Fetal Wound Repair Research Articles

The Mechanism of Excisional Fetal Wound Repair in Vitro Is Responsive to Growth Factors

The Mechanism of Excisional Fetal Wound Repair in Vitro Is Responsive to Growth Factors

Myofibroblast persistence in fetal sheep wounds is associated with scar formation

The scarless repair capabilities of the fetus are influenced by the size of the wound and the gestational age of the fetus. Whereas small wounds heal scarlessly, large wounds in the same fetus heal with scar. Myofibroblasts are specialized fibroblasts that express α-smooth muscle actin (α-SMA), a contractile cytoskeletal protein. The authors hypothesized that small fetal wounds that heal scarlessly will have a relative absence of myofibroblasts, whereas large wounds that heal with scar will have abundant myofibroblasts. In this study, an incisional wound and four punch biopsy wounds of 2, 4, 6, and 10 mm diameter were placed on the backs of 60- to 90-day-gestation fetal sheep (term, 145 days). Fourteen days after wounding, the healed fetal wounds were harvested, the repair morphology was determined (scarless, transitional repair, or scar), and the expression of α-SMA was analyzed by immunohistochemistry. In the second part of this study the authors analyzed the temporal expression of α-SMA in fetal wounds at 1, 2, 3, and 7 days after wounding in 70-day-gestation fetal sheep. In the 14-day wounds, the authors found that α-SMA was not expressed in any incisional or 2-mm wound that healed scarlessly, but it was expressed in all wounds that healed with scar. Overall, α-SMA expression strongly correlated with increasing wound size ( P < .005). Myofibroblasts were seen as early as 24 hours after wounding, and at 3 and 7 days all wounds showed strong expression of α-SMA. These results demonstrate that although myofibroblasts are induced early in fetal wound repair, by 14 days there is a notable lack of myofibroblasts in wounds that heal scarlessly and an abundance of myofibroblasts in those wounds that scar. By determining the factors that regulate the disappearance of the myofibroblast in scarless fetal wounds, the authors hope to gain new insights into the mechanisms of scarless fetal repair.

Wound size and gestational age modulate scar formation in fetal wound repair

The early-gestation fetus heals incisional skin wounds rapidly and scarlessly. The morphology with which the fetus heals excisional skin wounds remains unclear. To characterize excisional fetal wound repair, and to determine whether there is a developmentally regulated wound-size threshold beyond which fetal skin heals with scar, the authors created excisional wounds in fetal lambs of varying gestational age. Time-mated pregnant ewes carrying 22 fetuses at 60 to 90 days' gestation (term, 145 days) underwent laparotomy and hysterotomy. An incisional wound and four circular, punch biopsy wounds of 2, 4, 6, and 10 mm in diameter were placed on the back of each fetal lamb and marked with India ink. The wounds were harvested at 14 days' postwounding and examined grossly and microscopically after serial sectioning and histological staining. Morphological features of all wounds were graded. By 14 days' postwounding all fetal wounds had healed completely. For lambs at each gestational age, increasing wound size was strongly associated with an increase in the frequency of scar. Also, as gestational age increased from 60 to 90 days' gestation the frequency of scarless repair decreased. By understanding the cellular and molecular processes that mediate scar formation with increasing wound size and advancing gestational age, the authors hope to gain further insight into the mechanisms of scarless fetal wound repair.

The differential regulation and secretion of proteinases from fetal and neonatal fibroblasts by growth factors

One of the major differences between fetal and adult wound repair is the unique ability of fetal wounds to heal without scarring. Since scar formation is a function of extracellular matrix deposition, the regulation of this component is fundamental in tissue remodeling. In this study, we have characterized the differences in the secretion of matrix-degrading proteases, namely urokinase plasminogen activator and gelatinase A and B, from fetal and neonatal fibroblasts. In addition, we examined the modulation of these protease levels by growth factors known to be important in wound repair. The results indicate that the secretion of these proteases differ significantly between the two cell types. The levels of urokinase plasminogen activator and its inhibitor were notably higher in media conditioned by neonatal fibroblasts in comparison to fetal samples. In contrast, the basal level of gelatinase A was comparable in both cell types, whilst the level of gelatinase B was elevated in the fetal fibroblasts. Transforming growth factor-β1 reduced the level of urokinase plasminogen activator and stimulated the secretion of plasminogen activator inhibitor-1 and progelatinase B in both neonatal and fetal fibroblasts. However, only progelatinase A and an activated form of gelatinase B were significantly elevated in fetal fibroblasts. In contrast, platelet-derived growth factor stimulated urokinase plasminogen activator, its inhibitor and both gelatinase A and B, an effect which was more apparent in fetal fibroblasts. This difference in protease regulation may be reflected in the differing rate and quality of tissue remodeling observed during adult vs fetal wound repair.

