Studies on human scar tissue proteoglycans

Modeling of Old Scars: Histopathological, Biochemical and Thermal Analysis of the Scar Tissue Maturation

Simple Summary

Severe skin scars (i.e., hypertrophic and keloid) induce physical and emotional discomfort and functional disorders such as contractures and body part deformations. Scar’s response to treatment depends on “maturity”, which increases with time but is not merely proportional to it. When “fresh”, scars are relatively more treatable by conservative methods, while the treatment is only partially efficient. In contrast, surgery is a preferred approach for the older scars, but it is associated with a risk of the scar regrowth and worsening after excision if unrecognized immature scar tissue remains in the operated lesion. Therefore, to develop better treatment and diagnostics of scars, understanding of the scar maturation is essential. This requires biologically accurate experimental models of skin scarring. The current models only mimic the early stages of skin scar development. They are useful for testing new scar-preventing approaches while not addressing the problem of the older scars that exist for years. In our study, we demonstrate a new rabbit model of “old” scars and explore what happens to the scar tissue during maturation. We define measurable signs to delineate the scar development stages and discuss how this knowledge can improve scar diagnostics and treatment.

Abstract

Mature hypertrophic scars (HSs) remain a challenging clinical problem, particularly due to the absence of biologically relevant experimental models as a standard rabbit ear HS model only reflects an early stage of scarring. The current study aims to adapt this animal model for simulation of mature HS by validating the time of the scar stabilization using qualitative and quantitative criteria. The full-thickness skin and perichondrium excision wounds were created on the ventral side of the rabbit ears. The tissue samples were studied on post-operation days (PODs) 30, 60, 90 and 120. The histopathological examination and morphometry were applied in parallel with biochemical analysis of protein and glycosaminoglycans (GAGs) content and amino acid composition. The supramolecular organization of collagen was explored by differential scanning calorimetry. Four stages of the rabbit ear HS maturation were delineated and attributed with the histolomorphometrical and physicochemical parameters of the tissue. The experimental scars formed in 30 days but stabilized structurally and biochemically only on POD 90–120. This evidence-based model can be used for the studies and testing of new treatments of the mature HSs.

Interleukin-31, Interleukin-31RA, and OSMR Expression Levels in Post-burn Hypertrophic Scars

BACKGROUND

Although several studies have shown the role of interleukin-31 (IL-31) and its receptors in inducing pruritus in certain skin disorders, knowledge of its role in post-burn hypertrophic scars is insufficient. Therefore, the histopathological expression levels of IL-31, IL-31 receptor alpha (IL-31RA), and oncostatin M receptor (OSMR) in post-burn hypertrophic scar tissues were investigated and compared with normal tissue expression levels.

METHODS

Samples of hypertrophic scar tissue were obtained from 20 burn patients through punch biopsy. Normal samples were obtained from areas adjacent to the burn injury site of the same patients. Samples were placed in 10% neutral buffered formalin, embedded in paraplast, and processed into serial 5-μm sections. Immunohistochemistry results were semi-quantitatively evaluated for IL-31, IL-31RA, and OSMR. By hematoxylin and eosin staining, epidermal and dermal thickness were assessed with a microscope and digital camera. Intensities were rated on a scale of 1 to 4.

RESULTS

Percentages for IL-31, IL-31RA, and OSMR in the epidermal basal layer cell cytoplasm were significantly greater in the burn scar tissue compared to normal skin, as well as the dermal and epidermal thickness (p < .05). There was a significant difference in IL-31 epidermal basal layer intensity in burn scar tissue compared to normal skin (p < .05). Besides the OSMR basal layer intensity, IL-31 and IL-31RA intensities between the burn scar and normal tissues were not significant. However, correlations were significant, indicating that the greater the infiltration percentage, the higher the intensity (p < .05).

CONCLUSIONS

IL-31, IL-31RA, and OSMR expression levels are increased in hypertrophic scars compared with normal tissue.

Inflammatory and Physiological Consequences of Debridement of Fibrous Tissue after Volumetric Muscle Loss Injury

Volumetric muscle loss (VML) injuries present chronic loss of muscle fibers followed by expansive fibrotic tissue deposition. Regenerative medicine therapies are under development to promote regeneration. However, mitigation of the expansive fibrous tissue is required for integration with the remaining muscle. Using a porcine VML model, delayed debridement of injury fibrosis was performed 3 months post‐VML and observed for an additional 4 weeks. A second group underwent the initial VML and was observed for 4 weeks, allowing comparison of initial fibrosis formation and debrided groups. The following salient observations were made: (i) debridement neither exacerbated nor ameliorated strength deficits; (ii) debridement results in recurrent fibrotic tissue deposition of a similar magnitude and composition as acute VML injury; and (iii) similarly upregulated transcriptional fibrotic and transcriptional pathways persist 4 weeks after initial VML or delayed debridement. This highlights the need for future studies to investigate adjunctive antifibrotic treatments for the fibrosed musculature.

