Regulation of wound healing by growth factors and cytokines

The contribution of platelets in the production of cryoprecipitates for use in a fibrin glue

BACKGROUND AND OBJECTIVES

Cryoprecipitate has a wide application for use as a fibrin glue. In some situations, platelets are added to the preparation in order to enhance the fibrin glue.

MATERIALS AND METHODS

Fresh plasma was collected by apheresis from the same donor to produce 250 ml of platelet-rich plasma (PRP) or platelet-poor plasma (PPP) (n = 12 each). Cryoprecipitate was then produced following the standards of the American Association of Blood Banks and resuspended to a total volume of 8 ml, from which aliquots were removed and assayed. Clot formation was measured using the thromboelastogram.

RESULTS

The protein content of the two preparations was identical for PRP and PPP. Results for fibrinogen (PPP 475 +/- 220 mg; PRP 399 +/- 215 mg), Factor VIII (PPP 186 +/- 67 IU; PRP 175 +/- 70 IU) and von Willebrand Factor (PPP 260 +/- 104 IU; PRP 221 +/- 88 IU) were not significantly different. The concentration of platelet-derived growth factor was markedly higher (a 100-fold increase at 3778 +/- 1036 ng) when platelets were added to the plasma. There was a small, but not statistically significant, difference in the rate of clot formation (R = 2.3 for PPP and 3.8 for PRP) and clot strength (MA = 63.4 for PPP and 56.6 for PRP) between PPP and PRP cryoprecipitates when measured using the thromboelastogram.

CONCLUSIONS

Platelets do not significantly increase the concentration of the usual constituents of cryoprecipitate; however, the levels of platelet-derived growth factor are markedly enhanced. Therefore, there are advantages for using PRP to enhance the growth of new tissue.

Regulation of epidermal homeostasis and repair by phosphoinositide 3-kinase

The epidermis undergoes continuous self-renewal to maintain its protective function. Whereas growth factors are known to modulate overall skin homeostasis, the intracellular signaling pathways, which control the delicate balance between proliferation and differentiation in keratinocytes, are largely unknown. Here we show transient upregulation of the phosphoinositide 3-kinase (PI3K) catalytic subunits p110α and p110β in differentiating keratinocytes in vitro, expression of these subunits in the epidermis of normal and wounded skin, and enhanced Akt phosphorylation in the hyperproliferative wound epidermis. Stimulation of PI3K activity in cultured keratinocytes by stable expression of an inducible, constitutively active PI3K mutant promoted cell proliferation and inhibited terminal differentiation in keratinocyte monocultures and induced the formation of a hyperplastic, disorganized and poorly differentiated epithelium in organotypic skin cultures. Activation of PI3K signaling also caused reorganization of the actin cytoskeleton and induced keratinocyte migration in vitro and in skin organ cultures. The identification of 122 genes, which are differentially expressed after induction of PI3K signaling provides insight into the molecular mechanisms underlying the observed effects of active PI3K on keratinocytes and indicates that hyperproliferation may be achieved at the expense of genome integrity. These results identify PI3K as an important intracellular regulator of epidermal homeostasis and repair.

Biology of the hair follicle: the basics

The mammalian hair follicle represents a unique, highly regenerative neuroectodermal-mesodermal interaction system that contains numerous stem cells. It is the only organ in the mammalian organism that undergoes life-long cycles of rapid growth (anagen), regression (catagen), and resting periods (telogen). These transformations are controlled by changes in the local signaling milieu, based on changes in expression/activity of a constantly growing number of cytokines, hormones, neurotransmitters, and their cognate receptors as well as of transcription factors and enzymes that have become recognized as key mediators of hair follicle cycling. Transplantation experiments have shown that the driving force of cycling, the "hair cycle clock," is located in the hair follicle itself. However, the exact underlying molecular mechanisms that drive this oscillator system remain unclear. These controls of hair follicle cycling are of great clinical interest because hair loss or unwanted hair growth largely reflect undesired changes in hair follicle cycling. To develop therapeutic agents for the management of these hair cycle abnormalities, it is critical to decipher and pharmacologically target the key molecular controls that underlie the enigmatic "hair cycle clock."

Mast cells are required for normal healing of skin wounds in mice

Mast cells (MCs) have recently been reported to play a pivotal role in the elicitation of inflammatory reactions that are beneficial to the host, e.g., during innate immune responses to bacteria. To explore whether MCs also contribute to wound repair, we studied experimentally induced skin wounds in MC-deficient Kit(W)/Kit(W-v) mice, normal Kit+/+ mice, and MC-reconstituted Kit(W)/Kit(W-v) mice. Wound closure was significantly impaired in the absence of MCs during the first 6 days of wound healing and histomorphometric analyses of MC degranulation at the wound edges revealed distance-dependent MC activation, i.e., MC degranulation was most prominent directly adjacent to the wound. In addition, Kit(W)/Kit(W-v) mice showed impaired extravasation and recruitment of neutrophils to the wounded areas. Notably, wound closure, extravasation, and neutrophil recruitment were found to be normal in MC-reconstituted Kit(W)/Kit(W-v) mice. Therefore, we examined whether MCs promote wound healing by releasing histamine or TNF-alpha. Interestingly, wound closure was reduced in mice treated with an H1-receptor antagonist but not after treatment with an H2-receptor antagonist or in the absence of TNF-alpha. Taken together, our findings indicate that MC activation and histamine release are required for normal cutaneous wound healing.

CD18 in monogenic and polygenic inflammatory processes of the skin

The beta 2 integrin family (CD11/CD18) of leukocyte adhesion molecules plays a key role in inflammation. Absence of the common chain (CD18) leads to leukocyte adhesion deficiency-1 (LAD1) in humans. We here summarize data of two genetically defined mice models of beta 2 integrin deficiency, one with a CD18 null mutation (CD18-/-), and the other one with a hypomorphic CD18 mutation (CD18hypo). Firstly, we focus on the underlying mechanism of a severely impaired wound healing in CD18-/- mice, outlining a scenario in which a defective extravasation and phagocytosis of CD18-/- neutrophils results in delayed myofibroblast-dependent wound contraction owing to a deficient transforming growth factor-beta 1 release. Based on this, we have identified a potential therapy that fully rescued the impaired wound healing in CD18-/- mice. Secondly, we expand on a CD18hyp0 PL/J mouse model closely resembling human psoriasis. Apart from common clinical and pathophysiological features, this psoriasiform dermatitis also depends on the presence of activated CD4+ T cells. We here recapitulate the influence of a reduced CD18 gene expression on T-cell function, also with regard to CD18 gene-dose effects, and its contribution to the pathogenesis of this disease. Taken together, these unique features make this model a valuable tool for investigations into the pathogenesis of human psoriasis--including its polygenic base--and future preclinical studies.

Functions of the peroxisome proliferator-activated receptor (PPAR) alpha and beta in skin homeostasis, epithelial repair, and morphogenesis

The three peroxisome proliferator-activated receptors (PPAR alpha, PPAR beta, and PPAR gamma) are ligand-activated transcription factors belonging to the nuclear hormone receptor superfamily. They are regarded as being sensors of physiological levels of fatty acids and fatty acid derivatives. In the adult mouse skin, they are found in hair follicle keratinocytes but not in interfollicular epidermis keratinocytes. Skin injury stimulates the expression of PPAR alpha and PPAR beta at the site of the wound. Here, we review the spatiotemporal program that triggers PPAR beta expression immediately after an injury, and then gradually represses it during epithelial repair. The opposing effects of the tumor necrosis factor-alpha and transforming growth factor-beta-1 signalling pathways on the activity of the PPAR beta promoter are the key elements of this regulation. We then compare the involvement of PPAR beta in the skin in response to an injury and during hair morphogenesis, and underscore the similarity of its action on cell survival in both situations.

