Applied Neurobiology Group, Institute of Comparative Medicine, University of Glasgow, Bearsden, Glasgow, Scotland.
J Neurosci Res. 2010 Aug 1;88(10):2135-45. doi: 10.1002/jnr.22379.
The rumpshaker mutation of the murine myelin proteolipid protein 1 (Plp1) gene generates misfolded PLP/DM20 protein, resulting in dysmyelination, increased oligodendrocyte apoptosis, and death prior to P40 when expressed on the C57 BL/6 background. In this study, we used transgenic complementation to normalize the levels of PLP/DM20 in myelin with wild-type protein to determine whether loss of normal PLP function or gain of toxic function is responsible for dysmyelination in the rumpshaker. Restoring myelin PLP/DM20 levels extended the survival time to at least P60, significantly reduced the density of apoptotic cells, increased myelin volume, and restored normal periodicity of myelin. Biochemical analysis found that several myelin proteins that are reduced in rumpshaker, including MAG, CNP, and SirT2, are markedly elevated at peak myelination (P20) in the rumpshaker transgenic mouse. Myelin basic protein, however, remained low at peak myelination but was restored at P60 when myelin had matured and entered into a maintenance phase. Markers of the unfolded protein response (UPR), BiP and XBP1, remained activated with the introduction of wild-type PLP. These data demonstrate that restoring wild-type PLP/DM20 levels in rumpshaker improves the phenotype and the integrity of myelin, but hypomyelination persists and stress pathways remain activated. This suggests that both gain- and loss-of-function mechanisms are involved in the pathogenesis of the rumpshaker.
鼠髓鞘蛋白脂蛋白 1（Plp1）基因的 rumpshaker 突变会产生错误折叠的 PLP/DM20 蛋白，导致髓鞘发育不良、少突胶质细胞凋亡增加，并在 C57BL/6 背景下表达时在 P40 之前死亡。在这项研究中，我们使用转基因互补来使髓鞘中的 PLP/DM20 水平正常化，以确定丢失正常 PLP 功能还是获得毒性功能是 rumpshaker 中髓鞘发育不良的原因。恢复髓鞘 PLP/DM20 水平将存活时间延长至至少 P60，显著降低凋亡细胞的密度，增加髓鞘体积，并恢复髓鞘的正常周期性。生化分析发现，在 rumpshaker 中减少的几种髓鞘蛋白，包括 MAG、CNP 和 SirT2，在 rumpshaker 转基因小鼠的髓鞘形成高峰期（P20）明显升高。然而，髓鞘碱性蛋白在髓鞘形成高峰期仍然较低，但在 P60 时恢复，此时髓鞘已经成熟并进入维持阶段。未折叠蛋白反应 (UPR) 的标志物 BiP 和 XBP1 在引入野生型 PLP 时仍然保持激活。这些数据表明，在 rumpshaker 中恢复野生型 PLP/DM20 水平可改善表型和髓鞘的完整性，但低髓鞘化仍然存在，应激途径仍然保持激活。这表明 gain- 和 loss-of-function 机制都参与了 rumpshaker 的发病机制。
