Biology subjects

Ghevaert, C.

Publications and source records attributed to Ghevaert, C..

7 recordsLinked to original sources

bioRxiv2026

Modelling human haematopoietic stem cell commitment ex vivo identifies IL-33 as a regulator of megakaryopoiesis

Commitment events to specific blood lineages arise from single hematopoietic stem cells (HSCs) and are influenced by stress, inflammation and disease. However, the understanding of how such events are regulated in human haematopoiesis is limited by the lack of tractable in vitro models. In this study, we introduce a novel Early Progenitor Differentiation (EPD) assay to study the initial lineage commitment of human 49+ HSCs, in a system faithfully recapitulating cell states observed in vivo. Combining single cell -omics approaches and single cell functional assays, we show that IL-33 acts directly on human 49f+ HSCs activating the MAPK pathway to enhance their commitment towards Megakaryocytic-Erythroid-Mast cell Progenitors and subsequently megakaryopoiesis. This occurs without affecting HSC self-renewal via accelerated establishment of chromatin programmes associated with Erythroid and Megakaryocyte and mast cells lineages. Our findings demonstrate the utility of the EPD model to identify molecular regulators of human HSC differentiation and uncover a new role of IL-33 in haematopoiesis.

cell biology↗

bioRxiv2026

ATP11A and ATP11C are plasma membrane phosphatidylserine flippases in in vitro human megakaryocytes.

Thrombotic diseases are the major worldwide cause of cardiovascular death. Platelets prevent blood loss following injury (haemostasis), but inappropriate and excessive platelet activation can lead to thrombosis. Platelet activation must be tightly controlled. Pro-coagulant platelets expose phosphatidylserine (PS), enabling coagulation complex assembly, enhancing thrombin generation and thrombosis. PS is normally restricted to the inner leaflet of the plasma membrane by flippase (aminophospholipid translocase) activity. However, the flippase protein(s) responsible for this crucial activity in platelets remains unidentified. The P4 ATPases ATP11A and ATP11C, regulated by their obligatory partner CDC50A, flip PS at the plasma membrane in a range of different cell types. To investigate platelet flippases, human induced pluripotent stem cells (hiPSCs) were forward-programmed into CD41+/CD42+ megakaryocytes, the platelet precursor. Wildtype (WT) forward-programmed megakaryocytes showed similar flippase activity to human platelets with internalisation of NBD-PS that could be inhibited by high cytosolic Ca2+ or N-ethylmaleimide (NEM). We then generated CDC50A, ATP11A or ATP11C single knockout and ATP11A/11C double knockout (DKO) hiPSCs using CRISPR-Cas9. CDC50A-KO, ATP11A-KO, ATP11C-KO and DKO hiPSC clones successfully formed CD41a+/CD42a+ mature megakaryocytes. CDC50A-KO megakaryocytes bound Annexin V when unstimulated and had no remaining NEM-sensitive flippase activity indicating the involvement of a P4-ATPase. Although ATP11A-KO and ATP11C-KO megakaryocytes had similar flippase activity to WT clones, DKO clones had inhibited NBD-PS internalisation compared to WT and had no remaining NEM-sensitive flippase activity. This indicates that the CDC50A-regulated P4-ATPases ATP11A and ATP11C act together at the megakaryocyte plasma membrane and are responsible for PS flippase activity and therefore likely responsible in human platelets.

cell biology↗

bioRxiv2023

Circulating Platelets Modulate Oligodendrocyte Progenitor Cell Differentiation During Remyelination

Revealing unknown cues that regulate oligodendrocyte progenitor cell (OPC) function in remyelination is important to optimise the development of regenerative therapies for multiple sclerosis (MS). Platelets are present in chronic non-remyelinated lesions of MS and an increase in circulating platelets has been described in experimental autoimmune encephalomyelitis (EAE) mice, an animal model for MS. However, the contribution of platelets to remyelination remains unexplored. Here we show platelet aggregation in proximity to OPCs in areas of experimental demyelination. Partial depletion of circulating platelets impaired OPC differentiation and remyelination, without altering blood-brain barrier stability and neuroinflammation. Transient exposure to platelets enhanced OPC differentiation in vitro, whereas sustained exposure suppressed this effect. In a mouse model of thrombocytosis (CALRHET), there was a sustained increase in platelet aggregation together with a reduction of newly-generated oligodendrocytes following toxin-induced demyelination. These findings reveal a complex bimodal contribution of platelet to remyelination and provide insights into remyelination failure in MS.

