Biomechanical Forces and Oxidative Stress: Implications for Pulmonary Vascular Disease

Significance: Oxidative stress in the cell is characterized by excessive generation of reactive oxygen species (ROS). Superoxide (O₂^-) and hydrogen peroxide (H₂O₂) are the main ROS involved in the regulation of cellular metabolism. As our fundamental understanding of the underlying causes of lung disease has increased it has become evident that oxidative stress plays a critical role. Recent Advances: A number of cells in the lung both produce, and respond to, ROS. These include vascular endothelial and smooth muscle cells, fibroblasts, and epithelial cells as well as the cells involved in the inflammatory response, including macrophages, neutrophils, eosinophils. The redox system is involved in multiple aspects of cell metabolism and cell homeostasis. Critical Issues: Dysregulation of the cellular redox system has consequential effects on cell signaling pathways that are intimately involved in disease progression. The lung is exposed to biomechanical forces (fluid shear stress, cyclic stretch, and pressure) due to the passage of blood through the pulmonary vessels and the distension of the lungs during the breathing cycle. Cells within the lung respond to these forces by activating signal transduction pathways that alter their redox state with both physiologic and pathologic consequences. Future Directions: Here, we will discuss the intimate relationship between biomechanical forces and redox signaling and its role in the development of pulmonary disease. An understanding of the molecular mechanisms induced by biomechanical forces in the pulmonary vasculature is necessary for the development of new therapeutic strategies.

LPS-induced Acute Lung Injury Involves NF-κB-mediated Downregulation of SOX18

One of the early events in the progression of LPS-mediated acute lung injury in mice is the disruption of the pulmonary endothelial barrier resulting in lung edema. However, the molecular mechanisms by which the endothelial barrier becomes compromised remain unresolved. The SRY (sex-determining region on the Y chromosome)-related high-mobility group box (Sox) group F family member, SOX18, is a barrier-protective protein through its ability to increase the expression of the tight junction protein CLDN5. Thus, the purpose of this study was to determine if downregulation of the SOX18-CLDN5 axis plays a role in the pulmonary endothelial barrier disruption associated with LPS exposure. Our data indicate that both SOX18 and CLDN5 expression is decreased in two models of in vivo LPS exposure (intraperitoneal, intratracheal). A similar downregulation was observed in cultured human lung microvascular endothelial cells (HLMVECs) exposed to LPS. SOX18 overexpression in HLMVECs or in the mouse lung attenuated the LPS-mediated vascular barrier disruption. Conversely, reduced CLDN5 expression (siRNA) reduced the HLMVEC barrier-protective effects of SOX18 overexpression. The mechanism by which LPS decreases SOX18 expression was identified as transcriptional repression through binding of NF-κB (p65) to a SOX18 promoter sequence located between -1,082 and -1,073 bp with peroxynitrite contributing to LPS-mediated NF-κB activation. We conclude that NF-κB-dependent decreases in the SOX18-CLDN5 axis are essentially involved in the disruption of human endothelial cell barrier integrity associated with LPS-mediated acute lung injury.

EXPRESS: Surfing the Right Ventricular Pressure Waveform: Methods to assess Global, Systolic and Diastolic RV Function from a Clinical Right Heart Catheterization

Right ventricular (RV) function strongly associates with mortality in patients with pulmonary arterial hypertension (PAH). Current methods to determine RV function require temporal measurements of pressure and volume. The aim of the study was to investigate the feasibility of using right heart catheterization (RHC) measurements to estimate systolic and diastolic RV function. RV pressure and volume points were fit to P = α(eβV-1) to assess diastolic stiffness coefficient (β) and end-diastolic elastance (Eed). Single-beat methods were used to assess RV contractility (Ees). The effects of a non-zero unstressed RV volume (V0), RHC-derived stroke volume (SVRHC), and normalization of the end-diastolic volume (EDV) on estimates of β, Eed, and Ees were tested using Bland–Altman analysis in an incident PAH cohort (n = 32) that had both a RHC and cardiac magnetic resonance (CMR) test. RHC-derived measures of RV function were used to detect the effect of prostacyclin therapy in an incident PAH cohort and the severity of PAH in prevalent PAH (n = 21). A non-zero V0 had a minimal effect on β with a small bias and limits of agreement (LOA). Stroke volume (SV) significantly influenced estimates of β and Ees with a large LOA. Normalization of EDV had minimal effect on both β and Eed. RHC-derived β and Eed increased due to the severity of PAH and decreased due to three months of prostacyclin therapy. It is feasible to detect therapeutic changes in specific stiffness and elastic properties of the RV from signal-beat pressure-volume loops by using RHC-derived SV and normalizing RV EDV.

