Klebsiella pneumoniae type VI secretion system: a weapon for innate immunity warfare

抗菌素耐药性(AMR)这一全球性问题正迅速成为现代重大科学和健康问题之一。毫不奇怪，AMR被列入英国政府最近发布的可能在未来5年直接影响英国的《公民紧急情况国家风险登记册》。如果一种耐药微生物大范围爆发，估计会有超过8万人死亡。新抗生素的开发是缓慢而困难的工作，但细菌耐药性正在减少我们现有药物的武器库。后抗生素时代--在这个时代，常见的感染和轻微的伤害可能会导致死亡--远非世界末日般的幻想，而是21世纪的一种非常现实的可能性。奥尼尔最近在AMR上发表的评估报告强调了全球面临的威胁，称“全球每年已有数十万人死于耐药感染，到2050年，这一数字可能会超过1000万”。特别令人关切的是，耐多药革兰氏阴性细菌，特别是肺炎克雷伯氏菌引起的感染日益普遍。由于极具抗药性的菌株，这种病原体已被英国政府、美国疾病控制和预防中心以及世界卫生组织列为“对人类健康的紧急威胁”。然而，从分子和细胞水平研究肺炎克雷伯菌致病机制的证据很少。因此，更好地了解克雷伯菌的病理生理机制，以便能够设计新的策略来治疗克雷伯菌感染是迫切和必要的。以前的实验室研究支持这样的观点，即克雷伯菌颠覆了宿主防御机制的激活，从而在肺中生存。虽然我们在理解病原体操纵的细胞通路以阻止炎症方面取得了进展，但在破译克雷伯菌使用的抗免疫因子方面仍存在很大差距。通过应用涵盖细胞和分子微生物学、先天免疫学、结构生物信息学的多学科方法，以及利用酿酒酵母表达异源蛋白，我们将着手利用肺炎克雷伯菌VI型分泌系统(T6SS)传递的效应器如何阻止细胞固有免疫激活的基础知识。T6SS是最近发现的一种纳米机械，细菌利用它向受体细胞(竞争对手细菌和/或真核细胞)运送蛋白质。我们将从分子水平对克雷伯氏菌T6SS进行表征。我们将剖析T66S传递的蛋白质如何对抗信号通路的激活，该通路控制着感染后的大多数宿主防御反应。最后，我们将阐述一种迄今未知的基于线粒体动力学的克雷伯氏菌毒力策略。利用宿主-病原体界面为新的抗菌疗法开辟了道路。干扰病原体的毒力和/或被病原体为了自身利益劫持的信号通路是一种特别引人注目的方法，因为与旨在杀死病原体或防止其生长的传统策略相比，这被认为对发展抗药性施加的选择性压力较小。因此，人们相信，如果在研究过程中发现并验证这些靶点，将会引起制药公司的极大兴趣。

The global problem of antimicrobial resistance (AMR) is fast becoming one of the major scientific and health issues of modern times. No surprisingly, AMR is included in the recently release UK government "National Risk Register of Civil Emergencies" that may directly affect the UK over the next 5 years. More than 80,000 deaths are estimated if there is a widespread outbreak of a resistant microbe. The development of new antibiotics is slow and difficult work but bacterial resistance is decreasing our arsenal of existing drugs. A post-antibiotic era - in which common infections and minor injuries can kill - far from being an apocalyptic fantasy, is a very real possibility for the 21st Century. The recent O'Neill review on AMR sets out the global threat by highliting that "drug-resistant infections already kill hundreds of thousands a year globally, and by 2050 that figure could be more than 10 million". Of particular concern is the mounting prevalence of infections caused by multidrug resistant Gram-negative bacteria, in particular Klebsiella pneumoniae. This pathogen has been singled out as an "urgent threat to human health" by the UK Government, the U.S. Centers for Disease Control and Prevention, and the World Health Organization due to extremely drug resistant strains. However, there is scant evidence on K. pneumoniae pathogenesis at the molecular and cellular level. Therefore, it is both urgent and necessary to better understand its pathophysiology to be able to design new strategies to treat Klebsiella infections.Previous studies from the laboratory support the notion that Klebsiella subverts the activation of host defence mechanisms to survive in the lung. While we have progressed on understanding the cellular pathways manipulated by the pathogen to block inflammation, there is a major gap on decoding the anti-immune factors employed by Klebsiella. By applying a multidisciplinar approach encompassing cellular and molecular microbiology, innate immunity, structural bioinformatics; and exploiting Saccharomyces cerevisiae to express heterologous proteins, we will embark on harnessing basic knowledge about how Klebsiella pneumoniae type VI secretion system (T6SS)-delivered effectors block the activation of cell intrinsic immunity. T6SS is a recently discovered nanomachinery that bacteria use to deliver proteins to a recipient cell (either a competitor bacteria and/or an eukaryotic cell). We will characterize Klebsiella T6SS at the molecular level. We will dissect how T66S-delivered proteins antagonize the activation of the signalling pathway controlling the majority of host defense responses upon infection. And, finally, we will illuminate a hithertho unknown Klebsiella virulence strategy based on targeting mitochondrial dynamics.Harnessing the host-pathogen interface opens the avenue for new antimicrobial therapeutics. Interference with pathogen virulence and/or signalling pathways hijacked by pathogens for their own benefit is an especially compelling approach, as it is thought to apply less selective pressure for the development of resistance than traditional strategies, which are aimed at killing pathogens or preventing their growth. It is therefore believed that such targets - if found and validated during the research - will meet big interest at pharmaceutical companies.