A cartilage-derived growth factor enhances hyaluronate synthesis and diminishes sulfated glycosaminoglycan synthesis in chondrocytes

An Fgf-Shh signaling hierarchy regulates early specification of the zebrafish skull

The neurocranium generates most of the craniofacial skeleton and consists of prechordal and postchordal regions. Although development of the prechordal is well studied, little is known of the postchordal region. Here we characterize a signaling hierarchy necessary for postchordal neurocranial development involving Fibroblast growth factor (Fgf) signaling for early specification of mesodermally-derived progenitor cells. The expression of hyaluron synthetase 2 (has2) in the cephalic mesoderm requires Fgf signaling and Has2 function, in turn, is required for postchordal neurocranial development. While Hedgehog (Hh)-deficient embryos also lack a postchordal neurocranium, this appears primarily due to a later defect in chondrocyte differentiation. Inhibitor studies demonstrate that postchordal neurocranial development requires early Fgf and later Hh signaling. Collectively, our results provide a mechanistic understanding of early postchordal neurocranial development and demonstrate a hierarchy of signaling between Fgf and Hh in the development of this structure.

Verapamil protects against cartilage degradation in osteoarthritis by inhibiting Wnt/β-catenin signaling

In past years, the canonical Wnt/β-catenin signaling pathway has emerged as a critical regulator of cartilage development and homeostasis. FRZB, a soluble antagonist of Wnt signaling, has been studied in osteoarthritis (OA) animal models and OA patients as a modulator of Wnt signaling. We screened for FDA-approved drugs that induce FRZB expression and suppress Wnt/β-catenin signaling. We found that verapamil, a widely prescribed L-type calcium channel blocker, elevated FRZB expression and suppressed Wnt/β-catenin signaling in human OA chondrocytes. Expression and nuclear translocation of β-catenin was attenuated by verapamil in OA chondrocytes. Lack of the verapamil effects in LiCl-treated and FRZB-downregulated OA chondrocytes also suggested that verpamil suppressed Wnt signaling by inducing FRZB. Verapamil enhanced gene expressions of chondrogenic markers of ACAN encoding aggrecan, COL2A1 encoding collagen type II α1, and SOX9, and suppressed Wnt-responsive AXIN2 and MMP3 in human OA chondrocytes. Verapamil ameliorated Wnt3A-induced proteoglycan loss in chondrogenically differentiated ATDC5 cells. Verapamil inhibited hypertrophic differentiation of chondrocytes in the explant culture of mouse tibiae. Intraarticular injection of verapamil inhibited OA progression as well as nuclear localizations of β-catenin in a rat OA model. We propose that verapamil holds promise as a potent therapeutic agent for OA by upregulating FRZB and subsequently downregulating Wnt/β-catenin signaling.

Hyaluronic acid and chondroitin sulfate content of osteoarthritic human knee cartilage: site-specific correlation with weight-bearing force based on femorotibial angle measurement

This study analyzed glycosaminoglycan (GAG) content in specific compartments of the knee joint to determine the impact of malalignment and helped refine indications for osteotomy. To assess malalignment, the radiological femorotibial angle (FTA) was measured and knee joints were also graded for OA severity with the Kellgren/Lawrence (K/L) classification. Cartilage samples were obtained from 36 knees of 32 OA patients undergoing total knee replacement surgery. Explants were harvested from the medial femoral condyle (MFC), lateral femoral condyle (LFC), patellar groove (PG), and lateral posterior femoral condyle (LPC). Concentrations of hyaluronic acid (HA) and chondroitin sulfate (CS) were measured by high-performance liquid chromatography (HPLC). With OA severity, the average FTA significantly increased. HA and CS content in MFC was negatively correlated with radiographic FTA. In LFC, HA ratio, which is HA content in lateral condyle divided by medial condyle and chondroitin 6 sulfate, increased until about 190 degrees FTA. Importantly, at >190 degrees these contents were significantly decreased. HA and CS content of the femoral condyle shows topographic differences that are related to OA grade and weight-bearing force based on FTA. The clinical relevance is that osteotomy may not be indicated for patients with severe varus (>190 degrees) abnormalities.

