From scarless fetal wounds to keloids: Molecular studies in wound healing

Genetic influence on scar vascularity after burn injury in individuals of European ancestry: A prospective cohort study

After burn injury there is considerable variation in scar outcome, partially due to genetic factors. Scar vascularity is one characteristic that varies between individuals, and this study aimed to identify genetic variants contributing to different scar vascularity outcomes. An exome-wide array association study and gene pathway analysis was performed on a prospective cohort of 665 patients of European ancestry treated for burn injury, using their scar vascularity (SV) sub-score, part of the modified Vancouver Scar Scale (mVSS), as an outcome measure. DNA was genotyped using the Infinium HumanCoreExome-24 BeadChip, imputed to the Haplotype Reference Consortium panel. Associations between genetic variants (single nucleotide polymorphisms) and SV were estimated using an additive genetic model adjusting for sex, age, % total body surface area and number of surgical procedures, utilising linear and multinomial logistic regression. No individual genetic variants achieved the cut-off threshold for significance. Gene sets were also analysed using the Functional Mapping and Annotation (FUMA) platform, in which biological processes indirectly related to angiogenesis were significantly represented. This study suggests that SNPs in genes associated with angiogenesis may influence SV, but further studies with larger datasets are essential to validate these findings.

Insights into the role of adipose-derived stem cells and secretome: potential biology and clinical applications in hypertrophic scarring

Scar tissue is the inevitable result of repairing human skin after it has been subjected to external destructive stimuli. It leads to localized damage to the appearance of the skin, accompanied by symptoms such as itching and pain, which reduces the quality of life of the patient and causes serious medical burdens. With the continuous development of economy and society, there is an increasing demand for beauty. People are looking forward to a safer and more effective method to eliminate pathological scarring. In recent years, adipose-derived stem cells (ADSCs) have received increasing attention from researchers. It can effectively improve pathological scarring by mediating inflammation, regulating fibroblast proliferation and activation, and vascular reconstruction. This review focuses on the pathophysiological mechanisms of hypertrophic scarring, summarizing the therapeutic effects of in vitro, in vivo, and clinical studies on the therapeutic effects of ADSCs in the field of hypertrophic scarring prevention and treatment, the latest application techniques, such as cell-free therapies utilizing ADSCs, and discussing the advantages and limitations of ADSCs. Through this review, we hope to further understand the characterization of ADSC and clarify the effectiveness of its application in hypertrophic scarring treatment, so as to provide clinical guidance.

The transcriptional profile of keloidal Schwann cells

Recently, a specific Schwann cell type with profibrotic and tissue regenerative properties that contributes to keloid formation has been identified. In the present study, we reanalyzed published single-cell RNA sequencing (scRNA-seq) studies of keloids, healthy skin, and normal scars to reliably determine the specific gene expression profile of keloid-specific Schwann cell types in more detail. We were able to confirm the presence of the repair-like, profibrotic Schwann cell type in the datasets of all three studies and identified a specific gene-set for these Schwann cells. In contrast to keloids, in normal scars, the number of Schwann cells was not increased, nor was their gene expression profile distinctly different from that of Schwann cells of normal skin. In addition, our bioinformatics analysis provided evidence for a role of transcription factors of the AP1, STAT, and KLF families, and members of the IER genes in the dedifferentiation process of keloidal Schwann cells. Together, our analysis strengthens the role of the profibrotic Schwann cell type in the formation of keloids. Knowledge of the exact gene expression profile of these Schwann cells will facilitate their identification in other organs and diseases.

Telomerized fibroblasts as a candidate 3d in vitro model of pathological hypertrophic scars

The search for the optimal cell model for studying the pathogenesis of pathological scars is a pressing challenge. This study aimed at evaluating the feasibility of using telomerized fibroblasts for the in vitro 3D modeling of pathological hypertrophic scars. NF and Fb-hTERT cells were cultured as monolayers and spheroids in the absence and in the presence of TGFβ1. The metabolic activity of the cultured cells was assessed using the MTT assay. Cell migration was estimated using the scratch assay. The expression of genes associated with fibrous scar tissue growth was measured by qRT-PCR. Fb-hTERT cells were more metabolically active than NF cells in the presence of TGFβ1 (for 1 ng/ml: 179 ± 12% vs. 135 ± 13% respectively; p < 0,05). Spheroids grown from Fb-hTERT cells were significantly larger than those derived from NF cells. In the presence of TGFβ1, the expression of proteins associated with extracellular matrix production (COL1A1, COL3A1, FN1) was lower in Fb-hTERT cells than in NF cells (more than 25, 20 and 2-fold, respectively; p < 0.05). Intact NF cells were more active in closing the scratch than Fb-hTERT cells: on day 2, the gap closure rate was 2.28 times higher in NF cells (p < 0.05). Exposure to TGFβ1 stimulated Fb-hTERT, unlike NF cells, to close the gap 2 times faster on day 2 (p < 0.05). Thus, telomerized fibroblasts have a few phenotypic traits observed in keloid fibroblasts; still there are some limitations that should be accounted for when using Fb-hTERT cells for the modeling of pathological hypertrophic scars.

