Scar formation: the spectral nature of fetal and adult wound repair

Avotermin: A Novel Antiscarring Agent

Published literature shows that both physicians and their patients are highly concerned about scarring, even relatively minor scars and those that can be concealed by clothing. Furthermore, both patients and their physicians value any opportunities to improve or minimize scarring. While a range of treatment paradigms have been evaluated, no single therapy has been adopted as a universally accepted standard of care and, currently, there are no marketed pharmaceuticals for the prophylactic reduction of scarring. Many of the available treatments are used empirically and most have not been evaluated in robust prospective, randomized, controlled clinical trials. To address this unmet medical need, translational research into the molecular mechanisms of scarring has led to the discovery and commercial development of a new class of prophylactic medicines that promote the regeneration of normal skin and improve scar appearance. Avotermin, the first agent identified in this class, is the clinical application of human recombinant transforming growth factor β3 (TGFβ3), a key protein involved in scar-free healing observed in embryos. Controlled, double-blind, randomized phase I/II clinical studies have shown that avotermin, administered as an intradermal injection at the time of surgery, leads to both short-term and longer-term (at ≥12 months) improvements in the appearance of scars compared with placebo and standard wound care.

The role of the epidermis in the control of scarring: evidence for mechanism of action for silicone gel

Hypertrophic scars can be reduced by the application of silicone dressing; however, the detailed mechanism of silicone action is still unknown. It is known that silicone gel sheets cause a hydration of the epidermal layer of the skin. An in vitro co-culture experiment has shown that hydration of keratinocytes has a suppressive effect on the metabolism of the underlying fibroblasts resulting in reduced collagen deposition. We tested the hypothesis that silicone sheeting in vivo has a beneficial effect on scarring by reducing keratinocyte stimulation, with a resulting decrease in dermal thickness, hence scar hypertrophy. Silicone adhesive gel sheets were applied to scars in our rabbit ear model of hypertrophic scarring 14 days postwounding for a total of 16 days. Scarring was measured in this model by the scar elevation index (SEI), a ratio of the area of newly formed dermis to the area of the dermis of unwounded skin, and the epidermal thickness index (ETI), a ratio of the averaged epidermal height of the scar to the epidermal thickness of normal epidermis. Specific staining [anti-PCNA (proliferating cell nuclear antigen) and Masson trichrome] was performed to reveal differences in scar morphology. SEIs were significantly reduced after silicone gel sheet application versus untreated scars corresponding to a 70% reduction in scar hypertrophy. Total occlusion reduced scar hypertrophy by 80% compared to semi-occlusion. ETIs of untreated scars were increased by more than 100% compared to uninjured skin. Silicone gel treatment significantly reduced epidermal thickness by more than 30%. Our findings demonstrate that 2 weeks of silicone gel application at a very early onset of scarring reduces dermal and epidermal thickness which appears to be due to a reduction in keratinocyte stimulation. Oxygen can be ruled out as a mechanism of action of silicone occlusive treatment. Hydration of the keratinocytes seems to be the key stimulus.

The hidden cost of skin scars: quality of life after skin scarring

BACKGROUND

Surprisingly little is known about how skin scars affect patients' lives, though specialist clinical impressions suggest their impact is related to both their physical and psychosocial effects. Facial scars have been shown to cause high levels of anxiety and self-consciousness, but further work has been neglected. We aimed to explore the influence of skin scars on patients' quality of life (QoL) and identify potential implications for clinical practice.

METHODS

We adopted a needs-based approach to QoL and conducted semi-structured interviews with scar patients at a specialist clinic. Transcribed data underwent interpretative phenomenological analysis to identify common themes in individuals' personal experiences.

RESULTS

Thirty-four scar patients (24 women; aged 14-70 years, mean=35.7 years, SD=17.9 years) with a wide range of scar type, severity and onset were recruited. Five hundred and seventy-three statements were identified from interview transcripts relating to need impairment by skin scars. These were subsequently classified into 44 themes covering five main areas: physical comfort and functioning; acceptability to self and others; social functioning; confidence in the nature and management of the condition; emotional well-being. The majority of respondents were unhappy with their scar's appearance due to their perceived stigma and psychological associations, and thus adopted different coping behaviours to hide or compensate for them. Often this made them unsociable and interfered with their communication skills, personal relationships, work life and leisure activities. Concerns about the diagnosis and persistent nature of scars were common, whilst unempathic management by general physicians and frustrations of current treatment compounded distress.

CONCLUSIONS

There are five main areas of impact on the needs of scar patients that should be addressed in their management, which are greater and more complex than previously considered. Support services should be made available, along with clinician and public education to improve management and help reduce patient distress. A need for a carefully designed measure of scar-related QoL is also indicated, for use in clinical settings and trials.

High-dose ultraviolet light exposure reduces scar hypertrophy in a rabbit ear model

BACKGROUND

The effects of ultraviolet light exposure on scar pigmentation are well documented. There is a commonly held belief among physicians that sun exposure may also worsen the appearance of fresh scars and result in excess collagen deposition. However, few studies have documented a relationship between ultraviolet light exposure and hypertrophic scarring. This study sought to evaluate the effect of ultraviolet light exposure on scar hypertrophy in an established rabbit model of cutaneous scarring.

METHODS

Four 7-mm ulcers were created on the ventral ears of eight rabbits. Starting on postoperative day 15, half of the wounds were exposed to ultraviolet-B radiation daily for either 7 or 14 days. Ultraviolet-B-exposed (n = 16) and control (n = 16) scars were harvested on postoperative day 32 for histologic and reverse-transcriptase polymerase chain reaction analysis.

RESULTS

Exposure to ultraviolet-B radiation for 7 or 14 days was associated with a 52 percent (p < 0.01) or 74 percent (p < 0.05) reduction in scar volume, respectively, compared with controls. In wounds subjected to ultraviolet-B radiation for 14 days, collagen type I-alpha2 mRNA expression was 29 percent lower than in controls (p < 0.05). There was no difference in the mRNA expression of transforming growth factor-beta1.

CONCLUSION

: These short-term observations demonstrate that ultraviolet-B radiation exposure reduces scar hypertrophy in this clinically relevant animal model. A reduction in collagen production or increase in collagen breakdown may account for this result. However, sunscreen should still be used as primary protection when skin is exposed to direct sunlight.

The biology of hernia formation

Abdominal wall hernias occur when tissue structure and function are lost at the load-bearing muscle, tendon, and fascial layer. The fundamental biologic mechanisms are primary fascial pathology or surgical wound failure. In both cases, cellular and extracellular molecular matrix defects occur. Primary abdominal wall hernias have been associated with extracellular matrix diseases. Incisional hernias and recurrent inguinal hernias more often involve a combination of technical and biologic limitations. Defects in wound healing and extracellular matrix synthesis contribute to the high incidence of incisional hernia formation following laparotomy.

