Localized vessel expression of lipoprotein lipase in rabbits leads to rapid lipid deposition in the balloon-injured arterial wall

Urotensin II Enhances Advanced Aortic Atherosclerosis Formation and Delays Plaque Regression in Hyperlipidemic Rabbits

Accumulated evidence shows that elevated urotensin II (UII) levels are associated with cardiovascular diseases. However, the role of UII in the initiation, progression, and regression of atherosclerosis remains to be verified. Different stages of atherosclerosis were induced in rabbits by a 0.3% high cholesterol diet (HCD) feeding, and either UII (5.4 μg/kg/h) or saline was chronically infused via osmotic mini-pumps. UII promoted atherosclerotic fatty streak formation in ovariectomized female rabbits (34% increase in gross lesion and 93% increase in microscopic lesion), and in male rabbits (39% increase in gross lesion). UII infusion significantly increased the plaque size of the carotid and subclavian arteries (69% increase over the control). In addition, UII infusion significantly enhanced the development of coronary lesions by increasing plaque size and lumen stenosis. Histopathological analysis revealed that aortic lesions in the UII group were characterized by increasing lesional macrophages, lipid deposition, and intra-plaque neovessel formation. UII infusion also significantly delayed the regression of atherosclerosis in rabbits by increasing the intra-plaque macrophage ratio. Furthermore, UII treatment led to a significant increase in NOX2 and HIF-1α/VEGF-A expression accompanied by increased reactive oxygen species levels in cultured macrophages. Tubule formation assays showed that UII exerted a pro-angiogenic effect in cultured endothelial cell lines and this effect was partly inhibited by urantide, a UII receptor antagonist. These findings suggest that UII can accelerate aortic and coronary plaque formation and enhance aortic plaque vulnerability, but delay the regression of atherosclerosis. The role of UII on angiogenesis in the lesion may be involved in complex plaque development.

Lipoprotein lipase: Biosynthesis, regulatory factors, and its role in atherosclerosis and other diseases

Lipoprotein lipase (LPL) is a rate-limiting enzyme that catalyzes hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins including chylomicrons (CM), low-density lipoproteins (LDL) and very low-density lipoproteins (VLDL). A variety of parenchymal cells can synthesize and secrete LPL. Recent studies have demonstrated that complicated processes are involved in LPL biosynthesis, secretion and transport. The enzyme activity of LPL is regulated by many factors, such as apolipoproteins, angiopoietins, hormones and miRNAs. In this article, we also reviewed the roles of LPL in atherosclerosis, coronary heart disease, cerebrovascular accident, Alzheimer disease and chronic lymphocytic leukemia. LPL in different tissues exerts differential physiological functions. The role of LPL in atherosclerosis is still controversial as reported in the literature. Here, we focused on the properties of LPL derived from macrophages, endothelial cells and smooth muscle cells in the vascular wall. We also explore the existence of crosstalk between LPL and those cells when the molecule mainly plays a proatherogenic role. This review will provide insightful knowledge of LPL and open new therapeutic perspectives.

Association between Lipoprotein Lipase Polymorphism and the Risk of Stroke: A Meta-analysis

BACKGROUND

Several studies have studied the relationship between lipoprotein lipase (LPL) HindIII gene polymorphism and stroke susceptibility. However, the conclusions remain controversial. To clarify the association of LPL gene HindIII polymorphism and stroke susceptibility, we therefore conducted a comprehensive meta-analysis.

MATERIALS AND METHODS

The PubMed, Web of Science, EMBASE, and Google Scholar databases were systemically searched to indentify available studies. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated under the allelic, dominant, homozygous, heterozygous, and recessive models. The data were analyzed by using Stata 12.0 (StataCorp, College Station, TX).

RESULTS

Ten studies were enrolled, including a total of 2122 cases and 2235 controls. The overall results showed that LPL HindIII variants were associated with a decreased risk of stroke (G versus T: OR = .78, 95% CI = .70-.87, P < .001; GG + TG versus TT: OR = .76, 95% CI = .67-.87, P < .001; GG versus TT: OR = .69, 95% CI = .53-.90, P = .006; TG versus TT: OR = .78, 95% CI = .68-.90, P <.001; GG versus TG + TT: OR = .74, 95% CI = .57-.95, P = .02). Stratified analysis by ethnicity (Asian and non-Asian) indicated that LPL HindIII variants were associated with a decreased risk of stroke in the Asian population, but not in the non-Asian population. In the subgroup analysis by stroke subtype, the results suggested that LPL HindIII variants contributed to a decrease in both ischemic stroke and hemorrhagic stroke risks.

