Spinal Mechanisms Underlying SCI-Induced Pain: Implications for Targeted Therapy

描述（由申请人提供）：慢性疼痛是美国的一种公共卫生流行病，脊髓损伤（SCI）不仅会导致运动、感觉和认知功能的缺陷，而且还会导致慢性、严重和经常持续的疼痛，这种疼痛在很大程度上对常规治疗（SCI-PAIN）有抵抗力。在多达85%的SCI患者中，疼痛在最初的损伤后数周或数月开始，包括伤害性刺激引起的疼痛（痛觉过敏），对先前无害刺激的疼痛（异常性疼痛）和自发性疼痛。这种持续的疼痛可以是弥漫性的，双侧的，通常延伸到脊髓损伤的尾部。SCI疼痛的延迟表达和疼痛症状的弥漫性定位表明，病理生理学反映的不仅仅是失神经脊髓节段的直接影响。事实上，SCI疼痛的这些特征强烈表明脊髓背角发生了适应不良的可塑性。药物开发的一个重要焦点是确定参与与SCI疼痛持续性相关的脊髓可塑性的新治疗靶点/分子。脑源性神经营养因子（BDNF）是一个很有前途的新的治疗靶点，它调节脊髓的伤害性感受。BDNF通过与其全长细胞表面受体原肌球蛋白相关激酶B（trk B.FL）结合并启动细胞内信号传导而发挥其对伤害感受性处理的作用。除了trkB.FL，trkB基因座还产生广泛表达的选择性剪接截短亚型trkB. T1，但这种受体亚型在伤害感受中的功能在很大程度上是未知的。TrkB.T1在几种非疼痛和疼痛相关的病理状态中上调，我们已经报道了小鼠中该受体的遗传缺失在几种慢性疼痛模型中提供了对热痛觉过敏和机械异常性疼痛的发展的显著保护。对于这一提议至关重要的是，我们有初步数据显示，在我们小组开发的中度挫伤SCI小鼠模型中，trkB.T1缺失导致运动恢复显著改善，并减少异常性疼痛。我们进行了差异基因表达的研究，以检查潜在的转录机制，调节这些改善，并发现上调的关键细胞周期基因与神经元凋亡后，实验性SCI，没有上调的trkB.T1空脊髓。这些结果表明，trkB.T1可能是一个令人兴奋的新的分子靶点。在这项研究中，我们将使用体外和体内方法系统地评估trkB.T1对细胞周期基因的调节是否有助于SCI-PAIN，并确定是否可以单独或联合靶向细胞周期基因或trkB.T1以增强疗效，以开发新的治疗干预措施来减少或改善SCI-PAIN。

DESCRIPTION (provided by applicant): Chronic pain is a public health epidemic in the U.S., affecting more than 116 million people and costing greater than $600 billion per year to treat. Spinal cord injury (SCI) results not only in debilitating motor, sensory and cognitive deficits, bu also in a chronic, severe and often unrelenting pain that is largely resistant to conventional treatments (SCI-PAIN). Occurring in as many as 85% of SCI patients, pain starts weeks or months after the original insult, and includes increased pain with noxious stimulation (hyperalgesia), pain in response to previously innocuous stimuli (allodynia), and spontaneous pain. This unremitting pain can be diffuse, bilateral, and usually extends to locations caudal to the spinal injury. The delayed expression of SCI- PAIN and the diffuse localization of painful symptoms suggest that the pathophysiology reflects more than the direct effects at the denervated spinal segments. Indeed, these features of SCI-PAIN strongly suggest the occurrence of maladaptive plasticity in the spinal dorsal horn. An important focus for drug development has been to identify new therapeutic targets/molecules that participate in the spinal cord plasticity associated with the persistence of SCI-PAIN. One promising new therapeutic target, Brain-derived Neurotrophic Factor (BDNF), modulates nociception in the spinal cord. BDNF exerts its effects on nociceptive processing by binding to its full-length, cell surface receptor tropomyosin-related kinase B (trkB.FL) and initiating intracellular signaling. In addition to trkB.FL, the trkB locus also produces a widely-expressed alternatively-spliced truncated isoform, trkB.T1, but the function of this receptor isoform in nociception is largely unknown. TrkB.T1 is upregulated in several non-pain and pain related pathological states and we have reported that the genetic deletion of this receptor in mouse provides significant protection from the development of thermal hyperalgesia and mechanical allodynia across several models of chronic pain. Crucial to this proposal, we have preliminary data showing that trkB.T1 deletion results in significantly improved locomoter recovery and reduced allodynia in a moderate contusion injury mouse model of SCI developed by our group. We conducted differential gene expression studies to examine the potential transcriptional mechanisms regulating these improvements, and found that upregulation of key cell cycle genes correlating with neuronal apoptosis after experimental SCI, are not upregulated in the trkB.T1 null spinal cord. These results suggest that trkB.T1 may be an exciting new molecular target. In this study, we will systematically evaluate, using in vitro and in vivo approaches, whether trkB.T1 regulation of cell cycle genes contributes to SCI-PAIN and determine whether targeting cell cycle genes or trkB.T1, separately or in combination for enhanced effectiveness, can be utilized to develop novel therapeutic interventions to reduce or ameliorate SCI-PAIN.