Differential expression of laminin alpha chains during proliferative and differentiation stages in a model for skin morphogenesis

The purpose of this study was to determine the mRNA and protein expression of laminin alpha chains at various stages of in vitro skin morphogenesis. Fibroblasts in mono-cultures express low levels of the mRNA of laminin alpha1,alpha2, alpha3 and alpha4 chains. When co-cultured with keratinocytes for 28 days, they expressed the mRNA for all these chains. Keratinocytes in monolayer expressed the laminin alpha3 chain mRNA and very low levels of the mRNA of the alpha1 and alpha2 chains, although, when recombined with fibroblasts they also expressed laminin alpha1and alpha2 mRNA, but not the laminin alpha4 mRNA. Immunocytochemistry of cells in co-culture showed that laminin alpha1, alpha3 and alpha5 chains were expressed in the epidermis, while the laminin alpha2, beta1, and gamma1 chains were noted in the dermis and at the epidermo-dermal interface. The laminin alpha1chain was first expressed during the proliferative stage (14-21 days) and the laminin alpha2 and alpha5 chains appeared later, during the differentiation stage (28-42 days). The above results suggest that epithelial-mesenchymal interactions are involved in the expression of laminin alpha chain mRNA during in vitro skin morphogenesis. In addition, there is distinct temporal and spatial expression of these chains during proliferative and differentiation stages, possibly reflecting different functions.

There is binding of collagen IV to beta 1 integrin during early skin basement membrane assembly

This study is concerned with the mechanism of basement membrane assembly in an in vitro 3-dimensional skin-culture system. Dermal fibroblasts alone can synthesize collagen IV, perlecan, and nidogen, but cannot assemble them into a basement membrane. When keratinocytes are added to the culture, however, linear assembly of collagen IV, perlecan, and nidogen is noted at the epidermo-dermal interface. Northern blots and in situ hybridization showed that perlecan and nidogen mRNAs derive exclusively from fibroblasts, while the alpha 2 (IV) collagen chain is expressed by both keratinocytes and fibroblasts, although the major source is in the mesenchyma (80%). Prior to the development of the lamina densa, collagen IV colocalizes with beta 1 integrins, most likely alpha 1 beta 1 and alpha 2 beta 1, which are known receptors for this collagen. Blocking experiments with the AIIB2 mAb (anti-beta 1 integrin subunit) and by peptide inhibition with the CB3(IV) collagen fragment disrupted the assembly of collagen IV. This study suggests that the initiation of basement-membrane formation involves binding of collagen IV molecules to keratinocyte cell-matrix integrins. These complexes act as nucleation sites for further polymerization of collagen IV molecules mostly derived from fibroblasts, by a process of self-assembly.

Initiation of skin basement membrane formation at the epidermo-dermal interface involves assembly of laminins through binding to cell membrane receptors

To study the mechanism of basement membrane formation, we determined by immunochemistry temporal and spatial expression of laminin-5 (Ln-5), laminin-1 (Ln-1) and their integrin receptors during early skin morphogenesis. A 3-dimensional skin culture was used that allows the study of the sequential molecular events of basement membrane formation at the epidermodermal interface. During early anchorage of keratinocytes to the extracellular matrix there is expression of Ln-5, BP-230 antigen and alpha3, beta1 integrin subunits. During epidermal stratification and prior to the formation of the lamina densa there is assembly of Ln-5, Ln-1, collagen IV and nidogen accompanied by keratinocyte basal clustering of alpha2, alpha3, alpha6, beta1, and beta4+ integrin subunits. The assembly pattern of Ln-1 and Ln-5 can be disturbed with functional antibodies against the beta1 (AIIB2) and alpha6 (GoH3) integrin subunits. Ln-1 assembly can also be disturbed with antibodies against its E8 domain and by competitive inhibition with a synthetic peptide (AG-73) derived from its G-4 domain. Quantitative RT-PCR showed that the dermis contributes about 80% of the laminin gamma)1 chain mRNA while 20% is produced by the epidermis which emphasizes its dual tissue origin and the major contribution of the mesenchyma in laminin production. The laminin gamma2 chain mRNA, present in Ln-5, was mostly of epidermal origin. This study presents evidence that during the initiation of basement membrane formation, laminins bind to keratinocyte plasma membrane receptors and thus may serve as nucleation sites for further polymerization of these compounds by a self-assembly process.

