In different pathological situations, cardiac cells undergo hyperosmotic stress and cell shrinkage. This change in cellular volume has been associated with contractile dysfunction and cell death. However, the intracellular mechanisms involved in hyperosmotic stress-induced cell death have not been investigated in depth in adult cardiac myocytes. Given that osmotic stress has been shown to promote endoplasmic reticulum stress (ERS), a recognized trigger for apoptosis, we examined whether hyperosmotic stress triggers ERS in adult cardiac myocytes and if so whether this mechanism mediates hyperosmotic stress-induced cell death. Adult rat cardiomyocytes cultured overnight in a hypertonic solution (HS) containing mannitol as the osmolite, showed increased expression of ERS markers, GRP78, CHOP and cleaved-Caspase-12, compared with myocytes in isotonic solution (IS), suggesting that hyperosmotic stress induces ERS. In addition, HS significantly reduced cell viability and increased TUNEL staining and the expression of active Caspase-3, indicative of apoptosis. These effects were prevented with the addition of the ERS inhibitor, 4-PBA, indicating that hyperosmotic stress-induced apoptosis is mediated by ERS. Hyperosmotic stress-induced apoptosis was also prevented when cells were cultured in the presence of a Ca2+-chelating agent (EGTA) or the CaMKII inhibitor (KN93), suggesting that hyperosmotic stress-induced ERS is mediated by a Ca2+ and CaMKII-dependent mechanism. Similar results were observed when hyperosmotic stress was induced using glucose as the osmolite. We conclude that hyperosmotic stress promotes ERS by a CaMKII-dependent mechanism leading to apoptosis of adult cardiomyocytes. More importantly, we demonstrate that hyperosmotic stress-triggered ERS contributes to hyperglycemia-induced cell death.

中文翻译：

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高渗应激促进成年大鼠心肌细胞内质网应激依赖性凋亡。

在不同的病理情况下，心肌细胞会经受高渗应激和细胞收缩。细胞体积的这种变化与收缩功能障碍和细胞死亡有关。然而，尚未深入研究成年心肌细胞中涉及高渗应激诱导的细胞死亡的细胞内机制。考虑到渗透压已经显示出促进内质网应激（ERS）的作用，后者是细胞凋亡的公认触发因素，我们检查了高渗透压是否会触发成年心肌细胞中的ERS，如果是，那么这种机制是否会介导高渗透压诱导的细胞死亡。在含有甘露醇作为渗透压的高渗溶液（HS）中过夜培养的成年大鼠心肌细胞，其ERS标志物，GRP78，CHOP和裂解的Caspase-12，与等渗溶液（IS）中的心肌细胞相比，提示高渗应激可诱导ERS。此外，HS显着降低了细胞活力，增加了TUNEL染色和活性Caspase-3的表达，这表明细胞凋亡。通过添加ERS抑制剂4-PBA可以防止这些作用，表明高渗应激诱导的细胞凋亡是由ERS介导的。当在Ca2 +螯合剂（EGTA）或CaMKII抑制剂（KN93）存在下培养细胞时，高渗应激诱导的细胞凋亡也得到了阻止，这表明高渗应激诱导的ERS是由Ca2 +和CaMKII依赖性机制介导的。当使用葡萄糖作为渗透压诱导高渗应激时，观察到相似的结果。我们得出结论，高渗应激通过导致成年心肌细胞凋亡的CaMKII依赖性机制促进ERS。更重要的是，我们证明了高渗应激触发的ERS有助于高血糖诱导的细胞死亡。