Unravelling the functions of Peptidyl-Prolyl Isomerase A in axonal transport and neuromuscular junction development and maintenance.

伴侣蛋白是每个细胞中必不可少的因子。通过控制蛋白质的正确折叠和组装，它们确保蛋白质在不同水平上的正确结构和功能。对于其他区室，周围神经系统（PNS）的活性受到适当的伴侣活性的影响，因为蛋白质的正确折叠和功能在细胞体、轴突和末端突触水平上是必要的。神经肌肉连接（NMJ）是一种三方突触，由神经元、肌肉和末端雪旺细胞共同创造和维持PNS与组织之间的联系。在PNS中，雪旺细胞可分为四组：包裹神经轴突并允许信号传递的髓鞘细胞，包裹轴突并使其分离的非髓鞘细胞，与神经元细胞体相关的卫星细胞，以及在NMJ中对突触生长、功能和维持至关重要的突触周围细胞。肽酰脯氨酸异构酶A （Peptidyl-Prolyl Isomerase A， PPIA）又称亲环蛋白A，是一种主要定位于中枢神经系统（CNS）的普遍表达的伴侣蛋白，在神经元中表达量最高。在中枢神经系统中，PPIA与神经元生长有关，它的缺失会导致聚集蛋白的增加。文献证据指出PPIA可能参与轴突运输和树突形成。PPIA可以通过不同的细胞类型在细胞外空间释放，并通过与其受体EMMPRIN（细胞外基质金属蛋白酶诱导剂）结合，可以作为促炎分子、趋化因子或基质金属蛋白酶（MMPs）释放的诱导剂。MMPs参与轴突生长和NMJ的形成和维持。除了PPIA在神经元中的高表达外，目前还没有研究涉及PPIA在PNS和外周突触（如NMJ）水平上的表达、释放和功能。本研究旨在首次探讨PPIA在PNS，特别是外周轴突和NMJs水平上的参与。我们将研究PPIA在运动神经元轴突延伸、引导和运输中的功能，以及PPIA在神经元、肌肉和雪旺细胞之间的信号传导中参与NMJ形成和维持的细胞内和细胞外的作用。我们期望描述PPIA在轴突生理学中的重要作用，从货物运输到肌肉中的突触沉降，并解读其在构成NMJ的不同细胞群中的作用，以及它们之间的交流。通过提出的研究计划，我们的目标是产生有助于理解和表征PNS的垫脚石结果，细胞群体在NMJ水平上的相互作用，以及从未被描述过的多任务伴侣蛋白如PPIA在上述隔室中的参与。

Chaperone proteins are essential factors in every cells. By governing the proper folding and assembly of proteins they ensure the correct structure and function of proteins at different levels. As for others compartments, the activity of peripheral nervous system (PNS) is influenced by a proper chaperones activity since the correct folding and function of proteins are necessary in the cell body, along the axon and at the terminal synaptic level. The neuromuscular junction (NMJ) is as tripartite synapse where neurons, muscles and terminal Schwann cells cooperate to create and maintain the connection between the PNS and tissues. In the PNS, Schwann cells can be divided into four main groups: the myelinating cells that wrap the axons in nerves and allows signal to be transmitted, the non-myelinating cells that wrap axons and keep them separated, the satellite cells that associate with neuronal cells body, and the perisynaptic cells that are essential at the NMJ for synaptic growth, function and maintenance. Peptidyl-Prolyl Isomerase A (PPIA), also known as cyclophilin A, is a ubiquitously expressed chaperone mainly localized in the central nervous system (CNS) with highest expression in neurons. In the CNS, PPIA has been implicated in neuronal growth and its absence induces an increase of aggregated proteins. Evidence from literature points out the possible involvement of PPIA in axonal transport and arborisation. PPIA can be released in the extracellular space by different cell types and, by binding to its receptor EMMPRIN (extracellular matrix metalloproteinase inducer), it can work as a proinflammatory molecule, as chemoattractant factor or as an inducer of matrix metalloproteinases (MMPs) release. MMPs are implicated in axonal growth and NMJ formation and maintenance. Except for its high expression in neurons, no studies have addressed the expression, release, and function of PPIA in the PNS and at the level of peripheral synapses like the NMJ. The present research program aims to investigate for the first time the involvement of PPIA in the PNS and, in particular, at the level of peripheral axons and NMJs. We will investigate the function of PPIA in axonal elongation, guidance and transport in motor neurons and the intracellular and extracellular involvement of PPIA in the signaling among neurons, muscles and Schwann cells in NMJ formation and maintenance. We expect to describe an essential role for PPIA in axonal physiology, from transport of cargos to synapse settlement in muscles, and to decipher its role both inside the different cellular populations that constitute the NMJ, and in their communication. With the proposed research program, we aim to produce steppingstone results that will contribute in the understanding and characterization of the PNS, the interplay of cellular populations at the NMJ level and a never described involvement of a multitasking chaperone protein like PPIA in the aforementioned compartments.