The Keloid Disorder: Heterogeneity, Histopathology, Mechanisms and Models

Keloids constitute an abnormal fibroproliferative wound healing response in which raised scar tissue grows excessively and invasively beyond the original wound borders. This review provides a comprehensive overview of several important themes in keloid research: namely keloid histopathology, heterogeneity, pathogenesis, and model systems. Although keloidal collagen versus nodules and α-SMA-immunoreactivity have been considered pathognomonic for keloids versus hypertrophic scars, conflicting results have been reported which will be discussed together with other histopathological keloid characteristics. Importantly, histopathological keloid abnormalities are also present in the keloid epidermis. Heterogeneity between and within keloids exists which is often not considered when interpreting results and may explain discrepancies between studies. At least two distinct keloid phenotypes exist, the superficial-spreading/flat keloids and the bulging/raised keloids. Within keloids, the periphery is often seen as the actively growing margin compared to the more quiescent center, although the opposite has also been reported. Interestingly, the normal skin directly surrounding keloids also shows partial keloid characteristics. Keloids are most likely to occur after an inciting stimulus such as (minor and disproportionate) dermal injury or an inflammatory process (environmental factors) at a keloid-prone anatomical site (topological factors) in a genetically predisposed individual (patient-related factors). The specific cellular abnormalities these various patient, topological and environmental factors generate to ultimately result in keloid scar formation are discussed. Existing keloid models can largely be divided into in vivo and in vitro systems including a number of subdivisions: human/animal, explant/culture, homotypic/heterotypic culture, direct/indirect co-culture, and 3D/monolayer culture. As skin physiology, immunology and wound healing is markedly different in animals and since keloids are exclusive to humans, there is a need for relevant human in vitro models. Of these, the direct co-culture systems that generate full thickness keloid equivalents appear the most promising and will be key to further advance keloid research on its pathogenesis and thereby ultimately advance keloid treatment. Finally, the recent change in keloid nomenclature will be discussed, which has moved away from identifying keloids solely as abnormal scars with a purely cosmetic association toward understanding keloids for the fibroproliferative disorder that they are.

Monocytes co-cultured with reconstructed keloid and normal skin models skew towards M2 macrophage phenotype

Several abnormalities have been reported in the peripheral blood mononuclear cells of keloid-forming patients and particularly in the monocyte cell fraction. The goal of this in vitro study was to determine whether monocytes from keloid-prone patients contribute to the keloid phenotype in early developing keloids, and whether monocyte differentiation is affected by the keloid microenvironment. Therefore, keloid-derived keratinocytes and fibroblasts were used to reconstruct a full thickness, human, in vitro keloid scar model. The reconstructed keloid was co-cultured with monocytes from keloid-forming patients and compared to reconstructed normal skin co-cultured with monocytes from non-keloid-formers. The reconstructed keloid showed increased contraction, dermal thickness (trend) and α-SMA+ staining, but co-culture with monocytes did not further enhance the keloid phenotype. After 2-week culture, all monocytes switched from a CD11c^high/CD14^high/CD68^low to a CD11c^high/CD14^low/CD68^high phenotype. However, only monocytes co-cultured with either reconstructed keloid scar or normal skin models skewed towards the more fibrotic M2-macrophage phenotype. There was negligible fibroblast and fibrocyte differentiation in mono- and co-cultured monocytes. These results indicate that monocytes differentiate into M2 macrophages when in the vicinity of early regenerating and repairing tissue, independent of whether the individual is prone to normal or keloid scar formation.

Reconstructed human keloid models show heterogeneity within keloid scars

Keloid scars are often described as having an actively growing peripheral margin with a regressing centre. The aim of this study was to examine the possible heterogeneity within keloids and the involvement of different regions within and around keloid scars in the pathogenesis, using an in vitro keloid scar model. In vitro skin models were constructed from keratinocytes and fibroblasts from normal skin and different regions within and around keloid scars: periphery, centre, and (adjacent) surrounding-normal-skin regions. Additionally, fibroblasts were isolated from the superficial-central and deep-central regions of the keloid and combined with central keratinocytes. All keloid regions showed increased contraction compared to normal skin models, particularly in central regions. Myofibroblasts were present in all keloid regions but were more abundant in models containing central-deep keloid fibroblasts. Secretion of anti-fibrotic HGF and extracellular matrix collagen IV gene expression was reduced in the central deep keloid compared to normal skin. No significant differences between peripheral and central regions within keloids were observed for inflammatory cytokine CCL20, CCL27, CXCL8, IL-6 and IL-18 secretion. Parameters for surrounding-normal-skin showed similarities to both non-lesional normal skin and keloids. In conclusion, a simple but elegant method of culturing keloid-derived keratinocytes and fibroblasts in an organotypic 3D scar model was developed, for the dual purpose of studying the underlying pathology and ultimately testing new therapeutics. In this study, these tissue engineered scar models show that the central keloid region shows a more aggressive keloid scar phenotype than the periphery and that the surrounding-normal-skin also shares certain abnormalities characteristic for keloids.

Stem Cell-Based Therapeutics to Improve Wound Healing

Issues surrounding wound healing have garnered deep scientific interest as well as booming financial markets invested in novel wound therapies. Much progress has been made in the field, but it is unsurprising to find that recent successes reveal new challenges to be addressed. With regard to wound healing, large tissue deficits, recalcitrant wounds, and pathological scar formation remain but a few of our most pressing challenges. Stem cell-based therapies have been heralded as a promising means by which to surpass current limitations in wound management. The wide differentiation potential of stem cells allows for the possibility of restoring lost or damaged tissue, while their ability to immunomodulate the wound bed from afar suggests that their clinical applications need not be restricted to direct tissue formation. The clinical utility of stem cells has been demonstrated across dozens of clinical trials in chronic wound therapy, but there is hope that other aspects of wound care will inherit similar benefit. Scientific inquiry into stem cell-based wound therapy abounds in research labs around the world. While their clinical applications remain in their infancy, the heavy investment in their potential makes it a worthwhile subject to review for plastic surgeons, in terms of both their current and future applications.

