Lectin-like oxidized low density lipoprotein receptor-1 (LOX-1), the main oxidized low-density lipoprotein (OxLDL) in endothelial cells, is upregulated in atherosclerotic lesions and is involved in several cellular processes that regulate the pathogenesis of atherosclerosis. The LOX-1 expressed on the cell surface can be proteolytically cleaved and released in a soluble form (sLOX-1) in the circulation under pathological conditions. Serum levels of sLOX-1, in fact, are elevated at the early stages of acute coronary syndrome and are associated with coronary plaque vulnerability and with the presence of multiple complex coronary lesions. Moreover, in subjects with stable CAD, levels of serum sLOX-1 are associated with the presence of lesions in the proximal and mid-segments of the left anterior descending artery that are the most prone to rupture; in subjects undergoing percutaneous coronary intervention, baseline preprocedural serum sLOX-1 levels are associated with the incidence of periprocedural myocardial infarction. Altogether, these findings suggest that circulating levels of sLOX-1 might be a diagnostic and prognostic marker for atherosclerotic-related events.
We investigated the association between soluble lectin-like oxidized LDL receptor 1 (sLOX-1) levels and obesity in older women. Fifty-one (10 lean, 22 overweight, and 19 obese) postmenopausal women were included in this small retrospective analysis. Plasma sLOX-1 levels were measured using a chemiluminescent ELISA. Plasma levels of sLOX-1 were significantly higher in obese women (55.33±4.49 pg/mL) compared to lean (30.91±6.19 pg/mL, p=0.002) and overweight women (38.31±4.18 pg/mL, p=0.017). Plasma sLOX-1 levels were positively associated with body weight, BMI, total body fat, and trunk fat. The relationship between sLOX-1 and BMI was attenuated after adjustment for age, HRT, and body fat. In conclusion, obese women have higher sLOX-1 levels, which may reflect increased LOX-1 expression in adipose tissue.
obesity; postmenopausal women; receptors
Background/Objective. It is known that menopause or lack of endogenous estrogen is a risk factor for endothelial dysfunction and CAD. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is involved inmultiple phases of vascular dysfunction.The purpose of the current study was to determine the association between soluble LOX-1 (sLOX-1) and pregnancy followed by delivery in women of reproductive age. Materials/Methods. Sixty-eight subjects with pregnancy followed by delivery (group 1) and 57 subjects with nongravidity (group 2) were included in this study. Levels of sLOX-1 were measured in serum by EL SA. Results. Plasma levels of sLOX-1 were significantly lower in Group 1 than Group 2 in women of reproductive age (0.52 ± 0.18 ng/mL and 0.78 ± 0.13, resp., P < 0.001). There were strong correlations between sLOX-1 levels and the number of gravida (r = −0.645, P < 0.001). The levels of sLOX-1 highly correlated with the number of parous (r = −0.683, P < 0.001). Conclusion. Our study demonstrated that serum sLOX-1 levels were associated with pregnancy followed by delivery that might predict endothelial dysfunction. We conclude that pregnancy followed by delivery may delay the beginning and progress of arteriosclerosis and its clinical manifestations in women of reproductive age.
Elevated circulating levels of soluble lectin-like oxidized low-density lipoprotein receptor-1 (sLOX-1) have been observed in obese persons and are reduced by weight loss. However, it is not known if combining caloric restriction (CR) with exercise training is better in reducing sLOX-1 levels than CR alone.
We examined whether the addition of aerobic exercise to a weight loss intervention differentially affects sLOX-1 levels in 61 abdominally obese postmenopausal women randomly assigned to a CR only (n=22), CR + moderate-intensity exercise (n=22), or CR + vigorous-intensity exercise (n=17) intervention for 20 weeks. The caloric deficit was ~2,800 kcal/week for all groups.
The intervention groups were similar at baseline with respect to body weight, body composition, lipids, and blood pressure. However, plasma sLOX-1 levels were higher in the CR only group (99.90 ± 8.23 pg/ml) compared to both the CR + moderate-intensity exercise (69.39 ± 8.23 pg/ml, p=0.01) and CR + vigorous-intensity exercise (72.83 ± 9.36 pg/ml, p=0.03) groups. All three interventions significantly reduced body weight (~14%), body fat, and waist and hip circumferences to a similar degree. These changes were accompanied by a 23% reduction in sLOX-1 levels overall (−19.00 ± 30.08 pg/ml, p<0.0001), which did not differ among intervention groups (p=0.13). Changes in body weight, body fat, and VO2 max were not correlated with changes in sLOX-1 levels. In multiple regression analyses in all women combined, baseline sLOX-1 levels (β = − 0.70 ± 0.06, p<0.0001), age (β = 0.92 ± 0.43, p=0.03) and baseline BMI (β = 1.88 ± 0.66, p=0.006) were independent predictors of the change in sLOX-1 with weight loss.
