Hyaluronan--magic glue for the regulation of the immune response?

Inflammatory alterations of the extracellular matrix in the tumor microenvironment

Complex interactions between cancer cells and host stromal cells result in the formation of the "tumor microenvironment", where inflammatory alterations involve the infiltration of tumor-associated fibroblasts and inflammatory leukocytes that contribute to the acquisition of malignant characteristics, such as increased cancer cell proliferation, invasiveness, metastasis, angiogenesis, and avoidance of adaptive immunity. The microenvironment of a solid tumor is comprised not only of cellular compartments, but also of bioactive substances, including cytokines, growth factors, and extracellular matrix (ECM). ECM can act as a scaffold for cell migration, a reservoir for cytokines and growth factors, and a signal through receptor binding. During inflammation, ECM components and their degraded fragments act directly and indirectly as inflammatory stimuli in certain cases and regulate the functions of inflammatory and immune cells. One such ECM component, hyaluronan, has recently been implicated to modulate innate immune cell function through pattern recognition toll-like receptors and accelerate the recruitment and activation of tumor-associated macrophages in inflamed cancers. Here, we will summarize the molecular mechanism linking inflammation with ECM remodeling in the tumor microenvironment, with a particular emphasis on the role of hyaluronan in controlling the inflammatory response.

Innate and adaptive immune responses in obliterative airway disease in rat tracheal allografts

BACKGROUND

We assessed cellular innate and adaptive immune responses in a rat heterotopic tracheal allograft model during the development of obliterative airway disease.

METHODS

Syngeneic tracheal grafts were transplanted heterotopically from DA to DA rats and fully MHC-mismatched allografts from DA to WF rats. The recipients received either no immunosuppression or two different doses of cyclosporine and were euthanized at 3, 10 and 30 days. Non-transplanted DA tracheas served as controls. Histologic, immunohistochemical and real-time RT-PCR analyses were performed.

RESULTS

The syngrafts had normal epithelium at 10 days and no tracheal occlusion was seen at 30 days. In non-immunosuppressed allografts, almost total loss of epithelium was observed at 10 days, culminating in tracheal occlusion at 30 days. The activation of innate immune response was observed during the ischemic period at 3 days in both groups. Influx of the infiltrating inflammatory cells was more prominent in the allografts. In syngrafts, mRNA expression of pro-inflammatory, but also tolerogenic, cytokines was significantly upregulated, whereas Th1 and Th17 priming factors were significantly downregulated. In allografts, prominent mRNA expression of pro-inflammatory cytokines was seen and adaptive Th1 and Th17 alloresponses were increased. Cyclosporine treatment reduced tracheal occlusion and inhibited both tolerogenic and pro-inflammatory T-cell responses in allografts.

CONCLUSIONS

Ischemia induced a self-limiting, alloantigen-independent innate immune response in syngrafts. In allografts, the predominant pro-inflammatory milieu and alloantigen-dependent Th1 and Th17 responses were linked to the development of obliterative airway disease and were inhibited by cyclosporine treatment.

Hyaluronan as an immune regulator in human diseases

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

Diels-Alder Click cross-linked hyaluronic acid hydrogels for tissue engineering

Hyaluronic acid (HA) is a naturally occurring polymer that holds considerable promise for tissue engineering applications. Current cross-linking chemistries often require a coupling agent, catalyst, or photoinitiator, which may be cytotoxic, or involve a multistep synthesis of functionalized-HA, increasing the complexity of the system. With the goal of designing a simpler one-step, aqueous-based cross-linking system, we synthesized HA hydrogels via Diels-Alder "click" chemistry. Furan-modified HA derivatives were synthesized and cross-linked via dimaleimide poly(ethylene glycol). By controlling the furan to maleimide molar ratio, both the mechanical and degradation properties of the resulting Diels-Alder cross-linked hydrogels can be tuned. Rheological and degradation studies demonstrate that the Diels-Alder click reaction is a suitable cross-linking method for HA. These HA cross-linked hydrogels were shown to be cytocompatible and may represent a promising material for soft tissue engineering.

