Telomere length is a determinant of emphysema susceptibility

Telomere attrition and restoration in the normal teleost Oryzias latipes are linked to growth rate and telomerase activity at each life stage

Telomere shortening occurs when cells divide, both in vitro and in vivo. On the other hand, telomerase is able to maintain telomere length in cells by adding TTAGGG repeats to the ends of telomeres. However, the interrelationships existing among telomere length, telomerase activity and growth in vertebrates remain to be clarified. In the present study we measured telomere length (terminal restriction fragment length), telomerase activity and body growth of Oryzias latipes from the embryo stage until senescence. During the rapid growth stage (age 0–7 months), telomeres shortened in parallel with decreasing telomerase activity. Then, during adolescence (age 7 months – 1 year), telomeres lengthened quickly as growth slowed and telomerase activity increased. In the adult stage (age 1–4 years) characterized by little growth, telomerase activity decreased gradually and telomeres shortened. Our data indicate that telomere attrition and restoration are linked to growth and telomerase activity, and suggest that critical loss of telomere homeostasis is associated with mortality in this animal.

Accelerated telomere attrition in children and teenagers with α1-antitrypsin deficiency

Numerous studies have shown that oxidative stress accelerates telomere shortening in several lung pathologies. Since oxidative stress is involved in the pathophysiology of α1-antitrypsin deficiency (AATD), we hypothesised that telomere shortening would be accelerated in AATD patients. This study aimed to assess telomere length in AATD patients and to study its association with α1-antitrypsin phenotypes.

Telomere length, telomerase activity, telomerase reverse transcriptase (hTERT) expression and biomarkers of oxidative stress were measured in 62 children and teenagers (aged 2–18 years) diagnosed with AATD and 18 controls (aged 3–16 years).

Our results show that intermediate-risk (MZ; SZ) and high-risk (ZZ) AATD patients have significantly shorter telomeres and increased oxidative stress than controls. Correlation studies indicate that telomere length was related to oxidative stress markers in AATD patients. Multiple hypothesis testing revealed an association between telomere length, telomerase activity, hTERT expression and AATD phenotypes; high-risk patients showed shorter telomeres, lower hTERT expression and decreased telomerase activity than intermediate-risk and low-risk patients.

AATD patients show evidence of increased oxidative stress leading to telomere attrition. An association between telomere and α1-antitrypsin phenotypes is observed suggesting that telomere length could be a promising biomarker for AATD disease progression.

Inflammaging increases susceptibility to cigarette smoke-induced COPD

Chronic obstructive pulmonary disease (COPD) is related to an abnormal chronic inflammatory response of the lung to mainly cigarette smoke (CS) and the disease risk is increased in aged individuals. The source of this chronic inflammation is due to the repeated and progressive activation of immune cells. We hypothesize that in a chronic CS-induced mouse model, the predisposition to COPD pathogenesis in aged mice is characterized by an elevated immune response compared to young animals. We measured several characteristics of COPD in young and old mice (2 and 12 months of age) exposed to CS for 3 months. CS-exposed aged mice exhibited increased lung compliance (0.061 ± 0.008 vs. 0.055 ± 0.006 ml/cm H2O, p < 0.01), emphysema development (35.36 ± 0.71 vs. 25.31 ± 0.005 μm; p < 0.01) and airway remodeling (2.15 ± 0.37 vs. 1.09 ± 0.64 μm3/μm2; p < 0.01) compared to control animals, which was not seen in CS-exposed young mice. Quantification of lung tissue inflammation revealed a significantly greater volume of inducible bronchus-associated lymphoid tissue structures in aged mice after CS exposure (5.94 ± 2.89 vs. 2.37 ± 1.69 μm3/μm2; p < 0.01). Our results indicate that age-induced lung inflammation is further elevated after CS exposure in old mice, potentially via an age-induced change in immune cell susceptibility to CS thereby accelerating the pathophysiological hallmarks of COPD.

ROS, Cell Senescence, and Novel Molecular Mechanisms in Aging and Age-Related Diseases

The aging process worsens the human body functions at multiple levels, thus causing its gradual decrease to resist stress, damage, and disease. Besides changes in gene expression and metabolic control, the aging rate has been associated with the production of high levels of Reactive Oxygen Species (ROS) and/or Reactive Nitrosative Species (RNS). Specific increases of ROS level have been demonstrated as potentially critical for induction and maintenance of cell senescence process. Causal connection between ROS, aging, age-related pathologies, and cell senescence is studied intensely. Senescent cells have been proposed as a target for interventions to delay the aging and its related diseases or to improve the diseases treatment. Therapeutic interventions towards senescent cells might allow restoring the health and curing the diseases that share basal processes, rather than curing each disease in separate and symptomatic way. Here, we review observations on ROS ability of inducing cell senescence through novel mechanisms that underpin aging processes. Particular emphasis is addressed to the novel mechanisms of ROS involvement in epigenetic regulation of cell senescence and aging, with the aim to individuate specific pathways, which might promote healthy lifespan and improve aging.

Impact of Comorbidities on Mortality in Patients with Idiopathic Pulmonary Fibrosis

INTRODUCTION

Comorbidities significantly influence the clinical course of idiopathic pulmonary fibrosis (IPF). However, their prognostic impact is not fully understood. We therefore aimed to determine the impact of comorbidities, as individual and as whole, on survival in IPF.

METHODS

The database of a tertiary referral centre for interstitial lung diseases was reviewed for comorbidities, their treatments, their frequency and survival in IPF patients.

RESULTS

272 patients were identified of which 12% had no, 58% 1-3 and 30% 4-7 comorbidities, mainly cardiovascular, pulmonary and oncologic comorbidities. Median survival according to the frequency of comorbidities differed significantly with 66 months for patients without comorbidities, 48 months when 1-3 comorbidities were reported and 35 months when 4-7 comorbidities were prevalent (p = 0.004). A multivariate Cox proportional hazard analyses identified other cardiac diseases and lung cancer as significant predictors of death, gastro-oesophageal reflux disease (GERD) and diastolic dysfunction had a significant positive impact on survival. A significant impact of comorbidities associated therapies on survival was not discovered. This included the use of proton pump inhibitors at baseline, which was not associated with a survival benefit (p = 0.718). We also established a predictive tool for highly prevalent comorbidities, termed IPF comorbidome which demonstrates a new relationship of IPF and comorbidities.

