TSG-6: a multifunctional protein associated with inflammation

Therapeutic potential of mesenchymal stem cells for pulmonary complications associated with preterm birth

Preterm infants frequently suffer from pulmonary complications resulting in significant morbidity and mortality. Physiological and structural lung immaturity impairs perinatal lung transition to air breathing resulting in respiratory distress. Mechanical ventilation and oxygen supplementation ensure sufficient oxygen supply but enhance inflammatory processes which might lead to the establishment of a chronic lung disease called bronchopulmonary dysplasia (BPD). Current therapeutic options to prevent or treat BPD are limited and have salient side effects, highlighting the need for new therapeutic approaches. Mesenchymal stem cells (MSCs) have demonstrated therapeutic potential in animal models of BPD. This review focuses on MSC-based therapeutic approaches to treat pulmonary complications and critically compares results obtained in BPD models. Thereby bottlenecks in the translational systems are identified that are preventing progress in combating BPD. Notably, current animal models closely resemble the so-called "old" BPD with profound inflammation and injury, whereas clinical improvements shifted disease pathology towards a "new" BPD in which arrest of lung maturation predominates. Future studies need to evaluate the utility of MSC-based therapies in animal models resembling the "new" BPD though promising in vitro evidence suggests that MSCs do possess the potential to stimulate lung maturation. Furthermore, we address the mode-of-action of MSC-based therapies with regard to lung development and inflammation/fibrosis. Their therapeutic efficacy is mainly attributed to an enhancement of regeneration and immunomodulation due to paracrine effects. In addition, we discuss current improvement strategies by genetic modifications or precondition of MSCs to enhance their therapeutic efficacy which could also prove beneficial for BPD therapies.

TNFAIP6 is a potential biomarker of disease activity in inflammatory bowel disease

AIM

Ideal biomarkers are needed for evaluating the activity of inflammatory bowel disease (IBD). We aimed to investigate the value of TNFAIP6 as a biomarker.

MATERIALS & METHODS

Inflamed colonic samples and serum samples were collected from patients with Crohn's disease (CD), patients with ulcerative colitis (UC), and normal controls. SPSS 18.0 was used for statistical analysis.

RESULTS

Serum TNFAIP6 was higher in IBD patients than in normal controls and correlated with the inflammatory indicators. Compared with active patients, TNFAIP6 was decreased in both CD and UC patients in remission. Furthermore, TNFAIP6 concentrations consistent with TNF-α level, correlated well with disease location and extent of both CD and UC.

CONCLUSION

Serum TNFAIP6 may be a promising biomarker for evaluating the disease activity of IBD, demonstrating the diagnostic value in disease location differentiation.

The Anti-inflammatory Protein TSG-6 Regulates Chemokine Function by Inhibiting Chemokine/Glycosaminoglycan Interactions

TNF-stimulated gene-6 (TSG-6) is a multifunctional protein secreted in response to pro-inflammatory stimuli by a wide range of cells, including neutrophils, monocytes, and endothelial cells. It has been shown to mediate anti-inflammatory and protective effects when administered in disease models, in part, by reducing neutrophil infiltration. Human TSG-6 inhibits neutrophil migration by binding CXCL8 through its Link module (Link_TSG6) and interfering with the presentation of CXCL8 on cell-surface glycosaminoglycans (GAGs), an interaction that is vital for the function of many chemokines. TSG-6 was also found to interact with chemokines CXCL11 and CCL5, suggesting the possibility that it may function as a broad specificity chemokine-binding protein, functionally similar to those encoded by viruses. This study was therefore undertaken to explore the ability of TSG-6 to regulate the function of other chemokines. Herein, we demonstrate that Link_TSG6 binds chemokines from both the CXC and CC families, including CXCL4, CXCL12, CCL2, CCL5, CCL7, CCL19, CCL21, and CCL27. We also show that the Link_TSG6-binding sites on chemokines overlap with chemokine GAG-binding sites, and that the affinities of Link_TSG6 for these chemokines (K_D values 1–85 nm) broadly correlate with chemokine-GAG affinities. Link_TSG6 also inhibits chemokine presentation on endothelial cells not only through a direct interaction with chemokines but also by binding and therefore masking the availability of GAGs. Along with previous work, these findings suggest that TSG-6 functions as a pluripotent regulator of chemokines by modulating chemokine/GAG interactions, which may be a major mechanism by which TSG-6 produces its anti-inflammatory effects in vivo.

Anti-inflammatory protein tumor necrosis factor-α-stimulated protein 6 (TSG-6) promotes early gingival wound healing: an in vivo study

BACKGROUND

Human multipotent mesenchymal stromal cells (hMSCs) produce tumor necrosis factor (TNF)-α-stimulated protein 6 (TSG-6). TSG-6 modulates proinflammatory cytokine cascades and enhances tissue repair. This study tests the effects of recombinant human TSG-6 (rhTSG-6) on gingival wound healing within the first 2 days post-surgery.

METHODS

After gingival resection in 120 Sprague-Dawley rats, 2 µg rhTSG-6 in 5-µL phosphate-buffered saline (PBS) or the same volume of only PBS solution was injected into gingival tissue approximating the surgical wound. Control animals did not receive injections. Tissue biopsies and blood were collected at 1 to 2, 6 to 8, 24, and 48 hours post-surgery (n = 10 per group). Specimens were analyzed via histologic analysis and enzyme-linked immunosorbent assay (ELISA) for quantification and comparison of inflammatory markers interleukin (IL)-1β, IL-6, TNF-α, and myeloperoxidase (MPO). Wound photographs were taken for a double-masked clinical assessment at each time period. Weights were recorded for all animals pre- and post-surgery.

RESULTS

Animals injected with rhTSG-6 had significantly less severe clinical inflammation at 6 to 8 (P = 0.01228), 24 (P = 0.01675), and 48 (P = 0.0186) hours. Sham and control animals had more weight loss at 24 and 48 hours. Sham and control animals had more pronounced cellular infiltrate. rhTSG-6-treated animals had significantly less MPO (P = 0.027) at 24 hours and IL-1β (P = 0.027) at 24 and 48 hours. IL-6 showed a marginal significant difference at 6 to 8 hours, but there was no significant difference for TNF-α.

CONCLUSION

rhTSG-6 reduced postoperative gingival inflammation by reducing levels of proinflammatory cytokines and cellular infiltrate and may offer significant promise as an anti-inflammatory agent for gingival surgery.

Paracrine in vivo inhibitory effects of adipose tissue-derived mesenchymal stromal cells in the early stages of the acute inflammatory response

BACKGROUND AIMS

Excessive or unresolved inflammation leads to tissue lesions. Adipose tissue-derived mesenchymal stromal cells (AMSCs) have shown protective effects that may be dependent on the modulation of inflammation by secreted factors.

METHODS

We used the zymosan-induced mouse air pouch model at two time points (4 h and 18 h) to evaluate the in vivo effects of AMSCs and their conditioned medium (CM) on key steps of the early inflammatory response. We assessed the effects of AMSCs and CM on leukocyte migration and myeloperoxidase activity. The levels of chemokines, cytokines and eicosanoids in exudates were measured by use of enzyme-linked immunoassay or radio-immunoassay. In addition, the expression of cyclooxygenase-2 and microsomal prostaglandin E synthase-1 (mPGES-1) was studied by use of Western blotting and the phosphorylation of p65 nuclear factor-κB (NF-κB) by immunofluorescence.

RESULTS

All inflammatory parameters were significantly reduced by CM and AMSCs to a similar extent at 4 h after zymosan injection with lower effects at 18 h. The observed inhibition of leukocyte migration was associated with reduced levels of chemokines and leukotriene B4. Interleukin-1β, interleukin-6, tumor necrosis factor-α and tumor necrosis factor-stimulated gene 6 levels were significantly decreased. The downregulation of mPGES-1 was associated with inhibition of prostaglandin E2 production. Our results suggest that these anti-inflammatory effects are related, in part, to the inhibition of NF-κB activation.

CONCLUSIONS

AMSCs dampen the early process of inflammation in the zymosan-induced mouse air pouch model through paracrine mechanisms. These results support the potential utility of these cells as a source of novel treatment approaches for inflammatory pathologies.

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.

