Stearoyl-CoA Desaturase Isoform Research Articles

SCD4 deficiency decreases cardiac steatosis and prevents cardiac remodeling in mice fed a high-fat diet

Stearoyl-CoA desaturase (SCD) is a lipogenic enzyme that catalyzes formation of the first double bond in the carbon chain of saturated fatty acids. Four isoforms of SCD have been identified in mice, the most poorly characterized of which is SCD4, which is cardiac-specific. In the present study, we investigated the role of SCD4 in systemic and cardiac metabolism. We used WT and global SCD4 KO mice that were fed standard laboratory chow or a high-fat diet (HFD). SCD4 deficiency reduced body adiposity and decreased hyperinsulinemia and hypercholesterolemia in HFD-fed mice. The loss of SCD4 preserved heart morphology in the HFD condition. Lipid accumulation decreased in the myocardium in SCD4-deficient mice and in HL-1 cardiomyocytes with knocked out Scd4 expression. This was associated with an increase in the rate of lipolysis and, more specifically, adipose triglyceride lipase (ATGL) activity. Possible mechanisms of ATGL activation by SCD4 deficiency include lower protein levels of the ATGL inhibitor G0/G1 switch protein 2 and greater activation by protein kinase A under lipid overload conditions. Moreover, we observed higher intracellular Ca2+ levels in HL-1 cells with silenced Scd4 expression. This may explain the activation of protein kinase A in response to higher Ca2+ levels. Additionally, the loss of SCD4 inhibited mitochondrial enlargement, NADH overactivation, and reactive oxygen species overproduction in the heart in HFD-fed mice. In conclusion, SCD4 deficiency activated lipolysis, resulting in a reduction of cardiac steatosis, prevented the induction of left ventricular hypertrophy, and reduced reactive oxygen species levels in the heart in HFD-fed mice.

EXTH-23. PRECLINICAL EFFICACY OF A TARGETED, BRAIN PENETRANT INHIBITOR OF FATTY ACID DESATURATION IN GLIOBLASTOMA

Abstract There is increasing evidence that targeting de novo fatty acid synthesis could be effective for the treatment of primary and metastatic brain tumors, but brain penetrant inhibitors of this pathway are still lacking. We have previously reported that Stearoyl CoA Desaturase (SCD), a desaturase enzyme which converts saturated fatty acids into their unsaturated counterparts is a therapeutic target in glioblastoma (GBM). We showed that SCD exerts a cytoprotective role by protecting GBM cells against lipotoxicity and is essential for maintaining self-renewal and tumor initiating properties in GBM stem cells (GSCs). Using a panel of patient derived GSCs, mouse orthotopic GSC models, isogenic astrocytes models of gliomagenesis as well as in silico analysis, we report that in addition to SCD1, a second SCD isoform is also essential for GSCs maintenance. Further we demonstrate that while EGFR/PI3K/AKT signaling promotes lipogenesis, the activation of RAS/MEK/ERK signaling creates a metabolic vulnerability and sensitizes to SCD inhibitors. We tested a first-in-class, clinically relevant SCD inhibitor and showed that this compound effectively inhibits fatty acid desaturation in GSCs in a mouse orthotopic GSC model. Importantly, using different GSCs mouse models, we demonstrate that this SCD inhibitor can effectively increase overall survival as a monotherapy. Further, SCD inhibition impairs DNA-damage repair via homologous recombination thereby sensitizing to the standard of care therapeutics for GBM, ionizing radiation and temozolomide (TMZ). Consequently, combining this inhibitor with TMZ in mouse orthotopic GSC models leads to a significantly increased overall survival. Altogether, our results provide a deeper understanding of de novo fatty acid dynamics in GBM and support the clinical testing of a new SCD inhibitor, with favorable pharmacokinetic and pharmacodynamic properties, in patients diagnosed with GBM.

Stearoyl-CoA Desaturase-2 in Murine Development, Metabolism, and Disease.

