Distinctive integrin expression in the newly forming epidermis during wound healing in humans

Epidermal stem cells: the cradle of epidermal determination, differentiation and wound healing

The field of epidermal stem cells has dramatically advanced in the last decade, leading to a better understanding of the molecular factors, signalling pathways and cellular events that identify and characterize stem cells, thus revealing their immense potential for therapeutic use. Furthermore, multipotent epidermal stem cells present the major advantage of easy accessibility with the discovery of their specific location within the bulge of the hair follicle. This review focuses on the most recent findings on epidermal stem cells, and their potential role in initial epidermal commitment, differentiation and wound healing processes in the skin.

Immunopathogenesis of conjunctival remodelling in vernal keratoconjunctivitis

PURPOSE

To study the processes involved in mediating conjunctival remodelling in vernal keratoconjunctivitis (VKC) by investigating the expression of integrin receptors, epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), transforming growth factor-beta(TGF-beta), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), and Ki67 antigen, which is a marker for cell proliferation.

METHODS

Conjunctival biopsy specimens from 16 patients with active VKC and nine control subjects were studied by immunohistochemical techniques using monoclonal and polyclonal antibodies directed against the integrin alpha3 and alpha6 subunits, EGFR, VEGF, TGF-beta, bFGF, PDGF, and Ki67 antigen. The phenotype of inflammatory cells expressing growth factors was examined by double immunohistochemistry.

RESULTS

In the normal conjunctiva, very weak immunoreactivity was observed for EGFR and VEGF in epithelial cells, and for alpha3 and alpha6 integrin subunits on basal epithelial cells, and on vascular endothelial cells in the upper substantia propria. There was no immunoreactivity for the other antibodies. In VKC specimens, strong staining for alpha3 and alpha6 integrin subunits was observed on the membranes of basal and suprabasal epithelial cells, and all vascular endothelial cells. Immunoreactivity for Ki67 antigen was observed in the nuclei of the basal and suprabasal epithelial cells. Strong immunoreactivity was observed for EGFR in the deeper layers of the epithelium, and for VEGF in all epithelial cells. Inflammatory cells expressing EGFR, VEGF, TGF-beta, bFGF, and PDGF were noted in 8, 9, 11, 10, and 10 specimens, respectively. The majority of inflammatory cells expressing growth factors were eosinophils (45+/-4%) and monocytes/macrophages (35+/-4%).

CONCLUSIONS

Chronic conjunctival inflammation in VKC is associated with increased staining of alpha3, and alpha6 integrin subunits, EGFR, VEGF, TGF-beta, bFGF, and PDGF that might mediate conjunctival remodelling.

Integrin-dependent Functions of the Angiogenic Inducer NOV (CCN3)

The novel angiogenic inducer CCN3 (NOV, nephroblastoma overexpressed) is a matricellular protein of the CCN family, which also includes CCN1 (CYR61), CCN2 (CTGF), CCN4 (WISP-1), CCN5 (WISP-2), and CCN6 (WISP-3). CCN3 is broadly expressed in derivatives of all three germ layers during mammalian development, and its deranged expression is associated with vascular injury and a broad range of tumors. We have shown that CCN3 promotes proangiogenic activities in vascular endothelial cells through integrin receptors and induces neovascularization in vivo (Lin, C. G., Leu, S. J., Chen, N., Tebeau, C. M., Lin, S. X., Yeung, C. Y., and Lau, L. F. (2003) J. Biol. Chem. 278, 24200-24208). In this study, we show that CCN3 is highly expressed in granulation tissue of cutaneous wounds 5-7 days after injury and is capable of inducing responses in primary fibroblasts consistent with wound healing. Purified CCN3 supports primary skin fibroblast adhesion through integrins alpha(5)beta(1) and alpha(6)beta(1) and induces fibroblast chemotaxis through integrin alpha(v)beta(5). We show that CCN3 is a novel ligand of alpha(v)beta(5) in a solid phase binding assay. Although not mitogenic on its own, CCN3 also enhances basic fibroblast growth factor-induced DNA synthesis. Furthermore, CCN3 up-regulates MMP-1 and PAI-1 expression but interacts with TGF-beta1 in an antagonistic or synergistic manner to regulate the expression of specific genes. These findings, together with its angiogenic activity, support a role for CCN3 in cutaneous wound healing in skin fibroblasts and establish its matricellular mode of action through integrin receptors.

An In Vivo Model of Wound Healing in Genetically Modified Skin-Humanized Mice

Cutaneous wound-healing disorders are a major health problem that requires the development of innovative treatments. Whithin this context, the search for reliable human wound-healing models that allow us to address both mechanistic and therapeutic matters is warranted. In this study, we have developed a novel invivo wound-healing model in a genetically modified human context. Our model is based on the regeneration of human skin on the back of nude mice by transplantation of a cultured bioengineered skin equivalent previously designed in our laboratory. In this setting, human keratinocytes in the epidermal compartment were genetically modified with a retroviral vector encoding the enhanced green fluorescent protein (EGFP). After stable engraftment of the EGFP skin was achieved (9-12 wk after grafting), a small circular full thickness wound was performed on this mature human skin. A wide variety of parameters involved in wound healing were monitored, including tissue architecture, cell proliferation, epidermal differentiation, dermal remodelling, and basement membrane regeneration. Wounded gene-targeted skin-humanized mice re-capitulated native skin wound-healing features. In addition, when keratinocyte growth factor (KGF), a growth factor that has been shown to improve wound healing, was added to wounds during 3 d, the re-epithelialization was significantly accelerated. The present wound-healing model system provides a suitable in vivo tool to test gene transfer strategies for human skin repair. It also serves as a complementary platform for studies in genetically modified mice and as a model to evaluate pharmaceutical therapeutic approaches for impaired wound healing.

In Vivo Model of Wound Healing Based on Transplanted Tissue-Engineered Skin

Advances in understanding the complex process of wound healing and development of novel growth factor and gene therapies would benefit from models that mimic closely the physiology of human wounds. To this end, we developed a hybrid wound-healing model based on human tissue-engineered skin transplanted onto athymic mice. Grafted tissues were infiltrated with mouse mesenchymal cells as native and foreign dermal regions fused together. Immunohistochemical staining for human involucrin revealed that the transplanted epithelium maintained its human origin, whereas the dermis was infiltrated by numerous mouse fibroblasts and blood vessels. Grafted tissues were wounded with a 4-mm punch to create full-thickness excisional wounds. At 1 and 2 weeks, the tissues were excised and assessed for reepithelialization, differentiation, and neovascularization. Interestingly, the average rate of keratinocyte migration (120 microm/day) was similar to migration rates observed in human subjects and significantly lower than migration in mouse epidermis. Immunohistochemical staining for keratin 10, laminin, and involucrin revealed a normal pattern of differentiation in the neoepidermis. Neovascularization was significantly elevated in the granulation tissue at 1 week and subsided to the level of unwounded tissue at 2 weeks postwounding. Our data suggest that skin equivalents grafted to a mouse model may serve as a realistic model of human wound regeneration. Because skin equivalents can be prepared with patient cells and genetically modified to stimulate or suppress gene expression, this model may be ideal for addressing mechanistic questions and evaluating the efficacy of biomaterials and gene therapeutics for promoting wound healing.

