Marcksl1 modulates endothelial cell mechanoresponse to haemodynamic forces to control blood vessel shape and size

Plxnd1-mediated mechanosensing of blood flow controls the caliber of the Dorsal Aorta via the transcription factor Klf2

The cardiovascular system generates and responds to mechanical forces. The heartbeat pumps blood through a network of vascular tubes, which adjust their caliber in response to the hemodynamic environment. However, how endothelial cells in the developing vascular system integrate inputs from circulatory forces into signaling pathways to define vessel caliber is poorly understood. Using vertebrate embryos and in vitro-assembled microvascular networks of human endothelial cells as models, flow and genetic manipulations, and custom software, we reveal that Plexin-D1, an endothelial Semaphorin receptor critical for angiogenic guidance, employs its mechanosensing activity to serve as a crucial positive regulator of the Dorsal Aorta's (DA) caliber. We also uncover that the flow-responsive transcription factor KLF2 acts as a paramount mechanosensitive effector of Plexin-D1 that enlarges endothelial cells to widen the vessel. These findings illuminate the molecular and cellular mechanisms orchestrating the interplay between cardiovascular development and hemodynamic forces.

A cell-and-plasma numerical model reveals hemodynamic stress and flow adaptation in zebrafish microvessels after morphological alteration

The development of a functional cardiovascular system ensures a sustainable oxygen, nutrient and hormone delivery system for successful embryonic development and homeostasis in adulthood. While early vessels are formed by biochemical signaling and genetic programming, the onset of blood flow provides mechanical cues that participate in vascular remodeling of the embryonic vascular system. The zebrafish is a prolific animal model for studying the quantitative relationship between blood flow and vascular morphogenesis due to a combination of favorable factors including blood flow visualization in optically transparent larvae. In this study, we have developed a cell-and-plasma blood transport model using computational fluid dynamics (CFD) to understand how red blood cell (RBC) partitioning affect lumen wall shear stress (WSS) and blood pressure in zebrafish trunk blood vascular networks with altered rheology and morphology. By performing live imaging of embryos with reduced hematocrit, we discovered that cardiac output and caudal artery flow rates were maintained. These adaptation trends were recapitulated in our CFD models, which showed reduction in network WSS via viscosity reduction in the caudal artery/vein and via pressure gradient weakening in the intersegmental vessels (ISVs). Embryos with experimentally reduced lumen diameter showed reduced cardiac output and caudal artery flow rate. Factoring in this trend into our CFD models, simulations highlighted that lumen diameter reduction increased vessel WSS but this increase was mitigated by flow reduction due to the adaptive network pressure gradient weakening. Additionally, hypothetical network CFD models with different vessel lumen diameter distribution characteristics indicated the significance of axial variation in lumen diameter and cross-sectional shape for establishing physiological WSS gradients along ISVs. In summary, our work demonstrates how both experiment-driven and hypothetical CFD modeling can be employed for the study of blood flow physiology during vascular remodeling.

Sertoli cell-enriched proteins in mouse and human testicular interstitial fluid

Sertoli cells support the development of sperm and the function of various somatic cells in the interstitium between the tubules. Sertoli cells regulate the function of the testicular vasculature and the development and function of the Leydig cells that produce testosterone for fertility and virility. However, the Sertoli cell-derived factors that regulate these cells are largely unknown. To define potential mechanisms by which Sertoli cells could support testicular somatic cell function, we aimed to identify Sertoli cell-enriched proteins in the testicular interstitial fluid (TIF) between the tubules. We previously resolved the proteome of TIF in mice and humans and have shown it to be a rich source of seminiferous tubule-derived proteins. In the current study, we designed bioinformatic strategies to interrogate relevant proteomic and genomic datasets to identify Sertoli cell-enriched proteins in mouse and human TIF. We analysed proteins in mouse TIF that were significantly reduced after one week of acute Sertoli cell ablation in vivo and validated which of these are likely to arise primarily from Sertoli cells based on relevant mouse testis RNASeq datasets. We used a different, but complementary, approach to identify Sertoli cell-enriched proteins in human TIF, taking advantage of high-quality human testis genomic, proteomic and immunohistochemical datasets. We identified a total of 47 and 40 Sertoli cell-enriched proteins in mouse and human TIF, respectively, including 15 proteins that are conserved in both species. Proteins with potential roles in angiogenesis, the regulation of Leydig cells or steroidogenesis, and immune cell regulation were identified. The data suggests that some of these proteins are secreted, but that Sertoli cells also deposit specific proteins into TIF via the release of extracellular vesicles. In conclusion, we have identified novel Sertoli cell-enriched proteins in TIF that are candidates for regulating somatic cell-cell communication and testis function.

