bims-microg 2024-09-29 papers

bims-microg

Biomed News

on Microglia in Health and Disease

Issue of 2024‒09‒29
33 papers selected by
Marcus Karlstetter, Universität zu Köln

IRF8 defines the epigenetic landscape in postnatal microglia, thereby directing their transcriptome programs.
Transport of β-amyloid from brain to eye causes retinal degeneration in Alzheimer's disease.
Microglia Mediate Metabolic Dysfunction from Common Air Pollutants through NF-κB Signaling.
Repeated LPS induces training and tolerance of microglial responses across brain regions.
Understanding genetics, sex and signaling: Implications of sex-dependent APOE4-neutrophil-microglia interactions for Alzheimer's and tauopathies.
Glycation Produces Topologically Different α-Synuclein Oligomeric Strains and Modulates Microglia Response via the NLRP3-Inflammasome Pathway.
Blockage of ATGL-mediated breakdown of lipid droplets in microglia alleviates neuroinflammatory and behavioural responses to lipopolysaccharides.
Engineering of Human Blood-Induced Microglia-like Cells for Reverse-Translational Brain Research.
Microglia in retinal diseases: From pathogenesis towards therapeutic strategies.
Neonatal inflammation impairs developmentally-associated microglia and promotes a highly reactive microglial subset.
APOE4 affects neutrophil-microglia crosstalk in Alzheimer's disease.
Extracellular cleavage of microglia-derived progranulin promotes diet-induced obesity.
Integrative transcriptomic analysis reveals Cd72 as a novel pro-inflammatory factor in microglia following experimental ischemic stroke.
Microglia inversely regulate the level of perineuronal nets with the treatment of lipopolysaccharide and valproic acid.
Shh regulates M2 microglial polarization and fibrotic scar formation after ischemic stroke.
Glucocorticoids induce HMGB1 release in primary cultured rat cortical microglia.
EXPRESS: Human microglia polarization following infection with the Lyme disease spirochete.
Immunocompetent Brain Organoids with Microglia Allow Advanced Aging Research.
Pentylenetetrazole-Induced Seizures Cause Short-Term Changes in the Phenotype of Microglial and Astroglial Cells in the Hippocampus and Temporal Cortex of Young Male Wistar Rats.
Loss of TREM2 diminishes CAA despite an overall increase of amyloid load in Tg-SwDI mice.
Esketamine improves cognitive function in sepsis-associated encephalopathy by inhibiting microglia-mediated neuroinflammation.
ARL11 knockdown alleviates spinal cord injury by inhibiting neuroinflammation and M1 activation of microglia in mice.
Novel human iPSC models of neuroinflammation in neurodegenerative disease and regenerative medicine.
Angiotensin II, blood-brain barrier permeability, and microglia interplay during the transition from pre-to hypertensive phase in spontaneously hypertensive rats.
Zebrafish models of human-duplicated gene SRGAP2 reveal novel functions in microglia and visual system development.
Remimazolam attenuates lipopolysaccharide-induced neuroinflammation and cognitive dysfunction.
Transcriptome analysis unveils PLSCR1 associated with microglial polarization in neuropathic pain.
High-dose dexamethasone regulates microglial polarization via the GR/JAK1/STAT3 signaling pathway after traumatic brain injury.
Gelsevirine ameliorates sepsis-associated encephalopathy by inhibiting the STING signalling-mediated pyroptosis pathway in microglia.
Uncovering Plaque-Glia Niches in Human Alzheimer's Disease Brains Using Spatial Transcriptomics.
Epigenetic adaptation drives monocyte differentiation into microglia-like cells upon engraftment into the retina.
Protective lifelines: Tunneling nanotubes connect neurons and microglia.
Isolation of Hypothalamic Microglia from Freshly Perfused Adult Mouse Brain by Magnetic-Activated Cell Sorting.

Nat Immunol. 2024 Oct;25(10): 1928-1942

IRF8 defines the epigenetic landscape in postnatal microglia, thereby directing their transcriptome programs.

Keita Saeki, Richard Pan, Eunju Lee, Daisuke Kurotaki, Keiko Ozato.

Microglia are innate immune cells in the brain. Transcription factor IRF8 (interferon regulatory factor 8) is highly expressed in microglia. However, its role in postnatal microglia development is unknown. We demonstrate that IRF8 binds stepwise to enhancer regions of postnatal microglia along with Sall1 and PU.1, reaching a maximum after day 14. IRF8 binding correlated with a stepwise increase in chromatin accessibility, which preceded the initiation of microglia-specific transcriptome. Constitutive and postnatal Irf8 deletion led to a loss of microglia identity and gain of disease-associated microglia (DAM)-like genes. Combined analysis of single-cell (sc)RNA sequencing and single-cell transposase-accessible chromatin with sequencing (scATAC-seq) revealed a correlation between chromatin accessibility and transcriptome at a single-cell level. IRF8 was also required for microglia-specific DNA methylation patterns. Last, in the 5xFAD model, constitutive and postnatal Irf8 deletion reduced the interaction of microglia with amyloidβ plaques and the size of plaques, lessening neuronal loss. Together, IRF8 sets the epigenetic landscape, which is required for postnatal microglia gene expression.

DOI: https://doi.org/10.1038/s41590-024-01962-2
J Exp Med. 2024 Nov 04. pii: e20240386. [Epub ahead of print]221(11):

Transport of β-amyloid from brain to eye causes retinal degeneration in Alzheimer's disease.

Qiuchen Cao, Shige Yang, Xiaowei Wang, Huaiqing Sun, Weijie Chen, Yuliang Wang, Junying Gao, Yanchi Wu, Qiuhua Yang, Xue Chen, Songtao Yuan, Ming Xiao, Maiken Nedergaard, Yuqing Huo, Qinghuai Liu.

The eye is closely connected to the brain, providing a unique window to detect pathological changes in the brain. In this study, we discovered β-amyloid (Aβ) deposits along the ocular glymphatic system in patients with Alzheimer's disease (AD) and 5×FAD transgenic mouse model. Interestingly, Aβ from the brain can flow into the eyes along the optic nerve through cerebrospinal fluid (CSF), causing retinal degeneration. Aβ is mainly observed in the optic nerve sheath, the neural axon, and the perivascular space, which might represent the critical steps of the Aβ transportation from the brain to the eyes. Aquaporin-4 facilitates the influx of Aβ in brain-eye transport and out-excretion of the retina, and its absence or loss of polarity exacerbates brain-derived Aβ induced damage and visual impairment. These results revealed brain-to-eye Aβ transport as a major contributor to AD retinopathy, highlighting a new therapeutic avenue in ocular and neurodegenerative disease.

DOI: https://doi.org/10.1084/jem.20240386
Diabetes. 2024 Sep 25. pii: db240110. [Epub ahead of print]

Microglia Mediate Metabolic Dysfunction from Common Air Pollutants through NF-κB Signaling.

Lucas K Debarba, Hashan S M Jayarathne, Lukas Stilgenbauer, Ana L Terra Dos Santos, Lisa Koshko, Sydney Scofield, Ryan Sullivan, Abhijit Mandal, Ulrike Klueh, Marianna Sadagurski.

The prevalence of Type 2 Diabetes (T2D) poses a significant health challenge yet the contribution of air pollutants to T2D epidemics remains understudied. Several studies demonstrated a correlation between exposure to volatile organic compounds (VOCs) in indoor/outdoor environments, and T2D. Here, we conducted the first meta-analysis, establishing a robust association between exposure to benzene, a prevalent airborne VOC, and insulin resistance in humans across all ages. We utilized a controlled benzene exposure system, continuous glucose monitoring (CGM) approach and indirect calorimetry in mice, to investigate the underlying mechanisms. Following exposure, disruptions in energy homeostasis, accompanied by modifications in the hypothalamic transcriptome and alterations in insulin and immune signaling, were observed exclusively in males, leading to a surge in blood glucose levels. In agreement, RNA-sequencing of microglia reveals increased expression of genes associated with immune response and NF-κB signaling. Selective ablation of IKKβ in immune cells (Cx3cr1GFPΔIKK) or exclusively in microglia (Tmem119ERΔIKK) in adult mice alleviated benzene-induced gliosis, restored energy homeostasis, hypothalamic gene expression, and protected against hyperglycemia. We conclude that the microglial NF-κB pathway plays a critical role in chemical-induced metabolic disturbances, revealing a vital pathophysiological mechanism linking exposure to airborne toxicants and the onset of metabolic diseases.

