A Review of Fetal Scarless Healing
Wound healing is a complex process involving a number of processes. Fetal regeneration has been shown to have a number of differences compared to scar-forming healing. This review discusses the number of differences identified in fetal regeneration. Understanding these differences may result in new therapeutic targets which may reduce or even prevent scarring in adult healing.
Since the 1970s it has been well established that early human fetuses can heal cutaneous wounds without the formation of scar tissue . This regeneration appears organ specific, as in early fetuses which heal cutaneous wounds with perfect regeneration other organs such as the gut heal with the formation of scar tissue. Studies on the marsupial embryo, Monodelphis domestica, have shown that fetal regeneration is not due to the moist, sterile environment of the uterus . Further, this regenerative phenotype is cell specific with fetal skin transplanted subcutaneously onto adults continuing to show a regenerative phenotype  whereas skin from the adult transplanted onto the fetus demonstrate an adult-like scarring phenotype .
Wound healing is an inherent response resulting in restoration of tissue integrity. It is a complex process involving cell migration, proliferation, differentiation, apoptosis, and the synthesis and remodelling of the extra cellular matrix (ECM). A number of factors are involved in the various stages of tissue repair including cell-cell interactions, cell-matrix interactions, a number of different cell types, and a large number of growth factors and cytokines. The regenerative phenotype of the fetus has shown a difference in a number of processes involved in wound healing, which may be manipulated to reduce or even prevent scarring.
Fetal wound healing compared to adult wound healing has been shown to have a different and reduced inflammatory response [5, 6]. The levels of immune cells are reduced which include macrophages, which are also less activated, and, in addition, the presence of inflammatory cells is short lived in fetal wound healing compared to the adult [5–7]. The reduced number of inflammatory cells also means lower expression levels of some growth factors and cytokines and for a shorter duration of time [8, 9]. However, studies have shown that fetuses which are artificially stimulated to produce an inflammatory response show an adult-like response with scar formation [10, 11]. It appears that no single immune cell is essential for wound healing [12–14] with PU.1 knockout mice, which lack both macrophages and neutrophils, showing improved rates of reepithelisation and reduced scarring compared to their wild-type equivalents .
The proinflammatory cytokines interleukin-6 (IL-6) and interleukin-8 (IL-8) have been found to be decreased during scarless fetal repair even when fetal fibroblasts are stimulated with platelet-derived growth factor (PDGF) [16, 17]. IL-10 is known to be a major regulator in suppressing the inflammatory response, including IL-6 and IL-8, and IL-10 also inhibits the migration of inflammatory cells to sites of injury [18–22]. Knockout animals for IL-10 demonstrate scar formation in fetal wounds which would have healed without a scar  while over expression of IL-10 in adult wounds, using genetic manipulation, decreased the inflammatory response, decreased abnormal collagen deposition, and restored normal architecture .
Cyclooxygenase-2 (COX-2), part of the arachidonic acid cascade, is upregulated in response to an inflammatory response such as an injury. COX-2 functions by producing prostaglandins which control many aspects of inflammation. A murine model of scarless healing demonstrated low levels of COX-2 and prostaglandin-2 (PGE2), whereas the addition of exogenous PGE2 induced scar formation in a fetal model of wound healing . Blocking the COX-2 enzyme in adult wounds results in a fetal-like phenotype with reduced scarring . However, both fetal and adult fibroblasts show expression of the PGE2 receptors . PGE2 inhibited fibroblast migration, in both the fetus and adult, through the EP2/EP4-cAMP protein kinase A pathway, though fetal fibroblasts appeared refractory requiring a higher concentration to achieve the same effect. The inhibition of adult fibroblast migration by PGE2 correlated with the disruption of the actin cytoskeleton, and PGE2 also inhibited the contraction of adult derived fibroblast populated collagen lattices. PGE2 however, did not disrupt the actin cytoskeleton in fetal-derived fibroblasts and further did not prevent fetal fibroblast populated collagen lattices contraction , possibly because fetal fibroblasts are thought to have a more migratory phenotype .
3. Extra Cellular Matrix (ECM)
The ECM is known to play an important role in wound healing as it can play a part in regulating growth factors and cytokines and alter cell behaviour . Fetal wounds have been shown to have increased levels of glycosaminoglycans such as hyaluronic acid (HA) and chondroitin sulfate, which are long unbranched polysaccharides comprising of repeating disaccharides found on the cell surface or in the ECM. HA is found at higher levels and for a longer duration in fetal wounds compared to adult wounds [30, 31]. This increased expression is possibly due to the reduced activity of hyaluronidase in the fetus  while fetal fibroblasts also express higher levels of the hyaluronic acid receptor (CD44) compared to adult fibroblasts . Exogenous addition of HA reduces the formation of scar tissue in adults [34, 35] while reducing HA expression results in a phenotype more akin to adult healing . Increased levels of HA as identified in the fetus promotes both the proliferation and migration of a number of cell types ; HA-rich matrices can bind growth factors and cytokines which can result in temporal and spatial differences of these factors.
Glycoproteins, such as fibronectin, laminin, and tenascin C, bind integrins, collagen, and proteoglycans and are integral components of the ECM playing a role in cell adherence . Fibronectin is involved in the migration of a number of cells involved in wound healing including fibroblasts, keratinocytes, and endothelial cells. The fibronectin family consists of numerous splice variants in humans with a number of variants being involved in both fetal development and wound healing [39–41]. Fibronectin which is part of the provisional matrix, shows similar temporal and spatial expression in both fetal and adult sheep and mice [42, 43] while another animal model (rabbit) suggests that fetal wounds show an earlier expression of fibronectin . Tenascin C has shown earlier deposition in fetal wounds which may be associated with the rapid reepithelisation seen in fetal wounds [42, 43]. The wounded fetal human skin has shown increased expression of integrin subunits α2, α3, α6, and β4, (laminin and collagen receptors) and neoexpression of α5, αV, and β6 (fibronectin and tenascin C receptors), and this may further explain the fetuses’ ability to reepithelise wounds rapidly with a reduced presence of inflammatory cells .
