In the brain, key focal points for control of metabolic function and feeding behavior are melanocortin receptors MC3R and MC4R. These receptors respond to two ligands, alpha-melanocyte stimulating hormone (a-MSH) and the agouti-related protein (AgRP), which act in opposite ways to promote negative and positive energy balance, respectively. Recent research demonstrates the profound importance of AgRP releasing neurons in metabolism and body weight homeostasis. The goal of this program is to understand the molecular basis of AgRP action, thus enabling new strategies for treating diverse conditions linked to obesity and metabolic diseases. New findings from our lab are significantly reshaping our understanding of a-MSH and AgRP action. The current paradigm posits that these molecules act to stimulate or suppress production of the cAMP second messenger. However, using protein design, we demonstrated that AgRP mutations in segments outside of the MCR binding core exert a profound influence on long term feeding, while leaving receptor affinity and cAMP suppression completely unchanged relative to wild-type. Moreover, new collaborative results find that AgRP promotes the opening of inward rectifying potassium channels through a cAMP independent mechanism, an effect that is directly dependent on these peripheral AgRP segments.
Aim 1 of this application will expand these studies by identifying how AgRP sequence and conformation drive potassium channel currents. This will be tested through protein design, NMR structure determination, as well as with a new human AgRP obesity-linked mutant identified by whole exome analysis.
Aim 2 will examine how syndecan-3, a negatively charged, membrane bound proteoglycan, facilitates AgRP signaling. This will be accomplished with biophysical experiments and through comparison studies where designed proteins are administered to wild-type and syndecan-3 knockout mice, followed by feeding trials and brain tissue imaging.
Aim 3 will expand on AgRP design efforts to produce stable proteins to test the role of proteolytic resistance in promoting long-term AgRP action, and as leads for treating cancer cachexia, a wasting condition characterized by extreme loss of appetite and lean tissue degradation.

Public Health Relevance

Obesity is one of the greatest public health concerns facing Western society. The condition arises from an imbalance between energy intake and expenditure and contributes to diabetes, high blood pressure, high blood cholesterol, coronary artery disease and certain cancers. In the brain, AgRP releasing neurons play a central role in controlling feeding behavior and metabolic function. Despite the deepening appreciation of the homeostatic role of AgRP neurons, the understanding of what happens once AgRP is released remains at an elementary level. This research program uses protein structure determination, protein engineering, pharmacology and in vivo experiments to uncover the molecular details responsible for AgRP regulation of the central melanocortin receptors. The goals are to advance the understanding this fundamental homeostatic system and to reveal new therapeutic approaches. In addition, protein design is used to improve AgRP stability in order to test the role proteolytic resistance in long-term AgRP action, and to develop new protein leads for treating wasting syndromes.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Molecular and Cellular Endocrinology Study Section (MCE)
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Sechi, Salvatore
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University of California Santa Cruz
Schools of Arts and Sciences
Santa Cruz
United States
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Hendricks, Audrey E; Bochukova, Elena G; Marenne, Gaƫlle et al. (2017) Rare Variant Analysis of Human and Rodent Obesity Genes in Individuals with Severe Childhood Obesity. Sci Rep 7:4394
Palomino, Rafael; Lee, Hsiau-Wei; Millhauser, Glenn L (2017) The agouti-related peptide binds heparan sulfate through segments critical for its orexigenic effects. J Biol Chem 292:7651-7661