Oxidized Low Density Lipoprotein Induces Bone Morphogenetic Protein-2 in Coronary Artery Endothelial Cells via Toll-like Receptors 2 and 4

Abstract

Vascular calcification is a common complication in atherosclerosis. Bone morphogenetic protein-2 (BMP-2) plays an important role in atherosclerotic vascular calcification. The aim of this study was to determine the effect of oxidized low density lipoprotein (oxLDL) on BMP-2 protein expression in human coronary artery endothelial cells (CAECs), the roles of Toll-like receptor (TLR) 2 and TLR4 in oxLDL-induced BMP-2 expression, and the signaling pathways involved. Human CAECs were stimulated with oxLDL. The roles of TLR2 and TLR4 in oxLDL-induced BMP-2 expression were determined by pretreatment with neutralizing antibody, siRNA, and overexpression. Stimulation with oxLDL increased cellular BMP-2 protein levels in a dose-dependent manner (40-160 μg/ml). Pretreatment with neutralizing antibodies against TLR2 and TLR4 or silencing of these two receptors reduced oxLDL-induced BMP-2 expression. Overexpression of TLR2 and TLR4 enhanced the cellular BMP-2 response to oxLDL. Furthermore, oxLDL was co-localized with TLR2 and TLR4. BMP-2 expression was associated with activation of nuclear factor-κB (NF-κB), p38 mitogen-activated protein kinase (MAPK), and extracellular signal-regulated kinase (ERK)1/2. Inhibition of NF-κB and ERK1/2 reduced BMP-2 expression whereas inhibition of p38 MAPK had no effect. In conclusion, oxLDL induces BMP-2 expression through TLR2 and TLR4 in human CAECs. The NF-κB and ERK1/2 pathways are involved in the signaling mechanism. These findings underscore an important role for TLR2 and TLR4 in mediating the BMP-2 response to oxLDL in human CAECs and indicate that these two immunoreceptors contribute to the mechanisms underlying atherosclerotic vascular calcification.