NOTCH1 is a mechanosensor in adult arteries

HES1 potentiates high salt stress response as an enhancer of NFAT5-DNA binding

High salt conditions and subsequent hyperosmolarity are injurious cellular stresses that can activate immune signaling. Nuclear factor of activated T-cells 5 (NFAT5) is an essential transcription factor that induces osmoprotective genes such as aldose reductase (AR) and betaine-GABA transporter 1 (BGT1). High salt stress-mediated NFAT5 activation is also reported to accelerate the inflammatory response and autoimmune diseases. However, the systemic regulation of NFAT5 remains unclear. Here, we performed a genome-wide siRNA screen to comprehensively identify the regulators of NFAT5. We monitored NFAT5 nuclear translocation and identified one of the Notch signaling effectors, Hairy and enhancer of split-1 (HES1), as a positive regulator of NFAT5. HES1 was induced by high salinity via ERK signaling and facilitated NFAT5 recruitment to its target promoter region, resulting in the proper induction of osmoprotective genes and cytoprotection under high salt stress. These findings suggest that, though HES1 is well known as a transcriptional repressor, it positively regulates NFAT5-dependent transcription in the context of a high salinity/hyperosmotic response.

Another Notch in the Belt of Rheumatoid Arthritis

Notch ligands and receptors, including JAG1/2, DLL1/4, and Notch1/3, are enriched on macrophages (MΦs), fibroblast-like synoviocytes (FLS), and/or endothelial cells in rheumatoid arthritis (RA) compared with normal synovial tissues (ST). Power Doppler ultrasound-guided ST studies reveal that the Notch family is highly involved in early active RA, especially during neovascularization. In contrast, the Notch family is not implicated during the erosive stage, evidenced by their lack of correlation with radiographic damage in RA ST. Toll-like receptors and tumor necrosis factor (TNF) are the common inducers of Notch expression in RA MΦs, FLS, and endothelial cells. Among Notch ligands, JAG1 and/or DLL4 are most inducible by inflammatory responses in RA MΦs or endothelial cells and transactivate their receptors on RA FLS. TNF plays a central role on Notch ligands, as anti-TNF good responders display JAG1/2 and DLL1/4 transcriptional downregulation in RA ST myeloid cells. In in vitro studies, TNF increases Notch3 expression in MΦs, which is further amplified by RA FLS addition. Specific disease-modifying antirheumatic drugs reduced JAG1 and Notch3 expression in MΦ and RA FLS cocultures. Organoids containing FLS and endothelial cells have increased expression of JAG1 and Notch3. Nonetheless, Methotrexate, interleukin-6 receptor (IL-6R) antibodies, and B cell blockers are mostly ineffective at decreasing Notch family expression. NF-κB, MAPK, and AKT pathways are involved in Notch signaling, whereas JAK/STATs are not. Although Notch blockade has been effective in RA preclinical studies, its small molecule inhibitors have failed in phase I and II studies, suggesting that alternative strategies may be required to intercept their function.

Mitigating Vascular Inflammation by Mimicking AIBP Mechanisms: A New Therapeutic End for Atherosclerotic Cardiovascular Disease

Atherosclerosis, characterized by the accumulation of lipoproteins and lipids within the vascular wall, underlies a heart attack, stroke, and peripheral artery disease. Endothelial inflammation is the primary component driving atherosclerosis, promoting leukocyte adhesion molecule expression (e.g., E-selectin), inducing chemokine secretion, reducing the production of nitric oxide (NO), and enhancing the thrombogenic potential. While current therapies, such as statins, colchicine, anti-IL1β, and sodium-glucose cotransporter 2 (SGLT2) inhibitors, target systemic inflammation, none of them addresses endothelial cell (EC) inflammation, a critical contributor to disease progression. Targeting endothelial inflammation is clinically significant because it can mitigate the root cause of atherosclerosis, potentially preventing disease progression, while reducing the side effects associated with broader anti-inflammatory treatments. Recent studies highlight the potential of the APOA1 binding protein (AIBP) to reduce systemic inflammation in mice. Furthermore, its mechanism of action also guides the design of a potential targeted therapy against a particular inflammatory signaling pathway. This review discusses the unique advantages of repressing vascular inflammation or enhancing vascular quiescence and the associated benefits of reducing thrombosis. This approach offers a promising avenue for more effective and targeted interventions to improve patient outcomes.

Endothelial cell elongation and alignment in response to shear stress requires acetylation of microtubules

The innermost layer of the vessel wall is constantly subjected to recurring and relenting mechanical forces by virtue of their direct contact with blood flow. Endothelial cells of the vessel are exposed to distension, pressure, and shear stress; adaptation to these hemodynamic forces requires significant remodeling of the cytoskeleton which includes changes in actin, intermediate filaments, and microtubules. While much is known about the effect of shear stress on the endothelial actin cytoskeleton; the impact of hemodynamic forces on the microtubule network has not been investigated in depth. Here we used imaging techniques and protein expression analysis to characterize how pharmacological and genetic perturbations of microtubule properties alter endothelial responses to laminar shear stress. Our findings revealed that pharmacological suppression of microtubule dynamics blocked two typical responses to laminar shear stress: endothelial elongation and alignment. The findings demonstrate the essential contribution of the microtubule network to changes in cell shape driven by mechanical forces. Furthermore, we observed a flow-dependent increase in microtubule acetylation that occurred early in the process of cell elongation. Pharmacological manipulation of microtubule acetylation showed a direct and causal relationship between acetylation and endothelial elongation. Finally, genetic inactivation of aTAT1, a microtubule acetylase, led to significant loss of acetylation as well as inhibition of cell elongation in response to flow. In contrast, loss of HDAC6, a microtubule deacetylase, resulted in robust microtubule acetylation with cells displaying faster kinetics of elongation and alignment. Taken together, our findings uncovered the critical contributions of HDAC6 and aTAT1, that through their roles in the regulation of microtubule acetylation, are key mediators of endothelial mechanotransduction.

Insights into the post-translational modifications in heart failure

Heart failure (HF), as the terminal manifestation of multiple cardiovascular diseases, causes a huge socioeconomic burden worldwide. Despite the advances in drugs and medical-assisted devices, the prognosis of HF remains poor. HF is well-accepted as a myriad of subcellular dys-synchrony related to detrimental structural and functional remodelling of cardiac components, including cardiomyocytes, fibroblasts, endothelial cells and macrophages. Through the covalent chemical process, post-translational modifications (PTMs) can coordinate protein functions, such as re-localizing cellular proteins, marking proteins for degradation, inducing interactions with other proteins and tuning enzyme activities, to participate in the progress of HF. Phosphorylation, acetylation, and ubiquitination predominate in the currently reported PTMs. In addition, advanced HF is commonly accompanied by metabolic remodelling including enhanced glycolysis. Thus, glycosylation induced by disturbed energy supply is also important. In this review, firstly, we addressed the main types of HF. Then, considering that PTMs are associated with subcellular locations, we summarized the leading regulation mechanisms in organelles of distinctive cell types of different types of HF, respectively. Subsequently, we outlined the aforementioned four PTMs of key proteins and signaling sites in HF. Finally, we discussed the perspectives of PTMs for potential therapeutic targets in HF.

Endothelial γ-protocadherins inhibit KLF2 and KLF4 to promote atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of mortality worldwide. Laminar shear stress from blood flow, sensed by vascular endothelial cells, protects from ASCVD by upregulating the transcription factors KLF2 and KLF4, which induces an anti-inflammatory program that promotes vascular resilience. Here we identify clustered γ-protocadherins as therapeutically targetable, potent KLF2 and KLF4 suppressors whose upregulation contributes to ASCVD. Mechanistic studies show that γ-protocadherin cleavage results in translocation of the conserved intracellular domain to the nucleus where it physically associates with and suppresses signaling by the Notch intracellular domain. γ-Protocadherins are elevated in human ASCVD endothelium; their genetic deletion or antibody blockade protects from ASCVD in mice without detectably compromising host defense against bacterial or viral infection. These results elucidate a fundamental mechanism of vascular inflammation and reveal a method to target the endothelium rather than the immune system as a protective strategy in ASCVD.