Assessment and management of chronic pressure ulcers in the elderly

Pressure ulcers remain a complex and costly problem to the health care system. As the population ages, a greater number of individuals will be at high risk for developing pressure ulcers. An understanding of the physiologic changes that occur with aging skin is important in preventing and treating chronic wounds. Risk factor assessment and modification, when possible, can help to reduce the development of pressure ulcerations. Although the goal continues to be prevention, once a pressure ulcer does occur, a systematic and comprehensive approach to assessment and treatment is necessary to reduce healing times.

Molecular balance of capillary tube formation versus regression in wound repair: role of matrix metalloproteinases and their inhibitors

In this review, we discuss the identification of distinct matrix metalloproteinases (MMPs) and their inhibitors that differentially control the processes of capillary tube formation (morphogenesis) versus capillary tube regression in three-dimensional (3D) collagen matrices. This work directly relates to both granulation tissue formation and regression during wound repair. The membrane metalloproteinase, MT1-MMP (MMP-14), is required for endothelial cell (EC) tube formation using in vitro assays that mimic vasculogenesis or angiogenic sprouting in 3D collagen matrices. These events are markedly blocked by small interfering RNA (siRNA) suppression of MT1-MMP in ECs or by addition of tissue inhibitor of metalloproteinases (TIMPs)-2,-3, and -4 but not TIMP-1. In contrast, MMP-1 and MMP-10 are strongly induced during EC tube formation to regulate the process of tube regression (following activation by serine proteases) rather than formation. TIMP-1, which selectively inhibits soluble MMPs, blocks tube regression by inhibiting MMP-1 and MMP-10 while having no influence on EC tube formation. siRNA suppression of MMP-1 and MMP-10 markedly blocks tube regression without affecting tube formation. Furthermore, we discuss that pericyte-induced stabilization of EC tube networks in our model system appears to occur through EC-derived TIMP-2 and pericyte-derived TIMP-3 to block both the capillary tube formation and regression pathways.

Evidence of Innervation in Talc-Induced Pleural Adhesions

STUDY OBJECTIVES

To conduct a detailed morphologic and ultrastructural study of pleural adhesions following talc pleurodesis.

METHODS

Talc with a main particle size of 8.36 +/- 0.2 mum (mean +/- SEM) and at a dose of 200 mg/kg in a 2-mL slurry was instilled via a small catheter into the pleural cavity of 10 male rabbits. Five rabbits were killed at 1 week, and five rabbits were killed at 1 month after instillation. At autopsy, after macroscopically observing the pleural cavity, adhesions were excised from opposing pleural surfaces and processed for histopathologic, immunocytochemical, and ultrastructural study.

RESULTS

At 1 week, all adhesions examined were mesothelium-covered fibrovascular bands containing well-developed blood and lymphatic vessels establishing a structural continuity between both pleural layers. Nerves were present in adhesions from 20% of the rabbits. They consisted of a single fascicle containing 5 to 20 thin myelinated axons of various diameters (1 to 6 microm) uniformly distributed throughout the nerve section. The anatomic location of the adhesion did not appear to influence its overall morphology.

CONCLUSIONS

As early as at 1 week, adhesions are well-formed structures more resembling newly formed pleural tissue than a simple scar. Nerve fibers in pleural adhesions are reported for the first time, which suggests that these adhesions are potentially capable of conducting pain stimuli. Further studies are required in order to confirm our results in human pleural adhesions.

Gene therapy in wound healing: present status and future directions

Gene therapy was traditionally considered a treatment modality for patients with congenital defects of key metabolic functions or late-stage malignancies. The realization that gene therapy applications were much vaster has opened up endless opportunities for therapeutic genetic manipulations, especially in the skin and external wounds. Cutaneous wound healing is a complicated, multistep process with numerous mediators that act in a network of activation and inhibition processes. Gene delivery in this environment poses a particular challenge. Numerous models of gene delivery have been developed, including naked DNA application, viral transfection, high-pressure injection, liposomal delivery, and more. Of the various methods for gene transfer, cationic cholesterol-containing liposomal constructs are emerging as a method with great potential for non-viral gene transfer in the wound. This article aims to review the research on gene therapy in wound healing and possible future directions in this exciting field.

Sequential patterns of chemokine- and chemokine receptor-synthesis following vessel wall injury in porcine coronary arteries

Inflammation plays a central role in vascular repair, and spreads into perivascular tissue (PVT) following angioplasty. Chemokines (CK) and chemokine receptors (CKR) are key determinants of inflammatory chemotaxis. We sought to assess the arterial and perivascular expression of the CK CCL2 and CXCL2, and the CKR CCR2, CCR5, and CXCR4 in balloon-injured porcine coronary arteries. Vascular cells that express specific CK and CKR mRNA during post-angioplasty time course were detected by in situ hybridization (ISH), and expression was quantified by real time RT-PCR in PVT. CCL2 was maximal in PVT from 2 to 24h post injury, coincident with local macrophage-activation. Expression was upregulated in media and adventitia from 24h to 3 days, and in neointima at 7 days. CXCL2 was detected in media at 2 and 4h, and also in some neointimal cells. CCR2 and CCR5 were maximal in PVT at 24h and 3 days, respectively. Expression shifted to media and adventitia at 2 and 3 days, and to neointima and adventitia at 7 days, and was low at 14 days. CXCR4 was low in PVT, but was upregulated in media and adventitia at 2 and 3 days, as well as in neointima and adventitia at 7 days. In conclusion, PVT is the primary source of inflammatory CK and CKR early post-angioplasty. Specific sequential patterns of CK- and CKR-synthesis are identified that may regulate phase-specific chemotaxis by spatio-temporally differential expression during coronary response to injury.

Non-adenine based purines accelerate wound healing

Wound healing is a complex sequence of cellular and molecular processes that involves multiple cell types and biochemical mediators. Several growth factors have been identified that regulate tissue repair, including the neurotrophin nerve growth factor (NGF). As non-adenine based purines (NABPs) are known to promote cell proliferation and the release of growth factors, we investigated whether NABPs had an effect on wound healing. Full-thickness, excisional wound healing in healthy BALB/c mice was significantly accelerated by daily topical application of NABPs such as guanosine (50% closure by days 2.5′.8). Co-treatment of wounds with guanosine plus anti-NGF reversed the guanosine-promoted acceleration of wound healing, indicating that this effect of guanosine is mediated, at least in part, by NGF. Selective inhibitors of the NGF-inducible serine/threonine protein kinase (protein kinase N), such as 6-methylmercaptopurine riboside abolished the acceleration of wound healing caused by guanosine, confirming that activation of this enzyme is required for this effect of guanosine. Treatment of genetically diabetic BKS.Cg-m+/+lepr db mice, which display impaired wound healing, with guanosine led to accelerated healing of skin wounds (25% closure by days 2.8′.0). These results provide further confirmation that the NABP-mediated acceleration of cutaneous wound healing is mediated via an NGF-dependent mechanism. Thus, NABPs may offer an alternative and viable approach for the treatment of wounds in a clinical setting.

