Selective HDAC6 inhibition prevents TNF-α-induced lung endothelial cell barrier disruption and endotoxin-induced pulmonary edema

Downregulation of HDAC6 mitigates lung ischemia/reperfusion injury depending on activation of Nrf2/HO-1 signaling pathway and inactivation of ERK/NF-κB signaling pathway

INTRODUCTION

Lung ischemia/reperfusion injury (LIRI) is a pathological process caused by the deficiency and subsequent reperfusion of oxygen and blood to the lung. Literature reports that the catalytic activity and expression of HDAC6 can be induced in response to IRI. HDAC6 inhibition confers protective effects against a series of IRI and also exerts pulmonary protection against various lung damage. The present study was formulated to investigate the functional role of HDAC6 inhibitor in LIRI and to probe into the intrinsic mechanisms underlying the protective role of HDAC6 inhibitor against LIRI.

METHODS

Lung epithelial cell line MLE-12 cells were subjected to H/R injury to construct in vitro cell culture model of LIRI. For functional experiments, MLE-12 cells were pre-treated with various concentrations of selective HDAC6 inhibitor ACY-1215 (1, 5, 10 μM) to evaluate the biological role of HDAC6 in LIRI. For rescue experiments, MLE-12 cells were pre-treated with Nrf2 inhibitor ML385 (10 μM) or ERK activator LM22B-10 (50 μM) to discuss the molecular mechanisms.

RESULTS

It was verified that HDAC6 inhibition repressed H/R-induced apoptosis, oxidative stress, inflammation and mitochondrial dysfunction of MLE-12 cells. HDAC6 inhibition activated Nrf2/HO-1 signaling pathway and inactivated ERK/NF-κB signaling pathway in MLE-12 cells. The repressing effects of HDAC6 inhibition on H/R-induced apoptosis, oxidative stress, inflammation and mitochondrial dysfunction of MLE-12 cells were partially abolished upon pre-treatment with Nrf2 inhibitor ML385 or ERK activator LM22B-10.

CONCLUSION

HDAC6 inhibition may mitigate H/R-induced lung epithelial cell injury depending on activation of Nrf2/HO-1 signaling pathway and inactivation of ERK/NF-κB signaling pathway.

Selective HDAC6 inhibition protects against blood-brain barrier dysfunction after intracerebral hemorrhage

BACKGROUNDS

Blood-brain barrier (BBB) disruption after intracerebral hemorrhage (ICH) significantly induces neurological impairment. Previous studies showed that HDAC6 knockdown or TubA can protect the TNF-induced endothelial dysfunction. However, the role of HDAC6 inhibition on ICH-induced BBB disruption remains unknown.

METHODS

Hemin-induced human brain microvascular endothelial cells (HBMECs) and collagenase-induced rats were employed to investigated the underlying impact of the HDAC6 inhibition in BBB lesion and neuronal dysfunction after ICH.

RESULTS

We found a significant decrease in acetylated α-tubulin during early phase of ICH. Both 25 or 40 mg/kg of TubA could relieve neurological deficits, perihematomal cell apoptosis, and ipsilateral brain edema in ICH animal model. TubA or specific siRNA of HDAC6 inhibited apoptosis and reduced the endothelial permeability of HBMECs. HDAC6 inhibition rescued the degradation of TJ proteins and repaired TJs collapses after ICH induction. Finally, the results suggested that the protective effects on BBB after ICH induction were exerted via upregulating the acetylated α-tubulin and reducing stress fiber formation.

CONCLUSIONS

Inhibition of HDAC6 expression showed beneficial effects against BBB disruption after experimental ICH, which suggested that HDAC6 could be a novel and promising target for ICH treatment.

Zinc-Dependent Histone Deacetylases in Lung Endothelial Pathobiology

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and, as such, provides a semi-selective barrier between the blood and the interstitial space. Compromise of the lung EC barrier due to inflammatory or toxic events may result in pulmonary edema, which is a cardinal feature of acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS). The EC functions are controlled, at least in part, via epigenetic mechanisms mediated by histone deacetylases (HDACs). Zinc-dependent HDACs represent the largest group of HDACs and are activated by Zn2+. Members of this HDAC group are involved in epigenetic regulation primarily by modifying the structure of chromatin upon removal of acetyl groups from histones. In addition, they can deacetylate many non-histone histone proteins, including those located in extranuclear compartments. Recently, the therapeutic potential of inhibiting zinc-dependent HDACs for EC barrier preservation has gained momentum. However, the role of specific HDAC subtypes in EC barrier regulation remains largely unknown. This review aims to provide an update on the role of zinc-dependent HDACs in endothelial dysfunction and its related diseases. We will broadly focus on biological contributions, signaling pathways and transcriptional roles of HDACs in endothelial pathobiology associated mainly with lung diseases, and we will discuss the potential of their inhibitors for lung injury prevention.

Selective and Bioavailable HDAC6 2-(Difluoromethyl)-1,3,4-oxadiazole Substrate Inhibitors and Modeling of Their Bioactivation Mechanism

Histone deacetylase 6 (HDAC6) is a unique member of the HDAC family mainly targeting cytosolic nonhistone substrates, such as α-tubulin, cortactin, and heat shock protein 90 to regulate cell proliferation, metastasis, invasion, and mitosis in tumors. We describe the identification and characterization of a series of 2-(difluoromethyl)-1,3,4-oxadiazoles (DFMOs) as selective nonhydroxamic acid HDAC6 inhibitors. By comparing structure-activity relationships and performing quantum mechanical calculations of the HDAC6 catalytic mechanism, we show that potent oxadiazoles are electrophilic substrates of HDAC6 and propose a mechanism for the bioactivation. We also observe that the inherent electrophilicity of the oxadiazoles makes them prone to degradation in water solution and the generation of potentially toxic products cannot be ruled out, limiting the developability for chronic diseases. However, the oxadiazoles demonstrate high oral bioavailability and low in vivo clearance and are excellent tools for studying the role of HDAC6 in vitro and in vivo in rats and mice.

Hydrogen Sulfide Ameliorates SARS-CoV-2-Associated Lung Endothelial Barrier Disruption

Recent studies have confirmed that lung microvascular endothelial injury plays a critical role in the pathophysiology of COVID-19. Our group and others have demonstrated the beneficial effects of H2S in several pathological processes and provided a rationale for considering the therapeutic implications of H2S in COVID-19 therapy. Here, we evaluated the effect of the slow-releasing H2S donor, GYY4137, on the barrier function of a lung endothelial cell monolayer in vitro, after challenging the cells with plasma samples from COVID-19 patients or inactivated SARS-CoV-2 virus. We also assessed how the cytokine/chemokine profile of patients' plasma, endothelial barrier permeability, and disease severity correlated with each other. Alterations in barrier permeability after treatments with patient plasma, inactivated virus, and GYY4137 were monitored and assessed by electrical impedance measurements in real time. We present evidence that GYY4137 treatment reduced endothelial barrier permeability after plasma challenge and completely reversed the endothelial barrier disruption caused by inactivated SARS-CoV-2 virus. We also showed that disease severity correlated with the cytokine/chemokine profile of the plasma but not with barrier permeability changes in our assay. Overall, these data demonstrate that treatment with H2S-releasing compounds has the potential to ameliorate SARS-CoV-2-associated lung endothelial barrier disruption.

