Paxillin Regulates Pulmonary Arterial Smooth Muscle Cell Function in Pulmonary Hypertension

Hypoxia-induced YAP activation and focal adhesion turnover to promote cell migration in mesenchymal TNBC cells

BACKGROUND

Hypoxia is commonly characterized by malignant tumors that promote the aggressiveness and metastatic potential of cancer. Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, with approximately 46% capacity related to distant metastasis. Transcriptional factor yes-associated protein (YAP), a core component of the Hippo pathway, is associated with poor prognosis and outcome in cancer metastasis. Here, we explored the effect of hypoxia-mediated YAP activation and focal adhesions (FAs) turnover in mesenchymal TNBC cell migration.

METHODS

We characterized the effect of hypoxia on YAP in different breast cancer cell lines using a hypoxia chamber and CoCl₂ .

RESULTS

Hypoxia-induced YAP nuclear translocation is significantly observed in normal breast epithelial cells, non-TNBC cells, mesenchymal TNBC cells, but not in basal-like TNBC cells. Functionally, we demonstrated that YAP activation was required for hypoxia to promote mesenchymal TNBC cell migration. Furthermore, hypoxia induced the localization of FAs at the leading edge of mesenchymal TNBC cells. In contrast, verteporfin (VP), a YAP inhibitor, significantly reduced the migration and the recruitment of nascent FAs at the cell periphery under hypoxia conditions, which only showed in mesenchymal TNBC cells.

CONCLUSIONS

Our data support the hypothesis that YAP is novel factor and positively responsible for hypoxia-promoting mesenchymal TNBC cell migration. Our findings provide further evidence and outcomes to help prevent the progression of TNBC.

SPARC, a Novel Regulator of Vascular Cell Function in Pulmonary Hypertension

BACKGROUND

Pulmonary hypertension (PH) is a life-threatening disease, characterized by excessive pulmonary vascular remodeling, leading to elevated pulmonary arterial pressure and right heart hypertrophy. PH can be caused by chronic hypoxia, leading to hyper-proliferation of pulmonary arterial smooth muscle cells (PASMCs) and apoptosis-resistant pulmonary microvascular endothelial cells (PMVECs). On reexposure to normoxia, chronic hypoxia-induced PH in mice is reversible. In this study, the authors aim to identify novel candidate genes involved in pulmonary vascular remodeling specifically in the pulmonary vasculature.

METHODS

After microarray analysis, the authors assessed the role of SPARC (secreted protein acidic and rich in cysteine) in PH using lung tissue from idiopathic pulmonary arterial hypertension (IPAH) patients, as well as from chronically hypoxic mice. In vitro studies were conducted in primary human PASMCs and PMVECs. In vivo function of SPARC was proven in chronic hypoxia-induced PH in mice by using an adeno-associated virus-mediated Sparc knockdown approach.

RESULTS

C57BL/6J mice were exposed to normoxia, chronic hypoxia, or chronic hypoxia with subsequent reexposure to normoxia for different time points. Microarray analysis of the pulmonary vascular compartment after laser microdissection identified Sparc as one of the genes downregulated at all reoxygenation time points investigated. Intriguingly, SPARC was vice versa upregulated in lungs during development of hypoxia-induced PH in mice as well as in IPAH, although SPARC plasma levels were not elevated in PH. TGF-β1 (transforming growth factor β1) or HIF2A (hypoxia-inducible factor 2A) signaling pathways induced SPARC expression in human PASMCs. In loss of function studies, SPARC silencing enhanced apoptosis and reduced proliferation. In gain of function studies, elevated SPARC levels induced PASMCs, but not PMVECs, proliferation. Coculture and conditioned medium experiments revealed that PMVECs-secreted SPARC acts as a paracrine factor triggering PASMCs proliferation. Contrary to the authors' expectations, in vivo congenital Sparc knockout mice were not protected from hypoxia-induced PH, most probably because of counter-regulatory proproliferative signaling. However, adeno-associated virus-mediated Sparc knockdown in adult mice significantly improved hemodynamic and cardiac function in PH mice.

CONCLUSIONS

This study provides evidence for the involvement of SPARC in the pathogenesis of human PH and chronic hypoxia-induced PH in mice, most likely by affecting vascular cell function.

