The current approach into signaling pathways in pulmonary arterial hypertension and their implication in novel therapeutic strategies

Methylation-mediated silencing of PTPRD induces pulmonary hypertension by promoting pulmonary arterial smooth muscle cell migration via the PDGFRB/PLCγ1 axis

OBJECTIVE

Pulmonary hypertension is a lethal disease characterized by pulmonary vascular remodeling and is mediated by abnormal proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs). Platelet-derived growth factor BB (PDGF-BB) is the most potent mitogen for PASMCs and is involved in vascular remodeling in pulmonary hypertension development. Therefore, the objective of our study is to identify novel mechanisms underlying vascular remodeling in pulmonary hypertension.

METHODS

We explored the effects and mechanisms of PTPRD downregulation in PASMCs and PTPRD knockdown rats in pulmonary hypertension induced by hypoxia.

RESULTS

We demonstrated that PTPRD is dramatically downregulated in PDGF-BB-treated PASMCs, pulmonary arteries from pulmonary hypertension rats, and blood and pulmonary arteries from lung specimens of patients with hypoxic pulmonary arterial hypertension (HPAH) and idiopathic PAH (iPAH). Subsequently, we found that PTPRD was downregulated by promoter methylation via DNMT1. Moreover, we found that PTPRD knockdown altered cell morphology and migration in PASMCs via modulating focal adhesion and cell cytoskeleton. We have demonstrated that the increase in cell migration is mediated by the PDGFRB/PLCγ1 pathway. Furthermore, under hypoxic condition, we observed significant pulmonary arterial remodeling and exacerbation of pulmonary hypertension in heterozygous PTPRD knock-out rats compared with the wild-type group. We also demonstrated that HET group treated with chronic hypoxia have higher expression and activity of PLCγ1 in the pulmonary arteries compared with wild-type group.

CONCLUSION

We propose that PTPRD likely plays an important role in the process of pulmonary vascular remodeling and development of pulmonary hypertension in vivo .

Potential role of sympathetic activity on the pathogenesis of massive pulmonary embolism with circulatory shock in rabbits

BACKGROUND

We recently showed that intravenous sodium nitroprusside treatment (SNP) could relieve the pulmonary vasospasm of pulmonary embolism (PE) and non-pulmonary embolism (non-PE) regions in a rabbit massive pulmonary embolism (MPE) model associated with shock. The present study explored the potential role of cardiopulmonary sympathetic activity on the pathogenesis and the impact of vasodilators on cardiopulmonary sympathetic activity in this model.

METHODS

Rabbits were randomly divided into sham operation group (S group, n = 8), model group (M, equal volume of saline intravenously, n = 11), SNP group (3.5 μg/kg/min intravenously, n = 10) and diltiazem group (DLZ, 6.0 μg/kg/min intravenously, n = 10).

RESULTS

MPE resulted in reduced mean arterial pressure and increased mean pulmonary arterial pressure as well as reduced PaO2 in the M, SNP and DLZ groups. Tyrosine hydroxylase (TH), neuropeptide Y (NPY) and endothelin-1 (ET-1) expression levels were significantly increased, while nitric oxide (NO) levels were reduced in both PE and non-PE regions in the M group. Both SNP and DLZ decreased mean pulmonary arterial pressure, reversed shock status, downregulated the expression of TH, NPY and ET-1, and increased NO levels in PE and non-PE regions.

CONCLUSION

Present results indicate that upregulation of the sympathetic medium transmitters TH and NPY in whole lung tissues serves one of the pathological features of MPE. The vasodilators SNP and DLZ could relieve pulmonary vasospasm in both embolization and non-embolization regions and reverse circulatory shock, thereby indirectly downregulating the sympathetic activation of the whole lung tissues and breaking a vicious cycle related to sympathetic activation in this model.

Maprotiline Prevents Monocrotaline-Induced Pulmonary Arterial Hypertension in Rats

Pulmonary arterial hypertension (PAH) is a progressive disease caused by increased pulmonary artery pressure and pulmonary vascular resistance, eventually leading to right heart failure until death. Soluble guanylate cyclase (sGC) has been regarded as an attractive drug target in treating PAH. In this study, we discovered that maprotiline, a tetracyclic antidepressant, bound to the full-length recombinant sGC with a high affinity (K_D = 0.307 μM). Further study demonstrated that maprotiline concentration-dependently inhibited the proliferation of hypoxia-induced human pulmonary artery smooth muscle cells. Moreover, in a monocrotaline (MCT) rat model of PAH, maprotiline (ip, 10 mg/kg once daily) reduced pulmonary hypertension, inhibited the development of right ventricular hypertrophy and pathological changes of the pulmonary vascular remodeling. Taken together, our studies showed that maprotiline may contribute to attenuate disease progression of pulmonary hypertension.

