Peripheral orexin agonist administration as a potential therapy for weight gain and obesity in polygenic New Zealand obese mouse

• Grant number: 21/10671-6
• Support type: Scholarships abroad - Research Internship - Doctorate
• Effective date (Start): January 07, 2022
• Effective date (End): May 28, 2022
• Field of knowledge: Biological Sciences - Physiology - Physiology of Organs and Systems
• Principal researcher: Camila Aparecida Machado de Oliveira
• Grantee: Izabelle Dias Benfato
• Supervisor abroad: Catherine Kotz
• Home Institution: Instituto de Saúde e Sociedade (ISS). Universidade Federal de São Paulo (UNIFESP). Campus Baixada Santista. Santos , SP, Brazil
• Research place: University of Minnesota (U of M), United States
• Associated to the scholarship: 17/26075-8 - Central control of spontaneous physical activity in mice submitted or not to caloric restriction during aging process, BP.DR

Abstract

Spontaneous physical activity (SPA) and its associated thermogenesis, non-exercise activity thermogenesis (NEAT) are important components of total daily energy expenditure and can protect against obesity. In the current PhD project, we used calorie restriction (30%) as an intervention to mitigate the age-associated decline in SPA and investigate the brain areas and the molecules involved, with special attention to orexin. Orexin, a hypothalamic neurotransmitter, is the major candidate in the positive modulation of SPA, thanks to the valuable work of Professor Kotz. Low levels of orexin are associated with obesity and reduced physical activity in humans and animals. Several studies from Dr. Kotz laboratory have demonstrated that enhancing orexin tone increases SPA in mice and rats, which was accompanied by increases in energy expenditure, indicating that orexin-based treatments could protect against development of obesity and its associated diseases. New Zealand Obese (NZO) mice are a well-established polygenic model of obesity. They are heavier than control mice at weaning age and develop severe obesity even when maintained on a standard diet. Based on the knowledge of orexin on SPA and energy expenditure, the aim of this project is to evaluate whether orexin function on SPA can be amplified using an orexin-agonist sufficiently to slow weight gain in the NZO animal model of obesity at different stages of life. Importantly, this agonist is exclusively developed and tested by Dr. Kotz and her collaborators. Age- and weight-matched male young (1 month) and aged (10-12 months) wild type and NZO mice will be used. Animals will be housed individually in the Promethion Indirect Calorimetry caging system for continuous and simultaneous measure of SPA, energy expenditure and food intake. They will be distributed in two groups: Control (n =8) and Treatment (n=8). All animals will receive a once-daily intraperitoneal injection of either saline (Control) or orexin agonist (RTIOXA-47; 40mg/kg, Treatment). Injections will be performed a minimum of 5 days per week for 4 weeks, just prior to onset of dark (active) period. Body composition (fat and lean mass) will be measured once every two weeks by EchoMRI. In addition, food intake and body weight will also be measured manually once every two days. At end of the study, half of the animals of all phenotypes will be euthanized. Blood samples will be collected via cardiac puncture and brains will be collected for protein and gene expression studies. Half the mice in each group (n = 4/group) will have brains sectioned and processed for orexin immunohistochemistry to determine extent of orexin neuron loss. For the remaining mice (n = 4/group), micropunches will be obtained from the rostral lateral hypothalamus (rLH), flash-frozen, and RNA will be extracted for analysis of gene expression via real-time qRT-PCR. The collected blood will be analysed for blood glucose and plasma insulin levels. Data will be initially evaluated for normality for determination of the most appropriate statistical analysis using SPSS software (IBM®). The significance will be set at p < 0.05. The central hypothesis is that peripheral orexin agonist administration will increase SPA levels and ameliorate obesity in the NZO mouse. (AU)