title: Activation of liver X receptor regulates substrate oxidation in white adipocytes.
abstract: Liver X receptors (LXRs) are nuclear receptors with established roles in cholesterol, lipid, and carbohydrate metabolism, although their function in adipocytes is not well characterized. Increased adipose tissue mass in obesity is associated with increased adipocyte lipolysis. Fatty acids (FA) generated by lipolysis can be oxidized by mitochondrial beta-oxidation, reesterified, or released from the adipocyte. The latter results in higher circulating levels of free FAs, in turn causing obesity-related metabolic complications. However, mitochondrial beta-oxidation can at least in part counteract an increased output of FA into circulation. In this study, we provide evidence that activation of LXRs up-regulates mitochondrial beta-oxidation in both human and murine white adipocytes. We also show that the expression of a kinase regulating the cellular fuel switch, pyruvate dehydrogenase kinase 4 (PDK4), is up-regulated by the LXR agonist GW3965 in both in vitro differentiated human primary adipocytes and differentiated murine 3T3-L1 cells. Moreover, activation of LXR causes PDK4-dependent phosphorylation of the pyruvate dehydrogenase complex, thereby decreasing its activity and attenuating glucose oxidation. The specificity of the GW3965 effect on oxidation was confirmed by RNA interference targeting LXRs. We propose that LXR has an important role in the regulation of substrate oxidation and the switch between lipids and carbohydrates as cellular fuel in both human and murine white adipocytes.
authors: Department of Medicine, Karolinska Institutet, Lipid Laboratory, Neuroventenskap, Novum, Huddinge, SE-141 86 Stockholm, Sweden. britta.stenson@ki.se
authors: Britta M
authors: BM
authors: Stenson
authors: Mikael
authors: M
authors: Rydén
authors: Knut R
authors: KR
authors: Steffensen
authors: Kerstin
authors: K
authors: Wåhlén
authors: Amanda T
authors: AT
authors: Pettersson
authors: Johan W
authors: JW
authors: Jocken
authors: Peter
authors: P
authors: Arner
authors: Jurga
authors: J
authors: Laurencikiene
mesh_terms: D041721:3T3-L1 Cells; D052438:Adipocytes, White / Q000378:metabolism*; D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D001596:Benzylamines / Q000494:pharmacology; D002454:Cell Differentiation; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D000071518:Liver X Receptors; D051379:Mice; D057093:Orphan Nuclear Receptors; D010084:Oxidation-Reduction; D019308:Palmitic Acid / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D001565:Benzoates; D001596:Benzylamines; D004268:DNA-Binding Proteins; C473027:GW 3965; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D011768:Pyruvate Dehydrogenase Complex; D018160:Receptors, Cytoplasmic and Nuclear; D019308:Palmitic Acid; D011494:Protein Kinases; C403287:pyruvate dehydrogenase kinase 4