Section of Physiology of Lipid Metabolism, Institute of Physiology, Center for Physiology, Pathophysiology and Immunology, Medical University of Vienna, Vienna, Austria.
PLoS One. 2009 Nov 16;4(11):e7791. doi: 10.1371/journal.pone.0007791.
Our recognition of the mitochondria as being important sites of fatty acid biosynthesis is continuously unfolding, especially in light of new data becoming available on compromised fatty acid synthase type 2 (FASII) in mammals. For example, perturbed regulation of murine 17beta-HSD8 encoding a component of the mitochondrial FASII enzyme 3-oxoacyl-thioester reductase is implicated in polycystic kidney disease. In addition, over-expression in mice of the Mecr gene coding for 2-trans-enoyl-thioester reductase, also of mitochondrial FASII, leads to impaired heart function. However, mouse knockouts for mitochondrial FASII have hitherto not been reported and, hence, there is a need to develop alternate metazoan models such as nematodes or fruit flies. Here, the identification of Caenorhabditis elegans W09H1.5/MECR-1 as a 2-trans-enoyl-thioester reductase of mitochondrial FASII is reported. To identify MECR-1, Saccharomyces cerevisiae etr1Delta mutant cells were employed that are devoid of mitochondrial 2-trans-enoyl-thioester reductase Etr1p. These yeast mutants fail to synthesize sufficient levels of lipoic acid or form cytochrome complexes, and cannot respire or grow on non-fermentable carbon sources. A mutant yeast strain ectopically expressing nematode mecr-1 was shown to contain reductase activity and resemble the self-complemented mutant strain for these phenotype characteristics. Since MECR-1 was not intentionally targeted for compartmentalization using a yeast mitochondrial leader sequence, this inferred that the protein represented a physiologically functional mitochondrial 2-trans-enoyl-thioester reductase. In accordance with published findings, RNAi-mediated knockdown of mecr-1 in C. elegans resulted in life span extension, presumably due to mitochondrial dysfunction. Moreover, old mecr-1(RNAi) worms had better internal organ appearance and were more mobile than control worms, indicating a reduced physiological age. This is the first report on RNAi work dedicated specifically to curtailing mitochondrial FASII in metazoans. The availability of affected survivors will help to position C. elegans as an excellent model for future pursuits in the emerging field of mitochondrial FASII research.
我们对线粒体作为脂肪酸生物合成的重要部位的认识不断深入，特别是在新数据表明哺乳动物中脂肪酸合酶 2（FASII）受损的情况下。例如，编码线粒体 FASII 酶 3-氧酰基硫酯还原酶的组成部分的 17β-HSD8 的调节失调与多囊肾病有关。此外，在线虫中过度表达编码线粒体 FASII 的 2-反式烯酰-硫酯还原酶的 Mecr 基因会导致心脏功能受损。然而，迄今为止尚未报道线粒体 FASII 的小鼠敲除体，因此需要开发替代的后生动物模型，如线虫或果蝇。在这里，我们报告了秀丽隐杆线虫 W09H1.5/MECR-1 作为线粒体 FASII 的 2-反式烯酰-硫酯还原酶的鉴定。为了鉴定 MECR-1，使用了缺乏线粒体 2-反式烯酰-硫酯还原酶 Etr1p 的酿酒酵母 etr1Delta 突变体细胞。这些酵母突变体不能合成足够水平的硫辛酸或形成细胞色素复合物，不能在非发酵碳源上呼吸或生长。异位表达线虫 mecr-1 的酵母突变体菌株被证明含有还原酶活性，并且类似于这些表型特征的自我互补突变体菌株。由于 MECR-1 没有使用酵母线粒体前导序列有意进行区室化，因此推断该蛋白代表一种生理功能上的线粒体 2-反式烯酰-硫酯还原酶。与已发表的研究结果一致，在线虫中 RNAi 介导的 mecr-1 敲低导致寿命延长，推测这是由于线粒体功能障碍所致。此外，年老的 mecr-1(RNAi) 线虫的内部器官外观更好，比对照线虫更具移动性，表明生理年龄降低。这是首次专门针对后生动物中线粒体 FASII 的 RNAi 工作的报告。受影响的幸存者的出现将有助于将秀丽隐杆线虫定位为未来在新兴的线粒体 FASII 研究领域的出色模型。
