Molecular mechanisms of human synapse formation induced by secreted bloodborne factors

突触是神经元之间的单一连接，能够在大脑中快速传递和处理信息。突触的形成由两种类型的组织分子引导：在神经元细胞表面表达的粘附分子和脑内或其他器官外部产生的分泌因子。特别令人感兴趣的是在血液中循环的“全身因素”，这些因素已被证明可以增强小鼠的学习和记忆。这项研究的目的是了解这些系统性因素是否以及如何作用于人类神经元来调节突触的形成。首先，我们将使用从干细胞中衍生的人类神经元来筛选结构蛋白、生长因子和激素，以了解它们对突触数量和活动的直接影响。这将通过用每种全身因子处理人类神经元并测量神经元网络的活性和个体神经元对电刺激的突触反应的变化来实现。其次，我们将结合联合收割机生物化学和基因编辑方法来鉴定与系统因子结合并引发内部细胞反应以触发突触组装和活动的神经元受体蛋白。最后，我们将生成具有专门组织层的人类“迷你脑”类器官，该组织层在内部类器官流体和外部环境之间形成选择性屏障。我们将测试系统性因素是否可以跨越这一选择性屏障，并使用高分辨率显微镜和电网络活动的全球测量来研究对类器官突触形成的潜在影响。我们的机制见解将建立系统环境和脑功能之间的因果关系，并可能最终为突触丢失驱动的神经退行性疾病的治疗策略提供信息。

Synapses are unitary connections between neurons that enable rapid transfer and processing of information in the brain. Synapse formation is guided by two types of organizer molecules: adhesion molecules expressed at the neuronal cell surface and secreted factors produced inside the brain or externally by other organs. Of particular interest are "systemic factors" circulating in the bloodstream that have been shown to enhance learning and memory in mice. The goal of this research is to understand whether and how these systemic factors act on human neurons to regulate synapse formation. First, we will use human neurons derived from stem cells to screen structural proteins, growth factors and hormones for direct effects on synapse number and activity. This will be accomplished by treating the human neurons with each systemic factor and measuring changes in the activity of neuronal networks and in the synaptic responses of individual neurons to electrical stimulation. Second, we will combine biochemical and gene editing approaches to identify neuronal receptor proteins that bind to the systemic factors and elicit internal cellular responses to trigger synapse assembly and activity. Finally, we will generate human "mini-brain" organoids with a specialized tissue layer that forms a selective barrier between the internal organoid fluid and the external environment. We will test whether systemic factors can cross this selective barrier and examine potential effects on organoid synapse formation using high-resolution microscopy and global measurements of electrical network activity. Our mechanistic insights will establish a causal link between the systemic environment and brain function and may ultimately inform therapeutic strategies for neurodegenerative diseases driven by synapse loss.