Pathology of pulmonary hypertension

Early Intervention of Tongxinluo () on Right Ventricular Function Assessed by Echocardiography in Rats with Pulmonary Arterial Hypertension Induced by Monocrotaline

OBJECTIVE

To investigate the effect of early intervention of Tongxinluo (, TXL) on right ventricular function (RVF) of rats with pulmonary arterial hypertension (PAH) induced by monocrotaline (MCT).

METHODS

A total of 30 adult male Sprague-Dawley rats were assigned to 5 groups with complete random experiment design: Sham group (Sham), MCT group, TXL group, sildenafil (SIL) group and combination group (TXL+SIL), 6 rats in each group. Rats were injected with 50 mg/kg MCT solution for inducing PAH model except for those in the sham group. From the day of modeling, rats of TXL, SIL and TXL+SIL groups were given TXL (1.2 g/kg), SIL (10 mg/kg) and combination solution (TXL:1.2 g/kg, SIL: 10 mg/kg) respectively, and rats in Sham and MCT groups were given normal saline (5 mL/kg). The samples were collected and tested after 21 consecutive days of intragastric administration. Echocardiography was used to measure the related indices of RVF, including pulmonary arterial flow spectrum, pulmonary artery diameter (PAD), right ventricular wall thickness (RVWT), right ventricular diameter (RVD), tricuspidannular plane systolic excursion (TAPSE), right atrium transverse diameter (RAT), and inferior vena cava diameter (IVCD). Elastic Verhoeff-Van Gieson staining was adopted to measure the percentage of wall thickness (WT%) of pulmonary arteriols. Hematoxylin-eosin staining was used to measure the cross-sectional area (CSA) of right ventricular cardiomyocytes.

RESULTS

MCT-induced PAH rat model was successfully established. In MCT group the wall of pulmonary arterioles exhibited a prominent-increase thickness, PAD, RVWT, RVD, RAT, IVCD, WT%, right ventricular hypertrophy index (RVHI) as well as CSA of RV cardiomyocyte significantly increased (all P<0.01), and TAPSE markedly decreased (P<0.01). At the same time, TXL prominently improved all of the above indices (all P<0.01). In comparison with SIL, TXL significantly reduced RVD (P<0.05) and decreased CAS of RV cardiomyocytes (P<0.01), but TAPSE in SIL group was much larger than in TXL group (P<0.01). Moreover, TAPSE in TXL+SIL group was larger than that in TXL group (P<0.01), while the two groups performed equally well in terms of the other indices.

CONCLUSION

Early intervention of TXL could inhibit pulmonary arterioles remodeling, and improve RVF by attenuating right ventricular hypertrophy, and TXL has a stronger effect on inhibiting right ventricular remodeling than SIL.

Endoplasmic reticulum stress and pulmonary hypertension

Pulmonary hypertension is a fatal disease of which pulmonary vasculopathy is the main pathological feature resulting in the mean pulmonary arterial pressure higher than 25 mmHg. Moreover, pulmonary hypertension remains a tough problem with unclear molecular mechanisms. There have been dozens of studies about endoplasmic reticulum stress during the onset of pulmonary hypertension in patients, suggesting that endoplasmic reticulum stress may have a critical effect on the pathogenesis of pulmonary hypertension. The review aims to summarize the rationale to elucidate the role of endoplasmic reticulum stress in pulmonary hypertension. Started by reviewing the mechanisms responsible for the unfolded protein response following endoplasmic reticulum stress, the potential link between endoplasmic reticulum stress and pulmonary hypertension were introduced, and the contributions of endoplasmic reticulum stress to different vascular cells, mitochondria, and inflammation were described, and finally the potential therapies of attenuating endoplasmic reticulum stress for pulmonary hypertension were discussed.

Real-Life Experience with Selexipag as an Add-On Therapy to Oral Combination Therapy in Patients with Pulmonary Arterial or Distal Chronic Thromboembolic Pulmonary Hypertension: A Retrospective Analysis

BACKGROUND

Patients with pulmonary arterial hypertension (PAH) and distal chronic thromboembolic pulmonary hypertension (CTEPH) who still reveal risk factors of worse prognosis on double combination therapy may benefit from add-on therapy with the novel oral selective prostacyclin receptor agonist selexipag.

METHODS

We reviewed all patients with PAH/distal CTEPH in the Zurich cohort who received selexipag as add-on to oral combination therapy and retrieved New York Heart Association (NYHA) functional class, 6-min walk distance (6MWD), NT-pro-BNP, quality of life questionnaires (CAMPHOR and EuroQoL), tricuspid pressure gradient (TPG) by echocardiography and cardiopulmonary exercise test parameters (power output and oxygen uptake).

RESULTS

Twenty-three patients with PAH/CTEPH (20/3), 14 females, median (quartiles) age 56 (46; 66) years received an oral triple therapy containing selexipag at a median dose of 2000 (1600; 3100) mcg during 221 (113; 359) days. The following parameters were stabilized from baseline to last FU: 6MWD (440 (420; 490) to 464 (420; 526) m), NYHA class (three to two), NT-pro-BNP (326 (167; 1725) to 568 (135; 1856)  ng/l), TPG, power output, and oxygen uptake. Quality of life reflected by the CAMPHOR and EuroQoL improved.

CONCLUSIONS

Early initiation of triple oral combination therapy including selexipag in PAH/CTEPH with intermediate risk factor profile may help to stabilize functional class, exercise performance, and pulmonary hemodynamics in a real-life setting and potentially improves quality of life. Whether these beneficial effects can be truly attributed to the addition of selexipag should be addressed in future randomized controlled trials.

Triple-tyrosine kinase inhibition attenuates pulmonary arterial hypertension and neointimal formation

The present study examined the effects of simultaneous inhibition of vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) receptor signaling with BIBF1000, a novel triple tyrosine kinase inhibitor on preventing and reversing the progression of severe pulmonary arterial hypertension (PAH) in an experimental model in rats. Left pneumonectomized male Wistar rats were injected with monocrotaline to induce PAH. Treatment with BIBF1000 from day 1 to day 21 after monocrotaline injection attenuated PAH development, as evidenced by lower values for pulmonary artery pressure (mPAP), right ventricular pressure (RVSP), pulmonary arterial neointimal formation, and the ratio of right ventricular weight to left ventricular and septum weight [RV/(LV+S)] on day 21 compared to control rats. Treatment with BIBF1000 from day 21 to day 42 after monocrotaline injection reversed established PAH as shown by normalized values for mPAP and RVSP, RV/(LV+S) ratio, pulmonary arterial occlusion scores, levels of heart and lung fibrosis, as well as improved survival. Treatment with BIBF1000 reduced inflammatory cell recruitment in bronchoalveolar lavage and lung tissues, reduced CD-68 positive macrophages and expression of proliferating cell nuclear antigen in the perivascular areas, and reduced TNF-α and growth factor productions, and inhibited the phosphorylation of AKT and GSK3β in lungs. In addition, BIBF1000 inhibited pulmonary artery smooth muscle cells migration and proliferation from rat pulmonary artery explant cultures. Simultaneous inhibition of VEGF, PDGF, and FGF receptor signaling by BIBF1000 prevents and reverses the progression of severe pulmonary arterial hypertension and vascular remodeling in this experimental model.