Increased expression levels of integrin alphavbeta5 on scleroderma fibroblasts

Integrin alphavbeta5 is a receptor for vitronectin, a plasma glycoprotein that is also distributed in extracellular matrix of various tissues. Matrix-bound vitronectin has the potential to stabilize the active form of plasminogen activator inhibitor-1, resulting in the inhibition of the plasmin-mediated pericellular proteolytic cascade. In this study, we compared the levels of alphavbeta5 and matrix-bound vitronectin between normal and scleroderma fibroblasts and investigated the association with fibrosis. We demonstrated that alphavbeta5 was up-regulated on scleroderma fibroblasts. The up-regulated alphavbeta5 contributed to the increase in vitronectin-binding ability in scleroderma fibroblasts, which led to the vitronectin-dependent activation of plasminogen activator inhibitor-1. In immunohistochemistry, the alphav and beta5 subunits were stained strongly on scleroderma fibroblasts and the amount of vitronectin was increased in the pericellular matrix of those cells. The transient overexpression of alphavbeta5 on normal fibroblasts enhanced the human alpha2(I) collagen promoter activity through Sp-1 and Smad3 as well as the vitronectin-dependent plasminogen activator inhibitor-1 activity. This effect on the promoter activity was also observed in the absence of vitronectin and completely disappeared in the presence of anti-alphavbeta5 antibody. These results indicate that the up-regulated alphavbeta5 may contribute to the phenotypical alteration of scleroderma fibroblasts, while at the same time suppressing the plasmin-mediated pericellular proteolytic cascade.

Inflammatory events are involved in acne lesion initiation

The earliest subclinical acne "lesion" is a microcomedone, of which hyperproliferation of the follicular epithelium is a characteristic feature. Inflammatory cells have been observed at the periphery of these "lesions". This study investigated whether inflammatory events occur pre or post hyperproliferative changes. Cellular, vascular, and proliferative markers were examined by immunohistochemical techniques on biopsies of clinically normal follicles from uninvolved skin and early inflamed lesions from acne patients. Control follicles were obtained from non-acne subjects. Follicles from uninvolved skin exhibited no microcomedonal features. Proliferation in the epithelium was comparable to controls and was significantly lower than in inflamed lesions. Numbers of CD3+, CD4+ T cells were elevated in the perifollicular and papillary dermis although levels were not equivalent to those in papules. The number of macrophages was also greatly increased and similar to those in papules. There were no changes in blood vessel numbers or vascular intercellular adhesion molecule 1 expression but E-selectin expression was increased to levels found in papules and vascular adhesion molecule 1 levels were upregulated. Levels of the pro-inflammatory cytokine interleukin-1 were also upregulated perifollicularly. Moreover, aberrant integrin expression was demonstrated in the epidermis around these uninvolved follicles and inflamed lesions whereas the basement membrane was still intact. These results provide novel evidence for vascular endothelial cell activation and involvement of inflammatory responses in the very earliest stages of acne lesion development.

Acute wound healing an overview

The ability to heal an injury is a biologic necessity for all organisms, with mammals lagging in proficiency when compared with lower life forms that have the ability to regenerate differentiated structures. Technology and increased scientific knowledge have established a coordinated interplay that has improved the ability to manage wounds in a logical manner, and, on occasion, to accelerate the healing process. Insight into the complex chain of events leading to the formation of scar is a necessity for every individual who attempts wound management.

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.

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.

Effect of fibroblasts on epidermal regeneration

BACKGROUND

There is little information on specific interactions between dermal fibroblasts and epidermal keratinocytes. The use of engineered skin equivalents consisting of organotypic cocultures of keratinocytes and fibroblasts offers an attractive approach for such studies.

OBJECTIVES

To examine the role fibroblasts play in generation and maintenance of reconstructed epidermis.

METHODS

Human keratinocytes were seeded on collagen matrices populated with increasing numbers of fibroblasts and cultured for 2 weeks at the air-liquid interface.

RESULTS

In the absence of fibroblasts, stratified epidermis with only three or four viable cell layers was formed. In the presence of fibroblasts, keratinocyte proliferation was stimulated and epidermal morphology was improved. Epidermal morphogenesis was also markedly improved in epidermis generated in organotypic keratinocyte monocultures grown in medium derived from dermal equivalents or from organotypic keratinocyte-fibroblast cocultures. These observations clearly indicate the proliferation-stimulating activity of soluble factors released from fibroblasts. Under all experimental conditions, onset of keratinocyte differentiation was shown by the expression of keratin 10 in all suprabasal cell layers. With increasing numbers of fibroblasts incorporated into the collagen matrix, the expression of markers associated with keratinocyte activation, e.g. keratins 6, 16 and 17 and the cornified envelope precursor SKALP decreased, and involucrin localization shifted toward the granulosum layer. This fibroblast-mediated effect was even more pronounced when the fibroblasts were precultured in the collagen matrices for 1 week instead of overnight. The basement membrane proteins collagen VII and laminin 5 were present at the epithelial-matrix border. The expression of integrin alpha 6 beta 4 and of E-cadherin was comparable with that seen in native skin and was not significantly modulated by fibroblasts. Under all experimental conditions the expression of integrin subunits alpha 2, alpha 3 and beta 1 was upregulated, indicating keratinocyte activation.

CONCLUSIONS

Our results illustrate that numbers of fibroblasts in the collagen matrix and their functional state is a critical factor for establishment of normal epidermal morphogenesis.

