周围神经损伤后趋化因子CXCL12的表达调节及介导病理性痛的分子机制

Peripheral nerve injury and inflammation often results in pathological pain, but the underlying mechanism still remain largely unknown. It has been reported, recently, that some chemokines are involved in the development of chronic pain. The CXCL12, one of the important chemokines which also known as stromal cell derived-factor-1 (SDF-1), and its cognate receptor CXCR4 express constitutively in brain, spinal cord and dorsal root ganglia (DRG) in normal rats. However, few study has systemically observed the role of CXCL12/CXCR4 signaling in the pathogensis of neuropathic pain following peripheral nerve injury. Our present preliminary exprement revealed that lumbar 5 spinal nerve ligation (L5 SNL) induced increased-expression of CXCL12 and CXCR4 in rats spinal dorsal horn. Intrathecal injection of AMD3100, a specific antagonist of CXCR4, alliviated the L5 SNL-induced allodynia. It indicated that the upregulation of CXCL12 and CXCR4 in spinal cord might contributate to the development of neuropathic pain. To further verify the hypothesis, we have designed the following experiments in this progrom.(1) The expression of CXCL12 and CXCR4 in rats dorsal root ganglia and spinal cord following L5 SNL. (2) The regulation of CXCL12 and CXCR4 expression in DRG and spinal cord following L5 SNL. (3) The role of CXCL12/CXCR4 upregulation in DRG and spinal cord in the pathogenesis of neuropathic pain following L5 SNL. (4) The intracellular signal pathway of CXCL12/CXCR4-mediated neuropathic pain. The results might be provided a new therapeutic target to the treatment of neuropathic pain in clinic.

神经损伤和炎症可引起病理性痛，其发病机理仍不清楚。近年发现一些趋化因子参与介导慢性痛。趋化因子CXCL12及其受体CXCR4在正常大鼠脑、脊髓和背根神经节(DRG)有结构性表达，但目前有关CXCL12/CXCR4系统在神经损伤后的表达调节及介导病理性痛的分子机制仍缺乏系统研究。我们的预实验发现大鼠腰5脊神经结扎(L5 SNL)可引起CXCL12、CXCR4在脊髓背角上调，鞘内注射CXCR4阻断剂AMD3100 可减轻L5 SNL引起的痛觉过敏，结果提示CXCL12/CXCR4上调可能参与介导神经病理性痛。为进一步证明这一假说，本研究拟进行以下实验：①L5 SNL后CXCL12/CXCR4在大鼠DRG和脊髓的表达变化；②L5 SNL后CXCL12/CXCR4的表达调控；③CXCL12/CXCR4系统在L5 SNL大鼠病理性痛中的作用；④CXCL12/CXCR4介导病理性痛的信号通路。

以往的研究发现CXCL12及其受体CXCR4在大鼠DRG和脊髓背角有结构性的表达；足底注射CXCL12可引起大鼠产生痛觉过敏；阻断CXCL12/CXCR4信号通路可减轻大鼠癌性痛。本项目系统观察了CXCL12/CXCR4通路激活在坐骨神经部分损伤（spared nerve injury, SNI）引起大鼠神经病理性痛中的作用及其机制。结果发现：（1）大鼠SNI后可引起CXCL12和CXCR4在L4/5 DRGs和脊髓背角的表达上调。在DRG两者既表达于神经元，也表达于卫星样胶质细胞；在脊髓背角CXCL12表达于神经元和小胶质细胞，而CXCR4表达于神经元和星形胶质细胞。（2）鞘内微量注射CXCR4受体阻断剂AMD3100可剂量依赖性地减轻SNI引起的大鼠痛觉过敏；于SNI的第七天鞘内或腹腔注射AMD3100，以及鞘内微量注射CXCL12中和抗体均可使已经形成的大鼠神经病理性痛得到部分缓解。（3）SNI也引起了TNF-α在大鼠DRG和脊髓背角的持续上调；腹腔注射TNF-α合成抑制剂Thalidomide不仅能减轻大鼠SNI的痛觉过敏，而且显著抑制CXCL12在DRG和脊髓背角的表达。（4）SNI引起的ERK在脊髓背角的激活可被鞘内注射AMD3100所阻断；而且鞘内注射CXCL12诱导的的痛觉过敏可被ERK激活抑制剂PD98059所阻断。上述结果表明：SNI引起的CXCL12/CXCR4在DRG和脊髓背角的上调通过激活ERK信号途径参与了大鼠神经病理性痛的形成。. CXCL12/CXCR4信号途径在慢性痛中的作用得到了广泛关注，但其在术后痛中的作用还没有相关的报道。本研究采用大鼠足底切口模型（Plantar Incision, PI）观察了CXCL12/CXCR4在术后急性痛中的作用。结果发现：大鼠PI后可引起CXCL12/CXCR4在同侧脊髓背角的上调，鞘内注射AMD3100或CXCL12中和抗体均能减轻术后急性痛的症状，同时抑制脊髓ERK的激活。PI也引起了磷酸化NF-κB p65的上调，鞘内阻断NF-κB的激活可抑制PI引起的CXCL12的上调。上述结果表明：脊髓NF-κB激活通过上调CXCL12参与了大鼠足底切口痛。. 此外，本人也参与了TLR4/NF-κB在大鼠足底和DRG的激活介导术后痛的研究。