Magnolol ameliorates pneumonectomy and monocrotaline-induced pulmonary arterial hypertension in rats through inhibition of angiotensin II and endothelin-1 expression

BACKGROUND

Magnolol, a major bioactive component extracted from Magnolia officinalis, exerts several beneficial effects, such as anti-inflammatory and anti-hypertensive activities.

PURPOSE

In this study, we investigated whether magnolol has a protective effect on pneumonectomy and monocrotaline-induced pulmonary arterial hypertension (PAH) in rats.

DESIGN/METHODS

The alterations of right ventricular (RV) hypertrophy, pulmonary vascular remodeling, histopathological parameters, and related gene expression and signaling pathways in lungs by magnolol treatment were studied in the PAH rats.

RESULTS

Administration of magnolol greatly ameliorated the characteristic features of PAH, including increased pulmonary arterial pressure, RV hypertrophy, and pulmonary vascular remodeling. Moreover, magnolol inhibited angiotensin-converting enzyme (ACE)/angiotensin II (Ang II)/Ang II type 1 receptor (AT-1R) cascade, whereas upregulates ACE2 in the lungs of PAH rats. The overexpression of endothelin-1 (ET-1) and ET_A receptor occurred in the PAH rats was significantly attenuated by magnolol through inhibition of Akt/ERK1/2/GSK3β/β-catenin pathway. Compared with that of untreated PAH rats, higher expression of endothelial nitric oxide synthase, and lower expression of inducible nitric oxide synthase and O₂^- production in lungs were observed in magnolol-treated PAH rats.

CONCLUSION

We demonstrated that treatment with magnolol reduces the development of PAH induced by pneumonectomy and monocrotaline in rats, and suppressing Ang II and ET-1-mediated processes may contribute to its protective effects. These findings suggest that magnolol may be a potential agent for PAH therapy.

Baicalein Ameliorates Pulmonary Arterial Hypertension Caused by Monocrotaline through Downregulation of ET-1 and ETAR in Pneumonectomized Rats

Baicalein (BE) extracted from Scutellaria baicalensis Georgi is able to alleviate various cardiovascular and inflammatory diseases. However, the effects of BE on pulmonary arterial hypertension (PAH) remain unknown. Therefore, the present study aimed to examine whether BE ameliorates pneumonectomy and monocrotaline-induced PAH in rats and further investigate the underlying molecular mechanisms. Administration of BE greatly attenuated the development of PAH as evidenced by an improvement of its characteristic features, including elevation of right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary vascular remodeling. Moreover, the increased protein expression of endothelin-1 (ET-1) and ETA receptor (ETAR), superoxide overproduction, and activation of Akt/ERK1/2/GSK3[Formula: see text]/[Formula: see text]-catenin pathway that occurred in the lungs of PAH rats were markedly reversed by BE treatment. Compared with the untreated PAH rats, higher expression of endothelial nitric oxide synthase (eNOS), but lower levels of inducible nitric oxide synthase and vWF were observed in BE-treated PAH rats. Collectively, treatment with BE remarkably attenuates the pathogenesis of PAH, and the protection of BE may be associated with suppressing Akt/Erk1/2/GSK3[Formula: see text]/[Formula: see text]-catenin/ET-1/ETAR signaling and preventing endothelial dysfunction. These results suggest that BE is a potential agent for treatment of PAH.

FGF21 attenuates hypoxia‑induced dysfunction and apoptosis in HPAECs through alleviating endoplasmic reticulum stress

Vascular endothelial apoptosis and dysfunction have a crucial role in triggering pathological vascular remodeling of hypoxia‑induced pulmonary arterial hypertension (PAH). Fibroblast growth factor (FGF)21, an endocrine regulator, has recently been reported to protect cardiac endothelial cells from damage and suppress inflammatory responses. In addition, FGF21 is reported to be involved in endoplasmic reticulum stress (ERS). Previous studies have suggested that ERS participates in the development of PAH, and attenuation of ERS could be an effective therapeutic strategy for the protection of pulmonary arteries. However, whether FGF21 has a protective function via suppression of ERS in pulmonary arterial endothelial cells in hypoxia remains unclear. The present study aimed to explore whether FGF21 could reduce the hypoxia‑induced apoptosis of human pulmonary arterial endothelial cells (HPAECs) and prevent endothelial dysfunction via the inhibition of ERS. HPAECs were divided into six groups: Normoxia, hypoxia, hypoxia plus FGF21, hypoxia plus salubrinal (an ERS inhibitor), hypoxia plus tunicamycin (an ERS agonist), and hypoxia plus tunicamycin plus FGF21. The endoplasmic reticulum ultrastructure in HPAECs was assessed by transmission electron microscopy, and proliferation and apoptosis were examined by cell counting kit‑8 and terminal deoxyribonucleotide transferase‑mediated dUTP nick end‑labelling assays, respectively. The expression levels of ERS‑related proteins, including binding immunoglobulin protein (BiP), protein kinase R‑like endoplasmic reticulum kinase (PERK), phosphorylated (p‑) PERK, transcription factor C/EBP homologous protein (CHOP), B‑cell lymphoma-2 (Bcl‑2) and caspase‑4 were detected by western blotting. Transwell migration chamber assays were performed, and the concentration of nitric oxide (NO)/endothelin‑1 (ET‑1) in the culture medium was determined to examine endothelial function. The results revealed that hypoxia increased the % of apoptotic cells and diminished the viability of HPAECs, accompanied by an upregulation of ERS‑dependent apoptosis by increasing the expression of the proapoptotic caspase‑4 and decreasing the antiapoptotic Bcl‑2. Additionally, hypoxia upregulated the expression of representative proteins in the PERK branch of ERS, including BiP, p‑PERK and CHOP, while it downregulated the expression of PERK. Furthermore, the secretion of NO/ET‑1 and the migration rate of HPAECs were downregulated under conditions of hypoxia. FGF21 significantly attenuated the hypoxia‑induced apoptosis and dysfunction of HPAECs through alleviating the aforementioned changes in ERS‑dependent signaling pathways. In conclusion, ERS may be a crucial mechanism in the hypoxia‑induced apoptosis and endothelial dysfunction of HPAECs. FGF21 may attenuate the hypoxia‑induced apoptosis and dysfunction of HPAECs through alleviating ERS, via the PERK/CHOP signaling pathway and inhibition of caspase‑4 expression.

