Fournier A E, McKerracher L
Faculté de Médecine, Département de Pathologie, Université de Montréal, and McGill University, C.P. 6128, Succursale Centre-ville Montréal, Québec H3C 3J7, Canada.
J Neurosci. 1997 Jun 15;17(12):4623-32. doi: 10.1523/JNEUROSCI.17-12-04623.1997.
Axonal regrowth after injury is accompanied by changes in the expression of tubulin, but the contributions of substrate molecules and neurotrophic factors in regulating these changes in vivo are not known. Adult rat retinal ganglion cells (RGCs) were examined after intraorbital axotomy, after application of a peripheral nerve (PN) graft to stimulate regeneration, and after axotomy and treatment with brain-derived neurotrophic factor (BDNF). After these treatments we used in situ hybridization to study mRNA levels for betaI, betaII, betaIII, betaIVa, and Talpha1 tubulin isotypes. Levels of mRNA for all isotypes were downregulated after intraorbital axotomy. During regrowth of injured RGC axons, mRNA levels for betaII, betaIII, and Talpha1 isotypes were upregulated specifically and dramatically, suggesting that elevated expression of these isotypes is correlated specifically with axonal regrowth. A corresponding increase in betaIII protein levels was detected by immunocytochemistry. The betaI and betaIVa mRNAs were not increased during regeneration. BDNF did not elicit a specific increase in the mRNA levels for the betaIII and Talpha1 isotypes and had only a small effect on mRNA levels for the betaII isotype. Therefore, despite the ability of BDNF to support the survival of injured RGCs and to enhance neurite outgrowth of retinal neurons in vitro, the in vivo application of BDNF alone is unable to induce the program of changes in growth-associated tubulins that accompany regeneration of RGC axons into PN grafts. We speculate that, in addition to BDNF, cooperative signaling with substrate molecules is required to allow RGCs to regenerate and exhibit tubulin isotype switching.
损伤后的轴突再生伴随着微管蛋白表达的变化，但体内底物分子和神经营养因子在调节这些变化中的作用尚不清楚。在眶内轴突切断术后、应用周围神经（PN）移植物刺激再生后以及轴突切断并给予脑源性神经营养因子（BDNF）治疗后，对成年大鼠视网膜神经节细胞（RGCs）进行了检查。在这些处理后，我们使用原位杂交来研究βI、βII、βIII、βIVa和Tα1微管蛋白亚型的mRNA水平。眶内轴突切断术后，所有亚型的mRNA水平均下调。在受损RGC轴突再生过程中，βII、βIII和Tα1亚型的mRNA水平特异性且显著上调，表明这些亚型表达的升高与轴突再生特异性相关。通过免疫细胞化学检测到βIII蛋白水平相应增加。在再生过程中，βI和βIVa mRNA没有增加。BDNF并没有引起βIII和Tα1亚型mRNA水平的特异性增加，对βII亚型mRNA水平的影响也很小。因此，尽管BDNF能够支持受损RGCs的存活并在体外增强视网膜神经元的神经突生长，但单独在体内应用BDNF无法诱导RGC轴突向PN移植物再生时伴随的生长相关微管蛋白变化程序。我们推测，除了BDNF之外，还需要与底物分子的协同信号传导，以使RGCs再生并表现出微管蛋白亚型转换。