Stearoyl-CoA Desaturase-2 (SCD2) is a member of the Stearoyl-CoA Desaturase (SCD) family of enzymes that catalyze the rate-limiting step in monounsaturated fatty acid (MUFA) synthesis. The MUFAs palmitoleoyl-CoA (16:1n7) and oleoyl-CoA (18:1n9) are the major products of SCD2. Palmitoleoyl-CoA and oleoyl-CoA have various roles, from being a source of energy to signaling molecules. Under normal feeding conditions, SCD2 is ubiquitously expressed and is the predominant SCD isoform in the brain. However, obesogenic diets highly induce SCD2 in adipose tissue, lung, and kidney. Here we provide a comprehensive review of SCD2 in mouse development, metabolism, and various diseases, such as obesity, chronic kidney disease, Alzheimer′s disease, multiple sclerosis, and Parkinson′s disease. In addition, we show that bone mineral density is decreased in SCD2KO mice under high-fat feeding conditions and that SCD2 is not required for preadipocyte differentiation or the expression of PPARγ in vivo despite being required in vitro.

Genes controlling polyunsaturated fatty acid synthesis are developmentally regulated in broiler chicks

ABSTRACT 1. The objective of this study was to characterise the regulation of the pathways that synthesise long-chain polyunsaturated fatty acids (PUFA) on developing adipose deposits in broiler embryos and chicks. Subcutaneous adipose depots were harvested from embryos and embryonic d E13, E15 and E17. Subcutaneous, abdominal and crop (neck) adipose, as well as liver, were collected at 7 and 14 d post-hatch. 2. Targeted RNA sequencing was used to quantify expression of 6 elongation of very long-chain fatty acid (ELOVL) genes, two isoforms of stearoyl-CoA desaturase (SCD and SCD5), and three fatty acid desaturases (FADS1, FADS2, and FADS6) in each depot and in the liver. Expression levels of marker genes for fatty acid oxidation and adipogenesis (peroxisome proliferator-activated receptor gamma (PPARG)) were quantified. Fatty acid composition of subcutaneous adipose was analysed using gas chromatograph–mass spectrometry (GC/MS). 3. Genes in the PUFA synthetic pathway were differentially expressed across developmental ages and between depots. These include elongase and desaturase genes, that have not previously been characterised in chicken. Correlation analyses identified subsets of co-regulated genes and fatty acids and highlighted relationships that may influence adipose metabolism and development. 4. It was concluded that PUFA synthesis is an active and dynamically regulated pathway in developing adipose deposits in the broiler chick. These data highlighted potential novel roles for specific elongase and desaturase genes in adipose deposition and metabolism.

Global deficiency of stearoyl-CoA desaturase-2 protects against diet-induced adiposity

In mouse, there are four stearoyl-CoA desaturase isoforms (SCD1-4) that catalyze the synthesis of monounsaturated fatty acids. Previously, we have shown that mice harboring a whole body deletion of the SCD1 isoform (SCD1KO) are protected from diet and genetically induced adiposity. Here, we report that global deletion of the SCD2 isoform (SCD2KO) provides a similar protective effect against the onset of both high-fat diet (HFD) and high-carbohydrate diet (HCD) induced adiposity. After 10 weeks of HFD feeding or 6 weeks of HCD feeding, SCD2KO mice failed to gain weight and had decreased fat mass. On HFD, SCD2KO mice remained glucose and insulin tolerant. Lastly, the markers for energy expenditure, UCP1 and PGC-1α, were increased in the brown adipose tissue of HFD fed SCD2KO mice.

186 Stearoyl-CoA desaturase-5 is upregulated in basal cell carcinoma: A role in aberrant cell proliferation in human skin

