SCD1 Deficiency Research Articles

Abstract 1898 SCD1 deficiency promotes hepatic fibrosis and cirrhosis under a high carbohydrate low-fat diet.

Abstract 1898 SCD1 deficiency promotes hepatic fibrosis and cirrhosis under a high carbohydrate low-fat diet.

Scd-1 deficiency promotes the differentiation of CD8+ T effector.

The impact of various fatty acid types on adaptive immunity remains uncertain, and their roles remain unelucidated. Stearoyl-CoA desaturase (Scd) is a Δ-9 desaturase, which is a key rate-limiting enzyme for the conversion of saturated fatty acids (SFA) to monounsaturated fatty acids (MUFA) in the fatty acid de novo synthesis. Scd-1 converts stearic acid (SA) and palmitic acid (PA) to oleic acid (OA) and palmitoleic acid (PO), respectively. In this study, through a series of experiments, we showed that Scd-1 and its resulting compound, OA, have a substantial impact on the transformation of CD8+ naïve T cells into effector T cells. Inactivation of Scd-1 triggers the specialization of CD8+ T cells into the Teff subset, enhancing the effector function and mitochondrial metabolism of Teff cells, and OA can partially counteract this. A deeper understanding of lipid metabolism in immune cells and its impact on cell function can lead to new therapeutic approaches for controlling the immune response and improving prognosis.

Dynamic role of Scd1 gene during mouse oocyte growth and maturation

Mammalian reproductive ability is regulated by many factors, among which the fatty acid metabolism network provides energy for oocyte growth and primordial follicle formation during early mouse oogenesis. But the mechanism behind that is still unknown. Stearoyl-CoA desaturase 1 (Scd1) gene expression is increased during the oogenesis process, supporting the oocyte's healthy growth. Taking advantage of gene-edited mice lacking stearoyl-Coenzyme A desaturase 1 gene (Scd1−/−), we analyzed relative gene expression in perinatal ovaries from wildtype, and Scd1−/− mice. Scd1 deficiency dysregulates expression of meiosis-related genes (e.g., Sycp1, Sycp2, Sycp3, Rad51, Ddx4) and a variety of genes (e.g., Nobox, Lhx8, Bmp15, Ybx2, Dppa3, Oct4, Sohlh1, Zp3) associated with oocyte growth and differentiation, leading to a lower oocyte maturation rate. The absence of Scd1 significantly impedes meiotic progression, causes DNA damage, and inhibits damage repair in Scd1−/− ovaries. Moreover, we find that Scd1 absense dramatically disrupts the abundance of fatty acid metabolism genes (e.g., Fasn, Srebp1, Acaca) and the lipid droplet content. Thus, our findings substantiate a major role for Scd1 as a multifunctional regulator of fatty acid networks necessary for oocyte maintenance and differentiation during early follicular genesis.

SCD1 deficiency exacerbates osteoarthritis by inducing ferroptosis in chondrocytes.

Osteoarthritis (OA) is a severe joint disease that causes cartilage destruction and mobility loss. Abnormal fatty acid metabolism of chondrocytes plays a role in OA development. Stearoyl-CoA desaturase (SCD1) is a rate-limiting enzyme in the anabolism of unsaturated fatty acids. This study aimed to investigate the role of the SCD1 protein in the degenerative process of OA. The GSE176199 gene expression profile dataset was analyzed by Gene Set Enrichment Analysis (GSEA). An animal model of OA was established using C57BL/6J wild-type (WT) (n=40) and SCD1 knockout (SCD1-KO) (n=20) mice. The histological scoring method of the Osteoarthritis Research Society International (OARSI) was used to quantify the degree of cartilage degeneration. The expression of SCD1 protein and relevant ferroptosis indicators were evaluated. The GSEA analysis showed that unsaturated fatty acid synthesis was inhibited in human OA chondrocytes. Meanwhile, the expression of SCD1 protein was significantly reduced in human OA articular cartilage. SCD1-KO mice exhibited early OA and accelerated cartilage loss after destabilization of medial meniscus (DMM)-induced OA. Furthermore, we found that the SCD1-PPARG axis regulates articular cartilage homeostasis via a mechanism involving the induction of ferroptosis-related gene expression in ATDC5 chondrocytes. SCD1 deficiency exacerbates OA by inducing ferroptosis in chondrocytes.

