One systemic administration of transforming growth factor-beta 1 reverses age- or glucocorticoid-impaired wound healing

Aging fibroblasts present reduced epidermal growth factor (EGF) responsiveness due to preferential loss of EGF receptors

Wound healing is compromised in aging adults in part due to decreased responsiveness of fibroblasts to extracellular signals. However, the cellular mechanisms underlying this phenomenon are not known. Aged dermal fibroblasts with reduced remaining replicative capacities demonstrated decreased epidermal growth factor (EGF)-induced cell migrative and cell proliferative capacities, as reported previously. Thus, as cells approach senescence, programmed in vivo or in vitro, EGF responsiveness is preferentially lost. To define the rate-limiting signaling event, we found that the activity of two different EGF receptor (EGFR)-signaling pathways to cell migration (phospholipase-C gamma) and/or mitogenesis (extracellular signal/regulated-mitogen-activated kinases) were decreased in near senescent cells despite unchanged levels of effector molecules. Aged cells presented decreased levels of EGFR, although insulin receptor and transferrin receptor levels were relatively unchanged. EGFR mRNA levels and production of new transcripts decreased during aging, suggesting that this preferential loss of EGFR was due to diminished production, which more than counteracts the reduced ligand-induced receptor loss. Since these data suggested that the decrement in EGF was rate-limiting, higher levels of EGFR were established in near senescent cells by electroporation of EGFR cDNA. These cells presented higher levels of EGFR and recovered their EGF-induced migration and proliferation responsiveness. Thus, the defect in EGF responsiveness of aged dermal fibroblasts is secondary to reduced EGFR message transcription. Our experimental model suggests that EGFR gene delivery might be an effective future therapy for compromised wound healing.

Glucocorticoid-regulated gene expression during cutaneous wound repair

Glucocorticoids exert a deleterious effect on the wound healing process, which has been suggested to result from the anti-inflammatory action of these steroids. In addition, recent studies have demonstrated that glucocorticoids regulate the expression of various genes at the wound site which are likely to encode key players in the wound repair process. Using a murine full-thickness excisional wound healing model, we analyzed the effect of dexamethasone on the expression of various cytokines, growth factors, enzymes, and extracellular matrix molecules in normal and wounded skin. We demonstrate that the proinflammatory cytokines interleukin-1 alpha and -beta, tumor necrosis factor alpha, keratinocyte growth factor, transforming growth factors beta 1, beta 2, and beta 3 and their receptors, platelet-derived growth factors and their receptors, tenascin-C, stromelysin-2, macrophage metalloelastase, and enzymes involved in the generation of nitric oxide are targets of glucocorticoid action in wounded skin. These results indicate that anti-inflammatory steroids inhibit wound repair at least in part by influencing the expression of these key regulatory molecules.

Transforming growth factor-beta1 expression in cultured corneal fibroblasts in response to injury

The mechanisms underlying TGF-beta regulation in response to injury are not fully understood. We have developed an in vitro wound model to evaluate the expression and localization of transforming growth factor-beta1 in rabbit corneal fibroblasts in response to injury. Experiments were conducted in the presence or absence of serum so that the effect of the injury could be distinguished from exogenous wound mediators. Cultures were wounded and evaluations conducted over a number of time points. Expression of TGF-beta1 RNA was determined using Northern blot analysis and in situ hybridization, while the TGF-beta receptors were identified by affinity cross-linking. Injury increased the expression of TGF-beta1 mRNA in cells at the wound edge after 30 min; this response was amplified by the addition of serum. TGF-beta1 mRNA expression was observed in a number of cells distal from the wound. After wound closure, TGF-beta1 mRNA was negligible and resembled unwounded cultures. The half-life of TGF-beta1 mRNA was two times greater in the wounded cultures, indicating that the injury itself maintained the expression, while cell migration was present. Analogous to these findings, we found that binding of TGF-beta to its receptors was maximal at the wound edge, decreasing with time and distance from the wound. These results indicate that injury increases the level of expression of TGF-beta1 mRNA and maintains a higher level of receptor binding during events in wound repair and that these might facilitate the migratory and synthetic response of stromal fibroblasts.

Loss of Smad3 modulates wound healing

TGF-beta plays a central and critical role in tissue repair. The recent identification of TGF-beta signal transduction pathways involving Smad proteins has now made it possible to explore their contribution to the activities of TGF-beta in vivo. Both Smad3 and its closely related homolog Smad2 act as latent nuclear transcriptional activators and mediate intracellular signaling by TGF-betas and activin, each of which regulates cellular functions pivotal to cutaneous wound healing. Mice null for Smad3 (Smad3(ex8/ex8)) survive into adulthood and show accelerated cutaneous wound healing characterized by an increased rate of re-epithelialization and a reduced local inflammatory infiltrate. These data implicate Smad3 in specific pathways of tissue repair and suggest that it could be a target for the development of therapeutic strategies to modulate wound healing.

Hypertrophic scar tissues and fibroblasts produce more transforming growth factor-beta1 mRNA and protein than normal skin and cells

Transforming growth factor-beta1 is a well-known fibrogenic cytokine produced by many types of cells including dermal fibroblasts. To investigate whether this fibrogenic cytokine is involved in development of hypertrophic scar, transforming growth factor-beta1 gene expression was evaluated in small skin samples. Because a sufficient quantity of normal skin from patients with hypertrophic scar is not readily available, a reverse transcription-polymerase chain reaction technique was used. Quantitation of gene expression by reverse transcription-polymerase chain reaction is difficult partly due to the lack of suitable complementary RNA standards. We have established a convenient, reliable procedure to construct an internal standard for transforming growth factor-beta1 starting with a gene specific polymerase chain reaction product. After digestion of the polymerase chain reaction product with endonuclease, a small piece of cDNA from human procollagen alpha1(I) cDNA with compatible ends was inserted into the polymerase chain reaction-DNA fragment. The recombinant cDNA was re-amplified by polymerase chain reaction and subcloned into a plasmid containing bacteriophage T7 and T3 promoters. Complementary RNA was prepared from the recombinant plasmid and amplified by reverse transcription-polymerase chain reaction together with the tissue or cellular RNA. After amplification, the products were electrophoresed in an agarose gel containing ethidium bromide. The bands for internal standard and transforming growth factor-beta1 mRNA were scanned, digitized, and plotted against the amount of internal standard complementary RNA added in the reverse transcription-polymerase chain reaction. The number of mRNA molecules/cell was calculated. We examined the transforming growth factor-beta1 mRNA in hypertrophic scar tissue and in normal skin and found that hypertrophic scar tissues expressed five-fold more transforming growth factor-beta1 mRNA than normal skin per unit of wet weight. We used this procedure to quantitate transforming growth factor-beta1 mRNA expression in 5 pairs of fibroblast cultures derived from hypertrophic scar and normal skin. The results showed that hypertrophic scar fibroblast cultures contain significantly more molecules of mRNA for transforming growth factor-beta1 than normal cells (116 +/- 6 vs. 97 +/- 7, p = 0.017, n = 5). These results were supported by Northern analysis for transforming growth factor-beta1 mRNA in the cells and enzyme-linked immunosorbent assay for TGF-beta1 protein in fibroblast-conditioned medium. In conclusion, hypertrophic scar tissue and fibroblasts produce more mRNA and protein for transforming growth factor-beta1, which may be important in hypertrophic scar formation. The construction of the gene specific internal standard for reverse transcription-polymerase chain reaction is a simple and reliable procedure useful to quantitate gene expression in a small amount of tissue or number of cells.

