Ovarian estradiol supports sexual behavior but not energy homeostasis in female marmoset monkeys.

OBJECTIVE: In adult female rodents, ovarian estradiol (E2) regulates body weight, adiposity, energy balance, physical activity, glucose-insulin homeodynamics, and lipid metabolism, while protecting against diet-induced obesity. The same E2 actions are presumed to occur in primates, but confirmatory studies have been lacking. METHODS: We investigated the consequences of ovariectomy (OVX) and E2 replacement in female marmoset monkeys on major metabolic and morphometric endpoints. Sexual behavior and uterine diameters were assessed as positive controls for E2 treatment efficacy. Metabolic parameters were measured 1 mo prior to OVX, and 3 and 6 mo thereafter. During OVX, animals received empty or E2-containing silastic s.c. implants. To test the interaction between E2 and diet, both treatment groups were assigned to either a higher fat diet (HFD) or a low-fat diet (LFD). RESULTS: As anticipated, OVX animals exhibited diminished frequency (p = 0.04) of sexually receptive behavior and increased rejection behavior (p = 0.04) toward their male partners compared with E2-treated OVX females. OVX also decreased (p = 0.01) uterine diameter. There were no treatment effects on total caloric intake. There were no significant effects of OVX, E2 treatment, or diet on body weight, body composition, energy expenditure, physical activity, fasting glucose, or glucose tolerance. Regardless of E2 treatment, serum triglycerides were higher (p = 0.05) in HFD than LFD females. Postmortem qPCR analysis of hypothalamic tissues revealed higher mRNA expression (p < 0.001) for PGR in E2-treated monkeys versus OVX controls regardless of diet, but no differences between groups in other selected metabolic genes. In contrast, regardless of E2 treatment, there was a decreased mRNA expression of PGC1α (PPARGC1A), HTR1A, and HTR5A in HFD compared with LFD females. CONCLUSIONS: Our findings, overall, document a greatly diminished role for ovarian E2 in the metabolic physiology of a female primate, and encourage consideration that primates, including humans, evolved metabolic control systems regulated by extra-ovarian E2 or are generally less subject to E2 regulation.

Extraovarian gonadotropin negative feedback revealed by aromatase inhibition in female marmoset monkeys.

Whereas the ovary produces the majority of estradiol (E2) in mature female primates, extraovarian sources contribute to E2 synthesis and action, including the brain E2-regulating hypothalamic gonadotropin-releasing hormone. In ovary-intact female rodent models, aromatase inhibition (AI) induces a polycystic ovary syndrome-like hypergonadotropic hyperandrogenism due to absent E2-mediated negative feedback. To examine the role of extraovarian E2 on nonhuman primate gonadotropin regulation, the present study uses letrozole to elicit AI in adult female marmoset monkeys. Sixteen female marmosets (Callithrix jacchus; >2 yr) were randomly assigned to ovary-intact or ovariectomy (OVX) conditions and subsequently placed on a daily oral regimen of either ~200 µl vehicle alone (ovary-intact Control, n = 3; OVX, n = 3) or 1 mg ⋅ kg-1 ⋅ day-1 letrozole in vehicle (ovary-intact AI, n = 4; OVX + AI, n = 6). Blood samples were collected every 10 days, and plasma chorionic gonadotropin (CG) and steroid hormone levels were determined by validated radioimmunoassay and liquid chromatography/tandem mass spectrometry, respectively. Ovary-intact, AI-treated and OVX females exhibited elevated CG (P < 0.01, P = 0.004, respectively) compared with controls, and after 30 days, OVX + AI females exhibited a suprahypergonadotropic phenotype (P = 0.004) compared with ovary-intact + AI and OVX females. Androstenedione (P = 0.03) and testosterone (P = 0.05) were also elevated in ovary-intact, AI-treated females above all other groups. The current study thus confirms in a nonhuman primate that E2 depletion and diminished negative feedback in ovary-intact females engage hypergonadotropic hyperandrogenism. Additionally, we demonstrate that extraovarian estrogens, possibly neuroestrogens, contribute to female negative feedback regulation of gonadotropin release.

Hepatic oleate regulates liver stress response partially through PGC-1α during high-carbohydrate feeding.

