Recent investigations suggest that reducing stearoyl CoA desaturase (SCD) 1 expression confers protection against obesity and insulin resistance, whereas others show that increasing SCD1 expression protects cells from lipotoxicity. The overall aim of this thesis was to establish the role of SCD1 expression in fatty acid metabolism and insulin stimulated glucose disposal in skeletal muscle. In vitro and in vivo studies were conducted to investigate the relationship between fatty acid subtype, SCD1 expression and fuel metabolism. The role of fatty acid subtype on fatty acid metabolite accumulation and insulin resistance was initially examined in rats. Rats were provided with a low fat diet or a high fat diet consisting of predominantly saturated (SAT) or polyunsaturated fatty acids (PUFA). Rats fed a SAT diet were insulin resistant and had increased skeletal muscle diacylglycerol content whereas rats fed a PUFA diet retained insulin sensitivity and accumulated triacylglycerol rather than diacylglycerol. Interestingly, SCD1 mRNA and protein content were elevated in SAT rats compared with PUFA fed and control fed rats, indicating a possible involvement of SCD1 in the aetiology of insulin resistance. Subsequently, SCD1 expression was examined in the skeletal muscle of various rodent models of genetic and diet-induced obesity. SCD1 content was consistently upregulated in the skeletal muscle of obese rodents. To determine whether SCD1 contributes to or protects from fatty-acid induced insulin resistance, SCD1 levels were transiently altered in L6 skeletal muscle myotubes. Short interfering (si) RNA was used to decrease SCD1 content and a pcDNA3.1/HygromSCD1 vector was introduced to increase SCD1 content. Reducing SCD1 protein resulted in marked esterification of exogenous fatty acids into diacylglycerol and ceramide. Insulin-stimulated Akt (acute transforming retrovirus thymoma) phosphorylation and 2-deoxyglucose uptake were reduced with SCD1 siRNA. Exposure of L6 myotubes to palmitate abolished insulin-stimulated glucose uptake in both control and SCD1 siRNA myotubes. Transient overexpression of SCD1 resulted in triacylglycerol esterification but attenuated ceramide and diacylglycerol accumulation and protected myotubes from fatty acid-induced insulin resistance. Further, these changes were associated with reduced phosphorylation of c-Jun Amino-Terminal Kinase (JNK) and the inhibitor of IêB kinase (IKK), both of which impair insulin signalling. These studies indicated that SCD1 protects from cellular toxicity in L6 myotubes by preventing excessive accumulation of bioactive lipid metabolites. Collectively, these experiments indicate that increasing SCD1 expression may be a protective mechanism designed to prevent insulin resistance in obese phenotypes.

This thesis investigates the contributions of fatty acids (FA) to adipokine dysregulation and inflammation. Differentiated 3T3-L1 adipocytes were treated with palmitic, stearic, palmitoleic, and oleic acids and changes in adipokine gene expression were measured. Here it was determined that saturated FA (SFA) increased the expression of RANTES and monounsaturated FA (MUFA) decreased the expression of RANTES and IL-6; demonstrating that FA differentially regulate adipokine expression. Relationships between plasma levels of SFA, MUFA and C-reactive protein (CRP) were also identified in a human observational study, further demonstrating the link between FA and inflammation Moreover, an association was also found between stearoyl-CoA desaturase 1 (SCD1) activity and CRP, demonstrating that SCD1 activity contributes to the inflammatory state. Genetic variation in SCD1 was also found to alter plasma FA and CRP levels, thus contributing to systemic inflammation. Taken together, these results demonstrate that SFA and MUFA influence adipokine dysregulation and systemic inflammation.

No description available.

