Mechanism of triglyceride lowering in mice expressing human apolipoprotein A5

Cholesterol transport and beyond: Illuminating the versatile functions of HDL apolipoproteins through structural insights and functional implications

High-density lipoproteins (HDLs) play a vital role in lipid metabolism and cardiovascular health, as they are intricately involved in cholesterol transport and inflammation modulation. The proteome of HDL particles is indeed complex and distinct from other components in the bloodstream. Proteomics studies have identified nearly 285 different proteins associated with HDL; however, this review focuses more on the 15 or so traditionally named "apo" lipoproteins. Important lipid metabolizing enzymes closely working with the apolipoproteins are also discussed. Apolipoproteins stand out for their integral role in HDL stability, structure, function, and metabolism. The unique structure and functions of each apolipoprotein influence important processes such as inflammation regulation and lipid metabolism. These interactions also shape the stability and performance of HDL particles. HDLs apolipoproteins have multifaceted roles beyond cardiovascular diseases (CVDs) and are involved in various physiological processes and disease states. Therefore, a detailed exploration of these apolipoproteins can offer valuable insights into potential diagnostic markers and therapeutic targets. This comprehensive review article aims to provide an in-depth understanding of HDL apolipoproteins, highlighting their distinct structures, functions, and contributions to various physiological processes. Exploiting this knowledge holds great potential for improving HDL function, enhancing cholesterol efflux, and modulating inflammatory processes, ultimately benefiting individuals by limiting the risks associated with CVDs and other inflammation-based pathologies. Understanding the nature of all 15 apolipoproteins expands our knowledge of HDL metabolism, sheds light on their pathological implications, and paves the way for advancements in the diagnosis, prevention, and treatment of lipid and inflammatory-related disorders.

APOA5 deficiency causes hypertriglyceridemia by reducing amounts of lipoprotein lipase in capillaries

Apolipoprotein AV (APOA5) deficiency causes hypertriglyceridemia in mice and humans. For years, the cause remained a mystery, but the mechanisms have now come into focus. Here, we review progress in defining APOA5's function in plasma triglyceride metabolism. Biochemical studies revealed that APOA5 binds to the angiopoietin-like protein 3/8 complex (ANGPTL3/8) and suppresses its ability to inhibit the activity of lipoprotein lipase (LPL). Thus, APOA5 deficiency is accompanied by increased ANGPTL3/8 activity and lower levels of LPL activity. APOA5 deficiency also reduces amounts of LPL in capillaries of oxidative tissues (e.g., heart, brown adipose tissue). Cell culture experiments revealed the likely explanation: ANGPTL3/8 detaches LPL from its binding sites on the surface of cells, and that effect is blocked by APOA5. Both the low intracapillary LPL levels and the high plasma triglyceride levels in Apoa5-/- mice are normalized by recombinant APOA5. Carboxyl-terminal sequences in APOA5 are crucial for its function; a mutant APOA5 lacking 40-carboxyl-terminal residues cannot bind to ANGPTL3/8 and lacks the ability to change intracapillary LPL levels or plasma triglyceride levels in Apoa5-/- mice. Also, an antibody against the last 26 amino acids of APOA5 reduces intracapillary LPL levels and increases plasma triglyceride levels in wild-type mice. An inhibitory ANGPTL3/8-specific antibody functions as an APOA5-mimetic reagent, increasing intracapillary LPL levels and lowering plasma triglyceride levels in both Apoa5-/- and wild-type mice. That antibody is a potentially attractive strategy for treating elevated plasma lipid levels in human patients.

Genetic and biochemical analysis of severe hypertriglyceridemia complicated with acute pancreatitis or with low post-heparin lipoprotein lipase mass

Severe hypertriglyceridemia is a pathological condition caused by genetic factors alone or in combination with environmental factors, sometimes leading to acute pancreatitis (AP). In this study, exome sequencing and biochemical analyses were performed in 4 patients with hypertriglyceridemia complicated by obesity or diabetes with a history of AP or decreased post-heparin LPL mass. In a patient with a history of AP, SNP rs199953320 resulting in LMF1 nonsense mutation and APOE rs7412 causing apolipoprotein E2 were both found in heterozygous form. Three patients were homozygous for APOA5 rs2075291, and one was heterozygous. ELISA and Western blot analysis of the serum revealed the existence of apolipoprotein A-V in the lipoprotein-free fraction regardless of the presence or absence of rs2075291; furthermore, the molecular weight of apolipoprotein A-V was different depending on the class of lipoprotein or lipoprotein-free fraction. Lipidomics analysis showed increased serum levels of sphingomyelin and many classes of glycerophospholipid; however, when individual patients were compared, the degree of increase in each class of phospholipid among cases did not coincide with the increases seen in total cholesterol and triglycerides. Moreover, phosphatidylcholine, lysophosphatidylinositol, and sphingomyelin levels tended to be higher in patients who experienced AP than those who did not, suggesting that these phospholipids may contribute to the onset of AP. In summary, this study revealed a new disease-causing gene mutation in LMF1, confirmed an association between overlapping of multiple gene mutations and severe hypertriglyceridemia, and suggested that some classes of phospholipid may be involved in the pathogenesis of AP.

Macromolecular Interactions of Lipoprotein Lipase (LPL)

Lipoprotein lipase (LPL) is a critical enzyme in humans that provides fuel to peripheral tissues. LPL hydrolyzes triglycerides from the cores of lipoproteins that are circulating in plasma and interacts with receptors to mediate lipoprotein uptake, thus directing lipid distribution via catalytic and non-catalytic functions. Functional losses in LPL or any of its myriad of regulators alter lipid homeostasis and potentially affect the risk of developing cardiovascular disease-either increasing or decreasing the risk depending on the mutated protein. The extensive LPL regulatory network tunes LPL activity to allocate fatty acids according to the energetic needs of the organism and thus is nutritionally responsive and tissue dependent. Multiple pharmaceuticals in development manipulate or mimic these regulators, demonstrating their translational importance. Another facet of LPL biology is that the oligomeric state of the enzyme is also central to its regulation. Recent structural studies have solidified the idea that LPL is regulated not only by interactions with other binding partners but also by self-associations. Here, we review the complexities of the protein-protein and protein-lipid interactions that govern LPL structure and function.

Hypertriglyceridemia in Apoa5-/- mice results from reduced amounts of lipoprotein lipase in the capillary lumen

Why apolipoprotein AV (APOA5) deficiency causes hypertriglyceridemia has remained unclear, but we have suspected that the underlying cause is reduced amounts of lipoprotein lipase (LPL) in capillaries. By routine immunohistochemistry, we observed reduced LPL staining of heart and brown adipose tissue (BAT) capillaries in Apoa5-/- mice. Also, after an intravenous injection of LPL-, CD31-, and GPIHBP1-specific mAbs, the binding of LPL Abs to heart and BAT capillaries (relative to CD31 or GPIHBP1 Abs) was reduced in Apoa5-/- mice. LPL levels in the postheparin plasma were also lower in Apoa5-/- mice. We suspected that a recent biochemical observation - that APOA5 binds to the ANGPTL3/8 complex and suppresses its capacity to inhibit LPL catalytic activity - could be related to the low intracapillary LPL levels in Apoa5-/- mice. We showed that an ANGPTL3/8-specific mAb (IBA490) and APOA5 normalized plasma triglyceride (TG) levels and intracapillary LPL levels in Apoa5-/- mice. We also showed that ANGPTL3/8 detached LPL from heparan sulfate proteoglycans and GPIHBP1 on the surface of cells and that the LPL detachment was blocked by IBA490 and APOA5. Our studies explain the hypertriglyceridemia in Apoa5-/- mice and further illuminate the molecular mechanisms that regulate plasma TG metabolism.

