Mechanism of the susceptibility of remodeled pulmonary vessels to drug-induced cell killing

Identifying Potential Mitochondrial Proteome Signatures Associated with the Pathogenesis of Pulmonary Arterial Hypertension in the Rat Model

Pulmonary arterial hypertension (PAH) is a severe and progressive disease that affects the heart and lungs and a global health concern that impacts individuals and society. Studies have reported that some proteins related to mitochondrial metabolic functions could play an essential role in the pathogenesis of PAH, and their specific expression and biological function are still unclear. We successfully constructed a monocrotaline- (MCT-) induced PAH rat model in the present research. Then, the label-free quantification proteomic technique was used to determine mitochondrial proteins between the PAH group (n = 6) and the normal group (n = 6). Besides, we identified 1346 mitochondrial differentially expressed proteins (DEPs) between these two groups. Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to analyze the mainly mitochondrial DEPs' biological functions and the signal pathways. Based on the protein-protein interaction (PPI) network construction and functional enrichment, we screened 19 upregulated mitochondrial genes (Psmd1, Psmc4, Psmd13, Psmc2, etc.) and 123 downregulated mitochondrial genes (Uqcrfs1, Uqcrc1, Atp5c1, Atp5a1, Uqcrc2, etc.) in rats with PAH. Furthermore, in an independent cohort dataset and experiments with rat lung tissue using qPCR, validation results consistently showed that 6 upregulated mitochondrial genes (Psmd2, Psmc4, Psmc3, Psmc5, Psmd13, and Psmc2) and 3 downregulated mitochondrial genes (Lipe, Cat, and Prkce) were significantly differentially expressed in the lung tissue of PAH rats. Using the RNAInter database, we predict potential miRNA target hub mitochondrial genes at the transcriptome level. We also identified bortezomib and carfilzomib as the potential drugs for treatment in PAH. Finally, this study provides us with a new perspective on critical biomarkers and treatment strategies in PAH.

Innovative Anti-Inflammatory and Pro-resolving Strategies for Pulmonary Hypertension: High Blood Pressure Research Council of Australia Award 2019

Pulmonary hypertension is a rare, ostensibly incurable, and etiologically diverse disease with an unacceptably high 5-year mortality rate (≈50%), worse than many cancers. Irrespective of pathogenic origin, dysregulated immune processes underlie pulmonary hypertension pathobiology, particularly pertaining to pulmonary vascular remodeling. As such, a variety of proinflammatory pathways have been mooted as novel therapeutic targets. One such pathway involves the family of innate immune regulators known as inflammasomes. In addition, a new and emerging concept is differentiating between anti-inflammatory approaches versus those that promote pro-resolving pathways. This review will briefly introduce inflammasomes and examine recent literature concerning their role in pulmonary hypertension. Moreover, it will explore the difference between inflammation-suppressing and pro-resolution approaches and how this links to inflammasomes. Finally, we will investigate new avenues for targeting inflammation in pulmonary hypertension via more targeted anti-inflammatory or inflammation resolving strategies.

Oxygen sensing, mitochondrial biology and experimental therapeutics for pulmonary hypertension and cancer

The homeostatic oxygen sensing system (HOSS) optimizes systemic oxygen delivery. Specialized tissues utilize a conserved mitochondrial sensor, often involving NDUFS2 in complex I of the mitochondrial electron transport chain, as a site of pO₂-responsive production of reactive oxygen species (ROS). These ROS are converted to a diffusible signaling molecule, hydrogen peroxide (H₂O₂), by superoxide dismutase (SOD2). H₂O₂ exits the mitochondria and regulates ion channels and enzymes, altering plasma membrane potential, intracellular Ca²⁺ and Ca²⁺-sensitization and controlling acute, adaptive, responses to hypoxia that involve changes in ventilation, vascular tone and neurotransmitter release. Subversion of this O₂-sensing pathway creates a pseudohypoxic state that promotes disease progression in pulmonary arterial hypertension (PAH) and cancer. Pseudohypoxia is a state in which biochemical changes, normally associated with hypoxia, occur despite normal pO₂. Epigenetic silencing of SOD2 by DNA methylation alters H₂O₂ production, activating hypoxia-inducible factor 1α, thereby disrupting mitochondrial metabolism and dynamics, accelerating cell proliferation and inhibiting apoptosis. Other epigenetic mechanisms, including dysregulation of microRNAs (miR), increase pyruvate dehydrogenase kinase and pyruvate kinase muscle isoform 2 expression in both diseases, favoring uncoupled aerobic glycolysis. This Warburg metabolic shift also accelerates cell proliferation and impairs apoptosis. Disordered mitochondrial dynamics, usually increased mitotic fission and impaired fusion, promotes disease progression in PAH and cancer. Epigenetic upregulation of dynamin-related protein 1 (Drp1) and its binding partners, MiD49 and MiD51, contributes to the pathogenesis of PAH and cancer. Finally, dysregulation of intramitochondrial Ca²⁺, resulting from impaired mitochondrial calcium uniporter complex (MCUC) function, links abnormal mitochondrial metabolism and dynamics. MiR-mediated decreases in MCUC function reduce intramitochondrial Ca²⁺, promoting Warburg metabolism, whilst increasing cytosolic Ca²⁺, promoting fission. Epigenetically disordered mitochondrial O₂-sensing, metabolism, dynamics, and Ca²⁺ homeostasis offer new therapeutic targets for PAH and cancer. Promoting glucose oxidation, restoring the fission/fusion balance, and restoring mitochondrial calcium regulation are promising experimental therapeutic strategies.

