Evaluation and Treatment of Endoplasmic Reticulum (ER) Stress in Right Ventricular Dysfunction during Monocrotaline-Induced Rat Pulmonary Arterial Hypertension

Downregulation of PDCD4 through STAT3/ATF6/autophagy mediates MIF-induced PASMCs proliferation/migration and vascular remodeling

To address the molecular mechanisms underlying macrophage migration inhibitory factor (MIF) induced pulmonary artery smooth muscle cells (PASMCs) proliferation, migration and vascular remodeling in pulmonary hypertension (PH), primary cultured rat PASMCs and monocrotaline (MCT)-induced rats with PH were applied in the present study. The results showed that MIF increased signal transducer and activator of transcription 3 (STAT3) phosphorylation, and then stimulated activating transcription factor 6 (ATF6) activation, subsequently triggered autophagy activation, which further led to programmed cell death factor 4 (PDCD4) lysosomal degradation, and eventually promoted PASMCs proliferation/migration. In lung tissues of MCT rats, MIF protein expression was elevated, phosphorylation of STAT3 and activation of ATF6 were increased, activation of autophagy was evident, and reduction of PDCD4 was observed. Intervention with MIF inhibitor 4-Iodo-6-phenylpyrimidine (4-IPP), ATF6 blocker melatonin or autophagy inhibitor chloroquine, confirmed the in vitro interaction among MIF, STAT3, ATF6, autophagy and PDCD4 in MCT induced rats with PH. Targeting MIF/STAT3/ATF6/autophagy/PDCD4 axis effectively prevented the development of PH by suppressing PASMCs proliferation and vascular remodeling. In conclusions, we demonstrate that MIF activates the STAT3/ATF6/autophagy cascade and then degrades PDCD4 leading to PASMCs proliferation/migration and pulmonary vascular remodeling, suggesting that intervention this axis might have potential value in management of PH.

Down-regulation of the mitochondrial fusion protein Opa1/Mfn2 promotes cardiomyocyte hypertrophy in Su5416/hypoxia-induced pulmonary hypertension rats

BACKGROUND

Maladaptive right ventricular (RV) remodeling is the most important pathological feature of pulmonary hypertension (PH), involving processes such as myocardial hypertrophy and fibrosis. A growing number of studies have shown that mitochondria-associated endoplasmic reticulum membranes (MAMs) are involved in various physiological and pathological processes, such as calcium homeostasis, lipid metabolism, inflammatory response, mitochondrial dynamics, and autophagy/mitophagy. The abnormal expression of MAMs-related factors is closely related to the occurrence and development of heart-related diseases. However, the role of MAM-related factors in the maladaptive RV remodeling of PH rats remains unclear.

METHODS AND RESULTS

We first obtained the transcriptome data of RV tissues from PH rats induced by Su5416 combined with hypoxia treatment (SuHx) from the Gene Expression Omnibus (GEO) database. The results showed that two MAMs-related genes (Opa1 and Mfn2) were significantly down-regulated in RV tissues of SuHx rats, accompanied by significant up-regulation of cardiac hypertrophy-related genes (such as Nppb and Myh7). Subsequently, using the SuHx-induced PH rat model, we found that the downregulation of mitochondrial fusion proteins Opa1 and Mfn2 may be involved in maladaptive RV remodeling by accelerating mitochondrial dysfunction. Finally, at the cellular level, we found that overexpression of Opa1 and Mfn2 could inhibit hypoxia-induced mitochondrial fission and reduce ROS production in H9c2 cardiomyocytes, thereby retarded the progression of cardiomyocyte hypertrophy.

CONCLUSIONS

The down-regulation of mitochondrial fusion protein Opa1/Mfn2 can accelerate cardiomyocyte hypertrophy and then participate in maladaptive RV remodeling in SuHx-induced PH rats, which may be potential targets for preventing maladaptive RV remodeling.

Interleukin-6 and pulmonary hypertension: from physiopathology to therapy

Pulmonary hypertension (PH) is a progressive, pulmonary vascular disease with high morbidity and mortality. Unfortunately, the pathogenesis of PH is complex and remains unclear. Existing studies have suggested that inflammatory factors are key factors in PH. Interleukin-6 (IL-6) is a multifunctional cytokine that plays a crucial role in the regulation of the immune system. Current studies reveal that IL-6 is elevated in the serum of patients with PH and it is negatively correlated with lung function in those patients. Since IL-6 is one of the most important mediators in the pathogenesis of inflammation in PH, signaling mechanisms targeting IL-6 may become therapeutic targets for this disease. In this review, we detailed the potential role of IL-6 in accelerating PH process and the specific mechanisms and signaling pathways. We also summarized the current drugs targeting these inflammatory pathways to treat PH. We hope that this study will provide a more theoretical basis for targeted treatment in patients with PH in the future.