Comprehensive Lipid Profiling Recapitulates Enhanced Lipolysis and Fatty Acid Metabolism in Intimal Foamy Macrophages From Murine Atherosclerotic Aorta

Lipid accumulation in macrophages is a prominent phenomenon observed in atherosclerosis. Previously, intimal foamy macrophages (FM) showed decreased inflammatory gene expression compared to intimal non-foamy macrophages (NFM). Since reprogramming of lipid metabolism in macrophages affects immunological functions, lipid profiling of intimal macrophages appears to be important for understanding the phenotypic changes of macrophages in atherosclerotic lesions. While lipidomic analysis has been performed in atherosclerotic aortic tissues and cultured macrophages, direct lipid profiling has not been performed in primary aortic macrophages from atherosclerotic aortas. We utilized nanoflow ultrahigh-performance liquid chromatography-tandem mass spectrometry to provide comprehensive lipid profiles of intimal non-foamy and foamy macrophages and adventitial macrophages from Ldlr-/- mouse aortas. We also analyzed the gene expression of each macrophage type related to lipid metabolism. FM showed increased levels of fatty acids, cholesterol esters, phosphatidylcholine, lysophosphatidylcholine, phosphatidylinositol, and sphingomyelin. However, phosphatidylethanolamine, phosphatidic acid, and ceramide levels were decreased in FM compared to those in NFM. Interestingly, FM showed decreased triacylglycerol (TG) levels. Expressions of lipolysis-related genes including Pnpla2 and Lpl were markedly increased but expressions of Lpin2 and Dgat1 related to TG synthesis were decreased in FM. Analysis of transcriptome and lipidome data revealed differences in the regulation of each lipid metabolic pathway in aortic macrophages. These comprehensive lipidomic data could clarify the phenotypes of macrophages in the atherosclerotic aorta.

Comparison of the structure-function properties of wild-type human apoA-V and a C-terminal truncation associated with elevated plasma triglycerides

Background

Plasma triglycerides (TGs) are causally associated with coronary artery disease and acute pancreatitis. Apolipoprotein A-V (apoA-V, gene APOA5) is a liver-secreted protein that is carried on triglyceride-rich lipoproteins and promotes the enzymatic activity of lipoprotein lipase (LPL), thereby reducing TG levels. Little is known about apoA-V structure-function; naturally occurring human APOA5 variants can provide novel insights.

Methods

We used hydrogen-deuterium exchange mass spectrometry to determine the secondary structure of human apoA-V in lipid-free and lipid-associated conditions and identified a C-terminal hydrophobic face. Then, we used genomic data in the Penn Medicine Biobank to identify a rare variant, Q252X, predicted to specifically eliminate this region. We interrogated the function of apoA-V Q252X using recombinant protein in vitro and in vivo in apoa5 knockout mice.

Results

Human apoA-V Q252X carriers exhibited elevated plasma TG levels consistent with loss of function. Apoa5 knockout mice injected with AAV vectors expressing wildtype and variant APOA5-AAV recapitulated this phenotype. Part of the loss of function is due to reduced mRNA expression. Functionally, recombinant apoA-V Q252X was more readily soluble in aqueous solutions and more exchangeable with lipoproteins than WT apoA-V. Despite lacking the C-terminal hydrophobic region (a putative lipid binding domain) this protein also decreased plasma TG in vivo.

Conclusions

Deletion of apoA-V's C-terminus leads to reduced apoA-V bioavailability in vivo and higher TG levels. However, the C-terminus is not required for lipoprotein binding or enhancement of intravascular lipolytic activity. WT apoA-V is highly prone to aggregation, and this property is markedly reduced in recombinant apoA-V lacking the C-terminus.

Association of the APOA-5 Genetic Variant rs662799 with Metabolic Changes after an Intervention for 9 Months with a Low-Calorie Diet with a Mediterranean Profile

In cross-sectional studies, the genetic variant rs662799 of the APOA5 gene is associated with high serum triglyceride concentrations, and in some studies, the effect of short-term dietary interventions has been evaluated. The aim of the present investigation was to evaluate the role of this genetic variant in metabolic changes after the consumption of a low-calorie diet with a Mediterranean pattern for 9 months. A population of 269 Caucasian obese patients was recruited. Adiposity and biochemical parameters were measured at the beginning (basal level) and after 3 and 9 months of the dietary intervention. The rs662799 genotype was assessed with a dominant analysis (TT vs. CT + CC). The APOA5 variant distribution was: 88.1% (n = 237) (TT), 11.5% (n = 31) (TC) and 0.4% (n = 1) (CC). There were significant differences only in triglyceride levels at all times of the study between the genotype groups. After 3 and 9 months of dietary intervention, the following parameters improved in both genotype groups: adiposity parameters, systolic pressure, total cholesterol, LDL cholesterol, leptin, adiponectin and the leptin/adiponectin ratio. The intervention significantly decreased insulin levels, HOMA-IR and triglyceride levels in non-C allele carriers (Delta 9 months TT vs. TC + CC). i.e., insulin levels (delta: −3.8 + 0.3 UI/L vs. −1.2 + 0.2 UI/L; p = 0.02), HOMA-IR levels (delta: −1.2 + 0.2 units vs. −0.3 + 0.1 units; p = 0.02), triglyceride levels (delta: −19.3 + 4.2 mg/dL vs. −4.2 + 3.0 mg/dL; p = 0.02). In conclusion, non-C allele carriers of rs662799 of the APOA5 gene showed a decrease of triglyceride, insulin and HOMA-IR levels after consuming a low-calorie diet with a Mediterranean pattern; we did not observe this effect in C allele carriers, despite a significant weight loss.

Lipoprotein size is a main determinant for the rate of hydrolysis by exogenous LPL in human plasma

LPL is a key player in plasma triglyceride metabolism. Consequently, LPL is regulated by several proteins during synthesis, folding, secretion, and transport to its site of action at the luminal side of capillaries, as well as during the catalytic reaction. Some proteins are well known, whereas others have been identified but are still not fully understood. We set out to study the effects of the natural variations in the plasma levels of all known LPL regulators on the activity of purified LPL added to samples of fasted plasma taken from 117 individuals. The enzymatic activity was measured at 25°C using isothermal titration calorimetry. This method allows quantification of the ability of an added fixed amount of exogenous LPL to hydrolyze triglyceride-rich lipoproteins in plasma samples by measuring the heat produced. Our results indicate that, under the conditions used, the normal variation in the endogenous levels of apolipoprotein C1, C2, and C3 or the levels of angiopoietin-like proteins 3, 4, and 8 in the fasted plasma samples had no significant effect on the recorded activity of the added LPL. Instead, the key determinant for the LPL activity was a lipid signature strongly correlated to the average size of the VLDL particles. The signature involved not only several lipoprotein and plasma lipid parameters but also apolipoprotein A5 levels. While the measurements cannot fully represent the action of LPL when attached to the capillary wall, our study provides knowledge on the interindividual variation of LPL lipolysis rates in human plasma.

Hepatic transcriptome analysis identifies genes, polymorphisms and pathways involved in the fatty acids metabolism in sheep

Fatty acids (FA) in ruminants, especially unsaturated FA (USFA) have important impact in meat quality, nutritional value, and flavour quality of meat, and on consumer’s health. Identification of the genetic factors controlling the FA composition and metabolism is pivotal to select sheep that produce higher USFA and lower saturated (SFA) for the benefit of sheep industry and consumers. Therefore, this study was aimed to investigate the transcriptome profiling in the liver tissues collected from sheep with divergent USFA content in longissimus muscle using RNA deep-sequencing. From sheep (n = 100) population, liver tissues with higher (n = 3) and lower (n = 3) USFA content were analysed using Illumina HiSeq 2500. The total number of reads produced for each liver sample were ranged from 21.28 to 28.51 million with a median of 23.90 million. Approximately, 198 genes were differentially regulated with significance level of p-adjusted value <0.05. Among them, 100 genes were up-regulated, and 98 were down-regulated (p<0.01, FC>1.5) in the higher USFA group. A large proportion of key genes involved in FA biosynthesis, adipogenesis, fat deposition, and lipid metabolism were identified, such as APOA5, SLC25A30, GFPT1, LEPR, TGFBR2, FABP7, GSTCD, and CYP17A. Pathway analysis revealed that glycosaminoglycan biosynthesis- keratan sulfate, adipokine signaling, galactose metabolism, endocrine and other factors-regulating calcium metabolism, mineral metabolism, and PPAR signaling pathway were playing important regulatory roles in FA metabolism. Importantly, polymorphism and association analyses showed that mutation in APOA5, CFHR5, TGFBR2 and LEPR genes could be potential markers for the FA composition in sheep. These polymorphisms and transcriptome networks controlling the FA variation could be used as genetic markers for FA composition-related traits improvement. However, functional validation is required to confirm the effect of these SNPs in other sheep population in order to incorporate them in the sheep breeding program.

APOA-5 Genetic Variant rs662799: Role in Lipid Changes and Insulin Resistance after a Mediterranean Diet in Caucasian Obese Subjects

Background and Aims

This APOA5-1131C allele is related with a higher serum triglyceride levels and perhaps a different metabolic response to a dietary intervention. The aim of the present investigation was to evaluate SNP rs662799 in the APOA5 gene and its associations with metabolic effects after a hypocaloric diet with Mediterranean pattern.

