Reduction of Na/K-ATPase Potentiates Marinobufagenin-induced Cardiac Dysfunction and Myocyte Apoptosis
Reduction of Na/K-ATPase Potentiates Marinobufagenin-induced Cardiac Dysfunction and Myocyte Apoptosis
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DOI：
10.1074/jbc.m111.304451
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发表时间：
2012-05-11
影响因子：
4.8
通讯作者：
Tian, Jiang
中科院分区：
文献类型：
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作者：
Liu, Changxuan;Bai, Yan;Tian, Jiang
心力衰竭患者的心脏Na/K-ATP酶降低。Na/K-ATP酶α 1的减少也有助于动物模型中心肌收缩力的缺乏。我们以前的研究表明，细胞Na/K-ATP酶的减少导致细胞生长抑制和细胞死亡在肾近曲小管细胞。为了测试Na/K-ATP酶的减少与强心类固醇的增加相结合是否会导致心肌细胞死亡和心功能障碍，我们检查了Na/K-ATP酶α 1杂合子敲除小鼠（α 1（+/-））与野生型（WT）同窝小鼠在输注海蟾毒配基（MBG）后的心脏功能。还从WT和α 1（+/-）小鼠中分离成年心肌细胞用于体外实验。结果表明，MBG输注增加了α 1（+/-）小鼠的心肌细胞凋亡并诱导了显著的左心室扩张，但在WT同窝小鼠中没有。在机制上，发现在WT肌细胞中，MBG激活Src/Akt/mTOR信号通路，这进一步增加核糖体S6激酶（S6 K）和BAD（Bcl-2相关死亡启动子）的磷酸化并保护细胞免于凋亡。在α 1（+/-）心肌细胞中，磷酸化BAD的基础水平高于WT心肌细胞，但MBG未能诱导其TOR途径的进一步激活。Na/K-ATP酶的减少也引起这些细胞中caspase 9的激活，但不引起caspase 8的激活。使用新生心肌细胞的培养物，我们证明了雷帕霉素对mTOR通路的抑制也使MBG能够激活caspase 9并诱导心肌细胞凋亡。
Decreases in cardiac Na/K-ATPase have been documented in patients with heart failure. Reduction of Na/K-ATPase alpha 1 also contributes to the deficiency in cardiac contractility in animal models. Our previous studies demonstrate that reduction of cellular Na/K-ATPase causes cell growth inhibition and cell death in renal proximal tubule cells. To test whether reduction of Na/K-ATPase in combination with increased cardiotonic steroids causes cardiac myocyte death and cardiac dysfunction, we examined heart function in Na/K-ATPase alpha 1 heterozygote knock-out mice (alpha 1(+/-)) in comparison to wild type (WT) littermates after infusion of marinobufagenin (MBG). Adult cardiac myocytes were also isolated from both WT and alpha 1(+/-) mice for in vitro experiments. The results demonstrated that MBG infusion increased myocyte apoptosis and induced significant left ventricle dilation in alpha 1(+/-) mice but not in their WT littermates. Mechanistically, it was found that in WT myocytes MBG activated the Src/Akt/mTOR signaling pathway, which further increased phosphorylation of ribosome S6 kinase (S6K) and BAD (Bcl-2-associated death promoter) and protected cells from apoptosis. In alpha 1(+/-) myocytes, the basal level of phospho-BAD is higher compared with WT myocytes, but MBG failed to induce further activation of them TOR pathway. Reduction of Na/K-ATPase also caused the activation of caspase 9 but not caspase 8 in these cells. Using cultures of neonatal cardiac myocytes, we demonstrated that inhibition of the mTOR pathway by rapamycin also enabled MBG to activate caspase 9 and induce myocyte apoptosis.