Adhesion molecule expression in fibroblasts - Alteration in fibroblast biology after transfection with LOX-1 plasmids

The endothelial lectinlike, oxidatively ( ox-) modified LDL receptor LOX- 1 is a critical player in the pathogenesis of atherosclerosis and myocardial ischemia. Ox- LDL binding of LOX- 1 results in the expression of various adhesion molecules, which attract monocytes to endothelial cells, an initial step in atherogenesis. We wished to examine the role of the ox- LDL/ LOX- 1 signaling pathway in fibroblasts, which naturally express low levels of LOX- 1. Rat cardiac fibroblasts were transfected with either cytomegalovirus ( CMV)- LOX-1(wt) ( amino acids [ aa] 1 to 273) or CMV- LOX- 1(1-261) ( an ox- LDL - binding negative mutant, aa 1 to 261) plasmid. Western blots showed that LOX- 1 protein expression was increased significantly in cells transfected with CMV- LOX- 1(wt) or CMV- LOX- 1(1-261) plasmid ( P < 0.01 vs control). Fibroblasts transfected with CMV- LOX- 1wt showed ox- LDL binding, whereas fibroblasts without transfection and those transfected with CMV- LOX- 1(1-261) did not bind ox- LDL. Compared with untransfected cells, ox- LDL treatment ( 50 mu g/ mL, 24 hours) markedly induced the expression of the leukocyte adhesion molecules intercellular adhesion molecule- 1 ( ICAM- 1), and vascular cell adhesion molecule- 1 ( VCAM)- 1 as well as matrix metalloproteinase ( MMP)- 1 in cells transfected with CMV- LOX- 1(wt) ( P < 0.05) but not in cells transfected with CMV- LOX- 1(1-261). Concurrently, ox- LDL treatment enhanced the phosphorylation of p38 mitogen- activated protein kinase ( MAPK) ( P < 0.05 vs control) in CMV- LOX- 1(wt) - transfected cells. These data suggest that in cardiac fibroblasts, ox- LDL binds to LOX- 1 and activates p38 MAPK, followed by the expression of ICAM- 1, VCAM- 1, and MMP- 1. Thus, fibroblasts transform into an endothelial phenotype on transfection with CMV- LOX- 1(wt) and subsequent exposure to ox- LDL. This study provides a useful model system ( plasmid- transfected fibroblasts) to study the molecular biology of LOX- 1.