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Correspondence to:
James M. Ntambi, ntambi{at}biochem.wisc.edu (E-mail)
Stearoyl-CoA desaturase (SCD) catalyzes the de novo biosynthesis of oleate and palmitoleate, which are the major fatty acids found in triglycerides, cholesteryl esters, and phospholipids. A high carbohydrate (lipogenic) diet induces lipogenic gene expression by sterol regulatory element binding protein 1 (SREBP-1c)-mediated gene transcription, leading to an increase in the synthesis of triglycerides. The lipogenic diet fed to mice with a null mutation in the SCD1 gene (SCD-/-) fails to induce the synthesis of triglycerides in liver, despite the induction of expression of SREBP-1 and its target genes, fatty acid synthase and glycerol-3-phosphate acyltransferase. The lipogenic diet led to a decrease in the levels of triglyceride, but an increase in the level of cholesteryl esters of saturated fatty acids. Feeding a lipogenic diet supplemented with high levels of oleate to the SCD-/- mice resulted in incorporation of oleate in the liver of SCD-/- mice, but failed to restore triglycerides to the levels in the normal mouse. Triglyceride synthesis, as measured by the incorporation of [3H]glycerol, was dramatically reduced in the liver of SCD-/- mouse fed a lipogenic diet compared with the normal mouse.
These observations demonstrate that induction of triglyceride synthesis is highly dependent on SCD1 gene expression. — Miyazaki, M., Y-C. Kim, and J. M. Ntambi. A lipogenic diet in mice with a disruption of the stearoyl-CoA desaturase 1 gene reveals a stringent requirement of endogenous monounsaturated fatty acids for triglyceride synthesis. J. Lipid Res. 2001. 42: 1018;–1024.
Supplementary key words:
triglycerides, cholesteryl esters, gene expression, SREBP
Stearoyl-CoA desaturase (SCD) is a key enzyme involved in the biosynthesis of unsaturated fatty acids, as well as the regulation of this process. It catalyzes the
Several isoforms of SCD exist in the mouse genome. SCD1 and SCD2, which are products of different genes, are the most well characterized (3) (11) (12). Most organs of different mouse strains express SCD1 and SCD2 with the exception of liver, which expresses mainly the SCD1 isoform. SCD2 is constitutively expressed in the brain (11), and is expressed at high levels in livers of mice that overexpress the truncated nuclear form of SREBP-1a (7). SCD3 is expressed mainly in the skin (12). Several in vivo studies have shown that SCD1 gene expression is highly regulated by dietary changes, hormonal factors, developmental processes, and peroxisomal proliferators (12), implicating the role of SCD in several physiological processes.
Recent studies using the asebia mutant mouse model have begun to address the role of SCD1 gene expression and its products, the monounsaturated fatty acids, in physiological processes (13) (14) (15). The asebia mouse mutation (ab), an autosomal recessive trait characterized by hypoplastic sebaceous glands, arose more than 30 years ago in a colony of BALB/c Crg/Ga mice (15) (16). A similar mutation, designated abj, arose spontaneously in the BALB/cJ inbred strain at the Jackson Laboratory (Bar Harbor, ME), and was found to be allelic to asebia (16) (17). Using positional and high resolution genetic mapping, the abj mutation was localized to chromosome 19 and has recently been determined to be in the SCD1 gene (14). Further characterization of the asebia mice showed that they express the SCD2 mRNA isoform in various tissues, but lack the SCD1 gene function (13) (14). In addition to the presence of hypoplastic sebaceous glands, the asebia mice appear hairless with a short sparse hair coat and dry scaly skin (14). The mice also suffer from corneal opacities and hypoplastic meibomian glands, implicating the SCD1 in normal ocular barrier function. In addition, we recently showed that the livers of asebia mice are deficient in hepatic triglycerides and cholesteryl esters (13), suggesting that the SCD1 gene plays an important role in cholesterol and lipoprotein metabolism. The mechanisms leading to these various phenotypes are not yet known, but are postulated to involve deficiencies in the de novo biosynthesis of sufficient monounsaturated fatty acids, mainly oleate and palmitoleate, that serve as the major substrates for the biosynthesis of neutral lipids.
