Opto-RhoGEFs, an optimized optogenetic toolbox to reversibly control Rho GTPase activity on a global to subcellular scale, enabling precise control over vascular endothelial barrier strength

The inner layer of blood vessels consists of endothelial cells, which form the physical barrier between blood and tissue. This vascular barrier is tightly regulated and is defined by cell-cell contacts through adherens and tight junctions. To investigate the signaling that regulates vascular barrier strength, we focused on Rho GTPases, regulators of the actin cytoskeleton and known to control junction integrity. To manipulate Rho GTPase signaling in a temporal and spatial manner we applied optogenetics. Guanine-nucleotide exchange factor (GEF) domains from ITSN1, TIAM1, and p63RhoGEF, activating Cdc42, Rac, and Rho, respectively, were integrated into the optogenetic recruitment tool improved light-induced dimer (iLID). This tool allows for Rho GTPase activation at the subcellular level in a reversible and non-invasive manner by recruiting a GEF to a specific area at the plasma membrane, The membrane tag of iLID was optimized and a HaloTag was applied to gain more flexibility for multiplex imaging. The resulting optogenetically recruitable RhoGEFs (Opto-RhoGEFs) were tested in an endothelial cell monolayer and demonstrated precise temporal control of vascular barrier strength by a cell-cell overlap-dependent, VE-cadherin-independent, mechanism. Furthermore, Opto-RhoGEFs enabled precise optogenetic control in endothelial cells over morphological features such as cell size, cell roundness, local extension, and cell contraction. In conclusion, we have optimized and applied the optogenetic iLID GEF recruitment tool, that is Opto-RhoGEFs, to study the role of Rho GTPases in the vascular barrier of the endothelium and found that membrane protrusions at the junction region can rapidly increase barrier integrity independent of VE-cadherin.

Size-Dependent Polymeric Nanoparticle Distribution in a Static versus Dynamic Microfluidic Blood Vessel Model: Implications for Nanoparticle-Based Drug Delivery

Nanoparticles (NPs) have been widely investigated in the nanomedicine field. One of the main challenges is to accurately predict the NP distribution and fate after administration. Microfluidic platforms acquired huge importance as tools to model the in vivo environment. In this study, we leveraged a microfluidic platform to produce FITC-labeled poly(lactide-co-glycolide)-block-poly(ethylene glycol) (PLGA-PEG) NPs with defined sizes of 30, 50, and 70 nm. The study aimed to compare the ability of NPs with differences of 20 nm in size to cross an endothelial barrier using static (Transwell inserts) and dynamic (microfluidic perfusion device) in vitro models. Our results evidence a size-dependent NP crossing in both models (30 > 50 > 70 nm) and highlight the bias deriving from the static model, which does not involve shear stresses. The permeation of each NP size was significantly higher in the static system than in the dynamic model at the earliest stages. However, it gradually decreased to levels comparable with those of the dynamic model. Overall, this work highlights clear differences in NP distribution over time in static versus dynamic conditions and distinct size-dependent patterns. These findings reinforce the need for accurate in vitro screening models that allow for more accurate predictions of in vivo performance.

Endothelial Cell SMAD6 Balances ACVRL1/Alk1 Function to Regulate Adherens Junctions and Hepatic Vascular Development

BMP signaling is critical to blood vessel formation and function, but how pathway components regulate vascular development is not well-understood. Here we find that inhibitory SMAD6 functions in endothelial cells to negatively regulate ALK1/ACVRL1-mediated responses, and it is required to prevent vessel dysmorphogenesis and hemorrhage in the embryonic liver vasculature. Reduced Alk1 gene dosage rescued embryonic hepatic hemorrhage and microvascular capillarization induced by Smad6 deletion in endothelial cells in vivo . At the cellular level, co-depletion of Smad6 and Alk1 rescued the destabilized junctions and impaired barrier function of endothelial cells depleted for SMAD6 alone. At the mechanistic level, blockade of actomyosin contractility or increased PI3K signaling rescued endothelial junction defects induced by SMAD6 loss. Thus, SMAD6 normally modulates ALK1 function in endothelial cells to regulate PI3K signaling and contractility, and SMAD6 loss increases signaling through ALK1 that disrupts endothelial junctions. ALK1 loss-of-function also disrupts vascular development and function, indicating that balanced ALK1 signaling is crucial for proper vascular development and identifying ALK1 as a "Goldilocks" pathway in vascular biology regulated by SMAD6.

