Hepatic farnesyl diphosphate synthase expression is suppressed by polyunsaturated fatty acids.
Dietary vegetable oils and fish oils rich in PUFA (polyunsaturated fatty acids) exert hypocholesterolaemic and hypotriglyceridaemic effects in rodents. The plasma cholesterol-lowering properties of PUFA are due partly to a diminution of cholesterol synthesis and of the activity of the rate-limiting enzyme HMG-CoA reductase (3-hydroxy-3-methylglutaryl-CoA reductase). To better understand the mechanisms involved, we examined how tuna fish oil and individual n-3 and n-6 PUFA affect the expression of hepatic FPP synthase (farnesyl diphosphate synthase), a SREBP (sterol regulatory element-binding protein) target enzyme that is subject to negative-feedback regulation by sterols, in co-ordination with HMG-CoA reductase. Feeding mice on a tuna fish oil diet for 2 weeks decreased serum cholesterol and triacylglycerol levels, by 50% and 60% respectively. Hepatic levels of FPP synthase and HMG-CoA reductase mRNAs were also decreased, by 70% and 40% respectively. Individual n-3 and n-6 PUFA lowered FPP synthase and HMG-CoA reductase mRNA levels in H4IIEC3 rat hepatoma cells to a greater extent than did stearate and oleate, with the largest inhibitory effects occurring with arachidonate, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). We observed a similar inhibitory effect on protein levels of FPP synthase. The suppressive effect of PUFA on the FPP synthase mRNA level was not due to a decrease in mRNA stability, but to transcription inhibition. Moreover, a lower nuclear availability of both SREBP-1 and SREBP-2 mature forms was observed in HepG2 human hepatoblastoma cells treated with arachidonate, EPA or DHA. Taken together, these data suggest that PUFA can down-regulate hepatic cholesterol synthesis through inhibition of HMG-CoA reductase and FPP synthase, at least in part through impairment of the SREBP pathway.
Laboratoire de Biologie Moléculaire et Cellulaire (GDR CNRS no. 2583), Université de Bourgogne, 21000 Dijon, France. catherine.corcos@univ-brest.fr
Catherine
C
Le Jossic-Corcos
Céline
C
Gonthier
Isabelle
I
Zaghini
Emmanuelle
E
Logette
Ishaiahu
I
Shechter
Paulette
P
Bournot
D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002784:Cholesterol / Q000097:blood; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004032:Diet; D015536:Down-Regulation / Q000187:drug effects; D005231:Fatty Acids, Unsaturated / Q000008:administration & dosage / Q000494:pharmacology*; D005395:Fish Oils / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D051228:Geranyltranstransferase; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D051379:Mice; D011401:Promoter Regions, Genetic / Q000235:genetics; D020871:RNA Stability / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014280:Triglycerides / Q000097:blood; D014413:Tuna; D017962:alpha-Linolenic Acid / Q000494:pharmacology
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D005231:Fatty Acids, Unsaturated; D005395:Fish Oils; D012333:RNA, Messenger; C497387:SREBF1 protein, human; C497390:SREBF2 protein, human; C497388:Srebf1 protein, mouse; C497389:Srebf1 protein, rat; C497391:Srebf2 protein, mouse; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors; D014280:Triglycerides; D017962:alpha-Linolenic Acid; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D019883:Alkyl and Aryl Transferases; D051228:Geranyltranstransferase