Combined hyperlipidemia in transgenic mice overexpressing human apolipoprotein Cl

Analyzing the impact and mechanism of bisphenol A on testicular lipid metabolism in Gobiocypris rarus through integrated lipidomics and transcriptomics

Bisphenol A (BPA) is one of the most common environmental endocrine chemicals, known for its estrogenic effects that can interfere with male spermatogenesis. Lipids play crucial roles in sperm production, capacitation, and motility as important components of the sperm plasma membrane. However, limited research has explored whether BPA affects lipid metabolism in the testes of male fish and subsequently impacts spermatogenesis. In this study, we employed Gobiocypris rarus rare minnow as a research model and exposed them to environmentally relevant concentrations of BPA (15 μg/L) for 5 weeks. We assessed sperm morphology and function and analyzed changes in testicular lipid composition and transcriptomics. The results demonstrated a significant increase in the sperm head membrane damage rate, along with reduced sperm motility and fertilization ability due to BPA exposure. Lipidomics analysis revealed that BPA increased the content of 11 lipids while decreasing the content of 6 lipids in the testes, particularly within glycerophospholipids, glycerolipids, and sphingolipid subclasses. Transcriptomics results indicated significant up-regulation in pathways such as cholesterol metabolism, peroxisome proliferator-activated receptor signaling, and fat digestion and absorption, with significant alterations in key genes related to lipid metabolism, including apolipoprotein A-I, apolipoprotein C-I, and translocator protein. These findings suggest that BPA exposure can induce testicular lipid metabolism disruption in rare minnows, potentially resulting in abnormalities in rare minnow spermatogenesis.

Identifying potential therapeutic targets of mulberry leaf extract for the treatment of type 2 diabetes: a TMT-based quantitative proteomic analysis

BACKGROUND

Mulberry (Morus alba L.) leaf, as a medicinal and food homologous traditional Chinese medicine, has a clear therapeutic effect on type 2 diabetes mellitus (T2DM), yet its underlying mechanisms have not been totally clarified. The study aimed to explore the mechanism of mulberry leaf in the treatment of T2DM through tandem mass tag (TMT)-based quantitative proteomics analysis of skeletal muscle.

METHODS

The anti-diabetic activity of mulberry leaf extract (MLE) was evaluated by using streptozotocin-induced diabetic rats at a dose of 4.0 g crude drug /kg p.o. daily for 8 weeks. Fasting blood glucose, body weight, food and water intake were monitored at specific intervals, and oral glucose tolerance test and insulin tolerance test were conducted at the 7th and 8th week respectively. At the end of the experiment, levels of glycated hemoglobin A1c, insulin, free fat acid, leptin, adiponectin, total cholesterol, triglyceride, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were assessed and the pathological changes of rat skeletal muscle were observed by HE staining. TMT-based quantitative proteomic analysis of skeletal muscle and bioinformatics analysis were performed and differentially expressed proteins (DEPs) were validated by western blot. The interactions between the components of MLE and DEPs were further assessed using molecular docking.

RESULTS

After 8 weeks of MLE intervention, the clinical indications of T2DM such as body weight, food and water intake of rats were improved to a certain extent, while insulin sensitivity was increased and glycemic control was improved. Serum lipid profiles were significantly reduced, and the skeletal muscle fiber gap and atrophy were alleviated. Proteomic analysis of skeletal muscle showed that MLE treatment reversed 19 DEPs in T2DM rats, regulated cholesterol metabolism, fat digestion and absorption, vitamin digestion and absorption and ferroptosis signaling pathways. Key differential proteins Apolipoprotein A-1 (ApoA1) and ApoA4 were successfully validated by western blot and exhibited strong binding activity to the MLE's ingredients.

CONCLUSIONS

This study first provided skeletal muscle proteomic changes in T2DM rats before and after MLE treatment, which may help us understand the molecular mechanisms, and provide a foundation for developing potential therapeutic targets of anti-T2DM of MLE.

Quartet of APOCs and the Different Roles They Play in Diabetes

APOA1 and APOB are the structural proteins of high-density lipoprotein and APOB-containing lipoproteins, such as low-density lipoprotein and very low-density lipoprotein, respectively. The 4 smaller APOCs (APOC1, APOC2, APOC3, and APOC4) are exchangeable apolipoproteins; they are readily transferred among high-density lipoproteins and APOB-containing lipoproteins. The APOCs regulate plasma triglyceride and cholesterol levels by modulating substrate availability and activities of enzymes interacting with lipoproteins and by interfering with APOB-containing lipoprotein uptake through hepatic receptors. Of the 4 APOCs, APOC3 has been best studied in relation to diabetes. Elevated serum APOC3 levels predict incident cardiovascular disease and progression of kidney disease in people with type 1 diabetes. Insulin suppresses APOC3 levels, and accordingly, elevated APOC3 levels associate with insulin deficiency and insulin resistance. Mechanistic studies in a mouse model of type 1 diabetes have demonstrated that APOC3 acts in the causal pathway of diabetes-accelerated atherosclerosis. The mechanism is likely due to the ability of APOC3 to slow the clearance of triglyceride-rich lipoproteins and their remnants, thereby causing an increased accumulation of atherogenic lipoprotein remnants in lesions of atherosclerosis. Less is known about the roles of APOC1, APOC2, and APOC4 in diabetes.

Role of apolipoprotein C1 in lipoprotein metabolism, atherosclerosis and diabetes: a systematic review

Apolipoprotein C1 (apoC1) is a small size apolipoprotein whose exact role is not totally clarified but which seems to modulate significantly the metabolism of lipoproteins. ApoC1 is involved in the metabolism of triglyceride-rich lipoproteins by inhibiting the binding of very low density lipoproteins (VLDL) to VLDL-receptor (VLDL-R), to low density lipoprotein receptor (LDL-R) and to LDL receptor related protein (LRP), by reducing the activity of lipoprotein lipase (LPL) and by stimulating VLDL production, all these effects leading to increase plasma triglycerides. ApoC1 takes also part in the metabolism of high density lipoproteins (HDL) by inhibiting Cholesterol Ester Transfer Protein (CETP). The functionality of apoC1 on CETP activity is impaired in diabetes that might account, at least in part, for the increased plasma CETP activity observed in patients with diabetes. Its different effects on lipoprotein metabolism with a possible role in the modulation of inflammation makes the net impact of apoC1 on cardiometabolic risk difficult to figure out and apoC1 might be considered as pro-atherogenic or anti-atherogenic depending on the overall metabolic context. Making the link between total plasma apoC1 levels and the risk of cardio-metabolic diseases is difficult due to the high exchangeability of this small protein whose biological effects might depend essentially on its association with VLDL or HDL. The role of apoC1 in humans is not entirely elucidated and further studies are needed to determine its precise role in lipid metabolism and its possible pleiotropic effects on inflammation and vascular wall biology. In this review, we will present data on apoC1 structure and distribution among lipoproteins, on the effects of apoC1 on VLDL metabolism and HDL metabolism and we will discuss the possible links between apoC1, atherosclerosis and diabetes.

Association of lipid metabolism-related gene promoter methylation with risk of coronary artery disease

BACKGROUND

Coronary artery disease (CAD) is a complex disease that is influenced by environmental and genetic factors. Lipid levels are regarded as a major risk factor for CAD, and epigenetic mechanisms might be involved in the regulation of CAD development. This study was designed to investigate the association between the DNA methylation status of 8 lipid metabolism-related genes and the risk of CAD in the Chinese Han population.

METHODS

A total of 260 individuals were sampled in this study, including 120 CAD cases and 140 normal healthy controls. DNA methylation status was tested via targeted bisulfite sequencing.

RESULTS

The results indicated a significant association between hypomethylation of the APOC3, CETP and APOC1 gene promoters and the risk of CAD. Individuals with higher methylation levels of the APOA5 and LIPC gene promoters had increased risks for CAD. In addition, ANGPTL4 methylation level was significantly associated with CAD in males but not females. There were no significant differences in the methylation levels of the APOB and PCSK9 gene promoters between CAD patients and controls.

CONCLUSIONS

The methylation status of the APOC3, APOA5, LIPC, CETP and APOC1 gene promoters may be associated with the development of CAD.

Genetic deletion of Abcc6 disturbs cholesterol homeostasis in mice

Genetic studies link adenosine triphosphate-binding cassette transporter C6 (ABCC6) mutations to pseudoxanthoma elasticum (PXE). ABCC6 sequence variations are correlated with altered HDL cholesterol levels and an elevated risk of coronary artery diseases. However, the role of ABCC6 in cholesterol homeostasis is not widely known. Here, we report reduced serum cholesterol and phytosterol levels in Abcc6-deficient mice, indicating an impaired sterol absorption. Ratios of cholesterol precursors to cholesterol were increased, confirmed by upregulation of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase (Hmgcr) expression, suggesting activation of cholesterol biosynthesis in Abcc6-/- mice. We found that cholesterol depletion was accompanied by a substantial decrease in HDL cholesterol mediated by lowered ApoA-I and ApoA-II protein levels and not by inhibited lecithin-cholesterol transferase activity. Additionally, higher proprotein convertase subtilisin/kexin type 9 (Pcsk9) serum levels in Abcc6-/- mice and PXE patients and elevated ApoB level in knockout mice were observed, suggesting a potentially altered very low-density lipoprotein synthesis. Our results underline the role of Abcc6 in cholesterol homeostasis and indicate impaired cholesterol metabolism as an important pathomechanism involved in PXE manifestation.

