Mechanisms of obesity and related pathologies: role of apolipoprotein E in the development of obesity

Relationships Between APOE, Type 2 Diabetes, and Cardiovascular Disease in Postmenopausal Women

BACKGROUND

The apolipoprotein E (APOE) ε4 allele, type 2 diabetes mellitus (T2DM), and cardiovascular disease (CVD) are well-established risk factors for dementia. Relationships between APOE and incidence of T2DM and CVD are not fully understood but may shed light on the mechanisms underlying dementia pathogenesis.

METHODS

Postmenopausal women (N = 6 795) from the Women's Health Initiative hormone therapy clinical trial with APOE genotyping and no prior diagnosis of T2DM or CVD were included. We examined associations of APOE status (APOE2+ [ε2/ε2, ε2/ε3], APOE3 [ε3/ε3], and APOE4+ [ε4/ε4, ε3/ε4] carriers) with incidence of T2DM, coronary heart disease, stroke, and total CVD events using Cox regression. CVD outcomes were examined in baseline non-statin users and adjusted for statin initiation over follow-up to account for possible confounding by statins.

RESULTS

Among all participants (mean age 66.7 ± 6.5 years, 100% non-Hispanic White), 451 (6.6%) were using statins at baseline. Over the follow-up (mean 14.9 and 16.0 years for T2DM and CVD, respectively), 1 564 participants developed T2DM and 1 578 developed CVD. T2DM incidence did not differ significantly by APOE status (ps ≥ .09). Among non-statin users, APOE4+ had higher incidence of total CVD (hazard ratio [95% confidence interval] = 1.18 [1.02-1.38], p = .03) compared with APOE3 carriers, but risks for coronary heart disease (1.09 [0.87-1.36], p = .47) and stroke (1.14 [0.91-1.44], p = .27) were not significantly elevated when examined individually. CVD outcomes did not differ between APOE2+ and APOE3 carriers (ps ≥ 0.11).

CONCLUSIONS

T2DM risk did not differ by APOE status among postmenopausal women, but APOE4+ carriers not using statins had an increased risk of total CVD events.

Generational Diet-Induced Obesity Remodels the Omental Adipose Proteome in Female Mice

Obesity, a complex condition that involves genetic, environmental, and behavioral factors, is a non-infectious pandemic that affects over 650 million adults worldwide with a rapidly growing prevalence. A major contributor is the consumption of high-fat diets, an increasingly common feature of modern diets. Maternal obesity results in an increased risk of offspring developing obesity and related health problems; however, the impact of maternal diet on the adipose tissue composition of offspring has not been evaluated. Here, we designed a generational diet-induced obesity study in female C57BL/6 mice that included maternal cohorts and their female offspring fed either a control diet (10% fat) or a high-fat diet (45% fat) and examined the visceral adipose proteome. Solubilizing proteins from adipose tissue is challenging due to the need for high concentrations of detergents; however, the use of a detergent-compatible sample preparation strategy based on suspension trapping (S-Trap) enabled label-free quantitative bottom-up analysis of the adipose proteome. We identified differentially expressed proteins related to lipid metabolism, inflammatory disease, immune response, and cancer, providing valuable molecular-level insight into how maternal obesity impacts the health of offspring. Data are available via ProteomeXchange with the identifier PXD042092.

Insights into the roles of Apolipoprotein E in adipocyte biology and obesity

Apolipoprotein E (APOE) is a multifunctional protein expressed by various cell types, including hepatocytes, adipocytes, immune cells of the myeloid lineage, vascular smooth muscle cells, astrocytes, etc. Initially, APOE was discovered as an arginine-rich peptide within very-low-density lipoprotein, but it was subsequently found in triglyceride-rich lipoproteins in humans and other animals, where its presence facilitates the clearance of these lipoproteins from circulation. Recent epidemiolocal studies and experimental research in mice suggest a link between ApoE and obesity. The latest findings highlight the role of endogenous adipocyte ApoE in regulating browning of white adipose tissue, beige adipocyte differentiation, thermogenesis and energy homeostasis. This review focuses on the emerging evidence showing the involvement of ApoE in the regulation of obesity and its associated metabolic diseases.

Relationship between Nutrition, Lifestyle, and Neurodegenerative Disease: Lessons from ADH1B, CYP1A2 and MTHFR

In the present review, the main features involved in the susceptibility and progression of neurodegenerative disorders (NDDs) have been discussed, with the purpose of highlighting their potential application for promoting the management and treatment of patients with NDDs. In particular, the impact of genetic and epigenetic factors, nutrients, and lifestyle will be presented, with particular emphasis on Alzheimer’s disease (AD) and Parkinson’s disease (PD). Metabolism, dietary habits, physical exercise and microbiota are part of a complex network that is crucial for brain function and preservation. This complex equilibrium can be disrupted by genetic, epigenetic, and environmental factors causing perturbations in central nervous system homeostasis, contributing thereby to neuroinflammation and neurodegeneration. Diet and physical activity can directly act on epigenetic modifications, which, in turn, alter the expression of specific genes involved in NDDs onset and progression. On this subject, the introduction of nutrigenomics shed light on the main molecular players involved in the modulation of health and disease status. In particular, the review presents data concerning the impact of ADH1B, CYP1A2, and MTHFR on the susceptibility and progression of NDDs (especially AD and PD) and how they may be exploited for developing precision medicine strategies for the disease treatment and management.

On the effect of flavonoids and dietary fibre in lingonberries on atherosclerotic plaques, lipid profiles and gut microbiota composition in Apoe-/- mice

It has not been clarified whether the anti-atherosclerotic effect of lingonberry can be ascribed to its content of flavonoids or dietary fibre or both. The aim of this study was to evaluate the metabolic effects of whole lingonberries compared with isolated flavonoid and fibre fractions on atherosclerotic plaques, plasma lipid profiles, gut microbiota and microbiota-dependent metabolites in an Apoe^-/- mouse model. Mice fed whole lingonberries showed the lowest amount of atherosclerotic plaques, while mice fed the fibre fraction had the highest formation of caecal butyric acid. Flavonoids, rather than dietary fibre, were suggested to be the components that favour proliferation of Akkermansia, as judged by the lowest abundance of this bacterium in mice fed the fibre fraction. All groups fed lingonberry diets had both, lower Firmicutes/Bacteroidetes ratios and creatinine concentrations, compared with the control. To conclude, different components in lingonberries are associated with different physiological effects in Apoe^-/- mice.

Positive Effects of a Mediterranean Diet Supplemented with Almonds on Female Adipose Tissue Biology in Severe Obesity

It has been suggested that weight-loss-independent Mediterranean diet benefits on cardiometabolic health and diabetes prevention may be mediated, at least in part, through the modulation of white adipose tissue (WAT) biology. This study aimed to evaluate the short-term effects of a dietary intervention based on the Mediterranean diet supplemented with almonds (MDSA) on the main features of obesity-associated WAT dysfunction. A total of 38 women with obesity were randomly assigned to a 3-month intervention with MDSA versus continuation of their usual dietary pattern. Subcutaneous (SAT) and visceral adipose tissue (VAT) biopsies were obtained before and after the dietary intervention, and at the end of the study period, respectively. MDSA favored the abundance of small adipocytes in WAT. In SAT, the expression of angiogenesis genes increased after MDSA intervention. In VAT, the expression of genes implicated in adipogenesis, angiogenesis, autophagy and fatty acid usage was upregulated. In addition, a higher immunofluorescence staining for PPARG, CD31+ cells and M2-like macrophages and increased ADRB1 and UCP2 protein contents were found compared to controls. Changes in WAT correlated with a significant reduction in circulating inflammatory markers and LDL-cholesterol levels. These results support a protective effect of a Mediterranean diet supplemented with almonds on obesity-related WAT dysfunction.