DOI: https://doi.org/10.2337/db24-0110
J Neuroinflammation. 2024 Sep 20. 21(1): 233

Repeated LPS induces training and tolerance of microglial responses across brain regions.

Jennifer Kim, Olivia Sullivan, Kristen Lee, Justin Jao, Juan Tamayo, Abdullah Muhammad Madany, Brandon Wong, Paul Ashwood, Annie Vogel Ciernia.

  BACKGROUND: Neuroinflammation is involved in the pathogenesis of almost every central nervous system disorder. As the brain's innate immune cells, microglia fine tune their activity to a dynamic brain environment. Previous studies have shown that repeated bouts of peripheral inflammation can trigger long-term changes in microglial gene expression and function, a form of innate immune memory.METHODS AND RESULTS: In this study, we used multiple low-dose lipopolysaccharide (LPS) injections in adult mice to study the acute cytokine, transcriptomic, and microglia morphological changes that contribute to the formation of immune memory in the frontal cortex, hippocampus, and striatum, as well as the long-term effects of these changes on behavior. Training and tolerance of gene expression was shared across regions, and we identified 3 unique clusters of DEGs (2xLPS-sensitive, 4xLPS-sensitive, LPS-decreased) enriched for different biological functions. 2xLPS-sensitive DEG promoters were enriched for binding sites for IRF and NFkB family transcription factors, two key regulators of innate immune memory. We quantified shifts in microglia morphological populations and found that while the proportion of ramified and rod-like microglia mostly remained consistent within brain regions and sexes with LPS treatment, there was a shift from ameboid towards hypertrophic morphological states across immune memory states and a dynamic emergence and resolution of events of microglia aligning end-to-end with repeated LPS.
CONCLUSIONS: Together, findings support the dynamic regulation of microglia during the formation of immune memories in the brain and support future work to exploit this model in brain disease contexts.

Keywords:  Gene expression; Gene regulation; Innate immune memory; Microglia; Microglia morphology

DOI:  https://doi.org/10.1186/s12974-024-03198-1
Signal Transduct Target Ther. 2024 Sep 23. 9(1): 252

Understanding genetics, sex and signaling: Implications of sex-dependent APOE4-neutrophil-microglia interactions for Alzheimer's and tauopathies.

Natja Haag, Juliane Bremer, Hans Zempel.

DOI: https://doi.org/10.1038/s41392-024-01967-1
ACS Chem Neurosci. 2024 Sep 25.

Glycation Produces Topologically Different α-Synuclein Oligomeric Strains and Modulates Microglia Response via the NLRP3-Inflammasome Pathway.

Manisha Kumari, Krishna Singh Bisht, Kriti Ahuja, Rajender K Motiani, Tushar Kanti Maiti.

  α-Synuclein, a key player in Parkinson's disease and other synucleinopathies, possesses an inherently disordered structure that allows for versatile structural changes during aggregation. Microglia, the brain immune cells, respond differently to various α-synuclein strains, influencing their activation and release of harmful molecules, leading to neuronal death. Post-translational modifications, such as glycation in α-synuclein, add a layer of complexity to microglial activation. This study aimed to explore the impact of glycation on α-synuclein aggregation and microglial responses, which have not been studied before. Biophysical analyses revealed that glycated α-synuclein oligomers had distinct morphologies with a more negative and hydrophobic surface, preventing fibril formation and interfering with membrane interactions. Notably, there was increased cytosolic Ca2+ dysregulation, redox stress, and mitochondrial instability compared to cells exposed to unmodified α-synuclein oligomers. Additionally, glycated α-synuclein oligomers exhibited impaired binding to Toll-like receptor 2, compromising downstream signaling. Surprisingly, these oligomers promoted TLR4 endocytosis and degradation. In our experiments with oligomers, glycated α-synuclein oligomers preferred NLRP3 inflammasome-mediated neuroinflammation, contributing differently from unmodified α-synuclein oligomers. In summary, this study unveils the mechanism underlying the effect of glycation on α-synuclein oligomers and highlights the conformation-specific microglial responses toward extracellular α-synuclein.

Keywords:  NOD- LRR- and pyrin domain-containing protein 3 (NLRP3); Parkinson’s disease; glycated α-synuclein; microglia; toll-like receptors 2; α-synuclein

DOI:  https://doi.org/10.1021/acschemneuro.4c00057
Brain Behav Immun. 2024 Sep 24. pii: S0889-1591(24)00629-9. [Epub ahead of print]

Blockage of ATGL-mediated breakdown of lipid droplets in microglia alleviates neuroinflammatory and behavioural responses to lipopolysaccharides.

Representative of consortium

  Lipid droplets (LD) are triglyceride storing organelles that have emerged as an important component of cellular inflammatory responses. LD lipolysis via adipose triglyceride lipase (ATGL), the enzyme that catalyses the rate-limiting step of triglyceride lipolysis, regulates inflammation in peripheral immune and non-immune cells. ATGL elicits both pro- and anti-inflammatory responses in the periphery in a cell-type dependent manner. The present study determined the impact of ATGL inhibition and microglia-specific ATGL genetic loss-of-function on acute inflammatory and behavioural responses to pro-inflammatory insult. First, we evaluated the impact of lipolysis inhibition on lipopolysaccharide (LPS)-induced expression and secretion of cytokines and phagocytosis in mouse primary microglia cultures. Lipase inhibitors (ORlistat and ATGListatin) and LPS led to LD accumulation in microglia. Pan-lipase inhibition with ORlistat alleviated LPS-induced expression of IL-1β and IL-6. Specific inhibition of ATGL had a similar action on CCL2, IL-1β and IL-6 expression in both neonatal and adult microglia cultures. CCL2 and IL-6 secretion were also reduced by ATGListatin or knockdown of ATGL. ATGListatin increased phagocytosis in neonatal cultures independently from LPS treatment. Second, targeted and untargeted lipid profiling revealed that ATGListatin reduced LPS-induced generation of pro-inflammatory prostanoids and modulated ceramide species in neonatal microglia. Finally, the role of microglial ATGL in neuroinflammation was assessed using a novel microglia-specific and inducible ATGL knockout mouse model. Loss of microglial ATGL in adult male mice dampened LPS-induced expression of IL-6 and IL-1β and microglial density. LPS-induced sickness- and anxiety-like behaviours were also reduced in mice with loss of ATGL in microglia. Together, our results demonstrate potent anti-inflammatory effects produced by pharmacological or genetic inhibition of ATGL-mediated triglyceride lipolysis and thereby propose that supressing microglial LD lipolysis has beneficial actions in acute neuroinflammatory conditions.

Keywords:  Adipose triglyceride lipase; Interleukin-6; Lipid droplet; Microglia; Neuroinflammation

DOI:  https://doi.org/10.1016/j.bbi.2024.09.027
J Vis Exp. 2024 Sep 06.

Engineering of Human Blood-Induced Microglia-like Cells for Reverse-Translational Brain Research.

Sota Kyuragi, Shogo Inamine, Masahiro Ohgidani, Takahiro A Kato.

Recent investigations employing animal models have highlighted the significance of microglia as crucial immunological modulators in various neuropsychiatric and physical diseases. Postmortem brain analysis and positron emission tomography imaging are representative research methods that evaluate microglial activation in human patients; the findings have revealed the activation of microglia in the brains of patients presenting with various neuropsychiatric disorders and chronic pain. Nonetheless, the aforementioned technique merely facilitates the assessment of limited aspects of microglial activation. In lieu of brain biopsy and the induced pluripotent stem cell technique, we initially devised a technique to generate directly induced microglia-like (iMG) cells from freshly derived human peripheral blood monocytes by supplementing them with granulocyte-macrophage colony-stimulating factor and interleukin 34 for 2 weeks. These iMG cells can be employed to perform dynamic morphological and molecular-level analyses concerning phagocytic capacity and cytokine releases following cellular-level stress stimulation. Recently, comprehensive transcriptome analysis has been used to verify the similarity between human iMG cells and brain primary microglia. The patient-derived iMG cells may serve as key surrogate markers for predicting microglial activation in human brains and have aided in the unveiling of previously unknown dynamic pathophysiology of microglia in patients with Nasu-Hakola disease, fibromyalgia, bipolar disorder, and Moyamoya disease. Therefore, the iMG-based technique serves as a valuable reverse-translational tool and provides novel insights into elucidating dynamic the molecular pathophysiology of microglia in a variety of mental and physical diseases.

