Pathophysiological role of lipid molecules produced by 12/l5-lipoxygenase

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Lipoxygenase incorporates a molecular oxygen regiospecifically and stereospeciflcally into unsaturated fatty acids. There are four classes of enzymes in mammalian tissues; 5-, 8-, 12-, and 15-lipoxygenases, named by the number indicating oxygenation site of arachidonic acid as a substrate. Among the enzymes, 12-lipoxygenases are widely distributed in various tissues and species, and there are three isoforms: platelet, leukocyte and epidermis types. Since the leukocyte 12-lipoxygenase and 15-lipoxygenase-1 are highly related in their primary structures and enzymological properties, these enzymes are collectively called as 12/15-lipoxygenase. A number of evidences support the role of 12/15-lipoxygenase in LDL oxidation. In order to investigate precise mechanisms of the 12/15-lipoxygenase-mediated LDL oxidation, we established a mouse macrophage-like J774A1 cell line overexpressing porcine leukocyte 12-lipoxygenase. The presence of regio- and stereospeciflcally oxygenated product of cholesteryl linoleate in the LDL indicates that the 12/15-lipoxygenase is responsible for cell-mediated LDL oxidation. We also showed that LDL receptor-related protein (LRP) was required for the enzyme-mediated LDL oxidation by macrophages. Furthermore, cholesterol ester selectively transferred from the LDL particle to the plasma membrane via LRP is oxygenated by 12/15-lipoxygenase translocated to this membrane: