Toll-Like Receptor-9 Polymorphisms in Sarcoidosis and Chronic Obstructive Pulmonary Disease

Expanding role of deoxyribonucleic acid-sensing mechanism in the development of lifestyle-related diseases

In lifestyle-related diseases, such as cardiovascular, metabolic, respiratory, and kidney diseases, chronic inflammation plays a causal role in their pathogenesis; however, underlying mechanisms of sterile chronic inflammation are not well-understood. Previous studies have confirmed the damage of cells in these organs in the presence of various risk factors such as diabetes, dyslipidemia, and cigarette smoking, releasing various endogenous ligands for pattern recognition receptors. These studies suggested that nucleic acids released from damaged tissues accumulate in these tissues, acting as an endogenous ligand. Undamaged DNA is an integral factor for the sustenance of life, whereas, DNA fragments, especially those from pathogens, are potent activators of the inflammatory response. Recent studies have indicated that inflammatory responses such as the production of type I interferon (IFN) induced by DNA-sensing mechanisms which contributes to self-defense system in innate immunity participates in the progression of inflammatory diseases by the recognition of nucleic acids derived from the host, including mitochondrial DNA (mtDNA). The body possesses several types of DNA sensors. Toll-like receptor 9 (TLR9) recognizes DNA fragments in the endosomes. In addition, the binding of DNA fragments in the cytosol activates cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase (cGAS), resulting in the synthesis of the second messenger cyclic GMP-AMP (cGAMP). The binding of cGAMP to stimulator of interferon genes (STING) activates NF-κB and TBK-1 signaling and consequently the production of many inflammatory cytokines including IFNs. Numerous previous studies have demonstrated the role of DNA sensors in self-defense through the recognition of DNA fragments derived from pathogens. Beyond the canonical role of TLR9 and cGAS-STING, this review describes the role of these DNA-sensing mechanism in the inflammatory responses caused by endogenous DNA fragments, and in the pathogenesis of lifestyle-related diseases.

Innate and Adaptive Immunity in Noninfectious Granulomatous Lung Disease

Sarcoidosis and chronic beryllium disease are noninfectious lung diseases that are characterized by the presence of noncaseating granulomatous inflammation. Chronic beryllium disease is caused by occupational exposure to beryllium containing particles, whereas the etiology of sarcoidosis is not known. Genetic susceptibility for both diseases is associated with particular MHC class II alleles, and CD4⁺ T cells are implicated in their pathogenesis. The innate immune system plays a critical role in the initiation of pathogenic CD4⁺ T cell responses as well as the transition to active lung disease and disease progression. In this review, we highlight recent insights into Ag recognition in chronic beryllium disease and sarcoidosis. In addition, we discuss the current understanding of the dynamic interactions between the innate and adaptive immune systems and their impact on disease pathogenesis.

Experimental models of sarcoidosis

PURPOSE OF REVIEW

Sarcoidosis is a disease caused by a complex combination of genetic susceptibility, immune networks and infectious and/or environmental agents. The onset and phenotypic variability of sarcoidosis remain poorly elucidated, not only due to the lack of clearly identified causes, but also because it is widely considered that no reliable model of this disease is available. In this review, we discuss the various models of granulomatous diseases in order to challenge this assertion.

RECENT FINDINGS

A large number of models of granulomatous diseases are available, both cellular models used to study the natural history of granulomas and experimental animal models mostly developed in rodents.

SUMMARY

Although none of the available models fully reproduces sarcoidosis, most of them generate various data supporting key concepts. Selected models with a high level of confidence among those already published may provide various pieces of the sarcoidosis jigsaw puzzle, whereas clinical data can provide other elements. A 'systems biology' approach for modelling may be a way of piecing together the various pieces of the puzzle. Finally, experimental models and a systemic approach should be considered to be tools for preclinical evaluation of the efficacy of drugs prior to testing in clinical trials.

