Biology subjects

Durrant, C. S.

Publications and source records attributed to Durrant, C. S..

12 recordsLinked to original sources

bioRxiv2026

Sexually dimorphic behavioural signatures of tau toxicity in adult Drosophila

Tau pathology is central to Alzheimers disease and related tauopathies, yet mechanisms driving neuronal dysfunction and degeneration downstream of pathological changes in tau remain poorly understood. Drosophila melanogaster models provide a genetically tractable system with an intact nervous system and short lifespan that allows investigation of mechanisms of many diseases. However, in Drosophila, developmental expression of human tau frequently causes lethality and developmental phenotypes, limiting the study of neurodegenerative disease processes. Further, sex is rarely considered in Drosophila studies of tau pathology despite clear sex differences being observed in many aspects of human tauopathies. Here, we used an inducible, pan-neuronal GeneSwitch system to express human tau isoforms exclusively in adulthood, enabling the dissection of tau toxicity independent of development. We combined longitudinal behavioural monitoring with lifespan and neurodegeneration analyses, and performed a targeted genetic screen to identify modifiers of tau-induced dysfunction. Adult-onset tau expression produced striking, sexually dimorphic effects on survival and behaviour. Neuronal expression of the human tau isoform with 4 microtubule binding repeats and neither alternatively spliced N-terminal exon (0N4R tau) caused pronounced neurodegeneration and reduced lifespan, which was exacerbated in flies expressing the phospho-mimetic 0N4R-TauE14 variant. Tau expression produced sexually dimorphic effects on survival and behaviour, with females exhibiting a greater reduction in lifespan, while the induction-dependent increase in vacuolar neurodegeneration was broadly comparable between sexes. Behaviourally, tau expression induced elevated daytime inactivity in females, whereas males exhibited hyperactivity, revealing opposing functional outcomes between sexes. A targeted genetic screen further identified modifiers of tau-dependent behavioural impairment. APOE2 expression in glia, syndecan overexpression in neurons, and increased global expression of the chaperone heat shock protein 90 all reduced 0N4R-TauE14-induced behavioural changes. Seventeen candidate perturbations enhanced the TauE14-induced behavioural phenotype, including manipulations of APOE3, CLU, INPP5D/INPP5K, BIN1/Amph, synaptogyrin, LRP1, NPC1, and Hsp90 pathways. Together, these findings establish an adult-onset Drosophila model of tauopathy that uncouples neurotoxicity from development, reveals sex as a major determinant of tau-induced behavioural outcomes in flies, and uncovers genetic modulators of tau-induced dysfunction. This work highlights the importance of incorporating sex as a biological variable and provides a platform for mechanistic and translational studies of tauopathy.

neuroscience↗

bioRxiv2025

FMRP regulates adult human cortical excitability via cyclic-AMP signalling

Fragile X Syndrome (FXS) is a common inherited neurodevelopmental condition, resulting from loss of Fragile X Messenger Ribonuclear Protein (FMRP). Rodent models of FXS display cellular hyperexcitability, but it is not known to what extent this is the case in intact human neurons. Depleting FMRP in human brain slice cultures reveals cyclic-AMP-dependent cellular hyperexcitability which is corrected by phosphodiesterase 4D inhibition and may be independent of neurodevelopment.

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bioRxiv2025

Absence of short-term axon initial segment plasticity in human, mouse, and rat cortical circuits

Maintaining neuronal output with respect to input in the physiological range relies on the ability of neurons to update their responsiveness to inputs dependent on changing activity levels. Termed homeostatic plasticity, the mechanisms that neurons employ to control their responsiveness are varied, and proposed to include structural changes to a key neuronal structure - the axon initial segment (AIS). As the site of action potential initiation, the AIS has been postulated to rapidly change its length in response to increased or decreased cellular and circuit activity. To date, AIS structural plasticity has only been tested in tissue cultures and rodent models. In our current study, we assess the ability of neurons to alter their AIS length over a variety of timescales in ex vivo rodent and human brain slices, human neurons derived from induced pluripotent stem cells, and in mice dark-reared during early life; using a combination of electrophysiology and immunohistochemistry. We find no evidence for changes to AIS length following depolarisation for up to 3 hours, despite positive controls confirming modulated activity. However, we do find that neuronal physiological properties are altered by changes in activity - but these are largely independent of action potential initiation associated with the AIS. In summary, we find no evidence supporting a role for AIS structural plasticity in mouse, rat, or human cortical neurons.

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bioRxiv2024

Phylogenetic divergence of GABAB receptor signalling in neocortical networks over adult life.