Hyaluronan and hyaluronan-binding proteins in cartilaginous tissues

Recent developments in the biology of hyaluronan in cartilage are reviewed. The homology between the hyaluronan-binding sites of cartilage proteoglycan and link protein is discussed. Previous reports indicate that an increased concentration of extracellular hyaluronan inhibits 35S-proteoglycan synthesis by several types of chondrocyte. We report data showing that this response varies in its reproducibility and sensitivity to low concentrations of hyaluronan in rat chondrosarcoma chondrocytes and pig laryngeal chondrocytes in suspension culture. Two newly recognized hyaluronan-binding proteins have been isolated from extracts of Swarm rat chondrosarcoma. The major protein has a molecular mass of 102 kDa and the less prominent protein a molecular mass of 91 kDa. The latter may be derived from the former. Neither protein cross-reacts with antisera against cartilage proteoglycan HABR (hyaluronan-binding region), link protein, hyaluronectin or type II collagen.

Isolation and characterization of microvascular endothelial cells from chicken fat pads

Microvascular endothelial cells from abdominal fat pads of 6-wk-old broiler chickens were isolated to provide an in vitro system to study their physiological functions. The isolation procedure produced clumps of 10-30 cells, which attached to culture vessels in 4 h and attained confluency in 2 wk. At confluency, cells had a cobblestone appearance but were not contact inhibited and detached from the bottom of the culture vessel 2 wk after reaching confluency. The cells internalized acetylated low density lipoproteins, a characteristic of endothelial cells. This property was used to obtain pure endothelial cell cultures using the cell sorter. When cultured over Matrigel, a reconstituted matrix, the cells aligned themselves into chordlike structures and formed branching microvessels. Cells plated on type I collagen-coated culture flasks occasionally formed chordlike structures and proliferated at a faster rate than cells plated on Matrigel. Cells cultured on laminin-coated plates were slender and had long cytoplasmic extensions; however, cells cultured on uncoated plastic had fibroblastic morphology. These properties are similar to those described for microvessel endothelial cells isolated from tissues of other species.

Transforming growth factor-beta 1 and fibroblast growth factors in rat growth plate

Chondrocytes in the growth plate progress in an orderly fashion from resting through proliferating to hypertrophic cells. In the region of hypertrophic chondrocytes, the cartilage is invaded by capillary loops and endochondral ossification is initiated. It is currently believed that growth factors may regulate the proliferation and maturation of chondrocytes and the synthesis of extracellular matrix in the growth plate. The ordered sequence of proliferation and differentiation observed in the growth plate provides a unique opportunity to study the role of acidic fibroblast growth factor, basic fibroblast growth factor, and transforming growth factor-beta 1 in the regulation of these processes. In this study, expression of the mRNA of these growth factors was examined using total RNA extracted from the physis and epiphysis of rat tibias. Transforming growth factor-beta 1 mRNA was detected by Northern hybridization. Expression of the genes encoding acidic and basic fibroblast growth factors was demonstrated by polymerase chain reaction amplification. In addition, using polyclonal antibodies against these growth factors, we localized them by immunohistochemical analysis. Strong intracellular staining with a predominantly nuclear pattern was observed in chondrocytes from the proliferating and upper hypertrophic zones. In contrast, chondrocytes in the resting zone stained only faintly for the presence of these growth factors. Some chondrocytes in the resting zone adjacent to the proliferating zone stained with these antibodies, and the antibodies also stained cells in the zone of Ranvier, which regulates latitudinal bone growth. Lastly, the location of transforming growth factor-beta 1 was examined further with use of a polyclonal antipeptide antibody specific for its extracellular epitope.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of proliferation and osteochondrogenic differentiation of periosteum-derived cells by transforming growth factor-beta and basic fibroblast growth factor

