Stearoyl-CoA Desaturase 1 Is a Key Determinant of Membrane Lipid Composition in 3T3-L1 Adipocytes

MUFA synthesis and stearoyl-CoA desaturase as a new pharmacological target for modulation of lipid and alpha-synuclein interaction against Parkinson's disease synucleinopathy

Protein pathology spreading within the nervous system, accompanies neurodegeneration and a spectrum of motor and cognitive dysfunctions. Currently available therapies against Parkinson's disease and other synucleinopathies are mostly symptomatic and fail to slow the disease progression in the long term. Modification of α-synuclein (αS) aggregation and toxicity of its pathogenic forms is one of the main goals in neuroprotective approach. Since the discovery of lipid component of Lewy bodies, fatty acids became a crucial, yet little explored target for research. MUFAs (monounsaturated fatty acids) are substrates for lipids, such as phospholipids, triglycerides and cholesteryl esters. They regulate membrane fluidity, take part in signal transduction, cellular differentiation and other fundamental processes. αS and MUFA interactions are essential for Lewy body pathology. αS increases levels of MUFAs, mainly oleic acid, which in turn can enhance αS toxicity and aggregation. Thus, reduction of MUFAs synthesis by inhibition of stearoyl-CoA desaturase (SCD) activity could be the new way to prevent aggravation of αS pathology. Due to the limited distribution in peripheral tissues, SCD5 is a potential target in novel therapies and therefore could be an important starting point in search for disease-modifying neuroprotective therapy. Here we summarize facts about physiology and pathology of αS, explain recently discovered lipid-αS interactions, review SCD function and involved mechanisms, present available SCD inhibitors and discuss their pharmacological potential in disease management. Modulation of MUFA synthesis, decreasing αS and lipid toxicity is clearly essential, but unexplored avenue in pharmacotherapy of Parkinson's disease and synucleinopathies.

Targeting dysregulated lipid metabolism in the tumor microenvironment

The reprogramming of lipid metabolism and its association with oncogenic signaling pathways within the tumor microenvironment (TME) have emerged as significant hallmarks of cancer. Lipid metabolism is defined as a complex set of molecular processes including lipid uptake, synthesis, transport, and degradation. The dysregulation of lipid metabolism is affected by enzymes and signaling molecules directly or indirectly involved in the lipid metabolic process. Regulation of lipid metabolizing enzymes has been shown to modulate cancer development and to avoid resistance to anticancer drugs in tumors and the TME. Because of this, understanding the metabolic reprogramming associated with oncogenic progression is important to develop strategies for cancer treatment. Recent advances provide insight into fundamental mechanisms and the connections between altered lipid metabolism and tumorigenesis. In this review, we explore alterations to lipid metabolism and the pivotal factors driving lipid metabolic reprogramming, which exacerbate cancer progression. We also shed light on the latest insights and current therapeutic approaches based on small molecular inhibitors and phytochemicals targeting lipid metabolism for cancer treatment. Further investigations are worthwhile to fully understand the underlying mechanisms and the correlation between altered lipid metabolism and carcinogenesis.

A comparative analyses of lipid ratios representing desaturase enzyme activity between preterm and term infants within the first ten weeks of life

BACKGROUND

Desaturase enzymes play a key role in several pathways including biosynthesis of poly- and mono- unsaturated fatty acids (PUFAs, MUFA). In preterm infants, desaturase enzyme activity (DA) may be a rate-limiting step in maintaining PUFAs levels during this critical developmental window and impact on long term metabolic health. The study tested the hypothesis that DA is altered in preterm infants compared to term infants in early life and may be a marker of risk or contribute to later alterations in metabolic health.

METHODS

Lipidomic analyses were conducted using blood samples from two established UK-based cohorts, involving very preterm (n = 105) and term (n = 259) infants. Blood samples were taken from term infants at birth, two and six weeks and from preterm infants when established on enteral feeds and at term corrected age. DA of the 2 groups of infants were estimated indirectly from product/precursor lipids ratios of phosphatidylcholine (PC) and triglycerides (TG) species and reported according to their postmenstrual and postnatal ages.

RESULTS

There were changes in lipid ratios representing desaturase enzyme activity in preterm infants in the first weeks of life with higher delta 6 desaturases (D6D) triglyceride (TG) indices but significantly lower delta 9 desaturase (D9D) and D6D(PC) indices. In comparison to term infants, preterm have lower delta 5 desaturase (D5D) but higher D6D indices at all postnatal ages. Although point levels of desaturase indices were different, trajectories of changes in these indices over time were similar in preterm and term infants.