Methods

A population of 363 Caucasian obese patients was enrolled. Anthropometric parameters and serum parameters (lipid profile, insulin, homeostasis model assessment (HOMA-IR), glucose, C reactive protein, adiponectin, resistin, and leptin levels) were measured, at basal time and after 3 months. All patients were genotyped in the rs662799 polymorphism.

Results

The APOA5 variant distribution was as follows: 89.3% (n = 324) (TT) were homozygous for the T allele, 10.5% (n = 38) (TC) were heterozygous, and 0.2% (n = 1) (CC) were homozygous for the C allele. Triglyceride levels were higher in patients with the C allele. After dietary intervention, BMI, weight, fat mass, waist circumference, systolic blood pressure, adiponectin, leptin, and adiponectin/leptin ratio improved significantly in both genotype groups TT and TC+CC. After dietary intervention, insulin levels (delta: −3.6 ± 0.8 UI/L vs. −1.5 ± 0.6 UI/L; P = 0.03), HOMA-IR (delta: −1.5 ± 0.4 units vs. −0.3 ± 0.2 units; P = 0.02), and triglyceride levels (delta: −19.3 ± 4.2 mg/dL vs. −3.2 ± 3.1 mg/dL; P = 0.02) decreased in non-C allele carriers.

Conclusions

C allele carriers of rs662799 of the APOA5 gene did not show an improvement in triglyceride, insulin, and HOMA-IR levels after a significant weight loss due to a hypocaloric diet with a Mediterranean pattern.

Metabolic-associated fatty liver disease and lipoprotein metabolism

BACKGROUND

Non-alcoholic fatty liver disease, or as recently proposed 'metabolic-associated fatty liver disease' (MAFLD), is characterized by pathological accumulation of triglycerides and other lipids in hepatocytes. This common disease can progress from simple steatosis to steatohepatitis, and eventually end-stage liver diseases. MAFLD is closely related to disturbances in systemic energy metabolism, including insulin resistance and atherogenic dyslipidemia.

SCOPE OF REVIEW

The liver is the central organ in lipid metabolism by secreting very low density lipoproteins (VLDL) and, on the other hand, by internalizing fatty acids and lipoproteins. This review article discusses recent research addressing hepatic lipid synthesis, VLDL production, and lipoprotein internalization as well as the lipid exchange between adipose tissue and the liver in the context of MAFLD.

MAJOR CONCLUSIONS

Liver steatosis in MAFLD is triggered by excessive hepatic triglyceride synthesis utilizing fatty acids derived from white adipose tissue (WAT), de novo lipogenesis (DNL) and endocytosed remnants of triglyceride-rich lipoproteins. In consequence of high hepatic lipid content, VLDL secretion is enhanced, which is the primary cause of complex dyslipidemia typical for subjects with MAFLD. Interventions reducing VLDL secretory capacity attenuate dyslipidemia while they exacerbate MAFLD, indicating that the balance of lipid storage versus secretion in hepatocytes is a critical parameter determining disease outcome. Proof of concept studies have shown that promoting lipid storage and energy combustion in adipose tissues reduces hepatic lipid load and thus ameliorates MAFLD. Moreover, hepatocellular triglyceride synthesis from DNL and WAT-derived fatty acids can be targeted to treat MAFLD. However, more research is needed to understand how individual transporters, enzymes, and their isoforms affect steatosis and dyslipidemia in vivo, and whether these two aspects of MAFLD can be selectively treated. Processing of cholesterol-enriched lipoproteins appears less important for steatosis. It may, however, modulate inflammation and consequently MAFLD progression.

APOA5 Variant rs662799, Role in Cardiovascular Traits and Serum Adipokine Levels in Caucasian Obese Subjects

BACKGROUND AND AIMS

This ApoA5-1131C allele of rs662799 variant is related with a higher serum triglyceride levels, and it contributes to increase risk of cardiovascular disease. The aim of the present investigation was to evaluate single nucleotide polymorphism rs662799 in APOA5 gene and its associations with cardiovascular risk factors, MS, and serum adipokine levels.

METHODS

The study involved a population of 1,002 Caucasian obese subjects. Measurements of body weight, waist circumference, fat mass, arterial blood pressure, blood glucose, C-reactive protein, insulin levels, insulin resistance (HOMA-IR), lipid profile, and adipokines levels were recorded. Genotype of ApoA5 gene polymorphism (rs662799) and prevalence of metabolic syndrome (MS) were evaluated.

RESULTS

The distribution of the rs662799 polymorphism in this adult population (n = 1,002) was 88.3% (n = 885) (TT), 11.4% (n = 114) (TC), and 0.3% (n = 3) (CC). No significant differences were found between the 2 genotypes in the anthropometric data, MS, or blood pressure. Triglyceride levels were higher in C-allele carriers (delta total group: 19.7 ± 2.1 mg/dL: p = 0.02) than non C-allele carriers. HDL-cholesterol levels were lower in C-allele carriers (delta total group: -6.7 ± 1.1 mg/dL: p = 0.02) than non C-allele carriers. Adiponectin levels were lower in C-allele carriers (delta total group: -11.6 ± 1.0 mg/dL: p = 0.02) too. In C-allele carriers, logistic regression analysis showed an increased risk of hypertriglyceridemia (odds ratio [OR] = 2.1, 95% confidence interval [CI] = 1.2-3.4, p = 0.001) and percentage of low-HDL-C (OR = 2.2, 95% CI = 1.3-3.7, p = 0.002) after adjusting by body mass index and age.

CONCLUSIONS

C-allele carriers of rs662799 of APOA5 gene showed high rates of low levels of HDL and hypertriglyceridemia, with differences in triglyceride, HDL cholesterol, and adiponectin levels in Caucasian obese subjects.

Inadvertent nucleotide sequence alterations during mutagenesis: highlighting the vulnerabilities in mouse transgenic technology

In the last three decades, researchers have utilized genome engineering to alter the DNA sequence in the living cells of a plethora of organisms, ranging from plants, fishes, mice, to even humans. This has been conventionally achieved by using methodologies such as single nucleotide insertion/deletion in coding sequences, exon(s) deletion, mutations in the promoter region, introducing stop codon for protein truncation, and addition of foreign DNA for functional elucidation of genes. However, recent years have witnessed the advent of novel techniques that use programmable site-specific nucleases like CRISPR/Cas9, TALENs, ZFNs, Cre/loxP system, and gene trapping. These have revolutionized the field of experimental transgenesis as well as contributed to the existing knowledge base of classical genetics and gene mapping. Yet there are certain experimental/technological barriers that we have been unable to cross while creating genetically modified organisms. Firstly, while interfering with coding strands, we inadvertently change introns, antisense strands, and other non-coding elements of the gene and genome that play integral roles in the determination of cellular phenotype. These unintended modifications become critical because introns and other non-coding elements, although traditionally regarded as “junk DNA,” have been found to play a major regulatory role in genetic pathways of several crucial cellular processes, development, homeostasis, and diseases. Secondly, post-insertion of transgene, non-coding RNAs are generated by host organism against the inserted foreign DNA or from the inserted transgene/construct against the host genes. The potential contribution of these non-coding RNAs to the resulting phenotype has not been considered. We aim to draw attention to these inherent flaws in the transgenic technology being employed to generate mutant mice and other model organisms. By overlooking these aspects of the whole gene and genetic makeup, perhaps our current understanding of gene function remains incomplete. Thus, it becomes important that, while using genetic engineering techniques to generate a mutant organism for a particular gene, we should carefully consider all the possible elements that may play a potential role in the resulting phenotype. This perspective highlights the commonly used mouse strains and the most probable associated complexities that have not been considered previously, resulting in possible limitations in the currently utilized transgenic technology. This work also warrants the use of already established mouse lines in further research.

Lipoprotein Lipase and Its Regulators: An Unfolding Story

Lipoprotein lipase (LPL) is one of the most important factors in systemic lipid partitioning and metabolism. It mediates intravascular hydrolysis of triglycerides packed in lipoproteins such as chylomicrons and very-low-density lipoprotein (VLDL). Since its initial discovery in the 1940s, its biology and pathophysiological significance have been well characterized. Nonetheless, several studies in the past decade, with recent delineation of LPL crystal structure and the discovery of several new regulators such as angiopoietin-like proteins (ANGPTLs), glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1), lipase maturation factor 1 (LMF1) and Sel-1 suppressor of Lin-12-like 1 (SEL1L), have completely transformed our understanding of LPL biology.

