LOX-1+and+LOXIN

Interestingly, we noticed [by Western blot] a relative increase in the amount of LOXIN in cells derived from subjects homozygous for the “non-risk” haplotype (Figure 4B). . . . It is worth noting that a very low dose of LOXIN [delivered via DNA transfection to human monocyte-derived macrophages], corresponding to a ratio of 1:4 with LOX-1, resulted in a 72% reduction in the number of apoptotic cells, and a 1:1 ratio of the 2 plasmids used for transfection completely prevented the phenotype.
 * EXON 5 EXCLUSION --> LOXIN:** An association of poly- morphisms in the human //OLR1// gene and MI susceptibility has been recently reported. 14,15 In particular, we have identi- fied 7 different single nucleotide polymorphisms (SNPs), 6 of them located within introns 4, 5, and 3 􏰎 UTR (untranslated region), comprised in a linkage disequilibrium (LD) block strongly associated with the elevated risk to develop MI. 14 . . . Using a minigene approach, we show that SNPs located in the LD block regulate the level of the new fully functional transcript by modulating the retention of exon 5 of the //OLR1// gene. . . . the //OLR1///LOXIN mRNA ratio was 33% higher in human monocyte-derived macrophages of subjects homozygous for the “risk” haplotype compared with homozygous for the “non-risk” haplotype (Figure 2A). . . . we extended these studies by constructing minigenes carrying the “risk” and “non-risk” haplotypes with genomic sequences containing intron 4, exon 5, and intron 5 (Figure 2B). These constructs were transfected in COS-7 fibroblasts and the ratio of unspliced (exon 5 􏰉 ) to spliced (exon 5 􏰐 ) transcript was analyzed by real time isoform- specific PCR. As can be seen in Figure 2C, the ratio was 27% higher in RNA extracted from cells transfected with mini- genes carrying the “risk” haplotype. . ..


 * CLINICAL EXPLANATION:** A cen- tral tenet of atherosclerosis has been the concept that LDL undergoes modification into oxidized LDL (oxLDL) in tissues like the arterial wall. Uptake of oxLDL by macrophages and other vascular cells incites a cascade of events that promote inflammation, atherosclerosis, and eventually plaque rupture. A major advance in this area came with the identification of the lectin-like oxidized LDL receptor 1 (LOX-1) that, upon activation by ox-LDL binding, induces multiple proatherosclerotic responses in endothelial cells (ECs) as well as smooth muscle cells and macrophages, in- cluding production of reactive oxygen species, release of matrix-degrading metalloproteinases, recruitment of leukocytes (increasing chemoattractant cytokines and adhesion molecule expression), reduced levels of endothelial nitric oxide synthase, and more apoptosis (4, 5 ). Mice lacking LOX-1 are protected against ath- erosclerosis, whereas transgenic LOX-1 overexpression increases atherosclerotic lesion size. A genetic variant in LOX-1 in humans that interferes with ox-LDL bind- ing is associated with decreased atherosclerosis, al- though the results with genetic LOX-1 variants have been variable. Together, these data raise key clinical issues: does LOX-1 activity predict clinical cardiovas- cular events? . . . [In a correlative study in Suita, Japan,] After adjusting for many (but not all) known cardiovascular risk factors such as sex, age, smoking,hypertension,diabetes,non– high-densityli- poproteins, and lipid-lowering drug use, the highest quar- tile of the LOX index was still associated with a significant increase in risk for coronary heart disease and stroke. [[file:Clinical LOX-1.pdf]]

In addition to the Rho and Rac pathways, the following signal transduction pathways have been reported to be activated via LOX-1: p38 mitogen-activated protein kinase C (MAPK), 23,24 p44/42MAPK, 11 protein kinase C, 25 protein kinase B, 26 ERK1/2, 27 protein tyrosine kinase 28 and NF-κB. Among them, LOX-1-mediated NF-κB activation by oxLDL is crucial for increasing the expressions of the following adhesion molecules: E- and P-selectins, intracellular sion molecule-1 (ICAM-1), vascular cell adhesion molecule- 1 (VCAM-1) and monocyte chemotactic protein-1 (MCP- 1), 25,29,30 which brings proinflammatory changes to the vessel wall. Additionally, LOX-1 activation changes endothelial cells and smooth muscle cells prone to apoptosis by increasing the Bcl-2-associated X protein (Bax)/Bcl-2 ratio (Figure 2). 6
 * EXPRESSION OF LOX-1:** LOX-1 is expressed not only in endothelial cells, but also in macrophages, 5 vascular smooth muscle cells 6 and plate- lets. 7
 * FUNCTION OF LOX-1:** LOX-1 binding to oxLDL enhances nitric oxide (NO) catabolism as a result of superoxide generation, and decreases NO release via attenuated endothelial NO synthase (eNOS) activity. LOX-1 has been recently shown to form a complex with MT1-MMP under a basal condition. 22 When oxLDL binds to LOX-1 it induces rapid RhoA and Rac1 activation via MT1-MMP, which results in NADPH oxidase activation and eNOS downregulation. 22 The imbalance of NO and oxidative stress resulting from the binding of oxLDL to LOX-1 causes oxLDL-induced endothelial dysfunction leading to atherosclerosis.
 * MOUSE STUDIES:** On a high-fat diet, compared with ApoEKO mice, LOXtg/ApoEKO mice showed more pronounced oxLDL accumulation, oxidative stress detected by8-hydroxy-2’ -deoxyguanosine(8-OH-dG),increased expression of ICAM-1 and VCAM-1, and infiltration of macrophages in the heart vessels. Furthermore, atheroma- like lesions in the intramyocardial vessels increased 10-fold in LOXtg/ApoEKO mice compared with ApoEKO mice. We also generated LOX-1-deficient mice by deleting a part of the lectin-like domain that is essential for ligand binding. 32 LOX-1-deficient mice were resistant to oxLDL-induced impairment of endothelium-dependent vasorelaxation. 32 When crossed with atherosclerosis-prone LDL receptor (LDLR) KO mice, the formation of atherosclerotic lesions was significantly reduced in the aorta of LOX-1/LDLR double KO mice.