Microbiota-Gut-Brain Axis in Neurological Disorders: From Leaky Barriers Microanatomical Changes to Biochemical Processes

BACKGROUND

The gastrointestinal tract and the central nervous system are distinct because of evident morpho-functional features. Nonetheless, evidence indicates that these systems are bidirectionally connected through the gut-brain axis, defined as the signaling that takes place between the gastrointestinal tract and central nervous system, which plays in concert with the gut microbiota, i.e., the myriad of microorganisms residing in the lumen of the human intestine. In particular, it has been described that gut microbiota abnormalities, referred to as dysbiosis, may affect both central nervous system development and physiology.

OBJECTIVE

Starting from the possible mechanisms through which gut microbiota variations were found to impact several central nervous system disorders, including Autism Spectrum Disorder and Alzheimer's Disease, we will focus on intriguing, although poorly investigated, aspects such as the epithelial and vascular barrier integrity. Indeed, several studies suggest a pivotal role of gut microbiota in maintaining the efficiency of both the intestinal barrier and blood-brain barrier. In particular, we report evidence indicating an impact of gut microbiota on intestinal barrier and blood-brain barrier homeostasis and discuss the differences and the similarities between the two barriers. Moreover, to stimulate further research, we review various tests and biochemical markers that can be used to assess intestinal and blood-brain barrier permeability.

CONCLUSION

We suggest that the evaluation of intestinal and blood-brain barrier permeability in neurological patients may not only help to better understand central nervous system disorders but also pave the way for finding new molecular targets to treat patients with neurological impairment.

Long-Term Oral Administration of Salidroside Alleviates Diabetic Retinopathy in db/db Mice

Diabetic retinopathy (DR), a microvascular complication of diabetes mellitus, is the leading cause of vision loss in the working-age population worldwide. Unfortunately, current clinical treatments cannot completely prevent the occurrence and development of DR. Salidroside (Sal) is a medicinal supplement that has antioxidative and cytoprotective properties. This study aimed to investigate the therapeutic effect of Sal on DR. Briefly, Sal treatment was applied to wide-type mice and db/db mice (a widely used diabetic mice) at 25 mg/kg by oral gavage once daily from 8 weeks to 20 weeks. Mice's bodyweight, blood glucose, total cholesterol, triglyceride, high density lipoprotein and low density lipoprotein were recorded and analyzed. Retinal trypsin digestion and evans blue dye assay were used to detect retinal microvessel changes and function. Retinal glutathione and malondialdehyde content measurements were applied to assess retinal oxidative stress. Full-length transcriptome analysis was performed to explore the underlying mechanisms of Sal protection. Our results found that Sal treatment could successfully relieve blood glucose and blood lipid abnormalities, and reduce retinal oxidative stress level in diabetic mice. Also, Sal treatment repaired the abnormal transcriptome caused by diabetes, alleviated the microvascular lesion of the fundus in diabetic mice, and protected retinal normal barrier function. This study enriches the indications of Sal in the treatment of diabetic diseases, providing practical research ideas for the comprehensive preventions and treatments of DR.

Baicalin Protects Vascular Tight Junctions in Piglets During Glaesserella parasuis Infection

Glaesserella parasuis (G. parasuis) can cause Glässer's disease and severely affect swine industry worldwide. This study is an attempt to address the issue of the capability of G. parasuis to damage the vascular barrier and the effects of baicalin on vascular tight junctions (TJ) in order to investigate the interactions between the pathogen and the porcine vascular endothelium. Piglets were challenged with G. parasuis and treated with or without baicalin. The expressions of vascular TJ genes were examined using RT-PCR. The distribution patterns of TJ proteins were detected by immunofluorescence. The involved signaling pathways were determined by Western blot assays on related proteins. G. parasuis can downregulate TJ expression and disrupt the distribution of TJ proteins. Baicalin can alleviate the downregulation of vascular TJ mRNA, maintain the distribution, and prevent the abnormalities of TJ. These results provide ample evidence that baicalin has the capacity to protect vascular TJ damaged by G. parasuis through inhibiting PKC and MLCK/MLC pathway activation. As a result, baicalin is a promising candidate for application as a natural agent for the prevention and control of G. parasuis infection.

eNOS-induced vascular barrier disruption in retinopathy by c-Src activation and tyrosine phosphorylation of VE-cadherin

Background:

Hypoxia and consequent production of vascular endothelial growth factor A (VEGFA) promote blood vessel leakiness and edema in ocular diseases. Anti-VEGFA therapeutics may aggravate hypoxia; therefore, therapy development is needed.

