Raquel R. Bunge

Blockade of IL-6 Trans Signaling Attenuates Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease with progressive fibrosis and death within 2–3 y of diagnosis. IPF incidence and prevalence rates are increasing annually with few effective treatments available. Inhibition of IL-6 results in the attenuation of pulmonary fibrosis in mice. It is unclear whether this is due to blockade of classical signaling, mediated by membrane-bound IL-6Rα, or trans signaling, mediated by soluble IL-6Rα (sIL-6Rα). Our study assessed the role of sIL-6Rα in IPF. We demonstrated elevations of sIL-6Rα in IPF patients and in mice during the onset and progression of fibrosis. We demonstrated that protease-mediated cleavage from lung macrophages was important in production of sIL-6Rα. In vivo neutralization of sIL-6Rα attenuated pulmonary fibrosis in mice as seen by reductions in myofibroblasts, fibronectin, and collagen in the lung. In vitro activation of IL-6 trans signaling enhanced fibroblast proliferation and extracellular matrix protein production, effects relevant in the progression of pulmonary fibrosis. Taken together, these findings demonstrate that the production of sIL-6Rα from macrophages in the diseased lung contributes to IL-6 trans signaling that in turn influences events crucial in pulmonary fibrosis.

Adenosine A2B receptor and hyaluronan modulate pulmonary hypertension associated with Chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death worldwide. The development of pulmonary hypertension (PH) in patients with COPD is strongly associated with increased mortality. Chronic inflammation and changes to the lung extracellular matrix (ECM) have been implicated in the pathogenesis of COPD, yet the mechanisms that lead to PH secondary to COPD remain unknown. Our experiments using human lung tissue show increased expression levels of the adenosine A2B receptor (ADORA2B) and a heightened deposition of hyaluronan (HA; a component of the ECM) in remodeled vessels of patients with PH associated with COPD. We also demonstrate that the expression of HA synthase 2 correlates with mean pulmonary arterial pressures in patients with COPD, with and without a secondary diagnosis of PH. Using an animal model of airspace enlargement and PH, we show that the blockade of ADORA2B is able to attenuate the development of a PH phenotype that correlates with reduced levels of HA deposition in the vessels and the down-regulation of genes involved in the synthesis of HA.

Hypoxia-induced deoxycytidine kinase contributes to epithelial proliferation in pulmonary fibrosis.

RATIONALE Idiopathic pulmonary fibrosis (IPF) is a deadly lung disease with few therapeutic options. Apoptosis of alveolar epithelial cells, followed by abnormal tissue repair characterized by hyperplastic epithelial cell formation, is a pathogenic process that contributes to the progression of pulmonary fibrosis. However, the signaling pathways responsible for increased proliferation of epithelial cells remain poorly understood. OBJECTIVES To investigate the role of deoxycytidine kinase (DCK), an important enzyme for the salvage of deoxynucleotides, in the progression of pulmonary fibrosis. METHODS DCK expression was examined in the lungs of patients with IPF and mice exposed to bleomycin. The regulation of DCK expression by hypoxia was studied in vitro and the importance of DCK in experimental pulmonary fibrosis was examined using a DCK inhibitor and alveolar epithelial cell-specific knockout mice. MEASUREMENTS AND MAIN RESULTS DCK was elevated in hyperplastic alveolar epithelial cells of patients with IPF and in mice exposed to bleomycin. Increased DCK was localized to cells associated with hypoxia, and hypoxia directly induced DCK in alveolar epithelial cells in vitro. Hypoxia-induced DCK expression was abolished by silencing hypoxia-inducible factor 1α and treatment of bleomycin-exposed mice with a DCK inhibitor attenuated pulmonary fibrosis in association with decreased epithelial cell proliferation. Furthermore, DCK expression, and proliferation of epithelial cells and pulmonary fibrosis was attenuated in mice with conditional deletion of hypoxia-inducible factor 1α in the alveolar epithelium. CONCLUSIONS Our findings suggest that the induction of DCK after hypoxia plays a role in the progression of pulmonary fibrosis by contributing to alveolar epithelial cell proliferation.

Macrophage bone morphogenic protein receptor 2 depletion in idiopathic pulmonary fibrosis and Group III pulmonary hypertension.

Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease of unknown etiology. The development of pulmonary hypertension (PH) is considered the single most significant predictor of mortality in patients with chronic lung diseases. The processes that govern the progression and development of fibroproliferative and vascular lesions in IPF are not fully understood. Using human lung explant samples from patients with IPF with or without a diagnosis of PH as well as normal control tissue, we report reduced BMPR2 expression in patients with IPF or IPF+PH. These changes were consistent with dampened P-SMAD 1/5/8 and elevated P-SMAD 2/3, demonstrating reduced BMPR2 signaling and elevated TGF-β activity in IPF. In the bleomycin (BLM) model of lung fibrosis and PH, we also report decreased BMPR2 expression compared with control animals that correlated with vascular remodeling and PH. We show that genetic abrogation or pharmacological inhibition of interleukin-6 leads to diminished markers of fibrosis and PH consistent with elevated levels of BMPR2 and reduced levels of a collection of microRNAs (miRs) that are able to degrade BMPR2. We also demonstrate that isolated bone marrow-derived macrophages from BLM-exposed mice show reduced BMPR2 levels upon exposure with IL6 or the IL6+IL6R complex that are consistent with immunohistochemistry showing reduced BMPR2 in CD206 expressing macrophages from lung sections from IPF and IPF+PH patients. In conclusion, our data suggest that depletion of BMPR2 mediated by a collection of miRs induced by IL6 and subsequent STAT3 phosphorylation as a novel mechanism participating to fibroproliferative and vascular injuries in IPF.