Augmentation of Histone Deacetylase 6 Activity Impairs Mitochondrial Respiratory Complex I in Ischemic/Reperfused Diabetic Hearts

BACKGROUND

Diabetes augments activity of histone deacetylase 6 (HDAC6) and generation of tumor necrosis factor α (TNFα) and impairs the physiological function of mitochondrial complex I (mCI) which oxidizes reduced nicotinamide adenine dinucleotide (NADH) to nicotinamide adenine dinucleotide to sustain the tricarboxylic acid cycle and β-oxidation. Here we examined how HDAC6 regulates TNFα production, mCI activity, mitochondrial morphology and NADH levels, and cardiac function in ischemic/reperfused diabetic hearts.

METHODS

HDAC6 knockout, streptozotocin-induced type 1 diabetic, and obese type 2 diabetic db/db mice underwent myocardial ischemia/reperfusion injury in vivo or ex vivo in a Langendorff-perfused system. H9c2 cardiomyocytes with and without HDAC6 knockdown were subjected to hypoxia/reoxygenation injury in the presence of high glucose. We compared the activities of HDAC6 and mCI, TNFα and mitochondrial NADH levels, mitochondrial morphology, myocardial infarct size, and cardiac function between groups.

RESULTS

Myocardial ischemia/reperfusion injury and diabetes synergistically augmented myocardial HDCA6 activity, myocardial TNFα levels, and mitochondrial fission and inhibited mCI activity. Interestingly, neutralization of TNFα with an anti-TNFα monoclonal antibody augmented myocardial mCI activity. Importantly, genetic disruption or inhibition of HDAC6 with tubastatin A decreased TNFα levels, mitochondrial fission, and myocardial mitochondrial NADH levels in ischemic/reperfused diabetic mice, concomitant with augmented mCI activity, decreased infarct size, and ameliorated cardiac dysfunction. In H9c2 cardiomyocytes cultured in high glucose, hypoxia/reoxygenation augmented HDAC6 activity and TNFα levels and decreased mCI activity. These negative effects were blocked by HDAC6 knockdown.

CONCLUSIONS

Augmenting HDAC6 activity inhibits mCI activity by increasing TNFα levels in ischemic/reperfused diabetic hearts. The HDAC6 inhibitor, tubastatin A, has high therapeutic potential for acute myocardial infarction in diabetes.

Selective HDAC6 inhibitor TubA offers neuroprotection after intracerebral hemorrhage via inhibiting neuronal apoptosis

A large body of evidence has demonstrated that neuronal apoptosis is involved in the pathological process of secondary brain injury following intracerebral hemorrhage (ICH). Additionally, our previous studies determined that the inhibition of HDAC6 activity by tubacin or specific shRNA can attenuate neuronal apoptosis in an oxygen-glucose deprivation reperfusion model. However, whether the pharmacological inhibition of HDAC6-attenuated neuronal apoptosis in ICH remains unclear. In this study, we used hemin-induced SH-SY5Y cells to simulate a hemorrhage state in vitro and adopted a collagenase-induced ICH rat model in vivo to assess the effect of the HDAC6 inhibition. We found a significant increase in HDAC6 during the early stages of ICH. As expected, the acetylated α-tubulin significantly decreased in correlation with the expression of HDAC6. Medium and high doses (25, 40 mg/kg) of TubA, a selective inhibitor of HDAC6, both reduced neurological impairments, histological impairments, and ipsilateral brain edema in vivo. TubA or HDAC6 siRNA both alleviated neuronal apoptosis in vivo and in vitro. Finally, HDAC6 inhibition increased the level of acetylated α-tubulin and Bcl-2 and lowered the expression of Bax and cleaved caspase-3 post-ICH. In general, these results suggested that the pharmacological inhibition of HDAC6 may act as a novel and promising therapeutic target for ICH therapy by up-regulating acetylated α-tubulin and reducing neuronal apoptosis.

HDAC6 inhibitor ACY-1083 shows lung epithelial protective features in COPD

Airway epithelial damage is a common feature in respiratory diseases such as COPD and has been suggested to drive inflammation and progression of disease. These features manifest as remodeling and destruction of lung epithelial characteristics including loss of small airways which contributes to chronic airway inflammation. Histone deacetylase 6 (HDAC6) has been shown to play a role in epithelial function and dysregulation, such as in cilia disassembly, epithelial to mesenchymal transition (EMT) and oxidative stress responses, and has been implicated in several diseases. We thus used ACY-1083, an inhibitor with high selectivity for HDAC6, and characterized its effects on epithelial function including epithelial disruption, cytokine production, remodeling, mucociliary clearance and cell characteristics. Primary lung epithelial air-liquid interface cultures from COPD patients were used and the impacts of TNF, TGF-β, cigarette smoke and bacterial challenges on epithelial function in the presence and absence of ACY-1083 were tested. Each challenge increased the permeability of the epithelial barrier whilst ACY-1083 blocked this effect and even decreased permeability in the absence of challenge. TNF was also shown to increase production of cytokines and mucins, with ACY-1083 reducing the effect. We observed that COPD-relevant stimulations created damage to the epithelium as seen on immunohistochemistry sections and that treatment with ACY-1083 maintained an intact cell layer and preserved mucociliary function. Interestingly, there was no direct effect on ciliary beat frequency or tight junction proteins indicating other mechanisms for the protected epithelium. In summary, ACY-1083 shows protection of the respiratory epithelium during COPD-relevant challenges which indicates a future potential to restore epithelial structure and function to halt disease progression in clinical practice.

