Marked alveolar apoptosis/proliferation imbalance in end-stage emphysema

Impaired Alveolar Re-Epithelialization in Pulmonary Emphysema

Alveolar type II (ATII) cells are progenitors in alveoli and can repair the alveolar epithelium after injury. They are intertwined with the microenvironment for alveolar epithelial cell homeostasis and re-epithelialization. A variety of ATII cell niches, transcription factors, mediators, and signaling pathways constitute a specific environment to regulate ATII cell function. Particularly, WNT/β-catenin, YAP/TAZ, NOTCH, TGF-β, and P53 signaling pathways are dynamically involved in ATII cell proliferation and differentiation, although there are still plenty of unknowns regarding the mechanism. However, an imbalance of alveolar cell death and proliferation was observed in patients with pulmonary emphysema, contributing to alveolar wall destruction and impaired gas exchange. Cigarette smoking causes oxidative stress and is the primary cause of this disease development. Aberrant inflammatory and oxidative stress responses result in loss of cell homeostasis and ATII cell dysfunction in emphysema. Here, we discuss the current understanding of alveolar re-epithelialization and altered reparative responses in the pathophysiology of this disease. Current therapeutics and emerging treatments, including cell therapies in clinical trials, are addressed as well.

Senescence: Pathogenic Driver in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is recognized as a disease of accelerated lung aging. Over the past two decades, mounting evidence suggests an accumulation of senescent cells within the lungs of patients with COPD that contributes to dysregulated tissue repair and the secretion of multiple inflammatory proteins, termed the senescence-associated secretory phenotype (SASP). Cellular senescence in COPD is linked to telomere dysfunction, DNA damage, and oxidative stress. This review gives an overview of the mechanistic contributions and pathologic consequences of cellular senescence in COPD and discusses potential therapeutic approaches targeting senescence-associated signaling in COPD.

The arginine methyltransferase PRMT7 promotes extravasation of monocytes resulting in tissue injury in COPD

Extravasation of monocytes into tissue and to the site of injury is a fundamental immunological process, which requires rapid responses via post translational modifications (PTM) of proteins. Protein arginine methyltransferase 7 (PRMT7) is an epigenetic factor that has the capacity to mono-methylate histones on arginine residues. Here we show that in chronic obstructive pulmonary disease (COPD) patients, PRMT7 expression is elevated in the lung tissue and localized to the macrophages. In mouse models of COPD, lung fibrosis and skin injury, reduced expression of PRMT7 associates with decreased recruitment of monocytes to the site of injury and hence less severe symptoms. Mechanistically, activation of NF-κB/RelA in monocytes induces PRMT7 transcription and consequential mono-methylation of histones at the regulatory elements of RAP1A, which leads to increased transcription of this gene that is responsible for adhesion and migration of monocytes. Persistent monocyte-derived macrophage accumulation leads to ALOX5 over-expression and accumulation of its metabolite LTB4, which triggers expression of ACSL4 a ferroptosis promoting gene in lung epithelial cells. Conclusively, inhibition of arginine mono-methylation might offer targeted intervention in monocyte-driven inflammatory conditions that lead to extensive tissue damage if left untreated.

Cigarette Smoke Particle-Induced Lung Injury and Iron Homeostasis

It is proposed that the mechanistic basis for non-neoplastic lung injury with cigarette smoking is a disruption of iron homeostasis in cells after exposure to cigarette smoke particle (CSP). Following the complexation and sequestration of intracellular iron by CSP, the host response (eg, inflammation, mucus production, and fibrosis) attempts to reverse a functional metal deficiency. Clinical manifestations of this response can present as respiratory bronchiolitis, desquamative interstitial pneumonitis, pulmonary Langerhans’ cell histiocytosis, asthma, pulmonary hypertension, chronic bronchitis, and pulmonary fibrosis. If the response is unsuccessful, the functional deficiency of iron progresses to irreversible cell death evident in emphysema and bronchiectasis. The subsequent clinical and pathological presentation is a continuum of lung injuries, which overlap and coexist with one another. Designating these non-neoplastic lung injuries after smoking as distinct disease processes fails to recognize shared relationships to each other and ultimately to CSP, as well as the common mechanistic pathway (ie, disruption of iron homeostasis).

GLIPR1 Protects Against Cigarette Smoke-Induced Airway Inflammation via PLAU/EGFR Signaling

Background

Chronic obstructive pulmonary disease (COPD) is a major health problem associated with high mortality worldwide. Cigarette smoke (CS) exposure is the main cause of COPD. Glioma pathogenesis-related protein 1 (GLIPR1) plays a key role in cell growth, proliferation, and invasion; however, the role of GLIPR1 in COPD remains unclear.

Methods

To clarify the involvement of GLIPR1 in COPD pathogenesis, Glipr1 knockout (Glipr1-/-) mice were generated. Wild-type (WT) and Glipr1-/- mice were challenged with CS for 3 months. To illustrate how GLIPR1 regulates CS-induced airway damage, knockdown experiments targeting GLIPR1 and PLAU, as well as overexpression experiments of PLAU, were performed with human bronchial epithelial cells.

Results

Compared with WT mice, Glipr1-/- mice showed exacerbated CS-induced airway damage including lung inflammation, airway wall thickening, and alveolar destruction. After CS exposure, total proteins, total white cells, neutrophils, lymphocytes, IL-6, and matrix metalloproteinase-9 increased significantly in lung of Glipr1-/- mice than those in lung of WT mice. Furthermore, in vivo and in vitro experiments demonstrated that silencing of GLIPR1 inactivated PLAU/EGFR signaling and promoted caspase-1-dependent pyroptosis (a mode of inflammatory cell death) induced by CS and CS extract exposure, respectively. In vitro experiments further revealed the interaction between GLIPR1 and PLAU, and silencing of PLAU blocked EGFR signaling and promoted pyroptosis, while overexpression of PLAU activated EGFR signaling and reversed pyroptosis.

Conclusion

To conclude, GLIPR1 played a pivotal role in COPD pathogenesis and protected against CS-induced inflammatory response and airway damage, including cell pyroptosis, through the PLAU/EGFR signaling. Thus, GLIPR1 may play a potential role in COPD treatment.

Cigarette smoke activates the parthanatos pathway of cell death in human bronchial epithelial cells

Tobacco smoke negatively affects human bronchial epithelial (HBE) cells and is directly implicated in the etiology of smoking related respiratory diseases. Smoke exposure causes double-stranded DNA breaks and DNA damage activates PARP-1, the key mediator of the parthanatos pathway of cell death. We hypothesize that smoke exposure activates the parthanatos pathway in HBE cells and represents a cell death mechanism that contributes to smoking related lung diseases. We exposed fully differentiated, primary HBE cells grown at the air liquid interface to cigarette smoke and evaluated them for parthanatos pathway activation. Smoke exposure induced mitochondrial to nuclear translocation of Apoptosis-Inducing Factor (AIF) and Endonuclease G (EndoG) within the first three hours characteristic of the parthanatos pathway. Exposing cells to an increasing number of cigarettes revealed that significant activation of the parthanatos pathway occurs after exposure to higher levels of smoke. Use of the specific PARP-1 inhibitor, BMN673, abrogated the effect of smoke induced activation of the parthanatos pathway. Smoke-mediated activation of the parthanatos pathway is increased in HBE cells originating from habitual smokers compared to non-smokers. This suggests that chronic smoke exposure leads to an increase in smoke-mediated activation of the parthanatos pathway and implicates its contribution in the pathogenesis of smoke-related lung diseases.