Biomechanical Screening of Cell Therapies for Vocal Fold Scar

Candidate cell sources for vocal fold scar treatment include mesenchymal stromal cells from bone marrow (BM-MSC) and adipose tissue (AT-MSC). Mechanosensitivity of MSC can alter highly relevant aspects of their behavior, yet virtually nothing is known about how MSC might respond to the dynamic mechanical environment of the larynx. Our objective was to evaluate MSC as a potential cell source for vocal fold tissue engineering in a mechanically relevant context. A vibratory strain bioreactor and cDNA microarray were used to evaluate the similarity of AT-MSC and BM-MSC to the native cell source, vocal fold fibroblasts (VFF). Posterior probabilities for each of the microarray transcripts fitting into specific expression patterns were calculated, and the data were analyzed for Gene Ontology (GO) enrichment. Significant wound healing and cell differentiation GO terms are reported. In addition, proliferation and apoptosis were evaluated with immunohistochemistry. Results revealed that VFF shared more GO terms related to epithelial development, extracellular matrix (ECM) remodeling, growth factor activity, and immune response with BM-MSC than with AT-MSC. Similarity in glycosaminoglycan and proteoglycan activity dominated the ECM analysis. Analysis of GO terms relating to MSC differentiation toward osteogenic, adipogenic, and chondrogenic lineages revealed that BM-MSC expressed fewer osteogenesis GO terms in the vibrated and scaffold-only conditions compared to polystyrene. We did not evaluate if vibrated BM-MSC recover osteogenic expression markers when returned to polystyrene culture. Immunostaining for Ki67 and cleaved caspase 3 did not vary with cell type or mechanical condition. We conclude that VFF may have a more similar wound healing capacity to BM-MSC than to AT-MSC in response to short-term vibratory strain. Furthermore, BM-MSC appear to lose osteogenic potential in the vibrated and scaffold-only conditions compared to polystyrene, potentially attenuating the risk of osteogenesis for in vivo applications.

Chondrogenic and fibrotic process in the ligamentum flavum of patients with lumbar spinal canal stenosis

STUDY DESIGN

A histological, biological, and immunohisto-chemical study of human lumbar ligamentum flavum.

OBJECTIVE

To analyze changes in the hypertrophied ligamentum flavum and clarify their etiology.

SUMMARY OF BACKGROUND DATA

Hypertrophy of the ligamentum flavum has been considered a major contributor to the development of lumbar spinal canal stenosis (LSCS). Although previous studies have reported some factors related to ligamentum flavum hypertrophy, its etiology is still unclear.

METHODS

Ligamentum flavum samples were collected from 20 patients with LSCS (LSCS group) and 10 patients with lumbar disc herniation (LDH group) as a control. The thickness of the ligamentum flavum was measured histologically. The amounts of elastic fibers and proteoglycans were assessed by Elastica-Masson staining and alcian blue staining, respectively. Gene and protein expressions related to fibrosis, inflammation, and chondrogenesis were analyzed by quantitative reverse transcription-polymerase chain reaction and immunohistochemistry. The total genes of the 2 groups were compared by DNA microarray analysis.

RESULTS

The ligamentum flavum was significantly thicker in the LSCS group, which had a smaller amount of elastic fibers and a larger amount of proteoglycans. The gene expression related to fibrosis was significantly higher in the LSCS group; however, the immunoreactivities of collagen types I and III were weaker on the dorsal side of the ligamentum flavum in the LSCS group. The gene expression related to chondrogenesis and proteoglycan synthesis was significantly higher in the LSCS group. There was no significant difference in the gene expression related to inflammation between the 2 groups.

CONCLUSION

Synthesis of the collagenous fibers and degradation of the elastic and collagenous fibers are both accelerated in the ligamentum flavum of patient with LSCS, which may be the reason for hypertrophy of the tissue. In addition, chondrogenesis and proteoglycan synthesis may have critical roles in the pathogenesis of the ligamentum flavum hypertrophy.

LEVEL OF EVIDENCE

5.

Myofibroblast differentiation: main features, biomedical relevance, and the role of reactive oxygen species

SIGNIFICANCE

Myofibroblasts are prototypical fibrotic cells, which are involved in a number of more or less pathological conditions, from foreign body reactions to scarring, from liver, kidney, or lung fibrosis to neoplastic phenomena. The differentiation of precursor cells (not only of fibroblastic nature) is characterized by a complex interplay between soluble factors (growth factors such as transforming growth factor β1, reactive oxygen species [ROS]) and material properties (matrix stiffness).

RECENT ADVANCES

The last 15 years have seen very significant advances in the identification of appropriate differentiation markers, in the understanding of the differentiation mechanism, and above all, the involvement of ROS as causative and persistence factors.

CRITICAL ISSUES

The specific mechanisms of action of ROS remain largely unknown, although evidence suggests that both intracellular and extracellular phenomena play a role.