BACKGROUND & AIMS: High-carbohydrate diets contribute to the development of liver stress and fatty liver disease. While saturated fatty acids are known to induce liver stress, the role of monounsaturated fatty acids (MUFA), synthesized by the stearoyl-CoA desaturase (SCD) family of enzymes, in regulation of liver function during lipogenic dietary conditions remains largely unknown. The major products of SCD-catalyzed reactions are oleate (18:1n-9) and palmitoleate (16:1n-7). METHODS: We generated mouse models with restricted exogenous MUFA supply and reduced endogenous MUFA synthesis, in which SCD1 global knockout (GKO) or liver-specific knockout (LKO) mice were fed a lipogenic high-sucrose very low-fat (HSVLF) or high-carbohydrate (HC) diet. In a gain-of-function context, we introduced liver-specific expression of either human SCD5, which synthesizes 18:1n-9, or mouse Scd3, which synthesizes 16:1n-7, into SCD1 GKO mice and fed the HSVLF diet. RESULTS: Lipogenic high-carbohydrate diets induced hepatic endoplasmic reticulum (ER) stress and inflammation in SCD1 GKO and LKO mice. Dietary supplementation with 18:1n-9, but not 18:0, prevented the HSVLF diet-induced hepatic ER stress and inflammation in SCD1 LKO mice, while hepatic SCD5, but not Scd3, expression reduced the ER stress and inflammation in GKO mice. Additional experiments revealed liver-specific deletion of the transcriptional coactivator PGC-1α reduced hepatic inflammatory and ER stress response gene expression in SCD1 LKO mice. CONCLUSIONS: Our results demonstrate an indispensable role of hepatic oleate in protection against lipogenic diet-induced hepatic injury, and PGC-1α potentiates the ER stress response under conditions of restricted dietary oleate coupled to reduced capacity of endogenous hepatic oleate synthesis. LAY SUMMARY: Susceptibility to metabolic dysfunction is influenced by genetic and environmental factors. In this study we show that modulation of two genes regulates the liver response, including ER stress and inflammation, to a high-carbohydrate low-fat diet. We reveal that hepatic availability of oleate, a monounsaturated fatty acid, is important for maintenance of liver health.

Hepatic oleate regulates adipose tissue lipogenesis and fatty acid oxidation.

Hepatic steatosis is associated with detrimental metabolic phenotypes including enhanced risk for diabetes. Stearoyl-CoA desaturases (SCDs) catalyze the synthesis of MUFAs. In mice, genetic ablation of SCDs reduces hepatic de novo lipogenesis (DNL) and protects against diet-induced hepatic steatosis and adiposity. To understand the mechanism by which hepatic MUFA production influences adipose tissue stores, we created two liver-specific transgenic mouse models in the SCD1 knockout that express either human SCD5 or mouse SCD3, that synthesize oleate and palmitoleate, respectively. We demonstrate that hepatic de novo synthesized oleate, but not palmitoleate, stimulate hepatic lipid accumulation and adiposity, reversing the protective effect of the global SCD1 knockout under lipogenic conditions. Unexpectedly, the accumulation of hepatic lipid occurred without induction of the hepatic DNL program. Changes in hepatic lipid composition were reflected in plasma and in adipose tissue. Importantly, endogenously synthesized hepatic oleate was associated with suppressed DNL and fatty acid oxidation in white adipose tissue. Regression analysis revealed a strong correlation between adipose tissue lipid fuel utilization and hepatic and adipose tissue lipid storage. These data suggest an extrahepatic mechanism where endogenous hepatic oleate regulates lipid homeostasis in adipose tissues.

Positional cloning of Sorcs1, a type 2 diabetes quantitative trait locus.

We previously mapped the type 2 diabetes mellitus-2 locus (T2dm2), which affects fasting insulin levels, to distal chromosome 19 in a leptin-deficient obese F2 intercross derived from C57BL/6 (B6) and BTBR T+ tf/J (BTBR) mice. Introgression of a 7-Mb segment of the B6 chromosome 19 into the BTBR background (strain 1339A) replicated the reduced insulin linked to T2dm2. The 1339A mice have markedly impaired insulin secretion in vivo and disrupted islet morphology. We used subcongenic strains derived from 1339A to localize the T2dm2 quantitative trait locus (QTL) to a 242-kb segment comprising the promoter, first exon and most of the first intron of the Sorcs1 gene. This was the only gene in the 1339A strain for which we detected amino acid substitutions and expression level differences between mice carrying B6 and BTBR alleles of this insert, thereby identifying variation within the Sorcs1 gene as underlying the phenotype associated with the T2dm2 locus. SorCS1 binds platelet-derived growth factor, a growth factor crucial for pericyte recruitment to the microvasculature, and may thus have a role in expanding or maintaining the islet vasculature. Our identification of the Sorcs1 gene provides insight into the pathway underlying the pathophysiology of obesity-induced type 2 diabetes mellitus.

