Caveolin-1-eNOS signaling promotes p190RhoGAP-A nitration and endothelial permeability

Inflammatory lung injury is associated with endothelial cell mitochondrial fission and requires the nitration of RhoA and cytoskeletal remodeling

Higher levels of extracellular nicotinamide phosphoribosyltransferase (eNAMPT), a TLR4 agonist, are associated with poor clinical outcomes in sepsis-induced acute lung injury (ALI). Little is known regarding the mechanisms by which eNAMPT is involved in ALI. Our recent work has identified a crucial role for mitochondrial dysfunction in ALI. Thus, this study aimed to determine if eNAMPT-mediated inflammatory injury is associated with the loss of mitochondrial function. Our data show that eNAMPT disrupted mitochondrial bioenergetics. This was associated with cytoskeleton remodeling and the loss of endothelial barrier integrity. These changes were associated with enhanced mitochondrial fission and blocked when Rho-kinase (ROCK) was inhibited. The increases in mitochondrial fission were also associated with the nitration-mediated activation of the small GTPase activator of ROCK, RhoA. Blocking RhoA nitration decreased eNAMPT-mediated mitochondrial fission and endothelial barrier dysfunction. The increase in fission was linked to a RhoA-ROCK mediated increase in Drp1 (dynamin-related protein 1) at serine(S)616. Another TLR4 agonist, lipopolysaccharide (LPS), also increased mitochondrial fission in a Drp1 and RhoA-ROCK-dependent manner. To validate our findings in vivo, we challenged C57BL/6 mice with eNAMPT in the presence and absence of the Drp1 inhibitor, Mdivi-1. Mdivi-1 treatment protected against eNAMPT-induced lung inflammation, edema, and lung injury. These studies demonstrate that mitochondrial fission-dependent disruption of mitochondrial function is essential in TLR4-mediated inflammatory lung injury and identify a key role for RhoA-ROCK signaling. Reducing mitochondrial fission could be a potential therapeutic strategy to improve ARDS outcomes.

ARAP3 protects from excessive formylated peptide-induced microvascular leakage by acting on endothelial cells and neutrophils

Vascular permeability is temporarily heightened during inflammation, but excessive inflammation-associated microvascular leakage can be detrimental, as evidenced in the inflamed lung. Formylated peptides regulate vascular leakage indirectly via formylated peptide receptor-1 (FPR1)-mediated recruitment and activation of neutrophils. Here we identify how the GTPase-activating protein ARAP3 protects against formylated peptide-induced microvascular permeability via endothelial cells and neutrophils. In vitro, Arap3-/- endothelial monolayers were characterised by enhanced formylated peptide-induced permeability due to upregulated endothelial FPR1 and enhanced vascular endothelial cadherin internalisation. In vivo, enhanced inflammation-associated microvascular leakage was observed in Arap3-/- mice. Leakage of plasma protein into the lungs of Arap3-/- mice increased within hours of formylated peptide administration. Adoptive transfer experiments indicated this was dependent upon ARAP3 deficiency in both immune and non-immune cells. Bronchoalveolar lavages of formylated peptide-challenged Arap3-/- mice contained neutrophil extracellular traps (NETs). Pharmacological inhibition of NET formation abrogated excessive microvascular leakage, indicating a critical function of NETs in this context. The observation that Arap3-/- mice developed more severe influenza suggests these findings are pertinent to pathological situations characterised by abundant formylated peptides. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Caveolin-1 protects endothelial cells from extensive expansion of transcellular tunnel by stiffening the plasma membrane

Large transcellular pores elicited by bacterial mono-ADP-ribosyltransferase (mART) exotoxins inhibiting the small RhoA GTPase compromise the endothelial barrier. Recent advances in biophysical modeling point toward membrane tension and bending rigidity as the minimal set of mechanical parameters determining the nucleation and maximal size of transendothelial cell macroaperture (TEM) tunnels induced by bacterial RhoA-targeting mART exotoxins. We report that cellular depletion of caveolin-1, the membrane-embedded building block of caveolae, and depletion of cavin-1, the master regulator of caveolae invaginations, increase the number of TEMs per cell. The enhanced occurrence of TEM nucleation events correlates with a reduction in cell height due to the increase in cell spreading and decrease in cell volume, which, together with the disruption of RhoA-driven F-actin meshwork, favor membrane apposition for TEM nucleation. Strikingly, caveolin-1 specifically controls the opening speed of TEMs, leading to their dramatic 5.4-fold larger widening. Consistent with the increase in TEM density and width in siCAV1 cells, we record a higher lethality in CAV1 KO mice subjected to a catalytically active mART exotoxin targeting RhoA during staphylococcal bloodstream infection. Combined theoretical modeling with independent biophysical measurements of plasma membrane bending rigidity points toward a specific contribution of caveolin-1 to membrane stiffening in addition to the role of cavin-1/caveolin-1-dependent caveolae in the control of membrane tension homeostasis.

Plasma TNFRSF11B as a New Predictive Inflammatory Marker of Sepsis-ARDS with Endothelial Dysfunction

Inflammation plays an important role in the development of sepsis-acute respiratory distress syndrome (ARDS). Olink inflammation-related biomarker panels were used to analyze the levels of 92 inflammation-related proteins in plasma with sepsis-ARDS (n = 25) and healthy subjects (n = 25). There were significant differences in 64 inflammatory factors, including TNFRSF11B in sepsis-ARDS, which was significantly higher than that in controls. Functional analysis showed that TNFRSF11B was closely focused on signal transduction, immune response, and inflammatory response. The TNFRSF11B level in sepsis-ARDS plasma, LPS-induced mice, and LPS-stimulated HUVECs significantly increased. The highest plasma concentration of TNFRSF11B in patients with sepsis-ARDS was 10-20 ng/mL, and 10 ng/mL was selected to stimulate HUVECs. Western blot results demonstrated that the levels of syndecan-1, claudin-5, VE-cadherin, occludin, aquaporin-1, and caveolin-1 in TNFRSF11B-stimulated HUVECs decreased, whereas that of connexin-43 increased in TNFRSF11B-stimulated HUVECs. To the best of the authors' knowledge, this study was the first to reveal elevated TNFRSF11B in sepsis-ARDS associated with vascular endothelial dysfunction. In summary, TNFRSF11B may be a new potential predictive and diagnostic biomarker for vascular endothelium damage in sepsis-ARDS.

The Muscarinic Acetylcholine M2 Receptor-Induced Nitration of p190A by eNOS Increases RhoA Activity in Cardiac Myocytes

p190RhoGAP, which exists in two paralogs, p190RhoGAP-A (p190A) and p190RhoGAP-B (p190B), is a GTPase activating protein (GAP) contributing to the regulation of the cellular activity of RhoGTPases. Recent data showed that M2 muscarinic acetylcholine receptor (M2R) stimulation in neonatal rat cardiac myocytes (NRCM) induces the binding of p190RhoGAP to the long isoform of the regulator of G protein signaling 3 (RGS3L). This complex formation alters the substrate preference of p190RhoGAP from RhoA to Rac1. By analyzing carbachol-stimulated GAP activity, we show herein that p190A, but not p190B, alters its substrate preference in NRCM. Based on data that the RhoGAP activity of p190A in endothelial cells is diminished upon nitration by endothelial nitric oxide synthase (eNOS)-derived peroxynitrite, we studied whether carbachol-induced NO/peroxynitrite formation contributes to the carbachol-induced RhoA activation in NRCM. Interestingly, the carbachol-induced RhoA activation in NRCM was suppressed by the eNOS-preferring inhibitor L-NIO as well as the non-selective NOS inhibitor L-NAME. Using L-NIO, we firstly verified the carbachol-induced NO production concurrent with eNOS activation and, secondly, the carbachol-induced nitration of p190A in NRCM. By co-immunoprecipitation, the carbachol-induced complex formation of eNOS, p190A, RGS3L and caveolin-3 was detected. We thus conclude that the NO production by M2R-induced eNOS activation in caveolae in NRCM is required for the nitration of p190A, leading to the binding to RGS3L and the change in substrate preference from RhoA to Rac1. In line with this interpretation, the disruption of caveolae in NRCM by methyl-β-cyclodextrin suppressed carbachol-induced RhoA activation in NRCM to a similar extent as the inhibition of NO production.