The proteoglycans decorin and fibromodulin which are known to regulate collagen fibrillogenesis, growth factor activity, and cellular proliferation have shown variation in fetal wound healing. Decorin showed reduced expression in fetal fibroblasts and fetal skin compared to adult fibroblasts and skin . While decorin was upregulated during adult wound healing, it has also been shown that reduced or delayed expression of decorin is associated with pathological scarring in a number of adult models [47, 48]. Fibromodulin, a further proteoglycan, showed an increase protein expression in scarless wounds compared to scarring  and similarly to decorin  is believed to alter the biological activity of TGF-β.
Fetal and adult wounds show a number of differences in collagen synthesis; these differences include speed of deposition, variations in collagen ratios and quantity of collagen itself [51–53]. Studies suggest that fetal fibroblasts not only show increased collagen III expression, but the new collagen is deposited in a fine reticular or basket weave pattern similar to uninjured skin [54, 55]. However uninjured fetal skin does show increased collagen III compared to collagen type I [51–53]. Others have suggested that the collagen deposited by fetuses is less mature with less cross-linking reducing rigidity but not affecting tensile strength . This reduced collagen cross-linking may be due to a lower expression of lysyl oxidase, which is known to play a role in both collagen cross-linking and influences collagen architecture . Chin et al.  also showed that fetal fibroblasts show increased expression of the collagen receptor DDR1 thought to be important for both collagen expression and organization. Though fetuses may show increased collagen production they do not exhibit excessive collagen deposition, and this may be through rapid turnover of the ECM components.
Fetal wounds show increased levels of the urokinase plasminogen activator and matrix metalloproteinases (MMPs) while their inhibitors (PAI-1 and TIMPs) are reduced during fetal wound healing [58–60]. Higher levels of MMPs result in matrix degradation compared to matrix deposition. Dang et al.  showed that scarless fetal healing expresses MMP-1, MMP-9, and MMP-14 mRNA quicker and at higher levels than fibrotic fetal wounds. While MMP-2 and TIMP1 and TIMP 3 expression are not altered during scarless healing, whereas fibrotic wounds show decreased levels of MMP2 but with an increase in TIMPs .
4. Myofibroblasts and Contraction
Fetal studies have indicated that, unlike adult wound closure, fetal wounds close through an actin cable which acts like a purse string . This cable assembles within minutes of an injury and requires a GTPase, Rho, to reepithelise fetal wounds . Studies have shown that this cable may contain myosin which acts in a zipper-like manner to close incisional wounds in fetal skin , and paxillin mRNA expression was upregulated and colocalised with actin in the fetus but not in the adult . Adult wound closure involves active movements of connective tissue and epidermis. The adult wound contracts to bring the two sides of the wound edges in close proximity to allow the epidermis to migrate and cover the exposed connective tissue .
Granulation tissue is thought to play a considerable part in wound contraction in adult wound healing. Migrating adult fibroblasts are capable of generating some tensile strength to start contraction, and the myofibroblast (differentiated fibroblast expressing alpha smooth muscle actin) is the main cell responsible for wound contraction. Differentiation of fibroblasts to myofibroblasts requires a combination of growth factors, mechanical cues, and the presence of the EDA variant of fibronectin. The presence of myofibroblasts in fetal wounds remains controversial with a murine model showing no alpha smooth muscle actin expression (except associated with blood vessels ), which was further replicated in a fetal sheep model . However, Cass et al.  did detect myofibroblasts in fetal wound healing but at earlier time points than in postnatal (scarring) wound healing. Furthermore, others in an in vitro study have shown that human fetal fibroblasts can differentiate into myofibroblasts when stimulated with exogenous TGF-β1 but again at earlier time points than postnatal fibroblasts .
5. Growth Factors
Growth factors and their receptors play a vital role in wound healing with a number of aberrations associated with abnormal wound healing such as pathological scarring. A number of growth factors have shown different expression in fetal or scarless wound healing compared to adult or scarring wound healing (Table 1).
The TGF-β family is multifunctional and is believed to be important in both tissue repair and scarring. The three isoforms of TGF-β are synthesized as latent precursors which require activation before they can exert their biological activity through binding to their heteromeric receptor complexes. Fetal wound healing has shown a rapid induction of TGF-β1 mRNA in fetal repair but at lower levels and with a more rapid clearance from the wound site compared to adult wounds [8, 69, 70]. Interestingly TGF-β2 levels, also considered to be profibrotic, was found to be lower in adult-like repair compared to fetal repair . The third isoform, TGF-β3, is expressed in adult animal wound healing [69, 71], though its expression is delayed , and with lower levels  compared to fetal wounds and in in vitro studies . Studies have shown that blocking TGF-β1 and TGF-β2 may reduce scar tissue formation [72, 73]. Whereas, the addition of exogenous TGF-β3 has in some animal models shown improved scar formation . Further, early human clinical studies showed that exogenous TGF-β3 if administered prior to the injury could reduce scarring . However, other studies using a different animal model have shown that TGF-β3 had no effect in reducing scar tissue formation . There have been three TGF-β receptors identified (TβRI, TβRII, and TβRIII), and variations in the TGF-β receptor expressions have been identified in fetal wound healing [8, 77].
Epidermal growth factor (EGF) is known to be involved in wound healing and is thought to be mitogenic for a number of cell types including fibroblasts and keratinocytes. EGF mRNA showed decreased levels with increasing gestational age (scarring) . Surprisingly, the profibrotic platelet-derived growth factor (PDGF) mRNA has also been shown to be elevated in fetal skin compared to adult skin  though similar to TGF-β it appears to have quicker clearance in fetal wound healing . However, fetal wounds when treated with exogenous growth factors such as PDGF showed a fibrotic response, with increased inflammation, fibroblast recruitment and collagen deposition indicating that fetal wound can respond in an adult manner in response to exogenous PDGF . The fibroblast growth factors (FGF) stimulate proliferation and regulate migration and differentiation in a number of target cells . FGF isoforms are regulated in a complex manner during fetal skin development, and though most do not change expression in scarless healing, both FGF7 and FGF10 were found to be downregulated . The FGF receptor 2 (FGFR2) was down regulated in wound healing, in both scar-forming and scarless healing, but the downregulation was earlier and more sustained in scarless healing . While bFGF (otherwise known as FGF2) and the FGF receptor-1 (flg) expressions were found to be higher in fetal skin than later gestational skin .
