Dysfunctional intracellular trafficking in the pathobiology of pulmonary arterial hypertension

The Golgi Apparatus: A Key Player in Innate Immunity

The Golgi apparatus, long recognized for its roles in protein processing and vesicular trafficking, has recently been identified as a crucial contributor to innate immune signaling pathways. This review discusses our expanding understanding of the Golgi apparatus's involvement in initiating and activating these pathways. It highlights the significance of membrane connections between the Golgi and other organelles, such as the endoplasmic reticulum, mitochondria, endosomes, and autophagosomes. These connections are vital for the efficient transmission of innate immune signals and the activation of effector responses. Furthermore, the article delves into the Golgi apparatus's roles in key immune pathways, including the inflammasome-mediated activation of caspase-1, the cGAS-STING pathway, and TLR/RLR signaling. Overall, this review aims to provide insights into the multifunctional nature of the Golgi apparatus and its impact on innate immunity.

Endothelial Dec1-PPARγ Axis Impairs Proliferation and Apoptosis Homeostasis Under Hypoxia in Pulmonary Arterial Hypertension

Background: The hypoxia-induced pro-proliferative and anti-apoptotic characteristics of pulmonary arterial endothelial cells (PAECs) play critical roles in pulmonary vascular remodeling and contribute to hypoxic pulmonary arterial hypertension (PAH) pathogenesis. However, the mechanism underlying this hypoxic disease has not been fully elucidated.

Methods: Bioinformatics was adopted to screen out the key hypoxia-related genes in PAH. Gain- and loss-function assays were then performed to test the identified hypoxic pathways in vitro. Human PAECs were cultured under hypoxic (3% O₂) or normoxic (21% O₂) conditions. Hypoxia-induced changes in apoptosis and proliferation were determined by flow cytometry and Ki-67 immunofluorescence staining, respectively. Survival of the hypoxic cells was estimated by cell counting kit-8 assay. Expression alterations of the target hypoxia-related genes, cell cycle regulators, and apoptosis factors were investigated by Western blot.

Results: According to the Gene Expression Omnibus dataset (GSE84538), differentiated embryo chondrocyte expressed gene 1-peroxisome proliferative-activated receptor-γ (Dec1-PPARγ) axis was defined as a key hypoxia-related signaling in PAH. A negative correlation was observed between Dec1 and PPARγ expression in patients with hypoxic PAH. In vitro observations revealed an increased proliferation and a decreased apoptosis in PAECs under hypoxia. Furthermore, hypoxic PAECs exhibited remarkable upregulation of Dec1 and downregulation of PPARγ. Dec1 was confirmed to be crucial for the imbalance of proliferation and apoptosis in hypoxic PAECs. Furthermore, the pro-surviving effect of hypoxic Dec1 was mediated through PPARγ inhibition.

Conclusion: For the first time, Dec1-PPARγ axis was identified as a key determinant hypoxia-modifying signaling that is necessary for the imbalance between proliferation and apoptosis of PAECs. These novel endothelial signal transduction events may offer new diagnostic and therapeutic options for patients with hypoxic PAH.

Plasma miR-451 with echocardiography serves as a diagnostic reference for pulmonary hypertension

Due to the lack of typical clinical symptoms, the average delay time for diagnosis of pulmonary hypertension (PH) is longer than 2 years. It is urgent to find biomarkers for PH diagnosis. In this study we investigated whether plasma microRNAs (miRNAs) can be used as biomarkers for PH diagnosis. We used microarray to identify dynamic miRNAs between PH and non-PH patients. The candidate miRNAs were verified using qRT-PCR in a mouse model of PH, which was induced by monocrotaline (MCT) injection. We observed that miR-21, miR-126, miR-145, miR-191 and miR-150 had no differences between control mice and MCT-treated mice; but plasma miR-451 was significantly decreased in the 2wk-MCT group, with no further decrease in the 4wk-MCT group. Plasma miR-451 was also markedly decreased in PH patients, whereas miR-21, miR-126, miR-150 and miR-320 did not show differences between 53 PH patients and 54 non-PH patients. Receiver operating characteristic curves (ROCs) were constructed from the patient data to assess the clinical diagnostic values of circulating miR-451 and Doppler echocardiography (D-ECHO). The areas under the curve (AUCs) of ROCs for miR-451 and D-ECHO were 0.710 and 0.766, respectively. Combination of miR-451 and D-ECHO with AUC of 0.825 was superior to the use of either miR-451 or D-ECHO alone for PH diagnosis. In conclusion, plasma miR-451 has a moderate diagnostic value in PH comparable to that of D-ECHO, and the combination of miR-451 with D-ECHO has better diagnostic value than either method alone, which may have implications for PH diagnosis.

