Sorting out cholesterol and coronary artery disease

Diagnostic potential of SORT1 gene in coronary artery disease

BACKGROUND

Genome-wide association studies identify SORT1 gene associated with risk of coronary artery disease (CAD). Sortilin protein enhances LDL absorption, form cell development, and atherosclerosis in macrophages.

AIM

We therefore explored SORT1 expression in CAD patients and its gene expression's predictive usefulness for the severity of the disease.

METHODOLOGY

This is a case control study and Quantitative real-time PCR; Sandwich ELISA and western blotting were used to determine the expression of SORT1 gene at the mRNA and protein level in two hundred healthy controls and two hundred patients with various CAD syndromes.

RESULTS

CAD patients exhibit higher SORT1 gene expression in CAD patients, a higher concentration of sortilin in their plasma, and distinct expression patterns in various CAD syndromes. The study reveals a positive correlation between gene expression and the severity of coronary artery stenosis, the number of diseased vessels, and the presence of diabetes. ROC curve analysis of SORT1 gene expression both at mRNA and protein level showed strong discrimination between significant CAD and control subjects.

CONCLUSION

Therefore, elevated SORT1 gene expression in various CAD syndromes may be a potential biomarker for the disease.

Serum sortilin as a predictor of stroke in patients with intermediate carotid artery stenosis

BACKGROUND

Sortilin was an important molecular protein involved in the pathogenesis of atherosclerosis. Besides, serum sortilin was associated with adverse cerebrovascular events. Atherosclerotic stenosis in the carotid artery is a major etiology for ischemic stroke. The risk of stroke in patients with intermediate carotid artery stenosis (CAS) was unknown. Hence, the aim of the present study was to evaluate the relationship between serum sortilin levels and stroke in patients with intermediate CAS.

METHODS

A total of 195 intermediate CAS patients were included in this cross-sectional study. The patients were divided into two groups as symptomatic (N = 95) and asymptomatic (N = 100) patients. Patients with a transient ischemic attack (TIA), retinal ischemic event, or ischemic stroke resulting from the narrowed carotid artery were considered to be symptomatic. Serum sortilin concentrations were measured using the enzyme-linked immunosorbent assay.

RESULTS

Serum sortilin level was significantly higher in the symptomatic group than in the severe asymptomatic group (1.53 ± 0.25 ng/mL vs 1.34 ± 0.19 ng/mL, p < 0.001). Besides, high serum sortilin levels (odds ratio = 4.91, 95% confidence intervals 1.24-19.51, p = 0.023) were identified as independent predictors of symptomatic carotid plaque. In the receiver operating characteristic curve analysis, serum sortilin levels higher than 1.34 ng/mL predicted stroke/TIA with a sensitivity of 66.3% and a specificity of 67% (AUC = 0.725, p < 0.001).

CONCLUSIONS

Serum sortilin level is increased in the presence of symptomatic intermediate CAS and may have clinical value in the management of patients with carotid artery disease.

Sortilin and Homocysteine as Potential Biomarkers for Coronary Artery Diseases

Purpose

The aim of this study was to assess the relationship of coronary artery disease (CAD) with levels of homocysteine and sortilin in Egyptian patients.

Background

CAD is a primary contributor to cardiac disease and a prominent cause of death globally.

Patients and Methods

We enrolled 45 patients with CAD evaluated by coronary CT angiography and 42 control subjects without CAD. Plasma-homocysteine and -sortilin levels were measured with a commercial ELISA kit.

Results

Elevated levels of homocysteine and sortilin were observed in the CAD patients compared to controls (13.75±1.40 vs 7.73±2.06 μmol/L, P=0 and 160.91±32.17 vs 143.02±32.30 ng/dL, P=0.02, respectively). Significantly higher total cholesterol, low density–lipoprotein cholesterol and triglycerides (P<0.05) and lower high density–lipoprotein cholesterol (P<0.05) were seen among patients with CAD than the control group. Sortilin levels were positively associated with homocysteine levels (r=0.32, P=0.006), total cholesterol (r=0.61, P=0), low density–lipoprotein cholesterol (r=0.37, P=0.001), triglycerides (r=0.91, P=0), troponin I (r=0.82, P=0), Gensini score (r=0.93, P=0) and high-sensitivity CRP (r=0.87, P=0) in all subjects. Homocysteine has a significantly negative association with high density–lipoprotein cholesterol (r=−0.42, P=0).

