Identification of ALOX5 as a gene regulating adiposity and pancreatic function

Exploring the Role of Glycine Metabolism in Coronary Artery Disease: Insights from Human Genetics and Mouse Models

Background: Circulating glycine levels have been associated with reduced risk of coronary artery disease (CAD) in humans but these associations have not been observed in all studies. We evaluated whether the relationship between glycine levels and atherosclerosis was causal using genetic analyses in humans and feeding studies in mice. Methods: Serum glycine levels were evaluated for association with risk of CAD in the UK Biobank. Genetic determinants of glycine levels were identified through a genome-wide association study (GWAS) and used to evaluate the causal relationship between glycine and risk of CAD by Mendelian randomization (MR). A dietary supplementation study was carried out with atherosclerosis-prone apolipoprotein E deficient (ApoE-/-) mice to determine the effects of increased circulating glycine levels on cardiometabolic traits and aortic lesion formation. Results: Among 105,718 UK Biobank subjects, elevated serum glycine levels were associated with significantly reduced risk of prevalent CAD (Quintile 5 vs. Quintile 1 OR = 0.76, 95% CI 0.67-0.87; p < 0.0001) and incident CAD (Quintile 5 vs. Quintile 1 HR = 0.70, 95% CI 0.65-0.77; p < 0.0001) after adjustment for age, sex, ethnicity, anti-hypertensive and lipid-lowering medications, blood pressure, kidney function, and diabetes. A GWAS meta-analysis with 230,947 subjects identified 61 loci for glycine levels, of which 26 were novel. MR analyses provided modest evidence that genetically elevated glycine levels were causally associated with reduced systolic blood pressure and risk of type 2 diabetes, but did not provide significant evidence for an association with decreased risk of CAD. Glycine supplementation in mice had no effects on cardiometabolic traits or atherosclerotic lesion development. Conclusions: While expanding the genetic architecture of glycine metabolism, MR analyses and in vivo feeding studies did not provide evidence that the clinical association of this amino acid with atherosclerosis represents a causal relationship.

Identification of Important Genes Associated with the Development of Atherosclerosis

Atherosclerosis is one of the most important medical problems due to its prevalence and significant contribution to the structure of temporary and permanent disability and mortality. Atherosclerosis is a complex chain of events occurring in the vascular wall over many years. Disorders of lipid metabolism, inflammation, and impaired hemodynamics are important mechanisms of atherogenesis. A growing body of evidence strengthens the understanding of the role of genetic and epigenetic factors in individual predisposition and development of atherosclerosis and its clinical outcomes. In addition, hemodynamic changes, lipid metabolism abnormalities, and inflammation are closely related and have many overlapping links in regulation. A better study of these mechanisms may improve the quality of diagnosis and management of such patients.

Effect of Genetic and Dietary Perturbation of Glycine Metabolism on Atherosclerosis in Humans and Mice

Objective

Epidemiological and genetic studies have reported inverse associations between circulating glycine levels and risk of coronary artery disease (CAD). However, these findings have not been consistently observed in all studies. We sought to evaluate the causal relationship between circulating glycine levels and atherosclerosis using large-scale genetic analyses in humans and dietary supplementation experiments in mice.

Methods

Serum glycine levels were evaluated for association with prevalent and incident CAD in the UK Biobank. A multi-ancestry genome-wide association study (GWAS) meta-analysis was carried out to identify genetic determinants for circulating glycine levels, which were then used to evaluate the causal relationship between glycine and risk of CAD by Mendelian randomization (MR). A glycine feeding study was carried out with atherosclerosis-prone apolipoprotein E deficient (ApoE-/-) mice to determine the effects of increased circulating glycine levels on amino acid metabolism, metabolic traits, and aortic lesion formation.

Results

Among 105,718 subjects from the UK Biobank, elevated serum glycine levels were associated with significantly reduced risk of prevalent CAD (Quintile 5 vs. Quintile 1 OR=0.76, 95% CI 0.67-0.87; P<0.0001) and incident CAD (Quintile 5 vs. Quintile 1 HR=0.70, 95% CI 0.65-0.77; P<0.0001) in models adjusted for age, sex, ethnicity, anti-hypertensive and lipid-lowering medications, blood pressure, kidney function, and diabetes. A meta-analysis of 13 GWAS datasets (total n=230,947) identified 61 loci for circulating glycine levels, of which 26 were novel. MR analyses provided modest evidence that genetically elevated glycine levels were causally associated with reduced systolic blood pressure and risk of type 2 diabetes, but did provide evidence for an association with risk of CAD. Furthermore, glycine-supplementation in ApoE-/- mice did not alter cardiometabolic traits, inflammatory biomarkers, or development of atherosclerotic lesions.

Conclusions

Circulating glycine levels were inversely associated with risk of prevalent and incident CAD in a large population-based cohort. While substantially expanding the genetic architecture of circulating glycine levels, MR analyses and in vivo feeding studies in humans and mice, respectively, did not provide evidence that the clinical association of this amino acid with CAD represents a causal relationship, despite being associated with two correlated risk factors.

Genetic and Epigenetic Regulation of Lipoxygenase Pathways and Reverse Cholesterol Transport in Atherogenesis

Atherosclerosis is one of the most important medical and social problems of modern society. Atherosclerosis causes a large number of hospitalizations, disability, and mortality. A considerable amount of evidence suggests that inflammation is one of the key links in the pathogenesis of atherosclerosis. Inflammation in the vascular wall has extensive cross-linkages with lipid metabolism, and lipid mediators act as a central link in the regulation of inflammation in the vascular wall. Data on the role of genetics and epigenetic factors in the development of atherosclerosis are of great interest. A growing body of evidence is strengthening the understanding of the significance of gene polymorphism, as well as gene expression dysregulation involved in cross-links between lipid metabolism and the innate immune system. A better understanding of the genetic basis and molecular mechanisms of disease pathogenesis is an important step towards solving the problems of its early diagnosis and treatment.

Effects of Arachidonic Acid and Its Metabolites on Functional Beta-Cell Mass

Arachidonic acid (AA) is a polyunsaturated 20-carbon fatty acid present in phospholipids in the plasma membrane. The three primary pathways by which AA is metabolized are mediated by cyclooxygenase (COX) enzymes, lipoxygenase (LOX) enzymes, and cytochrome P450 (CYP) enzymes. These three pathways produce eicosanoids, lipid signaling molecules that play roles in biological processes such as inflammation, pain, and immune function. Eicosanoids have been demonstrated to play a role in inflammatory, renal, and cardiovascular diseases as well type 1 and type 2 diabetes. Alterations in AA release or AA concentrations have been shown to affect insulin secretion from the pancreatic beta cell, leading to interest in the role of AA and its metabolites in the regulation of beta-cell function and maintenance of beta-cell mass. In this review, we discuss the metabolism of AA by COX, LOX, and CYP, the roles of these enzymes and their metabolites in beta-cell mass and function, and the possibility of targeting these pathways as novel therapies for treating diabetes.

