Biology subjects

Ruminot, I.

Publications and source records attributed to Ruminot, I..

5 recordsLinked to original sources

bioRxiv2025

Acute stimulation of glucose metabolism by H2O2 sustains theNADPH steady-state under oxidative stress

Oxidative stress reprograms metabolic flux from glycolysis to the pentose phosphate pathway. Recently, it has been proposed that NADPH acts as a key molecule in pentose phosphate pathway regulation by exerting negative feedback through tonic inhibition of glucose-6-phosphate dehydrogenase. Interestingly, recent studies show that NADPH levels remain stable during acute exposure to hydrogen peroxide in the presence of glucose, ruling out NADPH-dependent feedback inhibition. We hypothesize that hydrogen peroxide triggers a feedforward activation mechanism, increasing NADPH production even before any detectable NADPH depletion. To probe this hypothesis, we used a panel of genetically encoded fluorescent indicators to monitor glucose, NADPH, F1,6BP, and pyruvate in single cells with high temporal resolution. Our results reveal that hydrogen peroxide rapidly activates glucose transport and consumption rates, enabling cells to preserve NADPH steady-state levels during early oxidative stress. Notably, this response precedes NADPH depletion, implying an anticipatory phenomenon that boosts NADPH production prior to its consumption. Furthermore, hydrogen peroxide induced an acute perturbation of F1,6BP steady-state and an increase of pyruvate accumulation. The pharmacological inhibition of the PPPs gateway enzymes, glucose-6-phosphate dehydrogenase and transketolase, abolished the hydrogen peroxide-dependent alterations in F1,6BP steady-state levels and pyruvate accumulation, respectively. These findings suggest that a substantial fraction of glucose-derived carbon flux is diverted to the pentose phosphate pathway under oxidative stress, underscoring the importance of feedforward control in maintaining redox balance.

biochemistry↗

bioRxiv2025

APOE genotype-dependent differences in human astrocytic energy metabolism

The main genetic risk factor for Alzheimers disease (AD) is the presence of the apolipoprotein E4 (APOE4) allele. While APOE4 increases the risk of developing AD, the APOE2 allele is protective and APOE3 is risk-neutral. In the brain, APOE is primarily expressed by astrocytes and plays a key role in various processes including cholesterol and lipid transport, neuronal growth, synaptic plasticity, immune response and energy metabolism. Disruptions in brain energy metabolism are considered a major contributor to AD pathophysiology, raising a key question about how different APOE isoforms affect the energy metabolism of human astrocytes. In this study, we generated astrocytes (iAstrocytes) from APOE-isogenic human induced pluripotent stem cells (iPSCs), expressing either APOE2, APOE3, APOE4 or carrying an APOE knockout (APOE-KO), and investigated APOE genotype-dependent changes in energy metabolism. ATP Seahorse assay revealed a reduced mitochondrial and glycolytic ATP production in APOE4 iAstrocytes. In contrast, proteomic GO enrichment analysis and mitochondrial stress tests indicated increased mitochondrial respiration and activity in APOE4 iAstrocytes, accompanied with elevated proton leak, while mitochondrial fusion and fission protein levels remain unchanged. Glycolysis stress tests also demonstrated enhanced glycolysis and glycolytic capacity in APOE4 iAstrocytes while genetically encoded nanosensor-based FLIM analysis revealed that APOE does not affect lactate dynamics. Mass spectrometry-based metabolomic analysis identified various energy and glucose metabolism-related pathways that were differentially regulated in APOE4 compared to the other genotypes, including mitochondrial electron transport chain and glycolysis. In general, APOE2 and APOE-KO iAstrocytes showed a very similar phenotype in all functional assays and differences between APOE2/APOE-KO and APOE4 were stronger than between APOE3 and APOE4. Our study provides evidence for APOE genotype-dependent effects on astrocyte energy metabolism and highlights alterations in the bioenergetic processes of the brain as important pathomechanisms in AD.

neuroscience↗

bioRxiv2024

Lactate-carried Mitochondrial Energy Overflow

We addressed the question of mitochondrial lactate metabolism using genetically-encoded sensors. The organelle was found to contain a dynamic lactate pool that leads to dose- and time-dependent protein lactylation. In neurons, mitochondrial lactate reported blood lactate levels with high fidelity. The exchange of lactate across the inner mitochondrial membrane was found to be mediated by a high affinity H+-coupled transport system involving the mitochondrial pyruvate carrier MPC. Assessment of electron transport chain activity and determination of lactate flux showed that mitochondria are tonic lactate producers, a phenomenon driven by energization and stimulated by hypoxia. We conclude that an overflow mechanism caps the redox level of mitochondria, while saving energy in the form of lactate. One Sentence SummaryMitochondrial lactate production

biochemistry↗

bioRxiv2021

Inhibition of the sodium-dependent HCO3 -transporter SLC4A4, produces a cystic fibrosis-like airway disease phenotype.

Bicarbonate secretion is a fundamental process involved in maintaining acid-base homeostasis. Disruption of bicarbonate entry into airway lumen, as has been observed in cystic fibrosis, produces several defects in lung function due to thick mucus accumulation. Bicarbonate is critical for correct mucin deployment and there is increasing interest in understanding its role in airway physiology, particularly in the initiation of lung disease in children affected by cystic fibrosis, in the absence of detectable bacterial infection. The current model of anion secretion in mammalian airways consists of CFTR and TMEM16A as apical anion exit channels, with limited capacity for bicarbonate transport compared to chloride. However, both channels can couple to SLC26A4 anion exchanger to maximise bicarbonate secretion. Nevertheless, current models lack any details about the identity of the basolateral protein(s) responsible for bicarbonate uptake into airway epithelial cells. We report herein that the electrogenic, sodium-dependent, bicarbonate cotransporter, SLC4A4, is expressed in the basolateral membrane of human and mouse airways, and that its pharmacological inhibition or genetic silencing reduces bicarbonate secretion. In fully differentiated primary human airway cells, SLC4A4 inhibition induced an acidification of the airways surface liquid and markedly reduced the capacity of cells to recover from an acid load. Studies in the Slc4a4-null mice revealed a previously unreported lung phenotype, characterized by mucus accumulation and reduced mucociliary clearance. Collectively, our results demonstrate that the reduction of SLC4A4 function induced a CF-like phenotype, even when chloride secretion remained intact, highlighting the important role SLC4A4 plays in bicarbonate secretion and mammalian airway function.

physiology↗

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↗