Dendritic Spines on AgRP Neurons as Communication Hubs Controlling Feeding

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DESCRIPTION (provided by applicant): Agouti-related peptide (AgRP)-expressing neurons in the arcuate nucleus of the hypothalamus are critical regulators of energy balance. AgRP neurons are anabolic: optogenetic or pharmaco-genetic stimulation of AgRP neurons drives intense feeding behavior and promotes obesity; disruption of these neurons in adult mice causes severe anorexia. Given the important roles played by AgRP neurons, there is great interest in understanding the factors that regulate their activity. Most previous studies have been placed on examining their direct regulation by circulating factors, such as leptin, insulin, and ghrelin. Their synaptic regulation by neurotransmitters released from other neurons in the brain, however, has been greatly overlooked. This is unfortunate because defective synaptic transmission on these neurons could also contribute to eating disorders. Furthermore, it is likely that the mechanism-of-action for hormonal regulation of AgRP neurons, for example by ghrelin, is modulation of afferent synaptic transmission. Through the recent work at Dr. Brad Lowell group (Prof of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School), the candidate has found that glutamatergic synaptic transmission plays a key role in AgRP neurons. In particular, he discovered that AgRP neurons but not the adjacent POMC neurons have dendritic spines, 1um3 protrusions where majority of glutamatergic synapses reside and within which glutamate NMDA receptors operate to control synaptic plasticity. In addition, he found that the fasting- induced activation of AgRP neurons and its related feeding behavior are paralleled (and likely caused) by a marked increase in the number of spines (i.e. spinogenesis), and this is dependent on postsynaptic NMDARs. Thus, glutamatergic transmission and its plasticity, as modulated by postsynaptic NMDARs, play critical roles in controlling AgRP neuron activity and their related feeding behaviors. These findings, which are recently published on Neuron, provide the candidate a unique opportunity to interrogate synaptic regulations in the feeding circuits. However, to pursue such studies, some state-of-art technologies (such as electrophysiology combined with 2-photon microscope imaging), which are beyond the scope of Dr. Lowell's lab and not available at BIDMC, are required. Toward these ends, the candidate is now trained by Dr. Bernardo Sabatini (Prof of Neurobiology, HHMI, Dept. of Neurobiology, Harvard Medical School), to use such advanced technologies to study structural and functional properties of spines. In this K01 mentored career development award, under the mentorship of Dr. Sabatini, and co- mentorship of Dr. Lowell, the candidate proposes to obtain acquisition in both scientific knowledge and in technologies (electrophysiology combined with 2-photon microscope imaging) related to synapse studies, and develop other necessary skills toward his career independence (immediate goal). The candidate is now Instructor in Medicine at BIDMC and Harvard Medical School. Once he finishes training with Dr. Sabatini, he will be transitioned to Assistant Professor at BIDMC and establish his own laboratory, become an independent investigator in the area of nutrition, obesity and neuroscience research, and apply multi- disciplinary methodology to understand synaptic plasticity in hypothalamic neurons controlling feeding, energy expenditure, and fuel metabolisms (long-term goal). Therefore, the K01 award will provide the candidate protected time to obtain necessary training before he becomes independent. At the same time, the proposed project in this award will greatly help the candidate to obtain subsequent R01 grant support.