Platelets modulate endothelial cell response to dynamic shear stress through PECAM-1

Effects of Panax notoginseng saponins on alleviating low shear induced endothelial inflammation and thrombosis via Piezo1 signalling

ETHNOPHARMACOLOGICAL RELEVANCE

Panax notoginseng saponins (PNS) are the major effective components of Panax notoginseng (burk) F.H.Chen which is one of the classic promoting blood circulation herbs in traditional Chinese medicine. PNS is widely used in China for the treatment of cerebral ischemic stroke. Pathological low shear stress is a causal factor in endothelial inflammation and thrombosis. However, the mechanism of PNS against low shear related endothelial inflammation is still unclear.

AIM TO THE STUDY

This study aims to investigate the effects of PNS against endothelial inflammation induced by low shear stress and to explore the underlying mechanical and biological mechanisms.

MATERIALS AND METHODS

Mouse model of carotid partial ligation for inducing low endothelial shear stress was established, the pharmacodynamic effect and mechanism of PNS against endothelial inflammation induced by low shear stress through Piezo1 were explored. Yoda1-evoked Piezo1 activation and expression in human umbilical vein endothelial cells (HUVECs) were determined at static condition. Microfluidic channel systems were used to apply shear stress on HUVECs and Piezo1 siRNA HUVECs to determine PECAM-1, p-YAP and VCAM-1 expression. And platelet rich plasma (PRP) was introduced to low shear treated endothelial cells surface to observe the adhesion and activation by fluorescence imaging and flowcytometry.

RESULTS

PNS attenuated endothelial inflammation and improved blood flow in a reasonable dose response pattern in carotid partial ligation mouse model by influencing Piezo1 and PECAM-1 expression, while suppressing yes-associated protein (YAP) nuclear translocation. We found Piezo1 sensed abnormal shear stress and transduced these mechanical signals by different pathways in HUVECs, and PNS relieved endothelial inflammation induced by low shear stress through Piezo1. We also found Piezo1 signalling has interaction with PECAM-1 under low shear stress, which were involved in platelets adhesion to endothelial cells. Low shear stress increased YAP nuclear translocation and increased VCAM-1 expression in HUVECs which might activate platelets. PNS inhibited low shear induced Piezo1 and PECAM-1 expression and YAP nuclear translocation in HUVECs, furthermore inhibited platelet adhesion and activation on dysfunctional endothelial cells induced by low shear stress.

CONCLUSION

PNS ameliorated endothelial inflammation and thrombosis induced by low shear stress through modulation of the Piezo1 channel, PECAM-1 expression, and YAP nuclear translocation. PNS might serve as a potential therapeutic candidate for ameliorating endothelial inflammation induced by abnormal blood shear stress.

From Crypts to Cancer: A Holistic Perspective on Colorectal Carcinogenesis and Therapeutic Strategies

Colorectal cancer (CRC) represents a significant global health burden, with high incidence and mortality rates worldwide. Recent progress in research highlights the distinct clinical and molecular characteristics of colon versus rectal cancers, underscoring tumor location's importance in treatment approaches. This article provides a comprehensive review of our current understanding of CRC epidemiology, risk factors, molecular pathogenesis, and management strategies. We also present the intricate cellular architecture of colonic crypts and their roles in intestinal homeostasis. Colorectal carcinogenesis multistep processes are also described, covering the conventional adenoma-carcinoma sequence, alternative serrated pathways, and the influential Vogelstein model, which proposes sequential APC, KRAS, and TP53 alterations as drivers. The consensus molecular CRC subtypes (CMS1-CMS4) are examined, shedding light on disease heterogeneity and personalized therapy implications.

Physiological platelet aggregation assay to mitigate drug-induced thrombocytopenia using a microphysiological system

Developing a reliable method to predict thrombocytopenia is imperative in drug discovery. Here, we establish an assay using a microphysiological system (MPS) to recapitulate the in-vivo mechanisms of platelet aggregation and adhesion. This assay highlights the role of shear stress on platelet aggregation and their interactions with vascular endothelial cells. Platelet aggregation induced by soluble collagen was detected under agitated, but not static, conditions using a plate shaker and gravity-driven flow using MPS. Notably, aggregates adhered on vascular endothelial cells under gravity-driven flow in the MPS, and this incident increased in a concentration-dependent manner. Upon comparing the soluble collagen-induced aggregation activity in platelet-rich plasma (PRP) and whole blood, remarkable platelet aggregate formation was observed at concentrations of 30 µg/mL and 3 µg/mL in PRP and whole blood, respectively. Moreover, ODN2395, an oligonucleotide, induced platelet aggregation and adhesion to vascular endothelial cells. SYK inhibition, which mediated thrombogenic activity via glycoprotein VI on platelets, ameliorated platelet aggregation in the system, demonstrating that the mechanism of platelet aggregation was induced by soluble collagen and oligonucleotide. Our evaluation system partially recapitulated the aggregation mechanisms in blood vessels and can contribute to the discovery of safe drugs to mitigate the risk of thrombocytopenia.

