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Background: Pulmonary hypertension (PH) is a life-threatening disease, characterized by excessive pulmonary vascular remodeling, leading to elevated pulmonary arterial pressure and right heart hypertrophy. PH can be caused by chronic hypoxia, leading to hyper-proliferation of pulmonary arterial smooth muscle cells (PASMCs) and apoptosis-resistant pulmonary microvascular endothelial cells (PMVECs). On reexposure to normoxia, chronic hypoxia-induced PH in mice is reversible. In this study, the authors aim to identify novel candidate genes involved in pulmonary vascular remodeling specifically in the pulmonary vasculature., Methods: After microarray analysis, the authors assessed the role of SPARC (secreted protein acidic and rich in cysteine) in PH using lung tissue from idiopathic pulmonary arterial hypertension (IPAH) patients, as well as from chronically hypoxic mice. In vitro studies were conducted in primary human PASMCs and PMVECs. In vivo function of SPARC was proven in chronic hypoxia-induced PH in mice by using an adeno-associated virus-mediated Sparc knockdown approach., Results: C57BL/6J mice were exposed to normoxia, chronic hypoxia, or chronic hypoxia with subsequent reexposure to normoxia for different time points. Microarray analysis of the pulmonary vascular compartment after laser microdissection identified Sparc as one of the genes downregulated at all reoxygenation time points investigated. Intriguingly, SPARC was vice versa upregulated in lungs during development of hypoxia-induced PH in mice as well as in IPAH, although SPARC plasma levels were not elevated in PH. TGF-β1 (transforming growth factor β1) or HIF2A (hypoxia-inducible factor 2A) signaling pathways induced SPARC expression in human PASMCs. In loss of function studies, SPARC silencing enhanced apoptosis and reduced proliferation. In gain of function studies, elevated SPARC levels induced PASMCs, but not PMVECs, proliferation. Coculture and conditioned medium experiments revealed that PMVECs-secreted SPARC acts as a paracrine factor triggering PASMCs proliferation. Contrary to the authors' expectations, in vivo congenital Sparc knockout mice were not protected from hypoxia-induced PH, most probably because of counter-regulatory proproliferative signaling. However, adeno-associated virus-mediated Sparc knockdown in adult mice significantly improved hemodynamic and cardiac function in PH mice., Conclusions: This study provides evidence for the involvement of SPARC in the pathogenesis of human PH and chronic hypoxia-induced PH in mice, most likely by affecting vascular cell function.

Background: The pathogenesis of life-threatening cardiopulmonary diseases such as pulmonary hypertension (PH) and chronic obstructive pulmonary disease (COPD) originates from a complex interplay of environmental factors and genetic predispositions that is not fully understood. Likewise, little is known about developmental abnormalities or epigenetic dysregulations that might predispose for PH or COPD in adult individuals., Methods: To identify pathology-associated epigenetic alteration in diseased lung tissues, we screened a cohort of human patients with PH and COPD for changes of histone modifications by immunofluorescence staining. To analyze the function of H4K20me2/3 in lung pathogenesis, we developed a series of Suv4-20h1 knockout mouse lines targeting cardiopulmonary progenitor cells and different heart and lung cell types, followed by hemodynamic studies and morphometric assessment of tissue samples. Molecular, cellular, and biochemical techniques were applied to analyze the function of Suv4-20h1-dependent epigenetic processes in cardiopulmonary progenitor cells and their derivatives., Results: We discovered a strong reduction of the histone modifications of H4K20me2/3 in human patients with COPD but not patients with PH that depend on the activity of the H4K20 di-methyltransferase SUV4-20H1. Loss of Suv4-20h1 in cardiopulmonary progenitor cells caused a COPD-like/PH phenotype in mice including the formation of perivascular tertiary lymphoid tissue and goblet cell hyperplasia, hyperproliferation of smooth muscle cells/myofibroblasts, impaired alveolarization and maturation defects of the microvasculature leading to massive right ventricular dilatation and premature death. Mechanistically, SUV4-20H1 binds directly to the 5'-upstream regulatory element of the superoxide dismutase 3 ( Sod3 ) gene to repress its expression. Increased levels of the extracellular SOD3 enzyme in Suv4-20h1 mutants increases hydrogen peroxide concentrations, causing vascular defects and impairing alveolarization., Conclusions: Our findings reveal a pivotal role of the histone modifier SUV4-20H1 in cardiopulmonary codevelopment and uncover the developmental origins of cardiopulmonary diseases. We assume that the study will facilitate the understanding of pathogenic events causing PH and COPD and aid the development of epigenetic drugs for the treatment of cardiopulmonary diseases.

