Right ventricular stiffening and anisotropy alterations in pulmonary hypertension: Mechanisms and relations to function.

Aims: Pulmonary hypertension (PH) results in an increase in RV afterload, leading to RV dysfunction and failure. The mechanisms underlying maladaptive RV remodeling are poorly understood. In this study, we investigated the multiscale and mechanistic nature of RV free wall (RVFW) biomechanical remodeling and its correlations with RV function adaptations. Methods and Results: Mild and severe models of PH, consisting of hypoxia (Hx) model in Sprague-Dawley (SD) rats (n=6 each, Control and PH) and Sugen-hypoxia (SuHx) model in Fischer (CDF) rats (n=6 each, Control and PH), were used. Organ-level function and tissue-level stiffness and microstructure were quantified through in-vivo and ex-vivo measures, respectively. Multiscale analysis was used to determine the association between fiber-level remodeling, tissue-level stiffening, and organ-level dysfunction. Animal models with different PH severity provided a wide range of RVFW stiffening and anisotropy alterations in PH. Decreased RV-pulmonary artery (PA) coupling correlated strongly with stiffening but showed a weaker association with the loss of RVFW anisotropy. Machine learning classification identified the range of adaptive and maladaptive RVFW stiffening. Multiscale modeling revealed that increased collagen fiber tautness was a key remodeling mechanism that differentiated severe from mild stiffening. Myofiber orientation analysis indicated a shift away from the predominantly circumferential fibers observed in healthy RVFW specimens, leading to a significant loss of tissue anisotropy. Conclusion: Multiscale biomechanical analysis indicated that although hypertrophy and fibrosis occur in both mild and severe PH, certain fiber-level remodeling events, including increased tautness in the newly deposited collagen fibers and significant reorientations of myofibers, contributed to excessive biomechanical maladaptation of the RVFW leading to severe RV-PA uncoupling. Collagen fiber remodeling and the loss of tissue anisotropy can provide an improved understanding of the transition from adaptive to maladaptive remodeling. Translational perspective: Right ventricular (RV) failure is a leading cause of mortality in patients with pulmonary hypertension (PH). RV diastolic and systolic impairments are evident in PH patients. Stiffening of the RV wall tissue and changes in the wall anisotropy are expected to be major contributors to both impairments. Global assessments of the RV function remain inadequate in identifying patients with maladaptive RV wall remodeling primarily due to their confounded and weak representation of RV fiber and tissue remodeling events. This study provides novel insights into the underlying mechanisms of RV biomechanical remodeling and identifies the adaptive-to-maladaptive transition across the RV biomechanics-function spectrum. Our analysis dissecting the contribution of different RV wall remodeling events to RV dysfunction determines the most adverse fiber-level remodeling to RV dysfunction as new therapeutic targets to curtail RV maladaptation and, in turn, RV failure in PH.

Reduced exercise capacity occurs before intrinsic skeletal muscle dysfunction in experimental rat models of pulmonary hypertension.

Reduced exercise capacity in pulmonary hypertension (PH) significantly impacts quality of life. However, the cause of reduced exercise capacity in PH remains unclear. The objective of this study was to investigate whether intrinsic skeletal muscle changes are causative in reduced exercise capacity in PH using preclinical PH rat models with different PH severity. PH was induced in adult Sprague-Dawley (SD) or Fischer (CDF) rats with one dose of SU5416 (20 mg/kg) injection, followed by 3 weeks of hypoxia and additional 0-4 weeks of normoxia exposure. Control s rats were injected with vehicle and housed in normoxia. Echocardiography was performed to assess cardiac function. Exercise capacity was assessed by VO2 max. Skeletal muscle structural changes (atrophy, fiber type switching, and capillary density), mitochondrial function, isometric force, and fatigue profile were assessed. In SD rats, right ventricular systolic dysfunction is associated with reduced exercise capacity in PH rats at 7-week timepoint in comparison to control rats, while no changes were observed in skeletal muscle structure, mitochondrial function, isometric force, or fatigue profile. CDF rats at 4-week timepoint developed a more severe PH and, in addition to right ventricular dysfunction, the reduced exercise capacity in these rats is associated with skeletal muscle atrophy; however, mitochondrial function, isometric force, and fatigue profile in skeletal muscle remain unchanged. Our data suggest that cardiopulmonary impairments in PH are the primary cause of reduced exercise capacity, which occurs before intrinsic skeletal muscle dysfunction.