Ursolic Acid Protected Lung of Rats From Damage Induced by Cigarette Smoke Extract

Background: We found previously that ursolic acid (UA) administration could alleviate cigarette smoke-induced emphysema in rats partly through the unfolded protein response (UPR) PERK-CHOP and Nrf2 pathways, thus alleviating endoplasmic reticulum stress (ERS)-associated oxidative stress and cell apoptosis. We hypothesized that other UPR pathways may play similar roles in cigarette smoke extract (CSE)-induced emphysema. So, we sought to investigate the dynamic changes and effects of UPR and the downstream apoptotic pathways. Further, we investigated whether UA could alleviate CSE-induced emphysema and airway remodelling in rats, whether and when it exerts its effects through UPR pathways as well as Smads pathways.

Methods: One hundred eight Sprague Dawley (SD) rats were randomly divided into three groups: Sham group, CSE group, and UA group, and each group was further divided into three subgroups, administered CSE (vehicle) for 2, 3, or 4 weeks; each subgroup had 12 rats. We examined pathological changes, analyzed the three UPR signaling pathways and subsequent ERS, intrinsic and extrinsic apoptotic pathway indicators, as well as activation of Smad2,3 molecules in rat lungs.

Results: Exposure to CSE for 3 or 4 weeks could apparently induce emphysema and airway remodeling in rats, including gross and microscopic changes, alteration of mean alveolar number (MAN), mean linear intercept (MLI), and mean airway thickness in lung tissue sections. UA intervention could significantly alleviate CSE-induced emphysema and airway remodeling in rats. UA exerted its effects through ameliorating apoptosis by down regulating UPR signalling pathways and subsequent apoptosis pathways, as well as, downregulating p-Smad2 and p-Smad3 molecules.

Conclusions: UA attenuated CSE-induced emphysema and airway remodeling, exerting its effects partly through regulation of three UPR pathways, amelioration downstream apoptotic pathways, and alleviating activation of Smad2 and Smad3.

S100A8 Protects Human Primary Alveolar Type II Cells against Injury and Emphysema

Pulmonary emphysema is characterized by alveolar wall destruction, and cigarette smoking is the main risk factor in this disease development. S100A8 is a member of the S100 protein family, with an oxidative stress-related and antiinflammatory role. The mechanisms of human alveolar type II (ATII) cell injury contributing to emphysema pathophysiology are not completely understood. We wanted to determine whether S100A8 can protect ATII cells against injury induced by cigarette smoke and this disease development. We used freshly isolated ATII cells from nonsmoking and smoking organ donors, as well as patients with emphysema to determine S100A8 function. S100A8 protein and mRNA levels were low in individuals with this disease and correlated with its severity as determined by using lung tissue from areas with mild and severe emphysema obtained from the same patient. Its expression negatively correlated with high oxidative stress as observed by 4-hydroxynonenal levels. We also detected decreased serine phosphorylation within S100A8 by PKAα in this disease. This correlated with increased S100A8 ubiquitination by SYVN1. Moreover, we cultured ATII cells isolated from nonsmokers followed by treatment with cigarette smoke extract. We found that this exposure upregulated S100A8 expression. We also confirmed the cytoprotective role of S100A8 against cell injury using gain- and loss-of-function approaches in vitro. S100A8 knockdown sensitized cells to apoptosis induced by cigarette smoke. In contrast, S100A8 overexpression rescued cell injury. Our results suggest that S100A8 protects ATII cells against injury and cigarette smoke-induced emphysema. Targeting S100A8 may provide a potential therapeutic strategy for this disease.

Differential expression of heat shock proteins and activation of mitogen-activated protein kinases in A549 alveolar epithelial cells exposed to cigarette smoke extract

NEW FINDINGS

What is the central question of this study? What is the effect of cigarette smoke on cell death, oxidative damage, expression of heat shock proteins (HSPs) and activation of mitogen-activated protein kinases (MAPKs) in A549 alveolar epithelial cells? What is the main finding and its importance? Cigarette smoke induces cytotoxicity and oxidative damage to A549 cells, increases expression of different HSPs and activates MAPK signalling pathways. This could be related to inflammatory response and apoptosis observed in lungs of patients with smoking-related diseases.

ABSTRACT

Cigarette smoking is one of the main risk factors for development of chronic obstructive pulmonary disease (COPD). We previously reported that cigarette smoke (CS) induces damage to proteins and their ineffective degradation. Here, we hypothesize that CS could induce oxidative stress and cytotoxicity in lung epithelial cells through alterations of heat shock protein (HSP) expression and mitogen-activated protein kinase (MAPK) signalling pathways. We exposed A549 alveolar epithelial cells to various concentrations of cigarette smoke extract (CSE). Higher concentrations of CSE caused apoptosis of A549 cells after 4 h, while after 24 h cell viability was decreased, and lactate dehydrogenase in cell culture medium was increased as well as the number of necrotic cells. Concentrations of malondialdehyde (MDA) were elevated, while total thiol groups were decreased. Changes in the expression of HSPs (HSP70, HSP32 and HSP27) were time-dependent. After 6 h, CSE caused an increase in the expression of HSP70 and HSP32, while after 8 h all examined HSPs were up-regulated and remained increased up to 48 h. Treatment of A549 cells with CSE stimulated phosphorylation of extracellular signal-regulated kinase and p38 in a dose-dependent manner, while c-Jun N-terminal kinase activation was not detected. By using specific inhibitors, we demonstrated that MAPKs and HSPs interplay in CSE effects. In conclusion, our results show that MAPKs and HSPs are involved in the mechanism underlying CSE-induced cytotoxicity and oxidative damage to A549 alveolar epithelial cells. These processes could be related to inflammatory response and apoptosis observed in lungs of patients with smoking-related diseases, such as COPD.

Matrix metalloproteinases in emphysema

Several studies have implicated a causative role for specific matrix metalloproteinases (MMPs) in the development and progression of cigarette smoke-induced chronic obstructive pulmonary disease (COPD) and its severe sequela, emphysema. However, the precise function of any given MMP in emphysema remains an unanswered question. Emphysema results from the degradation of alveolar elastin - among other possible mechanisms - a process that is often thought to be caused by elastolytic proteinases made by macrophages. In this article, we discuss the data suggesting, supporting, or refuting causative roles of macrophage-derived MMPs, with a focus on MMPs-7, -9, -10, -12, and 28, in both the human disease and mouse models of emphysema. Findings from experimental models suggest that some MMPs, such as MMP-12, may directly breakdown elastin, whereas others, particularly MMP-10 and MMP-28, promote the development of emphysema by influencing the proteolytic and inflammatory activities of macrophages.

An Increased Proportion of Apoptosis in CD4⁺ T Lymphocytes Isolated from the Peripheral Blood in Patients with Stable Chronic Obstructive Pulmonary Disease

BACKGROUND

The pathophysiology of chronic obstructive pulmonary disease (COPD) includes inflammation, oxidative stress, an imbalance of proteases and antiproteases and apoptosis which has been focused on lately. Abnormal apoptotic events have been demonstrated in both epithelial and endothelial cells, as well as in inflammatory cells including neutrophils and lymphocytes in the lungs of COPD patients. An increased propensity of activated T lymphocytes to undergo apoptosis has been observed in the peripheral blood of COPD patients. Therefore, the apoptosis of T lymphocytes without activating them was investigated in this study.

METHODS

Twelve control subjects, 21 stable COPD patients and 15 exacerbated COPD patients were recruited in the study. The T lymphocytes were isolated from the peripheral blood using magnetically activated cell sorting. Apoptosis of the T lymphocytes was assessed with flow cytometry using Annexin V and 7-aminoactinomycin D. Apoptosis of T lymphocytes at 24 hours after the cell culture was measured so that the T lymphocyte apoptosis among the control and the COPD patients could be compared.

