Houseweart Megan K, Pennacchio Len A, Vilaythong Alex, Peters Christoph, Noebels Jeffrey L, Myers Richard M
Department of Genetics, School of Medicine, Stanford University, Stanford, California 94305, USA.
J Neurobiol. 2003 Sep 15;56(4):315-27. doi: 10.1002/neu.10253.
The inherited epilepsy Unverricht-Lundborg disease (EPM1) is caused by loss-of-function mutations in the cysteine protease inhibitor, cystatin B. Because cystatin B inhibits a class of lysosomal cysteine proteases called cathepsins, we hypothesized that increased proteolysis by one or more of these cathepsins is likely to be responsible for the seizure, ataxia, and neuronal apoptosis phenotypes characteristic of EPM1. To test this hypothesis and to identify which cysteine cathepsins contribute to EPM1, we have genetically removed three candidate cathepsins from cystatin B-deficient mice and tested for rescue of their EPM1 phenotypes. Whereas removal of cathepsins L or S from cystatin B-deficient mice did not ameliorate any aspect of the EPM1 phenotype, removal of cathepsin B resulted in a 36-89% reduction in the amount of cerebellar granule cell apoptosis depending on mouse age. The incidence of an incompletely penetrant eye phenotype was also reduced upon removal of cathepsin B. Because the apoptosis and eye phenotypes were not abolished completely and the ataxia and seizure phenotypes experienced by cystatin B-deficient animals were not diminished, this suggests that another molecule besides cathepsin B is also responsible for the pathogenesis, or that another molecule can partially compensate for cathepsin B function. These findings establish cathepsin B as a contributor to the apoptotic phenotype of cystatin B-deficient mice and humans with EPM1. They also suggest that the identification of cathepsin B substrates may further reveal the molecular basis for EPM1.
遗传性癫痫——翁韦里希特-伦德伯格病（EPM1）由半胱氨酸蛋白酶抑制剂胱抑素B的功能丧失性突变引起。由于胱抑素B抑制一类称为组织蛋白酶的溶酶体半胱氨酸蛋白酶，我们推测一种或多种此类组织蛋白酶的蛋白水解作用增强可能是导致EPM1特征性癫痫发作、共济失调和神经元凋亡表型的原因。为了验证这一假设并确定哪些半胱氨酸组织蛋白酶与EPM1有关，我们从胱抑素B缺陷小鼠中通过基因手段去除了三种候选组织蛋白酶，并测试其EPM1表型是否得到挽救。从胱抑素B缺陷小鼠中去除组织蛋白酶L或S并未改善EPM1表型的任何方面，而去除组织蛋白酶B可使小脑颗粒细胞凋亡量减少36% - 89%，具体减少幅度取决于小鼠年龄。去除组织蛋白酶B后，不完全显性的眼部表型发生率也有所降低。由于凋亡和眼部表型并未完全消除，且胱抑素B缺陷动物所经历的共济失调和癫痫发作表型也未减轻，这表明除组织蛋白酶B外，另一种分子也参与了发病机制，或者另一种分子可以部分补偿组织蛋白酶B的功能。这些发现证实组织蛋白酶B是导致胱抑素B缺陷小鼠和患有EPM1的人类出现凋亡表型的一个因素。它们还表明，鉴定组织蛋白酶B的底物可能会进一步揭示EPM1的分子基础。