Human apolipoprotein A-II reduces atherosclerosis in knock-in rabbits

BACKGROUND AND AIMS

Apolipoprotein A-II (apoAII) is the second major apolipoprotein of the high-density lipoprotein (HDL) particle, after apoAI. Unlike apoAI, the biological and physiological functions of apoAII are unclear. We aimed to gain insight into the specific roles of apoAII in lipoprotein metabolism and atherosclerosis using a novel rabbit model.

METHODS

Wild-type (WT) rabbits are naturally deficient in apoAII, thus their HDL contains only apoAI. Using TALEN technology, we replaced the endogenous apoAI in rabbits through knock-in (KI) of human apoAII. The newly generated apoAII KI rabbits were used to study the specific function of apoAII, independent of apoAI.

RESULTS

ApoAII KI rabbits expressed exclusively apoAII without apoAI, as confirmed by RT-PCR and Western blotting. On a standard diet, the KI rabbits exhibited lower plasma triglycerides (TG, 52%, p < 0.01) due to accelerated clearance of TG-rich particles and higher lipoprotein lipase activity than the WT littermates. ApoAII KI rabbits also had higher plasma HDL-C (28%, p < 0.05) and their HDL was rich in apoE, apoAIV, and apoAV. When fed a cholesterol-rich diet for 16 weeks, apoAII KI rabbits were resistant to diet-induced hypertriglyceridemia and developed significantly less aortic atherosclerosis compared to WT rabbits. HDL isolated from rabbits with apoAII KI had similar cholesterol efflux capacity and anti-inflammatory effects as HDL isolated from the WT rabbits.

CONCLUSIONS

ApoAII KI rabbits developed less atherosclerosis than WT rabbits, possibly through increased plasma HDL-C, reduced TG and atherogenic lipoproteins. These results suggest that apoAII may serve as a potential target for the treatment of atherosclerosis.

In-silico therapeutic investigations of arjunic acid and arjungenin as an FXR agonist and validation in 3T3-L1 adipocytes

The present study was to illustrate the agonistic property of arjungenin and arjunic acid towards farnesoid X receptor protein (FXR).The pharmacokinetic properties like molecular interactions, absorption, distribution, metabolism, elimination and toxicity (ADMET) of the ligands were checked through in-silico studies. Protein-ligand docking was carried out using autodock software. Molecular docking analysis confirmed strong binding energy and interaction of arjungenin and arjunic acid with the target protein and the ADMET profiles identified for both compounds were promising.Further in vitro studies were performed in 3T3-L1 adipocyte to verify the agonistic property of arjungenin and arjunic acid. Oil red O staining was done to check differentiation induction. Adiponectin, leptin, triglycerides and total cholesterol levels were quantified. The mRNA expression of FXR, Cyp7a1, PPAR-γ and SREBP-1c were quantified using fluorescent real-time PCR. Cytotoxicity assay was confirmed that up to 150 μM concentration there is no significant cell death on treatment with arjunic acid and arjungenin. Treatment with arjungenin and arjunic acid confirms increased differentiation of the cells with significant (P < 0.05) increase in adiponectin (118.07% and 132.92%) and leptin (133.52% and 149.74%) protein levels compared to the negative control group. After treatment with arjungenin and arjunic acid in 3T3-L1 preadipocytes the mRNA expression of FXR, PPAR-γ and SREBP-1c were significantly (P < 0.01) increased and cyp7a1 was significantly (P < 0.01) decreased when compared with the negative control group. Overall, our results suggest that arjungenin and arjunic acid acts as an FXR agonist and may be useful for rational therapeutic strategies as a novel drug to treat cholesterol mediated metabolic syndrome and insulin resistance.

Magnolol-mediated regulation of plasma triglyceride through affecting lipoprotein lipase activity in apolipoprotein A5 knock-in mice

Hyperlipidemia is a risk factor of arteriosclerosis, stroke, and other coronary heart disease, which has been shown to correlate with single nucleotide polymorphisms of genes essential for lipid metabolism, such as lipoprotein lipase (LPL) and apolipoprotein A5 (APOA5). In this study, the effect of magnolol, the main active component extracted from Magnolia officinalis, on LPL activity was investigated. A dose-dependent up-regulation of LPL activity, possibly through increasing LPL mRNA transcription, was observed in mouse 3T3-L1 pre-adipocytes cultured in the presence of magnolol for 6 days. Subsequently, a transgenic knock-in mice carrying APOA5 c.553G>T variant was established and then fed with corn oil with or without magnolol for four days. The baseline plasma triglyceride levels in transgenic knock-in mice were higher than those in wild-type mice, with the highest increase occurred in homozygous transgenic mice (106 mg/dL vs 51 mg/dL, p<0.01). After the induction of hyperglyceridemia along with the administration of magnolol, the plasma triglyceride level in heterozygous transgenic mice was significantly reduced by half. In summary, magnolol could effectively lower the plasma triglyceride levels in APOA5 c.553G>T variant carrier mice and facilitate the triglyceride metabolism in postprandial hypertriglyceridemia.

Apolipoprotein A5 3'-UTR variants and cardiometabolic traits in Koreans: results from the Korean genome and epidemiology study and the Korea National Health and Nutrition Examination Survey

BACKGROUND/OBJECTIVES

This study aimed to test the association between APOA5 3'-UTR variants (rs662799) and cardiometabolic traits in Koreans.

SUBJECTS/METHODS

For this study, epidemiological data, Apolipoprotein A5 (APOA5) genotype information, and lymphoblastoid cell line (LCL) biospecimens from a subset of the Ansung-Ansan cohort within the Korean Genome and Epidemiology study (KoGES-ASAS; n = 7,704) as well as epidemiological data along with genomic DNA biospecimens of participants from a subset of the Korea National Health and Nutrition Examination Survey (KNHANES 2011-12; n = 2,235) were obtained. APOA5 mRNA expression was also measured.

RESULTS

APOA5 rs662799 genotype distributions in both the KoGES-ASAS and KNHANES groups were 50.6% for TT, 41.3% for TC, and 8.1% for CC, which are similar to those in previous reports. In both groups, minor C allele carriers, particularly subjects with CC homozygosity, had lower high-density lipoprotein (HDL) cholesterol and higher triglyceride levels than TT homozygotes. Linear regression analysis showed that the minor C allele significantly contributed to reduction of circulating HDL cholesterol levels [β = −2.048, P < 0.001; β = −2.199, P < 0.001] as well as elevation of circulating triglyceride levels [β = 0.053, P < 0.001; β = 0.066, P < 0.001] in both the KoGES-ASAS and KNHANES groups. In addition, higher expression levels of APOA5 in LCLs of 64 healthy individuals were negatively associated with body mass index (r = −0.277, P = 0.027) and circulating triglyceride level (r = −0.340, P = 0.006) but not significantly correlated with circulating HDL cholesterol level. On the other hand, we observed no significant difference in the mRNA level of APOA5 according to APOA5 rs662799 polymorphisms.

CONCLUSIONS

The C allele of APOA5 rs662799 was found to be significantly associated with cardiometabolic traits in a large Korean population from the KoGES-ASAS and KNHANES. The effect of this genotype may be associated with post-transcriptional regulation, which deserves further experimental confirmation.

Glucose added to a fat load suppresses the postprandial triglyceridemia response in carriers of the -1131C and 56G variants of the APOA5 gene

Apolipoprotein A-V plays an important role in the determination of plasma triglyceride (TG) concentration. We aimed to determine whether polymorphisms -1131T>C (rs662799) and 56C>G (rs3135506) of the APOA5 gene have an impact on the course of postprandial lipemia induced by a fat load and a fat load with added glucose. Thirty healthy male volunteers, seven heterozygous for the -1131C variant and three for the 56G variant (HT) carriers, and 20 wild-type (WT) carriers underwent two 8-hour tests of postprandial lipemia - one after an experimental breakfast consisting of 75 g of fat and second after a breakfast consisting of 75 g of fat and 25 g of glucose. HT carriers had a higher postprandial response after fat load than WT carriers (AUC TG: 14.01+/-4.27 vs. 9.84+/-3.32 mmol*h/l, respectively, p=0.016). Glucose added to the test meal suppressed such a difference. Heterozygous carriers of the variants of APOA5 (-1131C and 56G) display more pronounced postprandial lipemia after pure fat load than WT carriers. This statistically significant difference disappears when glucose is added to a fat load, suggesting that meal composition modulates the effect of these polymorphisms on the magnitude of postprandial lipemia.

