Contraction of collagen lattices by fibroblasts from patients and animals with heritable disorders of connective tissue

The Role of Cell Adhesion and Cytoskeleton Dynamics in the Pathogenesis of the Ehlers-Danlos Syndromes and Hypermobility Spectrum Disorders

The Ehlers-Danlos syndromes (EDS) are a group of 13 disorders, clinically defined through features of joint hypermobility, skin hyperextensibility, and tissue fragility. Most subtypes are caused by mutations in genes affecting the structure or processing of the extracellular matrix (ECM) protein collagen. The Hypermobility Spectrum Disorders (HSDs) are clinically indistinguishable disorders, but are considered to lack a genetic basis. The pathogenesis of all these disorders, however, remains poorly understood. Genotype-phenotype correlations are limited, and findings of aberrant collagen fibrils are inconsistent and associate poorly with the subtype and severity of the disorder. The defective ECM, however, also has consequences for cellular processes. EDS/HSD fibroblasts exhibit a dysfunctional phenotype including impairments in cell adhesion and cytoskeleton organization, though the pathological significance of this has remained unclear. Recent advances in our understanding of fibroblast mechanobiology suggest these changes may actually reflect features of a pathomechanism we herein define. This review departs from the traditional view of EDS/HSD, where pathogenesis is mediated by the structurally defective ECM. Instead, we propose EDS/HSD may be a disorder of membrane-bound collagen, and consider how aberrations in cell adhesion and cytoskeleton dynamics could drive the abnormal properties of the connective tissue, and be responsible for the pathogenesis of EDS/HSD.

Scar and contracture: biological principles

Dysregulated wound healing and pathologic fibrosis cause abnormal scarring, leading to poor functional and aesthetic results in hand burns. Understanding the underlying biologic mechanisms involved allows the hand surgeon to better address these issues, and suggests new avenues of research to improve patient outcomes. In this article, the authors review the biology of scar and contracture by focusing on potential causes of abnormal wound healing, including depth of injury, cytokines, cells, the immune system, and extracellular matrix, and explore therapeutic measures designed to target the various biologic causes of poor scar.

Mechanical tension and integrin alpha 2 beta 1 regulate fibroblast functions

The extracellular matrix (ECM) environment in connective tissues provides fibroblasts with a structural scaffold and modulates cell shape, but it also profoundly influences the fibroblast phenotype. Here we studied fibroblasts cultured in a three-dimensional network of native collagen, which was either mechanically stressed or relaxed. Mechanical load induces fibroblasts that synthesize abundant ECM and a characteristic array of cytokines/chemokines. This phenotype is reminiscent of late granulation tissue or scleroderma fibroblasts. By contrast, relaxed fibroblasts are characterized by induction of proteases and a subset of cytokines that does not overlap with that of mechanically stimulated cells. Thus, the biochemical composition and physical nature of the ECM exert powerful control over the phenotypes of fibroblasts, ranging from "synthetic" to "inflammatory" phenotypes. Interactions between fibroblasts and collagen fibrils are mostly mediated by a subset of beta 1 integrin receptors. Fibroblasts utilize alpha 1 beta 1, alpha 2 beta 1, and alpha 11 beta 1 integrins for establishing collagen contacts and transducing signals. In vitro assays and mouse genetics have demonstrated individual tasks served by each receptor, but also functional redundancy. Unraveling the integrated functions of fibroblasts, collagen integrin receptors, collagen fibrils, and mechanical tension will be important to understand the molecular mechanisms underlying tissue repair and fibrosis.

Contractile forces generated by striae distensae fibroblasts embedded in collagen lattices

Striae distensae are characterized by linear, smooth bands of atrophic-appearing skin that are reddish at first and finally white. They are due to stretching of the skin, as in rapid weight gain, or mechanical stress, as in weight lifting. The pathogenesis of striae distensae is unknown but probably relates to changes in the fibroblast phenotype. In order to characterize striae distensae fibroblasts, alpha-smooth muscle actin expression and contractile forces were studied. Five healthy women with early erythematous striae and five healthy women with older striae were selected. Paired biopsies were taken from the center of lesional striae and adjacent normal skin. Fibroblasts were obtained by an explant technique and expanded in vitro in Dulbecco's modified Eagle's medium. Contractile forces generated by fibroblasts in collagen lattices were measured with the Glasbox device developed in our laboratory. Alpha-smooth muscle actin expression was studied by immunofluorescence labeling of cells and by flow cytometry. Fibroblasts from early striae distensae were the richest cells in alpha-smooth muscle actin filaments and generated the highest contractile forces. Their peak contractile force was 26% greater than normal fibroblasts. There was a 150% higher level of alpha-smooth muscle actin content in fibroblasts from early striae distensae compared with fibroblasts from normal skin. In contrast, there was no significant difference in force generation between old striae fibroblasts and normal fibroblasts with cells expressing no alpha-smooth muscle actin. The contractile properties of fibroblasts from striae distensae varies depending on the stage of the disease. In early striae distensae, fibroblasts acquire a more contractile phenotype, corresponding to that of myofibroblasts.