Weight loss interventions of equal energy deficit have similar effects on sLOX-1 levels in overweight and obese postmenopausal women, with the addition of aerobic exercise having no added benefit when performed in conjunction with CR.
obesity; weight loss; caloric restriction; aerobic exercise; soluble receptor
The human cutaneous circulation is an accessible and representative regional circulation for investigating mechanisms of microvascular dysfunction, a systemic disease process occurring early in the pathogenesis of atherosclerosis. Elevated concentrations of low-density lipoproteins ([LDL]) are highly atherogenic and independently associated with the severity of coronary atherosclerosis through their actions on the lectin-like oxidized LDL receptors (LOX-1). We hypothesized that cutaneous microvascular dysfunction, as measured by a decrement in endothelial nitric oxide- (NO-) dependent vasodilation during local heating, would be correlated with serum [LDL], oxidized [LDL], and soluble LOX-1 receptors [sLOX-1]. Intradermal microdialysis fibers were placed in the skin of 53 otherwise healthy men and women (aged 52±8 years) whose serum [LDL] ranged from 72 to 233 mg/dL. Skin blood flow was measured by laser Doppler flowmetry over a local forearm skin site as it was heated (42 °C) to induce sustained local vasodilation. After flux plateaued, L-NAME was infused to block endothelial NO synthase in order to determine the NO-dependent portion of the vasodilatory response. Data were normalized to maximal cutaneous vascular conductance (CVC). NO-dependent vasodilation was reduced as a linear function of [LDL] (R2=0.303, p<0.001), oxidized [LDL] (R2=0.214, p<0.001), and [sLOX-1] (R2=0.259, p=0.026) but was unrelated to high-density lipoprotein (HDL) concentration (R2=0.003, p=0.68). Hypercholesterolemia-induced microvascular dysfunction is related to various LDL markers and involves a reduction in NO-dependent vasodilation that appears to be a progressive process measurable in the skin microcirculation.
Oxidized low-density lipoprotein (OxLDL) contributes to the atherosclerotic plaque formation and progression by several mechanisms, including the induction of endothelial cell activation and dysfunction, macrophage foam cell formation, and smooth muscle cell migration and proliferation. Vascular wall cells express on their surface several scavenger receptors that mediate the cellular effects of OxLDL. The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is the main OxLDL receptor of endothelial cells, and it is expressed also in macrophages and smooth muscle cells. LOX-1 is almost undetectable under physiological conditions, but it is upregulated following the exposure to several proinflammatory and proatherogenic stimuli and can be detected in animal and human atherosclerotic lesions. The key contribution of LOX-1 to the atherogenic process has been confirmed in animal models; LOX-1 knockout mice exhibit reduced intima thickness and inflammation and increased expression of protective factors; on the contrary, LOX-1 overexpressing mice present an accelerated atherosclerotic lesion formation which is associated with increased inflammation. In humans, LOX-1 gene polymorphisms were associated with increased susceptibility to myocardial infarction. Inhibition of the LOX-1 receptor with chemicals or antisense nucleotides is currently being investigated and represents an emerging approach for controlling OxLDL-LOX-1 mediated proatherogenic effects.
LOX-1 is an endothelial receptor for oxidized low-density lipoprotein (oxLDL), a key molecule in the pathogenesis of atherosclerosis.The basal expression of LOX-1 is low but highly induced under the influence of proinflammatory and prooxidative stimuli in vascular endothelial cells, smooth muscle cells, macrophages, platelets and cardiomyocytes. Multiple lines of in vitro and in vivo studies have provided compelling evidence that LOX-1 promotes endothelial dysfunction and atherogenesis induced by oxLDL. The roles of LOX-1 in the development of atherosclerosis, however, are not simple as it had been considered. Evidence has been accumulating that LOX-1 recognizes not only oxLDL but other atherogenic lipoproteins, platelets, leukocytes and CRP. As results, LOX-1 not only mediates endothelial dysfunction but contributes to atherosclerotic plaque formation, thrombogenesis, leukocyte infiltration and myocardial infarction, which determine mortality and morbidity from atherosclerosis. Moreover, our recent epidemiological study has highlighted the involvement of LOX-1 in human cardiovascular diseases. Further understandings of LOX-1 and its ligands as well as its versatile functions will direct us to ways to find novel diagnostic and therapeutic approaches to cardiovascular disease.
