. Similarly we will use molecular approaches to increase or decrease NPAT in immortal cell lines representative of different tissues. This allows us to compare effects of increased or decreased production of NPAT proteins on specific functions of liver, pancreas and brain. We will also make cells that produce the genetic variants in NPAT found in the human patients and study how this effects NPAT biology and metformin action. Our overarching aim is to establish why NPAT gene sequences influence the response to therapy in people with diabetes. This information will help clinicians decide on the best early treatment options for people with diabetes and help scientists develop more effective therapies for this common disease.