Synapse Engulfment Research Articles

Physical Exercise Decreases Complement-Mediated Synaptic Loss and Protects Against Cognitive Impairment by Inhibiting Microglial Tmem9-ATP6V0D1 in Alzheimer's Disease.

Physical exercise is known to slow synaptic neurodegeneration and cognitive aging in Alzheimer's disease (AD). The benefits of physical exercise are related to reduced amyloid beta (Aβ) deposition and increased synaptic plasticity. Yet little is known about the mechanisms that mediate these effects. Here, we show that physical exercise down-regulated the microglial Tmem9 protein, inhibited C1q activation, and decreased C1q-dependent microglial synapse engulfment, eventually ameliorating cognitive impairment in 5xFAD mice. Furthermore, using oAβ cultured-BV2 invitro, we show that downregulation of microglial Tmem9 was sufficient to restrain complement activity and decrease microglia-mediated synaptic loss, whereas overexpression of microglial Tmem9 tended to promote complement activation and induced synaptic loss, abolishing exercise-associated protection. Finally, we show that microglial Tmem9 contributed to complement activation by regulating ATP6V0D1, a vesicular (H+) ATP-dependent proton pump (V-ATPase) subunit that regulates V-ATPase assembly. Together, our results demonstrate that exercise is a potential treatment for AD patients. In an AD mouse model, it decreased the levels of microglial Tmem9 to inhibit the activation of complement, alleviated complement-dependent synaptic loss, and eventually ameliorated emotional and cognitive disorders.

Microglial activation states and their implications for Alzheimer's Disease.

Alzheimer's Disease (AD) is a chronic neurodegenerative disorder characterized by the accumulation of toxic amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFTs) of tau protein in the brain. Microglia, key immune cells of the central nervous system, play an important role in AD development and progression, primarily through their responses to Aβ and NFTs. Initially, microglia can clear Aβ, but in AD, chronic activation overwhelms protective mechanisms, leading to sustained neuroinflammation that enhances plaque toxicity, setting off a damaging cycle that affects neurons, astrocytes, cerebral vasculature, and other microglia. Current AD treatments have been largely ineffective, though emerging immunotherapies focusing on plaque removal show promise, but often overlook the role of neuroinflammation. Activated microglia display a complex range of phenotypes that can be broadly broken into pro- or anti-inflammatory states, although this dichotomy does not describe the significant overlap between states. Aβ can strongly induce inflammatory activity, triggering the production of reactive oxygen species, inflammatory cytokines (e.g., TNF-α, IL-1β, IL-6), synapse engulfment, blood-brain barrier compromise, and impaired Aβ clearance. These processes contribute to neural tissue loss, manifesting as cognitive decline such as impaired executive function and memory. Conversely, anti-inflammatory activation exerts neuroprotective effects by suppressing inflammatory pathways and releasing neurotrophic factors that aid neuron repair and protection. Induction of anti-inflammatory states may offer a dual therapeutic approach to address both neuroinflammation and plaque accumulation in AD. This approach suggests potential strategies to modulate microglial phenotypes, aiming to restore neuroprotective functions and mitigate disease progression by simultaneously targeting inflammation and plaque pathology.

Prolactin deficiency drives diabetes-associated cognitive dysfunction by inducing microglia-mediated synaptic loss

