1. Docosahexaenoic acid inhibits proteolytic processing of sterol regulatory element-binding protein-1c (SREBP-1c) via activation of AMP-activated kinase.
- Author
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Deng X, Dong Q, Bridges D, Raghow R, Park EA, and Elam MB
- Subjects
- AMP-Activated Protein Kinases genetics, Animals, Cell Line, Tumor, Hyperlipidemias drug therapy, Hyperlipidemias genetics, Hyperlipidemias pathology, Insulin genetics, Insulin metabolism, Liver pathology, Mechanistic Target of Rapamycin Complex 1, Multiprotein Complexes genetics, Multiprotein Complexes metabolism, Obesity diet therapy, Obesity genetics, Obesity pathology, Phosphorylation drug effects, Phosphorylation genetics, Rats, Sterol Regulatory Element Binding Protein 1 genetics, TOR Serine-Threonine Kinases genetics, TOR Serine-Threonine Kinases metabolism, AMP-Activated Protein Kinases metabolism, Docosahexaenoic Acids pharmacology, Hyperlipidemias metabolism, Liver metabolism, Obesity metabolism, Proteolysis drug effects, Sterol Regulatory Element Binding Protein 1 metabolism
- Abstract
In hyperinsulinemic states including obesity and T2DM, overproduction of fatty acid and triglyceride contributes to steatosis of the liver, hyperlipidemia and hepatic insulin resistance. This effect is mediated in part by the transcriptional regulator sterol responsive element binding protein-1c (SREBP-1c), which stimulates the expression of genes involved in hepatic fatty acid and triglyceride synthesis. SREBP-1c is up regulated by insulin both via increased transcription of nascent full-length SREBP-1c and by enhanced proteolytic processing of the endoplasmic reticulum (ER)-bound precursor to yield the transcriptionally active n-terminal form, nSREBP-1c. Polyunsaturated fatty acids of marine origin (n-3 PUFA) prevent induction of SREBP-1c by insulin thereby reducing plasma and hepatic triglycerides. Despite widespread use of n-3 PUFA supplements to reduce triglycerides in clinical practice, the exact mechanisms underlying their hypotriglyceridemic effect remain elusive. Here we demonstrate that the n-3 PUFA docosahexaenoic acid (DHA; 22:5 n-3) reduces nSREBP-1c by inhibiting regulated intramembrane proteolysis (RIP) of the nascent SREBP-1c. We further show that this effect of DHA is mediated both via activation of AMP-activated protein kinase (AMPK) and by inhibition of mechanistic target of rapamycin complex 1 (mTORC1). The inhibitory effect of AMPK on SREBP-1c processing is linked to phosphorylation of serine 365 of SREBP-1c in the rat. We have defined a novel regulatory mechanism by which n-3 PUFA inhibit induction of SREBP-1c by insulin. These findings identify AMPK as an important negative regulator of hepatic lipid synthesis and as a potential therapeutic target for hyperlipidemia in obesity and T2DM., (Published by Elsevier B.V.)
- Published
- 2015
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