Studies were conducted to investigate: 1) desaturation of dietary trans-vaccenic acid (TVA, trans11-18:1) to the cis9,trans11-18:2 isomer of conjugated linoleic acid (9/11CLA), 2) effects of two conjugated linoleic acid isomers [9/11CLA or trans10,cis12-18:2 (10/12CLA)] and TVA on enzyme activities and mRNA abundance for lipogenic enzymes, and 3) regulation of stearoyl-CoA desaturase (SCD) gene transcription. In the first study, lactating mice were fed 3% linoleic acid (LA), or 2% LA plus 1% stearic acid (SA), 1% TVA, or 1% CLA mixture. Dietary TVA enriched the 9/11CLA content of carcass, liver, and mammary tissue of lactating mice. A similar enhancement of 9/11CLA also was observed in liver, but not carcass, of suckling pups nursing TVA-fed dams. The CLA mixture decreased mammary acetyl-CoA carboxylase (ACC) activity compared with other treatments. However, total fatty acid content of mammary tissue was reduced only when compared with TVA. In the second experiment, lactating mice were fed 3% canola oil (OA), or 2% OA plus 1% SA, 1% TVA, 1% 9/11CLA, or 1% 10/12CLA. Dietary TVA, 9/11CLA, and 10/12CLA decreased mRNA abundance for ACC and fatty acid synthase (FAS) in mammary tissue, suggesting each had the potential to reduce de novo fatty acid synthesis. However, only the CLA isomers decreased ACC activity in mammary tissue and concentration of medium-chain fatty acids (MCFA = 12:0+14:0+16:0) in milk fat. The 10/12CLA isomer caused greater reductions in MCFA and milk fat percentage than the 9/11CLA, indicating that 10/12CLA is the primary CLA isomer affecting lipid metabolism in the mammary gland. Dietary TVA, 9/11CLA, or 10/12CLA decreased SCD enzyme activity and mRNA abundance in mammary tissue. In study 3, mouse (COMMA-D/MME) and bovine (Mac-T) mammary epithelial cells were transfected with the putative promoter (600 bp) of SCD gene. The 9/11CLA reduced SCD gene transcription in mouse cells, but not bovine cells. Transcription, however, was reduced in both cell lines by 10/12CLA, linoleic acid, and linolenic acid. Thus, reduced SCD transcription in response to the CLA isomers in mouse mammary cells in vitro may provide an explanation for reduced SCD enzyme activity and mRNA abundance in mammary tissue when lactating mice were fed either of the CLA isomers. In contrast, stearic acid, oleic acid, and TVA did not affect SCD transcription. Although TVA did not reduce SCD transcription in mouse mammary cells in vitro, it did reduce SCD enzyme activity and mRNA abundance in mammary tissue when fed to lactating mice. The results suggested TVA may influence SCD mRNA processing or stability in the nucleus after transcription. Despite the reduction in SCD mRNA and enzyme activity, however, substantial quantities of TVA were desaturated to the 9/11CLA isomer when TVA was fed to lactating mice in the first two studies. Thus, dietary TVA provides an alternate supply of the anticarcinogenic 9/11CLA isomer in tissues. / Ph. D.

Studies were conducted to investigate the tissue distribution of stearoyl-CoA desaturase-1 (SCD) and the regulation of SCD1 protein expression by dietary fat, insulin, polyunsaturated fatty acids (PUFA), and linoleic acid (cis-9, cis-12 18:2). The first study examined tissue distribution of SCD1 protein in Holstein calves (n=6/diet) fed one of four milk replacer diets for a nine wk period after which they were sacrificed. Milk replacer diets varied in fat content and were formulated and administered as follows: 0.4 kg/d 20% protein, 20% fat (20:20; CON), 0.97 kg/d (28:20; HPLF), 0.97 kg/d (28:28; HPHF), or 1.46 kg/d (28:28; HPHF+). Samples of subcutaneous adipose tissue (AT), perirenal AT, omental AT, duodenum, proximal jejunum, distal jejunum, ileum, and liver were collected from calves fed the HPHF+ diet to determine SCD1 tissue distribution. Tissue homogenates were prepared and used for Western blotting. Additionally, dietary effects were analyzed on tissues expressing SCD1 protein for all 24 calves. The second study investigated the regulation of SCD1 protein expression by insulin, fatty acids increasing in degree of unsaturation, and increasing concentrations of linoleic (18:2) acid. Subcutaneous AT was collected from Smith Valley Meats in Rich Creek, VA and used to prepare explants cultured in treatment media for 24 h. Treatments consisted of insulin at 0, 7, 14, and 21 nM; stearic (18:0), oleic (18:1), linoleic (18:2), and linolenic (18:3) acids at 100 μM; and linoleic (18:2) acid at concentrations of 0, 25, 50, 75, and 100 μM. Tissue explant homogenates were used for Western blotting to detect SCD1. In the first study, we found that SCD1 protein was detectable in subcutaneous AT, perirenal AT, and omental AT; however, it was not detectable in liver or small intestine samples. Also, the HPHF+ diet increased SCD1 protein expression in subcutaneous AT and perireanl AT. In the second study, SCD1 protein expression increased linearly with insulin concentration. There was no fatty acid treatment effect, but there was a negative linear effect with increase in degree of unsaturation. Finally, there was no effect on SCD1 protein expression with linoleic acid increasing in concentration. In conclusion, results indicate that SCD1 protein expression was detected in bovine AT depots, regulated by dietary fat, insulin, and by PUFA . / Master of Science