Pulmonary Endothelial Mechanical Sensing and Signaling, a Story of Focal Adhesions and Integrins in Ventilator Induced Lung Injury

Patients with critical illness such as acute lung injury often undergo mechanical ventilation in the intensive care unit. Though lifesaving in many instances, mechanical ventilation often results in ventilator induced lung injury (VILI), characterized by overdistension of lung tissue leading to release of edemagenic agents, which further damage the lung and contribute to the mortality and progression of pulmonary inflammation. The endothelium is particularly sensitive, as VILI associated mechanical stress results in endothelial cytoskeletal rearrangement, stress fiber formation, and integrity loss. At the heart of these changes are integrin tethered focal adhesions (FAs) which participate in mechanosensing, structure, and signaling. Here, we present the known roles of FA proteins including c-Src, talin, FAK, paxillin, vinculin, and integrins in the sensing and response to cyclic stretch and VILI associated stress. Attention is given to how stretch is propagated from the extracellular matrix through integrins to talin and other FA proteins, as well as signaling cascades that include FA proteins, leading to stress fiber formation and other cellular responses. This unifying picture of FAs aids our understanding in an effort to prevent and treat VILI.

Pathogenic Role of mTORC1 and mTORC2 in Pulmonary Hypertension

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G protein-coupled receptors and tyrosine kinase receptors signal through the phosphoinositide 3-kinase/Akt/mTOR pathway to induce cell proliferation, survival, and growth. mTOR is a kinase present in 2 functionally distinct complexes, mTORC1 and mTORC2.

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Functional disruption of mTORC1 by knockout of Raptor (regulatory associated protein of mammalian target of rapamycin) in smooth muscle cells ameliorated the development of experimental PH.

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Functional disruption of mTORC2 by knockout of Rictor (rapamycin insensitive companion of mammalian target of rapamycin) caused spontaneous PH by up-regulating platelet-derived growth factor receptors.

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Use of mTOR inhibitors (e.g., rapamycin) to treat PH should be accompanied by inhibitors of platelet-derived growth factor receptors (e.g., imatinib).

Concentric lung vascular wall thickening due to enhanced proliferation of pulmonary arterial smooth muscle cells is an important pathological cause for the elevated pulmonary vascular resistance reported in patients with pulmonary arterial hypertension. We identified a differential role of mammalian target of rapamycin (mTOR) complex 1 and complex 2, two functionally distinct mTOR complexes, in the development of pulmonary hypertension (PH). Inhibition of mTOR complex 1 attenuated the development of PH; however, inhibition of mTOR complex 2 caused spontaneous PH, potentially due to up-regulation of platelet-derived growth factor receptors in pulmonary arterial smooth muscle cells, and compromised the therapeutic effect of the mTOR inhibitors on PH. In addition, we describe a promising therapeutic strategy using combination treatment with the mTOR inhibitors and the platelet-derived growth factor receptor inhibitors on PH and right ventricular hypertrophy. The data from this study provide an important mechanism-based perspective for developing novel therapies for patients with pulmonary arterial hypertension and right heart failure.

Mechanisms Behind Resistance to PI3K Inhibitor Treatment Induced by the PIM Kinase

Cancer resistance to PI3K inhibitor therapy can be in part mediated by increases in the PIM1 kinase. However, the exact mechanism by which PIM kinase promotes tumor cell resistance is unknown. Our study unveils the pivotal control of redox signaling by PIM kinases as a driver of this resistance mechanism. PIM1 kinase functions to decrease cellular ROS levels by enhancing nuclear factor erythroid 2-related factor 2 (NRF2)/antioxidant response element activity. PIM prevents cell death induced by PI3K-AKT-inhibitory drugs through a noncanonical mechanism of NRF2 ubiquitination and degradation and translational control of NRF2 protein levels through modulation of eIF4B and mTORC1 activity. Importantly, PIM also controls NAD(P)H production by increasing glucose flux through the pentose phosphate shunt decreasing ROS production, and thereby diminishing the cytotoxicity of PI3K-AKT inhibitors. Treatment with PIM kinase inhibitors reverses this resistance phenotype, making tumors increasingly susceptible to small-molecule therapeutics, which block the PI3K-AKT pathway.

