Cytoskeletal dynamics and lung fluid balance

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.

Immunological alterations in the endothelial barrier: a new predictive and therapeutic paradigm for sepsis

INTRODUCTION

Despite the fact incidence and mortality vary widely among regions, sepsis remains a major cause of morbidity and cost worldwide. The importance of the endothelial barrier in sepsis and infectious diseases is increasingly recognized; however, the underlying pathophysiology of the endothelial barrier in sepsis remains poorly understood.

AREAS COVERED

Here we review the advances in basic and clinical research for relevant papers in PubMed database. We attempt to provide an updated overview of immunological alterations in endothelial dysfunction, discussing the central role of endothelial barrier involved in sepsis to provide new predictive and therapeutic paradigm for sepsis.

EXPERT OPINION

Given its physiological and immunological functions in infectious diseases, the endothelial barrier has been dramatically altered in sepsis, suggesting that endothelial dysfunction may play a critical role in the pathogenesis of sepsis. Although many reliable biomarkers have been investigated to monitor endothelial activation and injury in an attempt to find diagnostic and therapeutic tools, there are no specific therapies to treat sepsis due to its complex pathophysiology. Since sepsis is initiated by both hyperinflammation and immunoparalysis occurring simultaneously, a 'one-treatment-fits-all' strategy for sepsis-induced immune injury and immunoparalysis is bound to fail, and an individualized 'precision medicine' approach is required.

SIRT1-Rab7 axis attenuates NLRP3 and STING activation through late endosomal-dependent mitophagy during sepsis-induced acute lung injury

BACKGROUND

Acute lung injury (ALI) is a leading cause of mortality in patients with sepsis due to proinflammatory endothelial changes and endothelial permeability defects. Mitochondrial dysfunction is recognized as a critical mediator in the pathogenesis of sepsis-induced ALI. Although mitophagy regulation of mitochondrial quality is well recognized, little is known about its role in lung ECs during sepsis-induced ALI. Sirtuin 1 (SIRT1) is a histone protein deacetylase involved in inflammation, mitophagy, and cellular senescence. Here, the authors show a type of late endosome-dependent mitophagy that inhibits NLRP3 and STING activation through SIRT1 signaling during sepsis-induced ALI.

METHODS

C57BL/6J male mice with or without administration of the SIRT1 inhibitor EX527 in the CLP model and lung ECs in vitro were developed to identify mitophagy mechanisms that underlie the cross-talk between SIRT1 signaling and sepsis-induced ALI.

RESULTS

SIRT1 deficient mice exhibited exacerbated sepsis-induced ALI. Knockdown of SIRT1 interfered with mitophagy through late endosome Rab7, leading to the accumulation of damaged mitochondria and inducing excessive mitochondrial reactive oxygen species (mtROS) generation and cytosolic release of mitochondrial DNA (mtDNA), which triggered NLRP3 inflammasome and the cytosolic nucleotide sensing pathways (STING) over-activation. Pharmacological inhibition of STING and NLRP3 i n vivo or genetic knockdown in vitro reversed SIRT1 deficiency mediated endothelial permeability defects and endothelial inflammation in sepsis-induced ALI. Moreover, activation of SIRT1 with SRT1720 in vivo or overexpression of SIRT1 in vitro protected against sepsis-induced ALI.

CONCLUSION

These findings suggest that SIRT1 signaling is essential for restricting STING and NLRP3 hyperactivation by promoting endosomal-mediated mitophagy in lung ECs, providing potential therapeutic targets for treating sepsis-induced ALI.

Histologic and proteomic remodeling of the pulmonary veins and arteries in a porcine model of chronic pulmonary venous hypertension

AIMS

In heart failure (HF), pulmonary venous hypertension (PVH) produces pulmonary hypertension (PH) with remodeling of pulmonary veins (PV) and arteries (PA). In a porcine PVH model, we performed proteomic-based bioinformatics to investigate unique pathophysiologic mechanisms mediating PA and PV remodeling.

METHODS AND RESULTS

Large PV were banded (PVH, n = 10) or not (Sham, n = 9) in piglets. At sacrifice, PV and PA were perfusion labelled for vessel-specific histology and proteomics. The PA and PV were separately sampled with laser-capture micro-dissection for mass spectrometry. Pulmonary vascular resistance [Wood Units; 8.6 (95% confidence interval: 6.3, 12.3) vs. 2.0 (1.7, 2.3)] and PA [19.9 (standard error of mean, 1.1) vs. 10.3 (1.1)] and PV [14.2 (1.2) vs. 7.6 (1.1)] wall thickness/external diameter (%) were increased in PVH (P < 0.05 for all). Similar numbers of proteins were identified in PA (2093) and PV (2085) with 94% overlap, but biological processes differed. There were more differentially expressed proteins (287 vs. 161), altered canonical pathways (17 vs. 3), and predicted upstream regulators (PUSR; 22 vs. 6) in PV than PA. In PA and PV, bioinformatics indicated activation of the integrated stress response and mammalian target of rapamycin signalling with dysregulated growth. In PV, there was also activation of Rho/Rho-kinase signalling with decreased actin cytoskeletal signalling and altered tight and adherens junctions, ephrin B, and caveolae-mediated endocytosis signalling; all indicating disrupted endothelial barrier function. Indeed, protein biomarkers and the top PUSR in PV (transforming growth factor-beta) suggested endothelial to mesenchymal transition in PV. Findings were similar in human autopsy specimens.

CONCLUSION

These findings provide new therapeutic targets to oppose pulmonary vascular remodeling in HF-related PH.

