Endothelin and the tumor microenvironment: a finger in every pie.

The tumor microenvironment (TME) plays a central role in the development of cancer. Within this complex milieu, the endothelin (ET) system plays a key role by triggering epithelial-to-mesenchymal transition, causing degradation of the extracellular matrix and modulating hypoxia response, cell proliferation, composition, and activation. These multiple effects of the ET system on cancer progression have prompted numerous preclinical studies targeting the ET system with promising results, leading to considerable optimism for subsequent clinical trials. However, these clinical trials have not lived up to the high expectations; in fact, the clinical trials have failed to demonstrate any substantiated benefit of targeting the ET system in cancer patients. This review discusses the major and recent advances of the ET system with respect to TME and comments on past and ongoing clinical trials of the ET system.

Case Report: Durable therapy response to Osimertinib in rare EGFR Exon 18 mutated NSCLC.

Up to 20% of all non-small cell lung cancer patients harbor tumor specific driver mutations that are effectively treated with tyrosine kinase inhibitors. However, for the rare EGFR deletion-insertion mutation of exon 18, there is very little evidence regarding the effectiveness of tyrosine kinase inhibitors. A particular challenge for clinicians in applying tyrosine kinase inhibitors is not only diagnosing a mutation but also interpreting rare mutations with unclear therapeutic significance. Thus, we present the case of a 65-year-old Caucasian male lung adenocarcinoma patient with an EGFR Exon 18 p.Glu709_Thr710delinsAsp mutation of uncertain therapeutic relevance. This patient initially received two cycles of standard platinum-based chemotherapy without any therapeutic response. After administration of Osimertinib as second line therapy, the patient showed a lasting partial remission for 12 months. Therapy related toxicities were limited to mild thrombocytopenia, which ceased after dose reduction of Osimertinib. To our knowledge, this is the first report of effective treatment of this particular mutation with Osimertinib. Hence, we would like to discuss Osimertinib as a viable treatment option in EGFR Exon 18 p.Glu709_Thr710delinsAsp mutated lung adenocarcinoma.

[Whipple's triad with high and low insulin levels]. / Whipple-Trias mit erhöhten und erniedrigten Insulinspiegeln.

A 69-year-old female patient and a 70-year-old male patient were admitted to hospital with recurrent, severe hypoglycemic episodes and a typical manifestation of Whipple's triad. In the female, elevated levels of insulin, C­peptide and pro-insulin together with pathological findings during a fasting test proved the presence of an insulinoma, which could be detected by Ga-68-DOTATOC-PET-CT in the pancreas. There was a very rare co-existence of a neuroendocrine Merkel cell carcinoma. In the male, levels of insulin and C­peptide were suppressed and a diagnosis of paraneoplastic hypoglycemia by IGF­2 secretion was made with increased glucose disposal in skeletal muscle proven by 18F­FDG-PET-CT.

Outpatient palliative care during the COVID-19 pandemic: a retrospective single centre analysis in Germany.

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic has challenged health care systems worldwide. In Germany, patients in a palliative care setting have the opportunity to receive treatment by a specialised mobile outpatient palliative care team (OPC). The given retrospective single centre analysis describes the use of OPC structures for terminally ill COVID-19 patients during the height of the pandemic in Germany and aims to characterise this exceptional OPC patient collective. METHODS: First, death certificates were analysed in order to collect data about the place of death of all deceased COVID-19 patients (n = 471) within our local governance district. Second, we investigated whether advance care planning structures were established in local nursing homes (n = 30) during the height of the COVID-19 pandemic in 2020. Third, we examined patient characteristics of COVID-19 negative (n = 1579) and COVID-19 positive (n = 28) patients treated by our tertiary care centre guided OPC service. RESULTS: The analysis of death certificates in our local district revealed that only 2.1% of all deceased COVID-19 patients had succumbed at their home address (n = 10/471). In contrast, 34.0% of COVID-19 patients died in nursing homes (n = 160/471), whereas 63.5% died in an inpatient hospital setting (n = 299/471). A large proportion of these hospitalised patients died on non-intensive care unit wards (38.8%). Approximately 33.0% of surveyed nursing homes had a palliative care council service and 40.0% of them offered advance care planning (ACP) structures for their nursing home residents. In our two OPC collectives we observed significant differences concerning clinical characteristics such as the Index of Eastern Cooperative Oncology Group [ECOG] (p = 0.014), oncologic comorbidity (p = 0.004), as well as referrer and primary patient location (p = 0.001, p = 0.033). CONCLUSIONS: Most COVID-19 patients in our governance district died in an inpatient setting. However, the highest number of COVID-19 patients in our governance district who died in an outpatient setting passed away in nursing homes where palliative care structures should be further expanded. COVID-19 patients who died under the care of our OPC service had considerably fewer oncologic comorbidities. Finally, to relieve conventional health care structures, we propose the expansion of established OPC structures for treating terminally ill COVID-19 patients.

