Aggravated restenosis and atherogenesis in ApoCIII transgenic mice but lack of protection in ApoCIII knockouts: the effect of authentic triglyceride-rich lipoproteins with and without ApoCIII

A novel mouse model of familial combined hyperlipidemia and atherosclerosis

Within the context of residual cardiovascular risk in post-statin era, emerging evidence from epidemiologic and human genetic studies have demonstrated that triglyceride (TG)-rich lipoproteins and their remnants are causally related to cardiovascular risk. While, carriers of loss-of-function mutations of ApoC3 have low TG levels and are protected from cardiovascular disease (CVD). Of translational significance, siRNAs/antisense oligonucleotide (ASO) targeting ApoC3 is beneficial for patients with atherosclerotic CVD. Therefore, animal models of atherosclerosis with both hypercholesterolemia and hypertriglyceridemia are important for the discovery of novel therapeutic strategies targeting TG-lowering on top of traditional cholesterol-lowering. In this study, we constructed a novel mouse model of familial combined hyperlipidemia through inserting a human ApoC3 transgene (hApoC3-Tg) into C57BL/6 J mice and injecting a gain-of-function variant of adeno-associated virus-proprotein convertase subtilisin/kexin type 9 (AAV-PCSK9)-D377Y concurrently with high cholesterol diet (HCD) feeding for 16 weeks. In the last 10 weeks, hApoC3-Tg mice were orally treated with a combination of atorvastatin (10 mg·kg-1·d-1) and fenofibrate (100 mg·kg-1·d-1). HCD-treated hApoC3-Tg mice demonstrated elevated levels of serum TG, total cholesterol (TC) and low density lipoprotein-cholesterol (LDL-C). Oral administration of atorvastatin and fenofibrate significantly decreased the plaque sizes of en face aorta, aortic sinus and innominate artery accompanied by improved lipid profile and distribution. In summary, this novel mouse model is of considerable clinical relevance for evaluation of anti-atherosclerotic drugs by targeting both hypercholesterolemia and hypertriglyceridemia.

APOA1/C3/A4/A5 Gene Cluster at 11q23.3 and Lipid Metabolism Disorders: From Epigenetic Mechanisms to Clinical Practices

The APOA1/C3/A4/A5 cluster is an essential component in regulating lipoprotein metabolism and maintaining plasma lipid homeostasis. A genome-wide association analysis and Mendelian randomization have revealed potential associations between genetic variants within this cluster and lipid metabolism disorders, including hyperlipidemia and cardiovascular events. An enhanced understanding of the complexity of gene regulation has led to growing recognition regarding the role of epigenetic variation in modulating APOA1/C3/A4/A5 gene expression. Intensive research into the epigenetic regulatory patterns of the APOA1/C3/A4/A5 cluster will help increase our understanding of the pathogenesis of lipid metabolism disorders and facilitate the development of new therapeutic approaches. This review discusses the biology of how the APOA1/C3/A4/A5 cluster affects circulating lipoproteins and the current progress in the epigenetic regulation of the APOA1/C3/A4/A5 cluster.

Elevated apolipoprotein C3 augments diabetic kidney disease and associated atherosclerosis in type 2 diabetes

Diabetes increases the risk of both cardiovascular disease and kidney disease. Notably, most of the excess cardiovascular risk in people with diabetes is in those with kidney disease. Apolipoprotein C3 (APOC3) is a key regulator of plasma triglycerides, and it has recently been suggested to play a role in both type 1 diabetes-accelerated atherosclerosis and kidney disease progression. To investigate if APOC3 plays a role in kidney disease in people with type 2 diabetes, we analyzed plasma levels of APOC3 from the Veterans Affairs Diabetes Trial. Elevated baseline APOC3 levels predicted a greater loss of renal function. To mechanistically test if APOC3 plays a role in diabetic kidney disease and associated atherosclerosis, we treated black and tan, brachyury, WT and leptin-deficient (OB; diabetic) mice, a model of type 2 diabetes, with an antisense oligonucleotide (ASO) to APOC3 or a control ASO, all in the setting of human-like dyslipidemia. Silencing APOC3 prevented diabetes-augmented albuminuria, renal glomerular hypertrophy, monocyte recruitment, and macrophage accumulation, partly driven by reduced ICAM1 expression. Furthermore, reduced levels of APOC3 suppressed atherosclerosis associated with diabetes. This suggests that targeting APOC3 might benefit both diabetes-accelerated atherosclerosis and kidney disease.

Effects of a dietary intervention with lacto-ovo-vegetarian and Mediterranean diets on apolipoproteins and inflammatory cytokines: results from the CARDIVEG study

BACKGROUND

Apolipoproteins have been recently proposed as novel markers of cardiovascular disease (CVD) risk. However, evidence regarding effects of diet on apolipoproteins is limited.

AIM

To compare the effects of Mediterranean diet (MD) and lacto-ovo vegetarian diet (VD) on apolipoproteins and traditional CVD risk factors in participants with low-to-moderate CVD risk.

METHODS

Fifty-two participants (39 women; 49.1 ± 12.4 years), followed MD and VD for 3 months each. Medical and dietary information was collected at the baseline. Anthropometric parameters and blood samples were obtained at the beginning and the end of interventions.

RESULTS

MD and VD resulted in significant improvement in anthropometric and lipid profiles. Both diets led to a reduction in most of the inflammatory parameters. As for apolipoproteins, a significant change was observed for ApoC-I after VD (+ 24.4%; p = 0.020). MD led to a negative correlation between ApoC-III and carbohydrates (R = - 0.29; p = 0.039) whereas VD between ApoD and saturated fats (R = - 0.38; p = 0.006). A positive correlation emerged after VD between HDL and ApoD (R = 0.33; p = 0.017) and after MD between plasma triglycerides and ApoC-I (R = 0.32; p = 0.020) and ApoD (R = 0.30; p = 0.031). IL-17 resulted to be positively correlated with ApoB after MD (R = 0.31; p = 0.028) and with ApoC-III after VD (R = 0.32; p = 0.019). Subgroup analysis revealed positive effects on apolipoproteins from both diets, especially in women, individuals older than 50 years-old or with < 3 CVD risk factors.

CONCLUSIONS

Both diets seem to improve CVD risk, however, MD showed a greater positive effect on apolipoproteins in some subgroups, thus suggesting how diet may influence new potential markers of CVD risk.

TRIAL REGISTRATION

registered at clinicaltrials.gov (identifier: NCT02641834) on December 2015.

Development of New Genome Editing Tools for the Treatment of Hyperlipidemia

Hyperlipidemia is a medical condition characterized by high levels of lipids in the blood. It is often associated with an increased risk of cardiovascular diseases such as heart attacks and strokes. Traditional treatment approaches for hyperlipidemia involve lifestyle modifications, dietary changes, and the use of medications like statins. Recent advancements in genome editing technologies, including CRISPR-Cas9, have opened up new possibilities for the treatment of this condition. This review provides a general overview of the main target genes involved in lipid metabolism and highlights the progress made during recent years towards the development of new treatments for dyslipidemia.

A Review of Progress on Targeting LDL Receptor-Dependent and -Independent Pathways for the Treatment of Hypercholesterolemia, a Major Risk Factor of ASCVD

Since the discovery of the LDL receptor in 1973 by Brown and Goldstein as a causative protein in hypercholesterolemia, tremendous amounts of effort have gone into finding ways to manage high LDL cholesterol in familial hypercholesterolemic (HoFH and HeFH) individuals with loss-of-function mutations in the LDL receptor (LDLR) gene. Statins proved to be the first blockbuster drug, helping both HoFH and HeFH individuals by inhibiting the cholesterol synthesis pathway rate-limiting enzyme HMG-CoA reductase and inducing the LDL receptor. However, statins could not achieve the therapeutic goal of LDL. Other therapies targeting LDLR include PCSK9, which lowers LDLR by promoting LDLR degradation. Inducible degrader of LDLR (IDOL) also controls the LDLR protein, but an IDOL-based therapy is yet to be developed. Among the LDLR-independent pathways, such as angiopoietin-like 3 (ANGPTL3), apolipoprotein (apo) B, apoC-III and CETP, only ANGPTL3 offers the advantage of treating both HoFH and HeFH patients and showing relatively better preclinical and clinical efficacy in animal models and hypercholesterolemic individuals, respectively. While loss-of-LDLR-function mutations have been known for decades, gain-of-LDLR-function mutations have recently been identified in some individuals. The new information on gain of LDLR function, together with CRISPR-Cas9 genome/base editing technology to target LDLR and ANGPTL3, offers promise to HoFH and HeFH individuals who are at a higher risk of developing atherosclerotic cardiovascular disease (ASCVD).

