OPTN

Researchers uncovered the mechanistic details behind how several proteins interact to help cells recognize and remove damaged mitochondria. Optineurin (OPTN) and its interactions are needed to provide a contact site for another protein, Tank-binding kinase 1 (TBK1), during this process. The OPTN-TBK1 relationship is necessary for these mitochondria to be recognized and eliminated from the cell. This mechanism may have relevance for developing drugs to treat Parkinson's disease. Autophagy is a process used by cells as a recycling system to transport and break down organelles and other cytosolic components, which become enveloped in a membrane called the autophagosome (Fig 1). When this involves the removal of damaged mitochondria, commonly called the "powerhouse" of the cell, it is known as mitophagy. In a recent article published in The EMBO Journal, a team led by researchers at Tokyo Medical and Dental University (TMDU) elucidated the molecular details of how an enzyme called Tank-binding kinase 1 (TBK1) participates in a disease-relevant mitophagy mechanism. Although autophagy has been characterized as a more general process meant to degrade and clear various cellular components, recent data have suggested that certain pathways are specifically involved in the autophagy of particular organelle types that are damaged or no longer needed. The researchers became interested in mitophagy mediated by molecules called PINK1 and Parkin, as they are proteins that have been pathologically linked to Parkinson's disease. "Mitophagy-related defects have been directly implicated in the neurodegeneration observed in Parkinson's disease patients," says Koji Yamano, lead author of the study. "Normally, PINK1 and Parkin work together to mark damaged mitochondria for removal by adding a chain of molecules called ubiquitin. This mark allows proteins called autophagy adaptors to associate with the mitochondria and bring in the autophagy machinery for autophagosome development." Although TBK1 is known to participate in PINK1/Parkin-mediated mitophagy, a detailed mechanism how it activates remained unclear. Using various molecular biology techniques, the team found that deleting the gene encoding TBK1 prevented association of an autophagy adaptor called optineurin (OPTN) during Parkin-mediated mitophagy (Fig 2). Additionally, deleting the OPTN gene prevented autophosphorylation of TBK1, which is necessary for it to function. Further work suggested that the interactions between OPTN and ubiquitin, as well as between OPTN and the developing autophagosome, were all needed for OPTN and TBK1 to come together at the contact site between damaged mitochondria and the pre-autophagosome membrane. Without this contact site, TBK1 autophosphorylation could not occur. The researchers also generated molecules called monobodies in their lab that could specifically bind OPTN and inhibit its physical interactions. The monobodies prevented OPTN accumulation at the mitophagy contact sites (Fig 3A). This subsequently blocked TBK1 activation (Fig 3B) and thereby mitochondrial degradation. These experiments further emphasized the importance of the OPTN-TBK1 relationship to support proper mitophagy. "Because PINK1 and Parkin are critical contributors to the molecular basis of Parkinson's disease, understanding the mechanistic details related to the mitophagy process mediated by these molecules is very important," explains Yamano. This study demonstrates a positive and reciprocal relationship between OPTN and TBK1 that is necessary for autophagosomes to begin forming on damaged mitochondria. The impactful finding may lead to the development of novel drugs to treat Parkinson's disease.