Leukotriene C4 synthase is a novel PPARγ target gene, and leukotriene C4 and D4 activate adipogenesis through cysteinyl LT1 receptors in adipocytes

Leukotriene (LT) C₄ synthase (LTC4S) catalyzes the conversion from LTA₄ to LTC_4, which is a proinflammatory lipid mediator in asthma and other inflammatory diseases. LTC₄ is metabolized to LTD₄ and LTE₄, all of which are known as cysteinyl (Cys) LTs and exert physiological functions through CysLT receptors. LTC4S is expressed in adipocytes. However, the function of CysLTs and the regulatory mechanism in adipocytes remain unclear. In this study, we investigated the expression of LTC4S and production of CysLTs in murine adipocyte 3T3-L1 cells and their underlying regulatory mechanisms. Expression of LTC4S and production of LTC₄ and CysLTs increased during adipogenesis, whereas siRNA-mediated suppression of LTC4S expression repressed adipogenesis by reducing adipogenic gene expression. The CysLT1 receptor, one of the two LTC₄ receptors, was expressed in adipocytes. LTC₄ and LTD₄ increased the intracellular triglyceride levels and adipogenic gene expression, and their enhancement was suppressed by co-treatment with pranlukast, a CysLT1 receptor antagonist. Moreover, the expression profiles of LTC4S gene/protein during adipogenesis resembled those of peroxisome proliferator-activated receptor (PPAR) γ. LTC4S expression was further upregulated by treatment with troglitazone, a PPARγ agonist. Promoter-luciferase and chromatin immunoprecipitation assays showed that PPARγ directly bound to the PPAR response element of the LTC4S gene promoter in adipocytes. These results indicate that the LTC4S gene expression was enhanced by PPARγ, and LTC₄ and LTD₄ activated adipogenesis through CysLT1 receptors in 3T3-L1 cells. Thus, LTC4S and CysLT1 receptors are novel potential targets for the treatment of obesity.

NOTUM promotes thermogenic capacity and protects against diet-induced obesity in male mice

We recently showed that NOTUM, a liver-secreted Wnt inhibitor, can acutely promote browning of white adipose. We now report studies of chronic overexpression of NOTUM in liver indicating that it protects against diet-induced obesity and improves glucose homeostasis in mice. Adeno-associated virus (AAV) vectors were used to overexpress GFP or mouse Notum in the livers of male C57BL/6J mice and the mice were fed an obesifying diet. After 14 weeks of high fat, high sucrose diet feeding, the AAV-Notum mice exhibited decreased obesity and improved glucose tolerance compared to the AAV-GFP mice. Gene expression and immunoblotting analysis of the inguinal fat and brown fat revealed increased expression of beige/brown adipocyte markers in the AAV-Notum group, suggesting enhanced thermogenic capacity by NOTUM. A β3 adrenergic receptor agonist-stimulated lipolysis test suggested increased lipolysis capacity by NOTUM. The levels of collagen and C–C motif chemokine ligand 2 (CCL2) in the epididymal white adipose tissue of the AAV-Notum mice were significantly reduced, suggesting decreased fibrosis and inflammation, respectively. RNA sequencing analysis of inguinal white adipose of 4-week chow diet-fed mice revealed a highly significant enrichment of extracellular matrix (ECM) functional cluster among the down-regulated genes in the AAV-Notum group, suggesting a potential mechanism contributing to improved glucose homeostasis. Our in vitro studies demonstrated that recombinant human NOTUM protein blocked the inhibitory effects of WNT3A on brown adipocyte differentiation. Furthermore, NOTUM attenuated WNT3A’s effects on upregulation of TGF-β signaling and its downstream targets. Overall, our data suggest that NOTUM modulates adipose tissue function by promoting thermogenic capacity and inhibiting fibrosis through inhibition of Wnt signaling.

Characterization of Autozygosity in Pigs in Three-Way Crossbreeding

Crossbreeding in livestock can be used to increase genetic diversity. The resulting increase in variability is related to the heterozygosity of the crossbred animal. The evolution of diversity during crossbreeding can be assessed using genomic data. The objective of this study was to describe patterns of runs of homozygosity (ROH) in animals resulting from three-way crossbreeding, from parental pure lines, and in their crossbred offspring. The crossbreeding scheme consisted of a first crossbreeding Pietrain boars and Large White sows, after which the offspring of the Pietrain × Large White were crossed with Duroc boars. The offspring of the second crossbreeding are called G0, the offspring of G0 boars and G0 sows are called G1. All the animals were genotyped using the Illumina SNP60 porcine chip. After filtering, analyses were performed with 2,336 animals and 48,579 autosomal single nucleotide polymorphism (SNP). The mean ROH-based inbreeding coefficients were shown to be 0.27 ± 0.05, 0.23 ± 0.04, and 0.26 ± 0.04 for Duroc, Large White, and Pietrain, respectively. ROH were detected in the Pietrain × Large White crossbred but the homozygous segments were fewer and smaller than in their parents. Similar results were obtained in the G0 crossbred. However, in the G1 crossbreds the number and the size of ROH were higher than in G0 parents. Similar ROH hotspots were detected on SSC1, SSC4, SSC7, SSC9, SSC13, SSC14, and SSC15 in both G0 and G1 animals. Long ROH (>16 Mb) were observed in G1 animals, suggesting regions with low recombination rates. The conservation of these homozygous segments in the three crossbred populations means that some haplotypes were shared between parental breeds. Gene annotation in ROH hotspots in G0 animals identified genes related to production traits including carcass composition and reproduction. These findings advance our understanding of how to manage genetic diversity in crossbred populations.

Leukotriene A4 hydrolase deficiency protects mice from diet-induced obesity by increasing energy expenditure through neuroendocrine axis

Obesity is a health problem worldwide, and brown adipose tissue (BAT) is important for energy expenditure. Here, we explored the role of leukotriene A₄ hydrolase (LTA₄ H), a key enzyme in the synthesis of the lipid mediator leukotriene B₄ (LTB₄ ), in diet-induced obesity. LTA₄ H-deficient (LTA₄ H-KO) mice fed a high-fat diet (HFD) showed a lean phenotype, and bone-marrow transplantation studies revealed that LTA₄ H-deficiency in non-hematopoietic cells was responsible for this lean phenotype. LTA₄ H-KO mice exhibited greater energy expenditure, but similar food intake and fecal energy loss. LTA₄ H-KO BAT showed higher expression of thermogenesis-related genes. In addition, the plasma thyroid-stimulating hormone and thyroid hormone concentrations, as well as HFD-induced catecholamine secretion, were higher in LTA₄ H-KO mice. In contrast, LTB₄ receptor (BLT1)-deficient mice did not show a lean phenotype, implying that the phenotype of LTA₄ H-KO mice is independent of the LTB₄ /BLT1 axis. These results indicate that LTA₄ H mediates the diet-induced obesity by reducing catecholamine and thyroid hormone secretion.

The association between the rs4987105 of 5-lipoxygenase (ALOX5) gene and gestational glucose metabolism in Chinese population

Objective

The arachidonate 5-lipoxygenase (ALOX5) pathway has been investigated in diverse chronic inflammatory diseases including metabolic disorders. Recently, the ALOX5 polymorphism rs4987105 was identified to confer susceptibility to type 2 diabetes mellitus (T2DM), implicating its role in regulating glucose homeostasis. Gestational diabetes mellitus (GDM) shares similar pathogenic mechanism with T2DM. Thus, we aimed to evaluate the association between rs4987105 and gestational glucose metabolism in Chinese pregnant women.

Results

A total of 380 unrelated Chinese pregnant women including 241 GDM patients and 139 controls were included in this study. The genotypes of rs4987105 were examined by the Agena MassARRAY iPLEX platform, the association between rs4987105 and fasting plasma glucose (FPG) levels at 24–28 gestational weeks was evaluated using different statistical methods. We found that carriers of rs4987105 CT/TT genotypes exhibited significantly lower FPG levels (P = 0.011). In addition, we observed a significant association between rs4987105 and FPG levels after adjusting confounding variables in the linear regression analysis using dominant genetic model (b = − 0.218; P = 0.01). The present study for the first time reported that the rs4987105 of 5-lipoxygenase (ALOX5) gene was associated with gestational glucose metabolism in Chinese pregnant women.