DOI: https://doi.org/10.3791/66819
Biochem Pharmacol. 2024 Sep 20. pii: S0006-2952(24)00550-1. [Epub ahead of print] 116550

Microglia in retinal diseases: From pathogenesis towards therapeutic strategies.

Ruihan Xiao, Xi Huang, Sheng Gao, Jianan Duan, Yun Zhang, Meixia Zhang.

  Microglia, a widely dispersed cohort of immune cells in the retina, are intricately involved in a diverse range of pivotal biological processes, including inflammation, vascular development, complement activation, antigen presentation, and phagocytosis. Within the retinal milieu, microglia are crucial for the clearance of dead cells and cellular debris, release of anti-inflammatory agents, and orchestration of vascular network remodeling to maintain homeostasis. In addition, microglia are key mediators of neuroinflammation. Triggered by oxidative stress, elevated intraocular pressure, genetic anomalies, and immune dysregulation, microglia release numerous inflammatory cytokines, contributing to the pathogenesis of various retinal disorders. Recent studies on the ontogeny and broad functions of microglia in the retina have elucidated their characteristics during retinal development, homeostasis, and disease. Furthermore, therapeutic strategies that target microglia and their effector cytokines have been developed and shown positive results for some retinal diseases. Therefore, we systematically review the microglial ontogeny in the retina, elucidate their dual roles in retinal homeostasis and disease pathogenesis, and demonstrate microglia-based targeted therapeutic strategies for retinal diseases.

Keywords:  Homeostasis; Microglia; Pathogenesis; Retinal diseases; Targeted therapeutic strategies

DOI:  https://doi.org/10.1016/j.bcp.2024.116550
Brain Behav Immun. 2024 Sep 23. pii: S0889-1591(24)00623-8. [Epub ahead of print]

Neonatal inflammation impairs developmentally-associated microglia and promotes a highly reactive microglial subset.

Adrien Dufour, Ariane Heydari-Olya, Sophie Foulon, Clémence Réda, Amazigh Mokhtari, Valérie Faivre, Jennifer Hua, Cindy Bokobza, Andrew D Griffiths, Philippe Nghe, Pierre Gressens, Andrée Delahaye-Duriez, Juliette Van Steenwinckel.

Microglia and border-associated macrophages play critical roles in both immunity and neurodevelopment. The disruption of microglial development trajectories by neonatal inflammation is an important issue in research on neurodevelopmental disorders (NDDs), as models have suggested a strong association between inflammation and cognitive deficits. Here, we explored by single-cell RNA sequencing and flow cytometry the impact of neonatal inflammation in a mouse NDD model on the brain myeloid cell subsets. A specific subset of microglia expressing the complement receptor C5ar1 has been identified, in which inflammatory pathways are most strongly activated. Based on transcriptional similarity, this subset appears to originate from the most mature and "homeostatic" microglia at this stage of development and demonstrated hypersensitivity to inflammation. Besides that, Spp1-microglia supporting oligodendrocyte differentiation, primitive and proliferative microglia were reduced by the inflammation. These findings suggest major changes in microglial subsets developmental trajectories and reactivity contributing to NDDs induced by neonatal inflammation.

DOI: https://doi.org/10.1016/j.bbi.2024.09.019
Trends Immunol. 2024 Sep 24. pii: S1471-4906(24)00210-2. [Epub ahead of print]

APOE4 affects neutrophil-microglia crosstalk in Alzheimer's disease.

Eleonora Terrabuio, Gabriela Constantin.

Circulating immune cells contribute to the pathogenesis of Alzheimer's disease (AD), but their role is poorly understood. Rosenzweig et al. recently identified a subset of interleukin (IL)-17+ neutrophils that inhibit neuroprotective microglia in female APOE4 carriers. Blockade of IL-17 signaling or APOE4 deletion in neutrophils restored microglial responses and reduced murine amyloid pathology.

DOI: https://doi.org/10.1016/j.it.2024.09.002
Diabetes. 2024 Sep 20. pii: db240097. [Epub ahead of print]

Extracellular cleavage of microglia-derived progranulin promotes diet-induced obesity.

Chae Beom Park, Chan Hee Lee, Kae Won Cho, Sunghun Shin, Won Hee Jang, Junyeong Byeon, Yu Rim Oh, Sung Jun Kim, Jae Woo Park, Gil Myoung Kang, Se Hee Min, Seyun Kim, Rina Yu, Min-Seon Kim.

Hypothalamic innate immune responses to dietary fats underpin the pathogenesis of obesity, in which microglia play a critical role. Progranulin (PGRN) is an evolutionarily -conserved secretory protein containing seven-and-a-half granulin (GRN) motifs. It is cleaved into GRNs by multiple proteases. In the central nervous system, PGRN is highly expressed in microglia. To investigate the role of microglia-derived PGRN in metabolism regulation, we established a mouse model with a microglia-specific deletion of the Grn gene, that encodes PGRN. Mice with microglia-specific Grn gene depletion displayed dietdependent metabolic phenotypes. Under normal diet-fed conditions, microglial Grn gene depletion produced adverse outcomes like fasting hyperglycemia and aberrant activation of hypothalamic microglia. However, when fed a high fat diet (HFD), these mice exhibited beneficial effects, including less obesity, glucose dysregulation, and hypothalamic inflammation. These differing phenotypes appear linked to increased extracellular cleavage of anti-inflammatory PGRN into proinflammatory GRNs in the hypothalamus during overnutrition. In support of this, inhibiting PGRN cleavage attenuated HFD-induced hypothalamic inflammation and obesity progression. Our results suggest that the extracellular cleavage of microglia-derived PGRN plays a significant role in promoting hypothalamic inflammation and obesity during periods of overnutrition. Therefore, therapies that inhibit PGRN cleavage may be beneficial for combating dietinduced obesity.

DOI: https://doi.org/10.2337/db24-0097
Exp Neurol. 2024 Sep 24. pii: S0014-4886(24)00300-5. [Epub ahead of print] 114974

Integrative transcriptomic analysis reveals Cd72 as a novel pro-inflammatory factor in microglia following experimental ischemic stroke.

Haojie Ding, Xuan Shi, Junwei Ma, Chang Cao, Yangyang Liu, Jinxin Lu, Lei Bai, Xiang Li, Haiying Li.

  Ischemic stroke remains a leading cause of global mortality and disability, with neuroinflammation playing a critical role in determining patient outcomes. Microglia, the brain's resident immune cells, can both exacerbate neuroinflammation and neuronal damage by releasing neurotoxic mediators and engaging in excessive phagocytosis, while also aiding recovery through the production of anti-inflammatory cytokines and debris clearance. However, the molecular mechanisms governing microglial activation and polarization after ischemic stroke are not well elucidated. In this study, we combined integrative transcriptomic analyses with experimental validation in a murine model of middle cerebral artery occlusion/reperfusion (MCAO/R) to explore microglial heterogeneity and identify key regulatory factors in ischemic stroke. Bioinformatics analysis identified Cd72 as a novel pro-inflammatory modulator within ischemia-associated microglial phenotypes. We observed significant upregulation of Cd72 in microglia following MCAO/R, and selective knockdown of Cd72 using CX3CR1Cre/ERT2 mice and Cre recombinase-dependent adeno-associated virus reduced MCAO/R-induced infarct volume, neuronal apoptosis, and neurological deficits. Furthermore, Cd72 expression in microglia was positively correlated with pro-inflammatory pathways and cytokines, including TNF-α, IL-1β, and IL-6. Knockdown of Cd72 significantly reduced these pro-inflammatory factors, highlighting its potential as a therapeutic target for mitigating inflammation in ischemic stroke. In conclusion, this study identifies Cd72 as a critical pro-inflammatory regulator in microglia following ischemic stroke, with its knockdown effectively reducing neuroinflammation and associated brain injury, highlighting Cd72 as a promising therapeutic target.

