Endoplasmic Reticulum Stress Gene Induction and Protection From Ischemia/Reperfusion Injury in the Hearts of Transgenic Mice With a Tamoxifen-Regulated Form of ATF6

Abstract

Abstract-Ischemia/reperfusion (I/R) affects the integrity of the endoplasmic reticulum (ER), the site of synthesis and folding of numerous proteins. Therefore, I/R may activate the unfolded protein response (UPR), resulting in the induction of a collection of ER stress proteins, many of which are protective and function to resolve the ER stress. In this study, we showed that when mouse hearts were subjected to ex vivo I/R, the levels of 2 ER stress-inducible markers of the UPR, the ER-targeted cytoprotective chaperones glucose-regulated proteins 78 and 94 (GRP78 and GRP94), were increased, consistent with I/R-mediated UPR activation in the heart. The UPR-mediated activation of ATF6 (Activation of Transcription Factor 6) induces cytoprotective ER stress proteins, including GRP78 and GRP94. To examine whether ATF6 protects the myocardium from I/R injury in the heart, we generated transgenic (TG) mice featuring cardiac-restricted expression of a novel tamoxifen-activated form of ATF6, ATF6-MER. When NTG and ATF6-MER TG mice were treated with or without tamoxifen for 5 days, only the hearts from the tamoxifen-treated TG mice exhibited increased levels of many ER stress-inducible mRNAs and proteins; for example, GRP78 and GRP94 transcript levels were increased by 8-and 15-fold, respectively. The tamoxifen-treated TG mouse hearts also exhibited better functional recovery from ex vivo I/R, as well as significantly reduced necrosis and apoptosis. These results suggest that the UPR is activated in the heart during I/R and that, as a result, the ATF6 branch of the UPR may induce expression of proteins that can function to reduce I/R injury.

δPKC participates in the endoplasmic reticulum stress-induced response in cultured cardiac myocytes and ischemic heart

“…Studies in transgenic mice expressing the activation transcription factor 6, ATF6, also suggest that ER stress may participate in ischemia-reperfusion injury [9]. During ischemia-reperfusion injury, ER stress may be excessively activated, since in addition to the increased expression of the chaperone protein, GRP78, there is a significant increase in the pro-apoptotic kinase, phosphorylated-JNK.…”

“…δPKC translocation to the ER mediates, at least in part, ER stress response of the myocardium in a model of ischemia-reperfusion injury Inhibition of δPKC protects the heart from ischemia-reperfusion injury partly through reducing mitochondria-mediated cell death [13,16]. Increasing evidence suggests that ischemia/ reperfusion in the heart also activates the ER stress response resulting in cellular injury [5,8,9,[30][31][32]. Based on our in vitro results, we next determined whether inhibition of δPKC protects the myocardium from ER stress in an ex vivo model of ischemia and reperfusion injury.…”

“…In addition, recent evidence suggests that cardiac ischemia and hypoxia induce UPR [5,8,9]. Elevated UPR response is found in isolated cardiac myocytes subjected to hypoxia, as well as in a mouse model of myocardial infarction.…”

“…The transcription factor 6, ATF6, is one of the ER membrane resident proteins induced by ER stress. Transgenic mice expressing ATF6 subjected to ischemia-reperfusion injury show increased cardiac levels of ER stress-induced proteins such as GRP78 and a lower level of cell death and apoptosis [9]. Therefore, ER stress appears to be an important component of ischemia and reperfusioninduced apoptosis of the myocardium.…”

Endoplasmic reticulum stress: a novel mechanism and therapeutic target for cardiovascular diseases

“…Martindale et al obtained results inconsistent with the above opinions. They suggested that the UPR is activated in the heart during I/R, and as a result, the ATF6 branch of UPR-induced expression of proteins, including GRP78 and GRP94, can reduce I/R injury [109] . I/R injury rats are accompanied by myocardial infarction (MI), and increased myocardial infarct size and myocardial enzyme activity were observed [106] .…”