Immortal brown adipocytes from p53-knockout mice: Differentiation and expression of uncoupling proteins

Brown adipose tissue (BAT) is the specific site for metabolic heat producti on in mammals. To establish a novel immortal brown adipocyte cell line, the stromal-vascular fraction containing preadipocytes was obtained from inter scapular BAT of mice deficient of a tumor-suppressor gene p53. The p53-defi cient cells, tentatively named as HB2 cells, could be cultured in vitro aft er repeated passages and differentiated into adipocytes in the presence of insulin, T-3 and/or troglitazone, expressing some adipocyte-specific genes and accumulating intracellular lipid droplets. The mRNA level of uncoupling protein 1 (UCP1), a mitochondrial protein specifically present in brown ad ipocytes, was undetectable in HB2 preadipocytes, but increased after adipos e differentiation. In HB2 adipocytes, UCP1 mRNA expression was markedly act ivated after stimulation of the beta-adrenergic receptor pathway. The mRNA of UCP2 and UCP3, recently cloned isoforms of UCP1, were also detected in H B2 adipocytes, but their levels were not influenced by adrenergic stimulati on. Thus HB2 cells seem useful for in vitro studies of BAT and UCP function s. (C) 1999 Academic Press.