Improving functional connectivity following transplantation of cone photoreceptors

遗传性视网膜疾病和年龄相关性黄斑变性（AMD）是英国不可逆失明的主要原因。遗传性视网膜营养不良的发病率为1 / 2,500，通常发生在儿童或成年早期，而老年性黄斑变性的发病率为1:3，超过75岁。到2050年，英国受视力损失影响的人数将翻一番，达到400万人。据估计，视力损失每年将给英国经济造成280亿英镑的直接和间接损失。目前，我们缺乏有效的治疗方法，迫切需要开发新的治疗方法。这两种情况都涉及视网膜中感光锥细胞和杆状感光细胞的丧失。光感受器替代旨在通过移植健康细胞来恢复视力，理想情况下，这些细胞来自可再生来源。一旦移植，这些细胞必须与宿主视网膜内的靶细胞（称为双极细胞）形成新的连接（突触）。移植后恢复功能连接是中枢神经系统修复的一个雄心勃勃的目标。尽管如此，对于高灵敏度日光视力至关重要的黄斑只占很小的面积，实现有用的视力可能需要相对较少的功能性光感受器细胞，因此即使是低效率的锥状光感受器移植也可能带来临床效益。干细胞生物学在过去十年中取得了非凡的进展，我们和其他人现在有能力从各种干细胞来源中产生大量可移植的光感受器。虽然有一些报道表明在移植的光感受器和宿主双极细胞之间形成了新的连接，但实现强大的功能性突触连接仍然是一个重大挑战，特别是在晚期视网膜疾病中，视网膜可以经历许多，通常是抑制性的变化。我们有新的和令人兴奋的数据，证明了通过移植人类干细胞来源的光感受器来挽救视觉功能（小鼠模型）晚期视网膜疾病的可行性。最重要的是，这种拯救似乎确实是由供体和宿主神经元之间新突触连接的形成所介导的。在这个项目中，我们将建立干细胞来源的锥状光感受器移植后突触连接的完整程度，这可以用现有的方法来实现。然后，我们寻求开发新的方法来进一步改善功能连接，以便在晚期退行性视网膜疾病的动物模型中恢复日光视力。为此，我们将开展以下调查：我们将(i)使用目前报道的方案进行实验，以确定移植细胞和宿主眼睛之间的功能连接程度；（ii）确定可能限制移植后新功能连接数量的重要相互作用，并制定改善连接和恢复视力的策略。总之，这些实验使用小鼠和人类胚胎干细胞衍生的供体细胞和啮齿动物的晚期视网膜疾病模型，将为我们提供一个框架，以发展类似的方法来治疗人类疾病。

Hereditary retinal disease and age-related macular degeneration (AMD) are major causes of irreversible blindness in the UK. Inherited retinal dystrophies affect 1 in 2,500, usually during childhood or early adulthood, while AMD affects 1:3 over the age of 75. The number of number of people in the UK affected by sight loss is set to double, to 4 million, by 2050 and sight loss is estimated to cost the UK economy £28bn a year, directly and indirectly. At present, we lack effective treatments for these conditions and there is an urgent requirement to develop new therapies. Both conditions involve the loss of the light sensitive cone and rod photoreceptor cells in the retina. Photoreceptor replacement aims to restore vision by the transplantation of healthy cells, ideally derived from a renewable source. Once transplanted these cells must form new connections (synapses) with their target cells, called bipolar cells, within the host retina. Restoring functional connectivity following transplantation is an ambitious goal for CNS repair. Nonetheless, the macula, which is crucial for high acuity daylight vision occupies a small area and relatively few functional photoreceptor cells may be required to achieve useful vision, so even low efficiency cone photoreceptor transplantation may result in clinical benefit. Stem cell biology has seen extraordinary progress in the past decade and we, and others, now have the ability to generate of large numbers of transplantable photoreceptors from a variety of stem cell sources. While there are some reported indications of new connections being formed between transplanted photoreceptors and host bipolar cells, achieving robust functional synaptic connectivity remains a significant challenge, particularly in advanced retinal disease, where the retina can undergo many, often inhibitory, changes. We have new and exciting data that demonstrates the feasibility of rescuing visual function (mouse models of) advanced retinal disease by transplantation of human stem cell-derived photoreceptors. Most importantly, this rescue does indeed appear to be mediated by the formation of new synaptic connections between the donor and host neurons. In this project, we will establish the full extent of synaptic connections following transplantation of stem cell-derived cone photoreceptors that can be achieved used current methods. We then seek to develop new methods to further improve functional connectivity in order to restore daylight vision in animal models of advanced degenerative retinal disease. We will conduct the following investigations to achieve this goal. We will (i) perform experiments to establish the extent of functional connectivity between transplanted cells and the host eye using current reported protocols, (ii) identify important interactions that may limit the number of new functional connections made after transplantation and develop strategies to improve connectivity and restore vision. Together, these experiments using both murine and human embryonic stem cell-derived donor cells and rodent models of advanced retinal disease will provide the framework for us to move to developing similar approaches to treat human disease.