Circadian dysfunction is a common attribute of many neurodegenerative diseases, most of which are associated with neuroinflammation. Circadian rhythm dysfunction has been associated with inflammation in the periphery, but the role of the core clock in neuroinflammation remains poorly understood. Here we demonstrate that Rev-erbα, a nuclear receptor and circadian clock component, is a mediator of microglial activation and neuroinflammation. We observed time-of-day oscillation in microglial immunoreactivity in the hippocampus, which was disrupted in Rev-erbα −/− mice. Rev-erbα deletion caused spontaneous microglial activation in the hippocampus and increased expression of proinflammatory transcripts, as well as secondary astrogliosis. Transcriptomic analysis of hippocampus from Rev-erbα −/− mice revealed a predominant inflammatory phenotype and suggested dysregulated NF-κB signaling. Primary Rev-erbα −/− microglia exhibited proinflammatory phenotypes and increased basal NF-κB activation. Chromatin immunoprecipitation revealed that Reverbα physically interacts with the promoter regions of several NF-κB-related genes in primary microglia. Loss of Rev-erbα in primary astrocytes had no effect on basal activation but did potentiate the inflammatory response to lipopolysaccharide (LPS). In vivo, Reverbα −/− mice exhibited enhanced hippocampal neuroinflammatory responses to peripheral LPS injection, while pharmacologic activation of Rev-erbs with the small molecule agonist SR9009 suppressed LPSinduced hippocampal neuroinflammation. Rev-erbα deletion influenced neuronal health, as conditioned media from Rev-erbα-deficient primary glial cultures exacerbated oxidative damage in cultured neurons. Reverbα −/− mice also exhibited significantly altered cortical resting-state functional connectivity, similar to that observed in neurodegenerative models. Our results reveal Rev-erbα as a pharmacologically accessible link between the circadian clock and neuroinflammation.Rev-erbα | circadian | microglia | neuroinflammation C ircadian clocks allow organisms to precisely synchronize internal physiological processes with their external environment. A conserved transcriptional-translational feedback loop known as the core circadian clock controls cycles of protein expression that produce transcriptional and physiologic rhythms. This core circadian clock consists of the transcriptional activators BMAL1 and CLOCK, which drive transcription of their own transcriptional repressors, including CRYPTOCHROME (CRY), PE-RIOD (PER), and REV-ERB proteins (1). The circadian system regulates a variety of critical cellular processes, including aspects of metabolism, inflammation, and redox homeostasis (2). Disruptions of the clock or its associated proteins have been implicated in pathological conditions ranging from cancer to neurodegenerative diseases (2-4). However, the roles of cellular circadian clocks in brain health and neuroinflammation are still poorly understood.Aberrant glial cell activation and neuroinflammation are hallmarks of many neuro...

Late onset Alzheimer’s disease (LOAD) is a genetically complex and clinically heterogeneous disease. Recent large-scale genome wide association studies (GWAS) have identified more than twenty loci that modify risk for AD. Despite the identification of these loci, little progress has been made in identifying the functional variants that explain the association with AD risk. Thus, we sought to determine whether the novel LOAD GWAS single nucleotide polymorphisms (SNPs) alter expression of LOAD GWAS genes and whether expression of these genes is altered in AD brains. The majority of LOAD GWAS SNPs occur in gene dense regions under large linkage disequilibrium (LD) blocks, making it unclear which gene(s) are modified by the SNP. Thus, we tested for brain expression quantitative trait loci (eQTLs) between LOAD GWAS SNPs and SNPs in high LD with the LOAD GWAS SNPs in all of the genes within the GWAS loci. We found a significant eQTL between rs1476679 and PILRB and GATS, which occurs within the ZCWPW1 locus. PILRB and GATS expression levels, within the ZCWPW1 locus, were also associated with AD status. Rs7120548 was associated with MTCH2 expression, which occurs within the CELF1 locus. Additionally, expression of several genes within the CELF1 locus, including MTCH2, were highly correlated with one another and were associated with AD status. We further demonstrate that PILRB, as well as other genes within the GWAS loci, are most highly expressed in microglia. These findings together with the function of PILRB as a DAP12 receptor supports the critical role of microglia and neuroinflammation in AD risk.