Right Ventricular Architectural Remodeling and Functional Adaptation in Pulmonary Hypertension.

BACKGROUND: Global indices of right ventricle (RV) function provide limited insights into mechanisms underlying RV remodeling in pulmonary hypertension (PH). While RV myocardial architectural remodeling has been observed in PH, its effect on RV adaptation is poorly understood. METHODS: Hemodynamic assessments were performed in 2 rodent models of PH. RV free wall myoarchitecture was quantified using generalized Q-space imaging and tractography analyses. Computational models were developed to predict RV wall strains. Data from animal studies were analyzed to determine the correlations between hemodynamic measurements, RV strains, and structural measures. RESULTS: In contrast to the PH rats with severe RV maladaptation, PH rats with mild RV maladaptation showed a decrease in helical range of fiber orientation in the RV free wall (139º versus 97º; P=0.029), preserved global circumferential strain, and exhibited less reduction in right ventricular-pulmonary arterial coupling (0.029 versus 0.017 mm/mm Hg; P=0.037). Helical range correlated positively with coupling (P=0.036) and stroke volume index (P<0.01). Coupling correlated with global circumferential strain (P<0.01) and global radial strain (P<0.01) but not global longitudinal strain. CONCLUSIONS: Data analysis suggests that adaptive RV architectural remodeling could improve RV function in PH. Our findings suggest the need to assess RV architecture within routine screenings of PH patients to improve our understanding of its prognostic and therapeutic significance in PH.

Chitinase 3 like 1 contributes to the development of pulmonary vascular remodeling in pulmonary hypertension.

Chitinase 3 like 1 (CHI3L1) is the prototypic chitinase-like protein mediating inflammation, cell proliferation, and tissue remodeling. Limited data suggest CHI3L1 is elevated in human pulmonary arterial hypertension (PAH) and is associated with disease severity. Despite its importance as a regulator of injury/repair responses, the relationship between CHI3L1 and pulmonary vascular remodeling is not well understood. We hypothesize that CHI3L1 and its signaling pathways contribute to the vascular remodeling responses that occur in pulmonary hypertension (PH). We examined the relationship of plasma CHI3L1 levels and severity of PH in patients with various forms of PH, including group 1 PAH and group 3 PH, and found that circulating levels of serum CHI3L1 were associated with worse hemodynamics and correlated directly with mean pulmonary artery pressure and pulmonary vascular resistance. We also used transgenic mice with constitutive knockout and inducible overexpression of CHI3L1 to examine its role in hypoxia-, monocrotaline-, and bleomycin-induced models of pulmonary vascular disease. In all 3 mouse models of pulmonary vascular disease, pulmonary hypertensive responses were mitigated in CHI3L1-null mice and accentuated in transgenic mice that overexpress CHI3L1. Finally, CHI3L1 alone was sufficient to induce pulmonary arterial smooth muscle cell proliferation, inhibit pulmonary vascular endothelial cell apoptosis, induce the loss of endothelial barrier function, and induce endothelial-mesenchymal transition. These findings demonstrate that CHI3L1 and its receptors play an integral role in pulmonary vascular disease pathobiology and may offer a target for the treatment of PAH and PH associated with fibrotic lung disease.

A machine learning model to estimate myocardial stiffness from EDPVR.