Severe hypertriglyceridemia caused by Gpihbp1 deficiency facilitates vascular remodeling through increasing endothelial activation and oxidative stress

Hypertriglyceridemia (HTG) is an independent risk factor for atherosclerosis. However, its impact on non-atherosclerotic cardiovascular diseases remains largely unknown. Glycosylphosphatidylinositol anchored high-density lipoprotein binding protein 1 (GPIHBP1) is essential for the hydrolysis of circulating triglycerides and loss of functional GPIHBP1 causes severe HTG. In this study, we used Gpihbp1 knockout (GKO) mice to investigate the potential effects of HTG on non-atherosclerotic vascular remodeling. We compared the aortic morphology and gene expressions between three-month-old and ten-month-old GKO mice and their age-matched wild-type controls. We also conducted similar comparisons between GKO mice and wild-type controls in an angiotensin II (AngII)-induced vascular remodeling model. Our data showed that the intima-media wall of ten-month-old GKO mice but not three-month-olds was significantly thickened compared to wild-type controls. Moreover, ten-month-old GKO mice but not three-month-olds had increased aortic macrophage infiltration and perivascular fibrosis, along with increased endothelial activation and oxidative stress. Similarly, the AngII-induced vascular remodeling, as well as endothelial activation and oxidative stress, were also exacerbated in the GKO mice compared to wild-type controls. In conclusion, we demonstrated that severe HTG caused by Gpihbp1 deficiency could facilitate the onset and progression of non-atherosclerotic vascular remodeling through endothelial activation and oxidative stress in mice.

Effects of shear stress on vascular endothelial functions in atherosclerosis and potential therapeutic approaches

Different blood flow patterns in the arteries can alter the adaptive phenotype of vascular endothelial cells (ECs), thereby affecting the functions of ECs and are directly associated with the occurrence of lesions in the early stages of atherosclerosis (AS). Atherosclerotic plaques are commonly found at curved or bifurcated arteries, where the blood flow pattern is dominated by oscillating shear stress (OSS). OSS can induce ECs to transform into pro-inflammatory phenotypes, increase cellular inflammation, oxidative stress response, mitochondrial dysfunction, metabolic abnormalities and endothelial permeability, thereby promoting the progression of AS. On the other hand, the straight artery has a stable laminar shear stress (LSS), which promotes the transformation of ECs into an anti-inflammatory phenotype, improves endothelial cell function, thereby inhibits atherosclerotic progression. ECs have the ability to actively sense, integrate, and convert mechanical stimuli by shear stress into biochemical signals that further induces intracellular changes (such as the opening and closing of ion channels, activation and transcription of signaling pathways). Here we not only outline the relationship between functions of vascular ECs and different forms of fluid shear stress in AS, but also aim to provide new solutions for potential atherosclerotic therapies targeting intracellular mechanical transductions.

Postprandial triglyceride-rich lipoproteins promote the adipogenic differentiation of adipose-derived mesenchymal stem cells via the LRP1/caveolin-1/AKT1 pathway

Diet-induced obesity (OB) is usually accompanied by hypertriglyceridemia, which is characterized by the accumulation of triglyceride (TG)-rich lipoprotein (TRL) particles in the circulation. We previously found that postprandial TRL combined with insulin induced the adipogenic differentiation of 3T3-L1 preadipocytes, which may represent a key mechanism underlying obesity. However, the specific mechanism and signaling pathway involved in this process remain to be fully elucidated. In this study, we found that, in the postprandial state, patients with obesity had significantly higher levels of TG and remnant cholesterol (RC) than normal-weight controls. In vitro, we found that postprandial TRL, together with insulin, promoted the adipogenic differentiation of adipose-derived mesenchymal stem cells (AMSCs), as evidenced by the increased expression of lipogenesis-related genes and their protein products, including low-density lipoprotein related protein 1 (LRP1). Besides, caveolin-1 (Cav-1) expression was also significantly upregulated under this condition. Cav-1 and LRP1 were observed to interact, and then led to the activation of the PI3K/AKT1 signaling pathway. Meanwhile, the inhibition of LRP1 or Cav-1 significantly attenuated the adipogenic differentiation of AMSCs and downregulated AKT1 phosphorylation levels. Moreover, treatment with a selective AKT1 inhibitor significantly suppressed postprandial TRL and insulin-induced adipogenesis in AMSCs. Combined, our results demonstrated that, in association with insulin, postprandial TRL can promote the adipogenic differentiation of AMSCs in a manner that is dependent on the LRP1/Cav-1-mediated activation of the PI3K/AKT1 signaling pathway. Our findings indicated that a postprandial increase in TRL content is a critical factor in the pathogenesis of hypertriglyceridemia and diet-induced obesity.

APOC-III: a Gatekeeper in Controlling Triglyceride Metabolism

PURPOSE OF REVIEW

Apolipoprotein C-III (ApoC-III) is a widely known player in triglyceride metabolism, and it has been recently recognized as a polyhedric factor which may regulate several pathways beyond lipid metabolism by influencing cardiovascular, metabolic, and neurological disease risk. This review summarizes the different functions of ApoC-III and underlines the recent findings related to its multifaceted pathophysiological role.

RECENT FINDINGS

The role of ApoC-III has been implicated in HDL metabolism and in the development of atherosclerosis, inflammation, and ER stress in endothelial cells. ApoC-III has been recently considered an important player in insulin resistance mechanisms, lipodystrophy, diabetic dyslipidemia, and postprandial hypertriglyceridemia (PPT). The emerging evidence of the involvement of ApoC-III in the in the pathogenesis of Alzheimer's disease open the way to further study if modification of ApoC-III level slows disease progression. Furthermore, ApoC-III is clearly linked to cardiovascular disease (CVD) risk, and progression of coronary artery disease (CAD) as well as the calcification of aortic valve and recent clinical trials has pointed out the inhibition of ApoC-III as a promising approach to manage hypertriglyceridemia and prevent CVD. Several evidences highlight the role of ApoC-III not only in triglyceride metabolism but also in several cardio-metabolic pathways. Results from recent clinical trials underline that the inhibition of ApoC-III is a promising therapeutical strategy for the management of severe hypertriglyceridemia and in CVD prevention.

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.

CRISPR/CAS9: A promising approach for the research and treatment of cardiovascular diseases

The development of gene-editing technology has been one of the biggest advances in biomedicine over the past two decades. Not only can it be used as a research tool to build a variety of disease models for the exploration of disease pathogenesis at the genetic level, it can also be used for prevention and treatment. This is done by intervening with the expression of target genes and carrying out precise molecular targeted therapy for diseases. The simple and flexible clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene-editing technology overcomes the limitations of zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs). For this reason, it has rapidly become a preferred method for gene editing. As a new gene intervention method, CRISPR/Cas9 has been widely used in the clinical treatment of tumours and rare diseases; however, its application in the field of cardiovascular diseases is currently limited. This article reviews the application of the CRISPR/Cas9 editing technology in cardiovascular disease research and treatment, and discusses the limitations and prospects of this technology.