In the present study, we fed a lipogenic diet to mice, and examined the role of SCD1 gene expression in the induction of de novo synthesis of hepatic triglycerides. Normally, a lipogenic diet induces SCD1 gene expression and other lipogenic genes, resulting in increased levels of monounsaturated fatty acids and triglycerides in liver. This feeding regimen allowed us to analyze the fate of endogenously synthesized monounsaturated fatty acids without interference from exogenous sources. We showed that a lipogenic diet failed to induce triglyceride synthesis in a SCD-/- mouse, despite the induction of expression of SREBP-1 and two of its target genes, FAS and GPAT. Feeding a lipogenic diet supplemented with high levels of triolein to the SCD-/- mice resulted in incorporation of oleate into the liver of SCD-/- mice, but failed to restore triglycerides to the levels found in the normal mouse. Further, the rate of triglyceride synthesis, as measured by the incorporation of [3H]glycerol, was dramatically reduced in the livers of SCD-/- mice. Taken together, our results show that the expression of SCD1 is important for the de novo synthesis of monounsaturated fatty acids that act as the main substrates for the dietary induction of triglyceride biosynthesis in liver. Because triglycerides are a major source of stored energy, and most of the hepatic triglycerides are secreted in the form of VLDL for transport to other tissues, the dietary regulation of SCD gene expression may play a larger role in energy and lipoprotein metabolism than was previously thought.
Animals and diets
Materials
Lipid analysis
Isolation and analysis of RNA
In vivo assay for triglyceride synthesis using [3H]glycerol
Fig 1 shows a Northern blot of total RNA isolated from the livers of SCD-/- and SCD+/- mice that were fed a chow diet or a lipogenic diet for 2 days and analyzed the expression of SCD1, SREBP-1, FAS, and GPAT mRNAs. There were no noticeable alterations in food intake between the SCD-/- and the wild-type controls. The expression of these genes is induced by a lipogenic diet, resulting in increased levels of fatty acids and triglycerides (2) (3) (4). As shown previously (13), the SCD1 mRNA is not detectable in liver of SCD1-/- mice, whereas SCD+/- mice that are phenotypically indistinguishable from normal mice (14) express the 4.9-kb SCD1 mRNA. The SREBP-1, FAS, and GPAT mRNA were detectable in SCD-/- and SCD+/- animals on a chow diet. Upon feeding with a lipogenic diet, the SCD1 mRNA expression was induced 12-fold only in the SCD+/- mouse, whereas the SREBP-1, FAS, and GPAT mRNAs were induced 9.5-, 22-, and 6.5-fold, respectively, in both the SCD-/- and SCD+/- mouse. pAL 15 mRNA expression used as a loading control did not change in both groups of animals on either chow diet or lipogenic diet.
Fig 2 shows TLC analysis of lipids extracted from liver of SCD-/- and SCD+/- mice fed a chow diet or a lipogenic diet. The levels of cholesteryl esters and triglycerides of SCD-/- mice on a chow diet were lower than those of SCD+/- mice, consistent with our previous results (13). When the mice were fed a lipogenic diet, there was a marked increase in triglyceride levels in livers of SCD +/- mice, whereas SCD-/- mice showed a marked reduction in the triglyceride levels. The cholesteryl ester fraction was increased in both SCD+/- and SCD-/- mice. Table 1 shows that the triglyceride content in liver of SCD+/- mice increased by 2.3-fold, whereas the triglyceride content in the SCD1-/- mice decreased by 59% compared with the animals on a chow diet. The cholesteryl ester fraction was increased by 4.1- and 5.0-fold, respectively, in the livers of the SCD+/- and SCD-/- mice.
Table 2 shows the relative percentage compositions of the major fatty acids measured in the total lipid fraction, as well as in the triglyceride, cholesteryl ester, and phospholipid fractions of livers of SCD+/- and SCD-/- mice fed a lipogenic or chow diet. In the total lipid fraction, the SCD1+/- livers from mice fed a lipogenic diet compared with a chow diet had a 54% increase in the relative amount of 16:1, and a 45% increase in 18:1. In the triglyceride fraction, the relative amount of 16:1 increased by 42%, whereas that of 18:1 increased by 26%. In the liver cholesteryl ester fraction, the relative amount of 16:1 and 18:1 increased by 28% and 15%, respectively. The phospholipid fraction showed a 44% and 38% increase, respectively, in 16:1 and 18:1. In the total lipid fraction, the SCD1-/- livers from mice fed a lipogenic diet compared with the SCD+/- mice had a 100% decrease in the relative amount of 16:1 and a 63% decrease in 18:1. In the hepatic triglyceride fraction, the relative amount of 16:1 decreased by 76%, whereas that of 18:1 decreased by 70%. The liver cholesteryl ester fraction of SCD1-/- mice showed a 67% decrease of 16:1 and a 69% decrease of 18:1, whereas the phospholipid fraction showed a 78% decrease in 16:1 and a 55% decrease in 18:1.