Les patients SLA et les souris modèles présentent un dysfonctionnement métabolique qui coïncide avec le changement de concentration de différentes espèces lipidiques. Notre hypothèse est qu’un tel dysfonctionnement métabolique au niveau musculaire conduirait aux premiers changements observés dans la SLA. Nous avons montré que l’expression de la stéaroyl-coenzyme A désaturase 1 (SCD1), une enzyme clé de la synthèse des acides gras mono-insaturés à partir des acides gras saturés, est diminuée dans le muscle avant les premiers symptômes moteurs observés chez les souris modèles de SLA. Dans ce modèle murin, les altérations en acides gras au niveau circulant et hépatique, traduisant les changements de SCD1,apparaissent lors des premiers symptômes de la pathologie. De plus, l’inhibition pharmacologique de l’activité de SCD1 mime le phénotype métabolique des souris modèles de SLA. Notre étude a ainsi montré que la diminution de la SCD1 joue un rôle important pour l’activité neuromusculaire. Elle module les besoins énergétiques, maintien l’activité musculaire par augmentation du métabolisme oxydatif et agit sur l’expression de gènes impliqués dans le développement et le fonctionnement de la jonction neuromusculaire. De plus, l’ablation du gène SCD1 stimule la récupération fonctionnelle musculaire après lésion du nerf. L’inhibition pharmacologique de SCD1 apporte également une protection au muscle. Nous avons pu conclure de cette étude qu’une modification de l’expression de SCD1 ainsi que du profil d’acides gras peut apporter une protection au muscle pour lutter contre la pathologie. En outre, des inhibiteurs de l’activité enzymatique de la SCD1 pourraient être développés comme traitement thérapeutique dans la SLA. / ALS patients and mouse model manifest metabolic dysfunctions that coincide with the modified levels of various lipid species. We postulated that metabolic dysfunctions in muscles function as a leading preliminary change in ALS. We have noted that the expression of stearoyl-CoA desaturase 1 (SCD1), a key enzyme that synthesises monounsaturated fatty acids (MUFAs) from saturated fatty acids (SFAs), is diminished even at pre-symptomatic stage in the muscles of an ALS mouse model. In these mice, alterations in circulating and hepatic fatty acid composition, resulting from SCD1 modification, arise at a critical stage of disease onset. Of note, inhibition of SCD1 enzymatic activity by a specific pharmacological agent mimics the metabolicphenotype of the ALS mouse model. Our study also elucidates that the lack of SCD1 plays a vital role in neuromuscular function. It modulates energy supply, and maintains muscle activity by increasing oxidative metabolism and the expression of genes involved in neuromuscular junction development and function. In addition, ablation of SCD1 gene stimulates functional recovery of muscles after a nerve lesion. Pharmacological SCD1 inhibition also provides a protection to muscle function. We conclude that alteration in SCD1 expression and related altered fatty acid profile may protect muscles against pathology. Therefore, SCD1 inhibitors can be developed as a therapeutic intervention.

La sclérose latérale amyotrophique est une maladie neurodégénérative associée à un dysfonctionnement métabolique. Des altérations du métabolisme des lipides, décrites chez les patients SLA et les animaux modèles, pourraient participer à la mise en place des premières étapes de la maladie. L’objectif de cette thèse était d’étudier le rôle de la stéaroyl-coenzyme A désaturase 1 (SCD1), une enzyme clé du métabolisme des lipides, dans la SLA. En étudiant le profil d’acides gras périphériques dans un modèle de souris SLA, les souris SOD1m, nous avons vu une diminution de l’activité de la SCD1 dès les stades précoces (subcliniques) de la maladie. Cette diminution pourrait expliquer, à elle seule, les altérations du métabolisme des lipides caractéristiques de la SLA. La répercussion de la perte de l’activité de la SCD1 sur l’axe moteur a été étudiée. Une délétion du gène ou une inhibition pharmacologique de la SCD1 améliore la récupération fonctionnelle après lésion du nerf sciatique chez la souris sauvage. Nous avons cherché à voir si la perte d’activité de la SCD1 trouvée chez les souris SOD1m est un mécanisme de protection mis en place pour lutter contre l’évolution de la SLA. Nous avons traité des souris SOD1m avec un inhibiteur de l’activité de la SCD1. Le traitement a conduit à une augmentation du métabolisme oxydatif, une préservation de l’intégrité neuromusculaire ainsi qu’une amélioration de la survie des motoneurones. Nousconcluons que l’inhibition de la SCD1 représente une cible thérapeutique prometteuse dans la SLA. / Amyotrophic lateral sclerosis is a neurodegenerative disease, associated with metabolic dysfunction. Alteration of lipid metabolism has been documented in ALS patients and animal models, and could participate to the first pathological steps of the disease. The objective of this thesis was to study the role of stearoyl-CoA desaturase 1 (SCD1), a key enzyme of lipid metabolism, in ALS. By studying the profile of peripheral fatty acids in an animal model of ALS, the SOD1 mice, we found that SCD1 activity was strongly reduced at early (sub-clinical) disease stage, and that this reduction could explain in itself the alteration of lipid metabolism characteristic of ALS. The impact of loss of SCD1 activity for the motor axis was then studied. Genetic deletion or pharmacological inhibition of SCD1 enhanced functional recovery after sciatic nerve injury in mice. Wefurther explored if the loss of SCD1 activity found in SOD1 mice is a protective mechanism elicited in response to ALS. We treated SOD1 mice with an inhibitor of SCD1 activity. The treatment resulted in exacerbated muscular oxidative metabolism,preservation of neuromuscular integrity and enhanced motor neuron survival. We conclude that inhibition of SCD1 represents a promising therapeutic target for ALS.