Utility and Drawbacks of Chimeric Antigen Receptor T Cell (CAR-T) Therapy in Lung Cancer.

The present treatments for lung cancer include surgical resection, radiation, chemotherapy, targeted therapy, and immunotherapy. Despite advances in therapies, the prognosis of lung cancer has not been substantially improved in recent years. Chimeric antigen receptor (CAR)-T cell immunotherapy has attracted growing interest in the treatment of various malignancies. Despite CAR-T cell therapy emerging as a novel potential therapeutic option with promising results in refractory and relapsed leukemia, many challenges limit its therapeutic efficacy in solid tumors including lung cancer. In this landscape, studies have identified several obstacles to the effective use of CAR-T cell therapy including antigen heterogeneity, the immunosuppressive tumor microenvironment, and tumor penetration by CAR-T cells. Here, we review CAR-T cell design; present the results of CAR-T cell therapies in preclinical and clinical studies in lung cancer; describe existing challenges and toxicities; and discuss strategies to improve therapeutic efficacy of CAR-T cells.

[Adjuvant Lung Cancer Therapy in the Elderly: Comparative Analysis of Indication, Adherence to Therapy, and Long Term Survival]. / Adjuvante Therapie betagter Lungenkrebspatienten: Komparative Analyse von Indikationsstellung, Therapieadhärenz und Langzeitüberleben.

BACKGROUND: Lung cancer is frequently diagnosed among elderly patients. However, this patient group is under-represented in or excluded from clinical trials and, therefore, evidence-based treatment is challenging. It is uncertain whether there are differences in the feasibility of adjuvant therapies between older and younger patients with NSCLC. The objective of this study was the analysis of treatment recommendations, adherence to adjuvant therapy, and overall survival in patients of at least 70 years of age with resected stage II, III or oligometastatic IV NSCLC in comparison to younger patients. METHODS: 316 patients with NSCLC stage II to IV oligo resected with curative intent at the Giessen University Hospital between 2008 and 2019 were included, 115 of them 70 years or older. Patient and tumor characteristics, treatment type and survival data were extracted from the oncological database of the Mittelhessen lung cancer centre. Primary endpoints were indication and adherence to adjuvant treatment. Secondary endpoints were therapy-associated morbidity and overall survival. RESULTS: Elderly received significantly fewer recommendations for adjuvant therapy, both chemotherapy (OR=0.509) and radiochemotherapy (OR=0.455). Compared to younger patients, elderly patients commenced therapy significantly less often (OR=4.49) and were less likely to complete treatment (OR=0.423). The 5-year survival rates of treated elderly patients treated exceeded those of untreated elderly (Stage II, 51.9 vs 31.8%; stage III, 29.0 vs 25.8%), and were inferior to the survival rates of the younger patients (stage II, 69.8 vs. 69.8%; stage III 52.8 vs. 19.7%). CONCLUSION: In general, adjuvant therapy appears to be useful and feasible in selected patients over 70 years of age. However, its implementation and success are limited compared to younger patients. Adjuvant therapy is recommended and performed less frequently in older patients. The number of elderly patients treated remained unchanged over time, despite an increasing amount of therapy recommendations. Since the postoperative course, comorbidities, frailty and the toxicity of the therapy play a major role, the assessment of each individual case in an interdisciplinary oncological conference should serve as the basis for therapy decisions instead of age. Further studies are needed to collect representative data for the general elderly population. Newer, potentially better tolerated drugs such as tyrosine kinase inhibitors or immune checkpoint inhibitors appear to be promising.