CONCLUSION

Comorbidities are frequent in IPF patients. Some comorbidities, especially lung cancer, mainly influence survival in IPF, while others such as GERD may inherit a more favourable effect. Moreover, their cumulative incidence impacts survival.

Pathophysiology of Emphysema and Implications

This article serves as a CME-available, enduring material summary of the following COPD9_USA presentations: "Overview of Lung Injury in COPD: Types and Key Questions" Presenter: Caroline Owen, MD, PhD Emphysema as a Disease of Deficient Tissue Repair/Maintenance" Presenter: Rubin Tuder, MD.

Telomere length in interstitial lung diseases

BACKGROUND

Interstitial lung disease (ILD) is a heterogeneous group of rare diseases that primarily affect the pulmonary interstitium. Studies have implicated a role for telomere length (TL) maintenance in ILD, particularly in idiopathic interstitial pneumonia (IIP). Here, we measure TL in a wide spectrum of sporadic and familial cohorts of ILD and compare TL between patient cohorts and control subjects.

METHODS

A multiplex quantitative polymerase chain reaction method was used to measure TL in 173 healthy subjects and 359 patients with various ILDs, including familial interstitial pneumonia (FIP). The FIP cohort was divided into patients carrying TERT mutations, patients carrying SFTPA2 or SFTPC mutations, and patients without a proven mutation (FIP-no mutation).

RESULTS

TL in all cases of ILD was significantly shorter compared with those of control subjects (P range: .038 to < .0001). Furthermore, TL in patients with idiopathic pulmonary fibrosis (IPF) was significantly shorter than in patients with other IIPs (P = .002) and in patients with sarcoidosis (P < .0001). Within the FIP cohort, patients in the FIP-telomerase reverse transcriptase (TERT) group had the shortest telomeres (P < .0001), and those in the FIP-no mutation group had TL comparable to that of patients with IPF (P = .049). Remarkably, TL of patients with FIP-surfactant protein (SFTP) was significantly longer than in patients with IPF, but similar to that observed in patients with other sporadic IIPs.

CONCLUSIONS

The results show telomere shortening across all ILD diagnoses. The difference in TL between the FIP-TERT and FIP-SFTP groups indicates the distinction between acquired and innate telomere shortening. Short TL in the IPF and FIP-no mutation groups is indicative of an innate telomere-biology defect, while a stress-induced, acquired telomere shortening might be the underlying process for the other ILD diagnoses.

Effect of obesity on telomere length: Systematic review and meta-analysis

OBJECTIVE

The main objective of this systematic review is to assess the effects of obesity on telomere length.

METHODS

The following databases were searched: MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), LILACS, SPORTdiscus, and Web of Science from inception to August 2014. The search was performed using the following combinations of terms: telomere AND "overweight" OR "obesity" OR "adiposity," without language restriction.

RESULTS

Sixty-three original studies were included in this systematic review, comprising 119,439 subjects. Thirty-nine studies showed either weak or moderate correlation between obesity and telomere length; however, they showed an important heterogeneity.

CONCLUSIONS

There is a tendency toward demonstrating negative correlation between obesity and telomere length. The selected studies showed weak to moderate correlation for the main search, and there was an important heterogeneity. For this reason, the causal relationship of obesity and telomere length remains open. Additional controlled longitudinal studies are needed to investigate this issue.

Telomerase Deficiency Causes Alveolar Stem Cell Senescence-associated Low-grade Inflammation in Lungs

Mutations of human telomerase RNA component (TERC) and telomerase reverse transcriptase (TERT) are associated with a subset of lung aging diseases, but the mechanisms by which TERC and TERT participate in lung diseases remain unclear. In this report, we show that knock-out (KO) of the mouse gene Terc or Tert causes pulmonary alveolar stem cell replicative senescence, epithelial impairment, formation of alveolar sacs, and characteristic inflammatory phenotype. Deficiency in TERC or TERT causes a remarkable elevation in various proinflammatory cytokines, including IL-1, IL-6, CXCL15 (human IL-8 homolog), IL-10, TNF-α, and monocyte chemotactic protein 1 (chemokine ligand 2 (CCL2)); decrease in TGF-β1 and TGFβRI receptor in the lungs; and spillover of IL-6 and CXCL15 into the bronchoalveolar lavage fluids. In addition to increased gene expressions of α-smooth muscle actin and collagen 1α1, suggesting myofibroblast differentiation, TERC deficiency also leads to marked cellular infiltrations of a mononuclear cell population positive for the leukocyte common antigen CD45, low-affinity Fc receptor CD16/CD32, and pattern recognition receptor CD11b in the lungs. Our data demonstrate for the first time that telomerase deficiency triggers alveolar stem cell replicative senescence-associated low-grade inflammation, thereby driving pulmonary premature aging, alveolar sac formation, and fibrotic lesion.

Understanding Idiopathic Interstitial Pneumonia: A Gene-Based Review of Stressed Lungs

Pulmonary fibrosis is the main cause of severe morbidity and mortality in idiopathic interstitial pneumonias (IIP). In the past years, there has been major progress in the discovery of genetic factors that contribute to disease. Genes with highly penetrant mutations or strongly predisposing common risk alleles have been identified in familial and sporadic IIP. This review summarizes genes harbouring causative rare mutations and replicated common predisposing alleles. To date, rare mutations in nine different genes and five risk alleles fulfil this criterion. Mutated genes represent three genes involved in surfactant homeostasis and six genes involved in telomere maintenance. We summarize gene function, gene expressing cells, and pathological consequences of genetic alterations associated with disease. Consequences of the genetic alteration include dysfunctional surfactant processing, ER stress, immune dysregulation, and maintenance of telomere length. Biological evidence shows that these processes point towards a central role for alveolar epithelial type II cell dysfunction. However, tabulation also shows that function and consequence of most common risk alleles are not known. Most importantly, the predisposition of the MUC5B risk allele to disease is not understood. We propose a mechanism whereby MUC5B decreases surface tension lowering capacity of alveolar surfactant at areas with maximal mechanical stress.

