The amyloid precursor protein regulates synaptic transmission at medial perforant path synapses

The perforant path provides the main cortical excitatory input to the hippocampus. Due to its important role in information processing and coding, entorhinal projections to the dentate gyrus have been studied in considerable detail. Nevertheless, a characterization of synaptic transmission between individual connected pairs of entorhinal stellate cells and dentate granule cells is still pending. Here, we have used organotypic entorhino-hippocampal tissue cultures, in which the entorhino-dentate (EC-GC) projection is present and EC-GC pairs can be studied using whole-cell patch clamp recordings. Using cultures of wildtype mice, the properties of EC-GC synapses formed by afferents from the lateral and medial entorhinal cortex were compared and differences in short-term plasticity were revealed. Since the perforant path is severely affected in Alzheimer´s disease, we used cultures of APP-deficient mice to address the role of the amyloid-precursor protein (APP) at this synapse. APP-deficiency caused alterations in excitatory neurotransmission at medial perforant path synapses that were accompanied by transcriptomic and ultrastructural changes. Moreover, the deletion of pre- but not postsynaptic APP through the local injection of Cre-expressing AAVs in conditional APPflox/flox tissue cultures increased the efficacy of neurotransmission at perforant path synapses. Together, these data suggest a physiological role for presynaptic APP at medial perforant path synapses, which may be adversely affected under conditions of altered APP processing. Overall design: Comparative gene expression profiling analysis of RNA-seq data for dentate gyrus samples from APP-deficient and wildtype animals.

穿通通路（perforant path）是向海马体（hippocampus）提供主要皮层兴奋性输入的神经通路。鉴于其在信息处理与编码中的关键作用，学界对内嗅皮层向齿状回（dentate gyrus）的投射已开展了相当细致的研究。然而，针对单个配对连接的内嗅皮层星状细胞与齿状回颗粒细胞之间突触传递的特征描述仍未完成。本研究采用器官型内嗅皮层-海马组织培养体系：该体系保留了内嗅皮层-齿状回（EC-GC）投射通路，且可通过全细胞膜片钳记录（whole-cell patch clamp recordings）对EC-GC细胞对进行研究。研究以野生型小鼠（wildtype mice）的组织培养物为材料，对比了外侧内嗅皮层与内侧内嗅皮层传入纤维所形成的EC-GC突触的特性，揭示了二者在短时程可塑性（short-term plasticity）上的差异。鉴于穿通通路在阿尔茨海默病（Alzheimer´s disease）中会受到严重损害，本研究同时使用APP敲除小鼠（APP-deficient mice）的组织培养物，探究淀粉样前体蛋白（amyloid-precursor protein, APP）在该突触中的功能。APP敲除会改变内侧穿通通路突触的兴奋性神经传递（excitatory neurotransmission），并伴随转录组学（transcriptomic）与超微结构（ultrastructural）层面的改变。此外，在条件性APPflox/flox组织培养物中，通过局部注射表达Cre的腺相关病毒（Cre-expressing AAVs）删除突触前APP（而非突触后APP），可提升穿通通路突触的神经传递效能。综上，本研究数据表明，突触前APP在内侧穿通通路突触中发挥生理功能，且该功能可能在APP加工异常的情况下受到不利影响。整体实验设计：对APP敲除小鼠与野生型动物的齿状回样本进行RNA测序（RNA-seq）数据分析，开展对比基因表达谱分析。