The control of vascular integrity by endothelial cell junctions: molecular basis and pathological implications

Effects of Different Fermented Feeds on Production Performance, Cecal Microorganisms, and Intestinal Immunity of Laying Hens

Simple Summary

Fermented feed exerts beneficial effects on intestinal microorganisms, host health, and production performance. However, the effect of fermented feed on laying hens is uncertain due to the different types of inoculated probiotics, fermentation substrates, and fermentation technology. Hence, this experiment was conducted to investigate the effects of fermented feed with different compound strains on the performance and intestinal health of laying hens. Supplement fermented feed reduced the feed conversion ratio and promoted egg quality. Both dietary treatment (fermented feed A produced Bacillus subtilis, Lactobacillus, and Yeast and fermented feed B produced by C. butyricum and L. salivarius) influenced intestinal immunity and regulated cecal microbial structure. This may be because the metabolites of microorganisms in fermented feed and the reduced pH value inhibited the colonization of harmful bacteria, improved the intestinal morphology, and then had a positive impact on the production performance and albumen quality of laying hens.

Abstract

This experiment was conducted to investigate the effects of different compound probiotics on the performance, cecal microflora, and intestinal immunity of laying hens. A total of 270 Jing Fen No.6 (22-week-old) were randomly divided into 3 groups: basal diet (CON); basal diet supplemented with 6% fermented feed A by Bacillussubtilis,Lactobacillus, and Yeast (FA); and with 6% fermented feed B by C. butyricum and L. salivarius (FB). Phytic acid, trypsin inhibitor, β-glucan concentrations, and pH value in fermented feed were lower than the CON group (p < 0.05). The feed conversion ratio (FCR) in the experimental groups was decreased, while albumen height and Haugh unit were increased, compared with the CON group (p < 0.05). Fermented feed could upregulate the expression of the signal pathway (TLR4/MyD88/NF-κB) to inhibit mRNA expression of pro-inflammatory cytokines (p < 0.05). Fermented feed promoted the level of Romboutsia (in the FA group) Butyricicoccus (in the FB group), and other beneficial bacteria, and reduced opportunistic pathogens, such as Enterocooccus (p < 0.05). Spearman’s correlations showed that the above bacteria were closely related to albumen height and intestinal immunity. In summary, fermented feed can decrease the feed conversion ratio, and improve the performance and intestinal immunity of laying hens, which may be related to the improvement of the cecal microflora structure.

Autophagy modulates endothelial junctions to restrain neutrophil diapedesis during inflammation

The migration of neutrophils from the blood circulation to sites of infection or injury is a key immune response and requires the breaching of endothelial cells (ECs) that line the inner aspect of blood vessels. Unregulated neutrophil transendothelial cell migration (TEM) is pathogenic, but the molecular basis of its physiological termination remains unknown. Here, we demonstrated that ECs of venules in inflamed tissues exhibited a robust autophagic response that was aligned temporally with the peak of neutrophil trafficking and was strictly localized to EC contacts. Genetic ablation of EC autophagy led to excessive neutrophil TEM and uncontrolled leukocyte migration in murine inflammatory models, while pharmacological induction of autophagy suppressed neutrophil infiltration into tissues. Mechanistically, autophagy regulated the remodeling of EC junctions and expression of key EC adhesion molecules, facilitating their intracellular trafficking and degradation. Collectively, we have identified autophagy as a modulator of EC leukocyte trafficking machinery aimed at terminating physiological inflammation.

The Disruption of the Endothelial Barrier Contributes to Acute Lung Injury Induced by Coxsackievirus A2 Infection in Mice

Sporadic occurrences and outbreaks of hand, foot, and mouth disease (HFMD) caused by Coxsackievirus A2 (CVA2) have frequently reported worldwide recently, which pose a great challenge to public health. Epidemiological studies have suggested that the main cause of death in critical patients is pulmonary edema. However, the pathogenesis of this underlying comorbidity remains unclear. In this study, we utilized the 5-day-old BALB/c mouse model of lethal CVA2 infection to evaluate lung damage. We found that the permeability of lung microvascular was significantly increased after CVA2 infection. We also observed the direct infection and apoptosis of lung endothelial cells as well as the destruction of tight junctions between endothelial cells. CVA2 infection led to the degradation of tight junction proteins (e.g., ZO-1, claudin-5, and occludin). The gene transcription levels of von Willebrand factor (vWF), endothelin (ET), thrombomodulin (THBD), granular membrane protein 140 (GMP140), and intercellular cell adhesion molecule-1 (ICAM-1) related to endothelial dysfunction were all significantly increased. Additionally, CVA2 infection induced the increased expression of inflammatory cytokines (IL-6, IL-1β, and MCP-1) and the activation of p38 mitogen-activated protein kinase (MAPK). In conclusion, the disruption of the endothelial barrier contributes to acute lung injury induced by CVA2 infection; targeting p38-MAPK signaling may provide a therapeutic approach for pulmonary edema in critical infections of HFMD.

The protective effect of harpagoside on angiotensin II (Ang II)-induced blood-brain barrier leakage in vitro

Hypertension and its associated dysfunction of the blood-brain barrier (BBB) contribute to cerebral small vessel disease (cSVD). Angiotensin II (Ang II), a vasoactive peptide of the renin-angiotensin system (RAS), is not only a pivotal molecular signal in hypertension but also causes BBB leakage, cSVD, and cognitive impair. Harpagoside, the major bioactive constituent of Scrophulariae Radix, has been commonly used for the treatment of multiple diseases including hypertension in China. The effect of harpagoside on Ang II-induced BBB damage is unclear. We employed an immortalized endothelial cell line (bEnd.3) to mimic a BBB monolayer model in vitro and investigated the effect of harpagoside on BBB and found that harpagoside alleviated Ang II-induced BBB destruction, inhibited Ang II-associated cytotoxicity in a concentration-dependent manner and attenuated Ang II-induced reactive oxygen species (ROS) impair by downregulation of Nox2, Nox4, and COX-2. Harpagoside prevented Ang II-induced apoptosis via keeping Bax/Bcl-2 balance, decreasing cytochrome c release, and inactivation of caspase-8, caspase-9, and caspase-3 (the mitochondria-dependent and death receptor-mediated apoptosis pathways). Moreover, harpagoside can alleviate Ang II-induced BBB damage through upregulation of tight junction proteins and decrease of caveolae-mediated endocytosis. Thus, harpagoside might be a potential drug to treat Ang II-induced cSVD.

Vascular Normalization: A New Window Opened for Cancer Therapies

Preclinical and clinical antiangiogenic approaches, with multiple side effects such as resistance, have not been proved to be very successful in treating tumor blood vessels which are important targets for tumor therapy. Meanwhile, restoring aberrant tumor blood vessels, known as tumor vascular normalization, has been shown not only capable of reducing tumor invasion and metastasis but also of enhancing the effectiveness of chemotherapy, radiation therapy, and immunotherapy. In addition to the introduction of such methods of promoting tumor vascular normalization such as maintaining the balance between proangiogenic and antiangiogenic factors and targeting endothelial cell metabolism, microRNAs, and the extracellular matrix, the latest molecular mechanisms and the potential connections between them were primarily explored. In particular, the immunotherapy-induced normalization of blood vessels further promotes infiltration of immune effector cells, which in turn improves immunotherapy, thus forming an enhanced loop. Thus, immunotherapy in combination with antiangiogenic agents is recommended. Finally, we introduce the imaging technologies and serum markers, which can be used to determine the window for tumor vascular normalization.

Platelet-derived growth factor B restores vascular barrier integrity and diminishes permeability in ovarian hyperstimulation syndrome

Although advances in the prediction and management of ovarian hyperstimulation syndrome (OHSS) have been introduced, complete prevention is not yet possible. Previously, we and other authors have shown that vascular endothelial growth factor, angiopoietins (ANGPTs) and sphingosine-1-phosphate are involved in OHSS etiology. In addition, we have demonstrated that ovarian protein levels of platelet-derived growth factor (PDGF) ligands -B and -D decrease in an OHSS rat model, whilst PDGFR-β and ANGPT2 remain unchanged. In the present work, we investigated the role of PDGF-B in OHSS by evaluating ligand protein levels in follicular fluid (FF) from women at risk of developing OHSS and by using an immature rat model of OHSS. We demonstrated that PDGF-B and PDGF-D are lower in FF from women at risk of developing OHSS compared to control patients (P < 0.05). In the OHSS rat model, PDGF-B (0.5 µg/ovary) administration decreased ovarian weight (P < 0.05), reduced serum progesterone (P < 0.05) and lowered the percentage of cysts (P < 0.05), compared to untreated OHSS rats, but had no effect on the proportion of follicles or corpora lutea (CL). PDGF-B treatment also restored the expression of steroidogenic acute regulatory protein (P < 0.05) and P450 cholesterol side-chain cleavage enzyme (P < 0.01) to control levels. In addition, PDGF-B increased the peri-endothelial cell area in CL and cystic structures, and reduced vascular permeability compared to untreated OHSS ovaries. Lastly, PDGF-B increased the levels of junction proteins claudin-5 (P < 0.05), occludin (P < 0.05) and β-catenin (P < 0.05), while boosting the extracellular deposition of collagen IV surrounding the ovarian vasculature (PP < 0.01), compared to OHSS alone. In conclusion, our findings indicate that PDGF-B could be another crucial mediator in the onset and development of OHSS, which may lead to the development of novel prediction markers and therapeutic strategies.

