Rosiglitazone up-regulates lipoprotein lipase, hormone-sensitive lipase and uncoupling protein-1, and down-regulates insulin-induced fatty acid synthase gene expression in brown adipocytes of Wistar rats.
OBJECTIVE
Although thiazolidinediones are now widely used to treat type 2 diabetes, their mechanism of action remains largely unknown. They are agonists for the transcription factor PPARgamma, and in addition to their insulin-sensitising effects, they can promote adipogenesis and control gene expression in adipose tissues. We have explored the effect of rosiglitazone on insulin-mediated induction of pivotal genes involved in lipid metabolism and thermogenesis in brown fat. The genes studied were: (1) lipoprotein lipase (lpl), which is involved in lipid uptake; (2) hormone-sensitive lipase (hsl), which mobilises fatty acids from stored triglycerides; (3) fatty acid synthase (fas), which regulates de novo lipogenesis; and (4) the uncoupling proteins (ucp) 1 and 3, which control thermogenesis.


METHODS
We used fetal rat primary brown adipocytes cultured with insulin, rosiglitazone or both combined. Then, we studied gene expression by northern and western blotting, as well as 'run-on' and gel-shift assays to identify binding of potential transcription factors to the fas promoter.


RESULTS
Exposure to rosiglitazone for 24 h induced ucp-1, lpl and hsl gene expression and when rosiglitazone was combined with insulin a synergistic effect on lpl and ucp-3 mRNA expression was produced. These effects were consistent with increased LPL and HSL activities as well as respiration rates, mainly in response to exogenous palmitate. In contrast, treatment with rosiglitazone did not alter FAS mRNA basal levels but prevented the induction elicited by insulin in a time- and dose-dependent manner. Correspondingly diminished FAS protein levels and activity, as well as cellular lipid content, were observed, indicating an antilipogenic action of rosiglitazone in brown adipocytes. Furthermore, rosiglitazone impaired insulin increase in the FAS transcription rate by antagonising insulin-induced binding of upstream stimulatory factors to the E-box consensus sequence in the FAS promoter and insulin-induced binding of activating protein-1.


CONCLUSIONS
Rosiglitazone prevents insulin-induced up-regulation of the main lipogenic enzyme but increases the expression of those enzymes involved in lipid uptake and mobilisation, favouring fatty acid utilisation through uncoupled respiration.
Teruel
T
T
Department of Biochemistry and Molecular Biology II, Faculty of Pharmacy, Complutense University, 28040, Madrid, Spain.
Hernandez
R
R
Rial
E
E
Martin-Hidalgo
A
A
Lorenzo
M
M
D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D002001:Adipose Tissue, Brown / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D000818:Animals; D001833:Body Temperature Regulation; D002352:Carrier Proteins / Q000235:genetics*; D018929:Cell Culture Techniques; D064429:Fatty Acid Synthases / Q000235:genetics*; D005786:Gene Expression Regulation; D015971:Gene Expression Regulation, Enzymologic; D007328:Insulin / Q000494:pharmacology*; D007473:Ion Channels; D008071:Lipoprotein Lipase / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D024101:Mitochondrial Proteins; D051381:Rats; D017208:Rats, Wistar; D000077154:Rosiglitazone; D002787:Sterol Esterase / Q000235:genetics*; D045162:Thiazolidinediones / Q000494:pharmacology*; D000071256:Uncoupling Protein 1
D002352:Carrier Proteins; D007328:Insulin; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D045162:Thiazolidinediones; C000604373:Ucp1 protein, rat; D000071256:Uncoupling Protein 1; D000077154:Rosiglitazone; D064429:Fatty Acid Synthases; D002787:Sterol Esterase; D008071:Lipoprotein Lipase