Endothelial Poldip2 regulates sepsis-induced lung injury via Rho pathway activation

AIMS

Sepsis-induced lung injury is associated with significant morbidity and mortality. Previously, we showed that heterozygous deletion of polymerase δ-interacting protein 2 (Poldip2) was protective against sepsis-induced lung injury. Since endothelial barrier disruption is thought to be the main mechanism of sepsis-induced lung injury, we sought to determine if the observed protection was specifically due to the effect of reduced endothelial Poldip2.

METHODS AND RESULTS

Endothelial-specific Poldip2 knock-out mice (EC-/-) and their wild-type littermates (EC+/+) were injected with saline or lipopolysaccharide (18 mg/kg) to model sepsis-induced lung injury. At 18 h post-injection mice, were euthanized and bronchoalveolar lavage (BAL) fluid and lung tissue were collected to assess leucocyte infiltration. Poldip2 EC-/- mice showed reduced lung leucocyte infiltration in BAL (0.21 ± 0.9×106 vs. 1.29 ± 1.8×106 cells/mL) and lung tissue (12.7 ± 1.8 vs. 23 ± 3.7% neutrophils of total number of cells) compared to Poldip2 EC+/+ mice. qPCR analysis of the lung tissue revealed a significantly dampened induction of inflammatory gene expression (TNFα 2.23 ± 0.39 vs. 4.15 ± 0.5-fold, IκBα 4.32 ± 1.53 vs. 8.97 ± 1.59-fold), neutrophil chemoattractant gene expression (CXCL1 68.8 ± 29.6 vs. 147 ± 25.7-fold, CXCL2 65 ± 25.6 vs. 215 ± 27.3-fold) and a marker of endothelial activation (VCAM1 1.25 ± 0.25 vs. 3.8 ± 0.38-fold) in Poldip2 EC-/- compared to Poldip2 EC+/+ lungs. An in vitro model using human pulmonary microvascular endothelial cells was used to assess the effect of Poldip2 knock-down on endothelial activation and permeability. TNFα-induced endothelial permeability and VE-cadherin disruption were significantly reduced with siRNA-mediated knock-down of Poldip2 (5 ± 0.5 vs. 17.5 ± 3-fold for permeability, 1.5 ± 0.4 vs. 10.9 ± 1.3-fold for proportion of disrupted VE-cadherin). Poldip2 knock-down altered expression of Rho-GTPase-related genes, which correlated with reduced RhoA activation by TNFα (0.94 ± 0.05 vs. 1.29 ± 0.01 of relative RhoA activity) accompanied by redistribution of active-RhoA staining to the centre of the cell.

CONCLUSION

Poldip2 is a potent regulator of endothelial dysfunction during sepsis-induced lung injury, and its endothelium-specific inhibition may provide clinical benefit.

Mechanotransduction Regulates the Interplays Between Alveolar Epithelial and Vascular Endothelial Cells in Lung

Mechanical stress plays a critical role among development, functional maturation, and pathogenesis of pulmonary tissues, especially for the alveolar epithelial cells and vascular endothelial cells located in the microenvironment established with vascular network and bronchial-alveolar network. Alveolar epithelial cells are mainly loaded by cyclic strain and air pressure tension. While vascular endothelial cells are exposed to shear stress and cyclic strain. Currently, the emerging evidences demonstrated that non-physiological mechanical forces would lead to several pulmonary diseases, including pulmonary hypertension, fibrosis, and ventilation induced lung injury. Furthermore, a series of intracellular signaling had been identified to be involved in mechanotransduction and participated in regulating the physiological homeostasis and pathophysiological process. Besides, the communications between alveolar epithelium and vascular endothelium under non-physiological stress contribute to the remodeling of the pulmonary micro-environment in collaboration, including hypoxia induced injuries, endothelial permeability impairment, extracellular matrix stiffness elevation, metabolic alternation, and inflammation activation. In this review, we aim to summarize the current understandings of mechanotransduction on the relation between mechanical forces acting on the lung and biological response in mechanical overloading related diseases. We also would like to emphasize the interplays between alveolar epithelium and vascular endothelium, providing new insights into pulmonary diseases pathogenesis, and potential targets for therapy.

Tunicamycin Protects against LPS-Induced Lung Injury

The pulmonary endothelium is a dynamic semipermeable barrier that orchestrates tissue-fluid homeostasis; regulating physiological and immunological responses. Endothelial abnormalities are caused by inflammatory stimuli interacting with intracellular messengers to remodel cytoskeletal junctions and adhesion proteins. Those phenomena are associated with sepsis, acute lung injury, and acute respiratory distress syndrome. The molecular processes beyond those responses are the main interest of our group. Unfolded protein response (UPR) is a highly conserved molecular pathway resolving protein-folding defects to counteract cellular threats. An emerging body of evidence suggests that UPR is a promising target against lung and cardiovascular disease. In the present study, we reveal that Tunicamycin (TM) (UPR inducer) protects against lipopolysaccharide (LPS)-induced injury. The barrier function of the inflamed endothelium was evaluated in vitro (transendothelial and paracellular permeability); as well as in mice exposed to TM after LPS. Our study demonstrates that TM supports vascular barrier function by modulating actomyosin remodeling. Moreover, it reduces the internalization of vascular endothelial cadherin (VE-cadherin), enhancing endothelial integrity. We suggest that UPR activation may deliver novel therapeutic opportunities in diseases related to endothelial dysregulation.

