自发性脊髓再生中MIF的非炎性功能研究

Uncontrolled, excessive inflammation contributes to the second tissue damage of traumatic spinal cord, and macrophage migration inhibitory factor (MIF) has been found to be a key molecule involved in the process. It is interesting to note that several regenerative-competent vertebrates have evolved to circumvent the second damages during the spontaneous spinal cord regeneration.So, the question arises as to how MIF attenuates inflammatory responses and what the non-inflammatory function of MIF is, as well as what the underlying mechanisms are. Our previous study revealed that MIF did not trigger the inflammatory response of gecko injured spinal cord. MIF decreased the inflammation and promoted the spinal cord regeneration by differential spatial-temporal expression in the tail stump and injured spinal cord following tail amputation, where it acted reverse functions on the macrophages and glial cells. To address its special functions in the spontaneous spinal cord regeneration, we are going to shed light on the effects of MIF on the various cells in the spinal cord and the underlying signal mechanisms; we will further exmaine the effects on the spinal cord regeneration by interference of MIF and its co-factors; we also try to find out the key regulators of MIF, which is differentially expressed in order to circumvent the inflammatory reaction, by transcriptome sequence and gene network analysis. At last, we are going to perform the in vivo validation to the important regulators. By the comparative studies of pro-inflammatory cytokine MIF, we attempt to provide some clues for the control of the second tissue damage of traumatic spinal cord in mammals.

过度激活的炎症反应是脊髓继发性损伤的关键因素之一，诸多研究表明，巨噬细胞迁移抑制分子MIF是触发炎症反应的核心分子。有趣的是，低等脊椎动物脊髓损伤后却能够规避炎症反应再生脊髓，那么MIF在自发性脊髓再生中是如何消减炎症反应，它的非炎性功能及信号调节机制又是什么？我们前期工作发现，MIF没有引发多疣壁虎断尾脊髓的炎症反应；MIF在断尾末端组织和损伤脊髓中通过时空差异表达，对炎症细胞和胶质细胞产生截然不同的细胞学效应，降低炎症反应，调节脊髓再生。在此基础上，本课题拟深入阐明其对脊髓中不同细胞的影响，揭示其细胞学效应的分子调控机制；在体干预损伤脊髓中MIF以及下游通路分子的表达，检测其对脊髓再生的影响；结合转录组测序和核心信号流分析模型，寻找调节MIF时空差异表达以规避炎症反应的关键分子，并体内外验证。通过对MIF促炎分子的功能和信号途径的比较学研究，为控制高等哺乳动物脊髓继发性损伤提供线索。

高等哺乳动物脊髓损伤后，往往引发过度激活的炎症反应，引起脊髓的二次损伤。炎症细胞或者损伤的神经细胞通过主动或被动方式释放促炎因子，与炎症细胞和胶质细胞膜表面受体相互作用激活炎症反应。有趣的是，一些低等脊椎动物脊髓损伤后可以规避过度激活的炎症反应而再生脊髓。揭示其中的分子机制可以为控制高等哺乳动物的中枢炎症提供重要的参考。诸多研究表明，巨噬细胞迁移抑制因子MIF是触发炎症反应的核心分子。哺乳动物中枢神经损伤后，MIF与炎症细胞膜受体CD74相互作用，促进炎症因子的产生。那么MIF在自发性脊髓再生中是如何消减炎症反应，它的非炎性功能及信号调节机制又是什么，目前尚不清楚。课题组采用多疣壁虎断尾再生模型研究了MIF在损伤脊髓中的功能。壁虎脊髓损伤后，MIF在神经元、少突胶质细胞和星形胶质细胞中表达上调；这些神经细胞产生的MIF通过激活RhoA蛋白，促进炎症细胞在损伤脊髓处的集聚；MIF与炎症细胞CD74受体结合，激活胞内MAPKs激酶，释放适度的炎症因子；同时MIF促进炎症细胞对组织碎片的吞噬；MIF不会激活壁虎星形胶质细胞的炎症反应，但通过上调IL-8的表达促进星形胶质细胞的迁移，进而促进脊髓再生；以大鼠损伤脊髓为模型的比较学研究发现，大鼠小胶质细胞和星形胶质细胞均表达MIF，MIF通过激活星形胶质细胞内MAPKs激酶，激活炎症反应；同时，MIF刺激星形胶质细胞CCL5等趋化因子的产生，促进炎症细胞向脊髓损伤处迁移，引发过度的炎症反应。该结果阐明了可再生低等脊椎动物中枢系统中，胶质细胞具有不同的生理功能，炎症因子的非致炎效应在很大程度上依赖于该胶质细胞生理功能的特化。上述结果对控制高等哺乳动物中枢炎症具有重要的参考价值。