Functional Toll-Like Receptor 9 Expression and CXCR3 Ligand Release in Pulmonary Sarcoidosis

Sarcoidosis is a granulomatous disease characterized by a T-helper type 1 (Th1) cell-dominated alveolitis. As a role of bacteria in the pathogenesis of sarcoidosis has been discussed, Toll-like receptors (TLRs) may be involved in the initiation of a first immune reaction. We analyzed expression and functional relevance of several TLRs in bronchoalveolar lavage (BAL) cells from patients with pulmonary sarcoidosis. In parallel, we determined the release of C-X-C motif chemokine 9 (CXCL9), CXCL10, and CXCL11 by BAL cells from patients with pulmonary sarcoidosis. Nucleotide-binding oligomerization domain-containing protein (NOD) 1 and 2, TLR2, TLR6, and TLR9 expression by BAL cells was analyzed by real-time RT-PCR and cell surface expression by flow cytometry. Chemokine release was measured in BAL cell culture supernatants by ELISA. We found increased TLR9 mRNA expression in patients with sarcoidosis with chest X-ray type I and II and TLR9 protein expression in BAL cells from patients with chest X-ray type II and III. Stimulation with CpG nucleotides increased CXCL10 release by BAL cells from patients with sarcoidosis type II significantly compared with control subjects or other patients with sarcoidosis. In contrast, no increase in TNF, IL-12p40, or CXCL8 was detected. Spontaneous release of CXCL10, but not CXCL9 or CXCL11, by cultured BAL cells was also highest in cells from patients with chest X-ray type II. We found a significant association between TLR9 expression and CD4⁺ lymphocytes in BAL. Our data demonstrate that TLR9 ligands may contribute to the immunopathogenesis of sarcoidosis via induction of CXCL10 release in the alveolar macrophages.

Immune-related gene polymorphisms in pulmonary diseases

Between the DNA sequences of two randomly-selected human genomes, which consist of over 3 billion base pairs and twenty five thousand genes, there exists only 0.1% variation and 99.9% sequence identity. During the last couple of decades, extensive genome-wide studies have investigated the association between single-nucleotide polymorphisms (SNPs), the most common DNA variations, and susceptibility to various diseases. Because the immune system's primary function is to defend against myriad infectious agents and diseases, the large number of people who escape serious infectious diseases underscores the tremendous success of this system at this task. In fact, out of the third of the global human population infected with Mycobacterium tuberculosis during their lifetime, only a few people develop active disease, and a heavy chain smoker may inexplicably escape all symptoms of chronic obstructive pulmonary disease (COPD), lung cancer, and other smoke-associated lung diseases. This may be attributable to the genetic makeup of the individual(s), including their SNPs, which provide some resistance to the disease. Pattern recognition receptors (PRRs), transcription factors, cytokines and chemokines all play critical roles in orchestrating immune responses and their expression/activation is directly linked to human disease tolerance. Moreover, genetic variations present in the immune-response genes of various ethnicities may explain the huge differences in individual outcomes to various diseases and following exposure to infectious agents. The current review focuses on recent advances in our understanding of pulmonary diseases and the relationship of genetic variations in immune response genes to these conditions.

Toll-like receptors and autophagy in interstitial lung diseases

Interstitial lung diseases (ILDs) include a number of diseases whose pathogenesis still is not fully understood. Idiopathic pulmonary fibrosis (IPF), the most frequent and severe form of ILDs is an epithelial-driven disease and the treatment consists of the use of antifibrotic agents. In the rest of ILDs an inflammation-driven pathway is believed to be the main pathogenetic mechanism and treatment consists of the use of immunomodulatory agents. In both groups it is believed that infection can play an important role in the development and progression of the diseases. The immune system can recognize exogenous threats or endogenous stress through specialized receptors namely pattern recognition receptors (PRRs) which in turn, initiate downstream signaling pathways to control immune responses. Recently, a link between PRRs and autophagy, a specialized biological process involved in maintaining cellular homeostasis but also involved in various immunologic processes, has been described. In this review, we focus on the reciprocal influences of PRRs with particular emphasis on Toll-like receptors and autophagy in modulating innate immune responses.

Fungal cell wall agents and bacterial lipopolysaccharide in organic dust as possible risk factors for pulmonary sarcoidosis

Background

Composition of organic dust is very complex, involving particles of microbial, animal and plant origin. Several environmental exposure studies associate microbial cell wall agents in organic dust with various respiratory symptoms and diseases. The aim of the present study was to investigate the in vitro effects of the co-exposure of fungal cell wall agents (FCWAs) and bacterial lipopolysaccharide (LPS) on inflammatory immune responses of peripheral blood mononuclear cells (PBMCs) from patients with pulmonary sarcoidosis.

