Persistence and Sexual Dimorphism of Gut Dysbiosis and Pathobiome after Sepsis and Trauma.

OBJECTIVE: To evaluate the persistence of intestinal microbiome dysbiosis and gut-plasma metabolomic perturbations following severe trauma or sepsis weeks after admission in patients experiencing chronic critical illness (CCI). SUMMARY: Trauma and sepsis can lead to gut dysbiosis and alterations in the plasma and fecal metabolome. However, the impact of these perturbations and correlations between gut dysbiosis and the plasma metabolome in chronic critical illness have not been studied. METHODS: A prospective observational cohort study was performed with healthy subjects, severe trauma patients, patients with sepsis residing in an intensive care unit (ICU) for 2-3 weeks. A high-throughput multi-omics approach was utilized to evaluate the gut microbial and gut-plasma metabolite responses in critically ill trauma and sepsis patients 14-21 days after ICU admission. RESULTS: Patients in the sepsis and trauma cohorts demonstrated strikingly depleted gut microbiome diversity, with significant alterations and specific pathobiome patterns in the microbiota composition compared to healthy subjects. Further subgroup analyses based on sex revealed resistance to changes in microbiome diversity among female trauma patients compared to healthy counterparts. Sex-specific changes in fecal metabolites were also observed after trauma and sepsis, while plasma metabolite changes were similar in both males and females. CONCLUSIONS: Dysbiosis induced by trauma and sepsis persists up to 14-21 days after onset and is sex-specific, underscoring the implication of pathobiome and entero-septic microbial-metabolite perturbations in post-sepsis and post-trauma CCI. This indicates resilience to infection or injury in females' microbiome and should inform and facilitate future precision/personalized medicine strategies in the intensive care unit.

Gut mycobiome dysbiosis after sepsis and trauma.

BACKGROUND: Sepsis and trauma are known to disrupt gut bacterial microbiome communities, but the impacts and perturbations in the fungal (mycobiome) community after severe infection or injury, particularly in patients experiencing chronic critical illness (CCI), remain unstudied. METHODS: We assess persistence of the gut mycobiome perturbation (dysbiosis) in patients experiencing CCI following sepsis or trauma for up to two-to-three weeks after intensive care unit hospitalization. RESULTS: We show that the dysbiotic mycobiome arrays shift toward a pathobiome state, which is more susceptible to infection, in CCI patients compared to age-matched healthy subjects. The fungal community in CCI patients is largely dominated by Candida spp; while, the commensal fungal species are depleted. Additionally, these myco-pathobiome arrays correlate with alterations in micro-ecological niche involving specific gut bacteria and gut-blood metabolites. CONCLUSIONS: The findings reveal the persistence of mycobiome dysbiosis in both sepsis and trauma settings, even up to two weeks post-sepsis and trauma, highlighting the need to assess and address the increased risk of fungal infections in CCI patients.

Sex, sepsis and the brain: defining the role of sexual dimorphism on neurocognitive outcomes after infection.

Sexual dimorphisms exist in multiple domains, from learning and memory to neurocognitive disease, and even in the immune system. Male sex has been associated with increased susceptibility to infection, as well as increased risk of adverse outcomes. Sepsis remains a major source of morbidity and mortality globally, and over half of septic patients admitted to intensive care are believed to suffer some degree of sepsis-associated encephalopathy (SAE). In the short term, SAE is associated with an increased risk of in-hospital mortality, and in the long term, has the potential for significant impairment of cognition, memory, and acceleration of neurocognitive disease. Despite increasing information regarding sexual dimorphism in neurologic and immunologic systems, research into these dimorphisms in sepsis-associated encephalopathy remains critically understudied. In this narrative review, we discuss how sex has been associated with brain morphology, chemistry, and disease, sexual dimorphism in immunity, and existing research into the effects of sex on SAE.

Metformin inhibits RAN translation through PKR pathway and mitigates disease in C9orf72 ALS/FTD mice.