Comparing the contractile properties of human fibroblasts in leg ulcers with normal fibroblasts

OBJECTIVE

The tissue contraction phenomenon associated with wound healing is of prime importance for wound closure. Contractile properties of human fibroblasts from chronic venous leg ulcers were compared with those of normal fibroblasts using in vitro models.

METHOD

Biopsies were taken from the uninvolved skin of the thigh, the epithelialised ulcer edge and the non-epithelialised ulcer centre in four patients (average age: 78 years). Fibroblasts were obtained by an explant technique and expanded in vitro in Dulbecco's Modified Eagle's Medium supplemented with 10% foetal calf serum and used for the assays at their fourth passage. Intracellular alpha-smooth muscle actin expression (alphaSM-actin) was studied by immunofluorescence labelling of cells cultured in monolayer. Contractile properties were evaluated using three-dimensional collagen lattices.

RESULTS

Fibroblasts from the ulcer centre were the richest cells in actin filaments. Both populations of venous ulcer fibroblasts contracted more rapidly and to a greater extent than normal fibroblasts. The peak contractile forces developed by fibroblasts from the ulcer centre and the ulcer edge were 30% and 18% greater than normal fibroblasts respectively.

CONCLUSION

Some functions of fibroblasts, in particular the generation of contractile forces and the formation of cytoplasmic actin filaments, seem not to be affected in chronic venous ulcers.

DECLARATION OF INTEREST

This study was supported by the Fondation Coloplast pour la Qualite de la Vie of France.

Factor XIII a-positive dermal dendrocytes and shear wave propagation in human skin

BACKGROUND

The in vivo interdependence between the phenotypic characteristics of dermal cells and the strain imposed on the tissue has not been studied thoroughly in humans. In particular the mechanical force modulation of Factor XIII a expression in dermal dendrocytes (DD) remains unknown.

MATERIALS AND METHODS

The present study compares the numerical density of Factor XIII a-positive DD and the in vivo shear wave velocity in the skin. The investigation was performed in 20 men of normal weight and 20 obese men before and after entering a slimming process.

RESULTS

Excess cutaneous fat places the skin under increased intrinsic tension. The resonance running time measurement (RRTM) and the DD density were significantly reduced in overweight individuals. After a short-term but intense slimming process, the same individuals showed a trend to normalization of these two parameters without, however, reaching significance. Pooling all data yielded a significant logarithmic correlation between RRTM values and densities in Factor XIII a-positive DD.

CONCLUSION

Factor XIII a expression in human DD may be partially regulated by the intrinsic resting tensions in the skin.

Skin tensile strength modulation by compressive garments in burn patients. A pilot study

Compression therapy is frequently used to prevent hypertrophy of post-burn scars. This pilot study was performed in 6 patients to assess non-invasive changes induced in the tensile strength of the skin before any clinical improvement can be perceived. Assessments were performed using a computerized suction device delivering three 5 s cycles of 500 mbar depression. Measurements were made at one-month intervals for three months after initiating the garment compression therapy. Comparisons were made between the intact skin, the ungrafted and grafted post-burn scars and the graft donor sites. Data show that garment compression therapy alters the tensile strength in the skin of all test sites. The most reliable variations consist of an increase in both the extensibility and elasticity of the tissues submitted to traction.

Keratinocytes modulate the biosynthetic phenotype of dermal fibroblasts at a pretranslational level in a human skin equivalent

In this study we investigated the influence of keratinocytes on the phenotype of fibroblasts in an in vitro human skin equivalent. Keratinocytes were seeded at the surface of fibroblast-populated mechanically restrained type I collagen gels (lattices). Lattices without keratinocytes were handled in parallel as controls. After 2 and 4 days in culture, the keratinocyte layer was removed and the steady-state level of the mRNA for the main extracellular matrix macromolecules and interstitial collagenase produced by the fibroblasts was measured by Northern and dot blot analysis. A 50% decrease in the amount of procollagen type I and type III mRNAs was observed after 2 and 4 days of coculture while collagenase gene expression was upregulated by 300% when compared with control lattices. No significant modulation of type IV and type VI collagen, elastin or laminin B1 mRNA levels was found. Fibronectin mRNA levels in fibroblasts were significantly increased only on day 4. All the observed changes could be reproduced using a conditioned medium collected from a lattice covered with keratinocytes added to a lattice containing fibroblasts alone. These results indicate that in an in vitro reconstituted skin, keratinocytes are able to modulate the biosynthetic phenotype of fibroblasts at a pretranslational level through a paracrine signalling pathway.