Fig 3 shows the content (mg/g of liver) of the monounsaturated and saturated fatty acids measured in the triglyceride, cholesteryl ester, and phospholipid fractions in the livers of SCD+/- and SCD-/- mice fed a lipogenic diet or chow diet. In the triglyceride fraction of the SCD+/- mouse on a lipogenic diet, the amount of monounsaturated fatty acids increased by 3.1-fold, whereas that of saturated fatty acids increased by 1.9-fold when compared with the chow diet. The liver of SCD-/- mice showed a 97% reduction in the monounsaturated fatty acids compared with the SCD+/- mice. The triglyceride fraction of the SCD1-/- mice showed a 36% decrease in the contents of saturated fatty acids (16:0 and 18:0) compared with the liver of animals on a chow diet. The cholesteryl ester fraction showed a greater than 8.2-fold increase in the content of saturated fatty acids in both the SCD-/- and SCD+/- mice. These data indicate that the increased levels of cholesteryl ester observed in the SCD-/- mouse in response to a lipogenic diet (Fig 2, Table 1) is most likely due to incorporation of saturated fatty acids, mainly 18:0 and 16:0, in this fraction. The phospholipid fraction also incorporated saturated fatty acids, but to a lesser extent than the cholesteryl ester fraction. Because very low levels of saturated fatty acids were incorporated in the triglyceride fraction, the results would suggest that the triglycerides synthesized in response to lipogenic diet contain mainly monounsaturated fatty acids.
To determine whether dietary oleate could substitute for the endogenously synthesized oleate and restore the hepatic triglycerides of the SCD-/- mice to the levels observed in the heterozygous mice, we supplemented the lipogenic diets with high levels of 18:1 (50% of total fat) as triolein, and fed it to the mice for 2 days. There were no noticeable alterations in food intake between the SCD-/- and the wild-type controls. Total liver extracts were prepared, and the lipid fractions were analyzed by TLC. The fatty acid composition of the liver was analyzed by gas-liquid chromatography. Table 3 shows that feeding diets supplemented with triolein to the SCD-/- mice resulted in an increase in the levels of 18:1 in the liver. However, as shown ( Fig 4), there was no recovery in the levels of triglycerides in the SCD-/- mice to the levels observed in the SCD+/- mice fed a lipogenic diet or even to the levels of the SCD-/- mice fed a chow diet. This observation suggests that the increase in the levels of triglycerides in liver in response to a lipogenic diet is largely dependent on the presence of endogenously synthesized oleate.
To establish that the low levels of triglycerides in the SCD-/- mice are due to lower triglyceride synthesis rates, we used [3H]glycerol as a precursor of lipid synthesis to directly measure newly synthesized triglyceride in livers of SCD+/- and SCD-/- mice fed a lipogenic diet. Fig 5 shows that the triglyceride synthetic rate was 7-fold higher in the liver of the heterozygous mice, but only 1.25-fold in the liver of the SCD-/- mice. This figure also shows that although triglyceride synthesis was reduced, that of the phospholipid fraction was increased in both the SCD-/- and SCD+/- mice.
It is well known that feeding a lipogenic diet to rodents induces SCD1 gene expression and several other lipogenic genes, leading to high levels of monounsaturated fatty acids and triglycerides (2) (3) (4). This feeding regimen allows for the analysis of the fate of de novo synthesized fatty acids without interference from exogenous sources. Using this feeding regimen, we showed that a lipogenic diet fails to induce triglyceride synthesis in SCD-/- mice, despite the induction of expression of SREBP-1, as well as two of its target genes, FAS and GPAT, involved in saturated fatty acid and triglyceride synthesis, respectively. The triglyceride levels, instead, were decreased. We have established that the lower hepatic triglyceride levels are due to a lower rate of triglyceride synthesis in the mutant mice. Because the SCD+/- and the SCD-/- mice consumed equivalent amounts of food, the decrease in the triglyceride levels in the mutant mouse could be due to increased ß-oxidation. We also demonstrated that dietary monounsaturated fatty acids could not substitute for the ones endogenously synthesized by SCD as substrates for adequate triglyceride synthesis in liver.
The consequences of regulating the SCD1 gene expression by diet may be relevant to lipoprotein metabolism. The majority of de novo synthesis of fatty acids in liver is directed toward triglyceride synthesis and secretion (7). The deficiency in triglyceride levels that we observed could have been due to increased synthesis or secretion of VLDL-TG. However, the lipoprotein profile previously performed on plasma of the SCD-/- showed that these mice have very low levels of triglycerides in the VLDL, LDL, and HDL lipoprotein fractions (13). The current results, therefore, suggest that in the absence of cellular monounsaturated fatty acids due to SCD1 deficiency, the levels of hepatic triglycerides are reduced, leading to lower levels of plasma VLDL-TG.