Paxillin controls actin stress fiber formation and migration of vascular smooth muscle cells by directly binding to the active Fyn

Rho-kinase (ROK)-mediated migration of vascular smooth muscle cells plays a crucial role in cardiovascular diseases. Previously we demonstrated Fyn tyrosine kinase as an upstream molecule of ROK to mediate actin stress fiber formation that plays an important role in cell migration, but the molecular mechanism between the two kinases was unclear. To discover a novel signaling molecule that exists between Fyn and ROK, we identified paxillin acting downstream of the active Fyn by combined use of pulldown assay and mass spectrometry. Immunofluorescence staining confirmed co-localization of Fyn and paxillin at the ends of actin stress fibers in human coronary artery smooth muscle cells (CASMCs). Surface plasmon resonance assay demonstrated direct binding between constitutively active Fyn (CA-Fyn) and N-terminus of paxillin (N-pax). The sphingosylphosphorylcholine (SPC)-induced ROK activation, actin stress fiber formation and cell migration were inhibited by paxillin knockdown, which were rescued by full-length paxillin (FL-pax) but not N-pax. N-pax co-localized with CA-Fyn at the cytosol and overexpression of N-pax inhibited the SPC-induced actin stress fiber formation and cell migration, indicating that the direct binding of FL-pax and CA-Fyn at the ends of actin stress fibers is essential for the ROK-mediated actin stress fiber formation and cell migration. Paxillin, as a novel signalling molecule, mediates the SPC-induced actin stress fiber formation and migration in human CASMCs via the Fyn/paxillin/ROK signalling pathway by direct binding of active Fyn.

Adenylate Kinase 4-A Key Regulator of Proliferation and Metabolic Shift in Human Pulmonary Arterial Smooth Muscle Cells via Akt and HIF-1α Signaling Pathways

Increased proliferation of pulmonary arterial smooth muscle cells (PASMCs) in response to chronic hypoxia contributes to pulmonary vascular remodeling in pulmonary hypertension (PH). PH shares numerous similarities with cancer, including a metabolic shift towards glycolysis. In lung cancer, adenylate kinase 4 (AK4) promotes metabolic reprogramming and metastasis. Against this background, we show that AK4 regulates cell proliferation and energy metabolism of primary human PASMCs. We demonstrate that chronic hypoxia upregulates AK4 in PASMCs in a hypoxia-inducible factor-1α (HIF-1α)-dependent manner. RNA interference of AK4 decreases the viability and proliferation of PASMCs under both normoxia and chronic hypoxia. AK4 silencing in PASMCs augments mitochondrial respiration and reduces glycolytic metabolism. The observed effects are associated with reduced levels of phosphorylated protein kinase B (Akt) as well as HIF-1α, indicating the existence of an AK4-HIF-1α feedforward loop in hypoxic PASMCs. Finally, we show that AK4 levels are elevated in pulmonary vessels from patients with idiopathic pulmonary arterial hypertension (IPAH), and AK4 silencing decreases glycolytic metabolism of IPAH-PASMCs. We conclude that AK4 is a new metabolic regulator in PASMCs interacting with HIF-1α and Akt signaling pathways to drive the pro-proliferative and glycolytic phenotype of PH.

Identification of hub genes related to the progression of type 1 diabetes by computational analysis

BACKGROUND

Type 1 diabetes (T1D) is a serious threat to childhood life and has fairly complicated pathogenesis. Profound attempts have been made to enlighten the pathogenesis, but the molecular mechanisms of T1D are still not well known.

METHODS

To identify the candidate genes in the progression of T1D, expression profiling by high throughput sequencing dataset GSE123658 was downloaded from Gene Expression Omnibus (GEO) database. The differentially expressed genes (DEGs) were identified, and gene ontology (GO) and pathway enrichment analyses were performed. The protein-protein interaction network (PPI), modules, target gene - miRNA regulatory network and target gene - TF regulatory network analysis were constructed and analyzed using HIPPIE, miRNet, NetworkAnalyst and Cytoscape. Finally, validation of hub genes was conducted by using ROC (Receiver operating characteristic) curve and RT-PCR analysis. A molecular docking study was performed.