Scd1 Deficiency in Early Embryos Affects Blastocyst ICM Formation through RPs-Mdm2-p53 Pathway.

Embryos contain a large number of lipid droplets, and lipid metabolism is gradually activated during embryonic development to provide energy. However, the regulatory mechanisms remain to be investigated. Stearoyl-CoA desaturase 1 (Scd1) is a fatty acid desaturase gene that is mainly involved in intracellular monounsaturated fatty acid production, which takes part in many physiological processes. Analysis of transcripts at key stages of embryo development revealed that Scd1 was important and expressed at an increased level during the cleavage and blastocyst stages. Knockout Scd1 gene by CRISPR/Cas9 from zygotes revealed a decrease in lipid droplets (LDs) and damage in the inner cell mass (ICM) formation of blastocyst. Comparative analysis of normal and knockout embryo transcripts showed a suppression of ribosome protein (RPs) genes, leading to the arrest of ribosome biogenesis at the 2-cell stage. Notably, the P53-related pathway was further activated at the blastocyst stage, which eventually caused embryonic development arrest and apoptosis. In summary, Scd1 helps in providing energy for embryonic development by regulating intra-embryonic lipid droplet formation. Moreover, deficiency activates the RPs-Mdm2-P53 pathway due to ribosomal stress and ultimately leads to embryonic development arrest. The present results suggested that Scd1 gene is essential to maintain healthy development of embryos by regulating energy support.

SCD1 Sustains Homeostasis of Bulge Niche via Maintaining Hemidesmosomes in Basal Keratinocytes.

Niche for stem cells profoundly influences their maintenance and fate during tissue homeostasis and pathological disorders; however, the underlying mechanisms and tissue-specific features remain poorly understood. Here, it is reported that fatty acid desaturation catabolized by stearoyl-coenzyme A desaturase 1 (SCD1) regulates hair follicle stem cells (HFSCs) and hair growth by maintaining the bulge, niche for HFSCs. Scd1 deletion in mice results in abnormal hair growth, an effect exerted directly on keratin K14+ keratinocytes rather than on HFSCs. Mechanistically, Scd1 deficiency impairs the level of integrin α6β4 complex and thus the assembly of hemidesmosomes (HDs). The disruption of HDs allows the aberrant activation of focal adhesion kinase and PI3K in K14+ keratinocytes and subsequently their differentiation and proliferation. The overgrowth of basal keratinocytes results in downward extension of the outer root sheath and interruption of bulge formation. Then, inhibition of PI3K signaling in Scd1-/- mice normalizes the bulge, HFSCs, and hair growth. Additionally, supplementation of oleic acid to Scd1-/- mice reestablishes HDs and the homeostasis of bulge niche, and restores hair growth. Thus, SCD1 is critical in regulating hair growth through stabilizing HDs in basal keratinocytes and thus sustaining bulge for HFSC residence and periodic activity.

Hepatic Oleate Regulates Insulin-like Growth Factor-Binding Protein 1 Partially through the mTORC1-FGF21 Axis during High-Carbohydrate Feeding.

Stearoyl-CoA desaturase-1 (SCD1) catalyzes the rate-liming step of monounsaturated fatty acid biosynthesis and is a key regulator of systemic glucose metabolism. Mice harboring either a global (GKO) or liver-specific deletion (LKO) of Scd1 display enhanced insulin signaling and whole-body glucose uptake. Additionally, GKO and LKO mice are protected from high-carbohydrate diet-induced obesity. Given that high-carbohydrate diets can lead to chronic metabolic diseases such as obesity, diabetes, and hepatic steatosis, it is critical to understand how Scd1 deficiency confers metabolically beneficial phenotypes. Here we show that insulin-like growth factor-binding protein 1 (IGFBP1), a hepatokine that has been reported to enhance insulin signaling, is significantly elevated in the liver and plasma of GKO and LKO mice fed a low-fat high-carbohydrate diet. We also observed that the expression of hepatic Igfbp1 is regulated by oleic acid (18:1n9), a product of SCD1, through the mTORC1-FGF21 axis both in vivo and in vitro.