The use of a lipogenic diet supplemented with high levels of triolein enabled us to test the possibility that the liver could utilize dietary monounsaturated fatty acids instead of those generated in vivo by SCD for de novo synthesis of triglycerides. Dietary oleate or palmitoleate from the small intestine would reach the liver mainly as glycerol esters of chylomicron remnants. The triglycerides are then cleaved into free glycerol and free oleate and palmitoleate in the lysosomes. Because the SCD-/- mice possess normal activity of GPAT (13), this enzyme would then use the freed oleate and palmitoleate as substrates for triglyceride synthesis. We found that feeding a lipogenic diet rich in monounsaturated fatty acids did not correct the deficiency in triglyceride levels in the SCD-/- mice, despite an increase in the levels of 16:1 and 18:1 in the liver. This observation suggests that although the monounsaturated fatty acids reach the liver, they do not necessarily become fatty acyl-CoA substrates at the site of de novo synthesis of liver triglycerides. It is possible that dietary monounsaturated fatty acids and those synthesized endogenously constitute different pools and end up in different environments of the endoplasmic reticulum or cellular compartments where they may be utilized for different purposes. A possible physiological explanation for the requirement of dietary induction of SCD expression is to produce more readily accessible substrates within the vicinity of GPAT to aid in the efficient esterification of glycerol 3-phosphate for triglyceride synthesis.
Feeding a lipogenic diet to the SCD-/- mice led to further accumulation of saturated fatty acids in liver. We found that the saturated fatty acids made endogenously were incorporated into the cholesteryl ester and, to a lesser extent, in the phospholipid fraction, resulting in an increase in the levels of these lipids in liver of both the SCD-/- and SCD+/- mice. However, the saturated fatty acids failed to elevate the levels of the triglyceride fraction in the SCD-/- mice. This observation thus suggests that the endogenously synthesized oleate or palmitoleate, which arise from SCD activity in the endoplasmic reticulum, are critical substrates for the synthesis of triglycerides by GPAT. The results also indicate a more stringent requirement of monounsaturated fatty acids as substrates of diacylglycerol acyltransferase than ACAT. The diacylglycerol acyltransferase step may be important in selecting monounsaturated fatty acids over saturated fatty acids, providing a mechanism to funnel saturated fatty acids into metabolic pools.
The mouse and rat genomes contain several SCD genes, two of which (SCD1 and SCD2) are well characterized (3) (11). These two genes, which are products of two separate genes, are highly homologous at both the nucleotide and amino acid sequence levels, but exhibit divergent tissue-specific expression. Most organs of different mouse strains express SCD1 and SCD2, with the exception of liver, which expresses mainly the SCD1 isoform. In liver, a lipogenic diet and insulin induce SCD1 gene expression, but SCD2 is silent under both conditions (3) (23). The insulin induction of SCD1 gene expression is thought to be mediated by the truncated nuclear form of the SREBP-1c. Liver SCD2 becomes expressed at higher levels only in livers of mice that overexpress SREBP-1 (7). Thus, the transcription of both SCD1 and SCD2 can be regulated by SREBP-1c. We have shown previously that SCD2 mRNA is present in the SCD-/- mice (13), and although expressed at low levels, would be expected to be induced by SREBP-1-mediated gene transcription. However, despite the induction of SREBP-1 by a lipogenic diet and the expression of SCD2 in liver of the SCD-/- mice, the levels of triglycerides remained low, suggesting that SCD2 could not compensate for the SCD1 deficiency. These results point to SCD1 gene expression as a key control point in the induction of triglyceride synthesis in liver.
In conclusion, the present work demonstrates that dietary induction of triglyceride synthesis in mouse liver is highly dependent on the expression of the SCD1 gene. SCD2 cannot compensate for the deficiency. We propose that the synthesis of triglycerides requires endogenously synthesized monounsaturated fatty acids by SCD1 as critical substrates. Dietary monounsaturated fatty acids can get into the liver, but cannot be utilized to synthesize enough triglycerides. Because most of the hepatic triglycerides are packaged and incorporated into VLDL-TG and transported to tissues such as adipose tissue for storage, the induction of SCD1 gene expression can have a wide range of effects on lipoprotein metabolism in normal and disease states. For instance, high SCD activity has been correlated with high levels of triglycerides in plasma (24). Hypertriglyceridemia is a risk factor for cardiovascular disease, and high SCD expression may be a major cause of this condition in humans. Thus, the regulation of SCD may have broad implications for its potential use as a target in the treatment of human hypertriglyceridemia.
Abbreviations: FAS, fatty acid synthase; GPAT, glycerol-3-phosphate acyltransferase; SCD, stearoyl-CoA desaturase; SREBP-1, sterol regulatory element binding protein 1.
We thank Dr. Alan Attie for useful discussions and critical review of the manuscript. This work was supported, in part, by a grant from the American Heart Association and Xenon Genetics.
Manuscript received January 18, 2001; and in revised form March 12, 2001
Copyright © 2001 by Lipid Research, Inc.