LOX-1; Endothelial cells; Atherosclerosis; Oxidized LDL
Increased plasma C-reactive protein (CRP) levels are associated with the occurrence and severity of acute coronary syndrome. We investigated whether CRP can be generated in vascular endothelial cells (ECs) after exposure to the most electronegative subfraction of low-density lipoprotein (LDL), L5, which is atherogenic to ECs. Because L5 and CRP are both ligands for the lectin-like oxidized LDL receptor-1 (LOX-1), we also examined the role of LOX-1.
Methods and Results
Plasma LDL samples isolated from asymptomatic hypercholesterolemic (LDL cholesterol [LDL-C] levels, 154.6±20 mg/dL; n = 7) patients and normocholesterolemic (LDL-C levels, 86.1±21 mg/dL; P<0.001; n = 7) control individuals were chromatographically resolved into 5 subfractions, L1-L5. The L5 percentage (L5%) and the plasma L5 concentration ([L5] = L5% × LDL-C) in the patient and control groups were 8.1±2% vs. 2.3±1% (P<0.001) and 12.6±4 mg/dL vs. 1.9±1 mg/dL (P<0.001), respectively. In hypercholesterolemic patients treated with atorvastatin for 6 months (10 mg/day), [L5] decreased from 12.6±4 mg/dL to 4.5±1.1 mg/dL (P = 0.011; n = 5), whereas both [L5] and L5% returned to baseline levels in 2 noncompliant patients 3 months after discontinuation. In cultured human aortic ECs (HAECs), L5 upregulated CRP expression in a dose- and time-dependent manner up to 2.5-fold (P<0.01), whereas the least electronegative subfraction, L1, had no effect. DiI-labeled L1, internalized through the LDL receptor, became visible inside HAECs within 30 seconds. In contrast, DiI-labeled L5, internalized through LOX-1, became apparent after 5 minutes. L5-induced CRP expression manifested at 30 minutes and was attenuated by neutralizing LOX-1. After 30 minutes, L5 but not L1 induced reactive oxygen species (ROS) production. Both L5-induced ROS and CRP production were attenuated by ROS inhibitor N-acetyl cysteine.
Our results suggest that CRP, L5, and LOX-1 form a cyclic mechanism in atherogenesis and that reducing plasma L5 levels with atorvastatin disrupts the vascular toxicity of L5.
The human lectin-like oxidized low density lipoprotein receptor 1 LOX-1, encoded by the ORL1 gene, is the major scavenger receptor for oxidized low density lipoprotein in endothelial cells. Here we report on the functional effects of a coding SNP, c.501G>C, which produces a single amino acid change (K>N at codon 167). Our study was aimed at elucidating whether the c.501G>C polymorphism changes the binding affinity of LOX-1 receptor altering its function. The presence of p.K167N mutation reduces ox-LDL binding and uptake. Ox-LDL activated extracellular signal-regulated kinases 1 and 2 (ERK 1/2) is inhibited. Furthermore, ox-LDL induced biosynthesis of LOX-1 receptors is dependent on the p.K167N variation. In human macrophages, derived from c.501G>C heterozygous individuals, the ox-LDL induced LOX-1 46 kDa band is markedly lower than in induced macrophages derived from c.501G>C controls. Investigation of p.K167N mutation through molecular dynamics simulation and electrostatic analysis suggests that the ox-LDL binding may be attributed to the coupling between the electrostatic potential distribution and the asymmetric flexibility of the basic spine residues. The N/N-LOX-1 mutant has either interrupted electrostatic potential and asymmetric fluctuations of the basic spine arginines.
The lectin-like oxidized LDL receptor LOX-1 (encoded by OLR1) is believed to play a key role in atherogenesis and some reports suggest an association of OLR1 polymorphisms with myocardial infarction (MI). We tested whether single nucleotide polymorphisms (SNPs) in OLR1 are associated with clinically significant CAD in the Atherosclerotic Disease, VAscular FuNction, & Geneti C Epidemiology (ADVANCE) study.
