review article lox-1, oxldl, and...

Hindawi Publishing CorporationMediators of InflammationVolume 2013 Article ID 152786 12 pageshttpdxdoiorg1011552013152786

Review ArticleLOX-1 OxLDL and Atherosclerosis

Angela Pirillo12 Giuseppe Danilo Norata134 and Alberico Luigi Catapano23

1 Center for the Study of Atherosclerosis E Bassini Hospital 20092 Cinisello Balsamo Italy2 IRCCS Multimedica 20162 Milan Italy3 Department of Pharmacological and Biomolecular Sciences Universita degli Studi di Milano 20133 Milan Italy4Centre for Diabetes The Blizard Institute Barts and The London School of Medicine amp Dentistry Queen Mary UniversityLondon E1 2AT UK

Correspondence should be addressed to Angela Pirillo angelapirilloguestunimiit

Received 30 April 2013 Accepted 16 June 2013

Academic Editor Asım Orem

Copyright copy 2013 Angela Pirillo et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Oxidized low-density lipoprotein (OxLDL) contributes to the atherosclerotic plaque formation and progression by severalmechanisms including the induction of endothelial cell activation and dysfunction macrophage foam cell formation and smoothmuscle cell migration and proliferation Vascular wall cells express on their surface several scavenger receptors that mediate thecellular effects of OxLDL The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is the main OxLDL receptor ofendothelial cells and it is expressed also inmacrophages and smoothmuscle cells LOX-1 is almost undetectable under physiologicalconditions but it is upregulated following the exposure to several proinflammatory and proatherogenic stimuli and can be detectedin animal and human atherosclerotic lesions The key contribution of LOX-1 to the atherogenic process has been confirmed inanimal models LOX-1 knockout mice exhibit reduced intima thickness and inflammation and increased expression of protectivefactors on the contrary LOX-1 overexpressing mice present an accelerated atherosclerotic lesion formation which is associatedwith increased inflammation In humans LOX-1 gene polymorphisms were associated with increased susceptibility to myocardialinfarction Inhibition of the LOX-1 receptor with chemicals or antisense nucleotides is currently being investigated and representsan emerging approach for controlling OxLDL-LOX-1 mediated proatherogenic effects

1 Introduction

Atherosclerosis is a chronic inflammatory vascular diseasehaving as ultimate outcome the atheromatous plaque afocal lesion located within the intima of large and mediumsized arteries [1 2] Subendothelial retention of low den-sity lipoprotein (LDL) and its oxidative modification rep-resent the initial event in atherogenesis which is followedby infiltration and activation of blood inflammatory cellsOxidized LDL (OxLDL) in fact activates endothelial cells(ECs) by inducing the expression of several cell surfaceadhesion molecules which mediate the rolling and adhesionof blood leukocytes (monocytes and T cells) after adhesionto the endothelium leukocytes migrate into the intima inresponse to chemokines Monocytes then differentiate intomacrophages that upregulate both toll-like receptors (TLRs)involved in macrophage activation and scavenger receptors(SRs) that internalize apoptotic cell fragments bacterial

endotoxins and OxLDL leading to lipid accumulation andfoam cell formation [2] Macrophage activation leads to therelease of proinflammatory cytokines reactive oxygen species(ROS) proteolytic enzymes involved in matrix degradationand thus in atherosclerotic plaque destabilization T cellsrespond to local peptide antigens present on the surfaceof antigen-presenting cells become activated and releaseproinflammatory cytokines [2]

OxLDL acts via binding to several SRs including SR-ASR-BI CD36 and lectin-like oxidized low-density lipopro-tein receptor-1 (LOX-1) [3] LOX-1 is a type II integral mem-brane glycoprotein consisting of a short N-terminal cyto-plasmic domain a transmembrane domain a neck regionwhich regulates receptor oligomerization and an extracel-lular C-type lectin-like extracellular domain involved inligand binding (Figure 1) [4] LOX-1 has been identifiedfirst in ECs as the major OxLDL receptor [5] howeveralso macrophages and smooth muscle cells express LOX-1

2 Mediators of Inflammation

NH2

Cytoplasmic domain

Trans-membrane domain

Extracellular stalk region

(neck domain)

Extracellular lectin-like domain

COOH

(residues 1ndash33)(residues 34ndash60) (residues 61ndash139)

(residues 140ndash273)

Figure 1 Schematic representation of LOX-1 structure LOX-1 consists of four domains a cytoplasmic N-terminal domain a singletransmembrane domain an extracellular neck domain and an extracellular lectin-like domain

together with other SRs [6] Basal cellular LOX-1 expressionis very low but it can be induced by several proinflammatoryand proatherogenic stimuli [7 8] In vitro LOX-1 expres-sion is induced by many stimuli related to atherosclerosisincluding proinflammatory cytokines such as tumor necrosisfactor alpha (TNF120572) interleukin-1 (IL-1) and interferon-gamma (IFN120574) angiotensin II endothelin-1 OxLDL andother modified lipoproteins free radicals and fluid shearstress [8ndash10] (Table 1) In vivo the expression of LOX-1is upregulated in the presence of pathological conditionsincluding atherosclerosis hypertension and diabetes [8](Figure 2) In human atherosclerotic lesions LOX-1 is overex-pressed in ECs especially in the early stage of atherogenesisin advanced atherosclerotic plaques LOX-1 is overexpressedin ECs of neovascular formations [11] Furthermore LOX-1 ishighly expressed by intimal smooth muscle cells (SMCs) andmacrophages in human carotid atherosclerotic plaques [11]suggesting the roles for LOX-1 in endothelial activation andin foam cell formation Finally the results obtained in LOX-1 knockout or LOX-1 overexpressing mice have suggested akey contribution of LOX-1 in the inflammatory response andlipid deposition in heart vessels [12 13]

Besides OxLDL LOX-1 binds multiple ligands includingother forms of modified lipoproteins advanced glycationend-products activated platelets and apoptotic cells [8ndash10](Table 2) LOX-1 also binds delipidated OxLDL suggestingthat LOX-1 recognizes the modified apolipoprotein B fur-thermore LOX-1 binds with higher affinity tomildly oxidizedLDL rather than extensively oxidized LDL suggesting theability to recognize also oxidized lipids (ie lipids that arecovalently bound to the protein and are not removed by thedelipidation process) [3] (Table 2) OxLDL is rapidly inter-nalized into cells following the interaction with LOX-1 thisinternalization process is inhibited by LOX-1-blocking anti-bodywhich acts by preventing the binding ofOxLDLwith thereceptor [14] After the endocytosis of the complex OxLDL-LOX-1 the receptor is uncoupled from OxLDL and both arelocated in separate compartments within the cytosol [14]

LOX-1 is mainly localized in caveolaelipid rafts (choles-terol-enriched membrane microdomains) in the plasmamembrane its function is modulated by the cholesterol con-tent ofmembrane cholesterol depletion induces themislocal-ization of LOX-1 which results in a more diffuse distributionof the receptor in the plasmamembrane (without a reductionof the amount of receptor exposed on the cell surface) andin a marked reduction of LOX-1-mediated OxLDL bindingand uptake [15] This finding suggests that the clustered

Table 1 LOX-1 inducers

Proinflammatory cytokinesTumor necrosis factor 120572 (TNF120572)Interleukin-1 (IL-1)Interferon 120574 (IFN120574)Lipopolysaccharide (LPS)C-reactive protein (CRP)

Modified lipoproteinsOxLDL (copper-oxidized LDL)15-Lipoxygenase-modified LDL15-Lipoxygenase-modified HDL3

Glycoxidized-LDLLysophosphatidylcholine (LPC)Palmitic acid

Hypertension-related stimuliAngiotensin IIEndothelin-1Fluid shear stress

Hyperglycemic stimuliHigh glucoseAdvanced glycation end-products (AGEs)

Other stimuliHomocysteineFree radicals

distribution of LOX-1 in specific membrane microdomains isessential for an efficient interaction with OxLDL and for theinternalization of OxLDL-LOX-1 complexes

2 LOX-1-Mediated Endothelial Dysfunction

21 LOX-1 Upregulation by OxLDL Endothelial dysfunctionrepresents a very early stage in the atherogenic processand is a pathological condition characterized by alterationsin anti-inflammatory and anticoagulant properties and byimpaired ability to regulate vascular tone LOX-1 is the mainreceptor for OxLDL in ECs [5] and OxLDL through LOX-1 contributes to the induction of endothelial dysfunctionby several mechanisms (Figure 3) Basal LOX-1 expression isvery low but it can be induced by proinflammatory cytokines

Mediators of Inflammation 3

Platelets

Smooth muscle cells

Macrophages

Heart failure

Transplantation

Atherosclerosis

Diabetes

Hypertension

Ischemiareperfusion

Endothelial cells

uarr LOX-1

Figure 2 In vivo stimuli of LOX-1 Several pathological conditions can upregulate LOX-1 expression resulting in vascular wall cell activation