CONCLUSION

Our meta-analysis suggested that LPL HindIII variants were associated with a decreased risk of stroke in the Asian population, but not in the non-Asian population.

Cholesterol efflux from THP-1 macrophages is impaired by the fatty acid component from lipoprotein hydrolysis by lipoprotein lipase

Lipoprotein lipase (LPL) is an extracellular lipase that primarily hydrolyzes triglycerides within circulating lipoproteins. Macrophage LPL contributes to atherogenesis, but the mechanisms behind it are poorly understood. We hypothesized that the products of lipoprotein hydrolysis generated by LPL promote atherogenesis by inhibiting the cholesterol efflux ability by macrophages. To test this hypothesis, we treated human THP-1 macrophages with total lipoproteins that were hydrolyzed by LPL and we found significantly reduced transcript levels for the cholesterol transporters ATP binding cassette transporter A1 (ABCA1), ABCG1, and scavenger receptor BI. These decreases were likely due to significant reductions for the nuclear receptors liver-X-receptor-α, peroxisome proliferator activated receptor (PPAR)-α, and PPAR-γ. We prepared a mixture of free fatty acids (FFA) that represented the ratios of FFA species within lipoprotein hydrolysis products, and we found that the FFA mixture also significantly reduced cholesterol transporters and nuclear receptors. Finally, we tested the efflux of cholesterol from THP-1 macrophages to apolipoprotein A-I, and we found that the treatment of THP-1 macrophages with the FFA mixture significantly attenuated cholesterol efflux. Overall, these data show that the FFA component of lipoprotein hydrolysis products generated by LPL may promote atherogenesis by inhibiting cholesterol efflux, which partially explains the pro-atherogenic role of macrophage LPL.

Amelioration of hypertriglyceridemia with hypo-alpha-cholesterolemia in LPL deficient mice by hematopoietic cell-derived LPL

Background

Macrophage-derived lipoprotein lipase (LPL) has been shown uniformly to promote atherosclerotic lesion formation while the extent to which it affects plasma lipid and lipoprotein levels varies in wild-type and hypercholesterolemic mice. It is known that high levels of LPL in the bulk of adipose tissue and skeletal muscle would certainly mask the contribution of macrophage LPL to metabolism of plasma lipoprotein. Therefore, we chose LPL deficient (LPL^-/-) mice with severe hypertriglyceridemia as an alternative model to assess the role of macrophage LPL in plasma lipoprotein metabolism via bone marrow transplant, through which LPL will be produced mainly by hematopoietic cell-derived macrophages.

Methods and Results

Hypertriglyceridemic LPL^-/- mice were lethally irradiated, then transplanted with bone marrow from wild-type (LPL^+/+) or LPL^-/- mice, respectively. Sixteen weeks later, LPL^+/+ →LPL^-/- mice displayed significant reduction in plasma levels of triglyceride and cholesterol (408±44.9 vs. 2.7±0.5×10³ and 82.9±7.1 vs. 229.1±30.6 mg/dl, p<0.05, respectively), while a 2.7-fold increase in plasma high density lipoprotein- cholesterol (p<0.01) was observed, compared with LPL^-/-→LPL^-/- control mice. The clearance rate for the oral fat load test in LPL^+/+ →LPL^-/- mice was faster than that in LPL^-/-→LPL^-/- mice, but slower than that in wild-type mice. Liver triglyceride content in LPL^+/+→LPL^-/- mice was also significantly increased, compared with LPL^-/-→LPL^-/- mice (6.8±0.7 vs. 4.6±0.5 mg/g wet tissue, p<0.05, n = 6). However, no significant change was observed in the expression levels of genes involved in hepatic lipid metabolism between the two groups.

Conclusions

Hematopoietic cell-derived LPL could efficiently ameliorate severe hypertriglyceridemia and hypo-alpha-cholesterolemia at the compensation of increased triglyceride content of liver in LPL^-/- mice.

