Skin wounds in the MRL/MPJ mouse heal with scar

Adult MRL/MpJ mice regenerate cartilage during repair of through-and-through ear punch wounds. However, the ability of this mouse strain to heal isolated cutaneous wounds by regeneration or with scar is unknown. The purpose of this study was to characterize the rate of reepithelialization and collagen architecture in dermal wounds from MRL/MpJ mice compared with C57bl/6 and Balb/c strains. Full-thickness incisional (5 mm) and excisional (2 mm diameter) skin wounds were made on the dorsum of 7-week-old MRL/MpJ, C57bl/6, and Balb/c mice. Ear punch wounds were made simultaneously on each animal. Reepithelialization was complete by 48 hours for incisional skin wounds in each strain. All excisional wounds showed incomplete reepithelialization at 24, 48, and 72 hours. At 14 days, all skin wounds had grossly healed. In contrast to the ear wounds made in C57bl/6 and Balb/c mice, MRL/MpJ ear wounds were completely healed by day 28. Dorsal skin wound sections at 14 and 28 days revealed dense collagen deposition and similar degrees of fibrosis between the three strains of mice. In conclusion, in contrast to wound healing in the ear, MRL/MpJ mouse dorsal cutaneous wounds heal similarly to C57bl/6 and Balb/c mice with dermal collagen deposition and scar formation.     

Dendritic cells modulate burn wound healing by enhancing early proliferation

Adequate wound healing is vital for burn patients to reduce the risk of infections and prolonged hospitalization. Dendritic cells (DCs) are antigen presenting cells that release cytokines and are central for the activation of innate and acquired immune responses. Studies have showed their presence in human burn wounds; however, their role in burn wound healing remains to be determined. This study investigated the role of DCs in modulating healing responses within the burn wound. A murine model of full‐thickness contact burns was used to study wound healing in the absence of DCs (CD11c promoter‐driven diphtheria toxin receptor transgenic mice) and in a DC‐rich environment (using fms‐like tyrosine kinase‐3 ligand, FL‐ a DC growth factor). Wound closure was significantly delayed in DC‐deficient mice and was associated with significant suppression of early cellular proliferation, granulation tissue formation, wound levels of TGFβ1 and formation of CD31⁺ vessels in healing wounds. In contrast, DC enhancement significantly accelerated early wound closure, associated with increased and accelerated cellular proliferation, granulation tissue formation, and increased TGFβ1 levels and CD31⁺ vessels in healing wounds. We conclude that DCs play an important role in the acceleration of early wound healing events, likely by secreting factors that trigger the proliferation of cells that mediate wound healing. Therefore, pharmacological enhancement of DCs may provide a therapeutic intervention to facilitate healing of burn wounds.     

Wound healing in a fetal,adult, and scar tissue model: A comparative study

Early gestation fetal wounds heal without scar formation. Understanding the mechanism of this scarless healing may lead to new therapeutic strategies for improving adult wound healing. The aims of this study were to develop a human fetal wound model in which fetal healing can be studied and to compare this model with a human adult and scar tissue model. A burn wound (10 × 2 mm) was made in human ex vivo fetal, adult, and scar tissue under controlled and standardized conditions. Subsequently, the skin samples were cultured for 7, 14, and 21 days. Cells in the skin samples maintained their viability during the 21‐day culture period. Already after 7 days, a significantly higher median percentage of wound closure was achieved in the fetal skin model vs. the adult and scar tissue model (74% vs. 28 and 29%, respectively, p<0.05). After 21 days of culture, only fetal wounds were completely reepithelialized. Fibroblasts migrated into the wounded dermis of all three wound models during culture, but more fibroblasts were present earlier in the wound area of the fetal skin model. The fast reepithelialization and prompt presence of many fibroblasts in the fetal model suggest that rapid healing might play a role in scarless healing.     

The murine excisional wound model: Contraction revisited

Rodent models of healing are considered limited because of the perception that rodent wounds heal by contraction while humans heal by reepithelialization The purpose of this report is to present evidence that simple murine excisional wounds provide a valid and reproducible wound model that heals by both contraction and reepithelialization. Previous studies have shown that, although rodent wounds contract by up to 80%, much of this contraction occurs only after epithelial closure. To confirm these previous findings, we measured re‐epithelialization and contraction in three separate mouse strains, (BALB/c, db/+, and db/db); reepithelialization and contraction each accounted for ～40 to 60% of the initial closure of full thickness excisional wounds. After closure, the wound continues to contract and this provides the impression of dominant closure by contraction. In conclusion, the simple excisional rodent wound model produces a well defined and readily identifiable wound bed over which the process of reepithelialization is clearly measurable.     

