Jia Yichang, Jucius Thomas J, Cook Susan A, Ackerman Susan L
Howard Hughes Medical Institute and The Jackson Laboratory, Bar Harbor, Maine 04609.
The Jackson Laboratory, Bar Harbor, Maine 04609.
J Neurosci. 2015 Feb 18;35(7):3001-9. doi: 10.1523/JNEUROSCI.3678-14.2015.
Folding of transmembrane and secretory proteins occurs in the lumen of the endoplasmic reticulum (ER) before transportation to the cell surface and is monitored by the unfolded protein response (UPR) signaling pathway. The accumulation of unfolded proteins in the ER activates the UPR that restores ER homeostasis by regulating gene expression that leads to an increase in the protein-folding capacity of the ER and a decrease in the ER protein-folding load. However, prolonged UPR activity has been associated with cell death in multiple pathological conditions, including neurodegeneration. Here, we report a spontaneous recessive mouse mutation that causes progressive cerebellar granule cell death and peripheral motor axon degeneration. By positional cloning, we identify the mutation in this strain as a retrotransposon insertion in the Clcc1 gene, which encodes a putative chloride channel localized to the ER. Furthermore, we demonstrate that the C3H/HeSnJ inbred strain has late onset cerebellar degeneration due to this mutation. Interestingly, acute knockdown of Clcc1 expression in cultured cells increases sensitivity to ER stress. In agreement, GRP78, the major HSP70 family chaperone in the ER, is upregulated in Clcc1-deficient granule cells in vivo, and ubiquitinated proteins accumulate in these neurons before their degeneration. These data suggest that disruption of chloride homeostasis in the ER disrupts the protein-folding capacity of the ER, leading to eventual neuron death.
跨膜蛋白和分泌蛋白在内质网（ER）腔中折叠，然后运输到细胞表面，其过程受未折叠蛋白反应（UPR）信号通路监控。内质网中未折叠蛋白的积累会激活UPR，后者通过调节基因表达来恢复内质网稳态，从而导致内质网蛋白折叠能力增强，内质网蛋白折叠负荷降低。然而，在包括神经退行性变在内的多种病理情况下，UPR的长期激活与细胞死亡有关。在此，我们报告了一种自发的隐性小鼠突变，该突变导致进行性小脑颗粒细胞死亡和外周运动轴突变性。通过定位克隆，我们确定该品系中的突变是Clcc1基因中的一个反转录转座子插入，该基因编码一种定位于内质网的假定氯离子通道。此外，我们证明C3H/HeSnJ近交系由于该突变而出现迟发性小脑变性。有趣的是，在培养细胞中急性敲低Clcc1表达会增加细胞对内质网应激的敏感性。同样，内质网中主要的HSP70家族伴侣蛋白GRP78在体内Clcc1缺陷的颗粒细胞中上调，泛素化蛋白在这些神经元变性之前就开始积累。这些数据表明，内质网中氯离子稳态的破坏会扰乱内质网的蛋白折叠能力，最终导致神经元死亡。
