Biology subjects

Lloyd, M.

Publications and source records attributed to Lloyd, M..

7 recordsLinked to original sources

bioRxiv2026

Hyperglycaemia reversibly disrupts circadian behaviour in mice

Disrupted sleep and circadian rhythms are among the most common features of diabetes, and are known to raise the risk of developing the disease. Whether the relationship also runs the other way, with diabetes itself disrupting the clock, has remained unresolved. Using an inducible mouse model of diabetes, in which hyperglycaemia can be induced and then reversed within the same animal, we show that elevated blood glucose is a reversible cause of circadian disruption. Raising blood glucose reduced the amplitude of circadian rest-activity rhythms by 50%, in proportion to the degree of hyperglycaemia, and shortened the free-running period of the clock. Restoring normoglycaemia reversed both effects. Diabetic animals had a delayed phase of activity onset, i.e. later chronotype, and re-entrained more slowly after a simulated jet lag. However, phase shifting to nocturnal light pulses was intact, suggesting normal photic responses. Brain glucose and O-GlcNAcylation, a nutrient-sensitive protein modification, were both elevated in diabetic animals, showing that peripheral hyperglycaemia reaches the brain and alters its metabolic state, and providing a molecular readout of that exposure. Together, these findings establish that a peripheral metabolic state is a reversible determinant of circadian rest-activity behaviour, completing a bidirectional link between blood glucose and the clock and arguing that the two must be treated together rather than in isolation.

neuroscience↗

bioRxiv2026

Intact learning and memory in mice incapable of de novo myelination

Motor skill learning stimulates and requires generation of oligodendrocytes (OLs) from their precursors (OLPs) in the adult mouse brain, but the functional role(s) of the newly formed OLs is not known. We asked whether new compact myelin sheaths are required, by genetic block of myelin basic protein (MBP) synthesis in adult OLPs and their newly-differentiating OL progeny, using tamoxifen-inducible Cre-lox recombination. Newly-differentiating OLs in these Mbp-cKO mice are unable to assemble compact myelin or normal nodes of Ranvier. Despite this, Mbp-cKOs learned a motor skill just as well as their wild type littermates. They also demonstrated normal contextual fear conditioning. Therefore, neither motor nor fear learning depends on rapid saltatory conduction in newly-myelinated circuits. Mbp-cKOs also formed normal long-term motor and contextual fear memories. Moreover, OL lineage-specific knockout of Monocarboxylate transporter-1 (Mct1), believed to be responsible for transferring metabolic substrates from OLs into axons, did not affect learning or memory consolidation. Myelin regulatory factor (Myrf)-cKOs, in which newly-differentiating OLs die and are rapidly eliminated, confirmed that newly formed OLs are required for learning and memory. Together, the data suggest that learning and memory depends on a non-canonical property of pre-myelinating or myelinating OLs, distinct from myelins cardinal role in speeding action potentials.

neuroscience↗

bioRxiv2024

CRISPR-enabled control of gene expression sets the isotopic composition of microbial methane

The stable isotopic composition of biogenic methane varies substantially in the environment and is routinely used to fingerprint its source. However, the underlying cause of this variation is debated. Here, we experimentally manipulate the growth rate of the model methanogen, Methanosarcina acetivorans, using CRISPR mutagenesis to generate a tunable version of the key and final enzyme in methanogenesis, methyl-coenzyme M reductase (MCR). We demonstrate that the carbon and hydrogen isotopic composition of methane change as a function of MCR expression and growth rate. Using an isotope enabled metabolic model we show that these changes stem from a substrate-independent increase in reversibility of methanogenic enzymes. Overall, these data provide a novel framework for calibrating growth coupled changes in the isotopic composition of biogenic methane.

microbiology↗

bioRxiv2024

Selective suppression of oligodendrocyte-derived amyloid beta rescues neuronal dysfunction in Alzheimer's Disease

Reduction of amyloid beta (A{beta}) has been shown to be effective in treating Alzheimers Disease (AD), but the underlying assumption that neurons are the main source of pathogenic A{beta} is untested. Here we challenge this prevailing belief by demonstrating that oligodendrocytes are an important source of A{beta}, and play a key role in promoting abnormal neuronal hyperactivity in AD. We show that selectively suppressing oligodendrocyte A{beta} production improves AD brain pathology and restores neuronal function in vivo. Our findings suggest that targeting oligodendrocyte A{beta} production could be a promising therapeutic strategy for treating AD.