2ME2 increase radiation-induced apoptosis of keloid fibroblasts by targeting HIF-1α in vitro

BACKGROUND

Radiation therapy is considered to be a treatment for keloid scarring; however, radioresistance has been shown to be a serious impediment to treatment efficacy. There is therefore a need for the discovery of novel critical molecular targets whose inhibition might enhance the radiotherapeutic response. An elevated level of hypoxia inducible factor (HIF)-1α expression after radiation therapy in keloid fibroblasts has been demonstrated in our recent experiments. Therefore, we suggested there was a possible close relationship between HIF-1α and keloid radioresistance. The current study aimed to investigate whether target HIF-1α may enhance the radiotherapeutic efficacy of keloids.

METHODS

2-methoxyestradiol (2ME2) was applied to inhibit HIF-1α expression, and the treatment results were assessed by cell proliferation, apoptosis and radiosensitivity. A lentivirus-mediated small interfering RNA (siRNA) transduction method was used to block the expression of HIF-1α gene.

RESULTS

Both mRNA and protein levels can be effectively inhibited after the knockdown of HIF-1α, leading to a significant increase of radiation-induced apoptosis in keloid fibroblasts. Our experiment also demonstrated that 2ME2 could effectively inhibit the protein expression of HIF-1α, which significantly increased the late stage of radiation-induced apoptosis of keloid fibroblasts.

CONCLUSIONS

The present study indicates that HIF-1α might serve as a therapeutic target for keloids. Furthermore, suppression of HIF-1α by 2ME2 may be a promising therapeutic adjuvant in radiation therapy for keloids.

Molecular signalings in keloid disease and current therapeutic approaches from natural based compounds

CONTEXT

Keloid is an excessive dermal scar occurring in response to skin injuries. Several therapeutic strategies have been proposed to ease the aggressiveness of keloid scarring. Even though the principle mechanism underlying the disease propagation still remains unidentified, several signaling pathways were highly focused as plausible pathways involving keloid formation, including transforming growth factor-beta 1 (TGF-β1), mitogen-activated protein kinase (MAPK), insulin-like growth factor-I (IGF-I), and integrin pathways. Natural compounds containing multiple bioeffective properties such as quercetin, asiaticoside, Astragalus membranaceus Bunge. (Leguminosae), and Salvia miltiorrhiza Bunge. (Lamiaceae) extracts, curcuminoids, oxymatrine, madecassoside, and Aneilema keisak Hassk. (Commelinaceae) are claimed as candidates for therapeutic treatment against keloid disorder.

OBJECTIVE

This review investigates current mechanisms regarding keloid formation and provides scientific evidence supporting the therapeutic potential of natural compounds.

METHODS

This review obtained and analyzed a number of literature data items from various databases including Pubmed, ScienceDirect, and Elton B. Stephens Company (EBSCO).

RESULT

Several phytochemical compounds are able to suppress keloid scar development through manipulating various components in the complex signaling cascades.

CONCLUSION

The present review may be helpful to future studies that further examine the molecular mechanism of keloid etiology as well as investigate the anti-keloid property in natural compounds.

Phenotypic and functional modulation of 20-30 year old dermal fibroblasts by mid- and late-gestational keratinocytes in vitro

Fetal wound healing occurs rapidly and without scar formation early in gestation, but the mechanisms underlying this scarless healing are poorly understood. This study explores the phenotypic and functional modulation of 20-30 year old dermal fibroblasts by mid- and late-gestational keratinocytes (KCs) in vitro. Human KCs of different gestational ages were isolated, characterized, and co-cultured with human 20-30 year old fibroblasts. Gene expression and protein levels of TGF-β family members, precollagen, collagen, matrix metalloproteinases (MMPs), and the tissue inhibitors of metalloproteinases (TIMPs) were measured in the fibroblasts. Mid-gestational KCs promoted faster proliferation and migration of fibroblasts than late-gestational KCs. Additionally, significant differences in gene expression and protein levels of some markers were observed in fibroblasts co-cultured with mid- or late-gestational KCs. Fibroblasts co-cultured with mid-gestational KCs for 48 h exhibited downregulated gene expression of precollagen 1, collagen 1, TGF-β1, TGF-β2, TIMP-2 and TIMP-3, while precollagen 3, collagen 3, TGF-β3, and MMP-1, -2, -3, -9 and -14 were upregulated. In contrast, late-gestational KCs exhibited downregulated TIMP-1, TIMP-2 and TIMP-3 levels, while collagen 1, TGF-β2, TGF-β3, and MMP-2, -3, -9 and -14 were upregulated. Moreover, statistically significant differences in expression levels of precollagen 1, precollagen 3, collagen 1, TGF-β1, -β2, and -β3, MMP-1, -3 and MMP-14, TIMP-1 and TIMP-2 were found between fibroblasts co-cultured with mid- and late-gestational KCs. Furthermore, cytokine levels of IL-1a and HB-EGF were found to be statistically different between conditioned medium from mid- and late-gestational KCs. Therefore, the gestational age of KCs appears to have an important effect on scarless wound healing in the human fetus.

A two-component pre-seeded dermal-epidermal scaffold

We have developed a bilayered dermal-epidermal scaffold for application in the treatment of full-thickness skin defects. The dermal component gels in situ and adapts to the lesion shape, delivering human dermal fibroblasts in a matrix of fibrin and cross-linked hyaluronic acid modified with a cell adhesion-promoting peptide. Fibroblasts were able to form a tridimensional matrix due to material features such as tailored mechanical properties, presence of protease-degradable elements and cell-binding ligands. The epidermal component is a robust membrane containing cross-linked hyaluronic acid and poly-l-lysine, on which keratinocytes were able to attach and to form a monolayer. Amine-aldehyde bonding at the interface between the two components allows the formation of a tightly bound composite scaffold. Both parts of the scaffold were designed to provide cell-type-specific cues to allow for cell proliferation and form a construct that mimics the skin environment.