HMGB1-induced activation of ER stress contributes to pulmonary artery hypertension in vitro and in vivo

BACKGROUND

HMGB1 and ER stress have been considered to participate in the progression of pulmonary artery hypertension (PAH). However, the molecular mechanism underlying HMGB1 and ER stress in PAH remains unclear. This study aims to explore whether HMGB1 induces pulmonary artery smooth muscle cells (PASMCs) functions and pulmonary artery remodeling through ER stress activation.

METHODS

Primary cultured PASMCs and monocrotaline (MCT)-induced PAH rats were applied in this study. Cell proliferation and migration were determined by CCK-8, EdU and transwell assay. Western blotting was conducted to detect the protein levels of protein kinase RNA-like endoplasmic reticulum kinase (PERK), activating transcription factor-4 (ATF4), seven in absentia homolog 2 (SIAH2) and homeodomain interacting protein kinase 2 (HIPK2). Hemodynamic measurements, immunohistochemistry staining, hematoxylin and eosin staining were used to evaluate the development of PAH. The ultrastructure of ER was observed by transmission electron microscopy.

RESULTS

In primary cultured PASMCs, HMGB1 reduced HIPK2 expression through upregulation of ER stress-related proteins (PERK and ATF4) and subsequently increased SIAH2 expression, which ultimately led to PASMC proliferation and migration. In MCT-induced PAH rats, interfering with HMGB1 by glycyrrhizin, suppression of ER stress by 4-phenylbutyric acid or targeting SIAH2 by vitamin K3 attenuated the development of PAH. Additionally, tetramethylpyrazine (TMP), as a component of traditional Chinese herbal medicine, reversed hemodynamic deterioration and vascular remodeling by targeting PERK/ATF4/SIAH2/HIPK2 axis.

CONCLUSIONS

The present study provides a novel insight to understand the pathogenesis of PAH and suggests that targeting HMGB1/PERK/ATF4/SIAH2/HIPK2 cascade might have potential therapeutic value for the prevention and treatment of PAH.

Cannabidiol alleviates right ventricular fibrosis by inhibiting the transforming growth factor β pathway in monocrotaline-induced pulmonary hypertension in rats

Cannabidiol (CBD) is a non-intoxicating compound of Cannabis with anti-fibrotic properties. Pulmonary hypertension (PH) is a disease that can lead to right ventricular (RV) failure and premature death. There is evidence that CBD reduces monocrotaline (MCT)-induced PH, including reducing right ventricular systolic pressure (RVSP), vasorelaxant effect on pulmonary arteries, and decreasing expression of profibrotic markers in the lungs. The aim of our study was to investigate the effect of chronic administration of CBD (10 mg/kg daily for 21 days) on profibrotic parameters in the RVs of MCT-induced PH rats. In MCT-induced PH, we found an increase in profibrotic parameters and parameters related to RV dysfunction, i.e. plasma pro-B-type natriuretic peptide (NT-proBNP), cardiomyocyte width, interstitial and perivascular fibrosis area, amount of fibroblasts and fibronectin, as well as overexpression of the transforming growth of factor β1 (TGF-β1), galectin-3 (Gal-3), suppressor of mothers against decapentaplegic 2 (SMAD2), phosphorylated SMAD2 (pSMAD2) and alpha-smooth muscle actin (α-SMA). In contrast, vascular endothelial cadherin (VE-cadherin) levels were decreased in the RVs of MCT-induced PH rats. Administration of CBD reduced the amount of plasma NT-proBNP, the width of cardiomyocytes, the amount of fibrosis area, fibronectin and fibroblast expression, as well as decreased the expression of TGF-β1, Gal-3, SMAD2, pSMAD2, and increased the level of VE-cadherin. Overall, CBD has been found to have the anti-fibrotic potential in MCT-induced PH. As such, CBD may act as an adjuvant therapy for PH, however, further detailed investigations are recommended to confirm our promising results.

Apolipoprotein A5 ameliorates MCT induced pulmonary hypertension by inhibiting ER stress in a GRP78 dependent mechanism

Background

Pulmonary arterial hypertension (PAH) is a chronic, progressive lung vascular disease accompanied by elevated pulmonary vascular pressure and resistance, and it is characterized by increased pulmonary artery smooth muscle cell (PASMC) proliferation. Apolipoprotein A5 (ApoA5) improves monocrotaline (MCT)-induced PAH and right heart failure; however, the underlying mechanism remains unknown. Here we speculate that ApoA5 has a protective effect in pulmonary vessels and aim to evaluate the mechanism.

Methods

ApoA5 is overexpressed in an MCT-induced PAH animal model and platelet-derived growth factor (PDGF)-BB-induced proliferating PASMCs. Lung vasculature remodeling was measured by immunostaining, and PASMC proliferation was determined by cell counting kit‐8 and 5‐ethynyl‐2'‐deoxyuridine5‐ethynyl‐2'‐deoxyuridine incorporation assays. Coimmunoprecipitation-mass spectrometry was used to investigate the probable mechanism. Next, its role and mechanism were further verified by knockdown studies.

