The fetal fibroblast: the effector cell of scarless fetal skin repair.

Human fetal skin heals without scar formation when it is transplanted to a subcutaneous location on an adult athymic mouse and subsequently wounded. In contrast, human fetal skin of identical gestational age heals with scar formation when transplanted to a cutaneous location on the athymic mouse recipient. To determine if mouse (adult) or human (fetal) fibroblasts are healing the graft wounds, we performed indirect immunohistochemistry for mouse and human collagen types I and III. Full-thickness skin grafts (n = 51) from human fetuses at 18 weeks' (n = 4) or 24 weeks' (n = 2) gestational age were placed onto athymic mice in two locations: cutaneously onto a fascial bed and subcutaneously in a pocket under the murine panniculus carnosus. Linear incisions were made in each graft 7 days after transplantation. Grafts were harvested at 7, 14, and 21 days after wounding and stained with hematoxylin and eosin or Mallory's trichrome. Immunohistochemistry for either human collagen type I or type III or for mouse collagen type I was performed. The subcutaneous grafts healed with human collagen types I and III in a scarless pattern. The wound collagen pattern was reticular and unrecognizable from the surrounding dermis. Hair follicles and sebaceous gland patterns were unchanged in the wounded dermis. Conversely, the cutaneous grafts healed with mouse collagen in a scar pattern with disorganized collagen fibers and no appendages. Mouse collagen scar was present along the base of the cutaneous grafts and as a thin capsule around the subcutaneous grafts. We conclude that (1) subcutaneous grafts heal with human fetal collagen and no scar formation, and (2) cutaneous grafts heal with mouse collagen in a scar pattern. Fetal fibroblasts can heal fetal skin wounds without scar despite being perfused by adult serum and inflammatory cells in an adult environment. These data suggest that the fetal fibroblast is the major effector cell for scarless fetal skin repair.

Adult skin wounds in the fetal environment heal with scar formation.

OBJECTIVE: This study investigated the influence of the fetal environment on the healing characteristics of adult skin. SUMMARY BACKGROUND DATA: The remarkable ability of the fetus to heal without scarring is poorly understood. The unique qualities of fetal wound healing may be caused by the fetal environment, the fetal tissues, or a combination of both. There are numerous differences between the prenatal and postnatal environments that may play a role in the unique fetal response to injury. METHODS: Full-thickness adult sheep skin was transplanted onto the backs of 60-day-gestation fetal lambs (term, 145 days of gestation). The adult skin grafts were thus perfused by fetal blood and bathed in amniotic fluid. Previous work has demonstrated that, before midgestation, fetal lambs do not reject allogenic skin grafts. Forty days later (100 days of gestation), incisional wounds were made on both the adult skin graft and the adjacent fetal skin. The wounds were harvested 14 days postwounding and analyzed by both light microscopy and immunohistochemical testing using antibodies to collagen types I, III, and VI. RESULTS: The wounds in the adult skin grafts healed with scar formation. This observation contrasts strongly with the scarless healing of the incisional fetal skin wounds. CONCLUSIONS: This study suggests that scarless fetal skin healing properties are intrinsic to fetal skin and are not primarily the result of the fetal environment.

Fetal wound healing. The ontogeny of scar formation in the non-human primate.

OBJECTIVE: This study determined how scar formation develops in a non-human primate model of fetal skin repair. SUMMARY BACKGROUND DATA: A transition from healing scarlessly to healing with scar formation characterizes skin repair in rat and sheep fetuses. New knowledge of the regulatory processes occurring in the fetal wound at the initial stages of scar formation may provide insights into the early mechanisms of scar formation. METHODS: Full-thickness wounds were made in fetal rhesus monkey lips from 75 through 114 days gestation (n = 6, term = 165 days). Wounds were harvested at 14 days postwounding and processed for histology (hematoxylin & eosin, Masson's trichrome) as well as immunohistochemistry (human type I or type III collagen). RESULTS: Wounds healed with complete restoration of normal tissue architecture in the 75-day gestation fetus. However in the 85-100 day gestation fetuses, wounds healed with an absence of hair follicles and sebaceous glands, but the dermal collagen pattern remained reticular and similar to that in unwounded dermis. At 107 days, a thin scar was present in the wound, thereby demonstrating a transition to scar formation between 100 and 107 days gestation (early 3rd trimester) in the non-human primate. CONCLUSIONS: In the non-human primate fetus, a transition from scarless repair to adult-type repair with scar formation occurs in the early third trimester. These data provide insight into the transition process; the ontogeny of scar formation is characterized initially by wounds healing without the presence of epidermal appendages but with a normal reticular dermal collagen pattern, which we term the "transition wound."

