Abstract 6: ADAMTS13 Reduces VWF-Mediated Acute Myocardial Ischemia/Reperfusion Injury in Mice

Background and objective: ADAMTS13 cleaves von Willebrand factor (VWF), a large multimeric protein that plays an important role in thrombus formation by binding to platelets following vascular injury. Epidemiological studies implicate elevated VWF levels and reduced ADAMTS13 activity in plasma as risk factors for myocardial infarction, but it remains unknown whether the ADAMTS13/VWF axis contributes to myocardial infarction pathogenesis. We tested the hypothesis that ADAMTS13 reduces VWF-mediated myocardial ischemia/reperfusion injury in mice. Methods: Myocardial infarction was induced in male mice (8-10 weeks of age) by ligating the left anterior descending coronary artery for 30 minutes followed by 23.5 hours of reperfusion. The extent of myocardium damage was evaluated by measuring infarct size (%) in 2 mm serial sections stained with 2% triphenyl-2, 3, 4-tetrazolium-chloride. Results: Adamts13 -/- mice had significantly larger infarcts (mean ± SEM: 21.4 ± 1.3%, P <0.05) than WT mice (16.9 ± 1.2%) after myocardial ischemia/reperfusion injury. Adamts13+/- mice, which have a 50% reduction in ADAMTS13 activity, had similar sized infarcts (16.6 ± 1.3%) compared to those in WT mice. Because VWF remains the only known substrate of ADAMTS13 in multiple experimental models, we hypothesized that ADAMTS13 reduces myocardial injury through its proteolytic effect on hyper adhesive ULVWF and /or VWF. To test this hypothesis, we used a VWF-blocking antibody. Interestingly, WT mice treated with the VWF-blocking antibody showed a marked reduction in infarct size (7.9 ± 0.6%, P < 0.001) compared with WT mice treated with control Ig (17.5 ± 1.5 %). Finally, Adamts13 -/- mice treated with the VWF-blocking antibody had infarct sizes (8.0 ± 1.5%) that were similar to those WT mice treated with VWF-blocking antibody, demonstrating that increased infarct size in the Adamts13 -/- mice in this acute myocardial ischemia/reperfusion injury model is VWF-dependent. Conclusion: These findings reveal a new role for anti-thrombotic enzyme ADAMTS13 in reducing VWF-mediated myocardial ischemia/reperfusion injury.

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Abstract 1000: Dichotomous Roles Of TNF-α Receptors p55 And p75 In Acute Ischemia/reperfusion Injury And Late Ischemic Preconditioning

Circulation ◽

10.1161/circ.116.suppl_16.ii_198 ◽

2007 ◽

Vol 116 (suppl_16) ◽

Author(s):

Michael P Flaherty ◽

Yiru Guo ◽

Xian-Liang Tang ◽

Sumit Tiwari ◽

Greg Hunt ◽

...

Keyword(s):

Myocardial Ischemia ◽

Infarct Size ◽

Reperfusion Injury ◽

Ischemic Preconditioning ◽

Coronary Occlusion ◽

Ischemia Reperfusion Injury ◽

Ischemia Reperfusion ◽

Acute Myocardial Ischemia ◽

Myocardial Ischemia Reperfusion Injury ◽

Myocardial Ischemia Reperfusion

We have previously demonstrated that TNF-alpha signaling is critical for the development of protection afforded by the late phase of ischemic preconditioning (PC). In the current study, we investigated the roles of p55 (TNFR-I) and p75 (TNFR-II) in acute myocardial ischemia/reperfusion injury as well as late PC. Wild-type (WT, B6 and B6,129 strains), TNF-a−/−, p55−/−, p75−/−, and p55−/−/p75−/− double-knockout mice underwent a 30-min coronary occlusion followed by 4 h of reperfusion with or without six cycles of coronary occlusion/reperfusion (O/R) 24 h earlier. Six cycles of O/R reduced infarct size 24 h later in B6 as well as B6,129 WT mice, indicating a rob ust late PC effect (Figure ). This infarct-sparing effect of late PC was abolished in the absence of TNF-a, p55, p75, and both p55/p75, indicating that TNF-a signaling is critical for the development of late PC protection; and that signaling via both p55 and p75 is necessary for the development of protection. In nonpreconditioned TNF-a−/− and p75−/− mice, infarct size was similar to that observed in strain-matched WT mice (Figure ). However, infarct size in nonpreconditioned p55−/− mice was reduced compared with nonpreconditioned WT mice (46.8 ± 2.8% vs. 63.4 ± 3.2%, P < 0.05, Figure ). These observations were confirmed via linear regression analysis of myocardial risk region and infarct size. We conclude that nonredundant TNF-a signaling via both p55 and p75 is crucial for the development of late PC protection. However, the reduction in infarct size in naïve p55−/− mice indicates a deleterious role of this receptor during acute myocardial ischemia/reperfusion injury.

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Abstract 16598: The Role of Paraoxonase 2 in Myocardial Ischemia/Reperfusion Injury

Circulation ◽

10.1161/circ.132.suppl_3.16598 ◽

2015 ◽

Vol 132 (suppl_3) ◽

Author(s):

Jingyuan Li ◽

Victor R Grijalva ◽

Srinivasa T Reddy ◽

Mansoureh Eghbali

Keyword(s):

Myocardial Ischemia ◽

Infarct Size ◽

Er Stress ◽

Reperfusion Injury ◽

Ischemia Reperfusion Injury ◽

Ischemia Reperfusion ◽

Ros Production ◽

Myocardial Ischemia Reperfusion Injury ◽

Myocardial Ischemia Reperfusion

Objectives: Paraoxonases (PON) gene family consists of three proteins PON1, PON2, and PON3. PON2 is an intracellular membrane-associated protein that is widely expressed in vascular cells and many tissues. At the subcellular level, PON2 is localized to both the ER and mitochondria, and protects against oxidative stress. Hypothesis: The aim of this study was to investigate the role of PON2 in myocardial ischemia reperfusion injury. Methods: PON2 deficient (PON2-/-) and WT male mice were subjected to in-vivo ischemia/reperfusion injury. The left anterior descending coronary artery was occluded for 30 min followed by 24 hr of reperfusion. The infarct size, mitochondrial calcium retention capacity (CRC) and reactive oxygen species (ROS) generation were measured. The expression of C/EBP homologous protein (CHOP), GSK3b and phosphate GSK3b protein were examined by Western Blot. The number of animals was 5-7/group and data were expressed as mean±SEM. T test were used for statistical analysis. Probability values <0.05 were considered statistically significant. Results: The infarct size was ~2 fold larger in PON2 deficient mice compared to WT mice (p<0.05). The threshold for opening of mitochondrial permeability transition pore (mPTP) in response to calcium overload was much lower in PON2-/- mice compared with WT mice (173±19 in PON2-/-, 250±41 in WT, nmol/mg-mitochondrial protein, p<0.05). The ROS production was ~2 fold higher in isolated cardiac mitochondria from PON2-/- mice compared with WT mice (p<0.05). ER stress protein CHOP increased significantly in PON2-/- mice compared to WT mice (normalized to WT: 1±0.05 in WT, 1.66±0.08 in PON2-/-, p<0.001). Phospho-GSK3b level was significantly downregulated in in PON2-/- mice compared to WT mice (pGSK3b/GSK3b normalized to WT: 1±0.06 in WT 0.67±0.08 in PON2-/-, p<0.05). Conclusions: PON2 regulates myocardial ischemia/reperfusion injury via inhibiting the opening of mPTP, which is associated with reduced mitochondria ROS production, deactivation of ER stress signaling CHOP and GSK3b.

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