TGF-beta 1 stimulates expression of keratinocyte integrins during re-epithelialization of cutaneous wounds

Growth factors in wound healing

Enhancement of wound healing was limited to good surgical technique, maintenance of a clean wound with appropriate dressings, and debridement. The ability to heal wounds has been advanced through the recognition that healing in a moist environment is improved over that of a desiccated wound. Pharmacologic approaches to wound healing did not exist until the last few decades, when it was recognized that growth factors are normally present in the wound environment and that in animal models and a few clinical studies, the addition of growth factors could enhance healing. In 1998, platelet-derived growth factor was approved for clinical use. This approach is still the subject of intense investigation and clinical trials. This article analyzes current knowledge on growth factors as therapeutic agents and speculates on their future potential, with an analysis of successes and failures to date.

TGF-beta1-mediated inhibition of HK-2 cell migration

Restoration of proximal tubular cell (PTC) integrity and function after ischemic injury involves cell proliferation and migration. Hypoxia is a known stimulus for PTC TGF-beta1 synthesis. This study examines the effect of TGF-beta1 on PTC migration. A model of PTC injury was used consisting of mechanically wounding a monolayer of HK2 cells followed by repopulation of the denuded area by time lapse photomicroscopy. Repopulation was the result of cell migration but not proliferation. Addition of TGF-beta1 led to a marked inhibition of cell migration increased expression of paxillin and vincullin and their incorporation into dense focal adhesion plaques. This was associated with increased association of focal adhesion components with the f-actin cytoskeleton. There was also increased beta3 integrin expression and increased synthesis of the matrix component fibronectin. The effect on migration and focal adhesion reorganisation was abrogated by inhibitors of the RhoA downstream target ROCK, suggesting that signaling events resulting from altered beta3 integrin expression initiate the TGF-beta1 response. These results suggest that, by inhibition of cell migration, increased expression of TGF-beta1 after ischemia delays recovery of proximal tubule structure and function. We speculate that this may contribute to permanent alteration in renal tubular function after severe ischemic injury.

Wound healing effects of porcine placental extracts on rats with thermal injury

BACKGROUND

Placental extracts have been used as Chinese folk medicines to accelerate wound healing. However, the molecular mechanism of placental extracts on wound healing has not been identified. It is known that fibroblast growth factors (FGF) and transforming growth factors (TGF) are two key factors involved in wound healing.

OBJECTIVES

To determine the molecular mechanism of placental extracts on wound healing.

METHODS

The protein levels of both growth factors in rat skins with thermal injury were therefore studied to explore the molecular mechanism of placental extracts on wound healing. As cell proliferation is essential for wound healing, effects of placental extracts on fibroblast proliferation were also determined.

RESULTS

As compared with the controls, the S phase of fibroblasts was significantly increased by 1.5-, 1.7- and 4.7-fold for 1, 10 and 30 mg mL(-1) of placental extracts, respectively. The increase of the S phase was not due to the minute amount of sex hormones in the placental extracts as the addition of equivalent amounts of hormones showed no increase of the S phase. In addition, a 2.5-fold increase of TGF-beta1 in wound skin biopsy was noticed with 30 mg mL(-1) of porcine placental extracts. The FGF levels in the wound skin receiving 30 mg mL(-1) of porcine placental extracts were also significantly increased compared with the controls.

CONCLUSIONS

These ex vivo data support the observation that the application of 30 mg mL(-1) of placental extracts reduced the wound healing time by about 50%. To the best of our knowledge, this is the first report to explore the molecular mechanisms of porcine placental extracts on wound healing. These results may provide the insight into the potential use of porcine placental extracts as an alternative medicine for accelerating wound healing.

Keratinocyte motility induced by TGF-beta1 is accompanied by dramatic changes in cellular interactions with laminin 5

Transforming growth factor-beta1 (TGF-beta1) has the ability to induce epithelial cell migration while stopping proliferation. In this study, we show that, concomitant to promoting migration of normal human keratinocytes in vitro, TGF-beta1 induced a marked decrease in their adhesion capacity to processed alpha3-containing laminin 5-coated surfaces. Indeed, the expression levels of alpha3 and alpha6 integrin subunit mRNA and protein, as well as the cell surface alpha3beta1 and alpha6beta4 integrins, were down-regulated. Recent studies showed that keratinocytes over express and deposit laminin 5 during migration and we have shown that laminin 5 found in the matrix of TGF-beta1 induced migrating keratinocytes is present in its unprocessed form [Décline and Rousselle, 2001: J. Cell Sci. 114:811-823]. We show here that TGF-beta1 treatment of the cells promoted a significant increase in their adhesion to the alpha3 chain carboxy-terminal LG4/5 subdomain and that this interaction is likely to be mediated by a heparan sulfate proteoglycan type of receptor. Our results indicate that alpha6beta4 and alpha3beta1 integrin interactions with laminin 5 are diminished during migration while a specific interaction occurs between an additional cellular receptor and the alpha3 LG4/5 module present on unprocessed laminin 5.

Immunomodulatory effects of peptide T on human keratinocyte cells

BACKGROUND

Peptide T (PT) is an octapeptide shown to resolve psoriatic lesions. PT is from the V2 region of HIV-1 gp120, an exterior envelope glycoprotein that is a target for host immune responses. The anti-inflammatory mechanisms of PT are not well understood.

OBJECTIVES

We studied the immunomodulatory effects of PT on the human keratinocyte cells.

METHODS

Cultured human keratinocytes were treated with PT, proteins extracted and analysed by Western blotting and reverse transcriptase polymerase chain reaction.

RESULTS

Our findings show reduced expression of intercellular adhesion molecule 1 and an increase in transforming growth factor (TGF)-beta and heat shock protein (HSP)-70 in human keratinocyte cells treated with PT. The HSP-70 increase is modulated by TGF-beta. In fact, we demonstrated that anti-TGF-beta antibodies reduce HSP-70 overexpression. In addition, we show a modulation of alphav integrins after 4 hours of treatment with PT. These receptors favour keratinocyte migration and epidermal regeneration. It has been reported that overexpression of HSP results in dramatic changes to intermediate filaments. These proteins act on keratin intermediate filaments and determine their retraction. The consequence is cell-cell contact detachment and inhibition of cellular hyperproliferation.

CONCLUSIONS

Our results support the beneficial effect of PT found in vivo, suggesting, moreover, the primary role of keratinocytes upon which PT acts directly by stimulating the anti-inflammatory function and favouring the regeneration of tissue.

Fibrin promotes migration in a three-dimensional in vitro model of wound regeneration

We developed an in vitro model of wound reepithelialization based on engineered composite skin equivalents of human keratinocytes. Such organotypic cultures are unique in that regulatory mechanisms of cell growth and differentiation can be investigated under conditions mimicking those in vivo. We employed this model system to evaluate fibrin as a substrate for keratinocyte growth and migration after incisional wounding. Our results show that fibrin decreases the length of the lag phase of keratinocyte activation and increases the consistency of the healing response. In addition, the response of these skin equivalents to wounding mimicks that of animal models in terms of the kinetics of reepithelialization, the spatiotemporal distribution of proliferating cells in and around the wound, the unique phenotype exhibited by the cells in the newly formed epidermis, the upregulation of key molecular anchors that initiate cell migration, and the formation of basement membrane during wound closure. Our results suggest that this model can be used to study molecular mechanisms of reepithelialization and evaluate biomaterials as vehicles for controlled delivery of genes and proteins to promote wound healing.