RESULTS

A total of 284 DEGs were identified, consisting of 142 up regulated genes and 142 down regulated genes. The gene ontology (GO) and pathways of the DEGs include cell-cell signaling, vesicle fusion, plasma membrane, signaling receptor activity, lipid binding, signaling by GPCR and innate immune system. Four hub genes were identified and biological process analysis revealed that these genes were mainly enriched in cell-cell signaling, cytokine signaling in immune system, signaling by GPCR and innate immune system. ROC curve and RT-PCR analysis showed that EGFR, GRIN2B, GJA1, CAP2, MIF, POLR2A, PRKACA, GABARAP, TLN1 and PXN might be involved in the advancement of T1D. Molecular docking studies showed high docking score.

CONCLUSIONS

DEGs and hub genes identified in the present investigation help us understand the molecular mechanisms underlying the advancement of T1D, and provide candidate targets for diagnosis and treatment of T1D.

Basement Membrane Remodeling Controls Endothelial Function in Idiopathic Pulmonary Arterial Hypertension

The extracellular matrix (ECM) increasingly emerges as an active driver in several diseases, including idiopathic pulmonary arterial hypertension (IPAH). The basement membrane (BM) is a specialized class of ECM proteins. In pulmonary arteries, the BM is in close contact and direct proximity to vascular cells, including endothelial cells. So far, the role of the BM has remained underinvestigated in IPAH. Here, we aimed to shed light on the involvement of the BM in IPAH, by addressing its structure, composition, and function. On an ultrastructural level, we observed a marked increase in BM thickness in IPAH pulmonary vessels. BM composition was distinct in small and large vessels and altered in IPAH. Proteoglycans were mostly responsible for distinction between smaller and larger vessels, whereas BM collagens and laminins were more abundantly expressed in IPAH. Type IV collagen and laminin both strengthened endothelial barrier integrity. However, only type IV collagen concentration dependently increased cell adhesion of both donor and IPAH-derived pulmonary arterial endothelial cells (PAECs) and induced nuclear translocation of mechanosensitive transcriptional coactivator of the hippo pathway YAP (Yes-activated protein). On the other hand, laminin caused cytoplasmic retention of YAP in IPAH PAECs. Accordingly, silencing of COL4A5 and LAMC1, respectively, differentially affected tight junction formation and barrier integrity in both donor and IPAH PAECs. Collectively, our results highlight the importance of a well-maintained BM homeostasis. By linking changes in BM structure and composition to altered endothelial cell function, we here suggest an active involvement of the BM in IPAH pathogenesis.

Endothelial Basement Membrane Components and Their Products, Matrikines: Active Drivers of Pulmonary Hypertension?

Pulmonary arterial hypertension (PAH) is a vascular disease that is characterized by elevated pulmonary arterial pressure (PAP) due to progressive vascular remodeling. Extracellular matrix (ECM) deposition in pulmonary arteries (PA) is one of the key features of vascular remodeling. Emerging evidence indicates that the basement membrane (BM), a specialized cluster of ECM proteins underlying the endothelium, may be actively involved in the progression of vascular remodeling. The BM and its steady turnover are pivotal for maintaining appropriate vascular functions. However, the pathologically elevated turnover of BM components leads to an increased release of biologically active short fragments, which are called matrikines. Both BM components and their matrikines can interfere with pivotal biological processes, such as survival, proliferation, adhesion, and migration and thus may actively contribute to endothelial dysfunction. Therefore, in this review, we summarize the emerging role of the BM and its matrikines on the vascular endothelium and further discuss its implications on lung vascular remodeling in pulmonary hypertension.

Long non-coding RNAs influence the transcriptome in pulmonary arterial hypertension: the role of PAXIP1-AS1

In idiopathic pulmonary arterial hypertension (IPAH), global transcriptional changes induce a smooth muscle cell phenotype characterised by excessive proliferation, migration, and apoptosis resistance. Long non‐coding RNAs (lncRNAs) are key regulators of cellular function. Using a compartment‐specific transcriptional profiling approach, we sought to investigate the link between transcriptional reprogramming by lncRNAs and the maladaptive smooth muscle cell phenotype in IPAH. Transcriptional profiling of small remodelled arteries from 18 IPAH patients and 17 controls revealed global perturbations in metabolic, neuronal, proliferative, and immunological processes. We demonstrated an IPAH‐specific lncRNA expression profile and identified the lncRNA PAXIP1‐AS1 as highly abundant. Comparative transcriptomic analysis and functional assays revealed an intrinsic role for PAXIP1‐AS1 in orchestrating the hyperproliferative and migratory actions of IPAH smooth muscle cells. Further, we showed that PAXIP1‐AS1 mechanistically interferes with the focal adhesion axis via regulation of expression and phosphorylation of its downstream target paxillin. Overall, we show that changes in the lncRNA transcriptome contribute to the disease‐specific transcriptional landscape in IPAH. Our results suggest that lncRNAs, such as PAXIP1‐AS1, can modulate smooth muscle cell function by affecting multiple IPAH‐specific transcriptional programmes. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Src-mediated phosphorylation converts FHL1 from tumor suppressor to tumor promoter