Hypoxia-induced deoxycytidine kinase expression contributes to apoptosis in chronic lung disease

Chronic obstructive pulmonary disease (COPD) is characterized by persistent inflammation and tissue remodeling and is a leading cause of death in the United States. Increased apoptosis of pulmonary epithelial cells is thought to play a role in COPD development and progression. Identification of signaling pathways resulting in increased apoptosis in COPD can be used in the development of novel therapeutic interventions. Deoxyadenosine (dAdo) is a DNA breakdown product that amplifies lymphocyte apoptosis by being phosphorylated to deoxyadenosine triphosphate (dATP). dAdo is maintained at low levels by adenosine deaminase (ADA). This study demonstrated that mice lacking ADA developed COPD manifestations in association with elevated dAdo and dATP levels and increased apoptosis in the lung. Deoxycitidine kinase (DCK), a major enzyme for dAdo phosphorylation, was up‐regulated in mouse and human airway epithelial cells in association with air‐space enlargement. Hypoxia was identified as a novel regulator of DCK, and inhibition of DCK resulted in diminished dAdo‐mediated apoptosis in the lungs. Our results suggest that activating the dAdo‐DCK‐dATP pathway directly results in increased apoptosis in the lungs of mice with air‐space enlargement and suggests a novel therapeutic target for the treatment of COPD.—Weng, T., Karmouty‐Quintana, H., Garcia‐Morales, L. J., Molina, J. G., Pedroza, M., Bunge, R. R., Bruckner, B. A., Loebe, M., Seethamraju, H., and Blackburn, M. R. Hypoxia‐induced deoxycytidine kinase expression contributes to apoptosis in chronic lung disease. FASEB J. 27, 2013–2026 (2013). www.fasebj.org

Altered Hypoxic–Adenosine Axis and Metabolism in Group III Pulmonary Hypertension

Group III pulmonary hypertension (PH) is a highly prevalent and deadly lung disorder with limited treatment options other than transplantation. Group III PH affects patients with ongoing chronic lung injury, such as idiopathic pulmonary fibrosis (IPF). Between 30 and 40% of patients with IPF are diagnosed with PH. The diagnosis of PH has devastating consequences to these patients, leading to increased morbidity and mortality, yet the molecular mechanisms involved in the development of PH in patients with chronic lung disease remain elusive. Our hypothesis was that the hypoxic-adenosinergic system is enhanced in patients with group III PH compared with patients with IPF with no PH. Explanted lung tissue was analyzed for markers of the hypoxic-adenosine axis, including expression levels of hypoxia-inducible factor (HIF)-1A, adenosine A2B receptor, CD73, and equilibrative nucleotide transporter-1. In addition, we assessed whether altered mitochondrial metabolism was present in these samples. Increased expression of HIF-1A was observed in tissues from patients with group III PH. These changes were consistent with increased evidence of adenosine accumulation in group III PH. A novel observation of our study was of evidence suggesting altered mitochondrial metabolism in lung tissue from group III PH leading to increased succinate levels that are able to further stabilize HIF-1A. Our data demonstrate that the hypoxic-adenosine axis is up-regulated in group III PH and that subsequent succinate accumulation may play a part in the development of group III PH.

Superior mesenteric artery mycotic aneurysm in patients with left ventricular assist device support and intravenous drug abuse.

Mycotic aneurysm of the superior mesenteric artery (SMA) is one of the complications associated with infective endocarditis. However, there are no previous case reports in the literature describing mycotic SMA aneurysm after left ventricular assist device (LVAD) implantation. We describe the case of a 31-year-old male diagnosed with congestive heart failure due to nonischemic dilated cardiomyopathy who underwent LVAD implantation for bridge to heart transplantation. The postoperative course was uneventful, and the patient was maintained on anticoagulation and antiplatelet therapy. There were no signs of pump failure or device-related infections. However, 7 months post-LVAD support, the patient complained of abdominal symptoms (nausea and vomiting) with low-grade fever. Computed tomography identified an aneurysmal change of the SMA (2.2 × 1.8 cm). There was no evidence of thrombus or septic vegetation inside the heart. Aneurysm and segmental small bowel resection was performed. Pathological study revealed typical findings of mycotic aneurysm with significant infiltration of inflammatory cells. The patient, however, expired due to concurrent brain hemorrhage. Postmortem study indicated no sign of pump thrombus or septic emboli inside the pump or inflow/outflow conduit. This case report presents a rare mycotic aneurysm that developed in the SMA after chronic LVAD support.

Large Cardiac Tumor Managed With Resection and Two Ventricular Assist Devices

Symptomatic cardiac tumors can lead to a rapid clinical deterioration and death. Prompt surgical resection is ideal in this situation as it is the only proven treatment to date. We report the radical resection of a large malignant cardiac tumor that obstructed the right ventricular outflow tract. Extensive resection precluded reconstruction and limited the ability to implant a total artificial heart; thus, 2 paracorporeal devices were implanted instead.