Hepatic oleate regulates one-carbon metabolism during high carbohydrate feeding.

Obesity is a major risk factor for type 2 diabetes, coronary heart disease, and strok. These diseases are associated with profound alterations in gene expression in metabolic tissues. Epigenetic-mediated regulation of gene expression is one mechanism through which environmental factors, such as diet, modify gene expression and disease predisposition. However, epigenetic control of gene expression in obesity and insulin resistance is not fully characterized. We discovered that liver-specific stearoyl-CoA desaturase-1 (Scd1) knockout mice (LKO) fed a high-carbohydrate low-fat diet exhibit dramatic changes in hepatic gene expression and metabolites of the folate cycle and one-carbon metabolism respectively for the synthesis of S-adenosylmethionine (SAM). LKO mice show an increased ratio of S-adenosylmethionine to S-adenosylhomocysteine, a marker for increased cellular methylation capacity. Furthermore, expression of DNA and histone methyltransferase genes is up-regulated while the mRNA and protein levels of the non-DNA methyltransferases including phosphatidylethanolamine methyltransferase (PEMT), Betaine homocysteine methyltransferase (Bhmt), and the SAM-utilizing enzymes such as glycine-N-methyltransferase (Gnmt) and guanidinoacetate methyltransferase (Gamt) are generally down-regulated. Feeding LKO mice a high carbohydrate diet supplemented with triolein, but not tristearin, and increased endogenous hepatic synthesis of oleate but not palmitoleate in Scd1 global knockout mice normalized one carbon gene expression and metabolite levels. Additionally, changes in one carbon gene expression are independent of the PGC-1α-mediated ER stress response previously reported in the LKO mice. Together, these results highlight the important role of oleate in maintaining one-carbon cycle homeostasis and point to observed changes in one-carbon metabolism as a novel mediator of the Scd1 deficiency-induced liver phenotype.

Inositol-Requiring Enzyme 1α-Mediated Synthesis of Monounsaturated Fatty Acids as a Driver of B Cell Differentiation and Lupus-like Autoimmune Disease.

OBJECTIVE: To explore the molecular mechanisms underlying dysregulation of lipid metabolism in the pathogenesis of systemic lupus erythematosus (SLE). METHODS: B cells in peripheral blood from patients with SLE and healthy controls were stained with BODIPY dye for detection of lipids. Mice with targeted knockout of genes for B cell-specific inositol-requiring enzyme 1α (IRE-1α) and stearoyl-coenzyme A desaturase 1 (SCD-1) were used for studying the influence of the IRE-1α/SCD-1/SCD-2 pathway on B cell differentiation and autoantibody production. The preclinical efficacy of IRE-1α suppression as a treatment for lupus was tested in MRL.Faslpr mice. RESULTS: In cultures with mouse IRE-1α-null B cells, supplementation with monounsaturated fatty acids largely rescued differentiation of plasma cells from B cells, indicating that the compromised capacity of B cell differentiation in the absence of IRE-1α may be attributable to a defect in monounsaturated fatty acid synthesis. Moreover, activation with IRE-1α/X-box binding protein 1 (XBP-1) was required to facilitate B cell expression of SCD-1 and SCD-2, which are 2 critical enzymes that catalyze monounsaturated fatty acid synthesis. Mice with targeted Scd1 gene deletion displayed a phenotype that was similar to that of IRE-1α-deficient mice, with diminished B cell differentiation into plasma cells. Importantly, in B cells from patients with lupus, both IRE-1α expression and Xbp1 messenger RNA splicing were significantly increased, and this was positively correlated with the expression of both Scd1 and Scd2 as well as with the amount of B cell lipid deposition. In MRL.Faslpr mice, both genetic and pharmacologic suppression of IRE-1α protected against the pathologic development and progression of lupus-like autoimmune disease. CONCLUSION: The results of this study reveal a molecular link in the dysregulation of lipid metabolism in the pathogenesis of lupus, demonstrating that the IRE-1α/XBP-1 pathway controls plasma cell differentiation through SCD-1/SCD-2-mediated monounsaturated fatty acid synthesis. These findings provide a rationale for targeting IRE-1α and monounsaturated fatty acid synthesis in the treatment of patients with SLE.

