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Soluble TREM2 ameliorates pathological phenotypes by modulating microglial functions in an Alzheimer's disease model.

ABSTRACT: Triggering receptor expressed on myeloid cells 2 (TREM2) is a microglial surface receptor genetically linked to the risk for Alzheimer's disease (AD). A proteolytic product, soluble TREM2 (sTREM2), is abundant in the cerebrospinal fluid and its levels positively correlate with neuronal injury markers. To gain insights into the pathological roles of sTREM2, we studied sTREM2 in the brain of 5xFAD mice, a model of AD, by direct stereotaxic injection of recombinant sTREM2 protein or by adeno-associated virus (AAV)-mediated expression. We found that sTREM2 reduces amyloid plaque load and rescues functional deficits of spatial memory and long-term potentiation. Importantly, sTREM2 enhances microglial proliferation, migration, clustering in the vicinity of amyloid plaques and the uptake and degradation of Aβ. Depletion of microglia abolishes the neuroprotective effects of sTREM2. Our study demonstrates a protective role of sTREM2 against amyloid pathology and related toxicity and suggests that increasing sTREM2 can be explored for AD therapy.

SUBMITTER: Zhong L

PROVIDER: S-EPMC6433910 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:1,7-bis(4-hydroxy-3-methoxyphenyl)heptane-3,5-dione (tetrahydrocurcumin, THC) is a major bioactive metabolite of curcumin (the principal active ingredient of Curcuma longa L.), and overcomes the low bioavailability of curcumin, demonstrating the potential anti-inflammatory, antioxidant and neuroprotective properties, etc, some of which were considered to be even superior to curcumin. In the present study, the protective properties of THC in the hippocampus of APP/PS1 mice, and the effects of THC against Aβ-induced toxicity in BV-2 cells were explored. The data in vitro showed that Aβ induced decreased cell viability, and cell cycle arrest and apoptosis in BV-2 cells, which could be ameliorated by THC. In vivo, THC administration was able to rescue learning and memory, and reduce Aβ burden in the hippocampus of APP/PS1 mice. By comprehensive proteomic analysis of the hippocampus of mice, a total of 157 differentially expressed proteins were identified in APP/PS1 mice treated with THC (comparing with APP/PS1 mice), which were enriched in “T cell activation”, “lymphocyte proliferation” and “protein oligomerization”, etc. The results of Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis suggested that the effects of THC on the cell cycle and apoptosis were mostly related to the “Ras signaling pathway” and “JAK−STAT signaling pathway”, etc. Using Western blot and ELISA, the down-regulation of Gab2 and K-Ras, and the up-regulation of caspase-3, TGF-β1 and TNF-ɑ were found in APP/PS1 mice. THC attenuated the abnormal expression of Gab2, K-Ras, caspase-3 and TNF-ɑ, and up-regulated Bag1 and TGF-β1 expression in APP/PS1 mice. In BV-2 cells, Aβ induced the down-regulation of Gab2, K-Ras and TGF-β1, and the overexpression of caspase-3, PARP1, cleaved-PARP1 and TNF-ɑ, which were markedly restored by THC. Moreover, THC up-regulated Bag1 expression in BV-2 cells treated with Aβ. The decreased transcriptional expression levels of Ccnd2 and Cdkn1a was also observed in Aβ-treated BV-2 cells. THC treatment alleviated down-regulation of Ccnd2, but did not affect the abnormal transcriptional expression of Cdkn1a caused by Aβ in BV-2 cells. For the first time, we identified that the action of THC in preventing AD was associated with inhibition of cell cycle arrest and apoptosis of microglia via the Ras/ERK signaling pathway, shedding new light on the role of THC in alleviating the progression of AD.

Project description:BackgroundAlzheimer's disease (AD) patients exhibit memory disruptions and profound sleep disturbances, including disruption of deep non-rapid eye movement (NREM) sleep. Slow-wave activity (SWA) is a major restorative feature of NREM sleep and is important for memory consolidation.MethodsWe generated a mouse model where GABAergic interneurons could be targeted in the presence of APPswe/PS1dE9 (APP) amyloidosis, APP-GAD-Cre mice. An electroencephalography (EEG) / electromyography (EMG) telemetry system was used to monitor sleep disruptions in these animals. Optogenetic stimulation of GABAergic interneurons in the anterior cortex targeted with channelrhodopsin-2 (ChR2) allowed us to examine the role GABAergic interneurons play in sleep deficits. We also examined the effect of optogenetic stimulation on amyloid plaques, neuronal calcium as well as sleep-dependent memory consolidation. In addition, microglial morphological features and functions were assessed using confocal microscopy and flow cytometry. Finally, we performed sleep deprivation during optogenetic stimulation to investigate whether sleep restoration was necessary to slow AD progression.ResultsAPP-GAD-Cre mice exhibited impairments in sleep architecture including decreased time spent in NREM sleep, decreased delta power, and increased sleep fragmentation compared to nontransgenic (NTG) NTG-GAD-Cre mice. Optogenetic stimulation of cortical GABAergic interneurons increased SWA and rescued sleep impairments in APP-GAD-Cre animals. Furthermore, it slowed AD progression by reducing amyloid deposition, normalizing neuronal calcium homeostasis, and improving memory function. These changes were accompanied by increased numbers and a morphological transformation of microglia, elevated phagocytic marker expression, and enhanced amyloid β (Aβ) phagocytic activity of microglia. Sleep was necessary for amelioration of pathophysiological phenotypes in APP-GAD-Cre mice.ConclusionsIn summary, our study shows that optogenetic targeting of GABAergic interneurons rescues sleep, which then ameliorates neuropathological as well as behavioral deficits by increasing clearance of Aβ by microglia in an AD mouse model.

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Soluble TREM2 ameliorates pathological phenotypes by modulating microglial functions in an Alzheimer's disease model.

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