Exploitation of metadherin as a regulator of hepatic energy metabolism

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The metabolic syndrome, a collection of obesity, hepatic steatosis, and insulin resistance is a major public health crisis, with unmet medical need. Non-surgical intervention strategies including lifestyle modification are generally ineffective due to poor compliance. We must therefore continue to identify and develop novel strategies and therapeutic targets. An essential initiating feature is excess triglyceride accumulation in the liver, which can progress through inflammation and fibrosis to steatohepatitis, cirrhosis, and hepatocellular carcinoma. Glucocorticoid (Gc) signalling in the liver has been implicated at all stages of progression. Moreover, metabolic complication is a persistent and limiting issue in long-term Gc treatment in inflammatory disease.In seeking mechanisms to address metabolic complications of Gc action we discovered the Gc receptor (GR) binds to metadherin, a multifunctional protein scaffold, implicated in liver lipid metabolism, inflammation and cancer. We discovered that metadherin is essential for Gc transactivation, but not transrepression, and that this is accomplished by regulating GR recruitment to enhancer elements. In mice lacking metadherin, Gc action in the liver was profoundly altered with a major shift in Gc-responsive lipid metabolic genes, and also a striking hyperglycaemic response. In the metadherin null mice, we also observed genome wide changes in H3K27Ac, a mark of active enhancers, in response to acute Gc challenge; likely indicating an underlying re-wiring of the GR cistrome. We have established mouse models of glucocorticoid excess, and found a marked induction of hepatic triglyceride, with lipid droplet accumulation; thus optimising a model of Gc-induced hepatosteatosis. We will now use this mode and more conventional diet-induced obesity, to define control mechanisms in GR action, and the role of metadherin.We will define how metadherin regulates GR function. We have evidence that metadherin promotes interaction with kinases required to modify the GR. We will now comprehensively define post-translational modification, using new mass spectrometry approaches, and link receptor modification to function. As altered GR trafficking (as may explain failure of recruitment to enhancers in response to metadherin disruption), we will employ single molecule resolution live cell imaging to track GR movement, and use fluorescence correlation spectroscopy to measure interaction with metadherin in real time.We hypothesise that metadherin, a known scaffold protein, promotes protein-protein interaction to regulate cellular responses to environmental stress, such as energy excess in the liver. To find metadherin effector mechanisms, we will define post-translational dynamics of metadherin, and use proteomics to identify metadherin client proteins, and in normal and fatty liver. We will specifically measure interactions with the 36 liver-expressed nuclear receptors, using a targeted, quantitative mass spectrometry approach.Finally, we will examine the physiological consequence of metadherin action in vivo with selective genetic targeting of metadherin in hepatocytes in mice under normal conditions and during diet-induced obesity and chronic Gc treatment. Together, this programme of work will define a new regulatory mode in Gc signaling and reveal a potential new therapeutic target ,which has the intriguing potential to selectively modify metabolic consequence of GR action.