Hypertriglyceridemic acute pancreatitis in emergency department: Typical clinical features and genetic variants

OBJECTIVE

To investigate the clinical characteristics of patients with hypertriglyceridemic acute pancreatitis (HTGAP), and the molecular foundation contributing to hypertriglyceridemia in such patients.

METHODS

Clinical data from 329 patients with acute pancreatitis (AP) were analyzed. The patients were divided into the HTGAP group, with fasting serum triglyceride (TG) levels ≥500 mg/dL (5.65 mmol/L), and the non-HTGAP (NHTGAP) group. Targeted next-generation sequencing was applied to 11 HTGAP patients to identify the genetic mutations associated with hypertriglyceridemia, including apolipoprotein A-V (APOA5), APOC2, APOC3 and APOE, BLK, LPL, GPIHBP1 and LMF1.

RESULTS

Patients in the HTGAP group, compared with those in the NHTGAP group, had a higher mortality rate (7.5% vs 0.7%, P = 0.001), more commonly seen severe AP (17.5% vs 5.2%, P = 0.004) as well as a higher recurrence rate (32.4% vs 19.9%, P = 0.070). DNA sequencing showed that two patients carried the same compound of p.G185C and p.V153M heterozygous mutations located in the APOA5 gene. Two patients carried a homozygous variation of p.C14F, in the GPIHBP1 gene. One patient had a homozygous variation of p.R176C in the APOE gene. And a rare heterozygous LMF1 gene mutation of p.P562R was detected in two patients.

CONCLUSIONS

HTGAP was significantly severe than NHTGAP, with a high recurrence rate. Genetic information may be useful in the clinical setting for the investigation of the pathogenesis of HTGAP and its interventions.

Association analysis of APOA5 rs662799 and rs3135506 polymorphisms with obesity in Moroccan patients

The aim of the present study is to explore the association between the APOA5 polymorphisms and haplotypes with obesity in Moroccan patients. The study was performed in 459 subjects, Obese (n=164) and non-obese (n=295). All subjects were genotyped for the APOA5 -1131T>C (rs662799) and c.56C>G (rs3135506) polymorphisms. The contribution of APOA5 polymorphisms and haplotypes in the increased risk of obesity were explored using logistic regression analyses. The -1131T>C and c.56C>G polymorphisms were significantly associated with obesity. Both polymorphisms were strongly associated with increased BMI. Analysis of constructed haplotypes showed a significant association between CG haplotype and susceptibility to obesity (OR [95%CI]=3.09 [1.93-4.97]; P<0.001). These results support a potential role for APOA5 common variants and related haplotypes as risk factors for obesity.

Transcriptome Analysis Reveals Regulation of Gene Expression for Lipid Catabolism in Young Broilers by Butyrate Glycerides

BACKGROUND & AIMS

Butyrate has been shown to potently regulate energy expenditure and lipid metabolism in animals, yet the underlying mechanisms remain to be fully understood. The aim of this study was to investigate the molecular mechanisms of butyrate (in the form of butyrate glycerides, BG)-induced lipid metabolism at the level of gene expression in the jejunum and liver of broilers.

METHODOLOGY/PRINCIPAL FINDINGS

Two animal experiments were included in this study. In Experiment 1, two hundred and forty male broiler chickens were equally allocated into two groups: 1) basal diet (BD), 2) BG diets (BD + BG). Growth performance was compared between treatments for the 41-day trial. In Experiment 2, forty male broiler chickens were equally allocated into two groups. The general experimental design, group and management were the same as described in Experiment 1 except for reduced bird numbers and 21-day duration of the trial. Growth performance, abdominal fat deposition, serum lipid profiles as well as serum and tissue concentrations of key enzymes involved in lipid metabolism were compared between treatments. RNA-seq was employed to identify both differentially expressed genes (DEGs) and treatment specifically expressed genes (TSEGs). Functional clustering of DEGs and TSEGs and signaling pathways associated with lipid metabolism were identified using Ingenuity Pathways Analysis (IPA) and DAVID Bioinformatics Resources 6.7 (DAVID-BR). Quantitative PCR (qPCR) assays were subsequently conducted to further examine the expression of genes in the peroxisome proliferator-activated receptors (PPAR) signaling pathway identified by DAVID-BR. Dietary BG intervention significantly reduced abdominal fat ratio (abdominal fat weight/final body weight) in broilers. The decreased fat deposition in BG-fed chickens was in accordance with serum lipid profiles as well as the level of lipid metabolism-related enzymes in the serum, abdominal adipose, jejunum and liver. RNA-seq analysis indicated that dietary BG intervention induced 79 and 205 characterized DEGs in the jejunum and liver, respectively. In addition, 255 and 165 TSEGs were detected in the liver and jejunum of BG-fed group, while 162 and 211 TSEGs genes were observed in the liver and jejunum of BD-fed birds, respectively. Bioinformatic analysis with both IPA and DAVID-BR further revealed a significant enrichment of DEGs and TSEGs in the biological processes for reducing the synthesis, storage, transportation and secretion of lipids in the jejunum, while those in the liver were for enhancing the oxidation of ingested lipids and fatty acids. In particular, transcriptional regulators of THRSP and EGR-1 as well as several DEGs involved in the PPAR-α signaling pathway were significantly induced by dietary BG intervention for lipid catabolism.

CONCLUSIONS

Our results demonstrate that BG reduces body fat deposition via regulation of gene expression, which is involved in the biological events relating to the reduction of synthesis, storage, transportation and secretion, and improvement of oxidation of lipids and fatty acids.

Increased apolipoprotein A5 expression in human and rat non-alcoholic fatty livers

Apolipoprotein A5 (apoA5) is a potent regulator of triglyceride (TG) metabolism and therefore may contribute to the pathogenesis of non-alcoholic fatty liver disease (NAFLD), a disease characterised by excessive TG-rich lipid droplets in hepatocytes. To test this hypothesis, we examined the mRNA expression of apoA5 in paediatric NAFLD livers in comparison to healthy controls. According to microarray and quantitative real-time PCR, human NAFLD livers exhibited elevated apoA5 expression compared to healthy controls. The apoA5 expression levels were positively correlated with hepatic TG storage and a marker for lipid droplets (perilipin), but were not correlated with plasma TG levels. These observations were confirmed with a NAFLD rat model. Interestingly, apoA5 expression was not altered in cultured fat-laden HepG2 cells, demonstrating that fat storage does not induce apoA5 in NAFLD livers. Therefore, the correlation between apoA5 and intracellular fat storage is likely explained by the potent effect of apoA5 in promoting intracellular fat storage. Our NAFLD patients and rats had elevated insulin resistance, which may have a role in elevating apoA5 expression in NAFLD livers. Our data support the hypothesis that apoA5 promotes hepatic TG storage and therefore contributes to the pathogenesis of NAFLD, and may represent a potential target for therapeutic intervention.

Association of G894T eNOS, 4G/5G PAI and T1131C APOA5 polymorphisms with susceptibility to myocardial infarction in Morocco

Background

Myocardial infarction (MI) is a common multifactorial disease. Numerous studies have found that genetic plays an essential role in MI occurrence. The main objective of our case–control study is to explore the association of G894T eNOS (rs1799983), 4G/5G PAI (rs1799889) and T1131C APOA5 (rs662799) polymorphisms with MI susceptibility in the Moroccan population.

Methods and results

118 MI patients were recruited vs 184 healthy controls. DNA samples were genotyped by PCR-RFLP method using MboI, BslI and MseI restriction enzymes respectively for the G894T eNOS, 4G/5G PAI and T1131C APOA5 polymorphisms. Our results show that the G894T eNOS was significantly associated with increased risk of MI under the three genetic transmission models (dominant: OR = 1.64, 95% CI = 1.05–2.58, P = 0.003; recessive: OR = 2.15, 95% CI = 0.74–6.16, P = 0.03; additive: OR = 1.54, 95% CI = 1.06–2.23, P = 0.001). The T1131C APOA5 polymorphism was associated to MI risk in recessive and additive models (OR = 1.53, 95% CI = 0.72–3.2, P = 0.04 and OR = 1.78, 95% CI = 1.26–2.51, P = 0.03 respectively). For the 4G/5G PAI variant, even the cases and controls groups were not in Hardy–Weinberg Equilibrium (HWE), the dominant and additive models show a statistically significant association with MI risk (OR = 7.96, 95%CI = 3.83–16.36, P = 0.01 and OR = 1.96, 95% CI = 1.4–2.72, P = 0.03 respectively).

