Polyunsaturated fatty acids are FXR ligands and differentially regulate expression of FXR targets.
Polyunsaturated fatty acids (PUFAs) have been previously reported as agonists of peroxisome proliferatoractivated receptor and antagonists of the liver X receptor. The activities on these two nuclear receptors have been attributed to their beneficial effects such as improvement of dyslipidemia and insulin sensitivity and decrease of hepatic lipogenesis. Here we report that PUFAs are ligands of farnesoid X receptor (FXR), a nuclear receptor for bile acids. In a conventional FXR binding assay, arachidonic acid (AA, 20:4), docosahexaenoic acid (DA, 22:6), and linolenic acid (LA, 18:3) had an affinity of 2.6, 1.5, and 3.5 microM, respectively. In a cell-free coactivator association assay, AA, DA, and LA decreased FXR agonist-induced FXR activation with IC(50)s ranging from 0.9 to 4.7 microM. In HepG2 cells, PUFAs regulated the expression of two FXR targets, BSEP and kininogen, in an opposite fashion, although both genes were transactivated by FXR. All three PUFAs dose-dependently enhanced FXR agonist-induced BSEP expression but decreased FXR agonist-induced human kininogen mRNA. Saturated fatty acids such as stearic acid (SA, 18:0) and palmitic acid (PA, 16:0) did not bind to FXR and did not change BSEP or kininogen expression. The pattern of BSEP and kininogen regulation by PUFAs is closely similar to that of the guggulsterone, previously reported as a selective bile acid receptor modulator. Our results suggest that PUFAs may belong to the same class of FXR ligands as guggulsterone, and that the selective regulation of FXR targets may contribute to the beneficial effects of PUFAs in lipid metabolism.
Zhao
Annie
A
Department of Cardiovascular Diseases, Merck Research Laboratories, Rahway, New Jersey 07065, USA.
Yu
Jinghua
J
Lew
Jane-L
JL
Huang
Li
L
Wright
Samuel D
SD
Cui
Jisong
J
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D016718:Arachidonic Acid / Q000378:metabolism; D045744:Cell Line, Tumor; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000819:agonists / Q000378:metabolism*; D004281:Docosahexaenoic Acids / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism / Q000494:pharmacology*; D005453:Fluorescence; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D007704:Kininogens / Q000378:metabolism*; D008024:Ligands; D016133:Polymerase Chain Reaction / Q000379:methods; D012333:RNA, Messenger / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors / Q000819:agonists / Q000378:metabolism*; D017962:alpha-Linolenic Acid / Q000378:metabolism; D000099150:Receptor, Farnesoid X-Activated
D018528:ATP-Binding Cassette Transporters; D016718:Arachidonic Acid; D017931:DNA Primers; D004268:DNA-Binding Proteins; D004281:Docosahexaenoic Acids; D005231:Fatty Acids, Unsaturated; D007704:Kininogens; D008024:Ligands; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D017962:alpha-Linolenic Acid; D000099150:Receptor, Farnesoid X-Activated