Secretome and Tunneling Nanotubes: A Multilevel Network for Long Range Intercellular Communication between Endothelial Cells and Distant Cells

As a cellular interface between the blood and tissues, the endothelial cell (EC) monolayer is involved in the control of key functions including vascular tone, permeability and homeostasis, leucocyte trafficking and hemostasis. EC regulatory functions require long-distance communications between ECs, circulating hematopoietic cells and other vascular cells for efficient adjusting thrombosis, angiogenesis, inflammation, infection and immunity. This intercellular crosstalk operates through the extracellular space and is orchestrated in part by the secretory pathway and the exocytosis of Weibel Palade Bodies (WPBs), secretory granules and extracellular vesicles (EVs). WPBs and secretory granules allow both immediate release and regulated exocytosis of messengers such as cytokines, chemokines, extracellular membrane proteins, coagulation or growth factors. The ectodomain shedding of transmembrane protein further provide the release of both receptor and ligands with key regulatory activities on target cells. Thin tubular membranous channels termed tunneling nanotubes (TNTs) may also connect EC with distant cells. EVs, in particular exosomes, and TNTs may contain and transfer different biomolecules (e.g., signaling mediators, proteins, lipids, and microRNAs) or pathogens and have emerged as a major triggers of horizontal intercellular transfer of information.

Meningitic Escherichia coli α-hemolysin aggravates blood-brain barrier disruption via targeting TGFβ1-triggered hedgehog signaling

Bacterial meningitis is a life-threatening infectious disease with severe neurological sequelae and a high mortality rate, in which Escherichia coli is one of the primary Gram-negative etiological bacteria. Meningitic E. coli infection is often accompanied by an elevated blood–brain barrier (BBB) permeability. BBB is the structural and functional barrier composed of brain microvascular endothelial cells (BMECs), astrocytes, and pericytes, and we have previously shown that astrocytes-derived TGFβ1 physiologically maintained the BBB permeability by triggering a non-canonical hedgehog signaling in brain microvascular endothelial cells (BMECs). Here, we subsequently demonstrated that meningitic E. coli infection could subvert this intercellular communication within BBB by attenuating TGFBRII/Gli2-mediated such signaling. By high-throughput screening, we identified E. coli α-hemolysin as the critical determinant responsible for this attenuation through Sp1-dependent TGFBRII reduction and triggering Ca²⁺ influx and protein kinase A activation, thus leading to Gli2 suppression. Additionally, the exogenous hedgehog agonist SAG exhibited promising protection against the infection-caused BBB dysfunction. Our work revealed a hedgehog-targeted pathogenic mechanism during meningitic E. coli-caused BBB disruption and suggested that activating hedgehog signaling within BBB could be a potential protective strategy for future therapy of bacterial meningitis.

Tissue Kallikrein Exacerbating Sepsis-Induced Endothelial Hyperpermeability is Highly Predictive of Severity and Mortality in Sepsis

AIM

Sepsis, an acute, life-threatening dysregulated response to infection, affects practically all aspects of endothelial function. Tissue kallikrein (TK) is a key enzyme in the kallikrein-kinin system (KKS) which has been implicated in endothelial permeability. Thus, we aimed to establish a potentially novel association among TK, endothelial permeability, and sepsis demonstrated by clinical investigation and in vitro studies.

METHODS

We performed a clinical investigation with the participation of a total of 76 controls, 42 systemic inflammatory response syndrome (SIRS) patients, and 150 patients with sepsis, who were followed-up for 28 days. Circulating TK levels were measured with an enzyme-linked immunosorbent assay. Then, the effect of TK on sepsis-induced endothelial hyperpermeability was evaluated by in vitro study.

RESULTS

Data showed a gradual increase in TK level among controls and the patients with SIRS, sepsis, and septic shock (0.288±0.097 mg/l vs 0.335±0.149 vs 0.495±0.170 vs 0.531±0.188 mg/l, respectively, P <0.001). Further analysis revealed that plasma TK level was positively associated with the severity and mortality of sepsis and negatively associated with event-free survival during 28 days of follow-up (relative risk, 3.333; 95% CI, 2.255-4.925; p < 0.001). With a septic model of TK and kallistatin in vitro, we found that TK exacerbated sepsis-induced endothelial hyperpermeability by downregulating zonula occluden-1 (ZO-1) and vascular endothelial (VE)-cadherin, and these could be reversed by kallistatin, an inhibitor of TK.

CONCLUSION

TK can be used in the diagnosis of sepsis and assessment of severity and prognosis of disease. Inhibition of TK may be a novel therapeutic target for sepsis through increasing ZO-1 and VE-cadherin, as well as downregulating endothelial permeability.

The Angiotensin-Converting Enzyme Inhibitory State Promotes the Transformation of Non-Small Cell Lung Cancer Blood Supply Pattern Toward Vasculogenic Mimicry Formation

Tumor microenvironment plays an important role in tumor proliferation, metastasis, and angiogenesis. Local RAS is a key factor to tumor proliferation and metastasis in NSCLC microenvironment, but its role on angiogenesis and VM formation remains unclear. Although overwhelming majority of previous studies suggested that VM is well established in aggressive tumor and facilitates tumor growth and metastasis, we put forward different views from another angle. We proved that status of tumor blood supply patterns, including VM channels and endothelial vessels, can dynamically exchange with each other along with local RAS fluctuations in microenvironment. Quantitatively, ACE2/ACEI promotes VM formation via Nodal/Notch4 activation; while structurally, ACE2/ACEI leads to a strong and solid structure of VM via inhibition of VE-cadherin internalization. These changes induced by ACE2/ACEI relate to relatively low metastasis rate and comforting prognoses of NSCLC patients.

LncRSPH9-4 Facilitates Meningitic Escherichia coli-Caused Blood-Brain Barrier Disruption via miR-17-5p/MMP3 Axis

Brain microvascular endothelial cells (BMECs) constitute the structural and functional basis for the blood–brain barrier (BBB) and play essential roles in bacterial meningitis. Although the BBB integrity regulation has been under extensive investigation, there is little knowledge regarding the roles of long non-coding RNAs (lncRNAs) in this event. The present study aimed to investigate the roles of one potential lncRNA, lncRSPH9-4, in meningitic E. coli infection of BMECs. LncRSPH9-4 was cytoplasm located and significantly up-regulated in meningitic E. coli-infected hBMECs. Electrical cell-substrate impedance sensing (ECIS) measurement and Western blot assay demonstrated lncRSPH9-4 overexpression in hBMECs mediated the BBB integrity disruption. By RNA-sequencing analysis, 639 mRNAs and 299 miRNAs were significantly differentiated in response to lncRSPH9-4 overexpression. We further found lncRSPH9-4 regulated the permeability in hBMECs by competitively sponging miR-17-5p, thereby increasing MMP3 expression, which targeted the intercellular tight junctions. Here we reported the infection-induced lncRSPH9-4 aggravated disruption of the tight junctions in hBMECs, probably through the miR-17-5p/MMP3 axis. This finding provides new insights into the function of lncRNAs in BBB integrity during meningitic E. coli infection and provides the novel nucleic acid targets for future treatment of bacterial meningitis.

The BMP Pathway in Blood Vessel and Lymphatic Vessel Biology

Bone morphogenetic proteins (BMPs) were originally identified as the active components in bone extracts that can induce ectopic bone formation. In recent decades, their key role has broadly expanded beyond bone physiology and pathology. Nowadays, the BMP pathway is considered an important player in vascular signaling. Indeed, mutations in genes encoding different components of the BMP pathway cause various severe vascular diseases. Their signaling contributes to the morphological, functional and molecular heterogeneity among endothelial cells in different vessel types such as arteries, veins, lymphatic vessels and capillaries within different organs. The BMP pathway is a remarkably fine-tuned pathway. As a result, its signaling output in the vessel wall critically depends on the cellular context, which includes flow hemodynamics, interplay with other vascular signaling cascades and the interaction of endothelial cells with peri-endothelial cells and the surrounding matrix. In this review, the emerging role of BMP signaling in lymphatic vessel biology will be highlighted within the framework of BMP signaling in the circulatory vasculature.