Stearoyl-CoA desaturase (SCD), a Δ9-desaturase that converts saturated fatty acids into monounsaturated fatty acids, is an important regulator of lipogenesis, cell proliferation and differentiation. To date, four mouse (14) and two human (1 and 5) isoforms of SCD have been identified. Human SCD-1 is abundantly expressed in lipogenic tissues, while increased expression of SCD-5 has been reported in the brain and pancreas. Importantly, both isoforms convert stearate to its unsaturated counterpart oleate. Mice lacking SCD-1 are protected from obesity and are characterized by suppressed fatty acid synthesis and enhanced oxidation. The biological function(s) of SCDs in the human skin are not well understood. Here we report that both isoforms, in particular SCD-5, is robustly expressed in human epidermal keratinocytes. Pharmacological inhibition of SCD-1 in keratinocytes resulted in induction of endoplasmic reticulum (ER) stress and activation of mTOR signaling. Parallel studies in skin specific SCD-1 KO mouse model indicated a similar increase in ER stress with activation of NF-κb and mTOR/S6 signaling. In normal keratinocytes, SCD-1 deficiency was not accompanied with significant alterations in oleate-to-stearate or palmitoleate-to-palmitate ratio. However, elevated oleate-to-stearate ratio in basal carcinoma cells compared to normal keratinocytes signified increased SCD activity in the malignant phenotype. Tissues from patients with basal cell carcinoma showed upregulated SCD-5 transcripts in tumor compared to non-lesional control skin. Intriguingly, increases in SCD-5 mRNA expression in tumor tissues were inversely proportional to SCD-1 levels. Western blot analysis validated elevated SCD-5 protein expression and activation of mTOR/S6 signaling in tumor tissues. Our studies provide novel insight into a potential regulatory loop driving aberrant cell proliferation through modulation of fatty acid metabolism in the human skin.

Bovine brain region-specific stearoyl-CoA desaturase expression and fatty acid composition.

In this study, we sought to determine the relationship between stearoyl-CoA desaturase (SCD) gene isoform expression in the bovine brain and the accumulation of 18:1n-9. Two SCD gene isoforms are found in cows-SCD1 and SCD5. Samples of six brain regions (cerebellum, frontal cortex, hippocampus, hypothalamus, midbrain, and pons) were collected from animals at four different ages (neonates, weanlings, yearlings, and adults) for mRNA isolation and fatty acid analysis. Expression of SCD1 and SCD5 mRNA was compared across age groups to determine its developmental regulation. Fatty acid composition and SCD isoform mRNA expression were compared to examine the correlation of SCD1 and SCD5 with 18:1n-9 content in different brain regions. We found statistically significant correlations between SCD1 and SCD5 mRNA expression and the ratio of 18:1n-9 to 18:0 across age groups, with stronger correlations observed for SCD5. Similarly, there was a significant correlation between the ratio of 18:1n-9 to 18:0 and SCD5 mRNA expression across brain regions. SCD1 mRNA and the 18:1n-9 to 18:0 ratio were negatively correlated in the hippocampus. There was no trend of increasing 18:1n-9 content or SCD expression with age. Correlations indicated a stronger relationship between SCD5 mRNA expression and the 18:1n-9 to 18:0 ratio, potentially indicating a strong contribution of the SCD5 isoform to brain 18:1n-9 content. This is the first study examining a potential role for SCD5 in providing 18:1n-9 for brain lipids.

Stearoyl‐CoA desaturase‐3 mediates the regulation of adipose and hepatic murine lipid metabolism (605.1)

Stearoyl‐CoA desaturase (SCD) is a critical enzyme involved in de novo lipogenesis and catalyzes the Δ9 desaturation of saturated fatty acids. Four SCD isoforms have been identified in mouse (SCD1‐4); SCD isoform 3 exhibits unique substrate specificity and tissue expression. While SCD1, 2, and 4 convert palmitate and stearate to palmitoleate and oleate, respectively, SCD3 preferentially desaturates palmitate. SCD3 expression is restricted to skin, harderian glands, preputial glands and differentiating adipocytes. To determine the role of SCD3 in murine lipid metabolism, we created a mouse model in which SCD3 is globally knocked out. Despite the limited tissue expression of this isoform, SCD3‐/‐ mice exhibit a global phenotype when fed a lipogenic low‐fat high‐carbohydrate diet. In contrast to SCD1 deletion, which protects mice from diet‐induced obesity and hepatic steatosis, deletion of SCD3 deletion predisposes mice to increased hepatic triglyceride accumulation under high‐carbohydrate feeding compared to SCD3flox mice. Gene expression studies in white adipose tissue reveal that SCD3 deletion and high‐carbohydrate feeding cause a transcriptional remodeling of subcutaneous white adipose tissue. Expression of genes involved in de novo lipogenesis, fatty acid oxidation, and uncoupling are simultaneously increased in the subcutaneous depot of SCD3‐/‐ mice.Grant Funding Source: Supported by NIH National Research Service Award T32 GM07215.