RESULTS

Stable COPD patients had increased rates of CD4⁺ T lymphocyte apoptosis at 24 hours after the cell culture, more than the CD4⁺ T lymphocyte apoptosis which appeared in the control group, while the COPD patients with acute exacerbation had an amplified response of CD4⁺ T lymphocyte apoptosis as well as of CD8⁺ T lymphocyte apoptosis at 24 hours after the cell culture.

CONCLUSION

Stable COPD patients have more apoptosis of CD4⁺ T lymphocytes, which can be associated with the pathophysiology of COPD in stable conditions.

Immunomodulatory effects of two different physical therapy modalities in patients with chronic obstructive pulmonary disease

[Purpose] Counteracting the systemic cytokine release and its inflammatory effects by improving respiratory muscle strength and controlling lung inflammation may be important for improving immune system in patients with chronic obstructive pulmonary disease, So the aim of the present study was to evaluate the effect of low level laser therapy and inspiratory muscle training on interleukin-6 (IL-6) as a marker of inflammation and CD4+/CD8+ ratio as a marker for T Lymphocytes in these patients. [Subjects and Methods] Forty male patients with stable COPD participated in the study, their ages ranged between 55−65 years. They were randomly divided into group (A) who received inspiratory muscle training and group (B) who received low level laser (LLL) acupuncture stimulation for about 8 week. [Results] There was a reduction in the concentration of plasma IL-6 associated with an increase in CD4+/CD8+ ratio in both groups, but laser was superior to inspiratory muscle training. IL-6 and CD4+/CD8+ were negatively correlated. [Conclusion] Both inspiratory muscle training and low level laser therapy are effective physical therapy modalities in promoting immune disturbances. The results also supported the superior role of LLLT over IMT in managing immune disturbances.

Reduced Frizzled Receptor 4 Expression Prevents WNT/β-Catenin-driven Alveolar Lung Repair in Chronic Obstructive Pulmonary Disease

RATIONALE

Chronic obstructive pulmonary disease (COPD), in particular emphysema, is characterized by loss of parenchymal alveolar tissue and impaired tissue repair. Wingless and INT-1 (WNT)/β-catenin signaling is reduced in COPD; however, the mechanisms thereof, specifically the role of the frizzled (FZD) family of WNT receptors, remain unexplored.

OBJECTIVES

To identify and functionally characterize specific FZD receptors that control downstream WNT signaling in impaired lung repair in COPD.

METHODS

FZD expression was analyzed in lung homogenates and alveolar epithelial type II (ATII) cells of never-smokers, smokers, patients with COPD, and two experimental COPD models by quantitative reverse transcriptase-polymerase chain reaction, immunoblotting, and immunofluorescence. The functional effects of cigarette smoke on FZD4, WNT/β-catenin signaling, and elastogenic components were investigated in primary ATII cells in vitro and in three-dimensional lung tissue cultures ex vivo. Gain- and loss-of-function approaches were applied to determine the effects of FZD4 signaling on alveolar epithelial cell wound healing and repair, as well as on expression of elastogenic components.

MEASUREMENTS AND MAIN RESULTS

FZD4 expression was reduced in human and experimental COPD lung tissues as well as in primary human ATII cells from patients with COPD. Cigarette smoke exposure down-regulated FZD4 expression in vitro and in vivo, along with reduced WNT/β-catenin activity. Inhibition of FZD4 decreased WNT/β-catenin-driven epithelial cell proliferation and wound closure, and it interfered with ATII-to-ATI cell transdifferentiation and organoid formation, which were augmented by FZD4 overexpression. Moreover, FZD4 restoration by overexpression or pharmacological induction led to induction of WNT/β-catenin signaling and expression of elastogenic components in three-dimensional lung tissue cultures ex vivo.

CONCLUSIONS

Reduced FZD4 expression in COPD contributes to impaired alveolar repair capacity.

Neutrophilic Inflammation in the Immune Responses of Chronic Obstructive Pulmonary Disease: Lessons from Animal Models

Chronic obstructive pulmonary disease (COPD) is a major cause of mortality worldwide, which is characterized by chronic bronchitis, destruction of small airways, and enlargement/disorganization of alveoli. It is generally accepted that the neutrophilic airway inflammation observed in the lungs of COPD patients is intrinsically linked to the tissue destruction and alveolar airspace enlargement, leading to disease progression. Animal models play an important role in studying the underlying mechanisms of COPD as they address questions involving integrated whole body responses. This review aims to summarize the current animal models of COPD, focusing on their advantages and disadvantages on immune responses and neutrophilic inflammation. Also, we propose a potential new animal model of COPD, which may mimic the most characteristics of human COPD pathogenesis, including persistent moderate-to-high levels of neutrophilic inflammation.

Pro-apoptotic Noxa is involved in ablative focal irradiation-induced lung injury

Although lung injury including fibrosis is a well‐documented side effect of lung irradiation, the mechanisms underlying its pathology are poorly understood. X‐rays are known to cause apoptosis in the alveolar epithelial cells of irradiated lungs, which results in fibrosis due to the proliferation and differentiation of fibroblasts and the deposition of collagen. Apoptosis and BH3‐only pro‐apoptotic proteins have been implicated in the pathogenesis of pulmonary fibrosis. Recently, we have established a clinically analogous experimental model that reflects focal high‐dose irradiation of the ipsilateral lung. The goal of this study was to elucidate the mechanism underlying radiation‐induced lung injury based on this model. A radiation dose of 90 Gy was focally delivered to the left lung of C57BL/6 mice for 14 days. About 9 days after irradiation, the mice began to show increased levels of the pro‐apoptotic protein Noxa in the irradiated lung alongside increased apoptosis and fibrosis. Suppression of Noxa expression by small interfering RNA protected cells from radiation‐induced cell death and decreased expression of fibrogenic markers. Furthermore, we showed that reactive oxygen species participate in Noxa‐mediated, radiation‐induced cell death. Taken together, our results show that Noxa is involved in X‐ray‐induced lung injury.

COPD immunopathology

The immunopathology of chronic obstructive pulmonary disease (COPD) is based on the innate and adaptive inflammatory immune responses to the chronic inhalation of cigarette smoking. In the last quarter of the century, the analysis of specimens obtained from the lower airways of COPD patients compared with those from a control group of age-matched smokers with normal lung function has provided novel insights on the potential pathogenetic role of the different cells of the innate and acquired immune responses and their pro/anti-inflammatory mediators and intracellular signalling pathways, contributing to a better knowledge of the immunopathology of COPD both during its stable phase and during its exacerbations. This also has provided a scientific rationale for new drugs discovery and targeting to the lower airways. This review summarises and discusses the immunopathology of COPD patients, of different severity, compared with control smokers with normal lung function.