Integrin expression in the dermis during scar formation in humans

To evaluate changes leading to human wound reorganization we examined by immunohistochemistry the expression of several extracellular matrix (ECM) receptors (alpha2 chain of VLA-2, alpha3 chain of VLA-3, alpha6 chain of VLA-6, alphav, and beta1/beta3 chains of integrins) in a series of biopsies of human skin wounds healing by primary intention. The first time point investigated in this study was day 6 after injury, i.e. when a fibrin clot has been almost completely replaced by the granulation tissue. Gradual changes in integrin expression in granulation tissue and in the dermal scar were observed from the first time point investigated and were characterized by an up-regulation of alpha2beta1 complex, alphav integrin subunit, and beta1 integrin subunit. At day 27, the expression of the alpha2 chain of VLA-2 in the scar decreased. The expression of alphav and beta1 integrin subunits decreased but was still detectable by day 35. Vitronectin expression from day 7 onwards was also increased and colocalized to the area of the wounded dermis, and decreased by day 27. Our data suggests that, during the remodelling of the provisional matrix of the wound, dermal fibroblasts express transiently mainly alpha2 and alphav subunits of integrins associated with up-regulation of the beta1 subunit. It seems that up-regulation of some chains of integrins may be involved in the control of deposition of ECM components associated with wound healing.

Dynamic characterization of the molecular events during in vitro epidermal wound healing

The aim of this study was to characterize some of the molecular events stimulated in vitro in response to injury within a confluent culture of normal epidermal keratinocytes as a model to understand the mechanisms of wound healing. To this end, an original device was developed specifically designed to perform calibrated injuries of great lengths within mono-stratified or pluri-stratified keratinocyte cultures. The experiments performed in this study validate this device as an appropriate tool for studying epidermal wound healing; this is because it performs mechanical injuries that stimulate the expression of multiple healing markers also known to be upregulated during wound healing in vivo (growth factors, cytokines, proteinases, extracellular matrix proteins). Using this device, it was demonstrated in human keratinocytes: mechanical injuries (i) immediately stimulate the tyrosine phosphorylation of numerous cellular proteins; (ii) induce molecular cascades leading to the activation of p21ras, mitogen-activated protein kinases, extracellular signal-regulated kinases 1/2, c-Jun NH2 terminal kinase, and p38 mitogen-activated protein kinase; and (iii) increase the phosphorylation of their respective substrates, c-jun and activator transcription factor 1. Wounding of these cells also results in increases in the DNA binding activities of several jun/fos activator protein-1 transcription factor complexes. It is important to note that the development of an appropriate wounding system was essential for performing this study, as use of a classical wounding procedure did not enable the detection of the biologic parameters reported above. In conclusion, these data indicate that using the appropriate system, it is possible to identify the signaling pathways activated in normal human keratinocyte cells after injury. In this study, it was shown that the mitogen-activated protein kinase pathways and activator protein-1 are stimulated in response to physical injury, and may be involved in regulating the expression of healing markers.

The cellular proliferative phase of the wound repair process

The proliferative--or new-tissue formation--phase of wound healing is complex. This article examines the changes that occur to cells during this stage and the effect on the extracellular matrix environment.

Characterization of the living skin equivalent as a model of cutaneous re-epithelialization

The living skin equivalent, a three-dimensional organotypic model, has been widely used to investigate many aspects of cutaneous biology. However, there are relatively few studies assessing how faithfully the skin equivalent reproduces normal skin biology. The skin equivalent was fabricated by seeding human epidermal keratinocytes onto the upper surface of a hydrated collagen lattice populated with human dermal fibroblasts and subsequently raised to the air-liquid interface where keratinocyte stratification and differentiation led to the formation of a tissue which showed many common morphological features to that of normal skin. Histology and immunohistochemical detection of keratinocyte integrins and matrix metalloproteinases (MMPs) were used as cytological markers to assess the accuracy of the model during cutaneous re-epithelialization. Analysis of expression of keratinocyte integrins revealed that whilst there were a number of similarities to normal skin, skin equivalent keratinocytes appeared to be 'activated' and hyper-proliferating. Wounding of the skin equivalent, by complete bisection, induced re-epithelialization from both wound edges within 8-12 h, which completely restored the epidermis within 4 days. This migration, like that in vivo, was associated with nascent expression of MMPs and upregulation of certain integrins. However, whilst integrin expression, was similar to in vivo re-epithelialization, there were subtle differences in the level of expression and distribution of certain integrins.

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

Discoidin domain receptor 2 regulates fibroblast proliferation and migration through the extracellular matrix in association with transcriptional activation of matrix metalloproteinase-2

Discoidin domain receptor 2 (DDR2) is a tyrosine kinase receptor expressed in mesenchymal tissues, the ligand of which is fibrillar collagen. We have compared DDR2 signaling in skin fibroblasts derived from DDR2(-/-) and DDR2(+/-) mice. Proliferation of DDR2(-/-) fibroblasts was significantly decreased compared with DDR2(+/-) cells. DDR2(-/-) fibroblasts exhibited markedly impaired capacity to migrate through a reconstituted basement membrane (Matrigel) in response to a chemotactic stimulus, which correlated with diminished matrix metalloproteinase-2 (MMP-2) activity by gelatin zymography and diminished MMP-2 transcription of a minimal MMP-2 promoter. In contrast, a lack of DDR2 had no effect on cell motility or alpha-smooth muscle actin or vinculin expression. Additionally, expression of type I collagen was greatly reduced in DDR2(-/-) cells. Stable reconstitution of either wild-type DDR2 or constitutively active chimeric DDR2 in DDR2(-/-) cells by retroviral infection restored cell proliferation, migration through a reconstituted basement membrane (Matrigel), and MMP-2 levels to those of DDR2(+/-) fibroblasts. These data establish a role for DDR2 in critical events during wound repair.

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.

Inhibition of integrin-linked kinase/protein kinase B/Akt signaling: mechanism for ganglioside-induced apoptosis

Ganglioside GT1b inhibits keratinocyte attachment to and migration on a fibronectin matrix by binding to alpha(5)beta(1) and preventing alpha(5)beta(1) interaction with fibronectin. The role of gangliosides in triggering keratinocyte apoptosis, however, is unknown. Addition of GT1b to keratinocyte-derived SCC12 cells, grown in serum-free medium but exposed to fibronectin, suppressed Bad phosphorylation, activated caspase-9, and inhibited cyclin D and E expression, resulting in cell cycle arrest at G(1) phase and initiation of apoptosis. The mechanism of GT1b activation of caspase-9 involved inhibition of beta(1) integrin serine/threonine phosphorylation and decreased phosphorylation of both integrin-linked kinase and protein kinase B/Akt at its Ser-473 site, leading to cytochrome c release from mitochondria. Consistently, blockade of GT1b function with anti-GT1b antibody specifically activated the Ser-473 site of Akt, markedly suppressing apoptosis. The ganglioside-induced inhibition of Akt phosphorylation was GT1b-specific and was not observed when cells were treated with other keratinocyte gangliosides, including GD3. These studies suggest that the modulation of keratinocyte cell cycle and survival by GT1b is mediated by its direct interaction with alpha(5)beta(1) and resultant inhibition of the integrin/integrin-linked kinase/protein kinase B/Akt signaling pathway.

