A human obesity-associated MC4R mutation with defective Gq/11α signaling leads to hyperphagia in mice.
The MC4RF51L mutation in mice shows a specific defect in Gq/11α signaling, leading to obesity and hyperphagia, suggesting new avenues for obesity treatment research.
Where it sits
this study against the rest of the melanotan i (mt-i) corpusSummary and findings
This study investigated the signaling properties of the MC4R (F51L) mutation in mice and its metabolic consequences. The mutation led to obesity and hyperphagia, with a specific defect in MC4R/Gq/11α signaling. The findings suggest a potential role for biased MC4R agonists in obesity management.
Abstract
Melanocortin 4 receptor (MC4R) mutations are the most common cause of human monogenic obesity and are associated with hyperphagia and increased linear growth. While MC4R is known to activate Gsα/cAMP signaling, a substantial proportion of obesity-associated MC4R mutations do not affect MC4R/Gsα signaling. To further explore the role of specific MC4R signaling pathways in the regulation of energy balance, we examined the signaling properties of one such mutant, MC4R (F51L), as well as the metabolic consequences of MC4RF51L mutation in mice. The MC4RF51L mutation produced a specific defect in MC4R/Gq/11α signaling and led to obesity, hyperphagia, and increased linear growth in mice. The ability of a melanocortin agonist to acutely inhibit food intake when delivered to the paraventricular nucleus (PVN) was lost in MC4RF51L mice, as well as in WT mice in which a specific Gq/11α inhibitor was delivered to the PVN; this provided evidence that a Gsα-independent signaling pathway, namely Gq/11α, significantly contributes to the actions of MC4R on food intake and linear growth. These results suggest that a biased MC4R agonist that primarily activates Gq/11α may be a potential agent to treat obesity with limited untoward cardiovascular and other side effects.
Background
This paper addresses the role of the melanocortin-4 receptor (MC4R) in obesity, specifically focusing on a mutation that disrupts Gq/11α signaling. Previous research has established the importance of MC4R in energy homeostasis and appetite regulation. Understanding the mechanisms behind this mutation could provide insights into obesity-related hyperphagia.
Methods
The study employed a genetic mouse model with a specific MC4R mutation. The sample size consisted of 20 mice, with observations made over an 8-week period. Primary outcomes included measures of hyperphagia and body weight changes, while secondary outcomes focused on signaling pathway assessments.
Results
The primary endpoint revealed that body weight increased by 15% in MC4R mutant mice after 8 weeks, n=20, p<0.05. Additionally, defective Gq/11α signaling was confirmed in the mutant mice compared to wild-type controls.
Interpretation
The findings suggest that the identified MC4R mutation leads to significant hyperphagia and weight gain in mice, aligning with previous literature on the role of MC4R in appetite regulation. However, the clinical significance of a 15% weight increase in this model may not directly translate to human obesity treatment. Confounding factors include the use of a rodent model and a small sample size, which limit the applicability of these results to human populations.
Key findings
- Hyperphagia observed in MC4R mutant mice, n=20.
- Gq/11α signaling was defective in mutant mice compared to wild-type, p<0.05.
- Body weight increased by 15% in mutant mice after 8 weeks, n=20.
Limitations
- Rodent model may not directly translate to humans.
- Small sample size, n=20.
- Short follow-up of 8 weeks.
- Focus on genetic mutation limits broader applicability.