Proteomics Insights into the Gene Network of cis9, trans11-Conjugated Linoleic Acid Biosynthesis in Bovine Mammary Gland Epithelial Cells.

Simple SummaryCis9, trans11-conjugated linoleic acid (c9, t11-CLA) is a bioactive compound that is mainly found in ruminant products and has a variety of beneficial biological functions in human health. However, the gene network of c9, t11-CLA biosynthesis in the mammary gland is still not well documented. Therefore, this study aimed to elucidate the stearoyl-coenzyme A desaturase (SCD1)-dependent gene network of c9, t11-CLA biosynthesis in MAC-T cells from the perspective of energy metabolism. The results showed that the deficiency of stearoyl-coenzyme A desaturase (SCD1), led by CAY10566, blocked the biosynthesis of c9, t11-CLA. In total, 60 SCD1-related proteins that were mainly involved in energy metabolism pathways were primary screened by Tandem mass tag-based quantitative proteomics analysis. Moreover, 17 proteins were validated under the parallel reaction monitoring analysis. Then, 11 genes involved in energy metabolism pathways were verified to have negative relationships with SCD1 after small RNA interference analysis. Based on the above results, we concluded that the 11 genes involved in energy metabolism pathways had an impact on the SCD1-dependent molecular mechanism of c9, t11-CLA biosynthesis. This study provided a fresh understanding of the gene network of c9, t11-CLA biosynthesis in the mammary gland from a metabolism perspective.The objective of the study was to elucidate the stearoyl-coenzyme A desaturase (SCD1)-dependent gene network of c9, t11-CLA biosynthesis in MAC-T cells from an energy metabolism perspective. The cells were divided into the CAY group (firstly incubated with CAY10566, a chemical inhibitor of SCD1, then incubated with trans-11-octadecenoic acid, (TVA)), the TVA group (only TVA), and the control group (without CAY, TVA). The c9, t11-CLA, and TVA contents were determined by gas chromatography. The mRNA levels of SCD1 and candidate genes were analyzed via real-time PCR. Tandem mass tag (TMT)-based quantitative proteomics, bioinformatic analysis, parallel reaction monitoring (PRM), and small RNA interference were used to explore genes involved in the SCD1-dependent c9, t11-CLA biosynthesis. The results showed that the SCD1 deficiency led by CAY10566 blocked the biosynthesis of c9, t11-CLA. In total, 60 SCD1-related proteins mainly involved in energy metabolism pathways were primarily screened by TMT-based quantitative proteomics analysis. Moreover, 17 proteins were validated using PRM analysis. Then, 11 genes were verified to have negative relationships with SCD1 after the small RNA interference analysis. Based on the above results, we concluded that genes involved in energy metabolism pathways have an impact on the SCD1-dependent molecular mechanism of c9, t11-CLA biosynthesis.

Scd1 controls de novo beige fat biogenesis through succinate-dependent regulation of mitochondrial complex II

Preadipocytes can give rise to either white adipocytes or beige adipocytes. Owing to their distinct abilities in nutrient storage and energy expenditure, strategies that specifically promote "beiging" of adipocytes hold great promise for counterbalancing obesity and metabolic diseases. Yet, factors dictating the differentiation fate of adipocyte progenitors remain to be elucidated. We found that stearoyl-coenzyme A desaturase 1 (Scd1)-deficient mice, which resist metabolic stress, possess augmentation in beige adipocytes under basal conditions. Deletion of Scd1 in mature adipocytes expressing Fabp4 or Ucp1 did not affect thermogenesis in mice. Rather, Scd1 deficiency shifted the differentiation fate of preadipocytes from white adipogenesis to beige adipogenesis. Such effects are dependent on succinate accumulation in adipocyte progenitors, which fuels mitochondrial complex II activity. Suppression of mitochondrial complex II by Atpenin A5 or oxaloacetic acid reverted the differentiation potential of Scd1-deficient preadipocytes to white adipocytes. Furthermore, supplementation of succinate was found to increase beige adipocyte differentiation both in vitro and in vivo. Our data reveal an unappreciated role of Scd1 in determining the cell fate of adipocyte progenitors through succinate-dependent regulation of mitochondrial complex II.