Primary adhered neutrophils increase JNK1-MARCKSL1-mediated filopodia to promote secondary neutrophil transmigration

During inflammation, leukocytes extravasate the vasculature to areas of inflammation in a process termed transendothelial migration. Previous research has shown that transendothelial migration hotspots exist, areas in the vasculature that are preferred by leukocytes to cross. Several factors that contribute to hotspot-mediated transmigration have been proposed already, but whether one leukocyte transmigration hotspot can be used subsequently by a second wave of leukocytes and thereby can increase the efficiency of leukocyte transmigration is not well understood. Here, we show that primary neutrophil adhesion to the endothelium triggers endothelial transmigration hotspots, allowing secondary neutrophils to cross the endothelium more efficiently. Mechanistically, we show that primary neutrophil adhesion increases the number of endothelial apical filopodia, resulting in an increase in the number of adherent secondary neutrophils. Using fluorescence resonance energy transfer (FRET)-based biosensors, we found that neutrophil adhesion did not trigger the activity of the small GTPase Cdc42. We used kinase translocation reporters to study the activity of mitogen-activated protein (MAP) kinases and Akt in endothelial cells on a single-cell level with a high temporal resolution during the process of leukocyte transmigration and found that c-Jun N-terminal kinase (JNK) is rapidly activated upon neutrophil adhesion, whereas extracellular regulated kinase (ERK), p38, and Akt are not. Additionally, we show that short-term chemical inhibition of endothelial JNK successfully prevents the adhesion of neutrophils to the endothelium. Furthermore, we show that neutrophil-induced endothelial JNK1 but not JNK2 increases the formation of filopodia and thereby the adhesion of secondary neutrophils. JNK1 needs its downstream substrate MARCKSL1 to trigger additional apical filopodia and consequently neutrophil adhesion. Overall, our data show that primary neutrophils can trigger the endothelial transmigration hotspot by activating JNK1 and MARCKSL1 to induce filopodia that trigger more neutrophils to transmigrate at the endothelial hotspot area.

Endothelial Senescence and Its Impact on Angiogenesis in Alzheimer's Disease

Endothelial cells are constantly exposed to environmental stress factors that, above a certain threshold, trigger cellular senescence and apoptosis. The altered vascular function affects new vessel formation and endothelial fitness, contributing to the progression of age-related diseases. This narrative review highlights the complex interplay between senescence, oxidative stress, extracellular vesicles, and the extracellular matrix and emphasizes the crucial role of angiogenesis in aging and Alzheimer's disease. The interaction between the vascular and nervous systems is essential for the development of a healthy brain, especially since neurons are exceptionally dependent on nutrients carried by the blood. Therefore, anomalies in the delicate balance between pro- and antiangiogenic factors and the consequences of disrupted angiogenesis, such as misalignment, vascular leakage and disturbed blood flow, are responsible for neurodegeneration. The implications of altered non-productive angiogenesis in Alzheimer's disease due to dysregulated Delta-Notch and VEGF signaling are further explored. Additionally, potential therapeutic strategies such as exercise and caloric restriction to modulate angiogenesis and vascular aging and to mitigate the associated debilitating symptoms are discussed. Moreover, both the roles of extracellular vesicles in stress-induced senescence and as an early detection marker for Alzheimer's disease are considered. The intricate relationship between endothelial senescence and angiogenesis provides valuable insights into the mechanisms underlying angiogenesis-related disorders and opens avenues for future research and therapeutic interventions.

