Apolipoprotein E4 potentiates amyloid beta peptide-induced lysosomal leakage and apoptosis in neuronal cells.
We assessed the isoform-specific effects of apolipoprotein (apo) E on the response of Neuro-2a cells to the amyloid beta peptide (Abeta1-42). As determined by the intracellular staining pattern and the release of beta-hexosaminidase into the cytosol, apoE4-transfected cells treated with aggregated Abeta1-42 showed a greater tendency toward lysosomal leakage than neo- or apoE3-transfected cells. Abeta1-42 caused significantly greater cell death and more than 2-fold greater DNA fragmentation in apoE4-secreting than in apoE3-secreting or control cells. H2O2 or staurosporine enhanced cell death and apoptosis in apoE4-transfected cells but not in apoE3-transfected cells. A caspase-9 inhibitor abolished the potentiation of Abeta1-42-induced apoptosis by apoE4. Similar results were obtained with conditioned medium from cells secreting apoE3 or apoE4. Cells preincubated for 4 h with a source of apoE3 or apoE4, followed by removal of apoE from the medium and from the cell surface, still exhibited the isoform-specific response to Abeta1-42, indicating that the potentiation of apoptosis required intracellular apoE, presumably in the endosomes or lysosomes. Studies of phospholipid (dimyristoylphosphatidylcholine) bilayer vesicles encapsulating 5-(and-6)-carboxyfluorescein dye showed that apoE4 remodeled and disrupted the phospholipid vesicles to a greater extent than apoE3 or apoE2. In response to Abeta1-42, vesicles containing apoE4 were disrupted to a greater extent than those containing apoE3. These findings are consistent with apoE4 forming a reactive molecular intermediate that avidly binds phospholipid and may insert into the lysosomal membrane, destabilizing it and causing lysosomal leakage and apoptosis in response to Abeta1-42.
Ji
Zhong-Sheng
ZS
Gladstone Institute of Neurological Disease, University of California, San Francisco, California 94141-9100, USA.
Miranda
R Dennis
RD
Newhouse
Yvonne M
YM
Weisgraber
Karl H
KH
Huang
Yadong
Y
Mahley
Robert W
RW
D016229:Amyloid beta-Peptides / Q000737:chemistry*; D000818:Animals; D053327:Apolipoprotein E4; D001057:Apolipoproteins E / Q000737:chemistry*; D017209:Apoptosis; D053938:DNA Fragmentation; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D009474:Neurons / Q000378:metabolism*; D020033:Protein Isoforms; D019311:Staurosporine / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
D016229:Amyloid beta-Peptides; D053327:Apolipoprotein E4; D001057:Apolipoproteins E; D004791:Enzyme Inhibitors; D020033:Protein Isoforms; D006861:Hydrogen Peroxide; D019311:Staurosporine; D004134:Dimyristoylphosphatidylcholine