Department of Biochemistry, University of Alberta, Edmonton, AB, Canada.
Mol Cell Biochem. 2010 May;338(1-2):47-57. doi: 10.1007/s11010-009-0337-5. Epub 2009 Dec 1.
The mammalian Na(+)/H(+) exchanger isoform 1 (NHE1) is a ubiquitously expressed membrane protein that regulates intracellular pH in the myocardium and other tissues. NHE1 is an important mediator of myocardial damage that occurs after ischemia-reperfusion injury. It has also been implicated in apoptotic damage in many tissues and its expression and activity are elevated in disease states in the myocardium. In this study, we examined the effect of additional exogenous NHE1 expression on isolated cardiomyocytes susceptibility to ischemia/reperfusion damage. Exogenous NHE1 elevated Na(+)/H(+) exchanger expression and activity when introduced into isolated cardiomyocytes through an adenoviral system. Isolated cardiomyocytes were subjected to simulated ischemia and reperfusion after infection with either control or NHE1-containing adenovirus. Cells were placed into an anaerobic chamber and effects of NHE1 expression after hypoxia/reoxygenation were examined. Hypoxia/reoxygenation increased caspase-3-like activity in controls, and the effect was greatly magnified in cells expressing NHE1 protein. It also elevated the percentage of apoptotic cardiomyocytes, which was also aggravated by expression of NHE1 protein. Hypoxia/reoxygenation also increased phospho-ERK levels. Elevated NHE1 expression was coincidental with increased expression of the ER stress protein, protein disulfide isomerase (PDI) and calreticulin (CRT). Our results demonstrate that increased NHE1 protein expression makes cells more susceptible to damage induced by hypoxia/reoxygenation in isolated cardiomyocytes. They suggest that elevated NHE1 in cardiovascular disease could predispose the human myocardium to enhanced apoptotic damage.
哺乳动物 Na(+)/H(+) 交换体亚型 1（NHE1）是一种广泛表达的膜蛋白，可调节心肌和其他组织的细胞内 pH 值。NHE1 是缺血再灌注损伤后心肌损伤的重要介导者。它还与许多组织中的细胞凋亡损伤有关，其表达和活性在心肌疾病状态下升高。在这项研究中，我们研究了额外的外源性 NHE1 表达对分离的心肌细胞对缺血/再灌注损伤的敏感性的影响。通过腺病毒系统将外源性 NHE1 导入分离的心肌细胞时，可升高 Na(+)/H(+) 交换表达和活性。感染对照或含 NHE1 的腺病毒后，将分离的心肌细胞置于缺氧/复氧条件下。将细胞置于缺氧室中，并检查缺氧/复氧后 NHE1 表达的影响。缺氧/复氧增加了对照组中 caspase-3 样活性，而在表达 NHE1 蛋白的细胞中，这种作用大大增强。它还增加了凋亡心肌细胞的百分比，这也因 NHE1 蛋白的表达而加重。缺氧/复氧还增加了磷酸化 ERK 水平。NHE1 表达的升高与内质网应激蛋白蛋白二硫键异构酶（PDI）和钙网蛋白（CRT）的表达增加有关。我们的结果表明，增加的 NHE1 蛋白表达使细胞对缺氧/复氧诱导的损伤更加敏感。它们表明，心血管疾病中升高的 NHE1 可能使人类心肌更容易受到增强的细胞凋亡损伤。