Pseudomonas aeruginosa biofilm hampers murine central wound healing by suppression of vascular epithelial growth factor

Biofilm‐infected wounds are clinically challenging. Vascular endothelial growth factor and host defence S100A8/A9 are crucial for wound healing but may be suppressed by biofilms. The natural course of Pseudomonas aeruginosa biofilm infection was compared in central and peripheral zones of burn‐wounded, infection‐susceptible BALB/c mice, which display delayed wound closure compared to C3H/HeN mice. Wounds were evaluated histopathologically 4, 7 or 10 days post‐infection. Photoplanimetry evaluated necrotic areas. P. aeruginosa biofilm suppressed vascular endothelial growth factor levels centrally in BALB/c wounds but increased peripheral levels 4–7 days post‐infection. Central zones of the burn wound displayed lower levels of central vascular endothelial growth factor as observed 4 and 7 days post‐infection in BALB/c mice compared to their C3H/HeN counterparts. Biofilm suppressed early, centrally located S100A8/A9 in BALB/c and centrally and peripherally later on in C3H/HeN wounds as compared to uninfected mice. Peripheral polymorphonuclear‐dominated inflammation and larger necrosis were observed in BALB/c wounds. In conclusion, P. aeruginosa biofilm modulates wounds by suppressing central, but inducing peripheral, vascular endothelial growth factor levels and reducing host response in wounds of BALB/c mice. This suppression is detrimental to the resolution of biofilm‐infected necrosis.     

Different wound healing properties of dermis,adipose, and gingiva mesenchymal stromal cells

Oral wounds heal faster and with better scar quality than skin wounds. Deep skin wounds where adipose tissue is exposed, have a greater risk of forming hypertrophic scars. Differences in wound healing and final scar quality might be related to differences in mesenchymal stromal cells (MSC) and their ability to respond to intrinsic (autocrine) and extrinsic signals, such as human salivary histatin, epidermal growth factor, and transforming growth factor beta1. Dermis‐, adipose‐, and gingiva‐derived MSC were compared for their regenerative potential with regards to proliferation, migration, and matrix contraction. Proliferation was assessed by cell counting and migration using a scratch wound assay. Matrix contraction and alpha smooth muscle actin was assessed in MSC populated collagen gels, and also in skin and gingival full thickness tissue engineered equivalents (reconstructed epithelium on MSC populated matrix). Compared to skin‐derived MSC, gingiva MSC showed greater proliferation and migration capacity, and less matrix contraction in full thickness tissue equivalents, which may partly explain the superior oral wound healing. Epidermal keratinocytes were required for enhanced adipose MSC matrix contraction and alpha smooth muscle actin expression, and may therefore contribute to adverse scarring in deep cutaneous wounds. Histatin enhanced migration without influencing proliferation or matrix contraction in all three MSC, indicating that salivary peptides may have a beneficial effect on wound closure in general. Transforming growth factor beta1 enhanced contraction and alpha smooth muscle actin expression in all three MSC types when incorporated into collagen gels. Understanding the mechanisms responsible for the superior oral wound healing will aid us to develop advanced strategies for optimal skin regeneration, wound healing and scar formation.     

Tissue profiling MALDI mass spectrometry reveals prominent calcium-binding proteins in the proteome of regenerative MRL mouse wounds

MRL/MpJ‐Fas^lpr mice exhibit the ability to regenerate ear tissue excised by dermal punches. This is an exceptional model to identify candidate proteins that may regulate regeneration in typically nonregenerative tissues. Identification of key molecules involved in regeneration can broaden our understanding of the wound‐healing process and generate novel therapeutic approaches. Tissue profiling by matrix‐assisted laser desorption ionization mass spectrometry is a rapid, powerful proteomic tool that allows hundreds of proteins to be detected from specific regions of intact tissue specimens. To identify these candidate molecules, protein expression in ear punches was examined after 4 and 7 days using tissue profiling of MRL/MpJ‐Fas^lpr mice and the nonregenerative mouse strain C57BL/6J. Spectral analysis revealed distinct proteomic differences between the regenerative and nonregenerative phenotypes, including the calcium‐binding proteins calgranulin A and B, calgizzarin, and calmodulin. Spatial distributions for these differentially expressed proteins within the injured regions were confirmed by immunohistochemistry.     