Fatty Acid Metabolite Profiling Reveals Oxylipins as Markers of Brown but Not Brite Adipose Tissue

Metabolites of omega-6 and omega-3 polyunsaturated fatty acids are important signaling molecules implicated in the control of adipogenesis and energy balance regulation. Some of these metabolites belonging to the group of oxylipins have been associated with non-shivering thermogenesis in mice mediated by brown or brite adipose tissue. We aimed to identify novel molecules with thermogenic potential and to clarify the relevance of these findings in a translational context. Therefore, we characterized and compared the oxylipin profiles of murine and human adipose tissues with different abundance of brown or brite adipocytes. A broad panel of 36 fatty acid metabolites was quantified in brown and white adipose tissues of C57BL/6J mice acclimatized to different ambient temperatures and in biopsies of human supraclavicular brown and white adipose tissue. The oxylipin profile of murine brite adipose tissue was not distinguishable from white adipose tissue, suggesting that adipose tissue browning in vivo is not associated with major changes in the oxylipin metabolism. Human brown and white adipose tissue also exhibited similar metabolite profiles. This is in line with previous studies proposing human brown adipose tissue to resemble the nature of murine brite adipose tissue representing a heterogeneous mixture of brite and white adipocytes. Although the global oxylipin profile served as a marker for the abundance of thermogenic adipocytes in bona fide brown but not white adipose tissue, we identified 5-HETE and 5,6-EET as individual compounds consistently associated with the abundance of brown or brite adipocytes in human BAT and murine brite fat. Further studies need to establish whether these candidates are mere markers or functional effectors of thermogenic capacity.

Functional Characterization of Knock-In Mice Expressing a 12/15-Lipoxygenating Alox5 Mutant Instead of the 5-Lipoxygenating Wild-Type Enzyme

Aims: Most mammalian genomes involve several genes encoding for functionally distinct arachidonate lipoxygenase (ALOX isoforms). Proinflammatory leukotrienes are formed via the ALOX5 pathway, but 12/15-lipoxygenating ALOX isoforms have been implicated in the biosynthesis of pro-resolving mediators. In vitro mutagenesis of the triad determinants abolished the leukotriene synthesizing activity of ALOX5, but the biological consequences of these alterations have not been studied. To fill this gap, we created Alox5 knock-in mice, which express the 12/15-lipoxygenating Phe359Trp + Ala424Ile + Asn425Met Alox5 triple mutant and characterized its phenotypic alterations. Results: The mouse Alox5 triple mutant functions as arachidonic acid 15-lipoxygenating enzyme, which also forms 12S-hydroxy and 8S-hydroxy arachidonic acid. In contrast to the wild-type enzyme, the triple mutant effectively oxygenates linoleic acid to 13S-hydroxy linoleic acid (13S-HODE), which functions as activating ligand of the type-2 nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ). Knock-in mice expressing the mutant enzyme are viable, fertile, and develop normally. The mice cannot synthesize proinflammatory leukotrienes but show significantly attenuated plasma levels of lipolytic endocannabinoids. When aging, the animals gained significantly more body weight, which may be related to the fivefold higher levels of 13-HODE in the adipose tissue. Innovation: These data indicate for the first time that in vivo mutagenesis of the triad determinants of mouse Alox5 abolished the biosynthetic capacity of the enzyme for proinflammatory leukotrienes and altered the catalytic properties of the protein favoring the formation of 13-HODE. Conclusion:In vivo triple mutation of the mouse Alox5 gene impacts the body weight homeostasis of aging mice via augmented formation of the activating PPARγ ligand 13-HODE.

5-Lipoxygenase (ALOX5): Genetic susceptibility to type 2 diabetes and vitamin D effects on monocytes

The arachidonate 5-lipoxygenase (ALOX5) pathway has been implicated in chronic inflammatory disease which may be influenced by vitamin D due to vitamin D response elements (VDRE). We investigated an ALOX5 polymorphism (rs4987105) in patients with type 2 diabetes (T2D) and the in vitro effects of calcitriol (1,25(OH)₂D₃) on ALOX5 metabolism in monocytes of T2D patients and healthy controls (HC). 533 T2D and 473 HC were genotyped for the rs4987105 polymorphism. In addition, the 25(OH)D₃ and 1,25(OH)₂D₃ plasma levels were measured in both cohorts. Further C-reactive protein (CRP) was determined in T2D patients. Our results demonstrate, that genotype CC and the allele C of ALOX5 rs4987105 polymorphism were more frequent in T2D compared to HC (OR = 1.44; 95% CI: 1.12-1.84; p < 0.05). Lower levels of both vitamin D metabolites (p < 0.0001 respectively) were found in the CC genotyped T2D patients compared to CC genotyped HC. In addition, CC genotyped T2D patients had higher levels of CRP compared to CT and TT genotyped T2D patients, (p < 0.01). In order to evaluate the impact of calcitriol in primary isolated monocytes, we isolated monocytes of 20 T2D patients and 20 HC. The cells were treated with 1,25(OH)₂D₃ and interleukin-1beta (IL-1β) for 24 h. The following genes were analysed for expression changes: ALOX5, leukotriene A4 hydrolase (LTA4H), leukotriene B4 receptor type 1 (LTB4R1) and CD14. Treatment with IL-1β+1,25(OH)₂D₃ increased ALOX5, LTA4H and LTB4R1 and CD14 mRNA in both T2D patients and HC (p < 0.0001, respectively). In addition, IL-1β+1,25(OH)₂D₃ treatment led to higher ALOX5, LTA4H and CD14 mRNA levels in T2D patients compared to HC (p < 0.001, p < 0.05, p ≤ 0.05, respectively). In conclusion, ALOX5 rs4987105 allele C confers susceptibility to T2D, lower vitamin D metabolites and higher CRP levels complement this association. Additionally, IL-1β+1,25(OH)₂D₃ treatment on, ALOX5, LTA4H and CD14 mRNA indicate a diabetes specific modulation. These findings identify a novel pathway in T2D potentially amenable for individualized therapeutic targeting.

Exposure to Nanoscale Particulate Matter from Gestation to Adulthood Impairs Metabolic Homeostasis in Mice

Emerging evidence from epidemiological and animal studies suggests that exposure to traffic-related air pollutants and particulate matter less than 2.5 µm in diameter (PM_2.5) contributes to development of obesity and related metabolic abnormalities. However, it is not known whether nanoscale particulate matter (nPM) with aerodynamic diameter ≤200 nm have similar adverse metabolic effects. The goal of the present study was to determine the effects of prenatal and early life exposure to nPM on metabolic homeostasis in mice. C57BL/6 J mice were exposed to nPM or filtered air from gestation until 17 weeks of age and characterized for metabolic and behavioral parameters. In male mice, nPM exposure increased food intake, body weight, fat mass, adiposity, and whole-body glucose intolerance (p < 0.05). Consistent with these effects, male mice exposed to nPM displayed alterations in the expression of metabolically-relevant neuropeptides in the hypothalamus and decreased expression of insulin receptor signaling genes in adipose (p < 0.05). There were no differences in exploratory behavior or motor function, fasting lipid levels, or the inflammatory profile of adipose tissue. Our results provide evidence that chronic nPM exposure from gestation to early adulthood in male mice promotes metabolic dysregulation in part through modulation of feeding behavior and in the absence of an obesogenic diet.

Functional peroxisomes are required for β-cell integrity in mice

Objectives

Peroxisomes play a crucial role in lipid and reactive oxygen species metabolism, but their importance for pancreatic β-cell functioning is presently unknown. To examine the contribution of peroxisomal metabolism to β-cell homeostasis in mice, we inactivated PEX5, the import receptor for peroxisomal matrix proteins, in an inducible and β-cell restricted manner (Rip-Pex5^−/− mice).

