Fibronectin and hyaluronan in bronchoalveolar lavage fluid from young patients with chronic obstructive pulmonary diseases

The role of α7-nAChR-mediated PI3K/AKT pathway in lung cancer induced by nicotine

Nicotine enters the environment mainly through human activity, as well as natural sources. This review article examines the increasing evidence implicating nicotine in the initiation and progression of lung cancer. Moreover, it primarily focuses on elucidating the activation mechanism of phosphoinositide 3-kinase (PI3K)/protein kinase B (PKB, also known as AKT) signaling pathway, regulated by α7 subtype nicotinic acetylcholine receptor (α7-nAChR), in relation to the proliferation, invasion, and metastasis of lung cancer cells induced by nicotine, as well as nicotine-mediated anti-apoptotic effects. This process involves PI3K/AKT phosphorylated-B-cell lymphoma-2 (Bcl-2) family proteins, PI3K/AKT/mammalian target of rapamycin (mTOR), PI3K/AKT/nuclear factor-κB (NF-κB), hepatocyte growth factor (HGF)/cellular-mesenchymal epithelial transition factor (c-Met)-induced PI3K/AKT and PI3K/AKT activated-hypoxia-inducible factor-1α (HIF-1α)/vascular endothelial growth factor (VEGF) pathways. In addition, we also deliberated on the related challenges and upcoming prospects within this field. These lay the foundation for further study on nicotine, lung tumorigenesis, and PI3K/AKT related molecular mechanisms. This work has the potential to significantly contribute to the treatment and prognosis of gastric cancer in smokers. Besides, the crucial significance of PI3K/AKT signaling pathway in multiple molecular pathways also suggests that its target antagonists may inhibit the development and progression of lung cancer, providing a possible new perspective for solving the problem of nicotine-promoted lung cancer. The emerging knowledge about the carcinogenic mechanisms of nicotine action should be considered during the environmental assessment of tobacco and other nicotine-containing products.

Airway Smooth Muscle Cell Mitochondria Damage and Mitophagy in COPD via ERK1/2 MAPK

Chronic obstructive pulmonary disease (COPD) is characterized by irreversible deterioration of the airway wall. Cigarette smoking is the major trigger, and in vitro studies showed that cigarette smoke extract (CSE) induced mitophagy in airway epithelial cells via oxidative stress, but this mechanism was not studied in airway smooth muscle cells (ASMCs). Primary ASMCs isolated from COPD patients or non-disease donors were investigated for CSE-induced remodeling and mitochondria structure. Proteins were assessed by Western blots for remodeling: collagen type-I, α-smooth muscle actin (α-SMA) and fibronectin; autophagy: beclin-1, protein62 (p62), light chain (LC)3A/B; mitochondria activity: mitochondrially encoded cytochrome c oxidase II & -IV (MTCO2, MTCO4), peroxisome proliferator activated receptor gamma coactivator 1α (PGC-1α); lysosomes: early endosome antigen 1, lysosome activated membrane protein 1; and cell signaling: extracellular signal regulated kinase (ERK1/2). Lysotracker and Mitotracker were used to monitor mitochondria morphology and organelle co-localization. Compared with controls, untreated COPD ASMCs showed lower collagen type-I and α-SMA expressions, but increased fibronectin levels. CSE further downregulated collagen type-I and α-SMA expression, but upregulated fibronectin. CSE decreased PGC-1α, MTCO2, and MTCO4, but increased beclin-1, p62, and LC3. CSE upregulated mitophagy and lysosomes activity via ERK1/2 phosphorylation. In vitro, cigarette smoke induced the deterioration of ASMCs, which might explain the tissue loss and structural remodeling in COPD bronchi. The results suggest that preventing exceeded mitophagy in ASMCs might present a novel therapeutic target for COPD.

The role of Hyaluronan synthesis and degradation in the critical respiratory illness COVID-19

Hyaluronan (HA) is a polysaccharide found in all tissues as an integral component of the extracellular matrix (ECM) that plays a central regulatory role in inflammation. In fact, HA matrices are increasingly considered as a barometer of inflammation. A number of proteins specifically recognize the HA structure and these interactions modify cell behavior and control the stability of the ECM. Moreover, inflamed airways are remarkably rich with HA and are associated with various inflammatory diseases including cystic fibrosis, influenza, sepsis, and more recently coronavirus disease 2019 (COVID-19). COVID-19 is a worldwide pandemic caused by a novel coronavirus called SARS-CoV-2, and infected individuals have a wide range of disease manifestations ranging from asymptomatic to severe illness. Critically ill COVID-19 patient cases are frequently complicated by development of acute respiratory distress syndrome (ARDS), which typically leads to poor outcomes with high mortality rate. In general, ARDS is characterized by poor oxygenation accompanied with severe lung inflammation, damage, and vascular leakage and has been suggested to be linked to an accumulation of HA within the airways. Here, we provide a succinct overview of known inflammatory mechanisms regulated by HA in general, and those both observed and postulated in critically ill patients with COVID-19.

