Makoto Kakutani

Increased Expression of Lectinlike Oxidized Low Density Lipoprotein Receptor-1 in Initial Atherosclerotic Lesions of Watanabe Heritable Hyperlipidemic Rabbits

A novel lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) was recently identified in bovine aortic endothelial cells. It is strongly suggested to have a potential role in the initiation and development of atherosclerosis. In this study, we have isolated cDNA clones encoding the rabbit homologue of LOX-1 by screening a rabbit placenta cDNA library. In amino acid sequence and domain structure organization, the rabbit LOX-1 is highly conserved with the human counterpart. Transfection of rabbit LOX-1 cDNA to HEK-293 cells confers on them the activity to bind and internalize oxidized low density lipoprotein. Rabbit LOX-1 was identified as a 45-kDa protein by Western blot analysis with a specific monoclonal antibody. Notably, analyses by reverse transcription-polymerase chain reaction and Western blot revealed that LOX-1 was accumulated in 8-week-old Watanabe heritable hyperlipidemic rabbit aortas compared with normal rabbit aortas. Immunostaining confirmed that the augmented expression of LOX-1 was primarily localized within the intima at the earliest stages of atherogenesis. The most prominent staining was in the endothelial cells of lesions. Furthermore, the distinctive staining of LOX-1 was identified in the endothelium of non-lesion areas of Watanabe heritable hyperlipidemic rabbit aortas. Taken together, these findings support the possibility that LOX-1 might be involved in the initiation of atherosclerosis.

LOX-1, an endothelial receptor for oxidized LDL Implications for induction of endothelium dysfunction in the pathogenesis of vascular diseases

LOX-1, Lectin-like oxidized LDL receptor-1 is the major receptor for oxidized LDL preferentially expressed in endothelial cells. LOX-1 is a 50 KD membrane glycoprotein that structurally belongs to C-type lectin family. It is highly expressed in the endothelium of arteries as well as vascular rich organs. LOX-1 is also inducibly expressed in differentiated macrophages and transformed smooth muscle cells. In cultured endothelial cells, the expression of LOX-1 is unregulated by TNF-a, phorbol esters, shear stress, and Ox-LDL. In vivo, LOX-1 has been shown to be inducibly expressed in the atherosclerotic regions, and upregulated in the aortas and veins of hypertensive states. The ligands specificity of LOX-1 included Ox-LDL, acetyl LDL, and multiple negatively charged phospholipids. Consistently, the LOX-1 expression cells will bind and phagocytose aged/apoptotic cells characterized by exposing negatively charged phosphatidylserine in the cell surface. Taken together, as an endothelial specific scavenger receptor, LOX-1 are responsible for removing circulating cellular debris and waste in the physiological conditions. However, recognizing and excessive insudatation of Ox-LDL by LOX-1 will induce endothelial dysfunction thus initiate atherogenesis. A further study of the molecular mechanisms underlying LOX-1 ligands-receptor interaction will provide insights into the pathogenesis of athersclerosis and and other vascular diseases.

Calcium-dependent platelet aggregation through the interaction between phosphatidylserine and LOX-1

Aims Platelet aggregation at the injured surface of blood vessels plays a crucial role in arterial thrombosis. Platelet aggregation in plasma has been analysed in the presence of calcium chelator to avoid coagulation. Here, we describe a novel mechanism of platelet aggregation that involves calcium-dependent binding between phosphatidylserine (PS) and lectin-like oxidized LDL receptor-1 (LOX-1), and the contribution of platelet LOX-1 to arterial thrombosis.nnMethods and results In vitro , LOX-1 gene deletion and anti-LOX-1 antibody suppressed the aggregation of platelets from mice and humans, respectively, in the absence of calcium-chelating citrate, but not in the presence of citrate. LOX-1 blockade and annexin V, in parallel, suppressed platelet aggregation and shifted the population of aggregates from large to small in size. Simultaneous application of anti-LOX-1 antibody and annexin V did not exert additive suppressive effects on aggregation. On activation, platelets exposed LOX-1 and PS and bound to a PS-coated surface in an LOX-1-dependent manner. In vivo , both LOX-1 deletion and anti-LOX-1 antibody significantly suppressed thrombus formation in mice and rats, respectively. Furthermore, platelet transfusion from LOX-1 knockout to wild-type mice still showed the suppressive effects of LOX-1 gene deletion, suggesting that platelet LOX-1 promoted thrombus formation.nnConclusion LOX-1 blockade could be a novel approach to prevent platelet aggregation and thrombosis.