A model of scarless human fetal wound repair is deficient in transforming growth factor beta.

A model of scarless human fetal wound repair is deficient in transforming growth factor beta.

Effect of Fetal Serum on Fibroblast Pericellular Matrix Formation

Hyaluronic acid (HA)-dependent pericellular matrices (PCM) play a role in embryonic differentiation of mesodermal cells. Fetal fibroblasts have significantly larger PCMs than postnatal fibroblasts. To determine if this property is intrinsic to fetal fibroblasts or induced by factors in the fetal environment, we studied the effect of fetal bovine serum (FBS) of varying gestational age on human fetal, newborn, and adult fibroblast PCM formation. Cultured human fetal, newborn, and adult fibroblasts were plated in triplicate at a density of 1 × 105cells and incubated in medium alone, medium containing 10% pooled FBS, or FBS from the first, second, or third trimesters. The cells were photographed and morphometric analysis of PCM was performed by the erythrocyte exclusion technique. PCM size was expressed as a ratio of the maximal width of the cell matrix to the maximal width of the cell. The unpaired Student'sttest was used for statistical analysis. The earlier the gestational age of FBS used, the larger the PCM observed in fetal and newborn fibroblasts. The PCM of fetal fibroblasts was significantly larger (P< 0.001) than that of newborn and adult fibroblasts at each gestational age of FBS tested (fetal >> newborn > adult). Medium containing pooled FBS caused a significant (P< 0.001) increase in PCM size in all cell lines compared with serum-free medium. There are both intrinsic and extrinsic factors which affect PCM size. These factors which affect HA-dependent PCM size may contribute to a permissive microenvironment for cell migration, proliferation, and development which may be important for scarless fetal wound repair.

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

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

Fetal wound healing: an overview

The ability of fetal tissues to heal without scarring has prompted extensive research into the biochemical and molecular differences between fetal and postnatal wound healing. A thorough understanding of the basic mechanisms of fetal wound repair may to lead to approaches to correct or prevent the clinical problems encountered in abnormal adult wound healing and fetal surgery. This article contrasts the normal healing response in adults with fetal repair in animal models, highlighting investigations of extracellular matrix expression, cytokine profiles, and cellular dynamics.

Cells, matrix, growth factors, and the surgeon: The biology of scarless fetal wound repair: N.S. Adzick and H.P. Lorenz. Ann Surg 220:10–18, (July), 1994

Cells, matrix, growth factors, and the surgeon: The biology of scarless fetal wound repair: N.S. Adzick and H.P. Lorenz. Ann Surg 220:10–18, (July), 1994

A model of scarless human fetal wound repair is deficient in transforming growth factor beta

Human fetal skin heals via scarless regeneration, whereas adult skin heals with scar. Scarless repair may reflect a distinct cytokine milieu. We studied the role of the cytokine transforming growth factor beta (TGFβ) using an established model of scarless human fetal skin repair in which human fetal skin is transplanted into a subcutaneous pocket on the flank of an adult nude mouse. In this model, wounded 16-week-gestation human fetal skin heals without scar, whereas wounded adult skin heals with scar. Seven days after transplantation, incisional wounds were made in the skin grafts. In the first phase of the study, wounds were harvested from 1 hour to 4 weeks postwounding, and immunohistochemistry was performed for TGFβ (isoform nonspecific), TGFβ 1, and TGFβ 2. Scarfree wounds in the fetal skin grafts did not show TGFβ staining. In contrast, wounds in adult grafts that heal with scar demonstrated isoform nonspecific TGFβ staining from 6 hours through 21 days, TGFβ 1 from 6 hours through 21 days, and TGFβ 2 from 12 hours through 7 days. In the second phase of the study, a slow-release disk with 0.01, 0.1, 1.0, or 10 μg of TGFβ 1 was placed beneath the fetal skin graft at the time of wounding. Fourteen days postwounding, there was marked scarring in the fetal grafts treated with TGFβ 1, and the size of the scar was proportional to the amount of TGFβ 1 applied. The relative lack of TGFβ, a cytokine known to promote fibrosis, may be one reason why the fetus heals by regeneration rather than scarring. In contrast, the fibrosis characteristic of postnatal wound repair may be associated with an excess of TGFβ. These findings suggest that anti-TGFβ therapeutic strategies may ameliorate scar formation in children and adults.

