人类多种疾病中mtDNA拷贝数的变化

线粒体是细胞能量和自由基代谢中心,在细胞生命活动中发挥着重要作用,而mt DNA拷贝数是决定线粒体功能的重要因素。由于mt DNA缺乏组蛋白的保护和损伤修复系统,又暴露在氧化磷酸化产生的高氧环境中,易受损引起拷贝数变化,从而影响线粒体的功能。大量研究表明,多种疾病的发生发展与mt DNA拷贝数变化密切相关。该文综述了癌症、神经退行性疾病、心脑血管疾病、精神疾病等各种疾病中mt DNA拷贝数的变化情况,以期从中发现疾病相关mt DNA拷贝数的变化规律和调控机制。     

线粒体DNA与DNA甲基化的关系

线粒体DNA（mitochondrial DNA,mtDNA）遗传信息量虽小,却控制着线粒体一些最基本的性质,对细胞及其功能有着重要影响。mtDNA的损伤与衰老、肿瘤等疾病的发生有关。DNA甲基化是调节基因表达的重要方式之一。mtDNA基因的表达受核DNA（nuclear DNA,nDNA）的调控,mtDNA和nDNA协同作用参与机体代谢调节和发病。本文就近年来mtDNA与DNA甲基化的关系作一综述。     

运动与衰老:线粒体功能和氧化还原的调控

衰老与线粒体功能衰退和氧化还原失衡紧密相关。随着年龄的增加,肌肉线粒体的DNA丰度和蛋白质的合成不断的下降,线粒体代谢过程中的副产物自由基增加导致脂质,蛋白质和核酸等大分子的氧化损伤不断累积。衰老相关的线粒体功能的下降和氧化还原失衡影响运动功能,导致胰岛素抵抗和神经退行性疾病,因而对于调节寿命起到重要的作用。因而线粒体可能是决定寿命的重要因素。大量研究证实长期运动训练可以很大程度预防和改善衰老相关疾病,其机制可能是通过促进线粒体生成和激活内源性抗氧化防御体系而提高线粒体功能和调控氧化还原平衡。因此,长期的运动训练预防衰老相关疾病和提高老年人的生命质量很可能是通过调控线粒体功能和氧化还原平衡而发挥作用。     

线粒体DNA异常与肿瘤

能量代谢重编程是肿瘤细胞一个重要的标志特征,而由线粒体DNA(mitochondrial DNA,mtDNA)结构及功能异常引起的线粒体功能障碍是其机制之一。人类mtDNA为位于线粒体基质中由16569bp组成的双链闭合环状分子,编码与氧化磷酸化电子传递链相关的13种多肽以及与线粒体蛋白合成相关的22种tRNA和2种rRNA。近年来,人们发现多种肿瘤组织及细胞中存在mtDNA序列的多类型突变或拷贝数的变异,且mtDNA的这些异常与肿瘤的发生发展、早期诊断及放化疗监测等密切相关。异常的mtDNA因削弱线粒体产能、增加细胞内活性氧(reactive oxygen species,ROS)水平、打破Ca2+稳态,从而赋予肿瘤细胞代谢重编程、凋亡抵抗等侵袭性进程。针对mtDNA异常在肿瘤发生发展中的作用及机制研究,将为肿瘤的早期诊断及靶向治疗提供新的策略。     

线粒体未折叠蛋白反应分子机制的研究进展

线粒体未折叠蛋白反应(UPR~(mt))作为新发现的细胞内应激机制,直接影响老化、神经退行性疾病、癌症等疾病的发生发展.UPR~(mt)是线粒体为了维持其内部蛋白质的平衡,启动由核DNA编码的线粒体热休克蛋白和蛋白酶等基因群转录活化程序的应激反应.深入探究UPR~(mt)的作用机制对阐明老化和线粒体相关疾病的发病机理具有指导意义.本文主要阐述了线粒体未折叠蛋白反应的诱导因素、线虫和哺乳动物细胞中最新的未折叠蛋白应激反应的信号传导通路、调控因子、具体作用机制以及线粒体未折叠蛋白反应与衰老、免疫等疾病的联系,旨在为这些疾病提供新的理论基础和治疗靶点.     