The role that angiogenesis and in particular VEGF has in scar formation remains unclear. Scarless fetal repair has not only shown reduced angiogenesis in fetal wounds , but growth factors associated with angiogenesis show reduced or no expression [25, 70, 79]. Wilgus et al. showed in a murine model that scarless fetal repair heals without either increased VEGF or vascularity . However, other studies have suggested an increase in VEGF mRNA . The variation of the results may be due to the wound model itself, that is, incisional versus excisional, different time and methods used and variations in animal model.
Insulin-like growth factors (IGF) are known profibrotic mitogens known to play a role in wound healing and fetal development. Treating wounds with exogenous IGF-I has been shown to accelerate wound healing through increased collagen synthesis and its mitogenic effect on keratinocytes and fibroblasts [84, 85]. IGF-1 has been implicated in fibrotic conditions including pathological scars possibly due to the increase in collagen synthesis [86, 87]. However, human fetal fibroblasts showed a lower mitogenic response to IGF-I and with a lower level of collagen synthesis compared to adult fibroblasts .
6. Cell Signalling, Transcription, and Gene Expression
Fetal wound healing and fetal derived cells have indicated that there may be differences in intracellular signalling following the binding of the ligand (growth factor) to its receptor. Martin et al.  demonstrated that TGF-β1 is rapidly cleared from fetal scarless wounds. While others have shown that the phosphorylation of receptors and some intracellular signalling proteins differ between fetal and adult fibroblasts [68, 88, 89]. The TGF-β1 signalling pathway has been shown to be short lived in human fetal fibroblasts after stimulation with exogenous TGF-β1 , while others found no difference [90, 91]. Variation in results between the studies may be explained through different species (human and mouse) and different intracellular proteins studied (Smad 2 or Smad 3 or Smad 2/3).
Wound healing requires the expression of a number of genes which are regulated by a number of transcription factors such as activator protein 1 (AP1) and the Hox genes. The AP-1 transcription factor is a heterodimeric protein composed of Fos, and Jun and activating transcription factor protein family members. AP-1 induction has been demonstrated in fetal mouse skin, while c-Fos protein was demonstrated to be upregulated in the epidermis after wounding [62, 92]. The increase in AP-1 and c-Fos is linked to Rho, a GTPase, which is linked to the formation of the actin cable in fetal wound closure. Others, have also shown that AP-1 transcription factors were induced after wounding in both scarless and scarring wounds. However, c-fos and c-jun induction was transient in fetal skin while AP-1 expression persisted in scarring tissue .
Hox protein activity is essential during embryogenesis, and the Hox genes have been implicated in limb regeneration [94, 95]. A number of Hox genes are expressed in both fetal and adult skin [96, 97], however, fetal wounds show an increase in expression of a number of the Hox genes during fetal scarless repair [98, 99].Though HoxB 13 was downregulated in fetal scarless wounds  and in an adult model, Hoxb13 knockout animals showed a more fetal-like healing phenotype .
Gene expression in fetal fibroblasts shows difference gene expression compared to adult fibroblasts in response to TGF-β1 in a number of experimental models [101, 102]. Colwell et al.  using genomic microarray demonstrated that fetal wounds have greater increased expression in the fraction of genes immediately after injury. As time after injury lengthened, adult wounds showed the fraction of genes with increased expression increasing. By twenty four hours after injury there were fewer genes with differential expression between the fetus and adult, with the majority having greater expression found in the adult wound . Chen et al.  showed that there were fifty three genes (0.93%) differentially expressed between early gestational skin and late gestational skin from rats; 27 genes were upregulated including FGF8, follistatin, and 26 genes were downregulated including beta-catenin in fetal skin when compared to adult skin .
7. Apoptosis, Proliferation, and Migration
A number of studies suggest that fetal fibroblasts proliferate more rapidly than adult fibroblasts . Though others suggest that there is no difference between fetal epidermal proliferation and adult proliferation .
Apoptosis is an important process in wound healing occurring in inflammatory cells, myofibroblasts, and vascular cells, for example. Studies have shown that scarless healing shows no difference in total caspase 3 or any cleavage of caspase 3 compared to scarring healing in a murine model. However, scarless healing showed an increase in cleaved caspase 7 after wounding while scar-forming wounds showed no increase. Further scarless healing showed increased levels of cleaved PARP while scar-forming healing only showed a small amount of cleaved PARP .
8. Problems in Fetal Wound-Healing Research
A number of animal models have been used to study fetal wound healing in vivo [54, 67, 107]. In addition a number of in vitro studies have used human fetal-derived cells [68, 88, 90]. The use of different species in wound healing studies can make direct comparisons either difficult or impossible with different species demonstrating variations in a number of wound-healing processes. Further complications in comparing fetal wound healing are in the wound itself with some studies using incisional wounds, excisional wounds, or even wounds created by burns. Interestingly the ability of the fetus to heal excisional wounds with perfect regeneration has been shown to be species dependent [54, 108]. Further some fetal excisional wounds undergo contraction (sheep)  while others show no contraction in closing excisional wounds (rabbits and monkeys) [107, 108].
The precise mechanism of fetal regeneration remains unclear with a number of differences identified between the fetal and adult wound healing (Table 2). A number of potential antiscarring therapeutics have evolved from understanding fetal regeneration though to date none have completely prevented scar formation. Recent studies have further suggested a role for fetal cells in difficult-to-heal wounds  through their promoting effect on adhesion, proliferation, and migration of existing cells.
Further work is required to understand how fetal cells promote regeneration and wound healing and if this can be promoted in adult wound repair. Work will also need to study the role that stem cells play in both adult and fetal wound repair. However, understanding fetal wound healing and regeneration will impact adult repair in the future and may lead to the reduction or even prevention in the formation of scar tissue in a number of organs.