Human embryoid body-derived stem cells in tissue engineering-enhanced migration in co-culture with bladder smooth muscle and urothelium

OBJECTIVES

To evaluate the affinity between human stem cells and human bladder cells by analyzing their migration and proliferation patterns in co-culture. Human stem cells have great potential for tissue engineering purposes. Co-culture of stem cells with mature cells may promote differentiation.

METHODS

Equal numbers of green fluorescent protein-labeled human embryonic germ cell derivates (SDECs) were plated, either alone or in the presence of red fluorescence-labeled (PKH 26) human bladder smooth muscle cells (SMCs) or urothelial cells (UROs). The co-cultures shared the same media (EGM2MV). The migration patterns of the different cell lines were measured daily, using an integrated grid, for 8 days with fluorescence microscopy.

RESULTS

SDECs, grown alone, had a robust basal migration rate of between 0.3 and 0.7 mm/day compared with SMCs, which had a rate of 0.1 to 0.3 mm/day and UROs with a rate of 0.1 to 0.2 mm/day. Stem cell migration was enhanced in co-culture with SMCs or UROs to 0.5 to 1.0 mm/day. Migration of SDECs was more linear, directed toward SMCs or UROs, compared with the circumferential growth when plated alone. SMCs, more than UROs, migrated more rapidly in the presence of stem cells.

CONCLUSIONS

Human stem cells showed improved migration in the presence of mature human bladder cells and were attracted to them, as shown by the altered direction of growth. Thus, co-culture of human stem cells with host SMCs can enhance seeding of matrices due to positive chemotaxis. Identifying the responsible factors may help to augment chemotaxis between desired cell types and optimize tissue regeneration.

Current insights into the formation and breakdown of hemidesmosomes

Hemidesmosomes are multiprotein adhesion complexes that promote epithelial stromal attachment in stratified and complex epithelia. Modulation of their function is of crucial importance in a variety of biological processes, such as differentiation and migration of keratinocytes during wound healing and carcinoma invasion, in which cells become detached from the substrate and acquire a motile phenotype. Although much is known about the signaling potential of the alpha6beta4 integrin in carcinoma cells, the events that coordinate the disassembly of hemidesmosomes during differentiation and wound healing remain unclear. The binding of alpha6beta4 to plectin has a central role in hemidesmosome assembly and it is becoming clear that disrupting this interaction is a crucial event in hemidesmosome disassembly. In addition, further insight into the functional interplay between alpha3beta1 and alpha6beta4 has contributed to our understanding of hemidesmosome disassembly and cell migration.

Lack of alpha2-antiplasmin improves cutaneous wound healing via over-released vascular endothelial growth factor-induced angiogenesis in wound lesions

BACKGROUND

The fibrinolytic system is supposed to play an important role in the degradation of extracellular matrices for physiological and pathological tissue remodeling; however, the detailed mechanism regarding how this system affects cutaneous wound healing remains to be clarified.

METHODS AND RESULTS

We performed experimental cutaneous wounding in mice with a deficiency of alpha(2)-antiplasmin (alpha(2)AP), which is a potent and specific plasmin inhibitor. We found that an accelerated wound closure was observed in alpha(2)AP-deficient (alpha(2)AP-/-) mice in comparison with wild type (WT) mice. Moreover, we observed that a greater increase of angiogenesis occurred in the process of wound healing in alpha(2)AP-/- mice than in the WT mice. Intriguingly, mRNA expression of vascular endothelial growth factor (VEGF), which is the best characterized positive regulator of angiogenesis, in wound lesions was found to show a greater increase in the early phase of the healing process in alpha(2)AP-/- mice than in WT mice. In addition, the amount of released-VEGF from the explanted fibroblasts of alpha(2)AP-/- mice increased dramatically more than in the WT mice. Finally, the intra-jugular administration of anti-VEGF antibody clearly suppressed the increased angiogenesis and accelerated wound closure in the wound lesion of alpha(2)AP-/- mice.

CONCLUSION

The lack of alpha(2)AP markedly causes an over-release of VEGF from the fibroblasts in cutaneous wound lesions, thereby inducing angiogenesis around the area, and thus resulting in an accelerated-wound closure.

CONCLUSIONS

This is the first report to describe the crucial role that alpha(2)AP plays following angiogenesis in the process of wound healing. Our results provide new insight into the role of alpha(2)AP on cutaneous wound healing.

Keratinocyte growth factor expression and activity in cancer: implications for use in patients with solid tumors

Keratinocyte growth factor (KGF) is a locally acting epithelial mitogen that is produced by cells of mesenchymal origin and has an important role in protecting and repairing epithelial tissues. Use of recombinant human KGF (palifermin) in patients with hematologic malignancies reduces the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. These results suggest that KGF may be useful in the treatment of patients with other kinds of tumors, including those of epithelial origin. However, its application in this context raises issues that were not pertinent to its use in hematologic cancer because epithelial tumor cells, unlike blood cells, often express the KGF receptor (FGFR2b). Thus, it is important to examine whether KGF could promote the growth of epithelial tumors or protect such tumor cells from the effects of chemotherapy agents. Analyses of KGF and FGFR2b expression in tumor specimens and of KGF activity on transformed cells in vitro and in vivo do not indicate a definitive role for KGF in tumorigenesis. On the contrary, restoring FGFR2b expression to certain malignant cells can induce cell differentiation or apoptosis. However, other observations suggest that, in specific situations, KGF may contribute to epithelial tumorigenesis. Thus, further studies are warranted to examine the nature and extent of KGF involvement in these settings. In addition, clinical trials in patients with solid tumors are underway to assess the potential benefits of using KGF to protect normal tissue from the adverse effects of chemoradiotherapy and its possible impact on clinical outcome.

A role for the mitogen-activated protein kinase kinase kinase 1 in epithelial wound healing

The mitogen-activated protein kinase kinase (MEK) kinase 1 (MEKK1) mediates activin B signals required for eyelid epithelium morphogenesis during mouse fetal development. The present study investigates the role of MEKK1 in epithelial wound healing, another activin-regulated biological process. In a skin wound model, injury markedly stimulates MEKK1 expression and activity, which are in turn required for the expression of genes involved in extracellular matrix (ECM) homeostasis. MEKK1 ablation or down-regulation by interfering RNA significantly delays skin wound closure and impairs activation of Jun NH2-terminal kinases, induction of plasminogen activator inhibitor (PAI)-1, and restoration of cell-cell junctions of the wounded epidermis. Conversely, expression of wild-type MEKK1 accelerates reepithelialization of full-thickness skin and corneal debridement wounds by mechanisms involving epithelial cell migration, a cell function that is partially abolished by neutralizing antibodies for PAI-1 and metalloproteinase III. Our data suggest that MEKK1 transmits wound signals, leading to the transcriptional activation of genes involved in ECM homeostasis, epithelial cell migration, and wound reepithelialization.

