Calcium-Independent Phospholipase A2β-Akt Signaling Is Involved in Lipopolysaccharide-Induced NADPH Oxidase 1 Expression and Foam Cell Formation

Abstract

Foam cell formation is the most important process in atherosclerosis, and low density lipoprotein oxidation by reactive oxygen species (ROS) is the key step in the conversion of macrophages to foam cells. This study reveals the control mechanism of the gene for NADPH oxidase 1 (Nox1), which produces ROS in the formation of foam cells by stimulating TLR4. Treatment of macrophages by the TLR4 agonist LPS stimulated ROS production and ROS-mediated macrophage to foam cell conversion. This LPS-induced ROS production and foam cell formation could be abrogated by pretreatment of macrophages with N-acetyl cysteine or apocynin. LPS increased Nox1 promoter activity, and resultant expression of mRNA and protein. Small interfering RNA mediated inhibition of Nox1 expression decreased LPS-induced ROS production and foam cell formation. LPS-mediated Nox1 expression and the responses occurred in a calcium-independent phospholipase A2 (iPLA2)-dependent manner. The iPLA2β-specific inhibitor S-BEL or iPLA2β small interfering RNA attenuated LPS-induced Nox1 expression, ROS production, and foam cell formation. In addition, activation of iPLA2β by LPS caused Akt phosphorylation and was followed by increased Nox1 expression. These results suggest that the binding of LPS and TLR4 increases Nox1 expression through the iPLA2β-Akt signaling pathway, and control ROS production and foam cell formation.

NOX/NADPH Oxidase, the Superoxide-Generating Enzyme: Its Transcriptional Regulation and Physiological Roles

“…Its expression is induced by vasoactive factors such as Ang II and platelet-derived growth factor (PDGF) and has been thought to be involved in proliferation and hypertrophy of VSMC (2,24). Expression of NOX1 was also reported in macrophages (25) and mast cells (26). In these cells, NOX1 was suggested to be involved in foam cell formation and interleukin (IL)-1β-induced IL-8 secretion contributing to angiogenesis, respectively.…”

“…The NOX1 mRNA species expressed in the mouse macrophage was the a-type. The induction was mediated by NF-κB, and a NF-κB binding site was found at −91/−82 of the mouse a-type NOX1 promoter (25). Induction of NOX1 by LPS was also reported in gastric mucosal cells (27).…”

“…NOX1 was reported to be expressed in mouse macrophages (25). Stimulation with a TLR4 agonist LPS induced the expression of NOX1, and generated O 2 − was thought to be involved in form cell formation.…”

Premetastatic milieu explained by TLR4 agonist-mediated homeostatic inflammation

“…48 In addition, S100A8 is capable of inducing NOS2, 49 and TLR4 signaling is closely linked with ROS generation. [50][51][52] Thus, endogenous ligand may serve to balance TLR4-mediated NF-kB signaling that is sensitive to redox.…”

Resveratrol Inhibits Inflammation Induced by Heat-Killed Listeria monocytogenes

“…20 Stimulation of HKLM, a well-known TLR2 agonist, resulted in a rapid increase in Nox-1 mRNA expression in Raw264.7 cells (Fig. 1A).…”