Culturing chick muscle cells on glycosaminoglycan substrates: attachment and differentiation

Mechanobiology of Hyaluronan: Connecting Biomechanics and Bioactivity in Musculoskeletal Tissues

Hyaluronan (HA) plays well-recognized mechanical and biological roles in articular cartilage and synovial fluid, where it contributes to tissue structure and lubrication. An understanding of how HA contributes to the structure of other musculoskeletal tissues, including muscle, bone, tendon, and intervertebral discs, is growing. In addition, the use of HA-based therapies to restore damaged tissue is becoming more prevalent. Nevertheless, the relationship between biomechanical stimuli and HA synthesis, degradation, and signaling in musculoskeletal tissues remains understudied, limiting the utility of HA in regenerative medicine. In this review, we discuss the various roles and significance of endogenous HA in musculoskeletal tissues. We use what is known and unknown to motivate new lines of inquiry into HA biology within musculoskeletal tissues and in the mechanobiology governing HA metabolism by suggesting questions that remain regarding the relationship and interaction between biological and mechanical roles of HA in musculoskeletal health and disease.

A regenerative niche for stem cells

Production of hyaluronic acid allows regenerative signaling in muscle stem cells after injury.

Functionalization of hyaluronic acid hydrogels with ECM-derived peptides to control myoblast behavior

Volumetric muscle loss (VML) occurs when skeletal muscle injury is too large for the body to fully self-repair. Typically, fibrotic tissue fills the void, which reduces muscle functionality and limb movement. Although a wide variety of natural and synthetic scaffolds have been studied with the purpose of providing the appropriate structural support, to date no scaffold has significantly restored muscle functionality after VML. Satellite cells, adult stem cells within the muscle capable of restoring smaller injuries, are sensitive to the stiffness and composition of the surrounding environment. Scaffolds that only address structural support are not sufficient to restore functionality and instead need to be designed to both promote satellite cell activation and prevent excessive fibroblast recruitment. The objective of this study was to design a scaffold that mimicked the regenerative environment and determine how the biomechanical properties differentially influence myogenic precursor and connective tissue cells. One of the main extracellular matrix (ECM) molecules upregulated during regeneration is hyaluronic acid (HA). Therefore, thiol-modified HA and poly(ethylene glycol) diacrylate hydrogels were generated and functionalized with peptides based on ECM known to influence regeneration, including fibronectin, laminin and tenascin-C. Scaffolds with different stiffness were created by varying HA content. The influence of HA stiffness and peptide functionalization on myogenic precursor and connective tissue cell proliferation, migration and gene expression was quantified. Our results indicated that HA hydrogels functionalized with the laminin peptide, IKVAV, show potential due to the enhanced promotion of myogenic cell behaviors including migration, proliferation and an increase in relevant transcription factors. STATEMENT OF SIGNIFICANCE: The goal of this study was to identify hyaluronic acid (HA) hydrogels with peptide and stiffness combinations that will direct muscle-derived cells towards regenerating phenotypes. While the interaction of skeletal muscle with RGD-functionalized HA hydrogels has been investigated, none of the other peptides described in this study had been used in the context of HA-based scaffolds and skeletal muscle-derived cells. Notably, the response of cells to variations in mechanics was dependent on ECM coating and lineage. The 3% HA functionalized with the laminin peptide, IKVAV, showed the most promise for future in vivo studies, as these hydrogels best promoted myoblast cell proliferation, attachment and spreading, enhanced migration over connective tissue cells and upregulated transcription factors associated with activated satellite cells.

Sericin accelerates the production of hyaluronan and decreases the incidence of polyspermy fertilization in bovine oocytes during in vitro maturation

Fetal bovine serum (FBS) has been widely used as a supplement in the maturation medium of bovine oocytes in vitro. However, serum contains many undefined factors and is potentially infectious to humans and animals. As a serum replacement, we evaluated the feasibility of using the silk protein, sericin, derived from the cocoons of silkworm. To examine the rates of oocyte maturation and fertilization, cumulus-oocyte complexes were cultured in TCM-199 supplemented with 0.01%, 0.05%, 0.1% or 0.15% sericin or 5% FBS. The sizes of the perivitelline space that might relate to polyspermy, the expressions of Has2 and CD44 mRNA, the amount of hyaluronan (hyaluronic acid: HA) contained in the oocytes and the rates of blastocyst formation following insemination were then compared between the oocytes cultured with 0.05% sericin and 5% FBS, because the polyspermy rates in oocytes cultured with 0.05% sericin were significantly lower than in those cultured with 5% FBS. After in vitro maturation (IVM), the mean size of the perivitelline space was significantly greater in oocytes cultured with sericin than in those cultured with FBS, although the rates of nuclear maturation, fertilization and blastocyst formation of oocytes under both IVM conditions were not significantly different. The expression of HAS2 and CD44 mRNA and the amount of HA in the denuded oocytes cultured with 0.05% sericin were significantly greater than in those cultured with FBS. These results indicate the feasibility of sericin as an alternative protein supplement for IVM in bovine oocytes.

Hyaluronan synthesis and myogenesis: a requirement for hyaluronan synthesis during myogenic differentiation independent of pericellular matrix formation

Exogenous hyaluronan is known to alter muscle precursor cell proliferation, migration, and differentiation, ultimately inhibiting myogenesis in vitro. The aim of the current study was to investigate the role of endogenous hyaluronan synthesis during myogenesis. In quantitative PCR studies, the genes responsible for synthesizing hyaluronan were found to be differentially regulated during muscle growth, repair, and pathology. Although all Has genes (Has1, Has2, and Has3) were differentially regulated in these models, only Has2 gene expression consistently associated with myogenic differentiation. During myogenic differentiation in vitro, Has2 was the most highly expressed of the synthases and increased after induction of differentiation. To test whether this association between Has2 expression and myogenesis relates to a role for Has2 in myoblast differentiation and fusion, C2C12 myoblasts were depleted of Has2 by siRNA and induced to differentiate. Depletion of Has2 inhibited differentiation and caused a loss of cell-associated hyaluronan and the hyaluronan-dependent pericellular matrix. The inhibition of differentiation caused by loss of hyaluronan was confirmed with the hyaluronan synthesis inhibitor 4-methylumbelliferone. In hyaluronan synthesis-blocked cultures, restoration of the pericellular matrix could be achieved through the addition of exogenous hyaluronan and the proteoglycan versican, but this was not sufficient to restore differentiation to control levels. These data indicate that intrinsic hyaluronan synthesis is necessary for myoblasts to differentiate and form syncytial muscle cells, but the hyaluronan-dependent pericellular matrix is not sufficient to support differentiation alone; additional hyaluronan-dependent cell functions that are yet unknown may be required for myogenic differentiation.