Methods

PBMCs from 22 patients with pulmonary sarcoidosis and 20 healthy subjects were isolated and stimulated in vitro with FCWAs (soluble and particulate (1 → 3)-β-D-glucan, zymosan and chitosan) and/or LPS. Subsequently, cytokines were measured by ELISA and the mRNA expression of dectin-1, toll-like receptor 2 (TLR2), TLR4 and mannose receptor (MR) was analysed by real-time RT-PCR.

Results

Patients with sarcoidosis had a significantly higher secretion of inflammatory cytokines tumour necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), IL-10 and IL-12 (1.7-fold, 2.0-fold, 2.2-fold, and 2.8-fold, respectively; all p < 0.05) after in vitro co-stimulation of PBMCs with FCWAs and LPS. We showed that PBMCs from patients with sarcoidosis had a higher baseline mRNA expression of dectin-1, TLR2, TLR4 and MR (6-fold, 11-fold, 18-fold, and 4-fold, respectively). Furthermore, we found a reduced expression of dectin-1, TLR2 and TLR4 after stimulation with FCWAs and/or LPS, although the reduction was significantly weaker in patients than in healthy subjects.

Conclusions

In conclusion, co-stimulation with FCWAs and LPS of PBMC from patients with sarcoidosis caused a weaker reduction of dectin-1, TLR2, TLR4 receptors expression, which could increase the sensitivity of PBMCs, leading to excessive inflammatory cytokine responses and result in the development or progression of pulmonary sarcoidosis.

Cellular Players in the Immunopathogenesis of Sarcoidosis

Current hypotheses on the pathogenesis of sarcoidosis assume that it is induced by a nondegradable antigen inducing immune reactions, which are mediated by a panel of immune cells of the innate and adoptive immune system. This immune reaction leads to an accumulation of immune cells that is mainly alveolar macrophages, T cells, and neutrophils in the lung. As the antigen persists and cannot be eliminated, the ongoing immune reaction results in granuloma formation and remodeling of the lung. The current review aims to elucidate the different roles of the cellular players in the immunopathogenesis of sarcoidosis.

Toll-like receptors in the pathogenesis of pulmonary fibrosis

Pulmonary fibrosis (PF) constitutes the end stage of a broad range of heterogeneous interstitial lung diseases, characterized by the destruction of the pulmonary parenchyma, deposition of extracellular matrix and dramatic changes in the phenotype of both fibroblasts and alveolar epithelial cells. More than 200 causes of pulmonary fibrosis have been identified so far, yet the most common form is idiopathic pulmonary fibrosis (IPF). IPF is a lethal lung disorder of unknown etiology with a gradually increasing worldwide incidence and a median survival of 3-5 years from the time of diagnosis. Despite intense research efforts, the pathogenesis remains elusive and no effective treatment is available. Accumulating body of evidence suggests an abnormal wound healing response followed by extracellular matrix deposition, destruction of lung architecture, ultimately leading to respiratory failure. The contribution of immune system in lung fibrogenesis had been largely underscored due to the absence of response to immunosuppressive agents; however, the premise that lung fibrosis has an immunologic background has been recently revived. Toll-like receptors (TLRs) are pattern recognition receptors (PRRs), which link innate and adaptive immune response and regulate wound healing. TLRs promote tissue repair or fibrosis in many disease settings including lung fibrosis, albeit with profound differences depending on the cellular microenvironment. This review summarizes the current state of knowledge regarding the mechanistic implications between TLRs and lung fibrosis and highlights the therapeutic potential of targeting TLR signaling at the ligand or receptor level.

TLR9 expression is required for the development of cigarette smoke-induced emphysema in mice

The expression of Toll-like receptor (TLR)-9, a pathogen recognition receptor that recognizes unmethylated CpG sequences in microbial DNA molecules, is linked to the pathogenesis of several lung diseases. TLR9 expression and signaling was investigated in animal and cell models of chronic obstructive pulmonary disease (COPD). We observed enhanced TLR9 expression in mouse lungs following exposure to cigarette smoke. Tlr9(-/-) mice were resistant to cigarette smoke-induced loss of lung function as determined by mean linear intercept, total lung capacity, lung compliance, and tissue elastance analysis. Tlr9 expression also regulated smoke-mediated immune cell recruitment to the lung; apoptosis; expression of granulocyte-colony stimulating factor (G-CSF), the CXCL5 protein, and matrix metalloproteinase-2 (MMP-2); and protein tyrosine phosphatase 1B (PTP1B) activity in the lung. PTP1B, a phosphatase with anti-inflammatory abilities, was identified as binding to TLR9. In vivo delivery of a TLR9 agonist enhanced TLR9 binding to PTP1B, which inactivated PTP1B. Ptp1b(-/-) mice had elevated lung concentrations of G-CSF, CXCL5, and MMP-2, and tissue expression of type-1 interferon following TLR9 agonist administration, compared with wild-type mice. TLR9 responses were further determined in fully differentiated normal human bronchial epithelial (NHBE) cells isolated from nonsmoker, smoker, and COPD donors, and then cultured at air liquid interface. NHBE cells from smokers and patients with COPD expressed more TLR9 and secreted greater levels of G-CSF, IL-6, CXCL5, IL-1β, and MMP-2 upon TLR9 ligand stimulation compared with cells from nonsmoker donors. Although TLR9 combats infection, our results indicate that TLR9 induction can affect lung function by inactivating PTP1B and upregulating expression of proinflammatory cytokines.

