Lee Sang Hun, Lutz David, Mossalam Mohanad, Bolshakov Vadim Y, Frotscher Michael, Shen Jie
Department of Neurology, Brigham & Women's Hospital, Harvard Medical School, Boston, MA, 02115, USA.
Institute for Structural Neurobiology, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, D-20246, Hamburg, Germany.
Mol Neurodegener. 2017 Jun 15;12(1):48. doi: 10.1186/s13024-017-0189-5.
Presenilins play a major role in the pathogenesis of Alzheimer's disease, in which the hippocampus is particularly vulnerable. Previous studies of Presenilin function in the synapse, however, focused exclusively on the hippocampal Schaffer collateral (SC) pathway. Whether Presenilins play similar or distinct roles in other hippocampal synapses is unknown.
To investigate the role of Presenilins at mossy fiber (MF) synapses we performed field and whole-cell electrophysiological recordings and Ca imaging using acute hippocampal slices of postnatal forebrain-restricted Presenilin conditional double knockout (PS cDKO) and control mice at 2 months of age. We also performed quantitative electron microscopy (EM) analysis to determine whether mitochondrial content is affected at presynaptic MF boutons of PS cDKO mice. We further conducted behavioral analysis to assess spatial learning and memory of PS cDKO and control mice at 2 months in the Morris water maze.
We found that long-term potentiation and short-term plasticity, such as paired-pulse and frequency facilitation, are impaired at MF synapses of PS cDKO mice. Moreover, post-tetanic potentiation (PTP), another form of short-term plasticity, is also impaired at MF synapses of PS cDKO mice. Furthermore, blockade of mitochondrial Ca efflux mimics and occludes the PTP deficits at MF synapses of PS cDKO mice, suggesting that mitochondrial Ca homeostasis is impaired in the absence of PS. Quantitative EM analysis showed normal number and area of mitochondria at presynaptic MF boutons of PS cDKO mice, indicating unchanged mitochondrial content. Ca imaging of dentate gyrus granule neurons further revealed that cytosolic Ca increases induced by tetanic stimulation are reduced in PS cDKO granule neurons in acute hippocampal slices, and that inhibition of mitochondrial Ca release during high frequency stimulation mimics and occludes the Ca defects observed in PS cDKO neurons. Consistent with synaptic plasticity impairment observed at MF and SC synapses in acute PS cDKO hippocampal slices, PS cDKO mice exhibit profound spatial learning and memory deficits in the Morris water maze.
Our findings demonstrate the importance of PS in the regulation of synaptic plasticity and mitochondrial Ca homeostasis in the hippocampal MF pathway.
早老素在阿尔茨海默病的发病机制中起主要作用，其中海马体特别脆弱。然而，先前关于早老素在突触中功能的研究仅聚焦于海马体的谢弗侧支（SC）通路。早老素在其他海马体突触中是否发挥相似或不同的作用尚不清楚。
为了研究早老素在苔藓纤维（MF）突触中的作用，我们使用出生后前脑限制性早老素条件性双敲除（PS cDKO）小鼠和2月龄对照小鼠的急性海马体切片进行了场电位和全细胞膜片钳电生理记录以及钙成像。我们还进行了定量电子显微镜（EM）分析，以确定PS cDKO小鼠突触前MF终扣处的线粒体含量是否受到影响。我们进一步进行了行为分析，以评估2月龄PS cDKO小鼠和对照小鼠在莫里斯水迷宫中的空间学习和记忆能力。
我们发现，PS cDKO小鼠的MF突触处长期增强以及短期可塑性，如双脉冲和频率易化，均受损。此外，强直后增强（PTP），另一种短期可塑性形式，在PS cDKO小鼠的MF突触处也受损。此外，线粒体钙外流的阻断模拟并掩盖了PS cDKO小鼠MF突触处的PTP缺陷，表明在缺乏PS的情况下线粒体钙稳态受损。定量EM分析显示，PS cDKO小鼠突触前MF终扣处线粒体的数量和面积正常，表明线粒体含量未改变。齿状回颗粒神经元的钙成像进一步显示，急性海马体切片中PS cDKO颗粒神经元在强直刺激诱导下的胞质钙增加减少，并且高频刺激期间线粒体钙释放的抑制模拟并掩盖了在PS cDKO神经元中观察到的钙缺陷。与急性PS cDKO海马体切片中MF和SC突触处观察到的突触可塑性损伤一致，PS cDKO小鼠在莫里斯水迷宫中表现出严重的空间学习和记忆缺陷。
我们的研究结果证明了PS在调节海马体MF通路中的突触可塑性和线粒体钙稳态方面的重要性。
