Obesity and obstructive sleep apnea tend to coexist and are associated with inflammation, insulin resistance, dyslipidemia, and high blood pressure, but their causal relation to these abnormalities is unclear.
We randomly assigned 181 patients with obesity, moderate-to-severe obstructive sleep apnea, and serum levels of C-reactive protein (CRP) greater than 1.0 mg per liter to receive treatment with continuous positive airway pressure (CPAP), a weight-loss intervention, or CPAP plus a weight-loss intervention for 24 weeks. We assessed the incremental effect of the combined interventions over each one alone on the CRP level (the primary end point), insulin sensitivity, lipid levels, and blood pressure.
Among the 146 participants for whom there were follow-up data, those assigned to weight loss only and those assigned to the combined interventions had reductions in CRP levels, insulin resistance, and serum triglyceride levels. None of these changes were observed in the group receiving CPAP alone. Blood pressure was reduced in all three groups. No significant incremental effect on CRP levels was found for the combined interventions as compared with either weight loss or CPAP alone. Reductions in insulin resistance and serum triglyceride levels were greater in the combined-intervention group than in the group receiving CPAP only, but there were no significant differences in these values between the combined-intervention group and the weight-loss group. In per-protocol analyses, which included 90 participants who met prespecified criteria for adherence, the combined interventions resulted in a larger reduction in systolic blood pressure and mean arterial pressure than did either CPAP or weight loss alone.
In adults with obesity and obstructive sleep apnea, CPAP combined with a weight-loss intervention did not reduce CRP levels more than either intervention alone. In secondary analyses, weight loss provided an incremental reduction in insulin resistance and serum triglyceride levels when combined with CPAP. In addition, adherence to a regimen of weight loss and CPAP may result in incremental reductions in blood pressure as compared with either intervention alone.
Recombinant adeno-associated viral vectors based on serotype 8 (AAV8) transduce liver with superior tropism following intravenous (IV) administration. Previous studies conducted by our lab demonstrated that AAV8-mediated transfer of the human low-density lipoprotein receptor (LDLR) gene driven by a strong liver-specific promoter (thyroxin-binding globulin [TBG]) leads to high level and persistent gene expression in the liver. The approach proved efficacious in reducing plasma cholesterol levels and resulted in the regression of atherosclerotic lesions in a murine model of homozygous familial hypercholesterolemia (hoFH). Prior to advancing this vector, called AAV8.TBG.hLDLR, to the clinic, we set out to investigate vector biodistribution in an hoFH mouse model following IV vector administration to assess the safety profile of this investigational agent. Although AAV genomes were present in all organs at all time points tested (up to 180 days), vector genomes were sequestered mainly in the liver, which contained levels of vector 3 logs higher than that found in other organs. In both sexes, the level of AAV genomes gradually declined and appeared to stabilize 90 days post vector administration in most organs although vector genomes remained high in liver. Vector loads in the circulating blood were high and close to those in liver at the early time point (day 3) but rapidly decreased to a level close to the limit of quantification of the assay. The results of this vector biodistribution study further support a proposed clinical trial to evaluate AAV8 gene therapy for hoFH patients.
The ATP-binding cassette transporter A1 (ABCA1) is a key mediator of cellular cholesterol efflux and HDL maturation. ABCA1 mRNA has an unusually long 3’ untranslated region, which makes it highly susceptible to microRNA (miRNA) targeting and repression. As such, multiple miRNAs have been reported to directly target ABCA1, including miR-33a/b, miR-26, miR-106b, and miR-758. Many of these miRNAs participate in feed-forward or feedback networks in controlling cholesterol and lipid homeostasis. Antisense oligonucleotide-based inhibition of miR-33 was found to increase HDL-C levels and regress atherosclerosis in mice and non-human primates. In this edition of Circulation Research, two separate studies identified novel miRNA networks driven by nuclear receptor induced miR-144 targeting of ABCA1 and cholesterol efflux. The first study reports that miR-144 serves to buffer uncontrolled ABCA1 activation in response to high cholesterol states and liver X receptor (LXR) activation in macrophages and liver. The second study highlights the role of miR-144 and ABCA1 in promotion of bile acid secretion in response to farensoid X receptor (FXR) activation in the liver. These studies suggest that anti-miR-144, like anti-miR-33, could be a novel approach to targeting HDL and reverse cholesterol transport.
