Background: Plasma low density lipoproteins (LDL) play a key role in the pathogenesis of atherosclerosis. LDL modify gene expression in vascular cells leading to disturbances in the functional state of the vessel wall.
Methods: Expression levels of C-4 sterol methyl oxidase gene (ERG25), sterol regulatory element binding protein (SREBP)-1 and -2 were evaluated in porcine aortic endothelial cells (PAEC), porcine and human smooth muscle cells (SMC) and in the vascular wall from normolipemic and hyperlipemic pigs by RT-PCR. SREBP-1 protein levels were assessed by Western blot and SREBP-SRE binding by EMSA. SREBP-2 was overexpressed by transient transfection with lipofectin.
Results: We have identified expression of the ERG25 in vascular cells and analyzed its regulation by LDL. ERG25, an enzyme involved in cholesterol biosynthesis, is expressed in vascular endothelial and SMC from porcine and human origin and is downregulated by LDL in a time- and dose-dependent manner. Downregulation of ERG25 by LDL was abolished by an inhibitor of neutral cysteine proteases (N-acetyl-leucyl-leucyl-norleucinal) that abrogates SREBP catabolism. LDL downregulated SREBP-2 mRNA levels but not SREBP-1 expression in these cells and both ERG25 and SREBP-2 gene expression was significantly decreased in the vascular wall of diet-induced hypercholesterolemic swine. Finally, in cell transfection experiments SREBP-2 overexpression blocks ERG25 downregulation caused by LDL.
Conclusions: Our results indicate that LDL modulate ERG25 expression in the vascular wall and suggest the involvement of SREBP-2 in this mechanism.