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

MiR-216a reduces apoptosis of pulmonary microvascular endothelial cells in COPD by targeting DNMT1

INTRODUCTION

Abnormal apoptosis of pulmonary microvascular endothelial cells (PMVECs) participates in the pathogenesis of COPD. Studies have shown that microRNAs (miRNAs) contribute to the pathogenesis of pulmonary diseases by regulating cell apoptosis. The present study aimed to investigate the effects of miR-216a in cigarette smoke extract (CSE)-induced apoptosis of PMVECs in COPD and explore the potential mechanisms.

METHODS

The emphysema model mice were treated with CSE and CS exposure. The expression of miR-216a and DNA methyltransferase 1 (DNMT1) was assessed in emphysema mice and COPD patients. The miR-216a mimic and Lenti-DNMT1 were transfected into PMVECs to identify the underlying mechanisms. The expression levels of miR-216a and DNMT1 were detected by real-time quantitative polymerase chain reaction (RT-qPCR) or Western blot. Moreover, cell apoptosis was examined by flow cytometry assays.

RESULTS

The results show that the expression of miR-216a was decreased, whereas the expression of DNMT1 was increased in the lung tissue of emphysema mice and COPD patients. In addition, the expression of miR-216a was significantly reduced in CSE-treated PMVECs, and the overexpression of miR-216a attenuated CSE-induced PMVEC apoptosis. Furthermore, the expression of DNMT1 was increased in the CSE-induced PMVECs and then was reduced after the overexpression of miR-216a in the CSE-stimulated PMVECs. Luciferase reporter assays confirmed the target reaction between miR-216a and DNMT1. Also, the overexpression of DNMT1 was able to reverse the anti-apoptotic effect of miR-216a in CSE-induced PMVECs.

CONCLUSIONS

The results indicate that miR-216a may play a crucial role in CSE-induced apoptosis by directly regulating its target gene DNMT1 in COPD. It provides insights into the function of MiR-216a/DNMT1 as a potential molecule in COPD.

Early Origins of Chronic Obstructive Pulmonary Disease: Prenatal and Early Life Risk Factors

The main risk factor for chronic obstructive pulmonary disease (COPD) is active smoking. However, a considerable amount of people with COPD never smoked, and increasing evidence suggests that adult lung disease can have its origins in prenatal and early life. This article reviews some of the factors that can potentially affect lung development and lung function trajectories throughout the lifespan from genetics and prematurity to respiratory tract infections and childhood asthma. Maternal smoking and air pollution exposure were also analyzed among the environmental factors. The adoption of preventive strategies to avoid these risk factors since the prenatal period may be crucial to prevent, delay the onset or modify the progression of COPD lung disease throughout life.

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).

Advances in Smoking Related In Vitro Inhalation Toxicology: A Perspective Case of Challenges and Opportunities from Progresses in Lung-on-Chip Technologies

The inhalation toxicology of multifaceted particulate matter from the environment, cigarette smoke, and e-cigarette liquid vapes is a major research topic concerning the adverse effect of these items on lung tissue. In vitro air-liquid interface (ALI) culture models hold more potential in an inhalation toxicity assessment. Apropos to e-cigarette toxicity, the multiflavor components of the vapes pose a complex experimental bottleneck. While an appropriate ALI setup has been one part of the focus to overcome this, parallel attention towards the development of an ideal exposure system has pushed the field forward. With the advent of microfluidic devices, lung-on-chip (LOC) technologies show enormous opportunities in in vitro smoke-related inhalation toxicity. In this review, we provide a framework, establish a paradigm about smoke-related inhalation toxicity testing in vitro, and give a brief overview of breathing LOC experimental design concepts. The capabilities with optimized bioengineering approaches and microfluidics and their fundamental pros and cons are presented with specific case studies. The LOC model can imitate the structural, functional, and mechanical properties of human alveolar-capillary interface and are more reliable than conventional in vitro models. Finally, we outline current perspective challenges as well as opportunities of future development to smoking lungs-on-chip technologies based on advances in soft robotics, machine learning, and bioengineering.