Targeting EB3-IP3R3 Interface with Cognate Peptide Protects from Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a lung disease characterized by acute onset of noncardiogenic pulmonary edema, hypoxemia, and respiratory insufficiency. The current treatment for ARDS is mainly supportive in nature, providing a critical need for targeted pharmacological management. We addressed this medical problem by developing a pharmacological treatment for pulmonary vascular leakage, a culprit of alveolar damage and lung inflammation. Our novel therapeutic target is the microtubule accessory factor EB3 (end binding protein 3), which contributes to pulmonary vascular leakage by amplifying pathological calcium signaling in endothelial cells in response to inflammatory stimuli. EB3 interacts with IP3R3 (inositol 1,4,5-trisphosphate receptor 3) and orchestrates calcium release from endoplasmic reticulum stores. Here, we designed and tested the therapeutic benefits of a 14-aa peptide named CIPRI (cognate IP3 receptor inhibitor), which disrupted EB3-IP3R3 interaction in vitro and in lungs of mice challenged with endotoxin. Treatment with CIPRI or depletion of IP3R3 in lung microvascular endothelial monolayers mitigated calcium release from endoplasmic reticulum stores and prevented a disassembly of vascular endothelial cadherin junctions in response to the proinflammatory mediator α-thrombin. Furthermore, intravenous administration of CIPRI in mice mitigated inflammation-induced lung injury, blocked pulmonary microvascular leakage, prevented activation of NFAT (nuclear factor of activated T cells) signaling, and reduced production of proinflammatory cytokines in the lung tissue. CIPRI also improved survival of mice from endotoxemia and polymicrobial sepsis. Together, these data demonstrate that targeting EB3-IP3R3 interaction with a cognate peptide is a promising strategy to address hyperpermeability of microvessels in inflammatory lung diseases.

Endothelial Transcytosis in Acute Lung Injury: Emerging Mechanisms and Therapeutic Approaches

Acute Lung Injury (ALI) is characterized by widespread inflammation which in its severe form, Acute Respiratory Distress Syndrome (ARDS), leads to compromise in respiration causing hypoxemia and death in a substantial number of affected individuals. Loss of endothelial barrier integrity, pneumocyte necrosis, and circulating leukocyte recruitment into the injured lung are recognized mechanisms that contribute to the progression of ALI/ARDS. Additionally, damage to the pulmonary microvasculature by Gram-negative and positive bacteria or viruses (e.g., Escherichia coli, SARS-Cov-2) leads to increased protein and fluid permeability and interstitial edema, further impairing lung function. While most of the vascular leakage is attributed to loss of inter-endothelial junctional integrity, studies in animal models suggest that transendothelial transport of protein through caveolar vesicles, known as transcytosis, occurs in the early phase of ALI/ARDS. Here, we discuss the role of transcytosis in healthy and injured endothelium and highlight recent studies that have contributed to our understanding of the process during ALI/ARDS. We also cover potential approaches that utilize caveolar transport to deliver therapeutics to the lungs which may prevent further injury or improve recovery.

srGAP2 deactivates RhoA to control the duration of thrombin-mediated endothelial permeability

The endothelial barrier is a tightly regulated gateway in the transport of material between circulation and the tissues. Inflammatory mediators such as thrombin are able to open paracellular spaces in the endothelial monolayer to allow the extravasation of plasma proteins and leukocytes. Here we show that the protein SLIT-ROBO Rho GTPase-activating protein 2 (srGAP2) plays a critical role in regulating the extent of thrombin-mediated opening. We show that srGAP2 is not required for normal barrier function in resting endothelial cells, but that depletion of srGAP2 significantly increases the magnitude and duration of junctional opening in response to thrombin. We show that srGAP2 acts to switch off RhoA signaling after the contraction phase of thrombin-induced permeability, allowing respreading of cells and reformation of the barrier. srGAP2 is also required for effective restoration of the barrier after treatment with two other vasoactive agents that active RhoA - TNFα and angiotensin II. Taken together, we show that srGAP2 has a general function in controlling RhoA signaling in endothelial permeability, acting to limit the degree and duration of opening, by triggering the switch from endothelial cell contraction to respreading.

A computational model of mutual antagonism in the mechano-signaling network of RhoA and nitric oxide

BACKGROUND

RhoA is a master regulator of cytoskeletal contractility, while nitric oxide (NO) is a master regulator of relaxation, e.g., vasodilation. There are multiple forms of cross-talk between the RhoA/ROCK pathway and the eNOS/NO/cGMP pathway, but previous work has not studied their interplay at a systems level. Literature review suggests that the majority of their cross-talk interactions are antagonistic, which motivates us to ask whether the RhoA and NO pathways exhibit mutual antagonism in vitro, and if so, to seek the theoretical implications of their mutual antagonism.

RESULTS

Experiments found mutual antagonism between RhoA and NO in epithelial cells. Since mutual antagonism is a common motif for bistability, we sought to explore through theoretical simulations whether the RhoA-NO network is capable of bistability. Qualitative modeling showed that there are parameters that can cause bistable switching in the RhoA-NO network, and that the robustness of the bistability would be increased by positive feedback between RhoA and mechanical tension.

CONCLUSIONS

We conclude that the RhoA-NO bistability is robust enough in silico to warrant the investment of further experimental testing. Tension-dependent bistability has the potential to create sharp concentration gradients, which could contribute to the localization and self-organization of signaling domains during cytoskeletal remodeling and cell migration.

Critical Role of Mortalin/GRP75 in Endothelial Cell Dysfunction Associated with Acute Lung Injury

Mortalin/GRP75 (glucose regulated protein 75), a member of heat shock protein 70 family of chaperones, is involved in several cellular processes including proliferation and signaling, and plays a pivotal role in cancer and neurodegenerative disorders. In this study, we sought to determine the role of mortalin/GRP75 in mediating vascular inflammation and permeability linked to the pathogenesis of acute lung injury (ALI). In an aerosolized bacterial lipopolysaccharide inhalation mouse model of ALI, we found that administration of mortalin/GRP75 inhibitor mean kinetic temperature-077, both prophylactically and therapeutically, protected against polymorphonuclear leukocytes influx into alveolar airspaces, microvascular leakage, and expression of pro-inflammatory mediators such as interleukin-1β, E-selectin, and tumor necrosis factor TNFα. Consistent with this, thrombin-induced inflammation in cultured human endothelial cells (EC) was also protected upon before and after treatment with mean kinetic temperature-077. Similar to pharmacological inhibition of mortalin/GRP75, siRNA-mediated depletion of mortalin/GRP75 also blocked thrombin-induced expression of proinflammatory mediators such as intercellular adhesion molecule-1 and vascular adhesion molecule-1. Mechanistic analysis in EC revealed that inactivation of mortalin/GRP75 interfered with the binding of the liberated NF-κB to the DNA, thereby leading to inhibition of downstream expression of adhesion molecules, cytokines, and chemokines. Importantly, thrombin-induced Ca signaling and EC permeability were also prevented upon mortalin/GRP75 inactivation/depletion. Thus, this study provides evidence for a novel role of mortalin/GRP75 in mediating EC inflammation and permeability associated with ALI.

The mitochondrial thioredoxin reductase system (TrxR2) in vascular endothelium controls peroxynitrite levels and tissue integrity

The mitochondrial thioredoxin/peroxiredoxin system encompasses NADPH, thioredoxin reductase 2 (TrxR2), thioredoxin 2, and peroxiredoxins 3 and 5 (Prx3 and Prx5) and is crucial to regulate cell redox homeostasis via the efficient catabolism of peroxides (TrxR2 and Trxrd2 refer to the mitochondrial thioredoxin reductase protein and gene, respectively). Here, we report that endothelial TrxR2 controls both the steady-state concentration of peroxynitrite, the product of the reaction of superoxide radical and nitric oxide, and the integrity of the vascular system. Mice with endothelial deletion of the Trxrd2 gene develop increased vascular stiffness and hypertrophy of the vascular wall. Furthermore, they suffer from renal abnormalities, including thickening of the Bowman's capsule, glomerulosclerosis, and functional alterations. Mechanistically, we show that loss of Trxrd2 results in enhanced peroxynitrite steady-state levels in both vascular endothelial cells and vessels by using a highly sensitive redox probe, fluorescein-boronate. High steady-state peroxynitrite levels were further found to coincide with elevated protein tyrosine nitration in renal tissue and a substantial change of the redox state of Prx3 toward the oxidized protein, even though glutaredoxin 2 (Grx2) expression increased in parallel. Additional studies using a mitochondria-specific fluorescence probe (MitoPY1) in vessels revealed that enhanced peroxynitrite levels are indeed generated in mitochondria. Treatment with Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin [Mn(III)TMPyP], a peroxynitrite-decomposition catalyst, blunted intravascular formation of peroxynitrite. Our data provide compelling evidence for a yet-unrecognized role of TrxR2 in balancing the nitric oxide/peroxynitrite ratio in endothelial cells in vivo and thus establish a link between enhanced mitochondrial peroxynitrite and disruption of vascular integrity.