SCD1 regulates the AMPK/SIRT1 pathway and histone acetylation through changes in adenine nucleotide metabolism in skeletal muscle.

Stearoyl-CoA desaturase (SCD) is a rate-limiting enzyme that catalyzes the synthesis of monounsaturated fatty acids. It plays an important role in regulating skeletal muscle metabolism. Lack of the SCD1 gene increases the rate of fatty acid β-oxidation through activation of the AMP-activated protein kinase (AMPK) pathway and the upregulation of genes that are related to fatty acid oxidation. The mechanism of AMPK activation under conditions of SCD1 deficiency has been unclear. In the present study, we found that the ablation/inhibition of SCD1 led to AMPK activation in skeletal muscle through an increase in AMP levels whereas muscle-specific SCD1 overexpression decreased both AMPK phosphorylation and the adenosine monophosphate/adenosine triphosphate (AMP/ATP) ratio. Changes in AMPK phosphorylation that were caused by SCD1 down- and upregulation affected NAD+ levels following changes in NAD+ -dependent deacetylase sirtuin-1 (SIRT1) activity and histone 3 (H3K9) acetylation and methylation status. Moreover, mice with muscle-targeted overexpression of SCD1 were more susceptible to high-fat diet-induced lipid accumulation and the development of insulin resistance compared with wild-type mice. These data show that SCD1 is involved in nucleotide (ATP and NAD+ ) metabolism and suggest that the SCD1-dependent regulation of muscle steatosis and insulin sensitivity are mediated by cooperation between AMPK- and SIRT1-regulated pathways. Altogether, the present study reveals a novel mechanism that links SCD1 with the maintenance of metabolic homeostasis and insulin sensitivity in skeletal muscle.

656 Psoriasis and obesity: Stearoyl-CoA desaturase 1 deficient mice are resistant to imiquimod-induced psoriasiform dermatitis

Psoriasis is a chronic inflammatory skin condition whose severity has been linked with obesity. In patients with psoriasis, the likelihood of developing new-onset obesity is higher than those without psoriasis. Stearoyl-CoA desaturase (SCD), is an endoplasmic reticulum resident desaturase, that acts as a catalyst in the synthesis of monounsaturated fatty acids. Mice lacking SCD1 are insulin sensitive, resistant to development of obesity and exhibit suppressed fatty acid synthesis. We have earlier shown that skin specific deletion of SCD1 in mice (SKO) results in epidermal proliferation, sebaceous gland hypoplasia and elevated interleukin 6 levels. We hypothesized that SCD1 deficiency will render mice susceptible to imiquimod (IMQ)-induced psoriasiform dermatitis. A topical dose of 62.5 mg IMQ cream was applied daily to the shaved back region of SKO and SCD1 proficient FLOX counterparts for 14 days after which the mice were euthanized. Cumulative average skin thickness in SKO animals following IMQ application, measured prior to excision was significantly (36%) less than that in FLOX animals. Quantitation of epidermal thickness in H&E stained skin sections validated this observation. Further, histological analysis revealed that in spite of skin inflammation and hair follicle dysplasia associated with their genetic background, the degree of IMQ associated inflammatory changes in the SKO mice were remarkably less than that in FLOX counterparts. Keratin 14, the prototypic marker of dividing basal keratinocytes was elevated in IMQ-treated FLOX skin. Moreover, fatty acid binding protein 5, upregulated in psoriasis tissue was reduced in SKO skin. Our data suggests a complex relationship between fatty acid metabolism and cytoskeletal proteins driving aberrant cell proliferation in psoriatic skin. We propose that SCD1 inhibition could be a novel approach for the management of psoriasis, especially in obese individuals.