neuroscience↗

bioRxiv2022

Low input capture Hi-C (liCHi-C) identifies promoter-enhancer interactions at high-resolution

Long-range interactions between regulatory elements and promoters are key in gene transcriptional control; however, their study requires large amounts of starting material, which is not compatible with clinical scenarios nor the study of rare cell populations. Here we introduce low input capture Hi-C (liCHi-C) as a cost-effective, flexible method to map and robustly compare promoter interactomes at high resolution. As proof of its broad applicability, we implement liCHi-C to study normal and malignant human hematopoietic hierarchy in clinical samples. We demonstrate that the dynamic promoter architecture identifies developmental trajectories and orchestrates transcriptional transitions during cell-state commitment. Moreover, liCHi-C enables the identification of new disease-relevant cell types, genes and pathways potentially deregulated by non-coding alterations at distal regulatory elements. Finally, we show that liCHi-C can be harnessed to uncover genome-wide structural variants, resolve their breakpoints and infer their pathogenic effects. Collectively, our optimized liCHi-C method expands the study of 3D chromatin organization to unique, low-abundance cell populations, and offers an opportunity to uncover novel factors and regulatory networks involved in disease pathogenesis.

genomics↗

bioRxiv2021

Platelet generation from circulating megakaryocytes is triggered in the lung vasculature

Platelets, small hemostatic blood cells, are derived from megakaryocytes, although the generation process is not clear. Only small numbers of platelets have been produced in systems outside the body, where bone marrow and lung are proposed as sites of platelet generation. Here we show that perfusion of megakaryocytes ex vivo through the mouse lung vasculature generates very large numbers of platelets, up to 3,000 per megakaryocyte. Despite their large size, megakaryocytes were able repeatedly to passage through the lung vasculature, leading to enucleation and fragmentation to generate platelets intravascularly. Using the ex vivo lung and a novel in vitro microfluidic chamber we determined the contributions of oxygenation, ventilation and endothelial cell health to platelet generation, and showed a critical role for the actin regulator TPM4. One-Sentence SummaryMegakaryocytes form platelets intravascularly in the lung, dependent upon oxygenation, endothelium and megakaryocyte TPM4

physiology↗

bioRxiv2021

Mapping the biogenesis of forward programmed megakaryocytes from induced pluripotent stem cells

Platelet deficiency, known as thrombocytopenia, can cause haemorrhage and is treated with platelet transfusions. We developed a system for the production of platelet precursor cells, megakaryocytes, from pluripotent stem cells. These cultures can be maintained for >100 days, implying culture renewal by megakaryocyte progenitors (MKPs). However, it is unclear whether the MKP state in vitro mirrors the state in vivo, and MKPs cannot be purified using conventional surface markers. We performed single cell RNA sequencing throughout in vitro differentiation and mapped each state to its equivalent in vivo. This enabled the identification of 5 surface markers which reproducibly purify MKPs, allowing us an insight into their transcriptional and epigenetic profiles. Finally, we performed culture optimisation, increasing MKP production. Altogether, this study has mapped parallels between the MKP states in vivo and in vitro and allowed the purification of MKPs, accelerating the progress of in vitro-derived transfusion products towards the clinic.

developmental biology↗

bioRxiv2019

Antiviral signalling in human IPSC-derived neurons recapitulates neurodevelopmental disorder phenotypes

Maternal immune activation increases the risk of neurodevelopmental disorders. Elevated cytokines, such as interferon-gamma (IFN{gamma}), in offsprings brains play a central role. IFN{gamma} activates an antiviral cellular state, limiting viral entry and replication. In addition, IFN{gamma} has been implicated in brain development. Here, we hypothesise that IFN{gamma}-induced antiviral signalling contributes to molecular and cellular phenotypes associated with neurodevelopmental disorders. We find that transient IFN{gamma} treatment of neural progenitors derived from human induced pluripotent stem cells (hIPSCs) persistently increases neurite outgrowth, phenocopying hIPSC-neurons from autistic individuals. IFN{gamma} upregulates antiviral PML bodies and MHC class I (MHCI) genes, which persists through neuronal differentiation. Critically, IFN{gamma}-induced neurite outgrowth requires both PML and MHCI. We also find that IFN{gamma} disproportionately alters expression of autism and schizophrenia risk genes, suggesting convergence between these genetic and environmental risk factors. Together, these data indicate that IFN{gamma}-induced antiviral signalling may contribute to neurodevelopmental disorder aetiology.

neuroscience↗