Pathological effects of glyoxalase I inhibition in SH-SY5Y neuroblastoma cells.
In Alzheimer's disease (AD), in aging, and under conditions of oxidative stress, the levels of reactive carbonyl compounds continuously increase. Accumulating carbonyl levels might be caused by an impaired enzymatic detoxification system. The major dicarbonyl detoxifying system is the glyoxalase system, which removes methylglyoxal in order to minimize cellular impairment. Although a reduced activity of glyoxalase I was evident in aging brains, it is not known how raising the intracellular methylglyoxal level influences neuronal function and the phosphorylation pattern of tau protein, which is known to be abnormally hyperphosphorylated in AD. To simulate a reduced glyoxalase I activity, we applied an inhibitor of glyoxalase I, p-bromobenzylglutathione cyclopentyl diester (pBrBzGSCp(2)), to SH-SY5Y neuroblastoma cells to induce chronically elevated methylglyoxal concentrations. We have shown that 10 microM pBrBzGSCp(2) leads to a fourfold elevation of the methylglyoxal level after 24 hr. In addition, glyoxalase I inhibition leads to reduced cell viability, strongly retracted neuritis, increase in [Ca(2+)](i), and activation of caspase-3. However, pBrBzGSCp(2) did not lead to tau "hyper"-phosphorylation despite activation of p38 mitogen-activated protein kinase and c-Jun NH(2)-terminal kinase but rather activated protein phosphatases 2 and induced tau dephosphorylation at the Ser(202)/Thr(205) and Ser(396)/Ser(404) epitopes. Preincubation with the carbonyl scavenger aminoguanidine prevented tau dephosphorylation, indicating the specific effect of methylglyoxal. Also, pretreatment with the inhibitor okadaic acid prevented tau dephosphorylation, indicating that methylglyoxal activates PP-2A. In summary, our data suggest that a reduced glyoxalase I activity mimics some changes associated with neurodegeneration, such as neurite retraction and apoptotic cell death.
Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA. kuhb@medizin.uni-leipzig.de
Björn
B
Kuhla
Hans-Joachim
HJ
Lüth
Dietrich
D
Haferburg
Michael
M
Weick
Andreas
A
Reichenbach
Thomas
T
Arendt
Gerald
G
Münch
D000544:Alzheimer Disease / Q000378:metabolism / Q000503:physiopathology; D017209:Apoptosis / Q000502:physiology*; D001921:Brain / Q000201:enzymology* / Q000503:physiopathology; D053148:Caspase 3; D020169:Caspases / Q000187:drug effects / Q000378:metabolism; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007791:Lactoylglutathione Lyase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009410:Nerve Degeneration / Q000201:enzymology* / Q000503:physiopathology; D016501:Neurites / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D009447:Neuroblastoma; D019636:Neurodegenerative Diseases / Q000378:metabolism / Q000503:physiopathology; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D010749:Phosphoprotein Phosphatases / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011765:Pyruvaldehyde / Q000378:metabolism; D013997:Time Factors; D016875:tau Proteins / Q000187:drug effects / Q000378:metabolism
D004791:Enzyme Inhibitors; D016875:tau Proteins; D011765:Pyruvaldehyde; D010749:Phosphoprotein Phosphatases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D007791:Lactoylglutathione Lyase