Modelling of the MCH system involved in Obesity: novel approaches in Comparative Biology – ObEdit

The melanin-concentrating hormone (MCH) is a major hypothalamic peptide involved in energy homeostasis. MCH binds to its two receptors MCHR1 and MCHR2, which are expressed in the human brain. Strikingly, MCHR2 is absent in rodent genomes (rat, mouse). While mouse strains over-expressing or deleted for the MCHR1 gene exhibit alterations in feeding behavior and body weight, extrapolating on a similar role of MCH in humans is purely speculative. To address this issue, we will use two animal models: the minipig, an omnivorous animal model expressing MCHR2, as well as our unique model of humanized mice expressing the human MCHR2 transgene. Based on a collaboration between the teams of Dr. JL Nahon (Coordinator/Partner 1; IPMC, Valbonne , France), Prof. V. Michelet (Partner 2; ICN, CNRS/UCA, Nice, France) and Prof. R Barrès (Partner 3; CBMR, Univ. Copenhagen, Denmark), we have planned experimental Work-Packages (WP) in addition to the Leadership task (WP1) as follows:
WP2: Mapping MCH/MCHR1/2 brain expression in pigs and humanized mice (Partners 1 and 3). In-situ hybridization/RNAscope identification of hMCHR2 mRNA in both animal models (and both sexes) will inform about the cellular distribution of MCHR2 transcripts and will be compared to that of MCHR1. Based on this cellular mapping, we will perform single cell transcriptomics to determine the magnitude of MCH/MCHR1/2 expression in the various brain cell types from pigs and humanized mice. Single nuclei will be extracted, FACS-sorted and used for RNA-sequencing using Nextera XT (at the Single Cell Sequencing Platform/CBMR). We will use a hierarchical annotation strategy and we will study the association between high level of MCH/MCHR1/2 expression and distinct transcriptomic patterns using pathway and gene ontologies analyses.
WP3: To determine the contribution of hMCHR2 on feeding behaviour, glucose homeostasis and energy balance in humanized mice (Partner 1). We will investigate which components of feeding behaviour and energy expenditure are modified following feeding of high-fat diets (HFD) containing various omega 3 to omega 6 ratios. We will assess the impact of MCHR2 expression on the development of fat mass and insulin resistance at homeostatic (fat storage and partitioning) and non-homeostatic (motivation, rewarding) levels of energy balance regulation. The animals (groups of 15 mice of both sexes) will be housed under controlled laboratory conditions with a 12-h light/dark cycle and a temperature of 28 ±2°C (thermoneutrality). All experiments will be conducted in the ANIMEX-IPMC animal facility. Standard protocols will be used to monitor blood glucose and insulin responses.
WP4: Study of MCHR2 role on food behaviour and energy balance using a pharmacological approach (Partners 1, 2, 3). We are currently synthetising selective MCHR2 antagonists based on an Amgen component. Moreover, new synthetic methodologies will be developed to generate libraries of chiral building blocks as key analogs, to discover novel and active hits. Then, we will determine progressive changes in glycemia, feeding behavior and other goal-oriented behaviors (motor behavior, stress response) in placebo and MCHR2 antagonist-treated minipigs and humanized mice. First, several doses of each antagonist and derivatives will be first tested in MCHR2 humanized mice of both sexes. Full phenotyping characterization will then be carried out using a selected dose. Second, three months-old minipigs will receive a placebo or a selected synthetic compound and will be subjected to a chow diet and then HFD. These experiments will be performed in private, state-of-the art animal facility located in BIONEA (Sophia Antipolis, France).
Through the identification of key brain pathways by which MCH controls energy metabolism, the results arising from our study are ideally placed to provide breakthroughs at the fundamental and pre-clinical level.