Type I Interferon Receptor Signaling in Astrocytes Regulates Hippocampal Synaptic Plasticity and Cognitive Function of the Healthy CNS

SARS-CoV-2-Induced Type I Interferon Signaling Dysregulation in Olfactory Networks Implications for Alzheimer's Disease

Type I interferon signaling (IFN-I) perturbations are major drivers of COVID-19. Dysregulated IFN-I in the brain, however, has been linked to both reduced cognitive resilience and neurodegenerative diseases such as Alzheimer's. Previous works from our group have proposed a model where peripheral induction of IFN-I may be relayed to the CNS, even in the absence of fulminant infection. The aim of our study was to identify significantly enriched IFN-I signatures and genes along the transolfactory route, utilizing published datasets of the nasal mucosa and olfactory bulb amygdala transcriptomes of COVID-19 patients. We furthermore sought to identify these IFN-I signature gene networks associated with Alzheimer's disease pathology and risk. Gene expression data involving the nasal epithelium, olfactory bulb, and amygdala of COVID-19 patients and transcriptomic data from Alzheimer's disease patients were scrutinized for enriched Type I interferon pathways. Gene set enrichment analyses and gene-Venn approaches were used to determine genes in IFN-I enriched signatures. The Agora web resource was used to identify genes in IFN-I signatures associated with Alzheimer's disease risk based on its aggregated multi-omic data. For all analyses, false discovery rates (FDR) <0.05 were considered statistically significant. Pathways associated with type I interferon signaling were found in all samples tested. Each type I interferon signature was enriched by IFITM and OAS family genes. A 14-gene signature was associated with COVID-19 CNS and the response to Alzheimer's disease pathology, whereas nine genes were associated with increased risk for Alzheimer's disease based on Agora. Our study provides further support to a type I interferon signaling dysregulation along the extended olfactory network as reconstructed herein, ranging from the nasal epithelium and extending to the amygdala. We furthermore identify the 14 genes implicated in this dysregulated pathway with Alzheimer's disease pathology, among which HLA-C, HLA-B, HLA-A, PSMB8, IFITM3, HLA-E, IFITM1, OAS2, and MX1 as genes with associated conferring increased risk for the latter. Further research into its druggability by IFNb therapeutics may be warranted.

In sickness and in health-Type I interferon and the brain

Type I interferons (IFN-I) represent a group of pleiotropic cytokines renowned for their antiviral activity and immune regulatory functions. A multitude of studies have unveiled a critical role of IFN-I in the brain, influencing various neurological processes and diseases. In this mini-review, I highlight recent findings on IFN-I's effects on brain aging, Alzheimer's disease (AD) progression, and central nervous system (CNS) homeostasis. The multifaceted influence of IFN-I on brain health and disease sheds light on the complex interplay between immune responses and neurological processes. Of particular interest is the cGAS-STING-IFN-I axis, which extensively participates in brain aging and various forms of neurodegeneration. Understanding the intricate role of IFN-I and its associated pathways in the CNS not only advances our comprehension of brain health and disease but also presents opportunities for developing interventions to modify the process of neurodegeneration and prevent age-related cognitive decline.

The Sixth Sense: Self-nucleic acid sensing in the brain

Our innate immune system uses pattern recognition receptors (PRRs) as a first line of defense to detect microbial ligands and initiate an immune response. Viral nucleic acids are key ligands for the activation of many PRRs and the induction of downstream inflammatory and antiviral effects. Initially it was thought that endogenous (self) nucleic acids rarely activated these PRRs, however emerging evidence indicates that endogenous nucleic acids are able to activate host PRRs in homeostasis and disease. In fact, many regulatory mechanisms are in place to finely control and regulate sensing of self-nucleic acids by PRRs. Sensing of self-nucleic acids is particularly important in the brain, as perturbations to nucleic acid sensing commonly leads to neuropathology. This review will highlight the role of nucleic acid sensors in the brain, both in disease and homeostasis. We also indicate the source of endogenous stimulatory nucleic acids where known and summarize future directions for the study of this growing field.

Type I interferon signaling, cognition and neurodegeneration following COVID-19: update on a mechanistic pathogenetic model with implications for Alzheimer's disease

COVID-19's effects on the human brain reveal a multifactorial impact on cognition and the potential to inflict lasting neuronal damage. Type I interferon signaling, a pathway that represents our defense against pathogens, is primarily affected by COVID-19. Type I interferon signaling, however, is known to mediate cognitive dysfunction upon its dysregulation following synaptopathy, microgliosis and neuronal damage. In previous studies, we proposed a model of outside-in dysregulation of tonic IFN-I signaling in the brain following a COVID-19. This disruption would be mediated by the crosstalk between central and peripheral immunity, and could potentially establish feed-forward IFN-I dysregulation leading to neuroinflammation and potentially, neurodegeneration. We proposed that for the CNS, the second-order mediators would be intrinsic disease-associated molecular patterns (DAMPs) such as proteopathic seeds, without the requirement of neuroinvasion to sustain inflammation. Selective vulnerability of neurogenesis sites to IFN-I dysregulation would then lead to clinical manifestations such as anosmia and cognitive impairment. Since the inception of our model at the beginning of the pandemic, a growing body of studies has provided further evidence for the effects of SARS-CoV-2 infection on the human CNS and cognition. Several preclinical and clinical studies have displayed IFN-I dysregulation and tauopathy in gene expression and neuropathological data in new cases, correspondingly. Furthermore, neurodegeneration identified with a predilection for the extended olfactory network furthermore supports the neuroanatomical concept of our model, and its independence from fulminant neuroinvasion and encephalitis as a cause of CNS damage. In this perspective, we summarize the data on IFN-I as a plausible mechanism of cognitive impairment in this setting, and its potential contribution to Alzheimer's disease and its interplay with COVID-19.

The Exon Junction Complex Factor RBM8A in Glial Fibrillary Acid Protein-Expressing Astrocytes Modulates Locomotion Behaviors

The role of RNA Binding Motif Protein 8a (RBM8A), an exon junction complex (EJC) component, in neurodevelopmental disorders has been increasingly studied for its crucial role in regulating multiple levels of gene expression. It regulates mRNA splicing, translation, and mRNA degradation and influences embryonic development. RBM8A protein is expressed in both neurons and astrocytes, but little is known about RBM8A's specific role in glial fibrillary acid protein (GFAP)-positive astrocytes. To address the role of RBM8A in astrocytes, we generated a conditional heterozygous knockout (KO) mouse line of Rbm8a in astrocytes using a GFAP-cre line. We confirmed a decreased expression of RBM8A in astrocytes of heterozygous conditional KO mice via RT-PCR and Sanger sequencing, as well as qRT-PCR, immunohistochemistry, and Western blot. Interestingly, these mice exhibit significantly increased movement and mobility, alongside sex-specific altered anxiety in the open field test (OFT) and elevated plus maze (OPM) tests. These tests, along with the rotarod test, suggest that these mice have normal motor coordination but hyperactive phenotypes. In addition, the haploinsufficiency of Rbm8a in astrocytes leads to a sex-specific change in astrocyte density in the dentate gyrus. This study further reveals the contribution of Rbm8a deletion to CNS pathology, generating more insights via the glial lens of an Rbm8a model of neurodevelopmental disorder.