Functionalization of multilayered DNA-coatings with bone morphogenetic protein 2

The focus of the present study was to functionalize multilayered DNA-coatings with the osteoinductive factor bone morphogenetic protein 2 (BMP-2) using different loading modalities. The multilayered DNA-coatings were built up from either poly-d-lysine (PDL) or poly(allylamine hydrochloride) (PAH) and DNA using electrostatic self-assembly (ESA). The amounts of BMP-2 loaded into the multilayered DNA-coatings and its subsequent release characteristics were determined using radiolabeled BMP-2. Additionally, the effect of BMP-2 functionalized multilayered DNA-coatings on the in vitro behavior of bone marrow-derived osteoblast-like cells was evaluated in terms of proliferation, differentiation, mineralization, and cell morphology. The results demonstrate the feasibility of multilayered DNA-coatings to be functionalized by embedding BMP-2 according to three different loading modalities: superficial (s), deep (d), and double-layer (dl). BMP-2 was incorporated proportionally into the multilayered DNA-coatings as: s+(4*d)=dl. All differently loaded multilayered DNA-coatings showed an initial burst release followed by an incremental sustained release of the remaining BMP-2. In vitro experiments demonstrated that the loaded factor remained biologically active, as an accelerated calcium deposition was observed on s- and dl-loaded multilayered DNA-coatings, without affecting cell proliferation. In contrast, d-loaded multilayered DNA-coatings influenced osteoblast-like cell behavior by decreasing the deposition of calcium.

Delayed wound healing and epidermal hyperproliferation in mice lacking JunB in the skin

The cutaneous response to injury and stress comprises a temporary change in the balance between epidermal proliferation and differentiation as well as an activation of the immune system. Soluble factors play an important role in the regulation of these complex processes by coordinating the intercellular communication between keratinocytes, fibroblasts, and inflammatory cells. In this study, we demonstrate that JunB, a member of the activator protein-1 transcription factor family, is an important regulator of cytokine expression and thus critically involved in the cutaneous response to injury and stress. Mice lacking JunB in the skin develop normally, indicating that JunB is neither required for cutaneous organogenesis, nor homeostasis. However, upon wounding and treatment with the phorbol ester 12-O-decanoyl-phorbol-13-acetate, JunB-deficiency in the skin likewise resulted in pronounced epidermal hyperproliferation, disturbed differentiation, and prolonged inflammation. Furthermore, delayed tissue remodelling was observed during wound healing. These phenotypic skin abnormalities were associated with JunB-dependent alterations in expression levels and kinetics of important mediators of wound repair, such as granulocyte macrophage colony-stimulating factor, growth-regulated protein-1, macrophage inflammatory protein-2, and lipocalin-2 in both the dermal and epidermal compartment of the skin, and a reduced ability of wound contraction of mutant dermal fibroblasts in vitro.

Beta-catenin regulates wound size and mediates the effect of TGF-beta in cutaneous healing

After cutaneous injury, a variety of cell types are activated to reconstitute the epithelial and dermal components of the skin. beta-Catenin plays disparate roles in keratinocytes and fibroblasts, inhibiting keratinocyte migration and activating fibroblast proliferation, suggesting that beta-catenin could either inhibit or enhance the healing process. How beta-catenin functions in concert with other signaling pathways important in the healing process is unknown. Wound size was examined in mice expressing conditional null or conditional stabilized alleles of beta-catenin, regulated by an adenovirus expressing cre-recombinase. The size of the wounds in the mice correlated with the protein level of beta-catenin. Using mice expressing these conditional alleles, we found that the wound phenotype imparted by Smad3 deficiency and by the injection of TGFbeta before wounding is mediated in part by beta-catenin. TGFbeta was not able to regulate proliferation in beta-catenin null fibroblasts, whereas keratinocyte proliferation rate was independent of beta-catenin. When mice are treated with lithium, beta-catenin-mediated signaling was activated in cutaneous wounds, which healed with a larger size. These results demonstrate a crucial role for beta-catenin in regulating cutaneous wound size. Furthermore, these data implicate mesenchymal cells as playing a critical role regulating wound size.

Platelet-derived growth factor (PDGF) isoform and PDGF receptor expression in drug-induced gingival overgrowth and hereditary gingival fibrosis

OBJECTIVE

To investigate possible associations between platelet-derived growth factor (PDGF), PDGF receptor expression and macrophages in drug-induced and hereditary gingival overgrowth.

MATERIALS AND METHODS

Tissues from patients with drug-induced gingival overgrowth (DIGO) (n = 10) and hereditary gingival fibrosis (n = 10) were studied and compared with 'control' gingiva (n = 10). Expression of PDGF and its alpha and beta receptors was investigated immunohistochemically and by RT-PCR. Macrophages were identified by immunostaining for CD68.

RESULTS

PDGF isoforms and receptors were detected in most cells within all specimens. There were no differences in the numbers of macrophages, or fibroblasts expressing PDGF or receptors, between groups. The level of PDGF expression by fibroblasts, determined by absorbance measurements, was similar between groups for PDGF A. Significantly lower levels of total PDGF and the receptors were detected in drug-induced overgrowth compared to those in hereditary fibrosis (P < 0.004) and control specimens (P < 0.034). All specimens expressed mRNA for PDGF A, PDGF B and alpha and beta receptors.

CONCLUSIONS

These data do not support a pivotal role for macrophage-derived PDGF B in the pathogenesis of DIGO. They suggest that fibroblasts in drug-induced lesions have a lowered capacity to produce, and respond to, PDGF, a property not shared by fibroblasts associated with hereditary fibrosis.

Mig6 is a negative regulator of EGF receptor-mediated skin morphogenesis and tumor formation

The growing number of recently identified negative feedback regulators of receptor tyrosine kinases (RTKs) highlights the importance of signal attenuation and modulation for correct signaling outcome. Mitogen-inducible gene 6 (Mig6 also known as RALT or Gene 33) is a multiadaptor protein thought to be involved in the regulation of RTK and stress signaling. Here, we show that deletion of the mouse gene encoding Mig6 (designated Errfi1, which stands for ERBB receptor feedback inhibitor 1) causes hyperactivation of endogenous epidermal growth factor receptor (EGFR) and sustained signaling through the mitogen-activated protein kinase (MAPK) pathway, resulting in overproliferation and impaired differentiation of epidermal keratinocytes. Furthermore, Errfi1-/- mice develop spontaneous tumors in various organs and are highly susceptible to chemically induced formation of skin tumors. A tumor-suppressive role for Mig6 is supported by our finding that MIG6 is downregulated in various human cancers. Inhibition of endogenous Egfr signaling with the Egfr inhibitor gefitinib (Iressa) or replacement of wild-type Egfr with the kinase-deficient protein encoded by the hypomorphic Egfr(wa2) allele completely rescued skin defects in Erffi1-/- mice. Carcinogen-induced tumors displayed by Errfi1-/- mice were highly sensitive to gefitinib. These results indicate that Mig6 is a specific negative regulator of Egfr signaling in skin morphogenesis and is a novel tumor suppressor of Egfr-dependent carcinogenesis.

