Biology subjects

Lythgoe, M. F.

Publications and source records attributed to Lythgoe, M. F..

14 recordsLinked to original sources

bioRxiv2024

Evidence for reduced choroid plexus volume in the aged brain

BackgroundThe choroid plexus plays an important role in brain homeostasis, including the active secretion of cerebrospinal fluid. Its function and structure have been reported to be affected by normal ageing. However, existing measures of choroid plexus volume may be complicated by partial volume (in vivo MRI) and tissue fixation artefacts (histology). In this study, we investigate possible changes in choroid plexus volume within the lateral ventricles of aged mice utilising two structural MRI protocols explicitly designed for time-efficient, high-resolution in vivo imaging of the choroid plexus. MethodsTwo MRI sequences were utilised to examine in vivo choroid plexus volume in the lateral ventricles of young ([~]6 months) and aged ([~]24 months) mouse brains: 1) an ultra-long echo-time T2 weighted fast-spin-echo and 2) a multi-TE T2* mapping protocol. A test-retest study was performed on a subset of the data to examine the reproducibility of choroid plexus volume estimation. A two-way ANOVA test was performed to determine possible differences in choroid plexus volume in young and aged mouse groups across the two distinct MRI protocols. ResultsReproducibility tests showed a low test-retest variability of the manual segmentation pipeline for both MRI protocols. A statistically significant reduction of in vivo choroid plexus volume was found in the aged mouse brain. This finding is concordant with previous histology studies that have observed a reduction in epithelial cell height with ageing across a wide range of species. ConclusionsWe present an in vivo investigation of changes to lateral ventricle choroid plexus volume in the mouse brain utilising a manual segmentation approach based on two bespoke MRI protocols designed for time-efficient high resolution imaging of the choroid plexus. Furthermore, based on these protocols, we provide evidence for a reduction in choroid plexus volume in the aged brain. This research provides insight for studies utilising MRI measurements of choroid plexus volume as a biomarker of age-related neurologic conditions as it indicates that the ageing process itself does not result in hypertrophy of the choroid plexus, but a decrease in tissue volume.

neuroscience↗

bioRxiv2024

Influence of the Glymphatic System on α-Synuclein Propagation: Role of Aquaporin-4 and the Dystrophin-Associated Protein Complex

Propagation and aggregation of prion proteins, such as tau and -synuclein (Syn), are key pathological features of neurodegenerative diseases. Extracellular clearance pathways, such as the glymphatic system, may play a crucial role in the removal of these toxic proteins from the brain. Primarily active during sleep, this system relies on aquaporin-4 (AQP4) water channel expression and polarisation to astrocytic endfeet, facilitating interstitial solute clearance. Glymphatic dysfunction has recently been implicated in Parkinsons disease, however the precise mechanisms underlying the pathogenic effect of this dysfunction remain unclear. This includes how impaired glymphatic function influences Syn propagation dynamics, and the role of propagating Syn itself on glymphatic function. In this study, we used a mouse model of Syn propagation to elucidate the impact of Syn aggregation on glymphatic function, by measuring CSF-ISF exchange and assessing AQP4 and associated endfoot complex proteins in the brain over time and across different regions. Our results show that direct injection of Syn pre-formed fibrils leads to reduced expression of the AQP4 endfoot complex, but propagation of endogenous Syn induces an enhancement of glymphatic function suggesting compensatory upregulation in response to increasing endogenous Syn load. To determine the influence of glymphatic dysfunction on Syn propagation dynamics, we then employed a pharmacological approach to inhibit glymphatic function in this model. Acute glymphatic inhibition significantly reduced brain to CSF Syn clearance, and chronic treatment exacerbated Syn pathology, neurodegeneration, and motor behavioural deficits in mice. Together our findings show that Syn clearance and propagation are modulated by glymphatic function and suggest that AQP4 complex dysregulation may contribute to glymphatic impairment associated with Parkinsons diseases. Summary for the non-scientific communityThe glymphatic system clears brain waste during sleep. Lopes et al. show that -synuclein, a protein linked to Parkinsons, is cleared by this system. Using a mouse model of the disease, they suggest that aquaporin-4 water channels may impair glymphatic function, contributing to -synuclein buildup in patients brains.

