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Genome-wide analysis of gene expression in brain of Neil3-deficient Alzheimer's disease mouse model

ABSTRACT: Oxidative stress generating DNA damage has been shown to be a key characteristic in Alzheimer’s disease (AD). However, how it affects the pathogenesis of AD is not yet fully understood. NEIL3 is a DNA glycosylase initiating oxidative DNA repair and with a distinct expression pattern in proliferating cells. In brain, its function has been linked to hippocampal-dependent memory and to induction of neurogenesis after stroke and in prion disease. Here, we generated a novel AD mouse model deficient for Neil3 to study the impact of impaired oxidative base lesion repair on the pathogenesis of AD. Our results demonstrate an age-dependent decrease in amyloid-β (Aβ) plaque deposition in female NEIL3-deficient AD mice. Moreover, male NEIL3-deficient AD mice show reduced neural stem cell proliferation in the adult hippocampus and impaired working memory. These effects seem to be independent of DNA repair as both sexes show increased level of oxidative base lesions in the hippocampus upon loss of NEIL3. Thus, our findings suggest a sex-dependent role of NEIL3 in the progression of AD by altering cerebral Aβ accumulation and promoting adult hippocampal neurogenesis to maintain cognitive function.

ORGANISM(S): Mus musculus

PROVIDER: GSE197199 | GEO | 2022/11/15

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 an unremitting neurodegenerative disorder characterized by cerebral amyloid-β (Aβ) accumulation and gradual decline in cognitive function. Changes in brain energy metabolism arise in the preclinical phase of AD, suggesting an important metabolic component of early AD pathology. Neurons and astrocytes function in close metabolic collaboration, which is essential for the recycling of neurotransmitters in the synapse. However, how this metabolic interplay may be affected during the early stages of AD development has not been sufficiently investigated. Here, we provide an integrative analysis of cellular metabolism during the early stages of Aβ accumulation in the cerebral cortex and hippocampus of the 5xFAD mouse model of AD. Our electrophysiological examination revealed an increase in spontaneous excitatory signaling in hippocampal brain slices of 5xFAD mice. This hyperactive neuronal phenotype coincided with decreased hippocampal TCA cycle metabolism mapped by stable 13C isotope tracing. Particularly, reduced astrocyte TCA cycle activity led to decreased glutamine synthesis, in turn hampering neuronal GABA synthesis in the 5xFAD hippocampus. In contrast, cerebral cortical slices of 5xFAD mice displayed an elevated capacity for oxidative glucose metabolism suggesting a metabolic compensation. When we explored the brain proteome and metabolome of the 5xFAD mice, we found limited changes, supporting that the functional metabolic disturbances between neurons and astrocytes are early events in AD pathology. In addition, we show that synaptic mitochondrial and glycolytic function was impaired selectively in the 5xFAD hippocampus, whereas non-synaptic mitochondrial function was maintained. These findings were supported by ultrastructural analyses demonstrating disruptions in mitochondrial morphology, particularly in the 5xFAD hippocampus. Collectively, our study reveals complex region and cell specific metabolic adaptations, in the early stages of amyloid pathology, which may be fundamental for the progressing synaptic dysfunction in AD.

Project description:Oxidative stress is a major risk factor for Alzheimer’s disease (AD), which is characterized by brain atrophy, amyloid plaques, neurofibrillary tangles, and loss of neurons. 8-Oxoguanine, a major oxidatively generated nucleobase highly accumulated in the AD brain, is known to cause neurodegeneration. In mammalian cells, several enzymes play essential roles in minimizing the 8-oxoguanine accumulation in DNA. MUTYH with adenine DNA glycosylase activity excises adenine inserted opposite 8-oxoguanine in DNA. MUTYH is reported to actively contribute to the neurodegenerative process in Parkinson and Huntington diseases and some mouse models of neurodegenerative diseases by accelerating neuronal dysfunction and microgliosis under oxidative conditions; however, whether or not MUTYH is involved in AD pathogenesis remains unclear. In the present study, we examined the contribution of MUTYH to the AD pathogenesis. Using postmortem human brains, we showed that various types of MUTYH transcripts and proteins are expressed in most hippocampal neurons and glia in both non-AD and AD brains. We further introduced MUTYH deficiency into AppNL-G-F/NL-G-F knock-in AD model mice, which produce humanized toxic amyloid-β without the overexpression of APP protein, and investigated the effects of MUTYH deficiency on the behavior, pathology, gene expression, and neurogenesis. MUTYH deficiency improved memory impairment in AppNL-G-F/NL-G-F mice, accompanied by reduced microgliosis. Gene expression profiling strongly suggested that MUTYH is involved in the microglial response pathways under AD pathology and contributes to the phagocytic activity of disease-associated microglia. We also found that MUTYH deficiency ameliorates impaired neurogenesis in the hippocampus, thus improving memory impairment. In conclusion, we propose that MUTYH, which is expressed in the hippocampus of AD patients as well as non-AD subjects, actively contributes to memory impairment by inducing microgliosis with poor neurogenesis in the preclinical AD phase and that MUTYH is a novel therapeutic target for AD, as its deficiency is highly beneficial for ameliorating AD pathogenesis.

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Genome-wide analysis of gene expression in brain of Neil3-deficient Alzheimer's disease mouse model

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