Loss of the melanocortin-4 receptor in mice causes dilated cardiomyopathy

Area of Science:

• Cardiovascular Science
• Metabolic Disorders
• Genetics

Background:

• Melanocortin-4 receptor (MC4R) deficiency is the most common cause of monogenic obesity.
• MC4R deficiency is linked to reduced autonomic tone and bradycardia, suggesting potential cardiovascular protection.
• The cardiovascular implications of MC4R deficiency, particularly concerning heart function, remain incompletely understood.

Purpose of the Study:

• To investigate the direct impact of melanocortin-4 receptor absence on cardiac function.
• To determine if MC4R deficiency causes cardiomyopathy independently of obesity.
• To elucidate the molecular mechanisms underlying MC4R deficiency-induced cardiac dysfunction.

Main Methods:

• Generation and analysis of melanocortin-4 receptor knockout (MC4R-/-) mice.
• Assessment of cardiac structure and function using echocardiography and histological analysis.
• Evaluation of mitochondrial morphology, cardiomyocyte organization, and myocardial bioenergetics.

Main Results:

• MC4R absence in mice leads to dilated cardiomyopathy with reduced contractility and increased left ventricular diameter.
• The observed cardiomyopathy is independent of obesity, as diet-induced obese mice lacking MC4R do not exhibit systolic dysfunction.
• Ultrastructural analysis reveals mitochondrial abnormalities and cardiomyocyte disorganization in MC4R-/- hearts.
• Myocardial tissue from MC4R-/- mice shows increased ADP-stimulated respiratory capacity, coupled with elevated reactive oxygen species production.

Conclusions:

• Melanocortin-4 receptor deletion is identified as a novel cause of dilated cardiomyopathy and heart failure.
• Cardiac dysfunction in MC4R deficiency is not solely attributable to obesity but involves direct effects on myocardial tissue.
• Increased mitochondrial respiration and reactive oxygen species production are key features of MC4R deficiency-induced heart failure, highlighting a new clinical concern.