Involvement of H- and N-Ras isoforms in transforming growth factor-beta1-induced proliferation and in collagen and fibronectin synthesis

Transforming growth factor beta1 (TGF-beta1) has a relevant role in the origin and maintenance of glomerulosclerosis and tubule-interstitial fibrosis. TGF-beta and Ras signaling pathways are closely related: TGF-beta1 overcomes Ras mitogenic effects and Ras counteracts TGF-beta signaling. Tubule-interstitial fibrosis is associated to increases in Ras, Erk, and Akt activation in a renal fibrosis model. We study the role of N- and H-Ras isoforms, and the involvement of the Ras effectors Erk and Akt, in TGF-beta1-mediated extracellular matrix (ECM) synthesis and proliferation, using embrionary fibroblasts from double knockout (KO) mice for H- and N-Ras (H-ras(-/-)/N-ras(-/-)) isoforms and from heterozygote mice (H-ras(+/-)/N-ras(+/-)). ECM synthesis is increased in basal conditions in H-ras(-/-)/N-ras(-/-) fibroblasts, this increase being higher after stimulation with TGF-beta1. TGF-beta1-induced fibroblast proliferation is smaller in H-ras(-/-)/N-ras(-/-) than in H-ras(+/-)/N-ras(+/-) fibroblasts. Erk activation is decreased in H-ras(-/-)/N-ras(-/-) fibroblasts; inhibition of Erk activation reduces fibroblast proliferation. Akt activation is higher in double KO fibroblasts than in heterozygotes; inhibition of Akt activation also inhibits ECM synthesis. We suggest that H- and N-Ras isoforms downregulate ECM synthesis, and mediate proliferation, in part through MEK/Erk activation. PI3K-Akt pathway activation may be involved in the increase in ECM synthesis observed in the absence of H- and N-Ras.

Stat3 contributes to keloid pathogenesis via promoting collagen production, cell proliferation and migration

Keloids, partially considered as benign tumors, represent the most extreme example of cutaneous scarring that uniquely afflicts humans as a pathological response to wound healing. It is characterized by excessive deposition of collagen and other extracellular matrix components by dermal fibroblasts. Upon cutaneous injury, cocktails of chemokines, cytokines and growth factors are secreted temporally and spatially to direct appropriate responses from neutrophils, macrophages, keratinocytes and fibroblasts to facilitate normal wound healing. Signal transducer and activator of transcription 3 (Stat3) is an oncogene and a latent transcription factor activated by various cytokines and growth factors. We investigated the possible role of Stat3 in keloid scar pathogenesis by examining skin tissue and cultured fibroblasts from keloid-scarred patients. We observed enhanced expression and phosphorylation of Stat3 in keloid scar tissue, and in cultured keloid fibroblasts (KFs) in vitro. Increased activation of Janus kinase (Jak)2, but not Jak1, was detected in KFs, and suppression of Jak2 by its inhibitor repressed Stat3 Y705 phosphorylation. Inhibition of Stat3 expression and phosphorylation by short interfering RNA or Cucurbitacin I resulted in the loss of collagen production, impaired proliferation and delayed cell migration in KFs. We show, for the first time, a role of Stat3 in keloid pathogenesis. Inhibitors of Stat3 may be useful therapeutic strategies for the prospective treatment of keloid scars.

Masters and servants of the force: The role of matrix adhesions in myofibroblast force perception and transmission

Fibroblast-to-myofibroblast differentiation - a key event in the development of fibrocontractive diseases and in wound granulation tissue contraction - is hallmarked by the formation of stress fibers and the neo-expression of alpha-smooth muscle actin. Incorporation of the smooth muscle actin isoform into stress fibers confers to myofibroblasts a high contractile activity which is transmitted to the extracellular matrix at sites of specialized adhesions, termed 'fibronexus' in tissue and 'supermature focal adhesions' in two-dimensional cell culture. Myofibroblast differentiation requires a mechanically restrained environment in conjunction with the action of growth factors like transforming growth factor beta and specialized matrix molecules like the ED-A splice variant of fibronectin. This mini-review discusses the roles of myofibroblast adhesions in sensing matrix stress, in transmitting contractile force to the extracellular environment and in creating the high intracellular tension that is required for myofibroblast development.

Improved mutants from directed evolution are biased to orthologous substitutions

We have engineered human epidermal growth factor (EGF) by directed evolution through yeast surface display for significantly enhanced affinity for the EGF receptor (EGFR). Statistical analysis of improved EGF mutants isolated from randomly mutated yeast-displayed libraries indicates that mutations are biased towards substitutions at positions exhibiting significant phylogenetic variation. In particular, mutations in high-affinity EGF mutants are statistically biased towards residues found in orthologous EGF species. This same trend was also observed with other proteins engineered through directed evolution in our laboratory (EGFR, interleukin-2) and in a meta-analysis of reported results for engineered subtilisin. By contrast, reported loss-of-function mutations in EGF were biased towards highly conserved positions. Based on these findings, orthologous mutations were introduced into a yeast-displayed EGF library by a process we term shotgun ortholog scanning mutagenesis (SOSM). EGF mutants with a high frequency of the introduced ortholog mutations were isolated through screening the library for enhanced binding affinity to soluble EGFR ectodomain. These mutants possess a 30-fold increase in binding affinity over wild-type EGF to EGFR-transfected fibroblasts and are among the highest affinity EGF proteins to be engineered to date. Collectively, our findings highlight a general approach for harnessing information present in phylogenetic variability to create useful genetic diversity for directed evolution. Our SOSM method exploits the benefits of library diversity obtained through complementary methods of error-prone PCR and DNA shuffling, while circumventing the need for acquisition of multiple genes for family or synthetic shuffling.

Oncostatin M expression is functionally connected to neutrophils in the early inflammatory phase of skin repair: implications for normal and diabetes-impaired wounds

In this study, we investigated the role of the cytokine oncostatin M (OSM) for wound biology. OSM and its specific OSM receptor subunit beta (OSMRbeta) were induced upon injury. OSM induction paralleled the early influx of polymorphonuclear neutrophils (PMN) into the wound. OSM protein was localized in PMN in very early wounds, whereas OSMRbeta could be detected on macrophages, keratinocytes, and fibroblasts later in repair. To establish a functional connection between PMN and OSM expression in wounds, we depleted mice from circulating PMN by injecting an anti-PMN monoclonal antibody (Ly-6G). PMN-depleted wounds were characterized by a nearly complete loss of OSM but not OSMRbeta mRNA and protein expression within the initial 16-24 hours after injury. PMN-rich chronic wounds from diabetic ob/ob mice were characterized by a strongly elevated OSM mRNA and protein expression as compared to healthy animals. Moreover, a leptin-mediated improvement of chronic wounds in ob/ob mice was paralleled by a complete inhibition of PMN influx associated again with a dramatic loss of OSM expression at the wound site. These data constitute strong evidence that OSM expression during wound inflammation is functionally connected to PMN infiltration.

Acceleration of wound healing in traumatic ulcers by absorbable collagen sponge containing recombinant basic fibroblast growth factor

The objective of this study was to examine the safety and efficacy of topical application of recombinant basic fibroblast growth factor loaded on a kind of absorbable collagen sponge (rbFGF/ACS) in patients with chronic traumatic ulcers. This double-blind controlled trial included 58 patients with chronic traumatic ulcers. The patients were randomized into two groups. After debridement, the wounds were covered with rbFGF/ACS and then bound up with sterile gauze in the rbFGF/ACS group (n = 30), or bound up with petrolatum sterile gauze in the placebo group (n = 28). The complete closure of the wounds was assessed by photography. The wounds that failed to heal were defined as incomplete healing after 3 weeks. Compared with the placebo group, rbFGF/ACS significantly increased the incidence of complete wound closure by 68% (90.0% versus 53.6%, P = 0.0019) after 3 weeks and shortened the time to achieve complete wound closure by 24% (10.6 days versus 13.9 days, P = 0.0171). There was no difference in side effects between the two groups. rbFGF/ACS significantly increased the incidence of complete wound closure, shortened the complete healing time and improved the healing quality of chronic traumatic ulcers. The safety profile in the rbFGF/ACS group was similar to that in placebo group.