Background: Vascular smooth muscle cells (VSMCs) show a remarkable phenotypic plasticity, allowing acquisition of contractile or synthetic states, but critical information is missing about the physiologic signals, promoting formation, and maintenance of contractile VSMCs in vivo. BMP9 and BMP10 (bone morphogenetic protein) are known to regulate endothelial quiescence after secretion from the liver and right atrium, whereas a direct role in the regulation of VSMCs was not investigated. We studied the role of BMP9 and BMP10 for controlling formation of contractile VSMCs., Methods: We generated several cell type-specific loss- and gain-of-function transgenic mouse models to investigate the physiologic role of BMP9, BMP10, ALK1 (activin receptor-like kinase 1), and SMAD7 in vivo. Morphometric assessments, expression analysis, blood pressure measurements, and single molecule fluorescence in situ hybridization were performed together with analysis of isolated pulmonary VSMCs to unravel phenotypic and transcriptomic changes in response to absence or presence of BMP9 and BMP10., Results: Concomitant genetic inactivation of Bmp9 in the germ line and Bmp10 in the right atrium led to dramatic changes in vascular tone and diminution of the VSMC layer with attenuated contractility and decreased systemic as well as right ventricular systolic pressure. On the contrary, overexpression of Bmp10 in endothelial cells of adult mice dramatically enhanced formation of contractile VSMCs and increased systemic blood pressure as well as right ventricular systolic pressure. Likewise, BMP9/10 treatment induced an ALK1-dependent phenotypic switch from synthetic to contractile in pulmonary VSMCs. Smooth muscle cell-specific overexpression of Smad7 completely suppressed differentiation and proliferation of VSMCs and reiterated defects observed in adult Bmp9/10 double mutants. Deletion of Alk1 in VSMCs recapitulated the Bmp9/10 phenotype in pulmonary but not in aortic and coronary arteries. Bulk expression analysis and single molecule RNA-fluorescence in situ hybridization uncovered vessel bed-specific, heterogeneous expression of BMP type 1 receptors, explaining phenotypic differences in different Alk1 mutant vessel beds., Conclusions: Our study demonstrates that BMP9 and BMP10 act directly on VSMCs for induction and maintenance of their contractile state. The effects of BMP9/10 in VSMCs are mediated by different combinations of BMP type 1 receptors in a vessel bed-specific manner, offering new opportunities to manipulate blood pressure in the pulmonary circulation.