Update on recent key publications in lung oncology: picking up speed.

INTRODUCTION: As incidence rates for lung cancer are still very high and lung cancer remains the most deadly cancer since the turn of the millennium, efforts have been made to find new approaches in cancer research. This systematic review highlights how therapeutic options were extended and how the development of new drugs has picked up speed during the last 20 years. METHODS: A systematic search was performed in PubMed, Cochrane Library and the European Union Trial Register and 443 records were identified. Our inclusion criteria constituted completed phase I, II and III studies investigating drugs approved by the European Medicines Agency (EMA). Overall, 127 articles were analysed. RESULTS: During the 5 year interval from 2015 to 2020, significantly more drugs were approved after phase III, and occasionally after phase II, trials than between 2000 and 2005 (p=0.002). Furthermore, there was a significant time difference (p=0.00001) indicating an increasingly briefer time interval between the publication of phase I and phase III results in the last few years. DISCUSSION: Due to novel therapeutic approaches, numerous new drugs in lung oncology were approved. This has improved symptoms and prognoses in patients with advanced lung cancer. However, faster approval could make it difficult to scrutinise new options regarding safety and efficacy with sufficient diligence.

Changes in Pain Medication Profile among Patients Admitted to Specialized Home Palliative Care in Relation to Referral Source: An Exploratory Study.

Pain is a common symptom leading to referrals to specialized home palliative care (SHPC) services and is known to affect patients' quality of life. To date, little is known about the impact of referral source on its management. To assess changes to pain medication profile in the course of SHPC and to identify potential differences in relation to referral source. This exploratory study is a retrospective analysis of 501 electronic medical records of a SHPC team in Germany. This included the assessment of baseline pain medication profiles according to the WHO analgesic ladder and changes to analgesic treatment in the course of SHPC with respect to referral source. At the time of admission, 77.4% of patients referred by a hospital and 78.8% of patients referred by the outpatient sector received a fixed analgesic regimen. In all, 61.9% of the inpatient group versus 62.9% of the outpatient group were treated with opioids, and 79.0% received modifications to pain medication at one point in time following admission. Thereby, patients referred by the outpatient sector received significantly earlier modifications and more supplementations of pain medication. Our study suggests positive development in the prescription of opioid analgesics compared to earlier studies in Germany. On the one hand, it highlights the relevance of thorough assessment and responsive evaluation of pain in SHPC, and on the other hand it reveals possible training needs of referring physicians, particularly those working in the outpatient sector. Our results inspired further research examining more closely the links between referral source and pain management.

Lipoteichoic acids from Staphylococcus aureus stimulate proliferation of human non-small-cell lung cancer cells in vitro.

Pulmonary infections are frequent complications in lung cancer and may worsen its outcome and survival. Inflammatory mediators are suspected to promote tumor growth in non-small-cell lung cancer (NSCLC). Hence, bacterial pathogens may affect lung cancer growth by activation of inflammatory signalling. Against this background, we investigated the effect of purified lipoteichoic acids (LTA) of Staphylococcus aureus (S. aureus) on cellular proliferation and liberation of interleukin (IL)-8 in the NSCLC cell lines A549 and H226. A549 as well as H226 cells constitutively expressed TLR-2 mRNA. Even in low concentrations, LTA induced a prominent increase in cellular proliferation of A549 cells as quantified by automatic cell counting. In parallel, metabolic activity of A549 cells was enhanced. The increase in proliferation was accompanied by an increase in IL-8 mRNA expression and a dose- and time-dependent release of IL-8. Cellular proliferation as well as the release of IL-8 was dependent on specific ligation of TLR-2. Interestingly, targeting IL-8 by neutralizing antibodies completely abolished the LTA-induced proliferation of A549 cells. The pro-proliferative effect of LTA could also be reproduced in the squamous NSCLC cell line H226. In summary, LTA of S. aureus induced proliferation of NSCLC cell lines of adeno- and squamous cell carcinoma origin. Ligation of TLR-2 followed by auto- or paracrine signalling by endogenously synthesized IL-8 is centrally involved in LTA-induced tumor cell proliferation. Therefore, pulmonary infections may exert a direct pro-proliferative effect on lung cancer growth.