New insights into and novel applications for platelet-rich fibrin therapies

The therapeutic use of autologous platelet-rich plasma constitutes a relatively new biotechnology that has been a breakthrough in the stimulation and acceleration of soft-tissue and bone healing. The efficiency of this process lies in the local and continuous delivery of a wide range of growth factors and proteins, mimicking the needs of the physiological wound healing and reparative tissue processes. Consequently, the application of platelet-rich plasma has been extended to many different fields, including orthopedics, sports medicine, dentistry, cosmetic and periodontal medicine and cosmetic, plastic and maxillofacial surgery. This article highlights the use of this technology and discusses some of the obstacles and challenges that need to be addressed to maintain progress in this field.

Inflammation in epithelial skin tumours: old stories and new ideas

The essential contribution of inflammation to tumour development and progression has gained increasing acceptance. For epithelial skin cancer, the observation that tumours arise in sites of chronic irritation and inflammation dates back to 1828 and has stimulated a whole field of research. Chemically-induced mouse skin tumours requiring inflammatory agents such as 12-O-tetradecanoylphorbol 13-acetate (TPA) for tumour-promotion have greatly contributed to our understanding of multi-stage carcinogenesis and have given important insights into the functional interaction between inflammatory micro-environment and epithelial tumour, especially when used in combination with transgenic animals. Data from these and additional new model systems clearly emphasise that the tumour-promoting micro-environment is indispensable for tumour formation and progression. It strongly resembles the wound and is largely orchestrated by inflammatory cells allowing tumour cells to co-opt signalling molecules of the innate immune system to promote their growth, invasion and metastasis. Consequently, anti-inflammatory drugs are of great clinical interest in prevention and treatment of epithelial skin cancers.

Tissue regeneration using macrophage migration inhibitory factor-impregnated gelatin microbeads in cutaneous wounds

Migration inhibitory factor (MIF) responds to tissue damage and regulates inflammatory and immunological processes. To elucidate the function of MIF in cutaneous wound healing, we analyzed MIF knockout (KO) mice. After the excision of wounds from the dorsal skin of MIF KO and wild-type (WT) mice, healing was significantly delayed in MIF KO mice compared to WT mice. Lipopolysaccharide treatment significantly increased [(3)H]thymidine uptake in WT mouse fibroblasts compared to MIF KO mouse fibroblasts. Furthermore, there was a significant reduction in fibroblast and keratinocyte migration observed in MIF KO mice after 1-oleoyl-2-lysophosphatidic acid treatment. We subsequently examined whether MIF-impregnated gelatin slow-release microbeads could accelerate skin wound healing. Injection of more than 1.5 microg/500 microl of MIF-impregnated gelatin microbeads around a wound edge accelerated wound healing compared to a single MIF injection without the use of microbeads. MIF-impregnated gelatin microbeads also accelerated skin wound healing in C57BL/6 mice and diabetic db/db mice. Furthermore, incorporating MIF-impregnated gelatin microbeads into an artificial dermis implanted into MIF KO mice accelerated procollagen production and capillary formation. These findings suggest that MIF is crucial in accelerating cutaneous wound healing and that MIF-impregnated gelatin microbeads represent a promising treatment to facilitate skin wound healing.

Macrophage migration inhibitory factor: a central regulator of wound healing

Age-associated differences in estrogen levels critically modify the cutaneous wound healing response. Using a microarray-based approach, we profiled changes in gene expression within the wounds of mice that were wild type or null for the pro-inflammatory cytokine macrophage migration inhibitory factor (MIF) in the presence or absence of estrogen. This experimental design identified more than 600 differentially expressed genes and established MIF as a key player in the wound healing process, regulating many novel repair/inflammation-associated gene targets. Moreover, MIF affected virtually all of the effects of reduced estrogen on wound repair. In humans, serum and wound levels of MIF increased with age and were strongly down-regulated by estrogen in vivo. Estrogen-regulated MIF transcription in vitro via a nuclear factor kappaB-dependent mechanism. These findings have wide-ranging implications for the many pathophysiological states in which MIF plays an important regulatory role and suggest a potential therapeutic role for MIF in modulating clinical conditions associated with age-related decline in estrogen levels.

The suppressor of cytokine signaling-3 is upregulated in impaired skin repair: implications for keratinocyte proliferation

In this study, we determined regulation and function of the suppressor of cytokine signaling (SOCS)-3 in acute and impaired murine skin repair. Upon skin injury, SOCS-3 was induced and expressed during the inflammatory phase of repair. SOCS-3 protein expression was localized in a subset of non-proliferating keratinocytes within the developing wound margin epithelia. Growth factors (EGF, transforming growth factor-alpha), nitric oxide (NO), and pro-inflammatory cytokines were inducers of SOCS-3 mRNA and protein expression in cultured human (HaCaT) and primary murine keratinocytes. Stable overexpression of SOCS-3 in HaCaT keratinocytes interfered with cytokine-induced signal transducers and activators of transcription-3 phosphorylation and inhibited serum-stimulated proliferation of the cells. Moreover, overexpression of SOCS-3 led to final differentiation of keratinocytes, which was comparable to the Ca(2+)-induced differentiation process in the cells. Finally, we determined SOCS-3 expression in two models of impaired skin repair: NO-deficient and diabetic wound healing. In line with observations from normal repair and SOCS-3 overexpression experiments, reduced keratinocyte proliferation within atrophied neo-epithelia in both models of impaired healing was associated with a marked increase in SOCS-3-expressing wound keratinocytes. In summary, this study suggests a potential novel function of SOCS-3 in regulating keratinocyte proliferation and differentiation in vitro and during skin repair in vivo.

Emerging new drugs for wound repair

Every year, millions of people experience burns, suffer from nonhealing wounds, or have acute wounds that become complicated by infection, dehiscence or problematic scarring. Effective wound treatment requires carefully considered interventions often requiring multiple clinic or hospital visits. The resulting costs of wound care are staggering, and more efficacious and cost-effective therapies are needed to decrease this burden. Unfortunately, the expenses and difficulties encountered in performing clinical trials have led to a relatively slow growth of new treatment options for the wound management. Research efforts attempting to examine wound pathophysiology have been hampered by the lack of an adequate chronic wound healing model, and the complexity of the wound healing cascade has limited attempts at pharmacological modification. As such, currently available wound healing therapies are only partially effective. Therefore, many new therapies are emerging that target various aspects of wound repair and the promise of new therapeutic interventions is on the immediate horizon.

Induction of vascular endothelial growth factor messenger ribonucleic acid expression in stored micrografts by aminoguanidine

BACKGROUND AND OBJECTIVES

Aminoguanidine (AMG) has been found to inhibit apoptotic cell death in hair follicle micrografts and improves the viability of isolated micrografts during the storage period in hair restoration surgery. In this study, we investigated the effect of AMG on messenger ribonucleic acid (mRNA) synthesis of growth factors in stored micrografts and primary cultures of follicle-derived cell populations.