Table 2 LOX-1 ligands

Modified lipoproteins Other ligandsOxLDL (copper-oxidized LDL) Apoptotic cells15-Lipoxygenase-oxidized LDL Activated platelets

15-Lipoxygenase-oxidized HDL3Advanced glycationend-products (AGEs)

Glycoxidized LDLDelipidated OxLDLHOCl-modified HDL

generated in a local environmentwithin the arterial wall or byother atherogenic stimuli including OxLDL [8]

OxLDLupregulates LOX-1mRNAandprotein expressionin a dose-dependent manner [16] OxLDL-mediated upregu-lation of LOX-1 is suppressed by pretreatment of cells withantisense to LOX-1 mRNA [17] suggesting that OxLDLmodulates its own receptor through interaction with LOX-1 In vitro LOX-1 expression can be upregulated in ECs alsoby 15-lipoxygenase-modified LDL andLOX-1 overexpressionincreases the association of 15-lipoxygenase-modified LDLto ECs [9] supporting the hypothesis that also minimallyoxidized LDL may contribute to LOX-1 induction and to ECactivation LOX-1 upregulation occurs also in ECs exposed to15-lipoxygenase-modified HDL

3 this modified lipoprotein is

also a ligand for LOX-1 [10]

22 LOX-1 Mediates OxLDL-Induced EC Activation Afteradhesion to the endothelium monocytes migrate into theintima where they differentiate into macrophages accumu-late lipids and become foam cells Recruitment of monocytesinvolves both chemokines and adhesion molecules Mono-cyte chemoattractant protein-1 (MCP-1) is a chemotacticprotein formonocytes incubation of ECswithOxLDL signif-icantly increases MCP-1 expression and monocyte adhesionto ECs these effects are both suppressed in the presence ofan antisense to LOX-1 mRNA [18] Activation of mitogen-activated protein kinase (MAPK) is required for OxLDL-mediated induction ofMCP-1 and antisense to LOX-1mRNA

completely inhibits the OxLDL-induced MAPK activation[18] Additional chemokines are upregulated by LOX-1 acti-vation in response to OxLDL including IL-8 chemokine (C-X-C motif) ligands 2 and 3 (CXCL2 and CXCL3) [19]

Upregulation of endothelial adhesion molecules con-tributes to the leukocyte adhesion OxLDL significantlyincreases the expression of E-selectin P-selectin vascular celladhesion molecule-1 (VCAM-1) and intercellular adhesionmolecule-1 (ICAM-1) in ECs [20] These effects are mediatedby LOX-1 since antisense to LOX-1 mRNA decreases bothLOX-1 expression and adhesion molecule upregulation inresponse to OxLDL [20] In addition pretreatment of ECswith a statin or with polyinosinic acid or carrageenan (twoknown ligands of LOX-1) lowers OxLDL-induced expressionof LOX-1 as well as adhesion molecules confirming thatLOX-1 activation plays an important role in OxLDL-inducedexpression of adhesion molecules [20 21] ICAM-1 expres-sion is upregulated in LOX-1-overexpressing ECs exposed to15-lipoxygenase-modified LDL [9] providing a role for min-imally modified LDL (mmLDL) as proinflammatory particle

Nuclear factor kappa B (NF-120581B) which is activated byseveral proinflammatory cytokinesmodulates the expressionof proinflammatory genes including adhesion moleculescytokines and chemokines and is also involved in LOX-1 upregulation [8 22] OxLDL following the binding withLOX-1 activates NF-120581B preincubation of ECs with anti-LOX-1 antibody markedly attenuates the transcription factoractivation [23]

The stimulation of CD40CD40L signaling results in theinduction of proatherogenic pathways (including the expres-sion of adhesion molecules and proinflammatory cytokines)and in EC activation [24] Incubation of human coronaryartery endothelial cells (HCAECs) with OxLDL increases theexpression of CD40 andCD40L while the inhibition of LOX-1 with a blocking antibody reduces the OxLDL-mediatedincrease of CD40 [25]

23 OxLDL-LOX-1 Interaction Impairs Endothelium-Depend-ent Relaxation ECs due to their location at the interfacebetween blood and the vessel wall play a crucial role in


OxLDL

Macrophage

OxLDL

SMC Platelet

LOX-1

OxLDL

Endothelial cell

LOX-1LOX-1LOX-1

OxLDL

uarrEndothelial activation

uarr EC apoptosis∙ uarr Caspase activation∙ darr Antiapoptotic proteins∙ uarr FAS expressionOther effects∙ uarr MMPs∙ uarr PAI-1∙ darr LDL receptor

∙ NF-kB activation∙ MCP-1∙ Adhesion molecules∙ CD40

darr EC-dependent vasorelaxation∙ darr NO∙ uarr Arginase II∙ uarr ET-1∙ uarr ACE

∙ uarr ROSuarr Cell proliferation

uarr Apoptosis

uarr OxLDL uptake

uarr Foam cell formation

uarr OxLDL uptake

uarr foam cell formation

uarr OxLDL uptake

uarr Cell activation

Figure 3 Role of LOX-1 in atherosclerosisOxLDLbinding to LOX-1 induces endothelial activation anddysfunction supports the recruitmentof circulating leukocytes triggers foam cell formation and sustains migration and proliferation of smooth muscle cells thus contributing tothe development of the atherosclerotic plaque Furthermore OxLDL-LOX-1 interaction may also contribute to plaque destabilization byinducing smooth muscle cell apoptosis and the release of matrix degrading enzymes (MMPs)

the control of vascular tone and homeostasis through theproduction of several vasoactive mediators Among themnitric oxide (NO) is produced by endothelial NO synthase(eNOS) in response to several stimuli functions mainly asa vasodilator inhibits leukocyte-endothelial cell adhesionplatelet adhesion and aggregation and smooth muscle cellproliferation and stimulates angiogenesis [26] In diseaseconditions ECs exhibit a reduced NO bioavailability due toan increased degradation of NO in response to an enhancedoxidative stress [26]The release ofNOby ECs can be reducedby OxLDLOxLDL displaces eNOS from its caveolae mem-brane localization by depleting caveolae of cholesterol thusinhibiting NO generation [27] Furthermore OxLDL inac-tivates NO through an oxidative mechanism by increasingcellular production of reactive oxygen species (ROS) and inparticular superoxide [28] Anti-LOX-1monoclonal antibodyreduces superoxide formation and increases intracellularNO level suggesting the involvement of LOX-1 in theseOxLDL-induced effects [28] Additionally OxLDL activatesendothelial arginase II (which regulates NO production bycompeting with eNOS for the common substrate L-arginine)through the dissociation of arginase from the microtubule

cytoskeleton resulting in a decreased NO production anda raise of ROS [29 30] The increased arginase activity isinhibited by monoclonal antibody to LOX-1 furthermoreECs from LOX-1 knockout (KO) mice do not increasearginase activity and exhibit reduced changes in NO andsuperoxide production in response to OxLDL [30] thusconfirming the involvement of LOX-1 in OxLDL-mediatedarginase activity Further neutralizing antibodies to LOX-1restore NO-mediated coronary arteriolar dilation in ApoEKO mice [31]

Dysfunctional ECs can also generate vasoconstrictorfactors including endothelin-1 (ET-1) and angiotensin II(Ang II) ET-1 is a potent vasoconstrictor proinflammatoryand mitogenic peptide produced by injured vascular ECs inresponse to several stimuli a tight interaction exists betweenET-1 and OxLDL OxLDL stimulates the generation of ET-1 and ET-1 enhances the uptake of OxLDL in ECs bypromoting the expression of LOX-1 [32] Incubation of ECswith OxLDL increases ET-1 mRNA and protein expressionan effect inhibited by anti-LOX-1 antibody [33]

Renin-angiotensin systemmay contribute to the endothe-lial dysfunction angiotensin-converting enzyme (ACE)


which converts Ang I to Ang II is mainly expressed in ECs[34] Ang II induces LOX-1 expression and facilitates OxLDLuptake by ECs [35] in turn OxLDL increases the expressionof ACE in a concentration- and time-dependent mannerThe upregulation of ACE expression in response to OxLDLis mediated by LOX-1 as pretreatment of ECs with LOX-1-blocking antibody significantly reduces the OxLDL-inducedexpression of ACE [36]

24 LOX-1 Mediates OxLDL-Induced Apoptosis of ECs Incu-bation with high concentrations of OxLDL induces cellularchanges thatmay result in cell deathOxLDLmay induce bothnecrosis and apoptosis the last is a highly regulated processand involves multiple pathways including ROS generationcaspase and protein kinase activation alteration of calciumhomeostasis and alteration of proapoptoticantiapoptoticgene expression [37] EC apoptosis results in increasedvascular permeability to cells and lipids smooth muscle cellproliferation and increased coagulation thus contributing tothe development of atherosclerotic lesions

OxLDL induces EC apoptosis through LOX-1 in factinhibition with antisense to LOX-1 mRNA or with chemicalinhibitors of LOX-1 significantly reduces the number ofapoptotic cells in response to OxLDL [17] NF-120581B activationfollowing EC exposure toOxLDL acts as a signal transductionmechanism in LOX-1-mediated apoptosis and antisense toLOX-1 significantly inhibits OxLDL-induced NF-120581B activa-tion [17]