In-vivo estimation of mechanical properties of the myocardium is essential for patient-specific diagnosis and prognosis of cardiac disease involving myocardial remodeling, including myocardial infarction and heart failure with preserved ejection fraction. Current approaches use time-consuming finite-element (FE) inverse methods that involve reconstructing and meshing the heart geometry, imposing measured loading, and conducting computationally expensive iterative FE simulations. In this paper, we propose a machine learning (ML) model that feasibly and accurately predicts passive myocardial properties directly from select geometric, architectural, and hemodynamic measures, thus bypassing exhaustive steps commonly required in cardiac FE inverse problems. Geometric and fiber-orientation features were chosen to be readily obtainable from standard cardiac imaging protocols. The end-diastolic pressure-volume relationship (EDPVR), which can be obtained using a single-point pressure-volume measurement, was used as a hemodynamic (loading) feature. A comprehensive ML training dataset in the geometry-architecture-loading space was generated, including a wide variety of partially synthesized rodent heart geometry and myofiber helicity possibilities, and a broad range of EDPVRs obtained using forward FE simulations. Latin hypercube sampling was used to create 2500 examples for training, validation, and testing. A multi-layer feed-forward neural network (MFNN) was used as a deep learning agent to train the ML model. The model showed excellent performance in predicting stiffness parameters [Formula: see text] and [Formula: see text] associated with fiber direction ([Formula: see text] and [Formula: see text]). After conducting permutation feature importance analysis, the ML performance further improved for [Formula: see text] ([Formula: see text]), and the left ventricular volume and endocardial area were found to be the most critical geometric features for accurate predictions. The ML model predictions were evaluated further in two cases: (i) rat-specific stiffness data measured using ex-vivo mechanical testing, and (ii) patient-specific estimation using FE inverse modeling. Excellent agreements with ML predictions were found for both cases. The trained ML model offers a feasible technology to estimate patient-specific myocardial properties, thus, bridging the gap between EDPVR, as a confounded organ-level metric for tissue stiffness, and intrinsic tissue-level properties. These properties provide incremental information relative to traditional organ-level indices for cardiac function, improving the clinical assessment and prognosis of cardiac diseases.

α7 Nicotinic acetylcholine receptor mediates right ventricular fibrosis and diastolic dysfunction in pulmonary hypertension.

Right ventricular (RV) fibrosis is a key feature of maladaptive RV hypertrophy and dysfunction and is associated with poor outcomes in pulmonary hypertension (PH). However, mechanisms and therapeutic strategies to mitigate RV fibrosis remain unrealized. Previously, we identified that cardiac fibroblast α7 nicotinic acetylcholine receptor (α7 nAChR) drives smoking-induced RV fibrosis. Here, we sought to define the role of α7 nAChR in RV dysfunction and fibrosis in the settings of RV pressure overload as seen in PH. We show that RV tissue from PH patients has increased collagen content and ACh expression. Using an experimental rat model of PH, we demonstrate that RV fibrosis and dysfunction are associated with increases in ACh and α7 nAChR expression in the RV but not in the left ventricle (LV). In vitro studies show that α7 nAChR activation leads to an increase in adult ventricular fibroblast proliferation and collagen content mediated by a Ca2+/epidermal growth factor receptor (EGFR) signaling mechanism. Pharmacological antagonism of nAChR decreases RV collagen content and improves RV function in the PH model. Furthermore, mice lacking α7 nAChR exhibit improved RV diastolic function and have lower RV collagen content in response to persistently increased RV afterload, compared with WT controls. These finding indicate that enhanced α7 nAChR signaling is an important mechanism underlying RV fibrosis and dysfunction, and targeted inhibition of α7 nAChR is a potentially novel therapeutic strategy in the setting of increased RV afterload.

Endothelial to mesenchymal transition during neonatal hyperoxia-induced pulmonary hypertension.

Bronchopulmonary dysplasia (BPD), a chronic lung disease in premature infants, results from mechanical ventilation and hyperoxia, amongst other factors. Although most BPD survivors can be weaned from supplemental oxygen, many show evidence of cardiovascular sequelae in adulthood, including pulmonary hypertension and pulmonary vascular remodeling. Endothelial-mesenchymal transition (EndoMT) plays an important role in mediating vascular remodeling in idiopathic pulmonary arterial hypertension. Whether hyperoxic exposure, a known mediator of BPD in rodent models, causes EndoMT resulting in vascular remodeling and pulmonary hypertension remains unclear. We hypothesized that neonatal hyperoxic exposure causes EndoMT, leading to the development of pulmonary hypertension in adulthood. To test this hypothesis, newborn mice were exposed to hyperoxia and then allowed to recover in room air until adulthood. Neonatal hyperoxic exposure gradually caused pulmonary vascular and right ventricle remodeling as well as pulmonary hypertension. Male mice were more susceptible to developing pulmonary hypertension compared to female mice, when exposed to hyperoxia as newborns. Hyperoxic exposure induced EndoMT in mouse lungs as well as in cultured lung microvascular endothelial cells (LMVECs) isolated from neonatal mice and human fetal donors. This was augmented in cultured LMVECs from male donors compared to those from female donors. Using primary mouse LMVECs, hyperoxic exposure increased phosphorylation of both Smad2 and Smad3, but reduced Smad7 protein levels. Treatment with a selective TGF-ß inhibitor SB431542 blocked hyperoxia-induced EndoMT in vitro. Altogether, we show that neonatal hyperoxic exposure caused vascular remodeling and pulmonary hypertension in adulthood. This was associated with increased EndoMT. These novel observations provide mechanisms underlying hyperoxia-induced vascular remodeling and potential approaches to prevent BPD-associated pulmonary hypertension by targeting EndoMT. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Endurance exercise training in pulmonary hypertension increases skeletal muscle electron transport chain supercomplex assembly.