Suppression of keratin 15 expression by transforming growth factor beta in vitro and by cutaneous injury in vivo

Transforming growth factor beta (TGF-beta) is a multifunctional cytokine which plays an important role in cutaneous wound repair. To gain insight into the mechanisms of action of this growth and differentiation factor in the skin, we searched for genes which are regulated by TGF-beta1 in cultured HaCaT keratinocytes. Using the differential display RT-PCR technology we identified a gene which was strongly downregulated by TGF-beta1. The identified cDNA includes sequences of the keratin 15 (K15) gene which encodes a component of the cytoskeleton of basal cells in stratified epithelia. Surprisingly, our cDNA also included an unknown sequence. Since this cDNA lacks an open reading frame, the corresponding mRNA is likely to be nonfunctional. However, we also demonstrate a strong negative regulation of the expression of the published, functional K15 variant. Expression of K15 was also suppressed by tumor necrosis factor alpha (TNF-alpha) and to a lesser extent by epidermal growth factor (EGF) and keratinocyte growth factor (KGF). By contrast, the major basal type I keratin, K14, was upregulated by TGF-beta1, whereas TNF-alpha, EGF, and KGF had no effect. Consistent with the in vitro data, we found a significant reduction of the K15 mRNA levels after skin injury, whereas K14 expression increased during the wound healing process. Immunostaining revealed the presence of K15 in all basal cells of the epidermis adjacent to the wound, but not in the hyperproliferative epithelium above the granulation tissue. These data demonstrate that K15 is excluded from the activated keratinocytes of the hyperthickened wound epidermis, possibly as a result of increased growth factor expression in injured skin.

TGF-beta and fibrosis

Transforming growth factor-beta (TGF-beta) isoforms are multifunctional cytokines that play a central role in wound healing and in tissue repair. TGF-beta is found in all tissues, but is particularly abundant in bone, lung, kidney and placental tissue. TGF-beta is produced by many but not all parenchymal cell types, and is also produced or released by infiltrating cells such as lymphocytes, monocytes/macrophages, and platelets. Following wounding or inflammation, all these cells are potential sources of TGF-beta. In general, the release and activation of TGF-beta stimulates the production of various extracellular matrix proteins and inhibits the degradation of these matrix proteins, although exceptions to these principles abound. These actions of TGF-beta contribute to tissue repair, which under ideal circumstances leads to the restoration of normal tissue architecture and may involve a component of tissue fibrosis. In many diseases, excessive TGF-beta contributes to a pathologic excess of tissue fibrosis that compromises normal organ function, a topic that has been the subject of numerous reviews [1-3]. In the following chapter, we will discuss the role of TGF-beta in tissue fibrosis, with particular emphasis on renal fibrosis.

Glucocorticoid receptor inhibits transforming growth factor-beta signaling by directly targeting the transcriptional activation function of Smad3

The transforming growth factor-beta (TGF-beta) family of cytokines and glucocorticoids regulate diverse biological processes through modulating the expression of target genes. Here we report that glucocorticoid receptor (GR) represses TGF-beta transcriptional activation of the type-1 plasminogen activator inhibitor (PAI-1) gene in a ligand-dependent manner. Similarly, GR represses TGF-beta activation of the TGF-beta responsive sequence containing Smad3/4-binding sites. Using mammalian two-hybrid assays, we demonstrate that GR inhibits transcriptional activation by both Smad3 and Smad4 C-terminal activation domains. Finally, we show that GR interacts with Smad3 both in vitro and in vivo. These results suggest a molecular basis for the cross-regulation between glucocorticoid and TGF-beta signaling pathways.

Optimisation of the biology of soft tissue repair

As identified in this review, over the past twenty years there have been a number of very exciting new developments in the quest to optimise soft tissue repair. Comparing fetal soft tissue injuries, which heal by regeneration, to the adult processes of healing by inflammation-induced scar formation has led to a number of insights into how the latter may be improved. Seeding wounds with embryonic stem cells, bridging gaps with cell-derived "engineered tissues", addition of exogenous hyaluronic acid and modification of wounds to either enhance the growth factors which have been implicated in regeneration (e.g. TGF-B3) or block those implicated in scar formation (eg. TGF-B1) have all shown promise. Our group has quantified numerous cellular, molecular, biomechanical and matrix abnormalities of scar in a rabbit model of ligament healing. Based on these studies which we review here, three matrix deficiencies have been identified which appear to have specific implications to scar weakness: organisational "flaws", abnormal hydroxypyridinoline collagen cross-link densities and abnormally small, slow-maturing collagen fibrils. In tests aimed at finding therapeutic solutions in this model, the addition of a 7ug bolus of TGF-B1 at day 21 or 2.5ng/day of TGF-B1 being pumped into a wound x 21 days increased the size of ligament scars but did not improve their material strength. It also did not alter any of the above-noted matrix deficiencies. A liposome-mediated anti-sense gene therapy approach aimed at decreasing the expression of the proteoglycan decorin in 21-day scars, however, has significantly increased the size of scar collagen fibrils as well as improved these scars mechanically. Based on these positive results from a single dose of only one targeted molecule, we believe that this gene therapy approach has great potential for further scar improvement. If combined with some of the other biological strategies reviewed above, a repair which is closer to true regenerative healing of ligaments, and all soft tissues, may eventually be achieved.

A time course study for the development of an immunocompromised wound model, using hydrocortisone

Although wound healing is essentially a physiologic process, some chronic wounds exhibit considerable delay in healing. Often these do not heal perfectly in individuals with low immune profiles. Thus, the present study was undertaken to develop an excision wound model in the immunocompromised state induced by pretreatment with hydrocortisone (HC) 40 mg/kg intramuscularly in male rats. Wounds of 8-mm diameter were made on the preshaved dorsal surface of rats using an Acuderm biopsy punch, following pretreatment with HC. After 14 days HC-treated animals exhibited atrophy of spleen and adrenal glands and a significant reduction of circulating lymphocytes and increase in neutrophils; these changes are indicative of immunosuppressive state of animals. The cell proliferation was significantly affected as shown by decreases in DNA (23%) and protein (11%). Furthermore, there were also significant reductions in tensile strength (37%) and hydroxyproline (33%) contents. These results were further supported by lack of contraction of wound edges. It is concluded that animals primed with HC 1 week prior to wounding developed prolonged immunosuppression, which significantly impaired the wound healing as compared with other groups. Thus, this can be experimentally employed as an immunocompromised wound model for evaluating compounds as novel wound healers suitable for immunocompromised subjects.

Collagen fiber orientation as quantified by small angle light scattering in wounds treated with transforming growth factor-beta2 and its neutalizing antibody

The purpose of this study was determine quantitative differences in collagen fiber orientation in a wound healing model in the presence of transforming growth factor-beta2 and anti-transforming growth factor-beta2,3 antibody. Full-thickness wounds were made in the paravertebral area of two young pigs. Wounds were treated once, topically, with either transforming growth factor-beta2 or anti-transforming growth factor-beta2 antibody, or with methylcellulose gel. Control wounds were left untreated. Tissue biopsies were obtained from each wound on days 7, 14 and 46 post wounding. Tissue sections were stained with hematoxylin and eosin, and collagen fiber preferred orientation was quantified using small angle light scattering. Our results indicated that wounds treated with transforming growth factor-beta2 and anti-transforming growth factor-beta2,3 antibody had a significantly higher degree of orientation of collagen fibers than normal unwounded skin on days 7, 14 and 46 (p < 0.001). Transforming growth factor-beta2- treated wounds had a higher degree of orientation of collagen fibers than control wounds on days 7 and 14 (p < 0.001), and control wounds displayed a higher degree of orientation than wounds treated with anti-transforming growth factor-beta2,3 and normal unwounded skin at all time points (p < 0.001). These results suggest that differences in the dermal collagen degree of orientation correlate with scarring, and show that small angle light scattering can be used quantitatively to assess differences in the collagen fiber architecture of dermal wounds.

