Transport of neurotrophic cytokines after spinal cord injury

足够的神经营养支持对于脊髓再生是必不可少的；然而，脊髓损伤(SCI)部位神经营养因子和神经营养因子的产生不足。血-脑/血-脊髓屏障(BBB/BSCB)介导外周选择性神经营养细胞因子的渗透。我们认为，脊髓损伤后，白血病抑制因子(LIF)在BSCB的转运系统上调，LIF的转运增强有利于功能恢复。为了验证LIF通过受体相关的转运穿过BSCB以及脊髓损伤后转运系统上调的假设，我们将测量12SI-LIF在血液到脊髓的转移，测试不同类别的转运抑制剂的效果，并比较 结果与表皮生长因子(125I-EGF)对照。我们预计12SI-LIF进入将被LIF受体抗体减少，而12SI-EGF进入将被多阳离子多肽和丹参素减少，但不被EGF受体抗体减少。这将支持LIF通过受体介导的转运穿过BSCB的概念，而EGF通过吸附内吞作用穿过BSCB。我们将进一步测定损伤后不同区域和时间段脊髓对125I-LIF和1251-EGF的摄取，并将结果与通透性测定结果进行比较 标记物(放射性标记的白蛋白和菊粉作为屏障破坏的指示物)，并测试受体抗体和内吞抑制剂对脊髓损伤后增加的放射性示踪剂摄取的影响。我们预计，脊髓损伤上调受体相关的转运(对于LIF)而不影响吸附跨细胞(对于EGF)，并且LIF转运的增强与内皮LIFRα受体表达的增加相关。为了验证LIF在穿过BSCB后有利于脊髓再生的假设，我们将确定轴突再生的组织学和电生理学证据。我们希望通过追踪，神经丝染色，以及 在外周分娩后，当诱发电位的转运上调时，LIF治疗会增加诱发电位在脊髓内的传导。这些变化将与行为表现的改善相一致。为了验证甲基强的松龙增强LIF的治疗效果和上调LIF转运的假说，我们不仅要检测这些再生参数，而且还要检测甲基强的松龙或联合治疗后的转运效果。通过完成这些研究，我们将证明脊髓损伤后神经营养细胞因子的运输可以被调节以促进功能恢复。因此，BBB/BSCB不仅是一个简单的屏障，而且是脊髓再生的大门。了解细胞因子在这一调控界面的转运机制将有助于设计新的治疗脊髓损伤的方法。

Adequate neurotrophic support is essential for spinal cord regeneration; however, production of neurotrophins and neurotrophic cytokines at the site of spinal cord injury (SCI) is insufficient. The blood-brain/blood-spinal cord barrier (BBB/BSCB) mediates permeation of selective neurotrophic cytokines from the periphery. We propose that the transport system for leukemia inhibitory factor (LIF) at the BSCB is upregulated after SCI, and that enhanced transport of LIF benefits functional recovery. To test the hypothesis that LIF crosses the BSCB by receptor-related transport and that the transport system is upregulated after SCI, we will measure blood-to-spinal cord transfer of 12SI-LIF, test the effects of different classes of transport inhibitors, and compare the results with that of epidermal growth factor (125I-EGF). We expect that 12SI-LIF entry will be decreased by a LIF receptor antibody whereas 12SI-EGF entry will be decreased by polycationic peptides and dansylcadaverin but not by an EGF receptor antibody. This will support the concept that LIF crosses the BSCB by receptor-mediated transport while EGF does so by adsorptive endocytosis. We will further determine spinal cord uptake of 125I-LIF and 1251-EGF in various regions and time course after injury, compare the results with those of permeability markers (radioactively labeled albumin and inulin as indicators of barrier disruption), and test the effects of receptor antibodies and endocytosis inhibitors on the increased radiotracer uptake after SCI. We expect that SCI upregulates receptor-related transport (for LIF) without affecting adsorptive transcytosis (for EGF), and that enhanced LIF transport correlates with increased endothelial LIFRalpha receptor expression. To test the hypothesis that LIF benefits spinal cord regeneration after crossing the BSCB, we will determine histological and electrophysiological evidence of axonal regeneration. We expect that tract tracing, neurofilament staining, and intraspinal conduction of evoked potentials will be increased by LIF treatment after peripheral delivery when its transport is upregulated. These changes will coincide with improved behavioral performance. To test the hypothesis that methylprednisolone potentiates the therapeutic effects of LIF and upregulates LIF transport, we will examine not only these regeneration parameters but also transport efficacy after methylprednisolone or combined treatment. By completing these studies, we will have demonstrated that transport of neurotrophic cytokines after SCI can be modulated to facilitate functional restoration. Therefore, the BBB/BSCB is not a simple barrier but also a gate for spinal cord regeneration. Understanding the mechanisms of cytokine transport at this regulatory interface would help in the design of new approaches to treat SCI.