The expression of transforming growth factor type beta in fetal and adult rabbit skin wounds

MSCs on an acellular dermal matrix (ADM) sourced from neonatal mouse skin regulate collagen reconstruction of granulation tissue during adult cutaneous wound healing

The novel strategy of MSCs seeded on ADM sourced from neonatal mouse skin promotes full-thickness cutaneous wound healing.

Fetal and adult fibroblasts display intrinsic differences in tendon tissue engineering and regeneration

Injured adult tendons do not exhibit optimal healing through a regenerative process, whereas fetal tendons can heal in a regenerative fashion without scar formation. Hence, we compared FFs (mouse fetal fibroblasts) and AFs (mouse adult fibroblasts) as seed cells for the fabrication of scaffold-free engineered tendons. Our results demonstrated that FFs had more potential for tendon tissue engineering, as shown by higher levels of tendon-related gene expression. In the in situ AT injury model, the FFs group also demonstrated much better structural and functional properties after healing, with higher levels of collagen deposition and better microstructure repair. Moreover, fetal fibroblasts could increase the recruitment of fibroblast-like cells and reduce the infiltration of inflammatory cells to the injury site during the regeneration process. Our results suggest that the underlying mechanisms of better regeneration with FFs should be elucidated and be used to enhance adult tendon healing. This may assist in the development of future strategies to treat tendon injuries.

Altered TGF-β signaling in fetal fibroblasts: what is known about the underlying mechanisms?

Scarless wound healing is a unique and intrinsic capacity of the fetal skin that is not fully understood. Further insight into the underlying mechanisms of fetal wound healing may lead to new therapeutic approaches promoting adult scarless wound healing. Differences between fetal and adult wound healing are found in the extracellular matrix, the inflammatory reaction and the levels of growth factors present in the wound. This review focuses specifically on transforming growth factor β (TGF-β), as this growth factor is prominently involved in wound healing and fibroblast-to-myofibroblast differentiation. Although fetal fibroblasts do respond to TGF-β, they lack a proliferative and a contractile response and display short-lived myofibroblast differentiation, autocrine response, and collagen up-regulation in comparison with adult fibroblasts. Curiously, prolonged TGF-β activation is associated with fibrosis, and therefore, this short-lived response in fetal fibroblasts might contribute to scarless healing. This review gives an overview of the current knowledge on TGF-β signaling and the intracellular TGF-β signaling pathway in fetal fibroblasts. Furthermore, this review also describes the various components that regulate the cellular TGF-β response and hypothesizes about the possible roles these components might play in the altered response of fetal fibroblasts to TGF-β.

Transforming Growth Factor-β and Endoglin Signaling Orchestrate Wound Healing

Physiological wound healing is a complex process requiring the temporal and spatial co-ordination of various signaling networks, biomechanical forces, and biochemical signaling pathways in both hypoxic and non-hypoxic conditions. Although a plethora of factors are required for successful physiological tissue repair, transforming growth factor beta (TGF-β) expression has been demonstrated throughout wound healing and shown to regulate many processes involved in tissue repair, including production of ECM, proteases, protease inhibitors, migration, chemotaxis, and proliferation of macrophages, fibroblasts of the granulation tissue, epithelial and capillary endothelial cells. TGF-β mediates these effects by stimulating signaling pathways through a receptor complex which contains Endoglin. Endoglin is expressed in a broad spectrum of proliferating and stem cells with elevated expression during hypoxia, and regulates important cellular functions such as proliferation and adhesion via Smad signaling. This review focuses on how the TGF-β family and Endoglin, regulate stem cell availability, and modulate cellular behavior within the wound microenvironment, includes current knowledge of the signaling pathways involved, and explores how this information may be applicable to inflammatory and/or angiogenic diseases such as fibrosis, rheumatoid arthritis and metastatic cancer.

Cellular and Molecular Characteristics of Scarless versus Fibrotic Wound Healing

The purpose of this paper is to compare and contrast the discrete biology differentiating fetal wound repair from its adult counterpart. Integumentary wound healing in mammalian fetuses is essentially different from wound healing in adult skin. Adult (postnatal) skin wound healing is a complex and well-orchestrated process spurred by attendant inflammation that leads to wound closure with scar formation. In contrast, fetal wound repair occurs with minimal inflammation, faster re-epithelialization, and without the accumulation of scar. Although research into scarless healing began decades ago, the critical molecular mechanisms driving the process of regenerative fetal healing remain uncertain. Understanding the molecular and cellular events during regenerative healing may provide clues that one day enable us to modulate adult wound healing and consequently reduce scarring.

Scarless fetal wound healing: a basic science review

SUMMARY

Scar formation is a major medical problem that can have devastating consequences for patients. The adverse physiological and psychological effects of scars are broad, and there are currently no reliable treatments to prevent scarring. In contrast to adult wounds, early gestation fetal skin wounds repair rapidly and in the absence of scar formation. Despite extensive investigation, the exact mechanisms of scarless fetal wound healing remain largely unknown. For some time, it has been known that significant differences exist among the extracellular matrix, inflammatory response, cellular mediators, and gene expression profiles of fetal and postnatal wounds. These differences may have important implications in scarless wound repair.