CONCLUSIONS

This study findings suggest the patterns of desaturase indices in preterm infants differ from that of term infants but their trajectories of change in the first 10 weeks of life were similar. These differences of DA if they persist in later life could contribute to the mechanism of diseases in preterm adulthood and warrant further investigations.

Protein Expression of AEBP1, MCM4, and FABP4 Differentiate Osteogenic, Adipogenic, and Mesenchymal Stromal Stem Cells

Mesenchymal stem cells (MSCs) gain an increasing focus in the field of regenerative medicine due to their differentiation abilities into chondrocytes, adipocytes, and osteoblastic cells. However, it is apparent that the transformation processes are extremely complex and cause cellular heterogeneity. The study aimed to characterize differences between MSCs and cells after adipogenic (AD) or osteoblastic (OB) differentiation at the proteome level. Comparative proteomic profiling was performed using tandem mass spectrometry in data-independent acquisition mode. Proteins were quantified by deep neural networks in library-free mode and correlated to the Molecular Signature Database (MSigDB) hallmark gene set collections for functional annotation. We analyzed 4108 proteins across all samples, which revealed a distinct clustering between MSCs and cell differentiation states. Protein expression profiling identified activation of the Peroxisome proliferator-activated receptors (PPARs) signaling pathway after AD. In addition, two distinct protein marker panels could be defined for osteoblastic and adipocytic cell lineages. Hereby, overexpression of AEBP1 and MCM4 for OB as well as of FABP4 for AD was detected as the most promising molecular markers. Combination of deep neural network and machine-learning algorithms with data-independent mass spectrometry distinguish MSCs and cell lineages after adipogenic or osteoblastic differentiation. We identified specific proteins as the molecular basis for bone formation, which could be used for regenerative medicine in the future.

Stearoyl-CoA Desaturase (SCD) Induces Cardiac Dysfunction with Cardiac Lipid Overload and Angiotensin II AT1 Receptor Protein Up-Regulation

Heart failure is a major cause of death worldwide with insufficient treatment options. In the search for pathomechanisms, we found up-regulation of an enzyme, stearoyl-CoA desaturase 1 (Scd1), in different experimental models of heart failure induced by advanced atherosclerosis, chronic pressure overload, and/or volume overload. Because the pathophysiological role of Scd1/SCD in heart failure is not clear, we investigated the impact of cardiac SCD upregulation through the generation of C57BL/6-Tg(MHCSCD)Sjaa mice with myocardium-specific expression of SCD. Echocardiographic examination showed that 4.9-fold-increased SCD levels triggered cardiac hypertrophy and symptoms of heart failure at an age of eight months. Tg-SCD mice had a significantly reduced left ventricular cardiac ejection fraction of 25.7 ± 2.9% compared to 54.3 ± 4.5% of non-transgenic B6 control mice. Whole-genome gene expression profiling identified up-regulated heart-failure-related genes such as resistin, adiponectin, and fatty acid synthase, and type 1 and 3 collagens. Tg-SCD mice were characterized by cardiac lipid accumulation with 1.6- and 1.7-fold-increased cardiac contents of saturated lipids, palmitate, and stearate, respectively. In contrast, unsaturated lipids were not changed. Together with saturated lipids, apoptosis-enhancing p53 protein contents were elevated. Imaging by autoradiography revealed that the heart-failure-promoting and membrane-spanning angiotensin II AT1 receptor protein of Tg-SCD hearts was significantly up-regulated. In transfected HEK cells, the expression of SCD increased the number of cell-surface angiotensin II AT1 receptor binding sites. In addition, increased AT1 receptor protein levels were detected by fluorescence spectroscopy of fluorescent protein-labeled AT1 receptor-Cerulean. Taken together, we found that SCD promotes cardiac dysfunction with overload of cardiotoxic saturated lipids and up-regulation of the heart-failure-promoting AT1 receptor protein.

SCD1, autophagy and cancer: implications for therapy

BACKGROUND

Autophagy is an intracellular degradation system that removes unnecessary or dysfunctional components and recycles them for other cellular functions. Over the years, a mutual regulation between lipid metabolism and autophagy has been uncovered.

METHODS

This is a narrative review discussing the connection between SCD1 and the autophagic process, along with the modality through which this crosstalk can be exploited for therapeutic purposes.

RESULTS

Fatty acids, depending on the species, can have either activating or inhibitory roles on autophagy. In turn, autophagy regulates the mobilization of fat from cellular deposits, such as lipid droplets, and removes unnecessary lipids to prevent cellular lipotoxicity. This review describes the regulation of autophagy by lipid metabolism in cancer cells, focusing on the role of stearoyl-CoA desaturase 1 (SCD1), the key enzyme involved in the synthesis of monounsaturated fatty acids. SCD1 plays an important role in cancer, promoting cell proliferation and metastasis. The role of autophagy in cancer is more complex since it can act either by protecting against the onset of cancer or by promoting tumor growth. Mounting evidence indicates that autophagy and lipid metabolism are tightly interconnected.

