Epidermal growth factor activates hyaluronan synthase 2 in epidermal keratinocytes and increases pericellular and intracellular hyaluronan

Chronic ultraviolet B irradiation causes loss of hyaluronic acid from mouse dermis because of down-regulation of hyaluronic acid synthases

Remodeling of the dermal extracellular matrix occurs during photoaging. Here, the effect of repetitive UVB irradiation on dermal hyaluronic acid (HA) was examined. C57/BL6 mice were chronically (182 days) irradiated with UVB, and consecutive skin biopsies were collected during the irradiation period and afterward (300 and 400 days of age). UVB caused marked loss of HA from the papillary dermis and down-regulation of HA synthase 1 (HAS1), HAS2, and HAS3 mRNA expression. In contrast, hyaluronidases (HYAL) 1, HYAL2, and HA receptor CD44 were unchanged. Furthermore, transforming growth factor beta-1 (TGF-beta1) and TGF-beta1-receptor II expression were decreased in UVB-irradiated biopsies, and TGF-beta1 strongly induced HAS1 and HAS2 expression in cultured dermal fibroblasts. Therefore, TGF-beta1 might be one factor involved in UVB-induced down-regulation of HAS enzymes. In addition, total cell number and the percentage of proliferating fibroblasts in the papillary dermis of UVB-irradiated mice were decreased. Down-regulation of HAS2 by lentiviral overexpression of short hairpin RNA in vitro caused inhibition of HA synthesis, DNA synthesis, and migration of dermal fibroblasts. In conclusion, chronic UVB irradiation induces loss of HA from the dermis, thereby contributing to the quiescent phenotype of dermal fibroblasts.

Cyclic movement stimulates hyaluronan secretion into the synovial cavity of rabbit joints

The novel hypothesis that the secretion of the joint lubricant hyaluronan (HA) is coupled to movement has implications for normal function and osteoarthritis, and was tested in the knee joints of anaesthetized rabbits. After washing out the endogenous synovial fluid HA (miscibility coefficient 0.4), secretion into the joint cavity was measured over 5 h in static joints and in passively cycled joints. The net static secretion rate (11.2 +/- 0.7 microg h(-1), mean +/- s.e.m., n = 90) correlated with the variable endogenous HA mass (mean 367 +/- 8 microg), with a normalized value of 3.4 +/- 0.2 microg h(-1) (100 microg)(-1) . Cyclic joint movement approximately doubled the net HA secretion rate to 22.6 +/- 1.2 microg h(-1) (n = 77) and raised the normalized percentage to 5.9 +/- 0.3 microg h(-1) (100 microg)(-1). Secretion was inhibited by 2-deoxyglucose and iodoacetate, confirming active secretion. The net accumulation rate underestimated true secretion rate due to some trans-synovial loss. HA turnover time (endogenous mass/secretion rate) was 17-30 h (static) to 8-15 h (moved) The results demonstrate for the first time that the active secretion of HA is coupled to joint usage. Movement-secretion coupling may protect joints against the damaging effects of repetitive joint use, replace HA lost during periods of immobility (overnight), and contribute to the clinical benefit of exercise therapy in moderate osteoarthritis.

Mannose inhibits hyaluronan synthesis by down-regulation of the cellular pool of UDP-N-acetylhexosamines

We found that d-mannose dose-dependently decreases hyaluronan synthesis in cultured epidermal keratinocytes to approximately 50%, whereas glucose, galactose, and fructose up to 20 mm concentration had no effect. The full inhibition occurred within 3 h following introduction of mannose and did not involve down-regulation of hyaluronan synthase (Has1-3) mRNA. Following introduction of mannose, there was an approximately 50% reduction in the cellular concentration of UDP-N-acetylhexosamines (UDP-HexNAc, i.e. UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine). On the other hand, 2 mm glucosamine in the culture medium increased UDP-HexNAc content, stimulated hyaluronan secretion, and negated the effect of mannose, supporting the notion that the inhibition by mannose on hyaluronan synthesis was because of down-regulated UDP-HexNAc content. The content of UDP-glucuronic acid, the other building block for hyaluronan synthesis, was not reduced by mannose but declined from 39 to 14% of controls by 0.2-1.0 mm 4-methylumbelliferone, another compound that inhibits hyaluronan synthesis. Applying 4-methylumbelliferone and mannose together produced the expected reductions in both UDP sugars but no additive reduction in hyaluronan production, indicating that the concentration of each substrate alone can limit hyaluronan synthesis. Mannose is a potentially useful tool in studies on hyaluronan-dependent cell functions, as demonstrated by reduced rates of keratinocyte proliferation and migration, functions known to depend on hyaluronan synthesis.

Induction of hyaluronan cables and monocyte adherence in epidermal keratinocytes

Hyaluronan attached to cell surface can form at least two very different structures; a pericellular coat close to plasma membrane and hyaluronan chains coalesced into "cables" that can span several cell lengths. The hyaluronan in cables, induced by many inflammatory agents, can bind leukocytes, whereas that in the pericellular coat does not contribute to leukocyte binding. Therefore, this structural change seems to have a major role in inflammation. In the present study we checked whether cells of squamous epithelium, like epidermal keratinocytes, can form hyaluronan cables and bind leukocytes. In addition, we checked whether hyaluronan synthesis is affected during the induction of cables. Control keratinocytes expressed pericellular hyaluronan as small patches on plasma membrane. But when treated with inflammatory agents or stressful conditions (tunicamycin, interleukin-1beta, tumor necrosis factor-alpha, and high glucose concentration), hyaluronan organization changed into cable-like structures that avidly bound monocytes. Simultaneously, the total amount of secreted hyaluronan was slightly decreased, and the expression levels of hyaluronan synthases (Has1-3) and CD44 were not significantly changed. The results show that epidermal keratinocytes can form cables and bind leukocytes under inflammatory provocation and that these effects are not dependent on stimulation of hyaluronan secretion.

Hyaluronan in tissue injury and repair

A hallmark of tissue injury and repair is the turnover of extracellular matrix components. This review focuses on the role of the glycosaminoglycan hyaluronan in tissue injury and repair. Both the synthesis and degradation of extracellular matrix are critical contributors to tissue repair and remodeling. Fragmented hyaluronan accumulates during tissue injury and functions in ways distinct from the native polymer. There is accumulating evidence that hyaluronan degradation products can stimulate the expression of inflammatory genes by a variety of immune cells at the injury site. CD44 is the major cell-surface hyaluronan receptor and is required to clear hyaluronan degradation products produced during lung injury; impaired clearance of hyaluronan results in persistent inflammation. However, hyaluronan fragment stimulation of inflammatory gene expression is not dependent on CD44 in inflammatory macrophages. Instead, hyaluronan fragments utilize both Toll-like receptor (TLR) 4 and TLR2 to stimulate inflammatory genes in macrophages. Hyaluronan also is present on the cell surface of lung alveolar epithelial cells and provides protection against tissue damage by interacting with TLR2 and TLR4 on these parenchymal cells. The simple repeating structure of hyaluronan appears to be involved in a number of important aspects of noninfectious tissue injury and repair that are dependent on the size and location of the polymer as well as the interacting cells. Thus, the interactions between the endogenous matrix component hyaluronan and its signaling receptors initiate inflammatory responses, maintain structural cell integrity, and promote recovery from tissue injury.

The effect of endogenous overexpression of hyaluronan synthases on material, morphological, and biochemical properties of uncrosslinked collagen biomaterials

Hyaluronan is an essential component of the native extracellular matrix that has often been added exogenously to biomaterials. The role of endogenously produced hyaluronan on soft tensile tissue mechanics, however, has been largely overlooked. To investigate this aspect of hyaluronan using a cell-mediated approach, cells overexpressing the hyaluronan synthases (has), namely has-1, has-2, has-3 or the empty vector control LXSN, were seeded within collagen gel scaffolds. The resulting engineered tissues were grown under static tension for 6 weeks. Following 6 weeks of culture, the samples were characterized to assess collagen gel contraction, matrix organization, production of hyaluronan, and tissue material properties. The engineered tissues containing cells transfected to overexpress one of the has isozymes had significantly increased retention of hyaluronan within the scaffold; elevated hyaluronan secretion into the culture medium (all but has-2); reduced contraction; reduced collagen density; and significantly altered material properties compared to the LXSN controls. These results indicate that the cell-mediated endogenous overproduction of hyaluronan within biomaterials alters their material, morphological and biochemical characteristics. This investigation, the first to examine the role of endogenously produced hyaluronan in engineered tissue mechanics, suggests that overproduction of hyaluronan in soft connective tissues can transform their biological and biomechanical functionality.