Binding of Hyaluronan to the Native Lymphatic Vessel Endothelial Receptor LYVE-1 Is Critically Dependent on Receptor Clustering and Hyaluronan Organization

The lymphatic endothelial receptor LYVE-1 has been implicated in both uptake of hyaluronan (HA) from tissue matrix and in facilitating transit of leukocytes and tumor cells through lymphatic vessels based largely on in vitro studies with recombinant receptor in transfected fibroblasts. Curiously, however, LYVE-1 in lymphatic endothelium displays little if any binding to HA in vitro, and this has led to the conclusion that the native receptor is functionally silenced, a feature that is difficult to reconcile with its proposed in vivo functions. Nonetheless, as we reported recently, LYVE-1 can function as a receptor for HA-encapsulated Group A streptococci and mediate lymphatic dissemination in mice. Here we resolve these paradoxical findings and show that the capacity of LYVE-1 to bind HA is strictly dependent on avidity, demanding appropriate receptor self-association and/or HA multimerization. In particular, we demonstrate the prerequisite of a critical LYVE-1 threshold density and show that HA binding may be elicited in lymphatic endothelium by surface clustering with divalent LYVE-1 mAbs. In addition, we show that cross-linking of biotinylated HA in streptavidin multimers or supramolecular complexes with the inflammation-induced protein TSG-6 enables binding even in the absence of LYVE-1 cross-linking. Finally, we show that endogenous HA on the surface of macrophages can engage LYVE-1, facilitating their adhesion and transit across lymphatic endothelium. These results reveal LYVE-1 as a low affinity receptor tuned to discriminate between different HA configurations through avidity and establish a new mechanistic basis for the functions ascribed to LYVE-1 in matrix HA binding and leukocyte trafficking in vivo.

Nuclear Magnetic Resonance Insight into the Multiple Glycosaminoglycan Binding Modes of the Link Module from Human TSG-6

Tumor necrosis factor-stimulated gene-6 (TSG-6) is a hyaluronan (HA)-binding protein that is essential for stabilizing and remodeling the extracellular matrix (ECM) during ovulation and inflammatory disease processes such as arthritis. The Link module, one of the domains of TSG-6, is responsible for binding hyaluronan and other glycosaminoglycans found in the ECM. In this study, we used a well-defined chondroitin sulfate (CS) hexasaccharide (ΔC444S) to determine the structure of the Link module, in solution, in its chondroitin sulfate-bound state. A variety of nuclear magnetic resonance techniques were employed, including chemical shift perturbation, residual dipolar couplings (RDCs), nuclear Overhauser effects, spin relaxation measurements, and paramagnetic relaxation enhancements from a spin-labeled analogue of ΔC444S. The binding site for ΔC444S on the Link module overlapped with that of HA. Surprisingly, ΔC444S binding induced dimerization of the Link module (as confirmed by analytical ultracentrifugation), and a second weak binding site that partially overlapped with a previously identified heparin site was detected. A dimer model was generated using chemical shift perturbations and RDCs as restraints in the docking program HADDOCK. We postulate that the molecular cross-linking enhanced by the multiple binding modes of the Link module might be critical for remodeling the ECM during inflammation/ovulation and might contribute to other functions of TSG-6.

Molecular analysis of the cumulus matrix: insights from mice with O-glycan-deficient oocytes

During follicle development, oocytes secrete factors that influence the development of granulosa and cumulus cells (CCs). In response to oocyte and somatic cell signals, CCs produce extracellular matrix (ECM) molecules resulting in cumulus expansion, which is essential for ovulation, fertilisation, and is predictive of oocyte quality. The cumulus ECM is largely made up of hyaluronan (HA), TNF-stimulated gene-6 (TSG-6, also known as TNFAIP6), pentraxin-3 (PTX3), and the heavy chains (HCs) of serum-derived inter-α-inhibitor proteins. In contrast to other in vivo models where modified expansion impairs fertility, the cumulus mass of C1galt1 Mutants, which have oocyte-specific deletion of core 1-derived O-glycans, is modified without impairing fertility. In this report, we used C1galt1 Mutant (C1galt1^FF:ZP3Cre) and Control (C1galt1^FF) mice to investigate how cumulus expansion is affected by oocyte-specific deletion of core 1-derived O-glycans without adversely affecting oocyte quality. Mutant cumulus–oocyte complexes (COCs) are smaller than Controls, with fewer CCs. Interestingly, the CCs in Mutant mice are functionally normal as each cell produced normal levels of the ECM molecules HA, TSG-6, and PTX3. However, HC levels were elevated in Mutant COCs. These data reveal that oocyte glycoproteins carrying core 1-derived O-glycans have a regulatory role in COC development. In addition, our study of Controls indicates that a functional COC can form provided all essential components are present above a minimum threshold level, and thus some variation in ECM composition does not adversely affect oocyte development, ovulation or fertilisation. These data have important implications for IVF and the use of cumulus expansion as a criterion for oocyte assessment.

The Compact and Biologically Relevant Structure of Inter-α-inhibitor Is Maintained by the Chondroitin Sulfate Chain and Divalent Cations

Inter-α-inhibitor is a proteoglycan of unique structure. The protein consists of three subunits, heavy chain 1, heavy chain 2, and bikunin covalently joined by a chondroitin sulfate chain originating at Ser-10 of bikunin. Inter-α-inhibitor interacts with an inflammation-associated protein, tumor necrosis factor-inducible gene 6 protein, in the extracellular matrix. This interaction leads to transfer of the heavy chains from the chondroitin sulfate of inter-α-inhibitor to hyaluronan and consequently to matrix stabilization. Divalent cations and heavy chain 2 are essential co-factors in this transfer reaction. In the present study, we have investigated how divalent cations in concert with the chondroitin sulfate chain influence the structure and stability of inter-α-inhibitor. The results showed that Mg(2+) or Mn(2+), but not Ca(2+), induced a conformational change in inter-α-inhibitor as evidenced by a decrease in the Stokes radius and a bikunin chondroitin sulfate-dependent increase of the thermodynamic stability. This structure was shown to be essential for the ability of inter-α-inhibitor to participate in extracellular matrix stabilization. In addition, the data revealed that bikunin was positioned adjacent to both heavy chains and that the two heavy chains also were in close proximity. The chondroitin sulfate chain interacted with all protein components and inter-α-inhibitor dissociated when it was degraded. Conventional purification protocols result in the removal of the Mg(2+) found in plasma and because divalent cations influence the conformation and affect function it is important to consider this when characterizing the biological activity of inter-α-inhibitor.

Podoplanin discriminates distinct stromal cell populations and a novel progenitor subset in the liver

Podoplanin/gp38(+) stromal cells present in lymphoid organs play a central role in the formation and reorganization of the extracellular matrix and in the functional regulation of immune responses. Gp38(+) cells are present during embryogenesis and in human livers of primary biliary cirrhosis. Since little is known about their function, we studied gp38(+) cells during chronic liver inflammation in models of biliary and parenchymal liver fibrosis and steatohepatitis. Gp38(+) cells were analyzed using flow cytometry and confocal microscopy, and the expression of their steady state and inflammation-associated genes was evaluated from healthy and inflamed livers. Gp38(+) cells significantly expanded in all three models of liver injury and returned to baseline levels during regression of inflammation. Based on CD133 and gp38 expression in the CD45(-)CD31(-)Asgpr1(-) liver cell fraction, numerous subsets could be identified that were negative for CD133 (gp38(hi)CD133(-), gp38(low)CD133(-), and gp38(-)CD133(-)). Moreover, among the CD133(+) cells, previously identified as progenitor population in injured liver, two subpopulations could be distinguished based on their gp38 expression (gp38(-)CD133(+) and CD133(+)gp38(+)). Importantly, the distribution of the identified subsets in inflammation illustrated injury-specific changes. Moreover, the gp38(+)CD133(+) cells exhibited liver progenitor cell characteristics similar to the gp38(-)CD133(+) population, thus representing a novel subset within the classical progenitor cell niche. Additionally, these cells expressed distinct sets of inflammatory genes during liver injury. Our study illuminates a novel classification of the stromal/progenitor cell compartment in the liver and pinpoints a hitherto unrecognized injury-related alteration in progenitor subset composition in chronic liver inflammation and fibrosis.

Human cytomegalovirus infection of human adipose-derived stromal/stem cells restricts differentiation along the adipogenic lineage

Human adipose-derived stromal/stem cells (ASCs) display potential to be used in regenerative stem cell therapies and as treatments for inflammatory and autoimmune disorders. Despite promising use of ASCs as therapeutics, little is known about their susceptibility to infectious agents. In this study, we demonstrate that ASCs are highly susceptible to human cytomegalovirus (HCMV) infection and permissive for replication leading to release of infectious virions. Additionally, many basic ASC functions are inhibited during HCMV infection, such as differentiation and immunomodulatory potential. To our knowledge this is the first study examining potential adverse effects of HCMV infection on ASC biology. Our results suggest, that an active HCMV infection during ASC therapy may result in a poor clinical outcome due to interference by the virus.

