Abstract 11367: HAX-1 Protects Hearts from Ischemia/Reperfusion Injury in vivo
Multiple cell death pathways are activated during cardiac ischemia/reperfusion (I/R) injury, resulting in cell death and compromised function. The HS-1 associated protein X-1 (HAX-1), an anti-apoptotic protein, has been reported to localize both to mitochondria and endoplasmic/sarcoplasmic reticulum (ER/SR), implicating its involvement in different cell death mechanisms. Interestingly, we found that the HAX-1 protein levels were reduced in hearts after I/R injury. To delineate the functional significance of increased HAX-1 expression in vivo, we generated a transgenic (TG) model with cardiac specific HAX-1 overexpression (∼2-fold) and subjected the hearts to I/R-induced injury. The HAX-1 TG hearts exhibited improved contractile performance after ex vivo I/R and decreased infarct-to-risk region ratio after in vivo myocardial infarction. This protective effect was associated with decreased activities of caspases 3 and 9. We also found that mitochondria isolated from HAX-1 TG hearts were resistant to swelling and permeability transition (MPT) induced by calcium. Cytochrome C release triggered by calcium and oxidative stress was also depressed in isolated TG mitochondria. Furthermore, the expression of cyclophilin D (cyp-D), a major MPT pore regulatory protein, was significantly decreased in TG hearts. Immunoprecipitation studies indicated HAX-1 may directly interact with cyp-D, implying that HAX-1 may be a novel regulator of the MPT pore, one of the major cell death pathways in mitochondria. In addition, HAX-1 TG hearts had reduced ER stress response after I/R, assessed by decreases in glucose regulated protein 94 (GRP94) expression and caspase 12 activation. Surprisingly, the attenuation of ER stress response by HAX-1 was related to the decreased expression of X-box binding protein 1 (XBP-1), a downstream target of the inositol-requiring enzyme 1 (IRE-1), indicating that HAX-1 may play a specific inhibitory role in the IRE-1 pathway. Taken together, these studies demonstrate that the beneficial effects of HAX-1 are mediated through both the mitochondria permeability transition and the ER stress response, suggesting a unique cardioprotective potential of HAX-1 in ischemia/reperfusion injury.
- © 2010 by American Heart Association, Inc.