Virus Egress Pathways

长期以来，病毒学领域的大部分领域都将细胞视为病毒构建模块的被动供应者，并专注于病毒如何利用单个细胞酶来转录其信使RNA或翻译病毒蛋白。Nihal Altan-Bonnet博士使用活细胞显微镜的动态工具取得了根本性的发现，揭示了病毒对宿主的利用如何超越单个分子，而是诱导细胞生理学和结构的彻底改变。 作为一个具有细胞生物学和生物物理学背景的局外人，Altan-Bonnet博士进入病毒学领域时并不效忠于任何特定的病毒-这在这个领域是不寻常的，因为大多数病毒学家都专注于研究一种病毒。相反，她有意地试图研究各种不同的病毒，以寻找病毒利用宿主细胞的一般原则和共同策略。这种更广泛的方法导致了几个突破性的发现。 其中第一个是发现许多病毒改变宿主脂质代谢以组装病毒复制平台。具体来说，Altan-Bonnet博士表明，宿主编码的脂质激酶，磷脂酰肌醇4-激酶，可以被多种不同的RNA病毒（包括脊髓灰质炎病毒，丙型肝炎病毒，肠道病毒D 68，鼻病毒）劫持。她表明，多种病毒聚集在这种脂质激酶上的原因是产生富含PI 4P脂质的复制区室，其中这种PI 4P脂质用作膜对接以募集、稳定和刺激病毒复制酶的催化活性。她的研究是制药公司（葛兰素史克，诺华）和大学（项目四斯坦福大学ViRX）开发针对宿主PI 4激酶的小分子作为泛病毒靶点的多项倡议的基础。 博士阿尔坦-博内的第二个突破性发现是发现了一种新的病毒感染单位：病毒隐藏在囊泡中，以隐蔽的方式传播。在这一发现之前，人们不仅认为病毒是以自由的单个粒子在宿主之间传播的，而且这种传播形式被认为是最致命的，因为它允许病毒广泛传播并感染尽可能多的宿主。尼哈尔斯的研究结果挑战了传统的概念，病毒传播的个人单位的感染，并占其演变的人口作为准物种或病毒变种。Altan-Bonnet博士透露，许多不同的病毒在没有裂解的情况下离开细胞，进入细胞外囊泡，最明显的是多个病毒颗粒一起旅行。她继续指出，这种传播形式比病毒作为单个粒子更具传染性和毒性，因为通过大量进入细胞，它们可以很容易地克服复制障碍-不仅来自宿主方面的障碍，而且还有内在障碍，如突变病毒变体或准物种，它们单独会受到阻碍，但通过大量旅行，它们可以从合作行为中受益。此外，隐藏在囊泡膜下的病毒受到保护，免受炎症和/或中和免疫反应的影响：这对于必须穿越胃肠道的恶劣环境同时保持其感染性的肠道病毒特别重要。 最近Altan-Bonnet博士已经证明，这些携带病毒的细胞外囊泡在胃肠道、粪便、气溶胶中高度稳定，并被人类和动物大量排出。 博士Altan-Bonnet对病毒有效传播的研究也导致她最近发现了一种全新的、可能与公共卫生更相关的肠道病毒诺如病毒、轮状病毒和星状病毒的传播途径，这些病毒共同感染了全球15亿人，造成了大量的死亡率和发病率（更不用说经济困难了）。在她的发现之前，肠道病毒被认为只在肠道中复制，并通过口腔-粪便途径在宿主中传播。她证明了这些肠道病毒在唾液腺中强大地复制（与肠道相当），并通过唾液传播，不仅在个体之间，而且通过哺乳在母亲和婴儿之间传播。这一发现可能为这些病毒的更简单的诊断开辟了道路，例如唾液测试，也可能促使公共卫生卫生实践的修订，到目前为止，这些实践仅专注于限制通过口腔-粪便途径传播的病毒，包括掩蔽。 最后，在COVID-19大流行期间，Altan-Bonnet博士运用她的成像技术窥视冠状病毒感染的细胞内部，以揭示这些病毒如何从细胞中退出并传播到其他细胞-这一领域显然尚未被研究过。大多数病毒，包括丙型肝炎，依赖于生物合成分泌途径（例如高尔基体）退出细胞，这被认为是冠状病毒的情况。但尼哈尔发现，这些病毒的独特之处在于，它们通过一种更奇特的细胞途径--溶酶体胞吐作用--离开细胞。在此过程中，病毒可以逃避细胞防御，因为它们通过溶酶体途径使溶酶体蛋白降解失活并改变细胞抗原呈递。这一发现是冠状病毒生命周期的一个基本方面，使用溶酶体作为出口，这可能是COVID患者表现出的全系统免疫功能障碍的根本原因之一。 总之，最近的大流行所带来的特殊情况，更加强调了像Altan-Bonnet博士那样对宿主-病原体相互作用的一般原理和分子/细胞细节进行研究的必要性。

Much of the field of virology has long viewed the cell as a passive supplier of viral building blocks and focused on how viruses exploit individual cellular enzymes for transcription of their messenger RNAs or translation of the viral proteins. Dr. Nihal Altan-Bonnet using the dynamic tools of live-cell microscopy has made fundamental discoveries, revealing how viral exploitation of the host goes beyond individual molecules and rather induces a complete shake up of cell physiology and architecture. As an outsider with a background in cellular biology and biophysics, Dr. Altan-Bonnet came into the field of virology without any allegiance to a particular virus- something unusual in this field as most virologists focus on the study of one virus. Instead she intentionally sought to study a wide variety of different viruses in order to search for general principles and common strategies viruses employ to exploit the host cell. This broader approach resulted in several groundbreaking discoveries. The first of which was the discovery that many viruses alter the host lipid metabolism to assemble viral replication platforms. Specifically, Dr. Altan-Bonnet showed that a host encoded lipid kinase, phosphatidyl inositol 4-kinase, can be hijacked by multiple different RNA viruses (including poliovirus, hepatitis C, Enterovirus D68, Rhinovirus). The reason for multiple viruses to converge on this lipid kinase she showed was to generate PI4P lipid enriched replication compartments where this PI4P lipid was used as a membrane dock to recruit, stabilize and stimulate the catalytic activities of viral replication enzymes. Her studies have been the basis of multiple initiatives by pharmaceutical companies (Glaxo, Novartis) and universities (Project Four Stanford ViRX) to develop small molecules against host PI4 kinases as panviral targets. Dr. Altan-Bonnet 's second groundbreaking discovery was the identification of a new form of viral infectious unit: viruses traveling en masse, cloaked inside