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

人脑是一个高度复杂的系统，由数十亿个神经元相互连接，形成功能性的神经回路。正常的脑功能依赖于神经元之间的有效交流，这一过程需要建立正常的神经网络活动模式。一些影响大脑的疾病是由于神经元之间的交流受损造成的，这就是为什么了解神经回路最初是如何建立的以及涉及的机制是至关重要的。我们特别感兴趣的是了解神经网络活动的出现是如何通过未成熟胎儿人类大脑和唐氏综合症（DS）中各种细胞类型的精确组成来控制的。退行性椎体滑移是一种常见的神经发育障碍，也是21号染色体三体（Ts21）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概括这种复杂染色体状况的模型系统的有限可用性的阻碍。未成熟人脑的细胞分析主要集中在死后的固定组织样本上，不能直接观察到电活动模式的形成等动态事件。这一局限性提出了如何研究退行性痴呆中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的方法，利用移植的供体来源的诱导多能干细胞（iPSC）和纵向体内成像来实时研究人类神经网络的建立。这种实验设计允许在几个星期内研究带血管的人类移植物中的人类神经网络活动，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在退行性椎体滑移中不太同步，这可能导致退行性椎体滑移的认知缺陷。我们还发现皮质体积减少，并确定了潜在的分子机制。随着开发策略来纠正DS胎儿大脑的线路缺陷的前景，我们将获得所有细胞类型的地图，这些细胞类型填充发育中的DS皮层。这张图谱将识别皮层细胞群缺失/减少或成熟延迟，这可以解释退行性痴呆大脑体积缩小及其活动模式改变的原因。我们将利用强大的遗传工具来探测DS大脑和移植到实验动物大脑中的人类细胞中的单个细胞的含量。因此，本研究计划的最终目的是对调节人类皮层回路建立的细胞和分子机制获得新的和基本的见解，希望这些知识将在未来转化为拯救退行性痴呆的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.