Hyaluronic acid, HAS1, and HAS2 are significantly upregulated during muscle hypertrophy

Hyaluronic acid (HA) is a component of the extracellular matrix (ECM) in most vertebrate tissues and is thought to play a significant role during development, wound healing, and regeneration. In vitro studies have shown that HA enhances muscle progenitor cell recruitment and inhibits premature myotube fusion, implicating a role for this glycosaminoglycan in functional repair. However, the spatiotemporal distribution of HA during muscle growth and repair was unknown. We hypothesized that inducing hypertrophy via synergist ablation would increase the expression of HA and the HA synthases (HAS1-HAS3). We found that HA and HAS1-HAS3 were significantly upregulated within the plantaris muscle in response to Achilles tenectomy. HA concentration significantly increased 2.8-fold after 2 days but decreased towards levels comparable to age-matched controls by 14 days. Using immunohistochemistry, we found the colocalization of HAS1-HAS3 with macrophages, blood vessel epithelia, and fibroblasts varied in response to time and/or tenectomy. At the level of gene expression, only HAS1 and HAS2 significantly increased with respect to both time and tenectomy. The profiles of additional genes that influence ECM composition during muscle repair, tenascin-C, type I collagen, the HA-degrading hyaluronidases (Hyal) and matrix metalloproteinases (MMP) were also investigated. Hyal1 and Hyal2 were highly expressed in skeletal muscle but did not change after tenectomy; however, indicators of hypertrophy, MMP-2 and MMP-14, were significantly upregulated from 2 to 14 days. These results indicate that HA levels dynamically change in response to a hypertrophic stimulus and various cells may participate in this mechanism of skeletal muscle adaptation.

Size of the perivitelline space and incidence of polyspermy in rabbit and hamster oocytes

Purpose

The size of the perivitelline space and the incidence of polyspermy were observed in ovulated and cultured oocytes from rabbits and hamsters with or without treatment by 4-methylumbelliferone (MU), an inhibitor of hyaluronic acid (HA) synthase, in order to examine the relationship between the incidence of polyspermy and the size of the perivitelline space. The amount of HA in the medium with MU-treated hamster oocytes was measured and compared with that in the medium with untreated oocytes.

Methods

The perivitelline space of oocytes with 1st polar bodies was measured by use of a micrometer under a microscope, and the incidence of polyspermy was observed in the oocytes after insemination. The amount of HA in the medium was examined using an enzyme-linked immunosorbent assay. The distribution of cortical granules was observed by staining with FITC-conjugated LCA.

Results

In both rabbit and hamster, the mean size of the perivitelline space was significantly smaller and the incidence of polyspermy was significantly higher in the cultured and MU-treated oocytes than in the ovulated and untreated oocytes. The mean amount of HA in the medium with MU-treated oocytes (8.96 pg) was significantly smaller than that in the medium with untreated oocytes (21.77 pg). The distribution of cortical granules did not differ among the ovulated, cultured, and MU-treated oocytes.

Conclusions

These findings suggest that the size of the perivitelline space is closely related to the incidence of polyspermy, and that the oocyte itself synthesizes and secretes the HA involved in the enlargement of the perivitelline space.

A transitional extracellular matrix instructs cell behavior during muscle regeneration

Urodele amphibians regenerate appendages through the recruitment of progenitor cells into a blastema that rebuilds the lost tissue. Blastemal formation is accompanied by extensive remodeling of the extracellular matrix. Although this remodeling process is important for appendage regeneration, it is not known whether the remodeled matrix directly influences the generation and behavior of blastemal progenitor cells. By integrating in vivo 3-dimensional spatiotemporal matrix maps with in vitro functional time-lapse imaging, we show that key components of this dynamic matrix, hyaluronic acid, tenascin-C and fibronectin, differentially direct cellular behaviors including DNA synthesis, migration, myotube fragmentation and myoblast fusion. These data indicate that both satellite cells and fragmenting myofibers contribute to the regeneration blastema and that the local extracellular environment provides instructive cues for the regenerative process. The fact that amphibian and mammalian myoblasts exhibit similar responses to various matrices suggests that the ability to sense and respond to regenerative signals is evolutionarily conserved.

Accumulation of Glycosaminoglycans in Radiation-induced Muscular Fibrosis

The content and biosynthesis of glycosaminoglycans (GAGs) were studied in the pig thigh muscle after acute local gamma-irradiation. Seven months following irradiation, the muscular tissue next to the irradiation cone was replaced by severe mutilating fibrosis delimited by an intermediary perifbrotic zone. Fibrosis, perifibrotic tissue and normal muscle, were sampled and incubated with [3H]glucosamine and [35S]sulphate, and GAGs were isolated following pronase digestion. Results showed a parallel increase of collagen and GAG content in perifibrotic and fibrotic tissues. Sulphated GAGs, heparan sulphate and dermatan sulphate were preferentially accumulated in fibrotic tissue, while the hyaluronic acid content increased only slightly. Synthesis of sulphated GAGs was more elevated in fibrotic tissue than in perifibrotic zone as compared with normal muscle. Seven months after irradiation well-developed fibrotic tissue continued to synthesize and to accumulate extracellular matrix macromolecules, indicating the invasive aspect of post-irradiation fibrosis.

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.

Topical hyaluronidase decreases hyaluronic acid and CD44 in human skin and in reconstituted human epidermis: evidence that hyaluronidase can permeate the stratum corneum

Hyaluronic acid (HA), a high molecular weight glycosaminoglycan of the extracellular matrix involved in growth, inflammation and wound healing, also contributes to the hydration and plastic properties of skin. Several drug and cosmetic formulations contain HA. We have initiated investigations that explore whether it is possible, by topical application, to modulate endogenous HA levels in skin. We developed a model epidermal culture system that exhibited a differentiated stratum corneum, and expressed HA and the HA receptor CD44, in a pattern similar to that observed in intact skin. Such in vitro skin equivalents are useful models for investigating the effect of topical drugs. HA and bacterial hyaluronidase were applied to the in vitro skin equivalent and to human skin. Their effects on endogenous HA and CD44 expression were examined using histochemical analysis. Topical HA treatment had no significant effect on HA or CD44 expression in either system. However, hyaluronidase decreased HA and CD44 expression in a dose-dependent manner in both the epidermal culture system and in skin. Apparently, HA is not able to permeate the epidermal culture system or human skin to a significant degree, but bacterial hyaluronidase does permeate both human skin and the culture system, depleting HA and decreasing CD44 expression. These effects were more prominent in the dermal than in the epidermal layers, suggesting that marked differences in HA metabolism exist in these two skin compartments. The ability of hyaluronidase to permeate the stratum corneum suggests that topical application may, additionally, be useful as a clinical modality.