The β-catenin/CBP signaling axis participates in sepsis-induced inflammatory lung injury

Sepsis-induced inflammatory lung injury is a key factor causing failure of the lungs and other organs, as well as death, during sepsis. In the present study, a caecal ligation and puncture (CLP)-induced sepsis model was established to investigate the effect of β-catenin on sepsis-induced inflammatory lung injury and the corresponding underlying mechanisms. C57BL/6 mice were randomly divided into five groups, namely, the sham, CLP, β-catenin knockout (KO) + CLP, XAV-939 + CLP, and ICG-001 + CLP groups; the XAV-939 + CLP and ICG-001 + CLP groups were separately subjected to intraperitoneal injections of the β-catenin inhibitors XAV-939 and ICG-001 for 1 week preoperatively and 2 days postoperatively, respectively. Forty-eight hours after CLP, we measured β-catenin expression in lung tissues and evaluated mouse mortality, histopathological characteristics of hematoxylin and eosin (H&E)-stained lung tissues, serum cytokine (tumor necrosis factor [TNF]-α, interleukin [IL]-10, and IL-1β) levels, lung myeloperoxidase (MPO) activity, and the number of apoptotic cells in the lung tissues. Our results indicated that both the inhibition of β-catenin expression and blockage of β-catenin/CREB-binding protein (CBP) interactions by ICG-001 effectively decreased mouse mortality, alleviated pathological lung injury, and reduced the serum TNF-α, IL-10, and IL-1β levels, in addition to reducing the lung MPO activity and the number of apoptotic cells in lung tissues of the sepsis model mice. Therefore, it can be deduced that the β-catenin/CBP signaling axis participates in regulating sepsis-induced inflammatory lung injury.

NF-κB-dependent repression of Sox18 transcription factor requires the epigenetic regulators histone deacetylases 1 and 2 in acute lung injury

In acute lung injury (ALI), the NF-κB-mediated downregulation of Sox18 gene expression leads to the disruption of the pulmonary endothelial barrier. Previous studies have suggested that the action of NF-κB as a transcriptional repressor also requires the action of class I histone deacetylases (HDACs). Thus, the purpose of this study was to investigate and further delineate the mechanism of Sox18 repression during lipopolysaccharide (LPS) induced ALI. Using selective inhibitors and specific siRNA-driven depletion of HDACs 1-3 in human lung microvascular endothelial cells (HLMVEC) we were able to demonstrate a critical role for HDACs 1 and 2 in the LPS-mediated repression of Sox18 gene expression and the loss of endothelial monolayer integrity. Moreover, our data demonstrate that HDAC1 associates with a transcription-repressive complex within the NF-κB-binding site of Sox18 promoter. Further, we were able to show that the selective inhibitor of HDAC1, tacedinaline, significantly reduced the endothelial permeability and injury associated with LPS challenge in the mouse lung. Taken together, our data demonstrate, for the first time, that transcription repressors HDACs 1 and 2 are involved in pathological mechanism of ALI and can be considered as therapeutic targets.

Glycyl-L-histidyl-L-lysine-Cu2+ attenuates cigarette smoke-induced pulmonary emphysema and inflammation by reducing oxidative stress pathway

Background: Chronic obstructive pulmonary disease (COPD) is a common respiratory disorder manifested as chronic airway inflammation and persistent airflow limitation with the essential mechanism as inflammatory response and oxidative stress induced by toxic exposures such as cigarette smoke (CS). Glycyl-L-histidyl-L-lysine (GHK) is a nontoxic tripeptide involved in the process of healing and regeneration as a natural product. With the combination of Cu(II), glycyl-L-histidyl-L-lysine-Cu²⁺ (GHK-Cu) improves antioxidative and anti-inflammatory bioavailability, and they might offer potential therapeutic properties for COPD. Thus, the present study aimed to identify the potential effects of GHK-Cu on emphysema induced by cigarette smoke.

Methods: In the in vivo experiment, C57BL/6J mice were exposed to CS for 12 weeks to induce pulmonary emphysema. GHK-Cu was injected intraperitoneally at doses of 0.2, 2 and 20 μg/g/day in 100 µl of saline on alternative days from the 1st day after CS exposure. The effects of GHK-Cu on the morphology of CS-induced emphysema, the inflammatory response and oxidative stress were evaluated. The antioxidative effect of GHK-Cu on human alveolar epithelial A549 cells was assessed in vitro.

Results: GHK-Cu treatment attenuated the CS-induced emphysematous changes and partially reversed the matrix metalloprotein -9 (MMP-9)/tissue inhibitor of metalloproteinases-1 (TIMP-1) imbalance in the lung tissue. GHK-Cu reduced the inflammation and oxidation by decreasing the expression of inflammatory cytokines (IL-1β and TNF-α) in the bronchoalveolar lavage and the enzymatic activity of MPO and MDA in the lung homogenate while restoring the T-AOC and GSH content. Furthermore, administration of GHK-Cu reversed the increase in NF-κB expression induced by CS and increased the Nrf2 level, as an antioxidant defense component, in mice with chronic CS exposure. In CSE-exposed human alveolar epithelial A549 cells, GHK-Cu also inhibited oxidative stress by suppressing MDA levels and restoring T-AOC and GSH levels, which were modulated by upregulating Nrf2 expression.

Conclusion: GHK-Cu treatment attenuated CS-induced emphysema by anti-inflammation by downregulating NF-κB and antioxidation via upregulation of the Nrf2/Keap1 in lung tissues.

Dichotomous Role of Tumor Necrosis Factor in Pulmonary Barrier Function and Alveolar Fluid Clearance

Alveolar-capillary leak is a hallmark of the acute respiratory distress syndrome (ARDS), a potentially lethal complication of severe sepsis, trauma and pneumonia, including COVID-19. Apart from barrier dysfunction, ARDS is characterized by hyper-inflammation and impaired alveolar fluid clearance (AFC), which foster the development of pulmonary permeability edema and hamper gas exchange. Tumor Necrosis Factor (TNF) is an evolutionarily conserved pleiotropic cytokine, involved in host immune defense against pathogens and cancer. TNF exists in both membrane-bound and soluble form and its mainly -but not exclusively- pro-inflammatory and cytolytic actions are mediated by partially overlapping TNFR1 and TNFR2 binding sites situated at the interface between neighboring subunits in the homo-trimer. Whereas TNFR1 signaling can mediate hyper-inflammation and impaired barrier function and AFC in the lungs, ligand stimulation of TNFR2 can protect from ventilation-induced lung injury. Spatially distinct from the TNFR binding sites, TNF harbors within its structure a lectin-like domain that rather protects lung function in ARDS. The lectin-like domain of TNF -mimicked by the 17 residue TIP peptide- represents a physiological mediator of alveolar-capillary barrier protection. and increases AFC in both hydrostatic and permeability pulmonary edema animal models. The TIP peptide directly activates the epithelial sodium channel (ENaC) -a key mediator of fluid and blood pressure control- upon binding to its α subunit, which is also a part of the non-selective cation channel (NSC). Activity of the lectin-like domain of TNF is preserved in complexes between TNF and its soluble TNFRs and can be physiologically relevant in pneumonia. Antibody- and soluble TNFR-based therapeutic strategies show considerable success in diseases such as rheumatoid arthritis, psoriasis and inflammatory bowel disease, but their chronic use can increase susceptibility to infection. Since the lectin-like domain of TNF does not interfere with TNF's anti-bacterial actions, while exerting protective actions in the alveolar-capillary compartments, it is currently evaluated in clinical trials in ARDS and COVID-19. A more comprehensive knowledge of the precise role of the TNFR binding sites versus the lectin-like domain of TNF in lung injury, tissue hypoxia, repair and remodeling may foster the development of novel therapeutics for ARDS.