Background: The angiogenic function of endothelial cells is regulated by numerous mechanisms, but the impact of long noncoding RNAs (lncRNAs) has hardly been studied. We set out to identify novel and functionally important endothelial lncRNAs., Methods: Epigenetically controlled lncRNAs in human umbilical vein endothelial cells were searched by exon-array analysis after knockdown of the histone demethylase JARID1B. Molecular mechanisms were investigated by RNA pulldown and immunoprecipitation, mass spectrometry, microarray, several knockdown approaches, CRISPR-Cas9, assay for transposase-accessible chromatin sequencing, and chromatin immunoprecipitation in human umbilical vein endothelial cells. Patient samples from lung and tumors were studied for MANTIS expression., Results: A search for epigenetically controlled endothelial lncRNAs yielded lncRNA n342419, here termed MANTIS, as the most strongly regulated lncRNA. Controlled by the histone demethylase JARID1B, MANTIS was downregulated in patients with idiopathic pulmonary arterial hypertension and in rats treated with monocrotaline, whereas it was upregulated in carotid arteries of Macaca fascicularis subjected to atherosclerosis regression diet, and in endothelial cells isolated from human glioblastoma patients. CRISPR/Cas9-mediated deletion or silencing of MANTIS with small interfering RNAs or GapmeRs inhibited angiogenic sprouting and alignment of endothelial cells in response to shear stress. Mechanistically, the nuclear-localized MANTIS lncRNA interacted with BRG1, the catalytic subunit of the switch/sucrose nonfermentable chromatin-remodeling complex. This interaction was required for nucleosome remodeling by keeping the ATPase function of BRG1 active. Thereby, the transcription of key endothelial genes such as SOX18 , SMAD6 , and COUP-TFII was regulated by ensuring efficient RNA polymerase II machinery binding., Conclusion: MANTIS is a differentially regulated novel lncRNA facilitating endothelial angiogenic function., (© 2017 The Authors.)

Background: Pulmonary hypertension (PH) is a life-threatening disease characterized by vascular remodeling and increased pulmonary vascular resistance. Chronic alveolar hypoxia in animals is often used to decipher pathways being regulated in PH. Here, we aimed to investigate whether chronic hypoxia-induced PH in mice can be reversed by reoxygenation and whether possible regression can be used to identify pathways activated during the reversal and development of PH by genome-wide screening., Methods and Results: Mice exposed to chronic hypoxia (21 days, 10% O2) were reoxygenated for up to 42 days. Full reversal of PH during reoxygenation was evident by normalized right ventricular pressure, right heart hypertrophy, and muscularization of small pulmonary vessels. Microarray analysis from these mice revealed s-adenosylmethionine decarboxylase 1 (AMD-1) as one of the most downregulated genes. In situ hybridization localized AMD-1 in pulmonary vessels. AMD-1 silencing decreased the proliferation of pulmonary arterial smooth muscle cells and diminished phospholipase Cγ1 phosphorylation. Compared with the respective controls, AMD-1 depletion by heterozygous in vivo knockout or pharmacological inhibition attenuated PH during chronic hypoxia. A detailed molecular approach including promoter analysis showed that AMD-1 could be regulated by early growth response 1, transcription factor, as a consequence of epidermal growth factor stimulation. Key findings from the animal model were confirmed in human idiopathic pulmonary arterial hypertension., Conclusions: Our study indicates that genome-wide screening in mice from a PH model in which full reversal of PH occurs can be useful to identify potential key candidates for the reversal and development of PH. Targeting AMD-1 may represent a promising strategy for PH therapy.

Background: Pulmonary arterial hypertension is characterized by a progressive increase in pulmonary vascular resistance caused by endothelial dysfunction, inward vascular remodeling, and severe loss of precapillary pulmonary vessel cross-sectional area. Asymmetrical dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, and its metabolizing enzyme dimethylarginine dimethylaminohydrolase (DDAH) play important roles in endothelial dysfunction. We investigated whether combined phosphodiesterase (PDE) 3 and 4 inhibition ameliorates endothelial function by regulating the ADMA-DDAH axis., Methods and Results: We investigated the effects of the PDE3/4 inhibitor tolafentrine in vitro on endothelial cell survival, proliferation, and apoptosis. Effects of tolafentrine on the endothelial nitric oxide synthase/nitric oxide pathway, DDAH expression, DDAH promoter activity, and cytokine release from endothelial cells and their subsequent influence on DDAH expression were investigated. In monocrotaline-induced pulmonary arterial hypertension in rats, the effects of inhaled tolafentrine on DDAH expression and activity were investigated. Real-time-polymerase chain reaction, immunocytochemistry, and PDE activity assays suggested high expression of PDE3 and PDE4 isoforms in endothelial cells. Treatment of endothelial cells with PDE3/4 inhibitor significantly decreased ADMA-induced apoptosis via a cAMP/PKA-dependent pathway by induction of DDAH2. Chronic nebulization of PDE3/4 inhibitor significantly attenuated monocrotaline-induced hemodynamic, gas exchange abnormalities, vascular remodeling, and right heart hypertrophy. Interestingly, PDE3/4 inhibitor treatment reduced ADMA and elevated nitric oxide/cGMP levels. Mechanistically, this could be attributed to direct modulatory effects of cAMP on the promoter region of DDAH2, which was consequently found to be increased in expression and activity. Furthermore, PDE3/4 inhibitor suppressed apoptosis in endothelial cells and increased vascularization in the lung., Conclusion: Combined inhibition of PDE3 and 4 regresses development of pulmonary hypertension and promotes endothelial regeneration by modulating the ADMA-DDAH axis.