Conclusion

Elevated homocysteine and sortilin levels are crucial risk factors of CAD in Egyptian patients.

Coronary Artery Disease Genetics Enlightened by Genome-Wide Association Studies

Many cardiovascular diseases are facilitated by strong inheritance. For example, large-scale genetic studies identified hundreds of genomic loci that affect the risk of coronary artery disease. At each of these loci, common variants are associated with disease risk with robust statistical evidence but individually small effect sizes. Only a minority of candidate genes found at these loci are involved in the pathophysiology of traditional risk factors, but experimental research is making progress in identifying novel, and, in part, unexpected mechanisms. Targets identified by genome-wide association studies have already led to the development of novel treatments, specifically in lipid metabolism. This review summarizes recent genetic and experimental findings in this field. In addition, the development and possible clinical usefulness of polygenic risk scores in risk prediction and individualization of treatment, particularly in lipid metabolism, are discussed.

Sortilin promotes macrophage cholesterol accumulation and aortic atherosclerosis through lysosomal degradation of ATP-binding cassette transporter A1 protein

Sortilin is closely associated with hyperlipidemia and the risk of atherosclerosis (AS). The role of sortilin and the underlying mechanism in peripheral macrophage are not fully understood. In this study, we investigated the effect of macrophage sortilin on ATP-binding cassette transporter A1 (ABCA1) expression, ABCA1-mediated cholesterol efflux, and aortic AS. Macrophage sortilin expression was upregulated by oxidized low-density lipoproteins (ox-LDLs) in both concentration- and time-dependent manners. Its expression reached the peak level when cells were incubated with 50 μg/ml ox-LDL for 24 h. Overexpression of sortilin in macrophage reduced cholesterol efflux, leading to an increase in intracellular total cholesterol, free cholesterol, and cholesterol ester. Sortilin was found to bind with ABCA1 protein and suppress macrophage ABCA1 expression, resulting in a decrease in cholesterol efflux from macrophages. The inhibitory effect of sortilin in cholesterol efflux was partially reversed by treatment with chloroquine, a lysosomal inhibitor. On the contrary, the ABCA1 protein level and ABCA1-mediated cholesterol efflux is increased by sortilin short hairpin RNA transfection. The fecal and biliary cholesterol 3H-sterol from cholesterol-laden mouse peritoneal macrophage was reduced by sortilin overexpression through lentivirus vector (LV)-sortilin in low-density lipoprotein receptor knockout mice, which was prevented by co-treatment with chloroquine. Treatment with LV-sortilin reduced plasma high-density lipoprotein and increased plasma ox-LDL levels. Accordingly, aortic lipid deposition and plaque area were exacerbated, and ABCA1 expression was reduced in mice in response to infection with LV-sortilin alone. These effects of LV-sortilin were partially reversed by chloroquine. Sortilin enhances lysosomal degradation of ABCA1 protein and suppresses ABCA1-mediated cholesterol efflux from macrophages, leading to foam cell formation and AS development.

There is an association between a genetic polymorphism in the ZNF259 gene involved in lipid metabolism and coronary artery disease

BACKGROUND

Recent genome-wide association studies (GWAS) have identified several genetic variants that influence the risk of dyslipidemia and coronary artery disease (CAD). In this study, we have examined the potential association of five SNPs variants related to lipid pathway, previously identified in GWAS studies (ZNF259 C>G, CETP I405VA/G, LPA C>T, LPLS447X and PSRC1 A>G) with CAD.

METHODS

Two hundred and ninety subjects including 194 patients with coronary artery disease and 96 controls were enrolled, followed by the analyses of anthropometric/biochemical parameters. Genotyping was carried out using Taq-Man real-time PCR based method. The association of the genetic polymorphisms with CAD was determined using univariate and multivariate analyses.