OxLDL also activates caspase-9 and caspase-3 in ECs andinduces the release of mitochondrial activators of caspaseswhile reducing the expression of the antiapoptotic proteinsB-cell lymphoma 2 (Bcl-2) and cellular inhibitor of apoptosisprotein 1 (c-IAP-1) [38] These effects are mediated by LOX-1 as pretreatment of cells with antisense to LOX-1 mRNAsignificantly decreasesOxLDL-induced activation of caspasesas well as the percentage of apoptotic cells [38]These findingsindicate that OxLDL through its receptor LOX-1 modulatesactivity and expression of relevant players in apoptosis

Fas is a death-receptor that triggers apoptosis whenactivated by its ligand FasL and is involved in OxLDL-induced apoptosis in fact OxLDL sensitizes vascular cellsto Fas-mediated apoptosis upregulating Fas surface expres-sion while OxLDL-induced apoptosis is reduced by FasL-neutralizing antibodies [37] LOX-1 activation is involvedin these effects as neutralizing LOX-1 antibody preventsOxLDL-induced activation of Fas-mediated apoptosis andinhibits OxLDL-induced modulation of surface Fas expres-sion in ECs [39]

25 OxLDL Increases Oxidative Stress through LOX-1 in ECsHigh levels of ROS are produced in several disease condi-tions including atherosclerosis and contribute to endothelialdysfunction ROS are involved in LDL oxidation and inturn OxLDL mediates many of its biological effects bygenerating more intracellular ROS through the bindingto LOX-1 anti-LOX-1 antibody markedly reduces OxLDL-induced ROS formation [23 40] OxLDL-induced increaseof ROS also results in NF-120581B activation [23] and in EC

apoptosis [40] both these effects are mediated by LOX-1 as pretreatment of the cells with LOX-1-blocking anti-body significantly reduces ROS production NF-120581B acti-vation and apoptosis rate in response to OxLDL [2340]

Endothelial NADPH oxidase a multisubunit enzymaticcomplex is a major source of ROS in vascular ECs andOxLDL induces a significant increase of NADPH oxidase-generated ROS in ECs [41] The binding of OxLDL to LOX-1 activates NADPH oxidase by inducing translocation ofspecific subunits on the cell membrane leading to a rapidincrease in intracellular ROS such as hydrogen peroxide andsuperoxide the latter reacts with intracellular NO therebycauses intracellular NO level to decrease and upregulatesLOX-1 expression thus resulting in further increase in ROSproduction [42]

p66Shc is a redox enzyme involved in mitochondrialROS generation and the translation of oxidative signals intoapoptosis higher levels of p66Shc have been found underpathological conditions and well correlated with oxidativestress in cardiovascular disease [43] When exposed toOxLDL ECs increase phosphorylation of p66Shc an effectthat is prevented by blockade or molecular silencing of LOX-1 [43] supporting a role for LOX-1 also in this OxLDL-mediated effect On the other hand lysophosphatidylcholine(LPC) a relevant component of OxLDL induced p66Shcactivation independently of LOX-1 [43]

In HCAECs OxLDL promotes intracellular ROS pro-duction and induces DNA oxidative damage [44] resultingin the regulation of several transcription factors includingNF-120581B and octamer-binding transcription factor-1 (Oct-1) Oct-1 acts as a transcriptional repressor for endothelialenzymes involved in the production of vasoactive moleculesthus providing a link between oxidative DNA damage andimpaired function of endothelium upon exposure to OxLDLOct-1 is also involved in OxLDL-induced LOX-1 promoteractivation and gene expression [45] Inhibition of LOX-1 attenuates OxLDL-mediated endothelial DNA damageOct-1DNA binding and reverses impaired production ofvasoactive compound [44]

26 Other Effects of OxLDL Mediated by LOX-1 in ECsIncubation of ECs with OxLDL modulates the expression ofseveral other genes associated with atherosclerosis and LOX-1 plays a crucial role in mediating such effects

Metalloproteinases (MMPs) are a family of matrix de-grading enzymes involved in vascular remodeling that con-tribute to the determination of atherosclerotic plaque stabil-ity their expression and activity are increased in atheroscle-rotic plaques [46] OxLDL increases the expression of MMP-1 and MMP-3 mRNA and protein in ECs without affect-ing the expression of tissue inhibitor of metalloproteinases(TIMPs) [47] suggesting an OxLDL-induced imbalancebetween MMPs and TIMPs LOX-1 activation mediates themodulation of MMPs by OxLDL LOX-1-blocking antibodyprevents the increase of MMPs in response to OxLDL [47]Similarly OxLDL enhances MMP-9 production in humanaortic ECs and anti-LOX-1 antibody inhibits this effect [48]


Angiogenesis is a highly regulated physiological pro-cess involved in several pathological conditions includinginflammation and atherosclerosis and requires disruption ofcell-cell contact EC migration proliferation and capillarytube formation Generation of small amount of ROS asthose induced by low concentrations of OxLDL (lt5 120583gmL)seems to be involved in this process Low concentrationsof OxLDL stimulate tube formation from ECs in vitro Thiseffect is inhibited by anti-LOX-1 antibody that also decreasesOxLDL-induced ROS generation NF-120581B activation andupregulation of vascular endothelial growth factor (VEGF)[49]

The plasminogen activator (PA) is involved in the con-trol of fibrinolysis within the vascular lumen plasminogenactivator inhibitor-1 (PAI-1) attenuates fibrinolysis throughinhibition of plasminogen activation and modulates cellularresponses increased expression of PAI-1 has been describedin atherosclerosis [50] OxLDL induces PAI-1 upregulationin cultured ECs through LOX-1 as showen by the inhibitoryeffect of anti-LOX-1-blocking antibody this finding suggestsan involvement of LOX-1 also in OxLDL-induced thromboticprocess [51]

The LDL receptor regulates plasma LDL-cholesterol lev-els OxLDL decreases the expression of LDL receptor ina concentration- and time-dependent manner in HCAECs[52] This effect is mediated by LOX-1 as cell pretreatmentwith LOX-1-blocking antibody or with antisense to LOX-1 mRNA reduces the effect of OxLDL on LDL-receptorexpression [52]

27 LOX-1 Mediates OxLDL-Induced Effects in EndothelialProgenitor Cells Endothelial progenitor cells (EPCs) areinvolved in the regeneration of the injured endothelium andin the neovascularization process which represents a com-pensatory mechanism in ischemic disease atherosclerosis isassociated with reduced numbers and impaired functionalityof EPCs [53] OxLDL has a negative effect on EPCs inducesEPC senescence inhibits VEGF-induced EPCdifferentiationdecreases EPC number and impairs their function [54ndash56] LOX-1 is expressed in EPCs and incubation of EPCswith OxLDL increases LOX-1 expression [57] an effectdepending on the interaction between OxLDL and LOX-1as confirmed by the use of an anti-LOX-1 antibody OxLDLalso induces EPC apoptosis in a dose-dependent mannerthus reducing their survival moreover OxLDL impairs EPCadhesive migratory and tube formation capacities [57] Allthese effects are attenuated by pretreatment with a LOX-1monoclonal antibody Furthermore OxLDL reduces eNOSexpression and NO production that may in part explain theinhibitory effect of OxLDL on EPC survival and function[57] Pretreatmentwith anti-LOX-1 antibody inhibits all theseOxLDL-induced effects

At low concentrations (lt10 120583gmL) OxLDL does notinduce apoptosis but accelerates EPC senescence this effectis significantly attenuated by LOX-1-blocking antibody or byatorvastatin (that reduces LOX-1 expression) [54] OxLDLsignificantly reduces telomerase activity (which plays a criti-cal role in cellular senescence) and impairs proliferation and

network formation capacity resulting in cellular dysfunction[54]

3 Role of LOX-1 in OxLDL-Induced SmoothMuscle Cell Proliferation and Apoptosis

LOX-1 is expressed also in smooth muscle cells (SMCs) [6]in vitro several stimuli including OxLDL and Ang II canupregulate LOX-1 expression in SMCs [58ndash60] in vivo LOX-1 protein is not detectable in the media of noninjured aortabut is present in SMCs two days after vascular injury or afterballoon-angioplasty [61] OxLDL and LOX-1 colocalize withSMCs of human restenotic lesions suggesting a role for LOX-1 in OxLDL-induced SMC proliferation and restenosis [61]

MicroRNAs are small noncoding RNAs that negativelymodulate gene expression through the binding with theirmRNAand play a role also in atherosclerosis [60]MicroRNAlet-7g targets LOX-1 gene and inhibits its expression OxLDLby inducing the transcription factor Oct-1 reduces let-7gexpression Let-7g mimic reduces OxLDL-induced LOX-1and Oct-1 upregulation as well as OxLDL-enhanced SMCproliferation and migration [60]

