Hyaluronan cross-linking: a protective mechanism in inflammation?

Tissue integrity signals communicated by high-molecular weight hyaluronan and the resolution of inflammation

The extracellular matrix polysaccharide hyaluronan (HA) exerts size-dependent effects on leukocyte behavior. Low-molecular weight HA is abundant at sites of active tissue catabolism and promotes inflammation via effects on Toll-like receptor signaling. Conversely, high-molecular weight HA is prevalent in uninjured tissues and is anti-inflammatory. We propose that the ability of high-molecular weight but not low-molecular weight HA to cross-link CD44 functions as a novel form of pattern recognition that recognizes intact tissues and communicates "tissue integrity signals" that promote resolution of local immune responses.

Recombinant human hyaluronidase PH20 does not stimulate an acute inflammatory response and inhibits lipopolysaccharide-induced neutrophil recruitment in the air pouch model of inflammation

Hyaluronidase (Hyal) and low m.w. hyaluronan (LMW HA) fragments have been widely reported to stimulate the innate immune response. However, most hyaluronidases used were purified from animal tissues (e.g., bovine testis Hyal [BTH]), and contain endotoxin and other unrelated proteins. We tested a highly purified recombinant human Hyal (rHuPH20) and endotoxin-free HA fragments from M(r) 5,000 to 1,500,000 in the rodent air pouch model of inflammation to determine their potential for stimulation of the innate immune response. Exogenous LMW HA fragments (average M(r) 200,000) failed to induce either cytokine/chemokine production or neutrophil infiltration into the air pouch. Challenging the air pouch with LPS or BTH stimulated production of cytokines and chemokines but rHuPH20 did not, suggesting that neither PH20 nor generation of LMW HA fragments in situ stimulates cytokine and chemokine production. LPS and BTH also induced neutrophil infiltration into the air pouch, which was not observed with rHuPH20 treatment. Endotoxin-depleted BTH had much reduced proinflammatory activity, suggesting that the difference in inflammatory responses between rHuPH20 and BTH is likely due to endotoxin contaminants in BTH. When rHuPH20 was dosed with LPS, the induction of cytokines and chemokines was the same as LPS alone, but neutrophil infiltration was inhibited, likely by interrupting HA-CD44 interaction. Our results indicate that neither rHuPH20 nor its directly generated HA catabolites have inflammatory properties in the air pouch model, and rHuPH20 can instead inhibit some aspects of inflammation, such as neutrophil infiltration into the air pouch.

Dynamic interfacial behavior of viscoelastic aqueous hyaluronic acid: effects of molecular weight, concentration and interfacial velocity

An aqueous hyaluronic acid (HA(aq)) pericellular coat, when mediating the tactile aspect of cellular contact inhibition, has three tasks: interface formation, mechanical signal transmission and interface separation. To quantify the interfacial adhesive behavior of HA(aq), we induce simultaneous interface formation and separation between HA(aq) and a model hydrophobic, hysteretic Si-SAM surface. While surface tension γ remains essentially constant, interface formation and separation depend greatly on concentration (5 ≤ C ≤ 30 mg mL(-1)), molecular weight (6 ≤ MW ≤ 2000 kDa) and interfacial velocity (0 ≤ V ≤ 3 mm s(-1)), each of which affect shear elastic and loss moduli G′ and G′′, respectively. Viscoelasticity dictates the mode of interfacial motion: wetting-dewetting, capillary necking, or rolling. Wetting-dewetting is quantified using advancing and receding contact angles θ(A) and θ(R), and the hysteresis between them, yielding data landscapes for each C above the [MW, V] plane. The landscape sizes, shapes, and curvatures disclose the interplay, between surface tension and viscoelasticity, which governs interfacial dynamics. Gel point coordinates modulus G and angular frequency ω appear to predict wetting-dewetting (G < 75 ω0.2), capillary necking (75 ω0.2 < G < 200 ω0.075) or rolling (G > 200ω0.075). Dominantly dissipative HA(aq) sticks to itself and distorts irreversibly before separating, while dominantly elastic HA(aq) makes contact and separates with only minor, reversible distortion. We propose the dimensionless number (G′V)/(ω(r)γ), varying from 10(-5) to 10(3) in this work, as a tool to predict the mode of interface formation-separation by relating interfacial kinetics with bulk viscoelasticity. Cellular contact inhibition may be thus aided or compromised by physiological or interventional shifts in [C, MW, V], and thus in (G′V)/(ω(r)γ), which affect both mechanotransduction and interfacial dynamics. These observations, understood in terms of physical properties, may be broadened to probe interfacial dynamics of other viscoelastic aqueous biopolymers.

Design of cell-matrix interactions in hyaluronic acid hydrogel scaffolds

The design of hyaluronic acid (HA)-based hydrogel scaffolds to elicit highly controlled and tunable cell response and behavior is a major field of interest in developing tissue engineering and regenerative medicine applications. This review will begin with an overview of the biological context of HA, which is needed to better understand how to engineer cell-matrix interactions in the scaffolds via the incorporation of different types of signals in order to direct and control cell behavior. Specifically, recent methods of incorporating various bioactive, mechanical and spatial signals are reviewed, as well as novel HA modifications and crosslinking schemes with a focus on specificity.

Reprint of: A rapid increase in macrophage-derived versican and hyaluronan in infectious lung disease

The goals of this study were to characterize the changes in chondroitin sulfate proteoglycans and hyaluronan in lungs in acute response to gram-negative bacterial infection and to identify cellular components responsible for these changes. Mice were treated with intratracheal (IT) live Escherichia coli, E. coli lipopolysaccharide (LPS), or PBS. Both E. coli and LPS caused rapid selective increases in mRNA expression of versican and hyaluronan synthase (Has) isoforms 1 and 2 associated with increased immunohistochemical and histochemical staining for versican and hyaluronan in the lungs. Versican was associated with a subset of alveolar macrophages. To examine whether macrophages contribute to versican and hyaluronan accumulation, in vitro studies with primary cultures of bone marrow-derived and alveolar macrophages were performed. Unstimulated macrophages expressed very low levels of versican and hyaluronan synthase mRNA, with no detectible versican protein or hyaluronan product. Stimulation with LPS caused rapid increases in versican mRNA and protein, a rapid increase in Has1 mRNA, and concomitant inhibition of hyaluronidases 1 and 2, the major hyaluronan degrading enzymes. Hyaluronan could be detected following chloroquine pre-treatment, indicating rapid turnover and degradation of hyaluronan by macrophages. In addition, the effects of LPS, the M1 macrophage classical activation agonist, were compared to those of IL-4/IL-13 or IL-10, the M2a and M2c alternative activation agonists, respectively. Versican and Has1 increased only in response to M1 activation. Finally, the up-regulation of versican and Has1 in the whole lungs of wild-type mice following IT LPS was completely abrogated in TLR-4(-/-) mice. These findings suggest that versican and hyaluronan synthesis may play an important role in the innate immune response to gram-negative lung infection.