FUTURE DIRECTIONS

Approaches based on antioxidant (ROS-scavenging) principles and on the potentiation of nitric oxide signaling hold much promise in view of a pharmacological therapy of fibrotic phenomena. However, how to make the active principles available at the target sites is yet a largely neglected issue.

The localisation of inflammatory cells and expression of associated proteoglycans in response to implanted chitosan

Implantation of a foreign material almost certainly results in the formation of a fibrous capsule around the implant however, mechanistic events leading to its formation are largely unexplored. Mast cells are an inflammatory cell type known to play a role in the response to material implants, through the release of pro-inflammatory proteases and cytokines from their α-granules following activation. This study examined the in vivo and in vitro response of mast cells to chitosan, through detection of markers known to be produced by mast cells or involved with the inflammatory response. Mast cells, identified as Leder stained positive cells, were shown to be present in response to material implants. Additionally, the mast cell receptor, c-kit, along with collagen, serglycin, perlecan and chondroitin sulphate were detected within the fibrous capsules, where distribution varied between material implants. In conjunction, rat mast cells (RBL-2H3) were shown to be activated following exposure to chitosan as indicated by the release of β-hexosaminidase. Proteoglycan and glycosaminoglycans produced by the cells showed similar expression and localisation when in contact with chitosan to when chemically activated. These data support the role that mast cells play in the inflammatory host response to chitosan implants, where mediators released from their α-granules impact on the formation of a fibrous capsule by supporting the production and organisation of collagen fibres.

Human xylosyltransferase-I - a new marker for myofibroblast differentiation in skin fibrosis

Skin fibrosis is a severe type of fibrotic disorder emerging in terms of hypertrophic scars or systemic sclerosis. Key event of fibrogenesis is the transition of fibroblasts to matrix-producing myofibroblasts. In the presence of fibrotic triggers, for instance secretion of profibrotic growth factors like transforming growth factor-β1 (TGF-β1) or mechanical strain, myofibroblasts persist. Current research focuses on discovering innovative myofibroblast biomarkers which are regulated in fibrotic development and accessible for antifibrotic inhibition. Here, we consider the suitability of xylosyltransferase-I (XT-I) as a myofibroblast biomarker in skin fibrosis. XT-I catalyzes the initial step of glycosaminoglycan biosynthesis. Its increase in enzymatic activity is known to refer only to manifested diseases which are characterized by an abnormal rate of proteoglycan biosynthesis. In this study, treatment of normal human dermal fibroblasts (NHDF) with TGF-β1 was followed by increased relative XYLT1 mRNA expression. Remarkably, this upregulation was strongly dependent on myofibroblast content, increasing during fibrogenesis. Moreover, XT activity increased time-dependently in response to progressive myofibroblast transformation. XYLT1 expression was inhibited by TGF-β receptor I (ALK5) inhibitor SB431542. In contrast, XYLT2 expression was only marginally affected by TGF-β1 as well as ALK5 inhibition. Our results strengthen the significance of XT expression and activity in fibrotic remodeling. Therefore, we propose XT activity, in addition to α-SMA expression, as a new biomarker for myofibroblast differentiation and fibrotic development. Further studies are now needed to evaluate the option to control and inhibit fibrotic remodeling by interfering with XT expression.

Elastic fiber assembly is disrupted by excessive accumulation of chondroitin sulfate in the human dermal fibrotic disease, keloid

Keloid is a fibrotic disease characterized by abnormal accumulation of extracellular matrix in the dermis. The keloid matrix contains excess collagen and glycosaminoglycans (GAGs), but lacks elastic fiber. However, the roles of these matrix components in the pathogenesis of keloid are largely unknown. Here, we show that elastin and DANCE (also known as fibulin-5), a protein required for elastic fiber formation, are not deposited in the extracellular matrix of keloids, due to excess accumulation of chondoitin sulfate (CS), although the expression of elastin and DANCE is not affected. Amount of CS accumulated in the keloid legion was 6.9-fold higher than in normal skin. Fibrillin-1, a scaffold protein for elastic fiber assembly, was abnormally distributed in the keloid matrix. Addition of purified CS to keloid fibroblast culture resulted in abnormal deposition of fibrillin-1, concomitant with significantly decreased accumulation of elastin and DANCE in the extracellular matrix. We propose that CS plays a crucial role in the development of keloid lesions through inhibition of elastic fiber assembly.