FHL1 has been recognized for a long time as a tumor suppressor protein that associates with both the actin cytoskeleton and the transcriptional machinery. We present in this study a paradigm that phosphorylated FHL1 functions as an oncogenic protein by promoting tumor cell proliferation. The cytosolic tyrosine kinase Src interacts with and phosphorylates FHL1 at Y149 and Y272, which switches FHL1 from a tumor suppressor to a cell growth accelerator. Phosphorylated FHL1 translocates into the nucleus, where it binds to the transcription factor BCLAF1 and promotes tumor cell growth. Importantly, the phosphorylation of FHL1 is increased in tissues from lung adenocarcinoma patients despite the down-regulation of total FHL1 expression. Kindlin-2 was found to interact with FHL1 and recruit FHL1 to focal adhesions. Kindlin-2 competes with Src for binding to FHL1 and suppresses Src-mediated FHL1 phosphorylation. Collectively, we demonstrate that FHL1 can either suppress or promote tumor cell growth depending on the status of the sites for phosphorylation by Src.

Matrix Mechanics Influence Fibroblast-Myofibroblast Transition by Directing the Localization of Histone Deacetylase 4

INTRODUCTION

The propagation of mechanochemical signals from the extracellular matrix to the cell nucleus has emerged as a central feature in regulating cellular differentiation and de-differentiation. This process of outside-in signaling and the associated mechanotransduction pathways have been well described in numerous developmental and pathological contexts. However, it remains less clear how mechanotransduction influences the activity of chromatin modifying enzymes that direct gene expression programs.

OBJECTIVES

The primary objective of this study was to explore how matrix mechanics and geometric confinement influence histone deacetylase (HDAC) activity in fibroblast culture.

METHODS

Polyacrylamide hydrogels were formed and functionalized with fibronectin patterns using soft lithography. Primary mouse embryonic fibroblasts (MEFs) were cultured on the islands until confluent, fixed, and immunolabeled for microscopy.

RESULTS

After 24 h MEFs cultured on soft hydrogels (0.5 kPa) show increased expression of class I HDACs relative to MEFs cultured on stiff hydrogels (100 kPa). A member of the class II family, HDAC4 shows a similar trend; however, there is a pronounced cytoplasmic localization on soft hydrogels suggesting a role in outside-in cytoplasmic signaling. Pharmacological inhibitor studies suggest that the opposing activities of extracellular related kinase 1/2 (ERK) and protein phosphatase 2a (PP2a) influence the localization of HDAC4. MEFs cultured on the soft hydrogels show enhanced expression of markers associated with a fibroblast-myofibroblast transition (Paxillin, αSMA).

CONCLUSIONS

We show that the phosphorylation state and cellular localization of HDAC4 is influenced by matrix mechanics, with evidence for a role in mechanotransduction and the regulation of gene expression associated with fibroblast-myofibroblast transitions. This work establishes a link between outside-in signaling and epigenetic regulation, which will assist efforts aimed at controlling gene regulation in engineered extracellular matrices.