The role of stearoyl‐CoA desaturase‐3 in lipid metabolism

Stearoyl‐CoA desaturase (SCD) is a rate‐limiting enzyme in de novo lipogenesis that catalyzes the synthesis of monounsaturated fatty acids from saturated fatty acids. Four SCD isoforms have been identified in mouse (SCD1–4); SCD isoform 3 exhibits unique tissue expression and substrate specificity. While SCD1, 2, and 4 convert palmitate and stearate to palmitoleate and oleate, respectively, SCD3 preferentially desaturates palmitate. SCD3 expression is restricted to skin, harderian glands, and preputial glands. Despite the limited tissue expression of this isoform, SCD3−/− mice exhibit a global phenotype when fed a lipogenic low‐fat high‐carbohydrate diet. While deletion of SCD1 protects mice from diet‐induced obesity and hepatic steatosis, SCD3 deletion predisposes mice to increased lipogenesis in white adipose tissue and hepatic triglyceride accumulation. Gene expression studies in the harderian gland reveal that deletion of SCD1 causes a dramatic decrease in Scd3, while deletion of SCD3 results in an increase in Scd1. We propose that the observed increase in lipogenesis upon the deletion of this lipogenic enzyme stems from a regulatory mechanism between SCD isoforms. Funded by NIH.

The role of fatty acid desaturases in epidermal metabolism

The lipid composition of skin is important to a variety of functions served by this organ. Therefore, skin expresses multiple enzymes that synthesize and metabolize lipids. An important class of lipid metabolism enzymes expressed in skin is the lipid desaturases. Various isoforms of stearoyl-CoA desaturase, a delta-9 desaturase, as well as a delta-6 desaturase alter the lipid composition of the skin, thereby affecting skin barrier homeostasis and consequently, whole body energy balance. This review will focus on the role of fatty acid desaturases in maintaining epidermal metabolism.

Loss of stearoyl-CoA desaturase 1 rescues cardiac function in obese leptin-deficient mice

The heart of leptin-deficient ob/ob mice is characterized by pathologic left ventricular hypertrophy along with elevated triglyceride (TG) content, increased stearoyl-CoA desaturase (SCD) activity, and increased myocyte apoptosis. In the present study, using an ob/ob;SCD1(-/-) mouse model, we tested the hypothesis that lack of SCD1 could improve steatosis and left ventricle (LV) function in leptin deficiency. We show that disruption of the SCD1 gene improves cardiac function in ob/ob mice by correcting systolic and diastolic dysfunction without affecting levels of plasma TG and FFA. The improvement is associated with reduced expression of genes involved in FA transport and lipid synthesis in the heart, as well as reduction in cardiac FFA, diacylglycerol, TG, and ceramide levels. The rate of FA beta-oxidation is also significantly lower in the heart of ob/ob;SCD1(-/-) mice compared with ob/ob controls. Moreover, SCD1 deficiency reduces cardiac apoptosis in ob/ob mice due to increased expression of antiapoptotic factor Bcl-2 and inhibition of inducible nitric oxide synthase and caspase-3 activities. Reduction in myocardial lipid accumulation and inhibition of apoptosis appear to be one of the main mechanisms responsible for improved LV function in ob/ob mice caused by SCD1 deficiency.

Regulation of ovine and porcine stearoyl coenzyme A desaturase gene promoters by fatty acids and sterols1