Fibroblast extracellular matrix gene expression in response to keratinocyte-releasable stratifin

Termination of wound-healing process requires a fine balance between connective tissue deposition and its hydrolysis. Previously, we have demonstrated that keratinocyte-releasable stratifin, also known as 14-3-3 sigma protein, stimulates collagenase (MMP-1) expression in dermal fibroblasts. However, role of extracellular stratifin in regulation of extracellular matrix (ECM) factors and other matrix metalloproteinases (MMPs) in dermal fibroblast remains unexplored. To address this question, large-scale ECM gene expression profile were analyzed in human dermal fibroblasts co-cultured with keratinocytes or treated with recombinant stratifin. Superarray pathway-specific microarrays were utilized to identify upregulation or downregulation of 96 human ECM and adhesion molecule genes. RT-PCR and Western blot were used to validate microarray expression profiles of selected genes. Comparison of gene profiles with the appropriate controls showed a significant (more than twofold) increase in expression of collagenase-1, stromelysin-1 and -2, neutrophil collagenase, and membrane type 5 MMP in dermal fibroblasts treated with stratifin or co-cultured with keratinocytes. Expression of type I collagen and fibronectin genes decreased in the same fibroblasts. The results of a dose-response experiment showed that stratifin stimulates the expression of stromelysin-1 (MMP-3) mRNA by dermal fibroblasts in a concentration-dependent fashion. Furthermore, Western blot analysis of fibroblast-conditioned medium showed a peak in MMP-3 protein levels 48 h following treatment with recombinant stratifin. In a lasting-effect study, MMP-3 protein was detected in fibroblast-condition medium for up to 72 h post removal of stratifin. In conclusion, our results suggest that keratinocyte-releasable stratifin plays a major role in induction of ECM degradation by dermal fibroblasts through stimulation of key MMPs, such as MMP-1 and MMP-3. Therefore, stratifin protein may prove to be a useful target for clinical intervention in controlling excessive wound healing in fibrotic conditions.

High resolution B-scan ultrasound of hypertrophic scars

BACKGROUND

Ultrasonography has provided the means for objective and non-invasive monitoring of the dynamics of some skin diseases. The pathologic scars (keloids and hypertrophic scars) that have an increased content of collagen, and have been not analyzed by high-frequency ultrasound so far. The purpose of the present study was to determine the ecographic features of these scars with a view in developing a reliable method for assessing the effectiveness of different therapeutic approaches.

METHODS

Six pathological scars from five patients were examined by a 20 MHz B-Scanner and compared with healthy skin of the same region. Densitometry analysis was performed with the aid of a dedicated software.

RESULTS

All the pathologic scars studied showed an easily identified echo-poor image clearly demarcated from the surrounding not involved tissue. When they were analyzed by densitometry, the lesions had highly significant reduced densitometric values (7.6+/-4.7) compared with regional healthy skin (31.79+/-10.8).

CONCLUSION

The high-frequency ultrasonography is a suitable objective and non-invasive method for discriminating healthy from pathologic skin in hypertrophic scars and keloids.

Keloid or Hypertrophic Scar

Keloid and hypertrophic scars are 2 types of excessive scarring observed clinically that require different therapeutic approaches. The clinical course and physical appearance define keloids and hypertrophic scars as separate entities; however, they are often confused because of an apparent lack of morphologic differences. Nevertheless, clinical differences between hypertrophic scars and keloids have long been recognized by plastic surgeons and dermatologists. Yet, translating these differences into morphologic or biochemical distinctions has prompted much conflict in the literature. The present report is an attempt to clarify the longstanding controversy regarding these 2 similar yet separate and nonidentical entities by highlighting the reported points of differentiation as well as the similarities.

Keratinocyte-derived growth factors play a role in the formation of hypertrophic scars

In predisposed individuals, wound healing can lead to hypertrophic scar or keloid formation, characterized by an overabundant extracellular matrix. It has recently been shown that hypertrophic scars are accompanied by abnormal keratinocyte differentiation and proliferation, and significantly increased acanthosis, compared with normal scars. This study addressed the question of whether the development of normal and hypertrophic scars is regulated by differences in the growth factor profiles of both the epidermis and the dermis. The presence of interleukin-1alpha (IL-1alpha), IL-1beta, tumour necrosis factor-alpha (TNF-alpha), platelet-derived growth factor (PDGF), transforming growth factor-beta1 (TGF-beta1), and basic fibroblast growth factor (bFGF) was investigated in biopsies taken from breast reduction scars at 3 and 12 months following surgery. The samples were analysed by immunohistological methods and categorized as scars that remained hypertrophic (HH), became normal (HN) or remained normal after 12 months (NN). The epidermal expression of IL-1alpha was significantly increased in NN scars compared with HN and HH scars 3 and 12 months following operation, whereas the dermal expression showed no difference. PDGF was significantly increased in the dermis of normal scars after 3 months and in both the epidermis and the dermis of hypertrophic scars after 12 months. IL-1beta, TNF-alpha, TGF-beta and bFGF showed no differences. It is hypothesized that impaired production of keratinocyte-derived growth factors, such as IL-1alpha, leads to a decrease in the catabolism of the dermal matrix, whereas augmented epidermal PDGF production leads to increased formation of the dermal matrix in hypertrophic scars. These observations support the possibility that the epidermis is involved in preventing the formation of hypertrophic scars.