The effect of exogenous unsaturated fatty acids on cellular fatty acid biosynthesis in mammary cells was examined. Under normal situations, even though the diet of a dairy cow contains considerable amounts of unsaturated fatty acids, viz. oleic acid (18:1) and linoleic acid (18:2), the major 18-carbon fatty acid that enters the circulation post-ruminally for delivery to the mammary gland is saturated fatty acid, viz. stearic acid (18:0). This is due to extensive ruminal biohydrogenation of unsaturated fatty acids. Studies have indicated that saturated fatty acids such as 18:0 are enhancers and that certain unsaturated fatty acids are inhibitors of de novo fatty acid synthesis in tissues such as the liver and adipose tissue. The present study investigated the effect of cis and trans isomers of 18:1 and 18:2 on de novo fatty acid synthesis and desaturation in mouse and bovine mammary epithelial cell cultures, and compared it with the effect caused by 18:0. In the first experiment 12.5, 25, 50 or 100 micromoles stearic acid (SA), oleic acid (OA), elaidic acid (EA), trans-vaccenic acid (TVA), linoleic acid (LA) or conjugated linoleic acid (CLA) were supplemented in the media of mouse mammary epithelial (MME) cells that were grown to confluence in Dulbecco's modified Eagle's medium (DMEM). As indicated by cellular palmitic acid (16:0) content and fatty acid synthetase (FAS) activity, when compared with SA all unsaturated fatty acid treatments inhibited de novo fatty acid synthesis in MME cells. In addition, OA at all concentrations and LA and CLA at 50 and 100 micromoles inhibited cellular stearoyl-CoA desaturase (SCD) activity and mRNA abundance. However, EA and TVA, when compared with SA, enhanced SCD activity and mRNA abundance at 12.5 and 25 micromoles. In the second experiment 25, 50 or 100 micromoles SA, OA, TVA, LA or CLA were supplemented in the media of bovine mammary epithelial cells that were grown to confluence in DMEM. As indicated by cellular 16:0 content, acetyl-CoA carboxylase (ACC) activity and FAS activity, treatment with the unsaturated fatty acids inhibited de novo fatty acid synthesis at all concentrations, when compared with SA. Unsaturated fatty acid treatments also reduced the abundance of ACC and FAS mRNA in the cells. When compared with SA at all treatment-concentrations, OA and LA inhibited whereas TVA and CLA enhanced cellular SCD activity and mRNA abundance in the bovine cells. In both cell types, CLA and TVA appeared to be the most potent inhibitors of saturated fatty acid biosynthesis. / Ph. D.

La recherche sur la maladie d’Alzheimer (MA) est concentrée, en grande partie, sur l’étude de ses principales caractéristiques histologiques, les plaques β-amyloïdes (Aβ) et les enchevêtrements neurofibrillaires. Cependant, les thérapies ciblant directement ces caractéristiques n’empêchent pas la progression de la MA. En plus de ces caractéristiques, la génétique a mis en évidence l’implication du métabolisme des lipides et de la réponse immunitaire dans la MA. Les perturbations du métabolisme lipidique est le prédicteur génétique le plus puissant du développement de la MA, mais ses mécanismes restent un mystère. Des travaux récents dans notre laboratoire ont montré que les triglycérides s’accumulent dans le cerveau des patients atteints de MA et des souris 3xTg, un modèle murin de la MA. Chez les souris 3xTg, ces triglycérides sont enrichis en acide oléique (AO), un acide gras monoinsaturé, et l’inhibition de l’enzyme de synthèse de l’AO, le stéaryle-CoA désaturase (SCD), réduit leur accumulation et contrecarre la perte précoce de la neurogenèse hippocampique et les troubles de mémoire. Nous avons donc testé si l’inhibition de la SCD peut inverser les changements dans le transcriptome et rétablir la fonction de l’hippocampe chez les souris 3xTg symptomatiques. En comparant aux souris contrôles, l’hippocampe de souris 3xTg possède des altérations transcriptomiques impliquées dans les processus reconnus pour être perturbés dans la MA. Leur hippocampe a également montré une baisse significative des épines dendritiques. De manière remarquable, les données de séquençage de l’ARN montrent que le traitement des souris 3xTg pendant un mois avec un inhibiteur de la SCD a sauvé des gènes liés à l’immunité et aux synapses. Les analyses tissulaires ont révélé que ce traitement a conduit à des améliorations de la densité des épines dendritiques. Nous avons également établi un modèle de microglie en culture et nos données préliminaires suggèrent que les oligomères Aβ pourrait être responsable de perturbations du métabolisme des lipides chez les microglies. En somme, ces études soulignent le potentiel d’un nouveau médicament ciblant SCD pour le traitement de la MA. / Alzheimer’s disease (AD) research has mainly focused on studying its main histological hallmarks, β-amyloid (Aβ) plaques, and neurofibrillary tangles. However, therapies directly targeting these hallmarks do not prevent AD progression. In addition to these hallmarks, genetics have highlighted the implication of lipid metabolism and immunity in AD. Disturbances in lipid metabolism are the single strongest genetic predictor of developing AD, but the underlying mechanisms remain poorly understood. Recent work in our laboratory showed that triglycerides accumulate in the brains of both AD patients and 3xTg mice, a mouse model of AD. In 3xTg mice, these triglycerides are enriched with monounsaturated fatty acid oleic acid (OA), and the inhibition of the OAsynthesizing enzyme stearoyl-CoA desaturase (SCD) reduced their accumulation and counteracts the early loss of hippocampal neurogenesis and memory deficits. Here, we tested whether SCD inhibition can reverse changes in the transcriptome and rescue hippocampal function in symptomatic 3xTg mice. Compared to their strain controls, the hippocampus of middle-aged, preplaque 3xTg mice showed transcriptomic alterations involved in processes recognized to be disrupted in AD. Their hippocampus also displayed significant reduction in dendritic spines. Remarkably, RNA sequencing data show that treatment of middle-aged 3xTg mice for one month with an SCD inhibitor rescued genes related to immunity and synapses. Tissue analyses revealed that this treatment led to improvements in dendritic spine density. We also established a model of microglia in culture and our preliminary data suggest that Aβ oligomers may be responsible for disruptions in microglial lipid metabolism. Together, these studies shed light on the potential of a novel drug target SCD for the treatment of AD.

<p>The development of the metabolic syndrome (MetS) and cardiovascular diseases have been suggested to be influenced more by the quality than the amount of dietary fat. The FA composition of serum lipids may be used as biomarkers of dietary fat quality. FAs can, however, also be endogenously synthesized by lipogenic enzymes such as elongases and desaturases. Three desaturases are important in humans: Stearoyl-CoA-desaturase (SCD), ∆6-desaturase (D6D) and ∆5-desaturase (D5D) and surrogate measures of desaturase activities can be estimated as product-to-precursor FA ratios.</p><p>In this thesis, we demonstrated that high SCD, D6D and low D5D estimated activities predicted MetS 20 years later, as well as cardiovascular and total mortality during a maximum of 33.7 years. The relation between D5D and MetS was independent of lifestyle and BMI, while the relation between SCD, D6D and MetS was confounded by BMI. Serum proportions of palmitic (16:0), palmitoleic (16:1) and dihomo-γ-linoleic acids were higher and the serum proportion of linoleic acid (LA) lower at baseline in those individuals who developed MetS. Further, LA was inversely related to mortality, while palmitic, palmitoleic and dihomo-γ-linoleic acids were directly associated with mortality. We also demonstrated that a diet rich in saturated fat “induced” a similar serum FA pattern (including estimated desaturase activities) that was associated with MetS, cardiovascular disease and mortality. We also propose that the SCD ratio [16:1/16:0] might be a novel and useful marker of dietary saturated fat, at least in Western high-fat diets. Finally, genetic variations in the human SCD1 gene were linked to obesity and insulin sensitivity, results that agree with data in SCD1 deficient mice.</p><p>This thesis suggests that dietary fat quality and endogenous desaturation may play a role in the development of metabolic and cardiovascular diseases and the results support current dietary guidelines.</p>