Type I Interferon Signalling and Ischemic Stroke: Mechanisms and Therapeutic Potentials

Type I interferon (IFN-I) signalling is intricately involved in the pathogenesis of multiple infectious diseases, autoimmune diseases, and neurological diseases. Acute ischemic stroke provokes overactivation of IFN-I signalling within the injured brain, particularly in microglia. Following cerebral ischemia, damage-associated molecular patterns (DAMPs) released from injured neural cells elicit marked proinflammatory episodes within minutes. Among these, self-nucleic acids, including nuclear DNA and mitochondrial DNA (mtDNA), have been recognized as a critical alarm signal to fan the flames of neuroinflammation, predominantly via inducing IFN-I signalling activation in microglia. The concept of interferon-responsive microglia (IRM), marked by upregulation of a plethora of IFN-stimulated genes, has been emergingly elucidated in ischemic mouse brains, particularly in aged ones. Among the pattern recognition receptors responsible for IFN-I induction, cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) plays integral roles in potentiating microglia-driven neuroinflammation and secondary brain injury after cerebral ischemia. Here, we aim to provide an up-to-date review on the multifaceted roles of IFN-I signalling, the detailed molecular and cellular mechanisms leading to and resulting from aberrant IFN-I signalling activation after cerebral ischemia, and the therapeutic potentials. A thorough exploration of these above points will inform our quest for IFN-based therapies as effective immunomodulatory therapeutics to complement the limited repertoire of thrombolytic agents, thereby facilitating the translation from bench to bedside.

Simvastatin Differentially Modulates Glial Functions in Cultured Cortical and Hypothalamic Astrocytes Derived from Interferon α/β Receptor Knockout mice

Astrocytes have key regulatory roles in central nervous system (CNS), integrating metabolic, inflammatory and synaptic responses. In this regard, type I interferon (IFN) receptor signaling in astrocytes can regulate synaptic plasticity. Simvastatin is a cholesterol-lowering drug that has shown anti-inflammatory properties, but its effects on astrocytes, a main source of cholesterol for neurons, remain to be elucidated. Herein, we investigated the effects of simvastatin in inflammatory and functional parameters of primary cortical and hypothalamic astrocyte cultures obtained from IFNα/β receptor knockout (IFNα/βR-/-) mice. Overall, simvastatin decreased extracellular levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), which were related to a downregulation in gene expression in hypothalamic, but not in cortical astrocytes. Moreover, there was an increase in anti-inflammatory interleukin-10 (IL-10) in both structures. Effects of simvastatin in inflammatory signaling also involved a downregulation of cyclooxygenase 2 (COX-2) gene expression as well as an upregulation of nuclear factor κB subunit p65 (NFκB p65). The expression of cytoprotective genes sirtuin 1 (SIRT1) and nuclear factor erythroid derived 2 like 2 (Nrf2) was also increased by simvastatin. In addition, simvastatin increased glutamine synthetase (GS) activity and glutathione (GSH) levels only in cortical astrocytes. Our findings provide evidence that astrocytes from different regions are important cellular targets of simvastatin in the CNS, even in the absence of IFNα/βR, which was showed by the modulation of cytokine production and release, as well as the expression of cytoprotective genes and functional parameters.

Proteomic profiling of interferon-responsive reactive astrocytes in rodent and human

Astrocytes are a heterogeneous population of central nervous system glial cells that respond to pathological insults and injury by undergoing a transformation called "reactivity." Reactive astrocytes exhibit distinct and context-dependent cellular, molecular, and functional state changes that can either support or disturb tissue homeostasis. We recently identified a reactive astrocyte sub-state defined by interferon-responsive genes like Igtp, Ifit3, Mx1, and others, called interferon-responsive reactive astrocytes (IRRAs). To further this transcriptomic definition of IRRAs, we wanted to define the proteomic changes that occur in this reactive sub-state. We induced IRRAs in immunopanned rodent astrocytes and human iPSC-differentiated astrocytes using TNF, IL1α, C1Q, and IFNβ and characterized their proteomic profile (both cellular and secreted) using unbiased quantitative proteomics. We identified 2335 unique cellular proteins, including IFIT2/3, IFITM3, OASL1/2, MX1/2/3, and STAT1. We also report that rodent and human IRRAs secrete PAI1, a serine protease inhibitor which may influence reactive states and functions of nearby cells. Finally, we evaluated how IRRAs are distinct from neurotoxic reactive astrocytes (NRAs). While NRAs are described by expression of the complement protein C3, it was not upregulated in IRRAs. Instead, we found ~90 proteins unique to IRRAs not identified in NRAs, including OAS1A, IFIT3, and MX1. Interferon signaling in astrocytes is critical for the antiviral immune response and for regulating synaptic plasticity and glutamate transport mechanisms. How IRRAs contribute to these functions is unknown. This study provides the basis for future experiments to define the functional roles of IRRAs in the context of neurodegenerative disorders.

It's a TRIM-endous view from the top: the varied roles of TRIpartite Motif proteins in brain development and disease

The tripartite motif (TRIM) protein family members have been implicated in a multitude of physiologies and pathologies in different tissues. With diverse functions in cellular processes including regulation of signaling pathways, protein degradation, and transcriptional control, the impact of TRIM dysregulation can be multifaceted and complex. Here, we focus on the cellular and molecular roles of TRIMs identified in the brain in the context of a selection of pathologies including cancer and neurodegeneration. By examining each disease in parallel with described roles in brain development, we aim to highlight fundamental common mechanisms employed by TRIM proteins and identify opportunities for therapeutic intervention.

4E-BP1-dependent translation in nociceptors controls mechanical hypersensitivity via TRIM32/type I interferon signaling

Activation of the mechanistic target of rapamycin complex 1 (mTORC1) contributes to the development of chronic pain. However, the specific mechanisms by which mTORC1 causes hypersensitivity remain elusive. The eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) is a key mTORC1 downstream effector that represses translation initiation. Here, we show that nociceptor-specific deletion of 4E-BP1, mimicking activation of mTORC1-dependent translation, is sufficient to cause mechanical hypersensitivity. Using translating ribosome affinity purification in nociceptors lacking 4E-BP1, we identified a pronounced translational up-regulation of tripartite motif-containing protein 32 (TRIM32), an E3 ubiquitin ligase that promotes interferon signaling. Down-regulation of TRIM32 in nociceptors or blocking type I interferon signaling reversed the mechanical hypersensitivity in mice lacking 4E-BP1. Furthermore, nociceptor-specific ablation of TRIM32 alleviated mechanical hypersensitivity caused by tissue inflammation. These results show that mTORC1 in nociceptors promotes hypersensitivity via 4E-BP1-dependent up-regulation of TRIM32/interferon signaling and identify TRIM32 as a therapeutic target in inflammatory pain.