Microtubules as Major Regulators of Endothelial Function: Implication for Lung Injury

Endothelial dysfunction has been attributed as one of the major complications in COVID-19 patients, a global pandemic that has already caused over 4 million deaths worldwide. The dysfunction of endothelial barrier is characterized by an increase in endothelial permeability and inflammatory responses, and has even broader implications in the pathogenesis of acute respiratory syndromes such as ARDS, sepsis and chronic illnesses represented by pulmonary arterial hypertension and interstitial lung disease. The structural integrity of endothelial barrier is maintained by cytoskeleton elements, cell-substrate focal adhesion and adhesive cell junctions. Agonist-mediated changes in endothelial permeability are directly associated with reorganization of actomyosin cytoskeleton leading to cell contraction and opening of intercellular gaps or enhancement of cortical actin cytoskeleton associated with strengthening of endothelial barrier. The role of actin cytoskeleton remodeling in endothelial barrier regulation has taken the central stage, but the impact of microtubules in this process remains less explored and under-appreciated. This review will summarize the current knowledge on the crosstalk between microtubules dynamics and actin cytoskeleton remodeling, describe the signaling mechanisms mediating this crosstalk, discuss epigenetic regulation of microtubules stability and its nexus with endothelial barrier maintenance, and overview a role of microtubules in targeted delivery of signaling molecules regulating endothelial permeability and inflammation.

Mechanical forces and metabolic changes cooperate to drive cellular memory and endothelial phenotypes

Endothelial cells line the innermost layer of arterial, venous, and lymphatic vascular tree and accordingly are subject to hemodynamic, stretch, and stiffness mechanical forces. Normally quiescent, endothelial cells have a hemodynamic set point and become "activated" in response to disturbed hemodynamics, which may signal impending nutrient or gas depletion. Endothelial cells in the majority of tissue beds are normally inactivated and maintain vessel barrier functions, are anti-inflammatory, anti-coagulant, and anti-thrombotic. However, under aberrant mechanical forces, endothelial signaling transforms in response, resulting cellular changes that herald pathological diseases. Endothelial cell metabolism is now recognized as the primary intermediate pathway that undergirds cellular transformation. In this review, we discuss the various mechanical forces endothelial cells sense in the large vessels, microvasculature, and lymphatics, and how changes in environmental mechanical forces result in changes in metabolism, which ultimately influence cell physiology, cellular memory, and ultimately disease initiation and progression.

The Short-Chain Fatty Acid Butyrate Attenuates Pulmonary Vascular Remodeling and Inflammation in Hypoxia-Induced Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive cardiovascular disorder in which local vascular inflammation leads to increased pulmonary vascular remodeling and ultimately to right heart failure. The HDAC inhibitor butyrate, a product of microbial fermentation, is protective in inflammatory intestinal diseases, but little is known regarding its effect on extraintestinal diseases, such as PH. In this study, we tested the hypothesis that butyrate is protective in a Sprague-Dawley (SD) rat model of hypoxic PH. Treatment with butyrate (220 mg/kg intake) prevented hypoxia-induced right ventricular hypertrophy (RVH), hypoxia-induced increases in right ventricular systolic pressure (RVSP), pulmonary vascular remodeling, and permeability. A reversal effect of butyrate (2200 mg/kg intake) was observed on elevated RVH. Butyrate treatment also increased the acetylation of histone H3, 25-34 kDa, and 34-50 kDa proteins in the total lung lysates of butyrate-treated animals. In addition, butyrate decreased hypoxia-induced accumulation of alveolar (mostly CD68+) and interstitial (CD68+ and CD163+) lung macrophages. Analysis of cytokine profiles in lung tissue lysates showed a hypoxia-induced upregulation of TIMP-1, CINC-1, and Fractalkine and downregulation of soluble ICAM (sICAM). The expression of Fractalkine and VEGFα, but not CINC-1, TIMP-1, and sICAM was downregulated by butyrate. In rat microvascular endothelial cells (RMVEC), butyrate (1 mM, 2 and 24 h) exhibited a protective effect against TNFα- and LPS-induced barrier disruption. Butyrate (1 mM, 24 h) also upregulated tight junctional proteins (occludin, cingulin, claudin-1) and increased the acetylation of histone H3 but not α-tubulin. These findings provide evidence of the protective effect of butyrate on hypoxic PH and suggest its potential use as a complementary treatment for PH and other cardiovascular diseases.

HDAC6 Activates ERK in Airway and Pulmonary Vascular Remodeling of COPD

Chronic obstructive pulmonary disease (COPD) is a multisystemic respiratory disease which is associated with progressive airway and pulmonary vascular remodeling due to the increased proliferation of bronchial and pulmonary arterial smooth muscle cells (BSMCs and PASMCs) and overproduction of extracellular matrix (ECM), e.g., collagen. Cigarette smoke (CS) and several mediators such as PDGF and IL-6 play critical role in the COPD pathogenesis. Histone deacetylase 6 (HDAC6) has been shown to be implicated in vascular remodeling. However, the HDAC6 signaling in airway and pulmonary vascular remodeling of COPD and the underlying mechanisms remain undetermined. Here we show that HDAC6 expression is upregulated in lungs of COPD patients and animal model. We also found that cigarette smoke extract (CSE), PDGF and IL-6 increase the protein levels and activation of HDAC6 in BSMCs and PASMCs. Furthermore, CSE and these stimulants induced deacetylation and phosphorylation of ERK1/2 and increased collagen synthesis and proliferation of BSMCs and PASMCs which were prevented by HDAC6 inhibition. Inhibition of ERK1/2 also diminished the CSE, PDGF and IL-6-caused elevation in collagen levels and cell proliferation. Pharmacological HDAC6 inhibition by tubastatin A prevented the CS-stimulated increases in the thickness of the bronchial and pulmonary arterial wall, airway resistance, emphysema as well as right ventricular (RV) systolic pressure (RVSP) and RV hypertrophy in rat model of COPD. These data demonstrate that the upregulated HDAC6 governs the collagen synthesis and proliferation of BSMCs and PASMCs leading to airway and vascular remodeling in COPD.

