Hyaluronic acid in the pulmonary secretions of patients with asthma

Defining the Versican Interactome in Lung Health and Disease

The extracellular matrix (ECM) imparts critical mechanical and biochemical information to cells in the lungs. Proteoglycans are essential constituents of the ECM and play a crucial role in controlling numerous biological processes, including regulating cellular phenotype and function. Versican, a chondroitin sulfate proteoglycan required for embryonic development, is almost absent from mature, healthy lungs and is re-expressed and accumulates in acute and chronic lung disease. Studies using genetically engineered mice show that the versican-enriched matrix can be pro- or anti-inflammatory depending on the cellular source or disease process studied. The mechanisms whereby versican develops a contextual ECM remain largely unknown. The primary goal of this review is to provide an overview of the interaction of versican with its many binding partners, the "versican interactome," and how through these interactions, versican is an integrator of complex extracellular information. Hopefully, the information provided in this review will be used to develop future studies to determine how versican and its binding partners can develop contextual ECMs that control select biological processes. While this review focuses on versican and the lungs, what is described can be extended to other proteoglycans, tissues, and organs.

Oral hymecromone decreases hyaluronan in human study participants

BACKGROUNDHyaluronan (HA), an extracellular matrix glycosaminoglycan, has been implicated in the pathophysiology of COVID-19 infection, pulmonary hypertension, pulmonary fibrosis, and other diseases, but is not targeted by any approved drugs. We asked whether hymecromone (4-methylumbelliferone [4-MU]), an oral drug approved in Europe for biliary spasm treatment that also inhibits HA in vitro and in animal models, could be repurposed as an inhibitor of HA synthesis in humans.METHODSWe conducted an open-label, single-center, dose-response study of hymecromone in healthy adults. Subjects received hymecromone at 1200 (n = 8), 2400 (n = 9), or 3600 (n = 9) mg/d divided into 3 doses daily, administered orally for 4 days. We assessed safety and tolerability of hymecromone and analyzed HA, 4-MU, and 4-methylumbelliferyl glucuronide (4-MUG; the main metabolite of 4-MU) concentrations in sputum and serum.RESULTSHymecromone was well tolerated up to doses of 3600 mg/d. Both sputum and serum drug concentrations increased in a dose-dependent manner, indicating that higher doses lead to greater exposures. Across all dose arms combined, we observed a significant decrease in sputum HA from baseline after 4 days of treatment. We also observed a decrease in serum HA. Additionally, higher baseline sputum HA levels were associated with a greater decrease in sputum HA.CONCLUSIONAfter 4 days of exposure to oral hymecromone, healthy human subjects experienced a significant reduction in sputum HA levels, indicating this oral therapy may have potential in pulmonary diseases where HA is implicated in pathogenesis.TRIAL REGISTRATIONClinicalTrials.gov NCT02780752.FUNDINGStanford Medicine Catalyst, Stanford SPARK, Stanford Innovative Medicines Accelerator program, NIH training grants 5T32AI052073-14 and T32HL129970.

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.

Hyaluronan and Its Interactions With Immune Cells in the Healthy and Inflamed Lung

Hyaluronan is a hygroscopic glycosaminoglycan that contributes to both extracellular and pericellular matrices. While the production of hyaluronan is essential for mammalian development, less is known about its interaction and function with immune cells. Here we review what is known about hyaluronan in the lung and how it impacts immune cells, both at homeostasis and during lung inflammation and fibrosis. In the healthy lung, alveolar macrophages provide the first line of defense and play important roles in immunosurveillance and lipid surfactant homeostasis. Alveolar macrophages are surrounded by a coat of hyaluronan that is bound by CD44, a major hyaluronan receptor on immune cells, and this interaction contributes to their survival and the maintenance of normal alveolar macrophage numbers. Alveolar macrophages are conditioned by the alveolar environment to be immunosuppressive, and can phagocytose particulates without alerting an immune response. However, during acute lung infection or injury, an inflammatory immune response is triggered. Hyaluronan levels in the lung are rapidly increased and peak with maximum leukocyte infiltration, suggesting a role for hyaluronan in facilitating leukocyte access to the injury site. Hyaluronan can also be bound by hyaladherins (hyaluronan binding proteins), which create a provisional matrix to facilitate tissue repair. During the subsequent remodeling process hyaluronan concentrations decline and levels return to baseline as homeostasis is restored. In chronic lung diseases, the inflammatory and/or repair phases persist, leading to sustained high levels of hyaluronan, accumulation of associated immune cells and an inability to resolve the inflammatory response.

Asthmatic bronchial epithelial cells promote the establishment of a Hyaluronan-enriched, leukocyte-adhesive extracellular matrix by lung fibroblasts

Background

Airway inflammation is a hallmark of asthma. Alterations in extracellular matrix (ECM) hyaluronan (HA) content have been shown to modulate the recruitment and retention of inflammatory cells. Bronchial epithelial cells (BECs) regulate the activity of human lung fibroblasts (HLFs); however, their contribution in regulating HLF production of HA in asthma is unknown. In this study, we tested the hypothesis that BECs from asthmatic children promote the generation of a pro-inflammatory, HA-enriched ECM by HLFs, which promotes the retention of leukocytes.

Methods

BECs were obtained from well-characterized asthmatic and healthy children ages 6–18 years. HLFs were co-cultured with BECs for 96 h and samples were harvested for analysis of gene expression, synthesis and accumulation of HA, and subjected to a leukocyte adhesion assay with U937 monocytes.

Results

We observed increased expression of HA synthases HAS2 and HAS3 in HLFs co-cultured with asthmatic BECs. Furthermore, we demonstrated greater total accumulation and increased synthesis of HA by HLFs co-cultured with asthmatic BECs compared to healthy BEC/HLF co-cultures. ECM generated by HLFs co-cultured with asthmatic BECs displayed increased HA-dependent adhesion of leukocytes in a separate in vitro binding assay.

Conclusions

Our findings demonstrate that BEC regulation of HA production by HLFs is altered in asthma, which may in turn promote the establishment of a more leukocyte-permissive ECM promoting airway inflammation in this disease.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0849-1) contains supplementary material, which is available to authorized users.

Nitric oxide alters hyaluronan deposition by airway smooth muscle cells

Asthma is a chronic inflammatory disease that is known to cause changes in the extracellular matrix, including changes in hyaluronan (HA) deposition. However, little is known about the factors that modulate its deposition or the potential consequences. Asthmatics with high levels of exhaled nitric oxide (NO) are characterized by greater airway reactivity and greater evidence of airway inflammation. Based on these data and our previous work we hypothesized that excessive NO promotes the pathologic production of HA by airway smooth muscle cells (SMCs). Exposure of cultured SMCs to various NO donors results in the accumulation of HA in the form of unique, cable-like structures. HA accumulates rapidly after exposure to NO and can be seen as early as one hour after NO treatment. The cable-like HA in NO-treated SMC cultures supports the binding of leukocytes. In addition, NO produced by murine macrophages (RAW cells) and airway epithelial cells also induces SMCs to produce HA cables when grown in co-culture. The modulation of HA by NO appears to be independent of soluble guanylate cyclase. Taken together, NO-induced production of leukocyte-binding HA by SMCs provides a new potential mechanism for the non-resolving airway inflammation in asthma and suggests a key role of non-immune cells in driving the chronic inflammation of the submucosa. Modulation of NO, HA and the consequent immune cell interactions may serve as potential therapeutic targets in asthma.