Developmental diversity and unique sensitivity to injury of lung endothelial subtypes during postnatal growth

At birth, the lung is still immature, heightening susceptibility to injury but enhancing regenerative capacity. Angiogenesis drives postnatal lung development. Therefore, we profiled the transcriptional ontogeny and sensitivity to injury of pulmonary endothelial cells (EC) during early postnatal life. Although subtype speciation was evident at birth, immature lung EC exhibited transcriptomes distinct from mature counterparts, which progressed dynamically over time. Gradual, temporal changes in aerocyte capillary EC (CAP2) contrasted with more marked alterations in general capillary EC (CAP1) phenotype, including distinct CAP1 present only in the early alveolar lung expressing Peg3, a paternally imprinted transcription factor. Hyperoxia, an injury that impairs angiogenesis induced both common and unique endothelial gene signatures, dysregulated capillary EC crosstalk, and suppressed CAP1 proliferation while stimulating venous EC proliferation. These data highlight the diversity, transcriptomic evolution, and pleiotropic responses to injury of immature lung EC, possessing broad implications for lung development and injury across the lifespan.

Development and evaluation of a risk score model based on a WNT score gene-associated signature for predicting the clinical outcome and the tumour microenvironment of hepatocellular carcinoma

Background: Hepatocellular carcinoma (HCC) is currently one of the most life-threatening diseases worldwide. However, the factors, genes, and processes involved in the mechanisms of HCC initiation, development, and metastasis remain to be identified.Methods: WNT signalling pathways may play important roles in cancer initiation and progression. Thus, it would be informative to construct a WNT signature-based gene model for the prognosis of HCC and the prediction of therapeutic efficacy. We curated genomic profiles for HCC from The Cancer Genome Atlas (TCGA) and divided them into training and internal validation datasets. We also used samples from GSE14520 and HCCDB18 as validation datasets and clustered them by ConsensusClusterPlus analysis. We applied WebGestaltR to the WNT score-associated differentially expressed genes (DEGs) and conducted a signalling pathway enrichment analysis. We assessed the tumour immune microenvironment with ESTIMATE, Microenvironment Cell Populations (MCP)-counter, single-sample gene set enrichment analysis (ssGSEA), and tumour immune dysfunction and exclusion (TIDE).Results: We performed a least absolute shrinkage and selection operator (LASSO) regression analysis to identify the prognosis-related hub genes, identified the risk and protective factor genes associated with HCC, classified them into two clusters, and found that Cluster 2 had a significantly better prognosis than Cluster 1. Moreover, the latter had advanced clinical features compared with the former. Uridine-cytosine kinase 1 (UCK1), myristoylated alanine-rich C-kinase substrate-like protein 1 (MARCKSL1), P-antigen family member 1 (PAGE1), and killer cell lectin-like receptor B1 (KLRB1) were detected and used to construct a simplified prognostic model for HCC. The high risk score subgroup showed a poorer prognosis than the low risk score subgroup, and the model assessed HCC prognosis consistently and effectively.Conclusions: The WNT score-related gene-based model designed and evaluated herein had strong prognostic and predictive ability for HCC and could, therefore, facilitate decision-making in the prognosis and therapeutic efficacy assessment of HCC.

Actin cytoskeleton in angiogenesis

Actin, one of the most abundant intracellular proteins in mammalian cells, is a critical regulator of cell shape and polarity, migration, cell division, and transcriptional response. Angiogenesis, or the formation of new blood vessels in the body is a well-coordinated multi-step process. Endothelial cells lining the blood vessels acquire several new properties such as front-rear polarity, invasiveness, rapid proliferation and motility during angiogenesis. This is achieved by changes in the regulation of the actin cytoskeleton. Actin remodelling underlies the switch between the quiescent and angiogenic state of the endothelium. Actin forms endothelium-specific structures that support uniquely endothelial functions. Actin regulators at endothelial cell-cell junctions maintain the integrity of the blood-tissue barrier while permitting trans-endothelial leukocyte migration. This review focuses on endothelial actin structures and less-recognised actin-mediated endothelial functions. Readers are referred to other recent reviews for the well-recognised roles of actin in endothelial motility, barrier functions and leukocyte transmigration. Actin generates forces that are transmitted to the extracellular matrix resulting in vascular matrix remodelling. In this review, we attempt to synthesize our current understanding of the roles of actin in vascular morphogenesis. We speculate on the vascular bed specific differences in endothelial actin regulation and its role in the vast heterogeneity in endothelial morphology and function across the various tissues of our body.