Pulmonary Artery Hypertension Model in Rats by Monocrotaline Administration

Pulmonary arterial hypertension (PAH) is a syndrome characterized by pulmonary vascular remodeling and vasoconstriction, leading to increased pulmonary vascular resistance, right ventricular pressure overload and, eventually, to right ventricular failure and premature death. Animal models have been an essential tool for understanding pulmonary hypertension pathophysiology and for the discovery and development of novel therapies.MCT-induced PAH in rats leads to a significant increase in RV pressure and pulmonary vascular remodeling, as well as greater RV hypertrophy. In this chapter, we describe protocols for inducing and assessing the monocrotaline (MCT) rat model, the most classical and widely used in vivo model of PAH. Using this protocol, rats reproducibly develop pulmonary hypertension with a mean pulmonary pressure of ~40 mmHg approximately 4 weeks after single MCT administration.

Defective cellular trafficking of the bone morphogenetic protein receptor type II by mutations underlying familial pulmonary arterial hypertension

Familial pulmonary arterial hypertension (FPAH) is a relatively rare but fatal disorder characterized by elevated arterial pressure caused by abnormal proliferation of endothelial cells of the arteries, which eventually leads to heart failure and death. FPAH is inherited as an autosomal dominant trait and is caused by heterozygous mutations in the BMPR2 gene encoding the bone morphogenetic protein type II receptor (BMPR2). BMPR2 belongs to the TGF β/BMP super-family of receptors involved in a signal transduction cascade via the SMAD signaling pathway. The BMPR2 polypeptide is composed of 1038 amino acids and consists of a ligand binding domain, a kinase domain and a cytoplasmic tail. To investigate the cellular and functional consequence of BMPR2 mutations, C-terminally FLAG-tagged constructs of eighteen pathogenic BMPR2 missense mutants were generated by site directed mutagenesis and expressed in HeLa and HEK-293T cell lines. The subcellular localizations of the mutant proteins were investigated using immunostaining and confocal microscopy. Post-translational modifications of the proteins were analyzed by Endoglycosidase H deglycosylation assay. Our results indicated that mutations in the ligand binding domain affecting highly conserved cysteine residues resulted in retention of the mutant proteins in the endoplasmic reticulum (ER), as evident from their co-localization with the ER resident protein calnexin. The kinase domain mutants showed both ER and plasma membrane (PM) distributions, while the cytoplasmic tail domain variants were localized exclusively to the PM. The subcellular localizations of the mutants were further confirmed by their characteristic glycosylation profiles. In conclusion, our results indicate that ER quality control (ERQC) is involved in the pathological mechanism of several BMPR2 receptor missense mutations causing FPAH, which can be explored as a potential therapeutic target in the future.

The Golgi apparatus regulates cGMP-dependent protein kinase I compartmentation and proteolysis

cGMP-dependent protein kinase I (PKGI) is an important effector of cGMP signaling that regulates vascular smooth muscle cell (SMC) phenotype and proliferation. PKGI has been detected in the perinuclear region of cells, and recent data indicate that proprotein convertases (PCs) typically resident in the Golgi apparatus (GA) can stimulate PKGI proteolysis and generate a kinase fragment that localizes to the nucleus and regulates gene expression. However, the role of the endomembrane system in PKGI compartmentation and processing is unknown. Here, we demonstrate that PKGI colocalizes with endoplasmic reticulum (ER), ER-Golgi intermediate compartment, GA cisterna, and trans-Golgi network proteins in pulmonary artery SMC and cell lines. Moreover, PKGI localizes with furin, a trans-Golgi network-resident PC known to cleave PKGI. ER protein transport influences PKGI localization because overexpression of a constitutively inactive Sar1 transgene caused PKGI retention in the ER. Additionally, PKGI appears to reside within the GA because PKGI immunoreactivity was determined to be resistant to cytosolic proteinase K treatment in live cells. The GA appears to play a role in PKGI proteolysis because overexpression of inositol 1,4,5-trisphosphate receptor-associated cGMP kinase substrate, not only tethered heterologous PKGI-β to the ER and decreased its localization to the GA, but also diminished PKGI proteolysis and nuclear translocation. Also, inhibiting intra-GA protein transport with monensin was observed to decrease PKGI cleavage. These studies detail a role for the endomembrane system in regulating PKGI compartmentation and proteolysis. Moreover, they support the investigation of mechanisms regulating PKGI-dependent nuclear cGMP signaling in the pulmonary vasculature with Golgi dysfunction.