Platelet and endothelial cell responses under concurrent shear stress and tensile strain

Thrombosis can lead to significant mortality and morbidity. Both platelets and vascular endothelial cells play significant roles in thrombosis. Platelets' response to blood flow-induced shear stress can vary greatly depending on shear stress magnitude, pattern and shear exposure time. Endothelial cells are also sensitive to the biomechanical environment. Endothelial cell activation and dysfunction can occur under low oscillatory shear stress and low tensile strain. Platelet and endothelial cell interaction can also be affected by mechanical conditions. The goal of this study was to investigate how blood flow-induced shear stress, vascular wall tensile strain, platelet-endothelial cell stress history, and platelet-endothelial cell interaction affect platelet thrombogenicity. Platelets and human coronary artery endothelial cells were pretreated with physiological and pathological shear stress and/or tensile strain separately. The pretreated cells were then put together and exposed to pulsatile shear stress and cyclic tensile strain simultaneously in a shearing-stretching device. Following treatment, platelet thrombin generation rate, platelet and endothelial cell activation, and platelet adhesion to endothelial cells was measured. The results demonstrated that shear stress pretreatment of endothelial cells and platelets caused a significant increase in platelet thrombin generation rate, cell surface phosphatidylserine expression, and adhesion to endothelial cells. Shear stress pretreatment of platelets and endothelial cells attenuated endothelial cell ICAM-1 expression under stenosis conditions, as well as vWF expression under recirculation conditions. These results indicate that platelets are sensitized by prior shearing, while in comparison, the interaction with shear stress-pretreated platelets may reduce endothelial cell sensitivity to pathological shear stress and tensile strain.

Updates on New Therapies for Patients with CKD

Individuals diagnosed with chronic kidney disease (CKD) continue to increase globally. This group of patients experience a disproportionately higher risk of cardiovascular (CV) events compared to the general population. Despite multiple guidelines-based medical management, patients with CKD continue to experience residual cardiorenal risk. Several potential mechanisms explain this excessive CV risk observed in individuals with CKD. Several new drugs have become available that could potentially transform CKD care, given their efficacy in this patient population. Nevertheless, use of these drugs presents certain benefits and challenges that are often underrecognized by prescribing these drugs. In this review, we aim to provide a brief discussion about CKD pathophysiology, limiting our discussion to recent published studies. We also explore benefits and limitations of newer drugs, including angiotensin receptor/neprilysin inhibitors (ARNI), sodium glucose transporter 2 inhibitors (SGLT2i), glucagon-like peptides-1 (GLP-1) agonists and finerenone in patients with CKD. Despite several articles covering this topic, our review provides an algorithm where subgroups of patients with CKD might benefit the most from such drugs based on the selection criteria of the landmark trials. Patients with CKD who have nephrotic range proteinuria beyond 5000 mg/g, or those with poorly controlled blood pressure (systolic ≥160 mm Hg or diastolic ≥100 mm Hg) remain understudied.

Endothelial Glycocalyx Injury in SARS-CoV-2 Infection: Molecular Mechanisms and Potential Targeted Therapy

This review aims at summarizing state-of-the-art knowledge on glycocalyx and SARS-CoV-2. The endothelial glycocalyx is a dynamic grid overlying the surface of the endothelial cell (EC) lumen and consists of membrane-bound proteoglycans and glycoproteins. The role of glycocalyx has been determined in the regulation of EC permeability, adhesion, and coagulation. SARS-CoV-2 is an enveloped, single-stranded RNA virus belonging to β-coronavirus that causes the outbreak and the pandemic of COVID-19. Through the respiratory tract, SARS-CoV-2 enters blood circulation and interacts with ECs possessing angiotensin-converting enzyme 2 (ACE2). Intact glycolyx prevents SARS-CoV-2 invasion of ECs. When the glycocalyx is incomplete, virus spike protein of SARS-CoV-2 binds with ACE2 and enters ECs for replication. In addition, cytokine storm targets glycocalyx, leading to subsequent coagulation disorder. Therefore, it is intriguing to develop a novel treatment for SARS-CoV-2 infection through the maintenance of the integrity of glycocalyx. This review aims to summarize state-of-the-art knowledge of glycocalyx and its potential function in SARS-CoV-2 infection.