Diazobutanone-assisted isobaric labelling of phospholipids and sulfated glycolipids enables multiplexed quantitative lipidomics using tandem mass spectrometry.

Mass spectrometry-based quantitative lipidomics is an emerging field aiming to uncover the intricate relationships between lipidomes and disease development. However, quantifying lipidomes comprehensively in a high-throughput manner remains challenging owing to the diverse lipid structures. Here we propose a diazobutanone-assisted isobaric labelling strategy as a rapid and robust platform for multiplexed quantitative lipidomics across a broad range of lipid classes, including various phospholipids and glycolipids. The diazobutanone reagent is designed to conjugate with phosphodiester or sulfate groups, while accommodating various functional groups on different lipid classes, enabling subsequent isobaric labelling for high-throughput multiplexed quantitation. Our method demonstrates excellent performance in terms of labelling efficiency, detection sensitivity, quantitative accuracy and broad applicability to various biological samples. Finally, we performed a six-plex quantification analysis of lipid extracts from lean and obese mouse livers. In total, we identified and quantified 246 phospholipids in a high-throughput manner, revealing lipidomic changes that may be associated with obesity in mice.

SCD1 activity in muscle increases triglyceride PUFA content, exercise capacity, and PPARδ expression in mice.

Stearoyl-CoA desaturase (SCD)1 converts saturated fatty acids into monounsaturated fatty acids. Using muscle overexpression, we sought to determine the role of SCD1 expression in glucose and lipid metabolism and its effects on exercise capacity in mice. Wild-type C57Bl/6 (WT) and SCD1 muscle transgenic (SCD1-Tg) mice were generated, and expression of the SCD1 transgene was restricted to skeletal muscle. SCD1 overexpression was associated with increased triglyceride (TG) content. The fatty acid composition of the muscle revealed a significant increase in polyunsaturated fatty acid (PUFA) content of TG, including linoleate (18:2n6). Untrained SCD1-Tg mice also displayed significantly increased treadmill exercise capacity (WT = 6.6 ± 3 min, Tg = 71.9 ± 9.5 min; P = 0.0009). SCD1-Tg mice had decreased fasting plasma glucose, glucose transporter (GLUT)1 mRNA, fatty acid oxidation, mitochondrial content, and increased peroxisome proliferator-activated receptor (PPAR)δ and Pgc-1 protein expression in skeletal muscle. In vitro studies in C2C12 myocytes revealed that linoleate (18:2n6) and not oleate (18:1n9) caused a 3-fold increase in PPARδ and a 9-fold increase in CPT-1b with a subsequent increase in fat oxidation. The present model suggests that increasing delta-9 desaturase activity of muscle increases metabolic function, exercise capacity, and lipid oxidation likely through increased PUFA content, which increases PPARδ expression and activity. However, the mechanism of action that results in increased PUFA content of SCD1-Tg mice remains to be elucidated.

Efficient in vivo neuronal genome editing in the mouse brain using nanocapsules containing CRISPR-Cas9 ribonucleoproteins.

Genome editing of somatic cells via clustered regularly interspaced short palindromic repeats (CRISPR) offers promise for new therapeutics to treat a variety of genetic disorders, including neurological diseases. However, the dense and complex parenchyma of the brain and the post-mitotic state of neurons make efficient genome editing challenging. In vivo delivery systems for CRISPR-Cas proteins and single guide RNA (sgRNA) include both viral vectors and non-viral strategies, each presenting different advantages and disadvantages for clinical application. We developed non-viral and biodegradable PEGylated nanocapsules (NCs) that deliver preassembled Cas9-sgRNA ribonucleoproteins (RNPs). Here, we show that the RNP NCs led to robust genome editing in neurons following intracerebral injection into the healthy mouse striatum. Genome editing was predominantly observed in medium spiny neurons (>80%), with occasional editing in cholinergic, calretinin, and parvalbumin interneurons. Glial activation was minimal and was localized along the needle tract. Our results demonstrate that the RNP NCs are capable of safe and efficient neuronal genome editing in vivo.