Mesenchymal stem/stromal cells precondition lung monocytes/macrophages to produce tolerance against allo- and autoimmunity in the eye

Intravenously administered mesenchymal stem/stromal cells (MSCs) engraft only transiently in recipients, but confer long-term therapeutic benefits in patients with immune disorders. This suggests that MSCs induce immune tolerance by long-lasting effects on the recipient immune regulatory system. Here, we demonstrate that i.v. infusion of MSCs preconditioned lung monocytes/macrophages toward an immune regulatory phenotype in a TNF-α-stimulated gene/protein (TSG)-6-dependent manner. As a result, mice were protected against subsequent immune challenge in two models of allo- and autoimmune ocular inflammation: corneal allotransplantation and experimental autoimmune uveitis (EAU). The monocytes/macrophages primed by MSCs expressed high levels of MHC class II, B220, CD11b, and IL-10, and exhibited T-cell-suppressive activities independently of FoxP3(+) regulatory T cells. Adoptive transfer of MSC-induced B220(+)CD11b(+) monocytes/macrophages prevented corneal allograft rejection and EAU. Deletion of monocytes/macrophages abrogated the MSC-induced tolerance. However, MSCs with TSG-6 knockdown did not induce MHC II(+)B220(+)CD11b(+) cells, and failed to attenuate EAU. Therefore, the results demonstrate a mechanism of the MSC-mediated immune modulation through induction of innate immune tolerance that involves monocytes/macrophages.

Inflammatory biomarkers in osteoarthritis

Osteoarthritis (OA) is highly prevalent and a leading cause of disability worldwide. Despite the global burden of OA, diagnostic tests and treatments for the molecular or early subclinical stages are still not available for clinical use. In recent years, there has been a large shift in the understanding of OA as a "wear and tear" disease to an inflammatory disease. This has been demonstrated through various studies using MRI, ultrasound, histochemistry, and biomarkers. It would of great value to be able to readily identify subclinical and/or sub-acute inflammation, particularly in such a way as to be appropriate for a clinical setting. Here we review several types of biomarkers associated with OA in human studies that point to a role of inflammation in OA.

Differential Interactive Effects of Cartilage Traumatization and Blood Exposure In Vitro and In Vivo

BACKGROUND

Sport injuries of the knee often lead to posttraumatic arthritis. In addition to direct damage of the cartilage, trauma-associated intra-articular bleeding may cause hemarthrosis. Both blood exposure and trauma are known to induce cell death and inflammation and to enhance proteoglycan release in cartilage.

HYPOTHESIS

Blood exposure increases chondrocyte death as well as inflammatory and degenerative processes in traumatized cartilage.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human macroscopically intact osteoarthritic (OA) cartilage explants were impacted by a drop-tower system (0.59 J) and cultivated with or without 10% blood. Interactive effects were studied concerning cell survival, gene expression, and the release of mediators over 24 hours and 96 hours. To evaluate the effects of trauma and hemarthrosis in vivo, a newly established blunt cartilage trauma model in the rabbit was used. Treatment of the knee joints of mature New Zealand White rabbits consisted of the following groups: control (C), arthrotomy (A), arthrotomy with cartilage trauma (AT; 1.0 J), and arthrotomy with cartilage trauma and blood injection (ATH). After 1 and 12 weeks, inflammatory mediators in the synovial fluid and histological changes of the cartilage were determined, and immunohistological staining was performed.

RESULTS

The in vitro studies revealed a significant additional or synergistic effect of blood exposure on trauma-induced chondrocyte death, interleukin (IL)-1β and prostaglandin-E2 (PGE2) release, and matrix metalloproteinase (MMP)/pro-MMP level. Singular arthrotomy in vivo induced a temporary inflammation. Histologically, cartilage trauma caused significant OA changes that were not aggravated by an additional hemarthrosis. Trauma led to a persistent deposition of terminal complement complex (TCC), being enhanced by hemarthrosis. However, trauma-induced formation of osteophytes and arthrotomy-induced elevation of tumor necrosis factor-α release were reduced by hemarthrosis.

CONCLUSION

While blood exposure clearly aggravated trauma-induced OA processes in the in vitro model, a singular blood injection revealed heterogeneous effects in vivo, enhancing TCC deposition but reducing trauma-induced osteophyte formation while the histological score of traumatized cartilage was not further impaired.

CLINICAL RELEVANCE

The results of this study indicate that a singular, limited bleeding event might not exacerbate early trauma-induced cartilage degeneration in joint injuries. An early removal of intra-articular blood may not prevent the final resulting cartilage damage.

Metal Ion-dependent Heavy Chain Transfer Activity of TSG-6 Mediates Assembly of the Cumulus-Oocyte Matrix

The matrix polysaccharide hyaluronan (HA) has a critical role in the expansion of the cumulus cell-oocyte complex (COC), a process that is necessary for ovulation and fertilization in most mammals. Hyaluronan is organized into a cross-linked network by the cooperative action of three proteins, inter-α-inhibitor (IαI), pentraxin-3, and TNF-stimulated gene-6 (TSG-6), driving the expansion of the COC and providing the cumulus matrix with its required viscoelastic properties. Although it is known that matrix stabilization involves the TSG-6-mediated transfer of IαI heavy chains (HCs) onto hyaluronan (to form covalent HC·HA complexes that are cross-linked by pentraxin-3) and that this occurs via the formation of covalent HC·TSG-6 intermediates, the underlying molecular mechanisms are not well understood. Here, we have determined the tertiary structure of the CUB module from human TSG-6, identifying a calcium ion-binding site and chelating glutamic acid residue that mediate the formation of HC·TSG-6. This occurs via an initial metal ion-dependent, non-covalent, interaction between TSG-6 and HCs that also requires the presence of an HC-associated magnesium ion. In addition, we have found that the well characterized hyaluronan-binding site in the TSG-6 Link module is not used for recognition during transfer of HCs onto HA. Analysis of TSG-6 mutants (with impaired transferase and/or hyaluronan-binding functions) revealed that although the TSG-6-mediated formation of HC·HA complexes is essential for the expansion of mouse COCs in vitro, the hyaluronan-binding function of TSG-6 does not play a major role in the stabilization of the murine cumulus matrix.

Regulation of synthesis and roles of hyaluronan in peritoneal dialysis

Hyaluronan (HA) is a ubiquitous extracellular matrix glycosaminoglycan composed of repeated disaccharide units of alternating D-glucuronic acid and D-N-acetylglucosamine residues linked via alternating β-1,4 and β-1,3 glycosidic bonds. HA is synthesized in humans by HA synthase (HAS) enzymes 1, 2, and 3, which are encoded by the corresponding HAS genes. Previous in vitro studies have shown characteristic changes in HAS expression and increased HA synthesis in response to wounding and proinflammatory cytokines in human peritoneal mesothelial cells. In addition, in vivo models and human peritoneal biopsy samples have provided evidence of changes in HA metabolism in the fibrosis that at present accompanies peritoneal dialysis treatment. This review discusses these published observations and how they might contribute to improvement in peritoneal dialysis.

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.

Mesenchymal Stem Cells Stabilize Atherosclerotic Vulnerable Plaque by Anti-Inflammatory Properties

Background and objectives

Formation and progression of atherosclerotic vulnerable plaque (VP) is the primary cause of many cardio-cerebrovascular diseases such as acute coronary syndrome and stroke. It has been reported that bone marrow mesenchymal stem cells (MSC) exhibit protective effects against many kinds of diseases including myocardial infarction. Here, we examined the effects of intravenous MSC infusion on a VP model and provide novel evidence of its influence as a therapy in this animal disease model.

Subjects and methods

Thirty healthy male New Zealand white rabbits were randomly divided into a MSC, VP or stable plaque (SP) group (n = 10/group) and received high fat diet and cold-induced common carotid artery intimal injury with liquid nitrogen to form atherosclerotic plaques. Serum hs-CRP, TNF-α, IL-6 and IL-10 levels were measured by ELISA at 1, 2, 3, 7, 14, 21 and 28 days after MSC transplantation. The animals were sacrificed at 4 weeks after MSC transplantation. Lesions in the right common carotid were observed using H&E and Masson staining, and the fibrous cap/lipid core ratio of atherosclerotic plaques were calculated. The expression of nuclear factor κB (NF-κB) and matrix metalloproteinase 1, 2, 9 (MMP-1,2,9) in the plaque were detected using immunohistochemistry, and apoptotic cells in the plaques were detected by TUNEL. In addition, the level of TNF-α stimulated gene/protein 6 (TSG-6) mRNA and protein were measured by quantitative Real-Time PCR and Western blotting, respectively.

