Evolutionary Conserved Mechanisms of Neuronal Degeneration and Regeneration

项目摘要 大脑功能的逐渐丧失和神经退行性变是不同门的衰老的共同特征。 了解中枢神经系统（CNS）如何在其一生中再生神经元是神经科学的一个主要领域。 对再生医学感兴趣神经干细胞（NSC）和CNS发育和生物学的研究 一直是一个活跃的研究领域，然而，我们对调节人类行为的精确发育程序的了解， 老化过程中的NSC动力学是有限的，这是由于长期NSC的罕见性，在老化过程中监测NSC的困难， 以及小鼠和人类大脑难以置信的复杂性。在这份提案中，我们试图了解基本的 神经元再生、变性和衰老的原理和进化保守元素 Schlosseri葡萄球菌，一种具有简单CNS的原始脊索动物，表现出可检测和频繁（每周）CNS 组织再生和退化在整个成年生活中，这可以在体内监测，由于其近 透明的身体。这些生物可以通过配子进行有性繁殖，也可以通过茎进行无性繁殖 细胞介导的出芽过程。随着新一代的芽发育成成熟的个体（zoids）， 经历了程序性细胞死亡的同步波。在每周的再生过程中， 退化周期新的大脑在幼芽中形成，与旧的类人猿大脑的破坏相一致 (Fig 1）。这个模型系统提供了一个独特的机会，研究细胞和分子机制，指导 年轻和年老菌落中CNS生成和退化的每周周期（例如<3 months vs. >9年），以及 以确定在其中枢神经系统DNA中积累的突变，这些干细胞在其一生中持续存在。的 葡萄球菌基因组编码数百个与哺乳动物同源的脑相关基因。我们采取了 一个系统的分子（转录组），细胞（流式细胞仪）形态和行为表征的老年人 和年轻的殖民地（图2）。Botryllus转录组分析揭示了393个与阿尔茨海默氏症相关的基因 在年轻和年老的集落之间差异表达疾病（图2C-D）。血液分析显示 在老葡萄球菌菌落中吞噬细胞的频率增加（图2A-B），类似于年龄相关的 在小鼠和人HSC中转移以有利于髓样细胞。形态和功能分析发现， 旧的集落较小，含有较少数量的细胞，对刺激的反应降低（图2 E-F）。 由于干细胞是唯一能够自我更新并在整个殖民地生命周期中得以维持的细胞， 假设NSC中随时间积累的基因突变是与年龄相关的主要原因， 神经退行性疾病为了验证这一假设，我们计划表征分子和细胞的多样性， 在年轻和年老的菌落中，分离其NSC，鉴定在NSC中积累的突变， 祖细胞DNA，并测试其对脑再生和功能的影响。

Project Summary Gradual loss of brain function and neurodegeneration are common features of aging throughout diverse phyla. Understanding how the central nervous system (CNS) regenerates neurons throughout its life is a major area of interest in regenerative medicine. The study of neural stem cells (NSC) and CNS development and biology has been an active field of research, however, our knowledge of the precise developmental programs that regulate NSC dynamics during aging is limited due to the rarity of long term NSCs, the difficulty of monitoring NSCs in- vivo, and the incredible complexity of mouse and human brains. In this proposal we seek to understand basic principles and evolutionary conserved elements of neuronal regeneration, degeneration and aging using Botryllus schlosseri, a primitive chordate with a simple CNS that exhibits assayable and frequent (weekly) CNS tissue regeneration and degeneration throughout adult life, that can be monitored in vivo thanks to its nearly transparent body. These organisms can reproduce either sexually through gametes, or asexually through a stem cell mediated budding process. As a new generation of buds develop into mature individuals (zooids) the bodies of the old zooids undergo a synchronized wave of programmed cell death. During this weekly regeneration and degeneration cycle new brains form within the young buds in concert with the destruction of the old zooids’ brain (Fig 1). This model system offers a unique opportunity to study the cellular and molecular mechanisms that direct weekly cycles of CNS generation and degeneration in young and old colonies (e.g. <3 months vs. >9 years) and to identify mutations that accumulate in the DNA of its CNS, stem cells that persist throughout its life. The Botryllus genome encodes hundreds of brain-associated genes with mammalian homologs. We have undertaken a systematic molecular (transcriptomic), cellular (FACS) morphological and behavioral characterization of old and young colonies (Fig 2). Botryllus transcriptome analyses revealed 393 genes that correlate with Alzheimer’s disease are differentially expressed between young and old colonies (Fig 2C-D). Blood analysis showed an increased frequency of phagocytic cells in old Botryllus colonies (Fig 2A-B), analogous to the age-associated shift in mouse and human HSC to favor myeloid cells. Morphological and functional analysis found that the brains of old colonies are smaller, contain a lower number of cells and have reduced response to stimuli (Fig 2E-F). Since stem cells are the only cells that self-renew and are maintained throughout the colony’s life, we hypothesize that genetic mutations that accumulate over time in NSC are the main cause of age associated neurodegenerative diseases. To test this hypothesis, we plan to characterize the molecular and cellular diversity of the Botryllus brain in young and old colonies, isolate its NSCs, identify mutations that accumulate in NSC and progenitor cells DNA, and test their effect on brain regeneration and function.