Emerging Approaches to Understanding Microvascular Endothelial Heterogeneity: A Roadmap for Developing Anti-Inflammatory Therapeutics

The endothelium is the inner layer of all blood vessels and it regulates hemostasis. It also plays an active role in the regulation of the systemic inflammatory response. Systemic inflammatory disease often results in alterations in vascular endothelium barrier function, increased permeability, excessive leukocyte trafficking, and reactive oxygen species production, leading to organ damage. Therapeutics targeting endothelium inflammation are urgently needed, but strong concerns regarding the level of phenotypic heterogeneity of microvascular endothelial cells between different organs and species have been expressed. Microvascular endothelial cell heterogeneity in different organs and organ-specific variations in endothelial cell structure and function are regulated by intrinsic signals that are differentially expressed across organs and species; a result of this is that neutrophil recruitment to discrete organs may be regulated differently. In this review, we will discuss the morphological and functional variations in differently originated microvascular endothelia and discuss how these variances affect systemic function in response to inflammation. We will review emerging in vivo and in vitro models and techniques, including microphysiological devices, proteomics, and RNA sequencing used to study the cellular and molecular heterogeneity of endothelia from different organs. A better understanding of microvascular endothelial cell heterogeneity will provide a roadmap for developing novel therapeutics to target the endothelium.

mTOR Inhibition Promotes Pneumonitis Through Inducing Endothelial Contraction and Hyperpermeability

Compromised endothelial (EC) barrier function is a hallmark of inflammatory diseases. Mammalian target of rapamycin (mTOR) inhibitors, widely applied as clinical therapies, cause pneumonitis through mechanisms not yet fully understood. This study aimed to elucidate the EC mechanisms underlying the pathogenesis of pneumonitis caused by mTOR inhibition (mTORi). Mice with EC-specific deletion of mTOR complex components (Mtor, Rptor or Rictor) were administered LPS to induce pulmonary injury. Cultured EC were treated with pharmacological inhibitors, small interfering RNA or overexpression-plasmids. EC barrier function was evaluated in vivo with Evan's blue assay and in vitro by measurement of transendothelial electrical resistance and albumin flux. mTORi increased basal and TNFα-induced EC permeability, which was caused by myosin light chain (MLC) phosphorylation-dependent cell contraction. Inactivation of mTOR kinase activity by mTORi triggered PKCδ/p38/NF-κB signaling that significantly upregulated TNFα-induced MLC kinase (MLCK) expression, while Raptor promoted the phosphorylation of PKCα/MYPT1 independent of its interaction with mTOR, leading to suppression of MLC phosphatase (MLCP) activity. EC-specific deficiency in mTOR, Raptor or Rictor aggravated lung inflammation in LPS-treated mice. These findings reveal that mTORi induces PKC-dependent endothelial MLC phosphorylation, contraction and hyperpermeability that promote pneumonitis.

Nitration of protein kinase G-Iα modulates cyclic nucleotide crosstalk via phosphodiesterase 3A: Implications for acute lung injury

Phosphodiesterase 3A (PDE3A) selectively cleaves the phosphodiester bond of cAMP and is inhibited by cGMP, making it an important regulator of cAMP–cGMP signaling crosstalk in the pulmonary vasculature. In addition, the nitric oxide–cGMP axis is known to play an important role in maintaining endothelial barrier function. However, the potential role of protein kinase G-Iα (PKG-Iα) in this protective process is unresolved and was the focus of our study. We describe here a novel mechanism regulating PDE3A activity, which involves a PKG-Iα–dependent inhibitory phosphorylation of PDE3A at serine 654. We also show that this phosphorylation is critical for maintaining intracellular cAMP levels in the pulmonary endothelium and endothelial barrier integrity. In an animal model of acute lung injury (ALI) induced by challenging mice with lipopolysaccharide (LPS), an increase in PDE3 activity and a decrease in cAMP levels in lung tissue was associated with reduced PKG activity upon PKG-Iα nitration at tyrosine 247. The peroxynitrite scavenger manganese (III) tetrakis(1-methyl-4-pyridyl)porphyrin prevented this increase in PDE3 activity in LPS-exposed lungs. In addition, site-directed mutagenesis of PDE3A to replace serine 654 with alanine yielded a mutant protein that was insensitive to PKG-dependent regulation. Taken together, our data demonstrate a novel functional link between nitrosative stress induced by LPS during ALI and the downregulation of barrier-protective intracellular cAMP levels. Our data also provide new evidence that PKG-Iα is critical for endothelial barrier maintenance and that preservation of its catalytic activity may be efficacious in ALI therapy.

Actin-binding protein, IQGAP1, regulates LPS-induced RPMVECs hyperpermeability and ICAM-1 upregulation via Rap1/Src signalling pathway

Pulmonary microvascular barrier dysfunction is a hallmark feature of acute lung injury (ALI). IQGAP1 is a ubiquitously expressed scaffolding protein known to regulate cancer metastasis, angiogenesis, and barrier stability. However, the function of IQGAP1 in lipopolysaccharide (LPS)-induced microvascular endothelial hyperpermeability remains poorly understood. In the present study, we demonstrated that IQGAP1 was markedly upregulated in LPS-induced ALI models and rat pulmonary microvascular endothelial cells (RPMVECs). Lentivirus-mediated knockdown of IQGAP1 significantly attenuated the formation of actin stress fibers, phosphorylation of myosin light chain (MLC), and disruption of VE-cadherin, thereby protecting the RPMVECs barrier failure from LPS damage. In addition, IQGAP1 depletion reduced the reactive oxygen species (ROS)-mediated increase in intracellular adhesion molecule-1 (ICAM-1) in RPMVECs stimulated with LPS. Mechanistically, we found that the upregulation of IQGAP1 affected the activity of Rap1 and the downstream phosphorylation of Src. In conclusion, these findings reveal an essential mechanism by which increased IQGAP1 in LPS-treated RPMVECs promotes barrier dysfunction and ICAM-1 upregulation, at least in part by regulating Rap1/Src signalling, indicating that IQGAP1 may be a potential therapeutic target to prevent endothelial hyperpermeability and inflammation in ALI.

