Oleoyl-CoA is the major de novo product of stearoyl-CoA desaturase 1 gene isoform and substrate for the biosynthesis of the Harderian gland 1-alkyl-2,3-diacylglycerol

Lipid Metabolism as a Potential Target of Liver Cancer

Hepatocellular carcinoma (HCC) stands as a severe malignant tumor with a profound impact on overall health, often accompanied by an unfavorable prognosis. Despite some advancements in the diagnosis and treatment of this disease, improving the prognosis of HCC remains a formidable challenge. It is noteworthy that lipid metabolism plays a pivotal role in the onset, development, and progression of tumor cells. Existing research indicates the potential application of targeting lipid metabolism in the treatment of HCC. This review aims to thoroughly explore the alterations in lipid metabolism in HCC, offering a detailed account of the potential advantages associated with innovative therapeutic strategies targeting lipid metabolism. Targeting lipid metabolism holds promise for potentially enhancing the prognosis of HCC.

A Conversation with James Ntambi

An interview with James M. Ntambi, professor of biochemistry and the Katherine Berns Van Donk Steenbock Professor in Nutrition, College of Agricultural and Life Sciences, at the University of Wisconsin-Madison, took place via Zoom in April 2022. He was interviewed by Patrick J. Stover, director of the Institute for Advancing Health through Agriculture and professor of nutrition and biochemistry and biophysics at Texas A&M University. Dr. James Ntambi is a true pioneer in the field of nutritional biochemistry. He was among the very first to discover and elucidate the role that diet and nutrients play in regulating metabolism through changes in the expression of metabolic genes, focusing on the de novo lipogenesis pathways. As an African immigrant from Uganda, his love of science and his life experiences in African communities suffering from severe malnutrition molded his scientific interests at the interface of biochemistry and nutrition. Throughout his career, he has been an academic role model, a groundbreaking nutrition scientist, and an educator. His commitment to experiential learning through the many study-abroad classes he has hosted in Uganda has provided invaluable context for American students in nutrition. Dr. Ntambi's passion for education and scientific discovery is his legacy, and the field of nutrition has benefited enormously from his unique perspectives and contributions to science that are defined by his scientific curiosity, his generosity to his students and colleagues, and his life experiences. The following is an edited transcript.

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.

Mechanism of SCD Participation in Lipid Droplet-Mediated Steroidogenesis in Goose Granulosa Cells

Stearoyl-CoA desaturase (SCD) is a key enzyme catalyzing the rate-limiting step in monounsaturated fatty acids (MUFAs) production. There may be a mechanism by which SCD is involved in lipid metabolism, which is assumed to be essential for goose follicular development. For this reason, a cellular model of SCD function in goose granulosa cells (GCs) via SCD overexpression and knockdown was used to determine the role of SCD in GC proliferation using flow cytometry. We found that SCD overexpression induced and SCD knockdown inhibited GCs proliferation. Furthermore, ELISA analysis showed that SCD overexpression increased the total cholesterol (TC), progesterone, and estrogen levels in GCs, while SCD knockdown decreased TC, progesterone, and estrogen levels (p < 0.05). Combining these results with those of related multi-omics reports, we proposed a mechanism of SCD regulating the key lipids and differentially expressed gene (DEGs) in glycerophospholipid and glycerolipid metabolism, which participate in steroidogenesis mediated by the lipid droplet deposition in goose GCs. These results add further insights into understanding the lipid metabolism mechanism of goose GCs.

Microbiota-Independent Spontaneous Dermatitis Associated With Increased Sebaceous Lipid Production in Tmem79-Deficient Mice

TMEM79 is a predisposing gene for atopic dermatitis (AD). Tmem79-deficient mice develop spontaneous dermatitis in a biphasic pattern. The 1^st-phase dermatitis is unique, as it occurs independent of microbiota status, whereas the 2^nd-phase dermatitis is microbiota-dependent. In this study, we sought to identify key factors mediating the development of 1^st-phase dermatitis. Structural analysis showed that sebaceous gland hyperplasia started from 1^st-phase dermatitis. Longitudinal RNA-sequencing analysis revealed significant activation of fatty acid lipid-metabolism pathways in 1^st-phase dermatitis, whereas Th17-based immune response genes were highly expressed in 2^nd-phase dermatitis. Quantitative reverse transcription-polymerase chain reaction analysis revealed that genes involved in fatty acid elongation and sebocyte differentiation were upregulated in 1^st-phase dermatitis. The results of thin-layer chromatography supported these findings with an increased abundance of wax esters, cholesterol esters, and fatty alcohols in hair lipids. Further gas chromatography-tandem mass spectrometry analysis showed an increase in total fatty acid production, including that of elongated C20-24 saturated and C18-24 mono-unsaturated fatty acids. Collectively, these results suggest that aberrant production of sebaceous long-chain fatty acids is associated with microbiota-independent dermatitis. Further investigation of Tmem79-deficient mice may clarify the role of certain fatty acids in dermatitis.

Rat prostaglandin EP3 receptor is highly promiscuous and is the sole prostanoid receptor family member that regulates INS-1 (832/3) cell glucose-stimulated insulin secretion

Chronic elevations in fatty acid metabolites termed prostaglandins can be found in circulation and in pancreatic islets from mice or humans with diabetes and have been suggested as contributing to the β‐cell dysfunction of the disease. Two‐series prostaglandins bind to a family of G‐protein‐coupled receptors, each with different biochemical and pharmacological properties. Prostaglandin E receptor (EP) subfamily agonists and antagonists have been shown to influence β‐cell insulin secretion, replication, and/or survival. Here, we define EP3 as the sole prostanoid receptor family member expressed in a rat β‐cell‐derived line that regulates glucose‐stimulated insulin secretion. Several other agonists classically understood as selective for other prostanoid receptor family members also reduce glucose‐stimulated insulin secretion, but these effects are only observed at relatively high concentrations, and, using a well‐characterized EP3‐specific antagonist, are mediated solely by cross‐reactivity with rat EP3. Our findings confirm the critical role of EP3 in regulating β‐cell function, but are also of general interest, as many agonists supposedly selective for other prostanoid receptor family members are also full and efficacious agonists of EP3. Therefore, care must be taken when interpreting experimental results from cells or cell lines that also express EP3.

Epidermal Acyl-CoA-binding protein is indispensable for systemic energy homeostasis

OBJECTIVES

The skin is the largest sensory organ of the human body and plays a fundamental role in regulating body temperature. However, adaptive alterations in skin functions and morphology have only vaguely been associated with physiological responses to cold stress or sensation of ambient temperatures. We previously found that loss of acyl-CoA-binding protein (ACBP) in keratinocytes upregulates lipolysis in white adipose tissue and alters hepatic lipid metabolism, suggesting a link between epidermal barrier functions and systemic energy metabolism.

METHODS

To assess the physiological responses to loss of ACBP in keratinocytes in detail, we used full-body ACBP^-/- and skin-specific ACBP^-/- knockout mice to clarify how loss of ACBP affects 1) energy expenditure by indirect calorimetry, 2) response to high-fat feeding and a high oral glucose load, and 3) expression of brown-selective gene programs by quantitative PCR in inguinal WAT (iWAT). To further elucidate the role of the epidermal barrier in systemic energy metabolism, we included mice with defects in skin structural proteins (ma/ma Flg^ft/ft) in these studies.