Results

ApoA5 level was decreased in MCT-induced PAH lung as well as PASMCs. Overexpression of ApoA5 could help to inhibit the remodeling of pulmonary artery smooth muscle. ApoA5 could inhibit PDGF-BB-induced PASMC proliferation and endoplasmic reticulum stress by increasing the expression of glucose-regulated protein 78 (GRP78). After knocking down GRP78, the protecting effects of ApoA5 have been blocked.

Conclusion

ApoA5 ameliorates MCT-induced PAH by inhibiting endoplasmic reticulum stress in a GRP78 dependent mechanism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-022-01680-4.

Sulforaphane Does Not Protect Right Ventricular Systolic and Diastolic Functions in Nrf2 Knockout Pulmonary Artery Hypertension Mice

PURPOSE

Nrf2 is a nuclear transcription factor and plays an important role in the regulation of oxidative stress and inflammation. We recently demonstrated that sulforaphane (SFN) protected mice from developing pulmonary arterial hypertension (PAH) and right ventricular (RV) dysfunction by elevating cardiac Nrf2 expression and function. Here we further investigate Nrf2 dependence for SFN-mediated prevention of PAH and RV dysfunction in an Nrf2 knockout mouse model.

METHODS

We used male global Nrf2-knockout mice and male C57/6 J wild type mice in the following groups: Control group received room air and vehicle control; SuHx group received SU5416 and 10% hypoxia for 4 weeks to induce PAH; SuHx+SFN group received both SuHx and sulforaphane, a Nrf2 activator, for 4 weeks. Transthoracic echocardiography was performed to quantify RV function and estimate pulmonary vascular resistance over 4 weeks. PAH was confirmed using invasive RV systolic pressure measurement at 4 weeks.

RESULTS

All Nrf2 knockout mice survived the 4-week SuHx induction of PAH. SuHx caused progressive RV diastolic/systolic dysfunction and increased RV systolic pressure. The development of RV diastolic dysfunction occurred earlier in the Nrf2 knockout PAH mice when compared with the wide type PAH mice. SFN partially or completely reversed SuHx-induced RV diastolic/systolic dysfunction and increased RV systolic pressure in wild-type mice, but not in Nrf2 knockout mice.

CONCLUSION

Our findings demonstrated the essential role of Nrf2 in SFN-mediated prevention of RV dysfunction and PAH, and increasing Nrf2 activity in patients with PAH may have therapeutic potential.

Xbp1s-Ddit3 promotes MCT-induced pulmonary hypertension

Pulmonary hypertension (PH) is a life-threatening disease characterized by vascular remodeling. Exploring new therapy target is urgent. The purpose of the present study is to investigate whether and how spliced x-box binding protein 1 (xbp1s), a key component of endoplasmic reticulum stress (ERS), contributes to the pathogenesis of PH. Forty male SD rats were randomly assigned to four groups: Control, Monocrotaline (MCT), MCT+AAV-CTL (control), and MCT+AAV-xbp1s. The xbp1s protein levels were found to be elevated in lung tissues of the MCT group. Intratracheal injection of adeno-associated virus serotype 1 carrying xbp1s shRNA (AAV-xbp1s) to knock down the expression of xbp1s effectively ameliorated the MCT-induced elevation of right ventricular systolic pressure (RVSP), total pulmonary resistance (TPR), right ventricular hypertrophy and medial wall thickness of muscularized distal pulmonary arterioles. The abnormally increased positive staining rates of proliferating cell nuclear antigen (PCNA) and Ki67 and decreased positive staining rates of terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) in pulmonary arterioles were also reversed in the MCT+AAV-xbp1s group. For mechanistic exploration, bioinformatics prediction of the protein network was performed on the STRING database, and further verification was performed by qRT-PCR, Western blots and co-immunoprecipitation (Co-IP). DNA damage-inducible transcript 3 (Ddit3) was identified as a downstream protein that interacted with xbp1s. Overexpression of Ddit3 restored the decreased proliferation, migration and cell viability caused by silencing of xbp1s. The protein level of Ddit3 was also highly consistent with xbp1s in the animal model. Taken together, our study demonstrated that xbp1s-Ddit3 may be a potential target to interfere with vascular remodeling in PH.

Hypoxia and the integrated stress response promote pulmonary hypertension and preeclampsia: Implications in drug development

Chronic hypoxia is a common cause of pulmonary hypertension, preeclampsia, and intrauterine growth restriction (IUGR). The molecular mechanisms underlying these diseases are not completely understood. Chronic hypoxia may induce the generation of reactive oxygen species (ROS) in mitochondria, promote endoplasmic reticulum (ER) stress, and result in the integrated stress response (ISR) in the pulmonary artery and uteroplacental tissues. Numerous studies have implicated hypoxia-inducible factors (HIFs), oxidative stress, and ER stress/unfolded protein response (UPR) in the development of pulmonary hypertension, preeclampsia and IUGR. This review highlights the roles of HIFs, mitochondria-derived ROS and UPR, as well as their interplay, in the pathogenesis of pulmonary hypertension and preeclampsia, and their implications in drug development.