Purification and lipid dependence of the recombinant hyaluronan synthases from Streptococcus pyogenes and Streptococcus equisimilis

The two hyaluronan synthases (HASs) from Streptococcus pyogenes (spHAS) and Streptococcus equisimilis (seHAS) were expressed in Escherichia coli as recombinant proteins containing His6 tails. Both enzymes were expressed as major membrane proteins, accounting for approximately 5-8% of the total membrane protein. Using nickel chelate affinity chromatography, the HASs were purified to homogeneity from n-dodecyl beta-D-maltoside extracts. High levels of HAS activity could be achieved only if the purified enzymes were supplemented with either bovine or E. coli cardiolipin (CL), although bovine CL gave consistently greater activity. Mass spectroscopic analysis revealed that the fatty acid compositions of these two CL preparations did not overlap. The two HAS enzymes showed similar but distinct activation profiles with the 10 other lipids tested. For example, phosphatidic acid and phosphatidylethanolamine stimulated seHAS, but not spHAS. Phosphatidylserine stimulated both enzymes. spHAS appears to be more CL-specific than seHAS, although both purified enzymes still contain endogenous CL that can not easily be removed. Both seHAS and spHAS were inhibited by phosphatidylcholine, sphingomyelin, and sulfatides and were not substantially stimulated by cerebrosides, phosphatidylglycerol, or phosphatidylinositol. With both HASs, CL increased the Km for UDP-GlcUA, but decreased the Km for UDP-GlcNAc and gave an overall stimulation of Vmax. A kinetic characterization of the two membrane-bound and purified HASs is presented in the accompanying paper (Tlapak-Simmons, V. L., Baggenstoss, B. A., Kumari, K., Heldermon, C., and Weigel, P. H. (1999) J. Biol. Chem. 274, 4246-4253). Both purified HASs became inactive after storage for approximately 5 days at 4 degreesC. Both purified enzymes also lost activity over 4-5 days when stored at -80 degreesC in the presence of CL, but reached a level of activity that then slowly decreased over a period of months. Although the purified enzymes stored in the absence of CL at -80 degreesC were much less active, the enzymes retained this same low level of activity for at least 5 weeks. When both spHAS and seHAS were stored without CL at -80 degreesC, even after 2 months, they could be stimulated by the addition of bovine CL to approximately 60% of the initial activity of the freshly purified enzyme.

Hyaluronan (hyaluronic acid) in human saliva

Hyaluronan (hyaluronic acid) is a glycosaminoglycan that functions as a constituent of ground substance, a mediator of cell proliferation and would healing, and that plays a prominent part in tumorigenesis as well as in embryogenesis. Its presence and possible role in saliva has been subjected to little study. Unstimulated and stimulated pure parotid and mixed saliva was obtained from 10 volunteers. The protein content of the samples was assayed and the hyaluronan concentration was evaluated by means of an enzyme immunosorbent-like assay using a hyaluronan-binding peptide. Stimulated whole saliva had the highest protein content (mean 1.26 mg/ml) followed by unstimulated parotid saliva (1.15 mg/ml), stimulated parotid saliva (0.95 mg/ml) and unstimulated whole saliva (0.93 mg/ml). Absolute hyaluronan concentrations were highest in unstimulated whole saliva (mean 459.2 ng (nanograms)/ml), and lowest in stimulated parotid saliva (82.7 ng/ml). When hyaluronan concentrations are expressed as ng/mg of protein, the highest are in the unstimulated whole saliva (mean 477.5 ng/mg protein) followed by stimulated parotid saliva (229.7 ng/mg), unstimulated parotid saliva (179.6 ng/mg) and stimulated whole saliva (159.9 ng/mg). There are wide variations in the levels of hyaluronan in human saliva depending on the type of saliva and the conditions at the time of collection. Regulation of hyaluronan metabolism represents an intricate balance between production and degradation, and it is unclear whether elevated concentrations of hyaluronan in response to tissue proliferation, regeneration or repair. The hyaluronan may contribute to the healing properties of saliva, assisting in protecting the oral mucosa and adding to the lubricating properties of saliva.

Acceleration of granulation tissue ingrowth by hyaluronic acid in artificial skin

Hyaluronic acid (HA), which is known to play an important role in wound healing, was incorporated in an artificial skin material and studied for its potential to create a wound bed which would support a skin graft. Collagen sponge based artificial skin was soaked in 0.3% HA in phosphate buffered saline and grafted onto skin defects in rats. Control grafts were soaked in normal saline solution. HA incorporated implants and control implants were simultaneously grafted onto wounds made on either side of the spine. To examine the effect of HA incorporation, the percentage area of cellular tuft infiltration and the number of capillaries present in the graft matrix were evaluated at 7 and 14 days after the operation. At postoperative day 7, there was a statistically significant difference in the number of capillaries in the matrix of the experimental versus the control implants. There was no difference in the percentage area of cellular tuft infiltration. At postoperative day 14, all implants exhibited better ingrowth of granulation tissue than at day 7. The differences between the experimental and control implants were statistically significant with respect to both the percentage area of cellular tuft infiltration and the number of capillaries. It is therefore concluded that in artificial skin HA incorporation accelerates the ingrowth of granulation tissue, making a more suitable graft bed.

Effects of hyaluronan on collagen fibrillar matrix contraction by fibroblasts

Hyaluronan, found in high concentrations in fetal tissues, appears to have a major role in preventing scar formation in fetal wounds. Nevertheless, its role in inhibiting wound contractures associated with scar formation has not been clearly demonstrated. Our current study evaluated the effects of hyaluronan using an in vitro floating collagen fibrillar matrix (CFM) contraction model. The results demonstrated that the contraction of CFM by fibroblasts was significantly reduced when high concentrations (> 1 mg/mL) of hyaluronan were present in the media. This phenomenon is unique to hyaluronan, because chondroitin sulfate was ineffective in this connection. Fibroblast migration and proliferation studies indicated that high concentrations of hyaluronan stimulated cell migration and had no cytotoxic effects. Some possible mechanisms by which high concentrations of hyaluronan reduced CFM contraction by fibroblasts were proposed. Because the viscosity of a hyaluronan solution is much greater than that of chondroitin sulfate, and this increases with concentration, we investigated whether this property in itself was an important factor in inhibiting CFM contraction. No direct correlation was found between the viscosity of glycosaminoglycans and their ability to reduce CFM contraction.