Perspective article: transforming growth factor-beta: crossroad of glucocorticoid and bleomycin regulation of collagen synthesis in lung fibroblasts

Fibrosis is a consequence of injury which is characterized by accumulation of excess collagen and other extracellular matrix components, resulting in the destruction of normal tissue architecture and function. Transforming growth factor-beta, a potent wound healing agent, has also been shown to be an agent that can produce fibrosis because it is a potent stimulator of collagen synthesis. Both glucocorticoids and bleomycin have recently been shown to affect collagen synthesis in opposite directions, by utilizing a common pathway of involving transforming growth factor-beta activator protein binding to the transforming growth factor-beta element. This article presents a mechanistic overview of collagen synthesis regulation by glucocorticoids and bleomycin through the transforming growth factor-beta pathway.

Recombinant human granulocyte-macrophage colony-stimulating factor applied locally in low doses enhances healing and prevents recurrence of chronic venous ulcers

BACKGROUND

Chronic venous leg ulcers have a major medical and economic impact on the elderly worldwide. Healing of the large ulcers (>10 cm2) occurs only in two-thirds of the patients and reulceration of healed ulcers recurs in one-third within 1 year. Because both healing and relapse rate influence greatly a patient's quality of life and the overall cost of treatment, every effort should be made to improve these two parameters.

OBJECTIVE

To determine the safety and efficacy of topical low-dose recombinant human granulocyte-macrophage colony-stimulating factor (rhu GM-CSF) for the treatment of venous ulcers, and to document any improvement in healing rates.

METHODS

Thirty-eight patients (29 women, 9 men; median age, 74 years) with chronic venous insufficiency were treated with topical rhu GM-CSF (5 microg/mL 0.9% sodium chloride solution), followed by application of a compression dressing. All subjects were treated as outpatients.

RESULTS

Complete healing was observed in 47 of the 52 ulcers (90.4%). The average healing time was 19 weeks. No systemic or local side-effects from the therapy were observed. Nine chronic ulcers, previously refractory to conventional treatment (pretreatment for more than 46 weeks), showed the same response rate (9/8, or 88.9%) and healing time (mean, 19 weeks). After 40 months, no reulceration of the healed ulcers was observed, but two patients developed new ulcers on the same leg. Healing remained stable, with excellent cosmetic results.

CONCLUSIONS

In this first study, topically applied low-dose rhu GM-CSF was a safe treatment for chronic venous leg ulcers. Healing rates were significantly increased and relapse rates were minimal.

Role of elevated plasma transforming growth factor-beta1 levels in wound healing

Transforming growth factor (TGF)-beta1 plays a central role in wound healing. Wounds treated with neutralizing antibody to TGF-beta1 have a lower inflammatory response, reduced early extracellular matrix deposition, and reduced later cutaneous scarring, indicating the importance of local tissue TGF-beta1. By contrast, increasing the local, tissue levels of TGF-beta1 increases the early extracellular matrix deposition but does not alter scar formation. Increased levels of plasma TGF-beta1 correlate with increased fibrogenesis in the lung, kidneys, and liver. The aim of the present study was to investigate the role of elevated systemic levels of TGF-beta1 on wound healing. We used transgenic mice that express high levels of active TGF-beta1 and have elevated plasma levels of TGF-beta1 and wild-type mice of the same strain as controls. Incisional wounds and subcutaneously implanted polyvinyl alcohol (PVA) sponges were analyzed. Surprisingly, cutaneous wounds in transgenic, TGF-beta1-overexpressing mice healed with reduced scarring accompanied by an increase in the immunostaining for TGF-beta3 and TGF-beta-receptor RII and a decrease in immunostaining for TGF-beta1 compared with wounds in control mice. By contrast, the PVA sponges showed the opposite response, with PVA sponges from transgenic mice demonstrating an enhanced rate of cellular influx and matrix deposition into the sponges accompanied by an increase in the immunostaining for all three TGF-beta isoforms and their receptors compared with PVA sponges from control mice. Together, the data demonstrate that increased circulating levels of TGF-beta1 do not always result in increased expression or activity in selected target tissues such as the skin. The two wound models, subcutaneously implanted PVA sponges and cutaneous incisional wounds, differ significantly in terms of host response patterns. Finally, the data reinforce our previous observations that the relative ratios of the three TGF-beta isoforms is critical for control of scarring.

Improved nerve regeneration with neutralization of transforming growth factor-beta1

OBJECTIVES

Recovery of injured peripheral nerves depends on a balance between Schwann cell regeneration and scar formation. Transforming growth factor-beta1 (TGF-beta1) has been implicated as a humoral stimulus in scar formation. The neutralization of TGF-beta1 has been beneficial in the reduction of fibrosis. This study was to identify the presence of TGF-beta1 in regenerating peripheral nerve and to measure motor nerve regeneration by the neutralization of TGF-beta1 in neural wounds.

STUDY DESIGN

A randomized study of rat sciatic nerve regeneration.

METHOD

Sciatic nerve axotomy was performed, followed by serial immunohistochemical staining by anti-TGF-beta1 at 12 to 216 hours (n = 5). Two groups (n = 10) with sciatic axotomy and epineural repair were treated with a 7-day perineural administration of neutralizing antibody of TGF-beta1 or saline carrier via subcutaneous silicone infusion port. A control group (n = 10) without axotomy with anti-TGF-beta1 administration was established. At 12 weeks the compound muscle action potential amplitude (CMAP) and the muscle twitch strength generated by the gastrocnemiussoleus muscle complex were measured.

RESULTS

TGF-beta1 was qualitatively present with maximal concentration by 72 to 144 hours. CMAP amplitude in the anti-TGF-beta1/axotomy group was 49.6% of the control and the axotomy/saline group was 31% of the control. Muscle twitch strength was 74% and 46.5%, respectively. These differences were statistically significant, P = .05.

CONCLUSIONS

The presence of TGF-beta1 at regenerating nerve sites was confirmed. The benefit of neutralization of transforming growth factor on CMAP and muscle twitch strength was shown. These results suggest improved regeneration at nerve injury sites with neutralization of TGF-beta1.

Adult respiratory distress syndrome - an update

In adults, acute lung injury or adult respiratory distress syndrome (ARDS) may complicate a wide range of serious medical and surgical conditions, only some of which involve direct pulmonary insult. The characteristic histological feature of ARDS is an intense inflammatory process in the lungs, which may progress to fibrosis. The earliest physiological characteristic is an increase in the protein permeability across the endothelial and epithelial barriers of the lungs. This clinical syndrome is characterized by arterial hypoxaemia and bilateral radiographic infiltrates, which represent protein-rich oedema fluid. In addition there is a neutrophilic and macrophage infiltrate. Pulmonary endothelium is actively involved in the development of ARDS. It alters cell-cell adhesion as the initial step in leucocyte migration which, in turn, changes the permeability that allows protein-rich fluid to move into the interstitium. The quantity of this interstitial oedema may be sufficient to cause bulk flow through the epithelial barrier. There is probably independent epithelial injury. Finally, the endothelium can release and metabolize vasoactive and inflammatory substances, such as endothelins, nitric oxide and cytokines, etc. No single substance is responsible for acute lung injury, but rather a complex interplay exists between diverse pro- and anti-inflammatory mediators.