RESULTS

CAD patients had a higher (p < 0.05) fasting blood glucose (FBG), total cholesterol (TC), high sensitivity C-reactive protein (hs-CRP), low-density lipoprotein cholesterol (LDL-C) and waist circumference. Results showed that subjects with CETP rs5882 genetic variant, AA&AG genotypes, had a higher risk of developing Coronary artery disease [OR: 2.1, 95% CI (1.2-4.1), p value = 0.015]. Also subjects who carried the G allele of the ZNF259 polymorphism were at an increased the risk of developing CAD [OR 1.86, 95% CI: 1.06-3.25, p value = 0.029] and had an increased TC, LDL and TG levels (p < 0.05). Furthermore, no statistically significant association was found between genetic polymorphisms of PSRC1 A>G, LPL S447X and LPA C>T and CAD.

CONCLUSION

We identified a relationship between a genetic variant in CETP and ZNF259 gene with CAD and CAD and lipid profile, respectively. Further investigation in a larger population may help to investigate the value of emerging marker as a risk stratification marker in CAD and its risk factors.

Generalized multifactor dimensionality reduction approaches to identification of genetic interactions underlying ordinal traits

The manifestation of complex traits is influenced by gene-gene and gene-environment interactions, and the identification of multifactor interactions is an important but challenging undertaking for genetic studies. Many complex phenotypes such as disease severity are measured on an ordinal scale with more than two categories. A proportional odds model can improve statistical power for these outcomes, when compared to a logit model either collapsing the categories into two mutually exclusive groups or limiting the analysis to pairs of categories. In this study, we propose a proportional odds model-based generalized multifactor dimensionality reduction (GMDR) method for detection of interactions underlying polytomous ordinal phenotypes. Computer simulations demonstrated that this new GMDR method has a higher power and more accurate predictive ability than the GMDR methods based on a logit model and a multinomial logit model. We applied this new method to the genetic analysis of low-density lipoprotein (LDL) cholesterol, a causal risk factor for coronary artery disease, in the Multi-Ethnic Study of Atherosclerosis, and identified a significant joint action of the CELSR2, SERPINA12, HPGD, and APOB genes. This finding provides new information to advance the limited knowledge about genetic regulation and gene interactions in metabolic pathways of LDL cholesterol. In conclusion, the proportional odds model-based GMDR is a useful tool that can boost statistical power and prediction accuracy in studying multifactor interactions underlying ordinal traits.

Sortilin and Its Multiple Roles in Cardiovascular and Metabolic Diseases

Cardiovascular disease is a leading cause of morbidity and mortality in the Western world. Studies of sortilin's influence on cardiovascular and metabolic diseases goes far beyond the genome-wide association studies that have revealed an association between cardiovascular diseases and the 1p13 locus that encodes sortilin. Emerging evidence suggests a significant role of sortilin in the pathogenesis of vascular and metabolic diseases; this includes type II diabetes mellitus via regulation of insulin resistance, atherosclerosis through arterial wall inflammation and calcification, and dysregulated lipoprotein metabolism. Sortilin is also known for its functional role in neurological disorders. It serves as a key receptor for cytokines, lipids, and enzymes and participates in pathological cargo loading to and trafficking of extracellular vesicles. This article provides a comprehensive review of sortilin's contributions to cardiovascular and metabolic diseases but focuses particularly on atherosclerosis. We summarize recent clinical findings that suggest that sortilin may be a cardiovascular risk biomarker and also discuss sortilin as a potential drug target.

[Genetic testing in polygenic diseases : Atrial fibrillation, arterial hypertension and coronary artery disease]

Genetic testing plays an increasing role in cardiovascular medicine. Advances in technology and the development of novel and more affordable (high throughput) methods have led to the identification of genetic risk factors in research and clinical practice. Also, this progress has simplified the screening of patients and individuals at risk. In case of rare monogenic diseases, diagnostics, risk stratification, and, in some cases, treatment decisions have become easier. For common, polygenic cardiovascular diseases, the situation is more complex due to interaction of modifiable external risk factors and nonmodifiable factors like genetic predisposition. Over the last few years, it has been shown that multiple genes are involved in the pathophysiology of these cardiovascular diseases rather than one single gene. In the following article, we give an overview of the genetic risk factors in polygenic cardiovascular diseases as atrial fibrillation, arterial hypertension and coronary artery disease. Furthermore, we aim to illustrate in which cases genetic testing is recommended in these diseases.