Investigation of the ability of several naturally occurring and synthetic polyanions to bind to and potentiate the biological activity of acidic fibroblast growth factor

The ability of several animal, plant, and bacterial derived polyanions (PAs) as well as synthetic PAs to compete with heparin for the binding of acidic fibroblast growth factor (aFGF) was correlated with their ability to potentiate the mitogenic and neurotrophic actions of this factor. Dextran sulphate, kappa-carrageenan, pentosan sulphate, polyanethole sulfonate, heparin, and fucoidin competed for the heparin binding site on aFGF at relatively low concentrations (< 50 micrograms/ml). lambda-carrageenan, iota-carrageenan, and polyvinyl sulphate exhibited lower affinity for aFGF, whereas hyaluronic acid, dermatan sulphate, chondroitin-6-sulphate, chondroitin-4-sulphate, and uncharged dextran displayed very low or no demonstrable affinity. Potentiation of the mitogenic action of aFGF for Balb/c 3T3 fibroblasts tended to be in general agreement with the aFGF binding affinity of the PAs. However, polyanethole sulfonate, the carrageenans, polyvinyl sulphate, fucoidin, and pentosan sulphate exerted a mitogenic action on the 3T3 cells that was independent of, and in addition to, the ability of these GAGs to potentiate the action of aFGF. The ability to potentiate the neurotrophic action of aFGF for E8 chick ciliary neurons was a general property of those PA with low or no activity in the mitogen assay. Thus hyaluronic acid, dermatan sulphate, chondroitin-4-sulphate, chondroitin-6-sulphate, and even unchanged dextran all potentiated aFGF induced neuronal survival. The differential effects of these PA in potentiating the biological activities of aFGF are discussed in relation to their ability to compete for the heparin-binding site of aFGF.

Ontogeny of hyaluronan secretion during early mouse development

The ontogeny of hyaluronan (HA) secretion during early mouse embryogenesis has been investigated using a biotin-labelled HA-binding complex from cartilage proteoglycan. HA is first secreted by visceral endoderm cells of the early egg cylinder on day 5.5 post coitum (p.c.), predominantly into the expanding yolk cavity. On day 6.5 p.c., HA is present in both the yolk and proamniotic cavities, but pericellular staining is restricted to the visceral endoderm and a population of embryonic ectoderm cells at the antimesometrial end of the proamniotic cavity. By the primitive streak stage, HA is secreted into the ectoplacental, exocoelomic, amniotic and yolk cavities, whilst the only cells exhibiting pericellular staining are those of the embryonic and extraembryonic mesoderm, including the allantois. Comparisons of HA-staining patterns of cultured whole blastocysts, microdissected trophectoderm fragments and immunosurgically isolated inner cell masses, revealed no trophoblast-associated HA secretion during outgrowth in vitro but significant synthetic activity by the endodermal derivatives of differentiating inner cell masses. To identify the cell lineages responsible for secretion of HA into the embryonic cavities and to investigate the origin of the HA observed around migrating mesoderm cells, day 7.5 p.c. primitive streak stage conceptuses were dissected into their various embryonic and extraembryonic cell lineages. HA secretion was observed after short-term suspension culture of mesoderm, embryonic ectoderm and embryonic endoderm, but was undetectable in fragments of ectoplacental cone, parietal yolk sac (primary giant trophoblast and parietal endoderm), extraembryonic ectoderm or extraembryonic endoderm. The level of synthesis by the HA-positive tissues was markedly enhanced by culture in medium containing serum, compared with that obtained following culture in medium supplemented with a defined serum substitute containing insulin, transferrin, selenous acid and linoleic acid. This suggests that additional growth factors, present in serum but absent from the serum substitute, are required for optimal HA synthesis by the HA-secreting tissues in vitro, and probably also in vivo. The implications of these events for implantation and the development of peri- and early post-implantation mouse embryos are discussed, and a new role for HA in the initial formation and expansion of the embryonic cavities is proposed.

Fetal cleft lip repair in rabbits: Histology and role of hyaluronic acid

This study examines the histologic and biochemical features of wound healing in a cleft lip model in the mid-third-trimester fetal rabbit. At days 1, 2, and 4 after the procedure, control, unrepaired, and repaired fetal heads were obtained, sectioned, and stained for histologic examination. The localization of hyaluronic acid in the wound was documented using a cartilage-derived hyaluronic acid-binding protein. In both repaired and unrepaired wounds, the fetal cleft healed without inflammatory cell infiltration or scar formation. Six months after birth, the repaired cleft showed complete regeneration of muscle across the wound and the collagen fibers were of normal density and orientation. Decreased hyaluronic acid deposition was observed in unrepaired clefts as compared with adjacent tissue; no such difference was detected in repaired clefts. Our findings support the hypothesis that a cleft lip repaired in utero heals without the scarring that accompanies postnatal repair. This may explain the lack of maxillary growth restriction after in utero cleft lip repair.

Perivitelline space of mammalian oocytes: extracellular matrix of unfertilized oocytes and formation of a cortical granule envelope following fertilization

Extracellular matrices (ECM) present around unfertilized and fertilized mammalian oocytes were studied ultrastructurally in samples prepared in the presence of ruthenium red to facilitate stabilization of extracellular materials. Unfertilized mouse, hamster, and human oocytes have an ECM comprising granules and filaments in their perivitelline spaces (PVS). This matrix is more abundant in the human than in hamsters and mice. The granule/filament matrix appears identical to the matrix seen between cumulus and corona radiata cells following ruthenium red processing and previously shown to comprise protein and hyaluronic acid. By including ruthenium red during fixation, it is possible to demonstrate the existence of cortical granule exudate in the PVS of fertilized oocytes from hamsters, mice, and humans. Much of the cortical granule exudate is trapped in the PVS and forms a new coat around the fertilized oocyte. This material is particulate when stained with ruthenium red and appears to be uniformly dispersed around the entire oocyte surface. We refer to this new coat as the cortical granule envelope. This envelope is observed in the PVS of all developmental stages up to and including blastocysts in all three species. Following hatching of mouse and hamster blastocysts, the cortical granule envelope is no longer present. Possible functions of this envelope are discussed.

Animal models for the study of fetal tissue repair

Recent experimental and clinical evidence suggests that the fetus responds to injury in a fashion fundamentally different from that of the adult. Acute inflammation is almost always absent, hyaluronic acid is a prominent component of the wound matrix, and collagen is deposited in a scarless manner. Using a variety of animal models and techniques, numerous investigators have begun to analyze the constituents of the fetal wound healing process in an attempt to understand the control mechanisms that endow the fetus with unique healing abilities. Since scarring and fibrosis dominate some diseases in almost every medical specialty, the ultimate clinical aim is to delineate the biological principles of fetal wound healing and then apply them to modulate adult wound healing problems.

