Qin Zheng-Hong, Wang Yumei, Kegel Kimberly B, Kazantsev Aleksey, Apostol Barbara L, Thompson Leslie Michels, Yoder Jennifer, Aronin Neil, DiFiglia Marian
Laboratory of Cellular Neurobiology, Masschusetts General Hospital and Harvard Medical School, Charlestown 02129, USA.
Hum Mol Genet. 2003 Dec 15;12(24):3231-44. doi: 10.1093/hmg/ddg346. Epub 2003 Oct 21.
The N-terminus of mutant huntingtin (htt) has a polyglutamine expansion and forms neuronal aggregates in the brain of Huntington's disease (HD) patients. Htt expression in vitro activates autophagy, but it is unclear whether autophagic/lysosomal pathways process htt, especially N-terminal htt fragments. We explored the role of autophagy in htt processing in three cell lines, clonal striatal cells, PC12 cells and rodent embryonic cells lacking cathepsin D. Blocking autophagy raised levels of exogenously expressed htt1-287 or 1-969, reduced cell viability and increased the number of cells bearing mutant htt aggregates. Stimulating autophagy promoted htt degradation, including breakdown of caspase cleaved N-terminal htt fragments. Htt expression increased levels of the lysosomal enzyme cathepsin D by an autophagy-dependent pathway. Cells without cathepsin D accumulated more N-terminal htt fragments and cells with cathepsin D were more efficient in degrading wt htt than mutant htt in vitro. These results suggest that autophagy plays a critical role in the degradation of N-terminal htt. Altered processing of mutant htt by autophagy and cathepsin D may contribute to HD pathogenesis.
突变型亨廷顿蛋白（htt）的N端存在多聚谷氨酰胺扩展，并在亨廷顿病（HD）患者大脑中形成神经元聚集体。体外表达的htt可激活自噬，但尚不清楚自噬/溶酶体途径是否参与htt的处理，尤其是N端htt片段的处理。我们在三种细胞系（克隆纹状体细胞、PC12细胞和缺乏组织蛋白酶D的啮齿动物胚胎细胞）中探究了自噬在htt处理中的作用。阻断自噬会提高外源表达的htt1-287或1-969的水平，降低细胞活力，并增加携带突变型htt聚集体的细胞数量。刺激自噬可促进htt降解，包括半胱天冬酶切割的N端htt片段的分解。htt表达通过自噬依赖性途径提高溶酶体酶组织蛋白酶D的水平。缺乏组织蛋白酶D的细胞积累了更多的N端htt片段，而在体外，有组织蛋白酶D的细胞在降解野生型htt方面比突变型htt更有效。这些结果表明自噬在N端htt的降解中起关键作用。自噬和组织蛋白酶D对突变型htt处理的改变可能有助于HD的发病机制。
