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1. Synthetic amyloid beta does not induce a robust transcriptional response in innate immune cell culture systems

   https://doi.org/10.1186/s12974-022-02459-1  

   Quiroga, I. Y. ; Cruikshank, A. E. ; Bond, M. L. ; Reed, K. S. M. ; Evangelista, B. A. ; Tseng, J. H. ; Ragusa, J. V. ; Meeker, R. B. ; Won, H. ; Cohen, S. ; et al ( April 2022 , Journal of Neuroinflammation)

   Alzheimer’s disease (AD) is a progressive neurodegenerative disease that impacts nearly 400 million people worldwide. The accumulation of amyloid beta (Aβ) in the brain has historically been associated with AD, and recent evidence suggests that neuroinflammation plays a central role in its origin and progression. These observations have given rise to the theory that Aβ is the primary trigger of AD, and induces proinflammatory activation of immune brain cells (i.e., microglia), which culminates in neuronal damage and cognitive decline. To test this hypothesis, many in vitro systems have been established to study Aβ-mediated activation of innate immune cells. Nevertheless, the transcriptional resemblance of these models to the microglia in the AD brain has never been comprehensively studied on a genome-wide scale.

   We used bulk RNA-seq to assess the transcriptional differences between in vitro cell types used to model neuroinflammation in AD, including several established, primary and iPSC-derived immune cell lines (macrophages, microglia and astrocytes) and their similarities to primary cells in the AD brain. We then analyzed the transcriptional response of these innate immune cells to synthetic Aβ or LPS and INFγ.

   We found that human induced pluripotent stem cell (hIPSC)-derived microglia (IMGL) are the in vitro cell model that best resembles primary microglia. Surprisingly, synthetic Aβ does not trigger a robust transcriptional response in any of the cellular models analyzed, despite testing a wide variety of Aβ formulations, concentrations, and treatment conditions. Finally, we found that bacterial LPS and INFγ activate microglia and induce transcriptional changes that resemble many, but not all, aspects of the transcriptomic profiles of disease associated microglia (DAM) present in the AD brain.

   These results suggest that synthetic Aβ treatment of innate immune cell cultures does not recapitulate transcriptional profiles observed in microglia from AD brains. In contrast, treating IMGL with LPS and INFγ induces transcriptional changes similar to those observed in microglia detected in AD brains.

    

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2. Circadian clock protein Rev-erbα regulates neuroinflammation

   https://doi.org/10.1073/pnas.1812405116  

   Griffin, Percy ; Dimitry, Julie M. ; Sheehan, Patrick W. ; Lananna, Brian V. ; Guo, Chun ; Robinette, Michelle L. ; Hayes, Matthew E. ; Cedeño, Michelle R. ; Nadarajah, Collin J. ; Ezerskiy, Lubov A. ; et al ( February 2019 , Proceedings of the National Academy of Sciences)

   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 Rev-erbα 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, Rev-erbα^−/−mice exhibited enhanced hippocampal neuroinflammatory responses to peripheral LPS injection, while pharmacologic activation of Rev-erbs with the small molecule agonist SR9009 suppressed LPS-induced hippocampal neuroinflammation. Rev-erbα deletion influenced neuronal health, as conditioned media from Rev-erbα–deficient primary glial cultures exacerbated oxidative damage in cultured neurons. Rev-erbα^−/−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.

    

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3. CD36‐Binding Amphiphilic Nanoparticles for Attenuation of α‐Synuclein‐Induced Microglial Activation

   https://doi.org/10.1002/anbr.202100120  

   Zhao, Nanxia ; Francis, Nicola L. ; Song, Shuang ; Kholodovych, Vladyslav ; Calvelli, Hannah R. ; Hoop, Cody L. ; Pang, Zhiping P. ; Baum, Jean ; Uhrich, Kathryn E. ; Moghe, Prabhas V. ( March 2022 , Advanced NanoBiomed Research)

   Neuroinflammation is one of the hallmarks contributing to Parkinson's disease (PD) pathology, where microglial activation occurs as one of the earliest events, triggered by extracellular α‐synuclein (aSYN) binding to the cluster of differentation 36 (CD36) receptor. Herein, CD36‐binding nanoparticles (NPs) containing tartaric acid–based amphiphilic macromolecules (AMs) are rationally designed to inhibit this aSYN–CD36 binding. In silico docking reveals that four AMs with varying alkyl side chain lengths present differential levels of CD36 binding affinity and that an optimal alkyl chain length promotes the strongest inhibitory activity toward aSYN–CD36 interactions. In vitro competitive binding assays indicate that the inhibitory activity of AM‐based NPs plateaus at intermediate side chain lengths of 12 and 18 carbons, supporting the in silico docking predictions. These intermediate‐length AM NPs also has significantly stronger effects on reducing aSYN internalization and inhibiting proinflammatory molecules tumor necrosis factor α (TNF‐α) and nitric oxide from aSYN‐challenged microglia. All four NPs modulate the gene expression of aSYN‐challenged microglia, downregulating proinflammatory genes TNF, interleukin 6 (IL‐6), and IL‐1β, and upregulating anti‐inflammatory genes transforming growth factor β (TGF‐β) and Arg1 expression. Herein, overall, a novel polymeric nanotechnology platform is represented that can be used to modulate aSYN‐induced microglial activation.