Divergent changes of p53 in pulmonary arterial endothelial and smooth muscle cells involved in the development of pulmonary hypertension

The tumor-suppressive role of p53, a transcription factor that regulates the expression of many genes, has been linked to cell cycle arrest, apoptosis, and senescence. The noncanonical function or the pathogenic role of p53 has more recently been implicated in pulmonary vascular disease. We previously reported that rapid nuclear accumulation of hypoxia-inducible factor (HIF)-1α in pulmonary arterial smooth muscle cells (PASMCs) upregulates transient receptor potential channels and enhances Ca²⁺ entry to increase cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt). Also, we observed differences in HIF-1α/2α expression in PASMCs and pulmonary arterial endothelial cells (PAECs). Here we report that p53 is increased in PAECs, but decreased in PASMCs, isolated from mice with hypoxia-induced pulmonary hypertension (PH) and rats with monocrotaline (MCT)-induced PH (MCT-PH). The increased p53 in PAECs from rats with MCT-PH is associated with an increased ratio of Bax/Bcl-2, while the decreased p53 in PASMCs is associated with an increased HIF-1α. Furthermore, p53 is downregulated in PASMCs isolated from patients with idiopathic pulmonary arterial hypertension compared with PASMCs from normal subjects. Overexpression of p53 in normal PASMCs inhibits store-operated Ca²⁺ entry (SOCE) induced by passive depletion of intracellularly stored Ca²⁺ in the sarcoplasmic reticulum, while downregulation of p53 enhances SOCE. These data indicate that differentially regulated expression of p53 and HIF-1α/2α in PASMCs and PAECs and the cross talk between p53 and HIF-1α/2α in PASMCs and PAECs may play an important role in the development of PH via, at least in part, induction of PAEC apoptosis and PASMC proliferation.

Diabetes Mellitus Associates with Increased Right Ventricular Afterload and Remodeling in Pulmonary Arterial Hypertension

BACKGROUND

Diabetes mellitus is associated with left ventricular hypertrophy and dysfunction. Parallel studies have also reported associations between diabetes mellitus and right ventricular dysfunction and reduced survival in patients with pulmonary arterial hypertension. However, the impact of diabetes mellitus on the pulmonary vasculature has not been well characterized. We hypothesized that diabetes mellitus and hyperglycemia could specifically influence right ventricular afterload and remodeling in patients with Group I pulmonary arterial hypertension, providing a link to their known susceptibility to right ventricular dysfunction.

METHODS

Using an adjusted model for age, sex, pulmonary vascular resistance, and medication use, associations of fasting blood glucose, glycated hemoglobin, and the presence of diabetes mellitus were evaluated with markers of disease severity in 162 patients with pulmonary arterial hypertension.

RESULTS

A surrogate measure of increased pulmonary artery stiffness, elevated pulmonary arterial elastance (P = .012), along with reduced log(pulmonary artery capacitance) (P = .006) were significantly associated with the presence of diabetes mellitus in patients with pulmonary arterial hypertension in a fully adjusted model. Similar associations between pulmonary arterial elastance and capacitance were noted with both fasting blood glucose and glycated hemoglobin. Furthermore, right ventricular wall thickness on echocardiography was greater in pulmonary arterial hypertension patients with diabetes, supporting the link between right ventricular remodeling and diabetes.

CONCLUSION

Cumulatively, these data demonstrate that an increase in right ventricular afterload, beyond pulmonary vascular resistance alone, may influence right ventricular remodeling and provide a mechanistic link between the susceptibility to right ventricular dysfunction in patients with both diabetes mellitus and pulmonary arterial hypertension.

ROS Signaling in the Pathogenesis of Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS)

The generation of reactive oxygen species (ROS) plays an important role for the maintenance of cellular processes and functions in the body. However, the excessive generation of oxygen radicals under pathological conditions such as acute lung injury (ALI) and its most severe form acute respiratory distress syndrome (ARDS) leads to increased endothelial permeability. Within this hallmark of ALI and ARDS, vascular microvessels lose their junctional integrity and show increased myosin contractions that promote the migration of polymorphonuclear leukocytes (PMNs) and the transition of solutes and fluids in the alveolar lumen. These processes all have a redox component, and this chapter focuses on the role played by ROS during the development of ALI/ARDS. We discuss the origins of ROS within the cell, cellular defense mechanisms against oxidative damage, the role of ROS in the development of endothelial permeability, and potential therapies targeted at oxidative stress.

Extracellular adenosine-induced Rac1 activation in pulmonary endothelium: Molecular mechanisms and barrier-protective role