Proteoglycans regulate the chemotaxis of dendritic cells derived from human peripheral blood monocytes

Dendritic cells (DCs) are a type of antigen-presenting cell which play an essential role in the immune system. The transition from immature DC (iDCs) to mature DCs (mDCs) requires appropriate maturation stimuli, such as pro-inflammatory cytokines or pathogen-derived components. Proteoglycans (PGs), which are composed of core proteins and the glycosaminoglycans that bind to them, are one of the main components of the extracellular matrix around pathogens such as bacteria. This study investigated the effects of PG extracted from the nasal septum cartilage of whale (W-PG) on the maturation of DCs derived from human peripheral blood monocytes. iDCs were prepared from human monocytes using granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). The iDCs were stimulated by W-PG alone. In another type of experiment, the iDCs were stimulated by MIX (tumor necrosis factor-alpha (TNF-alpha), IL-1beta, IL-6 and prostaglandin E(2) (PGE(2))) or a combination of MIX plus W-PG. The stimulation of W-PG alone did not induce the phenotypic maturation from iDCs. However, W-PG promoted the up-regulation of chemokine receptor CCR7-surface expression and the chemotactic responsiveness to CCR7 ligand macrophage inflammatory protein-3beta on MIX-stimulated mDCs although W-PG did not influence matrix metalloproteinase-9 activity which is an important factor in DC migration through the extracellular matrix. The findings that W-PG can selectively regulate the chemotactic activity of DCs in vitro under inflammatory conditions therefore indicate that the interaction of PGs with immune cells including DCs plays an important role in the immune response under the milieu of innate immunity.

Bioengineered hyaluronic acid elicited a nonantigenic T cell activation: implications from cosmetic medicine and surgery to nanomedicine

Hyaluronan is known to act as a filling material of extracellular matrices and as an adhesive substrate for cellular migration. Consequently, it is widely used in aesthetic medicine and surgery, and it would be expected to be used in nanomedicine. Previous clinical case reports associated hyaluronic acid implants to delayed immune-mediated adverse effects. A series of experiments to evaluate immune cell activation supported by this dermal filler and nanomedical biomaterial were performed. The study comprised a total of 12 individuals. Four healthy individuals, none with cosmetically injected dermal filler, were considered as control. Five individuals carried injections of hyaluronic acid dermal filler. Three individuals carried injections of hyaluronic acid dermal filler and presented delayed adverse effects related to the dermal filler. Hyaluronic acid-stimulated peripheral blood mononuclear cells (PBMC) produced low levels of pro-inflammatory cytokines. Phytohemagglutinine (PHA)-stimulated PBMC from patients with hyaluronic implants presenting adverse effects showed a slight increase in the production of interferon (IFN)-gamma and higher expression of CD25, CD69, or CD71. In conclusion, hyaluronic acid administration elicited a laboratory evidence of immune cell activation. Production of low levels of proinflammatory cytokines in vitro could be an observation for low-grade inflammation in vivo resulting in T cell activation.

Human fibroblasts support the expansion of IL-17-producing T cells via up-regulation of IL-23 production by dendritic cells

The initiation of immune responses is associated with the maturation of dendritic cells (DCs) and their migration to draining lymph nodes. En route activated DCs encounter cells of the tissue microenvironment, such as fibroblasts. Because we have shown that DCs interact with fibroblasts during immune responses, we studied the impact of skin fibroblasts on human monocyte-derived DC function and subsequent human T-cell (TC) differentiation. We show that fibroblasts support interleukin-23 (IL-23) secretion from DCs preactivated by lipopolysaccharide (DC(act)) compared with lipopolysaccharide-activated DCs alone. The underlying complex feedback-loop mechanism involves IL-1β/tumor necrosis factor-α (from DC(act)), which stimulate fibroblasts prostaglandin E(2) production. Prostaglandin E(2), in turn, acts on DC(act) and increases their IL-23 release. Furthermore, fibroblast-stimulated DC(act) are far superior to DC(act) alone, in promoting the expansion of Th17 cells in a Cox-2-, IL-23-dependent manner. Using CD4(+)CD45RO(+) memory TCs and CD4(+)CD45RA(+) naive TCs, we showed that fibroblasts induce a phenotype of DC(act) that promotes the expansion of Th17 cells. Moreover, in psoriasis, a prototypic immune response in which the importance of IL-23/Th17 is known, high expression of Cox-2 in fibroblasts was observed. In conclusion, skin fibroblasts are involved in regulation of IL-23 production in DCs and, as a result, of Th17 expansion.

IL-1R1/MyD88 signaling is critical for elastase-induced lung inflammation and emphysema

Lung emphysema and fibrosis are severe complications of chronic obstructive pulmonary disease, and uncontrolled protease activation may be involved in the pathogenesis. Using experimental elastase-induced acute inflammation, we demonstrate here that inflammation and development of emphysema is IL-1R1 and Toll/IL-1R signal transduction adaptor MyD88 dependent; however, TLR recognition is dispensable in this model. Elastase induces IL-1beta, TNF-alpha, keratinocyte-derived chemokine, and IL-6 secretion and neutrophil recruitment in the lung, which is drastically reduced in the absence of IL-1R1 or MyD88. Further, tissue destruction with emphysema and fibrosis is attenuated in the lungs of IL-1R1- and MyD88-deficient mice. Specific blockade of IL-1 by IL-1R antagonist diminishes acute inflammation and emphysema. Finally, IL-1beta production and inflammation are reduced in mice deficient for the NALP3 inflammasome component apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and we identified uric acid, which is produced upon elastase-induced lung injury, as an activator of the NALP3/ASC inflammasome. In conclusion, elastase-mediated lung pathology depends on inflammasome activation with IL-1beta production. IL-1beta therefore represents a critical mediator and a possible therapeutic target of lung inflammation leading to emphysema.

