Autophagy regulates the processing of amino terminal huntingtin fragments.
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.
Laboratory of Cellular Neurobiology, Masschusetts General Hospital and Harvard Medical School, Charlestown 02129, USA.
Zheng-Hong
ZH
Qin
Yumei
Y
Wang
Kimberly B
KB
Kegel
Aleksey
A
Kazantsev
Barbara L
BL
Apostol
Leslie Michels
LM
Thompson
Jennifer
J
Yoder
Neil
N
Aronin
Marian
M
DiFiglia
D000818:Animals; D001343:Autophagy / Q000502:physiology*; D002402:Cathepsin D / Q000378:metabolism; D002478:Cells, Cultured; D003470:Culture Media; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000378:metabolism*; D051379:Mice; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*
D003470:Culture Media; C086055:HTT protein, human; C506812:Htt protein, mouse; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D002402:Cathepsin D