Exposure to endosulfan increases endothelial permeability by transcellular and paracellular pathways in relation to cardiovascular diseases

Exposure to environmental pollutants results in out-of-balance of vascular homeostasis. Endothelial dysfunction leads to a disruption of the endothelial permeability characteristics, associated with cardiovascular diseases. We previously reported that endosulfan could cause endothelial dysfunction, but the role of endosulfan in permeability of endothelial cells has been unexplored. To elucidate molecular mechanism of endosulfan-induced changes in endothelial permeability, human umbilical vein endothelial cells (HUVECs) were exposed to endosulfan, followed by endothelial permeability analysis. The results showed that permeability of HUVECs was enhanced at 48 h after exposure to endosulfan in a dose-dependent manner. Immunofluorescence analysis demonstrated the disruptions of actin cytoskeleton and focal adhesion in endosulfan-exposed cells. Endosulfan activated MMP3/LAMC1/FAK signaling pathway, and downregulated ROCK and PXN in transcellular pathway. Endosulfan affected adherens junctions via E-cadherin and β-catenin, and impaired gap junctions through downregulation of Cx43 in paracellular pathway. We predicted four closely related human cardiovascular diseases in Nextbio, including shock, coronary arteriosclerosis, disorder of cardiac function and hypertensive disorder in relation to endosulfan exposure. Some genes such as ROCK2 and PXN were predicted to be key genes in these diseases. These findings suggest that endosulfan increased endothelial permeability by paracellular and transcellular pathways, implicating the potential correlation between endosulfan and cardiovascular diseases.

Paxillin: a crossroad in pathological cell migration

Paxilllin is a multifunctional and multidomain focal adhesion adapter protein which serves an important scaffolding role at focal adhesions by recruiting structural and signaling molecules involved in cell movement and migration, when phosphorylated on specific Tyr and Ser residues. Upon integrin engagement with extracellular matrix, paxillin is phosphorylated at Tyr31, Tyr118, Ser188, and Ser190, activating numerous signaling cascades which promote cell migration, indicating that the regulation of adhesion dynamics is under the control of a complex display of signaling mechanisms. Among them, paxillin disassembly from focal adhesions induced by extracellular regulated kinase (ERK)-mediated phosphorylation of serines 106, 231, and 290 as well as the binding of the phosphatase PEST to paxillin have been shown to play a key role in cell migration. Paxillin also coordinates the spatiotemporal activation of signaling molecules, including Cdc42, Rac1, and RhoA GTPases, by recruiting GEFs, GAPs, and GITs to focal adhesions. As a major participant in the regulation of cell movement, paxillin plays distinct roles in specific tissues and developmental stages and is involved in immune response, epithelial morphogenesis, and embryonic development. Importantly, paxillin is also an essential player in pathological conditions including oxidative stress, inflammation, endothelial cell barrier dysfunction, and cancer development and metastasis.

Deregulation of focal adhesion formation and cytoskeletal tension due to loss of A-type lamins

The nuclear lamina mechanically integrates the nucleus with the cytoskeleton and extracellular environment and regulates gene expression. These functions are exerted through direct and indirect interactions with the lamina's major constituent proteins, the A-type lamins, which are encoded by the LMNA gene. Using quantitative stable isotope labeling-based shotgun proteomics we have analyzed the proteome of human dermal fibroblasts in which we have depleted A-type lamins by means of a sustained siRNA-mediated LMNA knockdown. Gene ontology analysis revealed that the largest fraction of differentially produced proteins was involved in actin cytoskeleton organization, in particular proteins involved in focal adhesion dynamics, such as actin-related protein 2 and 3 (ACTR2/3), subunits of the ARP2/3 complex, and fascin actin-bundling protein 1 (FSCN1). Functional validation using quantitative immunofluorescence showed a significant reduction in the size of focal adhesion points in A-type lamin depleted cells, which correlated with a reduction in early cell adhesion capacity and an increased cell motility. At the same time, loss of A-type lamins led to more pronounced stress fibers and higher traction forces. This phenotype could not be mimicked or reversed by experimental modulation of the STAT3-IL6 pathway, but it was partly recapitulated by chemical inhibition of the ARP2/3 complex. Thus, our data suggest that the loss of A-type lamins perturbs the balance between focal adhesions and cytoskeletal tension. This imbalance may contribute to mechanosensing defects observed in certain laminopathies.