Repeat associated non-AUG (RAN) translation is found in a growing number of microsatellite expansion diseases, but the mechanisms remain unclear. We show that RAN translation is highly regulated by the double-stranded RNA-dependent protein kinase (PKR). In cells, structured CAG, CCUG, CAGG, and G4C2 expansion RNAs activate PKR, which leads to increased levels of multiple RAN proteins. Blocking PKR using PKR-K296R, the TAR RNA binding protein or PKR-KO cells, reduces RAN protein levels. p-PKR is elevated in C9orf72 ALS/FTD human and mouse brains, and inhibiting PKR in C9orf72 BAC transgenic mice using AAV-PKR-K296R or the Food and Drug Administration (FDA)-approved drug metformin, decreases RAN proteins, and improves behavior and pathology. In summary, targeting PKR, including by use of metformin, is a promising therapeutic approach for C9orf72 ALS/FTD and other expansion diseases.

Combinatorial model of amyloid ß and tau reveals synergy between amyloid deposits and tangle formation.

AIMS: To illuminate the pathological synergy between Aß and tau leading to emergence of neurofibrillary tangles (NFT) in Alzheimer's disease (AD), here, we have performed a comparative neuropathological study utilising three distinctive variants of human tau (WT tau, P301L mutant tau and S320F mutant tau). Previously, in non-transgenic mice, we showed that WT tau or P301L tau does not form NFT while S320F tau can spontaneously aggregate into NFT, allowing us to test the selective vulnerability of these different tau conformations to the presence of Aß plaques. METHODS: We injected recombinant AAV-tau constructs into neonatal APP transgenic TgCRND8 mice or into 3-month-old TgCRND8 mice; both cohorts were aged 3 months post injection. This allowed us to test how different tau variants synergise with soluble forms of Aß (pre-deposit cohort) or with frank Aß deposits (post-deposit cohort). RESULTS: Expression of WT tau did not produce NFT or altered Aß in either cohort. In the pre-deposit cohort, S320F tau induced Aß plaque deposition, neuroinflammation and synaptic abnormalities, suggesting that early tau tangles affect the amyloid cascade. In the post-deposit cohort, contemporaneous expression of S320F tau did not exacerbate amyloid pathology, showing a dichotomy in Aß-tau synergy based on the nature of Aß. P301L tau produced NFT-type inclusions in the post-deposit cohort, but not in the pre-deposit cohort, indicating pathological synergy with pre-existing Aß deposits. CONCLUSIONS: Our data show that different tau mutations representing specific folding variants of tau synergise with Aß to different extents, depending on the presence of cerebral deposits.

MhcII Regulates Transmission of α-Synuclein-Seeded Pathology in Mice.

MHCII molecules, expressed by professional antigen-presenting cells (APCs) such as T cells and B cells, are hypothesized to play a key role in the response of cellular immunity to α-synuclein (α-syn). However, the role of cellular immunity in the neuroanatomic transmission of α-syn pre-formed fibrillar (PFF) seeds is undetermined. To illuminate whether cellular immunity influences the transmission of α-syn seeds from the periphery into the CNS, we injected preformed α-syn PFFs in the hindlimb of the Line M83 transgenic mouse model of synucleinopathy lacking MhcII. We showed that a complete deficiency in MhcII accelerated the appearance of seeded α-syn pathology and shortened the lifespan of the PFF-seeded M83 mice. To characterize whether B-cell and T-cell inherent MhcII function underlies this accelerated response to PFF seeding, we next injected α-syn PFFs in Rag1-/- mice which completely lacked these mature lymphocytes. There was no alteration in the lifespan or burden of endstage α-syn pathology in the PFF-seeded, Rag1-deficient M83+/- mice. Together, these results suggested that MhcII function on immune cells other than these classical APCs is potentially involved in the propagation of α-syn in this model of experimental synucleinopathy. We focused on microglia next, finding that while microglial burden was significantly upregulated in PFF-seeded, MhcII-deficient mice relative to controls, the microglial activation marker Cd68 was reduced in these mice, suggesting that these microglia were not responsive. Additional analysis of the CNS showed the early appearance of the neurotoxic astrocyte A1 signature and the induction of the Ifnγ-inducible anti-viral response mediated by MhcI in the MhcII-deficient, PFF-seeded mice. Overall, our data suggest that the loss of MhcII function leads to a dysfunctional response in non-classical APCs and that this response could potentially play a role in determining PFF-induced pathology. Collectively, our results identify the critical role of MhcII function in synucleinopathies induced by α-syn prion seeds.