Endocytic deficiency induced by ITSN-1s knockdown alters the Smad2/3-Erk1/2 signaling balance downstream of Alk5

Recently, we demonstrated in cultured endothelial cells and in vivo that deficiency of an isoform of intersectin-1, ITSN-1s, impairs caveolae and clathrin-mediated endocytosis and functionally upregulates compensatory pathways and their morphological carriers (i.e. enlarged endocytic structures, membranous rings or tubules) that are normally underrepresented. We now show that these endocytic structures internalize the broadly expressed transforming growth factor β receptor I (TGFβ-RI or TGFBR1), also known as Alk5, leading to its ubiquitylation and degradation. Moreover, the apoptotic or activated vascular cells of the ITSN-1s-knockdown mice release Alk5-bearing microparticles to the systemic circulation. These interact with and transfer Alk5 to endocytosis-deficient endothelial cells, resulting in lung endothelial cell survival and phenotypic alteration towards proliferation through activation of Erk1 and Erk2 (also known as MAPK3 and MAPK1, respectively). We also show that non-productive assembly of the Alk5–Smad–SARA (Smad anchor for receptor activation, also known as ZFYVE9) signaling complex and preferential formation of the Alk5–mSos–Grb2 complex account for Erk1/2 activation downstream of Alk5 and proliferation of pulmonary endothelial cells. Taken together, our studies demonstrate a functional relationship between the intercellular transfer of Alk5 by microparticles and endothelial cell survival and proliferation, and define a novel molecular mechanism for TGFβ and Alk5-dependent Erk1/2^MAPK signaling that is significant for proliferative signaling and abnormal growth.

Pyrrolizidine Alkaloids: Potential Role in the Etiology of Cancers, Pulmonary Hypertension, Congenital Anomalies, and Liver Disease

Large outbreaks of acute food-related poisoning, characterized by hepatic sinusoidal obstruction syndrome, hemorrhagic necrosis, and rapid liver failure, occur on a regular basis in some countries. They are caused by 1,2-dehydropyrrolizidine alkaloids contaminating locally grown grain. Similar acute poisoning can also result from deliberate or accidental consumption of 1,2-dehydropyrrolizidine alkaloid-containing herbal medicines, teas, and spices. In recent years, it has been confirmed that there is also significant, low-level dietary exposure to 1,2-dehydropyrrolizidine alkaloids in many countries due to consumption of common foods such as honey, milk, eggs, salads, and meat. The level of 1,2-dehydropyrrolizidine alkaloids in these foods is generally too low and too intermittent to cause acute toxicity. However, these alkaloids are genotoxic and can cause slowly developing chronic diseases such as pulmonary arterial hypertension, cancers, cirrhosis, and congenital anomalies, conditions unlikely to be easily linked with dietary exposure to 1,2-dehydropyrrolizidine alkaloids, especially if clinicians are unaware that such dietary exposure is occurring. This Perspective provides a comprehensive review of the acute and chronic toxicity of 1,2-dehydropyrrolizidine alkaloids and their potential to initiate certain chronic diseases, and suggests some associative considerations or indicators to assist in recognizing specific cases of diseases that may have resulted from dietary exposure to these hazardous natural substances. If it can be established that low-level dietary exposure to 1,2-dehydropyrrolizidine alkaloids is a significant cause of some of these costly and debilitating diseases, then this should lead to initiatives to reduce the level of these alkaloids in the food chain.

In vivo knockdown of intersectin-1s alters endothelial cell phenotype and causes microvascular remodeling in the mouse lungs

Intersectin-1s (ITSN-1s) is a general endocytic protein involved in regulating lung vascular permeability and endothelial cells (ECs) survival, via MEK/Erk1/2^MAPK signaling. To investigate the in vivo effects of ITSN-1s deficiency and the resulting ECs apoptosis on pulmonary vasculature and lung homeostasis, we used an ITSN-1s knocked-down (KD_ITSN) mouse generated by repeated delivery of a specific siRNA targeting ITSN-1 gene (siRNA_ITSN). Biochemical and histological analyses as well as electron microscopy (EM) revealed that acute KD_ITSN [3-days (3d) post-siRNA_ITSN treatment] inhibited Erk1/2^MAPK pro-survival signaling, causing significant ECs apoptosis and lung injury; at 10d of KD_ITSN, caspase-3 activation was at peak, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive ECs showed 3.4-fold increase, the mean linear intercept (MLI) showed 48 % augment and pulmonary microvessel density as revealed by aquaporin-1 staining (AQP-1) decreased by 30 %, all compared to controls; pulmonary function was altered. Concomitantly, expression of several growth factors known to activate Erk1/2^MAPK and suppress Bad pro-apoptotic activity increased. KD_ITSN altered Smads activity, downstream of the transforming growth factor beta-receptor-1 (TβR1), as shown by subcellular fractionation and immunoblot analyses. Moreover, 24d post-siRNA_ITSN, surviving ECs became hyper-proliferative and apoptotic-resistant against ITSN-1s deficiency, as demonstrated by EM imaging, 5-bromo-deoxyuridine (BrdU) incorporation and Bad-Ser^112/155 phosphorylation, respectively, leading to increased microvessel density and repair of the injured lungs, as well as matrix deposition. In sum, ECs endocytic dysfunction and apoptotic death caused by KD_ITSN contribute to the initial lung injury and microvascular loss, followed by endothelial phenotypic changes and microvascular remodeling in the remaining murine pulmonary microvascular bed.