neuroscience↗

bioRxiv2024

A unique subset of pericystic endothelium associates with aberrant microvascular remodelling and impaired blood perfusion early in polycystic kidney disease

Hallmarks of autosomal dominant polycystic kidney disease (ADPKD), the most common hereditary kidney anomaly, include expanding fluid-filled epithelial cysts, inflammation, and fibrosis. Despite previous work showing the potential of vascular-based therapies, renal microvascular alterations in ADPKD, and their timing, are poorly understood. Using single-cell transcriptomics of human kidney microvasculature, we identify a population of endothelial cells adjacent to cysts in ADPKD. This pericystic endothelium, distinguishable by its expression of osteopontin (SPP1), has a distinct molecular profile compared to the common endothelial cell injury signature in other kidney diseases. SPP1+ pericystic endothelium was also present in an orthologous mouse model of ADPKD before overt kidney functional decline. By interrogating geometric, topological and fractal properties from three-dimensional imaging of early ADPKD mouse kidneys, we show that pericystic endothelium associates with disorganisation and non-uniformity of the renal cortical microvasculature. Concurrently, we detected region-specific reductions in cortical blood flow within ADPKD murine kidneys using arterial spin labelling. We conclude that ADPKD kidneys contain a unique subset of endothelium manifesting with aberrant remodelling and impaired blood perfusion. Its detection, prior to renal functional decline, advocates the vasculature as a therapeutic target to modulate or preserve renal function in early ADPKD.

pathology↗

bioRxiv2023

Glymphatic Inhibition Exacerbates Tau Propagation in an Alzheimers Disease Model

BackgroundThe aggregation and spread of misfolded amyloid structured proteins, such as tau and -synuclein, are key pathological features associated with neurodegenerative disorders, including Alzheimers and Parkinsons disease. These proteins possess a prion-like property, enabling their transmission from cell to cell leading to propagation throughout the central and peripheral nervous systems. While the mechanisms underlying their intracellular spread are still being elucidated, targeting the extracellular space has emerged as a potential therapeutic approach. The glymphatic system, a brain-wide pathway responsible for clearing extracellular metabolic waste from the central nervous system, has gained attention as a promising target for removing these toxic proteins. MethodsIn this study, we investigated the impact of long-term modulation of glymphatic function on tau aggregation and spread by chronically treating a mouse model of tau propagation with a pharmacological inhibitor of AQP4, TGN-020. Thy1-hTau.P301S mice were intracerebrally inoculated with tau into the hippocampus and overlying cortex, and subsequently treated with TGN-020 (3 doses/week, 50mg/kg TGN-020, i.p.) for 10-weeks. During this time, animal memory was studied using cognitive behavioural tasks, and structural MR images were acquired of the brain in vivo prior to brain extraction for immunohistochemical characterisation. ResultsOur findings demonstrate increased tau aggregation in the brain and transhemispheric propagation in the hippocampus and cortex following the inhibition of glymphatic clearance. Moreover, disruption of the glymphatic system aggravated recognition memory in tau inoculated mice and exacerbated regional changes in brain volume detected in the model. When initiation of drug treatment was delayed for several weeks post-inoculation, the aforementioned alterations were attenuated. ConclusionsThese results indicate that by modulating AQP4 function and, consequently, glymphatic clearance, it is possible to modify the propagation and pathological impact of tau in the brain, particularly during the initial stages of the disease. These findings highlight the critical role of the glymphatic system in preserving healthy brain homeostasis and offer valuable insights into the therapeutic implications of targeting this system for managing neurodegenerative diseases characterized by protein aggregation and spread.

neuroscience↗

bioRxiv2021

CO2 signalling mediates neurovascular coupling in the cerebral cortex

The mechanisms of neurovascular coupling remain incompletely understood. Here we show in experimental animal models that the neuronal activity-dependent increases in local cerebral blood flow in the somatosensory cortex are abolished by saturation of brain CO2-sensitive vasodilatory mechanism or disruption of brain HCO3-/CO2 transport, independently of baseline cerebral perfusion and brain tissue pH. These results suggest that increases in metabolic CO2 production and CO2 signalling play an important role in the development of neurovascular coupling response.