Tissue engineering of replacement skin: the crossroads of biomaterials, wound healing, embryonic development, stem cells and regeneration

Advanced therapies combating acute and chronic skin wounds are likely to be brought about using our knowledge of regenerative medicine coupled with appropriately tissue-engineered skin substitutes. At the present time, there are no models of an artificial skin that completely replicate normal uninjured skin. Natural biopolymers such as collagen and fibronectin have been investigated as potential sources of biomaterial to which cells can attach. The first generation of degradable polymers used in tissue engineering were adapted from other surgical uses and have drawbacks in terms of mechanical and degradation properties. This has led to the development of synthetic degradable gels primarily as a way to deliver cells and/or molecules in situ, the so-called smart matrix technology. Tissue or organ repair is usually accompanied by fibrotic reactions that result in the production of a scar. Certain mammalian tissues, however, have a capacity for complete regeneration without scarring; good examples include embryonic or foetal skin and the ear of the MRL/MpJ mouse. Investigations of these model systems reveal that in order to achieve such complete regeneration, the inflammatory response is altered such that the extent of fibrosis and scarring is diminished. From studies on the limited examples of mammalian regeneration, it may also be possible to exploit such models to further clarify the regenerative process. The challenge is to identify the factors and cytokines expressed during regeneration and incorporate them to create a smart matrix for use in a skin equivalent. Recent advances in the use of DNA microarray and proteomic technology are likely to aid the identification of such molecules. This, coupled with recent advances in non-viral gene delivery and stem cell technologies, may also contribute to novel approaches that would generate a skin replacement whose materials technology was based not only upon intelligent design, but also upon the molecules involved in the process of regeneration.

Heregulin-mediated ErbB2-ERK signaling activates hyaluronan synthases leading to CD44-dependent ovarian tumor cell growth and migration

Heregulin (HRG)-induced cell responses are mediated by the ErbB family of tyrosine kinase receptors. In this study we have investigated HRG activation of ErbB2, extracellular signal-regulated kinase (ERK) signaling, and their role in regulating hyaluronan synthase (HAS) activity in human ovarian tumor cells (SK-OV-3.ipl cells). Immunological and biochemical analyses indicate that ErbB2, ErbB3, and ErbB4 are all expressed in SK-OV-3.ipl cells and that ErbB4 (but not ErbB3) is physically linked to ErbB2 following HRG stimulation. Furthermore, our data indicate that the HRG-induced ErbB2.ErbB4 complexes stimulate ErbB2 tyrosine kinase, which induces both ERK phosphorylation and kinase activity. The activated ERK then increases the phosphorylation of HAS1, HAS2, and HAS3. Consequently, all three HAS isozymes are activated resulting in hyaluronan (HA) production. Because HRG-mediated HAS isozyme phosphorylation/activation can be effectively blocked by either AG825 (an ErbB2 inhibitor) or thiazolidinedione compound (an ERK blocker), we conclude that ErbB2-ERK signaling and HAS isozyme phosphorylation/HA production are functionally coupled in SK-OV-3.ipl cells. HRG also promotes HA- and CD44-dependent oncogenic events (e.g. CD44-Cdc42 association, p21-activated kinase 1 activation, and p21-activated kinase 1-filamin complex formation) and tumor cell-specific behaviors in an ErbB2-ERK signaling-dependent manner. Finally, we have found that the down-regulation of HAS isozyme expression (by transfecting cells with HAS1/HAS2/HAS3-specific small interfering RNAs) not only inhibits HRG-mediated HAS phosphorylation/activation and HA production but also impairs CD44-specific Cdc42-PAK1/filamin signaling, cytoskeleton activation and tumor cell behaviors. Taken together, these findings clearly indicate that HRG activation of ErbB2-ERK signaling modulates HAS phosphorylation/activation and HA production leading to CD44-mediated oncogenic events and ovarian cancer progression.

A rapid transient increase in hyaluronan synthase-2 mRNA initiates secretion of hyaluronan by corneal keratocytes in response to transforming growth factor beta

Keratocytes of the corneal stroma produce transparent extracellular matrix devoid of hyaluronan (HA); however, in corneal pathologies and wounds, HA is abundant. We previously showed primary keratocytes cultured under serum-free conditions to secrete matrix similar to that of normal stroma, but serum and transforming growth factor beta (TGFbeta) induced secretion of fibrotic matrix components, including HA. This study found HA secretion by primary bovine keratocytes to increase rapidly in response to TGFbeta, reaching a maximum in 12 h and then decreasing to <5% of the maximum by 48 h. Cell-free biosynthesis of HA by cell extracts also exhibited a transient peak at 12 h after TGFbeta treatment. mRNA for hyaluronan synthase enzymes HAS1 and HAS2 increased >10- and >50-fold, respectively, in 4-6 h, decreasing to near original levels after 24-48 h. Small interfering RNA against HAS2 inhibited the transient increase of HAS2 mRNA and completely blocked HA induction, but small interfering RNA to HAS1 had no effect on HA secretion. HAS2 mRNA was induced by a variety of mitogens, and TGFbeta acted synergistically to induce HAS2 by as much as 150-fold. In addition to HA synthesis, treatment with TGFbeta induced degradation of fluorescein-HA added to culture medium. These results show HA secretion by keratocytes to be initiated by a rapid transient increase in the HAS2 mRNA pool. The very rapid induction of HA expression in keratocytes suggests a functional role of this molecule in the fibrotic response of keratocytes to wound healing.

Integration of the activation of the human hyaluronan synthase 2 gene promoter by common cofactors of the transcription factors retinoic acid receptor and nuclear factor kappaB

Hyaluronan (HA) is a polysaccharide of the vertebrate extracellular matrix, produced by three related HA synthases (HASs) that influence numerous physiological processes. We screened the first 2250 bp of the HAS2 promoter for transcription factor response elements (REs) in silico and found 1 cluster of 2 retinoic acid (RA) REs, 3 discrete NF-kappaB factors, and 12 Sp1 REs. In parallel, we scanned nine overlapping promoter regions in HaCaT human immortalized keratinocytes using chromatin immunoprecipitation assays to identify binding of mediator, coactivator, and corepressor proteins and Sp1 transcription factor in response to all-trans-RA and tumor necrosis factor-alpha (TNF-alpha). We found that all-trans-RA modulated the binding of the RA receptor and several coregulators to the region containing the RARE cluster at position -1230. The importance of this region is supported in reporter gene assays by the all-trans-RA induction of the respective promoter region. Similarly, we showed by chromatin immunoprecipitation assays as well as by gel-shift assays with nuclear extracts that TNF-alpha induced NF-kappaB binding to regions at positions -380, -1420, and -1890, demonstrated its association with RNA polymerase II and cofactor proteins, and confirmed the functionality of the respective promoter regions in vivo. These findings partially explain the induction of HAS2 mRNA by all-trans-RA and TNF-alpha and provide an example how the action of different transcription factor families can use the same cofactors.

Polyplex-mediated gene transfer and cell cycle: effect of carrier on cellular uptake and intracellular kinetics, and significance of glycosaminoglycans

BACKGROUND

Here we report on studies that probe whether the intracellular kinetics of plasmid DNA (pDNA) and cell surface glycosaminoglycans (GAGs) are modified during the cell cycle in a way that can be correlated with changes in gene transfer efficiency with poly(ethyleneimine) (PEI) and poly-L-lysine (PLL) polyplexes.