Apolipoprotein C3 and circulating mediators of preadipocyte proliferation in states of lipodystrophy

Adipogenesis is a complex process controlled by intrinsic and extrinsic factors that regulate preadipocyte proliferation, adipogenic capacity and maturation of metabolic function. Here we show that insulin and IGF-1 receptors are essential for mature adipocyte survival and that deletion of both IR and IGF1R specifically in fat using a tamoxifen inducible-AdipoQ-Cre (Ai-DKO) leads to rapid and severe loss of adipocytes in all depots, associated with a metabolic syndrome characterized by hypertriglyceridemia, hyperglycemia, hyperinsulinemia, fatty liver, and pancreatic beta cell proliferation. In this model, this pathological phenotype reverses over a few weeks, in large part, due to preadipocyte proliferation and adipose tissue regeneration. Incubation of preadipocytes with serum from the Ai-DKO mice in vitro stimulates cell proliferation, and this effect can be mimicked by conditioned media from liver slices of Ai-DKO mice, but not by media of cultured Ai-DKO adipocytes, indicating a hepatic origin of the growth factor. Proteomic analysis of serum reveals apolipoprotein C3 (APOC3), a protein secreted by liver, as one of the most upregulated proteins in the Ai-DKO mice. In vitro, purified and delipidated APOC3 stimulates preadipocyte proliferation, however, knockdown of hepatic APOC3 in vivo in Ai-DKO mice is not sufficient to block adipose regeneration. Thus, lipodystrophy is associated with presence of increased preadipocyte-stimulating growth factors in serum. Our study indicates that APOC3 is one contributing factor to preadipocyte proliferation, however, other still-unidentified circulating growth factors are also likely present in Ai-DKO mice. Identification of these factors may provide a new approach to regulation of adipose mass in health and disease.

Interventional hepatic apoC-III knockdown improves atherosclerotic plaque stability and remodeling by triglyceride lowering

Apolipoprotein C-III (apoC-III) is a critical regulator of triglyceride metabolism and correlates positively with hypertriglyceridemia and cardiovascular disease (CVD). It remains unclear if therapeutic apoC-III lowering reduces CVD risk and if the CVD correlation depends on the lipid-lowering or antiinflammatory properties. We determined the impact of interventional apoC-III lowering on atherogenesis using an apoC-III antisense oligonucleotide (ASO) in 2 hypertriglyceridemic mouse models where the intervention lowers plasma triglycerides and in a third lipid-refractory model. On a high-cholesterol Western diet apoC-III ASO treatment did not alter atherosclerotic lesion size but did attenuate advanced and unstable plaque development in the triglyceride-responsive mouse models. No lesion size or composition improvement was observed with apoC-III ASO in the lipid-refractory mice. To circumvent confounding effects of continuous high-cholesterol feeding, we tested the impact of interventional apoC-III lowering when switching to a cholesterol-poor diet after 12 weeks of Western diet. In this diet switch regimen, apoC-III ASO treatment significantly reduced plasma triglycerides, atherosclerotic lesion progression, and necrotic core area and increased fibrous cap thickness in lipid-responsive mice. Again, apoC-III ASO treatment did not alter triglyceride levels, lesion development, and lesion composition in lipid-refractory mice after the diet switch. Our findings suggest that interventional apoC-III lowering might be an effective strategy to reduce atherosclerosis lesion size and improve plaque stability when lipid lowering is achieved.

Increased atherosclerosis in a mouse model of glycogen storage disease type 1a

Glycogen storage disease type 1a (GSD Ia) is an inborn error of carbohydrate metabolism. Despite severe hyperlipidemia, GSD Ia patients show limited atherogenesis compared to age-and-gender matched controls. Employing a GSD Ia mouse model that resembles the severe hyperlipidemia in patients, we here found increased atherogenesis in GSD Ia. These data provide a rationale for investigating atherogenesis in GSD Ia in a larger patient cohort.

Inflammatory Links Between Hypertriglyceridemia and Atherogenesis

PURPOSE OF REVIEW

Recent studies indicate an association between hypertriglyceridemia (HTG) and atherosclerotic cardiovascular disease (ASCVD). The purpose of this review is to discuss the potential mechanism connecting HTG and ASCVD risk and the potential efficacy of HTG-targeting therapies in ASCVD prevention.

RECENT FINDINGS

HTG, with elevations in triglyceride-rich lipoproteins (TGRL) and their remnants, are causal ASCVD risk factors. The mechanisms whereby HTG increases ASCVD risk are not well understood but may include multiple factors. Inflammation plays a crucial role in atherosclerosis. TGRL compared to low-density lipoproteins (LDL) correlate better with inflammation. TGRL remnants can penetrate endothelium and interact with macrophages leading to foam cell formation and inflammation in arterial walls, thereby contributing to atherogenesis. In addition, circulating monocytes can take up TGRL and become lipid-laden foamy monocytes, which infiltrate the arterial wall and may also contribute to atherogenesis. Novel therapies targeting HTG or inflammation are in development and have potential of reducing residual ASCVD risk associated with HTG. Clinical and preclinical studies show a causal role of HTG in promoting ASCVD, in which inflammation plays a vital role. Novel therapies targeting HTG or inflammation have potential of reducing residual ASCVD risk.

Targeting ApoC3 Paradoxically Aggravates Atherosclerosis in Hamsters With Severe Refractory Hypercholesterolemia

Rationale

ApoC3 plays a central role in the hydrolysis process of triglyceride (TG)-rich lipoproteins mediated by lipoprotein lipase (LPL), which levels are positively associated with the incidence of cardiovascular disease (CVD). Although targeting ApoC3 by antisense oligonucleotide (ASO), Volanesorsen markedly reduces plasma TG level and increase high-density lipoprotein cholesterol (HDL-C) in patients with hypertriglyceridemia (HTG), the cholesterol-lowering effect of ApoC3 inhibition and then the consequential outcome of atherosclerotic cardiovascular disease (ASCVD) have not been reported in patients of familial hypercholesterolemia (FH) with severe refractory hypercholesterolemia yet.

Objective

To investigate the precise effects of depleting ApoC3 on refractory hypercholesterolemia and atherosclerosis, we crossed ApoC3-deficient hamsters with a background of LDLR deficiency to generate a double knockout (DKO) hamster model (LDLR^−/−, XApoC3^−/−, DKO).

Approach and Results

On the standard laboratory diet, DKO hamsters had reduced levels of plasma TG and total cholesterol (TC) relative to LDLR^−/− hamsters. However, upon high-cholesterol/high-fat (HCHF) diet feeding for 12 weeks, ApoC3 deficiency reduced TG level only in female animals without affecting refractory cholesterol in the circulation, whereas apolipoprotein A1 (ApoA1) levels were significantly increased in DKO hamsters with both genders. Unexpectedly, loss of ApoC3 paradoxically accelerated diet-induced atherosclerotic development in female and male LDLR^−/− hamsters but ameliorated fatty liver in female animals. Further analysis of blood biological parameters revealed that lacking ApoC3 resulted in abnormal platelet (PLT) indices, which could potentially contribute to atherosclerosis in LDLR^−/− hamsters.

Conclusions

In this study, our novel findings provide new insight into the application of ApoC3 inhibition for severe refractory hypercholesterolemia and ASCVD.

Is Apo-CIII the new cardiovascular target? An analysis of its current clinical and dietetic therapies

AIMS

Recently, Apolipoprotein CIII (Apo-CIII) has gained remarkable attention since its overexpression has been strongly correlated to cardiovascular disease (CVD) occurrence. The aim of this review was to summarize the latest findings of Apo-CIII as a CVDs and diabetes risk factor, as well as the plausible mechanisms involved in the development of these pathologies, with particular emphasis on current clinical and dietetic therapies.

DATA SYNTHESIS

Apo-CIII is a small protein (∼8.8 kDa) that, among other functions, inhibits lipoprotein lipase, a key enzyme in lipid metabolism. Apo-CIII plays a fundamental role in the physiopathology of atherosclerosis, type-1, and type-2 diabetes. Apo-CIII has become a potential clinical target to tackle these multifactorial diseases. Dietetic (omega-3 fatty acids, stanols, polyphenols, lycopene) and non-dietetic (fibrates, statins, and antisense oligonucleotides) therapies have shown promising results to regulate Apo-CIII and triglyceride levels. However, more information from clinical trials is required to validate it as a new target for atherosclerosis and diabetes types 1 and 2.

CONCLUSIONS

There are still several pathways involving Apo-CIII regulation that might be affected by bioactive compounds that need further research. The mechanisms that trigger metabolic responses following bioactive compounds consumption are mainly related to higher LPL expression and PPARα activation, although the complete pathways are yet to be elucidated.