Characterization of integrin expression in the mouse ovary

Integrin alpha:beta heterodimers mediate cell contacts to the extracellular matrix and initiate intracellular signaling cascades in response to a variety of factors. Integrins interact with many determinants of cellular phenotypes and play roles in controlling the development, structural integrity, and function of every type of tissue. Despite their importance, little is known about the regulation of integrin subunits in the mammalian ovary and how they function in folliculogenesis. To determine their relevance to ovarian physiology, we have studied the expression of integrin subunit mRNAs by Northern blot analysis and in situ hybridization in ovaries of wild-type, growth differentiation factor 9 (Gdf 9) knockout, FSHbeta (Fshb) knockout, and inhibin alpha (Inha) knockout mice. Integrin alpha6 mRNA is expressed in oocytes and granulosa cells of single-layer follicles and in oocytes and theca cells of multilayer follicles. Integrin alpha6 is highly expressed in Gdf 9 knockout ovaries, which are enriched in oocytes and primary (single layer) follicles because of a block at this stage of follicular development. Integrin alpha(v) mRNA is most highly expressed in the granulosa cells of multilayer growing follicles, and therefore only low levels of expression are detectable in the Gdf 9 knockout ovaries. Integrin beta1 mRNA exhibits a broad expression pattern in ovaries, including oocytes, granulosa cells, theca cells, and corpora lutea. Integrin beta3 mRNA is expressed in theca and interstitial cells and is upregulated in corpora lutea. It is nearly undetectable in ovaries of Fshb knockout mice, which develop preantral follicles but have no luteal cells. Integrin beta5 mRNA is predominantly expressed in granulosa cells of multilayer follicles. It is expressed at high levels in the Fshb knockout mice and in a compartmentalized manner in the granulosa cell/Sertoli cell tumors that develop in the Inha knockout mice. Specific integrins are associated with ovarian cellular phenotypes in mice, which raises intriguing possibilities as to integrin functions in oocyte competence, follicular development, luteinization, and granulosa cell proliferation.

TGF-beta1 regulates TGF-beta1 and FGF-2 mRNA expression during fibroblast wound healing

AIMS

To evaluate the expression of transforming growth factor beta1 (TGF-beta1) and fibroblast growth factor 2 (FGF-2) mRNA in stromal cells in response to injury in the presence of either TGF-beta1 or FGF-2. It has been shown previously that heparan sulfate proteoglycans and FGF-2 are present transiently during wound repair in vivo and that an increase in TGF-beta1 mRNA is detected rapidly after injury.

METHODS

Primary corneal fibroblasts were cultured to confluency, serum starved, and linear wound(s) were made in medium containing TGF-beta1 or FGF-2. TGF-beta1 and FGF-2 mRNA expression were evaluated using both northern blot analysis and in situ hybridisation. Both dose dependent and time course experiments were performed. Whole eye organ culture experiments were also carried out and growth factor expression was assessed.

RESULTS

Injury and exogenous TGF-beta1 increased TGF-beta1 mRNA values. The increase in expression of FGF-2 mRNA was not detected until wound closure. In contrast, FGF-2 inhibited the expression of TGF-beta1. TGF-beta1 increased TGF-beta1 mRNA stability but did not alter that of FGF-2. Migration assay data demonstrated that unstimulated stromal cells could be activated to migrate to specific growth factors.

CONCLUSIONS

TGF-beta1 specifically enhances cellular responsiveness, as shown by increased stability after injury and the acquisition of a migratory phenotype. These data suggest that there is an integral relation during wound repair between TGF-beta1 and FGF-2.

Proteolytic events of wound-healing--coordinated interactions among matrix metalloproteinases (MMPs), integrins, and extracellular matrix molecules

During wound-healing, cells are required to migrate rapidly into the wound site via a proteolytically generated pathway in the provisional matrix, to produce new extracellular matrix, and, subsequently, to remodel the newly formed tissue matrix during the maturation phase. Two classes of molecules cooperate closely to achieve this goal, namely, the matrix adhesion and signaling receptors, the integrins, and matrix-degrading and -processing enzymes, the matrix metalloproteinases (MMPs). There is now substantial experimental evidence that blocking key molecules of either group will prevent or seriously delay wound-healing. It has been known for some time now that cell adhesion by means of the integrins regulates the expression of MMPs. In addition, certain MMPs can bind to integrins or other receptors on the cell surface involved in enzyme activation, thereby providing a mechanism for localized matrix degradation. By proteolytically modifying the existing matrix molecules, the MMPs can then induce changes in cell behavior and function from a state of rest to migration. During wound repair, the expression of integrins and MMPs is simultaneously up-regulated. This review will focus on those aspects of the extensive knowledge of fibroblast and keratinocyte MMPs and integrins in biological processes that relate to wound-healing.

Resistance of keratinocytes to TGFβ-mediated growth restriction and apoptosis induction accelerates re-epithelialization in skin wounds

The pleiotropic growth factor TGFβ plays an important role in regulating responses to skin injury. TGFβ targets many different cell types and is involved in all aspects of wound healing entailing inflammation,re-epithelialization, matrix formation and remodeling. To elucidate the role of TGFβ signal transduction in keratinocytes during cutaneous wound healing, we have used transgenic mice expressing a dominant negative type II TGFβ receptor exclusively in keratinocytes. We could demonstrate that this loss of TGFβ signaling in keratinocytes led to an accelerated re-epithelialization of full thickness excisional wounds accompanied by an increased proliferation in keratinocytes at the wound edge. Furthermore, we show that impaired TGFβ signaling in keratinocytes reduces apoptosis in re-epithelialized wounds of transgenic animals.

A cDNA array identified the transcription factor early growth response factor 1 (Egr1) as a target gene for TGFβ in late phases of the wound healing process. As a member of the immediate-early gene family, Egr1 is upregulated shortly after injury and induces the expression of growth factor genes. We could demonstrate that Egr1 expression is also upregulated in skin wounds which have already undergone re-epithelialization. In conclusion, we attribute the enhanced re-epithelialization in our transgenics to the resistance of keratinocytes to TGFβ-mediated growth restriction and apoptosis induction. We also propose a new role for TGFβ induced Egr1 in late phase wound repair.

A crucial role of β1 integrins for keratinocyte migration in vitro and during cutaneous wound repair

Integrins are ubiquitous transmembrane receptors that play crucial roles in cell-cell and cell-matrix interactions. In this study, we have determined the effects of the loss of β1 integrins in keratinocytes in vitro and during cutaneous wound repair. Flow cytometry of cultured β1-deficient keratinocytes confirmed the absence of β1 integrins and showed downregulation of α6β4 but not of αv integrins. β1-null keratinocytes were characterised by poor adhesion to various substrates, by a reduced proliferation rate and by a strongly impaired migratory capacity. In vivo, the loss of β1 integrins in keratinocytes caused a severe defect in wound healing. β1-null keratinocytes showed impaired migration and were more densely packed in the hyperproliferative epithelium. Surprisingly, their proliferation rate was not reduced in early wounds and even increased in late wounds. The failure in re-epithelialisation resulted in a prolonged inflammatory response, leading to dramatic alterations in the expression of important wound-regulated genes. Ultimately, β1-deficient epidermis did cover the wound bed, but the epithelial architecture was abnormal. These findings demonstrate a crucial role of β1 integrins in keratinocyte migration and wound re-epithelialisation.