BackgroundDiabetes-associated cognitive dysfunction, characterized by hippocampal synaptic loss as an early pathological feature, seriously threatens patients’ quality of life. Synapses are dynamic structures, and hormones play important roles in modulating the formation and elimination of synapses. The pituitary, the master gland of the body, releases several hormones with multiple roles in hippocampal synaptic regulation. In this study, we aimed to explore the relationship between pituitary hormones and cognitive decline in diabetes.MethodsA total of 744 patients with type 2 diabetes (T2DM) (445 men and 299 postmenopausal women) who underwent serum pituitary hormone level assessments, comprehensive cognitive evaluations and MRI scans were enrolled. Dynamic diet interventions were applied in both chow diet-fed mice and high-fat diet (HFD)-fed diabetic mice. The cognitive performance and hippocampal pathology of prolactin (PRL)-knockout mice, neuronal prolactin receptor (PRLR)-specific knockout mice and microglial PRLR-specific knockout mice were assessed. Microglial PRLR-specific knockout mice were fed an HFD to model diabetes. Diabetic mice received an intracerebroventricular infusion of recombinant PRL protein or vehicle.ResultsThis clinical study revealed that decreased PRL levels were associated with cognitive impairment and hippocampal damage in T2DM patients. In diabetic mice, PRL levels diminished before hippocampal synaptic loss and cognitive decline occurred. PRL loss could directly cause cognitive dysfunction and decreased hippocampal synaptic density. Knockout of PRLR in microglia, rather than neurons, induced hippocampal synaptic loss and cognitive impairment. Furthermore, blockade of PRL/PRLR signaling in microglia exacerbated abnormal microglial phagocytosis of synapses, further aggravating hippocampal synaptic loss and cognitive impairment in diabetic mice. Moreover, PRL infusion reduced microglia-mediated synaptic loss, thereby alleviating cognitive impairment in diabetic mice.ConclusionPRL is associated with cognitive dysfunction and hippocampal damage in T2DM patients. In diabetes, a decrease in PRL level drives hippocampal synaptic loss and cognitive impairment by increasing microglia-mediated synapse engulfment. Restoration of PRL levels ameliorates cognitive dysfunction and hippocampal synaptic loss in diabetic mice.

High-confidence and high-throughput quantification of synapse engulfment by oligodendrocyte precursor cells.

Oligodendrocyte precursor cells (OPCs) sculpt neural circuits through the phagocytic engulfment of synapses during development and adulthood. However, existing techniques for analyzing synapse engulfment by OPCs have limited accuracy. Here we describe the quantification of synapse engulfment by OPCs via a two-pronged cell biological approach that combines high-confidence and high-throughput methodologies. Firstly, an adeno-associated virus encoding a pH-sensitive, fluorescently tagged synaptic marker is expressed in neurons in vivo to differentially label presynaptic inputs, depending upon whether they are outside of or within acidic phagolysosomal compartments. When paired with immunostaining for OPC markers in lightly fixed tissue, this approach quantifies the engulfment of synapses by around 30-50 OPCs in each experiment. The second method uses OPCs isolated from dissociated brain tissue that are then fixed, incubated with fluorescent antibodies against presynaptic proteins, and analyzed by flow cytometry, enabling the quantification of presynaptic material within tens of thousands of OPCs in <1 week. The integration of both methods extends the current imaging-based assays, originally designed to quantify synaptic phagocytosis by other brain cells such as microglia and astrocytes, by enabling the quantification of synaptic engulfment by OPCs at individual and populational levels. With minor modifications, these approaches can be adapted to study synaptic phagocytosis by numerous glial cell types in the brain. The protocol is suitable for users with expertise in both confocal microscopy and flow cytometry. The imaging-based and flow cytometry-based protocols require 5 weeks and 2 d to complete, respectively.

Blockade of STING activation alleviates microglial dysfunction and a broad spectrum of Alzheimer’s disease pathologies

Abnormal glial activation promotes neurodegeneration in Alzheimer’s disease (AD), the most common cause of dementia. Stimulation of the cGAS-STING pathway induces microglial dysfunction and sterile inflammation, which exacerbates AD. We showed that inhibiting STING activation can control microglia and ameliorate a wide spectrum of AD symptoms. The cGAS-STING pathway is required for the detection of ectopic DNA and the subsequent immune response. Amyloid-β (Aβ) and tau induce mitochondrial stress, which causes DNA to be released into the cytoplasm of microglia. cGAS and STING are highly expressed in Aβ plaque-associated microglia, and neuronal STING is upregulated in the brains of AD model animals. The presence of the APOE ε4 allele, an AD risk factor, also upregulated both proteins. STING activation was necessary for microglial NLRP3 activation, proinflammatory responses, and type-I-interferon responses. Pharmacological STING inhibition reduced a wide range of AD pathogenic features in AppNL-G-F/hTau double-knock-in mice. An unanticipated transcriptome shift in microglia reduced gliosis and cerebral inflammation. Significant reductions in the Aβ load, tau phosphorylation, and microglial synapse engulfment prevented memory loss. To summarize, our study describes the pathogenic mechanism of STING activation as well as its potential as a therapeutic target in AD.