Novel molecular insights and public omics data in pulmonary hypertension

Pulmonary hypertension is a rare disease with high morbidity and mortality which mainly affects women of reproductive age. Despite recent advances in understanding the pathogenesis of pulmonary hypertension, the high heterogeneity in the presentation of the disease among different patients makes it difficult to make an accurate diagnosis and to apply this knowledge to effective treatments. Therefore, new studies are required to focus on translational and personalized medicine to overcome the lack of specificity and efficacy of current management. Here, we review the majority of public databases storing 'omics' data of pulmonary hypertension studies, from animal models to human patients. Moreover, we review some of the new molecular mechanisms involved in the pathogenesis of pulmonary hypertension, including non-coding RNAs and the application of 'omics' data to understand this pathology, hoping that these new approaches will provide insights to guide the way to personalized diagnosis and treatment.

Ghrelin Protects Lipopolysaccharide-Induced Acute Lung Injury Rats against Pulmonary Vascular Dysfunction by Inhibiting Inflammation

Objective. To determine the effect and mechanism of the anti-inflammatory agent ghrelin on pulmonary vascular dysfunction (PVD) in lipopolysaccharide- (LPS-) induced acute lung injury (ALI) rat models. Methods. Thirty-two adult male Sprague Dawley rats (n = 16/group) were randomly divided into ghrelin and saline groups, wherein ghrelin (10 nmol/kg) or saline was subcutaneously administered. After 30 min, eight rats from each group were randomly selected, and LPS (5 mg/kg) or saline was administered by intratracheal instillation to induce ALI. Four hours after establishing the ALI rat model, the mean pulmonary arterial pressure (mPAP), mean right ventricular systolic pressure (RVSP), levels of proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the bronchoalveolar lavage fluid (BALF), BALF cell count, wet-to-dry (W/D) lung weight ratios, and myeloperoxidase (MPO) activity in lung tissue for all four groups (ghrelin, ghrelin + ALI, saline, and saline + ALI) were measured. Immunohistochemical staining to detect alpha-smooth muscle actin (α-SMA) and proliferating cell nuclear antigen (PCNA) expression was performed to assess the intrapulmonary arterial wall thickness and the proliferation of smooth muscle cells, respectively. Results. The ghrelin-pretreated ALI rats showed lower mPAP, RVSP, PCNA expression, MPO activity, W/D lung weight ratio, TNF-α and IL-6 levels, and BALF cell count than the saline-pretreated ALI rats, but ghrelin had no effect on the intrapulmonary arterial wall thickness of ALI rats. Conclusion. Our results confirmed the association between inflammation and PVD in ALI and suggested that the suppression of inflammation by ghrelin pretreatment could protect LPS-induced ALI rats against PVD.

Endoplasmic reticulum stress and unfolded protein response in cardiovascular diseases

Cardiovascular diseases (CVDs), such as ischaemic heart disease, cardiomyopathy, atherosclerosis, hypertension, stroke and heart failure, are among the leading causes of morbidity and mortality worldwide. Although specific CVDs and the associated cardiometabolic abnormalities have distinct pathophysiological and clinical manifestations, they often share common traits, including disruption of proteostasis resulting in accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). ER proteostasis is governed by the unfolded protein response (UPR), a signalling pathway that adjusts the protein-folding capacity of the cell to sustain the cell's secretory function. When the adaptive UPR fails to preserve ER homeostasis, a maladaptive or terminal UPR is engaged, leading to the disruption of ER integrity and to apoptosis. ER stress functions as a double-edged sword, with long-term ER stress resulting in cellular defects causing disturbed cardiovascular function. In this Review, we discuss the distinct roles of the UPR and ER stress response as both causes and consequences of CVD. We also summarize the latest advances in our understanding of the importance of the UPR and ER stress in the pathogenesis of CVD and discuss potential therapeutic strategies aimed at restoring ER proteostasis in CVDs.

Transcriptomic Analysis of Right Ventricular Remodeling in Two Rat Models of Pulmonary Hypertension: Identification and Validation of Epithelial-to-Mesenchymal Transition in Human Right Ventricular Failure

BACKGROUND

Right ventricular (RV) dysfunction is a significant prognostic determinant of morbidity and mortality in pulmonary arterial hypertension (PAH). Despite the importance of RV function in PAH, the underlying molecular mechanisms of RV dysfunction secondary to PAH remain unclear. We aim to identify and compare molecular determinants of RV failure using RNA sequencing of RV tissue from 2 clinically relevant animal models of PAH.

METHODS

We performed RNA sequencing on RV from rats treated with monocrotaline or Sugen with hypoxia/normoxia. PAH and RV failure were confirmed by catheterization and echocardiography. We validated the RV transcriptome results using quantitative real-time polymerase chain reaction, immunofluorescence, and Western blot. Immunohistochemistry and immunofluorescence were performed on human RV tissue from control (n=3) and PAH-induced RV failure patients (n=5).