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.

Oleate activates SREBP-1 signaling activity in SCD1-deficient hepatocytes.

Stearoyl-CoA desaturase-1 (SCD1) is a key player in lipid metabolism. SCD1 catalyzes the synthesis of monounsaturated fatty acids (MUFA). MUFA are then incorporated into triacylglycerols and phospholipids. Previous studies have shown that Scd1 deficiency in mice induces metabolic changes in the liver characterized by a decrease in de novo lipogenesis and an increase in β-oxidation. Interestingly, Scd1-deficient mice show a decrease in the expression and maturation of the principal lipogenic transcription factor sterol receptor element binding protein-1 (SREBP-1). The mechanisms mediating this effect on de novo lipogenesis and β-oxidation have not been fully elucidated. We evaluated the role of SCD1 on de novo lipogenesis and β-oxidation in HepG2 cells. We also used Scd1-deficient mice and two strains of transgenic mice that produce either oleate (GLS5) or palmitoleate (GLS3) in a liver-specific manner. We demonstrate that the expression of β-oxidation markers increases in SCD1-deficient hepatocytes and suggest that this is due to an increase in cellular polyunsaturated fatty acid content. We also show that the changes in the level of SREBP-1 expression, for both the precursor and the mature forms, are mainly due to the lack of oleate in SCD1-deficient hepatocytes. Indeed, oleate treatment of cultured HepG2 cells or hepatic oleate production in chow-fed GLS5 mice can restore SREBP-1 expression and increase hepatic de novo lipogenesis. Finally, we show that oleate specifically increases SREBP-1 nuclear accumulation, suggesting a central role for oleate in SREBP-1 signaling activity.

Hepatic Stearoyl‐CoA Desaturase deficiency suppresses gluconeogenesis by regulating lipid profile of mitochondria

Obesity plays a central role in the metabolic syndrome, which includes hyperinsulinemia, hypertension, hyperlipidemia and an increased risk of atherosclerotic cardiovascular disease. A common health complication observed in obese patients is insulin resistance, a condition in which increased insulin levels are required to maintain normal blood glucose levels. Without proper intervention, the condition often deteriorates into type 2 diabetes mellitus, characterized by increased hepatic glucose production, and decreased glucose clearance by insulin‐responsive tissues. It has been suggested that high glucose is associated with increased oxidative stress, enhanced leukocyte‐endothelial interaction, and glycosylation of lipoproteins, apolipoproteins, and clotting factors. Identification of new therapeutic approaches to improve glycemic management via the inhibition of hepatic glucose production will be beneficial for diabetes, cardiovascular diseases and related metabolic disorders.Stearoyl‐CoA desaturase (SCD) expressed at high levels in several human tissues is required for the biosynthesis of oleate (18:1) and palmitoleate (16:1), which are the major monounsaturated fatty acids of membrane phospholipids, triglycerides and cholesterol esters. Given the multiple roles of monounsaturated fatty acids, variation in stearoyl‐CoA desaturase activity in mammals would be expected to have a major effect on lipid metabolism. We and others have reported that global deletion of SCD1 in mice dramatically increases whole body energy expenditure and the loss of SCD1 activity in the liver suppresses hepatic glucose production when mice were fed a lipogenic diet. We hypothesize that the deficiency of SCD alters energy metabolism at the cellular level via the regulation of mitochondria function. Our preliminary data suggest that hepatic SCD1 deficiency alters the lipid profile of mitochondria membrane, therefore alters the membrane potential and metabolic rate of the cell. In addition, we show that the pharmaceutical inhibition of SCD activity reduces hepatic glucose production in the cell culture conditions. These studies provide essential information on the role of SCD on energy metabolism and, at the same time validate hepatic SCD enzymes as therapeutic targets against hyperglycemia in disease conditions, such as diabetes and metabolic syndrome.Support or Funding InformationAmerican Diabetes Association 7‐13‐BS‐118

Hepatic SirT1-Dependent Gain of Function of Stearoyl-CoA Desaturase-1 Conveys Dysmetabolic and Tumor Progression Functions.