Regulation of Endothelial and Vascular Functions by Carbon Monoxide via Crosstalk With Nitric Oxide

Carbon monoxide (CO), generated by heme oxygenase (HO), has been considered a signaling molecule in both the cardiovascular and central nervous systems. The biological function of the HO/CO axis is mostly related to other gaseous molecules, including nitric oxide (NO), which is synthesized by nitric oxide synthase (NOS). Healthy blood vessels are essential for the maintenance of tissue homeostasis and whole-body metabolism; however, decreased or impaired vascular function is a high-risk factor of cardiovascular and neuronal diseases. Accumulating evidence supports that the interplay between CO and NO plays a crucial role in vascular homeostasis and regeneration by improving endothelial function. Moreover, endothelial cells communicate with neighboring cells, such as, smooth muscle cells, immune cells, pericytes, and astrocytes in the periphery and neuronal vascular systems. Endogenous CO could mediate the cell-cell communication and improve the physiological functions of the cardiovascular and neurovascular systems via crosstalk with NO. Thus, a forward, positive feedback circuit between HO/CO and NOS/NO pathways can maintain cardiovascular and neurovascular homeostasis and prevent various human diseases. We discussed the crucial role of CO-NO crosstalk in the cardiovascular and neurovascular systems.

Nateglinide Exerts Neuroprotective Effects via Downregulation of HIF-1α/TIM-3 Inflammatory Pathway and Promotion of Caveolin-1 Expression in the Rat's Hippocampus Subjected to Focal Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is a major cause of death and motor disabilities all over the world. It is a muti-factorial disorder associated with inflammatory, apoptotic, and oxidative responses. Nateglinide (NAT), an insulinotropic agent used for the treatment of type 2 diabetes mellitus, recently showed potential anti-inflammatory and anti-apoptotic effects. The aim of our study was to elucidate the unique neuroprotective role of NAT in the middle cerebral artery occlusion (MCAO)-induced stroke in rats. Fifty-six male rats were divided to 4 groups (n = 14 in each group): the sham-operated group, sham receiving NAT (50 mg/kg/day, p.o) group, ischemia/reperfusion (IR) group, and IR receiving NAT group (50 mg/kg/day, p.o). MCAO caused potent deficits in motor and behavioral functions of the rats. Significant increase in inflammatory and apoptotic biomarkers has been observed in rats' hippocampi. Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathway was significantly stimulated causing activation of series inflammatory biomarkers ending up neuro-inflammatory milieu. Pretreatment with NAT preserved rats' normal behavioral and motor functions. Moreover, NAT opposed the expression of hypoxia-inducible factor-1α (HIF-1α) resulting in downregulation of more inflammatory mediators namely, NF-κB, tumor necrosis factor-β (TNF-β), and the anti-survival gene PMAIP-1. NAT stimulated caveolin-1 (Cav-1) which prevented expression of oxidative biomarkers, nitric oxide (NO), and myeloperoxidase (MPO) and hamper the activation of apoptotic biomarker caspase-3. In conclusion, our work postulated that NAT exhibited its neuroprotective effects in rats with ischemic stroke via attenuation of different unique oxidative, apoptotic, and inflammatory pathways.

Human plasminogen-derived N-acetyl-Arg-Leu-Tyr-Glu antagonizes VEGFR-2 to prevent blood-retinal barrier breakdown in diabetic mice

Targeting the vascular endothelial growth factor (VEGF)/its receptor-2 (VEGFR-2) system has become a mainstay of treatment for many human diseases, including retinal diseases. We examined the therapeutic effect of recently developed N-acetylated Arg-Leu-Tyr-Glu (Ac-RLYE), a human plasminogen kringle-5 domain-derived VEGFR-2 antagonists, on the pathogenesis of diabetic retinopathy. Ac-RLYE inhibited VEGF-A-mediated VEGFR-2 activation and endothelial nitric oxide synthase (eNOS)-derived NO production in the retinas of diabetic mice. In addition, Ac-RLYE prevented the disruption of adherens and tight junctions and vascular leakage by inhibiting S-nitrosylation of β-catenin and tyrosine nitration of p190RhoGAP in the retinal vasculature of diabetic mice. Peptide treatment preserved the pericyte coverage of retinal capillaries by upregulating angiopoietin-2. These results suggest that Ac-RLYE potentially prevents blood-retinal barrier breakdown and vascular leakage by antagonizing VEGFR-2; Ac-RLYE can be used as a potential therapeutic drug for the treatment of diabetic retinopathy.

PV1 in Caveolae Controls Lung Endothelial Permeability

Caveolae are prominent plasmalemmal invaginations in endothelial cells, especially in the lung vasculature, which comprises a vast surface area. PV1 (plasmalemmal vesicle-associated protein-1), a 60-kD glycoprotein expressed in endothelial cells, is essential for generating spoke-like diaphragmatic structures that span the neck region of endothelial caveolae. However, their role in caveolae-mediated uptake and endothelial-barrier function is unknown. Here, we generated mice with endothelial cell-specific deletion of PV1 through tamoxifen-induced Cdh5.Cre.ERT2 (endothelial-specific vascular cadherin.Cre.estrogen receptor 2)-mediated excision of the floxed PV1 allele. We observed that loss of PV1 specifically in endothelial cells increased lung vascular permeability of fluid and protein, indicating that PV1 is required for maintenance of lung vascular-barrier integrity. Endothelial-specific PV1 deletion also increased caveolae-mediated uptake of tracer albumin compared with controls, promoted Au-albumin accumulation in the bulb of caveolae, and induced caveolar swelling. In addition, we observed the progressive loss of plasma proteins from the circulation and reduced arterial pressure resulting from transudation of water and protein as well as edema formation in multiple tissues, including lungs. These changes seen after endothelial-specific PV1 deletion occurred in the absence of disruption of endothelial junctions. We demonstrated that exposure of wild-type mice to endotoxin, which is known to cause acute lung injury and increase protein permeability, also significantly reduced PV1 protein expression. We conclude that the key function of PV1 is to regulate lung endothelial permeability through its ability to restrict the entry of plasma proteins such as albumin into caveolae and their transport through the endothelial barrier.

Post-translational modifications of S1PR1 and endothelial barrier regulation

Sphingosine-1-phosphate receptor-1 (S1PR1), a G-protein coupled receptor that is expressed in endothelium and activated upon ligation by the bioactive lipid sphingosine-1-phosphate (S1P), is an important vascular-barrier protective mechanism at the level of adherens junctions (AJ). Loss of endothelial barrier function is a central factor in the pathogenesis of various inflammatory conditions characterized by protein-rich lung edema formation, such as acute respiratory distress syndrome (ARDS). While several S1PR1 agonists are available, the challenge of arresting the progression of protein-rich edema formation remains to be met. In this review, we discuss the role of S1PRs, especially S1PR1, in regulating endothelial barrier function. We review recent findings showing that replenishment of the pool of cell-surface S1PR1 may be crucial to the effectiveness of S1P in repairing the endothelial barrier. In this context, we discuss the S1P generating machinery and mechanisms that regulate S1PR1 at the cell surface and their impact on endothelial barrier function.

Caveolin-1 upregulates Fut8 expression by activating the Wnt/β-catenin pathway to enhance HCC cell proliferative and invasive ability

Caveolin-1 (Cav-1), a critical structural protein of caveolae, plays an oncogenic role by participating in abnormal protein glycosylation in hepatocellular carcinoma (HCC). However, the mechanism by which Cav-1 regulates glycosylation and glycosyltransferase expression has yet to be fully defined. Here, we show that Cav-1 promotes the expression of α-1,6-fucosyltransferase (Fut8), which catalyzes the transfer of GDP-fucose to the core structure of the N-sugar chain. In this study, we show that the mouse HCC cell line, Hepa1-6, which has low Fut8 transcriptional and protein levels, also lacks Cav-1 expression, whereas the mouse HCC cell line, Hca-F, has strong Fut8 expression and high transcriptional and protein levels of Cav-1. Subsequently, Cav-1 overexpression in Hepa1-6 was found to activate Wnt/β-catenin signaling, which leads to downstream binding of the T cell factor/lymphoid enhancer factor to the Fut8 promoter region for activation of its transcription. In contrast, knockdown of Cav-1 expression in Hca-F caused the Wnt/β-catenin pathway to be significantly inhibited, which attenuates the expression of Fut8. We further show that Cav-1-induced upregulation of Fut8 expression enhanced proliferation and invasion by mouse HCC cells in vitro. Our current findings provide molecular evidence that Cav-1 plays an important role in regulating glycosyltransferase expression and may participate in abnormal glycosylation, which mediates the proliferation and invasion of HCC.