Interactions between neutrophils and non-small cell lung cancer cells: enhancement of tumor proliferation and inflammatory mediator synthesis.

The inflammatory tumor microenvironment plays a crucial role in tumor progression. In lung cancer, both bacterial infections and neutrophilia are associated with a poor prognosis. In this study, we characterized the effect of isolated human neutrophils on proliferation of the non-small cell lung cancer (NSCLC) cell line A549 and analyzed the impact of A549-neutrophil interactions on inflammatory mediator generation in naive and lipopolysaccharide (LPS)-exposed cell cultures. Co-incubation of A549 cells with neutrophils induced proliferation of resting and LPS-exposed A549 cells in a dose-dependent manner. In transwell-experiments, this effect was demonstrated to depend on direct cell-to-cell contact. This pro-proliferative effect of neutrophils on A549 cells could be attenuated by inhibition of neutrophil elastase activity, but not by oxygen radical neutralization. Correspondingly, neutrophil elastase secretion, but not respiratory burst, was specifically enhanced in co-cultures of A549 cells and neutrophils. Moreover, interference with COX-2 activity by indomethacin or the specific COX-2 inhibitor NS-398 also blunted the increased A549 proliferation in the presence of neutrophils. In parallel, a massive amplification of COX-2-dependent prostaglandin E2 synthesis was detected in A549-neutrophil co-cultures. These findings suggest that direct cell-cell interactions between neutrophils and tumor cells cause release of inflammatory mediators which, in turn, may enhance tumor growth in NSCLC.

Endotoxin induces proliferation of NSCLC in vitro and in vivo: role of COX-2 and EGFR activation.

Lung cancer is frequently complicated by pulmonary infections which may impair prognosis of this disease. Therefore, we investigated the effect of bacterial lipopolysaccharides (LPS) on tumor proliferation in vitro in the non-small cell lung cancer (NSCLC) cell line A549, ex vivo in a tissue culture model using human NSCLC specimens and in vivo in the A549 adenocarcinoma mouse model. LPS induced a time- and dose-dependent increase in proliferation of A549 cells as quantified by MTS activity and cell counting. In parallel, an increased expression of the proliferation marker Ki-67 and cyclooxygenase (COX)-2 was detected both in A549 cells and in ex vivo human NSCLC tissue. Large amounts of COX-2-derived prostaglandin (PG)E(2) were secreted from LPS-stimulated A549 cells. Pharmacological interventions revealed that the proliferative effect of LPS was dependent on CD14 and Toll-like receptor (TLR)4. Moreover, blocking of the epidermal growth factor receptor (EGFR) also decreased LPS-induced proliferation of A549 cells. Inhibition of COX-2 activity in A549 cells severely attenuated both PGE(2) release and proliferation in response to LPS. Synthesis of PGE(2) was also reduced by inhibiting CD14, TLR4 and EGFR in A549 cells. The proliferative effect of LPS on A549 cells could be reproduced in the A549 adenocarcinoma mouse model with enhancement of tumor growth and Ki-67 expression in implanted tumors. In summary, LPS induces proliferation of NSCLC cells in vitro, ex vivo in human NSCLC specimen and in vivo in a mouse model of NSCLC. Pulmonary infection may thus directly induce tumor progression in NSCLC.

Irradiation-dependent effects on tumor perfusion and endogenous and exogenous hypoxia markers in an A549 xenograft model.