α-Synuclein Induces Progressive Changes in Brain Microstructure and Sensory-Evoked Brain Function That Precedes Locomotor Decline.

In vivo functional and structural brain imaging of synucleinopathies in humans have provided a rich new understanding of the affected networks across the cortex and subcortex. Despite this progress, the temporal relationship between α-synuclein (α-syn) pathology and the functional and structural changes occurring in the brain is not well understood. Here, we examine the temporal relationship between locomotor ability, brain microstructure, functional brain activity, and α-syn pathology by longitudinally conducting rotarod, diffusion magnetic resonance imaging (MRI), resting-state functional MRI (fMRI), and sensory-evoked fMRI on 20 mice injected with α-syn fibrils and 20 PBS-injected mice at three timepoints (10 males and 10 females per group). Intramuscular injection of α-syn fibrils in the hindlimb of M83+/- mice leads to progressive α-syn pathology along the spinal cord, brainstem, and midbrain by 16 weeks post-injection. Our results suggest that peripheral injection of α-syn has acute systemic effects on the central nervous system such that structural and resting-state functional activity changes occur in the brain by four weeks post-injection, well before α-syn pathology reaches the brain. At 12 weeks post-injection, a separate and distinct pattern of structural and sensory-evoked functional brain activity changes was observed that are co-localized with previously reported regions of α-syn pathology and immune activation. Microstructural changes in the pons at 12 weeks post-injection were found to predict survival time and preceded measurable locomotor deficits. This study provides preliminary evidence for diffusion and fMRI markers linked to the progression of synuclein pathology and has translational importance for understanding synucleinopathies in humans.SIGNIFICANCE STATEMENT α-Synuclein (α-syn) pathology plays a critical role in neurodegenerative diseases such as Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. The longitudinal effects of α-syn pathology on locomotion, brain microstructure, and functional brain activity are not well understood. Using high field imaging, we show preliminary evidence that peripheral injection of α-syn fibrils induces unique patterns of functional and structural changes that occur at different temporal stages of α-syn pathology progression. Our results challenge existing assumptions that α-syn pathology must precede changes in brain structure and function. Additionally, we show preliminary evidence that diffusion and functional magnetic resonance imaging (fMRI) are capable of resolving such changes and thus should be explored further as markers of disease progression.

Combining P301L and S320F tau variants produces a novel accelerated model of tauopathy.

Understanding the biological functions of tau variants can illuminate differential etiologies of Alzheimer's disease (AD) and primary tauopathies. Though the end-stage neuropathological attributes of AD and primary tauopathies are similar, the etiology and behavioral outcomes of these diseases follow unique and divergent trajectories. To study the divergent physiological properties of tau variants on a uniform immunogenetic background, we created somatic transgenesis CNS models of tauopathy utilizing neonatal delivery of adeno-associated viruses expressing wild-type (WT) or mutant tau in non-transgenic mice. We selected four different tau variants-WT tau associated with AD, P301L mutant tau associated with frontotemporal dementia (FTD), S320F mutant tau associated with Pick's disease and a combinatorial approach using P301L/S320F mutant tau. CNS-targeted expression of WT and P301L mutant tau results in robust tau hyperphosphorylation without tangle pathology, gradually developing age-progressive memory deficits. In contrast, the S320F variant, especially in combination with P301L, produces an AD-type tangle pathology, focal neuroinflammation and memory impairment on an accelerated time scale. Using the doubly mutated P301L/S320F tau variant, we demonstrate that combining different mutations can have an additive effect on neuropathologies and associated co-morbidities, possibly hinting at involvement of unique functional pathways. Importantly, we also show that overexpression of wild-type tau as well as an FTD-associated tau variant can lead to cognitive deficits even in the absence of tangles. Together, our data highlights the synergistic neuropathologies and associated cognitive and synaptic alterations of the combinatorial tau variant leading to a robust model of tauopathy.