Pulmonary hypertension is associated with pronounced exercise intolerance (decreased V c O2 max) that can significantly impact quality of life. The cause of exercise intolerance in pulmonary hypertension remains unclear. Mitochondrial supercomplexes are large respiratory assemblies of individual electron transport chain complexes which can promote more efficient respiration. In this study, we examined pulmonary hypertension and exercise-induced changes in skeletal muscle electron transport chain protein expression and supercomplex assembly. Pulmonary arterial hypertension was induced in rats with the Sugen/Hypoxia model (10% FiO2, three weeks). Pulmonary arterial hypertension and control rats were assigned to an exercise training protocol group or kept sedentary for one month. Cardiac function and V c O2 max were assessed at the beginning and end of exercise training. Red (Type 1-oxidative muscle) and white (Type 2-glycolytic muscle) gastrocnemius were assessed for changes in electron transport chain complex protein expression and supercomplex assembly via SDS- and Blue Native-PAGE. Results showed that pulmonary arterial hypertension caused a significant decrease in V c O2 max via treadmill testing that was improved with exercise (P < 0.01). Decreases in cardiac output and pulmonary acceleration time due to pulmonary arterial hypertension were not improved with exercise. Pulmonary arterial hypertension reduced expression in individual electron transport chain complex protein expression (NDUFB8 (CI), SDHB (CII), Cox IV (CIV), but not UQCRC2 (CIII), or ATP5a (CV)) in red gastrocnemius muscle. Both red gastrocnemius and white gastrocnemius electron transport chain expression was unaffected by exercise. However, non-denaturing Blue Native-PAGE analysis of mitochondrial supercomplexes demonstrated increases with exercise training in pulmonary arterial hypertension in the red gastrocnemius but not white gastrocnemius muscle. Pulmonary arterial hypertension-induced exercise intolerance is improved with exercise and is associated with muscle type specific alteration in mitochondrial supercomplex assembly and expression of mitochondrial electron transport chain proteins.

Blockade of equilibrative nucleoside transporter 1/2 protects against Pseudomonas aeruginosa-induced acute lung injury and NLRP3 inflammasome activation.

Pseudomonas aeruginosa infections are increasingly multidrug resistant and cause healthcare-associated pneumonia, a major risk factor for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Adenosine is a signaling nucleoside with potential opposing effects; adenosine can either protect against acute lung injury via adenosine receptors or cause lung injury via adenosine receptors or equilibrative nucleoside transporter (ENT)-dependent intracellular adenosine uptake. We hypothesized that blockade of intracellular adenosine uptake by inhibition of ENT1/2 would increase adenosine receptor signaling and protect against P. aeruginosa-induced acute lung injury. We observed that P. aeruginosa (strain: PA103) infection induced acute lung injury in C57BL/6 mice in a dose- and time-dependent manner. Using ENT1/2 pharmacological inhibitor, nitrobenzylthioinosine (NBTI), and ENT1-null mice, we demonstrated that ENT blockade elevated lung adenosine levels and significantly attenuated P. aeruginosa-induced acute lung injury, as assessed by lung wet-to-dry weight ratio, BAL protein levels, BAL inflammatory cell counts, pro-inflammatory cytokines, and pulmonary function (total lung volume, static lung compliance, tissue damping, and tissue elastance). Using both agonists and antagonists directed against adenosine receptors A2AR and A2BR, we further demonstrated that ENT1/2 blockade protected against P. aeruginosa -induced acute lung injury via activation of A2AR and A2BR. Additionally, ENT1/2 chemical inhibition and ENT1 knockout prevented P. aeruginosa-induced lung NLRP3 inflammasome activation. Finally, inhibition of inflammasome prevented P. aeruginosa-induced acute lung injury. Our results suggest that targeting ENT1/2 and NLRP3 inflammasome may be novel strategies for prevention and treatment of P. aeruginosa-induced pneumonia and subsequent ARDS.