RESULTS

We show that the ACBP^-/- mice and skin-specific ACBP^-/- knockout mice exhibited increased energy expenditure, increased food intake, browning of the iWAT, and resistance to diet-induced obesity. The metabolic phenotype, including browning of the iWAT, was reversed by housing the mice at thermoneutrality (30 °C) or pharmacological β-adrenergic blocking. Interestingly, these findings were phenocopied in flaky tail mice (ma/ma Flg^ft/ft). Taken together, we demonstrate that a compromised epidermal barrier induces a β-adrenergic response that increases energy expenditure and browning of the white adipose tissue to maintain a normal body temperature.

CONCLUSIONS

Our findings show that the epidermal barrier plays a key role in maintaining systemic metabolic homeostasis. Thus, regulation of epidermal barrier functions warrants further attention to understand the regulation of systemic metabolism in further detail.

Lipid metabolism in colon cancer: Role of Liver X Receptor (LXR) and Stearoyl-CoA Desaturase 1 (SCD1)

Colorectal cancer (CRC) is one of the most commonly occurring cancers worldwide. Although several genetic alterations have been associated with CRC onset and progression, nowadays the reprogramming of cellular metabolism has been recognized as a fundamental step of the carcinogenic process. Intestinal tumor cells frequently display an aberrant activation of lipid metabolism. Indeed, to satisfy the growing needs of a continuous proliferation, cancer cells can either increase the uptake of exogenous lipids or upregulate the endogenous lipogenesis and cholesterol synthesis. Therefore, strategies aimed at limiting lipid accumulation are now under development in order to counteract malignancies. Two major players of lipids metabolism have been so far identified for their contribution to CRC development: the nuclear receptor Liver X Receptor (LXRs) and the enzyme Stearoyl-CoA Desaturase 1 (SCD1). Whereas LXR is mainly recognized for its role as a cholesterol sensor, finally promoting the loss of cellular cholesterol and whole-body homeostasis, SCD1 acts as the major regulator of new fatty acids, finely tuning the monounsaturated fatty acids (MUFA) to saturated fatty acids (SFA) ratio. Intriguingly, SCD1 is directly regulated by LXRs. Despite LXRs agonists have elicited great interest as a promising therapeutic target for cancer, LXR's ability to induce SCD1 and new fatty acids synthesis represent a major obstacle in the development of new effective treatments. Thus, further investigations are required to fully dissect the concomitant modulation of both players, to develop specific therapies aimed at blocking intestinal cancer cells proliferation, eventually counteracting CRC progression.

Involvement of overweight and lipid metabolism in the development of pulmonary hypertension under conditions of chronic intermittent hypoxia

There is growing evidence that exposure to hypoxia, regardless of the source, elicits several metabolic responses in individuals. These responses are constitutive and are usually observed under hypoxia but vary according to the type of exposure. The aim of this review was to describe the involvement of obesity and lipid metabolism in the development of high-altitude pulmonary hypertension and in the development of acute mountain sickness under chronic intermittent hypoxia. Overweight or obesity, which are common in individuals with long-term chronic intermittent hypoxia exposure (high-altitude miners, shift workers, and soldiers), are thought to play a major role in the development of acute mountain sickness and high-altitude pulmonary hypertension. This association may be rooted in the interactions between obesity-related metabolic and physical alterations, such as increased waist circumference and neck circumference, among others, which lead to critical ventilation impairments; these impairments aggravate hypoxemia at high altitude, thereby triggering high-altitude diseases. Overweight and obesity are strongly associated with higher mean pulmonary artery pressure in the context of long-term chronic intermittent hypoxia. Remarkably, de novo synthesis of triglycerides by the sterol regulatory element-binding protein-1c pathway has been demonstrated, mainly due to the upregulation of stearoyl-CoA desaturase-1, which is also associated with the same outcomes. Therefore, overweight, obesity, and other metabolic conditions may hinder proper acclimatization. The involved mechanisms include respiratory impairment, alteration of the nitric oxide pathways, inflammatory status, reactive oxygen species imbalance, and other metabolic changes; however, further studies are required.

SCD1 activity promotes cell migration via a PLD-mTOR pathway in the MDA-MB-231 triple-negative breast cancer cell line

BACKGROUND

Breast cancer is the most common cancer in women. Despite high survival rates in Western countries, treatments are less effective in metastatic cases and triple-negative breast cancer (TNBC) patient survival is the shortest across breast cancer subtypes. High expression levels of stearoyl-CoA desaturase-1 (SCD1) have been reported in breast cancer. The SCD1 enzyme catalyzes the formation of oleic acid (OA), a lipid stimulating the migration of metastatic breast cancer cells. Phospholipase activity is also implicated in breast cancer metastasis, notably phospholipase D (PLD).

METHODS

Kaplan-Meier survival plots generated from gene expression databases were used to analyze the involvement of SCD1 and PLD in several cancer subtypes. SCD1 enzymatic activity was modulated with a pharmaceutical inhibitor or by OA treatment (to mimic SCD1 over-activity) in three breast cancer cell lines: TNBC-derived MDA-MB-231 cells as well as non-TNBC MCF-7 and T47D cells. Cell morphology and migration properties were characterized by various complementary methods.

RESULTS

Our survival analyses suggest that SCD1 and PLD2 expression in the primary tumor are both associated to metastasis-related morbid outcomes in breast cancer patients. We show that modulation of SCD1 activity is associated with the modification of TNBC cell migration properties, including changes in speed, direction and cell morphology. Cell migration properties are regulated by SCD1 activity through a PLD-mTOR/p70S6K signaling pathway. These effects are not observed in non-TNBC cell lines.

CONCLUSION

Our results establish a key role for the lipid desaturase SCD1 and delineate an OA-PLD-mTOR/p70S6K signaling pathway in TNBC-derived MDA-MB-231 cell migration.

Role of Oleic Acid in the Gut-Liver Axis: From Diet to the Regulation of Its Synthesis via Stearoyl-CoA Desaturase 1 (SCD1)

The consumption of an olive oil rich diet has been associated with the diminished incidence of cardiovascular disease and cancer. Several studies have attributed these beneficial effects to oleic acid (C18 n-9), the predominant fatty acid principal component of olive oil. Oleic acid is not an essential fatty acid since it can be endogenously synthesized in humans. Stearoyl-CoA desaturase 1 (SCD1) is the enzyme responsible for oleic acid production and, more generally, for the synthesis of monounsaturated fatty acids (MUFA). The saturated to monounsaturated fatty acid ratio affects the regulation of cell growth and differentiation, and alteration in this ratio has been implicated in a variety of diseases, such as liver dysfunction and intestinal inflammation. In this review, we discuss our current understanding of the impact of gene-nutrient interactions in liver and gut diseases, by taking advantage of the role of SCD1 and its product oleic acid in the modulation of different hepatic and intestinal metabolic pathways.