Stearoyl CoA desaturase (SCD) is responsible for converting SFA into MUFA and plays an important role in regulating the fatty acid composition of tissues. Although the number of SCD isoforms differs among species, SCD-1 is the predominant isoform expressed in the major lipogenic tissues of all species studied. The SCD-1 gene promoter region has been cloned for several species, including the human, mouse, pig, and recently, the cow. In this study, we cloned and partially characterized the ovine SCD promoter region. Sequence alignment showed a high degree of similarity with published bovine (94%) and porcine (92%) sequences. This included a highly conserved PUFA response region, which was also similar to that found in the human SCD and mouse SCD-1 promoters. Previous studies have indicated that there may be species differences in the regulation of SCD promoter activity by fatty acids. Using promoter-reporter gene (luciferase) constructs transfected into both HEK 293 and McA-RH7777 cells (kidney- and liver-derived cell lines, respectively), we showed the activity of the SCD promoter from 4 different species (mouse, human, pig, and sheep) to be reduced in a dose-dependent manner by addition of unsaturated fatty acids to the media, with linoleic acid being more potent than oleic acid after a 24-h treatment at 60 microM. This effect was dependent on the presence of the PUFA response region. In each of the species studied, the PUFA response region of the SCD promoter was shown to have an active sterol response element, which responded to treatment of cells with sterol or overexpression of the truncated active form of sterol regulatory element binding protein-1c. Thus, any species differences in previously reported regulation of SCD expression by fatty acids are not due to differences in promoter structure between species, but are more likely to depend on the cell type being studied or the relative concentrations and distribution of sterol regulatory element binding proteins or other transcription factors.

Expression of Stearoyl-CoA desaturase isoforms in the brain and their changes in neuronal and glial cells during various kinds of brain injury

Expression of Stearoyl-CoA desaturase isoforms in the brain and their changes in neuronal and glial cells during various kinds of brain injury

Comparison of pig, sheep and chicken SCD5 homologs: Evidence for an early gene duplication event

Stearoyl-CoA desaturase (SCD) catalyzes the desaturation of saturated fatty acyl-CoA substrates at the delta-9 position. Multiple SCD isoforms are well characterized in rodents, especially in mice, where four isoforms have been described. In humans and cows, two SCD isoforms have been described: SCD1, which is a homolog of murine SCD1, and SCD5, which appears to be a distinct SCD gene rather than an ortholog of any of the four murine isoforms. In this paper, we describe for the first time SCD5 homologs in sheep, pigs and chickens. The SCD5 nucleotide sequences have notably higher GC content than SCD1 sequences, and the predicted protein sequences lack N-terminal PEST sequences typically found in SCD1 proteins. Similar to humans and bovines, the mRNA expression of sheep and pig SCD5 is greatest in the brain, and the mRNA expression of chicken SCD5 is greatest in the pancreas and brain. In contrast, SCD1 expression was found to be highest in adipose tissue in pigs and sheep, and liver in the chicken. This is the first report of an SCD5 homolog in a non-mammalian species, and suggests that SCD5 may be the result of an early gene duplication event that occurred before the divergence of mammals.

Dietary effects on mRNA levels of stearoyl-CoA desaturase isoforms in the hamster

Dietary effects on mRNA levels of stearoyl-CoA desaturase isoforms in the hamster

Role of stearoyl-CoA desaturase in human metabolic disease

Stearoyl-CoA desaturase (SCD) is a highly conserved Δ-9 desaturase that converts saturated fatty acids into monounsaturated fatty acids. Mice lacking the Scd1 gene are characterized by decreased adiposity and increased lipid oxidation and insulin sensitivity in liver and skeletal muscle. Two isoforms of SCD have also been identified in humans, and there appears to be an association between SCD expression and adiposity. This review will provide a brief update of recent progress in understanding the role of SCD in mediating the progression of disease in human populations, with a special emphasis on metabolic disease.

Identification and Characterization of Hamster Stearoyl‐CoA Desaturase Isoforms

Stearoyl-CoA desaturase (SCD) catalyzes the formation of monounsaturated fatty acids from saturated fatty acids. It plays a key role in lipid metabolism and energy expenditure in mammals. In mice, four SCD isoforms (SCD1-4) have been identified. Here we report the identification of cDNA sequences corresponding to SCD1, SCD2 and SCD3 of golden hamster. The deduced amino acid sequences of these hamster SCD (hmSCD) isoforms display a high degree of homologies to their mouse counterparts (mouse SCD). Polyclonal antibodies specific to rodent SCDs detected proteins of predicted size in the human embryonic kidney 293 cells transfected with hmSCD cDNAs. Microsome fractions prepared from these cells also displayed increased SCD activity versus cells transfected with vector alone. Real-time reverse transcription-polymerase chain reaction analysis revealed the highest expression of hmSCD1 in liver and adipose tissue, while the highest hmSCD2 expression was detected in the brain. Very low levels of hmSCD3 mRNA can be detected in the tissues tested. This report is the first description of three SCD isoforms in the hamster and will provide useful tools in the further study of fatty acids metabolism in this species.

