Biology subjects

Gerhardt, H.

Publications and source records attributed to Gerhardt, H..

At least 19 recordsLinked to original sources

bioRxiv2026

Neuroblastoma-derived small extracellular vesicles retaincellular identity and adrenergic/mesenchymal state signatures

Neuroblastoma is a heterogeneous pediatric malignancy characterized by distinct genomic subgroups and cell-state plasticity between adrenergic (ADRN) and mesenchymal (MES) phenotypes. While small extracellular vesicles (sEVs) mediate pre-metastatic niche priming, the degree to which sEV proteomes reflect parental genomic and phenotypic identity remains unresolved. Here, we isolated sEVs from six neuroblastoma cell models (IMR-5/75, BE(2)-C, GI-ME-N, CLB-GA, LAN-6, and SK-N-FI) representing three genomic subgroups (MYCN-amplified, TERT-rearranged, and unaltered) using OptiPrep density gradient centrifugation followed by size exclusion chromatography and ultrafiltration. High-resolution mass spectrometry of sEV proteomes revealed that sEVs carry highly reproducible protein signatures that tightly correlate with the parental genomic subgroups. Analyzing paired cell/sEV samples, we demonstrate cell-to-EV concordance of lineage-specific markers: ADRN sEVs selectively enriched L1CAM and dopamine {beta}-hydroxylase (DBH), whereas MES sEVs enriched SERPINE1 and type III collagen (COL3A1). These findings indicate that neuroblastoma-derived sEVs systematically preserve both the genomic landscape and the lineage transdifferentiation states of their cells of origin. This study establishes a robust molecular foundation for utilizing sEV-based proteomics as a surrogate to track cellular plasticity and for studying sEV-mediated microenvironmental remodeling.

cancer biology↗

bioRxiv2026

Tunable Laminar Perfusion Coordinates Endothelial and Perivascular Remodeling in Angiogenic Vasculature-on-Chip

Perfusable vascular microphysiological systems are increasingly used to model angiogenesis, tissue crosstalk, and disease. However, many platforms still rely on oscillatory, discontinuous, or poorly controlled perfusion regimes, limiting the study of sustained flow-dependent vascular remodeling. Here, we establish a tunable, unidirectional laminar flow workflow for long-term perfusion of angiogenic vasculature-on-chip cultures and use it to investigate endothelial, perivascular, and immune cell responses to sustained flow. Using an AIM Biotech microfluidic platform containing 14-day-old human umbilical vein endothelial cell-derived angiogenic sprouts and pericytes, continuous perfusion enabled intraluminal transport of 1 m tracer beads through vessels, demonstrating stable flow across the vascular bed. Sustained laminar flow induced endothelial remodeling at both the mother vessel and sprout levels, with cellular alignment evident in both compartments. Quantitative analysis of the mother vessel further revealed Golgi polarization against the direction of flow. Sustained perfusion also increased pericyte recruitment to angiogenic sprouts and reduced endothelial proliferation within the mother vessel, consistent with flow-driven vascular maturation and quiescence. Live-cell imaging further captured directional endothelial migration against the flow, lumen remodeling, and dynamic pericyte behavior under continuous perfusion. In immune-cell assays performed under continuous-flow conditions, interactions with untreated endothelium were limited, whereas inflammatory activation increased immune-cell adhesion and crawling. These observations suggest that sustained flow supports a quiescent endothelial phenotype and demonstrate the suitability of the platform for studying inflammatory activation and immune-vascular communication under controlled hemodynamic conditions. Beyond its biological relevance, the workflow provides practical advantages for live-cell imaging, low medium consumption, and downstream perturbation studies. Moreover, the modular design of the platform makes it well suited for vascular-organ crosstalk applications. Collectively, these results establish laminar flow angiogenic vasculature-on-chip as an experimentally tractable model for studying vascular mechanobiology, vascular maturation, and dynamic cell interactions under defined hemodynamic conditions.