Gene correction of integrin beta4-dependent pyloric atresia-junctional epidermolysis bullosa keratinocytes establishes a role for beta4 tyrosines 1422 and 1440 in hemidesmosome assembly

The cytoplasmic domain of beta4 integrin contains two pairs of fibronectin-like repeats separated by a connecting segment. The connecting segment harbors a putative tyrosine activation motif in which tyrosines 1422 and 1440 are phosphorylated in response to alpha6beta4 binding to laminin-5. Primary beta4-null keratinocytes, obtained from a newborn suffering from lethal junctional epidermolysis bullosa, were stably transduced with retroviruses carrying a full-length beta4 cDNA or a beta4 cDNA with phenylalanine substitutions at Tyr-1422 and Tyr-1440. Hemidesmosome assembly was evaluated on organotypic skin cultures. beta4-corrected keratinocytes were indistinguishable from normal cells in terms of alpha6beta4 expression, the localization of hemidesmosome components, and hemidesmosome structure and density, suggesting full genetic and functional correction of beta4-null keratinocytes. In cultures generated from beta4(Y1422F/Y1440F) keratinocytes, beta4 mutants as well as alpha6 integrin, HD1/plectin, and BP180 were not concentrated at the dermal-epidermal junction. Furthermore, the number of hemidesmosomes was strikingly reduced as compared with beta4-corrected keratinocytes. The rare hemidesmosomes detected in beta4(Y1422F/Y1440F) cells were devoid of sub-basal dense plates and of inner cytoplasmic plaques with keratin filament insertion. Collectively, our data demonstrate that the beta4 tyrosine activation motif is not required for the localization of alpha6beta4 at the keratinocyte plasma membrane but is essential for optimal assembly of bona fide hemidesmosomes.

Mechanisms of wound reepithelialization: hints from a tissue-engineered reconstructed skin to long-standing questions

Wound closure of epithelial tissues must occur efficiently to restore rapidly their barrier function. We have developed a tissue-engineered wound-healing model composed of human skin keratinocytes and fibroblasts to better understand the mechanisms of reepithelialization. It allowed us to quantify the reepithelialization rate, which was significantly accelerated in the presence of fibrin or platelet-rich plasma. The reepithelialization of these 6 mm excisional wounds required the contribution of keratinocyte proliferation, migration, stratification, and differentiation. The epidermis regenerated progressively from the surrounding wound margins. After 3 days, the neoepidermis showed a complete spectrum of changes. Near the wound margin, the differentiation of the neoepidermis (keratins 1/10, filaggrin, and loricrin) and regeneration of the dermoepidermal junction (laminin 5 and collagen IV) were more advanced than toward the wound center, where the proliferative index was significantly increased. The spatial distribution of keratinocytes distinguished by particular features suggests two complementary mechanisms of reepithelialization: 1) the passive displacement of the superficial layers near the wound margin that would rapidly regenerate a barrier function and 2) the crawling of keratinocytes over each other at the tip of the progressing neoepidermis. Therefore, this study brings a new perspective to long-standing questions concerning wound reepithelialization.

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.

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.

Gingival, dermal, and periodontal ligament fibroblasts express different extracellular matrix receptors

BACKGROUND

Fibroblasts are the predominant cells of the periodontal ligament and the gingiva and have important roles in the function and regeneration of the tooth support apparatus. The goal of this study was to investigate the possible differences in the adhesion properties and expression of extracellular matrix (ECM) receptors among different fibroblast populations.

METHODS

The adhesion of gingival (GF), dermal (DF), and periodontal ligament fibroblast (PDLF) cultures to ECM proteins (fibronectin, laminin, vitronectin, RGD peptide, collagen type I, and collagen type IV) adsorbed to tissue culture plastic was evaluated fluorometrically. Quantitative reverse transcription-polymerase chain reactions (RT-PCR) were performed using primers specific for 19 integrin subunits to quantify ECM receptor transcript expression.

RESULTS

Our data demonstrated that GF and PDLF adhere to vitronectin and collagen types I and IV more avidly than do DF. PDLF adhered well to laminin, whereas GF and DF did not. Quantitation of integrin expression demonstrated that the different fibroblast types expressed different integrin transcripts, further demonstrating their innate differences.

CONCLUSIONS

The 3 fibroblast types studied behave differently and expressed different ECM receptors. However, gingival fibroblasts and periodontal ligament fibroblasts are more similar in their attachment and integrin expression than either is to dermal fibroblasts. Therefore, experiments using DF will not necessarily be valid for oral tissues.

alpha v beta 6 Integrin upregulates matrix metalloproteinase 9 and promotes migration of normal oral keratinocytes

The integrin alpha v beta 6 is a fibronectin receptor that is undetectable on normal keratinocytes in situ, but is increased significantly in wound healing and in culture-established keratinocytes, suggesting that it may promote changes associated with cell motility. Using normal human oral keratinocytes we have shown that cultured cells express relatively high levels of alpha v beta 6 and this integrin has a functional role in both cell adhesion and migration towards fibronectin. We provide experimental evidence that the increased expression of alpha v beta 6 by normal human oral keratinocytes results in coordinate changes, which promote a more migratory phenotype. Thus increased expression of alpha v beta 6 results in a fibronectin-dependent increase in pro-matrix metalloproteinase 9, matrix metalloproteinase 9 activity increases normal human oral keratinocyte migration, and this may be further dependent on plasmin activation. The results suggest a key role for alpha v beta 6 in these processes and indicate a coordinated link between alpha v beta 6 expression and upregulation of matrix metalloproteinase 9. It appears that alpha v beta 6 may function in normal human oral keratinocyte migration through matrix-metalloproteinase-9-dependent and -independent mechanisms.

Effects of BisGMA and TEGDMA on proliferation, migration, and tenascin expression of human fibroblasts and keratinocytes

Previous studies have documented a marked cytotoxic potency of BisGMA and TEGDMA. The purpose of this investigation was to determine if these substances also affect proliferation, migration, and tenascin expression of primary human gingival fibroblasts (HGF) and immortalized human keratinocytes (HaCaT). These parameters play an important role in healing wounds. HGF and HaCaT cultures were incubated with TEGDMA and BisGMA. Cell proliferation (BrdU-assay) and migration (Boyden method) were determined 24 h after incubation. Tenascin expression was investigated four and seven days after treatment. Results were statistically evaluated by ANOVA using the Wilcoxon-Mann-Whitney test (p < 0.05). Proliferation of both cell types was significantly inhibited at concentrations > or = 0.25 mM (TEGDMA) or > or = 0.01 mM (BisGMA). Migration of HaCaT was significantly increased after incubation with BisGMA for 24 h. TEGDMA did not alter migration of HGF and HaCaT. In addition, TEGDMA had no effect on tenascin expression of both cell cultures. After 4 days of incubation, BisGMA (at a concentration of 0.01 mM) significantly reduced tenascin production of HaCaT cultures related to cell number. However, 7 days after treatment, BisGMA significantly increased tenascin expression of HGF and HaCaT cultures. Altogether, our results indicate that BisGMA can affect migration of keratinocytes and alters the expression of the extracellular matrix component tenascin. Thus, BisGMA may significantly influence the healing of injured oral tissues.