vesicles. Before this discovery, it was not only assumed that viruses traveled as free single particles from host to host but this form of travel was considered to be the most virulent as it allowed viruses to spread wide and infect as many hosts as possible. Nihals findings challenged the classical concept of virus transmission as individual units of infection and accounted for their evolution of populations as quasi-species or viral variants. Dr. Altan-Bonnet revealed that many different viruses exit cells without lysis, inside extracellular vesicles and most remarkably as multiple virus particles all traveling together. She went on to show that this form of transmission is much more infectious and virulent than viruses as single particles because by entering cells in high numbers they could easily overcome barriers to replication- barriers from not only the host side but also intrinsic barriers such as mutant viral variants or quasi-species that alone would be handicapped but by traveling en masse benefit from cooperative behavior. Additionally, cloaked under a vesicular membrane, viruses were protected from inflammatory and/or neutralizing immune responses: this is particularly significant for enteroviruses that must traverse the harsh environment of the gastrointestinal tract while maintaining their infectiousness. Recently Dr. Altan-Bonnet has demonstrated that these extracellular vesicles carrying viruses are highly stable in the gastrointestinal tract, in stool, in aerosol and are copiously shed by humans and animals. Dr. Altan-Bonnet's investigations into what makes viruses efficient at transmission led also to her recent discovery of an entirely new and likely more public health relevant transmission route for the enteric viruses norovirus, rotavirus and astrovirus, which combined infect 1.5 billion people globally causing much mortality and morbidity (not to mention economic hardship). Until her findings, enteric viruses were thought to solely replicate in intestines and spread through the oral-fecal route among hosts. She demonstrated that these enteric viruses replicate in salivary glands robustly ( on par with intestines) and spread through saliva, not only among individuals but also between mothers and infants through suckling. This finding potentially opens the way to simpler diagnostics for these viruses, such as saliva tests, and also may prompt revision of public health sanitary practices, which until now have been solely focused on limiting viral transmission by the oral-fecal route, to include masking. Finally during the COVID-19 pandemic, Dr. Altan-Bonnet applied her imaging skills to peer inside coronavirus infected cells to reveal how these viruses exit from cells and spread to others- an area that has remarkably not been studied. Most viruses, including hepatitis C, rely on the biosynthetic secretory pathway (e.g. Golgi apparatus) to exit out of cells and this was assumed to be the case for coronaviruses too. But Nihal discovered that these viruses are unique in that they piggy-back on a more exotic cellular pathway, lysosomal exocytosis, to exit from the cells. In the process, viruses can evade cell defenses as their passage through the lysosomal pathway inactivates lysosomal protein degradation and alter cellular antigen presentation. This discovery of a fundamental aspect of the coronavirus lifecycle, using lysosomes for exit, maybe one, if not the root cause, of the system wide immune dysfunction exhibited by COVID patients. To conclude, the extraordinary circumstances brought upon by the recent pandemic, emphasize even more the need for investigations, like Dr. Altan-Bonnet s, into the general principles and molecular/cellular details of host-pathogen interactions.