There is temporal and spatial expression of alpha1 (IV), alpha2 (IV), alpha5 (IV), alpha6 (IV) collagen chains and beta1 integrins during the development of the basal lamina in an "in vitro" skin model

Temporal and spatial expression of alpha1 (IV), alpha2 (IV), alpha3 (IV), alpha4 (IV), alpha5 (IV), and alpha6 (IV) collagen chains was studied during the formation of the basal lamina in an "in vitro" skin model. A sequential study was performed at 7-d and 14-d cultures (lamina densa absent) and at 28-, 36-, and 56-d cultures (lamina densa present). Expression of beta1, beta4, alpha1, alpha2, alpha3, alpha5, alpha6 integrin subunits and co-localization with collagen IV was studied by regular and laser confocal indirect immunofluorescence microscopy. mRNA expression of alpha2 (IV) and alpha6 (IV) chains was estimated by northern blots. The earliest expression of alpha1 (IV) and alpha2 (IV) collagen chains was noted in 7-d cultures restricted to basal keratinocytes. At 14-d cultures, alpha1 (IV) and alpha2 (IV) chains were noted in basal keratinocytes and as a broad band (10 microm) in the adjacent dermis. At this stage 80% of the alpha2 (IV) mRNA was expressed in the dermis and 20% in the epidermis. At 28-, 36-, and 56-d cultures the alpha1 (IV) and alpha2 (IV) chains were present in a linear distribution at the epidermo-dermal junction and in the upper dermis. The alpha6 (IV) collagen chains were expressed much later at 36-d cultures and the alpha5 (IV) at 56 d, both mostly in a linear distribution but also in the adjacent dermis. Alpha6 (IV) mRNA was demonstrated in the dermis of 36-d cultures. There was co-localization of collagen IV and beta1 integrin subunits in 14-d cultures at the matrix site of keratinocytes. Functional perturbation studies with AIIB2 monoclonal antibody (anti-beta1 subunits) and competitive inhibition with a collagen cyanogen bromide digestion derived fragment (CB3[IV]) that contains the collagen IV ligand for alpha1beta1, alpha2beta1 integrins, altered the pattern of collagen IV deposition.

Skin fibroblasts are the only source of nidogen during early basal lamina formation in vitro

The purpose of this study was to determine whether nidogen, the linkage protein of the basal lamina, is of epidermal or dermal origin. The development of the basal lamina was studied in an in vitro skin model. Preputial fibroblasts seeded onto a nylon mesh attached, proliferated, and developed a rich extracellular matrix (dermal model). Preputial keratinocytes were added to the dermal model to form a keratinocyte dermal model that ultrastructurally resembled in many respects human skin. Ultrastructural analysis revealed early stages of dermal development, including an incomplete basal lamina, aggregates of dermal filamentous material connecting to the lamina densa, bundles of 10-nm microfibrils, formation of premature hemidesmosomes, anchoring filaments, and anchoring fibrils. The cell origin of nidogen was determined in the dermal model and in the epidermal and dermal components of the keratinocyte dermal model. Specific antibodies and a cDNA probe for nidogen were used for immunofluorescence microscopy, Western and Northern blots, and for in situ hybridization studies. Our data show that fibroblasts are the only source of nidogen during early basal lamina formation. Although fibroblasts can synthesize nidogen and deposit it in the dermal matrix, no basal lamina will form unless they are recombined with keratinocytes. This suggests that the epidermis plays a major regulatory role in the production and assembly of nidogen into the basal lamina.

Collagen alterations in chronically sun-damaged human skin

The major histological characteristic of sun-damaged skin is the accumulation of an elastotic material that appears to replace collagen. This elastotic material consists primarily of elastin and histological studies suggest a large loss of collagen in the dermis of chronically sun-damaged skin. In this study, we examine the content and distribution of collagen and procollagen in sun-damaged human skin. The total collagen content of sun-damaged skin was 20% less than nonsolar-exposed skin (524 micrograms collagen per mg total protein in sun-damaged skin and 667 micrograms collagen per mg total protein in nonsolar-exposed skin). In addition, there was a 40% decrease in the content of intact amino propeptide moiety of type III procollagen in sun-damaged skin (0.68 U per 50 mg wet weight) as compared to nonsolar-exposed skin (1.12 U per 50 mg wet weight). The data suggest that this change in collagen content is due to increased degradation. The distribution of collagen in sun-damaged skin was examined by indirect immunofluorescence. Mild digestion of sun-damaged skin with elastase removed the elastin and revealed the presence of collagen in the elastotic material. Therefore, the elastin appears to mask the presence of collagen fibers in the dermis of sun-damaged skin.

Immunochemistry of a keratinocyte-fibroblast co-culture model for reconstruction of human skin

Our purpose was to determine differentiation markers of an in vitro co-culture model in which fibroblasts grown in a three-dimensional nylon mesh were recombined with human keratinocytes. The cultures were kept for 5 weeks and then processed for electron microscopy and immunochemistry. The specimens revealed an epidermis, a basal lamina, an anchoring zone, and a dermis. Epidermal differentiation was confirmed by the presence of K10-keratin, trichohyalin, and filaggrin. The basal lamina contained Type IV collagen, laminin, nidogen, and heparan sulfate. Type IV collagen, laminin, and nidogen were also noted in the extracellular matrix. Type VI collagen was present in the anchoring zone and also gave a reticulated pattern in the rest of the dermis. There was a heavy signal for tenascin and fibronectin throughout the dermis. Osteonectin was restricted to the epidermis and dermal fibroblasts. Fibrillin stained at the anchoring zone and dermis but elastin and vitronectin were negative, suggesting early formation of elastic fibrils. Collagen fibrils stained for Types I, III, and V, as well as the amino propeptide of Types I and III procollagen, suggesting newly synthesized collagen. Decorin was present throughout the dermis. The model described appears suitable for in vitro reconstruction of the skin and may be useful to study the development of various supramolecular skin structures.