bioengineering↗

bioRxiv2026

Endothelial YAP/TAZ rewiring under cardiometabolic stress drives sex-divergent vascular remodeling in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is widely linked to endothelial dysfunction, yet the molecular pathways translating cardiometabolic stress into microvascular remodeling remain poorly defined. Here, we identify endothelial YAP/TAZ signaling as a mechanistic regulator of sex-divergent vascular responses in HFpEF. Plasma proteomics from the UK Biobank revealed elevated circulating YAP1 levels associated with heart failure and increased mortality, particularly in male patients, where YAP1 coincided with increased levels of the endothelial activation marker ESM1. In a hypertensive cardiorenal mouse model, endothelial YAP/TAZ deletion preserved cardiac function, whereas endothelial TAZ gain-of-function aggravated disease. Under cardiometabolic stress (TNF and high glucose), endothelial cells exhibited sex-specific rewiring of YAP/TAZ-dependent transcriptional programs. Male endothelial cells showed increased extracellular YAP1 release, angiogenic instability with impaired extracellular matrix remodeling, whereas female cells adopted an immune-primed, stress-adaptive phenotype. Mechanistically, cardiometabolic stress uncoupled canonical YAP-TEAD transcription and engaged alternative cofactors, including VGLL3 and VGLL4, thereby reshaping the endothelial secretome and propagating sex-divergent microvascular remodeling. These findings identify endothelial YAP/TAZ rewiring as a molecular switch that converts cardiometabolic stress into sex-divergent microvascular remodeling in HFpEF and connect this process to circulating YAP1 and ESM1 in patients.

cell biology↗

bioRxiv2025

Disrupted endothelial cell-cell dynamics in ALK1 and SMAD4 deficiency drive arteriovenous malformations

Arteriovenous malformations (AVMs) are a hallmark of hereditary haemorrhagic telangiectasia (HHT) and arise from abnormal vascular remodelling. Although AVM formation has been associated with disruptions in the BMP9/10 signalling pathway, the distinct contributions of its components remain unclear. Here, we combine in vitro mosaic endothelial cell (EC) cultures with agent-based modelling (ABM) to investigate how knockdown of the BMP9/10 pathway components ALK1 and SMAD4 alters cell-cell interactions and collective vascular organisation. Using cell tracking data, we inferred the mechanical interactions between neighbouring ECs in 2D monolayers by applying Approximate Bayesian Computation to an ABM of cell migration. SMAD4 knockdown increased the motile forces generated by ECs, while ALK1 knockdown weakened the ability of cells to push apart and rearrange with their neighbours, both resulting in greater mixing and fluidity within the cell layer. When these altered interaction profiles were incorporated into an ABM of collective EC dynamics during vascular remodelling, they gave rise to distinct AVM-prone phenotypes. SMAD4-deficient populations exhibited local blockages as highly polarised cells migrated excessively, whereas ALK1-deficient populations disrupted vascular patterning by impairing coordinated polarity and neighbour separation, favouring flow reversal. Our findings suggest that canonical BMP9/10 pathway defects destabilise the biomechanical balance of endothelial interactions, leading to emergent collective behaviours that predispose vessels to AVM formation. Significance StatementArteriovenous malformations (AVMs) are abnormal connections between arteries and veins that disrupt blood flow and can cause stroke or life-threatening bleeding. They are a hallmark of hereditary haemorrhagic telangiectasia (HHT), a genetic vascular disorder, but the cellular events that initiate AVMs remain unclear. Using a combination of endothelial cell cultures and computational modelling, we show that loss of two key HHT-linked genes, ALK1 and SMAD4, disrupts the coordinated movement and interactions of endothelial cells. Although both deficiencies lead to AVM-like behaviours, they do so through distinct mechanisms. SMAD4 loss drives excessive collective migration, whereas ALK1 loss impairs polarity and neighbour separation. These findings provide a mechanistic framework for how genetic defects could contribute to cell-cell dynamics observed in vascular malformations.

cell biology↗

bioRxiv2025

Self-organized vascularized human liver spheroids: Serum-free culture conditions and use as tissue building blocks