Tissue-specific functional interaction between apolipoproteins A1 and E in cold-induced adipose organ mitochondrial energy metabolism

White (WAT) and brown (BAT) adipose tissue, the two main types of adipose organ, are responsible for lipid storage and non-shivering thermogenesis, respectively. Thermogenesis is a process mediated by mitochondrial uncoupling protein 1 (UCP1) which uncouples oxidative phosphorylation from ATP production, leading to the conversion of free fatty acids to heat. This process can be triggered by exposure to low ambient temperatures, caloric excess, and the immune system. Recently mitochondrial thermogenesis has also been associated with plasma lipoprotein transport system. Specifically, apolipoprotein (APO) E3 is shown to have a bimodal effect on WAT thermogenesis that is highly dependent on its site of expression. Similarly, APOE2 and APOE4 differentially affect BAT and WAT mitochondrial metabolic activity in processes highly modulated by APOA1. Furthermore, the absence of classical APOA1 containing HDL (APOA1-HDL), is associated with no measurable non-shivering thermogenesis in WAT of mice fed high fat diet. Based on these previous observations which indicate important regulatory roles for both APOA1 and APOE in adipose tissue mitochondrial metabolic activity, here we sought to investigate the potential roles of these apolipoproteins in BAT and WAT metabolic activation in mice, following stimulation by cold exposure (7 °C). Our data indicate that APOA1-HDL promotes metabolic activation of BAT only in the presence of very low levels (virtually undetectable) of APOE3-containing HDL (APOE3-HDL), which acts as an inhibitor in this process. In contrast, induction of WAT thermogenesis is subjected to a more complicated regulation which requires the combined presence of both APOA1-HDL and APOE3-HDL.

Diet, Microbiota and Brain Health: Unraveling the Network Intersecting Metabolism and Neurodegeneration

Increasing evidence gives support for the idea that extra-neuronal factors may affect brain physiology and its predisposition to neurodegenerative diseases. Epidemiological and experimental studies show that nutrition and metabolic disorders such as obesity and type 2 diabetes increase the risk of Alzheimer's and Parkinson's diseases after midlife, while the relationship with amyotrophic lateral sclerosis is uncertain, but suggests a protective effect of features of metabolic syndrome. The microbiota has recently emerged as a novel factor engaging strong interactions with neurons and glia, deeply affecting their function and behavior in these diseases. In particular, recent evidence suggested that gut microbes are involved in the seeding of prion-like proteins and their spreading to the central nervous system. Here, we present a comprehensive review of the impact of metabolism, diet and microbiota in neurodegeneration, by affecting simultaneously several aspects of health regarding energy metabolism, immune system and neuronal function. Advancing technologies may allow researchers in the future to improve investigations in these fields, allowing the buildup of population-based preventive interventions and development of targeted therapeutics to halt progressive neurologic disability.

Integrative phenotyping of glycemic responders upon clinical weight loss using multi-omics

Weight loss aims to improve glycemic control in obese but strong variability is observed. Using a multi-omics approach, we investigated differences between 174 responders and 201 non-responders, that had lost >8% body weight following a low-caloric diet (LCD, 800 kcal/d for 8 weeks). The two groups were comparable at baseline for body composition, glycemic control, adipose tissue transcriptomics and plasma ketone bodies. But they differed significantly in their response to LCD, including improvements in visceral fat, overall insulin resistance (IR) and tissue-specific IR. Transcriptomics analyses found down-regulation in key lipogenic genes (e.g. SCD, ELOVL5) in responders relative to non-responders; metabolomics showed increase in ketone bodies; while proteomics revealed differences in lipoproteins. Findings were consistent between genders; with women displaying smaller improvements owing to a better baseline metabolic condition. Integrative analyses identified a plasma omics model that was able to predict non-responders with strong performance (on a testing dataset, the Receiving Operating Curve Area Under the Curve (ROC AUC) was 75% with 95% Confidence Intervals (CI) [67%, 83%]). This model was based on baseline parameters without the need for intrusive measurements and outperformed clinical models (p = 0.00075, with a +14% difference on the ROC AUCs). Our approach document differences between responders and non-responders, with strong contributions from liver and adipose tissues. Differences may be due to de novo lipogenesis, keto-metabolism and lipoprotein metabolism. These findings are useful for clinical practice to better characterize non-responders both prior and during weight loss.

Impact of Apolipoprotein E gene polymorphism during normal and pathological conditions of the brain across the lifespan

The central nervous system (CNS) is the cellular substrate for the integration of complex, dynamic, constant, and simultaneous interactions among endogenous and exogenous stimuli across the entire human lifespan. Numerous studies on aging-related brain diseases show that some genes identified as risk factors for some of the most common neurodegenerative diseases - such as the allele 4 of APOE gene (APOE4) for Alzheimer's disease (AD) - have a much earlier neuro-anatomical and neuro-physiological impact. The impact of APOE polymorphism appears in fact to start as early as youth and early-adult life. Intriguingly, though, those same genes associated with aging-related brain diseases seem to influence different aspects of the brain functioning much earlier actually, that is, even from the neonatal periods and earlier. The APOE4, an allele classically associated with later-life neurodegenerative disorders as AD, seems in fact to exert a series of very early effects on phenomena of neuroplasticity and synaptogenesis that begin from the earliest periods of life such as the fetal ones.We reviewed some of the findings supporting the hypothesis that APOE polymorphism is an early modifier of various neurobiological aspects across the entire human lifespan - from the in-utero to the centenarian life - during both normal and pathological conditions of the brain.

Obesity and ageing: Two sides of the same coin

Conditions and comorbidities of obesity mirror those of ageing and age-related diseases. Obesity and ageing share a similar spectrum of phenotypes such as compromised genomic integrity, impaired mitochondrial function, accumulation of intracellular macromolecules, weakened immunity, shifts in tissue and body composition, and enhanced systemic inflammation. Moreover, it has been shown that obesity reduces life expectancy by 5.8 years in men and 7.1 years in women after the age of 40. Shorter life expectancy could be because obesity holistically accelerates ageing at multiple levels. Besides jeopardizing nuclear DNA and mitochondrial DNA integrity, obesity modifies the DNA methylation pattern, which is associated with epigenetic ageing in different tissues. Additionally, other signs of ageing are seen in individuals with obesity including telomere shortening, systemic inflammation, and functional declines. This review aims to show how obesity and ageing are "two sides of the same coin" through discussing how obesity predisposes an individual to age-related conditions, illness, and disease. We will further demonstrate how the mechanisms that perpetuate the early-onset of chronic diseases in obesity parallel those of ageing.