Intersectin-1s: an important regulator of cellular and molecular pathways in lung injury

Abstract Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are severe syndromes resulting from the diffuse damage of the pulmonary parenchyma. ALI and ARDS are induced by a plethora of local or systemic insults, leading to the activation of multiple pathways responsible for injury, resolution, and repair or scarring of the lungs. Despite the large efforts aimed at exploring the roles of different pathways in humans and animal models and the great strides made in understanding the pathogenesis of ALI/ARDS, the only viable treatment options are still dependent on ventilator and cardiovascular support. Investigation of the pathophysiological mechanisms responsible for initiation and resolution or advancement toward lung scarring in ALI/ARDS animal models led to a better understanding of the disease's complexity and helped in elucidating the links between ALI and systemic multiorgan failure. Although animal models of ALI/ARDS have pointed out a variety of new ideas for study, there are still limited data regarding the initiating factors, the critical steps in the progression of the disease, and the central mechanisms dictating its resolution or progression to lung scarring. Recent studies link deficiency of intersectin-1s (ITSN-1s), a prosurvival protein of lung endothelial cells, to endothelial barrier dysfunction and pulmonary edema as well as to the repair/recovery from ALI. This review discusses the effects of ITSN-1s deficiency on pulmonary endothelium and its significance in the pathology of ALI/ARDS.

Attenuating Endoplasmic Reticulum Stress as a Novel Therapeutic Strategy in Pulmonary Hypertension

Background—

Evidence suggestive of endoplasmic reticulum (ER) stress in the pulmonary arteries of patients with pulmonary arterial hypertension has been described for decades but has never been therapeutically targeted. ER stress is a feature of many conditions associated with pulmonary arterial hypertension like hypoxia, inflammation, or loss-of-function mutations. ER stress signaling in the pulmonary circulation involves the activation of activating transcription factor 6, which, via induction of the reticulin protein Nogo, can lead to the disruption of the functional ER-mitochondria unit and the increasingly recognized cancer-like metabolic shift in pulmonary arterial hypertension that promotes proliferation and apoptosis resistance in the pulmonary artery wall. We hypothesized that chemical chaperones known to suppress ER stress signaling, like 4-phenylbutyrate (PBA) or tauroursodeoxycholic acid, will inhibit the disruption of the ER-mitochondrial unit and prevent/reverse pulmonary arterial hypertension.

Methods and Results—

PBA in the drinking water both prevented and reversed chronic hypoxia–induced pulmonary hypertension in mice, decreasing pulmonary vascular resistance, pulmonary artery remodeling, and right ventricular hypertrophy and improving functional capacity without affecting systemic hemodynamics. These results were replicated in the monocrotaline rat model. PBA and tauroursodeoxycholic acid improved ER stress indexes in vivo and in vitro, decreased activating transcription factor 6 activation (cleavage, nuclear localization, luciferase, and downstream target expression), and inhibited the hypoxia-induced decrease in mitochondrial calcium and mitochondrial function. In addition, these chemical chaperones suppressed proliferation and induced apoptosis in pulmonary artery smooth muscle cells in vitro and in vivo.

Conclusions—

Attenuating ER stress with clinically used chemical chaperones may be a novel therapeutic strategy in pulmonary hypertension with high translational potential.

Idiopathic and heritable PAH perturb common molecular pathways, correlated with increased MSX1 expression

The majority of pulmonary arterial hypertension (PAH) is not associated with BMPR2 mutation, and major risk factors for idiopathic PAH are not known. The objective of this study was to identify a gene expression signature for IPAH. To accomplish this, we used Affymetrix arrays to probe expression levels in 86 patient samples, including 22 healthy controls, 20 IPAH patients, 20 heritable PAH patients (HPAH), and 24 BMPR2 mutation carriers that were as yet unaffected (UMC). Culturing the patient cells removes the signatures of drug effects and inflammation which have made interpretation of results from freshly isolated lymphocytes problematic. We found that gene expression signatures from IPAH patients clustered either with HPAH patients or in a single distinct group. There were no groups of genes changed in IPAH that were not also changed in HPAH. HPAH, IPAH, and UMC had common changes in metabolism, actin dynamics, adhesion, cytokines, metabolism, channels, differentiation, and transcription factors. Common to IPAH and HPAH but not UMC were an upregulation of vesicle trafficking, oxidative/nitrosative stress, and cell cycle genes. The transcription factor MSX1, which is known to regulate BMP signaling, was the most upregulated gene (4×) in IPAH patients. These results suggest that IPAH cases have a shared molecular origin, which is closely related to, but distinct from, HPAH. HPAH and IPAH share the majority of altered signaling pathways, suggesting that treatments developed to target the molecular etiology of HPAH will also be effective against IPAH.