|AP-1:||Activator protein 1|
|ECM:||Extra cellular matrix|
|EGF:||Epidermal growth factor|
|PDGF:||Platelet derived growth factor|
|TGF-β:||Transforming growth factor-beta.|
U. Rowlatt, “Intrauterine wound healing in a 20 week human fetus,” Virchows Archiv, vol. 381, no. 3, pp. 353–361, 1979.View at: Google Scholar
J. R. Armstrong and M. W. J. Ferguson, “Ontogeny of the skin and the transition from scar-free to scarring phenotype during wound healing in the pouch young of a marsupial, Monodelphis domestica,” Developmental Biology, vol. 169, no. 1, pp. 242–260, 1995.View at: Publisher Site | Google Scholar
H. P. Lorenz, M. T. Longaker, L. A. Perkocha, R. W. Jennings, M. R. Harrison, and N. S. Adzick, “Scarless wound repair: a human fetal skin model,” Development, vol. 114, no. 1, pp. 253–259, 1992.View at: Google Scholar
M. T. Longaker, D. J. Whitby, M. W. J. Ferguson, H. P. Lorenz, M. R. Harrison, and N. S. Adzick, “Adult skin wounds in the fetal environment heal with scar formation,” Annals of Surgery, vol. 219, no. 1, pp. 65–72, 1994.View at: Google Scholar
A. J. Cowin, M. P. Brosnan, T. M. Holmes, and M. W. Ferguson, “Endogenous inflammatory response to dermal wound healing in the fetal and adult mouse,” Developmental Dynamics, vol. 212, no. 3, pp. 385–393, 1998.View at: Google Scholar
J. Hopkinson-Woolley, D. Hughes, S. Gordon, and P. Martin, “Macrophage recruitment during limb development and wound healing in the embryonic and foetal mouse,” Journal of Cell Science, vol. 107, no. 5, pp. 1159–1167, 1994.View at: Google Scholar
B. C. Wulff, A. E. Parent, M. A. Meleski, L. A. Dipietro, M. E. Schrementi, and T. A. Wilgus, “Mast cells contribute to scar formation during fetal wound healing,” Journal of Investigative Dermatology, vol. 132, no. 2, pp. 458–465, 2012.View at: Google Scholar
A. J. Cowin, T. M. Holmes, P. Brosnan, and M. W. J. Ferguson, “Expression of TGF-β and its receptors in murine fetal and adult dermal wounds,” European Journal of Dermatology, vol. 11, no. 5, pp. 424–431, 2001.View at: Google Scholar
T. A. Wilgus, A. M. Ferreira, T. M. Oberyszyn, V. K. Bergdall, and L. A. DiPietro, “Regulation of scar formation by vascular endothelial growth factor,” Laboratory Investigation, vol. 88, no. 6, pp. 579–590, 2008.View at: Publisher Site | Google Scholar
F. W. Frantz, D. A. Bettinger, J. H. Haynes et al., “Biology of fetal repair: the presence of bacteria in fetal wounds induces an adult-like healing response,” Journal of Pediatric Surgery, vol. 28, no. 3, pp. 428–434, 1993.View at: Publisher Site | Google Scholar
S. Öztürk, M. Deveci, M. Sengezer, and Ö. Günhan, “Results of artificial inflammation in scarless foetal wound healing: an experimental study in foetal lambs,” British Journal of Plastic Surgery, vol. 54, no. 1, pp. 47–52, 2001.View at: Publisher Site | Google Scholar
E. I. Egozi, A. M. Ferreira, A. L. Burns, R. L. Gamelli, and L. A. DiPietro, “Mast cells modulate the inflammatory but not the proliferative response in healing wounds,” Wound Repair and Regeneration, vol. 11, no. 1, pp. 46–54, 2003.View at: Publisher Site | Google Scholar
A. M. Szpaderska, E. I. Egozi, R. L. Gamelli, and L. A. DiPietro, “The effect of thrombocytopenia on dermal wound healing,” Journal of Investigative Dermatology, vol. 120, no. 6, pp. 1130–1137, 2003.View at: Publisher Site | Google Scholar
J. V. Dovi, L. K. He, and L. A. DiPietro, “Accelerated wound closure in neutrophil-depleted mice,” Journal of Leukocyte Biology, vol. 73, no. 4, pp. 448–455, 2003.View at: Publisher Site | Google Scholar
P. Martin, D. D'Souza, J. Martin et al., “Wound healing in the PU.1 null mouse—tissue repair is not dependent on inflammatory cells,” Current Biology, vol. 13, no. 13, pp. 1122–1128, 2003.View at: Publisher Site | Google Scholar
K. W. Liechty, T. M. Crombleholme, D. L. Cass, B. Martin, and N. S. Adzick, “Diminished interleukin-8 (IL-8) production in the fetal wound healing response,” Journal of Surgical Research, vol. 77, no. 1, pp. 80–84, 1998.View at: Publisher Site | Google Scholar
K. W. Liechty, N. S. Adzick, and T. M. Crombleholme, “Diminished interleukin 6 (IL-6) production during scarless human fetal wound repair,” Cytokine, vol. 12, no. 6, pp. 671–676, 2000.View at: Publisher Site | Google Scholar
R. Alam, D. Kumar, D. Anderson-Walters, and P. A. Forsythe, “Macrophage inflammatory protein-1α and monocyte chemoattractant peptide- 1 elicit immediate and late cutaneous reactions and activate murine mast cells in vivo,” Journal of Immunology, vol. 152, no. 3, pp. 1298–1303, 1994.View at: Google Scholar
L. A. DiPietro, P. J. Polverini, S. M. Rahbe, and E. J. Kovacs, “Modulation of JE/MCP-1 expression in dermal wound repair,” American Journal of Pathology, vol. 146, no. 4, pp. 868–875, 1995.View at: Google Scholar