Fetal skin wound healing

The developing fetus has the ability to heal wounds by regenerating normal epidermis and dermis with restoration of the extracellular matrix (ECM) architecture, strength, and function. In contrast, adult wounds heal with fibrosis and scar. Scar tissue remains weaker than normal skin with an altered ECM composition. Despite extensive investigation, the mechanism of fetal wound healing remains largely unknown. We do know that early in gestation, fetal skin is developing at a rapid pace and the ECM is a loose network facilitating cellular migration. Wounding in this unique environment triggers a complex cascade of tightly controlled events culminating in a scarless wound phenotype of fine reticular collagen and abundant hyaluronic acid. Comparison between postnatal and fetal wound healing has revealed differences in inflammatory response, cellular mediators, cytokines, growth factors, and ECM modulators. Investigation into cell signaling pathways and transcription factors has demonstrated differences in secondary messenger phosphorylation patterns and homeobox gene expression. Further research may reveal novel genes essential to scarless repair that can be manipulated in the adult wound and thus ameliorate scar.

Progressive pulmonary fibrosis is mediated by TGF-beta isoform 1 but not TGF-beta3

Tissue repair is a well-orchestrated biological process involving numerous soluble mediators, and an imbalance between these factors may result in impaired repair and fibrosis. Transforming growth factor (TGF)-beta is a key profibrotic element in this process and it is thought that its three isoforms act in a similar way. Here, we report that TGF-beta3 administered to rat lungs using transient overexpression initiates profibrotic effects similar to those elicited by TGF-beta1, but causes less severe and progressive changes. The data suggest that TGF-beta3 does not lead to inhibition of matrix degradation in the same way as TGF-beta1, resulting in non-fibrotic tissue repair. Further, TGF-beta3 is able to downregulate TGF-beta1-induced gene expression, suggesting a regulatory role of TGF-beta3. TGF-beta3 overexpression results in an upregulation of Smad proteins similar to TGF-beta1, but is less efficient in inducing the ALK 5 and TGF-beta type II receptor (TbetaRII). We provide evidence that this difference may contribute to the progressive nature of TGF-beta1-induced fibrotic response, in contrast to the limited fibrosis observed following TGF-beta3 overexpression. TGF-beta3 is important in "normal wound healing", but is outbalanced by TGF-beta1 in "fibrotic wound healing" in the lung.

Rosiglitazone Suppresses Cyclosporin-Induced Chronic Transplant Dysfunction and Prolongs Survival of Rat Cardiac Allografts

BACKGROUND

The lack of effective treatment for chronic transplant dysfunction restricts the long-term survival of solid organ allografts. Peroxisome proliferator-activated receptor ligands can suppress vascular inflammation. The aim of this study was to analyze the effects of rosiglitazone on chronic transplant dysfunction in a rat cardiac transplant model.

METHODS

Inbred male Fisher 344 (F344, RT1lvl) and Lewis (LEW, RT1(1)) rats were subjected to heterotopic abdominal heart transplantation according to standard procedures. Cyclosporine A was administered intraperitoneally to cover acute rejection, and rosiglitazone was administered orally by gavage daily from 3 days before the operation to the end of experiments.

RESULTS

Rosiglitazone significantly prolonged the survival of cardiac allografts in rats (F344 to LEW) that had received a 10-day course of cyclosporin A compared to treatment with immunosuppressant alone. Analysis of allografts at 120 days posttransplantation showed that rosiglitazone reduced the inflammatory cell infiltrate in both the vessels and graft parenchyma as were neointimal formation, vascular occlusion, and fibrosis. Expression of transforming growth factor-beta and related proteins was less abundant after cyclosporin A/rosiglitazone treatment.

CONCLUSIONS

The findings reported here demonstrate that rosiglitazone given under the cover of short-term treatment with cyclosporin A prolongs cardiac allograft survival and reduces the severity of chronic transplant dysfunction. This may be mediated in part through the downregulation of transforming growth factor-beta and related proteins. The combined effects of rosiglitazone and immunosuppressive drugs are potentially beneficial to patients receiving organ transplants.

Identification of a novel FcγRIII receptor that is up-regulated in fetal wound healing

The mid-gestation fetus is able to heal skin wounds rapidly and without scarring, an ability that is lost as development proceeds. The aim of this study was to identify novel genes involved in this process. We established an ex vivo wound model from embryonic rats and showed that over 72 hours, embryonic day 17 wounds reepithelialized and closed whereas day 19 wounds did not. To investigate the molecular basis of this phenomenon we analyzed changes in gene expression using differential display polymerase chain reaction. We characterized one transcript that was strongly up-regulated in the healing response of wounded, day 17 skin. It encodes a protein of 249 amino acids with striking similarity to the human low-affinity receptor for the Fc portion of IgG (FcgammaRIII), suggesting that it is a novel member of the FcgammaR family, which we named FcgammaRIII-X. A wound-healing timecourse shows that FcgammaRIII-X was up-regulated in healing, wounded day 17 skin but not in nonhealing, wounded day 19 skin and that its up-regulation was accelerated in skin with multiple wounds. We suggest that up-regulation of FcgammaRIII-X may contribute to scarless healing of fetal skin.

