Toll-Like Receptor 9 Plays a Pivotal Role in Angiotensin II–Induced Atherosclerosis

Background
Toll-like receptor (TLR) 9 recognizes bacterial DNA, activating innate immunity, whereas it also provokes inflammation in response to fragmented DNA released from mammalian cells. We investigated whether TLR9 contributes to the development of vascular inflammation and atherogenesis using apolipoprotein E–deficient (Apoe-/-) mice.
Methods and Results
Tlr9-deficient Apoe-/- (Tlr9-/-Apoe-/-) mice and Apoe-/- mice on a Western-type diet received subcutaneous angiotensin II infusion (1000 ng/kg per minute) for 28 days. Angiotensin II increased the plasma level of double-stranded DNA, an endogenous ligand of TLR9, in these mice. Genetic deletion or pharmacologic blockade of TLR9 in angiotensin II–infused Apoe-/- mice attenuated atherogenesis in the aortic arch (P<0.05), reduced the accumulation of lipid and macrophages in atherosclerotic plaques, and decreased RNA expression of inflammatory molecules in the aorta with no alteration of metabolic parameters. On the other hand, restoration of TLR9 in bone marrow in Tlr9-/-Apoe-/- mice promoted atherogenesis in the aortic arch (P<0.05). A TLR9 agonist markedly promoted proinflammatory activation of Apoe-/- macrophages, partially through p38 mitogen-activated protein kinase signaling. In addition, genomic DNA extracted from macrophages promoted inflammatory molecule expression more effectively in Apoe-/- macrophages than in Tlr9-/-Apoe-/- macrophages. Furthermore, in humans, circulating double-stranded DNA in the coronary artery positively correlated with inflammatory features of coronary plaques determined by optical coherence tomography in patients with acute myocardial infarction (P<0.05).
Conclusions
TLR9 plays a pivotal role in the development of vascular inflammation and atherogenesis through proinflammatory activation of macrophages. TLR9 may serve as a potential therapeutic target for atherosclerosis.

©2019 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License(https://creativecommons.org/licenses/by-nc/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.