Intramyocardial Sprouting Tip Cells Specify Coronary Arterialization

BACKGROUND

The elaborate patterning of coronary arteries critically supports the high metabolic activity of the beating heart. How coronary endothelial cells coordinate hierarchical vascular remodeling and achieve arteriovenous specification remains largely unknown. Understanding the molecular and cellular cues that pattern coronary arteries is crucial to develop innovative therapeutic strategies that restore functional perfusion within the ischemic heart.

METHODS

Single-cell transcriptomics and histological validation were used to delineate heterogeneous transcriptional states of the developing and mature coronary endothelium with a focus on sprouting endothelium and arterial cell specification. Genetic lineage tracing and high-resolution 3-dimensional imaging were used to characterize the origin and mechanisms of coronary angiogenic sprouting, as well as to fate-map selective endothelial lineages. Integration of single-cell transcriptomic data from ischemic adult mouse hearts and human embryonic data served to assess the conservation of transcriptional states across development, disease, and species.

RESULTS

We discover that coronary arteries originate from cells that have previously transitioned through a specific tip cell phenotype. We identify nonoverlapping intramyocardial and subepicardial tip cell populations with differential gene expression profiles and regulatory pathways. Esm1-lineage tracing confirmed that intramyocardial tip cells selectively contribute to coronary arteries and endocardial tunnels, but not veins. Notably, prearterial cells are detected from development stages to adulthood, increasingly in response to ischemic injury, and in human embryos, suggesting that tip cell-to-artery specification is a conserved mechanism.

CONCLUSIONS

A tip cell-to-artery specification mechanism drives arterialization of the intramyocardial plexus and endocardial tunnels throughout life and is reactivated upon ischemic injury. Differential sprouting programs govern the formation and specification of the venous and arterial coronary plexus.

Notch transcriptional target tmtc1 maintains vascular homeostasis

Proper lung function requires the maintenance of a tight endothelial barrier while simultaneously permitting the exchange of macromolecules and fluids to underlying tissue. Disruption of this barrier results in an increased vascular permeability in the lungs, leading to acute lung injury. In this study, we set out to determine whether transcriptional targets of Notch signaling function to preserve vascular integrity. We tested the in vivo requirement for Notch transcriptional signaling in maintaining the pulmonary endothelial barrier by using two complementary endothelial-specific Notch loss-of-function murine transgenic models. Notch signaling was blocked using endothelial-specific activation of an inhibitor of Notch transcriptional activation, Dominant Negative Mastermindlike (DNMAML; CDH5CreERT2), or endothelial-specific loss of Notch1 (Notch1f/f; CDH5CreERT2). Both Notch mutants increased vascular permeability with pan-Notch inhibition by DNMAML showing a more severe phenotype in the lungs and in purified endothelial cells. RNA sequencing of primary lung endothelial cells (ECs) identified novel Notch targets, one of which was transmembrane O-mannosyltransferase targeting cadherins 1 (tmtc1). We show that tmtc1 interacts with vascular endothelial cadherin (VE-cadherin) and regulates VE-cadherin egress from the endoplasmic reticulum through direct interaction. Our findings demonstrate that Notch signaling maintains endothelial adherens junctions and vascular homeostasis by a transcriptional mechanism that drives expression of critical factors important for processing and transport of VE-cadherin.

Hydrostatic pressure drives sprouting angiogenesis via adherens junction remodelling and YAP signalling

Endothelial cell physiology is governed by its unique microenvironment at the interface between blood and tissue. A major contributor to the endothelial biophysical environment is blood hydrostatic pressure, which in mechanical terms applies isotropic compressive stress on the cells. While other mechanical factors, such as shear stress and circumferential stretch, have been extensively studied, little is known about the role of hydrostatic pressure in the regulation of endothelial cell behavior. Here we show that hydrostatic pressure triggers partial and transient endothelial-to-mesenchymal transition in endothelial monolayers of different vascular beds. Values mimicking microvascular pressure environments promote proliferative and migratory behavior and impair barrier properties that are characteristic of a mesenchymal transition, resulting in increased sprouting angiogenesis in 3D organotypic model systems ex vivo and in vitro. Mechanistically, this response is linked to differential cadherin expression at the adherens junctions, and to an increased YAP expression, nuclear localization, and transcriptional activity. Inhibition of YAP transcriptional activity prevents pressure-induced sprouting angiogenesis. Together, this work establishes hydrostatic pressure as a key modulator of endothelial homeostasis and as a crucial component of the endothelial mechanical niche.

Capturing embryonic hematopoiesis in temporal and spatial dimensions

Hematopoietic stem cells (HSCs) possess the ability to sustain the continuous production of all blood cell types throughout an organism's lifespan. Although primarily located in the bone marrow of adults, HSCs originate during embryonic development. Visualization of the birth of HSCs, their developmental trajectory, and the specific interactions with their successive niches have significantly contributed to our understanding of the biology and mechanics governing HSC formation and expansion. Intravital techniques applied to live embryos or non-fixed samples have remarkably provided invaluable insights into the cellular and anatomical origins of HSCs. These imaging technologies have also shed light on the dynamic interactions between HSCs and neighboring cell types within the surrounding microenvironment or niche, such as endothelial cells or macrophages. This review delves into the advancements made in understanding the origin, production, and cellular interactions of HSCs, particularly during the embryonic development of mice and zebrafish, focusing on studies employing (live) imaging analysis.

Capturing physiological hemodynamic flow and mechanosensitive cell signaling in vessel-on-a-chip platforms

Recent advances in organ chip (or, "organ-on-a-chip") technologies and microphysiological systems (MPS) have enabled in vitro investigation of endothelial cell function in biomimetic three-dimensional environments under controlled fluid flow conditions. Many current organ chip models include a vascular compartment; however, the design and implementation of these vessel-on-a-chip components varies, with consequently varied impact on their ability to capture and reproduce hemodynamic flow and associated mechanosensitive signaling that regulates key characteristics of healthy, intact vasculature. In this review, we introduce organ chip and vessel-on-a-chip technology in the context of existing in vitro and in vivo vascular models. We then briefly discuss the importance of mechanosensitive signaling for vascular development and function, with focus on the major mechanosensitive signaling pathways involved. Next, we summarize recent advances in MPS and organ chips with an integrated vascular component, with an emphasis on comparing both the biomimicry and adaptability of the diverse approaches used for supporting and integrating intravascular flow. We review current data showing how intravascular flow and fluid shear stress impacts vessel development and function in MPS platforms and relate this to existing work in cell culture and animal models. Lastly, we highlight new insights obtained from MPS and organ chip models of mechanosensitive signaling in endothelial cells, and how this contributes to a deeper understanding of vessel growth and function in vivo. We expect this review will be of broad interest to vascular biologists, physiologists, and cardiovascular physicians as an introduction to organ chip platforms that can serve as viable model systems for investigating mechanosensitive signaling and other aspects of vascular physiology.

Resilience to diabetic retinopathy

Chronic elevation of blood glucose at first causes relatively minor changes to the neural and vascular components of the retina. As the duration of hyperglycemia persists, the nature and extent of damage increases and becomes readily detectable. While this second, overt manifestation of diabetic retinopathy (DR) has been studied extensively, what prevents maximal damage from the very start of hyperglycemia remains largely unexplored. Recent studies indicate that diabetes (DM) engages mitochondria-based defense during the retinopathy-resistant phase, and thereby enables the retina to remain healthy in the face of hyperglycemia. Such resilience is transient, and its deterioration results in progressive accumulation of retinal damage. The concepts that co-emerge with these discoveries set the stage for novel intellectual and therapeutic opportunities within the DR field. Identification of biomarkers and mediators of protection from DM-mediated damage will enable development of resilience-based therapies that will indefinitely delay the onset of DR.