    

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4. The inflammatory response to birth requires MyD88 and is driven by both mother and offspring

   https://doi.org/10.1016/j.bbi.2023.11.011  

   Gray, Jennifer M. ; Major, Kharli ; Castillo-Ruiz, Alexandra ; Shipley, Michael ; Gangappa, Shivaprakash ; Forger, Nancy G. ( January 2024 , Brain, Behavior, and Immunity)

   Birth is an inflammatory event for the newborn, characterized by elevations in interleukin (IL)-6, IL-10, and tumor necrosis factor (TNF)-α peripherally and/or centrally, as well as changes in brain microglia. However, the mechanism(s) underlying these responses is unknown. Toll-like receptors (TLRs) play crucial roles in innate immunity and initiate inflammatory cascades upon recognition of endogenous or exogenous antigens. Most TLR signaling depends on the adaptor molecule myeloid differentiation primary response 88 (MyD88). We independently varied MyD88 gene status in mouse dams and their offspring to determine whether the inflammatory response to birth depends on MyD88 signaling and, if so, whether that signaling occurs in the offspring, the mother, or both. We find that the perinatal surges in plasma IL-6 and brain expression of TNF-α depend solely on MyD88 gene status of the offspring, whereas postnatal increases in plasma IL-10 and TNF-α depend on MyD88 in both the pup and dam. Interestingly, MyD88 genotype of the dam primarily drives differences in offspring brain microglial density and has robust effects on developmental neuronal cell death. Milk cytokines were evaluated as a possible source of postnatal maternal influence; although we found high levels of CXCL1/GROα and several other cytokines in ingested post-partum milk, their presence did not require MyD88. Thus, the inflammatory response previously described in the late-term fetus and newborn depends on MyD88 (and, by extension, TLRs), with signaling in both the dam and offspring contributing. Unexpectedly, naturally-occuring neuronal cell death in the newborn is modulated primarily by maternal MyD88 gene status. 

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5. TREX1 is required for microglial cholesterol homeostasis and oligodendrocyte terminal differentiation in human neural assembloids

   https://doi.org/10.1038/s41380-023-02348-w  

   Goldberg, Gabriela ; Coelho, Luisa ; Mo, Guoya ; Adang, Laura A. ; Patne, Meenakshi ; Chen, Zhoutao ; Garcia-Bassets, Ivan ; Mesci, Pinar ; Muotri, Alysson R. ( December 2023 , Molecular Psychiatry)

   Three Prime Repair Exonuclease 1 (TREX1) gene mutations have been associated with Aicardi-Goutières Syndrome (AGS) – a rare, severe pediatric autoimmune disorder that primarily affects the brain and has a poorly understood etiology. Microglia are brain-resident macrophages indispensable for brain development and implicated in multiple neuroinflammatory diseases. However, the role of TREX1 – a DNase that cleaves cytosolic nucleic acids, preventing viral- and autoimmune-related inflammatory responses – in microglia biology remains to be elucidated. Here, we leverage a model of human embryonic stem cell (hESC)-derived engineered microglia-like cells, bulk, and single-cell transcriptomics, optical and transmission electron microscopy, and three-month-old assembloids composed of microglia and oligodendrocyte-containing organoids to interrogate TREX1 functions in human microglia. Our analyses suggest that TREX1 influences cholesterol metabolism, leading to an active microglial morphology with increased phagocytosis in the absence of TREX1. Notably, regulating cholesterol metabolism with an HMG-CoA reductase inhibitor, FDA-approved atorvastatin, rescues these microglial phenotypes. Functionally, TREX1 in microglia is necessary for the transition from gliogenic intermediate progenitors known as pre-oligodendrocyte precursor cells (pre-OPCs) to precursors of the oligodendrocyte lineage known as OPCs, impairing oligodendrogenesis in favor of astrogliogenesis in human assembloids. Together, these results suggest routes for therapeutic intervention in pathologies such as AGS based on microglia-specific molecular and cellular mechanisms.

    

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