Bortezomib Inhibits Hypoxia-Induced Proliferation by Suppressing Caveolin-1/SOCE/[Ca2+]i Signaling Axis in Human PASMCs

Background

Previous studies have demonstrated the ubiquitin-proteasome inhibitor bortezomib (BTZ) can effectively alleviate hypoxia-induced pulmonary hypertension (HPH) by suppressing the intracellular calcium homeostasis in pulmonary arterial smooth muscle cells (PASMCs). Further evaluation showed that the antiproliferation roles of BTZ are mainly mediated by inhibition of the intracellular calcium homeostasis. Caveolin-1 belongs to one of the key regulators of the intracellular calcium homeostasis in PASMCs, which can regulate the store-operated calcium entry (SOCE). However, the effects of BTZ on Caveolin-1 remain unclear.

Methods

Primarily cultured human PASMCs were used as the cell model. CCK-8 assay was performed to assess the PASMCs proliferation. Western blotting and real-time qPCR were used to detect the mRNA and protein expressions. Fura-2-based fluorescence imaging experiments were used to determine the intracellular calcium concentration ([Ca²⁺]_i). The protein synthesis inhibitor cycloheximide (CHX) was utilized to determine the protein degradation process.

Results

Firstly, in cultured human PASMCs, treatment of BTZ for 24 or 60 hours significantly downregulates Caveolin-1 at both mRNA and protein levels. Secondly, in the presence CHX, BTZ treatment also leads to downregulated protein expression and fastened protein degradation of Caveolin-1, indicating that BTZ can promote the Caveolin-1 protein degradation, other than the BTZ on Caveolin-1 mRNA transcription. Then, BTZ significantly attenuates the hypoxia-elevated baseline [Ca²⁺]_i, SOCE, and cell proliferation.

Conclusion

We firstly observed that the ubiquitin-proteasome inhibitor BTZ can inhibit the Caveolin-1 expression at both mRNA transcription and protein degradation processes, providing new mechanistic basis of BTZ on PASMC proliferation.

Endothelial Dysfunction in Pulmonary Hypertension: Cause or Consequence?

Pulmonary arterial hypertension (PAH) is a rare, complex, and progressive disease that is characterized by the abnormal remodeling of the pulmonary arteries that leads to right ventricular failure and death. Although our understanding of the causes for abnormal vascular remodeling in PAH is limited, accumulating evidence indicates that endothelial cell (EC) dysfunction is one of the first triggers initiating this process. EC dysfunction leads to the activation of several cellular signalling pathways in the endothelium, resulting in the uncontrolled proliferation of ECs, pulmonary artery smooth muscle cells, and fibroblasts, and eventually leads to vascular remodelling and the occlusion of the pulmonary blood vessels. Other factors that are related to EC dysfunction in PAH are an increase in endothelial to mesenchymal transition, inflammation, apoptosis, and thrombus formation. In this review, we outline the latest advances on the role of EC dysfunction in PAH and other forms of pulmonary hypertension. We also elaborate on the molecular signals that orchestrate EC dysfunction in PAH. Understanding the role and mechanisms of EC dysfunction will unravel the therapeutic potential of targeting this process in PAH.

COVID-19 patients may become predisposed to pulmonary arterial hypertension

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is causing the current pandemic of coronavirus disease 2019 (COVID-19) that have killed over one million people worldwide so far. To date, over forty million people have officially been identified to be infected with this virus with less than 3% death rate. Since many more people are expected to have been infected with this virus without the official diagnosis, the number of people who have recovered from the SARS-CoV-2 infection should be substantial. Given the large number of people recovered from either the mild SARS-CoV-2 infection or more severe COVID-19 conditions, it is critical to understand the long-term consequences of the infection by this virus. Our histological evaluations revealed that patients died of COVID-19 exhibited thickened pulmonary vascular walls, one important hallmark of pulmonary arterial hypertension (PAH). By contrast, such pulmonary vascular remodeling lesions were not found in patients died of SARS-CoV-1 during the 2002–2004 SARS outbreak or due to the infection by H1N1 influenza. The advancement in the treatment for the human immunodeficiency virus (HIV) infection has been remarkable that HIV-infected individuals now live for a long time, in turn revealing that these individuals become susceptible to developing PAH, a fatal condition. We herein hypothesize that SARS-CoV-2 is another virus that is capable to triggering the increased susceptibility of infected individuals to developing PAH in the future. Given the large number of people being infected with SARS-CoV-2 during this pandemic and that most people recover from severe, mild or asymptomatic conditions, it is imperative to generate scientific information on how the health of recovered individuals may be affected long-term. PAH is one lethal consequence that should be considered and needs to be monitored. This may also foster the research on developing therapeutic agents to prevent PAH, which has not so far been successful.

