Convertible adipose tissue in mice.

Area of Science:

• Adipose tissue biology
• Thermogenesis research
• Mitochondrial function

Background:

• White adipose tissue (WAT) and brown adipose tissue (BAT) have distinct roles in energy metabolism.
• The plasticity of adipose tissue in response to environmental stimuli is an area of active research.
• Uncoupling protein 1 (UCP1) is a key mediator of non-shivering thermogenesis in BAT.

Purpose of the Study:

• To investigate the potential for UCP expression and UCP-dependent thermogenesis in tissues typically classified as WAT.
• To characterize the morphological and molecular changes in inguinal WAT under cold stress.
• To determine the reversibility of cold-induced adaptations in adipose tissue.

Main Methods:

• Mice were subjected to cold acclimatization (4°C) and cold stress (-20°C).
• Analysis included slot-blot for UCP and lipoprotein lipase mRNA, immuno-electron microscopy for UCP localization, and morphological/morphometrical analysis.
• Cold-stressed mice were rewarmed (28°C) to assess the duration and reversibility of tissue conversion.

Main Results:

• Cold stress induced UCP mRNA and protein expression in inguinal WAT, with UCP localized to mitochondria, resembling BAT.
• Inguinal adipose tissue exhibited UCP-dependent thermogenesis and morphological characteristics of BAT.
• Upon rewarming, inguinal adipocytes downregulated UCP, mitochondria reverted to a non-uncoupled state, and the tissue regained WAT morphology.

Conclusions:

• Inguinal white adipose tissue can convert to a brown-like, UCP-expressing, thermogenic tissue under cold stress.
• This conversion is reversible, with the tissue reverting to a white adipose tissue phenotype upon rewarming.
• These findings identify a third type of adipose tissue in mice: convertible adipose tissue, highlighting adipose tissue plasticity.