Dayna J. Groskreutz

Respiratory Syncytial Virus Induces TLR3 Protein and Protein Kinase R, Leading to Increased Double-Stranded RNA Responsiveness in Airway Epithelial Cells

Respiratory syncytial virus (RSV) preferentially infects airway epithelial cells, causing bronchiolitis, upper respiratory infections, asthma exacerbations, chronic obstructive pulmonary disease exacerbations, and pneumonia in immunocompromised hosts. A replication intermediate of RSV is dsRNA. This is an important ligand for both the innate immune receptor, TLR3, and protein kinase R (PKR). One known effect of RSV infection is the increased responsiveness of airway epithelial cells to subsequent bacterial ligands (i.e., LPS). In this study, we examined a possible role for RSV infection in increasing amounts and responsiveness of another TLR, TLR3. These studies demonstrate that RSV infection of A549 and human tracheobronchial epithelial cells increases the amounts of TLR3 and PKR in a time-dependent manner. This leads to increased NF-κB activity and production of the inflammatory cytokine IL-8 following a later exposure to dsRNA. Importantly, TLR3 was not detected on the cell surface at baseline but was detected on the cell surface after RSV infection. The data demonstrate that RSV, via an effect on TLR3 and PKR, sensitizes airway epithelial cells to subsequent dsRNA exposure. These findings are consistent with the hypothesis that RSV infection sensitizes the airway epithelium to subsequent viral and bacterial exposures by up-regulating TLRs and increasing their membrane localization.

Constitutive ERK MAPK Activity Regulates Macrophage ATP Production and Mitochondrial Integrity

A unique feature of human alveolar macrophages is their prolonged survival in the face of a stressful environment. We have shown previously that the ERK MAPK is constitutively active in these cells and is important in prolonging cell survival. This study examines the role of the ERK pathway in maintaining mitochondrial energy production. The data demonstrate that ATP levels in alveolar macrophages depend on intact mitochondria and optimal functioning of the electron transport chain. Significant levels of MEK and ERK localize to the mitochondria and inhibition of ERK activity induces an early and profound depletion in cellular ATP coincident with a loss of mitochondrial transmembrane potential. The effect of ERK suppression on ATP levels was specific, since it did not occur with PI3K/Akt, p38, or JNK suppression. ERK inhibition led to cytosolic release of mitochondrial proteins and caspase activation. Both ERK inhibition and mitochondrial blockers induced loss of plasma membrane permeability and cell death. The cell death induced by ERK inhibition had hallmarks of both apoptotic (caspase activation) and necrotic (ATP loss) cell death. By blocking ERK inhibition-induced reactive oxygen species, caspase activation was prevented, although necrotic pathways continued to induce cell death. This suggests that mitochondrial dysfunction caused by ERK inhibition generates both apoptotic and necrotic cell death-inducing pathways. As a composite, these data demonstrate a novel mitochondrial role for ERK in maintaining mitochondrial membrane potential and ATP production in human alveolar macrophages.

Respiratory Syncytial Virus Decreases p53 Protein to Prolong Survival of Airway Epithelial Cells

Respiratory syncytial virus (RSV) is a clinically important pathogen. It preferentially infects airway epithelial cells causing bronchiolitis in infants, exacerbations in patients with obstructive lung disease, and life-threatening pneumonia in the immunosuppressed. The p53 protein is a tumor suppressor protein that promotes apoptosis and is tightly regulated for optimal cell growth and survival. A critical negative regulator of p53 is murine double minute 2 (Mdm2), an E3 ubiquitin ligase that targets p53 for proteasome degradation. Mdm2 is activated by phospho-Akt, and we previously showed that RSV activates Akt and delays apoptosis in primary human airway epithelial cells. In this study, we explore further the mechanism by which RSV regulates p53 to delay apoptosis but paradoxically enhance inflammation. We found that RSV activates Mdm2 1–6 h after infection resulting in a decrease in p53 6–24 h after infection. The p53 down-regulation correlates with increased airway epithelial cell longevity. Importantly, inhibition of the PI3K/Akt pathway blocks the activation of Mdm2 by RSV and preserves the p53 response. The effects of RSV infection are antagonized by Nutlin-3, a specific chemical inhibitor that prevents the Mdm2/p53 association. Nutlin-3 treatment increases endogenous p53 expression in RSV infected cells, causing earlier cell death. This same increase in p53 enhances viral replication and limits the inflammatory response as measured by IL-6 protein. These findings reveal that RSV decreases p53 by enhancing Akt/Mdm2-mediated p53 degradation, thereby delaying apoptosis and prolonging survival of airway epithelial cells.