Caveolins and lung function

The primary function of the mammalian lung is to facilitate diffusion of oxygen to venous blood and to ventilate carbon dioxide produced by catabolic reactions within cells. However, it is also responsible for a variety of other important functions, including host defense and production of vasoactive agents to regulate not only systemic blood pressure, but also water, electrolyte and acid-base balance. Caveolin-1 is highly expressed in the majority of cell types in the lung, including epithelial, endothelial, smooth muscle, connective tissue cells, and alveolar macrophages. Deletion of caveolin-1 in these cells results in major functional aberrations, suggesting that caveolin-1 may be crucial to lung homeostasis and development. Furthermore, generation of mutant mice that under-express caveolin-1 results in severe functional distortion with phenotypes covering practically the entire spectrum of known lung diseases, including pulmonary hypertension, fibrosis, increased endothelial permeability, and immune defects. In this Chapter, we outline the current state of knowledge regarding caveolin-1-dependent regulation of pulmonary cell functions and discuss recent research findings on the role of caveolin-1 in various pulmonary disease states, including obstructive and fibrotic pulmonary vascular and inflammatory diseases.

Caveolins and lung function

The primary function of the mammalian lung is to facilitate diffusion of oxygen to venous blood and to ventilate carbon dioxide produced by catabolic reactions within cells. However, it is also responsible for a variety of other important functions, including host defense and production of vasoactive agents to regulate not only systemic blood pressure, but also water, electrolyte and acid-base balance. Caveolin-1 is highly expressed in the majority of cell types in the lung, including epithelial, endothelial, smooth muscle, connective tissue cells, and alveolar macrophages. Deletion of caveolin-1 in these cells results in major functional aberrations, suggesting that caveolin-1 may be crucial to lung homeostasis and development. Furthermore, generation of mutant mice that under-express caveolin-1 results in severe functional distortion with phenotypes covering practically the entire spectrum of known lung diseases, including pulmonary hypertension, fibrosis, increased endothelial permeability, and immune defects. In this Chapter, we outline the current state of knowledge regarding caveolin-1-dependent regulation of pulmonary cell functions and discuss recent research findings on the role of caveolin-1 in various pulmonary disease states, including obstructive and fibrotic pulmonary vascular and inflammatory diseases.

Protein trafficking dysfunctions: Role in the pathogenesis of pulmonary arterial hypertension

Earlier electron microscopic data had shown that a hallmark of the vascular remodeling in pulmonary arterial hypertension (PAH) in man and experimental models includes enlarged vacuolated endothelial and smooth muscle cells with increased endoplasmic reticulum and Golgi stacks in pulmonary arterial lesions. In cell culture and in vivo experiments in the monocrotaline model, we observed disruption of Golgi function and intracellular trafficking with trapping of diverse vesicle tethers, SNAREs and SNAPs in the Golgi membranes of enlarged pulmonary arterial endothelial cells (PAECs) and pulmonary arterial smooth muscle cells (PASMCs). Consequences included the loss of cell surface caveolin-1, hyperactivation of STAT3, mislocalization of eNOS with reduced cell surface/caveolar NO and hypo-S-nitrosylation of trafficking-relevant proteins. Similar Golgi tether, SNARE and SNAP dysfunctions were also observed in hypoxic PAECs in culture and in PAECs subjected to NO scavenging. Strikingly, a hypo-NO state promoted PAEC mitosis and cell proliferation. Golgi dysfunction was also observed in pulmonary vascular cells in idiopathic PAH (IPAH) in terms of a marked cytoplasmic dispersal and increased cellular content of the Golgi tethers, giantin and p115, in cells in the proliferative, obliterative and plexiform lesions in IPAH. The question of whether there might be a causal relationship between trafficking dysfunction and vasculopathies of PAH was approached by genetic means using HIV-nef, a protein that disrupts endocytic and trans-Golgi trafficking. Macaques infected with a chimeric simian immunodeficiency virus (SIV) containing the HIV-nef gene (SHIV-nef), but not the non-chimeric SIV virus containing the endogenous SIV-nef gene, displayed pulmonary arterial vasculopathies similar to those in human IPAH. Only macaques infected with chimeric SHIV-nef showed pulmonary vascular lesions containing cells with dramatic cytoplasmic dispersal and increase in giantin and p115. Specifically, it was the HIV-nef–positive cells that showed increased giantin. Elucidating how each of these changes fits into the multifactorial context of hypoxia, reduced NO bioavailability, mutations in BMPR II, modulation of disease penetrance and gender effects in disease occurrence in the pathogenesis of PAH is part of the road ahead.

The monocrotaline model of pulmonary hypertension in perspective

Severe forms of pulmonary arterial hypertension (PAH) are characterized by various degrees of remodeling of the pulmonary arterial vessels, which increases the pulmonary vascular resistance and right ventricular afterload, thus contributing to the development of right ventricle dysfunction and failure. Recent years have seen advances in the understanding of the pathobiology of PAH; however, many important questions remain unanswered. Elucidating the pathobiology of PAH continues to be critical to design new effective therapeutic strategies, and appropriate animal models of PAH are necessary to achieve the task. Although the monocrotaline rat model of PAH has contributed to a better understanding of vascular remodeling in pulmonary hypertension, we question the validity of this model as a preclinically relevant model of severe plexogenic PAH. Here we review pertinent publications that either have been forgotten or ignored, and we reexamine the monocrotaline model in the context of human forms of PAH.