Isoform and tissue dependent impact of apolipoprotein E on adipose tissue metabolic activation: The role of apolipoprotein A1

Adipose organ is made of white (WAT) and brown (BAT) adipose tissue which are primarily responsible for lipid storage and energy production (heat and ATP) respectively. Metabolic activation of WAT may ascribe to this tissue characteristics of BAT, namely non-shivering thermogenesis and ATP production. Recent data indicate that apolipoproteins E (APOE) and A1 (APOA1) regulate WAT mitochondrial metabolic activation. Here, we investigated the functional cross-talk between natural human APOE2 and APOE4 isoforms with APOA1 in this process, using Apoe2^knock-in and Apoe4^knock-in mice. At baseline when Apoe2^knock-in and Apoe4^knock-in mice express both APOE and Apoa1, the Apoe2^knock-in strain appears to have higher mitochondrial oxidative phosphorylation levels and non-shivering thermogenesis in WAT compared to Apoe4^knock-in mice. When mice were switched to a high-fat diet for 18 weeks, circulating levels of endogenous Apoa1 in Apoe2^knock-in mice became barely detectable though significant levels of APOE2 were still present. This change was accompanied by a significant reduction in WAT mitochondrial Ucp1 expression while BAT Ucp1 was unaffected. Ectopic APOA1 expression in Apoe2^knock-in animals potently stimulated WAT but not BAT mitochondrial Ucp1 expression providing further evidence that APOA1 potently stimulates WAT non-shivering thermogenesis in the presence of APOE2. Ectopic expression of APOA1 in Apoe4^knock-in mice stimulated BAT but no WAT mitochondrial Ucp1 levels, suggesting that in the presence of APOE4, APOA1 is a trigger of BAT non-shivering thermogenesis. Overall, our data identified a tissue-specific role of the natural human APOE2 and APOE4 isoforms in WAT- and BAT-metabolic activation respectively, that appears dependent on circulating APOA1 levels.

Possible synergistic effect of apoE and LRP1 genotypes on metabolic syndrome development in Serbian patients

The modern way of life contributes to the higher frequency of a complex state medically called metabolic syndrome (MetS), which is an inevitable consequence of several most common diseases of modern civilization. Patients with MetS have three times higher risk of experiencing a heart attack or a stroke and twice higher possibility to die from them. Serbia holds the infamous third place in Europe in mortality from heart disease, just behind Russia and Ukraine. The study explores the correlation of every combination of genotypes of apoE (apolipoprotein E) and LRP1 (low density receptor- related protein 1) genes with presence of MetS, and the connection with each anthropometric and biochemical parameter in both tested groups. Study demonstrates the impact of genotype combinations on the emergence and development of the MetS in Serbia. 63 patients and 30 controls were included in the study, aged from 19 to 65. Each person genotype was determined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) profile. Odds ratio (OR) values showed that the presence of apoE e3e4/LRP1 CC genotype combination of genotypes in patients multiplies the chance (7.6 times) for the occurrence of the MetS in comparison to the presence of other genotype combinations. Determining the genetic basis of MetS is one of the necessary steps in the prevention of disease, saving the cost of treatment, and in the design of targeted therapies.

Cholesterol-Lowering Gene Therapy Prevents Heart Failure with Preserved Ejection Fraction in Obese Type 2 Diabetic Mice

Hypercholesterolemia may be causally related to heart failure with preserved ejection fraction (HFpEF). We aimed to establish a HFpEF model associated with hypercholesterolemia and type 2 diabetes mellitus by feeding a high-sucrose/high-fat (HSHF) diet to C57BL/6J low-density lipoprotein receptor (LDLr)^−/− mice. Secondly, we evaluated whether cholesterol-lowering adeno-associated viral serotype 8 (AAV8)-mediated LDLr gene transfer prevents HFpEF. AAV8-LDLr gene transfer strongly (p < 0.001) decreased plasma cholesterol in standard chow (SC) mice (66.8 ± 2.5 mg/dl versus 213 ± 12 mg/dl) and in HSHF mice (84.6 ± 4.4 mg/dl versus 464 ± 25 mg/dl). The HSHF diet induced cardiac hypertrophy and pathological remodeling, which were potently counteracted by AAV8-LDLr gene transfer. Wet lung weight was 19.0% (p < 0.001) higher in AAV8-null HSHF mice than in AAV8-null SC mice, whereas lung weight was normal in AAV8-LDLr HSHF mice. Pressure–volume loop analysis was consistent with HFpEF in AAV8-null HSHF mice and showed a completely normal cardiac function in AAV8-LDLr HSHF mice. Treadmill exercise testing demonstrated reduced exercise capacity in AAV8-null HSHF mice but a normal capacity in AAV8-LDLr HSHF mice. Reduced oxidative stress and decreased levels of tumor necrosis factor-α may mediate the beneficial effects of cholesterol lowering. In conclusion, AAV8-LDLr gene therapy prevents HFpEF.

Independent associations of TOMM40 and APOE variants with body mass index

The TOMM40-APOE variants are known for their strong, antagonistic associations with Alzheimer's disease and body weight. While a stronger role of the APOE than TOMM40 variants in Alzheimer's disease was suggested, comparative contribution of the TOMM40-APOE variants in the regulation of body weight remains elusive. We examined additive effects of rs2075650 and rs157580 TOMM40 variants and rs429358 and rs7412 APOE variants coding the ε2/ε3/ε4 polymorphism on body mass index (BMI) in age-aggregated and age-stratified cohort-specific and cohort-pooled analysis of 27,863 Caucasians aged 20-100 years from seven longitudinal studies. Minor alleles of rs2075650, rs429358, and rs7412 were individually associated with BMI (β = -1.29, p = 3.97 × 10^-9 ; β = -1.38, p = 2.78 × 10^-10 ; and β = 0.58, p = 3.04 × 10^-2 , respectively). Conditional analysis with rs2075650 and rs429358 identified independent BMI-lowering associations for minor alleles (β = -0.63, p = 3.99 × 10^-2 and β = -0.94, p = 2.17 × 10^-3 , respectively). Polygenic mega-analysis identified additive effects of the rs2075650 and rs429358 heterozygotes (β = -1.68, p = 3.00 × 10^-9 ), and the strongest BMI-lowering association for the rs2075650 heterozygous and rs429358 minor allele homozygous carriers (β = -4.11, p = 2.78 × 10^-3 ). Conditional analysis with four polymorphisms identified independent BMI-lowering (rs2075650, rs157580, and rs429358) and BMI-increasing (rs7412) associations of heterozygous genotypes with BMI. Age-stratified conditional analysis revealed well-powered support for a differential and independent association of the rs429358 heterozygote with BMI in younger and older individuals, β = 0.58, 95% confidence interval (CI) = -1.18, 2.35, p = 5.18 × 10^-1 for 3,068 individuals aged ≤30 years and β = -4.28, CI = -5.65, -2.92, p = 7.71 × 10^-10 for 6,052 individuals aged >80 years. TOMM40 and APOE variants are independently and additively associated with BMI. The APOE ε4-coding rs429358 polymorphism is associated with BMI in older individuals but not in younger individuals.