Structural and Functional Remodeling of the Brain Vasculature Following Stroke

Maintenance of cerebral blood vessel integrity and regulation of cerebral blood flow ensure proper brain function. The adult human brain represents only a small portion of the body mass, yet about a quarter of the cardiac output is dedicated to energy consumption by brain cells at rest. Due to a low capacity to store energy, brain health is heavily reliant on a steady supply of oxygen and nutrients from the bloodstream, and is thus particularly vulnerable to stroke. Stroke is a leading cause of disability and mortality worldwide. By transiently or permanently limiting tissue perfusion, stroke alters vascular integrity and function, compromising brain homeostasis and leading to widespread consequences from early-onset motor deficits to long-term cognitive decline. While numerous lines of investigation have been undertaken to develop new pharmacological therapies for stroke, only few advances have been made and most clinical trials have failed. Overall, our understanding of the acute and chronic vascular responses to stroke is insufficient, yet a better comprehension of cerebrovascular remodeling following stroke is an essential prerequisite for developing novel therapeutic options. In this review, we present a comprehensive update on post-stroke cerebrovascular remodeling, an important and growing field in neuroscience, by discussing cellular and molecular mechanisms involved, sex differences, limitations of preclinical research design and future directions.

Preeclampsia serum increases CAV1 expression and cell permeability of human renal glomerular endothelial cells via down-regulating miR-199a-5p, miR-199b-5p, miR-204

INTRODUCTION

To gain insight into mechanisms of preeclampsia (PE)-dependent proteinuria, this study focused on whether preeclampsia serum (PES) could induce hyperpermeability in human renal glomerular endothelial cells (HRGECs) via the miRNAs-Caveolin-1 (CAV-1)-dependent pathway.

METHODS

Bioinformatics approach was used to identify miRNAs targeting CAV1. Normal pregnancy serum (NPS) and severe PES were used to treat HRGECs monolayer to demonstrate if PES could induce the expression of identified miRNAs. A luciferase reporter assay was used to determine whether CAV1 was a direct target of miR-199a-5p, miR-199b-5p, and miR-204. The relationship between the expression of miR-199a-5p, miR-199b-5p, miR-204, and CAV1 in HRGECs was determined using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot. The gain-of-function and loss-of-function experiments were performed on HRGECs to investigate the effects of miR-199a-5p, miR-199b-5p, miR-204 on HRGECs permeability.

RESULTS

We identified that CAV1 3'UTR has putative binding sites for miR-199a-5p, miR-199b-5p, and miR-204, whereas miR-199a-5p does not appear to be a direct regulator of CAV1. We detected that PE serum downregulated the expression of miR-199a-5p, miR-199b-5p and miR-204, increased expression of CAV1 and increased cell monolayer permeability in HRGECs. The level of CAV1 and permeability decreased when miR-199b-5p or miR-204, but not miR-199a-5p, were overexpressed.

DISCUSSION

miR-199b-5p and miR-204 may play a role in PES-induced increasing permeability of HRGECs by regulating CAV1 expression.

miR-144-mediated Inhibition of ROCK1 Protects against LPS-induced Lung Endothelial Hyperpermeability

Dysfunctional endothelial cell (EC) barrier and increased lung vascular permeability is a cardinal feature of acute lung injury and sepsis that may result in a pathophysiological condition characterized by alveolar flooding, pulmonary edema, and subsequent hypoxemia. In lung ECs, activation of Rho-associated kinase-1 (ROCK1) phosphorylates myosin light chain (MLC)-associated phosphatase at its inhibitory site, which favors phosphorylation of MLC, stress fiber formation, and hyperpermeability during acute lung injury. The role of microRNA-144 (miR-144) has been well investigated in many human diseases, including cardiac ischemia/reperfusion-induced injury, lung cancer, and lung viral infection; however, its role in pulmonary EC barrier regulation remains obscure. Here, we investigated the miR-144-mediated mechanism in the protection of endothelial barrier function in an LPS-induced lung injury model. By using transendothelial electrical resistance and transwell permeability assay to examine in vitro permeability and immunofluorescence microscopy to determine barrier integrity, we showed that ectopic expression of miR-144 effectively blocked lung EC barrier disruption and hyperpermeability in response to proinflammatory agents. Furthermore, using a gain-and-loss-of-function strategy, overexpression of miR-144 significantly decreased ROCK1 expression. Concomitantly, miR-144 inhibits ROCK1-mediated phosphorylation of MLC phosphatase^Thr853 and thus phosphorylation of MLC^Thr18/Ser19 to counteract stress fiber formation in LPS-activated EC. Finally, in LPS-challenged mice, intranasal delivery of miR-144 mimic via liposomes attenuated endotoxemia-induced increases in lung wet/dry ratio, vascular permeability, and inflammation. In conclusion, these data suggest that miR-144-attenuated activation of inflammatory ROCK1/MLC pathway in vascular ECs is a promising therapeutic strategy to counter inflammatory lung injury.

Lung Endothelial Transcytosis

Transcytosis of macromolecules through lung endothelial cells is the primary route of transport from the vascular compartment into the interstitial space. Endothelial transcytosis is mostly a caveolae-dependent process that combines receptor-mediated endocytosis, vesicle trafficking via actin-cytoskeletal remodeling, and SNARE protein directed vesicle fusion and exocytosis. Herein, we review the current literature on caveolae-mediated endocytosis, the role of actin cytoskeleton in caveolae stabilization at the plasma membrane, actin remodeling during vesicle trafficking, and exocytosis of caveolar vesicles. Next, we provide a concise summary of experimental methods employed to assess transcytosis. Finally, we review evidence that transcytosis contributes to the pathogenesis of acute lung injury. © 2020 American Physiological Society. Compr Physiol 10:491-508, 2020.

Passing the Vascular Barrier: Endothelial Signaling Processes Controlling Extravasation

A central function of the vascular endothelium is to serve as a barrier between the blood and the surrounding tissue of the body. At the same time, solutes and cells have to pass the endothelium to leave or to enter the bloodstream to maintain homeostasis. Under pathological conditions, for example, inflammation, permeability for fluid and cells is largely increased in the affected area, thereby facilitating host defense. To appropriately function as a regulated permeability filter, the endothelium uses various mechanisms to allow solutes and cells to pass the endothelial layer. These include transcellular and paracellular pathways of which the latter requires remodeling of intercellular junctions for its regulation. This review provides an overview on endothelial barrier regulation and focuses on the endothelial signaling mechanisms controlling the opening and closing of paracellular pathways for solutes and cells such as leukocytes and metastasizing tumor cells.

Characterization of Kcnk3-Mutated Rat, a Novel Model of Pulmonary Hypertension

RATIONALE

Pulmonary arterial hypertension is a severe lethal cardiopulmonary disease. Loss of function mutations in KCNK3 (potassium channel subfamily K member 3) gene, which encodes an outward rectifier K⁺ channel, have been identified in pulmonary arterial hypertension patients.

OBJECTIVE

We have demonstrated that KCNK3 dysfunction is common to heritable and nonheritable pulmonary arterial hypertension and to experimental pulmonary hypertension (PH). Finally, KCNK3 is not functional in mouse pulmonary vasculature.

METHODS AND RESULTS

Using CRISPR/Cas9 technology, we generated a 94 bp out of frame deletion in exon 1 of Kcnk3 gene and characterized these rats at the electrophysiological, echocardiographic, hemodynamic, morphological, cellular, and molecular levels to decipher the cellular mechanisms associated with loss of KCNK3. Using patch-clamp technique, we validated our transgenic strategy by demonstrating the absence of KCNK3 current in freshly isolated pulmonary arterial smooth muscle cells from Kcnk3-mutated rats. At 4 months of age, echocardiographic parameters revealed shortening of the pulmonary artery acceleration time associated with elevation of the right ventricular systolic pressure. Kcnk3-mutated rats developed more severe PH than wild-type rats after monocrotaline exposure or chronic hypoxia exposure. Kcnk3-mutation induced a lung distal neomuscularization and perivascular extracellular matrix activation. Lungs of Kcnk3-mutated rats were characterized by overactivation of ERK1/2 (extracellular signal-regulated kinase1-/2), AKT (protein kinase B), SRC, and overexpression of HIF1-α (hypoxia-inducible factor-1 α), survivin, and VWF (Von Willebrand factor). Linked with plasma membrane depolarization, reduced endothelial-NOS expression and desensitization of endothelial-derived hyperpolarizing factor, Kcnk3-mutated rats presented predisposition to vasoconstriction of pulmonary arteries and a severe loss of sildenafil-induced pulmonary arteries relaxation. Moreover, we showed strong alteration of right ventricular cardiomyocyte excitability. Finally, Kcnk3-mutated rats developed age-dependent PH associated with low serum-albumin concentration.