CONCLUSION

Here, we discuss controversial findings of SCD1 as an autophagy inducer or inhibitor in cancer, highlighting how these activities may result in cancer promotion or inhibition depending upon the degree of cancer heterogeneity and plasticity.

Comparisons of adipogenesis- and lipid metabolism-related gene expression levels in muscle, adipose tissue and liver from Wagyu-cross and Holstein steers

The intramuscular fat (IMF) content and fatty acid composition are important meat quality traits that are mostly affected by the cattle breed. Muscle, adipose tissue and liver are important organs involved in the development of intramuscular adipose tissue. Thus, we hypothesized that there were marked differences in the adipogenesis and lipid metabolism of these tissues between Wagyu-cross and Holstein steers during the finishing phases. To test this hypothesis, we analyzed the expression levels of adipogenesis- and lipid metabolism-related genes in longissimus muscle (LM), subcutaneous fat (SCF) and liver from Wagyu-cross and Holstein steers at 26 months of age. The IMF content and fatty acid profile of LM were determined. Wagyu-cross steers had a higher IMF content and MUFA percentages in the LM than Holstein steers (P<0.05). The relative expression of FGF2, COL1A1, SREBP1c, SCD1, GRP78 and LEP was greater in the LM of Wagyu-cross steers than in Holstein steers (P<0.05). In contrast, Holstein steer SCF had higher (P<0.05) mRNA expression levels of FABP4 and ADIPOQ than Wagyu-cross steers. In the liver, the expression of SREBP1c and GRP78 in Wagyu-cross steers was significantly higher than that in Holstein steers (P<0.05). The results demonstrate that both intramuscular adipogenesis and fibrogenesis are enhanced in Wagyu-cross steers compared with Holstein steers during the finishing phase and that IMF deposition is positively correlated with the maturity of SCF and hepatic lipid accumulation in Wagyu-cross steers.

Deletion of fatty acid transport protein 2 (FATP2) in the mouse liver changes the metabolic landscape by increasing the expression of PPARα-regulated genes

Fatty acid transport protein 2 (FATP2) is highly expressed in the liver, small intestine, and kidney, where it functions in both the transport of exogenous long-chain fatty acids and the activation of very-long-chain fatty acids. Here, using a murine model, we investigated the phenotypic impacts of deleting FATP2, followed by a transcriptomic analysis using unbiased RNA-Seq to identify concomitant changes in the liver transcriptome. WT and FATP2-null (Fatp2-/-) mice (5 weeks) were maintained on a standard chow diet for 6 weeks. The Fatp2-/- mice had reduced weight gain, lowered serum triglyceride, and increased serum cholesterol levels and attenuated dietary fatty acid absorption. Transcriptomic analysis of the liver revealed 258 differentially expressed genes in male Fatp2-/- mice and a total of 91 in female Fatp2-/- mice. These genes mapped to the following gene ontology categories: fatty acid degradation, peroxisome biogenesis, fatty acid synthesis, and retinol and arachidonic acid metabolism. Targeted RT-quantitative PCR verified the altered expression of selected genes. Of note, most of the genes with increased expression were known to be regulated by peroxisome proliferator-activated receptor α (PPARα), suggesting that FATP2 activity is linked to a PPARα-specific proximal ligand. Targeted metabolomic experiments in the Fatp2-/- liver revealed increases of total C16:0, C16:1, and C18:1 fatty acids; increases in lipoxin A4 and prostaglandin J2; and a decrease in 20-hydroxyeicosatetraenoic acid. We conclude that the expression of FATP2 in the liver broadly affects the metabolic landscape through PPARα, indicating that FATP2 provides an important role in liver lipid metabolism through its transport or activation activities.

A high-throughput platform for detailed lipidomic analysis of a range of mouse and human tissues

Lipidomics is of increasing interest in studies of biological systems. However, high-throughput data collection and processing remains non-trivial, making assessment of phenotypes difficult. We describe a platform for surveying the lipid fraction for a range of tissues. These techniques are demonstrated on a set of seven different tissues (serum, brain, heart, kidney, adipose, liver, and vastus lateralis muscle) from post-weaning mouse dams that were either obese (> 12 g fat mass) or lean (<5 g fat mass). This showed that the lipid metabolism in some tissues is affected more by obesity than others. Analysis of human serum (healthy non-pregnant women and pregnant women at 28 weeks' gestation) showed that the abundance of several phospholipids differed between groups. Human placenta from mothers with high and low BMI showed that lean placentae contain less polyunsaturated lipid. This platform offers a way to map lipid metabolism with immediate application in metabolic research and elsewhere. Graphical abstract.