Long 3'UTRs predispose neurons to inflammation by promoting immunostimulatory double-stranded RNA formation

Loss of RNA homeostasis underlies numerous neurodegenerative and neuroinflammatory diseases. However, the molecular mechanisms that trigger neuroinflammation are poorly understood. Viral double-stranded RNA (dsRNA) triggers innate immune responses when sensed by host pattern recognition receptors (PRRs) present in all cell types. Here, we report that human neurons intrinsically carry exceptionally high levels of immunostimulatory dsRNAs and identify long 3'UTRs as giving rise to neuronal dsRNA structures. We found that the neuron-enriched ELAVL family of genes (ELAVL2, ELAVL3, and ELAVL4) can increase (i) 3'UTR length, (ii) dsRNA load, and (iii) activation of dsRNA-sensing PRRs such as MDA5, PKR, and TLR3. In wild-type neurons, neuronal dsRNAs signaled through PRRs to induce tonic production of the antiviral type I interferon. Depleting ELAVL2 in WT neurons led to global shortening of 3'UTR length, reduced immunostimulatory dsRNA levels, and rendered WT neurons susceptible to herpes simplex virus and Zika virus infection. Neurons deficient in ADAR1, a dsRNA-editing enzyme mutated in the neuroinflammatory disorder Aicardi-Goutières syndrome, exhibited intolerably high levels of dsRNA that triggered PRR-mediated toxic inflammation and neuronal death. Depleting ELAVL2 in ADAR1 knockout neurons led to prolonged neuron survival by reducing immunostimulatory dsRNA levels. In summary, neurons are specialized cells where PRRs constantly sense "self" dsRNAs to preemptively induce protective antiviral immunity, but maintaining RNA homeostasis is paramount to prevent pathological neuroinflammation.

Theiler's Murine Encephalomyelitis Virus Replicates in Primary Neuron Cultures and Impairs Spine Density Formation

In this study, we examined infection with the highly neurovirulent GDVII, the less neurovirulent DA strains, and with a mutant DA, which lacks the L* protein (L*-1) involved in viral persistence and demyelinating disease, to analyze the direct effects of Theiler's murine encephalomyelitis virus (TMEV) replication using primary cultures of mouse brain hippocampal neurons. All viruses replicate in cultured neurons, with GDVII having the highest titers and L*-1 the lowest. Accordingly, all were positive for viral antigen staining 3 days postinfection (dpi), and DA and L*-1 were also positive after 12 dpi. NeuN + immunostaining showed an early and almost complete absence of positive cells in cultures infected with GDVII, an approximately 50% reduction in cultures infected with DA, and fewer changes in L*-1 strains at 3 dpi. Accordingly, staining with chloromethyltetramethylrosamine orange (Mitotracker OrangeTM) as a parameter for cell viability showed similar results. Moreover, at 1 dpi, the strain DA induced higher transcript levels of neuroprotective genes such as IFN-Iβ, IRF7, and IRF8. At 3 dpi, strains GDVII and DA, but not the L*-1 mutant, showed lower PKR expression. In addition, confocal analysis showed that L*-1-infected neurons exhibited a decrease in spine density. Treatment with poly (I:C), which is structurally related to dsRNA and is known to trigger IFN type I synthesis, reduced spine density even more. These results confirmed the use of mouse hippocampal neuron cultures as a model to study neuronal responses after TMEV infection, particularly in the formation of spine density.

Selective neuroimmune modulation by type I interferon drives neuropathology and neurologic dysfunction following traumatic brain injury

Accumulating evidence suggests that type I interferon (IFN-I) signaling is a key contributor to immune cell-mediated neuropathology in neurodegenerative diseases. Recently, we demonstrated a robust upregulation of type I interferon-stimulated genes in microglia and astrocytes following experimental traumatic brain injury (TBI). The specific molecular and cellular mechanisms by which IFN-I signaling impacts the neuroimmune response and neuropathology following TBI remains unknown. Using the lateral fluid percussion injury model (FPI) in adult male mice, we demonstrated that IFN α/β receptor (IFNAR) deficiency resulted in selective and sustained blockade of type I interferon-stimulated genes following TBI as well as decreased microgliosis and monocyte infiltration. Molecular alteration of reactive microglia also occurred with diminished expression of genes needed for MHC class I antigen processing and presentation following TBI. This was associated with decreased accumulation of cytotoxic T cells in the brain. The IFNAR-dependent modulation of the neuroimmune response was accompanied by protection from secondary neuronal death, white matter disruption, and neurobehavioral dysfunction. These data support further efforts to leverage the IFN-I pathway for novel, targeted therapy of TBI.

Selective neuroimmune modulation by type I interferon drives neuropathology and neurologic dysfunction following traumatic brain injury

Accumulating evidence suggests that type I interferon (IFN-I) signaling is a key contributor to immune cell-mediated neuropathology in neurodegenerative diseases. Recently, we demonstrated a robust upregulation of type I interferon-stimulated genes in microglia and astrocytes following experimental traumatic brain injury (TBI). The specific molecular and cellular mechanisms by which IFN-I signaling impacts the neuroimmune response and neuropathology following TBI remains unknown. Using the lateral fluid percussion injury model (FPI) in adult male mice, we demonstrated that IFN α/β receptor (IFNAR) deficiency resulted in selective and sustained blockade of type I interferon-stimulated genes following TBI as well as decreased microgliosis and monocyte infiltration. Phenotypic alteration of reactive microglia also occurred with diminished expression of molecules needed for MHC class I antigen processing and presentation following TBI. This was associated with decreased accumulation of cytotoxic T cells in the brain. The IFNAR-dependent modulation of the neuroimmune response was accompanied by protection from secondary neuronal death, white matter disruption, and neurobehavioral dysfunction. These data support further efforts to leverage the IFN-I pathway for novel, targeted therapy of TBI.

Harnessing type I interferon-mediated immunity to target malignant brain tumors

Type I interferons have long been appreciated as a cytokine family that regulates antiviral immunity. Recently, their role in eliciting antitumor immune responses has gained increasing attention. Within the immunosuppressive tumor microenvironment (TME), interferons stimulate tumor-infiltrating lymphocytes to promote immune clearance and essentially reshape a "cold" TME into an immune-activating "hot" TME. In this review, we focus on gliomas, with an emphasis on malignant glioblastoma, as these brain tumors possess a highly invasive and heterogenous brain TME. We address how type I interferons regulate antitumor immune responses against malignant gliomas and reshape the overall immune landscape of the brain TME. Furthermore, we discuss how these findings can translate into future immunotherapies targeting brain tumors in general.