We have previously shown that Gs-coupled adenosine receptors (A2a) are primarily involved in adenosine-induced human pulmonary artery endothelial cell (HPAEC) barrier enhancement. However, the downstream events that mediate the strengthening of the endothelial cell (EC) barrier via adenosine signaling are largely unknown. In the current study, we tested the overall hypothesis that adenosine-induced Rac1 activation and EC barrier enhancement is mediated by Gs-dependent stimulation of cAMP-dependent Epac1-mediated signaling cascades. Adenoviral transduction of HPAEC with constitutively-active (C/A) Rac1 (V12Rac1) significantly increases transendothelial electrical resistance (TER) reflecting an enhancement of the EC barrier. Conversely, expression of an inactive Rac1 mutant (N17Rac1) decreases TER reflecting a compromised EC barrier. The adenosine-induced increase in TER was accompanied by activation of Rac1, decrease in contractility (MLC dephosphorylation), but not Rho inhibition. Conversely, inhibition of Rac1 activity attenuates adenosine-induced increase in TER. We next examined the role of cAMP-activated Epac1 and its putative downstream targets Rac1, Vav2, Rap1, and Tiam1. Depletion of Epac1 attenuated the adenosine-induced Rac1 activation and the increase in TER. Furthermore, silencing of Rac1 specific guanine nucleotide exchange factors (GEFs), Vav2 and Rap1a expression significantly attenuated adenosine-induced increases in TER and activation of Rac1. Depletion of Rap1b only modestly impacted adenosine-induced increases in TER and Tiam1 depletion had no effect on adenosine-induced Rac1 activation and TER. Together these data strongly suggest that Rac1 activity is required for adenosine-induced EC barrier enhancement and that the activation of Rac1 and ability to strengthen the EC barrier depends, at least in part, on cAMP-dependent Epac1/Vav2/Rap1-mediated signaling.

Endothelial HIF-2α contributes to severe pulmonary hypertension due to endothelial-to-mesenchymal transition

Pulmonary vascular remodeling characterized by concentric wall thickening and intraluminal obliteration is a major contributor to the elevated pulmonary vascular resistance in patients with idiopathic pulmonary arterial hypertension (IPAH). Here we report that increased hypoxia-inducible factor 2α (HIF-2α) in lung vascular endothelial cells (LVECs) under normoxic conditions is involved in the development of pulmonary hypertension (PH) by inducing endothelial-to-mesenchymal transition (EndMT), which subsequently results in vascular remodeling and occlusive lesions. We observed significant EndMT and markedly increased expression of SNAI, an inducer of EndMT, in LVECs from patients with IPAH and animals with experimental PH compared with normal controls. LVECs isolated from IPAH patients had a higher level of HIF-2α than that from normal subjects, whereas HIF-1α was upregulated in pulmonary arterial smooth muscle cells (PASMCs) from IPAH patients. The increased HIF-2α level, due to downregulated prolyl hydroxylase domain protein 2 (PHD2), a prolyl hydroxylase that promotes HIF-2α degradation, was involved in enhanced EndMT and upregulated SNAI1/2 in LVECs from patients with IPAH. Moreover, knockdown of HIF-2α (but not HIF-1α) with siRNA decreases both SNAI1 and SNAI2 expression in IPAH-LVECs. Mice with endothelial cell (EC)-specific knockout (KO) of the PHD2 gene, egln1 (egln1EC-/-), developed severe PH under normoxic conditions, whereas Snai1/2 and EndMT were increased in LVECs of egln1EC-/- mice. EC-specific KO of the HIF-2α gene, hif2a, prevented mice from developing hypoxia-induced PH, whereas EC-specific deletion of the HIF-1α gene, hif1a, or smooth muscle cell (SMC)-specific deletion of hif2a, negligibly affected the development of PH. Also, exposure to hypoxia for 48-72 h increased protein level of HIF-1α in normal human PASMCs and HIF-2α in normal human LVECs. These data indicate that increased HIF-2α in LVECs plays a pathogenic role in the development of severe PH by upregulating SNAI1/2, inducing EndMT, and causing obliterative pulmonary vascular lesions and vascular remodeling.

Hypoxia selectively upregulates cation channels and increases cytosolic [Ca2+] in pulmonary, but not coronary, arterial smooth muscle cells

Ca²⁺ signaling, particularly the mechanism via store-operated Ca²⁺ entry (SOCE) and receptor-operated Ca²⁺ entry (ROCE), plays a critical role in the development of acute hypoxia-induced pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension. This study aimed to test the hypothesis that chronic hypoxia differentially regulates the expression of proteins that mediate SOCE and ROCE [stromal interacting molecule (STIM), Orai, and canonical transient receptor potential channel TRPC6] in pulmonary (PASMC) and coronary (CASMC) artery smooth muscle cells. The resting cytosolic [Ca²⁺] ([Ca²⁺]_cyt) and the stored [Ca²⁺] in the sarcoplasmic reticulum were not different in CASMC and PASMC. Seahorse measurement showed a similar level of mitochondrial bioenergetics (basal respiration and ATP production) between CASMC and PASMC. Glycolysis was significantly higher in PASMC than in CASMC. The amplitudes of cyclopiazonic acid-induced SOCE and OAG-induced ROCE in CASMC are slightly, but significantly, greater than in PASMC. The frequency and the area under the curve of Ca²⁺ oscillations induced by ATP and histamine were also larger in CASMC than in PASMC. Na⁺/Ca²⁺ exchanger-mediated increases in [Ca²⁺]_cyt did not differ significantly between CASMC and PASMC. The basal protein expression levels of STIM1/2, Orai1/2, and TRPC6 were higher in CASMC than in PASMC, but hypoxia (3% O₂ for 72 h) significantly upregulated protein expression levels of STIM1/STIM2, Orai1/Orai2, and TRPC6 and increased the resting [Ca²⁺]_cyt only in PASMC, but not in CASMC. The different response of essential components of store-operated and receptor-operated Ca²⁺ channels to hypoxia is a unique intrinsic property of PASMC, which is likely one of the important explanations why hypoxia causes pulmonary vasoconstriction and induces pulmonary vascular remodeling, but causes coronary vasodilation.