METHODS

Synchronized D407 retinal cells were transfected with PEI and PLL polyplexes using a luciferase reporter. The free and/or loosely complexed nuclear pDNA was determined by real-time PCR, and compared with transgene expression, the rate of pinocytosis by FITC-dextran uptake and the content of cell surface GAGs.

RESULTS

The amount of free and/or loosely complexed nuclear pDNA between cell cycle phases varied approximately 4-20 times (G1 < S < G2/M). Both carriers delivered pDNA in a similar way into the nucleus (PLL vs. PEI < or = 3.5-fold), but PEI was approximately 10-100 times more efficient in gene expression than PLL (G1 < G2/M < S). The rate of pinocytosis increased up to 70-fold from G1 to middle S phase. Cell surface heparan and chondroitin sulfate increased 50-80%, and hyaluronan decreased 50% when the cells went from G1 through S to G2/M.

CONCLUSIONS

The data obtained indicates that no single parameter (pinocytosis, cell surface GAGs, nuclear uptake) solely accounts for the differential pDNA uptake or expression during cell cycle, and that the main difference in PLL- and PEI-mediated transfections seems to be at the nuclear level.

Tumor Microenvironment Modulates Hyaluronan Expression: The Lactate Effect

Hyaluronan (HA) synthesis is a tightly regulated process and is partly controlled by the microenvironment (e.g., lactate concentration). Experimental evidence has indicated that the melanoma cells that synthesize large amounts of HA exhibit enhanced tumor cell growth and increased metastatic capacity compared to those expressing smaller amounts. Because most studies have examined HA expression on melanoma cells in vitro, we compared the patterns of HA expression by B16-F1 and B16-F10 melanoma cells in vitro and in situ. Cell surface HA expression was assessed with the HA-binding peptide Pep-1. B16-F1 melanoma cells showed significantly higher levels of Pep-1 binding compared with B16-F10 cells in vitro. On the other hand, expression levels of HA were comparable between B16-F1 and B16-F10 melanoma cells in cryostat sections. These results show that B16-F1 cells express high levels of HA in vitro and in vivo, while B16-F10 cells express high concentrations of HA only in the context of skin tumors. Finally, B16-F10 melanoma cells, but not B16-F1 cells, expressed high concentrations of HA after stimulation with lactate. We propose that components of the tumor microenvironment (e.g., lactate) can induce melanoma cells to express HA and thus acquire an aggressive phenotype.

The role of hyaluronic acid in wound healing: assessment of clinical evidence

Hyaluronic acid (hyaluronan), a naturally occurring polymer within the skin, has been extensively studied since its discovery in 1934. It has been used in a wide range of medical fields as diverse as orthopedics and cosmetic surgery, but it is in tissue engineering that it has been primarily advanced for treatment. The breakdown products of this large macromolecule have a range of properties that lend it specifically to this setting and also to the field of wound healing. It is non-antigenic and may be manufactured in a number of forms, ranging from gels to sheets of solid material through to lightly woven meshes. Epidermal engraftment is superior to most of the available biotechnologies and, as such, the material shows great promise in both animal and clinical studies of tissue engineering. Ongoing work centers around the ability of the molecule to enhance angiogenesis and the conversion of chronic wounds into acute wounds.

Hyaluronan synthesis induces microvillus-like cell surface protrusions

Hyaluronan synthases (HASs) are plasma membrane enzymes that simultaneously elongate, bind, and extrude the growing hyaluronan chain directly into extracellular space. In cells transfected with green fluorescent protein (GFP)-tagged Has3, the dorsal surface was decorated by up to 150 slender, 3-20-microm-long microvillus-type plasma membrane protrusions, which also contained filamentous actin, the hyaluronan receptor CD44, and lipid raft microdomains. Enzymatic activity of HAS was required for the growth of the microvilli, which were not present in cells transfected with other GFP proteins or inactive GFP-Has3 mutants or in cells incubated with exogenous soluble hyaluronan. The microvilli induced by HAS3 were gradually withered by introduction of an inhibitor of hyaluronan synthesis and rapidly retracted by hyaluronidase digestion, whereas they were not affected by competition with hyaluronan oligosaccharides and disruption of the CD44 gene, suggesting independence of hyaluronan receptors. The data bring out the novel concept that the glycocalyx created by dense arrays of hyaluronan chains, tethered to HAS during biosynthesis, can induce and maintain prominent microvilli.

Immunologic roles of hyaluronan

Hyaluronan (HA), a large glycosaminoglycan composed of D-N-acetylglucosamine and D-glucuronic acid, is expressed in virtually all tissues and has long been considered to serve as a structural component or filling material in the tissue interstitium (Filler Theory). This idea was revised with the discovery of HA-binding proteins that introduced the concept that HA may also serve as an adhesive substrate for cellular trafficking (Adhesion Theory). Most recently, it has been shown that HA fragments can deliver maturational signals to dendritic cells (DCs) and high molecular weight HA polymers can deliver costimulatory signals to T-cells (Signaling Theory). Thus, HA may represent an important component of the immune system. Recently, we have evaluated the impact of HA on Langerhans cell (LC) maturation and migration using a novel peptide inhibitor of HA function, termed Pep-1 (GAHWQFNALTVR). As skin-specific members of the DC family, LCs are crucial for the initiation of cutaneous immune responses. Local injections of Pep-1 prevented hapten-induced LC migration from the epidermis, providing the first experimental evidence that HA facilitates their emigration. Moreover, Pep-1 also significantly inhibited the hapten-induced maturation of LCs in vivo as assessed by cell morphology, costimulatory molecule expression, and their ability to induce proliferation of allogeneic T-cells. HA therefore has dual functionality to facilitate LC migration and maturation, the two critical events for the initiation of adaptive immune responses. Finally, we have observed that DC-dependent, antigen-specific T-cell proliferation and cytokine secretion is blocked by Pep-1. These results have revealed a previously unrecognized role for HA in antigen presentation. Thus, far from an inert structural biopolymer, HA represents a multifunctional carbohydrate mediator of immune processes.

Differential regulation of hyaluronic acid synthase isoforms in human saphenous vein smooth muscle cells: possible implications for vein graft stenosis

Autologous saphenous vein bypass grafts (SVG) are frequently compromised by neointimal thickening and subsequent atherosclerosis eventually leading to graft failure. Hyaluronic acid (HA) generated by smooth muscle cells (SMC) is thought to augment the progression of atherosclerosis. The aim of the present study was (1) to investigate HA accumulation in native and explanted arterialized SVG, (2) to identify factors that regulate HA synthase (HAS) expression and HA synthesis, and (3) to study the function of the HAS2 isoform. In native SVG, expression of all 3 HAS isoforms was detected by RT-PCR. Histochemistry revealed that native and arterialized human saphenous vein segments were characterized by marked deposition of HA in association with SMC. Interestingly, in contrast to native SVG, cyclooxygenase (COX)-2 expression by SMC and macrophages was detected only in arterialized SVG. In vitro in human venous SMC HAS isoforms were found to be differentially regulated. HAS2, HAS1, and HA synthesis were strongly induced by vasodilatory prostaglandins via Gs-coupled prostaglandin receptors. In addition, thrombin induced HAS2 via activation of PAR1 and interleukin 1beta was the only factor that induced HAS3. By small interfering RNA against HAS2, it was shown that HAS2 mediated HA synthesis is critically involved in cell cycle progression through G1/S phase and SMC proliferation. In conclusion, the present study shows that HA-rich extracellular matrix is maintained after arterialization of vein grafts and might contribute to graft failure because of its proproliferative function in venous SMC. Furthermore, COX-2-dependent prostaglandins may play a key role in the regulation of HA synthesis in arterialized vein grafts.

