Pathological Hyaluronan Matrices in Cystic Fibrosis Airways and Secretions

The extracellular matrix and the immune system: A mutually dependent relationship

For decades, immunologists have studied the role of circulating immune cells in host protection, with a more recent appreciation of immune cells resident within the tissue microenvironment and the intercommunication between nonhematopoietic cells and immune cells. However, the extracellular matrix (ECM), which comprises at least a third of tissue structures, remains relatively underexplored in immunology. Similarly, matrix biologists often overlook regulation of complex structural matrices by the immune system. We are only beginning to understand the scale at which ECM structures determine immune cell localization and function. Additionally, we need to better understand how immune cells dictate ECM complexity. This review aims to highlight the potential for biological discovery at the interface of immunology and matrix biology.

Human Mesenchymal Stem Cell (hMSC) Donor Potency Selection for the "First in Cystic Fibrosis" Phase I Clinical Trial (CEASE-CF)

Human Mesenchymal Stem Cell (hMSC) immunotherapy has been shown to provide both anti-inflammatory and anti-microbial effectiveness in a variety of diseases. The clinical potency of hMSCs is based upon an initial direct hMSC effect on the pro-inflammatory and anti-microbial pathophysiology as well as sustained potency through orchestrating the host immunity to optimize the resolution of infection and tissue damage. Cystic fibrosis (CF) patients suffer from a lung disease characterized by excessive inflammation and chronic infection as well as a variety of other systemic anomalies associated with the consequences of abnormal cystic fibrosis transmembrane conductance regulator (CFTR) function. The application of hMSC immunotherapy to the CF clinical armamentarium is important even in the era of modulators when patients with an established disease still need anti-inflammatory and anti-microbial therapies. Additionally, people with CF mutations not addressed by current modulator resources need anti-inflammation and anti-infection management. Furthermore, hMSCs possess dynamic therapeutic properties, but the potency of their products is highly variable with respect to their anti-inflammatory and anti-microbial effects. Due to the variability of hMSC products, we utilized standardized in vitro and in vivo models to select hMSC donor preparations with the greatest potential for clinical efficacy. The models that were used recapitulate many of the pathophysiologic outcomes associated with CF. We applied this strategy in pursuit of identifying the optimal donor to utilize for the "First in CF" Phase I clinical trial of hMSCs as an immunotherapy and anti-microbial therapy for people with cystic fibrosis. The hMSCs screened in this study demonstrated significant diversity in antimicrobial and anti-inflammatory function using models which mimic some aspects of CF infection and inflammation. However, the variability in activity between in vitro potency and in vivo effectiveness continues to be refined. Future studies require and in-depth pursuit of hMSC molecular signatures that ultimately predict the capacity of hMSCs to function in the clinical setting.

Dysfunctional Extracellular Matrix Remodeling Supports Perianal Fistulizing Crohn's Disease by a Mechanoregulated Activation of the Epithelial-to-Mesenchymal Transition

BACKGROUND AND AIMS

Perianal fistula represents one of the most disabling manifestations of Crohn's disease (CD) due to complete destruction of the affected mucosa, which is replaced by granulation tissue and associated with changes in tissue organization. To date, the molecular mechanisms underlying perianal fistula formation are not well defined. Here, we dissected the tissue changes in the fistula area and addressed whether a dysregulation of extracellular matrix (ECM) homeostasis can support fistula formation.

METHODS

Surgical specimens from perianal fistula tissue and the surrounding region of fistulizing CD were analyzed histologically and by RNA sequencing. Genes significantly modulated were validated by real-time polymerase chain reaction, Western blot, and immunofluorescence assays. The effect of the protein product of TNF-stimulated gene-6 (TSG-6) on cell morphology, phenotype, and ECM organization was investigated with endogenous lentivirus-induced overexpression of TSG-6 in Caco-2 cells and with exogenous addition of recombinant human TSG-6 protein to primary fibroblasts from region surrounding fistula. Proliferative and migratory assays were performed.