Western-type diet differentially modulates osteoblast, osteoclast, and lipoblast differentiation and activation in a background of APOE deficiency

During the past few years, considerable evidence has uncovered a strong relationship between fat and bone metabolism. Consequently, alterations in plasma lipid metabolic pathways strongly affect bone mass and quality. We recently showed that the deficiency of apolipoprotein A-1 (APOA1), a central regulator of high-density lipoprotein cholesterol (HDL-C) metabolism, results in reduced bone mass in C57BL/6 mice. It is documented that apolipoprotein E (APOE), a lipoprotein know for its atheroprotective functions and de novo biogenesis of HDL-C, is associated with the accumulation of fat in the liver and other organs and regulates bone mass in mice. We further studied the mechanism of APOE in bone metabolism using well-characterized APOE knockout mice. We found that bone mass was remarkably reduced in APOE deficient mice fed Western-type diet (WTD) compared to wild type counterparts. Static (microCT-based) and dynamic histomorphometry showed that the reduced bone mass in APOΕ^-/- mice is attributed to both decreased osteoblastic bone synthesis and elevated osteoclastic bone resorption. Interestingly, histologic analysis of femoral sections revealed a significant reduction in the number of bone marrow lipoblasts in APOΕ^-/- compared to wild type mice under WTD. Analyses of whole bone marrow cells obtained from femora of both animal groups showed that APOE null mice had significantly reduced levels of the osteoblastic (RUNX2 and Osterix) and lipoblastic (PPARγ and CEBPα) cardinal regulators. Additionally, the modulators of bone remodeling RANK, RANKL, and cathepsin K were greatly increased, while OPG and the OPG/RANKL ratio were remarkably decreased in APOΕ^-/- mice fed WTD, compared to their wild-type counterparts. These findings suggest that APOE deficiency challenged with WTD reduces osteoblastic and lipoblastic differentiation and activity, whereas it enhances osteoclastic function, ultimately resulting in reduced bone mass, in mice.

Phenotype and genotype predictors of BMI variability among European adults

Background/Objective

Obesity is a complex and multifactorial disease resulting from the interactions among genetics, metabolic, behavioral, sociocultural and environmental factors. In this sense, the aim of the present study was to identify phenotype and genotype variables that could be relevant determinants of body mass index (BMI) variability.

Subjects/Methods

In the present study, a total of 1050 subjects (798 females; 76%) were included. Least angle regression (LARS) analysis was used as regression model selection technique, where the dependent variable was BMI and the independent variables were age, sex, energy intake, physical activity level, and 16 polymorphisms previously related to obesity and lipid metabolism.

Results

The LARS analysis obtained the following formula for BMI explanation: (64.7 + 0.10 × age [years] + 0.42 × gender [0, men; 1, women] + −40.6 × physical activity [physical activity level] + 0.004 × energy intake [kcal] + 0.74 × rs9939609 [0 or 1–2 risk alleles] + −0.72 × rs1800206 [0 or 1–2 risk alleles] + −0.86 × rs1801282 [0 or 1–2 risk alleles] + 0.87 × rs429358 [0 or 1–2 risk alleles]. The multivariable regression model accounted for 21% of the phenotypic variance in BMI. The regression model was internally validated by the bootstrap method (r² original data set = 0.208, mean r² bootstrap data sets = 0.210).

Conclusion

In conclusion, age, physical activity, energy intake and polymorphisms in FTO, APOE, PPARG and PPARA genes are significant predictors of the BMI trait.

Weighted gene co-expression network analysis of expression data of monozygotic twins identifies specific modules and hub genes related to BMI

Background

The therapeutic management of obesity is challenging, hence further elucidating the underlying mechanisms of obesity development and identifying new diagnostic biomarkers and therapeutic targets are urgent and necessary. Here, we performed differential gene expression analysis and weighted gene co-expression network analysis (WGCNA) to identify significant genes and specific modules related to BMI based on gene expression profile data of 7 discordant monozygotic twins.

Results

In the differential gene expression analysis, it appeared that 32 differentially expressed genes (DEGs) were with a trend of up-regulation in twins with higher BMI when compared to their siblings. Categories of positive regulation of nitric-oxide synthase biosynthetic process, positive regulation of NF-kappa B import into nucleus, and peroxidase activity were significantly enriched within GO database and NF-kappa B signaling pathway within KEGG database. DEGs of NAMPT, TLR9, PTGS2, HBD, and PCSK1N might be associated with obesity. In the WGCNA, among the total 20 distinct co-expression modules identified, coral1 module (68 genes) had the strongest positive correlation with BMI (r = 0.56, P = 0.04) and disease status (r = 0.56, P = 0.04). Categories of positive regulation of phospholipase activity, high-density lipoprotein particle clearance, chylomicron remnant clearance, reverse cholesterol transport, intermediate-density lipoprotein particle, chylomicron, low-density lipoprotein particle, very-low-density lipoprotein particle, voltage-gated potassium channel complex, cholesterol transporter activity, and neuropeptide hormone activity were significantly enriched within GO database for this module. And alcoholism and cell adhesion molecules pathways were significantly enriched within KEGG database. Several hub genes, such as GAL, ASB9, NPPB, TBX2, IL17C, APOE, ABCG4, and APOC2 were also identified. The module eigengene of saddlebrown module (212 genes) was also significantly correlated with BMI (r = 0.56, P = 0.04), and hub genes of KCNN1 and AQP10 were differentially expressed.

Conclusion

We identified significant genes and specific modules potentially related to BMI based on the gene expression profile data of monozygotic twins. The findings may help further elucidate the underlying mechanisms of obesity development and provide novel insights to research potential gene biomarkers and signaling pathways for obesity treatment. Further analysis and validation of the findings reported here are important and necessary when more sample size is acquired.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4257-6) contains supplementary material, which is available to authorized users.

APOE genotype influences insulin resistance, apolipoprotein CII and CIII according to plasma fatty acid profile in the Metabolic Syndrome

Metabolic markers associated with the Metabolic Syndrome (MetS) may be affected by interactions between the APOE genotype and plasma fatty acids (FA). In this study, we explored FA-gene interactions between the missense APOE polymorphisms and FA status on metabolic markers in MetS. Plasma FA, blood pressure, insulin sensitivity and lipid concentrations were determined at baseline and following a 12-week randomized, controlled, parallel, dietary FA intervention in 442 adults with MetS (LIPGENE study). FA-APOE gene interactions at baseline and following change in plasma FA were assessed using adjusted general linear models. At baseline E4 carriers had higher plasma concentrations of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and apolipoprotein B (apo B) compared with E2 carriers; and higher TC, LDL-C and apo B compared with E3/E3. Whilst elevated plasma n-3 polyunsaturated FA (PUFA) was associated with a beneficially lower concentration of apo CIII in E2 carriers, a high proportion of plasma C16:0 was associated with insulin resistance in E4 carriers. Following FA intervention, a reduction in plasma long-chain n-3 PUFA was associated with a reduction in apo CII concentration in E2 carriers. Our novel data suggest that individuals with MetS may benefit from personalized dietary interventions based on APOE genotype.