Distribution of seven ApoC-III glycoforms in plasma, VLDL, IDL, LDL and HDL of healthy subjects

Glycosylation of ApoC-III modulates its function in TG metabolism, with some variants being associated with a more atherogenic lipid profile. These associations have been studied in whole plasma but rarely in individual lipoprotein fractions. In this study, we aimed to measure the relative content of ApoC-III glycoforms in each lipoprotein fraction as a potential biomarker for TG metabolism and cardiovascular risk. Lipoprotein fractions were separated by differential ultracentrifugation of plasma samples from healthy subjects. Relative concentrations of seven ApoC-III variants were measured by MSIA. ApoC-III₁, ApoC-III_0b and ApoC-III₂ were the most abundant glycoforms. There was high interindividual variability in the distribution of glycoforms across the study population but a uniform proportion in all lipoprotein fractions of each given subject. Two ApoC-III variants, ApoC-III_0b and ApoC-III_1d, negatively correlated with plasma and VLDL triglycerides irrespectively of VLDL size and were associated with increased LDL size when transported in LDL particles. ApoC-III_0b also showed a negative correlation with lipoprotein-insulin resistance score. We have been able to measure seven ApoC-III glycoforms in each lipoprotein fraction, setting the basis for future studies exploring their role on cardiovascular risk. Some glycoforms suggest a less proatherogenic role on TG and lipoprotein metabolism. SIGNIFICANCE: Apo CIII has an important role on plasma TG metabolism through different mechanisms and it is also involved in type 1 and type 2 Diabetes Mellitus. Different glycosylated forms of Apo CIII exist and they show different roles. For this reason, this protein has gained interest in the las years and the relationship between ApoC-III glycoforms and lipids, lipoproteins and metabolic disorders has been increasingly studied in the last years. Apo CIII glycoforms have been previously analysed in plasma, and the function of the main four glycoforms has been assessed in a variety of cohorts; but in the present study, ApoC-III glycoforms are measured in each lipoprotein fraction, which may be of clinical interest.

Genetically Engineered Hamster Models of Dyslipidemia and Atherosclerosis

Animal models of human diseases play an extremely important role in biomedical research. Among them, mice are widely used animal models for translational research, especially because of ease of generation of genetically engineered mice. However, because of the great differences in biology between mice and humans, translation of findings to humans remains a major issue. Therefore, the exploration of models with biological and metabolic characteristics closer to those of humans has never stopped.Although pig and nonhuman primates are biologically similar to humans, their genetic engineering is technically difficult, the cost of breeding is high, and the experimental time is long. As a result, the application of these species as model animals, especially genetically engineered model animals, in biomedical research is greatly limited.In terms of lipid metabolism and cardiovascular diseases, hamsters have several characteristics different from rats and mice, but similar to those in humans. The hamster is therefore an ideal animal model for studying lipid metabolism and cardiovascular disease because of its small size and short reproduction period. However, the phenomenon of zygote division, which was unexpectedly blocked during the manipulation of hamster embryos for some unknown reasons, had plagued researchers for decades and no genetically engineered hamsters have therefore been generated as animal models of human diseases for a long time. After solving the problem of in vitro development of hamster zygotes, we successfully prepared enhanced green fluorescent protein (eGFP) transgenic hamsters by microinjection of lentiviral vectors into the zona pellucida space of zygotes. On this basis, we started the development of cardiovascular disease models using the hamster embryo culture system combined with the novel genome editing technique of clustered regularly interspaced short palindromic repeats (CRISPR )/CRISPR associated protein 9 (Cas9). In this chapter, we will introduce some of the genetically engineered hamster models with dyslipidemia and the corresponding characteristics of these models. We hope that the genetically engineered hamster models can be further recognized and complement other genetically engineered animal models such as mice, rats, and rabbits. This will lead to new avenues and pathways for the study of lipid metabolism and its related diseases.

CRISPR/Cas9-mediated knockout of APOC3 stabilizes plasma lipids and inhibits atherosclerosis in rabbits

Background

High levels of apolipoprotein C3 (APOC3) can lead to hypertriglyceridemia, which increases the risk of cardiovascular disease. We aim to create APOC3-knockout (KO) rabbits and explore the effects of APOC3 deletion on the occurrence and development of atherosclerosis.

Methods

An sgRNA anchored to exon 2 of APOC3 was designed to edit embryo genomes using the CRISPR/Cas9 system. The founder rabbits were sequenced, and their lipid profile, inflammatory cytokines, and atherosclerotic plaques were analyzed.

Results

When given a normal chow (NC) diet, all APOC3-KO rabbits had 50% lower triglyceride (TG) levels than those of the matched age control group. Additionally, their plasma lipoprotein lipase increased. When fed a high-fat diet, APOC3 deficiency was observed to be more conducive to the maintenance of plasma TG, total cholesterol, and low-density lipoprotein cholesterol levels, and the inhibition of the inflammatory response and the protection against atherosclerosis in rabbits.

Conclusion

APOC3 deficiency can delay the formation of atherosclerosis-induced HFD in rabbits, indicating this is a novel therapeutic target to treat atherosclerosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-021-01605-7.

Gene Therapy for Cardiovascular Disease: Basic Research and Clinical Prospects

In recent years, the vital role of genetic factors in human diseases have been widely recognized by scholars with the deepening of life science research, accompanied by the rapid development of gene-editing technology. In early years, scientists used homologous recombination technology to establish gene knock-out and gene knock-in animal models, and then appeared the second-generation gene-editing technology zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) that relied on nucleic acid binding proteins and endonucleases and the third-generation gene-editing technology that functioned through protein-nucleic acids complexes-CRISPR/Cas9 system. This holds another promise for refractory diseases and genetic diseases. Cardiovascular disease (CVD) has always been the focus of clinical and basic research because of its high incidence and high disability rate, which seriously affects the long-term survival and quality of life of patients. Because some inherited cardiovascular diseases do not respond well to drug and surgical treatment, researchers are trying to use rapidly developing genetic techniques to develop initial attempts. However, significant obstacles to clinical application of gene therapy still exists, such as insufficient understanding of the nature of cardiovascular disease, limitations of genetic technology, or ethical concerns. This review mainly introduces the types and mechanisms of gene-editing techniques, ethical concerns of gene therapy, the application of gene therapy in atherosclerosis and inheritable cardiovascular diseases, in-stent restenosis, and delivering systems.

Dietary-Induced Elevations of Triglyceride-Rich Lipoproteins Promote Atherosclerosis in the Low-Density Lipoprotein Receptor Knockout Syrian Golden Hamster

Elevated triglycerides are associated with an increased risk of cardiovascular disease (CVD). Therefore, it is very important to understand the metabolism of triglyceride-rich lipoproteins (TRLs) and their atherogenic role in animal models. Using low-density lipoprotein receptor knockout (LDLR^-/-) Syrian golden hamsters, this study showed that unlike LDLR^-/- mice, when LDLR^-/- hamsters were fed a high cholesterol high-fat diet (HFD), they had very high plasma levels of triglycerides and cholesterol. We found that LDLR^-/- hamsters exhibited increased serum TRLs and the ApoB100 and 48 in these particles after being fed with HFD. Treatment with ezetimibe for 2 weeks decreased these large particles but not the LDL. In addition, ezetimibe simultaneously reduced ApoB48 and ApoE in plasma and TRLs. The expression of LRP1 did not change in the liver. These findings suggested that the significantly reduced large particles were mainly chylomicron remnants, and further, the remnants were mainly cleared by the LDL receptor in hamsters. After 40 days on an HFD, LDLR^-/- hamsters had accelerated aortic atherosclerosis, accompanied by severe fatty liver, and ezetimibe treatment reduced the consequences of hyperlipidemia. Compared with the serum from LDLR^-/- hamsters, that from ezetimibe-treated LDLR^-/- hamsters decreased the expression of vascular adhesion factors in vascular endothelial cells and lipid uptake by macrophages. Our results suggested that in the LDLR^-/- hamster model, intestinally-derived lipoprotein remnants are highly atherogenic and the inflammatory response of the endothelium and foam cells from macrophages triggered atherosclerosis. The LDL receptor might be very important for chylomicrons remnant clearance in the Syrian golden hamster, and this may not be compensated by another pathway. We suggest that the LDLR^-/- hamster is a good model for the study of TRLs-related diseases as it mimics more complex hyperlipidemia.

