Mechanisms Modulating Cytoskeletal Dynamics During Schwann Cell Myelination

髓鞘形成允许动作电位在神经系统中快速传播。DYS和脱髓鞘障碍是影响年轻人的最常见的神经病理。髓鞘胶质细胞，如周围神经系统的雪旺细胞，在形态上经历了特定阶段的变化，使它们能够在轴突周围形成髓鞘。调控肌动蛋白动力学以响应外源性轴突和细胞外基质信号的信号通路在很大程度上是未知的。我们最近报道，ErbB和B1整合素受体的激活诱导了神经纤维瘤病2型肿瘤抑制因子Schwannomin的磷酸化。Schwannomin将受体连接到肌动蛋白细胞骨架上，并调节CDC42/racGTP酶的活性。因此，它被定位为将受体活性与肌动蛋白动力学联系起来，并触发髓鞘形成所需的细胞形态的变化。我们假设Sch通过p21激活的激酶(PAK)-LIM激酶-Cofilin途径调节肌动蛋白聚合。在目标1中，我们建议阐明Cofilin在雪旺细胞髓鞘形成过程中的作用。我们将在体外比较正常和粘连蛋白缺陷雪旺细胞对髓鞘轴突的能力。在目标2中，我们将评估NeuRegin和Laminin是否调节L1MK和Cofilin的磷酸化。我们将通过对正常和粘附素缺乏的雪旺细胞进行活体成像实验，确定雪旺细胞是否需要粘附素来响应NRG和层粘连蛋白刺激来重塑其质膜。这项工作的直接结果将是确定雪旺细胞使用的一种新途径，以产生与髓鞘形成相关的受体特异性形态变化。如果成功，这项工作将提供第一个由轴突和基底板配体启动的信号级联的完整图谱，最终终止于下游的效应蛋白-肌动蛋白。这些信息将影响越来越具体的药物靶点的确定，以开发髓鞘疾病和其他雪旺细胞疾病的单一和联合治疗方法，如神经纤维瘤病和神经鞘瘤病。

Myelination allows rapid propagation of action potentials in the nervous system. Dys- and demyelinating disorders are among the most common neurological pathologies affecting young adults. Myelinating glial cells such as Schwann cells of the peripheral nervous system undergo stage specific changes in morphology that enable them to elaborate myelin around an axon. The signaling pathways that regulate actin dynamics in response to extrinsic axonal and extracellular matrix cues are largely unknown. We recently reported that activation of ErbB and B1 integrin receptors induces phosphorylation of Schwannomin, the Neurofibromatosis type 2 tumor suppressor. Schwannomin links receptors to the actin cytoskeleton and modulates the activity of Cdc42/RacGTPase. Thus it is positioned to link receptor activity to actin dynamics and trigger changes in cellular morphology needed for myelination. We hypothesize that Sch modulates actin polymerization through a p21activated kinase (PAK) - LIM kinase - cofilin pathway. In Aim 1, we propose to elucidate the function of cofilin during Schwann cell myelination. We will compare the ability normal and cofilin-deficient Schwann cells to myelinate axons in vitro. In Aim 2, we will assess whether neuregulin and laminin regulate LlMK and cofilin phosphorylation. We will determine whether cofilin is needed for Schwann cells to remodel their plasma membrane in response to NRG and laminin stimulation by conducting live imaging experiments with normal and cofilin-deficient Schwann cells. The immediate outcome of this work will be to identify a novel pathway used by Schwann cells to produce receptor specific changes in morphology associated with myelination. If successful, this work will provide the first complete map of a signaling cascade initiated by axonal and basal lamina ligands that terminates at the final downstream effector protein, actin. This information will impact the identification of increasingly specific drug targets for development of single and combinatorial therapies for myelinating disorders and other Schwann cell disorders such as Neurofibromatosis and Schwannomatosis.