Circuit-based mechanisms of neuronal vulnerability in the adult EC

项目摘要/摘要。 内嗅皮层第二层(ECII)神经元是阿尔茨海默病(AD)中最早退化的细胞之一。ECII 轴突形成穿支通路，是进入海马体的主要皮质输入。穿孔剂通路支撑 记忆形成和空间导航贯穿一生，而这种输入的丧失与认知缺陷是一致的 它出现在公元早期。为了模拟AD中这种输入的丢失，Jankowsky实验室创造了一个化学遗传小鼠模型 穿透通路的破坏，其中ECII神经元亚群表达工程氯离子通道(GlyCl)以 防止动作电位的产生。我们出人意料地发现，内嗅神经元非常容易受到 沉默。在失活后不久，许多ECII神经元从齿状回收回轴突，表达前- 凋亡蛋白，然后从回路中消除。我们观察到类似的神经变性在消除后 神经递质与破伤风毒素(TeTX)的释放，证实神经元丢失不是GlyCl激活的伪影。 此外，这种沉默引起的退化并不被其他大脑区域所共享，因为前/副小结或 在神经元失活后，脾后皮质表现为细胞丢失。这表明内嗅器的特定特征 大脑皮层可能会使神经元对不活动产生脆弱性。一个可能的漏洞可能与 内嗅觉-海马环路。我们注意到，沉默后的ECII退化模式与 指导在发育过程中精炼穿孔途径的过程。在出生后早期，不活跃的ECII 神经元从回路中被修剪，这个过程是由局部活动的差异介导的，称为活动- 从属竞争。只有当神经元稀少地不活跃时-当所有细胞都相等时-投射才会被修剪 处于非活动状态，则不会删除任何内容。这项提议将检验关于驱动神经元死亡的细胞机制的两个假说 成熟的内嗅觉皮质。目标1将确定在成年ECII中是否存在依赖活动的竞争。 药理学和遗传学方法将被用来调节相对活动水平，以确定细胞死亡的方式 受相邻细胞活性差异的影响。目标2将确定突触后伙伴 促进ECII神经元存活。我们的初步数据表明，消除ECII释放的神经递质 神经元--没有阻断动作电位--足以引起变性。因此，我将使用药剂 以及减少齿状颗粒细胞中神经递质结合并消除其火灾能力的遗传方法 动作电位对ECII输入的反应。这将测试神经递质介导的信号传递或突触后 活动本身，是ECII神经元生存所必需的。来自这些目标的数据将决定活动中断可能 调节成人大脑中的细胞死亡。此外，这些数据可能表明，导致细胞死亡的机制在 出生后发育不一定局限于关键时期，但在某些特定时期内可能持续到成年期 小路。了解这些机制可能有助于未来对神经退行性疾病及其回路的研究 神经中断可能会导致神经元丢失。

Project summary/abstract. Entorhinal cortex layer II (ECII) neurons are some of the first cells to degenerate in Alzheimer’s Disease (AD). ECII axons form the perforant pathway and are the major cortical input into the hippocampus. The perforant pathway supports memory formation and spatial navigation throughout life, and loss of this input is consistent with the cognitive deficits that present early in AD. To mimic the loss of this input in AD, the Jankowsky lab created a chemogenetic mouse model of perforant pathway disruption in which a subset of ECII neurons express an engineered chloride channel (GlyCl) to prevent the generation of action potentials. We unexpectedly discovered that entorhinal neurons were highly vulnerable to silencing. Shortly after being inactivated, many ECII neurons retract their axons from the dentate gyrus, express pro- apoptotic proteins, and then are eliminated from the circuit. We observed similar neurodegeneration after eliminating neurotransmitter release with tetanus toxin (TeTX), confirming that neuronal loss is not an artifact of GlyCl activation. Further, this silencing-induced degeneration is not shared by other brain regions, as neither the pre/parasubiculum nor retrosplenial cortex exhibit cell loss after neuronal inactivation. This suggests that specific features of the entorhinal cortex may confer neuronal vulnerability to inactivity. One possible vulnerability could be related to the formation of entorhinal-hippocampal circuit. We noted that the pattern of ECII degeneration after silencing was strikingly similar to the processes that guide to refinement of the perforant pathway during development. In early post-natal periods, inactive ECII neurons are pruned from the circuit in a process that is mediated by local differences in activity, referred to as activity- dependent competition. Projections are only pruned when neurons are sparsely inactive - when all cells are equally inactive, none are removed. This proposal will test two hypotheses about the cellular mechanism driving neuronal death in the mature entorhinal cortex. Aim 1 will determine whether activity-dependent competition persists in the adult ECII. Pharmacological and genetic approaches will be used to modulate relative activity levels to determine how cell death is influenced by activity differences between neighboring cells. Aim 2 will determine whether post-synaptic partners promote the survival of ECII neurons. Our preliminary data suggests that eliminating neurotransmitter release from ECII neurons – without blocking action potentials - is sufficient to induce degeneration. I will therefore use pharmacological and genetic approaches to both reduce neurotransmitter binding in dentate granule cells and eliminate their ability to fire action potentials in response to ECII input. This will test whether neurotransmitter-mediate signaling, or post-synaptic activity itself, is required for ECII neuron survival. Data from these aims will determine how activity disruption may mediate cell death in the adult brain. Further, these data may suggest that mechanisms which drive cell death during postnatal development are not necessarily limited to critical periods but may persist into adulthood within certain pathways. Understanding these mechanisms may inform future studies on neurodegenerative disease and how circuit disruption may contribute to neuronal loss.