Blocking Toll-Like Receptors 7 and 9 Reduces Postinterventional Remodeling via Reduced Macrophage Activation, Foam Cell Formation, and Migration

Abstract

e72P ostinterventional remodeling is a critical determinant of long-term efficacy of percutaneous coronary interventions. Restenosis is characterized by acute elastic recoil and intimal hyperplasia attributable to inflammation, smooth muscle cell (SMC) proliferation, and extracellular matrix turnover. 1 Under hypercholesterolemic conditions, this is accompanied by influx and accumulation of low-density lipoprotein (LDL) cholesterol in the vessel wall that becomes oxidized and taken up by macrophages. Thereby these macrophages become foam cells and initiate a process of accelerated atherosclerosis.2 Previously, we and others described an important causal role for extracellular toll-like receptors (TLRs) in postinterventional remodeling. It has been shown that TLR4 and the MyD88-dependent pathway play an important role in restenosis and postinterventional accelerated atherosclerosis. [3][4][5][6] Similarly, a crucial role for TLR2 has been described. TLRs, as part of the innate immune system, are pattern recognition receptors known to recognize exogenous ligands that originate from bacteria or viruses as well as endogenous ligands. These endogenous ligands may be released after tissue damage or cell stress, processes that may be initiated by percutaneous coronary interventions. MyD88-dependent signaling is the dominant activation pathway of TLR signaling leading to nuclear factor-kappaB activation and upregulation of several proinflammatory cytokines. Because TLR2 and TLR4 are known to be expressed on the cell surface of vascular cells and activated in vascular disease processes via damageassociated molecular patterns as endogenous ligands, such as heat shock proteins, fibronectin containing extradomain A, tenascin-C, and high-mobility group box 1 (HMGB1), [8][9][10][11] research in the cardiovascular field mainly focused on TLR2 and TLR4. Objective-The role of toll-like receptors (TLRs) in vascular remodeling is well established. However, the involvement of the endosomal TLRs is unknown. Here, we study the effect of combined blocking of TLR7 and TLR9 on postinterventional remodeling and accelerated atherosclerosis. Methods and Results-In hypercholesterolemic apolipoprotein E*3-Leiden mice, femoral artery cuff placement led to strong increase of TLR7 and TLR9 presence demonstrated by immunohistochemistry. Blocking TLR7/9 with a dual antagonist in vivo reduced neointimal thickening and foam cell accumulation 14 days after surgery by 65.6% (P=0.0079). Intima/media ratio was reduced by 64.5% and luminal stenosis by 62.8%. The TLR7/9 antagonist reduced the arterial wall inflammation, with reduced macrophage infiltration, decreased cytoplasmic high-mobility group box 1 expression, and altered serum interleukin-10 levels. Stimulation of cultured macrophages with TLR7 and TLR9 ligands enhanced tumor necrosis factor-α expression, which is decreased by TLR7/9 antagonist coadministration. Additionally, the antagonist abolished the TLR7/9-enhanced low-density lipoprotein uptake. The antagonist also reduced oxidized lowden...

Protective Role for Toll-Like Receptor-9 in the Development of Atherosclerosis in Apolipoprotein E–Deficient Mice

“…Also, various diseases might differ in the overall complex response to TLR signaling. For example, postinterventional vascular remodeling is reduced by the combined blockade of TLR7 and TLR9, 31 whereas genetic deficiency of TLR7, as reported by Salagianni et al, 10 and TLR9, as reported here, causes acceleration of atherosclerosis. Notably, our data are consistent with recent findings indicating an emerging paradigm that endosomally located TLRs (eg, TLR3, TLR7) exert atheroprotection, whereas cell surface-located TLRs (eg, TLR2, TLR4) exert proatherosclerotic effects.…”

Toll-like Receptors in the Vascular System: Sensing the Dangers Within

“…Moreover, TLR3 plays a critical role in mediating atherosclerotic plaque instability, in part by modulation of macrophage matrix metalloproteinases-2 and -9 activities (Ishibashi et al, 2013). The contribution of endosomal TLR7 is beginning to emerge as a mediator of vascular remodeling and foam cell accumulation (Karper et al, 2012). Finally, endosomal TLR9 has been observed to propagate inflammation in response to vascular injury (Erridge et al, 2008;Lopez et al, 2012;Hirata et al, 2013), foam cell accumulation, and lesion formation (Niessner et al, 2006;Kim et al, 2009a;Sorrentino et al, 2010;Karper et al, 2012) and in LDL receptor-deficient mice (Ding et al, 2013).…”

Extracellular Ribonucleic Acids (RNA) Enter the Stage in Cardiovascular Disease

“…84,85 Moreover, mitochondrial DNA in conjunction with antimicrobial peptide leads to activation of TLR9-mediated inflammation and atherosclerotic lesion formation in Apoe −/− mice. 86 Given the conflicting data on the role of both TLR7 and TLR9, for example, in vascular inflammation, [87][88][89][90] it currently remains unclear whether effects of eRNA (and extracellular DNA) on atherosclerosis and myocardial infarction are in part mediated by triggering immune responses targeted against self-nucleic acids that require signaling via particular TLRs. It is conceivable that eRNA exerts cell type-specific mechanisms and that the multiple cardiovascular functions of selfeRNA are mainly transmitted independently of TLR signaling.…”