Inhibition of HDAC6 Activity Protects Against Endothelial Dysfunction and Atherogenesis in vivo: A Role for HDAC6 Neddylation

We previously reported that histone deacetylase 6 (HDAC6) has an important role in endothelial cell (EC) function in vitro. However, whether HDAC6 plays a role in atherogenesis in vivo and the mechanism(s) that control HDAC6 activity/expression in response to atherogenic stimuli are unclear. The goals of this study were to determine whether HDAC6 inhibitor tubacin attenuates atherogenesis and to elucidate specific molecular mechanism(s) that regulate endothelial HDAC6 expression/activity. We evaluated whether administration of tubacin attenuated or reversed the endothelial dysfunction and atherosclerosis induced in mice by a single intraperitoneal injection of adeno-associated viruses encoding liver-target PCSK9 gain-of-function mutant followed by a high fat diet (HFD) for 18 weeks. Tubacin significantly blunted PCSK9-induced increases in pulse wave velocity (index of vascular stiffness and overall vascular health) that are also seen in atherogenic mice. Furthermore, tubacin protected vessels from defective vasorelaxation, as evaluated by acetylcholine-mediated relaxation using wire myograph. Plaque burden defined by Oil Red O staining was also found to be significantly less in mice that received tubacin than in those that received PCSK9 alone. Inhibition of the NEDDylation pathway with MLN4924, an inhibitor of NEDD8-activating enzyme 1 (NAE1), significantly increased HDAC6 activity in HAECs. Interestingly, HDAC6 expression remained unchanged. Further, HAECs exposed to the atherogenic stimulus oxidized low-density lipoprotein (OxLDL) exhibited enhanced HDAC6 activity, which was attenuated by pretreatment with MLN4924. The HDAC6 NEDDylation molecular pathway might regulate genes related to endothelial control of vasomotor tone, reactivity, and atherosclerosis. Tubacin may represent a novel pharmacologic intervention for atherogenesis and other vasculopathies.

Inhibition of Class IIa HDACs improves endothelial barrier function in endotoxin-induced acute lung injury

Acute lung injury (ALI) is an acute inflammatory process arises from a wide range of lung insults. A major cause of ALI is dysfunction of the pulmonary vascular endothelial barrier but the mechanisms involved are incompletely understood. The therapeutic potential of histone deacetylase (HDAC) inhibitors for the treatment of cardiovascular and inflammatory diseases is increasingly apparent, but the mechanisms by which HDACs regulate pulmonary vascular barrier function remain to be resolved. We found that specific Class IIa HDACs inhibitor, TMP269, significantly attenuated the lipopolysaccharide (LPS)-induced human lung microvascular endothelial cells (HLMVEC) barrier compromise in vitro and improved vascular barrier integrity and lung function in murine model of ALI in vivo. TMP269 decreased LPS-induced myosin light chain phosphorylation suggesting the role for Class IIa HDACs in LPS-induced cytoskeleton reorganization. TMP269 did not affect microtubule structure and tubulin acetylation in contrast to the HDAC6-specific inhibitor, Tubastatin A suggesting that Class IIa HDACs and HDAC6 (Class IIb) regulate endothelial cytoskeleton and permeability via different mechanisms. Furthermore, LPS increased the expression of ArgBP2 which has recently been attributed to HDAC-mediated activation of Rho. Depletion of ArgBP2 abolished the ability of LPS to disrupt barrier function in HLMVEC and both TMP269 and Tubastatin A decreased the level of ArgBP2 expression after LPS stimulation suggesting that both Class IIa and IIb HDACs regulate endothelial permeability via ArgBP2-dependent mechanism. Collectively, our data strongly suggest that Class IIa HDACs are involved in LPS-induced ALI in vitro and in vivo via specific mechanism which involved contractile responses, but not microtubule reorganization.

Role of HDAC6 inhibition in sepsis-induced acute respiratory distress syndrome (Review)

Acute respiratory distress syndrome (ARDS) induced by sepsis contributes remarkably to the high mortality rate observed in intensive care units, largely due to a lack of effective drug therapies. Histone deacetylase 6 (HDAC6) is a class-IIb deacetylase that modulates non-nuclear protein functions via deacetylation and ubiquitination. Importantly, HDAC6 has been shown to exert anti-cancer, anti-neurodegeneration, and immunological effects, and several HDAC6 inhibitors have now entered clinical trials. It has also been recently shown to modulate inflammation, and HDAC6 inhibition has been demonstrated to markedly suppress experimental sepsis. The present review summarizes the role of HDAC6 in sepsis-induced inflammation and endothelial barrier dysfunction in recent years. It is proposed that HDAC6 inhibition predominantly ameliorates sepsis-induced ARDS by directly attenuating inflammation, which modulates the innate and adaptive immunity, transcription of pro-inflammatory genes, and protects endothelial barrier function. HDAC6 inhibition protects against sepsis-induced ARDS, thereby making HDAC6 a promising therapeutic target. However, HDAC inhibition may be associated with adverse effects on the embryo sac and oocyte, necessitating further studies.

SOCS3-microtubule interaction via CLIP-170 and CLASP2 is critical for modulation of endothelial inflammation and lung injury

Proinflammatory cytokines such as IL-6 induce endothelial cell (EC) barrier disruption and trigger an inflammatory response in part by activating the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. The protein suppressor of cytokine signaling-3 (SOCS3) is a negative regulator of JAK-STAT, but its role in modulation of lung EC barrier dysfunction caused by bacterial pathogens has not been investigated. Using human lung ECs and EC-specific SOCS3 knockout mice, we tested the hypothesis that SOCS3 confers microtubule (MT)-mediated protection against endothelial dysfunction. SOCS3 knockdown in cultured ECs or EC-specific SOCS3 knockout in mice resulted in exacerbated lung injury characterized by increased permeability and inflammation in response to IL-6 or heat-killed Staphylococcus aureus (HKSA). Ectopic expression of SOCS3 attenuated HKSA-induced EC dysfunction, and this effect required assembled MTs. SOCS3 was enriched in the MT fractions, and treatment with HKSA disrupted SOCS3-MT association. We discovered that-in addition to its known partners gp130 and JAK2-SOCS3 interacts with MT plus-end binding proteins CLIP-170 and CLASP2 via its N-terminal domain. The resulting SOCS3-CLIP-170/CLASP2 complex was essential for maximal SOCS3 anti-inflammatory effects. Both IL-6 and HKSA promoted MT disassembly and disrupted SOCS3 interaction with CLIP-170 and CLASP2. Moreover, knockdown of CLIP-170 or CLASP2 impaired SOCS3-JAK2 interaction and abolished the anti-inflammatory effects of SOCS3. Together, these findings demonstrate for the first time an interaction between SOCS3 and CLIP-170/CLASP2 and reveal that this interaction is essential to the protective effects of SOCS3 in lung endothelium.

Pre-exposure to mechanical ventilation and endotoxemia increases Pseudomonas aeruginosa growth in lung tissue during experimental porcine pneumonia

Background

Immune system suppression during critical care contributes to the risk of acquired bacterial infections with Pseudomonas (P.) aeruginosa. Repeated exposure to endotoxin can attenuate systemic inflammatory cytokine responses. Mechanical ventilation affects the systemic inflammatory response to various stimuli.