We studied the effects of transforming growth factor-beta and basic fibroblast growth factor on the regulation of proliferation and osteochondrogenic differentiation of periosteum-derived cells, which have the potential to differentiate into bone and hypertrophic cartilage in vitro. Histological observation revealed that transforming growth factor-beta stimulated chondrogenesis of periosteum-derived cells while basic fibroblast growth factor stimulated proliferation of fibroblast-like cells and inhibited osteochondrogenic differentiation. Immunohistochemical studies revealed that basic fibroblast growth factor inhibited the expression of osteocalcin. Transforming growth factor-beta enhanced uronic acid content but decreased DNA content, alkaline phosphatase activity, and calcium content. In contrast, basic fibroblast growth factor enhanced DNA content but decreased alkaline phosphatase activity, calcium content, and uronic acid content. In addition, transforming growth factor-beta shortened the time-course of gene expression of type-X collagen whereas basic fibroblast growth factor inhibited the gene expression. These results indicate that transforming growth factor-beta stimulates osteochondrogenic differentiation of periosteum-derived cells but inhibits proliferation. They also indicate that basic fibroblast growth factor stimulates proliferation of periosteum-derived cells but inhibits osteochondrogenic differentiation.

Isolation and localization of basic fibroblast growth factor-immunoreactive substance in the epiphyseal growth plate

Previous research in our laboratory has shown basic fibroblast growth factor (bFGF) to be a permissive mitogen for isolated avian growth plate chondrocytes. The present study was conducted to determine whether bFGF is present in avian growth plate and, if present, to determine its localization within the tissue. Immunohistochemical studies revealed that bFGF is present in the resting proliferative and hypertrophic calcifying zones of the growth plate but is absent from the prehypertrophic zone. Basic FGF appears to be associated with the extracellular matrix of the proliferative zone, but it is predominantly intracellular in the hypertrophic and mineralizing zone chondrocytes. Partial purification of cartilage-derived bFGF was performed on crude extracts of cartilage using heparin-Sepharose affinity chromatography. The presence of bFGF in the heparin-Sepharose column fractions was confirmed by immunoblotting and radioimmunoassay. Furthermore, western blot analysis of the extracts showed multiple protein bands having bFGF immunoreactivity, in the molecular weight range 14.4-18 kD. The data support the hypothesis that bFGF has a dual role in the growth plate. In the proliferative zone it acts as a chondrocyte mitogen, whereas when released from terminal hypertrophic chondrocytes, bFGF may serve as a chemotactic signal for metaphyseal blood vessel proliferation.

Intracellular signal transduction for serum activation of the hyaluronan synthase in eukaryotic cell lines

Hyaluronan synthase was activated in B6 cells or 3T3 fibroblasts by foetal calf serum with maximal activity after 6 h. Activation was inhibited by cycloheximide or by the protein kinase inhibitors H-7 or H-8, indicating that transcription as well as phosphorylation was required for activation. The activation by serum was markedly prolonged, when serum was added together with cholera toxin or theophylline. Without serum stimulation the hyaluronan synthase could also be activated by phorbol-12-myristate-13-acetate, by dibutyryl-c-AMP, or by forskolin. Increasing the intracellular Ca-ion concentration with a Ca-ionophore also led to an activation. The activation of the drugs was not synergistic. In isolated plasma membranes the synthase activity could be decreased by phosphatase treatment and enhanced by ATP in B6 cells and by ATP in the presence of phorbol-12-myristate-13-acetate in 3T3 fibroblasts. Stimulation correlated with increased transcription and phosphorylation of the 52 kD hyaluronan synthase at serine residues. The results led to the conclusion that hyaluronan synthase is induced by transcription and activated by phosphorylation by protein kinase C, c-AMP-dependent protein kinases, or Ca-ion-dependent protein kinases.

Platelet-derived growth factor stimulates hyaluronate but not proteoglycan synthesis by human gingival fibroblasts in vitro

The effect of PDGF-BB on human gingival fibroblasts was monitored in an in vitro system. PDGF was found to be mitogenic for these cells, although it required the presence of low concentrations of fetal calf serum to be active. Proteoglycan and hyaluronate synthesis was analyzed by labeling newly synthesized macromolecules with [35S]-sulfate or [3H]-glucosamine, respectively. Identification of specific glycosaminoglycans was achieved by selective enzymatic or chemical degradations. It was found that cells cultured in the presence of PDGF showed no discernible differences in proteoglycan synthesis relative to the control cultures. There were no alterations in amounts of proteoglycans synthesized, types of sulfated glycosaminoglycans synthesized, or relative hydrodynamic sizes of the proteoglycans. In contrast to the proteoglycans, hyaluronate synthesis was significantly increased in the presence of PDGF. The increase in [3H]-glucosamine incorporation into newly synthesized hyaluronate correlated with an increase in the activity of the enzyme hyaluronate synthetase but could not be accounted for entirely by changes in the specific activity of sugar nucleotide precursors, which did alter slightly under differing culture conditions. It is concluded from these results that PDGF stimulates gingival fibroblasts to proliferate and is associated with a differential effect of proteoglycan and hyaluronate synthesis. These observations may correlate with the observed early events associated with wound healing and repair.

