Role of AgRP and POMC neurons in glucose homeostasis and food intake in a model of insulin resistance

• Grant number: 24/09045-1
• Support Opportunities: Research Grants - Visiting Researcher Grant - International
• Start date: March 31, 2025
• End date: March 30, 2026
• Field of knowledge: Biological Sciences - Physiology - Physiology of Organs and Systems
• Principal Investigator: Lucila Leico Kagohara Elias
• Grantee: Lucila Leico Kagohara Elias
• Visiting researcher: Arikawe Adesina Paul
• Visiting researcher institution: University Of Lagos/Unilag, Nigeria
• Host Institution: Faculdade de Medicina de Ribeirão Preto (FMRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil
• Associated research grant: 18/18071-5 - Hydroelectrolytic and energy homeostasis: from cellular metabolism to endocrine systems in different phases of development, AP.TEM

Abstract

IntroductionFructose a major constituent of modern diet with same chemical formula as glucose was initially thought to be beneficial to diabetics due to its low glycemic index and its lesser suppression of food intake (Luc and Kim-anne, 2010). But its metabolism is different from that of glucose due to its complete hepatic extraction and rapid hepatic conversion into glucose, glycogen, lactate, and fat. This contributes to its effectiveness in inducing insulin resistance (IR) and type 2 diabetes in rodents and genetically predisposed humans. We have utilized fructose feeding to induce IR and subsequently type 2 diabetes in rodents (Arikawe et al., 2006 & 2012).Cells in Arcuate nucleus sense peripheral hormones like leptin and insulin signalling to activate anorexigenic and orexigenic neurons e.g. proopiomelanocortin (POMC) & Agouti-related peptide (AgRP), both of which play important roles in energy homeostasis. However, it remains unknown whether hypothalamic AgRP and/or POMC neuronal activity is directly involved in glycemic control, food intake and energy metabolism during diabetic situations. This study will utilize the DREADD technique to investigate the involvement of POMC and AgRP neurons on glucose homeostasis, food intake and energy metabolism in normal and genetic mice fed a high fructose diet. Objectives1.To determine if modulation of AgRP or POMC neurons using DREADD would alter blood glucose and food intake in insulin resistant normal and AgRPires-cre/POMC-cre adult male mice. 2.To highlight interplay of AgRP or POMC neuronal activity on glucose metabolism and glycemic control in AgRPires -cre and POMC-cre adult male mice following chronic fructose feeding.MethodologyNormal male C57BL/6 mice and male AgRP ires -cre and POMC-cre knockout mice will be randomly categorized into "before DREADD" and "after DREADD". The "before DREADD" mice will be divided into 2 groups: Control (CON); fed ad libitum with AIN-93G diet + untreated drinking water and Insulin resistant (IRG); fed ad libitum with a special diet containing 25% fructose mixed with AIN-93G w/w diet (Arikawe et al., 2006; 2012) and fed ad libitum with water supplemented with 20% fructose w/v for 8 weeks. Fasting blood glucose (FBG), fasting insulin (FIN), OGTT, homeostasis model assessment (HOMA) calculation for IR index, islet ²-cell function and insulin sensitivity index will be carried out in both groups. Mice will also be subjected to analysis of body composition using MRI Mini Spec and energy expenditure using the Comprehensive Laboratory Animal Monitoring System. This will be followed by DREADD stimulation while mice will continue feeding as stated above for an additional 4 weeks. There after FBG, FIN, OGTT and HOMA assessments stated above will be repeated. Furthermore, stereotactic and surgical procedures will be performed to quantify mCherry-positive AgRP or POMC neurons.The "after DREADD" animals will be divided into similar categories and subjected to all protocols as highlighted above with the only difference being the timing of DREADD stimulation, which will be carried out before fructose feeding. There after FBG, FIN, OGTT and HOMA assessments stated above will be repeated. Also, stereotactic and surgical procedures will be performed to quantify mCherry-positive AgRP or POMC neurons in these animals.The results will be expressed as mean ± SEM. Data will be statistically compared with one-way ANOVA using Prism 8.0 followed by Student-Newman-Keuls post-hoc for between-group comparisons and p<0.05 will be considered statistically significant.References1.Luc, T., Kim-anne, L., 2010. Fructose metabolism. Physiol. Rev. 90, 23-46.2.Arikawe, et al., 2006. Afr. J. Reprod. Health. 10, 106-113.3.Arikawe, et al., (2012). Nigerian Journal of Physiological Sciences, Vol. 27, (2): 171 - 179. (AU)