An accumulation of proteoglycans in scarred fascia

A little is known about proteoglycan (PG) changes, occuring in the course of scarring of tissues another than skin. The aim of present study was biochemical characterization of glycosaminoglycans (GAGs) and proteoglycans (PGs) of normal and scarred fascia. Samples of normal fascia lata were taken at autopsy from 23 individuals and samples of scarred fascia lata were removed from 23 patients at reoperations for femoral fracture. The obtained tissues were divided into two samples: first of them was submitted to GAG isolation and the second one to PG isolation. GAGs were extracted by extensive papain digestion followed by the fractionation using cetylpyridinium chloride. In order to qualitative and quantitative characterization GAGs were submitted to electrophoresis on cellulose acetate before and after treatment with enzymes, specifically depolymerizing some kinds of GAGs. PGs were extracted using 4 M guanidine HCl followed by purification by forming complexes with Alcian blue. PGs were submitted to gel permeation chromatography on Sepharose 4B. In order to obtain core proteins PGs were depolymerized with chondroitinase ABC. The purified PGs and their core proteins were separated with sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS/PAGE). It was found that total GAGs content was significantly elevated in scarred fascia. Both types of fascia contained chondroitin-, dermatan- and heparan sulphates and hyaluronic acid. Dermatan sulphates (DS) were the predominant GAGs of normal and scarred fascia. The contents of all GAG types were increased in scarred fascia. Both types of fascia contained two kinds of dermatan sulphate proteoglycans (DSPGs); first being similar to biglycan and the second one similar to decorin, as it was judged by molecular weight of their native molecules and core proteins as well as type of GAG components. Densitometric analysis showed that decorin is a predominant DSPG in both fascia types, but in scarred tissue the ratio of biglycan to decorin is considerably higher. Moreover, in scarred fascia a large chondroitin sulphate proteoglycan (CSPG) was also observed. The obtained results have shown that the scar formation is accompanied by quantitative and qualitative alterations in GAGs/PGs resembling those observed in hypertrophic skin scars. The biochemical modification of the scarred fascia lata may partly explain the clinically manifested damage to biomechanical properties of this tissue.

Elevated synthesis of biglycan and decorin in an ovine annular lesion model of experimental disc degeneration

The aim of this study was to extend our earlier observations on the changes that occur in the proteoglycans (PGs) of discs subjected to experimental injury to the annulus fibrosus (AF). We employed the alginate bead culture method to examine the metabolism of the dermatan sulphate (DS) containing PGs by cells derived from different regions of ovine discs that had been subjected to experimental annular injury. This was compared with the metabolism of the DS-PGs by cells isolated from equivalent regions of normal sham-operated discs. Six months after induction of the annular lesion, AF cells isolated from the lesion produced significantly higher levels of decorin and biglycan in alginate bead culture than did cells from equivalent zones of the controls. Decorin and biglycan were identified in culture media samples by immunoblotting, using specific antibodies (6-B-6, LF-96), and also by positive identification of their de-glycosylated core proteins. The core protein of the DS-PGs has been shown to inhibit type I/II collagen fibrillogenesis, to negatively regulate the action of transforming growth factor-beta (TGF-beta) and to diminish cellular proliferation in vitro; events which may be detrimental to tissue repair. The findings are therefore consistent with our previous observation the annular lesions in the avascular inner annulus have no capacity to heal.

Immunohistochemical localization of the proteoglycans decorin, biglycan and versican and transforming growth factor-beta in human post-burn hypertrophic and mature scars

The distributions of the small proteoglycans, decorin and biglycan and the large proteoglycan, versican, in normal skin and post-burn hypertrophic and mature scars, were compared using monoclonal and polyclonal antibodies to the core proteins. Biglycan and versican were virtually undetectable in normal dermis but readily seen in hypertrophic scars. Staining for decorin was strong throughout the dermis in normal skin but restricted to the deep dermis and a narrow zone under the epidermis in hypertrophic scar--areas which did not stain for versican. Decorin was absent or reduced in the nodules in these specimens. In mature post-burn scars, staining for all three proteoglycans demonstrated an intensity that was intermediate between that in normal dermis and that in the nodules of the hypertrophic scars. Transforming growth factor-beta was present in the nodules of hypertrophic scars but the deep dermis of these specimens stained most intensely for this cytokine which was also found in the dermis of mature scars but was not detectable in normal dermis. The apparent co-distribution of decorin and transforming growth factor-beta suggests that this proteoglycan may play an active role in the resolution of the scars. Changes in proteoglycan type and distribution could possibly account, at least in part, for the derangement of collagen and the altered physical properties of hypertrophic scar tissue.