A novel role for primary cilia in airway remodeling

Primary cilia (PC) are solitary cellular organelles that play critical roles in development, homeostasis, and disease pathogenesis by modulating key signaling pathways such as Sonic Hedgehog and calcium flux. The antenna-like shape of PC enables them also to facilitate sensing of extracellular and mechanical stimuli into the cell, and a critical role for PC has been described for mesenchymal cells such as chondrocytes. However, nothing is known about the role of PC in airway smooth muscle cells (ASMCs) in the context of airway remodeling. We hypothesized that PC on ASMCs mediate cell contraction and are thus integral in the remodeling process. We found that PC are expressed on ASMCs in asthmatic lungs. Using pharmacological and genetic methods, we demonstrated that PC are necessary for ASMC contraction in a collagen gel three-dimensional model both in the absence of external stimulus and in response to the extracellular component hyaluronan. Mechanistically, we demonstrate that the effect of PC on ASMC contraction is, to a small extent, due to their effect on Sonic Hedgehog signaling and, to a larger extent, due to their effect on calcium influx and membrane depolarization. In conclusion, PC are necessary for the development of airway remodeling by mediating calcium flux and Sonic Hedgehog signaling.

Hyaluronan as a therapeutic target in human diseases

Accumulation and turnover of extracellular matrix is a hallmark of tissue injury, repair and remodeling in human diseases. Hyaluronan is a major component of the extracellular matrix and plays an important role in regulating tissue injury and repair, and controlling disease outcomes. The function of hyaluronan depends on its size, location, and interactions with binding partners. While fragmented hyaluronan stimulates the expression of an array of genes by a variety of cell types regulating inflammatory responses and tissue repair, cell surface hyaluronan provides protection against tissue damage from the environment and promotes regeneration and repair. The interactions of hyaluronan and its binding proteins participate in the pathogenesis of many human diseases. Thus, targeting hyaluronan and its interactions with cells and proteins may provide new approaches to developing therapeutics for inflammatory and fibrosing diseases. This review focuses on the role of hyaluronan in biological and pathological processes, and as a potential therapeutic target in human diseases.

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.

Hyaluronan and Its Heavy Chain Modification in Asthma Severity and Experimental Asthma Exacerbation

Hyaluronan (HA) is a large (>1500 kDa) polysaccharide of the extracellular matrix that has been linked to severity and inflammation in asthma. During inflammation, HA becomes covalently modified with heavy chains (HC-HA) from inter-α-inhibitor (IαI), which functions to increase its avidity for leukocytes. Our murine model of allergic pulmonary inflammation suggested that HC-HA may contribute to inflammation, adversely effecting lower airway remodeling and asthma severity. Our objective was to characterize the levels of HA and HC-HA in asthmatic subjects and to correlate these levels with asthma severity. We determined the levels and distribution of HA and HC-HA (i) from asthmatic and control lung tissue, (ii) in bronchoalveolar lavage fluid obtained from non-severe and severe asthmatics and controls, and (iii) in serum and urine from atopic asthmatics after an experimental asthma exacerbation. HC-HA distribution was observed (i) in the thickened basement membrane of asthmatic lower airways, (ii) around smooth muscle cells of the asthmatic submucosa, and (iii) around reserve cells of the asthmatic epithelium. Patients with severe asthma had increased HA levels in bronchoalveolar lavage fluid that correlated with pulmonary function and nitric oxide levels, whereas HC-HA was only observed in a patient with non-severe asthma. After an experimental asthma exacerbation, serum HA was increased within 4 h after challenge and remained elevated through 5 days after challenge. Urine HA and HC-HA were not significantly different. These data implicate HA and HC-HA in the pathogenesis of asthma severity that may occur in part due to repetitive asthma exacerbations over the course of the disease.

Hyaluronan stimulates ex vivo B lymphocyte chemotaxis and cytokine production in a murine model of fungal allergic asthma

Allergic asthma is a chronic inflammatory disease of the airways characterized by excessive eosinophilic and lymphocytic inflammation with associated changes in the extracellular matrix (ECM) resulting in airway wall remodeling. Hyaluronan (HA) is a nonsulfated glycosaminoglycan ECM component that functions as a structural cushion in its high molecular mass (HMM) but has been implicated in metastasis and other disease processes when it is degraded to smaller fragments. However, relatively little is known about the role HA in mediating inflammatory responses in allergy and asthma. In the present study, we used a murine Aspergillus fumigatus inhalational model to mimic human disease. After observing in vivo that a robust B cell recruitment followed a massive eosinophilic egress to the lumen of the allergic lung and corresponded with the detection of low molecular mass HA (LMM HA), we examined the effect of HA on B cell chemotaxis and cytokine production in the ex vivo studies. We found that LMM HA functioned through a CD44-mediated mechanism to elicit chemotaxis of B lymphocytes, while high molecular mass HA (HMM HA) had little effect. LMM HA, but not HMM HA, also elicited the production of IL-10 and TGF-β1 in these cells. Taken together, these findings demonstrate a critical role for ECM components in mediating leukocyte migration and function which are critical to the maintenance of allergic inflammatory responses.

Hyaluronan fragments as mediators of inflammation in allergic pulmonary disease

Asthma is frequently caused and/or exacerbated by sensitization to allergens, which are ubiquitous in many indoor and outdoor environments. Severe asthma is characterized by airway hyperresponsiveness and bronchial constriction in response to an inhaled allergen, leading to a disease course that is often very difficult to treat with standard asthma therapies. As a result of interactions among inflammatory cells, structural cells, and the intercellular matrix of the allergic lung, patients with sensitization to allergens may experience a greater degree of tissue injury followed by airway wall remodeling and progressive, accumulated pulmonary dysfunction as part of the disease sequela. In addition, turnover of extracellular matrix (ECM) components is a hallmark of tissue injury and repair. This review focuses on the role of the glycosaminoglycan hyaluronan (HA), a component of the ECM, in pulmonary injury and repair with an emphasis on allergic asthma. Both the synthesis and degradation of the ECM are critical contributors to tissue repair and remodeling. Fragmented HA accumulates during tissue injury and functions in ways distinct from the larger native polymer. There is gathering evidence that HA degradation products are active participants in stimulating the expression of inflammatory genes in a variety of immune cells at the injury site. In this review, we will consider recent advances in the understanding of the mechanisms that are associated with HA accumulation and inflammatory cell recruitment in the asthmatic lung.