Senescence associated long non-coding RNA 1 regulates cigarette smoke-induced senescence of type II alveolar epithelial cells through sirtuin-1 signaling

OBJECTIVE

The primary aim of our study was to explore the mechanisms through which long non-coding RNA (lncRNA)-mediated sirtuin-1 (SIRT1) signaling regulates type II alveolar epithelial cell (AECII) senescence induced by a cigarette smoke-media suspension (CSM).

METHODS

Pharmacological SIRT1 activation was induced using SRT2104 and senescence-associated lncRNA 1 (SAL-RNA1) was overexpressed. The expression of SIRT1, FOXO3a, p53, p21, MMP-9, and TIMP-1 in different groups was detected by qRT-PCR and Western blotting; the activity of SA-β gal was detected by staining; the binding of SIRT1 to FOXO3a and p53 gene transcription promoters was detected by Chip.

RESULTS

We found that CSM increased AECII senescence, while SAL-RNA1 overexpression and SIRT1 activation significantly decreased levels of AECII senescence induced by CSM. Using chromatin immunoprecipitation, we found that SIRT1 bound differentially to transcriptional complexes on the FOXO3a and p53 promoters.

CONCLUSION

Our results suggested that lncRNA-SAL1-mediated SIRT1 signaling reduces senescence of AECIIs induced by CSM. These findings suggest a new therapeutic target to limit the irreversible apoptosis of lung epithelial cells in COPD patients.

The role of cigarette smoke-induced pulmonary vascular endothelial cell apoptosis in COPD

Chronic obstructive pulmonary disease (COPD) is one of the most common chronic respiratory diseases with high morbidity and mortality. It has become the fifth most burdened and the third most deadly disease in the global economy and increases year by year. The prevention and treatment of COPD are urgent. Smoking is the main and most common risk factor for COPD. Cigarette smoke (CS) contains a large number of toxic substances, can cause a series of changes in the trachea, lung tissue, pulmonary blood vessels, and promotes the occurrence and development of COPD. In recent years, the development of epigenetics and molecular biology have provided new guidance for revealing the pathogenesis, diagnosis, and treatment of diseases. The latest research indicates that pulmonary vascular endothelial cell apoptosis initiates and participates in the pathogenesis of COPD. In this review, we summarize the current research on the epigenetic mechanisms and molecular biology of CS-induced pulmonary vascular endothelial cell apoptosis in COPD, providing a new research direction for pathogenesis of COPD and a new target for the diagnosis, treatment, and prevention of COPD.

Bronchopulmonary dysplasia: what are its links to COPD?

Emerging evidence suggests that adverse early life events can affect long-term health trajectories throughout life. Preterm birth, in particular, is a significant early life event that affects approximately 10% of live births. Worldwide, prematurity is the number one cause of death in children less than 5 years of age and has been shown to disrupt normal lung development with lasting effects into adult life. Along with impaired lung development, interventions used to support gas exchange and other sequelae of prematurity can lead to the development of bronchopulmonary dysplasia (BPD). BPD is a chronic respiratory disease of infancy characterized by alveolar simplification, small airways disease, and pulmonary vascular changes. Although many survivors of BPD improve with age, survivors of BPD often have chronic lung disease characterized by airflow obstruction and intermittent pulmonary exacerbations. Long-term lung function trajectories as measured by FEV1 can be lower in children and adults with a history BPD. In this review, we discuss the epidemiology and manifestations of BPD and its long-term consequences throughout childhood and into adulthood. Available evidence suggests that disrupted lung development, genetic susceptibility and subsequent environment and infectious events that occur in prenatal and postnatal life likely increase the predisposition of children with BPD to develop early onset chronic obstructive pulmonary disease (COPD). The reviews of this paper are available via the supplemental material section.

