Abstract 11058: Aggravation of Cardiac Injury by Iron and Heme Oxygenase-1 in Viral Myocarditis
Introduction: Heme oxygenase-1 (HO-1) which is mostly described as protective molecule against oxidative stress-mediated injury during inflammatory processes is known to be induced by nitric oxide (NO) and to increase uptake of iron in specific cells. Based on our findings that coxsackievirus B3 (CVB3)-infected susceptible SWR/J mice but not resistant C57BL/6 mice show significant iron incorporation in damaged myocytes at later stages of myocarditis we aimed to investigate the molecular interplay of HO-1 expression and iron homeostasis in ongoing CVB3 myocarditis.
Methods and Results: In CVB3-infected susceptible SWR/J mice we found that increased oxidative activities are correlated with the upregulation of the heme oxygenase-1 (HO-1) mRNA and protein in macrophages and also in myocytes as determined by qRT-PCR, in situ hybridization and immunohistochemistry. In in vitro experiments we confirmed these results by demonstrating an increase of HO-1 mRNA in CVB3-infected RAW 264.7 macrophages. Nitric oxide (NO) is a well known stimulus of HO-1. In CVB3-infected SWR/J mouse hearts a high expression of nitric-oxide synthase (iNOS) mRNA was found in macrophages which correlated with enhanced activation of HO-1. Cell culture experiments revealed that blockage of NO production with L-NAME decreases HO-1 protein expression. In RAW 264.7 macrophages increased HO-1 expression was found to be associated with an increase in ROS production which could be blocked by tin-mesoporphyrin, suggesting that HO-1 may contribute to enhanced oxidative stress in CVB3-infected hearts. Interestingly, iron containing myocytes of SWR/J mice but not those of C57BL/6 mice revealed a high expression of HO-1 and were found to correspond with signs of apoptosis. Knockdown experiments in CVB3-infected HeLa cells by siRNA directed against HO-1 revealed a downregulation of caspase-3. Finally, iron was found to enhance virus replication in HeLa cells.
Conclusions: Iron is a proapoptotic factor for infected myocytes, enhancing viral replication and heart damage. HO-1, which is mainly known as a cytoprotective molecule, induces a paracrine signalling via ROS production in activated macrophages and mediates apoptosis of virus-infected and iron-loaded cardiomyocytes.
- © 2012 by American Heart Association, Inc.