The evolution of robust development and homeostasis in artificial organisms

During embryogenesis, multicellular animals are shaped via cell proliferation, cell rearrangement, and apoptosis. At the end of development, tissue architecture is then maintained through balanced rates of cell proliferation and loss. Here, we take an in silico approach to look for generic systems features of morphogenesis in multicellular animals that arise as a consequence of the evolution of development. Using artificial evolution, we evolved cellular automata-based digital organisms that have distinct embryonic and homeostatic phases of development. Although these evolved organisms use a variety of strategies to maintain their form over time, organisms of different types were all found to rapidly recover from environmental damage in the form of wounds. This regenerative response was most robust in an organism with a stratified tissue-like architecture. An evolutionary analysis revealed that evolution itself contributed to the ability of this organism to maintain its form in the face of genetic and environmental perturbation, confirming the results of previous studies. In addition, the exceptional robustness of this organism to surface injury was found to result from an upward flux of cells, driven in part by cell divisions with a stable niche at the tissue base. Given the general nature of the model, our results lead us to suggest that many of the robust systems properties observed in real organisms, including scar-free wound-healing in well-protected embryos and the layered tissue architecture of regenerating epithelial tissues, may be by-products of the evolution of morphogenesis, rather than the direct result of selection.

During development, multicellular animals are shaped by cell proliferation, cell rearrangement, and cell death to generate an adult whose form is maintained over time. Disruption of this finely balanced state can have devastating consequences, including aging, psoriasis, and cancer. Typically, however, development is robust, so that animals achieve the same final form even when challenged by environmental damage such as wounding. To see how morphogenetic robustness arises, we have taken an in silico approach to evolve digital organisms that exhibit distinct phases of growth and homeostasis. During the homeostasis period, organisms were found to use a variety of strategies to maintain their form. Remarkably, however, all recovered from severe wounds, despite having evolved in the absence of selection pressure to do so. This ability to regenerate was most striking in an organism with a tissue-like architecture, where it was enhanced by a directional flux of cells that drives tissue turnover. This identifies a stratified architecture, like that seen in human skin and gut, as an evolutionarily accessible and robust form of tissue organisation, and suggests that wound-healing may be a general feature of evolved morphogenetic systems. Both may therefore contribute to homeostasis, wound-healing, and regeneration in real animals.

Transforming growth factor-beta1-antisense modulates the expression of hepatocyte growth factor/scatter factor in keloid fibroblast cell culture

Abnormal wound healing processes can result in hypertrophic scars and keloids. Transforming growth factor-beta1 (TGF-beta1) and hepatocyte growth factor/scatter factor (HGF/SF) are biphasic growth factor cytokines in physiologic and pathophysiologic conditions. Findings have shown TGF-beta1 to be pivotal in the formation of keloid tissue. Therefore, neutralizing antibodies may allow wound healing without keloid formation. As reported, TGF-beta1 is antagonized by HGF/SF. Some authors have reported that exogenous administration of HGF/SF prevented scar formation. Hence, this study targeted TGF-beta1 and determined the levels of HGF/SF in fibroblast cell culture. Keloid tissue was taken from seven patients. Another seven patients with mature nonhypertrophic scar served as controls. All tissues were cultured, and fibroblast cultures were used for further experiments. The TGF-beta1 antisense was administered at 3 and 6 micromol/ml, and HGF/SF levels were determined after 16, 24, and 48 h of incubation. The levels of HGF/SF showed significant differences after incubation with antisense oligonucleotides. The increasing antisense levels resulted in increased HGF/SF levels (up to 87.66 pg/ml after 48 h of incubation). In conclusion, targeting TGF-beta1 resulted in significantly increased levels of HGF/SF. The clinical relevance could include the use of locally administered HGF/SF in protein or gene form to minimize formation of keloids. Nevertheless, wound healing is the result of many interacting cytokines, so neutralizing or targeting one protein could result in no significant effect.

Dermal fibroblasts derived from fetal and postnatal humans exhibit distinct responses to insulin like growth factors

Background

It has been well established that human fetuses will heal cutaneous wounds with perfect regeneration. Insulin-like growth factors are pro-fibrotic fibroblast mitogens that have important roles in both adult wound healing and during development, although their relative contribution towards fetal wound healing is currently unknown. We have compared responses to IGF-I and -II in human dermal fibroblast strains derived from early gestational age fetal (<14 weeks) and developmentally mature postnatal skin to identify any differences that might relate to their respective wound healing responses of regeneration or fibrosis.

Results

We have established that the mitogenic response of fetal cells to both IGF-I and -II is much lower than that seen in postnatal dermal fibroblasts. Further, unlike postnatal cells, fetal cells fail to synthesise collagen in response to IGF-I, whereas they do increase synthesis in response to IGF-II. This apparent developmentally regulated difference in response to these related growth factors is also reflected in changes in the tyrosine phosphorylation pattern of a number of proteins. Postnatal cells exhibit a significant increase in phosphorylation of ERK 1 (p44) in response to IGF-I and conversely the p46 isoform of Shc on IGF-II stimulation. Fetal cells however only show a significant increase in an unidentified 100 kDa tyrosine-phosphorylated protein on stimulation with IGF-II.

Conclusion

Dermal fibroblasts exhibit different responses to the two forms of IGF depending on their developmental maturity. This may relate to the developmental transition in cutaneous wound healing from regeneration to fibrosis.

The biology of hernias and the abdominal wall

The fundamental mechanism for hernia formation is loss of the mechanical integrity of abdominal wall structural tissue that results in the inability to offset and contain intra-abdominal forces during valsalva and loading of the torso. There is evidence that genetic or systemic extracellular matrix disorders may predispose patients to hernia formation. There is also evidence that acute laparotomy wound failure leads to hernia formation and increases the risk of recurrent hernia disease. It may be that hernia formation is a heterogeneous disease, not unlike cancer, where one population of patients express an extracellular matrix defect leading to primary hernia disease, while other subsets of patients acquire a defective, chronic wound phenotype following failed laparotomy and hernia repairs. It is evident that an improved understanding of structural tissue matrix biology will lead to improved results following abdominal wall reconstructions.

Regenerative approaches in the craniofacial region: manipulating cellular progenitors for oro-facial repair

This review aims to highlight the potential for regeneration that resides within the bony tissues of the craniofacial region. We examine the five main cues which determine osteogenic differentiation: heritage of the cell, mechanical cues, the influence of the matrix, growth factor stimulation and cell-to-cell contact. We review how successful clinical procedures, such as guided tissue regeneration and distraction osteogenesis exploit this resident ability. We explore the developmental origins of the flat bones of the skull to see how such programmes of differentiation may inform new therapies or regenerative techniques. Finally we compare and contrast existing approaches of hard tissue reconstruction with future approaches inspired by the regenerative medicine philosophy, with particular emphasis on the potential for using chondrocyte-inspired factors and replaceable scaffolds.

Bioengineering skin using mechanisms of regeneration and repair

The development and use of artificial skin in treating acute and chronic wounds has, over the last 30 years, advanced from a scientific concept to a series of commercially viable products. Many important clinical milestones have been reached and the number of artificial skin substitutes licensed for clinical use is growing, but they have yet to replace the current "gold standard" of an autologous skin graft. Currently available skin substitutes often suffer from a range of problems that include poor integration (which in many cases is a direct result of inadequate vascularisation), scarring at the graft margins and a complete lack of differentiated structures. The ultimate goal for skin tissue engineers is to regenerate skin such that the complete structural and functional properties of the wounded area are restored to the levels before injury. New synthetic biomaterials are constantly being developed that may enable control over wound repair and regeneration mechanisms by manipulating cell adhesion, growth and differentiation and biomechanics for optimal tissue development. In this review, the clinical developments in skin bioengineering are discussed, from conception through to the development of clinically viable products. Central to the discussion is the development of the next generation of skin replacement therapy, the success of which is likely to be underpinned with our knowledge of wound repair and regeneration.