Cyclic Change of Fatty Acid Composition in Meibum During the Menstrual Cycle

Purpose

To evaluate the fatty acid (FA) composition in the meibum of pre- and postmenopausal women and age-matched men.

Methods

This prospective study involved 24 healthy subjects; six premenopausal women in their 30s with a regular menstrual cycle (young-female [yF] group), six postmenopausal women in their 60s (elderly-female [eF] group), and 12 age-matched men (i.e., young-male [yM] and elderly-male [eM] groups, respectively). The menstrual cycle was divided into six phases (phase I–VI). Meibum was obtained from the meibomian gland orifices via a Daviel spoon, and its FA composition was then analyzed via gas chromatography mass spectrometry (GC-MS). Principal component analysis (PCA) was performed on the GC-MS results.

Results

The mean FA composition of all subjects was 40% saturated FAs (SFA) and 60% unsaturated FAs (UFAs). The PCA results of all groups indicated two categories (PC1 [77.5%] and PC2 [12.4%]); one consisting of yF-group samples of mainly phase II and III and the other consisting of the yF-group samples of the rest of the cycle, as well as from eF-group, yM-group, and eM-group samples. Each group had a distinctive nature. The FAs that most contributed to PC1 were C_14:0, C_16:0, and C_18:0 in a positive correlation, and C_18:1n9 in a negative correlation.

Conclusions

FA composition noticeably changes during the menstrual cycle and is somewhat affected by sex and age. The ratio of SFAs (C_16:0, C_18:0) to mono-UFAs (C_18:1n9) in the FA composition might have an impact on the lipid quality of meibum, thus suggesting alteration of its melting temperature and viscosity.

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.

Aberrant lipid metabolism as a therapeutic target in liver cancer

INTRODUCTION

Hepatocellular carcinoma (HCC) is one of the most common and lethal cancers. Progress has been made in treatment of HCC; however, improved outcomes are much needed. The increased metabolic needs of cancer cells underscore the importance of metabolic pathways in cancer cell survival. Lipid metabolism has a role in HCC development; aberrant overexpression of several key enzymes is seen in many solid human tumors. Areas covered: We discuss aberrant lipid metabolism and the promise of multiple targets, in particular related to HCC treatment. We searched PubMed and clinicaltrials.gov for published and unpublished studies from 2000 to 2019. These terms were used: lipids, fatty acid metabolism, lipid metabolism, liver cancer, HCC, de novo fatty acid synthesis, ATP citrate lyase, stearoyl CoA denaturase, fatty acid synthase, acetyl coenzyme A carboxylase, CD147, KLF4, monoglyceride lipase, AMP activated protein kinase. Expert opinion: The importance of dysregulation of fatty acid synthesis in cancer is a growing area of research. HCC demonstrates significant alteration in lipid metabolism, representing great potential as a target for novel therapeutics. Various agents have demonstrated promising anti-neoplastic activity. This strategy deserves further development for improved outcomes.

β-Cryptoxanthin-Biofortified Hen Eggs Enhance Vitamin A Status When Fed to Male Mongolian Gerbils

Background

Consumption of provitamin A carotenoid biofortified crops, such as maize, supports vitamin A (VA) status in animals and humans. Laying hens that consume β-cryptoxanthin-biofortified maize deposit β-cryptoxanthin into egg yolk.

Objective

We investigated whether β-cryptoxanthin-biofortified egg consumption would affect VA status of male Mongolian gerbils (Meriones unguiculatus) compared with white-yolked eggs.

Methods

β-Cryptoxanthin-biofortified egg yolk, produced in hens fed biofortified orange maize or tangerine-fortified maize feeds, was freeze-dried and fed to gerbils. White-yolked eggs were produced by feeding white maize to hens. Gerbils (n = 57) were fed VA-deficient feed for 28 d. After baseline (n = 7), treatments (n = 10/group) included oil control (VA-); 16.7% orange maize-biofortified, tangerine-fortified, or white-yolk egg feeds; or retinyl acetate as positive control (VA+) matched to daily preformed retinol intake from the eggs for 30 d. Preformed retinol did not differ between the egg yolks. Gerbil liver retinol, lipid, fatty acids, and cholesterol were determined.

Results

Liver retinol concentration (0.13 ± 0.03 µmol/g) and total hepatic VA (0.52 ± 0.12 µmol) were higher in gerbils fed orange maize-biofortified eggs than in all other groups. The VA- group was severely VA deficient (0.018 ±0.010 µmol/g; P < 0.05). Liver retinol was similar among VA+, tangerine-egg-, and white-egg-fed gerbils, but retinol reserves were higher in tangerine-egg-fed gerbils (0.35 ± 0.11 μmol) than in VA+ or VA- gerbils or at baseline (P < 0.05). Liver fat was 3.6 times (P < 0.0001) and cholesterol was 2.1 times (P < 0.004) higher in egg-fed groups that experienced hepatosteatosis. Liver fatty acid profiles reflected feed, but retinyl ester fatty acids did not.

Conclusions

The preformed retinol in the eggs enhanced gerbil VA status, and the β-cryptoxanthin-biofortified eggs from hens fed orange maize prevented deficiency. Biofortified maize can enhance VA status when consumed directly or through products from livestock fed orange maize.

Protein engineering: Regulatory perspectives of stearoyl CoA desaturase

Stearoyl Co A desaturase (SCD) is a rate-limiting lipogenic enzyme that plays an integral role in catalyzing the synthesis of monounsaturated fatty acids, chiefly oleate and palmitoleate. Both contribute a major part of the biological membrane. Numerous SCD isoforms exist in mouse and humans, i.e., SCD-1 to SCD-4 and SCD-1 and SCD-5, respectively. From the biological viewpoint, hyperexpression of SCD1 cause many metabolic disorders including obesity, insulin resistance, hypertension, and hypertriglyceridemia, etc. Herein, an effort has been made to highlight the value of protein engineering in controlling the SCD-1 expression with the involvement of different inhibitors as therapeutic agents. The first part of the review describes Stearoyl CoA desaturase index and different SCD isoforms. Various regulatory aspects of SCD are reviewed in four subsections, i.e., (1) hormonal regulation, (2) regulation by dietary carbohydrates, (3) regulation by green tea, and (4) regulation via polyunsaturated fatty acids (PUFAs). Moreover, the regulation of Stearoyl CoA desaturase expression in the metabolism of fats and carbohydrates is discussed. The third part mainly focuses on natural and synthetic inhibitors. Towards the end, information is also given on potential future considerations of SCD-1 inhibitors as metabolic syndrome therapeutics, yet additional work is required.

Pilot Study of a "Large-Eye," Surgically Induced Dry Eye Rabbit Model by Selective Removal of the Harderian, Lacrimal, and Meibomian Glands

Background/Aims

Establish a reliable rabbit dry eye (DE) model.

Methods

An interventional cohort study surgically removing glands contributing to the tear film. Eight rabbits were studied after removal of left lacrimal, Harderian, or both glands. Additional rabbits had Meibomian glands in the left eye thermally obstructed. All were followed for 10 weeks with phenol red thread (PRT) and slit-lamp examination with 2% fluorescein. We assessed corneal sensitivity using a Cochet-Bonnet esthesiometer. Outcome measures were severity/duration of reduced PRT, punctate epithelial erosions (PEE), and histologic evidence of corneal pannus.