Coactivator-Associated Arginine Methyltransferase-1 Function in Alveolar Epithelial Senescence and Elastase-Induced Emphysema Susceptibility

Chronic obstructive pulmonary disease (COPD) is characterized by an irreversible loss of lung function and is one of the most prevalent and severe diseases worldwide. A major feature of COPD is emphysema, which is the progressive loss of alveolar tissue. Coactivator-associated arginine methyltransferase-1 (CARM1) regulates histone methylation and the transcription of genes involved in senescence, proliferation, and differentiation. Complete loss of CARM1 leads to disrupted differentiation and maturation of alveolar epithelial type II (ATII) cells. We thus hypothesized that CARM1 regulates the development and progression of emphysema. To address this, we investigated the contribution of CARM1 to alveolar rarefication using the mouse model of elastase-induced emphysema in vivo and small interfering (si)RNA-mediated knockdown in ATII-like LA4 cells in vitro. We demonstrate that emphysema progression in vivo is associated with a time-dependent down-regulation of CARM1. Importantly, elastase-treated CARM1 haploinsufficient mice show significantly increased airspace enlargement (52.5 ± 9.6 μm versus 38.8 ± 5.5 μm; P < 0.01) and lung compliance (2.8 ± 0.32 μl/cm H2O versus 2.4 ± 0.4 μl/cm H2O; P < 0.04) compared with controls. The knockdown of CARM1 in LA4 cells led to decreased sirtuin 1 expression (0.034 ± 0.003 versus 0.022 ± 0.001; P < 0.05) but increased expression of p16 (0.27 ± 0.013 versus 0.31 ± 0.010; P < 0.5) and p21 (0.81 ± 0.088 versus 1.28 ± 0.063; P < 0.01) and higher β-galactosidase-positive senescent cells (50.57 ± 7.36% versus 2.21 ± 0.34%; P < 0.001) compared with scrambled siRNA. We further demonstrated that CARM1 haploinsufficiency impairs transdifferentiation and wound healing (32.18 ± 0.9512% versus 8.769 ± 1.967%; P < 0.001) of alveolar epithelial cells. Overall, these results reveal a novel function of CARM1 in regulating emphysema development and premature lung aging via alveolar senescence as well as impaired regeneration, repair, and differentiation of ATII cells.

Metabolomics screening identifies reduced L-carnitine to be associated with progressive emphysema

The progression of emphysema, a severe chronic lung disease, was found to be associated with reduced lung tissue-specific L-carnitine in a clinically relevant mouse model. Furthermore, supplementing mice with this metabolite improved lung function and impaired disease progression.

The aryl hydrocarbon receptor suppresses cigarette-smoke-induced oxidative stress in association with dioxin response element (DRE)-independent regulation of sulfiredoxin 1

The aryl hydrocarbon receptor (AhR) is a ubiquitously expressed receptor/transcription factor that mediates toxicological responses of environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Emerging evidence indicates that the AhR suppresses apoptosis and proliferation independent of exogenous ligands, including suppression of apoptosis by cigarette smoke, a key risk factor for chronic obstructive pulmonary disease (COPD). As cigarette smoke is a potent inducer of oxidative stress, a feature that may contribute to the development of COPD, we hypothesized that the AhR prevents smoke-induced apoptosis by regulating oxidative stress. Utilizing primary lung fibroblasts derived from AhR(+/+) and AhR(-/-) mice as well as A549 human lung adenocarcinoma cells deficient in AhR expression (A549-AhR(ko)), we first show that AhR(-/-) fibroblasts and A549-AhR(ko) epithelial cells have a significant increase in cigarette smoke extract (CSE)-induced oxidative stress compared to wild type. CSE induced a significant increase in the mRNA expression of key antioxidant genes, including Nqo1 and Srxn1, predominantly in AhR(+/+) fibroblasts, with significantly less induction in AhR(-/-) cells. The induction of Srxn1, but not Nqo1, was independent of dioxin-response element (DRE) binding as AhR(DBD/DBD) lung fibroblasts, which express an AhR incapable of binding the DRE, increased Srxn1 to a degree similar to wild-type cells in response to CSE. There was no difference in Nrf2 expression or activation based on AhR expression. Lung fibroblasts derived from COPD subjects have significantly less AhR protein expression compared with both never-smokers (Normal) and smokers (At Risk). Consequently, COPD-derived fibroblasts were less robust in their induction of both Nqo1 and Srxn1 mRNA after exposure to CSE, which also failed to activate the AhR in the COPD fibroblasts. Taken together, these results support a new role for the AhR in regulating antioxidant defense in lung structural cells, such that low AhR expression may facilitate the development or progression of COPD.

Increased innate and adaptive immune responses in induced sputum of young smokers

BACKGROUND AND OBJECTIVES

It is known that chronic obstructive pulmonary disease (COPD) development process is imperceptible and can be asymptomatic for 20 or more years. It is of great importance to diagnose early inflammatory changes that can lead to COPD in young asymptomatic cigarette smokers. The aim of our study was to analyze the cell spectrum of induced sputum (IS) of young cigarette smokers, with emphasis on T-regulatory cells.

MATERIALS AND METHODS

A total of 20 healthy nonallergic smokers, 20 nonsmokers and 20 COPD patients were enrolled in the study. After lung function measurements were taken, we performed sputum induction and analyzed sputum cells. We evaluated the cell count of FOXP3-positive, CD4⁺ and CD8⁺ T lymphocytes by immunocytochemistry staining, and the cell count of macrophages and neutrophils by May-Grünwald Giemsa staining.

RESULTS

Induced sputum of smokers contained a higher absolute amount of macrophages and neutrophils when compared to nonsmokers. FOXP3-positive cells in the sputum of young smokers showed a statistically significant increase when compared to nonsmokers. Induced sputum of COPD patients contained an increased absolute amount of neutrophils and FOXP3-positive Treg cells when compared to nonsmokers. Regression analysis showed that the amount of FOXP-3 positive cells, neutrophils and macrophages in the induced sputum was increasing with the number of pack years.

CONCLUSIONS

This study demonstrates that young smokers have early inflammatory changes in their airways that not only initiate nonspecific mechanisms recruiting neutrophils, but also involve specific immune mechanisms with recruitment of T regulatory lymphocytes. The lymphocyte response is probably adaptive.

Decreased proteasomal function accelerates cigarette smoke-induced pulmonary emphysema in mice

Chronic obstructive pulmonary disease (COPD) is a disease common in elderly people, characterized by progressive destruction of lung parenchyma and chronic inflammation of the airways. The pathogenesis of COPD remains unclear, but recent studies suggest that oxidative stress-induced apoptosis in alveolar cells contributes to emphysematous lung destruction. The proteasome is a multicatalytic enzyme complex that plays a critical role in proteostasis by rapidly destroying misfolded and modified proteins generated by oxidative and other stresses. Proteasome activity decreases with aging in many organs including lungs, and an age-related decline in proteasomal function has been implicated in various age-related pathologies. However, the role of the proteasome system in the pathogenesis of COPD has not been investigated. Recently, we have established a transgenic (Tg) mouse model with decreased proteasomal chymotrypsin-like activity, showing age-related phenotypes. Using this model, we demonstrate here that decreased proteasomal function accelerates cigarette smoke (CS)-induced pulmonary emphysema. CS-exposed Tg mice showed remarkable airspace enlargement and increased foci of inflammation compared with wild-type controls. Importantly, apoptotic cells were found in the alveolar walls of the affected lungs. Impaired proteasomal activity also enhanced apoptosis in cigarette smoke extract (CSE)-exposed fibroblastic cells derived from mice and humans in vitro. Notably, aggresome formation and prominent nuclear translocation of apoptosis-inducing factor were observed in CSE-exposed fibroblastic cells isolated from Tg mice. Collective evidence suggests that CS exposure and impaired proteasomal activity coordinately enhance apoptotic cell death in the alveolar walls that may be involved in the development and progression of emphysema in susceptible individuals such as the elderly.

