Role of Bcl-xl in synaptic plasticity in the hippocampus

描述（由申请人提供）：海马侧侧CA1突触的Schaffer突触传递的长期增强可能是记忆储存的基础。在阿尔茨海默病、帕金森氏病和其他神经退行性疾病中，突触的增强会随着突触的减少或收缩而变得功能失调。频繁活动后突触可塑性的一个重要方面是AMPA受体插入突触后质膜的增强。然而，除了突触后的变化之外，还会发生持久的突触前变化。在发育过程中，囊泡池的大小增加以处理更频繁发生的突触事件，但对成年CA1突触在高频事件后持久的突触前可塑性的作用尚未完全研究。突触前可塑性的一种形式是囊泡恢复到容易释放的池的速率的持久变化。在突触活动期间，囊泡释放可用性的减少表现为突触抑制；突触抑制后囊泡池的恢复速度影响突触的反应能力，因此可适应可塑性。我们之前已经发现抗死亡蛋白Bcl-xL不仅可以防止神经元的躯体死亡，还可以防止急性和长期的突触抑制。在某种程度上，Bcl-xL的作用是提高易释放的突触囊泡池的恢复速度。我们最近的初步数据表明，Bcl-xL直接与囊泡膜结合，在突触活动期间提高囊泡从质膜再摄取的速率。然而，除了囊泡再摄取外，我们的数据还表明，Bcl-xL通过调节突触代谢，可能影响储备池中囊泡的动员。这项应用的假设是，Bcl-xL通过提高线粒体效率，增加突触囊泡储备池的动员，从而引起突触强度的长期变化。在这个提议中，我们将通过测量在培养和体内海马神经元中受到刺激的活突触前钮扣中ATP水平和氧摄取的持续变化来研究线粒体效率的急性和长期变化。利用成像和记录技术，我们将区分Bcl-xL对质膜上囊泡再吸收的影响和对储备池动员的影响，以确定线粒体效率对不同囊泡再积累策略的影响。我们还将研究Bcl-x对神经元兴奋性抑制引起的囊泡池抑制的长期影响。与活性降低相反，突触活性的增加可能与ATP可用性的增强有关，直接促进下游靶点的磷酸化和激活，如突触蛋白，这些靶点可迅速将囊泡从储备池释放到易释放池。我们的研究将揭示在学习和记忆过程中加强突触或在突触功能障碍或神经变性过程中削弱突触的基本特性。

DESCRIPTION (provided by applicant): At the hippocampal Schaffer collateral to CA1 synapse long term enhancement of synaptic transmission may underlie memory storage. Synaptic strengthening can become dysfunctional in Alzheimer's disease, Parkinson's Disease and other neurodegenerative disorders as synapses decline or are retracted. One important aspect of synaptic plasticity after frequent activity is the enhanced insertion of AMPA receptors into the postsynaptic plasma membrane. In addition to postsynaptic changes, however, long lasting presynaptic changes occur. During development vesicle pool sizes increase to handle more frequently occurring synaptic events, but the role of long lasting presynaptic plasticity at the adult CA1 synapse after high frequency events has been incompletely studied. One form of presynaptic plasticity is a long lasting change in the rate at which vesicles recover to readily releasable pools. During synaptic activity, a decrease in availability of vesicles for release manifests as synaptic depression; the rate at which vesicle pools recover after synaptic depression affects the response capabilities of the synapse and is therefore amenable to plasticity. We have found previously that the anti-death protein Bcl-xL acts not only to prevent somatic death in neurons, but to prevent synaptic depression acutely and over the long term. In part Bcl-xL functions to enhance the rate of recovery of the readily releasable pool of synaptic vesicles. Our recent preliminary data show that Bcl-xL binds directly to vesicle membranes, enhancing the rate of vesicle re-uptake from the plasma membrane during synaptic activity. In addition to vesicle re-uptake, however, our data also show that Bcl-xL, by its regulation of synaptic metabolism, may affect mobilization of vesicles from the reserve pool. The hypothesis of this application is that Bcl-xL causes long term changes in synaptic strength by enhancing mitochondrial efficiency to increase mobilization of a reserve pool of synaptic vesicles. In this proposal, we will study acute and long term changes in mitochondrial efficiency by measuring ongoing changes in ATP levels and oxygen uptake in living presynaptic boutons undergoing stimulation in hippocampal neurons both in culture and in vivo. Using imaging and recording techniques, we will differentiate the effects of Bcl-xL on vesicle re-uptake at the plasma membrane from those on reserve pool mobilization to determine the effect of mitochondrial efficiency on different vesicle re-accumulation strategies. We will also study the effects of Bcl-x on long term changes in vesicle pool depression brought on by inhibition of neuronal excitability. In contrast to decreased activity, increased synaptic activity may be associated with enhanced ATP availability, directly promoting phosphorylation and activation of downstream targets such as synapsin that rapidly release vesicles from the reserve to the readily releasable pool. Our studies will shed light on basic properties that strengthen the synapse during learning and memory or weaken it during synaptic dysfunction or neurodegeneration.