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Increased Human like Alzheimer features in a Novel Mouse Model with Oxidative DNA Repair Dysfunction

ABSTRACT: The decline of cognitive function is a feature of normal human aging and is exacerbated in Alzheimer’s disease (AD). DNA repair declines in brain cells during normal aging and even more so in AD. Here we show that experimental reduction in levels of the base excision repair enzyme, DNA polymerase β (Polb) renders neurons vulnerable to age-related dysfunction and degeneration in a mouse model of AD. Whereas 3xTgAD mice exhibit age-related extracellular amyloid b-peptide (Ab) accumulation and cognitive deficits, but no neuronal death, 3xTg/Polb+/- mice accumulates intracellular Ab and neurons die in the hippocampus and cerebral cortex. The DNA repair-deficient 3xTgAD mice exhibited increased DNA strand breaks and apoptotic caspase activation with loss of hippocampal volume, and impaired synaptic plasticity and memory retention. Molecular profiling revealed remarkable similarities in gene expression alterations in brain cells of AD patients and 3xTgAD/Polb+/- mice including multiple abnormalities suggestive of impaired cellular bioenergetics. Our findings demonstrate that a modest decrement in oxidative DNA damage processing is sufficient to render neurons vulnerable to AD-related pathogenic molecular and cellular alterations that result in the dysfunction and death of neurons, and associated cognitive deficits.

ORGANISM(S): Mus musculus

PROVIDER: GSE60911 | GEO | 2015/01/05

SECONDARY ACCESSION(S): PRJNA259802

REPOSITORIES: GEO

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Project description:The decline of cognitive function is a feature of normal human aging and is exacerbated in AlzheimerM-bM-^@M-^Ys disease (AD). DNA repair declines in brain cells during normal aging and even more so in AD. Here we show that experimental reduction in levels of the base excision repair enzyme, DNA polymerase M-NM-2 (Polb) renders neurons vulnerable to age-related dysfunction and degeneration in a mouse model of AD. Whereas 3xTgAD mice exhibit age-related extracellular amyloid b-peptide (Ab) accumulation and cognitive deficits, but no neuronal death, 3xTg/Polb+/- mice accumulates intracellular Ab and neurons die in the hippocampus and cerebral cortex. The DNA repair-deficient 3xTgAD mice exhibited increased DNA strand breaks and apoptotic caspase activation with loss of hippocampal volume, and impaired synaptic plasticity and memory retention. Molecular profiling revealed remarkable similarities in gene expression alterations in brain cells of AD patients and 3xTgAD/Polb+/- mice including multiple abnormalities suggestive of impaired cellular bioenergetics. Our findings demonstrate that a modest decrement in oxidative DNA damage processing is sufficient to render neurons vulnerable to AD-related pathogenic molecular and cellular alterations that result in the dysfunction and death of neurons, and associated cognitive deficits. 4 mouse strains were used in these experiments, the 3xTgAD and Pol M-NM-2 (+/-) mice were bred at the National Institute on Aging (Baltimore, Maryland). The original line 3xTgAD line was generated as described previously (Oddo, et. al 2003) and possess APPswe, PS1M146V, and tauP301L mutations. DNA polymerase beta heterozygous mice, Pol M-NM-2 (+/-), were crossed with the 3xTgAD mice to generate a 3xTgAD/Pol M-NM-2 (+/-) mouse. The Wt strain is C57Bl/6. At 20 months of age these mice were euthanized by cervical dislocation, the brain removed from the skull and dissected into regions of interest, the prefrontal cortex was used for the microarray studies.