Effects of chondroitin sulfates with different structures on leukemia cells: U-937 cell proliferation and differentiation

Chondroitin sulfates extracted and purified by different manufacturers were tested to evaluate their effects on proliferation and differentiation processes of U-937 cells. The different chondroitin sulfates were evaluated for purity, structure and physicochemical properties. The three chondroitin sulfates utilized did not present other contaminant glycosaminoglycans and proteins and had about the same relative molecular mass but different disaccharide patterns and charge density. Chondroitin sulfates with small amounts of disulfated disaccharides and low charge density, at 5 micrograms/ml concentration, doubled (about + 133%) cell proliferation in comparison to controls. In contrast, chondroitin sulfates with large amounts of disulfated disaccharides and high sulfate to carboxyl ratio were less effective (about + 15%) in stimulating cell proliferation at low concentration. A decrease of U-937 cell proliferation was observed in proportion to the increased amounts of chondroitin sulfate with low sulfate to carboxyl ratio. On the contrary, chondroitin sulfate with large amounts of disulfated disaccharides produced increased cell proliferation depending on concentration. Small amounts (5-10 micrograms/ml) of chondroitin sulfates with low charge density reduced the differentiative process of U-937 cells. Chondroitin sulfate with large amounts of disulfated disaccharides and high charge density seemed to be able to produce a significant decrease of differentiative processes only at very high concentrations (1000 micrograms/ml). These contrasting effects of chondroitin sulfates with different disaccharide patterns (and structure) and charge density on a leukemia cell line could help to explain the regulation of proliferative and/or differentiative processes of hemopoietic cells. This is underlined by the changes of types, physicochemical properties and structure of glycosaminoglycans induced by different extracellular factors and agents.

Regulation of growth-plate chondrocytes by insulin-like growth-factor I and basic fibroblast growth factor

A study was performed in order to investigate the possible functional roles of insulin-like growth-factor I (IGFI) and basic fibroblast growth factor (bFGF) in the regulation of mitotic and metabolic activity of growth-plate chondrocytes. Chondrocytes from the distal radial growth plates of calves and the costal physeal cartilage of rats were exposed to these factors, individually and in combination, in primary monolayer culture, to assess their effects. The data showed that bFGF had both a greater potency and a greater efficacy as a mitogen for bovine growth-plate chondrocytes than did IGF-I. The maximum incorporation of 3H-thymidine by bFGF was 8.3 times that in serum-free (control) cultures; the maximum stimulation of incorporation by IGF-I was 2.5 times that in the control medium. In contrast, IGF-I stimulated a maximum incorporation of 35S-sulfate into glycosaminoglycans that was 2.6 times that in the IGF-I serum-free control cultures, while bFGF had no effect or was mildly inhibitory. When used together, these two factors acted synergistically. Incorporation of 3H-thymidine was more than two times greater than the sum of the effects of the growth factors when used alone and 20.5 times greater than that of the growth factor-free control cultures. Physeal chondrocytes from six-day-old rats were mitotically more responsive to bFGF than to IGF-I, but they were more responsive to IGF-I when they had been derived from twenty-eight-day-old rats. Interaction between bFGF and factors in the serum enhanced the mitotic activity of the rat chondrocytes, but bFGF did not interact with IGF-I under the same experimental conditions. In the presence of bFGF, there was a reduction in the stimulation by IGF-I of incorporation of 35S-sulfate and a decrease in the percentage of chondrocytes containing alkaline phosphatase. These growth factors also influenced cellular morphology in culture. In the presence of IGF-I or serum, the rat chondrocytes manifested the polygonal morphology typical of chondrocytes in culture, while bFGF promoted a more elongated spindle shape. Removal of bFGF and replacement by IGF-I restored the polygonal morphology, indicating that this transition is reversible.