Platelets at the Vessel Wall in Non-Thrombotic Disease

Platelets are small, anucleate entities that bud from megakaryocytes in the bone marrow. Among circulating cells, platelets are the most abundant cell, traditionally involved in regulating the balance between thrombosis (the terminal event of platelet activation) and hemostasis (a protective response to tissue injury). Although platelets lack the precise cellular control offered by nucleate cells, they are in fact very dynamic cells, enriched in preformed RNA that allows them the capability of de novo protein synthesis which alters the platelet phenotype and responses in physiological and pathological events. Antiplatelet medications have significantly reduced the morbidity and mortality for patients afflicted with thrombotic diseases, including stroke and myocardial infarction. However, it has become apparent in the last few years that platelets play a critical role beyond thrombosis and hemostasis. For example, platelet-derived proteins by constitutive and regulated exocytosis can be found in the plasma and may educate distant tissue including blood vessels. First, platelets are enriched in inflammatory and anti-inflammatory molecules that may regulate vascular remodeling. Second, platelet-derived microparticles released into the circulation can be acquired by vascular endothelial cells through the process of endocytosis. Third, platelets are highly enriched in mitochondria that may contribute to the local reactive oxygen species pool and remodel phospholipids in the plasma membrane of blood vessels. Lastly, platelets are enriched in proteins and phosphoproteins which can be secreted independent of stimulation by surface receptor agonists in conditions of disturbed blood flow. This so-called biomechanical platelet activation occurs in regions of pathologically narrowed (atherosclerotic) or dilated (aneurysmal) vessels. Emerging evidence suggests platelets may regulate the process of angiogenesis and blood flow to tumors as well as education of distant organs for the purposes of allograft health following transplantation. This review will illustrate the potential of platelets to remodel blood vessels in various diseases with a focus on the aforementioned mechanisms.

Platelets play a dual role in the pathophysiology of transfusion-related acute lung injury

Platelets are increasingly recognized as key regulators of inflammatory and immune responses, through their interaction with endothelium and immune cells. Therefore they might have a role in transfusion-related acute lung injury (TRALI), in which endothelial cells and neutrophils are the key players. In this study, by a classic TRALI animal model, combining a custom-designed system for intravital confocal microscopy of pulmonary microvasculature and a platelet tracking technique, we found that thrombin-activated platelets transfusion aggravated TRALI while resting platelets transfusion alleviated TRALI. Promoting endogenous platelets activation also aggravated TRALI while inhibiting endogenous platelets activation alleviated TRALI. Activated platelets interfered with the stability of endothelial barrier function while resting platelets modulated the activation of neutrophils. Anti-thrombin could alleviate TRALI, which was not reproduced upon anti-GPIIbIIIa or anti-P-selectin In conclusion, platelets might play a dual role (protective and pathogenic) in TRALI, the balance between the two roles is highly dependent on whether platelets are activated by thrombin or not. This might explain the conflicting results of previous researches studying the contribution of platelets in TRALI by platelet depletion technology, in which the induction of TRALI and the condition of animals were different, hence the state of platelets during TRALI was different. Moreover, anti-platelet-activation (such as anti-thrombin) might be a better approach than anti-activated-platelets (such as anti-P-selectin) to search for potential therapies in TRALI. Considering the involvement of thrombin-activated platelets in TRALI, anti-thrombin might be needed when blood component transfusion is performed.

Monocyte-Platelet Aggregates Triggered by CD31 Molecule in Non-ST Elevation Myocardial Infarction: Clinical Implications in Plaque Rupture

Despite the recent innovations in cardiovascular care, atherothrombosis is still a major complication of acute coronary syndromes (ACS). We evaluated the involvement of the CD31 molecule in thrombotic risk through the formation of monocyte-platelet (Mo-Plt) aggregates in patients with ACS with no-ST-segment elevation myocardial infarction (NSTEMI) on top of dual anti-platelet therapy (DAPT). We enrolled 19 control (CTRL) subjects, 46 stable angina (SA), and 86 patients with NSTEMI, of which, 16 with Intact Fibrous Cap (IFC) and 19 with Ruptured Fibrous Cap (RFC) as assessed by the Optical Coherence Tomography (OCT). The expression of CD31 on monocytes and platelets was measured. Following the coronary angiography, 52 NSTEMIs were further stratified according to thrombus grade (TG) evaluation. Finally, a series of ex vivo experiments verified whether the CD31 participates in Mo-Plt aggregate formation. In patients with NSTEMI, CD31 was reduced on monocytes and was increased on platelets, especially in NSTEMI presented with RFC plaques compared to those with IFC lesions, and in patients with high TG compared to those with zero/low TG. Ex vivo experiments documented an increase in Mo-Plt aggregates among NSTEMI, which significantly decreased after the CD31 ligation, particularly in patients with RFC plaques. In NSTEMI, CD31 participates in Mo-Plt aggregate formation in spite of optimal therapy and DAPT, suggesting the existence of alternative thrombotic pathways, as predominantly displayed in patients with RFC.