Original Article
A lipogenic diet in mice with a disruption of the stearoyl-CoA desaturase 1 gene reveals a stringent requirement of endogenous monounsaturated fatty acids for triglyceride synthesis
Makoto Miyazakia,
Young-Cheul Kima, and
James M. Ntambia,b
a Department of Biochemistry, University of Wisconsin, 433 Babcock Drive, Madison, WI 53706
b Department of Nutritional Sciences, University of Wisconsin, 433 Babcock Drive, Madison, WI 53706
ABSTRACT
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ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
INTRODUCTION
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ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
9-desaturation of long-chain fatty acids, leading to biosynthesis of palmitoleic (C16:1) and oleic (C18:1) acids as major products (1). Palmitoleic and oleic acids are the major monounsaturated fatty acids of triglycerides, cholesteryl esters, and membrane phospholipids. When fasted animals are subsequently fed a high carbohydrate (lipogenic) diet, there is a dramatic increase in the levels of SCD and several other enzymes involved in fatty acid and triglyceride synthesis such as acetyl-CoA carboxylase, fatty acid synthase (FAS), and glycerol-3-phosphate acyltransferase (GPAT) (2) (3). The coordinate induction of these enzymes is due to increased sterol regulatory element binding protein 1 (SREBP-1)-stimulated gene transcription (4) (5) (6) (7) (8). The induction of lipogenic gene transcription is followed by a prompt increase in fatty acids and triglycerides to the levels above those observed in animals fed normally (2). The majority of the excess triglycerides are incorporated and secreted by the liver as VLDL-TG for transport to other tissues (9). A high level of VLDL-TG in plasma is a risk factor for cardiovascular disease (10) and, therefore, identifying a control point in the pathway of triglyceride biosynthesis can be a selective target for treating the condition.
MATERIALS AND METHODS
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ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
Asebia homozygous (SCD-/-) and heterozygous (SCD+/-) mice, originally obtained from the Jackson Laboratory (Bar Harbor, ME), were reared and housed in a pathogen-free animal facility of the department of Biochemistry of the University of Wisconsin;–Madison, operating at a 12-h light/12-h dark cycle. The breeding of the animals was in accordance with the protocols approved by the Animal Care Research Committee of the University of Wisconsin;–Madison. In this study, the heterozygous mice are considered to have the normal phenotype (13) (14). At 16 weeks of age, the mice were fed, ad libitum for 2 days either chow diet (5008 test diet; PMI Nutrition International Inc., Richmond, IN), high carbohydrate diet (TD 99252, Harlan Teklad, Madison WI), or high carbohydrate diet supplemented with triolein (50% of total fat). The high carbohydrate diet contained, by weight, 21% casein, 14% maltodextrin, 55% sucrose, 5% cellulose, 3% mineral mix (AIN-93G-MX), and 1% vitamin mix (AIN-93-VX).
Radioactive [32P]dCTP (3,000 Ci/mmol) was obtained from DuPont Co. (Wilmington, DE). TLC plates (TLC Silica Gel G60) were from Merck (Darmstadt, Germany). [1,2,3-3H]-glycerol was obtained from American Radiolabeled Chemicals Inc. (St. Louis, MO). The cDNA probes for FAS and GPAT were obtained from Dr. H. Sul, University of California, Berkeley. All other chemicals were purchased from Sigma (St. Louis, MO).
Total lipids were extracted from liver according to the method of Bligh and Dyer (18), and were separated by silca gel TLC using petroleum ether;–diethyl ether;–acetic acid (80:30:1) as the developing solvent. The lipids were visualized by cupric sulfate in 8% phosphoric acid. The lipids were scraped, methylated, and analyzed by gas-liquid chromatography as previously described (13). Triheptadecanoylglcerol, heptadecanoyl cholesterol, and 1,2-dihepatadecanoyl-L-
-phosphatidylcholine (Sigma) were added prior to lipid extraction as internal standards for the quantitation of triglycerides, cholesteryl esters, and phospholipids, respectively.
Total RNA was isolated from livers using the acid guanidinium-phenol-chloroform extraction method (19). Twenty micrograms of total RNA were separated by 1.0% agarose/2.2 M formaldehyde gel electrophoresis, and transferred onto nylon membrane. The membrane was hybridized with 32P-labeled FAS (2), GPAT (20), SREBP-1c (21), and SCD1 cDNA probes (3). pAL15 cDNA probe (19) was used as a control for equal loading of RNA.