Ultrastructural and morphometric analysis of the separation of two thigh muscles in the chick

Limb muscles separate from one another in a complex but highly stereotyped sequence and spatial pattern. The process of separation is characterized by the progression of a region of increased extracellular space, the cleavage zone, along the proximodistal axis between the individual muscle anlagen. We analyzed ultrastructurally the muscles and cleavage zone during the separation of two representative muscles, the developing sartorius and iliotibialis in the chick thigh, to establish an accurate baseline for an analysis of the mechanisms of separation. Comparisons of the morphology and distribution of cells before and after separation show no evidence that muscles became separated by the massive influx of an exterior cell population; if populations invade the cleavage zone, they are small. We do find characteristic transitions within the cell population of the cleavage zone in situ that could accomplish cleavage without invoking massive cell movements. These progressive transitions within the cleavage zone include a loss of close cell-cell interactions, an increase in extracellular space, the assumption of a more stellate morphology by mesenchyme cells, and a gradual alteration in the composition of the extracellular matrix from one typical of early muscle to one typical of loose connective tissue. Myotubes do differentiate between the incipient muscles, ruling out the possibility that the location where muscles will separate is defined by sites where myotubes fail to differentiate. Instead, the myotubes in the cleavage zone gradually diminish in number and appear to be specifically recognized and removed from the cleavage zone by phagocytes. We suggest that the transitions within the cleavage zone, including the loss of muscle cells, are a result of the progressive differentiation of loose connective tissue. If so, then the spatial pattern and process of cleavage is a consequence of spatially programmed cell differentiation.

Studies in fetal wound healing. V. A prolonged presence of hyaluronic acid characterizes fetal wound fluid

Midgestation fetal wound healing is characterized by healing without fibrosis or scar formation. The mechanisms that underlie this remarkable process are mediated in part through a fetal wound extracellular matrix rich in hyaluronic acid. In this study a newly developed assay was used to determine the hyaluronic acid levels in fetal and adult wound fluid. Adult wound fluid had a rapid increase in hyaluronic acid, which peaked at 3 days and decreased to 0 by 7 days. In contrast levels of hyaluronic acid in fetal wound fluid increased rapidly and remained significantly elevated for 3 weeks. This prolonged presence of hyaluronic acid in the matrix of fetal wounds creates a 'permissive' wound environment that promotes fetal fibroblast movement and proliferation and inhibits cytodifferentiation. Such a matrix environment promotes healing by regeneration rather than by scarring. This observation has therapeutic implications. The prolonged application of hyaluronic acid or hyaluronate protein complexes to wounds in children or adults may modulate healing in a manner that makes the wounds more fetal-like.

Density-dependent expression of hyaluronic acid binding to vascular cells in vitro

Alterations in glycosaminoglycans and their receptors have been associated with changes in cell proliferation during development, wound healing, regeneration, and remodeling. We have previously found a differential effect of hyaluronic acid on the attachment of vascular cells in vitro; endothelial cell (EC) attachment was improved on hyaluronic acid-coated substrates, whereas that of smooth muscle cells (SMC) was reduced (Orlidge and D'Amore, 1986). To determine if hyaluronic acid binding sites are involved in these different substrate preferences, we have studied specific hyaluronic acid binding to cultured bovine aortic EC and SMC. Since very large numbers of cells are required for these binding assays (3 x 10(6)/data point), and since the level of hyaluronate binding to fixed and native SMC and EC was similar, fixed cells were used throughout this study. The effect of cell density on hyaluronic acid binding was investigated. No significant difference was observed between hyaluronic acid binding to sparse and high density SMC. On the other hand, a more than threefold elevation in specific hyaluronic acid binding was observed on low density EC when compared to binding on high density EC. Hyaluronic acid binding was found to be specific; excesses of heparan sulfate and chondroitin sulfate had no effect on the levels of specific binding. Finally, the effect of cell passage on SMC binding of hyaluronic acid was measured. Specific binding was measured from 1st to 12th passage cells and was found to increase with passage number so that by passage 12, hyaluronic acid binding was fourfold that of 1st passage cells. These data support the concept that SMC may become less differentiated upon continuous culture. Our results indicate quantitative changes in the level of hyaluronic acid binding to vascular cells as a function of their growth state. Further, these data correlate well with in vivo observations which suggest a role for hyaluronic acid in vascular development.

Ultrastructural and immunocytochemical study of bone-derived cells cultured in three-dimensional matrices: influence of chondroitin-4 sulfate on mineralization

Bone-derived cells were cultured in three-dimensional reconstituted matrices made of type I collagen or type I collagen chondroitin-4-sulfate. As observed by microscope, their characteristics were as follows: The cells deposited a faint extracellular matrix mainly composed of type I collagen. In the collagen-chondroitin-sulfate sponge fibers, a calcification process, which involved the deposition of hydroxyapatite crystals, was demonstrated. Mineralization occurred only in collagen chondroitin sulfate sponge fibers when seeded with bone-derived cells and was not seen with nonosteogenic cells, such as gingival fibroblasts. Gla protein was intracellularly visualized in both types of sponges seeded with bone-derived cells while an extracellular secretion was seen only in the collagen chondroitin sulfate sponge fibers where calcification occurred. These results suggest that collagen chondroitin sulfate promotes in vitro mineralization of three-dimensional collagen matrices when seeded with bone-derived cells.

Hyaluronic acid determinations: optimizing assay parameters

Assay conditions for determining hyaluronic acid levels in cultured cells have been examined. In cultures labeled with [3H]glucosamine, hyaluronic acid is measured by digestion with a highly specific hyaluronidase from Streptomyces hyaluronlyticus. Products obtained in the presence and absence of preliminary enzyme digestion are precipitated with cetylpyridinium chloride. The precipitation step has been optimized for ion concentration, glycosaminoglycan carrier and for cetylpyridinium chloride levels. Chondroitin sulfate is an effective carrier in the precipitation of radiolabeled product, while unlabeled hyaluronic acid is not. Addition of sulfate to the mixture yields a flocculent precipitate that facilitates subsequent steps of the determination. Optimizing these steps in hyaluronic acid determination can generate two- to three-fold increases in apparent levels of deposition in cultured cells.