Spray-assisted layer-by-layer assembly on hyaluronic acid scaffolds for skin tissue engineering

Tissue engineering approaches for the development of a single epidermal-dermal scaffold to treat full-thickness skin defects have been limited by difficulties in the fabrication of a bilayer scaffold combining the specific properties of the epidermis and the dermis. Here we present an innovative approach to developing a scaffold that holds promise for skin tissue engineering. We utilize the spray-assisted layer-by-layer assembly technique to deposit a polyelectrolyte multilayer film composed of hyaluronic acid and poly-L-lysine (the epidermal component) on a porous hyaluronic acid scaffold (the dermal component), in a rapid and controlled manner. The multilayer film promotes cell adhesion, contributing to regeneration of the epidermal barrier functions of skin. While human keratinocytes attached and proliferated on the coated porous scaffolds, they did not invade the porous dermal component, thus leaving room for seeding of relevant fibroblast cell types in this scaffold. This scaffold therefore holds promise for co-culture of different cells, which may be useful for treatment of full-thickness skin defects as well as other tissue engineering applications.

Dermal templates and the wound-healing paradigm: the promise of tissue regeneration

Dermal regeneration templates arguably represent the first and most clinically successful 'tissue engineering' solution designed for organ reconstruction. Wound healing in the skin normally occurs on a continuum. At one extreme of the continuum lies the promise of tissue regeneration and the complete restoration of normal structure and function. Unfortunately, in the adult, all too often, wound healing occurs at the other extreme of the continuum and the dermis is reconstituted as scar tissue. Dermal regeneration templates are designed to manage the wound-healing process and tip the scales toward regeneration. This review discusses the architecture and molecular composition of the skin and the events that mediate wound healing and scar formation. The development, evolution and commercialization of dermal templates are examined and the clinical and business considerations that drive the product-development cycle are discussed. In the near term, dermal templates cannot be expected to dramatically change in overall composition. Product development will be dominated by continued refinements of existing templates and the field of use will continue to expand as manufacturers seek to increase revenue and capture market share. Continued exploration of novel processing strategies, such as electrospinning, that can be used to fabricate nanoscale biomaterials, may provide a gateway to the next generation of dermal templates.

Fetal fibroblasts and keratinocytes with immunosuppressive properties for allogeneic cell-based wound therapy

Fetal skin heals rapidly without scar formation early in gestation, conferring to fetal skin cells a high and unique potential for tissue regeneration and scar management. In this study, we investigated the possibility of using fetal fibroblasts and keratinocytes to stimulate wound repair and regeneration for further allogeneic cell-based therapy development. From a single fetal skin sample, two clinical batches of keratinocytes and fibroblasts were manufactured and characterized. Tolerogenic properties of the fetal cells were investigated by allogeneic PBMC proliferation tests. In addition, the potential advantage of fibroblasts/keratinocytes co-application for wound healing stimulation has been examined in co-culture experiments with in vitro scratch assays and a multiplex cytokines array system. Based on keratin 14 and prolyl-4-hydroxylase expression analyses, purity of both clinical batches was found to be above 98% and neither melanocytes nor Langerhans cells could be detected. Both cell types demonstrated strong immunosuppressive properties as shown by the dramatic decrease in allogeneic PBMC proliferation when co-cultured with fibroblasts and/or keratinocytes. We further showed that the indoleamine 2,3 dioxygenase (IDO) activity is required for the immunoregulatory activity of fetal skin cells. Co-cultures experiments have also revealed that fibroblasts-keratinocytes interactions strongly enhanced fetal cells secretion of HGF, GM-CSF, IL-8 and to a lesser extent VEGF-A. Accordingly, in the in vitro scratch assays the fetal fibroblasts and keratinocytes co-culture accelerated the scratch closure compared to fibroblast or keratinocyte mono-cultures. In conclusion, our data suggest that the combination of fetal keratinocytes and fibroblasts could be of particular interest for the development of a new allogeneic skin substitute with immunomodulatory activity, acting as a reservoir for wound healing growth factors.

Phenotypical differences in connective tissue cells emerging from microvascular pericytes in response to overexpression of PDGF-B and TGF-β1 in normal skin in vivo

Fibrosis is a deleterious consequence of chronic inflammation in a number of human pathologies ultimately leading to organ dysfunction and failure. Two growth factors that are important in blood vessel physiology and tissue fibrosis, platelet-derived growth factor (PDGF)-B and transforming growth factor (TGF)-β1, were investigated. Adenoviral vectors were used to induce transient overexpression of these growth factors in mouse skin. Changes in tissue structure and protein and mRNA expressions were investigated. Both PDGF-B and TGF-β1 could initiate but neither could sustain angiogenesis. Instead, vascular regression was observed. Overexpression of both TGF-β1 and PDGF-B led to a marked macrophage influx and an expansion of the connective tissue cell population. Over time, this effect was sustained in mice treated with TGF-β1, whereas it was partially reversible in mice treated with PDGF-B. On the basis of structure and expression of phenotypical markers, the emerging connective tissue cell population may originate from microvascular pericytes. TGF-β1 induced expansion of connective tissue cells with a myofibroblast phenotype, whereas PDGF-B induced a fibroblast phenotype negative for α-smooth muscle actin. TGF-β1 and PDGF-B overexpressions mediated distinct effects on mRNA transcript levels of fibrillar procollagens, their modifying enzymes, small leucin-rich repeat proteoglycans, and matricellular proteins affecting both the composition and the quantity of the extracellular matrix. This study offers new insight into the effects of PDGF-B and TGF-β1 on the vasculature and connective tissue in vivo.