Researchers have solved a long-standing mystery about how a protein helps rid the body of damaged mitochondria, in findings that could help lead to potential new treatments for Parkinson's disease. While mitochondria play a crucial role in producing the energy our cells need to carry out their various functions, when damaged, they can have profound effects on cellular function and contribute to the development of various diseases. Broken-down mitochondria are usually removed and recycled through a garbage disposal process known as 'mitophagy'. PINK1 and Parkin are two proteins vital to this process, responsible for 'tagging' malfunctioning mitochondria for destruction. In Parkinson's disease, mutations in these proteins can result in the accumulation of damaged mitochondria in the brain, which can lead to motor symptoms such as tremors, stiffness and difficulty with movement. The new research, published in Molecular Cell, solves a mystery about how the protein Optineurin recognises unhealthy mitochondria 'tagged' by PINK1 and Parkin, enabling their delivery to our body's garbage disposal system. Associate Professor Michael Lazarou, a Laboratory Head in WEHI's Ubiquitin Signalling Division, said the discovery filled a vital knowledge gap that would transform our understanding of this cellular pathway. "Until this study, Optineurin's precise role in initiating our body's garbage disposal process was unknown," Assoc Prof Lazarou, who also holds a co-appointment with Monash University, said. "While there are many proteins that link damaged cellular materials to the garbage disposal machinery, we found that Optineurin does this in a highly unconventional way that is unlike anything else we've seen from similar proteins. "This finding is significant because the human brain relies on Optineurin to degrade its mitochondria through the garbage disposal system driven by PINK1 and Parkin. "Knowing how Optineurin does this provides us with a framework on how we might be able to target PINK1 and Parkin mitophagy in disease and prevent the build-up of damaged mitochondria in neurons as we age. "Achieving this would be instrumental to people with Parkinson's disease -- a condition that continues to impact more than 10 million people worldwide, including 80,000 Australians." Outlier discovery PINK1 acts as a 'watch-house' inside the mitochondria, responsible for monitoring their health. When it detects problems, it activates Parkin, which tags damaged mitochondria for removal. They work together to instruct our body to generate cellular 'garbage bags' around broken-down mitochondria and enlist the help of Optineurin to initiate this process. The new study revealed that Optineurin removes damaged mitochondria by binding to an enzyme known as TBK1. From there, they found that TBK1 goes on to activate a specific cellular machine that is key to generating these garbage bags around unhealthy mitochondria. First author Dr Thanh Nguyen said: "Other proteins don't need TBK1 to help them trigger this degradation process, making Optineurin a real outlier when it comes to how our bodies remove mitochondria. "This has allowed us to look at the features of this pathway involving TBK1 as a potential drug target, which is a significant step forward in our search for new Parkinson's disease treatments. "The ultimate goal would be to find a way to boost levels of PINK1/Parkin mitophagy in the body -- especially the brain -- so that damaged mitochondria can be removed more effectively. "We also hope to design a molecule that could mimic what Optineurin does, so damaged mitochondria could be removed even without PINK1 or Parkin." "Given Optineurin is critical in activating the garbage disposal system in our brains, this could then prevent the accumulation of damaged mitochondria in this region, which is a significant precursor to Parkinson's disease." Dr Nguyen said while clinical application of the research is years away, the discovery had laid the essential foundation needed to understand how Optineurin works and realise the pathway's potential as a future therapeutic