Chloroquine is a potent pulmonary vasodilator that attenuates hypoxia-induced pulmonary hypertension

BACKGROUND AND PURPOSE

Sustained pulmonary vasoconstriction and excessive pulmonary vascular remodelling are two major causes of elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension. The purpose of this study was to investigate whether chloroquine induced relaxation in the pulmonary artery (PA) and attenuates hypoxia-induced pulmonary hypertension (HPH).

EXPERIMENTAL APPROACH

Isometric tension was measured in rat PA rings pre-constricted with phenylephrine or high K⁺ solution. PA pressure was measured in mouse isolated, perfused and ventilated lungs. Fura-2 fluorescence microscopy was used to measure cytosolic free Ca²⁺ concentration levels in PA smooth muscle cells (PASMCs). Patch-clamp experiments were performed to assess the activity of voltage-dependent Ca²⁺ channels (VDCCs) in PASMC. Rats exposed to hypoxia (10% O₂ ) for 3 weeks were used as the model of HPH or Sugen5416/hypoxia (SuHx) for in vivo experiments.

KEY RESULTS

Chloroquine attenuated agonist-induced and high K⁺ -induced contraction in isolated rat PA. Pretreatment with l-NAME or indomethacin and functional removal of endothelium failed to inhibit chloroquine-induced PA relaxation. In PASMC, extracellular application of chloroquine attenuated store-operated Ca²⁺ entry and ATP-induced Ca²⁺ entry. Furthermore, chloroquine also inhibited whole-cell Ba²⁺ currents through VDCC in PASMC. In vivo experiments demonstrated that chloroquine treatment ameliorated the HPH and SuHx models.

CONCLUSIONS AND IMPLICATIONS

Chloroquine is a potent pulmonary vasodilator that may directly or indirectly block VDCC, store-operated Ca²⁺ channels and receptor-operated Ca²⁺ channels in PASMC. The therapeutic potential of chloroquine in pulmonary hypertension is probably due to the combination of its vasodilator, anti-proliferative and anti-autophagic effects.

Asymmetric Dimethylarginine Stimulates Akt1 Phosphorylation via Heat Shock Protein 70-Facilitated Carboxyl-Terminal Modulator Protein Degradation in Pulmonary Arterial Endothelial Cells

Asymmetric dimethylarginine (ADMA) induces the mitochondrial translocation of endothelial nitric oxide synthase (eNOS) through the nitration-mediated activation of Akt1. However, it is recognized that the activation of Akt1 requires phosphorylation events at threonine (T) 308 and serine (S) 473. Thus, the current study was performed to elucidate the potential effect of ADMA on Akt1 phosphorylation and the mechanisms that are involved. Exposure of pulmonary arterial endothelial cells to ADMA enhanced Akt1 phosphorylation at both threonine 308 and Ser473 without altering Akt1 protein levels, phosphatase and tensin homolog activity, or membrane Akt1 levels. Heat shock protein (Hsp) 90 plays a pivotal role in maintaining Akt1 activity, and our results demonstrate that ADMA decreased Hsp90-Akt1 interactions, but, surprisingly, overexpression of a dominant-negative Hsp90 mutant increased Akt1 phosphorylation. ADMA exposure or overexpression of dominant-negative Hsp90 increased Hsp70 levels, and depletion of Hsp70 abolished ADMA-induced Akt1 phosphorylation. ADMA decreased the interaction of Akt1 with its endogenous inhibitor, carboxyl-terminal modulator protein (CTMP). This was mediated by the proteasomal-dependent degradation of CTMP. The overexpression of CTMP attenuated ADMA-induced Akt1 phosphorylation at Ser473, eNOS phosphorylation at Ser617, and eNOS mitochondrial translocation. Finally, we found that the mitochondrial translocation of eNOS in our lamb model of pulmonary hypertension is associated with increased Akt1 and eNOS phosphorylation and reduced Akt1-CTMP protein interactions. In conclusion, our data suggest that CTMP is directly involved in ADMA-induced Akt1 phosphorylation in vitro and in vivo, and that increasing CTMP levels may be an avenue to treat pulmonary hypertension.