Transforming Growth Factor-β Gene Polymorphisms in Sarcoidosis Patients With and Without Fibrosis

STUDY OBJECTIVES

Pulmonary fibrosis develops in approximately 25% of patients with chronic sarcoidosis. Transforming growth factor (TGF)-beta1 plays a central role in fibrosis, and accruing reports address the implication of TGF-beta2 and TGF-beta3 in this process. We determined whether single-nucleotide polymorphisms (SNPs) in the TGF-beta1, TGF-beta2, and TGF-beta3 genes might contribute to pulmonary fibrosis in sarcoidosis patients.

SETTING

A hospital in the Netherlands.

DESIGN

Five SNPs per TGF-beta gene were investigated.

PATIENTS AND CONTROL SUBJECTS

Patients with either acute/self-remitting sarcoidosis (n = 50) and Löfgren syndrome (n = 46) or chronic disease with fibrosis (n = 24) and without fibrosis (n = 34) were assessed over a 4-year follow-up period. The control subjects included 315 individuals.

MEASUREMENTS AND RESULTS

Polymorphism frequencies were not discordant between the patients and control subjects. The TGF-beta3 4875 A allele was significantly higher in fibrotic patients (carrier frequency, 0.29) than in patients with acute/self-remitting (0.06) and chronic (0.03) sarcoidosis combined (corrected p = 0.01; odds ratio [OR], 7.9). The TGF-beta3 17369 C allele carrier frequency was significantly higher in fibrotic patients (0.29) compared to acute/self-remitting (0.08) and chronic (0.06) patients combined (corrected p = 0.05; OR, 5.1). Although not significant after correction, the TGF-beta3 15101 G allele carrier frequency was lower in fibrotic patients (0.79) compared to acute/self-remitting (0.94) and chronic (1.00) patients combined (p = 0.02; corrected p = 0.1; OR, 0.15). The TGF-beta2 59941 G allele was more abundant in fibrotic patients (carrier frequency, 0.62) compared to patients with acute/self-remitting (0.41) and chronic sarcoidosis combined (0.28) [p = 0.04; corrected p = 0.2; OR, 2.9]. TGF-beta1 gene polymorphisms were not associated with fibrosis.

CONCLUSIONS

This study is the first to suggest the implication of genetic variation of TGF-beta3 in the predilection for pulmonary fibrosis developing in sarcoidosis patients.

An In Vivo Mouse Excisional Wound Model of Scarless Healing

BACKGROUND

The purpose of this study was to develop a reproducible murine model of fetal scarless wound healing.

METHODS

One-millimeter excisional wounds were made in fetal skin at gestational days 16.5 (E17) and 18.5 (E19) (term = day 21.5, or E22) and marked with India ink. Fetal mortality was less than 30 percent in E17 fetuses and 0 percent in E19 fetuses. Control postnatal 2-mm open wounds were made in 3-week-old mice.

RESULTS

At 48 hours, E17 skin wounds had healed completely. E19 skin wounds also healed but were marked by skin irregularity at the wound site. Histologically, E17 wounds had fine reticular collagen architecture by trichrome staining and hair follicle regeneration. In contrast, E19 wounds healed with collagen deposition and scar formation and no hair follicle regeneration.

CONCLUSIONS

The authors have developed a reliable mouse model of fetal scarless repair to help elucidate the mechanism of scarless wound healing to take advantage of genetically modified animals. The knowledge gained may be used to manipulate scarring in the adult to produce a more fetal-like wound.

Hydrogen peroxide disrupts scarless fetal wound repair

Cutaneous wound healing is a complex process that leads to the formation of a permanent scar in adult skin. In contrast, early gestation fetal skin undergoes scarless repair. Normally, the repair process in the skin begins with an acute inflammatory response. However, one of the most important aspects of scarless fetal wound repair appears to be a lack of inflammation, suggesting that inflammation promotes scar formation in the skin. While it is well accepted that inflammation causes scar formation in the fetus, it is not known what specific factors produced during inflammation are responsible for these effects. Oxidants released by activated inflammatory cells have the potential to be involved, although this has never been examined. The present studies, using a murine fetal wound repair model, show that hydrogen peroxide interferes with scarless healing, possibly through the induction of transforming growth factor-beta1. Hydrogen peroxide also increased the proliferation of fetal fibroblasts, which could contribute to an increase in the fibrosis seen with hydrogen peroxide. Defining the factors produced during the inflammatory response that contribute to scar formation could be important for the development of new therapies designed to minimize scarring.

The fibroblast-populated collagen matrix as a model of wound healing: a review of the evidence

The fibroblast-populated collagen matrix (FPCM) has been utilized as an in vitro model of wound healing for more than 2 decades. It offers a reasonable approximation of the healing wound during the phases of established granulation tissue and early scar. The gross and microscopic morphology of the FPCM and the healing wound are similar at analogous phases. The processes of proliferation, survival/apoptosis, protein synthesis, and contraction act in similar directions in these two models, and the response to exogenous agents also is consistent between them. If its limitations are respected, then the FPCM can be used as a model of the healing wound.

