The late phases of wound healing: histological and ultrastructural studies of collagen and elastic-tissue formation

Fibrillin-1 and elastin are differentially expressed in hypertrophic scars and keloids

Hypertrophic scars and keloids are two forms of excessive cutaneous scarring. Considering the importance of extracellular matrix elements in tissue repair, a morphological and quantitative analysis of the elastic system components (fibrillin-1 and elastin) was performed in normal skin, normal scars, hypertrophic scars, and keloids. In superficial and deep dermis, fibrillin-1 volume density was significantly higher in normal skin compared with normal scars, hypertrophic scars, and keloids. The fibrillin-1 volume density did not show differences between hypertrophic scars and keloids in superficial or deep dermis. In superficial dermis, elastin volume density was higher in normal skin compared with normal scars, hypertrophic scars, and keloids. In deep dermis, the elastin volume density was higher in keloids compared with normal skins, normal scars, and hypertrophic scars. We showed that the distribution of fibrillin-1 and elastin is disrupted in all kinds of scars analyzed, but there are two patterns: one for normal scars and another for excessive scars.

Mechanical forces induce scar remodeling. Study in non-pressure-treated versus pressure-treated hypertrophic scars

Reparative process of second and third degree burns usually results in hypertrophic scar formation that can be treated by pressure. Although this method is efficient, its mechanisms of action are not known. In this work, we have studied the histological organization of hypertrophic scars submitted to pressure. Skin biopsies were performed 2 to 7 months after the onset of treatment in two adjacent regions of the scar, non-pressure- or pressure-treated and analyzed by immunohistochemistry and transmission electron microscopy for extracellular matrix organization and cellular morphology. In non-pressure-treated regions, fibrillin deposits did not present the classical candelabra-like pattern under epidermis and were reduced in dermis; in pressure-treated regions the amount was increased compared to non-pressure-treated regions but the organization was still disturbed. In non-pressure-treated regions, elastin was present in patch deposits; in pressure-treated regions elastin formed fibers, smaller than in normal dermis. Tenascin was present in the whole dermis in non-pressure-treated regions, whereas in pressure-treated regions it was observed only under epidermis and around vessels, as in normal skin. alpha-Smooth muscle actin-expressing myofibroblasts were absent in normal skin, present in large amounts in non-pressure-treated regions, and almost absent in pressure-treated regions. The disturbed ultrastructural organization of dermal-epidermal junction observed in non-pressure-treated regions disappeared after pressure therapy; typical features of apoptosis in fibroblastic cells and morphological aspects of collagen degradation were observed in pressure-treated regions. Our results show that, in hypertrophic scars, pressure therapy restores in part the extracellular matrix organization observed in normal scar and induces the disappearance of alpha-smooth muscle actin-expressing myofibroblasts, probably by apoptosis. We suggest that the pressure acts by accelerating the remission phase of the postburn reparative process.

Wound management of the airway mucosa: comparison with skin in a rabbit model

In comparison to the extensive study of skin wound healing, there have been few reports investigating mucosal wound healing. Our primary objective was to compare the natural progression of wound healing in airway mucosa to skin in a rabbit model. Split-thickness skin wounds and subglottic mucosal wounds created by drill injury were compared on days 0, 1, 3, 5, 7, 14 and 21 after injury. Histologic examination was performed by a veterinary pathologist blinded to sample identity. Subglottic wounds showed a 'fibrinous clot' overlying the epithelium, analogous to the fibrin crust in skin wounds. Re-epithelialization started on day 5 in the subglottic epithelium and was complete by day 14; fibroplasia and fibrosis in the lamina propria were present on days 7-21. This wound healing profile paralleled the skin epidermis and dermis, respectively. The epithelial changes, however, were temporally extended in the airway. Our secondary objective was to determine the effects of treating airway mucosa with a bioresorbable membrane, modified sodium hyaluronate and carboxymethylcellulose (modified HA/CMC), placed over the subglottic wounds of four rabbits after drill injury. Subglottic wounds treated with modified HA/CMC showed a more mature epithelium and less fibrosis on day 21. In this pilot study, the application of a bioresorbable membrane improved mucosal wound healing at both the epithelial and lamina propria levels. Clearly, a larger study must be performed to confirm this interesting observation.