Dermal fibroblasts promote the migration of dendritic cells

Migration of dendritic cells (DCs) from skin to lymph nodes on activation is an essential step in the initiation of an adequate immune response. The dermal microenvironment including stromal cells and their soluble factors might be involved in the regulation of DC migration. To focus on the role of dermal fibroblasts, we studied whether interaction of DCs with fibroblasts promotes the migration of DCs. DCs were co-cultured with resting fibroblasts or with tumor necrosis factor (TNF)alpha/IL-1beta-activated fibroblasts to mimic an inflammatory microenvironment. Interaction of DCs with TNFalpha/IL-1beta-stimulated fibroblasts increased the secretion of matrix metalloproteinase-9 (MMP-9) from DCs within 6 hours compared with DCs alone or DCs stimulated with lipopolysaccharide or TNFalpha/IL-1beta. In contrast, unstimulated fibroblasts did not affect MMP-9 secretion. IL-6 released by TNFalpha/IL-1beta-stimulated fibroblasts was identified as a factor responsible for fibroblast-stimulated MMP-9 secretion from DCs. In accordance with the elevated MMP-9 release, on co-culture with TNFalpha/IL-1beta-stimulated fibroblasts, DCs migrated significantly more effectively through matrigel matrices than did TNFalpha/IL-1beta-stimulated DCs. This was inhibited by a selective blocking of MMP-9, indicating the importance of MMP-9 for this migratory capacity of DCs. In summary, fibroblasts in the local dermal microenvironment are capable of potentiating the migratory capacity of DCs, and thus have the potential to actively participate in the regulation of a cutaneous immune response.

The hyaluronan receptor for endocytosis mediates hyaluronan-dependent signal transduction via extracellular signal-regulated kinases

The hyaluronan (HA) receptor for endocytosis (HARE) mediates the endocytotic clearance of HA and other glycosaminoglycans from lymph and blood. Two isoforms of human HARE, 315- and 190-kDa, are highly expressed in sinusoidal endothelial cells of liver, lymph node, and spleen; HARE is also in specialized cells in the eye, heart, brain, and kidney. Here we determined whether HA binding to HARE initiates intracellular signaling in Flp-In 293 cells stably expressing either the 315- and 190-kDa HARE or the 190-kDa HARE alone. HARE was co-immunoprecipitated with extracellular signal-regulated kinase 1 and 2 (ERK1/2), c-Jun N-terminal protein kinase (JNK), and p38 members of the mitogen-activated protein kinase signaling cascade. ERK phosphorylation increased in a dose- and time-dependent manner when HA was added to cells expressing full-length or 190-kDa HARE, but not cells with vector-only or a HARE(DeltaLink) construct with greatly decreased ( approximately 90%) HA uptake. HA did not induce phosphorylation of JNK or p38. A maximum increase in phospho-ERK1/2 occurred within 30 min at 5 mug/ml HA, and the response was dampened at >20 mug/ml HA. HA binding did not increase the level of HARE-ERK complexes, but did increase HARE phosphorylation. These findings demonstrate a novel functional response, when HARE binds HA, that leads to activation of ERK1/2, important mediators of intracellular signal transduction.

Review of long-term adverse effects associated with the use of chemically-modified animal and nonanimal source hyaluronic acid dermal fillers

Although only recently introduced, chemically-modified hyaluronic acid dermal fillers have gained widespread acceptance as "redefining" dermal fillers in the fields of dermatology and cosmetic facial surgery. Although hyaluronic acid-based dermal fillers have a low overall incidence of long-term side effects, occasional adverse outcomes, ranging from chronic lymphoplasmacytic inflammatory reactions to classic foreign body-type granulomatous reactions have been documented. These long-term adverse events are reviewed.