Improved metabolism and redox state with a novel preservation solution: implications for donor lungs after cardiac death (DCD)

Lungs donated after cardiac death (DCD) are an underutilized resource for a dwindling donor lung transplant pool. Our study investigates the potential of a novel preservation solution, Somah, to better preserve statically stored DCD lungs, for an extended time period, when compared to low-potassium dextran solution (LPD). We hypothesize that Somah is a metabolically superior organ preservation solution for hypothermic statically stored porcine DCD lungs, possibly improving lung transplant outcomes. Porcine DCD lungs (n = 3 per group) were flushed with and submerged in cold preservation solution. The lungs were stored up to 12 h, and samples were taken from lung tissue and the preservation medium throughout. Metabolomic and redox potential were analyzed using high performance liquid chromatography, mass spectrometry, and RedoxSYS®, comparing substrate and pathway utilization in both preservation solutions. Glutathione reduction was seen in Somah but not in LPD during preservation. Carnitine, carnosine, and n-acetylcarnosine levels were elevated in the Somah medium compared with LPD throughout. Biopsies of Somah exposed lungs demonstrated similar trends after 2 h, up to 12 h. Adenosine gradually decreased in Somah medium over 12 h, but not in LPD. An inversely proportional increase in inosine was found in Somah. Higher oxidative stress levels were measured in LPD. Our study suggests suboptimal metabolic preservation in lungs stored in LPD. LPD had poor antioxidant potential, cytoprotection, and an insufficient redox potential. These findings may have immediate clinical implications for human organs; however, further investigation is needed to evaluate DCD lung preservation in Somah as a viable option for transplant.

Endotoxin- and mechanical stress-induced epigenetic changes in the regulation of the nicotinamide phosphoribosyltransferase promoter

Mechanical ventilation, a lifesaving intervention for patients with acute respiratory distress syndrome (ARDS), also unfortunately contributes to excessive mechanical stress and impaired lung physiological and structural integrity. We have elsewhere established the pivotal role of increased nicotinamide phosphoribosyltransferase (NAMPT) transcription and secretion as well as its direct binding to the toll-like receptor 4 (TLR4) in the progression of this devastating syndrome; however, regulation of this critical gene in ventilator-induced lung injury (VILI) is not well characterized. On the basis of an emerging role for epigenetics in enrichment of VILI and CpG sites within the NAMPT promoter and 5'UTR, we hypothesized that NAMPT expression and downstream transcriptional events are influenced by epigenetic mechanisms. Concomitantly, excessive mechanical stress of human pulmonary artery endothelial cells or lipopolysaccharide (LPS) treatment led to both reduced DNA methylation levels in the NAMPT promoter and increased gene transcription. Histone deacetylase inhibition by trichostatin A or Sirt-1-silencing RNA attenuates LPS-induced NAMPT expression. Furthermore, recombinant NAMPT administration induced TLR4-dependent global H3K9 hypoacetylation. These studies suggest a complex epigenetic regulatory network of NAMPT in VILI and ARDS and open novel strategies for combating VILI and ARDS.

Hyper-activation of pp60Src limits nitric oxide signaling by increasing asymmetric dimethylarginine levels during acute lung injury

The molecular mechanisms by which the endothelial barrier becomes compromised during lipopolysaccharide (LPS) mediated acute lung injury (ALI) are still unresolved. We have previously reported that the disruption of the endothelial barrier is due, at least in part, to the uncoupling of endothelial nitric oxide synthase (eNOS) and increased peroxynitrite-mediated nitration of RhoA. The purpose of this study was to elucidate the molecular mechanisms by which LPS induces eNOS uncoupling during ALI. Exposure of pulmonary endothelial cells (PAEC) to LPS increased pp60^Src activity and this correlated with an increase in nitric oxide (NO) production, but also an increase in NOS derived superoxide, peroxynitrite formation and 3-nitrotyrosine (3-NT) levels. These effects could be simulated by the over-expression of a constitutively active pp60^Src (Y527FSrc) mutant and attenuated by over-expression of dominant negative pp60^Src mutant or reducing pp60^Src expression. LPS induces both RhoA nitration and endothelial barrier disruption and these events were attenuated when pp60^Src expression was reduced. Endothelial NOS uncoupling correlated with an increase in the levels of asymmetric dimethylarginine (ADMA) in both LPS exposed and Y527FSrc over-expressing PAEC. The effects in PAEC were also recapitulated when we transiently over-expressed Y527FSrc in the mouse lung. Finally, we found that the pp60-^Src-mediated decrease in DDAH activity was mediated by the phosphorylation of DDAH II at Y207 and that a Y207F mutant DDAH II was resistant to pp60^Src-mediated inhibition. We conclude that pp60^Src can directly inhibit DDAH II and this is involved in the increased ADMA levels that enhance eNOS uncoupling during the development of ALI.