Correlation of hyaluronic acid accumulation and the growth of preneoplastic mammary cells in collagen: a longitudinal study

Hyaluronic acid accumulation is characteristic of mammary tumor cells, and the amount that accumulates seems to correlate with the degree of malignancy of the producing cells. We have tested directly the relationship between hyaluronic acid accumulation and the replication rate of preneoplastic mammary cells in culture. We used nontumorigenic but immortal CL-S1 mouse mammary cells that were derived from a hyperplastic alveolar nodule. Using a collagen gel culture system, we found clear differences in the growth properties of cells before and after Passages 68 to 70. Late passage cells replicated earlier and faster than early passage cells in collagen and on plastic. The rate of cycling resembled that of tumorigenic mouse mammary cells during the first week of culture. Cells seeded at low densities cycled faster than those seeded at high densities during the second week in culture. Exogenous hyaluronic acid, at 10 to 1000 micrograms/ml, neither enhanced nor inhibited CL-S1 cell growth significantly in collagen, regardless of passage. However, by the third day in collagen, late passage cells produced 7 times more total glycosaminoglycans and 12 times more hyaluronic acid per cell than did early passage cells. Late passage cells also deposited 12 times more labeled hyaluronic acid in the matrix than did early passage cells, on a per-cell basis. After a decline in the deposition of hyaluronic acid in the extracellular matrix, growth ceased. The late passage cells did not grow in soft agar, indicating that they had not become neoplastic spontaneously during passage. However, their accelerated growth rate, coupled with the synthesis and secretion of large amounts of hyaluronic acid into the extracellular matrix, may characterize a distinct step in tumor progression in preneoplastic CL-S1 cells.

The effects of growth factors on DNA synthesis, proteoglycan synthesis and alkaline phosphatase activity in bovine dental pulp cells

Platelet-derived growth factor (PDGF), insulin-like growth factor-I and -II (IGF-I and -II), acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) stimulated [125I]-deoxyuridine incorporation about 13, 6.2-, 4.6-, 3.8-, 3.1- and 1.2-fold, respectively, above control values at a concentration of 50 ng/ml. Transforming growth factor-beta (TGF-beta) decreased incorporation about 30% at the same dose. aFGF, IGF-I, IGF-II, bFGF and TGF-beta increased [35S]-sulphate incorporation 231, 71, 64, 42 and 39%, respectively, in proliferating cells, while EGF, IGF-I, TGF-beta and PDGF decreased incorporation about 30%, and aFGF increased incorporation 80% in stationary-stage culture. TGF-beta, PDGF, aFGF and bFGF caused 65-40% inhibition of alkaline phosphatase activity in proliferating and stationary cultures. These findings suggest that the proliferation of pulp cells may be stimulated mainly by PDGF and IGF-I, and the production of extracellular matrix proteoglycan may be enhanced by aFGF, IGF-I and IGF-II. Furthermore, TGF-beta, PDGF, aFGF and bFGF may regulate the differentiation of pulp cells into odontoblasts.

Hyaluronan-dependent pericellular coats of chick embryo limb mesodermal cells: induction by basic fibroblast growth factor

Basic fibroblast growth factor (FGF) has been shown previously to be present in the chick embryonic limb during early stages of its development, at which time the limb mesodermal cells are proliferating within a hyaluronan-rich extracellular matrix. In this study, basic FGF was found to stimulate hyaluronan synthesis and production of hyaluronan-dependent pericellular coats by mesodermal cells from the chick embryo limb; acidic FGF, platelet-derived growth factor, epidermal growth factor, and retinoic acid either had a much smaller effect than basic FGF or an inhibitory effect. Transforming growth factor-beta stimulated hyaluronan synthesis and coat formation but, unlike basic FGF, this factor also stimulated chondroitin sulfate production by the mesodermal cells.

Bacillus Calmette-Guérin (BCG) influences cell proliferation and glycosaminoglycans of chondrocyte cultures

There are only few reports on the correlation between bacterial products and the GAG pattern of cartilage. Mycobacteria bovis (BCG) were applied to chondrocyte monolayer cultures for one week. The following parameters did change: cell proliferation increased, glycosaminoglycan synthesis and secretion decreased, hyaluronic acid in secreted and cell-associated glycosaminoglycans increased, a correlation between the degree of these changes and the degree of cell differentiation seems to exist. The contact of bacteria like BCG to chondrocytes may change the cellular metabolism. On the tissue level this may injure articular cartilage and thus support the concept of predamaged cartilage that is readily susceptible to further degradation.

