Rapid cell death is preceded by amyloid plaque-mediated oxidative stress

Abstract

Neuronal loss is the ultimate outcome in a variety of neurodegenerative diseases and central nerve system disorders. Understanding the sequelae of events that leads to cell death would provide insight into neuroprotective approaches. We imaged neurons in the living brain of a mouse model of Alzheimer's disease that overexpresses mutant human amyloid precursor protein and presenilin 1 and followed the death of individual neurons in real time. This mouse model exhibited limited neurodegeneration and atrophy, but we were able to identify a small fraction of vulnerable cells that would not have been detectable by using standard approaches. By exploiting a genetically encoded reporter of oxidative stress, we identified susceptible neurons by their increased redox potential. The oxidative stress was most dramatic in neurites near plaques, propagated to cell bodies, and preceded activation of caspases that led to cell death within 24 h. Thus, local oxidative stress surrounding plaques contributes to longrange toxicity and selective neuronal death in Alzheimer's disease.in vivo imaging | reduction-oxidation sensitive GFP A lzheimer's disease (AD) is underscored by neurodegeneration and is the most common form of dementia. The pathological hallmarks of this disease include amyloid plaques, neurofibrillary tangles, and neuronal loss. Early-onset familial AD is caused by genetic mutations of amyloid precursor protein (APP) or presenilin 1 and 2 (PS1 and PS2). Although recent genetic studies have revealed risk factors for late onset AD, the pathogenic pathways for sporadic AD remain largely unknown. The development of mouse models of AD that develop senile plaques similar to those found in AD patients was a critical step in identifying the role of amyloid β (Aβ) on neuronal function. A major disappointment of most of the mouse models is the lack of overt neuronal loss that is a hallmark of the human disease. Many, in fact, have used this lack of neuronal death as evidence that amyloid is not relevant to dementia in AD. We and others (1-4) have identified structural and functional alterations of neurons in the brains of APP mice that implicate amyloid-mediated toxicity, but we have never detected neuronal death. The ability to monitor cell death in an experimental model provides the opportunity to intervene with neuroprotective agents that could be applied to the spectrum of neurodegenerative diseases and CNS disorders.We were able to identify vulnerable cells by quantitatively imaging the redox potential of neurons in the living brain. Our hypothesis was that amyloid-mediated increases in oxidative stress are the initiators of the toxic cascade that leads to cell loss. Accumulating evidence supports a role for oxidative stress in the pathogenesis of neuronal degeneration and death in AD (5-8). The evidence supporting oxidative stress in AD comes largely from postmortem samples and includes increased lipid peroxidation, decreased polyunsaturated fatty acids (9-12), increased protein oxidation (13,14), and DNA oxidation (15, ...

In vivo imaging of immediate early gene expression reveals layer-specific memory traces in the mammalian brain

“…The EGFP signals were acquired using multiphoton imaging through a cranial window (30)(31)(32) (Fig. S2C).…”

“…Animal care was in accordance with the Institutional Guidelines of Tsinghua University. Three-to 5-mo-old mice received cranial window implantation as previously described (32) and recordings began 1 mo later. To implant the cranial window, the mouse was immobilized in custom-built stage-mounted ear bars and a nosepiece, similar to a stereotaxic apparatus.…”

“…On each session, a field of view was selected according to the marked blood vessel to perform the repetitive imaging on the same volume. To facilitate the location of cortical volumes from section to section, dextran Texas red (Dex Red; 70,000 molecular weight; Invitrogen) was injected into a lateral tail vein to create a fluorescent angiogram, as previously described (32).…”

Mint Proteins Are Required for Synaptic Activity-dependent Amyloid Precursor Protein (APP) Trafficking and Amyloid β Generation

“…However, it is now clearly recognized that they play a dynamic role in finely tuning cellular information and responses (29,30). Mint1 and Mint2 play more sophisticated roles in achieving functional regulation through autoinhibitory mechanisms (31,32). We have shown previously that Mint1 undergoes a conformational switch between a "closed" state that does not bind APP and an "open" state involved in APP binding and that this switch plays a central role in regulating A␤ production (31).…”

Application of APP/PS1 Transgenic Mouse Model for Alzheimer’s Disease

“…Some researchers have found that clearance of extracellular Aβ by the monoclonal antibody 3D6 or reactive oxygen species by N-tert-butylphenylnitrone (PBN) did not rescue the cellular oxidative stress in neurites surrounding Aβ plaques in APP/PS1 mouse. This non-rescue event suggests that once the redox potential increased within cells that the effect of external anti-oxidants are ineffective .This non-rescue event implies that prevention therapies will be more effective than treatment therapies or that longer durations of treatment will be necessary [36].…”