线粒体稳态失衡与心脏衰老及相关疾病

随着年龄的增长,衰老的心脏会发生左室肥厚、舒张功能不全、瓣膜功能下降、心肌纤维化增加、电传导异常等病理变化.线粒体作为真核细胞中调控代谢的关键细胞器,是细胞内合成ATP的重要场所.由于心脏一刻不停地收缩需要大量ATP提供能量,线粒体稳态对于维持正常的心脏功能至关重要,而线粒体稳态失衡则会导致心脏功能发生异常.本文主要阐述了衰老心脏中线粒体的异常变化,探讨了线粒体形态与数量变化、线粒体代谢异常、线粒体质量控制失衡、线粒体基因组和转录组改变等线粒体稳态失衡在常见衰老相关心脏疾病发生发展中的重要作用,总结了靶向线粒体干预衰老相关心脏疾病的现状与前景,为研究线粒体相关心脏疾病的细胞分子机制,治疗衰老相关的心脏疾病提供新的思路.     

综述: mTOR信号通路与衰老及衰老相关重大疾病

衰老引起多器官功能衰减,导致各种衰老相关代谢、心血管重大疾病发生和发展.哺乳动物雷帕霉素靶蛋白/雷帕霉素机能靶蛋白(mammalian/mechanistic target of rapamycin,mTOR)信号通路作为生长、发育、代谢、免疫、癌症等生理活动的主要调控者,通过影响细胞自噬、内质网应激、线粒体等形成复杂调控网络,在衰老与长寿中发挥关键作用.mTOR信号通路与许多衰老相关重大疾病(如代谢综合征、心血管疾病、神经退行性病变、肿瘤等)的发生发展密切相关,故以mTOR为靶点的药物开发与应用是未来延缓衰老及治疗衰老相关疾病的热点之一.     

mtDNA单倍型D4和B4a细胞线粒体功能及其影响衰老发生的机制研究

该文初步分析了两个与衰老发生抑制及促进的线粒体DNA(mitochondrial DNA,mtDNA)单倍型D4和B4a细胞的线粒体功能情况,并对其影响衰老的可能机制进行了探究。通过细胞融合构建两个核背景一致但mtDNA单倍型分别是D4和B4a的胞质杂合细胞。应用RT-PCR方法检测细胞mt DNA拷贝数以及线粒体基因的mRNA水平,氧电极法和非变性梯度聚丙烯酰胺凝胶电泳(blue native polyacrylamide gelelectrophoresis,BN-PAGE)技术检测细胞线粒体氧化呼吸能力及线粒体复合体水平,TMRM染料和DCFH-DA染料法检测细胞线粒体膜电位和活性氧(reactive oxygen species,ROS)生成水平。结果显示,D4单倍型细胞线粒体氧呼吸能力、膜电位水平以及线粒体基因(mt-ND1、mt-7S RNA)转录水平均明显高于B4a单倍型细胞,而ROS生成水平明显降低,mt DNA拷贝数则并无明显差异。该结果表明,在D4单倍型细胞中,通过提高某些线粒体基因的表达,使得线粒体呼吸复合体表达得到提升,继而提高线粒体氧化呼吸功能,降低细胞氧化损伤,从而延缓衰老的发生。     

mTOR信号通路与衰老及衰老相关重大疾病

衰老引起多器官功能衰减,导致各种衰老相关代谢、心血管重大疾病发生和发展.哺乳动物雷帕霉素靶蛋白/雷帕霉素机能靶蛋白(mammalian/mechanistic target of rapamycin,mTOR)信号通路作为生长、发育、代谢、免疫、癌症等生理活动的主要调控者,通过影响细胞自噬、内质网应激、线粒体等形成复杂调控网络,在衰老与长寿中发挥关键作用.mTOR信号通路与许多衰老相关重大疾病(如代谢综合征、心血管疾病、神经退行性病变、肿瘤等)的发生发展密切相关,故以mTOR为靶点的药物开发与应用是未来延缓衰老及治疗衰老相关疾病的热点之一.     

跨组织线粒体应激信号交流调控机体衰老研究进展

线粒体内蛋白质稳态的平衡对于细胞正常的生理功能非常关键。线粒体蛋白稳态失衡时,细胞会启动应激反应机制,即线粒体未折叠蛋白反应(mitochondrial unfolded protein response,UPRmt),修复线粒体功能,平衡细胞内稳态。尽管线粒体的严重损伤对机体是有害的,但在线虫(Caenorhabditis elegans)、果蝇(Drosophila melanogaste)及小鼠(Mus musculus)中都有研究表明线粒体的轻微损伤可以通过激活UPRmt,促进寿命延长。有趣的是,在没有直接经历线粒体损伤的细胞或组织中,UPRmt也能以非自主方式被诱导。不同组织间可以通过名为“mitokine”的细胞因子进行UPRmt的跨组织调控,系统性地协调机体整体的压力适应能力和抗衰老能力。该调控机制与衰老相关神经退行性疾病、癌症等多种疾病密切相关,近年来有关研究与日俱增。本文系统总结了线粒体应激及其组织间通讯的机制,并介绍了跨组织线粒体应激交流信号“mitokine”调控衰老进程的最新研究进展,以期为跨组织信号调控和机体衰老等研究提供参考。     