Human apolipoprotein C1 transgenesis reduces atherogenesis in hypercholesterolemic rabbits

BACKGROUND AND AIMS

Apolipoprotein (apo) C1 is a 6.6 kDa protein associated with HDL and VLDL. ApoC1 alters triglyceride clearance, and it also favors cholesterol accumulation in HDL, especially by inhibiting CETP in human plasma. Apart from studies in mice, which lack CETP, the impact of apoC1 on atherosclerosis in animal models expressing CETP, like in humans, is not known. This study aimed at determining the net effect of human apoC1 on atherosclerosis in rabbits, a species with naturally high CETP activity but with endogenous apoC1 without CETP inhibitory potential.

METHODS

Rabbits expressing a human apoC1 transgene (HuApoC1Tg) were generated and displayed significant amounts of human apoC1 in plasma.

RESULTS

After cholesterol feeding, atherosclerosis lesions were significantly less extensive (-22%, p < 0.05) and HDL displayed a reduced ability to serve as CETP substrates (-25%, p < 0.05) in HuApoC1Tg rabbits than in WT littermates. It was associated with rises in plasma HDL cholesterol level and PON-1 activity, and a decrease in the plasma level of the lipid oxidation markers 12(S)-HODE and 8(S)HETE. In chow-fed animals, the level of HDL-cholesterol was also significantly higher in HuApoC1Tg than in WT animals (0.83 ± 0.11 versus 0.73 ± 0.11 mmol/L, respectively, p < 0.05), and it was associated with significantly lower CETP activity (cholesteryl ester transfer rate, -10%, p < 0.05; specific CETP activity, -14%, p < 0.05).

CONCLUSIONS

Constitutive expression of fully functional human apoC1 in transgenic rabbit attenuates atherosclerosis. It was found to relate, at least in part, to the inhibition of plasma CETP activity and to alterations in plasma HDL.

Apolipoprotein C1 (APOC1): A Novel Diagnostic and Prognostic Biomarker for Clear Cell Renal Cell Carcinoma

Background: Apolipoprotein C1 (APOC1) has been proved to play a critical role in gastric, breast, lung, and pancreatic cancer. However, the relationship between APOC1 and urinary tumors remains unclear. This study aimed to assess the diagnostic and prognostic value of APOC1 in urinary tumors.

Methods: We performed a pan analysis of APOC1 mRNA expression in urinary cancer using the Gene Expression Profiling Interactive Analysis (GEPIA) database. To further investigate the prognostic value of APOC1 expression in urinary cancers, the Kaplan-Meier plotter database was used. Furthermore, we collected the tumor and adjacent normal samples of 32 ccRCC patients to perform qRT-PCR and western blotting assays. A total of 72 cases with ccRCC were analyzed using tissue microarrays (TMAs).

Results: Our results based on Kaplan-Meier plotter database indicated that a high expression of APOC1 may lead to poor overall survival (OS, p = 0.0019) in patients with ccRCC. Furthermore, the cancer stages and tumor grade of ccRCC appeared to be strongly linked with APOC1 expression according to UALCAN database. Hence, we reached a preliminary conclusion that APOC1 may play a key role in the tumorigenesis and progression of ccRCC. Furthermore, the Kaplan-Meier survival curve analyses of 72 clinical patients indicated that high expression of APOC1 was associated with poor progression-free survival (PFS, p = 0.007) and OS (p = 0.022). In addition, univariate Cox regression analysis confirmed the significant relationship between APOC1 expression and survival (p = 0.038). The TMAs analysis in combination with the patients' clinicopathological features was also performed. The expression of APOC1 was found to be significantly correlated with the tumor size (p = 0.018) and histological grade (p = 0.016).

Conclusions: In conclusion, the findings of our study suggest that APOC1 may serve as a novel diagnostic and prognostic biomarker for ccRCC. Further evidence on the mechanism of APOC1 promoting tumor progression may transform it to a new therapeutic target for the treatment of ccRCC.

Apolipoprotein C1: Its Pleiotropic Effects in Lipid Metabolism and Beyond

Apolipoprotein C1 (apoC1), the smallest of all apolipoproteins, participates in lipid transport and metabolism. In humans, APOC1 gene is in linkage disequilibrium with APOE gene on chromosome 19, a proximity that spurred its investigation. Apolipoprotein C1 associates with triglyceride-rich lipoproteins and HDL and exchanges between lipoprotein classes. These interactions occur via amphipathic helix motifs, as demonstrated by biophysical studies on the wild-type polypeptide and representative mutants. Apolipoprotein C1 acts on lipoprotein receptors by inhibiting binding mediated by apolipoprotein E, and modulating the activities of several enzymes. Thus, apoC1 downregulates lipoprotein lipase, hepatic lipase, phospholipase A2, cholesterylester transfer protein, and activates lecithin-cholesterol acyl transferase. By controlling the plasma levels of lipids, apoC1 relates directly to cardiovascular physiology, but its activity extends beyond, to inflammation and immunity, sepsis, diabetes, cancer, viral infectivity, and-not last-to cognition. Such correlations were established based on studies using transgenic mice, associated in the recent years with GWAS, transcriptomic and proteomic analyses. The presence of a duplicate gene, pseudogene APOC1P, stimulated evolutionary studies and more recently, the regulatory properties of the corresponding non-coding RNA are steadily emerging. Nonetheless, this prototypical apolipoprotein is still underexplored and deserves further research for understanding its physiology and exploiting its therapeutic potential.

A Novel Genes Signature Associated with the Progression of Polycystic Ovary Syndrome

To identify genes involving in the pathogenesis of polycystic ovary syndrome (PCOS). In this study, the comprehensive analysis of GSE8157 was downloaded. Overlapping genes of differentially expressed genes (DEGs) were identified, and enrichment analysis for these genes was performed. A modular network of differentially expressed genes was constructed by weighted gene co-expression network analyses (WGCNA), and a total of 322 differentially expressed genes in 5 stable modules were screened. The correlations of genes of the stable modules in BioGRID 3.4, STRING 10.5, HPRD9 databases were screened, and the interaction network of 104 DEGs was constructed. In addition, some genes and the key words were searched in CTD. A total of 596 differentially expressed genes were screened, including 379 genes that were up-regulated in case group and down-regulated in control group and treat group, and 217 genes that were down-regulated in case group and up-regulated in control group and treat group. The differentially expressed genes were enriched in PPAR signaling pathway, Neuroactive ligand-receptor interaction, cAMP signaling pathway, of which pathways were involved in the cancer development. Finally, 7 important target genes were identified, such as APOC3 was interacted with pioglitazone, ADCY2 involved in cAMP signaling pathway, and the genes (C3AR1, HRH2, GRIA1, MLNR and TAAR2) involved in neuroactive ligand-receptor interaction. In addition, the important target genes were significantly differential expression. These results implied that the 7 important target genes were played an important role in the development and progression of PCOS. Our study implied that genes had played a key role in the development and progression of PCOS, the results showed that microarray can be use as a method for the discovery of new biomarkers and therapeutic targets for PCOS.

Apolipoprotein profiling as a personalized approach to the diagnosis and treatment of dyslipidaemia

An elevated low-density lipoprotein cholesterol concentration is a classical risk factor for cardiovascular disease. This has led to pharmacotherapy in patients with atherosclerotic heart disease or high heart disease risk with statins to reduce serum low-density lipoprotein cholesterol. Even in patients in whom the target levels of low-density lipoprotein cholesterol are reached, there remains a significant residual cardiovascular risk; this is due, in part, to a focus on low-density lipoprotein cholesterol alone and neglect of other important aspects of lipoprotein metabolism. A more refined lipoprotein analysis will provide additional information on the accumulation of very low-density lipoproteins, intermediate density lipoproteins, chylomicrons, chylomicron-remnants and Lp(a) concentrations. Instead of measuring the cholesterol and triglyceride content of the lipoproteins, measurement of their apolipoproteins (apos) is more informative. Apos are either specific for a particular lipoprotein or for a group of lipoproteins. In particular measurement of apos in atherogenic particles is more biologically meaningful than the measurement of the cholesterol concentration contained in these particles. Applying apo profiling will not only improve characterization of the lipoprotein abnormality, but will also improve definition of therapeutic targets. Apo profiling aligns with the concept of precision medicine by which an individual patient is not treated as 'average' patient by the average (dose of) therapy. This concept of precision medicine fits the unmet clinical need for stratified cardiovascular medicine. The requirements for clinical application of proteomics, including apo profiling, can now be met using robust mass spectrometry technology which offers desirable analytical performance and standardization.

