PD-1/PD-L1信号通路在脊髓损伤后巨噬/小胶质细胞极化过程中的作用研究

The inflammatory response is one of the most important pathological processes to influence prognosis directly after spinal cord injury. The main inflammatory cells are infiltrated macrophages and residential activated microglia after spinal cord injury (SCI). Both of them can be polarized to M1 or M2 microphage based on environment they are located at to give different physiological functions. PD-1/PD-L1 pathway is a critical co-inhibitory signaling to regulate not only activity of lymphocytes, but also the function of macrophages. Our preliminary data showed that the transcripts of PD-1 and PD-L1 were gradually increased after SCI. PD-L1 as well as PD-1 expressed on macrophages/microglia which located at lesion site. The motor function was promoting to recovery with spinal cord crushing in TgPD-L1 mice. On the contrary, PD-1-/- mice became worse in their recovery of motor function after SCI. The M1 macrophages were obviously increased in PD-1-/- mice compared with wild type mice after SCI. And the iNOS, the specific marker of M1 macrophages was upregulated. These results showed that the PD-1/PD-L1 pathway played critical roles in macrophages/microglia polarization after SCI. It might influence the prognosis of injured spinal cord by regulating the polarization of macrophages/microglia after SCI. In this study, we are planning to clarify the mechanism of PD-1/PD-L1 pathway in regulating the polarization of macrophages/microglia in detail in vivo and in vitro with PD-1-/- and Tg PD-L1 mice after SCI. The results of this project will provide a new clinical therapeutic strategy for SCI in near future.

脊髓损伤后的炎症反应是脊髓损伤最为重要的病理过程之一，直接影响脊髓损伤的愈后。巨噬/小胶质细胞是脊髓损伤最主要的炎症细胞，它们可以极化为M1和M2型细胞，发挥不同的生理功能。PD-1/PD-L1信号通路是一条重要的共抑制性通路，它不仅调节淋巴细胞的活性，同时也调节巨噬细胞功能。我们前期研究显示：PD-1、PD-L1分子在脊髓损伤后表达水平逐渐增加；PD-1和PD-L1在巨噬/小胶质细胞表面均有表达；干预PD-1/PD-L1信号通路明显影响小鼠脊髓损伤后的运动功能恢复；PD-1-/-小鼠脊髓损伤后，M1型细胞数量增加，iNOS表达升高。这些结果说明：PD-1/PD-L1信号通路在脊髓损伤修复过程中具有重要作用。本课题采用PD-1-/-和TgPD-L1小鼠，通过体内和体外研究，详细阐明脊髓损伤后PD-1/PD-L1信号通路调节巨噬/小胶质细胞极化的分子机制，为今后脊髓损伤治疗提供新的理论基础。

项目研究背景：脊髓损伤是愈后非常差的常见中枢神经系统损伤疾病，再生医学的长足进步但却依然没有多少改变脊髓损伤的救治成功率。脊髓损伤后的炎症反应是脊髓损伤最为重要的病理过程之一，是影响损伤细胞内环境最主要的因素，直接影响脊髓损伤的愈后。巨噬/小胶质细胞是脊髓损伤炎症反应最主要的效应细胞，它们可以极化为M1和M2型细胞，发挥不同的生理功能。PD-1/PD-L1信号通路是一条重要的免疫抑制性通路，它不仅调节淋巴细胞的活性，同时也调节巨噬细胞功能。我们前期研究显示：PD-1、PD-L1分子在脊髓损伤后表达水平逐渐增加；PD-1和PD-L1在巨噬/小胶质细胞表面均有表达；干预PD-1/PD-L1信号通路明显影响小鼠脊髓损伤后的运动功能恢复；PD-1-/-小鼠脊髓损伤后，M1型细胞数量增加，iNOS表达升高。这些结果说明：PD-1/PD-L1信号通路在脊髓损伤修复过程中具有重要作用。.主要研究内容：本课题采用PD-1-/-和TgPD-L1小鼠，通过体内和体外研究，详细阐明脊髓损伤后PD-1/PD-L1信号通路调节巨噬/小胶质细胞极化的分子机制。.重要结果：PD-1和PD-L1分子在脊髓损伤后再巨噬/小胶质细胞表面高表达；PD-1缺陷促进巨噬/小胶质细胞向M1方向分化，不利于脊髓损伤后的功能恢复；PD-1肯能通过STAT1和STAT6调节巨噬细胞的极化；同时NF-kB也参与极化的调节。研究显示：PD-1/PD-L1在巨噬小胶质细胞表面发挥相互作用时，并不是作为共受体的形式发挥作用，揭示了PD-1/PD-L1不依赖于BCR或TCR信号通路的新机制。此外，PD-1在巨噬细胞表达后，其内部信号通路与在活化的T细胞不同，它并没有通过SHP-1/2分子下调来降低细胞的活性，很可能是通过mTOR信号通路完成。.科学意义：巨噬/小胶质细胞在脊髓损伤中的不同极化方向，决定了损伤区的不同内环境。M1有利于胶质瘢痕的形成，促进神经干细胞向星形胶质细胞分化，不利于损伤后功能恢复；而M2则有利于轴突再生，神经元和少突胶质细胞的分化，促进损伤的功能恢复。而PD-1是一个细胞表面分子，易于对其进行调节。如今阻断PD-1和PD-L1药物已经作为肿瘤治疗而应用于临床。该课题的研究，可以为通过调节PD-1/PD-L1信号通路的活性来促进脊髓损伤的修复奠定基础。