Astragalus Polysaccharides Attenuate Monocrotaline-Induced Pulmonary Arterial Hypertension in Rats

Astragalus polysaccharides (APS) have been shown to possess a variety of biological activities including anti-oxidant and anti-inflammation functions in a number of diseases. However, their function in pulmonary arterial hypertension (PAH) is still unknown. Rats received APS (200[Formula: see text]mg/kg once two days) for 2 weeks after being injected with monocrotaline (MCT; 60[Formula: see text]mg/kg). The pulmonary hemodynamic index, right ventricular hypertrophy, and lung morphological features of the rat models were examined, as well as the NO/eNOS ratio of wet lung and dry lung weight and MPO. A qRT-PCR and p-I[Formula: see text]B was used to assess IL-1[Formula: see text], IL-6 and TNF-[Formula: see text] and WB was used to detect the total I[Formula: see text]B. Based on these measurements, it was found that APS reversed the MCT-induced increase in mean pulmonary arterial pressure (mPAP) (from 32.731[Formula: see text]mmHg to 26.707[Formula: see text]mmHg), decreased pulmonary vascular resistance (PVR) (from 289.021[Formula: see text]mmHg[Formula: see text][Formula: see text] min/L to 246.351[Formula: see text]mmHg[Formula: see text][Formula: see text][Formula: see text]min/L), and reduced right ventricular hypertrophy (from 289.021[Formula: see text]mmHg[Formula: see text][Formula: see text][Formula: see text]min/L to 246.351 mmHg[Formula: see text][Formula: see text][Formula: see text]min/L) ([Formula: see text]0.05). In terms of pulmonary artery remodeling, the WT% and WA% decreased with the addition of APS. In addition, it was found that APS promoted the synthesis of eNOS and the secretion of NO, promoting vasodilation and APS decreased the MCT-induced elevation of MPO, IL-1[Formula: see text], IL-6 and TNF-[Formula: see text], reducing inflammation. Furthermore, APS was able to inhibit the activation of pho-I[Formula: see text]B[Formula: see text]. In couclusion, APS ameliorates MCT-induced pulmonary artery hypertension by inhibiting pulmonary arterial remodeling partially via eNOS/NO and NF-[Formula: see text]B signaling pathways.

H2S inhibits pulmonary arterial endothelial cell inflammation in rats with monocrotaline-induced pulmonary hypertension

This study aimed to determine whether hydrogen sulfide (H₂S) inhibits pulmonary arterial endothelial inflammation in rats with monocrotaline (MCT)-induced pulmonary hypertension and its possible mechanisms. Twenty-four male Wistar rats were divided randomly into control, MCT, and MCT+H₂S treatment groups. Human pulmonary arterial endothelial cells (HPAEC) were cultured and divided into four groups: control, MCT, MCT+H₂S, and H₂S. Pulmonary artery pressure was determined using a right cardiac catheterization procedure 3 weeks after MCT administration. Pulmonary vascular morphological changes and inflammatory infiltration were measured. Endogenous H₂S levels, cystathionine-γ-lyase (CSE) expression, and inflammatory cytokines were determined both in vivo and in vitro. In addition, phosphorylation of NF-κB p65 and IκBα was detected by western blotting, and NF-κB p65 nuclear translocation, as well as its DNA-binding activity, was determined. Pulmonary hypertension and vascular remolding developed 3 wks after MCT administration, with elevated lung tissue inflammatory infiltration and cytokine level associated with activation of the NF-κB pathway, both in vivo and in vitro. However, the endogenous H₂S/CSE pathway was downregulated in MCT rats. By contrast, an H₂S donor markedly reduced pulmonary artery pressure, pulmonary vascular structural remolding, and increased lung inflammatory infiltration and cytokine levels of MCT-treated rats. Meanwhile, H₂S reversed the activation of the NF-κB pathway successfully. The downregulated pulmonary arterial endothelial H₂S/CSE pathway is involved in the pulmonary inflammatory response in MCT-treated pulmonary hypertensive rats. H₂S attenuated endothelial inflammation by inhibiting the NF-κB pathway.

Modulation of Intersectin-1s Lung Expression Induces Obliterative Remodeling and Severe Plexiform Arteriopathy in the Murine Pulmonary Vascular Bed

Murine models of pulmonary arterial hypertension (PAH) that recapitulate the plexiform and obliterative arteriopathy seen in PAH patients and help in defining the molecular mechanisms involved are missing. Herein, we investigated whether intersectin-1s (ITSN) deficiency and prolonged lung expression of an ITSN fragment with endothelial cell (EC) proliferative potential (EH_ITSN), present in the lungs of PAH animal models and human patients, induce formation of plexiform/obliterative lesions and defined the molecular mechanisms involved. ITSN-deficient mice (knockout/heterozygous and knockdown) were subjected to targeted lung delivery of EH_ITSN via liposomes for 20 days. Immunohistochemistry and histological and morphometric analyses revealed a twofold increase in proliferative ECs and a 1.35-fold increase in proliferative α-smooth muscle actin-positive cells in the lungs of ITSN-deficient mice, transduced with the EH_ITSN relative to wild-type littermates. Treated mice developed severe medial wall hypertrophy, intima proliferation, and various forms of obliterative and plexiform-like lesions in pulmonary arteries, similar to PAH patients. Hemodynamic measurements indicated modest increases in the right ventricular systolic pressure and right ventricle hypertrophy. Transcriptional and protein assays of lung tissue indicated p38^MAPK-dependent activation of Elk-1 transcription factor and increased expression of c-Fos gene. This unique murine model of PAH-like plexiform/obliterative arteriopathy induced via a two-hit pathophysiological mechanism without hypoxia provides novel druggable targets to ameliorate and, perhaps, reverse the EC plexiform phenotype in severe human PAH.

4-Phenylbutyric Acid Induces Protection against Pulmonary Arterial Hypertension in Rats

BACKGROUND

Endoplasmic reticulum (ER) stress has been implicated in the pathophysiology of various pulmonary diseases via the activation of the unfolded protein response. However, the role of ER stress in pulmonary arterial hypertension (PAH) remains unclear. The well-known chemical chaperone 4-phenylbutyric acid (4-PBA) inhibits ER stress signaling. We hypothesized that known chemical chaperones, including 4-PBA, would inhibit the activation of ER stress and prevent and/or reverse PAH.

METHODS AND RESULTS

Male Wistar rats were randomly divided into four groups: a normal control group (NORMAL group), a PAH group, and two PAH model plus 4-PBA treatment groups. The latter two groups included rats receiving 4-PBA by gavage each day as a preventive measure (the PRE group, with PBA starting on the day of PAH induction and continuing for 4 weeks) or as a reversal measure (the REV group, with PBA starting on the third week of PAH induction and continuing for 2 weeks). The PAH model was induced by intraperitoneally administering monocrotaline. The mean pulmonary artery pressure and mean right ventricular pressure were lower in the REV and PRE groups than in the NORMAL group. Furthermore, 4-PBA improved pulmonary arterial remodeling and suppressed the expression of ER stress indicators.

CONCLUSION

Our findings indicate that PAH induces ER stress and provokes pulmonary arterial and right ventricular remodeling. Additionally, we show that attenuation of ER stress has the potential to be an effective therapeutic strategy for protecting pulmonary arteries.

Prolyl-4 Hydroxylase 2 (PHD2) Deficiency in Endothelial Cells and Hematopoietic Cells Induces Obliterative Vascular Remodeling and Severe Pulmonary Arterial Hypertension in Mice and Humans Through Hypoxia-Inducible Factor-2α

BACKGROUND

Vascular occlusion and complex plexiform lesions are hallmarks of the pathology of severe pulmonary arterial hypertension (PAH) in patients. However, the mechanisms of obliterative vascular remodeling remain elusive; hence, current therapies have not targeted the fundamental disease-modifying mechanisms and result in only modest improvement in morbidity and mortality.