RESULTS

We identified similar transcriptomic profiles of RV from monocrotaline- and Sugen with hypoxia-induced RV failure. Pathway analysis showed genes enriched in epithelial-to-mesenchymal transition, inflammation, and metabolism. Histological staining of human RV tissue from patients with RV failure secondary to PAH revealed significant RV fibrosis and endothelial-to-mesenchymal transition, as well as elevated cellular communication network factor 2 (top gene implicated in epithelial-to-mesenchymal transition/endothelial-to-mesenchymal transition) expression in perivascular areas compared with normal RV.

CONCLUSIONS

Transcriptomic signature of RV failure in monocrotaline and Sugen with hypoxia models showed similar gene expressions and biological pathways. We provide translational relevance of this transcriptomic signature using RV from patients with PAH to demonstrate evidence of epithelial-to-mesenchymal transition/endothelial-to-mesenchymal transition and protein expression of cellular communication network factor 2 (CTGF [connective tissue growth factor]). Targeting specific molecular mechanisms responsible for RV failure in monocrotaline and Sugen with hypoxia models may identify novel therapeutic strategies for PAH-associated RV failure.

Melo E, B. C. T. Coimbra L, Lapa MS, Acencio MMP, Freitas-Filho O, Capelozzi VL, Teixeira LR, Fernandes CJCS, Jatene FB, Laurindo FRM, Terra-Filho M. Shear stress-exposed pulmonary artery endothelial cells fail to upregulate HSP70 in chronic thromboembolic pulmonary hypertension

The pathophysiological mechanisms underlying chronic thromboembolic pulmonary hypertension (CTEPH) are still unclear. Endothelial cell (EC) remodeling is believed to contribute to this pulmonary disease triggered by thrombus and hemodynamic forces disbalance. Recently, we showed that HSP70 levels decrease by proatherogenic shear stress. Molecular chaperones play a major role in proteostasis in neurological, cancer and inflammatory/ infectious diseases. To shed light on microvascular responses in CTEPH, we characterized the expression of molecular chaperones and annexin A2, a component of the fibrinolytic system. There is no animal model that reproduces microvascular changes in CTEPH, and this fact led us to isolated endothelial cells from patients with CTEPH undergoing pulmonary endarterectomy (PEA). We exposed CTEPH-EC and control human pulmonary endothelial cells (HPAEC) to high- (15 dynes/cm2) or low- (5 dynes/cm2) shear stress. After high-magnitude shear stress HPAEC upregulated heat shock protein 70kDa (HSP70) and the HSP ER paralogs 78 and 94kDa glucose-regulated protein (GRP78 and 94), whereas CTEPH-ECs failed to exhibit this response. At static conditions, both HSP70 and HSP90 families in CTEPH-EC are decreased. Importantly, immunohistochemistry analysis showed that HSP70 expression was downregulated in vivo, and annexin A2 was upregulated. Interestingly, wound healing and angiogenesis assays revealed that HSP70 inhibition with VER-155008 further impaired CTEPH-EC migratory responses. These results implicate HSP70 as a novel master regulator of endothelial dysfunction in type 4 PH. Overall, we first show that global failure of HSP upregulation is a hallmark of CTEPH pathogenesis and propose HSP70 as a potential biomarker of this condition.

Genetic Deficiency and Pharmacological Stabilization of Mast Cells Ameliorate Pressure Overload-Induced Maladaptive Right Ventricular Remodeling in Mice

Although the response of the right ventricle (RV) to the increased afterload is an important determinant of the patient outcome, very little is known about the underlying mechanisms. Mast cells have been implicated in the pathogenesis of left ventricular maladaptive remodeling and failure. However, the role of mast cells in RV remodeling remains unexplored. We subjected mast cell-deficient WBB6F1-KitW/W-v (Kit^W/Kit^W-v) mice and their mast cell-sufficient littermate controls (MC^+/+) to pulmonary artery banding (PAB). PAB led to RV dilatation, extensive myocardial fibrosis, and RV dysfunction in MC^+/+ mice. In PAB Kit^W/Kit^W-v mice, RV remodeling was characterized by minimal RV chamber dilatation and preserved RV function. We further administered to C57Bl/6J mice either placebo or cromolyn treatment starting from day 1 or 7 days after PAB surgery to test whether mast cells stabilizing drugs can prevent or reverse maladaptive RV remodeling. Both preventive and therapeutic cromolyn applications significantly attenuated RV dilatation and improved RV function. Our study establishes a previously undescribed role of mast cells in pressure overload-induced adverse RV remodeling. Mast cells may thus represent an interesting target for the development of a new therapeutic approach directed specifically at the heart.

