Chemogenetic control of liver metabolism

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Hepatic glucose production (HGP) is the result of coordinated biochemical processes by which glycogen storage are catabolized to generate glucose (glycogenolysis), or glucose is produced from non-carbohydrate carbon substrates (gluconeogenesis). These processes are regulated by many G protein coupled receptors (GPCRs) expressed at the surface of the hepatocytes. As their names imply, GPCRs interact with G proteins located in the plasma membrane. When a ligand binds to the GPCR, it causes a conformational change that triggers the interaction between the GPCR and a nearby G protein. However, the downstream signaling events mediating the effects of GPCR activation on HPG are still misunderstood because of the lack of appropriate tools to selectively stimulate G proteins acutely. Here, I propose to harness the power of chemogenetics to selectively manipulate GPCR signaling in hepatocytes, as a mean of defining the complex biochemical reactions leading to HGP. Chemical genetics (chemogenetics) is an approach use to genetically engineer receptors that interact with previously unrecognized small molecule chemical actuators. This approach has been used to create modified GPCRs, called Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). Originally developed to control neuronal activity, DREADDs are emerging as key tools for selective pharmacological control of GPCR signaling in any cell type or organ. Recently, I reported the generation of a novel chemogenetic approach allowing acute stimulation of GsPCR and GiPCR signaling in adipocytes. This innovative model revealed important, previously unappreciated complex interactions of GPCR signaling in adipose tissue and demonstrated the usefulness of chemogenetic technology to better understand organ functions. I propose to combine state-of-the-art metabolic flux techniques with chemogenetics models to better understand the mechanisms mediating HGP. In particular, I propose to use chemogenetics to dissect two important metabolic pathways for HGP, namely glycogenolysis and gluconeogenesis in vitro (primary hepatocytes), ex vivo (perfused livers) and in vivo. Building on my previous work and expertise on liver metabolism and chemogenetic technology, this program aims to: 1) determine the sex-dependent mechanisms by which chemogenetic stimulation of liver GqPCR stimulate HGP; 2) evaluate how GqPCR signaling affects metabolic flux independent of changes in peripheral hormones in a perfused mouse liver model; 3) define the molecular cascade leading to HGP in primary hepatocytes. This Discovery Grant will define complex previously unknown mechanisms mediating HGP. Understanding this biology will provide a framework to better understand how different systems directly regulates liver metabolism. This program will also provide a powerful and sought after scientific and technical skill set for my students and the field to understand other regulatory factors involved in peripheral metabolism.