Amyloid 13 Protein Aggravates Neuronal Senescence an, d Cognitive Deficits in 5XFAD Mouse Model of Alzheimer s Disease

Background： Amyloid β （Aβ） has been established as a key factor for the pathological changes in the brains of patients with Alzheimer＇s disease （AD）, and cellular senescence is closely associated with aging and cognitive impairment. However, it remains blurred whether, in theAD brains, Aβ accelerates the neuronal senescence and whether this senescence, in turn, impairs the cognitive function. This study aimed to explore the expression of senescence-associated genes in the hippocampal tissue from young to aged 5XFAD mice and their age-matched wild type （WT） mice to determine whether senescent neurons are present in the transgenic AD mouse model. Methods： The 5XFAD mice and age-matched wild type mice, both raised from 1 to 18 months, were enrolled in the study. The senescence-associated genes in the hippocampus were analyzed and differentially expressed genes （DEGs） were screened by quantitative real-time polymerase chain reaction. Cognitive perfom3ance of the mice was evaluated by Y-maze and Morris water maze tests. Oligomeric Aβ（oAβ） （1-42） was applied to culture primary neurons to simulate the in vivo manifestation. Aging-related proteins were detected by Western blotting analysis and immunofluorescence. Results： In 5XFAD mice, of all the DEGs, the senescence-associated marker p16 was most significantly increased, even at the early age. It was mainly localized in neurons, with a marginal expression in astrocytes （labeled as glutamine synthetase）, nil expression in activated microglia （labeled as lba1）, and negatively correlated with the spatial cognitive impairments of 5XFAD mice. oAβ （1-42） induced the production of senescence-related protein p1 6, but not p53 in vitro, which was in line with the in vivo manifestation. Conclusions： oAβ-accelerated neuronal senescence may be associated with the cognitive impairment in 5XFAD mice. Senescence-associated marker p16 can serve as an indicator to estimate the cognitive prognosis for A D population.

Endoplasmic Reticulum Stress Induces the Early Appearance of Pro-apoptotic and Anti-apoptotic Proteins in Neurons of Five Familial Alzheimer＇s Disease Mice

Background： Amyloid β （Aβ） deposits and the endoplasmic reticulum stress （ERS） are both well established in the development and progression of Alzheimer＇s disease （AD）. However, the mechanism and role of Aβ-induced ERS in AD-associated pathological progression remain to be elucidated. Methods： The five familial AD （5×FAD） mice and wild-type （WT） mice aged 2, 7, and 12 months were used in the present study. Monis water maze test was used to evaluate their cognitive performance, lmmunofluorescence and Western blot analyses were used to examine the dynamic changes of pro-apoptotic （CCAAT/enhancer-binding protein homologous protein [CHOP] and cleaved caspase-12） and anti-apoptotic factors （chaperone glucose-regulated protein [GRP] 78 and endoplasmic reticulum-associated protein degradation-associated ubiquitin ligase synovial apoptosis inhibitor 1 [SYVN 1]） in the ERS-associated unfolded protein response （UPR） pathway. Results： Compared with age-matched WT mice, 5 xFAD mice showed higher cleaved caspase-3, lower neuron-positive staining at the age of 12 months, but earlier cognitive deficit at the age of 7 months （all P 〈 0.05）. Interestingly, for 2-month-old 5×FAD mice, the related proteins involved in the ERS-associated UPR pathway, including CHOP, cleaved caspase-12, GRP 78, and SYVN 1, were significantly increased when compared with those in age-matched WT mice （all P 〈 0.05）. Moreover, ERS occurred mainly in neurons, not in astrocytes. Conclusions： These findings suggest that compared with those of age-matched WT mice, ERS-associated pro-apoptotic and anti-apoptotic proteins are upregulated in 2-month-old 5×FAD mice, consistent with intracellular Aβ aggregation in neurons.

Reduction of Glucose Metabolism in Olfactory Bulb is an Earlier Alzheimer＇s Disease-related Biomarker in 5XFAD Mice

Background：Early diagnosis assumes a vital role in an effective treatment of Alzheimer＇s disease （AD）.Most of the current studies can only make anAD diagnosis after the manifestation of typical clinical symptoms.The present study aimed to investigate typical and other biomarkers of AD to find a possible early biomarker.Methods：A total of 14 5XFAD mice （at 3 and 6 months old）,with 14 age-matched wild-type （WT） mice as control,were enrolled in this case-control study.Morris water maze test was performed to evaluate the cognitive function;buried food pellet test and olfactory maze test were employed to investigate the olfactory function;immunofluorescence to detect amyloid deposition and positron emission tomography to examine 2-deoxy-2-（18F） fluoro-D-glucose （[18F]-FDG） uptake in the hippocampus and cerebral cortex.Results：With the increasing age,cognitive performance （P =0.0262） and olfactory function were significantly deteriorated （day 1 P =0.0012,day 2 P =0.0031,day 3 P =0.0160,respectively） and the （18F）-FDG uptake was markedly decreased in multi-cerebral regions including the olfactory bulb （P 〈 0.0001）,hippocampus （P =0.0121）,and cerebral cortex （P 〈 0.0001）.Of note,in 3-month-old 5XFAD mice,a significant decline of （18F）-FDG uptake in the olfactory bulb was found when compared with that of age-matched WT mice （P =0.023） while no significant difference was present when the uptakes in other cerebral regions were compared.Conclusions：The decline of （18F）-FDG uptake in the olfactory bulb occurs earlier than other incidents,serving as an earlier in vivo biological marker of AD in 5XFAD mice and making early diagnosis of AD possibly.