Hepatic stearoyl-CoA desaturase-1 deficiency protects mice from carbohydrate-induced adiposity and hepatic steatosis.

Stearoyl-CoA desaturase-1 (SCD1), a critical regulator of energy metabolism, catalyzes the synthesis of monounsaturated fats. To understand the tissue-specific role of SCD1 in energy homeostasis, we used Cre-lox technology to generate mice with a liver-specific knockout of Scd1 (LKO). LKO mice were protected from high-carbohydrate, but not high-fat (HF), diet-induced adiposity and hepatic steatosis. Additionally, on a high-sucrose, very low-fat (HSVLF) diet, lipogenesis and levels of nuclear SREBP-1 and ChREBP were significantly decreased in the livers of LKO relative to Scd1(lox/lox) (Lox) mice. HSVLF feeding in LKO mice caused hypoglycemia and hepatic carbohydrate reduction due to an impairment of gluconeogenesis. Oleate, but not stearate, supplementation normalized adiposity, gluconeogenesis, triglyceride secretion, and hepatic lipogenesis of LKO mice. These results indicate that hepatic SCD1 expression (and thus, oleate) is required for carbohydrate-induced adiposity, but SCD1 inhibition in extrahepatic tissues is required to protect mice from HF-induced obesity and insulin resistance.

Combined deletion of SCD1 from adipose tissue and liver does not protect mice from obesity.

Stearoyl-CoA desaturase 1 (SCD1) catalyzes the synthesis of monounsaturated fatty acids (MUFA) from saturated FA. Mice with whole-body or skin-specific deletion of SCD1 are resistant to obesity. Here, we show that mice lacking SCD1 in adipose and/or liver are not protected from either genetic- (agouti; A(y)/a) or diet-induced obesity (DIO) despite a robust reduction in SCD1 MUFA products in both subcutaneous and epididymal white adipose tissue. Adipose SCD1 deletion had no effect on glucose or insulin tolerance or on hepatic triglyceride (TG) accumulation. Interestingly, lack of SCD1 from liver lowered the MUFA levels of adipose tissue and vice versa, as reflected by the changes in FA composition. Simultaneous deletion of SCD1 from liver and adipose resulted in a synergistic lowering of tissue MUFA levels, especially in the A(y)/a model in which glucose tolerance was also improved. Lastly, we found that liver and plasma TG show nearly identical genotype-dependent differences in FA composition, indicating that FA composition of plasma TG is predictive for hepatic SCD1 activity and TG FA composition. The current study suggests that SCD1 deletion from adipose and/or liver is insufficient to elicit protection from obesity, but it supports the existence of extensive lipid cross-talk between liver and adipose tissue.

Aromatase Inhibition Eliminates Sexual Receptivity Without Enhancing Weight Gain in Ovariectomized Marmoset Monkeys.

Context: Ovarian estradiol supports female sexual behavior and metabolic function. While ovariectomy (OVX) in rodents abolishes sexual behavior and enables obesity, OVX in nonhuman primates decreases, but does not abolish, sexual behavior, and inconsistently alters weight gain. Objective: We hypothesize that extra-ovarian estradiol provides key support for both functions, and to test this idea, we employed aromatase inhibition to eliminate extra-ovarian estradiol biosynthesis and diet-induced obesity to enhance weight gain. Methods: Thirteen adult female marmosets were OVX and received (1) estradiol-containing capsules and daily oral treatments of vehicle (E2; n = 5); empty capsules and daily oral treatments of either (2) vehicle (VEH, 1 mL/kg, n = 4), or (3) letrozole (LET, 1 mg/kg, n = 4). Results: After 7 months, we observed robust sexual receptivity in E2, intermediate frequencies in VEH, and virtually none in LET females (P = .04). By contrast, few rejections of male mounts were observed in E2, intermediate frequencies in VEH, and high frequencies in LET females (P = .04). Receptive head turns were consistently observed in E2, but not in VEH and LET females. LET females, alone, exhibited robust aggressive rejection of males. VEH and LET females demonstrated increased % body weight gain (P = .01). Relative estradiol levels in peripheral serum were E2 >>> VEH > LET, while those in hypothalamus ranked E2 = VEH > LET, confirming inhibition of local hypothalamic estradiol synthesis by letrozole. Conclusion: Our findings provide the first evidence for extra-ovarian estradiol contributing to female sexual behavior in a nonhuman primate, and prompt speculation that extra-ovarian estradiol, and in particular neuroestrogens, may similarly regulate sexual motivation in other primates, including humans.

