Differential Roles of Each Orexin Receptor Signaling in Obesity

Area of Science:

• Neuroscience
• Metabolic Research
• Endocrinology

Background:

• Orexins are hypothalamic neuropeptides crucial for regulating feeding, energy expenditure, and sleep.
• While orexin deficiency causes obesity, the specific roles of orexin receptors (Ox1r, Ox2r) in long-term energy metabolism remain unclear.

Purpose of the Study:

• To metabolically characterize mice deficient in orexin receptor 1 (Ox1r) and orexin receptor 2 (Ox2r).
• To elucidate the distinct functions of Ox1r and Ox2r signaling in energy balance and body weight regulation.

Main Methods:

• Metabolic characterization of Ox1r-deficient and Ox2r-deficient mice.
• Assessment of diet-induced obesity, food intake, and energy expenditure on chow and high-fat diets.
• Evaluation of the interactive effects of diet and exercise (running wheel) on body weight.

Main Results:

• Ox1r-deficient mice were resistant to diet-induced obesity with similar food intake on chow and high-fat diets.
• Ox2r-deficient mice showed reduced energy expenditure on a high-fat diet.
• Neither Ox1r- nor Ox2r-deficient mice exhibited body weight gain comparable to orexin-deficient mice.
• The obesity-suppressing effect of exercise was diminished in orexin neuron-ablated mice.
• No abnormalities were found in the brown adipose tissue of orexin-deficient mice.

Conclusions:

• Each orexin receptor subtype (Ox1r and Ox2r) possesses a unique role in modulating energy metabolism.
• Orexin neurons are integral to the interplay between diet and physical activity in controlling body weight gain.