Hydrated keratinocytes reduce collagen synthesis by fibroblasts via paracrine mechanisms

Regulating collagen metabolism can control hypertrophic scars in cutaneous wounds. Hypertrophic scars can be reduced by occlusive dressings such as silicone sheeting; however, their mechanism is still unknown. We hypothesized that hydration of keratinocytes reduces the collagen secretion of fibroblasts by modifying the cytokine levels. Stratified human epidermal keratinocytes and confluent human dermal fibroblasts were co-cultured serum free for 72 hours. Keratinocytes were either kept at the air interface or hydrated. Messenger RNA (mRNA) levels of interleukin-1 (IL-1)alpha, IL-1beta, tumor necrosis factor alpha (TNF-alpha), keratinocyte growth factor (KGF), and procollagen-1 were analyzed by real-time reverse transcription-polymerase chain reaction. Secretion of cytokines into conditioned media was quantified by enzyme-linked immunosorbent assay and collagen content by Western blot. The content of collagen-I decreased by 44% in the presence of hydrated keratinocytes. Co-culture with air-treated keratinocytes decreased collagen-I only by 23%. Co-cultured hydrated keratinocytes had significantly higher TNF-alpha mRNA (172%) than hydrated keratinocytes. At the protein level, there was an overall trend toward increased TNF-alpha levels in hydrated cultures. IL-1beta secretion decreased significantly under hydration (42% monoculture, 58% co-culture). Co-culture stimulated a 240% increase of KGF mRNA in fibroblasts compared with monocultured fibroblasts. Fibroblasts secreted 4.5-fold more KGF in hydrated co-cultures and sixfold more KGF in air-treated co-cultures. Hydration of keratinocytes modifies important paracrine interactions between keratinocytes and fibroblasts and reduces collagen-1, which supports the hypothesis that hydration of the epidermis and restoration of water barrier function play an important role in scar formation.

Tissue engineering of replacement skin: the crossroads of biomaterials, wound healing, embryonic development, stem cells and regeneration

Advanced therapies combating acute and chronic skin wounds are likely to be brought about using our knowledge of regenerative medicine coupled with appropriately tissue-engineered skin substitutes. At the present time, there are no models of an artificial skin that completely replicate normal uninjured skin. Natural biopolymers such as collagen and fibronectin have been investigated as potential sources of biomaterial to which cells can attach. The first generation of degradable polymers used in tissue engineering were adapted from other surgical uses and have drawbacks in terms of mechanical and degradation properties. This has led to the development of synthetic degradable gels primarily as a way to deliver cells and/or molecules in situ, the so-called smart matrix technology. Tissue or organ repair is usually accompanied by fibrotic reactions that result in the production of a scar. Certain mammalian tissues, however, have a capacity for complete regeneration without scarring; good examples include embryonic or foetal skin and the ear of the MRL/MpJ mouse. Investigations of these model systems reveal that in order to achieve such complete regeneration, the inflammatory response is altered such that the extent of fibrosis and scarring is diminished. From studies on the limited examples of mammalian regeneration, it may also be possible to exploit such models to further clarify the regenerative process. The challenge is to identify the factors and cytokines expressed during regeneration and incorporate them to create a smart matrix for use in a skin equivalent. Recent advances in the use of DNA microarray and proteomic technology are likely to aid the identification of such molecules. This, coupled with recent advances in non-viral gene delivery and stem cell technologies, may also contribute to novel approaches that would generate a skin replacement whose materials technology was based not only upon intelligent design, but also upon the molecules involved in the process of regeneration.

Regeneration, tissue injury and the immune response

The involvement of the immune system in the response to tissue injury has raised the possibility that it might influence tissue, organ or appendage regeneration following injury. One hypothesis that has been discussed is that inflammatory aspects may preclude the occurrence of regeneration, but there is also evidence for more positive roles of immune components. The vertebrate eye is an immunoprivileged site where inflammatory aspects are inhibited by several immunomodulatory mechanisms. In various newt species the ocular tissues such as the lens are regenerative and it has recently been shown that the response to local injury of the lens involves activation of antigen-presenting cells which traffic to the spleen and return to displace and engulf the lens, thereby inducing regeneration from the dorsal iris. The activation of thrombin from prothrombin in the dorsal iris is one aspect of the injury response that is important in the initiation of regeneration. The possible relationships between the immune response and the regenerative response are considered with respect to phylogenetic variation of regeneration in general, and lens regeneration in particular.

Scarring occurs at a critical depth of skin injury: precise measurement in a graduated dermal scratch in human volunteers

BACKGROUND

The association between scarring and the depth of dermal injury or burn is clinically recognized but not quantified. The authors tested the hypothesis that there is a critical depth beyond which a fibrous scar develops.

METHODS

A novel jig produced a wound that was deep dermal at one end and superficial dermal at the other. Pilot studies in cadaveric and ex vivo breast skin confirmed the depth of injury. Healthy volunteers had a standardized dermal wound made on the lateral aspect of the hip. Digital photography recorded the surface appearance of wound healing and scar development. High-frequency ultrasound demonstrated the depth of the healing wound and subsequent scar in vivo.

RESULTS

One hundred thirteen human subjects participated in the clinical study. Mean length of follow up was 28.6 +/- 13.2 weeks. The deep dermal end of the wound healed with a visible scar and the superficial end had no visible residual mark after week 18. The initial length of injury was 51.3 +/- 0.6 mm, which reduced to a scar of 34.9 +/- 1.0 mm at 36 weeks (corresponding areas were 196.6 +/- 7.5 mm and 92.7 +/- 9.4 mm). High-frequency ultrasound analysis showed a gradual reduction in scar thickness at the deep end and no detectable scar at the shallow end. The transition point between scar and no scar marked the threshold depth for scarring. This was calculated as 0.56 +/- 0.03 mm, or 33.1 percent of normal hip skin thickness.

CONCLUSIONS

The dermal scratch provides a well-tolerated, standardized, and reproducible wound model for investigating the healing response to dermal injury of different depths. There is a threshold depth of dermal injury at which scarring develops.

Visual analogue scale scoring and ranking: a suitable and sensitive method for assessing scar quality?

BACKGROUND

The field of scar assessment lacks a standard methodology. Previous methods have focused on a wide range of scar types, resulting in poorer sensitivity and diminishing their discriminatory effectiveness.

METHODS

As part of a clinical trial investigating the scar-improving efficacy of transforming growth factor-beta3, the authors investigated the use of a visual analogue scale and scar ranking as scar assessment tools. Scar photographic images were assessed using a newly developed computerized scar assessment system by an external lay panel.

RESULTS

A total of 4296 scar images were collected for visual analogue scale assessment and 2148 scar pairs were collected for scar ranking. Intrarater consistency was 100 percent for the ranking data, with differences very close to zero for the visual analogue scale consistency data. Reducing the number of assessors in the external panel significantly improved intraclass correlation coefficients. From month 1 to month 12, the correlation coefficients for the difference in visual analogue scale score showed that the assessors reliably noted the changes in the maturing scars. Combining logistic regression with an area under the curve of 0.72 in a receiver operating characteristic curve analysis, the visual analogue scale score was shown to be a highly statistically significant predictor of a good scar.

