Citations

Microglia actively survey the brain and dynamically interact with neurons to maintain brain homeostasis. Microglial Gi protein–coupled receptors (Gi-GPCRs) play a critical role in microglia-neuron communications. However, the impact of temporally activating microglial Gi signaling on microglial dynamics and neuronal activity in the homeostatic brain remains largely unknown. In this study, we used Gi-based designer receptors exclusively activated by designer drugs (Gi-DREADD) to selectively and temporally modulate microglial Gi signaling pathway. By integrating this chemogenetic approach with in vivo two-photon imaging, we observed that exogenous activation of microglial Gi signaling transiently inhibited microglial process dynamics, reduced neuronal activity, and impaired neuronal synchronization. These altered neuronal functions were associated with a decrease in interactions between microglia and neuron somata. Together, this study demonstrates that acute, exogenous activation of microglial Gi signaling regulates neuronal circuit function, offering a potential pharmacological target for the neuromodulation through microglia.

AbstractBackgroundAccumulation of the amyloid‐β (Aβ) peptide into amyloid plaque is one of the key pathological markers of Alzheimer’s disease (AD). Apolipoprotein E (APOE) is known to modify AD risk and has been reported to influence Aβ accumulation in the brain in an isoform‐dependent manner. ApoE can be produced by various cell types in the brain, with astrocytes being the main producer. Increasing studies show that altering apoE levels can influence Aβ plaque pathology. However, it is not fully understood how apoE produced by specific cell types, such as astrocytes, contributes to amyloid pathology.MethodWe utilized mouse models expressing APOE isoforms in astrocytes and crossed them with 5xFAD mouse models of amyloidosis. We analyzed the changes to amyloid plaques and assessed the impact on cellular responses to amyloid plaques in condition of astrocytic APOE expression.ResultSpecific expression of APOE3 in astrocytes resulted in compact amyloid plaques and a large increase in plaque deposition, while the total plaque burden was reduced. Astrocytic APOE2 expression led to similar changes to amyloid plaques, but the fold change is lower comparing to that in astrocytic APOE3 models. Intriguingly, the total microglial response increased dramatically in condition of astrocytic APOE3 expression but not in condition of astrocytic APOE2 expression. Further, the ratio of plaque associated Lgals3/Iba1 is higher in condition of astrocytic APOE3 expression, indicating increased microglial activation. Additionally, astrocyte GFAP levels only increased in astrocytic APOE3 models, but not in astrocytic APOE2 models. Finally, APOE isoform effect on dystrophic neurites amount was also observed.ConclusionTogether, our study reveals an important role of astrocytic APOE on the deposition and accumulation of Aβ plaques as well as on Aβ‐associated downstream effects.

Abstract Background Nicotinamide adenosine dinucleotide phosphate oxidases (NOX) play important roles in mediating stress-induced depression. Three NOX isotypes are expressed mainly in the brain: NOX2, NOX3 and NOX4. In this study, the expression and cellular sources of these NOX isoforms was investigated in the context of stress-induced depression. Methods Chronic restraint stress (CRS)-induced depressive-like behaviour and cognitive deficits were evaluated by tail suspension tests, forced swimming tests and the Morris water maze test. Hippocampal NOX expression was determined by immunofluorescence staining and western blotting. The hippocampal levels of the brain-derived neurotrophic factor (BDNF) mRNA were determined via quantitative real-time –polymerase chain reaction. Glucocorticoid levels in the hippocampus were measured using ELISA kits. Results In the mouse CRS model, a significant increase in NOX2 expression was observed in the hippocampus, whereas no significant changes in NOX3 and NOX4 expression were detected. Next, NOX2 expression was primarily localised to neurons (NeuN+) but not microglia (Iba-1+) or astrocytes (GFAP+). Treatment with gp91ds-tat, a specific NOX2 inhibitor, effectively mitigated the behavioural deficits induced by CRS. The decreased expression of the BDNF mRNA in the hippocampus of CRS mice was restored upon gp91ds-tat treatment. A positive correlation was identified between neuronal NOX2 expression and serum glucocorticoid levels. Conclusions Our study indicated that neuronal NOX2 may be a critical mediator of depression-like behaviours and spatial cognitive deficits in mice subjected to CRS. Blockade of NOX2 signalling may be a promising therapeutic strategy for depression.

Abstract Mounting evidence indicates the involvement of peripheral immunity in the regulation of brain function, influencing aspects such as neuronal development, emotion, and cognitive abilities. Previous studies from our laboratory have revealed that neonatal hepatitis B vaccination can downregulate hippocampal neurogenesis, synaptic plasticity and spatial learning memory. In the current post-epidemic era characterized by universal vaccination, understanding the impact of acquired immunity on neuronal function and neuropsychiatric disorders, along with exploring potential underlying mechanisms, becomes imperative. We employed hepatitis B vaccine-induced CD3 positive T cells in immunodeficient mice to investigate the key mechanisms through which T cell subsets modulate hippocampal neurogenesis and anxiety-like behaviours. Our data revealed that mice receiving hepatitis B vaccine-induced T cells exhibited heightened anxiety and decreased hippocampal cell proliferation compared to those receiving phosphate-buffered saline-T cells or wild-type mice. Importantly, these changes were predominantly mediated by infiltrated CD8+ T cells into the brain, rather than CD4+ T cells. Transcriptome profiling of CD8+ T cells unveiled that C-X-C motif chemokine receptor 6 positive (CXCR6+) CD8+ T cells were recruited into the brain through microglial and astrocyte-derived C-X-C motif chemokine ligand 16 (CXCL16). This recruitment process impaired neurogenesis and induced anxiety-like behaviour via tumour necrosis factor-α-dependent mechanisms. Our findings highlight the role of glial cell derived CXCL16 in mediating the recruitment of CXCR6+CD8+ T cell subsets into the brain. This mechanism represents a potential avenue for modulating hippocampal neurogenesis and emotion-related behaviours after hepatitis B vaccination.

