AMP-Activated Protein Kinase Protects Cardiomyocytes against Hypoxic Injury through Attenuation of Endoplasmic Reticulum Stress

Abstract

Oxygen deprivation leads to the accumulation of misfolded proteins in the endoplasmic reticulum (ER), causing ER stress. Under conditions of ER stress, inhibition of protein synthesis and up-regulation of ER chaperone expression reduce the misfolded proteins in the ER. AMP-activated protein kinase (AMPK) is a key regulatory enzyme involved in energy homeostasis during hypoxia. It has been shown that AMPK activation is associated with inhibition of protein synthesis via phosphorylation of elongation factor 2 (eEF2) in cardiomyocytes. We therefore examined whether AMPK attenuates hypoxia-induced ER stress in neonatal rat cardiomyocytes. We found that hypoxia induced ER stress, as assessed by the expression of CHOP and BiP and cleavage of caspase 12. Knockdown of CHOP or caspase 12 through small interfering RNA (siRNA) resulted in decreased expression of cleaved poly(ADP-ribose) polymerase following exposure to hypoxia. We also found that hypoxia-induced CHOP expression and cleavage of caspase 12 were significantly inhibited by pretreatment with 5-aminoimidazole-4-carboxyamide-1-␤-D-ribofuranoside (AICAR), a pharmacological activator of AMPK. In parallel, adenovirus expressing dominant-negative AMPK significantly attenuated the cardioprotective effects of AICAR. Knockdown of eEF2 phosphorylation using eEF2 kinase siRNA abolished these cardioprotective effects of AICAR. Taken together, these findings demonstrate that activation of AMPK contributes to protection of the heart against hypoxic injury through attenuation of ER stress and that attenuation of protein synthesis via eEF2 inactivation may be the mechanism of cardioprotection by AMPK.

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

“…However, few studies have investigated the role of ER stress in the induction of apoptosis during ischemia/ reperfusion. Hypoxia induces the expression of XBP1 splicing and GRP78 in cultures of rat neonatal cardiac myocytes [5,8]. In a mouse model of myocardial infarction, an increased expression of GRP78 was observed in cells near the infarct four days after occlusion of the left anterior descending coronary artery [5].…”

“…This early rise in GRP78 expression after ischemia and reperfusion may be due to the experimental model used. Indeed, ER stress-induced injury occurs with different kinetics under pathological conditions [6,8].…”

“…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.…”

Molecular mechanisms of cardiotoxicity of tyrosine kinase inhibition

“…This raises the possibility that an offtarget effect of the drug could account for the apparent cardiotoxicity. Scanning the kinase interaction map identifies several candidates, including the ribosomal S6 kinase (RSK) family, which signals survival through inhibitory phosphorylation of the pro-apoptotic factor BAD, and AMP-activated protein kinase (AMPK), which has been reported to transduce pro-survival signals in the heart 46,70 . Indeed, the inhibitor-binding assay predicts that inhibition of RSKs and AMPK by sunitinib could be seen at clinically relevant concentrations 15 .…”