Genomic translational research: Paving the way to individualized cardiac functional analyses and personalized cardiology

For most of Medicine's past, the best that physicians could do to cope with disease prevention and treatment was based on the expected response of an average patient. Currently, however, a more personalized/precise approach to cardiology and medicine in general is becoming possible, as the cost of sequencing a human genome has declined substantially. As a result, we are witnessing an era of precipitous advances in biomedicine and bourgeoning understanding of the genetic basis of cardiovascular and other diseases, reminiscent of the resurgence of innovations in physico-mathematical sciences and biology-anatomy-cardiology in the Renaissance, a parallel time of radical change and reformation of medical knowledge, education and practice. Now on the horizon is an individualized, diverse patient-centered, approach to medical practice that encompasses the development of new, gene-based diagnostics and preventive medicine tactics, and offers the broadest range of personalized therapies based on pharmacogenetics. Over time, translation of genomic and high-tech approaches unquestionably will transform clinical practice in cardiology and medicine as a whole, with the adoption of new personalized medicine approaches and procedures. Clearly, future prospects far outweigh present accomplishments, which are best viewed as a promising start. It is now essential for pluridisciplinary health care providers to examine the drivers and barriers to the clinical adoption of this emerging revolutionary paradigm, in order to expedite the realization of its potential. So, we are not there yet, but we are definitely on our way.

Increased sortilin and its independent effect on circulating proprotein convertase subtilisin/kexin type 9 (PCSK9) in statin-naive patients with coronary artery disease

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has been shown to play a crucial role in the metabolism of low density lipoprotein receptor (LDLR). Sortilin, encoded by the dyslipidemia-related gene SORT1, is also an important regulator of lipoprotein metabolism. Animal studies have shown the potential role of sortilin in regulating secretion of PCSK9. However, the data for the relationship between serum sortilin and circulating PCSK9 in CAD patients are scarce.

METHODS

Eighty subjects were classified into a CAD group (n=43) and a non-CAD group (n=37) according to their clinical conditions and the results of coronary angiography (CAG). Serum PCSK9 and sortilin levels were measured with enzyme-linked immunosorbent assays.

RESULTS

CAD patients had markedly greater PCSK9 concentrations than controls [247.0(218.6317.4) vs 226.6(181.6270.3) ng/ml, P=0.007]. Moreover, serum PCSK9 levels were still higher in patients not receiving statin therapy, as compared with those in the control group [261.8(216.0,315.8) vs 221.0(176.8260.7)ng/ml, P=0.003]. Circulating sortilin tended to be higher in CAD patients than in non-CAD subjects, yet the difference is significant only between the statin-naive CAD patients and controls [4.96(4.38,6.57) vs 4.28(2.96,5.03) ng/ml, P=0.032]. Serum PCSK9 concentrations were positively associated with sortilin levels(r=0.37, P=0.001,n=80). Stratified analysis showed that there was stronger correlation between PCSK9 and sortilin in non-statin group (r=0.41, P=0.001,n=60) as well as in the non-CAD group (r=0.47, P=0.004,n=37) , whereas the correlation between them was disappeared in statin group and CAD group. Using stepwise multiple regression analysis with adjustment for age, gender, LDL-cholesterol, smoking and CAD, we found that the correlation between serum sortilin and PCSK9 levels remained significant in all subjects (P=0.01) as well as in statin-naive group (P=0.03).

CONCLUSION

Both circulating PCSK9 and sortilin levels are elevated in CAD patients. PCSK9 was independent related to sortilin, but their correlation was affected by the use of statin therapy.

Sortilin: A novel regulator in lipid metabolism and atherogenesis

Several lines of evidence have shown that SORT1 gene within 1p13.3 locus is an important modulator of the low-density lipoprotein-cholesterol (LDL-C) level and atherosclerosis risk. Here, we summarize the effects of SORT1, which codes for sortilin, on lipid metabolism and development of atherosclerosis and explore the mechanisms underlying sortilin effects on lipid metabolism especially in hepatocytes and macrophages. Recent epidemiological evidence demonstrated that sortilin has been implicated as the causative factor and regulates lipid metabolism in vivo. Hepatic sortilin overexpression leads to both increased and decreased LDL-C levels by several different mechanisms, suggesting the complex roles of sortilin in hepatic lipid metabolism. Macrophage sortilin causes internalization of LDL and probably a reduction in cholesterol efflux, resulting in the intracellular accumulation of excessive lipids. In addition, sortilin deficiency in an atherosclerotic mouse model results in decreased aortic atherosclerotic lesion. Sortilin involves in lipid metabolism, promotes the development of atherosclerosis, and possibly becomes a potential therapeutic target for atherosclerosis treatment.

