Kubo Takekazu, Endo Mitsuharu, Hata Katsuhiko, Taniguchi Junko, Kitajo Keiko, Tomura Sayaka, Yamaguchi Atsushi, Mueller Bernhard K, Yamashita Toshihide
Department of Neurobiology, Graduate School of Medicine, Chiba University, Chuo-ku, Chiba, Japan, and BioClues Inc., Nihonbashi, Chuo-ku, Tokyo, Japan.
J Neurochem. 2008 Apr;105(1):113-26. doi: 10.1111/j.1471-4159.2007.05125.x. Epub 2007 Nov 12.
Although myelin-associated neurite outgrowth inhibitors express their effects through RhoA/Rho-kinase, the downstream targets of Rho-kinase remain unknown. We examined the involvement of myosin II, which is one of the downstream targets of Rho-kinase, by using blebbistatin - a specific myosin II inhibitor - and small interfering RNA targeting two myosin II isoforms, namely, MIIA and MIIB. We found that neurite outgrowth inhibition by repulsive guidance molecule (RGMa) was mediated via myosin II, particularly MIIA, in cerebellar granule neurons. RGMa induced myosin light chain (MLC) phosphorylation by a Rho-kinase-dependent mechanism. After spinal cord injury in rats, phosphorylated MLC in axons around the lesion site was up-regulated, and this effect depends on Rho-kinase activity. Further, RGMa-induced F-actin reduction in growth cones and growth cone collapse were mediated by MIIA. We conclude that Rho-kinase-dependent activation of MIIA via MLC phosphorylation induces F-actin reduction and growth cone collapse and the subsequent neurite retraction/outgrowth inhibition triggered by RGMa.
尽管髓磷脂相关的神经突生长抑制因子通过RhoA/ Rho激酶发挥作用，但其下游靶点仍不清楚。我们通过使用肌球蛋白II的特异性抑制剂blebbistatin和靶向两种肌球蛋白II亚型（即MIIA和MIIB）的小干扰RNA，研究了作为Rho激酶下游靶点之一的肌球蛋白II的作用。我们发现，在小脑颗粒神经元中，排斥性导向分子（RGMa）对神经突生长的抑制作用是通过肌球蛋白II介导的，尤其是MIIA。RGMa通过Rho激酶依赖性机制诱导肌球蛋白轻链（MLC）磷酸化。大鼠脊髓损伤后，损伤部位周围轴突中的磷酸化MLC上调，且这种效应依赖于Rho激酶活性。此外，RGMa诱导的生长锥中F-肌动蛋白减少和生长锥塌陷是由MIIA介导的。我们得出结论，RGMa通过MLC磷酸化导致的MIIA的Rho激酶依赖性激活，诱导F-肌动蛋白减少和生长锥塌陷，以及随后由RGMa引发的神经突回缩/生长抑制。