Results

Two rabbits in the VP group died of lung infection and cerebral infarction respectively at 1 week after plaque injury by liquid nitrogen. Both H&E and Masson staining revealed that the plaques from the SP and MSC groups had more stable morphological structure and a larger fibrous cap/lipid core ratio than the VP group. Serum hs-CRP, TNF-α and IL-6 were significantly down-regulated, whereas IL-10 was significantly up-regulated in the MSC group compared with the VP group. .Immunohistochemistry analysis revealed that NF-κB and MMP expression was reduced in the MSC and SP groups compared to the VP group. Cell apoptosis decreased significantly in both the MSC and SP groups in comparison to the VP group. TSG-6 mRNA and protein expression were higher in the plaques of the MSC group compared to the VP and SP groups.

Conclusions

Our study results suggest that MSC transplantation can effectively stabilize vulnerable plaques in atherosclerotic rabbits. This may potentially offer a new clinical application of MSC in atherosclerosis.

Hyaluronan cable formation by ocular trabecular meshwork cells

Hyaluronan (HA) in the ocular trabecular meshwork (TM) is a critical modulator of aqueous humor outflow. Individual HA strands in the pericellular matrix can coalesce to form cable-like structures, which have different functional properties. Here, we investigated HA structural configuration by TM cells in response to various stimuli known to stimulate extracellular matrix (ECM) remodeling. In addition, the effects of HA cable induction on aqueous outflow resistance was determined. Primary TM cell cultures grown on tissue culture-treated plastic were treated for 12-48 h with TNFα, IL-1α, or TGFβ2. TM cells grown on silicone membranes were subject to mechanical stretch, which induces synthesis and activation of ECM proteolytic enzymes. HA structural configuration was investigated by HA binding protein (HAbp) staining and confocal microscopy. HAbp-labeled cables were induced by TNFα, TGFβ2 and mechanical stretch, but not by IL-1α. HA synthase (HAS) gene expression was quantitated by quantitative RT-PCR and HA concentration was measured by ELISA assay. By quantitative RT-PCR, HAS-1, -2, and -3 genes were differentially up-regulated and showed temporal differences in response to each treatment. HA concentration was increased in the media by TNFα, TGFβ2 and IL-1α, but mechanical stretch decreased pericellular HA concentrations. Immunofluorescence and Western immunoblotting were used to investigate the distribution and protein levels of the HA-binding proteins, tumor necrosis factor-stimulated gene-6 (TSG-6) and inter-α-inhibitor (IαI). Western immunoblotting showed that TSG-6 and IαI were increased by TNFα, TGFβ2 and IL-1α, but mechanical stretch reduced their levels. The underlying substrate appears to affect the identity of IαI·TSG-6·HA complexes since different complexes were detected when TM cells were grown on a silicone substrate compared to a rigid plastic surface. Porcine anterior segments were perfused with 10 μg/ml polyinosinic:polycytidylic acid (polyI:C), a potent inducer of HA cables, and outflow rates were monitored for 72 h. PolyI:C had no significant effect on outflow resistance in porcine anterior segments perfused at physiological pressure. Collectively, HAS gene expression, HA concentration and configuration are differentially modified in response to several treatments that induce ECM remodeling in TM cells. In ocular TM cells, our data suggests that the most important determinant of HA cable formation appears to be the ratio of HA chains produced by the different HAS genes. However, the act of rearranging pericellular HA into cable-like structures does not appear to influence aqueous outflow resistance.

Acute and temporal expression of tumor necrosis factor (TNF)-α-stimulated gene 6 product, TSG6, in mesenchymal stem cells creates microenvironments required for their successful transplantation into muscle tissue

Previously, we demonstrated that when mesenchymal stem cells (MSCs) from mouse ES cells were transplanted into skeletal muscle, more than 60% of them differentiated into muscles in the crush-injured tibialis anterior muscle in vivo, although MSCs neither differentiated nor settled in the intact muscle. Microenvironments, including the extracellular matrix between the injured and intact muscle, were quite different. In the injured muscle, hyaluronan (HA), heavy chains of inter-α-inhibitor (IαI), CD44, and TNF-α-stimulated gene 6 product (TSG-6) increased 24-48 h after injury, although basement membrane components of differentiated muscle such as perlecan, laminin, and type IV collagen increased gradually 4 days after the crush. We then investigated the microenvironments crucial for cell transplantation, using the lysate of C2C12 myotubules for mimicking injured circumstances in vivo. MSCs settled in the intact muscle when they were transplanted together with the C2C12 lysate or TSG6. MSCs produced and released TSG6 when they were cultured with C2C12 lysates in vitro. MSCs pretreated with the lysate also settled in the intact muscle. Furthermore, MSCs whose TSG6 was knocked down by shRNA, even if transplanted or pretreated with the lysate, could not settle in the muscle. Immunofluorescent staining showed that HA and IαI always co-localized or were distributed closely, suggesting formation of covalent complexes, i.e. the SHAP-HA complex in the presence of TSG6. Thus, TSG6, HA, and IαI were crucial factors for the settlement and probably the subsequent differentiation of MSCs.

Intravitreal TSG-6 suppresses laser-induced choroidal neovascularization by inhibiting CCR2+ monocyte recruitment

Choroidal neovascularization (CNV) is the hallmark of wet age-related macular degeneration (AMD), one of the leading causes of blindness in the elderly. Although the pathogenesis of CNV is not clear, a number of studies show that ocular-infiltrating macrophages and inflammation play a critical role in the development of CNV. TNFα-stimulated gene/protein (TSG)-6 is a multifunctional endogenous protein that has anti-inflammatory activities partly by regulating macrophage activation. Therefore, we here investigated the therapeutic potential of TSG-6 in a rat model of CNV induced by laser photocoagulation. Time course analysis showed that the expression of VEGF and pro-inflammatory cytokines in the choroid was up-regulated early after laser injury, and gradually decreased to baseline over 14 days. An intravitreal injection of TSG-6 suppressed the expression of VEGF and pro-inflammatory cytokines including CCL2, and reduced the size of CNV. Also, the number of Iba⁺ and CCR2⁺ cells including infiltrating macrophages was markedly lower in the CNV lesion of TSG-6-treated eyes. Further analysis identified CCR2⁺ CD11b⁺ CD11c⁺ cells and CCR2⁺ CD11b^-CD11c⁺ cells as the cell populations that were increased by laser injury and reduced by TSG-6 treatment. Together, the results demonstrate that TSG-6 inhibits inflammation and CCR2⁺ monocyte recruitment into the choroid, and suppresses the development of CNV.

Hyaluronan, Inflammation, and Breast Cancer Progression

Breast cancer-induced inflammation in the tumor reactive stroma supports invasion and malignant progression and is contributed to by a variety of host cells including macrophages and fibroblasts. Inflammation appears to be initiated by tumor cells and surrounding host fibroblasts that secrete pro-inflammatory cytokines and chemokines and remodel the extracellular matrix (ECM) to create a pro-inflammatory “cancerized” or tumor reactive microenvironment that supports tumor expansion and invasion. The tissue polysaccharide hyaluronan (HA) is an example of an ECM component within the cancerized microenvironment that promotes breast cancer progression. Like many ECM molecules, the function of native high-molecular weight HA is altered by fragmentation, which is promoted by oxygen/nitrogen free radicals and release of hyaluronidases within the tumor microenvironment. HA fragments are pro-inflammatory and activate signaling pathways that promote survival, migration, and invasion within both tumor and host cells through binding to HA receptors such as CD44 and RHAMM/HMMR. In breast cancer, elevated HA in the peri-tumor stroma and increased HA receptor expression are prognostic for poor outcome and are associated with disease recurrence. This review addresses the critical issues regarding tumor-induced inflammation and its role in breast cancer progression focusing specifically on the changes in HA metabolism within tumor reactive stroma as a key factor in malignant progression.