Mendelian Randomization versus Path Models: Making Causal Inferences in Genetic Epidemiology

OBJECTIVE

The term Mendelian randomization is popular in the current literature. The first aim of this work is to describe the idea of Mendelian randomization studies and the assumptions required for drawing valid conclusions. The second aim is to contrast Mendelian randomization and path modeling when different 'omics' levels are considered jointly.

METHODS

We define Mendelian randomization as introduced by Katan in 1986, and review its crucial assumptions. We introduce path models as the relevant additional component to the current use of Mendelian randomization studies in 'omics'. Real data examples for the association between lipid levels and coronary artery disease illustrate the use of path models.

RESULTS

Numerous assumptions underlie Mendelian randomization, and they are difficult to be fulfilled in applications. Path models are suitable for investigating causality, and they should not be mixed up with the term Mendelian randomization. In many applications, path modeling would be the appropriate analysis in addition to a simple Mendelian randomization analysis.

CONCLUSIONS

Mendelian randomization and path models use different concepts for causal inference. Path modeling but not simple Mendelian randomization analysis is well suited to study causality with different levels of 'omics' data.

[Genetic analyses as basis for a personalized medicine in patients with coronary artery disease]

Knowledge about the etiology of coronary artery disease (CAD) entered new dimensions using genome-wide association studies. The current situation is that 46 chromosomal loci have been identified to be associated with CAD with genome-wide significance, i.e. p<5×10(-8), in Western Europeans. As the individual DNA sequence remains unchanged after fertilization, the risk variants cannot occur due to confounders, such as secondary disease processes. Thus, it can be proposed that these variants are directly affecting a primary and thereby causal pathophysiological process in CAD. Interestingly, only 20% of the effects mediated by the identified loci can be explained by the influence of traditional risk factors. This implies that yet unknown mechanisms and, as a consequence, new therapeutic targets play an important role in the pathophysiology of CAD. However, the high allele frequency of risk loci was also surprising. In the diploid chromosome set Western European individuals carry on average 30-50 risk variants at the 46 loci. Considering this, every individual in the population carries a larger or smaller genetic predisposition for CAD. On the other hand it is remarkable that many risk allele carriers seem to be able to compensate the genetic risk: even in old age not everyone suffers from CAD. This indicates yet unknown gene-gene and gene-environment interactions and limits the current possibilities in individual risk prediction.

Sortilin and the risk of cardiovascular disease

Plasma low-density lipoprotein cholesterol (LDL-C) levels are a key determinant of the risk of cardiovascular disease, which is why many studies have attempted to elucidate the pathways that regulate its metabolism. Novel latest-generation sequencing techniques have identified a strong association between the 1p13 locus and the risk of cardiovascular disease caused by changes in plasma LDL-C levels. As expected for a complex phenotype, the effects of variation in this locus are only moderate. Even so, knowledge of the association is of major importance, since it has unveiled a new metabolic pathway regulating plasma cholesterol levels. Crucial to this discovery was the work of three independent teams seeking to clarify the biological basis of this association, who succeeded in proving that SORT1, encoding sortilin, was the gene in the 1p13 locus involved in LDL metabolism. SORT1 was the first gene identified as determining plasma LDL levels to be mechanistically evaluated and, although the three teams used different, though appropriate, experimental methods, their results were in some ways contradictory. Here we review all the experiments that led to the identification of the new pathway connecting sortilin with plasma LDL levels and risk of myocardial infarction. The regulatory mechanism underlying this association remains unclear, but its discovery has paved the way for considering previously unsuspected therapeutic targets and approaches.