Elastic fibers in scar tissue

The capacity of the skin to be stretched and to return to its resting position is correlated to the quantity and to the quality of the elastic fiber network. Although elastic fibers have been demonstrated in scars, the time course of their appearance in scars and their role in scar elasticity has not been elucidated. A study was therefore undertaken to evaluate the elastic fiber network in scars. The scars studied were from re-excision specimens following a biopsy performed for a benign or a malignant process. A total of 182 scars were evaluated in patients of different age groups. Miller's elastic tissue stain, considered to be superior to Verhoeff's van Giesen stain, was used. No elastic fibers were detected in any of 116 scars which were of less than 3 months' duration. In 66 scars present for over 3 months, a progressive increase in elastic fibers was present, first as focal and thin fibers, then as diffuse and thicker fibers. For scars of the same duration, a regional difference was noted in that scars from the back contained more and thicker elastic fibers than those from the cheek. When patients were stratified according to age, no appreciable difference was noted in the density of elastic fibers in both new and old scars between the different age groups. These results show that the synthesis of elastic tissue fibers in scars is a function of duration and site of the scar.

Mentolabial sulcus: a histologic study

This study deals with the structure of the lower lip in the region of the mentolabial sulcus with particular emphasis on the morphologic factors responsible for producing and maintaining the sulcus. The results of this study provide information about the anatomic framework as it pertains to reconstructive and aesthetic procedures on the lower face deformed by injuries.

Age-related changes in wound healing

Knowledge of the physiology of wound healing, in particular the recovery of the dermal and epidermal compartments and the co-ordination of these processes by the cytokine network, is of great importance to rational wound management. The individual components of the wound healing process have been studied using various in vitro and in vivo models, comparing young, adult and aged individuals. Many of the processes involved in wound healing are impaired in the elderly. However, in elderly patients not suffering from concomitant diseases, the rate of wound healing is normal or only slightly reduced. Various 'systemic factors' (endocrine and haematological diseases, nutritional deficiencies and medications) and 'regional disorders' (vascular and neural diseases) may impair wound healing. These complicating conditions occur more frequently in aged subjects. Failure of wound healing in the elderly is a chronic disabling condition, which occurs frequently in our society, requiring a major investment of medical care.

Ultrastructural study of a corneal keloid

A 69-year-old man developed keloid overgrowth on his left cornea in response to an injury from a fingernail. The lesion was removed by superficial lamellar keratectomy and was studied by electron microscopy, and light microscopy after immunoperoxidase staining for actin. The surgical specimen revealed disorganised, anteriorly atrophied and posteriorly vascularised connective tissue stroma. The epithelium was oedematous, thin, non-keratinised, and contained cells with features of myoblastic differentiation. Stromal fibroblasts were found in several distinct ultrastructural forms including young active fibroblasts, myofibroblasts, inactive fibroblasts (fibrocytes) and fibroblasts with prominently fibrillar cytoplasm. Fibroblasts with glycogen storage and/or pseudonuclear inclusions were also seen. Macrophages and lymphocytes were scattered in the stroma, and intact nerves were also present. An irregular 2-65 microns band of 10 nm filament meshwork existed at the posterior border of the keloid stroma, and deep localised patches of climatic degeneration were detected.

Development of the human fetal phreno-esophageal membrane and its role in the anti-reflux mechanism

The structural development of the phreno-esophageal membrane was studied in 34 human fetuses ranging from 9-26 weeks of age. Horizontal and coronal sections of the lower esophagus, cardia, and diaphragm were stained with Victoria Blue and Gomori's aldehyde fuchsin to show elastic fibers, and with peracetic-aldehyde fuchsin to show pre-elastic, oxytalan, and elastic fibers, being the elastic elements. The membrane was found to be present between the lower esophagus and diaphragm at 9 weeks. The peracetic-aldehyde fuchsin stain showed many elastic elements in this membrane, but the elastic stain showed only a few elastic fibers under 13 weeks. There was no basic structural change of the membrane from 9 to 26 weeks except for an increasing number of fibers and no basic difference from the anatomical arrangement described in the adult with fibers running from the fascial covering of the undersurface of the diaphragm upwards to the esophageal adventitia. Three dimensional observation revealed that the abdominal part of the esophagus was fixed caudally by the posterior part of the membrane. These findings suggest the position-stabilizing function of this membrane and the developmental co-operation between the hiatal crus and the lower esophageal sphincter as an anti-reflux mechanism.

