Polypeptide transforming growth factors isolated from bovine sources and used for wound healing in vivo

Pathogenesis of tumor stroma generation: a critical role for leaky blood vessels and fibrin deposition

Tumor stroma formation results from the interaction of tumor cells and their products with the host and certain of its normal defense mechanisms, particularly the clotting and fibrinolytic systems. It is a process in which tumor cells render local venules and veins hyperpermeable with the result that fibrinogen and other proteins extravasate and clot, forming an extravascular crosslinked fibrin gel. Coagulation is mediated by an interaction between extravasated plasma clotting factors and tumor-associated and perhaps other tissue procoagulants. Parallel activation of the fibrinolytic system leads to substantial fibrin turnover, but fibrin nonetheless accumulates in amounts, variable from tumor to tumor, that are sufficient to provide a provisional stroma. This provisional stroma imposes on tumor cells a structure that persists even as tumor cells multiply and as the fibrin provisional stroma is replaced by mature connective tissue. The provisional fibrin stroma also serves to regulate the influx of macrophages, and perhaps other inflammatory cells, but at the same time, and in ways that are not fully understood, facilitates the inward migration of new blood vessels and fibroblasts, integral components of mature tumor stroma. Ascites tumors differ from solid tumors in that fibrin gel is not ordinarily deposited in body cavities and, as a result, there is no provisional stroma to impose an initial structure. Tumor stroma generation resembles the process of wound healing in many respects. However, it differs in the mechanism of its initiation, and in the apparent lack of a role for platelets. It also differs fundamentally in that invading tumor cells continually render new vessels hyperpermeable to plasma, thus perpetuating the cycle of extravascular fibrin deposition. In this sense, tumors behave as wounds that do not heal. Largely neglected in this review has been discussion of the numerous cytokines, mitogens, and growth factors that are widely believed to play important roles in tumor angiogenesis and wound healing; i.e., PDGF, FGF, EGF, TGF alpha, TGF beta, TNF, interferons, etc. This omission has been intentional, and for two reasons. First, these cytokines have already received considerable attention [100,123-128]. Second, it is not yet clear how closely the actions of these molecules, as described in vitro, relate to their functions in vivo. At present we are deluged with a surfeit of factors that have the capacity to induce new blood vessel formation in angiogenesis assays; these factors include not only peptides but lipids and even ions [126,129-131].(ABSTRACT TRUNCATED AT 400 WORDS)

Type beta transforming growth factor regulates expression of genes encoding bone matrix proteins

TGF beta modulates the growth and differentiation of various cell types, in part by regulating the production of extracellular matrix proteins. In rat osteoblast-like cells TGF beta stimulates the production of collagen, osteopontin and osteonectin. On the other hand, TGF beta inhibits the production of osteocalcin, one of the most abundant non-collagenous bone matrix proteins, which is only expressed in osteoblasts. Inhibition of osteocalcin expression by TGF beta in the rat osteoblastic osteosarcoma, ROS 17/2.8 cells, occurs at least in part through transcriptional control.

Mitogenic and protein synthetic activity of tissue repair cells: control by the postsurgical macrophage

It is well known that fibroblasts are a main source of extracellular matrix synthesis necessary for tissue repair. In addition, macrophages secrete products that are known to modulate synthesis of extracellular matrix. Accordingly, we studied the incorporation of [3H]thymidine, [3H]proline, and [35S]sulfate into macromolecules produced by fibroblasts recovered from the site of peritoneal tissue repair cultured with and without spent media from postsurgical peritoneal macrophages. Rabbits underwent resection and reanastomosis of their small intestines. Peritoneal exudative cells (PEC) were then collected on postsurgical day 5 and day 10 as well as from nonsurgical controls, separated by discontinuous Percoll gradient centrifugation, and cultured for 48 h. A second group of rabbits underwent peritoneal wall abrasion from which fibroblast tissue repair cells (TRC) were collected from the site of injury at postsurgical day 7 and maintained in culture for varying times. Incorporation of radiolabeled precursors into DNA, collagen, and sulfated proteoglycans was determined. Incorporation of [3H]thymidine and [3H]proline into untreated TRC gradually decreased with culture duration. Conversely, [35S]sulfate incorporation gradually increased during prolonged culture. Macrophage spent media increased the levels of [3H]thymidine incorporation by the TRC. [3H]Proline and [35S]sulfate incorporation into TRC were also stimulated by macrophage spent media. However, this stimulation may be due to the enhanced proliferation of TRC by macrophage spent media. In conclusion, tissue repair fibroblasts are activated for postsurgical repair at the site of injury by many factors including secretory products from postsurgical macrophages.

Transforming growth factor beta increases cell surface binding and assembly of exogenous (plasma) fibronectin by normal human fibroblasts

