Letter by Hüttemann et al Regarding Article, "Ndufs2, a Core Subunit of Mitochondrial Complex I, Is Essential for Acute Oxygen-Sensing and Hypoxic Pulmonary Vasoconstriction".
Letter by Hüttemann et al Regarding Article, "Ndufs2, a Core Subunit of Mitochondrial Complex I, Is Essential for Acute Oxygen-Sensing and Hypoxic Pulmonary Vasoconstriction".
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Hüttemann 等人关于文章“Ndufs2，线粒体复合物 I 的核心亚基，对于急性氧感应和缺氧性肺血管收缩至关重要”的信函。
DOI：
10.1161/circresaha.119.315815
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发表时间：
2019
影响因子：
20.1
通讯作者：
Grossman,LawrenceI
中科院分区：
文献类型：
--
作者：
Hüttemann,Maik;Sommer,Natascha;Weissmann,Norbert;Grossman,LawrenceI
肺中的氧感是一种复杂的现象，并且对于在局部肺泡缺氧期间诱导缺氧性肺血管收缩（HPV）以逃避可能危及生命的低氧血症是必不可少的。与全身血管系统相反，当氧气稀缺时，全身血管系统会扩张以增加向靶器官的氧气输送，急性HPV导致肺某些区域的血管收缩，将血液从通风不良的肺泡分流到通风良好的肺泡，从而优化氧气提取。因此，HPV需要与全身血管系统不同的氧传感和信号传导机制。关于分子氧传感器引发级联反应最终导致HPV的争论仍然很多，有证据表明线粒体电子传递链改变超氧化物生成是早期事件。1，2这会导致肌浆和质膜离子通道的激活/抑制（包括电压门控钾通道的关闭），从而导致肺动脉平滑肌细胞内钙离子增加，引发血管收缩。3-5然而，一个重要的问题仍然存在：什么是感觉肺中氧浓度的分子机制，以及这是如何导致超氧化物增加的？我们感兴趣地看到最近的文章“Ndufs 2，线粒体复合物I的核心亚基，对急性氧感和肺血管收缩功能减退至关重要”，6为氧感单元增加了另一个潜在的参与者。我们希望提请读者注意一个重要的误解，但文章中提供的数据并不支持这一误解。如摘要中所述，作者声称，我们先前报告的肺特异性COX 4 I2（细胞色素c氧化酶亚基4亚型2）对HPV 7是必需的，但HPV不需要。作者从在线数据补充中的图5I中提供的数据得出了这个错误的结论，其中他们显示了培养细胞中COX 4 I2的部分siRNA敲低。尽管在Western印迹中呈现的对照细胞缺乏重复，信号非常弱，仅略高于背景，但作者报告说，COX 4 I2表达在敲除细胞中减少了约50%。使用该系统，他们表明当暴露于缺氧时，COX 4 I2敲除细胞中仍然存在可测量的钙释放增加（在线图5 J），然后得出结论，该基因对HPV不是必需的。重要的是，为了得出这样的结论，作者必须假设部分敲除导致完全单倍不足，这是不正确的，如下所述。首先，我们之前已经明确显示，在体内，使用Cox 4 i2敲除小鼠，Cox 4 i2是必不可少的急性HPV，因为HPV在敲除小鼠中被消除。7其次，我们还以随机方式分析了Sommer等人7图1B中Cox 4 i2 +/−杂合子小鼠与野生型和敲除小鼠的HPV，但原始文章中未包括数据：用常氧（21%O2、5%CO2和74%N2）或低氧（1%O2、5%CO2和94%N2）气体对离体小鼠肺通气10分钟。低通气导致HPV，检测为肺动脉压与常氧通气期间的压力（ΔPAP）相比的升高。野生型和Cox 4 i2 −/−敲除小鼠与Sommer等人7中图1B的组相同，并取自这些组，以与Cox 4 i2 +/−小鼠进行比较。ΔPAP（mm Hg±SE）为野生型1.0±0.11（n= 5; P< 0.001 vs Cox 4 i2 −/−小鼠），Cox 4 i2 +/−小鼠0.75±0.07（n= 6; P< 0.001 vs Cox 4 i2 −/−小鼠），Cox 4 i2 −/−小鼠0.1±0.05（n= 6）。
Oxygen sensing in the lung is a complex phenomenon and essential to induce hypoxic pulmonary vasoconstriction (HPV) during local alveolar hypoxia to escape potentially life-threatening hypoxemia. In contrast to the systemic vasculature, which expands when oxygen is scarce to increase oxygen delivery to target organs, acute HPV leads to vasoconstriction in certain areas of the lung to shunt blood from poorly-to well-ventilated alveoli, thereby optimizing oxygen extraction. Thus, HPV requires an oxygen sensing and signaling mechanism that is distinct from the systemic vasculature. There is still much debate about the molecular oxygen sensor that initiates a cascade eventually leading to HPV, and evidence suggests that altered superoxide generation by the mitochondrial electron transport chain is an early event. 