Collagen fibrillogenesis in a three-dimensional fibroblast cell culture system

The purpose of this study was to follow collagen fibril formation in a newly developed three dimensional cell culture system. Human neonatal foreskin fibroblasts were grown on a nylon mesh in Dulbecco's Modified Eagles Medium (DMEM) supplemented with 10% fetal calf serum and antibiotics. Fibrillogenesis was initiated by the addition of 50 micrograms/ml ascorbate to confluent cultures. Sample meshes were processed for electron microscopy or immuno-electron microscopy. Fibrils approximately 20-30 nm in diameter, with 67 nm periodicity, were first detected five days after the addition of ascorbate. As cultures progressed, cells organized into parallel layers between which collagen fibers continued to form and increase in diameter. By day 50, fiber diameter ranged from 30 to 80 nm and large bundles were seen. No collagen fibril formation occurred in control cultures to which no ascorbate was added. However, large amounts of microfibrils were observed. Antibodies against the aminopropeptide of type I procollagen were found to bind to fibrils with diameters less than 34 nm while antibodies against the aminopropeptide of type III collagen bound primarily to fibers which ranged from 35-54 nm in diameter. We believe that this system, which morphologically resembles a normal dermis, will serve as an excellent model for the study of collagen fibrillogenesis.

Culturing keratinocytes and fibroblasts in a three-dimensional mesh results in epidermal differentiation and formation of a basal lamina-anchoring zone

The purpose of this study was to characterize an in vitro co-culture model in which fibroblasts grown in a three-dimensional nylon mesh were recombined with human keratinocytes. The cultures were kept for 3 and 5 weeks and then processed for electron microscopy. Keratinocytes showed reconstruction of an epidermis consisting of a basal layer with hemidesmosomes, a stratified epithelium with tonofilaments and desmosomes, a granular layer with keratinosomes and keratohyaline granules, and a transitional stratum corneum. Anchoring filaments, lamina densa, anchoring fibrils, bundles of elastin-associated microfibrils (diameters 10 nm) and fine collagen fibrils were formed. Collagen fibrils near the epidermis were much thinner than those in the lower levels. The present study shows that the dermal model containing metabolically active fibroblasts in their natural environment will support epidermal morphogenesis and differentiation including the formation of a basal lamina and anchoring zone.

Immunochemical analysis of human kidney reticulin

This study characterized the nature of reticulin fibrils from human kidney cortex by immunochemical analysis. Controls consisted of type I collagen fibrils derived from the kidney parietal capsule. Most of the fibrils in the capsule ranged in diameter from 60 to 80 nm whereas reticulin fibrils from the cortex ranged from 30-45 nm. Immunochemistry by light and electron microscopic examinations was carried out with antibodies directed against type I and type III collagens, their corresponding aminopropeptides, and decorin (PG-II). The ratio of type I to type III collagen was determined by cyanogen bromide peptide digests. This study showed that reticulin fibrils are hybrids of type I and type III collagens. Double immunoelectron microscopic examination showed that fibrils 20-25 nm consisted mainly of type I collagen some of which retained their aminopropeptide. Larger fibrils 30-35 nm labeled simultaneously for type I and type III collagens. However, most fibrils with diameters between 40-55 nm labeled for type III collagen and its corresponding aminopropeptide. No decorin was detected at the surface of reticulin fibrils. Purified reticulin consisted of 82% type III and 18% type I collagen whereas collagen derived from the capsule revealed 76% type I and 24% type III. The presence of the aminopropeptide of type III procollagen in reticulin fibrils is a striking feature and may play a role in regulating their diameter.