Methods

After tamoxifen-induced recombination of the Pex5 gene at the age of 6 weeks, mice were fed either normal chow or a high-fat diet for 12 weeks and were subsequently phenotyped.

Results

Increased levels of very long chain fatty acids and reduced levels of plasmalogens in islets confirmed impairment of peroxisomal fatty acid oxidation and ether lipid synthesis, respectively. The Rip-Pex5^−/− mice fed on either diet exhibited glucose intolerance associated with impaired insulin secretion. Ultrastructural and biochemical analysis revealed a decrease in the density of mature insulin granules and total pancreatic insulin content, which was further accompanied by mitochondrial disruptions, reduced complex I activity and massive vacuole overload in β-cells. RNAseq analysis suggested that cell death pathways were affected in islets from HFD-fed Rip-Pex5^−/− mice. Consistent with this change we observed increased β-cell apoptosis in islets and a decrease in β-cell mass.

Conclusions

Our data indicate that normal peroxisome metabolism in β-cells is crucial to preserve their structure and function.

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Pex5 deletion in β-cells impairs glucose tolerance and reduces β-cell mass.

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Pex5-deficient β-cells display increased apoptosis.

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Peroxisomal loss causes mitochondrial deterioration and cytoplasmic vacuolization.

Genetic variation in the leukotriene pathway is associated with myocardial infarction in the Chinese population

Background

Genetic variation in the genes ALOX5 (arachidonate 5-lipoxygenase), ALOX5AP (arachidonate 5-lipoxygenase-activating protein) and LTA4H (leukotriene A4 hydrolase) has previously been shown to contribute to the risk of MI (myocardial infarction) in Caucasian and African American populations. All genes encode proteins playing a role in the synthesis of the pro-inflammatory leukotriene B mediators, possibly providing a link between MI and inflammation. The aim of the present study was to investigate whether these associations could be confirmed in the study of China MI patients. The study included 401 Han Chinese MI patients and 409 controls. Six tag single nucleotide polymorphisms (SNPs)—ALOX5 rs12762303 and rs12264801, ALOX5AP rs10507391, LTA4H rs2072512, rs2540487 and rs2540477—were selected. SNP genotyping was performed by an improved multiplex ligation detection reaction assay.

Results

The rs2540487 genotype was associated with the risk of MI in overdominant model (P = 0.008). rs12762303 and rs10507391 SNPs were significantly associated with lipid levels in MI patients (P < 0.006–0.008). Several SNPs interacted with alcohol consumption, cigarette smoking, and hypertension to modify TC, TG, LDL-C and CRE levels, and the risk of MI (P < 0.0017 for all). No association between the SNPs of LT pathway and susceptibility to MI was found (P > 0.05 for all).

Conclusions

Taken together, this study provides additional evidence that functional genetic variation of the LT pathway can mediate atherogenic processes and the risk of MI in Chinese.

5-LO inhibition ameliorates palmitic acid-induced ER stress, oxidative stress and insulin resistance via AMPK activation in murine myotubes

Leukotriene B4 (LTB4) production via the 5-lipoxygenase (5-LO) pathway contributes to the development of insulin resistance in adipose and hepatic tissues, but the role of LTB4 in skeletal muscle is relatively unknown. Here, the authors investigated the role of LTB4 in C2C12 myotubes in palmitic acid (PA)-induced ER stress, inflammation and insulin resistance. PA (750 μM) evoked lipotoxicity (ER stress, oxidative stress, inflammation and insulin resistance) in association with LTB4 production. 5-LO inhibition reduced all the lipotoxic effects induced by PA. On the other hand, PA did not induce cysteinyl leukotrienes (CysLTs), which themselves had no effect on ER stress and inflammation. The beneficial effects of 5-LO suppression from PA-induced lipotoxicity were related with AMPK activation. In ob/ob mice, once daily oral administration of zileuton (50, 100 mg/kg) for 5 weeks improved insulin resistance, increased AMPK phosphorylation, and reduced LTB4 and ER stress marker expression in skeletal muscle. These results show that 5-LO inhibition by either zileuton or 5-LO siRNA protects C2C12 myotubes from PA-induced lipotoxicity, at least partly via AMPK activation, and suggest that the in vivo insulin-sensitizing effects of zileuton are in part attributable to its direct action on skeletal muscle via LTB4 downregulation followed by AMPK activation.

Identification and profiling of microRNAs from ovary of estrous Kazakh sheep induced by nutritional status in the anestrous season

Estrous regulation in sheep has an important role in the sheep industry in improving production of meat and wool. It has been reported that an enhanced nutritional status can induce estrus resulting in an end of the anestrous season earlier than occurs in ewes with a lesser nutritional status. However, the endocrine and physiological mechanisms that induce the increased incidence of estrus remains unclear. In the present study, the differences in amounts and characteristics of miRNAs in ewes at estrus or during the anestrous season were screened by using the Illumina HiSeq sequencing technology. In total, 294 miRNAs, including 174 novel miRNA candidates, were identified in ewes with an enhanced nutritional status (OEN) through assessment of the OEN library for this group and 307 miRNAs including 186 novel miRNA candidates were identified in the ewes with a lesser nutritional status (OAN) through assessing the OAN library, among which there were nine conserved and 104 novel miRNAs in differential amounts between the two libraries. Based on poly (A) q-PCR, six miRNAs were assessed to verify the accuracy of the library database. Furthermore, the family of the known miRNAs, the target genes and related pathways were also analyzed. The results indicated that the nutritional status had important roles in estrous regulation in sheep. The PLA2G4D can directly regulate ovarian follicle development, or indirectly influence leptin secretion involved in the regulation of the reproductive endocrine and physiological systems during the anestrous season. The identification of significantly different miRNAs expanded the repertoire of sheep miRNAs that have been examined and could contribute to further studies on the molecular mechanism of regulation of initiation of estrous cycles in previously anestrous ewes as influenced by different nutritional status.

ALOX5AP Overexpression in Adipose Tissue Leads to LXA4 Production and Protection Against Diet-Induced Obesity and Insulin Resistance

Eicosanoids, such as leukotriene B4 (LTB4) and lipoxin A4 (LXA4), may play a key role during obesity. While LTB4 is involved in adipose tissue inflammation and insulin resistance, LXA4 may exert anti-inflammatory effects and alleviate hepatic steatosis. Both lipid mediators derive from the same pathway, in which arachidonate 5-lipoxygenase (ALOX5) and its partner, arachidonate 5-lipoxygenase-activating protein (ALOX5AP), are involved. ALOX5 and ALOX5AP expression is increased in humans and rodents with obesity and insulin resistance. We found that transgenic mice overexpressing ALOX5AP in adipose tissue had higher LXA4 rather than higher LTB4 levels, were leaner, and showed increased energy expenditure, partly due to browning of white adipose tissue (WAT). Upregulation of hepatic LXR and Cyp7a1 led to higher bile acid synthesis, which may have contributed to increased thermogenesis. In addition, transgenic mice were protected against diet-induced obesity, insulin resistance, and inflammation. Finally, treatment of C57BL/6J mice with LXA4, which showed browning of WAT, strongly suggests that LXA4 is responsible for the transgenic mice phenotype. Thus, our data support that LXA4 may hold great potential for the future development of therapeutic strategies for obesity and related diseases.