IL-1R1/MyD88 signaling and the inflammasome are essential in pulmonary inflammation and fibrosis in mice

The molecular mechanisms of acute lung injury resulting in inflammation and fibrosis are not well established. Here we investigate the roles of the IL-1 receptor 1 (IL-1R1) and the common adaptor for Toll/IL-1R signal transduction, MyD88, in this process using a murine model of acute pulmonary injury. Bleomycin insult results in expression of neutrophil and lymphocyte chemotactic factors, chronic inflammation, remodeling, and fibrosis. We demonstrate that these end points were attenuated in the lungs of IL-1R1- and MyD88-deficient mice. Further, in bone marrow chimera experiments, bleomycin-induced inflammation required primarily MyD88 signaling from radioresistant resident cells. Exogenous rIL-1beta recapitulated a high degree of bleomycin-induced lung pathology, and specific blockade of IL-1R1 by IL-1 receptor antagonist dramatically reduced bleomycin-induced inflammation. Finally, we found that lung IL-1beta production and inflammation in response to bleomycin required ASC, an inflammasome adaptor molecule. In conclusion, bleomycin-induced lung pathology required the inflammasome and IL-1R1/MyD88 signaling, and IL-1 represented a critical effector of pathology and therapeutic target of chronic lung inflammation and fibrosis.

Fabrication and characterization of porous hyaluronic acid-collagen composite scaffolds

Hyaluronic acid (HA) plays a vital role in many tissues, influencing water content and mechanical function, and has been shown to have positive biological effects on cell behavior in vitro. To begin to determine whether these benefits can be accessed if HA is incorporated into collagen-based scaffolds for tissue engineering, HA-collagen composite matrices were prepared and selected properties evaluated. HA-collagen scaffolds were cross-linked with carbodiimide and loss rates of HA in culture medium assessed. Scaffold pore structures were evaluated by light and electron microscopy. Adult canine chondrocytes were grown in selected HA-collagen scaffolds to assess the effects of HA on cell behavior. Homogenous HA-collagen slurries were achieved when polyionic complexes were suppressed. HA was uniformly distributed through the scaffolds, which demonstrated honeycomb-like pores with interconnectivity among pores increasing as HA content increased. Virtually all of the HA added to the collagen slurry was incorporated into the composite scaffolds that underwent a 7-day cross-linking protocol. After 5 days in culture medium, the HA content in the scaffolds was 5-7% regardless of initial HA loading. After only 2 weeks in culture cartilaginous tissue was found in the chondrocyte-seeded HA-collagen scaffolds. This study contributes to the understanding of the effects of HA content, pH, and cross-link treatment on pore characteristics and degradation behavior essential for the design of HA-collagen scaffolds. The demonstration that these scaffolds can be populated by chondrocytes and support in vitro formation of cartilaginous tissue warrants further investigation of this material system for tissue engineering.

The magic glue hyaluronan and its eraser hyaluronidase: a biological overview

Hyaluronan (HA) is a multifunctional high molecular weight polysaccharide found throughout the animal kingdom, especially in the extracellular matrix (ECM) of soft connective tissues. HA is thought to participate in many biological processes, and its level is markedly elevated during embryogenesis, cell migration, wound healing, malignant transformation, and tissue turnover. The enzymes that degrade HA, hyaluronidases (HAases) are expressed both in prokaryotes and eukaryotes. These enzymes are known to be involved in physiological and pathological processes ranging from fertilization to aging. Hyaluronidase-mediated degradation of HA increases the permeability of connective tissues and decreases the viscosity of body fluids and is also involved in bacterial pathogenesis, the spread of toxins and venoms, acrosomal reaction/ovum fertilization, and cancer progression. Furthermore, these enzymes may promote direct contact between pathogens and the host cell surfaces. Depolymerization of HA also adversely affects the role of ECM and impairs its activity as a reservoir of growth factors, cytokines and various enzymes involved in signal transduction. Inhibition of HA degradation therefore may be crucial in reducing disease progression and spread of venom/toxins and bacterial pathogens. Hyaluronidase inhibitors are potent, ubiquitous regulating agents that are involved in maintaining the balance between the anabolism and catabolism of HA. Hyaluronidase inhibitors could also serve as contraceptives and anti-tumor agents and possibly have antibacterial and anti-venom/toxin activities. Additionally, these molecules can be used as pharmacological tools to study the physiological and pathophysiological role of HA and hyaluronidases.

Human Langerhans cells express a specific TLR profile and differentially respond to viruses and Gram-positive bacteria

