Beta-amyloid (25-35) enhances lipid metabolism and protein ubiquitination in cultured neurons.
We investigated the effect of beta-amyloid (Abeta) (25-35), a cytotoxic fragment of Abeta peptide, on lipid metabolism and protein ubiquitination in cultured rat hippocampal neurons. After treatment with Abeta under conditions leading to apoptotis, as assessed by caspase activity assay, the total cell mass of lipids changed following a biphasic behavior, with an increase that reached a maximum after 16 hr of treatment, followed by a decrease. The increase at 16 hr was 15.3% in the case of phospholipids and 103.0% in the case of gangliosides and was due to enhanced biosynthesis as confirmed by increase of radioactivity incorporation (phospholipids +52.0%, gangliosides +193.1%) in cells fed with tritiated palmitic acid. No change with respect to cholesterol was observed. Strikingly, under these conditions, the ubiquitination state of cell proteins strongly increased. These effects were not observed with the (35-25) reverse sequence peptide. Similarly to Abeta, lactacystin treatment increased lipid synthesis and protein ubiquitination; only lactacystin, and not Abeta, induced a strong decrease of proteasome chimotrypsin activity. These results suggest that Abeta enhances protein ubiquitination, without inhibiting proteasomal activity, and lipid synthesis. These results may shed new light on the mechanisms of Abeta toxicity.
Cazzaniga
Emanuela
E
Department of Experimental and Environmental Medicine, University of Milano Bicocca, Monza, Italy. emanuela.cazzaniga@unimib.it
Bulbarelli
Alessandra
A
Cassetti
Arianna
A
Lonati
Elena
E
Re
Francesca
F
Palestini
Paola
P
Mutoh
Tatsuro
T
Masserini
Massimo
M
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D016229:Amyloid beta-Peptides / Q000494:pharmacology*; D000818:Animals; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D002918:Chymotrypsin / Q000037:antagonists & inhibitors; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology; D050356:Lipid Metabolism / Q000187:drug effects*; D008854:Microscopy, Electron; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D019308:Palmitic Acid / Q000378:metabolism; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D014316:Tritium; D025801:Ubiquitin / Q000378:metabolism*
D016229:Amyloid beta-Peptides; D015853:Cysteine Proteinase Inhibitors; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D025801:Ubiquitin; C074636:amyloid beta-protein (25-35); D014316:Tritium; C067713:lactacystin; D019308:Palmitic Acid; D002918:Chymotrypsin; D020169:Caspases; D000111:Acetylcysteine