Loss of Stearoyl-CoA desaturase-1 attenuates adipocyte inflammation: effects of adipocyte-derived oleate.

BACKGROUND AND PURPOSE: Adipose inflammation is crucial to the pathogenesis of metabolic disorders. This study aimed at identify the effects of stearoyl-CoA desaturase-1 (SCD1) on the inflammatory response of a paracrine network involving adipocytes, macrophages, and endothelial cells. METHODS AND RESULTS: Loss of SCD1 in both genetic (Agouti) and diet-induced obesity (high-fat diet) mouse models prevented inflammation in white adipose tissue and improved its basal insulin signaling. In SCD1-deficient mice, white adipose tissue exhibited lower inflammation, with a reduced response to lipopolysaccharide in isolated adipocytes, but not in peritoneal macrophages. Mimicking the in vivo paracrine regulation of white adipose tissue inflammation, SCD1-deficient adipocyte-conditioned medium attenuated the induction of tumor necrosis factor (TNF) alpha/interleukin 1beta gene expression in RAW264.7 macrophages and reduced the adhesion response in endothelial cells. We further demonstrated that the adipocyte-derived oleate (18:1n9), but not palmitoleate (16:1n7), mediated the inflammation in macrophages and adhesion responses in endothelial cells. CONCLUSIONS: Loss of SCD1 attenuates adipocyte inflammation and its paracrine regulation of inflammation in macrophages and endothelial cells. The reduced oleate level is linked to the inflammation-modulating effects of SCD1 deficiency.

Stearoyl-CoA desaturase and its relation to high-carbohydrate diets and obesity.

Obesity is currently a worldwide epidemic and public health burden that increases the risk for developing insulin resistance and several chronic diseases such as diabetes, cardiovascular diseases and non-alcoholic fatty liver disease. The multifactorial causes of obesity include several genetic, dietary and lifestyle variables that together result in an imbalance between energy intake and energy expenditure. Dietary approaches to limit fat intake are commonly prescribed to achieve the hypocaloric conditions necessary for weight loss. But dietary fat restriction is often accompanied by increased carbohydrate intake, which can dramatically increase endogenous fatty acid synthesis depending upon carbohydrate composition. Since both dietary and endogenously synthesized fatty acids contribute to the whole-body fatty acid pool, obesity can therefore result from excessive fat or carbohydrate consumption. Stearoyl-Coenzyme A desaturase-1 (SCD1) is a delta-9 fatty acid desaturase that converts saturated fatty acids into monounsaturated fatty acids (MUFA) and this activity is elevated by dietary carbohydrate. Mice lacking Scd1 are protected from obesity and insulin resistance and are characterized by decreased fatty acid synthesis and increased fatty acid oxidation. In this review, we address the association of high-carbohydrate diets with increased SCD activity and summarize the current literature on the subject of SCD1 and body weight regulation.

Adipose-specific deletion of stearoyl-CoA desaturase 1 up-regulates the glucose transporter GLUT1 in adipose tissue.