Annexin A2 inhibits the migration of PASMCs stimulated with HPS rat serum by down-regulating the expression of paxillin

Hepatopulmonary syndrome (HPS) has been classically associated with intrapulmonary vasodilatation (IPVD) and pulmonary vascular remodelling (PVR), which are the key pathophysiological components of HPS and concerned frequently in the studies of HPS. Little is known about the relevance of pulmonary artery smooth muscle cells (PASMCs) migration or the molecular mechanisms of PVR in HPS. Annexin A2 (ANXA2) plays crucial role in HPS-associated PVR and might activate the activity of paxillin which as a regulatory protein participates in the regulation of PASMCs function in PVR. In addition, it has been identified that ANXA2 could influence the cells migration by some important signaling pathways in many diseases, including lung cancer, pulmonary hypertensionand and liver cancer. In this study, we performed scratch wound motility assay, modified boyden chamber, reverse transcription PCR, western blot and co-immunoprecipitation to determine the role of ANXA2 on HPS-associated PVR. We found that HPS rat serum from a common bile duct ligation (CBDL) rat model enhanced the migration of PASMCs and increased the expression of ANXA2 in PASMCs. We reported that ANXA2 and paxillin could form a co-immunoprecipitation. After silencing ANXA2 with siRNA, we found that the up-regulation of paxillin expression, induced by the HPS rat serum, was reversed. Additionally, we found that down-regulation of ANXA2 could significantly inhibit the migration of PASMCs. These findings indicated that down-regulation of ANXA2 by siRNA results in the inhibition of the aberrant dysregulation of paxillin and migration of PASMCs, which suggesting a potential therapeutic effect on HPS-associated PVR.

Expression of mutant bone morphogenetic protein receptor II worsens pulmonary hypertension secondary to pulmonary fibrosis

Pulmonary fibrosis is often complicated by pulmonary hypertension (PH), and previous studies have shown a potential link between bone morphogenetic protein receptor II (BMPR2) and PH secondary to pulmonary fibrosis. We exposed transgenic mice expressing mutant BMPR2 and control mice to repetitive intraperitoneal injections of bleomycin for 4 weeks. The duration of transgene activation was too short for mutant BMPR2 mice to develop spontaneous PH. Mutant BMPR2 mice had increased right ventricular systolic pressure compared to control mice, without differences in pulmonary fibrosis. We found increased hypoxia-inducible factor (HIF)1-α stabilization in lungs of mutant-BMPR2-expressing mice compared to controls following bleomycin treatment. In addition, expression of the hypoxia response element protein connective tissue growth factor was increased in transgenic mice as well as in a human pulmonary microvascular endothelial cell line expressing mutant BMPR2. In mouse pulmonary vascular endothelial cells, mutant BMPR2 expression resulted in increased HIF1-α and reactive oxygen species production following exposure to hypoxia, both of which were attenuated with the antioxidant TEMPOL. These data suggest that expression of mutant BMPR2 worsens secondary PH through increased HIF activity in vascular endothelium. This pathway could be therapeutically targeted in patients with PH secondary to pulmonary fibrosis.

Endothelial HIF signaling regulates pulmonary fibrosis-associated pulmonary hypertension

Pulmonary hypertension (PH) complicating chronic parenchymal lung disease, such as idiopathic pulmonary fibrosis, results in significant morbidity and mortality. Since the hypoxia-inducible factor (HIF) signaling pathway is important for development of pulmonary hypertension in chronic hypoxia, we investigated whether HIF signaling in vascular endothelium regulates development of PH related to pulmonary fibrosis. We generated a transgenic model in which HIF is deleted within vascular endothelial cells and then exposed these mice to chronic intraperitoneal bleomycin to induce PH associated with lung fibrosis. Although no differences in the degree of fibrotic remodeling were observed, we found that endothelial HIF-deficient mice were protected against development of PH, including right ventricle and pulmonary vessel remodeling. Similarly, endothelial HIF-deficient mice were protected from PH after a 4-wk exposure to normobaric hypoxia. In vitro studies of pulmonary vascular endothelial cells isolated from the HIF-targeted mice and controls revealed that endothelial HIF signaling increases endothelial cell expression of connective tissue growth factor, enhances vascular permeability, and promotes pulmonary artery smooth muscle cell proliferation and wound healing ability, all of which have the potential to impact the development of PH in vivo. Taken together, these studies demonstrate that vascular endothelial cell HIF signaling is necessary for development of hypoxia and pulmonary fibrosis associated PH. As such, HIF and HIF-regulated targets represent a therapeutic target in these conditions.