Primaquine Diphosphate, a Known Antimalarial Drug, Blocks Vascular Leakage Acting Through Junction Stabilization

Endothelial barrier integrity is important for vascular homeostasis, and hyperpermeability participates in the progression of many pathological states, such as diabetic retinopathy, ischemic stroke, chronic bowel disease, and inflammatory disease. Here, using drug repositioning, we discovered that primaquine diphosphate (PD), previously known as an antimalarial drug, was a potential blocker of vascular leakage. PD inhibited the linear pattern of vascular endothelial growth factors (VEGF)-induced disruption at the cell boundaries, blocked the formation of VEGF-induced actin stress fibers, and stabilized the cortactin actin rings in endothelial cells. PD significantly reduced leakage in the Miles assay and mouse model of streptozotocin (STZ)-induced diabetic retinopathy. Targeted prediction programs and deubiquitinating enzyme activity assays identified a potential mechanism of action for PD and demonstrated that this operates via ubiquitin specific protease 1 (USP1). USP1 inhibition demonstrated a conserved barrier function by inhibiting VEGF-induced leakage in endothelial permeability assays. Taken together, these findings suggest that PD could be used as a novel drug for vascular leakage by maintaining endothelial integrity.

Mucopolysaccharide polysulfate promotes microvascular stabilization and barrier integrity of dermal microvascular endothelial cells via activation of the angiopoietin-1/Tie2 pathway

BACKGROUND

Mucopolysaccharide polysulfate (MPS) is a heparinoid and MPS-containing formulations are widely used as moisturizers for dry skin and to treat peripheral vascular insufficiency. Although MPS has therapeutic effects in skin diseases with microvascular abnormalities, the effects of MPS on microvascular function remain incompletely understood.

OBJECTIVE

The aim of this study was to evaluate the functional activities of MPS on human pericytes (HPC) and human dermal microvascular endothelial cells (HDMEC) in vitro, and on microvascular permeability of the skin.

METHODS

The protein expression of angiopoietin (Ang)-1 in HPC, and platelet-derived growth factor-BB (PDGF-BB) and phosphorylated tyrosine-protein kinase receptor 2 (Tie2) in HDMEC were measured in the presence or absence of MPS. The vascular barrier was evaluated by the expressions of claudin-5 and vascular endothelial (VE)-cadherin, and transendothelial electrical resistance (TEER).

RESULTS

In HPC, MPS dose-dependently enhanced Ang-1 secretion, which activated Tie2 in HDMEC. In HDMEC, MPS significantly increased the production of PDGF-BB, which is important for the recruitment of HPC to the vascular endothelium, and significantly increased the phosphorylation of Tie2, which results in the activation of the Ang-1/Tie2 signaling . MPS significantly increased the expression of tight junction protein claudin-5 and TEER in the HDMEC. Moreover, the intradermal injection of MPS prevented vascular endothelial growth factor-induced increase in vascular permeability in mouse skin.

CONCLUSION

We found that MPS promoted microvascular stabilization and barrier integrity in HDMEC via Ang-1/Tie2 activation. These results suggest that MPS might improve microvascular abnormalities in various diseases accompanied by disturbances in Ang-1/Tie2 signaling.

A novel BLOC1S5-related HPS-11 patient and zebrafish with bloc1s5 disruption

Hermansky-Pudlak Syndrome (HPS) cases present with a variable degree of OCA and bleeding tendency. HPS is categorized into eleven types based on eleven causative genes, and disease severity varies among different types. By whole-exome sequencing performed on a family trio and Sanger sequencing of candidate variants, we identified a novel homozygous variant (NM_201280.3: c.181delC, p.Val61*) in BLOC1S5 in the patient who presents OCA and mild bleeding diathesis, and his healthy parents are heterozygous carriers. The variant can be considered pathogenic based on the guideline American College of Medical Genetics and Genomics, and the patient is proposed to be affected with HPS-11. In this study, we also explored bloc1s5 in zebrafish. bloc1s5 mRNA can be detected during early development of zebrafish. bloc1s5 knockdown zebrafish present with retinal hypopigmentation, thrombocytes loss and pericardial edema, and dll4/notch1 signaling and vascular integrity signaling are down-regulated at mRNA level in bloc1s5 morphants. The data from the first HPS-11 patient in Chinese population expand phenotypic and genotypic spectrum of HPS-11. Disruption of bloc1s5 in zebrafish recapitulates HPS-11-like phenotypes, and the potential signaling pathways associated with bloc1s5 are proposed. Altogether, this study may facilitate genetic counseling of HPS and investigation about BLOC1S5.

CNS-Draining Meningeal Lymphatic Vasculature: Roles, Conundrums and Future Challenges

A genuine and functional lymphatic vascular system is found in the meninges that sheath the central nervous system (CNS). This unexpected (re)discovery led to a reevaluation of CNS fluid and solute drainage mechanisms, neuroimmune interactions and the involvement of meningeal lymphatics in the initiation and progression of neurological disorders. In this manuscript, we provide an overview of the development, morphology and unique functional features of meningeal lymphatics. An outline of the different factors that affect meningeal lymphatic function, such as growth factor signaling and aging, and their impact on the continuous drainage of brain-derived molecules and meningeal immune cells into the cervical lymph nodes is also provided. We also highlight the most recent discoveries about the roles of the CNS-draining lymphatic vasculature in different pathologies that have a strong neuroinflammatory component, including brain trauma, tumors, and aging-associated neurodegenerative diseases like Alzheimer's and Parkinson's. Lastly, we provide a critical appraisal of the conundrums, challenges and exciting questions involving the meningeal lymphatic system that ought to be investigated in years to come.

Resveratrol Attenuates Meningitic Escherichia coli-Mediated Blood-Brain Barrier Disruption

Meningitic Escherichia coli can infiltrate the central nervous system (CNS), consequently increasing the levels of proinflammatory cytokines and chemokines and deteriorating the integrity of the blood-brain barrier (BBB). Resveratrol has emerged in recent years as a compound with antioxidant and anti-inflammatory properties. However, it is still unknown how resveratrol affects meningitic E. coli-induced CNS dysfunction. Here, by using in vivo and in vitro BBB models, we demonstrated that resveratrol treatment significantly inhibited meningitic E. coli invasion of the BBB, protected the integrity of the BBB, and reduced neuroinflammation and lethality. In mechanism, resveratrol inhibited bacterial penetration of the BBB by attenuating the upregulation of caveolin-1 (CAV-1), a class of lipid rafts maintaining endothelial cell function. Resveratrol treatment also maintained BBB permeability by suppressing the ERK1/2-VEGFA signaling cascade. In vivo treatment of resveratrol decreased the production of inflammatory cytokines and improved the survival rate in mice challenged with meningitic E. coli. These findings collectively indicated that resveratrol could attenuate meningitic E. coli-induced CNS injury, which might constitute a new approach for future prevention and treatment of E. coli meningitis.

The Tumour Vasculature as a Target to Modulate Leucocyte Trafficking

Simple Summary

Tumour blood vessels, characterised by abnormal morphology and function, create an immunosuppressive tumour microenvironment via restricting the appropriate leucocyte subsets trafficking. Strategies to trigger phenotypic alteration in tumour vascular system to resemble normal vascular system, named vascular normalisation, promote effective trafficking of leucocytes into tumours through enhancing the interactions between leucocytes and endothelial cells. This review specifically demonstrates how targeting tumour blood vessels modulates the critical steps of leucocyte trafficking. Furthermore, selective regulation of leucocyte subsets trafficking in tumours can be achieved by vasculature-targeting strategies, contributing to improved immunotherapy and thereby delayed tumour progression.

Abstract

The effectiveness of immunotherapy against solid tumours is dependent on the appropriate leucocyte subsets trafficking and accumulating in the tumour microenvironment (TME) with recruitment occurring at the endothelium. Such recruitment involves interactions between the leucocytes and the endothelial cells (ECs) of the vessel and occurs through a series of steps including leucocyte capture, their rolling, adhesion, and intraluminal crawling, and finally leucocyte transendothelial migration across the endothelium. The tumour vasculature can curb the trafficking of leucocytes through influencing each step of the leucocyte recruitment process, ultimately producing an immunoresistant microenvironment. Modulation of the tumour vasculature by strategies such as vascular normalisation have proven to be efficient in facilitating leucocyte trafficking into tumours and enhancing immunotherapy. In this review, we discuss the underlying mechanisms of abnormal tumour vasculature and its impact on leucocyte trafficking, and potential strategies for overcoming the tumour vascular abnormalities to boost immunotherapy via increasing leucocyte recruitment.