Aim

To study the effect of pre-exposure to mechanical ventilation with and without endotoxin-induced systemic inflammation on P. aeruginosa growth and wet-to-dry weight measurements on lung tissue and plasma and bronchoalveolar lavage levels of tumor necrosis factor alpha, interleukins 6 and 10.

Methods

Two groups of pigs were exposed to mechanical ventilation for 24 hours before bacterial inoculation and six h of experimental pneumonia (total experimental time 30 h): A_30h+Etx (n = 6, endotoxin 0.063 μg x kg^-1 x h^-1) and B_30h (n = 6, saline). A third group, C_6h (n = 8), started the experiment at the bacterial inoculation unexposed to endotoxin or mechanical ventilation (total experimental time 6 h). Bacterial inoculation was performed by tracheal instillation of 1x10¹¹ colony-forming units of P. aeruginosa. Bacterial cultures and wet-to-dry weight ratio analyses were done on lung tissue samples postmortem. Separate group comparisons were done between A_30h+Etx vs.B_30h (Inflammation) and B_30h vs. C_6h (Ventilation Time) during the bacterial phase of 6 h.

Results

P. aeruginosa growth was highest in A_30h+Etx, and lowest in C_6h (Inflammation and Ventilation Time both p<0.05). Lung wet-to-dry weight ratios were highest in A_30h+Etx and lowest in B_30h (Inflammation p<0.01, Ventilation Time p<0.05). C_6h had the highest TNF-α levels in plasma (Ventilation Time p<0.01). No differences in bronchoalveolar lavage variables between the groups were observed.

Conclusions

Mechanical ventilation and systemic inflammation before the onset of pneumonia increase the growth of P. aeruginosa in lung tissue. The attenuated growth of P. aeruginosa in the non-pre-exposed animals (C_6h) was associated with a higher systemic TNF-α production elicited from the bacterial challenge.

Mechanisms of extracellular vesicle uptake in stressed retinal pigment epithelial cell monolayers

PURPOSE

Extracellular vesicles (EVs) can mediate long-distance communication in polarized RPE monolayers. Specifically, EVs from oxidatively stressed donor cells (stress EVs) rapidly reduced barrier function (transepithelial resistance, TER) in naïve recipient monolayers, when compared to control EVs. This effect on TER was dependent on dynamin-mediated EV uptake, which occurred rapidly with EVs from oxidatively stressed donor cells. Here, we further determined molecular mechanisms involved in uptake of EVs by naïve RPE cells.

METHODS

RPE cells were grown as monolayers in media supplemented with 1% FBS followed by transfer to FBS-free media. Cultures were used to collect control or stress EVs upon treatment with H₂O₂, others served as naïve recipient cells. In recipient monolayers, TER was used to monitor EV-uptake-based activity, live-cell imaging confirmed uptake. EV surface proteins were quantified by protein chemistry.

RESULTS

Clathrin-independent, lipid raft-mediated internalization was excluded as an uptake mechanism. Known ligand-receptor interactions involved in clathrin-dependent endocytosis include integrins and proteoglycans. Desialylated glycans and integrin-receptors on recipient cells were necessary for EV uptake and subsequent reduction of TER in recipient cells. Protein quantifications confirmed elevated levels of ligands and neuraminidase on stress EVs. However, control EVs could confer activity in the TER assay if exogenous neuraminidase or additional ligand was provided.

CONCLUSIONS

In summary, while EVs from both stressed cells and control contain cargo to communicate stress messages to naive RPE cells, stress EVs contain surface ligands that confer rapid uptake by recipient cells. We propose that EVs potentially contribute to RPE dysfunction in aging and disease.

Endothelial Cell Mechano-Metabolomic Coupling to Disease States in the Lung Microvasculature

Lungs are the most vascular part of humans, accepting the totality of cardiac output in a volume much smaller than the body itself. Due to this cardiac output, the lung microvasculature is subject to mechanical forces including shear stress and cyclic stretch that vary with the cardiac and breathing cycle. Vessels are surrounded by extracellular matrix which dictates the stiffness which endothelial cells also sense and respond to. Shear stress, stiffness, and cyclic stretch are known to influence endothelial cell state. At high shear stress, endothelial cells exhibit cell quiescence marked by low inflammatory markers and high nitric oxide synthesis, whereas at low shear stress, endothelial cells are thought to "activate" into a pro-inflammatory state and have low nitric oxide. Shear stress' profound effect on vascular phenotype is most apparent in the arterial vasculature and in the pathophysiology of vascular inflammation. To conduct the flow of blood from the right heart, the lung microvasculature must be rigid yet compliant. It turns out that excessive substrate rigidity or stiffness is important in the development of pulmonary hypertension and chronic fibrosing lung diseases via excessive cell proliferation or the endothelial-mesenchymal transition. Recently, a new body of literature has evolved that couples mechanical sensing to endothelial phenotypic changes through metabolic signaling in clinically relevant contexts such as pulmonary hypertension, lung injury syndromes, as well as fibrosis, which is the focus of this review. Stretch, like flow, has profound effect on endothelial phenotype; metabolism studies due to stretch are in their infancy.

Histone deacetylase 6 regulates endothelial MyD88-dependent canonical TLR signaling, lung inflammation, and alveolar remodeling in the developing lung

Lung endothelial cell (EC) immune activation during bacterial sepsis contributes to acute lung injury and bronchopulmonary dysplasia in premature infants. The epigenetic regulators of sepsis-induced endothelial immune activation, lung inflammation, and alveolar remodeling remain unclear. Herein, we examined the role of the cytoplasmic histone deacetylase, HDAC6, in regulating EC Toll-like receptor 4 (TLR4) signaling and modulating sepsis-induced lung injury in a neonatal model of sterile sepsis. In human primary microvascular endothelial cells (HPMEC), lipopolysaccharide (LPS)-induced MAPK, IKK-β, and p65 phosphorylation as well as inflammatory cytokine expression were exaggerated with the HDAC6 inhibitor tubastatin A, and by dominant-negative HDAC6 with a mutated catalytic domain 2. Expression of HDAC6 wild-type protein suppressed LPS-induced myeloid differentiation primary response 88 (MyD88) acetylation, p65 (Lys³¹⁰) acetylation, MyD88/TNF receptor-associated factor 6 (TRAF6) coimmunoprecipitation, and proinflammatory TLR4 signaling in HPMEC. In a neonatal mouse model of sepsis, the HDAC6 inhibitor tubastatin A amplified lung EC TLR4 signaling and vascular permeability. HDAC6 inhibition augmented LPS-induced MyD88 acetylation, MyD88/TRAF6 binding, p65 acetylation, canonical TLR4 signaling, and inflammation in the developing lung. Sepsis-induced decreases in the fibroblast growth factors FGF2 and FGF7 and increase in matrix metalloproteinase-9 were worsened with HDAC6 inhibition, while elastin expression was equally suppressed. Exaggerated sepsis-induced acute lung inflammation observed with HDAC6 inhibition worsened alveolar simplification evidenced by increases in mean linear intercepts and decreased radial alveolar counts. Our studies reveal that HDAC6 is a constitutive negative regulator of cytoplasmic TLR4 signaling in EC and the developing lung. The therapeutic efficacy of augmenting HDAC6 activity in neonatal sepsis to prevent lung injury needs to be evaluated.