Recent advances to Neuroprotection: repurposing drugs against neuroinflammatory disorders

Cell death is a natural mechanism for biological clearance for the maintenance of homeostasis in a dynamic microenvironment of the central nervous system. Stress and various factors can lead to imbalance between cellular genesis and cell death leading to dysfunctionality and a number of neuropathological disorders. Drug repurposing can help bypass development time and cost. A complete understanding of drug actions and neuroinflammatory pathways can lead to effective control of neurodegenerative disorders. This review covers recent advances in various neuroinflammatory pathways understanding, biomarkers, and drug repurposing for neuroprotection.

Type I interferon response in astrocytes promotes brain metastasis by enhancing monocytic myeloid cell recruitment

Cancer metastasis to the brain is a significant clinical problem. Metastasis is the consequence of favorable interactions between invaded cancer cells and the microenvironment. Here, we demonstrate that cancer-activated astrocytes create a sustained low-level activated type I interferon (IFN) microenvironment in brain metastatic lesions. We further confirm that the IFN response in astrocytes facilitates brain metastasis. Mechanistically, IFN signaling in astrocytes activates C-C Motif Chemokine Ligand 2 (CCL2) production, which further increases the recruitment of monocytic myeloid cells. The correlation between CCL2 and monocytic myeloid cells is confirmed in clinical brain metastasis samples. Lastly, genetically or pharmacologically inhibiting C-C Motif Chemokine Receptor 2 (CCR2) reduces brain metastases. Our study clarifies a pro-metastatic effect of type I IFN in the brain even though IFN response has been considered to have anti-tumor effects. Moreover, this work expands our understandings on the interactions between cancer-activated astrocytes and immune cells in brain metastasis.

Molecular and neuroimmune pharmacology of S1P receptor modulators and other disease-modifying therapies for multiple sclerosis

Multiple sclerosis (MS) is a neurological, immune-mediated demyelinating disease that affects people in the prime of life. Environmental, infectious, and genetic factors have been implicated in its etiology, although a definitive cause has yet to be determined. Nevertheless, multiple disease-modifying therapies (DMTs: including interferons, glatiramer acetate, fumarates, cladribine, teriflunomide, fingolimod, siponimod, ozanimod, ponesimod, and monoclonal antibodies targeting ITGA4, CD20, and CD52) have been developed and approved for the treatment of MS. All the DMTs approved to date target immunomodulation as their mechanism of action (MOA); however, the direct effects of some DMTs on the central nervous system (CNS), particularly sphingosine 1-phosphate (S1P) receptor (S1PR) modulators, implicate a parallel MOA that may also reduce neurodegenerative sequelae. This review summarizes the currently approved DMTs for the treatment of MS and provides details and recent advances in the molecular pharmacology, immunopharmacology, and neuropharmacology of S1PR modulators, with a special focus on the CNS-oriented, astrocyte-centric MOA of fingolimod.

Astrocytic TDP-43 dysregulation impairs memory by modulating antiviral pathways and interferon-inducible chemokines

Transactivating response region DNA binding protein 43 (TDP-43) pathology is prevalent in dementia, but the cell type-specific effects of TDP-43 pathology are not clear, and therapeutic strategies to alleviate TDP-43-linked cognitive decline are lacking. We found that patients with Alzheimer's disease or frontotemporal dementia have aberrant TDP-43 accumulation in hippocampal astrocytes. In mouse models, induction of widespread or hippocampus-targeted accumulation in astrocytic TDP-43 caused progressive memory loss and localized changes in antiviral gene expression. These changes were cell-autonomous and correlated with impaired astrocytic defense against infectious viruses. Among the changes, astrocytes had elevated levels of interferon-inducible chemokines, and neurons had elevated levels of the corresponding chemokine receptor CXCR3 in presynaptic terminals. CXCR3 stimulation altered presynaptic function and promoted neuronal hyperexcitability, akin to the effects of astrocytic TDP-43 dysregulation, and blockade of CXCR3 reduced this activity. Ablation of CXCR3 also prevented TDP-43-linked memory loss. Thus, astrocytic TDP-43 dysfunction contributes to cognitive impairment through aberrant chemokine-mediated astrocytic-neuronal interactions.

IFNAR signaling of neuroectodermal cells is essential for the survival of C57BL/6 mice infected with Theiler's murine encephalomyelitis virus

BACKGROUND

Theiler's murine encephalomyelitis virus (TMEV) is a single-stranded RNA virus that causes encephalitis followed by chronic demyelination in SJL mice and spontaneous seizures in C57BL/6 mice. Since earlier studies indicated a critical role of type I interferon (IFN-I) signaling in the control of viral replication in the central nervous system (CNS), mouse strain-specific differences in pathways induced by the IFN-I receptor (IFNAR) might determine the outcome of TMEV infection.

METHODS

Data of RNA-seq analysis and immunohistochemistry were used to compare the gene and protein expression of IFN-I signaling pathway members between mock- and TMEV-infected SJL and C57BL/6 mice at 4, 7 and 14 days post-infection (dpi). To address the impact of IFNAR signaling in selected brain-resident cell types, conditional knockout mice with an IFNAR deficiency in cells of the neuroectodermal lineage (NesCre^±IFNAR^fl/fl), neurons (Syn1Cre^±IFNAR^fl/fl), astrocytes (GFAPCre^±IFNAR^fl/fl), and microglia (Sall1Cre^ER±IFNAR^fl/fl) on a C57BL/6 background were tested. PCR and an immunoassay were used to quantify TMEV RNA and cytokine and chemokine expression in their brain at 4 dpi.

RESULTS

RNA-seq analysis revealed upregulation of most ISGs in SJL and C57BL/6 mice, but Ifi202b mRNA transcripts were only increased in SJL and Trim12a only in C57BL/6 mice. Immunohistochemistry showed minor differences in ISG expression (ISG15, OAS, PKR) between both mouse strains. While all immunocompetent Cre-negative control mice and the majority of mice with IFNAR deficiency in neurons or microglia survived until 14 dpi, lack of IFNAR expression in all cells (IFNAR^-/-), neuroectodermal cells, or astrocytes induced lethal disease in most of the analyzed mice, which was associated with unrestricted viral replication. NesCre^±IFNAR^fl/fl mice showed more Ifnb1, Tnfa, Il6, Il10, Il12b and Ifng mRNA transcripts than Cre^-/-IFNAR^fl/fl mice. IFNAR^-/- mice also demonstrated increased IFN-α, IFN-β, IL1-β, IL-6, and CXCL-1 protein levels, which highly correlated with viral load.