A novel tau-based rhesus monkey model of Alzheimer's pathogenesis.

INTRODUCTION: Alzheimer's disease (AD) is a devastating condition with no effective treatments, with promising findings in rodents failing to translate into successful therapies for patients. METHODS: Targeting the vulnerable entorhinal cortex (ERC), rhesus monkeys received two injections of an adeno-associated virus expressing a double tau mutation (AAV-P301L/S320F) in the left hemisphere, and control AAV-green fluorescent protein in the right ERC. Noninjected aged-matched monkeys served as additional controls. RESULTS: Within 3 months we observed evidence of misfolded tau propagation, similar to what is hypothesized to occur in humans. Viral delivery of human 4R-tau also coaptates monkey 3R-tau via permissive templating. Tau spreading is accompanied by robust neuroinflammatory response driven by TREM2+ microglia, with biomarkers of inflammation and neuronal loss in the cerebrospinal fluid and plasma. DISCUSSION: These results highlight the initial stages of tau seeding and propagation in a primate model, a more powerful translational approach for the development of new therapies for AD.

Integrative functional genomic analysis of intron retention in human and mouse brain with Alzheimer's disease.

Intron retention (IR) has been implicated in the pathogenesis of complex diseases such as cancers; its association with Alzheimer's disease (AD) remains unexplored. We performed genome-wide analysis of IR through integrating genetic, transcriptomic, and proteomic data of AD subjects and mouse models from the Accelerating Medicines Partnership-Alzheimer's Disease project. We identified 4535 and 4086 IR events in 2173 human and 1736 mouse genes, respectively. Quantitation of IR enabled the identification of differentially expressed genes that conventional exon-level approaches did not reveal. There were significant correlations of intron expression within innate immune genes, like HMBOX1, with AD in humans. Peptides with a high probability of translation from intron-retained mRNAs were identified using mass spectrometry. Further, we established AD-specific intron expression Quantitative Trait Loci, and identified splicing-related genes that may regulate IR. Our analysis provides a novel resource for the search for new AD biomarkers and pathological mechanisms.

Integrative approach to sporadic Alzheimer's disease: deficiency of TYROBP in a tauopathy mouse model reduces C1q and normalizes clinical phenotype while increasing spread and state of phosphorylation of tau.

TYROBP/DAP12 forms complexes with ectodomains of immune receptors (TREM2, SIRPß1, CR3) associated with Alzheimer's disease (AD) and is a network hub and driver in the complement subnetwork identified by multi-scale gene network studies of postmortem human AD brain. Using transgenic or viral approaches, we characterized in mice the effects of TYROBP deficiency on the phenotypic and pathological evolution of tauopathy. Biomarkers usually associated with worsening clinical phenotype (i.e., hyperphosphorylation and increased tauopathy spreading) were unexpectedly increased in MAPTP301S;Tyrobp-/- mice despite the improved learning behavior and synaptic function relative to controls with normal levels of TYROBP. Notably, levels of complement cascade initiator C1q were reduced in MAPTP301S;Tyrobp-/- mice, consistent with the prediction that C1q reduction exerts a neuroprotective effect. These observations suggest a model wherein TYROBP-KO-(knock-out)-associated reduction in C1q is associated with normalized learning behavior and electrophysiological properties in tauopathy model mice despite a paradoxical evolution of biomarker signatures usually associated with neurological decline.

Distinct differences in prion-like seeding and aggregation between Tau protein variants provide mechanistic insights into tauopathies.