neuroscience↗

bioRxiv2023

Beyond Alternans: Detection of Higher-Order Periodicity in Ex-Vivo Human Ventricles Before Induction of Ventricular Fibrillation

BackgroundRepolarization alternans, defined as period-2 oscillation in the repolarization phase of the action potentials, is one of the cornerstones of cardiac electrophysiology as it provides a mechanistic link between cellular dynamics and ventricular fibrillation (VF). Theoretically, higher-order periodicities (e.g., period-4, period-8,...) are expected but have very limited experimental evidence. MethodsWe studied explanted human hearts, obtained from the recipients of heart transplantation at the time of surgery, using optical mapping technique with transmembrane voltage-sensitive fluorescent dyes. The hearts were stimulated at an increasing rate until VF was induced. The signals recorded from the right ventricle endocardial surface just before the induction of VF and in the presence of 1:1 conduction were processed using the Principal Component Analysis and a combinatorial algorithm to detect and quantify higher-order dynamics. ResultsA prominent and statistically significant 1:4 peak (corresponding to period-4 dynamics) was seen in three of the six studied hearts. Local analysis revealed the spatiotemporal distribution of higher-order periods. Period-4 was localized to temporally stable islands. Higher-order oscillations (period-5, 6, and 8) were transient and primarily occurred in arcs parallel to the activation isochrones. DiscussionWe present evidence of higher-order periodicities and the co-existence of such regions with stable non-chaotic areas in ex-vivo human hearts before VF induction. This result is consistent with the period-doubling route to chaos as a possible mechanism of VF initiation, which complements the concordant to discordant alternans mechanism. The presence of higher-order regions may act as niduses of instability that can degenerate into chaotic fibrillation.

biophysics↗

bioRxiv2021

Proton export drives the Warburg Effect

Aggressive cancers commonly ferment glucose to lactic acid at high rates, even in the presence of oxygen. This is known as aerobic glycolysis, or the "Warburg Effect". It is widely assumed that this is a consequence of the upregulation of glycolytic enzymes. Oncogenic drivers can increase the expression of most proteins in the glycolytic pathway, including the terminal step of exporting H+ equivalents from the cytoplasm. Proton exporters maintain an alkaline cytoplasmic pH, which can enhance all glycolytic enzyme activities, even in the absence of oncogene-related expression changes. Based on this observation, we hypothesized that increased uptake and fermentative metabolism of glucose could be driven by the expulsion of H+ equivalents from the cell. To test this hypothesis, we stably transfected lowly-glycolytic MCF-7, U2-OS, and glycolytic HEK293 cells to express proton exporting systems: either PMA1 (yeast H+-ATPase) or CAIX (carbonic anhydrase 9). The expression of either exporter in vitro enhanced aerobic glycolysis as measured by glucose consumption, lactate production, and extracellular acidification rate. This resulted in an increased intracellular pH, and metabolomic analyses indicated that this was associated with an increased flux of all glycolytic enzymes upstream of pyruvate kinase. These cells also demonstrated increased migratory and invasive phenotypes in vitro, and these were recapitulated in vivo by more aggressive behavior, whereby the acid-producing cells formed higher grade tumors with higher rates of metastases. Neutralizing tumor acidity with oral buffers reduced the metastatic burden. Therefore, cancer cells with increased H+ export increase intracellular alkalization, even without oncogenic driver mutations, and this is sufficient to alter cancer metabolism towards a Warburg phenotype.

cancer biology↗

bioRxiv2019

Systematic Establishment of Robustness and Standards in Patient-Derived Xenograft Experiments and Analysis

Patient-Derived Xenografts (PDXs) are tumor-in-mouse models for cancer. PDX collections, such as those supported by the NCI PDXNet program, are powerful resources for preclinical therapeutic testing. However, variations in experimental design and analysis procedures have limited interpretability. To determine the robustness of PDX studies, the PDXNet tested temozolomide drug response for three pre-validated PDX models (sensitive, resistant, and intermediate) across four blinded PDX Development and Trial Centers (PDTCs) using independently selected SOPs. Each PDTC was able to correctly identify the sensitive, resistant, and intermediate models, and statistical evaluations were concordant across all groups. We also developed and benchmarked optimized PDX informatics pipelines, and these yielded robust assessments across xenograft biological replicates. These studies show that PDX drug responses and sequence results are reproducible across diverse experimental protocols. Here we share the range of experimental procedures that maintained robustness, as well as standardized cloud-based workflows for PDX exome-seq and RNA-Seq analysis and for evaluating growth.

cancer biology↗