Nakano M, Knowlton A A, Dibbs Z, Mann D L
Department of Medicine, Veterans Administration Medical Center, Baylor College of Medicine, Houston, Tex 77030, USA.
Circulation. 1998 Apr 14;97(14):1392-400. doi: 10.1161/01.cir.97.14.1392.
Previous studies in isolated cardiac myocytes have shown that tumor necrosis factor (TNF)-alpha provokes increased expression of 27- and 70-kD stress proteins as well as manganese superoxide dismutase, suggesting that TNF-alpha might play a role in mediating stress responses in the heart.
To determine whether TNF-alpha stimulation would protect isolated cardiac myocytes against environmental stress, myocyte cultures were pretreated with TNF-alpha for 12 hours and then subjected to continuous hypoxic injury (O2 content, 3 to 5 ppm) for 12 hours, followed by reoxygenation. Cell injury was assessed in terms of lactic dehydrogenase (LDH) release, 45Ca2+ uptake, and MTT metabolism. Pretreatment with TNF-alpha concentrations > or = 50 U/mL significantly attenuated LDH release by hypoxic cells compared with diluent-treated hypoxic cells. Similar findings were observed with respect to 45Ca2+ uptake and MTT metabolism in TNF-alpha-pretreated cells that were subjected to prolonged hypoxia. To determine the mechanism for the TNF-alpha-induced protective effect, the cells were pretreated with heat shock protein (HSP) 72 antisense oligonucleotides. These studies showed that the protective effect of TNF-alpha was not inhibited by antisense oligonucleotides, despite use of a concentration of antisense that was sufficient to attenuate the TNF-alpha-induced increase in HSP 72 expression. Subsequent studies using mutated TNF ligands showed that activation of both types 1 and 2 TNF receptors was sufficient to confer a protective response in isolated cardiac myocytes through an as yet unknown pathway(s).
Taken together, the above observations demonstrate that TNF-alpha pretreatment confers resistance to hypoxic stress in the adult cardiac myocyte through a novel mechanism that appears to be different from but not necessarily exclusive of the protective response conferred by HSP 72 expression.
先前对分离的心肌细胞进行的研究表明，肿瘤坏死因子（TNF）-α可促使27-kD和70-kD应激蛋白以及锰超氧化物歧化酶的表达增加，这表明TNF-α可能在介导心脏应激反应中发挥作用。
为了确定TNF-α刺激是否能保护分离的心肌细胞免受环境应激，心肌细胞培养物先用TNF-α预处理12小时，然后进行持续12小时的低氧损伤（氧含量为3至5 ppm），随后再进行复氧。通过乳酸脱氢酶（LDH）释放、45Ca2+摄取和MTT代谢来评估细胞损伤。与用稀释剂处理的低氧细胞相比，用浓度≥50 U/mL的TNF-α预处理可显著减弱低氧细胞的LDH释放。在经历长时间低氧的TNF-α预处理细胞中，关于45Ca2+摄取和MTT代谢也观察到了类似的结果。为了确定TNF-α诱导的保护作用的机制，细胞先用热休克蛋白（HSP）72反义寡核苷酸进行预处理。这些研究表明，尽管使用了足以减弱TNF-α诱导的HSP 72表达增加的反义寡核苷酸浓度，但TNF-α的保护作用并未被反义寡核苷酸抑制。随后使用突变的TNF配体进行的研究表明，1型和2型TNF受体的激活均足以通过一条尚不清楚的途径在分离的心肌细胞中赋予保护反应。
综上所述，上述观察结果表明，TNF-α预处理通过一种新机制赋予成年心肌细胞对低氧应激的抗性，该机制似乎与HSP 72表达赋予的保护反应不同，但不一定相互排斥。