Fractalkine Is Linked to the Necrosome Pathway in Acute Pulmonary Inflammation

Acute pulmonary inflammation affects over 10% of intensive care unit (ICU) patients and is associated with high mortality. Fractalkine (CX₃CL1) and its receptor, CX₃CR1, have been shown to affect pulmonary inflammation, but previous studies have focused on macrophages. In a murine model of acute pulmonary inflammation, we identified inflammatory hallmarks in C57BL/6J and CX₃CR1^−/− mice. Pulmonary inflammation was significantly enhanced in the CX₃CR1^−/− animals compared to the C57BL/6J animals, as assessed by microvascular permeability, polymorphonuclear neutrophil (PMN) migration into lung tissue and alveolar space. The CX₃CR1^−/− mice showed increased levels of apoptotic PMNs in the lungs, and further investigations revealed an increased activation of necrosome-related receptor-interacting serine/threonine-protein kinases 1 (RIPK1), 3 (RIPK3), and mixed-lineage kinase domain-like pseudokinase (MLKL). Phosphorylated MLKL leads to membrane rupture and damage-associated molecular pattern (DAMP) release, which further enhance inflammation. The release of DAMPs was significantly higher in the CX₃CR1^−/− mice and led to the activation of various cascades, explaining the increased inflammation. RIPK3 and MLKL inhibition improved the inflammatory response in human PMNs in vitro and confirmed our in vivo findings. In conclusion, we linked CX₃CL1 to the necrosome complex in pulmonary inflammation and demonstrated a pivotal role of the necrosome complex in human PMNs.

Extracellular adenosine enhances pulmonary artery vasa vasorum endothelial cell barrier function via Gi/ELMO1/Rac1/PKA-dependent signaling mechanisms

The vasa vasorum (VV), the microvascular network around large vessels, has been recognized as an important contributor to the pathological vascular remodeling in cardiovascular diseases. In bovine and rat models of hypoxic pulmonary hypertension (PH), we have previously shown that chronic hypoxia profoundly increased pulmonary artery (PA) VV permeability, associated with infiltration of inflammatory and progenitor cells in the arterial wall, perivascular inflammation, and structural vascular remodeling. Extracellular adenosine was shown to exhibit a barrier-protective effect on VV endothelial cells (VVEC) via cAMP-independent mechanisms, which involved adenosine A1 receptor-mediated activation of Gi-phosphoinositide 3-kinase-Akt pathway and actin cytoskeleton remodeling. Using VVEC isolated from the adventitia of calf PA, in this study we investigated in more detail the mechanisms linking Gi activation to downstream barrier protection pathways. Using a small-interference RNA (siRNA) technique and transendothelial electrical resistance assay, we found that the adaptor protein, engulfment and cell motility 1 (ELMO1), the tyrosine phosphatase Src homology region 2 domain-containing phosphatase-2, and atypical Gi- and Rac1-mediated protein kinase A activation are implicated in VVEC barrier enhancement. In contrast, the actin-interacting GTP-binding protein, girdin, and the p21-activated kinase 1 downstream target, LIM kinase, are not involved in this response. In addition, adenosine-dependent cytoskeletal rearrangement involves activation of cofilin and inactivation of ezrin-radixin-moesin regulatory cytoskeletal proteins, consistent with a barrier-protective mechanism. Collectively, our data indicate that targeting adenosine receptors and downstream barrier-protective pathways in VVEC may have a potential translational significance in developing pharmacological approach for the VV barrier protection in PH.

Arg mediates LPS-induced disruption of the pulmonary endothelial barrier

Acute Respiratory Distress Syndrome (ARDS) is a devastating disease process that involves dysregulated inflammation and decreased alveolar-capillary barrier function. Despite increased understanding of the pathophysiology, no effective targeted therapies exist to treat ARDS. Recent preclinical studies suggest that the multi-tyrosine kinase inhibitor, imatinib, which targets the Abl kinases c-Abl and Arg, has the potential to restore endothelial dysfunction caused by inflammatory agonists. Prior work demonstrates that imatinib attenuates LPS (lipopolysaccharide)-induced vascular leak and inflammation; however, the mechanisms underlying these effects remain incompletely understood. In the current study, we demonstrate that imatinib inhibits LPS-induced increase in the phosphorylation of CrkL, a specific substrate of Abl kinases, in human pulmonary endothelial cells. Specific silencing of Arg, and not c-Abl, attenuated LPS-induced pulmonary vascular permeability as measured by electrical cellular impedance sensing (ECIS) and gap formation assays. In addition, direct activation of Abl family kinases with the small molecule activator DPH resulted in endothelial barrier disruption that was attenuated by Arg siRNA. In complementary studies to characterize the mechanisms by which Arg mediates endothelial barrier function, Arg silencing was found to inhibit LPS-induced disruption of adherens junctions and phosphorylation of myosin light chains (MLC). Overall, these results characterize the mechanisms by which imatinib protects against LPS-induced endothelial barrier disruption and suggest that Arg inhibition may represent a novel strategy to enhance endothelial barrier function.

