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：钙网蛋白(calreticulin, CRT)和caspase-12 是重要的内质网(endoplasmic reticulum, ER)应激分子，本实验在心肌细胞低氧/ 复氧(hypoxia/reoxygenation, H/R)模型上观察低氧预处理(hypoxic preconditioning, HPC)对CRT 和 caspase-12 表达及活化的影响，探讨内质网应激(endoplasmic reticulum stress, ERS)在HPC 保护机制中的意义及其细胞信号转导机制。原代培养的Sprague-Dawley 乳鼠心肌细胞随机分为6 组：H/R 组、HPC+H/R 组、SB203580+HPC+H/R 组、SP600125+HPC+H/R 组、HPC 组和对照组。以细胞存活率、乳酸脱氢酶 (lactate dehydrogenase, LDH)活性及流式细胞术检测细胞损伤情况；Westernblot 方法检测CRT 和caspase-12 表达、活化及p38 丝裂素活化蛋白激酶 (mitogen-activated protein kinases, MAPK)、c-Jun N-terminal kinase (JNK)磷酸化水平。结果表明：(1) HPC 具有细胞保护作用，与H/R 组比较，HPC+H/R 组细胞凋亡率和LDH 漏出分别降低6.6% 和70.0%，存活率增高6.4%；HPC 前以特异性p38 MAPK 抑制剂 SB203580 预孵育消除HPC的保护作用，与HPC+H/R 组相比，细胞凋亡率和LDH 漏出分别增高5.4% 和2.1 倍，存活率降低5.4%，JNK 特异性抑制剂SP600125 预孵育对HPC 的保护作用无明显影响。 (2) H/R 明显上调CRT 表达(较对照组高8.1 倍)和caspase-12 活性(较对照组高33.2 倍) ；单独HPC 可诱导CRT 表达增多(较对照组高2.6 倍)，但上调程度较H/R 组低60%。H/R 前进行HPC 降低CRT过表达程度(降低72.4%)及caspase-12 活化水平(降低59.6%)。 (3) HPC 前应用p38 MAPK 抑制剂，抑制CRT 表达上调(分别较HPC+H/R 组和HPC 组低63.9% 和71.9%)，并消除HPC 减轻H/R 上调caspase-12 活性的作用(较HPC+H/R 组高7.1 倍) ；HPC 前抑制JNK 活性对CRT、caspase-12 表达和活化均无明显影响。上述结果提示：HPC 可激发适当的ERS，抑制H/R诱导的过度ERS，减少ER 凋亡信号介导的细胞凋亡。p38 MAPK 信号途径在HPC 诱导的ER 应激分子表达、抑制ER 凋亡信号分子活化等机制中发挥重要作用。

Calreticulin (CRT), an important Ca2+-binding molecular chaperone in the endoplasmic reticulum (ER), and caspase-12, a pivotalmolecule mediating ER-initiated apoptosis, are involved in the ER stress (ERS). Using primary cultured neonatal cardiomyocytes, CRTand caspase-12 expression and activation during hypoxic preconditioning (HPC) and hypoxia/reoxygenation (H/R) were studied toexplore the role of ERS in cardioprotection by HPC. And by using SB203580 and SP600125 [the specific inhibitors of p38 mitogenactivatedprotein kinase (MAPK) and c-Jun N-terminal kinase (JNK) ] separately, the role of p38 MAPK in HPC-induced ERS wasalso detected. Neonatal cardiomyocytes were prepared from Sprague-Dawley rats aged 24 h, and cultured in DMEM medium containing10% fetal bovine serum, and then randomly divided into six groups as follows: H/R, HPC+H/R, SB203580+HPC+H/R, SP600125+HPC+H/R, HPC and control groups. H/R was produced by 2-hour hypoxia/14-hour reoxygenation, and HPC by 20-minutehypoxia/24-hour reoxygenation. Morphological studies, estimation of lactate dehydrogenase (LDH) leakage and flow cytometry wereemployed to assess cell apoptosis and necrosis. CRT and caspase-12 expression and activation, levels of phospho-p38 MAPK andphospho-JNK were detected by Western blot. All experiments were repeated at least four separate times. The results obtained are asfollows: (1) HPC relieved the cell injury caused by H/R. Compared with that in H/R group, cells’ survival rate in HPC+H/R goup increasedby 6.4%, and the apotosis rate and LDH leakage in the cell culture medium decreased by 6.6% and 70.0%, respectively. (2) H/R inducedcaspase-12 activation (33.2-fold increase in comparison with control) and CRT expression (8.1-fold increase in comparison with control).HPC itself resulted in mild CRT up-regulation (2.6-fold increase in comparison with control), but the extent of up-regulation was lowerthan that induced by H/R. HPC before H/R was found to relieve the over-expression of CRT induced by H/R (72.4% decrease), and toinhibit the activation of caspase-12 (59.6% decrease). (3) The protection of HPC and HPC-induced up-expression of CRT andinhibition of caspase-12 activation were almost eliminated when the inhibitor of p38 MAPK, not of JNK, was present before HPC.These results suggest that HPC protects the neonatal cardiomyocytes from severe ERS-induced apoptosis during sustained H/Rthrough pre-invoking proper ERS response. Mild up-expression of CRT and inhibition of caspase-12 activation induced by HPC,which are important protection factors, are mediated by p38 MAPK, not by JNK.