Dendritic cells (DC) are APCs essential for the development of primary immune responses. In pluristratified epithelia, Langerhans cells (LC) are a critical subset of DC which take up Ags and migrate toward lymph nodes upon inflammatory stimuli. TLR allow detection of pathogen-associated molecular patterns (PAMP) by different DC subsets. The repertoire of TLR expressed by human LC is uncharacterized and their ability to directly respond to PAMP has not been systematically investigated. In this study, we show for the first time that freshly purified LC from human skin express mRNA encoding TLR1, TLR2, TLR3, TLR5, TLR6 and TLR10. In addition, keratinocytes ex vivo display TLR1-5, TLR7, and TLR10. Accordingly, highly enriched immature LC efficiently respond to TLR2 agonists peptidoglycan and lipoteichoic acid from Gram-positive bacteria, and to dsRNA which engages TLR3. In contrast, LC do not directly sense TLR7/8 ligands and LPS from Gram-negative bacteria, which signals through TLR4. TLR engagement also results in cytokine production, with marked differences depending on the PAMP detected. TLR2 and TLR3 ligands increase IL-6 and IL-8 production, while dsRNA alone stimulates TNF-alpha release. Strikingly, only peptidoglycan triggers IL-10 secretion, thereby suggesting a specific function in tolerance to commensal Gram-positive bacteria. However, LC do not produce IL-12p70 or type I IFNs. In conclusion, human LC are equipped with TLR that enable direct detection of PAMP from viruses and Gram-positive bacteria, subsequent phenotypic maturation, and differential cytokine production. This implies a significant role for LC in the control of skin immune responses.

Differential regulation of hyaluronan metabolism in the epidermal and dermal compartments of human skin by UVB irradiation

Hyaluronan (HA), a major component of the cutaneous extracellular-matrix, is involved in tissue repair. Human skin is exposed to and damaged by UVB-irradiation. Here, we investigate the regulation of HA metabolism in human skin during acute UVB-induced inflammation. Expression of HA synthesizing (HAS) and degrading enzymes hyaluronidase (HYAL) as evaluated by quantitative reverse transcribed PCR in response to UVB differed when fibroblasts and HaCaT-keratinocytes, representative cell types in dermis and epidermis, respectively, were compared. Both demonstrated temporally different expression patterns of these genes 3- and 24-hours post-irradiation. This resulted 24-hours post-irradiation in an increase in HAS gene expression in both fibroblasts and HaCaT-keratinocytes, and an increase in HYAL expression only in fibroblasts. HA-production as analyzed by the HA content of conditioned medium was reduced in HaCaT and fibroblast cultures 3-hours post-irradiation, whereas HA increased in HaCaT-cultures 24-hours post-irradiation but remained suppressed in fibroblasts-cultures. Consistently, immunohistochemical staining for HA in human skin 24-hours post-irradiation demonstrated an increased epidermal HA, but a decrease in the dermal compartment. Moreover, analysis of the HA content of dermal microdialysis-fluid revealed increased accumulation of HA degradation products 24-hours post-irradiation. These data demonstrate that there is a complex temporal and spatial regulation of HA-metabolism in skin in response to UVB irradiation.

Localization of CD44 and hyaluronan in the synovial membrane of the rat temporomandibular joint

Previous studies have pointed out a lack of adhesion structures in the synovial lining layer of the rat temporomandibular joint (TMJ) despite showing an epithelial arrangement. CD44, a major cell adhesion molecule, plays crucial roles as an anchor between cells and extracellular matrices by binding hyaluronan (HA) for the development of organs or the metastasis of tumors. The present study examined the localization of CD44 in the synovial membrane of the rat TMJ by immunocytochemistry for OX50, ED1, and Hsp25, which are markers for the rat CD44, macrophage-like type A, and fibroblast-like type B synoviocytes, respectively. Histochemistry for HA-binding protein (HABP) was also employed for the detection of HA. OX50 immunoreactions were found along the cell surface and, in particular, accumulated along the surface of the articular cavity. Observations by a double immunostaining and immunoelectron microscopy revealed that all the OX50-immunopositive cells were categorized as fibroblastic type B cells, which had many caveolae and a few vesicles reactive to intense OX50. However, the macrophage-like type A cells did not have any OX50 immunoreaction in the synovial lining layer. A strong HABP reaction was discernable in the extracellular matrix surrounding both OX50-positive and -negative cells in the synovial lining layers, exhibiting a meshwork distribution, but weak in its sublining layer. This localization pattern of CD44 and HABP might be involved in the formation of the epithelial arrangement of the synovial lining layer. Furthermore, OX50 immunonegativity in the type A cells suggests their low phagocytotic activity in the rat TMJ under normal conditions.