Dynamics of angiogenesis during wound healing: a coupled in vivo and in silico study

OBJECTIVE

The most critical determinant of restoration of tissue structure during wound healing is the re-establishment of a functional vasculature, which largely occurs via angiogenesis, specifically endothelial sprouting from the pre-existing vasculature.

MATERIALS AND METHODS

We used confocal microscopy to capture sequential images of perfused vascular segments within the injured panniculus carnosus muscle in the mouse dorsal skin-fold window chamber to quantify a range of microcirculatory parameters during the first nine days of healing. This data was used to inform a mathematical model of sequential growth of the vascular plexus. The modeling framework mirrored the experimental circular wound domain and incorporated capillary sprouting and endothelial cell (EC) sensing of vascular endothelial growth factor gradients.

RESULTS

Wound areas, vessel densities and vessel junction densities obtained from the corresponding virtual wound were in excellent agreement both temporally and spatially with data measured during the in vivo healing process. Moreover, by perturbing the proliferative ability of ECs in the mathematical model, this leads to a severe reduction in vascular growth and poor healing. Quantitative measures from this second set of simulations were found to correlate extremely well with experimental data obtained from animals treated with an agent that targets endothelial proliferation (TNP-470).

CONCLUSION

Our direct combination and comparison of in vivo longitudinal analysis (over time in the same animal) and mathematical modeling employed in this study establishes a useful new paradigm. The virtual wound created in this study can be used to investigate a wide range of experimental hypotheses associated with wound healing, including disorders characterized by aberrant angiogenesis (e.g., diabetic models) and the effects of vascular enhancing/disrupting agents or therapeutic interventions such as hyperbaric oxygen.

Keloid formation after syndactyly release in patients with associated macrodactyly: management with methotrexate therapy

We present a series of cases of keloid formation after release of syndactyly in the hands and feet of children with associated digital overgrowth. The use of methotrexate to suppress keloid formation after release of syndactyly and for control of recurrence after surgery for keloid is effective.

Combination of stromal cell-derived factor-1 and collagen-glycosaminoglycan scaffold delays contraction and accelerates reepithelialization of dermal wounds in wild-type mice

While dermal substitutes can mitigate scarring and wound contraction, a significant drawback of current dermal replacement technologies is the apparent delay in vascular ingrowth compared with conventional skin grafts. Herein, we examined the effect of the chemokine stromal cell-derived factor-1 (SDF-1) on the performance of a porous collagen-glycosaminoglycan dermal analog in excisional wounds in mice. C57BL/6 mice with 1 cm × 1 cm dorsal full-thickness wounds were covered with a collagen-glycosaminoglycan scaffold, followed by four daily topical applications of 1 μg SDF-1 or phosphate-buffered saline vehicle. Some animals were also pretreated with five daily doses of 300 mg/kg granulocyte colony-stimulating factor. Animals treated with SDF-1 and no granulocyte colony-stimulating factor reepithelialized 36% faster than vehicle controls (16 vs. 25 days), and exhibited less wound contraction on postwounding day 18 (∼ 35% greater wound area) plus three-fold longer neoepidermis formed than controls. Conversely, granulocyte colony-stimulating factor promoted contraction and no epidermal regeneration. Early (postwounding Day 3) inflammatory cell infiltration in the SDF-1-treated group was 86% less, while the fraction of proliferating cells (positive Ki67 staining) was 32% more, when compared with controls. These results suggest that SDF-1 simultaneously delays contraction and promotes reepithelialization and may improve the wound-healing performance of skin substitutes.

Strategies for prevention of scars: what can we learn from fetal skin?

Fetal wound healing occurs rapidly and without scar formation early in gestation. Studying the mechanisms of scarless repair can lead to novel scar-preventive approaches. In fetal wounds, collagen is deposited early and is fine and reticular with less cross-linking. Several important differences of fetal vs. postgestational wound-healing response have been determined, such as the presence of less inflammation, higher hyaluronic acid concentration and a greater ratio of collagen type III to type I. Compared with typical wounds, there are also altered ratios of signaling molecules, such as higher ratios of transforming growth factor (TGF)-β3 to TGF-β1 and -β2, and matrix metalloproteinases to tissue inhibitors of metalloproteinases. Furthermore, fetal fibroblasts do not exhibit TGF-β1-induced collagen production compared with their mature counterparts. Patterning genes (homeobox genes) involved in organogenesis are more active in the fetal period and are believed to be the "first domino" in the fetal cutaneous wound repair regulatory cascade. The recommended scar-preventive agents, such as Scarguard MD®, silicone gel and sheet, Seprafilm® Bioresorbable Membrane, topical hyaluronan, onion extract, oral tamoxifen and 585-nm pulsed dye laser are reviewed in this study. Despite the lack of supporting evidence, there is a widespread false presumption that the acceleration of healing with the widely assumed scar-preventive commercial agents is associated with decreased scar formation. Humans are erroneously inclined to make a negative correlation between the healing rate and the degree of scar formation, while such a correlation does not exist in reality. Despite the importance of scar prevention, no FDA-approved therapy for this purpose is available in the 21st century, which reflects the important challenges, such as the presence of redundant pathways, that these approaches are facing.

Role of vascular endothelial growth factor in keloids: a clinicopathologic study

BACKGROUND

Despite their benign nature, keloids are usually associated with considerable cosmetic effects and may lead to functional problems. Recently, it has been reported that vascular endothelial growth factor (VEGF), a potent angiogenic factor, is overexpressed in keloid tissue and may have a potential role in its evolution.