Ontogenetic transition in fetal wound transforming growth factor-beta regulation correlates with collagen organization

Fetal rat skin transitions from scarless fetal-type repair to adult-type repair with scar between day 16 (E16) and day 18 (E18) of gestation (term = 21.5 days). Deficient transforming growth factor (TGF)-beta 1 and -beta 2 injury response has been proposed as a mechanism for scarless fetal-type repair. However, previous fetal studies have inconsistently reported the degree of TGF-beta induction after injury. To minimize developmental variables in fetal versus adult TGF-beta regulation, we narrowed our study to wounded fetal animals. We hypothesize that TGF-beta ligand and receptor expression will be differentially regulated during the transition from early gestation (E16) wounds manifesting scarless fetal-type repair to late gestation (E19) wounds manifesting adult-type repair with scar. In this study, decreased and rapidly cleared TGF-beta 1 and -beta 2 expression accompanied by increased and prolonged TGF-beta 3 levels in wounded E16 animals correlated with organized collagen deposition. In contrast, increased and prolonged TGF-beta 1 and -beta 2 expression accompanied by decreased and delayed TGF-beta 3 expression in wounded E19 animals correlated with disorganized collagen architecture. Similarly, expression of TGF-beta receptors type I and II were also increased or prolonged in E19 animals. Our results implicate increased TGF-beta 1, -beta 2, and decreased TGF-beta 3 expression, as well as increased type I and II receptor expression in late gestation fetal scar formation.

Regulation of wound healing by growth factors and cytokines

Cutaneous wound healing is a complex process involving blood clotting, inflammation, new tissue formation, and finally tissue remodeling. It is well described at the histological level, but the genes that regulate skin repair have only partially been identified. Many experimental and clinical studies have demonstrated varied, but in most cases beneficial, effects of exogenous growth factors on the healing process. However, the roles played by endogenous growth factors have remained largely unclear. Initial approaches at addressing this question focused on the expression analysis of various growth factors, cytokines, and their receptors in different wound models, with first functional data being obtained by applying neutralizing antibodies to wounds. During the past few years, the availability of genetically modified mice has allowed elucidation of the function of various genes in the healing process, and these studies have shed light onto the role of growth factors, cytokines, and their downstream effectors in wound repair. This review summarizes the results of expression studies that have been performed in rodents, pigs, and humans to localize growth factors and their receptors in skin wounds. Most importantly, we also report on genetic studies addressing the functions of endogenous growth factors in the wound repair process.

Reduction of scar formation in full-thickness wounds with topical celecoxib treatment

Adult wound repair occurs with an initial inflammatory response, reepithelialization, and the formation of a permanent scar. Although the inflammatory phase is often considered a necessity for successful adult wound healing, fetal healing studies have shown the ability to regenerate skin and to heal wounds in a scarless manner in the absence of inflammation. The cyclooxygenase-2 (COX-2) enzyme, a known mediator of inflammation, has been shown to contribute to a variety of inflammatory conditions and to the development of cancer in many organs. To examine the role of COX-2 in the wound healing process, incisional wounds were treated topically with the anti-inflammatory COX-2 inhibitor celecoxib. Acutely, celecoxib inhibited several parameters of inflammation in the wound site. This decrease in the early inflammatory phase of wound healing had a significant effect on later events in the wound healing process, namely a reduction in scar tissue formation, without disrupting reepithelialization or decreasing tensile strength. Our data suggest that in the absence of infection, adult wound healing is able to commence with decreased inflammation and that anti-inflammatory drugs may be used to improve the outcome of the repair process in the skin by limiting scar formation.

Fetal wound healing current perspectives

Early in gestation, fetal wounds are capable of healing scarlessly. Scarless healing in the fetus is characterized by regeneration of an organized dermis with normal appendages and by a relative lack of inflammation. Although there is a transition period between scarless and scar-forming repair, scarless healing also depends on wound size and the organ involved. The ability to heal scarlessly, furthermore, appears to be intrinsic to fetal skin. Unique characteristics of fetal fibroblasts, inflammatory cells, extra-cellular matrix, cytokine profile, and developmental gene regulation may be responsible for the scarless phenotype of early gestation fetal wounds. With the current knowledge, only minimal success has been achieved with the topical application of neutralizing antibodies, antisense oligonucleotides, and growth factors to improve wound-healing outcomes. Thus, further investigation into the mechanisms underlying scarless repair is crucial in order to devise more effective therapies for scar reduction and the treatment of cirrhosis, scleroderma, and other diseases of excessive fibrosis.

Autocrine growth factor production by fetal, keloid, and normal dermal fibroblasts

OBJECTIVE

To evaluate differences in fibroblast autocrine growth factor production by human fetal, keloid, and normal adult dermal fibroblasts.

DESIGN

Serum-free cell lines of fetal, keloid, and normal adult dermal fibroblasts were established. Cell counts were performed and supernatants collected at 4, 24, and 72 hours. Cell-free supernatants were quantitatively assayed for transforming growth factor beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF).