Glucocorticoid-Augmented Efferocytosis Inhibits Pulmonary Pneumococcal Clearance in Mice by Reducing Alveolar Macrophage Bactericidal Function

Inhaled corticosteroids (ICS) increase community-acquired pneumonia (CAP) incidence in patients with chronic obstructive pulmonary disease (COPD) by unknown mechanisms. Apoptosis is increased in the lungs of COPD patients. Uptake of apoptotic cells (ACs) ("efferocytosis") by alveolar macrophages (AMøs) reduces their ability to combat microbes, including Streptococcus pneumoniae, the most common cause of CAP in COPD patients. Having shown that ICS significantly increase AMø efferocytosis, we hypothesized that this process, termed glucocorticoid-augmented efferocytosis, might explain the association of CAP with ICS therapy in COPD. To test this hypothesis, we studied the effects of fluticasone, AC, or both on AMøs of C57BL/6 mice in vitro and in an established model of pneumococcal pneumonia. Fluticasone plus AC significantly reduced TLR4-stimulated AMø IL-12 production, relative to either treatment alone, and decreased TNF-α, CCL3, CCL5, and keratinocyte-derived chemoattractant/CXCL1, relative to AC. Mice treated with fluticasone plus AC before infection with viable pneumococci developed significantly more lung CFUs at 48 h. However, none of the pretreatments altered inflammatory cell recruitment to the lungs at 48 h postinfection, and fluticasone plus AC less markedly reduced in vitro mediator production to heat-killed pneumococci. Fluticasone plus AC significantly reduced in vitro AMø killing of pneumococci, relative to other conditions, in part by delaying phagolysosome acidification without affecting production of reactive oxygen or nitrogen species. These results support glucocorticoid-augmented efferocytosis as a potential explanation for the epidemiological association of ICS therapy of COPD patients with increased risk for CAP, and establish murine experimental models to dissect underlying molecular mechanisms.

Sphingolipids as cell fate regulators in lung development and disease

Sphingolipids are a diverse class of signaling molecules implicated in many important aspects of cellular biology, including growth, differentiation, apoptosis, and autophagy. Autophagy and apoptosis are fundamental physiological processes essential for the maintenance of cellular and tissue homeostasis. There is great interest into the investigation of sphingolipids and their roles in regulating these key physiological processes as well as the manifestation of several disease states. With what is known to date, the entire scope of sphingolipid signaling is too broad, and a single review would hardly scratch the surface. Therefore, this review attempts to highlight the significance of sphingolipids in determining cell fate (e.g. apoptosis, autophagy, cell survival) in the context of the healthy lung, as well as various respiratory diseases including acute lung injury, acute respiratory distress syndrome, bronchopulmonary dysplasia, asthma, chronic obstructive pulmonary disease, emphysema, and cystic fibrosis. We present an overview of the latest findings related to sphingolipids and their metabolites, provide a short introduction to autophagy and apoptosis, and then briefly highlight the regulatory roles of sphingolipid metabolites in switching between cell survival and cell death. Finally, we describe functions of sphingolipids in autophagy and apoptosis in lung homeostasis, especially in the context of the aforementioned diseases.

Macrophage migration inhibitory factor is a novel determinant of cigarette smoke-induced lung damage

Cigarette smoke (CS) is the most common cause of chronic obstructive pulmonary diseases (COPD), including emphysema. CS exposure impacts all cell types within the airways and lung parenchyma, causing alveolar tissue destruction through four mechanisms: (1) oxidative stress; (2) inflammation; (3) protease-induced degradation of the extracellular matrix; and (4) enhanced alveolar epithelial and endothelial cell (EC) apoptosis. Studies in human pulmonary ECs demonstrate that macrophage migration inhibitory factor (MIF) antagonizes CS-induced apoptosis. Here, we used human microvascular ECs, an animal model of emphysema (mice challenged with chronic CS), and patient serum samples to address both the capacity of CS to alter MIF expression and the effects of MIF on disease severity. We demonstrate significantly reduced serum MIF levels in patients with COPD. In the murine model, chronic CS exposure resulted in decreased MIF mRNA and protein expression in the intact lung. MIF deficiency (Mif(-/-)) potentiated the toxicity of CS exposure in vivo via increased apoptosis of ECs, resulting in enhanced CS-induced tissue remodeling. This was linked to MIF's capacity to protect against double-stranded DNA damage and suppress p53 expression. Taken together, MIF appears to antagonize CS-induced toxicity in the lung and resultant emphysematous tissue remodeling by suppressing EC DNA damage and controlling p53-mediated apoptosis, highlighting a critical role of MIF in EC homeostasis within the lung.

Aryl hydrocarbon receptor-dependent regulation of miR-196a expression controls lung fibroblast apoptosis but not proliferation

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor implicated in the regulation of apoptosis and proliferation. Although activation of the AhR by xenobiotics such as dioxin inhibits the cell cycle and control apoptosis, paradoxically, AhR expression also promotes cell proliferation and survival independent of exogenous ligands. The microRNA (miRNA) miR-196a has also emerged as a regulator of proliferation and apoptosis but a relationship between the AhR and miR-196a is not known. Therefore, we hypothesized that AhR-dependent regulation of endogenous miR-196a expression would promote cell survival and proliferation. Utilizing lung fibroblasts from AhR deficient (AhR(-/-)) and wild-type (AhR(+/+)) mice, we show that there is ligand-independent regulation of miRNA, including low miR-196a in AhR(-/-) cells. Validation by qRT-PCR revealed a significant decrease in basal expression of miR-196a in AhR(-/-) compared to AhR(+/+) cells. Exposure to AhR agonists benzo[a]pyrene (B[a]P) and FICZ as well as AhR antagonist CH-223191 decreased miR-196a expression in AhR(+/+) fibroblasts concomitant with decreased AhR protein levels. There was increased proliferation only in AhR(+/+) lung fibroblasts in response to serum, corresponding to a decrease in p27(KIP1) protein, a cyclin-dependent kinase inhibitor. Increasing the cellular levels of miR-196a had no effect on proliferation or expression of p27(KIP1) in AhR(-/-) fibroblasts but attenuated cigarette smoke-induced apoptosis. This study provides the first evidence that AhR expression is essential for the physiological regulation of cellular miRNA levels- including miR-196a. Future experiments designed to elucidate the functional relationship between the AhR and miR-196a may delineate additional novel ligand-independent roles for the AhR.

Immune response in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major public health problem because of its high prevalence, rising incidence and associated socio-economic cost. The inhalation of toxic particles and gases, mostly tobacco smoke, is the main risk factor for COPD. Yet, not all smokers are equally susceptible to these toxic effects and only a percentage of them develop the disease (so-called 'susceptible smokers'). This, in combination with the observation that COPD shows familial aggregation, suggests that the genetic background of the smoker is a key element in the pathogenesis of the disease. On the other hand, it is well established that 'susceptible' smokers exhibit an enhanced inflammatory response of the lung parenchyma as compared with 'resistant' smokers (i.e., those who manage to maintain lung function within the normal age range despite their habit). Importantly, in COPD patients this inflammatory response does not resolve after quitting smoking, again at variance with resistant smokers. All in all, these observations suggest that the pathogenesis of COPD may involve, in some patients, an autoimmune component which contributes to the enhanced and persistent inflammatory response that characterizes the disease. Here we: i) review briefly the pathobiology of COPD; ii) present the available scientific evidence supporting a potential role for autoimmunity in COPD; iii) propose a three-step pathogenic hypothesis in the transition from smoking to COPD; and iv) discuss potential implications for the diagnosis and treatment of this frequent, growing, devastating and costly disease.