Apolipoprotein C-III in triglyceride-rich lipoprotein metabolism

PURPOSE OF REVIEW

Apolipoprotein (apo) C-III is a key player in triglyceride-rich lipoprotein metabolism and strongly associated with elevated plasma triglyceride levels. Several new studies added important insights on apoC-III and its physiological function confirming its promise as a valid therapeutic target.

RECENT FINDINGS

APOC3 is expressed in liver and intestine and regulates triglyceride-rich lipoprotein (TRL) catabolism and anabolism. The transcriptional regulation in both organs requires different regulatory elements. Clinical and preclinical studies established that apoC-III raises plasma triglyceride levels predominantly by inhibiting hepatic TRL clearance. Mechanistic insights into missense variants indicate accelerated renal clearance of apoC-III variants resulting in enhanced TRL catabolism. In contrast, an APOC3 gain-of-function variant enhances de novo lipogenesis and hepatic TRL production. Multiple studies confirmed the correlation between increased apoC-III levels and cardiovascular disease. This has opened up new therapeutic avenues allowing targeting of specific apoC-III properties in triglyceride metabolism.

SUMMARY

Novel in vivo models and APOC3 missense variants revealed unique mechanisms by which apoC-III inhibits TRL catabolism. Clinical trials with Volanesorsen, an APOC3 antisense oligonucleotide, report very promising lipid-lowering outcomes. However, future studies will need to address if acute apoC-III lowering will have the same clinical benefits as a life-long reduction.

Effects of apoC1 genotypes on the hormonal levels, metabolic profile and PAF-AH activity in Chinese women with polycystic ovary syndrome

Background

Elevated serum levels of apolipoprotein (apo) C1 may be an early protein marker of metabolic abnormality in women with polycystic ovary syndrome (PCOS). It is not clear, however, whether there are any relationships between the apoC1 rs4420638A/G and -317deletion (H1)/insertion (H2) polymorphisms and PCOS. We investigated the relationship between these two variants and the risk of PCOS, evaluated the genotypic effects on clinical, hormonal and metabolic indexes and plasma platelet-activating factor acetylhydrolase (PAF-AH) activity, and defined the association of apoC1 gene variants with apoE ε2/ε3/ε4 polymorphisms.

Methods

This is a cross-sectional study of 877 women with PCOS and 761 controls. The apoC1 rs4420638A/G genotype was determined by a Taqman real-time PCR allelic discrimination assay. The apoC1–317H1/H2 and apoE ε2/ε3/ε4 genotypes were measured using PCR and restriction fragment length polymorphism analysis. The clinical, hormonal and metabolic parameters and PAF-AH activity were measured.

Results

The frequencies of apoC1 rs4420638A/G and -317H1/H2 genotypes and alleles were similar between PCOS and control groups (P > 0.05). However, the rs4420638 G allele was related to increased serum luteinizing hormone, cholesterol and apoB levels, and the ratio of apoB to apoA1 (P < 0.05), and the -317H1H1 genotype was associated with a higher acne grade score and a higher ratio of apoB-PAF-AH to H-PAF-AH activity (P < 0.05) in patients with PCOS. We also demonstrated that the apoC1 rs4420638A/G and -317H1/H2 gene variants existed in moderate to reasonably high linkage disequilibrium with apoE ε2/ε3/ε4 polymorphisms in Chinese women.

Conclusion

The apoC1 rs4420638A/G and -317H1/H2 gene variants might be involved in endocrine abnormalities of reproductive axis, metabolic abnormalities and chronic inflammation in PCOS, although no association was observed between the apoC1 genetic variants and the risk of PCOS in Chinese women.

ApoC-III inhibits clearance of triglyceride-rich lipoproteins through LDL family receptors

Hypertriglyceridemia is an independent risk factor for cardiovascular disease, and plasma triglycerides (TGs) correlate strongly with plasma apolipoprotein C-III (ApoC-III) levels. Antisense oligonucleotides (ASOs) for ApoC-III reduce plasma TGs in primates and mice, but the underlying mechanism of action remains controversial. We determined that a murine-specific ApoC-III-targeting ASO reduces fasting TG levels through a mechanism that is dependent on low-density lipoprotein receptors (LDLRs) and LDLR-related protein 1 (LRP1). ApoC-III ASO treatment lowered plasma TGs in mice lacking lipoprotein lipase (LPL), hepatic heparan sulfate proteoglycan (HSPG) receptors, LDLR, or LRP1 and in animals with combined deletion of the genes encoding HSPG receptors and LDLRs or LRP1. However, the ApoC-III ASO did not lower TG levels in mice lacking both LDLR and LRP1. LDLR and LRP1 were also required for ApoC-III ASO-induced reduction of plasma TGs in mice fed a high-fat diet, in postprandial clearance studies, and when ApoC-III-rich or ApoC-III-depleted lipoproteins were injected into mice. ASO reduction of ApoC-III had no effect on VLDL secretion, heparin-induced TG reduction, or uptake of lipids into heart and skeletal muscle. Our data indicate that ApoC-III inhibits turnover of TG-rich lipoproteins primarily through a hepatic clearance mechanism mediated by the LDLR/LRP1 axis.

WAT apoC-I secretion: role in delayed chylomicron clearance in vivo and ex vivo in WAT in obese subjects

Reduced white adipose tissue (WAT) LPL activity delays plasma clearance of TG-rich lipoproteins (TRLs). We reported the secretion of apoC-I, an LPL inhibitor, from WAT ex vivo in women. Therefore we hypothesized that WAT-secreted apoC-I associates with reduced WAT LPL activity and TRL clearance. WAT apoC-I secretion averaged 86.9 ± 31.4 pmol/g/4 h and 74.1 ± 36.6 pmol/g/4 h in 28 women and 11 men with BMI ≥27 kg/m(2), respectively, with no sex differences. Following the ingestion of a (13)C-triolein-labeled high-fat meal, subjects with high WAT apoC-I secretion (above median) had delayed postprandial plasma clearance of dietary TRLs, assessed from plasma (13)C-triolein-labeled TGs and apoB48. They also had reduced hydrolysis and storage of synthetic (3)H-triolein-labeled ((3)H)-TRLs in WAT ex vivo (i.e., in situ LPL activity). Adjusting for WAT in situ LPL activity eliminated group differences in chylomicron clearance; while adjusting for plasma apoC-I, (3)H-NEFA uptake by WAT, or body composition did not. apoC-I inhibited in situ LPL activity in adipocytes in both a concentration- and time-dependent manner. There was no change in postprandial WAT apoC-I secretion. WAT apoC-I secretion may inhibit WAT LPL activity and promote delayed chylomicron clearance in overweight and obese subjects. We propose that reducing WAT apoC-I secretion ameliorates postprandial TRL clearance in humans.

Plasma apolipoprotein C1 concentration is associated with plasma triglyceride concentration, but not visceral fat, in patients with type 2 diabetes

INTRODUCTION

Apolipoprotein C1 (apoC1) is likely to play an important role in triglyceride (TG) metabolism. Mice overexpressing human apoC1 present decreased adipose tissue stores. This study aimed to determine whether apoC1 concentration influences fat mass and distribution and liver fat content (LFC) in patients with type 2 diabetes (T2D).

METHODS

ApoC1 concentrations were measured by ELISA in 113 T2D patients and 56 normolipidaemic-normoglycaemic subjects. Visceral and subcutaneous fat areas were determined by single-slice axial T1-weighted magnetic resonance imaging (MRI), while LFC was measured by hydrogen-1 ((1)H) MR spectroscopy.

RESULTS

ApoC1 concentrations were higher in T2D patients than in normolipidaemic-normoglycaemic subjects (P<0.0001), and did not correlate with visceral or subcutaneous fat areas, but significantly correlated with TG (P<0.0001) and LFC (P=0.02) in T2D patients. However, the correlation between apoC1 and LFC was lost after adjusting for TG. ApoC1 concentration was also significantly higher in T2D patients with TG<1.5mmol/L than in control subjects (P<0.0001), although both groups had similar TG levels. On multivariate analysis performed in T2D patients with TG<1.5mmol/L and control subjects, apoC1 concentration was independently and positively associated with type 2 diabetes (P<0.0001) and TG levels (P=0.03).

CONCLUSION

This study reports, for the first time, that apoC1 is increased in T2D patients and is significantly correlated with TG, whereas no association was found between apoC1 and adipose tissue. This indicates that, in T2D, apoC1 may play a role in TG metabolism, but is unlikely to modulate fat mass and distribution. This increased apoC1 concentration in T2D patients is not only explained by the increased TG level in T2D patients.