Engineering vascularized human liver tissue for in vitro models and in vivo applications remains a major challenge. Here, we describe a scalable approach to generate human liver spheroids with self-organized, lumen-containing vascular networks and demonstrate their use as building blocks for fabricating vascularized tissue layers. Spheroids were formed from HepaRG liver cells, human umbilical vein endothelial cells (HUVECs), and adipose tissue-derived mesenchymal stem cells (MSCs). The inclusion of MSCs prevented spatial segregation of hepatic and endothelial compartments and enabled endothelial network formation. We present two media that are suitable for culturing these spheroids: a serum-reduced medium and a defined serum-free medium containing GibcoTM KnockOut serum replacement. These media supported the long-term maintenance of hepatocytes in a metabolically active, relatively mature state, as well as the persistence of endothelial networks. Endothelial cell identity and organization were confirmed by VE-cadherin and ICAM-2 immunostaining and by transmission electron microscopy, which revealed adherens junctions and luminal morphologies consistent with a capillary-like organization. Spheroid-derived HUVECs established anastomoses with external endothelial channels in microfluidic devices. Moreover, endothelial sprouts emerging from the spheroids formed inter-spheroid connections within permissive hydrogels (fibrin or collagen-methylcellulose), a process that depended on the inter-spheroid distance. Finally, we demonstrate the fabrication of planar tissue layers with vascularly interconnected spheroids. Together, we identify key conditions, including cellular ratios, medium formulations, biomaterials, and spatial design criteria that enable the generation and assembly of vascularized liver spheroids as scalable tissue building blocks for tissue engineering applications. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=187 SRC="FIGDIR/small/684548v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@1b8c8a2org.highwire.dtl.DTLVardef@7c0ed2org.highwire.dtl.DTLVardef@b10886org.highwire.dtl.DTLVardef@a6ab4f_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2025

Isogenic monocytes improve the responsiveness of hiPSC cardiac spheroids to cardiac stressors

AimsHeart failure remains a leading cause of morbidity and mortality worldwide. Suitable in vitro models to accurately replicate the pathological environment in heart failure with reduced and preserved ejection fraction (HFrEF/HFpEF) are limited, hampering mechanistic studies and drug screening. In particular, these models rarely incorporate immune cells, which play a critical role in heart failure. To address these limitations, we developed an isogenic 3D induced pluripotent stem cell (iPSC)-derived cardiac spheroid model incorporating monocytes. Methods and resultsCardiac spheroids were assembled from three healthy female iPSC lines: three-cell-type (3CT) spheroids consisting of iPSC-derived cardiomyocytes, cardiac fibroblasts, and endothelial cells, and four-cell-type (4CT) spheroids additionally containing monocytes. After six days of culture, established spheroids were treated for 24 h with different known heart failure-associated triggers (glucose & tumour necrosis factor alpha (TNF) or ischaemia with/without reoxygenation). Differences between treated and control 3CT and 4CT spheroids were investigated at the cellular, molecular, and functional levels using confocal microscopy, RNA expression (qPCR and RNA sequencing), protein secretion using proximity extension assay technology (Olink), and functional analyses of beating rate, contraction, and relaxation. The results confirmed successful monocyte integration in 4CT spheroids, and only spheroids with monocytes (4CTs) exhibited changes in beating rate and relaxation duration upon stimulation, highlighting the necessity of incorporating immune cells to successfully mimic heart failure-associated functional changes. Along with a more pronounced global transcriptomic treatment response and inflammatory changes, additional transcriptomic alterations previously linked to heart failure in patients, as well as changes in metabolism, ion channels, and extracellular matrix pathways, were observed in 4CT compared with 3CT spheroids. ConclusionWe showed that immune cell incorporation enhances the functional and transcriptional responses of engineered cardiac tissue to relevant heart failure triggers in vitro and is essential for future studies to elucidate the cellular crosstalk and pathomechanisms. Translational perspectiveHeart failure continues to be a predominant cause of morbidity and mortality, necessitating the development of innovative therapeutic strategies, particularly in light of the rising prevalence of obesity and diabetes mellitus. We introduced an isogenic in vitro spheroid model comprising iPSC-derived cardiomyocytes, cardiac fibroblasts, endothelial cells, and monocytes to examine the effects of heart failure-associated triggers on cardiac tissue. Our findings indicate that spheroids incorporating monocytes exhibit a more pronounced response to heart failure-associated triggers and demonstrate greater differential transcriptional and functional responses than spheroids lacking immune cells. This model

cell biology↗

bioRxiv2025

Divergent endothelial mechanisms drive arteriovenous malformations in Alk1 and Smad4 loss-of-function