Homozygous achondroplasia: morphologic and biochemical study of cartilage

We have performed histochemical, immunohistochemical, electron microscopic, and biochemical studies on the upper tibial cartilage from a case of homozygous achondroplasia. The growth zone was narrow and disorganized. Columnization was absent except for a few areas with short rows of cells. Hypertrophy was reduced to scattered clusters of cells. The provisional calcification was patchy and primary trabeculae were thick and irregularly arranged. Islands of fibrous or fibrocartilagineous tissue were found along the growth zone. The matrix did not stain with safranin O and lacked metachromasia, except for pericellular rims around the hypertrophic cell clusters. Staining with antibodies against the large proteoglycan monomers and chondroitin-4-sulfate was weakly positive. Electron microscopic examination showed that only a few cells had degenerative signs. In most areas of the matrix, proteoglycan granules were absent. Areas with dense collagen fibers were seen. In contrast to the growth zone, the cartilage of the remaining epiphyses had normal histochemical, immunohistochemical, and electron microscopic appearance. The large proteoglycan monomers had a normal composition and hydrodynamic size. Type II and XI collagen, pepsin fragments of type IX collagen, and several noncollagenous proteins extracted from cartilage had a normal electrophoretic migration. It is suggested that a mutation affecting a matrix component or a regulatory pathway present only or predominantly in the growth area of the chondroepiphysis might explain the findings.

Stimulation of adult chondrocyte metabolism by a thyroid-derived factor

This paper reports the effects of adding partially purified bovine thyroid calcitonin, thyrocalcitonin, to adult bovine articular cartilage cells. Thyrocalcitonin stimulated chondrocyte proliferation fourfold under low serum (0.5%) culture conditions. In serum-free medium, thyrocalcitonin stimulated cell proliferation more than twofold. With high-density cultures in serum-free medium, chondrocyte glycosaminoglycan (GAG) synthesis was stimulated 60% by thyrocalcitonin. Cell-associated radioactivity was increased twofold. In contrast to thyrocalcitonin, addition of human and salmon calcitonin peptides as well as the thyroid hormones T3 and T4 had no effect on adult cartilage cell proliferation or GAG synthesis. The data reported here suggest the existence of a thyroid-derived factor, independent of calcitonin peptides or thyroid hormones, which stimulates adult articular chondrocyte metabolism.

Inhibition of sulphate incorporation by chondrocytes in intact cartilage by hyaluronate from foetal cartilage

A number of regulators are available in cartilage to effect the local control of matrix production by chondrocytes. A cartilage slice assay has been used in this study to investigate the influence of such regulators (extracted from foetal cartilage) on intact cartilage. A net inhibition of sulphation was found, rather than stimulation as reported for extracts rich in the somatomedin-like, cartilage derived factor (CDF). Inhibition was due, to a high molecular weight component identified as hyaluronic acid (based on enzyme sensitivity, chromatographic behaviour and temperature stability). Its inhibition of sulphation in intact cartilage was more profound than that produced by commercially available umbilical cord hyaluronate. We conclude that foetal cartilage hyaluronate is a far more potent inhibitor of sulphation than hyaluronate from other sources, suppressing sulphation even in the presence of a somatomedin-like activator and in intact cartilage, which responds poorly to commercial hyaluronate.

Developmental changes in fibroblast growth factor in the chicken embryo limb bud

Cell proliferation is a major event during early limb development. Significant levels of growth factor activity, as measured by stimulation of DNA synthesis in mouse BALB/c 3T3 cells, were found in extracts of chicken embryo limb buds at early stages of development. Extracts from stage-18 limbs (3 days of incubation) were 2 to 3 times more potent than were extracts from older stages, namely 22-24 (4 days), 26 (5 days), and 28 (6 days). Basic fibroblast growth factor (bFGF) was measured specifically using an RIA, and the amounts of factor obtained corresponded to the activities measured by the 3T3 cell-growth assay. In addition, most growth factor in the extracts bound with high affinity to heparin-Sepharose columns. Western (immunologic) blotting and immunoprecipitation with an antibody specific for bFGF revealed a protein of identical size to bFGF--i.e., 18 kDa, in the extracts. Thus, a growth factor with the properties of bFGF is present in the early limb, and the level of this factor is highest when proliferation is a predominant cellular event in the developing limb. These and other data suggest that fibroblast growth factor is a key regulatory factor in embryonic growth and morphogenesis.

