2021 BBSRC-NSF/BIO: Comparative analysis of immune response programmes employed by epithelial cells to fight natural infection in C. elegans

上皮细胞在动物表面形成关键屏障，在体内宿主环境和外部环境之间的交界处占据与感染具有战略相关性的位置。尽管越来越多的人认识到这些细胞对所有后生动物强大的天然免疫系统至关重要，但它们的研究比巨噬细胞等专业免疫细胞要少。线虫线虫为检测上皮细胞的免疫功能提供了一个强大的全动物系统。线虫没有已知的专业免疫细胞，相反，它们似乎严重依赖非专业免疫细胞，如上皮细胞。这一模型系统的实验可控性使人们能够研究有关上皮细胞如何感知和响应病原体攻击的基本问题，以及感染期间发生的相关生理扰动。线虫是如何检测感染的，人们对此知之甚少。其他动物的先天免疫研究通常集中在微生物相关分子模式(MAMP)是如何被感知来触发免疫反应的。相比之下，对线虫免疫的研究表明，这种宿主通常通过检测感染的影响来感知感染，这种影响被称为监视免疫，或效应器触发免疫。线虫可能使用效应器触发的免疫，以及MAMP触发的免疫，但对这两种免疫激活的分子机制知之甚少。此外，大多数线虫的研究都集中在对细菌感染的反应上，但线虫在野外可以被不同的微生物感染，包括普遍存在的真核病原体。在这里，我们建议研究线虫是如何对抗两类不同的天然真核病原体的感染的，即微孢子虫和卵菌。这些病原体代表了进化上不同的微生物谱系，其中微孢子虫与真菌有关，卵菌与褐藻和硅藻关系密切。这些真核病原体分支包括感染广泛的农业重要宿主的物种，包括昆虫、甲壳类动物、鱼类和植物。微孢子虫和卵菌也是线虫普遍存在的自然病原体，通过肠道(微孢子虫)或皮肤(卵菌)进入线虫体内，最终传播并杀死线虫。特罗梅尔和巴库拉斯实验室的研究发现，对这些不同的真核病原体具有共同的防御特征，这增加了一组共同的基因可能驱动肠道和皮肤上皮免疫的可能性。然而，线虫用来感知和对抗感染的这些免疫防御网络的结构在很大程度上仍然是未知的。我们将采取跨病原体比较的方法，以了解动物如何在正确的组织中启动适当的防御程序。剖析非专业免疫细胞对不同病原体的免疫机制是一个根本性的问题。线虫体内存在多种进化上保守的信号通路和免疫效应器。例如，几丁质酶样蛋白已被证明可以对抗线虫中的卵真菌感染，它们也在其他动物的炎症和疾病中发挥作用。此外，蛋白毒性应激与线虫对微孢子虫和卵菌的免疫应答密切相关，也与其他宿主的先天免疫和炎症反应有关。因此，这项工作将加深我们对上皮免疫的理解，并可能在水产养殖和农业中长期应用于治疗由微孢子虫和卵菌引起的许多疾病。

Epithelial cells form a critical barrier at animal surfaces, occupying positions of strategic relevance to infection being at the interface between the internal host environment and the external environment. Despite the growing appreciation of these cells as critical to a robust innate immune system in all metazoans, they are less well-studied than professional immune cells like macrophages. The small nematode Caenorhabditis elegans provides a powerful whole-animal system in which to examine immunity of epithelial cells. C. elegans does not have known professional immune cells, and instead appears to rely heavily on non-professional immune cells, such as epithelial cells. The experimental tractability of this model system enables the study of fundamental questions about how epithelial cells sense and respond to pathogen attacks, as well as the associated perturbations in physiology that occur during infection. How C. elegans detects infection is poorly understood. Innate immune studies in other animals usually focus on how microbial-associated molecular patterns (MAMPs) are sensed to trigger immune responses. In contrast, studies of C. elegans immunity have revealed that this host often senses infection through detecting the effects of infection, called surveillance immunity, or effector-triggered immunity. C. elegans likely uses effector-triggered immunity, as well as MAMP-triggered immunity, but relatively little is known about the molecular mechanisms of activation of either kind of immunity. Furthermore, most C. elegans studies have focused on response to bacterial infection, but C. elegans can be infected by diverse microbes in the wild, including ubiquitous eukaryotic pathogens.Here, we propose to study how C. elegans fights infection by two distinct clades of natural eukaryotic pathogens, namely microsporidia and oomycetes. These pathogens represent evolutionarily distinct lineages of microbes, with microsporidia being related to fungi and oomycetes being closely related to brown algae and diatoms. These eukaryotic pathogen clades include species that infect a wide range of agriculturally important hosts including insects, crustaceans, fish and plants. Microsporidia and oomycetes are also ubiquitous natural pathogens of C. elegans, entering through its intestine (microsporidia) or skin (oomycetes) to eventually spread and kill the nematodes. Work from the Troemel and Barkoulas labs has identified shared features in the defence to these diverse eukaryotic pathogens raising the possibility that a common set of genes may drive epithelial immunity in the intestine and the skin. However, it remains largely unknown what is the architecture of these immune defence networks the nematodes employ to sense and fight infection. We will pursue a cross-pathogen comparative approach to understand how the animals mount the appropriate defence programmes in the right tissues. Dissecting mechanisms of immunity in non-professional immune cells against diverse pathogens represents a fundamental problem. Various evolutionarily conserved signalling pathways and immune effectors are present in C. elegans. For example, chitinase-like proteins have been shown to antagonise oomycete infections in C. elegans and they also play a role in inflammation and disease in other animals. Furthermore, proteotoxic stress is closely linked to the immune responses against microsporidia and oomycetes in C. elegans, and is associated with innate immunity and inflammation in other hosts as well. Therefore, this work will deepen our understanding of epithelial immunity and may have long-term applications in aquaculture and agriculture to treat the many diseases caused by microsporidia and oomycetes.