Extracellular matrix in ovarian follicular development and disease

The ovarian follicle contains several different cell types and separate compartments and undergoes substantial development during its growth and maturation. Extracellular matrix (ECM) could be expected to play a major role in these processes. Most research on ECM in follicles has focused on the follicular basal lamina and its changing composition during folliculogenesis and on the specialised matrix formed at ovulation by the cumulus cells surrounding the oocyte and the zona pellucida. We review these aspects. Few naturally occurring gene mutations have identified unique roles for ECM molecules in follicular function. Presumably, any mutations leading to reduced fertility are eliminated quickly by natural selection and, when mutations are not eliminated, considerable redundancy occurs to ensure successful reproduction. In mice, in which the genome can be easily manipulated, the modification of matrix components associated with cumulus and oocytes has often resulted in partial infertility, suggesting redundancy. We provide an update of basal lamina components focusing on newer discoveries. In addition, we review matrix associated with the occyte and cumulus cells (excluding the zona pellucida) and other components of ECM. Where possible, we examine evidence for the role of the ECM in follicular development and diseases.

Plasma membrane residence of hyaluronan synthase is coupled to its enzymatic activity

Hyaluronan is a multifunctional glycosaminoglycan up to 10(7) Da molecular mass produced by the integral membrane glycosyltransferase, hyaluronan synthase (HAS). When expressed in keratinocytes, N-terminally tagged green fluorescent protein-HAS2 and -HAS3 isoenzymes were found to travel through endoplasmic reticulum (ER), Golgi, plasma membrane, and endocytic vesicles. A distinct enrichment of plasma membrane HAS was found in cell protrusions. The total turnover time of HAS3 was 4-5 h as judged by the green fluorescent protein signal decay and hyaluronan synthesis inhibition in cycloheximide-treated cells. The transfer from ER to Golgi took about 1 h, and the dwell time on the plasma membrane was less than 2 h in experiments with a relief and introduction, respectively, of brefeldin A. Constructs of HAS3 with 16- and 45-amino-acid C-terminal deletions mostly stayed within the ER, whereas a D216A missense mutant was localized within the Golgi complex but not the plasma membrane. Both types of mutations were almost or completely inactive, similar to the wild type enzyme that had its entry to the plasma membrane experimentally blocked by brefeldin A. Inhibition of hyaluronan synthesis by UDP-glucuronic acid starvation using 4-methyl-umbelliferone also prevented HAS access to the plasma membrane. The results demonstrate that 1) a latent pool of HAS exists within the ER-Golgi pathway; 2) this pool can be rapidly mobilized and activated by insertion into the plasma membrane; and 3) inhibition of HAS activity through mutation or substrate starvation results in exclusion of HAS from the plasma membrane.

Potential impact of a single nucleotide polymorphism in the hyaluronan synthase 1 gene in Waldenstrom's macroglobulinemia

The hyaluronan synthase 1 (HAS1) gene encodes a plasma membrane protein that synthesizes hyaluronan, an extracellular matrix molecule. Previously, in patients with Waldenstrom's macroglobulinemia (WM), we detected upregulation of HAS1 transcripts and identified aberrant splice variants of this gene. Aberrant splicing of HAS1 results from activation of cryptic splice sites. In turn, activation of cryptic donor and acceptor splice sites can be promoted by mutations occurring upstream of these sites and/or at the branch point of slicing. We measured the frequency of the HAS1 833A/G polymorphism (ie, single-nucleotide polymorphism; SNP) in patients with WM and healthy donors. Additionally, HAS1 gene expression was evaluated in the same group of patients. Our observations so far suggest that HAS1 833A/G SNPs contribute to aberrant splicing of this gene; this idea is supported by the fact that 833A/G SNP is located on an exonic splicing enhancer motif. Based on the results obtained thus far, we speculate that individuals with HAS1 833G/G genotype are predisposed toward aberrant HAS1 splicing and expression of HAS1 variants, resulting in an enhanced risk of developing WM. Study of a larger group of patients and healthy donors is needed to confirm these speculations and to evaluate the prognostic significance of these findings.

Gammadelta T cell-induced hyaluronan production by epithelial cells regulates inflammation

Nonhealing wounds are a major complication of diseases such as diabetes and rheumatoid arthritis. For efficient tissue repair, inflammatory cells must infiltrate into the damaged tissue to orchestrate wound closure. Hyaluronan is involved in the inflammation associated with wound repair and binds the surface of leukocytes infiltrating damaged sites. Skin gammadelta T cells play specialized roles in keratinocyte proliferation during wound repair. Here, we show that gammadelta T cells are required for hyaluronan deposition in the extracellular matrix (ECM) and subsequent macrophage infiltration into wound sites. We describe a novel mechanism of control in which gammadelta T cell-derived keratinocyte growth factors induce epithelial cell production of hyaluronan. In turn, hyaluronan recruits macrophages to the site of damage. These results demonstrate a novel function for skin gammadelta T cells in inflammation and provide a new perspective on T cell regulation of ECM molecules.

Hyaluronan synthase induction and hyaluronan accumulation in mouse epidermis following skin injury

Hyaluronan, a major extracellular matrix component in the epidermis, has been shown to control keratinocyte proliferation and differentiation in vitro. We assayed hyaluronan and hyaluronan synthases (has1-3) in mouse epidermis during fetal development, postnatal life, and trauma reaction in vivo. Hyaluronan increased in the epidermis when keratinocytes started to stratify on day E15, remained high until birth, and then rapidly declined, with corresponding changes in the mRNA levels of has2 and has3. The hyaluronan in adult mouse epidermis mainly resided around the orifices of the hair follicles, and the overall concentration was about one order of magnitude lower than in adult human epidermis. In adult mice, epidermal trauma caused by tape stripping rapidly increased hyaluronan, leading to a 6-fold increase in epidermal hyaluronan on day 3 following trauma. The hyaluronan response was associated with a strong induction of has2 and has3 mRNA, slightly higher CD44 expression, and considerable epidermal hyperplasia. The data show that the pre- and postnatal fluctuations in epidermal hyaluronan content correlate with the expression levels of has2 and has3. Stimulated hyaluronan synthesis through upregulated has expression is an inherent feature of the keratinocyte activation triggered by tissue trauma, and presumably important for a proper healing response.

The human hyaluronan synthase 2 gene is a primary retinoic acid and epidermal growth factor responding gene

Hyaluronan is an abundant and rapidly turned over matrix molecule between the vital cell layers of the epidermis and subject to large concentration changes associated with keratinocyte proliferation, migration, and differentiation induced by paracrine and endocrine factors like epidermal growth factor (EGF) and all-trans-retinoic acid (RA). We found that in REK cells EGF and all-trans-RA up-regulated hyaluronan synthase 2 (Has2) gene expression within 2 h 4-fold each and in HaCaT human immortal keratinocytes 8- and 33-fold, respectively. The first 10 kb of the human Has2 promoter were scanned in silico and in vitro for potential response elements of signal transducer and activator of transcription (STAT) or RA receptor (RAR) proteins. We identified a STAT-response element in the proximal promoter region and confirmed its functionality in response to EGF by chromatin immunoprecipitation (ChIP) assays. Direct in vitro binding of RARs to four RARE candidates within the Has2 promoter could not be observed at stringent gel shift conditions, but reporter gene assays demonstrated functionality of a complex of two of these RAREs located approximately 1200 bp upstream of the transcription start site. Moreover, ChIP assays using antibodies against nine nuclear proteins monitored all-trans-RA-dependent binding of RAR, retinoid X receptor, mediator protein, and RNA polymerase II and also histone 4 acetylation to a promoter region containing the complex RARE. Taken together, the human Has2 gene is a potent primary EGF and all-trans-RA responding gene with a complex regulation.

Regulation of hyaluronan synthases in mouse uterine cervix

We examined the expression pattern of hyaluronan synthase (HAS) mRNAs in the uterine cervix of pregnant mice. The expression levels of HAS-1 and -2 mRNAs peaked at delivery, whereas that of HAS-3 mRNA peaked on the 15th day of pregnancy. The regulation of HAS mRNA expression was examined in pregnant mouse uterine cervical fibroblasts. The expression of HAS-1, -2, and -3 mRNAs was significantly augmented by interleukin-1beta (IL-1beta). Progesterone significantly interfered with expression of HAS-1 and -2 mRNAs, but significantly increased the expression of HAS-3 mRNA. Low-molecular-weight hyaluronan significantly enhanced only the expression of HAS-1 mRNA. These results indicate that HAS in the uterine cervix is regulated in a complex manner by IL-1beta, progesterone, and low-molecular-weight hyaluronan, of which changes in the cervical tissue and serum closely participate in uterine cervical ripening and/or inflammation.