Hyaluronan: a simple polysaccharide with diverse biological functions

Hyaluronan (HA) is a linear polysaccharide with disaccharide repeats of d-glucuronic acid and N-acetyl-d-glucosamine. It is evolutionarily conserved and abundantly expressed in the extracellular matrix (ECM), on the cell surface and even inside cells. Being a simple polysaccharide, HA exhibits an astonishing array of biological functions. HA interacts with various proteins or proteoglycans to organize the ECM and to maintain tissue homeostasis. The unique physical and mechanical properties of HA contribute to the maintenance of tissue hydration, the mediation of solute diffusion through the extracellular space and the lubrication of certain tissues. The diverse biological functions of HA are manifested through its complex interactions with matrix components and resident cells. Binding of HA with cell surface receptors activates various signaling pathways, which regulate cell function, tissue development, inflammation, wound healing and tumor progression and metastasis. Taking advantage of the inherent biocompatibility and biodegradability of HA, as well as its susceptibility to chemical modification, researchers have developed various HA-based biomaterials and tissue constructs with promising and broad clinical potential. This paper illustrates the properties of HA from a matrix biology perspective by first introducing the principles underlying the biosynthesis and biodegradation of HA, as well as the interactions of HA with various proteins and proteoglycans. It next highlights the roles of HA in physiological and pathological states, including morphogenesis, wound healing and tumor metastasis. A deeper understanding of the mechanisms underlying the roles of HA in various physiological processes can provide new insights and tools for the engineering of complex tissues and tissue models.

Functional aspects of the interaction between interleukin-8 and sulfated glycosaminoglycans

During the immune response, the cytokine interleukin 8 (IL-8, CXCL8) functions as a strong chemoattractant for polymorphonuclear leukocytes helping to direct these cells to infected/injured sites. This review focuses on the interaction of IL-8 with sulfated glycosaminoglycans expressed on cell surfaces and the extracellular matrix. This interaction contributes to the recruitment of polymorphonuclear cells from blood, penetration of these cells through the vessel wall, and their directed migration to inflammatory sites. Regulatory aspects of the interplay between IL-8 and heparan sulfate, the most abundant glycosaminoglycan, are highlighted. In this field, the large natural heterogeneity of glycosaminoglycans represents a great challenge that impedes the modeling of IL-8 functions. The interaction of IL-8 with newly developed artificial sulfated hyaluronan derivatives is also considered as these artificial substrates are an important tool for development of new materials in regenerative medicine.

Hyaluronan, a crucial regulator of inflammation

Hyaluronan (HA), a major component of the extracellular matrix (ECM), plays a key role in regulating inflammation. Inflammation is associated with accumulation and turnover of HA polymers by multiple cell types. Increasingly through the years, HA has become recognized as an active participant in inflammatory, angiogenic, fibrotic, and cancer promoting processes. HA and its binding proteins regulate the expression of inflammatory genes, the recruitment of inflammatory cells, the release of inflammatory cytokines, and can attenuate the course of inflammation, providing protection against tissue damage. A growing body of evidence suggests the cell responses are HA molecular weight dependent. HA fragments generated by multiple mechanisms throughout the course of inflammatory pathologies, elicit cellular responses distinct from intact HA. This review focuses on the role of HA in the promotion and resolution of inflammation.

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.

Versican and the control of inflammation

Versican is an extracellular matrix (ECM) proteoglycan that interacts with cells by binding to non-integrin and integrin receptors and to other ECM components that associate with the cell surface. Recent studies have shown also that versican interacts with myeloid and lymphoid cells promoting their adhesion and production of inflammatory cytokines. Versican is produced by stromal cells, as well as leukocytes, and is markedly increased in inflammation. Inflammatory agonists, such as double-stranded RNA mimetics (e.g., poly I:C), stimulate stromal cells, smooth muscle cells and fibroblasts, to produce fibrillar ECMs enriched in versican and hyaluronan (HA) that interact with leukocytes promoting their adhesion. Interference with the incorporation of versican into this ECM blocks monocyte adhesion and dampens the inflammatory response. Tumor cells also express elevated levels of versican which interact with myeloid cells to promote an inflammatory response, through stimulating cytokine release, and metastasis. In addition, myeloid cells, such as macrophages in tumors, synthesize versican which affects tumor cell phenotypes, inflammation, and subsequent metastasis. Versican, by binding to hyaluronan, influences T lymphocyte phenotypes and in part controls the ability of these cells to synthesize and secrete cytokines that influence the immune response. Collectively, these studies indicate that versican as an ECM molecule plays a central role in inflammation and as a result it is emerging as a potential target promising wide therapeutic benefits.

A rapid increase in macrophage-derived versican and hyaluronan in infectious lung disease

The goals of this study were to characterize the changes in chondroitin sulfate proteoglycans and hyaluronan in lungs in acute response to gram-negative bacterial infection and to identify cellular components responsible for these changes. Mice were treated with intratracheal (IT) live Escherichia coli, E. coli lipopolysaccharide (LPS), or PBS. Both E. coli and LPS caused rapid selective increases in mRNA expression of versican and hyaluronan synthase (Has) isoforms 1 and 2 associated with increased immunohistochemical and histochemical staining for versican and hyaluronan in the lungs. Versican was associated with a subset of alveolar macrophages. To examine whether macrophages contribute to versican and hyaluronan accumulation, in vitro studies with primary cultures of bone marrow-derived and alveolar macrophages were performed. Unstimulated macrophages expressed very low levels of versican and hyaluronan synthase mRNA, with no detectible versican protein or hyaluronan product. Stimulation with LPS caused rapid increases in versican mRNA and protein, a rapid increase in Has1 mRNA, and concomitant inhibition of hyaluronidases 1 and 2, the major hyaluronan degrading enzymes. Hyaluronan could be detected following chloroquine pre-treatment, indicating rapid turnover and degradation of hyaluronan by macrophages. In addition, the effects of LPS, the M1 macrophage classical activation agonist, were compared to those of IL-4/IL-13 or IL-10, the M2a and M2c alternative activation agonists, respectively. Versican and Has1 increased only in response to M1 activation. Finally, the up-regulation of versican and Has1 in the whole lungs of wild-type mice following IT LPS was completely abrogated in TLR-4(-/-) mice. These findings suggest that versican and hyaluronan synthesis may play an important role in the innate immune response to gram-negative lung infection.

