Abstract 5170: Atrial Endothelial Impairment Induced by Toll-Like Receptor-4 Signaling May Cause Atrial Thrombogenesis

Abstract

Background Recently atrial endothelial dysfunction has gained more attention as an important cause for atrial thrombogenesis in patients with atrial fibrillation (AF). It was reported that AF patients with left ventricular hypertrophy or heart failure (HF) have higher thromboembolic risks than those without. Several reports showed that angiotensin II receptor blockers prevented occurrences of AF and thrombogenesis by inhibiting inflammation. However, little is known how AF causes atrial inflammation and thrombogenesis. We examined whether atrial inflammation through toll-like receptor (TLR)-4 signaling causes atrial thrombogenesis. Methods and result First, we examined serum and atrial tissue heat shock protein 60 (HSP60) levels, which have been known as a TLR-4 ligand, in patients with and without AF. Atrial HSP60 increased in HF patients with AF compared to those without AF whereas serum HSP60 level was lower in HF patients with AF compared to those without AF (NYHA class I and II). Then, we created thoracic transverse aortic constriction (TAC) model in TLR-4 knockout (KO) mice (n=15) and wild-type (WT) mice (n=20). We performed echocardiography at 4 weeks after TAC surgery. Then, the atrium was excised, and vascular cell adhesion molecule (VCAM)-1, endothelial nitric oxide synthase (eNOS), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and mitogen activated protein kinase p38 (p38) were analyzed by Western blotting. We observed less frequent occurrence of atrial thrombosis in TLR-4 KO-TAC mice (4/15) than WT-TAC mice (16/20). Decrease in eNOS phosphorylation and increase in VCAM-1 expression in WT-TAC mice were significantly attenuated in TLR-4 KO-TAC mice (P<0.05). Nuclear factor-kappa B (NFkB) was attenuated in TLR-4 KO-TAC mice compared to WT-TAC mice by electrophoretic mobility shift assay analysis. Phosphorylation of p38, but ERK and JNK was also attenuated in TLR-4 KO-TAC mice (P<0.05). These results suggested that activation of VCAM-1 and decreased eNOS through TLR-4/p38 and NFkB signaling may be associated with atrial thrombogenesis in AF. Conclusion Atrial inflammation caused by TLR-4 signaling may play a role in atrial thrombogenesis in heart failure mice model.