Methods:

Oxygen-induced retinopathy was used as a model to test the role of nitric oxide (NO) in pathological neovascularization and vessel permeability. Suppression of NO formation was achieved chemically using L-NMMA, or genetically, in endothelial NO synthase serine to alanine (S1176A) mutant mice.

Results:

Suppression of NO formation resulted in reduced retinal neoangiogenesis. Remaining vascular tufts exhibited reduced vascular leakage through stabilized endothelial adherens junctions, manifested as reduced phosphorylation of vascular endothelial (VE)-cadherin Y685 in a c-Src-dependent manner. Treatment with a single dose of L-NMMA in established retinopathy restored the vascular barrier and prevented leakage.

Conclusions:

We conclude that NO destabilizes adheren junctions, resulting in vascular hyperpermeability, by converging with the VEGFA/VEGFR2/c-Src/VE-cadherin pathway.

Funding:

This study was supported by the Swedish Cancer foundation (19 0119 Pj ), the Swedish Research Council (2020-01349), the Knut and Alice Wallenberg foundation (KAW 2020.0057) and a Fondation Leducq Transatlantic Network of Excellence Grant in Neurovascular Disease (17 CVD 03). KAW also supported LCW with a Wallenberg Scholar grant (2015.0275). WCS was supported by Grants R35 HL139945, P01 HL1070205, AHA MERIT Award. DV was supported by grants from the Deutsche Forschungsgemeinschaft, SFB1450, B03, and CRU342, P2.

Electroacupuncture Reduces Oocyte Number and Maintains Vascular Barrier Against Ovarian Hyperstimulation Syndrome by Regulating CD200

Ovarian hyperstimulation syndrome (OHSS) is a common complication caused by ovulatory stimulation therapy, which manifests as an increase in ovarian volume, an increase in the number of oocytes retrieved, and increased vascular permeability throughout the body and especially in ovarian tissue. In our previous study, we found that electroacupuncture (EA) could prevent the progression of OHSS, by mainly affecting ovary. However, the specific molecules and the mechanism of this process were still unknown. In order to explore the underlying mechanism, OHSS rat model was established and EA treatment was performed, which was followed by proteomic analysis of ovaries. Results showed a significant increase in the expression level of CD200 in the ovaries of OHSS group treated with EA than those of OHSS group. Clinical data showed that the level of CD200 in follicular fluid was negatively correlated with the number of oocytes retrieved and serum E2 level. Further in vitro experiments showed a concentration-dependent role of human chorionic gonadotropin (hCG) in reducing CD200 and CD200R levels, and increasing inflammatory cytokine levels in cultured KGN cells. In human umbilical vein endothelial cells (HUVECs), the vascular barrier function was improved by CM (cultural medium from KGN cell) which treated with CD200Fc (CD200R agonist). Meanwhile, the results of in vivo experiments indicated that EA reduced the number of ovarian corpora lutea, decreased inflammatory response, and improved the vascular barrier function by increasing the expression of CD200 and CD200R in rat ovaries. These findings suggest that EA treatment may reduce oocyte number and maintain vascular barrier against OHSS through ovarian anti-inflammatory response mediated by CD200. Therefore, this study is the first to identify CD200 as a main of EA in the ovary and elucidate the possible mechanism of EA on preventing and treating OHSS, which provide a scientific basis for CD200 as an effector and indicator in EA treatment.