Lipocalin-2-induced proliferative endoplasmic reticulum stress participates in Kawasaki disease-related pulmonary arterial abnormalities

Clinical cases have reported pulmonary arterial structural and functional abnormalities in patients with Kawasaki disease (KD); however, the underlying mechanisms are unclear. In this study, a KD rat model was established via the intraperitoneal injection of Lactobacillus casei cell wall extract (LCWE). The results showed that pulmonary arterial functional and structural abnormalities were observed in KD rats. Furthermore, proliferative endoplasmic reticulum stress (ER stress) was observed in the pulmonary arteries of KD rats. Notably, the level of lipocalin-2 (Lcn 2), a trigger factor of inflammation, was remarkably elevated in the plasma and lung tissues of KD rats; increased Lcn 2 levels following LCWE stimulation may result from polymorphonuclear neutrophils (PMNs). Correspondingly, in cultured pulmonary artery smooth muscle cells (PASMCs), Lcn 2 markedly augmented the cleavage and nuclear localization of activating transcription factor-6 (ATF6), upregulated the transcription of glucose regulated protein 78 (GRP78) and neurite outgrowth inhibitor (NOGO), and promoted PASMCs proliferation. However, proapoptotic C/EBP homologous protein (CHOP) and caspase 12 levels were not elevated. Treatment with 4-phenyl butyric acid (4-PBA, a specific inhibitor of ER stress) inhibited PASMCs proliferation induced by Lcn 2 and attenuated pulmonary arterial abnormalities and right ventricular hypertrophy and reduced right ventricular systolic pressure in KD rats. In conclusion, Lcn 2 remarkably facilitates proliferative ER stress in PASMCs, which probably accounts for KD-related pulmonary arterial abnormalities.

Protein Misfolding and Endoplasmic Reticulum Stress in Chronic Lung Disease: Will Cell-Specific Targeting Be the Key to the Cure?

Chronic lung disease accounts for a significant global burden with respect to death, disability, and health-care costs. Due to the heterogeneous nature and limited treatment options for these diseases, it is imperative that the cellular and molecular mechanisms underlying the disease pathophysiology are further understood. The lung is a complex organ with a diverse cell population, and each cell type will likely have different roles in disease initiation, progression, and resolution. The effectiveness of a given therapeutic agent may depend on the net effect on each of these cell types. Over the past decade, it has been established that endoplasmic reticulum stress and the unfolded protein response are involved in the development of several chronic lung diseases. These conserved cellular pathways are important for maintaining cellular proteostasis, but their aberrant activation can result in pathology. This review discusses the current understanding of endoplasmic reticulum stress and the unfolded protein response at the cellular level in the development and progression of various chronic lung diseases. We highlight the need for increased understanding of the specific cellular contributions of unfolded protein response activation to these pathologies and suggest that the development of cell-specific targeted therapies is likely required to further decrease disease progression and to promote resolution of chronic lung disease.

Glucagon-like peptide-1 receptor activation alleviates lipopolysaccharide-induced acute lung injury in mice via maintenance of endothelial barrier function

Glucagon-like peptide-1 (GLP-1), which is well known for regulating glucose homeostasis, exhibits multiple actions in cardiovascular disorders and renal injury. However, little is known about the effect of GLP-1 receptor (GLP-1R) activation on acute lung injury (ALI). In this study, we investigated the effect of GLP-1R on ALI and the potential underlying mechanisms with the selective agonist liraglutide. Our results show that GLP-1 levels decreased in serum, though they increased in bronchoalveolar lavage fluid (BALF) and lung tissue in a mouse model of lipopolysaccharide (LPS)-induced ALI. Liraglutide prevented LPS-induced polymorphonuclear neutrophil (PMN) extravasation, lung injury, and alveolar-capillary barrier dysfunction. In cultured human pulmonary microvascular endothelial cells (HPMECs), liraglutide protected against LPS-induced endothelial barrier injury by restoring intercellular tight junctions and adherens junctions. Moreover, liraglutide prevented PMN-endothelial adhesion by inhibiting the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), and thereafter suppressed PMN transendothelial migration. Furthermore, liraglutide suppressed LPS-induced activation of Rho/NF-κB signaling in HPMECs. In conclusion, our results show that GLP-1R activation protects mice from LPS-induced ALI by maintaining functional endothelial barrier and inhibiting PMN extravasation. These results also suggest that GLP-1R may be a potential therapeutic target for the treatment of ALI.

Glucagon-like peptide-1 (GLP-1) mediates the protective effects of dipeptidyl peptidase IV inhibition on pulmonary hypertension

Background

Pulmonary hypertension (PH) is a progressive disease leading to death ultimately. Our recently published data demonstrated that inhibiting dipeptidyl peptidase IV (DPP-4) alleviated pulmonary vascular remodeling in experimental PH. However, whether glucagon-like peptide-1 (GLP-1) mediated the protective effect of DPP-4 inhibition (DPP-4i) on PH is unclear.