Ultrastructural Changes of the Right Ventricular Myocytes in Pulmonary Arterial Hypertension

Background Pulmonary arterial hypertension ( PAH ) is a serious disease without cure. Elevated pulmonary vascular resistance puts strain on the right ventricle ( RV ) and patients die of RV failure. Subjecting Sprague-Dawley rats to SU 5416 injection and hypoxia promotes severe PAH with pulmonary vascular lesions similar to human disease and has been well utilized to investigate pulmonary vascular pathology. However, despite exhibiting severe RV fibrosis, these rats do not die. Recently, subjecting Fischer ( CDF ) rats to the same treatment to promote PAH was found to result in mortality. Thus, the present study performed detailed morphological characterizations of Fischer rats with PAH . Methods and Results Rats were subjected to SU 5416 injection and hypoxia for 3 weeks, followed by maintenance in normoxia. More than 90% of animals died within 6 weeks of the SU 5416 injection. Necropsy revealed the accumulation of fluid in the chest cavity, right ventricular hypertrophy and dilatation, hepatomegaly, and other indications of congestive heart failure. Time course studies demonstrated the progressive thickening of pulmonary arteries with the formation of concentric lamellae and plexiform lesions as well as RV fibrosis in PAH rats. Transmission electron microscopy demonstrated the destruction of the myofilaments, T-tubules, and sarcoplasmic reticulum. RV mitochondrial damage and fission were found in Fischer rats, but not in Sprague-Dawley rats, with PAH . Conclusions These results suggest that the destruction of RV mitochondria plays a role in the mechanism of PAH -induced death. The SU 5416/hypoxia model in Fischer rats should be useful for further investigating the mechanism of RV failure and finding effective therapeutic agents to increase the survival of PAH patients.

Morphological and Functional Characteristics of Animal Models of Myocardial Fibrosis Induced by Pressure Overload

Myocardial fibrosis is characterized by excessive deposition of myocardial interstitial collagen, abnormal distribution, and excessive proliferation of fibroblasts. According to the researches in recent years, myocardial fibrosis, as the pathological basis of various cardiovascular diseases, has been proven to be a core determinant in ventricular remodeling. Pressure load is one of the causes of myocardial fibrosis. In experimental models of pressure-overload-induced myocardial fibrosis, significant increase in left ventricular parameters such as interventricular septal thickness and left ventricular posterior wall thickness and the decrease of ejection fraction are some of the manifestations of cardiac damage. These morphological and functional changes have a serious impact on the maintenance of physiological functions. Therefore, establishing a suitable myocardial fibrosis model is the basis of its pathogenesis research. This paper will discuss the methods of establishing myocardial fibrosis model and compare the advantages and disadvantages of the models in order to provide a strong basis for establishing a myocardial fibrosis model.

Severe but reversible pulmonary hypertension in scleromyxedema and multiple myeloma: a case report

BACKGROUND

Scleromyxedema is a progressive, systemic connective tissue disorder characterized by fibro-mucous skin lesions and increased serum monoclonal immunoglobulin levels. Pulmonary involvement occurs in a subset of patients, though the overall prevalence of pulmonary lesions in scleromyxedema is unknown. Since pulmonary hypertension presumably occurs in these patients due to disease progression and development of additional conditions, treatment of the underlying plasma cell dyscrasia and connective tissue disorder may improve pulmonary hypertension symptoms.

CASE PRESENTATION

An elderly patient with scleromyxedema developed pulmonary hypertension refractory to vasodilator and diuretic therapy and subsequently multiple myeloma that responded to a combination therapy of bortezomib, cyclophosphamide, and dexamethasone treatment.

CONCLUSIONS

Treatment of the underlying disease(s) that contributed to pulmonary hypertension development with anti-neoplastic agents like bortezomib may improve cardiopulmonary symptoms secondary to reducing abnormal blood cell counts and paraprotein levels.