At higher concentrations OxLDL upregulates LOX-1expression and induces apoptosis of vascular SMCs [62](Figure 3) a process that may contribute to atheroscleroticplaque destabilization OxLDL-induced apoptosis is a con-sequence of LOX-1 upregulation as apoptosis is inhibitedby a neutralizing anti-LOX-1 antibody Furthermore OxLDLincreases the expression of the proapoptotic protein Bcl-2-associated X protein (Bax) and inhibits the expression ofthe antiapoptotic Bcl2 This effect is mediated by LOX-1as anti-LOX-1 antibody markedly inhibits OxLDL-inducedmodulation of these two proteins [62] LOX-1 colocalizeswith Bax in human atherosclerotic plaques particularly inrupture-prone shoulder region suggesting a role for LOX-1in the mechanisms that contribute to plaque destabilization[62]

Since SMCs can transform into foam cells LOX-1 mightbe a potential player in this process (Figure 3) Treatmentof SMCs with LPC increases LOX-1 expression [63] withconsequent LOX-1-mediated increase of OxLDL uptakeanti-LOX-1 antibody markedly inhibits the LPC-enhancedOxLDL uptake [63]

Bone marrow cells can potentially originate smoothmuscle progenitor cells (SMPCs) that may differentiate intosmooth muscle-like cells (SMLCs) in the damaged ves-sels [64] thus contributing to the atherogenic process Invitro long-term culture with platelet-derived growth factorPDGF-BB induces the differentiation of SMPCs into SMLCsthat express SMC-specific markers [65] OxLDL inhibitsPDGF-BB-induced differentiation of SMLCs as revealed bythe decrease of SMC marker expression in the presenceof OxLDL Furthermore OxLDL incubation induces lipiddroplet accumulation in the cytoplasm and LOX-1 surfaceexpression [65] Anti-LOX-1 antibody significantly reducesOxLDL uptake by SMLCs suggesting a role for LOX-1in the transdifferentiation of SMLCs into foam-like cells[65]


4 Role of LOX-1 in OxLDL-InducedEffects in Macrophages

Macrophages internalize OxLDL by several SRs includingSR-AIII SR-BI cluster of differentiation 36 (CD36) andLOX-1 resulting in lipid accumulation and transformationinto foam cells LOX-1 is not detectable in freshly isolatedhuman monocytes but its expression increases in differen-tiated macrophages [66] LOX-1 expression in macrophagescan be upregulated by several stimuli including OxLDLLPC high-glucose levels and proinflammatory cytokines[8] The contribution of LOX-1 in macrophage uptake anddegradation of OxLDL under normal conditions is small Nosignificant differences are observed between wild-type andLOX-1 deficient macrophages [67] probably due to the highexpression of other SRs that could mask the contribution ofLOX-1 However in cells stimulated with LPC LOX-1 expres-sion andOxLDL uptake and degradation increase in wilt typecells but not in LOX-1-deficient cells [67]These observationssuggest that LOX-1 gene inactivation does notmarkedlymod-ify OxLDL uptake in unstimulated macrophages as LOX-1accounts for 5ndash10ofOxLDLuptake by these cells but whenLOX-1 is upregulated internalization of OxLDL increases bymore than 40 [67] (Figure 2) Proinflammatory cytokinesupregulate LOX-1 and downregulate other SRs (SR-AIIIand CD36) suggesting that in inflamedmicroenvironmentswhere these cytokines are relatively abundant (such as inatherosclerotic lesions) LOX-1 might play a significant rolein macrophage OxLDL uptake

Monocytes may also differentiate into dendritic cells(DCs) a specific type of leukocytes that play a key rolein the initiation of innate and adaptive immune responsesand OxLDL affects both DC maturation and migration[68 69] LOX-1 is highly expressed on mature DCs andsignificantly contributes to OxLDL uptake as anti-LOX-1antibody reduced OxLDL uptake by 48 [70]

5 Role of LOX-1 in Platelet Activation

Platelets express several SRs some of which are constitu-tively expressed (including CD36) while LOX-1 appears onthe surface of platelets on activation [71] thus in restingplatelets CD36 mediates OxLDL binding to platelets whilein activated platelets in which OxLDL binding is increasedcompared to resting cells binding of OxLDL is mediated byboth CD36 and LOX-1 [71] Activated platelets internalizesignificant amount of OxLDL compared with resting platelets[72] (Figure 3) OxLDL induces platelet activation increasestheir ability to adhere to ECs induces an inflammatoryresponse and leads to platelet accumulation after vascularinjury In fact OxLDL-positive platelets induce adhesionmolecule expression on ECs reduce regeneration of ECsand induce foam cell formation [72] suggesting that OxLDL-activated platelets may contribute to vascular inflammationby several mechanisms

Dysfunctional endothelium exhibits procoagulant andadhesive properties to platelets and endothelial LOX-1 playsa major role in the platelet-endothelium interaction thus

enhancing endothelial dysfunction In fact LOX-1 binds alsoanionic phospholipids including those present on the surfaceof apoptotic cells or activated platelets [73] thus working asan adhesion molecule for platelets OxLDL partially inhibitsthe binding of platelets to LOX-1 indicating a high affinityof platelets for this receptor [73] The binding of activatedplatelets to endothelial LOX-1 induces the release of ET-1 further supporting the induction of endothelial dysfunc-tion [73] Furthermore the binding of activated platelet toendothelial LOX-1 induces ROS generation followed by areduction of NO bioavailability all effects are prevented byanti-LOX-1 antibody [74]

6 LOX-1 and AtherosclerosisExperimental Evidences

As previously described LOX-1 mediates many of the effectsof OxLDL that is EC growth dysfunction adhesion andactivation of monocytesmacrophages and all critical fea-tures of atherosclerosis LOX-1 mRNA has also been foundin human atherosclerotic plaques while negligible amountsare detectable in unaffected aortas [11] The key relevanceof LOX-1 in atherosclerosis has been demonstrated by keyexperiments in LOX-1 KO mice crossed to a mouse modelprone to develop atherosclerosis such as the LDL-R KOmouse Feeding thesemice with a cholesterol-rich diet resultsin a reduced binding of OxLDL to the aortic endotheliumand a preservation of endothelium-dependent vasorelaxationafter treatment with OxLDL compared to wild type animals[12] More importantly LOX-1 KOLDL-R KO animals showa significant reduction in atherosclerosis compared withLDL-R KO mice [12] This is associated with reduced NF-120581B expression as well as decreased inflammatory markersand also with an increased eNOS expression suggesting animproved endothelial function [12] Conversely mice over-expressing LOX-1 on ApoE KO background show a dramaticincrease in atherosclerosis compared to the nontransgenicmice [13] In hypercholesterolemic rabbits LOX-1 expressionis detected mainly in atherosclerotic plaques with a thinnerfibromuscular cap and is localized to the lipid core where itcorrelates with tissue factor expression and apoptosis [75]potentially connecting LOX-1 with plaque destabilization andrupture In line with this LOX-1 expression is increased inunstable plaques when the AMI-prone Watanabe heritablehyperlipidemic rabbit and control rabbits are injected with anantibody tracing LOX-1 [76]

Among the critical player in atherogenesis the activationof the rennin-angiotensin system and the consequent gener-ation of Ang II are thought to be critical factors Ang II via itstype 1 receptor (AT1 receptor) also upregulates the expressionof LOX-1 mRNA and OxLDL via LOX-1 upregulates theexpression of AT1 receptor [77] Of note hypertensive ratspresent an upregulation of LOX-1 expressionmainly in vascu-lar ECs [78ndash80] The mutually facilitatory cross-talk betweenLOX-1 and AT1 receptors may explain the coexistence ofmultiple risk factors in the same patient and the increasein atherosclerosis risk with the presence of multiple riskfactors In agreement with this assumption LOX-1 expression


is increased in several animal models of cardiometabolicdisorders including streptozotocin-induced diabetes [81] orischemia-reperfusion (IR) injury [82] LOX-1 deficiency isassociated with a more preserved left ventricular functionfollowing IR injury which resulted in a reduced oxidativestress collagen deposition and fibronectin expression thusresulting in a significant decrease inmyocardial injury as wellas in the accumulation of inflammatory cells [83 84]

Altogether the results from experimental atherosclerosissupport a proatherogenic role for LOX-1