Polymorphisms of the lipoprotein lipase gene are associated with atherosclerotic cerebral infarction in the Chinese

BACKGROUND

Lipoprotein lipase (LPL), which plays an essential role in plasma lipoprotein metabolism and transportation, appears to be a risk factor for ischemic vascular diseases. Several studies have recently reported the presence of relationship between HindIII, PvuII, Ser447Ter (C-->G) polymorphisms of LPL and ischemic vascular diseases.

PURPOSE

We first studied the relationship between LPL polymorphisms and the risk of atherosclerotic cerebral infarction (CI) by detecting the frequencies of LPL HindIII, PvuII and Ser447Ter genotypes and combined genotypes in the Chinese.

METHODS

We recruited 185 CI patients, confirmed by cranial computed tomography or magnetic resonance imaging/angiography, or both, and 186 control subjects. Polymerase chain reaction-restriction fragment length polymorphisms technique was used to detect HindIII, PvuII and Ser447Ter polymorphisms of the LPL gene.

RESULTS

The frequencies of the H+H+ genotype and H+ allele did not differ between CI and control groups. The frequencies of the P+P+ genotype and P+ allele gene were significantly higher in the CI group (P=0.040, P=0.015). The frequencies of CG+GG genotype and G allele were lower in the CI group (P<0.001, P<0.001). In the CI group, the individuals with P+P+ genotype had a significantly higher level of plasma triglyceride (TG) and a lower level of plasma high density lipoprotein cholesterol (HDL-c). CG+GG genotypes were correlated with significantly higher levels of plasma total cholesterol (TC), HDL-c and low density lipoprotein cholesterol (LDL-c) in the CI group. The frequencies of H+/C and P+/C combined genotypes were higher in the CI group than in controls (P<0.001, P<0.001). The frequency of H+/P+/C combined genotype was significantly higher in the CI group than in controls (P<0.001).

CONCLUSIONS

Our study suggests that PvuII and Ser447Ter polymorphisms are associated with lipid profile and CI.

Subendothelial lipoprotein retention as the initiating process in atherosclerosis: update and therapeutic implications

The key initiating process in atherogenesis is the subendothelial retention of apolipoprotein B-containing lipoproteins. Local biological responses to these retained lipoproteins, including a chronic and maladaptive macrophage- and T-cell-dominated inflammatory response, promote subsequent lesion development. The most effective therapy against atherothrombotic cardiovascular disease to date--low density lipoprotein-lowering drugs--is based on the principle that decreasing circulating apolipoprotein B lipoproteins decreases the probability that they will enter and be retained in the subendothelium. Ongoing improvements in this area include more aggressive lowering of low-density lipoprotein and other atherogenic lipoproteins in the plasma and initiation of low-density lipoprotein-lowering therapy at an earlier age in at-risk individuals. Potential future therapeutic approaches include attempts to block the interaction of apolipoprotein B lipoproteins with the specific subendothelial matrix molecules that mediate retention and to interfere with accessory molecules within the arterial wall that promote retention such as lipoprotein lipase, secretory sphingomyelinase, and secretory phospholipase A2. Although not the primary focus of this review, therapeutic strategies that target the proatherogenic responses to retained lipoproteins and that promote the removal of atherogenic components of retained lipoproteins also hold promise. The finding that certain human populations of individuals who maintain lifelong low plasma levels of apolipoprotein B lipoproteins have an approximately 90% decreased risk of coronary artery disease gives hope that our further understanding of the pathogenesis of this leading killer could lead to its eradication.

Overexpression of Mitofusin 2 inhibited oxidized low-density lipoprotein induced vascular smooth muscle cell proliferation and reduced atherosclerotic lesion formation in rabbit

Our previous studies have implies that Mitofusin 2 (Mfn2), which was progressively reduced in arteries from ApoE(-/-) mice during the development of atherosclerosis, may take part in pathogenesis of atherosclerosis. In this study, we found that overexpression of Mfn2 inhibited oxidized low-density lipoprotein or serum induced vascular smooth muscle cell proliferation by down-regulation of Akt and ERK phosphorylation. Then we investigated the in vivo role of Mfn2 on the development of atherosclerosis in rabbits using adenovirus expressing Mitofusin 2 gene (AdMfn2). By morphometric analysis we found overexpression of Mfn2 inhibited atherosclerotic lesion formation and intima/media ratio by 66.7% and 74.6%, respectively, compared with control group. These results suggest that local Mfn2 treatment suppresses the development of atherosclerosis in vivo in part by attenuating the smooth muscle cell proliferation induced by lipid deposition and vascular injury.