Transforming growth factor beta (TGF-beta) enhances the cell surface binding of 125I-fibronectin by cultured human fibroblasts. The effect of TGF-beta on cell surface binding was maximal after 2 h of exposure to TFG-beta and did not require epidermal growth factor or protein synthesis. The enhancement was dose dependent and was found with the 125I-labeled 70-kilodalton amino-terminal fragment of fibronectin as well as with 125I-fibronectin. Treatment of cultures with TGF-beta for 6 h resulted in a threefold increase in the estimated number of fibronectin binding sites. The increase in number of binding sites was accompanied by an increased accumulation of labeled fibronectin in detergent-insoluble extracellular matrix. The effect of TGF-beta was biphasic; after 6 h of exposure, less labeled fibronectin bound to treated cultures than to control cultures. Exposure of cells to TGF-beta for greater than 6 h caused a two- to threefold increase in the accumulation of cellular fibronectin in culture medium as detected by a quantitative enzyme-linked immunosorbent assay. The second phase of the biphasic effect and the increase in soluble cellular fibronectin were blocked by cycloheximide. Immunofluorescence staining of fibroblast cultures with antifibronectin revealed that TGF-beta caused a striking increase in fibronectin fibrils. The 70-kilodalton amino-terminal fragment of fibronectin, which blocks incorporation of fibronectin into extracellular matrix, blocked anchorage-independent growth of NRK-49F cells in the presence of epidermal growth factor. Our results show that an increase in the binding and rate of assembly of exogenous fibronectin is an early event preceding the increase in expression of extracellular matrix proteins. Such an early increase in cell surface binding of exogenous fibronectin may be a mechanism whereby TGF-beta can modify extracellular matrix characteristics rapidly after tissue injury or during embryonic morphogenesis.

Transforming growth factor-beta (TGF beta) is chemotactic for human monocytes and induces their expression of angiogenic activity

TGF beta stimulates human blood monocyte migration, with peak migratory response occurring consistently at a concentration of 16-100 fg/ml. Checkerboard analysis revealed both chemotactic and chemokinetic components to this response. At higher concentrations (10-100 pg/ml), TGF beta stimulated expression of angiogenic activity by monocytes. While mRNA for TNF alpha was undetectable in resting monocytes, high steady state levels of TNF alpha mRNA were rapidly induced in TGF beta-treated monocytes. TGF beta is secreted by a number of neoplastic cells as well as normal cells such as platelets and lymphocytes. TGF beta may recruit monocytes from the circulation, and subsequently activate them to express angiogenic activities such as TNF alpha, thus playing an important role in wound repair, inflammation and tumor growth.

Acceleration of tensile strength of incisions treated with EGF and TGF-beta

The ability of surgeons to accelerate wound healing through pharmacologic intervention is limited. The effects of locally applied, biosynthetic human epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) on tensile strength of experimental incisions were investigated. A single dose of EGF in saline failed to increase tensile strength over controls. Thus, EGF was incorporated into multilamellar liposomes, which prolonged the exposure of incisions to EGF (p less than 0.001). A single dose of EGF in multilamellar liposomes produced a 200% increase in wound tensile strength over controls between 7 and 14 days (p less than 0.05). Light and electron microscopy of the wounds revealed increased collagen formation and fibroblast proliferation. A single dose of TGB-beta in a collagen vehicle stimulated a 51% increase in wound tensile strength at 9 days (p less than 0.01). We conclude that addition of EGF and TGF-beta in appropriate vehicles stimulates early transient increases in wound tensile strength in normal rats.

The physiology of wound healing

Many of the biochemical events of wound healing are prisoners of the victim's physiologic state. Although the initial local events of inflammation occur normally in any viable tissue, the subsequent reparative capacities of macrophages, fibroblasts, and endothelial cells are seriously impaired by any compromise of local perfusion and oxygenation. In particular, the bacteriocidal capacities of granulocytes are heavily dependent on local oxygenation/perfusion, nutrition, and endocrine status. This article depicts the local mechanisms of repair with special attention to the means by which physiologic and nutritional support at the clinical level influence repair, even to a point at which wound healing may exceed contemporary expectations. Without appropriate physiologic, nutritional, and endocrine support, wound healing often fails totally. It is now possible, although not always easy, to achieve optimal physiologic support.

In situ hybridization--a useful tool for studies on collagen gene expression in cell culture as well as in normal and altered tissue

We report the application of antisense RNA probes for in situ hybridization to identify collagen type I and type III mRNA synthesizing fibroblasts under in vitro and in vivo conditions in normal and wounded human skin. Non-specific hybridization was excluded by specific distribution patterns of alpha 1(I)- and alpha 1(III) probes in mouse fetuses. In addition, the specificity of hybridization was checked by sense probes, radioactively labelled transcripts of Gemini vectors and a keratin probe. In normal skin weakly activated fibroblasts were sparsely scattered within the dermis, while in wound healing processes mRNA both for alpha 1(I) and for alpha 1(III) was dramatically increased, thus suggesting that collagen synthesis is at least partly regulated at a pretranslational level. In addition, the intensity of the labelling, as defined by image analysis and the distribution pattern of collagen mRNA synthesizing cells, provide strong evidence that wound healing by primary intention starts within the deep dermis.

Stimulatory effects of transforming growth factor-beta and epidermal growth factor on epidermal cell outgrowth from porcine skin explant cultures

Transforming growth factor-beta (TGF-beta) is known to stimulate dermal wound healing events (fibroplasia and fibrosis). In this study, the effect of TGF-beta on epidermal wound healing (re-epithelialization) was examined. Epidermal cell outgrowth from partial-thickness porcine skin explants was used as an in vitro model for epithelialization. All cultures were grown in medium with 1% fetal bovine serum, which was sufficient for explant viability but low enough to permit measurement of modulation by added factors. Because TGF-beta is known to act in concert with other growth factors, it was evaluated alone and in the presence of epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). The results indicate that TGF-beta produced earlier initiation of outgrowth, by 1-2 d compared with control cultures, and increased the rate of outgrowth during the migratory phase of culture (Days 1-3). Compared to controls, EGF alone produced a greater percentage of growing explants and an increased rate of outgrowth during the mitotic phase (Days 4-7). TGF-beta (1 or 10 ng/ml) and EGF (5 ng/ml) had an additive rather than a synergistic effect on outgrowth. PDGF-treated explants did not show enhanced growth when PDGF (2.5 units/ml) was added alone or together with TGF-beta and EGF. The ability of TGF-beta to produce earlier initiation of outgrowth was not due to an effect on mitosis, because TGF-beta did not increase the incorporation of [3H]thymidine into keratinocytes in the growing epidermal sheets. Rather, it is likely that TGF-beta facilitated keratinocyte migration, possibly by unmasking a receptor on the epidermal cell surface. These results suggest that TGF-beta may play a role in early epidermal wound healing.