Fibroblast growth factor-2 regulates the synthesis of hyaluronan by human periodontal ligament cells

Basic fibroblast growth factor (FGF-2) can enhance biological potentials of periodontal ligament cells and its topical application induces considerable periodontal tissue regeneration in vivo. In this study, we examined the effect of FGF-2 on the production of hyaluronan (HA), an extracellular matrix playing important roles in homeostasis and inflammatory/wound healing responses, by human periodontal ligament (HPDL) cells. An inhibition binding-protein assay revealed that FGF-2 significantly increased HA production by HPDL cells in a dose dependent manner. Analysis by HPLC revealed that in conditioned medium of FGF-2-treated HPDL cells HA had a higher molecular mass, compared to that of untreated HPDL cells. RT-PCR analysis revealed the enhancement of mRNA expression of hyaluronan synthase (HAS) 1 and HAS 2, both of which contribute to the production of HA with a high molecular mass, but not HAS 3 in the FGF-2-treated HPDL cells. In contrast, three isoforms of hyaluronidase (HYAL) transcript were unchanged in the FGF-2-treated HPDL cells. These results provide new evidence for the possible involvement of FGF-2 in the regulation of HA production and its appreciable roles in not only homeostasis but also regeneration of periodontal tissues.

Intracellular hyaluronan in arterial smooth muscle cells: association with microtubules, RHAMM, and the mitotic spindle

Although considered a pericellular matrix component, hyaluronan was recently localized in the cytoplasm and nucleus of proliferating cells, supporting earlier reports that hyaluronan was present in locations such as the nucleus, rough endoplasmic reticulum, and caveolae. This suggests that it can play roles both inside and outside the cell. Hyaluronan metabolism is coupled to mitosis and cell motility, but it is not clear if intracellular hyaluronan associates with cytoskeletal elements or plays a structural role. Here we report the distribution of intracellular hyaluronan, microtubules, and RHAMM in arterial smooth muscle cells in vitro. The general distribution of intracellular hyaluronan more closely resembled microtubule staining rather than actin filaments. Hyaluronan was abundant in the perinuclear microtubule-rich areas and was present in lysosomes, other vesicular structures, and the nucleolus. Partially fragmented fluorescein-hyaluronan was preferentially translocated to the perinuclear area compared with high-molecular-weight hyaluronan. In the mitotic spindle, hyaluronan colocalized with tubulin and with the hyaladherin RHAMM, a cell surface receptor and microtubule-associated protein that interacts with dynein and maintains spindle pole stability. Internalized fluorescein-hyaluronan was also seen at the spindle. Following telophase, an abundance of hyaluronan near the midbody microtubules at the cleavage furrow was also noted. In permeabilized cells, fluorescein-hyaluronan bound to RHAMM-associated microtubules. These findings suggest novel functions for hyaluronan in cellular physiology.

The hyaluronan synthesis inhibitor 4-methylumbelliferone prevents keratinocyte activation and epidermal hyperproliferation induced by epidermal growth factor

Since excessive epidermal hyaluronan is associated with hyperproliferative states and disturbed terminal differentiation of the keratinocytes, we hypothesized that 4-methylumbelliferone (4-MU), an inhibitor of hyaluronan synthesis, could counteract these phenotypic features. Cultured epidermal keratinocytes showed a concentration dependent, maximum 83% reduction of hyaluronan in the presence of 0.2-1.0 mM 4-MU, whereas less decline was seen in the synthesis of chondroitin and heparan sulfate. The reduced hyaluronan was associated with no apparent change in its molecular mass. The 4-MU-treated keratinocytes showed an accentuated epithelial morphology with a flat, round cell shape, increased stress fibers and large vinculin-positive adhesion plaques, cytoskeletal changes consistent with the markedly reduced migration rate observed in scratched monolayer cultures. High concentrations of 4-MU also caused a block in keratinocyte proliferation, reversible upon 4-MU withdrawal. In the epidermis of organotypic cultures, 4-MU prevented the hyaluronan accumulation and epidermal hypertrophy induced by epidermal growth factor. The present results concur with earlier data indicating that enhanced cell locomotion and proliferation are associated with hyaluronan synthesis in activated keratinocytes. Cell proliferation, however, was blocked more strongly than expected on the basis of the incomplete hyaluronan synthesis inhibition, and may represent a novel target of 4-MU. At any rate, 4-MU and equivalent hyaluronan synthesis inhibitors might be considered for situations where suppression of epidermal activation and hyperproliferation is warranted.

Hyaluronan participates in the epidermal response to disruption of the permeability barrier in vivo

Hyaluronan (hyaluronic acid, HA) is a glycosaminoglycan in the extracellular matrix of tissues that plays a role in cellular migration, proliferation and differentiation. Injury to the stratum corneum elicits an epidermal hyperproliferative response, a pathogenic feature in many cutaneous diseases including eczema and psoriasis. Because HA is abundant in the matrix between keratinocytes, we asked whether the presence of HA is required for epidermal hyperplasia to occur in response to barrier injury. Disruption of the stratum corneum, by acetone application on the skin of hairless mice, led to a marked accumulation of HA in the matrix between epidermal basal and spinous keratinocytes, and also within keratinocytes of the upper epidermis. To test whether HA may have a functional role in epidermal hyperplasia, we used Streptomyces hyaluronidase (StrepH), delivered topically, to degrade epidermal HA and blunt the accumulation of epidermal HA after acetone. StrepH signficantly reduced epidermal HA levels, and also significantly inhibited the development of epidermal hyperplasia. This reduction in epidermal thickness was not attributable to any decrease in keratinocyte proliferation, but rather to an apparent acceleration in terminal differentiation (ie, increased keratin 10 and filaggrin expression). Overall, the data show that HA is a significant participant in the epidermal response to barrier injury.

Elevated transcript level of hyaluronan synthase1 gene correlates with poor prognosis of human colon cancer

Hyaluronan plays important roles in the complex processes of tumor invasion and metastasis. It is now known that three hyaluronan synthase (HAS) isoforms catalyze hyaluronan synthesis, which raises the question of how they are involved in malignant tumor progression. In this study, we examined the correlation between tumor progression and transcriptional levels of three HAS isoforms in specimens of human colon cancers. Tumor tissues from 31 patients with different diagnostic grades were assessed to determine the level of each HAS isoform by real time RT-PCR. The mean expression coefficients for HAS1, HAS2 and HAS3 in the cancerous parts were 0.82-, 0.91- and 1.22-fold, respectively; of those in the noncancerous parts at Dukes' stage A; 1.00-, 0.95- and 1.06-fold, respectively, at stage B; and 1.95-, 1.16- and 1.19-fold, respectively, at stage C. In survival analysis, a significant correlation was observed between poor survival and the HAS1 transcript level. When the ratio of tumor to normal tissue in the HAS1 level was compared with that of the HA receptor transcript level, there was a positive correlation with that of the CD44 variant 6 level at Dukes' stage C. Our current results therefore suggest that HAS1 plays a role in the malignant progression of human colon cancer cells.

Differential Regulation by IL-1β and EGF of Expression of Three Different Hyaluronan Synthases in Oral Mucosal Epithelial Cells and Fibroblasts and Dermal Fibroblasts: Quantitative Analysis Using Real-Time RT-PCR

Using "real-time RT-PCR", we assessed the expression of three different hyaluronan synthase genes, HAS1, HAS2, and HAS3, by measuring their mRNA amounts in cultured human oral mucosal epithelial (COME) cells, oral mucosal fibroblasts, and dermal fibroblasts, and investigated the effects of interleukin-1beta (IL-1beta) and epidermal growth factor (EGF). When COME cells were treated with IL-1beta or EGF, early and marked increases and subsequent rapid decreases were observed for all HAS genes and, moreover, actual changes in hyaluronan synthesis subsequently occurred. The effects of IL-1beta stimulation were concentration-dependent and the maximal response to the EGF stimulation was observed at a low concentration (0.1 ng per mL). When two different types of fibroblasts were treated with IL-1beta or EGF, increased expression with different degrees and rates of three different HAS genes and subsequent increased synthesis of hyaluronan were also observed. In addition, HAS1 gene expression was not detectable in the mucosal fibroblasts, while weak HAS3 gene expression was detected in the dermal fibroblasts. Taken together, it is likely that the regulation of the expression of the three different HAS genes is different between oral mucosa and skin, which may be of significance for elucidating some of the differences between these tissues in wound healing.