Association of APOE gene polymorphism with lipid profile and coronary artery disease in Afro-Caribbeans

OBJECTIVES

Apolipoprotein E gene (APOE) polymorphism is associated with the lipid profile and cardio-vascular disease. However, these relationships vary between ethnic groups. We evaluated, for the first time in an Afro-Caribbean population, the distribution of APOE polymorphisms and their associations with coronary artery disease (CAD), the lipid profile and other cardio-metabolic risk factors.

METHODS

We studied 712 Afro-Caribbean subjects including 220 with documented CAD and 492 healthy subjects. TaqMan assays were performed to genotype rs7412 and rs429358, the two variants that determine the APOE alleles ε2, ε3 and ε4. The association between APOE genotype and the lipid profile was analysed by comparing ε2 carriers, ε3 homozygotes and ε4 carriers.

RESULTS

The frequencies of ε2, ε3 and ε4 in the overall sample were 8%, 70% and 22%, respectively. CAD was not associated with APOE polymorphism. The total cholesterol level was higher in ε4 carriers compared with ε2 carriers: 5.07 vs 4.59 mmol/L (P = 0.016). The LDL-cholesterol level was lower in APOE ε2 carriers compared with ε3 homozygotes and ε4 carriers: 2.65 vs 3.03 and 3.17 mmol/L, respectively (p = 0.002). The total cholesterol/HDL-cholesterol and LDL-cholesterol/HDL-cholesterol ratios were similar in the three allelic groups. APOE polymorphism was not associated with diabetes, hypertension, waist circumference or body mass index.

CONCLUSIONS

Our results indicate that APOE gene polymorphism is associated with the lipid profile but not with CAD in Afro-Caribbean people. This lack of association with CAD may be explained by the low atherogenic profile observed in ε4 carriers, which may warrant further investigation.

Obesity Accelerates Alzheimer-Related Pathology in APOE4 but not APOE3 Mice

Alzheimer's disease (AD) risk is modified by both genetic and environmental risk factors, which are believed to interact to cooperatively modify pathogenesis. Although numerous genetic and environmental risk factors for AD have been identified, relatively little is known about potential gene-environment interactions in regulating disease risk. The strongest genetic risk factor for late-onset AD is the ε4 allele of apolipoprotein E (APOE4). An important modifiable risk factor for AD is obesity, which has been shown to increase AD risk in humans and accelerate development of AD-related pathology in rodent models. Potential interactions between APOE4 and obesity are suggested by the literature but have not been thoroughly investigated. In the current study, we evaluated this relationship by studying the effects of diet-induced obesity (DIO) in the EFAD mouse model, which combines familial AD transgenes with human APOE3 or APOE4. Male E3FAD and E4FAD mice were maintained for 12 weeks on either a control diet or a Western diet high in saturated fat and sugars. We observed that metabolic outcomes of DIO were similar in E3FAD and E4FAD mice. Importantly, our data showed a significant interaction between diet and APOE genotype on AD-related outcomes in which Western diet was associated with robust increases in amyloid deposits, β-amyloid burden, and glial activation in E4FAD but not in E3FAD mice. These findings demonstrate an important gene-environment interaction in an AD mouse model that suggests that AD risk associated with obesity is strongly influenced by APOE genotype.

A long-term high-fat, high-sucrose diet in Bama minipigs promotes lipid deposition and amyotrophy by up-regulating the myostatin pathway

Skeletal muscle is as an important regulator of blood glucose and glycolipid metabolism and is closely related to motor ability. The underlying mechanisms by which dietary ectopic lipids in skeletal muscle prevents muscle growth remain elusive. We utilized miniature Bama swine as a model to mimic human obesity using prolonged dietary induction. After 23 months on a high-fat, high-sucrose diet, metabolic disorders were induced in the animals, which exhibited increased body weight, extensive lipid deposition in the skeletal muscle and amyotrophy. Microarray profiles demonstrated the up-regulation of genes related to fat deposition and muscle growth inhibition. We outline a clear potential pathway that in combination with increased 11β-hydroxysteroid dehydrogenase type 1, promotes expression of a major inhibitor, myostatin, by converting corticosterone to cortisol, which leads to the growth inhibition of skeletal muscle. This research provides new insights into the treatment of muscle diseases induced by obesity.

Obesity and sex interact in the regulation of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, for which a number of genetic, environmental, and lifestyle risk factors have been identified. A significant modifiable risk factor is obesity in mid-life. Interestingly, both obesity and AD exhibit sex differences and are regulated by sex steroid hormones. Accumulating evidence suggests interactions between obesity and sex in regulation of AD risk, although the pathways underlying this relationship are unclear. Inflammation and the E4 allele of apolipoprotein E have been identified as independent risk factors for AD and both interact with obesity and sex steroid hormones. We review the individual and cooperative effects of obesity and sex on development of AD and examine the potential contributions of apolipoprotein E, inflammation, and their interactions to this relationship.

Association between Apolipoprotein E Variants and Obesity-Related Traits in Mexican School Children

BACKGROUND/AIM

Genetic variation in apolipoprotein E (ApoE) has a key role in lipid metabolism. However, its contribution to the amount and distribution of body fat is under investigation. The aim of this study was to analyze the association between genetic variation in ApoE and obesity-related traits in Mexican school children.

MATERIAL AND METHODS

Anthropometric, body composition and physical activity measures were conducted using standard methods in 300 children (177 girls/123 boys) who fulfilled the inclusion criteria. DNA was isolated from saliva. ApoE genotypes were analyzed by allelic discrimination. The association between variation in ApoE and anthropometric and body composition measures was investigated using the General Linear Model.

RESULTS

The mean±SD values for age, body mass index (BMI) and waist circumference (WC) were 9.05±0.80 years, 19.01±3.83 and 67.98±10.97 cm, respectively. Approximately 46% of the participants were overweight or obese. A significant association between ApoE isoforms and WC was found after controlling for age, sex and the percentage of physical activity (p=0.025). Significant main effects were found for vigorous physical activity and light physical activity influencing the adiposity-related BMI (p<0.001) and WC (p=0.044), respectively.

CONCLUSIONS

Variation in ApoE and physical activity intensity were associated with adiposity-related phenotypes in Mexican school children.

A genetic risk tool for obesity predisposition assessment and personalized nutrition implementation based on macronutrient intake

There is little evidence about genetic risk score (GRS)-diet interactions in order to provide personalized nutrition based on the genotype. The aim of the study was to assess the value of a GRS on obesity prediction and to further evaluate the interactions between the GRS and dietary intake on obesity. A total of 711 seekers of a Nutrigenetic Service were examined for anthropometric and body composition measurements and also for dietary habits and physical activity. Oral epithelial cells were collected for the identification of 16 SNPs (related with obesity or lipid metabolism) using DNA zip-coded beads. Genotypes were coded as 0, 1 or 2 according to the number of risk alleles, and the GRS was calculated by adding risk alleles with such a criterion. After being adjusted for gender, age, physical activity and energy intake, the GRS demonstrated that individuals carrying >7 risk alleles had in average 0.93 kg/m(2) of BMI, 1.69 % of body fat mass, 1.94 cm of waist circumference and 0.01 waist-to-height ratio more than the individuals with ≤7 risk alleles. Significant interactions for GRS and the consumption of energy, total protein, animal protein, vegetable protein, total fat, saturated fatty acids, polyunsaturated fatty acids, total carbohydrates, complex carbohydrates and fiber intake on adiposity traits were found after adjusted for confounders variables. The GRS confirmed that the high genetic risk group showed greater values of adiposity than the low risk group and demonstrated that macronutrient intake modifies the GRS association with adiposity traits.

