Abstract 080: Role of High-mobility Group Box 1 in Angiotensin Converting Enzyme 2 -Mediated Cardioprotective Effects in a Mouse Model of Myocardial Ischemia

Abstract

Backgrounds: High-mobility group box 1 (HMGB1) activates inflammation process, and its elevation is associated with adverse clinical outcomes in patients with myocardial infarction (MI). Previous studies have demonstrated that angiotensin-converting enzyme 2 (ACE2), a key member of vasoprotective axis of the renin angiotensin system, provides protection against MI. However, the involvement of HMGB1 in ACE2-mediated protective effects in cardiovascular diseases has yet to be elucidated. Thus, we hypothesized that the cardioprotective effects of ACE2 are, in part, by inhibition of cardiac HMGB1 and inflammatory pathways. Methods and results: Transgenic (TG) mice that ubiquitously overexpress ACE2 were used for the study. ACE2 levels in the hearts of TG mice were 58-times higher than wild type (WT). Mice were subjected to coronary artery ligation surgery and cardiac functions were evaluated by echocardiography 4 weeks post MI. MI resulted in a 53% decrease in ejection fraction (EF) and a 42% infarct area of left free wall. However, ACE2 TG mice showed 60% improvement of EF over WT mice. This was associated with a 55% decrease in the infarct area. Additionally, MI caused a three times increase in plasma HMGB1 levels which was associated with elevated macrophage infiltration and proinflammatory cytokine levels. In comparison to WT-MI mice, ACE2 overexpression attenuated the increase in plasma HMGB1 by 25% and reduced the proinflammatory cytokine levels to normal in the TG mice. To investigate the modulatory effects of ACE2 on HMGB1, adult cardiomyocytes incubated with an ACE2 activator (DIZE), a selective ACE2 inhibitor (C16), and a combination of DIZE and C16 were exposed to hypoxic condition for three hours. Hypoxia (H) caused 35% cell death and 44% increase in the HMGB1 level (H: 23.6± 0.8 vs normoxia: 16.4± 1.2, ng/ml). DIZE significantly attenuated the cell death (2% cell death) and 37% decrease in HMGB1 levels (DIZE+H: 14.8± 2.5 ng/ml), which was blocked by a selective ACE2 inhibitor (C16+DIZE+H: 20.8± 2.9ng/ml). Conclusions: The protective effect of ACE2 against ischemia is correlated with decrease in HMGB1 and its downstream pro-inflammatory cascades. Thus, HMGB1 could be useful target for the development of novel treatment for MI.