Movies available on-line

Gallium nitrate accelerates partial thickness wound repair and alters keratinocyte integrin expression to favor a motile phenotype

The nitrate form of the Group III transitional element gallium (GN) increases expression of specific structural components of the provisional wound matrix (i.e., collagen type I, fibronectin) in human dermal fibroblasts. To evaluate the potential of GN as a therapeutic option in management of cutaneous trauma, GN-treated partial thickness porcine wounds and experimentally "injured" human keratinocyte (NHK) monolayer cultures were compared with mirror image control (i.e., saline-treated) sites. GN suppressed cell proliferation in both models, as determined by reduced Ki-67 reactivity and significant lengthening of keratinocyte cell cycle transit times, while effectively promoting reepithelialization. The primary effect of GN was apparently to promote cell migration, as neither epidermal thickness nor epidermal differentiation was altered as a result of GN exposure in vivo or in vitro. Significantly enhanced epidermal reepithelialization was associated with alterations in expression of several keratinocyte integrin subunits. GN induced a significant increase in alpha5 expression. alpha5beta1 switching is a characteristic of the motile phenotype in the setting of cutaneous injury. Concomitantly, GN treatment also induced a dramatic (70%) decrease in the expression of the alpha3 subunit; alpha3beta1 binds laminin 5 and is associated with hemidesmosome formation and reestablishment of a nonmotile phenotype. Taken together, the GN-induced changes in integrin expression favor acellular migration. While the molecular mechanism of GN action on resident cells of the skin remains to be defined, these data suggest that GN administration which represses MMP activity in the wound and increases matrix synthesis also accelerates NHK motility and, thereby, may be a useful therapeutic agent for wound repair.

Curcumin differentially regulates TGF-beta1, its receptors and nitric oxide synthase during impaired wound healing

Wound healing is a highly ordered process, requiring complex and coordinated interactions involving peptide growth factors of which transforming growth factor-beta (TGF-beta) is one of the most important. Nitric oxide is also an important factor in healing and its production is regulated by inducible nitric oxide synthase (iNOS). We have earlier shown that curcumin (diferuloylmethane), a natural product obtained from the plant Curcuma longa, enhances cutaneous wound healing in normal and diabetic rats. In this study, we have investigated the effect of curcumin treatment by topical application in dexamethasone-impaired cutaneous healing in a full thickness punch wound model in rats. We assessed healing in terms of histology, morphometry, and collagenization on the fourth and seventh days post-wounding and analyzed the regulation of TGF-beta1, its receptors type I (tIrc) and type II (tIIrc) and iNOS. Curcumin significantly accelerated healing of wounds with or without dexamethasone treatment as revealed by a reduction in the wound width and gap length compared to controls. Curcumin treatment resulted in the enhanced expression of TGF-beta1 and TGF-beta tIIrc in both normal and impaired healing wounds as revealed by immunohistochemistry. Macrophages in the wound bed showed an enhanced expression of TGF-beta1 mRNA in curcumin treated wounds as evidenced by in situ hybridization. However, enhanced expression of TGF-beta tIrc by curcumin treatment observed only in dexamethasone-impaired wounds at the 7th day post-wounding. iNOS levels were increased following curcumin treatment in unimpaired wounds, but not so in the dexamethasone-impaired wounds. The study indicates an enhancement in dexamethasone impaired wound repair by topical curcumin and its differential regulatory effect on TGF-beta1, it's receptors and iNOS in this cutaneous wound-healing model.

Fibrinogen and fibrin are anti-adhesive for keratinocytes: a mechanism for fibrin eschar slough during wound repair

During cutaneous wound repair the epidermis avoids the fibrin-rich clot; rather it migrates down the collagen-rich dermal wound margin and over fibronectin-rich granulation tissue. The mechanism(s) underlying keratinocyte movement in this precise pathway has not been previously addressed. Here we demonstrate that cultured human keratinocytes do not express functional fibrinogen/fibrin receptors, specifically alpha v beta 3. Biologic modifiers known to induce integrin expression or activation did not induce adhesion to fibrin, fibrinogen, or its fragments. Epidermal explant outgrowth and single epidermal cell migration failed to occur on either fibrin or fibrinogen. Surprisingly, fibrin and fibrinogen mixed at physiologic molar ratios with fibronectin abrogated keratinocyte attachment to fibronectin. Keratinocytes transduced with the beta 3 integrin subunit cDNA, expressed alpha v beta 3 on their surface and attached to and spread on fibrinogen and fibrin. beta-gal cDNA-transduced keratinocytes did not demonstrate this activity. Furthermore, beta 3 cDNA-transduced keratinocyte adhesion to fibrin was inhibited by LM609 monoclonal antibody to alpha v beta 3 in a concentration-dependent fashion. From these data, we conclude that normal human keratinocytes cannot interact with fibrinogen and its derivatives due to the lack of alpha v beta 3. Thus, fibrinogen and fibrin are authentic anti-adhesive for keratinocytes. This may be a fundamental reason why the migrating epidermis dissects the fibrin eschar from wounds.

The mast cell in wound healing

This review describes the role of the mast cell in the pathobiology of skin healing. After illustrating its main morphofunctional characteristics, with special reference to the dog and cat, we consider the involvement of the mast cell in the various phases of skin repair. With the aid of a wide array of newly formed or preformed mediators released by degranulation, the activated mast cell controls the key events of the healing phases: triggering and modulation of the inflammatory stage, proliferation of connective cellular elements and final remodelling of the newly formed connective tissue matrix. The importance of the mast cell in regulating healing processes is also demonstrated by the fact that a surplus or deficit of degranulated biological mediators causes impaired repair, with the formation of exuberant granulation tissue (e.g. keloids and hypertrophic scars), delayed closure (dehiscence) and chronicity of the inflammatory stage.

Wound epithelialization deficits in the transforming growth factor-alpha knockout mouse

In vitro, transforming growth factor-alpha is an important factor controlling epithelial cell proliferation and migration. However, the transforming growth factor-alpha knockout mouse has shown no wound epithelialization defect in tail amputation and full-thickness back wounds. To resolve this disparity, we combined a full-thickness head wound and a partial-thickness ear wound on the transforming growth factor-alpha knockout mouse for analysis of wound epithelialization with or without granulation tissue formation. Three-millimeter ear wounds were made on the transforming growth factor-alpha knockout and heterozygous control mice. Full-thickness head wounds were made using a 6-mm trephine on the crown of the skull. In the ear model, transforming growth factor-alpha knockout mice had significantly larger epithelial gaps versus control at post-operative day 3 and 5. Epithelial thickness at the wound edge of transforming growth factor-alpha deficient mice was also depressed at post-operative day 3 and post-operative day 5 compared to control mice. On post-operative day 8, most wounds of both groups were epithelialized. In contrast, no difference in epithelial gap or new granulation tissue was found in the head model. The data support the concept that transforming growth factor-alpha plays a significant early role in wound epithelialization in vivo but its deficit is compensated if accompanied by granulation tissue formation. The data further show the importance of appropriate wound models to address the role of vulnerary factors.