Stearoyl-CoA desaturase 1 (SCD1) deficiency protects mice from diet-induced obesity and insulin resistance. To understand the tissue-specific role of SCD1 in energy homeostasis, we have generated mice with an adipose-specific knockout of Scd1 (AKO), and report here that SCD1 deficiency increases GLUT1 expression in adipose tissue of AKO mice, but not global SCD1 knockout (GKO) mice. In 3T3-L1 adipocytes treated with an SCD inhibitor, basal glucose uptake and the cellular expression of GLUT1 were significantly increased while GLUT4 expression remained unchanged. Consistently, adipose-specific SCD1 knockout (AKO) mice had significantly elevated GLUT1 expression, but not GLUT4, in white adipose tissue compared to Lox counterparts. Concurrently, adiponectin expression was significantly diminished, whereas TNF-alpha expression was elevated. In contrast, in adipose tissue of GKO mice, GLUT4 and adiponectin expression were significantly elevated with lowered TNF-alpha expression and little change in GLUT1 expression, suggesting a differential responsiveness of adipose tissue to global- or adipose-specific SCD1 deletion. Taken together, these results indicate that adipose-specific deletion of SCD1 induces GLUT1 up-regulation in adipose tissue, associated with decreased adiponectin and increased TNF-alpha production, and suggest that GLUT1 may play a critical role in controlling glucose homeostasis of adipose tissue in adipose-specific SCD1-deficient conditions.

Probing the role of stearoyl-CoA desaturase-1 in hepatic insulin resistance.

Previous studies using stearoyl-CoA desaturase-1-deficient (SCD1-deficient) mice have shown that this enzyme plays an important role in many diseases of altered cellular metabolism including obesity, insulin resistance, and dyslipidemia. Although SCD1 activity is highest in lipogenic tissues such as the liver and adipose tissue, it is also present at lower levels in most tissues. To better understand the role of SCD1 in liver metabolism it is necessary to explore SCD1 deficiency in a more focused, tissue-specific manner. This commentary focuses on 2 recent studies published in the JCI that address this question using antisense oligonucleotide inhibition of SCD1. First, Jiang et al. have previously reported that long-term inhibition of SCD1 prevents the development of high-fat diet-induced obesity and hepatic steatosis. Second, Gutiérrez-Juárez et al. show in this issue that short-term inhibition of hepatic SCD1 is sufficient to prevent diet-induced hepatic insulin resistance, signifying an important role of hepatic SCD1 in liver insulin sensitivity (see related article beginning on page 1686).

Stearoyl-CoA desaturase-1 deficiency attenuates obesity and insulin resistance in leptin-resistant obese mice.

Obesity and adiposity greatly increase the risk for secondary conditions such as insulin resistance. Mice deficient in the enzyme stearoyl-CoA desaturase-1 (SCD1) are lean and protected from diet-induced obesity and insulin resistance. In order to determine the effect of SCD1 deficiency on various mouse models of obesity, we introduced a global deletion of the Scd1 gene into leptin-deficient ob/ob mice, leptin-resistant Agouti (A(y)/a) mice, and high-fat diet-fed obese (DIO) mice. SCD1 deficiency lowered body weight, adiposity, hepatic lipid accumulation, and hepatic lipogenic gene expression in all three mouse models. However, glucose tolerance, insulin, and leptin sensitivity were improved by SCD1 deficiency only in A(y)/a and DIO mice, but not ob/ob mice. These data uncouple the effects of SCD1 deficiency on weight loss from those on insulin sensitivity and suggest a beneficial effect of SCD1 inhibition on insulin sensitivity in obese mice that express a functional leptin gene.

Combined expression trait correlations and expression quantitative trait locus mapping.

Coordinated regulation of gene expression levels across a series of experimental conditions provides valuable information about the functions of correlated transcripts. The consideration of gene expression correlation over a time or tissue dimension has proved valuable in predicting gene function. Here, we consider correlations over a genetic dimension. In addition to identifying coregulated genes, the genetic dimension also supplies us with information about the genomic locations of putative regulatory loci. We calculated correlations among approximately 45,000 expression traits derived from 60 individuals in an F2 sample segregating for obesity and diabetes. By combining the correlation results with linkage mapping information, we were able to identify regulatory networks, make functional predictions for uncharacterized genes, and characterize novel members of known pathways. We found evidence of coordinate regulation of 174 G protein-coupled receptor protein signaling pathway expression traits. Of the 174 traits, 50 had their major LOD peak within 10 cM of a locus on Chromosome 2, and 81 others had a secondary peak in this region. We also characterized a Riken cDNA clone that showed strong correlation with stearoyl-CoA desaturase 1 expression. Experimental validation confirmed that this clone is involved in the regulation of lipid metabolism. We conclude that trait correlation combined with linkage mapping can reveal regulatory networks that would otherwise be missed if we studied only mRNA traits with statistically significant linkages in this small cross. The combined analysis is more sensitive compared with linkage mapping alone.