Decorin interacts with fibrillar collagen of embryonic and adult human skin

Biglycan (PG-I, BGN) and decorin (PG-II, DCN) are small proteoglycans that have been isolated in cartilage, skin, and bone. Although the function of biglycan is unknown, there is biochemical evidence that decorin interacts with fibrillar collagens (type I, type II). The purpose of this study was to perform immunofluorescence and immunoelectron microscopy and immunoblotting of human embryonic and adult skin with antibodies directed against biglycan and decorin. These antibodies were developed against synthetic peptides of the core proteins of biglycan (amino acid sequence 11-24) and decorin (amino acid sequence 5-17). Immunofluorescence microscopy showed that decorin stained embryonic and adult collagen fibrils. Biglycan did not stain collagen, but it appeared to stain the pericellular matrix of embryonic mesenchymal cells. Immunoelectron microscopy revealed labeling of all collagen fibrils with decorin antibodies regardless of their diameter, often at 60-nm periodicity. Positive stains suggest that most of the labeling was in the gap of the D-period (d and e bands) and also in one of the steps (c band). Decorin was identified by immunoblotting in fetal and adult skin. Also, significant amounts of core protein was identified lacking the dermatan sulfate chain. This study suggests that the core protein of decorin interacts with collagen fibrils although its specific function remains unknown.

Rotary shadowing of collagen monomers, oligomers, and fibrils during tendon fibrillogenesis

Collagen monomers, oligomers, and fibrillar structures were isolated from chick tendons at various stages of development and studied by rotary shadowing. Monomers of Type I collagen, solubilized in 0.15 M NaCl solutions, were mostly present as collagen, pN-collagen, and pC-collagen with few procollagen molecules. They did not form polymers, nor were they associated with a carrier. Dimers of fibrillar collagen molecules were arranged in a 4-D stagger, suggesting that this was the preferred molecular interaction for the initiation of collagen fibrillogenesis. Type XII collagen molecules were mostly free, but some were attached by their central globular domain to one end of free fibrillar collagen molecules. Tenascin and Type VI collagen were also identified. The fibril populations consisted of collagen and beaded structures. These fibrils consisted of beads (globular domains) about 23 nm in diameter, separated by a period about 27 nm in length. Beads were linked by filamentous structures. These beaded fibrils probably represent the microfibrils of elastin.

Self reactive repertoire of tight skin mouse: immunochemical and molecular characterization of anti-topoisomerase I autoantibodies

Tight skin (TSK) mice develop cutaneous hyperplasia accompanied by histopathological alterations of skin and collagen metabolism similar to those described in human scleroderma. Diffuse scleroderma, the most severe form of progressive systemic sclerosis, is associated with the production of autoantibodies specific for Scleroderma 70 antigen (topoisomerase I). Our studies show that there is an increase in the level of serum anti-topoisomerase I (topo I) autoantibodies in aged TSK mice. The monoclonal antibodies isolated from TSK mice bind to epitopes which interact with autoantibodies from scleroderma patients. A significant number of TSK monoclonal anti-topo I antibodies and serum immunoglobulin (Ig) from aged TSK mice bear a cross reactive idiotype (Id) recognized by a syngeneic monoclonal anti-Id antibody obtained from a 2 month-old TSK mouse. Analysis of V gene usage by monoclonal anti-topo I antibodies showed that the majority of these antibodies are encoded by VH genes derived from VHJ558 family pairing with VK genes from various families in a stochastic manner.

Dermal collagen fibrils are hybrids of type I and type III collagen molecules

It has been suggested that dermal collagen fibrils with 67-nm periodicity consist of hybrids of type I and type III collagens. This is based on the assumption that all these banded fibrils are coated with type III collagen regardless of their diameter. However, conclusive evidence for this form of hybridization is lacking. In order to clarify this problem dermal collagen fibrils were disrupted into microfibrils using 8 M urea. Single and double indirect immunoelectron microscopy showed type III collagen at the periphery of intact collagen fibrils but no labeling with type I collagen antibodies, suggesting that the epitopes for this collagen were masked. Disrupted collagen fibrils revealed type I collagen throughout the fibril except for the periphery which was coated with type III collagen. Almost no type III collagen was noted in the interior of the collagen fibrils. Since type III collagen is present only at the periphery it suggests that this collagen has a different role than type I collagen and may have a regulatory function in fibrillogenesis.

Type I and type III collagen interactions during fibrillogenesis

There is some evidence that type I and type III collagens may be present in the same fibril. In order to demonstrate this, double labeling immunofluorescence microscopy and immunoelectron microscopy were performed with antibodies directed against the collagen molecule and the aminopropeptide domains of type I and type III procollagens using embryonic (postabortion) and adult human skin. Double indirect and protein A immunoelectron microscopy were carried out with 5- and 15-nm gold particles. Skin extracts were also studied by immunoblotting. Double immunofluorescence microscopy with antibodies against type I and type III collagen molecules revealed patterns of fluorescence that were identical in both fetal and adult skins. Immunofluorescence microscopy using an antibody directed against the aminopropeptide of type III procollagen labeled the entire dermis in both embryonic and adult skins. In contrast, although the aminopropeptide of type I procollagen was present throughout embryonic dermis, it was markedly reduced in adult dermis, except for the epidermo-dermal junction. Double immunoelectron microscopy of fetal skin revealed labeling of the aminopropeptide of type I and type III procollagens on the same thin (20-30 nm) fibrils. Large type I fibrils (90-100 nm) were coated with type III collagen molecules and their corresponding aminopropeptide but not with the aminopropeptide of type I procollagen. The aminopropeptide of type I procollagen was present on thin fibrils only at the epidermo-dermal junction in adult skin. Immunoblotting of skin extracts revealed the presence of both pN-type III procollagen (collagen plus the aminopropeptide) and pN-type I procollagen in fetal skin, but only pN-type III in adult skin. This study demonstrates that type I and type III collagens coexist within the same fibril and that the aminopropeptide of type III procollagen is present at the surface of type I collagen fibrils that apparently have reached full growth.

