Regulation of glial activation and neuroinflammation are critical factors in the pathogenesis of Alzheimer’s disease (AD). YKL-40, a primarily astrocytic protein encoded by the gene Chi3l1, is a widely studied cerebrospinal fluid biomarker that increases with aging and early in AD. However, the function of Chi3l1/YKL-40 in AD is unknown. In a cohort of patients with AD, we observed that a variant in the human CHI3L1 gene, which results in decreased CSF YKL-40 expression, was associated with slower AD progression. At baseline, Chi3l1 deletion in mice had no effect on astrocyte activation while modestly promoting microglial activation. In a mouse APP/PS1 model of AD, Chi3l1 deletion decreased amyloid plaque burden and increased periplaque expression of the microglial lysosomal marker CD68, suggesting that Chi3l1 may suppress glial phagocytic activation and promote amyloid accumulation. Accordingly, Chi3l1 knockdown increased phagocytosis of zymosan particles and of β-amyloid peptide in both astrocytes and microglia in vitro. We further observed that expression of Chi3l1 is regulated by the circadian clock, as deletion of the core clock proteins BMAL1 or CLOCK/NPAS2 strongly suppresses basal Chi3l1 expression, whereas deletion of the negative clock regulators PER1/PER2 increased Chi3l1 expression. Basal Chi3l1 mRNA was nonrhythmic because of a long mRNA half-life in astrocytes. However, inflammatory induction of Chi3l1 was gated by the clock. Our findings reveal Chi3l1/YKL-40 as a modulator of glial phagocytic activation and AD pathogenesis in both mice and humans and suggest that the astrocyte circadian clock regulates inflammatory Chi3l1 induction.

Despite producing enormous amounts of cytoplasmic DNA, poxviruses continue to replicate efficiently by deploying an armory of proteins that counter host antiviral responses at multiple levels. Among these, poxvirus protein F17 dysregulates the host kinase mammalian target of rapamycin (mTOR) to prevent the activation of stimulator of interferon genes (STING) expression and impair the production of interferon-stimulated genes (ISGs). However, the host DNA sensor(s) involved and their impact on infection in the absence of F17 remain unknown. Here, we show that cyclic-di-GMP-AMP (cGAMP) synthase (cGAS) is the primary sensor that mediates interferon response factor (IRF) activation and ISG responses to vaccinia virus lacking F17 in both macrophages and lung fibroblasts, although additional sensors also operate in the latter cell type. Despite this, ablation of ISG responses through cGAS or STING knockout did not rescue defects in late-viral-protein production, and the experimental data pointed to other functions of mTOR in this regard. mTOR adjusts both autophagic and protein-synthetic processes to cellular demands. No significant differences in autophagic responses to wild-type or F17 mutant viruses could be detected, with autophagic activity differing across cell types or states and exhibiting no correlations with defects in viral-protein accumulation. In contrast, results using transformed cells or altered growth conditions suggested that late-stage defects in protein accumulation reflect failure of the F17 mutant to deregulate mTOR and stimulate protein production. Finally, rescue approaches suggest that phosphorylation may partition F17’s functions as a structural protein and mTOR regulator. Our findings reveal the complex multifunctionality of F17 during infection. IMPORTANCE Poxviruses are large, double-stranded DNA viruses that replicate entirely in the cytoplasm, an unusual act that activates pathogen sensors and innate antiviral responses. In order to replicate, poxviruses therefore encode a wide range of innate immune antagonists that include F17, a protein that dysregulates the kinase mammalian target of rapamycin (mTOR) to suppress interferon-stimulated gene (ISG) responses. However, the host sensor(s) that detects infection in the absence of F17 and its precise contribution to infection remains unknown. Here, we show that the cytosolic DNA sensor cGAS is primarily responsible for activating ISG responses in biologically relevant cell types infected with a poxvirus that does not express F17. However, in line with their expression of ∼100 proteins that act as immune response and ISG antagonists, while F17 helps suppress cGAS-mediated responses, we find that a critical function of its mTOR dysregulation activity is to enhance poxvirus protein production.

Human Cytomegalovirus (HCMV) is an opportunistic pathogen that causes substantial disease in neonates and immunocompromised individuals. Reverse genetic analysis of the HCMV genome is a powerful tool to dissect the roles that various viral genes play during infection. However, genetic engineering of HCMV is hampered by both the large size of the HCMV genome and HCMV's slow replication cycle. Currently, most laboratories that genetically engineer HCMV employ Bacterial Artificial Chromosome (BAC) mediated recombineering, which is a relatively lengthy process. We explored an alternative method of producing recombinant HCMV using the CRISPR/ Cas9 system. We employed both homologous recombination (HR) and Non-homologous endjoining (NHEJ)-based methods, and find that each approach is capable of efficiently mutating the HCMV genome, with optimal efficiencies of 42% and 81% respectively. Our results suggest that CRISPR-mediated genomic engineering of HCMV is competitive with BAC-mediated recombineering and provide a framework for using CRISPR/Cas9 for mutational analysis of the HCMV genome.

Impaired proteostasis is associated with normal aging and is accelerated in neurodegeneration. This impairment may lead to the accumulation of protein, which can be toxic to cells and tissue. In a subset of frontotemporal lobar degeneration with tau pathology (FTLD-tau) cases, pathogenic mutations in the microtubule-associated protein tau (MAPT) gene are sufficient to cause tau accumulation and neurodegeneration. However, the pathogenic events triggered by the expression of the mutant tau protein remain poorly understood. Here, we show that molecular networks associated with lysosomal biogenesis and autophagic function are disrupted in brains from FTLD-tau patients carrying a MAPT p.R406W mutation. We then used human induced pluripotent stem cell (iPSC)-derived neurons and 3D cerebral organoids from patients carrying the MAPT p.R406W mutation and CRISPR/Cas9, corrected controls to evaluate proteostasis. MAPT p.R406W was sufficient to induce morphological and functional deficits in the lysosomal pathway in iPSC-neurons. These phenotypes were reversed upon correction of the mutant allele with CRISPR/Cas9. Treatment with mTOR inhibitors led to tau degradation specifically in MAPT p.R406W neurons. Together, our findings suggest that MAPT p.R406W is sufficient to cause impaired lysosomal function, which may contribute to disease pathogenesis and serve as a cellular phenotype for drug screening.

No abstract

An emerging role for the circadian clock in autophagy and lysosome function has opened new avenues for exploration in the field of neurodegeneration. The daily rhythms of circadian clock proteins may coordinate gene expression programs involved not only in daily rhythms but in many cellular processes. In the brain, astrocytes are critical for sensing and responding to extracellular cues to support neurons. The core clock protein BMAL1 serves as the primary positive circadian transcriptional regulator and its depletion in astrocytes not only disrupts circadian function but also leads to a unique cell-autonomous activation phenotype. We report here that astrocyte-specific deletion of Bmal1 influences endolysosome function, autophagy, and protein degradation dynamics. In vitro, Bmal1 -deficient astrocytes exhibit increased endocytosis, lysosome-dependent protein cleavage, and accumulation of LAMP1- and RAB7-positive organelles. In vivo, astrocyte-specific Bmal1 knockout (aKO) brains show accumulation of autophagosome-like structures within astrocytes by electron microscopy. Transcriptional analysis of isolated astrocytes from young and aged Bmal1 aKO mice indicates broad dysregulation of pathways involved in lysosome function which occur independently of TFEB activation. Since a clear link has been established between neurodegeneration and endolysosome dysfunction over the course of aging, this work implicates BMAL1 as a key regulator of these crucial astrocyte functions in health and disease.