A single-cell transcriptomic map of the human developing cortex in Down syndrome

人类大脑是一个高度复杂的系统，由数十亿个相互连接的神经元组成，形成功能性神经回路。正常的大脑功能依赖于神经元之间的有效通信，这一过程需要建立正常的神经网络活动模式。影响大脑的几种疾病是由神经元之间的通信障碍引起的，这就是为什么必须了解神经回路最初是如何建立的以及所涉及的机制。我们特别感兴趣的是了解神经网络活动的出现如何受到未成熟胎儿大脑和唐氏综合征（DS）中各种细胞类型的精确组成的控制。DS是一种常见的神经发育障碍，是由21号染色体三体（Ts 21）引起的先天性智力残疾的主要原因。我们对潜在的细胞和分子机制的理解的进展受到了有限的模型系统的阻碍，这些模型系统概括了这种复杂的染色体条件。然而，未成熟人脑中的细胞分析集中在死后固定的组织样本上，这不能提供对动态事件的直接观察，例如电活动模式的形成。这一局限性提出了如何研究人类神经回路组装及其功能障碍的细胞和分子机制的问题。我的团队最近开发了一种新方法，使用移植的供体来源的诱导多能干细胞（iPSC）和纵向体内成像实时研究人类神经元网络的建立。这种实验设计允许在几周内研究血管化的人类移植物中的人类神经网络活性，克服了目前体外方法的几个限制（例如缺乏血管）。我们发现，神经元活动是不同步的DS，这可能有助于认知缺陷DS。我们还发现了皮质体积的减少，并确定了一个潜在的分子机制。随着前景的发展战略，以纠正缺陷的布线的胎儿大脑在DS，我们将获得一个地图的所有类型的细胞，其中填充发展中的DS皮质。该图谱将识别缺失/减少或成熟延迟的皮质细胞群，这可以解释DS大脑的尺寸减小及其活动模式改变。我们将利用强大的遗传工具，可以探测DS大脑中单个细胞的内容，以及移植到实验室动物大脑中的人类细胞。因此，本研究提案的最终目的是获得对调节人类皮层回路建立的细胞和分子机制的新的和基本的见解，希望这些知识将在未来转化为拯救DS网络活动缺陷的新方法，并指导治疗策略的发展。

The human brain is a highly complex system comprised of billions of neurons interconnected to each other to form functional neural circuits. Normal brain function is dependent on effective communication between neurons, a process that requires the establishment of normal patterns of neural network activity. Several diseases that affect the brain result from impairments in the communication between neurons, which is why it is essential to understand how neural circuits are initially established and the mechanisms involved. We are particularly interested in understanding how the emergence of neural network activity can be controlled by the precise composition of various cell types in the immature foetal human brain and in Down syndrome (DS). DS is a common neurodevelopmental disorder and a major cause of congenital intellectual disability caused by a trisomy of Chromosome 21 (Ts21). Advances in our understanding of the underlying cellular and molecular mechanisms have been hampered by the limited availability of model systems that recapitulate this complex chromosomal condition. Cellular analyses in the immature human brain though focus on post-mortem fixed tissue samples, which cannot provide direct observation of dynamic events such the formation of electrical activity patterns. This limitation raises the question of how to study the cellular and molecular mechanisms of human neural circuit assembly and their dysfunction in DS. My team has recently developed a new approach to study in real-time the establishment of human neuronal networks using transplanted donor-derived induced pluripotent stem cells (iPSC) and longitudinal in vivo imaging. This experimental design allows the study of human neural network activity in a vascularized human graft over several weeks, overcoming several limitations of current in vitro approaches (e.g. the lack of blood vessels). We showed that neuronal activity is less synchronous in DS, which could contribute to cognitive deficits in DS. We also found a reduction in cortical volume and identified a potential molecular mechanism. With the prospect of developing strategies to correct defects in the wiring of the fetal brain in DS, we will obtain a map of all the cell types, which populate the developing DS cortex. This map will identify cortical cell populations which are either missing/reduced or whose maturation is delayed, which could explain the reduced size of the DS brain and its altered activity patterns. We will take advantage of powerful genetic tools that allow to probe the content of individual cells in the DS brain and in human cells transplanted in the brain of laboratory animals. The ultimate aim of this research proposal is therefore to gain new and fundamental insights into the cellular and molecular mechanisms that regulate the establishment of human cortical circuits, in the hope that this knowledge will, in the future, translate into new ways to rescue the network activity deficits in DS and guide the development of therapeutic strategies.