Identification of common sequence motifs shared exclusively among selectively packed exosomal pathogenic microRNAs during rickettsial infections

We previously reported that microRNA (miR)23a and miR30b are selectively sorted into exosomes derived from rickettsia-infected endothelial cells (R-ECExos). Yet, the mechanism remains unknown. Cases of spotted fever rickettsioses have been increasing, and infections with these bacteria cause life-threatening diseases by targeting brain and lung tissues. Therefore, the goal of the present study is to further dissect the molecular mechanism underlying R-ECExos-induced barrier dysfunction of normal recipient microvascular endothelial cells (MECs), depending on their exosomal RNA cargos. Infected ticks transmit the rickettsiae to human hosts following a bite and injections of the bacteria into the skin. In the present study, we demonstrate that treatment with R-ECExos, which were derived from spotted fever group R parkeri infected human dermal MECs, induced disruptions of the paracellular adherens junctional protein VE-cadherin, and breached the paracellular barrier function in recipient pulmonary MECs (PMECs) in an exosomal RNA-dependent manner. We did not detect different levels of miRs in parent dermal MECs following rickettsial infections. However, we demonstrated that the microvasculopathy-relevant miR23a-27a-24 cluster and miR30b are selectively enriched in R-ECExos. Bioinformatic analysis revealed that common sequence motifs are shared exclusively among the exosomal, selectively-enriched miR23a cluster and miR30b at different levels. Taken together, these data warrant further functional identification and characterization of a monopartition, bipartition, or tripartition among ACA, UCA, and CAG motifs that guide recognition of microvasculopathy-relevant miR23a-27a-24 and miR30b, and subsequently results in their selective enrichments in R-ECExos.

The Role of Sphingolipids in Regulating Vascular Permeability in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a disease that causes scarring and fibrotic transformation of the lung parenchyma, resulting in the progressive loss of respiratory function and, often, death. Current treatments that target profibrotic factors can slow the rate of progression but are unable to ultimately stop it. In the past decade, many studies have shown that increased vascular permeability may be both a predictive and perpetuating factor in fibrogenesis. Consequently, there is a search for therapeutic targets to try and modulate vascular permeability in fibrotic lungs. One such class of targets that show great promise is sphingolipids. Sphingolipids are common in cell membranes and are increasingly recognized as critical to many cell signaling pathways, including those that affect the integrity of the vascular endothelial barrier. In this focused review we look at sphingolipids, particularly the sphingosine-1-phosphate (S1P) axis and its effects on vascular permeability, and how those effects may affect the pathogenesis of IPF. We further examine existing S1P modulators and their potential efficacy as therapeutics for IPF.

Significance of Pulmonary Endothelial Injury and the Role of Cyclooxygenase-2 and Prostanoid Signaling

The endothelium plays a key role in the dynamic balance of hemodynamic, humoral and inflammatory processes in the human body. Its central importance and the resulting therapeutic concepts are the subject of ongoing research efforts and form the basis for the treatment of numerous diseases. The pulmonary endothelium is an essential component for the gas exchange in humans. Pulmonary endothelial dysfunction has serious consequences for the oxygenation and the gas exchange in humans with the potential of consecutive multiple organ failure. Therefore, in this review, the dysfunction of the pulmonary endothel due to viral, bacterial, and fungal infections, ventilator-related injury, and aspiration is presented in a medical context. Selected aspects of the interaction of endothelial cells with primarily alveolar macrophages are reviewed in more detail. Elucidation of underlying causes and mechanisms of damage and repair may lead to new therapeutic approaches. Specific emphasis is placed on the processes leading to the induction of cyclooxygenase-2 and downstream prostanoid-based signaling pathways associated with this enzyme.

Circulating Exosomes from Alzheimer's Disease Suppress Vascular Endothelial-Cadherin Expression and Induce Barrier Dysfunction in Recipient Brain Microvascular Endothelial Cell

BACKGROUND

Blood-brain barrier (BBB) breakdown is a crucial aspect of Alzheimer's disease (AD) progression. Dysfunction in BBB is primarily caused by impaired tight junction and adherens junction proteins in brain microvascular endothelial cells (BMECs). The role of adherens junctions in AD-related BBB dysfunction remains unclear. Exosomes from senescent cells have unique characteristics and contribute to modulating the phenotype of recipient cells. However, it remains unknown if and how these exosomes cause BMEC dysfunction in AD.