Results

In the present study, GLP-1 receptor antagonist (exendin-3) abolished the protective effects of DPP-4 inhibitor (sitagliptin) on right ventricular systolic pressure (RVSP) and pulmonary vascular remodeling (PVR) in monocrotaline (MCT, 60 mg/kg)-induced PH in rat. Notably, activation of GLP-1 receptor by GLP-1 analogue liraglutide directly attenuated RVSP and PVR in MCT-induced PH, as well as bleomycin- and chronic hypoxia-induced PH. Moreover, liraglutide potently inhibited MCT-induced inflammation and suppressed MCT-induced down-regulation of vascular endothelial marker (VE-cadherin and vWF) in lung. In vitro studies showed liraglutide reversed TGF-β1 (5 ng/ml) combining IL-1β (5 ng/ml) induced endothelial-mesenchymal transition (EndMT) in human umbilical vein endothelial cells (HUVECs), which could be abolished by GLP-1 receptor antagonist (exendin-3). Furtermore, liraglutide suppressed TGF-β1-IL-1β-induced phosphorylation of both Smad3 and ERK1/2.

Conclusions

Our data suggest that GLP-1 mediated the protective effects of DPP-4i on pulmonary vascular and RV remodeling in experimental PH, which may be attributed to the inhibitory effect on EndMT.

Dipeptidyl peptidase IV (DPP-4) inhibition alleviates pulmonary arterial remodeling in experimental pulmonary hypertension

Dipeptidyl peptidase IV (DPP-4) is well known for its role in glucose homeostasis, and DPP-4 inhibitor (DPP-4i) exhibits multiple actions in cardiovascular diseases. However, the effect of DPP-4i on pulmonary hypertension (PH) remains unclear. Therefore, this study aims to investigate the effect of DPP-4i on pulmonary arterial remodeling in rats with PH and the potential underlying mechanisms. Our results show that DPP-4 was expressed in epithelial cells, endothelial cells, smooth muscle cells, and inflammatory cells in lung. DPP-4i (Sitagliptin) attenuated right ventricular systolic pressure (RVSP), right ventricle remodeling, hypertrophy of pulmonary arterial medial layer, inflammatory cell infiltration, and endothelial-mesenchymal transition (EndMT) in monocrotaline (MCT)-induced PH rats. Similarly, DPP-4i also alleviated bleomycin- and chronic hypoxia-induced PH in rats. In cultured human pulmonary arterial smooth muscle cells (PASMCs), DPP-4i inhibited platelet derived growth factor (PDGF)-BB-induced proliferation and migration, which was abolished by phosphatase and tensin homolog deleted on chromosome ten (PTEN) knockout. These results demonstrate that DPP-4 inhibition alleviates pulmonary arterial remodeling in experimental PH by inhibiting proliferation and migration of PASMCs.

Role of cardiac inflammation in right ventricular failure

Right ventricular failure (RVF) is the main determinant of mortality in patients with pulmonary arterial hypertension (PAH). Although the exact pathophysiology underlying RVF remains unclear, inflammation may play an important role, as it does in left heart failure. Perivascular pulmonary artery and systemic inflammation is relatively well studied and known to contribute to the initiation and maintenance of the pulmonary vascular insult in PAH. However, less attention has been paid to the role of cardiac inflammation in RVF and PAH. Consistent with many other types of heart failure, cardiac inflammation, triggered by systemic and local stressors, has been shown in RVF patients as well as in RVF animal models. RV inflammation likely contributes to impaired RV contractility, maladaptive remodelling and a vicious circle between RV and pulmonary vascular injury. Although the potential to improve RV function through anti-inflammatory therapy has not been tested, this approach has been applied clinically in left ventricular failure patients, with variable success. Because inflammation plays a dual role in the development of both pulmonary vascular pathology and RVF, anti-inflammatory therapies may have a potential double benefit in patients with PAH and associated RVF.

Inflammatory Mediators Drive Adverse Right Ventricular Remodeling and Dysfunction and Serve as Potential Biomarkers

Adverse right ventricular (RV) remodeling leads to ventricular dysfunction and failure that represents an important determinant of outcome in patients with pulmonary hypertension (PH). Recent evidence indicates that inflammatory activation contributes to the pathogenesis of adverse RV remodeling and dysfunction. It has been shown that accumulation of inflammatory cells such as macrophages and mast cells in the right ventricle is associated with maladaptive RV remodeling. In addition, inhibition of inflammation in animal models of RV failure ameliorated RV structural and functional impairment. Furthermore, a number of circulating inflammatory mediators have been demonstrated to be associated with RV performance. This work reviews the role of inflammation in RV remodeling and dysfunction and discusses anti-inflammatory strategies that may attenuate adverse structural alterations while promoting improvement of RV function.

New dynamic viewing of mast cells in pulmonary arterial hypertension (PAH): contributors or outsiders to cardiovascular remodeling

Background

In patients with pulmonary arterial hypertension (PAH), mast cells (MCs) are extensively observed around pulmonary vessels. However, their temporal and spatial variation during PAH development remains obscure. This study investigated the dynamic evolution of MCs in lungs and right ventricles (RV) to illuminate their role in pulmonary vascular and RV remodeling.