Effect of lymphotoxin and tumor necrosis factor on endothelial and connective tissue cell growth and function

In an approach to understand the immune basis of human vascular and fibrotic disorders, the effects of recombinant human tumor necrosis factor alpha (rTNF) and lymphotoxin (rLT) on the in vitro growth and function of vascular and connective tissue cells were studied. Both rTNF and rLT stimulated fibroblast growth and protein, fibronectin, and collagen synthesis in dose-dependent fashion. In contrast, endothelial cell (EC) growth was inhibited by both cytokines; true EC cytotoxicity was seen at high concentrations (greater than or equal to 500 mu/ml). Addition of recombinant interferon-gamma markedly enhanced EC cytotoxicity while the growth factor beta-transforming growth factor reversed EC growth inhibition. Both rTNF and rLT stimulated factor VIII-Ag synthesis by EC. These contrasting effects of rTNF and rLT on fibroblast and endothelial cell growth and function in vitro are intriguing because they are the same contrasting effects observed in vivo in connective tissue and vascular disorders, raising the possibility of a role for these cytokines in these disorders. Study of the in vitro and in vivo mechanisms of these diverse effects may contribute to the understanding of certain human disorders characterized by endothelial injury and fibroblast activation leading to fibrosis.

Transforming growth factor beta increases cell surface binding and assembly of exogenous (plasma) fibronectin by normal human fibroblasts

Transforming growth factor beta (TGF-beta) enhances the cell surface binding of 125I-fibronectin by cultured human fibroblasts. The effect of TGF-beta on cell surface binding was maximal after 2 h of exposure to TFG-beta and did not require epidermal growth factor or protein synthesis. The enhancement was dose dependent and was found with the 125I-labeled 70-kilodalton amino-terminal fragment of fibronectin as well as with 125I-fibronectin. Treatment of cultures with TGF-beta for 6 h resulted in a threefold increase in the estimated number of fibronectin binding sites. The increase in number of binding sites was accompanied by an increased accumulation of labeled fibronectin in detergent-insoluble extracellular matrix. The effect of TGF-beta was biphasic; after 6 h of exposure, less labeled fibronectin bound to treated cultures than to control cultures. Exposure of cells to TGF-beta for greater than 6 h caused a two- to threefold increase in the accumulation of cellular fibronectin in culture medium as detected by a quantitative enzyme-linked immunosorbent assay. The second phase of the biphasic effect and the increase in soluble cellular fibronectin were blocked by cycloheximide. Immunofluorescence staining of fibroblast cultures with antifibronectin revealed that TGF-beta caused a striking increase in fibronectin fibrils. The 70-kilodalton amino-terminal fragment of fibronectin, which blocks incorporation of fibronectin into extracellular matrix, blocked anchorage-independent growth of NRK-49F cells in the presence of epidermal growth factor. Our results show that an increase in the binding and rate of assembly of exogenous fibronectin is an early event preceding the increase in expression of extracellular matrix proteins. Such an early increase in cell surface binding of exogenous fibronectin may be a mechanism whereby TGF-beta can modify extracellular matrix characteristics rapidly after tissue injury or during embryonic morphogenesis.

Transforming growth factor beta (TGF-beta) induces fibrosis in a fetal wound model

The adult cellular response to tissue injury is characterized by acute inflammation followed eventually by fibroblast proliferation and collagen synthesis. Fetal tissue responses to injury differ markedly from those of the adult; an early acute inflammatory response is absent, few fibroblasts participate, and no collagen is deposited. The object of the present study was to analyze the effects of transforming growth factor beta (TGF-beta), an important regulatory molecule in adult healing events, on the fetal tissue response following wounding. Fetal cellular and extracellular matrix responses to injury were evaluated by placing subcutaneous wound implants containing TGF-beta (0.01 to 10 ng) in fetal rabbits at 24 days gestation (term = 31 days). Histologic responses one to seven days later were compared with fetal and adult control implants without TGF-beta. The histology of the adult implant was characterized by an early acute inflammatory response: by day 7 fibroblasts and collagen were predominant. In contrast, control implants removed from fetal rabbits had no histologic evidence of acute inflammation or fibroblast penetration and no collagen was deposited. When implants containing 1.0 ng TGF-beta were removed from fetal rabbits at seven days, a grossly fibrotic reaction was observed: histology confirmed marked fibroblast penetration with collagen deposition. Fetal implants containing 0.01 ng or 10 ng TGF-beta showed few fibroblasts but had increased numbers of inflammatory cells compared with controls. These observations demonstrate that the fetal response becomes adultlike with fibroblast proliferation and collagen accumulation when TGF-beta is added, thus documenting the responsiveness of the fetal system to adult repair signals.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor beta stimulates collagen-matrix contraction by fibroblasts: implications for wound healing

An important event during wound healing is the contraction of newly formed connective tissue (granulation tissue) by fibroblasts. The role of polypeptide growth factors in the process of wound contraction was investigated by analyzing the influence of transforming growth factor beta (TGF-beta), platelet-derived growth factor on the ability of fibroblasts to contract a collagen matrix in an in vitro system. TGF-beta, but not the other growth factors tested, markedly enhanced the ability of BHK-21,3T3-L1, and human foreskin fibroblasts to contract collagen gels. These results suggest that TGF-beta released from platelets and inflammatory cells at sites of tissue injury stimulates fibroblasts to contract the provisional wound matrix and that this effect contributes to the ability of TGF-beta to accelerate wound healing.

