Molecular mechanisms of synapse development and plasticity

通过使用基因敲低和敲除小鼠，我们证明了BAD-BAX-半胱天冬酶-3级联诱导NMDA受体依赖性LTD和AMPA受体内吞作用，但不诱导mGluR-LTD或突触传递的长时程增强作用（Li等人，Cell 2010; Jiao等人，Neuron 2011）。然而，与细胞凋亡不同，BAD仅短暂和轻度激活，导致不足以诱导细胞死亡的适度和短暂的半胱天冬酶-3激活。我们的研究结果揭示了LTD诱导的核心信号级联反应，并提供证据表明caspase-3激活的机制和定量差异对于确定它是否诱导LTD或凋亡至关重要。 为了确定BAD-BAX-caspase-3级联是否调节突触传递的其他特性，我们测量了诱发和自发兴奋性突触反应，并使用电子显微镜评估敲除小鼠突触的超微结构。为了确定促进LTD和AMPA受体内吞作用的BAD-BAX-caspase-3级联的下游效应物，我们与桑迪马基博士合作，寻找在LTD中裂解的caspase底物。我们将使用电生理学来确定所确定的caspase底物是否参与LTD诱导。 我们之前与Richard Youle博士合作研究了BAX在维持线粒体形态中的功能（Norris et al.，细胞死亡与分化（Cell Death and Differentiation）2010线粒体形态对于线粒体支持突触的发育和功能是重要的。为了测试BAD-BAX-半胱天冬酶-3级联是否调节线粒体形态，我们检查了BAD、BAX和半胱天冬酶-3敲除小鼠的线粒体。我们在BAD和BAX基因敲除的神经元中发现了一个片段化的线粒体表型和线粒体融合缺陷。因此，我们认为BAD是BAX维持神经元线粒体形态的重要激活剂。

By using gene knockdown and knockout mice, we demonstrated that the BAD-BAX-caspase-3 cascade is to induce NMDA receptor-dependent LTD and AMPA receptor endocytosis, but not for mGluR-LTD or long-term potentiation of synaptic transmission (Li et al., Cell 2010; Jiao et al., Neuron 2011). Unlike in apoptosis, however, BAD is activated only transiently and mildly leading to modest and transient caspase-3 activation insufficient to induce cell death. Our findings reveal a core signaling cascade for LTD induction and provide evidence that mechanistic and quantitative differences in caspase-3 activation are critical for determining whether it induces LTD or apoptosis. To determine if the BAD-BAX-caspase-3 cascade regulates other properties of synaptic transmission, we measured evoked and spontaneous excitatory synaptic response, and using electron microscopy to assess the ultrastructure of synapse in the knockout mice. To identify downstream effectors of the BAD-BAX-caspase-3 cascade that promotes LTD and AMPA receptor endocytosis, we collaborate with Dr. Sandy Markey to search for caspase substrates that are cleaved in LTD. We will use electrophysiology to determine if the identified caspase substrate is involved in LTD induction. We have previously collaborated with Dr. Richard Youle to examine the function of BAX in the maintenance of mitochondrial morphology (Norris et al., Cell Death and Differentiation 2010). Mitochondria morphology is important for mitochondria to support the development and function of synapses. To test whether the BAD-BAX-caspase-3 cascade regulates mitochondria morphology, we have examined mitochondria in BAD, BAX and caspase-3 knockout mice. We identified a fragmented mitochondrial phenotype and mitochondrial fusion defect in BAD and BAX knockout neurons. Therefore, we propose that BAD is an important activator of BAX for maintenance of mitochondria morphology in neurons.