Neutrophil-endothelial interactions of murine cells is not a good predictor of their interactions in human cells

All drugs recently developed in rodent models to treat inflammatory disease have failed in clinical trials. We therefore used our novel biomimetic microfluidic assay (bMFA) to determine whether the response of murine cells to inflammatory activation or anti-inflammatory treatment is predictive of the response in human cells. Under physiologically relevant flow conditions, permeability and transendothelial electrical resistance (TEER) of human or mouse lung microvascular endothelial cells (HLMVEC or MLMVEC), and neutrophil-endothelial cell interaction was measured. The differential impact of a protein kinase C-delta TAT peptide inhibitor (PKCδ-i) was also quantified. Permeability of HLMVEC and MLMVEC was similar under control conditions but tumor necrosis factor α (TNF-α) and PKCδ-i had a significantly higher impact on permeability of HLMVEC. TEER across HLMVEC was significantly higher than MLMVEC, but PKCδ-i returned TEER to background levels only in human cells. The kinetics of N-formylmethionyl-leucyl-phenylalanine (fMLP)-mediated neutrophil migration was significantly different between the two species and PKCδ-i was significantly more effective in attenuating human neutrophil migration. However, human and mouse neutrophil adhesion patterns to microvascular endothelium were not significantly different. Surprisingly, while intercellular adhesion molecule 1 (ICAM-1) was significantly upregulated on activated HLMVEC, it was not significantly upregulated on activated MLMVEC. Responses to activation and anti-inflammatory treatment in mice may not always be predictive of their response in humans.

MicroRNA-34a Promotes Endothelial Dysfunction and Mitochondrial-mediated Apoptosis in Murine Models of Acute Lung Injury

Recent evidence has shown that microRNAs (miRs) are involved in endothelial dysfunction and vascular injury in lung-related diseases. However, the potential role of miR-34a in the regulation of pulmonary endothelial dysfunction, vascular injury, and endothelial cells (ECs) apoptosis in acute lung injury (ALI)/acute lung respiratory distress syndrome is largely unknown. Here, we show that miR-34a-5p was upregulated in whole lungs, isolated ECs from lungs, and ECs stimulated with various insults (LPS and hyperoxia). Overexpression of miR-34a-5p in ECs exacerbated endothelial dysfunction, inflammation, and vascular injury, whereas the suppression of miR-34a-5p expression in ECs and miR-34a-null mutant mice showed protection against LPS- and hyperoxia-induced ALI. Furthermore, we observed that miR-34a-mediated endothelial dysfunction is associated with decreased miR-34a direct-target protein, sirtuin-1, and increased p53 expression in whole lungs and ECs. Mechanistically, we show that miR-34a leads to translocation of p53 and Bax to the mitochondrial compartment with disruption of mitochondrial membrane potential to release cytochrome C into the cytosol, initiating a cascade of mitochondrial-mediated apoptosis in lungs. Collectively, these data show that downregulating miR-34a expression or modulating its target proteins may improve endothelial dysfunction and attenuate ALI.

Nitric Oxide and Hydrogen Sulfide Regulation of Ischemic Vascular Growth and Remodeling

Ischemic vascular remodeling occurs in response to stenosis or arterial occlusion leading to a change in blood flow and tissue perfusion. Altered blood flow elicits a cascade of molecular and cellular physiological responses leading to vascular remodeling of the macro- and micro-circulation. Although cellular mechanisms of vascular remodeling such as arteriogenesis and angiogenesis have been studied, therapeutic approaches in these areas have had limited success due to the complexity and heterogeneous constellation of molecular signaling events regulating these processes. Understanding central molecular players of vascular remodeling should lead to a deeper understanding of this response and aid in the development of novel therapeutic strategies. Hydrogen sulfide (H₂ S) and nitric oxide (NO) are gaseous signaling molecules that are critically involved in regulating fundamental biochemical and molecular responses necessary for vascular growth and remodeling. This review examines how NO and H₂ S regulate pathophysiological mechanisms of angiogenesis and arteriogenesis, along with important chemical and experimental considerations revealed thus far. The importance of NO and H₂ S bioavailability, their synthesis enzymes and cofactors, and genetic variations associated with cardiovascular risk factors suggest that they serve as pivotal regulators of vascular remodeling responses. © 2019 American Physiological Society. Compr Physiol 9:1213-1247, 2019.

Protein kinase C-delta inhibition protects blood-brain barrier from sepsis-induced vascular damage

Background

Neuroinflammation often develops in sepsis leading to activation of cerebral endothelium, increased permeability of the blood-brain barrier (BBB), and neutrophil infiltration. We have identified protein kinase C-delta (PKCδ) as a critical regulator of the inflammatory response and demonstrated that pharmacologic inhibition of PKCδ by a peptide inhibitor (PKCδ-i) protected endothelial cells, decreased sepsis-mediated neutrophil influx into the lung, and prevented tissue damage. The objective of this study was to elucidate the regulation and relative contribution of PKCδ in the control of individual steps in neuroinflammation during sepsis.

Methods

The role of PKCδ in mediating human brain microvascular endothelial (HBMVEC) permeability, junctional protein expression, and leukocyte adhesion and migration was investigated in vitro using our novel BBB on-a-chip (B³C) microfluidic assay and in vivo in a rat model of sepsis induced by cecal ligation and puncture (CLP). HBMVEC were cultured under flow in the vascular channels of B³C. Confocal imaging and staining were used to confirm tight junction and lumen formation. Confluent HBMVEC were pretreated with TNF-α (10 U/ml) for 4 h in the absence or presence of PKCδ-i (5 μM) to quantify neutrophil adhesion and migration in the B³C. Permeability was measured using a 40-kDa fluorescent dextran in vitro and Evans blue dye in vivo.