The concept revolution of gut barrier: from epithelium to endothelium

Gut barrier controls the food tolerance as well as host defense against potential hazards. The gut epithelium has been extensively studied for its importance in the structure and function of gut barrier. Recently, a new concept of barrier, named gut vascular barrier (GVB) has been discovered in both mice and human. Subsequent studies identified the morphological characteristics of GVB, the involved signaling events and its association with clinical diseases. In current study, we will summarize recent breakthroughs of GVB, with particular attentions to the molecular basis of GVB dysfunction. We will perform bioinformatics analysis to compare the transcriptional profiles of endothelium between blood and lymphatic vessels, healthy and inflammatory bowel diseases (IBD), healthy and colorectal cancer in the absence or presence of liver metastasis. We will further discuss the significance of impaired GVB in associated diseases, including vascular diseases, IBD and cancer metastasis. Our study will provide insights into the new concept of gut barrier, and promote the development of new strategies toward the vascular endothelium in the management of various diseases.

Direct reprogramming of human smooth muscle and vascular endothelial cells reveals defects associated with aging and Hutchinson-Gilford progeria syndrome

Vascular dysfunctions are a common feature of multiple age-related diseases. However, modeling healthy and pathological aging of the human vasculature represents an unresolved experimental challenge. Here, we generated induced vascular endothelial cells (iVECs) and smooth muscle cells (iSMCs) by direct reprogramming of healthy human fibroblasts from donors of different ages and Hutchinson-Gilford Progeria Syndrome (HGPS) patients. iVECs induced from old donors revealed upregulation of GSTM1 and PALD1, genes linked to oxidative stress, inflammation and endothelial junction stability, as vascular aging markers. A functional assay performed on PALD1 KD VECs demonstrated a recovery in vascular permeability. We found that iSMCs from HGPS donors overexpressed bone morphogenetic protein (BMP)−4, which plays a key role in both vascular calcification and endothelial barrier damage observed in HGPS. Strikingly, BMP4 concentrations are higher in serum from HGPS vs. age-matched mice. Furthermore, targeting BMP4 with blocking antibody recovered the functionality of the vascular barrier in vitro, hence representing a potential future therapeutic strategy to limit cardiovascular dysfunction in HGPS. These results show that iVECs and iSMCs retain disease-related signatures, allowing modeling of vascular aging and HGPS in vitro.

Functions of Endothelial Cilia in the Regulation of Vascular Barriers

The vascular barrier between blood and tissues is a highly selective structure that is essential to maintain tissue homeostasis. Defects in the vascular barrier lead to a variety of cardiovascular diseases. The maintenance of vascular barriers is largely dependent on endothelial cells, but the precise mechanisms remain elusive. Recent studies reveal that primary cilia, microtubule-based structures that protrude from the surface of endothelial cells, play a critical role in the regulation of vascular barriers. Herein, we discuss recent advances on ciliary functions in the vascular barrier and suggest that ciliary signaling pathways might be targeted to modulate the vascular barrier.

Aging Suppresses Sphingosine-1-Phosphate Chaperone ApoM in Circulation Resulting in Maladaptive Organ Repair

Here, we show that the liver-derived apolipoprotein M (ApoM) protects the lung and kidney from pro-fibrotic insults and that this circulating factor is attenuated in aged mice. Aged mouse hepatocytes exhibit transcriptional suppression of ApoM. This leads to reduced sphingosine-1-phosphate (S1P) signaling via the S1P receptor 1 (S1PR1) in the vascular endothelial cells of lung and kidney. Suboptimal S1PR1 angiocrine signaling causes reduced resistance to injury-induced vascular leak and leads to organ fibrosis. Plasma transfusion from Apom transgenic mice but not Apom knockout mice blocked fibrosis in the lung. Similarly, infusion of recombinant therapeutics, ApoM-Fc fusion protein enhanced kidney and lung regeneration and attenuated fibrosis in aged mouse after injury. Furthermore, we identified that aging alters Sirtuin-1-hepatic nuclear factor 4α circuit in hepatocytes to downregulate ApoM. These data reveal an integrative organ adaptation that involves circulating S1P chaperone ApoM⁺ high density lipoprotein (HDL), which signals via endothelial niche S1PR1 to spur regeneration over fibrosis.

Apigenin and Ethaverine Hydrochloride Enhance Retinal Vascular Barrier In Vitro and In Vivo

Purpose

This study aims to develop an impedance-based drug screening platform that will help identify drugs that can enhance the vascular barrier function by stabilizing vascular endothelial cell junctions.