RESULTS

Population doubling times for fetal, keloid, and normal adult fibroblasts were 120.0, 88.1, and 128.4 hours, respectively. Differences in population doubling times did not reach statistical significance. Statistically significant differences between TGF-beta1 levels from fetal and normal adult fibroblasts were seen at 24 and 72 hours. Significant differences between TGF-beta1 levels from keloid and normal adult fibroblasts were also seen at 24 and 72 hours. Fetal fibroblasts demonstrated higher levels of bFGF than normal adult fibroblasts at each time point, but these differences were not statistically significant. No significant differences were observed between keloid and normal adult bFGF levels.

CONCLUSIONS

Both fetal and keloid fibroblasts produce significantly more TGF-beta1 than normal adult fibroblasts. Our data and the data of others suggest that fetal fibroblasts produce more bFGF than adult fibroblasts. The serum-free model we describe can be used to quantitatively measure autocrine growth factor production by cells that underlie clinically different types of wound healing. This model provides information that may allow us to better treat and prevent undesirable scarring.

Differential expression and regulation of extracellular matrix-associated genes in fetal and neonatal fibroblasts

Adults and neonates heal wounds by a repair process associated with scarring in contrast to scar-free wound healing in the fetus. In the present study, human dermal fetal fibroblasts, representing the scarless phenotype, and neonatal human dermal fibroblasts, representing scar-forming phenotype, were examined for potential differences that might influence the wound healing process. Fetal fibroblasts secreted four- to tenfold more latent transforming growth factor-beta1 depending on the cell strains compared. Fetal fibroblasts also produced higher levels of collagen protein and mRNA for most types of collagen (particularly type III) as compared to neonatal cells. Interestingly, mRNA for type V collagen was significantly reduced in fetal cells. Neonatal fibroblasts expressed significantly higher levels of latent transforming growth factor-beta1 binding protein mRNA, in contrast to almost undetectable levels in fetal fibroblasts. By ligand blot analysis, the levels of insulin-like growth factor binding protein-3, a reported mediator of transforming growth factor-beta1 activity, was eightfold higher in neonatal versus fetal fibroblasts. Approximately 20 other mRNAs for various cytokines, matrix molecules and receptors were examined and found to be similar between the two cell types. The phenotypic differences described in this article may represent potentially important mechanisms to explain the differences in the quality of wound repair observed in fetal versus adult/neonatal tissues.

Differential expression of fibromodulin, a transforming growth factor-beta modulator, in fetal skin development and scarless repair

Transforming growth factor-beta (TGF-beta1, -beta2, and -beta3) has been implicated in the ontogenetic transition from scarless fetal repair to adult repair with scar. Generally, TGF-beta exerts its effects through type I and II receptors; however, TGF-beta modulators such as latent TGF-beta binding protein-1 (LTBP-1), decorin, biglycan, and fibromodulin can bind and potentially inhibit TGF-beta activity. To more fully explore the role of TGF-beta ligands, receptors, and potential modulators during skin development and wound healing, we have used a rat model that transitions from scarless fetal-type repair to adult-type repair with scar between days 16 and 18 of gestation. We showed that TGF-beta ligand and receptor mRNA levels did not increase during the transition to adult-type repair in fetal skin, whereas LTBP-1 and fibromodulin expression decreased. In addition, TGF-beta1 and -beta3; type I, II, and III receptors; as well as LTBP-1, decorin, and biglycan were up-regulated during adult wound healing. In marked contrast, fibromodulin expression was initially down-regulated in adult repair. Immunostaining demonstrated significant fibromodulin induction 36 hours after injury in gestation day 16, but not day 19, fetal wounds. This inverse relationship between fibromodulin expression and scarring in both fetal and adult rat wound repair suggests that fibromodulin may be a biologically relevant modulator of TGF-beta activity during scar formation.

Increased expression of transforming growth factor-beta1, acidic fibroblast growth factor, and basic fibroblast growth factor in fetal versus adult fibroblast cell lines

OBJECTIVES

Fetal wound healing occurs without scar tissue formation. Differences in growth factor expression between fetal and adult fibroblasts have been explored. Recently we used RNA expression studies to demonstrate that transforming growth factor (TGF)-beta1, acidic fibroblast growth factor (alpha-FGF), and basic fibroblast growth factor (beta-FGF) could be detected in both fetal and adult fibroblast cell lines. In addition, adult fibroblasts showed greater relative expression of these growth factors than fetal fibroblasts. The aim of this study was to identify the level of protein expression in fetal and adult fibroblasts.

STUDY DESIGN/METHODS

Fetal and adult fibroblasts were grown in culture using standard and serum-free media. After protein extraction, Western blot studies were performed to detect the presence and amount of TGFbeta-1, alpha-FGF, and beta-FGF growth factor proteins. beta-Tubulin was used as a control.

RESULTS

TGFbeta-1, alpha-FGF, and beta-FGF proteins were detected in fetal and adult fibroblasts grown in standard and serum-free media. The fetal fibroblasts showed higher levels of all three growth factor proteins compared with the adult fibroblasts.

CONCLUSIONS

Western blot studies suggest higher levels of TGFbeta-1, alpha-FGF, and beta-FGF expression in fetal fibroblasts. It is clear that significant differences exist in the expression/production of these growth factors and it seems likely that further study of these differences will help elucidate the unique healing capabilities of fetal fibroblasts.