HDAC6 inhibition blocks inflammatory signaling and caspase-1 activation in LPS-induced acute lung injury

HDAC6 is a member of the class II histone deacetylase. HDAC6 inhibition possesses anti-inflammatory effects. However, the effects of HDAC6 inhibition in acute lung inflammation have not been studied. Here, we investigated the effects of a highly selective and potent HDAC6 inhibitor CAY10603 in LPS-induced acute inflammatory lung injury. We also conducted a series of experiments including immunoblotting, ELISA, and histological assays to explore the inflammatory signaling pathways modulated by the selective HDAC6 inhibition. We observed that HDAC6 activity was increased in the lung tissues after LPS challenge, which was associated with a decreased level of ɑ-tubulin acetylation in the lung tissues. HDAC6 inhibition by CAY10603 prevented LPS-induced ɑ-tubulin deacetylation in the lung tissues. HDAC6 inhibition also exhibited protective effects against LPS-induced acute lung inflammation, which was demonstrated by the reduced production of pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 and decreased leukocyte infiltration. Furthermore, HDAC6 inhibition blocked the decrease of E-cadherin level and inhibited the increase of MMP9 expression in the lung tissues, which could prevent the destruction of the lung architecture in LPS-induced inflammatory injury. Given the important roles of NFĸB and inflammasome activation in inflammatory responses, we investigated their regulation by HDAC6 inhibition in LPS-induced lung injury. Our results showed that HDAC6 inhibition blocked the activation of NFĸB by inhibiting IĸB phosphorylation in LPS-induced acute lung injury, and LPS-induced-inflammasome activity was reduced by HDAC6 inhibition as demonstrated by the decreased IL-1β and caspase-1 cleavage and activation. Collectively, our data suggest that selective HDAC6 inhibition suppresses inflammatory signaling pathways and alleviates LPS-induced acute lung inflammation.

Protective Effect of Tubastatin A in CLP-Induced Lethal Sepsis

We have found earlier that Tubastatin A (TubA), a selective inhibitor of histone deacetylase 6 (HDAC6), improves survival in a mouse model of lethal cecal ligation and puncture (CLP)-induced sepsis. However, the underlying mechanisms have not been fully established. This study sought to test the hypothesis that TubA could affect both lung and splenic functions. C57BL/6J mice were subjected to CLP, and randomized to receive either TubA (70 mg/kg) dissolved in dimethyl sulfoxide (DMSO), or DMSO alone, 1 h following CLP. Sham animals acted as control. Twenty-four hours later, lung tissue was harvested for pathological examination, and splenic tissue was harvested for bacterial colonization. In a parallel study, the spleen was collected 48 h following CLP, and single cell suspension was prepared. Splenocytes then underwent flow cytometry to analyze the immune cell population. RAW264.7 macrophages were treated with lipopolysaccharide (LPS) with or without the presence of TubA (10 μM) at 37 °C for 3 h to assess the effect on macrophage phagocytosis. We found that acute lung injury secondary to lethal sepsis was attenuated by TubA. Treatment with TubA restored the percentage of B lymphocytes, and significantly increased percentages of innate immune cells and macrophages compared to the vehicle-treated CLP group. Moreover, TubA significantly decreased the bacterial load in the spleen, and improved the phagocytic ability of RAW264.7 murine macrophages in vitro. Such findings may help to explain the beneficial effects of TubA treatment in a model of lethal sepsis, as previously reported.

Microtubule destabilization caused by particulate matter contributes to lung endothelial barrier dysfunction and inflammation

Exposure to particulate matter (PM) associated with air pollution remains a major public health concern, as it has been linked to significant increase in cardiopulmonary morbidity and mortality. Lung endothelial cell (EC) dysfunction is one of the hallmarks of cardiovascular events of lung exposure to PM. However, the role of PM in acute lung injury (ALI) exacerbation and delayed recovery remains incompletely understood. This study tested a hypothesis that PM augments lung injury and EC barrier dysfunction via microtubule-dependent mechanisms. Our data demonstrate that in pulmonary EC PM caused time- and dose-dependent remodeling of actin cytoskeleton and considerable destabilization of the microtubule (MT) network. These events led to the weakening of cell junctions and formation of actin stress fibers, resulting in disruption of lung EC monolayer and increased permeability. PM also caused ROS-dependent activation of MT-specific deacetylase, HDAC6. Suppression of HDAC6 activity by pharmacological inhibitors or siRNA-based depletion of HDAC6 abolished PM-induced EC permeability increase, which was accompanied by reduced activation of stress kinase signaling, inhibition of Rho cascade, decreased IL-6 production and suppressed activation of its downstream target STAT3. Pretreatment of pulmonary EC with IL-6 inhibitor led to inhibition of STAT3 activity and decreased PM-induced hyper-permeability. Because one of the major activators of Rho-GTPase, GEFH1, is localized on the MT, we examined its involvement in PM-caused EC barrier compromise. Inhibition of GEF-H1 activation significantly attenuated PM-induced permeability increase. Moreover, combined inhibition of IL-6 and GEF-H1 signaling exhibited additive protective effect. Taken together, these results demonstrate a critical involvement of MT-associated signaling in the PM-induced exacerbation of lung EC barrier compromise and inflammatory response.

Histone deacetylases in vascular permeability and remodeling associated with acute lung injury

Acute lung injury (ALI) is a severe progressive disorder that arises from a wide range of causes such as toxins or inflammation, resulting in significant morbidity and mortality. There are no effective therapeutic options apart from mechanical ventilation strategies. While the mechanisms that govern the clinically relevant process of increased EC permeability and remodeling associated with ALI are under intense investigation, our knowledge of the processes that determine barrier enhancement or preservation are far from completion. Recently, epigenetic mechanisms have emerged as a major regulator of enduring changes in cell behavior and the therapeutic potential of inhibiting histone deacetylases (HDACs) for the treatment of cardiovascular and inflammatory diseases has gained remarkable attention. Although HDACs have been shown to play an important role in regulating EC barrier function, the involved HDAC subtypes and mechanisms remain undefined. Further investigation of the HDAC signaling may provide therapeutic approaches for the prevention and treatment of ALI.