METHODS AND RESULTS

Mice with Tie2Cre-mediated disruption of Egln1 (encoding prolyl-4 hydroxylase 2 [PHD2]; Egln1(Tie2)) in endothelial cells and hematopoietic cells exhibited spontaneous severe PAH with extensive pulmonary vascular remodeling, including vascular occlusion and plexiform-like lesions, resembling the hallmarks of the pathology of clinical PAH. As seen in patients with idiopathic PAH, Egln1(Tie2) mice exhibited unprecedented right ventricular hypertrophy and failure and progressive mortality. Consistently, PHD2 expression was diminished in lung endothelial cells of obliterated pulmonary vessels in patients with idiopathic PAH. Genetic deletions of both Egln1 and Hif1a or Egln1 and Hif2a identified hypoxia-inducible factor-2α as the critical mediator of the severe PAH seen in Egln1(Tie2) mice. We also observed altered expression of many pulmonary hypertension-causing genes in Egln1(Tie2) lungs, which was normalized in Egln1(Tie2)/Hif2a(Tie2) lungs. PHD2-deficient endothelial cells promoted smooth muscle cell proliferation in part through hypoxia-inducible factor-2α-activated CXCL12 expression. Genetic deletion of Cxcl12 attenuated PAH in Egln1(Tie2) mice.

CONCLUSIONS

These studies defined an unexpected role of PHD2 deficiency in the mechanisms of severe PAH and identified the first genetically modified mouse model with obliterative vascular remodeling and pathophysiology recapitulating clinical PAH. Thus, targeting PHD2/hypoxia-inducible factor-2α signaling is a promising strategy to reverse vascular remodeling for treatment of severe PAH.

Therapeutic Benefits of Induced Pluripotent Stem Cells in Monocrotaline-Induced Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is characterized by progressive increases in vascular resistance and the remodeling of pulmonary arteries. The accumulation of inflammatory cells in the lung and elevated levels of inflammatory cytokines in the bloodstream suggest that inflammation may play a role in PAH. In this study, the benefits of induced pluripotent stem cells (iPSCs) and iPSC-conditioned medium (iPSC CM) were explored in monocrotaline (MCT)-induced PAH rats. We demonstrated that both iPSCs and iPSC CM significantly reduced the right ventricular systolic pressure and ameliorated the hypertrophy of the right ventricle in MCT-induced PAH rats in models of both disease prevention and disease reversal. In the prevention of MCT-induced PAH, iPSC-based therapy led to the decreased accumulation of inflammatory cells and down-regulated the expression of the IL-1β, IL-6, IL-12α, IL-12β, IL-23 and IFNγ genes in lung specimens, which implied that iPSC-based therapy may be involved in the regulation of inflammation. NF-κB signaling is essential to the inflammatory cascade, which is activated via the phosphorylation of the NF-κB molecule. Using the chemical inhibitor specifically blocked the phosphorylation of NF-κB, and in vitro assays of cultured human M1 macrophages implied that the anti-inflammation effect of iPSC-based therapy may contribute to the disturbance of NF-κB activation. Here, we showed that iPSC-based therapy could restore the hemodynamic function of right ventricle with benefits for preventing the ongoing inflammation in the lungs of MCT-induced PAH rats by regulating NF-κB phosphorylation.

Occlusive lung arterial lesions in endothelial-targeted, fas-induced apoptosis transgenic mice

Pulmonary arterial hypertension (PAH) is a lethal disease that is characterized by functional and structural abnormalities involving distal pulmonary arterioles that result in increased pulmonary vascular resistance and ultimately right heart failure. In experimental models of pulmonary hypertension, endothelial cell (EC) apoptosis is a necessary trigger for the development of obliterative lung arteriopathy, inducing the emergence of hyperproliferative and apoptosis-resistant vascular cells. However, it has not been established whether EC apoptosis is sufficient for the induction of complex lung arteriolar lesions. We generated a conditional transgenic system in mice to test the hypothesis that lung endothelial cell apoptosis is sufficient to induce a PAH phenotype. The Fas-induced apoptosis (FIA) construct was expressed under the control of endothelial-specific Tie2 promoter (i.e., EFIA mice), and administration of a small molecule dimerizing agent, AP20187, resulted in modest pulmonary hypertension, which was associated with obliterative vascular lesions localized to distal lung arterioles in a proportion of transgenic mice. These lesions were characterized by proliferating cells, predominantly CD68 macrophages. Although endothelial cell apoptosis was also seen in the kidney, evidence of subsequent arteriopathy was seen only in the lung. This model provides direct evidence that lung endothelial cell apoptosis acts as a trigger to initiate a PAH phenotype and provides initial insight into the potential mechanisms that underlie a lung-specific arterial response to endothelial injury.

Iptakalim attenuates hypoxia-induced pulmonary arterial hypertension in rats by endothelial function protection

The present study aimed to investigate the protective effects of iptakalim, an adenosine triphosphate (ATP)-sensitive potassium channel opener, on the inflammation of the pulmonary artery and endothelial cell injury in a hypoxia-induced pulmonary arterial hypertension (PAH) rat model. Ninety-six Sprague-Dawley rats were placed into normobaric hypoxia chambers for four weeks and were treated with iptakalim (1.5 mg/kg/day) or saline for 28 days. The right ventricle systolic pressures (RVSP) were measured and small pulmonary arterial morphological alterations were analyzed with hematoxylin and eosin staining. Enzyme-linked immunosorbent assay (ELISA) was performed to analyze the content of interleukin (IL)-1β and IL-10. Immunohistochemical analysis for ED1(+) monocytes was performed to detect the inflammatory cells surrounding the pulmonary arterioles. Western blot analysis was performed to analyze the expression levels of platelet endothelial cell adhesion molecule-1 (PECAM-1) and endothelial nitric oxide synthase (eNOS) in the lung tissue. Alterations in small pulmonary arteriole morphology and the ultrastructure of pulmonary arterial endothelial cells were observed via light and transmission electron microscopy, respectively. Iptakalim significantly attenuated the increase in mean pulmonary artery pressure, RVSP, right ventricle to left ventricle plus septum ratio and small pulmonary artery wall remodeling in hypoxia-induced PAH rats. Iptakalim also prevented an increase in IL-1β and a decrease in IL-10 in the peripheral blood and lung tissue, and alleviated inflammatory cell infiltration in hypoxia-induced PAH rats. Furthermore, iptakalim enhanced PECAM-1 and eNOS expression and prevented the endothelial cell injury induced by hypoxic stimuli. Iptakalim suppressed the pulmonary arteriole and systemic inflammatory responses and protected against the endothelial damage associated with the upregulation of PECAM-1 and eNOS, suggesting that iptakalim may represent a potential therapeutic agent for PAH.

Saudi Guidelines on the Diagnosis and Treatment of Pulmonary Hypertension: Intensive care management of pulmonary hypertension

Pulmonary hypertension (PH) in the Intensive Care Unit (ICU) may be due to preexisting pulmonary vascular lung disease, liver disease, or cardiac diseases. PH also may be caused by critical illnesses, such as acute respiratory distress syndrome (ARDS), acute left ventricular dysfunction and pulmonary embolism, or may occur after cardiac or thoracic surgery.