Transforming growth factor-beta1 fails to stimulate wound healing and impairs its signal transduction in an aged ischemic ulcer model: importance of oxygen and age

Clinical trials of exogenous growth factors in treating chronic wounds have been less successful than expected. One possible explanation is that most studies used animal models of acute wounds in young animals, whereas most chronic wounds occur in elderly patients with tissue ischemia. We described an animal model of age- and ischemia-impaired wound healing and analyzed the wound-healing response as well as the transforming growth factor (TGF)-beta1 effect in this model. Rabbits of increasing ages were made ischemic in the ear where dermal ulcers were created. Histological analysis showed that epithelium ingrowth and granulation tissue deposition were significantly impaired with increased age under ischemia. TGF-beta1 stimulated wound repair under both ischemic and non-ischemic conditions in young animals, although it showed no statistical difference in aged animals. Procollagen mRNA expression decreased under ischemic conditions and with aging. Neither TGF-beta1 nor procollagen alpha1(I) mRNA expression increased in response to TGF-beta1 treatment under ischemia in aged animals. Therefore, the wound-healing process is impaired additively by aging and ischemia. The lack of a wound-healing response to TGF-beta1 in aged ischemic wounds may play a role in the chronic wounds.

Induction of bone morphogenetic protein-6 in skin wounds. Delayed reepitheliazation and scar formation in BMP-6 overexpressing transgenic mice

Growth factors of the transforming growth factor-beta superfamily are involved in cutaneous wound healing. In this study we analyze the expression of the bone morphogenetic protein-6 (BMP-6) gene, a transforming growth factor-beta related gene, in skin wounds. In normal mouse skin high levels of BMP-6 mRNA and protein are expressed by postmitotic keratinocytes of stratified epidermis until day 6 after birth. BMP-6 expression is strongly reduced in adult epidermis with diminished mitotic activity. After skin injury we found large induction of BMP-6-specific RNA and protein in keratinocytes at the wound edge and keratinocytes of the newly formed epithelium as well as in fibroblast shaped cells in the wound bed. BMP-6-specific RNA was induced within 24 h after injury, whereas significant upregulation of BMP-6 on the protein level was detected only 2-3 d after injury. Protein was confined to outermost suprabasal epidermal layers, whereas BMP-6-specific RNA was distributed throughout all epidermal layers including basal keratinocytes and the leading edge of the migrating keratinocytes. We also detected high levels of BMP-6-specific RNA and protein in chronic human wounds of different etiology. In contrast to the overall distribution pattern of BMP-6-specific RNA, the protein was not detected in keratinocytes directly bordering the wound. In order to test the influence of BMP-6 abundance on the progress of wound healing, we analyzed the wound response of transgenic mice overexpressing BMP-6 in the epidermis. In these mice, reepitheliazation of skin wounds was significantly delayed, suggesting that strict spatial and temporal regulation of BMP-6 expression is necessary not only for formation but also for reestablishment of a fully differentiated epidermis.

Stimulation of collagen synthesis by the anabolic steroid stanozolol

There is evidence that anabolic steroids, which are derived from testosterone and have markedly less androgenic activity, promote tissue growth and enhance tissue repair; however, the mechanisms involved in their anabolic activities remain unclear. In this report, we measured the effect of the anabolic steroid stanozolol on cell replication and collagen synthesis in cultures of adult human dermal fibroblasts. Stanozolol (0.625-5 microg per ml) had no effect on fibroblast replication and cell viability (p = 0.764) but enhanced collagen synthesis (p < 0.01) in a dose-dependent manner (r = 0.907). Stanozolol also increased (by 2-fold) the mRNA levels of alpha1 (I) and alpha1 (III) procollagen and, to a similar extent, upregulated transforming growth factor-beta1 (TGF-beta1) mRNA and peptide levels (p < 0.001). There was no stimulation of collagen synthesis by testosterone. The stimulatory effects of stanozolol on collagen synthesis were blocked by a TGF-beta1 anti-sense oligonucleotide, by antibodies to TGF-beta, and in dermal fibroblast cultures derived from TGF-beta1 knockout mice. We conclude that collagen synthesis is increased by the anabolic steroid stanozolol and that, for the most part, this effect is due to TGF-beta1. These findings point to a novel mechanism of action of anabolic steroids.

Signal transduction in wound pharmacology

Growth factors such as TGF-beta, PDGF and FGF are thought to play important roles in wound healing. However, their biological activity and signal transduction during wound repair remain poorly understood. Growth factors are often ligands for receptor tyrosine kinase and receptor serine/threonine kinases. With recent advances in signal transduction by receptor kinases, we are beginning to understand the underlying mechanism of how growth factors may regulate cutaneous wound repair. In this paper, we will describe the pharmacological effects of growth factors on wound healing, and discuss the potential underlying signaling mechanisms. Thus, we hope to provide the basis for designing more specific therapeutics for wound healing in the near future.

Semiquantitative reverse transcription-polymerase chain reaction analysis of mRNA for growth factors and growth factor receptors from normal and healing rabbit medial collateral ligament tissue

Growth factors and their receptors play an essential role in the development, maturation, and response to injury of all tissues. A number of studies have explored the possibility of improving ligament healing with exogenous growth factors. However, limited data is available regarding the endogenous growth factor network in ligaments on which any exogenous growth factors must impact. The purpose of this study was to assess the endogenous growth factor network with molecular techniques. By the sensitive reverse transcription-polymerase chain reaction technique, transcripts for a number of growth factors and receptors were detected with RNA isolated from normal and healing rabbit medial collateral ligament tissues. These include transforming growth factor-beta1, insulin-like growth factors I and II, basic fibroblast growth factor, endothelin-1, and the receptors for insulin and insulin-like growth factor II. Semiquantitative reverse transcription-polymerase chain reaction analysis of RNA from normal and scar tissues from the medial collateral ligament revealed that the levels of several transcripts were elevated in the scar tissue. It was not possible to confirm biological activity because of the hypocellularity of the tissues; however, the results obtained indicate that the reverse transcription-polymerase chain reaction approach to defining the endogenous growth factor-receptor phenotype is feasible, and further definition should contribute to the development of rational approaches to exogenous therapy to improve healing.

Platelet-rich plasma: Growth factor enhancement for bone grafts

Platelet-rich plasma is an autologous source of platelet-derived growth factor and transforming growth factor beta that is obtained by sequestering and concentrating platelets by gradient density centrifugation. This technique produced a concentration of human platelets of 338% and identified platelet-derived growth factor and transforming growth factor beta within them. Monoclonal antibody assessment of cancellous cellular marrow grafts demonstrated cells that were capable of responding to the growth factors by bearing cell membrane receptors. The additional amounts of these growth factors obtained by adding platelet-rich plasma to grafts evidenced a radiographic maturation rate 1.62 to 2.16 times that of grafts without platelet-rich plasma. As assessed by histomorphometry, there was also a greater bone density in grafts in which platelet-rich plasma was added (74.0% +/- 11%) than in grafts in which platelet-rich plasma was not added (55.1% +/- 8%; p = 0.005).