Cigarette Smoke Triggers IL-33-associated Inflammation in a Model of Late-Stage Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a worldwide threat. Cigarette smoke (CS) exposure causes cardiopulmonary disease and COPD and increases the risk for pulmonary tumors. In addition to poor lung function, patients with COPD are susceptible to bouts of dangerous inflammation triggered by pollutants or infection. These severe inflammatory episodes can lead to additional exacerbations, hospitalization, further deterioration of lung function, and reduced survival. Suitable models of the inflammatory conditions associated with CS, which potentiate the downward spiral in patients with COPD, are lacking, and the underlying mechanisms that trigger exacerbations are not well understood. Although initial CS exposure activates a protective role for vascular endothelial growth factor (VEGF) functions in barrier integrity, chronic exposure depletes the pulmonary VEGF guard function in severe COPD. Thus, we hypothesized that mice with compromised VEGF production and challenged with CS would trigger human-like severe inflammatory progression of COPD. In this model, we discovered that CS exposure promotes an amplified IL-33 cytokine response and severe disease progression. Our VEGF-knockout model combined with CS recapitulates severe COPD with an influx of IL-33-expressing macrophages and neutrophils. Normally, IL-33 is quickly inactivated by a post-translational disulfide bond formation. Our results reveal that BAL fluid from the CS-exposed, VEGF-deficient cohort promotes a significantly prolonged lifetime of active proinflammatory IL-33. Taken together, our data demonstrate that with the loss of a VEGF-mediated protective barrier, the CS response switches from a localized danger to an uncontrolled long-term and long-range, amplified, IL-33-mediated inflammatory response that ultimately destroys lung function.

LncRNA‑mediated SIRT1/FoxO3a and SIRT1/p53 signaling pathways regulate type II alveolar epithelial cell senescence in patients with chronic obstructive pulmonary disease

The loss of alveolar structure and airspace enlargement are major pathological changes in chronic obstructive pulmonary disease (COPD). Type II alveolar epithelial cells (AECII) are involved in maintaining lung tissue repair and alveolar homeostasis. Long non‑coding RNAs (lncRNAs) are involved in multi‑regulating gene transcription, affecting processes including embryonic development, cell differentiation and cellular senescence. The primary aim of the present study was to explore the mechanisms of AECII senescence regulated by lncRNA‑mediated sirtuin 1 (SIRT1) and forkhead box O 3a (FoxO3a) signaling pathways in patients with COPD. Lung tissues from patients with COPD exhibited pathological characteristics and significantly increased senescence‑associated β‑galactosidase activity. Furthermore, the expression levels of senescence‑associated lncRNA1 (SAL‑RNA1), SIRT1 and FoxO3a were reduced, but SAL‑RNA2, SAL‑RNA3, p53 and p21 were upregulated in the lung tissues of patients with COPD compared with control. The results of the present study indicated that lncRNA‑mediated SIRT1/p53 and FoxO3a signaling pathways may regulate AECII senescence in the pathogenesis of COPD, which may provide a novel experimental basis for the treatment of COPD.

The Role of Mitochondria and Oxidative/Antioxidative Imbalance in Pathobiology of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a common preventable and treatable disease, characterized by persistent airflow limitation that is usually progressive and associated with an enhanced chronic inflammatory response in the airways and the lung to noxious particles or gases. The major risk factor of COPD, which has been proven in many studies, is the exposure to cigarette smoke. However, it is 15-20% of all smokers who develop COPD. This is why we should recognize the pathobiology of COPD as involving a complex interaction between several factors, including genetic vulnerability. Oxidant-antioxidant imbalance is recognized as one of the significant factors in COPD pathogenesis. Numerous exogenous and endogenous sources of ROS are present in pathobiology of COPD. One of endogenous sources of ROS is mitochondria. Although leakage of electrons from electron transport chain and forming of ROS are the effect of physiological functioning of mitochondria, there are various intra- and extracellular factors which may increase this amount and significantly contribute to oxidative-antioxidative imbalance. With the coexistence with impaired antioxidant defence, all these issues lead to oxidative and carbonyl stress. Both of these states play a significant role in pathobiology of COPD and may account for development of major comorbidities of this disease.

Altered expression of the CCN genes in the lungs of mice in response to cigarette smoke exposure and viral and bacterial infections