Project description:Alzheimer's disease (AD) is the most common type of dementia and is characterized by cognitive and behavioral impairment that significantly interferes with social functioning. Over the last decade, there has been an increased interest in whether sensory deficiency may be associated with the development of AD. Notably, the relationship between hearing impairment and AD is of great relevance, but still poorly understood. In this study, we found an early-onset hearing loss in 3xTgAD and 3xTgAD/Polβ+/− mouse models. The hearing assessment was measured by auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) recordings. Herein, we report that both 3xTgAD and 3xTgAD/Polβ+/− mice showed increased ABR thresholds between at 16 and 32 kHz at 4 weeks of age, much earlier than any AD behavioral changes. The ABR thresholds were significantly higher in 3xTgAD/Polβ+/− mice than in 3xTgAD mice at 16 kHz, and DPOAE signals were also reduced, indicating that DNA damage may affect hearing impairment in AD. Poly ADP-ribosylation levels and protein expression of DNA damage markers increased significantly and NAD+ levels were reduced in the cochlea of 3xTgAD and 3xTgAD/Polβ+/− mice. Remarkably, we observed the downregulation of phosphoglycerate mutase 2 (PGAM2) in cochlea and a decrease in the number of synaptic ribbons in the presynaptic zones of inner hair cells in 3xTgAD/Polβ+/− mice. We also find that the activity of sirtuin 3 (SIRT3) is downregulated in cochlea, indicative of impaired mitochondrial function. Taken together, hearing impairment may be a potential early marker of AD. In addition, these findings provide new insights into the mechanism of the relationship between hearing dysfunction and AD and suggest that DNA damage in the cochlea can contributes to the development of early hearing loss of AD. The hearing assessment was measured by auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) at 4 weeks of age, thereafter whole cochlea and auditory cortex tissue were collected from each mouse (WT, Polβ+/−, 3xTgAD, and 3xTgAD/Polβ+/−) and subjected to total RNA isolation to understand what metabolism-related gene expression changes in cochlea and auditory cortex.

Project description:Approximately 35 million people worldwide suffer from Alzheimer’s disease (AD). Existing therapeutics, while moderately effective, are currently unable to stem the widespread rise in AD prevalence. AD is associated with an increase in amyloid beta (A) oligomers and hyperphosphorylated tau, along with cognitive impairment and neurodegeneration. Several antidepressants have shown promise in improving cognition and alleviating oxidative stress in AD but have failed as long-term therapeutics. In this study, amitriptyline, an FDA-approved tricyclic antidepressant, was administered orally to aged and cognitively impaired transgenic AD mice (3xTgAD). After amitriptyline treatment, cognitive behavior testing demonstrated that there was a significant improvement in both long- and short-term memory retention. Amitriptyline treatment also caused a significant potentiation of non-toxic A monomer with a concomitant decrease in toxic oligomer A load, compared to vehicle-treated 3xTgAD controls. In addition, amitriptyline administration caused a significant increase in dentate gyrus neurogenesis as well as increases in expression of neurosynaptic marker proteins. Amitriptyline treatment resulted in increases in hippocampal brain-derived neurotrophic factor protein as well as increased tyrosine phosphorylation of its cognate receptor (TrkB). These results indicate that amitriptyline has significant beneficial actions in aged and damaged AD brains and that it shows promise as a tolerable novel therapeutic for the treatment of AD. Male 3xTgAD mice, 14 months of age, were maintained on a 12hr light dark cycle in pathogen free conditions. Animals received food and water ad libitum. The test group received 100ug/g body weight amitriptyline-hydrochloride per os in their drinking water (Sigma-Aldrich, St. Louis MO) for 4 months (n = 15), and the control group received water (n = 15). The Hippocampus and Cortex were removed from 3 replicates of each group and RNA purification was done using glass bead disruption followed by the RNEasy Mini Kit (Qiagen, Valencia, CA) according to the manufacturer's instructions. The RNA was examined for quantity and quality using an Agilent Bioanalyzer 2100 (Agilent Technologies, Palo Alto, CA). The samples were hybridized to Illumina's SentrixMouse Ref-8 v2. Expression BeadChips (Illumina, San Diego, CA).

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Increased Human like Alzheimer features in a Novel Mouse Model with Oxidative DNA Repair Dysfunction

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