Methods

Changes in permeability of cultured human retinal microvascular endothelial cells (HRMECs) monolayer were monitored in real-time with the xCELLigence RTCA system. Using this platform, we performed a primary screen of 2100 known drugs and confirmed hits using two additional secondary permeability assays: the transwell permeability assay and the XPerT assay. The cellular and molecular mechanisms of action and in vivo therapeutic efficacy were also assessed.

Results

Eleven compounds blocked interleukin 1 beta (IL-1β) induced hyperpermeability in the primary screen. Two of 11 compounds, apigenin and ethaverine hydrochloride, reproducibly blocked multiple cytokines induced hyperpermeability. In addition to HRMEC monolayers, the two compounds stabilized three other types of primary vascular endothelial cell monolayers. Preliminary mechanistic studies suggest that the two compounds stabilize the endothelium by blocking ADP-ribosylation factor 6 (ARF6) activation, which results in enhanced VE-cadherin membrane localization. The two compounds showed in vivo efficacy in an animal model of retinal permeability.

Conclusions

We developed an impedance-based cellular phenotypic drug screening platform that can identify drugs that enhance vascular barrier function. We found apigenin and ethaverine hydrochloride stabilize endothelial cell junctions and enhance the vascular barrier by blocking ARF6 activation and increasing VE-cadherin membrane localization.

Translational Relevance

The drugs identified from the phenotypic screen would have potential therapeutic efficacy in retinal vascular diseases regardless of the underlying mechanisms that promote vascular leak.

Quantifying the effects of engineered nanomaterials on endothelial cell architecture and vascular barrier integrity using a cell pair model

Engineered nanomaterials (ENMs) are increasingly used in consumer products due to their unique physicochemical properties, but the specific hazards they pose to the structural and functional integrity of endothelial barriers remain elusive. When assessing the effects of ENMs on vascular barrier function, endothelial cell monolayers are commonly used as in vitro models. Monolayer models, however, do not offer a granular understanding of how the structure-function relationships between endothelial cells and tissues are disrupted due to ENM exposure. To address this issue, we developed a micropatterned endothelial cell pair model to quantitatively evaluate the effects of 10 ENMs (8 metal/metal oxides and 2 organic ENMs) on multiple cellular parameters and determine how these parameters correlate to changes in vascular barrier function. This minimalistic approach showed concerted changes in endothelial cell morphology, intercellular junction formation, and cytoskeletal organization due to ENM exposure, which were then quantified and compared to unexposed pairs using a "similarity scoring" method. Using the cell pair model, this study revealed dose-dependent changes in actin organization and adherens junction formation following exposure to representative ENMs (Ag, TiO2 and cellulose nanocrystals), which exhibited trends that correlate with changes in tissue permeability measured using an endothelial monolayer assay. Together, these results demonstrate that we can quantitatively evaluate changes in endothelial architecture emergent from nucleo-cytoskeletal network remodeling using micropatterned cell pairs. The endothelial pair model therefore presents potential applicability as a standardized assay for systematically screening ENMs and other test agents for their cellular-level structural effects on vascular barriers.

Kindlin-2 interacts with endothelial adherens junctions to support vascular barrier integrity

KEY POINTS

A reduction in Kindlin-2 levels in endothelial cells compromises vascular barrier function. Kindlin-2 is a previously unrecognized component of endothelial adherens junctions. By interacting directly and simultaneously with β- or γ-catenin and cortical actin filaments, Kindlin-2 stabilizes adherens junctions. The Kindlin-2 binding sites for β- and γ-catenin reside within its F1 and F3 subdomains. Although Kindlin-2 does not associate directly with tight junctions, its downregulation also destabilizes these junctions. Thus, impairment of both adherens and tight junctions may contribute to enhanced leakiness of vasculature in Kindlin-2^+/- mice.