Capsaicin-induced Ca2+ signaling is enhanced via upregulated TRPV1 channels in pulmonary artery smooth muscle cells from patients with idiopathic PAH

Capsaicin is an active component of chili pepper and a pain relief drug. Capsaicin can activate transient receptor potential vanilloid 1 (TRPV1) channels to increase cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt). A rise in [Ca²⁺]_cyt in pulmonary artery smooth muscle cells (PASMCs) is an important stimulus for pulmonary vasoconstriction and vascular remodeling. In this study, we observed that a capsaicin-induced increase in [Ca²⁺]_cyt was significantly enhanced in PASMCs from patients with idiopathic pulmonary arterial hypertension (IPAH) compared with normal PASMCs from healthy donors. In addition, the protein expression level of TRPV1 in IPAH PASMCs was greater than in normal PASMCs. Increasing the temperature from 23 to 43°C, or decreasing the extracellular pH value from 7.4 to 5.9 enhanced capsaicin-induced increases in [Ca²⁺]_cyt; the acidity (pH 5.9)- and heat (43°C)-mediated enhancement of capsaicin-induced [Ca²⁺]_cyt increases were greater in IPAH PASMCs than in normal PASMCs. Decreasing the extracellular osmotic pressure from 310 to 200 mOsmol/l also increased [Ca²⁺]_cyt, and the hypo-osmolarity-induced rise in [Ca²⁺]_cyt was greater in IPAH PASMCs than in healthy PASMCs. Inhibition of TRPV1 (with 5'-IRTX or capsazepine) or knockdown of TRPV1 (with short hairpin RNA) attenuated capsaicin-, acidity-, and osmotic stretch-mediated [Ca²⁺]_cyt increases in IPAH PASMCs. Capsaicin induced phosphorylation of CREB by raising [Ca²⁺]_cyt, and capsaicin-induced CREB phosphorylation were significantly enhanced in IPAH PASMCs compared with normal PASMCs. Pharmacological inhibition and knockdown of TRPV1 attenuated IPAH PASMC proliferation. Taken together, the capsaicin-mediated [Ca²⁺]_cyt increase due to upregulated TRPV1 may be a critical pathogenic mechanism that contributes to augmented Ca²⁺ influx and excessive PASMC proliferation in patients with IPAH.

Endothelial cell signaling and ventilator-induced lung injury: molecular mechanisms, genomic analyses, and therapeutic targets

Mechanical ventilation is a life-saving intervention in critically ill patients with respiratory failure due to acute respiratory distress syndrome (ARDS). Paradoxically, mechanical ventilation also creates excessive mechanical stress that directly augments lung injury, a syndrome known as ventilator-induced lung injury (VILI). The pathobiology of VILI and ARDS shares many inflammatory features including increases in lung vascular permeability due to loss of endothelial cell barrier integrity resulting in alveolar flooding. While there have been advances in the understanding of certain elements of VILI and ARDS pathobiology, such as defining the importance of lung inflammatory leukocyte infiltration and highly induced cytokine expression, a deep understanding of the initiating and regulatory pathways involved in these inflammatory responses remains poorly understood. Prevailing evidence indicates that loss of endothelial barrier function plays a primary role in the development of VILI and ARDS. Thus this review will focus on the latest knowledge related to 1) the key role of the endothelium in the pathogenesis of VILI; 2) the transcription factors that relay the effects of excessive mechanical stress in the endothelium; 3) the mechanical stress-induced posttranslational modifications that influence key signaling pathways involved in VILI responses in the endothelium; 4) the genetic and epigenetic regulation of key target genes in the endothelium that are involved in VILI responses; and 5) the need for novel therapeutic strategies for VILI that can preserve endothelial barrier function.

Scottish Anatomy Departments: Adapting to Change

Objectives

To document changes to the academic infrastructure of Scottish departments of anatomy over the past 20 years and compare the strategic approaches adopted by each institution to ensure continued provision of the subject to medical students

Design

Interviews with principal anatomy staff members to obtain targeted information (staff numbers, staff recruitment, student numbers, staff:student ratio and contact hours in the medical curriculum) by investigating three temporal snapshots chosen at 10 year intervals (academic years 1983/4, 1993/4 and 2003/4)

Participants

Principal teaching staff members from the anatomy departments at the five Scottish medical schools: University of Aberdeen, University of Dundee, University of Edinburgh, University of Glasgow and the University of St Andrews. Additional information was forthcoming from the admissions office of each University.

Results

Over the past 20 years the Scottish anatomy schools have weathered a variety of external and internal influences and each school has adopted very individual strategies to the delivery and maintenance of their subject. Some schools have unquestionably been more affected than others but all have responded in a unique way to the demands of the disciplines they choose to subserve. In general, each school has seen a decline in the compliment of teachers (staff + demonstrators) whereas the student number has increased dramatically. Each department has micromanaged its proportions of lectures, dissecting room practical time and tutorials to best fit their student base, staff capabilities and the requirements of, and/or alterations to, the medical curriculum offered in their institution.