Targeted Proteomics Identifies Paraoxonase/Arylesterase 1 (PON1) and Apolipoprotein Cs as Potential Risk Factors for Hypoalphalipoproteinemia in Diabetic Subjects Treated with Fenofibrate and Rosiglitazone

Low levels of high-density lipoprotein cholesterol (HDL-C) and high triglyceride levels contribute to the excess rate of cardiovascular events seen in subjects with type 2 diabetes. Fenofibrate treatment partially reverses dyslipidemia in these subjects. However, a paradoxical marked reduction in HDL-C and HDL's major protein, apolipoprotein A-I, is a complication of fenofibrate in combination with rosiglitazone, an insulin-sensitizing agent. Risk factors for this condition, termed hypoalphalipoproteinemia, have yet to be identified. Using a case-control study design with subjects enrolled in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial, we tested the hypothesis that alterations in HDL's protein cargo predispose diabetic subjects to fenofibrate/rosiglitazone-induced hypoalphalipoproteinemia. HDL was isolated from blood obtained from controls (no decreases or increase in HDL-C while receiving fenofibrate/rosiglitazone therapy) and cases (developed hypoalphalipoproteinemia after fenofibrate/rosiglitazone treatment) participating in the ACCORD study before they began fenofibrate/rosiglitazone treatment. HDL proteins were quantified by targeted parallel reaction monitoring (PRM) and selected reaction monitoring (SRM) with isotope dilution. This approach demonstrated marked increases in the relative concentrations of paraoxonase/arylesterase 1 (PON1), apolipoprotein C-II (APOC2), apolipoprotein C-I, and apolipoprotein H in the HDL of subjects who developed hypoalphalipoproteinemia. The case and control subjects did not differ significantly in baseline HDL-C levels or other traditional lipid risk factors. We used orthogonal biochemical techniques to confirm increased levels of PON1 and APOC2. Our observations suggest that an imbalance in HDL proteins predisposes diabetic subjects to develop hypoalphalipoproteinemia on fenofibrate/rosiglitazone therapy.

Mining the genome for lipid genes

Mining of the genome for lipid genes has since the early 1970s helped to shape our understanding of how triglycerides are packaged (in chylomicrons), repackaged (in very low density lipoproteins; VLDL), and hydrolyzed, and also how remnant and low-density lipoproteins (LDL) are cleared from the circulation. Gene discoveries have also provided insights into high-density lipoprotein (HDL) biogenesis and remodeling. Interestingly, at least half of these key molecular genetic studies were initiated with the benefit of prior knowledge of relevant proteins. In addition, multiple important findings originated from studies in mouse, and from other types of non-genetic approaches. Although it appears by now that the main lipid pathways have been uncovered, and that only modulators or adaptor proteins such as those encoded by LDLRAP1, APOA5, ANGPLT3/4, and PCSK9 are currently being discovered, genome wide association studies (GWAS) in particular have implicated many new loci based on statistical analyses; these may prove to have equally large impacts on lipoprotein traits as gene products that are already known. On the other hand, since 2004 - and particularly since 2010 when massively parallel sequencing has become de rigeur - no major new insights into genes governing lipid metabolism have been reported. This is probably because the etiologies of true Mendelian lipid disorders with overt clinical complications have been largely resolved. In the meantime, it has become clear that proving the importance of new candidate genes is challenging. This could be due to very low frequencies of large impact variants in the population. It must further be emphasized that functional genetic studies, while necessary, are often difficult to accomplish, making it hazardous to upgrade a variant that is simply associated to being definitively causative. Also, it is clear that applying a monogenic approach to dissect complex lipid traits that are mostly of polygenic origin is the wrong way to proceed. The hope is that large-scale data acquisition combined with sophisticated computerized analyses will help to prioritize and select the most promising candidate genes for future research. We suggest that at this point in time, investment in sequence technology driven candidate gene discovery could be recalibrated by refocusing efforts on direct functional analysis of the genes that have already been discovered. This article is part of a Special Issue entitled: From Genome to Function.

Glycation of apolipoprotein C1 impairs its CETP inhibitory property: pathophysiological relevance in patients with type 1 and type 2 diabetes

OBJECTIVE Apolipoprotein (apo)C1 is a potent physiological inhibitor of cholesteryl ester transfer protein (CETP). ApoC1 operates through its ability to modify the electrostatic charge at the lipoprotein surface. We aimed to determine whether the inhibitory ability of apoC1 is still effective in vivo in patients with diabetes and whether in vitro glycation of apoC1 influences its electrostatic charge and its CETP inhibitory effect. RESEARCH DESIGN AND METHODS ApoC1 concentrations and CETP activity were measured in 70 type 1 diabetic (T1D) patients, 113 patients with type 2 diabetes, and 83 control subjects. The consequences of in vitro glycation by methylglyoxal on the electrostatic properties of apoC1 and on its inhibitory effect on CETP activity were studied. An isoelectric analysis of apoC1 was performed in patients with T1D and in normolipidemic-normoglycemic subjects. RESULTS An independent negative correlation was found between CETP activity and apoC1 in control subjects but not in patients with diabetes. HbA1c was independently associated with CETP activity in T1D patients. In vitro glycation of apoC1 modified its electrostatic charge and abrogated its ability to inhibit CETP activity in a concentration-dependent manner. The isoelectric point of apoC1 in T1D patients was significantly lower than that in control subjects. CONCLUSIONS The ability of apoC1 to inhibit CETP activity is impaired in patients with diabetes. Glycation of apoC1 leads to a change in its electrostatic properties that might account, at least in part, for a loss of constitutive CETP inhibition and an increase in plasma CETP activity in patients with diabetes.

Apolipoproteins C-I and C-III inhibit lipoprotein lipase activity by displacement of the enzyme from lipid droplets

Apolipoproteins (apo) C-I and C-III are known to inhibit lipoprotein lipase (LPL) activity, but the molecular mechanisms for this remain obscure. We present evidence that either apoC-I or apoC-III, when bound to triglyceride-rich lipoproteins, prevent binding of LPL to the lipid/water interface. This results in decreased lipolytic activity of the enzyme. Site-directed mutagenesis revealed that hydrophobic amino acid residues centrally located in the apoC-III molecule are critical for attachment to lipid emulsion particles and consequently inhibition of LPL activity. Triglyceride-rich lipoproteins stabilize LPL and protect the enzyme from inactivating factors such as angiopoietin-like protein 4 (angptl4). The addition of either apoC-I or apoC-III to triglyceride-rich particles severely diminished their protective effect on LPL and rendered the enzyme more susceptible to inactivation by angptl4. These observations were seen using chylomicrons as well as the synthetic lipid emulsion Intralipid. In the presence of the LPL activator protein apoC-II, more of apoC-I or apoC-III was needed for displacement of LPL from the lipid/water interface. In conclusion, we show that apoC-I and apoC-III inhibit lipolysis by displacing LPL from lipid emulsion particles. We also propose a role for these apolipoproteins in the irreversible inactivation of LPL by factors such as angptl4.

Constitutive inhibition of plasma CETP by apolipoprotein C1 is blunted in dyslipidemic patients with coronary artery disease

Plasma cholesteryl ester transfer protein (CETP) promotes the cholesterol enrichment of apoB-containing lipoproteins (VLDL and LDL) at the expense of HDL. Recent studies demonstrated that apoC1 is a potent CETP inhibitor in plasma of healthy, normolipidemic subjects. Our goal was to establish whether the modulation of CETP activity by apoC1 is influenced by dyslipidemia in patients with documented coronary artery disease (CAD). In the total CAD population studied (n = 240), apoC1 levels correlated negatively with CETP activity, independently of apoE-epsilon, CETP-Taq1B, and apoC1-Hpa1 genotypes. In multivariate analysis, the negative relationship was observed only in normolipidemic patients, not in those with hypercholesterolemia, hypertriglyceridemia, or combined hyperlipidemia. In the normolipidemic subjects, apoC1 levels were positively associated with higher HDL- to LDL-cholesterol ratio (r = 0.359, P < 0.001). It is concluded that apoC1 as a CETP inhibitor no longer operates on cholesterol redistribution in high-risk patients with dyslipidemia, probably due to increasing amounts of VLDL-bound apoC1, which is inactive as a CETP inhibitor. Patients with dyslipidemia could experience major benefits from treatment with pharmacological CETP inhibitors, which might compensate for blunted endogenous inhibition.

Apolipoprotein C-I binds more strongly to phospholipid/triolein/water than triolein/water interfaces: a possible model for inhibiting cholesterol ester transfer protein activity and triacylglycerol-rich lipoprotein uptake

Apolipoprotein C-I (apoC-I) is an important constituent of high-density lipoprotein (HDL) and is involved in the accumulation of cholesterol ester in nascent HDL via inhibition of cholesterol ester transfer protein and potential activation of lecithin:cholesterol acyltransferase (LCAT). As the smallest exchangeable apolipoprotein (57 residues), apoC-I transfers between lipoproteins via a lipid-binding motif of two amphipathic α-helices (AαHs), spanning residues 7-29 and 38-52. To understand apoC-I's behavior at hydrophobic lipoprotein surfaces, oil drop tensiometry was used to compare the binding to triolein/water (TO/W) and palmitoyloleoylphosphatidylcholine/triolein/water (POPC/TO/W) interfaces. When apoC-I binds to either interface, the surface tension (γ) decreases by ~16-18 mN/m. ApoC-I can be exchanged at both interfaces, desorbing upon compression and readsorbing on expansion. The maximal surface pressures at which apoC-I begins to desorb (Π(max)) were 16.8 and 20.7 mN/m at TO/W and POPC/TO/W interfaces, respectively. This suggests that apoC-I interacts with POPC to increase its affinity for the interface. ApoC-I is more elastic on POPC/TO/W than TO/W interfaces, marked by higher values of the elasticity modulus (ε) on oscillations. At POPC/TO/W interfaces containing an increasing POPC:TO ratio, the pressure at which apoC-I begins to be ejected increases as the phospholipid surface concentration increases. The observed increase in apoC-I interface affinity due to higher degrees of apoC-I-POPC interactions may explain how apoC-I can displace larger apolipoproteins, such as apoE, from lipoproteins. These interactions allow apoC-I to remain bound to the interface at higher Π values, offering insight into apoC-I's rearrangement on triacylglycerol-rich lipoproteins as they undergo Π changes during lipoprotein maturation by plasma factors such as lipoprotein lipase.