The CCN proteins are key signaling and regulatory molecules involved in many biological functions and contribute to malignant and non-malignant lung diseases. Despite the high morbidity and mortality of the lung respiratory infectious diseases, there is very little data related to the expression of the CCNs during infection. We investigated in mice the pulmonary mRNA expression levels of five CCNs (1 to 5) in response to influenza A virus (IAV) and bacterial agents (Nontypeable Haemophilus influenzae (NTHi), lipopolysaccharide (LPS) and lipoteichoic acid (LTA)). IAV, NTHi, LPS or LTA were instilled intranasally into mice. Mice were also exposed for 4days or 8weeks to cigarette smoke alone or prior infection to IAV in order to determine if CS modifies the CCN response to a viral infection. All challenges induced a robust inflammation. The mRNA expression of CCN1, CCN2 and CCN3 was decreased after short exposure to CS whereas prolonged exposure altered the expression of CCN1, CCN3 and CCN4. Influenza A virus infection increased CCN1, 2, 4 and 5 mRNA levels but expression of CCN3 was significantly decreased. Acute CS exposure prior infection had little effect on the expression of CCN genes but prolonged exposure abolished the IAV-dependent induction. Treatment with LPS or LTA and infection with NTHi revealed that both Gram-positive and Gram-negative bacteria rapidly modulate the expression of the CCN genes. Our findings reveal that several triggers of lung inflammation influence differently the CCN genes. CCN3 deserves special attention since its mRNA expression is decreased by all the triggers studied.

Murine models of cardiovascular comorbidity in chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) have an increased risk for cardiovascular disease (CVD). Currently, COPD patients with atherosclerosis (i.e., the most important underlying cause of CVD) receive COPD therapy complemented with standard CVD therapy. This may, however, not be the most optimal treatment. To investigate the link between COPD and atherosclerosis and to develop specific therapeutic strategies for COPD patients with atherosclerosis, a substantial number of preclinical studies using murine models have been performed. In this review, we summarize the currently used murine models of COPD and atherosclerosis, both individually and combined, and discuss the relevance of these models for studying the pathogenesis and development of new treatments for COPD patients with atherosclerosis. Murine and clinical studies have provided complementary information showing a prominent role for systemic inflammation and oxidative stress in the link between COPD and atherosclerosis. These and other studies showed that murine models for COPD and atherosclerosis are useful tools and can provide important insights relevant to understanding the link between COPD and CVD. More importantly, murine studies provide good platforms for studying the potential of promising (new) therapeutic strategies for COPD patients with CVD.

Transforming growth factor-β superfamily in obstructive lung diseases. more suspects than TGF-β alone

Asthma and chronic obstructive pulmonary disease are respiratory disorders and a major global health problem with increasing incidence and severity. Genes originally associated with lung development could be relevant in the pathogenesis of chronic obstructive pulmonary disease/asthma, owing to either an early-life origin of adult complex diseases or their dysregulation in adulthood upon exposure to environmental stressors (e.g., smoking). The transforming growth factor (TGF)-β superfamily is conserved through evolution and is involved in a range of biological processes, both during development and in adult tissue homeostasis. TGF-β1 has emerged as an important regulator of lung and immune system development. However, considerable evidence has been presented for a role of many of the other ligands of the TGF-β superfamily in lung pathology, including activins, bone morphogenetic proteins, and growth differentiation factors. In this review, we summarize the current knowledge on the mechanisms by which activin, bone morphogenetic protein, and growth differentiation factor signaling contribute to the pathogenesis of obstructive airway diseases.

Inhibitory effects of Stemona tuberosa on lung inflammation in a subacute cigarette smoke-induced mouse model

BACKGROUND

Stemona tuberosa has long been used in Korean and Chinese medicine to ameliorate various lung diseases such as pneumonia and bronchitis. However, it has not yet been proven that Stemona tuberosa has positive effects on lung inflammation.

METHODS

Stemona tuberosa extract (ST) was orally administered to C57BL/6 mice 2 hr before exposure to CS for 2 weeks. Twenty-four hours after the last CS exposure, mice were sacrificed to investigate the changes in the expression of cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), chemokines such as keratinocyte-derived chemokine (KC) and inflammatory cells such as macrophages, neutrophils, and lymphocytes from bronchoalveolar lavage fluid (BALF). Furthermore, we compared the effect of ST on lung tissue morphology between the fresh air, CS exposure, and ST treatment groups.

RESULTS

ST significantly decreased the numbers of total cells, macrophages, neutrophils, and lymphocytes in the BALF of mice that were exposed to CS. Additionally, ST reduced the levels of cytokines (TNF-α, IL-6) and the tested chemokine (KC) in BALF, as measured by enzyme-linked immunosorbent assay (ELISA). We also estimated the mean alveolar airspace (MAA) via morphometric analysis of lung tissues stained with hematoxylin and eosin (H&E). We found that ST inhibited the alveolar airspace enlargement induced by CS exposure. Furthermore, we observed that the lung tissues of mice treated with ST showed ameliorated epithelial hyperplasia of the bronchioles compared with those of mice exposed only to CS.