Iduronic acid-rich proteoglycans (PGIdoA) and human post-burn scar maturation: isolation and characterization

Proteoglycans (PGs) were extracted from human hypertrophic and normal scar tissues from two different stages of maturation after burn injury, under dissociative conditions (4 M guanidinium chloride containing proteinase inhibitors). The extracts were fractionated by ion-exchange chromatography, followed by ethanol precipitation, to give PG-containing iduronic acid (PGIdoA). The size of the PGIdoA decreased with the maturation of scars. Glycosaminoglycan (GAG) chains from PGIdoA were released by alkaline borohydride treatment, and their M(r) values were evaluated by polyacrylamide gel electrophoresis. The M(r) values for PGIdoA protein cores of the hypertrophic scars (5+ years and 2-5 years) and normal scar (5+ years and 2-5 years) were 22.6, 25, 19 and 21 kDa, respectively. The iduronic acid content of PGIdoA from both types of scar increased in their maturation phase. The M(r) values of PGIdoA decreased with maturation. PGIdoA carried the sulfate group mainly attached at C-4 of the 2-amino-2-deoxy-D-galactose residue. The NH2-terminal amino acid sequences of all the PGIdoA were similar to those of normal human skin or bone PG II (decorin) (i.e., Asp-Glu-Ala-B-Gly-Ile-Gly-Pro-Glu-Val-Pro-Asp-Asp-Arg).

Glycosaminoglycan composition of uninjured skin and of scar tissue in fetal, newborn and adult sheep

Few details are available on the heterogeneity of glycosaminoglycans (GAGs) in healing fetal wound tissue. We used a sensitive assay for hexosamines to examine changes occurring in the development of normal sheep skin and of wound healing tissue in PVA sponges inserted subcutaneously at different stages of gestation. It was assumed that glucosamine was derived mainly from hyaluronan and galactosamine mainly from dermatan sulphate and chondroitin sulphate. Hexosamine-containing tissue infiltrating the sponges was deposited more rapidly in the first week than in the second week. Three days after wounding, approximately 70% of the total GAGs in wound tissue was hyaluronan. The proportion of hyaluronan then fell progressively and by the 14th day contributed 57% to the total GAGs. In uninjured skin the contribution of hyaluronan to the total GAGs fell progressively with increasing fetal maturity, the level being 70% at 75 days gestation, but only 35-40% in newborn or adult skin. At no stage of development was there a sudden change in GAG composition suggestive of a transition from regeneration to scar formation. It is concluded that hyaluronan may play an important role in the biochemical sequence leading to collagen fibrillogenesis and mature scar formation.

Extracellular matrix analogs as carriers for growth factors: in vitro fibroblast behavior

Repair of connective tissue involves interactions between growth factors (GFs) and extracellular matrix (ECM) molecules. On the other hand, biological biomaterials could be used to carry and deliver GFs to stimulate wound healing. In the present study, fibroblasts were cultivated in a serum-free culture medium onto collagen (type I), hyaluronic acid, chondroitin sulfate, fibronectin, or fibrin. FGF, EGF, or PDGF was incorporated within those substrates. Using immuno- and radiolabeling assays, the distribution of GFs within the ECM analogs was relatively uniform and GFs retained in substrates were dependent on the substrates. Fibroblast replication was determined by the incorporation of [3H]-thymidine and compared to control groups. On collagen or chondroitin sulfate, the incorporation of GFs did not significantly improve cell proliferation. On hyaluronic acid, the incorporation of FGF and PDGF enhanced cell replication at 48 h. The incorporation of PDGF in fibronectin enhanced cell replication. On fibrin, the incorporation of PDGF, EGF, and FGF significantly enhanced cell replication. However, cell replication on FGF-incorporated fibrin was higher by 48 h than that on fibrin in the presence of FGF-supplemented culture medium. Fibrin sustains the biological activity of GFs, FGF in particular, and can be a carrier for GF that stimulates cell replication.

Proteoglycans in human burn hypertrophic scar from a patient with Ehlers-Danlos syndrome

Proteoglycans (PGs) from human burn hypertrophic scar of a patient with Ehlers-Danlos syndrome were extracted with 4M guanidinium chloride and purified by DEAE-cellulose chromatography. Differential ethanol precipitation of the PG fraction obtained after ion-exchange chromatography yielded two low mol.-wt. PGs, on rich in glucuronic acid (PGGLCA; Mr 66 kDa) and the other rich in iduronic acid (PGIDOA; Mr 48 kDa). In PGGLCA, 84% of the glycosaminoglycan chains are composed of GlcA----GalNAc(SO4) units, whereas in PGIDOA, the chains contain 95% IdoA----GalNAc(SO4) disaccharide units. Upon treatment with testicular hyaluronidase, the PGs gave different-sized oligosaccharides. Chondroitinase ABC digestion of PGGLCA or PGIDOA gave a single protein core (Mr approximately 20 kDa). The presence of glucosamine and sialic acid in PGGLCA and PGIDOA suggests that both contain N-linked oligosaccharides.

Proteoglycan synthesis in human skin and burn scar explant cultures

The synthesis of proteoglycans (PG) by normal human skin, and normal and hypertrophic scars were compared using tissue explants in culture. Newly synthesized PG were labelled with [35S]Na2SO4. Significant differences were found in the proportion of [35S]-radio-labelled incorporation of PG in the tissue and accumulation of [35S]PG in culture medium in the different tissues. The rate of PG biosynthesis in all three tissue types occurred in two phases. There was an initial phase of PG synthesis occurring at 0-3 h and a later phase that occurred at 3-18 h [35S]-labelled PG were isolated and characterized by Sepharose CL-6B chromatography and cellulose acetate electrophoresis. The results showed that the hypertrophic scar tissue and its culture medium contained higher proportions of dermatan sulphate (DS), chondroitin sulphate (CS) and DS' PG than the normal skin fractions. These results suggest that abnormal scarring is related to a change in the level of PG synthesis during the burn injury repair process.