Differential expression of genes in milk of dairy cattle during lactation

The milk fat globule (MFG) is one of the most representative of mammary gland tissues and can be utilized to study gene expression of lactating cows during lactation. In this study, RNA-seq technology was employed to detect differential expression of genes in MFGs at day 10 and day 70 after calving between two groups of cows with extremely high (H group) and low (L group) 305-day milk yield, milk fat yield and milk protein yield. In total, 1232, 81, 429 and 178 significantly differentially expressed genes (false discovery rate q < 0.05) were detected between H10 and L10, H70 and L70, H10 and H70, and L10 and L70 respectively. Gene Ontology enrichment and pathway analysis revealed that these differentially expressed genes were enriched in biological processes involved in mammary gland development, protein and lipid metabolism process, signal transduction, cellular process, differentiation and immune function. Among these differentially expressed genes, 178 (H10 vs. L10), 4 (H70 vs. L70), 68 (H10 vs. H70) and 22 (L10 vs. L70) were found to be located within previously reported QTL regions for milk production traits. Based on these results, some promising candidate genes for milk production traits in dairy cattle were suggested.

Changes of the expressions of multiple metabolism genes in rat pancreatic islets after ventromedial hypothalamic lesioning

It was recently reported that ventromedial hypothalamic lesions change the expression of cell proliferation-related genes and morphology-related genes in rat pancreatic islets. This study has examined how gene families involved in metabolism are regulated in rat pancreatic islets after VMH lesions formation. Total pancreatic islets RNA was extracted, and differences in the gene expression profiles between rats at day 3 after VMH lesioning and sham-VMH-lesioned rats were investigated using DNA microarray and real-time polymerase chain reaction. The VMH lesions regulated the genes that are involved in functions related to metabolism in the pancreas islets. Real-time polymerase chain reaction also confirmed that gene expressions of arachidonate 15-lipoxygenase (Alox15) was up-regulated and pancreatic lipase (Pnlip) was downregulated at day 3 after the VMH lesions. Ventromedial hypothalamic lesions may change the expression of multiple metabolism genes in rat pancreatic islets.

Minireview: 12-Lipoxygenase and Islet β-Cell Dysfunction in Diabetes

The insulin producing islet β-cells have increasingly gained attention for their role in the pathogeneses of virtually all forms of diabetes. Dysfunction, de-differentiation, and/or death of β-cells are pivotal features in the transition from normoglycemia to hyperglycemia in both animal models of metabolic disease and humans. In both type 1 and type 2 diabetes, inflammation appears to be a central cause of β-cell derangements, and molecular pathways that modulate inflammation or the inflammatory response are felt to be prime targets of future diabetes therapy. The lipoxygenases (LOs) represent a class of enzymes that oxygenate cellular polyunsaturated fatty acids to produce inflammatory lipid intermediates that directly and indirectly affect cellular function and survival. The enzyme 12-LO is expressed in all metabolically active tissues, including pancreatic islets, and has received increasing attention for its role in promoting cellular inflammation in the setting of diabetes. Genetic deletion models of 12-LO in mice reveal striking protection from metabolic disease and its complications and an emerging body of literature has implicated its role in human disease. This review focuses on the evidence supporting the proinflammatory role of 12-LO as it relates to islet β-cells, and the potential for 12-LO inhibition as a future avenue for the prevention and treatment of metabolic disease.

Exploring N(1)-p-fluorobenzyl-cymserine as an inhibitor of 5-lipoxygenase as a candidate for type 2 diabetes and neurodegenerative disorder treatment

Developing a single selective ligand to a target relevant to two mechanistically interlinked diseases, such as type 2 diabetes mellitus (T2DM) and a neurodegenerative disorder, like Parkinson's disease or Alzheimer's disease, provides the potential for an effective treatment that may impact both. The enzyme 5-lipoxygenase (5-LOX) has been revealed responsible for producing fatty acid molecules, leukotrienes. These leukotrienes are known to produce inflammatory responses in asthma and allergic reactions, to induce a reduction of tyrosine hydroxylase in brain, and are involved in the development of cardiac strokes, obesity and type 2 diabetes. N(1)-p-fluorobenzyl-cymserine (FBC), an analogue of cymserine and a known cholineterase inhibitor, was evaluated for inhibition of pleiotropic 5-LOX in our study. The stable 3D structure of 5-LOX was obtained from the Protein Data Bank (PDB) database and was implied for homology modeling of four reported mutant models. Each generated model was submitted to the Protein Model Database (PMDB) and employed for measuring inhibition and ligand efficiency of FBC with support of molecular docking. For each model, normal as well as mutant, FBC yielded remarkable inhibition constant values, with exothermic free binding energies. The current study revealed a highly reactive narrow fissure near the non-heme iron binding pocket of 5-LOX that contains residues crucial for 5-LOX stability and FBC binding. Investigating the binding of FBC with stabilized and destabilized 5-LOX structures confirmed it as a candidate therapeutic inhibitor worthy of assessment in preclinical models of T2DM and neurodegeneration.

The effects of Leptin and Adiponectin on Pdx1, Foxm1, and PPARγ Transcription in Rat Islets of Langerhans

BACKGROUND

Leptin and adiponectin are two hormones, which are released from adipocytes in order to control energy expenditure. Both hormones are also involved in glucose homeostasis through control of insulin secretion from pancreatic islets. Since Pdx1, PPARγ, and foxm1 play important roles in islets function, it is essential to understand how these genes are regulated in the islets of Langerhans.

OBJECTIVES

We have designed an experiment to identify the effect of leptin and adiponectin treatment on Pdx1, PPARγ, and foxm1 transcription.

MATERIALS AND METHODS

Islets were isolated from adult male rats by collagenase and incubated with different concentrations of leptin and adiponectin for 24 hours. Next, by means of real time PCR, we evaluated the gene transcription related to a housekeeping gene. The effect of leptin and adiponectin on insulin secretion was evaluated by ELISA.

RESULTS

Leptin decreased PPARγ transcription and insulin secretion, while adiponectin significantly increased Pdx1 and PPARγ transcription and insulin secretion in rat islets. The transcription of foxm1 did not change in the islet cells treated with leptin or adiponectin.

CONCLUSIONS

These findings indicate the possibility that Pdx1 and PPARγ transcription is a mediator of leptin and adiponectin function in control of insulin secretion and glucose homeostasis in pancreatic islets.

5-lipoxygenase-activating protein as a modulator of olanzapine-induced lipid accumulation in adipocyte

Experiments were performed in 3T3-L1 preadipocytes differentiated in vitro into adipocytes. Cells were treated with olanzapine and a 5-lipoxygenase (5-LOX) activating protein (FLAP) inhibitor MK-886. Lipid content was measured using an Oil Red O assay; 5-LOX and FLAP mRNA content was measured using quantitative real-time PCR; the corresponding protein contents were measured using quantitative Western blot assay. Olanzapine did not affect the cell content of 5-LOX mRNA and protein; it decreased FLAP mRNA and protein content at day five but not 24 hours after olanzapine addition. In the absence of MK-886, low concentrations of olanzapine increased lipid content only slightly, whereas a 56% increase was induced by 50 μM olanzapine. A 5-day cotreatment with 10 μM MK-886 potentiated the lipid increasing action of low concentrations of olanzapine. In contrast, in the presence of 50 μM olanzapine nanomolar and low micromolar concentrations of MK-886 reduced lipid content. These data suggest that FLAP system in adipocytes is affected by olanzapine and that it may modify how these cells respond to the second-generation antipsychotic drugs (SGADs). Clinical studies could evaluate whether the FLAP/5-LOX system could play a role in setting a variable individual susceptibility to the metabolic side effects of SGADs.