7 Genetics of LOX-1 and Atherosclerosis

LOX-1 is encoded by the oxidized low-density lipoprotein(lectin-like) receptor 1 (OLR1) gene mapped to chromosome12p13 [85] The association of polymorphisms in the humanOLR1 gene with the susceptibility to myocardial infarction(MI) has been reported [85 86] In particular six singlenucleotide polymorphisms (SNPs) located within introns 45 and 31015840 UTR (untranslated region) that are comprised ina linkage disequilibrium (LD) block are strongly associatedwith the elevated risk to develop MI [86] The observationthat the SNPs related to an increased risk of MI do notaffect the coding sequence of the gene suggests the possibilitythat the SNPs could give rise to a functional product suchas messenger RNA (mRNA) isoforms as a consequence ofalternative splicing Indeed it has been shown that the SNPslocated in the LD block regulate the level of the new fullyfunctional transcript bymodulating the retention of exon 5 ofthe OLR1 gene [85] The alternative splicing of OLR1 mRNAleads to different ratios of LOX-1 full receptor and LOXIN(lack of exon 5) an isoform lacking part of the C-terminuslectin-like domain which is a functional domain LOXINthrough heterooligomerization with LOX-1 [87] blocks thenegative effects of LOX-1 activation and this variant has afunctional role on plaque instability and therefore in thepathogenesis of MI [86] Ex vivo data show that macrophagesfrom subjects carrying the ldquononriskrdquo allele at OLR1 gene dis-play increased expression of LOXIN resulting in protectionagainst OxLDL-mediated apoptosis [87]

Later an SNP on exon 4 rs11053646 (G501C) whichleads to an amino acidic substitution (lysine to asparagine atposition 167 K167N) has been studied Of note basic residuesin the lectin domain are important for strengthening theligand binding substitution of this residue (K167N) causes achange on the positive isopotential surface and thereby resultsin reduced binding and internalization of OxLDL [88] Thisstudy performed on CV-1 (simian) in Origin and carryingthe SV40 (COS-1) cells overexpressing either GG (KK) or CC(NN) LOX-1 showed that GG (KK) COS-1 cells bind andinternalize less OxLDL than CC (NN) [88]

The K167N SNP has been identified among others in theORL-1 gene to be associated with acute MI and coronaryartery disease (CAD) [89ndash91] The frequencies of the KKgenotype and the K allele are higher in the CAD group thanin controls (119875 lt 005) while the opposite is true for NNgenotype (119875 lt 005) [92] The relevance of LOX-1 SNPshas been tested also in relation to markers of atherosclerosis

Among them ultrasound detection and quantification of thecommon carotid artery wall thickness (intima-media thick-ness IMT) are considered a surrogate marker of subclinicalatherosclerosis [93 94] The association between the non-synonymous substitution K167N (rs11053646) and IMT hasbeen tested in 2141 samples from the Progression of Lesionsin the Intima of the Carotid (PLIC) study (a prospectivepopulation-based study) [95] Significantly increased IMThas been observed in male carriers of the minor C (N) allelecompared to GC and GG (KN and KK) genotypes [95] Agender-specific association has been also described betweenthe C (N) allele and prevalence of carotid plaque also in acohort of Dominican-Hispanic origin [96]

Functional analysis onmacrophages suggests a decreasedassociation to OxLDL in NN carriers compared to KNand KK carriers which is also associated with a reducedOLR1mRNAexpression [95]Macrophages fromNNcarrierspresent also a specific inflammatory gene expression patterncompared to cells from KN and KK carriers [95] How thesedata obtained with human primarymacrophages relate withthose obtained in a transfected fibroblast-like cell line derivedfrommonkey kidney tissue is unclear and further studies arewarranted to clarify this issue [88]

In summary genetic alterations favoring LOXIN isoformproduction coupled to the observation that this isoformexerts a dominant-negative effect on LOX-1 function make itan attractive new target for prevention and treatment of ini-tiation progression and clinical consequences of atheroscle-rosis such as plaque instability acute myocardial infarctionand ischemia reperfusion injury

8 Concluding Remarks

OxLDL plays multiple roles in atherosclerosis LOX-1 scav-enger receptor mediates many of the OxLDL-induced effectsand the OxLDL-LOX-1 interaction can alter the expression ofseveral genes resulting in the induction of cellular dysfunc-tion proliferation and apoptosis A recent study showed thatLOX-1 inhibition in ApoE KO mice using a schizophyllan-based antisense oligonucleotide therapy resulted in reducedLOX-1 expression in the arterial wall [97] Blocking theexpression andor function of LOX-1 results in the improve-ment of cellular functions and reduction of atheroscle-rotic lesion formation suggesting that LOX-1 might be anattractive therapeutic target for the management and theprevention of atherosclerosis

References

[1] P Libby ldquoInflammation in atherosclerosisrdquo ArteriosclerosisThrombosis and Vascular Biology vol 32 no 9 pp 2045ndash20512012

[2] G K Hansson A K Robertson and C Soderberg-NauclerldquoInflammation and atherosclerosisrdquo Annual Review of Pathol-ogy vol 1 pp 297ndash329 2006

[3] I Levitan S Volkov and P V Subbaiah ldquoOxidized LDL diver-sity patterns of recognition and pathophysiologyrdquoAntioxidantsand Redox Signaling vol 13 no 1 pp 39ndash75 2010


[4] S Dunn R S Vohra J E Murphy S Homer-VanniasinkamJ H Walker and S Ponnambalam ldquoThe lectin-like oxidizedlow-density-lipoprotein receptor a pro-inflammatory factor invascular diseaserdquo Biochemical Journal vol 409 no 2 pp 349ndash355 2008

[5] T Sawamura N Kume T Aoyama et al ldquoAn endothelialreceptor for oxidized low-density lipoproteinrdquoNature vol 386no 6620 pp 73ndash77 1997

[6] G Draude N Hrboticky and R L Lorenz ldquoThe expression ofthe lectin-like oxidized low-density lipoprotein receptor (LOX-1) on human vascular smooth muscle cells and monocytes andits down-regulation by lovastatinrdquo Biochemical Pharmacologyvol 57 no 4 pp 383ndash386 1999

[7] J L Mehta J Chen P L Hermonat F Romeo and G NovellildquoLectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) a critical player in the development of atherosclerosis andrelated disordersrdquoCardiovascular Research vol 69 no 1 pp 36ndash45 2006

[8] S Xu S Ogura J Chen P J Little J Moss and P Liu ldquoLOX-1 in atherosclerosis biological functions and pharmacologicalmodifiersrdquo Cellular and Molecular Life Sciences 2012

[9] A Pirillo A Reduzzi N Ferri H Kuhn A Corsini and AL Catapano ldquoUpregulation of lectin-like oxidized low-densitylipoprotein receptor-1 (LOX-1) by 15-lipoxygenase-modifiedLDL in endothelial cellsrdquoAtherosclerosis vol 214 no 2 pp 331ndash337 2011

[10] A Pirillo P Uboldi N Ferri A Corsini H Kuhn and AL Catapano ldquoUpregulation of lectin-like oxidized low densitylipoprotein receptor 1 (LOX-1) expression in human endothelialcells by modified high density lipoproteinsrdquo Biochemical andBiophysical Research Communications vol 428 no 2 pp 230ndash233 2012

[11] H Kataoka N Kume S Miyamoto et al ldquoExpression oflectinlike oxidized low-density lipoprotein receptor-1 in humanatherosclerotic lesionsrdquo Circulation vol 99 no 24 pp 3110ndash3117 1999

[12] J L Mehta N Sanada C P Hu et al ldquoDeletion of LOX-1 reduces atherogenesis in LDLR knockout mice fed highcholesterol dietrdquo Circulation Research vol 100 no 11 pp 1634ndash1642 2007

[13] K Inoue Y Arai H Kurihara T Kita and T SawamuraldquoOverexpression of lectin-like oxidized low-density lipoproteinreceptor-1 induces intramyocardial vasculopathy in apolipopro-tein E-null micerdquo Circulation Research vol 97 no 2 pp 176ndash184 2005

[14] M W Twigg K Freestone S Homer-Vanniasinkam and SPonnambalam ldquoThe LOX-1 scavenger receptor and its implica-tions in the treatment of vascular diseaserdquo Cardiology Researchand Practice vol 2012 Article ID 632408 6 pages 2012

[15] S Matarazzo M C Quitadamo R Mango S Ciccone GNovelli and S Biocca ldquoCholesterol-lowering drugs inhibitlectin-like oxidized low-density lipoprotein-1 receptor functionbymembrane raft disruptionrdquoMolecular Pharmacology vol 82no 2 pp 246ndash254 2012

[16] J L Mehta and D Y Li ldquoIdentification and autoregulationof receptor for ox-LDL in cultured human coronary arteryendothelial cellsrdquo Biochemical and Biophysical Research Com-munications vol 248 no 3 pp 511ndash514 1998

[17] D Li and J L Mehta ldquoUpregulation of endothelial receptorfor oxidized LDL (LOX-1) by oxidized LDL and implicationsin apoptosis of coronary artery endothelial cells evidencefrom use of antisense LOX-1 mRNA and chemical inhibitorsrdquo

Arteriosclerosis Thrombosis and Vascular Biology vol 20 no4 pp 1116ndash1122 2000

[18] D Li and J L Mehta ldquoAntisense to LOX-1 inhibits oxi-dized LDL-mediated upregulation of monocyte chemoattrac-tant protein-1 and monocyte adhesion to human coronaryartery endothelial cellsrdquo Circulation vol 101 no 25 pp 2889ndash2895 2000