Hyaluronan deposition and co-localization with inflammatory cells and collagen in a murine model of fungal allergic asthma

OBJECTIVE

Allergic asthma is a chronic inflammatory disease of the airways characterized by excessive inflammation and remodeling of the extracellular matrix (ECM) and associated cells of the airway wall. Under inflammatory conditions, hyaluronan (HA), a major component of the ECM, undergoes dynamic changes, which may in turn affect the recruitment and activation of inflammatory cells leading to acute and chronic immunopathology of allergic asthma.

METHODS

In the present study, we measured the changes in HA levels generated at sites of inflammation, and examined its effect on inflammatory responses and collagen deposition in an Aspergillus fumigatus murine inhalational model of allergic asthma.

RESULTS

We found that HA levels are elevated in allergic animals and that the increase correlated with the influx of inflammatory cells 5 days after the second allergen challenge. This increase in HA levels appeared largely due to upregulation of hyaluronidase-1 (HYAL1) and hyaluronidase-2 (HYAL2). Furthermore, HA co-localizes with areas of new collagen synthesis and deposition.

CONCLUSIONS

Overall, our findings contribute to the growing literature that focuses on the components of ECM as inflammatory mediators rather than mere structural support products. The evidence of HA localization in fungal allergic asthma provides the impetus to study HA more closely with allergic leukocytes in murine models. Further studies examining HA's role in mediating cellular responses may help to develop targets for treatment in patients with severe asthma due to fungal sensitization.

Hyaluronan activation of the Nlrp3 inflammasome contributes to the development of airway hyperresponsiveness

BACKGROUND

The role of the Nlrp3 inflammasome in nonallergic airway hyperresponsiveness (AHR) has not previously been reported. Recent evidence supports both interleukin (IL) 1β and short fragments of hyaluronan (HA) as contributors to the biological response to inhaled ozone.

OBJECTIVE

Because extracellular secretion of IL-1β requires activation of the inflammasome, we investigated the role of the inflammasome proteins ASC, caspase1, and Nlrp3 in the biological response to ozone and HA.

METHODS

C57BL/6J wild-type mice and mice deficient in ASC, caspase1, or Nlrp3 were exposed to ozone (1 ppm for 3 hr) or HA followed by analysis of airway resistance, cellular inflammation, and total protein and cytokines in bronchoalveolar lavage fluid (BALF). Transcription levels of IL-1β and IL-18 were determined in two populations of lung macrophages. In addition, we examined levels of cleaved caspase1 and cleaved IL-1β as markers of inflammasome activation in isolated alveolar macrophages harvested from BALF from HA-treated mice.

RESULTS

We observed that genes of the Nlrp3 inflammasome were required for development of AHR following exposure to either ozone or HA fragments. These genes are partially required for the cellular inflammatory response to ozone. The expression of IL-1β mRNA in alveolar macrophages was up-regulated after either ozone or HA challenge and was not dependent on the Nlrp3 inflammasome. However, soluble levels of IL-1β protein were dependent on the inflammasome after challenge with either ozone or HA. HA challenge resulted in cleavage of macrophage-derived caspase1 and IL-1β, suggesting a role for alveolar macrophages in Nlrp3-dependent AHR.

CONCLUSIONS

The Nlrp3 inflammasome is required for the development of ozone-induced reactive airways disease.

Genes of innate immunity and the biological response to inhaled ozone

Ambient ozone has a significant impact on human health. We have made considerable progress in understanding the fundamental mechanisms that regulate the biological response to ozone. It is increasingly clear that genes of innate immunity play a central role in both infectious and noninfectious lung disease. The biological response to ambient ozone provides a clinically relevant environmental exposure that allows us to better understand the role of innate immunity in noninfectious airways disease. In this brief review, we focus on (1) specific cell types in the lung modified by ozone, (2) ozone and oxidative stress, (3) the relationship between genes of innate immunity and ozone, (4) the role of extracellular matrix in reactive airways disease, and (5) the effect of ozone on the adaptive immune system. We summarize recent advances in understanding the mechanisms that ozone contributes to environmental airways disease.

TSG-6 protein is crucial for the development of pulmonary hyaluronan deposition, eosinophilia, and airway hyperresponsiveness in a murine model of asthma

Hyaluronan (HA) deposition is often correlated with mucosal inflammatory responses, where HA mediates both protective and pathological responses. By modifying the HA matrix, Tnfip6 (TNF-α-induced protein-6; also known as TSG-6 (TNF-stimulated gene-6)) is thought to potentiate anti-inflammatory and anti-plasmin effects that are inhibitory to leukocyte extravasation. In this study, we examined the role of endogenous TSG-6 in the pathophysiological responses associated with acute allergic pulmonary inflammation. Compared with wild-type littermate controls, TSG-6(-/-) mice exhibited attenuated inflammation marked by a significant decrease in pulmonary HA concentrations measured in the bronchoalveolar lavage and lung tissue. Interestingly, despite the equivalent induction of both humoral and cellular Th2 immunity and the comparable levels of cytokines and chemokines typically associated with eosinophilic pulmonary inflammation, airway eosinophilia was significantly decreased in TSG-6(-/-) mice. Most importantly, contrary to their counterpart wild-type littermates, TSG-6(-/-) mice were resistant to the induction of airway hyperresponsiveness and manifested improved lung mechanics in response to methacholine challenge. Our study demonstrates that endogenous TSG-6 is dispensable for the induction of Th2 immunity but is essential for the robust increase in pulmonary HA deposition, propagation of acute eosinophilic pulmonary inflammation, and development of airway hyperresponsiveness. Thus, TSG-6 is implicated in the experimental murine model of allergic pulmonary inflammation and is likely to contribute to the pathogenesis of asthma.

Correlation of hyaluronan deposition with infiltration of eosinophils and lymphocytes in a cockroach-induced murine model of asthma

Asthma is a chronic inflammatory disease that exhibits airway remodeling with changes in the extracellular matrix (ECM). The role of the ECM in mediating these changes is poorly understood. Hyaluronan (HA), a major component of the ECM, has been implicated in many biological processes in diseases. This study investigates the processes involved in HA synthesis, deposition and localization during the propagation of cockroach-induced asthma. Mice were sensitized and challenged with cockroach antigen, and sacrificed at various time points during an 8-week challenge protocol. Analysis of bronchoalveolar lavage (BAL) fluid revealed an increase in total nucleated cells as early as 6h, which peaked at 6 days. Histopathologic analysis of the lung tissue revealed an influx of inflammatory cells at the peribronchial and perivascular regions starting at 12 h, which peaked at 6 days and persisted to 8 weeks. Eosinophils predominated in the early time points while lymphocytes predominated during the late time points. Quantitative polymerase chain reaction (PCR) data showed that hyaluronan synthase 1 (HAS1) mRNA peaked within 6 h and then declined. HAS2 mRNA also peaked within 6 h but remained elevated throughout the 8-week exposure course. HA levels in lung tissue and BAL increased at 12 h and peaked by 6 and 8 days, respectively. Inflammatory cells and new collagen formation localized in areas of HA deposition. Taken together, these data support a role for HA in the pathogenesis in asthma.