Myofibroblast induction with transforming growth factor-beta1 and -beta3 in cutaneous fetal excisional wounds

BACKGROUND/PURPOSE

In a noncontractile fetal rabbit model, the authors recently have shown the induction of excisional wound contraction with sustained-release cellulose implants formulated with transforming growth factor (TGF)-beta. The purpose of this study was to test the hypothesis that the excisional wound contraction in this model is associated with the induction of myofibroblasts in the surrounding dermis, demonstrated by the presence of alpha-smooth muscle actin.

METHODS

Cellulose discs were formulated with either 1.0 microg of TGF-beta1 (n = 6); 1.0 microg of TGF-beta3 (n = 9); 10 microg of TGF-beta3 (n = 6); or their carrier protein, bovine serum albumin (BSA; n = 9), for sustained-release over 5 days. Each disc was implanted into a subcutaneous pocket on the back of a fetal New Zealand White rabbit in utero on day 24 of gestation (term, 31 days). A full-thickness, 3-mm excisional wound (7.4 mm2) was then made next to the implanted cellulose disc. All fetuses were harvested at 3 days. The amount of alpha-smooth muscle (SM) actin in the dermis around the implants and wounds was determined using immunohistochemical techniques.

RESULTS

Excisional wounds exposed to 1.0 microg of TGF-beta1 (5.6+/-2.0 mm2), 1.0 microg of TGF-beta3 (6.9+/-1.0 mm2), and 10 microg of TGF-beta3 (2.7+/-1.0 mm2) were significantly smaller when compared with the BSA control group (12.8+/-1.1 mm2; P<.05). Furthermore, there was a significant increase in staining for alpha-SM actin in the TGF-beta1 (1.8+/-0.5) and 10 microg TGF-beta3 (2.8+/-0.2) groups in comparison with the scant staining in the BSA control group (0.5+/-0.2; P<.05).

CONCLUSIONS

TGF-beta1 and -beta3 induce alpha-SM actin and contraction of cutaneous excisional wounds in a fetal noncontractile model. This model of inducible cutaneous excisional wound contraction may be useful in further determining the role of the myofibroblast in wound contraction and the physiology underlying this poorly understood aspect of wound healing.

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.

Differential responses of collagen and glycosaminoglycan syntheses and cell proliferation to exogenous transforming growth factor beta 1 in the developing mouse skin fibroblasts in culture

Skin fibroblast cultures were established from mouse foetuses at days 14, 15, 16 and 18 of gestation and from newborn mice. Modulations of mitotic and biosynthetic phenotypes of the fibroblasts by transforming growth factor beta1 (TGFbeta1) were studied. Treatment of the fibroblasts with TGFbeta1 at doses of 1 and 10 ng/ml for 48 h resulted in significant stimulation of cell proliferation in the 15-, 16- and 18-day foetal fibroblasts and a slight stimulation in the 14-day foetal fibroblasts. Treatment with TGFbeta1 resulted in stimulation of collagen synthesis approximately 2-fold in the 18-day foetal and newborn fibroblasts, but failed to stimulate it in the 14-, 15- and 16-day foetal fibroblasts. TGFbeta1 stimulated glycosaminoglycan (GAG) synthesis throughout all developmental stages approximately 1.8-2.6 fold. Histological study demonstrated that skin wounds made at day 16 of gestation were replaced with normal-appearing dermis, but at day 18 the wounds left dermal fibrosis and lack of hair follicles. These results indicate that the modulations of fibroblast phenotypes (proliferation and syntheses of collagen and GAG) in response to TGFbeta1 occur at different stages of gestation. Ontogenic transitions of skin wound healing and collagen synthetic phenotype with TGFbeta1 treatment in cultured fibroblasts occurred between days 16 and 18 of gestation, suggesting that the unresponsiveness of collagen synthesis to exogenous TGFbeta1 in cell culture may be related to the phenomenon of scarless wounds in the foetus.

TGF-beta1 alters the healing of cutaneous fetal excisional wounds

BACKGROUND/PURPOSE

In a number of species, fetal wound healing differs from the adult in the absence of inflammation, fibrosis, scar formation, and excisional wound contraction. The lack of inflammation also may explain the relative absence of any cytokine levels at the wound site, such as transforming growth factor (TGF)-beta, and therefore the unique characteristics of fetal wound healing. The authors hypothesized that exogenous TGF-beta1 would induce contraction, inflammation, fibrosis, and scar formation in cutaneous excisional wounds in the fetal rabbit.

METHODS

Cellulose discs (3 mm in diameter) were formulated with either 1.0 microg TGF-beta1 (n = 6) or bovine serum albumin (BSA; n = 7), as a control, for sustained-release over 3 days. Each disc was implanted into the subcutaneous tissue on the backs of fetal New Zealand White Rabbits in utero on day 24 of gestation (term, 31 days). A full-thickness, 3-mm excisional wound (7.4 mm2) was then made next to the implanted cellulose disc. All wounds were harvested 3 days later.

