Inhibition of tissue transglutaminase promotes Aβ-induced apoptosis in SH-SY5Y cells.
OBJECTIVE
Tissue transglutaminase (tTG) catalyzes proteins, including β-amyloid (Aβ), to cross-link as a γ-glutamyl-ε-lysine structure isopeptide, which is highly resistant to proteolysis. Thus, tTG plays an important role in protein accumulation in Alzheimer's disease (AD). In the present study, we examined the effect of an irreversible tTG inhibitor, NTU283, on Aβ mimic-induced AD pathogenesis in SH-SY5Y cells.


METHODS
Western blot and in-cell Western analyses were used to detect tTG and isopeptide (representing the enzyme activity of tTG) protein levels. Moreover, Hoechst and PI co-staining was performed, and caspase-3 and caspase-7 activities and the Bax/Bcl-2 ratio were determined to evaluate the effects of NTU283 on apoptosis.


RESULTS
The results confirmed that tTG activity was inhibited by NTU283 20-500 μmol/L in a concentration-dependent manner in SH-SY5Y cells. Contrary to our expectations, however, the isopeptide bonds were increased when cells were co-treated with Aβ and NTU283. In addition, NTU283 alone did not induce apoptosis in SH-SY5Y cells. However, when co-applied with Aβ, NTU283 promoted rather than inhibited Aβ-induced apoptosis. Consistent with the apoptotic rate, pretreating cells with different concentrations of NTU283 and Aβ significantly increased the activities of caspase-3 and caspase-7 as well as the ratio of Bax/Bcl-2.


CONCLUSIONS
Irreversible inhibition of tTG activity did not block but rather promoted Aβ-induced apoptosis, which indicated that tTG has complex functions in AD pathogenesis.
Shanghai Key Laboratory of New Drug Design, School of Pharmacy, East China University of Science and Technology, Shanghai 200237, China.|Department of Nuclear Medicine, Fudan University Shanghai Cancer Center, Shanghai 200032, China.|Department of Oncology, Shanghai Medical College, Fudan University, Shanghai 200032, China.
Ji
J
Zhang
Shanghai Key Laboratory of New Drug Design, School of Pharmacy, East China University of Science and Technology, Shanghai 200237, China.
Yi-Rong
YR
Ding
Shanghai Key Laboratory of New Drug Design, School of Pharmacy, East China University of Science and Technology, Shanghai 200237, China.
Rui
R
Wang
D000544:Alzheimer Disease / Q000188:drug therapy; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology* / Q000633:toxicity; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases / Q000037:antagonists & inhibitors*
C000613701:1,3-dimethyl-2-((2-oxopropyl)sulfanyl)-1H-imidazol-3-ium; D016229:Amyloid beta-Peptides; D007093:Imidazoles; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins
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