Mechanosensitive FHL2 tunes endothelial function

Endothelial tissues are essential mechanosensors in the vasculature and facilitate adaptation to various blood flow-induced mechanical cues. Defects in endothelial mechanoresponses can perturb tissue remodelling and functions leading to cardiovascular disease progression. In this context, the precise mechanisms of endothelial mechanoresponses contributing to normal and diseased tissue functioning remain elusive. Here, we sought to uncover how flow-mediated transcriptional regulation drives endothelial mechanoresponses in healthy and atherosclerotic-prone tissues. Using bulk RNA sequencing, we identify novel mechanosensitive genes in response to healthy unidirectional flow (UF) and athero-prone disturbed flow (DF). We find that the transcription as well as protein expression of Four-and-a-half LIM protein 2 (FHL2) are enriched in athero-prone DF both in vitro and in vivo. We then demonstrate that the exogenous expression of FHL2 is necessary and sufficient to drive discontinuous adherens junction morphology and increased tissue permeability. This athero-prone phenotype requires the force-sensitive binding of FHL2 to actin. In turn, the force-dependent localisation of FHL2 to stress fibres promotes microtubule dynamics to release the RhoGEF, GEF-H1, and activate the Rho-ROCK pathway. Thus, we unravelled a novel mechanochemical feedback wherein force-dependent FHL2 localisation promotes hypercontractility. This misregulated mechanoresponse creates highly permeable tissues, depicting classic hallmarks of atherosclerosis progression. Overall, we highlight crucial functions for the FHL2 force-sensitivity in tuning multi-scale endothelial mechanoresponses.

Notch signaling regulates UNC5B to suppress endothelial proliferation, migration, junction activity, and retinal plexus branching

Notch signaling guides vascular development and function by regulating diverse endothelial cell behaviors, including migration, proliferation, vascular density, endothelial junctions, and polarization in response to flow. Notch proteins form transcriptional activation complexes that regulate endothelial gene expression, but few of the downstream effectors that enable these phenotypic changes have been characterized in endothelial cells, limiting our understanding of vascular Notch activities. Using an unbiased screen of translated mRNA rapidly regulated by Notch signaling, we identified novel in vivo targets of Notch signaling in neonatal mouse brain endothelium, including UNC5B, a member of the netrin family of angiogenic-regulatory receptors. Endothelial Notch signaling rapidly upregulates UNC5B in multiple endothelial cell types. Loss or gain of UNC5B recapitulated specific Notch-regulated phenotypes. UNC5B expression inhibited endothelial migration and proliferation and was required for stabilization of endothelial junctions in response to shear stress. Loss of UNC5B partially or wholly blocked the ability of Notch activation to regulate these endothelial cell behaviors. In the developing mouse retina, endothelial-specific loss of UNC5B led to excessive vascularization, including increased vascular outgrowth, density, and branchpoint count. These data indicate that Notch signaling upregulates UNC5B as an effector protein to control specific endothelial cell behaviors and inhibit angiogenic growth.

Molecular Mechanisms Regulating Vascular Endothelial Permeability

Vascular endothelial cells form a monolayer in the vascular lumen and act as a selective barrier to control the permeability between blood and tissues. To maintain homeostasis, the endothelial barrier function must be strictly integrated. During acute inflammation, vascular permeability temporarily increases, allowing intravascular fluid, cells, and other components to permeate tissues. Moreover, it has been suggested that the dysregulation of endothelial cell permeability may cause several diseases, including edema, cancer, and atherosclerosis. Here, we reviewed the molecular mechanisms by which endothelial cells regulate the barrier function and physiological permeability.

Endothelial Cell Flow-Mediated Quiescence Is Temporally Regulated and Utilizes the Cell Cycle Inhibitor p27

BACKGROUND

Endothelial cells regulate their cell cycle as blood vessels remodel and transition to quiescence downstream of blood flow-induced mechanotransduction. Laminar blood flow leads to quiescence, but how flow-mediated quiescence is established and maintained is poorly understood.

METHODS

Primary human endothelial cells were exposed to laminar flow regimens and gene expression manipulations, and quiescence depth was analyzed via time-to-cell cycle reentry after flow cessation. Mouse and zebrafish endothelial expression patterns were examined via scRNA-seq (single-cell RNA sequencing) analysis, and mutant or morphant fish lacking p27 were analyzed for endothelial cell cycle regulation and in vivo cellular behaviors.

RESULTS

Arterial flow-exposed endothelial cells had a distinct transcriptome, and they first entered a deep quiescence, then transitioned to shallow quiescence under homeostatic maintenance conditions. In contrast, venous flow-exposed endothelial cells entered deep quiescence early that did not change with homeostasis. The cell cycle inhibitor p27 (CDKN1B) was required to establish endothelial flow-mediated quiescence, and expression levels positively correlated with quiescence depth. p27 loss in vivo led to endothelial cell cycle upregulation and ectopic sprouting, consistent with loss of quiescence. HES1 and ID3, transcriptional repressors of p27 upregulated by arterial flow, were required for quiescence depth changes and the reduced p27 levels associated with shallow quiescence.

CONCLUSIONS

Endothelial cell flow-mediated quiescence has unique properties and temporal regulation of quiescence depth that depends on the flow stimulus. These findings are consistent with a model whereby flow-mediated endothelial cell quiescence depth is temporally regulated downstream of p27 transcriptional regulation by HES1 and ID3. The findings are important in understanding endothelial cell quiescence misregulation that leads to vascular dysfunction and disease.

Mechanosensitive membrane domains regulate calcium entry in arterial endothelial cells to protect against inflammation

Endothelial cells (ECs) in the descending aorta are exposed to high laminar shear stress, and this supports an antiinflammatory phenotype. High laminar shear stress also induces flow-aligned cell elongation and front-rear polarity, but whether these are required for the antiinflammatory phenotype is unclear. Here, we showed that caveolin-1-rich microdomains polarize to the downstream end of ECs that are exposed to continuous high laminar flow. These microdomains were characterized by high membrane rigidity, filamentous actin (F-actin), and raft-associated lipids. Transient receptor potential vanilloid (TRPV4) ion channels were ubiquitously expressed on the plasma membrane but mediated localized Ca2+ entry only at these microdomains where they physically interacted with clustered caveolin-1. These focal Ca2+ bursts activated endothelial nitric oxide synthase within the confines of these domains. Importantly, we found that signaling at these domains required both cell body elongation and sustained flow. Finally, TRPV4 signaling at these domains was necessary and sufficient to suppress inflammatory gene expression and exogenous activation of TRPV4 channels ameliorated the inflammatory response to stimuli both in vitro and in vivo. Our work revealed a polarized mechanosensitive signaling hub in arterial ECs that dampened inflammatory gene expression and promoted cell resilience.

Endocardial primary cilia and blood flow are required for regulation of EndoMT during endocardial cushion development

Blood flow is critical for heart valve formation, and cellular mechanosensors are essential to translate flow into transcriptional regulation of development. Here, we identify a role for primary cilia in vivo in the spatial regulation of cushion formation, the first stage of valve development, by regionally controlling endothelial to mesenchymal transition (EndoMT) via modulation of Kruppel-like Factor 4 (Klf4) . We find that high shear stress intracardiac regions decrease endocardial ciliation over cushion development, correlating with KLF4 downregulation and EndoMT progression. Mouse embryos constitutively lacking cilia exhibit a blood-flow dependent accumulation of KLF4 in these regions, independent of upstream left-right abnormalities, resulting in impaired cushion cellularization. snRNA-seq revealed that cilia KO endocardium fails to progress to late-EndoMT, retains endothelial markers and has reduced EndoMT/mesenchymal genes that KLF4 antagonizes. Together, these data identify a mechanosensory role for endocardial primary cilia in cushion development through regional regulation of KLF4.