L. A. DiPietro, M. Burdick, Q. E. Low, S. L. Kunkel, and R. M. Strieter, “Mip-1α as a critical macrophage chemoattractant in murine wound repair,” Journal of Clinical Investigation, vol. 101, no. 8, pp. 1693–1698, 1998.View at: Google Scholar
S. J. Fortunato, R. Menon, K. F. Swan, and S. J. Lombardi, “Interleukin-10 inhibition of interleukin-6 in human amniochorionic membrane: transcriptional regulation,” American Journal of Obstetrics and Gynecology, vol. 175, no. 4, pp. 1057–1065, 1996.View at: Publisher Site | Google Scholar
S. J. Fortunato, R. Menon, and S. J. Lombardi, “The effect of transforming growth factor and interleukin-10 on interleukin-8 release by human amniochorion may regulate histologic chorioamnionitis,” American Journal of Obstetrics and Gynecology, vol. 179, no. 3, pp. 794–799, 1998.View at: Publisher Site | Google Scholar
K. W. Liechty, H. B. Kim, N. S. Adzick, and T. M. Crombleholme, “Fetal wound repair results in scar formation in interleukin-10-deficient mice in a syngeneic murine model of scarless fetal wound repair,” Journal of Pediatric Surgery, vol. 35, no. 6, pp. 866–873, 2000.View at: Google Scholar
W. H. Peranteau, L. Zhang, N. Muvarak et al., “IL-10 overexpression decreases inflammatory mediators and promotes regenerative healing in an adult model of scar formation,” Journal of Investigative Dermatology, vol. 128, no. 7, pp. 1852–1860, 2008.View at: Publisher Site | Google Scholar
T. A. Wilgus, V. K. Bergdall, K. L. Tober et al., “The impact of cyclooxygenase-2 mediated inflammation on scarless fetal wound healing,” American Journal of Pathology, vol. 165, no. 3, pp. 753–761, 2004.View at: Google Scholar
T. A. Wilgus, Y. Vodovotz, E. Vittadini, E. A. Clubbs, and T. M. Oberyszyn, “Reduction of scar formation in full-thickness wounds with topical celecoxib treatment,” Wound Repair and Regeneration, vol. 11, no. 1, pp. 25–34, 2003.View at: Publisher Site | Google Scholar
V. C. Sandulache, A. Parekh, H. S. Li-Korotky, J. E. Dohar, and P. A. Hebda, “Prostaglandin E2 differentially modulates human fetal and adult dermal fibroblast migration and contraction: implication for wound healing,” Wound Repair and Regeneration, vol. 14, no. 5, pp. 633–643, 2006.View at: Publisher Site | Google Scholar
A. Parekh, V. C. Sandulache, A. S. Lieb, J. E. Dohar, and P. A. Hebda, “Differential regulation of free-floating collagen gel contraction by human fetal and adult dermal fibroblasts in response to prostaglandin E2 mediated by an EP2/cAMP-dependent mechanism,” Wound Repair and Regeneration, vol. 15, no. 3, pp. 390–398, 2007.View at: Publisher Site | Google Scholar
G. S. Schultz and A. Wysocki, “Interactions between extracellular matrix and growth factors in wound healing,” Wound Repair and Regeneration, vol. 17, no. 2, pp. 153–162, 2009.View at: Publisher Site | Google Scholar
M. T. Longaker, E. S. Chiu, N. S. Adzick, M. Stern, M. R. Harrison, and R. Stern, “Studies in fetal wound healing: V. A prolonged presence of hyaluronic acid characterizes fetal wound fluid,” Annals of Surgery, vol. 213, no. 4, pp. 292–296, 1991.View at: Google Scholar
T. Sawai, N. Usui, K. Sando et al., “Hyaluronic acid of wound fluid in adult and fetal rabbits,” Journal of Pediatric Surgery, vol. 32, no. 1, pp. 41–43, 1997.View at: Publisher Site | Google Scholar
D. C. West, D. M. Shaw, P. Lorenz, N. S. Adzick, and M. T. Longaker, “Fibrotic healing of adult and late gestation fetal wounds correlates with increased hyaluronidase activity and removal of hyaluronan,” International Journal of Biochemistry and Cell Biology, vol. 29, no. 1, pp. 201–210, 1997.View at: Publisher Site | Google Scholar
S. M. Alaish, D. Yager, R. F. Diegelmann, I. K. Cohen, and N. S. Adzick, “Biology of fetal wound healing: hyaluronate receptor expression in fetal fibroblasts,” Journal of Pediatric Surgery, vol. 29, no. 8, pp. 1040–1043, 1994.View at: Publisher Site | Google Scholar
M. Hu, E. E. Sabelman, Y. Cao, J. Chang, and V. R. Hentz, “Three-dimensional hyaluronic acid grafts promote healing and reduce scar formation in skin incision wounds,” Journal of Biomedical Materials Research, vol. 67, no. 1, pp. 586–592, 2003.View at: Google Scholar
J. A. Iocono, H. P. Ehrlich, K. A. Keefer, and T. M. Krummel, “Hyaluronan induces scarless repair in mouse limb organ culture,” Journal of Pediatric Surgery, vol. 33, no. 4, pp. 564–567, 1998.View at: Publisher Site | Google Scholar
B. A. Mast, R. F. Diegelmann, T. M. Krummel, and I. K. Cohen, “Hyaluronic acid modulates proliferation, collagen and protein synthesis of cultured fetal fibroblasts,” Matrix, vol. 13, no. 6, pp. 441–446, 1993.View at: Google Scholar
B. P. Toole, T. N. Wight, and M. I. Tammi, “Hyaluronan-cell interactions in cancer and vascular disease,” Journal of Biological Chemistry, vol. 277, no. 7, pp. 4593–4596, 2002.View at: Publisher Site | Google Scholar