Alterations in dermal collagen in ultraviolet irradiated hairless mice

Chronic exposure of the skin to sunlight results in severe dermal connective tissue damage that is characterized by the basophilic degeneration of collagen and the accumulation of an elastotic material. The aim of this study was to identify changes in collagen (the major structural protein of the skin) in ultraviolet irradiated mouse skin using immunochemical and biochemical techniques. Specific antibodies directed against the aminopropeptide of type III procollagen were used in immunofluorescence and immunoblotting studies. Immunofluorescent staining of irradiated and nonirradiated mice skin showed that the aminopropeptide of type III procollagen was distributed throughout the dermis in a pattern similar to that observed for type I collagen. Extracts of irradiated (5 and 10 weeks) and nonirradiated skins were then subjected to immunoblotting techniques. Levels of pN alpha 1, type III procollagen (measured by radioimmunoassay) were reduced in the extracts prepared from skins of mice that were irradiated for 5 and 10 weeks. Immunoelectron microscopy verified the loss of pN alpha 1 type III procollagen in irradiated skin. Collagen fibers of nonirradiated skin demonstrated normal labeling with antibody directed against the aminopropeptide of type III procollagen. In contrast, collagen fibers of 10 week irradiated skin failed to label with this antibody. The pN alpha 1 type III collagen is known to coat type I collagen fibers of normal skin. Therefore, its absence from the surface of type I collagen fibers of irradiated skin may play a role in the development of the elastotic material.

Procollagen intermediates during tendon fibrillogenesis

The purpose of this study was to correlate ultrastructural features of tendon collagen fibrils at various stages of development with the presence of procollagen, pN-collagen, pC-collagen, and the free amino propeptides and carboxyl propeptide of type I procollagen. Tendons from 10-, 14-, and 18-day chicken embryos reveal small, well-defined intercellular compartments containing collagen fibrils with diameters showing a unimodal distribution. At 21 days (hatching) and 9 days (post hatching) and at 5 weeks (post hatching), the compartments are larger, less well-defined, and there is multimodal distribution of tendon fibril diameters. Procollagen and the intermediates pN-collagen and pC-collagen are present in tendons up to 18 days. Thereafter there is a marked reduction in procollagen, whereas the intermediates persist throughout all stages of development. Similarly, free amino propeptides and carboxyl propeptides of type I procollagen were found at all stages. The amino propeptide of type III procollagen was restricted to the peritendineum until 7 weeks post hatching. At that time, a network of fibrils containing the amino propeptide of type III procollagen was seen delineating well-circumscribed compartments of collagen fibrils throughout the entire tendon. This study supports the notion that pN- and pC-collagen have an extracellular role and participate in collagen fibrillogenesis.

Identification of collagen fibrils in scleroderma skin

Skin from early and late stages of scleroderma has been shown to contain large amounts of thin (30-40 nm diameter) collagen fibrils that may be present in bundles or intermingled with large diameter fibrils (90-120 nm). The nature of these fibrils is unknown. Skin biopsies were obtained from involved areas of nine patients with progressive systemic sclerosis (PSS), one case of generalized morphea, one case of morphea, and six normal controls. Intact skin was analyzed by immunoelectron microscopy (IEM), while extracts were subjected to sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE), Western immunoblotting, radioimmunoassay (RIA), and enzyme-linked immunosorbent assay (ELISA). Fine fibrils 20-40 nm in diameter in the mid to lower dermis of scleroderma skin were labeled with antibodies directed against the aminopropeptide (AP) of type III procollagen. Antibodies directed against the AP of type I procollagen labelled fine fibrils in the lower dermis. Larger fibrils (80-120 nm) did not label. pN alpha 1 (III) was found to be present in both normal and scleroderma skin. Extracts of scleroderma skin contained 2.5 times the amount of pN (III) collagen and 3.0 times the amount of fibronectin as did extracts of normal skin. The data indicate that the increase in thin fibrils in scleroderma skin is most likely due to an increase in type III collagen, which retains the AP at its surface.

