Department of Pathology, Cardiovascular Division, Johns Hopkins University, Baltimore, MD 21205.
Circ Res. 2012 Jun 8;110(12):1596-603. doi: 10.1161/CIRCRESAHA.112.267732. Epub 2012 Apr 19.
Mitochondria are semiautonomous cellular organelles with their own genome, which not only supply energy but also participate in cell death pathways. MicroRNAs (miRNAs) are usually 19 to 25 nt long, noncoding RNAs, involved in posttranscriptional gene regulation by binding to the 3'-untranslated regions of target mRNA, which impact on diverse cellular processes.
To determine if nuclear miRNAs translocate into the mitochondria and regulate mitochondrial function with possible pathophysiological implications in cardiac myocytes.
We find that miR-181c is encoded in the nucleus, assembled in the cytoplasm, and finally translocated into the mitochondria of cardiac myocytes. Immunoprecipitation of Argonaute 2 from the mitochondrial fraction indicates binding of cytochrome c oxidase subunit 1 (mt-COX1) mRNA from the mitochondrial genome with miR-181c. Also, a luciferase reporter construct shows that mi-181c binds to the 3'UTR of mt-COX1. To study whether miR-181c regulates mt-COX1, we overexpressed precursor miR-181c (or a scrambled sequence) in primary cultures of neonatal rat ventricular myocytes. Overexpression of miR-181c did not change mt-COX1 mRNA but significantly decreased mt-COX1 protein, suggesting that miR-181c is primarily a translational regulator of mt-COX1. In addition to altering mt-COX1, overexpression of miR-181c results in increased mt-COX2 mRNA and protein content, with an increase in both mitochondrial respiration and reactive oxygen species generation in neonatal rat ventricular myocytes. Thus, our data show for the first time that miR-181c can enter and target the mitochondrial genome, ultimately causing electron transport chain complex IV remodeling and mitochondrial dysfunction.
Nuclear miR-181c translocates into the mitochondria and regulates mitochondrial genome expression. This unique observation may open a new dimension to our understanding of mitochondrial dynamics and the role of miRNA in mitochondrial dysfunction.
线粒体是具有自身基因组的半自主细胞细胞器，不仅提供能量，还参与细胞死亡途径。microRNAs（miRNAs）通常长 19 到 25 个核苷酸，是一种非编码 RNA，通过与靶 mRNA 的 3'非翻译区结合来参与转录后基因调控，从而影响多种细胞过程。
确定核 miRNAs 是否易位到线粒体并调节线粒体功能，这可能对心肌细胞的病理生理有影响。
我们发现 miR-181c 编码在核内，在细胞质中组装，最终易位到心肌细胞的线粒体中。从线粒体部分免疫沉淀 Argonaute 2 表明，来自线粒体基因组的细胞色素 c 氧化酶亚基 1（mt-COX1）mRNA 与 miR-181c 结合。此外，荧光素酶报告基因构建体表明，miR-181c 结合到 mt-COX1 的 3'UTR。为了研究 miR-181c 是否调节 mt-COX1，我们在原代培养的新生大鼠心室肌细胞中过表达前体 miR-181c（或乱序序列）。miR-181c 的过表达并未改变 mt-COX1 mRNA，但显著降低了 mt-COX1 蛋白，表明 miR-181c 主要是 mt-COX1 的翻译调节剂。除了改变 mt-COX1 外，miR-181c 的过表达还导致 mt-COX2 mRNA 和蛋白含量增加，同时增加了新生大鼠心室肌细胞中线粒体呼吸和活性氧的产生。因此，我们的数据首次表明，miR-181c 可以进入并靶向线粒体基因组，最终导致电子传递链复合物 IV 重塑和线粒体功能障碍。
核 miR-181c 易位到线粒体并调节线粒体基因组表达。这一独特的观察结果可能为我们理解线粒体动力学和 miRNA 在线粒体功能障碍中的作用开辟了一个新的维度。
