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There is need for biomarkers that improve the diagnostic work-up of neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson's disease (PD), which can be used in both clinical practice and trials. In this talk I will focus on recent advances in blood-based biomarkers, and how these can be combined with other easily accessible and low-cost biomarkers to improve detection of early AD. For example, we have recently shown that combining plasma P-tau with brief cognitive tests of memory and executive function can with high accuracy predict future development of AD in patients with subjective cognitive decline or mild cognitive impairment, which outperformed the baseline clinical assessment of dementia experts. Further, I will discuss steps needed to be taken before AD-relevant blood-based biomarkers can be implemented in clinical practice globally. There will also be a discussion on how blood and PET biomarkers can improve clinical trials evaluating disease modifying therapies, when it comes to enrichment of study participants to be included in the trials as well as when measuring relevant effects of the treatments. Finally, I will discuss the potential use of novel seeding aggregation assays for a-synuclein pathology for early detection of Lewy body disease in the context of selecting appropriate participants for clinical trials.

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The intraneuronal or extracellular accumulation of neurotoxic beta-sheet structured amyloids represent key pathological hallmarks of several neurodegenerative disease. While the brain has been considered an immune-privileged organ, increasing evidence suggests that innate immune cells are intimately involved in disease evolution and progression.

Microglia play a pivotal role for this innate immune response and are activated by binding of protein aggregates to pattern recognition receptors. This binding may activate pathways that are involved in phagocytosis and degradation. On the other hand, immune activation of microglia may lead to the release of inflammatory mediators and distracts microglia from their physiological functions and tasks. Microglial distribution of neurotoxic beta-sheet structured cargo may help stressed cells to cope with the inflammatory activation and contribute to the overall successful clearance. Importantly, disease causing mutations and risk polymorphisms for neurodegenerative disease such as Parkinson’s disease and Alzheimer’s disease are being tested for the potential to influence cargo distribution through tunneling nanotubes. Likewise, immune cells help each other by sharing intact mitochondria in order to cover the increased energy demand during an inflammatory challenge. The capability of microglia providing such help to neighboring cells may be key to prevent neurodegeneration.

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ApoE4 is the most prevalent and clinically most important risk factor for late-onset Alzheimer’s disease (AD). Three major ApoE isoforms exist in humans which differ by the presence of a positively charged arginine or a neutral cysteine at residues 112 and 158, respectively. The main biophysical difference between these different ApoE isoforms therefore is their net charge, and disease risk correlates with their isoelectric point (IEP). The higher the IEP, the greater the disease risk. The IEP of ApoE4 closely matches the pH of the early endosomes, which undergo swelling and impaired trafficking upon endocytosis of ApoE4. We showed previously that this trafficking defect can be completely abolished by pharmacologically inhibiting or genetically reducing NHE6, the main proton leak channel specifically in early endosomes. We now show that genetic disruption of NHE6 prevents amyloid accumulation in a humanized APP knocking mouse model, abolishes all functional differences between ApoE isoforms and restores synaptic dysfunction in humanized ApoE4 knockin mice. These findings reveal NHE6 as a novel rational therapeutic target for the prevention of late-onset AD.

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In Alzheimer disease (AD) models, microglia appear to influence amyloid-β (Aβ) linked tau seeding and spreading. We have been studying the effects of microglia, genes expressed by microglia, and genes expressed by microglia and other cells on Aβ-linked tau seeding and spreading. In the context of Aβ depositon, we asked whether microglial removal as well as removal with repopulation decreased Aβ driven tau seeding and spreading. We found that both TREM2 KO and microglial ablation dramatically enhance tau seeding and spreading around plaques. Interestingly, although repopulated microglia clustered around plaques, they had a reduction in disease associated microglia (DAM) gene expression and elevated tau seeding/spreading. Together, these data suggest that TREM2-dependent activation of the DAM phenotype is essential in delaying Aβ-induced pathological tau propagation. We are in the process of determining the role of apoE generally and apoE specifically deposited in plaques on Aβ-induced tau seeding and spreading.