Endoscopic creation and repair of fetal cleft lip.

In utero repair of several life-threatening malformations in the human fetus is now a clinical reality, yet fetal surgery still poses significant risks to both the mother and the unborn child. Preterm labor is a major problem and is directly related to the large hysterotomy required for fetal exposure. Endoscopic surgical manipulation of the fetus, through small uterine "ports," solves this problem and may eventually permit fetal intervention for non-life-threatening malformations. In this pilot study we demonstrated the feasibility of performing endoscopic surgery on the fetus in situ. A lip incision was created and repaired using endoscopic microsurgical techniques in midgestation fetal lambs. This represents the first application of this technique for in utero fetal intervention.

A model for fetal cleft lip repair in lambs.

Fetal wounds heal without inflammation and scar formation. This phenomenon may, in the future, be applicable to human cleft lip and palate repair. However, extensive experimental work must first be done to document the benefits of in utero repair. We developed a large animal model for creation and repair of a complete cleft lip and alveolus using fetal lambs. The cleft lip and alveolus deformity was created in eight 75-day-gestation fetuses (term = 145 days) and either repaired in three layers or left unrepaired. There were four sham-operated fetuses, and all animals were alive at harvest. Repaired, unrepaired, and control fetuses were harvested at 7, 14, 21, and 70 days following surgery. The unrepaired fetuses demonstrated a complete cleft lip and alveolus with an oronasal fistula. The maxilla was asymmetrical, with the greater segment deviated toward the cleft and with decreased anterior maxillary width. In contrast, repaired cleft lip and alveolus animals showed no scar, normal thickness of the lip, and a symmetrical maxilla. Histologic analysis of the repaired wounds showed evidence of tissue regeneration without scar formation. The results of this preliminary study indicate that the fetal lamb cleft lip and alveolus model is technically feasible with an excellent survival rate. Healing occurs without scar formation. In the repaired animals, the maxilla was symmetrical. This model will be used to document facial growth following in utero repair of a cleft lip and alveolus.

Immunohistochemical localization of growth factors in fetal wound healing.

Fetal wound healing occurs rapidly, in a regenerative fashion, and without scar formation, by contrast with adult wound healing, where tissue repair results in scar formation which limits tissue function and growth. The extracellular matrix deposited in fetal wounds contains essentially the same structural components as that in the adult wound but there are distinct differences in the spatial and temporal distribution of these components. In particular the organization of collagen in the healed fetal wound is indistinguishable from the normal surrounding tissue. Rapidity of healing, lack of an inflammatory response, and an absence of neovascularization also distinguish fetal from adult wound healing. The mechanisms controlling these differing processes are undefined but growth factors may play a critical role. The distribution of growth factors in healing fetal wounds is unknown. We have studied, by immunohistochemistry, the localization of platelet-derived growth factor (PDGF), transforming growth factor beta (TGF beta), and basic fibroblast growth factor (bFGF), in fetal, neonatal, and adult mouse lip wounds. TGF beta and bFGF were present in neonatal and adult wounds, but were not detected in the fetal wounds, while PDGF was present in fetal, neonatal, and adult wounds. This pattern correlates with the known effects in vitro of these factors, the absence of an inflammatory response and neovascularization in the fetal wound, and the patterns of collagen deposition in both fetal and adult wounds. The results suggest that it may be possible to manipulate the adult wound to produce more fetal-like, scarless, wound healing.