neuroscience↗

bioRxiv2019

89Zr-oxine labelling and PET imaging shows lung delivery of a cell/gene cancer therapy

PurposeMSCTRAIL is a new stem cell-based therapy for lung cancer, currently in phase I evaluation (ClinicalTrials.gov ref: NCT03298763). Biodistribution of cell therapies is rarely assessed in clinical trials, despite cell delivery to the target site often being critical to presumed mechanism of action. This preclinical study demonstrates that MSCTRAIL biodistribution dynamics can be detected non-invasively using 89Zr-oxine labelling and PET imaging, thus supporting use of this cell tracking technology in phase II evaluation.\n\nMethodsMSCTRAIL were radiolabelled with a range of 89Zr-oxine doses, and assayed for cell viability, phenotype and therapeutic efficacy post-labelling. Cell biodistribution was imaged in a mouse model of lung cancer using PET imaging and bioluminescence imaging (BLI) to confirm cell viability and location in vivo up to 1 week post-injection.\n\nResultsMSCTRAIL retained therapeutic efficacy and MSC phenotype at doses up to and above those required for clinical imaging. The effect of 89Zr-oxine labelling on cell proliferation rate was dose and time-dependent. PET imaging showed delivery of MSCTRAIL to the lungs in a mouse model of lung cancer, with PET signal correlating with the presence of viable cells as assessed by bioluminescence imaging, ex vivo autoradiography and matched fluorescence imaging on lung tissue sections. Human dosimetry estimates were produced using simulations and preclinical biodistribution data.\n\nConclusion89Zr-oxine labelling and PET imaging present an attractive method of evaluating the biodistribution of new cell-therapies, such as MSCTRAIL. This offers to improve understanding of mechanism of action, migration dynamics and interpatient variability of MSCTRAIL and other cell-based therapies.

cell biology↗

bioRxiv2019

Stem cell delivery to kidney via minimally invasive ultrasound-guided renal artery injection in mice

Cell-based therapies are promising treatments for various kidney diseases. However, the major hurdle in initiating therapeutic responses is the inefficiency of injection routes to deliver cells to the kidney parenchyma. Systemic injection, such as intravenous injection only delivers a small proportion of cells to the kidney. Whereas direct delivery, such as renal artery injection require surgical procedures. A minimally invasive renal artery injection was therefore developed to enhance cell delivery to kidney. In this study, luciferase expressing human adipocyte derived stem cells (ADSC) were labelled with gold nanorods (GNR) and injected into the renal artery using ultrasound guidance. The ADSCs were tracked using bioluminescence and photoacoustic imaging serially over 7 days. Imaging confirmed that the majority of signal was within the kidney, indicative of successful injection and that signal remained stable for 3 days. Histology showed co-localization of GNRs with ADSC staining throughout the kidney with no indication of injury caused by injection. These findings demonstrate that ultrasound-guided renal artery injection is feasible in mice and can successfully deliver a large proportion of cells which are retained within the kidney for 3 days. Therefore, the techniques developed here will be useful for optimising cell therapy in kidney diseases.

cell biology↗

bioRxiv2017

Combining optical imaging of cleared tissue with mathematical modelling to predict drug delivery and therapeutic response

Understanding how drugs are delivered to diseased tissue, and their subsequent spatial and temporal distribution, is a key factor in the development of effective, targeted therapies. However, the interaction between the pathophysiology of diseased tissue and individual therapeutic agents can be complex, and can vary significantly between individuals. In cancer, suboptimal dosing resulting from poor delivery can cause reduced treatment efficacy, upregulation of resistance mechanisms and can even stimulate growth. Preclinical tools to better understand drug delivery are therefore urgently required, which incorporate the inherent variability and heterogeneity of human disease. To meet this need, we have combined multiscale mathematical modelling, high-resolution optical imaging of intact, optically-cleared tumour tissue from animal models, and in vivo magnetic resonance imaging (MRI). Our framework, named REANIMATE (REAlistic Numerical Image-based Modelling of biologicAl Tissue substratEs) allows large tissue samples to be investigated as if it were a living sample, in detailed, highly controlled, computational experiments. Specifically, we show that REANIMATE can be used to predict the heterogeneous delivery of specific therapeutic agents, in disparate two murine xenograft models of human colorectal carcinoma. Given the wide adoption of optical clearing equipment in biomedical research laboratories, REANIMATE enables a new paradigm in cancer drug development, which could also be applied to other disease areas.