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The rate of progression of Alzheimer disease varies substantially across patients, yet it is uncertain why there are such marked individual differences. We explored the possibility that differences in tau propagation might contribute to this variability, and are also exploring other possible drivers of decline: apoE genotype, vascular pathological co-occurrence, and inflammatory changes.

We measured tau propagation of cortical soluble tau, measured from frozen autopsy material derived from patients who had been followed longitudinally at our Center. We measured bioactivity in an in vitro test, and found increased bioactivity in the individuals who had had a faster rate of progression. These both also correlated with biophysical properties of tau, specific patterns of post translational modifications as assessed by mass spectroscopy (with Dr Judith Steen), and ability to “seed” tau aggregates in a mouse model. We are currently studying the specific post translational modifications and trying to understand both their role in altering propagation kinetics as well as the activation of the enzymes responsible for specific PTMs, and to extend the assays to the hundred fold smaller amounts of bioactive tau present in AD patient lumbar spinal fluid.

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The mechanisms of the cognitive dysfunction caused by vascular factors (vascular cognitive impairment) or neurodegeneration (Alzheimer’s disease, AD) have traditionally been considered distinct, but there is increasing evidence that alterations in cerebral blood vessels play a role both in vascular and neurodegenerative dementias. Indeed, amyloid-beta and tau, major pathogenic factors in AD, have profound cerebrovascular effects. While the cerebrovascular effects of amyloid-beta are well described, recent data indicate that also tau has a profound impact on neurovascular regulation. However, the cerebrovascular dysfunction of tau is mechanistically distinct from that of amyloid beta. In mouse models of tau accumulation tau suppresses the increase in cerebral blood flow produced by neural activity in the somatosensory cortex but, at variance with amyloid-beta, does not impair the ability of cerebral endothelial cells to regulate blood flow. The mechanisms of the effect involve tau-mediated uncoupling of neuronal nitric oxide from NMDA receptors, leading to suppression of glutamate-dependent nitric oxide production, which, in turn, dampens the increase in blood flow produced by synaptic activity. The deficit of neuronal nitric oxide also leads to interneuron network dysfunction and increased neuronal excitability. These finding indicate that both tau and amyloid-beta target the cerebral microvasculature through mechanistically distinct pathogenic processes. The resulting vascular dysfunction may cooperate with amyloid-beta and tau-induced synaptic dysfunction and contribute to cognitive impairment. In the absence of mechanism-based approaches to counteract dementia, targeting cerebrovascular function may offer the opportunity to mitigate the public health impact of one of the most disabling human afflictions.

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A number of disease-modifying therapies (DMT) for Alzheimer’s disease (AD) are being tested in clinical trials, whereas those conducted in the dementia stages have largely failed, underscoring the necessity of early intervention. Notably, positive outcomes of recent anti-amyloid-β trials have been made possible by molecular imaging and fluid biomarkers, underscoring the needs of biomarkers that surrogate the clinical and pathophysiological progression of AD. Longitudinal observational studies as represented by AD Neuroimaging Initiative (ADNI) in the North America and the Japanese ADNI have contributed greatly towards the goal of very early treatment at the prodromal and preclinical AD stages by delineating the early natural course of AD and facilitating the development of biomarkers. Furthermore, secondary prevention trials on the preclinical, i.e., asymptomatic, stage of AD are highlighted as the future direction of development of AD DMTs. To overcome the difficulties in recruiting and correctly characterizing the preclinical AD candidates, establishing trial ready cohorts (TRC) of preclinical and prodromal AD is an effective approach. We have started J-TRC comprised of a webstudy for on-line registration and screening, followed by the on-site study to characterize the elderly volunteers by in-person visits conducting psychometry, amyloid PET and blood biomarkers. J-TRC webstudy so far recruited ~6900 web registrations, and the J-TRC onsite study screened ~250 volunteers and enrolled ~60 participants with intermediate to positive amyloid levels. These clinical activities, accelerated by the development and implementation of biomarkers, will pave the way toward the successful development of AD DMTs targeting its very early stages.

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Aims: In 2018 a workgroup commissioned by the National Institute on Aging and Alzheimer’s Association (NIA-AA) published a research framework in which Alzheimer’s disease (AD) is defined by the underlying pathologic processes rather than by the presence of an etiologically non-specific syndrome or syndromes. This shifts the definition of AD from a syndromal to a biological construct.

