Biology subjects

Andrews, K.

Publications and source records attributed to Andrews, K..

6 recordsLinked to original sources

bioRxiv2025

Dexamethasone-Induced p57-Mediated Quiescence Drives Chemotherapy Resistance in Sonic Hedgehog Medulloblastoma

Medulloblastoma (MB), the most common malignant pediatric brain tumor, remains difficult to cure upon relapse, with only 12.4% of patients surviving five years post-recurrence. While specific quiescent tumor cell populations are known to contribute to treatment-resistance, the molecular mechanisms that maintain quiescence remain poorly defined. Here, we identify the cell cycle inhibitor p57 as a regulator of quiescence and chemotherapy resistance in Sonic Hedgehog (SHH) MB. Nuclear p57 was enriched in Sox2+ and Nestin+ stem-like MB cells compared to proliferative Atoh1+ cells. Inducing p57 expression in SHH MB cells led to a six-fold increase in G0-phase cells and conferred resistance to the frontline chemotherapeutic vincristine. Clinically, dexamethasone is a glucocorticoid given to nearly all MB patients to manage cerebral edema and is administered with wide variability in timing and dosing. We show that dexamethasone significantly increased nuclear p57 levels and expanded the G0 population in both Ptch1+/- and Ptch1+/-;Trp53-/- SHH MB mouse models. Pre-treatment with dexamethasone reduced vincristine sensitivity in SHH MB cells. Together, our findings reveal a clinically relevant and previously unrecognized mechanism of treatment resistance, whereby dexamethasone, despite its benefits in managing edema, may inadvertently contribute to tumor persistence or recurrence by driving a quiescent, drug-resistant state. Addressing the lack of standardization in steroid use or targeting p57 may improve treatment response and reduce recurrence in patients diagnosed with SHH MB.

cancer biology↗

bioRxiv2024

Ezh2 Delays Activation of Differentiation Genes During Normal Cerebellar Granule Neuron Development and in Medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumour in children. The Sonic Hedgehog (SHH)-medulloblastoma subtype arises from the cerebellar granule neuron lineage. Terminally differentiated neurons are incapable of undergoing further cell division, so an effective treatment for this tumour could be to force neuronal differentiation. Differentiation therapy provides a potential alternative for patients with medulloblastoma who harbor mutations that impair cell death pathways (TP53), which is associated a with high mortality. To this end, our goal was to explore epigenetic regulation of cerebellar granule neuron differentiation in medulloblastoma cells. Key regulators were discovered using chromatin immunoprecipitation with high-throughput sequencing. DNA-bound protein and chromatin protein modifications were investigated across all genes. We discovered that Ezh2-mediated tri-methylation of the H3 histone (H3K27me3), occurred on more than half of the 787 genes whose transcription normally increases as granule neurons terminally differentiate. Conditional knockout of Ezh2 led to early initiation of differentiation in granule neuron precursors (GNPs), but only after cell cycle exit had occurred. Similarly, in MB cells, neuronal differentiation could be induced by preventing H3K27me3 modifications using an Ezh2 inhibitor (UNC1999), but only when UNC1999 was combined with forced cell cycle exit driven by a CDK4/6 inhibitor (Palbociclib). Ezh2 emerges as a powerful restraint upon post-mitotic differentiation during normal GNP development and combination of Ezh2 inhibition with cell cycle exit leads to MB cell differentiation.

cancer biology↗

bioRxiv2024

Learn!Bio - A time-limited cross-sectional study on biosciences students' pathway to resilience during and post the Covid-19 pandemic at an UK university from 2020-2023 and insights into future teaching approaches.

Higher education in biosciences is significantly informed by hands-on field trips and practical laboratory skills-training. With the first Covid-19 national lock-down in England in March 2020, on-campus education at higher education institutions was swiftly moved to alternative provisions, including online only options, a mix of synchronous or asynchronous blended, or hybrid adaptions. Students enrolled on an undergraduate bioscience programme have been faced with unprecedented changes and interruptions to their education. This study aimed to evaluate bioscience students ability to adjust to a fast-evolving learning environment and to capture students journey building up resilience and graduate attributes. Bioscience undergraduate students in years 1-3 at the biology department at a Northwest English university participated in this anonymous, cross-sectional, mixed-method study with open and closed questions evaluating their perception and feedback to remote and blended learning provisions during the Covid-19 pandemic and post pandemic learning capturing academic years 2019/20 to 2022/23. The Covid-19 pandemic and the consequent restriction of personal social interaction resulted in an significant decrease in the mental wellbeing of undergraduate bioscience students in this study, cumulating in poor or very poor self-rating of wellbeing in spring 2021; while at the same time students showed evidence of advanced adaption to the new learning and social environment by acquisition of additional technical, social and professional graduate-level skills, indicative of an, albeit unconscious, transition to resilience. Post pandemic, bioscience students worry about the increased living costs and are strongly in favour of a mixture of face-to-face and blended learning approaches. Our results show that bioscience students can experience poor mental health while developing resilience, indicating tailored support can aid students resilience performance. Students have adjusted with ease to digital teaching provisions and expect higher education institutions continue to offer both, face-to-face, and blended teaching, reducing the burden on students significantly risen living costs.

scientific communication and education↗

bioRxiv2023

Effect of antiretroviral protease inhibitors on Plasmodium falciparum erythrocyte egress and invasion