DNA damage response at telomeres contributes to lung aging and chronic obstructive pulmonary disease

Cellular senescence has been associated with the structural and functional decline observed during physiological lung aging and in chronic obstructive pulmonary disease (COPD). Airway epithelial cells are the first line of defense in the lungs and are important to COPD pathogenesis. However, the mechanisms underlying airway epithelial cell senescence, and particularly the role of telomere dysfunction in this process, are poorly understood. We aimed to investigate telomere dysfunction in airway epithelial cells from patients with COPD, in the aging murine lung and following cigarette smoke exposure. We evaluated colocalization of γ-histone protein 2A.X and telomeres and telomere length in small airway epithelial cells from patients with COPD, during murine lung aging, and following cigarette smoke exposure in vivo and in vitro. We found that telomere-associated DNA damage foci increase in small airway epithelial cells from patients with COPD, without significant telomere shortening detected. With age, telomere-associated foci increase in small airway epithelial cells of the murine lung, which is accelerated by cigarette smoke exposure. Moreover, telomere-associated foci predict age-dependent emphysema, and late-generation Terc null mice, which harbor dysfunctional telomeres, show early-onset emphysema. We found that cigarette smoke accelerates telomere dysfunction via reactive oxygen species in vitro and may be associated with ataxia telangiectasia mutated-dependent secretion of inflammatory cytokines interleukin-6 and -8. We propose that telomeres are highly sensitive to cigarette smoke-induced damage, and telomere dysfunction may underlie decline of lung function observed during aging and in COPD.

Identification of a Potential Regulatory Variant for Colorectal Cancer Risk Mapping to Chromosome 5q31.1: A Post-GWAS Study

Large-scale genome-wide association studies (GWAS) have established chromosome 5q31.1 as a susceptibility locus for colorectal cancer (CRC), which was still lack of causal genetic variants. We searched potentially regulatory single nucleotide polymorphisms (SNPs) in the overlap region between linkage disequilibrium (LD) block of 5q31.1 and regulatory elements predicted by histone modifications, then tested their association with CRC via a case-control study. Among three candidate common variants, we found rs17716310 conferred significantly (heterozygous model: OR = 1.273, 95% confidence interval (95%CI) = 1.016–1.595, P = 0.036) and marginally (dominant model: OR = 1.238, 95%CI = 1.000–1.532, P = 0.050) increase risk for CRC in a Chinese population including 695 cases and 709 controls. This variation was suggested to be regulatory altering the activity of enhancer that control PITX1 expression. Using epigenetic information such as chromatin immunoprecipitation-sequencing (ChIP-seq) data might help researchers to interpret the results of GWAS and locate causal variants for diseases in post-GWAS era.

A Genome-Wide Association Study of Emphysema and Airway Quantitative Imaging Phenotypes

RATIONALE

Chronic obstructive pulmonary disease (COPD) is defined by the presence of airflow limitation on spirometry, yet subjects with COPD can have marked differences in computed tomography imaging. These differences may be driven by genetic factors. We hypothesized that a genome-wide association study (GWAS) of quantitative imaging would identify loci not previously identified in analyses of COPD or spirometry. In addition, we sought to determine whether previously described genome-wide significant COPD and spirometric loci were associated with emphysema or airway phenotypes.

OBJECTIVES

To identify genetic determinants of quantitative imaging phenotypes.

METHODS

We performed a GWAS on two quantitative emphysema and two quantitative airway imaging phenotypes in the COPDGene (non-Hispanic white and African American), ECLIPSE (Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints), NETT (National Emphysema Treatment Trial), and GenKOLS (Genetics of COPD, Norway) studies and on percentage gas trapping in COPDGene. We also examined specific loci reported as genome-wide significant for spirometric phenotypes related to airflow limitation or COPD.

MEASUREMENTS AND MAIN RESULTS

The total sample size across all cohorts was 12,031, of whom 9,338 were from COPDGene. We identified five loci associated with emphysema-related phenotypes, one with airway-related phenotypes, and two with gas trapping. These loci included previously reported associations, including the HHIP, 15q25, and AGER loci, as well as novel associations near SERPINA10 and DLC1. All previously reported COPD and a significant number of spirometric GWAS loci were at least nominally (P < 0.05) associated with either emphysema or airway phenotypes.

CONCLUSIONS

Genome-wide analysis may identify novel risk factors for quantitative imaging characteristics in COPD and also identify imaging features associated with previously identified lung function loci.

The relationship between COPD and lung cancer

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COPD is a risk factor for lung cancer beyond their shared aetiology.

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Both are driven by oxidative stress.

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Both are linked to cellular aging, senescence and telomere shortening.

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Both have been linked to genetic predisposition.

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Both show altered epigenetic regulation of gene expression.

Both COPD and lung cancer are major worldwide health concerns owing to cigarette smoking, and represent a huge, worldwide, preventable disease burden. Whilst the majority of smokers will not develop either COPD or lung cancer, they are closely related diseases, occurring as co-morbidities at a higher rate than if they were independently triggered by smoking.

Lung cancer and COPD may be different aspects of the same disease, with the same underlying predispositions, whether this is an underlying genetic predisposition, telomere shortening, mitochondrial dysfunction or premature aging. In the majority of smokers, the burden of smoking may be dealt with by the body’s defense mechanisms: anti-oxidants such as superoxide dismutases, anti-proteases and DNA repair mechanisms. However, in the case of both diseases these fail, leading to cancer if mutations occur or COPD if damage to the cell and proteins becomes too great.

Alternatively COPD could be a driving factor in lung cancer, by increasing oxidative stress and the resulting DNA damage, chronic exposure to pro-inflammatory cytokines, repression of the DNA repair mechanisms and increased cellular proliferation. Understanding the mechanisms that drive these processes in primary cells from patients with these diseases along with better disease models is essential for the development of new treatments.

Short telomeres, telomeropathy, and subclinical extrapulmonary organ damage in patients with interstitial lung disease

BACKGROUND

Human telomere disease consists of a wide spectrum of disorders, including pulmonary, hepatic, and bone marrow abnormalities. The extent of bone marrow and liver abnormalities in patients with interstitial lung disease (ILD) and short telomeres is unknown.

METHODS

The lung transplant clinic established a prospective protocol to identify short telomeres in patients with ILD not related to connective tissue disease or sarcoidosis. Patients with short telomeres underwent bone marrow biopsies, liver biopsies, or both as part of the evaluation for transplant candidacy.