METHODS

Twenty patients with keloids were included in this study and classified into two groups according to the treatment received: intralesional triamcinolone acetonide 20 mg/mL (group 1) and cryotherapy spray technique (group 2). Treatment was continued until clearance or for a maximum of six sessions, and the follow-up period was 1 year. Skin biopsies were taken from patients before and after treatment to evaluate keloid pathology and from patients and 10 healthy controls to detect the immunohistochemical expression of VEGF.

RESULTS

Histopathologic examination revealed a remarkable resolution of the nodular arrangement of collagen after therapy, particularly in group 1. A statistically significant difference in VEGF expression was found between patients before therapy and controls, and between patients before and after therapy in each group. There was no significant difference in the treatment outcome between intralesional steroids and cryotherapy. No significant correlation was observed between the clinical variables of keloids and both VEGF expression and clinical response to therapy.

CONCLUSION

VEGF seems to play an important role in the pathogenesis of keloids and may be a useful guide in the evaluation of keloid therapeutics. Modulation of its production may provide a valuable treatment for keloids.

Molecular dissection of abnormal wound healing processes resulting in keloid disease

Keloids are locally aggressive scars that typically invade into healthy surrounding skin and cause both physical and psychosocial distress to the patient. These pathological scars occur following minimal skin trauma after a variety of causes including burns and trauma. Although the pathogenesis of keloid disease is not well understood, it is considered to be the end product of an abnormal healing process. The aim of this review was to investigate the molecular and cellular pathobiology of keloid disease in relation to the normal wound healing process. The molecular aberrances in keloids that correlate with the molecular mechanisms in normal wound healing can be categorized into three groups: (1) extracellular matrix proteins and their degradation, (2) cytokines and growth factors, and (3) apoptotic pathways. With respect to cellular involvements, fibroblasts are the most well-studied cell population. However, it is unclear whether the fibroblast is the causative cell; they are modulated by other cell populations in wound repair, such as keratinocytes and macrophages. This review presents a detailed account of individual phases of the healing process and how they may potentially be implicated in aberrant raised scar formation, which may help in clarifying the mechanisms involved in keloid disease pathogenesis.

Inhibition of HSP27 phosphorylation by a cell-permeant MAPKAP Kinase 2 inhibitor

Heat shock protein 27 (HSP27) has been implicated in many intracellular signaling processes. Since the phosphorylation of HSP27 can modulate its activity, the ability to inhibit phosphorylation of HSP27 might have clinical relevance especially with regard to the treatment of fibrosis. We have developed a cell-permeant peptide inhibitor of MAPKAP Kinase 2 (MK2), an enzyme that phosphorylates HSP27, by combining a previously described peptide substrate of MK2 with a cell penetrating peptide. This novel MK2 inhibitor (MK2i) reduced HSP27 phosphorylation by MK2 in vitro. At 10 microM, MK2i inhibited TGF-beta1-induced HSP27 phosphorylation in serum-starved human keloid fibroblasts. In addition, 10 microM MK2i decreased TGF-beta1-induced expression of connective tissue growth factor and collagen type I within serum-starved keloid fibroblasts. Thus, MK2i represents a potential therapeutic for the treatment of fibrotic disorders.

Integrin alpha1beta1 is involved in the differentiation into myofibroblasts in adult reactive tissues in vivo

Connective tissue cell activation is of importance during reactive conditions such as solid tumour growth, wound healing and pannus formation in rheumatoid arthritis. Here, we have compared connective tissue cells of mesenchymal origin in human tissues from these conditions and their normal counterparts using a panel of cell-type-specific markers. In particular, we investigated variations of integrin expression among connective tissue cell phenotypes. Connective tissue cell populations were defined based on their association with the microvasculature and their expression of activation markers. The phenotype of these cells varied according to the type of pathological connective tissue examined. Our morphological data from human tissues suggested that the alpha(1)beta(1) integrin, a collagen/laminin receptor, is involved in the differentiation of precursor cells into myofibroblasts. To mechanistically investigate this hypothesis, we employed experimental models for carcinoma growth and wound healing utilizing alpha(1) integrin-deficient mice. The data confirmed that the alpha(1)beta(1) integrin is of importance not only for the differentiation of mesenchymal cells into myofibroblasts but also for the neovascularization and connective tissue organization and emphasize the importance of myofibroblasts in the pathophysiology of tissue repair, inflammation and tumour growth.

Chronic wound healing by fetal cell therapy may be explained by differential gene profiling observed in fetal versus old skin cells

Engineering of fetal tissue has a high potential for the treatment of acute and chronic wounds of the skin in humans as these cells have high expansion capacity under simple culture conditions and one organ donation can produce Master Cell Banks which can fabricate over 900 million biological bandages (9 x 12cm). In a Phase 1 clinical safety study, cases are presented for the treatment of therapy resistant leg ulcers. All eight patients, representing 13 ulcers, tolerated multiple treatments with fetal biological bandages showing no negative secondary effects and repair processes similar to that seen in 3rd degree burns. Differential gene profiling using Affymetrix gene chips (analyzing 12,500 genes) were accomplished on these banked fetal dermal skin cells compared to banked dermal skin cells of an aged donor in order to point to potential indicators of wound healing. Families of genes involved in cell adhesion and extracellular matrix, cell cycle, cellular signaling, development and immune response show significant differences in regulation between banked fetal and those from banked old skin cells: with approximately 47.0% of genes over-expressed in fetal fibroblasts. It is perhaps these differences which contribute to efficient tissue repair seen in the clinic with fetal cell therapy.