CONCLUSIONS

These results indicate that Stemona tuberosa has significant effects on lung inflammation in a subacute CS-induced mouse model. According to these outcomes, Stemona tuberosa may represent a novel therapeutic herb for the treatment of lung diseases including COPD.

Therapeutic effects of amniotic fluid-derived mesenchymal stromal cells on lung injury in rats with emphysema

Background

In chronic obstructive pulmonary disease (COPD), two major pathological changes that occur are the loss of alveolar structure and airspace enlargement. To treat COPD, it is crucial to repair damaged lung tissue and regenerate the lost alveoli. Type II alveolar epithelial cells (AECII) play a vital role in maintaining lung tissue repair, and amniotic fluid-derived mesenchymal stromal cells (AFMSCs) possess the characteristics of regular mesenchymal stromal cells. However, it remains untested whether transplantation of rat AFMSCs (rAFMSCs) might alleviate lung injury caused by emphysema by increasing the expression of surfactant protein (SP)A and SPC and inhibiting AECII apoptosis.

Methods

We analyzed the phenotypic characteristics, differentiation potential, and karyotype of rAFMSCs, which were isolated from pregnant Sprague–Dawley rats. Moreover, we examined the lung morphology and the expression levels of SPA and SPC in rats with emphysema after cigarette-smoke exposure and intratracheal lipopolysaccharide instillation and rAFMSC transplantation. The ability of rAFMSCs to differentiate was measured, and the apoptosis of AECII was evaluated.

Results

In rAFMSCs, the surface antigens CD29, CD44, CD73, CD90, CD105, and CD166 were expressed, but CD14, CD19, CD34, and CD45 were not detected; rAFMSCs also strongly expressed the mRNA of octamer-binding transcription factor 4, and the cells could be induced to differentiate into adipocytes and osteocytes. Furthermore, rAFMSC treatment up-regulated the levels of SPA, SPC, and thyroid transcription factor 1 and inhibited AECII apoptosis, and rAFMSCs appeared to be capable of differentiating into AECII-like cells. Lung injury caused by emphysema was alleviated after rAFMSC treatment.

Conclusions

rAFMSCs might differentiate into AECII-like cells or induce local regeneration of the lung alveolar epithelium in vivo after transplantation and thus could be used in COPD treatment and lung regenerative therapy.

Glucocorticoids recruit Tgfbr3 and Smad1 to shift transforming growth factor-β signaling from the Tgfbr1/Smad2/3 axis to the Acvrl1/Smad1 axis in lung fibroblasts

Glucocorticoids represent the mainstay therapy for many lung diseases, providing outstanding management of asthma but performing surprisingly poorly in patients with acute respiratory distress syndrome, chronic obstructive pulmonary disease, lung fibrosis, and blunted lung development associated with bronchopulmonary dysplasia in preterm infants. TGF-β is a pathogenic mediator of all four of these diseases, prompting us to explore glucocorticoid/TGF-β signaling cross-talk. Glucocorticoids, including dexamethasone, methylprednisolone, budesonide, and fluticasone, potentiated TGF-β signaling by the Acvrl1/Smad1/5/8 signaling axis and blunted signaling by the Tgfbr1/Smad2/3 axis in NIH/3T3 cells, as well as primary lung fibroblasts, smooth muscle cells, and endothelial cells. Dexamethasone drove expression of the accessory type III TGF-β receptor Tgfbr3, also called betaglycan. Tgfbr3 was demonstrated to be a "switch" that blunted Tgfbr1/Smad2/3 and potentiated Acvrl1/Smad1 signaling in lung fibroblasts. The Acvrl1/Smad1 axis, which was stimulated by dexamethasone, was active in lung fibroblasts and antagonized Tgfbr1/Smad2/3 signaling. Dexamethasone acted synergistically with TGF-β to drive differentiation of primary lung fibroblasts to myofibroblasts, revealed by acquisition of smooth muscle actin and smooth muscle myosin, which are exclusively Smad1-dependent processes in fibroblasts. Administration of dexamethasone to live mice recapitulated these observations and revealed a lung-specific impact of dexamethasone on lung Tgfbr3 expression and phospho-Smad1 levels in vivo. These data point to an interesting and hitherto unknown impact of glucocorticoids on TGF-β signaling in lung fibroblasts and other constituent cell types of the lung that may be relevant to lung physiology, as well as lung pathophysiology, in terms of drug/disease interactions.