BackgroundHereditary hemorrhagic telangiectasia is a genetic disorder caused by loss-of-function mutations in components of the bone morphogenetic protein signaling pathway, leading to arteriovenous malformations. Most prior work has treated BMP-component mutations as mechanistically interchangeable, yet whether distinct genes converge on a shared mechanism remains unclear. We aimed to understand the molecular relationship between BMP signaling and endothelial flow response that leads to AVM formation. MethodsWe expose human endothelial monolayers treated with siRNA against SMAD4 or ALK1 to laminar flow and analyze flow-responsive transcriptomics, flow-responsive BMP signaling activation dynamics, cell polarity and morphology. We analyze the cell-autonomous and non-cell-autonomous migration dynamics of ECs treated with siSMAD4 or siALK1. Using the postnatal mouse retina model, we study EC distribution changes over time in mosaic settings, and assess the remodelling capabilities of Smad4iECKO or Alk1iECKO, relative to littermate controls. ResultsThis study shows that mutations in SMAD4 or ALK1 lead to fundamentally distinct mechanisms of malformation formation. SMAD4 deficiency enhances endothelial responses to blood flow, including transcriptional activation and migration against flow, causing excessive capillary pruning and the development of single large shunts. In contrast, ALK1 deficiency disrupts flow sensing, impairs cell polarization and migration, and promotes a persistent angiogenic state, resulting in dense, hypervascularized networks. RNA sequencing reveals that these transcriptional changes precede flow onset, suggesting early defects in endothelial fate specification. Mosaic in vitro models show that mutant cells co-opt neighboring wild-type cells, while in vivo tracking confirms mutation-specific migration behavior. ConclusionsThese findings reveal divergent cellular programs driving arteriovenous malformations and underscore the need for gene-specific diagnostic and therapeutic strategies. Clinical PerspectiveO_ST_ABSWhat is New?C_ST_ABSO_LIThis study identifies gene-specific mechanisms of AVM formation in endothelial cells with SMAD4 or ALK1 loss-of-function, two major mutations underlying Hereditary Hemorrhagic Telangiectasia. C_LIO_LIUsing multiple side-by-side analyses, the study reveals that SMAD4 deficiency enhances flow-mediated remodeling, while ALK1 deficiency impairs flow sensing and promotes angiogenic persistence. C_LIO_LIRNA sequencing showed that several transcriptional differences precede the onset of flow, indicating early divergence in endothelial cell fate specification and mechanosensory behavior. C_LIO_LIMosaic culture and retinal models demonstrate that mutant cells exert distinct non-cell-autonomous effects on wild-type endothelial cells. C_LI What Are the Clinical Implications?O_LIThis work challenges the prevailing assumption of a unified pathogenic pathway in HHT and supports a model of mutation-specific AVM pathogenesis, with distinct cellular and molecular drivers. C_LIO_LIThe findings provide a mechanistic basis for the variable clinical presentation seen in patients with different HHT mutations. C_LIO_LIIdentification of early transcriptional signatures, such as persistent ANGPT2 or DPP4 upregulation, may offer new biomarkers or therapeutic targets for early intervention before AVMs become clinically symptomatic. C_LIO_LIPersonalized therapeutic strategies could reduce reliance on invasive treatments and shift toward mechanism-based, precision medicine approaches in HHT and related vascular disorders. C_LI

developmental biology↗

bioRxiv2024

Mechanosensitive PIEZO2 channels shape coronary artery development

The coronary arteries develop under substantial mechanical loads. However, the role of mechanosensitive ion channels has barely been addressed in this system. Here we demonstrate the expression of the mechanosensitive ion channel PIEZO2 in specific coronary endothelial cell populations during a crucial phase of vascular modeling. Piezo2 positive coronary endothelial cells display distinct transcriptional profiles and have mechanically activated ionic currents. Strikingly, Piezo2-/- mouse embryos and mice with human pathogenic variants of PIEZO2 display coronary vessel malformations and left ventricular hyperplasia. We conclude that an optimal balance of PIEZO2 channel function is indispensable for coronary vessel formation, integrity, and remodeling and likely for proper cardiac function.

developmental biology↗

bioRxiv2024

Mechanical Strain Activates Planar Cell Polarity Signaling to Coordinate Vascular Cell Dynamics

Mechanical stimuli, particularly laminar blood flow, play a crucial role in shaping the vascular system. Changes in the rate of blood flow manifest in altered shear stress, which activates signaling cascades that drive vascular remodeling. Consistently, dysregulation of the endothelial response to fluid shear forces and aberrant flow patterns both lead to pathological conditions, including impaired blood vessel development and atherosclerosis. Despite its importance, the mechanisms driving the coordinated cell behavior underlying vascular remodeling are not fully understood. Combining classical cell biological approaches with advanced image analysis, mathematical modeling, biomimetic strategies, and in vivo studies, we identify the planar cell polarity (PCP) protein Vangl1 as an enforcer of flow-dependent cell dynamics in the vascular system. We demonstrate that shear stress triggers the relocation of Vangl1 from an internal reservoir to the plasma membrane at the initiation of cell remodeling. Membrane enrichment of Vangl1 is mediated by a Coronin1C-dependent shift in the equilibrium between endo- and exocytosis and results in the spatial reorganization of another essential PCP protein, Frizzled6 (Fzd6). The resulting mutual exclusion of the core PCP proteins Fzd6 and Vangl1 augments differential junctional and cytoskeletal dynamics along the flow axis. Loss of Vangl1 limits the ability of endothelial cells to respond to shear forces in a coordinated fashion, resulting in irregular cell alignment along the flow direction and erroneous vessel sprouting. Together, these studies introduce core PCP signaling as a determinant of collective cell dynamics and organization of the vascular system.