OBJECTIVE

This study aimed to investigate the impact of AD circulating exosomes on brain endothelial dysfunction.

METHODS

Exosomes were isolated from sera of AD patients and age- and sex-matched cognitively normal controls using size-exclusion chromatography. The study measured the biomechanical nature of BMECs' endothelial barrier, the lateral binding forces between live BMECs. Paracellular expressions of the key adherens junction protein vascular endothelial (VE)-cadherin were visualized in BMEC cultures and a 3D BBB model using human BMECs and pericytes. VE-cadherin signals were also examined in brain tissues from AD patients and normal controls.

RESULTS

Circulating exosomes from AD patients reduced VE-cadherin expression levels and impaired barrier function in recipient BMECs. Immunostaining analysis demonstrated that AD exosomes damaged VE-cadherin integrity in a 3D microvascular tubule formation model. The study found that AD exosomes weakened BBB integrity depending on their RNA content. Additionally, diminished microvascular VE-cadherin expression was observed in AD brains compared to controls.

CONCLUSION

These findings highlight the significant role of circulating exosomes from AD patients in damaging adherens junctions of recipient BMECs, dependent on exosomal RNA.

Steen solution protects pulmonary microvascular endothelial cells and preserves endothelial barrier after lipopolysaccharide-induced injury

OBJECTIVES

Acute respiratory distress syndrome represents the devastating result of acute lung injury, with high mortality. Limited methods are available for rehabilitation of lungs affected by acute respiratory distress syndrome. Our laboratory has demonstrated rehabilitation of sepsis-injured lungs via normothermic ex vivo and in vivo perfusion with Steen solution (Steen). However, mechanisms responsible for the protective effects of Steen remain unclear. This study tests the hypothesis that Steen directly attenuates pulmonary endothelial barrier dysfunction and inflammation induced by lipopolysaccharide.

METHODS

Primary pulmonary microvascular endothelial cells were exposed to lipopolysaccharide for 4 hours and then recovered for 8 hours in complete media (Media), Steen, or Steen followed by complete media (Steen/Media). Oxidative stress, chemokines, permeability, interendothelial junction proteins, and toll-like receptor 4-mediated pathways were assessed in pulmonary microvascular endothelial cells using standard methods.

RESULTS

Lipopolysaccharide treatment of pulmonary microvascular endothelial cells and recovery in Media significantly induced reactive oxygen species, lipid peroxidation, expression of chemokines (eg, chemokine [C-X-C motif] ligand 1 and C-C motif chemokine ligand 2) and cell adhesion molecules (P-selectin, E-selectin, and vascular cell adhesion molecule 1), permeability, neutrophil transmigration, p38 mitogen-activated protein kinase and nuclear factor kappa B signaling, and decreased expression of tight and adherens junction proteins (zonula occludens-1, zonula occludens-2, and vascular endothelial-cadherin). All of these inflammatory pathways were significantly attenuated after recovery of pulmonary microvascular endothelial cells in Steen or Steen/Media.

CONCLUSIONS

Steen solution preserves pulmonary endothelial barrier function after lipopolysaccharide exposure by promoting an anti-inflammatory environment via attenuation of oxidative stress, toll-like receptor 4-mediated signaling, and conservation of interendothelial junctions. These protective mechanisms offer insight into the advancement of methods for in vivo lung perfusion with Steen for the treatment of severe acute respiratory distress syndrome.