The Effects of Sevoflurane and Aβ Interaction on CA1 Dendritic Spine Dynamics and MEGF10-Related Astrocytic Synapse Engulfment.

General anesthetics may accelerate the neuropathological changes related to Alzheimer's disease (AD), of which amyloid beta (Aβ)-induced toxicity is one of the main causes. However, the interaction of general anesthetics with different Aβ-isoforms remains unclear. In this study, we investigated the effects of sevoflurane (0.4 and 1.2 maximal alveolar concentration (MAC)) on four Aβ species-induced changes on dendritic spine density (DSD) in hippocampal brain slices of Thy1-eGFP mice and multiple epidermal growth factor-like domains 10 (MEGF10)-related astrocyte-mediated synaptic engulfment in hippocampal brain slices of C57BL/6 mice. We found that both sevoflurane and Aβ downregulated CA1-dendritic spines. Moreover, compared with either sevoflurane or Aβ alone, pre-treatment with Aβ isoforms followed by sevoflurane application in general further enhanced spine loss. This enhancement was related to MEGF10-related astrocyte-dependent synaptic engulfment, only in AβpE3 + 1.2 MAC sevoflurane and 3NTyrAβ + 1.2 MAC sevoflurane condition. In addition, removal of sevoflurane alleviated spine loss in Aβ + sevoflurane. In summary, these results suggest that both synapses and astrocytes are sensitive targets for sevoflurane; in the presence of 3NTyrAβ, 1.2 MAC sevoflurane alleviated astrocyte-mediated synaptic engulfment and exerted a lasting effect on dendritic spine remodeling.

Emerging evidence of context-dependent synapse elimination by phagocytes in the CNS.

Precise synapse elimination is essential for the establishment of a fully developed neural circuit during brain development and higher function in adult brain. Beyond immune and nutrition support, recent groundbreaking studies have revealed that phagocytic microglia and astrocytes can actively and selectively eliminate synapses in normal and diseased brains, thereby mediating synapse loss and maintaining circuit homeostasis. Multiple lines of evidence indicate that the mechanisms of synapse elimination by phagocytic glia are not universal but rather depend on specific contexts and detailed neuron-glia interactions. The mechanism of synapse elimination by phagocytic glia is dependent on neuron-intrinsic factors and many innate immune and local apoptosis-related molecules. During development, microglial synapse engulfment in the visual thalamus is primarily influenced by the classic complement pathway, whereas in the barrel cortex, the fractalkine pathway is dominant. In Alzheimer's disease, microglia employ complement-dependent mechanisms for synapse engulfment in tauopathy and early β-amyloid pathology, but microglia are not involved in synapse loss at late β-amyloid stages. Phagocytic microglia also engulf synapses in a complement-dependent way in schizophrenia, anxiety, and stress. In addition, phagocytic astrocytes engulf synapses in a MEGF10-dependent way during visual development, memory, and stroke. Furthermore, the mechanism of a phenomenon that phagocytes selectively eliminate excitatory and inhibitory synapses is also emphasized in this review. We hypothesize that elucidating context-dependent synapse elimination by phagocytic microglia and astrocytes may reveal the molecular basis of synapse loss in neural disorders and provide a rationale for developing novel candidate therapies that target synapse loss and circuit homeostasis.