RESULTS

A markedly different organization of ECM was found across fistula and surrounding fistula regions with an increased expression of integrins and matrix metalloproteinases and hyaluronan (HA) staining in the fistula, associated with increased newly synthesized collagen fibers and mechanosensitive proteins. Among dysregulated genes associated with ECM, TNFAI6 (gene encoding for TSG-6) was as significantly upregulated in the fistula compared with area surrounding fistula, where it promoted the pathological formation of complexes between heavy chains from inter-alpha-inhibitor and HA responsible for the formation of a crosslinked ECM. There was a positive correlation between TNFAI6 expression and expression of mechanosensitive genes in fistula tissue. The overexpression of TSG-6 in Caco-2 cells promoted migration, epithelial-mesenchymal transition, transcription factor SNAI1, and HA synthase (HAs) levels, while in fibroblasts, isolated from the area surrounding the fistula, it promoted an activated phenotype. Moreover, the enrichment of an HA scaffold with recombinant human TSG-6 protein promoted collagen release and increase of SNAI1, ITGA4, ITGA42B, and PTK2B genes, the latter being involved in the transduction of responses to mechanical stimuli.

CONCLUSIONS

By mediating changes in the ECM organization, TSG-6 triggers the epithelial-mesenchymal transition transcription factor SNAI1 through the activation of mechanosensitive proteins. These data point to regulators of ECM as new potential targets for the treatment of CD perianal fistula.

Biochemical, biophysical, and immunological characterization of respiratory secretions in severe SARS-CoV-2 infections

Thick, viscous respiratory secretions are a major pathogenic feature of COVID-19, but the composition and physical properties of these secretions are poorly understood. We characterized the composition and rheological properties (i.e., resistance to flow) of respiratory secretions collected from intubated COVID-19 patients. We found the percentages of solids and protein content were greatly elevated in COVID-19 compared with heathy control samples and closely resembled levels seen in cystic fibrosis, a genetic disease known for thick, tenacious respiratory secretions. DNA and hyaluronan (HA) were major components of respiratory secretions in COVID-19 and were likewise abundant in cadaveric lung tissues from these patients. COVID-19 secretions exhibited heterogeneous rheological behaviors, with thicker samples showing increased sensitivity to DNase and hyaluronidase treatment. In histologic sections from these same patients, we observed increased accumulation of HA and the hyaladherin versican but reduced tumor necrosis factor-stimulated gene-6 staining, consistent with the inflammatory nature of these secretions. Finally, we observed diminished type I interferon and enhanced inflammatory cytokines in these secretions. Overall, our studies indicated that increases in HA and DNA in COVID-19 respiratory secretion samples correlated with enhanced inflammatory burden and suggested that DNA and HA may be viable therapeutic targets in COVID-19 infection.

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.

Biochemical, Biophysical, and Immunological Characterization of Respiratory Secretions in Severe SARS-CoV-2 (COVID-19) Infections.. [PMID: 35411348 PMCID: PMC8996635 DOI: 10.1101/2022.03.28.22272848] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Thick, viscous respiratory secretions are a major pathogenic feature of COVID-19 disease, but the composition and physical properties of these secretions are poorly understood. We characterized the composition and rheological properties (i.e. resistance to flow) of respiratory secretions collected from intubated COVID-19 patients. We find the percent solids and protein content are greatly elevated in COVID-19 compared to heathy control samples and closely resemble levels seen in cystic fibrosis, a genetic disease known for thick, tenacious respiratory secretions. DNA and hyaluronan (HA) are major components of respiratory secretions in COVID-19 and are likewise abundant in cadaveric lung tissues from these patients. COVID-19 secretions exhibit heterogeneous rheological behaviors with thicker samples showing increased sensitivity to DNase and hyaluronidase treatment. In histologic sections from these same patients, we observe increased accumulation of HA and the hyaladherin versican but reduced tumor necrosis factor–stimulated gene-6 (TSG6) staining, consistent with the inflammatory nature of these secretions. Finally, we observed diminished type I interferon and enhanced inflammatory cytokines in these secretions. Overall, our studies indicate that increases in HA and DNA in COVID-19 respiratory secretion samples correlate with enhanced inflammatory burden and suggest that DNA and HA may be viable therapeutic targets in COVID-19 infection.

