Biology subjects

McGeachan, R. I.

Publications and source records attributed to McGeachan, R. I..

3 recordsLinked to original sources

bioRxiv2025

Amyloid-beta pathology increases synaptic engulfment by glia in feline cognitive dysfunction syndrome: A naturally occurring model of Alzheimer's disease

Feline cognitive dysfunction syndrome (CDS) is an age-related neurodegenerative disorder, comparable to dementia in people, characterised by behavioural changes such as increased vocalisation, altered social interactions, sleep-wake cycle, disorientation and house-soiling. Although the underlying mechanisms remain poorly understood, pathologies similar to those observed in Alzheimers disease (AD), have been identified in the brains of aged or CDS-affected cats, including brain atrophy, neuronal loss, amyloid-beta plaques, tau pathology, and cerebral amyloid angiopathy. Neuroinflammation and synapse loss, other important hallmarks of AD, may also play important roles in feline ageing and CDS, but these are yet to be explored. Several mechanisms of synapse loss have been described in human AD and mouse models of amyloidopathy, including synaptic accumulation of amyloid-beta, and the aberrant induction of synaptic engulfment by microglia and astrocytes. In this study, immunohistochemistry and confocal microscopy were used to examine the parietal cortex of young (n=7), aged (n=10), and CDS-affected (n=8) cats. Linear mixed effect modelling revealed that amyloid-beta accumulates within synapses in the aged and CDS-affected brain. Additionally, in the aged and CDS groups there was microgliosis, astrogliosis and increased synaptic engulfment by microglia and astrocytes in regions with A{beta} plaques. Further, microglia and astrocytes show increased internalisation of amyloid-beta-containing synapses near plaques. These findings suggest that amyloid-beta exerts a pathogenic effect in the feline brain, with mechanisms mirroring those seen in human AD.

neuroscience↗

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.

neuroscience↗

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.

neuroscience↗