Dependence of Golgi apparatus integrity on nitric oxide in vascular cells: implications in pulmonary arterial hypertension

Although reduced bioavailability of nitric oxide (NO) has been implicated in the pathogenesis of pulmonary arterial hypertension (PAH), its consequences on organellar structure and function within vascular cells is largely unexplored. We investigated the effect of reduced NO on the structure of the Golgi apparatus as assayed by giantin or GM130 immunofluorescence in human pulmonary arterial endothelial (HPAECs) and smooth muscle (HPASMCs) cells, bovine PAECs, and human EA.hy926 endothelial cells. Golgi structure was also investigated in cells in tissue sections of pulmonary vascular lesions in idiopathic PAH (IPAH) and in macaques infected with a chimeric simian immunodeficiency virus containing the human immunodeficiency virus (HIV)-nef gene (SHIV-nef) with subcellular three-dimensional (3D) immunoimaging. Compounds with NO scavenging activity including 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), methylene blue, N-acetylcysteine, and hemoglobin markedly fragmented the Golgi in all cell types evaluated as did monocrotaline pyrrole, while LY-83583, sildenafil, fasudil, Y-27632, Tiron, Tempol, or H(2)O(2) did not. Golgi fragmentation by NO scavengers was inhibited by diethylamine NONOate, was evident in HPAECs after selective knockdown of endothelial nitric oxide synthase using small interfering RNA (siRNA), was independent of microtubule organization, required the GTPase dynamin 2, and was accompanied by depletion of α-soluble N-ethylmaleimide-sensitive factor (NSF) acceptor protein (α-SNAP) from Golgi membranes and codispersal of the SNAP receptor (SNARE) Vti1a with giantin. Golgi fragmentation was confirmed in endothelial and smooth muscle cells in pulmonary arterial lesions in IPAH and the SHIV-nef-infected macaque with subcellular 3D immunoimaging. In SHIV-nef-infected macaques Golgi fragmentation was observed in cells containing HIV-nef-bearing endosomes. The observed Golgi fragmentation suggests that NO plays a significant role in modulating global protein trafficking patterns that contribute to changes in the cell surface landscape and functional signaling in vascular cells.

Pulmonary hypertension associated with HIV infection: pulmonary vascular disease: the global perspective

The success of antiretroviral therapies in improving the survival of patients infected with HIV and reducing HIV-associated opportunistic infections is undisputed. Nevertheless, long-term outcomes such as noninfectious cardiovascular complications, including cardiomegaly, pericarditis, myocarditis, and pulmonary arterial hypertension, are now serious concerns. The lung is a frequent target organ for disorders associated with HIV infection. HIV-related pulmonary arterial hypertension (HRPAH) affects more individuals who are infected with HIV than individuals who are uninfected. Moreover, the long-standing estimated prevalence of HRPAH in developed countries (calculated at 0.5%) is increasing as more clinician-scientists unify their efforts to screen patients who are pulmonary asymptomatic for pulmonary arterial hypertension. In order to decrease mortality, efforts are directed at early detection, diagnosis, and therapeutic interventions before the disease compromises patients' quality of life. This article reviews the logistics of screening approaches for HRPAH and discusses the substantial disease burden currently faced by developing countries, where the prevalence of HIV infection is higher and complicated by hyperendemic risk factors, limited access to antiretrovirals, and lack of screening tools. We also present mechanistic insights into HRPAH, including the role of HIV proteins and their potential use as screening tools, and, finally, areas that still need intense research.

Golgi, trafficking, and mitosis dysfunctions in pulmonary arterial endothelial cells exposed to monocrotaline pyrrole and NO scavenging

Although the administration of monocrotaline (MCT) into experimental animals is in widespread use today in investigations of pulmonary arterial hypertension (PAH), the underlying cellular and subcellular mechanisms that culminate in vascular remodeling are incompletely understood. Bovine pulmonary arterial endothelial cells (PAECs) in culture exposed to monocrotaline pyrrole (MCTP) develop "megalocytosis" 18-24 h later characterized by enlarged hyperploid cells with enlarged Golgi, mislocalization of endothelial nitric oxide synthase away from the plasma membrane, decreased cell-surface/caveolar nitric oxide (NO), and hypo-S-nitrosylation of caveolin-1, clathrin heavy chain, and N-ethylmaleimide-sensitive factor. We investigated whether MCTP did in fact affect functional intracellular trafficking. The NO scavenger (4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) and the NO donor diethylamine NONOate were used for comparison. Both MCTP and c-PTIO produced distinctive four- to fivefold enlarged PAECs within 24-48 h with markedly enlarged/dispersed Golgi, as visualized by immunostaining for the Golgi tethers/matrix proteins giantin, GM130, and p115. Live-cell uptake of the Golgi marker C(5) ceramide revealed a compact juxtanuclear Golgi in untreated PAECs, brightly labeled enlarged circumnuclear Golgi after MCTP, but minimally labeled Golgi elements after c-PTIO. These Golgi changes were reduced by NONOate. After an initial inhibition during the first day, both MCTP and c-PTIO markedly enhanced anterograde secretion of soluble cargo (exogenous vector-expressed recombinant horseradish peroxidase) over the next 4 days. Live-cell internalization assays using fluorescently tagged ligands showed that both MCTP and c-PTIO inhibited the retrograde uptake of acetylated low-density lipoprotein, transferrin, and cholera toxin B. Moreover, MCTP, and to a variable extent c-PTIO, reduced the cell-surface density of all receptors assayed (LDLR, TfnR, BMPR, Tie-2, and PECAM-1/CD31). In an important distinction, c-PTIO enhanced mitosis in PAECs but MCTP inhibited mitosis, even that due to c-PTIO, despite markedly exaggerated Golgi dispersal. Taken together, these data define a broad-spectrum Golgi and subcellular trafficking dysfunction syndrome in endothelial cells exposed to MCTP or NO scavenging.