CONCLUSIONS

Ifi202b and Trim12a expression levels likely contribute to mouse strain-specific susceptibility to TMEV-induced CNS lesions. Restriction of viral replication is strongly dependent on IFNAR signaling of neuroectodermal cells, which also controls the expression of key pro- and anti-inflammatory cytokines during viral brain infection.

Repeated performance of spatial memory tasks ameliorates cognitive decline in APP/PS1 mice

BACKGROUND

Alzheimer's disease (AD) is a burden on the public health system because it is a neurodegenerative disease that is incurable and for which there is no successful treatment. AD patients suffer from symptoms for many years, with progressive loss of cognitive and functional abilities. In addition to the features of AD, described as amyloid plaques and neurofibrillary tangles, neuroinflammatory processes, genetic factors, and lifestyle also play important roles. Increasing evidence for lifestyle factors includes possible changes due to smoking, social engagement, and physical activity.

METHODS

Morris water maze behavioral tasks were performed to analyze the formation of spatial memory. APPswe/PS1dE9 mice with a remarkable increase in amyloid-β production associated with certain behavioral abnormalities comparable to AD symptoms and age-matched wild-type littermates were trained several times at 3, 6, 9, and 12 months of age and compared with untrained groups at 9 and 12 months of age. Performance during the acquisition phase, in the reference memory test, and in searching strategies were analyzed.

RESULTS

9- and 12-month-old APP/PS1 mice showed cognitive impairment, especially in the reference memory test and searching strategies. This cognitive deterioration was reversed in 9- and 12-month-old APP/PS1 mice that had been previously trained several times. Even in the reversal test, in which memory formation must be adapted to the new platform position, several trained APP/PS1 mice performed better.

CONCLUSION

Repeated spatial memory training in the water maze showed positive effects on memory formation in APP/PS1 mice. Interestingly, the cohort that had been previously trained several times was able to use increased hippocampus-dependent strategies, similar to the WT mice. This may suggest that cognitively demanding and physically active tasks can improve cognitive function.

Breaking down the cellular responses to type I interferon neurotoxicity in the brain

Since their original discovery, type I interferons (IFN-Is) have been closely associated with antiviral immune responses. However, their biological functions go far beyond this role, with balanced IFN-I activity being critical to maintain cellular and tissue homeostasis. Recent findings have uncovered a darker side of IFN-Is whereby chronically elevated levels induce devastating neuroinflammatory and neurodegenerative pathologies. The underlying causes of these 'interferonopathies' are diverse and include monogenetic syndromes, autoimmune disorders, as well as chronic infections. The prominent involvement of the CNS in these disorders indicates a particular susceptibility of brain cells to IFN-I toxicity. Here we will discuss the current knowledge of how IFN-Is mediate neurotoxicity in the brain by analyzing the cell-type specific responses to IFN-Is in the CNS, and secondly, by exploring the spectrum of neurological disorders arising from increased IFN-Is. Understanding the nature of IFN-I neurotoxicity is a crucial and fundamental step towards development of new therapeutic strategies for interferonopathies.

HLA-A, HSPA5, IGFBP5 and PSMA2 Are Restriction Factors for Zika Virus Growth in Astrocytic Cells

(1) Background: Zika virus (ZIKV), an arbo-flavivirus, is transmitted via Aeges aegyptii mosquitoes Following its major outbreaks in 2013, 2014 and 2016, WHO declared it a Public Health Emergency of International Concern. Symptoms of ZIKV infection include acute fever, conjunctivitis, headache, muscle & joint pain and malaise. Cases of its transmission also have been reported via perinatal, sexual and transfusion transmission. ZIKV pathologies include meningo-encephalitis and myelitis in the central nervous system (CNS) and Guillain-Barré syndrome and acute transient polyneuritis in the peripheral nervous system (PNS). Drugs like azithromycin have been tested as inhibitors of ZIKV infection but no vaccines or treatments are currently available. Astrocytes are the most abundant cells in the CNS and among the first cells in CNS infected by ZIKV; (2) Methods: We previously used SOMAScan proteomics to study ZIKV-infected astrocytic cells. Here, we use mass spectrometric analyses to further explain dysregulations in the cellular expression profile of glioblastoma astrocytoma U251 cells. We also knocked down (KD) some of the U251 cellular proteins using siRNAs and observed the impact on ZIKV replication and infectivity; (3) Results & Conclusions: The top ZIKV dysregulated cellular networks were antimicrobial response, cell death, and energy production while top dysregulated functions were antigen presentation, viral replication and cytopathic impact. Th1 and interferon signaling pathways were among the top dysregulated canonical pathways. siRNA-mediated KD of HLA-A, IGFBP5, PSMA2 and HSPA5 increased ZIKV titers and protein synthesis, indicating they are ZIKV restriction factors. ZIKV infection also restored HLA-A expression in HLA-A KD cells by 48 h post-infection, suggesting interactions between this gene product and ZIKV.

The role of type I IFN in autoimmune and autoinflammatory diseases with CNS involvement

Type I interferons (IFNs) are major mediators of innate immunity, with well-known antiviral, antiproliferative, and immunomodulatory properties. A growing body of evidence suggests the involvement of type I IFNs in the pathogenesis of central nervous system (CNS) manifestations in the setting of chronic autoimmune and autoinflammatory disorders, while IFN-β has been for years, a well-established therapeutic modality for multiple sclerosis (MS). In the present review, we summarize the current evidence on the mechanisms of type I IFN production by CNS cellular populations as well as its local effects on the CNS. Additionally, the beneficial effects of IFN-β in the pathophysiology of MS are discussed, along with the contributory role of type I IFNs in the pathogenesis of neuropsychiatric lupus erythematosus and type I interferonopathies.

The role of α-tubulin tyrosination in controlling the structure and function of hippocampal neurons

Microtubules (MTs) are central components of the neuronal cytoskeleton and play a critical role in CNS integrity, function, and plasticity. Neuronal MTs are diverse due to extensive post-translational modifications (PTMs), particularly detyrosination/tyrosination, in which the C-terminal tyrosine of α-tubulin is cyclically removed by a carboxypeptidase and reattached by a tubulin-tyrosine ligase (TTL). The detyrosination/tyrosination cycle of MTs has been shown to be an important regulator of MT dynamics in neurons. TTL-null mice exhibit impaired neuronal organization and die immediately after birth, indicating TTL function is vital to the CNS. However, the detailed cellular role of TTL during development and in the adult brain remains elusive. Here, we demonstrate that conditional deletion of TTL in the neocortex and hippocampus during network development results in a pathophysiological phenotype defined by incomplete development of the corpus callosum and anterior commissures due to axonal growth arrest. TTL loss was also associated with a deficit in spatial learning, impaired synaptic plasticity, and reduced number of spines in hippocampal neurons, suggesting that TTL also plays a critical role in hippocampal network development. TTL deletion after postnatal development, specifically in the hippocampus and in cultured hippocampal neurons, led to a loss of spines and impaired spine structural plasticity. This indicates a novel and important function of TTL for synaptic plasticity in the adult brain. In conclusion, this study reveals the importance of α-tubulin tyrosination, which defines the dynamics of MTs, in controlling proper network formation and suggests TTL-mediated tyrosination as a new key determinant of synaptic plasticity in the adult brain.