Fibrin and wound healing

Although hemostasis is the major role of fibrin in wound repair, once the clot is present the wound cells must deal with it. The invasion and clearing of fibrin by these cells involves multiple complex processes that may go array XXX and delay wound repair. A good example, of the latter is leg ulcers. These chronic wounds contain a plethora of proteases that digest fibronectin and growth factors in the fibrin clot resulting in a corrupt provisional matrix that no longer supports reepithelialization or granulation tissue formation. Every good wound care provider knows that these wounds will not heal unless the corrupt matrix is removed by vigorous debridement that stimulates the accumulation of a competent provisional matrix.

Keratins and the keratinocyte activation cycle

In wound healing and many pathologic conditions, keratinocytes become activated: they turn into migratory, hyperproliferative cells that produce and secrete extracellular matrix components and signaling polypeptides. At the same time, their cytoskeleton is also altered by the production of specific keratin proteins. These changes are orchestrated by growth factors, chemokines, and cytokines produced by keratinocytes and other cutaneous cell types. The responding intracellular signaling pathways activate transcription factors that regulate expression of keratin genes. Analysis of these processes led us to propose the existence of a keratinocyte activation cycle, in which the cells first become activated by the release of IL-1. Subsequently, they maintain the activated state by autocrine production of proinflammatory and proliferative signals. Keratins K6 and K16 are markers of the active state. Signals from the lymphocytes, in the form of Interferon-gamma, induce the expression of K17 and make keratinocytes contractile. This enables the keratinocytes to shrink the provisional fibronectin-rich basement membrane. Signals from the fibroblasts, in the form of TGF-beta, induce the expression of K5 and K14, revert the keratinocytes to the healthy basal phenotype, and thus complete the activation cycle.

CYR61 stimulates human skin fibroblast migration through Integrin alpha vbeta 5 and enhances mitogenesis through integrin alpha vbeta 3, independent of its carboxyl-terminal domain

CYR61, an angiogenic factor and a member of the CCN protein family, is an extracellular matrix-associated, heparin-binding protein that mediates cell adhesion, promotes cell migration, and enhances growth factor-stimulated cell proliferation. CYR61 induces angiogenesis and promotes tumor growth in vivo and is expressed in dermal fibroblasts during cutaneous wound healing. It has been demonstrated recently that adhesion of primary skin fibroblasts to CYR61 is mediated through integrin alpha(6)beta(1) and cell surface heparan sulfate proteoglycans, resulting in adhesive signaling and up-regulation of matrix metalloproteinases 1 and 3. CYR61 is composed of four discrete structural domains that bear sequence similarities to the insulin-like growth factor-binding proteins, von Willebrand factor type C repeat, thrombospondin type 1 repeat, and a carboxyl-terminal (CT) domain that resembles cysteine knots found in some growth factors. In this study, we show that a CYR61 mutant (CYR61DeltaCT) that has the CT domain deleted is unable to support adhesion of primary human skin fibroblasts but is still able to stimulate chemotaxis and enhance basic fibroblast growth factor-induced mitogenesis similar to wild type. In addition, fibroblast migration to CYR61 is mediated through integrin alpha(v)beta(5) but not integrins alpha(6)beta(1) or alpha(v)beta(3). Furthermore, we show that CYR61 binds directly to purified integrin alpha(v)beta(5) in vitro. By contrast, CYR61 enhancement of basic fibroblast growth factor-induced DNA synthesis is mediated through integrin alpha(v)beta(3), a known receptor for CYR61 that mediates CYR61-dependent cell adhesion and chemotaxis in vascular endothelial cells. Thus, CYR61 promotes primary human fibroblast adhesion, migration, and mitogenesis through integrins alpha(6)beta(1), alpha(v)beta(5), and alpha(v)beta(3), respectively. Together, these findings establish CYR61 as a novel ligand for integrin alpha(v)beta(5) and show that CYR61 interacts with distinct integrins to mediate disparate activities in a cell type-specific manner.

Integrin expression is upregulated during early healing in a canine intrasynovial flexor tendon repair and controlled passive motion model

To explore crucial early molecular events involved in contact healing of the intrasynovial flexor tendon, integrin expression was evaluated at the transcriptional and post-transcriptional levels during the first two weeks following injury, repair and controlled passive motion in a canine model. Specifically, immunohistochemical and reverse transcription polymerase chain reaction (RT-PCR) techniques were employed to evaluate expression of the fibronectin, vitronectin and endothelial cell binding integrin receptor subunits alpha5, alphav and alpha6, along with the common beta1 subunit. The two techniques revealed increasing expression of the four subunits over the two week post-repair period. Immunohistochemistry revealed that beta1 and alpha5 expression was concentrated in the epitenon layer near the repair site and interiorly within the wound area, while alpha6 was associated with capillary-forming endothelial cells near the wound. RT-PCR and quantitation by NIH image analysis demonstrated peak messenger RNA expression of beta1 and alpha5 at ten days post-repair and peak expression of alpha6 and alphav at 15 days. The results in this study correlate well with previous results demonstrating increased fibronectin deposition and angiogenesis during the same time period in a similar injury/repair model.

Keratinocyte migration requires alpha2beta1 integrin-mediated interaction with the laminin 5 gamma2 chain

Keratinocyte migration is an absolute requirement for correct epithelialization during the process of wound healing. This process requires changes in extracellular matrix ligand expression as well as changes in ligand-binding affinity of the corresponding cellular integrins. In this study, we attempt to understand the role of laminin 5 in migration by investigating the integrin-mediated interactions of migrating keratinocytes with their newly synthesized laminin 5. We chose to induce migration of freshly isolated NHK in vitro by exposing them to TGF-beta1 which, in addition to promoting epithelial cell migration, is also known to prevent cell proliferation. This important feature allowed the study to be focused on cell migration without interfering with cell proliferation. We confirm that keratinocyte migration on plastic, fibronectin or collagen IV substrates requires endogenous laminin 5 deposition, which is predominantly detected under its unprocessed form. Despite a crucial role for laminin 5 in migration, we show that this process is accompanied by a significant decrease in adhesion to purified laminin 5. Moreover, we provide evidence that the alpha2beta1 integrin interaction with newly synthesized laminin 5 renders the cells more adherent and retards migration. Conversely, we provide evidence that the alpha2beta1 integrin-laminin 5 interaction is absolutely required for keratinocyte migration and that the alpha2beta1 integrin is responsible for cell spreading on laminin 5. Finally, we demonstrate that the alpha2beta1 integrin binding to laminin 5 occurs within the short arm of the gamma2 subunit.

Bioactive interleukin-8 is expressed in wounds and enhances wound healing

BACKGROUND

Wound healing is a sequential biological process that involves the integration of chemotaxis of neutrophils, mitosis and migration of keratinocytes, and remodeling of the scar, all of which are regulated by specific soluble mediators. To modulate wound healing specific mediators have to be identified and functionally characterized. Therefore we addressed this study on the polymorphonuclear leukocyte (PMN) attractant interleukin-8 (IL-8) and its function in epidermal wound healing.