Growth factors reverse the impaired sprouting of microvessels from aged mice

Aging is accompanied by impaired angiogenesis and deficient expression of several angiogenic growth factors. To test the hypothesis that replacement of these factors would improve angiogenesis in aged animals, we cultured microvessels derived from the epididymal fat pad of aged and young mice ("aged" and "young" microvessels) in three-dimensional collagen gels for 2 weeks and measured their sprouting (formation of branch points) in response to fetal bovine serum (FBS), endothelial cell growth supplement (ECGS), and the specific growth factors transforming growth factor-beta1 (TGF-beta1), vascular endothelial growth factor (VEGF), insulin-like growth factor-1 (IGF-1), and basic fibroblast growth factor (bFGF). In the presence of culture medium with 1% FBS (Minimal medium), sprouting of aged microvessels was significantly less than sprouting of young microvessels. The addition of high levels of FBS and ECGS to Minimal medium enhanced the sprouting of microvessels from aged mice to a greater degree than that of young mice, such that the difference between the two age groups was no longer significant. Formation of branch points by aged microvessels was also significantly increased by Minimal medium supplemented with TGF-beta1, bFGF, IGF-1, or VEGF (listed in order of highest to lowest stimulation). Sprouts generated in the presence of VEGF possessed a particularly high percentage of endothelial cells. Mitomycin C did not diminish the degree of sprouting induced by TGF-beta1, VEGF, or IGF-1, a result indicating that early stages of angiogenesis, including formation of branch points, do not require cell division. From our findings in vitro, we propose that age-related deficiencies in angiogenesis in vivo are likely to be due, in part, to a decrease in angiogenic growth factors in the extracellular milieu.

Glucocorticoid dynamics and impaired wound healing in diabetes mellitus

The aim of the present study was to examine corticosterone dynamics and its role in the pathogenesis of impaired wound healing in diabetes mellitus (DM). The streptozotocin-treated rat was used as an animal model for type I DM. A linear skin incision and subcutaneously implanted polyvinyl alcohol sponge disks were considered as wound-healing models. The data regarding corticosterone dynamics revealed diabetes-related increments in plasma corticosterone concentrations at various time intervals during the diurnal cycle (9:00 a.m., 12:00 noon, and 3:00 p.m.) Moreover, a reduction in the levels of hippocampal glucocorticoid receptors was also evident in this disease state. Immobilization-induced stress elevated plasma corticosterone levels in both control and 30-day diabetic rats. Although the diabetic rat seems capable of appropriately initiating a corticosterone stress response, it is dramatically impaired in its capacity to terminate it. A progressive decrease in collagen deposition on polyvinyl alcohol sponge and wounded skin tensile strength was seen as a function of the duration of diabetes. Similarly, polyvinyl alcohol sponges retrieved from 30-day diabetic rats also showed a marked reduction in the expression of mRNA transcripts for type I and type III collagen. A simulation of the impairment in wound-healing potential in DM was achieved by treating control animals with a supraphysiological dose of hydrocortisone. It is worthy of note that an endocrinological paradigm involving adrenalectomy and replacement therapy with hydrocortisone significantly improved the wound-related parameters, including collagen metabolism and wounded skin tensile strength in the streptozotocin diabetic rats. Overall, our data provide evidence that the diabetic state is associated with hypercortisolemia and that this phenomenon may contribute to impaired wound healing in DM.

Neovascularization in aged mice: delayed angiogenesis is coincident with decreased levels of transforming growth factor beta1 and type I collagen

Angiogenesis, the growth of new vessels from existing microvasculature, is delayed in aged animals. In this study we asked whether this impairment might be due, in part, to changes in the expression of a growth factor, transforming growth factor-beta1 (TGF-beta1), and a matrix protein, type I collagen, which have been shown to regulate angiogenesis in vivo. We implanted polyvinyl alcohol sponges subcutaneously in the dorsa of young and aged mice and examined the sponges 7 to 21 days later for the presence of invasive fibrovascular bundles. Blood vessel ingrowth and proliferative activity were assessed by immunostain for von Willebrand factor and Ki-67, respectively. The fibrovascular bundles were also analyzed for TGF-beta1 and type I collagen. Relative to young mice, angiogenic invasion of sponges in aged mice was similar at 7 days, was diminished significantly (70%) at 14 days, but was again similar by 21 days after implantation. The expression of TGF-beta1 and type I collagen mRNA and protein in fibrovascular bundles was coincident but was also delayed (42 to 47%) at 14 days in the aged mice. Moreover, levels of active TGF-beta1 were decreased (48%) in the sera of aged relative to young mice. The delay in angiogenesis in aged mice was thus associated with decreased expression of TGF-beta1 and type I collagen by neovascular bundles. We conclude that changes in the levels of growth factors and proteins in the extracellular matrix contribute to impaired angiogenesis in aging.

Estrogen accelerates cutaneous wound healing associated with an increase in TGF-beta1 levels

The cellular and molecular mechanisms underlying the effects of aging on human cutaneous wound healing are poorly understood, and the possible role of reproductive hormones in this process has never been investigated. We report that aging in healthy females was associated with a reduced rate of cutaneous wound healing, but an improved quality of scarring both microscopically and macroscopically, and with reduced levels of transforming growth factor-beta1 (TGF-beta1) immunostaining and steady-state mRNA in the wound. These age-related changes were reversed by the systemic administration of hormone replacement therapy (HRT). Moreover, ovariectomized young female rodents exhibited a marked delay in repair of acute incisional wounds, which was reversed by the topical application of estrogen. The cellular mechanism underlying these changes appears to involve an estrogen-induced increase in latent TGF-beta1 secretion by dermal fibroblasts. These results suggest that both the rate and quality of wound healing depend on reproductive hormone levels.

Recombinant human transforming growth factor beta 3 accelerates gastric ulcer healing in rats

BACKGROUND

Gastric ulcer healing is mediated by various endogenous growth factors. In this experimental study effect of locally and systemically applied recombinant human transforming growth factor beta 3 (rhTGF-beta 3) on gastric ulcer healing was investigated in the rat.

METHODS AND RESULTS

Gastric ulcers were induced with a cryoprobe, and ulcer healing was evaluated 7 days after local infiltration (0.5 micrograms, 1.0 microgram, 2.5 micrograms, and 50 micrograms) or systemic (intravenous) application of TGF-beta 3 (500 micrograms/kg body weight). Compared with controls, a dose-dependent stimulation of ulcer healing (as evidenced by a reduction in ulcer size) was observed 7 days after local infiltration of TGF-beta 3 (1.0 microgram, 2.5 micrograms, and 50 micrograms). Corresponding increases in the levels of proliferating cell nuclear antigen (PCNA) and intracellular TGF-beta 3 expression and a downregulation of the TGF-beta type-II receptor expression were also observed in the granulation tissue of the ulcer margins. Systemic application of TGF-beta 3 produced effects similar to those observed after local treatment with 50 micrograms of the compound.

CONCLUSION

Local and systemic TGF-beta 3 treatment accelerates gastric ulcer healing in rats.

Pressure ulcer accelerated healing with local injections of granulocyte macrophage-colony stimulating factor

This is the first report of granulocyte macrophage-colony stimulating factor (GM-CSF) inducing accelerated healing of a sacral pressure ulcer in a bedridden patient with bilateral hemiplegia. GM-CSF was diluted and injected locally around and into the ulcer bed every 2-3 days for 2 weeks, then weekly for 4 weeks until complete healing occurred. A new firm granulation tissue was noted within a few days. The ulcer showed 85% healing within 2 weeks and 100% by 2 months. Healing started from the periphery and from within the ulcer bed at sites of GM-CSF injections. It was slower at areas where there was complete necrosis and detachment of skin from underlying tissue. The ulcer remained closed until the patient's sudden death 9 months later. A biopsy of granulation tissue showed inflammatory cells and reactive fibroblasts. The potential role of GM-CSF and growth factors in pressure ulcer therapy and wound healing are discussed.