The selective mGluR5 agonist CHPG attenuates SO2-induced oxidative stress and inflammation through TSG-6/NF-κB pathway in BV2 microglial cells

Sulfur dioxide (SO2) is a common air pollutant and can cause harmful insults on neurons. Microglial activation has been implicated in the signaling cascades that contribute to neuronal cell death in various neurological disorders. In the present study, we found that SO2 derivatives decreased cell viability via inducing oxidative stress, inflammatory responses and apoptotic cell death in BV2 microglial cells. Pretreatment with (RS)-2-chloro-5-hydroxyphenylglycine (CHPG), an mGluR5 agonist, significantly attenuated the SO2-induced cytotoxicity, which was fully prevented by the mGluR5 antagonist MPEP. CHPG increased the expression of TNF-α stimulated gene/protein 6 (TSG-6), but decreased the activation of nuclear factor-κB (NF-κB) after SO2 derivatives treatment in BV2 cells. In addition, knockdown of TSG-6 expression by specific targeted short interfering RNA (siRNA) partially reversed the protection induced by CHPG. Therefore, our findings reveal a mechanistic basis for exploring the association between SO2 exposure and neurological disorders, and also for opening up therapeutic approaches of ameliorating neuronal injury resulting from exposure in atmospheric polluting environment.

Tumor necrosis factor-inducible gene 6 promotes liver regeneration in mice with acute liver injury

INTRODUCTION

Tumor necrosis factor-inducible gene 6 protein (TSG-6), one of the cytokines released by human mesenchymal stem/stromal cells (hMSC), has an anti-inflammatory effect and alleviates several pathological conditions; however, the hepatoprotective potential of TSG-6 remains unclear. We investigated whether TSG-6 promoted liver regeneration in acute liver failure.

METHODS

The immortalized hMSC (B10) constitutively over-expressing TSG-6 or empty plasmid (NC: Negative Control) were established, and either TSG-6 or NC-conditioned medium (CM) was intraperitoneally injected into mice with acute liver damage caused by CCl4. Mice were sacrificed at 3 days post-CM treatment.

RESULTS

Higher expression and the immunosuppressive activity of TSG-6 were observed in CM from TSG-6-hMSC. The obvious histomorphological liver injury and increased level of liver enzymes were shown in CCl4-treated mice with or without NC-CM, whereas those observations were markedly ameliorated in TSG-6-CM-treated mice with CCl4. Ki67-positive hepatocytic cells were accumulated in the liver of the CCl4+TSG-6 group. RNA analysis showed the decrease in both of inflammation markers, tnfα, il-1β, cxcl1 and cxcl2, and fibrotic markers, tgf-β1, α-sma and collagen α1, in the CCl4+TSG-6 group, compared to the CCl4 or the CCl4+NC group. Protein analysis confirmed the lower expression of TGF-β1 and α-SMA in the CCl4+TSG-6 than the CCl4 or the CCl4+NC group. Immunostaining for α-SMA also revealed the accumulation of the activated hepatic stellate cells in the livers of mice in the CCl4 and CCl4+NC groups, but not in the livers of mice from the CCl4+TSG-6 group. The cultured LX2 cells, human hepatic stellate cell line, in TSG-6-CM showed the reduced expression of fibrotic markers, tgf-β1, vimentin and collagen α1, whereas the addition of the TSG-6 antibody neutralized the inhibitory effect of TSG-6 on the activation of LX2 cells. In addition, cytoplasmic lipid drops, the marker of inactivated hepatic stellate cell, were detected in TSG-6-CM-cultured LX2 cells, only. The suppressed TSG-6 activity by TSG-6 antibody attenuated the restoration process in livers of TSG-6-CM-treated mice with CCl4.

CONCLUSIONS

These results demonstrated that TSG-6 contributed to the liver regeneration by suppressing the activation of hepatic stellate cells in CCl4-treated mice, suggesting the therapeutic potential of TSG-6 for acute liver failure.

Oxidation of glycosaminoglycans by free radicals and reactive oxidative species: A review of investigative methods

Glycosaminoglycans, in particular hyaluronan (HA), and proteoglycans are components of the extracellular matrix (ECM). The ECM plays a key role in the regulation of cellular behaviour and alterations to it can modulate both the development of human diseases as well as controlling normal biochemical processes such as cell signalling and pro-inflammatory responses. For these reasons, in vitro fragmentation studies of glycosaminoglycans by free radicals and oxidative species are seen to be relevant to the understanding of in vivo studies of damage to the ECM. A wide range of investigative techniques have therefore been applied to gain insights into the relative fragmentation effects of several reactive oxidative species with the ultimate goal of determining mechanisms of fragmentation at the molecular level. These methods are reviewed here.

Anti-inflammatory cytokine TSG-6 inhibits hypertrophic scar formation in a rabbit ear model

Hypertrophic scars are characterized by excessive fibrosis and extracellular matrix (ECM) deposition and can be functionally and cosmetically problematic; however, there are few satisfactory treatments for controlling hypertrophic scars. The inflammatory cells and cytokines involved in excessive inflammation during wound healing facilitate fibroblast proliferation and collagen deposition, leading to pathologic scar formation. TSG-6 exhibits anti-inflammatory activity. This study examined the effect of recombinant TSG-6 on inflammation in hypertrophic scars using a rabbit ear model. Six 7-mm, full-thickness, circular wounds were made on the ears of 12 rabbits. TSG-6 and PBS were intradermally injected into the right and left ear wounds, respectively. The methods of TEM and TUNEL were used to detect fibroblast apoptosis. The expressions of inflammatory factors: IL-1β, IL-6 and TNF-α, were detected by immunohistochemistry and real time polymerase chain reaction. Collagen I and III expression detected by immunohistochemistry and Masson׳s trichrome staining and SEI (scar elevation index) was used to evaluate the extent of scarring. TSG-6 injection mitigated the formation of a hypertrophic scar in the rabbit ear. TSG-6-treated wounds exhibited decreased inflammation compared with the control group, as evidenced by the lower levels of IL-1β, IL-6, TNF-α and MPO. The SEI and the synthesis of collagens I and III were significantly decreased in the TSG-6-treated scars compared with control scars. The apoptosis rate was higher in the TSG-6-treated scars. TSG-6 exhibited anti-inflammatory effects during the wound healing process and cicatrization and significantly diminished hypertrophic scar formation in a rabbit ear model.

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.

Concise Review: Mesenchymal Stem Cells Ameliorate Tissue Injury via Secretion of Tumor Necrosis Factor-α Stimulated Protein/Gene 6

Numerous reports have described therapeutic benefits in various disease models after administration of the adult stem/progenitor cells from bone marrow or other tissues referred to as mesenchymal stem cells/multipotent mesenchymal stromal cells (MSCs). They all showed that one of the important effects of MSCs is to act against excessive inflammatory responses and repair the damaged tissues. The therapeutic benefits of MSCs were initially interpreted by their migration, engraftment, and differentiation into target tissues. However, remarkable anatomical structural repairs and functional improvements were increasingly observed with a small number of or even no MSCs in the injured tissues. This suggests that most beneficial effects are largely due to paracrine secretions or cell-to-cell contacts that have multiple effects involving modulation of inflammatory and immune responses. Currently, the therapeutic benefits of MSCs are in part explained by the cells being activated by signals from injured tissues to express an anti-inflammatory protein, tumor-necrosis-factor-α-induced protein 6. This important mechanism of action has attracted increasing attention, and therefore we conducted this review to summarize the latest research.

TSG-6 as a biomarker to predict efficacy of human mesenchymal stem/progenitor cells (hMSCs) in modulating sterile inflammation in vivo

Human mesenchymal stem/progenitor cells (hMSCs) from bone marrow and other tissues are currently being administered to large numbers of patients even though there are no biomarkers that accurately predict their efficacy in vivo. Using a mouse model of chemical injury of the cornea, we found that bone-marrow-derived hMSCs isolated from different donors varied widely in their efficacy in modulating sterile inflammation. Importantly, RT-PCR assays of hMSCs for the inflammation-modulating protein TSG-6 expressed by the TNFα-stimulated gene 6 (TSG-6 or TNFAIP6) predicted their efficacy in sterile inflammation models for corneal injury, sterile peritonitis, and bleomycin-induced lung injury. In contrast, the levels of TSG-6 mRNA were negatively correlated with their potential for osteogenic differentiation in vitro and poorly correlated with other criteria for evaluating hMSCs. Also, a survey of a small cohort suggested that hMSCs from female donors compared with male donors more effectively suppressed sterile inflammation, expressed higher levels of TSG-6, and had slightly less osteogenic potential.

The gene expression profile of cumulus cells reveals altered pathways in patients with endometriosis

PURPOSE

The objective of this experimental study was to compare the global gene expression profile of CC of mature oocytes in 18 patients with severe endometriosis and CC in 18 control patients affected by a severe male factor.