RESULTS

One hundred twenty-seven patients met ILD categorization for inclusion. Thirty were suspected to have short telomeres, and 15 had the diagnosis confirmed. Eight of 13 (53%) patients had bone marrow abnormalities. Four patients had hypocellular marrow associated with macrocytosis and relatively normal blood counts, which resulted in changes to planned immunosuppression at the time of transplant. Four patients with more severe hematologic abnormalities were not listed because of myelodysplastic syndrome (two); monoclonal gammopathy of unclear significance (one); and hypocellular marrow, decreased megakaryocyte lineage associated with thrombocytopenia (one). Seven patients underwent liver biopsies, and six had abnormal liver pathology. These abnormalities did not affect listing for lung transplant, and liver biopsies are no longer routinely obtained.

CONCLUSIONS

Subclinical bone marrow and liver abnormalities can be seen in patients with ILD and short telomeres, in some cases in the absence of clinically significant abnormalities in peripheral blood counts and liver function tests. A larger study examining the implication of these findings on the outcome of patients with ILD and short telomeres is needed.

The short and long telomere syndromes: paired paradigms for molecular medicine

Recent advances have defined a role for abnormally short telomeres in a broad spectrum of genetic disorders. They include rare conditions such as dyskeratosis congenita as well pulmonary fibrosis and emphysema. Now, there is new evidence that some familial cancers, such as melanoma, are caused by mutations that lengthen telomeres. Here, we examine the significance of these short and long telomere length extremes for understanding the molecular basis of age-related disease and cancer.

Keeping it together: Pulmonary alveoli are maintained by a hierarchy of cellular programs

The application of in vivo genetic lineage tracing has advanced our understanding of cellular mechanisms for tissue renewal in organs with slow turnover, like the lung. These studies have identified an adult stem cell with very different properties than classically understood ones that maintain continuously cycling tissues such as the intestine. A portrait has emerged of an ensemble of cellular programs that replenish the cells that line the gas exchange (alveolar) surface, enabling a response tailored to the extent of cell loss. A capacity for differentiated cells to undergo direct lineage transitions allows for local restoration of proper cell balance at sites of injury. We present these recent findings as a paradigm for how a relatively quiescent tissue compartment can maintain homeostasis throughout a lifetime punctuated by injuries ranging from mild to life-threatening, and discuss how dysfunction or insufficiency of alveolar repair programs produce serious health consequences like cancer and fibrosis.

Sirtuin 1 and aging theory for chronic obstructive pulmonary disease

Chronic Obstructive Pulmonary disease (COPD) is an inflammatory syndrome that represents an increasing health problem, especially in the elderly population. Drug therapies are symptomatic and inadequate to contrast disease progression and mortality. Thus, there is an urgent need to clarify the molecular mechanisms responsible for this condition in order to identify new biomarkers and therapeutic targets. Processes including oxidant/antioxidant, protease/antiprotease, and proliferative/antiproliferative balance and control of inflammatory response become dysfunctional during aging as well as in COPD. Recently it was suggested that Sirtuin 1 (SIRT1), an antiaging molecule involved in the response to oxidative stress and chronic inflammation, is implicated in both development and progression of COPD. The present review focuses on the involvement of SIRT1 in the regulation of redox state, inflammation, and premature senescence, all crucial characteristics of COPD phenotypes. Recent evidence corroborating the statement of the “aging theory for COPD” was also discussed.

Mice with Pulmonary Fibrosis Driven by Telomere Dysfunction

Idiopathic pulmonary fibrosis (IPF) is a degenerative disease of the lungs with an average survival post-diagnosis of 2-3 years. New therapeutic targets and treatments are necessary. Mutations in components of the telomere-maintenance enzyme telomerase or in proteins important for telomere protection are found in both familial and sporadic IPF cases. However, the lack of mouse models that faithfully recapitulate the human disease has hampered new advances. Here, we generate two independent mouse models that develop IPF owing to either critically short telomeres (telomerase-deficient mice) or severe telomere dysfunction in the absence of telomere shortening (mice with Trf1 deletion in type II alveolar cells). We show that both mouse models develop pulmonary fibrosis through induction of telomere damage, thus providing proof of principle of the causal role of DNA damage stemming from dysfunctional telomeres in IPF development and identifying telomeres as promising targets for new treatments.

Combined pulmonary fibrosis and emphysema (CPFE): an entity different from emphysema or pulmonary fibrosis alone

Chronic obstructive pulmonary disease (COPD) and idiopathic interstitial pneumonias (IIP), with different radiological, pathological, functional and prognostic characteristics, have been regarded as separate entities for a long time. However, there is an increasing recognition of the coexistence of emphysema and pulmonary fibrosis in individuals. The association was first described as a syndrome by Cottin in 2005, named "combined pulmonary fibrosis and emphysema (CPFE)", which is characterized by exertional dyspnea, upper-lobe emphysema and lower-lobe fibrosis, preserved lung volume and severely diminished capacity of gas exchange. CPFE is frequently complicated by pulmonary hypertension, acute lung injury and lung cancer and prognosis of it is poor. Treatments for CPFE patients with severe pulmonary hypertension are less effective other than lung transplantation. However, CPFE has not yet attracted wide attention of clinicians and there is no research systematically contrasting the differences among CPFE, emphysema/COPD and IIP at the same time. The authors will review the existing knowledge of CPFE and compare them to either entity alone for the first time, with the purpose of improving the awareness of this syndrome and exploring novel effective therapeutic strategies in clinical practice.

Blue journal conference. Aging and susceptibility to lung disease

The aging of the population in the United States and throughout the developed world has increased morbidity and mortality attributable to lung disease, while the morbidity and mortality from other prevalent diseases has declined or remained stable. Recognizing the importance of aging in the development of lung disease, the American Thoracic Society (ATS) highlighted this topic as a core theme for the 2014 annual meeting. The relationship between aging and lung disease was discussed in several oral symposiums and poster sessions at the annual ATS meeting. In this article, we used the input gathered at the conference to develop a broad framework and perspective to stimulate basic, clinical, and translational research to understand how the aging process contributes to the onset and/or progression of lung diseases. A consistent theme that emerged from the conference was the need to apply novel, systems-based approaches to integrate a growing body of genomic, epigenomic, transcriptomic, and proteomic data and elucidate the relationship between biologic hallmarks of aging, altered lung function, and increased susceptibility to lung diseases in the older population. The challenge remains to causally link the molecular and cellular changes of aging with age-related changes in lung physiology and disease susceptibility. The purpose of this review is to stimulate further research to identify new strategies to prevent or treat age-related lung disease.