BMPR2 Loss Activates AKT by Disrupting DLL4/NOTCH1 and PPARγ Signaling in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive cardiopulmonary disease characterized by pathologic vascular remodeling of small pulmonary arteries. Endothelial dysfunction in advanced PAH is associated with proliferation, apoptosis resistance, and endothelial to mesenchymal transition (EndoMT) due to aberrant signaling. DLL4, a cell membrane associated NOTCH ligand, plays a pivotal role maintaining vascular integrity. Inhibition of DLL4 has been associated with the development of pulmonary hypertension, but the mechanism is incompletely understood. Here we report that BMPR2 silencing in pulmonary artery endothelial cells (PAECs) activated AKT and suppressed the expression of DLL4. Consistent with these in vitro findings, increased AKT activation and reduced DLL4 expression was found in the small pulmonary arteries of patients with PAH. Increased NOTCH1 activation through exogenous DLL4 blocked AKT activation, decreased proliferation and reversed EndoMT. Exogenous and overexpression of DLL4 induced BMPR2 and PPRE promoter activity, and BMPR2 and PPARG mRNA in idiopathic PAH (IPAH) ECs. PPARγ, a nuclear receptor associated with EC homeostasis, suppressed by BMPR2 loss was induced and activated by DLL4/NOTCH1 signaling in both BMPR2-silenced and IPAH ECs, reversing aberrant phenotypic changes, in part through AKT inhibition. Directly blocking AKT or restoring DLL4/NOTCH1/PPARγ signaling may be beneficial in preventing or reversing the pathologic vascular remodeling of PAH.

Transient low shear-stress preconditioning influences long-term endothelial traction and alignment under high shear flow

Endothelial cells (ECs) within the vascular system encounter fluid shear stress (FSS). High, laminar FSS promotes vasodilation and anti-inflammatory responses, whereas low or disturbed FSS induces dysfunction and inflammation. However, the adaptation of endothelial cells (ECs) to dynamically changing FSS patterns remains underexplored. Here, by combining traction force microscopy with a custom flow chamber, we examined human umbilical vein endothelial cells adapting their traction during transitions from short-term low shear to long-term high shear stress. We discovered that the initial low FSS elevates the traction by only half of the amount in response to direct high FSS even after flow changes to high FSS. However, in the long term under high FSS, the flow started with low FSS triggers a substantial second rise in traction for over 10 h. In contrast, the flow started directly with high FSS results in a quick traction surge followed by a huge reduction below the baseline traction in <30 min. Importantly, we find that the orientation of traction vectors is steered by initial shear exposure. Using Granger causality analysis, we show that the traction that aligns in the flow direction under direct high FSS functionally causes cell alignment toward the flow direction. However, EC traction that orients perpendicular to the flow that starts with temporary low FSS functionally causes cell orientation perpendicular to the flow. Taken together, our findings elucidate the significant influence of initial short-term low FSS on lasting changes in endothelial traction that induces EC alignment.NEW & NOTEWORTHY In our study, we uncover that preconditioning with low shear stress yields enduring impacts on endothelial cell traction and orientation, persisting even after transitioning to high-shear conditions. Using Granger causality analysis, we demonstrate a functional link between the direction of cell traction and subsequent cellular alignment across varying shear environments.

Hemodynamics regulate spatiotemporal artery muscularization in the developing circle of Willis

Vascular smooth muscle cells (VSMCs) envelop vertebrate brain arteries, playing a crucial role in regulating cerebral blood flow and neurovascular coupling. The dedifferentiation of VSMCs is implicated in cerebrovascular diseases and neurodegeneration. Despite its importance, the process of VSMC differentiation on brain arteries during development remains inadequately characterized. Understanding this process could aid in reprogramming and regenerating differentiated VSMCs in cerebrovascular diseases. In this study, we investigated VSMC differentiation on the zebrafish circle of Willis (CoW), comprising major arteries that supply blood to the vertebrate brain. We observed that the arterial expression of CoW endothelial cells (ECs) occurs after their migration from the cranial venous plexus to form CoW arteries. Subsequently, acta2+ VSMCs differentiate from pdgfrb+ mural cell progenitors upon recruitment to CoW arteries. The progression of VSMC differentiation exhibits a spatiotemporal pattern, advancing from anterior to posterior CoW arteries. Analysis of blood flow suggests that earlier VSMC differentiation in anterior CoW arteries correlates with higher red blood cell velocity wall shear stress. Furthermore, pulsatile blood flow is required for differentiation of human brain pdgfrb+ mural cells into VSMCs as well as VSMC differentiation on zebrafish CoW arteries. Consistently, the flow-responsive transcription factor klf2a is activated in ECs of CoW arteries prior to VSMC differentiation, and klf2a knockdown delays VSMC differentiation on anterior CoW arteries. In summary, our findings highlight the role of blood flow activation of endothelial klf2a as a mechanism regulating the initial VSMC differentiation on vertebrate brain arteries.

HEG1 Protects Against Atherosclerosis by Regulating Stable Flow-Induced KLF2/4 Expression in Endothelial Cells

BACKGROUND

Atherosclerosis preferentially occurs in arterial regions of disturbed blood flow, and stable flow (s-flow) protects against atherosclerosis by incompletely understood mechanisms.

METHODS

Our single-cell RNA-sequencing data using the mouse partial carotid ligation model was reanalyzed, which identified Heart-of-glass 1 (HEG1) as an s-flow-induced gene. HEG1 expression was studied by immunostaining, quantitive polymerase chain reaction, hybridization chain reaction, and Western blot in mouse arteries, human aortic endothelial cells (HAECs), and human coronary arteries. A small interfering RNA-mediated knockdown of HEG1 was used to study its function and signaling mechanisms in HAECs under various flow conditions using a cone-and-plate shear device. We generated endothelial-targeted, tamoxifen-inducible HEG1 knockout (HEG1iECKO) mice. To determine the role of HEG1 in atherosclerosis, HEG1iECKO and littermate-control mice were injected with an adeno-associated virus-PCSK9 [proprotein convertase subtilisin/kexin type 9] and fed a Western diet to induce hypercholesterolemia either for 2 weeks with partial carotid ligation or 2 months without the surgery.

RESULTS

S-flow induced HEG1 expression at the mRNA and protein levels in vivo and in vitro. S-flow stimulated HEG1 protein translocation to the downstream side of HAECs and release into the media, followed by increased messenger RNA and protein expression. HEG1 knockdown prevented s-flow-induced endothelial responses, including monocyte adhesion, permeability, and migration. Mechanistically, HEG1 knockdown prevented s-flow-induced KLF2/4 (Kruppel-like factor 2/4) expression by regulating its intracellular binding partner KRIT1 (Krev interaction trapped protein 1) and the MEKK3-MEK5-ERK5-MEF2 pathway in HAECs. Compared with littermate controls, HEG1iECKO mice exposed to hypercholesterolemia for 2 weeks and partial carotid ligation developed advanced atherosclerotic plaques, featuring increased necrotic core area, thin-capped fibroatheroma, inflammation, and intraplaque hemorrhage. In a conventional Western diet model for 2 months, HEG1iECKO mice also showed an exacerbated atherosclerosis development in the arterial tree in both sexes and the aortic sinus in males but not in females. Moreover, endothelial HEG1 expression was reduced in human coronary arteries with advanced atherosclerotic plaques.

CONCLUSIONS

Our findings indicate that HEG1 is a novel mediator of atheroprotective endothelial responses to flow and a potential therapeutic target.

Eph-ephrin signaling couples endothelial cell sorting and arterial specification

Cell segregation allows the compartmentalization of cells with similar fates during morphogenesis, which can be enhanced by cell fate plasticity in response to local molecular and biomechanical cues. Endothelial tip cells in the growing retina, which lead vessel sprouts, give rise to arterial endothelial cells and thereby mediate arterial growth. Here, we have combined cell type-specific and inducible mouse genetics, flow experiments in vitro, single-cell RNA sequencing and biochemistry to show that the balance between ephrin-B2 and its receptor EphB4 is critical for arterial specification, cell sorting and arteriovenous patterning. At the molecular level, elevated ephrin-B2 function after loss of EphB4 enhances signaling responses by the Notch pathway, VEGF and the transcription factor Dach1, which is influenced by endothelial shear stress. Our findings reveal how Eph-ephrin interactions integrate cell segregation and arteriovenous specification in the vasculature, which has potential relevance for human vascular malformations caused by EPHB4 mutations.