Increased Smooth Muscle Kv11.1 Channel Expression in Pulmonary Hypertension and Protective Role of Kv11.1 Channel Blocker Dofetilide

Kv11.1 potassium channels are essential for heart repolarization. Prescription medication that blocks Kv11.1 channels lengthens the ventricular action potential and causes cardiac arrhythmias. Surprisingly little is known about the Kv11.1 channel expression and function in the lung tissue. Here we report that Kv11.1 channels were abundantly expressed in the large pulmonary arteries (PAs) of healthy lung tissues from humans and rats. Kv11.1 channel expression was increased in the lungs of humans affected by chronic obstructive pulmonary disease-associated pulmonary hypertension and in the lungs of rats with pulmonary arterial hypertension (PAH). In healthy lung tissues from humans and rats, Kv11.1 channels were confined to the large PAs. In humans with chronic obstructive pulmonary disease-associated pulmonary hypertension and in rats with PAH, Kv11.1 channels were expressed in both the large and small PAs. The increase in Kv11.1 channel expression closely followed the time-course of the development of pulmonary vascular remodeling in PAH rats. Treatment of PAH rats with dofetilide, an Kv11.1 channel blocker approved by the US Food and Drug Administration for use in the treatment of arrythmia, inhibited PAH-associated pulmonary vascular remodeling. Taken together, the findings from this study uncovered a novel role of Kv11.1 channels in lung function and their potential as new drug targets in the treatment of pulmonary hypertension. The protective effect of dofetilide raises the possibility of repurposing this antiarrhythmic drug for the treatment of patients with pulmonary hypertension.

Inhibition of Siah2 ubiquitin ligase ameliorates monocrotaline-induced pulmonary arterial remodeling through inactivation of YAP

AIMS

It has been shown that up-regulation of E3 ubiquitin ligase seven-in-absentia-homolog 2 (Siah2) and activation of Hippo signaling pathway effector yes-associated protein (YAP) are involved in the development of pulmonary arterial hypertension (PAH). However, it is still unclear whether Siah2 activates YAP in monocrotaline (MCT)-induced PAH rat models.

MAIN METHODS

Intraperitoneal injection of MCT was used to induce PAH rat models. The right ventricular systolic pressure (RVSP), right ventricle hypertrophy index (RVHI), percentage of medial wall thickness (%MT), α-SMA, Ki-67 and TUNEL staining were performed to evaluate the development of PAH. Protein levels of Siah2, Lats1/2, YAP phosphorylation and total YAP, and the subcellular localization of YAP were examined using immunoblotting. Proteasome activity was measured by an assay kit.

KEY FINDINGS

The protein level of Siah2 was significantly increased in MCT-induced PAH rats, this was accompanied with the proteasome-dependent degradation of Lats1/2 and subsequent up-regulation and dephosphorylation of YAP and its nuclear localization. Administration of PAH rats with Siah2 inhibitor Vitamin K3 or proteasome inhibitor MG-132 dramatically suppressed MCT-induced down-regulation of Lats1/2 and activation of YAP, finally reduced RVSP, RVHI, %MT, pulmonary arterial muscularization, pulmonary arterial smooth muscle cells (PASMCs) proliferation and enhanced PASMCs apoptosis in PAH rats.

SIGNIFICANCE

Siah2 contributes to the development of MCT-induced PAH by destabilizing Lats1/2 and subsequently stimulating YAP activation. Inhibition of Siah2 or proteasome alleviates pulmonary arterial remodeling through inactivation of YAP, indicating Siah2 ubiquitin ligase as a novel target might have potential value in the management of PAH.

Mitochondrial HSP90 Accumulation Promotes Vascular Remodeling in Pulmonary Arterial Hypertension

RATIONALE

Pulmonary arterial hypertension (PAH) is a vascular remodeling disease with a poor prognosis and limited therapeutic options. Although the mechanisms contributing to vascular remodeling in PAH are still unclear, several features, including hyperproliferation and resistance to apoptosis of pulmonary artery smooth muscle cells (PASMCs), have led to the emergence of the cancer-like concept. The molecular chaperone HSP90 (heat shock protein 90) is directly associated with malignant growth and proliferation under stress conditions. In addition to being highly expressed in the cytosol, HSP90 exists in a subcellular pool compartmentalized in the mitochondria (mtHSP90) of tumor cells, but not in normal cells, where it promotes cell survival.

OBJECTIVES

We hypothesized that mtHSP90 in PAH-PASMCs represents a protective mechanism against stress, promoting their proliferation and resistance to apoptosis.

METHODS

Expression and localization of HSP90 were analyzed by Western blot, immunofluorescence, and immunogold electron microscopy. In vitro, effects of mtHSP90 inhibition on mitochondrial DNA integrity, bioenergetics, cell proliferation and resistance to apoptosis were assessed. In vivo, the therapeutic potential of Gamitrinib, a mitochondria-targeted HSP90 inhibitor, was tested in fawn-hooded and monocrotaline rats.

MEASUREMENTS AND MAIN RESULTS

We demonstrated that, in response to stress, HSP90 preferentially accumulates in PAH-PASMC mitochondria (dual immunostaining, immunoblot, and immunogold electron microscopy) to ensure cell survival by preserving mitochondrial DNA integrity and bioenergetic functions. Whereas cytosolic HSP90 inhibition displays a lack of absolute specificity for PAH-PASMCs, Gamitrinib decreased mitochondrial DNA content and repair capacity and bioenergetic functions, thus repressing PAH-PASMC proliferation (Ki67 labeling) and resistance to apoptosis (Annexin V assay) without affecting control cells. In vivo, Gamitrinib improves PAH in two experimental rat models (monocrotaline and fawn-hooded rat).

