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，在脊髓损伤（SCI）部位产生的神经营养因子和神经营养细胞因子是不足的。血脑/血脊髓屏障（BBB/BSCB）介导选择性神经营养细胞因子从外周的渗透。我们认为，白血病抑制因子（LIF）在BSCB的运输系统是上调SCI后，增强运输LIF的功能恢复。为了验证LIF通过受体相关转运穿过BSCB以及SCI后转运系统上调的假设，我们将测量12 SI-LIF的血液至脊髓的转运，测试不同类别转运抑制剂的作用，并比较12 SI-LIF在脊髓中的表达。 结果与表皮生长因子（125 I-EGF）的结果一致。我们预期LIF受体抗体会降低12 SI-LIF进入，而聚阳离子肽和丹磺酰尸胺会降低12 SI-EGF进入，但EGF受体抗体不会降低。这将支持LIF通过受体介导的转运而EGF通过吸附性内吞作用穿过BSCB的概念。我们将进一步测定损伤后不同部位和不同时间段脊髓对125 I-LIF和1251-EGF的摄取，并与渗透性结果进行比较 标记物（放射性标记的白蛋白和菊粉作为屏障破坏的指标），并测试受体抗体和内吞抑制剂对SCI后放射性示踪剂摄取增加的影响。我们预期SCI上调受体相关转运（LIF）而不影响吸附转胞吞作用（EGF），并且增强的LIF转运与内皮LIFR α受体表达增加相关。为了验证LIF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。我们希望神经束追踪，神经丝染色， 当其转运被上调时，在外周递送后通过LIF处理将增加诱发电位的脊柱内传导。这些变化将与行为表现的改善相一致。为了检验甲泼尼龙增强LIF的治疗效果并上调LIF转运的假设，我们将不仅检查这些再生参数，还检查甲泼尼龙或联合治疗后的转运功效。通过完成这些研究，我们将证明SCI后神经营养细胞因子的转运可以被调节以促进功能恢复。因此，BBB/BSCB不是简单的屏障，而是脊髓再生的大门。了解细胞因子在这个调控界面的转运机制将有助于设计治疗SCI的新方法。

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.