[1,2,3-3H]glycerol was dissolved in 0.9% NaCl at a concentration of 50 µCi/0.15 ml. Mice that had been fed high carbohydrate diet or chow diet were injected intraperitoneally with 50 µCi of [3H]glycerol 15 min before being sacrificed (22). Hepatic lipids were extracted using Bligh and Dyer's method and separated by TLC using hexane;–ether;–acetic acid (90:30:1, v/v) as developing solvent. Each lipid extract was scraped off the plate, and the radioactivity was measured using a liquid scintillation counter.
RESULTS
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ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Figure 1.
Northern blot analysis for the expression of SCD1, SREBP-1, FAS, and GPAT mRNA from livers of SCD1-/- and heterozygous (+/-) mice fed a chow (C) or lipogenic diet (CHO). Total RNA (20 µg) pooled from four mice of each group was subjected to Northern analysis followed by hybridization with labeled probes specific for SCD1, SREBP-1, FAS, and GPAT. A cDNA probe for pAL15 (19) was used to confirm equal loading of RNA.
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Figure 2.
TLC of lipid extracts from livers of SCD1-/- and heterozygous (SCD+/-) mice fed chow or lipogenic diet for 2 days. Total lipids were extracted from livers of heterozygous and SCD1-/- mice. Lipid extracts were pooled and analyzed by TLC. Equivalent amounts of lipid extract (from 2.5 mg of tissue homogenate) were loaded in each lane. Each lane represents lipids from livers of three mice.
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Table 1.
Phenotypic differences in neutral lipid content between SCD-/- and SCD+/- mice
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Table 2.
Fatty acid composition of livers from SCD+/- and SCD-/- mice fed lipogenic diet or chow diet
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Figure 3.
The contents of saturated and monounsaturated fatty acids in triglyceride, cholesteryl ester, and phosholipid fractions of SCD-/- and SCD+/- mice fed a chow diet or a lipogenic diet. Triheptadecanoylglycerol, heptadecanoyl cholesteryl, and 1,2-dihepatadecanoyl-L- -phosphatidylcholine were added prior to lipid extraction as internal standards for the quantitation of triglycerides, cholesteryl esters, and phospholipids, respectively. Lipid extracts were pooled and analyzed by TLC, methyl esterified, and quantitated by gas-liquid chromatography.
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Figure 4.
TLC of lipid extracts from livers of SCD-/- mice fed high oleate (CHO+18:1) diet for 2 days. Total lipids were extracted from livers of SCD-/- mice. Lipid extracts were pooled and analyzed by TLC as described in Materials and Methods. Equivalent amounts of lipid extract (from 2.5 mg of tissue homogenate) were loaded in each lane. Each lane represents lipids from liver of one mouse.
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Table 3.
Fatty acid composition of livers from high oleate diet-fed SCD-/- mice
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Figure 5.
The rate of glycerolipid synthesis in liver. Mice fed chow diet or lipogenic diet for 2 days were intraperitoneally injected with 50 µCi of [3H]glycerol 15 min before being sacrificed. After extraction of hepatic lipids, phospholipids and triglycerides were separated, and the radioactivity was determined. Data are expressed as a percentage of the values of chow diet-fed heterozygous mice.
DISCUSSION
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ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
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FOOTNOTES 
ACKNOWLEDGMENTS
REFERENCES
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MATERIALS AND METHODS
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J. N. van der Veen, R. Havinga, V. W. Bloks, A. K. Groen, and F. Kuipers Cholesterol feeding strongly reduces hepatic VLDL-triglyceride production in mice lacking the liver X receptor {alpha} J. Lipid Res., February 1, 2007; 48(2): 337 - 347. [Abstract] [Full Text] [PDF]
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 H. Sampath, M. Miyazaki, A. Dobrzyn, and J. M. Ntambi Stearoyl-CoA Desaturase-1 Mediates the Pro-lipogenic Effects of Dietary Saturated Fat J. Biol. Chem., January 26, 2007; 282(4): 2483 - 2493. [Abstract] [Full Text] [PDF]