METHOD

Hair follicles were obtained from 10 different patients undergoing routine micrograft transplant and were stored for 5 hours at room temperature in phosphate-buffered saline containing different concentrations of AMG. After a culture period of 72 hours, quantitative changes of mRNA for basic fibroblast growth factor (bFGF), insulin-like growth factor 1 (IGF-1), and vascular endothelial growth factor (VEGF) were determined by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Primary cell cultures of dermal papilla and outer root sheath cells were stimulated for 72 hours with AMG followed by RT-PCR measurement of growth factor mRNA.

RESULTS

A dose-dependent induction of VEGF mRNA could be demonstrated in stored micrografts after stimulation with AMG (unstimulated: 1.0 [0.7-2.2]; AMG 10 pg/mL: 5.6 [3.1-9.7], p < .05; AMG 50 pg/mL: 6.9 [5.7-10.0], p < .05; AMG 100 microg/mL: 17.1 [14.1-22.3], p < .001). Expression of bFGF mRNA and IGF-1 mRNA levels was not influenced by AMG stimulation. Stimulation of cultured dermal papilla and outer root sheath cells demonstrated 14-fold induction of VEGF mRNA by AMG in outer root sheath cells (unstimulated: 1.0 [0.8-1.4]; AMG 100 pg/mL: 14.0 [12.5-16.1], p < .01), and no changes in VEGF mRNA levels were detected in dermal papilla cells.

CONCLUSIONS

Our study demonstrated induction of VEGF mRNA in stored micrografts by AMG. Although the clinical relevance in post-transplant hair growth and wound healing needs further evaluation, the possibility of actively influencing growth factor production in isolated micrografts during the storage period is the basis for the development of hair follicle growth-promoting storage solutions in the future.

Factors affecting soft tissue around dental implants: a review of the literature

Much of the focus in the early dental implant literature is on the bone-to-titanium interface because a successful osseointegrated implant requires direct bone contact to the implant surface. The research on soft tissue around dental implants has focused on the partially edentulous patient and, in particular, on the maxillary anterior dentition. Few studies have evaluated soft tissue around dental implants in completely edentulous patients over time. This paper reviews the pertinent literature on soft-tissue healing in both partially and completely edentulous dental implant patients from a Medline search of the English peer-reviewed literature from 1980 to 2004.

Uterine dehiscence in term pregnant patients with one previous cesarean delivery: growth factor immunoexpression and collagen content in the scarred lower uterine segment

OBJECTIVE

This study aimed at investigating the relationship between the occurrence of uterine dehiscence in term pregnant scarred uteri and the presence of altered biochemical behavior of the scarring process.

STUDY DESIGN

Collagen content and the expression of transforming growth factor-beta and its isoforms transforming growth factor-beta1 and transforming growth factor-beta3, connective tissue growth factor, basic fibroblast growth factor, vascular endothelial growth factor, platelet-derived growth factor, and tumor necrosis factor-alpha in myometrium of lower uterine segment were assessed in 19 otherwise healthy term patients with one previous cesarean delivery who were not in labor. We were searching for differences between patients who showed uterine dehiscence (9 cases) and patients who showed a normal-appearing scarred lower uterine segment (10 cases). We also evaluated all these features in lower uterine segment from unscarred uteri of 10 otherwise healthy patients who were not in labor.

RESULTS

In the case of uterine dehiscence, the scarred lower uterine segment showed a higher collagen content, a reduction of pan transforming growth factor-beta expression because of a marked decrease or absence of transforming growth factor-beta3, a reduction of connective tissue growth factor, an increase in basic fibroblast growth factor and a slight enhancement in vascular endothelial growth factor, platelet-derived growth factor, and tumor necrosis factor-alpha expression.

CONCLUSION

These findings contribute to meliorate our knowledge about uterine scar healing and allow us to hypothesize that uterine dehiscence of a scarred uterus may be related to altered biochemical behavior of the scarring process.

Skin cell isolation and expansion for cell transplantation is limited in patients using tobacco, alcohol, or are exhibiting diabetes mellitus

The aim of this exploratory study was to investigate the isolation and expansion of keratinocytes and fibroblasts from donors with certain medical histories. Biopsies were taken from donors (N=32) falling into one or more of the following categories: a history of heavy smoking and/or alcohol abuse, drug abuse, diabetes mellitus or steroid treatment. Cells from donors who did not fall into any of the above-mentioned categories were used as controls. Proliferation and growth behaviour of cells were analyzed by measurement of passage duration, absorbance (MTT-assay) and light microscopy. Donors with a specific medical history required larger biopsy areas than the control group for isolating a sufficient number of fibroblasts and keratinocytes. Times to confluence were significantly prolonged and absorbances (MTT) were significantly reduced in several donor groups when compared to control cultures. Biopsies from donors with steroid treatment, drug abuse and combined nicotine and alcohol abuse could not be established beyond passage 0 degrees or 1 degree, respectively. We conclude that isolation and expansion of skin cells from donors with certain medical histories may require larger biopsies, prolonged expansion times or may even result in failure. These findings may therefore be of clinical importance in the field of autologous skin cell transplantation.

Targeting matrix metalloproteases to improve cutaneous wound healing

Wound repair is a physiological event in which tissue injury initiates a repair process leading to restoration of structure and function of the tissue. Cutaneous wound repair can be divided into a series of overlapping phases including formation of fibrin clot, inflammatory response, granulation tissue formation incorporating re-epithelialisation and angiogenesis and finally, matrix formation and remodelling. Matrix metalloproteases (MMPs) are a family of neutral proteases that play a vital role throughout the entire wound healing process. They regulate inflammation, degrade the extracellular matrix (ECM) to facilitate the migration of cells and remodel the new ECM. However, excessive MMP activity contributes to the development of chronic wounds. Selective control of MMP activity may prove to be a valuable therapeutic approach to promote healing of chronic ulcers. Recent evidence indicates that the anticoagulant, activated protein C may be useful in the treatment of non-healing wounds by preventing excessive protease activity through inhibition of inflammation and selectively increasing MMP-2 activity to enhance angiogenesis and re-epithelialisation.

Focal adhesion size controls tension-dependent recruitment of alpha-smooth muscle actin to stress fibers

Expression of α-smooth muscle actin (α-SMA) renders fibroblasts highly contractile and hallmarks myofibroblast differentiation. We identify α-SMA as a mechanosensitive protein that is recruited to stress fibers under high tension. Generation of this threshold tension requires the anchoring of stress fibers at sites of 8–30-μm-long “supermature” focal adhesions (suFAs), which exert a stress approximately fourfold higher (∼12 nN/μm²) on micropatterned deformable substrates than 2–6-μm-long classical FAs. Inhibition of suFA formation by growing myofibroblasts on substrates with a compliance of ≤11 kPa and on rigid micropatterns of 6-μm-long classical FA islets confines α-SMA to the cytosol. Reincorporation of α-SMA into stress fibers is established by stretching 6-μm-long classical FAs to 8.1-μm-long suFA islets on extendable membranes; the same stretch producing 5.4-μm-long classical FAs from initially 4-μm-long islets is without effect. We propose that the different molecular composition and higher phosphorylation of FAs on supermature islets, compared with FAs on classical islets, accounts for higher stress resistance.

