Over 50% of patients who survive neuroinvasive infection with West Nile virus (WNV) exhibit chronic cognitive sequelae1,2. Although thousands of cases of WNV-mediated memory dysfunction accrue annually3, the mechanisms responsible for these impairments are unknown. The classical complement cascade, a key component of innate immune pathogen defence, mediates synaptic pruning by microglia during early postnatal development4,5. Here we show that viral infection of adult hippocampal neurons induces complement-mediated elimination of presynaptic terminals in a murine WNV neuroinvasive disease model. Inoculation of WNV-NS5-E218A, a WNV with a mutant NS5(E218A) protein6,7 leads to survival rates and cognitive dysfunction that mirror human WNV neuroinvasive disease. WNV-NS5-E218A-recovered mice (recovery defined as survival after acute infection) display impaired spatial learning and persistence of phagocytic microglia without loss of hippocampal neurons or volume. Hippocampi from WNV-NS5-E218A-recovered mice with poor spatial learning show increased expression of genes that drive synaptic remodelling by microglia via complement. C1QA was upregulated and localized to microglia, infected neurons and presynaptic terminals during WNV neuroinvasive disease. Murine and human WNV neuroinvasive disease post-mortem samples exhibit loss of hippocampal CA3 presynaptic terminals, and murine studies revealed microglial engulfment of presynaptic terminals during acute infection and after recovery. Mice with fewer microglia (Il34−/− mice with a deficiency in IL-34 production) or deficiency in complement C3 or C3a receptor were protected from WNV-induced synaptic terminal loss. Our study provides a new murine model of WNV-induced spatial memory impairment, and identifies a potential mechanism underlying neurocognitive impairment in patients recovering from WNV neuroinvasive disease.

In Alzheimer disease, the microtubule-associated protein tau dissociates from the neuronal cytoskeleton and aggregates to form cytoplasmic inclusions. Although hyper-phosphorylation of tau Ser and Thr residues is an established trigger of tau misfunction and aggregation, tau modifications extend to Lys residues as well, raising the possibility that different modification signatures depress or promote aggregation propensity depending on site occupancy. To identify Lys-residue modifications associated with normal tau function, soluble tau proteins isolated from four cognitively normal human brains were characterized by mass spectrometry methods. The major detectable Lys modification was found to be methylation, which appeared in the form of mono- and di-methyl Lys residues distributed among at least eleven sites. Unlike tau phosphorylation sites, the frequency of Lys methylation was highest in the microtubule binding repeat region that mediates both microtubule binding and homotypic interactions. When purified recombinant human tau was modified in vitro through reductive methylation, its ability to promote tubulin polymerization was retained, whereas its aggregation propensity was greatly attenuated at both nucleation and extension steps. These data establish Lys methylation as part of the normal tau post-translational modification signature in human brain, and suggest that it can function in part to protect against pathological tau aggregation.

BackgroundMicroglia are resident macrophages of the central nervous system (CNS) locally maintained through colony-stimulating factor 1 receptor (CSF1R) signaling. Microglial depletion via CSF1R inactivation improves cognition in mouse models of neuroinflammation, but limits virologic control in the CNS of mouse models of neurotropic infections by unknown mechanisms. We hypothesize that CSF1R plays a critical role in myeloid cell responses that restrict viral replication and locally restimulate recruited antiviral T cells within the CNS.MethodsThe impact of CSF1R signaling during West Nile virus infection was assessed in vivo using a mouse model of neurotropic infection. Pharmacological inactivation of CSF1R was achieved using PLX5622 prior to infection with virulent or attenuated strains of West Nile virus (WNV), an emerging neuropathogen. The subsequent effect of CSF1R antagonism on virologic control was assessed by measuring mortality and viral titers in the CNS and peripheral organs. Immune responses were assessed by flow cytometric-based phenotypic analyses of both peripheral and CNS immune cells.ResultsMice treated with CSF1R antagonist prior to infection exhibited higher susceptibility to lethal WNV infection and lack of virologic control in both the CNS and periphery. CSFR1 antagonism reduced B7 co-stimulatory signals on peripheral and CNS antigen-presenting cells (APCs) by depleting CNS cellular sources, which limited local reactivation of CNS-infiltrating virus-specific T cells and reduced viral clearance.ConclusionsOur results demonstrate the impact of CSF1R antagonism on APC activation in the CNS and periphery and the importance of microglia in orchestrating the CNS immune response following neurotropic viral infection. These data will be an important consideration when assessing the benefit of CSF1R antagonism, which has been investigated as a therapeutic for neurodegenerative conditions, in which neuroinflammation is a contributing factor.Electronic supplementary materialThe online version of this article (10.1186/s12974-019-1397-4) contains supplementary material, which is available to authorized users.