The apolipoprotein C-I content of very-low-density lipoproteins is associated with fasting triglycerides, postprandial lipemia, and carotid atherosclerosis

Background. Experimental studies in animals suggest that apolipoprotein (apo) C-I is an important regulator of triglycerides in fasting and postprandial conditions and associated with carotid atherosclerosis. Methods. A cross-sectional study was conducted with 81 subjects, aged 56–80 years recruited from a population health survey. The participants underwent a fat tolerance test (1 g fat per Kg body weight) and carotid atherosclerosis was determined by ultrasound examination. VLDL particles, Sf 20–400, were isolated and their lipid composition and apoC-I content determined. Results. The carotid plaque area increased linearly with the number of apoC-I molecules per VLDL particles (P = 0.048) under fasting conditions. Fasting triglycerides increased across tertiles of apoC-I per VLDL particle in analyses adjusted for apoC-II and -C-III, apoE genotype and traditional cardiovascular risk factors (P = 0.011). The relation between apoC-I in VLDL and serum triglycerides was conveyed by triglyceride enrichment of VLDL particles (P for trend <0.001. The amount of apoC-I molecules per VLDL was correlated with the total (r = 0.41, P < 0.0001) and incremental (r = 0.35, P < 0.001) area under the postprandial triglyceride curve. Conclusions. Our findings support the concept that the content of apoC-I per VLDL particle is an important regulator of triglyceride metabolism in the fasting and postprandial state and associated with carotid athrosclerosis.

Apolipoprotein C-I genotype and serum levels of triglycerides, C-reactive protein and coronary heart disease

Apolipoprotein C-I (apoCI) is implicated in lipid metabolism and inflammatory response, both important risk factors for human heart disease. However, most findings come from in vitro or animal studies, whereas data on human apoCI are sparse. To elucidate the role of apoCI in human disease, we analyzed a functional polymorphism in the promoter region of the apoCI gene in relation to blood lipids, C-reactive protein (CRP), coronary artery disease (CAD), and myocardial infarction (MI). Rs11568822 is a 4-base pair insertion/deletion (Ins/Del) polymorphism, and the Ins allele leads to a higher transcription in vitro compared with the Del allele. This polymorphism was analyzed in the Intergene study, a case-control study for CAD (N = 1236), and the Stockholm Heart Epidemiology Program, a case-control study for MI (N = 2774). Subjects homozygous for the Ins genotype had significantly higher serum levels of triglycerides (P = .01 and P = .006) and lower serum levels of CRP (P = .02 and P < .0001) compared with all other subjects in both studies. Similar results were obtained when analyzing only the controls of both studies (P = .002 and P = .0002, triglycerides; P = .002 and P < .0001, CRP). However, apoCI was not associated with CAD or MI. In conclusion, our data show that apoCI genotype is associated with serum levels of triglycerides and CRP, confirming the role of apoCI in lipid metabolism and suggesting that it also influences inflammation.

Metabolism of very-low-density lipoprotein and low-density lipoprotein containing apolipoprotein C-III and not other small apolipoproteins

OBJECTIVE

We aimed to clarify the influence of apolipoprotein C-III (apoCIII) on human apolipoprotein B metabolism.

METHODS AND RESULTS

We studied the kinetics of 4 very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL) types containing: (1) otherApos-CIII-: none of apoCIII, apoAII, apoCI, apoCII, or apoE; (2) otherApos+CIII-: no apoCIII but at least one of the others; (3) otherApos-CIII+: apoCIII, but not any others; and (4) otherApos+CIII+: apoCIII and at least one other. VLDL and IDL otherApos-CIII+ and otherApos-CIII- had similar rates of lipolytic conversion to smaller particles. However, light LDL otherApos-CIII+ compared with otherApos-CIII- had much faster conversion to dense LDL as did light LDL otherApos+CIII+ compared with otherApos+CIII-. VLDL and IDL otherApos-CIII+ had minimal direct removal from circulation, whereas VLDL and IDL otherApos+CIII-, rich in apoE, showed fast clearance. Lipoproteins in fraction otherApos+CIII+ also rich in apoE had very low clearance.

CONCLUSIONS

The results suggest that apoCIII strongly inhibits hepatic uptake of VLDL and IDL overriding the opposite influence of apoE when both are present. The presence of apoCIII on dense VLDL is not associated with slow conversion to IDL, a lipoprotein lipase-dependent process; but when on light LDL, apoCIII is associated with enhanced conversion to dense LDL, a process involving hepatic lipase.

APOC1 T45S polymorphism is associated with reduced obesity indices and lower plasma concentrations of leptin and apolipoprotein C-I in aboriginal Canadians

Apolipoprotein (apo) C-I is a constituent of chylomicrons, very low density lipoprotein, and high density lipoprotein. The role of apo C-I in human metabolism is incompletely defined. We took advantage of a naturally occurring amino acid polymorphism that is present in aboriginal North Americans, namely apo C-I T45S. We assessed the hypothesis that metabolic traits, including obesity-related and lipoprotein-related traits, would differ between carriers and noncarriers of apo C-I T45S. A genotyping assay was developed for APOC1 T45S and genotypes were determined in a sample of 410 Canadian Oji-Cree subjects. The allele frequency of the apo C-I S45 allele was approximately 8% in this sample. We observed the apo C-I S45 allele was significantly associated with 1) lower percent body fat (P < 0.05), 2) lower waist circumference (P = 0.058), 3) lower serum leptin levels (P < 0.05), and 4) lower plasma apo C-I levels (P < 0.0001), using a newly developed ELISA-based method. Taken together, these results suggest that at the whole human phenotype level, apo C-I is associated with the complex metabolic trait of obesity as well as with serum leptin levels.

Apolipoprotein CI is a physiological regulator of cholesteryl ester transfer protein activity in human plasma but not in rabbit plasma

Plasma cholesteryl ester transfer protein (CETP) activity is high in rabbits, intermediate in humans, and nondetectable in rodents. Human apolipoprotein CI (apoCI) was found to be a potent inhibitor of CETP. The aim of this study was to compare the ability of rabbit and human apoCI to modulate the interaction of CETP with HDLs and to evaluate to which extent apoCI contributes to plasma cholesteryl ester transfer rate in normolipidemic humans and rabbits. Rabbit apoCI gene was cloned and sequenced, rabbit and human apoCI were purified to homogeneity, and their ability to modify the surface charge properties and the CETP inhibitory potential of HDL were compared. It is demonstrated that unlike human apoCI, rabbit apoCI does not modulate cholesteryl ester transfer rate in total plasma. Whereas both human and rabbit apoCI readily associate with HDL, only human apoCI was found to modify the electrostatic charge of HDL. In humans, both CETP and apoCI at normal, physiological levels contribute significantly to the plasma cholesteryl ester transfer rate. In contrast, CETP is the sole major determinant of cholesteryl ester transfer in normolipidemic rabbit plasma as a result of the inability of rabbit apoCI to change HDL electronegativity.

Can serum apolipoprotein C-I demonstrate metabolic abnormality early in women with polycystic ovary syndrome?

OBJECTIVE

To evaluate the role of apolipoprotein C-I (apoC-I) levels and assess relationships between apoC-I and clinical features in women with polycystic ovary syndrome (PCOS).

DESIGN

Prospective study.

SETTING

Reproductive Center of Peking University Third Hospital.

PATIENT(S)

Thirty patients with PCOS with insulin resistance, 30 patients with PCOS without insulin resistance, and 30 control individuals.

INTERVENTION(S)

Fasting serum samples.

MAIN OUTCOME MEASURE(S)

Measures of serum apoC-I, androgens, total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, apoA1, apoB, heat-shock C-reactive protein, glucose, and homeostasis model assessment of insulin resistance (HOMA-IR).

