Temperature-sensitive phenotype in mice lacking pituitary adenylate cyclase-activating polypeptide

Area of Science:

• Endocrinology
• Neurobiology
• Metabolic Research

Background:

• Pituitary adenylate cyclase-activating polypeptide (PACAP) is a conserved hormone involved in metabolism and stress response.
• PACAP's role in thermoregulation, particularly in neonates and rodents, remains unclear.
• PACAP null mice exhibit temperature sensitivity, impacting survival rates at lower ambient temperatures.

Purpose of the Study:

• To investigate the mechanism by which PACAP absence affects thermoregulation.
• To determine the impact of PACAP deficiency on brown adipose tissue function and catecholamine levels.
• To elucidate the role of PACAP in adaptive thermogenesis under cold stress.

Main Methods:

• Comparison of survival rates of PACAP null mice and wild-type controls at different ambient temperatures (21°C vs. 24°C).
• Analysis of brown adipocyte differentiation and expression of thermogenic enzymes (hormone-sensitive lipase, uncoupling protein 1).
• Measurement of catecholamine (norepinephrine, dopamine) levels in adrenal medulla, plasma, and brown adipose tissue.

Main Results:

• PACAP null mice showed significantly lower survival rates at 21°C compared to 24°C.
• Brown adipocytes in PACAP null mice differentiated normally and expressed key thermogenic enzymes.
• Norepinephrine and dopamine levels were significantly reduced in the brown adipose tissue of PACAP null mice.
• PACAP null mice exhibited greater core body temperature loss at 21°C.

Conclusions:

• PACAP is crucial for maintaining adequate heat production under mild cold stress.
• The absence of PACAP leads to insufficient norepinephrine stimulation of brown adipose tissue, impairing thermogenesis.
• PACAP deficiency compromises the sympathetic response necessary for adaptive thermogenesis in rodents.