Genetically-engineered hamster models: applications and perspective in dyslipidemia and atherosclerosis-related cardiovascular disease

Cardiovascular disease is the leading cause of morbidity and mortality in both developed and developing countries, in which atherosclerosis triggered by dyslipidemia is the major pathological basis. Over the past 40 years, small rodent animals, such as mice, have been widely used for understanding of human atherosclerosis-related cardiovascular disease (ASCVD) with the advantages of low cost and ease of maintenance and manipulation. However, based on the concept of precision medicine and high demand of translational research, the applications of mouse models for human ASCVD study would be limited due to the natural differences in metabolic features between mice and humans even though they are still the most powerful tools in this research field, indicating that other species with biological similarity to humans need to be considered for studying ASCVD in future. With the development and breakthrough of novel gene editing technology, Syrian golden hamster, a small rodent animal replicating the metabolic characteristics of humans, has been genetically modified, suggesting that gene-targeted hamster models will provide new insights into the precision medicine and translational research of ASCVD. The purpose of this review was to summarize the genetically-modified hamster models with dyslipidemia to date, and their potential applications and perspective for ASCVD.

Downregulation of NK cell activities in Apolipoprotein C-III-induced hyperlipidemia resulting from lipid-induced metabolic reprogramming and crosstalk with lipid-laden dendritic cells

OBJECTIVE

Apolipoprotein C-III (Apoc3) is a key component of triglyceride-rich lipoproteins (TRL). The Apoc3-transgenic mice are characterized by high levels of plasma triglyceride and free fatty acids (FFAs). Apoc3 stimulates human monocytes via activation of the NLRP3 inflammasome. Considering the NK cell downregulation in obese individuals and the possible stimulatory-effects of macrophages, variations of NK cell functions and underlying mechanisms were investigated in mice with Apoc3-induced hyperlipidemia.

METHODS

Variations of activities and glycolipid metabolism in NK cells of the Apoc3-transgenic mice with hyperlipidemia were detected. Molecular mechanisms of lipid-induced metabolic-reprogramming in NK cells were analyzed based on the transcriptome sequencing. Finally, effects of DCs in mice with hyperlipidemia on NK cell functions were determined.

RESULTS

Impaired number and function of NK cells in Apoc3^TG mice was involved with the increased fatty acid oxidation and decreased glycolysis. Increased uptake of FFAs in Apoc3^TG-NK cells contributed to the peroxisome proliferator-activated receptor (PPAR) activation and the downstream PTEN-AKT-mTOR/FOXO1 signaling pathway. Inhibition of PPAR or CPT1α only partly reversed the IFN-γ production of Apoc3^TG-NK cells, but completely restored IFN-γ secretion by palmitic acid-treated NK cells ex vivo, indicating that other factors contributed to the Apoc3^TG-NK cell downregulation. Meanwhile, Apoc3^TG-DCs, which contained more lipids in the cytoplasm, depended on reactive oxygen species (ROS) to increase the expressions PD-L1, TGF-β1, and NKG2D ligands and suppress NK cell activities. DCs of the Apoc3^TG-CD36^-/+ hybrid mice with less intracellular lipids and ROS production could not inhibit NK cells, indicating that intracellular FFAs promoted the immune-modulatory function of DCs.

CONCLUSIONS

The downregulation of NK cell activities in individuals with Apoc3-induced hyperlipidemia was due to the increased fatty acid oxidation in NK cells and the bystander suppression caused by lipid-laden DCs. The dual recovery function of NK cells and DCs would improve the prognosis of patients with metabolic syndrome.

Apolipoprotein C3 aggravates diabetic nephropathy in type 1 diabetes by activating the renal TLR2/NF-κB pathway

OBJECTIVE

Apolipoprotein C3 (ApoC3) is a regulator of triglyceride metabolism and inflammation, and its plasma levels are positively correlated with the progression of diabetic nephropathy (DN) in patients. However, the role and underlying mechanism of ApoC3 in DN remain unclear.

METHODS

Diabetes was induced in ApoC3 transgenic (Tg) and knockout (KO) mice by injection of streptozotocin. We studied the effect of ApoC3 on type 1 DN after 4 months of diabetes. Plasma glucose and lipid levels, renal function parameters and inflammation- and fibrogenesis-related gene and protein expression levels were studied. In vitro, human mesangial cells (HMCs) were incubated with high levels of glucose or/and triglyceride-rich lipoproteins (TRLs) with a high or low ApoC3 content isolated from Tg or wild-type (WT) mice, respectively, to explore the mechanisms of ApoC3 on development of DN.

RESULTS

We found that compared to WT mice, Tg mice exhibited hypertriglyceridemia (HTG), aggravated early renal function injury and inflammation, enlarged glomerular and mesangial surface areas, renal lipid deposition and elevated fibrogenesis-related gene expression levels after 4 months of diabetes. ApoC3 overexpression activated the renal Toll-like receptor 2 (TLR2) and nuclear factor-κB (NF-κB) signaling pathways and increased the renal gene and protein expression levels of the downstream inflammatory factors TNF-α, VCAM-1 and MCP-1. Unfortunately, we did not find that ApoC3 deficiency had an obvious protective effect against DN. In vitro, we found that TRLs with a high ApoC3 content increased the gene and protein expression levels of inflammation- and fibrogenesis-related factors in HMCs compared to those following administration of the same concentration of TRLs with a low ApoC3 content. These effects of ApoC3 were inhibited by blockade of TLR2 or NF-κB.

CONCLUSIONS

These findings suggest that ApoC3 aggravates early-stage DN by activating the renal TLR2/NF-κB pathway which is partially independent of HTG.

Lowering apolipoprotein CIII protects against high-fat diet-induced metabolic derangements

Increased levels of apolipoprotein CIII (apoCIII), a key regulator of lipid metabolism, result in obesity-related metabolic derangements. We investigated mechanistically whether lowering or preventing high-fat diet (HFD)–induced increase in apoCIII protects against the detrimental metabolic consequences. Mice, first fed HFD for 10 weeks and thereafter also given an antisense (ASO) to lower apoCIII, already showed reduced levels of apoCIII and metabolic improvements after 4 weeks, despite maintained obesity. Prolonged ASO treatment reversed the metabolic phenotype due to increased lipase activity and receptor-mediated hepatic uptake of lipids. Fatty acids were transferred to the ketogenic pathway, and ketones were used in brown adipose tissue (BAT). This resulted in no fat accumulation and preserved morphology and function of liver and BAT. If ASO treatment started simultaneously with the HFD, mice remained lean and metabolically healthy. Thus, lowering apoCIII protects against and reverses the HFD-induced metabolic phenotype by promoting physiological insulin sensitivity.

Apolipoprotein C-III and cardiovascular diseases: when genetics meet molecular pathologies

Cardiovascular diseases (CVD) have overtaken infectious diseases and are currently the world's top killer. A quite strong linkage between this type of ailments and elevated plasma levels of triglycerides (TG) has been always noticed. Notably, this risk factor is mired in deep confusion, since its role in atherosclerosis is uncertain. One of the explanations that aim to decipher this persistent enigma was provided by apolipoprotein C-III (apoC-III), a small protein historically recognized as an important regulator of TG metabolism. Preeminently, hundreds of studies have been carried out in order to explore the APOC3 genetic background, as well as to establish a correlation between its variants and dyslipidemia-related disorders, pointing to an earnest predictive power for future outcomes. Among several polymorphisms reported within the APOC3, the SstI site in its 3'-untranslated region (3'-UTR) was the most consistently and robustly associated with an increased CVD risk. As more genetic data supporting its importance in cardiovascular events aggregate, it was declared, correspondingly, that apoC-III exerts various atherogenic effects, either by intervening in the function and catabolism of many lipoproteins, or by inducing endothelial inflammation and smooth muscle cells (SMC) proliferation. This review was designed to shed the light on the structural and functional aspects of the APOC3 gene, the existing association between its SstI polymorphism and CVD, and the specific molecular mechanisms that underlie apoC-III pathological implications. In addition, the translation of all these gathered knowledges into preventive and therapeutic benefits will be detailed too.