Treatment of Pulmonary Hypertension With Angiotensin II Receptor Blocker and Neprilysin Inhibitor Sacubitril/Valsartan.

BACKGROUND: Angiotensin II has been implicated in maladaptive right ventricular (RV) hypertrophy and fibrosis associated with pulmonary hypertension (PH). Natriuretic peptides decrease RV afterload by promoting pulmonary vasodilation and inhibiting vascular remodeling but are degraded by neprilysin. We hypothesized that angiotensin receptor blocker and neprilysin inhibitor, sacubitril/valsartan (Sac/Val, LCZ696), will attenuate PH and improve RV function by targeting both pulmonary vascular and RV remodeling. METHODS: PH was induced in rats using the SU5416/hypoxia model (Su/Hx), followed by 6-week treatment with placebo, Sac/Val, or Val alone. There were 4 groups: CON-normoxic animals with placebo (n=18); PH-Su/Hx rats+placebo (n=34); PH+Sac/Val (N=24); and PH+Val (n=16). RESULTS: In animals with PH, treatment with Sac/Val but not Val resulted in significant reduction in RV pressure (mm Hg: PH: 62±4, PH+Sac/Val: 46±5), hypertrophy (RV/LV+S: PH: 0.74±0.06, PH+Sac/Val: 0.46±0.06), collagen content (µg/50 µg protein: PH: 8.2±0.3, PH+Sac/Val: 6.4±0.4), pressures and improvement in RVs (mm/s: PH: 31.2±1.8, PH+Sac/Val: 43.1±3.6) compared with placebo. This was associated with reduced pulmonary vascular wall thickness, increased lung levels of ANP (atrial natriuretic peptide), BNP (brain-type natriuretic peptide), and cGMP, and decreased plasma endothelin-1 compared with PH alone. Also, PH+Sac/Val animals had altered expression of PKC isozymes in RV tissue compared with PH alone. CONCLUSIONS: Sac/Val reduces pulmonary pressures, vascular remodeling, as well as RV hypertrophy in a rat model of PH and may be appropriate for treatment of pulmonary hypertension and RV dysfunction.

Activation of Anoctamin-1 Limits Pulmonary Endothelial Cell Proliferation via p38-Mitogen-activated Protein Kinase-Dependent Apoptosis.

Hyperproliferative endothelial cells (ECs) play an important role in the pathogenesis of pulmonary arterial hypertension (PAH). Anoctamin (Ano)-1, a calcium-activated chloride channel, can regulate cell proliferation and cell cycle in multiple cell types. However, the expression and function of Ano1 in the pulmonary endothelium is unknown. We examined whether Ano1 was expressed in pulmonary ECs and if altering Ano1 activity would affect EC survival. Expression and localization of Ano1 in rat lung microvascular ECs (RLMVECs) was assessed using immunoblot, immunofluorescence, and subcellular fractionation. Cell counts, flow cytometry, and caspase-3 activity were used to assess changes in cell number and apoptosis in response to the small molecule Ano1 activator, Eact. Changes in mitochondrial membrane potential and mitochondrial reactive oxygen species (mtROS) were assessed using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine, iodide (mitochondrial membrane potential dye) and mitochondrial ROS dye, respectively. Ano1 is expressed in RLMVECs and is enriched in the mitochondria. Activation of Ano1 with Eact reduced RLMVEC counts through increased apoptosis. Ano1 knockdown blocked the effects of Eact. Ano1 activation increased mtROS, reduced mitochondrial membrane potential, increased p38 phosphorylation, and induced release of apoptosis-inducing factor. mtROS inhibition attenuated Eact-mediated p38 phosphorylation. Pulmonary artery ECs isolated from patients with idiopathic PAH (IPAH) had higher expression of Ano1 and increased cell counts compared with control subjects. Eact treatment reduced cell counts in IPAH cells, which was associated with increased apoptosis. In summary, Ano1 is expressed in lung EC mitochondria. Activation of Ano1 promotes apoptosis of pulmonary ECs and human IPAH-pulmonary artery ECs, likely via increased mtROS and p38 phosphorylation, leading to apoptosis.