CONCLUSIONS

The authors have shown the visual analogue scale scar scoring and scar ranking methods to be consistent, reliable, valid, and feasible. These methods for scar assessment are highly sensitive and capable of reliably measuring differences in scar quality, making them valuable techniques, reaching an unmet clinical need, and enabling investigation of changes in scar quality (e.g., with time or after therapeutic intervention).

Effect of extracts from the Chinese and European mole cricket on wound epithelialization and neovascularization: in vivo studies in the hairless mouse ear wound model

Until the end of World War II, oily extracts from the European mole cricket, Gryllotalpa gryllotalpa Linné, were used for treating nonhealing wounds and burns. In traditional Chinese medicine, extracts from the Chinese mole cricket, Gryllotalpa africana Beauvois, have been used to treat boils, abscesses, and ulcers successfully for over two centuries and are still being used today. The aim of this study was twofold: first, to measure the effect mole cricket extracts have on wound epithelialization and neovascularization, and second, to identify the active compounds in the Chinese and German mole cricket extracts. For the first aim, the hairless mouse ear wound model was used. The findings showed that wounds treated with the mole cricket extracts epithelialized significantly faster than control wounds 12.7+/-0.9 and 13.2+/-1.4 days vs. 16.3+/-2.2 days (mean+/-SD, p<0.05), respectively. While the rate of wound neovascularization was significantly increased in the first 3 days postwounding from that point on, the rate in treated wounds was the same as in controls. To identify the active compounds in the mole cricket extracts, the extracts were fractionated and tested in a foreskin basal keratinocyte cell culture assay. In this assay, the migration of keratinocytes is similar to skin cell migration or reepithelialization in a healing wound. Using this method, we found the active compound in the mole cricket extracts to be linoleic acid methyl ester. All other fatty acid structures that were isolated were found to be inactive.

Ontogeny of expression of transforming growth factor-beta and its receptors and their possible relationship with scarless healing in human fetal skin

Fetal cutaneous wounds that occur in early gestation heal without scar formation. Although much work has been done to characterize the role of transforming growth factor-beta (TGF-beta) isoforms and their receptors in the wound healing process, their roles in scarless wound repair observed in early gestation and their functions in human fetal skin development, and structural and functional maintenance are still not well understood. In this study, we explore the expression and distribution characteristics of three TGF-beta isoforms and their receptors, TGF-betaRI (TBRI) and TGF-betaRII (TBRII), in fetal and postnatal skins to understand the relevance of these five proteins to skin development and elucidate the mechanism(s) underlying the phenotypic transition from scarless to scar-forming healing observed during fetal gestation. Fetal skin biopsies of human embryo were obtained from spontaneous abortions at different gestational ages from 13 to 32 weeks and postnatal skin specimens were collected from patients undergoing plastic surgery. Gene expression and positive immunohistochemical signals of TGF-beta(1), TGF-beta(2), TGF-beta(3), TBRI, and TBRII could all be detected in fetal and postnatal skins. In early gestation, gene expression of TGF-beta(1), TBRI, and TBRII was weaker and protein contents were less compared with postnatal skins (p < 0.05). In contrast, more TGF-beta(2) mRNA transcript was found in early gestation than in late gestation and in postnatal skins, whereas protein content of this growth factor increased during gestation. Lastly, mRNA transcript and protein contents of TGF-beta(3) were apparently higher in early gestation compared to postnatal skin (p < 0.05). In postnatal skin, granules containing the three TGF-beta isoforms were mainly distributed in the cytoplasm and extracellular matrix of epidermal cells, interfollicular keratinocytes, and some fibroblasts. TBRI and TBRII were chiefly located in the cellular membrane of epidermal keratinocytes and some fibroblasts. The endogenous three TGF-beta isoforms and their receptors may be involved in the development of embryonic skin and in the maintenance of cutaneous structure and function, and also in postnatal wound healing. The differential levels of TGF-beta isoforms may provide either a predominantly antiscarring or profibrotic signal upon wounding depending on the gestational period. Lower expression of their receptors in early gestational skins may be a reason for the reduced ability to perceive ligands, ultimately leading to scar-free healing.

Clinical management of skin scarring

Not all scars are the same. They vary from normal skin scars to distinct types of abnormal scars, such as hypertrophic and disfiguring keloids. Physicians need to identify different types of skin scars and treat them appropriately. Misdiagnosis and mismanagement of scars can be costly for both the patient and physician. Patients with scars often face aesthetic, physical, psychological, and social consequences that result in substantial emotional and financial costs. This article reviews the spectrum of abnormal scar types and problems associated with scarring.

Scar-free healing: from embryonic mechanisms to adult therapeutic intervention

In man and domestic animals, scarring in the skin after trauma, surgery, burn or sports injury is a major medical problem, often resulting in adverse aesthetics, loss of function, restriction of tissue movement and/or growth and adverse psychological effects. Current treatments are empirical, unreliable and unpredictable: there are no prescription drugs for the prevention or treatment of dermal scarring. Skin wounds on early mammalian embryos heal perfectly with no scars whereas wounds to adult mammals scar. We investigated the cellular and molecular differences between scar-free healing in embryonic wounds and scar-forming healing in adult wounds. Important differences include the inflammatory response, which in embryonic wounds consists of lower numbers of less differentiated inflammatory cells. This, together with high levels of morphogenetic molecules involved in skin growth and morphogenesis, means that the growth factor profile in a healing embryonic wound is very different from that in an adult wound. Thus, embryonic wounds that heal without a scar have low levels of TGFbeta1 and TGFbeta2, low levels of platelet-derived growth factor and high levels of TGFbeta3. We have experimentally manipulated healing adult wounds in mice, rats and pigs to mimic the scar-free embryonic profile, e.g. neutralizing PDGF, neutralizing TGFbeta1 and TGFbeta2 or adding exogenous TGFbeta3. These experiments result in scar-free wound healing in the adult. Such experiments have allowed the identification of therapeutic targets to which we have developed novel pharmaceutical molecules, which markedly improve or completely prevent scarring during adult wound healing in experimental animals. Some of these new drugs have successfully completed safety and other studies, such that they have entered human clinical trials with approval from the appropriate regulatory authorities. Initial trials involve application of the drug or placebo in a double-blind randomized design, to experimental incision or punch biopsy wounds under the arms of human volunteers. Based on encouraging results from such human volunteer studies, the lead drugs have now entered human patient-based trials e.g. in skin graft donor sites. We consider the evolutionary context of wound healing, scarring and regeneration. We hypothesize that evolutionary pressures have been exerted on intermediate sized, widespread, dirty wounds with considerable tissue damage e.g. bites, bruises and contusions. Modem wounds (e.g. resulting from trauma or surgery) caused by sharp objects and healing in a clean or sterile environment with close tissue apposition are new occurrences, not previously encountered in nature and to which the evolutionary selected wound healing responses are somewhat inappropriate. We also demonstrate that both repair with scarring and regeneration can occur within the same animal, including man, and indeed within the same tissue, thereby suggesting that they share similar mechanisms and regulators. Consequently, by subtly altering the ratio of growth factors present during adult wound healing, we can induce adult wounds to heal perfectly with no scars, with accelerated healing and with no adverse effects, e.g. on wound strength or wound infection rates. This means that scarring may no longer be an inevitable consequence of modem injury or surgery and that a completely new pharmaceutical approach to the prevention of human scarring is now possible. Scarring after injury occurs in many tissues in addition to the skin. Thus scar-improving drugs could have widespread benefits and prevent complications in several tissues, e.g. prevention of blindness after scarring due to eye injury, facilitation of neuronal reconnections in the central and peripheral nervous system by the elimination of glial scarring, restitution of normal gut and reproductive function by preventing strictures and adhesions after injury to the gastrointestinal or reproductive systems, and restoration of locomotor function by preventing scarring in tendons and ligaments.