The accumulation of aberrantly aggregated MAPT (microtubule-associated protein Tau) defines a spectrum of tauopathies, including Alzheimer's disease. Mutations in the MAPT gene cause frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17), characterized by neuronal pathological Tau inclusions in the form of neurofibrillary tangles and Pick bodies and in some cases glial Tau pathology. Increasing evidence points to the importance of prion-like seeding as a mechanism for the pathological spread in tauopathy and other neurodegenerative diseases. Herein, using a cell culture model, we examined a multitude of genetic FTDP-17 Tau variants for their ability to be seeded by exogenous Tau fibrils. Our findings revealed stark differences between FTDP-17 Tau variants in their ability to be seeded, with variants at Pro301 and Ser320 showing robust aggregation with seeding. Similarly, we elucidated the importance of certain Tau protein regions and unique residues, including the role of Pro301 in inhibiting Tau aggregation. We also revealed potential barriers in cross-seeding between three-repeat and four-repeat Tau isoforms. Overall, these differences alluded to potential mechanistic differences between wildtype and FTDP-17 Tau variants, as well as different Tau isoforms, in influencing Tau aggregation. Furthermore, by combining two FTDP-17 Tau variants (either P301L or P301S with S320F), we generated aggressive models of tauopathy that do not require exogenous seeding. These models will allow for rapid screening of potential therapeutics to alleviate Tau aggregation without the need for exogenous Tau fibrils. Together, these studies provide novel insights in the molecular determinants that modulate Tau aggregation.

Neurite orientation dispersion and density imaging reveals white matter and hippocampal microstructure changes produced by Interleukin-6 in the TgCRND8 mouse model of amyloidosis.

Extracellular ß-amyloid (Aß) plaque deposits and inflammatory immune activation are thought to alter various aspects of tissue microstructure, such as extracellular free water, fractional anisotropy and diffusivity, as well as the density and geometric arrangement of axonal processes. Quantifying these microstructural changes in Alzheimer's disease and related neurodegenerative dementias could serve to monitor or predict disease course. In the present study we used high-field diffusion magnetic resonance imaging (dMRI) to investigate the effects of Aß and inflammatory interleukin-6 (IL6), alone or in combination, on in vivo tissue microstructure in the TgCRND8 mouse model of Alzheimer's-type Aß deposition. TgCRND8 and non-transgenic (nTg) mice expressing brain-targeted IL6 or enhanced glial fibrillary protein (EGFP controls) were scanned at 8 months of age using a 2-shell, 54-gradient direction dMRI sequence at 11.1 T. Images were processed using the diffusion tensor imaging (DTI) model or the neurite orientation dispersion and density imaging (NODDI) model. DTI and NODDI processing in TgCRND8 mice revealed a microstructure pattern in white matter (WM) and hippocampus consistent with radial and longitudinal diffusivity deficits along with an increase in density and geometric complexity of axonal and dendritic processes. This included reduced FA, mean, axial and radial diffusivity, and increased orientation dispersion (ODI) and intracellular volume fraction (ICVF) measured in WM and hippocampus. IL6 produced a 'protective-like' effect on WM FA in TgCRND8 mice, observed as an increased FA that counteracted a reduction in FA observed with endogenous Aß production and accumulation. In addition, we found that ICVF and ODI had an inverse relationship with the functional connectome clustering coefficient. The relationship between NODDI and graph theory metrics suggests that currently unknown microstructure alterations in WM and hippocampus are associated with diminished functional network organization in the brain.

α-Synuclein and astrocytes: tracing the pathways from homeostasis to neurodegeneration in Lewy body disease.

α-Synuclein is a soluble protein that is present in abundance in the brain, though its normal function in the healthy brain is poorly defined. Intraneuronal inclusions of α-synuclein, commonly referred to as Lewy pathology, are pathological hallmarks of a spectrum of neurodegenerative disorders referred to as α-synucleinopathies. Though α-synuclein is expressed predominantly in neurons, α-synuclein aggregates in astrocytes are a common feature in these neurodegenerative diseases. How and why α-synuclein ends up in the astrocytes and the consequences of this dysfunctional proteostasis in immune cells is a major area of research that can have far-reaching implications for future immunobiotherapies in α-synucleinopathies. Accumulation of aggregated α-synuclein can disrupt astrocyte function in general and, more importantly, can contribute to neurodegeneration in α-synucleinopathies through various pathways. Here, we summarize our current knowledge on how astrocytic α-synucleinopathy affects CNS function in health and disease and propose a model of neuroglial connectome altered by α-synuclein proteostasis that might be amenable to immune-based therapies.