The carboxylpropeptide of type I procollagen in skin fibrillogenesis

Previous studies suggested that the aminopropeptide of type I procollagen may initiate fibril formation. The purpose of this investigation was to study the location of the carboxylpropeptide of type I procollagen during collagen fibrillogenesis. Chick embryonic and posthatching skin specimens were studied by immunofluorescence and immunoelectron microscopy and by immunoblotting with antibodies against the amino and carboxylpropeptide of type I procollagen. The carboxylpropeptide was demonstrated at the surface of collagen fibrils, 20-40 nm in diameter (10-day embryos) and in fibrils, 40-65 nm (21-day embryos). In addition, the carboxylpropeptide was found at the cell surface and free in the ground substance. The aminopropeptide was only seen in fibrils, 20-30 nm in diameter, as previously reported. Ratios of pN-collagen/pC-collagen increased from 16 days embryonic to 3 and 9 days postembryonic skins. This study suggests that both pN-collagen (aminopropeptide plus collagen) and pC-collagen (carboxylpropeptide plus collagen) participate in fibrillogenesis.

Amino and carboxyl propeptides in bone collagen fibrils during embryogenesis

Collagen fibrillogenesis was studied in tibiae of chick embryos, 9, 11, and 14 days old. Specimens were incubated with antibodies against the amino and the carboxyl propeptides of type-I collagen and subjected to ferritin-labelling immuno-electron microscopy. The amino propeptide was found in thin fibrils, 20-40 nm in diameter, distributed at 60-nm periodicity. The carboxyl propeptide antibody labelled a wide spectrum of fibrils, although the majority were in the range of 40-100 nm, distinctly larger than those labelled with the amino propeptide antibody. The presence of pN (amino propeptide plus collagen) and pC (carboxyl propeptide plus collagen) collagen was also demonstrated by Western blotting in all specimens. This study suggests that the sequence of propeptide removal may regulate collagen fibril diameter.

Collagen synthesis regulation by the aminopropeptide of procollagen I in normal and scleroderma fibroblasts

The effect of the aminopropeptide of type I procollagen, Col 1(I), on collagen synthesis by normal and scleroderma fibroblasts was investigated. Collagen synthesis was inhibited by about 42% when normal fibroblasts were labeled with 3H-proline in the presence of 4 microM Col 1(I). In contrast, collagen synthesis by scleroderma fibroblasts was inhibited to a lesser degree, about 19%. Furthermore, scleroderma fibroblasts with elevated rates of collagen synthesis (2.5-5 times normal) were inhibited by only about 10%. The data suggest that the increased accumulation of collagen in the skin of scleroderma patients may be related to a defect in the regulation of collagen synthesis by the aminopropeptide.

Collagen synthesis in scleroderma: selection of fibroblast populations during subcultures

In progressive systemic scleroderma, excessive deposition of collagen leads to fibrosis of several tissues including the skin. It has been found that different populations of fibroblasts are present in scleroderma skin; these can be obtained by establishing cell cultures from different layers of the involved skin. Excessive overproduction of collagen was noted in primary cultures of cells obtained from deeper layers of the skin of patients in an early stage of the disease, whereas control fibroblasts did not manifest significant variations dependent on the layers of skin used to initiate the cultures. The synthesis of type-I and -III collagen was found to be altered concomitantly. The production of collagen and collagenous proteins was then followed during subcultivations of overproducing fibroblasts. In many cell strains, increased synthesis of collagen and/or non-collagenous proteins had already been lost after the first subcultivation, whereas overproduction was stable in others. However, after five passages, most of the cultures showed normal collagen synthesis, which probably indicates a loss of phenotype due to successive subcultures or overgrowth by another population of fibroblasts.

Lymphokine/monokine inhibition of fibroblast proliferation and collagen production: role in progressive systemic sclerosis (PSS)

A normal fibrotic response to inflammatory stimuli appears to be dependent on the balanced production of a number of stimulatory and inhibitory fibroblast-regulatory mediators by activated mononuclear cells (MNL). To investigate whether altered mediator production contributes to the fibrosis observed in progressive systemic sclerosis (PSS), we stimulated human peripheral blood MNL with concanavalin A (Con A) and lipopolysaccharide (LPS) to produce macromolecular mediators that inhibit the proliferation and the collagen production of cultured normal human fibroblasts. The two Con A-induced mediators were lymphokines (LK) as they were exclusively produced by activated T cells and they coeluted from a Sephacryl S-200 column with a Mr of 50,000. In contrast, the two LPS-induced mediators were monokines (MK) as they were exclusively produced by activated monocytes, and they coeluted in the Mr 20,000 range. Each pair of inhibitory LK and MK may also be distinct as inhibition of collagen production still occurred in proliferatively quiescent cultures. A quantitative comparison of the levels of fibroblast-inhibitory LK/MK produced by normal volunteers and long-term PSS patients revealed that although PSS MNL produced normal levels of both collagen production inhibitory mediators, they were aberrant producers of both proliferation inhibitory mediators, being hypo-producers (-49%) of the LK and hyper-producers (+196%) of the MK. These results suggest that reduced production of proliferation inhibitory LK may allow stimulatory mediators to induce the unrestricted fibroblast proliferation observed in early active PSS, which then may be stabilized in long-term PSS by the increased production of proliferation inhibitory MK.