Respiratory Syncytial Virus Synergizes with Th2 Cytokines to Induce Optimal Levels of TARC/CCL17

Respiratory syncytial virus (RSV) is a ubiquitous virus that preferentially infects airway epithelial cells, causing asthma exacerbations and severe disease in immunocompromised hosts. Acute RSV infection induces inflammation in the lung. Thymus- and activation-regulated chemokine (TARC) recruits Th2 cells to sites of inflammation. We found that acute RSV infection of BALB/c mice increased TARC production in the lung. Immunization of BALB/c mice with individual RSV proteins can lead to the development of Th1- or Th2-biased T cell responses in the lung after RSV infection. We primed animals with a recombinant vaccinia virus expressing either the RSV fusion (F) protein or the RSV attachment (G) protein, inducing Th1- and Th2-biased pulmonary memory T cell responses, respectively. After RSV infection, TARC production significantly increased in the vaccinia virus G-primed animals only. These data suggest a positive feedback loop for TARC production between RSV infection and Th2 cytokines. RSV-infected lung epithelial cells cultured with IL-4 or IL-13 demonstrated a marked increase in the production of TARC. The synergistic effect of RSV and IL-4/IL-13 on TARC production reflected differential induction of NFκB and STAT6 by the two stimuli (both are in the TARC promoter). These findings demonstrate that RSV induces a chemokine TARC that has the potential to recruit Th2 cells to the lung.

Respiratory Syncytial Virus Limits α Subunit of Eukaryotic Translation Initiation Factor 2 (eIF2α) Phosphorylation to Maintain Translation and Viral Replication

The impact of respiratory syncytial virus (RSV) on morbidity and mortality is significant in that it causes bronchiolitis in infants, exacerbations in patients with obstructive lung disease, and pneumonia in immunocompromised hosts. RSV activates protein kinase R (PKR), a cellular kinase relevant to limiting viral replication (Groskreutz, D. J., Monick, M. M., Powers, L. S., Yarovinsky, T. O., Look, D. C., and Hunninghake, G. W. (2006) J. Immunol. 176, 1733–1740). It is activated by autophosphorylation, likely triggered by a double-stranded RNA intermediate during replication of the virus. In most instances, ph-PKR targets the α subunit of eukaryotic translation initiation factor 2 (eIF2α) protein via phosphorylation, leading to an inhibition of translation of cellular and viral protein. However, we found that although ph-PKR increases in RSV infection, significant eIF2α phosphorylation is not observed, and inhibition of protein translation does not occur. RSV infection attenuates eIF2α phosphorylation by favoring phosphatase rather than kinase activity. Although PKR is activated, RSV sequesters PKR away from eIF2α by binding of the kinase to the RSV N protein. This occurs in conjunction with an increase in the association of the phosphatase, PP2A, with eIF2α following PKR activation. The result is limited phosphorylation of eIF2α and continued translation of cellular and viral proteins.

Cigarette Smoke Alters Respiratory Syncytial Virus–Induced Apoptosis and Replication

Individuals exposed to cigarette smoke have a greater number and severity of viral infections, including respiratory syncytial virus (RSV) infections, than do nonsmokers, but the cellular mechanism is unknown. Our objective was to determine the mechanism by which cigarette smoke augments viral infection. We hypothesize that cigarette smoke causes necrosis and prevents virus-induced cellular apoptosis, and that this is associated with increased inflammation and viral replication. Primary airway epithelial cells were exposed to cigarette smoke extract for 2 days, followed by 1 day of RSV exposure. Western blot detection of cleaved caspases 3 and 7 showed less apoptosis when cells were treated with cigarette smoke before viral infection. This finding was confirmed with ELISA and TUNEL detection of apoptosis. Measures of cell viability, including propidium iodide staining, ATP assay, and cell counts, indicated that cigarette smoke causes necrosis rather than virus-induced apoptosis. Using plaque assay and fluorescently-labeled RSV, we showed that although there were less live cells in the cigarette smoke-pretreated group, viral load was increased. The effect was inhibited by pretreatment of cells with N-acetylcysteine and aldehyde dehydrogenase, suggesting that the effect was primarily mediated by reactive aldehydes. Cigarette smoke causes necrosis rather than apoptosis in viral infection, resulting in increased inflammation and enhanced viral replication.