ADVANCE is a population-based case-control study of subjects receiving care within Kaiser Permanente of Northern California including a subset of participants of the Coronary Artery Risk Development in Young Adults (CARDIA) study. We first resequenced the promoter, exonic, and splice site regions of OLR1 and then genotyped four single nucleotide polymorphisms (SNPs), including a non-synonymous SNP (rs11053646, Lys167Asn) as well as an intronic SNP (rs3736232) previously associated with CAD.
In 1,809 cases with clinical CAD and 1,734 controls, the minor allele of the coding SNP was nominally associated with a lower odds ratio (OR) of CAD across all ethnic groups studied (minimally adjusted OR 0.8, P = 0.007; fully adjusted OR 0.8, P = 0.01). The intronic SNP was nominally associated with an increased risk of CAD (minimally adjusted OR 1.12, p = 0.03; fully adjusted OR 1.13, P = 0.03). However, these associations were not replicated in over 13,200 individuals (including 1,470 cases) in the Atherosclerosis Risk in Communities (ARIC) study.
Our results do not support the presence of an association between selected common SNPs in OLR1 and the risk of clinical CAD.
Lectin-like oxidized low-density lipoprotein (LDL) receptor-1 (LOX-1) is the major receptor for oxidized LDL (oxLDL), and plays a key role in the pathogenesis of atherosclerosis and cardiovascular diseases. Monoclonal antibodies (mAbs) specific for human LOX-1 (hLOX-1) were generated by a phage display technique using chickens immunized with recombinant hLOX-1 (rhLOX-1). A total of 53 independent scFv clones reactive for rhLOX-1 were obtained. Of the 53 clones, 49 recognized the C-type lectin-like domain (CTL domain), which contributes to the binding of oxLDL. Of these, 45 clones inhibited oxLDL-binding with LOX-1. Furthermore, some of these clones cross-reacted with rabbit, pig and/or mouse LOX-1. For possible application as therapeutic agents in the future, two cross-reactive mAbs were re-constructed as chicken-human chimeric antibodies. The chimeric antibodies showed similar characteristics compared to the original antibodies, and inhibited oxLDL binding to LOX-1 expressed on CHO cells. The results obtained in this study indicate that anti-LOX-1 mAbs might be useful tools for functional analyses and development of therapeutic agents for cardiovascular indications such as atherosclerosis.
LOX-1; oxLDL; chicken monoclonal antibody; chimeric antibody; neutralizing antibody
Increased prevalence of atherosclerotic cardiovascular disease in HIV-infected patients has been observed. The cause of this accelerated atherosclerosis is a matter of controversy. As clinical studies are complicated by a multiplicity of risk-factors and a low incidence of hard endpoints, studies in animal models could be attractive alternatives.
We evaluated gene expression of lectin-like oxidized-low-density-lipoprotein receptor-1 (LOX-1), vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) in HIV-1 transgenic (HIV-1Tg) rats; these genes are all thought to play important roles in early atherogenesis. Furthermore, the plasma level of sICAM-1 was measured. We found that gene expressions of LOX-1 and VCAM-1 were higher in the aortic arch of HIV-1Tg rats compared to controls. Also, the level of sICAM-1 was elevated in the HIV-1Tg rats compared to controls, but the ICAM-1 gene expression profile did not show any differences between the groups.
HIV-1Tg rats have gene expression patterns indicating endothelial dysfunction and accelerated atherosclerosis in aorta, suggesting that HIV-infection per se may cause atherosclerosis. This transgenic rat model may be a very promising model for further studies of the pathophysiology behind HIV-associated cardiovascular disease.
The oxidized-LDL receptor LOX-1 plays a crucial role in atherosclerosis. We sought to detect and assess atherosclerotic plaque in vivo using SPECT/CT and magnetic resonance imaging (MRI) using a molecular probe targeted at LOX-1.
Methods & Results
Apo E−/− mice on Western diet and LDLR−/− and LDLR−/−/LOX-1−/− mice on atherogenic diet were used. Imaging probes consisted of liposomes decorated with LOX-1 antibodies (LOX-1) or nonspecific IgG (nIgG), 111In or gadolinium (Gd), and DiI fluorescence markers. In vivo imaging was performed 24 hrs after intravenous injection (150 µl) of LOX-1 (or nIgG) probes labeled with either 111In (600 µCi) or Gd (0.075 mmol/kg) followed by aortic excision for phosphor imaging and Sudan IV staining or fluorescence imaging and H&E staining. The LOX-1 probe was also co-localized with specific cell types, apoptosis, and MMP9 expression using frozen aortic sections.