METHODS

For each group, the CC were pooled, RNA was extracted and a microarray performed. For validating the microarray, a quantitative real-time PCR was performed in the CC of an independent set of patients with endometriosis (n = 5) and controls (n = 7).

RESULTS

595 differentially expressed genes (320 down-regulated, 275 up-regulated, p < 0.05, fold change ≥1.5) were identified. The most significant changes were observed in genes involved in the chemokine signaling and cell-cell or cell-extracellular matrix adhesion pathways. Several genes of these pathways were down-regulated in endometriosis. Individual RT-PCR assays confirmed the microarray for ten genes.

CONCLUSIONS

Several genes involved in the chemokine mediated-signaling pathway and in the functional cross-talk between CC and the oocyte are down-regulated in endometriosis CC. The impairment of these processes could explain the reduction of oocyte competence in endometriosis. This preliminary knowledge could be the starting point for a more detailed elucidation of the relationship between endometriosis and oocyte competence.

Mesenchymal stem cells inhibit lipopolysaccharide-induced inflammatory responses of BV2 microglial cells through TSG-6

Microglia are the primary immunocompetent cells in brain tissue and microglia-mediated inflammation is associated with the pathogenesis of various neuronal disorders. Recently, many studies have shown that mesenchymal stem cells (MSCs) display a remarkable ability to modulate inflammatory and immune responses through the release of a variety of bioactive molecules, thereby protecting the central nervous system. Previously, we reported that MSCs have the ability to modulate inflammatory responses in a traumatic brain injury model and that the potential mechanisms may be partially attributed to upregulated TNF-α stimulated gene/protein 6 (TSG-6) expression. However, whether TSG-6 exerts an anti-inflammatory effect by affecting microglia is not fully understood. In this study, we investigated the anti-inflammatory effects of MSCs and TSG-6 in an in vitro lipopolysaccharide (LPS)-induced BV2 microglial activation model. We found that MSCs and TSG-6 significantly inhibited the expression of pro-inflammatory mediators in activated microglia. However, MSC effects on microglia were attenuated when TSG-6 expression was silenced. In addition, we found that the activation of nuclear factor (NF)-κB and mitogen-activated protein kinase (MAPK) pathways in LPS-stimulated BV2 microglial cells was significantly inhibited by TSG-6. Furthermore, we found that the presence of CD44 in BV2 microglial cells was essential for MSC- and TSG-6-mediated inhibition of pro-inflammatory gene expression and of NF-κB and MAPK activation in BV2 microglial cells. The results of this study suggest that MSCs can modulate microglia activation through TSG-6 and that TSG-6 attenuates the inflammatory cascade in activated microglia. Our study indicates that novel mechanisms are responsible for the immunomodulatory effect of MSCs on microglia and that MSCs, as well as TSG-6, might be promising therapeutic agents for the treatment of neurotraumatic injuries or neuroinflammatory diseases associated with microglial activation.

Effects of RU486 and indomethacin on meiotic maturation, formation of extracellular matrix, and progesterone production by porcine oocyte-cumulus complexes

This study was designed to determine whether inhibition of either cyclooxygenase-2 (COX-2) by indomethacin or progesterone receptor (PR) by PR antagonist, RU486, affects oocyte maturation, progesterone production, and covalent binding between hyaluronan (HA) and heavy chains of inter-α trypsin inhibitor, as well as expression of cumulus expansion-associated proteins (HA-binding protein, tumor necrosis factor α-induced protein 6, pentraxin 3) in oocyte-cumulus complexes (OCCs). The experiments were based on freshly isolated porcine OCC cultures in which the consequences of PR and COX-2 inhibition on the final processes of oocyte maturation were determined. Granulosa cells (GCs) and OCCs were cultured in medium supplemented with FSH/LH (both 100 ng/mL) in the presence/absence of RU486 or indomethacin. Western blot analysis, (3)H-glucosamine hydrochloride assay, immunofluorescence, and radioimmunoassay were performed. Only treatment with RU486 (25 μM) caused a decrease in the number of oocytes that reached germinal vesicle breakdown and metaphase II stage compared with indomethacin (100 μM) or FSH/LH treatment alone after 44 h. All treated OCCs synthesized an almost equal amount of HA. Heavy chains (of inter-α trypsin inhibitor)-HA covalent complexes were formed during in vitro FSH/LH-stimulated expansion in RU486- or indomethacin-treated OCCs. Follicle-stimulating hormone/LH-induced progesterone production by OCCs was increased in the presence of RU486 after 44 h. In contrast, a decrease of FSH/LH-stimulated progesterone production by GCs was detected in the presence of either RU486 or indomethacin after 72 h. We suggest that the PR-dependent pathway may be involved in the regulation of oocyte maturation. Both PR and COX-2 regulate FSH/LH-stimulated progesterone production by OCCs and GCs.

Therapeutic effect of TSG-6 engineered iPSC-derived MSCs on experimental periodontitis in rats: a pilot study

Background

We derived mesenchymal stem cells (MSCs) from rat induced pluripotent stem cells (iPSCs) and transduced them with tumor necrosis factor alpha-stimulated gene-6 (TSG-6), to test whether TSG-6 overexpression would boost the therapeutic effects of iPSC-derived MSCs in experimental periodontitis.

Methods

A total of 30 female Sprague-Dawley (SD) rats were randomly divided into four groups: healthy control group (Group-N, n = 5), untreated periodontitis group (Group-P, n = 5), iPS-MSCs-treated and iPSC-MSCs/TSG-6-treated periodontitis groups (Group-P1 and P2, n = 10 per group). Experimental periodontitis was established by ligature and infection with Porphyromonas gingivalis around the maxillae first molar bilaterally. MSC-like cells were generated from rat iPSCs, and transducted with TSG-6. iPSC-MSCs or iPSC-MSCs/TSG-6 were administrated to rats in Group-P1 or P2 intravenously and topically, once a week for three weeks. Blood samples were obtained one week post-injection for the analysis of serum pro-inflammatory cytokines. All animals were killed 3 months post-treatment; maxillae were then dissected for histological analysis, tartrate-resistant acid phosphatase (TRAP) staining, and morphological analysis of alveolar bone loss.

Results

Administration of iPSC-MSC/TSG-6 significantly decreased serum levels of IL-1β and TNF-α in the Group-P2 rats (65.78 pg/ml and 0.56 pg/ml) compared with those in Group-P (168.31 pg/ml and 1.15 pg/ml respectively) (p<0.05). Both alveolar bone loss and the number of TRAP-positive osteoclasts showed a significant decrease in rats that received iPSC-MSC/TSG-6 treatment compared to untreated rats in Group-P (p<0.05),

Conclusions

We demonstrated that overexpression of TSG-6 in rat iPSC-derived MSCs were capable of decreasing inflammation in experimental periodontitis and inhibiting alveolar bone resorption. This may potentially serve as an alternative stem-cell-based approach in the treatment and regeneration of periodontal tissues.

Characterization of a novel recombinant hyaluronan binding protein for tissue hyaluronan detection

Tumor necrosis factor-Stimulated Gene 6 protein (TSG-6) is a hyaluronan (HA)-binding glycoprotein containing an HA-binding Link module. Because of its well-defined structure, HA binding properties and small size, TSG-6 is an excellent candidate as an alternative to animal-derived HA-binding protein (HABP) for the detection of HA. The present work describes the generation and characterization of a novel recombinant HA-binding probe obtained by fusion of a modified TSG-6 Link module with mutationally inactivated heparin-binding sequence and the Fc portion of human IgG1 (TSG-6-ΔHep-Fc) for tissue HA detection in histological samples. Direct binding assays indicated strong binding of TSG-6-ΔHep-Fc to HA, with little residual binding to heparin. Histolocalization of HA in formalin-fixed, paraffin-embedded tissue sections using biotin-TSG-6-ΔHep-Fc resulted in hyaluronidase-sensitive staining patterns similar to those obtained with biotin-HABP, but with improved sensitivity. HA was detected in many human tissues, and was most abundant in soft connective tissues such as the skin dermis and the stroma of various glands. Digital image analysis revealed a linear correlation between biotin-HABP and biotin-TSG-6-ΔHep-Fc staining intensity in a subset of normal and malignant human tissues. These results demonstrate that TSG-6-ΔHep-Fc is a sensitive and specific probe for the detection of HA by histological methods.