Has2 Regulates the Development of Ovalbumin-Induced Airway Remodeling and Steroid Insensitivity in Mice

HAS2 is a member of the gene family encoding the hyaluronan synthase 2, which can generate high-molecular-weight hyaluronan (HMW-HA). Our previous study identified HAS2 as a candidate gene for increased susceptibility to adult asthma. However, whether HAS2 dysfunction affects airway remodeling and steroid insensitivity is still limited. Therefore, this study aimed to clarify the Has2 dysfunction, triggering severe airway remodeling and steroid insensitivity in a murine model of asthma. Has2 heterozygous-deficient (Has2^+/−) mice and their wild-type littermates have been evaluated in a model of chronic ovalbumin (OVA) sensitization and challenge. Mice present a higher sensitivity to OVA and higher IL-17 release as well as eosinophilic infiltration. RNA sequencing demonstrated the downregulation of EIF2 signaling pathways, TGF-β signaling pathways, and heat shock proteins with Th17 bias in Has2^+/−-OVA mice. The combined treatment with anti-IL-17A antibody and dexamethasone reduces steroid insensitivity in Has2^+/−-OVA mice. Has2 attenuation worsens eosinophilic airway inflammation, airway remodeling, and steroid insensitivity. These data highlight that HAS2 and HMW-HA are important for controlling intractable eosinophilic airway inflammation and remodeling and could potentially be exploited for their therapeutic benefits in patients with asthma.

Modulation of hyaluronan signaling as a therapeutic target in human disease

The extracellular matrix is an active participant, modulator and mediator of the cell, tissue, organ and organismal response to injury. Recent research has highlighted the role of hyaluronan, an abundant glycosaminoglycan constituent of the extracellular matrix, in many fundamental biological processes underpinning homeostasis and disease development. From this basis, emerging studies have demonstrated the therapeutic potential of strategies which target hyaluronan synthesis, biology and signaling, with significant promise as therapeutics for a variety of inflammatory and immune diseases. This review summarizes the state of the art in this field and discusses challenges and opportunities in what could emerge as a new class of therapeutic agents, that we term "matrix biologics".

Enhancing Cystic Fibrosis Immune Regulation

In cystic fibrosis (CF), sustained infection and exuberant inflammation results in debilitating and often fatal lung disease. Advancement in CF therapeutics has provided successful treatment regimens for a variety of clinical consequences in CF; however effective means to treat the pulmonary infection and inflammation continues to be problematic. Even with the successful development of small molecule cystic fibrosis transmembrane conductance regulator (CFTR) correctors and potentiators, there is only a modest effect on established infection and inflammation in CF patients. In the pursuit of therapeutics to treat inflammation, the conundrum to address is how to overcome the inflammatory response without jeopardizing the required immunity to manage pathogens and prevent infection. The key therapeutic would have the capacity to dull the inflammatory response, while sustaining the ability to manage infections. Advances in cell-based therapy have opened up the avenue for dynamic and versatile immune interventions that may support this requirement. Cell based therapy has the capacity to augment the patient’s own ability to manage their inflammatory status while at the same time sustaining anti-pathogen immunity. The studies highlighted in this manuscript outline the potential use of cell-based therapy for CF. The data demonstrate that 1) total bone marrow aspirates containing Cftr sufficient hematopoietic and mesenchymal stem cells (hMSCs) provide Cftr deficient mice >50% improvement in survival and improved management of infection and inflammation; 2) myeloid cells can provide sufficient Cftr to provide pre-clinical anti-inflammatory and antimicrobial benefit; 3) hMSCs provide significant improvement in survival and management of infection and inflammation in CF; 4) the combined interaction between macrophages and hMSCs can potentially enhance anti-inflammatory and antimicrobial support through manipulating PPARγ. These data support the development of optimized cell-based therapeutics to enhance CF patient’s own immune repertoire and capacity to maintain the balance between inflammation and pathogen management.

