Unexpected deposition of brown fat in mammary gland during postnatal development.

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

• Level A · Stronger Clinical Evidence
• Level B · Emerging clinical evidence with positive signals
• Level C · Early human research exploring benefits
• Level D · Scientific groundwork from lab and animal studies
• Emerging · Emerging topic under active research

Abstract (original English)

Mammary fat tissue is crucial for mammary ductal morphogenesis in both fetal and adult mice. There are two kinds of adipocytes, the energy-storing white and the energy-dissipating brown adipocyte. The precise identity of the types of adipocyte in the mammary gland has never been investigated but was always assumed to be only white fat. In this study, we show that both white and brown adipocytes are present in the postnatal mammary gland. The amount of brown adipose tissue (BAT) examined by histology and electron microscopy correlates with the transcript levels of uncoupling protein 1, which is a mitochondrial carrier expressed exclusively in BAT. Uncoupling protein 1 mRNAs are the highest during prepuberty, decrease upon puberty, and are finally undetectable in the adult mammary gland. The analysis of a BAT-depleted mouse model showed that depletion of mammary BAT in early postnatal development induces epithelial differentiation. Alveolar structures were formed along all ducts and were functional since they produced beta-casein. However, mammary transplantation experiments indicated that a systemic effect was responsible for epithelium differentiation. Our data suggest that BAT negatively regulates the differentiation of mammary epithelial cells in a systemic manner during prepubertal ductal outgrowth.

Evidence level

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

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