[19] M D Mattaliano C Huard W Cao et al ldquoLOX-1-dependenttranscriptional regulation in response to oxidized LDL treat-ment of human aortic endothelial cellsrdquo American Journal ofPhysiology vol 296 no 6 pp C1329ndashC1337 2009

[20] D Li H Chen F Romeo T Sawamura T Saldeen and JL Mehta ldquoStatins modulate oxidized low-density lipoprotein-mediated adhesion molecule expression in human coronaryartery endothelial cells role of LOX-1rdquo Journal of Pharmacologyand Experimental Therapeutics vol 302 no 2 pp 601ndash6052002

[21] H Zhu M Xia M Hou et al ldquoOx-LDL plays dual effectin modulating expression of inflammatory molecles throughLOX-1 pathway in human umbilical vein endothelial cellsrdquoFrontiers in Bioscience vol 10 no 2 pp 2585ndash2594 2005

[22] T Lawrence ldquoThenuclear factorNF-kappaB pathway in inflam-mationrdquo Cold Spring Harbor Perspectives in Biology vol 1 no 6Article ID a001651 2009

[23] L Cominacini A Fratta Pasini U Garbin et al ldquoOxidized lowdensity lipoprotein (ox-LDL) binding to ox-LDL receptor-1 inendothelial cells induces the activation of NF-120581B through anincreased production of intracellular reactive oxygen speciesrdquoJournal of Biological Chemistry vol 275 no 17 pp 12633ndash126382000

[24] D Lievens W J Eijgelaar E A L Biessen M J A P Daemenand E Lutgens ldquoThe multi-functionality of CD40L and itsreceptor CD40 in atherosclerosisrdquoThrombosis andHaemostasisvol 102 no 2 pp 206ndash214 2009

[25] D Li L Liu H Chen T Sawamura and J L Mehta ldquoLOX-1an oxidized LDL endothelial receptor induces CD40CD40Lsignaling in human coronary artery endothelial cellsrdquo Arte-riosclerosis Thrombosis and Vascular Biology vol 23 no 5 pp816ndash821 2003

[26] U Forstermann and W C Sessa ldquoNitric oxide synthasesregulation and functionrdquo European Heart Journal vol 33 no7 pp 829ndash837 2012

[27] A Blair P W Shaul I S Yuhanna P A Conrad and E JSmart ldquoOxidized low density lipoprotein displaces endothelialnitric-oxide synthase (eNOS) from plasmalemmal caveolae andimpairs eNOS activationrdquo Journal of Biological Chemistry vol274 no 45 pp 32512ndash32519 1999

[28] L Cominacini A Rigoni A F Pasini et al ldquoThe binding ofoxidized low density lipoprotein (ox-LDL) to ox-LDL receptor-1 reduces the intracellular concentration of nitric oxide inendothelial cells through an increased production of superox-iderdquo Journal of Biological Chemistry vol 276 no 17 pp 13750ndash13755 2001

[29] S Ryoo C A Lemmon K G Soucy et al ldquoOxidized low-density lipoprotein-dependent endothelial arginase II activa-tion contributes to impaired nitric oxide signalingrdquo CirculationResearch vol 99 no 9 pp 951ndash960 2006

[30] S Ryoo A Bhunia F Chang A Shoukas D E Berkowitzand L H Romer ldquoOxLDL-dependent activation of arginase IIis dependent on the LOX-1 receptor and downstream RhoAsignalingrdquo Atherosclerosis vol 214 no 2 pp 279ndash287 2011


[31] X Xu X Gao B J Potter J-M Cao and C Zhang ldquoAnti-LOX-1 rescues endothelial function in coronary arterioles inatherosclerotic ApoE knockout micerdquo Arteriosclerosis Throm-bosis and Vascular Biology vol 27 no 4 pp 871ndash877 2007

[32] J Pernow A Shemyakin and F Bohm ldquoNew perspectiveson endothelin-1 in atherosclerosis and diabetes mellitusrdquo LifeSciences vol 91 no 13-14 pp 507ndash516 2012

[33] K Sakurai L Cominacini U Garbin et al ldquoInduction ofendothelin-1 production in endothelial cells via co-operativeaction between CD40 and lectin-like oxidized LDL receptor(LOX-1)rdquo Journal of Cardiovascular Pharmacology vol 44supplement 1 pp S173ndashS180 2004

[34] F Montecucco A Pende and F Mach ldquoThe renin-angiotensinsystem modulates inflammatory processes in atherosclerosisevidence from basic research and clinical studiesrdquoMediators ofInflammation vol 2009 Article ID 752406 13 pages 2009

[35] HMorawietz U Rueckschloss B Niemann et al ldquoAngiotensinII induces LOX-1 the human endothelial receptor for oxidizedlow-density lipoproteinrdquo Circulation vol 100 no 9 pp 899ndash902 1999

[36] D Li R M Singh L Liu et al ldquoOxidized-LDL through LOX-1 increases the expression of angiotensin converting enzymein human coronary artery endothelial cellsrdquo CardiovascularResearch vol 57 no 1 pp 238ndash243 2003

[37] R Salvayre N Auge H Benoist and A Negre-Salvayre ldquoOxi-dized low-density lipoprotein-induced apoptosisrdquoBiochimica etBiophysica Acta vol 1585 no 2-3 pp 213ndash221 2002

[38] J Chen J L Mehta N Haider X Zhang J Narula and DLi ldquoRole of caspases in Ox-LDL-induced apoptotic cascade inhuman coronary artery endothelial cellsrdquo Circulation Researchvol 94 no 3 pp 370ndash376 2004

[39] T Imanishi T Hano T Sawamura S Takarada and I NishioldquoOxidized low density lipoprotein potentiation of Fas-inducedapoptosis through lectin-like oxidized-low density lipoproteinreceptor-1 in human umbilical vascular endothelial cellsrdquo Cir-culation Journal vol 66 no 11 pp 1060ndash1064 2002

[40] X-P Chen K-L Xun Q Wu T-T Zhang J-S Shi and G-H Du ldquoOxidized low density lipoprotein receptor-1 mediatesoxidized low density lipoprotein-induced apoptosis in humanumbilical vein endothelial cells role of reactive oxygen speciesrdquoVascular Pharmacology vol 47 no 1 pp 1ndash9 2007

[41] U Rueckschloss J Galle J Holtz H-R Zerkowski and HMorawietz ldquoInduction of NAD(P)H oxidase by oxidized low-density lipoprotein in human endothelial cells antioxidativepotential of hydroxymethylglutaryl coenzyme A reductaseinhibitor therapyrdquo Circulation vol 104 no 15 pp 1767ndash17722001

[42] H-C Ou T-Y Song Y-C Yeh et al ldquoEGCG protects againstoxidized LDL-induced endothelial dysfunction by inhibitingLOX-1-mediated signalingrdquo Journal of Applied Physiology vol108 no 6 pp 1745ndash1756 2010

[43] Y Shi F Cosentino G G Camici et al ldquoOxidized low-densitylipoprotein activates p66shc via lectin-like oxidized low-densitylipoprotein receptor-1 protein kinase c-120573 and c-jun n-terminalkinase kinase in human endothelial cellsrdquo ArteriosclerosisThrombosis and Vascular Biology vol 31 no 9 pp 2090ndash20972011

[44] T Thum and J Borlak ldquoLOX-1 receptor blockade abrogatesoxLDL-induced oxidativeDNAdamage and prevents activationof the transcriptional repressor Oct-1 in human coronaryarterial endotheliumrdquo Journal of Biological Chemistry vol 283no 28 pp 19456ndash19464 2008

[45] J Chen Y Liu H Liu P L Hermonat and J L MehtaldquoLectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) transcriptional regulation by Oct-1 in human endothelialcells implications for atherosclerosisrdquo Biochemical Journal vol393 part 1 pp 255ndash265 2006

[46] P Liu M Sun and S Sader ldquoMatrix metalloproteinases incardiovascular diseaserdquo The Canadian Journal of Cardiologyvol 22 supplement B pp 25Bndash30B 2006

[47] D Li L Liu H Chen T Sawamura S Ranganathan and JL Mehta ldquoLOX-1 mediates oxidized low-density lipoprotein-induced expression of matrix metalloproteinases in humancoronary artery endothelial cellsrdquoCirculation vol 107 no 4 pp612ndash617 2003

[48] L Li and G Renier ldquoThe oral anti-diabetic agent gli-clazide inhibits oxidized LDL-mediated LOX-1 expressionmetalloproteinase-9 secretion and apoptosis in human aorticendothelial cellsrdquo Atherosclerosis vol 204 no 1 pp 40ndash462009

[49] A Dandapat C Hu L Sun and J L Mehta ldquoSmall con-centrations of OXLDL induce capillary tube formation fromendothelial cells via LOX-1-dependent redox-sensitive path-wayrdquo Arteriosclerosis Thrombosis and Vascular Biology vol 27no 11 pp 2435ndash2442 2007

[50] I Diebold D Kraicun S Bonello and A Gorlach ldquoThe lsquoPAI-1paradoxrsquo in vascular remodellingrdquoThrombosis andHaemostasisvol 100 no 6 pp 984ndash991 2008