biophysics↗

bioRxiv2017

Investigating low-velocity fluid flow in tumours using convection-MRI

Several distinct fluid flow phenemena occur in solid tumours, including intravascular blood flow and interstitial convection. To probe low-velocity flow in tumors resulting from raised interstitial fluid pressure, we have developed a novel magnetic resonance imaging (MRI) technique named convection-MRI. It uses a phase-contrast acquisition with a dual-inversion vascular nulling preparation to separate intra- and extra-vascular flow. Here, we report the results of experiments in flow phantoms, numerical simulations and tumor xenograft models to investigate the technical feasibility of convection-MRI. We report a good correlation between estimates of effective fluid pressure from convection-MRI with gold-standard, invasive measurements of interstitial fluid pressure in mouse models of human colorectal carcinoma and show that convection-MRI can provide insights into the growth and response to vascular-targeting therapy in colorectal cancers.

biophysics↗

bioRxiv2017

Development of noninvasive biomarkers of response to proteasome inhibitor therapy (ixazomib) by imaging disrupted protein homeostasis in mouse models of solid tumors

With clinically-approved proteasome inhibitors now a standard of care for multiple myeloma, and increasing interest in their use in solid tumors, methods for monitoring therapeutic response in vivo are critically required. Here, we show that tumor protein homeostasis can be noninvasively monitored, using chemical exchange (CEST) magnetic resonance imaging (MRI) as a surrogate marker for proteasome inhibition, alongside diffusion MRI and relaxometry. We show that the in vivo CEST signal associated with amides and amines increases in proportion to proteasome inhibitor dose (ixazomib) and the magnitude of therapeutic effect in colorectal cancer xenografts. Moreover, we show that SW1222 and LS174T human colorectal cancer cell lines demonstrate differing sensitivities to ixazomib, which was reflected in our MRI measurements. We also found evidence of a mild stimulation in tumor growth at low ixazomib doses. Our results therefore identify CEST MRI as a promising method for safely and noninvasively monitoring changes in tumor protein homeostasis.

biophysics↗

bioRxiv2017

Non-invasive measurement of hepatic venous oxygen saturation (ShvO2) with quantitative susceptibility mapping in normal mouse liver and livers bearing colorectal metastases

PurposeThe purpose of this prospective study was to investigate the potential of QSM to non-invasively measure hepatic venous oxygen saturation (ShvO2).\n\nMaterials & MethodsAll animal studies were performed in accordance with the UK Home Office Animals Science Procedures Act (1986) and UK National Cancer Research Institute (NCRI) guidelines. QSM data was acquired from a cohort of mice (n=10) under both normoxic (medical air, 21% O2/ balance N), and hyperoxic conditions (100% O2). Susceptibility measurements were taken from large branches of the portal and hepatic vein under each condition and were used to calculate venous oxygen saturation in each vessel. Blood was extracted from the IVC of three mice under norm- and hyperoxic conditions, and oxygen saturation was measured using a blood gas analyser to act as a gold standard. QSM data was also acquired from a cohort of mice bearing colorectal liver metastases (CRLM). SvO2 was calculated from susceptibility measurements made in the portal and hepatic veins, and compared to the healthy animals.\n\nResultsSvO2 calculated from QSM measurements showed a significant increase of 14.93% in the portal vein (p < 0.05), and an increase of 21.39% in the hepatic vein (p < 0.01). Calculated results showed excellent agreement with those from the blood gas analyser (26.14% increase). ShvO2 was significantly lower in the disease cohort (30.18 {+/-} 11.6%), than the healthy animals (52.67 {+/-} 17.8%) (p < 0.05), but differences in the portal vein were not significant.\n\nConclusionQSM is a feasible tool for non-invasively measuring hepatic venous oxygen saturation and can detect differences in oxygen consumption in livers bearing colorectal metastases.