Polypeptide growth factors: targeted delivery systems

Growth factors are becoming extremely valuable tools in our attempts to understand the mechanisms that modulate cellular activities. Their targeting to appropriate cells and maintaining adequate pharmacological levels becomes essential, particularly in view of the different effects that these compounds have on various cells and the dose dependence of their response. Within this context, this review focuses primarily on the delivery of growth factors involved in the processes of wound healing and tissue repair.

Acute wound failure

The causes and treatment of acute failure of the abdominal incision are reviewed, along with a summary of studies on fascial healing. Emphasis is placed on taking large bites of tissue during closure to prevent dehiscence. Patient-related risk factors are viewed as less important in the causation of wound failure.

Altered wound arginine metabolism by corticosterone and retinoic acid

Arginine metabolism plays an important role in many aspects of inflammation and wound healing. In this study, we tested the hypothesis that steroids and vitamin A have differential effects on arginine metabolism and thereby may provide a mechanism by which steroids impair wound healing, and vitamin A improves this impairment. Rats were treated with subcutaneous corticosterone pellets 2 days prior to wounding. Intraperitoneal injections of all-trans retinoic acid in peanut oil were administered at the same time and repeated 2 and 4 days later. Polyvinyl alcohol sponges were implanted subcutaneously through a dorsal incision. On Postwounding Days 1, 5, 10, and 15, wound fluid was recovered from the sponges and assayed for nitrite/nitrate (NOx), citrulline, arginine, and ornithine concentrations as well as arginase activity. Steroid treatment decreased the metabolism of arginine to nitric oxide in the early phase of wound healing, and retinoic acid did not change this relationship. Corticosterone also decreased metabolism of arginine to ornithine in the later wound. This depression was inhibited by concomitant administration of retinoic acid. Considering the importance of nitric oxide in host defense and ornithine as a precursor for polyamine and proline synthesis, these data provide a mechanism by which vitamin A improves wound strength, but does not improve wound infection rates in steroid-treated animals.

The effects of ageing on wound healing: immunolocalisation of growth factors and their receptors in a murine incisional model

A number of reports suggest that the process of ageing impairs wound repair and that strategies to manipulate the age-related wound healing environment are necessary in order to stimulate repair. The process of cutaneous wound repair is controlled by growth factors in an autocrine and paracrine fashion: it is therefore surprising that the localisation of specific growth factors and their receptors has not been documented in wound healing with respect to chronological age. In this study the temporal profile of growth factor and receptor immunostaining was assessed within acute incisional wounds in an ageing mouse colony. A delay in appearance of platelet derived growth factor (PDGF) A and B isoforms, and PDGF-alpha and -beta receptors was evident with increasing animal age, paralleled by a similar finding for epidermal growth factor (EGF) and EGF receptor. Transforming growth factor (TGF)-beta 1 and 2 isoforms were increased at all time points in the wounds of younger animals, but the TGF-beta 3 isoform increased in intensity from d 7 postwounding in the old mice wounds, and basic fibroblast growth factor (bFGF) from d 14. The quantity and distribution patterns of the various growth factors and their receptors may explain the age-related differences in wound healing speed and quality, and possibly suggest new therapeutic targets for manipulating wound healing in the aged.

Reversal of in vivo drug resistance by the transforming growth factor-beta inhibitor decorin

Transforming growth factor-beta (TGF-beta) has been implicated in the in vivo resistance of the EMT-6/CTX and EMT-6/ CDDP murine mammary tumors. Both of these tumors have a higher number of intratumoral vessels than the EMT-6/ parent tumor. Animals bearing the resistant tumors have higher plasma levels of TGF-beta than animals bearing the parent tumors; however, upon treatment with cytotoxic therapies there is a greater rise in plasma TGF-beta levels in animals bearing the parent tumor than in animals bearing the resistant tumors. In situ hybridization for TGF-beta mRNA and immunohistochemical staining for TGF-beta protein showed that the resistant tumor levels of this growth factor are higher than those of the parent tumor prior to treatment; however, after cytotoxic therapy the increase in TGF-beta is greater in the parent tumor than in the resistant tumors. Treatment of tumor-bearing animals with the naturally occurring TGF-beta inhibitor decorin did not alter the sensitivity of the parent tumor to cyclophosphamide or to CDDP as determined by tumor cell survival assay. However, administration of decorin increased the sensitivity of the EMT-6/CTX tumor to cyclophosphamide and of the EMT-6/CDDP tumor to CDDP so that the drug resistance of these tumors was nearly ablated. A similar pattern was observed in the drug response of the bone marrow granulocyte-macrophage colony-stimulating factor of animals bearing each of the 3 tumors.

Dexamethasone abrogates the fibrogenic effect of transforming growth factor-beta in rat granuloma and granulation tissue fibroblasts

Administration of TGF-beta, a fibrogenic inflammatory growth factor, promotes fibrosis and scarring. Dexamethasone, an anti-inflammatory steroid, inhibits wound healing and reduces fibrosis. The current studies were initiated to determine whether the co-administration of dexamethasone was able to abrogate the fibrogenic effect of TGF-beta. Polyvinyl alcohol sponges were implanted subcutaneously on the abdominal area of rats and directly injected with vehicle, dexamethasone, TGF-beta, or dexamethasone plus TGF-beta. Dexamethasone was able to block the fibrogenic effect of TGF-beta. Collagen and noncollagen protein synthesis was measured as a function of TGF-beta or dexamethasone concentrations in fibroblasts isolated from granulation tissue. Addition of dexamethasone to cultures treated simultaneously with TGF-beta blocked the fibrogenic response of TGF-beta. To study the molecular regulation of collagen gene expression by TGF-beta or dexamethasone, fibroblasts derived from granulation tissue were stably transfected with the ColCat 3.6 plasmid, which contains the rat pro alpha1(I) collagen promoter linked to the chloramphenicol acetyltransferase (CAT) gene. Dexamethasone decreased CAT activity whereas TGF-beta increased the activity of this reporter gene. The increase in CAT activity observed with TGF-beta treatment was significantly decreased when dexamethasone was added to the cultures, although CAT activity did not return to control level. Since collagen synthesis in fibroblasts treated simultaneously with dexamethasone and TGF-beta1 was found to be the same as that of untreated samples, the data indicate that there is a dexamethasone-mediated posttranscriptional regulation of pro alpha1(I) collagen mRNA. These studies demonstrate that at the in vivo level, the cellular level, and the molecular level, dexamethasone is able to block the fibrogenic effect of TGF-beta.

Transforming growth factor beta s and wound healing

The Transforming Growth Factor beta superfamily (TGF beta) is one of the most complex groups of cytokines with widespread effects on many aspects of growth and development. The TGF beta isoforms and other family members, e.g. Activins and BMPs, have diverse effects in similar physiological situations. TGF beta is involved in the wound healing process. The three mammalian isoforms (TGF beta 1, 2 and 3) and recently other family members, e.g. Activin, have been localised in healing wounds. Manipulation of the ratios of TGF beta superfamily members, particularly the ratio of TGF beta 1 relative to TGF beta 3, reduces scarring and fibrosis. Such manipulations include reducing the levels of TGF beta 1/TGF beta 2 using neutralising antibodies or preventing the activation of TGF beta s. In chronic or impaired wounds the exogenous addition of TGF beta superfamily members accelerates aspects of the healing process. This review summarises evidence for the role of TGF beta superfamily members in wound healing and how modulation of TGF beta levels can prevent scarring and fibrosis.