Exercise mitigates flow recirculation and activates metabolic transducer SCD1 to catalyze vascular protective metabolites

Exercise promotes pulsatile shear stress in the arterial circulation and ameliorates cardiometabolic diseases. However, exercise-mediated metabolic transducers for vascular protection remain under-investigated. Untargeted metabolomic analysis demonstrated that wild-type mice undergoing voluntary wheel running exercise expressed increased endothelial stearoyl-CoA desaturase 1 (SCD1) that catalyzes anti-inflammatory lipid metabolites, namely, oleic (OA) and palmitoleic acids (PA), to mitigate NF-κB-mediated inflammatory responses. In silico analysis revealed that exercise augmented time-averaged wall shear stress but mitigated flow recirculation and oscillatory shear index in the lesser curvature of the mouse aortic arch. Following exercise, endothelial Scd1-deleted mice (Ldlr-/- Scd1EC-/-) on high-fat diet developed persistent VCAM1-positive endothelium in the lesser curvature and the descending aorta, whereas SCD1 overexpression via adenovirus transfection mitigated endoplasmic reticulum stress and inflammatory biomarkers. Single-cell transcriptomics of the aorta identified Scd1-positive and Vcam1-negative endothelial subclusters interacting with other candidate genes. Thus, exercise mitigates flow recirculation and activates endothelial SCD1 to catalyze OA and PA for vascular endothelial protection.

The Role of Mechanotransduction in Contact Inhibition of Locomotion and Proliferation

Contact inhibition (CI) represents a crucial tumor-suppressive mechanism responsible for controlling the unbridled growth of cells, thus preventing the formation of cancerous tissues. CI can be further categorized into two distinct yet interrelated components: CI of locomotion (CIL) and CI of proliferation (CIP). These two components of CI have historically been viewed as separate processes, but emerging research suggests that they may be regulated by both distinct and shared pathways. Specifically, recent studies have indicated that both CIP and CIL utilize mechanotransduction pathways, a process that involves cells sensing and responding to mechanical forces. This review article describes the role of mechanotransduction in CI, shedding light on how mechanical forces regulate CIL and CIP. Emphasis is placed on filamin A (FLNA)-mediated mechanotransduction, elucidating how FLNA senses mechanical forces and translates them into crucial biochemical signals that regulate cell locomotion and proliferation. In addition to FLNA, trans-acting factors (TAFs), which are proteins or regulatory RNAs capable of directly or indirectly binding to specific DNA sequences in distant genes to regulate gene expression, emerge as sensitive players in both the mechanotransduction and signaling pathways of CI. This article presents methods for identifying these TAF proteins and profiling the associated changes in chromatin structure, offering valuable insights into CI and other biological functions mediated by mechanotransduction. Finally, it addresses unanswered research questions in these fields and delineates their possible future directions.

Identification of abdominal aortic aneurysm subtypes based on mechanosensitive genes

BACKGROUND

Rupture of abdominal aortic aneurysm (rAAA) is a fatal event in the elderly. Elevated blood pressure and weakening of vessel wall strength are major risk factors for this devastating event. This present study examined whether the expression profile of mechanosensitive genes correlates with the phenotype and outcome, thus, serving as a biomarker for AAA development.

METHODS

In this study, we identified mechanosensitive genes involved in AAA development using general bioinformatics methods and machine learning with six human datasets publicly available from the GEO database. Differentially expressed mechanosensitive genes (DEMGs) in AAAs were identified by differential expression analysis. Molecular biological functions of genes were explored using functional clustering, Protein-protein interaction (PPI), and weighted gene co-expression network analysis (WGCNA). According to the datasets (GSE98278, GSE205071 and GSE165470), the changes of diameter and aortic wall strength of AAA induced by DEMGs were verified by consensus clustering analysis, machine learning models, and statistical analysis. In addition, a model for identifying AAA subtypes was built using machine learning methods.

RESULTS

38 DEMGs clustered in pathways regulating 'Smooth muscle cell biology' and 'Cell or Tissue connectivity'. By analyzing the GSE205071 and GSE165470 datasets, DEMGs were found to respond to differences in aneurysm diameter and vessel wall strength. Thus, in the merged datasets, we formally created subgroups of AAAs and found differences in immune characteristics between the subgroups. Finally, a model that accurately predicts the AAA subtype that is more likely to rupture was successfully developed.

CONCLUSION

We identified 38 DEMGs that may be involved in AAA. This gene cluster is involved in regulating the maximum vessel diameter, degree of immunoinflammatory infiltration, and strength of the local vessel wall in AAA. The prognostic model we developed can accurately identify the AAA subtypes that tend to rupture.

Low Shear in Short-Term Impacts Endothelial Cell Traction and Alignment in Long-Term

Within the vascular system, endothelial cells (ECs) are exposed to fluid shear stress (FSS), a mechanical force exerted by blood flow that is critical for regulating cellular tension and maintaining vascular homeostasis. The way ECs react to FSS varies significantly; while high, laminar FSS supports vasodilation and suppresses inflammation, low or disturbed FSS can lead to endothelial dysfunction and increase the risk of cardiovascular diseases. Yet, the adaptation of ECs to dynamically varying FSS remains poorly understood. This study focuses on the dynamic responses of ECs to brief periods of low FSS, examining its impact on endothelial traction-a measure of cellular tension that plays a crucial role in how endothelial cells respond to mechanical stimuli. By integrating traction force microscopy (TFM) with a custom-built flow chamber, we analyzed how human umbilical vein endothelial cells (HUVECs) adjust their traction in response to shifts from low to high shear stress. We discovered that initial exposure to low FSS prompts a marked increase in traction force, which continues to rise over 10 hours before slowly decreasing. In contrast, immediate exposure to high FSS causes a quick spike in traction followed by a swift reduction, revealing distinct patterns of traction behavior under different shear conditions. Importantly, the direction of traction forces and the resulting cellular alignment under these conditions indicate that the initial shear experience dictates long-term endothelial behavior. Our findings shed light on the critical influence of short-lived low-shear stress experiences in shaping endothelial function, indicating that early exposure to low FSS results in enduring changes in endothelial contractility and alignment, with significant consequences for vascular health and the development of cardiovascular diseases.

Endothelial Jagged1 levels and distribution are post-transcriptionally controlled by ZFP36 decay proteins

Vascular morphogenesis requires a delicate gradient of Notch signaling controlled, in part, by the distribution of ligands (Dll4 and Jagged1). How Jagged1 (JAG1) expression is compartmentalized in the vascular plexus remains unclear. Here, we show that Jag1 mRNA is a direct target of zinc-finger protein 36 (ZFP36), an RNA-binding protein involved in mRNA decay that we find robustly induced by vascular endothelial growth factor (VEGF). Endothelial cells lacking ZFP36 display high levels of JAG1 and increase angiogenic sprouting in vitro. Furthermore, mice lacking Zfp36 in endothelial cells display mispatterned and increased levels of JAG1 in the developing retinal vascular plexus. Abnormal levels of JAG1 at the sprouting front alters NOTCH1 signaling, increasing the number of tip cells, a phenotype that is rescued by imposing haploinsufficiency of Jag1. Our findings reveal an important feedforward loop whereby VEGF stimulates ZFP36, consequently suppressing Jag1 to enable adequate levels of Notch signaling during sprouting angiogenesis.