Activation of the sweet taste receptor, T1R3, by the artificial sweetener sucralose regulates the pulmonary endothelium.

A hallmark of acute respiratory distress syndrome (ARDS) is pulmonary vascular permeability. In these settings, loss of barrier integrity is mediated by cell-contact disassembly and actin remodeling. Studies into molecular mechanisms responsible for improving microvascular barrier function are therefore vital in the development of therapeutic targets for reducing vascular permeability in ARDS. The sweet taste receptor T1R3 is a G protein-coupled receptor, activated following exposure to sweet molecules, to trigger a gustducin-dependent signal cascade. In recent years, extraoral locations for T1R3 have been identified; however, no studies have focused on T1R3 within the vasculature. We hypothesize that activation of T1R3, in the pulmonary vasculature, plays a role in regulating endothelial barrier function in settings of ARDS. Our study demonstrated expression of T1R3 within the pulmonary vasculature, with a drop in expression levels following exposure to barrier-disruptive agents. Exposure of lung microvascular endothelial cells to the intensely sweet molecule sucralose attenuated LPS- and thrombin-induced endothelial barrier dysfunction. Likewise, sucralose exposure attenuated bacteria-induced lung edema formation in vivo. Inhibition of sweet taste signaling, through zinc sulfate, T1R3, or G-protein siRNA, blunted the protective effects of sucralose on the endothelium. Sucralose significantly reduced LPS-induced increased expression or phosphorylation of the key signaling molecules Src, p21-activated kinase (PAK), myosin light chain-2 (MLC2), heat shock protein 27 (HSP27), and p110α phosphatidylinositol 3-kinase (p110αPI3K). Activation of T1R3 by sucralose protects the pulmonary endothelium from edemagenic agent-induced barrier disruption, potentially through abrogation of Src/PAK/p110αPI3K-mediated cell-contact disassembly and Src/MLC2/HSP27-mediated actin remodeling. Identification of sweet taste sensing in the pulmonary vasculature may represent a novel therapeutic target to protect the endothelium in settings of ARDS.

Effect of α7 nicotinic acetylcholine receptor activation on cardiac fibroblasts: a mechanism underlying RV fibrosis associated with cigarette smoke exposure.

Right ventricular (RV) dysfunction is associated with numerous smoking-related illnesses, including chronic obstructive pulmonary disease (COPD), in which it is present even in the absence of pulmonary hypertension. It is unknown whether exposure to cigarette smoke (CS) has direct effects on RV function and cardiac fibroblast (CF) proliferation or collagen synthesis. In this study, we evaluated cardiac function and fibrosis in mice exposed to CS and determined mechanisms of smoke-induced changes in CF signaling and fibrosis. AKR mice were exposed to CS for 6 wk followed by echocardiography and evaluation of cardiac hypertrophy, collagen content, and pulmonary muscularization. Proliferation and collagen content were evaluated in primary isolated rat CFs exposed to CS extract (CSE) or nicotine. Markers of cell proliferation, fibrosis, and proliferative signaling were determined by immunoblot or Sircol collagen assay. Mice exposed to CS had significantly decreased RV function, as determined by tricuspid annular plane systolic excursion. There were no changes in left ventricular parameters. RV collagen content was significantly elevated, but there was no change in RV hypertrophy or pulmonary vascular muscularization. CSE directly increased CF proliferation and collagen content in CF. Nicotine alone reproduced these effects. CSE and nicotine-induced fibroblast proliferation and collagen content were mediated through α7 nicotinic acetylcholine receptors and were dependent on PKC-α, PKC-δ, and reduced p38-MAPK phosphorylation. CS and nicotine have direct effects on CFs to induce proliferation and fibrosis, which may negatively affect right heart function.