Cartography of Pathway Signal Perturbations Identifies Distinct Molecular Pathomechanisms in Malignant and Chronic Lung Diseases

Lung diseases are described by a wide variety of developmental mechanisms and clinical manifestations. Accurate classification and diagnosis of lung diseases are the bases for development of effective treatments. While extensive studies are conducted toward characterization of various lung diseases at molecular level, no systematic approach has been developed so far. Here we have applied a methodology for pathway-centered mining of high throughput gene expression data to describe a wide range of lung diseases in the light of shared and specific pathway activity profiles. We have applied an algorithm combining a Pathway Signal Flow (PSF) algorithm for estimation of pathway activity deregulation states in lung diseases and malignancies, and a Self Organizing Maps algorithm for classification and clustering of the pathway activity profiles. The analysis results allowed clearly distinguish between cancer and non-cancer lung diseases. Lung cancers were characterized by pathways implicated in cell proliferation, metabolism, while non-malignant lung diseases were characterized by deregulations in pathways involved in immune/inflammatory response and fibrotic tissue remodeling. In contrast to lung malignancies, chronic lung diseases had relatively heterogeneous pathway deregulation profiles. We identified three groups of interstitial lung diseases and showed that the development of characteristic pathological processes, such as fibrosis, can be initiated by deregulations in different signaling pathways. In conclusion, this paper describes the pathobiology of lung diseases from systems viewpoint using pathway centered high-dimensional data mining approach. Our results contribute largely to current understanding of pathological events in lung cancers and non-malignant lung diseases. Moreover, this paper provides new insight into molecular mechanisms of a number of interstitial lung diseases that have been studied to a lesser extent.

Immunogenetics of Disease-Causing Inflammation in Sarcoidosis

Sarcoidosis is a systemic inflammatory disorder characterised by tissue infiltration by mononuclear phagocytes and lymphocytes with associated non-caseating granuloma formation. Originally described as a disorder of the skin, sarcoidosis can involve any organ with wide-ranging clinical manifestations and disease course. Recent studies have provided new insights into the mechanisms involved in disease pathobiology, and we now know that sarcoidosis has a clear genetic basis largely involving human leukocyte antigen (HLA) genes. In contrast to Mendelian-monogenic disorders--which are generally due to specific and relatively rare mutations often leading to a single amino acid change in an encoded protein--sarcoidosis results from genetic variations relatively common in the general population and involving multiple genes, each contributing an effect of varying magnitude. However, an individual may have the necessary genetic profile and yet the disease will not develop unless an environmental or infectious factor is encountered. Genetics appears also to contribute to the huge variability in clinical phenotype and disease behaviour. Moreover, it has been established that sarcoidosis granulomatous inflammation is a highly polarized T helper 1 immune response that starts with an antigenic stimulus followed by T cell activation via a classic HLA class II-mediated pathway. A complex network of lymphocytes, macrophages, and cytokines is pivotal in the orchestration and evolution of the granulomatous process. Despite these advances, the aetiology of sarcoidosis remains elusive and its pathogenesis incompletely understood. As such, there is an urgent need for a better understanding of disease pathogenesis, which hopefully will translate into the development of truly effective therapies.