Liver gene expression analysis reveals endoplasmic reticulum stress and metabolic dysfunction in SCD1-deficient mice fed a very low-fat diet.

We previously reported that mice deficient in stearoyl-CoA desaturase-1 (Scd1) and maintained on a very low-fat (VLF) diet for 10 days developed severe loss of body weight, hypoglycemia, hypercholesterolemia, and many cholestasis-like phenotypes. To better understand the metabolic changes associated with these phenotypes, we performed microarray analysis of hepatic gene expression in chow- and VLF-fed female Scd1+/+ and Scd1-/- mice. We identified an extraordinary number of differentially expressed genes (>4,000 probe sets) in the VLF Scd1-/- relative to both VLF Scd1+/+ and chow Scd1-/- mice. Transcript levels were reduced for genes involved in detoxification and several facets of fatty acid metabolism including biosynthesis, elongation, desaturation, oxidation, transport, and ketogenesis. This pattern is attributable to the decreased mRNA abundance of several genes encoding key transcription factors, including LXRalpha, RXRalpha, FXR, PPARalpha, PGC-1beta, SREBP1c, ChREBP, CAR, DBP, TEF, and HLF. A robust induction of endoplasmic reticulum (ER) stress is indicated by enhanced splicing of XBP1, increased expression of the stress-induced transcription factors CHOP and ATF3, and elevated expression of several genes involved in the integrated stress and unfolded protein response pathways. The gene expression profile is also consistent with induction of an acute inflammatory response and macrophage recruitment. These results highlight the importance of monounsaturated fatty acid synthesis for maintaining metabolic homeostasis in the absence of sufficient dietary unsaturated fat and point to a novel cellular nutrient-sensing mechanism linking fatty acid availability and/or composition to the ER stress response.

Stearoyl-CoA desaturase deficiency, hypercholesterolaemia, cholestasis and diabetes.

Previous studies have shown that mice deficient in Scd1 have a dramatically reduced level of liver triglyceride and an improvement in insulin sensitivity. The mice are lean and partially protected from obesity induced by leptin deficiency or high fat diets. These results predicted that Scd1(-/-) mice would be protected from the increased serum triglyceride levels that result from a lipogenic diet and might also might protect a diabetes-susceptible obese mouse strain from diabetes. We studied Scd1(-/-) mice on a very low-fat high-carbohydrate lipogenic diet. The animals were almost entirely devoid of high density lipoprotein (HDL). Nonetheless, they were hypercholesterolaemic due to a large increase in low density lipoprotein (LDL). They had a high level of serum bilirubin and bile acids, and the appearance of lipoprotein-X, indicative of cholestasis. These changes were reversible with oil containing both mono- and polyunsaturated fat, but not entirely reversible with just triolein, suggesting that Scd1 deficiency increased the requirement for polyunsaturated fat. We performed hyperinsulinemic-euglycemic clamp experiments and found that the Scd1(-/-) mice on a normal chow diet had dramatically improved insulin sensitivity. But, surprisingly, leptin(ob/ob) Scd1(-/-) mice had worse diabetes than leptin(ob/ob) Scd1(wt/wt) mice. Thus, despite its effects on insulin sensitivity, Scdl deficiency worsens diabetes in leptin-deficient obese mice.

Stearoyl-CoA desaturase deficiency, hypercholesterolemia, cholestasis, and diabetes.

Previous studies showed that mice deficient in Scd1 had a reduced level of liver triglyceride and an improvement in insulin sensitivity. We studied Scd1(-/-) mice on a very low-fat, high-carbohydrate lipogenic diet. The animals were almost entirely devoid of high-density lipoprotein (HDL). Nonetheless, they were hypercholesterolemic and had cholestasis. These changes were reversible with oil containing both mono- and polyunsaturated fat, but not entirely reversible with just triolein, suggesting that Scd1 deficiency increased the requirement for polyunsaturated fat. We also found that the Scd1(-/-) mice on a normal chow diet had dramatically improved insulin sensitivity. However, leptin(ob/ob) Scd1(-/-) mice had worse diabetes than leptin(ob/ob) Scd1(wt/wt) mice.