PKC δ and ßII regulate angiotensin II-mediated fibrosis through p38: a mechanism of RV fibrosis in pulmonary hypertension.

Pulmonary hypertension (PH) eventually leads to right ventricular (RV) fibrosis and dysfunction that is associated with increased morbidity and mortality. Although angiotensin II plays an important role in RV remodeling associated with hypoxic PH, the molecular mechanisms underlying RV fibrosis in PH largely remain unresolved. We hypothesized that PKC-p38 signaling is involved in RV collagen accumulation in PH and in response to angiotensin II stimulation. Adult male Sprague-Dawley rats were exposed to 3 wk of normoxia or hypoxia (10% FiO2 ) as a model of PH. Hypoxic rats developed RV hypertrophy and fibrosis associated with an increase in PKC ßII and δ protein expression and p38 dephosphorylation in freshly isolated RV cardiac fibroblasts. Further mechanistic studies were performed in cultured primary cardiac fibroblasts stimulated with angiotensin II, a key activator of ventricular fibrosis in PH. Angiotensin II induced a reduction in p38 phosphorylation that was attenuated following chemical inhibition of PKC ßII and δ. Molecular and chemical inhibition of PKC ßII and δ abrogated angiotensin II-induced cardiac fibroblast proliferation and collagen deposition in vitro. The effects of PKC inhibition on proliferation and fibrosis were reversed by chemical inhibition of p38. Conversely, constitutive activation of p38 attenuated angiotensin II-induced increase of cardiac fibroblast proliferation and collagen accumulation. PKC ßII- and δ-dependent inactivation of p38 regulates cardiac fibroblast proliferation and collagen deposition in response to angiotensin II, which suggests that the PKC-p38 signaling in cardiac fibroblasts may be involved and important in the pathophysiology of RV fibrosis in PH.

NS1619-induced vasodilation is enhanced and differentially mediated in chronically hypoxic lungs.

PURPOSE: To identify the effect of the benzimidazalone derivative, NS1619, on modulating pulmonary vascular tone in lungs from rats exposed to normoxia (21% FiO2) or chronic hypoxia (10% FiO2) for three weeks. METHODS: Isolated perfused lungs were preconstricted (U46619), and dose-dependent vasodilation to NS1619 was assessed. To elucidate the mechanisms responsible, NS1619 vasodilatory responses were assessed following inhibition of large-conductance Ca(2+)-activated (BKCa; iberiotoxin and paxilline), L-type Ca2+ (nifedipine), K+ (tetraethylammonium), Cl- (niflumic acid), and cation/TRP (lanthanum) channels, as well as nitric oxide synthase (L-NAME). RESULTS: Compared to normoxia, NS1619-induced vasodilation was significantly greater following hypoxia; however, NO-dependent vasodilation and BKCa-mediated vasodilation, in response to NS1619, were similar in the normoxic and hypoxic lungs. In contrast, direct activation of L-type Ca2+ and non-BKCa K+ channel was involved in the NS1619-induced vasodilation only in hypoxic lungs. CONCLUSIONS: NS1619 causes pulmonary vasodilation by affecting multiple complementary pathways, including stimulation of NO production, activation of BKCa channels, other TEA-sensitive K+ channels, and L-type Ca2+ channels, and could be considered as a therapeutic agent in hypoxic PH.

Cigarette smoke-induced lung endothelial apoptosis and emphysema are associated with impairment of FAK and eIF2α.