In sporadic Alzheimer’s disease (AD), neurofibrillary lesion formation is preceded by extensive post-translational modification of the microtubule associated protein tau. To identify the modification signature associated with tau lesion formation at single amino acid resolution, immunopurified paired helical filaments were isolated from AD brain and subjected to nanoflow liquid chromatography–tandem mass spectrometry analysis. The resulting spectra identified monomethylation of lysine residues as a new tau modification. The methyl-lysine was distributed among seven residues located in the projection and microtubule binding repeat regions of tau protein, with one site, K254, being a substrate for a competing lysine modification, ubiquitylation. To characterize methyl lysine content in intact tissue, hippocampal sections prepared from post mortem late-stage AD cases were subjected to double-label confocal fluorescence microscopy using anti-tau and anti-methyl lysine antibodies. Anti-methyl lysine immunoreactivity colocalized with 78 ± 13% of neurofibrillary tangles in these specimens. Together these data provide the first evidence that tau in neurofibrillary lesions is post-translationally modified by lysine methylation.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-011-0893-0) contains supplementary material, which is available to authorized users.

Aims-Granulovacuolar degeneration involves the accumulation of large, double membranebound bodies within certain neurons during the course of Alzheimer's disease and other adultonset dementias. Because of the two-layer membrane morphology, it has been proposed that the bodies are related to autophagic organelles. The aim of this study was to test this hypothesis, and determine the approximate stage at which the pathway stalled in Alzheimer's disease.Methods-Spatial colocalization of autophagic and endocytic markers with casein kinase 1 delta, a marker for GVD bodies, was evaluated in hippocampal sections prepared from postmortem Braak stage IV and V Alzheimer's disease cases using double-label confocal fluorescence microscopy.Results-GVD bodies colocalized weakly with early-stage autophagy markers LC3 and p62, but strongly with late-stage marker LAMP1 (lysosome-associated membrane protein 1), which decorated their surrounding membranes. GVD bodies also colocalized strongly with CHMP2B (charged multivesicular body protein 2B), which colocalized with the core granule, but less strongly with lysosomal marker cathepsin D.Conclusions-The resultant immunohistochemical signature suggests that GVD bodies contain late-stage autophagic markers, and accumulate at the nexus of autophagic and endocytic pathways. . The data further suggest that failure to complete autolysosome formation may be an important correlate of GVD body accumulation.

Neurotropic RNA viruses continue to emerge and are increasingly linked to diseases of the central nervous system (CNS) despite viral clearance. Indeed, the overall mortality of viral encephalitis in immunocompetent individuals is low, suggesting efficient mechanisms of virologic control within the CNS. Both immune and neural cells participate in this process, which requires extensive innate immune signaling between resident and infiltrating cells, including microglia and monocytes, that regulate the effector functions of antiviral T and B cells as they gain access to CNS compartments. While these interactions promote viral clearance via mainly neuroprotective mechanisms, they may also promote neuropathology and, in some cases, induce persistent alterations in CNS physiology and function that manifest as neurologic and psychiatric diseases. This review discusses mechanisms of RNA virus clearance and neurotoxicity during viral encephalitis with a focus on the cytokines essential for immune and neural cell inflammatory responses and interactions. Understanding neuroimmune communications in the setting of viral infections is essential for the development of treatments that augment neuroprotective processes while limiting ongoing immunopathological processes that cause ongoing CNS disease.

Hypothesis: Although the risks for operating room distractions and interruptions (ORDIs) are acknowledged, most research on this topic is unrealistic, inconclusive, or methodologically unsound. We hypothesized that realistic ORDIs induce errors in a simulated surgical procedure performed by novice surgeons. Design, Setting, and Participants: Eighteen secondyear, third-year, and research-year surgical residents completed a within-subjects experiment on a laparoscopic virtual reality simulator. Based on 9 months of operating room observations, 4 distractions and 2 interruptions were designed and timed to occur during critical stages in simulated laparoscopic cholecystectomy. The control factor was the absence or presence of ORDIs, with order randomly counterbalanced across the subjects. Main Outcome Measures: The primary outcome measure was surgical errors measured by the simulator as damage to arteries, bile duct, or other organs. The second outcome measure was whether the participants remembered a prospective memory task assigned prior to the procedure and important to operative conduct. Results: Major surgical errors were committed in 8 of 18 simulated procedures (44%) with ORDIs vs only 1 of 18 (6%) without ORDIs (P = .02). Interrupting questions caused the most errors. Sidebar conversations were the next most likely distraction to lead to errors. Ten of 18 participants (56%) forgot the prospective memory task with ORDIs, while 4 of 18 (22%) forgot the task without ORDI (P =.04). All 8 surgical errors with ORDIs occurred after 1 PM (P =.001). Conclusions: Typical ORDIs have the potential to cause operative errors in surgical trainees. This performance deficit was prevalent in the afternoon.

Background: Vaccination against Tau reduces pathology in vivo; however, the mechanism of action remains unclear. Results: Antibodies promote uptake of Tau fibrils in microglia or block uptake in neurons in a size-and epitope-dependent manner. Conclusion: Antibodies have multiple potential mechanisms. Significance: Establishing specific mechanisms of antibody activity may help in design and optimization of more effective agents.