The scarless heart and the MRL mouse

The ability to regenerate tissues and limbs in its most robust form is seen in many non-mammalian species. The serendipitous discovery that the MRL mouse has a profound capacity for regeneration in some ways rivalling the classic newt and axolotl species raises the possibility that humans, too, may have an innate regenerative ability. The adult MRL mouse regrows cartilage, skin, hair follicles and myocardium with near perfect fidelity and without scarring. This is seen in the ability to close through-and-through ear holes, which are generally used for lifelong identification of mice, and the anatomic and functional recovery of myocardium after a severe cryo-injury. We present histological, biochemical and genetic data indicating that the enhanced breakdown of scar-like tissue may be an underlying factor in the MRL regenerative response. Studies as to the source of the cells in the regenerating MRL tissue are discussed. Such studies appear to support multiple mechanisms for cell replacement.

Differential proliferative response of fetal and adult human skin fibroblasts to transforming growth factor-beta

Since pronounced differences exist between the fetal and adult repair processes, we studied the proliferative response of skin fibroblasts from these two stages to transforming growth factor-beta (TGF-beta), a cytokine with a broad range of activities in tissue repair. Here, we present evidence that TGF-beta inhibits fetal human skin fibroblasts, while it is stimulatory for adult ones. This proliferative effect of TGF-beta was found to be concentration- dependent, but isoform-independent. Furthermore, even a transient exposure of the cells to this growth factor was sufficient to exert its stimulatory or inhibitory action. Accordingly, we have studied the immediate responses provoked by TGF-beta in major signaling pathways, and we have found that it induces a rapid activation of the SMAD pathway, i.e., phosphorylation and nuclear translocation of SMAD2, followed by dephosphorylation, most probably due to degradation by the proteasome. However, similar intensity and kinetics of this activation have been observed in both fetal and adult fibroblasts. On the other hand, curcumin, a natural product with wound healing properties that inhibits several intracellular signaling pathways, was found to completely abrogate the inhibitory effect of TGF-beta1 on human fetal skin fibroblasts, without affecting the stimulatory action on fibroblasts from adult donors. In conclusion, there is a major radical in the proliferative response of fetal and adult human skin fibroblasts to TGF-beta, possibly reflecting the different repair strategies followed in these two stages of development.

Comparison of surgical versus endovascular occlusion models in pig femoral arteries

PURPOSE

To compare an endovascular technique with a well established surgical approach to achieve long-term occlusions of large porcine arteries while preserving the integrity of periarterial tissue.

METHODS

The femoral arteries in 11 pigs were occluded using surgical techniques on one side and blinded stent-grafts in the contralateral vessel. Feasibility, safety, primary and long-term success, and the extent of vascularization were determined over a 3-month period by conventional angiography and histological analysis. A subgroup of animals (n=5) was treated with a locally administered plasmid coding for vascular endothelial growth factor (pVEGF165) to compare both occlusion techniques under conditions of collateral growth induction.

RESULTS

The primary and long-term success rates for both occlusion models were 100%. Surgical occlusion of arteries resulted in a significant amount of scar dehiscence and local groin infection compared to the endograft-occluded side. There was no significant difference in capillary densities and collateralization of periarterial areas in a comparison of the occlusion technique: the cross-sectional area of the superficial femoral artery (SFA) was 300 +/- 24 mm2 for endovascular occlusion versus 320 +/- 23 mm2 for surgical occlusion (p=0.559). In the profunda femoris artery, respective values were 418 +/- 35 and 448 +/- 18 mm2 (p=0.474). The local delivery of pVEGF165 resulted in a significant increase in collateral growth in both occlusion models with comparable neovascularization: cross-sectional SFA area increased from 310 +/- 16 to 428 +/- 13 mm2 (p<0.0001); in the PFA, the area increased from 422 +/- 19 to 658 +/- 49 mm2 (p<0.0001).

CONCLUSIONS

Endovascular arterial occlusions using blinded stent-grafts allow easy and safe creation of long-term occlusions. Previously described collateralization following surgical occlusions was not observed, indicating that those collaterals may be associated with wound healing rather than ischemia. The occlusion of arteries using blinded stent-grafts in pigs may therefore be an appropriate model for assessing the effects of angiogenic factors in vivo.

Three-dimensional hyaluronic acid grafts promote healing and reduce scar formation in skin incision wounds

Hyaluronic acid (HA) has been found to play important roles in tissue regeneration and wound-healing processes. Fetal tissue with a high concentration of HA heals rapidly without scarring. The present study employed HA formed into three-dimensional strands with or without keratinocytes to treat full-thickness skin incision wounds in rats. Wound closure rates of HA strand grafts both with and without keratinocytes were substantially enhanced. The closure times of both HA grafts were less than 1 day (average 16 h), about 1/7 that of the contralateral control incisions (114 h, p <.01). Average wound areas after 10 days were HA-only graft: 0.151 mm2 +/- 0.035; HA + cell grafts: 0.143 mm2 +/- 0.036 and controls: 14.434 mm2 +/- 1.175, experimental areas were 1% of the controls (p < 0.01). Transforming growth factor (TGF) beta1 measured by immunostaining was remarkably reduced in HA-treated wounds compared to the controls. In conclusion, HA grafts appeared to produce a fetal-like environment with reduced TGF-beta1, which is known to be elevated in incipient scars. The HA strands with or without cultured cells may potentially improve clinical wound healing as well as reduce scar formation.

Plasminogen activator/plasmin system: a major player in wound healing?

The role of the plasminogen activator/plasmin system in fibrinolysis has been well established. Indeed, clinicians worldwide have successfully utilized recombinant tissue-type plasminogen activator as first-line treatment of acute myocardial infarction for almost 2 decades. Outside the field of cardiology, there has been increasing excitement regarding the possible contribution of this system in many other important biological processes, including cell adhesion, cell migration, cell-cell signaling, tumor invasion and metastasis, ovulation, and wound healing. In this review, we present evidence in the current literature that the plasminogen activator/plasmin system does have a role in wound healing, looking at both normal and abnormal healing. Furthermore, the invaluable insights provided by numerous transgenic animal experiments are summarized.

Acute wound healing: the biology of acute wound failure

Acute wound healing failure is an important source of morbidity and mortality for surgical patients. Many incisional hernias, gastrointestinal anastomotic leaks, and vascular pseudoaneurysms occur despite patient optimization and standardized surgical technique. Modern surgical experience suggests that biologic and mechanical pathways overlap during "normal" acute wound healing. The cellular and molecular processes activated to repair tissue from the moment of injury are under the control of biologic and mechanical signals. Successful acute wound healing occurs when a dynamic balance is met between the loads placed across a provisional matrix and the feedback and feed-forward responses of repair cells.