Cell permeant peptide analogues of the small heat shock protein, HSP20, reduce TGF-beta1-induced CTGF expression in keloid fibroblasts

A growing body of evidence suggests the involvement of connective tissue growth factor (CTGF) in the development and maintenance of fibrosis and excessive scarring. As the expression of this protein requires an intact actin cytoskeleton, disruption of the cytoskeleton represents an attractive strategy to decrease CTGF expression and, consequently, excessive scarring. The small heat-shock-related protein (HSP20), when phosphorylated by cyclic nucleotide signaling cascades, displaces phospho-cofilin from the 14-3-3 scaffolding protein leading to activation of cofilin as an actin-depolymerizing protein. In the present study, we evaluated the effect of AZX100, a phosphopeptide analogue of HSP20, on transforming growth factor-beta-1 (TGF-beta1)-induced CTGF and collagen expression in human keloid fibroblasts. We also examined the effect of AZX100 on scar formation in vivo in dermal wounds in a Siberian hamster model. AZX100 decreased the expression of CTGF and type I collagen induced by TGF-beta1, endothelin, and lysophosphatidic acid. Treatment with AZX100 decreased stress fiber formation and altered the morphology of human dermal keloid fibroblasts. In vivo, AZX100 significantly improved collagen organization in a Siberian hamster scarring model. Taken together, these results suggest the potential use of AZX100 as a strategy to prevent excessive scarring and fibrotic disorders.

Fetal wound healing using a genetically modified murine model: the contribution of P-selectin

PURPOSE

During early gestation, fetal wounds heal with paucity of inflammation and absent scar formation. P-selectin is an adhesion molecule that is important for leukocyte recruitment to injury sites. We used a murine fetal wound healing model to study the specific contribution of P-selectin to scarless wound repair.

METHODS

Linear excisional wounds were created on the dorsa of E15.5 and E17.5 gestation fetuses in wild-type and P-selectin (-/-) mice (term = 19 days). Wounds were harvested at various time-points after wounding and analyzed using histology and immunohistochemistry.

RESULTS

The E15.5 wounds in both wild-type and P-selectin (-/-) fetuses healed scarlessly and with minimal inflammation, whereas E17.5 wounds healed with fibrosis and inflammation. However, the scars of the P-selectin (-/-) wounds appeared slightly different than wild-type. There were significantly more inflammatory cells in E17.5 wild-type wounds 6 hours after injury (P < .001), but the difference was no longer significant by 24 hours. Finally, reepithelialization was slower in the E15.5 knockout wounds compared to their wild-type counterparts.

CONCLUSIONS

Absence of P-selectin delays inflammatory cell recruitment and reepithelialization of fetal wounds; however, scar formation still occurs in late gestation wounds. The contribution of specific molecules to fetal wound healing can be elucidated using murine knockout or transgenic models.

Favorable Tissue Effects of Quantum Molecular Resonance Device (Vesalius®) Compared with Standard Electrocautery

BACKGROUND

Electrosurgical devices are largely employed in thoracic surgery but their use is burdened by extensive necrosis and second intention healing.

METHODS

A rat model of thoracotomy was performed on 46 adult male rats using a standard electrocautery or a new quantum molecular resonance (QMR) instrument called Vesalius. Skin, muscle and lung specimens were obtained immediately and 2 weeks after surgery to evaluate acute and late effects.

RESULTS

Both in the short- and long-term study, Vesalius produced less severe tissue damage than that of standard electrocautery.

CONCLUSIONS

The use of the QMR device may provide an alternative to gold-standard electrosurgical devices in thoracic surgery.

Progress and potential for regenerative medicine

Regenerative medicine focuses on new therapies to replace or restore lost, damaged, or aging cells in the human body to restore function. This goal is being realized by collaborative efforts in nonmammalian and human development, stem cell biology, genetics, materials science, bioengineering, and tissue engineering. At present, understanding existing reparative processes in humans and exploring the latent ability to regenerate tissue remains the focus in this field. This review covers recent work in limb regeneration, fetal wound healing, stem cell biology, somatic nuclear transfer, and tissue engineering as a foundation for developing new clinical therapies to augment and stimulate human regeneration.

Profiling of genes differentially expressed in a rat of early and later gestational ages with high-density oligonucleotide DNA array

The early gestational fetus heals dermal wounds rapidly and scarlessly. This phenomenon appears to be intrinsic to fetal skin and is probably modulated by interplay of many genes. We ventured to study differences in gene expression between earlier gestational skin (EGS) and later gestational skin (LGS) with the aid of high-density oligonucleotide DNA array to explore the molecular mechanism underlying scarless healing. Total RNA was isolated from fetal Wistar rat skin of the scarless (E15) and scar-forming (E18) periods of gestation (term=21.5 days), and purified to mRNAs. Both the mRNAs from EGS and LGS were reversely transcribed to cDNAs, and were labeled with the incorporation of fluorescent dCTP for preparing the hybridization probes through single primer amplification reaction and Klenow labeling methods. The mixed probes were then hybridized to the oligonucleotide DNA arrays that contained 5,705 DNA fragments representing 5,705 rat genes. After highly stringent washing, the microarray was scanned for fluorescent signals to display the differentially expressed genes between two groups of tissues. Among 5,705 rat genes, there were 53 genes (0.93%) with differentially expressed levels between EGS and LGS; 27 genes, including fibroblast growth factor 8 and follistatin, were up-regulated (0.47%); and 26 genes, containing lymphoid enhancer binding factor-1 and beta-catenin, were down-regulated (0.46%) in fetal skin of scarless period vs. scar-forming period. Analyses of genes related to ion channels, growth factors, extracellular matrix and cellular skeleton, and movement confirmed that our molecular data obtained by oligonucleotide DNA array were consistent with the published biochemical and clinical findings of fetal scarless healing. Stronger expression of fibroblast growth factor 8, follistatin, and weaker expression of lymphoid enhancer binding factor-1 and beta-catenin in EGS vs. LGS were also testified with reverse transcription-polymerase chain reaction and Western blotting methods. Oligonucleotide DNA array was a powerful tool for investigating different gene expression between scarless and scar-forming periods of gestation in the rat fetal skin. Many genes were involved in the phenotypic transition from scarless to scar-forming wound repair during gestation. Further analysis of the obtained genes will help to understand the molecular mechanism of fetal scarless healing.