PURPOSE: Hypoxia is a major determinant of tumor radiosensitivity, and microenvironmental changes in response to ionizing radiation (IR) are often heterogenous. We analyzed IR-dependent changes in hypoxia and perfusion in A549 human lung adenocarcinoma xenografts. MATERIALS AND METHODS: Immunohistological analysis of two exogenously added chemical hypoxic markers, pimonidazole and CCI-103F, and of the endogenous marker Glut-1 was performed time dependently after IR. Tumor vessels and apoptosis were analyzed using CD31 and caspase-3 antibodies. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and fluorescent beads (Hoechst 33342) were used to monitor vascular perfusion. RESULTS: CCI-103F signals measuring the fraction of hypoxic areas after IR were significantly decreased by approximately 50% when compared with pimonidazole signals, representing the fraction of hypoxic areas from the same tumors before IR. Interestingly, Glut-1 signals were significantly decreased at early time point (6.5 h) after IR returning to the initial levels at 30.5 h. Vascular density showed no difference between irradiated and control groups, whereas apoptosis was significantly induced at 10.5 h post-IR. DCE-MRI indicated increased perfusion 1 h post-IR. CONCLUSIONS: The discrepancy between the hypoxic fractions of CCI-103F and Glut-1 forces us to consider the possibility that both markers reflect different metabolic alterations of tumor microenvironment. The reliability of endogenous markers such as Glut-1 to measure reoxygenation in irradiated tumors needs further consideration. Monitoring tumor microvascular response to IR by DCE-MRI and measuring tumor volume alterations should be encouraged.

Fhl-1, a new key protein in pulmonary hypertension.

BACKGROUND: Pulmonary hypertension (PH) is a severe disease with a poor prognosis. Different forms of PH are characterized by pronounced vascular remodeling, resulting in increased vascular resistance and subsequent right heart failure. The molecular pathways triggering the remodeling process are poorly understood. We hypothesized that underlying key factors can be identified at the onset of the disease. Thus, we screened for alterations to protein expression in lung tissue at the onset of PH in a mouse model of hypoxia-induced PH. METHODS AND RESULTS: Using 2-dimensional polyacrylamide gel electrophoresis in combination with matrix-assisted laser desorption/ionization time-of-flight analysis, we identified 36 proteins that exhibited significantly altered expression after short-term hypoxic exposure. Among these, Fhl-1, which is known to be involved in muscle development, was one of the most prominently upregulated proteins. Further analysis by immunohistochemistry, Western blot, and laser-assisted microdissection followed by quantitative polymerase chain reaction confirmed the upregulation of Fhl-1, particularly in the pulmonary vasculature. Comparable upregulation was confirmed (1) after full establishment of hypoxia-induced PH, (2) in 2 rat models of PH (monocrotaline-treated and hypoxic rats treated with the vascular endothelial growth factor receptor antagonist SU5416), and (3) in lungs from patients with idiopathic pulmonary arterial hypertension. Furthermore, we demonstrated that regulation of Fhl-1 was hypoxia-inducible transcription factor dependent. Abrogation of Fhl-1 expression in primary human pulmonary artery smooth muscle cells by small-interfering RNA suppressed, whereas Fhl-1 overexpression increased, migration and proliferation. Coimmunoprecipitation experiments identified Talin1 as a new interacting partner of Fhl-1. CONCLUSIONS: Protein screening identified Fhl-1 as a novel protein regulated in various forms of PH, including idiopathic pulmonary arterial hypertension.

NOX4 regulates ROS levels under normoxic and hypoxic conditions, triggers proliferation, and inhibits apoptosis in pulmonary artery adventitial fibroblasts.