Results

Fluorescein staining demonstrated signs of dryness including PEE in all of the interventional eyes. The subjective measurement of epithelial erosions correlated with decreased tear production. PRT measurements in the control eyes averaged 31.54 mm (±1.83) and 22.71 mm (±1.60) in the eight left eyes, without loss of corneal sensitivity.

Conclusions

Surgical removal of either the Harderian or lacrimal gland results in statistically significant decreases in tear volume and the development of severe DE. Removal of both glands results in the occurrence of a DE of comparable severity/duration to removal of either the lacrimal or Harderian gland alone. Meibomian gland obstruction contributes less to the DE model.

Meibomian glands, meibum, and meibogenesis

Meibum is a lipid-rich secretion that is produced by fully differentiated meibocytes in the holocrine Meibomian glands (MG) of humans and most mammals. The secretion is a part of a defense mechanism that protects the ocular surface from hazardous environmental factors, and from desiccation. Meibomian lipids that have been identified in meibum are very diverse and unique in nature. The lipid composition of meibum is different from virtually any other lipid pool found in the human body. In fact, meibum is quite different from sebum, which is the closest secretion that is produced by anatomically, physiologically, and biochemically related sebaceous glands. However, meibum of mice have been shown to closely resemble that of humans, implying similar biosynthetic mechanisms in MG of both species. By analyzing available genomic, immunohistochemical, and lipidomic data, we have envisioned a unifying network of enzymatic reactions that are responsible for biosynthesis of meibum, which we call meibogenesis. Our current theory is based on an assumption that most of the biosynthetic reactions of meibogenesis are catalyzed by known enzymes. However, the main features that make meibum unique - the ratio of identified classes of lipids, the extreme length of its components, extensive ω-hydroxylation of fatty acids and alcohols, iso- and anteiso-branching of meibomian lipids (e.g. waxes), and the presence of rather unique complex lipids with several ester bonds - make it possible that either the activity of known enzymes is altered in MG, or some unknown enzymes contribute to the processes of meibogenesis, or both. Studies are in progress to elucidate meibogenesis on molecular level.

Enriching Islet Phospholipids With Eicosapentaenoic Acid Reduces Prostaglandin E2 Signaling and Enhances Diabetic β-Cell Function

Prostaglandin E₂ (PGE₂) is derived from arachidonic acid, whereas PGE₃ is derived from eicosapentaenoic acid (EPA) using the same downstream metabolic enzymes. Little is known about the impact of EPA and PGE₃ on β-cell function, particularly in the diabetic state. In this work, we determined that PGE₃ elicits a 10-fold weaker reduction in glucose-stimulated insulin secretion through the EP3 receptor as compared with PGE₂ We tested the hypothesis that enriching pancreatic islet cell membranes with EPA, thereby reducing arachidonic acid abundance, would positively impact β-cell function in the diabetic state. EPA-enriched islets isolated from diabetic BTBR Leptin^ob/ob mice produced significantly less PGE₂ and more PGE₃ than controls, correlating with improved glucose-stimulated insulin secretion. NAD(P)H fluorescence lifetime imaging showed that EPA acts downstream and independently of mitochondrial function. EPA treatment also reduced islet interleukin-1β expression, a proinflammatory cytokine known to stimulate prostaglandin production and EP3 expression. Finally, EPA feeding improved glucose tolerance and β-cell function in a mouse model of diabetes that incorporates a strong immune phenotype: the NOD mouse. In sum, increasing pancreatic islet EPA abundance improves diabetic β-cell function through both direct and indirect mechanisms that converge on reduced EP3 signaling.

A novel approach to the discovery of anti-tumor pharmaceuticals: searching for activators of liponecrosis

A recently conducted chemical genetic screen for pharmaceuticals that can extend longevity of the yeast Saccharomyces cerevisiae has identified lithocholic acid as a potent anti-aging molecule. It was found that this hydrophobic bile acid is also a selective anti-tumor chemical compound; it kills different types of cultured cancer cells if used at concentrations that do not compromise the viability of non-cancerous cells. These studies have revealed that yeast can be successfully used as a model organism for high-throughput screens aimed at the discovery of selectively acting anti-tumor small molecules. Two metabolic traits of rapidly proliferating fermenting yeast, namely aerobic glycolysis and lipogenesis, are known to be similar to those of cancer cells. The mechanisms underlying these key metabolic features of cancer cells and fermenting yeast have been established; such mechanisms are discussed in this review. We also suggest how a yeast-based chemical genetic screen can be used for the high-throughput development of selective anti-tumor pharmaceuticals that kill only cancer cells. This screen consists of searching for chemical compounds capable of increasing the abundance of membrane lipids enriched in unsaturated fatty acids that would therefore be toxic only to rapidly proliferating cells, such as cancer cells and fermenting yeast.

Free fatty acid profiling of marine sentinels by nanoLC-EI-MS for the assessment of environmental pollution effects

The present work aims to elucidate the free fatty acid (FFA) profile of the mussel Mytilus galloprovincialis caged in an anthropogenically impacted area and in a reference site through an innovative and validated analytical approach for the assessment of biological alterations induced by marine pollution. The FFA pattern is involved in the regulation of different cellular pathways and differs with respect to metabolic stimuli. To this purpose, the lipid fraction of mussels coming from both sampling areas was extracted and the FFA fractions were isolated and purified by a solid phase extraction; then, nano-scale liquid chromatography coupled to electron ionization mass spectrometry (nanoLC-EI-MS) was employed for the characterization of the two samples. A total of 19 and 17 FFAs were reliably identified in the mussels coming from the reference and polluted site, respectively. Significant qualitative and quantitative differences found in saturated, monounsaturated and polyunsaturated species may be exploited as typical pollution biomarkers (e.g. alteration of the fatty acid biosynthetic system and lipotoxicity) and explain adverse and compromising effects (e.g. oxidative stress and inflammatory processes) related to environmental pollution.

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.

miR-378 Activates the Pyruvate-PEP Futile Cycle and Enhances Lipolysis to Ameliorate Obesity in Mice

Obesity has been linked to many health problems, such as diabetes. However, there is no drug that effectively treats obesity. Here, we reveal that miR-378 transgenic mice display reduced fat mass, enhanced lipolysis, and increased energy expenditure. Notably, administering AgomiR-378 prevents and ameliorates obesity in mice. We also found that the energy deficiency seen in miR-378 transgenic mice was due to impaired glucose metabolism. This impairment was caused by an activated pyruvate-PEP futile cycle via the miR-378-Akt1-FoxO1-PEPCK pathway in skeletal muscle and enhanced lipolysis in adipose tissues mediated by miR-378-SCD1. Our findings demonstrate that activating the pyruvate-PEP futile cycle in skeletal muscle is the primary cause of elevated lipolysis in adipose tissues of miR-378 transgenic mice, and it helps orchestrate the crosstalk between muscle and fat to control energy homeostasis in mice. Thus, miR-378 may serve as a promising agent for preventing and treating obesity in humans.