Telomere dysfunction causes alveolar stem cell failure

Telomere syndromes have their most common manifestation in lung disease that is recognized as idiopathic pulmonary fibrosis and emphysema. In both conditions, there is loss of alveolar integrity, but the underlying mechanisms are not known. We tested the capacity of alveolar epithelial and stromal cells from mice with short telomeres to support alveolar organoid colony formation and found that type 2 alveolar epithelial cells (AEC2s), the stem cell-containing population, were limiting. When telomere dysfunction was induced in adult AEC2s by conditional deletion of the shelterin component telomeric repeat-binding factor 2, cells survived but remained dormant and showed all the hallmarks of cellular senescence. Telomere dysfunction in AEC2s triggered an immune response, and this was associated with AEC2-derived up-regulation of cytokine signaling pathways that are known to provoke inflammation in the lung. Mice uniformly died after challenge with bleomycin, underscoring an essential role for telomere function in AEC2s for alveolar repair. Our data show that alveoloar progenitor senescence is sufficient to recapitulate the regenerative defects, inflammatory responses, and susceptibility to injury that are characteristic of telomere-mediated lung disease. They suggest alveolar stem cell failure is a driver of telomere-mediated lung disease and that efforts to reverse it may be clinically beneficial.

The genetic basis of idiopathic pulmonary fibrosis

Throughout the past decade, there have been substantial advances in understanding the pathogenesis of idiopathic pulmonary fibrosis (IPF). Recently, several large genome-wide association and linkage studies have identified common genetic variants in more than a dozen loci that appear to contribute to IPF risk. In addition, family-based studies have led to the identification of rare genetic variants in genes related to surfactant function and telomere biology, and mechanistic studies suggest pathophysiological derangements associated with these rare genetic variants are also found in sporadic cases of IPF. Current evidence suggests that rather than existing as distinct syndromes, sporadic and familial cases of IPF (familial interstitial pneumonia) probably reflect a continuum of genetic risk. Rapidly evolving bioinformatic and molecular biology techniques, combined with next-generation sequencing technologies, hold great promise for developing a comprehensive, integrated approach to defining the fundamental molecular mechanisms that underlie IPF pathogenesis.

Accelerated ageing of the lung in COPD: new concepts

The rise in life expectancy worldwide has been accompanied by an increased incidence of age-related diseases, representing an enormous burden on healthcare services and society. All vital organs lose function with age, and this is well described in the lung, with a progressive decline in pulmonary function after the age of about 25 years. The lung ages, like any other organ, with progressive functional impairment and reduced capacity to respond to environmental stresses and injury. Normal physiological ageing results in enlarged alveolar spaces and loss of lung elasticity in the elderly known as 'senile emphysema', whereas in COPD there is destruction of the alveolar walls and fibrosis of peripheral airways. However, COPD shows striking age-associated features, such as an increase in cellular senescence, stem cell exhaustion, increased oxidative stress, alteration in the extracellular matrix and a reduction in endogenous antiageing molecules and protective pathways such as autophagy. In this review we discuss the evidence showing how oxidative stress induces accelerated ageing by upregulating the phosphatidylinositol-4,5-bisphosphate 3-kinase/AKT/mechanistic target of rapamycin signalling pathway resulting in depletion of stem cells, defective autophagy, reduced antioxidant responses and defective mitochondrial function thus generating further oxidative stress. Understanding the mechanisms of accelerated ageing in COPD may identify novel therapeutic approaches.

Hallmarks of the ageing lung

Ageing is the main risk factor for major non-communicable chronic lung diseases, including chronic obstructive pulmonary disease, most forms of lung cancer and idiopathic pulmonary fibrosis. While the prevalence of these diseases continually increases with age, their respective incidence peaks at different times during the lifespan, suggesting specific effects of ageing on the onset and/or pathogenesis of chronic obstructive pulmonary disease, lung cancer and idiopathic pulmonary fibrosis. Recently, the nine hallmarks of ageing have been defined as cell-autonomous and non-autonomous pathways involved in ageing. Here, we review the available evidence for the involvement of each of these hallmarks in the pathogenesis of chronic obstructive pulmonary disease, lung cancer, or idiopathic pulmonary fibrosis. Importantly, we propose an additional hallmark, “dysregulation of the extracellular matrix”, which we argue acts as a crucial modifier of cell-autonomous changes and functions, and as a key feature of the above-mentioned lung diseases.

Mechanisms of development of multimorbidity in the elderly

In ageing populations many patients have multiple diseases characterised by acceleration of the normal ageing process. Better understanding of the signalling pathways and cellular events involved in ageing shows that these are characteristic of many chronic degenerative diseases, such as chronic obstructive pulmonary disease (COPD), chronic cardiovascular and metabolic diseases, and neurodegeneration. Common mechanisms have now been identified in these diseases, which show evidence of cellular senescence with telomere shortening, activation of PI3K–AKT–mTOR signalling, impaired autophagy, mitochondrial dysfunction, stem cell exhaustion, epigenetic changes, abnormal microRNA profiles, immunosenescence and low grade chronic inflammation (“inflammaging”). Many of these pathways are driven by chronic oxidative stress. There is also a reduction in anti-ageing molecules, such as sirtuins and Klotho, which further accelerates the ageing process. Understanding these molecular mechanisms has identified several novel therapeutic targets and several drugs have already been developed that may slow the ageing process, as well as lifestyle interventions, such as diet and physical activity. This indicates that in the future new treatment approaches may target the common pathways involved in multimorbidity and this area of research should be given high priority. Thus, COPD should be considered as a component of multimorbidity and common disease pathways, particularly accelerated ageing, should be targeted.

Interstitial lung disease: NHLBI Workshop on the Primary Prevention of Chronic Lung Diseases

Population-based, longitudinal studies spanning decades linking risk factors in childhood, adolescence and early adulthood to incident clinical interstitial lung disease (ILD) events in late adulthood have not been performed. In addition, no observational or randomized clinical trials have been conducted; therefore, there is presently no evidence to support the notion that reduction of risk factor levels in early life prevents ILD events in adult life. Primary prevention strategies are host-directed interventions designed to modify adverse risk factors (i.e., smoking) with the goal of preventing the development of ILD, whereas primordial prevention for ILD can be defined as the elimination of external risk factors (i.e., environmental pollutants). As no ILD primary prevention studies have been previously conducted, we propose that research studies that promote implementation of primary prevention strategies could, over time, make a subset of ILD preventable. Herein, we provide a number of initial steps required for the future implementation of prevention strategies; this statement discusses the rationale and available evidence that support potential opportunities for primordial and primary prevention, as well as fertile areas for future research of preventive intervention in ILD.