Inhaled high molecular weight hyaluronan ameliorates respiratory failure in acute COPD exacerbation: a pilot study

Background

Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) carry significant morbidity and mortality. AECOPD treatment remains limited. High molecular weight hyaluronan (HMW-HA) is a glycosaminoglycan sugar, which is a physiological constituent of the lung extracellular matrix and has notable anti-inflammatory and hydrating properties.

Research question

We hypothesized that inhaled HMW-HA will improve outcomes in AECOPD.

Methods

We conducted a single center, randomized, placebo-controlled, double-blind study to investigate the effect of inhaled HMW-HA in patients with severe AECOPD necessitating non-invasive positive-pressure ventilation (NIPPV). Primary endpoint was time until liberation from NIPPV.

Results

Out of 44 screened patients, 41 were included in the study (21 for placebo and 20 for HMW-HA). Patients treated with HMW-HA had significantly shorter duration of NIPPV. HMW-HA treated patients also had lower measured peak airway pressures on the ventilator and lower systemic inflammation markers after liberation from NIPPV. In vitro testing showed that HMW-HA significantly improved mucociliary transport in air–liquid interface cultures of primary bronchial cells from COPD patients and healthy primary cells exposed to cigarette smoke extract.

Interpretation

Inhaled HMW-HA shortens the duration of respiratory failure and need for non-invasive ventilation in patients with AECOPD. Beneficial effects of HMW-HA on mucociliary clearance and inflammation may account for some of the effects (NCT02674880, www.clinicaltrials.gov).

Hyaluronan is abundant in COVID-19 respiratory secretions

COVID-19 respiratory infections are associated with copious, adherent respiratory secretions that prolong chronic ventilation and contribute to the morbidity and mortality caused by the disease. We hypothesized that hyaluronan, an extracellular matrix glycosaminoglycan produced at sites of active inflammation that promotes edema in other settings, might be a component of these secretions. To interrogate this, we examined the respiratory secretions collected from eight intubated patients with COVID-19, six control patients with cystic fibrosis (CF), a different respiratory disease also associated with thick adherent secretions, and eight healthy controls. In this sample set we found that hyaluronan content is increased approximately 20-fold in both CF and COVID-19 patients compared to healthy controls. The hyaluronan in COVID-19 samples was comprised of low-molecular weight fragments, the hyaluronan form most strongly linked with pro-inflammatory functions. Hyaluronan is similarly abundant in histologic sections from cadaveric lung tissue from COVID-19 patients. These findings implicate hyaluronan in the thick respiratory secretions characteristic of COVID-19 infection. Therapeutic strategies targeting hyaluronan should be investigated further for potential use in patients with COVID-19.

Endothelial Progenitor Cells Modulate Inflammation-Associated Stroke Vasculome

Stroke remains a major unmet clinical need that warrants novel therapies. Following an ischemic insult, the cerebral vasculature secretes inflammatory molecules, creating the stroke vasculome profile. The present study evaluated the therapeutic effects of endothelial cells on the inflammation-associated stroke vasculome. qRT-PCR analysis revealed that specific inflammation-related vasculome genes BRM, IκB, Foxf1, and ITIH-5 significantly upregulated by oxygen glucose deprivation (OGD. Interestingly, co-culture of human endothelial cells (HEN6) with human endothelial cells (EPCs) during OGD significantly blocked the elevations of BRM, IκB, and Foxf1, but not ITIH-5. Next, employing the knockdown/antisense technology, silencing the inflammation-associated stroke vasculome gene, IκB, as opposed to scrambled knockdown, blocked the EPC-mediated protection of HEN6 against OGD. In vivo, stroke animals transplanted with intracerebral human EPCs (300,000 cells) into the striatum and cortex 4 h post ischemic stroke displayed significant behavioral recovery up to 30 days post-transplantation compared to vehicle-treated stroke animals. At 7 days post-transplantation, quantification of the fluorescent staining intensity in the cortex and striatum revealed significant upregulation of the endothelial marker RECA1 and a downregulation of the stroke-associated vasculome BRM, IKB, Foxf1, ITIH-5 and PMCA2 in the ipsilateral side of cortex and striatum of EPC-transplanted stroke animals relative to vehicle-treated stroke animals. Altogether, these results demonstrate that EPCs exert therapeutic effects in experimental stroke possibly by modulating the inflammation-plagued vasculome.