Increase in Blood-Brain Barrier (BBB) Permeability Is Regulated by MMP3 via the ERK Signaling Pathway

BACKGROUND

The blood-brain barrier (BBB) regulates the exchange of molecules between the brain and peripheral blood and is composed primarily of microvascular endothelial cells (BMVECs), which form the lining of cerebral blood vessels and are linked via tight junctions (TJs). The BBB is regulated by components of the extracellular matrix (ECM), and matrix metalloproteinase 3 (MMP3) remodels the ECM's basal lamina, which forms part of the BBB. Oxidative stress is implicated in activation of MMPs and impaired BBB. Thus, we investigated whether MMP3 modulates BBB permeability.

METHODS

Experiments included in vivo assessments of isoflurane anesthesia and dye extravasation from brain in wild-type (WT) and MMP3-deficient (MMP3-KO) mice, as well as in vitro assessments of the integrity of monolayers of WT and MMP3-KO BMVECs and the expression of junction proteins.

RESULTS

Compared to WT mice, measurements of isoflurane usage and anesthesia induction time were higher in MMP3-KO mice and lower in WT that had been treated with MMP3 (WT+MMP3), while anesthesia emergence times were shorter in MMP3-KO mice and longer in WT+MMP3 mice than in WT. Extravasation of systemically administered dyes was also lower in MMP3-KO mouse brains and higher in WT+MMP3 mouse brains, than in the brains of WT mice. The results from both TEER and Transwell assays indicated that MMP3 deficiency (or inhibition) increased, while MMP3 upregulation reduced barrier integrity in either BMVEC or the coculture. MMP3 deficiency also increased the abundance of TJs and VE-cadherin proteins in BMVECs, and the protein abundance declined when MMP3 activity was upregulated in BMVECs, but not when the cells were treated with an inhibitor of extracellular signal related-kinase (ERK).

CONCLUSION

MMP3 increases BBB permeability following the administration of isoflurane by upregulating the ERK signaling pathway, which subsequently reduces TJ and VE-cadherin proteins in BMVECs.

The region-selective regulation of endothelial claudin-5 expression and signaling in brain health and disorders

The neurovascular unit (NVU) consists of neurons, glial cells, microvascular cells, and extracellular matrix, and is involved in a variety of physiological and pathological processes in the central nervous system (CNS). Within the NVU, the microvascular endothelial cells and pericytes principally contribute to maintaining the integrity of the blood-brain barrier (BBB). Various types of cells are connected to each other in the NVU by diverse cell adhesion molecules, of which claudin-5 (CLDN5) is by far the most abundantly expressed tight-junction protein in brain microvascular endothelial cells and absolutely required for the maintenance of the BBB. This review highlights recent progress in understanding the region-specific regulation and dysregulation of CLDN5 expression in CNS health and disorders. We also discuss how CLDN5 expression is regionally disrupted within the NVU. In addition, we focus on the link between cell adhesion and transcription factor signalings and describe the possible involvement of CLDN5-adhesion signaling in brain health and disorders.

Saffron anti-metastatic properties, ancient spice novel application

Crocus sativus L. (saffron), was applied as a spice, food colorant and medicine since four millennia ago and has been used as a remedy for various maladies. In the last three decades, the anti-primary tumor properties of saffron and its main carotenoids, crocin and crocetin, have been well explored. Despite the fact that metastasis is the leading cause of death in cancer patients, the anti-metastatic potential of saffron and its carotenoids has been surveyed only this decade. This review aims to provide an unprecedented overview of the anti-metastatic effects of saffron, crocin and crocetin, and the mechanisms underlying these effects. Investigations on various cancers demonstrated the anti-migratory, anti-invasion, anti-angiogenic potentials of saffron and its carotenoids, as well as their effects suppressing cell-ECM adhesion and enhancing cell-cell attachment. Saffron and its carotenoids exert their impact through different mechanisms such as reduction of CD34 and suppression of Wnt/β-catenin, Ras/ERK, P38, DCLK1, EMT, matrix metalloproteinases and urokinases. Crocin displayed more effective anti-metastatic potency, in comparison with saffron extract and crocetin. The bioaccessibility/bioavailability, nontoxicity on normal cells, confirmed anti-tumor efficiency and the recent evidence on the anti-metastatic potential of saffron and its carotenoids, recommends them as a propitious multipotent dietary agent and herbal medicine.

Angiogenesis: A Cellular Response to Traumatic Injury

ABSTRACT

The development of new vasculature plays a significant role in a number of chronic disease states, including neoplasm growth, peripheral arterial disease, and coronary artery disease, among many others. Traumatic injury and hemorrhage, however, is an immediate, often dramatic pathophysiologic insult that can also necessitate neovascularization to promote healing. Traditional understanding of angiogenesis involved resident endothelial cells branching outward from localized niches in the periphery. Additionally, there are a small number of circulating endothelial progenitor cells that participate directly in the process of neovessel formation. The bone marrow stores a relatively small number of so-called pro-angiogenic hematopoietic progenitor cells-that is, progenitor cells of a hematopoietic potential that differentiate into key structural cells and stimulate or otherwise support local cell growth/differentiation at the site of angiogenesis. Following injury, a number of cytokines and intercellular processes are activated or modulated to promote development of new vasculature. These processes initiate and maintain a robust response to vascular insult, allowing new vessels to canalize and anastomose and provide timely oxygen delivering to healing tissue. Ultimately as we better understand the key players in the process of angiogenesis we can look to develop novel techniques to promote healing following injury.

Engineering the Lymphatic Network: A Solution to Lymphedema

Secondary lymphedema is a life-long disorder characterized by chronic tissue swelling and inflammation that obstruct interstitial fluid circulation and immune cell trafficking. Regenerating lymphatic vasculatures using various strategies represents a promising treatment for lymphedema. Growth factor injection and gene delivery have been developed to stimulate lymphangiogenesis and augment interstitial fluid resorption. Using bioengineered materials as growth factor delivery vehicles allows for a more precisely targeted lymphangiogenic activation within the injured site. The implantation of prevascularized lymphatic tissue also promotes in situ lymphatic capillary network formation. The engineering of larger scale lymphatic tissues, including lymphatic collecting vessels and lymph nodes constructed by bioengineered scaffolds or decellularized animal tissues, offers alternatives to reconnecting damaged lymphatic vessels and restoring lymph circulation. These approaches provide lymphatic vascular grafting materials to reimpose lymphatic continuity across the site of injury, without creating secondary injuries at donor sites. The present work reviews molecular mechanisms mediating lymphatic system development, approaches to promoting lymphatic network regeneration, and strategies for engineering lymphatic tissues, including lymphatic capillaries, collecting vessels, and nodes. Challenges of advanced translational applications are also discussed.

Enhanced endothelial barrier function by monoclonal antibody activation of vascular endothelial cadherin

Excessive vascular permeability occurs in inflammatory disease processes. Vascular endothelial cadherin (VE-cadherin) is an adhesion protein that controls vascular permeability. We identified monoclonal antibodies (mAbs) to human VE-cadherin that activate cell adhesion and inhibit the increased permeability of endothelial cell monolayers induced by thrombin receptor activator peptide-6 (TRAP-6). Two mAbs, 8A12c and 3A5a, reduce permeability, whereas an inhibitory mAb, 2E11d, enhances permeability. Activating mAbs also reduce permeability induced by tumor necrosis factor-α (TNF-α) and vascular endothelial cell growth factor (VEGF). The activating mAbs also stabilize the organization of the adherens junctions that are disrupted by TRAP-6, VEGF, or TNF-α. The activating mAbs act directly on the adhesive function of VE-cadherin because they did not block the accumulation of actin filaments stimulated by TRAP-6 and enhance physical cell-cell adhesion of VE-cadherin-expressing tissue culture cells. Therefore, VE-cadherin function can be regulated at the cell surface to control endothelial permeability.NEW & NOTEWORTHY Excessive vascular permeability is a serious complication of many inflammatory disease conditions. We have developed monoclonal antibodies that inhibit increases in endothelial monolayer permeability induced by several signaling factors by activating VE-cadherin mediated adhesion and stabilizing cell junctions. These antibodies and/or the mechanisms they reveal may lead to important therapeutics to treat vascular leakiness and inflammation.