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.

Differential activation of migration by hypoxia in keratinocytes isolated from donors of increasing age: implication for chronic wounds in the elderly

Chronic wound healing conditions are often observed in elderly patients with poor tissue oxygenation. Impaired re-epithelialization is a hallmark of these wounds, which is seen in both clinical studies and in our animal models of impaired healing. To investigate the pathogenic mechanism of chronic wounds, we studied the effect of hypoxia on migration of keratinocytes isolated from human donors of increasing age. Keratinocytes from elderly donors had depressed migratory activity when exposed to hypoxia, as opposed to an increase in migration in young cells. Analysis of underlying biochemical changes demonstrated a differential activation of matrix metalloproteinases by hypoxia in keratinocytes isolated from the young and the old. Matrix metalloproteinases-1 and -9 and tissue inhibitor of matrix metalloproteinase-1 were strongly upregulated by hypoxia in young cells, whereas no induction was observed in aged cells. Furthermore, transforming growth factor-beta 1 signaling appears to be involved in the keratinocyte differential response to hypoxia, as transforming growth factor-beta type I receptor was upregulated by hypoxia in young cells, while there was no induction in aged cells. Transforming growth factor-beta neutralizing reagents blocked hypoxia-induced matrix metalloproteinase-1, matrix metalloproteinase-9 expression, and hypoxia-induced cell migration as well. Our results suggest that an age-related decrease in response to hypoxia plays a crucial part in the pathogenesis of retarded re-epithelialization in wound.

ICAM-1 and alpha3beta1 expression by bronchial epithelial cells and their in vitro modulation by inflammatory and anti-inflammatory mediators

BACKGROUND

Adhesion molecules are involved in inflammatory and repair processes of the bronchial epithelium. ICAM-1 is mainly involved in inflammatory reactions, whereas integrins, such as alpha3beta1, are mainly involved in repair processes.

METHODS

Using bronchial biopsies from 10 asthmatics and eight controls, we first evaluated by immunohistochemistry expression of alpha3beta1 and ICAM-1 in intact and damaged epithelium. Then, using the human pulmonary epithelial cell line WI-26 VA, we studied, by flow-cytometry, the modulation of ICAM-1 and alpha3beta1 expression, and, by ELISA, the release of fibronectin by proinflammatory cytokines, such as IL-5, and anti-inflammatory cytokines, such as IL-4, TGF-beta, and EGF.

RESULTS

alpha3beta1 expression was slightly higher in asthma than in controls, as well as in damaged epithelium than in undamaged epithelium. ICAM-1 expression was higher in asthma than in controls, and similarly distributed in intact or damaged epithelium. In vitro, alpha3beta1 was significantly increased by TGF-beta, EGF, and IL-4, and significantly decreased by IL-5. Fibronectin release was significantly increased by TGF-beta and IL-4, unchanged by EGF, and slightly but significantly decreased by IL-5. ICAM-1 expression was significantly decreased by TGF-beta and IL-4, unchanged by EGF, and significantly increased by IL-5.

CONCLUSIONS

These differences in adhesion molecule expression and fibronectin release may be important in epithelial cell inflammation and repair.

Wound healing in jellyfish striated muscle involves rapid switching between two modes of cell motility and a change in the source of regulatory calcium

Small wounds (1.2 mm in diameter) made in the sheet of myoepithelial cells forming the "swimming" muscle of the jellyfish, Polyorchis penicillatus, were closed within 10 h by epithelial cells migrating centripetally to the wound center. Some 24 to 48 h later these cells redifferentiated into fully contractile muscle cells. Labeling with bromodeoxyuridine failed to reveal any cell proliferation during this process. Phenotype switching (within 1 h) from contractile muscle cells to migratory cells did not require synthesis of new protein as shown by treatment with 40 microM cycloheximide. Excitation-contraction coupling in undamaged muscle depended on entry of Ca(2+) through voltage-gated ion channels, as shown by a block of contractility by 40 microM nitrendipine and also on calcium released from intracellular stores since caffeine (10 mM) caused a 25% reduction in contractile force. In contrast, migratory cells did not require a source of extracellular calcium since migration was unimpeded by low (1 microM) free Ca(2+) or nitrendipine. Instead, modulatory calcium was derived from intracellular stores since caffeine (10 mM) and thapsigargin (10 microM) slowed migration. This lack of dependence on calcium influx in migratory cells was further confirmed by a dramatic down-regulation in voltage-gated inward current as shown by whole-cell patch recordings.

Delayed wound healing in CXCR2 knockout mice

Previous studies demonstrated that the CXC chemokine, MGSA/GRO-alpha and its receptor, CXCR2, are expressed during wound healing by keratinocytes and endothelial cells at areas where epithelialization and neovascularization occur. The process of wound healing is dependent on leukocyte recruitment, keratinocyte proliferation and migration, and angiogenesis. These processes may be mediated in part by CXC chemokines, such as interleukin-8 and MGSA/GRO-alpha. To examine further the significance of CXC chemokines in wound healing, full excisional wounds were created on CXCR2 wild-type (+/+), heterozygous (+/-), or knockout (-/-) mice. Wounds were histologically analyzed for neutrophil and monocyte infiltration, neovascularization and epithelialization at days 3, 5, 7, and 10 postwounding. The CXCR2 -/- mice exhibited defective neutrophil recruitment, an altered temporal pattern of monocyte recruitment, and altered secretion of interleukin-1beta. Significant delays in wound healing parameters, including epithelialization and decreased neovascularization, were also observed in CXCR2 -/- mice. In vitro wounding experiments with cultures of keratinocytes established from -/- and +/+ mice revealed a retardation in wound closure in CXCR2 -/- keratinocytes, suggesting a role for this receptor on keratinocytes in epithelial resurfacing that is independent of neutrophil recruitment. These in vitro and in vivo studies further establish a pathophysiologic role for CXCR2 during cutaneous wound repair.

