Ultrastable targeted multifunctional hybrid nanomaterials for long-term stem cell tracking

干细胞科学开始认识到它的潜力，许多患者现在受益于新的干细胞疗法，通常涉及患者自己的骨髓来源干细胞的移植。然而，为了在干细胞医学方面取得进一步的进展，以便更多的患者能够从这些开创性的疗法中受益，需要技术发展，以便能够在移植后密切监测干细胞的行为。干细胞监测至关重要，因为如果干细胞迁移到目标器官以外的其他器官和组织，可能会给患者带来严重的健康问题。除了这些重要的安全问题外，干细胞监测也是必要的，以帮助我们了解细胞如何调节其积极作用。在这个项目中，我们的目标是开发一种使用一种名为磁共振成像(MRI)的非侵入性方法来监测干细胞的技术，这种方法不会对患者造成伤害。我们提出的这项技术是基于跟踪超顺磁性氧化铁纳米颗粒(SPIONS)的。SPIONS的主要优点是，由于它们的纳米尺寸，它们可以很容易地被引入细胞中，而不会产生有害的副作用。此外，由于铁是人体中的一种天然物质，实际上也是一种重要的营养物质，因为它是携氧分子--血红蛋白的基本成分，它不太可能对患者造成任何伤害，而且此前已确定氧化铁具有生物相容性。目前阻碍SPION用于干细胞追踪的一个主要障碍是，在大多数情况下，它们不会被干细胞保留超过几周。干细胞的治疗或不良反应可能会远远超过两周，因此，迫切需要一种能够在移植后更长时间内追踪细胞的步骤改变技术。SPION的细胞保持性如此之差的原因之一是，当SPION进入细胞时，SPION被定位在称为内小体的细胞隔室中，由于其酸性环境，导致SPION降解。另一个原因是，这些细胞使用一种被称为“逆向内吞作用”的过程，主动地将内小体的内容移回细胞外空间。这个项目解决了物理学家和干细胞生物学家之间跨学科合作的挑战。我们将为SPION设计和化学合成新的涂层，以保护它们免受降解，并防止它们被逆转内吞。为了确定最有效的涂层，我们将使用我们团队开发的一种新的成像技术，该技术允许我们监控SPION在培养皿中单个细胞内的保留时间。在该项目的最后阶段，我们将选择最有希望的SPION来标记小鼠骨髓来源的干细胞，这种干细胞被认为可以促进肾脏损伤的恢复。这些标记的干细胞将被移植到受损肾脏的小鼠体内，我们将使用磁共振成像来监测干细胞在较长时间内的行为。我们预测，在这个项目的过程中产生的新型SPION将对我们在移植后的长期(几个月)追踪干细胞的能力产生重大影响。尽管骨髓源性干细胞是当前项目的重点，但我们预计新型SPION将对更广泛的干细胞界有用，因为它们适合标记其他临床相关的干细胞类型，如胚胎干细胞，预计明年将进入英国治疗老年性黄斑变性的临床试验。此外，SPION可以用来标记各种类型的干细胞，这些干细胞有可能治疗帕金森氏症、糖尿病和心脏病等疾病。

Stem cell science is beginning to realise its potential, with many patients now benefiting from novel stem cell therapies, usually involving transplantation of the patient's own bone marrow-derived stem cells. However, to make further progress in stem cell medicine so that more patients can benefit from these pioneering therapies, technological developments are required so that the behaviour of the stem cells can be closely monitored following transplantation. Stem cell monitoring is crucial, because, if the cells migrate to other organs and tissues besides the target organ, they could cause serious health problems for the patient. Apart from these important safety issues, stem cell monitoring is also necessary to help us understand how the cells mediate their positive effects. In this project, we aim to develop the technology to monitor stem cells using a non-invasive method called magnetic resonance imaging (MRI) that will not cause harm to the patient. The technology we propose is based on tracking superparamagnetic iron oxide nanoparticles, or 'SPIONs'. The main advantage of SPIONs is that, because of their nanoscale dimensions, they can be easily introduced into cells without detrimental side effects. Furthermore, because iron is a natural substance in the human body and indeed an important nutrient, as it is an essential component of the oxygen-carryng molecule, haemoglobin, it is unlikely to cause any harm to patients and iron oxides have previously been established to be biocompatible.A major obstacle that currently prevents the use of SPIONs for stem cell tracking is that in most cases they are not retained by the stem cells for more than a few weeks. Therapeutic or adverse effects of the stem cells would potentially manifest well beyond two weeks and, therefore, there is a strong need for a step change technology enabling cell tracking for much longer periods following transplantation. One of the reasons why cellular retention of SPIONs is so poor is that upon entry into the cells, the SPIONs become localised in a cellular compartment called the endosome, which due to its acid environment, causes the SPIONs to degrade. A further reason is that the cells use a process called 'retro-endocytosis' to actively remove the contents of endosomes back into the extracellular space. This project addresses the challenge in an interdisciplinary collaboration between physical scientists and stem cell biologists. We will design and chemically synthesise novel coatings for the SPIONs that will protect them from degradation and prevent them from being retro-endocytosed. To identify the most effective coatings, we will use a new imaging technology developed by our group that allows us to monitor the retention time of the SPIONs within single cells in a culture dish. In the final stages of the project we will select the most promising SPIONs to label mouse bone marrow-derived stem cells, which are known to promote recovery from kidney damage. These labelled stem cells will then be transplanted into mice that have damaged kidneys, and we will use MRI to monitor the behaviour of the stem cells over a prolonged time course.We predict that the novel SPIONs generated during the course of this project will make a significant impact on our ability to track stem cells in the long-term (several months) following transplantation. Although bone marrow-derived stem cells are the focus of the current project, we anticipate that the novel SPIONs will be of use to the wider stem cell community, due to their adaptability for labelling other clinically relevant stem cell types, such as embryonic stem cells, which are expected to enter clinical trials in the UK next year for the treatment of age-related macular degeneration. Furthermore, the SPIONs could be used to label various stem cells types that have potential for the treatment of conditions such as Parkinson's Disease, Diabetes and Heart Disease.