CONCLUSIONS

Our data show for the first time that accumulation of mtHSP90 is a feature of PAH-PASMCs and a key regulator of mitochondrial homeostasis contributing to vascular remodeling in PAH.

Effects of Bcl-2/Bcl-xL Inhibitors on Pulmonary Artery Smooth Muscle Cells

Pulmonary arterial hypertension (PAH) is a fatal disease without satisfactory therapeutic options. By the time patients are diagnosed with this disease, the remodeling of pulmonary arteries has already developed due to the abnormal growth of pulmonary vascular cells. Therefore, agents that reduce excess pulmonary vascular cells have therapeutic potential. Bcl-2 is known to function in an antioxidant pathway to prevent apoptosis. The present study examined the effects of inhibitors of the anti-apoptotic proteins Bcl-2 and Bcl-x_L. ABT-263 (Navitoclax), ABT-199 (Venetoclax), ABT-737, and Obatoclax, which all promoted the death of cultured human pulmonary artery smooth muscle cells. Further examinations using ABT-263 showed that Bcl-2/Bcl-x_L inhibition indeed promoted apoptotic programmed cell death. ABT-263-induced cell death was inhibited by antioxidants. ABT-263 also promoted autophagy; however, the inhibition of autophagy did not suppress ABT-263-induced cell death. This is in contrast to other previously studied drugs, including anthracyclines and proteasome inhibitors, which were found to mediate autophagy to induce cell death. The administration of ABT-263 to rats with PAH in vivo resulted in the reversal of pulmonary vascular remodeling. Thus, promoting apoptosis by inhibiting anti-apoptotic Bcl-2 and Bcl-x_L effectively kills pulmonary vascular smooth muscle cells and reverses pulmonary vascular remodeling.

Insights on the epigenetic mechanisms underlying pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH), characterized by localized increased arterial blood pressure in the lungs, is a slow developing long-term disease that can be fatal. PAH is characterized by inflammation, vascular tone imbalance, pathological pulmonary vascular remodeling, and right-sided heart failure. Current treatments for PAH are palliative and development of new therapies is necessary. Recent and relevant studies have demonstrated that epigenetic processes may exert key influences on the pathogenesis of PAH and may be promising therapeutic targets in the prevention and/or cure of this condition. The aim of the present mini-review is to summarize the occurrence of epigenetic-based mechanisms in the context of PAH physiopathology, focusing on the roles of DNA methylation, histone post-translational modifications and non-coding RNAs. We also discuss the potential of epigenetic-based therapies for PAH.

Ligand-mediated dephosphorylation signaling for MAP kinase

Extracellular signal-regulated kinase (ERK), also known as classical mitogen-activated protein kinase, plays critical roles in cell regulation. ERK is activated through phosphorylation by a cascade of protein kinases including MEK. Various ligands activate the MEK/ERK pathway through receptor-dependent cell signaling. In cultured cells, many ligands such as growth factors, hormones, cytokines and vasoactive peptides elicit transient activation of MEK/ERK, often peaking at ~10 min after the cell treatment. Here, we describe a novel biological event, in which ligand-mediated cell signaling results in the dephosphorylation of MEK/ERK. Neuromedin N and neurotensin, peptides derived from the same precursor polypeptide, elicit cell signaling through the neurotensin receptors. In cultured human pulmonary artery smooth muscle cells (PASMCs), but not in human pulmonary artery endothelial cells (PAECs), we found that both neuromedin N and neurotensin promoted the dephosphorylation of ERK and MEK. Human PASMCs were found to express neurotensin receptor (NTR)-1, -2 and -3, while human PAECs only express NTR3. Neuromedin N-mediated dephosphorylation was suppressed by small chemical inhibitors of protein phosphatase 1/2A and peptidyl-prolyl isomerase. Transmission electron microscopy showed the formation of endocytic vesicles in response to neuromedin N treatment, and dephosphorylation did not occur when sorting nexin 9, a critical regulator of the endocytic vesicle formation, was knocked down. We conclude that neuromedin N and neurotensin elicit a unique dephosphorylation signaling in the MEK/ERK pathway that is regulated by endocytosis. Considering the pathophysiological importance of the MEK/ERK pathway, this discovery of the dephosphorylation mechanism should advance the field of cell signaling.