Methods: The research framework addresses both diagnosis (definition) and staging of AD. Biomarker and cognitive staging are performed independently from each other. AD can be documented by post-mortem examination or in vivo by biomarkers. Biomarkers are grouped into those of β-amyloid deposition, pathologic tau, and neurodegeneration (AT(N). Both imaging and biofluid (CSF and plasma) biomarkers exist within each AT(N) group.

Results: Since publication of the research framework, significant advances have occurred in development of plasma AT(N) biomarkers. Both plasma Ab42/40, particularly mass spec methods, and pTau perform well diagnostically against clinical, PET, CSF or autopsy standards. Most of these data, however, were generated from highly selected samples.

Conclusions: Due to advances in plasma biomarkers, widespread application of a biological definition of AD and AT(N) biomarker phenotyping now seems possible. This has significant implications for design of clinical trials, observational research, and clinical care. However, many unanswered questions exist concerning the appropriate roles and the interplay between traditional expensive or invasive AD biomarkers (CSF and imaging) and newer plasma biomarkers. In particular, it is less clear how well plasma biomarkers perform at the earliest, most subtle stages of disease progression, and in community settings.

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Current theories of Alzheimer’s disease (AD) pathogenesis postulate that β-amyloid facilitates spread of pathological tau from the entorhinal cortex (ERC) to neocortically connected targets. Much remains unclear about this model, including the role of neural activity. We studied normal older participants from the Berkeley Aging Cohort Study using PET measures of β-amyloid and tau, and functional MRI. We investigated relationships between functional connectivity, neural activity during performance of a memory task, and patterns and rates of tau deposition. First, we show that functional connectivity between the hippocampus and medial parietal cortex (MPC) is related to tau deposition in MPC, thus providing evidence that the pathway from ERC to neocortex transits via the hippocampus. We also show that neural activity in the medial temporal lobe (MTL) at baseline is related to the rate of subsequent tau deposition. Higher activation in ERC and parahippocampal cortex during a memory task in ERC is related to faster tau accumulation in these regions. In order to investigate these effects on MTL function, we examined the phenomenon of repetition suppression, whereby neural activity is normally suppressed for the repeated presentation of a previous stimulus. We found that tau was associated with increased neural activity during the memory task, and was also associated with reduced repetition suppression. Together these findings support a model whereby tau spreads to neocortex via the hippocampus, with higher neural activity related to both higher rates of tau deposition and dysfunction of the MTL memory system.

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Background and Objective: Clinician-based rating scales or questionnaires for gait are subjective and sensor-based analysis is limited in accessibility. To develop an easily accessible and objective tool to evaluate gait, we analyzed gait from a single 2-dimensional (2D) video.

Methods: We prospectively recorded 2D videos of PD patients (n=16) and healthy controls (n=15) performing the timed up and go test (TUG). The gait was simultaneously evaluated with a pressure-sensor (GAITRite). We estimated the 3D position of toes and heels with a deep-learning based pose-estimation algorithm and calculated gait parameters including step/stride length, step/stride time, gait velocity, cadence and variability for step/stride length and step/stride time which was validated with the GAITRite. Then, we applied the algorithm to previously recorded and archived videos of PD patients (n=32) performing the TUG.

Results: From the validation experiment, gait parameters (step length, step time, stride length, stride time, gait velocity, cadence) derived from video tracking were in excellent agreement with the parameters obtained with the GAITRite. (Intraclass correlation coefficient > 0.9). The variability for step/stride length and step/stride time were in moderate agreement (Intraclass correlation coefficient > 0.6) with the GAITRite. From the analysis with the archived videos, step/stride length, gait velocity was significantly correlated (Absolute R > 0.4, p < 0.005) with the Freezing of gait questionnaire, Unified PD Rating scale part III total score, HY stage and postural instability. Furthermore, the video-based tracking objectively measured improvement of step/stride length, gait velocity with antiparkinsonian medication.

Conclusion: 2D video-based tracking could objectively evaluate gait.