Differences in adhesion and collagen gel contraction between fibroblasts from various types of odontogenic cyst

Fibroblasts were grown from explants of normal gingiva and foreskin, and from walls of dentigerous, radicular and residual cysts, as well as keratocysts of basal-cell naevus syndrome and non-syndrome origin. Dentigerous-cyst fibroblast adhesion to poly-L-lysine-coated glass was unaffected by all adhesion-related glycoproteins. Chondroitin sulphate, fibronectin and heparan sulphate enhanced attachment of all other fibroblasts. Chondroitin-sulphate and fibronectin-enhanced adhesion was blocked by an arg-gly-asp peptide. Fibronectin, chondroitin sulphate and laminin all promoted collagen lattice contraction using normal gingival fibroblasts and low-serum media. Fibronectin had a greater effect than chondroitin sulphate and laminin. In media with standard serum, all cyst fibroblast lines examined demonstrated similar gel contraction curves with the exception of dentigerous cyst-derived fibroblasts, which contracted at decreased rates. Suppression of gel contraction was seen with dentigerous-cyst fibroblasts with all extracellular matrix glycoproteins and low serum. Dentigerous-cyst fibroblast attachment to glass and behaviour in gel lattices suggest that these cells express different functional attachment factors from other cyst fibroblast types.

Measurement of mechanical forces generated by skin fibroblasts embedded in a three-dimensional collagen gel

Mechanical activities developed by cells play a significant role in the embryogenesis, development, and physiopathology of pluricellular organisms. A technique is described to measure in vitro the traction force developed by cells seeded into a three-dimensional polymeric collagen lattice. It is based on the use of strain gauges generating an electrical signal upon tension that is amplified and recorded. The intensity of the signal depends on the number and type of cells, cytoskeleton integrity, concentration of collagen in the lattice support, and fetal calf serum in the culture medium. Skin fibroblasts from humans and animals produce traction forces ranging from 100 to 1000 mg per million cells. In the gel under tension, the cells are in mechanical dynamic equilibrium with their support. It is suggested that the mechanical activity of fibroblasts and the control of the tension that they operate on the lattice support participate in the structural organization of the dermis and in its physiologic tension.

Variability in the retraction of collagen lattices by scleroderma fibroblasts--relationship to protein synthesis and clinical data

Skin fibroblasts from 18 scleroderma patients were seeded into collagen lattices and their ability to retract their substratum was compared with that of control fibroblasts from healthy donors. When considered as a whole, scleroderma fibroblasts retracted lattices earlier and more intensely than controls. Analysis of individual results demonstrated that morphea and diffuse systemic sclerosis (dSSc) fibroblasts had different kinetics of lattice retraction. Fibroblasts which contracted lattices more intensely than controls were found to produce increased levels of fibronectin. A comparison of the retraction of collagen lattices by fibroblasts from involved (IS) and uninvolved skin (US) of the same patients (n = 4) showed that those from IS retracted the lattices more than fibroblasts from normal donors, whereas a high variability was found with fibroblasts from US. The increased retraction of collagen lattices seems to be a feature of the more severe forms of scleroderma.

Heterogeneity in dermatosparaxis is shown by contraction of collagen gels

Dermal fibroblasts from sheep exhibiting a mild form of dermatosparaxis were able to contract reconstituted, fibrillar collagen gels at the same rate as control dermal fibroblasts, indicating a normal interaction between the cells and a collagenous matrix. An extract from dermatosparactic skin was shown, after partial purification, to have N-proteinase activity, although the level of activity was much lower than found in normal skin. These data show that dermatosparaxis is a heterogeneous disease, since in the severe forms of the disease the defect has been characterized as an absence of N-proteinase and an inability of the cells to interact with and contract collagen gels.

The ageing dermis: the main cause for the appearance of 'old' skin

Ageing of the skin is associated with progressive atrophy of the dermis, as well as changes in the architectural organization, leading to folds and wrinkles. As the dermis comprises living tissue, dermal changes are not simply the sum of age-related changes occurring in the mesenchymal cells and the supporting macromolecular structures. Chronological ageing reduces the life of fibroblasts in vitro and, to some extent, in vivo; their potential for division being lower in the elderly. Fibroblasts replicate in vitro but only divide very slowly in vivo. Both endogenous factors, e.g. nutritional and endocrine status, and environmental factors, e.g. UV radiation, toxic compounds or free radicals, affect the functions of fibroblasts and the physical and chemical nature of the supporting macromolecules. Mechanical forces also play an important role in the architectural deterioration of the dermis. In vitro models have been developed using dermal cells and supporting tissue to investigate the factors involved in the ageing process.

