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Toxicity induced by aberrant protein aggregates in Alzheimer's disease ( AD) causes synaptic disconnection and concomitant progressive neurodegeneration that eventually impair cognitive function. cAMP-response element-binding protein ( CREB) is a transcription factor involved in the molecular switch that converts short-term to long-term memory. Although disturbances in CREB function have been suggested to cause memory deficits in both AD and AD animal models, the mechanism of CREB dysfunction is still unclear. Here, we show that the dopamine- and cAMP-regulated phosphoprotein 32 kDa ( DARPP-32), a key inhibitor of protein phosphate-1 ( PP-1) that regulates CREB phosphorylation, is cleaved by activated calpain in both AD brains and neuronal cells treated with amyloid-β or okadaic acid, a protein phosphatase-2A inhibitor that induces tau hyperphosphorylation and neuronal death. We found that DARPP-32 is mainly cleaved at Thr153 by calpain and that this cleavage of DARPP-32 reduces CREB phosphorylation via loss of its inhibitory function on PP1. Our results suggest a novel mechanism of DARPP-32- CREB signalling dysregulation in AD. [ABSTRACT FROM AUTHOR]

Abstract: Mitochondrial dysfunction is a prominent feature of neurodegenerative diseases and aging. A recent study showed that phosphorylation of dynamin-related protein 1 (Drp1) is increased in Alzheimer''s disease (AD) brains compared to control brains, indicating that mitochondrial fission is increased in AD brains. Here, we showed that Drp1 phosphorylation and mitochondrial fission were also increased in rat cortical neurons treated with okadaic acid (OA), which inhibits protein phosphatase-2A (PP2A) and induces AD-like tau phosphorylation and neuronal death. Concurrent with this abnormal increase in mitochondrial fission, mitochondrial reactive oxygen species (ROS) were also increased, suggesting mitochondrial damage and detrimental effects on cell survival. Parkin, which is necessary for mitophagy of abnormal mitochondria and has been shown to be decreased in AD brains, and K48-linked polyubiquitin were also decreased in OA-treated neurons, suggesting that the mitophagic process required to degrade detrimental ROS-generating mitochondria is disabled. Collectively, our results demonstrate that abnormal mitochondrial fission, ROS generation, and inefficient mitophagy all occur in PP2A-inhibited neurons, as in AD brains, and suggest that this model could be used in developing inhibitors of mitochondrial fission or ROS generation. [Copyright &y& Elsevier]

The link between Val232Met variant of phospholipase D3 (PLD3) and late-onset Alzheimer's disease (AD) is still obscure. While it may not affect directly the amyloid precursor protein function, PLD3 could be regulating multiple cellular compartments. Here, we investigated the function of wild-type human PLD3 (PLD3WT) and the Val232Met variant (PLD3VM) in the presence of β-amyloid (Aβ) in a Drosophila melanogaster model of AD. We expressed PLD3WT in CNS of the Aβ-model flies and monitored its effect on the ER stress, cell apoptosis and recovery the Aβ-induced cognitive impairment. The expression reduced ER stress and neuronal apoptosis, which resulted in normalized antioxidative phospholipids levels and brain protection. A specific O-glycosylation at pT271 in PLD3 is essential for its normal trafficking and cellular localization. The V232 M substitution impairs this O-glycosylation, leading to enlarged lysosomes and plausibly aberrant protein recycling. PLD3VM was less neuroprotective, and while, PLD3WT expression enhances the lysosomal functions, V232 M attenuated PLD3's trafficking to the lysosomes. Thus, the V232 M mutation may affect AD pathogenesis. Further understanding of the mechanistic role of PLD3 in AD could lead to developing novel therapeutic agents. • A specific O-glycosylation at pT271 in PLD3 is essential for its normal trafficking and cellular localization. • PLD3WT expression is neuroprotective, while pV232M attenuated PLD3's glycosylation, trafficking and lead to enlarged lysosomal structures. • The mechanistic role of PLD3 in AD could lead to developing novel therapeutic agents. [ABSTRACT FROM AUTHOR]