Hyaluronan fragments: an information-rich system

Hyaluronan is a straight chain, glycosaminoglycan polymer of the extracellular matrix composed of repeating units of the disaccharide [-D-glucuronic acid-beta1,3-N-acetyl-D-glucosamine-beta1,4-]n. Hyaluronan is synthesized in mammals by at least three synthases with products of varying chain lengths. It has an extraordinary high rate of turnover with polymers being funneled through three catabolic pathways. At the cellular level, it is degraded progressively by a series of enzymatic reactions that generate polymers of decreasing sizes. Despite their exceedingly simple primary structure, hyaluronan fragments have extraordinarily wide-ranging and often opposing biological functions. There are large hyaluronan polymers that are space-filling, anti-angiogenic, immunosuppressive, and that impede differentiation, possibly by suppressing cell-cell interactions, or ligand access to cell surface receptors. Hyaluronan chains, which can reach 2 x 10(4) kDa in size, are involved in ovulation, embryogenesis, protection of epithelial layer integrity, wound repair, and regeneration. Smaller polysaccharide fragments are inflammatory, immuno-stimulatory and angiogenic. They can also compete with larger hyaluronan polymers for receptors. Low-molecular-size polymers appear to function as endogenous "danger signals", while even smaller fragments can ameliorate these effects. Tetrasaccharides, for example, are anti-apoptotic and inducers of heat shock proteins. Various fragments trigger different signal transduction pathways. Particular hyaluronan polysaccharides are also generated by malignant cells in order to co-opt normal cellular functions. How the small hyaluronan fragments are generated is unknown, nor is it established whether the enzymes of hyaluronan synthesis and degradation are involved in maintaining proper polymer sizes and concentration. The vast range of activities of hyaluronan polymers is reviewed here, in order to determine if patterns can be detected that would provide insight into their production and regulation.

The signal-to-noise ratio as a measure of HA oligomer concentration: a MALDI-TOF MS study

MALDI-TOF MS (matrix-assisted laser desorption and ionization time-of-flight mass spectrometry) was used to determine ng amounts of defined hyaluronan (HA) oligomers obtained by enzymatic digestion of high molecular weight HA with testicular hyaluronate lyase. The signal-to-noise (S/N) ratio of the positive and negative ion spectra represents a reliable concentration measure: Amounts of HA down to about 40 fmol could be determined and there is a linear correlation between the S/N ratio and the HA amount between about 0.8 pmol and 40 fmol. However, the detection limits depend considerably on the size of the HA oligomer with larger oligomers being less sensitively detectable. The advantages and drawbacks of the S/N ratio as concentration measure are discussed.

Snake venom hyaluronidase: a therapeutic target

The diffusion of toxins from the site of a bite into the circulation is essential for successful envenomation. Degradation of hyaluronic acid in the extracellular matrix (ECM) by venom hyaluronidase is a key factor in this diffusion. Hyaluronidase not only increases the potency of other toxins but also damages the local tissue. In spite of its important role, little attention has been paid to this enzyme. Hyaluronidase exists in various isoforms and generates a wide range of hyaluronic acid degradation products. This suggests that beyond its role as a spreading factor venom hyaluronidase deserves to be explored as a possible therapeutic target for inhibiting the systemic distribution of venom and also for minimizing local tissue destruction at the site of the bite.

SHAP potentiates the CD44-mediated leukocyte adhesion to the hyaluronan substratum

CD44-hyaluronan (HA) interaction is involved in diverse physiological and pathological processes. Regulation of interacting avidity is well studied on CD44 but rarely on HA. We discovered a unique covalent modification of HA with a protein, SHAP, that corresponds to the heavy chains of inter-alpha-trypsin inhibitor family molecules circulating in blood. Formation of the SHAP.HA complex is often associated with inflammation, a well known process involving the CD44-HA interaction. We therefore examined the effect of SHAP on the CD44-HA interaction-mediated lymphocyte adhesion. Under both static and flowing conditions, Hut78 cells (CD44-positive) and CD44-transfected Jurkat cells (originally CD44-negative) adhered preferentially to the immobilized SHAP.HA complex than to HA. The enhanced adhesion is exclusively mediated by the CD44-HA interaction, because it was inhibited by HA, but not IalphaI, and was completely abolished by pretreating the cells with anti-CD44 antibodies. SHAP appears to potentiate the interaction by increasing the avidity of HA to CD44 and altering their distribution on cell surfaces. Large amounts of the SHAP.HA complex accumulate in the hyperplastic synovium of rheumatoid arthritis patients. Leukocytes infiltrated to the synovium were strongly positive for HA, SHAP, and CD44 on their surfaces, suggesting a role for the adhesion-enhancing effect of SHAP in pathogenesis.

A Blank Slate? Layer-by-Layer Deposition of Hyaluronic Acid and Chitosan onto Various Surfaces