Regardless of the underlying cause of PH, the final common pathway for hemodynamic deterioration and death is RV failure, which is the most challenging aspect of patient management. Therapy is thus aimed at acutely relieving RV overload by decreasing PVR and reversing RV failure with pulmonary vasodilators and inotropes.

The role of the renin-angiotensin-aldosterone system in the pathobiology of pulmonary arterial hypertension (2013 Grover Conference series)

Pulmonary arterial hypertension (PAH) is associated with aberrant pulmonary vascular remodeling that leads to increased pulmonary artery pressure, pulmonary vascular resistance, and right ventricular dysfunction. There is now accumulating evidence that the renin-angiotensin-aldosterone system is activated and contributes to cardiopulmonary remodeling that occurs in PAH. Increased plasma and lung tissue levels of angiotensin and aldosterone have been detected in experimental models of PAH and shown to correlate with cardiopulmonary hemodynamics and pulmonary vascular remodeling. These processes are abrogated by treatment with angiotensin receptor or mineralocorticoid receptor antagonists. At a cellular level, angiotensin and aldosterone activate oxidant stress signaling pathways that decrease levels of bioavailable nitric oxide, increase inflammation, and promote cell proliferation, migration, extracellular matrix remodeling, and fibrosis. Clinically, enhanced renin-angiotensin activity and elevated levels of aldosterone have been detected in patients with PAH, which suggests a role for angiotensin and mineralocorticoid receptor antagonists in the treatment of PAH. This review will examine the current evidence linking renin-angiotensin-aldosterone system activation to PAH with an emphasis on the cellular and molecular mechanisms that are modulated by aldosterone and may be of importance for the pathobiology of PAH.

The adventitia: Essential role in pulmonary vascular remodeling

A rapidly emerging concept is that the vascular adventitia acts as a biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. It is the most complex compartment of the vessel wall and comprises a variety of cells including fibroblasts, immunomodulatory cells, resident progenitor cells, vasa vasorum endothelial cells, and adrenergic nerves. In response to vascular stress or injury, resident adventitial cells are often the first to be activated and reprogrammed to then influence tone and structure of the vessel wall. Experimental data indicate that the adventitial fibroblast, the most abundant cellular constituent of adventitia, is a critical regulator of vascular wall function. In response to vascular stresses such as overdistension, hypoxia, or infection, the adventitial fibroblast is activated and undergoes phenotypic changes that include proliferation, differentiation, and production of extracellular matrix proteins and adhesion molecules, release of reactive oxygen species, chemokines, cytokines, growth factors, and metalloproteinases that, collectively, affect medial smooth muscle cell tone and growth directly and that stimulate recruitment and retention of circulating inflammatory and progenitor cells to the vessel wall. Resident dendritic cells also participate in "sensing" vascular stress and actively communicate with fibroblasts and progenitor cells to simulate repair processes that involve expansion of the vasa vasorum, which acts as a conduit for further delivery of inflammatory/progenitor cells. This review presents the current evidence demonstrating that the adventitia acts as a key regulator of pulmonary vascular wall function and structure from the "outside in."

Therapeutic efficacy of AAV1.SERCA2a in monocrotaline-induced pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is characterized by dysregulated proliferation of pulmonary artery smooth muscle cells leading to (mal)adaptive vascular remodeling. In the systemic circulation, vascular injury is associated with downregulation of sarcoplasmic reticulum Ca(2+)-ATPase 2a (SERCA2a) and alterations in Ca(2+) homeostasis in vascular smooth muscle cells that stimulate proliferation. We, therefore, hypothesized that downregulation of SERCA2a is permissive for pulmonary vascular remodeling and the development of PAH.

METHODS AND RESULTS

SERCA2a expression was decreased significantly in remodeled pulmonary arteries from patients with PAH and the rat monocrotaline model of PAH in comparison with controls. In human pulmonary artery smooth muscle cells in vitro, SERCA2a overexpression by gene transfer decreased proliferation and migration significantly by inhibiting NFAT/STAT3. Overexpresion of SERCA2a in human pulmonary artery endothelial cells in vitro increased endothelial nitric oxide synthase expression and activation. In monocrotaline rats with established PAH, gene transfer of SERCA2a via intratracheal delivery of aerosolized adeno-associated virus serotype 1 (AAV1) carrying the human SERCA2a gene (AAV1.SERCA2a) decreased pulmonary artery pressure, vascular remodeling, right ventricular hypertrophy, and fibrosis in comparison with monocrotaline-PAH rats treated with a control AAV1 carrying β-galactosidase or saline. In a prevention protocol, aerosolized AAV1.SERCA2a delivered at the time of monocrotaline administration limited adverse hemodynamic profiles and indices of pulmonary and cardiac remodeling in comparison with rats administered AAV1 carrying β-galactosidase or saline.

CONCLUSIONS

Downregulation of SERCA2a plays a critical role in modulating the vascular and right ventricular pathophenotype associated with PAH. Selective pulmonary SERCA2a gene transfer may offer benefit as a therapeutic intervention in PAH.

The adventitia: essential regulator of vascular wall structure and function

The vascular adventitia acts as a biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. It is the most complex compartment of the vessel wall and is composed of a variety of cells, including fibroblasts, immunomodulatory cells (dendritic cells and macrophages), progenitor cells, vasa vasorum endothelial cells and pericytes, and adrenergic nerves. In response to vascular stress or injury, resident adventitial cells are often the first to be activated and reprogrammed to influence the tone and structure of the vessel wall; to initiate and perpetuate chronic vascular inflammation; and to stimulate expansion of the vasa vasorum, which can act as a conduit for continued inflammatory and progenitor cell delivery to the vessel wall. This review presents the current evidence demonstrating that the adventitia acts as a key regulator of vascular wall function and structure from the outside in.

Targeting the adventitial microenvironment in pulmonary hypertension: A potential approach to therapy that considers epigenetic change

Experimental data indicate that the adventitial compartment of blood vessels, in both the pulmonary and systemic circulations, like the connective tissue stroma in tissues throughout the body, is a critical regulator of vessel wall function in health and disease. It is clear that adventitial cells, and in particular the adventitial fibroblast, are activated early following vascular injury, and play essential roles in regulating vascular wall structure and function through production of chemokines, cytokines, growth factors, and reactive oxygen species (ROS). The recognition of the ability of these cells to generate and maintain inflammatory responses within the vessel wall provides insight into why vascular inflammatory responses, in certain situations, fail to resolve. It is also clear that the activated adventitial fibroblast plays an important role in regulating vasa vasorum growth, which can contribute to ongoing vascular remodeling by acting as a conduit for delivery of inflammatory and progenitor cells. These functions of the fibroblast clearly support the idea that targeting chemokine, cytokine, adhesion molecule, and growth factor production in activated fibroblasts could be helpful in abrogating vascular inflammatory responses and thus in ameliorating vascular disease. Further, the recent observations that fibroblasts in vascular and fibrotic diseases may maintain their activated state through epigenetic alterations in key inflammatory and pro-fibrotic genes suggests that current therapies used to treat pulmonary hypertension may not be sufficient to induce apoptosis or to inhibit key inflammatory signaling pathways in these fibroblasts. New therapies targeted at reversing changes in the acetylation or methylation status of key transcriptional networks may be needed. At present, therapies specifically targeting abnormalities of histone deacytelase (HDAC) activity in fibroblast-like cells appear to hold promise.