Role of hyaluronan and hyaluronan-binding proteins in lung pathobiology

Hyaluronan (HA) has diverse functions in normal lung homeostasis and pulmonary disease. HA constitutes the major glycosaminoglycan in lung tissue, with HA degradation products, produced by hyaluronidase enzymes and reactive oxygen species, being implicated in several lung diseases, including acute lung injury, asthma, chronic obstructive pulmonary disease, and pulmonary hypertension. The differential activities of HA and its degradation products are due, in part, to regulation of multiple HA-binding proteins, including cluster of differentiation 44 (CD44), Toll-like receptor 4 (TLR4), HA-binding protein 2 (HABP2), and receptor for HA-mediated motility (RHAMM). Recent research indicates that exogenous administration of high-molecular-weight HA can serve as a novel therapeutic intervention for lung diseases, including lipopolysaccharide (LPS)-induced acute lung injury, sepsis/ventilator-induced lung injury, and airway hyperreactivity. This review focuses on the regulatory role of HA and HA-binding proteins in lung pathology and discusses the capacity of HA to augment and inhibit various lung diseases.

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.

Hyaluronan deposition and correlation with inflammation in a murine ovalbumin model of asthma

Asthma is a chronic inflammatory disease of the airways characterized by airway remodeling, which includes changes in the extracellular matrix (ECM). However the role of the ECM in mediating these changes is poorly understood. Hyaluronan (HA), a major component of the ECM, has been implicated in asthma as well as in many other biological processes. Our study investigates the processes involved in HA synthesis, deposition, localization and degradation during an acute and chronic murine model of ovalbumin (OVA)-induced allergic pulmonary inflammation. Mice were sensitized, challenged to OVA and sacrificed at various time points during an 8-week challenge protocol. Bronchoalveolar lavage (BAL) fluids, blood, and lung tissue were collected for study. RNA, HA, protein and histopathology were analyzed. Analyses of lung sections and BAL fluids revealed an early deposition and an increase in HA levels within 24 h of antigen exposure. HA levels peaked at day 8 in BAL, while inflammatory cell recovery peaked at day 6. Hyaluronan synthase (HAS)1 and HAS2 on RNA levels peaked within 2 h of antigen exposure, while hyaluronidase (HYAL)1 and HYAL2 on RNA levels decreased. Both inflammatory cell infiltrates and collagen deposition co-localized with HA deposition within the lungs. These data support a role for HA in the pathogenesis of inflammation and airway remodeling in a murine model of asthma. HA deposition appears largely due to up regulation of HAS1 and HAS2. In addition, HA appears to provide the scaffolding for inflammatory cell accumulation as well as for new collagen synthesis and deposition.

Deficiency in the serum-derived hyaluronan-associated protein-hyaluronan complex enhances airway hyperresponsiveness in a murine model of asthma

BACKGROUND

Serum-derived hyaluronan (HA)-associated proteins (SHAPs), the heavy chains of inter-α-trypsin inhibitor, covalently bind to HA to form the SHAP-HA complex. The SHAP-HA complex is involved in the pathophysiology of inflammatory diseases, including rheumatoid arthritis. We investigated whether this complex is also involved in airway allergy.

METHODS

SHAP-HA-deficient (bikunin knockout, KO) mice and wild-type (WT) mice were immunized twice by intraperitoneal injection of ovalbumin (OVA) and exposed to aerosol OVA for 30 min each day for 2 weeks. Twenty-four hours after the final OVA challenge, airway responsiveness to inhaled methacholine (MCh) was measured, and analysis of bronchoalveolar lavage fluid (BALF) and lung histological studies were done.

RESULTS

Compared to WT mice, KO mice showed higher airway hyperresponsiveness to inhaled MCh and higher late-phase responses to OVA whereas the early-phase responses were similar. Cell differentials of BALF showed an increased number of macrophages and neutrophils in KO mice. Furthermore, decreased concentrations of soluble tumor necrosis factor receptor-1 (sTNFR1) were found in BALF from KO mice whereas the levels of Th1 and Th2 cytokines were not different from WT mice. Immunochemical study of the lung tissues revealed stronger staining of sTNFR1 in KO than in WT mice.

CONCLUSIONS

Our results suggest that in this murine asthma model, the SHAP-HA complex has an inhibitory role in the development of airway hyperresponsiveness and allergic airway inflammation which may be attributed, at least in part, to negative feedback mechanisms exerted by sTNFR1, the shedding of which from the cell surface might also be promoted by the SHAP-HA complex.

Hyaluronan mediates ozone-induced airway hyperresponsiveness in mice

Ozone is a common urban environmental air pollutant and significantly contributes to hospitalizations for respiratory illness. The mechanisms, which regulate ozone-induced bronchoconstriction, remain poorly understood. Hyaluronan was recently shown to play a central role in the response to noninfectious lung injury. Therefore, we hypothesized that hyaluronan contributes to airway hyperreactivity (AHR) after exposure to ambient ozone. Using an established model of ozone-induced airways disease, we characterized the role of hyaluronan in airway hyperresponsiveness. The role of hyaluronan in response to ozone was determined by using therapeutic blockade, genetically modified animals, and direct challenge to hyaluronan. Ozone-exposed mice demonstrate enhanced AHR associated with elevated hyaluronan levels in the lavage fluid. Mice deficient in either CD44 (the major receptor for hyaluronan) or inter-alpha-trypsin inhibitor (molecule that facilitates hyaluronan binding) show similar elevations in hyaluronan but are protected from ozone-induced AHR. Mice pretreated with hyaluronan-binding peptide are protected from the development of ozone-induced AHR. Overexpression of hyaluronan enhances the airway response to ozone. Intratracheal instillation of endotoxin-free low molecular weight hyaluronan induces AHR dependent on CD44, whereas instillation of high molecular weight hyaluronan protects against ozone-induced AHR. In conclusion, we demonstrate that hyaluronan mediates ozone-induced AHR, which is dependent on the fragment size and both CD44 and inter-alpha-trypsin inhibitor. These data support the conclusion that pulmonary matrix can contribute to the development of airway hyperresponsiveness.