RESULTS

At harvest, the excisional wounds in the TGF-beta1 group had contracted (5.6 +/- 2.0 mm2), whereas those in the control group had expanded (13.5 +/- 1.2 mm2, P< .01). The surrounding dermis in the TGF-beta1 group had 16.3 inflammatory cells per grid block compared with 12.4 cells in the control group (not significant). In addition, a greater amount of fibrosis was induced by the TGF-beta1 implant (1.7 +/- 0.3) than the control implant (0.4 +/- 0.2) on a scale of 0 to 3, P < .01. In situ hybridization analysis showed an increase in procollagen type 1alpha1 gene expression in the surrounding dermis of the TGF-beta1 group (36.7 +/- 3.6 grains per grid block) compared with the control group (7.1 +/- 0.9 grains per grid block, P < .001).

CONCLUSIONS

These results demonstrate that the cytokine TGF-beta1 can induce fetal excisional wounds to contract, stimulate fibrosis, and increase procollagen type 1alpha1 gene expression. These findings further suggest that the absence of TGF-beta1 atthe wound site may be responsible in part for the lack of a postnatal healing response.

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.

Angiogenesis in pathological and surgical scars

We identified immunohistochemically vessels within cutaneous scars to test the hypothesis that they are qualitatively and quantitatively different in pathological and normally healing scars. The vascular density within and adjacent to 58 cutaneous scars was measured on histological sections stained for factor VIII-related antigen. Four scar types were studied; surgical scars (n = 25), hypertrophic scars (n = 10), keloid (n = 12), and periocular scars (n = 11). Statistical analyses were performed to test the hypothesis that vessel numbers were different in the varying types of scar. Results were also compared with mast cell counts previously derived from the same tissues. A significant reduction was found in the vascular density in keloids compared with surgical and hypertrophic scars (P < .05). No correlation was found between the vascular density and the number of mast cells in the lesions. We have shown quantitatively that keloids have a reduced vascular component compared with hypertrophic scars and normally healing surgical scars at periocular and systemic sites. The formation of keloid scars may be related to their reduced level of vascularization mediated through tissue hypoxia.

Temporal and spatial expression of transforming growth factor-beta in the healing patellar ligament of the rat

We investigated the temporal and spatial expression of transforming growth factor-beta in the healing patellar ligament of the rat by immunohistochemistry. The mid-portion of the medial half of the patellar ligament in 14-week-old male Wistar rats was cut transversely with a scalpel. On day 1 after ligament injury, diffuse staining for transforming growth factor-beta was observed in the extracellular matrix filling the wound, and the staining in the adjacent ligament tissue was as weak as it was in the normal ligament. On day 3, the intensity of the diffuse extracellular staining decreased, and the staining was observed in correspondence with the cellular distribution in the wound site and in the adjacent uninjured ligament tissue. On day 7, the intense staining was widely distributed over the whole length of the ligament tissue. On day 28, the staining for transforming growth factor-beta was still observed at the wound site and in the adjacent uninjured ligament tissue, where the staining was reduced in intensity but still stronger than it was in the normal ligament. On day 56, the expression of transforming growth factor-beta was still detectable at the wound site; however, in the adjacent uninjured ligament tissue, it had almost subsided to the normal level. The results of the present study suggest that ligament healing may be accompanied by extensive changes in the expression of transforming growth factor-beta over the whole length of ligament tissue.

The mechanism of excisional fetal wound repair in vitro is responsive to growth factors

We have investigated the ability of fetal rat skin to heal an excisional wound in vitro. Skin from the backs of E17-E19 rats was wounded using a 1-mm diameter cutting needle and suspended in culture on a 6-pin cradle for 72 h. Neither contraction nor epithelial closure was observed within wounds created in skin from E19 embryos. In contrast, wounds in E17 skin contracted to 35-50% of their original area over 72 h, although, in the absence of serum, complete wound closure was not observed. Addition of FBS at the time of culture resulted in the movement of the epithelium over the dermal margins of the wound to effect complete closure. Histological sections through these healed wounds revealed an epithelial bridge spanning the dermal margins of the wound. A similar mechanism of repair was observed in the presence of day 14 adult wound fluid. The response of wounds in E17 skin to a range of growth factors was then assessed in an attempt to reproduce the serum response under defined conditions. Insulin-like growth factor I or epidermal growth factor did not significantly affect wound closure. Basic fibroblast growth factor, transforming growth factor-beta, or platelet-derived growth factor did promote wound closure although, in contrast to the serum-induced response, wound histology revealed repair had been achieved by dermal fibroblasts that occupied the space between the epithelial margins of the healed wound. We have therefore shown that the epithelial component of fetal wound repair proceeds in organ-cultured fetal skin in the absence of an adhesive substrate over which to migrate and is dependent on the source of trophic factors. The inability of skin taken from the E19 embryo to heal in vitro suggests a developmental switch in the mechanism of wound epithelialization.

