Exploiting stem cell biology for liver fluke control

肝吸虫(片形吸虫属)是一种扁虫寄生虫，感染各种哺乳动物，包括人和反刍动物，如牛、山羊和绵羊。在人类中，这种寄生虫导致了肝片吸虫病，这是一种被忽视的热带疾病，据估计有1700万人被感染。这种蠕虫影响全球粮食安全，因为它破坏牲畜的健康和生产力，导致肝片吸虫病，估计每年在全球造成约30亿美元的损失。主要的担忧是：动植物卫生局将肝吸虫列为英国最常见的绵羊和牛的蠕虫寄生虫；最近对英国流行率变化的估计预测，到2050年，肝片吸虫病的风险将达到前所未有的水平；农民依赖于药物的管理，这些药物由于耐药性而变得越来越不有效。成虫生活在胆管中，幼虫被植物包裹；幼虫吞噬后，从肠道通过肝脏迁移到胆管。幼虫是主要的病原体，当它从肠道移动到胆管时，会对肝脏造成严重损害。正是在这个阶段，可以杀死羔羊和绵羊，而在这个阶段，只有一种有效的药物--三氯苯达唑(TCBZ)。至关重要的是，对TCBZ的抗药性威胁到世界许多地区畜牧业的可持续性，因此需要新的杀线虫剂和/或疫苗。肝吸虫研究的主要障碍包括缺乏良好的基因组资源，缺乏功能研究的模型系统，以及依赖基于宿主动物的活体实验来了解吸虫生物学。新的生物信息资源以及在实验室中在宿主外培养幼年吸虫的能力，意味着现在可以进行吸虫发育生物学的实验，从而刺激了这一项目。我们培养成长中的幼虫的能力，持续的时间框架，以及选择性地破坏基因靶点的能力，为改变肝吸虫生物学的方法和发现新的药物靶点提供了机会。我们发现肝吸虫干细胞对它们的生长和发育至关重要，因此是一个有吸引力的新药靶点资源。虽然干细胞在化疗和耐药中的关键作用已在癌症领域得到证实，但它们在寄生虫-药物相互作用中的作用和在寄生虫控制中的潜在开发尚未被研究。我们的初步数据揭示了这些干细胞在肝吸虫生长中的关键作用，并表明它们在寄生虫-药物相互作用中发挥作用，鼓励它们开发新的药物靶点。在这个项目中，在一个工业伙伴的支持下，我们提议发现与肝吸虫干细胞生物学有关的关键基因，并评估它们作为新的杀吸虫剂新药靶点的潜力。为此，我们建议对幼年肝吸虫干细胞中表达的基因产生新的生物信息学资源。我们还将评估干细胞在寄生虫-药物相互作用中的重要性，以帮助了解它们在肝吸虫如何耐受/从药物暴露中恢复的作用。我们将研究寄生虫药物敏感性和干细胞生物学之间的关系，以及破坏肝吸虫干细胞对寄生虫药物治疗反应的后果。最后，我们将使用我们建立的功能基因组学工具评估肝吸虫干细胞基因子集作为新药物靶点的潜力。我们的行业合作伙伴将把优先考虑和验证的靶点输入新药筛选，以启动控制肝吸虫的新药的发现。这里采取的方法与肝吸虫有直接关系，与引起动物和人类各种重要疾病的其他寄生虫有间接关系。

Liver fluke (Fasciola species) are flatworm parasites that infect diverse mammals including humans and ruminant livestock such as cattle, goats and sheep. In humans, the parasite causes the disease fascioliasis which is a neglected tropical disease with an estimated 17 million people believed to be infected. The worm impacts global food security as it undermines the health and productivity of livestock in which it causes fasciolosis, estimated to cause losses of ~$US3 billion/year worldwide. Major concerns are that: the Animal and Plant Health Agency list liver fluke as the most commonly diagnosed helminth parasite of sheep and cattle in UK; recent estimates of changing prevalence in the UK have forecast unprecedented levels of fasciolosis risk by 2050; farmers rely on the administration of drugs which are becoming less effective due to drug resistance. Adult worms live in the bile ducts and juveniles occur encysted on vegetation; after being swallowed the juveniles excyst and migrate from the intestine through the liver to the bile ducts. The juvenile worm is the key pathogen, causing profound damage to the liver as it moves from the intestine to the bile duct. It is this stage that can kill lambs and sheep and the stage against which there is only one effective drug, triclabendazole (TCBZ). Critically, TCBZ-resistance threatens the sustainability of livestock farming in many regions of the world such that new flukicides and/or a vaccine are needed. Key impediments to research studies on liver fluke have included the lack of good genomic resources, the absence of a model system for functional studies and the reliance on host animal-based in vivo experiments to inform fluke biology. The new bioinformatic resources as well as the ability to culture the juvenile fluke in the laboratory outside of a host, mean that experiments on fluke developmental biology are now possible, stimulating this project. Our ability to culture growing juveniles, for sustained timeframes, and to selectively disrupt gene targets provides an opportunity to transform approaches to liver fluke biology and the discovery of new drug targets. We have found that liver fluke stem cells are critical to their growth and development and as such, are an appealing resource for new drug targets. Whilst the critical role played by stem cells in chemotherapy and drug resistance is established in the cancer field, their role in parasite-drug interactions and potential exploitation in parasite control have not been investigated. Our preliminary data expose a critical role for these stem cells in liver fluke growth and indicate that they play a role in parasite-drug interaction, encouraging their exploitation for the discovery of new drug targets. In this project, supported by an industrial partner, we propose to discover key genes involved in liver fluke stem cell biology and to evaluate their potential as novel drug targets for new flukicides. To do this we propose to generate new bioinformatics resources on the genes expressed in juvenile liver fluke stem cells. We will also evaluate the importance of stem cells to parasite-drug interactions to help inform their role in how liver fluke parasites tolerate/recover from drug exposure. We will study the relationships between parasite drug sensitivities and stem cell biology and the consequences of disrupting liver fluke stem cells on parasite responses to drug treatments. Finally, we will evaluate a sub-set of liver fluke stem cell genes for their potential as new drug targets using the functional genomics tools we have established. Prioritized and validated targets will be entered into new drug screens by our industrial collaborator to initiate the discovery of new drugs to control liver fluke. The approaches taken here have direct relevance to liver fluke and indirect relevance to other parasitic worms that cause a diverse range of important diseases of animals and humans.