Stearoyl-CoA desaturase (scd1a) is epigenetically regulated by broodstock nutrition in gilthead sea bream (Sparus aurata)

The aim of this study was to generate new knowledge on fish epigenetics, assessing the effects of linolenic acid (ALA) conditioning of broodstock in the offspring of the marine fish Sparus aurata. Attention was focused on gene organization, methylation signatures and gene expression patterns of fatty acid desaturase 2 (fads2) and stearoyl-CoA desaturase 1a (scd1a). Blat searches in the genomic IATS-CSIC database (www.nutrigroup-iats.org/seabreamdb) highlighted a conserved exon-intron organization, a conserved PUFA response region, and CG islands at the promoter regions of each gene. The analysed CpG positions in the fads2 promoter were mostly hypomethylated and refractory to broodstock nutrition. The same response was achieved after conditioning of juvenile fish to low water oxygen concentrations, thus methylation susceptibility at individual CpG sites seems to be stringently regulated in fish of different origin and growth trajectories. Conversely, the scd1a promoter was responsive to broodstock nutrition and the offspring of parents fed the ALA-rich diet shared an increased DNA-methylation, mainly in CpG sites neighbouring SP1 and HNF4α binding sites. Cytosine methylation at these sites correlated inversely with the hepatic scd1a expression of the offspring. Co-expression analyses supported that the HNF4α-dependent regulation of scd1a is affected by DNA methylation. The phenotypic output is a regulated liver fat deposition through changes in scd1 expression, which would also allow the preservation of fatty acid unsaturation levels in fish fed reduced levels of n-3 LC-PUFA. Collectively, these findings reveal a reliable mechanism by which parent's nutrition can shape scd1a gene expression in the fish offspring.

Stearoyl-CoA Desaturase 1 as a Therapeutic Target for the Treatment of Cancer

A distinctive feature of cancer cells of various origins involves alterations of the composition of lipids, with significant enrichment in monounsaturated fatty acids. These molecules, in addition to being structural components of newly formed cell membranes of intensely proliferating cancer cells, support tumorigenic signaling. An increase in the expression of stearoyl-CoA desaturase 1 (SCD1), the enzyme that converts saturated fatty acids to ∆9-monounsaturated fatty acids, has been observed in a wide range of cancer cells, and this increase is correlated with cancer aggressiveness and poor outcomes for patients. Studies have demonstrated the involvement of SCD1 in the promotion of cancer cell proliferation, migration, metastasis, and tumor growth. Many studies have reported a role for this lipogenic factor in maintaining the characteristics of cancer stem cells (i.e., the population of cells that contributes to cancer progression and resistance to chemotherapy). Importantly, both the products of SCD1 activity and its direct impact on tumorigenic pathways have been demonstrated. Based on these findings, SCD1 appears to be a significant player in the development of malignant disease and may be a promising target for anticancer therapy. Numerous chemical compounds that exert inhibitory effects on SCD1 have been developed and preclinically tested. The present review summarizes our current knowledge of the ways in which SCD1 contributes to the progression of cancer and discusses opportunities and challenges of using SCD1 inhibitors for the treatment of cancer.

Canonical Wnt Signaling Remodels Lipid Metabolism in Zebrafish Hepatocytes following Ras Oncogenic Insult

There is limited understanding of the effects of major oncogenic pathways and their combinatorial actions on lipid composition and transformation during hepatic tumorigenesis. Here, we report a negative correlation of Wnt/Myc activity with steatosis in human hepatocellular carcinoma (HCC) and perform in vivo functional studies using three conditional transgenic zebrafish models. Double-transgenic zebrafish larvae conditionally expressing human CTNNB1mt and zebrafish tcf7l2 or murine Myc together with krasv12 in hepatocytes led to severe hepatomegaly and significantly attenuated accumulation of lipid droplets and cell senescence triggered by krasv12 expression alone. UPLC-MS-based, nontargeted lipidomic profiling and transcriptome analyses revealed that Wnt/Myc activity promotes triacylglycerol to phospholipid transformation and increases unsaturated fatty acyl groups in phospholipids in a Ras-dependent manner. Small-scale screenings suggested that supplementation of certain free fatty acids (FA) or inhibition of FA desaturation significantly represses hepatic hyperplasia of double-transgenic larvae and proliferation of three human HCC cells with and without sorafenib. Together, our studies reveal novel Ras-dependent functions of Wnt signaling in remodeling the lipid metabolism of cancerous hepatocytes in zebrafish and identify the SCD inhibitor MK8245 as a candidate drug for therapeutic intervention.Significance: These findings identify FA desaturation as a significant downstream therapeutic target for antagonizing the combinatorial effects of Wnt and Ras signaling pathways in hepatocellular carcinoma.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/19/5548/F1.large.jpg Cancer Res; 78(19); 5548-60. ©2018 AACR.