Telomere Shortening in Blood Leukocytes of Patients with Chronic Obstructive Pulmonary Disease

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is characterized by airflow limitation that is not completely reversible by administration of inhaled bronchodilators. Many studies propose that telomere length shortening might have occurred in COPD patients. We aimed to determine the telomere length in COPD patients and compare the results of non-smoking and smoking control subjects.

MATERIALS AND METHODS

In our case-control study, 84 clinically stable COPD patients were recruited on admission to Masih Daneshvari Hospital. Eighty-five healthy controls were also selected including 45 non-smokers and 40 smokers admitted for diseases other than COPD. Spirometry was done for all subjects. Telomere length was measured by quantitative real time PCR as described by Cawthon. The telomere repeat copy number (T) to single-gene copy number (S) ratio was calculated using the comparative Ct method.

RESULTS

The mean ±SD of age was 64.33±10.04 years in patients and 65.06 ±10.02 years in controls (P=0.693). The mean ±SD of FEV1 was 1.62±0.75 L in patients, 2.84±0.54 L in smoker controls and 2.83±0.56 L in non-smoker controls; significant differences were detected in this regard between cases and controls (P<0.001). T/S ratio was significantly lower in COPD patients (0.61±0.08) than in the control subjects (0.69±0.09) (P<0.001). However, telomere length was shorter in the patients than in controls in each age group (P<0.001). Additionally, there were no statistically significant differences in telomere length between the smoker and non-smoker control subjects. Regarding the correlation between BMI and telomere length, there were no significant differences among the patients and control groups.

CONCLUSION

In conclusion, we found that telomere length in COPD patients was shorter than that in smoker and non-smoker controls, irrespective of age, sex, spirometric variables, BMI and history of cigarette smoking.

Telomerase mutations in smokers with severe emphysema

Mutations in the essential telomerase genes TERT and TR cause familial pulmonary fibrosis; however, in telomerase-null mice, short telomeres predispose to emphysema after chronic cigarette smoke exposure. Here, we tested whether telomerase mutations are a risk factor for human emphysema by examining their frequency in smokers with chronic obstructive pulmonary disease (COPD). Across two independent cohorts, we found 3 of 292 severe COPD cases carried deleterious mutations in TERT (1%). This prevalence is comparable to the frequency of alpha-1 antitrypsin deficiency documented in this population. The TERT mutations compromised telomerase catalytic activity, and mutation carriers had short telomeres. Telomerase mutation carriers with emphysema were predominantly female and had an increased incidence of pneumothorax. In families, emphysema showed an autosomal dominant inheritance pattern, along with pulmonary fibrosis and other telomere syndrome features, but manifested only in smokers. Our findings identify germline mutations in telomerase as a Mendelian risk factor for COPD susceptibility that clusters in autosomal dominant families with telomere-mediated disease including pulmonary fibrosis.

Relationships of pulmonary function, inflammation, and T-cell activation and senescence in an HIV-infected cohort

OBJECTIVE

To determine associations between circulating markers of immune activation, immune cell senescence, and inflammation with HIV-associated abnormalities of pulmonary function.

DESIGN

HIV infection is an independent risk factor for abnormal pulmonary function. Immune activation, immune senescence, and chronic inflammation are characteristics of chronic HIV infection that have been associated with other HIV-associated comorbidities and may be related to pulmonary disease in this population.

METHODS

Participants from an HIV-infected cohort (n = 147) completed pulmonary function testing (PFT). Markers of T-cell activation and senescence were determined by flow cytometry, and plasma levels of interleukin-6, interleukin-8, and C-reactive protein (CRP) were measured, as was telomere length of peripheral blood mononuclear cells (PBMC). Regression models adjusting for clinical risk factors were constructed to examine relationships between biomarkers and PFT outcomes.

RESULTS

Activated CD25(+) T cells and activated/senescent CD69(+)/CD57(+)/CD28(null) CD4(+) T cells, interleukin-6, and CRP were associated with PFT abnormalities. Shortening of PBMC telomere length correlated with airflow obstruction and diffusing impairment. Paradoxically, circulating senescent CD57(+)/CD28(null) CD8(+) T cells were associated with better PFT outcomes.

CONCLUSION

Circulating T cells expressing markers of activation and inflammatory cytokine levels are independently correlated with PFT abnormalities in HIV-infected persons. Overall telomere shortening was also associated with pulmonary dysfunction. The paradoxical association of senescent CD8(+) T cells and better PFT outcomes could suggest an unrecognized beneficial compensatory function of such cells or a redistribution of these cells from the circulation to local compartments. Further studies are needed to differentiate and characterize functional subsets of local pulmonary and circulating T-cell populations in HIV-associated pulmonary dysfunction.

[Cellular senescence and pulmonary disease: COPD as an example]

The biological mechanisms of aging, and more specifically cellular senescence, are increasingly a subject of research. Cellular senescence may be a common determinant of many age-related diseases, including some chronic lung diseases such as chronic obstructive pulmonary disease (COPD) or idiopathic pulmonary fibrosis. Many arguments suggest that these diseases are associated with premature senescence of lung cells, which may be involved in the pathophysiology of respiratory alterations. Furthermore, these diseases are associated with systemic manifestations, such as bone loss, muscle wasting and atherosclerosis, which impact on symptoms and prognosis. Whether these alterations are related to a common pathogenic mechanism or develop independently in patients with COPD remains an open question. In this review, we will focus on cellular senescence and COPD. Two concepts will be discussed: (1) the role of cell senescence in the pathophysiology of lung destruction, vascular remodeling and inflammation in COPD, (2) the possible link between the pulmonary and systemic manifestations of COPD which could reflect a general process of accelerated aging.