The NADPH oxidases are involved in vascular remodeling processes and oxygen sensing. Hypoxia-induced pulmonary arterial remodeling results in thickening of the vessel wall and reduction of the area of vessel lumen, leading to pulmonary hypertension and cor pulmonale. The proliferation of pulmonary artery adventitial fibroblasts (PAFB) is critically involved in this process. In this study, we analyzed the role of the non-phagocytic NADPH oxidase subunits NOX1 and NOX4 in PAFB. NOX4 was predominantly expressed in comparison to NOX1 at mRNA levels. Under hypoxic conditions, NOX4 was significantly upregulated at mRNA and protein levels. Silencing of NOX4 by siRNA caused reduction of ROS levels under both normoxic and hypoxic (24 h) conditions and suppressed the significant hypoxic-induced ROS increase. PAFB proliferation was significantly decreased in cells transfected with NOX4 siRNA, whereas apoptosis was enhanced. Also, the expression of NOX4 was studied in PAFB isolated from the lungs of patients with idiopathic pulmonary arterial hypertension (IPAH). Interestingly, a significant increase of NOX4 mRNA expression was observed under hypoxic conditions in PAFB from the lungs with IPAH compared to healthy donors. In conclusion, NOX4 maintains ROS levels under normoxic and hypoxic conditions and enhances proliferation and inhibits apoptosis of PAFB.

The angiotensin II receptor 2 is expressed and mediates angiotensin II signaling in lung fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a severe interstitial lung disease unresponsive to currently available therapies. In IPF, initial alveolar epithelial cell damage leads to activation of fibroblast-(myo)fibroblasts, which deposit an increased amount of a collagen-rich extracellular matrix. Angiotensin II (ANGII) signaling, mediated via angiotensin II receptor type 1 (AGTR1) or type 2 (AGTR2), controls tissue remodeling in fibrosis, but the relevance of AGTR2 remains elusive. In the present study, we demonstrated increased expression of AGTR1 und AGTR2 in human and rodent lung tissues from patients with IPF and mice subjected to bleomycin-induced fibrosis, respectively. Both AGTR1 und AGTR2 localized to interstitial fibroblasts. Quantitative analysis of cell surface expression in primary mouse fibroblasts revealed a significant increase of AGTR2 surface expression in fibrotic fibroblasts, whereas AGTR1 surface expression levels remained similar. ANGII treatment of normal fibroblasts led to enhanced migration and proliferation, which was abrogated after pretreatment with losartan (LOS), an AGTR1 inhibitor. In contrast, in fibrotic fibroblasts, migration and proliferation was modified only by AGTR2, but not AGTR1 inhibition (using PD123319). ANGII-induced effects were mediated via phosphorylation of the mitogen-activated protein kinases p38 and p42/44, which was blocked via LOS and PD123319, respectively. Similar effects of AGTR1 and AGTR2 inhibition were observed using conditioned media of alveolar epithelial cells, a prominent source of ANGII in the lung in vivo. In summary, we conclude that ANGII signaling occurs primarily via AGTR1 in normal fibroblasts, while AGTR2-mediated effects are dominant on activated (myo)-fibroblasts, a receptor switch that may perturb epithelial-mesenchymal interaction, thereby further perpetuating fibrogenesis.

Hyperoxia modulates TGF-beta/BMP signaling in a mouse model of bronchopulmonary dysplasia.

Prematurely born infants who require oxygen therapy often develop bronchopulmonary dysplasia (BPD), a debilitating disorder characterized by pronounced alveolar hypoplasia. Hyperoxic injury is believed to disrupt critical signaling pathways that direct lung development, causing BPD. We investigated the effects of normobaric hyperoxia on transforming growth factor (TGF)-beta and bone morphogenetic protein (BMP) signaling in neonatal C57BL/6J mice exposed to 21% or 85% O(2) between postnatal days P1 and P28. Growth and respiratory compliance were significantly impaired in pups exposed to 85% O(2), and these pups also exhibited a pronounced arrest of alveolarization, accompanied by dysregulated expression and localization of both receptor (ALK-1, ALK-3, ALK-6, and the TGF-beta type II receptor) and Smad (Smads 1, 3, and 4) proteins. TGF-beta signaling was potentiated, whereas BMP signaling was impaired both in the lungs of pups exposed to 85% O(2) as well as in MLE-12 mouse lung epithelial cells and NIH/3T3 and primary lung fibroblasts cultured in 85% O(2). After exposure to 85% O(2), primary alveolar type II cells were more susceptible to TGF-beta-induced apoptosis, whereas primary pulmonary artery smooth muscle cells were unaffected. Exposure of primary lung fibroblasts to 85% O(2) significantly enhanced the TGF-beta-stimulated production of the alpha(1) subunit of type I collagen (Ialpha(1)), tissue inhibitor of metalloproteinase-1, tropoelastin, and tenascin-C. These data demonstrated that hyperoxia significantly affects TGF-beta/BMP signaling in the lung, including processes central to septation and, hence, alveolarization. The amenability of these pathways to genetic and pharmacological manipulation may provide alternative avenues for the management of BPD.