Background: Inhibition of tyrosine kinases, including platelet-derived growth factor receptor, can reduce pulmonary arterial pressure in experimental and clinical pulmonary hypertension. We hypothesized that inhibition of the serine/threonine kinases Raf-1 (also termed c-Raf) and b-Raf in addition to inhibition of tyrosine kinases effectively controls pulmonary vascular and right heart remodeling in pulmonary hypertension., Methods and Results: We investigated the effects of the novel multikinase inhibitor sorafenib, which inhibits tyrosine kinases as well as serine/threonine kinases, in comparison to imatinib, a tyrosine kinase inhibitor, on hemodynamics, pulmonary and right ventricular (RV) remodeling, and downstream signaling in experimental pulmonary hypertension. Fourteen days after monocrotaline injection, male rats were treated orally for another 14 days with sorafenib (10 mg/kg per day), imatinib (50 mg/kg per day), or vehicle (n=12 to 16 per group). RV systolic pressure was decreased to 35.0+/-1.5 mm Hg by sorafenib and to 54.0+/-4.4 mm Hg by imatinib compared with placebo (82.9+/-6.0 mm Hg). In parallel, both sorafenib and imatinib reduced RV hypertrophy and pulmonary arterial muscularization. The effects of sorafenib on RV systolic pressure and RV mass were significantly greater than those of imatinib. Sorafenib prevented phosphorylation of Raf-1 and suppressed activation of the downstream ERK1/2 signaling pathway in RV myocardium and the lungs. In addition, sorafenib but not imatinib antagonized vasopressin-induced hypertrophy of the cardiomyoblast cell line H9c2., Conclusions: The multikinase inhibitor sorafenib prevents pulmonary remodeling and improves cardiac and pulmonary function in experimental pulmonary hypertension. Sorafenib exerts direct myocardial antihypertrophic effects, which appear to be mediated via inhibition of the Raf kinase pathway. The combined inhibition of tyrosine and serine/threonine kinases may provide an option to treat pulmonary arterial hypertension and associated right heart remodeling.

Background: Pulmonary hypertension (PH) is a severe disease with a poor prognosis. Different forms of PH are characterized by pronounced vascular remodeling, resulting in increased vascular resistance and subsequent right heart failure. The molecular pathways triggering the remodeling process are poorly understood. We hypothesized that underlying key factors can be identified at the onset of the disease. Thus, we screened for alterations to protein expression in lung tissue at the onset of PH in a mouse model of hypoxia-induced PH., Methods and Results: Using 2-dimensional polyacrylamide gel electrophoresis in combination with matrix-assisted laser desorption/ionization time-of-flight analysis, we identified 36 proteins that exhibited significantly altered expression after short-term hypoxic exposure. Among these, Fhl-1, which is known to be involved in muscle development, was one of the most prominently upregulated proteins. Further analysis by immunohistochemistry, Western blot, and laser-assisted microdissection followed by quantitative polymerase chain reaction confirmed the upregulation of Fhl-1, particularly in the pulmonary vasculature. Comparable upregulation was confirmed (1) after full establishment of hypoxia-induced PH, (2) in 2 rat models of PH (monocrotaline-treated and hypoxic rats treated with the vascular endothelial growth factor receptor antagonist SU5416), and (3) in lungs from patients with idiopathic pulmonary arterial hypertension. Furthermore, we demonstrated that regulation of Fhl-1 was hypoxia-inducible transcription factor dependent. Abrogation of Fhl-1 expression in primary human pulmonary artery smooth muscle cells by small-interfering RNA suppressed, whereas Fhl-1 overexpression increased, migration and proliferation. Coimmunoprecipitation experiments identified Talin1 as a new interacting partner of Fhl-1., Conclusions: Protein screening identified Fhl-1 as a novel protein regulated in various forms of PH, including idiopathic pulmonary arterial hypertension.