Rapid epithelialisation of fetal wounds is associated with the early deposition of tenascin.

Wound healing is a complex process involving the interaction of many cell types with the extracellular matrix (ECM). Fetal skin wound healing differs from that in the adult in that it occurs rapidly and without scar formation. The mechanisms underlying these differing processes may be related to the fetal environment, the stage of differentiation of the fetal cells or the ECM deposited in the wound. The spatial and temporal distribution of two components of the ECM, fibronectin and tenascin, were studied by immunostaining of cryosections from trunk wounds of fetal and adult sheep. Epithelialisation was complete earlier in the fetal wound than in the adult. The distribution of fibronectin was similar in fetal and adult wounds but tenascin was present earlier in the fetal wound. Fibronectin has several roles in wound healing including acting as a substratum for cell migration and as a mediator of cell adhesion through cell surface integrins. The attachment of fibroblasts to fibronectin is inhibited by tenascin and during development the appearance of tenascin in the ECM of migratory pathways correlates with the initiation of cell migration. Similarly, the appearance of tenascin in healing wounds may initiate cell migration. Tenascin was present in these wounds prior to cell migration and the rapid epithelialisation of fetal wounds may be due to the early appearance of tenascin in the wound.

The extracellular matrix of lip wounds in fetal, neonatal and adult mice.

Wound healing in the fetus occurs rapidly, by a regenerative process and without an inflammatory response, resulting in complete restitution of normal tissue function. By contrast, in the adult, wounds heal with scar formation, which may impair function and inhibit further growth. The cellular mechanisms underlying these differing forms of wound healing are unknown but the extracellular matrix (ECM), through its effects on cell function, may play a key role. We have studied the ECM in upper lip wounds of adult, neonatal and fetal mice at days 14, 16 and 18 of gestation. The spatial and temporal distribution of collagen types I, III, IV, V and VI, fibronectin, tenascin, laminin, chondroitin and heparan sulphates were examined immunohistochemically. Results from the fetal groups were essentially similar whilst there were distinct differences between fetus, neonate and adult. Fibronectin was present at the surface of the wound in all groups at 1 h post-wounding. Tenascin was also present at the wound surface but the time at which it was first present differed between fetus (1 h), neonate (12 h) and adult (24 h). The time of first appearance paralleled the rate of wound healing which was most rapid in the fetus and slowest in the adult. Tenascin inhibits the cell adhesion effect of fibronectin and during development the appearance of tenascin correlates with the initiation of cell migration. During wound healing the appearance of tenascin preceded cell migration and the rapid closure of fetal wounds may be due to the early appearance of tenascin in the wound. Collagen types I, III, IV, V and VI were present in all three wound groups but the timing and pattern of collagen deposition differed, with restoration of the normal collagen pattern in the fetus and a scar pattern in the adult. This confirms that lack of scarring in fetal wounds is due to the organisation of collagen within the wound and not simply lack of collagen formation. The distribution of chondroitin sulphate differed between normal fetal and adult tissues and between fetal and adult wounds. Its presence in the fetal wound may alter collagen fibril formation. No inflammatory response was seen in the fetal wounds. The differences in the ECM of fetal and adult wounds suggests that it may be possible to alter the adult wound so that it heals by a fetal-like process without scar formation, loss of tissue function or restriction of growth.

Fetal diaphragmatic wounds heal with scar formation.

Fetal wound healing is fundamentally different from wound healing in the adult. Although experimental work in mice, rats, rabbits, monkeys, and sheep has demonstrated that fetal healing occurs without inflammation and scarring, all of these studies have been limited to fetal skin wounds. Whether all fetal tissues heal in a regenerative-like fashion is unknown. Amniotic fluid exposure may play an important role in scarless fetal skin wound healing, but the effect of amniotic fluid on fetal mesothelial wound healing has not been characterized. To investigate these questions we created bilateral linear diaphragmatic wounds in 100-day gestation fetal lambs (term = 145 days). The right thoracotomy was closed to exclude amniotic fluid. In contrast, the left thoracotomy was fashioned into an Eloesser flap which permitted the left diaphragmatic wound to be continually bathed in amniotic fluid. Wounds were harvested after 1, 2, 7, or 14 days and analyzed by light microscopy and immunohistochemistry with antibodies to collagen types I, III, IV, and VI. Whether bathed in or excluded from amniotic fluid, the mesothelial-lined diaphragm healed with scar formation and without evidence of muscle regeneration. Interestingly, diaphragmatic wounds exposed to amniotic fluid were covered by a thick fibrous collagen peel similar to that seen in gastroschisis bowel. These findings indicate that not all fetal tissues share the unique scarless healing properties of fetal skin.