Effects of transforming growth factor type beta upon bone cell populations grown either in monolayer or semisolid medium

Bone has been shown to store large amounts of transforming growth factor type beta (TGF beta) and this has recently been found to be synthesized by bone-forming cells. We report on studies undertaken to examine the effects of platelet-derived TGF beta on different bone cell populations, isolated from 1-day postnatal rat calvaria by sequential enzymatic digestion. In addition, we tried to determine which of these cell populations synthesize TGF beta. In this regard, evidence was collected to indicate that cell populations which were shown to be enriched with osteoblast-like cells synthesize TGF beta. Although the production of the factor appeared to be limited to a particular cell type, its action was found to be of a more general character, as all cell populations were found to respond to TGF beta. Contrary to earlier reports, TGF beta was shown to be inhibitory upon cell proliferation. In this context, growth of cells released during early digestions was reduced considerably more than growth of those released during late digestions. Studies on the effect upon protein synthesis revealed that TGF beta specifically inhibited collagen but not the synthesis of noncollagenous proteins. The synthesis of collagen was altered to a greater extent in cells isolated during late digestions than in cells of the early populations. Further information on the TGF beta-mediated effects on bone cell biology was provided by data showing that both alkaline phosphatase and cAMP production in response to PTH was greatly reduced by TGF beta. Finally, experiments performed to determine whether TGF beta induces any of the bone cell populations to acquire the transformed phenotype revealed that only populations previously shown to be enriched with osteoblast-like cells formed colonies in soft agarose.(ABSTRACT TRUNCATED AT 400 WORDS)

Transforming growth factor-beta-like activity in tumors of the central nervous system

Transforming growth factor type beta (TGF-beta) is a ubiquitous peptide with wide-ranging regulatory functions. This paper reports the initial isolation of TGF-beta activity from human glial and mesenchymally derived tumors and a human glial tumor cell line. While its physiological function at the molecular level is not yet defined, it is believed that this peptide plays a central role in the control of growth and transformation, with the exact role it plays being a function of the entire set of growth factors present in a given cell.

Regulation of fibronectin biosynthesis by dexamethasone, transforming growth factor beta, and cAMP in human cell lines

The regulation of fibronectin (FN) biosynthesis by dexamethasone (a synthetic glucocorticoid), forskolin (an activator of adenylate cyclase), and transforming growth factor beta (TGF-beta) was examined in six human cell lines. Dexamethasone treatment produced the largest increase in FN biosynthesis in the fibrosarcoma cell line, HT-1080 (approximately 45-fold). This seems to result from a dexamethasone-mediated increase in FN mRNA stability which increases the message half-life from approximately 11 to 26 h. The relative instability of FN mRNA in the fibrosarcoma (t1/2 11 h) compared to normal fibroblasts (70 h) appears to result from the particular transformed phenotype of the HT-1080 cells. Forskolin and TGF-beta increase the rate of FN gene transcription in most of the cell lines. These effects (four- to six-fold) occur rapidly and do not require protein synthesis in the responsive cell lines which include normal fibroblasts. However, in the fibrosarcoma (HT-1080), a surprisingly large induction (20-30-fold) is observed and this induction is different from that in the normal fibroblasts and the other cell lines in that both protein synthesis and a lag period are required. Synergism is seen with dexamethasone and either forskolin or TGF-beta in HT-1080 cells increasing the rate of FN biosynthesis approximately 200-fold to a level similar to normal fibroblasts. This seems to result from a combination of FN mRNA stabilization (dexamethasone) and increased transcription (forskolin and TGF-beta).

Depletion of salivary gland epidermal growth factor by sialodacryoadenitis virus infection in the Wistar rat

Male and female Wistar rats 2 to 15 months of age were inoculated intranasally with sialoda-cryoadenitis (SDA) virus and killed at 8 to 21 days post-inoculation (PI). Submandibular glands were evaluated by light and electron microscopy, and levels of salivary gland epidermal growth factor (EGF) were quantitated by cytochemistry and competitive radioreceptor assay. Apical granules in the epithelial cells of the granular convoluted tubules (GCT) were selectively depleted during the acute and convalescent stages of the disease. In addition, levels of immunoreactive EGF were reduced in affected submandibular glands, especially at 8 to 14 days PI with SDA virus, but some evidence of EGF depletion was seen at up to 3 weeks PI. A corresponding transient depletion of EGF receptor reactive salivary EGF was seen between 1 and 3 weeks after experimental SDA infection. These studies suggest that a clinical (or subclinical) infection with SDA virus could have significant effects on experimental studies on EGF-dependent functions, including reproductive physiology and carcinogenesis.