A 60-y-old chylomicronemia patient homozygous for missense mutation (G188E) in the lipoprotein lipase gene showed no accelerated atherosclerosis

BACKGROUND

Familial lipoprotein lipase (LPL) deficiency is a rare autosomal recessive disorder caused by mutations in the LPL gene. Patients with LPL deficiency have chylomicronemia; however, whether they develop accelerated atherosclerosis remains unclear.

METHODS

We investigated clinical and mutational characteristics of a 60-y-old Japanese patient with chylomicronemia.

RESULTS

The patient's fasting plasma triglyceride levels were >9.0 mmol/l. In postheparin plasma, one fifth of the normal LPL protein mass was present; however, LPL activity was undetectable. Molecular analysis of the LPL gene showed the patient to be a homozygote of missense mutation replacing glycine with glutamine at codon 188 (G188E), which had been known to produce mutant LPL protein lacking lipolytic activity. Ultrasonographic examination of the patient's carotid and femoral arteries showed no accelerated atherosclerosis. Moreover, 64-slice mechanical multidetector-row computer tomography (MDCT) angiography did not detect any accelerated atherosclerotic lesions in the patient's coronary arteries. The patient had none of the risk factors such as smoking, hypertension, and diabetes.

CONCLUSIONS

Our case suggests that accelerated atherosclerosis may not develop in patients with LPL deficiency, when they have no risk factors.

Lipoproteins and protection of the arterial wall against infection: the "response to the threat of infection" hypothesis

The exact reason why lipoproteins are found in the arterial intima is not understood. On the basis of recent findings presented in the literature, we are proposing a hypothesis that the accumulation of lipoprotein in the arterial intima is originally a physiological process, part of our defences against infection designed to protect susceptible segments of the arterial wall from microbial invasion. In addition to the intrinsic antimicrobial activities of the deposited lipids, the formation of fibrin-based matrices within the intima is promoted, fibrinolysis is inhibited, the lipid content exerts a vasoconstrictive influence and smooth muscle cells are mobilised into the intima, all these phenomenons being instrumental in fighting off an infectious menace. Oxidized lipids (including oxysterols and lysophosphatidylcholine) resulting from the oxidation of lipoproteins close to sites of infection and inflammation are disseminated through the circulatory system and act as alarm signals at arterial walls, promoting the penetration and retention of lipoproteins in the intimal tissue of the most susceptible segments of the arterial network. Oxidized lipids in the intima constitute part of first-line antimicrobial defences and their presence acts as a signal to immune effector cells (notably macrophages and lymphocytes) which trigger the acquired immune response when foreign antigens are encountered.

Expression of LPL in Endothelial-Intact Artery Results in Lipid Deposition and Vascular Cell Adhesion Molecule-1 Upregulation in Both LPL and ApoE-Deficient Mice

Objective— Overexpression of lipoprotein lipase (LPL) in deendothelialized artery led to profound localized lipid deposition. In this study the role of LPL in atherogenesis in endothelial-intact carotid arteries was assessed in genetically hyperlipidemic LPL- and ApoE-deficient mice.

Methods and Results— Human wild-type LPL (hLPLwt), catalytically inactive LPL (hLPL194), or control alkaline phosphatase (hAP) were expressed in endothelial-intact carotid arteries via adenoviral vectors. Compared with Ad-hAP, lipid deposition in the arterial wall increased 10.0- and 5.1-fold for Ad-hLPLwt and Ad-hLPL194 in LPL-deficient mice, and 10.6- and 6.2-fold in ApoE-deficient mice, respectively. Vascular cell adhesion molecule-1 (VCAM-1) was upregulated in Ad-hLPLwt and Ad-hLPL194 transferred arteries.

Conclusions— Endothelial cell associated LPL, either active or inactive, in the arterial wall is a strong proatherosclerotic factor in both LPL- and ApoE-deficient mice.