Collagen synthesis in generalized morphea

Synthesis of collagen and non-collagenous proteins was measured in fibroblast cultures derived from different layers of the dermis from a patient with an early stage of localized scleroderma. Increased synthesis of collagen was found in fibroblasts grown from the subcutaneous fat of this patient, whereas cells obtained from the papillary dermis revealed normal metabolism. These data agree with the results obtained in previous experiments with cells derived from patients with progressive systemic sclerosis in primary culture, thus indicating that the two diseases have a common pathomechanism. Several subcultures of the activated fibroblast populations were also studied. Normal collagen synthesis in these cultures was observed after the fifth passage, probably indicating selection of cell populations or loss of the previous phenotype.

Collagen fibril formation during embryogenesis

Chicken embryo skin of different ages and adult skin were labeled with antibodies against the amino propeptide and carboxyl propeptide of type I collagen and processed for indirect immunoelectron microscopy by the ferritin technique. The results indicate that the formation of thin collagen fibrils involves polymerization of pN-collagen. Fibrils that are thicker than 35-40 nm do not appear to contain the amino propeptide. How fibrils increase in size is not clear, but growth may involve mechanisms such as lateral aggregation of subfibril structures or fusion of thin fibrils. Carboxyl propeptides were localized near or in contact with thin collagen fibrils, but they did not appear to be arranged in a periodic manner along the fibrils. In experiments using antibodies against the amino propeptides of type III collagen, fibrils 20-40 nm in diameter were also labeled in a periodic fashion. pN-Collagen chains were extracted from embryonic skin and identified by NaDodSO4/polyacrylamide gel electrophoresis and by immunoblotting. The presence of significant amounts of pN-collagen in skin from 10- and 12-day chicken embryos agreed well with the labeling of amino propeptides by immunoelectron microscopy. This study provides evidence for the role of the amino propeptide in collagen fibrillogenesis in embryonic skin.

Increased procollagen mRNA levels in scleroderma skin fibroblasts

Procollagen messenger RNA activity in scleroderma and normal skin fibroblasts was measured using a cell-free translation assay. Radioactive translation products were fractionated by electrophoresis and the ratio of procollagen to total incorporation was determined from densitometric scans of gel fluorograms. In 4 scleroderma cell lines 1.78% (+/- 0.10) of incorporated [35S]-methionine was in procollagen, compared to 1.00% (+/- 0.20) in 5 normal controls. These values are consistent with previously reported increases in the rates of collagen synthesis obtained with intact cells and show that most if not all of the increase can be explained on the basis of elevated translatable procollagen messenger RNA in scleroderma fibroblasts.

Ultrastructural identification of extension aminopropeptides of type I and III collagens in human skin

Human skin was labeled with purified antibodies against type II and III collagens and against their extension aminopropeptides by using the ferritin technique. Both aminopropeptides were visualized mainly along thin collagenous fibrils (diameter, 20-40 nm) and rarely in nonfibrillar regions of the skin. The labeling showed a periodicity of 60-65 nm resembling the D (67 nm) stagger of collagen molecules. Blocking of antibodies with aminopropeptides and treatment of tissues with procollagen NH2-terminal protease abolished labeling. Antibodies against type I collagen uniformly labeled approximately equal to 80% of the fibrils (diameter, 20-80 nm), while reaction with antibodies against type III collagen was restricted to thin fibrils. It is currently thought that the aminopropeptides of procollagen molecules are cleaved after they are released from the cell and before fibril formation. Our data indicate that aminopropeptides are removed at the fibrillar level and that fibril growth can be regulated by extracellular procollagen processing.

Variability in collagen and fibronectin synthesis by scleroderma fibroblasts in primary culture

Primary cultures of fibroblasts obtained from the papillary, reticular and subcutaneous layer of scleroderma skin were analyzed for protein synthesis by metabolic labeling and radioimmunoassays. Several of these cultures showed a 10- to 20-fold increase in the production of total protein and collagen as well as of fibronectin and type III procollagen as compared to cells from unaffected individuals. Most of the increases were noted in the reticular and subcutaneous layers. With cells from other patients increased synthesis was found in some of the explants or for only some of the products. The heterogeneity observed here could represent heterogeneity in the disease, in the cells studied or in the state of the disease at the time the cells were obtained.

Immunoelectron microscopy of type III collagen in normal and scleroderma skin

Normal and scleroderma skin was studied by indirect immuno-electron microscopy with specific antibodies against Type III collagen. Fine collagen fibrils, 200-400 A in diameter were labeled with antitype III collagen antibodies. These antibodies attached to the collagen fibril forming rings with a 650 A periodicity. Fibrils with more than 600 A in diameter were only labeled with antitype I collagen antibodies. Type III collagen was found around small blood vessels, adipocytes and smooth muscle cells, thus, corresponding to the distribution of reticulin.