Role of hyaluronan and reactive oxygen species in tissue kallikrein-mediated epidermal growth factor receptor activation in human airways

In human airways, oxidative stress-induced submucosal gland cell hypertrophy and hyperplasia, histological features of chronic bronchitis, have been linked to epidermal growth factor receptor (EGFR) activation. To explore mechanisms of oxidative stress-induced EGFR activation and signaling, primary cultures of human tracheal submucosal gland (SMG) cells were used to assess EGFR ligand release, EGFR phosphorylation, p44/42 MAPK phosphorylation, and mucin 5AC synthesis in response to reactive oxygen species generated by xanthine/xanthine oxidase (X/XO). Exposure to X/XO increased release of epidermal growth factor (EGF) from these cells, thereby activating EGFR, phosphorylating MAPK, and increasing mucin 5AC production. The importance of EGF was confirmed by transfection of small interfering RNA inhibiting pro-EGF production, which resulted in inhibition of EGFR and MAPK phosphorylation despite X/XO exposure. Blocking signaling by using specific protease inhibitors showed that tissue kallikrein (TK) processed pro-EGF in response to X/XO. Airway TK is bound and inactivated by luminal hyaluronan (HA), and treatment of submucosal gland cells with X/XO induced HA depolymerization and TK activation. These events were blocked by reactive oxygen species scavengers and addition of exogenous excess HA and TK inhibitors. Thus, HA plays a crucial role in regulating airway TK activity and thereby TK-mediated release of active EGF from human SMG cells. Sustained HA depolymerization is expected to cause TK activation, EGF release, and EGFR signaling and to lead to SMG cell hypertrophy and hyperplasia as well as mucus hypersecretion with subsequent airflow obstruction.

Induction of hyaluronic acid synthase 2 (HAS2) in human vascular smooth muscle cells by vasodilatory prostaglandins

Hyaluronic acid (HA) is a prominent constituent of the extracellular matrix of atherosclerotic vascular lesions in humans known to modulate vascular smooth muscle phenotype. The regulation of HA synthesis by vasodilatory prostaglandins was analyzed in human arterial smooth muscle cells (SMCs). The prostacyclin analogue, iloprost (100 nmol/L), markedly increased pericellular formation of HA coats and HA secretion into the cell culture medium in human arterial SMCs (8.7+/-1.6-fold). Expression of HA synthase 2 (HAS2) was determined by semiquantitative RT-PCR and found to be strongly upregulated at concentrations of iloprost between 1 and 100 nmol/L after 3 hours. Furthermore, endogenous cyclooxygenase-2 (COX2) activity was required for basal expression of HAS2 mRNA in SMCs in vitro. Total HA secretion in response to iloprost was markedly decreased by RNA interference (RNAi), specific for HAS2. In addition, siRNA targeting HAS2 strongly increased the spreading of human SMCs compared with mock-transfected cells. HAS2 mRNA levels were also stimulated by a selective prostacyclin receptor (IP) agonist, cicaprost (10 nmol/L), prostaglandin E(2) (10 nmol/L), and the EP(2) receptor agonist, butaprost (1 micromol/L). Induction of HAS2 mRNA and HA synthesis by prostaglandins was mimicked by stable cAMP analogues and forskolin. In human atherectomy specimens from the internal carotid artery, HA deposits and COX2 expression colocalized frequently. In addition, strong EP(2) receptor expression was detected in SMCs in HA-rich areas. Therefore, upregulation of HAS2 expression via EP(2) and IP receptors might contribute to the accumulation of HA during human atherosclerosis, thereby mediating proatherosclerotic functions of COX2.

Selective expression and functional characteristics of three mammalian hyaluronan synthases in oncogenic malignant transformation

Malignant transformation of fibroblasts and epithelial cells is often accompanied by increased hyaluronan production and accumulation. Despite recent progress in the study of hyaluronan biosynthesis, the mechanisms underlying the transformation-induced overproduction of hyaluronan have not been elucidated. Here we report that activity and transcriptional levels of hyaluronan synthase (HAS) significantly increased after oncogenic malignant transformation of a rat 3Y1 fibroblast cell line. Of three HAS isoforms (HAS1, HAS2, and HAS3), only HAS2 gene expression was increased in the v-Ha-ras transformed 3Y1 cells, which show less malignancy. In contrast, both HAS1 and HAS2 expressions were elevated in the highly malignant cells transformed with v-src and/or v-fos. To assess the contribution of HAS expression to the oncogenic malignant transformation, we established stable cell transfectants expressing sense and antisense HAS genes. Antisense suppression of the HAS2 expression significantly decreased hyaluronan production in the cells transformed by the oncogenic v-Ha-ras and eventually led to a reduction in tumorigenicity in the rat peritoneum. The introduction of the HAS1 and HAS2 genes promoted the growth of subcutaneous tumors in a manner dependent on the levels of hyaluronan synthesis. Significant growth promotion was observed within a wide range of HAS1 expression. In contrast, the growth stimulation was only seen within a narrow range of HAS2 expression, and high levels of HAS2 expression even inhibited tumor growth. These results suggest that proper regulation of the expression of each HAS isoform is required for optimal malignant transformation and tumor growth.

Keratinocyte growth factor stimulates migration and hyaluronan synthesis in the epidermis by activation of keratinocyte hyaluronan synthases 2 and 3

Keratinocyte growth factor (KGF) activates keratinocyte migration and stimulates wound healing. Hyaluronan, an extracellular matrix glycosaminoglycan that accumulates in wounded epidermis, is known to promote cell migration, suggesting that increased synthesis of hyaluronan might be associated with the KGF response in keratinocytes. Treatment of monolayer cultures of rat epidermal keratinocytes led to an elongated and lifted cell shape, increased filopodial protrusions, enhanced cell migration, accumulation of intermediate size hyaluronan in the culture medium and within keratinocytes, and a rapid increase of hyaluronan synthase 2 (Has2) mRNA, suggesting a direct influence on this gene. In stratified, organotypic cultures of the same cell line, both Has2 and Has3 with the hyaluronan receptor CD44 were up-regulated and hyaluronan accumulated in the epidermis, the spinous cell layer in particular. At the same time the expression of the early differentiation marker keratin 10 was inhibited, whereas filaggrin expression and epidermal permeability were less affected. The data indicate that Has2 and Has3 belong to the targets of KGF in keratinocytes, and support the idea that enhanced hyaluronan synthesis acts an effector for the migratory response of keratinocytes in wound healing, whereas it may delay keratinocyte terminal differentiation.

Pericellular matrix formation by renal tubule epithelial cells in relation to crystal binding

BACKGROUND/AIM

Retention of crystals in the kidney ultimately leads to renal stone formation. Hyaluronan (HA) has been identified as binding molecule for calcium oxalate monohydrate crystals. The association of high molecular mass (M(r)) HA with cell surface receptors such as CD44 gives rise to pericellular matrix (PCM) formation by many eukaryotic cells in culture. Here, we study the ability of several renal tubular cell lines to assemble PCMs and to synthesize high-M(r) HA during proliferation in relation to crystal retention.

METHODS

PCM assembly by MDCK-I, MDCK-II, and LLC-PK1 cells was visualized by particle exclusion assay. Metabolic labeling studies were performed to estimate the cellular production of HA. The expression of CD44 and HA was studied using fluorescent probes, and crystal binding was quantified with radiolabeled calcium oxalate monohydrate.