Keywords:  Bulk RNA sequencing; Cd72; Ischemic stroke; Microglia; Neuroinflammation; Single-cell RNA sequencing

DOI:  https://doi.org/10.1016/j.expneurol.2024.114974
Neurosci Lett. 2024 Sep 18. pii: S0304-3940(24)00370-7. [Epub ahead of print]842 137992

Microglia inversely regulate the level of perineuronal nets with the treatment of lipopolysaccharide and valproic acid.

Luping Liu, Tianxiang Li, Jinlong Chang, Xiaojiao Xia, Jun Ju.

  Perineuronal nets (PNNs) are extracellular matrix which mostly surround the inhibitory neurons. They are changed in several brain diseases, such as autism spectrum disorder, but the mechanism of PNNs degradation is still unclear. In this study, we investigated the role of microglial cells in regulating PNNs levels. Specifically, 1 day or 3 days after a single dose of lipopolysaccharide (LPS, 0.25 mg/kg) increased the density of microglia and further reduced the density of PNNs in both hippocampus CA1 and visual cortex. Minocycline, an inhibitor of microglia activation, took effect time-dependently. Minocycline for 7 days before a single LPS injection (0.25 mg/kg) inhibited microglia increase and PNNs loss, but minocycline for 3 days did not work. Finally, in a valproic acid (VPA)-treated autism mouse model, microglia were reduced while PNNs+ cells were increased in both hippocampus CA1 and visual cortex. In summary, the microglia are involved in the balanced level of PNNs, while in the autism model, the altered level of PNNs might be due to the microglia hypofunction.

Keywords:  Autism spectrum disorder; Lipopolysaccharide; Microglia; Minocycline; Perineuronal nets

DOI:  https://doi.org/10.1016/j.neulet.2024.137992
Neurochem Int. 2024 Sep 20. pii: S0197-0186(24)00189-X. [Epub ahead of print]180 105862

Shh regulates M2 microglial polarization and fibrotic scar formation after ischemic stroke.

Qinghuan Yang, Peiran Jiang, Hao Tang, Jun Wen, Li Zhou, Yong Zhao, Ling Wang, Jiani Wang, Qin Yang.

  BACKGROUND: Fibrotic scar formation is a critical pathological change impacting tissue reconstruction and functional recovery after ischemic stroke. The regulatory mechanisms behind fibrotic scarring in the central nervous system (CNS) remain largely unknown. While macrophages are known to play a role in fibrotic scar formation in peripheral tissues, the involvement of microglia, the resident immune cells of the CNS, in CNS fibrosis requires further exploration. The Sonic Hedgehog (Shh) signaling pathway, pivotal in embryonic development and tissue regeneration, is also crucial in modulating fibrosis in peripheral tissues. However, the impact and regulatory mechanisms of Shh on fibrotic scar formation post-ischemic stroke have not been thoroughly investigated.METHODS: This study explores whether Shh can regulate fibrotic scar formation post-ischemic stroke and its underlying mechanisms through in vivo and in vitro manipulation of Shh expression.
RESULTS: Our results showed that Shh expression was upregulated in the serum of acute ischemic stroke patients, as well as in the serum, CSF, and ischemic regions of MCAO/R mice. Moreover, the upregulation of Shh expression was positively correlated with fibrotic scar formation and M2 microglial polarization. Shh knockdown inhibited fibrotic scar formation and M2 microglial polarization while aggravating neurological deficits in MCAO/R mice. In vitro, adenoviral knockdown or Smoothened Agonist (SAG) activation of Shh expression in BV2 cells following OGD/R regulated their polarization and influenced the expression of TGFβ1 and PDGFA, subsequently affecting fibroblast activation.
CONCLUSION: These results suggest that Shh regulates M2 microglial polarization and fibrotic scar formation after cerebral ischemia.

Keywords:  Fibrotic scar; Ischemic stroke; Microglia; Shh

DOI:  https://doi.org/10.1016/j.neuint.2024.105862
Neuroscience. 2024 Sep 19. pii: S0306-4522(24)00483-4. [Epub ahead of print]560 56-66

Glucocorticoids induce HMGB1 release in primary cultured rat cortical microglia.

Kazue Hisaoka-Nakashima, Yuka Takeuchi, Yukino Saito, Takahisa Shimoda, Yoki Nakamura, Dengli Wang, Keyue Liu, Masahiro Nishibori, Norimitsu Morioka.

  Stress, a risk factor for major depressive disorder and Alzheimer disease, leads to the release of high-mobility group box-1 (HMGB1) protein, which in turn causes neuroinflammation. The mechanism underlying stress-induced HMGB1 release is unknown, but stress-associated glucocorticoids could be involved. Primary cultured rat cortical microglia and neurons were treated with corticosterone, a stress-associated glucocorticoid, and HMGB1 release was measured by ELISA and western blotting to test this hypothesis. With corticosterone treatment, significant HMGB1 was released in microglia but not in neuronal cell cultures. HMGB1 mRNA expression and HMGB1 protein expression in microglia were not affected by corticosterone treatment. Thus, the source of extracellular HMGB1 released into the medium is likely to be existing nuclear HMGB1 rather than newly synthesized HMGB1. Corticosterone-induced HMGB1 release in microglia culture was significantly attenuated by blocking glucocorticoid receptors but not mineralocorticoid receptors. Dexamethasone, a selective glucocorticoid receptor agonist, and dexamethasone-bovine serum albumin (BSA), a membrane-impermeable glucocorticoid receptor agonist used to confirm the membrane receptor-mediated effects of glucocorticoids, increased the release of HMGB1. Immunocytochemistry showed that HMGB1 translocated from the nucleus to the cytoplasm following dexamethasone or dexamethasone-BSA treatment through glucocorticoid receptors. The present findings suggest that glucocorticoids stimulate microglial membrane glucocorticoid receptors and trigger cytoplasmic translocation and extracellular release of nuclear HMGB1. Thus, under stress conditions, glucocorticoids induce microglial HMGB1 release, leading to a neuroinflammatory state that could mediate neurological disorders.

Keywords:  Glucocorticoid; HMGB1; Major depressive disorder; Microglia; Neuroinflammation; Stress

DOI:  https://doi.org/10.1016/j.neuroscience.2024.09.031
J Investig Med. 2024 Sep 26. 10815589241290206

EXPRESS: Human microglia polarization following infection with the Lyme disease spirochete.

Idris Akinlusi, Brian Kan, Ted Shi, Jose Barragan, Carlos Bouchot, Jorge L Cervantes.

  Infection with Borrelia burgdorferi (Bb) can spread and cause CNS involvement, known as neuroborreliosis. Microglia phagocytose bacteria, mediate inflammation, and elicit an immune response towards the spirochete. Like other tissue macrophages, microglia can polarize into two different modulatory phenotypes, M1 and M2.We explored human microglial polarization changes upon infection with Bb.HMC3 human microglia cell line was infected with Bb for 24 hours. Expression of polarization markers was evaluated via flow cytometry at 4 and 24 hours. Secreted immunological mediators were evaluated using a multiplex ELISA system at 4,18, and 24 hours.An early decrease followed by a later increase in expression of M1 polarization marker iNOS was observed at 4 hours, and 24 hours, respectively. A decrease in M2 marker CX3CR1 occurred at 24 hours. There were no changes in expression of M1 markers CD14, or in M2 markers CD163 and CD206. Multiplex ELISA evidenced an increase in secretion of activation markers MIP-1α, MIP- 1β, IP-10, chemotactic factor MCP-1, M1 polarization cytokine IL-8, and VEGF, at 4, 18, and 24 hours.A decrease of iNOS at 4 hours of infection suggests a diminished production of reactive nitrogen species that are a critical component of innate defense against infection. Increased iNOS and simultaneously decreased expression of CX3CR1 at 24 hours, may suggest initiation of neuroprotective regulation of microglia recruitment to neuroinflammation. The dynamics of major inflammatory cytokines appear to be important in the microglial response to Bb should be further studied as these could become therapeutic targets in neuroborreliosis.