Analysis of genomic responses in a rat lung model treated with a humidifier sterilizer containing polyhexamethyleneguanidine phosphate

The antimicrobial biocide polyhexamethyleneguanidine (PHMG) phosphate is the main ingredient in the commercially available humidifier disinfectant. PHMG phosphate-based humidifier disinfectants can cause pulmonary fibrosis and induce inflammatory and fibrotic responses both in vivo and in vitro. However, toxicological mechanisms including genomic alterations induced by inhalation exposure to PHMG phosphate have not been elucidated. Therefore, this study evaluated the toxicological effects of the PHMG phosphate-containing humidifier disinfectant. We used DNA microarray to identify global gene expression changes in rats treated with PHMG phosphate-containing humidifier disinfectant for 4 weeks and 10 weeks. Functional significance of differentially expressed genes (DEGs) was estimated by gene ontology (GO) analysis. Four weeks post-exposure, 320 and 392 DEGs were identified in female and male rats, respectively (>2-fold, p<0.05). Ten weeks post-exposure, 1290 and 995 DEGs were identified in females and males, respectively. Of these, 119 and 556 genes overlapped between females and males at 4 weeks and 10 weeks, respectively, post-PHMG phosphate exposure. In addition, 21 genes were upregulated and 4 genes were downregulated in response to PHMG phosphate in a time-dependent manner. Thus, we predict that changes in genomic responses could be a significant molecular mechanism underlying PHMG phosphate toxicity. Further studies are required to determine the detailed mechanism of PHMG phosphate-induced pulmonary toxicity.

COPD Exacerbations Are Associated With Proinflammatory Degradation of Hyaluronic Acid

BACKGROUND

COPD is characterized by chronic airway inflammation and remodeling, with serious modifications of the extracellular matrix (ECM). Hyaluronic acid (HA) is an abundant ECM molecule in the lung with various biologic functions that depend on its molecular weight (MW). High-MW HA exhibits antiinflammatory and immunosuppressive effects, whereas low-MW HA is proinflammatory. In this study, we investigated whether acute exacerbations of COPD (AECOPDs), which affect patient quality of life and survival, are associated with altered HA turnover in BAL.

METHODS

We used BAL from patients with stable COPD (n = 53) or during AECOPD (n = 44) matched for demographics and clinical characteristics and BAL from control subjects (n = 15). HA, HA synthase-1 (HAS-1), and hyaluronidase (HYAL) values were determined by enzyme-linked immunosorbent assay, and HYAL activity was determined by HA zymography. The MW of HA was analyzed by agarose electrophoresis.

RESULTS

Levels of HA, HAS-1, and HYAL were significantly increased in BAL of patients with stable COPD and during exacerbations compared with control subjects. HYAL activity was significantly increased in BAL of patients with AECOPD, resulting in an increase of low-MW HA during exacerbations. In patients with AECOPD, we also observed a significant negative correlation of HA and HYAL levels with FEV1 % predicted but not with diffusing capacity of lung for carbon monoxide % predicted, indicating that increased HA degradation may be more associated with airway obstruction than with emphysema.

CONCLUSIONS

AECOPDs are associated with increased HYAL activity in BAL and subsequent degradation of HA, which may contribute to airway inflammation and subsequent lung function decline during exacerbations.

The Rise and Fall of Hyaluronan in Respiratory Diseases

In normal airways, hyaluronan (HA) matrices are primarily located within the airway submucosa, pulmonary vasculature walls, and, to a lesser extent, the alveoli. Following pulmonary injury, elevated levels of HA matrices accumulate in these regions, and in respiratory secretions, correlating with the extent of injury. Animal models have provided important insight into the role of HA in the onset of pulmonary injury and repair, generally indicating that the induction of HA synthesis is an early event typically preceding fibrosis. The HA that accumulates in inflamed airways is of a high molecular weight (>1600 kDa) but can be broken down into smaller fragments (<150 kDa) by inflammatory and disease-related mechanisms that have profound effects on HA pathobiology. During inflammation in the airways, HA is often covalently modified with heavy chains from inter-alpha-inhibitor via the enzyme tumor-necrosis-factor-stimulated-gene-6 (TSG-6) and this modification promotes the interaction of leukocytes with HA matrices at sites of inflammation. The clearance of HA and its return to normal levels is essential for the proper resolution of inflammation. These data portray HA matrices as an important component of normal airway physiology and illustrate its integral roles during tissue injury and repair among a variety of respiratory diseases.