Extracellular vesicle-mediated long-range communication in stressed retinal pigment epithelial cell monolayers

Retinal pigment epithelium (RPE) alterations in age-related macular degeneration occur in patches, potentially involving long-distance communication between damaged and healthy areas. Communication along the epithelium might be mediated by extracellular vesicles (EVs). To test this hypothesis, EVs were collected from supernatants of polarized ARPE-19 and primary porcine RPE monolayers for functional and biochemical assays. EVs from oxidatively stressed donor cells reduced barrier function in recipient RPE monolayers when compared to control EVs. The effect on barrier function was dependent on EV uptake, which occurred rapidly with EVs from oxidatively stressed donor cells. Mass spectrometry-based proteomic analysis of EVs identified HDAC6, which is known to reduce tight junction stability. Activity assays confirmed the presence of HDAC6 in EVs, and EV transfer assays using HDAC6 inhibitors confirmed its effect in monolayers. These findings demonstrate that EVs can communicate stress messages to healthy RPE cells, potentially contributing to RPE dysfunction.

HDAC6 inhibition prevents TNF-α-induced caspase 3 activation in lung endothelial cell and maintains cell-cell junctions

Pro-inflammatory mediators such as TNF-α induce caspase activation in endothelial cells, which leads to degradation of cellular proteins, induction of apoptotic signaling, and endothelial cell dysfunction. New therapeutic agents that can inhibit caspase activation may provide protection against inflammatory injury to endothelial cells. In the present study, we examined the effects of selective histone deacetylase 6 (HDAC6) inhibition on TNF-α induced caspase 3 activation and cell-cell junction dysfunction in lung endothelial cells. We also assessed the protective effects of HDAC6 inhibition against lung inflammatory injury in a mouse model of endotoxemia. We demonstrated that selective HDAC6 inhibition or knockdown of HDAC6 expression was able to prevent caspase 3 activation in lung endothelial cells and maintain lung endothelial cell-cell junctions. Mice pre-treated with HDAC6 inhibitors exhibited decreased endotoxin-induced caspase 3 activation and reduced lung vascular injury as indicated by the retention of cell-cell junction protein VE-Cadherin level and alleviated lung edema. Collectively, our data suggest that HDAC6 inhibition is a potent therapeutic strategy against inflammatory injury to endothelial cells.

Astaxanthin alleviated acute lung injury by inhibiting oxidative/nitrative stress and the inflammatory response in mice

The purpose of the present study was to assess the effect of astaxanthin (ASX) treatment on the acute lung injury (ALI) induced by cecal ligation and puncture (CLP) in mice. Mice were randomly allocated into the following groups: (1) the saline control group, in which mice were given saline before sham operation; (2) the ASX control group, in which mice received ASX before sham operation; (3) the ALI group, in which mice were given saline before CLP operation; and (4) the ALI+ASX group, in which mice received ASX before CLP operation. ASX was dissolved in olive oil and administrated by oral gavage for 14days consecutively before the CLP or sham operation. In experiment 1, Kaplan-Meier survival analysis was conducted for 72h after CLP. In experiment 2, blood, bronchoalveolar lavage fluid (BALF) and lung tissues were collected at 24h after the CLP or sham operation to determine the severity of lung injury. The results showed that ASX treatment could significantly decrease the CLP-induced mortality rate in mice. Meanwhile, ASX treatment significantly attenuated CLP-induced lung histopathological injury, inflammatory infiltration, total protein and albumin concentration, and total cell and neutrophil counts in the BALF. Furthermore, ASX treatment alleviated oxidative/nitrative stress, inflammation levels and pulmonary apoptosis in lung tissues. In addition, ASX treatment markedly down-regulated the expression of inducible nitric oxide synthase (i-NOS), nitrotyrosine (NT) and nuclear factor-kappa B (NF-Κb) P65 in the lung tissues compared with that in the ALI group. Astaxanthin treatment had markedly protective effect against ALI in mice, and the potential mechanism is associated with its ability to inhibit the inflammatory response, oxidative/nitrative stress, and pulmonary apoptosis, as well as down-regulate NF-κB P65 expression.

Mito-xenophagic killing of bacteria is coordinated by a metabolic switch in dendritic cells

Chlamydiae are bacterial pathogens that grow in vacuolar inclusions. Dendritic cells (DCs) disintegrate these compartments, thereby eliminating the microbes, through auto/xenophagy, which also promotes chlamydial antigen presentation via MHC I. Here, we show that TNF-α controls this pathway by driving cytosolic phospholipase (cPLA)2-mediated arachidonic acid (AA) production. AA then impairs mitochondrial function, which disturbs the development and integrity of these energy-dependent parasitic inclusions, while a simultaneous metabolic switch towards aerobic glycolysis promotes DC survival. Tubulin deacetylase/autophagy regulator HDAC6 associates with disintegrated inclusions, thereby further disrupting their subcellular localisation and stability. Bacterial remnants are decorated with defective mitochondria, mito-aggresomal structures, and components of the ubiquitin/autophagy machinery before they are degraded via mito-xenophagy. The mechanism depends on cytoprotective HSP25/27, the E3 ubiquitin ligase Parkin and HDAC6 and promotes chlamydial antigen generation for presentation on MHC I. We propose that this novel mito-xenophagic pathway linking innate and adaptive immunity is critical for effective DC-mediated anti-bacterial resistance.

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.

Inhibition of HDAC6 protects against rhabdomyolysis-induced acute kidney injury

Histone deacetylase 6 (HDAC6) inhibition has been reported to protect against ischemic stroke and prolong survival after sepsis in animal models. However, it remains unknown whether HDAC6 inhibition offers a renoprotective effect after acute kidney injury (AKI). In this study, we examined the effect of tubastatin A (TA), a highly selective inhibitor of HDAC6, on AKI in a murine model of glycerol (GL) injection-induced rhabdomyolysis. Following GL injection, the mice developed severe acute tubular injury as indicated by renal dysfunction; expression of neutrophil gelatinase-associated lipocalin (NGAL), an injury marker of renal tubules; and an increase of TdT-mediated dUTP nick-end labeling (TUNEL)-positive tubular cells. These changes were companied by increased HDAC6 expression in the cytoplasm of renal tubular cells. Administration of TA significantly reduced serum creatinine and blood urea nitrogen levels as well as attenuated renal tubular damage in injured kidneys. HDAC6 inhibition also resulted in decreased expression of NGAL, reduced apoptotic cell, and inactivated caspase-3 in the kidney after acute injury. Moreover, injury to the kidney increased phosphorylation of nuclear factor (NF)-κB and expression of multiple cytokines/chemokines including tumor necrotic factor-α and interleukin-6 and monocyte chemoattractant protein-1, as well as macrophage infiltration. Treatment with TA attenuated all those responses. Finally, HDAC6 inhibition reduced the level of oxidative stress by suppressing malondialdehyde (MDA) and preserving expression of superoxide dismutase (SOD) in the injured kidney. Collectively, these data indicate that HDAC6 contributes to the pathogenesis of rhabdomyolysis-induced AKI and suggest that HDAC6 inhibitors have therapeutic potential for AKI treatment.