MATERIALS AND METHODS

Peptide purification, bioassays for PMN chemotaxis, and sequential IL-8 measurements were performed on human wound fluid from burn blisters and skin graft donor sites. Histology for IL-8 immunoreactivity was included. In vitro human keratinocytes were assayed for proliferation, migration, and integrin expression after IL-8 treatment. Wounding experiments with topical IL-8 were performed in a chimeric mouse model.

RESULTS

IL-8 was found to be the major bioactive chemoattractant for PMNs in human blister and skin graft donor site wound fluids (mean levels ranging from 173 ng/ml Postoperative Day (POD) 1 to 2130 ng/ml (POD 5)). Released intracellular epidermal IL-8 immunoreactivity at the wound edge was considered as an immediate source of IL-8 while NH(2)-terminal analysis revealed the 77-amino-acid residue form as a second source of IL-8 possibly PMN derived. In vitro experiments on the effect of recombinant human (rh) IL-8 on keratinocyte proliferation revealed a rise in cell number (4.8-fold, ED(50) = 0.6 ng/ml), which was accompanied by an increase in cells in S phase and overexpression of the integrin subunit alpha6. In vivo topically applied IL-8 (1 microg/ml) on human skin grafts in a chimeric mouse model enhanced reepithelialization in IL-8 treated animals over controls due to elevated numbers of mitotic keratinocytes. Wound contraction was significantly diminished by topical IL-8.

CONCLUSIONS

These results indicate the sequential function of endogenous IL-8 in all phases of human wound healing. Topical IL-8 may be useful in impaired wound healing.

Occlusion following laser resurfacing promotes reepithelialization and wound healing

One of the critical parameters that has not been examined carefully following laser skin resurfacing is the effect of eschar on the wound healing process. Because occlusive dressings minimize the occurrence of eschar, the present study was undertaken to evaluate the effect of occlusion following laser resurfacing. It is clear that CO2 lasers promote epidermal cell loss and variable amounts of dermal injury. To characterize the wound repair process after laser treatment, biopsy specimens were obtained 2 to 4 days after treatment. Specimens from 15 patients were examined; the preauricular biopsy specimens were paired such that one specimen was from skin that had been occluded and the other specimen (from the same patient) was from skin treated without occlusion. Skin specimens were examined by indirect immunofluorescence using antibodies to specific epidermal and dermal antigens. The results indicate that the keratinocytes that repopulate the epidermis migrate from the hair follicles and express keratin 17, an intermediate filament protein expressed in keratinocytes during the early stages of wound healing. The migration of keratin 17-expressing cells begins 48 hours following laser resurfacing in skin treated with occlusion, whereas cell migration from the follicles of skin treated without occlusion is delayed. In summary, occlusion promotes enhanced cell migration and diminished eschar formation, resulting in more rapid healing.

Adhesion receptors in health and disease

Cell adhesion molecules have been recognized to play a major role in a variety of physiological and pathological phenomena. They determine the specificity of cell-cell binding and the interactions between cells and extracellular matrix proteins. Some of them may also function as receptors that trigger intracellular pathways and participate in cellular processes like migration, proliferation, differentiation, and cell death. The receptors that mediate adhesion between epithelial cells that are discussed in this review include integrins, selectins, the immunoglobulin superfamily members, and cadherins. The intent of this review is to inform the reader about recent advances in cellular and molecular functions of certain receptors, specifically those that are considered important in cell adhesion. We have deliberately not provided all-inclusive detailed information on every molecule, but instead, have presented a generalized overview in order to give the reader a global perspective. This information will be useful in enhancing the reader's understanding of the molecular pathology of diseases and recognizing the potential role of these receptors and ligands as therapeutic agents.

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.

Normal development, wound healing, and adenovirus susceptibility in beta5-deficient mice

Integrins have been shown to play important roles in embryonic development, wound healing, metastasis, and other biological processes. alphavbeta5 is a receptor for RGD-containing extracellular matrix proteins that has been suggested to be important in cutaneous wound healing and adenovirus infection. To examine the in vivo function of this receptor, we have generated mice lacking beta5 expression, using homologous recombination in embryonic stem cells. Mice homozygous for a null mutation of the beta5 subunit gene develop, grow, and reproduce normally. Keratinocytes harvested from beta5(-/-) mice demonstrate impaired migration on and adhesion to the alphavbeta5 ligand, vitronectin. However, the rate of healing of cutaneous wounds is not different in beta5(-/-) and beta5(+/+) mice. Furthermore, keratinocytes and airway epithelial cells obtained from null mice show adenovirus infection efficiency equal to that from wild-type mice. These data suggest that alphavbeta5 is not essential for normal development, reproduction, adenovirus infection, or the healing of cutaneous wounds.

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.

Effect of topical rh-TGF-beta 1 on second intention wound healing in horses

OBJECTIVE

To investigate the effects on wound healing of transforming growth factor-beta 1 as a topical treatment to full-thickness, excisional wounds of the distal limb of horses.

DESIGN

A randomised block study using four horses, each with wounds assigned to four treatment groups.

ANIMALS

Four adult Standardbred geldings.

PROCEDURE

Four, 4 cm2, full-thickness wounds were created on the dorsomedial and dorsolateral aspect of the metacarpus or metatarsus of each limb of four horses, giving a total of 64 wounds. For each limb, wounds were randomly assigned to four treatment groups: no treatment (control), carrier (Methyl Cellulose gel), 50 ng/wound rhTGF-beta 1 in carrier, and 500 ng/wound rhTGF-beta 1 in carrier. Wounds were treated on day 0 and day 8. Effects of treatment were evaluated on the basis of the presence of exuberant granulation tissue requiring excision, number of times excision was required, total wound area, area of epithelialisation, area of granulation, and histological evaluation of biopsy samples of wounds on day 8 and excised wounds on day 21.

RESULTS

Topical application of TGF-beta 1 at the two concentrations studied had no significant effect on the total area of wounds (P = 0.7), the area of granulation tissue (P = 0.78), the area of epithelialisation (P = 0.92), histological assessment or subjective clinical assessment of wounds.

CONCLUSION

TGF-beta 1 had no beneficial effects on wound healing. Additional trials are needed to test if it has value for wound treatment in horses.

Curcumin enhances wound healing in streptozotocin induced diabetic rats and genetically diabetic mice

Tissue repair and wound healing are complex processes that involve inflammation, granulation and tissue remodeling. Interactions of different cells, extracellular matrix proteins and their receptors are involved in wound healing, and are mediated by cytokines and growth factors. Previous studies from our laboratory have shown that curcumin (diferuloylmethane), a natural product obtained from the rhizomes of Curcuma longa, enhanced cutaneous wound healing in rats and guinea pigs. In this study, we have evaluated the efficacy of curcumin treatment by oral and topical applications on impaired wound healing in diabetic rats and genetically diabetic mice using a full thickness cutaneous punch wound model. Wounds of animals treated with curcumin showed earlier re-epithelialization, improved neovascularization, increased migration of various cells including dermal myofibroblasts, fibroblasts, and macrophages into the wound bed, and a higher collagen content. Immunohistochemical localization showed an increase in transforming growth factor-beta1 in curcumin-treated wounds compared to controls. Enhanced transforming growth factor-beta1 mRNA expression in treated wounds was confirmed by in situ hybridization, and laser scan cytometry. A delay in the apoptosis patterns was seen in diabetic wounds compared to curcumin treated wounds as shown by terminal deoxynucleotidyl transferase-mediated deoxyuridyl triphosphate nick end labeling analysis. Curcumin was effective both orally and topically. These results show that curcumin enhanced wound repair in diabetic impaired healing, and could be developed as a pharmacological agent in such clinical settings.