Distribution of T-cell subsets in BAL fluid of patients with mild to moderate COPD depends on current smoking status and not airway obstruction

BACKGROUND

COPD is characterized by chronic inflammation. CD8+ T cells and CD4+ T cells have both been implicated in the inflammatory response. We investigated whether the lymphocyte and T-cell subpopulations in BAL differ between patients with COPD who are current smokers and those who are ex-smokers.

METHODS

Forty never smokers, 40 smokers with normal lung function, and 38 patients with COPD, GOLD (Global Initiative for Chronic Obstructive Pulmonary Disease) stage I-II (27 smokers and 11 ex-smokers) underwent BAL. Using flow cytometry, cells were analyzed from BAL and blood for T-cell subsets, B cells, natural killer cells, and natural killer T (NKT)-like cells. The differentiation status of CD4+ T cells was also determined.

RESULTS

Smokers with or without COPD had higher percentages of CD8+ T cells and NKT-like cells in BAL than did never smokers and ex-smokers with COPD. Most of the NKT-like cells were CD8+. In contrast, the percentages of CD4+ T cells were lower in the smoking than in the nonsmoking groups. In blood, the frequency of CD4+ T cells was increased in the two smoking groups. Current smokers also had increased numbers of activated (CD69+) naive and effector CD4+ T cells in BAL compared with nonsmokers, particularly in patients with COPD. In male smokers with COPD, the percentage of CD8+ T cells in BAL positively correlated with the number of cigarettes per day.

CONCLUSIONS

Current smoking status has a greater impact than airway obstruction on the distribution of T-cell subsets in BAL of patients with mild to moderate COPD. This fact must be considered when the role of T cells in COPD is evaluated. Our results stress the importance of subgrouping patients with COPD in terms of smoking.

The role of bronchial epithelial cell apoptosis in the pathogenesis of COPD

There is an increased airway inflammation in the pathogenesis of chronic obstructive pulmonary disease (COPD), and it has been suggested that there may also be problem in the apoptosis and renewal of cells. However, there are limited human airway cell studies, in particular those from larger airways such as bronchi. We cultured primary human bronchial epithelial cells (HBECs) from bronchial explants of smokers (n = 6) without COPD and smokers with COPD (n = 8). Apoptosis was studied by fluorescence activated cell sorting. qRT-PCR was used to assess mRNA expression for proteins involving apoptosis including p21(CIP1/WAF1), p53, caspase-8 and caspase-9. Although there was no difference in the rate of viable cells between cells from smokers and COPDs, the level of early apoptotic cells was significantly increased in COPD cells [mean ± standard error of mean (SEM) = 4.86 ± 3.2 %, p = 0.015] as compared to smokers (mean ± SEM = 2.71 ± 1.62 %). In contrast, the rate of late apoptotic cells was significantly decreased in COPD cells (mean ± SEM = 9.82 ± 5.71 %) comparing to smokers (mean ± SEM = 15.21 ± 5.08 %, p = 0.003). Although expression of mRNA for p21(CIP1/WAF1) and caspase-9 was similar in both groups, p53 and caspase-8 mRNA expression was significantly greater in COPD cells. These findings suggest that HBEC apoptosis is increased in COPD, and that this involves p53 and caspase-8 pathways.

Macrophage migration inhibitory factor deficiency in chronic obstructive pulmonary disease

The pathogenesis of chronic obstructive pulmonary disease (COPD) remains poorly understood. Cellular senescence and apoptosis contribute to the development of COPD; however, crucial regulators of these underlying mechanisms remain unknown. Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that antagonizes both apoptosis and premature senescence and may be important in the pathogenesis of COPD. This study examines the role of MIF in the pathogenesis of COPD. Mice deficient in MIF (Mif(-/-)) or the MIF receptor CD74 (Cd74(-/-)) and wild-type (WT) controls were aged for 6 mo. Both Mif(-/-) and Cd74(-/-) mice developed spontaneous emphysema by 6 mo of age compared with WT mice as measured by lung volume and chord length. This was associated with activation of the senescent pathway markers p53/21 and p16. Following exposure to cigarette smoke, Mif(-/-) mice were more susceptible to the development of COPD and apoptosis compared with WT mice. MIF plasma concentrations were measured in a cohort of 224 human participants. Within a subgroup of older current and former smokers (n = 72), MIF concentrations were significantly lower in those with COPD [8.8, 95%CI (6.7-11.0)] compared with those who did not exhibit COPD [12.7 ng/ml, 95%CI (10.6-14.8)]. Our results suggest that both MIF and the MIF receptor CD74 are required for maintenance of normal alveolar structure in mice and that decreases in MIF are associated with COPD in human subjects.

Ceramides: a potential therapeutic target in pulmonary emphysema

Background

The aim of this manuscript was to characterize airway ceramide profiles in a rodent model of elastase-induced emphysema and to examine the effect of pharmacological intervention directed towards ceramide metabolism.

Methods

Adult mice were anesthetized and treated with an intratracheal instillation of elastase. Lung function was measured, broncho-alveolar lavage fluid collected and histological and morphometrical analysis of lung tissue performed within 3 weeks after elastase injection, with and without sphingomyelinase inhibitors or serine palmitoyltransferase inhibitor. Ceramides in broncho-alveolar lavage (BAL) fluid were quantified by tandem mass spectrometry.

Results

BAL fluid showed a transient increase in total protein and IgM, and activated macrophages and neutrophils. Ceramides were transiently upregulated at day 2 after elastase treatment. Histology showed persistent patchy alveolar destruction at day 2 after elastase installation. Acid and neutral sphingomyelinase inhibitors had no effect on BAL ceramide levels, lung function or histology. Addition of a serine palmitoyltransferase inhibitor ameliorated lung function changes and reduced ceramides in BAL.

Conclusions

Ceramides were increased during the acute inflammatory phase of elastase-induced lung injury. Since addition of a serine palmitoyltransferase inhibitor diminished the rise in ceramides and ameliorated lung function, ceramides likely contributed to the early phase of alveolar destruction and are a potential therapeutic target in the elastase model of lung emphysema.

Herpes virus infection is associated with vascular remodeling and pulmonary hypertension in idiopathic pulmonary fibrosis

Background

Pulmonary hypertension (PH) represents an important complication of idiopathic pulmonary fibrosis (IPF) with a negative impact on patient survival. Herpes viruses are thought to play an etiological role in the development and/or progression of IPF. The influence of viruses on PH associated with IPF is unknown. We aimed to investigate the influence of viruses in IPF patients focusing on aspects related to PH. A laboratory mouse model of gamma-herpesvirus (MHV-68) induced pulmonary fibrosis was also assessed.

Methods

Lung tissue samples from 55 IPF patients and 41 controls were studied by molecular analysis to detect various viral genomes. Viral molecular data obtained were correlated with mean pulmonary arterial pressure (mPAP) and arterial remodelling. Different clinical and morphological variables were studied by univariate and multivariate analyses at time of transplant and in the early post-transplant period. The same lung tissue analyses were performed in MHV-68 infected mice.

Results

A higher frequency of virus positive cases was found in IPF patients than in controls (p = 0.0003) and only herpes virus genomes were detected. Viral cases showed higher mPAP (p = 0.01), poorer performance in the six minute walking test (6MWT; p = 0.002) and higher frequency of primary graft (PGD) dysfunction after lung transplant (p = 0.02). Increased arterial thickening, particularly of the intimal layer (p = 0.002 and p = 0.004) and higher TGF-β expression (p = 0.002) were demonstrated in viral cases. The remodelled vessels showed increased vessel cell proliferation (Ki-67 positive cells) in the proximity to metaplastic epithelial cells and macrophages. Viral infection was associated with higher mPAP (p = 0.03), poorer performance in the 6MWT (p = 0.008) and PGD (p = 0.02) after adjusting for other covariates/intermediate factors. In MHV-68 infected mice, morphological features were similar to those of patients.