R. S. Cotran, V. Kumar, and T. Collins, Pathologic Basis of Disease, WB Saunders Company, Philadelphia, Pa, USA, 1999.
J. E. Schwarzbauer, “Alternative splicing of fibronectin: three variants, three functions,” BioEssays, vol. 13, no. 10, pp. 527–533, 1991.View at: Google Scholar
F. Pagani, L. Zagato, C. Vergani, G. Casari, A. Sidoli, and F. E. Baralle, “Tissue-specific splicing pattern of fibronectin messenger RNA precursor during development and aging in rat,” Journal of Cell Biology, vol. 113, no. 5, pp. 1223–1229, 1991.View at: Google Scholar
A. F. Muro, A. K. Chauhan, S. Gajovic et al., “Regulated splicing of the fibronectin EDA exon is essential for proper skin wound healing and normal lifespan,” Journal of Cell Biology, vol. 162, no. 1, pp. 149–160, 2003.View at: Publisher Site | Google Scholar
D. J. Whitby and M. W. J. Ferguson, “The extracellular matrix of lip wounds in fetal, neonatal and adult mice,” Development, vol. 112, no. 2, pp. 651–668, 1991.View at: Google Scholar
D. J. Whitby, M. T. Longaker, M. R. Harrison, N. S. Adzick, and M. W. J. Ferguson, “Rapid epithelialisation of fetal wounds is associated with the early deposition of tenascin,” Journal of Cell Science, vol. 99, no. 3, pp. 583–586, 1991.View at: Google Scholar
M. T. Longaker, D. J. Whitby, M. W. J. Ferguson et al., “Studies in fetal wound healing: III. Early deposition of fibronectin distinguishes fetal from adult wound healing,” Journal of Pediatric Surgery, vol. 24, no. 8, pp. 799–805, 1989.View at: Google Scholar
D. L. Cass, K. M. Bullard, K. G. Sylvester et al., “Epidermal integrin expression is upregulated rapidly in human fetal wound repair,” Journal of Pediatric Surgery, vol. 33, no. 2, pp. 312–316, 1998.View at: Publisher Site | Google Scholar
S. R. Beanes, C. Dang, C. Soo et al., “Down-regulation of decorin, a transforming growth factor-beta modulator, is associated with scarless fetal wound healing,” Journal of Pediatric Surgery, vol. 36, no. 11, pp. 1666–1671, 2001.View at: Publisher Site | Google Scholar
P. G. Scott, C. M. Dodd, A. Ghahary, Y. J. Shen, and E. E. Tredget, “Fibroblasts from post-burn hypertrophic scar tissue synthesize less decorin than normal dermal fibroblasts,” Clinical Science, vol. 94, no. 5, pp. 541–547, 1998.View at: Google Scholar
K. Sayani, C. M. Dodd, B. Nedelec et al., “Delayed appearance of decorin in healing burn scars,” Histopathology, vol. 36, no. 3, pp. 262–272, 2000.View at: Publisher Site | Google Scholar
C. Soo, F. Y. Hu, X. Zhang et al., “Differential expression of fibromodulin, a transforming growth factor-β modulator, in fetal skin development and scarless repair,” American Journal of Pathology, vol. 157, no. 2, pp. 423–433, 2000.View at: Google Scholar
Z. Zhang, T. M. Garron, X. J. Li et al., “Recombinant human decorin inhibits TGF-β1-induced contraction of collagen lattice by hypertrophic scar fibroblasts,” Burns, vol. 35, no. 4, pp. 527–537, 2009.View at: Publisher Site | Google Scholar
K. R. Knight, D. A. Lepore, R. S. C. Horne et al., “Collagen content of uninjured skin and scar tissue in foetal and adult sheep,” International Journal of Experimental Pathology, vol. 74, no. 6, pp. 583–591, 1993.View at: Google Scholar
H. N. Lovvorn, D. T. Cheung, M. E. Nimni, N. Perelman, J. M. Estes, and N. S. Adzick, “Relative distribution and crosslinking of collagen distinguish fetal from adult sheep wound repair,” Journal of Pediatric Surgery, vol. 34, no. 1, pp. 218–223, 1999.View at: Publisher Site | Google Scholar
J. R. Merkel, B. R. DiPaolo, G. G. Hallock, and D. C. Rice, “Type I and Type III collagen content of healing wounds in fetal and adult rats,” Proceedings of the Society for Experimental Biology and Medicine, vol. 187, no. 4, pp. 493–497, 1988.View at: Google Scholar
S. R. Goldberg, R. P. McKinstry, V. Sykes, and D. A. Lanning, “Rapid closure of midgestational excisional wounds in a fetal mouse model is associated with altered transforming growth factor-β isoform and receptor expression,” Journal of Pediatric Surgery, vol. 42, no. 6, pp. 966–973, 2007.View at: Publisher Site | Google Scholar
R. Carter, K. Jain, V. Sykes, and D. Lanning, “Differential expression of procollagen genes between mid- and late-gestational fetal fibroblasts,” Journal of Surgical Research, vol. 156, no. 1, pp. 90–94, 2009.View at: Publisher Site | Google Scholar
A. S. Colwell, T. M. Krummel, M. T. Longaker, and H. P. Lorenz, “Early-gestation fetal scarless wounds have less lysyl oxidase expression,” Plastic and Reconstructive Surgery, vol. 118, no. 5, pp. 1125–1129, 2006.View at: Publisher Site | Google Scholar
G. S. Chin, S. Lee, M. Hsu et al., “Discoidin domain receptors and their ligand, collagen, are temporally regulated in fetal rat fibroblasts in vitro,” Plastic and Reconstructive Surgery, vol. 107, no. 3, pp. 769–776, 2001.View at: Google Scholar
E. Y. Huang, H. Wu, E. R. Island et al., “Differential expression of urokinase-type plasminogen activator and plasminogen activator inhibitor-1 in early and late gestational mouse skin and skin wounds,” Wound Repair and Regeneration, vol. 10, no. 6, pp. 387–396, 2002.View at: Publisher Site | Google Scholar
Z. M. Peled, E. D. Phelps, D. L. Updike et al., “Matrix metalloproteinases and the ontogeny of scarless repair: the other side of the wound healing balance,” Plastic and Reconstructive Surgery, vol. 110, no. 3, pp. 801–811, 2002.View at: Google Scholar
C. M. Dang, S. R. Beanes, C. Soo et al., “Decreased expression of fibroblast and keratinocyte growth factor isoforms and receptors during scarless repair,” Plastic and Reconstructive Surgery, vol. 111, no. 6, pp. 1969–1979, 2003.View at: Publisher Site | Google Scholar
P. Martin and J. Lewis, “Actin cables and epidermal movement in embryonic wound healing,” Nature, vol. 360, no. 6400, pp. 179–183, 1992.View at: Publisher Site | Google Scholar