Fibronectin and its integrin receptors in cancer

The adhesive extracellular matrix protein fibronectin and its integrin receptors play important roles at several stages of tumor development. Tumor cells are generally less adhesive than normal cells and deposit less extracellular matrix. The loosened matrix adhesion that results may contribute to the ability of tumor cells to leave their original position in the tissue. Normal cells, when detached, stop growing and undergo anoikis (apoptosis caused by loss of adhesion). Integrin-activated pathways mediated by focal adhesion kinase (FAK) and the adapter protein She seem to be particularly important in anchorage dependence; many oncoproteins are capable of shunting these pathways. Malignant cells circumvent anchorage dependence with the help of oncoproteins. Once invading tumor cells have gained access to the circulation, adhesion to the endothelia and other tissue components facilitates the establishment of tumor colonies at distant sites. Specific tissue affinities may underlie the tendency of some tumors to metastasize preferentially to certain tissues. Interfering with tumor cell attachment with integrin-binding peptides has been shown to be an effective antimetastatic strategy in animal experiments. Tumor angiogenesis is yet another aspect of malignancy wherein extracellular matrices and integrins are important. Angiogenic endothelial cells in tumor vessels depend on the alpha v family of integrins for survival. Inhibiting angiogenesis with compounds that block the activity of alpha v integrins, and targeting drugs into tumors through these integrins, show promise as new anticancer strategies.

Alpha9 and beta8 integrin expression correlates with the merger of the developing mouse eyelids

As previously reported, alpha9 integrin is expressed between the merged or fused eyelids of mice at birth, and changes in alpha9 localization occur during lid opening. To determine whether alpha9 and/or additional integrin subunits mediate the emergence and temporary fusion of the eyelids, immunofluorescence and confocal microscopy were used to evaluate the localization of various integrin subunits in the developing ocular surface of the mouse. No detectable beta5, beta6, or beta7 integrins were observed on the epithelia of the ocular surface. alpha2, alpha3, alphav, and beta1 integrins were most abundant in the basal cells beginning at 13.5 days post conception and remained primarily localized to the basal cell layers throughout development. beta4 was localized at the basal surface of the epidermal basal cells beginning at 13.5 days post conception but was not found on the corneal epithelial basal cells until after birth. alpha9 and beta8 integrins were present on suprabasal cells of the epidermis at the leading edge of the eyelid before merger and on the epithelial bridge that forms immediately after these tissues merge, suggesting that they play a role in the initial fusion of the epithelial tissues of the eyelid and in stabilizing the epithelial junction. After birth and into adulthood, beta8 was retained within the suprabasal cell layers of the epidermis, whereas alpha9 became localized to the basal cells of the epidermis, the conjunctiva, and the limbus. The lack of co-localization of beta4 with either alpha9 or beta8 in double-labeling studies suggests that alpha9 and beta8 are restricted to the lateral and apical aspects of those cells in which they are expressed. The presence of tenascin-C and laminin-5 at the epithelial junction site suggests that alpha9: tenascin-C and beta4: laminin-5 interactions may play a role in stabilizing the fusion between lids early on but do not appear to be involved in the movement of the lids across the cornea. The data presented identify specific integrins and matrix proteins that are likely to mediate eyelid fusion.

In vitro modulation of keratinocyte wound healing integrins by zinc, copper and manganese

Although the trace elements zinc, copper and manganese are used in vivo for their healing properties, their mechanism of action is still only partially known. Some integrins expressed by basal layer keratinocytes play an essential part in healing, notably alpha2beta1, alpha3beta1, alpha6beta4 and alphaVbeta5, whose expression and distribution in epidermis are modified during the re-epithelialization phase. This study demonstrates how the expression of these integrins are modulated in vitro by trace elements. Integrin expression was studied in proliferating keratinocytes in monolayer cultures and in reconstituted skin that included a differentiation state. After 48 h incubation with zinc gluconate (0.9, 1.8 and 3.6 microg/mL), copper gluconate (1, 2 and 4 microg/mL), manganese gluconate (0.5, 1 and 2 microg/mL) and control medium, integrin expression was evaluated by FACScan and immunohistochemistry. Induction of alpha2, alpha3, alphaV and alpha6 was produced by zinc gluconate 1.8 microg/mL in monolayers, of alpha2, alpha6 and beta1 by copper gluconate 2 and 4 microg/mL and of all the integrins studied except alpha3 by manganese gluconate 1 microg/mL. Thus, alpha6 expression was induced by all three trace elements. The inductive effect of zinc was particularly notable on integrins affecting cellular mobility in the proliferation phase of wound healing (alpha3, alpha6, alphaV) and that of copper on integrins expressed by suprabasally differentiated keratinocytes during the final healing phase (alpha2, beta1 and alpha6), while manganese had a mixed effect.

Sensitivity of cross-reacting antihuman antibodies in formalin-fixed porcine skin: including antibodies to proliferation antigens and cytokeratins with specificity in the skin

Although no animal is a perfect skin model for the study of toxicological and therapeutic agents, structurally the pig may be superior to even non-human primates. Because our work involves effects of toxicological and therapeutic agents on the skin, we wanted to identify stains which may prove useful as well as determine cross-reactivity of some newer antihuman antibodies. We performed a battery of formalin-fixed skin from weanling pigs and minipigs. The battery of antibodies included LCA, CD3, OPD-4, CD34, UCHL-1, L-26, KP-1, MAC-387, Factor XIIIa, Leu-7, S-100 protein, HMB-45, GFAP, synaptophysin, neurofilament protein, ubiquitin, vimentin, type IV collagen, laminin, fibronectin, Factor VIII related antigen, Desmin-M, smooth muscle actin, cytokeratin 7, cytokeratin 20, AEI/AE3, CAM 5.2, EMA, GCDFP, Ki-67, and PCNA. Immunohistochemical stains for CD3, Leu-7, S-100 protein, type IV collagen, laminin, Factor VIII related antigen, GFAP, synaptophysin, neurofilament protein, ubiquitin, smooth muscle actin, vimentin, Desmin-M, cytokeratin 7, cytokeratin 20, AE1/AE3, CAM 5.2, Ki-67 and PCNA showed consistent cross-reactivity. In formalin-fixed tissue, only antibodies to lymphoreticular cells showed poor cross-reactivity. A high percentage of the remaining antibodies did show good cross-reactivity but with some interesting similarities and differences in specificity.

Demystified ... adhesion molecules

The cell adhesion molecules are ubiquitous recognition molecules that allow cells to communicate with one another and their environment. Through these molecules, complex alterations in the cytoplasmic messenger pathways and the microfilamentous cytoskeleton can lead to profound alterations in cell division, differentiation, behaviour, and function (fig 9). It is difficult to conceive of a group of molecules that could be more important to pathologists and to their understanding of disease processes.