Keywords:  Bacterial Infections; Inflammation; Nervous System Diseases

DOI:  https://doi.org/10.1177/10815589241290206
Methods Mol Biol. 2024 Sep 25.

Immunocompetent Brain Organoids with Microglia Allow Advanced Aging Research.

Raiane Oliveira Ferreira, Amanda Faria Assoni, Monize Valéria Ramos da Silva, Letícia Alves da Rocha, Mateus Vidigal de Castro, Débora Bertola, Mayana Zatz.

  Aging is a complex and multifactorial process that significantly affects brain function and health, since it is commonly associated with the emergence of neurodegenerative diseases. Recent advances in stem cell technology have facilitated the development of brain organoids, three-dimensional structures that mimic key aspects of brain architecture and functionality. By incorporating microglia, the resident monocyte-derived immune cells of the central nervous system, immunocompetent brain organoids can provide a more physiologically relevant model for studying brain aging. This chapter explores the methodology of immunocompetent brain organoids for advanced aging research, detailing protocols for their generation from a co-culture of neural stem cells and primitive macrophage progenitors.

Keywords:  Aging; Brain-organoid; Immunocompetent; Microglia; Stem cell

DOI:  https://doi.org/10.1007/7651_2024_565
J Neurosci Res. 2024 Sep;102(9): e25385

Pentylenetetrazole-Induced Seizures Cause Short-Term Changes in the Phenotype of Microglial and Astroglial Cells in the Hippocampus and Temporal Cortex of Young Male Wistar Rats.

Maria V Zakharova, Anna A Kovalenko, Olga E Zubareva, Alexander P Schwarz, Tatiana Y Postnikova, Alina M Trofimova, Aleksey V Zaitsev.

  Astrocytes and microglia can adopt two distinct phenotypes in various pathological processes: neurotoxic A1/M1 and neuroprotective A2/M2. Recent evidence suggests that these cells play a significant role in epileptogenesis. The objective of this study was to characterize the phenotype of astrocytes and microglial cells in the hippocampus and temporal cortex of young male Wistar rats at 3 h, 1, 3, and 7 days after pentylenetetrazole-induced seizures. RT-qPCR was employed to examine the expression of glial genes (Gfap, Aif1, Slc1a1, Slc1a2, Slc1a3, Itpr2, Gdnf, Bdnf, Fgf2, Tgfb, Il1b, Tnf, Il1rn, Lcn2, S100a10, Nlrp3, Arg1). The most notable alterations in the expression of glial genes were observed on the first day following seizures in the temporal cortex. An increase in the expression of the Gfap, Slc1a2, Slc1a1, Il1b, Tnfa, Bdnf, and Fgf2 genes, and the A2 astrocyte condition marker S100a10, was observed. An increase in the expression of the Gfap and Slc1a2 genes was observed in the hippocampus on the first day after seizures. However, in contrast to the changes observed in the cortex, the changes in the hippocampus were opposite for the Il1rn, Bdnf, Tgfb, and Arg1 genes. Nevertheless, the alterations in GFAP and EAAT2 protein levels were not corroborated by Western blot analysis. Conversely, a more comprehensive immunohistochemical analysis confirmed an augmentation in the number of GFAP-positive cells in the hippocampus 1 day after seizures. Based on the presented evidence, we can conclude that a single convulsive seizure episode in 3-week-old rats results in transient astroglial activation and polarization to a neuroprotective phenotype (A2).

Keywords:  astroglia polarization; microglia polarization; neuroinflammation; pentylenetetrazole; seizures

DOI:  https://doi.org/10.1002/jnr.25385
Alzheimers Dement. 2024 Sep 23.

Loss of TREM2 diminishes CAA despite an overall increase of amyloid load in Tg-SwDI mice.

Rui Zhong, Yingzheng Xu, Jesse W Williams, Ling Li.

  INTRODUCTION: The microglial receptor triggering receptor expressed on myeloid cells 2 (TREM2) is a major risk factor for Alzheimer's disease (AD). Experimentally, Trem2 deficiency affects parenchymal amyloid beta (Aβ) deposition. However, the role of TREM2 in cerebrovascular amyloidosis, especially cerebral amyloid angiopathy (CAA), remains unexplored.METHODS: Tg-SwDI (SwDI) mice, a CAA-prone model of AD, and Trem2 knockout mice were crossed to generate SwDI/TWT, SwDI/THet, and SwDI/TKO mice, followed by pathological and biochemical analyses at 16 months of age.
RESULTS: Loss of Trem2 led to a dramatic decrease in CAA and microglial association, despite a marked increase in overall brain Aβ load. Single nucleus RNA sequencing analysis revealed that in the absence of Trem2, microglia were activated but trapped in transition to the fully reactive state, with distinct responses of vascular cells.
DISCUSSION: Our study provides the first evidence that TREM2 differentially modulates parenchymal and vascular Aβ pathologies, offering significant implications for both TREM2- and Aβ-targeting therapies for AD.
HIGHLIGHTS: Triggering receptor expressed on myeloid cells 2 (TREM2) differentially modulates brain parenchymal and vascular amyloidosis. Loss of Trem2 markedly reduces cerebral amyloid angiopathy despite an overall increase of amyloid beta load in Tg-SwDI mice. Microglia are trapped in transition to the fully reactive state without Trem2. Perivascular macrophages and other vascular cells have distinct responses to Trem2 deficiency. Balanced TREM2-targeting therapies may be required for optimal outcomes.

Keywords:  Alzheimer's disease; cerebral amyloid angiopathy; cerebrovascular cells; microglia; triggering receptor expressed on myeloid cells 2

DOI:  https://doi.org/10.1002/alz.14222
Eur J Pharmacol. 2024 Sep 21. pii: S0014-2999(24)00704-0. [Epub ahead of print]983 177014

Esketamine improves cognitive function in sepsis-associated encephalopathy by inhibiting microglia-mediated neuroinflammation.

Hui Li, Wen Hu, Zhen Wu, Bin Tian, Yimin Ren, Xiaohua Zou.

  Microglia-mediated neuroinflammation is critical in the pathogenesis of sepsis-associated encephalopathy(SAE). Identifying the key factors that inhibit microglia-mediated neuroinflammation holds promise as a potential target for preventing and treating SAE. Esketamine, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, has been proposed to possess protective and therapeutic properties against neuroinflammatory disorders. This study provides evidence that the administration of Esketamine in SAE mice improves cognitive impairments and alleviates neuronal damage by inhibiting the microglia-mediated neuroinflammation. The BDNF receptor antagonist K252a was employed in both vivo and in vitro experiments. The findings indicate that K252a successfully counteracted the beneficial effects of Esketamine on microglia and cognitive behavior in mice with SAE. Consequently, these results suggest that Esketamine inhibits microglia-mediated neuroinflammation by activating the BDNF pathway, and mitigating neuronal damage and cognitive dysfunction associated with SAE.

Keywords:  BDNF; Esketamine; Microglia; Neuroinflammation; Sepsis-associated encephalopathy

DOI:  https://doi.org/10.1016/j.ejphar.2024.177014
Biochim Biophys Acta Mol Basis Dis. 2024 Sep 20. pii: S0925-4439(24)00516-7. [Epub ahead of print]1871(1): 167522

ARL11 knockdown alleviates spinal cord injury by inhibiting neuroinflammation and M1 activation of microglia in mice.

Haocong Zhang, Liangbi Xiang, Hong Yuan, Hailong Yu.

