The effects of oxidized low density lipoproteins on inducible mouse macrophage gene expression are gene and stimulus dependent

Abstract

Oxidized LDL has been previously reported to suppress the expression of genes induced in mononuclear phagocytes by inflammatory stimuli. In this study we extend these findings to demonstrate that the suppressive effects of oxidized LDL vary depending upon the gene being monitored and the stimulus being used to induce or enhance its expression. The expression of a selection of LPS-inducible genes exhibited differential sensitivity to pretreatment with oxidized LDL. Furthermore, the ability of oxidized LDL to suppress gene expression varied markedly with the inducing stimulus used. TNFα and IP-10 mRNA expression induced by IFNγ and IL-2 was markedly more sensitive to suppression by oxidized LDL than that induced by LPS. The cooperative effects of IFNγ and LPS on the expression of the inducible nitric oxide synthase gene were suppressed by oxidized LDL while the antagonistic effect of IFNγ on LPS-induced expression of the TNF receptor type II mRNA was not altered. The suppressive activity of LDL was acquired only after extensive oxidation and was localized in the extractable lipid component. These results suggest a potent and direct connection between the oxidative modification of LDL and the chronic inflammation seen in atherogenic lesions. Furthermore, the appreciable selectivity of oxidized LDL in mediating secondary control of cytokine gene expression demonstrates that the active material(s) is targeted to disrupt specific intracellular signaling pathways.