Apolipoprotein E synthesized by adipocyte and apolipoprotein E carried on lipoproteins modulate adipocyte triglyceride content

Excessive energy storage of adipose tissue makes contribution to the occurrence and progression of obesity, which accompanies with multiple adverse complications, such as metabolic syndrome, cardiovascular diseases. It is well known that apolipoprotein E, as a component of lipoproteins, performs a key role in maintaining plasma lipoproteins homeostasis. Interestingly, apolipoprotein E is highly expressed in adipocyte and has positive relation with body fat mass. Apolipoprotein E knock-out mice show small fat mass compared to wild type mice. Moreover, adipocyte deficiency in apolipoprotein E shows impaired lipoproeteins internalization and triglyceride accumulation. Apolipopreotein E-deficient lipoproteins can not induce preadipocyte to form round full-lipid adipocyte, whereas apolipoprotein E-containing lipoproteins can. This article mainly reviews the modulation of apolipoprotein E synthesized by adipocyte and apolipoprotein E carried on lipoproteins in adipocyte triglyceride content.

The low density lipoprotein receptor modulates the effects of hypogonadism on diet-induced obesity and related metabolic perturbations

Here, we investigated how LDL receptor deficiency (Ldlr(-/-)) modulates the effects of testosterone on obesity and related metabolic dysfunctions. Though sham-operated Ldlr(-/-) mice fed Western-type diet for 12 weeks became obese and showed disturbed plasma glucose metabolism and plasma cholesterol and TG profiles, castrated mice were resistant to diet-induced obesity and had improved glucose metabolism and reduced plasma TG levels, despite a further deterioration in their plasma cholesterol profile. The effect of hypogonadism on diet-induced weight gain of Ldlr(-/-) mice was independent of ApoE and Lrp1. Indirect calorimetry analysis indicated that hypogonadism in Ldlr(-/-) mice was associated with increased metabolic rate. Indeed, mitochondrial cytochrome c and uncoupling protein 1 expression were elevated, primarily in white adipose tissue, confirming increased mitochondrial metabolic activity due to thermogenesis. Testosterone replacement in castrated Ldlr(-/-) mice for a period of 8 weeks promoted diet-induced obesity, indicating a direct role of testosterone in the observed phenotype. Treatment of sham-operated Ldlr(-/-) mice with the aromatase inhibitor exemestane for 8 weeks showed that the obesity of castrated Ldlr(-/-) mice is independent of estrogens. Overall, our data reveal a novel role of Ldlr as functional modulator of metabolic alterations associated with hypogonadism.

β3-Adrenoceptor activation attenuates atherosclerotic plaque formation in ApoE(-/-) mice through lowering blood lipids and glucose

AIM

To examine the effects of β3-adrenoceptor (β3-AR) activation on atherosclerotic plaque development in ApoE(-/-) mice.

METHODS

Thirty six week-old male ApoE(-/-) mice on a high-fat diet were treated with atorvastatin (10 mg·kg(-1)·d(-1), po), BRL37344 (β3-AR agonist, 1.65 or 3.30 μg/kg, ip, twice a week) or SR52390A (β3-AR antagonist, 50 μg/kg, ip, twice a week) for 12 weeks. Wild-type C57BL/6J mice receiving a normal diet were taken as healthy controls. At the end of the treatments, serum levels of triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), non-high density lipoprotein cholesterol (nHDL-C), glucose and insulin were measured. The thoracic aortas were dissected out, the area of atherosclerotic plaques and extent of fibrosis in the plaques were examined using HE and Masson's trichome staining, respectively.

RESULTS

Compared to wild-type mice, ApoE(-/-) mice fed on a high-fat diet exhibited prominent hyperlipidemia and insulin resistance, associated with large area of atherosclerotic plaques and great extent of fibrosis in aortas. Atorvastatin significantly decreased the serum levels of TC and nHDL-C, and reduced the plaque area and collagen content in aortas. BRL37344 significantly decreased the serum levels of TG, TC, nHDL-C, glucose and insulin, and increased HDL-C and the insulin sensitivity, and dose-dependently reduced the plaque area and collagen content in aortas. SR52390A treatment did not affect any parameters studied.

CONCLUSION

The β3-AR agonist impedes the progression of atherosclerosis in ApoE(-/-) mice, through improvement of the lipid and glucose profiles.

Expression of inflammation-related genes is altered in gastric tissue of patients with advanced stages of NAFLD

Obesity is associated with chronic low-grade inflammation perpetuated by visceral adipose. Other organs, particularly stomach and intestine, may also overproduce proinflammatory molecules. We examined the gene expression patterns in gastric tissue of morbidly obese patients with nonalcoholic fatty liver disease (NAFLD) and compared the changes in gene expression in different histological forms of NAFLD. Stomach tissue samples from 20 morbidly obese NAFLD patients who were undergoing sleeve gastrectomy were profiled using qPCR for 84 genes encoding inflammatory cytokines, chemokines, their receptors, and other components of inflammatory cascades. Interleukin 8 receptor-beta (IL8RB) gene overexpression in gastric tissue was correlated with the presence of hepatic steatosis, hepatic fibrosis, and histologic diagnosis of nonalcoholic steatohepatitis (NASH). Expression levels of soluble interleukin 1 receptor antagonist (IL1RN) were correlated with the presence of NASH and hepatic fibrosis. mRNA levels of interleukin 8 (IL8), chemokine (C-C motif) ligand 4 (CCL4), and its receptor chemokine (C-C motif) receptor type 5 (CCR5) showed a significant increase in patients with advanced hepatic inflammation and were correlated with the severity of the hepatic inflammation. The results of our study suggest that changes in expression patterns for inflammatory molecule encoding genes within gastric tissue may contribute to the pathogenesis of obesity-related NAFLD.

Lipoprotein metabolism in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), an escalating health problem worldwide, covers a spectrum of pathologies characterized by fatty accumulation in hepatocytes in early stages, with potential progression to liver inflammation, fibrosis, and failure. A close, yet poorly understood link exists between NAFLD and dyslipidemia, a constellation of abnormalities in plasma lipoproteins including triglyceride-rich very low density lipoproteins. Apolipoproteins are a group of primarily liver-derived proteins found in serum lipoproteins; they not only play an extracellular role in lipid transport between vital organs through circulation, but also play an important intracellular role in hepatic lipoprotein assembly and secretion. The liver functions as the central hub for lipoprotein metabolism, as it dictates lipoprotein production and to a significant extent modulates lipoprotein clearance. Lipoprotein metabolism is an integral component of hepatocellular lipid homeostasis and is implicated in the pathogenesis, potential diagnosis, and treatment of NAFLD.