Fibrosis of pulmonary vascular remodeling in carotid artery-jugular vein shunt pulmonary artery hypertension model of rats

OBJECTIVE

The aim of the present study was to observe the changes of hemodynamics, stereology in pulmonary vascular remodeling and messenger RNA (mRNA) expressions of transforming growth factor beta 1, and receptors in carotid artery-jugular vein (CA-JV) shunt pulmonary artery hypertension model of rats.

METHODS

Thirty-six Sprague-Dawley rats were randomized into three groups: CA-JV group, monocrotaline (MCT) administration group, and control group. Left CA-JV shunts were established in CA-JV group. Dorsal subcutaneous injections of MCT (60 mg kg(-1)) were received in MCT group. Ligations of left common carotid artery and external jugular vein were performed in control group. Right ventricular systolic pressure (RVSP) measurement, histological evaluation of the pulmonary tissue, and mRNA levels of transforming growth factor beta 1 (TGFß1), receptor 1 and receptor 2, were investigated after 6 weeks on MCT group, and after 12 weeks on both control and CA-JV groups.

RESULTS

Compared with control group, RVSP, percentage of fibrous tissue (F%) in pulmonary arterioles, mRNA levels of TGFß1, and receptors of CA-JVand MCT groups increased significantly. Severe hemodynamics change was found in MCT groups. On the other hand, CA-JV group demonstrated more obvious fibrogenesis and TGFß1 signals' upregulation in two pulmonary artery hypertension (PAH) models.

CONCLUSIONS

CA-JV shunt model of rats was a well-established PAH animal model simulating congenital heart disease with systemic-pulmonary shunt.

Nicorandil attenuates monocrotaline-induced vascular endothelial damage and pulmonary arterial hypertension

Background

An antianginal K_ATP channel opener nicorandil has various beneficial effects on cardiovascular systems; however, its effects on pulmonary vasculature under pulmonary arterial hypertension (PAH) have not yet been elucidated. Therefore, we attempted to determine whether nicorandil can attenuate monocrotaline (MCT)-induced PAH in rats.

Materials and Methods

Sprague-Dawley rats injected intraperitoneally with 60 mg/kg MCT were randomized to receive either vehicle; nicorandil (5.0 mg·kg⁻¹·day⁻¹) alone; or nicorandil as well as either a K_ATP channel blocker glibenclamide or a nitric oxide synthase (NOS) inhibitor N^ω-nitro-l-arginine methyl ester (l-NAME), from immediately or 21 days after MCT injection. Four or five weeks later, right ventricular systolic pressure (RVSP) was measured, and lung tissue was harvested. Also, we evaluated the nicorandil-induced anti-apoptotic effects and activation status of several molecules in cell survival signaling pathway in vitro using human umbilical vein endothelial cells (HUVECs).

Results

Four weeks after MCT injection, RVSP was significantly increased in the vehicle-treated group (51.0±4.7 mm Hg), whereas it was attenuated by nicorandil treatment (33.2±3.9 mm Hg; P<0.01). Nicorandil protected pulmonary endothelium from the MCT-induced thromboemboli formation and induction of apoptosis, accompanied with both upregulation of endothelial NOS (eNOS) expression and downregulation of cleaved caspase-3 expression. Late treatment with nicorandil for the established PAH was also effective in suppressing the additional progression of PAH. These beneficial effects of nicorandil were blocked similarly by glibenclamide and l-NAME. Next, HUVECs were incubated in serum-free medium and then exhibited apoptotic morphology, while these changes were significantly attenuated by nicorandil administration. Nicorandil activated the phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK) pathways in HUVECs, accompanied with the upregulation of both eNOS and Bcl-2 expression.

Conclusions

Nicorandil attenuated MCT-induced vascular endothelial damage and PAH through production of eNOS and anti-apoptotic factors, suggesting that nicorandil might have a promising therapeutic potential for PAH.

Endoplasmic reticulum stress enters a Nogo zone

The debilitating disease pulmonary arterial hypertension (PAH) is characterized by an elevation in blood pressure in the lung arteries caused by vessel-blocking vascular-cell proliferation. This vascular remodeling is thought to result in part from defects in the endoplasmic reticulum stress response and mitochondrial dysfunction in pulmonary artery smooth muscle cells. In this issue of Science Translational Medicine, Sutendra et al. show that the vascular remodeling protein Nogo-B plays a role in the development of PAH in response to hypoxia-induced stress. The new findings finger Nogo-B as a possible therapeutic target for PAH.

Senescent endothelial progenitor cells from dogs with pulmonary arterial hypertension: a before-after self-controlled study

Previous studies have underlined the importance of endothelial dysfunction and microvascular occlusion in the pathogenesis of pulmonary artery hypertension (PAH). Since the endothelial progenitor cells (EPCs) are involved in maintaining endothelial homeostasis, we observed the change of peripheral EPCs in canines before and after PAH onset. PAH was induced by intra-pulmonary artery injection of dehydromonocrotaline (DHMC) in nine beagles. Before and 48 h and 6 weeks after DHMC injection, 40 ml peripheral blood was obtained from the femoral vein. Circulating EPCs were identified as CD133 + KDR + cells and numerated by fluorescence-activated cell sorter; the EPCs functional capacity was determined by in vitro tubule-forming assay. The senescence of EPCs was determined by beta-galactosidase staining. At each time point, 2 ml blood from femoral artery was obtained for arterial oxygen pressure (PaO(2)). Forty-eight hours after DHMC injection, treated beagles suffered from hypoxemia; however, both the number and the tubule-forming capacity of EPCs were transiently raised. Six weeks later, PAH was confirmed by obviously high mean pulmonary arterial pressure (20.2 +/- 1.64 vs. 11.3 +/- 2.0 mmHg, p < 0.05) and low PaO(2) (69.30 +/- 9.15 vs. 95.94 +/- 1.43 mmHg, p < 0.01) in beagles after DHMC treatment, and their EPCs exhibited a predominant decrease in either the number (206.1 +/- 26.8 vs. 632.8 +/- 42.8 cells/ml blood, p < 0.01) or the tubule-forming capacity (21.1 +/- 2.8 vs. 11.2 +/- 2.8 tubules/x200 field, p < 0.01). Additionally, senescence-associated beta-galactosidase-positive EPCs were significantly increased. Our data suggested that, after the acute stage of DHMC injury to pulmonary vessels, the EPCs from PAH beagles suffered from exhaustion and senescence.