A novel “sandwich” assay for quantifying chemo-regulated cell migration within 3-dimensional matrices: Wound healing cytokines exhibit distinct motogenic activities compared to the transmembrane assay

The extracellular matrix profoundly affects cellular response to soluble motogens. In view of this critical aspect of matrix functionality, we have developed a novel assay to quantify chemo-regulated cell migration within biologically relevant 3-dimensional matrices. In this "sandwich" assay, target cells are plated at the interface between an upper and lower matrix compartment, either in the presence of an isotropic (uniform) or anisotropic (gradient) spatial distribution of test motogen. Cell migration in response to the different conditions is ascertained by quantifying their subsequent disposition within the upper and lower matrix compartments. The objective of this study has been to compare the motogenic activities of platelet-derived growth factor (PDGF-AB) and transforming growth factor-beta isoforms (TGF-beta1, -beta2 and -beta3) in the sandwich assay and the commonly employed transmembrane assay. As previously reported, dermal fibroblasts exhibited a motogenic response to isotropic and anisotropic distributions of all tested cytokines in the transmembrane assay. In contrast, only PDGF-AB and TGF-beta3 were active in the sandwich assay, each eliciting directionally unbiased (symmetrical) migration into the upper and lower type I collagen matrices in response to an isotropic cytokine distribution and a directionally biased response to an anisotropic distribution. TGF-beta1 and -beta2 were completely devoid of motogenic activity. These results are consistent with the reported differential bioactivities of PDGF and TGF-beta3 compared to TGF-beta1 and -beta2 in animal models of wound healing and suggest that the sandwich assay provides a means of obtaining physiologically relevant data regarding chemo-regulated cell migration.

Stress and wound healing

Over the past decade it has become clear that stress can significantly slow wound healing: stressors ranging in magnitude and duration impair healing in humans and animals. For example, in humans, the chronic stress of caregiving as well as the relatively brief stress of academic examinations impedes healing. Similarly, restraint stress slows healing in mice. The interactive effects of glucocorticoids (e.g. cortisol and corticosterone) and proinflammatory cytokines [e.g. interleukin-1beta (IL-1beta), IL-1alpha, IL-6, IL-8, and tumor necrosis factor-alpha] are primary physiological mechanisms underlying the stress and healing connection. The effects of stress on healing have important implications in the context of surgery and naturally occurring wounds, particularly among at-risk and chronically ill populations. In research with clinical populations, greater attention to measurement of health behaviors is needed to better separate behavioral versus direct physiological effects of stress on healing. Recent evidence suggests that interventions designed to reduce stress and its concomitants (e.g., exercise, social support) can prevent stress-induced impairments in healing. Moreover, specific physiological mechanisms are associated with certain types of interventions. In future research, an increased focus on mechanisms will help to more clearly elucidate pathways linking stress and healing processes.

Ribozymes and siRnas: from structure to preclinical applications

The discovery that nucleic acids mediated the inhibition of gene expression in a sequence-specific manner has provided the scientific community with a potentially important tool to analyse gene function and validate drug targets. Selective inhibition of gene expression by ribozymes and small interfering RNAs (siRNAs) is being explored for potential therapeutics against viral infections, inflammatory disorders, haematological diseases and cancer. In order to be used as pharmaceutical drugs, chemical modifications are necessary to increase their stability in vivo. However, such modifications should not affect either the ribozyme cleavage activity or the incorporation of the siRNAs into the RNA interference (RNAi) targeting complex and subsequent mRNA cleavage. To attain stability, ribozymes and siRNAs must also overcome several other problems, including accessibility to target messenger RNAs (mRNAs), efficient delivery to target cells and unwanted non-specific effects.

Modulation of cutaneous wound healing by ozone: Differences between young and aged mice

Cutaneous tissues are frequently exposed to prooxidative environments, including UV radiation and air pollutants. Among the latter, ozone (O(3)) is of particular concern because of its high and dominating presence in photochemical smog. It is well known that O(3) depletes small molecular weight antioxidants, oxidizes proteins, induces lipid peroxidation and activates cellular responses in various tissues. Using an in vivo model (SKH-1 hairless mice), the interaction between O(3) exposure (0.5ppmx6h/day) and age was examined in relation to cutaneous wound healing. Compared to younger (8 weeks) mice, older (18 months) mice exposed to O(3) (day 0 to day 9 after wounding) exhibited delayed wound closure, increased lipid peroxidation (measured as 4-HNE protein adducts) and protein oxidation (measured as carbonyls concentration) and decreased levels of P-IkappaBalpha and TGFbeta protein. These findings support the hypothesis that oxidant pollutant exposure and age interact so as to disrupt normal wound healing processes.

The Effect of AgK114 on Wound Healing

AgK114 is a newly isolated membrane-associated protein which is expressed on keratinocytes. Its expression is restricted to dermal sheath cells near sebaceous glands in normal skin. However, it is transiently induced by UV exposure or injury stimulation (Tatefuji T. et al., Biol. Pharm. Bull., 27, 1742-1749, 2004). Thus, the expression pattern of AgK114 suggested its potential role in wound healing response. We report here that expression of AgK114 is induced in the initial 24 h at the edge keratinocytes during keratinocyte migration, followed by disappearance once epithelialization is completed in the murine excisional wound model. We also demonstrate that exogenous recombinant mouse AgK114FL promoted wound healing process. Mouse AgK114FL up-regulated pro-matrix-metalloproteinase-9, vascular endothelial growth factor, transforming growth factor-beta, IL-6, and IL-1beta production in the early stage of wound tissue. Moreover, mouse AgK114FL induced the matrix-metalloproteinase-9 activity of wound fibroblasts prepared from impaired skin in the presence of proinflammatory cytokines. These results suggest that the AgK114 participates in the wound response during the healing process, and promotes wound repair.

In vitro and in vivo protein sampling by combined microdialysis and ultrafiltration

Cytokines, chemokines and growth factors regulate inflammation, resistance to infection and tissue repair. Understanding their function within tissues is a priority in evolving therapy for a number of disease processes. Yet, the existence of complex networks of these factors in the tissue microenvironment has made understanding of their interactions difficult. We demonstrate the capability of microdialysis probes to recover small proteins efficiently in vitro. Further we show that microdialysis of human tissues allows for protein recovery from tissue interstitial fluid. This technology, combined with a multiplexed immunoassay, facilitates the simultaneous measurement of cytokines and chemokines in response to injury in the oral mucosa of human subjects in vivo.

Peroxisome proliferator-activated receptor-beta as a target for wound healing drugs

Healing of cutaneous wounds, which is crucial for survival after an injury, proceeds via a well-tuned pattern of events including inflammation, re-epithelialisation, and matrix and tissue remodelling. These events are regulated spatio-temporally by a variety of growth factors and cytokines. The inflammation that immediately follows injury increases the expression of peroxisome proliferator-activated receptor (PPAR)-beta in the wound edge keratinocytes and triggers the production of endogenous PPARbeta ligands that activate the newly produced receptor. This elevated PPARbeta activity results in increased resistance of the keratinocytes to the apoptotic signals released during wounding, allowing faster re-epithelialisation. The authors speculate that, in parallel, ligand activation of PPARbeta in infiltrated macrophages attenuates the inflammatory response, which also promotes repair. Thus, current understanding of the roles of PPARbeta in different cell types implicated in tissue repair has revealed an intriguing intercellular cross-talk that coordinates, spatially and temporally, inflammation, keratinocyte survival, proliferation and migration, which are all essential for efficient wound repair. These novel insights into the orchestrating roles of PPARbeta during wound healing may be helpful in the development of drugs for acute and chronic wound disorders.