Matrix proteins from smoke-exposed fibroblasts are pro-proliferative

Airway remodeling decreases lung function in chronic obstructive pulmonary disease (COPD). Extracellular matrix (ECM) deposition is increased in remodeled airways and drives cellular processes of proliferation, migration, and inflammation. We investigated the role of cigarette smoke in altering the ECM deposited from human lung fibroblasts. Lung fibroblasts isolated from patients with COPD or other lung disease were exposed to cigarette smoke extract (CSE) and 5 ng/ml transforming growth factor-β1 for 72 hours; in some experiments, inhibitors of signaling molecules were added. Deposition of perlecan, fibronectin, and elastin were measured by ELISA, as was release of IL-8 and IL-13. Unstimulated fibroblast cells were reseeded onto deposited matrix and assessed for proliferation and cytokine release. CSE (5%) increased deposition of fibronectin and perlecan from only COPD fibroblasts. Fibronectin and perlecan deposition was attenuated by addition of the NF-κB inhibitor, BMS-345541, and the signal transduction and activator of transcription-1/3 inhibitor, pyridone 6, respectively. CSE (5%) increased IL-8 release from COPD fibroblasts more than non-COPD fibroblasts. This increase was attenuated by BMS-345541. Matrix deposited after 5% CSE stimulation increased proliferation of fibroblasts, but did not alter cytokine release. ECM produced from COPD fibroblasts after CSE exposure has proproliferative effects. Thus, the ECM in patients with COPD may create an environment that promotes airway remodeling.

Hyaluronan as an immune regulator in human diseases

Accumulation and turnover of extracellular matrix components are the hallmarks of tissue injury. Fragmented hyaluronan stimulates the expression of inflammatory genes by a variety of immune cells at the injury site. Hyaluronan binds to a number of cell surface proteins on various cell types. Hyaluronan fragments signal through both Toll-like receptor (TLR) 4 and TLR2 as well as CD44 to stimulate inflammatory genes in inflammatory cells. Hyaluronan is also present on the cell surface of epithelial cells and provides protection against tissue damage from the environment by interacting with TLR2 and TLR4. Hyaluronan and hyaluronan-binding proteins regulate inflammation, tissue injury, and repair through regulating inflammatory cell recruitment, release of inflammatory cytokines, and cell migration. This review focuses on the role of hyaluronan as an immune regulator in human diseases.

Differential regulation of hyaluronan-induced IL-8 and IP-10 in airway epithelial cells

Airway epithelium is emerging as a regulator of local inflammation and immune responses. However, the cellular and molecular mechanisms responsible for the immune modulation by these cells have yet to be fully elucidated. At the cellular level, the hallmarks of airway inflammation are mucus gland hypertrophy with excess mucus production, accumulation of inflammatory mediators, inflammation in the airway walls and lumen, and breakdown and turnover of the extracellular matrix. We demonstrate that fragments of the extracellular matrix component hyaluronan induce inflammatory chemokine production in primary airway epithelial cells grown at an air-liquid interface. Furthermore, hyaluronan fragments use two distinct molecular pathways to induce IL-8 and IFN-gamma-inducible protein 10 (IP-10) chemokine expression in airway epithelial cells. Hyaluronan-induced IL-8 requires the MAP kinase pathway, whereas hyaluronan-induced IP-10 utilizes the NF-kappaB pathway. The induction is specific to low-molecular-weight hyaluronan fragments as other glycosaminoglycans do not induce IL-8 and IP-10 in airway epithelial cells. We hypothesize that not only is the extracellular matrix a target of destruction in airway inflammation but it plays a critical role in perpetuating inflammation through the induction of cytokines, chemokines, and modulatory enzymes in epithelial cells. Furthermore, hyaluronan, by inducing IL-8 and IP-10 by distinct pathways, provides a unique target for differential regulation of key inflammatory chemokines.

Differences in local versus systemic TNFalpha production in COPD: inhibitory effect of hyaluronan on LPS induced blood cell TNFalpha release

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is characterised by both airway inflammation and systemic changes. To elucidate the relationship between local and systemic inflammation, tumour necrosis factor alpha (TNFalpha) production by sputum cells and blood cells of patients with COPD and controls was compared and the effect of the extracellular matrix compound hyaluronan (HA) on TNFalpha release was studied.