STING inhibition suppresses microglia-mediated synapses engulfment and alleviates motor functional deficits after stroke

Ischemic stroke is the leading cause of adult disability. Ischemia leads to progressive neuronal death and synapse loss. The engulfment of stressed synapses by microglia further contributes to the disruption of the surviving neuronal network and related brain function. Unfortunately, there is currently no effective target for suppressing the microglia-mediated synapse engulfment. Stimulator of interferon genes (STING) is an important participant in innate immune response. In the brain, microglia are the primary cell type that mediate immune response after brain insult. The intimate relationship between STING and microglia-mediated neuroinflammation has been gradually established. However, whether STING affects other functions of microglia remains elusive. In this study, we found that STING regulated microglial phagocytosis of synapses after photothrombotic stroke. The treatment of STING inhibitor H151 significantly improved the behavioral performance of injured mice in grid-walking test, cylinder test, and adhesive removal test after stroke. Moreover, the puncta number of engulfed SYP or PSD95 in microglia was reduced after consecutive H151 administration. Further analysis showed that the mRNA levels of several complement components and phagocytotic receptors were decreased after STING inhibition. Transcriptional factor STAT1 is known for regulating most of the decreased molecules. After STING inhibition, the nucleus translocation of phosphorylated STAT1 was also suppressed in microglia. Our data uncovered the novel regulatory effects of STING in microglial phagocytosis after stroke, and further emphasized STING as a potential drug-able target for post-stroke functional recovery.

Microglial sex differences in innate high anxiety and modulatory effects of minocycline

Microglia modulate synaptic refinement in the central nervous system (CNS). We have previously shown that a mouse model with innate high anxiety-related behavior (HAB) displays higher CD68+ microglia density in the key regions of anxiety circuits compared to mice with normal anxiety-related behavior (NAB) in males, and that minocycline treatment attenuated the enhanced anxiety of HAB male. Given that a higher prevalence of anxiety is widely reported in females compared to males, little is known concerning sex differences at the cellular level. Herein, we address this by analyzing microglia heterogeneity and function in the HAB and NAB brains of both sexes. Single-cell RNA sequencing revealed ten distinct microglia clusters varied by their frequency and gene expression profile. We report striking sex differences, especially in the major microglia clusters of HABs, indicating a higher expression of genes associated with phagocytosis and synaptic engulfment in the female compared to the male. On a functional level, we show that female HAB microglia engulfed a greater amount of hippocampal vGLUT1+ excitatory synapses compared to the male. We moreover show that female HAB microglia engulfed more synaptosomes compared to the male HAB in vitro. Due to previously reported effects of minocycline on microglia, we finally administered oral minocycline to HABs of both sexes and showed a significant reduction in the engulfment of synapses by female HAB microglia. In parallel to our microglia-specific findings, we further showed an anxiolytic effect of minocycline on female HABs, which is complementary to our previous findings in the male HABs. Our study, therefore, identifies the altered function of synaptic engulfment by microglia as a potential avenue to target and resolve microglia heterogeneity in mice with innate high anxiety.

Protective Mechanism of Polysaccharide ORP-1 Isolated from Oudemansiella raphanipes against Age-Related Cognitive Decline through the Microbiota-Gut-Brain Axis.

Age-related cognitive decline is primarily attributed to the progressive weakening of synaptic function and loss of synapses, while age-related gut microbial dysbiosis is known to impair synaptic plasticity and cognitive behavior by metabolic alterations. To improve the health of the elderly, the protective mechanisms of Oudemansiella raphanipes polysaccharide (ORP-1) against age-related cognitive decline are investigated. The results demonstrate that ORP-1 and its gut microbiota-derived metabolites SCFAs restore a healthy gut microbial population to handle age-related gut microbiota dysbiosis mainly by increasing the abundance of beneficial bacteria Dubosiella, Clostridiales, and Prevotellaceae and reducing the abundance of harmful bacteria Desulfovibrio, strengthen intestinal barrier integrity by abolishing age-related alterations of tight junction (TJ) and mucin 2 (MUC2) proteins expression, diminish age-dependent increase in circulating inflammatory factors, ameliorate cognitive decline by reversing memory- and synaptic plasticity-related proteins levels, and restrain hyperactivation of microglia-mediated synapse engulfment and neuroinflammation. These findings expand the understanding of prebiotic-microbiota-host interactions.

Astrocytes Excessively Engulf Synapses in a Mouse Model of Alzheimer's Disease.