Role of MicroRNAs, Aptamers in Neuroinflammation and Neurodegenerative Disorders

Exploring the microRNAs and aptamers for their therapeutic role as biological drugs has expanded the horizon of its applicability against various human diseases, explicitly targeting the genetic materials. RNA-based therapeutics are widely being explored for the treatment and diagnosis of multiple diseases, including neurodegenerative disorders (NDD). Latter includes microRNA, aptamers, ribozymes, and small interfering RNAs (siRNAs), which control the gene expression mainly at the transcriptional strata. One RNA transcript translates into different protein types; hence, therapies targeted at the transcriptional sphere may have prominent and more extensive effects than alternative therapeutics. Unlike conventional gene therapy, RNAs, upon delivery, can either altogether abolish or alter the synthesis of the protein of interest, therefore, regulating their activities in a controlled and diverse manner. NDDs like Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, Prion disease, and others are characterized by deposition of misfolded protein such as amyloid-ß, tau, α-synuclein, huntingtin and prion proteins. Neuroinflammation, one of the perquisites for neurodegeneration, is induced during neurodegenerative pathogenesis. In this review, we discuss microRNAs and aptamers' role as two different RNA-based approaches for their unique ability to regulate protein production at the transcription level, hence offering many advantages over other biologicals. The microRNA acts either by alleviating the malfunctioning RNA expression or by working as a replacement to lost microRNA. On the contrary, aptamer act as a chemical antibody and forms an aptamer-target complex.

IL-37 expression reduces acute and chronic neuroinflammation and rescues cognitive impairment in an Alzheimer's disease mouse model

The anti-inflammatory cytokine interleukin-37 (IL-37) belongs to the IL-1 family but is not expressed in mice. We used a human IL-37 (hIL-37tg) expressing mouse, which has been subjected to various models of local and systemic inflammation as well as immunological challenges. Previous studies reveal an immunomodulatory role of IL-37, which can be characterized as an important suppressor of innate immunity. Here, we examined the functions of IL-37 in the central nervous system and explored the effects of IL-37 on neuronal architecture and function, microglial phenotype, cytokine production and behavior after inflammatory challenge by intraperitoneal LPS-injection. In wild-type mice, decreased spine density, activated microglial phenotype and impaired long-term potentiation (LTP) were observed after LPS injection, whereas hIL-37tg mice showed no impairment. In addition, we crossed the hIL-37tg mouse with an animal model of Alzheimer’s disease (APP/PS1) to investigate the anti-inflammatory properties of IL-37 under chronic neuroinflammatory conditions. Our results show that expression of IL-37 is able to limit inflammation in the brain after acute inflammatory events and prevent loss of cognitive abilities in a mouse model of AD.

Maternal high-dense diet programs interferon type I signaling and microglia complexity in the nucleus accumbens shell of rats showing food addiction-like behavior

OBJECTIVE

This study aimed to characterize the molecular immune networks and microglia reactivity in the nucleus accumbens (NAc) shell affected by fetal nutritional programming leading to addiction-like behavior in the offspring of Wistar rats. Fetal nutritional programming by energy-dense foods leads to addiction-like behavior in the offspring. Exposure to energy-dense foods also activates systemic and central inflammation in the offspring.

METHODS

Females Wistar rats were exposed to cafeteria (CAF) diet or control diet for 9 weeks (prepregnancy, pregnancy and lactation), and male offspring at 2 months of age were diagnosed with food addiction-like behavior using operant conditioning. Global microarray analysis, RTqPCR, proinflammatory plasma profile and microglia immunostaining were performed in the NAc shell of male rats. SIM-A9 microglia cells were stimulated with IFN-α and palmitic acid, and microglia activation and phagocytosis were determined by RTqPCR and incubation of green-fluorescent latex beads, respectively.

RESULTS

Microarray analysis in the NAc shell of the male offspring exposed to CAF during development and diagnosed with addiction-like behavior showed increasing in the type I interferon-inducible gene, Ift1 , gene network. Genomic and cellular characterization also confirmed microglia hyperreactivity and upregulation of the Ifit1 in the NAc shell of animals with addiction-like behavior. In-vitro models demonstrated that microglia do respond to IFN-α promoting a time-dependent genomic expression of Ift1, IL-1β and IL-6 followed by increased phagocytosis.

CONCLUSION

Prenatal exposure to energy-dense foods primes the IFN type I signaling and microglia complexity in the NAc shell of rats diagnosed with food addiction-like behavior.

Type-I-interferon signaling drives microglial dysfunction and senescence in human iPSC models of Down syndrome and Alzheimer's disease

Microglia are critical in brain development and Alzheimer's disease (AD) etiology. Down syndrome (DS) is the most common genetic developmental disorder and risk factor for AD. Surprisingly, little information is available on the impact of trisomy of human chromosome 21 (Hsa21) on microglial functions during DS brain development and in AD in DS. Using induced pluripotent stem cell (iPSC)-based organoid and chimeric mouse models, we report that DS microglia exhibit an enhanced synaptic pruning function, which alters neuronal synaptic functions. In response to human brain tissue-derived pathological tau, DS microglia undergo cellular senescence and exhibit elevated type-I-interferon signaling. Mechanistically, knockdown of Hsa21-encoded type I interferon receptors, IFNARs, rescues the DS microglial phenotypes both during brain development and in response to pathological tau. Our findings provide in vivo evidence that human microglia respond to pathological tau by exhibiting dystrophic phenotypes. Targeting IFNARs may improve DS microglial functions and prevent senescence.

The Role of Mesenchymal Stem Cells in Regulating Astrocytes-Related Synapse Dysfunction in Early Alzheimer’s Disease

Alzheimer’s disease (AD), a neurodegenerative disease, is characterized by the presence of extracellular amyloid-β (Aβ) aggregates and intracellular neurofibrillary tangles formed by hyperphosphorylated tau as pathological features and the cognitive decline as main clinical features. An important cellular correlation of cognitive decline in AD is synapse loss. Soluble Aβ oligomer has been proposed to be a crucial early event leading to synapse dysfunction in AD. Astrocytes are crucial for synaptic formation and function, and defects in astrocytic activation and function have been suggested in the pathogenesis of AD. Astrocytes may contribute to synapse dysfunction at an early stage of AD by participating in Aβ metabolism, brain inflammatory response, and synaptic regulation. While mesenchymal stem cells can inhibit astrogliosis, and promote non-reactive astrocytes. They can also induce direct regeneration of neurons and synapses. This review describes the role of mesenchymal stem cells and underlying mechanisms in regulating astrocytes-related Aβ metabolism, neuroinflammation, and synapse dysfunction in early AD, exploring the open questions in this field.