Type of culture medium determines properties of cultivated retinal endothelial cells: induction of substantial phenotypic conversion by standard DMEM

Contradictory behavior of microvascular retinal endothelial cells (REC) - a reliable in vitro model to study retinal diseases - have recently been reported which might result from cultivating the cells in standard DMEM not optimized for this cell type. Therefore, we studied DMEM's effects on phenotype and behavior of immortalized bovine REC. Cells were cultivated in endothelial cell growth medium (ECGM) until a confluent monolayer was reached and then further kept for 1-4 days in ECGM, DMEM, or mixes thereof all supplemented with 5% fetal bovine serum, endothelial cell growth supplement, 90 μg/ml heparin, and 100 nM hydrocortisone. Within hours of cultivation in DMEM, the cell index - measured to assess the cell layer's barrier function - dropped to ~5% of the initial value and only slowly recovered, not only accompanied by stronger expression of HSP70 mRNA and secretion of interleukin-6, but also by lower expressions of tight junction proteins claudin-5, claudin-1 or of the marker of cell type conversion caveolin-1. Altered subcellular localizations of EC-typic claudin-5, vascular endothelial cadherin and von Willebrand factor were also observed. Taken together, all experiments with (retinal) EC cultivated in common DMEM need to be interpreted very cautiously and should at least include phenotypic validation.

Molecular Mechanisms Controlling Lymphatic Endothelial Junction Integrity

The lymphatic system is essential for lipid absorption/transport from the digestive system, maintenance of tissue fluid and protein homeostasis, and immune surveillance. Despite recent progress toward understanding the cellular and molecular mechanisms underlying the formation of the lymphatic vascular system, the nature of lymphatic vessel abnormalities and disease in humans is complex and poorly understood. The mature lymphatic vasculature forms a hierarchical network in which lymphatic endothelial cells (LECs) are joined by functionally specialized cell-cell junctions to maintain the integrity of lymphatic vessels. Blind-ended and highly permeable lymphatic capillaries drain interstitial fluid via discontinuous, button-like LEC junctions, whereas collecting lymphatic vessels, surrounded by intact basement membranes and lymphatic smooth muscle cells, have continuous, zipper-like LEC junctions to transport lymph to the blood circulatory system without leakage. In this review, we discuss the recent advances in our understanding of the mechanisms by which lymphatic button- and zipper-like junctions play critical roles in lymphatic permeability and function in a tissue- and organ-specific manner, including lacteals of the small intestine. We also provide current knowledge related to key pathways and factors such as VEGF and RhoA/ROCK signaling that control lymphatic endothelial cell junctional integrity.

Astrocyte-Derived TGFβ1 Facilitates Blood-Brain Barrier Function via Non-Canonical Hedgehog Signaling in Brain Microvascular Endothelial Cells

The blood-brain barrier is a specialized structure in mammals, separating the brain from the bloodstream and maintaining the homeostasis of the central nervous system. The barrier is composed of various types of cells, and the communication between these cells is critical to blood-brain barrier (BBB) function. Here, we demonstrate the astrocyte-derived TGFβ1-mediated intercellular communication between astrocytes and brain microvascular endothelial cells (BMECs). By using an in vitro co-culture model, we observed that the astrocyte-derived TGFβ1 enhanced the tight junction protein ZO-1 expression in BMECs and the endothelial barrier function via a non-canonical hedgehog signaling. Gli2, the core transcriptional factor of the hedgehog pathway, was demonstrated to modulate ZO-1 expression directly. By the dual-luciferase reporter system and chromatin immunoprecipitation, we further identified the exact sites on Smad2/3 that bound to the gli2 promotor and on Gli2 that bound to the zo-1 promotor. Our work highlighted the TGFβ1-mediated intercellular communication of astrocytes with BMECs in BBB, which shall extend current knowledge on the BBB homeostasis physiologically, and more importantly suggests TGFβ1 as a potential effector for future prevention and amelioration of BBB dysfunction.

BML-111, the lipoxin A4 agonist, modulates VEGF or CoCl2-induced migration, angiogenesis and permeability in tumor-derived endothelial cells

Tumor angiogenesis plays a vital role in carcinogenesis, cancer progression, and metastasis. Lipoxin A₄ (LXA₄) is an endogenously-produced family of effective anti-inflammatory with a potent inhibitory effect on angiogenesis. However, BML-111, a LXA₄ agonist, its governing tumor-derived endothelial cells (Td-EC) mechanisms remain unknown. In the present study, we utilized VEGF or CoCl₂ to mimic tumor microenvironment in vitro to study the effect of BML-111 on angiogenesis and permeability of Td-EC, and preliminarily explore its specific mechanism. Data suggested that BML-111 inhibited viability, migration and angiogenesis in VEGF or CoCl₂-treated Td-EC by modulating MMP2/9-TIMP1, and decreasing the production of HIF-1α and COX-2 level. In addition, we observed that BML-111 inhibited Td-EC permeability induced by VEGF or CoCl₂, through the stabilization of VE-cadherin/β-catenin-dependent adherens junctions and TRPC1 pathway. Nevertheless, these effects could be blocked by BOC-2 which was the specific inhibitor of FPR2/ALX (the receptor of LXA₄).These results suggest that BML-111 may have inhibitory effects on VEGF or CoCl₂-induced migration, angiogenesis and permeability in tumor-derived endothelial cells.

Endothelial Barrier Integrity Is Disrupted In Vitro by Heme and by Serum From Sickle Cell Disease Patients

Free extracellular heme has been shown to activate several compartments of innate immunity, acting as a danger-associated molecular pattern (DAMP) in hemolytic diseases. Although localized endothelial barrier (EB) disruption is an important part of inflammation that allows circulating leukocytes to reach inflamed tissues, non-localized/deregulated disruption of the EB can lead to widespread microvascular hyperpermeability and secondary tissue damage. In mouse models of sickle cell disease (SCD), EB disruption has been associated with the development of a form of acute lung injury that closely resembles acute chest syndrome (ACS), and that can be elicited by acute heme infusion. Here we explored the effect of heme on EB integrity using human endothelial cell monolayers, in experimental conditions that include elements that more closely resemble in vivo conditions. EB integrity was assessed by electric cell-substrate impedance sensing in the presence of varying concentrations of heme and sera from SCD patients or healthy volunteers. Heme caused a dose-dependent decrease of the electrical resistance of cell monolayers, consistent with EB disruption, which was confirmed by staining of junction protein VE-cadherin. In addition, sera from SCD patients, but not from healthy volunteers, were also capable to induce EB disruption. Interestingly, these effects were not associated with total heme levels in serum. However, when heme was added to sera from SCD patients, but not from healthy volunteers, EB disruption could be elicited, and this effect was associated with hemopexin serum levels. Together our in vitro studies provide additional support to the concept of heme as a DAMP in hemolytic conditions.

p90RSK-MAGI1 Module Controls Endothelial Permeability by Post-translational Modifications of MAGI1 and Hippo Pathway

Previously, we reported that post-translational modifications (PTMs) of MAGI1, including S741 phosphorylation and K931 de-SUMOylation, both of which are regulated by p90RSK activation, lead to endothelial cell (EC) activation. However, roles for p90RSK and MAGI1-PTMs in regulating EC permeability remain unclear despite MAGI1 being a junctional molecule. Here, we show that thrombin (Thb)-induced EC permeability, detected by the electric cell-substrate impedance sensing (ECIS) based system, was decreased by overexpression of dominant negative p90RSK or a MAGI1-S741A phosphorylation mutant, but was accelerated by overexpression of p90RSK, siRNA-mediated knockdown of magi1, or the MAGI1-K931R SUMOylation mutant. MAGI1 depletion also increased the mRNA and protein expression of the large tumor suppressor kinases 1 and 2 (LATS1/2), which inhibited YAP/TAZ activity and increased EC permeability. Because the endothelial barrier is a critical mediator of tumor hypoxia, we also evaluated the role of p90RSK activation in tumor vessel leakiness by using a relatively low dose of the p90RSK specific inhibitor, FMK-MEA. FMK-MEA significantly inhibited tumor vessel leakiness at a dose that does not affect morphology and growth of tumor vessels in vivo. These results provide novel insights into crucial roles for p90RSK-mediated MAGI1 PTMs and the Hippo pathway in EC permeability, as well as p90RSK activation in tumor vessel leakiness.

Endothelial Responses in Sepsis

Endothelial cells (ECs) are vascular, nonconventional immune cells that play a major role in the systemic response after bacterial infection to limit its dissemination. Triggered by exposure to pathogens, microbial toxins, or endogenous danger signals, EC responses are polymorphous, heterogeneous, and multifaceted. During sepsis, ECs shift toward a proapoptotic, proinflammatory, proadhesive, and procoagulant phenotype. In addition, glycocalyx damage and vascular tone dysfunction impair microcirculatory blood flow, leading to organ injury and, potentially, life-threatening organ failure. This review aims to cover the current understanding of the EC adaptive or maladaptive response to acute inflammation or bacterial infection based on compelling recent basic research and therapeutic clinical trials targeting microvascular and endothelial alterations during septic shock.