Omega-3-derived mediators counteract obesity-induced adipose tissue inflammation

Chronic low-grade inflammation in adipose tissue has been recognized as a key step in the development of obesity-associated complications. In obesity, the accumulation of infiltrating macrophages in adipose tissue and their phenotypic switch to M1-type dysregulate inflammatory adipokine production leading to obesity-linked insulin resistance. Resolvins are potent anti-inflammatory and pro-resolving mediators endogenously generated from omega-3 fatty acids that act as "stop-signals" of the inflammatory response promoting the resolution of inflammation. Recently, a deficit in the production of these endogenous anti-inflammatory signals has been demonstrated in obese adipose tissue. The restoration of their levels by either exogenous administration of these mediators or feeding omega-3-enriched diets, improves the inflammatory status of adipose tissue and ameliorates metabolic dysfunction. Here, we review the current knowledge on the role of these endogenous autacoids in the resolution of adipose tissue inflammation with special emphasis on their functional actions on macrophages.

Fatty acids induce leukotriene C4 synthesis in macrophages in a fatty acid binding protein-dependent manner

Obesity results in increased macrophage recruitment to adipose tissue that promotes a chronic low-grade inflammatory state linked to increased fatty acid efflux from adipocytes. Activated macrophages produce a variety of pro-inflammatory lipids such as leukotriene C4 (LTC4) and 5-, 12-, and 15-hydroxyeicosatetraenoic acid (HETE) suggesting the hypothesis that fatty acids may stimulate eicosanoid synthesis. To assess if eicosanoid production increases with obesity, adipose tissue of leptin deficient ob/ob mice was analyzed. In ob/ob mice, LTC4 and 12-HETE levels increased in the visceral (but not subcutaneous) adipose depot while the 5-HETE levels decreased and 15-HETE abundance was unchanged. Since macrophages produce the majority of inflammatory molecules in adipose tissue, treatment of RAW264.7 or primary peritoneal macrophages with free fatty acids led to increased secretion of LTC4 and 5-HETE, but not 12- or 15-HETE. Fatty acid binding proteins (FABPs) facilitate the intracellular trafficking of fatty acids and other hydrophobic ligands and in vitro stabilize the LTC4 precursor leukotriene A4 (LTA4) from non-enzymatic hydrolysis. Consistent with a role for FABPs in LTC4 synthesis, treatment of macrophages with HTS01037, a specific FABP inhibitor, resulted in a marked decrease in both basal and fatty acid-stimulated LTC4 secretion but no change in 5-HETE production or 5-lipoxygenase expression. These results indicate that the products of adipocyte lipolysis may stimulate the 5-lipoxygenase pathway leading to FABP-dependent production of LTC4 and contribute to the insulin resistant state.

Role of leukotriene B₄ receptor signaling in human preadipocyte differentiation

We investigated the role of leukotriene B(4) (LTB(4))-leukotriene receptor (BLT) signaling in preadipocyte differentiation into mature adipocytes. Blockade of BLT signaling by treatment with lipoxygenase inhibitors, a BLT antagonist, and small interfering RNAs for BLTs in human and mouse preadipocytes isolated from adipose tissues showed acceleration of differentiation into mature adipocytes. DNA microarray analysis revealed regulation of transforming growth factor, beta-induced 68 kDa (TGFBI) expression through the BLT signaling pathway during adipocyte differentiation. Knockdown of TGFBI also showed acceleration of preadipocyte differentiation. The LTB(4)-BLT signaling pathway may negatively regulate preadipocyte differentiation via induction of TGFBI expression as a rate-limiting system to control adipocyte differentiation.

Adipocytes secrete leukotrienes: contribution to obesity-associated inflammation and insulin resistance in mice

Leukotrienes (LTs) are potent proinflammatory mediators, and many important aspects of innate and adaptive immune responses are regulated by LTs. Key members of the LT synthesis pathway are overexpressed in adipose tissue (AT) during obesity, resulting in increased LT levels in this tissue. We observed that several mouse adipocyte cell lines and primary adipocytes from mice and humans both can secrete large amounts of LTs. Furthermore, this production increases with a high-fat diet (HFD) and positively correlates with adipocyte size. LTs produced by adipocytes play an important role in attracting macrophages and T cells in in vitro chemotaxis assays. Mice that are deficient for the enzyme 5-lipoxygenase (5-LO), and therefore lack LTs, exhibit a decrease in HFD-induced AT macrophage and T-cell infiltration and are partially protected from HFD-induced insulin resistance. Similarly, treatment of HFD-fed wild-type mice with the 5-LO inhibitor Zileuton also results in a reduction of AT macrophages and T cells, accompanied by a decrease in insulin resistance. Together, these findings suggest that LTs represent a novel target in the prevention or treatment of obesity-associated inflammation and insulin resistance.

Resolution of inflammation in obesity-induced liver disease

Low-grade inflammation in adipose tissue is recognized as a critical event in the development of obesity-related co-morbidities. This chronic inflammation is powerfully augmented through the infiltration of macrophages, which together with adipocytes, perpetuate a vicious cycle of inflammatory cell recruitment and secretion of free fatty acids and deleterious adipokines that predispose to greater incidence of metabolic complications. In the last decade, many factors have been identified to contribute to mounting unresolved inflammation in obese adipose tissue. Among them, pro-inflammatory lipid mediators (i.e., leukotrienes) derived from the omega-6 polyunsaturated arachidonic acid have been shown to play a prominent role. Of note, the same lipid mediators that initially trigger the inflammatory response also signal its termination by stimulating the formation of anti-inflammatory signals. Resolvins and protectins derived from the omega-3 polyunsaturated docosahexaenoic and eicosapentaenoic acids have emerged as a representative family of this novel class of autacoids with dual anti-inflammatory and pro-resolving properties that act as “stop-signals” of the inflammatory response. This review discusses the participation of these endogenous autacoids in the resolution of adipose tissue inflammation, with a special emphasis in the amelioration of obesity-related metabolic dysfunctions, namely insulin resistance and non-alcoholic fatty liver disease.

PTGS-2-PTGER2/4 signaling pathway partially protects from diabetogenic toxicity of streptozotocin in mice

Prostanoids are suggested to participate in diabetes pathology, but their roles are controversially discussed. The purpose of the current study was to examine the role of cyclooxygenase (prostaglandin synthase [PTGS]) enzymes and prostaglandin (PG) E(2) signaling pathways in streptozotocin (STZ)-induced type 1 diabetes. Blood glucose, insulin, and survival rate were studied in mice with targeted disruption of the genes for PTGS and PGE receptors (PTGERs). PGE(2) was found as the main prostanoid formed by the pancreas. Contrarily to PTGS-1, deficiency of PTGS-2 activity significantly amplified STZ effect, causing dramatic loss of insulin production and rise in blood glucose and death rate. STZ metabolism was unaffected by PTGS deficiency. Diabetogenicity of STZ in PTGER1(-/-), PTGER2(-/-), PTGER3(-/-), and PTGER4(-/-) mice was comparable to control mice. In striking contrast, combined knockout of PTGER2 and PTGER4 by blocking PTGER4 in PTGER2(-/-) mice strongly enhanced STZ pathology. Treatment of PTGS-2(-/-) and wild-type mice with PTGER2/PTGER4 agonists partially protected against STZ-induced diabetes and restored β-cell function. Our data uncover a previously unrecognized protective role of PTGS-2-derived PGE(2) in STZ-induced diabetes mediated by the receptor types PTGER2 and PTGER4. These findings offer the possibility to intervene in early progression of type 1 diabetes by using PTGER-selective agonists.

Association of PLA2G4A with myocardial infarction is modulated by dietary PUFAs

BACKGROUND

Leukotrienes are proinflammatory molecules derived from dietary PUFAs and have been associated with cardiovascular disease (CVD). We previously reported that an A→G variant (rs12746200) of the cytosolic phospholipase A2 group IVA gene (PLA2G4A), which encodes the enzyme that liberates PUFAs from cellular membranes for leukotriene synthesis, decreases the risk of CVD.