Topical vascular endothelial growth factor reverses delayed wound healing secondary to angiogenesis inhibitor administration

The prevention of new blood vessel growth is an increasingly attractive strategy to limit tumor growth. However, it remains unclear whether anti-angiogenesis approaches will impair wound healing, a process thought to be angiogenesis dependent. Results of previous studies differ as to whether angiogenesis inhibitors delay wound healing. We evaluated whether endostatin at tumor-inhibiting doses delayed excisional wound closure. C57/BL6J mice were treated with endostatin or phosphate-buffered solution 3 days prior to the creation of two full-thickness wounds on the dorsum. Endostatin was administered daily until wound closure was complete. A third group received endostatin, but also had daily topical vascular endothelial growth factor applied locally to the wound. Wound area was measured daily and the wounds were analyzed for granulation tissue formation, epithelial gap, and wound vascularity. Endostatin-treated mice showed a significant delay in wound healing. Granulation tissue formation and wound vascularity were significantly decreased, but reepithelialization was not effected. Topical vascular endothelial growth factor application to wounds in endostatin-treated mice resulted in increased granulation tissue formation, increased wound vascularity, and wound closure approaching that of control mice. This study shows that the angiogenesis inhibitor endostatin delays wound healing and that topical vascular endothelial growth factor is effective in counteracting this effect.     

Mature B cells accelerate wound healing after acute and chronic diabetic skin lesions

Chronic wounds affect 12–15% of patients with diabetes and are associated with a drastic decrease in their quality of life. Here, we demonstrate that purified mature naive B220⁺/CD19⁺/IgM⁺/IgD⁺ B cells improve healing of acute and diabetic murine wounds after a single topical application. B cell treatment significantly accelerated acute wound closure by 2–3 days in wild‐type mice and 5–6 days in obese diabetic mice. The treatment led to full closure in 43% of chronic diabetic wounds, as compared to only 5% in saline‐treated controls. Applying equivalent numbers of T cells or disrupted B cells failed to reproduce these effects, indicating that live B cells mediated pro‐healing responses. Topically applied B cell treatment was associated with significantly reduced scar size, increased collagen deposition and maturation, enhanced angiogenesis, and increased nerve growth into and under the healing wound. β‐III tubulin+ nerve endings in scars of wounds treated acutely with B cells showed increased relative expression of growth‐associated protein 43. The improved healing associated with B cell treatment was supported by significantly increased fibroblast proliferation and decreased apoptosis in the wound bed and edges, altered kinetics of neutrophil infiltration, as well as an increase in TGF‐β and a significant reduction in MMP2 expression in wound granulation tissue. Our findings indicate that the timeline and efficacy of wound healing can be experimentally manipulated through the direct application of mature, naive B cells, which effectively modify the balance of mature immune cell populations within the wound microenvironment and accelerate the healing process.     

Orf virus IL‐10 accelerates wound healing while limiting inflammation and scarring

Interleukin (IL)‐10 plays a critical role in controlling wound inflammation and scar formation. Orf virus, a zoonotic parapoxvirus, induces proliferative skin lesions that resolve with minimal scarring. Orf virus encodes a range of factors that subvert the host's response to infection, including a homolog of IL‐10. This study investigated, using a murine full‐thickness wound model, whether purified orf virus IL‐10 (ovIL‐10) can regulate skin repair and scarring. Repeat injections of ovIL‐10 into wounded skin accelerated wound closure. Histological analyses of wound sections revealed that treatment with ovIL‐10 accelerated wound reepithelialization, granulation tissue coverage of the wound bed, and improved wound revascularization. In addition, wounds treated with ovIL‐10 showed a reduction in macrophage infiltration, myofibroblast differentiation, and wound contraction. Treatment of wounds with ovIL‐10 also resulted in a reduction in visible scarring that was consistent with the extent of scar tissue formed. Quantitative polymerase chain reaction analysis confirmed that ovIL‐10 reduced the expression of key mediators of inflammation and granulation tissue formation. These findings show that ovIL‐10, like mammalian IL‐10, limits inflammation and scar tissue formation and reveal a new role for both mammalian and viral IL‐10 in mediating tissue repair.     

