Expression and Subcellular Localization of Estrogen Receptors α and β in Human Fetal Brown Adipose Tissue

Context: Brown adipose tissue (BAT) has the unique ability of generating heat due to the expression of mitochondrial uncoupling protein 1 (UCP1). A recent discovery regarding functional BAT in adult humans has increased interest in the molecular pathways of BAT development and functionality. An important role for estrogen in white adipose tissue was shown, but the possible role of estrogen in human fetal BAT (fBAT) is unclear. Objective: The objective of this study was to determine whether human fBAT expresses estrogen receptor alpha (ER alpha) and ER beta. In addition, we examined their localization as well as their correlation with crucial proteins involved in BAT differentiation, proliferation, mitochondriogenesis and thermogenesis including peroxisome proliferator-activated receptor gamma (PPAR gamma), proliferating cell nuclear antigen (PCNA), PPAR gamma-coactivator-1 alpha (PGC-1 alpha), and UCP1. Design: The fBAT was obtained from 4 human male fetuses aged 15, 17, 20, and 23 weeks gestation. ER alpha and ER beta expression was assessed using Western blotting, immunohistochemistry, and immunocytochemistry. Possible correlations with PPAR gamma, PCNA, PGC-1 alpha, and UCP1 were examined by double immunofluorescence. Results: Both ER alpha and ER beta were expressed in human fBAT, with ER alpha being dominant. Unlike ER beta, which was present only in mature brown adipocytes, we detected ER alpha in mature adipocytes, preadipocytes, mesenchymal and endothelial cells. In addition, double immunofluorescence supported the notion that differentiation in fBAT probably involves ER alpha. Immunocytochemical analysis revealed mitochondrial localization of both receptors. Conclusion: The expression of both ER alpha and ER beta in human fBAT suggests a role for estrogen in its development, primarily via ER alpha. In addition, our results indicate that fBAT mitochondria could be targeted by estrogens and pointed out the possible role of both ERs in mitochondriogenesis.