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Systemically administering AgomiR-378 prevents and ameliorates obesity in mice

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miR-378 transgenic mice show energy deficiency due to impaired glucose metabolism

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The impairment is caused by miR-378-activated pyruvate-PEP futile cycle in muscle

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miR-378 governs energy homeostasis by increased lipolysis via targeting Scd1 in fat

Futile cycles are generally regarded as energetically wasteful processes that are avoided in metabolic pathways. Zhang et al. demonstrate miR-378-activated pyruvate-phosphoenolpyruvate futile cycle plays a regulatory benefit for the energy homeostasis by orchestrating inter-organ crosstalk between skeletal muscle and fat in mice, resulting its implication in preventing and treating obesity.

The expression of the SCD1 gene and its correlation with fattening and carcass traits in sheep

Abstract. Stearoyl-CoA desaturase 1 (SCD1) is a critical enzyme that catalyzes the synthesis of monounsaturated fatty acids and is involved in several signaling pathways related to lipid metabolism. The objective of the present study was to estimate the expression of the SCD1 gene in three different ovine tissues strongly associated with lipid homeostasis. The SCD1 gene expression measurement was performed on three tissues (liver, subcutaneous fat, perirenal fat) originated from 15 old-type Polish Merino sheep. The SCD1 transcript abundance was evaluated based on the two most stable endogenous controls (RPS2 – ribosomal protein S2; ATP5G2 – H(+)-transporting ATP synthase). The highest expression of the SCD1 gene was observed in ovine subcutaneous fat compared to perirenal fat and liver. Furthermore, the present research indicated the significant correlation between ovine SCD1 transcript abundance and several important production traits. The expression of the SCD1 gene in liver and perirenal fat highly positively correlated with the feed : gain ratio, test of daily gain and age of the animals at slaughter. Moreover, in both tissues, the SCD1mRNA level positively correlated with weight and content of perirenal fat and subcutaneous fat (R =  0.64, 0.8, 0.6, respectively) and negatively with assessment of external fat content with the use of the EUROP scale (R = −0.64). The SCD1 expression in subcutaneous fat also corresponds with back fat of blade chop and thickness of longissimus dorsi muscles evaluated using USG (ultrasonography) (R =  −0.6 and 0.62, respectively). The significant correlation between SCD1 transcript abundance and fattening and slaughtering traits indicate the ability to improve important production traits in sheep via modification of expression of the SCD1 gene.

Saturated phosphatidic acids mediate saturated fatty acid-induced vascular calcification and lipotoxicity

Recent evidence indicates that saturated fatty acid-induced (SFA-induced) lipotoxicity contributes to the pathogenesis of cardiovascular and metabolic diseases; however, the molecular mechanisms that underlie SFA-induced lipotoxicity remain unclear. Here, we have shown that repression of stearoyl-CoA desaturase (SCD) enzymes, which regulate the intracellular balance of SFAs and unsaturated FAs, and the subsequent accumulation of SFAs in vascular smooth muscle cells (VSMCs), are characteristic events in the development of vascular calcification. We evaluated whether SMC-specific inhibition of SCD and the resulting SFA accumulation plays a causative role in the pathogenesis of vascular calcification and generated mice with SMC-specific deletion of both Scd1 and Scd2. Mice lacking both SCD1 and SCD2 in SMCs displayed severe vascular calcification with increased ER stress. Moreover, we employed shRNA library screening and radiolabeling approaches, as well as in vitro and in vivo lipidomic analysis, and determined that fully saturated phosphatidic acids such as 1,2-distearoyl-PA (18:0/18:0-PA) mediate SFA-induced lipotoxicity and vascular calcification. Together, these results identify a key lipogenic pathway in SMCs that mediates vascular calcification.

Differential distribution of lipids in epidermis, gastrodermis and hosted Symbiodinium in the sea anemone Anemonia viridis

Cnidarian-dinoflagellate symbiosis mainly relies on nutrient recycling, thus providing both partners with a competitive advantage in nutrient-poor waters. Essential processes related to lipid metabolism can be influenced by various factors, including hyperthermal stress. This can affect the lipid content and distribution in both partners, while contributing to symbiosis disruption and bleaching. In order to gain further insight into the role and distribution of lipids in the cnidarian metabolism, we investigated the lipid composition of the sea anemone Anemonia viridis and its photosynthetic dinoflagellate endosymbionts (Symbiodinium). We compared the lipid content and fatty acid profiles of the host cellular layers, non-symbiotic epidermal and symbiont-containing gastrodermal cells, and those of Symbiodinium, in a mass spectrometry-based assessment. Lipids were more concentrated in Symbiodinium cells, and the lipid class distribution was dominated by polar lipids in all tissues. The fatty acid distribution between host cell layers and Symbiodinium cells suggested potential lipid transfers between the partners. The lipid composition and distribution was modified during short-term hyperthermal stress, mainly in Symbiodinium cells and gastrodermis. Exposure to elevated temperature rapidly caused a decrease in polar lipid C18 unsaturated fatty acids and a strong and rapid decrease in the abundance of polar lipid fatty acids relative to sterols. These lipid indicators could therefore be used as sensitive biomarkers to assess the physiology of symbiotic cnidarians, especially the effect of thermal stress at the onset of cnidarian bleaching. Overall, the findings of this study provide some insight on key lipids that may regulate maintenance of the symbiotic interaction.

Compromised epidermal barrier stimulates Harderian gland activity and hypertrophy in ACBP-/- mice

Acyl-CoA binding protein (ACBP) is a small, ubiquitously expressed intracellular protein that binds C14-C22 acyl-CoA esters with very high affinity and specificity. We have recently shown that targeted disruption of the Acbp gene leads to a compromised epidermal barrier and that this causes delayed adaptation to weaning, including the induction of the hepatic lipogenic and cholesterogenic gene programs. Here we show that ACBP is highly expressed in the Harderian gland, a gland that is located behind the eyeball of rodents and involved in the production of fur lipids and lipids used for lubrication of the eye lid. We show that disruption of the Acbp gene leads to a significant enlargement of this gland with hypertrophy of the acinar cells and increased de novo synthesis of monoalkyl diacylglycerol, the main lipid species produced by the gland. Mice with conditional targeting of the Acbp gene in the epidermis recapitulate this phenotype, whereas generation of an artificial epidermal barrier during gland development reverses the phenotype. Our findings indicate that the Harderian gland is activated by the compromised epidermal barrier as an adaptive and protective mechanism to overcome the barrier defect.