Synapse loss is one of the most critical features in Alzheimer's disease (AD) and correlates with cognitive decline. Astrocytes mediate synapse elimination through multiple EGF-like domains 10 (MEGF10) pathways in the developing and adult brain to build the precise neural connectivity. However, whether and how astrocytes mediate synapse loss in AD remains unknown. We here find that the phagocytic receptor MEGF10 of astrocytes is significantly increased in vivo and in vitro, which results in excessive engulfment of synapses by astrocytes in APP/PS1 mice. We also observe that the astrocytic lysosomal-associated membrane protein 1 (LAMP1) is significantly elevated, colocalized with the engulfed synaptic puncta in APP/PS1 mice, and astrocytic lysosomes contain more engulfed synaptic puncta in APP/PS1 mice relative to wild type mice. Together, our data provide evidence that astrocytes excessively engulf synapses in APP/PS1 mice, which is mediated by increased MEGF10 and activated lysosomes. The approach targeting synapse engulfment pathway in astrocytes would be a potent therapy for AD.

A circRNA ceRNA network involved in cognitive dysfunction after chronic cerebral hypoperfusion.

Chronic Cerebral Hypoperfusion (CCH) is associated with cognitive dysfunction, the underlying mechanisms of which remain elusive, hindering the development of effective therapeutic approaches. In this study, we employed an established CCH animal model to delve into neuropathological alterations like oxidative stress, inflammation, neurotransmitter synthesis deficits, and other morphological alterations. Our findings revealed that while the number of neurons remained unchanged, there was a significant reduction in neuronal fibers post-CCH, as evidenced by microtubule-associated protein 2 (MAP2) staining. Moreover, myelin basic protein (MBP) staining showed exacerbated demyelination of neuronal fibers. Furthermore, we observed increased neuroinflammation, proliferation, and activation of astrocytes and microglia, as well as synaptic loss and microglial-mediated synapse engulfment post-CCH. Utilizing RNA sequencing, differential expression analysis displayed alterations in both mRNAs and circRNAs. Following gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, both showed significant enrichment in immunological and inflammation-related terms and pathways. Importantly, the differentially expressed circular RNAs (DE circRNAs) exhibited a notable coexpression pattern with DE mRNAs. The ternary circRNA-miRNA-mRNA competing endogenous RNAs (ceRNA) network was constructed, and subsequent analysis reiterated the significance of neuroimmunological and neuroinflammatory dysfunction in CCH-induced neuropathological changes and cognitive dysfunction. This study underscores the potential role of circRNAs in these processes, suggesting them as promising therapeutic targets to mitigate the detrimental effects of CCH.

Low-dose PLX5622 treatment prevents neuroinflammatory and neurocognitive sequelae after sepsis

BackgroundSepsis-associated encephalopathy (SAE) is characterized by symptoms of delirium including hallucinations, impaired concentration, agitation, or coma and is associated with poor outcome in the early phase of sepsis. In addition, sepsis survivors often suffer from persisting memory deficits and impaired executive functions. Recent studies provide evidence that microglia are involved in the pathophysiology of SAE.MethodsHere, we investigated whether pharmacological depletion of microglia using PLX5622 (1200 ppm or 300 ppm) in the acute phase of sepsis is able to prevent long-term neurocognitive decline in a male mouse model of polymicrobial sepsis or lipopolysaccharide-induced sterile neuroinflammation. Therefore, we performed the novel object recognition test at different time points after sepsis to address hippocampus-dependent learning. To further assess synapse engulfment in microglia, colocalization analysis was performed using high-resolution 3D Airyscan imaging of Iba1 and Homer1. We also investigated the effect of PLX5622 on acute astrocyte and chronic microglia proliferation in the hippocampus after sepsis induction using immunofluorescence staining.ResultsHigh-dose application of the colony stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 (1200 ppm) seven days prior to sepsis induction lead to 70–80% microglia reduction but resulted in fatal outcome of bacterial sepsis or LPS induced inflammation. This is likely caused by severely compromised host immune response upon PLX5622-induced depletion of peripheral monocytes and macrophages. We therefore tested partial microglia depletion using a low-dose of PLX5622 (300 ppm) for seven days prior to sepsis which resulted in an increased survival in comparison to littermates subjected to high-dose CSF1R inhibiton and to a stable microglia reduction of ~ 40%. This partial microglia depletion in the acute stage of sepsis largely prevented the engulfment and microglia-induced stripping of postsynaptic terminals. In addition, PLX5622 low-dose microglia depletion attenuated acute astrogliosis as well as long-term microgliosis and prevented long-term neurocognitive decline after experimental sepsis.ConclusionsWe conclude that partial microglia depletion before the induction of sepsis may be sufficient to attenuate long-term neurocognitive dysfunction. Application of PLX5622 (300 ppm) acts by reducing microglia-induced synaptic attachement/engulfment and preventing chronic microgliosis.