Methods

The PAH model was established by a single intra-peritoneal injection of monocrotaline (MCT, 60 mg/kg) in rats. On day 0, 3, 7, 14, and 28 after MCT injection, lung and RV tissues were harvested for staining with hematoxylin and eosin (HE), Gomori aldehyde fuchsin (GAF), toluidine blue (TB) and picrosirius red (PSR). Immunohistochemistry was performed to evaluate the levels of α-SMA, CD68 and tryptase. A simple RV remolding model was produced as well by pulmonary artery banding (PAB). RV tissues were collected to determine the degree of MCs infiltration.

Results

After MCT challenge, elevated mean pulmonary arterial pressure (mPAP), increased RV systolic pressure (RVSP), pulmonary arterial media hypertrophy as well as distal vascular muscularization gradually occurred with time. MCs recruitment along with CD68+ macrophages accumulation was observed around distal pulmonary vessels and in alveolar septa. Excessive infiltration and degranulation of MCs were detected in MCT-treated group in lung tissues but not in RV. In addition, no exacerbation of MCs infiltration and degranulation in RV was noted in PAB-treated rats, suggesting few contributions of MCs to RV remodeling.

Conclusions

Our findings implied a crucial role of MCs in the remodeling of pulmonary vessels, not RV, which probably through releasing cytokines such as tryptase. The present study enriches the knowledge about PAH, providing a potential profile of MCs as a switch for the treatment of PAH.

Fasudil inhibits neutrophil-endothelial cell interactions by regulating the expressions of GRP78 and BMPR2

Regulation of leukocyte-endothelial cell interactions and of vascular permeability plays a critical role in the maintenance of functional pulmonary microvascular barriers. Little is yet known about the effect of the Rho-associated protein kinase (ROCK) inhibitor fasudil on leukocyte-endothelial cell interactions or the underlying mechanism. In the present study, as evaluated using co-culture systems of neutrophils and human pulmonary microvascular endothelial cells (HPMECs), fasudil dose-dependently suppressed neutrophil chemotaxis by decreasing the production of chemotactic factors in lipopolysaccharide (LPS)-treated HPMECs. The inhibitory role of fasudil in neutrophil chemotaxis was mediated by down-regulation of the chaperone glucose-regulated protein 78 (GRP78), since the inhibition was abolished by 4-phenyl butyric acid (a chemical chaperone mimicking GRP78). In addition, fasudil inhibited LPS-induced neutrophil-endothelial adhesion by reducing the expression of intercellular adhesion molecule (ICAM)-1. By use of lentiviral transfection in HPMECs, bone morphogenic protein receptor 2 (BMPR2) overexpression suppressed the LPS-induced increase of both ICAM-1 expression and neutrophil-endothelial adhesion, whereas knocking down BMPR2 abolished the inhibitory role of fasudil in both ICAM-1 expression and neutrophil-endothelial adhesion. Moreover, fasudil alleviated LPS-induced hyperpermeability of HPMEC monolayers by leading to the recovery of intercellular junctions, thereafter reduced neutrophil transendothelial cell migration. Therefore, fasudil inhibited leukocyte-endothelial cell interactions and vascular hyperpermeability through modulation of GRP78 and BMPR2 expression, suggesting a potential role for ROCK as a switch for inhibiting leukocyte-endothelial cell interactions.

Glucagon-Like Peptide-1 Mediates the Protective Effect of the Dipeptidyl Peptidase IV Inhibitor on Renal Fibrosis via Reducing the Phenotypic Conversion of Renal Microvascular Cells in Monocrotaline-Treated Rats

Chronic kidney diseases are characterized by renal fibrosis with excessive matrix deposition, leading to a progressive loss of functional renal parenchyma and, eventually, renal failure. Renal microcirculation lesions, including the phenotypic conversion of vascular cells, contribute to renal fibrosis. Here, renal microcirculation lesions were established with monocrotaline (MCT, 60 mg/kg). Sitagliptin (40 mg/kg/d), a classical dipeptidyl peptidase-4 (DPP-4) inhibitor, attenuated the renal microcirculation lesions by inhibiting glomerular tuft hypertrophy, glomerular mesangial expansion, and microvascular thrombosis. These effects of sitagliptin were mediated by glucagon-like peptide-1 receptor (GLP-1R), since they were blocked by the GLP-1R antagonist exendin-3 (Ex-3, 40 ug/kg/d). The GLP-1R agonist liraglutide showed a similar renal protective effect in a dose-independent manner. In addition, sitagliptin, as well as liraglutide, alleviated the MCT-induced apoptosis of renal cells by increasing the expression of survival factor glucose-regulated protein 78 (GRP78), which was abolished by the GLP-1R antagonist Ex-3. Sitagliptin and liraglutide also effectively ameliorated the conversion of vascular smooth muscle cells (SMCs) from a synthetic phenotype to contractile phenotype. Moreover, sitagliptin and liraglutide inhibited endothelial-mesenchymal transition (EndMT) via downregulating transforming growth factor-β1 (TGF-β1). Collectively, these findings suggest that DPP-4 inhibition can reduce microcirculation lesion-induced renal fibrosis in a GLP-1-dependent manner.