Tobacco smoke induced COPD/emphysema in the animal model-are we all on the same page?

Chronic Obstructive Pulmonary Disease (COPD) is one of the foremost causes of death worldwide. It is primarily caused by tobacco smoke, making it an easily preventable disease, but facilitated by genetic α-1 antitrypsin deficiency. In addition to active smokers, health problems also occur in people involuntarily exposed to second hand smoke (SHS). Currently, the relationship between SHS and COPD is not well established. Knowledge of pathogenic mechanisms is limited, thereby halting the advancement of new treatments for this socially and economically detrimental disease. Here, we attempt to summarize tobacco smoke studies undertaken in animal models, applying both mainstream (direct, nose only) and side stream (indirect, whole body) smoke exposures. This overview of 155 studies compares cellular and molecular mechanisms as well as proteolytic, inflammatory, and vasoreactive responses underlying COPD development. This is a difficult task, as listing of exposure parameters is limited for most experiments. We show that both mainstream and SHS studies largely present similar inflammatory cell populations dominated by macrophages as well as elevated chemokine/cytokine levels, such as TNF-α. Additionally, SHS, like mainstream smoke, has been shown to cause vascular remodeling and neutrophil elastase-mediated proteolytic matrix breakdown with failure to repair. Disease mechanisms and therapeutic interventions appear to coincide in both exposure scenarios. One of the more widely applied interventions, the anti-oxidant therapy, is successful for both mainstream and SHS. The comparison of direct with indirect smoke exposure studies in this review emphasizes that, even though there are many overlapping pathways, it is not conclusive that SHS is using exactly the same mechanisms as direct smoke in COPD pathogenesis, but should be considered a preventable health risk. Some characteristics and therapeutic alternatives uniquely exist in SHS-related COPD.

Second hand smoke and COPD: lessons from animal studies

Exposure to second hand smoke is a major cause of chronic obstructive pulmonary disease (COPD) in the non-smoker. In this review we explore the use of animal smoke exposure models and their insight into disease pathogenesis. The methods of smoke exposure, including exposure delivery systems, are described. Key findings from the acute and chronic smoke exposure models are outlined, including descriptions of the inflammation processes, proteases involved, oxidative stress, and apoptosis. Finally, alternatives to rodent models of lung disease are presented.

A Relationship between Epithelial Maturation, Bronchopulmonary Dysplasia, and Chronic Obstructive Pulmonary Disease

Premature infants frequently develop bronchopulmonary dysplasia (BPD). Lung immaturity and impaired epithelial differentiation contribute together with invasive oxygen treatment to BPD onset and disease progression. Substantial evidence suggests that prematurity is associated with long term pulmonary consequences. Moreover, there is increasing concern that lung immaturity at birth may increase the risk of developing chronic obstructive pulmonary disease (COPD). The mechanisms contributing to this phenomenon remains unknown, largely as a consequence of inadequate experimental models and clinical follow-up studies. Recent evidence suggests that defective transcriptional regulation of epithelial differentiation and maturation may contribute to BPD pathogenesis as well as early onset of COPD. The transcriptional regulators CCAAT/enhancer-binding protein (C/EBP)α and C/EBPβ, SMAD family member (Smad)3, GATA binding protein (GATA)6, and NK2 homeobox (NKX)2-1 are reported to be involved in processes contributing to pathogenesis of both BPD and COPD. Increased knowledge of the mechanisms contributing to early onset COPD among BPD survivors could translate into improved treatment strategies and reduced frequency of respiratory disorders among adult survivors of BPD. In this paper, we introduce critical transcriptional regulators in epithelial differentiation and summarize the current knowledge on the contribution of impaired epithelial maturation to the pathogenesis of inflammatory lung disorders.

TGF-β-Smad3 signaling in emphysema and pulmonary fibrosis: an epigenetic aberration of normal development?