Where the Action Is-Leukocyte Recruitment in Atherosclerosis

Atherosclerosis is the leading cause of death worldwide and leukocyte recruitment is a key element of this phenomenon, thus allowing immune cells to enter the arterial wall. There, in concert with accumulating lipids, the invading leukocytes trigger a plethora of inflammatory responses which promote the influx of additional leukocytes and lead to the continued growth of atherosclerotic plaques. The recruitment process follows a precise scheme of tethering, rolling, firm arrest, crawling and transmigration and involves multiple cellular and subcellular players. This review aims to provide a comprehensive up-to-date insight into the process of leukocyte recruitment relevant to atherosclerosis, each from the perspective of endothelial cells, monocytes and macrophages, neutrophils, T lymphocytes and platelets. In addition, therapeutic options targeting leukocyte recruitment into atherosclerotic lesions-or potentially arising from the growing body of insights into its precise mechanisms-are highlighted.

Peristaltic on-chip pump for tunable media circulation and whole blood perfusion in PDMS-free organ-on-chip and Organ-Disc systems

Organ-on-chip (OoC) systems have become a promising tool for personalized medicine and drug development with advantages over conventional animal models and cell assays. However, the utility of OoCs in industrial settings is still limited, as external pumps and tubing for on-chip fluid transport are dependent on error-prone, manual handling. Here, we present an on-chip pump for OoC and Organ-Disc systems, to perfuse media without external pumps or tubing. Peristaltic pumping is implemented through periodic compression of a flexible pump layer. The disc-shaped, microfluidic module contains four independent systems, each lined with endothelial cells cultured under defined, peristaltic perfusion. Both cell viability and functionality were maintained over several days shown by supernatant analysis and immunostaining. Integrated, on-disc perfusion was further used for cytokine-induced cell activation with physiologic cell responses and for whole blood perfusion assays, both demonstrating the versatility of our system for OoC applications.

gC1qR Antibody Can Modulate Endothelial Cell Permeability in Angioedema

Angioedema is characterized by swelling of the skin or mucous membranes. Overproduction of the vasodilator bradykinin (BK) is an important contributor to the disease pathology, which causes rapid increase in vascular permeability. BK formation on endothelial cells results from high molecular weight kininogen (HK) interacting with gC1qR, the receptor for the globular heads of C1q, the first component of the classical pathway of complement. Endothelial cells are sensitive to blood-flow-induced shear stress and it has been shown that shear stress can modulate gC1qR expression. This study aimed to determine the following: (1) how BK or angioedema patients' (HAE) plasma affected endothelial cell permeability and gC1qR expression under shear stress, and (2) if monoclonal antibody (mAb) 74.5.2, which recognizes the HK binding site on gC1qR, had an inhibitory effect in HK binding to endothelial cells. Human dermal microvascular endothelial cells (HDMECs) grown on Transwell inserts were exposed to shear stress in the presence of HAE patients' plasma. Endothelial cell permeability was measured using FITC-conjugated bovine serum albumin. gC1qR expression and HK binding to endothelial cell surface was measured using solid-phase ELISA. Cell morphology was quantified using immunofluorescence microscopy. The results demonstrated that BK at 1 µg/mL, but not HAE patients' plasma and/or shear stress, caused significant increases in HDMEC permeability. The mAb 74.5.2 could effectively inhibit HK binding to recombinant gC1qR, and reduce HAE patients' plasma-induced HDMEC permeability change. These results suggested that monoclonal antibody to gC1qR, i.e., 74.5.2, could be potentially used as an effective therapeutic reagent to prevent angioedema.

Platelet adhesion potential estimation in a normal and diseased coronary artery model: effects of shear stress magnitude versus shear stress history

Platelets play a salient role in the pathogenesis of coronary diseases; primarily through their adhesion to other platelets, endothelial cells and plasma proteins. It is necessary for platelets to activate in order for them to adhere to these different substrates. One of the key regulatory mechanical factors in platelet activation is shear stress, which has been shown to alter multiple platelet functions through the activation of mechanoreceptors. Our goal was to investigate how different numerical shear stress tracking techniques affect platelet adhesion estimates within physiologically relevant computational models. Previously, we developed a physiological coronary artery computational fluid dynamics model. Shear stress waveforms, obtained from these models, were used to monitor in vitro platelet and endothelial cell adhesion marker expression. In this work, the adhesion marker expression data was regressed to obtain numerical functions for receptor expression predictions. These functions were input into a customized adhesion model utilizing different shear stress tracking techniques. For the normal vascular conditions and minimal pathological disease models, shear stress tracking did not significantly affect the adhesion estimates. However, for the severe pathological model, the two shear stress tracking methods had vastly different estimates. Therefore, shear stress tracking methods must be chosen accurately to predict platelet adhesion potentials for accurate modeling techniques.