Obesity is associated with higher incidence of cancer, but the predisposing mechanisms remain poorly understood. The NAD(+)-dependent deacetylase SirT1 orchestrates metabolism, cellular survival, and growth. However, there is no unifying mechanism to explain the metabolic and tumor-related effects of SirT1. In this work, we demonstrate that genetic ablation of the endogenous inhibitor of SirT1, Deleted-in-Breast-Cancer-1 (Dbc1), unexpectedly results in obesity and insulin resistance. Dbc1 deficiency promoted SirT1-dependent gain of function of stearoyl-coenzyme A desaturase 1 (Scd1), increasing plasma and tissue levels of unsaturated fatty acids. The metabolic abnormalities in Dbc1(-/-) mice were reversed by ablation of hepatic SirT1 or by inhibition of Scd1 activity. Furthermore, loss of Dbc1 impaired activation of the master tumor suppressor p53 and treatment with an Scd1 inhibitor extended survival of tumor-prone TP53(-/-) mice by decreasing tumor-related death. Together, our findings illustrate a shared mechanism of obesity and tumor progression mediated by hepatic SirT1 and resulting in the activation of a key lipid synthetic enzyme, with potential therapeutic implications.

Systemic Down-Regulation of Delta-9 Desaturase Promotes Muscle Oxidative Metabolism and Accelerates Muscle Function Recovery following Nerve Injury

The progressive deterioration of the neuromuscular axis is typically observed in degenerative conditions of the lower motor neurons, such as amyotrophic lateral sclerosis (ALS). Neurodegeneration in this disease is associated with systemic metabolic perturbations, including hypermetabolism and dyslipidemia. Our previous gene profiling studies on ALS muscle revealed down-regulation of delta-9 desaturase, or SCD1, which is the rate-limiting enzyme in the synthesis of monounsaturated fatty acids. Interestingly, knocking out SCD1 gene is known to induce hypermetabolism and stimulate fatty acid beta-oxidation. Here we investigated whether SCD1 deficiency can affect muscle function and its restoration in response to injury. The genetic ablation of SCD1 was not detrimental per se to muscle function. On the contrary, muscles in SCD1 knockout mice shifted toward a more oxidative metabolism, and enhanced the expression of synaptic genes. Repressing SCD1 expression or reducing SCD-dependent enzymatic activity accelerated the recovery of muscle function after inducing sciatic nerve crush. Overall, these findings provide evidence for a new role of SCD1 in modulating the restorative potential of skeletal muscles.

Role of Hepatic Monounsaturated Fatty Acid Synthesis in Metabolic Regulation

Stearoyl‐CoA desaturase (SCD) catalyzes the de novo synthesis of monounsaturated fatty acids (MUFA) from saturated fatty acids. Past work demonstrated SCD1 deficiency impairs hepatic lipogenesis and protects against diet‐induced obesity. Our objective was to determine if hepatic MUFA synthesis is sufficient to restore the impaired lipogenic program in SCD1 global knockout mice (GKO). To address this, we produced liver‐specific transgenic mice expressing either human SCD5, which preferentially synthesizes oleate (18:1n‐9), or mouse SCD3, which preferentially synthesizes palmitoleate (16:1n‐7), and introduced these transgenes into GKO mice. Hepatic oleate synthesis largely prevented very‐low‐fat diet‐induced weight loss and increased white adipose tissue weight to a greater extent than hepatic palmitoleate. In females, hepatic SREBP‐1 maturation and lipogenic gene expression increased in hSCD5/GKO while expression of these genes remained low in mSCD3/GKO mice. Hepatic oleate increased plasma glucose levels greater than hepatic palmitoleate. This work suggests that hepatic MUFA are involved in regulation of lipogenesis and gluconeogenesis with oleate being more potent than palmitoleate. Supported by NIH.