Conclusion

Our results suggest that G894T eNOS and T1131C APOA5 polymorphisms may be considered as genetic markers of MI among the Moroccan population. Further studies including larger sample sizes and exploring more genetic associations are needed to confirm our results and to better understand the susceptibility to MI.

Apolipoprotein A-V is present in bile and its secretion increases with lipid absorption in Sprague-Dawley rats

Apolipoprotein (apo) A-V is a protein synthesized only in the liver that dramatically modulates plasma triglyceride levels. Recent studies suggest a novel role for hepatic apoA-V in regulating the absorption of dietary triglycerides, but its mode of action on the gut remains unknown. The aim of this study was to test for apoA-V in bile and to determine whether its secretion is regulated by dietary lipids. After an overnight recovery, adult male Sprague-Dawley bile fistula rats indeed secreted apoA-V into bile at a constant rate under fasting conditions. An intraduodenal bolus of intralipid (n = 12) increased the biliary secretion of apoA-V but not of other apolipoproteins, such as A-I, A-IV, B, and E. The lipid-induced increase of biliary apoA-V was abolished under conditions of poor lymphatic lipid transport, suggesting that the stimulation is regulated by the magnitude of lipids associated with chylomicrons transported into lymph. We also studied the secretion of apoA-V into bile immediately following bile duct cannulation. Biliary apoA-V increased over time (∼6-fold increase at hour 16, n = 8) but the secretions of other apolipoproteins remained constant. Replenishing luminal phosphatidylcholine and taurocholate (n = 9) only enhanced apoA-V secretion in bile, suggesting that the increase was not due to depletion of phospholipids or bile salts. This is the first study to demonstrate that apoA-V is secreted into bile, introducing a potential route of delivery of hepatic apoA-V to the gut lumen. Our study also reveals the uniqueness of apoA-V secretion into bile that is regulated by mechanisms different from other apolipoproteins.

Genetics of non-conventional lipoprotein fractions

Lipoprotein subclass measures associate with cardiometabolic disease risk. Currently the information that lipoproteins convey on disease risk over that of traditional demographic and lipid measures is minimal, and so their use is clinics is limited. However, lipoprotein subclass perturbations represent some of the earliest manifestations of metabolic dysfunction, and their etiology is partially distinct from lipids, so information on the genetic etiology of lipoproteins offers promise for improved risk prediction, and unique mechanistic insights into IR and atherosclerosis. Here, I review the genetic variants validated as associating with lipoprotein measures to date, and show that the majority of identified variants have functionality that is best understood as related to lipid measures. Until we focus on the genes as they relate to lipoprotein subclass production, we are limiting our understanding of biological mechanisms underlying cardiometabolic disease.

Interaction of dietary fat intake with APOA2, APOA5 and LEPR polymorphisms and its relationship with obesity and dyslipidemia in young subjects

BACKGROUND

Diet is an important environmental factor that interacts with genes to modulate the likelihood of developing disorders in lipid metabolism and the relationship between diet and genes in the presence of other chronic diseases such as obesity. The objective of this study was to analyze the interaction of a high fat diet with the APOA2 (rs3813627 and rs5082), APOA5 (rs662799 and rs3135506) and LEPR (rs8179183 and rs1137101) polymorphisms and its relationship with obesity and dyslipidemia in young subjects.

METHODS

The study included 200 young subjects aged 18 to 25 years (100 normal-weight and 100 obese subjects). Dietary fat intake was measured using the frequency food consumption questionnaire. Genotyping of polymorphisms was performed by PCR-RFLP.

RESULTS

Individuals carrying the APOA5 56 G/G genotype with a high saturated fatty acid consumption (OR = 2.7, p = 0.006) and/or total fat (OR = 2.4, p = 0.018), associated with an increased risk of obesity. We also found that A/G + G/G genotypes of the 668 A/G polymorphism in the LEPR gene with an intake ≥ 12 g/d of saturated fatty acids, have 2.9 times higher risk of obesity (p = 0.002), 3.8 times higher risk of hypercholesterolemia (p = 0.002) and 2.4 times higher risk of hypertriglyceridemia (p = 0.02), than those with an intake <12 g/d of saturated fatty acids. Similarly, LEPR 668 A/G + G/G carriers with a high fat total intake had 3.0 times higher risk of obesity (p = 0.002) and 4.1 times higher risk of hypercholesterolemia (p = 0.001).

CONCLUSION

Our results suggest that dietary fat intake modifies the effect of APOA5 and LEPR polymorphisms on serum triglycerides, cholesterol levels and obesity in young subjects.

Mice lacking prostaglandin E receptor subtype 4 manifest disrupted lipid metabolism attributable to impaired triglyceride clearance

Upon high-fat feeding, prostaglandin E receptor subtype 4 (EP4)-knockout mice gain less body weight than their EP4(+/+) littermates. We investigated the cause of the lean phenotype. The mice showed a 68.8% reduction in weight gain with diminished fat mass that was not attributable to reduced food intake, fat malabsorption, or increased energy expenditure. Plasma triglycerides in the mice were elevated by 244.9%. The increase in plasma triglycerides was independent of changes in hepatic very low density lipoprotein (VLDL)-triglyceride production or intestinal chylomicron-triglyceride synthesis. However, VLDL-triglyceride clearance was drastically impaired in the EP4-knockout mice. The absence of EP4 in mice compromised the activation of lipoprotein lipase (LPL), the key enzyme responsible for trafficking of plasma triglycerides into peripheral tissues. Deficiency in EP4 reduced hepatic mRNA expression of the transcriptional factor cAMP response element binding protein H (by 36.8%) and LPL activators, including apolipoprotein (Apo)a5 (by 40.2%) and Apoc2 (by 61.3%). In summary, the lean phenotype of EP4-deficient mice resulted from reduction in adipose tissue and accretion of other peripheral organs caused by impaired triglyceride clearance. The findings identify a new metabolic dimension in the physiologic role played by endogenous EP4.

Genetic Variants Associated with Gestational Hypertriglyceridemia and Pancreatitis

Severe hypertriglyceridemia is a well-known cause of pancreatitis. Usually, there is a moderate increase in plasma triglyceride level during pregnancy. Additionally, certain pre-existing genetic traits may render a pregnant woman susceptible to development of severe hypertriglyceridemia and pancreatitis, especially in the third trimester. To elucidate the underlying mechanism of gestational hypertriglyceridemic pancreatitis, we undertook DNA mutation analysis of the lipoprotein lipase (LPL), apolipoprotein C2 (APOC2), apolipoprotein A5 (APOA5), lipase maturation factor 1 (LMF1), and glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1) genes in five unrelated pregnant Chinese women with severe hypertriglyceridemia and pancreatitis. DNA sequencing showed that three out of five patients had the same homozygous variation, p.G185C, in APOA5 gene. One patient had a compound heterozygous mutation, p.A98T and p.L279V, in LPL gene. Another patient had a compound heterozygous mutation, p.A98T & p.C14F in LPL and GPIHBP1 gene, respectively. No mutations were seen in APOC2 or LMF1 genes. All patients were diagnosed with partial LPL deficiency in non-pregnant state. As revealed in our study, genetic variants appear to play an important role in the development of severe gestational hypertriglyceridemia, and, p.G185C mutation in APOA5 gene appears to be the most common variant implicated in the Chinese population. Antenatal screening for mutations in susceptible women, combined with subsequent interventions may be invaluable in the prevention of potentially life threatening gestational hypertriglyceridemia-induced pancreatitis.

Apolipoprotein A-V deficiency enhances chylomicron production in lymph fistula mice

Apolipoprotein A-V (apoA-V), a liver-synthesized apolipoprotein discovered in 2001, strongly modulates fasting plasma triglycerides (TG). Little is reported on the effect of apoA-V on postprandial plasma TG, an independent predictor for atherosclerosis. Overexpressing apoA-V in mice suppresses postprandial TG, but mechanisms focus on increased lipolysis or clearance of remnant particles. Unknown is whether apoA-V suppresses the absorption of dietary lipids by the gut. This study examines how apoA-V deficiency affects the steady-state absorption and lymphatic transport of dietary lipids in chow-fed mice. Using apoA-V knockout (KO, n = 8) and wild-type (WT, n = 8) lymph fistula mice, we analyzed the uptake and lymphatic transport of lipids during a continuous infusion of an emulsion containing [(3)H]triolein and [(14)C]cholesterol. ApoA-V KO mice showed a twofold increase in (3)H (P < 0.001) and a threefold increase in (14)C (P < 0.001) transport into the lymph compared with WT. The increased lymphatic transport was accompanied by a twofold reduction (P < 0.05) in mucosal (3)H, suggesting that apoA-V KO mice more rapidly secreted [(3)H]TG out of the mucosa into the lymph. ApoA-V KO mice also produced chylomicrons more rapidly than WT (P < 0.05), as measured by the transit time of [(14)C]oleic acid from the intestinal lumen to lymph. Interestingly, apoA-V KO mice produced a steadily increasing number of chylomicron particles over time, as measured by lymphatic apoB output. The data suggest that apoA-V suppresses the production of chylomicrons, playing a previously unknown role in lipid metabolism that may contribute to the postprandial hypertriglyceridemia associated with apoA-V deficiency.