OBJECTIVE

We sought to replicate these initial observations with a more clinically relevant phenotype, such as myocardial infarction (MI), and to determine whether dietary PUFAs mediate this association.

DESIGN

In a Costa Rican case-control data set (n = 3971), rs12746200 was genotyped and was tested for an association with MI. Functional experiments were carried out to determine whether rs12746200 led to differences in mRNA expression.

RESULTS

Risk of MI was significantly lower in AG/GG subjects than in AA homozygotes (OR: 0.86; 95% CI: 0.75, 0.99; P = 0.040). The reduced risk of MI was observed primarily in AG/GG subjects who were above the median for intake of dietary omega-6 (n-6) PUFAs (OR: 0.71; 95% CI: 0.59, 0.87; P-interaction = 0.005). A similar analysis with dietary omega-3 (n-3) PUFAs did not show a statistically significant nutrigenetic association (P-interaction = 0.23). Functional analysis in human aortic endothelial cells showed that the carriers of the G allele had significantly lower PLA2G4A gene expression (P = 0.014), consistent with the atheroprotective association of this variant.

CONCLUSION

These results replicate the association of rs12746200 with CVD phenotypes and provide evidence that the protective association of this functional PLA2G4A variant is mediated by dietary PUFAs.

Association of ALOX15 gene polymorphisms with obesity-related phenotypes in Chinese nuclear families with male offspring

AIM

Genetic variation in ALOX12, which encoded human 12-lipoxygenase, was found to be associated with fat mass in young Chinese men. The objective of this study was to investigate the relationship between single nucleotide polymorphisms (SNPs) and haplotypes in the ALOX15 gene and obesity-related phenotypes in Chinese nuclear families with male offspring.

METHODS

We recruited 1,296 subjects from 427 nuclear families with male offspring and genotyped five SNPs (rs9894225, rs748694, rs2619112, rs2619118, and rs916055) in the ALOX15 gene locus. The total fat mass (TFM), trunk fat mass (tFM), leg fat mass (LFM) and arm fat mass (AFM) were measured using dual-energy X-ray absorptiometry (DXA). The percentage of fat mass (PFM) was the ratio of TFM and body weight. The association between SNPs and haplotypes of ALOX15 and obesity-related phenotypic variation was measured using quantitative transmission disequilibrium test (QTDT).

RESULTS

Using QTDT to measure family-based genetic association, we found that rs916055 had a statistically significant association with PFM (P=0.038), whereas rs916055 had a marginal but statistically insignificant association with tFM (P=0.093). The multiple-parameter 1000 permutations test agreed with the family-based association results: both showed that rs916055 had a statistically significant association with PFM (P=0.033).

CONCLUSION

rs916055 in ALOX15 gene was significantly associated with the percentage of fat mass in Chinese nuclear families with male offspring in the family-based association study using QTDT approach.

Eicosanoids, β-cell function, and diabetes

Arachidonic acid (AA) is metabolized by cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes into eicosanoids, which are involved in diverse diseases, including type 1 and type 2 diabetes. During the last 30 years, evidence has been accumulated that suggests important functions for eicosanoids in the control of pancreatic β-cell function and destruction. AA metabolites of the COX pathway, especially prostaglandin E(2) (PGE(2)), appear to be significant factors to β-cell dysfunction and destruction, participating in the pathogenesis of diabetes and its complications. Several elegant studies have contributed to the sorting out of the importance of 12-LOX eicosanoids in cytokine-mediated inflammation in pancreatic β cells. The role of CYP eicosanoids in diabetes is yet to be explored. A recent publication has demonstrated that stabilizing the levels of epoxyeicosatrienoic acids (EETs), CYP eicosanoids, by inhibiting or deleting soluble epoxide hydrolase (sEH) improves β-cell function and reduces β-cell apoptosis in diabetes. In this review we summarize recent findings implicating these eicosanoid pathways in diabetes and its complications. We also discuss the development of animal models with targeted gene deletion and specific enzymatic inhibitors in each pathway to identify potential targets for the treatment of diabetes and its complications.

The 5-lipoxygenase/leukotriene pathway in obesity, insulin resistance, and fatty liver disease

PURPOSE OF REVIEW

Obesity is a major risk factor for metabolic syndrome-related comorbidities such as insulin resistance, type-II diabetes, and nonalcoholic fatty liver disease (NAFLD). A wealth of evidence indicates that the associated pathologies of the metabolic syndrome are aggravated by the presence of a chronic state of 'low-grade' inflammation in the adipose tissue. This article discusses recent data implicating lipoxygenases and especially 5-lipoxygenase and its derived products, the leukotrienes, in mounting adipose tissue inflammation and related pathologies in obesity.

RECENT FINDINGS

Overexpression of selected members of the 5-lipoxygenase pathway and increased leukotriene production are common findings in excessive visceral fat depots. In these conditions, 5-lipoxygenase products exert potent proinflammatory actions including induction of nuclear factor-κB and secretion of proinflammatory and insulin resistant adipokines (i.e., monocyte chemotactic protein-1, tumor necrosis factor-α, macrophage inflammatory protein-1γ, and interleukin-6) by adipose tissue. The 5-lipoxygenase pathway also plays a major role in mounting inflammation in hepatic tissue and has emerged as a pathogenic factor in obesity-induced NAFLD. Similar role in NAFLD has been proposed for the 12/15-lipoxygenase pathway.

SUMMARY

Modulation of lipoxygenases represents a novel target in the prevention of adipose tissue and hepatic dysfunction related to the metabolic syndrome.

Genetic contribution of the leukotriene pathway to coronary artery disease

We evaluated the genetic contribution of the leukotriene (LT) pathway to risk of coronary artery disease (CAD) in 4,512 Caucasian and African American subjects ascertained through elective cardiac evaluation. Of the three previously associated variants, the shorter "3" and "4" alleles of a promoter repeat polymorphism in ALOX5 increased risk of CAD in African Americans (OR = 1.4, 95% CI 1.0-1.9; p = 0.04), whereas a haplotype of LTA4H (HapK) was associated with CAD in Caucasians (OR = 1.2, 95% CI 1.01-1.4; p = 0.03). In Caucasians, first-stage analysis of 254 haplotype-tagging SNPs in 15 LT pathway genes with follow-up of 19 variants in stage 2 revealed an LTA4H SNP (rs2540477) that increased risk of CAD (OR = 1.2, 95% CI 1.1-1.5; p = 0.003) and a PLA2G4A SNP (rs12746200) that decreased risk of CAD (OR = 0.7, 95% CI 0.6-0.9; p = 0.0007). The PLA2G4A rs12746200 variant also decreased risk of experiencing a major adverse cardiac event (MACE = myocardial infarction, stroke, or death) over 3 years of follow-up (HR = 0.7, 95% CI 0.5-0.9; p = 0.01), consistent with its cardioprotective effect. Functional experiments demonstrated that stimulated monocytes from carriers of LTA4H variants HapK or rs2540477 had 50% (p = 0.002) and 33% (p = 0.03) higher LTB(4) production, respectively, compared to non-carriers. These ex vivo results are consistent with LTB(4) being the direct product of the reaction catalyzed by LTA4H and its role in promoting monocyte chemotaxis to sites of inflammation, including the artery wall of atherosclerotic lesions. Taken together, this study provides additional evidence that functional genetic variation of the LT pathway can mediate atherogenic processes and the risk of CAD in humans.