Severe acute pancreatitis: capillary permeability model linking systemic inflammation to multiorgan failure

Severe acute pancreatitis (SAP) includes persistent systemic inflammation (SIRS) and multiorgan failure (MOF). The mechanism of transition from SIRS to MOF is unclear. We developed a fluid compartment model and used clinical data to test predictions. The model includes vascular, interstitial and "third-space" compartments with variable permeability of plasma proteins at the capillaries. Consented patients from University of Pittsburgh Medical Center Presbyterian Hospital were studied. Preadmission and daily hematocrit (HCT), blood urea nitrogen (BUN), creatine (Cr), albumin (Alb), and total protein (TP) were collected, and nonalbumin plasma protein (NAPP = TP minus the Alb) was calculated. Subjects served as their own controls for trajectory analysis. Of 57 SAP subjects, 18 developed MOF (5 died), and 39 were non-MOF (0 died). Compared with preadmission levels, admission HCT increased in MOF +5.00 [25%-75% interquartile range, IQR] versus non-MOF -0.10 [-1.55, 1.40] (P < 0.002) with HCT > +3 distinguishing MOF from non-MOF (odds ratio 17.7, P = 0.014). Preadmission Alb fell faster in MOF than non-MOF (P < 0.01). By day 2, TP and NAPP dropped in MOF but not non-MOF (P < 0.001). BUN and Cr levels increased in MOF (P = 0.001), but BUN-to-Cr ratios remained constant. Pancreatic necrosis was more common in MOF (56%) than non-MOF (23%). Changing capillary permeability to allow loss of NAPP in this model predicts loss of plasma oncotic pressure and reduced vascular volume, hypotension with prerenal azotemia and acute kidney dysfunction, pancreas necrosis, and pulmonary edema from capillary leak in the lung with acute respiratory distress syndrome. Sequential biomarker analysis in humans with or without MOF is consistent with this model. This study is registered on https://clinicaltrials.gov at NCT03075605.NEW & NOTEWORTHY Acute pancreatitis is a sudden inflammatory response to pancreatic injury that may spread to systemic inflammation, multiorgan failure, and death in some patients. With the use of the predictions of a new mechanistic model, we compared patients with severe acute pancreatitis with or without multiorgan failure. All biomarkers of capillary leak and clinical features of multiorgan failure were accurately predicted. This provides a new paradigm for understanding and developing new treatments for patients with severe acute pancreatitis.

A modified microchip-based flow chamber system for evaluating thrombogenicity in patients with thrombocytopenia

BACKGROUND

In the intensive care unit (ICU), patients with thrombocytopenia are at high risk for bleeding and should be assessed for their thrombogenic potential. However, the analytical conditions of conventional hemostatic tests are unsuitable for the evaluation of low-platelet samples. Here we aimed to establish suitable analytical conditions with the Total Thrombus-formation Analysis System (T-TAS) for quantitative assessment of thrombogenic potential in patients with thrombocytopenia and to investigate how T-TAS values relate to bleeding symptoms and the effects of platelet transfusion.

METHODS

Modified chips with a different chamber depth were developed for the analysis of low-platelet samples in the T-TAS. We included 10 adult patients admitted to the ICU of Kagoshima University Hospital who required platelet transfusion. Patients were divided into major and minor bleeding groups according to their bleeding scale before platelet transfusion. The thrombogenic potential of these patients before and after platelet transfusion was assessed with hemostatic function tests, including rotational thromboelastometry, multiplate aggregometry, and the T-TAS.

RESULTS

Analysis of low-platelet samples revealed that, compared with the conventional chip (80-μm-deep chamber), the modified chip (50-μm-deep chamber) achieved higher sensitivity in detecting elevation of flow pressure caused by growth of an occlusive thrombus in the T-TAS analytical chamber. All patients in the minor bleeding group retained thrombogenic potential that occluded the modified chip (occlusion time 16.3 ± 3.3 min), whereas most patients in the major bleeding group were unable to occlude the modified chip during the 30-min measurement (P <  0.01). The recovery of thrombogenic potential after platelet transfusion was confirmed with the T-TAS and correlated with the function, rather than the count, of transfused platelets. Among all evaluated parameters in hemostatic function tests, only the T-TAS showed significant differences in occlusion time and area under the curve both between the minor and major bleeding groups and between pre- and post-platelet transfusion.

CONCLUSIONS

We developed a modified microchip-based flow chamber system that reflects the hemostatic function of patients with thrombocytopenia.

Dual function of perivascular fibroblasts in vascular stabilization in zebrafish

Blood vessels are vital to sustain life in all vertebrates. While it is known that mural cells (pericytes and smooth muscle cells) regulate vascular integrity, the contribution of other cell types to vascular stabilization has been largely unexplored. Using zebrafish, we identified sclerotome-derived perivascular fibroblasts as a novel population of blood vessel associated cells. In contrast to pericytes, perivascular fibroblasts emerge early during development, express the extracellular matrix (ECM) genes col1a2 and col5a1, and display distinct morphology and distribution. Time-lapse imaging reveals that perivascular fibroblasts serve as pericyte precursors. Genetic ablation of perivascular fibroblasts markedly reduces collagen deposition around endothelial cells, resulting in dysmorphic blood vessels with variable diameters. Strikingly, col5a1 mutants show spontaneous hemorrhage, and the penetrance of the phenotype is strongly enhanced by the additional loss of col1a2. Together, our work reveals dual roles of perivascular fibroblasts in vascular stabilization where they establish the ECM around nascent vessels and function as pericyte progenitors.

Blood vessels are essential to sustain life in humans. Defects in blood vessels can lead to serious diseases, such as hemorrhage, tissue ischemia, and stroke. However, how blood vessel stability is maintained by surrounding support cells is still poorly understood. Using the zebrafish model, we identify a new population of blood vessel associated cells termed perivascular fibroblasts, which originate from the sclerotome, an embryonic structure that is previously known to generate the skeleton of the animal. Perivascular fibroblasts are distinct from pericytes, a known population of blood vessel support cells. They become associated with blood vessels much earlier than pericytes and express several collagen genes, encoding main components of the extracellular matrix. Loss of perivascular fibroblasts or mutations in collagen genes result in fragile blood vessels prone to damage. Using cell tracing in live animals, we find that a subset of perivascular fibroblasts can differentiate into pericytes. Together, our work shows that perivascular fibroblasts play two important roles in maintaining blood vessel integrity. Perivascular fibroblasts secrete collagens to stabilize newly formed blood vessels and a sub-population of these cells also functions as precursors to generate pericytes to provide additional vascular support.

Repairing blood-CNS barriers: Future therapeutic approaches for neuropsychiatric disorders

Central nervous system (CNS) drug development faces significant difficulties that translate into high rates of failure and lack of innovation. The pathophysiology of neurological and psychiatric disorders often results in the breakdown of blood-CNS barriers, disturbing the CNS microenvironment and worsening disease progression. Therefore, restoring the integrity of blood-CNS barriers may have a beneficial influence in several CNS disorders and improve treatment outcomes. In this review, pathways that may be modulated to protect blood-CNS barriers from neuroinflammatory and oxidative insults are featured. First, the participation of the brain endothelium and glial cells in disruption processes is discussed. Then, the relevance of regulatory systems is analysed, specifically the hypothalamic-pituitary axis, the renin-angiotensin system, sleep and circadian rhythms, and glutamate neurotransmission. Lastly, compounds of endogenous and exogenous origin that are known to mediate the repair of blood-CNS barriers are presented. We believe that enhancing the protection of blood-CNS barriers is a promising therapeutic strategy to pursue in the future.

Striatal Acetylcholine Helps to Preserve Functional Outcomes in a Mouse Model of Stroke

Acetylcholine (ACh) has been suggested to facilitate plasticity and improve functional recovery after different types of brain lesions. Interestingly, numerous studies have shown that striatal cholinergic interneurons are relatively resistant to acute ischemic insults, but whether ACh released by these neurons enhances functional recovery after stroke is unknown. We investigated the role of endogenous striatal ACh in stroke lesion volume and functional outcomes following middle cerebral artery occlusion to induce focal ischemia in striatum-selective vesicular acetylcholine transporter-deficient mice (stVAChT-KO). As transporter expression is almost completely eliminated in the striatum of stVAChT-KO mice, ACh release is nearly abolished in this area. Conversely, in other brain areas, VAChT expression and ACh release are preserved. Our results demonstrate a larger infarct size after ischemic insult in stVAChT-KO mice, with more pronounced functional impairments and increased mortality than in littermate controls. These changes are associated with increased activation of GSK-3, decreased levels of β-catenin, and a higher permeability of the blood–brain barrier in mice with loss of VAChT in striatum neurons. These results support a framework in which endogenous ACh secretion originating from cholinergic interneurons in the striatum helps to protect brain tissue against ischemia-induced damage and facilitates brain recovery by supporting blood–brain barrier function.

