AbstractPoster presentation: Wednesday posterP4-053: JNK regulates APP processing

The accumulation of Amyloid beta peptide (Aβ) in senile plaques is widely believed to play a central role in Alzheimer's disease (AD). Aβ peptides (β1–40 and β1–42), derive from the proteolytic processing of the Amyloid Precursor Protein (APP). The exact mechanism by which these peptides trigger neuronal death is not well defined. However, the disturbance of the calcium homeostasis and the activation of caspases and c–Jun N–terminal kinase (JNK) are factors involved in the death process induced by Aβ. It has recently been demonstrated that the JNK scaffold protein, JIP–1, interacts with the cytoplasmic domain of APP, suggesting that JIP–1 and JNK may play important roles in the metabolism of APP. It has also been established that APP is phosphorylated at Thr 668 by JNK. This phosphorylation in the cytoplasmic domain of APP may result in a regulation of the APP processing. We examined here the role of JNK in AD pathogenesis using a specific cell–permeable JNK inhibitor peptide, D–JNKI–1, and two different in vitro models: primary cortical neurons and H4–15x cells, stably transfected with human APP695 carrying Swedish mutation. Cortical neurons and H4 cells were treated with increasing concentrations of D–JNKI–1 for 24h and western blot analysis of secreted APP (APPs) was conducted on both culture media and cell lysates. We observed a dose–response effect of D–JNKI–1, with a powerful reduction in APPs production. In fact, in cortical neurons, D–JNKI–1 (6μM) reduced by about 80% the level of APPs in both lysates and media, and this also correlated with a decrease in the media of Aβ fragments (40%). In the H4–15x using 80μM D–JNKI–1 we obtained 70% reduction in APPs production and 45% decrease of Aβ fragments. In both cellular models D–JNKI–1 prevented phosphorylation of APP at Thr 668 in a dose–dependent way. These data indicate an important role of JNK signalling pathway in the regulation of APP metabolism: in our models the proteolytic production of APPs and β1–40/1–42 was strongly reduced by the application of a specific JNK inhibitor that prevented the APP phosphorylation.