Redox Biology of Right-Sided Heart Failure

Right-sided heart failure is the major cause of death among patients who suffer from various forms of pulmonary hypertension and congenital heart disease. The right ventricle (RV) and left ventricle (LV) originate from different progenitor cells and function against very different blood pressures. However, differences between the RV and LV formed after birth have not been well defined. Work from our laboratory and others has accumulated evidence that redox signaling, oxidative stress and antioxidant regulation are important components that define the RV/LV differences. The present article summarizes the progress in understanding the roles of redox biology in the RV chamber-specificity. Understanding the mechanisms of RV/LV differences should help develop selective therapeutic strategies to help patients who are susceptible to and suffering from right-sided heart failure. Modulations of redox biology may provide effective therapeutic avenues for these conditions.

Natural reversal of pulmonary vascular remodeling and right ventricular remodeling in SU5416/hypoxia-treated Sprague-Dawley rats

Aims

Pulmonary arterial hypertension (PAH) is a lethal disease and improved therapeutic strategies are needed. Increased pulmonary arterial pressure, due to vasoconstriction and vascular remodeling, causes right ventricle (RV) failure and death in patients. The treatment of Sprague-Dawley rats with SU5416 injection and exposure to chronic hypoxia for three weeks followed by maintenance in normoxia promote progressive and severe PAH with pathologic features that resemble human PAH. At 5–17 weeks after the SU5416 injection, PAH is developed with pulmonary vascular remodeling as well as RV hypertrophy and fibrosis. The present study investigated subsequent events that occur in these PAH animals.

Methods & results

At 35 weeks after the SU5416 injection, rats still maintained high RV pressure, but pulmonary vascular remodeling was significantly reduced. Metabolomics analysis revealed that lungs of normal rats and rats from the 35-week time point had different metabolomics profiles. Despite the maintenance of high RV pressure, fibrosis was resolved at 35-weeks. Masson’s trichrome stain and Western blotting monitoring collagen 1 determined 12% fibrosis in the RV at 17-weeks, and this was decreased to 5% at 35-weeks. The level of myofibroblasts was elevated at 17-weeks and normalized at 35-weeks.

Conclusions

These results suggest that biological systems possess natural ways to resolve pulmonary and RV remodeling. The resolution of RV fibrosis appears to involve the reduction of myofibroblast-dependent collagen synthesis. Understanding these endogenous mechanisms should help improve therapeutic strategies to treat PAH and RV failure.

Docetaxel Reverses Pulmonary Vascular Remodeling by Decreasing Autophagy and Resolves Right Ventricular Fibrosis

Pulmonary arterial hypertension remains a fatal disease despite the availability of approved vasodilators. Since vascular remodeling contributes to increased pulmonary arterial pressure, new agents that reduce the thickness of pulmonary vascular walls have therapeutic potential. Thus, antitumor agents that are capable of killing cells were investigated. Testing of various antitumor drugs identified that docetaxel is a superior drug for killing proliferating pulmonary artery smooth muscle cells compared with other drugs, including gemcitabine, methotrexate, and ifosfamide. The administration of docetaxel to rats with severe pulmonary arterial hypertension reversed pulmonary vascular remodeling and reduced right ventricular pressure. Docetaxel was found to decrease autophagy as monitored by LC3B-II and p62 expression. The small interfering RNA knockdown of Beclin-1 or LC3B potentiated docetaxel-induced cell death, and knocking down p62 inhibited the docetaxel effects. The suppressed autophagic process is due to the ability of docetaxel to decrease Beclin-1 protein expression in a proteasome-dependent manner. Mass spectrometry identified a novel docetaxel-inducible Beclin-1 binding protein, namely, myosin-9. Knocking down myosin-9 inhibited docetaxel-induced cell death. In damaged right ventricles of pulmonary arterial hypertension rats, docetaxel remarkably promoted the resolution of fibrosis and the regeneration of myocardium. Thus, docetaxel is capable of reversing pulmonary vascular remodeling and resolving right ventricle fibrosis and is a promising therapeutic agent for the treatment of pulmonary arterial hypertension and right heart failure.

Oxidative profiling of the failing right heart in rats with pulmonary hypertension

Right heart failure is the major cause of death among patients with pulmonary arterial hypertension (PAH). Understanding the biology of the right ventricle (RV) should help developing new therapeutic strategies. Rats subjected to the injection of Sugen5416 (an inhibitors of vascular endothelial growth factor receptor) plus the ovalbumin immunization had increased pulmonary arterial pressure and severe vascular remodeling. RVs of these rats were hypertrophied and had severe cardiac fibrosis. No apoptosis was, however, detected. Metabolomics analysis revealed that oxidized glutathione, xanthine and uric acid had increased in PAH RVs, suggesting the production of reactive oxygen species by xanthine oxidase. PAH RVs were also found to have a 30-fold lower level of α-tocopherol nicotinate, consistent with oxidative stress decreasing antioxidants and also demonstrating for the first time that the nicotinate ester of vitamin E is endogenously expressed. Oxidative/nitrosative protein modifications including S-glutathionylation, S-nitrosylation and nitrotyrosine formation, but not protein carbonylation, were found to be increased in RVs of rats with PAH. Mass spectrometry identified that S-nitrosylated proteins include heat shock protein 90 and sarcoplasmic reticulum Ca²⁺-ATPase. These results demonstrate that RV failure is associated with the promotion of specific oxidative and nitrosative stress.