A Candidate Single Nucleotide Polymorphism in the 3' Untranslated Region of Stearoyl-CoA Desaturase Gene for Fatness Quality and the Gene Expression in Berkshire Pigs

Fatness qualities in pigs measured by the amount of fat deposition and composition of fatty acids (FAs) in pork have considerable effect on current breeding goals. The stearoyl-CoA desaturase (SCD) gene plays a crucial role in the conversion of saturated FAs into monounsaturated FAs (MUFAs), and hence, is among the candidate genes responsible for pig fatness traits. Here, we identified a single nucleotide polymorphism (SNP, c.*2041T>C) in the 3′ untranslated region by direct sequencing focused on coding and regulatory regions of porcine SCD. According to the association analysis using a hundred of Berkshire pigs, the SNP was significantly associated with FA composition (MUFAs and polyunsaturated FAs [PUFAs]), polyunsaturated to saturated (P:S) FA ratio, n-6:n-3 FA ratio, and extent of fat deposition such as intramuscular fat and marbling (p<0.05). In addition, the SNP showed a significant effect on the SCD mRNA expression levels (p = 0.041). Based on our results, we suggest that the SCD c.*2041T>C SNP plays a role in the gene regulation and affects the fatness qualities in Berkshire pigs.

Hepatic oleate regulates adipose tissue lipogenesis and fatty acid oxidation

Hepatic steatosis is associated with detrimental metabolic phenotypes including enhanced risk for diabetes. Stearoyl-CoA desaturases (SCDs) catalyze the synthesis of MUFAs. In mice, genetic ablation of SCDs reduces hepatic de novo lipogenesis (DNL) and protects against diet-induced hepatic steatosis and adiposity. To understand the mechanism by which hepatic MUFA production influences adipose tissue stores, we created two liver-specific transgenic mouse models in the SCD1 knockout that express either human SCD5 or mouse SCD3, that synthesize oleate and palmitoleate, respectively. We demonstrate that hepatic de novo synthesized oleate, but not palmitoleate, stimulate hepatic lipid accumulation and adiposity, reversing the protective effect of the global SCD1 knockout under lipogenic conditions. Unexpectedly, the accumulation of hepatic lipid occurred without induction of the hepatic DNL program. Changes in hepatic lipid composition were reflected in plasma and in adipose tissue. Importantly, endogenously synthesized hepatic oleate was associated with suppressed DNL and fatty acid oxidation in white adipose tissue. Regression analysis revealed a strong correlation between adipose tissue lipid fuel utilization and hepatic and adipose tissue lipid storage. These data suggest an extrahepatic mechanism where endogenous hepatic oleate regulates lipid homeostasis in adipose tissues.

Oleic acid synthesized by stearoyl-CoA desaturase (SCD-1) in the lateral periventricular zone of the developing rat brain mediates neuronal growth, migration and the arrangement of prospective synapses

Our previous work has shown that oleic acid synthesized by astrocytes in response to serum albumin behaves as a neurotrophic factor in neurons, upregulating the expression of GAP-43 and MAP-2 proteins, which are respectively markers of axonal and dendrite growth. In addition, oleic acid promoted neuron migration and aggregation, resulting in clusters of neurons connected each other by the newly formed neurites. In this work we show that the presence of albumin or albumin plus oleic acid increases neuron migration in cultured explants of the lateral periventricular zone, resulting in an increase in the number of GAP-43-positive neurons leaving the explant. Upon silencing stearoyl-CoA desaturase-1 (SCD-1), a key enzyme in oleic acid synthesis by RNA of interference mostly prevented the effect of albumin but not that of albumin plus oleic acid, suggesting that the oleic acid synthesized due to the effect of albumin would be responsible for the increase in neuron migration. Oleic acid increased doublecortin (DCX) expression in cultured neurons, explants and organotypic slices, suggesting that DCX may mediate in the effect of oleic acid on neuron migration. The effect of oleic acid on neuron migration may be destined for the formation of synapses because the presence of oleic acid increased the expression of synaptotagmin and that of postsynaptic density protein (PDS-95), respectively markers of the pre- and postsynaptic compartments. In addition, confocal microscopy revealed the occurrence of points of colocalization between synaptotagmin and PDS-95, which is consistent with the idea that oleic acid promotes synapse arrangement.

Stearoyl CoA desaturase is required to produce active, lipid-modified Wnt proteins

Wnt proteins contain palmitoleic acid, an unusual lipid modification. Production of an active Wnt signal requires the acyltransferase Porcupine and depends on the attachment of palmitoleic acid to Wnt. The source of this monounsaturated fatty acid has not been identified, and it is not known how Porcupine recognizes its substrate and whether desaturation occurs before or after fatty acid transfer to Wnt. Here, we show that stearoyl desaturase (SCD) generates a monounsaturated fatty acid substrate that is then transferred by Porcupine to Wnt. Treatment of cells with SCD inhibitors blocked incorporation of palmitate analogs into Wnt3a and Wnt5a and reduced Wnt secretion as well as autocrine and paracrine Wnt signaling. The SCD inhibitor effects were rescued by exogenous addition of monounsaturated fatty acids. We propose that SCD is a key molecular player responsible for Wnt biogenesis and processing and that SCD inhibition provides an alternative mechanism for blocking Wnt pathway activation.

Human breast cancer tissues contain abundant phosphatidylcholine(36∶1) with high stearoyl-CoA desaturase-1 expression

Breast cancer is the leading cause of cancer and mortality in women worldwide. Recent studies have argued that there is a close relationship between lipid synthesis and cancer progression because some enzymes related to lipid synthesis are overexpressed in breast cancer tissues. However, lipid distribution in breast cancer tissues has not been investigated. We aimed to visualize phosphatidylcholines (PCs) and lysoPCs (LPCs) in human breast cancer tissues by performing matrix assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS), which is a novel technique that enables the visualization of molecules comprehensively. Twenty-nine breast tissue samples were obtained during surgery and subjected to MALDI-IMS analysis. We evaluated the heterogeneity of the distribution of PCs and LPCs on the tissues. Three species [PC(32∶1), PC(34∶1), and PC(36∶1)] of PCs with 1 mono-unsaturated fatty acid chain and 1 saturated fatty acid chain (MUFA-PCs) and one [PC(34∶0)] of PCs with 2 saturated fatty acid chains (SFA-PC) were relatively localized in cancerous areas rather than the rest of the sections (named reference area). In addition, the LPCs did not show any biased distribution. The relative amounts of PC(36∶1) compared to PC(36∶0) and that of PC(36∶1) to LPC(18∶0) were significantly higher in the cancerous areas. The protein expression of stearoyl-CoA desaturase-1 (SCD1), which is a synthetic enzyme of MUFA, showed accumulation in the cancerous areas as observed by the results of immunohistochemical staining. The ratios were further analyzed considering the differences in expressions of the estrogen receptor (ER), human epidermal growth factor receptor 2 (HER2), and Ki67. The ratios of the signal intensity of PC(36∶1) to that of PC(36∶0) was higher in the lesions with positive ER expression. The contribution of SCD1 and other enzymes to the formation of the observed phospholipid composition is discussed.