Versican and the regulation of cell phenotype in disease

BACKGROUND

Versican is an extracellular matrix (ECM) proteoglycan that is present in the pericellular environment of most tissues and increases in many different diseases. Versican interacts with cells to influence the ability of cells to proliferate, migrate, adhere and assemble an ECM.

SCOPE OF REVIEW

The structure of the versican molecule is briefly reviewed and studies highlighting those factors that promote versican synthesis and degradation and their impact on cell phenotype in disease are discussed. Particular attention is given to vascular disease, but other diseases where versican is important are covered as well, most notably different forms of cancers. Attention is given to mechanisms(s) by which versican influences cell behaviors through either direct or indirect processes. Versican produced by either stromal cells or myeloid cells can have a major impact influencing immunity and inflammation. Finally, studies controlling versican accumulation that either delay or inhibit the progression of disease will be highlighted.

MAJOR CONCLUSIONS

Versican is one component of the ECM that can influence the ability of cells to proliferate, migrate, adhere, and remodel the ECM. Targeting versican as a way to control cell phenotype offers a novel approach in the treatment of disease.

SIGNIFICANCE

ECM molecules such as versican contribute to the structural integrity of tissues and interact with cells through direct and indirect means to regulate, in part, cellular events that form the basis of disease. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Can viscosupplementation be used in the hip? An Italian perspective

Viscosupplementation is the intra-articular administration of preparations containing hyaluronic acid or hyaluronate intended to restore the normal biological properties of hyaluronic acid normally found in synovial fluid. Infiltration of hyaluronic acid in the arthritic hip is a more recent technique than viscosupplementation of the knee due to the greater technical difficulty of infiltration to the hip, which requires fluoroscopic or ultrasound guidance. The introduction of high-molecular-weight hyaluronic acid in the treatment permits a single administration and has helped diffuse hip infiltration treatment. A single infiltration reduces patient discomfort caused by the procedure and allows treatment of a larger number of patients. Although the literature has unequivocally proven the possibility of reducing pain in patients affected by hip arthritis following infiltration, the molecular weight and density, the number of infiltrations required for long-term results, and the most appropriate indications for infiltration treatment have yet to be clarified. Selecting the patient is the first obstacle to be overcome. Therefore, infiltration should be considered as an option for patients with initial pain symptoms who have not yet been listed for joint prosthesis surgery. The radiographic criteria require at least a partly preserved joint space, and the clinical criteria of persistent hip pain and full joint mobility seem to be sufficiently effective for selection.

Self-assembly and elasticity of hierarchical proteoglycan–hyaluronan brushes††Electronic supplementary information (ESI) available: Variations in areal mass density upon SLB and SAv monolayer formation determined by SE (Fig. S1). See DOI: 10.1039/c3sm51213d

We assemble aggrecan-containing hyaluronan brushes to study how the supramolecular structure and dynamics relate to material properties in hyaluronan-rich pericellular matrices.

Spatially confined yet strongly hydrated assemblies made from the proteoglycan aggrecan and the polysaccharide hyaluronan (HA) are major, functionally important components of the pericellular space around chondrocytes, and in cartilage. To better understand, how mechanical properties arise from the supramolecular structure and dynamics of such assemblies, we have studied the effect of aggrecan on the physico-chemical properties of well-defined, planar HA brushes. From interaction studies by quartz crystal microbalance with dissipation monitoring and spectroscopic ellipsometry, and compression studies by combined colloidal probe atomic force/reflection interference contrast microscopy, we find that aggrecan readily intercalates into HA brushes in a reversible manner. Aggrecan induces a drastic swelling of HA brushes, generating self-assembled films of several micrometers in thickness that are highly hydrated (>99%), elastic and very soft. The Young modulus in the linear compression regime is well below 100 Pa, and reaches several kPa at strong compression. The implications of these findings for biological function are discussed.

The impact of intradermal injections of modified hyaluronic acid on the morphological skin condition in female patients with involutional changes

Goal. To provide a clinical assessment of the efficacy and tolerance of hyaluronic acid (HA) drugs modified with vitamin С and amino acids in patients with involutional skin changes. Methods. As many as 90 female patients underwent a course of treatment for age-related skin changes including three procedures of intradermal injections of modified HA. The skin condition was assessed prior to and after the treatment by using non-invasive methods (corneometry, pH-metry, sebometry, elastometry, visio-scanning, ultrasonic derma-scanning and confocal laser scanning microscopy). Results. The authors demonstrated good tolerance of modified HA and skin condition improvement (better elasticity, moisture level, improvement of the skin structure and microrelief, reduction in the intensity of expression and static wrinkles, restoration of color uniformity and elimination of xerosis manifestations). Conclusion. The study results are sufficient to recommend modified HA drugs for correcting involutional skin changes.

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.

Deregulation of hyaluronan synthesis, degradation and binding promotes breast cancer

Clinical and experimental data indicate that hyaluronan accumulates in breast cancer compared with normal breast epithelium, which correlates to poor prognosis. In this review, we discuss the expression of genes encoding enzymes that synthesize or degrade hyaluronan, i.e. hyaluronan synthases and hyaluronidases or bind hyaluronan, i.e. CD44 and receptor for hyaluronan-mediated motility (RHAMM, also designated as HMMR or CD168), in relation to breast cancer progression. Hyaluronan and hyaluronan receptors have multi-faceted roles in signalling events in breast cancer. A better understanding of the molecular mechanisms underlying these signalling pathways is highly warranted and may lead to improvement of cancer treatment.

