Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Department of Medical Genetics , Brain Research Centre, University of British Columbia, Vancouver, British Columbia, Canada V5Z 4H4.
J Neurosci. 2010 Nov 10;30(45):15019-29. doi: 10.1523/JNEUROSCI.2071-10.2010.
Caspase cleavage of huntingtin (htt) and nuclear htt accumulation represent early neuropathological changes in brains of patients with Huntington's disease (HD). However, the relationship between caspase cleavage of htt and caspase activation patterns in the pathogenesis of HD remains poorly understood. The lack of a phenotype in YAC mice expressing caspase-6-resistant (C6R) mutant htt (mhtt) highlights proteolysis of htt at the 586 aa caspase-6 (casp6) site as a key mechanism in the pathology of HD. The goal of this study was to investigate how proteolysis of htt at residue 586 plays a role in the pathogenesis of HD and determine whether inhibiting casp6 cleavage of mhtt alters cell-death pathways in vivo. Here we demonstrate that activation of casp6, and not caspase-3, is observed before onset of motor abnormalities in human and murine HD brain. Active casp6 levels correlate directly with CAG size and inversely with age of onset. In contrast, in vivo expression of C6R mhtt attenuates caspase activation. Increased casp6 activity and apoptotic cell death is evident in primary striatal neurons expressing caspase-cleavable, but not C6R, mhtt after NMDA application. Pretreatment with a casp6 inhibitor rescues the apoptotic cell death observed in this paradigm. These data demonstrate that activation of casp6 is an early marker of disease in HD. Furthermore, these data provide a clear link between excitotoxic pathways and proteolysis and suggest that C6R mhtt protects against neurodegeneration by influencing the activation of neuronal cell-death and excitotoxic pathways operative in HD.
Caspase 对 huntingtin（htt）的切割以及 htt 在细胞核中的聚集是亨廷顿病（HD）患者大脑中早期神经病理学改变的标志。然而，Caspase 对 htt 的切割与 HD 发病机制中 caspase 激活模式之间的关系仍不清楚。在表达 caspase-6 抗性（C6R）突变 htt（mhtt）的 YAC 小鼠中缺乏表型，突出了 htt 在 586 aa caspase-6（casp6）位点的蛋白水解作用作为 HD 病理学的关键机制。本研究的目的是研究 htt 在残基 586 处的蛋白水解作用如何在 HD 的发病机制中发挥作用，并确定抑制 mhtt 的 casp6 切割是否改变体内细胞死亡途径。在这里，我们证明 caspase-6 的激活，而不是 caspase-3 的激活，在人类和鼠类 HD 大脑运动异常出现之前就已经发生。活性 casp6 水平与 CAG 大小直接相关，与发病年龄成反比。相比之下，体内表达 C6R mhtt 可减弱 caspase 的激活。在 NMDA 应用后，表达可被 caspase 切割的，但不是 C6R 的 mhtt 的原代纹状体神经元中，可明显观察到 casp6 活性增加和凋亡性细胞死亡。在这种模型中，用 casp6 抑制剂预处理可挽救观察到的凋亡性细胞死亡。这些数据表明，caspase-6 的激活是 HD 疾病的早期标志物。此外，这些数据提供了兴奋性毒性途径与蛋白水解之间的明确联系，并表明 C6R mhtt 通过影响在 HD 中起作用的神经元细胞死亡和兴奋性毒性途径的激活来保护神经变性。