RESULTS

PCMs were formed, and HA was expressed by most MDCK-I and some MDCK-II, but not by LLC-PK1 cells. All cell types expressed CD44 at their apical surface. MDCK-I and MDCK-II cells secreted, respectively, 14.7 +/- 1.6 and 0.5 +/- 0.2 pmol [3H]glucosamine incorporated in high-M(r) HA, whereas LLC-PK1 cells did not secrete HA. Streptomyces hyaluronidase treatment significantly decreased crystal binding (microg/cm2) to MDCK-I cells (from 8.6 +/- 0.4 to 3.9 +/- 0.9), but hardly to MDCK-II cells (from 10.2 +/- 0.2 to 9.6 +/- 0.1) or LLC-PK1 cells (from 10.2 +/- 0.8 to 9.9 +/- 0.3).

CONCLUSIONS

There are various forms of crystal binding to renal tubular cells in culture. Crystal attachment to MDCK-I and some MDCK-II cells involves PCM assembly that requires high-M(r) HA synthesis. HA production and PCM formation do not play a role in crystal binding to LLC-PK1 and the majority of MDCK-II cells. It remains to be determined which form of binding is involved in renal stone disease.

The human hyaluronan synthase genes: genomic structures, proximal promoters and polymorphic microsatellite markers

The glycosaminoglycan (GAG) hyaluronan (HA) is a key component of the vertebrate extracellular matrix (ECM) and is synthesised by the HA synthase (HAS) enzymes HAS1, HAS2 and HAS3 at the plasma membrane. Accumulating evidence emphasises the relevance of HA metabolism in an increasing number of processes of clinical interest including renal fibrosis and peritoneal mesothelial wound healing. In the present study, the genomic sequences and organisation of the genes encoding the human HAS isoforms were deduced, in silico, from reference cDNA and genomic sequence data. These data were confirmed in vitro by sequencing of PCR-amplified HAS exons and flanking genomic sequences, comparison with sequence data for the corresponding murine Has orthologues, rapid amplification of 5' cDNA ends analysis and luciferase reporter assays on putative proximal promoter sequences. The HAS1 gene comprised five exons, with the translation start site situated 9bp from the 3' end of exon 1. In contrast, the genomic structures for HAS2 and both HAS3 variants spanned four exons, exon 1 forming a discrete 5'-untranslated region (5'-UTR) and the translation start site lying at nucleotide 1 of exon 2. Dinucleotide microsatellite loci were identified in intron 1 of HAS1 and HAS2, and immediately upstream of the HAS3 gene and their utility as linkage markers demonstrated in genomic DNA (gDNA) studies. We thus present a comprehensive resource for mutation detection screening of all HAS exons and/or linkage analysis of each HAS gene in a variety of disorders for which they are attractive candidates.

Regulation of hyaluronan secretion into rabbit synovial joints in vivo by protein kinase C

Hyaluronan (HA) is important for joint cavitation, lubrication, volume regulation and synovial fluid drainage but little is known about the regulation of joint HA synthesis/secretion in vivo. We investigated whether HA secretion into joints in vivo can be regulated by protein kinase C (PKC). Secretion into the knee joint cavity of anaesthetised rabbits was measured over 6 h by washout and chromatography. Joints received intra-articular injections of Ringer vehicle (control) or an activator of classical PKC isoforms, phorbol-12-myristate-13-acetate (PMA), at 20-2000 ng ml(-1). The effects of PKC inhibition by bisindolylmaleimide (BIM) and protein synthesis inhibition by cycloheximide (CX) on basal and stimulated HA secretion were also studied. The endogenous HA mass, 181+/-8 microg (n=26, mean +/- S.E.M.), and basal secretion rate, 4.4+/-0.4 microg h(-1), indicated a turnover time of 41 h. Secretion rate showed a dose-dependent response to PMA (n=30), rising 5-fold to 21.7+/-5.0 microg h(-1) (n=5) at 2000 ng ml(-1) PMA (P<0.0001, one-way ANOVA). PMA-induced stimulation was partially suppressed by CX (HA secretion: 5.8+/-1.7 microg h(-1), n=8, P<0.01) and totally blocked by BIM (HA secretion: 3.2+/-0.6 microg h(-1), n=9, P<0.001). Basal HA secretion was unaffected by CX over 6 h (4.2+/-0.7 microg h(-1), n=8) but was reduced by 29 % by BIM (3.1+/-0.6 microg h(-1), n=10, P=0.03). It is concluded that: (1) PKC can stimulate HA secretion into joints in vivo through mechanisms involving protein synthesis de novo as well as phosphorylation; (2) basal HA secretion is only partially PKC dependent; and (3) hyaluronan synthase turnover time is >6 h in vivo, which is slower than in vitro (<2-3 h).

Hoxb13 knockout adult skin exhibits high levels of hyaluronan and enhanced wound healing

In contrast to adult cutaneous wound repair, early gestational fetal cutaneous wounds heal by a process of regeneration, resulting in little or no scarring. Previous studies indicate that down-regulation of HoxB13, a member of the highly conserved family of Hox transcription factors, occurs during fetal scarless wound healing. No down-regulation was noted in adult wounds. Here, we evaluate healing of adult cutaneous wounds in Hoxb13 knockout (KO) mice, hypothesizing that loss of Hoxb13 in adult skin should result in enhanced wound healing. Tensiometry was used to measure the tensile strength of incisional wounds over a 60-day time course; overall, Hoxb13 KO wounds are significantly stronger than wild-type (WT). Histological evaluation of incisional wounds shows that 7-day-old Hoxb13 KO wounds are significantly smaller and that 60-day-old Hoxb13 KO wounds exhibit a more normal collagen architecture compared with WT wounds. We also find that excisional wounds close at a faster rate in Hoxb13 KO mice. Biochemical and histochemical analyses show that Hoxb13 KO skin contains significantly elevated levels of hyaluronan. Because higher levels of hyaluronan and enhanced wound healing are characteristics of fetal skin, we conclude that loss of Hoxb13 produces a more "fetal-like" state in adult skin.

EGF upregulates, whereas TGF-beta downregulates, the hyaluronan synthases Has2 and Has3 in organotypic keratinocyte cultures: correlations with epidermal proliferation and differentiation

Hyaluronan, a major extracellular matrix molecule in the vital cell layers of skin epidermis, has been suggested to support proliferation and migration of keratinocytes, during challenges like wounding and inflammation. An organotypic keratinocyte culture originated from continuous rat epidermal keratinocyte cell line was subjected to the proliferative and antiproliferative growth factors epidermal growth factor and transforming growth factor beta, respectively, to study their influence on hyaluronan synthesis and epidermal morphology. Epidermal growth factor induced a 4-fold increase of epidermal hyaluronan concentration. This was associated with upregulation of the hyaluronan synthases Has2 and Has3, and the hyaluronan receptor CD44. 5-Bromo-2'-deoxyuridine labeling, basal cell height, and the thickness of vital epidermis were increased, reflecting the hyperplastic effects of epidermal growth factor. The expression of keratin 10 and the maturation of filaggrin were inhibited, and epidermal permeability barrier became less efficient, indicating compromised terminal differentiation by epidermal growth factor. In contrast, transforming growth factor beta reduced the content of hyaluronan and the mRNA of Has2 and Has3. At the same time, transforming growth factor beta suppressed keratinocyte proliferation and epidermal thickness, but retained intact differentiation. The results suggest that epidermal hyaluronan synthesis, controlled by epidermal growth factor and transforming growth factor beta through changes in the expression of Has2 and Has3, correlates with epidermal proliferation, thickness, and differentiation.

Hyaluronan synthase in trabecular meshwork cells

BACKGROUND/AIMS

Hyaluronan is present in the trabecular meshwork where it is involved in the pathophysiology of aqueous outflow environment. In this study, the expression and regulation of hyaluronan synthase (HAS), which is the enzyme synthesising hyaluronan, in trabecular meshwork cells were investigated.