Embelin attenuates adipogenesis and lipogenesis through activating canonical Wnt signaling and inhibits high-fat diet-induced obesity

BACKGROUND

Recent studies suggest that Embelin, a natural plant extract might have the potential to prevent body weight gain in rats. However, the mechanisms involved remain to be elucidated.

METHODS

Effects of Embelin on adipocyte differentiation and lipogenesis were studied in murine ST2 stromal cells and C3H10T1/2 mesenchymal cells. The mechanisms through which Embelin regulates adipogenic differentiation and lipogenesis were explored. The in vivo anti-obesity effects of Embelin in high-fat diet (HFD)-induced obesity mice and possible transcriptional impact were investigated.

RESULTS

Embelin treatment suppressed ST2 and C3H10T1/2 cells to proliferate, and differentiate into mature adipocytes, along with the inhibition of adipogenic factors peroxisome proliferator-activated receptor γ, CCAAT/enhancer binding protein-α, adipocyte protein 2 and adipsin. Embelin treatment also decreased the expression levels of lipogenic factors sterol regulatory element-binding protein 1, fatty acid synthase, acetyl-CoA carboxylase 1 and stearoyl-Coenzyme A desaturase 1. Embelin promoted the translocation of β-catenin from the cytoplasm into the nucleus in C3H10T1/2. The nuclear protein levels of β-catenin and TCF-4 were increased following Embelin treatment. Furthermore, Dickkopf-1 (Dkk1) expression was downregulated by Embelin, and overexpression of Dkk1 in C3H10T1/2 reversed the inhibition of adipogenesis and lipogenesis by Embelin. In vivo studies showed that Embelin treatment reduced the gain of body weight and fat, decreased the serum level of triglycerides, free fatty acid and total cholesterol, and improved glucose tolerance and insulin resistance in HFD-fed mice. Moreover, Embelin blocked induction of adipogenic and lipogenic factors and Dkk1 in adipose tissue in HFD-fed mice.

CONCLUSIONS

The present work provides evidences that Embelin is effective in inhibiting adipogenesis and lipogenesis in vitro and the mechanisms may involve canonical Wnt signaling. Embelin has the potential to prevent body weight gain and fat accumulation, and to improve obesity-related glucose tolerance impairment and insulin resistance in the HFD-fed mice.

Dihydroceramide desaturase inhibitors induce autophagy via dihydroceramide-dependent and independent mechanisms

BACKGROUND

Autophagy consists on the delivery of cytoplasmic material and organelles to lysosomes for degradation. Research on autophagy is a growing field because deciphering the basic mechanisms of autophagy is key to understanding its role in health and disease, and to paving the way to discovering novel therapeutic strategies. Studies with chemotherapeutic drugs and pharmacological tools support a role for dihydroceramides as mediators of autophagy. However, their effect on the autophagy outcome (cell survival or death) is more controversial.

METHODS

We have examined the capacity of structurally varied Des1 inhibitors to stimulate autophagy (LC3-II analysis), to increase dihydroceramides (mass spectrometry) and to reduce cell viability (SRB) in T98G and U87MG glioblastoma cells under different experimental conditions.

RESULTS

The compounds activity on autophagy induction took place concomitantly with accumulation of dihydroceramides, which occurred by both stimulation of ceramide synthesis de novo and reduction of Des1 activity. However, autophagy was also induced by the test compounds after preincubation with myriocin and in cells with a reduced capacity to produce dihydroceramides (U87DND). Autophagy inhibition with 3-methyladenine in the de novo dihydroceramide synthesis competent U87MG cells increased cytotoxicity, while genetic inhibition of autophagy in U87DND cells, poorly efficient at synthesizing dihydroceramides, augmented resistance to the test compounds.

CONCLUSION

Dihydroceramide desaturase 1 inhibitors activate autophagy via both dihydroceramide-dependent and independent pathways and the balance between the two pathways influences the final cell fate.

GENERAL SIGNIFICANCE

The cells capacity to biosynthesize dihydroceramides must be taken into account in proautophagic Des1 inhibitors-including therapies.