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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 modelmore »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 culturesmore »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. Prioritized polycystic kidney disease drug targets and repurposing candidates from pre-cystic and cystic mouse Pkd2 model gene expression reversion

   https://doi.org/10.1186/s10020-023-00664-z  

   Wilk, Elizabeth J. ; Howton, Timothy C. ; Fisher, Jennifer L. ; Oza, Vishal H. ; Brownlee, Ryan T. ; McPherson, Kasi C. ; Cleary, Hannah L. ; Yoder, Bradley K. ; George, James F. ; Mrug, Michal ; et al ( May 2023 , Molecular Medicine)

   Autosomal dominant polycystic kidney disease (ADPKD) is one of the most prevalent monogenic human diseases. It is mostly caused by pathogenic variants inPKD1orPKD2genes that encode interacting transmembrane proteins polycystin-1 (PC1) and polycystin-2 (PC2). Among many pathogenic processes described in ADPKD, those associated with cAMP signaling, inflammation, and metabolic reprogramming appear to regulate the disease manifestations. Tolvaptan, a vasopressin receptor-2 antagonist that regulates cAMP pathway, is the only FDA-approved ADPKD therapeutic. Tolvaptan reduces renal cyst growth and kidney function loss, but it is not tolerated by many patients and is associated with idiosyncratic liver toxicity. Therefore, additional therapeutic options for ADPKD treatment are needed.

   As drug repurposing of FDA-approved drug candidates can significantly decrease the time and cost associated with traditional drug discovery, we used the computational approach signature reversion to detect inversely related drug response gene expression signatures from the Library of Integrated Network-Based Cellular Signatures (LINCS) database and identified compounds predicted to reverse disease-associated transcriptomic signatures in three publicly availablePkd2kidney transcriptomic data sets of mouse ADPKD models. We focused on a pre-cystic model for signature reversion, as it was less impacted by confounding secondary disease mechanisms in ADPKD, and then compared the resulting candidates’ target differential expression inmore »the two cystic mouse models. We further prioritized these drug candidates based on their known mechanism of action, FDA status, targets, and by functional enrichment analysis.

   With this in-silico approach, we prioritized 29 unique drug targets differentially expressed inPkd2ADPKD cystic models and 16 prioritized drug repurposing candidates that target them, including bromocriptine and mirtazapine, which can be further tested in-vitro and in-vivo.

   Collectively, these results indicate drug targets and repurposing candidates that may effectively treat pre-cystic as well as cystic ADPKD.

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4. Single-cell RNA transcriptome analysis of CNS immune cells reveals CXCL16/CXCR6 as maintenance factors for tissue-resident T cells that drive synapse elimination

   https://doi.org/10.1186/s13073-022-01111-0  

   Rosen, Sarah F. ; Soung, Allison L. ; Yang, Wei ; Ai, Shenjian ; Kanmogne, Marlene ; Davé, Veronica A. ; Artyomov, Maxim ; Magee, Jeffrey A. ; Klein, Robyn S. ( September 2022 , Genome Medicine)

   Emerging RNA viruses that target the central nervous system (CNS) lead to cognitive sequelae in survivors. Studies in humans and mice infected with West Nile virus (WNV), a re-emerging RNA virus associated with learning and memory deficits, revealed microglial-mediated synapse elimination within the hippocampus. Moreover, CNS-resident memory T (T_RM) cells activate microglia, limiting synapse recovery and inducing spatial learning defects in WNV-recovered mice. The signals involved in T cell-microglia interactions are unknown.

   Here, we examined immune cells within the murine WNV-recovered forebrain using single-cell RNA sequencing to identify putative ligand-receptor pairs involved in intercellular communication between T cells and microglia. Clustering and differential gene analyses were followed by protein validation and genetic and antibody-based approaches utilizing an established murine model of WNV recovery in which microglia and complement promote ongoing hippocampal synaptic loss.