target. "Our next step is to work with WEHI's Parkinson's Disease Centre to validate our findings in neuronal model systems to understand why Optineurin behaves this way, which will provide further insight into how we can target Optineurin and TBK1 to enhance treatment options for people with PINK1/Parkin mutations in the future." The research involves a collaboration with Professor Sascha Martens' lab at the Max Perutz Labs, University of Vienna and was supported by the National Health and Medical Research Council (NHMRC), the Australian Research Council (ARC), the Human Frontiers Science Program and Aligning Science Across Parkinson's (ASAP) through the Michael J. Fox Foundation for Parkinson's Research (MJFF).

关键词肌萎缩侧索硬化症；Qalsody；研究进展肌萎缩侧索硬化症（ALS），俗称“渐冻症”，是一种渐进和致命的神经退行性疾病，由来自大脑和脊髓的运动神经元缺失引起，可导致四肢、躯干、胸部、腹部肌肉逐渐无力并萎缩，从而影响运动、交流、吞咽和呼吸功能，最终致死。据统计，全球范围内每10000人中大约有6-9个ALS患者，且患病率逐年增长。目前，ALS发病机制并不十分明确。据2023年3月英国谢菲尔德大学谢菲尔德转化神经科学研究所Pamela J. Shaw团队在Nature Reviews Drug Discovery期刊上发表的文章，ALS发病与遗传、氧化应激、兴奋性毒性、神经炎症反应、线粒体功能紊乱、DNA和RNA损伤、蛋白稳态受损、轴突损伤等有关，这些因素相互作用导致患者出现运动神经元损伤。复杂的发病机制导致ALS药物研发十分困难，目前全球获批治疗ALS的药物非常有限，已获批的药物包括利鲁唑、依达拉奉、Relyvrio和Qalsody。利鲁唑是是第一个获FDA和欧盟批准用于治疗ALS的药物。作为神经保护剂，利鲁唑可改善病人生存状态，但却无法阻止ALS病情的发展，目前已获批的剂型包括片剂、口腔膜剂和混悬剂。依达拉奉是一种脑保护剂（自由基清除剂），为期6个月的临床试验证明其能够减缓ALS相关的日常功能衰退。目前，已获批的剂型有静脉注射剂（如Radicava）和口服混悬剂（如Radicava ORS）。Relyvrio是苯丁酸钠(PB)和牛磺酸二醇(TURSO)组成的复方制剂，其靶向ALS和其他神经退行性疾病中的内质网和线粒体依赖性神经元退行性变通路，减少神经元死亡和功能障碍，可显著减缓ALS疾病进展和延长生存期。2022年，Relyvrio先后在加拿大和美国被批准用于治疗成人ALS。Qalsody（tofersen）是Ionis研发的一种反义寡核苷酸（ASO)药物，它能够与编码SOD1的 mRNA结合，被核糖核酸酶RNase-H降解，从而减少突变SOD1蛋白的生成。2023年4月，Qalsody被FDA批准用于治疗超氧化物歧化酶1 (SOD1)突变所致的ALS。此外，目前全球还有多款在研ALS新疗法，详见下表。在研ALS疗法药物类型多样，涉及间充质干细胞疗法、基因疗法（ASO疗法和腺相关病毒（AAV）介导基因疗法）、Treg细胞疗法等，且有多款进入临床后期。全球部分在研ALS药物来源：公开资料01干细胞疗法干细胞疗法可以通过多种途径进行神经损伤修复，具有治疗ALS等多种中枢神经系统疾病潜力。过去十几年，ALS干细胞疗法的开发和临床转化取得了巨大的成就，据不完全统计，clinicaltrials官网登记的干细胞治疗ALS的临床研究数量超过40项。其中间充质干细胞作为能够保护运动神经元（MN）、分化为多种神经细胞类型、调节免疫细胞作用和减少中枢神经系统（CNS）炎症的细胞而脱颖而出。据悉，Corestem公司的间充质干细胞疗法NeuroNata-R已于2014在韩国获有条件批准用于治疗ALS，目前NeuroNata-R 联合利鲁唑治疗ALS的3期临床试验正在进行中。此外，Brainstorm公司的间充质干细胞疗法NurOwn®进展也较快。2020年11月，Brainstorm宣布NurOwn®在治疗ALS的3期临床试验中未能达到主要终点指标和关键次要终点，不过NurOwn®在病情较轻的患者组中产生了具有临床意义的作用。2022年11月，FDA在未对NurOwn®的BLA进行审查情况下就否决了其上市申请。02基因疗法自1993年发现第一个ALS致病基因，迄今为止，已有近30个基因被证实与ALS的发病相关，最常见的致病基因突变主要包括SOD1、TARDBP、FUS、OPTN、SQSTM1、DAO、DCTN1、VAPB、SIGMAR1、GRN、C9orf72等。近30年来，全球多款治疗ALS的基因疗法已进入临床试验阶段。在研ALS基因疗法包括反义寡核苷酸（ASO）疗法、腺相关病毒（AAV）介导的基因沉默/传递等多种创新疗法，其中首款治疗ALS的ASO药物Qalsody已于今年4月在美国获批。此外，ASO疗法中的ION363进展也较快，目前已进入3期临床。ION363是一种针对FUS RNA的反义药物，可减少FUS蛋白的产生。在FUS-ALS小鼠模型中，反义介导的突变FUS蛋白的还原可防止运动神经元丢失。通过针对FUS-ALS的根本原因，ION363具有减少或预防FUS-ALS患者疾病进展的潜力。2021年4月，ION363治疗FUS突变ALS患者的3期临床试验启动。WAVELife Sciences开发WVE-004是的一款针对C9orf72基因突变导致的ALS和额颞叶痴呆（FTD）的ASO药物，旨在选择性靶向含有与C9orf72基因相关的六核苷酸重复扩增（G4C2）的转录变体，从而保留C9orf72蛋白。C9orf72中的G4C2扩增是ALS和FTD散发性和遗传性形式的最常见遗传原因之一。目前， WVE-004正在进行一项针对42名与C9ORF72相关的ALS或FTD患者的1/2期安全性研究。AAV介导的ALS基因疗法进展相对较慢，其中Apic Bio开发APB-102由重组AAVrh10载体组成，该载体表达微核糖核酸（miRNA），旨在敲低SOD1的表达，目的是减缓或潜在逆转SOD1突变患者ALS的进展，目前已进入1/2期临床。Eikonoklastes Therapeutics的ET-101（SynCav1）是由加州大学圣地亚哥分校Brian Head博士实验室首创，用于过表达Caveolin-1的一种AAV9基因疗法，Caveolin-1可以组织和调节神经肌肉信号传导和功能所必需的突触受体。研究结果显示，增加Caveolin-1可以对神经细胞产生保护作用，使神经细胞可以补偿潜在疾病引起的神经退行性过程，并且使得细胞保持健康并提高其功能性。2022年12月，ET-101获得FDA孤儿药认定，用于治疗散发性和家族性ALS。03其他药物Treg细胞疗法也被开发用于治疗ALS，如ALS001。ALS001是一种自体的Treg细胞疗法，已被FDA授予的孤儿药资格。其1期临床结果表明，ALS001能够对神经起到保护作用，减缓ALS的进展。此外，Atibuclimab、Tegoprubart（AT-1501）等单抗也开发用于治疗ALS。其中Atibuclimab是一款靶向CD14的单克隆抗体，由小鼠可变区和人类IgG4 Fc区组成，可调节感染和损伤引发的致病性炎症反应。2021年1月，FDA授予Atibuclimab治疗ALS的孤儿药资格。Tegoprubart是一种靶向CD40L单抗，可阻断CD40L通路的激活，在ALS的临床前动物模型显示，CD40L通路可以改善肌肉功能、延缓疾病进展和提高存活率。在健康志愿者和患有ALS的成人开展的1a/1b期单次递增剂量试验显示，Tegoprubart在所有剂量下都表现出良好的耐受性，并显示出良好的安全性。而且，Tegoprubart在整个剂量范围内显示出线性剂量比例，半衰期长达26天。已公布的Tegoprubart治疗ALS的2a期临床试验结果显示：Tegoprubart表现出良好的耐受性，以及降低炎症相关生物标志物水平的作用。总结肌萎缩侧索硬化症(ALS)被WHO列为与艾滋病、癌症、白血病、类风湿等并列的五大绝症之一，然而目前该领域获批药物有限，ALS患者3年和5年死亡率分别为50%和80%。随着研究的深入，基因疗法、细胞疗法等药物治疗ALS的潜力已显现，期待未来有更好的ALS疗法获批上市，造福广大ALS患者。END👇关注药渡数据媒体矩阵