METHODS

Four study groups were included: 10 steroid free COPD patients, 8 steroid treated patients, 10 healthy smokers, and 11 healthy non-smokers. Sputum cells and blood were incubated for 24 hours with or without lipopolysaccharide (LPS) in the absence or presence of HA (122 kDa or HMW fragment). TNFalpha was measured by ELISA.

RESULTS

Sputum cells produced spontaneously high levels of TNFalpha but were unresponsive to LPS. Sputum cells from COPD patients (both steroid free and steroid treated) produced significantly less TNFalpha than cells from healthy non-smoking subjects (p=0.017 and p=0.001, respectively). In contrast, blood cells produced TNFalpha only in response to LPS. No differences were observed in TNFalpha production by blood cells between the patient groups and the control groups. HA (both fragments) partially blocked LPS (1 ng/ml) induced TNFalpha release by blood cells from all study groups, whereas TNFalpha production by sputum cells was not influenced by HA.

CONCLUSION

These data indicate a difference between local and systemic TNFalpha production. Sputum cells of patients with COPD produced less TNFalpha than controls, which could contribute to impaired local defence. An inhibitory effect of HA on TNFalpha release in blood cells was observed which was similar in both patients and controls.

Threat matrix: low-molecular-weight hyaluronan (HA) as a danger signal

Whether or not T cell receptor engagement leads to full activation or tolerance is determined by the context in which the antigen is encountered. Antigen presented by activated APCs in the presence of costimulation leads to full T cell activation, while antigen presented by resting APCs leads to tolerance. Pathogen-associated molecular patterns in the form of toll-like receptor ligands play a critical role in activating APCs and promoting T cell activation. In this review we hypothesize that low-molecular-weight species of the extracellular matrix polymer hyaluronan also performs this function by acting as an endogenous danger signal.

Adenosine induces fibronectin expression in lung epithelial cells: implications for airway remodeling

Adenosine is an extracellular nucleoside that is elevated in tissues during hypoxia and ischemia reperfusion and has been implicated in asthma and other lung disorders. There, adenosine is considered an important modulator of physiological functions and inflammation, but its effects on matrix expression and turnover during tissue remodeling are unknown. We examined the effects of adenosine on lung epithelial cells with particular attention to the expression of fibronectin, a matrix glycoprotein highly expressed in injured tissues that has been implicated in wound healing. In A549 lung epithelial cells, we found that adenosine induced expression of fibronectin mRNA and protein in a dose- and time-dependent manner and found that the stimulatory effect of adenosine was inhibited by specific adenosine receptor antagonists. Adenosine stimulation was associated with increased levels of intracellular cAMP and with phosphorylation and DNA binding of the cAMP response element binding protein (CREB), known for its ability to stimulate fibronectin gene transcription. To confirm the latter, A549 cells were transfected with a DNA construct containing the human fibronectin promoter connected to a luciferase reporter gene. Adenosine stimulated transcription of the gene, and this effect was blocked by inhibitors of protein kinase activation. Finally, we tested primary lung fibroblasts and primary alveolar epithelial type II cells and found increased fibronectin expression in response to adenosine. Overall, our observations suggest that adenosine might modulate tissue remodeling by stimulating fibronectin expression in lung epithelial cells through induction of purinergic receptor-mediated signals that target CREB phosphorylation and stimulate fibronectin gene transcription.

Enhanced levels of hyaluronan in lungs of patients with COPD: relationship with lung function and local inflammation

BACKGROUND

Chronic inflammation and airway remodelling are characteristics of chronic obstructive pulmonary disease (COPD). Hyaluronan (HA) is an extracellular matrix compound with proinflammatory activity. HA levels in induced sputum from patients with COPD were measured and related to local inflammation. The expression of hyaluronan synthase 2 (HAS2) and hyaluronidase 2 (HYAL2) was analysed in lung tissue.

METHODS

Sputum was obtained from 18 patients with COPD (forced expiratory volume in 1 second (FEV(1)) 62% predicted (range 20-76)) and 14 healthy smokers. HA and inflammatory markers were measured using ELISA assays. Lung sections were obtained from five patients with severe COPD (FEV(1) <30%) and from five smokers, and mRNA levels of HAS2 and HYAL2 were analysed by polymerase chain reaction.

RESULTS

HA levels were significantly higher in the sputum from patients with COPD than controls. The COPD population appeared to consist of two subpopulations with either high or moderate HA levels. The subgroup of patients with high HA levels had lower FEV(1) than the moderate HA group. In addition, neutrophil influx and levels of interleukin-8, and the soluble tumour necrosis factor receptors R55 and R75 were significantly higher in patients with high HA levels than in those with moderate HA levels and controls. Semiquantitative analysis revealed enhanced expression of HYAL2 in lung tissue of patients with severe COPD compared with control subjects.