WHO’s in Second?: A Practical Review of World Health Organization Group 2 Pulmonary Hypertension

World Health Organization (WHO) group 2 pulmonary hypertension (PH) due to left-side heart disease (ie, heart failure or left-sided valvular heart disease) is the most common form of PH in western countries. Distinguishing patients with WHO group 2 PH, particularly the subset of patients with PH due to heart failure with preserved ejection fraction (HFpEF), from those with WHO group 1 pulmonary arterial hypertension (PAH) is challenging. Separating the two conditions is of vital importance because treatment strategies differ completely. Furthermore, therapies that are indicated for WHO group 1 PAH may be harmful in patients with WHO group 2 PH. We review the somewhat confusing PH nomenclature and the WHO classification system and rationale behind it. We then focus on left-side heart disorders that cause PH. An aging population and advances in the medical management of common cardiovascular disorders have caused the prevalence of heart failure to rise significantly, with more than one-half of patients having HFpEF. We review contemporary studies that focus on clinical and echocardiographic findings that help to distinguish HFpEF from PAH in the patient with PH. We discuss the typical, and sometimes atypical, hemodynamic profiles that characterize these two groups, review challenges in the interpretation of data obtained by right-sided heart catheterization, and highlight special maneuvers that may be required for accurate diagnosis. Finally, we review the largely disappointing studies on the use of PAH-specific therapies in patients with WHO group 2 PH, including the use of prostacyclins, endothelin receptor antagonists, and the more promising phosphodiesterase-5 inhibitors.

Recognizing the Importance of Respiratory Syncytial Virus in Chronic Obstructive Pulmonary Disease

Acute exacerbations of chronic obstructive pulmonary disease (COPD) are responsible for a large proportion of the health care dollar expenditure, morbidity, and mortality related to COPD. Respiratory infections are the most common cause of acute exacerbations, but recent evidence indicates that the importance of respiratory syncytial virus (RSV) infection in COPD is under-appreciated. Improved detection of RSV using techniques based on the polymerase chain reaction accounts for much of the increased recognition of the importance of this virus in COPD patients. Furthermore, COPD patients may be more susceptible to RSV infection, possibly due to RSV-or immune response-induced pulmonary effects that are altered by age, environmental exposures, genetics, COPD itself, or a combination of these. However, although RSV infection occurs throughout life, viral and host factors that place COPD patients at increased risk are unclear. The complexities of RSV effects in COPD present opportunities for research with the goal of developing approaches to selectively modify damaging viral effects (e.g., altered airway function), while retaining beneficial immunity (e.g., clearance of virus) in COPD patients. This review explores the role RSV plays in acute exacerbations of COPD, the potential for RSV disease in chronic stable COPD, and newer concepts in RSV diagnosis, epidemiology, and host defense.

Recent Advances in Chest MedicineWHO's in Second?: A Practical Review of World Health Organization Group 2 Pulmonary Hypertension

World Health Organization (WHO) group 2 pulmonary hypertension (PH) due to left-side heart disease (ie, heart failure or left-sided valvular heart disease) is the most common form of PH in western countries. Distinguishing patients with WHO group 2 PH, particularly the subset of patients with PH due to heart failure with preserved ejection fraction (HFpEF), from those with WHO group 1 pulmonary arterial hypertension (PAH) is challenging. Separating the two conditions is of vital importance because treatment strategies differ completely. Furthermore, therapies that are indicated for WHO group 1 PAH may be harmful in patients with WHO group 2 PH. We review the somewhat confusing PH nomenclature and the WHO classification system and rationale behind it. We then focus on left-side heart disorders that cause PH. An aging population and advances in the medical management of common cardiovascular disorders have caused the prevalence of heart failure to rise significantly, with more than one-half of patients having HFpEF. We review contemporary studies that focus on clinical and echocardiographic findings that help to distinguish HFpEF from PAH in the patient with PH. We discuss the typical, and sometimes atypical, hemodynamic profiles that characterize these two groups, review challenges in the interpretation of data obtained by right-sided heart catheterization, and highlight special maneuvers that may be required for accurate diagnosis. Finally, we review the largely disappointing studies on the use of PAH-specific therapies in patients with WHO group 2 PH, including the use of prostacyclins, endothelin receptor antagonists, and the more promising phosphodiesterase-5 inhibitors.