Studies in fetal wound healing, VII. Fetal wound healing may be modulated by hyaluronic acid stimulating activity in amniotic fluid

Fetal wound healing occurs rapidly and without inflammation, fibrosis, or scar formation. It is a process fundamentally different from adult wound healing. The mechanisms that underlie such unique healing properties are unknown. However, hyaluronic acid, a glycosaminoglycan component of the extracellular matrix, is prominent throughout the course of fetal wound healing, and is thought to play a major role in the healing process. Amniotic fluid contains high levels of hyaluronic acid. Amniotic fluid also contains a number of potent growth factors that are critical for fetal development. In this report, a new factor in amniotic fluid that stimulates deposition of hyaluronic acid is described. This activity is measured in an in vitro assay system in which cultured fibrosarcoma cells are used as indicator cells. Amniotic fluid thus provides two separate mechanisms for the deposition of hyaluronic acid. One is by exogenous application directly onto fetal skin wounds; the second is by providing a factor to increase the production of hyaluronic acid endogenously, by stimulating cells around the wound site. The resulting hyaluronic acid-rich area may support the ability of the fetal wound to heal with its unique properties.

Changes in surface morphology and basal lamina of cultured muscle cells from Duchenne muscular dystrophy patients

Cultured muscle cells from Duchenne muscular dystrophy (DMD) patients show altered growth from the mononucleated stage: abnormal morphology, decreased adhesiveness, reduced number of population doublings and delayed fusion. On the basis of these findings, a study was undertaken to observe cell shape and surface morphology by scanning electron microscopy and to define the immunocytochemical localization of 4 basal lamina components (type IV collagen, laminin, fibronectin, heparan sulfate proteoglycan (HSPG]. Eight DMD muscle cultures with fusion indices higher than 65% were compared to muscle cultures from 10 age-matched controls. The following results were noted for the dystrophic muscle cells: (1) the cell surface was smooth with a few slender cell processes and anchorage extensions; (2) distribution of type IV collagen and laminin was heterogenous, with large patches (type IV collagen) or a reticulum (laminin); (3) in contrast, fibronectin and HSPG levels were clearly decreased. These molecules did not form a network but rather were arranged in thick filaments and patches. Cell surface morphology may be related to the decreases in fibronectin and HSPG, which could reflect a more general decrease in basal lamina. Such findings could explain the low adhesiveness of the cells from dystrophic cultures and the delayed fusion of myoblasts. Although these abnormalities were maximally expressed after myoblast fusion, they were already present in mononucleated cells and their connection with the primary defect in DMD, i.e., lack of dystrophin, must now be clarified.

Effects of medium and substratum on ovine satellite cell attachment, proliferation and differentiation in vitro

The ability of ovine-derived satellite cells to attach, proliferate and differentiate in response to seven horse serum-supplemented media and eleven substrata was evaluated in vitro. Satellite cells attached equally well when exposed to CRCM-30, Medium-199 and high glucose Dulbecco's modified Eagles medium (DMEM, P less than 0.05). Proliferation of satellite cells was greatest using McCoy's 5A, supplemented with 15% horse serum (P less than 0.05), and differentiation was most efficient with low glucose DMEM, supplemented with 1% horse serum (P less than 0.05). Pig-skin gelatin facilitated the greatest ovine satellite cell proliferative and differentiative responses when compared to the performance of ten other substrata (P less than 0.05). Further, 0.5 mg/16 mm2-well pig-skin gelatin appeared to be the optimum concentration of substratum for expression of satellite cell growth characteristics. Thus, consideration must be given to the processes of attachment and proliferation in experiments attempting to maximize satellite cell differentiation in vitro.

Studies in fetal wound healing. IV. Hyaluronic acid-stimulating activity distinguishes fetal wound fluid from adult wound fluid

Recent clinical and experimental evidence suggests that the fetus responds to injury in a fashion fundamentally different from that of the adult. Our initial experience with human open fetal surgery reinforces experimental observations that the fetal wounds heal without the scarring, inflammation, and contraction that often accompany adult wounds. In this study we examine fetal wound fluid in an attempt to elucidate the control mechanisms that endow the fetus with unique healing properties. The extracellular matrix of fetal wounds is rich in hyaluronic acid, a glycosaminoglycan found in high concentrations whenever there is tissue proliferation, regeneration, and repair. We establish that wound fluid from the fetus contains high levels of hyaluronic acid-stimulating activity that may underlie the elevated deposition of hyaluronic acid in the fetal wound matrix. In contrast there was no hyaluronic acid-stimulating activity present in adult wound fluid. Hyaluronic acid, in turn, fosters an extracellular environment permissive for cell motility and proliferation that may account for the unique properties observed in fetal wound healing.

Studies in fetal wound healing: I. A factor in fetal serum that stimulates deposition of hyaluronic acid

Fetal wound healing without scar formations, fibrosis, or contracture might be accompanied by major differences in the wound extracellular matrix. The matrix of fetal wounds is rich in hyaluronic acid, a glycosaminoglycan found in high concentrations whenever there is tissue proliferation, regeneration, and repair. Although hyaluronic acid is a critical molecule for both embryonic development and wound healing, no factor has yet been identified that modulates hyaluronic acid in a consistent manner. We describe here a substance present in fetal sheep serum that stimulates hyaluronic acid synthesis by cultured fibroblasts. This glycoprotein factor appears to be ubiquitous, present in fetal sheep and bovine serum, reaching a peak in each at 40% of the way through gestation. This factor is also present in amniotic fluid. It might control hyaluronic acid deposition. In turn, hyaluronic acid, by creating an extracellular environment permissive for cell motility and proliferation, might be critical for fetal development. We suggest that the same sequence of events underlie the unique properties observed in fetal wound healing.

Studies in fetal wound healing: II. A fetal environment accelerates fibroblast migration in vitro

We have used an in vitro model of wound healing using scratches made in a confluent monolayer of fibroblasts. The effects of fetal calf and postnatal calf serum on the migration of fibroblasts were compared. Differences between fetal and calf serum-incubated fibroblasts grown on coverslips were observed within 15 minutes of exposure. Cells in fetal serum began to change both shape and orientation and to move into the trough created by the scratch. The fibroblasts incubated in fetal calf serum completely filled in the trough within 16 hours while those incubated in calf serum did not do so even after 24 hours. We estimate that, at any point, there was a 50% lag time in the migration of the fibroblasts in the presence of postnatal calf serum. This difference in migration and filling was not a function of mitogenesis; the mitogenicity of the two sera were comparable. The results suggest that fibroblast migration in vitro is accelerated by the fetal serum. A similar mechanism may occur in vivo and may underlie the ability of the fetal wound to heal more rapidly.