The major proteoglycan of adult rabbit skeletal muscle. Relationship to small proteoglycans of other tissues

We have been interested in examining the putative biological role(s) of the major proteoglycan of adult skeletal muscle. The small proteoglycans of adult rabbit skeletal muscle and tendon were extracted and purified by sequential density-gradient ultracentrifugation, ion-exchange chromatography and gel filtration. They appeared to be homogeneous by the criterion of gel electrophoresis in SDS and to yield one major product, the core protein, after digestion with chondroitin ABC lyase, also observed after gel electrophoresis. Two major products were obtained when the intact proteoglycans were cleaved by CNBr, and those peptides were separated by SDS/PAGE and by ion-exchange chromatography. Sequencing of the N-terminal amino acids of either the intact proteoglycans or the CNBr-cleaved products allowed for comparison of the muscle and tendon proteoglycan with derived amino acid sequences previously reported for bovine bone proteoglycan. The bone and tendon proteoglycan sequences were remarkably similar, whereas those of the muscle proteoglycan differed from the other two molecules. The major site of glycosaminoglycan substitution was on a peptide fragment distant from the N-terminus, and a presumptive serine residue at position 4 from the N-terminus also appeared to be substituted, perhaps with a small glycosaminoglycan chain. These results provide some insight into the diversity of small proteoglycans of the PG-II class and provide a basis for exploring their mode of genetic expression.

Purification and characterization of iduronic acid-rich and glucuronic acid-rich proteoglycans implicated in human post-burn keloid scar

Small proteoglycans (PGs), extracted from human keloid scar tissue with 4M guanidinium chloride and fractionated by DEAE-cellulose chromatography, were separated by ethanol precipitation into one L-iduronic acid-rich and one D-glucuronic acid-rich fraction. The size of the L-iduronic acid-rich PG was 102 kDa with a 27 kDa glycosaminoglycan chain, that of the D-glucuronic acid-rich PG was 90 kDa with a 26 kDa glycosaminoglycan chain, and the protein core of both PGs was 14.5 kDa. The two PGs carried sulfate groups mostly attached at C-4 of the 2-amino-2-deoxy-D-galactose units. The N-terminal amino acid sequence of both was similar to human bone PGII (decorin), normal and hypertrophic scar, and human dermal tissue PG.

Isolation and some structure analyses of a copolymeric chondroitin sulfate-dermatan sulfate proteoglycan from post-burn, human hypertrophic scar

A D-glucuronic acid rich, copolymeric chondroitin sulfate (CS)-dermatan sulfate (DS) proteoglycan (PG) from post-burn hypertrophic scar tissue (HSc) was obtained by DEAE-cellulose chromatography and differential ethanol fractionation, and further purified on a Sepharose CL-6B column. CS-DS-PG protein content was 14% (w/w). The amino-terminal amino acid sequence of the first ten residues was as follows: NH2-Asp-Glu-Ala-B-Gly-Ile-Gly-Pro-Glu-Val. This sequence is identical to that of human embryonic fibroblast cell (IMR-90) CS-DS-PG, as well as to human HSc-DS-PG. After chondroitinase ABC treatment, two peptides (Mr 22,000 and 16,000 daltons) were detected by sodium dodecyl sulfate-(polyacryl)amide gel electrophoresis (SDS-PAGE). ELISA analysis using rabbit antiserum raised against a synthetic peptide that contained 15 amino acids in the same sequence as the amino terminus of human fetal membrane PG showed significant reactivity with HSc CS-DS-PG. HSc CS-DS-PG had an apparent Mr of approximately 78,000 daltons, as determined by Sepharose CL-6B chromatography and SDS-PAGE. Alkaline borohydride treatment of CS-DS-PG liberated CS-DS glycosaminoglycan (GAG) chains having an Mr of 29,000 daltons. The conversion of xylose to xylitol indicated that the GAG chains are attached to the PG protein core at O-3 through a xylosyl-seryl linkage. CS-DS-PG also contained both N and O-linked oligosaccharides and did not aggregate with hyaluronic acid. These results, together with those reported previously, showed that HSc CS-DS-PG and DS-PG have the same A1-A15 amino acid sequence at the amino terminus but different protein cores. HSc CS-DS-PG was completely digested with chondroitinase AC and is, therefore, distinctly different from HSc DS-PG.