Extracorporeal shock wave therapy suppresses the early proinflammatory immune response to a severe cutaneous burn injury*

Following severe burn injury, persistent inflammation perpetuated by surface eschar, bacterial colonisation and neutrophil proteolytic activity can impede normal healing and result in further tissue damage. Extracorporeal shock wave treatment (ESWT) has been shown in the clinical setting to promote the healing of burn and difficult‐to‐heal wounds; however, the mechanism is unclear. We investigated the role of ESWT on the early proinflammatory response using a severe, full‐thickness and highly inflammatory cutaneous burn wound in a murine model. Various wound‐healing parameters were measured and leukocyte infiltration quantitated. A panel of 188 candidate genes known to be involved in acute inflammation and wound healing was screened. We show that ESWT of burn wounds 1 hour postwounding significantly blunts polymorphonuclear neutrophil and macrophage infiltration into the wound. ESWT treatment potently attenuates both CC‐ and CXC‐chemokine expression, acute proinflammatory cytokine expression and extracellular matrix proteolytic activity at the wound margin. Given these findings and the clinical success of ESWT, we speculate that ESWT may be a potential therapeutic modality to treat severe wounds wherein excessive inflammatory responses involving increased levels of inflammatory cells, proinflammatory cytokines and proteases may become self‐resolving allowing wound healing to progresses by way of normal physiological repair processes.     

Transgenic mice overexpressing CD109 in the epidermis display decreased inflammation and granulation tissue and improved collagen architecture during wound healing

Transforming growth factor‐β (TGF‐β) is a multifunctional growth factor involved in all aspects of wound healing. TGF‐β accelerates wound healing, but an excess of its presence at the wound site has been implicated in pathological scar formation. Our group has recently identified CD109, a glycophosphatidylinositol‐anchored protein, as a novel TGF‐β coreceptor and inhibitor of TGF‐β signaling in vitro. To determine the effects of CD109 in vivo on wound healing, we generated transgenic mice overexpressing CD109 in the epidermis. In excisional wounds, we show that CD109 transgenic mice display markedly reduced macrophage and neutrophil recruitment, granulation tissue area, and decreased Smad2 and Smad3 phosphorylation, whereas wound closure remains unaffected as compared with wild‐type littermates. Futhermore, we demonstrate that the expression of the proinflammatory cytokines interleukin‐1α and monocyte chemoattractant protein‐1, and extracellular matrix components is markedly decreased during wound healing in CD109 transgenic mice. In incisional wounds, CD109 transgenic mice show improved dermal architecture, whereas the tensile strength of the wound remains unchanged. Taken together, our findings demonstrate that CD109 overexpression in the epidermis reduces inflammation and granulation tissue area and improves collagen organization in vivo.     

Quantitative and reproducible murine model of excisional wound healing

The goal of animal wound healing models is to replicate human physiology and predict therapeutic outcomes. There is currently no model of wound healing in rodents that closely parallels human wound healing. Rodents are attractive candidates for wound healing studies because of their availability, low cost, and ease of handling. However, rodent models have been criticized because the major mechanism of wound closure is contraction, whereas in humans reepithelialization and granulation tissue formation are the major mechanisms involved. This article describes a novel model of wound healing in mice utilizing wound splinting that is accurate, reproducible, minimizes wound contraction, and allows wound healing to occur through the processes of granulation and reepithelialization. Our results show that splinted wounds have an increased amount of granulation tissue deposition as compared to controls, but the rate of reepithelialization is not affected. Thus, this model eliminates wound contraction and allows rodents' wounds to heal by epithelialization and granulation tissue formation. Given these analogies to human wound healing, we believe that this technique is a useful model for the study of wound healing mechanisms and for the evaluation of new therapeutic modalities.     