SPECT/CT imaging of the LOX-1 probe showed aortic arch hotspots in Apo E−/− mice (n=8), confirmed by phosphor imaging. MRI showed significant Gd enhancement in atherosclerotic plaques in LDLR−/− mice with the LOX-1 (n=7), but not nIgG, probe (n=5). No signal enhancement was observed in LDLR−/−/LOX-1−/− mice injected with LOX-1 probe (n=5). These results were confirmed by ex-vivo fluorescence imaging. The LOX-1 probe bound preferentially to the plaque shoulder, a region with vulnerable plaque features including extensive LOX-1 expression, macrophage accumulation, apoptosis and MMP9 expression.
LOX-1 can be used as a target for molecular imaging of atherosclerotic plaque in vivo. Furthermore, LOX-1 imaging may identify rupture-prone atherosclerotic plaque.
Molecular imaging; LOX-1; atherosclerotic plaque; SPECT; MRI
AIM: To investigate the effects of sleeve gastrectomy on adipose tissue infiltration and lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) expression in rat aortas.
METHODS: Twenty-four rats were randomized into three groups: normal chow (control), high fat diet (HD) and high fat diet with sleeve gastrectomy (SG). After surgery, the HD and SG groups were fed a high fat diet. Animals were sacrificed and plasma high density lipoprotein (HDL) and low density lipoprotein (LDL) levels were determined. LOX-1 protein and LOX-1 mRNA expression was also measured. Aortas were stained with Nile red to visualize adipose tissue.
RESULT: Body weights were higher in the HD group compared to the other groups. HDL levels in control, HD, and SG groups were 32.9 ± 6.2 mg/dL, 43.4 ± 4.0 mg/dL and 37.5 ± 4.3 mg/dL, respectively. LDL levels in control, HD, and SG groups were 31.8 ± 4.5 mg/dL, 53.3 ± 5.1 mg/dL and 40.5 ± 3.7 mg/dL, respectively. LOX-1 protein and LOX-1 mRNA expression was greater in the HD group versus the other groups. Staining for adipose tissue in aortas was greater in the HD group in comparison to the other groups. Thus, a high fat diet elevates LOX-1 protein and mRNA expression in aorta.
CONCLUSION: Sleeve gastrectomy decreases plasma LDL levels, and downregulates LOX-1 protein and mRNA expression.
Sleeve gastrectomy; Morbid obesity; High fat diet; Aorta; Lipoprotein receptor-1 expression
Lectin-like oxidized LDL receptor-1 (LOX-1) is an endothelial receptor for oxidized LDL (oxLDL) and plays multiple roles in the development of cardiovascular diseases. We screened more than 400 foodstuff extracts for identifying materials that inhibit oxLDL binding to LOX-1. Results showed that 52 extracts inhibited LOX-1 by more than 70% in cell-free assays. Subsequent cell-based assays revealed that a variety of foodstuffs known to be rich in procyanidins such as grape seed extracts and apple polyphenols, potently inhibited oxLDL uptake in Chinese hamster ovary (CHO) cells expressing LOX-1. Indeed, purified procyanidins significantly inhibited oxLDL binding to LOX-1 while other ingredients of apple polyphenols did not. Moreover, chronic administration of oligomeric procyanidins suppressed lipid accumulation in vascular wall in hypertensive rats fed with high fat diet. These results suggest that procyanidins are LOX-1 inhibitors and LOX-1 inhibition might be a possible underlying mechanism of the well-known vascular protective effects of red wine, the French Paradox.
LOX-1; cardiovascular diseases; lipid accumulation; procyanidin; French Paradox
Cardiovascular disease is the leading cause of death. The disease is due to atherosclerosis which is characterized by lipid and fat accumulation in arterial blood vessel walls. A key causative event is the accumulation of oxidised low density lipoprotein particles within vascular cells, and this is mediated by scavenger receptors. One such molecule is the LOX-1 scavenger receptor that is expressed on endothelial, vascular smooth muscle, and lymphoid cells including macrophages. LOX-1 interaction with OxLDL particles stimulates atherosclerosis. LOX-1 mediates OxLDL endocytosis via a clathrin-independent internalization pathway. Transgenic animal model studies show that LOX-1 plays a significant role in atherosclerotic plaque initiation and progression. Administration of LOX-1 antibodies in cellular and animal models suggest that such intervention inhibits atherosclerosis. Antiatherogenic strategies that target LOX-1 function using gene therapy or small molecule inhibitors would be new ways to address the increasing incidence of vascular disease in many countries.
