Aldehyde Dehydrogenase-2 Deficiency Aggravates Cardiac Dysfunction Elicited by Endoplasmic Reticulum Stress Induction

Jianquan Liao,Junbo Ge,Toyoshi Isse,Yeqing Xie,Aijun Sun,Yunzeng Zou,Toshihiro Kawamoto

doi:10.2119/molmed.2011.00466

Abstract

Mitochondrial aldehyde dehydrogenase-2 (ALDH2) has been characterized as an important mediator of endogenous cytoprotection in the heart. This study was designed to examine the role of ALDH2 knockout (KO) in the regulation of cardiac function after endoplasmic reticulum (ER) stress. Wild-type (WT) and ALDH2 KO mice were subjected to a tunicamycin challenge, and the echocardiographic property was examined. Protein levels of six items--78 kDa glucose-regulated protein (GRP78), phosphorylation of eukaryotic initiation factor 2 subunit α (p-eIF2α), CCAAT/enhancer-binding protein homologous protein (CHOP), phosphorylation of Akt, p47(phox) nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and 4-hydroxynonenal--were determined by using Western blot analysis. Cytotoxicity and apoptosis were estimated using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl-tetrazolium bromide (MTT) assay and caspase-3 activity, respectively. ALDH2 deficiency exacerbated cardiac contractile dysfunction and promoted ER stress after ER stress induction, manifested by the changes of ejection fraction and fractional shortening. In vitro study revealed that tunicamycin significantly upregulated the levels of GRP78, p-eIF2α, CHOP, p47(phox) NADPH oxidase and 4-hydroxynonenal, which was exacerbated by ALDH2 knockdown and abolished by ALDH2 overexpression, respectively. Overexpression of ALDH2 abrogated tunicamycin-induced dephosphorylation Akt. Inhibition of phosphatidylinositol 3-kinase using LY294002 did not affect ALDH2-conferred protection against ER stress, although LY294002 reversed the antiapoptotic action of ALDH2 associated with p47(phox) NADPH oxidase. These results suggest a pivotal role of ALDH2 in the regulation of ER stress and ER stress-induced apoptosis. The protective role of ALDH2 against ER stress-induced cell death was probably mediated by Akt via a p47(phox) NADPH oxidase-dependent manner. These findings indicate the critical role of ALDH2 in the pathogenesis of ER stress in heart disease.

Highlights

The endoplasmic reticulum (ER) is a multifunctional intracellular organelle involved in multiprocesses within the cell, including synthesis and folding of secretory and membrane proteins, Ca2+ homeostasis and lipid biosynthesis [1,2,3]
The antiapoptosis property of aldehyde dehydrogenase-2 (ALDH2), evaluated by MTT assay and caspase-3 activity, was abrogated by LY294002 (Figure 6). These results indicate that ALDH2-forced expression was associated with increased resistance of cardiomyocytes to tunicamycin-induced cytotoxicity and apoptosis, whereas ALDH2 silencing by small interfering ribonucleic acid (siRNA) potentiated tunicamycin-induced cell death through Akt signaling
The salient findings from the present study demonstrated that ALDH2 deficiency was susceptible to cardiotoxicity in response to ER stress induction, characterized by impaired cardiac function

Summary

Introduction

The endoplasmic reticulum (ER) is a multifunctional intracellular organelle involved in multiprocesses within the cell, including synthesis and folding of secretory and membrane proteins, Ca2+ homeostasis and lipid biosynthesis [1,2,3]. ER stress develops in response to a wide variety of cellular stressors, such as heat, hypoxia, metabolic starvation, angiotensin II, tumor necrosis factor-α and change in lipid metabolism [4]. These stressors reduce the protein-folding capacity and disrupt the homeostatic functions of the ER, leading to the accumulation and aggregation of unfolded and misfolded protein in ER, a condition called “ER stress” [5]. ER stress appears to be a candidate instigator for pathological cell death and functional change intimately involved in the maintenance of cardiovascular homeo-

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