Capillary alterations in scleroderma

Electron microscopy of capillaries was performed in scleroderma skin. The main alterations were (1) gaps, vacuolization and eventual destruction of endothelial cells, (2) reduplication of the basal lamina, (3) perivascular cellular infiltrates consisting of lymphocytes, plasma cells, macrophages, or monocytes, and (4) fibroblasts and pericytes with enlarged, rough endoplasmic reticulum (RER) accompanied by perivascular fibrosis. Perivascular cellular infiltrates and endothelial cell damage appear to precede the stage of fibrosis.

Collagen in the cellular and fibrotic stages of scleroderma

The collagen in localized and systemic scleroderma skin was studied by light microscopy with silver impregnation (50 patients), electron microscopy (14 patients), and immunofluorescence microscopy using specific antibodies against Type I and Type III collagens (12 patients). In the cellular stage, the dermis and adipose tissue revealed perivascular or diffuse cellular infiltrates (mostly lymphocytes, plasma cells, and macrophages), accompanied by deposition of Type III collagen. The lower dermis also showed an increase in Type III collagen. In the fibrotic stage, the papillary layer showed a reduction and/or clumping of Type III collagen as compared to normal skin. The lower dermis and the adipose tissue revealed compact collagen consisting exclusively of Type I collagen or a mixture of Type I and Type III collagen. The pattern of Type III collagen distribution was similar to that of reticulin, thus suggesting that at least some reticulin fibrils may represent Type III collagen.

Ultrastructure of cutaneous cellular infiltrates in scleroderma

Electron microscopy of the skin was performed in ten patients with systemic and four with localized scleroderma. The following three groups of cells were identified: (1) mature lymphocytes, T lymphoblasts, immature plasma cells, and plasma cells; (2) fibroblasts, fibrocytes, and fibroblast-like cells; and (3) macrophages, undifferentiated mesenchymal cells, and monocytes. Inthose specimens with mononuclear cell infiltrates, the most common cells were lymphocytic-types, macrophages, and fibroblasts with well developed rough endoplasmic reticulum. In the specimens at the fibrotic stage, fibroblasts and histiocytic-type cells predominated. This study suggests that cellular and humoral immunity may play a role in the pathophysiology of scleroderma.

[3H]Thymidine labeling of dermal endothelial cells in scleroderma

The purpose of this study was to estimate [3H] thymidine labeling of endothelial cells of skin capillaries in localized scleroderma (LS) and systemic scleroderma (SS). Skin specimens from 14 patients with SS, 5 with LS, and 9 matched controls were studied by in vitro autoradiography. Capillaries from patients with SS showed a statistically significant increase in endothelial cell labeling when compared to vessels from controls (p less than 0.0005).

Cellular infiltrates in scleroderma skin

The purpose of this study was to determine the frequency, distribution, and nature of cellular infiltrates in 108 skin biopsies from patients with systemic scleroderma (SS) and localized scleroderma (LS). Cellular infiltrates, perivascular or diffuse, were noted in 49% of SS and 84% of LS patients and consisted of lymphocytes, plasma cells, and macrophages. No correlation was noted between the presence or severity of skin cellular infiltrates and serum serologic abnormalities.

Skin capillary changes in early systemic scleroderma. Electron microscopy and "in vitro" autoradiography with tritiated thymidine

Skin biopsy specimens obtained from involved and noninvolved areas in a patient with early diffuse systemic scleroderma were processed for histology, electron microscopy, and "in vitro" autoradiography with tritiated thymidine. The affected area revealed cellular infiltrates around the eccrine sweat glands, consisting of plasma cells and lymphocytes. The capillaries showed thickening of the basement lamina, damage of endothelial cells, and obstruction of their lumens. However, in some vessels, endothelial cells were preserved and appeared in prophase. Autoradiography with tritiated thymidine showed a marked increase in endothelial and periendothelial cell labeling. Blood immunological studies revealed an increase in B-lymphocytes, IgG, and IgA and the presence of antinuclear and antismooth muscle antibodies.

Connective tissue synthesis by cultured scleroderma fibroblasts. I. In vitro collagen synthesis by normal and scleroderma dermal fibroblasts

The authors have been unable to demonstrate an increase in collagen synthesis by fibroblasts isolated from sclerodermatous skin. In order to elucidate this problem further, scleroderma fibroblasts were biopsied from upper dermis, from lower (including subcutaneous) dermis, and from adjacent clinically noninvolved skin. All cell lines failed to show a significant increase in collagen synthesis when they were compared to control fibroblast lines. One difference among them was that fibroblasts from involved areas showed a rate of collagen synthesis equal to or less than cells isolated from adjacent clinically noninvolved sites.