Expression of the neuronal adaptor protein X11alpha protects against memory dysfunction in a transgenic mouse model of Alzheimer's disease

A novel mechanism of memory loss in Alzheimer's disease mice via the degeneration of entorhinal-CA1 synapses

The entorhinal cortex (EC) is one of the most vulnerable brain regions that is attacked during the early stage of Alzheimer's disease (AD). Here, we report that the synaptic terminals of pyramidal neurons in the EC layer II (ECII_PN) directly innervate CA1 parvalbumin (PV) neurons (CA1_PV) and are selectively degenerated in AD mice, which exhibit amyloid-β plaques similar to those observed in AD patients. A loss of ECII_PN-CA1_PV synapses disables the excitatory and inhibitory balance in the CA1 circuit and impairs spatial learning and memory. Optogenetic activation of ECII_PN using a theta burst paradigm rescues ECII_PN-CA1_PV synaptic defects and intercepts the decline in spatial learning and memory. These data reveal a novel mechanism of memory loss in AD mice via the selective degeneration of the ECII_PN-CA1_PV pathway.

Systematic review of the relationship between amyloid-β levels and measures of transgenic mouse cognitive deficit in Alzheimer's disease

Amyloid-β (Aβ) is believed to directly affect memory and learning in Alzheimer’s disease (AD). It is widely suggested that there is a relationship between Aβ₄₀ and Aβ₄₂ levels and cognitive performance. In order to explore the validity of this relationship, we performed a meta-analysis of 40 peer-reviewed, published AD transgenic mouse studies that quantitatively measured Aβ levels in brain tissue after assessing cognitive performance. We examined the relationship between Aβ levels (Aβ₄₀, Aβ₄₂, or the ratio of Aβ₄₂ to Aβ₄₀) and cognitive function as measured by escape latency times in the Morris water maze or exploratory preference percentage in the novel object recognition test. Our systematic review examined five mouse models (Tg2576, APP, PS1, 3xTg, APP(OSK)-Tg), gender, and age. The overall result revealed no statistically significant correlation between quantified Aβ levels and experimental measures of cognitive function. However, enough of the trends were of the same sign to suggest that there probably is a very weak qualitative trend visible only across many orders of magnitude. In summary, the results of the systematic review revealed that mice bred to show elevated levels of Aβ do not perform significantly worse in cognitive tests than mice that do not have elevated Aβ levels. Our results suggest two lines of inquiry: 1) Aβ is a biochemical “side effect” of the AD pathology; or 2) learning and memory deficits in AD are tied to the presence of qualitatively “high” levels of Aβ but are not quantitatively sensitive to the levels themselves.

Cellular, synaptic, and biochemical features of resilient cognition in Alzheimer's disease

Although neuritic plaques and neurofibrillary tangles in older adults are correlated with cognitive impairment and severity of dementia, it has long been recognized that the relationship is imperfect, as some people exhibit normal cognition despite high levels of Alzheimer's disease (AD) pathology. We compared the cellular, synaptic, and biochemical composition of midfrontal cortices in female subjects from the Religious Orders Study who were stratified into three subgroups: (1) pathological AD with normal cognition ("AD-Resilient"), (2) pathological AD with AD-typical dementia ("AD-Dementia"), and (3) pathologically normal with normal cognition ("Normal Comparison"). The AD-Resilient group exhibited preserved densities of synaptophysin-labeled presynaptic terminals and synaptopodin-labeled dendritic spines compared with the AD-Dementia group, and increased densities of glial fibrillary acidic protein astrocytes compared with both the AD-Dementia and Normal Comparison groups. Further, in a discovery-type antibody microarray protein analysis, we identified a number of candidate protein abnormalities that were associated with a particular diagnostic group. These data characterize cellular and synaptic features and identify novel biochemical targets that may be associated with resilient cognitive brain aging in the setting of pathological AD.

Aggressive behavior, cognitive impairment, and depressive symptoms in elderly subjects

Patients with dementia often have neuropsychiatric symptoms. The objective of this study was to evaluate the relationship between neuropsychiatric symptoms and progressive cognitive decline by assessing cognitive impairment, depressive symptoms, and aggressive behavior in a sample of elderly subjects. The study sample consisted of 201 subjects admitted to nursing homes. For the purpose of the present study each subject was evaluated using the Mini-Mental State Examination, the Geriatric Depression Scale, and the Modified Overt Aggression Scale. The results show that aggressive behavior and depressive symptoms are associated with progressive cognitive decline in elderly subjects. Early assessment of these conditions can promote rational therapeutic strategies that may improve the quality of life and delay institutionalization for elderly patients.

An X11alpha/FSBP complex represses transcription of the GSK3beta gene promoter

X11alpha is a neuronal adaptor protein that interacts with the amyloid precursor protein (APP) through a centrally located phosphotyrosine binding domain to inhibit the production of Abeta peptide that is deposited in Alzheimer's disease brains. X11alpha also contains two C-terminal postsynaptic density-95, large discs, zona occludens 1 (PDZ) domains, and we show here that through its PDZ domains, X11alpha interacts with a novel transcription factor, fibrinogen silencer binding protein. Moreover, we show that an X11alpha/fibrinogen silencer binding protein complex signals to the nucleus to repress glycogen synthase kinase-3beta promoter activity. Glycogen synthase kinase-3beta is a favoured candidate kinase for phosphorylating tau in Alzheimer's disease. Our findings show a new function for X11alpha that may impact on Alzheimer's disease pathogenesis.

Deficiency of the copper chaperone for superoxide dismutase increases amyloid-β production

The copper chaperone for superoxide dismutase (CCS) binds to both the β-site AβPP cleaving enzyme (BACE1) and to the neuronal adaptor protein X11α. BACE1 initiates AβPP processing to produce the amyloid-β (Aβ) peptide deposited in the brains of Alzheimer's disease patients. X11α also interacts directly with AβPP to inhibit Aβ production. However, whether CCS affects AβPP processing and Aβ production is not known. Here we show that loss of CCS increases Aβ production in both CCS knockout neurons and CCS siRNA-treated SHSY5Y cells and that this involves increased AβPP processing at the BACE1 site.