Direct and indirect effects of liraglutide on hypothalamic POMC and NPY/AgRP neurons – Implications for energy balance and glucose control

Zhenyan He, Yong Gao, Linh Lieu, Sadia Afrin, Jianhong Cao, Natalie J. Michael, Yanbin Dong, Jia Sun, Hongbo Guo, Kevin W. Williams

Glucagon-like peptide 1 (GLP-1) is a gut derived hormone that plays a key role in regulation of glucose metabolism. In addition, GLP-1 suppresses feeding. The acute effects of GLP-1 receptor activation in melanocortin neurons mirrors that of the description of leptin. Liraglutide is a GLP-1 receptor agonist. He et al. find that leptin and GLP-1 directly modulate neuronal excitability of melanocortin neurons in an additive manner. They also describe a melanocortin pre-synaptic network altered in response to GLP-1.

Objective: The long-acting glucagon-like peptide-1 receptor (GLP-1R) agonist, liraglutide, stimulates insulin secretion and efficiently suppresses food intake to reduce body weight. As such, liraglutide is growing in popularity in the treatment of diabetes and chronic weight management. Within the brain, liraglutide has been shown to alter the activity of hypothalamic proopiomelanocortin (POMC) and Neuropeptide Y/Agouti-related peptide (NPY/AgRP) neurons. Moreover, the acute activities of POMC and NPY neurons have been directly linked to feeding behavior, body weight, and glucose metabolism. Despite the increased usage of liraglutide and other GLP-1 analogues as diabetic and obesity interventions, the cellular mechanisms by which liraglutide alters the activity of metabolically relevant neuronal populations are poorly understood.

Methods: In order to resolve this issue, we utilized neuron-specific transgenic mouse models to identify POMC and NPY neurons for patch-clamp electrophysiology experiments.

Results: We found that liraglutide directly activated arcuate POMC neurons via TrpC5 channels, sharing a similar mechanistic pathway to the adipose-derived peptide leptin. Liraglutide also indirectly increases excitatory tone to POMC neurons. In contrast, liraglutide inhibited NPY/AgRP neurons through post-synaptic GABAA receptors and enhanced activity of pre-synaptic GABAergic neurons, which required both TrpC5 subunits and K-ATP channels. In support of an additive role of leptin and liraglutide in suppressing food intake, leptin potentiated the acute effects of liraglutide to activate POMC neurons. TrpC5 subunits in POMC neurons were also required for the intact pharmacological effects of liraglutide on food intake and body weight. Thus, the current study adds to recent work from our group and others, which highlight potential mechanisms to amplify the effects of GLP-1 agonists in vivo. Moreover, these data highlight multiple sites of action (both pre- and post-synaptic) for GLP-1 agonists on this circuit.

Conclusions: Taken together, our results identify critical molecular mechanisms linking GLP-1 analogues in arcuate POMC and NPY/AgRP neurons with metabolism.