Ifngr1 and Stat1 mediated canonical Ifn-γ signaling drives nigrostriatal degeneration.

Brain expression of AAV-Ifn-γ leads to reactive gliosis, nigrostriatal degeneration and midbrain calcification in wild type mice. This mouse model phenocopies idiopathic basal ganglia calcification which is associated with Parkinsonian symptoms. To understand how the nigro-striatal pathway is selectively vulnerable to Ifn-γ, we determined if the phenotype is driven by canonical signaling intermediates, Ifngr1 and Stat1. Using focused bioinformatic analysis and rotarod testing, we show that neuroinflammation and motor abnormalities precede the appearance of midbrain neuropathologies in the brains of Ifn-γ mouse model. To test whether canonical Ifn-γ signaling is a key driver of progressive nigrostriatal degeneration, we overexpressed Ifn-γ in the brains of Ifngr1-/- and Stat1-/- mice. Expression of Ifn-γ in Ifngr1-/- mice did not result in any neuroinflammation, midbrain calcinosis or nigrostriatal degenerative pathology. Interestingly, in Stat1-/- mice, Ifn-γ expression resulted in gliosis without recapitulating the neurodegenerative phenotype. Overall, our data shows that canonical Ifn-γ signaling triggers midbrain calcinosis and nigrostriatal neurodegeneration, providing mechanistic insights into cytokine-driven selective neuronal vulnerability. Our study establishes the broader relevance of inflammatory signaling in neurodegenerative diseases and can potentially identify novel immunological targets for Parkinsonian syndromes.

Motor neuron loss and neuroinflammation in a model of α-synuclein-induced neurodegeneration.

Mechanisms underlying α-synuclein (αSyn) mediated neurodegeneration are poorly understood. Intramuscular (IM) injection of αSyn fibrils in human A53T transgenic M83+/- mice produce a rapid model of α-synucleinopathy with highly predictable onset of motor impairment. Using varying doses of αSyn seeds, we show that αSyn-induced phenotype is largely dose-independent. We utilized the synchrony of this IM model to explore the temporal sequence of αSyn pathology, neurodegeneration and neuroinflammation. Longitudinal tracking showed that while motor neuron death and αSyn pathology occur within 2 months post IM, astrogliosis appears at a later timepoint, implying neuroinflammation is a consequence, rather than a trigger, in this prionoid model of synucleinopathy. Initiating at 3 months post IM, immune activation dominates the pathologic landscape in terminal IM-seeded M83+/- mice, as revealed by unbiased transcriptomic analyses. Our findings provide insights into the role of neuroinflammation in αSyn mediated proteostasis and neurodegeneration, which will be key in designing potential therapies.

Combination of Aß Suppression and Innate Immune Activation in the Brain Significantly Attenuates Amyloid Plaque Deposition.

Anti-Aß clinical trials are currently under way to determine whether preventing amyloid deposition will be beneficial in arresting progression of Alzheimer disease. Both clinical and preclinical studies suggest that antiamyloid strategies are only effective if started at early stages of the disease process in a primary prevention strategy. Because this approach will be difficult to deploy, strategies for secondary prevention aimed at later stages of disease are also needed. In this study, we asked whether combining innate immune activation in the brain with concurrent Aß suppression could enhance plaque clearance and could improve pathologic outcomes in mice with moderate amyloid pathologic disorder. Starting at 5 months of age, tet-off amyloid precursor protein transgenic mice were treated with doxycycline (dox) to suppress further amyloid precursor protein/Aß production, and at the same time mice were intracranially injected with adeno-associated virus 1 expressing murine IL-6 (AAV1-mIL-6). Three months later, mice treated with the combination of Aß suppression and AAV1-mIL-6 showed significantly less plaque pathologic disorder than dox or AAV1-mIL-6 only groups. The combination of AAV1-mIL-6 + dox treatment lowered total plaque burden by >60% versus untreated controls. Treatment with either dox or AAV1-mIL-6 alone was less effective than the combination. Our results suggest a synergistic mechanism by which the up-regulation of mIL-6 was able to improve plaque clearance in the setting of Aß suppression.