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Y.-L. Zhang, A. Hernandez-Ono, P. Siri, S. Weisberg, D. Conlon, M. J. Graham, R. M. Crooke, L.-S. Huang, and H. N. Ginsberg Aberrant Hepatic Expression of PPAR{gamma}2 Stimulates Hepatic Lipogenesis in a Mouse Model of Obesity, Insulin Resistance, Dyslipidemia, and Hepatic Steatosis J. Biol. Chem., December 8, 2006; 281(49): 37603 - 37615. [Abstract] [Full Text] [PDF]
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M. T. Flowers, A. K. Groen, A. T. Oler, M. P. Keller, Y. Choi, K. L. Schueler, O. C. Richards, H. Lan, M. Miyazaki, F. Kuipers, et al. Cholestasis and hypercholesterolemia in SCD1-deficient mice fed a low-fat, high-carbohydrate diet J. Lipid Res., December 1, 2006; 47(12): 2668 - 2680. [Abstract] [Full Text] [PDF]
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G. Rizki, L. Arnaboldi, B. Gabrielli, J. Yan, G. S. Lee, R. K. Ng, S. M. Turner, T. M. Badger, R. E. Pitas, and J. J. Maher Mice fed a lipogenic methionine-choline-deficient diet develop hypermetabolism coincident with hepatic suppression of SCD-1 J. Lipid Res., October 1, 2006; 47(10): 2280 - 2290. [Abstract] [Full Text] [PDF]
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 K. Chu, M. Miyazaki, W. C. Man, and J. M. Ntambi Stearoyl-Coenzyme A Desaturase 1 Deficiency Protects against Hypertriglyceridemia and Increases Plasma High-Density Lipoprotein Cholesterol Induced by Liver X Receptor Activation. Mol. Cell. Biol., September 1, 2006; 26(18): 6786 - 6798. [Abstract] [Full Text] [PDF]
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H. Cao, K. Maeda, C. Z. Gorgun, H.-J. Kim, S.-Y. Park, G. I. Shulman, J. K. Kim, and G. S. Hotamisligil Regulation of metabolic responses by adipocyte/ macrophage Fatty Acid-binding proteins in leptin-deficient mice. Diabetes, July 1, 2006; 55(7): 1915 - 1922. [Abstract] [Full Text] [PDF]
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S. B. Biddinger, M. Miyazaki, J. Boucher, J. M. Ntambi, and C. R. Kahn Leptin Suppresses Stearoyl-CoA Desaturase 1 by Mechanisms Independent of Insulin and Sterol Regulatory Element-Binding Protein-1c. Diabetes, July 1, 2006; 55(7): 2032 - 2041. [Abstract] [Full Text] [PDF]
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 S. Vankoningsloo, A. De Pauw, A. Houbion, S. Tejerina, C. Demazy, F. de Longueville, V. Bertholet, P. Renard, J. Remacle, P. Holvoet, et al. CREB activation induced by mitochondrial dysfunction triggers triglyceride accumulation in 3T3-L1 preadipocytes J. Cell Sci., April 1, 2006; 119(7): 1266 - 1282. [Abstract] [Full Text] [PDF]
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 M. Miyazaki, A. Dobrzyn, P. M. Elias, and J. M. Ntambi Stearoyl-CoA desaturase-2 gene expression is required for lipid synthesis during early skin and liver development PNAS, August 30, 2005; 102(35): 12501 - 12506. [Abstract] [Full Text] [PDF]
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N. Scaglia and R. A. Igal Stearoyl-CoA Desaturase Is Involved in the Control of Proliferation, Anchorage-independent Growth, and Survival in Human Transformed Cells J. Biol. Chem., July 8, 2005; 280(27): 25339 - 25349. [Abstract] [Full Text] [PDF]
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A. Dobrzyn, P. Dobrzyn, M. Miyazaki, H. Sampath, K. Chu, and J. M. Ntambi Stearoyl-CoA Desaturase 1 Deficiency Increases CTP:Choline Cytidylyltransferase Translocation into the Membrane and Enhances Phosphatidylcholine Synthesis in Liver J. Biol. Chem., June 17, 2005; 280(24): 23356 - 23362. [Abstract] [Full Text] [PDF]
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 S. M. Rahman, A. Dobrzyn, S.-H. Lee, P. Dobrzyn, M. Miyazaki, and J. M. Ntambi Stearoyl-CoA desaturase 1 deficiency increases insulin signaling and glycogen accumulation in brown adipose tissue Am J Physiol Endocrinol Metab, February 1, 2005; 288(2): E381 - E387. [Abstract] [Full Text] [PDF]
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S.-H. Lee, A. Dobrzyn, P. Dobrzyn, S. M. Rahman, M. Miyazaki, and J. M. Ntambi Lack of stearoyl-CoA desaturase 1 upregulates basal thermogenesis but causes hypothermia in a cold environment J. Lipid Res., September 1, 2004; 45(9): 1674 - 1682. [Abstract] [Full Text] [PDF]
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P. Cohen and J. M. Friedman Leptin and the Control of Metabolism: Role for Stearoyl-CoA Desaturase-1 (SCD-1) J. Nutr., September 1, 2004; 134(9): 2455S - 2463S. [Abstract] [Full Text] [PDF]