Platelets Do Not Alter Flow-Mediated Dilation or Arterial Conduction in vivo

The aim of this study was to investigate whether platelets contribute to shear stress and vascular conductance in the iliac vascular bed in vivo. Flow-mediated dilation of pig iliac was induced by downstream injection of acetylcholine (50 μg), and separately, conductance (ΔF/ΔP) was calculated. This was carried out before and after removal of 1 L of arterial blood in 240 mL increments, and each 240 mL was spun in a centrifuge (1,500 rcf for 7 min); platelet-rich plasma was replaced with equal volume of heparinised saline and reinjected. The circulating platelet count fell from 369 × 109/L (n = 5) to 165 × 109/L (p = 0.01; n = 4; Student's unpaired t). An increase in flow led to an increase in the iliac diameter by 0.49 ± 0.03 mm (mean ± SEM) before platelet reduction and 0.55 ± 0.05 mm after (p = 0.36, Student's paired t, n = 5); the change in arterial conductance was also not significantly affected by platelet reduction, control: 1.44 ± 0.34 mL/min/mm Hg, after platelet reduction: 1.39 ± 0.04 mm (p = 0.55, Student's paired t, n = 4). Therefore, platelets do not contribute to shear stress or conductance in vivo.

The glycocalyx: a central regulator of vascular function

The endothelial glycocalyx is a specialized extracellular matrix that covers the apical side of vascular endothelial cells, projecting into the lumen of blood vessels. The composition of the glycocalyx has been studied in great detail, and it is known to be composed of a mixture of proteoglycans, glycosaminoglycans, and glycoproteins. Although this structure was once believed to be a passive physical barrier, it is now recognized as a multifunctional and dynamic structure that participates in many vascular processes, including but not limited to vascular permeability, inflammation, thrombosis, mechanotransduction, and cytokine signaling. Because of its participation in many physiological and pathophysiological states, comprehensive knowledge of the glycocalyx will aid future vascular biologists in their research. With that in mind, this review discusses the biochemical structure of the glycocalyx and its function in many vascular physiological processes. We also briefly review a more recent discovery in glycocalyx biology, the placental glycocalyx.

The trend of indirect anastomosis formation in a 2-vessel occlusion plus encephalo-myo-synangiosis rat model

Background

Basic research on the factors influencing indirect anastomosis formation in a 2-vessel occlusion plus encephalo-myo-synangiosis (2VO + EMS) rat model is conducive to improving the efficacy of indirect revascularization surgery in the clinic. However, the time point at which anastomosis between the rat temporal muscle (TM) and brain naturally has the greatest effect after encephalo-myo-synangiosis (EMS) remains unknown. Therefore, we conducted this study to explore the peak time of indirect anastomosis formation in the 2VO + EMS rat model.

Methods

Forty 2VO + EMS rats were randomly divided into five groups (n=8) according to the length of time (by week) after EMS, and 2VO rats were used as the control group (n=8). The expression of vascular endothelial growth factor (VEGF) and CD31 on the EMS side of the brain, perfusion ratio [improvement of cerebral blood perfusion (CBP) on the EMS side] and Morris water maze (MWM) results were compared between groups. Furthermore, the trends of the above variables were explored over weeks.

Results

Overall, the expression of VEGF and CD31, the perfusion ratio and the cognitive improvement in the 2VO + EMS rat model gradually increased over weeks after EMS. The VEGF and CD31 expression (as detected by immunofluorescence), perfusion ratio and number of times crossing the platform area peaked at 4 weeks after EMS. In addition, both the escape latency and the time spent in the target quadrant peaked in the fifth week after EMS.

Conclusions

After establishing the 2VO + EMS rat model, the degree of endothelial cell (EC) proliferation and CBP improvement on the EMS side of the brain peaked at 4 weeks after EMS, whereas the cognitive improvement peaked in the fifth week.

