Temporal relationship of autophagy and apoptosis in neurons challenged by low molecular weight β-amyloid peptide.
Bottom Line: On the other hand, Aβ activated autophagy by inducing autophagic vesicle formation and autophagy related gene 12 (ATG12), and up-regulated the lysoso-mal machinery for the degradation of autophagosomes.Moreover, we demonstrated that activation of autophagy by Aβ preceded that of apoptosis, with death associated protein kinase phosphorylation as the potential molecular link.More importantly, under Aβ toxicity, neurons exhibiting high level of autophagosome formation were absent of apoptotic features, and inhibition of autophagy by 3-methylade-nine advanced neuronal apoptosis, suggesting that autophagy can protect neurons from Aβ-induced apoptosis.
Affiliation: Laboratory of Neurodegenerative Diseases, Department of Anatomy, The University of Hong Kong, Pokfulam, Hong Kong, China.Show MeSH
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Mentions: We tried to confirm this hypothesis by manipulating autophagy by the chemical inhibitor 3-MA  which inhibits PI3K. Without 3-MA, we demonstrated that low MW Aβ significantly increased the levels of both LC3-I and LC3-II at 24 hrs, which indicated the activation of autophagy, when compared to the vehicle-treated control (Fig. 13). When neurons were co-treated with 10 mM of 3-MA for 24 hrs, the levels of LC3-I and II of the 10 μM Aβ treated group were comparable to the vehicle-treated control, indicating that autophagy was inhibited by 3-MA. LC3 levels after 20 μM Aβ treatment were lower in the 3-MA group than that without 3-MA but higher than the vehicle control with 3-MA. This indicated that 10 mM 3-MA did not completely abolish autophagy induced by 20 μM Aβ. When we examined the effect of autophagy inhibition on apoptosis, we first demonstrated that the levels of cleaved cas-pase 3 in vehicle-treated control with or without 10 mM 3-MA were comparable (Fig. 13), suggesting 3-MA did not cause a cytotoxic effect in neurons. When neurons were treated with Aβ, cleaved caspase 3 levels increased with dose, which agrees with our Western blot analysis in Fig. 2. However, when the neurons were co-treated with 10 mM of 3-MA, the levels of cleaved cas-pase 3 markedly increased in all doses of Aβ treatment, suggesting that inhibition of autophagy advanced apoptosis. This further supports our hypothesis that neurons can be protected from Aβ-induced apoptosis by activating autophagy.
Affiliation: Laboratory of Neurodegenerative Diseases, Department of Anatomy, The University of Hong Kong, Pokfulam, Hong Kong, China.