Integrin alpha 5 beta 1 expression is required for inhibition of keratinocyte migration by ganglioside GT1b

Polysialoganglioside GT1b, a keratinocyte membrane glycosphingolipid, inhibits normal keratinocyte adhesion and migration on a fibronectin matrix. The specificity of the inhibition for cells plated on a fibronectin matrix and competition of GT1b inhibition with peptide RGDS suggest that GT1b abrogates the alpha 5 beta 1/fibronectin interaction. We examined the effects of GT1b on the adhesion and migration of keratinocyte-derived cell lines and correlated GT1b responsiveness and alpha 5 beta 1 integrin expression. GT1b (5 nM) significantly inhibited migration of normal human keratinocytes, immortalized keratinocytes, and squamous cell carcinoma SCC12F2 cells on fibronectin, but not on collagen I. Concentrations as high as 5 microM had no effect on SCC13 or HaCaT cells. Likewise, GT1b inhibited fibronectin-dependent cell adhesion of normal human keratinocytes, immortalized keratinocytes, and SCC12F2 cells, but had no effect on SCC13 or HaCaT cells. Flow cytometric and Western immunoblot analysis of integrin expression showed significantly decreased alpha 5 and beta 1 integrin expression in SCC13 and HaCaT cells compared to normal keratinocytes, immortalized keratinocytes, and SCC12F2 cells. Incubation with TGF-beta 1 increased alpha 5 beta 1 integrin expression and induced responsiveness to GT1b in HaCaT cells. These data imply that GT1b "response" requires sufficient expression of alpha 5 beta 1 and further suggest that the mechanism of the inhibitory effect of GT1b involves GT1b/alpha 5 beta 1 interaction.

Epidermal differentiation and basement membrane formation by HaCaT cells in surface transplants

The immortal human keratinocyte line HaCaT has been employed in many studies as paradigm for epidermal keratinocytes. In order to demonstrate its potential to form stable epidermal structures in response to connective tissue, this was challenged in surface transplants on nude mice, where normal keratinocytes rebuild a typical epidermis within two weeks. During the initial regeneration phase (day 1-4) multilayered but poorly organized epithelia formed with proliferating cells in all layers in analogy to normal keratinocytes. Similarly, with tissue consolidation (around day 7) proliferation was reduced and restricted to cells in basal position marked by keratin K14 and beta1-integrin immunostaining. The strong suprabasal reaction for K1 and K10, the appearance of the late markers K2e, filaggrin and loricrin as well as the polarized distribution of alpha2beta1 and alpha3beta1 indicated advancing tissue normalization (day 14). Keratinization further improved at around three weeks switching from the initial parakeratotic to the regular orthokeratotic type which was prominent at six weeks. Accordingly, most ultrastructural features typical for epidermis or normal keratinocyte grafts were detectable including a complete basement membrane (BM) with regular attachment structures. Matrix- and BM-components appeared sequentially with marked linear deposition of laminin-5 (day 4) followed by accumulation of collagen-IV and 'classical' BM-laminin between one and two weeks. With the general codistribution of integrin alpha6beta4 and BM-molecules (day 14) collagen-VII lining of BM became prominent, while epithelium and host connective tissue were still separated by the collagen matrix. In accordance with the delayed orthokeratinization, wound-matrix molecules (fibronectin, tenascin) persisted longer than in normal keratinocyte transplants. Finally, grafts of long-term passaged (no. 310) cells demonstrated a remarkable stability in the expression of epidermal markers. Thus, the immortalized HaCaT cells reveal a generally high competence to realize an epidermal phenotype in a natural environment and appear therefore qualified for in vitro studies on structural and regulatory aspects of keratinocyte physiology and pathology.

Epidermal integrin expression is upregulated rapidly in human fetal wound repair

BACKGROUND/PURPOSE

The fetus heals skin wounds rapidly and scarlessly. The mechanisms that mediate the rapid reepithelialization that is seen in this process are unknown. Integrins are a family of cell surface receptors that bind fibronectin, tenascin, collagen, and other extracellular matrix proteins that are deposited rapidly in fetal wounds. The authors hypothesized that epidermal integrin receptors specific for fibronectin and other wound matrix proteins are upregulated rapidly during human fetal repair.

METHODS

To investigate the spatial and temporal expression of integrins in scarless fetal repair, fetal skin from six human abortuses (16 to 23 weeks' gestation) was transplanted subcutaneously into severe combined immunodeficient mice. After graft take, full-thickness incisional wounds were made in the grafts, and grafts were harvested at various time-points from 4 hours to 28 days after wounding. Integrin receptor protein expression was analyzed at each time-point using immunohistochemistry with monoclonal antibodies specific for the receptors that bind fibronectin, tenascin, collagen, and laminin (alpha5, alpha(v), beta6, alpha2, alpha3, alpha6, and beta4).

RESULTS

In this model, wounded human fetal skin grafts reepithelialized rapidly (within 24 to 36 hours) and healed scarlessly. Within 4 hours of wounding, the grafts showed increased, suprabasal expression (alpha2, alpha3, alpha6, beta4) or neoexpression (alpha5, alpha(b), beta6) of integrins at the epidermal wound edge. This increased expression persisted until reepithelialization was complete.

CONCLUSIONS

Early upregulation of integrins in fetal wounds may permit rapid keratinocyte migration and reepithelialization, and may be important in limiting the induction of inflammatory mediators and scar.

Suprabasal expression of epidermal alpha 2 beta 1 and alpha 3 beta 1 integrins in skin treated with topical retinoic acid

In normal adult human skin, expression of epidermal integrins is confined to keratinocytes in the basal layer. However, suprabasal expression of alpha 2, alpha 3 and beta 1 integrin subunits is noted in hyperproliferative epidermis in wound repair and psoriasis. In this study, we examined the effect of topical all-trans-retinoic acid (RA), known to induce epidermal hyperplasia, on expression of integrins in human epidermis. Immunostaining of vehicle-treated skin revealed expression of alpha 2, alpha 3 and beta 1, as well as alpha 6 and beta 4 integrin subunits entirely on basal keratinocytes. Topical application of RA (0.1%) for 2 weeks resulted in marked suprabasal expression of alpha 2, alpha 3 and beta 1 integrin subunits, whereas alpha 6 and beta 4 staining remained on basal keratinocytes. Staining for putative ligands of alpha 2 beta 1 and alpha 3 beta 1 integrins, i.e. type IV collagen, laminin-5 and fibronectin, was not detected in the epidermal layer in RA- or vehicle-treated skin. Treatment of HaCaT keratinocytes in culture with RA (1 mumol/L) enhanced alpha 2 and beta 1 mRNA abundance. Furthermore, RA slightly up-regulated the expression of alpha 2, alpha 3 and beta 1 integrin subunits on primary epidermal keratinocytes and HaCaT cells in culture with no effect on cell proliferation. These results provide evidence that RA-elicited epidermal hyperplasia is associated with aberrant suprabasal expression of alpha 2 beta 1 and alpha 3 beta 1 integrins, and that this also involves direct stimulation of keratinocyte integrin expression by RA.

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.