Piceatannol alleviates glucolipotoxicity induced vascular barrier injury through inhibition of the ROS/NF-kappa B signaling pathway

Vascular barrier dysfunction is considered as the initial and critical event in atherosclerosis progression. Recent studies have revealed that treatment with piceatannol (PIC) alleviates both acute and chronic responses to vascular injury. We investigated whether PIC treatment would have beneficial effects on glucolipotoxicity-induced endothelial barrier dysfunction. Target proteins of PIC were identified from several online databases. Then, we confirmed the effect of PIC on endothelial barrier function. PIC treatment mitigated the impairment of endothelial cell motility, adhesion and migration ability associated with high glucose/lipid stimulation. PIC stabilized cytoskeletal reorganization and expression of cell cytoskeletal associated proteins GTPase. PIC reversed changes in critical vascular junction proteins and thus preserved endothelial barrier function and permeability. Finally, we confirmed that reducing of nuclear factor kappa B (NF-κB)/p65 activation and elimination of reactive oxygen species (ROS) were involved in the protective effect of PIC against glucolipotoxicity-induced vascular barrier injury. We identify PIC as a promising therapeutic strategy for glucolipotoxicity-induced endothelial barrier injury.

Exosomally Targeting microRNA23a Ameliorates Microvascular Endothelial Barrier Dysfunction Following Rickettsial Infection

Spotted fever group rickettsioses caused by Rickettsia (R) are devastating human infections, which mainly target microvascular endothelial cells (ECs) and can induce lethal EC barrier dysfunction in the brain and lungs. Our previous evidence reveals that exosomes (Exos) derived from rickettsial-infected ECs, namely R-ECExos, can induce disruption of the tight junctional (TJ) protein ZO-1 and barrier dysfunction of human normal recipient brain microvascular endothelial cells (BMECs). However, the underlying mechanism remains elusive. Given that we have observed that microRNA23a (miR23a), a negative regulator of endothelial ZO-1 mRNA, is selectively sorted into R-ECExos, the aim of the present study was to characterize the potential functional role of exosomal miR23a delivered by R-ECExos in normal recipient BMECs. We demonstrated that EC-derived Exos (ECExos) have the capacity to deliver oligonucleotide RNAs to normal recipient BMECs in an RNase-abundant environment. miR23a in ECExos impairs normal recipient BMEC barrier function, directly targeting TJ protein ZO-1 mRNAs. In separate studies using a traditional in vitro model and a novel single living-cell biomechanical assay, our group demonstrated that miR23a anti-sense oligonucleotide-enriched ECExos ameliorate R-ECExo-provoked recipient BMEC dysfunction in association with stabilization of ZO-1 in a dose-dependent manner. These results suggest that Exo-based therapy could potentially prove to be a promising strategy to improve vascular barrier function during bacterial infection and concomitant inflammation.

Adaptation of endothelial cells to shear stress under atheroprone conditions by modulating internalization of vascular endothelial cadherin and vinculin

Background

Endothelial cells play a pivotal role in cardiovascular physiology and pathology by providing a barrier to the bloodstream. In the current study, we investigated the phenotype and barrier function of endothelial cells in response to shear stress under pro-atherogenic conditions.

Methods

Endothelial cells were exposed to laminar shear stress (LSS) in a parallel-plate flow chamber containing oxidized low-density lipoprotein (oxLDL) in the perfusion solution, or remained static. We quantified the response of endothelial monolayers to LSS and oxLDL in terms of cell viability, barrier integrity, vascular endothelial cadherin (VE-cadherin) availability, focal adhesion (FA) remodeling, and monocyte-endothelial interactions.

Results

Our results showed that oxLDL stimulation and static conditions synergized to enhance endothelial barrier disruption. Under the same oxLDL challenge, the application of 25 dynes/cm² LSS on the endothelial monolayer decreased the passage of fluorescein isothiocyanate (FITC)-dextran by 37.79%, increased transendothelial electrical resistance (TEER) by 24.97% compared with static cells (P<0.05), which was accompanied by reduced intercellular gap formation, relatively solid cell-substrate adhesion. Compared with static cells, endothelial cells exposed to both laminar flow and oxLDL had less small FAs, less monocyte adhesion and transmigration, and alleviated overexpression of VCAM-1 and MCP-1. Meanwhile, the oxLDL-induced internalization of VE-cadherin and vinculin were also attenuated by laminar flow, and this change was more pronounced at LSS of 25 dynes/cm² than 5 dynes/cm².

Conclusions

Static conditions favor, whereas physiologically higher levels of LSS ameliorate endothelial barrier disruption under pro-atherogenic stress, which is related to the improved availability of VE-cadherin and vinculin on the cell surface.