Targeting Platelet in Atherosclerosis Plaque Formation: Current Knowledge and Future Perspectives

Besides their role in hemostasis and thrombosis, it has become increasingly clear that platelets are also involved in many other pathological processes of the vascular system, such as atherosclerotic plaque formation. Atherosclerosis is a chronic vascular inflammatory disease, which preferentially develops at sites under disturbed blood flow with low speeds and chaotic directions. Hyperglycemia, hyperlipidemia, and hypertension are all risk factors for atherosclerosis. When the vascular microenvironment changes, platelets can respond quickly to interact with endothelial cells and leukocytes, participating in atherosclerosis. This review discusses the important roles of platelets in the plaque formation under pro-atherogenic factors. Specifically, we discussed the platelet behaviors under disturbed flow, hyperglycemia, and hyperlipidemia conditions. We also summarized the molecular mechanisms involved in vascular inflammation during atherogenesis based on platelet receptors and secretion of inflammatory factors. Finally, we highlighted the studies of platelet migration in atherogenesis. In general, we elaborated an atherogenic role of platelets and the aspects that should be further studied in the future.

Endothelial JAK2V617F mutation leads to thrombosis, vasculopathy, and cardiomyopathy in a murine model of myeloproliferative neoplasm

OBJECTIVE

Cardiovascular complications are the leading cause of morbidity and mortality in patients with myeloproliferative neoplasms (MPNs). The acquired kinase mutation JAK2V617F plays a central role in these disorders. Mechanisms responsible for cardiovascular dysfunction in MPNs are not fully understood, limiting the effectiveness of current treatment. Vascular endothelial cells (ECs) carrying the JAK2V617F mutation can be detected in patients with MPNs. The goal of this study was to test the hypothesis that the JAK2V617F mutation alters endothelial function to promote cardiovascular complications in patients with MPNs.

APPROACH AND RESULTS

We employed murine models of MPN in which the JAK2V617F mutation is expressed in specific cell lineages. When JAK2V617F is expressed in both blood cells and vascular ECs, the mice developed MPN and spontaneous, age-related dilated cardiomyopathy with an increased risk of sudden death as well as a prothrombotic and vasculopathy phenotype on histology evaluation. In contrast, despite having significantly higher leukocyte and platelet counts than controls, mice with JAK2V617F-mutant blood cells alone did not demonstrate any cardiac dysfunction, suggesting that JAK2V617F-mutant ECs are required for this cardiovascular disease phenotype. Furthermore, we demonstrated that the JAK2V617F mutation promotes a pro-adhesive, pro-inflammatory, and vasculopathy EC phenotype, and mutant ECs respond to flow shear differently than wild-type ECs.

CONCLUSIONS

These findings suggest that the JAK2V617F mutation can alter vascular endothelial function to promote cardiovascular complications in MPNs. Therefore, targeting the MPN vasculature represents a promising new therapeutic strategy for patients with MPNs.

In Vitro Models of the Blood-Brain Barrier

Knowledge about the transport of active compounds across the blood-brain barrier is of essential importance for drug development. Systemically applied drugs for the central nervous system (CNS) must be able to cross the blood-brain barrier in order to reach their target sites, whereas drugs that are supposed to act in the periphery should not permeate the blood-brain barrier so that they do not trigger any adverse central adverse effects. A number of approaches have been pursued, and manifold in silico, in vitro, and in vivo animal models were developed in order to be able to make a better prediction for humans about the possible penetration of active substances into the CNS. In this particular case, however, in vitro models play a special role, since the data basis for in silico models is usually in need of improvement, and the predictive power of in vivo animal models has to be checked for possible species differences. The blood-brain barrier is a dynamic, highly selective barrier formed by brain capillary endothelial cells. One of its main tasks is the maintenance of homeostasis in the CNS. The function of the barrier is regulated by cells of the microenvironment and the shear stress mediated by the blood flow, which makes the model development most complex. In general, one could follow the credo "as easy as possible, as complex as necessary" for the usage of in vitro BBB models for drug development. In addition to the description of the classical cell culture models (transwell, hollow fiber) and guidance how to apply them, the latest developments (spheroids, microfluidic models) will be introduced in this chapter, as it is attempted to get more in vivo-like and to be applicable for high-throughput usage with these models. Moreover, details about the development of models based on stem cells derived from different sources with a special focus on human induced pluripotent stem cells are presented.