METHODS

Cultured bovine trabecular meshwork cells (BTMCs) were used. HAS expression in BTMCs was examined by RT-PCR. The effects of transforming growth factor beta (TGF-beta) and platelet derived growth factor BB (PDGF-BB) on HAS expression in BTMCs were examined by quantitative RT-PCR. The HAS2 expression by TGF-beta and PDGF-BB at the protein level was also confirmed immunohistochemically. The production of hyaluronan from BTMCs was detected by high performance liquid chromatography (HPLC).

RESULTS

Three HAS isoforms were expressed in BTMCs at the mRNA level. Among HAS isoforms, only the expression of HAS2 mRNA was increased by the administration of TGF-beta or PDGF-BB. HAS2 upregulation by these growth factors was also confirmed at the protein level. Further, hyaluronan production from BTMCs was stimulated by TGF-beta or PDGF-BB.

CONCLUSION

Expression of HAS in trabecular meshwork may maintain the hyaluronan content in the aqueous outflow pathway. Its production is regulated by TGF-beta and PDGF-BB. The regulation of the expression of HAS in trabecular meshwork might be useful for modulating the aqueous outflow environment.

Relationship between lymph and tissue hyaluronan in skin and skeletal muscle

The size of hyaluronan was compared between tissue and lymph using a combination of agarose gel electrophoresis and radiometric assay. Prenodal lymph was collected from heel skin and the gastrocnemius muscle in anesthetized rabbits. The major fraction of hyaluronan in both tissues had a molecular weight >4 million. Lymph contained primarily low-molecular-weight hyaluronan (<0.79 x 10(6)), which was absent from tissue. Volume loading produced a preferential increase in the flux of low-molecular-weight hyaluronan, indicating that tissue contains a small quantity of mobile, low-molecular-weight hyaluronan. The maximum daily removal of hyaluronan by lymph was <1% of the tissue content. The amount of lysosomal hyaluronidase activity in tissue was more than enough to account for a rapid turnover of hyaluronan. The data support the conclusion that lymph drainage is not significant in the normal catabolism of hyaluronan and may represent a small amount that becomes detached from the pericellular and extracellular matrixes.

Changed lamellipodial extension, adhesion plaques and migration in epidermal keratinocytes containing constitutively expressed sense and antisense hyaluronan synthase 2 (Has2) genes

Hyaluronan is a major component of the epidermal extracellular matrix, is actively synthesized by keratinocytes and shows fast matrix turnover in the stratified epithelium. We probed the importance of hyaluronan synthesis in keratinocytes by establishing cell lines carrying the exogenous hyaluronan synthase 2 (Has2) gene in sense and antisense orientations to increase and decrease their hyaluronan synthesis, respectively. Compared with cell lines transfected with the vector only, most clones containing the Has2 sense gene migrated faster in an in vitro wounding assay, whereas Has2 antisense cells migrated more slowly. Has2 antisense clones showed delayed entry into the S phase of cell cycle following plating, smaller lamellipodia and less spreading on the substratum. The decrease of hyaluronan on the undersurface of Has2 antisense cells was associated with an increased area of adhesion plaques containing vinculin. Exogenous hyaluronan added to the keratinocyte cultures had a minor stimulatory effect on migration after wounding but did not restore the reduced migratory ability of Has2 antisense cells. Hyaluronan decasaccharides that displace receptor bound hyaluronan in keratinocytes, and Streptomyces hyaluronidase sufficient to remove most cell surface hyaluronan had little effect on cell migration. The results suggest that the dynamic synthesis of hyaluronan directed by Has2, rather than the abundance of pericellular hyaluronan, controls keratinocyte migration, a cell function vital for the repair of squamous epithelia following wounding.

Abnormal accumulation of hyaluronan matrix diminishes contact inhibition of cell growth and promotes cell migration

Elevated hyaluronan biosynthesis and matrix deposition correlates with cell proliferation and migration. We ectopically expressed three isoforms of hyaluronan synthase (HAS1, HAS2, or HAS3) in nontransformed rat 3Y1 cells and observed a de novo, massive formation of a hyaluronan matrix that resulted in a partial loss of contact-mediated inhibition of cell growth and migration. All three HAS transfectants showed an enhanced motility in scratch wound assays, and a significant increase in their confluent cell densities. In high-density cultures, the HAS transfectants had a fibroblastic cell shape and markedly formed overlapping cell layers. This phenotype was more pronounced in the HAS2 transfectants than HAS1 or HAS3 transfectants, and occurred with significant alterations in the microfilament organization and N-cadherin distribution at the cell-cell border. Inhibition of a phosphatidylinositol 3-kinase (PI3-kinase) pathway resulted in reacquisition of the normal phenotype of HAS2 transfectants, suggesting that the intracellular PI3-kinase signaling regulates diminution of contact inhibition induced by formation of the massive hyaluronan matrix. Our observations suggest that hyaluronan and its matrix can modulate contact inhibition of cell growth and migration, and provide evidence for functional differences between hyaluronan synthesized by the different HAS proteins.

Hyaluronan synthase 3 regulates hyaluronan synthesis in cultured human keratinocytes

Three human hyaluronan synthase genes (HAS1, HAS2, and HAS3) have been cloned, but the functional differences between these HAS genes remains obscure. The purpose of this study was to examine which of the HAS genes are selectively regulated in epidermis. We examined the relation of changes between hyaluronan production and HAS gene expression when cytokines were added to cultured human keratinocytes. Interferon-gamma increased hyaluronan production whereas transforming growth factor beta decreased it. Both cytokines affected preferentially high-molecular-mass (> 106 Da) hyaluronan production. Consistent with the change in hyaluronan synthesis, we found that interferon-gamma markedly upregulated HAS3 mRNA whereas transforming growth factor beta downregulated HAS3 transcript levels. The expression of HAS1 mRNA was not significantly affected by either cytokine, and HAS2 mRNA expression was undetectable under either basal or cytokine-stimulated conditions by northern blot using total RNA. Furthermore, in situ mRNA hybridization showed that mouse epidermal keratinocytes abundantly expressed HAS3 mRNA from the basal to the granular cell layers, suggesting that HAS3 functions in epidermis. These findings suggest that HAS3 gene expression plays a crucial role in the regulation of hyaluronan synthesis in the epidermis.

Hyaluronan enters keratinocytes by a novel endocytic route for catabolism

Hyaluronan synthesized in the epidermis has an exceptionally short half-life, indicative of its catabolism by epidermal keratinocytes. An intracellular pool of endogenously synthesized hyaluronan, from 1 to 20 fg/cell, inversely related to cell density, was observed in cultured rat epidermal keratinocytes. More than 80% of the intracellular hyaluronan was small (<90 kDa). Approximately 25% of newly synthesized hyaluronan was endocytosed by the keratinocytes and had a half-life of 2-3 h. A biotinylated aggrecan G(1) domain/link protein probe demonstrated hyaluronan in small vesicles of approximately 100 nm diameter close to the plasma membrane, and in large vesicles and multivesicular bodies up to 1300 nm diameter around the nucleus. Hyaluronan did not co-localize with markers of lysosomes. However, inhibition of lysosomal acidification with NH(4)Cl or chloroquine, or treating the cells with the hyaluronidase inhibitor apigenin increased intracellular hyaluronan staining, suggesting that it resided in prelysosomal endosomes. Competitive displacement of hyaluronan from surface receptors using hyaluronan decasaccharides, resulted in a rapid disappearance of this endosomal hyaluronan (t(12) approximately 5 min), indicating its transitory nature. The ultrastructure of the hyaluronan-containing vesicles, co-localization with marker proteins for different vesicle types, and application of specific uptake inhibitors demonstrated that the formation of hyaluronan-containing vesicles did not involve clathrin-coated pits or caveolae. Treatment of rat epidermal keratinocytes with the OX50 monoclonal antibody against the hyaluronan receptor CD44 increased endosomal hyaluronan. However, no CD44-hyaluronan co-localization was observed intracellularly unless endosomal trafficking was retarded by monensin, or cultivation at 20 degrees C, suggesting CD44 recycling. Rat epidermal keratinocytes thus internalize a large proportion of their newly synthesized hyaluronan into non-clathrin-coated endosomes in a receptor mediated way, and rapidly transport it to slower degradation in the endosomal/lysosomal system.