ABSTRACT

Endothelial cells (EC) establish a physical barrier between the blood and surrounding tissue. Impairment of this barrier can occur during inflammation, ischaemia or sepsis and cause severe organ dysfunction. Kindlin-2, which is primarily recognized as a focal adhesion protein in EC, was not anticipated to have a role in vascular barrier. We tested the role of Kindlin-2 in regulating vascular integrity using several different approaches to decrease Kindlin-2 levels in EC. Reduced levels of Kindlin-2 in Kindlin-2^+/- mice aortic endothelial cells (MAECs) from these mice, and human umbilical ECs (HUVEC) treated with Kindlin-2 siRNA showed enhanced basal and platelet-activating factor (PAF) or lipopolysaccharide-stimulated vascular leakage compared to wild-type (WT) counterparts. PAF preferentially disrupted the Kindlin-2^+/- MAECs barrier to BSA and dextran and reduced transendothelial resistance compared to WT cells. Kindlin-2 co-localized and co-immunoprecipitated with vascular endothelial cadherin-based complexes, including β- and γ-catenin and actin, components of adherens junctions (AJ). Direct interaction of Kindlin-2 with β- and γ-catenin and actin was demonstrated in co-immunoprecipitation and surface plasmon resonance experiments. In thrombin-stimulated HUVECs, Kindlin-2 and cortical actin dissociated from stable AJs and redistributed to radial actin stress fibres of remodelling focal AJs. The β- and γ-catenin binding site resides within the F1 and F3 subdomains of Kindlin-2 but not the integrin binding site in F3. These results establish a previously unrecognized and vital role of Kindlin-2 with respect to maintaining the vascular barrier by linking Vascuar endothelial cadherin-based complexes to cortical actin and thereby stabilizing AJ.

Capillary collagen as the physical transport barrier in drug delivery to tumor microenvironment

The capillary wall is among the most important barriers that controls mass exchange between tumor microenvironment and systemic circulation. There are numerous studies on endothelial cells role in this mass exchange, but the role of capillary collagen of Type-IV in transport of small molecules and nanotherapeutics is less known. Our recent study revealed that the capillary wall collagen modulates the drug transport across the wall, and that it can be taken as a biophysical marker for drug transport. In our in vivo investigations with the 3LL and 4T1 tumors we noticed the differences in the collagen content in capillary walls. The imaging analysis and transport computational model of the capillary microenvironment showed that the penetration of doxorubicin (DOX) and pegylated liposomal doxorubicin (PLD) is substantially reduced by larger collagen content in the capillaries of the 3LL tumors. The results pointed to the importance of transport oncophysics, which opens a new avenue with respect to classical biology in understanding and improving drug delivery by nanotherapeutics, and aims to better explain the therapeutic resistance.

Role of high-mobility group box-1 protein in disruption of vascular barriers and regulation of leukocyte-endothelial interactions

High-mobility group box-1 protein (HMGB1) is a highly conserved non-histone DNA-binding protein present in the nuclei and cytoplasm of nearly all cell types. The results from recent research provide evidence that HMGB1 is secreted into the extracellular milieu and acts as a pro-inflammatory cytokine and exhibits angiogenic effects to fire the immunological response against the pathological effects. Recently, a great deal of evidence has indicated the critical importance of HMGB1 in mediating vascular barriers dysfunction by modulating the expression of adhesion molecules, such as intercellular adhesion molecule-1, vascular cell adhesion protein 1 and E-selectin on the surface of endothelial cells. Such process promotes the adhesion and migration of leukocytes across the endothelium, leading to breakdown of vascular barriers (blood-brain barrier and blood-retinal barrier) via modulating the expression, content, phosphorylation, and distribution of tight junction proteins. Therefore, here we give an abridged review to understand the mechanistic link between HMGB1 and vascular barriers dysfunction, including interaction with cell-surface receptors and intracellular signaling pathways.

Endothelial permeability and VE-cadherin: a wacky comradeship

The endothelium forms a selective semi-permeable barrier controlling bidirectional transfer between blood vessel and irrigated tissues. This crucial function relies on the dynamic architecture of endothelial cell-cell junctions, and in particular, VE-cadherin-mediated contacts. VE-cadherin indeed chiefly organizes the opening and closing of the endothelial barrier, and is central in permeability changes. In this review, the way VE-cadherin-based contacts are formed and maintained is first presented, including molecular traits of its expression, partners, and signaling. In a second part, the mechanisms by which VE-cadherin adhesion can be disrupted, leading to cell-cell junction weakening and endothelial permeability increase, are described. Overall, the molecular basis for VE-cadherin control of the endothelial barrier function is of high interest for biomedical research, as vascular leakage is observed in many pathological conditions and human diseases.