Results

During sepsis, PKCδ is activated in the rat brain resulting in membrane translocation, a step that is attenuated by treatment with PKCδ-i. Similarly, TNF-α-mediated activation of PKCδ and its translocation in HBMVEC are attenuated by PKCδ-i in vitro. PKCδ inhibition significantly reduced TNF-α-mediated hyperpermeability and TEER decrease in vitro in activated HBMVEC and rat brain in vivo 24 h after CLP induced sepsis. TNF-α-treated HBMVEC showed interrupted tight junction expression, whereas continuous expression of tight junction protein was observed in non-treated or PKCδ-i-treated cells. PKCδ inhibition also reduced TNF-α-mediated neutrophil adhesion and migration across HBMVEC in B³C. Interestingly, while PKCδ inhibition decreased the number of adherent neutrophils to baseline (no-treatment group), it significantly reduced the number of migrated neutrophils below the baseline, suggesting a critical role of PKCδ in regulating neutrophil transmigration.

Conclusions

The BBB on-a-chip (B³C) in vitro assay is suitable for the study of BBB function as well as screening of novel therapeutics in real-time. PKCδ activation is a key signaling event that alters the structural and functional integrity of BBB leading to vascular damage and inflammation-induced tissue damage. PKCδ-TAT peptide inhibitor has therapeutic potential for the prevention or reduction of cerebrovascular injury in sepsis-induced vascular damage.

Cortical Actin Dynamics in Endothelial Permeability

The pulmonary endothelial cell forms a critical semi-permeable barrier between the vascular and interstitial space. As part of the blood-gas barrier in the lung, the endothelium plays a key role in normal physiologic function and pathologic disease. Changes in endothelial cell shape, defined by its plasma membrane, determine barrier integrity. A number of key cytoskeletal regulatory and effector proteins including non-muscle myosin light chain kinase, cortactin, and Arp 2/3 mediate actin rearrangements to form cortical and membrane associated structures in response to barrier enhancing stimuli. These actin formations support and interact with junctional complexes and exert forces to protrude the lipid membrane to and close gaps between individual cells. The current knowledge of these cytoskeletal processes and regulatory proteins are the subject of this review. In addition, we explore novel advancements in cellular imaging that are poised to shed light on the complex nature of pulmonary endothelial permeability.

Protein functional effector sncRNAs (pfeRNAs) in lung cancer

PIWI-interacting RNA Likes (piR-Ls) were recently reported to regulate functions of their target phospho-Proteins (p-Proteins) in somatic lung cells. However, the mechanism underlying this functionality remains unclear. piR-Ls interact with their targets through direct binding but do not follow base-pairing rules, known to have important roles at levels of transcription, RNA processing and translation for small non-coding RNA (sncRNA). These observations imply a fundamentally different type of sncRNA with behavior that causes a molecular response in their target p-Proteins. Furthermore, the interaction of piR-Ls with their targets regulates the functional efficacy of target p-Proteins. In addition, except for writers (kinase) and erasers (phosphatase), the functional efficacy of p-Proteins on their readers still remains unknown. It is reasonable to consider the existence of protein functional effector sncRNAs (pfeRNAs), which were identified by deep sequencing the immunoprecipitation products of antibodies targeting phosphorylated residues in proteins, as well as by functional analysis. pfeRNAs harbor unique features in size distribution, 3' terminal modification, shared core sequences, and functional manner, and could be new players in lung physiological and pathological conditions.

A phosphorylation-wide sncRNA screen reveals Protein Functional Effector sncRNAs (pfeRNAs) in human lung somatic cells

We recently reported that PIWI-interacting RNAs likes (piR-Ls) could regulate functions of the interacting phosphorylated proteins (p-Proteins). In addition, except for writers and erasers, functional efficacy of p-Proteins on their readers still remains unknown. We, therefore, reasoned there was a type of sncRNAs which could regulate functional efficacy of p-Proteins. Here, we profiled sncRNAs interacting with phosphorylated -Ser, -Thr and -Tyr residues in 3 HBE and 4 lung SCC cell lines, investigated effects and mechanisms of phosphorylated-residue-interacting sncRNAs. Our results demonstrated sncRNAs regulating functional efficacy of p-Proteins and we thus referred them as Protein Functional Effector sncRNAs (pfeRNAs). pfeRNAs were distributed among 26 to 50 nucleotides, shared some core sequences and showed distinctive expression patterns between HBE and SCC cells. Core sequences 417 (CS417), showing consistent upregulation in all 4 SCC cells, bound directly to p-Nucleolin (NCL), which was dependent on the key elements CGCG of CS417 and p-Ser619 of NCL. The CS417/p-NCL interaction was critical for functional efficacy of p-NCL in basic activities of lung normal and cancer cells. Thus, we revealed a novel type of pfeRNAs controlling functional efficacy of p-Proteins in lung somatic cells.