Differential effect of wounding on actin and its associated proteins, paxillin and gelsolin, in fetal skin explants

Skin from the embryonic day 17 rat retains the ability to epithelialize an excisional wound when isolated in serum-supplemented suspension culture. This ability is lost by embryonic day 19. We have investigated this effect of gestational age on fetal epithelial wound closure by correlating the involvement of filamentous actin (F-actin) and its associated proteins, paxillin and gelsolin, in the wound margins of embryonic day 17 and 19 rat skins, with the ability to close a full thickness excisional wound. Using fluorescent-phalloidin histochemistry and scanning confocal microscopy, actin polymerization was observed some five to six cells back from the margin of wounds in the embryonic day 17 skin as early as 3 h postwounding. As the wounds closed over the following 48-72 h, the actin further condensed around the epithelial margin before dispersing after wound closure. In contrast, no organization of actin was seen in the epithelial margin of wounds in skin from the embryonic day 19 embryos. Instead, actin filaments were observed surrounding the dermal wound margins. Chemical or mechanical disruption of the actin in wounded embryonic day 17 skins prevented epithelial closure, although wound repair was independent of cell division. In particular, incising the wound margin 24 h after wounding resulted in the "springing-open" of the embryonic day 17 wound but not the embryonic day 19 wound, reflecting the development of tension in the embryonic day 17 wound margin. Expression of paxillin mRNA was upregulated following wounding at embryonic day 17 but not at embryonic day 19. Paxillin was also observed to colocalize with actin in embryonic day 17 wounds, but not embryonic day 19 wounds, indicating a potential role for paxillin in epithelial repair of the fetal wound. In contrast, gelsolin mRNA was upregulated in embryonic day 19 fetal skin but not at embryonic day 17 and gelsolin protein was observed surrounding actin filaments at embryonic day 19 but not embryonic day 17. These results demonstrate a change in the mechanism of wound epithelialization at the same gestational age that fetal wounds change from scar-free to scar-forming wound repair.

Regeneration of the ear after wounding in different mouse strains is dependent on the severity of wound trauma

The replacement and restoration of tissue mass after organ damage or injury in adult higher vertebrates is critical to the architecture and function of the organ. If replacement occurs with scar tissue, this often results in adverse effects on function and growth as well as an undesirable cosmetic appearance. However, certain mammals, such as the MRL/MpJ mouse, have shown a restricted capacity for regeneration, rather than scar tissue formation, after an excisional ear punch wound. To investigate the changes in tissue architecture leading to ear wound closure, initial ear wounding studies with a 2-mm clinical biopsy punch were performed on MRL/MpJ mice, by using C57BL/6 mice as a nonregenerative control strain. In contrast to previously reported studies on mouse ear regeneration, we observed that C57BL/6 mice in fact showed a limited regenerative capacity. One explanation for this difference could be attributed to the method of wounding used; both previous studies on mouse ear regeneration used a thumb punch, whereas our approach was to use a clinical biopsy punch. This approach led us to further investigate whether the severity of trauma applied influenced the rate of wound healing. We, therefore, compared the effects of the sharp clinical biopsy punch with that of a cruder thumb punch, and introduced a third strain of mouse, Balb/c, known to be a slow-healing strain. A new method to quantify ear punch hole closure was developed and a histologic investigation conducted up to 4 months after wounding. Image analysis data showed a reduction in original ear wound area of 85% in MRL/MpJ mice at 4 weeks and of 91.7% over 4 months by using a biopsy punch. In contrast, the crude thumb punch methodology resulted in an increase in wound area of up to 58% in Balb/c ears; thought to be due to increased necrosis of the wound site. All biopsy-punched wound areas plateaued in healing between days 28 and 112. Only 5 of 80 MRL/MpJ mouse ears showed no residual holes macroscopically after 28 days. Histologically, all strains of mice healed their ear wounds in a similar manner involving re-epithelialization, blastema-like formation, dermal extension, blood vessel formation, chondrogenesis, folliculogenesis, and skeletal muscle and fat differentiation. However, all regenerative features were more pronounced and accelerated in MRL/MpJ mice when compared with C57BL/6 and Balb/c biopsy-punched mouse ears.

Vascular endothelial growth factor (VEGF165) and its influence on angiogenesis versus arteriogenesis in different vascular beds

PURPOSE

To use local gene delivery to determine any district-specific influence of vascular endothelial growth factor (VEGF(165)) on angiogenesis and arteriogenesis in arteries of distinct developmental origin.

METHODS

Coronary and peripheral arteries were chronically occluded in 30 Pietrain pigs using a percutaneous approach and blinded stent-graft. DNA was delivered to the adventitia in dosages corresponding to 10% of the body weight-adapted amount used in clinical trials. The coronary arteries in 12 animals and the peripheral arteries in 12 animals were treated or used as controls (no occlusion or occlusion with transfection of the beta-galactosidase gene). Six additional animals were sacrificed at 1 or 3 weeks for expression analyses, while the other 24 animals were sacrificed at 5 months for expression analysis and histology. Angiography, polymerase chain reaction analyses, and immunohistochemistry were performed.

RESULTS

Expression of the VEGF gene was observed at 1 and 3 weeks following application, while transfected DNA was detected up to 5 months. New collaterals formed around occluded coronary arteries (2.63 +/- 0.69 fold, p<0.05 versus 1.24 +/- 0.40 fold for peripheral arteries), and angiographic arterial area increase was more pronounced in coronary (2.49 +/- 0.59 fold, p<0.05) than peripheral arteries (1.49 +/- 0.05 fold). There was no collateralization surrounding occluded peripheral arteries, but new arterial branches were seen (2.0 +/- 0.28, p<0.05 versus 1.07 +/- 0.31 for coronary).

CONCLUSIONS

The response to VEGF, whether it is predominantly angiogenesis or arteriogenesis, is dependent on the target vessel. These observed differences in the behavior of arteries may be related to their differing developmental origins, which may have important implications for future therapeutic strategies using VEGF in different vessels.

Thermal preconditioning prevents peritendinous adhesions and inflammation

Adhesion formation is one of the foremost obstacles to a reliably good outcome in tendon and joint surgery. Thermal preconditioning has been found to reduce the inflammatory response through the induction of molecular chaperone expression, a recently described family of cytoprotective intracellular proteins. The authors analyzed the effect of thermal preconditioning on the inflammatory response to surgery, on tendon healing, and on the formation of peritendinous adhesions in 16 New Zealand White rabbits. Very significant decreases in adhesion formation and in the gliding and dimensions of tendons in animals that had thermal preconditioning were found. Tendons from these animals also showed a decreased level of adhesion formation and a significantly diminished inflammatory response on histologic examination with no biomechanically significant deleterious effect on the strength of tendon healing on testing load to failure. These findings are consistent with induction of heat shock proteins by hyperthermic pretreatment. Such prevention of peritendinous adhesions and the inflammatory response to injury and surgery without compromising healing are findings that have significant implications for tendon surgery and all surgery involving joints and soft tissues.

Differential expression of collagen integrin receptor on fetal vs. adult skin fibroblasts: implication in wound contraction during healing

BACKGROUND

Fetal skin wound healing is characterized by an absence of contraction and scar formation, two important observations associated with adult healing often leading to pathological problems.

