Inhibition of Myelin Formation by Astrogliosis

长期培养的新生ICR小鼠的星形胶质细胞维持超过12周，没有细胞传代变得纤维化和肥大，并表现出强烈的免疫染色与抗GFAP抗体，类似于胶质星形胶质细胞的特征。在新生小鼠小脑组织中，贴在这些星形胶质细胞上的髓鞘形成被完全抑制，而贴在星形胶质细胞上的髓鞘形成维持不到3周。培养液中含有80%或更多的长期培养的星形胶质细胞的条件培养基显着抑制髓鞘形成的小脑组织中的胶原包被的24孔板，与含有星形胶质细胞的条件培养基维持不到3周。这些发现表明胶质星形胶质细胞产生髓鞘形成抑制因子，这可能部分解释多发性硬化慢性脱髓鞘斑块中髓鞘再生不良。其次，利用差异显示技术寻找胶质增生相关基因。我们获得了一个在长期培养的星形胶质细胞中被强烈诱导的基因，命名为OASIS。OASIS基因编码CREB/ATF基因家族的转录因子。OASIS mRNA的表达在小鼠大脑皮层中诱导响应冷冻损伤。OASIS阳性细胞的分布模式与GEAP阳性细胞的分布模式非常相似。这些结果支持长期培养的星形胶质细胞是一种良好的体外胶质细胞增生模型，并提示OASIS在胶质细胞增生中起作用。

Long-term cultured astrocytes of newborn ICR mice maintained for more than 12 weeks without cell passage became fibrous and hypertrophic, and exhibited intense immunostaining with anti-GFAP antibodies, characteristics analogous to gliotic astrocytes. In newborn mouse cerebellar tissue explanted on these astrocytes myelination was completely inhibited, while in that explanted on astrocytes maintained for less than 3 weeks myelination occurred vigorously. Culture medium containing 80% or more conditioned medium of longterm cultured astrocytes significantly inhibited myelin formation in cerebellar tissues explanted in collagen-coated 24-well plates, compared with that containing conditioned medium of astrocytes maintained for less than 3 weeks. These findings indicate that gliotic astrocytes produce myelination inhibition factor (s) which may partly explain the poor remyelination in chronic demyelination plaques of multiple sclerosis. Next, we searched for gliosis related genes by differential display method. We obtained a gene named OASIS which is strongly induced in the long-term cultured astrocytes. The OASIS gene encoded a putative transcription factor belonging to CREB/ATF gene family. The expression of the OASIS mRNA was induced in the mouse cerebral cortex in response to cryo-injury. The distribution pattern of the OASIS-positive cells was very similar to that of the GEAP-positive cells. These results support that long-term cultured astrocytes is a good model for gliosis in vitro, and suggest that OASIS plays a role for gliosis.