Number matters: control of mammalian mitochondrial DNA copy number

Regulation of mitochondrial biogenesis is essential for proper cellular functioning. Mitochondrial DNA （mtDNA） depletion and the resulting mitochondrial malfunction have been implicated in cancer, neurodegeneration, diabetes, aging, and many other human diseases. Although it is known that the dynamics of the mammalian mitochondrial genome are not linked with that of the nuclear genome, very little is known about the mechanism of mtDNA propagation. Nevertheless, our understanding of the mode of mtDNA replication has ad- vanced in recent years, though not without some controversies. This review summarizes our current knowledge of mtDNA copy number control in mammalian cells, while focusing on both mtDNA replication and turnover. Although mtDNA copy number is seemingly in excess, we reason that mtDNA copy number control is an important aspect of mitochondrial genetics and biogenesis and is essential for normal cellular function.     

Mouse models of mitochondrial DNA defects and their relevance for human disease

Qualitative and quantitative changes in mitochondrial DNA (mtDNA) have been shown to be common causes of inherited neurodegenerative and muscular diseases, and have also been implicated in ageing. These diseases can be caused by primary mtDNA mutations, or by defects in nuclear‐encoded mtDNA maintenance proteins that cause secondary mtDNA mutagenesis or instability. Furthermore, it has been proposed that mtDNA copy number affects cellular tolerance to environmental stress. However, the mechanisms that regulate mtDNA copy number and the tissue‐specific consequences of mtDNA mutations are largely unknown. As post‐mitotic tissues differ greatly from proliferating cultured cells in their need for mtDNA maintenance, and as most mitochondrial diseases affect post‐mitotic cell types, the mouse is an important model in which to study mtDNA defects. Here, we review recently developed mouse models, and their contribution to our knowledge of mtDNA maintenance and its role in disease.     

Visualization of Mitochondrial DNA Replication in Individual Cells by EdU Signal Amplification

Mitochondria are key regulators of cellular energy and mitochondrial biogenesis is an essential component of regulating mitochondria numbers in healthy cells^1-3. One approach for monitoring mitochondrial biogenesis is to measure the rate of mitochondrial DNA (mtDNA) replication⁴. We developed a sensitive technique to label newly synthesized mtDNA in individual cells in order to study mtDNA biogenesis. The technique combines the incorporation of 5-ethynyl-2''-deoxyuridine (EdU)^5-7 with a tyramide signal amplification (TSA)⁸ protocol to visualize mtDNA replication within subcellular compartments of neurons. EdU is superior to other thymidine analogs, such as 5-bromo-2-deoxyuridine (BrdU), because the initial click reaction to label EdU^5-7 does not require the harsh acid treatments or enzyme digests that are required for exposing the BrdU epitope. The milder labeling of EdU allows for direct comparison of its incorporation with other cellular markers^9-10. The ability to visualize and quantify mtDNA biogenesis provides an essential tool for investigating the mechanisms used to regulate mitochondrial biogenesis and would provide insight into the pathogenesis associated with drug toxicity, aging, cancer and neurodegenerative diseases. Our technique is applicable to sensory neurons as well as other cell types. The use of this technique to measure mtDNA biogenesis has significant implications in furthering the understanding of both normal cellular physiology as well as impaired disease states.     

Mitochondrial retrograde signaling at the crossroads of tumor bioenergetics,genetics and epigenetics

Mitochondria play a central role not only in energy production but also in the integration of metabolic pathways as well as signals for apoptosis and autophagy. It is becoming increasingly apparent that mitochondria in mammalian cells play critical roles in the initiation and propagation of various signaling cascades. In particular, mitochondrial metabolic and respiratory states and status on mitochondrial genetic instability are communicated to the nucleus as an adaptive response through retrograde signaling. Each mammalian cell contains multiple copies of the mitochondrial genome (mtDNA). A reduction in mtDNA copy number has been reported in various human pathological conditions such as diabetes, obesity, neurodegenerative disorders, aging and cancer. Reduction in mtDNA copy number disrupts mitochondrial membrane potential (Δψm) resulting in dysfunctional mitochondria. Dysfunctional mitochondria trigger retrograde signaling and communicate their changing metabolic and functional state to the nucleus as an adaptive response resulting in an altered nuclear gene expression profile and altered cell physiology and morphology. In this review, we provide an overview of the various modes of mitochondrial retrograde signaling focusing particularly on the Ca^2 +/Calcineurin mediated retrograde signaling. We discuss the contribution of the key factors of the pathway such as Calcineurin, IGF1 receptor, Akt kinase and HnRNPA2 in the propagation of signaling and their role in modulating genetic and epigenetic changes favoring cellular reprogramming towards tumorigenesis.     