Skeletal muscle fatty acids shift from oxidation to storage upon dexamethasone treatment in chickens

The effect of an exogenous glucocorticoid on the lipid metabolism and fatty acid pattern of skeletal muscle in broiler chickens (Gallus gallus domesticus) was investigated in vivo and in vitro. Male Arbor Acres chickens were subjected to dexamethasone (DEX) treatment for 3days. We found that DEX retarded body growth, facilitated lipid accumulation in adipose and skeletal muscle tissues, and elevated the thigh monounsaturated fatty acids (MUFA) to saturated fatty acids (SFA) ratio at fasted state. DEX-treated chickens exhibited increased stearoyl-CoA desaturase-1 (SCD1) activity and decreased carnitine palmitoyltransferase-1 (CPT1) activity in the thigh muscle under fasting conditions and in primary cultured myoblasts. Phosphorylation of AMP-activated protein kinase alpha at Thr172 did not occur in vivo but was increased in vitro by DEX. In cells exposed to DEX, fatty acid transport protein-1 mRNA expression and fatty acid storage were enhanced while fatty acid oxidation was repressed. In conclusion, in oxidative muscle of fasted chickens, DEX stimulated uptake of myocellular fatty acids which was stored with the modified MUFA to SFA ratio in a process that maybe involved SCD1 activation. The altered fatty acid composition together with the inactivation of CPT1 showed an increased tendency towards fatty acid accumulation as opposed to oxidation. These findings provide important insight concerning the influence of glucocorticoids on lipid metabolism.

Combined deletion of SCD1 from adipose tissue and liver does not protect mice from obesity

Stearoyl-CoA desaturase 1 (SCD1) catalyzes the synthesis of monounsaturated fatty acids (MUFA) from saturated FA. Mice with whole-body or skin-specific deletion of SCD1 are resistant to obesity. Here, we show that mice lacking SCD1 in adipose and/or liver are not protected from either genetic- (agouti; A(y)/a) or diet-induced obesity (DIO) despite a robust reduction in SCD1 MUFA products in both subcutaneous and epididymal white adipose tissue. Adipose SCD1 deletion had no effect on glucose or insulin tolerance or on hepatic triglyceride (TG) accumulation. Interestingly, lack of SCD1 from liver lowered the MUFA levels of adipose tissue and vice versa, as reflected by the changes in FA composition. Simultaneous deletion of SCD1 from liver and adipose resulted in a synergistic lowering of tissue MUFA levels, especially in the A(y)/a model in which glucose tolerance was also improved. Lastly, we found that liver and plasma TG show nearly identical genotype-dependent differences in FA composition, indicating that FA composition of plasma TG is predictive for hepatic SCD1 activity and TG FA composition. The current study suggests that SCD1 deletion from adipose and/or liver is insufficient to elicit protection from obesity, but it supports the existence of extensive lipid cross-talk between liver and adipose tissue.

The role of stearoyl-CoA desaturase in obesity, insulin resistance, and inflammation

Stearoyl-CoA desaturase 1 (SCD1) is an essential lipogenic enzyme that has been shown to play an intrinsic role in the development of obesity and related conditions, such as insulin resistance. Through the generation of various mouse models of SCD1 deficiency, we have come to understand that SCD1 plays a role, directly or indirectly, in diverse metabolic processes, including lipogenesis, fatty acid oxidation, insulin signaling, thermogenesis, and inflammation. This review will address recent advances in our understanding of this key regulator of cellular metabolic processes, including the role of SCD1 in maintaining skin barrier integrity and the role of skin SCD1 in the metabolic phenotype elicited by global SCD1 deficiency.

Bromovirus RNA replication compartment formation requires concerted action of 1a's self-interacting RNA capping and helicase domains

All positive-strand RNA viruses replicate their genomes in association with rearranged intracellular membranes such as single- or double-membrane vesicles. Brome mosaic virus (BMV) RNA synthesis occurs in vesicular endoplasmic reticulum (ER) membrane invaginations, each induced by many copies of viral replication protein 1a, which has N-terminal RNA capping and C-terminal helicase domains. Although the capping domain is responsible for 1a membrane association and ER targeting, neither this domain nor the helicase domain was sufficient to induce replication vesicle formation. Moreover, despite their potential for mutual interaction, the capping and helicase domains showed no complementation when coexpressed in trans. Cross-linking showed that the capping and helicase domains each form trimers and larger multimers in vivo, and the capping domain formed extended, stacked, hexagonal lattices in vivo. Furthermore, coexpressing the capping domain blocked the ability of full-length 1a to form replication vesicles and replicate RNA and recruited full-length 1a into mixed hexagonal lattices with the capping domain. Thus, BMV replication vesicle formation and RNA replication depend on the direct linkage and concerted action of 1a's self-interacting capping and helicase domains. In particular, the capping domain's strong dominant-negative effects showed that the ability of full-length 1a to form replication vesicles was highly sensitive to disruption by non-productively titrating lattice-forming self-interactions of the capping domain. These and other findings shed light on the roles and interactions of 1a domains in replication compartment formation and support prior results suggesting that 1a induces replication vesicles by forming a capsid-like interior shell.

Differential regulation of dihydroceramide desaturase by palmitate versus monounsaturated fatty acids: implications for insulin resistance

Much data implicate saturated fatty acids in deleterious processes associated with obesity, diabetes, and the metabolic syndrome. Many of these changes may be due to aberrant generation of bioactive lipids when saturated fatty acid availability to tissues is increased. On the other hand, studies are emerging that implicate the monounsaturated fatty acid oleate in protection from saturated fat mediated toxicity; however, the mechanisms are not well understood. Our data demonstrate a novel role for palmitate in increasing mRNA encoding DES1, which is the enzyme responsible for generating ceramide from its precursor dihydroceramide and thus controls synthesis of the bioactive lipid ceramide. Moreover, co-treatment with oleate prevented the increase in ceramide, and this occurred through attenuation of the increase in message and activity of DES1. Knockdown of DES1 also protected from palmitate-induced insulin resistance, and overexpression of this enzyme ameliorated the protective effect of oleate. Together, these findings provide insight into the mechanisms of oleate-mediated protection against metabolic disease and provide novel evidence for fatty acid-mediated regulation of a key enzyme of ceramide biosynthesis.

The role of fatty acid desaturases in epidermal metabolism

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

Ncb5or deficiency increases fatty acid catabolism and oxidative stress

The endoplasmic reticulum-associated NADH cytochrome b(5) oxidoreductase (Ncb5or) is widely distributed in animal tissues. Ncb5or(-/-) mice develop diabetes at age 7 weeks and have increased susceptibility to the diabetogenic oxidant streptozotocin. Ncb5or deficiency also results in lipoatrophy and increased hepatocyte sensitivity to cytotoxic effects of saturated fatty acids. Here we investigate the mechanisms of these phenomena in prediabetic Ncb5or(-/-) mice and find that, despite increased rates of fatty acid uptake and synthesis and higher stearoyl-CoA desaturase (SCD) expression, Ncb5or(-/-) liver accumulates less triacylglycerol (TAG) than wild type (WT). Increased fatty acid catabolism and oxidative stress are evident in Ncb5or(-/-) hepatocytes and reflect increased mitochondrial content, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) expression, fatty acid oxidation rates, oxidative stress response gene expression, and oxidized glutathione content. Ncb5or(-/-) hepatocytes readily incorporate exogenous fatty acids into TAG but accumulate more free fatty acids (FFA) and have greater palmitate-induced oxidative stress responses and cell death than WT, all of which are alleviated by co-incubation with oleate via TAG channeling. A high fat diet rich in palmitate and oleate stimulates both lipogenesis and fatty acid catabolism in Ncb5or(-/-) liver, resulting in TAG levels similar to WT but increased intracellular FFA accumulation. Hepatic SCD-specific activity is lower in Ncb5or(-/-) than in WT mice, although Ncb5or(-/-) liver has a greater increase in Scd1 mRNA and protein levels. Together, these findings suggest that increased FFA accumulation and catabolism and oxidative stress are major consequences of Ncb5or deficiency in liver.