Cortical circuit activity is controlled by GABA-mediated inhibition in a spatiotemporally restricted manner. Much is known about fast GABA currents, GABAB receptor (GABABR) signalling exerts powerful slow inhibition that controls synaptic, dendritic and neuronal activity. However, little is known about how GABABRs contribute to circuit-level inhibition over the lifespan of rodents and humans. In this study, we quantitatively determine the functional contribution of GABABR signalling to pre- and postsynaptic domains in rat and human cortical principal cells (PC). We find that postsynaptic GABABR differentially control pyramidal cell activity within the cortical column as a function of age and species, and that these receptors contribute to co-ordination of local information processing in a layer- and species-dependent manner. These data directly increase our knowledge of translationally relevant local circuit dynamics, with direct impact on understanding the role of GABABRs in the treatment of seizure disorders. HighlightsO_LIGABAB receptor signalling displays age and species differences in cortex C_LIO_LIGABAB receptor presynaptic inhibition is stronger in humans than rodents C_LIO_LIIn vitro oscillations in human cortex are strongly regulated by GABABRs C_LIO_LILevetiracetam enhances endogenous GABABR signalling in human cortex C_LI

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bioRxiv2024

Lowering glucose enhances BACE1 activity and Aβ generation in mouse brain slice cultures

Numerous environmental risk factors are now recognised as contributors to the onset and progression of Alzheimers disease (AD). It is probable that, in most instances, AD arises from a combination of genetic predisposition and environmental influences. In particular, there is a strong correlation between vascular impairment and dementia, yet the specific mechanisms by which vascular impairment and AD are linked, remain unknown. Hypoglycaemia can occur both due to vascular impairment, and due to fluctuating glucose levels in the context of diabetes, another risk factor for AD, and could potentially be involved in disease pathogenesis. To assess whether low glucose could contribute to the build-up of brain amyloid-{beta} (A{beta}) seen in AD, we exposed wildtype mouse organotypic hippocampal slice cultures (OHSCs) to varying glucose concentrations. Lowering glucose levels leads to an elevation in both A{beta}1-42 and A{beta}1-40 secreted into the culture medium, accompanied by an increased accumulation of A{beta} within the slice tissue. This effect is replicated in OHSCs derived from the TgCRND8 mouse model of overexpressed, mutant APP and in human SH-SY5Y cells. The heightened A{beta} levels are likely attributed to an upregulation of BACE1 activity, which is also observed with lowered glucose levels. In contrast, OHSCs subject to hypoxia exhibited no alterations in A{beta} levels whether singularly, or in combination of hypoglycaemia. Finally, we found that alternative energy sources such as pyruvate, fructose 1,6-bisphosphate, and lactate can alleviate heightened A{beta} levels, when given in combination with lowered glucose. This study underscores the capacity to induce an increase in A{beta} in a wildtype ex vivo system by selectively decreasing glucose levels.

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bioRxiv2024

Drosophila appear resistant to trans-synaptic tau propagation

Alzheimers disease (AD) is the most common cause of dementia in the elderly, prompting extensive efforts to pinpoint novel therapeutic targets for effective intervention. Among the hallmark features of AD is the development of neurofibrillary tangles comprised of hyperphosphorylated tau protein, whose progressive spread throughout the brain is associated with neuronal death. Trans-synaptic propagation of tau has been observed in mouse models and indirect evidence for tau spread via synapses has been observed in human AD. Halting tau propagation is a promising therapeutic target for AD, thus a scalable model system to screen for modifiers of tau spread would be very useful for the field. To this end, we sought to emulate the trans-synaptic spread of human tau (hTau) in Drosophila melanogaster. Employing the trans-Tango circuit mapping technique, we investigated whether tau spreads between synaptically connected neurons. Immunohistochemistry and confocal imaging were used to look for tau propagation. Examination of hundreds of flies expressing 4 different human tau constructs in two distinct neuronal populations reveal a robust resistance in Drosophila to the trans-synaptic spread of hTau. This resistance persisted in lines with concurrent expression of amyloid-{beta}, in lines with global hTau knock-in to provide a template for human tau in downstream neurons, and with manipulations of temperature. These negative data are important for the field as we establish that Drosophila expressing human tau in subsets of neurons are unlikely to be useful to perform screens to find mechanisms to reduce the trans-synaptic spread of tau. The inherent resistance observed in Drosophila may serve as a valuable clue, offering insights into strategies for impeding tau spread in future studies.