EphrinB2-EphB4 signalling provides Rho-mediated homeostatic control of lymphatic endothelial cell junction integrity

Endothelial integrity is vital for homeostasis and adjusted to tissue demands. Although fluid uptake by lymphatic capillaries is a critical attribute of the lymphatic vasculature, the barrier function of collecting lymphatic vessels is also important by ensuring efficient fluid drainage as well as lymph node delivery of antigens and immune cells. Here, we identified the transmembrane ligand EphrinB2 and its receptor EphB4 as critical homeostatic regulators of collecting lymphatic vessel integrity. Conditional gene deletion in mice revealed that EphrinB2/EphB4 signalling is dispensable for blood endothelial barrier function, but required for stabilization of lymphatic endothelial cell (LEC) junctions in different organs of juvenile and adult mice. Studies in primary human LECs further showed that basal EphrinB2/EphB4 signalling controls junctional localisation of the tight junction protein CLDN5 and junction stability via Rac1/Rho-mediated regulation of cytoskeletal contractility. EphrinB2/EphB4 signalling therefore provides a potential therapeutic target to selectively modulate lymphatic vessel permeability and function.

Lymph vessels are thin walled tubes that, similar to blood vessels, carry white blood cells, fluids and waste. Unlike veins and arteries, however, lymph vessels do not carry red blood cells and their main function is to remove excess fluid from tissues. The cells that line vessels in the body are called endothelial cells, and they are tightly linked together by proteins to control what goes into and comes out of the vessels. The chemical, physical and mechanical signals that control the junctions between endothelial cells are often the same in different vessel types, but their effects can vary.

The endothelial cells of both blood and lymph vessels have two interacting proteins on their membrane known as EphrinB2 and its receptor, EphB4. When these two proteins interact, the EphB4 receptor becomes activated, which leads to changes in the junctions that link endothelial cells together. Frye et al. examined the role of EphrinB2 and EphB4 in the lymphatic system of mice. When either EphrinB2 or EphB4 are genetically removed in newborn or adult mice, lymph vessels become disrupted, but no significant effect is observed on blood vessels. The reason for the different responses in blood and lymph vessels is unknown.

The results further showed that lymphatic endothelial cells need EphB4 and EphrinB2 to be constantly interacting to maintain the integrity of the lymph vessels. Further examination of human endothelial cells grown in the laboratory revealed that this constant signalling controls the internal protein scaffold that determines a cell’s shape and integrity. Changes in the internal scaffold affect the organization of the junctions that link neighboring lymphatic endothelial cells together.

The loss of signalling between EphrinB2 and EphB4 in lymph vessels reflects the increase in vessel leakage seen in response to bacterial infections and in some genetic conditions such as lymphoedema. Finding ways to control the signalling between these two proteins could help treat these conditions by developing drugs that improve endothelial cell integrity in lymph vessels.

Understanding immunopathology of severe dengue: lessons learnt from sepsis

Endothelial dysfunction leading to vascular permeability and plasma leakage are characteristic features of severe dengue and sepsis. However, the mechanisms underlying these immune-pathologies remain unclear. The risk of severe dengue and sepsis development depend on patient-related and pathogen-related factors. Additionally, comorbidities increase the risk of severe disease and their incidence hampers correct diagnosis and treatments. To date, there is no efficient therapy to combat severe dengue and sepsis. Here, we discuss the differences and similarities between the pathogenesis of severe dengue and that of bacterial sepsis. We identify gaps in knowledge that need to be better understood in order to move towards the rational development and/or usage of therapeutic strategies to ameliorate severe dengue disease.

Autophagy protein ATG7 is a critical regulator of endothelial cell inflammation and permeability

Endothelial cell (EC) inflammation and permeability are critical pathogenic mechanisms in many inflammatory conditions including acute lung injury. In this study, we investigated the role of ATG7, an essential autophagy regulator with no autophagy-unrelated functions, in the mechanism of EC inflammation and permeability. Knockdown of ATG7 using si-RNA significantly attenuated thrombin-induced expression of proinflammatory molecules such as IL-6, MCP-1, ICAM-1 and VCAM-1. Mechanistic study implicated reduced NF-κB activity in the inhibition of EC inflammation in ATG7-silenced cells. Moreover, depletion of ATG7 markedly reduced the binding of RelA/p65 to DNA in the nucleus. Surprisingly, the thrombin-induced degradation of IκBα in the cytosol was not affected in ATG7-depleted cells, suggesting a defect in the translocation of released RelA/p65 to the nucleus in these cells. This is likely due to suppression of thrombin-induced phosphorylation and thereby inactivation of Cofilin1, an actin-depolymerizing protein, in ATG7-depleted cells. Actin stress fiber dynamics are required for thrombin-induced translocation of RelA/p65 to the nucleus, and indeed our results showed that ATG7 silencing inhibited this response via inactivation of Cofilin1. ATG7 silencing also reduced thrombin-mediated EC permeability by inhibiting the disassembly of VE-cadherin at adherens junctions. Together, these data uncover a novel function of ATG7 in mediating EC inflammation and permeability, and provide a mechanistic basis for the linkage between autophagy and EC dysfunction.

Coronin 1B Controls Endothelial Actin Dynamics at Cell-Cell Junctions and Is Required for Endothelial Network Assembly

Development and homeostasis of blood vessels critically depend on the regulation of endothelial cell–cell junctions. VE-cadherin (VEcad)-based cell–cell junctions are connected to the actin cytoskeleton and regulated by actin-binding proteins. Coronin 1B (Coro1B) is an actin binding protein that controls actin networks at classical lamellipodia. The role of Coro1B in endothelial cells (ECs) is not fully understood and investigated in this study. Here, we demonstrate that Coro1B is a novel component and regulator of cell–cell junctions in ECs. Immunofluorescence studies show that Coro1B colocalizes with VEcad at cell–cell junctions in monolayers of ECs. Live-cell imaging reveals that Coro1B is recruited to, and operated at actin-driven membrane protrusions at cell–cell junctions. Coro1B is recruited to cell–cell junctions via a mechanism that requires the relaxation of the actomyosin cytoskeleton. By analyzing the Coro1B interactome, we identify integrin-linked kinase (ILK) as new Coro1B-associated protein. Coro1B colocalizes with α-parvin, an interactor of ILK, at the leading edge of lamellipodia protrusions. Functional experiments reveal that depletion of Coro1B causes defects in the actin cytoskeleton and cell–cell junctions. Finally, in matrigel tube network assays, depletion of Coro1B results in reduced network complexity, tube number and tube length. Together, our findings point toward a critical role for Coro1B in the dynamic remodeling of endothelial cell–cell junctions and the assembly of endothelial networks.

New Insights Into Immunological Therapy for Retinal Disorders

In the twentieth century, a conspicuous lack of effective treatment strategies existed for managing several retinal disorders, including age-related macular degeneration; diabetic retinopathy (DR); retinopathy of prematurity (ROP); retinitis pigmentosa (RP); uveitis, including Behçet's disease; and vitreoretinal lymphoma (VRL). However, in the first decade of this century, advances in biomedicine have provided new treatment strategies in the field of ophthalmology, particularly biologics that target vascular endothelial growth factor or tumor necrosis factor (TNF)-α. Furthermore, clinical trials on gene therapy specifically for patients with autosomal recessive or X-linked RP have commenced. The overall survival rates of patients with VRL have improved, owing to earlier diagnoses and better treatment strategies. However, some unresolved problems remain such as primary or secondary non-response to biologics or chemotherapy, and the lack of adequate strategies for treating most RP patients. In this review, we provide an overview of the immunological mechanisms of the eye under normal conditions and in several retinal disorders, including uveitis, DR, ROP, RP, and VRL. In addition, we discuss recent studies that describe the inflammatory responses that occur during the course of these retinal disorders to provide new insights into their diagnosis and treatment.