A study on skeletal myogenic cell movement in the developing avian limb bud

Quail limb mesenchyme containing myogenic cells of somitic origin were transplanted into chick limb buds to determine whether cell movement might play a role in avian limb myogenesis. In general, cell displacement was not detected 1-day after implantation: all quail cells were found at the graft site. Migration was evident 2-days after implantation but not all cell types were capable of movement; myogenic cells were very invasive while chondrocytes were relatively immobile. The spreading of myogenic cells was discernible up to 4-days after implantation and specifically in a proximodistal direction towards the apex of the limb.

Histochemical analysis of newly synthesized and accumulated sulfated glycosaminoglycans during musculogenesis in the embryonic chick leg

The leg musculature from 11, 14, and 17 day chick embryos was analyzed histochemically to investigate the temporal and spatial distribution of various types of sulfated glycosaminoglycans present during skeletal muscle development. Types of glycans were identified by selective degradation with specific glycosidases and nitrous acid coupled with Alcian blue staining procedures for sulfated polyanions and with [35S]sulfate autoradiography. On day 11, radiolabeled chondroitin sulfate glycosaminoglycans are localized extracellularly in both the myogenic and connective tissue cell populations. By day 17, incorporation of [35S]sulfate into chondroitin sulfate is substantially reduced, although Alcian blue-stained chondroitin sulfate molecules are still detectable. With increasing age and developmental state of the tissues, radiolabeled and stained dermatan sulfate and heparan sulfate progressively increase in relative quantity compared to chondroitin sulfate both in muscle and in associated connective tissue elements. These changes in glycosaminoglycans correlate well with similar changes previously determined biochemically and further document the alterations in extracellular matrix components during embryonic skeletal myogenesis.

Effect of selected denervations on glycoconjugate composition and tissue morphology during the initiation phase of limb regeneration in adult Ambystoma

This study was undertaken to assess the effects of various quantities of neural tissue on the temporal relationship of matrix glycoconjugates to the regeneration morphology. 1) Denervation before amputation revealed that a threshold level of nervous tissue was necessary to activate a regeneration response from the tissue, i.e., appearance of regeneration-specific morphologies and glycoconjugates. 2) Denervation after amputation demonstrated that the level of neural tissue necessary to maintain these responses was below the level necessary to activate the regeneration response. If neural tissue was completely removed there was a concomitant loss of regenerate morphologies and glycoconjugates. 3) Bilateral amputation of a neurogenically intact limb and its completely denervated contralateral limb revealed that the regeneration response was a localized phenomenon during the first 30 days after amputation. After 30 days the regeneration response appeared within the previously degenerated denervating limb. The results suggest that the factors controlling the regenerative response in adult Ambystoma are large diffusible substances that can be transported by the circulation and can affect the regenerative response in remote, previously activated, tissues.

Structural characterization of chick embryonic skeletal muscle chondroitin sulfate proteoglycan

Embryonic chick skeletal muscle has been shown to synthesize a distinct proteoglycan of large size with relatively large, highly 6-sulfated chondroitin sulfate glycosaminoglycans. Further analysis of these proteoglycans indicates that tryptic digestion gives rise to fragments with an average of two chondroitin sulfate chains per peptide. The skeletal muscle chondroitin sulfate proteoglycan also contains oligosaccharides whose characteristics suggest the presence of both O-linked and N-linked oligosaccharides. These characteristics include the average hydrodynamic size of the oligosaccharides as well as their localization. Approximately 10% of the putative O-linked oligosaccharides reside on the same tryptic fragments which contain the chondroitin sulfate chains, while the presumptive N-linked oligosaccharides appear to be present at sites distant from the chondroitin sulfate. Further support for this identification comes from radioisotopic labeling with [3H]mannose, which is incorporated exclusively into the putative N-linked oligosaccharides. Some of the O-linked oligosaccharides which are not in close apposition to the chondroitin sulfate seem to occur in clusters. The skeletal muscle chondroitin sulfate proteoglycan has the ability to interact in a link protein-stabilized fashion with hyaluronic acid. This ability as well as the estimated number of chondroitin sulfate chains per cluster and the estimated number of oligosaccharides per chondroitin sulfate chain have implications about the structure of the core protein of the skeletal muscle proteoglycan. The information presented is used to construct a model of these molecules; with this detailed model, attention can now be directed at other aspects of the skeletal muscle chondroitin sulfate proteoglycan, such as its role in myogenesis.

Fibronectin and glycosaminoglycan synthesis by fibrotic pig fibroblasts in primary culture

Synthesis of fibronectin and glycosamingoglycans (GAGs) was studied in fibroblasts from pigs with post-irradiation subcutaneous fibrosis. Fibrosis was developed in the femoral muscle by local gamma irradiation with a dose of 60 Gy. Normal fibroblasts were obtained from the healthy skin of the same animal. To measure GAG and fibronectin synthesis fibrotic and normal fibroblasts were labeled with 3H-glucosamine, 35S-sulfate and 35S-methionine. Fibrotic fibroblasts synthesized 2.5 times as much fibronectin as normal skin fibroblasts but total protein synthesis did not change. Parallel enhanced secretion of hyaluronic acid and dermatan sulfate into the cell culture medium were also observed. GAGs from the pericellular layer of trypsin-digested fibrotic fibroblasts exhibited increased 3H incorporation, but reduced 35S-sulfate incorporation. The largest reduction in the latter was observed for heparan sulfate. These results indicate that the fibroblasts from the well developed fibrotic tissue maintain enhanced synthesis of matrix macromolecules in primary cultures. Structural and/or metabolic changes in secreted GAGs, combined with the stimulation of tissue repair by growth factors may be responsible for the excessive deposition of collagen in post-irradiation fibrosis.

Vectorial secretion of proteoglycans by polarized rat uterine epithelial cells

We have studied proteoglycan secretion using a recently developed system for the preparing of polarized primary cultures of rat uterine epithelial cells. To mimic their native environment better and provide a system for discriminating apical from basolateral compartments, we cultured cells on semipermeable supports impregnated with biomatrix. Keratan sulfate proteoglycans (KSPG) as well as heparan sulfate-containing molecules (HS[PG]) were the major sulfated products synthesized and secreted by these cells. The ability of epithelial cells to secrete KSPG greatly increased in parallel with the development of cell polarity. Furthermore, KSPG secretion occurred preferentially to the apical medium in highly polarized cultures. In contrast, HS(PG) secretion did not increase along with development of polarity, although most HS(PG) (85%) were secreted apically as well. Pulse-chase studies indicated that highly polarized cultures secreted 80-90% of the sulfated macromolecules they synthesized, predominantly to the apical secretory compartment. The half-lives for KSPG and HS(PG) secretion were approximately 3 and 4 h, respectively. Parallel studies of cells cultured on tissue culture plastic-coated with biomatrix indicated that neither the state of confluency nor the biomatrix was primarily responsible for inducing the KSPG secretion observed in polarizing cultures. Experiments with uterine strips indicated that the steroid hormone, 17-beta-estradiol, markedly stimulated synthesis and secretion of sulfated macromolecules, but had no preferential effect on KSPG production. The ratio of KSPG to HS(PG) secretion from uterine strips was similar to that found in the apical medium of highly polarized cell cultures. Thus, the pattern of proteoglycan secretion observed in polarized cell cultures mimicked that observed for uterine cells, although the preferential increase in KSPG production by polarized cells could not be attributed to an estrogen response. Collectively, these studies describe the major sulfated molecules secreted by rat uterine epithelial cells under varying conditions and provide evidence for a novel influence of cell polarity on the cell's ability to secrete sulfated glycoconjugates.

