Journal
ARTERIOSCLEROSIS THROMBOSIS AND VASCULAR BIOLOGY
Volume 39, Issue 3, Pages 432-445Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1161/ATVBAHA.118.311874
Keywords
diet; inflammation; interleukin 6; osteoprotegerin; Toll-like receptor 2
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Funding
- Ministry of Science and Technology [105-2321-B-400-001, 106-2321-B-400-001, 102-2320-B-400-012-MY3]
- National Health Research Institutes (Taiwan) [CS-105-PP-11, CS-106-PP-11]
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Objective Vascular smooth muscle cell (VSMC) transformation to an osteochondrogenic phenotype is an initial step toward arterial calcification, which is highly correlated with cardiovascular disease-related morbidity and mortality. TLR2 (Toll-like receptor 2) plays a pathogenic role in the development of vascular diseases, but its regulation in calcification of arteries and VSMCs remains unclear. We postulate that TLR2-mediated inflammation participates in mediating atherosclerotic arterial calcification and VSMC calcification. Approach and Results We found that ApoE(-/-)Tlr2(-/-) genotype in mice suppressed high-fat diet-induced atherosclerotic plaques formation during initiation but progressively lost its preventative capacity, compared with ApoE(-/-) mice. However, TLR2 deficiency prohibited high-fat diet-induced advanced atherosclerotic calcification, chondrogenic metaplasia, and OPG (osteoprotegerin) downregulation in the calcified lesions. Incubation of VSMCs in a calcifying medium revealed that TLR2 agonists significantly increased VSMC calcification and chondrogenic differentiation. Furthermore, TLR2 deficiency suppressed TLR2 agonist-mediated VSMC chondrogenic differentiation and consequent calcification, which were triggered via the concerted actions of IL (interleukin)-6-mediated RANKL (receptor activator of nuclear factor B ligand) induction and OPG suppression. Inhibition experiments with pharmacological inhibitors demonstrated that IL-6-mediated RANKL induction is signaled by p38 and ERK1/2 (extracellular signal-regulated kinase 1/2) pathways, whereas the OPG is suppressed via NF-B (nuclear factor B) dependent signaling mediated by ERK1/2. Conclusions We concluded that on ligand binding, TLR2 activates p38 and ERK1/2 signaling to selectively modulate the upregulation of IL-6-mediated RANKL and downregulation of OPG. These signaling pathways act in concert to induce chondrogenic transdifferentiation of VSMCs, which in turn leads to vascular calcification during the pathogenesis of atherosclerosis.
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