Abstract
BackgroundDisturbances in clock genes affect almost all patients with Alzheimer’s disease (AD), as evidenced by their altered sleep/wake cycle, thermoregulation, and exacerbation of cognitive impairment. As microglia-mediated neuroinflammation proved to be a driver of AD rather than a result of the disease, in this study, we evaluated the relationship between clock gene disturbance and neuroinflammation in microglia and their contribution to the onset of AD.MethodsIn this study, the expression of clock genes and inflammatory-related genes was examined in MACS microglia isolated from 2-month-old amyloid precursor protein knock-in (APP-KI) and wild-type (WT) mice using cap analysis gene expression (CAGE) deep sequencing and RT-PCR. The effects of clock gene disturbance on neuroinflammation and relevant memory changes were examined in 2-month-old APP-KI and WT mice after injection with SR9009 (a synthetic agonist for REV-ERB). The microglia morphology was studied by staining, neuroinflammation was examined by Western blotting, and cognitive changes were examined by Y-maze and novel object recognition tests.ResultsCLOCK/BMAL1-driven transcriptional negative feedback loops were impaired in the microglia from 2-month-old APP-KI mice. Pro-inflammatory genes in microglia isolated from APP-KI mice were significantly higher than those isolated from WT mice at Zeitgeber time 14. The expression of pro-inflammatory genes was positively associated with NF-κB activation and negatively associated with the BMAL1 expression. SR9009 induced the activation of microglia, the increased expression of pro-inflammatory genes, and cognitive decline in 2-month-old APP-KI mice.ConclusionClock gene disturbance in microglia is involved in the early onset of AD through the induction of chronic neuroinflammation, which may be a new target for preventing or slowing AD.
Highlights
Disturbances in clock genes affect almost all patients with Alzheimer’s disease (AD), as evidenced by their altered sleep/wake cycle, thermoregulation, and exacerbation of cognitive impairment
Aberrant diurnal clock gene rhythms in cortical microglia isolated from amyloid precursor protein (APP)-KI mice In order to clarify the mechanisms underlying the effects of diurnal clock genes on the pathology of AD, we performed cap analysis gene expression (CAGE) RNA sequencing of microglia from a 2month-old WT and amyloid precursor protein knock-in (APP-KI) mice at ZT2 and ZT14
We identified 96,700 transcriptional start sites (TSS), 20% of which were upregulated and 19% of which were downregulated (FDR < 0.05, Log2Fc ≥ 1.5) at ZT2, 14% of which were upregulated, and 31% of which were downregulated at ZT14 in microglia from APP-KI mice compared to WT mice (Fig. 1a)
Summary
Disturbances in clock genes affect almost all patients with Alzheimer’s disease (AD), as evidenced by their altered sleep/wake cycle, thermoregulation, and exacerbation of cognitive impairment. Some microbes can remain latent in the nervous system with the potential for reactivation, and neuronal damage caused by direct microbial action and microbe-induced inflammation might occur years after the initial infection In line with this infection hypothesis of AD, we previously reported that virulence factors of Porphylomonas gingivalis, a major pathogen in periodontal disease, including lipopolysaccharide (LPS) and gingipains, were able to activate microglia to induce neuroinflammation through the activation of Toll-like receptor 2 and protease-activated receptor-2, respectively, [7, 8]. These observations suggest that excessive neuroinflammation mediated by microglia is a key driver of AD rather than a result of the disease
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