It is well accepted that TGF-β signaling has critical functional roles in lung development, injury, and repair. We showed previously that null mutation of Smad3, a critical node in the TGF-β pathway, protects mice against fibrosis induced by bleomycin. However, more recently we noticed that abnormal alveolarization also occurs in Smad3-deficient mice and that this is followed by progressive emphysema-like alveolar wall destruction mediated by MMP9. We now know that Smad3 cooperates with c-Jun to synergistically regulate a protein deacetylase SIRT1, by binding to an AP-1 site in the SIRT1 promoter. Consistently, Smad3 knockout lung at postnatal day 28 had reduced SIRT1 expression, which in turn resulted in increased histone acetylation at the binding sites of the transcription factors AP-1, NF-κB, and Pea3 on the MMP9 promoter, as well as increased acetylation of NF-κB. Thus, upon TGF-β activation, phosphorylated Smad3 can be translocated into the nucleus with Smad4, whereat Smad3 in turn collaborates with c-Jun to activate SIRT1 transcription. SIRT1 can deacetylate NF-κB at lysine 30, as well as histones adjacent to the transcription factor AP-1, NF-κB, and Pea3 binding sites of the MMP9 promoter, thereby suppressing MMP9 transcription, hence fixing MMP9 in the OFF mode. Conversely, when Smad3 is missing, this regulatory pathway is inactivated so that MMP9 is epigenetically turned ON. We postulate that these developmental epigenetic mechanisms by which Smad3 regulates MMP9 transcription cell autonomously may be important in modulating both emphysema and pulmonary fibrosis and that this could explain why both pathologies can appear within the same lung specimen.

Targeting TGFβ superfamily ligand accessory proteins as novel therapeutics for chronic lung disorders

Dysregulation of the transforming growth factor β (TGFβ) pathway has been implicated to underlie a number of disease indications including chronic lung disorders such as asthma, chronic obstructive pulmonary disease (COPD), interstitial pneumonias, and pulmonary arterial hypertension (PAH). Consequently, the pharmaceutical industry has devoted significant resources in the pursuit of TGFβ pathway inhibitors that target the cognate type I and II receptors and respective ligands. The progress of these approaches has been painfully slow, due in part to dose-limiting safety issues that result from the antagonism of a pathway that is responsible for regulating many fundamental biological processes including immune surveillance and cardiovascular responses. These disappointments have led many in the field to conclude that modulating the TGFβ pathway for chronic indications with a sufficient safety window using conventional approaches may be extremely difficult to achieve. Here we review the rationale and limitations of the use of TGFβ pathway inhibitors in chronic lung disorders and the possibility of targeting TGFβ superfamily ligand accessory proteins to allow rheostatic regulation of signaling to achieve efficacy while maintaining a sufficient therapeutic index.

Angiotensin receptor blockade attenuates cigarette smoke-induced lung injury and rescues lung architecture in mice

Chronic obstructive pulmonary disease (COPD) is a prevalent smoking-related disease for which no disease-altering therapies currently exist. As dysregulated TGF-β signaling associates with lung pathology in patients with COPD and in animal models of lung injury induced by chronic exposure to cigarette smoke (CS), we postulated that inhibiting TGF-β signaling would protect against CS-induced lung injury. We first confirmed that TGF-β signaling was induced in the lungs of mice chronically exposed to CS as well as in COPD patient samples. Importantly, key pathological features of smoking-associated lung disease in patients, e.g., alveolar injury with overt emphysema and airway epithelial hyperplasia with fibrosis, accompanied CS-induced alveolar cell apoptosis caused by enhanced TGF-β signaling in CS-exposed mice. Systemic administration of a TGF-β-specific neutralizing antibody normalized TGF-β signaling and alveolar cell death, conferring improved lung architecture and lung mechanics in CS-exposed mice. Use of losartan, an angiotensin receptor type 1 blocker used widely in the clinic and known to antagonize TGF-β signaling, also improved oxidative stress, inflammation, metalloprotease activation and elastin remodeling. These data support our hypothesis that inhibition of TGF-β signaling through angiotensin receptor blockade can attenuate CS-induced lung injury in an established murine model. More importantly, our findings provide a preclinical platform for the development of other TGF-β-targeted therapies for patients with COPD.