Endothelial cells and organ function: applications and implications of understanding unique and reciprocal remodelling

The microvasculature is a heterogeneous, dynamic and versatile component of the systemic circulation, with a unique ability to locally self-regulate and to respond to organ demand and environmental stimuli. Endothelial cells from different organs display considerable variation, but it is currently unclear to what extent functional properties of organ-specific endothelial cells are intrinsic, acquired and/or reprogrammable. Vascular function is a fundamental pillar of homeostasis, and dysfunction results in systemic consequences for the organism. Additionally, vascular failure can occur downstream of organ disease or environmental stress, often driving an exacerbation of symptoms and pathologies originally independent of the local circulation. The understanding of the molecular mechanisms underlying endothelial physiology and metabolism holds the promise to inform and improve diagnosis, prognosis and treatment options for a myriad of conditions as unrelated as cancer, neurodegeneration or pulmonary hypertension, and likely everything in between, if we consider that also treatments for such conditions are primarily distributed via the bloodstream. However, studying endothelial function has its challenges: the origin, isolation, culture conditions and preconditioning stimuli make this an extremely variable cell type to study and difficult to source. Animal models exist but are neither trivial to generate, nor necessarily adequately translatable to human disease. In this article, we aim to illustrate the breadth of microvascular functions in different environments, highlighting current and pioneering studies that have advanced our insight into the importance of the integrity of this tissue, as well as the limitations posed by its heterogeneity and plasticity.

Endothelial Cell Biomechanical Responses are Dependent on Both Fluid Shear Stress and Tensile Strain

Introduction

The goal of this study was to investigate how concurrent shear stress and tensile strain affect endothelial cell biomechanical responses.

Methods

Human coronary artery endothelial cells were exposed to concurrent pulsatile shear stress and cyclic tensile strain in a programmable shearing and stretching device. Three shear stress-tensile strain conditions were used: (1) pulsatile shear stress at 1 Pa and cyclic tensile strain at 7%, simulating normal stress/strain conditions in a healthy coronary artery; (2) shear stress at 3.7 Pa and tensile strain at 3%, simulating pathological stress/strain conditions near a stenosis; (3) shear stress at 0.7 Pa and tensile strain at 5%, simulating pathological stress/strain conditions in a recirculation zone. Cell morphology was quantified using immunofluorescence microscopy. Cell surface PECAM-1 phosphorylation, ICAM-1 expression, ERK1/2 and NF-κB activation were measured using ELISA or Western blot.

Results

Simultaneous stimulation from pulsatile shear stress and cyclic tensile strain induced a significant increase in cell area, compared to that induced by shear stress or tensile strain alone. The combined stimulation caused significant increases in PECAM-1 phosphorylation. The combined stimulation also significantly enhanced EC surface ICAM-1 expression (compared to that under shear stress alone) and transcriptional factor NF-κB activation (compared to that under control conditions).

Conclusion

Pulsatile shear stress and cyclic tensile strain could induce increased but not synergistic effect on endothelial cell morphology or activation. The combined mechanical stimulation can be relayed from cell membrane to nucleus. Therefore, to better understand how mechanical conditions affect endothelial cell mechanotransduction and cardiovascular disease development, both shear stress and tensile strain need to be considered.

Inflammatory cytokines in type 2 diabetes mellitus as facilitators of hypercoagulation and abnormal clot formation

BACKGROUND

The global burden of type 2 diabetes mellitus (T2DM), together with the presence of cardiovascular risk in this population, is reaching pandemic levels. A prominent feature of T2DM is chronic and systemic inflammation, with the accompanying presence of circulating and dysregulated inflammatory biomarkers; which in turn is associated with abnormal clot formation.

METHODS

Here, we investigate the correlation between abnormal blood clotting, using thromboelastography (TEG), clot ultrastructure using scanning electron microscopy (SEM) and the presence of a dysregulated inflammatory cytokine profile, by examining various circulating biomarkers.

RESULTS

Our results show that many biomarkers, across TEG, cytokine and lipid groups, were greatly dysregulated in the T2DM sample. Furthermore, our T2DM sample's coagulation profiles were significantly more hypercoagulable when compared to our heathy sample, and ultrastructural analysis confirmed a matted and denser clot structure in the T2DM sample.

CONCLUSIONS

We suggest that dysregulated circulating molecules may in part be responsible for a hypercoagulable state and vascular dysfunction in the T2DM sample. We propose further that a personalized approach could be of great value when planning treatment and tracking the patient health status after embarking on a treatment regimes, and that looking to novel inflammatory and vascular biomarkers might be crucial.

