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 oxLDLinduced 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 g/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-B (NF-B), p38 mitogen-activated protein kinase (MAPK), and extracellular signal-regulated kinase (ERK)1/2. Inhibition of NF-B 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-B 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.Calcification in intima is often associated with atherosclerosis. Atherosclerotic calcification of coronary artery is a significant risk for the unsuccessful coronary intervention and balloon-induced coronary artery dissection (1), and calcification is found to be an indicator of plaque instability (2). Although inhibition of atherosclerotic calcification might be a promising approach to stabilize atherosclerotic plaques, the molecular mechanism(s) underlying atherosclerotic vascular calcification remains incompletely understood.It is known that oxLDL 2 accumulation in the vascular wall provokes the development of atherosclerosis and vascular calcification (3). BMP-2 is an osteogenic factor. It is expressed in calcified human atherosclerotic plaque. Cells from the atherogenic aortic wall express BMP-2 in vitro and formed calcified nodules with prolonged culture (4). The BMP-2 mRNA level increased after oxLDL stimulation in human CAECs (5). However, it remains unclear whether oxLDL up-regulates BMP-2 protein levels in CAECs. Further, the signaling mechanism that regulates the cellular BMP-2 response to oxLDL is unknown.Accumulating evidence indicates that atherosclerosis is an inflammatory process involving a network of vascular cells, monocytes, and T lymphocytes. Proinflammatory mediators, including cytokines, chemokines, and growth factors...

The Innate Immune Response Mediated by TLRs in Atherosclerosis

“…mmLDL also caused the redistribution and patching of TLR2 on the cell surface, suggesting that there is a close association between these cell surface receptors (Chávez-Sánchez et al, 2010a). Similar data show that TLR2 and TLR4 colocalized with oxLDL (Su et al, 2011). Notably, mmLDL increases the expression of TLR2, rather than the expression of TLR4, in human monocytes and macrophages (Chávez-Sánchez et al, 2010a), suggesting that mmLDL may induce cross-talk between the TLR2 and TLR4 pathways of activation, resulting in amplified secretion of pro-inflammatory cytokines (Fan et al, 2006).…”

Interleukin-37 suppresses the osteogenic responses of human aortic valve interstitial cells in vitro and alleviates valve lesions in mice

“…Similarly, aortic valve thickening is essentially absent in TLR2 KO mice and TLR4 mutant mice fed with a high fat diet, indicating an important role of TLR2/4 in mediating aortic valve lesions. It is interesting that oxLDL deposition is evident in the aortic valve tissue of mice fed with high fat diet because oxLDL has been reported to function as a DAMP (29,40,41). In this regard, we reported that oxLDL induces BMP-2 expression in human coronary artery endothelial cells through TLR2/4 (29).…”

“…It is interesting that oxLDL deposition is evident in the aortic valve tissue of mice fed with high fat diet because oxLDL has been reported to function as a DAMP (29,40,41). In this regard, we reported that oxLDL induces BMP-2 expression in human coronary artery endothelial cells through TLR2/4 (29). The in vitro murine AVIC culture experiments revealed that TLR2 KO or TLR4 mutation greatly reduces oxLDL-induced BMP-2 expression, providing a possible mechanism for the in vivo effect of high fat diet on aortic valves.…”

“…Further, oxLDL deposition in the vascular wall is known to provoke atherosclerotic calcification (28). We have reported that oxLDL induces BMP-2 expression in human coronary artery endothelial cells through a mechanism dependent on TLR2 and TLR4 (29).…”

Molecular Biology of Atherosclerosis

“…For example, both receptors were shown to induce endothelial expression and secretion of bone morphogenic protein 2 (BMP2) through NF-B and ERK1/2 activation after exposure to oxLDL (1692). TLR4 binds LPS (and some other ligands) by way of the coreceptor CD14 after LPS is bound in serum to the acute phase reactant LPS binding protein (LBP, produced in liver).…”