The angiopietin-1-Tie2 pathway prevents rather than promotes pulmonary arterial hypertension in transgenic mice

The role of the angiopoietin-1 (Ang1)-Tie2 pathway in the pathogenesis of pulmonary arterial hypertension (PAH) is controversial. Although Ang1 is well known to prevent endothelial activation and injury in systemic vascular beds, this pathway has been suggested to mediate pulmonary vascular remodeling in PAH. Therefore, we used transgenic models to determine the effect of increased or decreased Tie2 activity on the development of PAH. We now report modest spontaneous elevation in right ventricular systolic pressure in Tie2-deficient mice (Tie2(+/-)) compared with wild-type (WT) littermate controls, which was exacerbated upon chronic exposure to the clinically relevant PAH triggers, serotonin (5-HT) or interleukin-6 (IL-6). Moreover, overexpression of Ang1 in transgenic mice had no deleterious effect on pulmonary hemodynamics and, if anything, blunted the response to 5-HT. Exposure to 5-HT or IL-6 also decreased lung Ang1 expression, further reducing Tie2 activity and inducing pulmonary apoptosis in the Tie2(+/-) group only. Similarly, cultured pulmonary artery endothelial cells subjected to Tie2 silencing demonstrated increased susceptibility to apoptosis after 5-HT treatment. Finally, treatment of Tie2-deficient mice with Z-VAD, a pan-caspase inhibitor, prevented the pulmonary hypertensive response to 5-HT. Thus, these findings firmly establish that endothelial survival signaling via the Ang1-Tie2 pathway is protective in PAH.

Pulmonary hypertension: diagnosis and management

Pulmonary arterial hypertension is a progressive, symptomatic, and ultimately fatal disorder for which substantial advances in treatment have been made during the past decade. Effective management requires timely recognition and accurate diagnosis of the disorder and appropriate selection among therapeutic alternatives. Despite progress in treatment, obstacles remain that impede the achievement of optimal outcomes. The current article provides an overview of the pathobiologic mechanisms of pulmonary arterial hypertension, including genetic substrates and molecular and cellular mechanisms, and describes the clinical manifestations and classification of pulmonary arterial hypertension. The article also reviews established approaches to evaluation and treatment, with emphasis on the appropriate application of calcium channel blockers, prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase 5 inhibitors. In addition, the authors discuss unresolved issues that may complicate patient management, such as the clinical importance of mild or exercise-related pulmonary arterial hypertension, and they identify avenues by which treatment may advance in the future through the use of combination treatment, outcomes assessment, and exploration of alternative pharmacologic strategies.

Pulmonary hypertension: diagnosis and management

Pulmonary arterial hypertension is a progressive, symptomatic, and ultimately fatal disorder for which substantial advances in treatment have been made during the past decade. Effective management requires timely recognition and accurate diagnosis of the disorder and appropriate selection among therapeutic alternatives. Despite progress in treatment, obstacles remain that impede the achievement of optimal outcomes. The current article provides an overview of the pathobiologic mechanisms of pulmonary arterial hypertension, including genetic substrates and molecular and cellular mechanisms, and describes the clinical manifestations and classification of pulmonary arterial hypertension. The article also reviews established approaches to evaluation and treatment, with emphasis on the appropriate application of calcium channel blockers, prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase 5 inhibitors. In addition, the authors discuss unresolved issues that may complicate patient management, such as the clinical importance of mild or exercise-related pulmonary arterial hypertension, and they identify avenues by which treatment may advance in the future through the use of combination treatment, outcomes assessment, and exploration of alternative pharmacologic strategies.

Peripheral blood B lymphocytes derived from patients with idiopathic pulmonary arterial hypertension express a different RNA pattern compared with healthy controls: a cross sectional study

BACKGROUND

Idiopathic pulmonary arterial hypertension (IPAH) is a progressive and still incurable disease. Research of IPAH-pathogenesis is complicated by the lack of a direct access to the involved tissue, the human pulmonary vasculature. Various auto-antibodies have been described in the blood of patients with IPAH. The purpose of the present work was therefore to comparatively analyze peripheral blood B lymphocyte RNA expression characteristics in IPAH and healthy controls.

METHODS

Patients were diagnosed having IPAH according to WHO (mean pulmonary arterial pressure > or = 25 mmHg, pulmonary capillary occlusion pressure < or = 15 mmHg, absence of another explaining disease). Peripheral blood B-lymphocytes of patients and controls were immediately separated by density gradient centrifugation and magnetic beads for CD19. RNA was thereafter extracted and analyzed by the use of a high sensitivity gene chip (Affymetrix HG-U133-Plus2) able to analyze 47000 transcripts and variants of human genes. The array data were analyzed by two different softwares, and up-and down-regulations were defined as at least 1.3 fold with standard deviations smaller than fold-changes.

RESULTS

Highly purified B-cells of 5 patients with IPAH (mean pulmonary artery pressure 51 +/- 13 mmHg) and 5 controls were analyzed. Using the two different analyzing methods we found 225 respectively 128 transcripts which were up-regulated (1.3-30.7 fold) in IPAH compared with healthy controls. Combining both methods, there were 33 overlapping up-regulated transcripts and no down-regulated B-cell transcripts.

CONCLUSION

Patients with IPAH have a distinct RNA expression profile of their peripheral blood B-lymphocytes compared to healthy controls with some clearly up-regulated genes. Our finding suggests that in IPAH patients B cells are activated.

Endothelial progenitor cell therapy for the treatment of coronary disease, acute MI, and pulmonary arterial hypertension: current perspectives

Since their identification in 1997, bone marrow derived endothelial progenitor cells (EPCs) have been studied for their role in the endogenous maintenance and repair of endothelium and their potential regenerative capacity beyond the endothelium. In particular, EPCs have been tested in cell therapy approaches with the aim of developing novel therapies for conditions currently lacking effective treatment options. In this review, we discuss the scientific background and clinical experience using EPC delivery or mobilization for the treatment of post-angioplasty restenosis, acute myocardial infarction and pulmonary arterial hypertension. Although these approaches are safe, efficacy has yet to be proven in large randomized clinical trials. Unfortunately, the biology of EPCs is still poorly understood. The success of future clinical trials depends on a better understanding of EPC biology and intelligent design.

Increased regulatory and decreased CD8+ cytotoxic T cells in the blood of patients with idiopathic pulmonary arterial hypertension

BACKGROUND

An association between pulmonary arterial hypertension (PAH) and various immune disorders is well established. Recently, the role of an intact immune system in protecting against pulmonary angioproliferation was shown in an animal model.

OBJECTIVE

To elucidate the role of T cells in human PAH, we comparatively studied T cell subclasses with emphasis on regulatory T cells (T(reg)) in the peripheral blood of patients with idiopathic pulmonary arterial hypertension (IPAH) and healthy controls.

METHODS

Isolated peripheral blood mononuclear cells from 36 patients diagnosed with IPAH and 33 healthy controls were stained with fluorescently labeled monoclonal antibodies against superficial T cell markers (CD3, CD4, CD8, CD25) and FoxP3, the intracellular marker of T(reg) cells. The relative cell distribution was analyzed by flow cytometry. The functionality of patient and control T(reg) cells was assessed by coculture of T(reg) with nonregulatory T cells from the same individual.

RESULTS

Significantly less CD8+ T cells (p = 0.02) and more CD25hi+ and FoxP3+CD4+ T cells were found in the peripheral blood of patients compared with controls (p = 0.009 and p < 0.001, respectively). The percentage of FoxP3+ cells within the CD25hi+CD4+ T(reg) cells was similar. T(reg) cell functionality was equal in patients and controls.

