Biology subjects

Livesey, F. J.

Publications and source records attributed to Livesey, F. J..

7 recordsLinked to original sources

bioRxiv2025

Synaptotoxic effects of extracellular tau are mediated by its microtubule-binding region

Immunotherapies targeting extracellular tau share the premise that interrupting cell-to-cell spread of tau pathology in Alzheimers disease (AD) will slow dementia pathogenesis. How these interventions affect the actions of synaptotoxic, extracellular tau species that may help mediate cognitive impairment is relatively unknown. Here, we assayed synaptic plasticity disruption in anaesthetised live rats caused by intracerebral injection of synaptotoxic tau present either in (a) secretomes of induced pluripotent stem cell-derived neurons (iNs) from people with Trisomy 21, the most common genetic cause of AD, or (b) aqueous extracts of human AD brain. Extracellular tau in iN secretomes was found to include fragments that contain the extended microtubule binding regions of tau, MTBR/R and adjacent C-terminal peptides. Immunodepletion or co-injection with antibodies targeting epitopes within these fragments prevented the acute disruption of synaptic plasticity by these patient-derived synaptotoxic tau preparations. Conversely, a recombinant human tau fragment encompassing the core MTBR/R- region present in tau fibrils, tau297-391 potently mimicked this deleterious action of patient-derived tau. MTBR/R-directed antibodies also rapidly reversed a very persistent synaptotoxic effect of soluble brain tau. Our findings reveal a hitherto relatively unexplored potential benefit of targeting MTBR/R.

neuroscience↗

bioRxiv2024

Altered neuronal network activity and connectivity in human Down Syndrome excitatory cortical neurons

Down syndrome (DS) is the most common genetic cause of intellectual disability, affecting one in 700 live births worldwide, and is caused by trisomy of the human chromosome 21 (Hsa21), yet the cellular and molecular mechanisms driving neuronal network dysfunction remain poorly understood. Here, we investigated whether trisomy 21 (TS21) alters the spontaneous synchronised activity of excitatory neuron networks, potentially contributing to the neurodevelopmental phenotypes of DS. By modelling human cortical development in vitro with TS21 and matched control human iPSCs from two DS donors, we investigated the impact of Hsa21 triplication on neural network activity and connectivity. Calcium imaging revealed an early and pronounced reduction in neuronal activity in TS21 cortical neurons, including a marked loss of synchronised bursting. These deficits persisted up to 80 days in vitro and for over 5 months in vivo following transplantation into the mouse forebrain, as shown by multiphoton calcium imaging through a cranial window. Viral trans-synaptic tracing identified significant reduction of neuronal connectivity in TS21 neuronal networks in vitro, suggesting that reduced network connectivity contributes to the dramatic reduction of synchronised bursting. Furthermore, TS21 neurons displayed significantly reduced expression of voltage-gated potassium channels, with single-neuron recordings confirming a reduction of hyperpolarization-activated currents. Together, these findings demonstrate long-lasting impairments in human cortical excitatory neuron network function associated with Trisomy 21.

neuroscience↗

bioRxiv2022

Synchronisation of apical constriction and cell cycle progression is a conserved behaviour of pseudostratified neuroepithelia informed by their tissue geometry

Neuroepithelial cells balance tissue growth requirement with the morphogenetic imperative of closing the neural tube. They apically constrict to generate mechanical forces which elevate the neural folds, but are thought to apically dilate during mitosis. However, we previously reported that mitotic neuroepithelial cells in the mouse posterior neuropore have smaller apical surfaces than non-mitotic cells. Here, we document progressive apical enrichment of non-muscle myosin-II in mitotic, but not non-mitotic, neuroepithelial cells with smaller apical areas. Live-imaging of the chick posterior neuropore confirms apical constriction synchronised with mitosis, reaching maximal constriction by anaphase, before division and re-dilation. Mitotic apical constriction amplitude is significantly greater than interphase constrictions. To investigate conservation in humans, we characterised early stages of iPSC differentiation through dual SMAD-inhibition to robustly produce pseudostratified neuroepithelia with apically enriched actomyosin. These cultured neuroepithelial cells achieve an equivalent apical area to those in mouse embryos. iPSC-derived neuroepithelial cells have large apical areas in G2 which constrict in M phase and retain this constriction in G1/S. Given that this differentiation method produces anterior neural identities, we studied the anterior neuroepithelium of the elevating mouse mid-brain neural tube. Instead of constricting, mid-brain mitotic neuroepithelial cells have larger apical areas than interphase cells. Tissue geometry differs between the apically convex early midbrain and flat posterior neuropore. Culturing human neuroepithelia on equivalently convex surfaces prevents mitotic apical constriction. Thus, neuroepithelial cells undergo high-amplitude apical constriction synchronised with cell cycle progression but the timing of their constriction if influenced by tissue geometry.