Production of IGF-II-related peptide by an anaplastic cell line (AT-3) established from the Dunning prostatic carcinoma of rats

AT-3 cells, one of anaplastic cell lines established from the Dunning prostatic carcinoma of rats, were able to grow under serum-free conditions in a state of suspension detached from a substratum. Radioimmunoassay using monoclonal antibody against rat insulin-like growth factor II (IGF-II) revealed the presence of IGF-II-related peptide in acid-ethanol extracts of lyophilized serum-free media conditioned by AT-3 cells. The peptide contents in the culture media increased with increase in cell number; 71 ng at 3.0 X 10(6) cells and 449 ng at 4.6 X 10(7) cells. IGF-II-related peptide was hardly detectable in acid-ethanol extracts of AT-3 cells harvested after 13-days culture. These results indicate that AT-3 cells produce IGF-II-related peptide and may release it into the culture media.

Hyaluronate accumulation and nerve-dependent growth during regeneration of larval Ambystoma limbs

Hyaluronate-mediated expansion of the extracellular matrix has been suggested as an important element of growth and morphogenesis in several developing systems. In vitro, various growth factors have been shown to stimulate hyaluronate synthesis as well as cell proliferation. A similar link between proliferation and hyaluronate production during in vivo growth is difficult to demonstrate, because in most systems the source of growth-promoting factors is either not known or not amenable to experimental manipulation. During amphibian limb regeneration, cell proliferation depends upon paracrine release of factors from axons in the limb stump, and the nerve supply can be eliminated or augmented experimentally for study of growth in this system. Denervated and amputated limbs of larval salamanders do not begin to regenerate until distal areas of the limb stumps are reinnervated. We have used such limbs to examine the effect exerted by the reappearance of nerves on the amount of hyaluronate in the tissue undergoing the growth response. Hyaluronate was demonstrated by the metachromatic dye Ethyl Stains-all, which stains hyaluronate blue while sulfated glycosaminoglycans (GAGs) and proteins in the extracellular matrix stain various shades of violet, and by microspectrophotometry of alcian-blue-stained GAGs in serial sections pretreated with buffer or with Streptomyces hyaluronidase (SH) to remove hyaluronate specifically. Both methods showed little hyaluronate in the distal region of limb stumps prior to reinnervation, while reinnervated stumps had amounts of hyaluronate similar to those of control blastemas. Autoradiography of 3H-glucosamine-labeled limbs indicated that hyaluronate in the blastemas of reinnervated limb stumps included material newly synthesized by cells throughout the growing tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfated glycosaminoglycans modify growth factor-induced neurite outgrowth in PC12 cells

Glycosaminoglycans (GAGs), localized on the surfaces of cells and in the basement membrane, modulate the growth and differentiation of many cell types. Recent studies have shown that heparin, a GAG found in mast cells, potentiates the ability of acidic fibroblast growth factor (aFGF) to induce neurite outgrowth in pheochromocytoma (PC12) cells. We examined the effect of a variety of GAGs on aFGF, basic fibroblast growth factor (bFGF), and nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells. The effects observed were dependent upon the specific GAG, the concentration of the GAG, and the growth factor. Heparin potentiated aFGF-induced neurite outgrowth in a concentration-dependent fashion; potentiation increased with increasing heparin concentrations of 0.01-100 micrograms/ml. At concentrations greater than 100 micrograms/ml, heparin potentiation decreased. The maximally active concentration of heparin (100 micrograms/ml) increased the potency of aFGF 102-fold. Increasing concentrations of heparan sulfate, dermatan sulfate, and chondroitin sulfate correlated with increasing aFGF potentiation. The maximally active concentrations of heparan sulfate (100 micrograms/ml), dermatan sulfate (10 mg/ml), and chondroitin sulfate (1 mg/ml) increased the activity of aFGF 11-, 110-, and 11-fold, respectively. Hyaluronic acid did not affect the neurite outgrowth-promoting activity of aFGF. Heparin also altered the activity of bFGF; increasing concentrations of heparin (0.01-1 micrograms/ml) correlated with increased potentiation. At concentrations greater than 1 microgram/ml, heparin concentration was inversely correlated with potentiation. Chondroitin sulfate only increased the percentage of neurite-bearing cells at concentrations greater than 10 micrograms/ml. Maximally active concentrations of heparin (1 microgram/ml) and chondroitin sulfate (1 mg/ml) increased the potency of bFGF 5-fold. The highest concentration of heparan sulfate studied (1 mg/ml) inhibited the activity of bFGF. Dermatan sulfate and hyaluronic acid (0.01-1000 micrograms/ml) had no effect on bFGF activity. Heparan sulfate and chondroitin sulfate showed concentration-dependent potentiation of NGF; maximally active concentrations of heparan sulfate (100 micrograms/ml) and chondroitin sulfate (1 mg/ml) increased the potency of NGF 3-fold, whereas heparin, dermatan sulfate and hyaluronic acid had no effect. None of the GAGs had any effect on PC12 neurite outgrowth when added alone. The specificity of the activity of the GAGs was verified by selective enzyme degradation.(ABSTRACT TRUNCATED AT 400 WORDS)

Porous collagen sponge wound dressings: in vivo and in vitro studies

Collagen-based materials can be formed into a three-dimensional sponge for use as a wound dressing and as a support for cell cultured skin components. Factors such as biocompatibility, morphological structure and addition of non-collagenous molecules to collagen are analyzed and discussed. Large pores or channels, interchannel communications and combinations of macromolecules of the connective tissue enhance wound tissue infiltration in vivo as well as cell growth in vitro into collagen sponges. The presence of such factors can be useful in patients with excised burn wounds and pressure skin ulcers.