RESULT(S)

We found differentially expressed proteins by use of the surface-enhanced laser adsorption/ionization (SELDI) protein chip in the serum of women with PCOS and controls. Of these, apoC-I, was highly up-regulated. ApoC-I is associated with glycometabolism and lipid metabolism, but its role in PCOS has been unknown. The serum levels of apoC-I in the patients with PCOS were statistically significantly elevated compared with those of controls, especially in women with insulin resistance. The lean PCOS women had higher apoC-I levels than controls. In patients with PCOS and without any abnormal serum lipid index, apoC-I levels were still higher than in controls. Analysis showed that apoC-I correlated with body mass index, triglycerides, high-density lipoprotein cholesterol, apoA1, and HOMA-IR.

CONCLUSION(S)

ApoC-I may have an important role in glucose and lipid metabolism, and may be useful for early demonstration of metabolic abnormality in women with PCOS.

ApoE and ApoC-I polymorphisms: association of genotype with cardiovascular disease phenotype in African Americans

Apolipoproteins (apo) E and C-I are components of triglyceride (TG)-rich lipoproteins and impact their metabolism. Functional polymorphisms have been established in apoE but not in apoC-I. We studied the relationship between apoE and apoC-I gene polymorphisms and plasma lipoproteins and coronary artery disease (CAD) in 211 African Americans and 306 Caucasians. In African Americans but not in Caucasians, apoC-I H2-carriers had significantly lower total and LDL cholesterol and apoB levels, and higher glucose, insulin, and HOMA-IR levels compared with H1 homozygotes. Differences across CAD phenotypes were seen for the apoC-I polymorphism. African-American H2-carriers without CAD had significantly lower total cholesterol (P < 0.001), LDL cholesterol (P < 0.001), and apoB (P < 0.001) levels compared with H1 homozygotes, whereas no differences were found across apoC-I genotypes for African Americans with CAD. Among African-American apoC-I H1 homozygotes, subjects with CAD had a profile similar to the metabolic syndrome (i.e., higher triglyceride, glucose, and insulin) compared with subjects without CAD. For African-American H2-carriers, subjects with CAD had a pro-atherogenic lipid pattern (i.e., higher LDL cholesterol and apoB levels), compared with subjects without CAD. ApoC-I genotypes showed an ethnically distinct phenotype relationship with regard to CAD and CAD risk factors.

Hepatic denervation impairs the assembly and secretion of VLDL-TAG

VLDL secretion is a regulated process that depends on the availability of lipids, apoB and MTP. Our aim was to investigate the effect of liver denervation upon the secretion of VLDL and the expression of proteins involved in this process. Denervation was achieved by applying a 85% phenol solution onto the portal tract, while control animals were treated with 9% NaCl. VLDL secretion was evaluated by the Tyloxapol method. The hepatic concentration of TAG and cholesterol, and the plasma concentration of TAG, cholesterol, VLDL-TAG, VLDL-cholesterol and HDL-cholesterol were measured, as well as mRNA expression of proteins involved in the process of VLDL assembly. Hepatic acinar distribution of MTP and apoB was evaluated by immunohistochemistry. Denervation increased plasma concentration of cholesterol (125.3 +/- 10.1 vs. 67.1 +/- 4.9 mg dL(-1)) and VLDL-cholesterol (61.6 +/- 5.6 vs. 29.4 +/- 3.3 mg dL(-1)), but HDL-cholesterol was unchanged (45.5 +/- 6.1 vs. 36.9 +/- 3.9 mg dL(-1)). Secretion of VLDL-TAG (47.5 +/- 23.8 vs. 148.5 +/- 27.4 mg dL h(-1)) and mRNA expression of CPT I and apoB were reduced (p < 0.01) in the denervated animals. MTP and apoB acinar distribution was not altered in the denervated animals, but the intensity of the reaction was reduced in relation to controls.

Inactivation of hepatic Foxo1 by insulin signaling is required for adaptive nutrient homeostasis and endocrine growth regulation

The forkhead transcription factor Foxo1 regulates expression of genes involved in stress resistance and metabolism. To assess the contribution of Foxo1 to metabolic dysregulation during hepatic insulin resistance, we disrupted Foxo1 expression in the liver of mice lacking hepatic Irs1 and Irs2 (DKO mice). DKO mice were small and developed diabetes; analysis of the DKO-liver transcriptome identified perturbed expression of growth and metabolic genes, including increased Ppargc1a and Igfbp1, and decreased glucokinase, Srebp1c, Ghr, and Igf1. Liver-specific deletion of Foxo1 in DKO mice resulted in significant normalization of the DKO-liver transcriptome and partial restoration of the response to fasting and feeding, near normal blood glucose and insulin concentrations, and normalization of body size. These results demonstrate that constitutively active Foxo1 significantly contributes to hyperglycemia during severe hepatic insulin resistance, and that the Irs1/2 --> PI3K --> Akt --> Foxo1 branch of insulin signaling is largely responsible for hepatic insulin-regulated glucose homeostasis and somatic growth.

Apolipoprotein C1 and apolipoprotein E are differentially expressed in atheroma of the carotid and femoral artery

BACKGROUND

A number of the genes and proteins as the causes of carotid atherosclerotic disease have been recently reported, but the major factors for atherosclerosis have still not been identified.

METHODS

The atherosclerotic atheromas were obtained during endarterectomy for each of 10 cases of diseased carotid and femoral arteries. As the nonatherosclerotic arteries, the iliac arteries were obtained during organ harvest from five cases of brain-dead donors, and the leg arteries were obtained during leg amputation from five cases of Buerger's disease. The total RNAs and proteins were isolated from the atheromas and arteries. The annealing control primer method was used to screen the differentially expressed mRNAs. To identify if the mRNA expression of screened gene was associated with the protein expression, we performed an immunohistochemical analysis.

RESULTS

We found that the apolipoprotein C1 (apo C1) gene was prominently expressed in the atheroma of the carotid and femoral arteries, as compared to the nonatherosclerotic arteries. Immunohistochemical analysis showed the high expression of apo C1 protein in the atheromas of the carotid and femoral arteries. Apo E protein was also highly expressed in atheromas compared with the nonatherosclerotic arteries, but there was no difference for apo C2 protein between those four groups of arteries.

DISCUSSION

The expression of apo C1 and apo E are closely associated with the susceptibility to the pathogenesis of atherosclerosis. This study suggests that these factors might play important roles in the future to screen for preventing atherosclerosis and for diagnostic testing of patients.

Hepatic lipid accumulation in apolipoprotein C-I-deficient mice is potentiated by cholesteryl ester transfer protein

The impact of apolipoprotein C-I (apoC-I) deficiency on hepatic lipid metabolism was addressed in mice in the presence or the absence of cholesteryl ester transfer protein (CETP). In addition to the expected moderate reduction in plasma cholesterol levels, apoCIKO mice showed significant increases in the hepatic content of cholesteryl esters (+58%) and triglycerides (+118%) and in biliary cholesterol concentration (+35%) as compared with wild-type mice. In the presence of CETP, hepatic alterations resulting from apoC-I deficiency were enforced, with up to 58% and 302% increases in hepatic levels of cholesteryl esters and triglycerides in CETPTg/apoCIKO mice versus CETPTg mice, respectively. Biliary levels of cholesterol, phospholipids, and bile acids were increased by 88, 77, and 20%, respectively, whereas total cholesterol, HDL cholesterol, and triglyceride concentrations in plasma were further reduced in CETPTg/apoCIKO mice versus CETPTg mice. Finally, apoC-I deficiency was not associated with altered VLDL production rate. In line with the previously recognized inhibition of lipoprotein clearance by apoC-I, apoC-I deficiency led to decreased plasma lipid concentration, hepatic lipid accumulation, and increased biliary excretion of cholesterol. The effect was even greater when the alternate reverse cholesterol transport pathway via VLDL/LDL was boosted in the presence of CETP.

Combined hyperlipidemia/hyperalphalipoproteinemia associated with premature spontaneous atherosclerosis in mice lacking hepatic lipase and low density lipoprotein receptor

BACKGROUND AND METHODS

Hepatic lipase (HL) is an enzyme which hydrolyzes triglycerides from plasma lipoproteins and thus takes part in the metabolism of triglyceride-rich lipoprotein remnants and high density lipoproteins. The search described here concentrated on the description of the double invalidation of the HL and LDL receptor genes in mice in order to better understand the possible role of HL in combined hyperlipidemia/hyperalphalipoproteinemia and development of atherosclerosis.

RESULTS

We show here that mice lacking both endogenous HL and LDL receptor (HL-/-:LDLR-/-) dramatically increased their plasma triglyceride-rich lipoproteins and their remnants as a consequence of reduced liver uptake. This result is strenghthened by the fact that HL-/-:LDLR-/- were found to overexpress LRP, LSR, and apoE genes. Interestingly, HL-/-:LDLR-/- mice showed premature spontaneous atherosclerosis and aortic lesions from 1-year-old animals were two-fold larger than those of LDLR-/- single mutants. We confirmed that HL-/- and wild-type mice did not develop atherosclerosis lesion even 1 year after birth.

CONCLUSIONS

Analysis of this double HL-LDLR knockout mouse model provides in vivo evidence that HL has a major role in the clearance of TRL remnants when LDLR is deficient and in the reduction of the development of atherosclerosis.

