Abstract 14944: Factor Xa Aggravates Atherosclerosis by Promoting Inflammasome Formation Through Suppressing Autophagy
Introduction: Growing body of evidence suggests that factor Xa (FXa), an endogenous coagulation factor, plays a critical role in promoting atherosclerosis. However, the mechanism how FXa facilitates atherogenesis remains unclear.
Hypothesis: FXa promotes progression of atherosclerosis through protease-activated receptor-2 (PAR-2)-mediated modulation of autophagy machinery and innate inflammatory response.
Methods and Results: Administration of 12 mg/kg/day of rivaroxaban (Riv), a direct FXa inhibitor, to the mice effectively elongated prothrombin time (Riv 12mg/kg/day: 14.6 ± 0.6*, Riv 6mg/kg/day: 9.2 ± 0.2*, Untreated: 7.1 ± 0.1 sec, *P < 0.05) and markedly suppressed plasma FXa activity (Riv 12mg/kg/day: 1.9 ± 0.1*, Riv 6mg/kg/day: 2.6 ± 0.3*, Untreated: 3.9 ± 0.3 RFU, *P < 0.05) compared with the mice treated with lower dose of Riv (6 mg/kg/day) or untreated mice. Riv treatment to ApoE-/- mice fed with a high-fat diet for 20 weeks markedly reduced the atherosclerotic areas in the sinus and whole aorta to 42.5 % (P > 0.05) and 50.4 % (P > 0.05), respectively. Moreover, Riv also reduced the inflammasome formation in the atherosclerotic lesions as evaluated by immunostaining of NLRP3. In vitro experiments using RAW264.7, a murine macrophage cell line, or mouse peritoneal macrophages demonstrated that treatment of 7-ketocholesterol (7KC), an atherosclerotic lesional oxysterol that promotes inflammation through inflammasome formation, significantly activated autophagy as evidenced by the increase in LC3-II protein and the number of autophagosomes. Treatment with FXa (50 nM) markedly induced phosphorylation of mTOR (Ser2448) and suppressed 7KC-induced autophagy, which was reversed in the presence of Riv (1 μM). In addition, Treatment with FXa significantly enhanced inflammasome formation induced by 7KC, which was blocked in the presence of Riv, as evaluated by the amount of NLRP3, caspase-1, and IL-1β. Importantly, however, treatment with FXa failed to block 7KC-induced autophagy and inflammasome activation in macrophages derived from PAR-2-/- mice.
Conclusion: FXa positively regulates the atherogenesis, possibly through PAR-2-mediated pathway by inhibiting autophagy which, in turn, promoting inflammasome activation in macrophages.
Author Disclosures: Y. Ito: None. Y. Maejima: None. N. Tamura: None. R. Watanabe: None. M. Isobe: None.
- © 2015 by American Heart Association, Inc.