A significant portion of mitochondrial proton leak in intact thymocytes depends on expression of UCP2
A significant portion of mitochondrial proton leak in intact thymocytes depends on expression of UCP2
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DOI：
10.1073/pnas.012410699
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发表时间：
2002-01-08
影响因子：
11.1
通讯作者：
Lowell, BB
中科院分区：
文献类型：
--
作者：
Krauss, S;Zhang, CY;Lowell, BB
解偶联蛋白同源物 UCP2 在多种哺乳动物细胞中表达。它被认为是氧化磷酸化的解偶联剂。先前已证明解偶联蛋白能够使质子穿过脂蛋白体系统中的磷脂双层。此外，对酵母过度表达蛋白质的线粒体的研究表明，它们可能在细胞中充当解偶联剂。然而，这个问题是有争议的，迄今为止，关于 UCP2 是否介导哺乳动物细胞中部分或全部基底线粒体质子泄漏，目前还缺乏明确的实验证据。在本研究中，通过使用从 UCP2 缺陷型和野生型 (WT) 小鼠中分离的胸腺细胞，我们解决了 UCP2 是否直接参与催化完整细胞中的质子泄漏的问题。在一系列线粒体膜电位 (DeltaPsi(m)) 上，UCP2 缺陷型小鼠胸腺细胞的质子泄漏活性低于 WT 小鼠。在 DeltaPsi(m) 的生理水平上，静息细胞中基础质子泄漏的很大一部分 (50%) 取决于 UCP2。值得注意的是，WT 小鼠全细胞中的质子泄漏对 4-[(E)-2-(5,6,7,8-四氢-5,5,8,8-四甲基-2-萘基)-1-丙烯基]苯甲酸 (TTNPB) 的刺激有反应，TTNPB 是一种已知的 UCP2 活性激活剂。与观察到的质子泄漏变化一致，UCP2 缺陷小鼠未经处理的胸腺细胞中 DeltaPsi(m) 和 ATP 水平增加。有趣的是，静息呼吸没有改变，这表明静息细胞中的 UCP2 功能可能与 ATP 产生的控制有关，而不是与底物氧化有关。这项研究证实，在内源水平表达的 UCP2 介导完整细胞中的质子泄漏。
The uncoupling protein homologue UCP2 is expressed in a variety of mammalian cells. It is thought to be an uncoupler of oxidative phosphorylation. Uncoupling proteins previously have been shown to be capable of translocating protons across phospholipid bilayers in proteoliposome systems. Furthermore, studies in mitochondria from yeast overexpressing the proteins have led to suggestions that they may act as uncouplers in cells. However, this issue is controversial, and to date, definitive experimental evidence is lacking as to whether UCP2 mediates part or all of the basal mitochondrial proton leak in mammalian cells in situ. In the present study, by using thymocytes isolated from UCP2-deficient and wild-type (WT) mice, we addressed the question whether UCP2 is directly involved in catalyzing proton leak in intact cells. Over a range of mitochondrial membrane potentials (DeltaPsi(m)), proton leak activity was lower in thymocytes from UCP2-deficient mice compared with WT mice. At physiological levels of DeltaPsi(m) a significant portion (50%) of basal proton leak in resting cells depended on UCP2. Of note, proton leak in whole cells from WT mice, but not UCP2-deficient mice, responded to stimulation by 4-[(E)-2-(5,6,7,8-tetra- hydro-5,5,8,8-tetramethyl-2-napthalenyl)-1-propenyl]benzoic acid (TTNPB), a known activator of UCP2 activity. Consistent with the observed changes in proton leak, DeltaPsi(m) and ATP levels were increased in untreated thymocytes from UCP2-deficient mice. Interestingly, resting respiration was unaltered, suggesting that UCP2 function in resting cells may be concerned with the control of ATP production rather than substrate oxidation. This study establishes that UCP2, expressed at endogenous levels, mediates proton leak in intact cells.