Although high-density lipoprotein (HDL) is known to inhibit endothelial adhesion molecule expression, the mechanism for this anti-inflammatory effect remains obscure. Surprisingly, we observed that HDL no longer decreased adhesion of U937 monocytoid cells to tumor necrosis factor (TNF)α-stimulated human endothelial cells (EC) in the presence of the general lipase inhibitor tetrahydrolipstatin. In considering endothelial mechanisms responsible for this effect, we found that endothelial lipase (EL) overexpression in both EC and non-EL–expressing NIH/3T3 mouse embryonic fibroblasts cells significantly decreased TNFα-induced VCAM1 expression and promoter activity in a manner dependent on HDL concentration and intact EL activity. Given recent evidence for lipolytic activation of peroxisome proliferator-activated receptors (PPARs)—nuclear receptors implicated in metabolism, atherosclerosis, and inflammation—we hypothesized HDL hydrolysis by EL is an endogenous endothelial mechanism for PPAR activation. In both EL-transfected NIH cells and bovine EC, HDL significantly increased PPAR ligand binding domain activation in the order PPAR-α≫-γ>-δ. Moreover, HDL stimulation induced expression of the canonical PPARα-target gene acyl-CoA-oxidase (ACO) in a PPARα-dependent manner in ECs. Conditioned media from EL-adenovirus transfected cells but not control media exposed to HDL also activated PPARα. PPARα activation by EL was most potent with HDL as a substrate, with lesser effects on LDL and VLDL. Finally, HDL inhibited leukocyte adhesion to TNFα-stimulated ECs isolated from wild-type but not PPARα-deficient mice. This data establishes HDL hydrolysis by EL as a novel, distinct natural pathway for PPARα activation and identifies a potential mechanism for HDL-mediated repression of VCAM1 expression, with significant implications for both EL and PPARs in inflammation and vascular biology.
adhesion molecules; endothelial cells; HDL cholesterol; high-density lipoproteins; lipase; PPARs; transcriptional regulation
Bone marrow derived endothelial progenitor cells (EPCs) are early precursors of mature endothelial cells which replenish aging and damaged endothelial cells. The authors studied a diabetic swine model to determine if induction of DM adversely affects either bone marrow or circulating EPCs and whether a HMG-CoA reductase inhibitor (statin) improves development and recruitment of EPCs in the absence of cholesterol lowering. Streptozotocin was administered to Yorkshire pigs to induce DM. One month after induction, diabetic pigs were treated with atorvastatin (statin, n = 10), ezetimibe (n = 10) or untreated (n = 10) and evaluated for number of bone marrow and circulating EPCs and femoral artery endothelial function. There was no effect of either medication on cholesterol level. One month after induction of DM prior to administration of drugs, the number of bone marrow and circulating EPCs significantly decreased (P < 0.0001) compared to baseline. Three months after DM induction, the mean proportion of circulating EPCs significantly increased in the atorvastatin group, but not in the control or ezetimibe groups. The control group showed progressive reduction in percentage of flow mediated vasodilatation (no dilatation at 3 months) whereas the atorvastatin group and ezetimibe exhibited vasodilatation, 6% and 4% respectively. DM results in significant impairment of bone marrow and circulating EPCs as well as endothelial function. The effect is ameliorated, in part, by atorvastatin independent of its cholesterol lowering effect. These data suggest a model wherein accelerated atherosclerosis seen with DM may, in part, result from reduction in EPCs which may be ameliorated by treatment with a statin.
diabetes mellitus; endothelium; endothelial progenitor cells; statin; inflammation; cytometry
Identification of the CETP, LIPG (encoding endothelial lipase) and APOC3 genes, and ana lysis of rare genetic variants in them, have allowed researchers to increase understanding of HDL metabolism significantly. However, development of cardiovascular risk-reducing therapeutics targeting the proteins encoded by these genes has been less straightforward. The failure of two CETP inhibitors is complex but illustrates a possible over-reliance on HDL cholesterol as a marker of therapeutic efficacy. The case of endothelial lipase exemplifies the importance of utilizing population-wide genetic studies of rare variants in potential therapeutic targets to gain information on cardiovascular disease end points. Similar population-wide studies of cardiovascular end points make apoC-III a potentially attractive target for lipid-related drug discovery. These three cases illustrate the positives and negatives of single-gene studies relating to HDL-related cardiovascular drug discovery; such studies should focus not only on HDL cholesterol and other components of the lipid profile, but also on the effect genetic variants have on cardiovascular end points.