Conclusion

Herpesviral infections may contribute to the development of PH in IPF patients.

Ceramide expression and cell homeostasis in chronic obstructive pulmonary disease

BACKGROUND

Increased expression of ceramide has been detected in emphysema. Ceramide promotes autophagy and apoptosis, which concur with cellular homeostasis.

OBJECTIVES

To determine whether ceramide expression is associated with the development of chronic obstructive pulmonary disease (COPD) and with altered cellular homeostasis in lung parenchyma.

METHODS

We studied 10 subjects with severe COPD, 13 with mild/moderate COPD, 11 with idiopathic pulmonary fibrosis (IPF), 12 non-COPD smokers, and 11 nonsmoking controls. The immunoreactivity for ceramide along with markers of autophagy (LC3B), apoptosis (cleaved caspase-3), and cell proliferation (MIB1) was quantified in alveolar walls.

RESULTS

Ceramide expression was increased in COPD patients compared with control smokers and was related to the impairment of gas exchange but not to the degree of airflow limitation. In COPD, an important activation of apoptosis and autophagy pathways was observed, particularly in patients with severe disease, that was not counterbalanced by cell proliferation. Upregulation of ceramide was observed even in subjects with IPF in whom activation of apoptosis and autophagy was negligible and cell proliferation was instead the most prominent feature.

CONCLUSIONS

Ceramide expression, which is increased in COPD and even more so in IPF, appears to be neither specific nor related to COPD severity, probably representing a broader marker of lung damage. In contrast, apoptosis and autophagy are characteristics of the COPD pathology, particularly in its most severe stage.

Genetic ablation of the aryl hydrocarbon receptor causes cigarette smoke-induced mitochondrial dysfunction and apoptosis

Cigarette smoke is the primary risk factor for chronic obstructive pulmonary disease (COPD). Alterations in the balance between apoptosis and proliferation are involved in the etiology of COPD. Fibroblasts and epithelial cells are sensitive to the oxidative properties of cigarette smoke, and whose loss may precipitate the development of COPD. Fibroblasts express the aryl hydrocarbon receptor (AhR), a transcription factor that attenuates pulmonary inflammation and may also regulate apoptosis. We hypothesized the AhR would prevent apoptosis caused by cigarette smoke. Using genetically deleted in vitro AhR expression models and an established method of cigarette smoke exposure, we report that AhR expression regulates fibroblasts proliferation and prevents morphological features of apoptosis, including membrane blebbing and chromatin condensation caused by cigarette smoke extract (CSE). Absence of AhR expression results in cleavage of PARP, lamin, and caspase-3. Mitochondrial dysfunction, including cytochrome c release, was associated with loss of AhR expression, indicating activation of the intrinsic apoptotic cascade. Heightened sensitivity of AhR-deficient fibroblasts was not the result of alterations in GSH, Nrf2, or HO-1 expression. Instead, AhR(-/-) cells had significantly less MnSOD and CuZn-SOD expression, enzymes that protects against oxidative stress. The ability of the AhR to suppress apoptosis was not restricted to fibroblasts, as siRNA-mediated knockdown of the AhR in lung epithelial cells also increased sensitivity to smoke-induced apoptosis. Collectively, these results suggest that cigarette smoke induced loss of lung structural support (i.e. fibroblasts, epithelial cells) caused by aberrations in AhR expression may explain why some smokers develop lung diseases such as COPD.

Idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is a devastating, age-related lung disease of unknown cause that has few treatment options. This disease was once thought to be a chronic inflammatory process, but current evidence indicates that the fibrotic response is driven by abnormally activated alveolar epithelial cells (AECs). These cells produce mediators that induce the formation of fibroblast and myofibroblast foci through the proliferation of resident mesenchymal cells, attraction of circulating fibrocytes, and stimulation of the epithelial to mesenchymal transition. The fibroblast and myofibroblast foci secrete excessive amounts of extracellular matrix, mainly collagens, resulting in scarring and destruction of the lung architecture. The mechanisms that link idiopathic pulmonary fibrosis with ageing and aberrant epithelial activation are unknown; evidence suggests that the abnormal recapitulation of developmental pathways and epigenetic changes have a role. In this Seminar, we review recent data on the clinical course, therapeutic options, and underlying mechanisms thought to be involved in the pathogenesis of idiopathic pulmonary fibrosis.

Cigarette smoke exposure aggravates air space enlargement and alveolar cell apoptosis in Smad3 knockout mice

The concept of genetic susceptibility factors predisposing cigarette smokers to develop emphysema stems from the clinical observation that only a fraction of smokers develop clinically significant chronic obstructive pulmonary disease. We investigated whether Smad3 knockout mice, which develop spontaneous air space enlargement after birth because of a defect in transforming growth factor-β (TGF-β) signaling, develop enhanced alveolar cell apoptosis and air space enlargement following cigarette smoke exposure. We investigated Smad3(-/-) and Smad3(+/+) mice at different adult ages and determined air space enlargement, alveolar cell proliferation, and apoptosis. Furthermore, laser-capture microdissection and real-time PCR were used to measure compartment-specific gene expression. We then compared the effects of cigarette smoke exposure on Smad3(-/-) and littermate controls. Smad3 knockout resulted in the development of air space enlargement in the adult mouse and was associated with decreased alveolar VEGF levels and activity and increased alveolar cell apoptosis. Cigarette smoke exposure aggravated air space enlargement and alveolar cell apoptosis. We also found increased Smad2 protein expression and phosphorylation, which was enhanced following cigarette smoke exposure, in Smad3-knockout animals. Double immunofluorescence analysis revealed that endothelial apoptosis started before epithelial apoptosis. Our data indicate that balanced TGF-β signaling is not only important for regulation of extracellular matrix turnover, but also for alveolar cell homeostasis. Impaired signaling via the Smad3 pathway results in alveolar cell apoptosis and alveolar destruction, likely via increased Smad2 and reduced VEGF expression and might represent a predisposition for accelerated development of emphysema due to cigarette smoke exposure.

[Structural abnormalities and inflammation in COPD: a focus on small airways]

Chronic obstructive pulmonary disease (COPD) is characterized by poorly reversible airflow limitation associated with airway remodelling and inflammation of both large and small airways. The site of airflow obstruction in COPD is located in the small airways, justifying a focus on this compartment. The structural abnormalities that are found in bronchioles with a diameter less than 2mm are characterized by increased airway wall thickness with peribronchial fibrosis, and by luminal obstruction by mucous exudates. Destruction of alveolar walls, the hallmark of emphysema, may be related to protease-antiprotease imbalance, and to mechanisms involving apoptosis, senescence, and autoimmunity. Cigarette smoke inhalation triggers the recruitment of innate immune cells (neutrophils and macrophages) and putatively adaptive immunity mediated via T and B lymphocytes and lymphoid follicles in the small airways. These data suggest a potential role for therapies that can target remodelling and inflammation in the small airways of patients with COPD.

Impairment of phagocytosis of apoptotic cells and its role in chronic airway diseases

Phagocytosis of dying cells is a complex and dynamic process coordinated by the interaction of many surface molecules, adaptors, and chemotactic molecules, and it is controlled at multiple levels. This well regulated clearance process is of utmost importance for the development and homeostasis of organisms because defective or inefficient phagocytosis may contribute to human pathologies. In this review we discuss recent advances in the knowledge of the molecular interactions involved in recognition and clearance of apoptotic cells and how derangement of these processes can contribute to the pathogenesis of chronic airway diseases such as chronic obstructive pulmonary disease, cystic fibrosis and asthma. We will briefly consider how different types of macrophages are implicated in chronic airway diseases. Finally, we will address possible therapeutic strategies, such as the use of macrolide antibiotics and statins, for modulating apoptotic cell clearance.

