Role of ERK and toll-like receptors in oxidised low-density lipoprotein mediated cell death.

Atherosclerosis is a chronic disease which involves the inflammation and thickening of arterial walls due to the deposition of lipid laden foam cells and fibrous elements which form the plaque. Low density lipoprotein (LDL) oxidation is a key atherogenic process that results in the formation of oxidised LDL (oxLDL) which is cytotoxic in nature. Oxidative stress response is triggered in various immune cells on exposure to oxLDL and when it becomes extreme, it causes cell death within the atherosclerotic plaque. NADPH oxidase (NOX) is a major oxidant source which generates superoxide radicals on activation by oxLDL. Cellular protein kinases such as extracellular signal-regulated kinase 1/2 (ERK 1/2) are implicated in the phosphorylation and activation of the controlling NOX subunit p47phox. This study aims to confirm previous studies on the kinetics of the oxLDL induced oxidative stress and the underlying mechanism driving the cytotoxic activation of NOX in U937 monocyte-like cells. This study also aims to determine if NOX 2 is activated by oxLDL via phosphorylation of ERK 1/2, measured by western blotting and confirm whether inhibition of ERK 1/2 blocks oxLDL induced cell death. Results show oxLDL addition led to increased phosphorylation of ERK. Inhibition of ERK inhibited the cell death by oxLDL. The ERK protein kinases are suggested to be activated via surface receptor pathways including the Toll-like receptors (TLRs), of which TLRs 2/6 and 4 have been implicated in inflammatory diseases. In this study, the effects of inhibiting TLRs 4 and 2/6 on oxLDL induced oxidant production and cell death were examined using two known inhibitors, TAK-242 and GIT-27 respectively. The individual and combined inhibition of TLRs 2, 4 and 6 did not have any significant effect on oxidative stress or cell death induced by oxLDL. This data suggests that other oxLDL binding receptors are responsible for activating the cascade which leads to NOX activation and cell death