anacetrapib; apoC-III; CETP; cholesterol; dalcetrapib; endothelial lipase; evacetrapib; genetics; HDL; ISI-APOCIIIRX; torcetrapib
Various pathological changes lead to the development of heart failure (HF). HDL is dysfunctional in both acute coronary syndrome, as measured by the HDL inflammatory index (HII) assay, and stable coronary disease, as measured by cholesterol efflux capacity. We therefore hypothesized that these functions of HDL are also impaired in subjects with ischaemic cardiomyopathy.
Methods and results
A case–control study was performed on subjects in the University of Pennsylvania Catheterization Study (PennCath) cohort of patients with angina. Cases had EF <50% and angiographic CAD (≥70% stenosis of any vessel; n = 23); controls included those with EF ≥55% and no CAD (n = 46). Serum from subjects was apolipoprotein-B depleted to isolate an HDL fraction. To measure HDL anti-oxidative capacity, the HDL fraction was incubated with LDL and a reporter lipid that fluoresces when oxidized. To measure cholesterol efflux capacity, the HDL fraction was also incubated with macrophages and tritium-labelled cholesterol. Mean HII was higher and efflux capacity lower in subjects with ischaemic cardiomyopathy (HII 0.26 vs. –0.028; efflux 0.80 vs. 0.92; P < 0.05). In a multivariable logistic regression model, both high HII and low efflux capacity were significant risk factors for HF [HII odds ratio (OR) 2.8, 95% confidence interval (CI) 2.0–3.9, P = 0.002; efflux OR 2.1, 95% CI 1.5–3.0, P = 0.03]. These effects persisted after adjustment for covariates and traditional risk factors for HF.
Subjects with reduced EF from ischaemia have lower HDL concentration and also impaired HDL function. HDL is a versatile lipoprotein particle with various anti-inflammatory and vasoprotective functions, whose impairment may contribute to ischaemic heart failure.
Heart failure; Coronary artery disease; HDL cholesterol
Editorials; high-density lipoprotein cholesterol; lipoproteins; obesity; adipose tissue; Reverse Cholesterol Transport
Postprandial triglyceridemia predicts cardiovascular events. Niacin might lower postprandial triglycerides (TG) by restricting free fatty acid (FFA). Immediate-release niacin reduced postprandial TGs, but extended-release niacin failed to do so when dosed the night before a fat challenge.
1) Determine whether extended-release niacin dosed before a fat challenge suppresses postprandial TG. 2) Determine whether postprandial TG is related to FFA restriction.
Double-blinded, placebo-controlled, random-order crossover experiment, where healthy volunteers took 2 g extended-release niacin or placebo 1 hour before heavy cream. We sampled blood over 12 hours, and report TG and FFA as means±SD for incremental area under the curve (iAUC) and nadir.
Combining 43 fat challenges from 22 subjects, postprandial TG iAUC was +312±200 on placebo vs +199±200 mg/dL*h on extended-release niacin (33% drop, p= 0.02). The incremental nadir for FFA was −0.07±0.15 on placebo vs −0.27±0.13 mmol/L on extended-release niacin (p<0.0001), and FFA iAUC fell from +2.9±1.5 to +1.5±1.5 mmol/L*h on extended-release niacin (20% drop, p=0.0015). The TG iAUC was strongly related to the post-dose drop in FFA (r=+0.58, p=0.0007).