Cutaneous wound healing in aging small mammals: a systematic review

As the elderly population grows, so do the clinical and socioeconomic burdens of nonhealing cutaneous wounds, the majority of which are seen among persons over 60 years of age. Human studies on how aging effects wound healing will always be the gold standard, but studies have ethical and practical hurdles. Choosing an animal model is dictated by costs and animal lifespan that preclude large animal use. Here, we review the current literature on how aging effects cutaneous wound healing in small animal models and, when possible, compare healing across studies. Using a literature search of MEDLINE/PubMed databases, studies were limited to those that utilized full‐thickness wounds and compared the wound‐healing parameters of wound closure, reepithelialization, granulation tissue fill, and tensile strength between young and aged cohorts. Overall, wound closure, reepithelialization, and granulation tissue fill were delayed or decreased with aging across different strains of mice and rats. Aging in mice was associated with lower tensile strength early in the wound healing process, but greater tensile strength later in the wound healing process. Similarly, aging in rats was associated with lower tensile strength early in the wound healing process, but no significant tensile strength difference between young and old rats later in healing wounds. From studies in New Zealand White rabbits, we found that reepithelialization and granulation tissue fill were delayed or decreased overall with aging. While similarities and differences in key wound healing parameters were noted between different strains and species, the comparability across the studies was highly questionable, highlighted by wide variability in experimental design and reporting. In future studies, standardized experimental design and reporting would help to establish comparable study groups, and advance the overall knowledge base, facilitating the translatability of animal data to the human clinical condition.     

Interferon‐gamma inhibits healing post scald burn injury

Impaired healing after severe burns remains a reason for prolonged hospitalization, opportunistic infections, and debilitating scarring. Interferon‐gamma (IFN‐γ) is an important immune regulator that has been shown to inhibit collagen synthesis by fibroblasts, resulting in delayed healing in incision wounds. To determine whether IFN‐γ plays similar roles in the healing process after severe burn, we induced scald injury in mice deficient or sufficient in IFN‐γ and examined local responses. In the absence of IFN‐γ, scalded areas healed faster. This was associated with attenuated local inflammatory responses, enhanced reepithelialization, increased proliferation of keratinocytes in reepithelialized leading edges, and up‐regulation of growth factors in burned skin areas. Furthermore, angiogenesis and myofibroblast formation commenced and terminated earlier in IFN‐γ^–/– mice compared with wild type (WT) controls. Our observations demonstrate that inhibition of IFN‐γ results in accelerated healing after burn injury by dampening excessive inflammation and facilitating reepithelialization, collagen deposition, and wound contraction.     

Mast cells modulate the inflammatory but not the proliferative response in healing wounds

Upon stimulation, mast cells release a heterogeneous group of factors that promote inflammation and influence cell proliferation. Mast cells accumulate at sites of injury, further suggesting a critical role in wound healing. To assess the importance of mast cells in tissue repair, we compared wound healing in mast cell-deficient WBB6F1/J-KitW/KitW-v (KitW/KitW-v) and wild type WBB6F1/++ (WT) mice. During the inflammatory phase, neutrophil infiltration into wounds of the KitW/KitW-v mice was significantly less than that of WT mice (84.6 +/- 10.3 vs. 218 +/- 26.0 cells/10 high-power fields at day 3, p < 0.001), while wound macrophage and T cell infiltration were similar in both strains. The decrease in neutrophils could not be explained by changes in tumor necrosis factor-alpha or macrophage inflammatory protein-2 levels, because the amounts of these two neutrophil chemoattractants were similar in both KitW/KitW-v and WT mice. Surprisingly, the absence of mast cells had no effect on the proliferative aspects of wound healing, including reepithelialization, collagen synthesis, and angiogenesis. Although mast cells are known to release proangiogenic mediators, vascular endothelial growth factor levels were similar in WT and KitW/KitW-v mice. Moreover, levels of fibroblast growth factor-2 were increased in KitW/KitW-v mice (4206 +/- 107 vs. 1865 +/- 249 pg/ml, p < 0.01). These results suggest that mast cells modulate the recruitment of neutrophils into sites of injury, yet indicate that mast cells are unlikely to exert a major influence on the proliferative response within healing wounds.     