Pulmonary artery smooth muscle cell hyperproliferation and metabolic shift triggered by pulmonary overcirculation

Vascular cell hyperproliferation and metabolic reprogramming contribute to the pathophysiology of pulmonary arterial hypertension (PAH). An important cause of PAH in children with congenital heart disease (CHD) is increased pulmonary blood flow (PBF). To better characterize this disease course we studied early changes in pulmonary artery smooth muscle cell (PASMC) proliferation and metabolism using a unique ovine model of pulmonary overcirculation. Consistent with PAH in adults, PASMCs derived from 4-wk-old lambs exposed to increased PBF (shunt) exhibited increased rates of proliferation. While shunt PASMCs also exhibited significant decreases in mitochondrial oxygen consumption, membrane potential, and tricarboxylic acid (TCA) cycle function, suggesting a switch to Warburg metabolism as observed in advanced PAH in adults, they unexpectedly demonstrated decreased glycolytic lactate production, likely due to enhanced flux through the pentose phosphate pathway (PPP). This may be a response to the marked increase in NADPH oxidase (Nox) activity and decreased NADPH/NADP+ ratios observed in shunt PASMCs. Consistent with these findings, pharmacological inhibition of Nox activity preferentially slowed the growth of shunt PASMCs in vitro. Our results therefore indicate that PASMC hyperproliferation is observed early in the setting of pulmonary overcirculation and is accompanied by a unique metabolic profile that is independent of HIF-1α, PDHK1, or increased glycolytic flux. Our results also suggest that Nox inhibition may help prevent pulmonary overcirculation-induced PAH in children born with CHD.

Anatomy in Scotland: 20 Years of Change

Background & Aims: To document changes in the educational infrastructure of anatomy in Scotland over the past 20 years. To investigate the possible impact of the GMC 1993 recommendations and assess the preparedness of Scottish anatomy to meet the implications of the proposed amendment to the 1984 Anatomy Act. Results: Over the past 20 years in Scotland, the total number of teaching staff in anatomy (full time, part time and honorary) has decreased by over 24%, full time teaching staff numbers have decreased by more than 33% and the number of clinical demonstrators by more than 70%. However, medical student intake has risen by 38% and the overall student number experiencing anatomical teaching (medicine, science and dentistry) has more than doubled, resulting in a current average staff:student ratio of 1:58. Anatomy contact hours between staff and medical students have decreased by just over 60% in the last 20 years. Conclusions: In the last 20 years, contact hours and staffing levels have decreased substantially in Scotland whilst student numbers (medical, science and dental) have increased significantly. On average the anatomical input to the medical curriculum decreased by 28% between 1983 and 1993 but post the CMC initiative, there was a further decrease of 43% resulting in current medical students in Scotland experiencing a 60% reduction in contact anatomy time compared to their peers in the early 1980's. The decline in anatomical infrastructure is not a reassuring indicator of its ability to meet substantial future demands.

Redox regulation of epidermal growth factor receptor signaling during the development of pulmonary hypertension

The development of pulmonary hypertension (PH) involves the uncontrolled proliferation of pulmonary smooth muscle cells via increased growth factor receptor signaling. However, the role of epidermal growth factor receptor (EGFR) signaling is controversial, as humans with advanced PH exhibit no changes in EGFR protein levels and purpose of the present study was to determine whether there are post-translational mechanisms that enhance EGFR signaling in PH. The EGFR inhibitor, gefinitib, significantly attenuated EGFR signaling and prevented the development of PH in monocrotaline (MCT)-exposed rats, confirming the contribution of EGFR activation in MCT induced PH. There was an early MCT-mediated increase in hydrogen peroxide, which correlated with the binding of the active metabolite of MCT, monocrotaline pyrrole, to catalase Cys377, disrupting its multimeric structure. This early oxidative stress was responsible for the oxidation of EGFR and the formation of sodium dodecyl sulfate (SDS) stable EGFR dimers through dityrosine cross-linking. These cross-linked dimers exhibited increased EGFR autophosphorylation and signaling. The activation of EGFR signaling did not correlate with pp60(src) dependent Y845 phosphorylation or EGFR ligand expression. Importantly, the analysis of patients with advanced PH revealed the same enhancement of EGFR autophosphorylation and covalent dimer formation in pulmonary arteries, while total EGFR protein levels were unchanged. As in the MCT exposed rat model, the activation of EGFR in human samples was independent of pp60(src) phosphorylation site and ligand expression. This study provides a novel molecular mechanism of oxidative stress stimulated covalent EGFR dimerization via tyrosine dimerization that contributes into development of PH.