Bletilla striata Polysaccharide Prevents Restenosis of Vein Graft Through Inhibiting Cell Proliferation in Rat Model

Coronary artery bypass grafting (CABG) is still the most effective method for the treatment of coronary heart disease at present. However, the restenosis of vein grafts following surgery is an important complication of CABG. In this study, Bletilla striata polysaccharide (BSP), which has anti-inflammatory and antiproliferative properties, was used to prevent or delay the proliferation of venous bridge endothelial cells in a rat model. We transplanted the autogenous jugular vein to the rat carotid artery, and wrapped it with BSP. We carried out experiments in 4 groups (with 24 rats in each group): a high-BSP dose group (the HBG group, 10 mg), a low-BSP dose group (the LBG group, 3 mg), a pluronic gel group (the gel group), and a control group. Vein grafts were then harvested after 3, 14, and 28 days. Following transplantation, we used color Doppler ultrasound to assess the patency of the transplanted vein. The grafted veins were stained with hematoxylin and eosin (H&E) and Masson to measure the thickness of the intima and media of the blood vessels. Proliferating cell nuclear antigen (PCNA) and vascular cell adhesion molecule-l (VCAM-1) were assessed in vein grafts by immunohistochemistry and western blotting. We detected a significant reduction in the proliferation of endothelial cells in the BSP group compared with the control group (P < 0.05). H&E and Masson's trichrome staining showed that the extent of intimal hyperplasia in transplanted veins from the high BSP group (HBS) (67.42 ± 0.54 µm) and low BSP group (LBS) (120.83 ± 1.87 µm) groups was significantly lower than that in the control group (257.03 ± 2.74 µm, P < 0.05), and that the extent of intimal hyperplasia in the HBS group was lower than that in the LBS group (P < 0.05). We found that the effect of BSP was dose-dependent, as high-dose BSP had a more significant inhibitory effect on cell proliferation than low-dose BSP (P < 0.05). The results of immunohistochemistry and western blotting showed that PCNA and VCAM-1 were significantly downregulated in the BSP treatment group on days 14 and 28 (P < 0.05). BSP inhibits the proliferation of vascular endothelial cells and reduces the expression of VCAM-1, thereby inhibiting the restenosis of graft veins.

ApoCIII: A multifaceted protein in cardiometabolic disease

ApoCIII has a well-recognized role in triglyceride-rich lipoproteins metabolism. A considerable amount of data has clearly highlighted that high levels of ApoCIII lead to hypertriglyceridemia and, thereby, may influence the risk of cardiovascular disease. However, recent findings indicate that ApoCIII might also act beyond lipid metabolism. Indeed, ApoCIII has been implicated in other physiological processes such as glucose homeostasis, monocyte adhesion, activation of inflammatory pathways, and modulation of the coagulation cascade. As the inhibition of ApoCIII is emerging as a new promising therapeutic strategy, the complete understanding of multifaceted pathophysiological role of this apoprotein may be relevant. Therefore, the purpose of this work is to review available evidences not only related to genetics and biochemistry of ApoCIII, but also highlighting the role of this apoprotein in triglyceride and glucose metabolism, in the inflammatory process and coagulation cascade as well as in cardiovascular disease.

Current Understanding of the Relationship of HDL Composition, Structure and Function to Their Cardioprotective Properties in Chronic Kidney Disease

In the general population, the ability of high-density lipoproteins (HDLs) to promote cholesterol efflux is a predictor of cardiovascular events, independently of HDL cholesterol levels. Although patients with chronic kidney disease (CKD) have a high burden of cardiovascular morbidity and mortality, neither serum levels of HDL cholesterol, nor cholesterol efflux capacity associate with cardiovascular events. Important for the following discussion on the role of HDL in CKD is the notion that traditional atherosclerotic cardiovascular risk factors only partially account for this increased incidence of cardiovascular disease in CKD. As a potential explanation, across the spectrum of cardiovascular disease, the relative contribution of atherosclerotic cardiovascular disease becomes less important with advanced CKD. Impaired renal function directly affects the metabolism, composition and functionality of HDL particles. HDLs themselves are a heterogeneous population of particles with distinct sizes and protein composition, all of them affecting the functionality of HDL. Therefore, a more specific approach investigating the functional and compositional features of HDL subclasses might be a valuable strategy to decipher the potential link between HDL, cardiovascular disease and CKD. This review summarizes the current understanding of the relationship of HDL composition, metabolism and function to their cardio-protective properties in CKD, with a focus on CKD-induced changes in the HDL proteome and reverse cholesterol transport capacity. We also will highlight the gaps in the current knowledge regarding important aspects of HDL biology.

Apolipoprotein CIII Deficiency Protects Against Atherosclerosis in Knockout Rabbits

OBJECTIVE

Apo (apolipoprotein) CIII mediates the metabolism of triglyceride (TG)-rich lipoproteins. High levels of plasma apoCIII are positively correlated with the plasma TG levels and increase the cardiovascular risk. However, whether apoCIII is directly involved in the development of atherosclerosis has not been fully elucidated. Approach and Results: To examine the possible roles of apoCIII in lipoprotein metabolism and atherosclerosis, we generated apoCIII KO (knockout) rabbits using ZFN (zinc finger nuclease) technique. On a normal standard diet, apoCIII KO rabbits exhibited significantly lower plasma levels of TG than those of WT (wild type) rabbits while total cholesterol and HDL (high-density lipoprotein) cholesterol levels were unchanged. Analysis of lipoproteins isolated by sequential ultracentrifugation revealed that reduced plasma TG levels in KO rabbits were accompanied by prominent reduction of VLDLs (very-low-density lipoproteins) and IDLs (intermediate-density lipoproteins). In addition, KO rabbits showed faster TG clearance rate after intravenous fat load than WT rabbits. On a cholesterol-rich diet, KO rabbits exhibited constantly and significantly lower levels of plasma total cholesterol and TG than WT rabbits, which was caused by a remarkable reduction of β-VLDLs-the major atherogenic lipoproteins. β-VLDLs of KO rabbits showed higher uptake by cultured hepatocytes and were cleared faster from the circulation than β-VLDLs isolated from WT rabbits. Both aortic and coronary atherosclerosis was significantly reduced in KO rabbits compared with WT rabbits.

CONCLUSIONS

These results indicate that apoCIII deficiency facilitates TG-rich lipoprotein catabolism, and therapeutic inhibition of apoCIII expression may become a novel means not only for the treatment of hyperlipidemia but also for atherosclerosis.

Emerging Targets for Cardiovascular Disease Prevention in Diabetes

Type 1 and type 2 diabetes mellitus (T1DM and T2DM) increase the risk of atherosclerotic cardiovascular disease (CVD), resulting in acute cardiovascular events, such as heart attack and stroke. Recent clinical trials point toward new treatment and prevention strategies for cardiovascular complications of T2DM. New antidiabetic agents show unexpected cardioprotective benefits. Moreover, genetic and reverse translational strategies have revealed potential novel targets for CVD prevention in diabetes, including inhibition of apolipoprotein C3 (APOC3). Modeling and pharmacology-based approaches to improve insulin action provide additional potential strategies to combat CVD. The development of new strategies for improved diabetes and lipid control fuels hope for future prevention of CVD associated with diabetes.

Is APOC3 the driver of cardiovascular disease in people with type I diabetes mellitus?

In this issue of the JCI, Kanter et al. make a strong case for implicating apolipoprotein C3 (APOC3) as a central player in atherosclerotic cardiovascular disease that is commonly seen in individuals with type 1 diabetes mellitus (T1DM). Kanter and colleagues suggest that insulin deficiency elevates plasma APOC3 as well as atherogenic triglyceride-rich (TG-rich) lipoproteins (TRLs). Using two mouse models of T1DM, the authors investigated APOC3-mediated inhibition of both TG hydrolysis by lipoprotein lipase and hepatic uptake of remnant lipoproteins. They suggest that poorly catabolized lipoproteins, enriched in both APOC3 and APOE content, are particularly atherogenic. Notably, treating both mouse models with an APOC3 antisense oligonucleotide lowered both plasma APOC3 and TRLs, and prevented atherosclerosis. These impactful mouse studies were supported by the initial finding that APOC3 predicted coronary artery disease events in participants of the prospective Coronary Artery Calcification in Type 1 Diabetes study with normal TG levels.

