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BackgroundMicroglial activation contributes to the neuropathology associated with chronic alcohol exposure and withdrawal, including the expression of inflammatory and anti-inflammatory genes. In the current study, we examined the transcriptome of primary rat microglial cells following incubation with alcohol alone, or alcohol together with a robust inflammatory stimulus.MethodsPrimary microglia were prepared from mixed rat glial cultures. Cells were incubated with 75 mM ethanol alone or with proinflammatory cytokines (“TII”: IL1β, IFNγ, and TNFα). Isolated mRNA was used for RNAseq analysis and qPCR. Effects of alcohol on phagocytosis were determined by uptake of oligomeric amyloid beta.ResultsAlcohol induced nitrite production in control cells and increased nitrite production in cells co-treated with TII. RNAseq analysis of microglia exposed for 24 h to alcohol identified 312 differentially expressed mRNAs (“Alc-DEs”), with changes confirmed by qPCR analysis. Gene ontology analysis identified phagosome as one of the highest-ranking KEGG pathways including transcripts regulating phagocytosis. Alcohol also increased several complement-related mRNAs that have roles in phagocytosis, including C1qa, b, and c; C3; and C3aR1. RNAseq analysis identified over 3000 differentially expressed mRNAs in microglia following overnight incubation with TII; and comparison to the group of Alc-DEs revealed 87 mRNAs modulated by alcohol but not by TII, including C1qa, b, and c. Consistent with observed changes in phagocytosis-related mRNAs, the uptake of amyloid beta1–42, by primary microglia, was reduced by alcohol.ConclusionsOur results define alterations that occur to microglial gene expression following alcohol exposure and suggest that alcohol effects on phagocytosis could contribute to the development of Alzheimer’s disease.Electronic supplementary materialThe online version of this article (10.1186/s12974-018-1184-7) contains supplementary material, which is available to authorized users.

The loss of noradrenergic neurons and subsequent reduction of brain noradrenaline (NA) levels are associated with the progression of Alzheimer's disease (AD). This seems to be due mainly to the ability of NA to reduce the activation of microglial cells. We previously observed that NA induces the production of the chemokine Fractalkine/CX3CL1 in neurons. The activation of microglial CX3CR1, sole receptor for CX3CL1, reduces the activation of microglia, which is known to largely contribute to the neuronal damage characteristic of AD. Therefore, alterations of CX3CR1 production in microglia could translate into the enhancement or inhibition of CX3CL1 anti-inflammatory effects. In order to determine if microglial CX3CR1 production is altered in AD and if NA can control it, CX3CR1 expression and synthesis were analyzed in 5xFAD mice and human AD brain samples. In addition, the effects of NA and its reuptake inhibitor reboxetine were analyzed in microglial cultures and mice respectively. Our results indicate that in AD CX3CR1 production is increased in the brain cortex and that reboxetine administration further increases it and enhances microglial reactivity toward amyloid beta plaques. However, direct administration of NA to primary rat microglia or human HMC3 cells inhibits CX3CR1 production, suggesting that microglia responses to NA may be altered in the absence of CX3CL1-producing neurons or other nonmicroglial external factors.

Fluoro-Jade is a fluorescein-derived fluorochrome which specifically binds to damaged neurons. Due to this characteristic, it is commonly used for the histochemical detection and quantification of neurodegeneration in mounted brain sections. Here, we describe an alternative and simpler histochemistry protocol based on the use of free-floating brain sections. For this purpose, we have used brain slices from wild-type and 5xFAD mice as well as from mice that received an intracerebral injection of oligomeric amyloid beta peptides. We observed that our histochemistry staining procedure allows for a well-defined labeling of degenerating neurons providing a better signal-to-noise ratio staining than the commonly used one. In addition, our modified protocol demonstrates the ability of Fluoro-Jade C to also fluorescently label amyloid beta plaques.