Macrophage Reprogramming with Anti-miR223-Loaded Artificial Protocells Enhances In Vivo Cancer Therapeutic Potential

Several immune cell-expressed miRNAs (miRs) are associated with altered prognostic outcome in cancer patients, suggesting that they may be potential targets for development of cancer therapies. Here, translucent zebrafish (Danio rerio) is utilized to demonstrate that genetic knockout or knockdown of one such miR, microRNA-223 (miR223), globally or specifically in leukocytes, does indeed lead to reduced cancer progression. As a first step toward potential translation to a clinical therapy, a novel strategy is described for reprogramming neutrophils and macrophages utilizing miniature artificial protocells (PCs) to deliver anti-miRs against the anti-inflammatory miR223. Using genetic and live imaging approaches, it is shown that phagocytic uptake of anti-miR223-loaded PCs by leukocytes in zebrafish (and by human macrophages in vitro) effectively prolongs their pro-inflammatory state by blocking the suppression of pro-inflammatory cytokines, which, in turn, drives altered immune cell-cancer cell interactions and ultimately leads to a reduced cancer burden by driving reduced proliferation and increased cell death of tumor cells. This PC cargo delivery strategy for reprogramming leukocytes toward beneficial phenotypes has implications also for treating other systemic or local immune-mediated pathologies.

Rab35 governs apicobasal polarity through regulation of actin dynamics during sprouting angiogenesis

In early blood vessel development, trafficking programs, such as those using Rab GTPases, are tasked with delivering vesicular cargo with high spatiotemporal accuracy. However, the function of many Rab trafficking proteins remain ill-defined in endothelial tissue; therefore, their relevance to blood vessel development is unknown. Rab35 has been shown to play an enigmatic role in cellular behaviors which differs greatly between tissue-type and organism. Importantly, Rab35 has never been characterized for its potential contribution in sprouting angiogenesis; thus, our goal was to map Rab35’s primary function in angiogenesis. Our results demonstrate that Rab35 is critical for sprout formation; in its absence, apicobasal polarity is entirely lost in vitro and in vivo. To determine mechanism, we systematically explored established Rab35 effectors and show that none are operative in endothelial cells. However, we find that Rab35 partners with DENNd1c, an evolutionarily divergent guanine exchange factor, to localize to actin. Here, Rab35 regulates actin polymerization through limiting Rac1 and RhoA activity, which is required to set up proper apicobasal polarity during sprout formation. Our findings establish that Rab35 is a potent brake of actin remodeling during blood vessel development.

The promiscuous GTPase Rab35 has been shown to be involved in many important cellular functions. In this article, Francis et al. illustrate how Rab35 acts as a critical brake to actin remodeling during sprouting angiogenesis and how it is necessary for proper blood vessel development.

FOXO1 represses sprouty 2 and sprouty 4 expression to promote arterial specification and vascular remodeling in the mouse yolk sac