Effect of transforming growth factor beta on cell proliferation and glycosaminoglycan synthesis by rabbit growth-plate chondrocytes in culture

The effects of the transforming growth factor beta (TGF-beta) on the growth and glycosaminoglycan synthesis of rabbit growth plate-chondrocytes in culture were studied. In serum-free medium, TGF-beta caused dose-dependent inhibition of DNA synthesis by chondrocytes, measured as [3H]thymidine incorporation (ED50 = 0.1-0.3 ng/ml). The inhibitory effect was maximal at a dose of 1 ng/ml, and extended for a duration of 16-42 h. In contrast, TGF-beta potentiated the synthesis of DNA stimulated by fetal calf serum (FCS). Addition of TGF-beta (1 ng/ml) to cultures containing 10% FCS increased [3H]thymidine incorporation to 1.6-times that in cultures with 10% FCS alone. Consistent with this finding, TGF-beta potentiated DNA synthesis stimulated by the purified growth factors such as platelet-derived growth factor (PDGF), epidermal growth factor (EGF) and fibroblast growth factor (FGF). The maximal stimulation of DNA synthesis by FGF (0.4 ng/ml) was further potentiated dose dependently by TGF-beta (ED50 = 0.1 ng/ml, maximum at 1 ng/ml). When the cultures were treated with the optimal concentrations of TGF-beta (1 ng/ml) and FGF (0.4 ng/ml), [3H]thymidine incorporation was 3-times higher than that of cultures treated with FGF alone. This TGF-beta-induced potentiation of DNA synthesis was associated with replication of chondrocytes, as shown by a marked increase in the amount of DNA during treatment of sparse cultures of the cells with the growth factors for 5 days. In contrast, TGF-beta caused dose-dependent stimulation of glycosaminoglycan synthesis in confluent cultures of growth-plate chondrocytes (ED50 = 0.3 ng/ml, maximum at 1 ng/ml). This stimulatory effect of TGF-beta was greater than that of insulin-like growth factor I (IGF-I) or PDGF. Furthermore, TGF-beta stimulated glycosaminoglycan synthesis additively with IGF-I or PDGF. Recently, it has been suggested that bone and articular cartilage are rich sources of TGF-beta, whereas epiphyseal growth cartilage is not. Thus, the present data indicate that TGF-beta may be important in bone formation by modulating growth and phenotypic expression of chondrocytes in the growth plate, possibly via a paracrine mechanism.

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.

In vivo incisional wound healing augmented by platelet-derived growth factor and recombinant c-sis gene homodimeric proteins

Human platelet-derived growth factor (hPDGF) is likely to be important in stimulating tissue repair, based upon its in vivo chemotactic and stimulatory activities for inflammatory cells and fibroblasts and upon the presence of PDGF and related proteins in platelets, macrophages, and activated fibroblasts, cell types that make up the milieu of the healing wound. Recombinant human c-sis (rPDGF-B), homodimers of the B chain of PDGF, were compared with hPDGF in vitro. rPDGF-B was immunologically similar to hPDGF and, at identical concentrations, similar to hPDGF in stimulating fibroblast mitogenesis and chemotaxis of polymorphonuclear leukocytes, monocytes, and fibroblasts. Purified hPDGF and rPDGF-B were also tested in vivo for potency in a model of tissue repair using a linear incision wound through rat dermis. A single application of hPDGF or rPDGF-B (2-20 micrograms/wound) in a slow release vehicle at the time of wounding resulted in a dose-dependent, statistically highly significant increase of breaking strength of treated wounds. Wound healing in animals treated with rPDGF-B was 170% stronger and accelerated by 2 d during the first week over control wounds and by 4-6 d over the next 2 wk. Histologic evaluation of growth factor-treated wounds correlated the in vitro chemotactic activity and the accelerated healing of wounds with a striking inflammatory cell infiltrate early after wounding, markedly increased formation of granulation tissue by 4-d, and increased fibrosis by 14 d in comparison to control wounds. The results thus demonstrate that rPDGF-B is fully active in in vitro tests of mitogenesis and chemotaxis and, for the first time, demonstrate directly that PDGF significantly advances wound healing in incisional wounds of experimental animals.

Differential effects of transforming growth factor-beta on the synthesis of extracellular matrix proteins by normal fetal rat calvarial bone cell populations

To determine the effects of transforming growth factor-beta (TGF-beta) on the different cell types that exist in bone, cell populations (I-IV), progressively enriched in osteoblastic cells relative to fibroblastic cells, were prepared from fetal rat calvaria using timed collagenase digestions. TGF-beta did not induce anchorage-independent growth of these cells, nor was anchorage-dependent growth stimulated in most populations studied, despite a two- to threefold increase in the synthesis of cellular proteins. In all populations the synthesis of secreted proteins increased 2-3.5-fold. In particular, collagen, fibronectin, and plasminogen activator inhibitor synthesis was stimulated. However, different degrees of stimulation of individual proteins were observed both within and between cell populations. A marked preferential stimulation of plasminogen activator inhibitor was observed in each population, together with a slight preferential stimulation of collagen; the effect on collagen expression being directed primarily at type I collagen. In contrast, the synthesis of SPARC (secreted protein acidic rich in cysteine/osteonectin was stimulated approximately two-fold by TGF-beta, but only in fibroblastic populations. Collectively, these results demonstrate that TGF-beta stimulates matrix production by bone cells and, through differential effects on individual matrix components, may also influence the nature of the matrix formed by different bone cell populations. In the presence of TGF-beta, osteoblastic cells lost their polygonal morphology and alkaline phosphatase activity was decreased, reflecting a suppression of osteoblastic features. The differential effects of TGF-beta on bone cell populations are likely to be important in bone remodeling and fracture repair.