The association of Chlamydia pneumoniae and atherosclerosis has been well documented. Recently, it has been demonstrated that C. pneumoniae upregulates expression of the lectin-like ox-LDL receptor (LOX-1) in endothelial cells. Many of the pro-atherogenic effects of ox-LDL occur through its activation of and uptake by LOX-1. This class E scavenger receptor contains a carbohydrate recognition domain common to the C type lectin family. Previously, we have demonstrated that the major outer membrane protein of the chlamydiae is glycosylated and glycan removal abrogates infectivity of C. pneumoniae for endothelial cells. In this study, we investigated whether C. pneumoniae binds to LOX-1. The results show that 1) infection of endothelial cells by C. pneumoniae is inhibited by ligands that bind to the LOX-1 receptor, but not by ligands binding to other scavenger receptors; 2) anti-LOX-1 antibody inhibits C. pneumoniae infectivity, while antibodies against other scavenger receptors do not; 3) anti-LOX-1 antibody inhibits attachment of C. pneumoniae to endothelial cells; and 4) C. pneumoniae co-localizes with LOX-1. These effects were not observed for Chlamydia trachomatis. In conclusion, C. pneumoniae binds to the LOX-1 receptor, which is known to promote atherosclerosis.
Chlamydia pneumoniae; LOX-1 receptor; Atherosclerosis
Oxidized low-density lipoprotein (ox-LDL) is an important risk factor in the development of atherosclerosis. LOX-1, a lectin-like receptor for ox-LDL, is present primarily on endothelial cells and upregulated by ox-LDL, tumor necrosis factor a, shear stress, and cytokines in atherosclerosis. Recent studies demonstrated that ginkgolide B, a platelet-activating factor receptor antagonist, has antiinflammatory and antioxidant effects on endothelial and nerve cells. The present study investigated the effects of ginkgolide B on LOX-1 expression and the possible mechanism of action. Our results showed that ginkgolide B inhibited LOX-1 and intercellular cell adhesion molecule-1 (ICAM-1) expression in ox-LDL-stimulated endothelial cells through a mechanism associated with the attenuation of Akt activation. Similar data were obtained by silencing Akt and LY294002. We also evaluated Sirt1 and nuclear factor erythroid 2-related factor 2 (Nrf2) expression. These molecules play a protective role in endothelial cell injury. The results showed that ginkgolide B increased Sirt1 expression in ox-LDL-treated cells. The inhibitory effects of ginkgolide B on LOX-1 and ICAM-1 expression were reduced in Sirt1 siRNA-transfected cells. Nrf2 expression was increased in ox-LDL-treated cells, and ginkgolide B downregulated Nrf2 expression. These results suggest that ginkgolide B reduces Nrf2 expression by inhibiting LOX-1 expression, consequently reducing oxidative stress injury in ox-LDL-stimulated cells. Altogether, these results indicate that the protective effect of ginkgolide B on endothelial cells may be attributable to a decrease in LOX-1 expression and an increase in Sirt1 expression in ox-LDL-stimulated endothelial cells, the mechanism of which is linked to the inhibition of Akt activation. Ginkgolide B may be a multiple-target drug that exerts protective effects in ox-LDL-treated human umbilical vein endothelial cells.
Oxidized low-density lipoproteins (oxLDL) and the lectin-like oxLDL receptor-1 (LOX-1) are upregulated in inflammation. Because of the importance of inflammation and capillary leakage in the impairment of the microcirculation, which in turn contributes to the development of sepsis and multiorgan failure, the role of oxidized LDL and LOX-1 as players of intestinal inflammation is of great interest. In fact, the blockade of LOX-1 during experimental endotoxemia was effective in reducing leukocyte activation. There are several mechanisms by which oxLDL can participate in local and systemic inflammation, including cell proliferation, apoptosis, capillary perfusion, leukocyte-endothelial cell interactions, and endothelial activation. This review highlights the evidence relating oxLDL and LOX-1 to proinflammatory disease mechanisms. We also indicate situations when oxLDL, because of exposure time, dose, or degree of oxidization, is involved in disease resolution. Modulation of LOX-1 response could be utilized for the treatment of local and systemic inflammation, but the successful use of this target requires further understanding of its broad effects.