Stauntonia chinensis injection relieves neuropathic pain by increasing the expression of PSD-95 and reducing the proliferation of phagocytic microglia.

Neuroinflammation induced by engulfment of synapses by phagocytic microglia plays a crucial role in neuropathic pain. Stauntonia chinensis is extracted from Stauntonia chinensis DC, which has been used as a traditional Chinese medicine to control trigeminal neuralgia or sciatica. However, the specific anti-neuralgia mechanism of Stauntonia chinensis is unknown. In this study, the analgesic effect of Stauntonia chinensis injection (SCI) in mice with neuropathic pain and the possible mechanisms are explored. We find that a local injection of 0.1 mL Stauntonia chinensis for 14 days can considerably relieve mechanical hyperalgesia and thermal hyperalgesia in mice with sciatic chronic constriction injury (CCI). Immunofluorescence staining shows that SCI reduces neuroinflammation in the spinal cord of CCI mice. RNA sequencing reveals that the expression of postsynaptic density protein 95 (PSD-95), a postsynaptic scaffold protein, is downregulated in the spinal cord of CCI mice, but upregulated after SCI administration. Immunofluorescence experiments also demonstrate that SCI administration reverses microglia proliferation and PSD-95 downregulation in CCI mice. These data suggest that SCI relieves neuropathic pain by increasing the expression of PSD-95 and reducing the proliferation of phagocytic microglia.

α-Synuclein propagation leads to synaptic abnormalities in the cortex through microglial synapse phagocytosis

The major neuropathologic feature of Parkinson’s disease is the presence of widespread intracellular inclusions of α-synuclein known as Lewy bodies. Evidence suggests that these misfolded protein inclusions spread through the brain with disease progression. Changes in synaptic function precede neurodegeneration, and this extracellular α-synuclein can affect synaptic transmission. However, whether and how the spreading of α-synuclein aggregates modulates synaptic function before neuronal loss remains unknown. In the present study, we investigated the effect of intrastriatal injection of α-synuclein preformed fibrils (PFFs) on synaptic activity in the somatosensory cortex using a combination of whole-cell patch-clamp electrophysiology, histology, and Golgi-Cox staining. Intrastriatal PFF injection was followed by formation of phosphorylated α-synuclein inclusions in layer 5 of the somatosensory cortex, leading to a decrease in synapse density, dendritic spines, and spontaneous excitatory post-synaptic currents, without apparent neuronal loss. Additionally, three-dimensional reconstruction of microglia using confocal imaging showed an increase in the engulfment of synapses. Collectively, our data indicate that propagation of α-synuclein through neural networks causes abnormalities in synaptic structure and dynamics prior to neuronal loss.

IFN-γ deficiency in the rostral ventrolateral medulla contributes to stress-induced hypertension by impairing microglial synaptic engulfment.