Mediators of inflammation and their effect on resident renal cells: implications in lupus nephritis

Lupus nephritis affects up to 70% of patients with systemic lupus erythematosus and is a major cause of morbidity and mortality. It is characterized by a breakdown of immune tolerance, production of autoantibodies, and deposition of immune complexes within the kidney parenchyma, resulting in local inflammation and subsequent organ damage. To date, numerous mediators of inflammation have been implicated in the development and progression of lupus nephritis, and these include cytokines, chemokines, and glycosaminoglycans. Of these, type I interferons (IFNs) can increase both gene and protein expression of cytokines and chemokines associated with lupus susceptibility, and interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and hyaluronan have been shown to elicit both pro- and anti-inflammatory effects on infiltrating and resident renal cells depending on the status of their microenvironment. Expression of IL-6, TNF-α, type I IFNs, and hyaluronan are increased in the kidneys of patients and mice with active lupus nephritis and have been shown to contribute to disease pathogenesis. There is also evidence that despite clinical remission, ongoing inflammatory processes may occur within the glomerular and tubulointerstitial compartments of the kidney, which further promote kidney injury. In this review, we provide an overview of the synthesis and putative roles of IL-6, TNF-α, IFN-α, and hyaluronan in the pathogenesis of lupus nephritis focusing on their effects on human mesangial cells and proximal renal tubular epithelial cells.

Sulfation of the bikunin chondroitin sulfate chain determines heavy chain·hyaluronan complex formation

Inter-α-trypsin inhibitor (IαI) is a complex comprising two heavy chains (HCs) that are covalently bound by an ester bond to chondroitin sulfate (CS), which itself is attached to Ser-10 of bikunin. IαI is essential for the trans-esterification of HCs onto hyaluronan (HA). This process is important for the stabilization of HA-rich matrices during ovulation and some inflammatory processes. Bikunin has been isolated previously by anion exchange chromatography with a salt gradient up to 0.5 M NaCl and found to contain unsulfated and 4-sulfated CS disaccharides. In this study, bikunin-containing fractions in plasma and urine were separated by anion exchange chromatography with a salt gradient of 0.1-1.0 M NaCl, and fractions were analyzed for their reactivity with the 4-sulfated CS linkage region antibody (2B6). The fractions that reacted with the 2B6 antibody (0.5-0.8 M NaCl) were found to predominantly contain sulfated CS disaccharides, including disulfated disaccharides, whereas the fractions that did not react with this antibody (0.1-0.5 M NaCl) contained unsulfated and 4-sulfated CS disaccharides. IαI in the 0.5-0.8 M NaCl plasma fraction was able to promote the trans-esterification of HCs to HA in the presence of TSG-6, whereas the 0.1-0.5 M NaCl fraction had a much reduced ability to transfer HC proteins to HA, suggesting that the CS containing 4-sulfated linkage region structures and disulfated disaccharides are involved in the HC transfer. Furthermore, these data highlight that the structure of the CS attached to bikunin is important for the transfer of HC onto HA and emphasize a specific role of CS chain sulfation.

A hexadecylamide derivative of hyaluronan (HYMOVIS®) has superior beneficial effects on human osteoarthritic chondrocytes and synoviocytes than unmodified hyaluronan

Background

Intra-articular hyaluronan (HA) injection provides symptomatic benefit in the treatment of osteoarthritis (OA). Previously we found superior beneficial effects in a large animal OA model of a hexadecylamide derivative compared with unmodified HA of the same initial molecular weight. The current study sought to define possible molecular mechanisms whereby this enhanced relief of symptoms was occurring.

Methods

Chondrocytes and synovial fibroblasts were isolated from tissues of patients undergoing arthroplasty for knee OA. Monolayer cultures of cells were treated with 0, 0.5, 1.0 or 1.5 mg/mL of unmodified HA (500–730 kDa) or a hexadecylamide derivative of HA of the same initial molecular weight (HYADD4®-G; HYMOVIS®) simultaneously or 1 hour before incubation with interleukin (IL)-1beta (2 ng/mL). Cultures were terminated 15 or 30 minutes later (chondrocytes and synovial fibroblasts, respectively) for quantitation of phosphorylated-(p)-JNK, p-NFkappaB, p-p38, or at 24 hours for quantitation of gene expression (MMP1 &13, ADAMTS4 &5, TIMP1 &3, CD44, COL1A1 &2A1, ACAN, PTGS2, IL6, TNF) and matrix metalloproteinase (MMP)-13 activity.

Results

The hexadecylamide derivative of HA had significantly better amelioration of IL-1beta-induced gene expression of key matrix degrading enzymes (MMP1, MMP13, ADAMTS5), and inflammatory mediators (IL6, PTGS2) by human OA chondrocytes and synovial fibroblasts. Pre-incubation of cells with the derivatized HA for 1 hour prior to IL-1beta exposure significantly augmented the inhibition of MMP1, MMP13, ADAMTS4 and IL6 expression by chondrocytes. The reduction in MMP13 mRNA by the amide derivative of HA was mirrored in reduced MMP-13 protein and enzyme activity in IL-1beta-stimulated chondrocytes. This was associated in part with a greater inhibition of phosphorylation of the cell signalling molecules JNK, p38 and NF-kappaB.

Conclusions

The present studies have demonstrated several potential key mechanisms whereby the intra-articular injection of a hexadecylamide derivative of HA may be acting in joints with OA.

Hyaluronan up-regulates growth and invasion of trophoblasts in an autocrine manner via PI3K/AKT and MAPK/ERK1/2 pathways in early human pregnancy

INTRODUCTION

As one of the key molecules in the extracellular matrix in human conceptus, hyaluronan (HA) has been receiving particular attention. Here, we have investigated the expression and regulation of different molecular weight HA on the biological behaviors of primary human trophoblasts during the first trimester of pregnancy.

METHODS

The expression of HA and HA synthetase (HAS) by human first trimester trophoblasts was analyzed in placentae from normal pregnancy or miscarriage by immunochemistry and real-time RT-PCR, respectively. ELISA was used to measure the secretion of HA by primary trophoblasts. The effects of HA on the proliferation, apoptosis and invasiveness of trophoblasts were examined. We also investigated the signaling pathways involved in HA activation in human trophoblasts.

