Low-density lipoprotein oxidized to various degrees activates ERK1/2 through Lox-1

Although the standard procedure for preparing extensively oxidized low-density lipoprotein (Ox-LDL) is to incubate it with 10 μM CuSO4 at 37 °C for 24 h, it is not well known how important the degree of oxidation of LDL is for inducing cell signaling. Since Lox-1 (an Ox-LDL receptor) contributes to cell proliferation through extracellular-signal-regulated kinase (ERK)1/2 activation and subsequently induces plaque growth, we analyzed ERK activity using LDL with various degrees of oxidation, from minimally Ox-LDL, which is mainly in human plasma, to extensively Ox-LDL using capillary electrophoresis (cITP). The cITP was a suitable tool for evaluating the degree of oxidation of LDL for analyzing the optimal conditions for the oxidation of LDL by CuSO4 to obtain LDL that was oxidized to a degree comparable to that in human plasma. In addition, both minimally and extensively Ox-LDL induced similar levels of ERK1/2 activation through Lox-1 in human coronary artery smooth muscle cells. These results indicate that both minimally and extensively Ox-LDL may be important for the progression of plaque growth through Lox-1. Since most previous reports have provided data only using extensively Ox-LDL, a re-evaluation is needed to analyze several signals that use LDL which has been oxidized to various degrees.