African Vegetables (Clerodendrum volibile Leaf and Irvingia gabonensis Seed Extracts) Effectively Mitigate Trastuzumab-Induced Cardiotoxicity in Wistar Rats.

Trastuzumab (TZM) is a humanized monoclonal antibody that has been approved for the clinical management of HER2-positive metastatic breast and gastric cancers but its use is limited by its cumulative dose and off-target cardiotoxicity. Unfortunately, till date, there is no approved antidote to this off-target toxicity. Therefore, an acute study was designed at investigating the protective potential and mechanism(s) of CVE and IGE in TZM-induced cardiotoxicity utilizing cardiac enzyme and oxidative stress markers and histopathological endpoints. 400 mg/kg/day CVE and IGE dissolved in 5% DMSO in sterile water were investigated in Wistar rats injected with 2.25 mg/kg/day/i.p. route of TZM for 7 days, using serum cTnI and LDH, complete lipid profile, cardiac tissue oxidative stress markers assays, and histopathological examination of TZM-intoxicated heart tissue. Results showed that 400 mg/kg/day CVE and IGE profoundly attenuated increases in the serum cTnI and LDH levels but caused no significant alterations in the serum lipids and weight gain pattern in the treated rats. CVE and IGE profoundly attenuated alterations in the cardiac tissue oxidative stress markers' activities while improving TZM-associated cardiac histological lesions. These results suggest that CVE and IGE could be mediating its cardioprotection via antioxidant, free radical scavenging, and antithrombotic mechanisms, thus, highlighting the therapeutic potentials of CVE and IGE in the management of TZM-mediated cardiotoxicity.

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.

Ferrous, but not ferric, iron maintains homeostasis in Histoplasma capsulatum triacylglycerides.

Iron is an indispensable micronutrient for virtually all microorganisms, where it acts as a cofactor of many enzymes involved in regulation of multiple cellular and physiological functions. This metal is also considered an important determinant contributing to the pathogenesis of fungal infectious diseases, and therefore the identification of iron-regulated metabolic processes occurring within the invading fungal cell can help the development of new antifungal therapeutic strategies. In this study, we examined relationships between iron availability and neutral storage lipids in Histoplasma capsulatum, a dimorphic fungus responsible for the most common respiratory and systemic mycosis in humans. Yeast cells were grown in a defined minimal medium supplemented with or without iron. Lipids were extracted from cells at the log and late stationary growth phases, then separated by thin-layer chromatography, and fatty acids were analyzed by gas chromatography. A culture age-related decrease in the unsaturated fatty acid content was observed in all four neutral lipid classes examined. Iron-related alterations could be seen in relation to triacylglycerol and free fatty acid pools, whereas no iron-dependent effects were detected in diacylglycerol and steryl ester fractions. Regarding triacylglycerols, the presence of iron positively affected the content of unsaturated fatty acids, and this stabilizing action of iron was notably increased when ferrous ions were added. Subsequent iron uptake studies showed a definite preference of H. capsulatum to acquire iron in its reduced, more soluble, ferrous form, and therefore, the availability of iron may be the underlying reason for the observed iron-maintained homeostasis in H. capsulatum triacylglycerols.

Polyunsaturated fatty acids do not activate AMP-activated protein kinase in mouse tissues.