Familial pulmonary fibrosis

The occurrence of pulmonary fibrosis in numerous individuals from the same family suggests a genetic cause for the disease. During the last 10 years, mutations involving proteins from the telomerase complex and from the surfactant system have been identified in association with pulmonary fibrosis. Mutations of TERT, the coding gene for the telomerase reverse transcriptase, are the most frequently identified mutations and are present in 15% of cases of familial pulmonary fibrosis. Other mutations (TERC, surfactant proteins genes) are only rarely evidenced in adults. Patients with mutations involving the telomerase complex may present with pulmonary fibrosis, hematologic, cutaneous or liver diseases. Other genetic variations associated with pulmonary fibrosis such as a polymorphism in the promoter of MUC5B or a polymorphism in TERT have been recently described, and could be considered to be part of a polygenic transmission. Evidence for mutations associated with the development of pulmonary fibrosis raises numerous clinical questions from establishing a diagnosis, providing counselling to deciding on therapy, and requires specific studies. From a pathophysiological point of view, the function of the genes highlights the central role of alveolar epithelium and aging in fibrogenesis.

The burden of image based emphysema and bronchiolitis in HIV-infected individuals on antiretroviral therapy

Background

With the widespread use of anti-retroviral therapy (ART), individuals infected with human immune deficiency virus (HIV) are increasingly experiencing morbidity and mortality from respiratory disorders. However, the prevalence or the risk factors associated with emphysema and bronchiolitis are largely unknown.

Methods

Thoracic computed tomography (CT) scans were performed in 1,446 patients infected with HIV who were on ART and who attended a tertiary care metabolic clinic (average age 48 years and 29% females). Detailed history and physical examination including anthropometric measurements were performed. Complete pulmonary function tests were performed in a subset of these patients (n = 364). No subjects were acutely ill with a respiratory condition at the time of CT scanning.

Findings

Nearly 50% of the subjects had CT evidence for emphysema, bronchiolitis or both with 13% (n = 195) showing bronchiolitis, 19% (n = 274) showing emphysema and 16% (n = 238) revealing both. These phenotypes were synergistically associated with reduced regular physical activity (p for interaction <.0001). The most significant risk factors for both phenotypes were cigarette smoking, intravenous drug use and peripheral leucocytosis. Together, the area-under-the curve statistics was 0.713 (p = 0.0037) for discriminating those with and without these phenotypes. There were no significant changes in lung volumes or flow rates related to these phenotypes, though the carbon monoxide diffusion capacity was reduced for the emphysema phenotype.

Interpretation

Emphysema and bronchiolitis are extremely common in HIV-infected patients who are treated with ART and can be identified by use of thoracic CT scanning.

Senescence-associated secretory phenotype and its possible role in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major disease of the lungs. It primarily occurs after a prolonged period of cigarette smoking. Chronic inflammation of airways and the alveolar space as well as lung tissue destruction are the hallmarks of COPD. Recently it has been shown that cellular senescence might play a role in the pathogenesis of COPD. Cellular senescence comprises signal transduction program, leading to irreversible cell cycle arrest. The growth arrest in senescence can be triggered by many different mechanisms, including DNA damage and its recognition by cellular sensors, leading to the activation of cell cycle checkpoint responses and activation of DNA repair machinery. Senescence can be induced by several genotoxic factors apart from telomere attrition. When senescence induction is based on DNA damage, senescent cells display a unique phenotype, which has been termed "senescence-associated secretory phenotype" (SASP). SASP may be an important driver of chronic inflammation and therefore may be part of a vicious cycle of inflammation, DNA damage, and senescence. This research perspective aims to showcase cellular senescence with relevance to COPD and the striking similarities between the mediators and secretory phenotype in COPD and SASP.

Ageing and the border between health and disease

Ageing is associated with a progressive degeneration of the tissues, which has a negative impact on the structure and function of vital organs and is among the most important known risk factors for most chronic diseases. Since the proportion of the world's population aged >60 years will double in the next four decades, this will be accompanied by an increased incidence of chronic age-related diseases that will place a huge burden on healthcare resources. There is increasing evidence that many chronic inflammatory diseases represent an acceleration of the ageing process. Chronic pulmonary diseases represents an important component of the increasingly prevalent multiple chronic debilitating diseases, which are a major cause of morbidity and mortality, particularly in the elderly. The lungs age and it has been suggested that chronic obstructive pulmonary disease (COPD) is a condition of accelerated lung ageing and that ageing may provide a mechanistic link between COPD and many of its extrapulmonary effects and comorbidities. In this article we will describe the physiological changes and mechanisms of ageing, with particular focus on the pulmonary effects of ageing and how these may be relevant to the development of COPD and its major extrapulmonary manifestations.

Senescence is involved in the pathogenesis of chronic obstructive pulmonary disease through effects on telomeres and the anti-aging molecule fibroblast growth factor 23

AIM

Fibroblast growth factor 23 knockout mice develop premature aging and emphysema, indicating that dysregulation of the normal aging process is involved in the pathobiology of chronic obstructive pulmonary disease. Thus, we explored the association among a coding single-nucleotide polymorphism of fibroblast growth factor 23, its protein concentration in serum and telomere length in patients with chronic obstructive pulmonary disease.

METHODS

The study involved 361 smokers; among whom, 244 were patients with chronic obstructive pulmonary disease. We genotyped a coding single-nucleotide polymorphism of fibroblast growth factor 23, rs7955866, and measured the telomere length of the peripheral blood cells. We also determined emphysema severity and airflow obstruction using computed tomography and pulmonary function tests, respectively. Furthermore, we analyzed the association between the disease phenotypes and fibroblast growth factor 23 genotypes or telomere length of peripheral blood leukocytes, as well as the association between the serum level of the studied protein and its genotypes.

RESULTS

The mice with A alleles on rs7955866 showed severe upper lung emphysema (P = 0.008). The serum concentration of the tested protein was lower in the mice with A allele than in the G homozygotes (P = 0.004). Telomere shortening was associated with airflow obstruction (P = 0.009), but not with upper lung emphysema.

CONCLUSIONS

A variation of fibroblast growth factor 23 with a reduced serum concentration appeared to promote emphysema formation. Telomere shortening in peripheral blood leukocytes was not associated with emphysema, but with airflow obstruction in chronic obstructive pulmonary disease through an independent mechanism.