CONCLUSIONS

We established the first Kcnk3-mutated rat model of PH. Our results confirm that KCNK3 loss of function is a key event in pulmonary arterial hypertension pathogenesis. This model presents new opportunities for understanding the initiating mechanisms of PH and testing biologically relevant therapeutic molecules in the context of PH.

Caveolin-1 promotes invasion and metastasis by upregulating Pofut1 expression in mouse hepatocellular carcinoma

Caveolin-1 (Cav-1) is an important structural protein of caveolae and plays an oncogene-like role by influencing protein glycosylation in hepatocellular carcinoma (HCC) cells. However, the mechanism by which Cav-1 promotes invasion and metastasis capacity has not been completely clarified. In this study, we demonstrate that Pofut1 is a fucosyltransferase induced by Cav-1. Mouse Hepa1-6 HCC cells lacking Cav-1 expression exhibited low transcription levels of Pofut1, whereas strong Pofut1 expression was found in high-metastasis-potential Hca-F cells with high levels of Cav-1. Cav-1 activated MAPK signaling and promoted phosphorylation of the transcription factors CREB, Sp1, HNF4A and c-Myc, which bound to the Pofut1 promoter region to induce its transcription. As Notch signaling receptors can be modified with O-fucose by Pofut1, we further showed that Cav-1-induced upregulation of Pofut1 expression activated the Notch pathway and thus enhanced invasion and metastasis by mouse HCC cells in vitro and in vivo. Collectively, our findings reveal a novel mechanism by which Cav-1 promotes tumor metastasis by upregulating expression of Pofut1, suggesting that Cav-1 may function as a new biomarker for HCC.

RAF dimers control vascular permeability and cytoskeletal rearrangements at endothelial cell-cell junctions

The endothelium functions as a semipermeable barrier regulating fluid homeostasis, nutrient, and gas supply to the tissue. Endothelial permeability is increased in several pathological conditions including inflammation and tumors; despite its clinical relevance, however, there are no specific therapies preventing vascular leakage. Here, we show that endothelial cell-restricted ablation of BRAF, a kinase frequently activated in cancer, prevents vascular leaking as well metastatic spread. BRAF regulates endothelial permeability by promoting the cytoskeletal rearrangements necessary for the remodeling of VE-Cadherin-containing endothelial cell-cell junctions and the formation of intercellular gaps. BRAF kinase activity and the ability to form complexes with RAS/RAP1 and dimers with its paralog RAF1 are required for proper permeability control, achieved mechanistically by modulating the interaction between RAF1 and the RHO effector ROKα. Thus, RAF dimerization impinges on RHO pathways to regulate cytoskeletal rearrangements, junctional plasticity, and endothelial permeability. The data advocate the development of RAF dimerization inhibitors, which would combine tumor cell autonomous effect with stabilization of the vasculature and antimetastatic spread.

Role of p120 Catenin in Epac1-Induced Chronic Postsurgical Pain in Rats

Chronic postsurgical pain (CPSP) is a chronic pain state that is difficult to be treated clinically. A series of complicated changes have been produced from nociceptive stimulation to the occurrence and development of postsurgical pain. Many mechanisms remain unclear. In order to study the role of intercellular gap junctions in inducing inflammatory microenvironment at the beginning of nociceptor after operation, the model of skin/muscle incision and retraction (SMIR) was established. We observed the changes of the expression of exchange proteins directly activated by cAMP-1 (Epac1) and p120 catenin (p120), the quantities of macrophages and endothelial cells, vascular endothelial permeability, and mechanical withdrawal threshold (MWT). It was found that macrophages and endothelial cells were functionally coupled through Epac1-p120. Adhesive linkage disorder remodeled the chronic, inflammatory, and eutrophic microenvironment at the beginning of nociceptor after operation through macrophages, endothelial cells, and endothelial paracellular pathways. It might be an early event and a key step in peripheral sensitization of CPSP. The expression of p120 in muscle tissue around the incision might become a prognostic marker for the conversion of acute postsurgical pain into CPSP. Targeted intervention of Epac1-p120 might be a clinical strategy for inhibiting the conversion of acute postsurgical pain into CPSP.

Graft-versus-host disease propagation depends on increased intestinal epithelial tight junction permeability

Graft-versus-host disease (GVHD) is a complication of hematopoietic stem cell transplantation (HSCT) that affects multiple organs. GVHD-associated intestinal damage can be separated into two distinct phases, initiation and propagation, which correspond to conditioning-induced damage and effector T cell activation and infiltration, respectively. Substantial evidence indicates that intestinal damage induced by pretransplant conditioning is a key driver of GVHD initiation. Here, we aimed to determine the impact of dysregulated intestinal permeability on the subsequent GVHD propagation phase. The initiation phase of GVHD was unchanged in mice lacking long MLCK (MLCK210), an established regulator of epithelial tight junction permeability. However, MLCK210-deficient mice were protected from sustained barrier loss and exhibited limited GVHD propagation, as indicated by reduced histopathology, fewer CD8+ effector T cells in the gut, and improved overall survival. Consistent with these findings, intestinal epithelial MLCK210 expression and enzymatic activity were similarly increased in human and mouse GVHD biopsies. Intestinal epithelial barrier loss mediated by MLCK210 is therefore a key driver of the GVHD propagation. These data suggest that inhibition of MLCK210-dependent barrier regulation may be an effective approach to limiting GVHD progression.

Impact of Metabolic Syndrome on Neuroinflammation and the Blood-Brain Barrier

Metabolic syndrome, which includes diabetes and obesity, is one of the most widespread medical conditions. It induces systemic inflammation, causing far reaching effects on the body that are still being uncovered. Neuropathologies triggered by metabolic syndrome often result from increased permeability of the blood-brain-barrier (BBB). The BBB, a system designed to restrict entry of toxins, immune cells, and pathogens to the brain, is vital for proper neuronal function. Local and systemic inflammation induced by obesity or type 2 diabetes mellitus can cause BBB breakdown, decreased removal of waste, and increased infiltration of immune cells. This leads to disruption of glial and neuronal cells, causing hormonal dysregulation, increased immune sensitivity, or cognitive impairment depending on the affected brain region. Inflammatory effects of metabolic syndrome have been linked to neurodegenerative diseases. In this review, we discuss the effects of obesity and diabetes-induced inflammation on the BBB, the roles played by leptin and insulin resistance, as well as BBB changes occurring at the molecular level. We explore signaling pathways including VEGF, HIFs, PKC, Rho/ROCK, eNOS, and miRNAs. Finally, we discuss the broader implications of neural inflammation, including its connection to Alzheimer's disease, multiple sclerosis, and the gut microbiome.

N-cadherin signaling via Trio assembles adherens junctions to restrict endothelial permeability

This work describes a role for endothelial N-cadherin in the regulation of endothelial permeability in the brain and lung. N-cadherin adhesions formed between endothelial cells and pericytes increase the abundance of VE-cadherin at adherens junctions through the RhoGEF Trio-dependent activation of RhoA and Rac1.

Vascular endothelial (VE)–cadherin forms homotypic adherens junctions (AJs) in the endothelium, whereas N-cadherin forms heterotypic adhesion between endothelial cells and surrounding vascular smooth muscle cells and pericytes. Here we addressed the question whether both cadherin adhesion complexes communicate through intracellular signaling and contribute to the integrity of the endothelial barrier. We demonstrated that deletion of N-cadherin (Cdh2) in either endothelial cells or pericytes increases junctional endothelial permeability in lung and brain secondary to reduced accumulation of VE-cadherin at AJs. N-cadherin functions by increasing the rate of VE-cadherin recruitment to AJs and induces the assembly of VE-cadherin junctions. We identified the dual Rac1/RhoA Rho guanine nucleotide exchange factor (GEF) Trio as a critical component of the N-cadherin adhesion complex, which activates both Rac1 and RhoA signaling pathways at AJs. Trio GEF1-mediated Rac1 activation induces the recruitment of VE-cadherin to AJs, whereas Trio GEF2-mediated RhoA activation increases intracellular tension and reinforces Rac1 activation to promote assembly of VE-cadherin junctions and thereby establish the characteristic restrictive endothelial barrier.