OBJECTIVES

We have studied the capacity of adult and fetal human skin fibroblasts to contract collagen gels, collagen being the major structural component of dermal matrix.

METHODS

In parallel with collagen gel contraction studies, we have used fluorescence-activated cell sorter analysis to study the levels of collagen receptors expressed at the surface of fibroblasts derived from fetal or adult skin samples.

RESULTS

Strong differences were detected between freshly isolated fetal and adult fibroblasts. Fetal fibroblasts had a very low capacity to contract collagen gel, whereas adult cells significantly contracted gels in the same conditions. The expression of alpha1, alpha2 and alpha3 integrin subunits was also significantly different depending of the donor age: alpha1 and alpha3 integrin subunit expression was lower in fetal cells compared with adult cells, whereas alpha2 integrin subunit expression was higher. When grown in monolayers, adult cells showed rapid changes in their contractile capacity and integrin expression while fetal cells were only affected after several passages.

CONCLUSIONS

These observations indicate that intrinsic differences between fetal and adult fibroblasts can strongly influence the quality of wound repair.

Local perivascular application of low amounts of a plasmid encoding for vascular endothelial growth factor (VEGF165) is efficient for therapeutic angiogenesis in pigs

Clinical trials have demonstrated therapeutic benefit in inducing angiogenesis in chronic occlusive arterial disease. The route of application mostly used was the intramuscular injection of high dosages of plasmid. Therefore, a local perivascular application of low amounts of vascular endothelial growth factor (VEGF) plasmid was used in an interventional occlusion model, and the effect of VEGF on coronary and peripheral occlusions compared in the same animal model. Coronary and peripheral arteries were chronically occluded in Pietrain pigs using a non-surgical, interventional approach. Adventitial delivery of the DNA for VEGF was performed with a needle injection catheter. The DNA was applied as lipoplexes using the novel cationic liposomes DOCSPER. Optimized transfer conditions were used. Angiography, polymerase chain reaction (PCR), reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry were undertaken within a follow-up period of 6 months. Expression of the transfected VEGF gene was observed at 1 and 3 weeks following application. The DNA was detected up to 5 months following application. Around occluded coronary arteries, there was formation of new collaterals and arterial prolongation, whereas surrounding occluded peripheral arteries there was no collateralization but development of new arterial branches was seen. Results demonstrate that the response to VEGF is also sufficient, when minimal amounts of plasmid encoding for VEGF are applied locally into the perivasculature allowing for more safety of this therapy. Comparison of treatment of chronic coronary and peripheral arterial disease revealed differences in angiogenesis following VEGF application during a total follow-up period of almost 6 months which may be related to their different developmental origins. This may have important implications for developing future therapeutic strategies using VEGF in different vessels.

Matrix metalloproteinases and the ontogeny of scarless repair: the other side of the wound healing balance

Early gestation mammalian fetuses possess the remarkable ability to heal cutaneous wounds in a scarless fashion. Over the past 20 years, scientists have been working to decipher the mechanisms underlying this phenomenon. Much of the research to date has focused on fetal correlates of adult wound healing that promote fibrosis and granulation tissue formation. It is important to remember, however, that wound repair consists of a balance between tissue synthesis, deposition, and degradation. Relatively little attention has been paid to this latter component of the fetal wound healing process. In this study, we examined the ontogeny of ten matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in nonwounded fetal rat skin and fibroblasts as a function of gestational age. We used a semiquantitative polymerase chain reaction protocol to analyze these important enzymes at time points that represent both the scarless and scar-forming periods of rat gestation. The enzymes evaluated were collagenase-1 (MMP-1), stromelysin-1 (MMP-3), gelatinase A (MMP-2), gelatinase B (MMP-9), membrane-type matrix metalloproteinases (MT-MMPs) 1, 2, and 3, and TIMPs 1, 2, and 3. Results demonstrated marked increases in gene expression for MMP-1, MMP-3 and MMP-9 that correlated with the onset of scar formation in nonwounded fetal skin. Similar results were noted in terms of MMP-9 gene expression in fetal fibroblasts. These results suggest that differences in the expression of these matrix metalloproteinases may have a role in the scarless wound healing phenotype observed early in fetal rat gestation. Furthermore, our data suggest that the differential expression of gelatinase B (MMP-9) may be mediated by the fetal fibroblasts themselves.

Wound remodelling and scarring

Wound healing usually results in a scar. No therapy currently exists for removing scars, so treatments focus on making them less obvious. Research is investigating how to prevent scars forming, inspired by what happens to foetuses in the womb.

Scar assessment tools: implications for current research

Scarring is considered a major medical problem that leads to cosmetic and functional sequelae. Scar tissue is clinically distinguished from normal skin by an aberrant color, rough surface texture, increased thickness (hypertrophy), occurrence of contraction, and firmness. Marked histologic differences are the change in dermal architecture and the presence of cells such as the myofibroblast. Many assessment tools are available for analysis of pathologic conditions of the skin; however, there is no general agreement as to the most appropriate tools for evaluation of scar tissue. This review critically discusses currently available objective measurement tools, subjective assessment tools, and potential devices that may be available in the future for scar assessment.

Neonatal rat cartilage has the capacity for tissue regeneration

One of the most relevant issues in future medicine is tissue regeneration. Transplantation medicine alone cannot solve the problem of incurable conditions of vital organs. One approach to this might be the replication of the spontaneous regeneration that is found in embryonic/neonatal tissue. In this study, a tissue model for basic investigation of regeneration mechanisms in vivo was established. We demonstrated by histology and immunohistochemical staining for types I and II collagen that neonatal rat cartilage unlike adult cartilage has the capacity for rapid scarfree regeneration after full-thickness incision. The underlying mechanism was identified in the preserved proliferative capacity of neonatal chondrocytes. This in vivo model should prove useful in further studies of the role of cellular (e.g., GA cell cycle regulators) and extracellular (e.g., cytokines) factors in tissue regeneration and wound healing.

Fetal rat amniotic fluid: transforming growth factor beta and fibroblast collagen lattice contraction

BACKGROUND

In several mammalian animal models, early-gestational-age fetal wounds heal without scar, but wounds of late gestational age heal with scar. This change in wound healing phenotype can be a result of both intrinsic (i.e., cellular characteristics) and extrinsic (i.e., environmental) factors. Our question was: Does amniotic fluid (AF) influence the change from scarless to scar-forming repair in the rat?

METHODS

Rat AF was investigated for its modulation of fibroblast-populated collagen lattice (FPCL) contraction and morphological changes of adult fibroblasts. AF was also assayed for transforming growth factor beta (TGF-beta) levels. Adult rat dermal fibroblasts in monolayer and incorporated into FPCLs were incubated with AF additions from gestational age 14, 16, 18, and 21 days at 10% (v/v).

RESULTS

Day 14 AF significantly stimulated FPCL contraction, but AF of 16, 18, and 21 days inhibited FPCL contraction. Fluorescence histology identified microtubules and microfilaments in AF treated adult rat dermal fibroblasts. The staining pattern of microtubules in Day 14 AF-treated fibroblasts showed denser structures at the cell center. Cells incubated with Day 16 or 18 AF showed fine peripheral microtubules. A mink lung epithelial cell bioassay was used to analyze concentrations of TGF-beta in AF. TGF-beta levels were greatly elevated in Day 14 AF, but were relatively low in Day 16, 18 and 21 AF. The inhibitor of FPCL contraction from AF of Days 16, 18, and 21 was not identified.

