Beta3-adrenergic receptors stimulate glucose uptake in brown adipocytes by two mechanisms independently of glucose transporter 4 translocation.
To identify the mechanisms whereby norepinephrine induces glucose uptake in brown adipose tissue, we used mouse brown adipocytes in culture. Proliferating brown adipocytes had high levels of glucose transporter (GLUT) 1 mRNA and low levels of GLUT4 mRNA. The ratio of GLUT4/GLUT1 mRNA expression increased during differentiation, and mature brown adipocytes had high levels of GLUT4 mRNA. The endogenous adrenergic neurotransmitter norepinephrine induced a potent increase in GLUT1 mRNA and a decrease of GLUT4 mRNA in mature brown adipocytes. The norepinephrine effect was mimicked by isoprenaline and CL 316243 and was thus mediated by beta3-adrenergic receptors. The cAMP analog 8-bromoadenosine-cAMP partly mimicked the response on GLUT1 mRNA increase and fully mimicked the GLUT4 mRNA decrease. We found no involvement of alpha1 or alpha2-adrenergic receptors on GLUT1 or GLUT4 mRNA transcription. Norepinephrine treatment led to a large increase of GLUT1 protein amount in brown adipocytes as visualized with immunocytochemical staining and subcellular fractionation. A large part of the newly synthesized GLUT1 was found in the plasma membrane (PM). The potent transcriptional inhibitor actinomycin D fully abolished this increase of GLUT1 protein at all time points examined. Norepinephrine treatment shifted GLUT4 from the PM to an intracellular vesicular compartment. Norepinephrine increased 2-deoxy-D-glucose uptake 2-fold at an early time point (1 h) and 4-fold at later time point (5 h). Addition of actinomycin D did not block the early phase but blocked a large part of the later phase of 2-deoxy-D-glucose uptake. These results imply that adrenergic stimulation through beta3-adrenergic receptors induces glucose uptake in brown adipocytes via two mechanisms: 1) a mechanism not dependent on GLUT1 and GLUT4 translocation, 2) a mechanism that is dependent on de novo synthesis of GLUT1 protein and increase of GLUT1 protein at the PM.
Dallner
O S
OS
The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, SE-106 91 Stockholm, Sweden.
Chernogubova
E
E
Brolinson
K A
KA
Bengtsson
T
T
D052437:Adipocytes, Brown / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003609:Dactinomycin / Q000494:pharmacology; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1 / Q000378:metabolism; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D051379:Mice; D009638:Norepinephrine / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D022702:Receptors, Adrenergic, beta-3 / Q000502:physiology*; D014018:Tissue Distribution / Q000187:drug effects
D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D022702:Receptors, Adrenergic, beta-3; C495678:Slc2a1 protein, mouse; D003609:Dactinomycin; D005947:Glucose; D009638:Norepinephrine