The Inter-α-Trypsin Inhibitor Family: Versatile Molecules in Biology and Pathology

Inter-α-trypsin inhibitor (IαI) family members are ancient and unique molecules that have evolved over several hundred million years of vertebrate evolution. IαI is a complex containing the proteoglycan bikunin to which heavy chain proteins are covalently attached to the chondroitin sulfate chain. Besides its matrix protective activity through protease inhibitory action, IαI family members interact with extracellular matrix molecules and most notably hyaluronan, inhibit complement, and provide cell regulatory functions. Recent evidence for the diverse roles of the IαI family in both biology and pathology is reviewed and gives insight into their pivotal roles in tissue homeostasis. In addition, the clinical uses of these molecules are explored, such as in the treatment of inflammatory conditions including sepsis and Kawasaki disease, which has recently been associated with severe acute respiratory syndrome coronavirus 2 infection in children.

Hyaluronan Fragmentation During Inflammatory Pathologies: A Signal that Empowers Tissue Damage

The mechanisms that modulate the response to tissue injury are not fully understood. Abnormalities in the repair response are associated with a variety of chronic disease states characterized by inflammation, followed subsequently by excessive ECM deposition. As cell-matrix interactions are able to regulate cellular homeostasis, modification of ECM integrity appears to be an unspecific factor in promoting the onset and progression of inflammatory diseases. Evidence is emerging to show that endogenous ECM molecules supply signals to damage tissues and cells in order to promote further ECM degradation and inflammation progression. Several investigations have been confirmed that HA fragments of different molecular sizes exhibit different biological effects and responses. In fact, the increased deposition of HA into the ECM is a strong hallmark of inflammation processes. In the context of inflammatory pathologies, highly polymerized HA is broken down into small components, which are able to exacerbate the inflammatory response by inducing the release of various detrimental mediators such as reactive oxygen species, cytokines, chemokines and destructive enzymes and by facilitating the recruitment of leukocytes. However, strategies involving the modulation of the HA fragment with specific receptors on cell surface could represent different promising effects for therapeutic scope. This review will focus on the inflammation action of small HA fragments in recent years obtained by in vivo reports.

A Retrospective Analysis of the Cartilage Kunitz Protease Inhibitory Proteins Identifies These as Members of the Inter-α-Trypsin Inhibitor Superfamily with Potential Roles in the Protection of the Articulatory Surface

Aim: The aim of this study was to assess if the ovine articular cartilage serine proteinase inhibitors (SPIs) were related to the Kunitz inter-α-trypsin inhibitor (ITI) family. Methods: Ovine articular cartilage was finely diced and extracted in 6 M urea and SPIs isolated by sequential anion exchange, HA affinity and Sephadex G100 gel permeation chromatography. Selected samples were also subjected to chymotrypsin and concanavalin-A affinity chromatography. Eluant fractions from these isolation steps were monitored for protein and trypsin inhibitory activity. Inhibitory fractions were assessed by affinity blotting using biotinylated trypsin to detect SPIs and by Western blotting using antibodies to α1-microglobulin, bikunin, TSG-6 and 2-B-6 (+) CS epitope generated by chondroitinase-ABC digestion. Results: 2-B-6 (+) positive 250, 220,120, 58 and 36 kDa SPIs were detected. The 58 kDa SPI contained α1-microglobulin, bikunin and chondroitin-4-sulfate stub epitope consistent with an identity of α1-microglobulin-bikunin (AMBP) precursor and was also isolated by concanavalin-A lectin affinity chromatography indicating it had N-glycosylation. Kunitz protease inhibitor (KPI) species of 36, 26, 12 and 6 kDa were autolytically generated by prolonged storage of the 120 and 58 kDa SPIs; chymotrypsin affinity chromatography generated the 6 kDa SPI. KPI domain 1 and 2 SPIs were separated by concanavalin lectin affinity chromatography, domain 1 displayed affinity for this lectin indicating it had N-glycosylation. KPI 1 and 2 displayed potent inhibitory activity against trypsin, chymotrypsin, kallikrein, leucocyte elastase and cathepsin G. Localisation of versican, lubricin and hyaluronan (HA) in the surface regions of articular cartilage represented probable binding sites for the ITI serine proteinase inhibitors (SPIs) which may preserve articulatory properties and joint function. Discussion/Conclusions: The Kunitz SPI proteins synthesised by articular chondrocytes are members of the ITI superfamily. By analogy with other tissues in which these proteins occur we deduce that the cartilage Kunitz SPIs may be multifunctional proteins. Binding of the cartilage Kunitz SPIs to HA may protect this polymer from depolymerisation by free radical damage and may also protect other components in the cartilage surface from proteolytic degradation preserving joint function.