RESULTS

The higher HAS2 expression and HA secretion were observed in normal villi than that of miscarriage, and the primary trophoblasts secreted HA continuously. High molecular weight HA (HMW-HA) and medium molecular weight HA (MMW-HA) promoted proliferation and invasiveness while inhibited apoptosis of trophoblasts. However, low molecular weight HA (LMW-HA) had no obvious effect on the growth or invasiveness of human trophoblasts. In addition, HMW-HA showed more efficiently than MMW-HA on the growth while MMW-HA displayed a more obvious effect on the invasiveness of trophoblasts than HMW-HA. HMW-HA activated PI3K/AKT and MAPK/ERK1/2 signaling pathways in trophoblasts. Blocking PI3K/AKT or MAPK/ERK1/2 signaling inhibited the HA-upregulated growth and invasiveness of human trophoblasts.

CONCLUSION

Our results suggest that higher level and greater molecular mass of HA can promote trophoblast growth and invasion in an autocrine manner, which was beneficial to placentation and maintenance of human early pregnancy.

Biological interplay between proteoglycans and their innate immune receptors in inflammation

An emerging body of evidence indicates that secreted proteoglycans act as signaling molecules, in addition to their canonical function in maintaining and regulating the architecture of various extracellular matrices. Proteoglycans interact with a number of receptors that regulate growth, motility and immune response. In part, as a consequence of their complex structure, proteoglycans can induce crosstalk among various families of receptors and can also interact with natural receptor ligands, often blocking and sequestering their bioactivity. In their soluble form, originating from either partial proteolytic processing or through de novo synthesis by activated cells, some proteoglycans can become potent danger signals, denoting tissue stress and injury. Recently, it has been shown that proteoglycans, especially those belonging to the small leucine-rich and hyaluronan-binding gene families as well as the glycosaminoglycan hyaluronan, act as endogenous ligands of the toll-like receptors, a group of central receptors regulating innate immunity. Furthermore, proteoglycans can activate intracellular inflammasomes and trigger sterile inflammation. In this review, we critically assess the signaling events induced by the proteoglycans biglycan, decorin, lumican and versican as well as hyaluronan during inflammation. We discuss the intriguing emerging notion that, in spite of structural diversity of biglycan, decorin, versican and hyaluronan, all of them signal through the same toll-like receptors, albeit triggering differential responses and biological outcomes. Finally, we review the modes of action of these endogenous ligands of toll-like receptors and their ability to specifically modify the final signaling events and the inflammatory response.

In situ forming hydrogels composed of oxidized high molecular weight hyaluronic acid and gelatin for nucleus pulposus regeneration

Encapsulation of nucleus pulposus (NP) cells within in situ forming hydrogels is a novel biological treatment for early stage intervertebral disc degeneration. The procedure aims to prolong the life of the degenerating discs and to regenerate damaged tissue. In this study we developed an injectable oxidized hyaluronic acid-gelatin-adipic acid dihydrazide (oxi-HAG-ADH) hydrogel. High molecular weight (1900 kDa) hyaluronic acid was crosslinked with various concentrations of gelatin to synthesize the hydrogels and their viscoelastic properties were analyzed. Interactions between the hydrogels, NP cells, and the extracellular matrix (ECM) were also evaluated, as were the effects of the hydrogels on NP cell gene expression. The hydrogels possess several clinical advantages, including sterilizability, low viscosity for injection, and ease of use. The viscoelastic properties of the hydrogels were similar to native tissue, as reflected in the complex shear modulus (∼11-14 kPa for hydrogels, 11.3 kPa for native NP). Cultured NP cells not only attached to the hydrogels but also survived, proliferated, and maintained their round morphology. Importantly, we found that hydrogels increased NP cell expression of several crucial ECM-related genes, such as COL2A1, AGN, SOX-9, and HIF-1A.

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

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

The role of hyaluronan and the extracellular matrix in islet inflammation and immune regulation

Type 1 diabetes (T1D) is a disease that in most individuals results from autoimmune attack of a single tissue type, the pancreatic islet. A fundamental, unanswered question in T1D pathogenesis is how the islet tissue environment influences immune regulation. This crosstalk is likely to be communicated through the extracellular matrix (ECM). Here, we review what is known about the ECM in insulitis and examine how the tissue environment is synchronized with immune regulation. In particular, we focus on the role of hyaluronan (HA) and its interactions with Foxp3+ regulatory T-cells (Treg). We propose that HA is a "keystone molecule" in the inflammatory milieu and that HA, together with its associated binding proteins and receptors, is an appropriate point of entry for investigations into how ECM influences immune regulation in the islet.

The Role of Hyaluronan and CD44 in the Pathogenesis of Lupus Nephritis

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease that affects multiorgan systems. Lupus nephritis is one of the most severe manifestations of SLE whereby immune-mediated inflammation can lead to permanent damage within the glomerular, tubulo-interstitial, and vascular compartments of the kidney, resulting in acute or chronic renal failure. The mechanisms that regulate host inflammatory responses and tissue injury are incompletely understood. Accumulating evidence suggests that hyaluronan and its interaction with its cell surface receptor CD44 plays an important role in mediating pathogenic mechanisms in SLE. This paper discusses the putative mechanisms through which hyaluronan and CD44 contribute to the pathogenesis of SLE, with particular emphasis on lupus nephritis.

Hyaluronan and hyaluronan binding proteins are normal components of mouse pancreatic islets and are differentially expressed by islet endocrine cell types

The pancreatic islet comprises endocrine, vascular, and neuronal cells. Signaling among these cell types is critical for islet function. The extracellular matrix (ECM) is a key regulator of cell-cell signals, and while some islet ECM components have been identified, much remains unknown regarding its composition. We investigated whether hyaluronan, a common ECM component that may mediate inflammatory events, and molecules that bind hyaluronan such as versican, tumor necrosis factor-stimulated gene 6 (TSG-6), and components of inter-α-trypsin inhibitor (IαI), heavy chains 1 and 2 (ITIH1/ITIH2), and bikunin, are normally produced in the pancreatic islet. Mouse pancreata and isolated islets were obtained for microscopy (with both paraformaldehyde and Carnoy's fixation) and mRNA. Hyaluronan was present predominantly in the peri-islet ECM, and hyaluronan synthase isoforms 1 and 3 were also expressed in islets. Versican was produced in α cells; TSG-6 in α and β cells; bikunin in α, β, and δ cells; and ITIH1/ITIH2 predominantly in β cells. Our findings demonstrate that hyaluronan, versican, TSG-6, and IαI are normal islet components and that different islet endocrine cell types contribute these ECM components. Thus, dysfunction of either α or β cells likely alters islet ECM composition and could thereby further disrupt islet function.

