Sakakima Harutoshi, Yoshida Yoshihiro, Kadomatsu Kenji, Yuzawa Yukio, Matsuo Seiichi, Muramatsu Takashi
School of Medical Sciences, Faculty of Medicine, Kagoshima University, 8-35-1, Sakuragaoka, Kagoshima, 890-8520, Japan.
Brain Res Dev Brain Res. 2004 Nov 25;153(2):251-60. doi: 10.1016/j.devbrainres.2004.09.006.
Midkine (MK), a heparin-binding growth factor, is produced in the developing and damaged nervous system. However, the role of MK in peripheral nerve injury has not been clarified. Here, we investigated MK expression in lumbar spinal motor neurons after rat sciatic nerve injury by immunohistochemical, in situ hybridization, and Western blot analyses. The rat sciatic nerve showed complete degeneration after local freezing. Numerous regenerated myelinated and thin nerve fibers were observed 3 weeks after injury. Intense MK immunoreactivity was detected in the ipsilateral spinal motor neurons of the anterior horn of the lumbar spinal cord after 1 day and in ipsilateral and contralateral spinal motor neurons from 4 days to 1 week after injury. It decreased after 2 weeks and again transiently increased in spinal motor neurons after 3 weeks. MK was found in the motor neurons and axon of the sciatic nerve. However, it was not detected in normal neurons and axon. In situ hybridization showed the expression of MK mRNA in lumbar spinal motor neurons of the anterior horn, but it was not present in Schwann cells or non-neuronal cells. Low-density lipoprotein receptor-related protein (LRP) immunoreactivity, a cell membrane receptor of MK, was observed in anterior horn motor neurons, but receptor-type protein tyrosine phosphatase zeta (PTPzeta) immunoreactivity as a signaling receptor complex of MK was not observed. LRP and PTPzeta immunoreactivities were observed in Schwann cells of the injured and uninjured sciatic nerve. Our findings suggest that MK is synthesized, released, and taken up in anterior horn motor neurons in an autocrine fashion with LRP. MK may have a role in degeneration and regeneration after peripheral nerve injury.
中期因子（MK）是一种肝素结合生长因子，在发育中的和受损的神经系统中产生。然而，MK在周围神经损伤中的作用尚未阐明。在此，我们通过免疫组织化学、原位杂交和蛋白质印迹分析，研究了大鼠坐骨神经损伤后腰脊髓运动神经元中MK的表达情况。大鼠坐骨神经局部冷冻后出现完全变性。损伤3周后观察到大量再生的有髓和细神经纤维。损伤1天后，在腰脊髓前角同侧脊髓运动神经元中检测到强烈的MK免疫反应性，损伤4天至1周后在同侧和对侧脊髓运动神经元中也检测到。2周后其减少，3周后在脊髓运动神经元中再次短暂增加。在坐骨神经的运动神经元和轴突中发现了MK。然而，在正常神经元和轴突中未检测到。原位杂交显示腰脊髓前角运动神经元中有MK mRNA表达，但在雪旺细胞或非神经元细胞中不存在。低密度脂蛋白受体相关蛋白（LRP）免疫反应性，即MK的细胞膜受体，在前角运动神经元中观察到，但未观察到作为MK信号受体复合物的受体型蛋白酪氨酸磷酸酶ζ（PTPzeta）免疫反应性。在受伤和未受伤的坐骨神经的雪旺细胞中观察到LRP和PTPzeta免疫反应性。我们的研究结果表明，MK在前角运动神经元中以自分泌方式与LRP一起合成、释放和摄取。MK可能在周围神经损伤后的变性和再生中起作用。