cell biology↗

bioRxiv2024

Polarity-JaM: An image analysis toolbox for cell polarity, junction and morphology quantification

Cell polarity involves the asymmetric distribution of cellular components such as signaling molecules and organelles within a cell, asymmetries of a cell"s shape as well as contacts with neighbouring cells. Gradients and mechanical forces often act as global cues that bias cell polarity and orientation, and polarity is coordinated by communication between adjacent cells. Advances in fluorescence microscopy combined with deep learning algorithms for image segmentation open up a wealth of possibilities to understand cell polarity behaviour in health and disease. We have therefore developed the open-source package Polarity-JaM, which offers versatile methods for performing reproducible exploratory image analysis. Multi-channel single cell segmentation is performed using a flexible and userfriendly interface to state-of-the-art deep learning algorithms. Interpretable single-cell features are automatically extracted, including cell and organelle orientation, cell-cell contact morphology, signaling molecule gradients, as well as collective orientation, tissue-wide size and shape variation. Circular statistics of cell polarity, including polarity indices, confidence intervals, and circular correlation analysis, can be computed using our web application. We have developed data graphs for comprehensive visualisation of key statistical measures and suggest the use of an adapted polarity index when the expected polarisation direction or the direction of a global cue is known a priori. The focus of our analysis is on fluorescence image data from endothelial cells (ECs) and their polarisation behaviour. ECs line the inside of blood vessels and are essential for vessel formation and repair, as well as for various cardiovascular diseases, cancer, and inflammation. However, the general architecture of the software will allow it to be applied to other cell types and image modalities. The package is built in in Python, allowing researchers to seamlessly integrate Polarity-JaM into their image and data analysis workflows, see https://polarityjam. readthedocs.io. In addition, a web application for statistical analysis, available at www.polarityjam.com, and a Napari plugin are available, each with a graphical user interface to facilitate exploratory analysis.

bioinformatics↗

bioRxiv2023

Pial collaterals develop through mosaic colonization of capillaries by arterial and microvascular endothelial cells

Collaterals are unique blood vessels present in many healthy tissues that cross-connect distal-end arterioles of adjacent arterial trees, thus providing alternate routes of perfusion. Stroke patients with superior pial collateral flow respond better to treatments and present with an overall improved prognostic outcome. However, how pial collaterals develop in the embryo and how they reactivate upon stroke remains unclear. Here, using lineage tracing in combination with three-dimensional imaging, we demonstrate that mouse embryos employ a novel mechanism to build pial collaterals, distinct from their outward remodeling following stroke. Endothelial cells (ECs) of arterial and microvascular origin invade already existing pre-collateral vascular structures in a process which we termed mosaic colonization. Arterialization of these pre-collateral vascular segments happens concurrently with mosaic colonization. Despite having a smaller proliferative capacity, embryonic arterial cells represent the majority of cells that migrate to form nascent collaterals; embryonic microvascular cells, despite their higher proliferative potential, form only about a quarter of collateral endothelial cells. Moreover, postnatal collateral growth relies much more on self-replenishment of arterial cells than on microvascular contribution. Following ischemic injury, pial collateral outward remodeling relies on local cell proliferation rather than recruitment of non-arterial cells. Together, these findings establish distinct cellular mechanisms underlying pial collateral development and ischemic remodeling, raising the prospect for future research to identify novel, collateral-specific therapeutic strategies for ischemic stroke.

developmental biology↗

bioRxiv2023

Reconstructing stochastic cell population trajectories reveals regulators and heterogeneity of endothelial flow-migration coupling driving vascular remodelling