Defective lung function following influenza virus is due to prolonged, reversible hyaluronan synthesis

Little is known about the impact of viral infections on lung matrix despite its important contribution to mechanical stability and structural support. The composition of matrix also indirectly controls inflammation by influencing cell adhesion, migration, survival, proliferation and differentiation. Hyaluronan is a significant component of the lung extracellular matrix and production and degradation must be carefully balanced. We have discovered an imbalance in hyaluronan production following resolution of a severe lung influenza virus infection, driven by hyaluronan synthase 2 from epithelial cells, endothelial cells and fibroblasts. Furthermore hyaluronan is complexed with inter-α-inhibitor heavy chains due to elevated TNF-stimulated gene 6 expression and sequesters CD44-expressing macrophages. We show that intranasal administration of exogenous hyaluronidase is sufficient to release inter-α-inhibitor heavy chains, reduce lung hyaluronan content and restore lung function. Hyaluronidase is already used to facilitate dispersion of co-injected materials in the clinic. It is therefore feasible that fibrotic changes following severe lung infection and inflammation could be overcome by targeting abnormal matrix production.

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Influenza causes prolonged changes in hyaluronan due to increased synthase activity

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Influenza induces persistent hyaluronan cross-linking by inter-alpha-inhibitor heavy chains

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Pockets of persistent hyaluronan are associated with CD44-expressing macrophages

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Digestion of hyaluronan with intranasal hyaluronidase restores lung function but upon cessation of treatment post-viral complications return

Rapid clearance of heavy chain-modified hyaluronan during resolving acute lung injury

BACKGROUND

Several inflammatory lung diseases display abundant presence of hyaluronic acid (HA) bound to heavy chains (HC) of serum protein inter-alpha-inhibitor (IαI) in the extracellular matrix. The HC-HA modification is critical to neutrophil sequestration in liver sinusoids and to survival during experimental lipopolysaccharide (LPS)-induced sepsis. Therefore, the covalent HC-HA binding, which is exclusively mediated by tumor necrosis factor α (TNFα)-stimulated-gene-6 (TSG-6), may play an important role in the onset or the resolution of lung inflammation in acute lung injury (ALI) induced by respiratory infection.

METHODS

Reversible ALI was induced by a single intratracheal instillation of LPS or Pseudomonas aeruginosa in mice and outcomes were studied for up to six days. We measured in the lung or the bronchoalveolar fluid HC-HA formation, HA immunostaining localization and roughness, HA fragment abundance, and markers of lung inflammation and lung injury. We also assessed TSG-6 secretion by TNFα- or LPS-stimulated human alveolar macrophages, lung fibroblast Wi38, and bronchial epithelial BEAS-2B cells.

RESULTS

Extensive HC-modification of lung HA, localized predominantly in the peri-broncho-vascular extracellular matrix, was notable early during the onset of inflammation and was markedly decreased during its resolution. Whereas human alveolar macrophages secreted functional TSG-6 following both TNFα and LPS stimulation, fibroblasts and bronchial epithelial cells responded to only TNFα. Compared to wild type, TSG-6-KO mice, which lacked HC-modified HA, exhibited modest increases in inflammatory cells in the lung, but no significant differences in markers of lung inflammation or injury, including histopathological lung injury scores.

