This work designs a class of biocompatible PEG-chitosan@CDs hybrid nanogels by integrating nonlinear poly(ethylene glycol) (PEG), chitosan, and graphitic carbon dots (CDs) into a single nanoparticle for two-photon fl uorescence (TPF) bioimaging, pH and near-infrared (NIR) light dual-responsive drug release, and synergistic therapy. Such hybrid nanogels can be simply prepared from a one-pot surfactant-free precipitation polymerization of the PEG macromonomers complexed with chitosan and CDs in water, resulting in a semi-interpenetration of chitosan chains and an immobilization of CDs in the nonlinear PEG networks. The embedded CDs in hybrid nanogels not only serve as an excellent confocal and TPF imaging contrast agent and fl uorescent pH-sensing probe, but also enhance the loading capacity of the hybrid nanogels for hydrophobic anticancer drug. The chitosan can induce a pH-sensitive swelling/deswelling of the hybrid nanogels for pH-regulated drug release over the physiologically important range of 5.0-7.4 and surface modulation of embedded CDs to realize fl uorescent pH sensing. The thermosensitive nonlinear PEG network can promote the drug release through the local heat produced by the embedded CDs under NIR irradiation. The in vitro results indicate that the hybrid nanogels demonstrated high therapeutic effi cacy through the synergistic effect of combined chemo-photothermal treatments.

The hyperphosphorylated microtubule-associated protein tau is present in several neurodegenerative diseases, although the causal relationship remains elusive. Few mouse models used to study Alzheimer-like dementia target tau phosphorylation. We created an inducible pseudophosphorylated tau (Pathological Human Tau, PH-Tau) mouse model to study the effect of conformationally modified tau in vivo. Leaky expression resulted in two levels of PH-Tau: low basal level and higher upon induction (4% and 14% of the endogenous tau, respectively). Unexpectedly, low PH-Tau resulted in significant cognitive deficits, decrease in the number of synapses (seen by EM in the CA1 region), reduction of synaptic proteins, and localization to the nucleus. Induction of PH-Tau triggered neuronal death (60% in CA3), astrocytosis, and loss of the processes in CA1. These findings suggest, that phosphorylated tau is sufficient to induce neurodegeneration and that two different mechanisms can induce cognitive impairment depending on the levels of PH-Tau expression.

Frequency of LATE neuropathologic change across the spectrum of Alzheimer's disease neuropathology: combined data from 13 community-based or population-based autopsy cohorts.

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BackgroundRepeated failure of drug candidates targeting Alzheimer’s disease (AD) in clinical trials likely stems from a lack of understanding of the molecular mechanisms underlying AD pathogenesis. Recent research has highlighted synergistic interactions between aggregated amyloid-β (Aβ) and tau proteins in AD, but the molecular details of how these interactions drive AD pathology remain elusive and speculative.MethodsHere, we test the hypothesis that Aβ potentiates intracellular tau aggregation, and show that oligomeric Aβ specifically exacerbates proteopathic seeding by tau. Using tau-biosensor cells, we show that treatment with sub-toxic concentrations of Aβ oligomers, but not monomers or fibrils, “primes” cells, making them more susceptible to tau seeding. The treatment with Aβ oligomers enhances intracellular tau aggregation in a dose-dependent manner when the cells are seeded with either recombinant or brain-derived tau fibrils, whereas little or no aggregation is observed in the absence of Aβ-oligomer priming.ResultsPriming by Aβ oligomers appears to be specific to tau, as α-synuclein seeding is unaffected by this treatment. Aβ oligomer-enhanced tau seeding also occurs in primary mouse neurons and human neuroblastoma cells. Using fluorescently labeled tau seeds, we find that treatment with Aβ oligomers significantly enhances the cellular uptake of tau seeds, whereas a known tau-uptake inhibitor blocks the effect of Aβ on tau uptake.ConclusionThe ability of Aβ to promote tau seeding suggests a specific and plausible mechanism by which extracellular Aβ initiates a deleterious cascade that is unique to AD. These data suggest that the Aβ-mediated potentiation of tau uptake into cells should also be taken into account when designing Aβ-targeted therapeutics.