Systemic scleroderma. Clinical and pathophysiologic aspects

Systemic scleroderma is a generalized disease of connective tissue involving mainly the skin, the gastrointestinal tract, the lungs, the heart, and the kidneys. It can be present in different forms, of which acroscleroderma, with limited cutaneous and extracutaneous involvement, and diffuse scleroderma within a more rapid progression are most characteristic. Circulating antibodies against antinucleolar antigens are present in most patients with systemic scleroderma. They are helpful for establishing a classification and for determining the prognosis of the disease; their involvement in the pathogenesis, however, is still unclear. Alterations of the blood vessels and induction of fibroblasts by potent mediators are thought to play an important role in the early phase of scleroderma. Therefore early diagnosis is required, which then can initiate vasoactive therapy. In patients with systemic scleroderma, who also suffer from additional myositis, interstitial lung diseases, or arthritis, anti-inflammatory treatment with prednisolone and azathioprine is suggested. Development and progression of fibrosis cannot yet be influenced sufficiently. Only D-penicillamine affecting cross-linking of collagen has been widely used in scleroderma and has some beneficial effect.

Growth regulation of skin cells by epidermal cell-derived factors: implications for wound healing

Epidermal cell-derived factors (EDF), present in extracts and supernatant fluids of cultured epidermal cells, were found to stimulate the proliferation of keratinocytes but to inhibit fibroblasts. In vitro, the effect of EDF on epidermal cells resulted in an increased number of rapidly proliferating colonies composed mainly of basal keratinocytes. Control cultures grown in the absence of EDF had a high proportion of terminally differentiated cells. In fibroblast cultures EDF inhibited the ability of fibroblasts to cause contraction of collagen sponges by 90%. Epidermal growth factor, basic fibroblast growth factor, platelet-derived growth factor, transforming growth factor beta, nerve growth factor, and extracts of WI-38 cells (human embryonic lung fibroblasts) did not have this inhibitory activity. Application of EDF to surgical wounds stimulated extensive migration and proliferation of keratinocytes from remnants of glands, hair follicles, and wound edges. The restoration of complete epidermal coverage of wounds treated with EDF occurred twice as rapidly as that of control wounds. In addition, regenerating dermis in the EDF-treated wounds contained 1/5th to 1/15th as many cells as wounds treated with epidermal growth factor, urogastrone, transforming growth factor, or phosphate-buffered saline. The use of EDF to enhance re-epithelization and to prevent scar formation is proposed.

Transforming growth factor beta increases mRNA for matrix proteins both in the presence and in the absence of changes in mRNA stability

Transforming growth factor-beta (TGF-beta) has been shown to stimulate synthesis of extracellular matrix proteins, both in animals and in cell culture. We found that mRNAs for alpha 1(I) collagen, fibronectin, and thrombospondin were markedly increased in TGF-beta-treated 3T3 (mouse) cells. For collagen and fibronectin this increase was 10-to 20-fold, as measured by quantitative blot hybridization analysis. A maximal value was reached at 16-24 hr, with a subsequent gradual decline. Concomitant treatment with cycloheximide prevented the stimulation observed with TGF-beta. Under conditions of confluent growth a clear increase in alpha 1(I) collagen mRNA stability was observed, whereas in subconfluent cells no change in mRNA half-life was found, despite an equally large increase in mRNA levels. We suggest that the mode of action of TGF-beta varies with the target cell and depends on the interplay of a number of complex cellular factors.

Localized production of TGF-beta mRNA in tumour promoter-stimulated mouse epidermis

Tumour promoters induce a wide spectrum of morphological and biochemical alterations when applied to mouse epidermis in vivo. These include the induction of RNA, DNA and protein synthesis during discrete phases of proliferation and differentiation. This constitutes an ideal model for studying molecular events underlying the disruption of epidermal homeostasis by TPA, and its subsequent re-establishment. Transforming growth factor-beta (TGF-beta) can induce either growth stimulation, inhibition, or differentiation, depending on the target cell. A function has been proposed for TGF-beta in wound healing and in tumour promotion, but the main source of TGF-beta is generally thought to be platelets, macrophages or lymphocytes, and a direct role for this growth factor in regulating tissue homeostasis in vivo has not been demonstrated. We show here that when the tumour promoter 12-tetradecanoyl-phorbol-13-acetate (TPA) is applied to the skin of mice, very high levels of TGF-beta messenger RNA are induced in the epidermal cells. In situ hybridization techniques show that the main site of TGF-beta synthesis is in the suprabasal differentiating epidermal cells. These results suggest that TGF-beta may be a natural regulator of epidermal homeostasis which is important in tumour promotion.

Regulation of platelet-derived growth factor gene expression by transforming growth factor beta and phorbol ester in human leukemia cell lines

We studied the expression of the genes encoding the A and B chains of platelet-derived growth factor (PDGF) in a number of human leukemia cell lines. Steady-state expression of the A-chain RNA was seen only in the promonocytic leukemia cell line U937 and in the T-cell leukemia cell line MOLT-4. It has previously been reported that both PDGF A and PDGF B genes are induced during megakaryoblastic differentiation of the K562 erythroleukemia cells and transiently during monocytic differentiation of the promyelocytic leukemia cell line HL-60 and U937 cells. In this study we show that PDGF A RNA expression was induced in HL-60 and Jurkat T-cell leukemia cells and increased in U937 and MOLT-4 cells after a 1- to 2-h stimulation with an 8 pM concentration of transforming growth factor beta (TGF-beta). PDGF A RNA remained at a constant, elevated level for at least 24 h in U937 cells, but returned to undetectable levels within 12 h in HL-60 cells. No PDGF A expression was induced by TGF-beta in K562 cells or in lung carcinoma cells (A549). Interestingly, essentially no PDGF B-chain (c-sis proto-oncogene) RNA was expressed simultaneously with PDGF A. In the presence of TGF-beta and protein synthesis inhibitors, PDGF A RNA was superinduced at least 20-fold in the U937 and HL-60 cells. PDGF A expression was accompanied by secretion of immunoprecipitable PDGF to the culture medium of HL-60 and U937 cells. The phorbol ester tumor promoter tetradecanoyl phorbol acetate also increased PDGF A expression with similar kinetics, but with a mechanism distinct from that of TGF-beta. These results suggest a role for TGF-beta in the differential regulation of expression of the PDGF genes.