Gamma protocadherins in vascular endothelial cells inhibit Klf2/4 to promote atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of mortality worldwide1. Laminar shear stress (LSS) from blood flow in straight regions of arteries protects against ASCVD by upregulating the Klf2/4 anti-inflammatory program in endothelial cells (ECs)2-8. Conversely, disturbed shear stress (DSS) at curves or branches predisposes these regions to plaque formation9,10. We previously reported a whole genome CRISPR knockout screen11 that identified novel inducers of Klf2/4. Here we report suppressors of Klf2/4 and characterize one candidate, protocadherin gamma A9 (Pcdhga9), a member of the clustered protocadherin gene family12. Pcdhg deletion increases Klf2/4 levels in vitro and in vivo and suppresses inflammatory activation of ECs. Pcdhg suppresses Klf2/4 by inhibiting the Notch pathway via physical interaction of cleaved Notch1 intracellular domain (NICD Val1744) with nuclear Pcdhg C-terminal constant domain (CCD). Pcdhg inhibition by EC knockout (KO) or blocking antibody protects from atherosclerosis. Pcdhg is elevated in the arteries of human atherosclerosis. This study identifies a novel fundamental mechanism of EC resilience and therapeutic target for treating inflammatory vascular disease.

Endothelial cell flow-mediated quiescence is temporally regulated and utilizes the cell cycle inhibitor p27

Background

Endothelial cells regulate their cell cycle as blood vessels remodel and transition to quiescence downstream of blood flow-induced mechanotransduction. Laminar blood flow leads to quiescence, but how flow-mediated quiescence is established and maintained is poorly understood.

Methods

Primary human endothelial cells were exposed to laminar flow regimens and gene expression manipulations, and quiescence depth was analyzed via time to cell cycle re-entry after flow cessation. Mouse and zebrafish endothelial expression patterns were examined via scRNA seq analysis, and mutant or morphant fish lacking p27 were analyzed for endothelial cell cycle regulation and in vivo cellular behaviors.

Results

Arterial flow-exposed endothelial cells had a distinct transcriptome, and they first entered a deep quiescence, then transitioned to shallow quiescence under homeostatic maintenance conditions. In contrast, venous-flow exposed endothelial cells entered deep quiescence early that did not change with homeostasis. The cell cycle inhibitor p27 (CDKN1B) was required to establish endothelial flow-mediated quiescence, and expression levels positively correlated with quiescence depth. p27 loss in vivo led to endothelial cell cycle upregulation and ectopic sprouting, consistent with loss of quiescence. HES1 and ID3, transcriptional repressors of p27 upregulated by arterial flow, were required for quiescence depth changes and the reduced p27 levels associated with shallow quiescence.

Conclusions

Endothelial cell flow-mediated quiescence has unique properties and temporal regulation of quiescence depth that depends on the flow stimulus. These findings are consistent with a model whereby flow-mediated endothelial cell quiescence depth is temporally regulated downstream of p27 transcriptional regulation by HES1 and ID3. The findings are important in understanding endothelial cell quiescence mis-regulation that leads to vascular dysfunction and disease.

Extracellular Matrix Cues Regulate Mechanosensing and Mechanotransduction of Cancer Cells

Extracellular biophysical properties have particular implications for a wide spectrum of cellular behaviors and functions, including growth, motility, differentiation, apoptosis, gene expression, cell-matrix and cell-cell adhesion, and signal transduction including mechanotransduction. Cells not only react to unambiguously mechanical cues from the extracellular matrix (ECM), but can occasionally manipulate the mechanical features of the matrix in parallel with biological characteristics, thus interfering with downstream matrix-based cues in both physiological and pathological processes. Bidirectional interactions between cells and (bio)materials in vitro can alter cell phenotype and mechanotransduction, as well as ECM structure, intentionally or unintentionally. Interactions between cell and matrix mechanics in vivo are of particular importance in a variety of diseases, including primarily cancer. Stiffness values between normal and cancerous tissue can range between 500 Pa (soft) and 48 kPa (stiff), respectively. Even the shear flow can increase from 0.1-1 dyn/cm2 (normal tissue) to 1-10 dyn/cm2 (cancerous tissue). There are currently many new areas of activity in tumor research on various biological length scales, which are highlighted in this review. Moreover, the complexity of interactions between ECM and cancer cells is reduced to common features of different tumors and the characteristics are highlighted to identify the main pathways of interaction. This all contributes to the standardization of mechanotransduction models and approaches, which, ultimately, increases the understanding of the complex interaction. Finally, both the in vitro and in vivo effects of this mechanics-biology pairing have key insights and implications for clinical practice in tumor treatment and, consequently, clinical translation.

Aspirin and Celecoxib Regulate Notch1/Hes1 Pathway to Prevent Pressure Overload-Induced Myocardial Hypertrophy

This study aimed to investigate the molecular mechanisms underlying the protective effects of cyclooxygenase (cox) inhibitors against myocardial hypertrophy.Rat H9c2 cardiomyocytes were induced by mechanical stretching. SD rats underwent transverse aortic constriction to induce pressure overload myocardial hypertrophy. Rats were subjected to echocardiography and tail arterial pressure in 12W. qPCR and western blot were used to detect the expression of Notch-related signaling. The inflammatory factors were tested by ELISA in serum, heart tissue, and cell culture supernatant.Compared with control, levels of pro-inflammatory cytokines IL-6, TNF-α, and IL-1β were increased and anti-inflammatory cytokine IL-10 was reduced in myocardial tissues and serum of rat models. Levels of Notch1 and Hes1 were reduced in myocardial tissues. However, cox inhibitor treatment (aspirin and celecoxib), the improvement of exacerbated myocardial hypertrophy, fibrosis, dysfunction, and inflammation was parallel to the activation of Notch1/Hes1 pathway. Moreover, in vitro experiments showed that, in cardiomyocyte H9c2 cells, application of ~20% mechanical stretching activated inflammatory mediators (IL-6, TNF-α, and IL-1β) and hypertrophic markers (ANP and BNP). Moreover, expression levels of Notch1 and Hes1 were decreased. These changes were effectively alleviated by aspirin and celecoxib.Cox inhibitors may protect heart from hypertrophy and inflammation possibly via the Notch1/Hes1 signaling pathway.

Mechanical regulation of the Notch signaling pathway

The mechanical regulation of Notch signaling is an emerging area of interest in cell biology. Notch is essential in many physiological processes in which mechanical stress plays an important role. This review provides an overview of the mechanoregulation of Notch signaling in multiple steps of the pathway. First, we discuss the current knowledge on the direct mechanoregulation of Notch receptor maturation and localization to the membrane and the effect of mechanical stress on the Notch components. Next, we explore how ligand-receptor interactions and membrane dynamics are possible subjects to mechano-regulation, emphasizing the role of cytoskeletal interactions, membrane stiffness, and endocytic complex formation. We further delve into the necessity of tension generation for negative regulatory region (NRR) domain unfolding, facilitated by ligand endocytosis and other microforces. Additionally, we examine the indirect mechano-regulation of S2 and S3 cleavages. Finally, we discuss the mechanoregulation of the Notch intracellular domain (NICD) trafficking and nuclear entry and the impact of mechanical stress on heterochromatin dynamics and nuclear NICD interactions. This review aims to draw attention to the intricate interplay between mechanical cues and Notch signaling regulation, offering novel insights into the multifaceted nature of cellular mechanobiology.

Integration of Chemo-mechanical signaling in response to fluid shear stress by the endothelium

Physical forces exert profound effects on cells affecting fate, function, and response to stressors. In the case of the endothelium, the layer that resides in the inner surface of blood vessels, the collective effect of hemodynamic forces influences the onset and severity of vascular pathologies. Justifiably, much emphasis has been placed in understanding how endothelial cells sense and respond to mechanical challenges, particularly hemodynamic shear stress. In this review, we highlight recent developments that have expanded our understanding of the molecular mechanisms underlying mechanotransduction. We describe examples of protein compartmentalization in response to shear stress, consider the contribution of the glycocalyx, and discuss the specific role ion channels in response to flow. We also highlight the recently recognized contribution of the receptor ALK5 in sensing turbulent flow. Research in the last three years has enriched our understanding of the molecular landscape responsible for recognizing and transducing shear stress responses, including novel transcriptional-dependent and transcriptional-independent mechanisms.