The PHSRN sequence induces extracellular matrix invasion and accelerates wound healing in obese diabetic mice

The PHSRN sequence of the plasma fibronectin (pFn) cell-binding domain induces human keratinocytes and fibroblasts to invade the naturally serum-free extracellular matrices of sea urchin embryos. The potency of acetylated, amidated PHSRN (Ac-PHSRN-NH(2)) is significantly increased, making it more active on a molar basis than the 120-kDa cell-binding domain of pFn. Arginine is important to this activity because PHSAN and PHSEN are inactive, as is a randomized sequence peptide, Ac-HSPNR-NH(2). One treatment with Ac-PHSRN-NH(2) stimulates reepithelialization and contraction of dermal wounds in healing-impaired, obese diabetic C57BL6/KsJ db/db mice. Wound closure is equally rapid in treated db/db and db/+ mice and may be more rapid than in untreated nondiabetic db/+ littermates. In contrast, treatment with either Ac-HSPNR-NH(2) or normal saline (NS) has no effect. Analysis of sectioned db/db wounds shows that, in contrast to treatment with Ac-HSPNR-NH(2) or NS, a single Ac-PHSRN-NH(2) treatment stimulates keratinocyte and fibroblast migration into wounds, enhances fibroplasia and vascularization in the provisional matrix, and stimulates the formation of prominent fibers that may be associated with wound contraction.

Re-epithelialization rate and protein expression in the suction-induced wound model: comparison between intact blisters, open wounds and calcipotriol-pretreated open wounds

We have investigated re-epithelialization following induction of suction blisters in humans in intact blisters, open wounds, i.e. blister roofs removed immediately after blister induction, and calcipotriol-pretreated open wounds. Intact blisters simulate blister healing in bullous disease, while open wounds simulate re-epithelialization during wound healing. Re-epithelialization was clearly faster in open wounds than in intact blisters, and was not affected by calcipotriol pretreatment. Bullous pemphigoid antigen 2 (BP180), bullous pemphigoid antigen 1 (BP230), plectin/hemidesmosomal 1 protein (HD1), laminin 5, laminin alpha5, laminin beta1, type VII collagen, tenascin-C, beta4, alphavbeta5, alpha5 and alpha9 integrins were studied in intact blisters and open wounds by immunohistochemistry. Hemidesmosomal plaque proteins BP230 and plectin/HD1, which connect the keratin cytoskeleton to the hemidesmosome, appeared earlier at the leading edge in intact blisters than in open wounds. Band-like immunostaining in the basement membrane for laminin 5, alpha5 and beta1 chains was continuous in blister bases, but partially discontinuous in open wound bases. The other antigens studied showed similar expression in intact blisters and open wounds. BP180, BP230, plectin/HD1, beta4 integrin, laminin 5 and tenascin-C expression were further studied in calcipotriol-pretreated open wounds. Calcipotriol did not affect the expression of these antigens. The immunohistochemical results suggest that the keratin cytoskeleton is linked to the basal plasma membrane of migrating basal cells via BP230 and plectin/HD1 earlier in the more slowly re-epithelializing blisters than in open wounds. An intact laminin sheath may inhibit keratinocyte migration in intact blisters.

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.

Facilitation of immune function, healing of pressure ulcers, and nutritional status in spinal cord injury patients

Multiple communicative pathways among nervous, endocrine, and immune systems facilitate physiological immunoregulation. Spinal cord injury (SCI) patients had strikingly decreased natural and adaptive immune responses by 2 weeks post injury. While NK-cell function was decreased, plasma ACTH and urine-free cortisol levels were increased. T cell function and activation were both diminished. With rehabilitation therapy, NK and T function increased; without rehabilitation, NK levels remained depressed. When rehabilitation ceased, NK function decreased. Cervical SCI patients had less NK and T function than thoracic injury patients. SCI patients also had reduced levels of cellular adhesion molecules (CAMs) that participate in immune function and wound healing. SCI patients with pressure ulcers were compared to those without pressure ulcers. LFA-1, VLA-4, and other surface markers were decreased on the lymphocytes of all SCI patients. SCI patients with pressure ulcers had lower CAM levels than did patients without pressure ulcers. Nutritional status was determined by zinc, albumin, and prealbumin levels. SCI patients had decreased albumin levels. Those with pressure ulcers had decreased prealbumin levels and zinc levels.

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.

Keratinocyte growth factor (KGF) promotes keratinocyte cell attachment and migration on collagen and fibronectin

Keratinocyte growth factor (KGF) induction of keratinocyte attachment and migration on provisional and basement membrane proteins was examined. KGF-treated keratinocytes showed increased attachment to collagen types I and IV and fibronectin, but, not to laminin-1, vitronectin, or tenascin. This increase was time- and dose-dependent. Increase in attachment occurred with 2 10 microg/ml of ECM proteins. This KGF-stimulated cell attachment was beta1 integrin-dependent but was not associated with stimulation of the cell surface expression nor affinity (activity) of the collagen integrin receptor (alpha2beta1) nor the fibronectin integrin receptors (alpha5beta1 or alphav). At the basal layer of KGF-treated cells significant accumulation of beta1 integrins was found at the leading edges, and actin stress fibers colocalized with beta1. KGF also induced migratory phenotype and stimulated keratinocyte migration on both fibronectin and collagen types I and IV but not on laminin-1, vitronectin nor tenascin. The results suggest that in addition to its proliferation promoting activity. KGF is able to modulate keratinocyte adhesion and migration on collagen and fibronectin. Our data suggest that KGF induced integrin avidity (clustering), a signaling event, which is not dependent on the alteration of cell surface integrin numbers.

Role of interactions between integrins and extracellular matrix components in healthy epithelial tissue and establishment of a long junctional epithelium during periodontal wound healing: a review

Following the surgical treatment of adult periodontitis, the epithelial regeneration of the periodontal attachment is non-physiological and thus unsatisfactory, if membranes or artificial bone material are not used. Re-epithelialization is based on the proliferation, migration, and differentiation of basal epithelial cells which are in contact with a wound matrix and whose molecular makeup differs from the extracellular matrix of intact regions. Interactions between basal epithelial cells and the extracellular matrix are mediated by special receptors on the cell surface which are known as integrins and belong to the family of cellular adhesion molecules (CAM). Various studies indicate that integrin-mediated interaction plays a decisive role in regulating the proliferation, migration, and differentiation of the epithelial cells. This review provides an overview of the in vivo and in vitro expression of integrins by epithelial cells and the interaction between integrins and extracellular matrix (ECM) in the case of a stationary epithelium and during wound healing. The regulation of these cell-cell and cell-matrix interactions may represent a method for inhibiting non-physiological epithelial regeneration on the molecular level.

