Induction of tauopathy in a mouse model of amyloidosis using intravenous administration of adeno-associated virus vectors expressing human P301L tau.

INTRODUCTION: Alzheimer's disease (AD) is a progressive neurodegenerative disease in which extracellular aggregates of the amyloid beta (Aß) peptide precede widespread intracellular inclusions of the microtubule-associated protein tau. The autosomal dominant form of AD requires mutations that increase production or aggregation of the Aß peptide. This has led to the hypothesis that amyloid deposition initiates downstream responses that lead to the hyperphosphorylation and aggregation of tau. METHODS: Here we use a novel approach, somatic gene transfer via intravenous adeno-associated virus (AAV), to further explore the effects of pre-existing amyloid deposits on tauopathy. APP+PS1 mice, which develop amyloid deposits at 3 to 6 months of age, and non-transgenic littermates were injected at 8 months of age intravenously with AAV-PHP.eB encoding P301L human tau. Tissue was collected at 13 months and tauopathy was assessed. RESULTS: Total human tau expression was observed to be relatively uniform throughout the brain, reflecting the vascular route of AAV administration. Phospho-tau deposition was not equal across brain regions and significantly increased in APP+PS1 mice compared to non-transgenic controls. Interestingly, the rank order of phospho-tau deposition of affected brain regions in both genotypes paralleled the rank order of amyloid plaque deposits in APP+PS1 mice. We also observed significantly increased MAPT RNA expression in APP+PS1 mice compared to non-transgenic despite equal AAV transduction efficiency between groups. DISCUSSION: This model has advantages over prior approaches with widespread uniform human tau expression throughout the brain and the ability to specify the stage of amyloidosis when the tau pathology is initiated. These data add further support to the amyloid cascade hypothesis and suggest RNA metabolism as a potential mechanism for amyloid-induced tauopathy.

Influence of Host Age on Intracranial AAV9 TauP301L Induced Tauopathy.

BACKGROUND: Advanced age is the greatest risk factor for the development of Alzheimer's disease (AD). This implies that some aspect of the aged milieu is possibly accelerating the development of AD related pathologies. OBJECTIVE: We hypothesized that intracranially injected with AAV9 tauP301L may cause a greater degree of pathology in old versus young mice. METHODS: Animals were injected with viral vectors overexpressing the mutant tauP301L or control protein (green fluorescent protein, GFP) into the brains of mature, middle-aged, and old C57BL/6Nia mice. The tauopathy phenotype was monitored four months after injection using behavioral, histological, and neurochemical measures. RESULTS: Phosphorylated-tau immunostaining (AT8) or Gallyas staining of aggregated tau increased with age, but other measures of tau accumulation were not significantly affected. Overall, AAV-tau injected mice had impaired radial arm water maze performance, increased microglial activation, and showed evidence of hippocampal atrophy. Aging impaired open field and rotarod performance in both AAV-tau and control mice. The efficiency of viral transduction and gene expression were the same at all animal ages. CONCLUSION: We conclude that tauP301L over expression results in a tauopathy phenotype with memory impairment and accumulation of aggregated tau. However, the effects of aging on this phenotype are modest and not detected by some markers of tau accumulation, similar to prior work on this topic. Thus, although age does influence the development of tauopathy, it is likely that other factors, such as ability to compensate for tau pathology, are more responsible for the increased risk of AD with advanced age.

Neural atrophy produced by AAV tau injections into hippocampus and anterior cortex of middle-aged mice.

Animal models of tauopathy help in understanding the role of mutations in tau pathobiology. Here, we used adeno-associated viral (AAV) vectors to administer three tau genetic variants (tauwild-type, tauP301L, and tauR406W) intracranially into 12-month-old C57BL/6Nia mice and collected tissue at 16 months. Vectors designed to express green fluorescent protein controlled for surgical procedures and exogenous protein expression by AAV. The tau genetic variants produced considerably different phenotypes. Tauwild-type and tauP301L caused memory impairments. The tauP301L caused increased amounts of aggregated tau, measured both neurochemically and histologically. Tauwild-type produced elevated levels of soluble tau and phosphorylated tau by ELISA and increased staining for phosphorylated forms of tau histologically. However, only the tauwild-type caused localized atrophy of brain tissue at the sites near the injection. The tauR406W had low protein expression and produced no atrophy or memory impairments. This supports the potential use of AAV expressing tauwild-type in aged mice to examine events leading to neurodegeneration in Alzheimer's disease pathology.