Dysfunction of Cerebrovascular Endothelial Cells: Prelude to Vascular Dementia

Vascular dementia (VaD) is the second most common type of dementia after Alzheimer's disease (AD), characterized by progressive cognitive impairment, memory loss, and thinking or speech problems. VaD is usually caused by cerebrovascular disease, during which, cerebrovascular endothelial cells (CECs) are vulnerable. CEC dysfunction occurs before the onset of VaD and can eventually lead to dysregulation of cerebral blood flow and blood-brain barrier damage, followed by the activation of glia and inflammatory environment in the brain. White matter, neuronal axons, and synapses are compromised in this process, leading to cognitive impairment. The present review summarizes the mechanisms underlying CEC impairment during hypoperfusion and pathological role of CECs in VaD. Through the comprehensive examination and summarization, endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) signaling pathway, Ras homolog gene family member A (RhoA) signaling pathway, and CEC-derived caveolin-1 (CAV-1) are proposed to serve as targets of new drugs for the treatment of VaD.

Targeting RNS/caveolin-1/MMP signaling cascades to protect against cerebral ischemia-reperfusion injuries: potential application for drug discovery

Reactive nitrogen species (RNS) play important roles in mediating cerebral ischemia-reperfusion injury. RNS activate multiple signaling pathways and participate in different cellular events in cerebral ischemia-reperfusion injury. Recent studies have indicated that caveolin-1 and matrix metalloproteinase (MMP) are important signaling molecules in the pathological process of ischemic brain injury. During cerebral ischemia-reperfusion, the production of nitric oxide (NO) and peroxynitrite (ONOO⁻), two representative RNS, down-regulates the expression of caveolin-1 (Cav-1) and, in turn, further activates nitric oxide synthase (NOS) to promote RNS generation. The increased RNS further induce MMP activation and mediate disruption of the blood-brain barrier (BBB), aggravating the brain damage in cerebral ischemia-reperfusion injury. Therefore, the feedback interaction among RNS/Cav-1/MMPs provides an amplified mechanism for aggravating ischemic brain damage during cerebral ischemia-reperfusion injury. Targeting the RNS/Cav-1/MMP pathway could be a promising therapeutic strategy for protecting against cerebral ischemia-reperfusion injury. In this mini-review article, we highlight the important role of the RNS/Cav-1/MMP signaling cascades in ischemic stroke injury and review the current progress of studies seeking therapeutic compounds targeting the RNS/Cav-1/MMP signaling cascades to attenuate cerebral ischemia-reperfusion injury. Several representative natural compounds, including calycosin-7-O-β-D-glucoside, baicalin, Momordica charantia polysaccharide (MCP), chlorogenic acid, lutein and lycopene, have shown potential for targeting the RNS/Cav-1/MMP signaling pathway to protect the brain in ischemic stroke. Therefore, the RNS/Cav-1/MMP pathway is an important therapeutic target in ischemic stroke treatment.

Lipopolysaccharide impairs permeability of pulmonary microvascular endothelial cells via Connexin40

The endotoxin lipopolysaccharide (LPS)-induced pulmonary endothelial barrier disruption is a key pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, the molecular mechanisms underlying LPS-impaired permeability of pulmonary microvascular endothelial cells (PMVECs) are not fully understood. Gap junctions, particularly Connexin40 (Cx40), are necessary for the maintenance of normal vascular function. In this study, we for the first time investigated the role of Cx40 in LPS-impaired permeability of PMVECs and provided potential therapeutic approaches based on mechanistic findings of Cx40 regulation by LPS stimuli. Rat PMVECs were isolated, cultured and identified with cell morphology, specific markers, ultrastructural characteristics and functional tests. Western blot analysis demonstrated that Cx40 is the major connexin highly expressed in PMVECs. Furthermore, by inhibiting Cx40 in a time-dependent manner, LPS impaired gap junction function and induced permeability injury of PMVECs. The key role of Cx40 decline in mediating detrimental effects of LPS was further confirmed in rescue experiments through Cx40 overexpression. Mechanistically, LPS stress on PMVECs inhibited the protein kinase C (PKC) pathway, which may synergize with the inflammatory nuclear factor kappaB (NFκB) signaling activation in suppressing Cx40 expression level and phosphorylation. Moreover, through pharmacological PKC activation or NFκB inhibition, Cx40 activity in PMVECs could be restored, leading to maintained barrier function under LPS stress. Our findings uncover a previously unrecognized role of Cx40 and its regulatory mechanisms in impaired endothelial integrity under endotoxin and inflammation, shedding light on intervention approaches to improve pulmonary endothelial barrier function in ALI and ARDS.

Nitric oxide donor [Ru(terpy)(bdq)NO]3+ induces uncoupling and phosphorylation of endothelial nitric oxide synthase promoting oxidant production

[Ru(terpy)(bdq)NO]3+ (TERPY) is a nitric oxide (NO) donor that promotes relaxation of the mesenteric artery and aorta in rats. We sought to investigate whether it acts as both an NO donor and endothelial NO synthase (eNOS) activator, as shown previously for nitroglycerin. Human umbilical vein endothelial cells (HUVECs) and human embryonic kidney 293 cells transfected with empty vector (HEK) or eNOS cDNA (HEK-eNOS) were treated with TERPY (1µM) for different lengths of time. eNOS expression, dimerization, and Ser1177 phosphorylation, caveolin-1 (Cav-1) oligomerization, Cav-1 Tyr14 phosphorylation were evaluated by Western blotting. Studies also assessed the production of reactive oxygen/nitrogen species (ROS/RNS) in HUVECs and HEK-eNOS cells. In HEK cells devoid of eNOS, TERPY released NO without additional stimulus indicating that is an NO donor. Moreover, in HEK-eNOS cells, TERPY-induced NO production that was blocked by L-NAME. In addition, TERPY increased ROS and ONOO- production which were blocked by more than 80% by BH4 (essential eNOS co-factor) and eNOS siRNA. These results suggest that TERPY-induced ROS and ONOO- production were originated from eNOS. HUVECs stimulated with TERPY showed increased eNOS Ser1177 and Cav-1 Tyr14 phosphorylation, and decreased eNOS dimerization, Cav-1 oligomerization, and Cav-1/eNOS interaction after 20min. It suggests that TERPY induces eNOS hyperactivation and uncoupling by disrupting Cav-1/eNOS interaction and depleting BH4. Endothelium-dependent vasodilation in response to NO donor TERPY is associated with eNOS activation and uncoupling, and thereby appears to be mediated, at least in part, via eNOS-dependent ROS/RNS production.

Angiogenic effects of apigenin on endothelial cells after hypoxia-reoxygenation via the caveolin-1 pathway

In the present study, we aimed to elucidate whether apigenin contributes to the induction of angiogenesis and the related mechanisms in cell hypoxia-reoxygenation injury. The role of apigenin was examined in human umbilical vein endothelial cell (HUVEC) viability, migration and tube formation in vitro. To investigate the related mechanisms, we used caveolin-1 short interfering RNA. The viability of HUVECs was measured using Cell Counting Kit-8 assays, HUVEC migration was analyzed by crystal violet staining, and a tube formation assay was performed using the branch point method. Expression of caveolin-1, vascular endothelial growth factor (VEGF), and endothelial nitric oxide synthase (eNOS) in HUVECs was examined by polymerase chain reaction and western blotting. Our data revealed that apigenin induced angiogenesis in vitro by increasing the tube formation ability of HUVECs, which was counteracted by caveolin-1 silencing. Compared to the NC group, Caveolin-1 and eNOS expression was upregulated by apigenin, whereas compared to the NC group, eNOS expression was increased upon caveolin-1 silencing. The expression of VEGF was increased by treatment with apigenin; however, compared to the NC group, caveolin-1 silencing did not affect VEGF expression, and apigenin did not increase VEGF expression in HUVECs after caveolin-1 silencing. These data suggest that apigenin may be a candidate therapeutic target for stroke recovery by promoting angiogenesis via the caveolin-1 signaling pathway.

Hypercapnic acidosis attenuates pressure-dependent increase in whole-lung filtration coefficient (Kf)

Hypercapnic acidosis (HCA) has beneficial effects in experimental models of lung injury by attenuating inflammation and decreasing pulmonary edema. However, HCA increases pulmonary vascular pressure that will increase fluid filtration and worsen edema development. To reconcile these disparate effects, we tested the hypothesis that HCA inhibits endothelial mechanotransduction and protects against pressure-dependent increases in the whole lung filtration coefficient (K_f). Isolated perfused rat lung preparation was used to measure whole lung filtration coefficient (K_f) at two levels of left atrial pressure (P_LA = 7.5 versus 15 cm H₂O) and at low tidal volume (LV_t) versus standard tidal volume (STV_t) ventilation. The ratio of K_f2/K_f1 was used as the index of whole lung permeability. Double occlusion pressure, pulmonary artery pressure, pulmonary capillary pressures, and zonal characteristics (ZC) were measured to assess effects of HCA on hemodynamics and their relationship to K_f2/K_f1. An increase in P_LA2 from 7.5 to 15 cm H₂O resulted in a 4.9-fold increase in K_f2/K_f1 during LV_t and a 4.8-fold increase during STV_t. During LV_t, HCA reduced K_f2/K_f1 by 2.7-fold and reduced STV_t K_f2/K_f1 by 5.2-fold. Analysis of pulmonary hemodynamics revealed no significant differences in filtration forces in response to HCA. HCA interferes with lung vascular mechanotransduction and prevents pressure-dependent increases in whole lung filtration coefficient. These results contribute to a further understanding of the lung protective effects of HCA.

Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability

The monolayer of endothelial cells lining the vessel wall forms a semipermeable barrier (in all tissue except the relatively impermeable blood-brain and inner retinal barriers) that regulates tissue-fluid homeostasis, transport of nutrients, and migration of blood cells across the barrier. Permeability of the endothelial barrier is primarily regulated by a protein complex called adherens junctions. Adherens junctions are not static structures; they are continuously remodeled in response to mechanical and chemical cues in both physiological and pathological settings. Here, we discuss recent insights into the post-translational modifications of junctional proteins and signaling pathways regulating plasticity of adherens junctions and endothelial permeability. We also discuss in the context of what is already known and newly defined signaling pathways that mediate endothelial barrier leakiness (hyperpermeability) that are important in the pathogenesis of cardiovascular and lung diseases and vascular inflammation.

RhoA S-nitrosylation as a regulatory mechanism influencing endothelial barrier function in response to G+-bacterial toxins

Disruption of the endothelial barrier in response to Gram positive (G⁺) bacterial toxins is a major complication of acute lung injury (ALI) and can be further aggravated by antibiotics which stimulate toxin release. The integrity of the pulmonary endothelial barrier is mediated by the balance of disruptive forces such as the small GTPase RhoA, and protective forces including endothelium-derived nitric oxide (NO). How NO protects against the barrier dysfunction is incompletely understood and our goal was to determine whether NO and S-nitrosylation can modulate RhoA activity and whether this mechanism is important for G⁺ toxin-induced microvascular permeability. We found that the G⁺ toxin listeriolysin-O (LLO) increased RhoA activity and that NO and S-NO donors inhibit RhoA activity. RhoA was robustly S-nitrosylated as determined by biotin-switch and mercury column analysis. MS revealed that three primary cysteine residues are S-nitrosylated including cys16, cys20 and cys159. Mutation of these residues to serine diminished S-nitrosylation to endogenous NO and mutant RhoA was less sensitive to inhibition by S-NO. G⁺-toxins stimulated the denitrosylation of RhoA which was not mediated by S-nitrosoglutathione reductase (GSNOR), thioredoxin (TRX) or thiol-dependent enzyme activity but was instead stimulated directly by elevated calcium levels. Calcium-promoted the direct denitrosylation of WT but not mutant RhoA and mutant RhoA adenovirus was more effective than WT in disrupting the barrier integrity of human lung microvascular endothelial cells. In conclusion, we reveal a novel mechanism by which NO and S-nitrosylation reduces RhoA activity which may be of significance in the management of pulmonary endothelial permeability induced by G⁺-toxins.

Regulation of Caveolin-1 and Junction Proteins by bFGF Contributes to the Integrity of Blood-Spinal Cord Barrier and Functional Recovery

The blood-spinal cord barrier (BSCB) plays important roles in the recovery of spinal cord injury (SCI), and caveolin-1 is essential for the integrity and permeability of barriers. Basic fibroblast growth factor (bFGF) is an important neuroprotective protein and contributes to the survival of neuronal cells. This study was designed to investigate whether bFGF is beneficial for the maintenance of junction proteins and the integrity of the BSCB to identify the relations with caveolin-1 regulation. We examined the integrity of the BSCB with Evans blue dye and fluorescein isothiocyanate-dextran extravasation, measured the junction proteins and matrix metalloproteinases, and evaluated the locomotor function recovery. Our data indicated that bFGF treatment improved the recovery of BSCB and functional locomotion in contusive SCI model rats, reduced the expression and activation of matrix metalloproteinase-9, and increased the expressions of caveolin-1 and junction proteins, including occludin, claudin-5, p120-catenin, and β-catenin. In the brain, in microvascular endothelial cells, bFGF treatment increased the levels of junction proteins, caveolin-1 small interfering RNA abolished the protective effect of bFGF under oxygen-glucose deprivation conditions, and the expression of fibroblast growth factor receptor 1 and co-localization with caveolin-1 decreased significantly, which could not be reversed by bFGF treatment. These findings provide a novel mechanism underlying the beneficial effects of bFGF on the BSCB and recovery of SCI, especially the regulation of caveolin-1.

Lower Serum Caveolin-1 Is Associated with Cerebral Microbleeds in Patients with Acute Ischemic Stroke

Caveolin-1 (Cav-1) plays pivotal roles in the endothelial damage following stroke. The present study aimed to investigate whether serum Cav-1 level is associated with the presence of cerebral small vessel disease (cSVD) in patients with acute ischemic stroke. To this end, 156 patients were consecutively enrolled. Cranial magnetic resonance imaging was analyzed to determine the surrogates of cSVD, including cerebral microbleeds (CMBs), silent lacunar infarcts (SLIs), and white matter hyperintensities (WMHs). After adjusting for potential confounders, patients with low Cav-1 level had a higher risk of CMBs than patients with high Cav-1 level (OR: 4.05, 95% CI: 1.77-9.30). However, there was no relationship between Cav-1 and the presence of SLIs or WMHs. When CMBs were stratified by location and number, a similar association was found in patients with deep or infratentorial CMBs (OR: 4.04, 95% CI: 1.59-10.25) and with multiple CMBs (OR: 3.18, 95% CI: 1.16-8.72). These results suggest lower serum Cav-1 levels may be associated with CMBs, especially those that are multiple and located in deep brain or infratentorial structures, in patients with acute ischemic stroke. Cav-1 may be involved in the pathophysiology of CMBs, and may act as a potential target for treating cSVD.

Caveolae protect endothelial cells from membrane rupture during increased cardiac output

This study provides direct in vivo evidence that endothelial cell caveolae disassemble and hence flatten out under increased mechanical stress and that the presence of caveolae protects endothelial cell plasma membranes from damage.

Caveolae are strikingly abundant in endothelial cells, yet the physiological functions of caveolae in endothelium and other tissues remain incompletely understood. Previous studies suggest a mechanoprotective role, but whether this is relevant under the mechanical forces experienced by endothelial cells in vivo is unclear. In this study we have sought to determine whether endothelial caveolae disassemble under increased hemodynamic forces, and whether caveolae help prevent acute rupture of the plasma membrane under these conditions. Experiments in cultured cells established biochemical assays for disassembly of caveolar protein complexes, and assays for acute loss of plasma membrane integrity. In vivo, we demonstrate that caveolae in endothelial cells of the lung and cardiac muscle disassemble in response to acute increases in cardiac output. Electron microscopy and two-photon imaging reveal that the plasma membrane of microvascular endothelial cells in caveolin 1^−/− mice is much more susceptible to acute rupture when cardiac output is increased. These data imply that mechanoprotection through disassembly of caveolae is important for endothelial function in vivo.

Redox biology in pulmonary arterial hypertension (2013 Grover Conference Series)

Through detailed interrogation of the molecular pathways that contribute to the development of pulmonary arterial hypertension (PAH), the separate but related processes of oxidative stress and cellular metabolic dysfunction have emerged as being critical pathogenic mechanisms that are as yet relatively untargeted therapeutically. In this review, we have attempted to summarize some of the important existing studies, to point out areas of overlap between oxidative stress and metabolic dysfunction, and to do so under the unifying heading of redox biology. We discuss the importance of precision in assessing oxidant signaling versus oxidant injury and why this distinction matters. We endeavor to advance the discussion of carbon-substrate metabolism beyond a focus on glucose and its fate in the cell to encompass other carbon substrates and some of the murkiness surrounding our understanding of how they are handled in different cell types. Finally, we try to bring these ideas together at the level of the mitochondrion and to point out some additional points of possible cognitive dissonance that warrant further experimental probing. The body of beautiful science regarding the molecular and cellular details of redox biology in PAH points to a future that includes clinically useful therapies that target these pathways. To fully realize the potential of these future interventions, we hope that some of the issues raised in this review can be addressed proactively.