Primary murine airway smooth muscle cells exposed to poly(I,C) or tunicamycin synthesize a leukocyte-adhesive hyaluronan matrix

Asthmatic attacks often follow viral infections with subsequent airway smooth muscle cell proliferation and the formation of an abnormal hyaluronan extracellular matrix with infiltrated leukocytes. In this study, we show that murine airway smooth muscle cells (MASM) treated with polyinosinic acid-polycytidylic acid (poly(I,C)), a double-stranded RNA that simulates a viral infection, synthesize an abnormal hyaluronan matrix that binds leukocytes (U937 cells). Synthesis of this matrix is initiated rapidly and accumulates linearly for approximately 10 h, reaching a plateau level approximately 7-fold higher than control cultures. MASM cells treated with tunicamycin, to induce endoplasmic reticulum stress, also rapidly initiate synthesis of the abnormal hyaluronan matrix with linear accumulation for approximately 10 h, but only reach a plateau level approximately 2-fold higher than control cultures. In contrast to poly(I,C), the response to tunicamycin depends on cell density, with pre-confluent cells producing more abnormal matrix per cell. Furthermore, U937 cell adhesion per hyaluronan content is higher in the sparse matrix produced in response to tunicamycin, suggesting that the structure in the poly(I,C)-induced matrix masks potential binding sites. When MASM cells were exposed to tunicamycin and poly(I,C) at the same time, U937 cell adhesion was partially additive, implying that these two toxins stimulate hyaluronan synthesis through two different pathways. We also characterized the size of hyaluronan produced by MASM cells, in response to poly(I,C) and tunicamycin, and we found that it ranges from 1500 to 4000 kDa, the majority of which was approximately 4000 kDa and not different in size than hyaluronan made by untreated cells.

High levels of hyaluronan in idiopathic pulmonary arterial hypertension

Hyaluronan (HA), a large glycosaminoglycan found in the ECM, has major roles in lung and vascular biology and disease. However, its role in idiopathic pulmonary arterial hypertension (IPAH) is unknown. We hypothesized that HA metabolism is abnormal in IPAH. We measured the plasma levels of HA in IPAH and healthy individuals. We also evaluated HA synthesis and the expression of HA synthases and hyaluronidases in pulmonary artery smooth muscle cells (PASMCs) from explanted lungs. Plasma HA levels were markedly elevated in IPAH compared with controls [HA (ng/ml, mean +/- SD): IPAH 325 +/- 80, control 28 +/- 9; P = 0.02]. In vitro, unstimulated IPAH PASMCs produced high levels of HA compared with control cells [HA in supernatant (microg/ml, mean +/- SD): IPAH 12 +/- 2, controls 6 +/- 0.9; P = 0.04]. HA levels were also higher in IPAH PASMC lysates. The increased HA was biologically relevant as shown by tissue staining and increased HA-specific binding of mononuclear cells to IPAH compared with control PASMCs [number of bound cells x 10(4) (mean +/- SD): IPAH 9.5 +/- 3, control 3.0 +/- 1; P = 0.01]. This binding was abrogated by the addition of hyaluronidase. HA synthase-2 and hyaluronidase-2 were predominant in control and IPAH PASMCs. Interestingly, the expressions of HA synthase-2 and hyaluronidase-2 were approximately 2-fold lower in IPAH compared with controls [HA synthase-2 (relative expression mean +/- SE): IPAH 4.3 +/- 0.02, control 7.8 +/- 0.1; P = 0.0004; hyaluronidase-2 (relative expression mean +/- SE): IPAH 4.2 +/- 0.06, control 7.6 +/- 0.07; P = 0.008]. Thus patients with IPAH have higher circulating levels of HA, and PASMCs derived from IPAH lungs produce more HA compared with controls. This is associated with increased tissue levels and increased binding of inflammatory cells suggesting a role for HA in remodeling and inflammation in IPAH.

Differentiated murine airway epithelial cells synthesize a leukocyte-adhesive hyaluronan matrix in response to endoplasmic reticulum stress

In this report, we describe a novel method for culturing murine trachea epithelial cells on a native basement membrane at an air-liquid interface to produce a pseudostratified, differentiated airway epithelium composed of ciliated and nonciliated cells. This model was used to examine hyaluronan synthesis by the airway epithelial cells (AECs) in response to poly(I,C) and tunicamycin. The former induces a response similar to viral infection, and the latter is a bacterial toxin known to induce endoplasmic reticulum (ER) stress. We found significant accumulation of hyaluronan on the apical surface of the AECs in response to ER stress, but, unlike previously reported results with smooth muscle cells, no increase in hyaluronan was observed in response to poly(I,C). Monocytic U937 cells adhered at 4 degrees C to the apical surface of the AECs subjected to ER stress by a mechanism almost entirely mediated by hyaluronan. The U937 cells spontaneously released themselves from the abnormal hyaluronan matrix when their metabolism was restored by shifting the temperature from 4 to 37 degrees C in a custom-made flow chamber. Time lapse confocal microscopy permitted live imaging of this interaction between the U937 cells and the hyaluronan matrix and their subsequent response at 37 degrees C. Within 45 min, we observed dynamic protrusions of the U937 cell plasma membrane into nearby hyaluronan matrix, resulting in the degradation of this matrix. Simultaneously, we observed some reorganization of the hyaluronan matrix, from a generalized, apical distribution to localized regions around the AEC tight junctions. We discuss the implications these results might have for the airway epithelium and its relation to airway inflammation and hyperresponsiveness associated with asthma and other airway diseases.

The peptidyl-prolyl isomerase Pin1 regulates the stability of granulocyte-macrophage colony-stimulating factor mRNA in activated eosinophils

The infiltration, accumulation and degranulation of eosinophils in the lung represents a hallmark of active asthma. In vivo or in vitro eosinophil activation triggers the secretion of the antiapoptotic cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF). We now identify Pin1, a cis-trans isomerase, as an essential component of the ribonucleoprotein complex responsible for GM-CSF mRNA stabilization, cytokine secretion and the survival of activated eosinophils. Pin1 regulated the association of the AU-rich element-binding proteins AUF1 and hnRNP C with GM-CSF mRNA, accelerating or slowing decay, respectively. These data indicate Pin1 is a key mediator of GM-CSF production.

The role of mRNA stability in airway remodelling

As a consequence of long-term exposure to inflammatory mediators, the airways of asthmatics become remodelled. Airway fibrosis becomes apparent, with thickening of the lamina recticularis and increased interstitial matrix deposition being typical features of an asthmatic airway. Mucus hypersecretion occurs, airway smooth muscle mass is increased and neovascularization is evident in the subepithelial mucosa. As development of a remodelled airway is correlated with deterioration of lung function in asthmatics, there is an urgent need for therapies that reduce airway inflammation and reverse structural changes in a remodelled airway. However, in order to design efficacious anti-remodelling agents we first need a greater understanding of the molecular mechanism/s underlying the development of airway remodelling. To date, however, most studies have primarily focused on the transcriptional regulation of genes that promote airway remodelling. Post-transcriptional mechanisms, such as control of mRNA stability, remain largely unexplored. Levels of cellular mRNA transcripts are regulated by controlling the rate at which the mRNA decays, thus investigation into the mechanisms underlying mRNA stability in asthma are of critical importance. Therefore, this review will present an overview of the control of mRNA stability and examine how mRNA stability may play a role in the development of airway remodelling in asthma.

