Tauopathies, including frontotemporal dementia (FTD) and Alzheimer’s disease (AD), are neurodegenerative diseases in which tau fibrils accumulate. Recent evidence supports soluble tau species as the major toxic species. How soluble tau accumulates and how it causes neurodegeneration remains unclear. Here we identified tau acetylation at K174 as an early change in AD brains and as a critical determinant in tau homeostasis and toxicity in mice. An acetyl-mimicking mutant (K174Q) slows down tau turnover and induces cognitive deficits in vivo. The acetyltransferase p300-induced tau acetylation is inhibited by a prescription drug salsalate/salicylate, which enhances tau turnover and reduces tau levels. In the PS19 transgenic mouse model of FTD, administering salsalate after disease onset inhibited p300 activity, lowered ac-K174 and total tau levels, rescued tau-induced memory deficits and prevented hippocampal atrophy. The tau-lowering and protective effects of salsalate/salicylate are diminished in neurons expressing K174Q tau. Targeting tau acetylation could be a new therapeutic strategy against human tauopathies.

SummaryLowering total tau levels is an attractive therapeutic strategy for Alzheimer's disease and other tauopathies. High-throughput screening in neurons derived from human induced pluripotent stem cells (iPSCs) is a powerful tool to identify tau-targeted therapeutics. However, such screens have been hampered by heterogeneous neuronal production, high cost and low yield, and multi-step differentiation procedures. We engineered an isogenic iPSC line that harbors an inducible neurogenin 2 transgene, a transcription factor that rapidly converts iPSCs to neurons, integrated at the AAVS1 locus. Using a simplified two-step protocol, we differentiated these iPSCs into cortical glutamatergic neurons with minimal well-to-well variability. We developed a robust high-content screening assay to identify tau-lowering compounds in LOPAC and identified adrenergic receptors agonists as a class of compounds that reduce endogenous human tau. These techniques enable the use of human neurons for high-throughput screening of drugs to treat neurodegenerative disease.

Summary Tau toxicity has been implicated in the emergence of synaptic dysfunction in Alzheimer’s disease (AD), but the mechanism by which tau alters synapse physiology and leads to cognitive decline is unclear. Here, we report abnormal acetylation of K274 and K281 on tau, identified in AD brains, promotes memory loss and disrupts synaptic plasticity by reducing postsynaptic KIBRA (KIdney/BRAin protein), a memory-associated protein. Transgenic mice expressing human tau with lysine-to-glutamine mutations to mimic K274 and K281 acetylation (tauKQ) exhibit AD-related memory deficits and impaired hippocampal long-term potentiation (LTP). TauKQ reduces synaptic KIBRA levels and disrupts activity-induced postsynaptic actin remodeling and AMPA receptor insertion. The LTP deficit was rescued by promoting actin polymerization or by KIBRA expression. In AD patients with dementia, we found enhanced tau acetylation is linked to loss of KIBRA. These findings suggest a novel mechanism by which pathogenic tau causes synaptic dysfunction and cognitive decline in AD pathogenesis.

Inhibitory interneurons regulate the oscillatory rhythms and network synchrony that are required for cognitive functions and disrupted in Alzheimer's disease (AD). Network dysrhythmias in AD and multiple neuropsychiatric disorders are associated with hypofunction of Nav1.1, a voltage-gated sodium channel subunit predominantly expressed in interneurons. We show that Nav1.1-overexpressing, but not wild-type, interneuron transplants derived from the embryonic medial ganglionic eminence (MGE) enhance behavior-dependent gamma oscillatory activity, reduce network hypersynchrony, and improve cognitive functions in human amyloid precursor protein (hAPP)-transgenic mice, which simulate key aspects of AD. Increased Nav1.1 levels accelerated action potential kinetics of transplanted fast-spiking and non-fast-spiking interneurons. Nav1.1-deficient interneuron transplants were sufficient to cause behavioral abnormalities in wild-type mice. We conclude that the efficacy of interneuron transplantation and the function of transplanted cells in an AD-relevant context depend on their Nav1.1 levels. Disease-specific molecular optimization of cell transplants may be required to ensure therapeutic benefits in different conditions.

Highlights d The FTD-causing V337M tau mutation impairs axon initial segment (AIS) plasticity d The V337M tau mutation impairs activity homeostasis d The V337M tau mutation leads to accumulation of EB3 in the AIS d EB3 is critical for regulating AIS plasticity and activity homeostasis

Highlights d APEX-mapped Tau interactome at subcellular and amino acid levels in human neurons d Activity-dependent binding of Tau to synaptic vesicle proteins during Tau secretion d FTD mutations reduce Tau binding to mitochondria proteins and impair bioenergetics d Tau interactors modified by FTD mutation are downregulated in human tauopathy Authors

BackgroundNeurons are highly polarized cells in which asymmetric axonal-dendritic distribution of proteins is crucial for neuronal function. Loss of polarized distribution of the axonal protein tau is an early sign of Alzheimer’s disease (AD) and other neurodegenerative disorders. The cytoskeletal network in the axon initial segment (AIS) forms a barrier between the axon and the somatodentritic compartment, contributing to axonal retention of tau. Although perturbation of the AIS cytoskeleton has been implicated in neurological disorders, the molecular triggers and functional consequence of AIS perturbation are incompletely understood.ResultsHere we report that tau acetylation and consequent destabilization of the AIS cytoskeleton promote the somatodendritic mislocalization of tau. AIS cytoskeletal proteins, including ankyrin G and βIV-spectrin, were downregulated in AD brains and negatively correlated with an increase in tau acetylated at K274 and K281. AIS proteins were also diminished in transgenic mice expressing tauK274/281Q, a tau mutant that mimics K274 and K281 acetylation. In primary neuronal cultures, the tauK274/281Q mutant caused hyperdynamic microtubules (MTs) in the AIS, shown by live-imaging of MT mobility and fluorescence recovery after photobleaching. Using photoconvertible tau constructs, we found that axonal tauK274/281Q was missorted into the somatodendritic compartment. Stabilizing MTs with epothilone D to restore the cytoskeletal barrier in the AIS prevented tau mislocalization in primary neuronal cultures.ConclusionsTogether, these findings demonstrate that tau acetylation contributes to the pathogenesis of neurodegenerative disease by compromising the cytoskeletal sorting machinery in the AIS.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-016-0109-0) contains supplementary material, which is available to authorized users.

Neurodegeneration is a major age-related pathology. Cognitive decline is characteristic of patients with Alzheimer's and related dementias and cancer patients after chemo-or radiotherapies. A recently emerged driver of these and other age-related pathologies is cellular senescence, a cell fate that entails a permanent cell cycle arrest and pro-inflammatory senescence-associated secretory phenotype (SASP). Although there is a link between inflammation and neurodegenerative diseases, there are many open questions regarding how cellular senescence affects neurodegenerative pathologies. Among the various cell types in the brain, astrocytes are the most abundant. Astrocytes have proliferative capacity and are essential for neuron survival. Here, we investigated the phenotype of primary human astrocytes made senescent by X-irradiation, and identified genes encoding glutamate and potassium transporters as specifically downregulated upon senescence. This down regulation led to neuronal cell death in co-culture assays. Unbiased RNA sequencing of transcripts expressed by non-senescent and senescent astrocytes confirmed that glutamate homeostasis pathway declines upon senescence. Our results suggest a key role for cellular senescence, particularly in astrocytes, in excitotoxicity, which may lead to neurodegeneration including Alzheimer's disease and related dementias.