Matrix metalloproteinases in repair

During repair, many different matrix metalloproteinases are produced by multiple cell types residing in various compartments within the wound environment. This diversity of enzymes, coupled with discreet cellular expression, implies that different matrix metalloproteinases serve different functions, acting on a variety of substrates, during wound healing. With few exceptions, however, the actual function and spectrum of functions of matrix metalloproteinases in vivo is not known. Even with the advent of genetically defined animal models, few studies have rigorously addressed the substrates and role of matrix metalloproteinases in wound repair. Before we can understand the role of matrix metalloproteinases in ulceration and disease, we need to determine the function these enzymes serve in normal tissues and repair.

Zyxin redistributes without upregulation in migrating human keratinocytes during wound healing

Cell migration, growth, and survival is modulated by focal adhesions linking extracellular matrix proteins, cell adhesion molecules, and the cytoskeleton. Zyxin is a focal adhesion phosphoprotein that shares homology with Listeria ActA protein in promoting actin filament assembly; it also has specialized protein-protein interface domains implicating an important role in cell growth and differentiation. We investigated the distribution of zyxin in normal and migrating human keratinocytes in wounds in vitro and in situ using confocal laser microscopy. Zyxin expression in high-density nonmigrating keratinocytes versus low-density migrating keratinocytes was determined by western immunoblotting and time lapse image analysis. In normal epidermis, zyxin exhibited a punctate staining pattern throughout the cytoplasm and was excluded from the intercellular spaces. In wounds, the punctate staining also localized in the edge of the migrating keratinocyte sheets; however, intercellular spaces were absent. Likewise, in vitro keratinocytes showed punctate staining throughout the cytoplasm. Migrating cultured keratinocytes next to wounds, however, had large focal contacts in the cell periphery where actin bundles converged at focal adhesions. Western immunoblots and confocal experiments with protein synthesis inhibition by cycloheximide confirmed that this difference in distribution of zyxin in migrating versus nonmigrating keratinocytes is due to the redistribution and not upregulation of zyxin. The abundance of zyxin and its relative change in distribution from normal to migrating keratinocytes in wounds is consistent with its role in cytoskeletal organization of actin bundles.

The alpha3 laminin subunit, alpha6beta4 and alpha3beta1 integrin coordinately regulate wound healing in cultured epithelial cells and in the skin

Previously, we demonstrated that proteolytic processing within the globular domain of the alpha3 subunit of laminin-5 (LN5) converts LN5 from a cell motility-inducing factor to a protein complex that can trigger the formation of hemidesmosomes, certain cell-matrix attachment sites found in epithelial cells. We have prepared a monoclonal antibody (12C4) whose epitope is located toward the carboxy terminus of the globular domain of the alpha3 laminin subunit. This epitope is lost from the alpha3 subunit as a consequence of proteolytic processing. Antibody 12C4 stains throughout the matrix of cells that fail to process the alpha3 laminin subunit, but does not recognize the matrix of confluent cultures of MCF-10A cells, which efficiently process their alpha3 laminin chain. In subconfluent populations of MCF-10A cells, 12C4 only stains matrix deposited at the outer edges of cell colonies. In these cells, integrin alpha3beta1 occasionally colocalizes with the staining generated by the 12C4 antibody but alpha6beta4 integrin does not. In wounded MCF-10A cell cultures, the 12C4 antibody stains the extracellular matrix beneath those cells at the very edge of the cellular sheet that moves to cover the wound site. A similar phenomenon is observed in human skin wounds, since we also detect expression of the unprocessed alpha3 laminin subunit at the leading tip of the sheet of epidermal cells that epithelializes skin wounds in vivo. In addition, using alpha3 laminin subunit and integrin function-inhibiting antibodies, we provide evidence that LN5 and its two integrin receptors (alpha6beta4 and alpha3beta1) appear necessary for wound healing to occur in MCF-10A cell culture wounds. We propose a model for healing of wounded epithelial tissues based on these results.

Delayed restoration of epidermal barrier function after suction blister injury in patients with diabetes mellitus

AIMS

Diabetes mellitus is a risk factor for compromised wound healing. The present study examines the restoration of the epidermal barrier function using the suction blister wound model.

METHODS

The healing process was evaluated over time by measuring water evaporation (WE) and blood flow (BF) in the wound area. Seventeen Type 1 diabetic males and 11 non-diabetic control males were studied.

RESULTS

At the onset, the WE of diabetic patients was 116 +/- 11 g x m(-2) x h(-1) and that of controls 95 +/- 13 g x m(-2) x h(-1) (P < 0.001). On the second day, the WE of diabetic patients was 90 +/- 21 g x m(-2) x h(-1) and that of controls 60 +/- 24 g x m(-2) x h(-1) (P < 0.02). The most profound difference was encountered during the fourth day, when the WE of diabetic patients was 40 +/- 17 g x m(-2) x h(-1) and that of controls 14 +/- 8 g x m(-2) x h(-1) (P < 0.001). The value recorded on the fourth day was 37% of the onset value in diabetic patients and 16% in controls (P < 0.001). Eight days after wounding the values were close to that of normal skin in both diabetic and control subjects. At the onset, the BF was 93 +/- 20 (arbitrary units) in diabetic men and 112 +/- 18 in controls (P = 0.02). On the second, fourth and eighth day there was no significant differences.

CONCLUSIONS

The results suggest that restoration of the epidermal barrier function is delayed in the patients with diabetes. There were also a trend toward an initially weaker inflammatory response.

Defects of basement membrane and hemidesmosome structure correlate with malignant phenotype and stromal interactions in HaCaT-Ras xenografts

Benign and malignant HaCaT-ras clones, derived from immortalized HaCaT cells were grown as nude mouse surface transplants rendering a human tumor progression model. Searching for malignancy-related alterations, the deposition, localization and mRNA of basement membrane and hemidesmosome components were analysed by immunofluorescence, in situ hybridization and electron microscopy. Initially, at 1 week epithelia of benign and malignant cells revealed a similarly low polarity and an enlarged 'activated basal' compartment, reflected by partial dislocation and extended pericellular staining of the hemidesmosome constituent integrin alpha 6 beta 4 seen by immunofluorescence. Whereas benign grafts eventually normalized, closely resembling grafts of HaCaT cells, malignant growth was correlated with a persisting epithelial activation state and continuing higher expression of alpha 6 (by immunofluorescence and in situ hybridization). The basement membrane components bullous pemphigoid antigen 1, laminin-5 and collagen IV exhibited a largely linear distribution at 1 week. However, in the malignant cell transplants initially minor basement membrane discontinuities became more severe at around 2 weeks, associated with close stromal cell contacts, angiogenesis and invasion. Most striking were basement membrane alterations seen by electron microscopy. At 1 week stretches of basement membrane had developed in malignant transplants, though to a much lesser extent than in benign specimens. With invasion these basement membrane structures mostly disappeared despite persistent although variable immunofluorescence, suggesting high turnover without ultrastructural assembly. The hemidesmosome structures were defective throughout, completely lacking anchoring plaques with keratin filaments, whereas they were still associated with basement membrane deposits. Thus, malignant HaCaT-ras transplants, while initially resembling regenerating wounds, revealed an increasing loss of tissue polarity and basement membrane structures, which seemed to be accelerated upon stromal cell contacts.