Stearoyl CoA desaturase 1: role in cellular inflammation and stress

Stearoyl CoA desaturase 1 (SCD1) catalyzes the rate-limiting step in the production of MUFA that are major components of tissue lipids. Alteration in SCD1 expression changes the fatty acid profile of these lipids and produces diverse effects on cellular function. High SCD1 expression is correlated with metabolic diseases such as obesity and insulin resistance, whereas low levels are protective against these metabolic disturbances. However, SCD1 is also involved in the regulation of inflammation and stress in distinct cell types, including β-cells, adipocytes, macrophages, endothelial cells, and myocytes. Furthermore, complete loss of SCD1 expression has been implicated in liver dysfunction and several inflammatory diseases such as dermatitis, atherosclerosis, and intestinal colitis. Thus, normal cellular function requires the expression of SCD1 to be tightly controlled. This review summarizes the current understanding of the role of SCD1 in modulating inflammation and stress.

Role of peroxisome proliferator-activated receptor {delta}/{beta} in hepatic metabolic regulation

Pharmacological activation of peroxisome proliferator-activated receptor δ/β (PPARδ/β) improves glucose handling and insulin sensitivity. The target tissues of drug actions remain unclear. We demonstrate here that adenovirus-mediated liver-restricted PPARδ activation reduces fasting glucose levels in chow- and high fat-fed mice. This effect is accompanied by hepatic glycogen and lipid deposition as well as up-regulation of glucose utilization and de novo lipogenesis pathways. Promoter analyses indicate that PPARδ regulates hepatic metabolic programs through both direct and indirect transcriptional mechanisms partly mediated by its co-activator, PPARγ co-activator-1β. Assessment of the lipid composition reveals that PPARδ increases the production of monounsaturated fatty acids, which are PPAR activators, and reduces that of saturated FAs. Despite the increased lipid accumulation, adeno-PPARδ-infected livers exhibit less damage and show a reduction in JNK stress signaling, suggesting that PPARδ-regulated lipogenic program may protect against lipotoxicity. The altered substrate utilization by PPARδ also results in a secondary effect on AMP-activated protein kinase activation, which likely contributes to the glucose-lowering activity. Collectively, our data suggest that PPARδ controls hepatic energy substrate homeostasis by coordinated regulation of glucose and fatty acid metabolism, which provide a molecular basis for developing PPARδ agonists to manage hyperglycemia and insulin resistance.

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

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

The key roles of elongases and desaturases in mammalian fatty acid metabolism: Insights from transgenic mice

In mammalian cells, elongases and desaturases play critical roles in regulating the length and degree of unsaturation of fatty acids and thereby their functions and metabolic fates. In the past decade, a great deal has been learnt about these enzymes and the first part of this review summarizes our current knowledge concerning these enzymes. More recently, several transgenic mouse models lacking either an elongase (Elovl3(-/-), Elovl4(-/-), Elovl5(-/-), Elovl6(-/-)) or a desaturase (Scd-1(-/-), Scd-2(-/-), Fads2(-/-)) have been developed and the second part of this review focuses on the insights gained from studies with these mice, as well as from investigations on cell cultures.

Stearoyl-CoA desaturase inhibitors: update on patented compounds

BACKGROUND

Stearoyl-CoA desaturase 1 (SCD1) has been implicated as a novel therapeutic target for the treatment of a variety of disease states, including hepatic steatosis, metabolic diseases, skin and eye disorders, and certain cancers.

OBJECTIVE/METHOD

This review focuses on the novel composition of matter patents in the area of small molecule SCD1 inhibitors, along with their pharmacological effects in relevant disease models. The prospect of targeting SCD1 inhibition as a novel therapeutic approach is discussed.

CONCLUSION

The rapid development of SCD1 inhibitors is evidenced by the increasing number of patent applications published and the number of promising preclinical compounds that have emerged in the past 5 years. Between January 2005 and February 2009, there were approximately 70 SCD1 inhibitor patent applications published.

Characterization of human SCD2, an oligomeric desaturase with improved stability and enzyme activity by cross-linking in intact cells

SCD (stearoyl-CoA desaturase) catalyses the conversion of saturated fatty acids into mono-unsaturated fatty acids, a critical step involved in lipid metabolism and various other biological functions. In the present study, we report the identification and characterization of a human gene that encodes a novel SCD enzyme (hSCD2). The hSCD2 gene codes for a 37.5-kDa protein that shares 61% and 57% sequence identity with the human SCD1 and mouse SCD2 enzymes respectively. The recombinant hSCD2 enzyme expressed in mammalian and Sf9 insect cells efficiently catalysed desaturation of both stearoyl- and palmitoyl-CoAs to the corresponding mono-unsaturated fatty acids. In comparison with the hSCD1 gene that is predominantly expressed in liver, hSCD2 is most abundantly expressed in pancreas and brain. Additionally, hSCD2 transcripts from adult and foetal tissues exhibit different sizes because of alternative splicing in the non-coding region, suggesting that hSCD2 expression is developmentally regulated. The recombinant human SCD2 and SCD1 transiently expressed in COS-7 cells exhibited as oligomeric proteins that consist of homodimers and oligomers when resolved by SDS/PAGE. The complex formation was independent of SCD protein expression levels, as supported by a relatively constant ratio of the level of dimers and oligomers to that of the monomers from COS-7 cells transiently transfected with different amounts of SCD expression vectors. Furthermore, treatment of intact COS-7 cells with a cross-linking reagent resulted in dose-dependent increases in the levels of SCD protein and activity, suggesting that oligomerization may play an important role in regulating the stability of SCD enzymes.

Leptin-mediated changes in hepatic mitochondrial metabolism, structure, and protein levels

Leptin reduces body weight in ob/ob mice by decreasing food intake and increasing energy expenditure; however, the mechanisms by which it does the latter are not known. Here we report that 30% of the weight loss induced by leptin treatment of ob/ob mice is due to changes in energy expenditure. In assessing leptin's effects on specific tissues, we found that hepatic basal metabolic rate was paradoxically decreased 1.7-fold with leptin treatment, which was the result of a 1.6-fold reduction in mitochondrial volume density and altered substrate oxidation kinetics. The altered kinetics were associated with a decrease in protein levels of 2 mitochondrial respiratory chain components--cytochrome c oxidase subunit VIa and cytochrome c oxidase subunit IV. In addition to reduced hepatic metabolism, there was reduced long chain fatty acid production and a 2.5-fold increase in hepatic lipid export, both of which explain the reduced steatosis in leptin-treated animals. These data help clarify the role of the liver in leptin-mediated weight loss and define the mechanisms by which leptin alters hepatic metabolism and corrects steatosis.