Methamphetamine Exposure in Adolescent Impairs Memory of Mice in Adulthood Accompanied by Changes in Neuroplasticity in the Dorsal Hippocampus

Methamphetamine (METH) has been shown to alter learning and memory by affecting the neuroplasticity of the dorsal hippocampus, a key structure that undergoes extensive remodeling during adolescence. In this study, we investigated whether mid-to-late adolescent exposure to METH leads to long-lasting memory impairment. To do this, adolescents (35–48 postnatal days) were exposed to different doses of METH for 14 days and then evaluated by the Morris water maze (MWM), new object recognition test (NORT), and the Y-maze, to investigate the learning and memory abilities of mice in their adolescence and adulthood, respectively. We also detected the mRNA levels of genes associated with neuroplasticity in the dorsal hippocampus. The synaptic ultrastructure and the number of neurons and astrocytes in the dorsal hippocampus were also determined by transmission electron microscopy (TEM) and immunofluorescence (IF). Exposure to METH in mid-to-late adolescence impaired spatial memory retrieval ability and the long-term recognition memory of mice in their adulthood, but not in their adolescence. Of note, the impairment of memory capacity in adulthood was accompanied by molecular and structural changes in synapses in the dorsal hippocampus. Our results indicate that mice exposed to METH in mid-to-late adolescence have impaired memory ability in their adulthood; this may be the result of abnormal changes in the structural plasticity of the dorsal hippocampus; the causal relationship between changes in synaptic structural plasticity and memory impairment needs to be further confirmed. In summary, our study provides evidence for the detrimental consequences of adolescent addiction and the prevention of adolescent drug abuse.

Cellular and molecular influencers of neuroinflammation in Alzheimer's disease: Recent concepts & roles

Alzheimer's disease (AD), an extremely common neurodegenerative disorder of the older generation, is one of the leading causes of death globally. Besides the conventional hallmarks i.e. Amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs), neuroinflammation also serves as a major contributing factor in the pathogenesis of AD. There are mounting evidences to support the fundamental role of cellular (microglia, astrocytes, mast cells, and T-cells) and molecular (cytokines, chemokines, caspases, and complement proteins) influencers of neuroinflammation in producing/promoting neurodegeneration and dementia in AD. Genome-wide association studies (GWAS) have revealed the involvement of various single nucleotide polymorphisms (SNPs) of genes related to neuroinflammation with the risk of developing AD. Modulating the release of the neuroinflammatory molecules and targeting their relevant mechanisms may have beneficial effects on the onset, progress and severity of the disease. Here, we review the distinct role of various mediators and modulators of neuroinflammation that impact the pathogenesis and progression of AD as well as incite further research efforts for the treatment of AD through a neuroinflammatory approach.

A new insight into mechanisms of interferon alpha neurotoxicity: Expression of GRIN3A subunit of NMDA receptors and NMDA-evoked exocytosis

Neurological and psychiatric side effects accompany the high-dose interferon-alpha (IFNA) therapy. The primary genes responsible for these complications are mostly unknown. Our genome-wide search in mouse and rat genomes for the conservative genes containing IFN-stimulated response elements (ISRE) in their promoters revealed a new potential target gene of IFNA, Grin3α, which encodes the 3A subunit of NMDA receptor. This study aimed to explore the impact of IFNA on the expression of Grin3α and Ifnα genes and neurotransmitters endo/exocytosis in the mouse brain. We administered recombinant human IFN-alpha 2b (rhIFN-α2b) intracranially, and 24 h later, we isolated six brain regions and used the samples for RT-qPCR and western blot analysis. Synaptosomes were isolated from the cortex to analyze endo/exocytosis with acridine orange and L-[14C]glutamate. IFNA induced an increase in Grin3α mRNA and GRIN3A protein, but a decrease in Ifnα mRNA and protein. IFNA did not affect the accumulation and distribution of L-[14C]glutamate and acridine orange between synaptosomes and the extra-synaptosomal space. It caused the more significant acridine orange release activated by NMDA or glutamate than from control mice's synaptosomes. In response to IFNA, the newly discovered association between elevated Grin3α expression and NMDA- and glutamate-evoked neurotransmitters release from synaptosomes implies a new molecular mechanism of IFNA neurotoxicity.

Long-Term Consequence of Non-neurotropic H3N2 Influenza A Virus Infection for the Progression of Alzheimer's Disease Symptoms

Influenza viruses until today are a leading cause of worldwide severe pandemics and represent a major threat to human and animal health. Although the primary target of influenza viruses is the lung, infection may manifest with acute and even chronic neurological complications (e.g., status epilepticus, encephalopathies, and encephalitis) potentially increasing the long-term risk for neurodegenerative diseases. We previously described that a peripheral influenza A virus (IAV) infection caused by non-neurotropic H3N2 (maHK68) variant leads to long-term neuroinflammation and synapse loss together with impaired memory formation in young adult mice. Processes of neuroinflammation have been associated with neurodegenerative diseases such as Alzheimer’s disease (AD) and prolonged or excessive innate immune responses are considered a risk factor for AD. Here, the role of purely peripheral IAV infection for the development and progression of AD in a transgenic mouse model (APP/PS1) was investigated. At 2 months of age, mice were infected with H3N2 IAV and the detailed analysis of microglia morphology revealed neuroinflammation in the hippocampus already of 6 months old non-infected APP/PS1 mice together with impaired spatial learning, however, microglia activation, amyloid-β plaques load and cognitive impairments were even more pronounced in APP/PS1 mice upon H3N2 infection. Moreover, CA1 hippocampal dendritic spine density was reduced even at 120 dpi compared to wild-type and also to non-infected APP/PS1 mice, whereas neuronal cells number was not altered. These findings demonstrate that non-neurotropic H3N2 IAV infection as a peripheral immune stimulation may exacerbate AD symptoms possibly by triggering microglial hyperactivation.