Given right before a fat meal, even a single dose of extended-release niacin suppresses postprandial triglyceridemia. This establishes that postprandial TG suppression is an acute pharmacodynamic effect of extended-release niacin, probably the result of marked FFA restriction. Further study is warranted to determine whether mealtime dosing would augment the clinical efficacy of extended-release niacin therapy.
adult; African Americans; clinical trial; dietary fats; drug; evaluation; free fatty acids; humans; hydroxybutyrate; ketones; lipoprotein; lipids; niacin; niacin/pharmacology; niacin/therapeutic use; postprandial; randomized controlled trial; triglycerides
High density lipoprotein; cholesterol efflux; reverse cholesterol transport; atherosclerosis; cardiovascular disease; vascular imaging
We performed a genome-wide association study on 1,292 individuals with abdominal aortic aneurysms (AAAs) and 30,503 controls from Iceland and The Netherlands, with a follow-up of top markers in up to 3,267 individuals with AAAs and 7,451 controls. The A allele of rs7025486 on 9q33 was found to associate with AAA, with an odds ratio (OR) of 1.21 and P = 4.6 × 10−10. In tests for association with other vascular diseases, we found that rs7025486[A] is associated with early onset myocardial infarction (OR = 1.18, P = 3.1 × 10−5), peripheral arterial disease (OR = 1.14, P = 3.9 × 10−5) and pulmonary embolism (OR = 1.20, P = 0.00030), but not with intracranial aneurysm or ischemic stroke. No association was observed between rs7025486[A] and common risk factors for arterial and venous diseases—that is, smoking, lipid levels, obesity, type 2 diabetes and hypertension. Rs7025486 is located within DAB2IP, which encodes an inhibitor of cell growth and survival.
Despite the critical importance of plasma lipoproteins in the development of atherosclerosis, varying degrees of evidence surround the causal associations of lipoproteins with coronary artery disease (CAD). These causal contributions can be assessed by employing genetic variants as unbiased proxies for lipid levels. A relatively large number of low-density lipoprotein cholesterol (LDL-C) variants strongly associate with CAD, confirming the causal impact of this lipoprotein on atherosclerosis. Although not as firmly established, genetic evidence supporting a causal role of triglycerides (TG) in CAD is growing. Conversely, high-density lipoprotein cholesterol (HDL-C) variants not associated with LDL-C or TG have not yet been shown to be convincingly associated with CAD, raising questions about the causality of HDL-C in atherosclerosis. Finally, genetic variants at the LPA locus associated with lipoprotein(a) [Lp(a)] are decisively linked to CAD, indicating a causal role for Lp(a). Translational investigation of CAD-associated lipid variants may identify novel regulatory pathways with therapeutic potential to alter CAD risk.
Genetics; GWAS; Mendelian randomization; Lipids; LDL-C; Lipoprotein(a); TG; HDL-C; PCSK9; SORT1; TRIB1; Apolipoprotein A5; Apolipoprotein C3; Lipoprotein lipase; Cholesterol ester transfer protein; Coronary artery disease; Lipid Traits
To identify loci for coronary artery calcification (CAC) in patients with chronic kidney disease (CKD).
CKD is associated with increased CAC and subsequent coronary heart disease (CHD) but the mechanisms remain poorly defined. Genetic studies of CAC in CKD may provide a useful strategy for identifying novel pathways in CHD.
We performed a candidate gene study (~2,100 genes; ~50,000 SNPs) of CAC within the Chronic Renal Insufficiency Cohort (CRIC) Study (n=1,509; 57% European, 43% African ancestry). SNPs with preliminary evidence of association with CAC in CRIC were examined for association with CAC in PennCAC (n=2,560) and Amish Family Calcification Study (AFCS; n=784) samples. SNPs with suggestive replication were further analyzed for association with myocardial infarction (MI) in the Pakistan Risk of Myocardial Infarction study (PROMIS) (n=14,885).
Of 268 SNPs reaching P <5×10−4 for CAC in CRIC, 28 SNPs in 23 loci had nominal support (P <0.05 and in same direction) for CAC in PennCAC or AFCS. Besides chr9p21 and COL4A1, known loci for CHD, these included SNPs having reported GWAS association with hypertension (e.g., ATP2B1). In PROMIS, four of the 23 suggestive CAC loci (chr9p21, COL4A1, ATP2B1 and ABCA4) had significant associations with MI consistent with their direction of effect on CAC.
We identified several loci associated with CAC in CKD that also relate to MI in a general population sample. CKD imparts a high risk of CHD and may provide a useful setting for discovery of novel CHD genes and pathways.