L-arginine reduces mitochondrial dysfunction and airway injury in murine allergic airway inflammation

Bronchial epithelial injury is the hall mark of asthma which is a chronic airway inflammatory disease. We have shown the mitochondrial ultrastructural changes and dysfunction in bronchial epithelia of OVA induced mice. Reduced L-arginine bioavailability in asthma leads to increased formation of peroxynitrite which could induce mitochondrial dysfunction. We have also shown that L-arginine administration attenuates experimental asthma and reduces peroxynitrite. In this study, we wanted to determine the effect of L-arginine on mitochondrial dysfunction and airway injury in allergic airway inflammation. To determine this, L-arginine was administered to ovalbumin sensitized and challenged mice during allergen challenges. Mitochondrial and cytosolic fractions were purified from the lung to determine key mitochondrial functions, and mitochondrial ultrastructural changes in bronchial epithelia of first generation bronchi were determined. It was found that L-arginine administration increased mitochondrial cytochrome c oxidase activity, reduced cytosolic cytochrome c, increased lung ATP levels, reduced DNA fragmentation in bronchial epithelia and restored the ultrastructural changes of mitochondria of bronchial epithelia. In addition, L-arginine administration reduced the widening of intercellular spaces between adjacent bronchial epithelia. These findings indicated that L-arginine administration reduced airway injury and restored mitochondrial dysfunction in murine allergic airway inflammation.

p53 mediates cigarette smoke-induced apoptosis of pulmonary endothelial cells: inhibitory effects of macrophage migration inhibitor factor

Exposure to cigarette smoke (CS) is the most common cause of emphysema, a debilitating pulmonary disease histopathologically characterized by the irreversible destruction of lung architecture. Mounting evidence links enhanced endothelial apoptosis causally to the development of emphysema. However, the molecular determinants of human endothelial cell apoptosis and survival in response to CS are not fully defined. Such determinants could represent clinically relevant targets for intervention. We show here that CS extract (CSE) triggers the death of human pulmonary macrovascular endothelial cells (HPAECs) through a caspase 9-dependent apoptotic pathway. Exposure to CSE results in the increased expression of p53 in HPAECs. Using the p53 inhibitor, pifithrin-α (PFT-α), and RNA interference (RNAi) directed at p53, we demonstrate that p53 function and expression are required for CSE-mediated apoptosis. The expression of macrophage migration inhibitory factor (MIF), an antiapoptotic cytokine produced by HPAECs, also increases in response to CSE exposure. The addition of recombinant human MIF prevents cell death from exposure to CSE. Further, the suppression of MIF or its receptor/binding partner, Jun activation domain-binding protein 1 (Jab-1), with RNAi enhances the sensitivity of human pulmonary endothelial cells to CSE via a p53-dependent (PFT-α-inhibitable) pathway. Finally, we demonstrate that MIF is a negative regulator of p53 expression in response to CSE, placing MIF upstream of p53 as an antagonist of CSE-induced apoptosis. We conclude that MIF can protect human vascular endothelium from the toxic effects of CSE via the antagonism of p53-mediated apoptosis.

Matrix modulation of compensatory lung regrowth and progenitor cell proliferation in mice

Mechanical stress is an important modulator of lung morphogenesis, postnatal lung development, and compensatory lung regrowth. The effect of mechanical stress on stem or progenitor cells is unclear. We examined whether proliferative responses of epithelial progenitor cells, including dually immunoreactive (CCSP and proSP-C) progenitor cells (CCSP+/SP-C+) and type II alveolar epithelial cells (ATII), are affected by physical factors found in the lung of emphysematics, including loss of elastic recoil, reduced elastin content, and alveolar destruction. Mice underwent single lung pneumonectomy (PNY) to modulate transpulmonary pressure (mechanical stress) and to stimulate lung regeneration. Control mice underwent sham thoracotomy. Plombage of different levels was employed to partially or completely abolish this mechanical stress. Responses to graded changes in transpulmonary pressure were assessed in elastin-insufficient mice (elastin +/-, ELN+/-) and elastase-treated mice with elastase-induced emphysema. Physiological regrowth, morphometry (linear mean intercept; Lmi), and the proliferative responses of CCSP+/SP-C+, Clara cells, and ATII were evaluated. Plombage following PNY significantly reduced transpulmonary pressure, regrowth, and CCSP+/SP-C+, Clara cell, and ATII proliferation following PNY. In the ELN+/- group, CCSP+/SP-C+ and ATII proliferation responses were completely abolished, although compensatory lung regrowth was not significantly altered. In contrast, in elastase-injured mice, compensatory lung regrowth was significantly reduced, and ATII but not CCSP+/SP-C+ proliferation responses were impaired. Elastase injury also reduced the baseline abundance of CCSP+/SP-C+, and CCSP+/SP-C+ were found to be displaced from the bronchioalveolar duct junction. These data suggest that qualities of the extracellular matrix including elastin content, mechanical stress, and alveolar integrity strongly influence the regenerative capacity of the lung, and the patterns of cell proliferation in the lungs of adult mice.

The possible role of granzyme B in the pathogenesis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a highly prevalent inflammatory lung condition characterized by airways disease and emphysema, and the precise mechanism of pathogenesis is poorly understood. The consistent features of COPD include protease-antiprotease imbalance, inflammation and accelerated aging caused by apoptosis or senescence. One family of molecules involved in all of these processes is the granzymes, serine proteases with the best-known member being granzyme B (GzmB). The majority of GzmB is released unidirectionally towards target cells, but GzmB can also be released nonspecifically and escape into the extracellular environment. GzmB is capable of cleaving extracellular matrix (ECM) proteins in vitro, and the accumulation of GzmB in the extracellular milieu during chronic inflammation in COPD could contribute to ECM degradation and remodelling and, consequently, the emphysematous phenotype in the lung. Preliminary studies suggest that increased GzmB expression is associated with increased COPD severity, and this may represent a promising new target for drug and biomarker discovery in COPD. In this paper, we review the potential pathogenic contributions of GzmB to the pathogenesis of COPD.

Elastin expression in very severe human COPD

Alveolar elastic fibres are key targets of proteases during the pathogenesis of chronic obstructive pulmonary disease (COPD). In the current study, we hypothesised that a response to injury leads to enhanced alveolar elastin gene expression in very severe COPD. Lung samples obtained from 43 patients, including 11 with very severe COPD (stage 4), 10 donors, 10 with moderate/severe COPD (stage 2-3) and 12 non-COPD subjects, were analysed for elastin mRNA expression by real-time RT-PCR and in situ hybridisation. Alveolar elastic fibres were visualised using Hart's staining of sections of frozen inflated lungs obtained from 11 COPD stage 4 patients and three donor lungs. Compared with donors, non-COPD and stage 2-3 COPD, elastin mRNA expression was significantly increased in very severe COPD lungs (12-fold change), and localised in situ hybridisation induced elastin expression to alveolar walls. Compared with donors, alveolar elastic fibres also comprised a greater volume fraction of total lung tissue in very severe COPD lungs (p<0.01), but elastic fibre content was not increased per lung volume, and desmosine content was not increased. The present study demonstrates enhanced alveolar elastin expression in very severe COPD. The efficiency of this potential repair mechanism and its regulation remain to be demonstrated.