Lipid- and receptor-binding regions of apolipoprotein E4 fragments act in concert to cause mitochondrial dysfunction and neurotoxicity.
Apolipoprotein (apo) E4, a 299-aa protein and a major risk factor for Alzheimer's disease, can be cleaved to generate C-terminal-truncated fragments that cause neurotoxicity in vitro and neurodegeneration and behavioral deficits in transgenic mice. To investigate this neurotoxicity, we expressed apoE4 with C- or N-terminal truncations or mutations in transfected Neuro-2a cells. ApoE4 (1-272) was neurotoxic, but full-length apoE4(1-299) and apoE4(1-240) were not, suggesting that the lipid-binding region (amino acids 241-272) mediates the neurotoxicity and that amino acids 273-299 are protective. A quadruple mutation in the lipid-binding region (I250A, F257A, W264R, and V269A) abolished the neurotoxicity of apoE4(1-272), and single mutations in the region of amino acids 273-299 (L279Q, K282A, or Q284A) made full-length apoE4 neurotoxic. Immunofluorescence staining showed that apoE4(1-272) formed filamentous inclusions containing phosphorylated tau in some cells and interacted with mitochondria in others, leading to mitochondrial dysfunction as determined by MitoTracker staining and flow cytometry. ApoE4(241-272) did not cause mitochondrial dysfunction or neurotoxicity, suggesting that the lipid-binding region alone is insufficient for neurotoxicity. Truncation of N-terminal sequences (amino acids 1-170) containing the receptor-binding region (amino acids 135-150) and triple mutations within that region (R142A, K146A, and R147A) abolished the mitochondrial interaction and neurotoxicity of apoE4(1-272). Further analysis showed that the receptor-binding region is required for escape from the secretory pathway and that the lipid-binding region mediates mitochondrial interaction. Thus, the lipid- and receptor-binding regions in apoE4 fragments act together to cause mitochondrial dysfunction and neurotoxicity, which may be important in Alzheimer's disease pathogenesis.
Chang
Shengjun
S
Gladstone Institute of Neurological Disease, 1650 Owens Street, San Francisco, CA 94158, USA.
ran Ma
Tian
T
Miranda
R Dennis
RD
Balestra
Maureen E
ME
Mahley
Robert W
RW
Huang
Yadong
Y
D000544:Alzheimer Disease / Q000378:metabolism; D000818:Animals; D053327:Apolipoprotein E4; D001057:Apolipoproteins E / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D045744:Cell Line, Tumor; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D008055:Lipids; D051379:Mice; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009474:Neurons / Q000187:drug effects* / Q000473:pathology*; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism / Q000633:toxicity; D018110:Receptors, Lipoprotein / Q000378:metabolism*
D053327:Apolipoprotein E4; D001057:Apolipoproteins E; D008055:Lipids; D010446:Peptide Fragments; D018110:Receptors, Lipoprotein