Thrombin Induces Inositol Trisphosphate-Mediated Spatially Extensive Responses in Lung Microvessels

Activation of plasma membrane receptors initiates compartmentalized second messenger signaling. Whether this compartmentalization facilitates the preferential intercellular diffusion of specific second messengers is unclear. Toward this, the receptor-mediated agonist, thrombin, was instilled into microvessels in a restricted region of isolated blood-perfused mouse lungs. Subsequently, the thrombin-induced increase in endothelial F-actin was determined using confocal fluorescence microscopy. Increased F-actin was evident in microvessels directly treated with thrombin and in those located in adjoining thrombin-free regions. This increase was abrogated by inhibiting inositol trisphosphate-mediated calcium release with Xestospongin C (XeC). XeC also inhibited the thrombin-induced increase in the amplitude of endothelial cytosolic Ca²⁺ oscillations. Instillation of thrombin and XeC into adjacent restricted regions increased F-actin in microvessels in the thrombin-treated and adjacent regions but not in those in the XeC-treated region. Thus, inositol trisphosphate, and not calcium, diffused interendothelially to the spatially remote thrombin-free microvessels. Thus, activation of plasma membrane receptors increased the ambit of inflammatory responses via a second messenger different from that used by stimuli that induce cell-wide increases in second messengers. Thrombin however failed to induce the spatially extensive response in microvessels of mice lacking endothelial connexin43, suggesting a role for connexin43 gap junctions. Compartmental second messenger signaling and interendothelial communication define the specific second messenger involved in exacerbating proinflammatory responses to receptor-mediated agonists.

Integration of endothelial protease-activated receptor-1 inflammatory signaling by ubiquitin

PURPOSE OF REVIEW

The maintenance and integrity of the endothelial barrier is essential for vascular homeostasis. Endothelial barrier dysfunction is mediated by various inflammatory factors, many of which act through G protein-coupled receptors including protease-activated receptors (PARs). PARs are expressed in multiple cell types in the vasculature and mediate cellular responses to thrombin, the key effector protease of the coagulation cascade. Thrombin activation of PAR1 induces endothelial barrier permeability through multiple pathways. Here, we discuss the mechanism by which thrombin activation of PAR1 promotes endothelial barrier breakdown and highlight recent advances that have provided new insight into molecular mechanisms that control endothelial barrier integrity.

RECENT FINDINGS

Although the signal transduction pathways induced by thrombin activation of PAR1 in endothelial cells have been extensively studied, the key regulatory mechanisms remain poorly understood. Posttranslational modifications are integral to the regulation of PAR1 signaling and recent studies suggest a novel function for ubiquitination of PAR1 in regulation of endothelial barrier permeability.

SUMMARY

An understanding of how endothelial barrier permeability is regulated by thrombin activation of PAR1 is important for the discovery of new drug targets that can be manipulated to control endothelial barrier permeability and prevent progression of vascular inflammation.

Lung Circulation

The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.

Metabolic Serum Profiles for Patients Receiving Allogeneic Stem Cell Transplantation: The Pretransplant Profile Differs for Patients with and without Posttransplant Capillary Leak Syndrome

Allogeneic stem cell transplantation is commonly used in the treatment of younger patients with severe hematological diseases, and endothelial cells seem to be important for the development of several posttransplant complications. Capillary leak syndrome is a common early posttransplant complication where endothelial cell dysfunction probably contributes to the pathogenesis. In the present study we investigated whether the pretreatment serum metabolic profile reflects a risk of posttransplant capillary leak syndrome. We investigated the pretransplant serum levels of 766 metabolites for 80 consecutive allotransplant recipients. Patients with later capillary leak syndrome showed increased pretherapy levels of metabolites associated with endothelial dysfunction (homocitrulline, adenosine) altered renal regulation of fluid and/or electrolyte balance (betaine, methoxytyramine, and taurine) and altered vascular function (cytidine, adenosine, and methoxytyramine). Additional bioinformatical analyses showed that capillary leak syndrome was also associated with altered purine/pyrimidine metabolism (i.e., metabolites involved in vascular regulation and endothelial functions), aminoglycosylation (possibly important for endothelial cell functions), and eicosanoid metabolism (also involved in vascular regulation). Our observations are consistent with the hypothesis that the pretransplant metabolic status can be a marker for posttransplant abnormal fluid and/or electrolyte balance.

Melatonin attenuates neurogenic pulmonary edema via the regulation of inflammation and apoptosis after subarachnoid hemorrhage in rats

Neurogenic pulmonary edema (NPE) is a serious non-neurological complication that can occur after a subarachnoid hemorrhage (SAH) and is associated with decreased survival and a poor neurological outcome. Melatonin is a strong antioxidant that has beneficial effects against SAH in rats, including reduced mortality and reduced neurological deficits. The molecular mechanisms underlying these clinical effects in the SAH model, however, have not been clearly identified. This study was undertaken to determine the influence of melatonin on SAH-induced NPE and the potential mechanism of these effects using the filament perforation model of SAH in male Sprague Dawley rats. Either melatonin (150 mg/kg) or a vehicle was given via an intraperitoneal injection 2 hr after an SAH induction. Lung samples were extracted 24 hr after SAH. The results show that the melatonin treatment attenuated SAH-induced NPE by preventing alveolar-capillary barrier dysfunctions via inhibiting the disruption of tight junction proteins (ZO-1 and occludin). Moreover, the treatment downregulated the levels of mature interleukin (IL) -1β, myeloperoxidase (MPO), and matrix metallopeptidase (MMP) 9 expression/activation, which were increased in the lung; also, melatonin treatment improved neurological deficits. Furthermore, the melatonin treatment markedly reduced caspase-3 activity and the number of TUNEL-positive cells in the lung. Taken together, these findings show that administration of melatonin attenuates NPE by preventing alveolar-capillary barrier dysfunctions via repressing the inflammatory response and by anti-apoptosis effects after SAH.