The effectiveness of coronavirus disease 2019 (COVID-19) vaccines against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) strain rapidly wanes over time. Growing evidence from epidemiological studies suggests that influenza vaccination is associated with a reduction in the risk of SARS-CoV-2 infection and COVID-19 severity. However, the underlying mechanisms remain elusive. Here, we investigate the cross-reactive immune responses of influenza vaccination to SARS-CoV-2 spike protein peptides based on in vitro study. Our data indicate enhanced activation-induced-marker (AIM) expression on CD4+ T cells in influenza-vaccination (IV)-treated peripheral blood mononuclear cells (PBMCs) upon stimulation with spike-protein-peptide pools. The fractions of other immune cell subtypes, including CD8+ T cells, monocytes, NK cells, and antigen-presenting cells, were not changed between IV-treated and control PBMCs following ex vivo spike-protein-peptide stimulation. However, the classical antiviral (IFN-γ) and anti-inflammatory (IL-1RA) cytokine responses to spike-protein-peptide stimulation were still enhanced in PBMCs from both IV-immunized adult and aged mice. Decreased expression of proinflammatory IL-1β, IL-12p40, and TNF-α is associated with inhibited levels of histone acetylation in PBMCs from IV-treated mice. Remarkably, prior immunity to SARS-CoV-2 does not result in modification of histone acetylation or hemagglutinin-protein-induced cytokine responses. This response is antibody-independent but can be mediated by manipulating the histone acetylation of PBMCs. These data experimentally support that influenza vaccination could induce modification of histone acetylation in immune cells and reveal the existence of potential cross-reactive immunity to SARS-CoV-2 antigens, which may provide insights for the adjuvant of influenza vaccine to limit COVID-19-related inflammatory responses.

CLEC4G, a glycan-binding receptor, has previously been demonstrated to inhibit Aβ generation, yet its brain localization and functions in Alzheimer’s disease (AD) are not clear. We explored the localization, function, and regulatory network of CLEC4G via experiments and analysis of RNA-seq databases. CLEC4G transcripts and proteins were identified in brain tissues, with the highest expression observed in neurons. Notably, AD was associated with reduced levels of CLEC4G transcripts. Bioinformatic analyses revealed interactions between CLEC4G and relevant genes such as BACE1, NPC1, PILRA, TYROBP, MGAT1, and MGAT3, all displaying a negative correlation trend. We further identified the upstream transcriptional regulators NR2F6 and XRCC4 for CLEC4G and confirmed a decrease in CLEC4G expression in APP/PS1 transgenic mice. This study highlights the role of CLEC4G in protecting against AD progression and the significance of CLEC4G for AD research and management.

Abstract Background Myeloid cells comprise up to 50% of the total tumor mass in glioblastoma (GBM) and have been implicated in promoting tumor progression and immunosuppression. Modulating the response of myeloid cells to the tumor has emerged as a promising new approach for cancer treatment. In this regard, we focus on the Triggering Receptor Expressed on Myeloid Cells 2 (TREM2), which has recently emerged as a novel immune modulator in peripheral tumors. Methods We studied the TREM2 expression profile in various patient tumor samples and conducted single-cell transcriptomic analysis in both GBM patients and the GL261 mouse glioma model. We utilized multiple mouse glioma models and employed state-of-the-art techniques such as invivo 2-photon imaging, spectrum flow cytometry, and in vitro co-culture assays to study TREM2 function in myeloid cell-mediated phagocytosis of tumor cells, antigen presentation, and response of CD4+ T cells within the tumor hemispheres. Results Our research revealed significantly elevated levels of TREM2 expression in brain tumors compared to other types of tumors in patients. TREM2 was predominantly localized in tumor-associated myeloid cells and was highly expressed in nearly all microglia, as well as various subtypes of macrophages. Surprisingly, in preclinical glioma models, TREM2 deficiency did not confer a beneficial effect; instead, it accelerated glioma progression. Through detailed investigations, we determined that TREM2 deficiency impaired the ability of tumor-myeloid cells to phagocytose tumor cells and led to reduced expression of MHCII. This deficiency further significantly decreased the presence of CD4+ T cells within the tumor hemispheres. Conclusions Our study unveiled a previously unrecognized protective role of tumor-myeloid TREM2. Specifically, we found that TREM2 enhances the phagocytosis of tumor cells and promotes an immune response by facilitating MHCII-associated CD4+ T-cell responses against gliomas.