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Recent studies highlight phosphorylated tau (p-tau) at threonine tau 217 (p-tau217) as a new promising plasma biomarker for pathological changes implicated in Alzheimer's disease (AD), but the specific brain pathological events related to the alteration in p-tau217 plasma levels are still largely unknown. Using immunostaining techniques of postmortem AD brain tissue, we show that p-tau217 is found in neurofibrillary tangles (NFTs) and neuropil threads that are also positive for p-tau181, 202, 202/205, 231, and 369/404. The p-tau217, but not the other five p-tau variants, was also prominently seen in vesicles structure positive for markers of granulovacuolar degeneration bodies and multi-vesicular bodies. Further, individuals with a high likelihood of AD showed significantly higher p-tau217 area fraction in 4 different brain areas (entorhinal cortex, inferior temporal gyrus, and superior frontal gyrus) compared to those with Primary age related tauopathy or other non-AD tauopathies. The p-tau217 area fraction correlated strongly with total amyloid-beta (Aβ) and NFT brain load when the whole group was analyzed. Finally, the mean p-tau217 area fraction correlated significantly with p-tau217 concentrations in antemortem collected plasma specifically in individuals with amyloid plaques and not in those without amyloid plaques. These studies highlight differences in cellular localization of different p-tau variants and suggest that plasma levels of p-tau217 reflect an accumulation of p-tau217 in presence of Aβ plaque load., (© 2021. The Author(s).)

Heterozygous NRXN1 deletions constitute the most prevalent currently known single-gene mutation associated with schizophrenia, and additionally predispose to multiple other neurodevelopmental disorders. Engineered heterozygous NRXN1 deletions impaired neurotransmitter release in human neurons, suggesting a synaptic pathophysiological mechanism. Utilizing this observation for drug discovery, however, requires confidence in its robustness and validity. Here, we describe a multicenter effort to test the generality of this pivotal observation, using independent analyses at two laboratories of patient-derived and newly engineered human neurons with heterozygous NRXN1 deletions. Using neurons transdifferentiated from induced pluripotent stem cells that were derived from schizophrenia patients carrying heterozygous NRXN1 deletions, we observed the same synaptic impairment as in engineered NRXN1 -deficient neurons. This impairment manifested as a large decrease in spontaneous synaptic events, in evoked synaptic responses, and in synaptic paired-pulse depression. Nrxn1 -deficient mouse neurons generated from embryonic stem cells by the same method as human neurons did not exhibit impaired neurotransmitter release, suggesting a human-specific phenotype. Human NRXN1 deletions produced a reproducible increase in the levels of CASK, an intracellular NRXN1 -binding protein, and were associated with characteristic gene-expression changes. Thus, heterozygous NRXN1 deletions robustly impair synaptic function in human neurons regardless of genetic background, enabling future drug discovery efforts., Competing Interests: Competing interest statement: This was an NIH-mandated academia–industry collaboration. The following authors were employees of companies with an active interest in the research: J.M. and M.M. of Fujifilm Cellular Dynamics and J.L.D. of Eli Lilly and Company.

Introduction: Genetic causes, or predisposition, are increasingly accepted to be part of the ethiopathogenesis of many neuropsychiatric diseases. While genes can be studied in any type of cells, their physiological function in human brain cells is difficult to evaluate, particularly in living subjects., Methods: As a first step towards the characterisation of human inducible pluripotent stem cell (iPSC)-derived neurons from autism spectrum disorder (ASD) patients, we used gene expression and functional studies to define the regional identity of the typical forebrain differentiation, demonstrate expression patterns of genes of interest in ASD and understand the properties of 'control' iPSC-derived neurons (iCell-Neurons™), with a focus on receptors and ion channels that play a central role in synaptic physio-pathology., Results and Discussion: The gene expression profile of the iCell-Neurons™ closely resembled that observed in neonatal prefrontal cortex tissues. Functional studies, performed mainly using calcium flux assays, demonstrated the presence of ionotropic glutamate (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl-D-aspartate) and gamma-aminobutyric acid type A receptors. Voltage-gated sodium and calcium channels were also identified using similar techniques., Conclusions: Overall, the results reported here suggest that iCell-Neurons™ are a good cellular model of a relatively immature forebrain human neuron population that can be used both as a control in comparison to patients cells, and as host cells in which mutations, insertions and deletions can be used in order to study the molecular mechanisms of ASD and other neurological disorders in an isogenic cellular background.

The microtubule-associated protein tau plays a critical role in the pathogenesis of Alzheimer's disease and several related disorders. In the disease tau aggregates into paired helical and straight filaments, which can form higher order neurofibrillary tangles in neurons and this pathology is associated with progressive neuronal loss and cognitive decline. Tau is a cytoplasmic protein and is thought to be released only from degenerating cells. In contrast, here we provide evidence that tau is constitutively secreted at a low level. We directly show tau release in cell culture model systems. In inducible transfected cell lines we observe that a small proportion of full-length tau is released from intact cells in a time dependent manner. We show that this tau is released by an unconventional secretion process, as the release is temperature dependent but not blocked by inhibitors of the conventional secretory pathway. We characterize the released tau as full length, not vesicle associated and containing Phospho-Tau (181P) proportional to its intracellular concentration. We demonstrate that tau secretion and its suppression by low temperature also occurs in human neurons differentiated from induced pluripotent stem cells. The constitutive tau secretion that we propose provides the most parsimonious explanation for the observed presence of tau in the CSF of healthy animals and human beings. If previously postulated pathogenic extracellular tau intermediates are released by this route, low level constitutive tau secretion could play a role in the spread of tau pathology in Alzheimer's disease and other human tauopathies., (Copyright © 2012 Elsevier Inc. All rights reserved.)