Hypertriglyceridemia and Atherosclerosis: Using Human Research to Guide Mechanistic Studies in Animal Models

Human studies support a strong association between hypertriglyceridemia and atherosclerotic cardiovascular disease (CVD). However, whether a causal relationship exists between hypertriglyceridemia and increased CVD risk is still unclear. One plausible explanation for the difficulty establishing a clear causal role for hypertriglyceridemia in CVD risk is that lipolysis products of triglyceride-rich lipoproteins (TRLs), rather than the TRLs themselves, are the likely mediators of increased CVD risk. This hypothesis is supported by studies of rare mutations in humans resulting in impaired clearance of such lipolysis products (remnant lipoprotein particles; RLPs). Several animal models of hypertriglyceridemia support this hypothesis and have provided additional mechanistic understanding. Mice deficient in lipoprotein lipase (LPL), the major vascular enzyme responsible for TRL lipolysis and generation of RLPs, or its endothelial anchor GPIHBP1, are severely hypertriglyceridemic but develop only minimal atherosclerosis as compared with animal models deficient in apolipoprotein (APO) E, which is required to clear TRLs and RLPs. Likewise, animal models convincingly show that increased clearance of TRLs and RLPs by LPL activation (achieved by inhibition of APOC3, ANGPTL3, or ANGPTL4 action, or increased APOA5) results in protection from atherosclerosis. Mechanistic studies suggest that RLPs are more atherogenic than large TRLs because they more readily enter the artery wall, and because they are enriched in cholesterol relative to triglycerides, which promotes pro-atherogenic effects in lesional cells. Other mechanistic studies show that hepatic receptors (LDLR and LRP1) and APOE are critical for RLP clearance. Thus, studies in animal models have provided additional mechanistic insight and generally agree with the hypothesis that RLPs derived from TRLs are highly atherogenic whereas hypertriglyceridemia due to accumulation of very large TRLs in plasma is not markedly atherogenic in the absence of TRL lipolysis products.

Large triglyceride-rich lipoproteins in hypertriglyceridemia are associated with the severity of acute pancreatitis in experimental mice

Hypertriglyceridemia severity is linked to acute pancreatitis prognosis, but it remains unknown why a portion of severe hypertriglyceridemia patients do not develop severe acute pancreatitis. To investigate whether hypertriglyceridemia subtypes affect acute pancreatitis progression, we analyzed two genetically modified hypertriglyceridemia mouse models—namely, glycosylphosphatidylinositol high-density lipoprotein binding protein 1 knockout (Gpihbp1−/−) and apolipoprotein C3 transgenic (ApoC3-tg) mice. Acute pancreatitis was induced by 10 intraperitoneal caerulein injections. Biochemical assays and pathological analysis were performed for the severity evaluation of acute pancreatitis. Plasma triglyceride-rich lipoproteins (TRLs), including chylomicrons and very low-density lipoprotein (VLDL), were collected via ultracentrifugation to evaluate their cytotoxic effects on primary pancreatic acinar cells (PACs). We found that the particle sizes of Gpihbp1−/− TRLs were larger than ApoC3-tg TRLs. Severe pancreatic injury with large areas of pancreatic necrosis in the entire lobule was induced in Gpihbp1−/− mice when plasma triglyceride levels were greater than 2000 mg/dL. However, ApoC3-tg mice with the same triglyceride levels did not develop large areas of pancreatic necrosis, even upon the administration of poloxamer 407 to further increase triglyceride levels. Meanwhile, in the acute pancreatitis model, free fatty acids (FFAs) in the pancreas of Gpihbp1−/− mice were greater than in ApoC3-tg mice. TRLs from Gpihbp1−/− mice released more FFAs and were more toxic to PACs than those from ApoC3-tg mice. Chylomicrons from patients showed the same effects on PACs as TRLs from Gpihbp1−/− mice. Gpihbp1−/− mice with triglyceride levels below 2000 mg/dL had milder pancreatic injury and less incidence of pancreatic necrosis than those with triglyceride levels above 2000 mg/dL, similar to Gpihbp1−/−mice with triglyceride levels above 2000 mg/dL but with fenofibrate administration. These findings demonstrated that hypertriglyceridemia subtypes with large TRL particles could affect acute pancreatitis progression and that chylomicrons showed more cytotoxicity than VLDL by releasing more FFAs.

Increased apolipoprotein C3 drives cardiovascular risk in type 1 diabetes

Type 1 diabetes mellitus (T1DM) increases the risk of atherosclerotic cardiovascular disease (CVD) in humans by poorly understood mechanisms. Using mouse models of T1DM-accelerated atherosclerosis, we found that relative insulin deficiency rather than hyperglycemia elevated levels of apolipoprotein C3 (APOC3), an apolipoprotein that prevents clearance of triglyceride-rich lipoproteins (TRLs) and their remnants. We then showed that serum APOC3 levels predict incident CVD events in subjects with T1DM in the Coronary Artery Calcification in Type 1 Diabetes (CACTI) study. To explore underlying mechanisms, we investigated the impact of Apoc3 antisense oligonucleotides (ASOs) on lipoprotein metabolism and atherosclerosis in a mouse model of T1DM. Apoc3 ASO treatment abolished the increased hepatic Apoc3 expression in diabetic mice - resulting in lower levels of TRLs - without improving glycemic control. APOC3 suppression also prevented arterial accumulation of APOC3-containing lipoprotein particles, macrophage foam cell formation, and the accelerated atherosclerosis in diabetic mice. Our observations demonstrate that relative insulin deficiency increases APOC3 and that this results in elevated levels of TRLs and accelerated atherosclerosis in a mouse model of T1DM. Because serum levels of APOC3 predicted incident CVD events in the CACTI study, inhibiting APOC3 might reduce CVD risk in T1DM patients.

Electronegative LDL: An Active Player in Atherogenesis or a By- Product of Atherosclerosis?

Low-density lipoproteins (LDLs) are the major plasma carriers of cholesterol. However, LDL particles must undergo various molecular modifications to promote the development of atherosclerotic lesions. Modified LDL can be generated by different mechanisms, but as a common trait, show an increased electronegative charge of the LDL particle. A subfraction of LDL with increased electronegative charge (LDL(-)), which can be isolated from blood, exhibits several pro-atherogenic characteristics. LDL(-) is heterogeneous, due to its multiple origins but is strongly related to the development of atherosclerosis. Nevertheless, the implication of LDL(-) in a broad array of pathologic conditions is complex and in some cases anti-atherogenic LDL(-) properties have been reported. In fact, several molecular modifications generating LDL(-) have been widely studied, but it remains unknown as to whether these different mechanisms are specific or common to different pathological disorders. In this review, we attempt to address these issues examining the most recent findings on the biology of LDL(-) and discussing the relationship between this LDL subfraction and the development of different diseases with increased cardiovascular risk. Finally, the review highlights the importance of minor apolipoproteins associated with LDL(-) which would play a crucial role in the different properties displayed by these modified LDL particles.

Endoplasmic Reticulum Stress: A Critical Molecular Driver of Endothelial Dysfunction and Cardiovascular Disturbances Associated with Diabetes

Physical inactivity and sedentary lifestyle contribute to the widespread epidemic of obesity among both adults and children leading to rising cases of diabetes. Cardiovascular disease complications associated with obesity and diabetes are closely linked to insulin resistance and its complex implications on vascular cells particularly endothelial cells. Endoplasmic reticulum (ER) stress is activated following disruption in post-translational protein folding and maturation within the ER in metabolic conditions characterized by heavy demand on protein synthesis, such as obesity and diabetes. ER stress has gained much interest as a key bridging and converging molecular link between insulin resistance, oxidative stress, and endothelial cell dysfunction and, hence, represents an interesting drug target for diabetes and its cardiovascular complications. We reviewed here the role of ER stress in endothelial cell dysfunction, the primary step in the onset of atherosclerosis and cardiovascular disease. We specifically focused on the contribution of oxidative stress, insulin resistance, endothelial cell death, and cellular inflammation caused by ER stress in endothelial cell dysfunction and the process of atherogenesis.

Increased inflammation, endoplasmic reticulum stress and oxidative stress in endothelial and macrophage cells exacerbate atherosclerosis in ApoCIII transgenic mice

Background

Overexpression of apolipoprotein CIII (ApoCIII) leads to hypertriglyceridemia (HTG) which promotes atherosclerosis development. However, it remains unclear whether ApoCIII affects the atherosclerosis alone by promoting the inflammation and endoplasmic reticulum (ER) stress, or in combination with HTG.