Systematic review and meta-analysis of interventions tested in animal models of pulmonary hypertension

A systematic review and meta-analysis was performed to test candidate therapeutic approaches in pulmonary hypertension (PH). The efficacy of 522 interventions with >200 unregistered drugs was tested on 7254 animals. We propose a modified formula to assess meta-data that concerns the contribution of PH animal model to the denoted efficacy of tested agents. The measure of efficacy expressed as a response ratio for right ventricle systolic pressure was 0.48 (95% CI, 0.46-0.50; P < 0.00001), mean pulmonary artery pressure was 0.54 (0.52-0.56; P < 0.00001), right ventricle hypertrophy was 0.49 (0.48-0.51; P < 0.00001) and pulmonary artery wall thickness was 0.58 (0.56-0.61; P < 0.00001). Only 41 out of 522 interventions were ineffective. The most potent agents to improve both haemodynamic and hypertrophic parameters were ATP-sensitive potassium channel openers with iptakalim, Rho/ROCK inhibitors with fasudil, RAAS regulators with adenosine and ACE2 activators, and anti-inflammatories with n-3 polyunsaturated fatty acids and NF-кB inhibitors.

Pulmonary Hypertension and Indicators of Right Ventricular Function

Pulmonary hypertension (PH) is a rare disease, whose underlying mechanisms are not fully understood. It is characterized by pulmonary arterial vasoconstriction and vessels wall thickening, mainly intimal and medial layers. Several molecular pathways have been studied, but their respective roles remain unknown. Cardiac repercussions of PH are hypertrophy, dilation, and progressive right ventricular dysfunction. Multiple echocardiographic parameters are being used, in order to assess anatomy and cardiac function, but there are no guidelines edited about their usefulness. Thus, it is now recommended to associate the best-known parameters, such as atrial and ventricular diameters or tricuspid annular plane systolic excursion. Cardiac catheterization remains necessary to establish the diagnosis of PH and to assess pulmonary hemodynamic state. Concerning energetic metabolism, free fatty acids, normally used to provide energy for myocardial contraction, are replaced by glucose uptake. These abnormalities are illustrated by increased (18)F-fluorodeoxyglucose ((18)F-FDG) uptake on positron emission tomography/computed tomography, which seems to be correlated with echocardiographic and hemodynamic parameters.

Salvianolic acid A attenuates vascular remodeling in a pulmonary arterial hypertension rat model

AIM

The current therapeutic approaches have a limited effect on the dysregulated pulmonary vascular remodeling, which is characteristic of pulmonary arterial hypertension (PAH). In this study we examined whether salvianolic acid A (SAA) extracted from the traditional Chinese medicine 'Dan Shen' attenuated vascular remodeling in a PAH rat model, and elucidated the underlying mechanisms.

METHODS

PAH was induced in rats by injecting a single dose of monocrotaline (MCT 60 mg/kg, sc). The rats were orally treated with either SAA (0.3, 1, 3 mg·kg(-1)·d(-1)) or a positive control bosentan (30 mg·kg(-1)·d(-1)) for 4 weeks. Echocardiography and hemodynamic measurements were performed on d 28. Then the hearts and lungs were harvested, the organ indices and pulmonary artery wall thickness were calculated, and biochemical and histochemical analysis were conducted. The levels of apoptotic and signaling proteins in the lungs were measured using immunoblotting.

RESULTS

Treatment with SAA or bosentan effectively ameliorated MCT-induced pulmonary artery remodeling, pulmonary hemodynamic abnormalities and the subsequent increases of right ventricular systolic pressure (RVSP). Furthermore, the treatments significantly attenuated MCT-induced hypertrophic damage of myocardium, parenchymal injury and collagen deposition in the lungs. Moreover, the treatments attenuated MCT-induced apoptosis and fibrosis in the lungs. The treatments partially restored MCT-induced reductions of bone morphogenetic protein type II receptor (BMPRII) and phosphorylated Smad1/5 in the lungs.

CONCLUSION

SAA ameliorates the pulmonary arterial remodeling in MCT-induced PAH rats most likely via activating the BMPRII-Smad pathway and inhibiting apoptosis. Thus, SAA may have therapeutic potential for the patients at high risk of PAH.

PDGF-dependent β-catenin activation is associated with abnormal pulmonary artery smooth muscle cell proliferation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by excessive pulmonary arterial smooth muscle cells (PASMCs) growth, partially in response to PDGF-BB but whether this is dependent on β-catenin (βC) activation is unclear. Compared to healthy cells, PAH PASMCs demonstrate higher levels of proliferation both at baseline and with PDGF-BB that correlate with GSK3β dependent βC activation. We show that βC knockdown but not Wnt5a stimulation reduces PDGF-BB dependent growth and normalizes PAH PASMCs proliferation. These findings support that cross-talk between PDGF and Wnt signaling modulates PASMC proliferation and suggest that βC targeted therapies could treat abnormal vascular remodeling in PAH.