Effect of sitagliptin plus metformin on β-cell function, islet integrity and islet gene expression in Zucker diabetic fatty rats

AIM

The combination of metformin and a dipeptidyl peptidase 4 (DPP-4) inhibitor has been shown to be an effective, safe, and well-tolerated treatment for type 2 diabetes. We evaluated β-cell function and morphological changes in islets in Zucker diabetic fatty (ZDF) rats following combined therapy with sitagliptin and metformin and investigated the expression of potentially relevant genes using cDNA microarrays.

METHODS

Nine-week-old ZDF rats were randomly divided into four treatment groups: no treatment (control); sitagliptin; metformin, and sitagliptin plus metformin. After 5 weeks of treatment, an oral glucose tolerance test was performed and plasma levels of active GLP-1 and islet morphology and gene expression were assessed.

RESULTS

Combination therapy reduced fasting glucose and postprandial plasma glucose levels and increased active GLP-1 levels, compared with monotherapy. Combination therapy also increased insulin secretion, the proportion of small islets, and the intensity of insulin staining. Furthermore, it increased the expression of genes involved in cell survival and growth and downregulated apoptosis-associated genes, relative to monotherapy.

CONCLUSIONS

Combination treatment with sitagliptin and metformin preserved β-cell function and β-cell integrity in ZDF rats. This may be associated with the transcriptional activation of anti-apoptotic and pro-survival genes, as well as the suppression of pro-apoptotic genes.

ALOX12 polymorphisms are associated with fat mass but not peak bone mineral density in Chinese nuclear families

OBJECTIVE

Arachidonate 12-lipoxygenase (ALOX12) is a member of the lipoxygenase superfamily, which catalyzes the incorporation of molecular oxygen into polyunsaturated fatty acids. The products of ALOX12 reactions serve as endogenous ligands for peroxisome proliferator-activated receptor γ (PPARG). The activation of the PPARG pathway in marrow-derived mesenchymal progenitors stimulates adipogenesis and inhibits osteoblastogenesis. Our objective was to determine whether polymorphisms in the ALOX12 gene were associated with variations in peak bone mineral density (BMD) and obesity phenotypes in young Chinese men.

METHODS

All six tagging single-nucleotide polymorphisms (SNPs) in the ALOX12 gene were genotyped in a total of 1215 subjects from 400 Chinese nuclear families by allele-specific polymerase chain reaction. The BMD at the lumbar spine and hip, total fat mass (TFM) and total lean mass (TLM) were measured using dual-energy X-ray absorptiometry. The pairwise linkage disequilibrium among SNPs was measured, and the haplotype blocks were inferred. Both the individual SNP markers and the haplotypes were tested for an association with the peak BMD, body mass index, TFM, TLM and percentage fat mass (PFM) using the quantitative transmission disequilibrium test (QTDT).

RESULTS

Using the QTDT, significant within-family association was found between the rs2073438 polymorphism in the ALOX12 gene and the TFM and PFM (P=0.007 and 0.012, respectively). Haplotype analyses were combined with our individual SNP results and remained significant even after correction for multiple testing. However, we failed to find significant within-family associations between ALOX12 SNPs and the BMD at any bone site in young Chinese men.

CONCLUSIONS

Our present results suggest that the rs2073438 polymorphism of ALOX12 contributes to the variation of obesity phenotypes in young Chinese men, although we failed to replicate the association with the peak BMD variation in this sample. Further independent studies are needed to confirm our findings.

Benefits of neuropsychiatric phenomics: example of the 5-lipoxygenase-leptin-Alzheimer connection

Phenomics is a systematic study of phenotypes on a genomewide scale that is expected to unravel, as of yet, unsuspected functional roles of the genome. It remains to be determined how to optimally approach and analyze the available phenomics databases to spearhead innovation in neuropsychiatry. By serendipitously connecting two unrelated phenotypes of increased blood levels of the adipokine leptin, a molecule that regulates appetite, in 5-lipoxygenase- (5-LOX) deficient mice and patients with a lower risk for Alzheimer's disease (AD), we postulated a leptin-mediated basis for beneficial effects of ALOX5 (a gene encoding 5-LOX) gene-deficiency in AD. We suggest that it might be possible to avoid relying on serendipity and develop data-mining tools capable of extracting from phenomics databases indications for such novel hypotheses. Hence, we provide an example of using a free-access Arrowsmith two-node search interface to identify ALOX5 as unsuspected putative mechanisms for the previously described clinical association between increased plasma levels of leptin and a lower risk of incident dementia and AD.

5-lipoxygenase activating protein signals adipose tissue inflammation and lipid dysfunction in experimental obesity

The presence of the so-called low-grade inflammatory state is recognized as a critical event in adipose tissue dysfunction, leading to altered secretion of adipokines and free fatty acids (FFAs), insulin resistance, and development of hepatic complications associated with obesity. This study was designed to investigate the potential contribution of the proinflammatory 5-lipoxygenase (5-LO) pathway to adipose tissue inflammation and lipid dysfunction in experimental obesity. Constitutive expression of key components of the 5-LO pathway, as well as leukotriene (LT) receptors, was detected in adipose tissue as well as in adipocyte and stromal vascular fractions. Adipose tissue from obese mice, compared with that from lean mice, exhibited increased 5-LO activating protein (FLAP) expression and LTB(4) levels. Incubation of adipose tissue with 5-LO products resulted in NF-kappaB activation and augmented secretion of proinflammatory adipokines such as MCP-1, IL-6, and TNF-alpha. In addition, LTB(4), but not LTD(4), reduced FFA uptake in primary adipocytes, whereas 5-LO inhibition suppressed isoproterenol-induced adipose tissue lipolysis. In mice with dietary obesity, elevated FLAP expression in adipose tissue was paralleled with macrophage infiltration, increased circulating FFA levels, and hepatic steatosis, phenomena that were reversed by FLAP inhibition with Bay-X-1005. Interestingly, FLAP inhibition induced AMP-activated protein kinase phosphorylation in parallel with decreases in hormone-sensitive lipase activity and the expression and secretion of TNF-alpha and IL-6. Similar effects were observed in differentiated 3T3-L1 adipocytes incubated with either Bay-X-1005 or the selective LTB(4) receptor antagonist U-75302. Taken together, these findings indicate that the 5-LO pathway signals the adipose tissue low-grade inflammatory state and steatogenic potential in experimental obesity.

Polyunsaturated fatty acids and cardiovascular disease: implications for nutrigenetics

Cardiovascular disease (CVD) arises as a result of genetic predisposition in the context of a disease-promoting environment. While several risk factors have been identified for CVD, such as elevated serum lipid levels and hypertension, most of the genes identified thus far do not appear to involve such 'conventional' risk factors. Moreover, the interactions between genes and environment, such as a diet high in certain fats, adds another level of complexity to CVD and renders identification of the underlying genetic factors even more difficult. Polyunsaturated fatty acids (PUFAs), such as the omega-6 and omega-3 fatty acids, which have multiple roles in membrane structure, lipid metabolism, blood clotting, blood pressure, and, in particular, inflammation, have been linked to the reduction in CVD. Linoleic (omega-6) and alpha-linolenic acid (omega-3) are essential fatty acids that can be converted into long-chain PUFAs, such as arachidonic acid (AA) and eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA), respectively. These long-chain PUFAs are metabolized by enzymatically catalyzed systems via cyclooxygenases and lipoxygenases. The 5-lipoxygenase (5-LO)/leukotriene (LT) biosynthesis pathway has been biochemically and genetically associated with CVD traits in mice and humans, particularly in the context of dietary AA and EPA/DHA. In this review, we summarize the biochemical metabolism of omega-3 and omega-6 PUFAs, evaluate the evidence for genetic and nutrigenetic contributions of 5-LO pathway genes to CVD, and discuss the potential of future studies that could identify other gene-dietary interactions between PUFAs and CVD traits.