Hyaluronic acid or TNF-alpha plus fibronectin triggers granulocyte macrophage-colony-stimulating factor mRNA stabilization in eosinophils yet engages differential intracellular pathways and mRNA binding proteins

Eosinophils (Eos) accumulate in airways and lung parenchyma of active asthmatics. GM-CSF is a potent inhibitor of Eos apoptosis both in vitro and in vivo and is produced by activated fibroblasts, mast cells, T lymphocytes as well as Eos. Cytokine release by Eos is preceded by GM-CSF mRNA stabilization induced by TNF-alpha plus fibronectin. Hyaluronic acid (HA) is a major extracellular matrix proteoglycan, which also accumulates in the lung during asthma exacerbations. In this study we have analyzed the effects of HA on Eos survival and GM-CSF expression. We demonstrate that like TNF-alpha plus fibronectin, HA stabilizes GM-CSF mRNA, increases GM-CSF secretion, and prolongs in vitro Eos survival. GM-CSF mRNA stabilization accounts for most of the observed GM-CSF mRNA accumulation and protein production. Unlike TNF-alpha plus fibronectin, GM-CSF mRNA stabilization induction by HA requires continuous extracellular signal-regulated kinase phosphorylation. Finally, to identify potential protein regulators responsible for GM-CSF mRNA stabilization, immunoprecipitation-RT-PCR studies revealed increased GM-CSF mRNA associated with YB-1, HuR, and heterogeneous nuclear ribonucleoprotein (hnRNP) C after TNF-alpha plus fibronectin but only hnRNP C after HA. Thus, our data suggest that both TNF-alpha plus fibronectin and HA, which are relevant physiological effectors in asthma, contributes to long-term Eos survival in vivo by enhancing GM-CSF production through two different posttranscriptional regulatory pathways involving extracellular signal-regulated kinase phosphorylation and RNA binding proteins YB-1, HuR, and hnRNP C.

Pro- and anti-inflammatory factors cooperate to control hyaluronan synthesis in lung fibroblasts

Hyaluronan (HA) is an important constituent of the extracellular matrix and accumulates during inflammatory lung diseases like asthma. Little is known about the factors that regulate HA synthesis by lung cells. Accordingly, we investigated the effect of T-helper 1 (TH1) and 2 (TH2) cytokines and the anti-inflammatory agents fluticasone and salmeterol on HA synthesis in human lung fibroblasts. Interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF)-alpha were the most potent stimulators of HA synthesis and when combined, caused synergistic increases in HA accumulation. Time-course analysis of HA accumulation and [3H]-glucosamine incorporation into HA demonstrated continued synthesis over the 24 h of stimulation. Peak synthesis at 6-12 h coincided with an increased proportion of high molecular weight HA. Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that IL-1beta and TNF-alpha induced HA synthase-2 messenger RNA (mRNA) 3 h following stimulation and remained elevated throughout the 24-h stimulation period. Fluticasone inhibited IL-1beta and TNF-alpha induced HA synthesis (44.5%) whereas salmeterol had no effect. When combined, fluticasone and salmeterol inhibited HA synthesis to a greater extent (85.2%). Further, fluticasone attenuated IL-1beta and TNF-alpha stimulated hyaluronan synthase-2 messenger RNA (mRNA), and the addition of salmeterol cooperatively enhanced this inhibition. These results indicate that enhanced synthesis of HA by the proinflammatory cytokines IL-1beta and TNF-alpha can be abrogated by specific corticosteroid and beta2 blocker combinations shown to be effective in the treatment of asthma.

Neutrophil-mediated degradation of lung proteoglycans: stimulation by tumor necrosis factor-alpha in sputum of patients with bronchiectasis

Neutrophil-mediated degradation of bronchial matrix has been proposed as a pathogenetic factor in bronchiectasis. We hypothesize that neutrophils, found in abundance in the bronchial lumens of patients with bronchiectasis, are capable of degrading lung matrix proteoglycans and that proinflammatory mediators in bronchial secretions of these patients can enhance the degradative action of neutrophils. We used rat bronchoalveolar proteoglycans entrapped in polyacrylamide gel beads as a substrate for test incubations with neutrophils from healthy volunteers and sputum sol from patients with idiopathic bronchiectasis. Coincubations with specimens of sputum sol and neutrophils showed proteoglycan degradation indices (PDIs) in excess of the sum of indices due to incubation with either heat-inactivated sputum sol or heat-inactivated neutrophils, suggesting sputum stimulation of the neutrophil response. Mediation of this stimulation by tumor necrosis factor (TNF)-alpha was suggested because (1) indices for the coincubations correlated with sputum levels of TNF-alpha and (2) an anti-TNF-alpha antibody completely attenuated the sputum-stimulated effect. Furthermore, recombinant human TNF-alpha required accompanying sputum sol to exert an enhancing effect on neutrophil-mediated proteoglycan degradation. Because neutrophil-mediated proteoglycan degradation in the coincubations was inhibited largely (90%) by Eglin C and much less so (8% to 20%) by ethylenediamine tetraacetic acid, we conclude that serine proteases secreted by neutrophils were mainly responsible for degradation of proteoglycans in the model matrix and that the secretion was stimulated by TNF-alpha in the presence of cofactors in the bronchial secretions of patients with bronchiectasis.

DNA from bronchial secretions modulates elastase inhibition by alpha(1)-proteinase inhibitor and oxidized secretory leukoprotease inhibitor

Previously we reported that DNA from sputum promotes the inhibition of human leukocyte elastase (HLE) by native secretory leukoprotease inhibitor (SLPI). This study shows that sputum DNA also promotes the inhibition by oxidized SLPI, a form of SLPI that may occupy a large fraction of the inhibitor in the lungs under conditions of high oxidative stress. With sputum DNA at 5 microg/ml, a concentration much lower than those in vivo, the inhibition constant (K(i) ) of oxidized SLPI against HLE is reduced from 31 nM to 23 to 920 pM, as compared with the K(i) of native SLPI, 58 pM, under the same conditions. On the other hand, sputum DNA retards inhibition of HLE by alpha(1)-proteinase inhibitor (alpha(1)-PI). The association rate of alpha(1)-PI and HLE is decreased from 1 x 10(7) M(-1) s(-1) in the absence of DNA to 2 to 6 x 10(6) M(-1) s(-1) in the presence of sputum DNA at 100 microg/ml. On the basis of results with an elastase-specific oligonucleotide aptamer, it was found that the downregulation of alpha(1)-PI activity can be attributed to an interaction between sputum DNA and multiple DNA-binding sites on HLE. DNA-binding sites on HLE also participate in the upregulation of oxidized SLPI activity. Data from this and our previous studies demonstrate that sputum DNA facilitates the association of HLE with native and oxidized SLPI, whereas it delays the association of HLE with alpha(1)-PI. We conclude that by modulating the inhibition of HLE, sputum DNA directly affects the balance between proteases and antiproteases in the lungs.

