C/EBP Homologous Protein Deficiency Attenuates Myocardial Reperfusion Injury by Inhibiting Myocardial Apoptosis and Inflammation

Abstract

Objective-To investigate whether and how the endoplasmic reticulum (ER) stress-induced, CCAAT/enhancer-binding protein-homologous protein (CHOP)-mediated pathway regulates myocardial ischemia/reperfusion injury. Methods and Results-Wild-type and chop-deficient mice underwent 50 minutes of left coronary artery occlusion followed by reperfusion. Expression of chop and spliced x-box binding protein-1 (sxbp1) mRNA was rapidly and significantly increased in reperfused myocardium of wild-type mice. chop-deficient mice exhibited markedly reduced injury size after reperfusion compared with wild-type mice, accompanied by a decreasing number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cardiomyocytes. Interestingly, myocardial inflammation, as assessed by expression of inflammatory cytokines and chemokines and numbers of infiltrated inflammatory cells, was also attenuated in chop-deficient mice. Moreover, expression of interleukin-6 mRNA in response to lipopolysaccharide was enhanced by simultaneous stimulation with thapsigargin, a potent ER stressor, in wild-type cardiomyocytes but not in chop-deficient cardiomyocytes. Finally, we found that superoxide was produced in reperfused myocardium and that intravenous administration of edaravone, a free radical scavenger, immediately before reperfusion significantly suppressed the superoxide overproduction and subsequent expression of sxbp1 and chop mRNA, followed by reduced injury size in wild-type mice. Conclusion-The ER stress-induced, CHOP-mediated pathway, which is activated in part by superoxide overproduction after reperfusion, exacerbates myocardial ischemia/reperfusion injury by inducing cardiomyocyte apoptosis and myocardial inflammation. Key Words: ischemic heart disease Ⅲ reactive oxygen species Ⅲ reperfusion injury Ⅲ CHOP Ⅲ ER stress T he endoplasmic reticulum (ER), one of the largest cellular organelles, is recognized as the principal site of synthesis, folding, assembly, and modification of numerous proteins. Various pathophysiological stimuli, which increase the demand for protein folding or disrupt folding capacity, cause accumulation of unfolded or misfolded proteins within the ER, a condition collectively known as ER stress. To overcome ER stress, cells activate specific signaling pathways in what is termed the ER stress response, the initial intent of which is to restore ER homeostasis and promote cell survival through alteration of cellular transcriptional and translational programs. However, if restoration fails, ER stress triggers a final response, namely, apoptosis, to protect the organism by eliminating damaged cells. Induction of C/EBP-homologous protein (CHOP), a member of the C/EBP transcription factor family, is a signaling event underlying ER stress-induced apoptosis, 1-3 and the involvement of CHOPmediated apoptosis has been demonstrated in various diseases, including diabetes, neurodegenerative diseases, brain ischemia, and even some cardiovascular diseases. [3][4][5] In the setting of acute myocardial infarction, early...

C/EBP homologous protein contributes to cytokine-induced pro-inflammatory responses and apoptosis in β-cells

“…On the other hand, none of those genes were regulated by CHOP (Supplementary Table 2). Recent studies indicate a role for CHOP in inflammation, [11][12][13] and we and others demonstrated that inflammation in b-cells largely depends on NF-kB. 3 We thus studied the impact of CHOP in cytokine-induced NF-kB activity.…”

“…This is in agreement with several studies on the CHOP KO mice revealing a role for CHOP in in vivo models of inflammation. [11][12][13] Moreover, CHOP KO mice are protected against diabetes induced by multiple low-dose streptozotocin (MLDSZT). 45 In contrast, backcrossing non-obese diabetic (NOD) mice with CHOP KO mice did not prevent diabetes, but delayed appearance of autoantibodies.…”

“…4,10 Besides its pro-apoptotic role, recent studies also indicated a proinflammatory role for CHOP. [11][12][13] It is well established that cytokines induce ER stress in b-cells. 4 However, the role of ER stress in cytokine-induced b-cell apoptosis remains controversial.…”

Endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation

“…CHOP contributes to rodent and human β-cell apoptosis and its expression is upregulated in islets from both T1D and T2D patients (Laybutt et al 2007, Cunha et al 2008. Besides its proapoptotic role, recent studies revealed a pro-inflammatory role for CHOP in different disease models, including myocardial inflammation (Miyazaki et al 2011), lung damage induced by LPS (Endo et al 2005), chemical hepatocarcinogenesis (DeZwaan-McCabe et al 2013), and high fat diet-induced diabetes (Maris et al 2012)…”

Signalling danger: endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation

“…The proinflammatory effect of CHOP in beta cells may require a second signal, provided by cytokines, since CHOP induction by CPA does not amplify NF-κB activation stimulated by a low concentration of IL-1β [20]. The role of CHOP in inflammatory responses (including chemokine and cytokine production) has been observed in different disease models, including myocardial inflammation [47], lung damage induced by LPS [48], inflammatory bowel disease [49] and obesity [15].…”