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M. Miyazaki, A. Dobrzyn, H. Sampath, S.-H. Lee, W. C. Man, K. Chu, J. M. Peters, F. J. Gonzalez, and J. M. Ntambi Reduced Adiposity and Liver Steatosis by Stearoyl-CoA Desaturase Deficiency Are Independent of Peroxisome Proliferator-activated Receptor-{alpha} J. Biol. Chem., August 13, 2004; 279(33): 35017 - 35024. [Abstract] [Full Text] [PDF]
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M. Miyazaki, A. Dobrzyn, W. C. Man, K. Chu, H. Sampath, H.-J. Kim, and J. M. Ntambi Stearoyl-CoA Desaturase 1 Gene Expression Is Necessary for Fructose-mediated Induction of Lipogenic Gene Expression by Sterol Regulatory Element-binding Protein-1c-dependent and -independent Mechanisms J. Biol. Chem., June 11, 2004; 279(24): 25164 - 25171. [Abstract] [Full Text] [PDF]
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F. Castro-Chavez, V. K. Yechoor, P. K. Saha, J. Martinez-Botas, E. C. Wooten, S. Sharma, P. O'Connell, H. Taegtmeyer, and L. Chan Coordinated Upregulation of Oxidative Pathways and Downregulation of Lipid Biosynthesis Underlie Obesity Resistance in Perilipin Knockout Mice: A Microarray Gene Expression Profile Diabetes, November 1, 2003; 52(11): 2666 - 2674. [Abstract] [Full Text] [PDF]
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S. M. Rahman, A. Dobrzyn, P. Dobrzyn, S.-H. Lee, M. Miyazaki, and J. M. Ntambi Stearoyl-CoA desaturase 1 deficiency elevates insulin-signaling components and down-regulates protein-tyrosine phosphatase 1B in muscle PNAS, September 16, 2003; 100(19): 11110 - 11115. [Abstract] [Full Text] [PDF]
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 J. J. Loor and J. H. Herbein Reduced Fatty Acid Synthesis and Desaturation Due to Exogenous trans10, cis12-CLA in Cows Fed Oleic or Linoleic Oil J Dairy Sci, April 1, 2003; 86(4): 1354 - 1369. [Abstract] [Full Text] [PDF]
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L. L. Listenberger, X. Han, S. E. Lewis, S. Cases, R. V. Farese Jr., D. S. Ory, and J. E. Schaffer Triglyceride accumulation protects against fatty acid-induced lipotoxicity PNAS, March 18, 2003; 100(6): 3077 - 3082. [Abstract] [Full Text] [PDF]
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A. D. Attie, R. M. Krauss, M. P. Gray-Keller, A. Brownlie, M. Miyazaki, J. J. Kastelein, A. J. Lusis, A. F. H. Stalenhoef, J. P. Stoehr, M. R. Hayden, et al. Relationship between stearoyl-CoA desaturase activity and plasma triglycerides in human and mouse hypertriglyceridemia J. Lipid Res., November 1, 2002; 43(11): 1899 - 1907. [Abstract] [Full Text] [PDF]
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J. M. Ntambi, M. Miyazaki, J. P. Stoehr, H. Lan, C. M. Kendziorski, B. S. Yandell, Y. Song, P. Cohen, J. M. Friedman, and A. D. Attie Loss of stearoyl-CoA desaturase-1 function protects mice against adiposity PNAS, August 20, 2002; 99(17): 11482 - 11486. [Abstract] [Full Text] [PDF]
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 X. Lin, G. Schonfeld, P. Yue, and Z. Chen Hepatic Fatty Acid Synthesis Is Suppressed in Mice With Fatty Livers Due to Targeted Apolipoprotein B38.9 Mutation Arterioscler. Thromb. Vasc. Biol., March 1, 2002; 22(3): 476 - 482. [Abstract] [Full Text] [PDF]
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M. Merkel, W. Velez-Carrasco, L. C. Hudgins, and J. L. Breslow Compared with saturated fatty acids, dietary monounsaturated fatty acids and carbohydrates increase atherosclerosis and VLDL cholesterol levels in LDL receptor-deficient, but not apolipoprotein E-deficient, mice PNAS, October 16, 2001; (2001) 231490498. [Abstract] [Full Text] [PDF]
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M. Miyazaki, H.-J. Kim, W. C. Man, and J. M. Ntambi Oleoyl-CoA Is the Major de Novo Product of Stearoyl-CoA Desaturase 1 Gene Isoform and Substrate for the Biosynthesis of the Harderian Gland 1-Alkyl-2,3-diacylglycerol J. Biol. Chem., October 12, 2001; 276(42): 39455 - 39461. [Abstract] [Full Text] [PDF]
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M. Merkel, W. Velez-Carrasco, L. C. Hudgins, and J. L. Breslow Compared with saturated fatty acids, dietary monounsaturated fatty acids and carbohydrates increase atherosclerosis and VLDL cholesterol levels in LDL receptor-deficient, but not apolipoprotein E-deficient, mice PNAS, November 6, 2001; 98(23): 13294 - 13299. [Abstract] [Full Text] [PDF]
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