CONCLUSION

These data indicate a relationship between HA levels, local inflammation and severity of disease, and suggest enhanced breakdown of HA in the lungs of patients with COPD.

Anti-Tissue Remodeling Effects of Corticosteroids

OBJECTIVES

Tissue remodeling often accompanies diseases such as COPD that are caused by or aggravated by tobacco exposure. Inhaled or systemic corticosteroids are frequently used for the treatment of these illnesses, and their beneficial effects are often ascribed to their anti-inflammatory properties. However, their role in tissue remodeling remains unclear. This study was designed to evaluate the role of corticosteroids in matrix expression in vitro.

DESIGN

We investigated the effects of the corticosteroid fluticasone propionate (FP) on the production of fibronectin by fibroblasts before and after stimulation by nicotine, a plant alkaloid found in tobacco. Fibronectin is an extracellular matrix glycoprotein found elevated in the alveolar lining fluid and airway walls of subjects with obstructive lung disease, and is considered a marker of tissue remodeling after injury.

RESULTS

FP, 1 micromol/L, inhibited the expression of fibronectin messenger RNA and protein in unstimulated NIH-3T3 cells and primary lung fibroblasts, as well as in fibroblasts stimulated with nicotine. The inhibitory effect of FP occurred at the level of gene transcription as demonstrated in lung fibroblasts expressing a construct containing the human fibronectin promoter connected to a luciferase reporter gene, but posttranscriptional effects also appeared involved. Electrophoresis mobility gel shift assays revealed that FP inhibited phosphorylation and DNA binding by the cyclic adenosine monophosphate response element binding protein, a transcription factor required for constitutive and nicotine-induced fibronectin expression.

CONCLUSIONS

Together, these data suggest that FP could diminish lung tissue remodeling by inhibiting the production of fibronectin in lung fibroblasts.

Nicotine and fibronectin expression in lung fibroblasts: implications for tobacco‐related lung tissue remodeling

Tobacco-related lung diseases are associated with alterations in tissue remodeling and are characterized by increased matrix deposition. Among the matrix molecules found to be highly expressed in tobacco-related lung diseases is fibronectin, a cell adhesive glycoprotein implicated in tissue injury and repair. We hypothesize that nicotine, a component of tobacco, stimulates the expression of fibronectin in lung fibroblasts via the activation of intracellular signals that lead to increased fibronectin gene transcription. In support of this, we found that nicotine stimulated the expression of fibronectin in lung fibroblasts and that its stimulatory effect was associated with activation of protein kinase C and mitogen-activated protein kinases, increased levels of intracellular cAMP, and phosphorylation and DNA binding of the transcription factor CREB. Increased transcription of the gene was dependent on cAMP-response elements (CREs) present on the 5' end of its gene promoter. The stimulatory effect of nicotine on fibronectin expression was abolished by alpha-bungarotoxin, an inhibitor of alpha7 nicotinic acetylcholine receptors (alpha7 AChRs). Of note, nicotine increased the expression of alpha7 nAChRs on fibroblasts. Our data suggest that nicotine induces lung fibroblasts to produce fibronectin by stimulating alpha7 nAChR-dependent signals that regulate the transcription of the fibronectin gene.

Enhancement of fibronectin expression in rat lung by ozone and an inflammatory stimulus

This study investigated the relationship of fibronectin expression and induction of pulmonary inflammation by ozone (O3). Rats were exposed to 0.8 parts/million O3 to induce lung inflammation. A second inflammatory stimulus, rabbit serum, was applied intratracheally to augment O3-induced inflammation. Bronchoalveolar lavage fluid (BALF) and lung tissues were analyzed for fibronectin protein and mRNA expression. Blood plasma was analyzed to investigate the potential of a minimally invasive procedure in predicting lung inflammation and fibronectin levels. Significant increases in the levels of fibronectin protein in the BALF and lung tissue after O3 exposure were further enhanced by pretreatment with normal serum. An increase in fibronectin mRNA following O3 exposure was also enhanced by serum pretreatment, which by itself had no effect on lung fibronectin mRNA expression. Plasma fibronectin levels were comparable in air-PBS and O3-PBS groups but increased in the O3-serum group. The results suggest leakage of fibronectin from blood plasma into the lung following intratracheal application of rabbit serum and upregulation of local synthesis following O3 exposure.