Molecular mechanism of PPARα action and its impact on lipid metabolism, inflammation and fibrosis in non-alcoholic fatty liver disease

Peroxisome proliferator-activated receptor α (PPARα) is a ligand-activated transcription factor belonging, together with PPARγ and PPARβ/δ, to the NR1C nuclear receptor subfamily. Many PPARα target genes are involved in fatty acid metabolism in tissues with high oxidative rates such as muscle, heart and liver. PPARα activation, in combination with PPARβ/δ agonism, improves steatosis, inflammation and fibrosis in pre-clinical models of non-alcoholic fatty liver disease, identifying a new potential therapeutic area. In this review, we discuss the transcriptional activation and repression mechanisms by PPARα, the spectrum of target genes and chromatin-binding maps from recent genome-wide studies, paying particular attention to PPARα-regulation of hepatic fatty acid and plasma lipoprotein metabolism during nutritional transition, and of the inflammatory response. The role of PPARα, together with other PPARs, in non-alcoholic steatohepatitis will be discussed in light of available pre-clinical and clinical data.

Bile acid nuclear receptor FXR and digestive system diseases

Bile acids (BAs) are not only digestive surfactants but also important cell signaling molecules, which stimulate several signaling pathways to regulate some important biological processes. The bile-acid-activated nuclear receptor, farnesoid X receptor (FXR), plays a pivotal role in regulating bile acid, lipid and glucose homeostasis as well as in regulating the inflammatory responses, barrier function and prevention of bacterial translocation in the intestinal tract. As expected, FXR is involved in the pathophysiology of a wide range of diseases of gastrointestinal tract, including inflammatory bowel disease, colorectal cancer and type 2 diabetes. In this review, we discuss current knowledge of the roles of FXR in physiology of the digestive system and the related diseases. Better understanding of the roles of FXR in digestive system will accelerate the development of FXR ligands/modulators for the treatment of digestive system diseases.

ApoA5 knockdown improves whole-body insulin sensitivity in high-fat-fed mice by reducing ectopic lipid content

ApoA5 has a critical role in the regulation of plasma TG concentrations. In order to determine whether ApoA5 also impacts ectopic lipid deposition in liver and skeletal muscle, as well as tissue insulin sensitivity, we treated mice with an antisense oligonucleotide (ASO) to decrease hepatic expression of ApoA5. ASO treatment reduced ApoA5 protein expression in liver by 60–70%. ApoA5 ASO-treated mice displayed approximately 3-fold higher plasma TG concentrations, which were associated with decreased plasma TG clearance. Furthermore, ApoA5 ASO-treated mice fed a high-fat diet (HFD) exhibited reduced liver and skeletal muscle TG uptake and reduced liver and muscle TG and diacylglycerol (DAG) content. HFD-fed ApoA5 ASO-treated mice were protected from HFD-induced insulin resistance, as assessed by hyperinsulinemic-euglycemic clamps. This protection could be attributed to increases in both hepatic and peripheral insulin responsiveness associated with decreased DAG activation of protein kinase C (PKC)-ε and PKCθ in liver and muscle, respectively, and increased insulin-stimulated AKT2 pho­sphory­lation in these tissues. In summary, these studies demonstrate a novel role for ApoA5 as a modulator of susceptibility to diet-induced liver and muscle insulin resistance through regulation of ectopic lipid accumulation in liver and skeletal muscle.

Intrinsic and extrinsic regulation of cardiac lipoprotein lipase following diabetes

Cardiac lipoprotein lipase (LPL) is a pivotal enzyme controlling heart metabolism by providing the majority of fatty acids required by this organ. From activation in cardiomyocytes to secretion to the vascular lumen, cardiac LPL is regulated by multiple pathways, which are altered during diabetes. Hence, dimerization/activation of LPL is modified following diabetes, a process controlled by lipase maturation factor 1. The role of AMP-activated protein kinase, protein kinase D, and heparan sulfate proteoglycans, intrinsic factors that regulate the intracellular transport of LPL is also shifted, and is discussed. More recent studies have identified several exogenous factors released from endothelial cells (EC) and adipose tissue that are required for proper functioning of LPL. In response to hyperglycemia, both active and latent heparanase are released from EC to facilitate LPL secretion. Diabetes also increased the expression of glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 (GPIHBP1) in EC, which mediates the transport of LPL across EC. Angiopoietin-like protein 4 secreted from the adipose tissue has the potential to reduce coronary LPL activity. Knowledge of these intrinsic and extrinsic factors could be used develop therapeutic targets to normalize LPL function, and maintain cardiac energy homeostasis after diabetes.

GW4064, a farnesoid X receptor agonist, upregulates adipokine expression in preadipocytes and HepG2 cells

AIM: To investigate the effect of GW4064 on the expression of adipokines and their receptors during differentiation of 3T3-L1 preadipocytes and in HepG2 cells.

METHODS: The mRNA expression of farnesoid X receptor (FXR), peroxisome proliferator-activated receptor-gamma 2 (PPAR-γ2), adiponectin, leptin, resistin, adiponectin receptor 1 (AdipoR1), adiponectin receptor 2 (AdipoR2), and the long isoform of leptin receptor (OB-Rb) and protein levels of adiponectin, leptin, and resistin were determined using fluorescent real-time PCR and enzyme linked immunosorbent assay, respectively, on days 0, 2, 4, 6, and 8 during the differentiation of 3T3-L1 preadipocytes exposed to GW4064. Moreover, mRNA expression of AdipoR2 and OB-Rb was also examined using fluorescent real-time PCR at 0, 12, 24, and 48 h in HepG2 cells treated with GW4064.

RESULTS: The mRNA expression of FXR, PPAR-γ2, adiponectin, leptin, resistin, AdipoR1, AdipoR2, and OB-Rb and protein levels of adiponectin, leptin, and resistin increased along with differentiation of 3T3-L1 preadipocytes (P < 0.05 for all). The mRNA expression of FXR, PPAR-γ2, adiponectin, leptin, and AdipoR2 in 3T3-L1 preadipocytes, and AdipoR2 and OB-Rb in HepG2 cells was significantly increased after treatment with GW4064, when compared with the control group (P < 0.05 for all). A similar trend was observed for protein levels of adipokines (including adiponectin, leptin and resistin). However, the expression of resistin, AdipoR1, and OB-Rb in 3T3-L1 cells did not change after treatment with GW4064.

CONCLUSION: The FXR agonist through regulating, at least partially, the expression of adipokines and their receptors could offer an innovative way for counteracting the progress of metabolic diseases such as nonalcoholic fatty liver disease.

A novel apolipoprotein C-II mimetic peptide that activates lipoprotein lipase and decreases serum triglycerides in apolipoprotein E-knockout mice

Apolipoprotein A-I (apoA-I) mimetic peptides are currently being developed as possible new agents for the treatment of cardiovascular disease based on their ability to promote cholesterol efflux and their other beneficial antiatherogenic properties. Many of these peptides, however, have been reported to cause transient hypertriglyceridemia due to inhibition of lipolysis by lipoprotein lipase (LPL). We describe a novel bihelical amphipathic peptide (C-II-a) that contains an amphipathic helix (18A) for binding to lipoproteins and stimulating cholesterol efflux as well as a motif based on the last helix of apolipoprotein C-II (apoC-II) that activates lipolysis by LPL. The C-II-a peptide promoted cholesterol efflux from ATP-binding cassette transporter ABCA1-transfected BHK cells similar to apoA-I mimetic peptides. Furthermore, it was shown in vitro to be comparable to the full-length apoC-II protein in activating lipolysis by LPL. When added to serum from a patient with apoC-II deficiency, it restored normal levels of LPL-induced lipolysis and also enhanced lipolysis in serum from patients with type IV and V hypertriglyceridemia. Intravenous injection of C-II-a (30 mg/kg) in apolipoprotein E-knockout mice resulted in a significant reduction of plasma cholesterol and triglycerides of 38 ± 6% and 85 ± 7%, respectively, at 4 hours. When coinjected with the 5A peptide (60 mg/kg), the C-II-a (30 mg/kg) peptide was found to completely block the hypertriglyceridemic effect of the 5A peptide in C57Bl/6 mice. In summary, C-II-a is a novel peptide based on apoC-II, which promotes cholesterol efflux and lipolysis and may therefore be useful for the treatment of apoC-II deficiency and other forms of hypertriglyceridemia.