Golgi dysfunction is a common feature in idiopathic human pulmonary hypertension and vascular lesions in SHIV-nef-infected macaques

Golgi dysfunction has been previously investigated as a mechanism involved in monocrotaline-induced pulmonary hypertension (PAH). In the present study, we addressed whether Golgi dysfunction might occur in pulmonary vascular cells in idiopathic PAH (IPAH) and whether there might be a causal relationship between trafficking dysfunction and vasculopathies of PAH. Quantitative immunostaining for the Golgi tethers giantin and p115 on human lung tissue from patients with IPAH (n = 6) compared with controls demonstrated a marked cytoplasmic dispersal of giantin- and p115-bearing vesicular elements in vascular cells in the proliferative, obliterative, and plexiform lesions in IPAH and an increase in the amounts of these Golgi tethers/matrix proteins per cell. The causality question was approached by genetic means using human immunodeficiency virus (HIV)-Nef, a protein that disrupts endocytic and trans-Golgi trafficking. Macaques infected with a chimeric simian immunodeficiency virus (SIV) containing the HIV-nef gene (SHIV-nef), but not the nonchimeric SIV virus containing the endogenous SIV-nef gene, displayed pulmonary arterial vasculopathies similar to those in human IPAH. Giantin and p115 levels and their subcellular distribution in pulmonary vascular cells in lungs of SHIV-nef infected macaques (n = 4) were compared with SIV-infected (n = 3) and an uninfected macaque control. Only macaques infected with chimeric SHIV-nef showed pulmonary vascular lesions containing cells with dramatic cytoplasmic dispersal and an increase in giantin and p115. Specifically, the HIV-Nef-positive cells showed increased giantin, p115, and the activated transcription factor PY-STAT3. These data represent the first test of the Golgi dysfunction hypothesis in IPAH and place trafficking and Golgi disruption in the chain of causality of pulmonary vasculopathies in the macaque model.

Cancer-cell-phenotype-dependent differential intracellular trafficking of unconjugated quantum dots

A diverse array of nanoparticles, including quantum dots (QDs), metals, polymers, liposomes, and dendrimers, are being investigated as therapeutics and imaging agents in cancer diseases. However, the role of the cancer-cell phenotype on the uptake and intracellular fate of nanoparticles in cancer cells remains poorly understood. Reported here is that differences in cancer-cell phenotypes can lead to significant differences in intracellular sorting, trafficking, and localization of nanoparticles. Unconjugated anionic QDs demonstrate dramatically different intracellular profiles in three closely related human-prostate-cancer cells used in the investigation: PC3, PC3-flu, and PC3-PSMA. QDs demonstrate punctated intracellular localization throughout the cytoplasm in PC3 cells. In contrast, the nanoparticles localize mainly at a single juxtanuclear location ("dot-of-dots") inside the perinuclear recycling compartment in PC3-PSMA cells, where they co-localize with transferrin and the prostate-specific membrane antigen. The results indicate that nanoparticle sorting and transport is influenced by changes in cancer-cell phenotype and can have significant implications in the design and engineering of nanoscale drug delivery and imaging systems for advanced tumors.