Expression of alpha-smooth muscle actin, TGF-beta 1 and TGF-beta type II receptor during connective tissue contraction

Closure of rat mesenteric perforation is considered to occur by connective tissue contraction, a process that has been shown to be stimulated by transforming growth factor-beta 1. In the present study, we assessed the expression of alpha-smooth muscle actin during closure by quantitative-reverse transcription-polymerase chain reaction and in situ hybridization. The expression of transforming growth factor-beta 1 and transforming growth factor-beta type II receptor was also estimated in mesenteric membranes and free peritoneal cells after wounding. A larger expression of alpha-smooth muscle actin was seen around the wound edges compared to unwounded tissue. Both alpha-smooth muscle actin and transforming growth factor-beta type II receptor were expressed during Days 0, 3, 5, 7, and 10. The expression of alpha-smooth muscle actin on Day 5 was > 100 times higher than on Day 0. Transforming growth factor-beta 1 was expressed in both membranes and free peritoneal cells of unoperated control animals but down-regulated after wounding, a finding that has not been reported previously. It reappeared on Days 7 and 10 in free peritoneal cells but not in perforated membranes. The enhanced expression of alpha-smooth muscle actin and down-regulation of transforming growth factor-beta 1 expression after wounding appears to be important phenomena in tissue contraction and repair.

Scar wars: implications of fetal wound healing for the pediatric burn patient

Scar formation and fibrosis often cause devastating disabilities in children suffering severe burn injury. In contrast to the child, the fetus has the ability to heal skin injury without scar formation, and instead with regeneration of epithelial and mesenchymal tissues and restoration of normal skin architecture. In this paper we review those unique features of the fetus and fetal wound healing that may contribute to the scarless repair process. It is hoped that an understanding of these remarkable reparative capabilities may lead to the development of new wound healing therapies that reduce or prevent scar formation and fibrosis in the management of children with burns.

Fetal and postnatal sera differentially modulate human dermal fibroblast phenotypic and functional features in vitro

Fetal wounds heal without scar formation, fibrosis, or contracture. Compared with adult wounds, they are characterized by major differences in the extracellular matrix and the absence of myofibroblastic cells. The reasons for these differences are not well known and determination of factors affecting the absence of scarring in the fetus may lead to strategies for controlling adult pathological scarring. In the present study, we have assessed the effects of serum on the behavior of normal human dermal fibroblasts. Using an in vitro approach, we investigated the effects of fetal and adult serum on cell properties such as growth rate, collagen synthesis, gelatinase activities, and differentiation to myofibroblasts using biochemical, morphological, and ultrastructural parameters. We studied the induction of alpha-smooth muscle (alpha-SM) actin in fibroblasts, and its correlation with increased collagen gel contraction by the cells. Our results showed that, compared with FBS (fetal bovine serum), postnatal calf serum (PCS) decreased mitogenic activity and collagenase synthesis but not collagen synthesis. Furthermore, cells cultured with PCS differentiated to myofibroblasts with an increase in cell diameter, number of stress fibers, alpha-SM actin expression, and collagen gel contraction. To characterize the molecules involved in this differentiation process, the amount of transforming growth factor beta (TGFbeta) in FBS and PCS was determined and the effect of neutralizing anti-TGFbeta antibody was evaluated. It was determined that FBS contained more TGFbeta than PCS, but that essentially all the TGFbeta was latent in both sera. However, results obtained with anti-TGFbeta antibody show that active TGFbeta is present when human dermal fibroblasts are cultured with medium containing PCS. These results suggest that, in the presence of PCS but not FBS, the cells either produce active TGFbeta or an enzyme that is able to activate latent serum TGFbeta. Alternatively, sera may contain two different forms of latent TGFbeta, the PCS form being activated by the dermal fibroblast cells. A similar mechanism may be involved, at least in part, in skin wound healing and may underlie the appearance of myofibroblasts in postnatal wounds.

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.

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.

A model of scarless human fetal wound repair is deficient in transforming growth factor beta

Human fetal skin heals via scarless regeneration, whereas adult skin heals with scar. Scarless repair may reflect a distinct cytokine milieu. We studied the role of the cytokine transforming growth factor beta (TGF beta) using an established model of scarless human fetal skin repair in which human fetal skin is transplanted into a subcutaneous pocket on the flank of an adult nude mouse. In this model, wounded 16-week-gestation human fetal skin heals without scar, whereas wounded adult skin heals with scar. Seven days after transplantation, incisional wounds were made in the skin grafts. In the first phase of the study, wounds were harvested from 1 hour to 4 weeks postwounding, and immunohistochemistry was performed for TGF beta (isoform nonspecific), TGF beta 1, and TGF beta 2. Scarfree wounds in the fetal skin grafts did not show TGF beta staining. In contrast, wounds in adult grafts that heal with scar demonstrated isoform nonspecific TGF beta staining from 6 hours through 21 days, TGF beta 1 from 6 hours through 21 days, and TGF beta 2 from 12 hours through 7 days. In the second phase of the study, a slow-release disk with 0.01, 0.1, 1.0, or 10 micrograms of TGF beta 1 was placed beneath the fetal skin graft at the time of wounding. Fourteen days postwounding, there was marked scarring in the fetal grafts treated with TGF beta 1, and the size of the scar was proportional to the amount of TGF beta 1 applied.(ABSTRACT TRUNCATED AT 250 WORDS)