Oral FGF21 delivery to limit its action to the liver

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The endocrine acting protein fibroblast growth factor 21 (FGF21) is an important metabolic regulator shown to reduce obesity and associated metabolic disorders in rodent models and non-human primates. The first clinical studies with FGF21 analogues confirmed the lowering of body weight, circulating lipids and insulin in humans and pointed to the liver as the most important target, particularly in patients suffering from lipid disorders and non-alcoholic fatty liver disease. Liver is also the main source of circulating FGF21 but little is known about direct hepatic effects of FGF21. The biology of FGF21 is quite complex and only partially understood due to its diverse metabolic functions in multiple target organs and ongoing controversies about the exact cellular targets and intracellular mechanisms. Also, pharmacologically increased plasma concentrations can lead to adverse side effects such as the reduction of bone mass.We hypothesize that the targeted delivery of FGF21 to the liver through an oral administration system will lead to metabolic improvements while avoiding adverse effects. In addition, oral delivery would allow an easy daily application. The main objectives of this project are (i) clarification of the hepatic specific effects of FGF21 action, and (ii) establishing the oral administration of FGF21 with the help of edible plants that express FGF21.For objective (i) the effects of recombinant FGF21 on liver and primary hepatocytes of wildtype and FGF21 ablated mice will be investigated. Using an unbiased transcriptomic and metabolomic approach, novel metabolic targets of FGF21 in hepatocytes will be identified and verified in vitro and in vivo. This will also serve to establish a robust and reliable read out system for analyzing hepatic effects of orally applied FGF21. For objective (ii) a plant expression system will be established. Edible plants provide an excellent system since the plant cells protect intracellular compounds from degradation in the stomach and release them in the intestine when the plant material is decomposed (in planta bioencapsulation). The intestinal release of FGF21 will lead to a high exposure of the liver to FGF21 through the portal vein, but low circulating levels due to the short half-life of FGF21 which is subject to rapid proteolysis. To improve the protective effect of the plant cell, FGF21 will be attached to an oilbinding domain. For transcytosis from the intestine into the blood transferrin is used as second fusion partner. It will be cleaved off in the serum via an endogenous protease. Using transiently produced, purified FGF21 variants, the effectiveness will be analysed in in vitro systems of a simulated gastrointestinal tract and the Ussing chamber system. The best variant will be used to stably transform edible oil-rich tobacco. Their bioavailability and metabolic effects will be investigated by feeding studies using FGF21 ablated and obese mice.