The cancer theory of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) remains a mysterious killer that, like cancer, is characterized by tremendous complexity. PAH development occurs under sustained and persistent environmental stress, such as inflammation, shear stress, pseudo-hypoxia, and more. After inducing an initial death of the endothelial cells, these environmental stresses contribute with time to the development of hyper-proliferative and apoptotic resistant clone of cells including pulmonary artery smooth muscle cells, fibroblasts, and even pulmonary artery endothelial cells allowing vascular remodeling and PAH development. Molecularly, these cells exhibit many features common to cancer cells offering the opportunity to exploit therapeutic strategies used in cancer to treat PAH. In this review, we outline the signaling pathways and mechanisms described in cancer that drive PAH cells' survival and proliferation and discuss the therapeutic potential of antineoplastic drugs in PAH.

Inhibition of ubiquitin proteasome function prevents monocrotaline-induced pulmonary arterial remodeling

AIMS

Previous study has indicated that inhibition of proteasome function ameliorates the development of pulmonary arterial hypertension (PAH), while its underlying mechanisms are still unclear. This study was performed to address these issues.

MATERIAL AND METHODS

Male Sprague-Dawley (SD) rats were divided into five groups: control group, PAH group, vehicle treated PAH group, MG-132 treated PAH group and bortezomib treated PAH group. PAH model was established by a single intraperitoneal injection of monocrotaline (MCT). MG-132 and bortezomib were administered to inhibit proteasome function. The right ventricular systolic pressure (RVSP), the right ventricle hypertrophy index (RVHI) and the percentage of medial wall thickness (%MT) were used to evaluate the development of PAH. Hematoxylin and eosin staining was performed to measure vascular remodeling. Immunoblotting was used to determine Akt phosphorylation, expression of PTEN and NEDD4, and the level of ubiquitinated-PTEN protein.

KEY FINDINGS

MCT increased RVSP, RVHI and %MT in rats, while these changes were suppressed by treatment of PAH rats with MG-132 or bortezomib. In PAH model, expression of PTEN was decreased and phosphorylation of Akt was increased, these were accompanied by an elevation of NEDD4 protein level. Treatment of PAH model with MG-132 or bortezomib increased PTEN expression and accumulation of ubiquitinated-PTEN protein and decreased Akt phosphorylation, while didn't change NEDD4 expression.

SIGNIFICANCE

Inhibition of proteasome function ameliorates pulmonary arterial remodeling by suppressing UPS-mediated PTEN degradation and subsequent inhibition of PI3K/Akt pathway, indicating that UPS might be a novel target for prevention of PAH.

Bortezomib alleviates experimental pulmonary hypertension by regulating intracellular calcium homeostasis in PASMCs

The ubiquitin-proteasome system is considered to be the key regulator of protein degradation. Bortezomib (BTZ) is the first proteasome inhibitor approved by the US Food and Drug Administration for treatment of relapsed multiple myeloma and mantle cell lymphoma. Recently, BTZ treatment was reported to inhibit right ventricular hypertrophy and vascular remodeling in hypoxia-exposed and monocrotaline-injected rats. However, the underlying mechanisms remain poorly understood. We previously confirmed that hypoxia-elevated basal intracellular Ca(2+) concentration ([Ca(2+)]i) and store-operated Ca(2+) entry (SOCE) in pulmonary artery smooth muscle cells (PASMCs) are involved in pulmonary vascular remodeling. In this study we aim to determine whether BTZ attenuates the hypoxia-induced elevation of [Ca(2+)] in PASMCs and the signaling pathway involved in this mechanism. Our results showed that 1) in hypoxia- and monocrotaline-induced rat pulmonary hypertension (PH) models, BTZ markedly attenuated the development and progression of PH, 2) BTZ inhibited the hypoxia-induced increase in cell proliferation, basal [Ca(2+)]i, and SOCE in PASMCs, and 3) BTZ significantly normalized the hypoxia-upregulated expression of hypoxia-inducible factor-1α, bone morphogenetic protein 4, canonical transient receptor potential isoforms 1 and 6, and the hypoxia-downregulated expression of peroxisome proliferator-activated receptor-γ in rat distal pulmonary arteries and PASMCs. These results indicate that BTZ exerts its protective role in the development of PH potentially by inhibiting the canonical transient receptor potential-SOCE-[Ca(2+)]i signaling axis in PASMCs.