Influence of hyaluronic acid on wound healing using composite porcine acellular dermal matrix grafts and autologous skin in rabbits

This study aims to explore the influence of hyaluronic acid (HA) on wound healing during xenogeneic porcine acellular dermal matrix (PADM) composite skin grafting. The results will facilitate the development of methods for improving graft contracture and poor elasticity of composite transplantation. Exogenous HA was added to composite PADM grafts and to thin autologous skin grafts during rabbit full-thickness skin wound repair. The influence of HA on wound healing was evaluated according to its contracture rate and its expression of collagen types I and III. The possible mechanism was then explored based on HA metabolism and vascularisation in the skin graft. The results show that exogenous HA relieves graft contracture on rabbit wound surfaces, increases collagen I and III expression and decreases the ratio between collagen types. HA stimulates the generation of more CD44 receptors to strengthen its enzymolysis. The resulting metabolites promote the vascularisation of the wound surface, which are conducive for mitigating graft contracture, and further improve the composite grafting effect.

Design of biomimetic cell-interactive substrates using hyaluronic acid hydrogels with tunable mechanical properties

Hyaluronic acid (HA) is a natural polysaccharide abundant in biological tissues with excellent potential for constructing synthetic extracellular matrix analogues. In this work, we established a simple and dependable approach to prepare hyaluronic acid-based hydrogels with controlled stiffness and cell recognition properties for use as cell-interactive substrates. This approach relied on a new procedure for the synthesis of methacrylate-modified HA macromers (HA-MA) and, on photorheometry allowing real time monitoring of gelation during photopolymerization. We showed in this way the ability to obtain gels that encompass the range of physiologically relevant elastic moduli while still maintaining the recognition properties of HA by specific cell surface receptors. These hydrogels were prepared from HA macromers having a degree of methacrylation <0.5, which allows to minimize compromising effects on the binding affinity of HA to its cell receptors due to high substitution on the one hand, and to achieve nearly 100% conversion of the methacrylate groups on the other. When the HA hydrogels were immobilized on glass substrates, it was observed that the attachment and the spreading of a variety of mammalian cells rely on CD44 and its coreceptor RHAMM. The attachment and spreading were also shown to be modulated by the elastic properties of the HA matrix. All together, these results highlight the biological potential of these HA hydrogel systems and the needs of controlling their chemical and physical properties for applications in cell culture and tissue engineering.

Long pentraxin 3/tumor necrosis factor-stimulated gene-6 interaction: a biological rheostat for fibroblast growth factor 2-mediated angiogenesis

OBJECTIVE

Angiogenesis is regulated by the balance between pro- and antiangiogenic factors and by extracellular matrix protein interactions. Fibroblast growth factor 2 (FGF2) is a major proangiogenic inducer inhibited by the interaction with the soluble pattern recognition receptor long pentraxin 3 (PTX3). PTX3 is locally coexpressed with its ligand tumor necrosis factor-stimulated gene-6 (TSG-6), a secreted glycoprotein that cooperates with PTX3 in extracellular matrix assembly. Here, we characterized the effect of TSG-6 on PTX3/FGF2 interaction and FGF2-mediated angiogenesis.

METHODS AND RESULTS

Solid phase binding and surface plasmon resonance assays show that TSG-6 and FGF2 bind the PTX3 N-terminal domain with similar affinity. Accordingly, TSG-6 prevents FGF2/PTX3 interaction and suppresses the inhibition exerted by PTX3 on heparan sulfate proteoglycan/FGF2/FGF receptor complex formation and on FGF2-dependent angiogenesis in vitro and in vivo. Also, endogenous PTX3 exerts an inhibitory effect on vascularization induced by FGF2 in a murine subcutaneous Matrigel plug assay, the inhibition being abolished in Ptx3-null mice or by TSG-6 treatment in wild-type animals.

CONCLUSION

TSG-6 reverts the inhibitory effects exerted by PTX3 on FGF2-mediated angiogenesis through competition of FGF2/PTX3 interaction. This may provide a novel mechanism to control angiogenesis in those pathological settings characterized by the coexpression of TSG-6 and PTX3, in which the relative levels of these proteins may fine-tune the angiogenic activity of FGF2.

Monocyte-to-macrophage differentiation: synthesis and secretion of a complex extracellular matrix

Although monocyte- and macrophage-derived molecules are known to promote extracellular matrix (ECM) disruption and destabilization, it is less appreciated that they also synthesize molecules contributing to ECM formation, stabilization, and function. We have identified and characterized the synthesis of proteoglycans and related proteins, some not previously known to be associated with macrophages. Proteoglycan extracts of [³⁵S]sulfate- and ³⁵S-trans amino acid-radiolabeled culture media from THP-1 monocytes induced to differentiate by treatment with phorbol myristate acetate revealed three major proteins of ∼25, 90, and 100 kDa following chondroitin ABC lyase digestion. The 25-kDa protein was predominant for monocytes, whereas the 90- and 100-kDa proteins were predominant for macrophages. Tandem mass spectrometry identified (i) the 25-kDa core protein as serglycin, (ii) the 90-kDa core protein as inter-α-inhibitor heavy chain 2 (IαIHC2), and (iii) the 100-kDa core as amyloid precursor-like protein 2 (APLP2). Differentiation was also associated with (i) a >500-fold increase in mRNA for TNF-stimulated gene-6, an essential cofactor for heavy chain-mediated matrix stabilization; (ii) a >800-fold increase in mRNA for HAS2, which is responsible for hyaluronan synthesis; and (iii) a 3-fold increase in mRNA for versican, which interacts with hyaluronan. Biochemical evidence is also presented for an IαIHC2-APLP2 complex, and immunohistochemical staining of human atherosclerotic lesions demonstrates similar staining patterns for APLP2 and IαIHC2 with macrophages, whereas serglycin localizes to the underlying glycosaminoglycan-rich region. These findings indicate that macrophages synthesize many of the molecules participating in ECM formation and function, suggesting a novel role for these molecules in the differentiation of macrophages in the development of atherosclerosis.

