Endocrine Abstracts

WAT and BAT are two different tissues devoted to store energy in the form of triglycerides. WAT provides the organism with fuel during intervals between meals. BAT oxidizes fatty acids to produce heat. BAT is activated by cold exposure, but it is also activated by food intake suggesting its involvement in anti-obesity mechanisms. The two tissues are contained into the adipose organ. This new concept implies that, in mammals, each fat depot contains both tissues. The relative percentage of WAT and BAT in the adipose organ can varies accordingly to environmental changes. Of note, the brown phenotype of the adipose organ is associated with resistance to diet-induced obesity in small mammals.

The main innovative part of the adipose organ concept is the possibility for the two different type of adipocytes to undergo reversible processes of transdifferentiation (a fully-differentiated cell type changes its phenotype into another fully-differentiated cell type). Several data from our lab suggest that part of the adipose organ plasticity is due to reversible transdifferentiation between white and brown adipocytes. These transdifferentiation phenomena in the adipose organ are not exclusive of these two cell types.

In fact, we recently observed that the white adipocytes of the mammary glands of mice, marked by specific expression of βGal (aP2/Cre-ROSA26R mice), during pregnancy are able to transform into milk secreting glandular epithelial cells and in the post-lactating period some glandular epithelial cells, marked by specific βGal expression (WAP/Cre-ROSA26R mice), escape from the process of apoptosis and transdifferentiate into white adipocytes.