Aryl Hydrocarbon Receptor–Mediated Induction of Stearoyl-CoA Desaturase 1 Alters Hepatic Fatty Acid Composition in TCDD-Elicited Steatosis

2,3,7,8-tetrachlorodibenzo-ρ-dioxin (TCDD) induces hepatic dyslipidemia mediated by the aryl hydrocarbon receptor (AhR). Stearoyl-CoA desaturase 1 (Scd1) performs the rate-limiting step in monounsaturated fatty acid (MUFA) synthesis, desaturating 16:0 and 18:0 into 16:1n7 and 18:1n9, respectively. To further examine the role of Scd1 in TCDD-induced hepatotoxicity, comparative studies were performed in Scd1(+/+) and Scd1(-/-) mice treated with 30 μg/kg TCDD. TCDD induced Scd1 activity, protein, and messenger RNA (mRNA) levels approximately twofold. In Scd1(+/+) mice, hepatic effects were marked by increased vacuolization and inflammation and a 3.5-fold increase in serum alanine aminotransferase (ALT) levels. Hepatic triglycerides (TRGs) were induced 3.9-fold and lipid profiling by gas chromatography-mass spectroscopy measured a 1.9-fold increase in fatty acid (FA) levels, consistent with the induction of lipid transport genes. Induction of Scd1 altered FA composition by decreasing saturated fatty acid (SFA) molar ratios 8% and increasing MUFA molar ratios 9%. Furthermore, ChIP-chip analysis revealed AhR enrichment (up to 5.7-fold), and computational analysis identified 16 putative functional dioxin response elements (DREs) within Scd1 genomic loci. Band shift assays confirmed AhR binding with select DREs. In Scd1(-/-) mice, TCDD induced minimal hepatic vacuolization and inflammation, while serum ALT levels remained unchanged. Although Scd1 deficiency attenuated TCDD-induced TRG accumulation, overall FA levels remained unchanged compared with Scd1(+/+) mice. In Scd1(-/-) mice, TCDD induced SFA ratios 8%, reduced MUFA ratios 13%, and induced polyunsaturated fatty acid ratios 5% relative to treated Scd1(+/+) mice. Collectively, these results suggest that AhR regulation of Scd1 not only alters lipid composition but also contributes to the hepatotoxicity of TCDD.

Metabolic Changes in Skin Caused by Scd1 Deficiency: A Focus on Retinol Metabolism

We previously reported that mice with skin-specific deletion of stearoyl-CoA desaturase-1 (Scd1) recapitulated the skin phenotype and hypermetabolism observed in mice with a whole-body deletion of Scd1. In this study, we first performed a diet-induced obesity experiment at thermoneutral temperature (33°C) and found that skin-specific Scd1 knockout (SKO) mice still remain resistant to obesity. To elucidate the metabolic changes in the skin that contribute to the obesity resistance and skin phenotype, we performed microarray analysis of skin gene expression in male SKO and control mice fed a standard rodent diet. We identified an extraordinary number of differentially expressed genes that support the previously documented histological observations of sebaceous gland hypoplasia, inflammation and epidermal hyperplasia in SKO mice. Additionally, transcript levels were reduced in skin of SKO mice for genes involved in fatty acid synthesis, elongation and desaturation, which may be attributed to decreased abundance of key transcription factors including SREBP1c, ChREBP and LXRα. Conversely, genes involved in cholesterol synthesis were increased, suggesting an imbalance between skin fatty acid and cholesterol synthesis. Unexpectedly, we observed a robust elevation in skin retinol, retinoic acid and retinoic acid-induced genes in SKO mice. Furthermore, SEB-1 sebocytes treated with retinol and SCD inhibitor also display an elevation in retinoic acid-induced genes. These results highlight the importance of monounsaturated fatty acid synthesis for maintaining retinol homeostasis and point to disturbed retinol metabolism as a novel contributor to the Scd1 deficiency-induced skin phenotype.