Platelet-derived growth factor induces fetal wound fibrosis

The fetal response to cutaneous injury differs markedly from that of the adult, proceeding with only minimal inflammation, minimal fibroblast proliferation, and only essential collagen deposition. Although the sequence of events in adult wound healing is well defined and thought to be controlled in part by potent polypeptide cytokines, relatively sparse information exists regarding growth factor involvement in fetal wound repair. Thus, the authors sought to examine the effect of platelet-derived growth factor (PDGF), a putative adult wound healing regulator, on the cellular and extracellular matrix events at a fetal wound site. SILASTIC ® wound implants containing 0, 1.0, 5.0, or 10.0 ng of human PDGF were placed subcutaneously on the backs of 24-day-gestation fetal rabbits (full term, 31 days) and then harvested after either 1, 3, or 5 days in utero. The specimens underwent standard histological processing and were evaluated in a blinded fashion. Compared with controls, PDGF-treated implants had a marked increase in acute inflammation, fibroblast recruitment, and collagen and hyaluronic acid deposition; these differences appeared to be largely time- and PDGF dose-dependent. Thus, the fetal system is responsive to an adult wound healing mediator, and these data suggest that fetal repair proceeds in the absence of PDGF.

Scarless human fetal skin repair is intrinsic to the fetal fibroblast and occurs in the absence of an inflammatory response

The fetus heals skin wounds without scar formation. Human fetal skin that is transplanted to a subcutaneous location on an adult athymic mouse and subsequently wounded heals without scar formation, whereas the same skin heals with scar formation when transplanted to a cutaneous location. In situ hybridization with species-specific DNA probes and immunohistochemistry were performed to characterize the healing process of human fetal skin in these two locations. Species-specific human and mouse DNA probes were constructed and used to probe graft wounds under high stringency in situ hybridization conditions. Immunostaining for species-specific fibroblasts, macrophages, and neutrophils was also performed. We found that the cutaneous human fetal grafts healed with scar and showed an influx of mouse fibroblasts and macrophages. In contrast, subcutaneous human fetal grafts showed exclusively human fetal fibroblasts in the wound environment, an absence of inflammatory cells, and scar-free repair. We conclude that the highly organized collagen deposition in scarless human fetal wound repair appears to be intrinsic to the human fetal fibroblasts and occurs in the absence of an adult-like inflammatory response.

Cells, Matrix, Growth Factors, and the Surgeon The Biology of Scarless Fetal Wound Repair

This review updates the surgeon about the cellular, matrix, and growth factor components of scarless fetal wound repair. Fetal skin wound healing is characterized by the absence of scar tissue formation. This unique repair process is not dependent on the sterile, aqueous intrauterine environment. The differences between fetal and adult skin wound healing appear to reflect processes intrinsic to fetal tissue, such as the unique fetal fibroblasts, a more rapid and ordered deposition and turnover of tissue components, and, particularly, a markedly reduced inflammatory infiltrate and cytokine profile. Scarless fetal wounds are relatively deficient in the inflammatory cytokine, transforming growth factor beta (TGF-beta). In contrast, the fibrosis characteristic of adult wound repair may be associated with TGF-beta excess. Recent experimental studies suggest that specific anti-TGF-beta therapeutic strategies can ameliorate scar formation in adult wound repair and fibrotic diseases. Inhibitors of TGF-beta may be important future drugs to control scar. Based on the scarless fetal wound repair model, a number of ways in which the matrix and cellular response of the healing adult wound might be manipulated to reduce scarring are reviewed.

Wound healing in fetal limb organ culture.

The in vitro wound healing responses in whole-limb organ culture of fetal rats at day 19 of gestation were compared with the intrauterine wound repair. In vitro, after a skin incision was made in the lower forelimb, the subcutaneous tissue and the dermis regenerated. Reepithelialization appeared within two to five days. Thus, the wound healing was comparable to the intrauterine fetal wound repair. The whole limb organ culture may be a useful and suitable in vitro test system to study the mechanisms involved in fetal wound healing to search for compounds required in fetal skin regeneration and to test factors tht might influence it.