Although poly(alpha-hydroxy esters), especially the PLGA family of lactic acid/glycolic acid copolymers, have many properties which make them promising materials for tissue engineering, the inherent chemistry of surfaces made from these particular polymers is problematic. In vivo, they promote a strong foreign-body response as a result of nonspecific adsorption and denaturation of serum proteins, which generally results in the formation of a nonfunctional fibrous capsule. Surface modification post-production of the scaffolds is an often-utilized approach to solving this problem, conceptually allowing the formation of a scaffold with mechanical properties defined by the bulk material and molecular-level interactions defined by the modified surface properties. A promising concept is the so-called "blank slate": essentially a surface that is rendered resistant to nonspecific protein adsorption but can be readily activated to covalently bind bio-functional molecules such as extracellular matrix proteins, growth factors or polysaccharides. This study focuses on the use of the quartz crystal microbalance (QCM) to follow the layer-by-layer (LbL) electrostatic deposition of high molecular weight hyaluronic acid and chitosan onto PLGA surfaces rendered positively charged by aminolysis, to form a robust, protein-resistant coating. We further show that this surface may be further functionalized via the covalent attachment of collagen IV, which may then be used as a template for the self-assembly of basement membrane components from dilute Matrigel. The response of NIH-3T3 fibroblasts to these surfaces was also followed and shown to closely parallel the results observed in the QCM.

Glycosaminoglycans and their proteoglycans: host‐associated molecular patterns for initiation and modulation of inflammation

Glycosaminoglycans, linear carbohydrates such as heparan sulfate and hyaluronan, participate in a variety of biological processes including cell-matrix interactions and activation of chemokines, enzymes and growth factors. This review will discuss progress in immunology and the science of wound repair that has revealed the importance of glycosaminoglycans, and their proteoglycans, in the inflammatory process. Heparan sulfate enables growth factor function and modifies enzyme/inhibitor functions, such as antithrombin III and heparin cofactor II. Heparan sulfate also interacts with cytokines/chemokines and participates in leukocyte selectin binding to promote the recruitment of leukocytes. Chondroitin sulfate/dermatan sulfate regulates growth factor activity and is an alternate modulator of heparin cofactor II. In addition, dermatan sulfate induces ICAM-1 expression on endothelial cells and also recruits leukocytes via selectin interactions. Hyaluronan alternatively participates in leukocyte recruitment via interaction with CD44, while activating various inflammatory cells, such as macrophages, through CD44-dependent signaling. Hyaluronan also signals through Toll-like receptor 4 to induce dendritic cell maturation and promote cytokine release by dendritic cells and endothelial cells. Taken together, the field of glycosaminoglycan biology provides new clues and explanations of the process of inflammation and suggests new therapeutic approaches to human disease.

Hyaluronan metabolism: a major paradox in cancer biology

Paradoxically, both hyaluronan (HA) and hyaluronidases, the enzymes that eliminate HA, can correlate with cancer progression. Levels of HA on the surface of tumor cells are indicators of poor outcome. Certain hyaluronidases, products of tumor suppressor genes eliminated in the course of tumor spread, are used clinically in anti-cancer chemotherapy regimens. Such information would indicate that cancer progression is inhibited by hyaluronidase. Yet progression of certain cancers correlates with levels of hyaluronidase activity. An attempt is made here to understand such apparent contradictions by examining details of HA metabolism. Anabolic and catabolic pathways are comprised of the HA synthases and hyaluronidases, respectively. There are several enzymes that synthesize HA, each under a different control mechanism, generating products of differing polymer size. The hyaluronidases degrade HA in step-wise fashion, the polymer decreasing in size in quantum steps, each size-specific polymer having a different biological activity. Superimposed on these are the potent hyaluronidase inhibitors, about which very little is known. These components of HA metabolism are reviewed here for possible roles in supporting or suppressing malignant transformation, growth, invasion and metastatic spread of tumors. Such a systematic approach may reveal mechanisms used in the course of cancer progression, resolve some of the apparent disparities, render new prognostic markers, and provide new targets for therapeutic intervention.

Hyaluronan catabolism: a new metabolic pathway

A new pathway of intermediary metabolism is described involving the catabolism of hyaluronan. The cell surface hyaluronan receptor, CD44, two hyaluronidases, Hyal-1 and Hyal-2, and two lysosomal enzymes, beta-glucuronidase and beta-N-acetylglucosaminidase, are involved. This metabolic cascade begins in lipid raft invaginations at the cell membrane surface. Degradation of the high-molecular-weight extracellular hyaluronan occurs in a series of discreet steps generating hyaluronan chains of decreasing sizes. The biological functions of the oligomers at each quantum step differ widely, from the space-filling, hydrating, anti-angiogenic, immunosuppressive 10(4)-kDa extracellular polymer, to 20-kDa intermediate polymers that are highly angiogenic, immuno-stimulatory, and inflammatory. This is followed by degradation to small oligomers that can induce heat shock proteins and that are anti-apoptotic. The single sugar products, glucuronic acid and a glucosamine derivative are released from lysosomes to the cytoplasm, where they become available for other metabolic cycles. There are 15 g of hyaluronan in the 70-kg individual, of which 5 g are cycled daily through this pathway. Some of the steps in this catabolic cascade can be commandeered by cancer cells in the process of growth, invasion, and metastatic spread.