Self-assembly of the microtubule-associated protein tau into neurotoxic oligomers, fibrils, and paired helical filaments, and cell-to-cell spreading of these pathological tau species are critical processes underlying the pathogenesis of Alzheimer’s disease and other tauopathies. Modulating the self-assembly process and inhibiting formation and spreading of such toxic species are promising strategies for therapy development. A challenge in investigating tau self-assembly in vitro is that, unlike most amyloidogenic proteins, tau does not aggregate in the absence of posttranslational modifications (PTM), aggregation inducers, or preformed seeds. The most common induction method is addition of polyanions, such as heparin; yet, this artificial system may not represent adequately tau self-assembly in vivo, which is driven by aberrant phosphorylation and other PTMs, potentially leading to in vitro data that do not reflect the behavior of tau and its interaction with modulators in vivo. To tackle these challenges, methods for in vitro phosphorylation of tau to produce aggregation-competent forms recently have been introduced (28784767Proc. Natl. Acad. Sci. U.S.A.201711490809085). However, the oligomerization, seeding, and interaction with assembly modulators of the different forms of tau have not been studied to date. To address these knowledge gaps, we compared here side-by-side the self-assembly and seeding activity of heparin-induced tau with two forms of in vitro phosphorylated tau and tested how the molecular tweezer CLR01, a negatively charged compound, affected these processes. Tau was phosphorylated by incubation either with activated extracellular signal-regulated kinase 2 or with a whole rat brain extract. Seeding activity was measured using a fluorescence-resonance energy transfer-based biosensor-cell method. We also used solution-state NMR to investigate the binding sites of CLR01 on tau and how they were impacted by phosphorylation. Our systematic structure–activity relationship study demonstrates that heparin-induced tau behaves differently from in vitro phosphorylated tau. The aggregation rates of the different forms are distinct as is the intracellular localization of the induced aggregates, which resemble brain-derived tau strains suggesting that heparin-induced tau and in vitro phosphorylated tau have different conformations, properties, and activities. CLR01 inhibits aggregation and seeding of both heparin-induced and in vitro phosphorylated tau dose-dependently, although heparin induction interferes with the interaction between CLR01 and tau.

The accumulation of hyperphosphorylated tau is a common feature of several dementias. Tau is one of the brain microtubule-associated proteins. Here we discuss tau's functions in microtubule assembly and stabilization and with regard to its interactions with other proteins. We describe and analyze important post-translational modifications: hyperphosphorylation, ubiquitination, glycation, glycosylation, nitration, polyamination, proteolysis, acetylation, and methylation. We discuss how these post-translational modifi cations can alter tau's biological function. We analyze the role of mitochondrial health in neurodegeneration. We propose that microtubules could be a therapeutic target and review different approaches. Finally, we consider whether tau accumulation or its conformational change is related to tau-induced neurodegeneration, and propose a mechanism of neurodegeneration.Keywords: tau; phosphorylation; neurodegeneration; tauopathies; mitochondria; microtubules; tubulin; kinases; phosphatases; Alzheimer's disease ·Review· IntroductionAlzheimer 's disease (AD), first described by Alois Alzheimer more than 100 years ago [1] , is a progressive neurodegenerative disorder, characterized by an insidious onset with irreversible cognitive declines that lead to profound mental deterioration causing dementia [2] . Two major forms of lesion characterize AD: amyloid as diffuse neurotic plaques primarily composed of the Aβ peptide [3] , which are mainly insoluble deposits of protein and cellular material, and neurofibrillary tangles composed of fi lamentous hyperphosphorylated tau protein that builds up inside the neuron [4,5] .Amyloid precursor protein (APP) is a highly conserved transmembrane protein [6] believed to play a role in synapse formation, synaptic plasticity, and neuronal survival [7][8][9] .In AD, APP is cleaved by β-and γ-secretases leading to the overproduction of an abnormal proteolytic byproduct called amyloid beta (Aβ) [10] . Upon cleavage fragments of Aβ of various sizes are released from the membrane and aggregate in the brain to form the characteristic plaques seen in AD. Plaques are composed primarily of the 40 and 42 amino-acid peptide fragments Aβ40 and Aβ42, the latter being the predominant species. In addition, Aβ42 is more prone to aggregation and deposition and therefore the cause of neurotoxicity, as well as synaptic loss [11] .The second lesion in AD is formed by aggregates of the microtubule-associated protein tau, which forms intracytoplasmic neuronal inclusions or neurofibrillary tangles when hyperphosphorylated [12] . Tau is associated with neurons of the central nervous system [13] and its main biological function is promoting the in vitro assembly and stabilization of microtubules in the cytoskeleton [14,15] . Tau is a phosphoprotein that is encoded by a single gene, MAPT, located on chromosome 17q21 [16] ; alternative splicing of the gene produces six major isoforms expressed in the adult human brain [17] . Isoforms derive their names from the number of microtubule-binding repeat s...

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