Impaired Innate COPD Alveolar Macrophage Responses and Toll-Like Receptor-9 Polymorphisms

Background

Dysfunctional innate responses of alveolar macrophages to nontypeable Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pneumoniae contribute to morbidity in chronic obstructive pulmonary disease (COPD). Our earlier studies discovered impaired COPD alveolar macrophage responses to Toll-like receptor (TLR) ligands of nontypeable H. influenzae and provide rationale for further evaluation of TLR signaling. While the role of TLR single nucleotide polymorphisms is increasingly recognized in inflammatory diseases, TLR single nucleotide polymorphisms in COPD have only recently been explored. We hypothesized that specific TLR polymorphisms are associated with dysfunctional innate immune COPD alveolar macrophage responses and investigated polymorphisms of TLR2(Arg753Gln), TLR4(Thr399Ile; Asp299Gly), and TLR9(T1486C; T1237C).

Methods

DNA was purified from cells of 1) healthy nonsmokers (n = 20); 2) COPD ex-smokers (n = 83); 3) COPD active smokers (n = 93). DNA amplifications (polymerase chain reaction) were performed for each SNP. Alveolar macrophages from each group were incubated with nontypeable H. influenzae, M. catarrhalis and S. pneumoniae. Cytokine induction of macrophage supernatants was measured and the association with TLR single nucleotide polymorphism expression was determined.

Results

No significant inter-group differences in frequency of any TLR SNP existed. However both TLR9 single nucleotide polymorphisms were expressed in high frequency. Among COPD ex-smokers, diminished IL-8 responsiveness to nontypeable H. influenzae, M. catarrhalis and S. pneumoniae was strongly associated with carriage of TLR9(T1237C) (p = 0.02; p = 0.008; p = 0.02), but not TLR9(T1486C). Carriage of TLR9(T1237C), but not TLR9(T1486C), correlated with diminished FEV₁%predicted (p = 0.037).

Conclusion

Our results demonstrate a notable association of TLR9(T1237C) expression with dysfunctional innate alveolar macrophage responses to respiratory pathogens and with severity of COPD.

Genetic variants in ADAM33 are associated with airway inflammation and lung function in COPD

BACKGROUND

Genetic factors play a role in the development and severity of chronic obstructive pulmonary disease (COPD). The pathogenesis of COPD is a multifactorial process including an inflammatory cell profile. Recent studies revealed that single nucleotide polymorphisms (SNPs) within ADAM33 increased the susceptibility to COPD through changing the airway inflammatory process and lung function.

METHODS

In this paper, we investigated associations of four polymorphisms (T1, T2, S2 and Q-1) of ADAM33 as well as their haplotypes with pulmonary function and airway inflammatory process in an East Asian population of patients with COPD.

RESULTS

We found that T1, T2 and Q-1 were significantly associated with the changes of pulmonary function and components of cells in sputum of COPD, and T1 and Q-1 were significantly associated with cytokines and mediators of inflammation in airway of COPD in recessive models. 10 haplotypes were significantly associated with transfer factor of the lung for carbon monoxide in the disease state, 4 haplotypes were significantly associated with forced expiratory volume in one second, and other haplotypes were associated with airway inflammation.

CONCLUSIONS

We confirmed for the first time that ADAM33 was involved in the pathogenesis of COPD by affecting airway inflammation and immune response in an East Asian population. Our results made the genetic background of COPD, a common and disabling disease, more apparent, which would supply genetic support for the study of the mechanism, classification and treatment for this disease.

Beneficial role of vitamin D3 in the prevention of certain respiratory diseases

There is evidence of aberrations in the vitamin D-endocrine system in subjects with respiratory diseases. Vitamin D deficiency is highly prevalent in patients with respiratory diseases, and patients who receive vitamin D have significantly larger improvements in inspiratory muscle strength and maximal oxygen uptake. Studies have provided an opportunity to determine which proteins link vitamin D to respiratory pathology, including the major histocompatibility complex class II molecules, vitamin D receptor, vitamin D-binding protein, chromosome P450, Toll-like receptors, poly(ADP-ribose) polymerase-1, and the reduced form of nicotinamide adenine dinucleotide phosphate. Vitamin D also exerts its effect on respiratory diseases through cell signaling mechanisms, including matrix metalloproteinases, mitogen-activated protein kinase pathways, the Wnt/β-catenin signaling pathway, prostaglandins, reactive oxygen species, and nitric oxide synthase. In conclusion, vitamin D plays a significant role in respiratory diseases. The best form of vitamin D for use in the treatment of respiratory diseases is calcitriol because it is the active metabolite of vitamin D3 and modulates inflammatory cytokine expression. Further investigation of calcitriol in respiratory diseases is needed.