Suppressive effects of hyaluronan on MMP-1 and RANTES production from chondrocytes

The purpose of the study was to examine the effects of hyaluronan (HA) on human chondrocytes in terms of production of MMP-1 and RANTES. Chondrocytes were obtained from patients with osteoarthritis (OA) or femoral neck fracture (control). Chondrocytes in monolayer culture were treated with various molecular weights (1.2, 50, 800 and 1,900 kD) of HA and then stimulated with IL-1beta. Production and expression of MMP-1 and RANTES were quantified by ELISA and real-time polymerase chain reaction (PCR). The response was blocked by anti-CD44 antibody. Production of MMP-1 was significantly suppressed by both 800- and 1,900-kD HA, while production of RANTES was suppressed by 1,900-kD HA. Expression of MMP-1 and RANTES mRNA was inhibited by 1,900-kD HA. Suppressive effects of HA on production of MMP-1 were canceled by treatment of anti-CD44 antibody. Higher CD44 expression was found in OA chondrocytes than in those of control. High-molecular-weight HA suppressed MMP-1 and RANTES production, mediated partly by CD44-HA interaction.

Extracellular Mycobacterial DNA-binding Protein 1 Participates in Mycobacterium-Lung Epithelial Cell Interaction through Hyaluronic Acid

Mycobacterium tuberculosis infects not only host macrophages but also nonprofessional phagocytes, such as alveolar epithelial cells. Glycosaminoglycans (GAGs) are considered as the component of mycobacterial adherence to epithelial cells. Here we show that extracellularly occurring mycobacterial DNA-binding protein 1 (MDP1) promotes mycobacterial infection to A549 human lung epithelial cells through hyaluronic acid (HA). Both surface plasmon resonance analysis and enzyme-linked immunosorbent assay revealed that MDP1 bound to HA, heparin, and chondroitin sulfate. Utilizing synthetic peptides, we next defined heparin-binding site of 20 amino acids from 31 to 50 of MDP1, which is responsible for the specific DNA-binding site of MDP1. MDP1 bound to A549 cells, and exogenous DNA and HA interfered with the interaction. The binding was also abolished by treatment of A549 cells with hyaluronidase, suggesting that HA participates in the MDP1-A549 cell interaction. Adherence of bacillus Calmette-Guérin (BCG) and M. tuberculosis to A549 cells was inhibited by addition of HA, DNA, and anti-MDP1 antibody, showing that MDP1 participates in the interaction between mycobacteria-alveolar epithelial cells. Simultaneous treatment of intratracheal BCG-infected mice with HA reduced the growth of BCG in vivo. Taken together, theses results suggest that HA participates in Mycobacterium-lung epithelium interaction and has potential for therapeutic and prophylactic interventions in mycobacterial infection.

Hyaluronan fragments stimulate endothelial recognition of injury through TLR4

Tissues must quickly recognize injury to respond to the rapid pace of microbial growth. In skin, dermal microvascular endothelial cells must also react to danger signals from the surrounding tissue and immediately participate by initiating the wound repair process. Components of the extracellular matrix such as hyaluronan are rapidly broken down into smaller molecular weight oligosaccharides in a wound, and these can activate a variety of biological processes. This study set out to determine if hyaluronan fragments released following injury can stimulate endothelial cells and what mechanism is responsible for this response. Using genechip microarray analysis, a response to hyaluronan fragments was detected in endothelial cells with the most significant increase observed for the chemokine IL-8. This observation was verified with qualitative reverse transcriptase-PCR and ELISA in human endothelial cell culture, and in a mouse model by observing serum levels of MIP-2 and KC following hyaluronan fragment administration in vivo. Activation was TLR4-dependent, as shown by use of TLR4 blocking antibody and TLR4-deficient mice, but not due to the presence of undetected contaminants as shown by inactivation following digestion with the hyaluronan-degrading enzyme chondroitinase ABC or incubation with the hyaluronan-specific blocking peptide Pep-1. Inactivation of LPS activity failed to diminish the action of hyaluronan fragments. These observations suggest that endogenous components of the extracellular matrix can stimulate endothelia to trigger recognition of injury in the initial stages of the wound defense and repair response.

Autoimmune response in cartilage-delivered peptides in a patient with osteoarthritis

Whatever the initiating factor of osteoarthritis (OA), the process ultimately unmasks the immunogenic determinants of chondrocytes, proteoglycans and collagens, which then triggers autoimmune reactions. Although the precise mechanism of the immune responses in the pathogenesis of OA requires further investigation, here I postulate that the presence of autoimmunity to cartilage components has an important role in the process of cartilage degradation in OA. Current studies strongly suggest that a immunoregulatory therapeutic strategy should be established.