Amyloid-β induces hepatic insulin resistance by activating JAK2/STAT3/SOCS-1 signaling pathway

Epidemiological studies indicate that patients with Alzheimer's disease (AD) have an increased risk of developing type 2 diabetes mellitus (T2DM), and experimental studies suggest that AD exacerbates T2DM, but the underlying mechanism is still largely unknown. This study aims to investigate whether amyloid-β (Aβ), a key player in AD pathogenesis, contributes to the development of insulin resistance, as well as the underlying mechanism. We find that plasma Aβ40/42 levels are increased in patients with hyperglycemia. APPswe/PSEN1dE9 transgenic AD model mice with increased plasma Aβ40/42 levels show impaired glucose and insulin tolerance and hyperinsulinemia. Furthermore, Aβ impairs insulin signaling in mouse liver and cultured hepatocytes. Aβ can upregulate suppressors of cytokine signaling (SOCS)-1, a well-known insulin signaling inhibitor. Knockdown of SOCS-1 alleviates Aβ-induced impairment of insulin signaling. Moreover, JAK2/STAT3 is activated by Aβ, and inhibition of JAK2/STAT3 signaling attenuates Aβ-induced upregulation of SOCS-1 and insulin resistance in hepatocytes. Our results demonstrate that Aβ induces hepatic insulin resistance by activating JAK2/STAT3/SOCS-1 signaling pathway and have implications toward resolving insulin resistance and T2DM.

A Mediterranean-style, low-glycemic-load diet decreases atherogenic lipoproteins and reduces lipoprotein (a) and oxidized low-density lipoprotein in women with metabolic syndrome

The objective was to assess the impact of a Mediterranean-style, low-glycemic-load diet (control group, n = 41) and the same diet plus a medical food (MF) containing phytosterols, soy protein, and extracts from hops and Acacia (MF group, n = 42) on lipoprotein atherogenicity in women with metabolic syndrome. Plasma lipids, apolipoproteins (apos), lipoprotein subfractions and particle size, low-density lipoprotein (LDL) oxidation, and lipoprotein (a) were measured at baseline, week 8, and week 12 of the intervention. Three-day dietary records were collected at the same time points to assess compliance. Compared with baseline, women decreased energy intake from carbohydrate (P < .001) and fat (P < .001), whereas they increased energy intake from protein (P < .001). A significant increase in energy from monounsaturated fatty acids was also observed as well as increases in eicosapentaenoic acid and docosahexaenoic acid, whereas trans-fatty acid intake was reduced (P < .00001). The atherogenic lipoproteins, large very low-density lipoprotein (P < .0001) and small LDL (P < .0001), were reduced, whereas the ratio of large high-density lipoprotein to smaller high-density lipoprotein particles was increased (P < .0001). Apolipoprotein B was reduced for all women (P < .0001), with a greater reduction in the MF group (P < .025). Oxidized LDL (P < .05) and lipoprotein (a) (P < .001) were reduced in both groups at the end of the intervention. Consumption of a Mediterranean-style diet reduces the risk for cardiovascular disease by decreasing atherogenic lipoproteins, oxidized LDL, and apo B. Inclusion of an MF may have an additional effect in reducing apo B.

Dietary omega 3 polyunsaturated fatty acids and Alzheimer's disease: interaction with apolipoprotein E genotype

Epidemiological studies suggest a protective role of omega-3 poly-unsaturated fatty acids (n-3 PUFA) against Alzheimer's disease (AD). However, most intervention studies of supplementation with n-3 PUFA have yielded disappointing results. One reason for such discordant results may result from inadequate targeting of individuals who might benefit from the supplementation, in particular because of their genetic susceptibility to AD. The ε4 allele of the apolipoprotein E gene (ApoE) is a genetic risk factor for late-onset AD. ApoE plays a key role in the transport of cholesterol and other lipids involved in brain composition and functioning. The action of n-3 PUFA on the aging brain might therefore differ according to ApoE polymorphism. The aim of this review is to examine the interaction between dietary fatty acids and ApoE genotype on the risk for AD. Carriers of the ε4 allele tend to be the most responsive to changes in dietary fat and cholesterol. Conversely, several epidemiological studies suggest a protective effect of long-chain n-3 PUFA on cognitive decline only in those who do not carry ε4 but with inconsistent results. An intervention study showed that only non-carriers had increased concentrations of long-chain n-3 PUFA in response to supplementation. The mechanisms underlying this gene-by-diet interaction on AD risk may involve impaired fatty acids and cholesterol transport, altered metabolism of n-3 PUFA, glucose or ketones, or modification of other risk factors of AD in ε4 carriers. Further research is needed to explain the differential effect of n-3 PUFA on AD according to ApoE genotype.

APOE genotype and cardio-respiratory fitness interact to determine adiposity in 8-year-old children from the Tasmanian Infant Health Survey

APOE plays a well established role in lipid metabolism. Animal model evidence suggests APOE may also be associated with adiposity, but this has not been thoroughly investigated in humans. We measured adiposity (BMI, truncal fat mass, waist circumference), physical activity (PA), cardiorespiratory fitness and APOE genotype (E2, E3, E4) in 292 8-year-old children from the Tasmanian Infant Health Survey (TIHS), an Australian population-based prospective birth cohort. Our aims were to examine the association of APOE with child adiposity, and to examine the interplay between this association and other measured factors. We found that APOE was associated with child lipid profiles. APOE was also associated with child adiposity measures. The association was E4 allele-specific, with adiposity lower in the E4-containing group (BMI: Mean difference -0.90 kg/m²; 95% confidence intervals (CI) -1.51, -0.28; p = 0.004). The association of APOE4 with lower BMI differed by fitness status (difference in effect p = 0.002), and was more evident among the less fit (mean difference -1.78 kg/m²; 95% CI -2.74, -0.83; p<0.001). Additionally, associations between BMI and lipids were only apparent in those of lower fitness who did not carry APOE4. Similar overall findings were observed when truncal fat mass and waist circumference were used as alternative adiposity measures. APOE4 and cardiorespitatory fitness could interact to influence child adiposity. In studies addressing the genetic determinants of childhood obesity, the context of child fitness should also be taken into account.

Apolipoproteins: metabolic role and clinical biochemistry applications

Lipoprotein metabolism is dependent on apolipoproteins, multifunctional proteins that serve as templates for the assembly of lipoprotein particles, maintain their structure and direct their metabolism through binding to membrane receptors and regulation of enzyme activity. The three principal functions of lipoproteins are contribution to interorgan fuel (triglyceride) distribution (by means of the fuel transport pathway), to the maintenance of the extracellular cholesterol pool (by means of the overflow pathway) and reverse cholesterol transport. The most important clinical application of apolipoprotein measurements in the plasma is in the assessment of cardiovascular risk. Concentrations of apolipoprotein B and apolipoprotein AI (and their ratio) seem to be better markers of cardiovascular risk than conventional markers such as total cholesterol and LDL-cholesterol. Apolipoprotein measurements are also better standardized than the conventional tests. We suggest that measurements of apolipoprotein AI and apolipoprotein B are included as a part of the specialist lipid profile. We also suggest that lipoprotein (a) should be measured as part of the initial assessment of dyslipidaemias because of its consistent association with cardiovascular risk. Genotyping of apolipoprotein E isoforms remains useful in the investigation of mixed dyslipidaemias. Lastly, the role of postprandial metabolism is increasingly recognized in the context of atherogenesis, obesity and diabetes. This requires better markers of chylomicrons, very-low-density lipoproteins and remnant particles. Measurements of apolipoprotein B48 and remnant lipoprotein cholesterol are currently the key tests in this emerging field.

