Endocrine Abstracts

The adipose tissue is an endocrine organ distributed over multiple depots and broadly categorised into two main subtypes: white adipose tissue which stores energy as lipids and brown adipose tissue which dissipates energy in the form of heat. Adipocytes from the white depots are able to switch from a white to a brown-like phenotype, a process called beiging. This phenomenon is stimulated by cold exposure or sympathetic nervous system activation and is associated with improved metabolic health. Weaning, defined as the switch from milk to solid diet is a crucial developmental period. In mice, pups start feeding on pellets as soon as 15 days of age and stop breastfeeding around 28 days of age. Dietary alterations or overfeeding of lactating mother have long-term effects on the metabolism of offspring in both rodents and humans. To understand how weaning affects the adipose tissue in mice, we have analysed the kinetics of adipose tissue remodelling between 21 days of age (P21) and 35 days of age (P35). We have harvested the visceral perigonadal white adipose tissue (gWAT), the subcutaneous inguinal white adipose tissue (iWAT) and the interscapular brown adipose tissue (BAT) at P21, P28 and P35. Between P21 and P35, mice are accumulating WAT while BAT mass remains constant. This process is accompanied by a decrease in the proportion of beige adipocytes, and a reduced innervation and vascularisation density. We next used a model a weaning retardation whereby after 21 days of lactation (P21), four pups from the litter are kept with the dam until P28 (delayed weaning, DW) while the rest of the pups are separated (standard weaning, SW). At P28, DW mice show a decreased body mass but with a higher proportion of fat mass compared to SW controls. Indeed, iWAT mass is increased in the DW condition. Interestingly, at P56, SW mice have higher body mass and adiposity. Finally, delayed weaning induces an increase in the cutaneous temperature of male offspring only, reaching a temperature close to that of females. These results highlight the importance of the weaning period for the development of adipose tissue. Sexually dimorphic phenotypes and the uncorrelated increase in body and fat masses upon delayed weaning suggest an involvement of sexual hormones that will be further investigated.