Molecular mechanisms of hypoxia-inducible factor-induced pulmonary arterial smooth muscle cell alterations in pulmonary hypertension

Oxygen (O2) is essential for the viability and function of most metazoan organisms and thus is closely monitored at both the organismal and the cellular levels. However, alveoli often encounter decreased O2 levels (hypoxia), leading to activation of physiological or pathophysiological responses in the pulmonary arteries. Such changes are achieved by activation of transcription factors. The hypoxia-inducible factors (HIFs) are the most prominent hypoxia-regulated transcription factors in this regard. HIFs bind to hypoxia-response elements (HREs) in the promoter region of target genes, whose expression and translation allows the organism, amongst other factors, to cope with decreased environmental O2 partial pressure (pO2). However, prolonged HIF activation can contribute to major structural alterations, especially in the lung, resulting in the development of pulmonary hypertension (PH). PH is characterized by a rise in pulmonary arterial pressure associated with pulmonary arterial remodelling, concomitant with a reduced intravascular lumen area. Patients with PH develop right heart hypertrophy and eventually die from right heart failure. Thus, understanding the molecular mechanisms of HIF regulation in PH is critical for the identification of novel therapeutic strategies. This review addresses the relationship of hypoxia and the HIF system with pulmonary arterial dysfunction in PH. We particularly focus on the cellular and molecular mechanisms underlying the HIF-driven pathophysiological processes.

α5 and αv integrins cooperate to regulate vascular smooth muscle and neural crest functions in vivo

The RGD-binding α5 and αv integrins have been shown to be key regulators of vascular smooth muscle cell (vSMC) function in vitro. However, their role on vSMCs during vascular development in vivo remains unclear. To address this issue, we have generated mice that lack α5, αv or both α5 and αv integrins on their vSMCs, using the SM22α-Cre transgenic mouse line. To our surprise, neither α5 nor αv mutants displayed any obvious vascular defects during embryonic development. By contrast, mice lacking both α5 and αv integrins developed interrupted aortic arches, large brachiocephalic/carotid artery aneurysms and cardiac septation defects, but developed extensive and apparently normal vasculature in the skin. Cardiovascular defects were also found, along with cleft palates and ectopically located thymi, in Wnt1-Cre α5/αv mutants, suggesting that α5 and αv cooperate on neural crest-derived cells to control the remodelling of the pharyngeal arches and the septation of the heart and outflow tract. Analysis of cultured α5/αv-deficient vSMCs suggests that this is achieved, at least in part, through proper assembly of RGD-containing extracellular matrix proteins and the correct incorporation and activation of latent TGF-β.

Hypoxia- or PDGF-BB-dependent paxillin tyrosine phosphorylation in pulmonary hypertension is reversed by HIF-1α depletion or imatinib treatment

Chronic exposure to hypoxia induces a pronounced remodelling of the pulmonary vasculature leading to pulmonary hypertension (PH). The remodelling process also entails increased proliferation and decreased apoptosis of pulmonary arterial smooth muscle cells (PASMC), processes regulated by the cytoskeletal protein paxillin. In this study, we aimed to examine the molecular mechanisms leading to deregulation of paxillin in PH. We detected a time-dependent increase in paxillin tyrosine 31 (Y31) and 118 (Y118) phosphorylation following hypoxic exposure (1 % O2) or platelet-derived growth factor (PDGF)-BB stimulation of primary human PASMC. In addition, both, hypoxia- and PDGF-BB increased the nuclear localisation of phospho-paxillin Y31 as indicated by immunofluorescence staining in human PASMC. Elevated paxillin tyrosine phosphorylation in human PASMC was attenuated by hypoxia-inducible factor (HIF)-1α depletion or by treatment with the PDGF-BB receptor antagonist, imatinib. Moreover, we observed elevated paxillin Y31 and Y118 phosphorylation in the pulmonary vasculature of chronic hypoxic mice (21 days, 10 % O2) which was reversible by imatinib-treatment. PDGF-BB-dependent PASMC proliferation was regulated via the paxillin-Erk1/2-cyclin D1 pathway. In conclusion, we suggest paxillin up-regulation and phosphorylation as an important mechanism of vascular remodelling underlying pulmonary hypertension.