Emerging concepts of developmental vascular remodelling recently identified that selectively labelled sprouting tip cells and/or venous endothelial cells (ECs) accumulate in developing arteries, suggesting directional migration of specific ECs drives artery formation. However, a general population analysis and detailed quantitative investigation of migratory mechanisms is so far lacking. Here, we developed a universally applicable quantitative approach and a computational model allowing to track and simulate stochastically labelled EC populations irrespective of labelling density and origin. Dynamic mapping of EC distributions in a bespoke coordinate system revealed how ECs move during the most active remodelling phases in the mouse retina. Simulation and parameter sensitivity analysis illustrated that the population shift from veins to arteries cannot be explained by random walk, but best fits to a tuneable dual force-field between shear-force induced directionality against blood flow, and hypoxia mediated VEGFA-gradients. High migration rates require only weak flow-migration coupling, whereas low migration rates require strong coupling to the flow direction. Functional analysis identified Cdc42 as the critical mediator of overall population movement from veins to arteries, yet with surprising heterogeneity suggesting the existence of distinct cell populations. This new quantitative understanding will enable future tailored intervention and tuning of the remodelling process.

developmental biology↗

bioRxiv2023

Single-cell profiling and zebrafish avatars reveal LGALS1 as immunomodulating target in glioblastoma

Glioblastoma (GBM) remains the most malignant primary brain tumor, with a median survival rarely exceeding 2 years. Tumor heterogeneity and an immunosuppressive microenvironment are key factors contributing to the poor response rates of current therapeutic approaches. GBM-associated macrophages (GAMs) often exhibit immunosuppressive features that promote tumor progression. However, their dynamic interactions with GBM tumor cells remain poorly understood. Here, we used patient-derived GBM stem cell cultures and combined single-cell RNA sequencing of GAM-GBM co-cultures and real-time in vivo monitoring of GAM-GBM interactions in orthotopic zebrafish xenograft models to provide insight into the cellular, molecular, and spatial heterogeneity. Our analyses revealed substantial heterogeneity across GBM patients in GBM-induced GAM polarization and the ability to attract and activate GAMs - features that correlated with patient survival. Differential gene expression analysis, immunohistochemistry on original tumor samples, and knock-out experiments in zebrafish subsequently identified LGALS1 as a primary regulator of immunosuppression. Overall, our work highlights that GAM-GBM interactions can be studied in a clinically relevant way using co-cultures and avatar models, while offering new opportunities to identify promising immune-modulating targets.

cancer biology↗

bioRxiv2022

Coronary vessel assembly involves patterned endocardial sprouting and tip-cell-to artery specification

The coronary vasculature comprises superficial coronary veins and deeper coronary arteries and capillaries that critically support the high metabolic activity of the beating heart. Understanding how different endothelial progenitor sources jointly shape and remodel the coronary vasculature into its adult pattern has recently attracted great research interest, and spurred much debate. Here, using lineage tracing tools in combination with three-dimensional imaging, live-imaging in explants and single-cell transcriptional profiling, we demonstrate that sprouting angiogenesis drives both sinus venosus and endocardial contribution to coronary plexus. Whereas previous studies limit endocardial contribution to coronary vessels to the interventricular septum and ventral aspect of the heart, our study demonstrates extensive endocardial sprouting angiogenesis in the free ventricular walls. In particular, we identify a distinct subpopulation of endocardial cells that express future coronary markers and reside in both the embryonic and adult ventricular wall endocardium. Most importantly, we provide evidence for sprouting angiogenesis from both endocardium and subepicardial plexus towards the inner myocardial wall to determine pre-arterial specification. Additionally, sprouting from the endocardium leads to the establishment of perfused connections to the advancing coronary plexus, also followed by transitioning to the pre-arterial cell state. Distinct molecular profiles characterize sprouting populations in the intramyocardial and subepicardial layers that shape the prospective coronary arteries and veins, respectively. Harnessing the endocardial progenitors and targeting the distinct sprouting populations may in the future serve to tailor cardiac vascular adaptations for therapeutic purposes.

developmental biology↗

bioRxiv2021

Emerging single cell endothelial heterogeneity supports sprouting tumour angiogenesis and growth