Flow-induced reprogramming of endothelial cells in atherosclerosis

Atherosclerotic diseases such as myocardial infarction, ischaemic stroke and peripheral artery disease continue to be leading causes of death worldwide despite the success of treatments with cholesterol-lowering drugs and drug-eluting stents, raising the need to identify additional therapeutic targets. Interestingly, atherosclerosis preferentially develops in curved and branching arterial regions, where endothelial cells are exposed to disturbed blood flow with characteristic low-magnitude oscillatory shear stress. By contrast, straight arterial regions exposed to stable flow, which is associated with high-magnitude, unidirectional shear stress, are relatively well protected from the disease through shear-dependent, atheroprotective endothelial cell responses. Flow potently regulates structural, functional, transcriptomic, epigenomic and metabolic changes in endothelial cells through mechanosensors and mechanosignal transduction pathways. A study using single-cell RNA sequencing and chromatin accessibility analysis in a mouse model of flow-induced atherosclerosis demonstrated that disturbed flow reprogrammes arterial endothelial cells in situ from healthy phenotypes to diseased ones characterized by endothelial inflammation, endothelial-to-mesenchymal transition, endothelial-to-immune cell-like transition and metabolic changes. In this Review, we discuss this emerging concept of disturbed-flow-induced reprogramming of endothelial cells (FIRE) as a potential pro-atherogenic mechanism. Defining the flow-induced mechanisms through which endothelial cells are reprogrammed to promote atherosclerosis is a crucial area of research that could lead to the identification of novel therapeutic targets to combat the high prevalence of atherosclerotic disease.

CAPILLARY LEAK AND EDEMA AFTER RESUSCITATION: THE POTENTIAL CONTRIBUTION OF REDUCED ENDOTHELIAL SHEAR STRESS CAUSED BY HEMODILUTION

ABSTRACT

Normal shear stress is essential for the normal structure and functions of the microcirculation. Hemorrhagic shock leads to reduced shear stress due to reduced tissue perfusion. Although essential for the urgent restoration of cardiac output and systemic blood pressure, large volume resuscitation with currently available solutions causes hemodilution, further reducing endothelial shear stress. In this narrative review, we consider how the use of currently available resuscitation solutions results in persistent reduction in endothelial shear stress, despite successfully increasing cardiac output and systemic blood pressure. We consider how this reduced shear stress causes (1) a failure to restore normal vasomotor function and normal tissue perfusion thus leading to persistent tissue hypoxia and (2) increased microvascular endothelial permeability resulting in edema formation and impaired organ function. We discuss the need for clinical research into resuscitation strategies and solutions that aim to quickly restore endothelial shear stress in the microcirculation to normal.

Mechanobiology of the endothelium in vascular health and disease: in vitro shear stress models

In recent years, there has been growing evidence that vascular pathologies arise in sites experiencing an altered haemodynamic environment. Fluid shear stress (FSS) is an important contributor to vascular homeostasis and regulates endothelial cell (EC) gene expression, morphology, and behaviour through specialised mechanosensitive signalling pathways. The presence of an altered FSS profile is a pathological characteristic of many vascular diseases, with the most established example being the preferential localisation of atherosclerotic plaque development. However, the precise haemodynamic contributions to other vascular pathologies including coronary artery vein graft failure remains poorly defined. To evaluate potential novel therapeutics for the treatment of vascular diseases via targeting EC behaviour, it is important to undertake in vitro experiments using appropriate culture conditions, particularly FSS. There are a wide range of in vitro models used to study the effect of FSS on the cultured endothelium, each with the ability to generate FSS flow profiles through which the investigator can control haemodynamic parameters including flow magnitude and directionality. An important consideration for selection of an appropriate model of FSS exposure is the FSS profile that the model can generate, in comparison to the physiological and pathophysiological haemodynamic environment of the vessel of interest. A resource bringing together the haemodynamic environment characteristic of atherosclerosis pathology and the flow profiles generated by in vitro methods of applying FSS would be beneficial to researchers when selecting the appropriate model for their research. Consequently, here we summarise the widely used methods of exposing cultured endothelium to FSS, the flow profile they generate and their advantages and limitations in investigating the pathological contribution of altered FSS to vascular disease and evaluating novel therapeutic targets for the treatment and prevention of vascular disease.

Transcriptional regulators of arterial and venous identity in the developing mammalian embryo

The complex and hierarchical vascular network of arteries, veins, and capillaries features considerable endothelial heterogeneity, yet the regulatory pathways directing arteriovenous specification, differentiation, and identity are still not fully understood. Recent advances in analysis of endothelial-specific gene-regulatory elements, single-cell RNA sequencing, and cell lineage tracing have both emphasized the importance of transcriptional regulation in this process and shed considerable light on the mechanism and regulation of specification within the endothelium. In this review, we discuss recent advances in our understanding of how endothelial cells acquire arterial and venous identity and the role different transcription factors play in this process.

A multiscale computational model of arterial growth and remodeling including Notch signaling

Blood vessels grow and remodel in response to mechanical stimuli. Many computational models capture this process phenomenologically, by assuming stress homeostasis, but this approach cannot unravel the underlying cellular mechanisms. Mechano-sensitive Notch signaling is well-known to be key in vascular development and homeostasis. Here, we present a multiscale framework coupling a constrained mixture model, capturing the mechanics and turnover of arterial constituents, to a cell-cell signaling model, describing Notch signaling dynamics among vascular smooth muscle cells (SMCs) as influenced by mechanical stimuli. Tissue turnover was regulated by both Notch activity, informed by in vitro data, and a phenomenological contribution, accounting for mechanisms other than Notch. This novel framework predicted changes in wall thickness and arterial composition in response to hypertension similar to previous in vivo data. The simulations suggested that Notch contributes to arterial growth in hypertension mainly by promoting SMC proliferation, while other mechanisms are needed to fully capture remodeling. The results also indicated that interventions to Notch, such as external Jagged ligands, can alter both the geometry and composition of hypertensive vessels, especially in the short term. Overall, our model enables a deeper analysis of the role of Notch and Notch interventions in arterial growth and remodeling and could be adopted to investigate therapeutic strategies and optimize vascular regeneration protocols.

Nuclear mechanosensing of the aortic endothelium in health and disease

The endothelium, the monolayer of endothelial cells that line blood vessels, is exposed to a number of mechanical forces, including frictional shear flow, pulsatile stretching and changes in stiffness influenced by extracellular matrix composition. These forces are sensed by mechanosensors that facilitate their transduction to drive appropriate adaptation of the endothelium to maintain vascular homeostasis. In the aorta, the unique architecture of the vessel gives rise to changes in the fluid dynamics, which, in turn, shape cellular morphology, nuclear architecture, chromatin dynamics and gene regulation. In this Review, we discuss recent work focusing on how differential mechanical forces exerted on endothelial cells are sensed and transduced to influence their form and function in giving rise to spatial variation to the endothelium of the aorta. We will also discuss recent developments in understanding how nuclear mechanosensing is implicated in diseases of the aorta.

Mechanotransduction: Forcing a change in metabolism

Epithelial and endothelial cells experience numerous mechanical cues throughout their lifetimes. Cells resist these forces by fortifying their cytoskeletal networks and adhesions. This reinforcement is energetically costly. Here we describe how these energetic demands are met. We focus on the response of epithelial and endothelial cells to mechanical cues, describe the energetic needs of epithelia and endothelia, and identify the mechanisms these cells employ to increase glycolysis, oxidative phosphorylation, and fatty acid metabolism. We discuss the similarities and differences in the responses of the two cell types.

