The lectin-like oxidized low-density lipoprotein receptor and its role in atherosclerosis

Rapamycin Inhibits Oxidized Low Density Lipoprotein Uptake in Human Umbilical Vein Endothelial Cells via mTOR/NF-κB/LOX-1 Pathway

Background

Lectin-like oxidized low-density lipoprotein-1 (LOX-1) is the major receptor for oxidized low density lipoprotein (ox-LDL) uptake in human umbilical vein endothelial cells (HUVECs). Previously, we found that rapamycin inhibited ox-LDL accumulation in HUVECs, and this effect was related to its role in increasing the activity of autophagy-lysosome pathway. In this study, we determined whether rapamycin could also reduce ox-LDL uptake in HUVECs and investigated the underlying signaling mechanisms.

Results

Flow cytometry and live cell imaging showed that rapamycin reduced Dil-ox-LDL accumulation in HUVECs. Furthermore, rapamycin reduced the ox-LDL-induced increase in LOX-1 mRNA and protein levels. Western blotting showed that rapamycin inhibited mechanistic target of rapamycin (mTOR), p70s6k and IκBα phosphorylation triggered by ox-LDL. Flow cytometry implied that mTOR, NF-κB knockdown and NF-κB inhibitors significantly reduced Dil-ox-LDL uptake. Moreover, immunofluorescent staining showed that rapamycin reduced the accumulation of p65 in the nucleus after ox-LDL treatment for 30 h. mTOR knockdown decreased LOX-1 protein production and IκBα phosphorylation induced by ox-LDL. NF-κB knockdown and NF-κB inhibitors reduced LOX-1 protein production, but did not inhibit mTOR phosphorylation stimulated by ox-LDL.

Conclusions

These findings demonstrate that rapamycin reduce mTOR phosphorylation and subsequently inhibit NF-κB activation and suppresses LOX-1, resulting in a reduction in ox-LDL uptake in HUVECs.

Rapamycin Promotes the Autophagic Degradation of Oxidized Low-Density Lipoprotein in Human Umbilical Vein Endothelial Cells

BACKGROUND/AIMS

Oxidized low-density lipoprotein (ox-LDL) has been extensively implicated in the initiation of atherosclerosis. Our previous studies reported that ox-LDL could activate autophagy in human umbilical vein endothelial cells (HUVECs). Because of this, subsequent studies were designed to elucidate the possible role of the autophagic inducer, rapamycin, on ox-LDL degradation in endothelial cells.

METHODS

Intracellular cholesterol content was measured using a tissue total cholesterol assay kit. ox-LDL trafficking within endothelial cells was analyzed by flow cytometry. Levels of proteins involved in the autophagic process, microtubule-associated protein 1 light chain 3 (MAP1-LC3), lysosome-associated membrane protein 1 (LAMP1), Beclin 1 and p62, were assessed by Western blot analysis.

RESULTS

We discovered that rapamycin could decrease the ox-LDL content in HUVECs at the 3-hour time point. Rapamycin also mediated an obvious increase in Dil-labeled ox-LDL (Dil-ox-LDL)/LC3 and Dil-ox-LDL/LAMP1 co-localization, which was inhibited by 3-methyladenine (3-MA), an autophagic inhibitor. In addition, significant co-localization of LC3 and LAMP1 occurred in cells pretreated with rapamycin. In the presence of rapamycin, p62 levels were reduced, and autophagic flux was enhanced.

CONCLUSION

These data demonstrate that the activation of the autophagy-lysosome pathway by rapamycin may accelerate ox-LDL degradation.

G501C polymorphism of the oxidized LDL receptor gene is associated with albuminuria in Chinese essential hypertension patients

Albuminuria is an independent predictor of renal and cardiovascular complications in hypertensive subjects. We previously showed that lectin-like oxidized low density lipoprotein receptor 1 (OLR-1) polymorphisms at G501C are associated with susceptibility to essential hypertension and serum C-reactive protein levels. We have now investigated a possible association between OLR-1 polymorphisms at G501C, genotyped by PCR-RFLP, and severity of albuminuria in 307 hypertensive Chinese subjects and 225 age- and sex-matched controls. Urine albumin concentration /urine creatinine concentrations (ACR) were measured to evaluate the severity of albuminuria. Hypertensive subjects had a significantly higher frequency of the CC genotype and the C allele of the OLR-1 polymorphism than controls; this was also true for . hypertensive subjects with macroalbuinuria and microalbuminuria compared to those with normoalbuminuria. The mean ACR levels and mean serum C-reactive protein levels in CC carriers were significantly higher than in GG and GC carriers. There was a significant, positive correlation between serum hs-C-reactive protein levels and ACR levels. We conclude that OLR-1 polymorphisms at G501C affect the severity of albuminuria in essential hypertension patients.

The G501C polymorphism of oxidized LDL receptor gene [OLR-1] is associated with susceptibility and serum C-reactive protein concentration in Chinese essential hypertensives

BACKGROUND

Oxidized LDL receptor gene 1 (OLR-1) polymorphism is reportedly associated with several cardiovascular conditions. However, its relationship with essential hypertension remains unknown. The aim of this study is to explore the association of OLR-1 polymorphism at position 501 in the open reading frame (G501C), with the susceptibility of essential hypertension.