  Spinal cord injury (SCI) is a severe central nervous system injury and microglia are major participants in neuroinflammation after injury. ADP-ribosylation factor-like GTPase 11 (ARL11) is a GTP-binding protein. Whether ARL11 is involved in the SCI progression is unknown. In the impactor-induced moderate SCI mouse model, ARL11 protein and mRNA expression were significantly increased in the injury site. LPS (100 ng/mL) and IFN-γ (20 ng/mL) were incubated with BV2 cells (immortalized mouse microglial cell line) to drive them into an M1-like phenotype. ARL11 up-regulation was also observed in activated microglia in SCI mice and LPS and IFN-γ treated BV2 cells. Basso Mouse Scale scores and inclined plate test revealed that ARL11 deletion promoted motor function recovery in SCI mice. Pathological examination showed ARL11 knockdown reduced spinal cord tissue damage, increased neuron numbers, and inhibited neuronal apoptosis in SCI mice. ARL11 knockdown notably inhibited IL-1β and IL-6 production in vivo and in vitro. Furthermore, ARL11 deletion significantly inhibited iNOS protein and mRNA expression in vivo and in vitro, and COX-2 expression in vivo. Mechanism studies revealed that ARL11 silencing decreased phosphorylated ERK1/2 protein expression. Additionally, ELF1 knockdown significantly inhibited ARL11 protein and mRNA expression in vitro. ELF1 acted as a transcription activator in regulating ARL11 expression by binding to the promoter. In conclusion, ARL11 knockdown protects neurons by inhibiting M1 microglia-induced neuroinflammation, thereby promoting motor functional recovery in SCI mice. This may occur in part under the regulation of ELF1. Our study provides a new molecular target for SCI treatment.

Keywords:  ARL11; ELF1; Microglia; Spinal cord injury

DOI:  https://doi.org/10.1016/j.bbadis.2024.167522
Trends Immunol. 2024 Sep 21. pii: S1471-4906(24)00190-X. [Epub ahead of print]

Novel human iPSC models of neuroinflammation in neurodegenerative disease and regenerative medicine.

Rose Ana Summers, Francesca Fagiani, David H Rowitch, Martina Absinta, Daniel S Reich.

  The importance of neuroinflammation in neurodegenerative diseases is becoming increasingly evident, and, in parallel, human induced pluripotent stem cell (hiPSC) models of physiology and pathology are emerging. Here, we review new advancements in the differentiation of hiPSCs into glial, neural, and blood-brain barrier (BBB) cell types, and the integration of these cells into complex organoids and chimeras. These advancements are relevant for modeling neuroinflammation in the context of prevalent neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). With awareness of current limitations, recent progress in the development and application of various hiPSC-derived models shows potential for aiding the identification of candidate therapeutic targets and immunotherapy approaches.

Keywords:  Alzheimer’s disease; Parkinson’s disease; cell differentiation; glia; hiPSC; microglia; multiple sclerosis; neuroinflammation; organoids

DOI:  https://doi.org/10.1016/j.it.2024.08.004
Front Physiol. 2024 ;15 1452959

Angiotensin II, blood-brain barrier permeability, and microglia interplay during the transition from pre-to hypertensive phase in spontaneously hypertensive rats.

Mariana Makuch-Martins, Camilla G Vieira-Morais, Sany M Perego, Adriana Ruggeri, Alexandre Ceroni, Lisete C Michelini.

  Background: Hypertension is characterized by upregulation of the renin-angiotensin system, increased blood-brain barrier (BBB) permeability, microglia activation within autonomic nuclei, and an intense sympathoexcitation. There is no information on the interplay of these events during the development of neurogenic hypertension. We sought to identify the interaction and time-course changes of Ang II availability, barrier dysfunction, microglia activation, and autonomic imbalance within autonomic areas during the development of neurogenic hypertension.Methods: Sequential changes of hemodynamic/autonomic parameters, BBB permeability, microglia structure/density (IBA-1), and angiotensin II (Ang II) immunofluorescence were evaluated within the paraventricular hypothalamic nucleus, nucleus of the solitary tract, and rostral ventrolateral medulla of Wistar and spontaneously hypertensive rats (SHRs) aged 4 weeks, 5 weeks, 6 weeks, 8 weeks, and 12 weeks. The somatosensory cortex and hypoglossal nucleus were also analyzed as non-autonomic control areas.
Results: Increased brain Ang II availability (4th-5th week) was the first observed change, followed by the incipient BBB leakage and increased microglia density (6th week). From the 5th-6th weeks on, BBB leakage, Ang II, and IBA-1 densities increased continuously, allowing a parallel increase in both Ang II-microglia colocalization and the transition of microglial cells from highly ramified in the basal surveillant condition (4th-5th week) to shorter process arbors, fewer endpoints, and enlarged soma in the disease-associate condition (6th week to the 12th week). Simultaneously with increased Ang II-microglia colocalization and microglia morphologic phenotypic changes, sympathetic activity and pressure variability increased, autonomic control deteriorated, and blood pressure increased. These responses were not specific for autonomic nuclei but also occurred at a lower magnitude in the somatosensory cortex and hypoglossal nucleus, indicating the predominance of hypertension-induced effects on autonomic areas. No changes were observed in age-matched controls where Ang II density did not change.
Conclusion: Brain Ang II density is the initial stimulus to drive coordinated changes in BBB permeability and microglial reactivity. Increased BBB dysfunction allows access of plasma Ang II and increases its local availability and the colocalization and activation of microglial cells. It is a potent stimulus to augments vasomotor sympathetic activity, autonomic imbalance, and pressure elevation during the establishment of hypertension.

Keywords:  angiotensin II; autonomic control; blood–brain barrier; microglia; spontaneously hypertensive rats

DOI:  https://doi.org/10.3389/fphys.2024.1452959
bioRxiv. 2024 Sep 11. pii: 2024.09.11.612570. [Epub ahead of print]

Zebrafish models of human-duplicated gene SRGAP2 reveal novel functions in microglia and visual system development.

José M Uribe-Salazar, Gulhan Kaya, KaeChandra Weyenberg, Brittany Radke, Keiko Hino, Daniela C Soto, Jia-Lin Shiu, Wenzhu Zhang, Cole Ingamells, Nicholas K Haghani, Emily Xu, Joseph Rosas, Sergi Simó, Joel Miesfeld, Tom Glaser, Scott C Baraban, Li-En Jao, Megan Y Dennis.

Recent expansion of duplicated genes unique in the Homo lineage likely contributed to brain evolution and other human-specific traits. One hallmark example is the expansion of the human SRGAP2 family, resulting in a human-specific paralog SRGAP2C . Introduction of SRGAP2C in mouse models is associated with altering cortical neuronal migration, axon guidance, synaptogenesis, and sensory-task performance. Truncated, human-specific SRGAP2C heterodimerizes with the full-length ancestral gene product SRGAP2A and antagonizes its functions. However, the significance of SRGAP2 duplication beyond neocortex development has not been elucidated due to the embryonic lethality of complete Srgap2 knockout in mice. Using zebrafish, we showed that srgap2 knockout results in viable offspring that phenocopy "humanized" SRGAP2C larvae. Specifically, human SRGAP2C protein interacts with zebrafish Srgap2, demonstrating similar Srgap2 functional antagonism observed in mice. Shared traits between knockout and humanized zebrafish larvae include altered morphometric features (i.e., reduced body length and inter-eye distance) and differential expression of synapse-, axogenesis-, vision-related genes. Through single-cell transcriptome analysis, we further observed a skewed balance of excitatory and inhibitory neurons that likely contributes to increased susceptibility to seizures displayed by Srgap2 mutant larvae, a phenotype resembling SRGAP2 loss-of-function in a child with early infantile epileptic encephalopathy. Single-cell data also pointed to strong microglia expression of srgap2 with mutants exhibiting altered membrane dynamics and likely delayed maturation of microglial cells. srgap2 -expressing microglia cells were also detected in the developing eye together with altered expression of genes related to axogenesis and synaptogenesis in mutant retinal cells. Consistent with the perturbed gene expression in the retina, we found that SRGAP2 mutant larvae exhibited increased sensitivity to broad and fine visual cues. Finally, comparing the transcriptomes of relevant cell types between human (+ SRGAP2C ) and non-human primates (- SRGAP2C ) revealed significant overlaps of gene alterations with mutant cells in our zebrafish models; this suggests that SRGAP2C plays similar roles altering microglia and the visual system in modern humans. Together, our functional characterization of zebrafish Srgap2 and human SRGAP2C in zebrafish uncovered novel gene functions and highlights the strength of cross-species analysis in understanding the development of human-specific features.

DOI: https://doi.org/10.1101/2024.09.11.612570
Behav Brain Res. 2024 Sep 23. pii: S0166-4328(24)00424-8. [Epub ahead of print] 115268

Remimazolam attenuates lipopolysaccharide-induced neuroinflammation and cognitive dysfunction.

