Unravelling the mechanisms of neurological damage during cryptococcal infection of the brain

大脑传染病的负担正在使非洲的社会经济发展丧失能力。其中一些疾病在非洲独一无二地流行，在全球研究和政策中通常都被忽视，这使得非洲神经科学家需要优先考虑这些挑战，并制定当地的解决方案。这类疾病的例子包括脑部真菌感染，如隐球菌性脑膜炎，在撒哈拉以南非洲，每年有20多万人死于这种疾病，还导致幸存者的神经功能障碍和残疾，其中大多数人处于经济多产的年龄。隐球菌性脑膜炎(CM)是艾滋病毒相关性脑膜炎的主要原因，其特点是使大脑虚弱、炎症性损伤，即使接受治疗，死亡的可能性也非常高。在撒哈拉以南非洲，由于无法获得安全有效的药物，死于CM及其并发症的人数进一步恶化。虽然已经做了很多工作来描述引起CM的真菌病原体的生物学，但我们对人体对真菌的反应知之甚少，特别是在大脑层面，这是那些死于这种疾病的人中受影响最严重的器官。想要研究CM脑损伤的研究人员面临的挑战之一是缺乏适当的实验模型来很好地代表这种疾病的真实临床形式，并具有足够好的分辨率来帮助描绘这种致命疾病导致的脑损伤的复杂机制。了解这些机制对于我们了解疾病如何发展至关重要，对于我们努力开发大多数非洲人民可以获得的更便宜、更安全的药物也是至关重要的。因此，这项研究的第一部分集中在介绍一种新的器官特异性、宿主特异性的实验模型，该模型可用于研究隐球菌感染期间脑损伤的潜在机制。提出的模型是基于使用啮齿动物和人脑组织切片，这些切片在培养中小心地保持活着，然后用新生隐球菌刺激，新生隐球菌是引起CM的真菌。我将研究大脑免疫细胞中关键炎症机制的激活，包括病原体识别受体、转录因子和其他在对抗真菌时释放的化学通讯分子。使用最先进的科学技术，我还将调查每种细胞类型对大脑对真菌的反应的贡献。为了补充使用这个新模型获得的数据，我提议的研究的第二部分旨在使用一个活的啮齿动物模型来概括CM的人类形式。使用这个模型，我们将能够描述真菌感染后在大脑中的哪里，最重要的是，我们将能够确定真菌细胞是否真的阻止了最近发现的大脑液体清除途径。这项研究将填补现有关于CM中大脑如何损伤的知识空白。然后，这些模型和方法将成为研究由细菌、寄生虫和病毒引起的其他中枢神经系统感染机制的平台，为亟需的新疗法的开发提供信息。

Lay summaryThe burden of infectious diseases of the brain is incapacitating to the socio-economic development of Africa. Some of the diseases are uniquely prevalent in Africa and are usually neglected in both global research and policy creating a need for African neuroscientists to prioritise and develop local solutions for these challenges. Examples of such diseases include fungal infections of the brain such as cryptococcal meningitis which kills more than 200 000 people each year in Sub-Saharan Africa and also causes neurological dysfunction and disability in survivors, most of which are of an economically productive age. Cryptococcal meningitis (CM) is the leading cause of HIV-associated meningitis, which is characterised by debilitating, inflammatory injury of the brain and a very high chance of death, even with treatment. In Sub-Saharan Africa, the number of people who die from CM and its complications is worsened by the unavailability and inaccessibility of safe and effective drugs. Although a lot of work has been done to describe the biology of the fungal pathogen that causes CM, we know very little about how the human body responds to the fungus especially at the level of the brain, which is the most affected organ in those who succumb to the disease. One of the challenges faced by researchers intending to study brain injury in CM is the lack of appropriate experimental models that provide a good representation of the real clinical form of the disease with good enough resolution to help delineate the complex mechanisms underlying brain damage from this fatal condition. Knowledge of these mechanisms is critical to our understanding of how the disease progresses, as well as to our efforts of developing cheaper and safer drugs that can be accessed by most African people. The first part of this study therefore focusses on introducing a new organ-specific, host-specific experimental model that could be used for studying mechanisms underlying brain injury during cryptococcal infection. The proposed model is based on using both rodent and human brain tissue slices which are carefully kept alive in culture then stimulated with Cryptococcus neoformans, the causative fungus for CM. I will investigate the activation of key inflammatory machinery in immune cells of the brain including receptors for pathogen recognition, transcription factors and other chemical communication molecules released when fighting the fungus. Using state-of-the-art scientific techniques, I will also investigate the contribution of each cell type to the brain's response to the fungus. To compliment data obtained using this novel model, the second part of my proposed research aims to use a living rodent model to recapitulate the human form of CM. Using this model we will be able to describe where in the brain the fungus goes after infection and most importantly, to establish if fungal cells indeed block the fluid clearance pathways of the brain which were discovered recently. This research will fill the existing knowledge gap on how the brain is injured in CM. This models and methods would then serve as a platform for studying the mechanisms of other infections of the CNS that are caused by bacteria, parasites and viruses to inform the development of the much-needed new therapies.