Constitutive expression of inter-α-inhibitor (IαI) family proteins and tumor necrosis factor-stimulated gene-6 (TSG-6) by human amniotic membrane epithelial and stromal cells supporting formation of the heavy chain-hyaluronan (HC-HA) complex

Recently, we reported HC-HA, a covalent complex formed between heavy chains (HCs) of inter-α-inhibitor (IαI) and hyaluronan (HA) by the catalytic action of tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6), is responsible for human amniotic membrane (AM) anti-inflammatory, anti-scarring, and anti-angiogenic actions. At the present time, the only well characterized source of IαI is serum being produced by the liver. This study showed that AM epithelial and stromal cells and stromal matrix all stained positively for HA, HC 1, 2, and 3, bikunin, and TSG-6. TSG-6 mRNA and protein were constitutively expressed by cultured AM epithelial and stromal cells without being up-regulated by TNF. In serum-free conditions, these cells expressed IαI, leading to the formation of HC-HA complex that contained both HC1 and HC2. In contrast, only HC1 was found in the HC-HA complex purified from AM. Local production of IαI, the HC-TSG-6 intermediate complex, and HC-HA were abolished when cells were treated with siRNA to HC1, HC2, bikunin (all of which impair the biosynthesis of IαI), or TSG-6 but not to HC3. Collectively, these results indicate that AM is another tissue in addition to the liver to constitutively produce IαI and that the HC-HA complex made by this tissue is different from that found at inflammatory sites (e.g. in asthma and arthritis) and in the matrix of the cumulus oocyte complex.

Combining colloidal probe atomic force and reflection interference contrast microscopy to study the compressive mechanics of hyaluronan brushes

We describe a method that combines colloidal probe atomic force microscopy (AFM) and reflection interference contrast microscopy (RICM) to characterize the mechanical properties of thin and solvated polymer films. When analyzing polymer films, a fundamental problem in colloidal probe AFM experiments is to determine the distance at closest approach between the probe and the substrate on which the film is deposited. By combining AFM and RICM in situ, forces and absolute distances can be measured simultaneously. Using the combined setup, we quantify the compressive mechanics of films of the polysaccharide hyaluronan that is end-grafted to a supported lipid bilayer. The experimental data, and comparison with polymer theory, show that hyaluronan films are well-described as elastic, very soft and highly solvated polymer brushes. The data on these well-defined films should be a useful reference for the investigation of the more complex hyaluronan-rich coats that surround many living cells.

Mechanical properties of tyramine substituted-hyaluronan enriched fascia extracellular matrix

Naturally occurring biomaterial scaffolds derived from extracellular matrix (ECM) have been the topic of recent investigation in the context of rotator cuff tendon repair. We previously reported a method to treat fascia ECM with high molecular weight tyramine substituted-hyaluronan (TS-HA) for use as a tendon augmentation scaffold. The presence of crosslinked TS-HA in fascia was associated with an increased macrophage and giant cell response compared to water-treated controls after implantation in a rat abdominal wall model. The objective of this study was to determine the extent to which TS-HA treatment was associated with mechanical property changes of fascia after implantation in the rat model. Fascia samples in all groups demonstrated time-dependent decreases in mechanical properties. TS-HA-treated fascia with crosslinking exhibited a lower toe modulus, a trend toward lower toe stiffness, and a higher transition strain than water-treated controls not only after implantation, but also at time zero. TS-HA treatment, with or without crosslinking, had no significant effect on time-zero or post-implantation load relaxation ratio, load relaxation rate, linear-region stiffness, or linear-region modulus. Our findings demonstrated that the particular TS-HA treatment employed in this study decreased the low-load elastic mechanical properties of fascia ECM, in keeping with the heightened macrophage and giant cell host response seen previously. This work provides a starting point and guidance for investigating alternative HA treatment strategies.

Pentraxins in humoral innate immunity

Innate immunity represents the first line of defence against pathogens and plays key roles in activation and orientation of the adaptive immune response. The innate immune system comprises both a cellular and a humoral arm. Components of the humoral arm include soluble pattern recognition molecules (PRMs) that recognise pathogens associated molecular patterns (PAMPs) and initiate the immune response in coordination with the cellular arm, therefore acting as functional ancestors of antibodies. The long pentraxin PTX3 is a prototypic soluble PRM that is produced at sites of infection and inflammation by both somatic and immune cells. Gene targeting of this evolutionarily conserved protein has revealed a non-redundant role in resistance to selected pathogens. Moreover, PTX3 exerts important functions at the crossroad between innate immunity, inflammation and female fertility. Here we review the studies on PTX3, with emphasis on pathogen recognition and crosstalk with other components of the innate immune system.

Inhibition of proteasomal proteolysis affects expression of extracellular matrix components and steroidogenesis in porcine oocyte-cumulus complexes

Porcine oocyte-cumulus complexes (OCCs) form an expanded cumulus extracellular matrix (ECM) in response to gonadotropins during meiotic maturation. Essential components of ECM are hyaluronan (HA), tumor necrosis factor α-induced protein 6 (TNFAIP6) and heavy chains (HC) of interalpha-trypsin inhibitor. To form expanded cumulus ECM, intermediate complexes (TNFAIP6-HC) must bind to HA to allow HC transfer onto HA. Protein turnover by the ubiquitin-proteasome pathway is poorly characterized in this process. It is known that the specific proteasomal inhibitor MG132 prevents cumulus expansion and formation of ECM. To determine whether inhibition of proteasomal proteolysis with MG132 affects cumulus cell steroidogenesis and expression of the cumulus expansion-related components (hyaluronan synthase type 2, HAS2, TNFAIP6) we cultured porcine OCCs and granulosa cells (GCs) in a medium supplemented with FSH/LH. Methods performed included real-time reverse transcription PCR, immunofluorescence and RIAs. The expression of TNFAIP6 and HAS2 transcripts increased significantly after the stimulation of OCCs and GCs with FSH/LH. In contrast, treatment with MG132 reduced the expression of TNFAIP6 and HAS2. Hyaluronan was detected with biotinylated HA-binding proteins within FSH/LH-stimulated expanded OCCs but not in those treated with MG132. Progesterone production, although increased almost three times after OCCs stimulation with FSH/LH, was significantly suppressed by MG132. The FSH/LH-stimulated a 40-fold increase in progesterone secretion by GCs was inhibited in the presence of MG132. In conclusion, MG132 affects progesterone secretion and expression of cumulus expansion-related components by cumulus and GCs, suggesting the requirement of ubiquitin-proteasome pathway-regulated protein turnover for formation of ECM during cumulus expansion in the preovulatory period in the pig.