Cytokine regulation of human lung fibroblast hyaluronan (hyaluronic acid) production. Evidence for cytokine-regulated hyaluronan (hyaluronic acid) degradation and human lung fibroblast-derived hyaluronidase

We characterized the mechanisms by which recombinant (r) tumor necrosis factor (TNF), IFN-gamma, and IL-1, alone and in combination, regulate human lung fibroblast hyaluronic acid (HA) production. Each cytokine stimulated fibroblast HA production. The combination of rTNF and rIFN-gamma resulted in a synergistic increase in the production of high molecular weight HA. This was due to a synergistic increase in hyaluronate synthetase activity and a simultaneous decrease in HA degradation. In contrast, when rTNF and rIL-1 were combined, an additive increase in low molecular weight HA was noted. This was due to a synergistic increase in hyaluronate synthetase activity and a simultaneous increase in HA degradation. Human lung fibroblasts contained a hyaluronidase that, at pH 3.7, depolymerized high molecular weight HA to 10-40 kD end products of digestion. However, hyaluronidase activity did not correlate with fibroblast HA degradation. Instead, HA degradation correlated with fibroblast-HA binding, which was increased by rIL-1 plus rTNF and decreased by rIFN-gamma plus rTNF. Recombinant IL-1 and rTNF weakly stimulated and rIL-1 and rTNF in combination further augmented the levels of CD44 mRNA in lung fibroblasts. In contrast, rIFN-gamma did not significantly alter the levels of CD44 mRNA in unstimulated or rTNF stimulated cells. These studies demonstrate that rIL-1, rTNF, and rIFN-gamma have complex effects on biosynthesis and degradation which alter the quantity and molecular weight of the HA produced by lung fibroblasts. They also show that fibroblast HA degradation is mediated by a previously unrecognized lysosomal-type hyaluronidase whose function may be regulated by altering fibroblast-HA binding. Lastly, they suggest that the CD44 HA receptor may be involved in this process.

Chondroitin sulfate in sputum from patients with cystic fibrosis and chronic bronchitis

In order to ascertain whether or not the presence of glycosaminoglycans in sputa of patients suffering from chronic bronchial disorders was related to tracheobronchial infection, an electrophoretic procedure was set up. The different acidic macromolecular components of sputum, namely nucleic acids, glycosaminoglycans, and bronchial glycopeptides could be identified in proteolyzed sputum using agarose electrophoresis before and after the action of different enzymes: nucleases, chondroitinases, hyaluronidase and heparinase. This procedure was used to analyze 13 sputum samples from patients suffering from cystic fibrosis (CF) and 12 sputum samples from patients suffering from chronic bronchitis. Chondroitin sulfate was identified in 11 infected sputum samples from patients with CF and also in the noninfected sputum from a patient with chronic bronchitis. These data suggest a relationship between the presence of chondroitin sulfate proteoglycans in sputum and severe tracheobronchial infection in CF.

Sulfated O-glycoproteins secreted by guinea pig trachea in organ culture

Organ culture of guinea pig trachea was performed in the presence of [35S]sulfate in order to characterize the sulfated glycoproteins released from the respiratory epithelium and mucosa. The sulfated macromolecules that were synthesized during a 6-h incorporation were separated by CsBr density-gradient centrifugation and gel-filtration chromatography successively. Most of the sulfated secreted macromolecules corresponded to a population of glycoproteins sensitive to reductive beta-elimination but resistant to both chondroitinase ABC and heparinase. These glycoproteins had different buoyant densities (ranging from 1.48 g/ml to 1.16 g/ml) and could be subfractionated according to molecular mass. A major part of the radioactivity was incorporated into high-molecular-mass mucins that were excluded from a Sepharose CL-2B column and did not penetrate into polyacrylamide gel in PAGE. However, a mixture of sulfated O-glycoproteins of much lower molecular mass was also characterized in addition to low amounts of chondroitin sulfate. Epithelial goblet cells are the predominant mucin-containing cells of the respiratory guinea pig trachea. Our results suggest that a wide range of sulfated O-glycoproteins are secreted by the guinea pig tracheal mucosa.

A hyaluronate secretor in the nasal mucosa: a cytochemical study using hyaluronidase-gold

The ultrastructural distribution of hyaluronate in the nasal mucosa of Wistar rats, especially in secretory cells, was examined by hyaluronidase-gold labeling using electron microscopy. The main secretor of hyaluronate in the nasal mucosa was found to be the goblet cells and not the nasal glands.

Dog tracheal epithelial cells in culture synthesize sulfated macromolecular glycoconjugates and release them from the cell surface upon exposure to extracellular proteinases

To determine whether glycoconjugates can be released into airways by surface epithelial cells that do not contain secretory granules and, if so, whether extracellular proteinases can affect this release, we studied dog tracheal epithelial cells after 8-10 days in culture. Ultrastructurally, these cells showed an extensive cell surface coat and no secretory granules. Cells were pulse labeled with radioactive sulfate (Na2 35SO4, 50 microCi/ml/24 h) and washed free of the unbound label. Release of sulfated products was then measured at 20-min intervals under basal conditions and again after 20 min of incubation with various extracellular proteinase. We found that these cells synthesized sulfated products and released them spontaneously and continuously into the medium. In addition, trypsin, Pseudomonas aeruginosa elastase, thermolysin, Staphylococcus aureus proteinase, mast cell chymase, plasmin, and kallikrein (each at 10(-7) M except plasmin, at 5 X 10(-6) M) increased the release of sulfated products to 77-667% over baseline release (p less than 0.01, n = 5 dogs for each); preliminary results showed that human neutrophil elastase was also very potent. The sulfated products released by trypsin had an apparent molecular weight of greater than or equal to 10(6) da as determined by gel filtration on Sepharose Cl-4B. Over 50% of these 35S-labeled products were digested to low-molecular-weight products (500-2000 da) upon incubation with endo-beta-galactosidase or with keratanase, suggesting that they are glycoconjugates containing poly(N-acetyllactosamine)-type carbohydrate chains. Decrease in cell staining by lectins specific for poly(N-acetyllactosamine), which accompanied the release of glycoconjugates, indicates that these sulfated glycoconjugates were released by proteinases from the apical cell surface. We conclude that cultured tracheal epithelial cells synthesize and transport sulfated macromolecular glycoconjugates to apical cell surfaces. These glycoconjugates are released from cell surfaces when exposed to extracellular proteinases. We therefore suggest that macromolecular glycoconjugates in airway secretions can originate not only from secretory granules but also from epithelial cell surfaces during airway inflammation.

Density gradient analysis of secretions produced in vitro by human and canine airway mucosa: identification of lipids and proteoglycans in such secretions

Human and canine airway mucosal explants synthesize and secrete high molecular weight glycoconjugates, incorporating 14C-glucosamine, a radioactive precursor to epithelial glycoprotein. Our examination of secretions produced by several individual specimens, however, did not reveal epithelial glycoprotein of typical buoyant density (1.5 g/ml in CsBr); only a high-density component with features of glycoprotein and proteoglycan. To provide sufficient material for characterization, secretions from several specimens of human and canine explants were separately pooled and subjected to DGU in CsBr. After removal of lipids and proteins, the glycoconjugates were recovered into five fractions of different density. 14C-glucosamine had been incorporated in all five fractions. Fractions 1-4 together accounted for 88% of the radiolabel but gas chromatography indicated that none of these contained epithelial glycoprotein. Their amino acid compositions were similar to those of proteoglycans and electrophoresis confirmed the presence of chondroitin sulfates A, B, C, heparan sulfate and hyaluronic acid. Sugars typical of epithelial glycoprotein were identified only in the glycoconjugate subfraction 5 of lowest density (and also lowest in yield) in which glycosaminoglycans were also identified. By addition of radioactive precursors, 14C acetate, 14C palmitate and 14C mevalonic acid to the culture medium and autoradiography of the secreted lipids we have shown that the tracheal explants actively synthesize lipids. Lipids accounted for a high proportion, almost half by weight, of the explant secretion. While neutral and phospholipids predominate, glycolipids were also identified.