J. Brock, K. Midwinter, J. Lewis, and P. Martin, “Healing of incisional wounds in the embryonic chick wing bud: characterization of the actin purse-string and demonstration of a requirement for Rho activation,” Journal of Cell Biology, vol. 135, no. 4, pp. 1097–1107, 1996.View at: Google Scholar
A. J. Cowin, N. Hatzirodos, J. T. Teusner, and D. A. Belford, “Differential effect of wounding on actin and its associated proteins, paxillin and gelsolin, in fetal skin explants,” Journal of Investigative Dermatology, vol. 120, no. 6, pp. 1118–1129, 2003.View at: Publisher Site | Google Scholar
S. Nodder and P. Martin, “Wound healing in embryos: a review,” Anatomy and Embryology, vol. 195, no. 3, pp. 215–228, 1997.View at: Publisher Site | Google Scholar
J. McCluskey and P. Martin, “Analysis of the tissue movements of embryonic wound healing—DiI studies in the limb bud stage mouse embryo,” Developmental Biology, vol. 170, no. 1, pp. 102–114, 1995.View at: Publisher Site | Google Scholar
J. M. Estes, J. S. Vande Berg, N. S. Adzick, T. E. MacGillivray, A. Desmouliere, and G. Gabbiani, “Phenotypic and functional features of myofibroblasts in sheep fetal wounds,” Differentiation, vol. 56, no. 3, pp. 173–181, 1994.View at: Publisher Site | Google Scholar
D. L. Cass, K. G. Sylvester, E. Y. Yang, T. M. Crombleholme, and N. S. Adzick, “Myofibroblast persistence in fetal sheep wounds is associated with scar formation,” Journal of Pediatric Surgery, vol. 32, no. 7, pp. 1017–1022, 1997.View at: Publisher Site | Google Scholar
K. J. Rolfe, J. Richardson, C. Vigor, L. M. Irvine, A. O. Grobbelaar, and C. Linge, “A role for TGF-β1-induced cellular responses during wound healing of the non-scarring early human fetus?” Journal of Investigative Dermatology, vol. 127, no. 11, pp. 2656–2667, 2007.View at: Publisher Site | Google Scholar
C. Soo, S. R. Beanes, F. Y. Hu et al., “Ontogenetic transition in fetal wound transforming growth factor-β regulation correlates with collagen organization,” American Journal of Pathology, vol. 163, no. 6, pp. 2459–2476, 2003.View at: Google Scholar
P. Martin, M. C. Dickson, F. A. Millan, and R. J. Akhurst, “Rapid induction and clearance of TGFβ1 is an early response to wounding in the mouse embryo,” Developmental Genetics, vol. 14, no. 3, pp. 225–238, 1993.View at: Google Scholar
J. H. Levine, H. L. Moses, L. I. Gold, and L. B. Nanney, “Spatial and temporal patterns of immunoreactive transforming growth factor β1, β2, and β3 during excisiona wound repair,” American Journal of Pathology, vol. 143, no. 2, pp. 368–380, 1993.View at: Google Scholar
M. Shah, D. M. Foreman, and M. W. J. Ferguson, “Control of scarring in adult wounds by neutralising antibody to transforming growth factor β,” The Lancet, vol. 339, no. 8787, pp. 213–214, 1992.View at: Publisher Site | Google Scholar
M. Shah, D. M. Foreman, and M. W. J. Ferguson, “Neutralising antibody to TGF-β1,2 reduces cutaneous scarring in adult rodents,” Journal of Cell Science, vol. 107, no. 5, pp. 1137–1157, 1994.View at: Google Scholar
M. Shah, D. M. Foreman, and M. W. J. Ferguson, “Neutralisation of TGF-β1 and TGF-β2 or exogenous addition of TGF-β3 to cutaneous rat wounds reduces scarring,” Journal of Cell Science, vol. 108, no. 3, pp. 985–1002, 1995.View at: Google Scholar
M. W. Ferguson, J. Duncan, J. Bond et al., “Prophylactic administration of avotermin for improvement of skin scarring: three double-blind, placebo-controlled, phase I/II studies,” The Lancet, vol. 373, no. 9671, pp. 1264–1274, 2009.View at: Publisher Site | Google Scholar
L. Wu, A. Siddiqui, D. E. Morris, D. A. Cox, S. I. Roth, and T. A. Mustoe, “Transforming growth factor β3 (TGFβ3) accelerates wound healing without alteration of scar prominence: histologic and competitive reverse- transcription-polymerase chain reaction studies,” Archives of Surgery, vol. 132, no. 7, pp. 753–760, 1997.View at: Google Scholar
W. Chen, X. Fu, S. Ge et al., “Ontogeny of expression of transforming growth factor-β and its receptors and their possible relationship with scarless healing in human fetal skin,” Wound Repair and Regeneration, vol. 13, no. 1, pp. 68–75, 2005.View at: Publisher Site | Google Scholar
Z. M. Peled, S. J. Rhee, M. Hsu, J. Chang, T. M. Krummel, and M. T. Longaker, “The ontogeny of scarless healing II: EGF and PDGF-B gene expression in fetal rat skin and fibroblasts as a function of gestational age,” Annals of Plastic Surgery, vol. 47, no. 4, pp. 417–424, 2001.View at: Google Scholar
J. H. Haynes, D. E. Johnson, B. A. Mast et al., “Platelet-derived growth factor induces fetal wound fibrosis,” Journal of Pediatric Surgery, vol. 29, no. 11, pp. 1405–1408, 1994.View at: Publisher Site | Google Scholar
D. M. Ornitz and N. Itoh, “Fibroblast growth factors,” Genome Biology, vol. 2, no. 3, article 3005, 2001.View at: Google Scholar
W. Chen, X. B. Fu, S. L. Ge, T. Z. Sun, and Z. Y. Sheng, “Ontogeny of expression of basic fibroblast growth factor and its receptors in human fetal skin,” Chinese Journal of Traumatology, vol. 8, no. 6, pp. 332–338, 2005.View at: Google Scholar
S. Ihara, Y. Motobayashi, E. Nagao, and A. Kistler, “Ontogenetic transition of wound healing pattern in rat skin occurring at the fetal stage,” Development, vol. 110, no. 3, pp. 671–680, 1990.View at: Google Scholar
A. S. Colwell, S. R. Beanes, C. Soo et al., “Increased angiogenesis and expression of vascular endothelial growth factor during scarless repair,” Plastic and Reconstructive Surgery, vol. 115, no. 1, pp. 204–212, 2005.View at: Publisher Site | Google Scholar
J. I. Jones and D. R. Clemmons, “Insulin-like growth factors and their binding proteins: biological actions,” Endocrine Reviews, vol. 16, no. 1, pp. 3–34, 1995.View at: Google Scholar
S. Beckert, S. Haack, H. Hierlemann et al., “Stimulation of steroid-suppressed cutaneous healing by repeated topical application of IGF-I: different mechanisms of action based upon the mode of IGF-I delivery,” Journal of Surgical Research, vol. 139, no. 2, pp. 217–221, 2007.View at: Publisher Site | Google Scholar