Establishing a functional circulatory system is required for post-implantation development during murine embryogenesis. Previous studies in loss-of-function mouse models showed that FOXO1, a Forkhead family transcription factor, is required for yolk sac (YS) vascular remodeling and survival beyond embryonic day (E) 11. Here, we demonstrate that at E8.25, loss of Foxo1 in Tie2-cre expressing cells resulted in increased sprouty 2 (Spry2) and Spry4 expression, reduced arterial gene expression and reduced Kdr (also known as Vegfr2 and Flk1) transcripts without affecting overall endothelial cell identity, survival or proliferation. Using a Dll4-BAC-nlacZ reporter line, we found that one of the earliest expressed arterial genes, delta like 4, is significantly reduced in Foxo1 mutant YS without being substantially affected in the embryo proper. We show that FOXO1 binds directly to previously identified Spry2 gene regulatory elements (GREs) and newly identified, evolutionarily conserved Spry4 GREs to repress their expression. Furthermore, overexpression of Spry4 in transient transgenic embryos largely recapitulates the reduced expression of arterial genes seen in conditional Foxo1 mutants. Together, these data reveal a novel role for FOXO1 as a key transcriptional repressor regulating both pre-flow arterial specification and subsequent vessel remodeling within the murine YS.

Endothelial cell mechanics and blood flow forces in vascular morphogenesis

The vertebrate cardiovascular system is made up by a hierarchically structured network of highly specialised blood vessels. This network emerges during early embryogenesis and evolves in size and complexity concomitant with embryonic growth and organ formation. Underlying this plasticity are actin-driven endothelial cell behaviours, which allow endothelial cells to change their shape and move within the vascular network. In this review, we discuss the cellular and molecular mechanisms involved in vascular network formation and how these intrinsic mechanisms are influenced by haemodynamic forces provided by pressurized blood flow. While most of this review focusses on in vivo evidence from zebrafish embryos, we also mention complementary findings obtained in other experimental systems.

A zebrafish toolbox for biomechanical signaling in cardiovascular development and disease

PURPOSE OF REVIEW

The zebrafish embryo has emerged as a powerful model organism to investigate the mechanisms by which biophysical forces regulate vascular and cardiac cell biology during development and disease. A versatile arsenal of methods and tools is available to manipulate and analyze biomechanical signaling. This review aims to provide an overview of the experimental strategies and tools that have been utilized to study biomechanical signaling in cardiovascular developmental processes and different vascular disease models in the zebrafish embryo. Within the scope of this review, we focus on work published during the last two years.

RECENT FINDINGS

Genetic and pharmacological tools for the manipulation of cardiac function allow alterations of hemodynamic flow patterns in the zebrafish embryo and various types of transgenic lines are available to report endothelial cell responses to biophysical forces. These tools have not only revealed the impact of biophysical forces on cardiovascular development but also helped to establish more accurate models for cardiovascular diseases including cerebral cavernous malformations, hereditary hemorrhagic telangiectasias, arteriovenous malformations, and lymphangiopathies.

SUMMARY

The zebrafish embryo is a valuable vertebrate model in which in-vivo manipulations of biophysical forces due to cardiac contractility and blood flow can be performed. These analyses give important insights into biomechanical signaling pathways that control endothelial and endocardial cell behaviors. The technical advances using this vertebrate model will advance our understanding of the impact of biophysical forces in cardiovascular pathologies.

Endothelial Extracellular Vesicles: From Keepers of Health to Messengers of Disease

Endothelium has a rich vesicular network that allows the exchange of macromolecules between blood and parenchymal cells. This feature of endothelial cells, along with their polarized secretory machinery, makes them the second major contributor, after platelets, to the particulate secretome in circulation. Extracellular vesicles (EVs) produced by the endothelial cells mirror the remarkable molecular heterogeneity of their parent cells. Cargo molecules carried by EVs were shown to contribute to the physiological functions of endothelium and may support the plasticity and adaptation of endothelial cells in a paracrine manner. Endothelium-derived vesicles can also contribute to the pathogenesis of cardiovascular disease or can serve as prognostic or diagnostic biomarkers. Finally, endothelium-derived EVs can be used as therapeutic tools to target endothelium for drug delivery or target stromal cells via the endothelial cells. In this review we revisit the recent evidence on the heterogeneity and plasticity of endothelial cells and their EVs. We discuss the role of endothelial EVs in the maintenance of vascular homeostasis along with their contributions to endothelial adaptation and dysfunction. Finally, we evaluate the potential of endothelial EVs as disease biomarkers and their leverage as therapeutic tools.