Glycosaminoglycans in the bronchial mucus of patients with chronic bronchitis and mucoid impaction of the bronchus

Glycosaminoglycans were isolated from mucus of patients with chronic bronchitis and mucoid impaction of the bronchus, whose contents were approximately 56 mumoles and 80 mumoles of hexosamine per g of dry weight of mucus respectively. Electrophoretic and chemical characterization and enzymatic susceptibility demonstrated that the glycosaminoglycans in mucus from both groups of the patients contained hyaluronic acid as the main constituent, with undersulphated chondroitin as a minor component. In addition, in mucus from the patient with mucoid impaction of the bronchus chondroitin sulphate and heparan sulphate or heparan sulphate-like substance were identified.

Immobilization of hyaluronate on cellulose fibres and its use for the isolation of cartilage components

Hyaluronate containing protein was isolated from rooster comb. An affinity chromatography matrix of cellulose hyaluronate was prepared. The matrix binds only aggregable proteoglycans, chondroitinase degraded proteoglycans and link protein.

Density gradient study of bronchial mucus aspirates from healthy volunteers (smokers and nonsmokers) and from patients with tracheostomy

Because it is difficult to obtain, little is known of bronchial mucus from the normal human airway; it has been mainly studied as sputum expectorated in chronic bronchitis with particular attention to epithelial glycoprotein. We have now applied density gradient methods to study this and other macromolecules and lipids in normal airway mucus. After lavage at bronchoscopy, mucus was aspirated from six normal volunteers, that include one light and two heavy smokers. This normal mucus has been compared with that obtained from four patients with tracheostomy because of respiratory muscle paralysis due to neurological disease. The normal aspirates contained small threads of mucus, the tracheostomy aspirates viscous blobs of jelly, a difference in physical appearance reflected in macromolecular yields, 0.3-1 mg/ml and 6-24 mg/ml respectively. On analytical ultracentrifugation normal mucus showed no discernible material in the buoyant density region typical of epithelial glycoprotein (1.5 g/ml): Virtually all the material migrated to the miniscus and was predominantly lipids and proteins. A trace amount of material recovered from a higher density region (greater than or equal to 1.6 g/ml) was found to contain both glycoprotein and proteoglycan. Aspirates from the heavy smokers contained appreciable amounts of material with typical buoyant density (approximately 1.5 g/ml) but still with features of proteoglycan. In contrast in tracheostomy aspirates epithelial glycoprotein of typical buoyant density and chemical composition accounted for up to 25% of nondialyzable material. We conclude that under normal conditions typical epithelial glycoprotein is virtually absent from airway mucus and that the glycoconjugate present has features of glycoprotein and proteoglycan.

The pulmonary extracellular lining

The extracellular lining of the lungs is reviewed. The pulmonary extracellular lining is a complex mixture of phospholipids, proteins and carbohydrates which is absolutely essential for the maintenance of normal pulmonary functions such as gas exchange. Without the lining the lungs would collapse. Alterations in the pulmonary extracellular lining may underlie some disease conditions induced by toxic agents, especially those which interfere with the formation of pulmonary surfactant. The extracellular lining could be used to detect and monitor damage and disease caused by agents toxic to the lungs. The lining contains many hydrolytic enzymes which may act to detoxify certain toxic agents such as those which contain ester groups. The pulmonary extracellular lining could play a significant role mediating the toxic action of inhaled agents as well as the removal of those agents from the lungs.

Alveolyn--structure and source: a review

Alveolyn is a unique secretory glycoprotein of 250,000 molecular weight (MW) that is found in distal pulmonary secretions. Several glycoproteins of 130,000 MW, 80,000 MW, 62,000 MW, and 36,000 MW have also been found to be present in the alveolar secretions, and it was found that these glycoproteins were proteolytic fragments of the much larger molecular glycoprotein. It is also a major protein in human amniotic fluid, presumably a product of alveolar secretions. It is also secreted by a clone of pulmonary fetal type II cells. Preliminary results indicate that two of the proteolytic fragments of 62,000 MW and 36,000 MW contain alternate collagenous and noncollagenous domains in the same polypeptide chain. The presence of collagenous domains in these glycoproteins was also confirmed by their susceptibility to digestion with collagenase and the presence of Gly-Pro-Hyp-Gly-type sequence in the peptide chain. Very little is known about the tertiary structure of the protein, except that its fragments bind phospholipids and probably facilitate transfer of the lipid to air-water interfaces.

Glycosaminoglycans and glycoproteins in bronchoalveolar lavage fluid from patients with pulmonary alveolar proteinosis

Bronchoalveolar lavage fluid from two cases of pulmonary alveolar proteinosis were analyzed for glycosaminoglycans and glycoproteins. The clinical courses of the two cases were entirely different. In one patient, signs and symptoms recurred despite repeated therapeutic bronchoalveolar lavages. In the other patient, three successive bronchoalveolar lavages brought about complete recovery. It was found that the bronchoalveolar lavage fluid from the former case contained various subtypes of glycosaminoglycans [hyaluronic acid, chondroitin sulfate A(C), dermatan sulfate, and heparan sulfate] and glycoprotein. On the other hand, the bronchoalveolar lavage fluid from the latter case contained glycoprotein, but no detectable amounts of glycosaminoglycans. There was only a slight qualitative difference in glycoprotein of bronchoalveolar lavage fluid between the two cases. The presence or absence of glycosaminoglycans in bronchoalveolar lavage fluid may be related to the prognosis of pulmonary alveolar proteinosis.

Quantitation of glycosaminoglycans of rabbit lung during delayed-type hypersensitivity reactions and granuloma formation

The specificity and kinetics of hyaluronic acid (HA) accumulation in relation to other glycosaminoglycans (GASs) were determined in rabbit lungs during an allergic granulomatous response to BCG, an allergic nongranulomatous response to tuberculoprotein, and during a foreign-body granulomatous response to carrageenan. Hyaluronic acid was the only GAG detected in the lung lavage fluids. Hyaluronic acid occurred in the airways on day two of the allergic granulomatous response, but its presence in the airway did not correlate with ensuing granuloma formation in the parenchyma. Generalized increases in GAG of the parenchyma also peaked on day two of the DTH responses. Generalized increases in GAG peaked on day five during the foreign-body granulomatous response to carrageenan. A persistently elevated level of HA in the lung tissue correlated with granuloma formation but not with the intensity of the response.