Reduced growth-factor requirement of keloid-derived fibroblasts may account for tumor growth

Keloids are benign dermal tumors that form during an abnormal wound-healing process in genetically susceptible individuals. Although growth of normal and keloid cells did not differ in medium containing 10% (vol/vol) fetal bovine serum, keloid cultures grew to significantly higher densities than normal cells in medium containing 5% (vol/vol) plasma or 1% fetal bovine serum. Conditioned medium from keloid cultures did not stimulate growth of normal cells in plasma nor did it contain detectable platelet-derived growth factor or epidermal growth factor. Keloid fibroblasts responded differently than normal adult fibroblasts to transforming growth factor beta. Whereas transforming growth factor beta reduced growth stimulation by epidermal growth factor in cells from normal adult skin or scars, it enhanced the activity of epidermal growth factor in cells from keloids. Normal and keloid fibroblasts also responded differently to hydrocortisone: growth was stimulated in normal adult cells and unaffected or inhibited in keloid cells. Fetal fibroblasts resembled keloid cells in their ability to grow in plasma and in their response to hydrocortisone. The ability of keloid fibroblasts to grow to higher cell densities in low-serum medium than cells from normal adult skin or from normal early or mature scars suggests that a reduced dependence on serum growth factors may account for their prolonged growth in vivo. Similarities between keloid and fetal cells suggest that keloids may result from the untimely expression of a growth-control mechanism that is developmentally regulated.

Human platelet alpha granules contain a nonspecific inhibitor of megakaryocyte colony formation: its relationship to type beta transforming growth factor (TGF-beta)

Whole blood serum (WBS) and platelet-poor plasma-derived serum (PDS) from the same normal subject were compared for their abilities to support human megakaryocyte (MK) colony formation. In all cases, PDS promoted the growth of a higher number (20-50%) of MK colonies than did WBS. Increasing amounts of WBS decreased the number of colonies, whereas increasing concentration of PDS had no marked effects. Crude platelet extracts or platelet secretory products from thrombin-activated platelets also elicited an inhibition of MK colony formation in a dose-dependent manner. A complete inhibition was found for a dose equivalent to 1.10(9) platelets/ml and a 50% inhibition in a range of 1.10(7)-1.10(8) platelets/ml. These platelet products were also inhibitory for erythroid progenitor growth. Platelets from two patients with gray platelet syndrome elicited only a minor inhibition of MK growth, suggesting that the platelet alpha granule is the origin of this inhibition. When platelet extracts were acid-treated, the biological activity of the inhibitor on CFU-MK and CFU-E growth was 20-50-fold higher. In addition, a potent stimulatory activity on the growth of day 7 CFU-GM was observed. The enhancement of biological activities by acid treatment suggests that type beta transforming growth factor (TGF-beta) could be involved in this platelet inhibitory activity. The homogeneous native TGF-beta (from 1 pg to 1 ng/ml) produced the same effects previously induced by platelet products. It totally inhibited CFU-MK growth (at a 500 pg/ml), it inhibited CFU-E growth, and it stimulated growth of day 7 CFU-GM in the presence of a colony-stimulating factor. The inhibition of CFU-MK growth was also observed on purified progenitors. In conclusion, these results suggest that TGF-beta may be implicated in negative autocrine regulation of megakaryopoiesis. However, since this molecule has ubiquitous biological activities, its physiologic relevance as a normal regulator of megakaryopoiesis requires further investigation.

Transforming growth factor beta and inhibition of hepatocellular proliferation

Transforming growth factor beta (TGF beta) is a recently characterized polypeptide that elicits diverse biologic actions in a wide range of cell types in vitro. TGF beta is a bifunctional growth regulator of fibroblasts with either growth stimulation or growth inhibition but inhibits the growth of most epithelial cells. In addition, TGF beta can either block or induce the differentiation of certain cells. TGF beta reversibly inhibits DNA synthesis in normal adult rat hepatocytes and in cells isolated from regenerating liver 12 h and 18 h after partial hepatectomy. However, at 3 h and 6 h after hepatectomy there is a decrease in sensitivity of hepatocytes to growth inhibition by TGF beta. Recent data from other laboratories indicate that TGF beta expression increases substantially in liver after partial hepatectomy and that administration of purified TGF beta in vivo inhibits DNA synthesis in regenerating rat liver. Together with our observations, these findings suggest that TGF beta may play a central role as a negative paracrine growth regulator in adult rat liver.