Lipoprotein lipase: from gene to atherosclerosis

Lipoprotein lipase (LPL) is a key enzyme in lipid metabolism and responsible for catalyzing lipolysis of triglycerides in lipoproteins. LPL is produced mainly in adipose tissue, skeletal and heart muscle, as well as in macrophage and other tissues. After synthesized, it is secreted and translocated to the vascular lumen. LPL expression and activity are regulated by a variety of factors, such as transcription factors, interactive proteins and nutritional state through complicated mechanisms. LPL with different distributions may exert distinct functions and have diverse roles in human health and disease with close association with atherosclerosis. It may pose a pro-atherogenic or an anti-atherogenic effect depending on its locations. In this review, we will discuss its gene, protein, synthesis, transportation and biological functions, and then focus on its regulation and relationship with atherosclerosis and potential underlying mechanisms. The goal of this review is to provide basic information and novel insight for further studies and therapeutic targets.

Increased risk of obesity related to total energy intake with the APOA5-1131T > C polymorphism in Korean premenopausal women

We hypothesized that triglyceride-raising apolipoprotein A5 (APOA5)-1131T > C may contribute to the increased risk of obesity associated with dietary intake in Korean premenopausal women whose minor allele frequency is higher than that in Western people. Genetically unrelated Korean premenopausal women (approximately 20-59 years, n = 1128) were genotyped for APOA5-1131T > C. Anthropometric, metabolic parameters and dietary intakes were analyzed. Odds ratios (ORs) for obesity risk (body mass index, ≥25.0 kg/m(2)) were calculated. Genotype distribution of APOA5-1131T > C of study subjects were like TT: 49.9%, TC: 40.8%, and CC: 9.3%. We found a significant interaction between APOA5-1131T > C and total energy intake (TEI) for obesity after adjusted for age, cigarette smoking, and alcohol consumption (P < .001). The risk of obesity in CC homozygotes compared with T carriers (TT + TC) was significantly increased, when the subjects consume higher TEI (≥2001 kcal/d (8372 kJ/d), median value of the population) (OR, 2.495; 95% confidence intervals, 1.325-4.696; P = .005), particularly, when they maintain negative balance between total energy expenditure and TEI (total energy expenditure/TEI, <1) (OR, 2.917; 95% confidence intervals, 1.451-5.864; P = .003). The contributions of APOA5-1131CC homozygotes to obesity risk in those who consume higher TEI were all significantly high regardless of percentage of energy intake from dietary macronutrients. Whereas, no significant association was observed in those who consume lower TEI (<2001 kcal/d). In addition, serum levels of triglyceride, high-density lipoprotein-cholesterol, and apolipoprotein A5 were associated with APOA5-1131T > C and TEI. These findings suggest that APOA5-1131CC homozygotes may influence the susceptibility of the individual to obesity, particularly, when they consume higher TEI, but the genetic effect may be attenuated, when people maintain low or adequate energy intake.

The association between APOA5 haplotypes and plasma lipids is not modified by energy or fat intake: the Czech HAPIEE study

BACKGROUND AND AIMS

Several smaller studies reported interactions between dietary factors and apolipoprotein A5 (APOA5) gene polymorphisms in determination of plasma lipids. We tested interactions between APOA5 haplotypes and dietary intake in determination of plasma triglycerides (TG) and other lipids.

METHODS AND RESULTS

Participants (5487 males and females aged 45-69) were classified according to the number (0, 1, 2+) of minor APOA5 alleles (using T-1131 > C; rs662799 and Ser19 > Trp; rs3135506 polymorphisms) and into three groups of low (bottom 25%), medium (26th-75th percentile) and high (top 25%) of intake of total energy and total, saturated and polyunsaturated fats, assessed by food frequency questionnaire. The age-sex adjusted geometric means of plasma TG increased with the number of minor alleles, from 1.57 (standard error 0.01), to 1.79 (0.02) to 2.29 (0.10) mmol/L (p < 0.00001) but TG did not differ between groups with low, medium and high total energy intake (p = 0.251). TG concentrations were highest in subjects with the combination of 2+ minor alleles and the highest energy intake (mean 2.59 [0.19], compared with 1.62 [0.03] in subjects with lowest energy intake and no minor allele) but the interaction between energy intake and APOA5 haplotypes was not statistically significant (p = 0.186). Analogous analyses with total, saturated and polyunsaturated fat intake yielded similar nonsignificant results. Effects of APOA5 and dietary intakes on total and HDL cholesterol were weaker and no interactions were significant.

CONCLUSION

In this Slavic Caucasian population sample, we did not detect the hypothesized interaction between common SNPs within the APOA5 gene and diet in determination of blood lipids.

An APOA5 3' UTR variant associated with plasma triglycerides triggers APOA5 downregulation by creating a functional miR-485-5p binding site

APOA5 c.*158C>T (rs2266788), located in the 3' UTR, belongs to APOA5 haplotype 2 (APOA5*2), which is strongly associated with plasma triglyceride levels and modulates the occurrence of both moderate and severe hypertriglyceridemia. Individuals with APOA5*2 display reduced APOA5 expression at the posttranscriptional level. However, the functionality of this haplotype remains unclear. We hypothesized that the hypertriglyceridemic effects of APOA5*2 could involve miRNA regulation in the APOA5 3' UTR. Bioinformatic studies have identified the creation of a potential miRNA binding site for liver-expressed miR-485-5p (MIRN485-5p) in the mutant APOA5 3' UTR with the c.*158C allele. In human embryonic kidney 293T (HEK293T) cells cotransfected with an APOA5 3' UTR luciferase reporter vector and a miR485-5p precursor, c.*158C allele expression was significantly decreased. Moreover, in HuH-7 cells endogenously expressing miR-485-5p, we observed that luciferase activity was significantly lower in the presence of the c.*158C allele than in the presence of the c.*158T allele, which was completely reversed by a miR-485-5p inhibitor. We demonstrated that the rare c.*158C APOA5 allele creates a functional target site for liver-expressed miR-485-5p. Therefore, we propose that the well-documented hypertriglyceridemic effect of APOA5*2 involves an APOA5 posttranscriptional downregulation mediated by miR-485-5p.

APOA5 genotype modulates 2-y changes in lipid profile in response to weight-loss diet intervention: the Pounds Lost Trial

BACKGROUND

The apolipoprotein A5 gene (APOA5) is a major gene that regulates lipid metabolism and is modulated by dietary factors. A novel variant rs964184 in APOA5 was identified to be associated with lipids in genome-wide association studies.

OBJECTIVE

We examined whether this variant modified changes in lipid concentrations in response to a 2-y weight-loss diet intervention in a randomized trial.

DESIGN

The current analyses were secondary analyses of a data set from the Pounds Lost Trial. We genotyped APOA5 rs964184 in 734 overweight or obese adults who were randomly assigned to one of 4 diets that differed in percentages of energy derived from fat, protein, and carbohydrate for 2 y. We evaluated changes in fasting serum concentrations of total cholesterol (TC), LDL cholesterol, HDL cholesterol, and triglyceride from baseline to 2 y of follow-up.

RESULTS

After a 2-y dietary intervention, we showed significant interactions between the APOA5 rs964184 polymorphism and dietary fat intake (low compared with high) in the determination of changes in TC, LDL cholesterol, and HDL cholesterol (P-interaction = 0.007, 0.017, and 0.006, respectively). In the low-fat intake group (20% of energy derived from fat), carriers of the risk allele (G allele) exhibited greater reductions in TC and LDL cholesterol than did noncarriers (P = 0.036 and 0.039, respectively), whereas in the high-fat diet group (40% of energy derived from fat), participants with the G allele had a greater increase in HDL cholesterol than did participants without this allele (P = 0.038).

CONCLUSION

Our data showed better improvement in lipid profiles from long-term low-fat diet intake in the APOA5 rs964184 risk allele.