What is new in clinical research in wound healing

Treating the underlying pathophysiology of the wound remains of utmost importance. Several new treatment modalities may soon be available as adjunctive treatments. The efficacy of some remains to be established in well-controlled clinical studies.

Integrated processes responsible for soft tissue healing

Wounded soft tissues undergo repair through a complex series of interrelated events that involve both physical and chemical activities. These processes are currently undergoing extensive investigation as efforts are directed toward achieving augmented and accelerated healing. Early wound-healing research focused on expanding traditional histologic descriptions of tissue healing by attempting to characterize the environment and biologic mediators responsible for healing. These initial studies successfully identified a number of agents and physiochemical factors present in healing wounds, but their precise roles and importance remain largely unknown. This review article summarizes the current literature on soft tissue healing. An effort has been made to correlate the activities of the major growth factors and cytokines with the individual reparative processes including the inflammatory response, hemostasis, fibroplasia, angiogenesis, and remodeling. Explanations and characteristics of growth factor function as well as brief descriptions of several major factors and their spectrum of activity are also provided.

Pathogenesis of scleroderma. Collagen

It is now evident that persistent overproduction of collagen and other connective tissue macromolecules results in excessive tissue deposition, and is responsible for the progressive nature of fibrosis in SSc. Up-regulation of collagen gene expression in SSc fibroblasts appears to be a critical event in the development of tissue fibrosis. The coordinate transcriptional activation of a number of extracellular matrix genes suggests a fundamental alteration in the regulatory control of gene expression in SSc fibroblasts. Trans-acting nuclear factors that bind to cis-acting elements in enhancer and promoter regions of the genes modulate the basal and inducible transcriptional activity of the collagen genes. The identity of the nuclear transcriptional factors that regulate normal collagen gene expression remains to be firmly established, and to date, no alterations in the level or in the activity of such DNA binding factors has been demonstrated in SSc fibroblasts. In addition to important interactions between fibroblasts and the extracellular matrix, cytokines and other cellular mediators can positively and negatively influence fibroblast collagen synthesis. Some of these signaling molecules may have physiologic roles, and their aberrant expression, or altered responsiveness of SSc fibroblasts to them, may result in the acquisition of the activated phenotype. The rapid expansion of knowledge regarding the effects of cytokines on extracellular matrix synthesis has led to an appreciation of the enormous complexity of regulatory networks that operate in the physiologic maintenance of connective tissue and which may be responsible for the occurrence of pathologic fibrosis. The ubiquitous growth factor TGF beta is the most potent inducer of collagen gene expression and connective tissue accumulation yet discovered. The expression of TGF beta in activated infiltrating mononuclear cells suggests a role for this cytokine as a mediator of fibroblast activation in SSc. Furthermore, the recognition that TGF beta is capable of inducing its own expression in a variety of cell types, coupled with the demonstration that a subpopulation of SSc dermal fibroblasts produces TGF beta, indicates the existence of a possible autocrine loop whereby lymphocyte-derived TGF beta in early SSc not only signals biosynthetic activation of fibroblasts in a paracrine manner, but autoinduces endogenous TGF beta production by the target fibroblasts themselves. Such an autocrine loop involving TGF beta may explain the persistent activation of collagen gene expression in SSc fibroblasts, and could be responsible for the progressive nature of fibrosis in SSc. Numerous other cytokines, as well as cell-matrix interactions, also modify collagen gene expression and can significantly influence the effects of TGF beta. Although their physiologic function in tissue remodeling or their involvement in abnormal fibrogenesis has not yet been conclusively demonstrated, the study of the biologic effects of these cytokines may provide important clues to understanding the pathogenesis of SSc, and to the development of rational drug therapy aimed at interrupting the abnormal fibrogenic process in this disease.

The impact of ischemia on wound healing is increased in old age but can be countered by hyperbaric oxygen therapy

The healing of normal incisional wounds and ischemic flap wounds was investigated in young (10 weeks) and old (102-104 weeks) rats, together with the effect of treatment with hyperbaric oxygen on day 0-3 of healing. After 10 days of healing all biomechanical strength parameters of normal wounds were decreased by 30-40% and of ischemic wounds by 40-51% in the old animals compared with the young controls. After 20 days all strength parameters of normal wounds and ischemic wounds were decreased by 29-37% and 46-58%, respectively, in the old rats compared with those of the young ones. Treatment with hyperbaric oxygen of ischemic wounds in old animals increased all strength parameters by 36-50% after 10 days and by 67-88% after 20 days. For young animals, the corresponding increase was only 21-35% after 10 days and no effect was seen after 20 days. The shrinkage of ischemic wounds was decreased by 48% in the old animals compared with the young ones. It can be concluded that ischemia intensifies the impairment of the healing seen in old age. On the other hand, treatment of ischemia with hyperbaric oxygen is much more effective in old animals, despite the fact that it also has a pronounced effect in young animals. Furthermore, the results suggest a decreased wound contraction with age.

Porous polysulfone coated with platelet-derived growth factor-BB stimulates proliferation of human periodontal ligament fibroblasts

The purpose of this study was to investigate if the treatment of porous polysulfone (PPSF) with various concentrations of platelet-derived growth factor-BB (PDGF-BB) would stimulate the proliferation of the adherent human periodontal ligament fibroblasts (HPDLF) in culture. Sterilized PPSF cylinders were immersed in an Eagle's minimum essential medium supplemented with 0.5% fetal bovine serum and 1% penicillin/streptomycin containing either 0, 10, 20, or 50 ng/ml of PDGF-BB for 24 hours. After 24 hours, the PPSF cylinders were removed and allowed to dry then placed in culture plates for each time point. Pooled HPDLF (8 x 10(4)) and 3H-thymidine in medium were pipetted into each well to cover the treated and control PPSF cylinders and plates were then incubated. At 1, 4, and 10 days the PPSF cylinders were removed and macromolecular precipitation was performed. Incorporation of 3H-thymidine was measured and a 2-way ANOVA with repeated measures was performed. In addition, determination of binding and release was performed using I125-PDGF-BB treated PPSF at 0, 2, 12, and 24 hours, and at 4 and 10 days. Results showed that the effects on HPDLF were significant for dose (P = 0.0012; F = 5.74) and time (P = 0.0001; F = 40.83). At 4 days, the percent increases above the control for the doses 10, 20, and 50 ng/ml were 192%, 310%, and 162% respectively. In conclusion, our findings suggest that treating PPSF with PDGF-BB results in a significant increase in the proliferation of HPDLF cells adherent to PPSF.

The role of microvasculature in normal and perturbed bone healing as revealed by intravital microscopy

Bone chamber intravital microscopy brings to the study of bone circulation a combination of the control volume of in vitro models and the chemical complexity of in vivo models. As an optical tool it provides a window to circulatory events at the tissue level of magnification. In particular, it allows measures of microvascular physiology 1) in space by magnifying local perfused vasculature and microcirculation at any instant and 2) in time by providing the same volume of tissue for weekly viewing of an evolving process such as bone healing. This hollow screw's windows have revealed: 1) a consistent order for vascular and bone progression during healing, 2) vascular changes in response to implanted polymers and 3) preliminary data about effects of hyperbaric oxygenation and pulsed electromagnetic fields on vascular aspects of healing. The parameters measured are osteogenesis, angiogenesis, blood supply and permeability.