Senescent HUVECs-secreted exosomes trigger endothelial barrier dysfunction in young endothelial cells

Accumulation of senescent endothelial cells can cause endothelium dysfunction which eventually leads to age-related vascular disorders. The senescent-associated secretory phenotype (SASP) cells secrete a plethora of soluble factors that negatively influence the surrounding tissue microenvironment. The present study sought to investigate the effects of exosomes, which are nano-sized extracellular vesicles known for intercellular communications secreted by SASP cells on young endothelial cells. Exosomes were isolated from the condition media of senescent human umbilical vein endothelial cells (HUVECs) and then confirmed by the detection of exosome specific CD63 and CD9 expressions, electron microscopy and acetylcholinesterase assay. The purified exosomes were used to treat young HUVECs. Exposure to exosomes repressed the expression of adherens junction proteins including vascular endothelial (VE)-cadherin and beta-catenin, decreased cell growth kinetics and impaired endothelial migration potential of young endothelial cells. These findings suggest that senescent HUVECs-secreted exosomes could disrupt barrier integrity that underpins endothelial barrier dysfunction in healthy young endothelial cells.

Ginsenoside Rg1 attenuates high glucose-induced endothelial barrier dysfunction in human umbilical vein endothelial cells by protecting the endothelial glycocalyx

Disruption of the endothelial barrier is essential for vascular complications associated with diabetes mellitus, and damage to the endothelial glycocalyx has been demonstrated to participate in this process. Ginsenoside Rg1 (Rg1), the major active component isolated from Panax notoginseng, is widely applied for the protection against vascular injury. The present study aimed to analyze the effect of high glucose on endothelial barrier function and its association with endothelial glycocalyx in human umbilical vein endothelial cells (HUVECs), and explore the potential benefits of Rg1 in protecting endothelial barrier function from high glucose-induced injury. The results indicated that high glucose induced a disorder of the endothelial glycocalyx and increased heparanase mRNA expression in HUVECs, which was reversed by Rg1 treatment. In addition, Rg1 treatment reduced transendothelial electrical resistance and transendothelial albumin passage after high-glucose stimulation. The present study suggested that high glucose caused a disruption in the endothelial glycocalyx and increased heparanase expression, which finally resulted in endothelial barrier dysfunction in HUVECs. Of note, Rg1 has a protective effect on high glucose-induced endothelial barrier dysfunction by attenuating the associated increase in heparanase expression.

Differential Mechanisms of Septic Human Pulmonary Microvascular Endothelial Cell Barrier Dysfunction Depending on the Presence of Neutrophils

Sepsis is characterized by injury of pulmonary microvascular endothelial cells (PMVEC) leading to barrier dysfunction. Multiple mechanisms promote septic PMVEC barrier dysfunction, including interaction with circulating leukocytes and PMVEC apoptotic death. Our previous work demonstrated a strong correlation between septic neutrophil (PMN)-dependent PMVEC apoptosis and pulmonary microvascular albumin leak in septic mice in vivo; however, this remains uncertain in human PMVEC. Thus, we hypothesize that human PMVEC apoptosis is required for loss of PMVEC barrier function under septic conditions in vitro. To assess this hypothesis, human PMVECs cultured alone or in coculture with PMN were stimulated with PBS or cytomix (equimolar interferon γ, tumor necrosis factor α, and interleukin 1β) in the absence or presence of a pan-caspase inhibitor, Q-VD, or specific caspase inhibitors. PMVEC barrier function was assessed by transendothelial electrical resistance (TEER), as well as fluoroisothiocyanate-labeled dextran and Evans blue-labeled albumin flux across PMVEC monolayers. PMVEC apoptosis was identified by (1) loss of cell membrane polarity (Annexin V), (2) caspase activation (FLICA), and (3) DNA fragmentation [terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)]. Septic stimulation of human PMVECs cultured alone resulted in loss of barrier function (decreased TEER and increased macromolecular flux) associated with increased apoptosis (increased Annexin V, FLICA, and TUNEL staining). In addition, treatment of septic PMVEC cultured alone with Q-VD decreased PMVEC apoptosis and prevented septic PMVEC barrier dysfunction. In septic PMN-PMVEC cocultures, there was greater trans-PMVEC macromolecular flux (both dextran and albumin) vs. PMVEC cultured alone. PMN presence also augmented septic PMVEC caspase activation (FLICA staining) vs. PMVEC cultured alone but did not affect septic PMVEC apoptosis. Importantly, pan-caspase inhibition (Q-VD treatment) completely attenuated septic PMN-dependent PMVEC barrier dysfunction. Moreover, inhibition of caspase 3, 8, or 9 in PMN-PMVEC cocultures also reduced septic PMVEC barrier dysfunction whereas inhibition of caspase 1 had no effect. Our data demonstrate that human PMVEC barrier dysfunction under septic conditions in vitro (cytomix stimulation) is clearly caspase-dependent, but the mechanism differs depending on the presence of PMN. In isolated PMVEC, apoptosis contributes to septic barrier dysfunction, whereas PMN presence enhances caspase-dependent septic PMVEC barrier dysfunction independently of PMVEC apoptosis.