Inflammatory tissue injury and immunosuppression are the major causes of death in sepsis. Novel therapeutic targets that can prevent excessive inflammation and improve immune responses during sepsis could be critical for treatment of this devastating disease. LOX-1 (lectin-like oxidized low-density lipoprotein receptor-1), a membrane protein expressed in endothelial cells, has been known to mediate vascular inflammation. In the present study, we demonstrated that LOX-1 deletion markedly improved the survival rate in a murine model of polymicrobial sepsis. Wild-type (LOX-1+/+) and LOX-1 knockout (LOX-1−/−) mice were subjected to cecal ligation and puncture (CLP) to induce sepsis. LOX-1 deletion significantly reduced systemic inflammation and inflammatory lung injury during sepsis, together with decreased production of proinflammatory cytokines and reduced lung edema formation. Furthermore, LOX-1 deletion improved host immune responses after the induction of sepsis, as indicated by enhanced bacterial clearance. Interestingly, we were able to demonstrate that LOX-1 is expressed in neutrophils. LOX-1 deletion prevented neutrophil overreaction and increased neutrophil recruitment to infection sites after sepsis induction, contributing at least partly to increased immune responses in LOX-1 knockout mice. Our study results indicate that LOX-1 is an important mediator of inflammation and neutrophil dysfunction in sepsis.
Lectin-like ox-LDL receptors (LOX-1) play a crucial role in the ox-LDL–induced pathological transformation of vessel-wall components, a crucial early step in atherogenesis. LOX-1 dynamics is quantitatively investigated in human endothelial cells (HUVECs) exposed to environmental nanotopographies. We demonstrate distinct nanotopography-induced cell phenotypes, characterized by different morphology, LOX-1 diffusivity and oligomerization state: HUVECs on flat surfaces exhibit the behavior found in pro-atherogenic conditions, while growth on nanogratings can interfere with LOX-1 dynamics and lead to a behavior characteristic of normal, non-pathological conditions.
Scavenger receptors play crucial roles in the pathogenesis of atherosclerosis, but their role in insulin resistance has not been explored. We hypothesized that scavenger receptors are present in human adipose tissue resident macrophages, and their gene expression is regulated by adiponectin and thaizolidinediones.
Methods and Results
The gene expression of scavenger receptors including scavenger receptor-A (SRA), CD36, and lectin-like oxidized LDL receptor-1 (LOX-1) were studied in subcutaneous adipose tissue of nondiabetic subjects and in vitro. Adipose tissue SRA expression was independently associated with insulin resistance. Pioglitazone downregulated SRA gene expression in adipose tissue of subjects with impaired glucose tolerance and decreased LOX-1 mRNA in vitro. Macrophage LOX-1 expression was decreased when macrophages were cocultured with adipocytes or when exposed to adipocyte conditioned medium. Adding adiponectin neutralizing antibody resulted in a 2-fold increase in LOX-1 gene expression demonstrating that adiponectin regulates LOX-1 expression.
Adipose tissue scavenger receptors are strongly associated with insulin resistance. Pioglitazone and adiponectin regulate gene expression of SRA and LOX-1, and this may have clinical implications in arresting the untoward sequalae of insulin resistance and diabetes, including accelerated atherosclerosis.
scavenger receptors; insulin resistance; pioglitazone; adiponectin
Anion-exchange chromatography resolves human plasma low-density lipoprotein (LDL) into 5 subfractions, with increasing negative surface charge in the direction of L1 to L5. Unlike the harmless L1 to L4, the exclusively atherogenic L5 is rejected by the normal LDL receptor (LDLR) but endocytosed into vascular endothelial cells through the lectin-like oxidized LDL receptor-1 (LOX-1). Analysis with SDS-PAGE and 2-dimensional electrophoresis showed that the protein framework of L1 was composed mainly of apolipoprotein (apo) B100, with an isoelectric point (pI) of 6.620. There was a progressively increased association of additional proteins, including apoE (pI 5.5), apoAI (pI 5.4), apoCIII (pI 5.1), and apo(a) (pI 5.5), from L1 to L5. LC/MSE was used to quantify protein distribution in all subfractions. On the basis of weight percentages, L1 contained 99% apoB-100 and trace amounts of other proteins. In contrast, L5 contained 60% apoB100 and substantially increased amounts of apo(a), apoE, apoAI, and apoCIII. The compositional characteristics contribute to L5’s electronegativity, rendering it unrecognizable by LDLR. LOX-1, which has a high affinity for negatively charged ligands, is known to mediate the signaling of proinflammatory cytokines. Thus, the chemical composition–oriented receptor selectivity hinders normal metabolism of L5, enhancing its atherogenicity through abnormal receptors, such as LOX-1.