Leguang Zhou, Mengzhe Xiao, Hongzhao Shi, Wenjie Liu, Lijuan Wang, Shangtao Zhou, Shenghua Chen, Yan Wang, Chengxi Liu.

  OBJECTIVE: Remimazolam, a novel benzodiazepine, is widely used as an anesthetic in endoscopic procedures; however, its effects on cognitive function remain unclear, limiting its broader application in general anaesthesia. Neuroinflammation is a well-established key factor in the etiology and progression of cognitive dysfunction, including conditions such as Alzheimer's disease, Parkinson's disease, postoperative delirium, and postoperative cognitive dysfunction. Preclinical studies have demonstrated that remimazolam exerts anti-inflammatory and neuroprotective effects, and clinical reports indicate a reduced incidence of postoperative delirium in patients treated with remimazolam. Nevertheless, whether remimazolam improves cognitive function through its anti-inflammatory properties remains uncertain. This study aimed to investigate the neuroprotective effects of remimazolam and its underlying mechanism in a lipopolysaccharide (LPS)-induced model of neuroinflammation, neuronal injury, and cognitive dysfunction METHODS: C57BL/6J male mice were administered LPS intraperitoneally to establish a model of neuroinflammation-induced cognitive impairment. A subset of mice received remimazolam via intraperitoneal injection 30minutes prior to LPS administration. Cognitive performance was evaluated using behavioural tests, including the Morris Water Maze (MWM), Novel Object Recognition (NOR) test, and Open Field Test (OFT). Hippocampal tissues were analyzed by haematoxylin-eosin (HE) staining to assess structural changes. Inflammatory markers, including Interleukin (IL)-6, IL-1β, and tumor necrosis factor-α, were quantified using enzyme-linked immunosorbent assay (ELISA) and real-time quantitative PCR. Immunofluorescence was used to detect translocator protein (TSPO) and markers of microglia activation (IBA-1, CD16/32, and CD206).RESULTS: (1) Remimazolam reversed LPS-induced cognitive deficits, as evidenced by shorter spatial exploration latency and increased platform crossings in the MWM, and an elevated recognition index in the NOR test. (2) Remimazolam improved hippocampal morphology, reducing LPS-induced neuronal damage. (3) Remimazolam significantly decreased levels of hippocampal inflammatory cytokines, inhibited microglial activation, promoted M2-type microglia polarization, and increased TSPO expression.
CONCLUSION: Remimazolam demonstrated neuroprotective and anti-neuroinflammatory effects in a mouse model of LPS-induced cognitive impairment. These effects are likely mediated through the regulation of TSPO, which inhibits microglial activation and promotes the polarization of microglia from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype.

Keywords:  Cognitive function; Microglia; Neuroinflammation; Remimazolam; Translocator protein

DOI:  https://doi.org/10.1016/j.bbr.2024.115268
Gene. 2024 Sep 21. pii: S0378-1119(24)00842-4. [Epub ahead of print]933 148961

Transcriptome analysis unveils PLSCR1 associated with microglial polarization in neuropathic pain.

Sheng Gao, Yuyan Sun, Shu Jia, Chunyang Meng.

  Neuropathic pain (NP) continues to be a significant problem that lacks effective treatment. Our study sought to explore a new promising gene target for the treatment of NP. Differential and enrichment analyses were performed on 24,197 genes and 12,088 genes from the NP microglial microarray and sequencing dataset. Candidate differentially expressed genes (DEGs), functions, and signaling pathways that are closely related to NP were identified by analyzing the bioinformatic results. For in vivo experiments, mice were divided into the sham and NP groups. The expressions of DEGs were validated to screen out the NP hub genes. For in vitro experiments, the hub genes in resting M0-BV2 and polarized M1-BV2 microglia were examined by immunofluorescence, flow cytometry, and qRT-PCR. DEGs in the NP microarray and sequencing data shared five candidate genes, CD244, MEGF9, PCGF2, PLSCR1, and NECAB2. The results of the in vivo experiment showed that the NP model group exhibited higher expression of PLSCR1 and MEGF9 compared to the sham group. The enrichment results of the DEGs revealed the biological processes of "response to lipopolysaccharide". PLSCR1 was highly expressed in the lipopolysaccharide-induced M1-BV2 microglia. PLSCR1 is a potential gene associated with microglial polarization in NP. These findings provide a new view on understanding the pathogenesis mechanism of NP.

Keywords:  Microglia; Neuropathic pain; PLSCR1; Polarization

DOI:  https://doi.org/10.1016/j.gene.2024.148961
Neural Regen Res. 2024 Sep 24.

High-dose dexamethasone regulates microglial polarization via the GR/JAK1/STAT3 signaling pathway after traumatic brain injury.

Mengshi Yang, Miao Bai, Yuan Zhuang, Shenghua Lu, Qianqian Ge, Hao Li, Yu Deng, Hongbin Wu, Xiaojian Xu, Fei Niu, Xinlong Dong, Bin Zhang, Baiyun Liu.

Although microglial polarization and neuroinflammation are crucial cellular responses after traumatic brain injury, the fundamental regulatory and functional mechanisms remain insufficiently understood. As potent anti-inflammatory agents, the use of glucocorticoids in traumatic brain injury is still controversial, and their regulatory effects on microglial polarization are not yet known. In the present study, we sought to determine whether exacerbation of traumatic brain injury caused by high-dose dexamethasone is related to its regulatory effects on microglial polarization and its mechanisms of action. In vitro cultured BV2 cells and primary microglia and a controlled cortical impact mouse model were used to investigate the effects of dexamethasone on microglial polarization. Lipopolysaccharide, dexamethasone, RU486 (a glucocorticoid receptor antagonist), and ruxolitinib (a Janus kinase 1 antagonist) were administered. RNA-sequencing data obtained from a C57BL/6 mouse model of traumatic brain injury were used to identify potential targets of dexamethasone. The Morris water maze, quantitative reverse transcription-polymerase chain reaction, western blotting, immunofluorescence and confocal microscopy analysis, and TUNEL, Nissl, and Golgi staining were performed to investigate our hypothesis. High-throughput sequencing results showed that arginase 1, a marker of M2 microglia, was significantly downregulated in the dexamethasone group compared with the traumatic brain injury group at 3 days post-traumatic brain injury. Thus dexamethasone inhibited M1 and M2 microglia, with a more pronounced inhibitory effect on M2 microglia in vitro and in vivo. Glucocorticoid receptor plays an indispensable role in microglial polarization after dexamethasone treatment following traumatic brain injury. Additionally, glucocorticoid receptor activation increased the number of apoptotic cells and neuronal death, and also decreased the density of dendritic spines. A possible downstream receptor signaling mechanism is the GR/JAK1/STAT3 pathway. Overactivation of glucocorticoid receptor by high-dose dexamethasone reduced the expression of M2 microglia, which plays an anti-inflammatory role. In contrast, inhibiting the activation of glucocorticoid receptor reduced the number of apoptotic glia and neurons and decreased the loss of dendritic spines after traumatic brain injury. Dexamethasone may exert its neurotoxic effects by inhibiting M2 microglia through the GR/JAK1/STAT3 signaling pathway.

DOI: https://doi.org/10.4103/NRR.NRR-D-23-01772
Phytomedicine. 2024 Sep 19. pii: S0944-7113(24)00728-1. [Epub ahead of print]135 156071

Gelsevirine ameliorates sepsis-associated encephalopathy by inhibiting the STING signalling-mediated pyroptosis pathway in microglia.

Qing-Quan Zeng, Jing Wang, Rong-Cai Yue, Fa-Sheng Wang, Ying Xu, Yan-Ping Su, Qiao-Ling Zhang, You-Wei Zheng, Gui-Fei Zhang, Bo Li, Chang-Xi Yu, Gui-Lin Jin.