Alpha-Catulin Co-Localizes With Vimentin Intermediate Filaments and Functions in Pulmonary Vascular Endothelial Cell Migration via ROCK

The ubiquitous α-catulin acts as a scaffold for distinct signalosomes including RhoA/ROCK; however, its function is not well understood. While α-catulin has homology to the cytoskeletal linkers α-catenin and vinculin, it appears to be functionally divergent. Here we further investigated α-catulin function in pulmonary vascular endothelial cells (VEC) on the premise that α-catulin has a unique cytoskeletal role. Examination of endogenous α-catulin intracellular localization by immunofluorescence revealed a highly organized cytosolic filamentous network suggestive of a cytoskeletal system in a variety of cultured VEC. Double-immunofluorescence analyses of VEC showed endogenous α-catulin co-localization with vimentin intermediate filaments. Similar to vimentin, α-catulin was found to distribute into detergent-soluble and -insoluble fractions. Treatment of VEC with withaferinA, an agent that targets vimentin filaments, disrupted the α-catulin network distribution and altered α-catulin solubility. Vimentin participates in cell migration, and withaferinA was found to inhibit VEC migration in vitro; similarly, α-catulin knock-down reduced VEC migration. Based on previous reports showing that ROCK modulates vimentin, we found that ROCK depletion attenuated VEC migration; furthermore, α-catulin depletion was shown to reduce ROCK-induced signaling. These findings indicate that α-catulin has a unique function in co-localization with vimentin filaments that contributes to VEC migration via a pathway that may involve ROCK signaling. J. Cell. Physiol. 231: 934-943, 2016. © 2015 Wiley Periodicals, Inc.

Microtubule-Associated Protein EB3 Regulates IP3 Receptor Clustering and Ca(2+) Signaling in Endothelial Cells

The mechanisms by which the microtubule cytoskeleton regulates the permeability of endothelial barrier are not well understood. Here, we demonstrate that microtubule-associated end-binding protein 3 (EB3), a core component of the microtubule plus-end protein complex, binds to inositol 1,4,5-trisphosphate receptors (IP3Rs) through an S/TxIP EB-binding motif. In endothelial cells, α-thrombin, a pro-inflammatory mediator that stimulates phospholipase Cβ, increases the cytosolic Ca(2+) concentration and elicits clustering of IP3R3s. These responses, and the resulting Ca(2+)-dependent phosphorylation of myosin light chain, are prevented by depletion of either EB3 or mutation of the TxIP motif of IP3R3 responsible for mediating its binding to EB3. We also show that selective EB3 gene deletion in endothelial cells of mice abrogates α-thrombin-induced increase in endothelial permeability. We conclude that the EB3-mediated interaction of IP3Rs with microtubules controls the assembly of IP3Rs into effective Ca(2+) signaling clusters, which thereby regulate microtubule-dependent endothelial permeability.

Mechanisms regulating endothelial permeability

The endothelial monolayer partitioning underlying tissue from blood components in the vessel wall maintains tissue fluid balance and host defense through dynamically opening intercellular junctions. Edemagenic agonists disrupt endothelial barrier function by signaling the opening of the intercellular junctions leading to the formation of protein-rich edema in the interstitial tissue, a hallmark of tissue inflammation that, if left untreated, causes fatal diseases, such as acute respiratory distress syndrome. In this review, we discuss how intercellular junctions are maintained under normal conditions and after stimulation of endothelium with edemagenic agonists. We have focused on reviewing the new concepts dealing with the alteration of adherens junctions after inflammatory stimulus.

Proline-rich region of non-muscle myosin light chain kinase modulates kinase activity and endothelial cytoskeletal dynamics

Disruption of the pulmonary endothelial barrier and subsequent vascular leak is a hallmark of acute lung injury. Dynamic rearrangements in the endothelial cell (EC) peripheral membrane and underlying cytoskeleton are critical determinants of barrier function. The cytoskeletal effector protein non-muscle myosin light chain kinase (nmMLCK) and the actin-binding regulatory protein cortactin are important regulators of the endothelial barrier. In the present study we functionally characterize a proline-rich region of nmMLCK previously identified as the possible site of interaction between nmMLCK and cortactin. A mutant nmMLCK construct deficient in proline residues at the putative sites of cortactin binding (amino acids 973, 976, 1019, 1022) was generated. Co-immunoprecipitation studies in human lung EC transfected with wild-type or mutant nmMLCK demonstrated similar levels of cortactin interaction at baseline and after stimulation with the barrier-enhancing agonist, sphingosine 1-phosphate (S1P). In contrast, binding studies utilizing recombinant nmMLCK fragments containing the wild-type or proline-deficient sequence demonstrated a two-fold increase in cortactin binding (p<0.01) to the mutant construct. Immunofluorescent microscopy revealed an increased stress fiber density in ECs expressing GFP-labeled mutant nmMLCK at baseline (p=0.02) and after thrombin (p=0.01) or S1P (p=0.02) when compared to wild-type. Mutant nmMLCK demonstrated an increase in kinase activity in response to thrombin (p<0.01). Kymographic analysis demonstrated an increased EC membrane retraction distance and velocity (p<0.01) in response to the barrier disrupting agent thrombin in cells expressing the mutant vs. the wild-type nmMLCK construct. These results provide evidence that critical prolines within nmMLCK (amino acids 973, 976, 1019, 1022) regulate cytoskeletal and membrane events associated with pulmonary endothelial barrier function.