Cell-mediated contraction of collagen lattices in serum-free medium: effect of serum and nonserum factors

This study was conducted to identify a defined, serum-free culture medium that supports cell dependent contraction of a collagen lattice. Collagen lattices were found to contract in cultures containing human foreskin fibroblasts (HFF) or rabbit aortic smooth muscle (RASM) cells incubated in serum-free medium. HFF and RASM cells required different supplements to contract the collagen gels. HFF cultured in Dulbecco's modified Eagle's (DME) medium supplemented with bovine serum albumin (BSA) and either endothelial cell growth supplement (EnGS), insulin (In), or platelet derived growth factor (PDGF) supported collagen lattice contraction. Replacement of BSA with casein without the addition of other supplements improved contraction. In contrast, RASM cells supplemented with BSA, EnGS, In, and PDGF were able to contract collagen gels only minimally. Similar to HFF, RASM cells cultured in DME medium supplemented with casein, but without the addition of other supplements, contracted collagen lattices. HFF-mediated collagen contraction was inhibited by prostaglandins E1 or E2, fibronectin, or ascorbic acid. The reported serum-free model provides a useful in vitro method to investigate the role of serum and nonserum factors regulating cell mediated-contraction of insoluble collagen fibrils.

Quantitative evaluation of the factors affecting the process of fibroblast-mediated collagen gel contraction by separating the process into three phases

Kinetics of collagen gel contraction by fibroblasts cultured in vitro was examined in detail for quantitative analysis. The process of collagen gel contraction was not expressed by a simple function of time. It appeared to consist of three distinct phases; a lag phase before the initiation of contraction, a rapid contraction phase and a slow contraction phase. Factors affecting the gel contraction can be classified into four groups. The first group includes increase in cell number, in culture temperature or in serum concentration, which strengthened the contraction in all the three phases, suggesting that they affected cellular activity particularly in interacting with collagen. The second group repressed the later two phases of contraction but not the first lag phase, typically increase in collagen concentration and a low dose of nocodazole or colcemid. Increasing population doubling levels of fibroblasts belongs to the third group which caused a reduced lag time but no change in the later two phases. Cytochalasin D at a low dose (0.03-0.1 microgram/ml) is another example of the third group which shortened the lag time. The last group did not change the contraction curves. Donor age of fibroblasts isolated from the skin is an example of this group. The rate of rapid contraction in the second phase was always found to be closely correlated with the degree of contraction at the end of the third phase, in a whole set of the factors above mentioned. The results suggest that the extent of the later two phases might be a reflection of the same cellular activity, particularly cytokinetical one. The lag time is directly related to the time for cells to become elongate in shape as observed by using the video-microscopy, suggesting that the lag phase is also governed by cytokinetical activity. The two cytokinetical activities are closely related, but may be distinct, since the factors affecting the collagen gel contraction can be differentiated into four groups.

A defective cell surface collagen-binding protein in dermatosparactic sheep fibroblasts

Fibroblasts from dermatosparactic sheep fail to contract collagen gels and show a reduced attachment to collagenous substrates. By comparing collagen-binding membrane proteins of normal (+/+), homozygote (-/-), and heterozygote (+/-) fibroblasts, we present evidence that the interaction of normal fibroblasts with native type I collagen involves a protein of apparent Mr = 34,000 which is absent from dermatosparactic fibroblasts and seems to be related to anchorin CII. This conclusion was reached from the following experiments: (a) On a blot of membrane proteins from normal fibroblasts radioactively labeled type I collagen bound predominantly to a protein band of 34 kD; dermatosparactic membranes revealed only a small amount of binding to a component with a molecular mass of 47 kD. (b) After separation of normal fibroblast membrane proteins on type I collagen-Sepharose, a collagen-binding component of 34 kD was found which was absent from the corresponding fraction of dermatosparactic membranes. (c) Antibodies to anchorin CII stained the surface of normal (+/+), but not of dermatosparactic (-/-) fibroblasts and labeled a 34-kD component after immunoblotting of normal fibroblast membrane proteins. (d) After metabolic labeling of fibroblasts with [35S]methionine and immunoprecipitation with anti-anchorin CII, 40- and 34-kD components were precipitated from extracts of normal fibroblasts, while the latter component was absent from affected cells. Similar differences were found after immunoblotting of membranes from whole normal or affected skin. These data indicate that dermatosparaxis of sheep involves a molecular defect of a collagen-binding protein. Therefore this disease represents a model to study the complex interaction of cells with the extracellular matrix on a molecular level.