Neutrophil-mediated vascular barrier injury: Role of neutrophil extracellular traps

Neutrophils play an essential role in host defense against infection or injury. While neutrophil activation is necessary for pathogen clearance and tissue repair, a hyperactive response can lead to tissue damage and microcirculatory disorders, a process involving complex neutrophil-endothelium cross talk. This review highlights recent research findings about neutrophil-mediated signaling and structural changes, including those induced by neutrophil extracellular traps, which ultimately lead to vascular barrier injury.

Endothelial tyrosine kinase receptor B prevents VE-cadherin cleavage and protects against atherosclerotic lesion development in ApoE-/- mice

Tyrosine kinase receptor B (TrkB) is a high-affinity receptor for brain-derived neurotrophic factor (BDNF). In addition to its nervous system functions, TrkB is also expressed in the aortic endothelium. However, the effects of endothelial TrkB signaling on atherosclerosis remained unknown. Immunofluorescence analysis revealed that TrkB expression is downregulated in the endothelium of atherosclerotic lesions from ApoE−/− mice compared with the atheroma-free aorta of WT mice. Endothelial TrkB knockdown led to increased lesion size, lipid deposition and inflammatory responses in the atherosclerotic lesions of the ApoE−/− mice compared with the control mice. Mechanistic studies showed that TrkB activation prevented VE-cadherin shedding by enhancing the interaction between vascular endothelial protein tyrosine phosphatase and VE-cadherin, maintaining VE-cadherin in a dephosphorylated state. Our data demonstrate that TrkB is an endothelial injury-response molecule in atherogenesis. Endothelial BDNF/TrkB signaling reduces VE-cadherin shedding and protects against atherosclerotic lesion development in ApoE−/− mice.

Myosin light chain kinase signaling in endothelial barrier dysfunction

Microvascular barrier dysfunction is a serious problem that occurs in many inflammatory conditions, including sepsis, trauma, ischemia-reperfusion injury, cardiovascular disease, and diabetes. Barrier dysfunction permits extravasation of serum components into the surrounding tissue, leading to edema formation and organ failure. The basis for microvascular barrier dysfunction is hyperpermeability at endothelial cell-cell junctions. Endothelial hyperpermeability is increased by actomyosin contractile activity in response to phosphorylation of myosin light chain by myosin light chain kinase (MLCK). MLCK-dependent endothelial hyperpermeability occurs in response to inflammatory mediators (e.g., activated neutrophils, thrombin, histamine, tumor necrosis factor alpha, etc.), through multiple cell signaling pathways and signaling molecules (e.g., Ca(++) , protein kinase C, Src kinase, nitric oxide synthase, etc.). Other signaling molecules protect against MLCK-dependent hyperpermeability (e.g., sphingosine-1-phosphate or cAMP). In addition, individual MLCK isoforms play specific roles in endothelial barrier dysfunction, suggesting that isoform-specific inhibitors could be useful for treating inflammatory disorders and preventing multiple organ failure. Because endothelial barrier dysfunction depends upon signaling through MLCK in many instances, MLCK-dependent signaling comprises multiple potential therapeutic targets for preventing edema formation and multiple organ failure. The following review is a discussion of MLCK-dependent mechanisms and cell signaling events that mediate endothelial hyperpermeability.