A preadipocyte clonal line from mouse brown adipose tissue: Short- and long-term responses to insulin and β-adrenergics

Abstract

A clonal cell line has been established from the interscapular brown adipose tissue (BAT) of the C 57 BL/6J +/+ mouse. The line, designated BFC-1, is aneuploid and exhibits both morphological and biochemical properties characteristic of mature adipocytes. Adipose conversion begins after confluence and is accompanied by ( a) an early emergence of lipoprotein lipase; ( b) a later emergence of glycerol-3-phosphate dehydrogenase and acid: CoA ligase; ( c) an increase in the average triglyceride content. Adipose conversion, estimated by activities of enzyme markers, is enhanced at any given time by the continuous presence in the culture medium of insulin and triiodothyronine, both within their physiological range of concentrations. In addition to both hormones, chronic exposure of confluent cells to β-adrenergics brings similar long-term effects on adipose conversion. The uptake of labelled 2-deoxyglucose by differentiated BFC-1 cells is stimulated by insulin; the half-maximum effect is observed at 1 nM insulin. Differentiated BFC-1 cells, in which endogenous triglycerides have been prelabelled on the fatty acid moiety, do respond to β-adrenergics by releasing radioactive fatty acids. The agonist potency order and the EC 50 value for each agonist are BRL 37344 (0.5 nM) > isoproterenol (1.5 nM) > norepinephrine (3 nM) > epinephrine (7 nM) > salbutamol (15 nM). The half-maximally and maximally effective concentrations of corticotropin to stimulate lipolysis are found to be 4 and 100 nM, respectively. The lipolytic response to isoproterenol is counteracted by prior addition of insulin or simultaneous addition of propranolol. Parallel studies performed on Ob17 cells, a clonal line established from mouse white adipose tissue (Négrel et al., Proc natl acad sci US 75 (1978) 6054) [22], show that the agonist potency order and the EC 50 value for each agonist are BRL 37344 (3 nM) > isoproterenol (10 nM) > norepinephrine (20 nM) > epinephrine (40 nM). Thus both BFC-1 cells and Ob17 cells show an atypical β-adrenoreceptor similar to that described in rat adipocytes (Arch et al., Nature 309 (1984) 163) [54], but tne sensitivity of BFC-1 cells toward β-agonists is found to be 6-fold higher than that of Ob17 cells. Thus the BFC-1 line represents a useful model for the study of short- and long-term responses to β-adrenergics.