T. T. Phan, I. J. Lim, B. H. Bay et al., “Role of IGF system of mitogens in the induction of fibroblast proliferation by keloid-derived keratinocytes in vitro,” American Journal of Physiology, vol. 284, no. 4, pp. C860–C869, 2003.View at: Google Scholar
A. Ghahary, Y. J. Shen, R. Wang, P. G. Scott, and E. E. Tredget, “Expression and localization of insulin-like growth factor-1 in normal and post-burn hypertrophic scar tissue in human,” Molecular and Cellular Biochemistry, vol. 183, no. 1-2, pp. 1–9, 1998.View at: Publisher Site | Google Scholar
K. J. Rolfe, A. D. Cambrey, J. Richardson, L. M. Irvine, A. O. Grobbelaar, and C. Linge, “Dermal fibroblasts derived from fetal and postnatal humans exhibit distinct responses to insulin like growth factors,” BMC Developmental Biology, vol. 7, article 124, 2007.View at: Publisher Site | Google Scholar
G. S. Chin, W. J. H. Kim, T. Y. Lee et al., “Differential expression of receptor tyrosine kinases and Shc in fetal and adult rat fibroblasts: toward defining scarless versus scarring fibroblast phenotypes,” Plastic and Reconstructive Surgery, vol. 105, no. 3, pp. 972–979, 2000.View at: Google Scholar
H. Pratsinis, C. C. Giannouli, I. Zervolea, S. Psarras, D. Stathakos, and D. Kletsas, “Differential proliferative response of fetal and adult human skin fibroblasts to transforming growth factor-β,” Wound Repair and Regeneration, vol. 12, no. 3, pp. 374–383, 2004.View at: Publisher Site | Google Scholar
A. S. Colwell, T. M. Krummel, M. T. Longaker, and H. P. Lorenz, “Fetal and adult fibroblasts have similar TGF-β-mediated, Smad-dependent signaling pathways,” Plastic and Reconstructive Surgery, vol. 117, no. 7, pp. 2277–2283, 2006.View at: Publisher Site | Google Scholar
P. Martin and C. D. Nobes, “An early molecular component of the wound healing response in rat embryos—induction of c-fos protein in cell at the epidermal wound margin,” Mechanisms of Development, vol. 38, no. 3, pp. 209–216, 1992.View at: Publisher Site | Google Scholar
S. Gangnuss, A. J. Cowin, I. S. Daehn et al., “Regulation of MAPK activation, AP-1 transcription factor expression and keratinocyte differentiation in wounded fetal skin,” Journal of Investigative Dermatology, vol. 122, no. 3, pp. 791–804, 2004.View at: Publisher Site | Google Scholar
J. P. Brockes, “Amphibian limb regeneration: rebuilding a complex structure,” Science, vol. 276, no. 5309, pp. 81–87, 1997.View at: Publisher Site | Google Scholar
D. M. Gardiner, M. A. Torok, L. M. Mullen, and S. V. Bryant, “Evolution of vertebrate limbs: robust morphology and flexible development,” American Zoologist, vol. 38, no. 4, pp. 659–671, 1998.View at: Google Scholar
E. J. Stelnicki, L. G. Komuves, A. O. Kwong et al., “HOX homeobox genes exhibit spatial and temporal changes in expression during human skin development,” Journal of Investigative Dermatology, vol. 110, no. 2, pp. 110–115, 1998.View at: Google Scholar
L. G. Kömüves, E. Michael, J. M. Arbeit et al., “HOXB4 homeodomain protein is expressed in developing epidermis and skin disorders and modulates keratinocyte proliferation,” Developmental Dynamics, vol. 224, no. 1, pp. 58–68, 2002.View at: Publisher Site | Google Scholar
K. Jain, V. Sykes, T. Kordula, and D. Lanning, “Homeobox genes Hoxd3 and Hoxd8 are differentially expressed in fetal mouse excisional wounds,” Journal of Surgical Research, vol. 148, no. 1, pp. 45–48, 2008.View at: Publisher Site | Google Scholar
E. J. Stelnicki, J. Arbeit, D. L. Cass, C. Saner, M. Harrison, and C. Largman, “Modulation of the human homeobox genes PRX-2 and HOXB13 in scarless fetal wounds,” Journal of Investigative Dermatology, vol. 111, no. 1, pp. 57–63, 1998.View at: Publisher Site | Google Scholar
J. A. Mack, S. R. Abramson, Y. Ben et al., “HOXB13 knockout adult skin exhibits high levels of hyaluronan and enhanced wound healing,” The FASEB Journal, vol. 17, no. 10, pp. 1352–1354, 2003.View at: Google Scholar
K. J. Rolfe, L. M. Irvine, A. O. Grobbelaar, and C. Linge, “Differential gene expression in response to transforming growth factor-β1 by fetal and postnatal dermal fibroblasts,” Wound Repair and Regeneration, vol. 15, no. 6, pp. 897–906, 2007.View at: Publisher Site | Google Scholar
A. S. Colwell, M. T. Longaker, and H. P. Lorenz, “Identification of differentially regulated genes in fetal wounds during regenerative repair,” Wound Repair and Regeneration, vol. 16, no. 3, pp. 450–459, 2008.View at: Publisher Site | Google Scholar
W. Chen, X. Fu, S. Ge et al., “Profiling of genes differentially expressed in a rat of early and later gestational ages with high-density oligonucleotide DNA array,” Wound Repair and Regeneration, vol. 15, no. 1, pp. 147–155, 2007.View at: Publisher Site | Google Scholar
M. R. Khorramizadeh, E. E. Tredget, C. Telasky, Q. Shen, and A. Ghahary, “Aging differentially modulates the expression of collagen and collagenase in dermal fibroblasts,” Molecular and Cellular Biochemistry, vol. 194, no. 1-2, pp. 99–108, 1999.View at: Publisher Site | Google Scholar
W. Gerstein, “Cell proliferation in human fetal epidermis,” Journal of Investigative Dermatology, vol. 57, no. 4, pp. 262–265, 1971.View at: Google Scholar
R. Carter, V. Sykes, and D. Lanning, “Scarless fetal mouse wound healing may initiate apoptosis through caspase 7 and cleavage of PARP,” Journal of Surgical Research, vol. 156, no. 1, pp. 74–79, 2009.View at: Publisher Site | Google Scholar
D. Sopher, “A study of wound healing in the fetal tissues of the cynomolgus monkey,” Laboratory Animal Handbooks, vol. 6, pp. 327–335, 1975.View at: Google Scholar
J. D. Burrington, “Wound healing in the fetal lamb,” Journal of Pediatric Surgery, vol. 6, no. 5, pp. 523–528, 1971.View at: Google Scholar
J. Hohlfeld, A. De Buys Roessingh, N. Hirt-Burri et al., “Tissue engineered fetal skin constructs for paediatric burns,” The Lancet, vol. 366, no. 9488, pp. 840–842, 2005.View at: Publisher Site | Google Scholar