Convergence of genes implicated in Alzheimer's disease on the cerebral cholesterol shuttle: APP, cholesterol, lipoproteins, and atherosclerosis

Polymorphic genes associated with Alzheimer's disease (see ) delineate a clearly defined pathway related to cerebral and peripheral cholesterol and lipoprotein homoeostasis. They include all of the key components of a glia/neurone cholesterol shuttle including cholesterol binding lipoproteins APOA1, APOA4, APOC1, APOC2, APOC3, APOD, APOE and LPA, cholesterol transporters ABCA1, ABCA2, lipoprotein receptors LDLR, LRP1, LRP8 and VLDLR, and the cholesterol metabolising enzymes CYP46A1 and CH25H, whose oxysterol products activate the liver X receptor NR1H2 and are metabolised to esters by SOAT1. LIPA metabolises cholesterol esters, which are transported by the cholesteryl ester transport protein CETP. The transcription factor SREBF1 controls the expression of most enzymes of cholesterol synthesis. APP is involved in this shuttle as it metabolises cholesterol to 7-betahydroxycholesterol, a substrate of SOAT1 and HSD11B1, binds to APOE and is tethered to LRP1 via APPB1, APBB2 and APBB3 at the cytoplasmic domain and via LRPAP1 at the extracellular domain. APP cleavage products are also able to prevent cholesterol binding to APOE. BACE cleaves both APP and LRP1. Gamma-secretase (PSEN1, PSEN2, NCSTN) cleaves LRP1 and LRP8 as well as APP and their degradation products control transcription factor TFCP2, which regulates thymidylate synthase (TS) and GSK3B expression. GSK3B is known to phosphorylate the microtubule protein tau (MAPT). Dysfunction of this cascade, carved out by genes implicated in Alzheimer's disease, may play a major role in its pathology. Many other genes associated with Alzheimer's disease affect cholesterol or lipoprotein function and/or have also been implicated in atherosclerosis, a feature of Alzheimer's disease, and this duality may well explain the close links between vascular and cerebral pathology in Alzheimer's disease. The definition of many of these genes as risk factors is highly contested. However, when polymorphic susceptibility genes belong to the same signaling pathway, the risk associated with multigenic disease is better related to the integrated effects of multiple polymorphisms of genes within the same pathway than to variants in any single gene [Wu, X., Gu, J., Grossman, H.B., Amos, C.I., Etzel, C., Huang, M., Zhang, Q., Millikan, R.E., Lerner, S., Dinney, C.P., Spitz, M.R., 2006. Bladder cancer predisposition: a multigenic approach to DNA-repair and cell-cycle-control genes. Am. J. Hum. Genet. 78, 464-479.]. Thus, the fact that Alzheimer's disease susceptibility genes converge on a clearly defined signaling network has important implications for genetic association studies.

Apolipoprotein CI stimulates the response to lipopolysaccharide and reduces mortality in Gram‐negative sepsis

Gram-negative sepsis is a major death cause in intensive care units. Accumulating evidence indicates the protective role of plasma lipoproteins such as high-density lipoprotein (HDL) in sepsis. It has recently been shown that septic HDL is almost depleted from apolipoprotein CI (apoCI), suggesting that apoCI may be a protective factor in sepsis. Sequence analysis revealed that apoCI possesses a highly conserved consensus KVKEKLK binding motif for lipopolysaccharide (LPS), an outer-membrane component of gram-negative bacteria. Through avid binding to LPS involving this motif, apoCI improved the presentation of LPS to macrophages in vitro and in mice, thereby stimulating the inflammatory response to LPS. Moreover, apoCI dose-dependently increased the early inflammatory response to Klebsiella pneumoniae-induced pneumonia, reduced the number of circulating bacteria, and protected mice against fatal sepsis. Our data support the hypothesis that apoCI is a physiological protector against infection by enhancing the early inflammatory response to LPS and suggest that timely increase of apoCI levels could be used to efficiently prevent and treat early sepsis.

Endogenous apoC-I increases hyperlipidemia in apoE-knockout mice by stimulating VLDL production and inhibiting LPL

Previous studies have shown that overexpression of human apolipoprotein C-I (apoC-I) results in moderate hypercholesterolemia and severe hypertriglyceridemia in mice in the presence and absence of apoE. We assessed whether physiological endogenous apoC-I levels are sufficient to modulate plasma lipid levels independently of effects of apoE on lipid metabolism by comparing apolipoprotein E gene-deficient/apolipoprotein C-I gene-deficient (apoe-/-apoc1-/-), apoe-/-apoc1+/-, and apoe-/-apoc1+/+ mice. The presence of the apoC-I gene-dose-dependently increased plasma cholesterol (+45%; P < 0.001) and triglycerides (TGs) (+137%; P < 0.001), both specific for VLDL. Whereas apoC-I did not affect intestinal [3H]TG absorption, it increased the production rate of hepatic VLDL-TG (+35%; P < 0.05) and VLDL-[35S]apoB (+39%; P < 0.01). In addition, apoC-I increased the postprandial TG response to an intragastric olive oil load (+120%; P < 0.05) and decreased the uptake of [3H]TG-derived FFAs from intravenously administered VLDL-like emulsion particles by gonadal and perirenal white adipose tissue (WAT) (-34% and -25%, respectively; P < 0.05). As LPL is the main enzyme involved in the clearance of TG-derived FFAs by WAT, and total postheparin plasma LPL levels were unaffected, these data demonstrate that endogenous apoC-I suffices to attenuate the lipolytic activity of LPL. Thus, we conclude that endogenous plasma apoC-I increases VLDL-total cholesterol and VLDL-TG dose-dependently in apoe-/- mice, resulting from increased VLDL particle production and LPL inhibition.

Apolipoprotein CI overexpression is not a relevant strategy to block cholesteryl ester transfer protein (CETP) activity in CETP transgenic mice

ApoCI (apolipoprotein CI) is a potent inhibitor of plasma CETP [CE (cholesteryl ester) transfer protein]. The relevance of apoCI overexpression as a method for CETP blockade in vivo was addressed in the present study in CETPTg/apoCITg mice (mice expressing both human CETP and apoCI). Despite a significant reduction in specific CETP activity in CETPTg/apoCITg mice compared with CETPTg mice [transgenic mouse to human CETP; 46.8+/-11.1 versus 101.8+/-25.7 pmol x h(-1).(mug of plasma CETP)(-1) respectively; P<0.05], apoCI overexpression increased both the CETP mass concentration (3-fold increase; P<0.05) and the hepatic CETP mRNA level (4-fold increase, P<0.005), leading to an increase in total plasma CE transfer activity (by 39%, P<0.05). The ratio of apoB-containing lipoprotein to HDL (high-density lipoprotein) CE was 10-fold higher in CETPTg/apoCITg mice than in apoCITg mice (P<0.0005). It is proposed that the increased CETP expression in CETPTg/apoCITg mice is a direct consequence of liver X receptor activation in response to the accumulation of cholesterol-rich apoB-containing lipoproteins. In support of the latter view, hepatic mRNA levels of other liver X receptor-responsive genes [ABCG5 (ATP-binding cassette transporter GS) and SREBP-1c (sterol-regulatory-binding protein-1c)] were higher in CETPTg/apoCITg mice compared with CETPTg mice. In conclusion, overexpression of apoCI, while producing a significant inhibitory effect on specific CETP activity, does not represent a suitable method for decreasing total CE transfer activity in CETPTg/apoCITg mice, owing to an hyperlipidaemia-mediated effect on CETP gene expression.

The apolipoprotein CI content of triglyceride-rich lipoproteins independently predicts early atherosclerosis in healthy middle-aged men

OBJECTIVES

In this study, we examined the apolipoprotein (apo) CI content of triglyceride-rich lipoproteins (TRLs) in relation to established coronary heart disease (CHD) risk factors and early atherosclerosis.

BACKGROUND

In Western society, the postprandial state constitutes a nearly constant stress on the vasculature and the metabolism of lipoproteins. Delayed clearance of postprandial TRL remnants has repeatedly been associated with premature CHD and may include the enrichment of these remnants with apoCI.

METHODS

We examined 72 healthy 50-year-old men with an apoE3/E3 genotype who had undergone an oral fat load test and B-mode ultrasound examination of the intima-media thickness (IMT) of the common carotid artery.

RESULTS

In the fasting state, plasma, very-low-density lipoprotein (VLDL), and low-density lipoprotein cholesterol, proinsulin, and apoB100-containing intermediate density lipoprotein levels were related to IMT (p < 0.05). In the postprandial state, IMT was related to triglycerides at 2 h (p < 0.01), large VLDL concentration at 3 h (p < 0.05), the apoCI plasma and TRL concentrations at 6 h (p < 0.05, p < 0.05), and the apoCI content of TRLs at 6 h (p < 0.002). Multivariate analysis revealed that the apoCI content of TRLs at 6 h (p < 0.0001), plasma triglyceride concentrations at 2 h (p < 0.006), and fasting plasma cholesterol concentration (p < 0.05) independently predicted IMT. In addition, the apoCI content of postprandial TRLs correlated strongly with the cholesterol content (r = 0.64, p < 0.0001).