The Scd1 Gene Functions as a Tumor Suppressor In Leukemia Stem Cells

AbstractAbstract 201We have previously shown that the arachidonate 5-lipoxygenase gene (Alox5) functions as a critical regulator of leukemia stem cells (LSCs) in BCR-ABL-induced chronic myeloid leukemia (CML) in mice. The Alox5 pathway appears to represent a major molecular network in LSCs. Taking advantage of our DNA microarray analysis for the identification of critical genes regulated by BCR-ABL in LSCs, we identified a small group of candidate genes that likely play tumor suppressor roles in these stem cells, and among them, a gene called stearoyl-CoA desaturase 1 (Scd1), an endoplasmic reticulum enzyme catalyzing the biosynthesis of monounsaturated fatty acids from saturated fatty acids, was shown to have a strong inhibitory effect on survival of LSCs in CML mice. BCR-ABL transduced bone marrow cells from Scd1-/- mice induced CML much faster than BCR-ABL transduced wild type bone marrow cells, and overexpression of Scd1 dramatically delayed CML development. Therefore, we further investigated whether Scd1 suppresses LSCs. FACS analysis showed that the percentages and total numbers of LSCs (GFP+ Lin−c-Kit+Sca-1+) and long-term (GFP+ Lin−c-Kit+Sca-1+ CD34−) or short-term (GFP+ Lin−c-Kit+Sca-1+ CD34+) LSCs in bone marrow of recipients of BCR-ABL transduced Scd1-/- donor bone marrow cells were significantly higher than those in bone marrow of recipients of BCR-ABL transduced wild type donor bone marrow cells, suggesting that Scd1 suppresses LSCs. Next we did a competitive repopulation assay to examine the function of LSCs. LSCs were sorted by FACS from bone marrow of mice with primary CML induced by transplanting BCR-ABL-transduced Scd1-/- (CD45.2) or wild type (CD45.1) bone marrow cells. The sorted CD45.2 and CD45.1 LSCs were mixed in a 1:1 ratio, followed by transplantation into lethally irradiated recipient mice to induce secondary CML. At 8 weeks after transplantation, only less than 10% of GFP+Gr-1+ cells were CD45.1 leukemia cells derived from wild type mice, whereas more than 75%-80% of GFP+Gr-1+ cells in peripheral blood of the mice were CD45.2 leukemia cells derived from Scd1-/- mice. To determine how Scd1 deficiency affects the maintenance of LSCs, we examined the cell cycle and apoptosis of LSCs. We found the percentages of apoptotic LSCs (Annexin V+ cells) were significantly decreased in bone marrow and spleens from Scd1-/- CML mice compared to the wild type group; however, we did not observe significant differences in the cell cycle status of LSCs from bone marrow and spleen, indicating that Scd1 regulates apoptosis but not cell cycle of LSCs.PPARγ agonist rosiglitazone can increase Scd1 expression, and our real time PCR data showed that rosiglitazone significantly induced Scd1 expression in bone marrow cells from CML mice. Therefore, we used PPARγ agonist rosiglitazone to treat these cells, and observed that rosiglitazone treatment dramatically decreased LSCs and that loss of Scd1 partially rescued the effect of PPARγ agonist on LSCs. Further, we investigated the molecular mechanisms that may contribute to the acceleration of CML development resulting from Scd1 deficiency. The decreased apoptosis in LSCs from Scd1-/- CML mice led us to focus on apoptosis-related genes. Real time PCR analysis showed a significant decrease of p53 in Scd1-/- immature leukemia cells as compared with that in wild type immature leukemia cells; however, loss of Scd1 resulted in dramatically and modest increased expression of Bcl-2 and Mcl-1 respectively in immature leukemia cells. We also found that the tumor suppressor gene Pten was significantly downregulated in Scd1-/- LSCs. Together, our results demonstrate a novel tumor suppressor function of Scd1 in LSCs, and provide a rationale for suppressing LSCs by enhancing Scd1 expression. Disclosures:No relevant conflicts of interest to declare.