Cartilaginous pseudocyst of the external auricle in children with atopic eczema.

Four children with severe atopic eczema developed painless endochondral pseudocysts of the external auricle. The lesions were bilateral in two cases. In one case the lesion spontaneously resolved; of the remaining five lesions, one contained haematoma and the other four contained serous fluid. The aetiology of these lesions and their association with atopic eczema are unclear, but repeated minor trauma from rubbing may play a part.

Studies in fetal wound healing, VI. Second and early third trimester fetal wounds demonstrate rapid collagen deposition without scar formation.

The mechanisms that underlie the lack of scarring in fetal wounds are unknown, but probably relate to the control of collagen fibrillogenesis. The role of collagen in the fetal wound matrix is controversial, and several wound implant models have been used to evaluate collagen deposition in fetal wounds. Unfortunately, these models create an artificial wound environment and may thereby affect the results. In order to study fetal wound collagen deposition in linear wounds without artificially altering the wound environment, we applied a highly sensitive immunohistochemical technique that uses antibodies to collagen types I, III, IV, and VI. We found that collagen was deposited in fetal wounds much more rapidly than in adult wounds. Wound collagen deposition occurred in a normal dermal and mesenchymal pattern in second and early third trimester fetal lambs. These findings are consistent with the observation that the fetus heals rapidly and without scar formation. In contrast, wounds in late gestation fetal lambs showed some evidence of scar formation. Further studies may suggest ways to alter the adult wound so that it heals in a fetal manner.

Studies in fetal wound healing: III. Early deposition of fibronectin distinguishes fetal from adult wound healing.

Wound healing in the fetus proceeds through a series of steps that differ in the fetus and the adult. At each phase of this complex process, there is signaling between the tissue cells and the wound microenvironment, signals that are mediated by and through the extracellular matrix. We postulate that these signals occur earlier in fetal wounds, resulting in more rapid repair. To investigate this, we compared the first 24 hours of wound healing in the rabbit fetus and adult, using antibodies against key extracellular matrix macromolecular components: laminin, fibronectin, and type-specific collagens I, III, IV, and V. Fibronectin was the first matrix component to be deposited, and was visualized as early as four hours after fetal wounding and 12 hours after adult wounding. There was no evidence of new laminin or collagen deposition in either the fetal or adult wounds at any time point examined. The early deposition of fibronectin, a matrix adhesion molecule that provides a scaffolding for epithelial migration, may underlie the rapid reepithelialization observed in fetal wounds.

Posterior circulation aneurysms. Results of direct operations.

Twenty-eight patients with aneurysms of the posterior circulation were managed by direct operations, 53.6% of these being done within 14 days of a subarachnoid hemorrhage. Transvenous cardiac pacing was used in 4 of the 13 patients with aneurysms of the basilar bifurcation in order to produce a short period of profound hypotension while final dissection and clip application was performed. There were nine patients with posterior-inferior cerebellar artery/vertebral-junction aneurysms, the only one dying having a large aneurysm. The operative technique used in the majority of the 13 patients with basilar bifurcation aneurysms involved subtotal temporal lobectomy, and the operative exposure so obtained was excellent. Five patients died, one of whom rebled from an aneurysm of the basilar artery origin that could only be wrapped, the total mortality being 17.9%. Seventeen (74%) of the 23 survivors were assessed as showing good results; 5 (22%) as showing fair results, and only 1 (4%) as showing a poor result.