Stearoyl-CoA desaturase 1 (SCD1) deficiency partitions fatty acids away from lipid synthesis towards fatty acid oxidation in liver and skeletal muscle in part due to activation of AMP-activated protein kinase (AMPK) pathway. The mechanism of AMPK activation by SCD1 mutation is unknown, however since SCD1-/- animals have increased relative amounts of polyunsaturated fatty acids (PUFA), we hypothesized that the increased levels of PUFA might be responsible for the activation of AMPK in SCD1 deficient mice. Therefore, the present study was undertaken to analyze the effect of PUFA on AMPK in liver, skeletal muscle, and heart. We fed mice ad libitum for 14 days with diet supplemented with fish oil (5% fat). As expected, fish oil supplementation significantly increased n-3 PUFA content in each of the analyzed tissues. Hepatic mRNA levels of fatty acid synthase and acyl-CoA oxidase decreased by 92% and increased by 60%, respectively, consistent with known PUFA effects. However, after 14 days of PUFA feeding, we did not find any changes in AMPK phosphorylation and protein content in mouse liver, skeletal muscle, and heart. The data suggest that PUFA are not involved in AMPK activation in mouse tissues and that the increased activity of AMPK in SCD1-/- mice is probably PUFA-independent.

Evidence that the anti-obesity effect of conjugated linoleic acid is independent of effects on stearoyl-CoA desaturase1 expression and enzyme activity.

The trans-10,cis-12 isomer of conjugated linoleic acid (CLA) reduces body fat gain in animals and inhibits stearoyl-CoA desaturase (SCD) activity in 3T3-L1 adipocytes. To test whether CLA's body fat reduction is mediated by SCD1, wild-type and SCD1-null mice were fed diet supplemented with 0.2% trans-10,cis-12 (t10c12) CLA for 4 weeks. The t10c12 CLA-supplemented diet significantly reduced body fat mass in both wild type and SCD1-null mice. Similarly, t10c12 CLA diet decreased blood triglyceride and free fatty acid levels regardless of SCD1 genotypes. Mice fed t10c12 CLA exhibited increased mRNA expression of fatty acid synthase and uncoupling protein 2 in both genotypes. Taken together, the effects of t10c12 CLA on reduction of body fat gain, blood parameters, and mRNA expression in both SCD1-null mice and wild-type mice were similar, indicating that the anti-obesity effect of t10c12 CLA may be independent of the effects of this CLA isomer on SCD1 gene expression and enzyme activity.

Identification and characterization of murine SCD4, a novel heart-specific stearoyl-CoA desaturase isoform regulated by leptin and dietary factors.

Stearoyl-CoA desaturase (SCD) is the rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids. Thus far, three isoforms of SCD (SCD1, SCD2, and SCD3) have been identified and characterized. Regulation of the SCD1 isoform has been shown to be an important component of the metabolic actions of leptin in liver, but the effects of leptin on SCD isoforms in other tissues have not been investigated. We found that although the mRNA levels of SCD1 and SCD2 were not affected by leptin deficiency in the hearts of ob/ob mice, the SCD activity and levels of monounsaturated fatty acids were increased, implying the existence of another SCD isoform. This observation has led to the cDNA cloning and characterization of a fourth SCD isoform (SCD4) that is expressed exclusively in the heart. SCD4 encodes a 352-amino acid protein that shares 79% sequence identity with the SCD1, SCD2, and SCD3 isoforms. Liver X receptor alpha (LXR alpha) agonists and a high carbohydrate fat-free diet induced SCD4 expression, but unlike SCD1, SCD4 expression was not repressed by dietary polyunsaturated fatty acids. SCD4 mRNA levels were elevated 5-fold in the hearts of leptin-deficient ob/ob mice relative to wild type controls. Treatment of ob/ob mice with leptin decreased mRNA levels of SCD4, whereas levels of SCD1 and SCD2 were not affected. Furthermore, in the hearts of SCD1-deficient mice, SCD4 mRNA levels were induced 3-fold, whereas the levels of SCD2 were not altered. The current studies identify a novel heart-specific SCD isoform that demonstrates tissue-specific regulation by leptin and dietary factors.