   Profiling of host transcriptome immune cells at 25 days post-infection in mice revealed a shift in forebrain homeostatic microglia to activated subpopulations with transcriptional signatures that have previously been observed in studies of neurodegenerative diseases. Importantly, CXCL16/CXCR6, a chemokine signaling pathway involved in T_RM cell biology, was identified as critically regulating CXCR6 expressing CD8⁺T_RM cell numbers within the WNV-recovered forebrain. We demonstrate that CXCL16 is highlymore »expressed by all myeloid cells, and its unique receptor, CXCR6, is highly expressed on all CD8⁺T cells. Using genetic and pharmacological approaches, we demonstrate that CXCL16/CXCR6 not only is required for the maintenance of WNV-specific CD8 T_RM cells in the post-infectious CNS, but also contributes to their expression of T_RM cell markers. Moreover, CXCR6⁺CD8⁺T cells are required for glial activation and ongoing synapse elimination.

   We provide a comprehensive assessment of the role of CXCL16/CXCR6 as an interaction link between microglia and CD8⁺T cells that maintains forebrain T_RM cells, microglial and astrocyte activation, and ongoing synapse elimination in virally recovered animals. We also show that therapeutic targeting of CXCL16 in mice during recovery may reduce CNS CD8⁺T_RM cells.

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5. Experimental colitis promotes sustained, sex-dependent, T-cell-associated neuroinflammation and parkinsonian neuropathology

   https://doi.org/10.1186/s40478-021-01240-4  

   Houser, Madelyn C. ; Caudle, W. Michael ; Chang, Jianjun ; Kannarkat, George T. ; Yang, Yuan ; Kelly, Sean D. ; Oliver, Danielle ; Joers, Valerie ; Shannon, Kathleen M. ; Keshavarzian, Ali ; et al ( August 2021 , Acta Neuropathologica Communications)

   The etiology of sporadic Parkinson’s disease (PD) remains uncertain, but genetic, epidemiological, and physiological overlap between PD and inflammatory bowel disease suggests that gut inflammation could promote dysfunction of dopamine-producing neurons in the brain. Mechanisms behind this pathological gut-brain effect and their interactions with sex and with environmental factors are not well understood but may represent targets for therapeutic intervention.

   We sought to identify active inflammatory mechanisms which could potentially contribute to neuroinflammation and neurological disease in colon biopsies and peripheral blood immune cells from PD patients. Then, in mouse models, we assessed whether dextran sodium sulfate-mediated colitis could exert lingering effects on dopaminergic pathways in the brain and whether colitis increased vulnerability to a subsequent exposure to the dopaminergic neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We assessed the involvement of inflammatory mechanisms identified in the PD patients in colitis-related neurological dysfunction in male and female mice, utilizing mice lacking the Regulator of G-Protein Signaling 10 (RGS10)—an inhibitor of nuclear factor kappa B (NFκB)—to model enhanced NFκB activity, and mice in which CD8⁺T-cells were depleted.

   High levels of inflammatory markers includingCD8Band NFκB p65 were found in colon biopsies from PD patients, and reduced levels of RGS10 were found in immune cells inmore »the blood. Male mice that experienced colitis exhibited sustained reductions in tyrosine hydroxylase but not in dopamine as well as sustained CD8⁺T-cell infiltration and elevatedIfngexpression in the brain. CD8⁺T-cell depletion prevented colitis-associated reductions in dopaminergic markers in males. In both sexes, colitis potentiated the effects of MPTP. RGS10 deficiency increased baseline intestinal inflammation, colitis severity, and neuropathology.

   This study identifies peripheral inflammatory mechanisms in PD patients and explores their potential to impact central dopaminergic pathways in mice. Our findings implicate a sex-specific interaction between gastrointestinal inflammation and neurologic vulnerability that could contribute to PD pathogenesis, and they establish the importance of CD8⁺T-cells in this process in male mice.

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