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bioRxiv2024

Opposing roles of physiological and pathological amyloid-β on synapses in live human brain slice cultures

In Alzheimers disease, it is theorised that amyloid beta (A{beta}) and tau pathology contribute to synapse loss. However, there is limited information on how endogenous levels of tau and A{beta} protein relate to patient characteristics, or how manipulating physiological levels of A{beta} impacts synapses, in living adult, human brain. Here, we employed live human brain slice cultures as a translational tool to assess endogenous tau and A{beta} release, pathology, and response to experimental manipulation. We found that the levels of A{beta}1-40 and tau detected in the culture medium depend on donor age, and brain region, respectively. Pharmacologically raising physiological A{beta} concentration enhanced levels of synaptic transcripts. Treatment of slices with A{beta}-containing Alzheimers disease brain extract resulted in postsynaptic A{beta} uptake and loss of presynaptic puncta. These data indicate that physiological and pathological A{beta} can have opposing effects on synapses in living human brain tissue.

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bioRxiv2023

Tau phosphorylated at serine 356 is associated with Alzheimer's disease pathology and can be lowered in mouse and human brain tissue using the NUAK inhibitor WZ4003

Tau hyperphosphorylation and aggregation is a common feature of many dementia-causing neurodegenerative diseases. Tau can be phosphorylated at up to 85 different sites, and there is increasing interest in whether tau phosphorylation at specific epitopes, by specific kinases, plays an important role in disease progression. The AMP-activated protein kinase (AMPK) related enzyme NUAK1 been identified as a potential mediator of tau pathology, whereby NUAK1-mediated phosphorylation of tau at Ser356 prevents the degradation of tau by the proteasome, further exacerbating tau hyperphosphorylation and accumulation. This study provides a detailed characterisation of the association of p-tau Ser356 with progression of Alzheimers disease pathology, identifying a Braak stage-dependent increase in p-tau Ser356 protein levels and an almost ubiquitous presence in neurofibrillary tangles. We also demonstrate, using sub-diffraction-limit resolution array tomography imaging, that p-tau Ser356 co-localises with synapses in AD post-mortem brain tissue, increasing evidence that this form of tau may play important roles in AD progression. To assess the potential impacts of pharmacological NUAK inhibition in an ex vivo system that retains multiple cell types and brain-relevant neuronal architecture, we treated postnatal mouse organotypic brain slice cultures from wildtype or APP/PS1 littermates with the commercially available NUAK1/2 inhibitor WZ4003. Whilst there were no genotype specific effects, we found that WZ4003 results in a culture-phase dependent loss of total tau and p-tau Ser356, which corresponds with a reduction in neuronal and synaptic proteins. By contrast, application of WZ4003 to live human brain slice cultures results in a specific lowering of p-tau Ser356, alongside increased neuronal tubulin protein. This work identifies differential responses of postnatal mouse organotypic brain slice cultures and adult human brain slice cultures to NUAK1 inhibition that will be important to consider in future work developing tau-targeting therapeutics for human disease.

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bioRxiv2021

Aβ toxicity rescued by protein retention in the ER

Accumulation of A{beta} in the brain is one of the hallmarks of Alzheimers disease (AD). In the adult Drosophila brain, human A{beta} over-expression is toxic and leads to deterioration of climbing ability and shortened lifespan. However, it remains unknown if A{beta} is inherently toxic or if it triggers toxic downstream pathways that lead to neurodegeneration. Here, we describe a novel, and previously unidentified, protective role of intracellular laminin chain accumulation. Despite high A{beta} levels, over-expression of the extracellular matrix protein subunit Laminin B1 (LanB1) resulted in a robust rescue of toxicity, highlighting a potential protective mechanism of resistance to A{beta}. Over-expression of other Laminin subunits and a Collagen IV subunit also significantly rescued A{beta} toxicity, while combining LanB1 with these subunits led to an even larger rescue. Imaging revealed that LanB1 was retained in the ER but had no effect on the secretion of A{beta} into the extracellular milieu. LanB1 rescued toxicity independently of the IRE1/XBP1-mediated branch of the ER stress response. Interestingly, over-expression of ER-targeted GFP also rescued A{beta} toxicity, indicating a potentially broader benefit of ER protein retention. Finally, in proof-of-principle lentiviral transduction experiments using murine organotypic hippocampal slice cultures, over-expression of mouse Lamb1 resulted in ER-retention in transduced cells, highlighting a conserved mechanism. Typically, retention of proteins in the ER is detrimental to cellular health, but in the context of neuronal A{beta} toxicity it may prove to be beneficial and a new therapeutic avenue for AD.