  BACKGROUND: Sepsis-associated encephalopathy (SAE) is among the most prevalent and deadly complications associated with sepsis, but satisfactory treatments and therapeutic agents are lacking. Gelsevirine, an active ingredient derived from Gelsemium elegans Benth., has shown promising effects in animal models of anxiety, ischaemic stroke and osteoarthritis. However, its protective effect against SAE and its mechanism of action are still unknown.PURPOSE: To elucidate the efficacy of gelsevirine against SAE and the mechanism of its protective effect through the STING signalling-mediated pyroptosis pathway.
METHODS: We constructed a mouse model of caecum ligation and puncture (CLP)-induced sepsis and explored the protective effects of gelsevirine in mice with SAE by assessing survival rates and behavioural alterations. To further explore its mechanism of action, we investigated the modulatory effects of gelsevirine on the levels of inflammatory factors, microglial activation and pyroptosis by Western blotting, immunohistochemistry staining and PCR. STING knockout mice were used to verify the protective effect of gelsevirine against SAE through the STING pathway.
RESULTS: Gelsevirine increased the survival rate of mice with SAE. The Morris water maze and open field tests revealed that gelsevirine significantly alleviated cognitive dysfunction and increased exploratory behaviour in mice with SAE. Gelsevirine inhibited the activation of microglia and decreased inflammatory factor levels in the hippocampus of mice with SAE. In mice with SAE and in vitro BV2 microglia, gelsevirine reduced levels of inflammatory factors and inhibited STING protein phosphorylation and microglial pyroptosis. However, after STING knockout, the inhibitory effect of gelsevirine on microglial pyroptosis was significantly weakened, and gelsevirine-mediated protective effects were abolished.
CONCLUSIONS: Gelsevirine increased the survival rate, ameliorated cognitive impairment, inhibited glial cell activation and reduced inflammation in the hippocampi of mice with SAE; the mechanism may be related to the inhibition of STING signalling pathway-mediated pyroptosis in microglia.

Keywords:  Gelsevirine; Microglia; Pyroptosis; Sepsis-associated encephalopathy; Sting

DOI:  https://doi.org/10.1016/j.phymed.2024.156071
bioRxiv. 2024 Sep 10. pii: 2024.09.05.611566. [Epub ahead of print]

Uncovering Plaque-Glia Niches in Human Alzheimer's Disease Brains Using Spatial Transcriptomics.

Denis R Avey, Bernard Ng, Ricardo A Vialle, Nicola A Kearns, Katia de Paiva Lopes, Artemis Iatrou, Sashini De Tissera, Himanshu Vyas, Devin M Saunders, Daniel J Flood, Jishu Xu, Shinya Tasaki, Chris Gaiteri, David A Bennett, Yanling Wang.

Amyloid-beta (Aβ) plaques and surrounding glial activation are prominent histopathological hallmarks of Alzheimer's Disease (AD). However, it is unclear how Aβ plaques interact with surrounding glial cells in the human brain. Here, we applied spatial transcriptomics (ST) and immunohistochemistry (IHC) for Aβ, GFAP, and IBA1 to acquire data from 258,987 ST spots within 78 postmortem brain sections of 21 individuals. By coupling ST and adjacent-section IHC, we showed that low Aβ spots exhibit transcriptomic profiles indicative of greater neuronal loss than high Aβ spots, and high-glia spots present transcriptomic changes indicative of more significant inflammation and neurodegeneration. Furthermore, we observed that this ST glial response bears signatures of reported mouse gene modules of plaque-induced genes (PIG), oligodendrocyte (OLIG) response, disease-associated microglia (DAM), and disease-associated astrocytes (DAA), as well as different microglia (MG) states identified in human AD brains, indicating that multiple glial cell states arise around plaques and contribute to local immune response. We then validated the observed effects of Aβ on cell apoptosis and plaque-surrounding glia on inflammation and synaptic loss using IHC. In addition, transcriptomic changes of iPSC-derived microglia-like cells upon short-interval Aβ treatment mimic the ST glial response and mirror the reported activated MG states. Our results demonstrate an exacerbation of synaptic and neuronal loss in low-Aβ or high-glia areas, indicating that microglia response to Aβ-oligomers likely initiates glial activation in plaque-glia niches. Our study lays the groundwork for future pathology genomics studies, opening the door for investigating pathological heterogeneity and causal effects in neurodegenerative diseases.

DOI: https://doi.org/10.1101/2024.09.05.611566
bioRxiv. 2024 Sep 14. pii: 2024.09.09.612126. [Epub ahead of print]

Epigenetic adaptation drives monocyte differentiation into microglia-like cells upon engraftment into the retina.

Jie Liu, Fengyang Lei, Bin Yan, Naiwen Cui, Jyoti Sharma, Victor Correa, Lara Roach, Savvas Nicolaou, Kristen Pitts, James Chodosh, Daniel E Maidana, Demetrios Vavvas, Milica A Margeta, Huidan Zhang, David Weitz, Raul Mostoslavsky, Eleftherios I Paschalis.

The identification of specific markers for microglia has been a long-standing challenge. Recently, markers such as P2ry12, TMEM119, and Fcrls have been proposed as microglia-specific and widely used to explore microglial functions within various central nervous system (CNS) contexts. The specificity of these markers was based on the assumption that circulating monocytes retain their distinct signatures even after infiltrating the CNS. However, recent findings reveal that infiltrating monocytes can adopt microglia-like characteristics while maintaining a pro-inflammatory profile upon permanent engraftment in the CNS.In this study, we utilize bone marrow chimeras, single-cell RNA sequencing, ATAC-seq, flow cytometry, and immunohistochemistry to demonstrate that engrafted monocytes acquire expression of established microglia markers-P2ry12, TMEM119, Fcrls-and the pan-myeloid marker Iba1, which has been commonly mischaracterized as microglia-specific. These changes are accompanied by alterations in chromatin accessibility and shifts in chromatin binding motifs that are indicative of microglial identity. Moreover, we show that engrafted monocytes dynamically regulate the expression of CX3CR1, CCR2, Ly6C, and transcription factors PU.1, CTCF, RUNX, AP-1, CEBP, and IRF2, all of which are crucial for shaping microglial identity. This study is the first to illustrate that engrafted monocytes in the retina undergo both epigenetic and transcriptional changes, enabling them to express microglia-like signatures. These findings highlight the need for future research to account for these changes when assessing the roles of monocytes and microglia in CNS pathology.Significance Statement: Monocytes can express putative microglia markers P2ry12, TMEM119, and Fcrls upon engraftment into the retina. Given their involvement in neuroinflammation, it is crucial to consider this overlap when utilizing these markers for experimental analysis.

DOI: https://doi.org/10.1101/2024.09.09.612126
Neuron. 2024 Sep 25. pii: S0896-6273(24)00572-5. [Epub ahead of print]112(18): 2991-2993

Protective lifelines: Tunneling nanotubes connect neurons and microglia.

Jonas J Neher, Mikael Simons.

Tunneling nanotubes (TNTs) facilitate the exchange of intracellular cargo between cells. In this issue of Neuron, Scheiblich et al.1 reveal that TNTs selectively mediate the bidirectional transfer of cytoplasmic protein aggregates from neurons to microglia and mitochondria from microglia to neurons, thereby preserving neuronal health.

DOI: https://doi.org/10.1016/j.neuron.2024.07.027
J Vis Exp. 2024 Sep 06.

Isolation of Hypothalamic Microglia from Freshly Perfused Adult Mouse Brain by Magnetic-Activated Cell Sorting.

Evangelia Kyriakidou, Giulia Cutugno, Camille Allard, Agnes Nadjar.

Microglia, as the resident macrophages of the brain, are essential for maintaining brain homeostasis. They shape neuronal circuits during development, survey their environment for debris or dead cells, as well as respond to infection and injury in the brain, among many other functions. However, their important role in neurodevelopment and synaptic plasticity and pathophysiology has not been fully defined, highlighting the need for further investigation. To gain a more comprehensive understanding of the role of microglia in these processes, we need to isolate microglia and characterize them genetically, metabolically, and functionally. However, the isolation of microglia from adult mice, especially from small brain structures, is challenging as they represent a small percentage of the total brain cells, and the yield of isolated microglia is often too low. Here, the magnetic isolation of microglia using CD11b+ microbeads allows us to sort microglial cells from the hypothalamus of a freshly perfused adult mouse brain. The current method allows us to achieve relatively high purity and yield in a short period while maintaining cell viability.

DOI: https://doi.org/10.3791/66769