Regulation and activities of amyloidogenic proteins APP and TGFBI in physiological and pathological protein aggregation

淀粉样蛋白的形成是正常可溶性蛋白聚集成不溶性纤维。常见于神经退行性疾病。例如，在阿尔茨海默氏症中，一种被称为APP的蛋白质的加工形式在患者体内自我聚集产生淀粉样斑块，这些斑块影响神经元的存活。同样，TGFBI蛋白的缺陷形式在角膜中产生淀粉样蛋白并导致失明。然而，淀粉样蛋白的形成不仅仅是病理性的。例如，一些激素通常形成惰性淀粉样蛋白结构，称为致密核，可以在分泌前储存在细胞中。对抗淀粉样蛋白疾病需要更好地了解淀粉样蛋白的形成是如何触发和控制的。但对患有阿尔茨海默病的患者和动物的研究主要集中在这一过程的最终产物，斑块和记忆丧失。事实上，对于像APP和TGFBI这样的蛋白质，我们一直不清楚它们是否正常参与蛋白质聚集，还是这是一种独特的病理过程。大的蛋白质聚集通常只在疾病中看到，而正常的蛋白质聚集通常涉及更小结构的组装，这使得使用适用于活细胞的显微镜技术很难跟踪这一过程。我们一直在研究果蝇致密核的形成。果蝇拥有相当于人类70%的疾病基因，包括APP和TGFBI。在果蝇中识别参与生物过程和疾病的基因，并观察这些过程在活组织中发生，通常要容易得多。事实上，这些动物被广泛用于研究阿尔茨海默氏症的退化过程。我们已经在苍蝇身上发现了一种特殊的类似前列腺的细胞，即次级细胞，它产生的致密核比其他细胞的核大1000多倍。这使我们能够追踪致密核的快速形成，以及这是如何在活组织中第一次得到控制的。值得注意的是，我们发现APP和TGFBI的苍蝇等价物在形成这些致密核中具有互补作用。TGFBI是蛋白质聚集发生所必需的，而APP则确保微核结构结合在一起形成单个巨核。如果在次生细胞中产生一种病理形式的APP，它会改变TGFBI在致密核中的组织并使其稳定，从而使它们在分泌时无法分散。利用在果蝇中可用的遗传方法，我们已经证明了次生细胞致密核形成的控制与人类斑块形成之间的相似之处，两者似乎都涉及称为外泌体的小膜滴。我们现在将研究APP和TGFBI如何共同控制次生细胞致密核的形成，以及当这些淀粉样蛋白的病理版本在这些细胞中产生时，这一过程是如何出错的。我们还将研究如何改变分泌蛋白通过分泌途径引导的方式来改变细胞中的这些蛋白质聚集事件，特别是关注APP或TGFBI的病理形式是否与正常蛋白表现不同。最后，我们将通过对患者和动物的研究，测试在阿尔茨海默病和神经退行性疾病中发挥作用的大量基因和细胞过程中，哪些参与了正常和病理的次生细胞中APP和TGFBI的聚集。然后我们将精确地计算出它们是如何影响这些过程的。我们的工作将使我们能够定义APP和TGFBI这两种疾病中重要的淀粉样蛋白如何在正常情况下驱动蛋白质聚集成不可溶的致密核心。我们将确定控制这一过程的基因，以及APP和TGFBI的病理形式如何干扰这一控制。然后，我们将与其他研究人员合作，确定哪些机制与人类淀粉样蛋白疾病有关，并开发阻断它们的方法。

Amyloidogenesis is the aggregation of normally soluble proteins into insoluble fibres. It is commonly observed in neurodegenerative disorders. For example, in Alzheimer's Disease, processed forms of a protein called APP self-aggregate to produce amyloid plaques in patients, and these plaques affect the survival of neurons. Similarly, defective forms of the TGFBI protein produce amyloid in the cornea and blindness. However, amyloid formation is not just pathological. For example, some hormones normally form inert amyloid structures called dense cores, which can be stored in cells prior to secretion.Combatting amyloid disease requires a better understanding of how amyloid formation is triggered and controlled. But studies in patients and in animals with Alzheimer's-like disease primarily focus on the end products of this process, plaques and memory loss. In fact, for proteins like APP and TGFBI, it has been unclear whether they are normally involved in protein aggregation or whether this is a uniquely pathological process. Large protein aggregates are typically only seen in disease, while normal protein aggregation generally involves the assembly of much smaller structures, making it difficult to follow this process using microscopy techniques suitable for living cells.We have been studying dense core formation in the fruit fly. Flies have equivalents of about 70% of human disease genes, including APP and TGFBI. It is often much easier to identify genes involved in biological processes and disease in flies and to watch these processes take place in living tissues. In fact, these animals are extensively used to study degenerative processes in Alzheimer's. We have identified a specific prostate-like cell in flies, the secondary cell, which makes dense cores that are over one thousand times larger than cores in other cells. This allowed us to follow the rapid formation of dense cores and how this is controlled for the first time in living tissues.Remarkably, we found that the fly equivalents of APP and TGFBI have complementary roles in making these dense cores. TGFBI is required for protein aggregation to take place, while APP ensures that micro-core structures coalesce together to make a single giant core. If a pathological form of APP is made in secondary cells, it changes the organisation of TGFBI in dense cores and stabilises them, so that they fail to disperse when secreted. Using the genetic approaches available in flies, we have already shown parallels between the control of dense core formation in secondary cells and plaque formation in humans, which both seem to involve small membranous droplets called exosomes.We will now study how APP and TGFBI work together to control dense core formation in secondary cells and how this process goes wrong when pathological versions of these amyloid proteins are made in these cells. We will also work out how altering the ways in which secreted proteins are guided through the secretory pathway changes these protein aggregation events in the cell, particularly focusing on whether pathological forms of APP or TGFBI behave differently to the normal proteins. Finally, we will test which of the large number of genes and cellular processes that have been suggested to play a role in Alzheimer's and neurodegeneration through studies in patients and animals are involved in normal and pathological APP and TGFBI aggregation in secondary cells. We will then work out precisely how they affect these processes.Our work will allow us to define how APP and TGFBI, two important amyloid proteins in disease, normally drive protein aggregation into insoluble dense cores. We will identify the genes that control this process and how pathological forms of APP and TGFBI interfere with this control. We will then be ideally positioned to collaborate with other researchers to determine which of these mechanisms is involved in amyloid disease in humans, and to develop approaches to block them.