1, 2 This leads to activation/inhibition of sarcoplasmic and plasmalemmal ion channels (including closure of voltage-gated potassium channels), which causes an increase in intracellular calcium in pulmonary artery smooth muscle cells, triggering vasoconstriction. 3–5 However, an essential question remains: what is the molecular mechanism that senses the oxygen concentration in the lung, and how does this lead to increased superoxide? We saw with interest the recent article “Ndufs2, a Core Subunit of Mitochondrial Complex I, Is Essential for Acute Oxygen-Sensing and Hypoxic Pulmonary Vasoconstriction,” 6 adding another potential player to the oxygen sensing unit. There is one important misinterpretation that we would like to bring to the readers’ attention, which is not supported by data provided in the article. As already stated in the abstract, the authors claim that lung-specific COX4I2 (cytochrome c oxidase subunit 4 isoform 2) previously reported by us to be essential for HPV, 7 is not required for HPV. The authors draw this false conclusion from data presented in Figure 5I in the Online Data Supplement, where they show a partial siRNA-based knockdown of COX4I2 in cultured cells. Despite the lack of replicates for the control cells presented in the Western blot with very weak signals that are only slightly above background, the authors report that COX4I2 expression is about 50% reduced in the knockdown cells. Using this system, they show that there is still a measurable increased calcium release in COX4I2 knockdown cells when exposed to hypoxia (Online Figure 5J), and then conclude that the gene is not essential for HPV. Importantly, to draw such a conclusion, the authors must presume that partial knockdown leads to full haploinsufficiency, which is incorrect as discussed below. First, we have previously unambiguously shown in vivo, using Cox4i2 knockout mice, that Cox4i2 is essential for acute HPV, since HPV is abolished in the knockout mice. 7 Second, we also analyzed HPV of Cox4i2+/− heterozygous mice at the same time as wildtype and knockout mice in Figure 1B in Sommer et al7 in a randomized fashion, but the data were not included in the original article: isolated mouse lungs were ventilated with normoxic (21% O2, 5% CO2, and 74% N2) or hypoxic (1% O2, 5% CO2, and 94% N2) gas for 10 minutes. Hypoxic ventilation resulted in HPV, detected as an increase in pulmonary arterial pressure compared with pressure during normoxic ventilation (ΔPAP). Wildtype and Cox4i2−/− knockout mice were identical with, and have been taken from, the groups of Figure 1B in Sommer et al7 for comparison with Cox4i2+/− mice. ΔPAP (mm Hg±SE) was 1.0±0.11 for wild-type (n= 5; P< 0.001 versus Cox4i2−/− mice), 0.75±0.07 for Cox4i2+/− mice (n= 6; P< 0.001 versus Cox4i2−/− mice), and 0.1±0.05 for Cox4i2−/− mice (n= 6 …