Histologic changes in skin associated with aging

This is a review of histologic changes noted in the skin of elderly individuals. Among the epidermal changes associated with skin aging are a flattened dermal-epidermal junction, giving the appearance of atrophy and cellular heterogeneity. The melanocyte density declines slowly, and the Langerhans cells decrease in number with advancing age. Among the dermal changes are attenuation in the number and diameter of elastic fibers in the papillary dermis, an increase in number and thickness of the same fibers in the reticular dermis, and a coarsening of collagen fibers with an increase in density of the collagen network. A decrease in the dermal cell population as well as a functional decline in glandular activity are also noted with intrinsic aging. A decline in hair number, rate of growth, and diameter, along with a slowing of the rate of growth of nails, have been well documented with progressive aging.

Elastosis in meningioma. A case report and electron microscopic study

A 55-year-old man underwent left frontoparietal craniotomy for total removal of a parasagittal meningioma. The tumor showed a predominant pattern of meningotheliomatous meningioma and a partial pattern of angiomatous, transitional and fibrous meningioma. A striking feature was the appearance of unusually numerous elastinophilic material in the intercellular stroma. We observed a process in which the progress of elastosis changed the appearance of meningotheliomatous meningioma to a hypocellular, and subsequently acellular fibroelastotic node. Three years after the first craniotomy, meningioma recurred at the same site. The recurrent tumor also showed the histological pattern of meningotheliomatous meningioma with stromal elastosis, as previously observed. This is the first report of a case of meningioma with stromal elastosis. The present case represents the first unequivocal demonstration of elastogenesis in meningioma.

Persistence of scleroderma-like phenotype in normal fibroblasts after prolonged exposure to soluble mediators from mononuclear cells

Supernatants of mononuclear cells (MNC-SN) were shown to increase synthesis of glycosaminoglycan (GAG) by cultured normal dermal fibroblasts. Fibroblasts from the skin of patients with progressive systemic sclerosis (PSS, scleroderma) were hyporesponsive. We exposed fibroblasts outgrowing from explants of normal adult skin to MNC-SN for up to 30 generations in culture. MNC-SN were obtained by incubating normal MNC with concanavalin A. Four experimental, 4 normal control, and 3 PSS control lines were passaged by trypsinizing and splitting the cultures 1:2 every 7 days. At the third and fifth passages, portions of the experimental fibroblasts were removed from MNC-SN, then passaged in medium alone. Cell counts, assays for GAG, and electron microscopy were performed and increases in GAG after brief reexposure to MNC-SN were determined at the third, fifth, and eighth passages. In normal dermal fibroblasts, baseline GAG production, measured by 3H-glucosamine uptake, was low and increased as much as 15 times after reexposure to MNC-SN. In contrast, production was high in both experimental and PSS lines, and increases after reexposure to MNC-SN were consistently small. This PSS-like behavior persisted in experimental fibroblasts removed from MNC-SN at the third and fifth passages. Growth of experimental and scleroderma fibroblasts was slower than that of control fibroblasts. Ultrastructurally, both scleroderma and experimental dermal fibroblasts differed from normal fibroblasts by their oval cellular shape, indentations in nuclear membrane, numerous organelles and bundles of microfilaments, prominent Golgi, and intranuclear inclusions. These experiments indicate that normal adult dermal fibroblasts subjected to MNC-SN in vitro acquire a scleroderma-like phenotype that persists for many generations.