Opioid receptor signaling via EGF receptor (EGFR) transactivation and ERK/MAPK phosphorylation initiates diverse cellular responses that are cell type-dependent. In astrocytes, multiple opioid receptor-mediated mechanisms of ERK activation exist that are temporally distinctive and feature different outcomes. Upon discovering that chronic opiate treatment of rats down-regulates thrombospondin 1 (TSP1) expression in the nucleus accumbens and cortex, we investigated the mechanism of action of this modulation in astrocytes. TSP1 is synthesized in astrocytes and is released into the extracellular matrix where it is known to play a role in synapse formation and neurite outgrowth. Acute morphine (hours) reduced TSP1 levels in astrocytes. Chronic (days) opioids repressed TSP1 gene expression and reduced its protein levels by opioid receptor and ERK-dependent mechanisms in astrocytes. Morphine also depleted TSP1 levels stimulated by TGF␤1 and abolished ERK activation induced by this factor. Chronic morphine treatment of astrocyte-neuron co-cultures reduced neurite outgrowth and synapse formation. Therefore, inhibitory actions of morphine were detected after both acute and chronic treatments. An acute mechanism of morphine signaling to ERK that entails depletion of TSP1 levels was suggested by inhibition of morphine activation of ERK by a function-blocking TSP1 antibody. This raises the novel possibility that acute morphine uses TSP1 as a source of EGF-like ligands to activate EGFR. Chronic morphine inhibition of TSP1 is reminiscent of the negative effect of opioids on EGFR-induced astrocyte proliferation via a phospho-ERK feedback inhibition mechanism. Both of these variations of classical EGFR transactivation may enable opiates to diminish neurite outgrowth and synapse formation.Astrocytes are the source of a diverse group of molecules that are required for synapse formation, function, and maintenance in neurons (1-7). Thrombospondin (TSP) 3 is a member of the astrocyte-derived intercellular signaling components that have been implicated in synaptogenesis and other neuronal glial interactions of the developing brain (8 -17). In addition, synaptic plasticity and other neuroadaptations involving astrocyte neuron interactions are thought to play a role in reward learning and addiction (18). Some chronic morphine-responsive genes (Homer1, PSD-95, and synaptotagmin1) may subserve the long lived neuronal and behavioral plasticity observed in regions of the mesolimbic reward system, and they are involved in synaptogenesis (19 -26).TSPs are multidomain, multimeric glycoproteins that are secreted into the extracellular matrix of many cells and serve as bridging molecules in cell-cell interactions (27,28). First discovered in platelet ␣-granules and secreted upon platelet activation, the superfamily of TSPs modulate varied functions of cell signaling and cell adhesion in a broad array of cell types. The five TSP genes are expressed in the CNS and peripheral nervous system where they play important roles in neural development. T...

Heterozygous genetic variants within the TREM2 gene show a strong association with increased Alzheimer’s disease (AD) risk. Amyloid beta–depositing mouse models haploinsufficient or null for Trem2 have identified important relationships among TREM2, microglia, and AD pathology; however, results are challenging to interpret in the context of varying microglial phenotypes and disease progression. We hypothesized that acute Trem2 reduction may alter amyloid pathology and microglial responses independent of genetic Trem2 deletion in mouse models. We developed antisense oligonucleotides (ASOs) that potently but transiently lower Trem2 messenger RNA throughout the brain and administered them to APP/PS1 mice at varying stages of plaque pathology. Late-stage ASO-mediated Trem2 knockdown significantly reduced plaque deposition and attenuated microglial association around plaque deposits when evaluated 1 mo after ASO injection. Changes in microglial gene signatures 1 wk after ASO administration and phagocytosis measured in ASO-treated cells together indicate that microglia may be activated with short-term Trem2 reduction. These results suggest a time- and/or dose-dependent role for TREM2 in mediating plaque deposition and microglial responses in which loss of TREM2 function may be beneficial for microglial activation and plaque removal in an acute context.