The cellular derivation and the life span of the myofibroblast

The presence of myofibroblasts in granulation tissue and various fibrotic settings is well established. Recent work on this cell has shown that myofibroblasts derive mainly from local fibroblasts, but also from pericytes and smooth muscle cells as well as from specialized cells such as perisinusoidal stellate cells of the liver and mesangial cells of the kidney glomerulus. During the healing of an open wound, myofibroblasts disappear by means of apoptosis when the wound is closed and granulation tissue gradually transforms into scar tissue. The possibility exists that an altered regulation of this process leads to the development of a hypertrophic scar.

Limited chondro-osteogenesis by recombinant human transforming growth factor-beta 1 in calvarial defects of adult baboons (Papio ursinus)

The therapeutic utility of a single application of recombinant human transforming growth factor-beta (hTGF-beta) has not been previously tested in large osseous wounds in primates. Sixteen calvarial defects, 25 mm in diameter, were prepared in four adult male baboons (Papio ursinus). In each animal, three defects were treated with increasing doses of hTGF-beta 1 in conjunction with baboon insoluble collagenous bone matrix as carrier (5, 30, and 100 micrograms of hTGF-beta 1/g of matrix). The fourth defect was implanted with collagenous matrix without hTGF-beta 1 as control. Serial undecalcified sections were prepared from the specimens harvested on day 30. Islands of cartilage and endochondral osteogenesis were found in hTGF-beta 1-treated defects, irrespective of the doses used. Histomorphometry of the defect site showed no significant differences between control and hTGF-beta 1-treated specimens with regard to bone and osteoid volumes. However, analysis of the regenerated tissue in proximity to the defect margins only showed that, on average, greater amounts of bone formed in specimens that were treated with 5 and 30 micrograms of hTGF-beta 1 when compared with controls. This suggests a possible effect on osteoblastic cells originating from the periosteal and endosteal spaces of the severed calvaria. Overall, however, this difference has no therapeutic implications for the healing of large cranial wounds in primates. The present findings indicate that a single application of hTGF-beta 1, in conjunction with collagenous matrix, results in limited chondro-osteogenesis in defects of membranous bone of adult baboons.

Tumor necrosis factor-alpha inhibits collagen alpha1(I) gene expression and wound healing in a murine model of cachexia

The mechanisms responsible for impaired wound healing in patients with cachexia-associated infection, inflammation, and cancer are unknown. As tumor necrosis factor (TNF)-alpha is elevated in these diseases, and TNF-alpha inhibits collagen alpha1(I) gene expression in cultured fibroblasts, we analyzed whether chronically elevated serum TNF-alpha affects collagen metabolism in vivo by inoculating nude mice with Chinese hamster ovary cells secreting TNF-alpha (TNF-alpha mice) or control Chinese hamster ovary cells (control mice). Before the onset of weight loss, TNF-alpha mice had a selective decrease in collagen synthesis and collagen alpha1(I) mRNA in the skin. In addition, TNF-alpha mice displayed impaired healing of incisional and excisional skin wounds, compared with control animals, before the onset of cachexia. The expression of transforming growth factor-beta1, a potent fibrogenic factor, was inhibited by TNF-alpha in the skin. In studies with transgenic mice expressing the human growth hormone under the direction of 5' regulatory regions of the human collagen alpha1(I) gene, TNF-alpha treatment inhibited the expression of the collagen alpha1(I) human growth hormone transgene containing -2.3 kb of the 5' region, whereas transgene expression directed by -0.44 kb of the 5' region was not affected. These experiments suggest that TNF-alpha may play an important role in the impaired wound healing of chronic diseases that are characterized by a high production of this cytokine and provide insights for potential therapeutic approaches.

Transforming growth factor-beta type-II receptor signalling: intrinsic/associated casein kinase activity, receptor interactions and functional effects of blocking antibodies

The transforming growth factor beta (TGF-beta) family of growth factors control proliferation, extracellular matrix synthesis and/ or differentiation in a wide variety of cells. However, the molecular mechanisms governing ligand binding, receptor oligomerization and signal transduction remain incompletely understood. In this study, we utilized a set of antibodies selective for the extracellular and intracellular domains of the TGF-beta type-II receptor as probes to investigate the intrinsic kinase activity of this receptor and its physical association in multimeric complexes with type-I and type-III receptors. The type-II receptor immuno-precipitated from human osteosarcoma cells exhibited autophosphorylation and casein kinase activity that was markedly stimulated by polylysine yet was insensitive to heparin. Affinity cross-linking of 125I-TGF-beta 1 ligand to cellular receptors followed by specific immunoprecipitation demonstrated that type-II receptors form stable complexes with both type-I and type-III receptors expressed on the surfaces of both human osteosarcoma cells and rabbit chondrocytes. Pretreatment of the cultured cells with an antibody directed against a distinct extracellular segment of the type-II receptor (anti-TGF-beta-IIR-NT) effectively blocked the 125I-TGF-beta labelling of type-I receptors without preventing the affinity labelling of type-II or type-III receptors, indicating a selective disruption of the type-I/type-II hetero-oligomers. The anti-TGF-beta-IIR-NT antibodies also blocked the TGF-beta-dependent induction of the plasminogen activator inhibitor (PAI-1) promoter observed in mink lung epithelial cells. However, the same anti-TGF-beta-IIR-NT antibodies did not prevent the characteristic inhibition of cellular proliferation by TGF-beta 1, as determined by [3H]thymidine incorporation into DNA. The selective perturbation of PAI-1 promoter induction versus cell-cycle-negative regulation suggests that strategic disruption of TGF-beta type-I and -II receptor interactions can effectively alter specific cellular responses to TGF-beta signalling.

Experimental glomerulosclerosis: Defektheilung of the kidney

Research in the role of cytokines in experimental glomerulonephritis has increased our understanding of the mechanisms that may be involved in the development of progressive renal disease. Glomerulosclerosis, the final common pathway in a variety of underlying kidney diseases, is characterized by increased extracellular matrix formation and cell proliferation. Transforming growth factor-beta (TGF-beta) and monocyte chemoattractant protein-1 (MCP-1) have been identified in animal models as mediators in the processes that follow renal injury. There is evidence of similar events occurring in other fibrotic disorders, suggesting that there is a common generic pathway of fibrosis. This review summarizes our knowledge of TGF-beta and MCP-1 in experimental kidney disease and compares these results with mechanisms described in other organs. We propose that glomerulosclerosis represents Defektheilung (healing by secondary intention) of the kidney after various injuries. The growing knowledge of the mechanisms involved will help advance future therapeutic interventions by directing the healing process toward primary healing.

Transforming growth factors beta1, beta2, and beta3 and their receptors are differentially regulated during normal and impaired wound healing

A series of studies has shown that application of transforming growth factor beta (TGF-beta) to a wound has a beneficial effect, especially in animals with wound healing disorders. In this study we have investigated the regulation of TGF-beta1, beta2, and beta3 and their receptors during the repair process. We found a large induction of all three TGF-beta isoforms and also of TGF-beta types I and II receptors, although the time course of induction and the absolute expression levels were different for these genes. Furthermore, each TGF-beta isoform had distinct sites of expression in the wound. Systemic treatment with glucocorticoids significantly altered the expression levels of TGF-betas and TGF-beta receptors. Whereas expression of TGF-beta1, TGF-beta2, and TGF-beta type II receptor was suppressed by glucocorticoids in normal and wounded skin, expression of TGF-beta3 and TGF-beta receptor type I mRNA was stimulated. These findings provide an explanation for the beneficial effect of exogenous TGF-beta in the treatment of impaired wound healing in glucocorticoid-treated animals. Furthermore, they suggest that a disturbed balance between the levels of the three TGF- beta isoforms and their receptors might underlie the wound healing defect seen in glucocorticoid-treated animals.