Spatial and temporal expression of parathyroid hormone-related protein during wound healing

Parathyroid hormone-related protein is produced by many normal tissues including the skin, where it regulates growth and differentiation of keratinocytes. To define better the role of parathyroid hormone-related protein in the skin, we investigated the spatial and temporal expression of parathyroid hormone-related protein and mRNA by immunohistochemistry and in situ hybridization during the healing of skin wounds, and the effects of topical administration of a parathyroid hormone-related protein agonist [parathyroid hormone-related protein (1-36)] and a parathyroid hormone-related protein antagonist [parathyroid hormone (7-34)] on the healing rate and morphology of the wounds. Wounds were produced on the back of guinea pigs with a 4 mm punch, and wound sites were collected at different time points during the healing process. Parathyroid hormone-related protein was expressed in normal skin by all viable keratinocyte layers, hair follicles, and adnexae. Following injury, migratory keratinocytes at wound margins and the newly restored epidermis expressed increased levels of parathyroid hormone-related protein. The remodeling phase was associated with progressive restoration of the pattern of parathyroid hormone-related protein expression in normal epidermis. Granulation tissue myofibroblasts and infiltrating macrophages also expressed parathyroid hormone-related protein. In vitro studies using THP-1 cells (a promonocytic cell line) confirmed that macrophages expressed parathyroid hormone-related protein, especially after activation. Topical application of parathyroid hormone related protein (1-36) or parathyroid hormone (7-34) did not result in significant changes in the healing rate and morphology of the wounds. These findings demonstrated that, in addition to keratinocytes, myofibroblasts and macrophages also represent sources of parathyroid hormone-related protein during the healing of skin wounds. Although the data suggest a role for parathyroid hormone-related protein in the healing of skin and in the restoration of epidermal homeostasis, parathyroid hormone-related protein does not appear to be required for proper re-epithelialization in response to injury, potentially because of redundancy in epidermal growth and wound healing, as has been shown for other paracrine and autocrine growth factors of the epidermis.

Monoclonal antibodies against integrin subunits alpha6 and beta1 inhibit migration of gingival epithelium in organ culture

BACKGROUND

The main problem in the posterior instrumental treatment of periodontitis is the re-epithelization of the periodontal defects, leading to the formation of an unphysiological, long junctional epithelium inhibiting the regeneration of periodontal attachment. A precondition for the re-epithelization is the interaction between epithelial cells and their extracellular matrix mediated by integrins. Integrins are cellular adhesion molecules (CAM), binding to different structures of the extracellular matrix, e.g., collagen, laminin, or fibronectin.

METHODS

Biopsy specimens of marginal gingiva, composed of epithelium and subepithelial connective tissue, were cultivated on microporous membranes in tissue culture plates. The culture medium was supplemented with monoclonal antibodies directed against human integrin subunits. The period of cultivation was 6 days and the medium was replaced daily. After cultivation, the tissue development was analyzed by histological and immunohistochemical methods.

RESULTS

We found that the combination of antibodies directed against the integrin subunits alpha6 and beta1 inhibited the migration of epithelium completely in 9 out of 10 cultures, whereas control cultures containing none or only irrelevant antibodies demonstrated connective tissues completely covered by epithelium.

CONCLUSIONS

Influencing the regeneration of periodontal tissue on a molecular basis by using antibodies directed against integrin subunits may be of future interest in postsurgical treatment of periodontal diseases.

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.

[Dorsal closure in Drosophila. A genetic model for wound healing?]

Dorsal closure (DC) is a morphogenetic movement that establishes the dorsal ectoderm of the drosophila embryo. During this process, the two lateral epithelia stretch toward the dorsal midline, the suture line of the two leading edges. Cell migration during DC relies both on cell shape change controlled by the activity of the JNK pathway in the leading edge cells and modification of cell adhesiveness, probably dependent upon activation of the Dpp (TGF-beta) pathway. Coupling of the JNK and TGF-beta pathways is essential. The sequence of the cellular and molecular events of DC highlights interesting common features with wound healing in vertebrates. Like DC, wound healing relies on the migration of epithelia bordered by leading edges controlling the direction and speed of the movement. This review summarizes recent data concerning the control of epithelial morphogenesis during DC and the bases of wound healing. The molecular and cellular events that underlie these two analogous migratory processes are detailed, discussed and compared. We suggest that DC is a good genetic model for wound healing studying.

Normalization of keratinocyte-type integrins during the establishment of the oral mucosa phenotype in vitro

In stratified epithelia, integrins play a fundamental role in mediating basal cell attachment to a variety of extracellular matrix molecules. To assess whether keratinocyte-specific integrins are expressed in a similar way as in the normal situation also under in vivo related conditions, we processed oral mucosa equivalents consisting of keratinocytes and fibroblasts from non-cornified gingiva. In this model histomorphology, the expression of differentiation-specific keratins and keratinocyte-type integrins exhibited similarity to the tissue of origin. The stages of tissue normalization were assessed on frozen sections by indirect immunofluorescence. The initial activated stage (1 week) was characterized by (i) incomplete epithelial organization and a weak presence of the suprabasal mucosa type keratin K4, (ii) diffuse expression of the integrin chains beta 1 and alpha 6 and (iii) abundance of the wound healing-associated integrin alpha v throughout the whole epithelium. After 2 weeks, the increase in epithelial organization was characterized by (i) the presence of a basal and suprabasal cell compartment, (ii) extension of K4 in the suprabasal compartment, (iii) extended expression of the keratinocyte integrins beta 1 and alpha 6 and (iv) concentration of alpha v integrin underneath basal cells. Further normalization of tissue architecture was indicated by (i) a slight increase in K4 extension, (ii) appearance of keratinocyte integrins beta 1 and alpha 6 in basal and parabasal cells and (iii) interruption of the band-like alpha v integrin immunolocalization at the subepithelial site. The findings in the in vitro model system indicate that these oral mucosa equivalents exhibit similarities to the in vivo situation of non-cornified gingiva, thus rendering them a suitable model for the assessment of stages during epithelial reconstruction or in vivo relevant studies on material effects.