An ultrathin poly(l‐lactic acid) nanosheet as a burn wound dressing for protection against bacterial infection

Burn wounds are highly susceptible to bacterial infection due to impairment of the skin's integrity. Therefore, prevention of bacterial colonization/infection in the wound is crucial for the management of burns, including partial‐thickness burn injuries. Although partial‐thickness burn injuries still retain the potential for reepithelialization, the complication of wound infection severely impairs the reepithelialization even in such superficial burn injuries. We recently developed a biocompatible nanosheet consisting of poly(l ‐lactic acid) (PLLA). The PLLA nanosheets have many useful and advantageous biological properties for their application as a wound dressing, such as sufficient flexibility, transparency, and adhesiveness. We herein investigated the suitability of the PLLA nanosheets as a wound dressing for partial‐thickness burn wounds in mice. The PLLA nanosheets tightly adhered to the wound without any adhesive agents. Although wound infection with Pseudomonas aeruginosa in the controls significantly impaired reepithelialization of burn wounds, dressing with the PLLA nanosheet markedly protected against bacterial wound infection, thereby improving wound healing in the mice receiving partial‐thickness burn injuries. The PLLA nanosheet also showed a potent barrier ability for protecting against bacterial penetration in vitro. The ultrathin PLLA nanosheet may be applied as a protective dressing to reduce environmental contamination of bacteria in a partial‐thickness burn wound.     

The anti‐inflammatory agent Propolis improves wound healing in a rodent model of experimental diabetes

Foot ulcers and poor wound healing are problematic for patients with diabetes. The beehive protectant Propolis can improve wound healing but whether it can improve healing in diabetic wounds has not been investigated. In this study, the effect of a single application of Propolis on epithelial closure, wound morphology, cellular infiltrate, and blood vessel density were investigated. Diabetes was induced in rats using streptozocin. After 6 weeks, diabetic and control animals were wounded and the wounds were treated with Propolis or saline as control. At days 6 and 12 animals were sacrificed and wounds were excised. Compared with controls, diabetes decreased epithelial closure and reepithelialization but had no effect on wound contraction. These delays were prevented by Propolis. At day 12, the impaired macrophage infiltration (C:1.49±0.09 vs. D:0.25±0.14), persistent neutrophil infiltration (C:0.22±0.19 vs. D:1.33±0.81), and increased myeloperoxidase activity (fourfold) in diabetic wounds were prevented by Propolis. Diabetes had no effect on wound volume, vessel number, or branch points. These novel data indicate that Propolis can accelerate wound healing in diabetes. As neutrophil infiltration is normalized, its mechanism of action may be through anti‐inflammatory pathways. This result and the established safety profile of Propolis provide a rationale for studying topical application of this agent in a clinical setting.     

Invariant NKT cells promote skin wound healing by preventing a prolonged neutrophilic inflammatory response

The wound‐healing process consists of the inflammation, proliferation, and remodeling phases. In chronic wounds, the inflammation phase is prolonged with persistent neutrophil infiltration. The inflammatory response is critically regulated by cytokines and chemokines that are secreted from various immune cells. Recently, we showed that skin wound healing was delayed and the healing process was impaired under conditions lacking invariant natural killer T (iNKT) cells, an innate immune lymphocyte with potent immuno‐regulatory activity. In the present study, we investigated the effect of iNKT cell deficiency on the neutrophilic inflammatory response during the wound healing process. Neutrophil infiltration was prolonged in wound tissue in mice genetically lacking iNKT cells (Jα18KO mice) than in wild‐type (WT) control mice on days 1 and 3 after wounding. MIP‐2, KC, and IL‐17A were produced at a significantly higher level in Jα18KO mice than in WT mice. In addition, neutrophil apoptosis was significantly reduced in the wound tissue in Jα18KO mice than in WT mice. Treatment with anti‐IL‐17A mAb, anti‐Gr‐1 mAb, or neutrophil elastase inhibitor reversed the impaired wound healing in Jα18KO mice. These results suggest that iNKT cells may promote the wound healing process through preventing the prolonged inflammatory response mediated by neutrophils.     

Impaired cutaneous wound healing in transforming growth factor‐β inducible early gene1 knockout mice

Transforming growth factor‐β inducible early gene (TIEG) is induced by transforming growth factor‐β (TGF‐β) and acts as the primary response gene in the TGF‐β/Smad pathway. TGF‐β is a multifunctional growth factor that affects dermal wound healing; however, the mechanism of how TGF‐β affects wound healing is still not well understood because of the complexity of its function and signaling pathways. We hypothesize that TIEG may play a role in dermal wound healing, with involvement in wound closure, contraction, and reepithelialization. In this study, we have shown that TIEG1 knockout (TIEG1^–/–) mice have a delay in wound closure related to an impairment in wound contraction, granulation tissue formation, collagen synthesis, and reepithelialization. We also found that Smad7 was increased in the wounds and appeared to play a role in this wound healing model in TIEG1^–/– mice.