Collagen fiber formation in repair tissue: development of strength and toughness

Dermal repair tissue shows a progressive increase in collagen content which may be related to the wound tensile strength. Wound strength and extensibility are lower than those found in normal skin. In animals, wounds closed by metal clips are chosen as a model to study the proliferative and remodeling phases of healing from a mechanical and morphological point of view. During the proliferative phase the low wound strength is associated with formation of collagen fibers of small diameter, later, (days 28-45) an acute change appears corresponding to the remodeling phase, with increased collagen fiber diameters observed by scanning electron microscopy and light microscopy, and increased tensile strength and toughness. By 180 days, wound strength and collagen fiber morphology were close to that observed in the normal skin. These observations show a direct relationship between collagen fiber diameter and tensile strength. In addition, packing density of collagen fibrils (determined by the birefringence retardation per unit thickness under polarized light) was unchanged until day 90, although collagen fiber diameters increased during this time.

Topical retinoic acid enhances the repair of ultraviolet damaged dermal connective tissue

Ultraviolet (UV) irradiation induces excessive accumulations of elastic fibers in animal and human skin. Collagen is damaged and glycosaminoglycans are vastly increased. Formerly considered an irreversible change, we recently showed, post-irradiation, that a band of normal connective tissue was laid down subepidermally . Because of its ability to stimulate fibroblasts and enhance healing of wounds, we thought it likely that retinoic acid (RA) would promote the formation of this subepidermal zone of reconstruction. Hairless mice were irradiated for 10 weeks with Westinghouse FS20 sunlamps for a total UV dose of 7 J/cm2. Then, 0.05% RA was applied for 5 and 10 weeks. Observations were made by light and electron microscopy. In contrast to controls treated with vehicle, the reconstruction zone was significantly wider in RA-treated mice. The enhanced repair was dose related. Histochemically and ultrastructurally, collagen was normal, fibroblasts were numerous and in a configuration of high metabolic activity.

Scanning electron microscopy of the structural reconstruction of the abdominal wall after experimental paramedian incision

The various healing stages of experimental paramedian incisions in the right rectus sheath of 36 albino rats were examined by utilizing the scanning electron and the light microscope. The successive reconstruction processes were visualized stereoscopically at a cellular level. During the inflammatory stage (7 days) various inflammatory cells accumulated around a wide network of trabeculae which traversed the gap of the wound. The fibrillogenetic stage increased in the period between the 2nd and 12th weeks postoperatively. Various stages of fiber maturation were visualized. Mechanisms of fiber formation, maturation, and junction between the newly formed fibers and the old healthy ones at the wound margin were also seen three dimensionally and described. The newly formed fibers were always arranged parallel to each other in a definite direction. This direction had a constant angular relationship to the long axis of the wound, i.e., the line of incision, regardless of the direction of the incision itself. This constant relationship might prove to be useful to the surgeon while choosing his incision in the anterior abdominal wall.

An ultrastructural study on periductal elastosis in human breast tumors

An ultrastructural study on elastosis of human breast tumors was made with special attention to the periductal elastosis and the cell responsible for elastic fiber formation. The elastosis was found prominently in scirrhous type of duct carcinoma. In the area of mild periductal elastosis, the elastic fibers with many microfibrils and a tiny central elastin were seen around the periductal fibroblasts which were characterized by attenuated cytoplasms with aggregates of microfilaments and slightly developed rough endoplasmic reticulum. With the thickening of the periductal wall, such an area was replaced by abundant mature elastic fibers with peripheral microfibrils and a few intervening ordinary fibroblasts. Therefore, it was suggested that the periductal fibroblasts which transformed into ordinary fibroblasts during the development of elastosis were primarily concerned with the elastic fiber formation. In the interlobular tissue in which both fibroblasts and myofibroblasts were present, the elastic fibers were larger than those of the periductal area and had less microfibrils in their periphery. The relationship between microfibrils and elastin during the early elastosis, maturation process of the elastic fibers, and cell modulation of the fibroblasts in the breast elastosis were discussed.