Fragile X‐associated tremor/ataxia syndrome: Regional decrease of mitochondrial DNA copy number relates to clinical manifestations

Fragile X‐associated tremor/ataxia syndrome (FXTAS) is a late‐onset neurodegenerative disorder that appears in at least one‐third of adult carriers of a premutation (55‐200 CGG repeats) in the fragile X mental retardation 1 (FMR1) gene. Several studies have shown that mitochondrial dysfunction may play a central role in aging and also in neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease as well as in FXTAS. It has been recently proposed that mtDNA copy number, measured by the number of mitochondrial genomes per nuclear genome (diploid), could be a useful biomarker of mitochondrial dysfunction. In order to elucidate the role of mtDNA variation in the pathogenesis of FXTAS, mtDNA copy number was quantified by digital droplet Polymerase chain reaction. In human brain samples, mtDNA levels were measured in the cerebellar vermis, dentate nucleus, parietal and temporal cortex, thalamus, caudate nucleus and hippocampus from a female FXTAS patient, a FMR1 premutation male carrier without FXTAS and from three male controls. The mtDNA copy number was further analyzed using this technology in dermal fibroblasts primary cultures derived from three FXTAS patients and three controls as well as in cortex and cerebellum of a CGG knock in FXTAS mice model. Finally, qPCR was carried out in human blood samples. Results indicate reduced mtDNA copy number in the specific brain region associated with disease progression in FXTAS patients, providing new insights into the role of mitochondrial dysfunction in the pathogenesis of FXTAS.     

Effects of X-irradiation on mitochondrial DNA damage and its supercoiling formation change

There have been a small number of reports of radiation-induced mtDNA damage, and mtDNA supercoiling formation change induced by ionizing radiation has not been investigated before. This study evaluated mtDNA damage and supercoiling formation change after X-irradiation. The human breast cancer cell line, MCF-7 cells were used for analysis. Modified supercoiling-sensitive real-time PCR approach was used to evaluate mitochondrial DNA supercoiling formation change and copy number; long-PCR method was applied for the quantification of mtDNA damage. MtDNA damage and formation change induced by high-dose irradiation was persistent in 24 h after irradiation and was not significant after low-dose irradiation. MtDNA copy number was slightly increased after high-dose irradiation and a transit increase was observed after low-dose irradiation. This is the first study to evaluate radiation-induced mitochondrial DNA supercoiling formation change using real-time PCR. Combined with data of ROS generation and dynamics of mitochondrial mass, our findings suggested that mtDNA is sensitive to radiation hazards, indicating mitochondrial biogenesis play an important role in radiation-induced cellular response.     

Decrease of MtDNA copy number affects mitochondrial function and involves in the pathological consequences of ischaemic stroke

The mtDNA copy number can affect the function of mitochondria and play an important role in the development of diseases. However, there are few studies on the mechanism of mtDNA copy number variation and its effects in IS. The specific mechanism of mtDNA copy number variation is still unclear. In this study, mtDNA copy number of 101 IS patients and 101 normal controls were detected by qRT‐PCR, the effect of D‐loop variation on mtDNA copy number of IS patients was explored. Then, a TFAM gene KD‐OE PC12 cell model was constructed to explore the effect of mtDNA copy number variation on mitochondrial function. The results showed that the mtDNA copy number level of the IS group was significantly lower than that of the normal control group (p < 0.05). The relative expression of TFAM gene mRNA in the cells of the OGD/R treatment group was significantly lower than that of the control group (p < 0.05). In addition, after TFAM gene knockdown and over‐expression plasmids were transfected into HEK 293T cells, mtDNA copy number and ATP production level of Sh‐TFAM transfection group was significantly decreased (p < 0.05), while mtDNA copy number and ATP production level of OE‐TFAM transfected group were significantly higher than that of blank control group and OE‐ctrl negative control group (p < 0.01). Our study demonstrated that mitochondrial D‐loop mutation and TFAM gene dysfunction can cause the decrease of mtDNA copy number, thus affecting the mitochondrial metabolism and function of nerve cells, participating in the pathological damage mechanism of IS.