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The melanocortin receptors: lessons from knockout models

A A Butler1, R D Cone

  • 1Neuropeptides Laboratory, Pennington Biomedical Research Center, Lousiana State university, Baton Rouge, LA70808, USA. butleraa@pbrc.edu

Neuropeptides
|October 3, 2002
PubMed

Insights

The melanocortin system regulates energy homeostasis. Melanocortin-4 receptor (MC4R) loss causes obesity, hyperphagia, and diabetes, unlike MC3R deficiency.

Area of Science:

  • Neuroendocrinology
  • Metabolic Regulation
  • Obesity Research

Background:

  • The melanocortin system plays a crucial role in regulating energy balance.
  • Genetic and pharmacological studies have implicated melanocortin receptors in appetite and metabolism.
  • The agouti gene product's antagonism of melanocortin-1 receptor (MC1R) is linked to coat color and potentially energy homeostasis.

Purpose of the Study:

  • To elucidate the distinct roles of melanocortin-3 receptor (MC3R) and melanocortin-4 receptor (MC4R) in energy homeostasis.
  • To compare the physiological consequences of MC3R and MC4R deficiency in knockout mouse models.
  • To investigate the mechanisms underlying obesity in melanocortin receptor knockout mice.

Main Methods:

  • Analysis of pro-opiomelanocortin (POMC), MC3R, and MC4R knockout mouse models.
  • Phenotypic characterization of knockout mice, including body weight, food intake, energy expenditure, and metabolic parameters.
  • Pharmacological studies investigating agouti's antagonism of MC4R.

Main Results:

  • MC4R knockout (KO) mice exhibit hyperphagia, impaired diet-induced thermogenesis, reduced physical activity, and develop type 2 diabetes.
  • MC3R KO mice are not hyperphagic, maintain normal metabolic responses to energy consumption, and do not develop diabetes.
  • MC4R antagonism by agouti recapitulates aspects of the lethal yellow mouse phenotype, highlighting MC4R's critical role in energy balance.

Conclusions:

  • MC4R is essential for regulating appetite, energy expenditure, and preventing obesity and associated metabolic disorders like type 2 diabetes.
  • MC3R's role in energy homeostasis appears distinct from MC4R, with its deficiency leading to increased adiposity through unclear mechanisms potentially involving nutrient partitioning or physical activity.
  • Targeting the melanocortin system, particularly MC4R, holds therapeutic potential for obesity and related metabolic diseases.

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