Promotion of wound collagen formation in normal and diabetic mice by quadrol

The rate of collagen deposition in implanted polytetrafluoroethylene (PTFE) tubing in non-diabetic and streptozotocin-induced (STZ) diabetic mice was measured during 14 days post-wounding. At the time of implantation, test groups received injections of either Quadrol [N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine], glucan, or buffer in an area adjacent to the wound site. The accumulation of collagen in the implants of Quadrol-treated non-diabetic animals was more than 200% above control on days 8 to 11 and was 50% above control on day 14. In Quadrol-treated STZ-diabetic mice, the collagen accumulation gradually increased from 50% above control on day 8 to 200% above control on day 14. Treatment with glucan increased the collagen accumulation in normal mice 200 to 300% above control from days 8 to 11 respectively and then 30% above control on day 14. Collagen accumulation in the implants of the glucan-treated STZ-diabetic mice was similar to the control group. These results indicate that Quadrol promotes in vivo collagen synthesis and that Quadrol may be effective as a stimulator of wound healing in diabetic and non-diabetic animals.

Platelet-derived growth factor enhances demineralized bone matrix-induced cartilage and bone formation

Subcutaneous implantation of demineralized bone matrix induces the local formation of cartilage and bone. In this study we have investigated the influence of adding various growth factors to the implant. Cartilage formation was monitored by measuring collagen II mRNA levels, and bone formation in the implant was assessed from alkaline phosphatase activity and calcium content. Supplements of the platelet-derived growth factor to implants in older rats increased and production of mRNA for collagen II, alkaline phosphatase activity, and the calcium content of the implant, whereas the other growth factors tested were without effect. The data suggest that under some conditions bone induction is submaximal and can be increased by local supplement of platelet-derived growth factor (PDGF). The present observations may have important therapeutic implications in the treatment of nonunions of fractures and impaired bone formation in the aged.

Chemotactic response of embryonic limb bud mesenchymal cells and muscle-derived fibroblasts to transforming growth factor-beta

Transforming growth factor beta (TGF-beta) was tested for its ability to stimulate a chemotactic response in Stage 24 embryonic chick limb bud mesenchymal cells and muscle-derived fibroblasts. TGF-beta stimulated dose-dependent chemotaxis in both cell populations. Maximal chemotaxis was achieved with a concentration of 5 ng/ml for limb bud cells and as low as 15 pg/ml for muscle-derived fibroblasts. TGF-beta was not chemokinetic at these levels. Several other proteins found in bone, namely fibronectin, type I collagen, and osteonectin, were not chemotactic. However, both Bone Gla-protein and basic-FGF were found to be chemotactic but less effective than TGF-beta. Comparison with extracts of adult bone indicates that while TGF-beta is a potent chemoattractant, it does not account for all the chemotactic activity found in adult bone.

Cytokines: molecular and biological characteristics

Cytokines are soluble molecules with many cells as the source of their origin and as targets for their actions. They are pleiotropic in their biological functions. Some cytokines are distinct with respect to their molecular structure yet they have overlapping biological properties (Interleukin 1 and tumor necrosis factors). Others are structurally distinct and often have contrasting biological activities (e.g. tumor necrosis factors and transforming growth factor-beta). In this article I have briefly reviewed the molecular and biological properties of four cytokines that appears to play an important role in the pathogenesis of certain immunoinflammatory disorders. It is also to be stressed that there are additional cytokines (e.g. granulocyte-monocyte colony stimulating factors, interleukin 2, interferons etc.) that could also play a role in the pathogenesis of immunoinflammatory disorders.

Transforming growth factor beta-1 in acute myocardial infarction in rats

TGF-beta 1 has been examined in the heart during myocardial infarction caused by ligation of the left coronary artery. Infarcted and uninfarcted myocardium have been compared by immunohistochemical staining of TGF-beta 1 and by Northern blot analysis of mRNA. Normal ventricular myocytes are strongly stained by an antibody to TGF-beta 1. Progressive loss of staining of these myocytes begins within 1 hr after coronary ligation. However, by 24-48 hr after ligation, intense staining of myocytes at the margin of infarcted areas is seen. Northern blots of infarcted myocardium 48 hr after ligation show a 3- to 4-fold increase in the principal 2.4 kb TGF-beta 1 mRNA; there is also a marked increase in a minor 1.9 kb transcript. In the same tissue samples, there is a 2-fold decrease in the mRNA for the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase. The results indicate a significant role for TGF-beta in the response of the heart to injury.

Type beta transforming growth factor (TGF beta) regulation of alkaline phosphatase expression and other phenotype-related mRNAs in osteoblastic rat osteosarcoma cells

TGF beta 1 from porcine platelets increased alkaline phosphatase (AP) activity in the rat osteoblastic cell line ROS 17/2.8 about three-fold. This effect was dose-dependent with an ED50 of about approximately 0.2 ng/ml and was larger during logarithmic growth than at confluence. TGF beta 1 inhibited cell growth by about 30% with similar dose dependence. Thirty min exposure to TGF beta 1 was sufficient to increase AP activity 3 days later by about two-fold but did not affect cell growth, suggesting dissociation between effects on proliferation and differentiation. The rise in AP activity started 6 h after TGF beta 1 addition and was blocked by cycloheximide and actinomycin D. TGF beta 1 also increased AP mRNA by two- to three-fold and this effect was not blocked by cycloheximide. The half-life of AP mRNA, estimated following the addition of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole was about ten h in both control and TGF beta 1-treated cells. The mRNAs for type I procollagen and osteonectin were also increased by TGF beta 1 but fibronectin mRNA was decreased. TGF beta 2 effects on AP and cell growth were similar to those of TGF beta 1, except for lack of activity following transient exposure. At saturating concentrations, TGF beta 2 (2 ng/ml) or dexamethasone (10(-7) M), which has similar effects on these cells, did not further augment the effects of TGF beta 1 (at 2 ng/ml). Above findings suggest that TGF beta promotes osteoblastic differentiation in rat osteosarcoma cells at least in part by acting at the pretranslational level.