Conserved brain myelination networks are altered in Alzheimer's and other neurodegenerative diseases.

INTRODUCTION: Comparative transcriptome analyses in Alzheimer's disease (AD) and other neurodegenerative proteinopathies can uncover both shared and distinct disease pathways. METHODS: We analyzed 940 brain transcriptomes including patients with AD, progressive supranuclear palsy (PSP; a primary tauopathy), and control subjects. RESULTS: We identified transcriptional coexpression networks implicated in myelination, which were lower in PSP temporal cortex (TCX) compared with AD. Some of these associations were retained even after adjustments for brain cell population changes. These TCX myelination network structures were preserved in cerebellum but they were not differentially expressed in cerebellum between AD and PSP. Myelination networks were downregulated in both AD and PSP, when compared with control TCX samples. DISCUSSION: Downregulation of myelination networks may underlie both PSP and AD pathophysiology, but may be more pronounced in PSP. These data also highlight conservation of transcriptional networks across brain regions and the influence of cell type changes on these networks.

Proteolysis of α-synuclein fibrils in the lysosomal pathway limits induction of inclusion pathology.

Progression of α-synuclein inclusion pathology may occur through cycles of release and uptake of α-synuclein aggregates, which induce additional intracellular α-synuclein inclusion pathology. This process may explain (i) the presence of α-synuclein inclusion pathology in grafted cells in human brains, and (ii) the slowly progressive nature of most human α-synucleinopathies. It also provides a rationale for therapeutic targeting of extracellular aggregates to limit pathology spread. We investigated the cellular mechanisms underlying intraneuronal α-synuclein aggregation following exposure to exogenous preformed α-synuclein amyloid fibrils. Exogenous α-synuclein fibrils efficiently attached to cell membranes and were subsequently internalized and degraded within the endosomal/lysosomal system. However, internalized α-synuclein amyloid fibrils can apparently overwhelm the endosomal/lysosomal machinery leading to the induction of intraneuronal α-synuclein inclusions comprised of endogenous α-synuclein. Furthermore, the efficiency of inclusion formation was relatively low in these studies compared to studies using primary neuronal-glial cultures over-expressing α-synuclein. Our study indicates that under physiologic conditions, endosomal/lysosomal function acts as an endogenous barrier to the induction of α-synuclein inclusion pathology, but when compromised, it may lower the threshold for pathology induction/transmission. Cover Image for this issue: doi: 10.1111/jnc.13787.

IFN-γ promotes τ phosphorylation without affecting mature tangles.

Inflammatory activation precedes and correlates with accumulating τ lesions in Alzheimer's disease and tauopathies. However, the relationship between neuroinflammation and etiology of pathologic τ remains elusive. To evaluate whether inflammatory signaling may promote or accelerate neurofibrillary tangle pathology, we explored the effect of recombinant adeno-associated virus (rAAV)-mediated overexpression of a master inflammatory cytokine, IFN-γ, on τ phosphorylation. In initial studies in primary neuroglial cultures, rAAV-mediated expression of IFN-γ did not alter endogenous τ production or paired helical filament τ phosphorylation. Next, we tested the effect of rAAV-mediated expression of IFN-γ in the brains of 2 mouse models of tauopathy: JNPL3 and rTg4510. In both models, IFN-γ increased 1) signal transducer and activator of transcription 1 levels and gliosis, and 2) hyperphosphorylation and conformational alterations of soluble τ compared with control cohorts. However, sarkosyl-insoluble phosphorylated τ levels and ubiquitin staining were unaltered in the IFN-γ cohorts. Notably, IFN-γ-induced τ hyperphosphorylation was associated with release of the inhibitory effect of glycogen synthase kinase 3ß function by decreasing Ser9 phosphorylation. Our data suggest that type II IFN signaling can promote τ phosphorylation by modulating cellular kinase activity, though this is insufficient in accelerating neuritic tangle pathology.