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bioRxiv2021

Tau assemblies do not behave like independently acting prion-like particles in mouse neural tissue

A fundamental property of infectious agents is their particulate nature: infectivity arises from independently-acting particles rather than as a result of collective action. Assemblies of the protein tau can exhibit seeding behaviour, potentially underlying the apparent spread of tau aggregation in many neurodegenerative diseases. Here we ask whether tau assemblies share with classical pathogens the characteristic of particulate behaviour. We used organotypic hippocampal slice cultures from P301S tau transgenic mice in order to precisely control the concentration of extracellular tau assemblies. Whilst untreated slices displayed no overt signs of pathology, exposure to tau assemblies could result in the formation of intraneuronal, hyperphosphorylated tau structures. However, seeding ability of tau assemblies did not titrate in a one-hit manner in neural tissue. The results suggest that seeding behaviour of tau only arises at supra-physiological concentrations, with implications for the interpretation of high-dose intracranial challenge experiments and the possible contribution of seeded aggregation to human disease.

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bioRxiv2019

Beta secretase 1-dependent amyloid precursor protein processing promotes excessive vascular sprouting through NOTCH3 signaling

Amyloid beta peptides (A{beta}) proteins play a key role in vascular pathology in Alzheimers Disease (AD) including impairment of the blood brain barrier and aberrant angiogenesis. Although previous work has demonstrated a pro-angiogenic role of A{beta}, the exact mechanisms by which amyloid precursor protein (APP) processing and endothelial angiogenic signalling cascades interact in AD remain a largely unsolved problem. Here, we report that increased endothelial sprouting in human-APP transgenic mouse (TgCRND8) tissue is dependent on {beta}-secretase (BACE1) processing of APP. Higher levels of A{beta} processing in TgCRND8 tissue coincides with decreased NOTCH3/JAG1 signalling, over-production of endothelial filopodia and increased numbers of vascular pericytes. Using a novel in vitro approach to study sprouting angiogenesis in TgCRND8 organotypic brain slice cultures (OBSCs), we find that BACE1 inhibition normalises excessive endothelial filopodia formation and restores NOTCH3 signalling. These data present the first evidence for the potential of BACE1 inhibition as an effective therapeutic target for aberrant angiogenesis in AD.\n\nSignificanceIn this study, we show that targeting amyloid beta processing provides an opportunity to selectively target tip cell filopodia-driven angiogenesis and develop therapeutic targets for vascular dysfunction related to aberrant angiogenesis in AD. Our data provide the first evidence for a safe level of BACE1 inhibition that can normalize excess angiogenesis in AD, without inducing vascular deficits in healthy tissue. Our findings may pave the way for the development of new angiogenesis dependent therapeutic strategies in Alzheimers Disease.

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bioRxiv2018

Microglia-dependent presynaptic disruption in an organotypic hippocampal slice culture model of neuroinflammation

BackgroundSystemic inflammation, such as occurs during sepsis, bone fracture, infections or post-operative trauma, has been linked to synapse loss and cognitive decline in human patients and animal models. Organotypic hippocampal slice cultures (OHSCs) represent an underused tool in neuroinflammation; retaining much of the neuronal architecture, synaptic connections and diversity of cell types present in the hippocampus in vivo whilst providing convenient access to manipulate and sample the culture medium and observe cellular reactions as in other in vitro methods. Here we report the development of an OHSC model of synaptic disruption after aseptic inflammation and investigate the underlying mechanism.\n\nMethodsOHSCs were generated from P6-P9 C57BL/6, the APP transgenic TgCRND8 model, or wild-type littermate mice according to the interface method. Aseptic inflammation was induced via addition of lipopolysaccharide (LPS) and cultures were analysed for changes in synaptic proteins via western blot. qPCR and ELISA analysis of the slice tissue and culture medium respectively determined changes in gene expression and protein secretion. Microglia were selectively depleted using the toxin clodronate and the effect of IL1{beta} was assessed using a specific neutralising monoclonal antibody.\n\nResultsAddition of LPS caused a loss of the presynaptic protein synaptophysin via a mechanism dependent on microglia and involving IL1{beta}. Washout of LPS via medium exchange allows for partial recovery of synaptic protein levels after 2 weeks. TgCRND8 OHSCs do not show alterations in IL1{beta} expression at a timepoint where they exhibit spontaneous synaptophysin loss, and LPS does not alter levels of APP or A{beta} in wild-type OHSCs. This indicates that although synaptophysin loss is seen in both systems, there is likely to be distinct underlying pathogenic mechanisms between the neuroinflammatory and amyloid models.\n\nConclusionsWe report the development of an OHSC model of LPS-induced synaptophysin loss and demonstrate a key role for microglia and involvement of IL1{beta}. We propose that distinct molecular mechanisms lead to synaptophysin protein loss in LPS-exposed versus TgCRND8 OHSCs and provide a new experimental paradigm for assessing chronic changes in synaptic proteins, and synaptic plasticity, following acute inflammatory insults.

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