Dysfunctional neurons and microglia in the rostral ventrolateral medulla (RVLM) have been implicated in the pathogenesis of stress-induced hypertension (SIH). Functional perturbation of microglial synaptic engulfment can induce aberrant brain circuit activity. IFN-γ is a pleiotropic cytokine that plays a role in regulating neuronal activity. However, existing research on the exploration of the effects of microglia on synapses in the RVLM is lacking, particularly on the function of IFN-γ in microglial synaptic engulfment involved in SIH. A SIH rat model was established by electric foot shocks combined with noise stimulation. The underlying mechanism of IFN-γ on synaptic density and microglial synaptic engulfment was investigated through in-vivo and in-vitro experiments involving gain of function, immunofluorescence, quantitative real-time PCR, western blot, and morphometric analysis. Furthermore, the function of IFN-γ in neuronal activity, renal sympathetic nerve activity (RSNA), and blood pressure (BP) regulation was determined through in-vivo and in-vitro experiments involving Ca2+ imaging, immunofluorescence, platinum-iridium electrode recording, ELISA, the femoral artery cannulation test, and the tail-cuff method. The BP, heart rate, RSNA, plasma norepinephrine, and the number of c-Fos-positive neurons in SIH rats increased compared with those in control rats. Pre and postsynaptic densities in the RVLM also increased in SIH rats. IFN-γ and CCL2 expression levels were significantly reduced in the RVLM of the SIH group, whose microglia also exhibited an impaired capacity for synapse engulfment. IFN-γ elevation increased CCL2 expression and microglial synaptic engulfment and decreased synaptic density in vivo and in vitro. However, CCL2 inhibition reversed these effects. Moreover, the reduction of neuronal excitability, RSNA, plasma norepinephrine, and BP by IFN-γ was abrogated through CCL2 expression. IFN-γ deficiency in the RVLM impaired the microglial engulfment of synapses by inhibiting CCL2 expression and increasing synaptic density and neuronal excitability, thereby contributing to SIH progression. Targeting IFN-γ may be considered a potential strategy to combat SIH.Graphical Abstract, http://links.lww.com/HJH/C203.

Interferon-alpha plays an important role in glial-mediated symptoms of neuropsychiatric systemic lupus erythematosus.

Abstract Systemic lupus erythematosus (SLE) is an autoimmune disease that leads to clinical pathology across organs, including the central nervous system (CNS). In up to 80% of patients with SLE, CNS manifestations can range from anxiety and fatigue to overt psychosis. While studies have demonstrated a hallmark increase in circulating interferon alpha (IFNα) in the peripheral blood and cerebrospinal fluid, the cellular mechanisms leading to neuropsychiatric lupus (NPSLE) remain unclear (Crow et. al., 2014). Using a mouse model of lupus which expresses an elevated IFNα signature and exhibits behaviors of NPSLE, we found a spatial pattern of interferon-stimulated genes (ISGs) in the brain parenchyma utilizing the multiplexed spatial transcriptomics platform MERFISH (Moffitt et. al., 2016). Guided by unbiased single nucleus sequencing highlighting astrocytes and oligodendrocytes as major glial cells enriched in ISG expression, we hypothesized that this spatial distribution implicates IFNα-driven glial activity against neuron function, thus disrupting regions of the CNS that manifests as NPSLE. We also investigated the role of IFNα on microglia activity and behavior changes using a cell-specific Cremouse model. Further functional assays reveal increased synapse engulfment by microglia upon IFNα activation. Despite waning ISGs levels in the periphery, levels in the brain persist along with behavior severity, pointing to a CNS source of IFNα. This body of work demonstrates how IFNα released locally by glial cells can mediate NPSLE development via disruption of neuron function. Deeper understanding of targetable pathways in IFNα signaling will expand the therapeutic potential of type 1 interferon-driven neuropsychiatric diseases.

The neuronal pentraxin Nptx2 regulates complement activity and restrains microglia-mediated synapse loss in neurodegeneration.