Prevention of ultraviolet damage to the dermis of hairless mice by sunscreens

To assess the ability of sunscreens to protect connective tissue from actinic damage, hairless mice were irradiated with Westinghouse FS20 sunlamps thrice weekly for 30 weeks. Each exposure, consisting mainly of UV-B and the less energetic UV-A, was approximately 6 human minimal erythema doses under these lights. One group of animals received irradiation only. The other 2 groups were treated, prior to irradiation, with sunscreens of either low or high sun protection factors (SPF 2 and SPF 15, respectively). Skin biopsies were taken at 10-week intervals and were stained with various histochemical stains to reveal changes in the dermis. The unprotected, irradiated animals showed a great increase in the following: reticulin fibers, elastic fibers to the extent of elastosis, neutral and acid mucopolysaccharides and melanin production. The SPF 15 sunscreen completely prevented these changes. The SPF 2 sunscreen was less effective. These effects were substantiated by ultrastructural examination of the tissues by electron microscopy. A surprising histologic finding was the repair capability of the dermis in the post-irradiation period.

Aggressive fibromatosis involving the paramandibular soft tissues. A study with the aid of electron microscopy

The distinction at the level of light microscopy between aggressive fibromatosis and low-grade malignancies with fibroblastic features may be difficult. An electron microscopic study of four cases of aggressive fibromatosis of the mandibular soft tissue was undertaken to determine whether any ultrastructural characteristics could be identified that would aid in a more uniform distinction between these lesions. The pertinent findings include the identification of cells of fibroblastic derivation showing a range of organelle-poor to organelle-rich features, cytoplasmic microfibrils, and dilated rough endoplasmic reticulum profiles. These features are discussed in the light of previously published findings of other forms of aggressive fibromatosis and closely related lesions. The study reaffirms that although electron microscopy may be useful in confirming the cell of origin in these lesions, the accurate diagnosis of fibrous tumors still rests with the proper correlation of clinical and light microscopic features. Clinical follow-up of the cases supports both the diagnosis of aggressive fibromatosis and the recommended treatment of adequate local excision.

Electron dense staining affinities of mouse oxytalan and elastic fibers

The staining affinity of electron dense stains to mouse palatal elastic fibers and periodontal oxytalan fibers was assessed and compared. Tissues were stained routinely with uranyl acetate and lead citrate or with elastic tissue stains including: (1) silver tetraphenylporphine sulfonate, (2) tannic acid technique, and (3) a high iron diamine sequence. Staining results were assessed with an electron microscope. Palatal elastic fibers demonstrated staining affinity to all elastic stain techniques. Oxytalan fibers did not demonstrate affinity to elastic fiber stains used. Based on electron dense stains, elastic and oxytalan fibers were dissimilar, in contrast to results reported utilizing light microscopic stains.

Myxoma of the mandible--a fibroblastic tumor

A case of myxoma of the mandible is described. The tumor was examined by both light and electron microscopy. Histochemistry showed an abundant acid mucopolysaccharide stroma, embedded in which were stellate cells with branching processes. Ultrastructurally, these cells were seen to be fibroblasts. Occasional myofibroblasts were seen in the tumor. No odontogenic epithelium was identified, and this component was not thought to be important in the histogenesis of the tumor.

Studies of elastic tissue formation in the developing bovine ligamentum nuchae

The foetal ligamentum nuchae showed two distinct stages of development, each characterised by its cell population and fibre products. Fibroblasts of the early phase have extensive ergastoplasm apparently associated with collagen production; those of the late phase have an "attenuated" cytoplasm and coincide with an increase of elastic tissue content. The elastic fibre comprised a core of fine elastin fibrils (100--130 nm diameter) and a surrounding mantle of microfibrillar protein. As development proceeded, the elastin fibrils appeared to coalesce with each other and also with elastin fibrils from adjacent fibres to form composite mature elastic fibre--a process which was accompanied by a loss of microfibrils. A characteristic of elastic fibres from adult ligament, not apparent in the foetal tissue, was that of bifurcation.

Ultrastructural features of proliferating fibroblasts in inflammatory granulomas

Proliferating fibroblasts in subcutaneous connective tissue of rats after injection of peanut oil or implantation of an almost insoluble synthetic material (silicap) were characterized electron microscopically. In tissue samples of both the foreign body granulomas typical fibroblasts with abundant rough endoplasmic reticulum and a peculiar cellular modulation resembling histiocytes concerning their organelle composition were found. The morphological picture of the latter cells does not allow the conclusion that their function must be a merely phagocytic one. True myofibroblasts as detected in other stages of connective tissue proliferation are not present. The capillary vessels show a clear proliferation of their vascular cells and migration of these cells with assumption of fibroblastic features is suggested basing on morphological observations.

