Mouse models for V103I and I251L gain of function variants of the human MC4R display decreased adiposity but are not protected against a hypercaloric diet

Abstract

Objective The melanocortin 4 receptor (MC4R) is a G protein-coupled receptor that plays major roles in the central control of energy balance. Loss-of-function mutations of MC4R constitute the most common monogenic cause of early-onset extreme obesity in humans, whereas gain-of-function mutations appear to be protective. In particular, two relatively frequent alleles carrying the non-synonymous coding mutations V103I or I251L are associated with lower risks of obesity and type-2 diabetes. Although V103I and I251L MC4Rs showed more efficient signalling in transfected cells, their specific effects in live animals remain unexplored. Here, we investigated whether the introduction of V103I and I251L mutations into the mouse MC4R leads to a lean phenotype and provides protection against an obesogenic diet. Methods Using CRISPR/Cas9, we generated two novel strains of mice carrying single-nucleotide mutations into the mouse Mc4r which are identical to those present in V103I and I251L MCR4 human alleles, and studied their phenotypic outcomes in mice fed with normal chow or a high-fat diet. In particular, we measured body weight progression, food intake and adiposity. In addition, we analysed glucose homeostasis through glucose and insulin tolerance tests. Results We found that homozygous V103I females displayed shorter longitudinal length and decreased abdominal white fat, whereas homozygous I251L females were also shorter and leaner due to decreased weight in all white fat pads examined. Homozygous Mc4r V103I/V103I and Mc4r I251L/I251L mice of both sexes showed improved glucose homeostasis when challenged in a glucose tolerance test, whereas Mc4r I251L/I251L females showed improved responses to insulin. Despite being leaner and metabolically more efficient, V103I and I251L mutants fed with a hypercaloric diet increased their fasting glucose levels and adiposity similar to their wild-type littermates. Conclusions Our results demonstrate that mice carrying V103I and I251L MC4R mutations displayed gain-of-function phenotypes that were more evident in females. However, hypermorphic MC4R mutants were as susceptible as their control littermates to the obesogenic and diabetogenic effects elicited by a long-term hypercaloric diet, highlighting the importance of healthy feeding habits even under favourable genetic conditions.

An Association between Diet and MC4R Genetic Polymorphism, in Relation to Obesity and Metabolic Parameters—A Cross Sectional Population-Based Study

“…Our study indicates that recommendations to decrease dietary fat < 30% are appropriate for carriers of protective MC4R genotypes. It has been found recently also by Rojo D. et al [ 39 ] that the protective mutations of MC4R do not protect against diabetogenic and adipogenic effects of a high-fat diet in animal model, which highlights the importance of the proper feeding habits even under favorable genetic conditions. On the other hand, intriguingly, our results suggest that in the carriers of MC4R risk genotypes, a dietary total fat intake might not affect metabolic parameters.…”

Guidelines on models of diabetic heart disease

“…One example is the generation of mouse models for mutations in the melanocortin 4 receptor, a G protein-coupled receptor. Specifically, the recent development of melanocortin 4 receptor hypermorphic mice revealed obesogenic and diabetogenic effects but did not characterize heart function ( 187 ).…”

Constitutive activity of the dopamine (D5) receptor, highly expressed in CA1 hippocampal neurons, selectively reduces CaV3.2 and CaV3.3 currents

“…A simple in vitro strategy is the use of increasing concentrations of the GPCR‐containing plasmid in the transfection mix, because it is expected that the levels of constitutive activity positively correlate with the amount GPCR expressed (Agosti et al, 2017; Cordisco Gonzalez et al, 2020; López Soto et al, 2015; Martinez Damonte et al, 2018; McCarthy et al, 2020; Tiberi & Caron, 1994). Moreover, GPCR‐mutants lacking basal activity that preserve the ability to respond their ligands are valuable tools to isolate the effects of constitutive activity from those of ligand‐evoked (Al‐Fulaij et al, 2008; Pantel et al, 2006; Rojo et al, 2020; Torz et al, 2020). Finally, the binding of inverse agonists reduces the constitutively active levels of a GPCR (Costa & Cotecchia, 2005).…”