[51] G V Sangle R Zhao and G X Shen ldquoTransmembranesignaling pathway mediates oxidized low-density lipoprotein-induced expression of plasminogen activator inhibitor-1 invascular endothelial cellsrdquo American Journal of Physiology vol295 no 5 pp E1243ndashE1254 2008

[52] B Hu D Li T Sawamura and J L Mehta ldquoOxidized LDLthrough LOX-1 modulates LDL-receptor expression in humancoronary artery endothelial cellsrdquo Biochemical and BiophysicalResearch Communications vol 307 no 4 pp 1008ndash1012 2003

[53] F Du J Zhou R Gong et al ldquoEndothelial progenitor cells inatherosclerosisrdquo Frontiers in Bioscience vol 17 no 6 pp 2327ndash2349 2011

[54] T Imanishi T Hano T Sawamura and I Nishio ldquoOxidizedlow-density lipoprotein induces endothelial progenitor cellsenescence leading to cellular dysfunctionrdquoClinical and Exper-imental Pharmacology and Physiology vol 31 no 7 pp 407ndash4132004

[55] T Imanishi T Hano Y Matsuo and I Nishio ldquoOxidized low-density lipoprotein inhibits vascular endothelial growth factor-induced endothelial progenitor cell differentiationrdquoClinical andExperimental Pharmacology and Physiology vol 30 no 9 pp665ndash670 2003

[56] X Wang J Chen Q Tao J Zhu and Y Shang ldquoEffectsof ox-LDL on number and activity of circulating endothelialprogenitor cellsrdquo Drug and Chemical Toxicology vol 27 no 3pp 243ndash255 2004

[57] X M Feng B Zhou Z Chen et al ldquoOxidized low densitylipoprotein impairs endothelial progenitor cells by regulation ofendothelial nitric oxide synthaserdquo Journal of Lipid Research vol47 no 6 pp 1227ndash1237 2006

[58] Y Sun and X Chen ldquoOx-LDL-induced LOX-1 expression invascular smooth muscle cells role of reactive oxygen speciesrdquoFundamental and Clinical Pharmacology vol 25 no 5 pp 572ndash579 2011

[59] R Limor M Kaplan T Sawamura et al ldquoAngiotensin IIincreases the expression of lectin-like oxidized low-density


lipoprotein receptor-1 in human vascular smooth muscle cellsvia a lipoxygenase-dependent pathwayrdquo American Journal ofHypertension vol 18 no 3 pp 299ndash307 2005

[60] K-C Chen I-C Hsieh E Hsi et al ldquoNegative feedbackregulation between microRNA let-7g and the oxLDL receptorLOX-1rdquo Journal of Cell Science vol 124 no 23 pp 4115ndash41242011

[61] H Eto M Miyata N Kume et al ldquoExpression of lectin-likeoxidized LDL receptor-1 in smooth muscle cells after vascularinjuryrdquo Biochemical and Biophysical Research Communicationsvol 341 no 2 pp 591ndash598 2006

[62] H Kataoka N Kume S Miyamoto et al ldquoOxidized LDLmodulates BaxBcl-2 through the lectinlike Ox-LDL receptor-1 in vascular smooth muscle cellsrdquo Arteriosclerosis Thrombosisand Vascular Biology vol 21 no 6 pp 955ndash960 2001

[63] T Aoyama M Chen H Fujiwara T Masaki and T SawamuraldquoLOX-1 mediates lysophosphatidylcholine-induced oxidizedLDL uptake in smooth muscle cellsrdquo FEBS Letters vol 467 no2-3 pp 217ndash220 2000

[64] N M Caplice T J Bunch P G Stalboerger et al ldquoSmoothmuscle cells in human coronary atherosclerosis can originatefrom cells administered atmarrow transplantationrdquo Proceedingsof the National Academy of Sciences of the United States ofAmerica vol 100 no 8 pp 4754ndash4759 2003

[65] J Yu Y Li M Li Z Qu and Q Ruan ldquoOxidized low den-sity lipoprotein-induced transdifferentiation of bone marrow-derived smooth muscle-like cells into foam-like cells in vitrordquoInternational Journal of Experimental Pathology vol 91 no 1pp 24ndash33 2010

[66] H Yoshida N Kondratenko S Green D Steinberg and OQuehenberger ldquoIdentification of the lectin-like receptor foroxidized low-density lipoprotein in humanmacrophages and itspotential role as a scavenger receptorrdquo Biochemical Journal vol334 part 1 pp 9ndash13 1998

[67] D F Schaeffer M Riazy K S Parhar et al ldquoLOX-1 augmentsoxLDL uptake by lysoPC-stimulated murine macrophages butis not required for oxLDL clearance from plasmardquo Journal ofLipid Research vol 50 no 8 pp 1676ndash1684 2009

[68] L Perrin-Cocon F Coutant S Agaugue S Deforges P Andreand V Lotteau ldquoOxidized low-density lipoprotein promotesmature dendritic cell transition from differentiatingmonocyterdquoJournal of Immunology vol 167 no 7 pp 3785ndash3891 2001

[69] T Nickel S Pfeiler C Summo et al ldquooxLDL downregulates thedendritic cell homing factors CCR7 and CCL21rdquo Mediators ofInflammation vol 2012 Article ID 320953 10 pages 2012

[70] T Nickel D Schmauss H Hanssen et al ldquooxLDL uptakeby dendritic cells induces upregulation of scavenger-receptorsmaturation and differentiationrdquo Atherosclerosis vol 205 no 2pp 442ndash450 2009

[71] M Chen M Kakutani T Naruko et al ldquoActivation-dependentsurface expression of LOX-1 in human plateletsrdquo Biochemicaland Biophysical Research Communications vol 282 no 1 pp153ndash158 2001

[72] K Daub P Seizer K Stellos et al ldquoOxidized LDL-activatedplatelets induce vascular inflammationrdquo Seminars inThrombosisand Hemostasis vol 36 no 2 pp 146ndash156 2010

[73] M Kakutani T Masaki and T Sawamura ldquoA platelet-endothelium interaction mediated by lectin-like oxidized low-density lipoprotein receptor-1rdquo Proceedings of the NationalAcademy of Sciences of the United States of America vol 97 no1 pp 360ndash364 2000

[74] L Cominacini A Fratta Pasini U Garbin et al ldquoThe platelet-endothelium interaction mediated by lectin-like oxidized low-density lipoprotein receptor-1 reduces the intracellular con-centration of nitric oxide in endothelial cellsrdquo Journal of theAmerican College of Cardiology vol 41 no 3 pp 499ndash507 2003

[75] Y Kuge N Kume S Ishino et al ldquoProminent lectin-likeoxidized low density lipoprotein (LDL) receptor-1 (LOX-1)expression in atherosclerotic lesions is associated with tissuefactor expression and apoptosis in hypercholesterolemic rab-bitsrdquo Biological and Pharmaceutical Bulletin vol 31 no 8 pp1475ndash1482 2008

[76] S Ishino T Mukai Y Kuge et al ldquoTargeting of lectinlike oxi-dized low-density lipoprotein receptor 1 (LOX-1) with99mTc-labeled anti-LOX-1 antibody potential agent for imaging ofvulnerable plaquerdquo Journal of Nuclear Medicine vol 49 no 10pp 1677ndash1685 2008

[77] XWangM I Phillips and J LMehta ldquoLOX-1 and angiotensinreceptors and their interplayrdquo Cardiovascular Drugs and Ther-apy vol 25 no 5 pp 401ndash417 2011

[78] M Nagase S Hirose and T Fujita ldquoUnique repetitive sequenceand unexpected regulation of expression of rat endothelialreceptor for oxidized low-density lipoprotein (LOX-1)rdquo Bio-chemical Journal vol 330 no 3 pp 1417ndash1422 1998

[79] K Ando and T Fujita ldquoRole of lectin-like oxidized low-densitylipoprotein receptor-1 (LOX-1) in the development of hyperten-sive organ damagerdquo Clinical and Experimental Nephrology vol8 no 3 pp 178ndash182 2004

[80] M Nagase K Ando T Nagase S Kaname T Sawamura andT Fujita ldquoRedox-sensitive regulation of LOX-1 gene expressionin vascular endotheliumrdquo Biochemical and Biophysical ResearchCommunications vol 281 no 3 pp 720ndash725 2001

[81] M Chen M Nagase T Fujita S Narumiya T Masaki andT Sawamura ldquoDiabetes enhances lectin-like oxidized LDLreceptor-1 (LOX-1) expression in the vascular endotheliumpossible role of LOX-1 ligand and AGErdquo Biochemical andBiophysical Research Communications vol 287 no 4 pp 962ndash968 2001

[82] D Li V Williams L Liu et al ldquoExpression of lectin-likeoxidized low-density lipoprotein receptors during ischemia-reperfusion and its role in determination of apoptosis and leftventricular dysfunctionrdquo Journal of the American College ofCardiology vol 41 no 6 pp 1048ndash1055 2003