Coronary artery calcification (CAC); chronic kidney disease (CKD); Chronic Renal Insufficiency Cohort Study (CRIC); myocardial infarction (MI); risk factors; candidate genes; single nucleotide polymorphisms (SNPs)
Recent studies involving HDL-raising therapeutics have greatly changed our understanding of this field. Despite effectively raising HDL-C levels, niacin remains of uncertain clinical benefit. Synthetic niacin receptor agonists are unlikely to raise HDL-C or have other beneficial effects on plasma lipids. Despite the failure in phase 3 of two CETP inhibitors, two potent CETP inhibitors that raise HDL-C levels by > 100% (and reduce LDL-C substantially) are in late stage clinical development. Infusions of recombinant HDL containing ‘wild-type’ apoA-I or apoA-I Milano, as well as autologous delipidated HDL, all demonstrated promising early results and remain in clinical development. A small molecule that causes upregulation of endogenous apoA-I production is also in clinical development. Finally, upregulation of macrophage cholesterol efflux pathways through agonism of liver X receptors or antagonism of miR-33 remains of substantial interest. The field of HDL therapeutics is poised to transition from the ‘HDL-cholesterol hypothesis’ to the ‘HDL flux hypothesis’ in which the impact on flux from macrophage to feces is deemed to be of greater therapeutic benefit than the increase in steady-state concentrations of HDL cholesterol.
Lipids; HDL; reverse cholesterol transport; niacin; GPR109A; cholesteryl ester transfer protein; CETP; anacetrapib; torcetrapib; dalcetrapib; evacetrapib; apoA-I; recombinant HDL; RVX-208; Liver X receptor; miR-33; cardiovascular disease
In addition to extensively characterized role of high density lipoprotein (HDL) in reverse cholesterol transport, bioactive lipids bound to HDL can also exert diverse vascular effects. Despite this, integration of HDL action in the vasculature with pathways that metabolize HDL and release bioactive lipids has been much less explored. The effects of HDL on endothelial cells (ECs) are mediated in part by HDL-associated sphingosine 1-phosphate (S1P), which binds to S1P1 receptors and promotes activation of eNOS and the kinase Akt. In these studies, we characterized the role of endothelial lipase (EL) in the control of endothelial signaling and biology, including those mediated by HDL-associated S1P.
Approach and Results
HDL-induced angiogenesis in aortic rings from EL-deficient (EL−/−) mice was markedly decreased versus wild-type controls. In cultured ECs, siRNA-mediated knockdown of EL abrogated HDL-promoted EC migration and tube formation. siRNA-mediated EL knockdown also attenuated HDL-induced phosphorylation of eNOS1179 and Akt473. S1P stimulation restored HDL-induced endothelial migration and Akt/eNOS phosphorylation that had been blocked by siRNA-mediated EL knockdown. HDL-induced EC migration and Akt/eNOS phosphorylation were completely inhibited by the S1P1 antagonist W146 but not by the S1P3 antagonist CAY10444.
Endothelial lipase is a critical determinant of the effects of HDL on S1P-mediated vascular responses and acts on HDL to promote activation of S1P1, leading to Akt/eNOS phosphorylation and subsequent endothelial migration and angiogenesis. The role of EL in HDL-associated S1P effects provides new insights into EL action, the responses seen through EL and HDL interaction, and S1P signaling.
HDL; endothelial lipase; endothelial cells; sphingosine 1-phosphate; angiogenesis
Endothelial–vascular smooth muscle cell communication has a critical role in cardiovascular homeostasis and the pathogenesis of atherosclerosis. A study now demonstrates extracellular-vesicle-mediated transfer of the atheroprotective microRNAs miR-143/145 between endothelial and vascular smooth muscle cells, providing compelling evidence that intercellular transport of miRNAs can influence a pathological process, namely atherosclerosis.
Autosomal recessive hypercholesterolemia (ARH) is a rare inherited disorder characterized by extremely high total and low-density lipoprotein cholesterol levels that has been previously linked to mutations in LDLRAP1. We identified a family with ARH not explained by mutations in LDLRAP1 or other genes known to cause monogenic hypercholesterolemia. The aim of this study was to identify the molecular etiology of ARH in this family.