CONCLUSION

Our findings of decreased CD8+ T cells and increased T(reg) cells in the peripheral blood of patients with IPAH are novel and may have implications for directing future research in the field to elucidate the differential role of T cells and the immune system in IPAH.

Dosage-dependent requirement of BMP type II receptor for maintenance of vascular integrity

Germ-line mutations in bone morphogenic protein type II receptor (Bmpr2) confer susceptibility to pulmonary arterial hypertension (PAH), which is characterized by obstructive vascular lesions in small arteries. The molecular and cellular mechanisms that account for the etiology of this disorder remain elusive, as does the role of Bmpr2 in postnatal tissue homeostasis. Here we show that in adult mice, stably silencing Bmpr2 expression by RNA interference does not increase pulmonary arterial resistance but results in severe mucosal hemorrhage, incomplete mural cell coverage on vessel walls, and gastrointestinal hyperplasia. We present evidence that BMP receptor signaling regulates vascular remodeling during angiogenesis by maintaining the expression of endothelial guidance molecules that promote vessel patterning and maturation and by counteracting growth factor–induced AKT activation. Attenuation of this function may cause vascular dysmorphogenesis and predisposition to angioproliferative diseases. Our findings provide a mechanistic link between PAH and other diseases associated with the BMP/TGF-β pathways, such as hereditary hemorrhagic telangiectasia and juvenile polyposis syndrome.

Hemolysis in sickle cell mice causes pulmonary hypertension due to global impairment in nitric oxide bioavailability

Pulmonary hypertension is a highly prevalent complication of sickle cell disease and is a strong risk factor for early mortality. However, the pathophysiologic mechanisms leading to pulmonary vasculopathy remain unclear. Transgenic mice provide opportunities for mechanistic studies of vascular pathophysiology in an animal model. By microcardiac catheterization, all mice expressing exclusively human sickle hemoglobin had pulmonary hypertension, profound pulmonary and systemic endothelial dysfunction, and vascular instability characterized by diminished responses to authentic nitric oxide (NO), NO donors, and endothelium-dependent vasodilators and enhanced responses to vasoconstrictors. However, endothelium-independent vasodilation in sickle mice was normal. Mechanisms of vasculopathy in sickle mice involve global dysregulation of the NO axis: impaired constitutive nitric oxide synthase activity (NOS) with loss of endothelial NOS (eNOS) dimerization, increased NO scavenging by plasma hemoglobin and superoxide, increased arginase activity, and depleted intravascular nitrite reserves. Light microscopy and computed tomography revealed no plexogenic arterial remodeling or thrombi/ emboli. Transplanting sickle marrow into wild-type mice conferred the same phenotype, and similar pathobiology was observed in a nonsickle mouse model of acute alloimmune hemolysis. Although the time course is shorter than typical pulmonary hypertension in human sickle cell disease, these results demonstrate that hemolytic anemia is sufficient to produce endothelial dysfunction and global dysregulation of NO.

Decreased left ventricular function, myocarditis, and coronary arteriolar medial thickening following monocrotaline administration in adult rats

Decreased right as well as left ventricular function can be associated with pulmonary hypertension (PH). Numerous investigations have examined cardiac function following induction of pulmonary hypertension with monocrotaline (MCT) assuming that MCT has no direct cardiac effect. We tested this assumption by examining left ventricular function and histology of isolated and perfused hearts from MCT-treated rats. Experiments were performed on 50 male Sprague-Dawley rats [348 +/- 6 g (SD)]. Thirty-seven rats received MCT (50 mg/kg sc; MCT group) while the remainder did not (Control group). Three weeks later, pulmonary artery pressure was assessed echocardiographically in 20 MCT and 8 Control rats. The hearts were then excised and perfused in the constant pressure Langendorff mode to determine peak left ventricular pressure (LVP), the peak instantaneous rate of pressure increase (+dP/dtmax) and decrease (-dP/dtmax), as well as the rate pressure product (RPP). Histological sections were subsequently examined. Pulmonary artery pressure was higher in the MCT-treated group compared with the Control group [12.9 +/- 6 vs. 51 +/- 35.3 mmHg (P < 0.01)]. Left ventricular systolic function and diastolic relaxation were decreased in the MCT group compared with the Control group (+dP/dtmax 4,178 +/- 388 vs. 2,801 +/- 503 mmHg/s, LVP 115 +/- 11 vs. 83 +/- 14 mmHg, RPP 33,688 +/- 1,910 vs. 23,541 +/- 3,858 beats x min(-1) x mmHg(-1), -dP/dtmax -3,036 +/- 247 vs. -2,091 +/- 389 mmHg/s; P < 0.0001). The impairment of cardiac function was associated with myocarditis and coronary arteriolar medial thickening. Similarly depressed ventricular function and inflammatory infiltration was seen in 12 rats 7 days after MCT administration. Our findings appear unrelated to the degree of PH and indicate a direct cardiotoxic effect of MCT.

Rescue of monocrotaline-induced pulmonary arterial hypertension using bone marrow-derived endothelial-like progenitor cells: efficacy of combined cell and eNOS gene therapy in established disease

Pulmonary arterial hypertension (PAH) is characterized by a progressive increase in pulmonary vascular resistance caused by narrowing and loss of pulmonary microvasculature, which in its late stages becomes refractory to traditional therapies. We hypothesized that bone marrow-derived endothelial progenitor cells (EPCs), which normally function to repair and regenerate blood vessels, would restore pulmonary hemodynamics and increase microvascular perfusion in the rat monocrotaline (MCT) model of PAH. Mononuclear cells were isolated from the bone marrow of syngeneic Fisher-344 rats by Ficoll gradient centrifugation and cultured for 7 to 10 days in endothelial growth medium. Fluorescently labeled endothelial-like progenitor cells (ELPCs) engrafted at the level of the distal pulmonary arterioles and incorporated into the endothelial lining in the MCT-injured lung. The administration of ELPCs 3 days after MCT nearly completely prevented the increase in right ventricular systolic pressure seen at 3 weeks with MCT alone (31.5+/-0.95 versus 48+/-3 mm Hg, respectively; P<0.001), whereas injection of skin fibroblasts had no protective effect (50.9+/-5.4 mm Hg). Delayed administration of progenitor cells 3 weeks after MCT prevented the further progression of PAH 2 weeks later (ie, 5 weeks after MCT), whereas only animals receiving ELPCs transduced with human endothelial NO-synthase (eNOS) exhibited significant reversal of established disease at day 35 (31+/-2 mm Hg, P<0.005) compared with day 21 (50+/-3 mm Hg). Fluorescent microangiography revealed widespread occlusion of pulmonary precapillary arterioles 3 weeks after MCT, whereas arteriolar-capillary continuity and microvascular architecture was preserved with the administration of syngeneic ELPCs. Moreover, the delivery of ELPCs to rats with established PAH resulted in marked improvement in survival, which was greatest in the group receiving eNOS-transduced cells. We conclude that bone marrow-derived ELPCs can engraft and repair the MCT-damaged lung, restoring microvasculature structure and function. Therefore, the regeneration of lung vascular endothelium by injection of progenitor cells may represent a novel treatment paradigm for patients with PAH.