A refined model for the TSG-6 link module in complex with hyaluronan: use of defined oligosaccharides to probe structure and function

Tumor necrosis factor-stimulated gene-6 (TSG-6) is an inflammation-associated hyaluronan (HA)-binding protein that contributes to remodeling of HA-rich extracellular matrices during inflammatory processes and ovulation. The HA-binding domain of TSG-6 consists solely of a Link module, making it a prototypical member of the superfamily of proteins that interacts with this high molecular weight polysaccharide composed of repeating disaccharides of D-glucuronic acid and N-acetyl-D-glucosamine (GlcNAc). Previously we modeled a complex of the TSG-6 Link module in association with an HA octasaccharide based on the structure of the domain in its HA-bound conformation. Here we have generated a refined model for a HA/Link module complex using novel restraints identified from NMR spectroscopy of the protein in the presence of 10 distinct HA oligosaccharides (from 4- to 8-mers); the model was then tested using unique sugar reagents, i.e. chondroitin/HA hybrid oligomers and an octasaccharide in which a single sugar ring was (13)C-labeled. The HA chain was found to make more extensive contacts with the TSG-6 surface than thought previously, such that a D-glucuronic acid ring makes stacking and ionic interactions with a histidine and lysine, respectively. Importantly, this causes the HA to bend around two faces of the Link module (resembling the way that HA binds to CD44), potentially providing a mechanism for how TSG-6 can reorganize HA during inflammation. However, the HA-binding site defined here may not play a role in TSG-6-mediated transfer of heavy chains from inter-α-inhibitor onto HA, a process known to be essential for ovulation.

TSG-6 inhibits neutrophil migration via direct interaction with the chemokine CXCL8

TNF-stimulated gene/protein-6 (TSG-6) is expressed by many different cell types in response to proinflammatory cytokines and plays an important role in the protection of tissues from the damaging consequences of acute inflammation. Recently, TSG-6 was identified as being largely responsible for the beneficial effects of multipotent mesenchymal stem cells, for example in the treatment of animal models of myocardial infarction and corneal injury/allogenic transplant. The protective effect of TSG-6 is due in part to its inhibition of neutrophil migration, but the mechanisms underlying this activity remain unknown. In this study, we have shown that TSG-6 inhibits chemokine-stimulated transendothelial migration of neutrophils via a direct interaction (KD, ∼ 25 nM) between TSG-6 and the glycosaminoglycan binding site of CXCL8, which antagonizes the association of CXCL8 with heparin. Furthermore, we found that TSG-6 impairs the binding of CXCL8 to cell surface glycosaminoglycans and the transport of CXCL8 across an endothelial cell monolayer. In vivo this could limit the formation of haptotactic gradients on endothelial heparan sulfate proteoglycans and, hence, integrin-mediated tight adhesion and migration. We further observed that TSG-6 suppresses CXCL8-mediated chemotaxis of neutrophils; this lower potency effect might be important at sites where there is high local expression of TSG-6. Thus, we have identified TSG-6 as a CXCL8-binding protein, making it, to our knowledge, the first soluble mammalian chemokine-binding protein to be described to date. We have also revealed a potential mechanism whereby TSG-6 mediates its anti-inflammatory and protective effects. This could inform the development of new treatments for inflammation in the context of disease or following transplantation.

TSG-6 activity as a novel biomarker of progression in knee osteoarthritis

OBJECTIVE

To establish whether there is an association between TSG-6 activity and osteoarthritis progression.

DESIGN

TSG-6 activity was determined in 132 synovial fluids from patients with OA of the knee, using a novel quantitative TSG-6 activity assay. The association between TSG-6 activities at baseline and four distinct disease progression states, determined at 3-year follow-up, was analyzed using logistic regression.

RESULTS

There was a statistically significant relationship between TSG-6 activity at baseline and all OA progression states over a 3-year period. Patient knees with TSG-6 activities in the top tenth percentile, compared to the median activity, had an odds ratio (OR) of at least 7.86 (confidence interval (CI) [3.2, 20.5]) for total knee arthroplasty (TKA) within 3 years, and of at least 5.20 (CI [1.8, 13.9]) after adjustment for confounding factors. Receiver operating characteristic (ROC) analysis for knee arthroplasty yielded a cut-off point of 13.3 TSG-6 activity units/ml with the following parameters: area under the curve 0.90 (CI [0.804, 0.996]), sensitivity 0.91 (CI [0.59, 0.99]), specificity 0.82 (CI [0.74, 0.88]) and a negative predictive value (NPV) of 0.99 (CI [0.934, 0.994]).

CONCLUSION

The TSG-6 activity is a promising independent biomarker for OA progression. Given the high NPV, this assay may be particularly suitable for identifying patients at low risk of rapid disease progression and to assist in the timing of arthroplasty.

Efficiencies of fragmentation of glycosaminoglycan chloramides of the extracellular matrix by oxidizing and reducing radicals: potential site-specific targets in inflammation?

Hypochlorous acid and its conjugate base, hypochlorite ions, produced under inflammatory conditions, may produce chloramides of glycosaminoglycans, these being significant components of the extracellular matrix (ECM). This may occur through the binding of myeloperoxidase directly to the glycosaminoglycans. The N-Cl group in the chloramides is a potential selective target for both reducing and oxidizing radicals, leading possibly to more efficient and damaging fragmentation of these biopolymers relative to the parent glycosaminoglycans. To investigate the effect of the N-Cl group, we used ionizing radiation to produce quantifiable concentrations of the reducing radicals, hydrated electron and superoxide radical, and also of the oxidizing radicals, hydroxyl, carbonate, and nitrogen dioxide, all of which were reacted with hyaluronan and heparin and their chloramides in this study. PAGE gels calibrated for molecular weight allowed the consequent fragmentation efficiencies of these radicals to be calculated. Hydrated electrons were shown to produce fragmentation efficiencies of 100 and 25% for hyaluronan chloramide (HACl) and heparin chloramide (HepCl), respectively. The role of the sulfate group in heparin in the reduction of fragmentation can be rationalized using mechanisms proposed by M.D. Rees et al. (J. Am. Chem. Soc.125:13719-13733; 2003), in which the initial formation of an amidyl radical leads rapidly to a C-2 radical on the glucosamine moiety. This is 100% efficient at causing glycosidic bond breakage in HACl but only 25% efficient in HepCl, the role of the sulfate group being to favor the nonfragmentary routes for the C-2 radical. The weaker reducing agent, the superoxide radical, did not cause fragmentation of either HACl or HepCl although kinetic reactivity had been demonstrated in earlier studies. Experiments using the oxidizing radicals, hydroxyl and carbonate, both potential in vivo species, showed significant increases in fragmentation efficiencies for both HACl and HepCl, relative to the parent molecules. The carbonate radical was shown to be involved in site-specific reactions at the N-Cl groups, reacting via abstraction of Cl, to produce the same amidyl radical produced by one-electron reductants such as the hydrated electron. As for the hydrated electrons, the data support fragmentation efficiencies of 100 and 29% for reaction of carbonate radicals at N-Cl for HACl and HepCl, respectively. For the weaker oxidant, nitrogen dioxide, no fragmentation was observed, probably because of a low kinetic reactivity and low reduction potential. It seems likely therefore that the N-Cl group can direct damage to extracellular matrix glycosaminoglycan chloramides, which may be produced under inflammatory conditions. The in vivo species, the carbonate radical, is also much more likely to be site-specific in its reactions with such components of the ECM than the hydroxyl radical.

Inter-α-inhibitor impairs TSG-6-induced hyaluronan cross-linking

Under inflammatory conditions and in the matrix of the cumulus-oocyte complex, the polysaccharide hyaluronan (HA) becomes decorated covalently with heavy chains (HCs) of the serum glycoprotein inter-α-inhibitor (IαI). This alters the functional properties of the HA as well as its structural role within extracellular matrices. The covalent transfer of HCs from IαI to HA is catalyzed by TSG-6 (tumor necrosis factor-stimulated gene-6), but TSG-6 is also known as a HA cross-linker that induces condensation of the HA matrix. Here, we investigate the interplay of these two distinct functions of TSG-6 by studying the ternary interactions of IαI and TSG-6 with well defined films of end-grafted HA chains. We demonstrate that TSG-6-mediated cross-linking of HA films is impaired in the presence of IαI and that this effect suppresses the TSG-6-mediated enhancement of HA binding to CD44-positive cells. Furthermore, we find that the interaction of TSG-6 and IαI in the presence of HA gives rise to two types of complexes that independently promote the covalent transfer of heavy chains to HA. One type of complex interacts very weakly with HA and is likely to correspond to the previously reported covalent HC·TSG-6 complexes. The other type of complex is novel and binds stably but noncovalently to HA. Prolonged incubation with TSG-6 and IαI leads to HA films that contain, in addition to covalently HA-bound HCs, several tightly but noncovalently bound molecular species. These findings have important implications for understanding how the biological activities of TSG-6 are regulated, such that the presence or absence of IαI will dictate its function.