[83] C Hu A Dandapat J Chen et al ldquoLOX-1 deletion alterssignals of myocardial remodeling immediately after ischemia-reperfusionrdquo Cardiovascular Research vol 76 no 2 pp 292ndash302 2007

[84] C Hu J Chen A Dandapat et al ldquoLOX-1 abrogation reducesmyocardial ischemia-reperfusion injury in micerdquo Journal ofMolecular and Cellular Cardiology vol 44 no 1 pp 76ndash832008

[85] R Mango I M Predazzi F Romeo and G Novelli ldquoLOX-1LOXIN the YinYang of atheroscleorosisrdquo CardiovascularDrugs andTherapy vol 25 no 5 pp 489ndash494 2011

[86] R Mango S Biocca F del Vecchio et al ldquoIn vivo and invitro studies support that a new splicing isoform of OLR1 geneis protective against acute myocardial infarctionrdquo CirculationResearch vol 97 no 2 pp 152ndash158 2005

[87] S Biocca I Filesi R Mango et al ldquoThe splice variantLOXIN inhibits LOX-1 receptor function through hetero-oligomerizationrdquo Journal of Molecular and Cellular Cardiologyvol 44 no 3 pp 561ndash570 2008


[88] S Biocca M Falconi I Filesi et al ldquoFunctional analysis andmolecular dynamics simulation of LOX-1 K167N polymor-phism reveal alteration of receptor activityrdquo PLoS One vol 4no 2 article e4648 2009

[89] R Mango F Clementi P Borgiani et al ldquoAssociation of singlenucleotide polymorphisms in the oxidised LDL receptor 1(OLR1) gene in patients with acute myocardial infarctionrdquoJournal of Medical Genetics vol 40 no 12 pp 933ndash936 2003

[90] R Ohmori Y Momiyama M Nagano et al ldquoAn oxidized low-density lipoprotein receptor gene variant is inversely associatedwith the severity of coronary artery diseaserdquoClinical Cardiologyvol 27 no 11 pp 641ndash644 2004

[91] M Tatsuguchi M Furutani J-I Hinagata et al ldquoOxidizedLDL receptor gene (OLR1) is associated with the risk ofmyocardial infarctionrdquo Biochemical and Biophysical ResearchCommunications vol 303 no 1 pp 247ndash250 2003

[92] O Kurnaz H Y Aydogan C S Isbir A Tekeli and T IsbirldquoIs LOX-1 K167N polymorphism protective for coronary arterydiseaserdquo In Vivo vol 23 no 6 pp 969ndash973 2009

[93] G D Norata K Garlaschelli L Grigore et al ldquoEffects of PCSK9variants on common carotid artery intima media thickness andrelation to ApoE allelesrdquo Atherosclerosis vol 208 no 1 pp 177ndash182 2010

[94] G D Norata S Raselli L Grigore et al ldquoSmall dense LDLand VLDL predict common carotid artery IMT and elicit aninflammatory response in peripheral blood mononuclear andendothelial cellsrdquo Atherosclerosis vol 206 no 2 pp 556ndash5622009

[95] I M Predazzi G D Norata L Vecchione et al ldquoAssociationbetween OLR1 K167N SNP and intima media thickness of thecommon carotid artery in the general populationrdquo PLoS Onevol 7 no 2 Article ID e31086 2012

[96] L Wang D Yanuck A Beecham et al ldquoA candidate gene studyrevealed sex-specific association between the OLR1 gene andcarotid plaquerdquo Stroke vol 42 no 3 pp 588ndash592 2011

[97] F Amati L Diano L Vecchione et al ldquoLOX-1 inhibition inApoE KO mice using a schizophyllan-based antisense oligonu-cleotide therapyrdquoMolecularTherapy Nucleic Acids vol 1 no 12article e58 2012

Submit your manuscripts athttpwwwhindawicom

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


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EndocrinologyInternational Journal of



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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Evidence-Based Complementary and Alternative Medicine

Volume 2014Hindawi Publishing Corporationhttpwwwhindawicom


NH2

Cytoplasmic domain

Trans-membrane domain

Extracellular stalk region

(neck domain)

Extracellular lectin-like domain

COOH

(residues 1ndash33)(residues 34ndash60) (residues 61ndash139)

(residues 140ndash273)

Figure 1 Schematic representation of LOX-1 structure LOX-1 consists of four domains a cytoplasmic N-terminal domain a singletransmembrane domain an extracellular neck domain and an extracellular lectin-like domain

together with other SRs [6] Basal cellular LOX-1 expressionis very low but it can be induced by several proinflammatoryand proatherogenic stimuli [7 8] In vitro LOX-1 expres-sion is induced by many stimuli related to atherosclerosisincluding proinflammatory cytokines such as tumor necrosisfactor alpha (TNF120572) interleukin-1 (IL-1) and interferon-gamma (IFN120574) angiotensin II endothelin-1 OxLDL andother modified lipoproteins free radicals and fluid shearstress [8ndash10] (Table 1) In vivo the expression of LOX-1is upregulated in the presence of pathological conditionsincluding atherosclerosis hypertension and diabetes [8](Figure 2) In human atherosclerotic lesions LOX-1 is overex-pressed in ECs especially in the early stage of atherogenesisin advanced atherosclerotic plaques LOX-1 is overexpressedin ECs of neovascular formations [11] Furthermore LOX-1 ishighly expressed by intimal smooth muscle cells (SMCs) andmacrophages in human carotid atherosclerotic plaques [11]suggesting the roles for LOX-1 in endothelial activation andin foam cell formation Finally the results obtained in LOX-1 knockout or LOX-1 overexpressing mice have suggested akey contribution of LOX-1 in the inflammatory response andlipid deposition in heart vessels [12 13]

Besides OxLDL LOX-1 binds multiple ligands includingother forms of modified lipoproteins advanced glycationend-products activated platelets and apoptotic cells [8ndash10](Table 2) LOX-1 also binds delipidated OxLDL suggestingthat LOX-1 recognizes the modified apolipoprotein B fur-thermore LOX-1 binds with higher affinity tomildly oxidizedLDL rather than extensively oxidized LDL suggesting theability to recognize also oxidized lipids (ie lipids that arecovalently bound to the protein and are not removed by thedelipidation process) [3] (Table 2) OxLDL is rapidly inter-nalized into cells following the interaction with LOX-1 thisinternalization process is inhibited by LOX-1-blocking anti-bodywhich acts by preventing the binding ofOxLDLwith thereceptor [14] After the endocytosis of the complex OxLDL-LOX-1 the receptor is uncoupled from OxLDL and both arelocated in separate compartments within the cytosol [14]

LOX-1 is mainly localized in caveolaelipid rafts (choles-terol-enriched membrane microdomains) in the plasmamembrane its function is modulated by the cholesterol con-tent ofmembrane cholesterol depletion induces themislocal-ization of LOX-1 which results in a more diffuse distributionof the receptor in the plasmamembrane (without a reductionof the amount of receptor exposed on the cell surface) andin a marked reduction of LOX-1-mediated OxLDL bindingand uptake [15] This finding suggests that the clustered

Table 1 LOX-1 inducers

Proinflammatory cytokinesTumor necrosis factor 120572 (TNF120572)Interleukin-1 (IL-1)Interferon 120574 (IFN120574)Lipopolysaccharide (LPS)C-reactive protein (CRP)

Modified lipoproteinsOxLDL (copper-oxidized LDL)15-Lipoxygenase-modified LDL15-Lipoxygenase-modified HDL3

Glycoxidized-LDLLysophosphatidylcholine (LPC)Palmitic acid

Hypertension-related stimuliAngiotensin IIEndothelin-1Fluid shear stress

Hyperglycemic stimuliHigh glucoseAdvanced glycation end-products (AGEs)

Other stimuliHomocysteineFree radicals

distribution of LOX-1 in specific membrane microdomains isessential for an efficient interaction with OxLDL and for theinternalization of OxLDL-LOX-1 complexes

2 LOX-1-Mediated Endothelial Dysfunction

21 LOX-1 Upregulation by OxLDL Endothelial dysfunctionrepresents a very early stage in the atherogenic processand is a pathological condition characterized by alterationsin anti-inflammatory and anticoagulant properties and byimpaired ability to regulate vascular tone LOX-1 is the mainreceptor for OxLDL in ECs [5] and OxLDL through LOX-1 contributes to the induction of endothelial dysfunctionby several mechanisms (Figure 3) Basal LOX-1 expression isvery low but it can be induced by proinflammatory cytokines


Platelets

Smooth muscle cells

Macrophages

Heart failure

Transplantation

Atherosclerosis

Diabetes

Hypertension

Ischemiareperfusion

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OxLDL






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Smooth muscle cells

Macrophages

Heart failure

Transplantation

Atherosclerosis

Diabetes

Hypertension

Ischemiareperfusion

Endothelial cells

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OxLDL

Macrophage

OxLDL

SMC Platelet

LOX-1

OxLDL

Endothelial cell

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OxLDL






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OxLDL

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OxLDL






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