CONCLUSIONS

Respiratory infection induces rapid HC modification of HA followed by fragmentation and clearance, with kinetics that parallel the onset and resolution phase of ALI, respectively. Alveolar macrophages may be an important source of pulmonary TSG-6 required for HA remodeling. The formation of HC-modified HA had a minor role in the onset, severity, or resolution of experimental reversible ALI induced by respiratory infection with gram-negative bacteria.

Hyaluronan interactions with innate immunity in lung biology

Lung disease is a leading cause of morbidity and mortality worldwide. Innate immune responses in the lung play a central role in the pathogenesis of lung disease and the maintenance of lung health, and thus it is crucial to understand factors that regulate them. Hyaluronan is ubiquitous in the lung, and its expression is increased following lung injury and in disease states. Furthermore, hyaladherins like inter-α-inhibitor, tumor necrosis factor-stimulated gene 6, pentraxin 3 and versican are also induced and help form a dynamic hyaluronan matrix in injured lung. This review synthesizes present knowledge about the interactions of hyaluronan and its associated hyaladherins with the lung immune system, and the implications of these interactions for lung biology and disease.

TSG-6: A multifunctional protein with anti-inflammatory and tissue-protective properties

Tumor necrosis factor- (TNF) stimulated gene-6 (TSG-6) is an inflammation-associated secreted protein that has been implicated as having important and diverse tissue protective and anti-inflammatory properties, e.g. mediating many of the immunomodulatory and beneficial activities of mesenchymal stem/stromal cells. TSG-6 is constitutively expressed in some tissues, which are either highly metabolically active or subject to challenges from the environment, perhaps providing protection in these contexts. The diversity of its functions are dependent on the binding of TSG-6 to numerous ligands, including matrix molecules such as glycosaminoglycans, as well as immune regulators and growth factors that themselves interact with these linear polysaccharides. It is becoming apparent that TSG-6 can directly affect matrix structure and modulate the way extracellular signalling molecules interact with matrix. In this review, we focus mainly on the literature for TSG-6 over the last 10 years, summarizing its expression, structure, ligand-binding properties, biological functions and highlighting TSG-6's potential as a therapeutic for a broad range of disease indications.

Chronic asthma and Mesenchymal stem cells: Hyaluronan and airway remodeling

BACKGROUND

Previous studies have demonstrated that ovalbumin sensitization promotes chronic asthma phenotype in murine asthma model. Human mesenchymal stem cells (hMSCs) are multipotent cells in vitro that have been shown to decrease inflammation and can reverse airway remodeling when infused into an in vivo chronic asthma model. However, the mechanism by which hMSCs reverse remodeling is still unclear. In this study, we hypothesized that hMSCs influence remodeling by decreasing extracellular matrix (ECM) deposition, more specifically by decreasing collagen I, collagen III, and hyaluronan synthesis.

METHODS

Chronic asthma phenotype was produced in an in vitro model with 3 T3 murine airway fibroblast cells by stimulating with GM-CSF. Collagen I and collagen III gene expression was investigated using RT-PCR and Taqman techniques. Hyaluronan was evaluated using FACE and Western Blots. The chronic asthma phenotype was produced in vivo in murine model using sensitization with ovalbumin with and without hMSC infusion therapy. ECM deposition (specifically trichrome staining, soluble and insoluble collagen deposition, and hyaluronan production) was evaluated. Image quantification was used to monitor trichrome staining changes.

RESULTS

GM-CSF which induced collagen I and collagen III production was down-regulated with hMSC using co-culture. In the in vivo model, Ovalbumin induced enhanced ECM deposition, soluble and insoluble collagen production, and lung elastance. hMSC infusions decreased ECM deposition as evidenced by decreases in soluble and insoluble collagen production.

CONCLUSION

hMSCs participate in improved outcomes of remodeling by reversing excess collagen deposition and changing hyaluronan levels.