Induction of the angiogenic phenotype by Hox D3

Angiogenesis is characterized by distinct phenotypic changes in vascular endothelial cells (EC). Evidence is provided that the Hox D3 homeobox gene mediates conversion of endothelium from the resting to the angiogenic/invasive state. Stimulation of EC with basic fibroblast growth factor (bFGF) resulted in increased expression of Hox D3, integrin alphavbeta3, and the urokinase plasminogen activator (uPA). Hox D3 antisense blocked the ability of bFGF to induce uPA and integrin alphavbeta3 expression, yet had no effect on EC cell proliferation or bFGF-mediated cyclin D1 expression. Expression of Hox D3, in the absence of bFGF, resulted in enhanced expression of integrin alphavbeta3 and uPA. In fact, sustained expression of Hox D3 in vivo on the chick chorioallantoic membrane retained EC in this invasive state and prevented vessel maturation leading to vascular malformations and endotheliomas. Therefore, Hox D3 regulates EC gene expression associated with the invasive stage of angiogenesis.

Depth of morphologic skin damage and viability after one, two, and three passes of a high-energy, short-pulse CO2 laser (Tru-Pulse) in pig skin

BACKGROUND

CO2 laser energy is absorbed by water, which is present in all tissue. The depth of penetration of CO2 lasers is narrow with minimal reflection, scatter, or transmission. However, thermal damage has limited the usefulness of conventional, continuous-wave CO2 lasers for debridement as demonstrated by wound healing studies. The development of high-energy CO2 lasers, with pulse durations that are less than the thermal relaxation time of tissue, have made vaporization of skin for resurfacing and wound debridement possible because of the decreased risk of thermal damage.

OBJECTIVE

This study was performed to evaluate thermal damage produced by a CO2 laser.

METHODS

Routine histopathologic examination and nitroblue-tetrazolium chloride (NBTC) staining were used to evaluate the depth of tissue damage and viability in weanling pig skin after one, two, and three passes of the laser.

RESULTS

At a pulse energy of 300 mJ, with a pulse duration of 60 microseconds, one pass of the laser produced vaporization of the epidermis with minimal thermal damage. Two passes produced areas of denatured collagen with loss of viable cells in the superficial papillary dermis. Three passes extended the damage into the papillary dermis.

CONCLUSION

Hyalinization of collagen appears to correspond well with the level of thermal damage as measured by NBTC staining. Our findings suggest that the energy necessary to vaporize the dermis may be greater than that needed to vaporize epidermis.

Human fibroblasts bind directly to fibrinogen at RGD sites through integrin alpha(v)beta3

Fibroblast migration into the blood clot initially filling a wound requires close interaction between fibroblasts and the matrix of the fibrin clot. However, very little is known about the specific receptor-ligand interactions that mediate fibroblast attachment to fibrin. Using an attachment assay developed to measure even relatively weak interactions, we demonstrate here that normal human dermal fibroblasts can attach to substrates coated with fibrinogen, fibrin, or the fibrinogen breakdown product I-9D. Fibroblast attachment to these ligands did not require the presence of fibronectin on the cell surface or as a component of the substrate. Cells treated with cycloheximide and monensin, to limit the synthesis and secretion of endogenous fibronectin, attached as well as untreated cells. The synthetic peptide GRGDS inhibited adhesion to fibrinogen, fibrin, and fibrinogen I-9D by about 60%, while the control peptide GRGES had no substantial effect. We conclude that attachment to these ligands is mediated at least partially by direct interactions between the substrates and one specific receptor, the integrin alpha(v)beta3. Affinity chromatography demonstrated that alpha(v)beta3 from detergent lysates of fibroblasts bound to a fibrinogen matrix and was eluted with EDTA. Furthermore, antibodies against the alpha(v)beta3 complex or against the alpha(v) subunit inhibited fibroblast attachment to fibrinogen and fibrin by 50-70%. An inhibitory antibody against the integrin beta1 subunit had no effect. The observation that integrin antagonists could not produce complete inhibition suggests that there may be other fibroblast cell surface proteins that can bind directly to fibrinogen.

Wound healing--aiming for perfect skin regeneration

The healing of an adult skin wound is a complex process requiring the collaborative efforts of many different tissues and cell lineages. The behavior of each of the contributing cell types during the phases of proliferation, migration, matrix synthesis, and contraction, as well as the growth factor and matrix signals present at a wound site, are now roughly understood. Details of how these signals control wound cell activities are beginning to emerge, and studies of healing in embryos have begun to show how the normal adult repair process might be readjusted to make it less like patching up and more like regeneration.

Fibronectin provides a conduit for fibroblast transmigration from collagenous stroma into fibrin clot provisional matrix

After injury, the wound space is filled with a fibrin/fibronectin clot containing growth factors released by platelets and monocytes. In response to these factors, fibroblasts migrate into the fibrin clot and contribute to the formation of granulation tissue. The functional mechanisms allowing fibroblasts to leave the collagenous matrix of normal connective tissue and invade the provisional matrix of the fibrin clot have not been fully defined. To investigate these mechanisms we established a new in vitro model which simulates specific aspects of early wound healing, that is, the migration of fibroblasts from a three-dimensional collagen matrix into a fibrin clot. This transmigration could be induced by physiological concentrations of platelet releasate or platelet-derived growth factor BB (PDGF-BB) in a concentration-dependent manner. At 24 hours irradiated fibroblasts invaded the fibrin gel almost as well as non-irradiated cells, indicating that transmigration was independent of proliferation. Plasminogen and its activators appear to be necessary for invasion of the fibrin clot since protease inhibitors decreased the amount of migration. These serine proteases, however, were not necessary for exit from the collagen gel as fibroblasts migrated out of the collagen gel onto a surface coated with fibrin fibrils even in the presence of inhibitors. Removal of fibronectin (FN) from either the collagen gel or the fibrin gel markedly decreased the number of migrating cells, suggesting that FN provides a conduit for transmigration. Cell movement in the in vitro model was inhibited by RGD peptide, and by monoclonal antibodies against the subunits of the alpha5 beta1 and alpha v beta3 integrin receptor. Thus, the functional requirements for fibroblast transmigration from collagen-rich to fibrin-rich matrices, such as occurs in early wound healing, have been partially defined using an in vitro paradigm of this important biologic process.

Transforming growth factor-beta1 inhibits basal melanogenesis in B16/F10 mouse melanoma cells by increasing the rate of degradation of tyrosinase and tyrosinase-related protein-1

Current evidence suggests that melanogenesis is controlled by epidermal paracrine modulators. We have analyzed the effects of transforming growth factor-beta1 (TGF-beta1) on the basal melanogenic activities of B16/F10 mouse melanoma cells. TGF-beta1 treatment (48 h) elicited a concentration-dependent decrease in basal tyrosine hydroxylase and 3,4-dihydroxyphenylalanine (Dopa) oxidase activities, to less than 30% of the control values but had no effect on dopachrome tautomerase activity (TRP-2). The inhibition affected to similar extents the Dopa oxidase activity associated to tyrosinase-related protein-1 (TRP-1) and tyrosinase. This inhibition was noticeable between 1 and 3 h after the addition of the cytokine, and maximal after 6 h of treatment. The decrease in the enzymatic activity was paralleled by a decrease in the abundance of the TRP-1 and tyrosinase proteins. TGF-beta1 mediated this effect by increasing the rate of degradation of tyrosinase and TRP-1. Conversely, after 48 h of treatment, the expression of the tyrosinase gene decreased only slightly, while TRP-1 and TRP-2 gene expression was not affected. An increased rate of proteolytic degradation of TRP-1 and tyrosinase seems the main mechanism accounting for the inhibitory effect of TGF-beta1 on the melanogenic activity of B16/F10 cells.