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)

Regulation of human lung fibroblast glycosaminoglycan production by recombinant interferons, tumor necrosis factor, and lymphotoxin

Mononuclear cells may be important regulators of fibroblast glycosaminoglycan (GAG) biosynthesis. However, the soluble factors mediating these effects, the importance of intercytokine interactions in this regulation and the mechanisms of these alterations remain poorly understood. We analyzed the effect of recombinant (r) tumor necrosis factor (TNF), lymphotoxin (LT), and gamma, alpha, and beta 1 interferons (INF-gamma, -alpha and -beta 1), alone and in combination, on GAG production by normal human lung fibroblasts. rTNF, rLT, and rINF-gamma each stimulated fibroblast GAG production. In addition, rIFN-gamma synergized with rTNF and rLT to further augment GAG biosynthesis. In contrast, IFN-alpha A, -alpha D, and -beta 1 neither stimulated fibroblast GAG production nor interacted with rTNF or rLT to regulate GAG biosynthesis. The effects of the stimulatory cytokines and cytokine combinations were dose dependent and were abrogated by the respective monoclonal antibodies. In addition, these cytokines did not cause an alteration in the distribution of GAG between the fibroblast cell layer and supernatant. However, the stimulation was at least partially specific for particular GAG moieties with hyaluronic acid biosynthesis being markedly augmented without a comparable increase in the production of sulfated GAGs. Fibroblast prostaglandin production did not mediate these alterations since indomethacin did not decrease the stimulatory effects of the cytokines. In contrast, protein and mRNA synthesis appeared to play a role since the stimulatory effects of the cytokines were abrogated by cyclohexamide and actinomycin D, respectively. In addition, the cytokines and cytokine combinations increased cellular hyaluronate synthetase activity in proportion to their effects on hyaluronic acid suggesting that induction of this enzyme(s) is important in this stimulatory process. These studies demonstrate that IFN-gamma, TNF, and LT are important stimulators of fibroblast GAG biosynthesis, that interactions between these cytokines may be important in this regulatory process, that these cytokines predominantly stimulate hyaluronic acid production and that this effect may be mediated by stimulation of fibroblast hyaluronate synthetase activity.

High and low affinity binding sites for basic fibroblast growth factor on cultured cells: absence of a role for low affinity binding in the stimulation of plasminogen activator production by bovine capillary endothelial cells

Scatchard analysis of binding of 125I-basic fibroblast growth factor (FGF) to baby hamster kidney (BHK) cells revealed the presence of two binding sites: a high affinity site with KD of 20 pM and 80,000 sites per cell and a low affinity site with KD of about 2 nM and 600,000 sites per cell. The binding to the two sites could be separated by first washing the cells with 2 M NaCl at pH 7.5 which released the low affinity binding and then extracting the cells with 0.5% Triton X-100 to recover the 125I-basic FGF bound to high affinity sites. The binding to the high affinity site was acid sensitive, suggesting that it represented binding to the receptor. Binding to the low affinity site could be competed strongly by heparin and less strongly by heparan sulfate but not by chondroitin sulfate, dermatan sulfate, or keratan sulfate. Treatment of BHK cells with heparinase abolished 62% of the low affinity binding, suggesting that the low affinity binding represented binding to cell-associated, heparin-like molecules. A variety of other cell types, including bovine capillary endothelial (BCE) cells, also demonstrated both low and high affinity binding sites. To test whether the low affinity binding might play a role in the basic FGF stimulation of plasminogen activator (PA) production by BCE cells, heparin was added to BCE cultures at concentrations which totally blocked binding of 125I-basic FGF to the low affinity sites. Addition of the heparin did not diminish the increased PA production induced by basic FGF. This suggests that the low affinity binding has no direct role in the stimulation of PA production in BCE cells.