Background: Pulmonary arterial hypertension (PAH) is a life-threatening disease, characterized by vascular smooth muscle cell hyperproliferation. The calcium/calmodulin-dependent phosphodiesterase 1 (PDE1) may play a major role in vascular smooth muscle cell proliferation., Methods and Results: We investigated the expression of PDE1 in explanted lungs from idiopathic PAH patients and animal models of PAH and undertook therapeutic intervention studies in the animal models. Strong upregulation of PDE1C in pulmonary arterial vessels in the idiopathic PAH lungs compared with healthy donor lungs was noted on the mRNA level by laser-assisted vessel microdissection and on the protein level by immunohistochemistry. In chronically hypoxic mouse lungs and lungs from monocrotaline-injected rats, PDE1A upregulation was detected in the structurally remodeled arterial muscular layer. Long-term infusion of the PDE1 inhibitor 8-methoxymethyl 3-isobutyl-1-methylxanthine in hypoxic mice and monocrotaline-injected rats with fully established pulmonary hypertension reversed the pulmonary artery pressure elevation, structural remodeling of the lung vasculature (nonmuscularized versus partially muscularized versus fully muscularized small pulmonary arteries), and right heart hypertrophy., Conclusions: Strong upregulation of the PDE1 family in pulmonary artery smooth muscle cells is noted in human idiopathic PAH lungs and lungs from animal models of PAH. Inhibition of PDE1 reverses structural lung vascular remodeling and right heart hypertrophy in 2 animal models. The PDE1 family may thus offer a new target for therapeutic intervention in pulmonary hypertension.

Background: Severe pulmonary hypertension is a disabling disease with high mortality, characterized by pulmonary vascular remodeling and right heart hypertrophy. Using wild-type and homozygous endothelial nitric oxide synthase (NOS3(-/-)) knockout mice with pulmonary hypertension induced by chronic hypoxia and rats with monocrotaline-induced pulmonary hypertension, we examined whether the soluble guanylate cyclase (sGC) stimulator Bay41-2272 or the sGC activator Bay58-2667 could reverse pulmonary vascular remodeling., Methods and Results: Both Bay41-2272 and Bay58-2667 dose-dependently inhibited the pressor response of acute hypoxia in the isolated perfused lung system. When wild-type (NOS3(+/+)) or NOS3(-/-) mice were housed under 10% oxygen conditions for 21 or 35 days, both strains developed pulmonary hypertension, right heart hypertrophy, and pulmonary vascular remodeling, demonstrated by an increase in fully muscularized peripheral pulmonary arteries. Treatment of wild-type mice with the activator of sGC, Bay58-2667 (10 mg/kg per day), or the stimulator of sGC, Bay41-2272 (10 mg/kg per day), after full establishment of pulmonary hypertension from day 21 to day 35 significantly reduced pulmonary hypertension, right ventricular hypertrophy, and structural remodeling of the lung vasculature. In contrast, only minor efficacy of chronic sGC activator therapies was noted in NOS3(-/-) mice. In monocrotaline-injected rats with established severe pulmonary hypertension, both compounds significantly reversed hemodynamic and structural changes., Conclusions: Activation of sGC reverses hemodynamic and structural changes associated with monocrotaline- and chronic hypoxia-induced experimental pulmonary hypertension. This effect is partially dependent on endogenous nitric oxide generated by NOS3.