Lung endothelial cell (EC) apoptosis has been implicated in the pathogenesis of emphysema. However, the mechanism underlying cigarette smoke (CS)-induced lung EC apoptosis and emphysema is not well defined. We have previously shown that cigarette smoke extract (CSE) decreased focal adhesion kinase (FAK) activity via oxidative stress in cultured lung EC. In this study, we compared FAK activation in the lungs of highly susceptible AKR mice and mildly susceptible C57BL/6 mice after exposure to CS for three weeks. We found that three weeks of CS exposure caused mild emphysema and increased lung EC apoptosis in AKR mice (room air: 12.8±5.6%; CS: 30.7±3.7%), but not in C57BL/6 mice (room air: 0±0%; CS: 3.5±1.7%). Correlated with increased lung EC apoptosis and early onset of emphysema, FAK activity was reduced in the lungs of AKR mice, but not of C57BL/6 mice. Additionally, inhibition of FAK caused lung EC apoptosis, whereas over-expression of FAK prevented CSE-induced lung EC apoptosis. These results suggest that FAK inhibition may contribute to CS-induced lung EC apoptosis and emphysema. Unfolded protein response (UPR) and autophagy have been shown to be activated by CS exposure in lung epithelial cells. In this study, we noted that CSE activated UPR and autophagy in cultured lung EC, as indicated by enhanced eIF2α phosphorylation and elevated levels of GRP78 and LC3B-II. However, eIF2α phosphorylation was significantly reduced by three-weeks of CS exposure in the lungs of AKR mice, but not of C57BL/6 mice. Markers for autophagy activation were not significantly altered in the lungs of either AKR or C57BL/6 mice. These results suggest that CS-induced impairment of eIF2α signaling may increase the susceptibility to lung EC apoptosis and emphysema. Taken together, our data suggest that inhibition of eIF2α and FAK signaling may play an important role in CS-induced lung EC apoptosis and emphysema.

C-type natriuretic peptide does not attenuate the development of pulmonary hypertension caused by hypoxia and VEGF receptor blockade.

AIMS: C-type natriuretic peptide (CNP) is a local regulator of vascular tone and remodeling in many vascular beds. However, the role of CNP in modulating pulmonary arterial hypertensive and vascular remodeling responses is unclear. The purpose of this study was to determine if CNP is capable of preventing the development of pulmonary hypertension (PH). MAIN METHODS: We used animal models of PH caused by chronic hypoxia alone or in combination with the vascular endothelial growth factor (VEGF) receptor blocker SU5416. We measured pulmonary hemodynamics, right ventricular hypertrophy and vascular remodeling effects in response to a continuous infusion of low dose or high dose CNP or vehicle placebo. KEY FINDINGS: Right ventricular hypertrophy and a marked elevation in right ventricular systolic pressure (RVSP) were seen in both models of PH. Rats treated with the combination of SU5416 and chronic hypoxia also developed pulmonary endothelial hyperproliferative lesions. Continuous intravenous infusion of CNP at either dose did not attenuate the development of PH, right ventricular hypertrophy or vascular remodeling in either of the models of PH despite a three-fold increase in serum CNP levels. SIGNIFICANCE: CNP does not prevent the development of PH in the chronic hypoxia or SU5416 plus hypoxia models of pulmonary hypertension suggesting that CNP may not play an important modulatory role in human PH.

Activation of endothelial BKCa channels causes pulmonary vasodilation.

BACKGROUND: Large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels cause hyperpolarization and can regulate vascular tone. In this study, we evaluated the effect of endothelial BK(Ca) activation on pulmonary vascular tone. METHODS: The presence of BK(Ca) channels in lung microvascular endothelial cells (LMVEC) and rat lung tissue was confirmed by RT-PCR, immunoblotting and immunohistochemistry. Isolated pulmonary artery (PA) rings and isolated ventilated-perfused rat lungs were used to assay the effects of BK(Ca) channel activation on endothelium-dependent vasodilation. RESULTS: Immunoblotting and RT-PCR revealed the presence of BK(Ca) channel alpha- and beta(4)-subunits in LMVEC. Immunohistochemical staining showed BK(Ca) channel alpha-subunit expression in vascular endothelium in rat lungs. In arterial ring studies, BK(Ca) channel activation by NS1619 enhanced endothelium-dependent vasodilation that was attenuated by tetraethylammonium and iberiotoxin. In addition, activation of BK(Ca) channels by C-type natriuretic peptide caused endothelial-dependent vasodilation that was blocked by iberiotoxin, L-NAME, and lanthanum. Furthermore, BK(Ca) activation by NS1619 caused a dose-dependent reduction in PA pressures that was attenuated by L-NAME. In vitro, BK(Ca) channel activation in LMVEC caused hyperpolarization and increased NO production. CONCLUSIONS: Pulmonary endothelium expresses BK(Ca) channels. Activation of endothelial BK(Ca) channels causes hyperpolarization and NO mediated endothelium-dependent vasodilation in micro- and macrovasculature in the lung.