Weight Regulation by GLP1R agonists via a non-canonical hypothalamic PKA-mTORC1 mediated pathway - PROJECT SUMMARY/ABSTRACT Glucagon-like peptide-1 receptor (GLP1R) agonists are an emerging class of drugs used to treat obesity due to their ability to lower body weight. While GLP1R action in the brain is essential for the weight-lowering effect of these drugs, little is known about the molecular mechanisms engaged by GLP1R agonists that promote weight loss. Studies conducted by our group made the novel discovery that the GLP1R agonist liraglutide stimulates activity of the nutrient-sensing protein complex mechanistic Target of Rapamycin Complex-1 (mTORC1) via phosphorylation of the mTORC1 accessory protein Raptor in Serine791 by the canonical GLP1R signaling target protein PKA. Furthermore, we show that global mutation of Serine791 in Raptor renders mice partially resistant to liraglutide-induced weight loss, indicating that this signaling mechanism contributes to the anorectic effect of GLP1R agonists. The goal of this project is to identify the key neuronal population and circuit in which GLP1R agonists engage this non-canonical PKA-mTORC1 interaction to promote weight loss. I hypothesize that GLP1R agonists promote weight loss by stimulating the PKA-mTORC1 interaction in Proopiomelanocortin (POMC) neurons of the Arcuate nucleus of the hypothalamus (ARCPOMC) that synapse onto Melanocortin- 4 Receptor-expressing neurons in the Paraventricular nucleus of the hypothalamus (PVHMC4R). The focus on ARCPOMC neurons is based on our preliminary findings that deletion of the GLP1R in POMC neurons significantly attenuates liraglutide-induced weight loss. ARCPOMC neurons synapse onto PVHMC4R neurons, and activation of this ARCPOMC → PVHMC4R circuit promotes weight loss. However, it is not known whether GLP1R- expressing ARCPOMC neurons form part of this functional ARCPOMC → PVHMC4R circuit. I will test my hypothesis using sophisticated genetically encoded protein activity reporters, transgenic mouse lines, imaging analyses, circuit mapping approaches, and metabolic phenotyping techniques. Aim 1 tests whether GLP1R activation specifically in ARCPOMC neurons promotes weight loss through the PKA- mTORC1 pathway. This includes in vivo measurements of PKA activity in ARCPOMC neurons in freely moving mice in response to GLP1R agonist treatment as well as performing comprehensive metabolic phenotyping tests in novel transgenic mice expressing a PKA-resistant Serine791 Raptor mutant specifically in POMC neurons. Aim 2 investigates whether GLP1R- expressing ARCPOMC neurons form an anatomical and functional ARCPOMC → PVHMC4R neurocircuit regulated via the PKA-mTORC1 signaling pathway in ARCPOMC neurons. This will involve rabies-virus based monosynaptic circuit mapping approaches and functional tests of neuronal activity. Completion of the experiments proposed in this application will provide me with extensive training in experimental design and data analysis and interpretation as well as in mastering concepts and methods relevant to neuroendocrinological regulation of metabolic phenotypes. My Sponsor and co-Sponsor are fully committed to my training and to helping me develop into an independent academic research scientist.