low-density lipoprotein; apolipoproteins; electronegative; LDL receptor; LOX-1; atherosclerosis
Oxidized LDL (ox-LDL) is a key factor in atherogenesis. It is taken up by endothelial cells primarily by ox-LDL receptor-1 (LOX-1). To elucidate transcriptional responses, we performed microarray analysis on human coronary artery endothelial cells (HCAECs) exposed to small physiologic concentration of ox-LDL- 5 µg/ml for 2 and 12 hours. At 12 hours, cultures treated with ox-LDL exhibited broad shifts in transcriptional activity involving almost 1500 genes (>1.5 fold difference, p<0.05). Resulting transcriptome was enriched for genes associated with cell adhesion (p<0.002), angiogenesis (p<0.0002) and migration (p<0.006). Quantitative PCR analysis revealed that LOX-1 expression in HCAECs is at least an order of magnitude greater than the expression of other major ox-LDL specific receptors CD36 and MSR1. In keeping with the data on LOX-1 expression, pre-treatment of HCAECs with LOX-1 neutralizing antibody resulted in across-the-board inhibition of cellular response to ox-LDL. Ox-LDL upregulated a number of pro-angiogenic genes including multiple receptors, ligands and transcription factors and altered the expression of a number of genes implicated in both stimulation and inhibition of apoptosis. From a functional standpoint, physiologic concentrations of ox-LDL stimulated tube formation and inhibited susceptibility to apoptosis in HCAECs. In addition, ox-LDL exposure resulted in upregulation of miR-1974, miR-1978 and miR-21 accompanied with significant over-presentation of their target genes in the downregulated portion of ox-LDL transcriptome. Our observations indicate that ox-LDL at physiologic concentrations induces broad transcriptional responses which are mediated by LOX-1, and are, in part, shaped by ox-LDL-dependent miRNAs. We also suggest that angiogenic effects of ox-LDL are partially based on upregulation of several receptors that render cells hypersensitive to angiogenic stimuli.
Rationale: To determine vascular signaling pathways involved in inhaled air pollution (vehicular engine emission) exposure–induced exacerbation of atherosclerosis that are associated with onset of clinical cardiovascular events.
Objectives: To elucidate the role of oxidized low-density lipoprotein (oxLDL) and its primary receptor on endothelial cells, the lectin-like oxLDL receptor (LOX-1), in regulation of endothelin-1 expression and matrix metalloproteinase activity associated with inhalational exposure to vehicular engine emissions.
Methods: Atherosclerotic apolipoprotein E knockout mice were exposed by inhalation to filtered air or mixed whole engine emissions (250 μg particulate matter [PM]/m3 diesel + 50 μg PM/m3 gasoline exhausts) 6 h/d for 7 days. Concurrently, mice were treated with either mouse IgG or neutralizing antibodies to LOX-1 every other day. Vascular and plasma markers of oxidative stress and expression proatherogenic factors were assessed. In a parallel study, healthy human subjects were exposed to either 100 μg PM/m3 diesel whole exhaust or high-efficiency particulate air and charcoal-filtered “clean” air (control subjects) for 2 hours, on separate occasions.
Measurements and Main Results: Mixed emissions exposure increased oxLDL and vascular reactive oxygen species, as well as LOX-1, matrix metalloproteinase-9, and endothelin-1 mRNA expression and also monocyte/macrophage infiltration, each of which was attenuated with LOX-1 antibody treatment. In a parallel study, diesel exhaust exposure in volunteer human subjects induced significant increases in plasma-soluble LOX-1.
Conclusions: These findings demonstrate that acute exposure to vehicular source pollutants results in up-regulation of vascular factors associated with progression of atherosclerosis, endothelin-1, and matrix metalloproteinase-9, mediated through oxLDL–LOX-1 receptor signaling, which may serve as a novel target for future therapy.
atherosclerosis; particulate matter; endothelin-1; matrix metalloproteinase; oxidized low-density lipoprotein