Clinical validation of genetic markers for improved risk estimation

Primary prevention is the most effective strategy for reducing the burden of cardiovascular disease; however, predicting cardiovascular risk in the asymptomatic population lacks precision. Traditional methods of estimating risk are based on the presence of certain risk factors, some of which (e.g. hypertension, dyslipidaemia) are modifiable. Cardiovascular risk is also determined by a plethora of genetic risk factors, and this is partially reflected by a positive family history of cardiovascular disease; however, family history may not always be an accurate indication of genetic cardiovascular risk. Genome-wide association studies have identified numerous genetic variants associated with increased cardiovascular risk and cardiovascular risk factors. The addition of genetic information to conventional risk scores has the potential to increase the discriminative power of the score. Genetic markers may be particularly helpful for predicting life-time risk of cardiovascular disease in younger subjects, which is often underestimated by traditional risk scores. Advances in our understanding of the genetics of cardiovascular risk provide opportunities for improving both the prevention and treatment of cardiovascular disease.

A shortcut to the lysosome: the mannose-6-phosphate-independent pathway

Lysosomal hydrolases have long been known to be responsible for the degradation of different substrates in the cell. These acid hydrolases are synthesized in the rough endoplasmic reticulum and transported through the Golgi apparatus to the trans-Golgi network (TGN). From there, they are delivered to endosomal/lysosomal compartments, where they finally become active due to the acidic pH characteristic of the lysosomal compartment. The majority of the enzymes leave the TGN after modification with mannose-6-phosphate (M6P) residues, which are specifically recognized by M6P receptors (MPRs), ensuring their transport to the endosomal/lysosomal system. Although M6P receptors play a major role in the intracellular transport of newly synthesized lysosomal enzymes in mammalian cells, several lines of evidence suggest the existence of alternative processes of lysosomal targeting. Among them, the two that are mediated by the M6P alternative receptors, lysosomal integral membrane protein (LIMP-2) and sortilin, have gained unequivocal support. LIMP-2 was shown to be implicated in the delivery of beta-glucocerebrosidase (GCase) to the lysosomes, whereas sortilin has been suggested to be a multifunctional receptor capable of binding several different ligands, including neurotensin and receptor-associated protein (RAP), and of targeting several proteins to the lysosome, including sphingolipid activator proteins (prosaposin and GM2 activator protein), acid sphingomyelinase and cathepsins D and H. Here, we review the current knowledge on these two proteins: their discovery, study, structural features and cellular function, with special attention to their role as alternative receptors to lysosomal trafficking. Recent studies associating both LIMP2 and sortilin to disease are also extensively reviewed.

Mendelian randomization: application to cardiovascular disease

In the absence of an ethical, practical, and economical randomized trial, the epidemiologist is left to explore other methods in efforts to assert causality. An approach based on genotypic variation has the potential to mitigate against some of the problems found within conventional observational studies. Genetic variations associated with risk factors of interest at the population level can be used as proxy measures for these risk factors and to generate estimates of causal effect. The potential and the possible limitations of this approach within the cardiovascular field are presented in this review.

Strategies beyond genome-wide association studies for atherosclerosis

Atherosclerotic diseases, including coronary artery disease (CAD) and myocardial infarction (MI), are the leading causes of death in the world. The genetic basis of CAD and MI, which are caused by multiple interacting endogenous and exogenous factors, has gained considerable interest in the last years as genome-wide association studies (GWASs) have identified many new susceptibility loci for CAD and MI, and the underlying genes provide new insights into the genetic architecture of these diseases. Here we summarize the recent findings from GWASs of atherosclerosis and discuss their functional and biological implications. We also discuss the different post-GWAS strategies that are currently used for refining the location of causal variants, understanding their role, and shedding light on molecular mechanisms explaining their association to CAD. We finally discuss potential clinical translations of GWAS findings for individual risk prediction, advanced clinical strategies, and personalized treatments.

Large-scale association analysis identifies 13 new susceptibility loci for coronary artery disease

We performed a meta-analysis of 14 genome-wide association studies of coronary artery disease (CAD) comprising 22,233 individuals with CAD (cases) and 64,762 controls of European descent followed by genotyping of top association signals in 56,682 additional individuals. This analysis identified 13 loci newly associated with CAD at P < 5 × 10⁻⁸ and confirmed the association of 10 of 12 previously reported CAD loci. The 13 new loci showed risk allele frequencies ranging from 0.13 to 0.91 and were associated with a 6% to 17% increase in the risk of CAD per allele. Notably, only three of the new loci showed significant association with traditional CAD risk factors and the majority lie in gene regions not previously implicated in the pathogenesis of CAD. Finally, five of the new CAD risk loci appear to have pleiotropic effects, showing strong association with various other human diseases or traits.