Methods

Transgenic (ApoCIIItg) mouse models were used to investigate the atherogenic role of ApoCIII. Since endothelial cells and macrophages play crucial roles in atherosclerosis, we examined whether triglyceride-rich lipoproteins (TRLs), the major lipoproteins, in plasma of ApoCIIItg mice affect inflammation and ER stress levels in these cells. To further investigate the role of ApoCIII and triglyceride, we incubated HUVECs cells and peritoneal macrophages with TRLs with or without ApoCIII.

Results

Increased inflammation and ER stress were found in the aorta of ApoCIIItg mice. TRLs increased ER stress and oxidative stress in HUVECs and macrophages in a dose dependent. Moreover, TRLs together with ApoCIII could induce a higher inflammation level than TRLs alone in these cells.

Conclusions

Both TRLs and ApoCIII contribute to the progression of atherosclerosis, and the modulation of TRLs and ApoCIII may represent a novel therapeutic approach against HTG induced atherosclerosis.

Proteomic Analysis of Charcoal-Stripped Fetal Bovine Serum Reveals Changes in the Insulin-like Growth Factor Signaling Pathway

Charcoal-stripped fetal bovine serum (CS-FBS) is commonly used to study androgen responsiveness and androgen metabolism in cultured prostate cancer (CaP) cells. Switching CaP cells from FBS to CS-FBS may reduce the activity of androgen receptor (AR), inhibit cell proliferation, or modulate intracellular androgen metabolism. The removal of proteins by charcoal stripping may cause changes in biological functions and has not yet been investigated. Here we profiled proteins in FBS and CS-FBS using an ion-current-based quantitative platform consisting of reproducible surfactant-aided precipitation/on-pellet digestion, long-column nanoliquid chromatography separation, and ion-current-based analysis. A total of 143 proteins were identified in FBS, among which 14 proteins including insulin-like growth factor 2 (IGF-2) and IGF binding protein (IGFBP)-2 and -6 were reduced in CS-FBS. IGF-1 receptor (IGF1R) and insulin receptor were sensitized to IGFs in CS-FBS. IGF-1 and IGF-2 stimulation fully compensated for the loss of AR activity to maintain cell growth in CS-FBS. Endogenous production of IGF and IGFBPs was verified in CaP cells and clinical CaP specimens. This study provided the most comprehensive protein profiles of FBS and CS-FBS and offered an opportunity to identify new protein regulators and signaling pathways that regulate AR activity, androgen metabolism, and proliferation of CaP cells.

ApoCIII as a Cardiovascular Risk Factor and Modulation by the Novel Lipid-Lowering Agent Volanesorsen

PURPOSE OF REVIEW

Apolipoprotein CIII (ApoCIII) is now recognized as a key regulator in severe hypertriglyceridemia, chylomicronemia, and conditions of triglyceride-rich lipoprotein (TRL) remnant excess due to its inhibition of lipoprotein lipase (LPL) and hepatic lipase, leading to decreased hepatic reuptake of TRLs, as well as enhanced synthesis and secretion of VLDL from the liver. ApoCIII gain-of-function mutations are associated with atherosclerosis and coronary heart disease (CHD), and contribute to the development of cardiometabolic syndrome, hypertriglyceridemia, and type 2 diabetes mellitus. Conversely, loss-of-function mutations in ApoCIII are associated with lower levels of plasma triglycerides (TG), attenuation of vascular inflammatory processes such as monocyte adhesion and endothelial dysfunction, and potentially, a reduction in the incidence and progression of atherosclerosis and cardioprotection.

RECENT FINDINGS

Evidence is now emerging that volanesorsen, a second-generation antisense oligonucleotide drug targeting ApoCIII messenger RNA resulting in decreases in TG in patients with familial chylomicronemia syndrome, severe hypertriglyceridemia, and metabolic dyslipidemia with type 2 diabetes giving support to the hypothesis that ApoCIII is a powerful inhibitor of LPL, and when reduced, endogenous clearance of TRLs can result in substantial reductions in TG levels. Discovery of the ApoCIII inhibitor volanesorsen opens a new era of lipid-lowering drugs for reduction in TG and potentially for reduction in LDL-C. Herein, this review will provide an update on the pathophysiology of ApoCIII-linked atherosclerosis and the development of the first drug to target ApoCIII, volanesorsen, as a promising lipid-lowering agent.

Association of apolipoprotein-CIII (apoC-III), endothelium-dependent vasodilation and peripheral neuropathy in a multi-ethnic population with type 2 diabetes

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a common complication of Type 2 diabetes (T2D). Apart from hyperglycemia, its pathogenesis is poorly understood. Apolipoprotein-CIII (apoC-III) associated with triglyceride metabolism, is a risk factor for cardiovascular disease. Its role in DPN is not well-established. We studied the associations of apoC-III, endothelial function and DPN.

METHODS

In patients with T2D, anthropometric data, fasting blood, and urine were collected for biochemistry and urine albumin/creatinine measurements (uACR). Endothelial function assessments were performed by laser Doppler flowmetry/imaging. DPN was considered present if there was an abnormal finding in monofilament (≤8 of 10 points) or neurothesiometer testing≥25V on either foot. Plasma apoC-III was assessed by ELISA.

RESULTS

Monofilament and neurothesiometer readings were measured in 1981 patients, mean age 57.4±10.8 years old. DPN prevalence was 10.8% (n=214). Patients with DPN compared to those without, were significantly older (p<0.0001), with longer duration of T2D (p<0.0001), had higher BMI (p=0.006), higher glucose (p=0.015) and HbA1c (p<0.0001), Systolic blood pressure (SBP) (p<0.0001), lower eGFR (p<0.0001), higher urine ACR (p<0.0001), poorer endothelium-dependent and endothelium-independent vasodilation (both p<0.0001), higher VCAM-1 (p<0.0001) and higher apoC-III [285.3 (195.2-405.6) vs 242.9(165.0-344.0) μg/ml]. After adjustment, log transformed apoC-III, remained independently associated with the presence of DPN (B=0.965, SE=0.397, p=0.015).

CONCLUSION

Plasma apoC-III is higher in patients with DPN. Apart from its known association with lipids and macrovascular complications, this study suggests its association with DPN. Whether regulating apoC-III metabolism may be an important new therapeutic approach to managing dyslipidemia and microvascular complications in T2D remains to be proven in future mechanistic and clinical studies.

Abnormal expression of long non-coding RNAs in myocardial infarction

Myocardial infarction (MI) is the leading cause of fatality worldwide. Our study aimed to investigate the dysregulated long non-coding RNA (lncRNA) in MI and elucidate the mechanism of it in MI. The lncRNA and mRNA expression profiling of the whole left ventricular tissue of MI mice model (8 mice) and Sham group (8 mice) was obtained based on microarray analysis. Differentially expressed lnRNAs/mRNA (DELs/DEMs) were identified in MI. DELs/DEMs co-expression network construction, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were conducted to predict the biological functions of DEMs. Quantitative real-time polymerase chain reaction (qRT-PCR) was subjected to validate the abnormally expressed DELs in left ventricular tissues of MI mice model. Total of 168 DELs (37 up- and 131 down-regulated) and 126 DEMs (87 up- and 39 down-regulated) were identified in MI compared with Sham group. The co-expression network of candidate DELs and DEMs was constructed, which covered 219 nodes and 1775 edges. The qRT-PCR validation results indicated that ENSMUST00000124047 was significantly down-regulated in MI group and AK166279 was significantly up-regulated in MI group. ENSMUST00000121611 and NR_015515 had the up-regulated tendency in MI group compared with Sham group. The DEMs in MI were significantly enriched in 41 signaling pathways including complement and coagulation cascades, cytokine-cytokine receptor interaction and chemokine signaling pathway. The expression profiling of dysregulated DELs in MI was identified. Our results might provide useful information for exploring the pathogenesis mechanism of MI.

The emerging role of apolipoprotein C-III: beyond effects on triglyceride metabolism

Apolipoprotein C-III has been referred to as an important participant in the metabolism of triglyceride-rich lipoproteins, leading to hypertriglyceridemia and thereafter cardiovascular disease. Accumulating evidence indicates that apolipoprotein C-III is a multifaceted protein which not only regulates triglyceride metabolism, but also participates in the atherosclerotic lesion formation and several other pathological processes involved in atherosclerosis. Based on data from experiments and clinical trials, some novel therapies such as antisense technology emerge.