Biology subjects

Mortiboys, H. J.

Publications and source records attributed to Mortiboys, H. J..

5 recordsLinked to original sources

bioRxiv2023

The Parkinson's Disease related mutant VPS35 (D620N) amplifies the LRRK2 response to endolysosomal stress

The identification of multiple genes linked to Parkinsons Disease invites the question as to how they may cooperate. We have generated isogenic cell lines that inducibly express either wild-type or a mutant form of the retromer component VPS35 (D620N), which has been linked to Parkinsons Disease. This has enabled us to test proposed effects of this mutation in a setting where the relative expression reflects the physiological occurrence. We confirm that this mutation compromises VPS35 association with the WASH complex, but find no defect in WASH recruitment to endosomes, nor in the distribution of lysosomal receptors, cation-independent mannose-6-phosphate receptor and Sortilin. We show VPS35 (D620N) enhances the activity of the Parkinsons associated kinase LRRK2 towards RAB12 under basal conditions. Furthermore, VPS35 (D620N) amplifies the LRRK2 response to endolysosomal stress resulting in enhanced phosphorylation of RABs 10 and 12. By comparing different types of endolysosomal stresses such as the ionophore nigericin and the membranolytic agent LLOMe, we are able to dissociate phospho-RAB accumulation from membrane rupture.

cell biology↗

bioRxiv2023

Deficits in mitochondrial function and glucose metabolism seen in sporadic and familial Alzheimers disease derived Astrocytes are ameliorated by increasing hexokinase 1 expression.

BackgroundAstrocytes have multiple roles including providing neurons with metabolic substrates and maintaining neurotransmitter synaptic homeostasis. Astrocyte glucose metabolism plays a key role in learning and memory with astrocytic glycogen a key substrate supporting memory encoding. The neuronal support provided by astrocytes has a high metabolic demand. Deficits in astrocytic mitochondrial metabolic functioning and glycolysis could impair neuronal function. Changes to cellular metabolism are seen early in Alzheimers disease (AD). Understanding cellular metabolism changes in AD astrocytes could be exploited as a new biomarker or synergistic therapeutic agent when combined with anti-amyloid treatments in AD. MethodsIn this project, we characterised mitochondrial and glycolytic function in astrocytes derived from patients with sporadic (n=6) and familial (PSEN1, n=3) forms of AD. Astrocytes were derived using direct reprogramming methods. Astrocyte metabolic outputs: ATP, and extracellular lactate levels were measured using luminescent and fluorescent protocols. Mitochondrial respiration and glycolytic function were measured using a Seahorse XF Analyzer. Hexokinase deficits identified where corrected by transfecting astrocytes with an adenovirus viral vector containing the hexokinase 1 gene. ResultsThere was a reduction of total cellular ATP of 20% (p=0.05 in sAD astrocytes) and of 48% (p<0.01) in fAD. A 44% reduction (p<0.05), and 80% reduction in mitochondrial spare capacity was seen in sAD and fAD astrocytes respectively. Reactive oxygen species (ROS) were increased in both AD astrocyte types (p=0.05). Mitochondrial complex I and II was significantly increased in sAD (p<0.05) but not in fAD. Astrocyte glycolytic reserve and extracellular lactate was significantly reduced when compared to controls in both sAD and fAD (p<0.05). We identified a deficit in the glycolytic pathway enzyme hexokinase, and correcting this deficit restored most of the metabolic phenotype in sAD but not fAD astrocytes. ConclusionAD astrocytes have abnormalities in functional capacity of mitochondria and the process of glycolysis. These functional deficits can be improved by correcting hexokinase expression deficits with adenoviral vectors. This suggests that hexokinase 1 deficiency could potentially be exploited as a new therapeutic target for AD.

neuroscience↗

bioRxiv2022

FBXL4 deficiency promotes mitophagy by elevating NIX.

The selective autophagy of mitochondria is linked to mitochondrial quality control and is critical to a healthy organism. We have conducted a CRISPR/Cas9 screen of human E3 ubiquitin ligases for influence on mitophagy under both basal cell culture conditions and following acute mitochondrial depolarisation. We identify two Cullin RING ligases, VHL and FBXL4 as the most profound negative regulators of basal mitophagy. We show that these converge through control of the mitophagy adaptors BNIP3 and BNIP3L/NIX through different mechanisms. FBXL4 suppression of BNIP3 and NIX levels is mediated via direct interaction and protein destabilisation rather than suppression of HIF1-mediated transcription. Depletion of NIX but not BNIP3 is sufficient to restore mitophagy levels. Our study enables a full understanding of the aetiology of early onset mitochondrial encephalomyopathy that is supported by analysis of a disease associated mutation. We further show that the compound MLN4924, which globally interferes with Cullin RING ligase activity, is a strong inducer of mitophagy providing a research tool in this context and a candidate therapeutic agent for conditions linked to mitochondrial dysfunction.

cell biology↗

bioRxiv2022

A p21-GFP zebrafish model of senescence for rapid testing of senolytics in vivo.

Senescence drives the onset and severity of multiple ageing-associated diseases as well as frailty. As a result, there has been an increased interest in mechanistic studies and in the search for compounds targeting senescent cells, known as senolytics. Mammalian models are commonly used to test senolytics and generate functional and toxicity data at the level of organs and systems, yet this is expensive and time consuming. Zebrafish share high homology in genes associated with human ageing and disease. They can be genetically-modified relatively easily. In larvae, most organs develop within 5 days of fertilisation and are transparent, which allows tracking of fluorescent cells in vivo in real time, testing drug off-target toxicity and assessment of cellular and phenotypic changes. Here, we have generated a transgenic zebrafish line that expresses green fluorescent protein (GFP) under the promoter of a key senescence marker, p21. We show an increase in p21:GFP+ cells in larvae following exposure to ionising radiation and with natural ageing. p21:GFP+ cells display other markers of senescence, including senescence-associated {beta}-galactosidase and IL6. The observed increase in senescent cells following irradiation is associated with a reduction in the thickness of muscle fibres and mobility, two important ageing phenotypes. We also show that quercetin and dasatinib, two senolytics currently in clinical trials, reduce the number of p21:GFP+ cells, in a rapid 5-day assay. This model provides an important tool to study senescence in a living organism, allowing the rapid selection of senolytics before moving to more expensive and time-consuming mammalian systems.

pharmacology and toxicology↗

bioRxiv2021

Co-aggregation with Apolipoprotein E modulates the function of Amyloid-β in Alzheimer's disease

Which isoforms of apolipoprotein E (apoE) we inherit determine our risk of developing late-onset Alzheimers Disease (AD), but the mechanism underlying this link is poorly understood. In particular, the relevance of direct interactions between apoE and amyloid-{beta} (A{beta}) remains controversial. Here, single-molecule imaging shows that all isoforms of apoE associate with A{beta} in the early stages of aggregation and then fall away as fibrillation happens. ApoE-A{beta} co-aggregates account for [~]50% of the mass of soluble A{beta} aggregates detected in the frontal cortices of homozygotes with the higher-risk APOE4 gene. Our results connect inherited APOE genotype with the risk of developing AD by demonstrating how, in an isoform- and lipidation-specific way, apoE modulates the aggregation, clearance and toxicity of A{beta}. Selectively removing non-lipidated apoE4-A{beta} co-aggregates enhances clearance of toxic A{beta} by glial cells, and reduces inflammation and membrane damage, demonstrating a clear path to AD therapeutics.

neuroscience↗