Mechanotransduction, immunoregulation, and metabolic functions of CD31 in cardiovascular pathophysiology

Biomechanical changes in the heart and vessels drive rapid and dynamic regulation of blood flow, a vital process for meeting the changing metabolic needs of the peripheral tissues at any given point in time. The fluid movement of the blood exerts haemodynamic stress upon the solid elements of the cardiovascular system: the heart, vessels, and cellular components of the blood. Cardiovascular diseases can lead to prolonged mechanical stress, such as cardiac remodelling during heart failure or vascular stiffening in atherosclerosis. This can lead to a significantly reduced or increasingly turbulent blood supply, inducing a shift in cellular metabolism that, amongst other effects, can trigger the release of reactive oxygen species and initiate a self-perpetuating cycle of inflammation and oxidative stress. CD31 is the most abundant constitutive co-signalling receptor glycoprotein on endothelial cells, which line the cardiovascular system and form the first-line of cellular contact with the blood. By associating with most endothelial receptors involved in mechanosensing, CD31 regulates the response to biomechanical stimuli. In addition, by relocating in the lipid rafts of endothelial cells as well as of cells stably interacting with the endothelium, including leucocytes and platelets, CD31–CD31 trans-homophilic engagement guides and restrains platelet and immune cell accumulation and activation and at sites of damage. In this way, CD31 is at the centre of mediating mechanical, metabolic, and immunological changes within the circulation and provides a single target that may have pleiotropic beneficial effects.

Quantification of Morphological Modulation, F-Actin Remodeling and PECAM-1 (CD-31) Re-distribution in Endothelial Cells in Response to Fluid-Induced Shear Stress under Various Flow Conditions

Cardiovascular diseases (CVDs) are the number one cause of death globally. Arterial endothelial cell (EC) dysfunction plays a key role in many of these CVDs, such as atherosclerosis. Blood flow-induced wall shear stress (WSS), among many other pathophysiological factors, is known to significantly contribute to EC dysfunction. The present study reports an in vitro investigation of the effect of quantified WSS on ECs, analyzing the EC morphometric parameters as well as cytoskeletal remodeling. The effects of four different flow cases (low steady laminar (LSL), medium steady laminar (MSL), non-zero-mean sinusoidal laminar (NZMSL) and laminar carotid (LCRD) waveforms) on EC area, perimeter, shape index (SI), angle of orientation, F-actin bundle remodeling and PECAM-1 localization were studied. For the first time, a flow facility was fully quantified for the uniformity of flow over ECs as well as for WSS determination (as opposed to relying on analytical equations). The SI and angle of orientation were found to be the most flow-sensitive morphometric parameters. A 2D Fast Fourier Transform based image processing technique was applied to analyze the F-actin directionality and an alignment index (AI) was defined accordingly. Also, a significant peripheral loss of PECAM-1 in ECs subjected to atheroprone cases (LSL and NZMSL) with high cell surface/cytoplasm stain of this protein is reported, which may shed light on of the mechanosensory role of PECAM-1 in mechanotransduction.

IL-17A promotes the formation of deep vein thrombosis in a mouse model

Deep venous thrombosis (DVT) is a significant problem in the health care industry worldwide. However, the factors and signaling pathways that trigger DVT formation are still largely unknown. In this study, we investigated the role of interleukin-17A (IL-17A) in DVT formation, focusing on the role of platelet aggregation, neutrophil infiltration, and endothelium cell (EC) activation. Notably, IL-17A levels increased in DVT patients as well as in a mouse DVT model. The DVT model mice were injected with recombinant mouse-IL-17A (rIL-17A) or anti-IL-17A monoclonal antibody (mAb) to further evaluate the effects of this cytokine. We found that rIL-17A promotes DVT formation, while IL-17A mAb represses DVT formation. Furthermore, platelet activation, highlighted by CD61 and CD49β expression, and aggregation were enhanced in platelets of rIL-17A-treated mice. rIL-17A also enhanced neutrophil infiltration by regulating the expression of macrophage inflammatory protein-2 (MIP-2) and the release of neutrophil extracellular traps (NETs). IL-17A mAb treatment inhibited both platelet activation and neutrophil activity. Moreover, rIL-17A appears to promote vein EC activation, while IL-17A mAb deters it. Taken together, these data suggest that IL-17A promotes DVT pathogenesis by enhancing platelet activation and aggregation, neutrophil infiltration, and EC activation and that anti-IL-17A mAb could be used for the treatment of DVT.

Molecular Sensors of Blood Flow in Endothelial Cells

Mechanical stress from blood flow has a significant effect on endothelial physiology, with a key role in initiating vasoregulatory signals. Disturbances in blood flow, such as in regions of disease-associated stenosis, arterial branch points, and sharp turns, can induce proatherogenic phenotypes in endothelial cells. The disruption of vascular homeostasis as a result of endothelial dysfunction may contribute to early and late stages of atherosclerosis, the underlying cause of coronary artery disease. In-depth knowledge of the mechanobiology of endothelial cells is essential to identifying mechanosensory complexes involved in the pathogenesis of atherosclerosis. In this review, we describe different blood flow patterns and summarize current knowledge on mechanosensory molecules regulating endothelial vasoregulatory functions, with clinical implications. Such information may help in the search for novel therapeutic approaches.