One-electron oxidation and reduction of glycosaminoglycan chloramides: a kinetic study

Hypochlorous acid and its acid-base counterpart, hypochlorite ions, produced under inflammatory conditions, may produce chloramides of glycosaminoglycans, these being significant components of the extracellular matrix (ECM). This may occur through the binding of myeloperoxidase directly to the glycosaminoglycans. The N-Cl group in the chloramides is a potential selective target for both reducing and oxidizing radicals, leading possibly to more efficient and damaging fragmentation of these biopolymers relative to the parent glycosaminoglycans. In this study, the fast reaction techniques of pulse radiolysis and nanosecond laser flash photolysis have been used to generate both oxidizing and reducing radicals to react with the chloramides of hyaluronan (HACl) and heparin (HepCl). The strong reducing formate radicals and hydrated electrons were found to react rapidly with both HACl and HepCl with rate constants of 1-1.7 × 10(8) and 0.7-1.2 × 10(8)M(-1)s(-1) for formate radicals and 2.2 × 10(9) and 7.2 × 10(8)M(-1)s(-1) for hydrated electrons, respectively. The spectral characteristics of the products of these reactions were identical and were consistent with initial attack at the N-Cl groups, followed by elimination of chloride ions to produce nitrogen-centered radicals, which rearrange subsequently and rapidly to produce C-2 radicals on the glucosamine moiety, supporting an earlier EPR study by M.D. Rees et al. (J. Am. Chem. Soc.125: 13719-13733; 2003). The oxidizing hydroxyl radicals also reacted rapidly with HACl and HepCl with rate constants of 2.2 × 10(8) and 1.6 × 10(8)M(-1)s(-1), with no evidence from these data for any degree of selective attack on the N-Cl group relative to the N-H groups and other sites of attack. The carbonate anion radicals were much slower with HACl and HepCl than hydroxyl radicals (1.0 × 10(5) and 8.0 × 10(4)M(-1)s(-1), respectively) but significantly faster than with the parent molecules (3.5 × 10(4) and 5.0 × 10(4)M(-1)s(-1), respectively). These findings suggest that these potential in vivo radicals may react in a site-specific manner with the N-Cl group in the glycosaminoglycan chloramides of the ECM, possibly to produce more efficient fragmentation. This is the first study therefore to conclusively demonstrate that reducing radicals react rapidly with glycosaminoglycan chloramides in a site-specific attack at the N-Cl group, probably to produce a 100% efficient biopolymer fragmentation process. Although less reactive, carbonate radicals, which may be produced in vivo via reactions of peroxynitrite with serum levels of carbon dioxide, also appear to react in a highly site-specific manner at the N-Cl group. It is not yet known if such site-specific attacks by this important in vivo species lead to a more efficient fragmentation of the biopolymers than would be expected for attack by the stronger oxidizing species, the hydroxyl radical. It is clear, however, that the N-Cl group formed under inflammatory conditions in the extracellular matrix does present a more likely target for both reactive oxygen species and reducing species than the N-H groups in the parent glycosaminoglycans.

Reaction of superoxide radicals with glycosaminoglycan chloramides: a kinetic study

Hypochlorous acid and its acid-base counterpart, hypochlorite ions, produced under inflammatory conditions, may produce chloramides of glycosaminoglycans, perhaps through the binding of myeloperoxidase directly to the glycosaminoglycans. The N-Cl group in the chloramides is a potential target for reducing species such as Cu(I) and superoxide radicals. Laser flash photolysis has been used here to obtain, for the first time, the rate constants for the direct reaction of superoxide radicals with the chloramides of hyaluronan and heparin. The rate constants were in the range 2.2-2.7 × 10(3)M(-1)s(-1). The rate constant for the reaction with the amino acid taurine was found to be much lower, at 3.5-4.0 × 10(2)M(-1)s(-1). This demonstration that superoxide anion radicals react directly with hyaluronan and heparin chloramides may support the mechanism first proposed by M.D. Rees et al. (Biochem. J.381, 175-184, 2004) for an efficient fragmentation of these glycosaminoglycans in the extracellular matrix under inflammatory conditions.

Anti-inflammatory effects of adult stem cells in sustained lung injury: a comparative study

Lung diseases are a major cause of global morbidity and mortality that are treated with limited efficacy. Recently stem cell therapies have been shown to effectively treat animal models of lung disease. However, there are limitations to the translation of these cell therapies to clinical disease. Studies have shown that delayed treatment of animal models does not improve outcomes and that the models do not reflect the repeated injury that is present in most lung diseases. We tested the efficacy of amnion mesenchymal stem cells (AM-MSC), bone marrow MSC (BM-MSC) and human amniotic epithelial cells (hAEC) in C57BL/6 mice using a repeat dose bleomycin-induced model of lung injury that better reflects the repeat injury seen in lung diseases. The dual bleomycin dose led to significantly higher levels of inflammation and fibrosis in the mouse lung compared to a single bleomycin dose. Intravenously infused stem cells were present in the lung in similar numbers at days 7 and 21 post cell injection. In addition, stem cell injection resulted in a significant decrease in inflammatory cell infiltrate and a reduction in IL-1 (AM-MSC), IL-6 (AM-MSC, BM-MSC, hAEC) and TNF-α (AM-MSC). The only trophic factor tested that increased following stem cell injection was IL-1RA (AM-MSC). IL-1RA levels may be modulated by GM-CSF produced by AM-MSC. Furthermore, only AM-MSC reduced collagen deposition and increased MMP-9 activity in the lung although there was a reduction of the pro-fibrogenic cytokine TGF-β following BM-MSC, AM-MSC and hAEC treatment. Therefore, AM-MSC may be more effective in reducing injury following delayed injection in the setting of repeated lung injury.

Administration of TSG-6 improves memory after traumatic brain injury in mice

Traumatic brain injury (TBI) causes multiple long-term defects including a loss of working memory that is frequently incapacitating. Administrations of mesenchymal stem/stromal cells (MSCs) previously produced beneficial effects in models of TBI as well as other disease models. In several models, the beneficial effects were explained by the MSCs being activated to express TSG-6, a multifunctional protein that modulates inflammation. In a mouse model of TBI, we found the initial mild phase of the inflammatory response persisted for at least 24h and was followed by secondary severe response that peaked at 3days. Intravenous human MSCs or TSG-6 during initial mild phase decreased neutrophil extravasation, expression of matrix metalloproteinase 9 by endothelial cells and neutrophils, and the subsequent blood brain barrier leakage in secondary phase. Administration of TSG-6 also decreased the lesion size at 2weeks. Importantly, the acute administration of TSG-6 within 24h of TBI was followed 6 to 10weeks later by improvements in memory, depressive-like behavior and the number of newly born-neurons. The data suggested that acute administration of TSG-6 may be an effective therapy for decreasing some of the long-term consequences of TBI.

Identification of biomarkers of response to IFNg during endotoxin tolerance: application to septic shock

The rapid development in septic patients of features of marked immunosuppression associated with increased risk of nosocomial infections and mortality represents the rational for the initiation of immune targeted treatments in sepsis. However, as there is no clinical sign of immune dysfunctions, the current challenge is to develop biomarkers that will help clinicians identify the patients that would benefit from immunotherapy and monitor its efficacy. Using an in vitro model of endotoxin tolerance (ET), a pivotal feature of sepsis-induced immunosuppression in monocytes, we identified using gene expression profiling by microarray a panel of transcripts associated with the development of ET which expression was restored after immunostimulation with interferon-gamma (IFN-γ). These results were confirmed by qRT-PCR. Importantly, this short-list of markers was further evaluated in patients. Of these transcripts, six (TNFAIP6, FCN1, CXCL10, GBP1, CXCL5 and PID1) were differentially expressed in septic patients’ blood compared to healthy blood upon ex vivo LPS stimulation and were restored by IFN-γ. In this study, by combining a microarray approach in an in vitro model and a validation in clinical samples, we identified a panel of six new transcripts that could be used for the identification of septic patients eligible for IFNg therapy. Along with the previously identified markers TNFa, IL10 and HLA-DRA, the potential value of these markers should now be evaluated in a larger cohort of patients. Upon favorable results, they could serve as stratification tools prior to immunostimulatory treatment and to monitor drug efficacy.