Unknown,Transcriptomics,Genomics,Proteomics

Dataset Information

In vivo response of microglia to Aβ and prostaglandin-E2 EP2 receptor signaling

ABSTRACT: Microglia, the innate immune cells of the central nervous system, perform critical inflammatory and non-inflammatory functions to maintain homeostasis and normal neural function. However in Alzheimer’s disease (AD), these beneficial functions become progressively impaired, contributing to synapse and neuron loss and cognitive impairment. The inflammatory cyclooxygenase-PGE2 pathway, including the PGE2 receptor EP2, is implicated in AD development, both in human epidemiology and in transgenic models of AD. To test the transcriptional responses of EP2-deficient microglia to Aβ in vivo, we used mice in which the EP2 receptor is conditionally deleted in microglia using the CD11b-Cre transgene and floxed alleles of the EP2 gene. By injecting these mice with Aβ ICV and isolating microglia from the brains, we have been able to establish the transcriptional response of microglia to Aβ in vivo and test how EP2 deletion in microglia affects this response. 8 month-old C57BL/6 mice, of the genotype CD11b-Cre; EP2+/+ or CD11b-Cre; EP2lox/lox, were injected I.C.V. with either Aβ or vehicle. 48 hours after injection, the mice were sacrificed and transcardially perfused with cold heparinized 0.9% NaCl. Brains were then removed from the mice and pooled, two brains of the same genotype per sample, to ensure adequate cell and RNA yield. The brains were then enzymatically dissociated for microglia isolation using the Neural Tissue Dissociation Kit (P), MACS Separation Columns (LS), and magnetic CD11b Microbeads from Miltenyi Biotec according to the manufacturer's protocol. Immediately after isolating the microglia, RNA was extracted from the cells for microarray analysis.

ORGANISM(S): Mus musculus

SUBMITTER: Katrin Andreasson

PROVIDER: E-GEOD-57181 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

Prostaglandin signaling suppresses beneficial microglial function in Alzheimer's disease models.

Johansson Jenny U JU Woodling Nathaniel S NS Wang Qian Q Panchal Maharshi M Liang Xibin X Trueba-Saiz Angel A Brown Holden D HD Mhatre Siddhita D SD Loui Taylor T Andreasson Katrin I KI

The Journal of clinical investigation 20141208 1

Microglia, the innate immune cells of the CNS, perform critical inflammatory and noninflammatory functions that maintain normal neural function. For example, microglia clear misfolded proteins, elaborate trophic factors, and regulate and terminate toxic inflammation. In Alzheimer's disease (AD), however, beneficial microglial functions become impaired, accelerating synaptic and neuronal loss. Better understanding of the molecular mechanisms that contribute to microglial dysfunction is an importa ...[more]

PMID: 25485684

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Project description:Microglia are innate immune cells of the brain that perform phagocytic and inflammatory functions in disease conditions. Transcriptomic studies of acutely-isolated microglia have provided novel insights into their molecular and functional diversity in homeostatic and neurodegenerative disease states. State-of-the-art mass spectrometric methods can comprehensively characterize proteomic alterations in microglia in neurodegenerative disorders, potentially providing novel functionally-relevant molecular insights that are not provided by transcriptomics. However, proteomic profiling of adult primary microglia in neurodegenerative disease conditions has not been performed. We performed quantitative proteomic analyses of purified CD11b+ acutely-isolated microglia adult mice in normal, acute neuroinflammatory (LPS-treatment) and chronic neurodegenerative states (5xFAD model of Alzheimer’s disease [AD]) using tandem mass tag mass spectrometry. Differential expression analyses were performed to characterize specific microglial proteomic changes in 5xFAD mice and identify overlap with LPS-induced pro-inflammatory changes. Our results were also contrasted with existing proteomic data from wild-type mouse microglia and from existing microglial transcriptomic data from wild-type and 5xFAD mice. Neuropathological validation studies of select proteins were performed in human AD and 5xFAD brains. Of 4,133 proteins identified, 187 microglial proteins were differentially expressed in the 5xFAD mouse model of AD pathology, including proteins with previously known (Apoe, Clu and Htra1) as well as previously unreported relevance to AD biology (Cotl1 and Hexb). Proteins upregulated in 5xFAD microglia shared significant overlap with pro-inflammatory changes observed in LPS-treated mice. Several proteins increased in human AD brain were also upregulated by 5xFAD microglia (Aβ peptide, Apoe, Htra1, Cotl1 and Clu). Cotl1 was identified as a novel microglia-specific marker with increased expression and strong association with AD neuropathology. Apoe protein was also detected within plaque-associated microglia in which Apoe and Aβ were highly co-localized suggesting a role for Apoe in phagocytic clearance of Aβ. We report the first comprehensive comparative proteomic study of adult mouse microglia derived from acute neuroinflammatory and AD models, representing a valuable resource to the neuroscience research community. We highlight shared and unique microglial proteomic changes in acute neuroinflammatory, aging and AD mouse models in addition to identifying novel roles for microglial proteins in human neurodegeneration.

Project description:Alzheimer’s Disease (AD) is the 6th leading cause of death in the US. It is established that neuroinflammation contributes to the synaptic loss, neuronal death, and symptomatic decline of AD patients. Accumulating evidence suggests a critical role for microglia, innate immune phagocytes of the brain. For instance, microglia release pro-inflammatory products such as IL-1β which is highly implicated in AD pathobiology. The mechanisms underlying the transition of microglia to proinflammatory promoters of AD remain largely unknown. To address this gap, we performed Representation Bisulfite Sequencing (RRBS) to profile global DNA methylation changes in human AD brains compared to no disease controls. We identified differential DNA methylation of CASPASE-4 (CASP4), which when expressed, can be involved in generation of IL-1β and is predominantly expressed in immune cells. DNA upstream of the CASP4 transcription start site was hypomethylated in human AD brains, which was correlated with increased expression of CASP4. Furthermore, microglia from a mouse model of AD (5xFAD) express increased levels of CASP4 compared to wild-type (WT) mice. To study the role of CASP4 in AD, we developed a novel mouse model of AD lacking CASP4 (5xFAD/Casp4-/-). The expression of CASP4 was associated with increased accumulation of pathologic protein aggregate amyloid-β (Aβ) in 5xFAD mice. Utilizing RNA sequencing, we determined that CASP4 promotes unique transcriptomic phenotypes in 5xFAD mouse brains, including alterations of neuroinflammatory and chemokine signaling pathways. Notably, in vitro, CASP4 promoted generation of IL-1β from macrophages and microglia in response to cytosolic Aβ through cleavage of downstream effector GASDERMIN-D (GSDMD). We are the first to describe a role for CASP4 and GSDMD in the generation of IL-1β in response to Aβ and the progression of pathologic inflammation in AD. Overall, our results demonstrate that overexpression of CASP4 due to differential methylation in AD microglia contributes to the progression of AD pathobiology, thus identifying CASP4 as a potential target for immunotherapies for the treatment of AD.

Dataset Information

In vivo response of microglia to Aβ and prostaglandin-E2 EP2 receptor signaling

Publications

Prostaglandin signaling suppresses beneficial microglial function in Alzheimer's disease models.

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