Hypoxia and the modulation of the actin cytoskeleton - emerging interrelations

Recent progress in understanding the influence of hypoxia on cell function has revealed new information about the interrelationship between the actin cytoskeleton and hypoxia; nevertheless, details remain cloudy. The dynamic regulation of the actin cytoskeleton during hypoxia is complex, varies in different cells and tissues, and also depends on the mode of hypoxia. Several molecular players and pathways are emerging that contribute to the modulation of the actin cytoskeleton and that affect the large repertoire of actin-binding proteins in hypoxia. This review describes and discusses the accumulated knowledge about actin cytoskeleton dynamics in hypoxia, placing special emphasis on the Rho family of small guanosine triphosphatases (Rho GTPases). Given that RhoA, Rac and Cdc42 are very well characterized, the review is focused on these family members of Rho GTPases. Notably, in several cell types and tissues, hypoxia, presumably via Rho GTPase signaling, induces actin rearrangement and actin stress fiber assembly, which is a prevalent modulation of the actin cytoskeleton in hypoxia.

Paxillin suppresses the proliferation of HPS rat serum treated PASMCs by up-regulating the expression of cytoskeletal proteins

Hepatopulmonary syndrome (HPS) is a triad of advanced liver disease, intrapulmonary vasodilatation (IPVD), and arterial hypoxemia. The arterial hypoxemia induces pulmonary vascular remodelling (PVR). In recent studies, the role of the proliferation of pulmonary artery smooth muscle cells (PASMCs) in PVR associated with HPS has been established; the changes in cytoskeletal proteins play an essential role in the proliferation of PASMCs. Little is known about the relevance of cytoskeletal protein expression or the molecular mechanisms of PVR associated with HPS. In addition, it has been identified that paxillin could influence the cytoskeletal protein expression by some important signaling pathways in many diseases, including lung cancer and liver cancer. In this study, we found that HPS rat serum from a common bile duct ligation (CBDL) rat model decreased the expression of cytoskeletal proteins (α-actin, α-tubulin, and destrin) and enhanced the expression levels of paxillin mRNA and protein in PASMCs. After silencing paxillin with siRNA, we found that the down-regulation of cytoskeletal protein expression, induced by the HPS rat serum, was reversed. Additionally, we reported that HPS rat serum improved the proliferation of PASMCs and down-regulation of paxillin could significantly inhibit this variation. These findings suggest that the up-regulation of cytoskeletal protein expression, induced by the paxillin, may cause the dysregulation of PASMC proliferation as well as play a fundamental role in PVR associated with HPS. In conclusion, down-regulation of paxillin by siRNA results in the inhibition of the dysregulation of cytoskeletal proteins and proliferation of PASMCs, suggesting a potential therapeutic effect on PVR associated with HPS.

Function of NADPH oxidase 1 in pulmonary arterial smooth muscle cells after monocrotaline-induced pulmonary vascular remodeling

AIMS

Chronic hypoxia induces pulmonary hypertension (PH) that is concomitant with pulmonary vascular remodeling. Reactive oxygen species (ROS) are thought to play a major role in this. Recent findings suggest that ROS production by NADPH oxidase 4 (Nox4) is important in this remodeling. We investigated whether ROS production by Nox is also important in an inflammatory model of monocrotaline (MCT)-induced PH. We examined ROS production, their possible sources, and their impact on the function of pulmonary arterial smooth muscle cells (PASMC) isolated from MCT-treated and healthy rats.

RESULTS

MCT-PASMC showed increased intracellular superoxide production, migration, and proliferation compared with healthy controls due to increased Nox1 expression. A comparison of PASMC from MCT- and nontreated rats revealed an up-regulation of Sod2, Nrf2, cyclin D1, and matrix metalloproteinase-9 (MMP-9) as well as an increased phosphorylation of cofilin and extracellular signal-regulated kinases (Erk). Expression of Sod2, Nrf2, and cyclin D1 and phosphorylation of cofilin and Erk were Nox1 dependent.

INNOVATION

The role of ROS in PH is not fully understood. Mitochondria and Nox have been suggested as sources of altered ROS generation in PH, yet it remains unclear whether increased or decreased ROS contributes to the development of PH. Our studies provide evidence that for different triggers of PH, different Nox isoforms regulate proliferation and migration of PASMC.

CONCLUSION

In contrast to hypoxia-induced PH, Nox1 but not Nox4 is responsible for pathophysiological proliferation and migration of PASMC in an inflammatory model of MCT-induced PH via increased superoxide production. Thus, different Nox isoforms may be targeted in different forms of PH.