In Alzheimer disease (AD), amyloid-β (Aβ) oligomer is suggested to play a critical role in imitating neurodegeneration, although its pathogenic mechanism remains to be determined. Recently, the cellular prion protein (PrP(C)) has been reported to be an essential co-factor in mediating the neurotoxic effect of Aβ oligomer. However, these previous studies focused on the synaptic plasticity in either the presence or the absence of PrP(C) and no study to date has reported whether PrP(C) is required for the neuronal cell death, the most critical element of neurodegeneration in AD. Here, we show that Prnp(-/-) mice are resistant to the neurotoxic effect of Aβ oligomer in vivo and in vitro. Furthermore, application of an anti-PrP(C) antibody or PrP(C) peptide prevents Aβ oligomer-induced neurotoxicity. These findings are the first to demonstrate that PrP(C) is required for Aβ oligomer-induced neuronal cell death, the pathology essential to cognitive loss.

We show that nuclear fragmentation in neurodegeneration is an early trigger for cell death initiated by deregulated Cdk5. Cdk5 induces nuclear dispersion by direct phosphorylation of lamins in neurons and in vivo Alzheimer's disease (AD) mouse models. Inhibition of nuclear fragmentation rescues neurons from cell death, underscoring the significance of this event in AD.

Retinoic acid, an essential factor derived from vitamin A, has been shown to have a variety of functions including roles as an antioxidant and in cellular differentiation. Since oxidative stress and de-differentiation of neurons appear to be common pathological elements of a number of neurodegenerative disorders, we speculated that retinoic acid may offer therapeutic promise. In this vein, recently compelling evidence indicates a role of retinoic acid in cognitive activities and anti-amyloidogenic properties. Here, we review the actions of retinoic acid that indicate that retinoic acid may have therapeutic properties ideally served for the treatment of neurodegenerative diseases such as Alzheimer's disease.

Cyclin-dependent kinase (Cdk) 5 and p38 activities are significantly increased in Alzheimer's Disease (AD). Both p38 and Cdk5 promote neurodegeneration upon deregulation. However, to date the mechanistic link between Cdk5 and p38 remains unclear. This study presents the first mechanism showing Cdk5 as a major regulator of p38 cascade in neurons and in transgenic mouse model of AD. Using b-amyloid and glutamate as the neurotoxic stimuli, our results show that deregulated Cdk5 induces p38 activation by increasing reactive oxygen species (ROS) in neuronal cells and in primary cortical neurons. Elimination of ROS inhibits p38 activation, revealing ROS as major stimuli of the p38 cascade.Importantly, Cdk5-mediated p38 activation increases c-Jun expression, thereby revealing a mechanistic link between deregulated Cdk5 and c-Jun level in AD brains. c-Jun is overexpressed in AD, and is believed to contribute significantly to neurodegeneration. Based on the proposed mechanism, Cdk5 inhibition is more neuroprotective relative to p38 and c-Jun, suggesting that Cdk5 is an upstream regulator of neurodegenerative pathways triggered by p38 and a preferable therapeutic target for AD.

Oxidative stress is an important factor, and one that acts in the earliest stages, of Alzheimer's disease (AD) pathogenesis. The reduction of oxidative stress has been tested as a therapy for AD. While the trial of vitamin E supplementation in moderately severe AD is the most promising so far, it also reveals the limitations of general antioxidant therapies that simply lower oxidative stress and, therefore, the complexity of the redox system. The multiple contributing factors that foster the clinical manifestations of AD should be considered when designing antioxidative stress therapy. In this article, we discuss the multiple pathogenic mechanisms of oxidative stress in AD and the potential targeting approaches.