Recent Advances and Impact of Chemotherapeutic and Antiangiogenic Nanoformulations for Combination Cancer Therapy

Traditional chemotherapy, along with antiangiogenesis drugs (combination cancer therapy), has shown reduced tumor recurrence and improved antitumor effects, as tumor growth and metastasis are often dependent on tumor vascularization. However, the effect of combination chemotherapy, including synergism and additive and even antagonism effects, depends on drug combinations in an optimized ratio. Hence, nanoformulations are ideal, demonstrating a great potential for the combination therapy of chemo-antiangiogenesis for cancer. The rationale for designing various nanocarriers for combination therapy is derived from organic (polymer, lipid), inorganic, or hybrid materials. In particular, hybrid nanocarriers that consist of more than one material construct provide flexibility for different modes of entrapment within the same carrier—e.g., physical adsorption, encapsulation, and chemical conjugation strategies. These multifunctional nanocarriers can thus be used to co-deliver chemo- and antiangiogenesis drugs with tunable drug release at target sites. Hence, this review attempts to survey the most recent advances in nanoformulations and their impact on cancer treatment in a combined regimen—i.e., conventional cytotoxic and antiangiogenesis agents. The mechanisms and site-specific co-delivery strategies are also discussed herein, along with future prospects.

The role of semaphorins in small vessels of the eye and brain

Small vessel diseases, such as ischemic retinopathy and cerebral small vessel disease (CSVD), are increasingly recognized in patients with diabetes, dementia and cerebrovascular disease. The mechanisms of small vessel diseases are poorly understood, but the latest studies suggest a role for semaphorins. Initially identified as axon guidance cues, semaphorins are mainly studied in neuronal morphogenesis, neural circuit assembly, and synapse assembly and refinement. In recent years, semaphorins have been found to play important roles in regulating vascular growth and development and in many pathophysiological processes, including atherosclerosis, angiogenesis after stroke and retinopathy. Growing evidence indicates that semaphorins affect the occurrence, perfusion and regression of both the macrovasculature and microvasculature by regulating the proliferation, apoptosis, migration, barrier function and inflammatory response of endothelial cells, vascular smooth muscle cells (VSMCs) and pericytes. In this review, we concentrate on the regulatory effects of semaphorins on the cell components of the vessel wall and their potential roles in microvascular diseases, especially in the retina and cerebral small vessel. Finally, we discuss potential molecular approaches in targeting semaphorins as therapies for microvascular disorders in the eye and brain.

Targeting miR-27a/VE-cadherin interactions rescues cerebral cavernous malformations in mice

Cerebral cavernous malformations (CCMs) are vascular lesions predominantly developing in the central nervous system (CNS), with no effective treatments other than surgery. Loss-of-function mutation in CCM1/krev interaction trapped 1 (KRIT1), CCM2, or CCM3/programmed cell death 10 (PDCD10) causes lesions that are characterized by abnormal vascular integrity. Vascular endothelial cadherin (VE-cadherin), a major regulator of endothelial cell (EC) junctional integrity is strongly disorganized in ECs lining the CCM lesions. We report here that microRNA-27a (miR-27a), a negative regulator of VE-cadherin, is elevated in ECs isolated from mouse brains developing early CCM lesions and in cultured ECs with CCM1 or CCM2 depletion. Furthermore, we show miR-27a acts downstream of kruppel-like factor (KLF)2 and KLF4, two known key transcription factors involved in CCM lesion development. Using CD5-2 (a target site blocker [TSB]) to prevent the miR-27a/VE-cadherin mRNA interaction, we present a potential therapy to increase VE-cadherin expression and thus rescue the abnormal vascular integrity. In CCM1- or CCM2-depleted ECs, CD5-2 reduces monolayer permeability, and in Ccm1 heterozygous mice, it restores dermal vessel barrier function. In a neonatal mouse model of CCM disease, CD5-2 normalizes vasculature and reduces vascular leakage in the lesions, inhibits the development of large lesions, and significantly reduces the size of established lesions in the hindbrain. Furthermore, CD5-2 limits the accumulation of inflammatory cells in the lesion area. Our work has established that VE-cadherin is a potential therapeutic target for normalization of the vasculature and highlights that targeting miR-27a/VE-cadherin interaction by CD5-2 is a potential novel therapy for the devastating disease, CCM.

Cerebral cavernous malformation (CCM) is a disease for which, hitherto, surgery has been the only option. This study shows that a potential therapeutic, CD5-2, inhibits lesion development and vascular leak in the brains of CCM neonatal mice by targeting the endothelial cell–specific adhesion molecule VE-cadherin and restoring the vascular integrity of CCM lesions.

Sulfated chitosan coated polylactide membrane enhanced osteogenic and vascularization differentiation in MC3T3-E1s and HUVECs co-cultures system

This study aimed to compare the effects of the two type chitosan derivatives, sulfated chitosan (SCS) and phosphorylated chitosan (PCS), coated on poly(d,l-lactide) (PDLLA) membrane via polydopamine, respectively, on vascularization and osteogenesis in vitro. Mouse preosteoblast cells (MC3T3-E1s) and human umbilical vein endothelial cells (HUVECs) were used as co-cultures system. The effects of two type membranes on calcium deposition, alkaline phosphatase (ALP) activity, vascularization related factors nitric oxide (NO) and angiogenic growth factor vascular endothelial growth factor (VEGF) were assessed. The changes of osteogenic and angiogenic related gene, and protein expression were evaluated too. In fact, SCS modified PDLLA membrane had the highest related gene and protein expression than other PDLLA membranes. Our results demonstrated that the SCS maybe a promising matrix for bone regeneration by co-cultures of ECs and OCs than PCS.

Flow Rate Affects Nanoparticle Uptake into Endothelial Cells

Nanoparticles are commonly administered through systemic injection, which exposes them to the dynamic environment of the bloodstream. Injected nanoparticles travel within the blood and experience a wide range of flow velocities that induce varying shear rates to the blood vessels. Endothelial cells line these vessels, and have been shown to uptake nanoparticles during circulation, but it is difficult to characterize the flow-dependence of this interaction in vivo. Here, a microfluidic system is developed to control the flow rates of nanoparticles as they interact with endothelial cells. Gold nanoparticle uptake into endothelial cells is quantified at varying flow rates, and it is found that increased flow rates lead to decreased nanoparticle uptake. Endothelial cells respond to increased flow shear with decreased ability to uptake the nanoparticles. If cells are sheared the same way, nanoparticle uptake decreases as their flow velocity increases. Modifying nanoparticle surfaces with endothelial-cell-binding ligands partially restores uptake to nonflow levels, suggesting that functionalizing nanoparticles to bind to endothelial cells enables nanoparticles to resist flow effects. In the future, this microfluidic system can be used to test other nanoparticle-endothelial cell interactions under flow. The results of these studies can guide the engineering of nanoparticles for in vivo medical applications.

Lymphatic Endothelial Cell Junctions: Molecular Regulation in Physiology and Diseases

Lymphatic endothelial cells (LECs) lining lymphatic vessels develop specialized cell-cell junctions that are crucial for the maintenance of vessel integrity and proper lymphatic vascular functions. Successful lymphatic drainage requires a division of labor between lymphatic capillaries that take up lymph via open "button-like" junctions, and collectors that transport lymph to veins, which have tight "zipper-like" junctions that prevent lymph leakage. In recent years, progress has been made in the understanding of these specialized junctions, as a result of the application of state-of-the-art imaging tools and novel transgenic animal models. In this review, we discuss lymphatic development and mechanisms governing junction remodeling between button and zipper-like states in LECs. Understanding lymphatic junction remodeling is important in order to unravel lymphatic drainage regulation in obesity and inflammatory diseases and may pave the way towards future novel therapeutic interventions.

Long non-coding RNA LASSIE regulates shear stress sensing and endothelial barrier function

Blood vessels are constantly exposed to shear stress, a biomechanical force generated by blood flow. Normal shear stress sensing and barrier function are crucial for vascular homeostasis and are controlled by adherens junctions (AJs). Here we show that AJs are stabilized by the shear stress-induced long non-coding RNA LASSIE (linc00520). Silencing of LASSIE in endothelial cells impairs cell survival, cell-cell contacts and cell alignment in the direction of flow. LASSIE associates with junction proteins (e.g. PECAM-1) and the intermediate filament protein nestin, as identified by RNA affinity purification. The AJs component VE-cadherin showed decreased stabilization, due to reduced interaction with nestin and the microtubule cytoskeleton in the absence of LASSIE. This study identifies LASSIE as link between nestin and VE-cadherin, and describes nestin as crucial component in the endothelial response to shear stress. Furthermore, this study indicates that LASSIE regulates barrier function by connecting AJs to the cytoskeleton.

Stanicek et al identify a shear stress-induced long non-coding RNA they name LASSIE, which stabilises junctions between endothelial cells through interactions with junctional and cytoskeletal proteins. This study provides insights into how a transcript that does not encode a protein controls endothelial response to forces associated with blood flow and endothelial barrier function.