Blood vessels supplying tumors are often dysfunctional and generally heterogeneous. The mechanisms underlying this heterogeneity remain poorly understood. Here, using multicolor lineage tracing, in vivo time-lapse imaging and single cell RNA sequencing in a mouse glioma model, we identify tumour-specific blood endothelial cells that originate from cells expressing the receptor for colony stimulating factor 1, Csf1r, a cytokine which controls macrophage biology. These Csf1r lineage endothelial cells (CLECs) form up to 10% of the tumour vasculature and express, besides classical blood endothelial cell markers, a gene signature that is distinct from brain endothelium but shares similarities with lymphatic endothelial cell populations. in silico analysis of pan-cancer single cell RNAseq datasets highlights the presence of a comparable subpopulation in the endothelium of a wide spectrum of human tumours. We show that CLECs actively contribute to sprouting and remodeling of tumour blood vessels and that selective depletion of CLECs reduces vascular branching and tumour growth. Our findings indicate that a non-tumour resident Csf1r-positive population is recruited to tumours, differentiates into blood endothelial cells to contribute to vascularization and, thereby, tumour growth.

cancer biology↗

bioRxiv2021

Svep1 stabilizes developmental vascular anastomosis in reduced flow conditions.

We report the discovery that flow and Svep1 are modulator of vessel anastomosis during developmental angiogenesis in zebrafish embryos. We show that loss of Svep1 and blood flow reduction both contribute to defective anastomosis of intersegmental vessels. We show that this defect in primary angiogenic sprouts is associated with an expansion of Apelin-positive tip cells and with reduced formation and lumenisation of the dorsal longitudinal anastomotic vessel. Mechanistically, our results suggest that flow and Svep1 act synergistically to modulate vascular network formation in the zebrafish trunk.

developmental biology↗

bioRxiv2020

Wasp controls oriented migration of endothelial cells to achieve functional vascular patterning

Endothelial cell migration and proliferation are essential for the establishment of a hierarchical organization of blood vessels and optimal distribution of blood. However, how these cellular processes are coordinated remains unknown. Here, using the zebrafish trunk vasculature we show that in future veins endothelial cells proliferate more than in future arteries and migrate preferentially towards neighboring arteries. In future arteries endothelial cells show a biphasic migration profile. During sprouting cells move away from the dorsal aorta, during remodelling cells stop or move towards the feeding aorta. The final morphology of blood vessels is thus established by local proliferation and oriented cell migration to and from neighboring vessels. Additionally, we identify WASp to be essential for this differential migration. Loss of WASp leads to irregular distribution of endothelial cells, substantially enlarged veins and persistent arteriovenous shunting. Mechanistically, we report that WASp drives the assembly of junctional associated actin filaments and is required for junctional expression of PECAM-1. Together, our data identify that functional vascular patterning in the zebrafish trunk utilizes differential cell movement regulated by junctional actin, and that interruption of differential migration may represent a pathomechanism in vascular malformations.

developmental biology↗

bioRxiv2020

Association between erythrocyte dynamics and vessel remodelling in developmental vascular networks

Sprouting angiogenesis is an essential vascularisation mechanism consisting of sprouting and remodelling. The remodelling phase is driven by rearrangements of endothelial cells (ECs) within the post-sprouting vascular plexus. Prior work has uncovered how ECs polarise and migrate in response to flow-induced wall shear stress (WSS). However, the question of how the presence of erythrocytes (well-known as RBCs) and their haemodynamics impact affects vascular remodelling remains unanswered. Here, we devise a computational framework to model cellular blood flow in developmental mouse retina. We demonstrate a previously unreported highly heterogeneous distribution of RBCs in primitive vasculature. Furthermore, we report a strong association between vessel regression and RBC depletion, and identify plasma skimming as the driving mechanism. Live imaging in a developmental zebrafish model confirms this association. Taken together, our results indicate that RBC dynamics are fundamental to establishing the regional WSS differences driving vascular remodelling via their ability to modulate effective viscosity. SummaryRecent studies demonstrate that during sprouting angiogenesis, blood flow provides crucial hydrodynamic cues (e.g. wall shear stress) for the remodelling of primitive plexuses towards a functional network. Notwithstanding, the role of RBCs in this process remains poorly understood. We report on the inherent heterogeneity of RBC perfusion within primitive vasculatures, and uncover a strong association between RBC depletion and vessel regression. Our work indicates the essential role of RBC dynamics in the establishment of regional WSS differences driving vascular remodelling. The RBC-driven process of pruning cell-depleted vessels not only importantly contributes to the optimal patterning of vascular networks during development, but also provides a remodelling mechanism to support clinical findings of microangiopathic complications associated with impaired RBC deformability in diseases such as diabetes mellitus and hypertension.

developmental biology↗