Type I Interferon Production of Plasmacytoid Dendritic Cells under Control

One of the most powerful and multifaceted cytokines produced by immune cells are type I interferons (IFNs), the basal secretion of which contributes to the maintenance of immune homeostasis, while their activation-induced production is essential to effective immune responses. Although, each cell is capable of producing type I IFNs, plasmacytoid dendritic cells (pDCs) possess a unique ability to rapidly produce large amounts of them. Importantly, type I IFNs have a prominent role in the pathomechanism of various pDC-associated diseases. Deficiency in type I IFN production increases the risk of more severe viral infections and the development of certain allergic reactions, and supports tumor resistance; nevertheless, its overproduction promotes autoimmune reactions. Therefore, the tight regulation of type I IFN responses of pDCs is essential to maintain an adequate level of immune response without causing adverse effects. Here, our goal was to summarize those endogenous factors that can influence the type I IFN responses of pDCs, and thus might serve as possible therapeutic targets in pDC-associated diseases. Furthermore, we briefly discuss the current therapeutic approaches targeting the pDC-type I IFN axis in viral infections, cancer, autoimmunity, and allergy, together with their limitations defined by the Janus-faced nature of pDC-derived type I IFNs.

Unraveling the Link Between Mitochondrial Dynamics and Neuroinflammation

Neuroinflammatory and neurodegenerative diseases are a major public health problem worldwide, especially with the increase of life-expectancy observed during the last decades. For many of these diseases, we still lack a full understanding of their etiology and pathophysiology. Nonetheless their association with mitochondrial dysfunction highlights this organelle as an important player during CNS homeostasis and disease. Markers of Parkinson (PD) and Alzheimer (AD) diseases are able to induce innate immune pathways induced by alterations in mitochondrial Ca2+ homeostasis leading to neuroinflammation. Additionally, exacerbated type I IFN responses triggered by mitochondrial DNA (mtDNA), failures in mitophagy, ER-mitochondria communication and mtROS production promote neurodegeneration. On the other hand, regulation of mitochondrial dynamics is essential for CNS health maintenance and leading to the induction of IL-10 and reduction of TNF-α secretion, increased cell viability and diminished cell injury in addition to reduced oxidative stress. Thus, although previously solely seen as power suppliers to organelles and molecular processes, it is now well established that mitochondria have many other important roles, including during immune responses. Here, we discuss the importance of these mitochondrial dynamics during neuroinflammation, and how they correlate either with the amelioration or worsening of CNS disease.

The NLRP3 inflammasome inhibitor OLT1177 rescues cognitive impairment in a mouse model of Alzheimer's disease

Numerous studies demonstrate that neuroinflammation is a key player in the progression of Alzheimer's disease (AD). Interleukin (IL)-1β is a main inducer of inflammation and therefore a prime target for therapeutic options. The inactive IL-1β precursor requires processing by the the nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome into a mature and active form. Studies have shown that IL-1β is up-regulated in brains of patients with AD, and that genetic inactivation of the NLRP3 inflammasome improves behavioral tests and synaptic plasticity phenotypes in a murine model of the disease. In the present study, we analyzed the effect of pharmacological inhibition of the NLRP3 inflammasome using dapansutrile (OLT1177), an oral NLRP3-specific inhibitor that is safe in humans. Six-month-old WT and APP/PS1 mice were fed with standard mouse chow or OLT1177-enriched chow for 3 mo. The Morris water maze test revealed an impaired learning and memory ability of 9-mo-old APP/PS1 mice (P = 0.001), which was completely rescued by OLT1177 fed to mice (P = 0.008 to untreated APP/PS1). Furthermore, our findings revealed that 3 mo of OLT1177 diet can rescue synaptic plasticity in this mouse model of AD (P = 0.007 to untreated APP/PS1). In addition, microglia were less activated (P = 0.07) and the number of plaques was reduced in the cortex (P = 0.03) following NLRP3 inhibition with OLT1177 administration. We also observed an OLT1177 dose-dependent normalization of plasma metabolic markers of AD to those of WT mice. This study suggests the therapeutic potential of treating neuroinflammation with an oral inhibitor of the NLRP3 inflammasome.

Langat virus infection affects hippocampal neuron morphology and function in mice without disease signs

Background

Tick-borne encephalitis virus (TBEV) is an important human pathogen that can cause the serious illness tick-borne encephalitis (TBE). Patients with clinical symptoms can suffer from severe meningoencephalitis with sequelae that include cognitive disorders and paralysis. While less than 30% of patients with clinical symptoms develop meningoencephalitis, the number of seropositive individuals in some regions indicates a much higher prevalence of TBEV infections, either with no or subclinical symptoms. The functional relevance of these subclinical TBEV infections and their influence on brain functions, such as learning and memory, has not been investigated so far.

Methods

To compare the effect of low and high viral replication in the brain, wildtype and Irf-7^−/− mice were infected with Langat virus (LGTV), which belongs to the TBEV-serogroup. The viral burden was analyzed in the olfactory bulb and the hippocampus. Open field, elevated plus maze, and Morris water maze experiments were performed to determine the impact on anxiety-like behavior, learning, and memory formation. Spine density of hippocampal neurons and activation of microglia and astrocytes were analyzed.

Results

In contrast to susceptible Irf-7^−/− mice, wildtype mice showed no disease signs upon LGTV infection. Detection of viral RNA in the olfactory bulb revealed CNS infections in wildtype and Irf-7^−/− mice. Very low levels of viral replication were detectable in the hippocampus of wildtype mice. Although wildtype mice develop no disease signs, they showed reduced anxiety-like behavior and impaired memory formation, whereas Irf-7^−/− mice were not affected. This impairment was associated with a significant decrease in spine density of neurons in the hippocampal CA1 region of wildtype mice. Microglia activation and astrogliosis were detected in the hippocampus.

Conclusion

In this study, we demonstrate that subclinical infections by viruses from the TBEV-serogroup affected anxiety-like behavior. Virus replication in the olfactory bulb induced far-reaching effects on hippocampal neuron morphology and impaired hippocampus-dependent learning and memory formation.

Long-Term Impact of Early-Life Stress on Hippocampal Plasticity: Spotlight on Astrocytes

Adverse experiences during childhood are among the most prominent risk factors for developing mood and anxiety disorders later in life. Early-life stress interventions have been established as suitable models to study the neurobiological basis of childhood adversity in rodents. Different models such as maternal separation, impaired maternal care and juvenile stress during the postweaning/prepubertal life phase are utilized. Especially within the limbic system, they induce lasting alterations in neuronal circuits, neurotransmitter systems, neuronal architecture and plasticity that are further associated with emotional and cognitive information processing. Recent studies found that astrocytes, a special group of glial cells, have altered functions following early-life stress as well. As part of the tripartite synapse, astrocytes interact with neurons in multiple ways by affecting neurotransmitter uptake and metabolism, by providing gliotransmitters and by providing energy to neurons within local circuits. Thus, astrocytes comprise powerful modulators of neuronal plasticity and are well suited to mediate the long-term effects of early-life stress on neuronal circuits. In this review, we will summarize current findings on altered astrocyte function and hippocampal plasticity following early-life stress. Highlighting studies for astrocyte-related plasticity modulation as well as open questions, we will elucidate the potential of astrocytes as new targets for interventions against stress-induced neuropsychiatric disorders.