Impact of TASK-1 in human pulmonary artery smooth muscle cells.

The excitability of pulmonary artery smooth muscle cells (PASMC) is regulated by potassium (K+) conductances. Although studies suggest that background K+ currents carried by 2-pore domain K+ channels are important regulators of resting membrane potential in PASMC, their role in human PASMC is unknown. Our study tested the hypothesis that TASK-1 leak K+ channels contribute to the K+ current and resting membrane potential in human PASMC. We used the whole-cell patch-clamp technique and TASK-1 small interfering RNA (siRNA). Noninactivating K+ current performed by TASK-1 K+ channels were identified by current characteristics and inhibition by anandamide and acidosis (pH 6.3), each resulting in significant membrane depolarization. Moreover, we showed that TASK-1 is blocked by moderate hypoxia and activated by treprostinil at clinically relevant concentrations. This is mediated via protein kinase A (PKA)-dependent phosphorylation of TASK-1. To further confirm the role of TASK-1 channels in regulation of resting membrane potential, we knocked down TASK-1 expression using TASK-1 siRNA. The knockdown of TASK-1 was reflected by a significant depolarization of resting membrane potential. Treatment of human PASMC with TASK-1 siRNA resulted in loss of sensitivity to anandamide, acidosis, alkalosis, hypoxia, and treprostinil. These results suggest that (1) TASK-1 is expressed in human PASMC; (2) TASK-1 is hypoxia-sensitive and controls the resting membrane potential, thus implicating an important role for TASK-1 K+ channels in the regulation of pulmonary vascular tone; and (3) treprostinil activates TASK-1 at clinically relevant concentrations via PKA, which might represent an important mechanism underlying the vasorelaxing properties of prostanoids and their beneficial effect in vivo.

Impact of HIF-1alpha and HIF-2alpha on proliferation and migration of human pulmonary artery fibroblasts in hypoxia.

Proliferation of adventitial fibroblasts of small intrapulmonary arteries (FBPA) has been disclosed as an early event in the development of pulmonary hypertension and cor pulmonale in response to hypoxia. We investigated the role of hypoxia-inducible transcription factors (HIF) in human FBPA exposed to hypoxia. Primary cultures of FBPA displayed a strong mitogenic response to 24 h hypoxia, whereas the rate of apoptosis was significantly suppressed. In addition, the migration of FBPA was strongly increased under hypoxic conditions but not the expression of alpha-smooth muscle actin. Hypoxia induced a marked up-regulation (protein level) of both HIF-1alpha and HIF-2alpha, alongside with nuclear translocation of these transcription factors. Specific inhibition of either HIF-1alpha or HIF-2alpha was achieved by RNA interference technology, as proven by HIF-1alpha and HIF-2alpha mRNA and protein analysis and expression analysis of HIF downstream target genes. With the use of this approach, the hypoxia-induced proliferative response of the FBPA was found to be solely HIF-2alpha dependent, whereas the migratory response was significantly reduced by both HIF-1alpha and HIF-2alpha interference. In conclusion, HIF up-regulation is essential for hypoxic cellular responses in human pulmonary artery adventitial fibroblasts such as proliferation and migration, mimicking the pulmonary hypertensive phenotype in vivo. Differential HIF subtype dependency was noted, with HIF-2alpha playing a predominant role, which may offer future intervention strategies.