Concise review: Mechanotransduction via p190RhoGAP regulates a switch between cardiomyogenic and endothelial lineages in adult cardiac progenitors

Mechanical cues can have pleiotropic influence on stem cell shape, proliferation, differentiation, and morphogenesis, and are increasingly realized to play an instructive role in regeneration and maintenance of tissue structure and functions. To explore the putative effects of mechanical cues in regeneration of the cardiac tissue, we investigated therapeutically important cardiosphere-derived cells (CDCs), a heterogeneous patient- or animal-specific cell population containing c-Kit(+) multipotent stem cells. We showed that mechanical cues can instruct c-Kit(+) cell differentiation along two lineages with corresponding morphogenic changes, while also serving to amplify the initial c-Kit(+) subpopulation. In particular, mechanical cues mimicking the structure of myocardial extracellular matrix specify cardiomyogenic fate, while cues mimicking myocardium rigidity specify endothelial fates. Furthermore, we found that these cues dynamically regulate the same molecular species, p190RhoGAP, which then acts through both RhoA-dependent and independent mechanisms. Thus, differential regulation of p190RhoGAP molecule by either mechanical inputs or genetic manipulation can determine lineage type specification. Since human CDCs are already in phase II clinical trials, the potential therapeutic use of mechanical or genetic manipulation of the cell fate could enhance effectiveness of these progenitor cells in cardiac repair, and shed new light on differentiation mechanisms in cardiac and other tissues.

ROS signaling and redox biology in endothelial cells

The purpose of this review is to provide an overview of redox mechanisms, sources and antioxidants that control signaling events in ECs. In particular, we describe which molecules are involved in redox signaling and how they influence the relationship between ECs and other vascular component with regard to angiogenesis. Recent and new tools to investigate physiological ROS signaling will be also discussed. Such findings are providing an overview of the ROS biology relevant for endothelial cells in the context of normal and pathological angiogenic conditions.

Angiopoietin-1 Regulates Brain Endothelial Permeability through PTPN-2 Mediated Tyrosine Dephosphorylation of Occludin

OBJECTIVE

Blood brain barrier (BBB) breakdown and increased endothelial permeability is a hallmark of neuro-vascular inflammation. Angiopoietin-1 (Ang-1), a Tie-2 receptor agonist ligand, is known to modulate barrier function of endothelial cells; however the molecular mechanisms related to Ang-1 mediated repair of Tight Junctions (TJs) in brain endothelium still remain elusive. In this study, we investigated a novel role of non-receptor protein tyrosine phosphatase N-2 (PTPN-2) in Ang-1 mediated stabilization of tight junction proteins.

METHOD AND RESULT

To study the barrier protective mechanism of Ang-1, we challenged human brain microvascular endothelial cells in-vitro, with a potent inflammatory mediator thrombin. By using confocal microscopy and transwell permeability assay, we show that pretreatment of brain endothelial cells with Ang-1 diminish thrombin mediated disruption of TJs and increase in endothelial permeability. We also found that Ang-1 inhibits thrombin induced tyrosine phosphorylation of Occludin and promote Occludin interaction with Zona Occludens-1 (ZO-1) to stabilize TJs. Interestingly, our study revealed that depletion of PTPN-2 by siRNAs abolishes Ang-1 ability to promote tyrosine dephosphorylation of Occludin, resulting Occludin disassociation from ZO-1 and endothelial hyperpermeability.

SUMMARY

Collectively, our findings suggest that in brain endothelial cells blocking PTPN-2 mediated tyrosine phosphorylation of Occludin is a novel mechanism to maintain BBB function, and may offer a key therapeutic strategy for neuro-inflammatory disorders associated with BBB disruption.

Rac1 functions as a reversible tension modulator to stabilize VE-cadherin trans-interaction

The role of the RhoGTPase Rac1 in stabilizing mature endothelial adherens junctions (AJs) is not well understood. In this paper, using a photoactivatable probe to control Rac1 activity at AJs, we addressed the relationship between Rac1 and the dynamics of vascular endothelial cadherin (VE-cadherin). We demonstrated that Rac1 activation reduced the rate of VE-cadherin dissociation, leading to increased density of VE-cadherin at AJs. This response was coupled to a reduction in actomyosin-dependent tension across VE-cadherin adhesion sites. We observed that inhibiting myosin II directly or through photo-release of the caged Rho kinase inhibitor also reduced the rate of VE-cadherin dissociation. Thus, Rac1 functions by stabilizing VE-cadherin trans-dimers in mature AJs by counteracting the actomyosin tension. The results suggest a new model of VE-cadherin adhesive interaction mediated by Rac1-induced reduction of mechanical tension at AJs, resulting in the stabilization of VE-cadherin adhesions.

Caveolae: molecular insights and therapeutic targets for stroke

INTRODUCTION

Caveolae are specialized plasma membrane micro-invaginations of most mammalian cell types. The organization and function of caveolae are carried out by their coat proteins, caveolins and adaptor proteins, cavins. Caveolae/caveolins physically interact with membrane-associated signaling molecules and function in cholesterol incorporation, signaling transduction and macromolecular transport/permeability.

AREAS COVERED

Recent investigations have implicated a check-and-balance role of caveolae in the pathophysiology of cerebral ischemia. Caveolin knockout mice displayed exacerbated ischemic injury, whereas caveolin peptide exerted remarkable protection against ischemia/reperfusion injury. This review attempts to provide a comprehensive synopsis of how caveolae/caveolins modulate blood-brain barrier permeability, pro-survival signaling, angiogenesis and neuroinflammation, and how this may contribute to a better understanding of the participation of caveolae in ischemic cascade. The role of caveolin in the preconditioning-induced tolerance against ischemia is also discussed.

EXPERT OPINION

Caveolae represent a novel target for cerebral ischemia. It remains open how to manipulate caveolin expression in a practical way to recapitulate the beneficial therapeutic outcomes. Caveolin peptides and associated antagomirs may be efficacious and deserve further investigations for their potential benefits for stroke.

Effect of oxidative stress on Rho kinase II and smooth muscle contraction in rat stomach

Recent studies have shown that both Rho kinase signaling and oxidative stress are involved in the pathogenesis of a number of human diseases, such as diabetes mellitus, hypertension, and atherosclerosis. However, very little is known about the effect of oxidative stress on the gastrointestinal (GI) smooth muscle Rho kinase pathway. The aim of the current study was to investigate the effect of oxidative stress on Rho kinase II and muscle contraction in rat stomach. The peroxynitrite donor 3-morpholinosydnonimine (SIN-1), hydrogen peroxide (H2O2), and peroxynitrite were used to induce oxidative stress. Rho kinase II expression and ACh-induced activity were measured in control and oxidant-treated cells via specifically designed enzyme-linked immunosorbent assay (ELISA) and activity assay kits, respectively. Single smooth muscle cell contraction was measured via scanning micrometry in the presence or absence of the Rho kinase blocker, Y-27632 dihydrochloride. All oxidant agents significantly increased ACh-induced Rho kinase II activity without affecting its expression level. Most important, oxidative stress induced by all three agents augmented ACh-stimulated muscle cell contraction, which was significantly inhibited by Y-27632. In conclusion, oxidative stress activates Rho kinase II and enhances contraction in rat gastric muscle, suggesting an important role in GI motility disorders associated with oxidative stress.

Caveolin expression changes in the neurovascular unit after juvenile traumatic brain injury: signs of blood-brain barrier healing?

Traumatic brain injury (TBI) is one of the major causes of death and disability in pediatrics, and results in a complex cascade of events including the disruption of the blood-brain barrier (BBB). A controlled-cortical impact on post-natal 17-day-old rats induced BBB disruption by IgG extravasation from 1 to 3 days after injury and returned to normal at day 7. In parallel, we characterized the expression of three caveolin isoforms, caveolin 1 (cav-1), caveolin 2 (cav-2) and caveolin 3 (cav-3). While cav-1 and cav-2 are expressed on endothelial cells, both cav-1 and cav-3 were found to be present on reactive astrocytes, in vivo and in vitro. Following TBI, cav-1 expression was increased in blood vessels at 1 and 7 days in the perilesional cortex. An increase of vascular cav-2 expression was observed 7 days after TBI. In contrast, astrocytic cav-3 expression decreased 3 and 7 days after TBI. Activation of endothelial nitric oxide synthase (eNOS) (via its phosphorylation) was detected 1 day after TBI and phospho-eNOS was detected both in association with blood vessels and with astrocytes. The molecular changes involving caveolins occurring in endothelial cells following juvenile-TBI might participate, independently of eNOS activation, to a mechanism of BBB repair while, they might subserve other undefined roles in astrocytes.