TAT opens the door.
TAT opens the door.
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DOI：
10.1038/mt.2008.24
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发表时间：
2008-04
期刊：
影响因子：
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通讯作者：
P. Vyas;R. Payne
中科院分区：
文献类型：
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作者：
P. Vyas;R. Payne
线粒体是复杂的细胞器，在细胞中执行许多关键活动。它们含有自身基因组的多个拷贝，该基因组编码人类中的13种蛋白质以及翻译它们所需的转移RNA和核糖体RNA。因此，几乎所有的数百种蛋白质都必须在细胞核中编码，并通过线粒体膜输入。在线粒体内，它们经历蛋白水解加工并靶向多个隔室和酶复合物。2有许多疾病是由线粒体基因组或那些核编码和靶向蛋白质的突变或缺陷引起的。这些疾病通常具有严重的健康后果，目前还没有治愈这些线粒体疾病的方法。线粒体疾病的修复必然比胞质基因产物的替换更复杂，并且必须不仅考虑到靶向和穿过线粒体中的多个膜的需要，而且还考虑到线粒体中的许多酶是疏水性的并且不容易溶解的事实。此外，许多线粒体基因缺陷作为主要或最突出的表型会导致严重的神经系统症状，并且穿过血脑屏障的药物递送是众所周知的困难。3因此，目前针对线粒体缺陷的治疗主要集中在使用小分子来增强通过电子传递链的通量，例如使用辅酶Q治疗OXPHOS疾病，4或改变底物的前体库以避免有缺陷的代谢途径，例如改变脂肪酸的饮食摄入量以避免中链酰基脱氢酶缺乏的中链脂质。[5]到目前为止，基因疗法和酶替代疗法（ERT）都没有用于线粒体缺陷，更不用说纠正血脑屏障缺陷了。然而，在本期《分子治疗》杂志中，Rapoport等人似乎向这个艰难的目标迈出了重要的一步。6在他们的报告中，作者使用蛋白质转录反式激活因子（TAT）结构域将硫辛酰胺脱氢酶（LAD）递送到患有LAD缺陷的患者的成纤维细胞中的线粒体。Rapoport及其同事令人信服地证明了TAT可以使LAD蛋白跨越细胞和线粒体膜。此外，这种转导的酶似乎能够取代大的多亚基复合物中的缺陷酶，以恢复接近正常的酶功能。LAD是线粒体基质中三种多组分酶复合物（α-酮酸脱氢酶复合物）的第三个催化亚基（E3），对碳水化合物和氨基酸的代谢至关重要。7 α-酮酸脱氢酶复合物由丙酮酸脱氢酶复合物、α-酮戊二酸脱氢酶复合物和支链酮酸脱氢酶复合物组成。7，8 LAD基因的A突变导致α-酮酸脱氢酶复合物的正常活性改变，导致乳酸血症、克雷布斯循环功能障碍和支链氨基酸降解受损。这些都是严重的代谢紊乱，患有这种疾病的患者在婴儿期可能会出现严重的神经系统症状，或者反复发作肝功能衰竭或肌红蛋白尿，这可能是致命的。9、10因此，为此开发ERT对人类健康有重大影响。
Mitochondria are complex organelles that perform many key activities in the cell. They contain multiple copies of their own genome, which encodes 13 proteins in humans and the transfer RNAs and ribosomal RNAs needed to translate them. 1 Thus, almost all of the hundreds of proteins needed for their function must be encoded in the nucleus and imported across the mitochondrial membranes. Within the mitochondria they undergo proteolytic processing and targeting to multiple compartments and enzyme complexes. 2 There are numerous diseases arising from mutations or defects in either the mitochondrial genome or those nuclear encoded and targeted proteins. These disorders typically have serious health consequences, and there are currently no cures for these mitochondrial disorders. Repair of mitochondrial disorders is necessarily more complex than replacement of a cytosolic gene product and must take into account not only the need to target and cross multiple membranes in mitochondria but also the fact that many enzymes in mitochondria are hydrophobic and not readily soluble. Additionally, many of the mitochondrial gene defects cause severe neurologic symptoms as the primary, or most prominent, phenotype, and drug delivery across the blood–brain barrier is notoriously difficult. 3 As a result, current therapies for mitochondrial defects focus primarily on the use of small molecules to enhance flux through the electron transport chain, such as with coenzyme Q for OXPHOS diseases, 4 or altering the precursor pool of substrate to avoid the defective metabolic pathway, such as changing dietary intake of fatty acids to avoid medium-chain lipids in medium-chain acyl-dehydrogenase deficiency. 5 Thus far, neither gene therapy nor enzyme-replacement therapy (ERT) has been accomplished for mitochondrial defects, much less to correct a defect across the blood–brain barrier. However, in this issue of Molecular Therapy, Rapoport et al. seem to have taken an important step toward this difficult goal. 6In their report the authors use the protein transactivator of transcription (TAT) domain to deliver lipoamide dehydrogenase (LAD) to mitochondria in fibroblasts from patients suffering from LAD deficiency. Rapoport and coworkers convincingly demonstrated that TAT could transduce the LAD protein across the cell and mitochondrial membranes. Furthermore, this transduced enzyme appears to be able to replace the defective enzyme in a large multisubunit complex to restore near-normal enzymatic function. LAD is the third catalytic subunit (E3) of three multicomponent enzymatic complexes (α-ketoacid dehydrogenase complexes) in the mitochondrial matrix that are crucial for the metabolism of carbohydrates and amino acids. 7 The α-ketoacid dehydrogenase complexes consist of pyruvate dehydrogenase complex, α-ketoglutarate dehydrogenase complex, and the branchedchain ketoacid dehydrogenase complex. 7, 8 A mutation of the LAD gene leads to alteration of the normal activity of α-ketoacid dehydrogenase complexes, resulting in lactic acidemia, dysfunction of the Krebs cycle, and impaired branched-chain amino acid degradation. These are serious metabolic disruptions, and patients with this disease can present with severe neurological symptoms in infancy, or recurrent episodes of liver failure or myoglobinuria that can be fatal. 9, 10 Thus, there is a significant human health impact to developing ERT for this