Approach and Results
We used exome sequencing to assess all protein coding regions of the genome in three family members and identified a homozygous exon 8 splice junction mutation (c.894G>A, also known as E8SJM) in LIPA that segregated with the diagnosis of hypercholesterolemia. Since homozygosity for mutations in LIPA is known to cause cholesterol ester storage disease (CESD), we performed directed follow-up phenotyping by non-invasively measuring hepatic cholesterol content. We observed abnormal hepatic accumulation of cholesterol in the homozygote individuals, supporting the diagnosis of CESD. Given previous suggestions of cardiovascular disease risk in heterozygous LIPA mutation carriers, we genotyped E8SJM in >27,000 individuals and found no association with plasma lipid levels or risk of myocardial infarction, confirming a true recessive mode of inheritance.
By integrating observations from Mendelian and population genetics along with directed clinical phenotyping, we diagnosed clinically unapparent CESD in the affected individuals from this kindred and addressed an outstanding question regarding risk of cardiovascular disease in LIPA E8SJM heterozygous carriers.
hypercholesterolemia; genetics; myocardial infarction
We performed a genome-wide association study (GWAS) and a multistage meta-analysis of type 2 diabetes (T2D) in Punjabi Sikhs from India. Our discovery GWAS in 1,616 individuals (842 case subjects) was followed by in silico replication of the top 513 independent single nucleotide polymorphisms (SNPs) (P < 10−3) in Punjabi Sikhs (n = 2,819; 801 case subjects). We further replicated 66 SNPs (P < 10−4) through genotyping in a Punjabi Sikh sample (n = 2,894; 1,711 case subjects). On combined meta-analysis in Sikh populations (n = 7,329; 3,354 case subjects), we identified a novel locus in association with T2D at 13q12 represented by a directly genotyped intronic SNP (rs9552911, P = 1.82 × 10−8) in the SGCG gene. Next, we undertook in silico replication (stage 2b) of the top 513 signals (P < 10−3) in 29,157 non-Sikh South Asians (10,971 case subjects) and de novo genotyping of up to 31 top signals (P < 10−4) in 10,817 South Asians (5,157 case subjects) (stage 3b). In combined South Asian meta-analysis, we observed six suggestive associations (P < 10−5 to < 10−7), including SNPs at HMG1L1/CTCFL, PLXNA4, SCAP, and chr5p11. Further evaluation of 31 top SNPs in 33,707 East Asians (16,746 case subjects) (stage 3c) and 47,117 Europeans (8,130 case subjects) (stage 3d), and joint meta-analysis of 128,127 individuals (44,358 case subjects) from 27 multiethnic studies, did not reveal any additional loci nor was there any evidence of replication for the new variant. Our findings provide new evidence on the presence of a population-specific signal in relation to T2D, which may provide additional insights into T2D pathogenesis.
Low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, and total cholesterol are heritable, modifiable, risk factors for coronary artery disease. To identify new loci and refine known loci influencing these lipids, we examined 188,578 individuals using genome-wide and custom genotyping arrays. We identify and annotate 157 loci associated with lipid levels at P < 5×10−8, including 62 loci not previously associated with lipid levels in humans. Using dense genotyping in individuals of European, East Asian, South Asian, and African ancestry, we narrow association signals in 12 loci. We find that loci associated with blood lipids are often associated with cardiovascular and metabolic traits including coronary artery disease, type 2 diabetes, blood pressure, waist-hip ratio, and body mass index. Our results illustrate the value of genetic data from individuals of diverse ancestries and provide insights into biological mechanisms regulating blood lipids to guide future genetic, biological, and therapeutic research.
Triglycerides are transported in plasma by specific triglyceride-rich lipoproteins; in epidemiologic studies, increased triglyceride levels correlate with higher risk for coronary artery disease (CAD). However, it is unclear whether this association reflects causal processes. We used 185 common variants recently mapped for plasma lipids (P<5×10−8 for each) to examine the role of triglycerides on risk for CAD. First, we highlight loci associated with both low-density lipoprotein cholesterol (LDL-C) and triglycerides, and show that the direction and magnitude of both are factors in determining CAD risk. Second, we consider loci with only a strong magnitude of association with triglycerides and show that these loci are also associated with CAD. Finally, in a model accounting for effects on LDL-C and/or high-density lipoprotein cholesterol, a polymorphism's strength of effect on triglycerides is correlated with the magnitude of its effect on CAD risk. These results suggest that triglyceride-rich lipoproteins causally influence risk for CAD.