Pulmonary arterial hypertension in primary amyloidosis

Amyloidosis involves extravascular deposition of fibrillar proteins within tissues and organs. Primary light chain amyloidosis represents the most common form of systemic amyloidosis involving deposition of monoclonal immunoglobulin light chains. Although pulmonary amyloid deposition is common in primary amyloidosis, clinically significant pulmonary amyloidosis is uncommon, and elevated pulmonary artery pressures are rarely observed in the absence of other underlying etiologies for pulmonary hypertension, such as elevated filling pressures secondary to cardiac amyloid. In this case report, we present a patient with primary light chain amyloidosis and pulmonary arterial hypertension in the setting of pulmonary vascular and right ventricular myocardial amyloid deposition.

Carfilzomib reverses pulmonary arterial hypertension

AIMS

Pulmonary arterial hypertension (PAH) remains a lethal disease with pronounced narrowing of pulmonary vessels due to abnormal cell growth. Agents that can reduce the pulmonary vascular thickness thus have therapeutic potential. The present study investigated the efficacy of carfilzomib (CFZ), a proteasome inhibitor and a cancer chemotherapeutic drug, on reversing PAH.

METHODS AND RESULTS

In two rat models of PAH, SU5416/hypoxia and SU5416/ovalbumin, CFZ effectively reversed pulmonary vascular remodelling with the promotion of apoptosis and autophagy. In human pulmonary artery smooth muscle cells, knocking down mediators of autophagy attenuated CFZ-induced cell death. The cell death role of autophagy was promoted by the participation of tumour protein p53-inducible nuclear protein 1. CFZ increased the protein ubiquitination, and siRNA knockdown of ubiquitin inhibited cell death, suggesting that CFZ-induced cell death is ubiquitin-dependent. Mass spectrometry demonstrated the ubiquitination of major vault protein and heat shock protein 90 in response to CFZ. The siRNA knockdown of these proteins enhanced CFZ-induced cell death, revealing that they are cell survival factors. CFZ reduced right-ventricular pressure and enhanced the efficacy of a vasodilator, sodium nitroprusside. While no indications of CFZ toxicity were observed in the right ventricle of PAH rats, apoptosis was promoted in the left ventricle. Apoptosis was prevented by dexrazoxane or by pifithrin-α without interfering with the efficacy of CFZ to reverse pulmonary vascular remodelling.

CONCLUSION

The addition of anti-tumour agents such as CFZ along with cardioprotectants to currently available vasodilators may be a promising way to improve PAH therapy.

Apoptosis-based therapy to treat pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is rare, but patients who are diagnosed with this disease still suffer from a lack of satisfactory treatment strategies to prolong survival. While currently approved drugs for PAH have some benefits, these vasodilators only have limited efficacy for eliminating pulmonary vascular remodeling and reducing mortality. Thus, our laboratory has been exploring the use of aggressive drugs, which are capable of causing apoptotic cell death, to treat PAH. We have so far found that three classes of anti-tumor agents, including anthracyclines, taxanes, and proteasome inhibitors, are capable of reducing pulmonary vascular thickness in rats with PAH. These drugs kill cells in remodeled pulmonary vessels without affecting the normal, healthy pulmonary vasculature, revealing that proliferating vascular cells in PAH patients are more sensitive to drug-induced apoptosis compared to the differentiated phenotype that is physiologically important for smooth muscle contraction. Since many apoptosis-inducing drugs cause cardiotoxicity in cancer patients, and because PAH patients already have a weakened heart, we focus on finding biological mechanisms that may reverse pulmonary vascular remodeling without promoting cardiotoxicity. We found two agents, dexrazoxane and pifithrin-α, that selectively inhibit cardiac muscle apoptosis without affecting the drug-induced apoptosis of the proliferating pulmonary vascular cells. Thus, we propose that the addition of apoptosis-inducing drugs and cardioprotectants to PAH therapies may be effective in treating patients and preventing right heart failure.

A Hypothesis Concerning the Biphasic Dose-response of Tumors to Angiostatin and Endostatin

This manuscript proposes a hypothesis to explain the U-shaped dose-response observed for angiostatin and other high-molecular-weight drugs in various anti-cancer bio-assays. The dose-response curves for angiostatin and endostatin (measured as suppression of tumor growth) go through an optimum (i.e., minimum tumor growth) and then becomes less effective at higher doses. The literature suggests that at lower doses the primary action of these high-molecular-weight drugs is to counteract the angiogenic effects of vascular endothelial growth factor (VEGF). To do this, the drugs must pass out of the blood vessel and enter the extra-cellular matrix (ECM) where VEGF induces the growth and fusion of tip cells. Ironically, VEGF actually facilitates access of the drugs to the ECM by making the vascular endothelium leaky. At higher doses, the high-molecular-weight drugs seem to reverse VEGF-induced permeability of the endothelium. Thus, at high dose rates, it is hypothesized that the drugs are not able to enter the ECM and block the angiogenic effects of VEGF there. As a result, high doses of the drugs do not suppress vascularization of the tumor or tumor growth. Moreover, if the permeability of the vessels is suppressed, the VEGF released by the stroma is concentrated in the ECM where it amplifies the angiogenic activity around the tumor.