Complement overactivation mediates microglial synapse elimination in neurological diseases such as Alzheimer's disease (AD) and frontotemporal dementia (FTD), but how complement activity is regulated in the brain remains largely unknown. We identified that the secreted neuronal pentraxin Nptx2 binds complement C1q and thereby regulates its activity in the brain. Nptx2-deficient mice show increased complement activity, C1q-dependent microglial synapse engulfment, and loss of excitatory synapses. In a neuroinflammation culture model and in aged TauP301S mice, adeno-associated virus (AAV)-mediated neuronal overexpression of Nptx2 was sufficient to restrain complement activity and ameliorate microglia-mediated synapse loss. Analysis of human cerebrospinal fluid (CSF) samples from a genetic FTD cohort revealed reduced concentrations of Nptx2 and Nptx2-C1q protein complexes in symptomatic patients, which correlated with elevated C1q and activated C3. Together, these results show that Nptx2 regulates complement activity and microglial synapse elimination in the brain and that diminished Nptx2 concentrations might exacerbate complement-mediated neurodegeneration in patients with FTD.

Endothelial TFEB signaling-mediated autophagic disturbance initiates microglial activation and cognitive dysfunction

ABSTRACT Cognitive impairment caused by systemic chemotherapy is a critical question that perplexes the effective implementation of clinical treatment, but related molecular events are poorly understood. Herein, we show that bortezomib exposure leads to microglia activation and cognitive impairment, this occurs along with decreased nuclear translocation of TFEB (transcription factor EB), which is linked to macroautophagy/autophagy disorder, STAT3 (signal transducer and activator of transcription 3) phosphorylation and IL23A (interleukin 23 subunit alpha) expression. Pharmacological enhancement of TFEB nuclear translocation by digoxin restores lysosomal function and reduces STAT3-dependent endothelial IL23A secretion. As a consequence, we found that brain endothelial-specific ablation of Il23a ameliorated both microglia activation and cognitive dysfunction. Thus, the endothelial TFEB-STAT3-IL23A axis in the brain represents a critical cellular event for initiating bortezomib-mediated aberrant microglial activation and synapse engulfment. Our results suggest the reversal of TFEB nuclear translocation may provide a novel therapeutic approach to prevent symptoms of cognitive dysfunction during clinical use of bortezomib. Abbreviations: AAV: adeno-associated virus; BBB: blood-brain barrier; BTZ: bortezomib; DG: digoxin; DGs: dentate gyrus; DLG4/PSD95: discs large MAGUK scaffold protein 4; HBMECs: human brain microvascular endothelial cells; HP: hippocampus; IL23A: interleukin 23 subunit alpha; MBVECs: mouse brain vascular endothelial cells; mPFC: medial prefrontal cortex; NORT: novel object recognition test; OLT: object location test; PLX5622: 6-fluoro-N-([5-fluoro-2-methoxypyridin-3-yl]methyl)-5-(5-methyl-1H-pyrrolo[2,3-b]pyridin-3- yl)methyl; PPP3/calcineurin: protein phosphatase 3; SBEs: STAT3 binding elements; shRNA: small hairpin RNA; SLC17A7/VGLUT1: solute carrier family 17 member 7; SLC32A1/VGAT: solute carrier family 32 member 1; STAT3: signal transducer and activator of transcription 3, TFEB: transcription factor EB; Ub: ubiquitin.

Microglia and astrocytes mediate synapse engulfment in a MER tyrosine kinase-dependent manner after traumatic brain injury.

Recent studies have shown that microglia/macrophages and astrocytes can mediate synaptic phagocytosis through the MER proto-oncokinase in developmental or stroke models, but it is unclear whether the same mechanism is also active in traumatic brain injury. In this study, we established a mouse model of traumatic brain injury and found that both microglia/macrophages and astrocytes phagocytosed synapses and expression of the MER proto-oncokinase increased 14 days after injury. Specific knockout of MER in microglia/macrophages or astrocytes markedly reduced injury volume and greatly improved neurobehavioral function. In addition, in both microglia/macrophages-specific and astrocytes-specific MER knock-out mice, the number of microglia/macrophage and astrocyte phagocytosing synapses was markedly decreased, and the total number of dendritic spines was increased. Our study suggested that MER proto-oncokinase expression in microglia/macrophages and astrocytes may play an important role in synaptic phagocytosis, and inhibiting this process could be a new strategy for treating traumatic brain injury.