CONCLUSIONS

Our results indicate that the apoCI content of postprandial TRLs is a novel independent risk factor for early atherosclerosis in normolipidemic healthy middle-aged men with possible implication for the enrichment of TRL remnant lipoproteins with cholesterol.

The common insertional polymorphism in the APOC1 promoter is associated with serum apolipoprotein C-I levels in Hispanic children

We examined the effect of APOC1-317insCGTT allele status (HpaI RFLP, deletion [H1] and insertion [H2] alleles) on serum apolipoprotein (apo) C-I level in 362 Hispanic children in the Columbia University BioMarkers Study. The H2 allele was present in 147 subjects (40.6%). Serum apoC-I was 20% lower in the presence of the H2 allele in APOE epsilon3/epsilon3 homozygotes (P=0.003) but did not differ by H2 status in epsilon4 carriers. Insufficient numbers of epsilon2 carriers (N=45) were present for analysis. In multivariate analysis in the epsilon3/epsilon3 context, after adjusting for potential covariate effects and familial aggregation, the mean effect of H2/* versus H1/H1 on apoC-I level, was estimated to be 2.15+/-0.55mg/dl (P<0.0025). Plasma triglyceride level was weakly correlated with serum apoC-I level (Pearson's r=0.17, P<0.001) but was highly correlated with serum apoC-III (Pearson's r=0.74, P<0.0001). Nevertheless, presence of the H2 allele was not significantly associated with serum apoC-III level. Thus, the effect of APOC1 genotype on serum apoC-I level was not due to apoC-I level serving as a surrogate for triglyceride level. The APOC1-317insCGTT allele is a commonly polymorphic genetic marker that is associated with serum apoC-I level in the APOE epsilon3/epsilon3 context. These findings suggest that the mechanism of the previously described association with plasma TG is, at least in part, related to the correlation of the polymorphism with the level of expression of apoC-I.

Effects of subchronic clozapine administration on serum glucose, cholesterol and triglyceride levels, and body weight in male BALB/c mice

Atypical antipsychotics, like clozapine, have fewer extrapyramidal side effects compared with typical antipsychotics, however, such treatment is associated with several adverse metabolic effects such as weight gain, hyperglycemia and hyperlipidemia in patients with schizophrenia. In this study, we investigated the effects of 30-day clozapine treatment on weight change, and serum fasting glucose, cholesterol and triglyceride levels in male BALB/c mice. The results demonstrate that 10.0 mg/kg clozapine group gained significantly less weight but had higher cholesterol compared with controls and the 2.0 mg/kg clozapine group. Our findings indicate the possibility of using mice to study the mechanisms of body weight change and lipid dysregulations induced by clozapine.

Severe hypertriglyceridemia in human APOC1 transgenic mice is caused by apoC-I-induced inhibition of LPL

Studies in humans and mice have shown that increased expression of apolipoprotein C-I (apoC-I) results in combined hyperlipidemia with a more pronounced effect on triglycerides (TGs) compared with total cholesterol (TC). The aim of this study was to elucidate the main reason for this effect using human apoC-I-expressing (APOC1) mice. Moderate plasma human apoC-I levels (i.e., 4-fold higher than human levels) caused a 12-fold increase in TG, along with a 2-fold increase in TC, mainly confined to VLDL. Cross-breeding of APOC1 mice on an apoE-deficient background resulted in a marked 55-fold increase in TG, confirming that the apoC-I-induced hyperlipidemia cannot merely be attributed to blockade of apoE-recognizing hepatic lipoprotein receptors. The plasma half-life of [3H]TG-VLDL-mimicking particles was 2-fold increased in APOC1 mice, suggesting that apoC-I reduces the lipolytic conversion of VLDL. Although total postheparin plasma LPL activity was not lower in APOC1 mice compared with controls, apoC-I was able to dose-dependently inhibit the LPL-mediated lipolysis of [3H]TG-VLDL-mimicking particles in vitro with a 60% efficiency compared with the main endogenous LPL inhibitor apoC-III. Finally, purified apoC-I impaired the clearance of [3H]TG-VLDL-mimicking particles independent of apoE-mediated hepatic uptake in lactoferrin-treated mice. Therefore, we conclude that apoC-I is a potent inhibitor of LPL-mediated TG-lipolysis.

Post-transcriptional regulation of apoC-I synthesis and secretion in human HepG2 cells

ApoC-I plays an important role in controlling plasma lipid metabolism, however little is known about factors regulating the hepatic synthesis and secretion of this apolipoprotein. In the present study, we have carried out experiments with human hepatoma (HepG2) cells, in order to determine the effect of different tissue culture conditions on cellular lipid levels and on the production of apoC-I (and apoE) at the protein and mRNA level. Cells incubated for 48 h with 10% human serum had significantly higher cellular triglyceride (22%, P<0.05) and cholesterol levels (19%, P<0.01), higher medium apoC-I and apoE levels (2.6- and 2.9-fold, respectively), but similar levels of apoC-I and apoE mRNA, compared to cells incubated with 10% human lipoprotein-deficient serum (LPDS). Serum containing only HDL, or containing HDL with LDL, also increased cellular lipids and increased secreted apoC-I and apoE levels without altering apoC-I and apoE mRNA levels. Incubation of cells with Intralipid triglyceride (625 microM), increased cellular triglyceride (2.8-fold, P<0.001), decreased cellular cholesterol (32%, P<0.01), decreased cellular and medium apoC-I (24 and 26%, P<0.01) and had no effect on apoC-I mRNA levels. Additional experiments in which cells were loaded with cholesterol (incubation with 10 microg/ml cholesterol plus 1 microg/ml 25-hydroxycholesterol) or depleted of cholesterol (statin treatment) confirmed that secretion of apoC-I by HepG2 cells was dependent on cellular cholesterol levels and independent of changes in apoC-I mRNA levels. These results demonstrate that cellular cholesterol rather than triglyceride levels play a role in controlling apoC-I production by HepG2 cells and that this regulation occurs at a post-transcriptional level.

Fatty acids increase presenilin-1 levels and γ-secretase activity in PSwt-1 cells

Presenilin-1 (PS1) is an important determinant of the gamma-secretase activity necessary for the generation of beta-amyloid (Abeta), likely the central pathogenic molecule in Alzheimer's disease. Most presenilin is rapidly degraded, and determinants of the level of the active cleaved form are unknown. We examined the influence of fatty acids on PS1 levels and gamma-secretase activity using stably transfected CHO cells that express human PS1 and the human amyloid precursor protein. Cells cultured with 0.4 mM oleic acid (OA), with 0.1 mM linoleic acid, or with a triglyceride emulsion expressed increased PS1 and Abeta. This effect was independent of any secondary increase in cellular cholesterol. Cells cultured in 0.4 mM OA also exhibited significantly increased gamma-secretase activity. PS1 mRNA levels were unchanged, and pulse-chase experiments indicated that OA slowed presenilin holoprotein degradation. Nontransfected human neuroblastoma cells also showed increased presenilin when cultured in 0.4 mM OA. Lipids may be important biological determinants of PS1 level and gamma-secretase activity.

Synthesis and secretion of apoC-I and apoE during maturation of human SW872 liposarcoma cells

Little is known about the regulation of apolipoprotein (apo) C-I production by human adipocytes. The aim of the present study, therefore, was to investigate the effect of different tissue culture conditions on the synthesis and secretion of apoC-I and apoE in human SW872 liposarcoma cells. After 3-4 d in culture (0.5 x 10(6) cells/well, DMEM/F-12 medium with 10% fetal calf serum), cells reached confluence and became growth arrested. The molar ratio of apoE:apoC-I in the cell was 8.9 +/- 0.6 and in the medium was 6.6 +/- 0.5. After 17 d in culture, SW872 cells contained significantly more cholesterol (100%) and triglyceride (3-fold) and secreted more apoC-I [4 vs. 17 d: 0.11 +/- 0.01 vs. 0.23 +/- 0.01 pmol/(10(6) cells . 24 h), P < 0.001] and apoE [0.7 +/- 0.1 vs. 3.1 +/- 0.3 pmol/(10(6) cells . 24 h), P < 0.001]. Cellular apoC-I increased 7-fold and apoE increased 16-fold. Cell maturation was associated with significantly higher levels of apoE mRNA but not apoC-I mRNA. Increases in cell lipids, apoC-I, and apoE were not dependent on the presence of extracellular lipids because similar changes occurred in cells incubated with lipoprotein-deficient serum or in cells incubated without serum. Treatment (7 d) of cells during maturation with insulin (10 or 1000 nmol/L) significantly reduced the secretion of apoC-I and apoE. These results demonstrate that in maturing SW872 cells, cholesterol and triglyceride accumulation in the presence or absence of extracellular lipids, is associated with increased apoC-I and apoE production. Furthermore, apoC-I and apoE production are differentially regulated at the transcriptional level, and long-term treatment with insulin has an inhibitory rather than stimulatory effect on apoC-I and apoE production.