Non-epithelial oral mucosal progenitor cell populations

This review considers the potential existence and role of stem or progenitor cell populations within the non-epithelial tissues of the oral mucosa. Currently, there is little published evidence supporting this hypothesis; however, because of the similarities in structure and function of the oral mucosa and skin, findings within the dermis of the skin may potentially reflect the situation within the oral mucosa. Over recent years, the identification of the skin as a local reservoir of adult stem cell populations and the idea that multipotent cell populations exist within the dermal tissues of skin has gained increasing credibility. Indeed, numerous multipotent progenitor cells have been identified within the dermis and resident appendages, all capable of differentiating into multiple cell lineages. Furthermore, a number of these cell populations have been implicated in the repair of these tissues following injury. There is increasing evidence suggesting that such populations of progenitor cells may also reside within the lamina propria. In this respect, the ability to isolate large numbers of multipotent progenitor cells from a tissue which when biopsied heals without a scar would be of great interest scientifically and commercially, particularly with respect to future therapeutic applications and the developing discipline of tissue engineering.

Emerging new drugs for scar reduction

Hypertropic and keloid scars cause both functional and cosmetic problems for those afflicted. Although people of all ages suffer from these conditions, the patients are often young and otherwise healthy, and become burdened with an activity limiting lesion or psychosocial stresses associated with a perceived aesthetic defect. Currently available treatment modalities are often inconvenient, occasionally painful, and have unwanted side effects. Despite the highest standard of care, treatment protocols are prone to failure with high rates of scar recurrence. Hypertropic and keloid scars are the result of an abnormal healing response and may result from an extended inflammatory phase in the wound healing process. Regardless of the causes, which remain elusive, excessive collagen deposition occurs relative to normal wounds. This extracellular matrix collagen accumulation makes a logical target for pharmacological interventions, and researchers are attempting to modify collagen-synthetic and -degradative pathways. In addition, growth factors and cytokines have been implicated in scar formation, and these factors are targeted for potential therapeutic use in scar management. Cytotoxic agents are also being evaluated for their potential utility in the reduction of tissue bulk associated with these excessive scar states. Given the wide range of potential therapeutic agents, the future market for scar therapy remains highly promising.

Principles and therapeutic implications of angiogenesis, vasculogenesis and arteriogenesis

The vasculature is the first organ to arise during development. Blood vessels run through virtually every organ in the body (except the avascular cornea and the cartilage), assuring metabolic homeostasis by supplying oxygen and nutrients and removing waste products. Not surprisingly therefore, vessels are critical for organ growth in the embryo and for repair of wounded tissue in the adult. Notably, however, an imbalance in angiogenesis (the growth of blood vessels) contributes to the pathogenesis of numerous malignant, inflammatory, ischaemic, infectious and immune disorders. During the last two decades, an explosive interest in angiogenesis research has generated the necessary insights to develop the first clinically approved anti-angiogenic agents for cancer and blindness. This novel treatment is likely to change the face of medicine in the next decade, as over 500 million people worldwide are estimated to benefit from pro- or anti-angiogenesis treatment. In this following chapter, we discuss general key angiogenic mechanisms in health and disease, and highlight recent developments and perspectives of anti-angiogenic therapeutic strategies.

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.

Angiogenesis, vasculogenesis, and induction of healing in chronic wounds

A key central stage of wound healing requires neovascularization of the wound base granulation tissue. In the adult, neovascularization is now known to occur by both angiogenesis and vasculogenesis. Understanding the biology of these 2 processes offers promising new therapeutic options for patients who suffer from chronic, nonhealing ischemic wounds. The authors review the current literature on the processes of angiogenesis and vasculogenesis and how it relates to wound healing.

Stages of wound healing and their clinical relevance

Wound healing describes the host mechanisms involved in the process of restoring the continuity of tissues after injury. Wound healing progresses through a continuum of overlapping stages characterized by macroscopic, microscopic, and biochemical events. An understanding of the relation between these events can enhance clinicians' skills in wound management.

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.

Microdeformational Wound Therapy

The vacuum-assisted closure (VAC) device causes microdeformations of the wound surface in contact with the foam. Because angiogenesis and matrix metalloproteinase (MMP) activity are altered in chronic wounds, we hypothesized that microdeformations stimulate capillary formation and affect MMP activity. A VAC device was used to deliver microdeformational wound therapy (MDWT) to the chronic wounds of 3 debilitated patients. Debrided tissue was obtained from wound areas with and without foam contact. Microvessel density and MMP activity were determined by immunohistochemistry and zymography, respectively. Microvessel density of MDWT-treated wounds was 4.5% (+/-0.8) compared with areas not covered by foam [1.6% (+/-0.1)] (P = 0.05) during the first week of treatment and 2.7% (+/-0.3) compared with untreated tissue [1.3% (+/-0.1)] (P = 0.03) during the second treatment week. Wounds subjected to MDWT had greater microvessel density compared with the same wound prior to treatment [1.5% (+/-0.3)] (P = 0.02). MMP-9/NGAL (neutrophil gelatinase-associated lipocalin), MMP-9, latent MMP-2, and active MMP-2 were reduced by 15%-76% in MDWT-treated wounds. MDWT provides a favorable wound-healing environment by increasing angiogenesis and decreasing MMP activity in chronic wounds.