Deficiency in apolipoprotein E has a protective effect on diet-induced nonalcoholic fatty liver disease in mice

Apolipoprotein E (apoE) mediates the efficient catabolism of the chylomicron remnants very low-density lipoprotein and low-density lipoprotein from the circulation, and the de novo biogenesis of high-density lipoprotein. Lipid-bound apoE is the natural ligand for the low-density lipoprotein receptor (LDLr), LDLr-related protein 1 and other scavenger receptors. Recently, we have established that deficiency in apoE renders mice resistant to diet-induced obesity. In the light of these well-documented properties of apoE, we sought to investigate its role in the development of diet-induced nonalcoholic fatty liver disease (NAFLD). apoE-deficient, LDLr-deficient and control C57BL/6 mice were fed a western-type diet (17.3% protein, 48.5% carbohydrate, 21.2% fat, 0.2% cholesterol, 4.5 kcal·g(-)) for 24 weeks and their sensitivity to NAFLD was assessed by histological and biochemical methods. apoE-deficient mice were less sensitive than control C57BL/6 mice to diet-induced NAFLD. In an attempt to identify the molecular basis for this phenomenon, biochemical and kinetic analyses revealed that apoE-deficient mice displayed a significantly delayed post-prandial triglyceride clearance from their plasma. In contrast with apoE-deficient mice, LDLr-deficient mice fed a western-type diet for 24 weeks developed significant accumulation of hepatic triglycerides and NAFLD, suggesting that apoE-mediated hepatic triglyceride accumulation in mice is independent of LDLr. Our findings suggest a new role of apoE as a key peripheral contributor to hepatic lipid homeostasis and the development of diet-induced NAFLD.

A functional mutation at position -155 in porcine APOE promoter affects gene expression

BACKGROUND

Apolipoprotein E, a component of the plasma lipoproteins, plays an important role in the transport and metabolism of cholesterol and other lipids. Three single nucleotide polymorphisms (SNPs) -491A>T, -219T>G and +113G>C in the regulatory region of human apolipoprotein E gene (APOE) change the promoter activity and are associated with a wide variety of disorders including Alzheimer disease (AD). Functional SNPs in porcine APOE gene 5' regulatory region have not been explored.

RESULTS

We examined SNPs within this region (from -831 to +855), and the analysis revealed that the T>A SNP at position -155 among these three polymorphism sites (-440, -155, +501) was found to exert a marked influence on the transcription of the porcine APOE gene. Electrophoretic mobility shift assays showed that the binding affinity of oligonucletides containing the -155A to transcription factor(s) was stronger than that of the -155T. Transient transfection assays and quantitative real-time PCR results revealed that the -155T>A variant enhanced the activity of the APOE promoter and was associated with increased APOE mRNA levels in vivo.

CONCLUSIONS

These data suggest that the -155T>A mutation in the promoter region of the porcine APOE gene is an important functional variant. The results provided new insights into aspects of pig genetics and might also facilitate the application of pigs in biomedical studies addressing important human diseases.

The APOE -219G/T and +113G/C polymorphisms affect insulin resistance among Turks

The -219G/T (rs405509) and +113G/C (rs440446) polymorphisms within the regulatory region of the apolipoprotein E (APOE) gene have been related to the transcriptional activity of the gene. We examined the effect of the stated polymorphisms and their construct haplotypes with the APOE ɛ2/ɛ3/ɛ4 polymorphism on lipid levels and insulin resistance in the Turkish Adult Risk Factor Study. Randomly selected 1774 adults (mean age, 55.0 ± 11.7 years; 51.2% women) participating in the population-based Turkish Adult Risk Factor Study were cross-sectionally analyzed for the -219G/T, +113G/C, and ɛ2/ɛ3/ɛ4 polymorphisms as well as their haplotypes. Insulin resistance was defined as the 70th percentile in the sample (>2.51) of the homeostatic model assessment (HOMA). The frequencies of the -219T and +113C alleles were 0.477 and 0.423, respectively; and those of haplotype 1 (GGɛ3) and haplotype 2 (TCɛ3) were 44.1% and 41.9%, respectively. The -219G/T and +113G/C genotypes (both P < .04) and diplotypes of haplotype 2 (TCɛ3) (P < .014) were inversely related to serum fasting insulin and the HOMA index, even after controlling for 8 relevant covariates, but not to serum lipids. Within the APOE3 group, haplotype 2 (TC-/TC+) heterozygotes had an odds ratio of 0.66 (95% confidence interval, 0.42-0.99) for HOMA of insulin resistance after adjusting for 8 covariates. APOE promoter polymorphisms and their diplotypes are independently related with serum fasting insulin levels and HOMA index among Turks.

The ε3 and ε4 alleles of human APOE differentially affect tau phosphorylation in hyperinsulinemic and pioglitazone treated mice

BACKGROUND

Impaired insulin signalling is increasingly thought to contribute to Alzheimer's disease (AD). The ε4 isoform of the APOE gene is the greatest genetic risk factor for sporadic, late onset AD, and is also associated with risk for type 2 diabetes mellitus (T2DM). Neuropathological studies reported the highest number of AD lesions in brain tissue of ε4 diabetic patients. However other studies assessing AD pathology amongst the diabetic population have produced conflicting reports and have failed to show an increase in AD-related pathology in diabetic brain. The thiazolidinediones (TZDs), peroxisome proliferator-activated receptor gamma agonists, are peripheral insulin sensitisers used to treat T2DM. The TZD, pioglitazone, improved memory and cognitive functions in mild to moderate AD patients. Since it is not yet clear how apoE isoforms influence the development of T2DM and its progression to AD, we investigated amyloid beta and tau pathology in APOE knockout mice, carrying human APOEε3 or ε4 transgenes after diet-induced insulin resistance with and without pioglitazone treatment.

METHODS

Male APOE knockout, APOEε3-transgenic and APOEε4-transgenic mice, together with background strain C57BL6 mice were kept on a high fat diet (HFD) or low fat diet (LFD) for 32 weeks, or were all fed HFD for 32 weeks and during the final 3 weeks animals were treated with pioglitazone or vehicle.

RESULTS

All HFD animals developed hyperglycaemia with elevated plasma insulin. Tau phosphorylation was reduced at 3 epitopes (Ser396, Ser202/Thr205 and Thr231) in all HFD, compared to LFD, animals independent of APOE genotype. The introduction of pioglitazone to HFD animals led to a significant reduction in tau phosphorylation at the Ser202/Thr205 epitope in APOEε3 animals only. We found no changes in APP processing however the levels of soluble amyloid beta 40 was reduced in APOE knockout animals treated with pioglitazone.