biophysics↗

bioRxiv2017

Deep learning diffusion fingerprinting to detect brain tumour response to chemotherapy

Artificial neural networks are being widely implemented for a range of different biomedical imaging applications.Convolutional neural networks are by far the most popular type of deep earning architecture,but often require very large datasets for robust training and evaluation We introduce deep learning diffusion fingerprinting (DLDF), which we have used to classifydiffusion-weighted magnetic resonance imaging voxels in a mouse model of glioblastoma (GL261 cell line), both prior to and in response to Temozolomide (TMZ) chemotherapy.We show that, even with limited training, DLDF can automatically segment brain tumours from normal brain, can automatically distinguish between young and older (after 9 days of growth) tumours and that DLDF can detect whether or not a tumour has been treated with chemotherapy.Our results also suggest that DLDF can detect localised changes in the underlying tumour microstructure, which are not evident using conventional measurements of the apparent diffusion coefficient (ADC).Tissue category maps generated by DLDF showed regions containing a mixture of normal brain and tumour cells, and in some cases evidence of tumour invasion across the corpus callosum, which were broadly consistent with histology.In conclusion, DLDF shows the potential for applying deep learning on a pixel-wise level,which reduces the need for vast training datasets and could easily be applied to other multi-dimensional imaging acquisitions\n\nAbbreviations

biophysics↗

bioRxiv2017

Quantitation of brain tumour microstructure response to Temozolomide therapy using non-invasive VERDICT MRI

There has been slow progress in the development of new therapeutic strategies for treating brain tumours, partly because assessment of treatment response is difficult and largely reliant on simple bi-dimensional measurements of MRI contrast-enhancing regions. Hence, there is a clinical need to develop improved imaging techniques for monitoring treatment response. In this study, we evaluate VERDICT (Vascular, Extracellular and Restricted Diffusion for Cytometry in Tumors) MRI in mouse glioblastomas for the quantification of tumour microstructure and assessment of response to Temozolomide (TMZ) chemotherapy, and, we investigate the feasibility of applying VERDICT MRI in a range of human gliomas. VERDICT MRI detected response to TMZ earlier than structural and apparent diffusion coefficient (ADC) measurements. A significant reduction in the cell radius parameter was detected three days earlier than ADC and six days earlier than structural MRI. Histological analysis showed the same trend as VERDICT of decreased intracellular volume fraction in the TMZ-treated mice. Vascular volume fraction was not altered by TMZ, which was consistent with optical projection tomography measurements. In patients, glioblastoma compartmental volume fractions showed good agreement with mouse glioblastoma parameters. The VERDICT parameters varied across the human gliomas, with raised intracellular volume fraction in the oligodendrogliomas and elevated cell radius in both low-grade tumours subtypes. In conclusion, our results suggest that VERDICT MRI is more sensitive at detecting TMZ response than structural or ADC measurements. In patients, VERDICT is feasible within clinical scan times, and performed best at characterising glioblastoma. Further optimisation should improve assessment of different glioma subtypes.

biophysics↗

bioRxiv2017

Impaired brain glymphatic flow in a rodent model of chronic liver disease and minimal hepatic encephalopathy

Neuronal function is exquisitely sensitive to alterations in extracellular environment. In patients with hepatic encephalopathy (HE), accumulation of metabolic waste products and noxious substances in the interstitial fluid of the brain may contribute to neuronal dysfunction and cognitive impairment. In a rat model of chronic liver disease, we used an emerging dynamic contrast-enhanced MRI technique to assess the efficacy of the glymphatic system, which facilitates clearance of solutes from the brain. We identified discrete brain regions (olfactory bulb, prefrontal cortex and hippocampus) of altered glymphatic flow, which aligned with cognitive/behavioural deficits. Although the underlying pathophysiological mechanisms remain unclear, this study provides the first experimental evidence of impaired glymphatic clearance in HE.

pathology↗