Smoking accelerates aging of the small airway epithelium

BACKGROUND

Aging involves multiple biologically complex processes characterized by a decline in cellular homeostasis over time leading to a loss and impairment of physiological integrity and function. Specific cellular hallmarks of aging include abnormal gene expression patterns, shortened telomeres and associated biological dysfunction. Like all organs, the lung demonstrates both physiological and structural changes with age that result in a progressive decrease in lung function in healthy individuals. Cigarette smoking accelerates lung function decline over time, suggesting smoking accelerates aging of the lung. Based on this data, we hypothesized that cigarette smoking accelerates the aging of the small airway epithelium, the cells that take the initial brunt of inhaled toxins from the cigarette smoke and one of the primary sites of pathology associated with cigarette smoking.

METHODS

Using the sensitive molecular parameters of aging-related gene expression and telomere length, the aging process of the small airway epithelium was assessed in age matched healthy nonsmokers and healthy smokers with no physical manifestation of lung disease or abnormalities in lung function.

RESULTS

Analysis of a 73 gene aging signature demonstrated that smoking significantly dysregulates 18 aging-related genes in the small airway epithelium. In an independent cohort of male subjects, smoking significantly reduced telomere length in the small airway epithelium of smokers by 14% compared to nonsmokers.

CONCLUSION

These data provide biologic evidence that smoking accelerates aging of the small airway epithelium.

Bone marrow failure and the telomeropathies

Our understanding of the pathophysiology of aplastic anemia is undergoing significant revision, with implications for diagnosis and treatment. Constitutional and acquired disease is poorly delineated, as lesions in some genetic pathways cause stereotypical childhood syndromes and also act as risk factors for clinical manifestations in adult life. Telomere diseases are a prominent example of this relationship. Accelerated telomere attrition is the result of mutations in telomere repair genes and genes encoding components of the shelterin complex and related proteins. Genotype-phenotype correlations show genes responsible for X-linked (DKC1) and severe recessive childhood dyskeratosis congenita, typically with associated mucocutaneous features, and others (TERC and TERT) for more subtle presentation as telomeropathy in adults, in which multiorgan failure may be prominent. Telomerase mutations also are etiologic in familial pulmonary fibrosis and cryptic liver disease. Detection of a telomere disease requires awareness in the clinic, appropriate laboratory testing of telomere content, and genetic sequencing. In treatment decisions, genetic screening of related donors for hematopoietic stem cell transplantation is critical, and androgen therapy may be helpful. Telomeres shorten normally with aging, as well as under environmental circumstances, with regenerative stress and oxidative damage. Telomere biology is complexly related to oncogenesis: telomere attrition is protective by enforcing senescence or apoptosis in cells with a long mitotic history, but telomere loss also can destabilize the genome by chromosome rearrangement and aneuploidy.

Cell biology of disease: Telomeropathies: an emerging spectrum disorder

A constellation of related genetic diseases are caused by defects in the telomere maintenance machinery. These disorders, often referred to as telomeropathies, share symptoms and molecular mechanisms, and mounting evidence indicates they are points along a spectrum of disease. Several new causes of these disorders have been recently discovered, and a number of related syndromes may be unrecognized telomeropathies. Progress in the clinical understanding of telomeropathies has in turn driven progress in the basic science of telomere biology. In addition, the pattern of genetic anticipation in some telomeropathies generates thought-provoking questions about the way telomere length impacts the course of these diseases.

Asthma epigenetics

Asthma is the most common chronic disease of childhood, and a growing body of evidence indicates that epigenetic variations may mediate the effects of environmental exposures on the development and natural history of asthma. Epigenetics is the study of mitotically or meiotically heritable changes in gene expression that occur without directly altering the DNA sequence. DNA methylation, histone modifications and microRNAs are major epigenetic variations in humans that are currently being investigated for asthma etiology and natural history. DNA methylation results from addition of a methyl group to the 5 position of a cytosine ring and occurs almost exclusively on a cytosine in a CpG dinucleotide. Histone modifications involve posttranslational modifications such as acetylation, methylation, phosphorylation and ubiquitination on the tails of core histones. MicroRNAs are short ~22 nucleotide long, non-coding, single-stranded RNAs that binds to complementary sequences in the target mRNAs, usually resulting in gene silencing. While many studies have documented relationships of environmental exposures that have been implicated in asthma etiology with epigenetic alterations, to date, few studies have directly linked epigenetic variations with asthma development. There are several methodological challenges in studying the epigenetics of asthma. In this chapter, the influence of epigenetic variations on asthma pathophysiology, methodological concerns in conducting epigenetic research and future direction of asthma epigenetics research are discussed.

Molecular processes that drive cigarette smoke-induced epithelial cell fate of the lung

Cigarette smoke contains numerous chemical compounds, including abundant reactive oxygen/nitrogen species and aldehydes, and many other carcinogens. Long-term cigarette smoking significantly increases the risk of various lung diseases, including chronic obstructive pulmonary disease and lung cancer, and contributes to premature death. Many in vitro and in vivo studies have elucidated mechanisms involved in cigarette smoke-induced inflammation, DNA damage, and autophagy, and the subsequent cell fates, including cell death, cellular senescence, and transformation. In this Translational Review, we summarize the known pathways underlying these processes in airway epithelial cells to help reveal future challenges and describe possible directions of research that could lead to better management and treatment of these diseases.

Telomere dynamics in mice and humans

Telomeres are ribonucleoprotein structures capping the end of every linear chromosome. In all vertebrates, they are composed of TTAGGG repeats coated with specific protecting proteins. Telomeres shorten with each mitotic cell division, but telomerase, a reverse transcriptase, elongate telomeres in very specific cells, such as embryonic and adult stem cells. Although telomere sequence is identical in mice and humans and telomeres serve the same role of protecting chromosomes and genetic information from damage and erosion in both species, abnormalities in telomere maintenance and in telomerase function do not coincide in phenotype in humans and mice. The telomeres of most laboratory mice are 5 to 10 times longer than in humans, but their lifespan is 30 times shorter. Complete absence of telomerase has little expression in phenotype over several generations in mice, whereas heterozygosity for telomerase mutations in humans is sufficient to result in organ regeneration defect and cancer development. Patients with telomerase deficiency and very short telomeres may develop aplastic anemia, pulmonary fibrosis, or cirrhosis, whereas telomerase-null murine models display only modest hematopoietic deficiency and develop emphysema when exposed to cigarette smoke. In summary, telomerase deficiency in both humans and mice accelerate telomere shortening, but its consequences in the different organs and in the organism diverge, mainly due to telomere length differences.