Abstract
The E3 ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C) is activated by the fizzy-related protein homolog/CDC20-like protein 1 (cdh1) in post-mitotic neurons. Growing evidence suggests that dysregulation of APC/C-Cdh1 is involved in neurodegenerative diseases. Here we show in neurons that oligomers of amyloid beta (Aβ), a peptide related to Alzheimer’s disease, cause proteasome-dependent degradation of cdh1. This leads to a subsequent increase in glutaminase (a degradation target of APC/C-Cdh1), which causes an elevation of glutamate levels and further intraneuronal Ca2+ dysregulation, resulting in neuronal apoptosis. Glutaminase inhibition prevents glutamate excitotoxicity and apoptosis in Aβ treated neurons. Furthermore, glutamate also decreases cdh1 and leads to accumulation of glutaminase, suggesting that there may be a positive feedback loop of cdh1 inactivation. We confirmed the main findings in vivo using microinjection of either Aβ or glutamate in the CA1 region of the rat hippocampus. We show here for the first time in vivo that both Aβ and glutamate cause nuclear exclusion of cdh1 and an increase in glutaminase. These results show that maintaining normal APC/C-Cdh1 activity may be a useful target in Alzheimer’s disease treatment.
Highlights
anaphase-promoting complex/cyclosome (APC/C)-Cdh[1] recognizes proteins by specific amino acid motifs like KEN-BOX or D-BOX sequences and targets them for degradation
To further test whether Aβ-induced decrease of cdh[1] is caused only by its degradation or whether it depends on changes in gene expression, we measured mRNA levels of cdh[1] and APC/C2, the catalytic subunit of the protein complex, using qPCR
APC/C-Cdh[1] plays an essential role in neurons, and dysregulation of this ubiquitin ligase has been associated with neurodegeneration[3]
Summary
APC/C-Cdh[1] recognizes proteins by specific amino acid motifs like KEN-BOX or D-BOX sequences and targets them for degradation. (g,h) Mean values ±SD of mRNA levels of cdh[1] and APC/C2 normalized against GAPDH in control conditions or with Aβtreatment for 24 h are shown. (i) Representative Western blot image of cdh[1] protein in neurons upon treatment with MG132, in control conditions, with Aβtreatment or with Aβ+MG132. (j) Blots of three independent experiments were quantified by densitometry and normalized against α-tubulin; the mean values ±SD are indicated (p < 0,05; p < 0,05). In addition we observed alterations of cdh[1] and glutaminase in the APP/PS1 mouse model of AD These results provide a molecular mechanism that contributes to glutamate excitotoxicity in AD, mediated by inhibition of APC/C-Cdh[1]
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