BackgroundAnti-retroviral protease inhibitors directly inhibit the growth of asexual blood stage malaria parasites, however, this activity is not fully understood. While mode of action hypotheses have included parasite aspartic protease (plasmepsin) inhibition, current data suggest that digestive vacuole plasmepsins I-IV are not essential for asexual parasite survival, that plasmepsins VI-VIII are not expressed in these parasites and that antiretroviral protease inhibitors are poor inhibitors of plasmepsin V. The remaining plasmepsins, IX and X, have recently been shown to be essential for merozoite egress and invasion, playing important roles in the processing of key proteins including the rhoptry bulb protein PfRAP1, and subtilisin-like serine protease PfSUB1, respectively. To further understand the antiplasmodial activity of antiretroviral protease inhibitors, here we investigated the impact of tipranavir, lopinavir, ritonavir and saquinavir on the processing of PfRAP1, the PfSUB1-processed PfMSP1, and the egress and invasion of P. falciparum parasites from human erythrocytes. MethodsThe effect of tipranavir, lopinavir, ritonavir and saquinavir on P. falciparum parasite egress and invasion was assessed using synchronized asexual blood stage P. falciparum parasites. Schizont rupture and purified merozoite invasion were performed with and without drug and quantified by flow cytometry analysis. The impact of selected antitretroviral protease inhibitors on PfRAP1 and PfMSP1 processing was assessed by Wesstern blot. ResultsThe effect of tipranavir, lopinavir, ritonavir and saquinavir on the egress and invasion of P. falciparum parasites from human erythrocytes varied considerably, but was low at concentrations shown to inhibit P. falciparum asexual parasite growth in vitro and negligible at clinically relevant concentrations. While the treatment of parasites with the antiretrovial protease inhibitors appeared to reduce the overall expression of PfRAP1 and PfMSP1, the processing of these proteins was not inhibited by concentrations known to inhibit parasite growth in vitro. ConclusionsThe limited activity of tipranavir, lopinavir, ritonavir and saquinavir on the egress and invasion of P. falciparum parasites from human erythrocytes and the processing of PfRAP1 and PfMSP1 suggests that plasmepsin IX and X are unlikely to be the primary targets of these drugs in these parasites.

microbiology↗

bioRxiv2023

Mitochondrial dysfunction underlies impaired neurovascular coupling following traumatic brain injury

Traumatic brain injury (TBI) involves an acute injury (primary damage), which may evolve in the hours to days after impact (secondary damage). Seizures and cortical spreading depolarization (CSD) are metabolically demanding processes that may worsen secondary brain injury. Metabolic stress has been associated with mitochondrial dysfunction, including impaired calcium homeostasis, reduced ATP production, and elevated ROS production. However, the association between mitochondrial impairment and vascular function after TBI is poorly understood. Here, we explored this association using a rodent closed head injury model. CSD resulted in neurobehavioral decline after TBI. Craniotomy was performed to elicit CSD via electrical stimulation or to induce seizures via 4-aminopyridine application. We measured vascular dysfunction following CSDs and seizures in TBI animals using laser doppler flowmetry. We observed a more profound reduction in local cortical blood flow in TBI animals compared to healthy controls. Following TBI, CSD resulted in mitochondrial dysfunction and pathological signs of increased oxidative stress adjacent to the vasculature. We explored these findings further using electron microscopy and found that TBI and CSDs resulted in vascular morphological changes and mitochondrial cristae damage in astrocytes, pericytes and endothelial cells. Overall, we provide evidence that CSDs induce mitochondrial dysfunction, impaired cortical blood flow, and neurobehavioral deficits in the setting of TBI. HighlightsCortical spreading depolarization after TBI causes behavioral decline in rats. Vasoconstriction and oligemia after cortical spreading depolarization is worse in TBI brains. Spreading depolarization causes impaired mitochondrial function. TBI and spreading depolarization result in constricted vessels and increased pericyte size. TBI and spreading depolarization result in mitochondrial damage in vascular cells. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=124 SRC="FIGDIR/small/549872v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@176a9a6org.highwire.dtl.DTLVardef@17bfc19org.highwire.dtl.DTLVardef@e3d74dorg.highwire.dtl.DTLVardef@4c194e_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2023

Thymidine kinase-independent click chemistry DNADetect probes for DNA proliferation assessment in malaria parasites

Metabolic chemical probes are small molecule reagents that utilise naturally occurring biosynthetic enzymes for in situ incorporation into biomolecules of interest. These reagents can be used to label, detect, and track important biological processes within living cells including protein synthesis, protein glycosylation and nucleic acid proliferation. A limitation of current chemical probes, which have largely focused on mammalian cells, is that they often cannot be applied to other organisms due to metabolic differences. For example, the thymidine derivative 5-ethynyl-2-deoxyuridine (EdU) is a gold standard metabolic chemical probe for assessing DNA proliferation in mammalian cells however is unsuitable for the study of malaria parasites due to Plasmodium species lacking the thymidine kinase enzyme that is essential for metabolism of EdU. Herein we report the design and synthesis of new thymidine-based probes that sidestep the requirement for a thymidine kinase enzyme in Plasmodium. Two of these DNADetect probes exhibit robust labelling of replicating asexual intraerythrocytic P. falciparum parasites, as determined by flow cytometry using copper catalysed azide-alkyne cycloaddition (CuAAC) to a fluorescent azide. The DNADetect chemical probes are synthetically accessible and thus can be made widely available to researchers as tools to further understand the biology of different Plasmodium species, including laboratory lines and clinical isolates.

microbiology↗