cell biology↗

bioRxiv2020

Whole genome CRISPR screens identify LRRK2-regulated endocytosis as a major mechanism for extracellular tau uptake by human neurons

Extracellular release and cellular uptake of pathogenic forms of the microtubule-associated protein tau contribute to the pathogenesis of several neurodegenerative diseases, including Alzheimers disease. Defining the cellular mechanisms and pathways for tau entry to human neurons is essential to understanding tauopathy pathogenesis and the rational design of disease-modifying therapeutics. Whole genome CRISPR loss-of-function screens in human iPSC-derived excitatory neurons, the major neuronal cell type affected in these diseases, enabled the delineation of the different cellular pathways for uptake of extracellular monomeric and fibrillar tau. Monomeric and fibrillar tau are both taken up by human neurons by receptor-mediated endocytosis, but involve different routes of entry at the neuronal surface: the low-density lipoprotein LRP1 is the primary receptor for monomeric tau, but contributes less to fibrillar tau entry. Similarly, endocytosis of monomeric tau is dependent on the familial Parkinsons disease gene LRRK2, but not required for endocytosis of fibrillar tau. These findings implicate LRP1 and LRRK2 in the pathogenesis of tauopathies and Parkinsons disease and identify LRRK2 as a potential therapeutic target for altering progression of these diseases.

neuroscience↗

bioRxiv2020

Molecular and cellular pathology of monogenic Alzheimer's disease at single cell resolution

Cell and molecular biology analyses of sporadic Alzheimers disease brain are confounded by clinical variability, ageing and genetic heterogeneity. Therefore, we used single-nucleus RNA sequencing to characterize cell composition and gene expression in the cerebral cortex in early-onset, monogenic Alzheimers disease. Constructing a cellular atlas of frontal cortex from 8 monogenic AD individuals and 8 matched controls, provided insights into which neurons degenerate in AD and responses of different cell types to AD at the cellular and systems level. Such responses are a combination of positively adaptive and deleterious changes, including large-scale changes in synaptic transmission and marked metabolic reprogramming in neurons. The nature and scale of the transcriptional changes in AD emphasizes the global impact of the disease across all brain cell types. One Sentence SummaryAlzheimers disease brain atlas provides insights into disease mechanisms

neuroscience↗

bioRxiv2019

Mutations in thyroid hormone receptor α1 cause premature neurogenesis and progenitor cell depletion in human cortical development

Mutations in the thyroid hormone receptor 1 gene (THRA) have recently been identified as a cause of intellectual deficit in humans. Patients present with structural abnormalities including microcephaly, reduced cerebellar volume and decreased axonal density. Here, we show that directed differentiation of THRA mutant patient-derived iPSCs to forebrain neural progenitors is markedly reduced, but mutant progenitor cells can generate deep and upper cortical layer neurons and form functional neuronal networks. Quantitative lineage tracing shows that THRA mutation-containing progenitor cells exit the cell cycle prematurely, resulting in reduced clonal output. Using a novel micropatterned chip assay, we find that spatial self-organisation of mutation-containing progenitor cells is impaired, consistent with downregulated expression of cell-cell adhesion genes. These results reveal for the first time that thyroid hormone receptor 1 is required for normal neural progenitor cell proliferation and organisation in human cerebral cortical development. They also exemplify novel quantitative approaches for studying neurodevelopmental disorders using patient-derived cells in vitro.

developmental biology↗

bioRxiv2018

Abnormal microtubule dynamics disrupt nucleocytoplasmic transport in tau-mediated frontotemporal dementia

The neuronal microtubule-associated protein tau (MAPT) is central to the pathogenesis of many dementias, including Alzheimers disease. Autosomal dominant mutations in MAPT cause inherited frontotemporal dementia (FTD), but the underlying pathogenic mechanisms are unclear. Using human stem cell models of FTD due to MAPT mutations, we find that tau becomes hyperphosphorylated and mislocalises to neuronal cell bodies and dendrites in cortical neurons, recapitulating a key early event in FTD. Mislocalised tau in the cell body leads to abnormal microtubule dynamics in FTD-MAPT neurons that grossly deform the nuclear membrane, resulting in defective nucleocytoplasmic transport. Neurons in the post-mortem human FTD-MAPT cortex have a high incidence of nuclear deformation, indicating that tau-mediated nuclear membrane dysfunction is an important pathogenic process in FTD. Defects in nucleocytoplasmic transport in FTD point to important commonalities in the pathogenic mechanisms of both tau-mediated dementias and ALS-FTD due to TDP-43 and C9orf72 mutations.

neuroscience↗