Baseline Clinical and Blood Biomarkers in Patients With Preataxic and Early-Stage Disease Spinocerebellar Ataxia 1 and 3.

BACKGROUND AND OBJECTIVES: In spinocerebellar ataxia, ataxia onset can be preceded by mild clinical manifestation, cerebellar and/or brainstem alterations, or biomarker modifications. READISCA is a prospective, longitudinal observational study of patients with spinocerebellar ataxia type 1 (SCA1) and 3 (SCA3) to provide essential markers for therapeutic interventions. We looked for clinical, imaging, or biological markers that are present at an early stage of the disease. METHODS: We enrolled carriers of a pathologic ATXN1 or ATXN3 expansion and controls from 18 US and 2 European ataxia referral centers. Clinical, cognitive, quantitative motor, neuropsychological measures and plasma neurofilament light chain (NfL) measurements were compared between expansion carriers with and without ataxia and controls. RESULTS: We enrolled 200 participants: 45 carriers of a pathologic ATXN1 expansion (31 patients with ataxia [median Scale for the Assessment and Rating of Ataxia: 9; 7-10] and 14 expansion carriers without ataxia [1; 0-2]) and 116 carriers of a pathologic ATXN3 expansion (80 patients with ataxia [7; 6-9] and 36 expansion carriers without ataxia [1; 0-2]). In addition, we enrolled 39 controls who did not carry a pathologic expansion in ATXN1 or ATXN3. Plasma NfL levels were significantly higher in expansion carriers without ataxia than controls, despite similar mean age (controls: 5.7 pg/mL, SCA1: 18.0 pg/mL [p < 0.0001], SCA3: 19.8 pg/mL [p < 0.0001]). Expansion carriers without ataxia differed from controls by significantly more upper motor signs (SCA1 p = 0.0003, SCA3 p = 0.003) and by the presence of sensor impairment and diplopia in SCA3 (p = 0.0448 and 0.0445, respectively). Functional scales, fatigue and depression scores, swallowing difficulties, and cognitive impairment were worse in expansion carriers with ataxia than those without ataxia. Ataxic SCA3 participants showed extrapyramidal signs, urinary dysfunction, and lower motor neuron signs significantly more often than expansion carriers without ataxia. DISCUSSION: READISCA showed the feasibility of harmonized data acquisition in a multinational network. NfL alterations, early sensory ataxia, and corticospinal signs were quantifiable between preataxic participants and controls. Patients with ataxia differed in many parameters from controls and expansion carriers without ataxia, with a graded increase of abnormal measures from control to preataxic to ataxic cohorts. TRIAL REGISTRATION INFORMATION: ClinicalTrials.gov NCT03487367.

Glucosylation Drives the Innate Inflammatory Response to Clostridium difficile Toxin A.

Clostridium difficile is a major, life-threatening hospital-acquired pathogen that causes mild to severe colitis in infected individuals. The tissue destruction and inflammation which characterize C. difficile infection (CDI) are primarily due to the Rho-glucosylating toxins A and B. These toxins cause epithelial cell death and induce robust inflammatory signaling by activating the transcription factor NF-κB, leading to chemokine and cytokine secretion. The toxins also activate the inflammasome complex, which leads to secretion of the pyrogenic cytokine IL-1ß. In this study, we utilized glucosylation-deficient toxin A to show that activation of the inflammasome by this toxin is dependent on Rho glucosylation, confirming similar findings reported for toxin B. We also demonstrated that tissue destruction and in vivo inflammatory cytokine production are critically dependent on the enzymatic activity of toxin A, suggesting that inhibiting toxin glucosyltransferase activity may be effective in combating this refractory disease.