A 96-wells fluidic system for high-throughput screenings under laminar high wall shear stress conditions

The ability of endothelial cells to respond to blood flow is fundamental for the correct formation and maintenance of a functional and hierarchically organized vascular network. Defective flow responses, in particular related to high flow conditions, have been associated with atherosclerosis, stroke, arteriovenous malformations, and neurodegenerative diseases. Yet, the molecular mechanisms involved in high flow response are still poorly understood. Here, we described the development and validation of a 96-wells fluidic system, with interchangeable cell culture and fluidics, to perform high-throughput screenings under laminar high-flow conditions. We demonstrated that endothelial cells in our newly developed 96-wells fluidic system respond to fluid flow-induced shear stress by aligning along the flow direction and increasing the levels of KLF2 and KLF4. We further demonstrate that our 96-wells fluidic system allows for efficient gene knock-down compatible with automated liquid handling for high-throughput screening platforms. Overall, we propose that this modular 96-well fluidic system is an excellent platform to perform genome-wide and/or drug screenings to identify the molecular mechanisms involved in the responses of endothelial cells to high wall shear stress.

Regulation of Notch1 Signalling by Long Non-Coding RNAs in Cancers and Other Health Disorders

Notch1 signalling plays a multifaceted role in tissue development and homeostasis. Currently, due to the pivotal role of Notch1 signalling, the relationship between NOTCH1 expression and the development of health disorders is being intensively studied. Nevertheless, Notch1 signalling is not only controlled at the transcriptional level but also by a variety of post-translational events. First is the ligand-dependent mechanical activation of NOTCH receptors and then the intracellular crosstalk with other signalling molecules-among those are long non-coding RNAs (lncRNAs). In this review, we provide a detailed overview of the specific role of lncRNAs in the modulation of Notch1 signalling, from expression to activity, and their connection with the development of health disorders, especially cancers.

Alcohol and vascular endothelial function: Biphasic effect highlights the importance of dose

BACKGROUND

Alcohol (ethanol) consumption has different influences on arterial disease, being protective or harmful depending on the amount and pattern of consumption. The mechanisms mediating these biphasic effects are unknown. Whereas endothelial cells play a critical role in maintaining arterial health, this study compared the effects of moderate and high alcohol concentrations on endothelial cell function.

METHODS

Human coronary artery endothelial cells (HCAEC) were treated with levels of ethanol associated with either low-risk/moderate drinking (i.e., 25 mM) or high-risk/heavy drinking (i.e., 50 mM) after which endothelial function was assessed. The effect of ethanol's primary metabolite acetaldehyde (10 and 25 μM) was also determined.

RESULTS

Moderate ethanol exposure (25 mM) improved HCAEC barrier integrity as determined by increased transendothelial electrical resistance (TEER), inhibited cell adhesion molecule (CAM) mRNA expression, decreased inflammatory cytokine (interferon-γ and interleukin 6) production, inhibited monocyte chemotactic protein-1 (MCP-1) expression and monocyte adhesion, and increased homeostatic Notch signaling. In contrast, exposure to high-level ethanol (50 mM) decreased TEER, increased CAM expression and inflammatory cytokine production, and stimulated MCP-1 and monocyte adhesion, with no effect on Notch signaling. Reactive oxygen species (ROS) generation and endothelial nitric oxide synthase activity were increased by both alcohol treatments, and to a greater extent in the 50 mM ethanol group. Acetaldehyde-elicited responses were generally the same as those of the high-level ethanol group.

CONCLUSIONS

Ethanol has biphasic effects on several endothelial functions such that a moderate level maintains the endothelium in a nonactivated state, whereas high-level ethanol causes endothelial dysfunction, as does acetaldehyde. These data show the importance of dose when considering ethanol's effects on arterial endothelium, and could explain, in part, the J-shaped relationship between alcohol concentration and atherosclerosis reported in some epidemiologic studies.

New Insights into the Reparative Angiogenesis after Myocardial Infarction

Myocardial infarction (MI) causes massive loss of cardiac myocytes and injury to the coronary microcirculation, overwhelming the limited capacity of cardiac regeneration. Cardiac repair after MI is finely organized by complex series of procedures involving a robust angiogenic response that begins in the peri-infarcted border area of the infarcted heart, concluding with fibroblast proliferation and scar formation. Efficient neovascularization after MI limits hypertrophied myocytes and scar extent by the reduction in collagen deposition and sustains the improvement in cardiac function. Compelling evidence from animal models and classical in vitro angiogenic approaches demonstrate that a plethora of well-orchestrated signaling pathways involving Notch, Wnt, PI3K, and the modulation of intracellular Ca2+ concentration through ion channels, regulate angiogenesis from existing endothelial cells (ECs) and endothelial progenitor cells (EPCs) in the infarcted heart. Moreover, cardiac repair after MI involves cell-to-cell communication by paracrine/autocrine signals, mainly through the delivery of extracellular vesicles hosting pro-angiogenic proteins and non-coding RNAs, as microRNAs (miRNAs). This review highlights some general insights into signaling pathways activated under MI, focusing on the role of Ca2+ influx, Notch activated pathway, and miRNAs in EC activation and angiogenesis after MI.

Endothelial mechanobiology in atherosclerosis

Cardiovascular disease (CVD) is a serious health challenge, causing more deaths worldwide than cancer. The vascular endothelium, which forms the inner lining of blood vessels, plays a central role in maintaining vascular integrity and homeostasis and is in direct contact with the blood flow. Research over the past century has shown that mechanical perturbations of the vascular wall contribute to the formation and progression of atherosclerosis. While the straight part of the artery is exposed to sustained laminar flow and physiological high shear stress, flow near branch points or in curved vessels can exhibit 'disturbed' flow. Clinical studies as well as carefully controlled in vitro analyses have confirmed that these regions of disturbed flow, which can include low shear stress, recirculation, oscillation, or lateral flow, are preferential sites of atherosclerotic lesion formation. Because of their critical role in blood flow homeostasis, vascular endothelial cells (ECs) have mechanosensory mechanisms that allow them to react rapidly to changes in mechanical forces, and to execute context-specific adaptive responses to modulate EC functions. This review summarizes the current understanding of endothelial mechanobiology, which can guide the identification of new therapeutic targets to slow or reverse the progression of atherosclerosis.

Mechanisms of endothelial flow sensing

Fluid shear stress plays a key role in sculpting blood vessels during development, in adult vascular homeostasis and in vascular pathologies. During evolution, endothelial cells evolved several mechanosensors that convert physical forces into biochemical signals, a process termed mechanotransduction. This Review discusses our understanding of endothelial flow sensing and suggests important questions for future investigation.

DLX5 regulates the osteogenic differentiation of spinal ligaments cells derived from ossification of the posterior longitudinal ligament patients via NOTCH signaling

Background

Ossification of the posterior longitudinal ligaments (OPLL) is common disorder characterized by heterotopic ossification of the spinal ligaments. Mechanical stimulation (MS) plays an important role in OPLL. DLX5 is an essential transcription factor required for osteoblast differentiation. However, the role of DLX5 during in OPLL is unclear. This study aims to investigate whether DLX5 is associated with OPLL progression under MS.

Methods

Stretch stimulation was applied to spinal ligaments cells derived from OPLL (OPLL cells) and non-OPLL (non-OPLL cells) patients. Expression of DLX5 and osteogenesis-related genes were determined by quantitative real-time polymerase chain reaction and Western blot. The osteogenic differentiation ability of the cells was measured using alkaline phosphatase (ALP) staining and alizarin red staining. The protein expression of DLX5 in the tissues and the nuclear translocation of NOTCH intracellular domain (NICD) was examined by immunofluorescence.

Results

Compared with non-OPLL cells, OPLL cells expressed higher levels of DLX5 in vitro and vivo (p < 0.01). Upregulated expression of DLX5 and osteogenesis-related genes (OSX, RUNX2, and OCN) were observed in OPLL cells induced with stretch stimulation and osteogenic medium, whereas there was no change in the non-OPLL cells (p < 0.01). Cytoplasmic NICD protein translocated from the cytoplasm to the nucleus inducing DLX5 under stretch stimulation, which was reduced by the NOTCH signaling inhibitors (DAPT) (p < 0.01).

Conclusions

These data suggest that DLX5 play a critical role in MS-induced progression of OPLL through NOTCH signaling, which provides a new insight into the pathogenesis of OPLL.