Ultrastructural cytology of regenerating tendon--an experimental study

Cellular differentiations in regenerating tendon tissue of rats and guinea pigs were examined by the aid of the electron microscope. Fibroblasts with certain variations were found as basic cell types. Corresponding to the organelle composition classical fibroblasts, fibroblasts with histiocyte-like features and fibroblasts with myoide differentiations (comparable to the so-called myofibroblasts) were identified. Furthermore, proliferating capillaries with remarkable pericytic activities among other things producing fibroblast-like features must be mentioned. This fact led to the conclusion, that a part of fibroblasts in the proliferating connective tissue during tendon repair may derive from pericytes. Our ultrastructural investigations showed proof of the great plasticity of fibroblasts which function as stem cells in connective tissue regeneration.

Cellular features in desmoid fibromatosis and well-differentiated fibrosarcomas: an electron microscopic study

In the study presented here the ultrastructural cellular features of three desmoids and four well-differentiated fibrosarcomas were compared. Electron microscopically, the tumors were almost identical relative to qualitative traits. The majority of cells corresponded to fibroblast-like cells with certain morphological variations. Especially cells with characteristics of myofibroblasts must be emphasized, whereas cells with an organelle composition of classical fibroblasts were surprisingly seldom. Considering the relations of cells to each other and to vessels the prevailing origin of tumor cells from preexisting fibroblasts is suggested.

Evolution of mesenchymal cells in fetal rat lung

The evolution of connective tissue cells in the developing fetal rat lung is studied under the electron microscope from the 15th until the 21st day of gestation and is compared to the evolution of epithelial cells. Three successive types of stem cells ("mesocytoblasts") are present during the first stages of lung development studied (15 to 18 days of gestation). These stem cells appear to be able to differentiate into fibroblasts or into smooth muscle cells, according to their localization along the broncho-alveolar tubule. Myoblasts are situated near the bronchial epithelium, whereas fibroblasts occur under the alveolar epithelium. Epithelo-mesenchymal interactions are assumed to play a role in this differentiation process. Synthesis of both, collagen and elastic fibers and of cytoplasmic filaments by fibroblasts as well as by myoblasts reveal the multiple potentialities of the mesenchymal stem cell and suggest a common origin. The early fibroblast in characterized by long cytoplasmic processes which contain numerous cytofilaments, and by the presence of collagen fibers in the vicinity of the cell. Later on, (20 days of gestation) the mature fibroblast of the lung mesenchyme shows areas of RER, glycogen and lipidic vacuoles in its cytoplasm. Cytofilaments are numerous within very long cytoplasmic processes and elastic and collagen fibers are very frequent beside the cytoplasmic membrane. The earliest fibroblast differentiation occurs under the epithelium of primitive respiratory bronchioles, which indicate the limit between the bronchial and the alveolar territories. Later on, differentiating fibroblasts are found throughout the whole alveolar walls. Connective tissue cells other than mesenchymal stem cells, fibroblasts or myoblasts are observed during lung development. Vacuolar cells, similar to Hofbauer cells, transiently appear on the 16th day of gestation. On the 20th and the 21st day macrophage-like cells are present in the septal space of the alveolar wall. The absence of intermediate stages of differentiation and parallel evolution of blood cells suggest that those connective tissue cells are differentiated elsewhere and have then migrated from blood into lung mesenchyme. No cell death has been observed in the developing lung.

Modified collagen membrane as a skin substitute: preliminary studies

Modified collagen membrane when compared to autograft, homograft, heterograft and silicone polymer membrane, demonstrated a superior adherence on split and full-thickness surfaces, but proved to be an inferior covering for granulating surfaces. Water vapor transport was found to be adequate and adaptable to modification. It was found to be permeable to most commonly used topical antibiotics, and no significant antigenicity could be demonstrated. In a controlled animal burn study, modified collagen membrane proved superior to homograft and heterograft in regard to mortality, time to grafting, bacteriology and autograft take. These studies provide a background for further laboratory and clinical studies now in progress.