CONCLUSION

It is proposed that the robust expression of TGF-beta or cytoskeletal changes induced by Day 14 AF contributes to enhanced FPCL contraction.

Fetal and adult human skin fibroblasts display intrinsic differences in contractile capacity

One of the differences between fetal and adult skin healing is the unique ability of fetal wounds to heal without contracture and scar formation. Studies have shown that the ratio between the three isoforms of TGFbeta is different in adult and fetal wounds. Thus, we analyzed the capacity of adult and fetal human skin fibroblasts to contract collagen gels after stimulation with TGFbeta isoforms. In control medium, fetal fibroblasts had a contractile capacity similar to that of adult fibroblasts. However, the growth capacity of fetal fibroblasts was completely inhibited, in contrast to adult fibroblasts. When cells were treated with TGFbeta, fetal fibroblasts showed an inhibition of their contractile capacity whereas adult fibroblasts further contracted gels. The contractile response was similar for all isoforms of TGFbeta although TGFbeta3 always had the strongest effect. We considered that the regulation of cell contractile capacity by TGFbeta may be dependent on receptor expression for this cytokine, on myofibroblast differentiation of the cells, or in cell links with matrix. Since TGFbeta receptor analysis did not show differences in receptor affinity, we studied the expression of alpha-smooth muscle (SM) actin, a fibroblast contractile marker and of three integrins, the cell surface receptors specific of the attachment of the fibroblasts with collagen matrix. We observed that the expression of alpha-SM actin and alpha3 and beta1 integrin subunits was increased when TGFbeta was added to the medium of adult fibroblasts whereas the levels of the alpha1 and alpha2 subunits were unchanged. In contrast, fetal fibroblasts treated with TGFbeta showed a decrease of alpha1, alpha2, and beta1 integrin expression but no change in alpha3 integrin and in alpha-SM actin expression. These results indicate that intrinsic differences between fetal and adult fibroblasts might explain their opposite responses to TGFbeta stimuli. The variations in their alpha-SM actin and integrin expression patterns represent potentially important mechanisms used by fetal fibroblasts to regulate their response to cytokines, and likely contribute to the resultant differences in the quality of wound repair.

Evaluation of endovascular techniques for creating a porcine femoral artery occlusion model

PURPOSE

To determine the optimal endovascular approach to achieve long-term occlusion of large arteries, while preserving the integrity of periarterial tissue, in an animal model of ischemia.

METHODS

Femoral artery occlusions were created in 16 pigs using detachable balloons, coils, or blinded stent-grafts. Feasibility, safety, primary and long-term success, and the degree of neovascularization were determined over a 6-month period by serial angiography and histological analyses. Four animals served as untreated controls.

RESULTS

Overall primary success for all occlusion devices was 100%. The 6-month occlusion rate using detachable balloons or coils was 33% and 0%, respectively; however, all arteries occluded with blinded stent-grafts remained obstructed to the end of the study. There was no significant difference in capillary densities and collateralization of periarterial areas when occluded arteries were compared with nonoccluded controls in the same animal. No increase in collateralization was observed following endovascular arterial occlusion.

CONCLUSIONS

Percutaneous insertion of blinded stent-grafts easily, safely, and reliably creates long-term arterial occlusion in pigs, which may make this a more appropriate model for studying the effects of angiogenic factors in vivo.

Ontogeny of expression of transforming growth factor-beta 1 (TGF-beta 1), TGF-beta 3, and TGF-beta receptors I and II in fetal rat fibroblasts and skin

Fetal cutaneous wounds that occur in early gestation heal without scar formation. Although much work has been done to characterize the role of transforming growth factor-beta (TGF-beta) isoforms in the adult wound repair process, their function in fetal scarless wound repair is not well understood. The authors hypothesized that the pattern of expression for TGF-beta isoforms and their receptors may influence the phenotypic transition from scarless to scar-forming repair observed during fetal gestation. Using time-dated fetal Sprague-Dawley rat fibroblasts and unwounded skin at gestational ages 14, 16, 18, and 21 days postcoitum of the scarless (< or =16 days) and scar-forming (>16 days) periods of gestation (term = 21.5 days), the authors analyzed the endogenous messenger RNA (mRNA) levels of TGF-beta 1 and TGF-beta 3 and their signaling receptors TGF-beta-RI and TGF-beta-RII. Northern blot analyses in both fibroblasts and unwounded skin revealed that levels of TGF-beta 1 were not differentially expressed, whereas more TGF-beta 3 mRNA transcript was found in early than in late gestation. Fibroblast expression of TGF-beta-RI showed no substantial differences, whereas expression of TGF-beta-RII increased during gestation. In contrast, expression of both TGF-beta-RI and TGF-beta-RII in unwounded skin showed decreasing levels as a function of gestational age. The differential levels of TGF-beta 1 and TGF-beta 3 suggest that the ratio of these cytokines may provide a predominantly antiscarring or profibrotic signal upon wounding during the scar-free or scar-forming periods of gestation, respectively. Furthermore, lower amounts of the ligand-binding TGF-beta-RII seen in early gestation fibroblasts suggest a decreased ability to perceive ligand during the period of scarless repair.

Discoidin domain receptors and their ligand, collagen, are temporally regulated in fetal rat fibroblasts in vitro

The biochemical regulation of collagen deposition during adult cutaneous wound repair is poorly understood. Likewise, how collagen is perceived and modulated in fetal scarless healing remains unknown. Recently, discoidin domain receptors-1 and 2 (DDR1 and DDR2) with tyrosine kinase activity have been identified as novel receptors for collagen. In light of these findings, it was speculated that the production of collagen receptors DDR1 and DDR2 by fetal fibroblasts may be temporally regulated to correlate with the ontogeny of embryonic scar formation. More specifically, because DDRs directly bind collagen and transmit the signals intracellularly, it was hypothesized that they may play an important role in fetal scarless healing by ultimately regulating and modulating collagen production and organization. As part of a fundamental assessment to elucidate the role of DDRs in scarless fetal wound repair, the endogenous expression of DDR1, DDR2, collagen I, and total collagen, as a function of fetal Sprague-Dawley rat skin fibroblasts of different gestational ages, representing scar-free (<E16.5 days) and scar-forming (>E16.5) periods was determined. Using explanted dermal fibroblasts of gestational days E13.5, E16.5, E18.5, and E21.5 (term gestation = 21.5 days) fetuses (n = 92), [3H]proline incorporation assay and Northern and Western blotting analysis were performed to compare the expressions of these molecules with scar-free and scar-forming stages of embryonic development. These results revealed a pattern of increasing collagen production with increasing gestational ages, whereas DDR1 expression decreased with increasing gestational age. This observation suggests that elevated levels of DDR1 may play an important role in scarless tissue regeneration by early gestation fetal fibroblasts. In contrast, DDR2 was expressed by fetal rat fibroblasts at a similar level throughout gestation. These data demonstrate for the first time the temporal expression of collagen and DDR tyrosine kinases in fetal rat fibroblasts as a function of gestational ages. Overall, these data suggest that differential temporal expression of the above-mentioned molecules during fetal skin development may play an important role in the ontogeny of scar formation. Future studies will involve the characterization of the biomolecular functions of these receptor kinases during fetal wound repair.