Blood pressure (BP) is a heritable determinant of risk for cardiovascular disease (CVD). To investigate genetic associations with systolic BP (SBP), diastolic BP (DBP), mean arterial pressure (MAP) and pulse pressure (PP), we genotyped ∼50 000 single-nucleotide polymorphisms (SNPs) that capture variation in ∼2100 candidate genes for cardiovascular phenotypes in 61 619 individuals of European ancestry from cohort studies in the USA and Europe. We identified novel associations between rs347591 and SBP (chromosome 3p25.3, in an intron of HRH1) and between rs2169137 and DBP (chromosome1q32.1 in an intron of MDM4) and between rs2014408 and SBP (chromosome 11p15 in an intron of SOX6), previously reported to be associated with MAP. We also confirmed 10 previously known loci associated with SBP, DBP, MAP or PP (ADRB1, ATP2B1, SH2B3/ATXN2, CSK, CYP17A1, FURIN, HFE, LSP1, MTHFR, SOX6) at array-wide significance (P < 2.4 × 10−6). We then replicated these associations in an independent set of 65 886 individuals of European ancestry. The findings from expression QTL (eQTL) analysis showed associations of SNPs in the MDM4 region with MDM4 expression. We did not find any evidence of association of the two novel SNPs in MDM4 and HRH1 with sequelae of high BP including coronary artery disease (CAD), left ventricular hypertrophy (LVH) or stroke. In summary, we identified two novel loci associated with BP and confirmed multiple previously reported associations. Our findings extend our understanding of genes involved in BP regulation, some of which may eventually provide new targets for therapeutic intervention.
The goal of this study was to understand the molecular basis for how the amino acid substitution C112R that distinguishes human apolipoprotein (apo) E4 from apoE3 causes the more pro-atherogenic plasma lipoprotein cholesterol distribution that is known to be associated with expression of apoE4.
Methods and Results
Adeno-associated viruses, serotype 8 (AAV8) were used to express different levels of human apoE3, apoE4 and several C-terminal truncation and internal deletion variants in C57BL/6 apoE-null mice which exhibit marked dysbetalipoproteinemia. Plasma obtained from these mice two weeks after the AAV8 treatment was analyzed for cholesterol and triglyceride levels as well as for the distribution of cholesterol between the lipoprotein fractions. Hepatic expression of apoE3 and apoE4 induced similar dose-dependent decreases in plasma cholesterol and triglyceride to the levels seen in control C57BL/6 mice. Importantly, at the same reduction in plasma total cholesterol, expression of apoE4 gave rise to higher very low density lipoprotein-cholesterol (VLDL-C) and lower high density lipoprotein-cholesterol (HDL-C) levels relative to the apoE3 situation. The C-terminal domain, and residues 261-272 in particular, play a critical role because deleting them markedly affected the performance of both isoforms.
ApoE4 possesses enhanced lipid and VLDL binding ability relative to apoE3 which gives rise to impaired lipolytic processing of VLDL in apoE4-expressing mice. These effects reduce VLDL remnant clearance from the plasma compartment and decrease the amount of VLDL surface components available for incorporation into the HDL pool, accounting for the more pro-atherogenic lipoprotein profile (higher VLDL-C/HDL-C ratio) occurring in apoE4-expressing animals compared to their apoE3 counterparts.
apolipoprotein E; cholesterol; high density lipoprotein; very low density lipoprotein; atherosclerosis
Atherosclerosis is a complex and heritable disease involving multiple cell types and the interactions of many different molecular pathways. The genetic and molecular mechanisms of atherosclerosis have in part been elucidated by mouse models; at least 100 different genes have been shown to influence atherosclerosis in mice. Importantly, unbiased genome-wide association studies have recently identified a number of novel loci robustly associated with atherosclerotic coronary artery disease (CAD). Here we review the genetic data elucidated from mouse models of atherosclerosis, as well as significant associations for human CAD. Furthermore, we discuss in greater detail some of these novel human CAD loci. The combination of mouse and human genetics has the potential to identify and validate novel genes that influence atherosclerosis, some of which may be candidates for new therapeutic approaches.
CAD; Lipids; Mice; GWAS; Genome-wide