METHODS

2-hundred eighty Chinese essential hypertensive and 284 control subjects were enrolled and genetic study was performed. The clinical data, i.e., sex, age, blood pressure, body mass index, smoking history, lipid profile and serum C-reactive protein concentration in both hypertensives and controls were obtained.

RESULTS

A significant difference in OLR-1 genotype distributions was noted between the hypertensives and the controls (GG: 67.9% vs. 70.8%; GC: 20.0% vs. 23.6%; CC: 12.1% vs. 5.6%, P=0.021). For G and C allele frequencies, the difference between these 2 groups was significant as well (G: 67.5% vs. 23.5%, C: 82.6% vs. 17.4%, P=0.011). Logistic regression analysis revealed that the CC genotype is an independent risk factor for hypertension (OR=3.036, 95% CI: 1.572-6.174, P=0.016). Furthermore, when the serum C-reactive protein concentration in the hypertensive group was studied according to OLR-1 genotypes, the serum CRP concentration in CC homozygous carriers were found significantly higher than that in GC and GG carriers (1.53+/-0.32, 1.31+/-0.32 and 2.94+/-1.29 respectively, P=0.002).

CONCLUSIONS

The CC genotype of OLR-1 G501C polymorphism is associated with susceptibility and serum C-reactive protein concentration in Chinese essential hypertensive population.

Lectin-like oxidized-LDL receptor-1 (LOX-1) polymorphisms influence cardiovascular events rate during statin treatment

BACKGROUND

Oxidized-LDL (ox-LDL) are involved in atherothrombosis by induction of endothelial dysfunction and thrombosis. The specific receptor lectin-like oxidized-LDL receptor-1 (LOX-1) is expressed in endothelial cells, monocytes and platelets. LOX-1 gene allelic variants (3'UTR/T) have been related with cardiovascular events and reduced anti-platelet activity induced by statins.

OBJECTIVES

To detect whether LOX-1 polymorphisms could affect statins effectiveness in cardiovascular prevention.

PATIENTS/METHODS

The present was a retrospective study performed in 751 white hypercholesterolemic subjects treated with increasing doses of atorvastatin (n=382, 247 male, 135 female) or simvastatin (n=369, 244 male, 125 female) up to 4 years, whose LDL target was 3.36 mmol/L according to the National Cholesterol Education Program, Adult Treatment Panel III (NCEP-ATPIII). Single nucleotide polymorphism were evaluated by allelic discrimination assays (PCR), lipid profile by enzymatic-colorimetric methods and C-reactive protein (CRP) by a nephelometric technique.

RESULTS

Twenty-three non-ST elevation (NSTEMI) and eleven ST-elevation myocardial infarction (STEMI) were encountered in the observational period without differences between treatments (p=0.175) and sex (p=0.139). Each symptomatic subject (10 reaching the appropriate LDL target and 24 with still undesirable LDL) had the 3'UTR/T allelic variant (adjusted O.R. 4.63, 95% C.I. 3.46-6.70, p<0.0001). Among patients not reaching LDL target the C allele resulted protective with respect to T carriers (p<0.00001). Also, similar changes of CRP resulted in different event rate between T and C carriers (p<0.001) in the whole cohort.

CONCLUSIONS

In the studied population LOX-1 genetic variants influence cardiovascular risk reduction induced by statins also in patients not reaching the LDL target. The previously described LOX-1-related antithrombotic actions of both statins employed could have a specific role in what observed, suggesting a genetic influence in statins LDL-lowering partially related actions.

The expression of recombinant human LOX-1 and identifying its mimic ligands by fluorescence polarization-based high throughput screening

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) was identified as a major receptor for oxidized low-density lipoprotein (oxLDL) in endothelial cells. LOX-1 critically mediates the endothelial dysfunction and the progression of atherosclerosis by oxLDL stimulation. It might be an important target for vascular endothelium. In order to obtain human LOX-1 and identify its mimic ligand for facilitating the study of LOX-1 function, a recombinant plasmid pPIC9K-His-hLOX-1 was structured and expressed human LOX-1 in Pichia pastoris GS115. Western blot analysis ensured the expressed recombinant human LOX-1 protein and a receptor-ligand binding assay showed that it had high binding affinity with oxLDL. With this receptor protein, a competitive fluorescence polarization-based high throughput screening method was established in a 384-well microplate to isolate the mimic ligands of human LOX-1. The evaluating parameter Z' value of 0.72 for this method showed that fluorescence polarization-based high throughput screening assay was robust and the results had a high reliability. By the fluorescence polarization-based high throughput screening assay, a total of 20,316 chemicals were screened, and 2 chemicals were identified that they have a high affinity with human LOX-1. Competitive uptake DiI-oxLDL assay by human LOX-1 transfected CHO-K1 cells further confirmed that two chemicals block the uptake of DiI-oxLDL. And the preliminary results indicated that isolated mimic ligands may act as a function of antagonist. The discovery of human LOX-1 mimic ligand would benefit to further study the function of LOX-1 and identify a novel avenue for prevention and treatment atherosclerosis.