Hyaluronan differently modulates TLR-4 and the inflammatory response in mouse chondrocytes

Hyaluronic acid (HA) may exert different action depending on its degree of polymerization. Small HA fragments induce proinflammatory responses, while highly polymerized HA exerts a protective effect in inflammatory pathologies such as rheumatoid arthritis. In both cases the toll-like receptor 4 (TLR-4) seems to be involved in the modulation of the inflammation process. The aim of this study was to investigate the influence of short HA oligosaccharides (HA 4-mers) and high molecular weight HA (HMWHA) in the inflammatory response in normal mouse chondrocytes. Messenger RNA and related protein levels were measured for TLR-4, tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and interleukin-18 (IL-18) in cells with and without the addition of HA. NF-kB activation was also evaluated. 4-mer HA treatment produced a significant up-regulation of all parameters considered while HMWHA did not exert any activity in untreated cells although it was able to reduce the effects of 4- mers HA significantly. Specific TLR-4 small interference RNA (siRNA) was used to confirm TLR-4 as the target of HA action. This study suggests that HA may modulate proinflammatory cytokines via its different degree of polymerization and inflammatory action may be modulated as a result of the interaction between HA and TLR-4.

Chain gangs: new aspects of hyaluronan metabolism

Hyaluronan is a matrix polymer prominent in tissues undergoing rapid growth, development, and repair, in embryology and during malignant progression. It reaches 10⁷ Daltons in size but also exists in fragmented forms with size-specific actions. It has intracellular forms whose functions are less well known. Hyaluronan occurs in all vertebrate tissues with 50% present in skin. Hyaluronan provides a scaffold on which sulfated proteoglycans and matrix proteins are organized. These supramolecular structures are able to entrap water and ions to provide tissues with hydration and turgor. Hyaluronan is recognized by membrane receptors that trigger intracellular signaling pathways regulating proliferation, migration, and differentiation. Cell responses are often dependent on polymer size. Catabolic turnover occurs by hyaluronidases and by free radicals, though proportions between these have not been determined. New aspects of hyaluronan biology have recently become realized: involvement in autophagy, in the pathology of diabetes., the ability to modulate immune responses through effects on T regulatory cells and, in its fragmented forms, by being able to engage several toll-like receptors. It is also apparent that hyaluronan synthases and hyaluronidases are regulated at many more levels than previously realized, and that the several hyaluronidases have functions in addition to their enzymatic activities.

Hyaluronan and versican in the control of human T-lymphocyte adhesion and migration

The ability of lymphocytes to migrate freely through connective tissues is vital to efficient immune function. How the extracellular matrix (ECM) may affect T-cell adhesion and migration is not well understood. We have examined the adhesion and migration of activated human T-lymphocytes on ECM made by fibroblast-like synoviocytes and lung fibroblasts. These cells were minimally interactive until treated with a viral mimetic, Poly I:C. This treatment promoted myofibroblast formation and engendered a higher-order structured ECM, rich in versican and hyaluronan, to which T-cells avidly adhered in a hyaluronidase-sensitive manner. This Poly I:C-induced matrix impeded T-cell spreading and migration on and through synoviocyte monolayers, while hyaluronidase treatment or adding versican antibody during matrix formation reversed the effect on T-cell migration. Hyaluronidase also reversed the spread myofibroblast morphology. These data suggest that the viscous hyaluronan- and versican-rich matrix binds and constrains T-lymphocytes. Using purified matrix components and solid state matrices of defined composition, we uncovered a role for versican in modulating hyaluronan-T-cell interactions. Versican prevented T-cell binding to soluble hyaluronan, as well as the amoeboid shape change on hyaluronan-coated dishes and T-cell penetration of collagen gels. Together, these data suggest that hyaluronan and versican play a role in T-cell trafficking and function in inflamed tissues.

High and low molecular weight hyaluronic acid differentially regulate human fibrocyte differentiation

Background

Following tissue injury, monocytes can enter the tissue and differentiate into fibroblast-like cells called fibrocytes, but little is known about what regulates this differentiation. Extracellular matrix contains high molecular weight hyaluronic acid (HMWHA; ∼2×10⁶ Da). During injury, HMWHA breaks down to low molecular weight hyaluronic acid (LMWHA; ∼0.8–8×10⁵ Da).

Methods and Findings

In this report, we show that HMWHA potentiates the differentiation of human monocytes into fibrocytes, while LMWHA inhibits fibrocyte differentiation. Digestion of HMWHA with hyaluronidase produces small hyaluronic acid fragments, and these fragments inhibit fibrocyte differentiation. Monocytes internalize HMWHA and LMWHA equally well, suggesting that the opposing effects on fibrocyte differentiation are not due to differential internalization of HMWHA or LMWHA. Adding HMWHA to PBMC does not appear to affect the levels of the hyaluronic acid receptor CD44, whereas adding LMWHA decreases CD44 levels. The addition of anti-CD44 antibodies potentiates fibrocyte differentiation, suggesting that CD44 mediates at least some of the effect of hyaluronic acid on fibrocyte differentiation. The fibrocyte differentiation-inhibiting factor serum amyloid P (SAP) inhibits HMWHA-induced fibrocyte differentiation and potentiates LMWHA-induced inhibition. Conversely, LMWHA inhibits the ability of HMWHA, interleukin-4 (IL-4), or interleukin-13 (IL-13) to promote fibrocyte differentiation.

Conclusions

We hypothesize that hyaluronic acid signals at least in part through CD44 to regulate fibrocyte differentiation, with a dominance hierarchy of SAP>LMWHA≥HMWHA>IL-4 or IL-13.

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.