Identification and Characterization of a Novel Bovine Stearoyl‐CoA Desaturase Isoform with Homology to Human SCD5

Stearoyl-CoA desaturase (SCD) is an enzyme responsible for the production of cis-9, trans-11 conjugated linoleic acid in ruminant fats, and for the synthesis of palmitoleoyl-CoA and oleoyl-CoA. To date, only one SCD isoform has been described in ruminant species, although multiple isoforms have been found in many other mammalian species. In this paper, we describe for the first time a second SCD isoform in cattle, which appears to be an ortholog of human SCD5 rather than a homolog of bovine SCD1 or any of the described murine SCD isoforms. As described in other SCD proteins, the predicted amino acid sequence of bovine SCD5 includes four transmembrane domains and three conserved histidine motifs. The amino-terminus of the predicted protein sequence of SCD5 lacks the PEST sequences typically found in SCD1 homologs, which are thought to target proteins for rapid degradation. Similar to human SCD5, the bovine SCD5 gene is organized into five exons and four introns, and is highly expressed in the brain. In other tissues examined, mRNA expression of SCD5 was minimal. Furthermore, the expression levels of SCD5 between brain gray and white matter are not different. This is the first description of a homolog of human SCD5 in a non-primate species.

A reduced protein diet induces stearoyl-CoA desaturase protein expression in pig muscle but not in subcutaneous adipose tissue: relationship with intramuscular lipid formation

A reduced protein diet (RPD) is known to increase the level of intramuscular lipid in pig meat with a smaller effect on the amount of subcutaneous adipose tissue. This might be due to tissue-specific activation of the expression of lipogenic enzymes by the RPD. The present study investigated the effect of a RPD, containing palm kernel oil, soyabean oil or palm oil on the activity and expression of one of the major lipogenic enzymes, stearoyl-CoA desaturase (SCD) and on the level of total lipids and the fatty acid composition of muscle and subcutaneous adipose tissue in pigs. The RPD significantly increased SCD protein expression and activity in muscle but not in subcutaneous adipose tissue. The level of MUFA and total fatty acids in muscle was also elevated when the RPD was fed, with only small changes in subcutaneous adipose tissue. A positive significant correlation between SCD protein expression and total fatty acids in muscle was found. The results suggest that an increase in intramuscular but not subcutaneous adipose tissue fatty acids under the influence of a RPD is related to tissue-specific activation of SCD expression. It is suggested that the SCD isoform spectra in pig subcutaneous adipose tissue and muscle might be different.

Membrane Topology of Mouse Stearoyl-CoA Desaturase 1

Stearoyl-CoA desaturase (SCD) is an integral membrane protein anchored in the endoplasmic reticulum. It catalyzes the biosynthesis of monounsaturated fatty acids that are required for the synthesis of triglycerides, cholesteryl esters, and phospholipids. Four mouse isoforms of SCD (SCD1-4) and two human isoforms have been characterized. In the current study, we characterize the topology of the mouse SCD1 isoform. Hydropathy analysis of the 355-amino acid mouse SCD1 protein predicts that the protein contains four transmembrane domains (TMDs) and three loops connecting the membrane-spanning domains. To define the topology of the protein, recombinant SCD1 constructs containing epitope tags were transiently expressed in HeLa cells and analyzed by indirect immunofluorescence and cysteine derivatization. Our data provide evidence that the N and C termini of SCD1 are oriented toward the cytosol with four transmembrane domains separated by two very short hydrophilic loops in the ER lumen and one large hydrophilic loop in the cytosol. In addition, based on the previous observation that SCD is a thiol enzyme, we sought to investigate whether the cysteine residues were essential for enzyme activity through mutagenesis studies, and our data suggest that the cysteines in SCD are not catalytically essential.