Depletion of the ATPase NSF from Golgi membranes with hypo-S-nitrosylation of vasorelevant proteins in endothelial cells exposed to monocrotaline pyrrole

Investigations of regulated S-nitrosylation and denitrosylation of vasorelevant proteins are a newly emergent area in vascular biology. We previously showed that monocrotaline pyrrole (MCTP)-induced megalocytosis of pulmonary arterial endothelial cells (PAECs), which underlies the development of pulmonary arterial hypertension, was associated with a Golgi blockade characterized by the trapping of diverse vesicle tethers, soluble N-ethylmaleimide-sensitive factor (NSF)-attachment protein receptors (SNAREs), and soluble NSF-attachment proteins (SNAPs) in the Golgi; reduced trafficking of caveolin-1 (cav-1) and endotheial nitric oxide (NO) synthase (eNOS) from the Golgi to the plasma membrane; and decreased caveolar NO. We have investigated whether NSF, the ATPase involved in all SNARE disassembly, might be the upstream target of MCTP and whether MCTP might regulate NSF by S-nitrosylation. Immunofluorescence microscopy and Golgi purification techniques revealed the discordant decrease of NSF by approximately 50% in Golgi membranes after MCTP despite increases in alpha-SNAP, cav-1, eNOS, and syntaxin-6. The NO scavenger (4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide failed to affect the initiation or progression of MCTP megalocytosis despite a reduction of 4,5-diaminofluorescein diacetate fluorescence and inhibition of S-nitrosylation of eNOS as assayed using the biotin-switch method. Moreover, the latter assay not only revealed constitutive S-nitrosylation of NSF, eNOS, cav-1, and clathrin heavy chain (CHC) in PAECs but also a dramatic 70-95% decrease in the S-nitrosylation of NSF, eNOS, cav-1, and CHC after MCTP. These data point to depletion of NSF from Golgi membranes as a mechanism for Golgi blockade after MCTP and to denitrosylation of vasorelevant proteins as critical to the development of endothelial cell megalocytosis.

Role of the TGF-beta/Alk5 signaling pathway in monocrotaline-induced pulmonary hypertension

RATIONALE

Pulmonary arterial hypertension is a progressive disease characterized by an elevation in the mean pulmonary artery pressure leading to right heart failure and a significant risk of death. Alterations in two transforming growth factor (TGF) signaling pathways, bone morphogenetic protein receptor II and the TGF-beta receptor I, Alk1, have been implicated in the pathogenesis of pulmonary hypertension (PH). However, the role of TGF-beta family signaling in PH and pulmonary vascular remodeling remains unclear.

OBJECTIVES

To determine whether inhibition of TGF-beta signaling will attenuate and reverse monocrotaline-induced PH (MCT-PH).

METHODS

We have used an orally active small-molecule TGF-beta receptor I inhibitor, SD-208, to determine the functional role of this pathway in MCT-PH.

MEASUREMENTS AND MAIN RESULTS

The development of MCT-PH was associated with increased vascular cell apoptosis, which paralleled TGF-beta signaling as documented by psmad2 expression. Inhibition of TGF-beta signaling with SD-208 significantly attenuated the development of the PH and reduced pulmonary vascular remodeling. These effects were associated with decreased early vascular cell apoptosis, adventitial cell proliferation, and matrix metalloproteinase expression. Inhibition of TGF-beta signaling with SD-208 in established MCT-PH resulted in a small but significant improvement in hemodynamic parameters and medial remodeling.

CONCLUSIONS

These findings provide evidence that increased TGF-beta signaling participates in the pathogenesis of experimental severe PH.

Cytoplasmic provenance of STAT3 and PY-STAT3 in the endolysosomal compartments in pulmonary arterial endothelial and smooth muscle cells: implications in pulmonary arterial hypertension

Lung vascular lesions in pulmonary arterial hypertension (PAH) are characterized by enlarged, vacuolated ("megalocytotic") pulmonary arterial endothelial (PAEC) and smooth muscle cells (PASMC). We have recently proposed that dysfunction of vesicle tethers, soluble N-ethylmaleimide-sensitive factor attachment proteins (SNAPs), and SNAP receptors (SNAREs), leading to disruptions of intracellular trafficking in the Golgi to plasma membrane (centrifugal) and the plasma membrane to cell interior (centripetal) directions is a key causal mechanism in this disease. In PAH, there was a reciprocal relationship between loss of caveolin-1 (cav-1) in PAECs and increased expression of "activated" tyrosine-phosphorylated STAT3 (PY-STAT3) associated with a block in centrifugal trafficking to/through the Golgi organelle. In the present study, we investigated 1) whether centripetal trafficking of STAT3 and PY-STAT3 in PAECs and PASMCs was membrane-associated, and 2) whether this might be affected in PAH. Immunofluorescence and live cell imaging studies showed that, in both PAEC and PASMC, STAT3 was associated with cytoplasmic vesicles partially colocalizing with markers of the endolysosomal compartments (clathrin, EEA1, Rab5, Rab11, and LAMP1). Overexpression of cav-1 increased the targeting of STAT3 to lysosomes and inhibited STAT3 transcriptional activity. Exposure of PAECs to monocrotaline (MCT) pyrrole, which causes PAH in the rat, led to a loss of caveolar STAT3 with increased sequestration of STAT3 and PY-STAT3 in endosomes. In vivo, marked cytoplasmic sequestration of activated PY-STAT3 was a common feature in PAEC in the rat/MCT model and in cells in the proliferative arterial and plexiform lesions in PAH in humans. These data highlight the epigenetic regulation of centripetal cytokine and growth-factor signaling pathways and its modulation in PAH.