Human skin and post-burn scar hyaluronan: demonstration of the association with collagen and other proteins

Hyaluronan (HA) extracted from tissues has been demonstrated to have an enhancing effect on the process of wound healing; the question arises whether this effect is due to the HA or to associated collagen and other proteins. In this study, HA has been extracted from human skin and scar tissue under dissociative conditions and isolated by DEAE-cellulose chromatography followed by CsCl gradient and Sepharose CL-6B chromatography. This highly purified HA was found to contain between 4 and 28% protein, with collagen constituting 5% of the total protein. A functional association between HA and a collagen protein complex is proposed.

Effect of proteoglycans on type I collagen fibre formation

Collagen fibrillogenesis is a multistep process involving assembly of molecules into fibrils and bundles of fibrils. The exact role of proteoglycans in collagen fibrillogenesis is unclear. The purpose of these studies is to study the effect of proteoglycans on collagen fibrillogenesis in vitro. Results of these studies suggest that the proteoglycans dermatan sulphate and chondroitin sulphate do not change the final turbidity and hence the diameter of fibrils formed during the early stages of fibrillogenesis. This suggests that proteoglycans may not influence the early phases of collagen assembly, such as nucleation. However, proteoglycans added during the final stages of collagen fibre formation in vitro cause changes in ultimate tensile strength. In the presence of the high-molecular-weight proteoglycan, the ultimate tensile strength is increased by a factor of 1.5 above that of the control, whilst in the presence of low-molecular weight chondroitin sulphate proteoglycan the tensile strength is significantly decreased. It is concluded that proteoglycans influence the later stages of fibre formation. The presence of high-molecular-weight chondroitin sulphate proteoglycan leads to efficient stress transfer between collagen fibrils, altering the ultimate tensile strength. The results of these studies will be useful in optimizing the design of collagen tendon-ligament prostheses.

Isolation and partial characterization of dermatan sulfate proteoglycans from human post-burn scar tissues

Dermatan sulfate (DS) proteoglycans (PGs) were extracted from human post-burn scar (Sc) tissues with 4M guanidinium chloride and isolated from the extracts by DEAE-cellulose chromatography and by differential ethanol precipitation. The DS.PGs were further purified by Sepharose CL-6B column chromatography. The average molecular weight (Mr) of hypertrophic scar (HSc) tissue DS.PGs was 39,000 based on sedimentation equilibrium measurements. Alkaline borohydride treatment of DS.PGs liberated glycosaminoglycan (GAG) chains and the presence of xylitol indicated that these chains were attached to protein core by xylosyl residues. The average Mr of the DS.GAG chain from HSc and normal scar (NSc) samples were 23,500 and 20,000 respectively. After digestion of the HSc and NSc, DS.PGs with chondroitinase ABC in the presence of proteinase inhibitors, two peptide components with Mr values of 21,500 and 17,000 were detected by SDS-polyacrylamide gel electrophoresis using reducing conditions. Analysis of the protein core fractions derived from NSc and HSc DS.PGs by Sepharose CL-6B column chromatography showed the presence of a single NH2-terminal amino acid (aspartic acid) and also that the fractions with different KAV values had an identical NH2-terminal sequence (A1-A5). The A1-A23 sequence of NSc DS.PG (major fraction, C): NH2Asp-Glu-Ala-O-Gly-Ile-Gly-Pro-Glu-Val-Pro-Asp-Asp-Arg-Asp-Phe-G lu-Pro- Ser-Leu-Gly-Pro-Val was the same as reported for a DS.PG isolated from human fetal membrane (HFM) tissue (Brennan et al., 1984). ELISA inhibition assay using monoclonal antibodies raised in rabbit against the NH2-terminal peptide (containing 15 amino acids) of human fetal membrane tissue were found to cross-react with HSc and NSc DS.PGs. Monoclonal antibodies to bovine skin DS.PGs protein core (Pearson et al., 1983) did not show any cross-reactivity with scar DS.PGs. These results show that the scar DS.PGs described here are different from normal bovine skin DS.PGs in the size and type of the protein core, and that in all the samples, the peptide components have the same NH2-terminal amino acid sequence.

Interleukin-1-induced changes in extracellular glycosaminoglycan composition of cutaneous scar-derived fibroblasts in culture

Fibroblast cultures established from explants of mature scar and skin tissue were analyzed with regard to extracellular glycosaminoglycan (GAG) composition and response to interleukin-1 (IL-1). Following a serum-free 48 hour label with [3H]glucosamine, pericellular and medium GAGs were isolated by precipitation with cetylpyridinium chloride (CPC) and analyzed by cellulose acetate electrophoresis. In addition, susceptibility of the precipitates to Streptomyces hyaluronidase, chondroitinase ABC and heparitinase was determined. Labeled conditioned medium from the scar-derived cells contained both dermatan sulfate (DS) and hyaluronate (HA), as compared to medium from the control (skin-derived) cells which contained predominantly DS. IL-1 induced the appearance of chondroitin 4-sulfate (C4-S) in the medium of the scar cells with no concurrent effect on either DS or HA, and increased the amount of HA in the medium fraction of normal skin cells. The pericellular fraction of the scar-derived cells contained chondroitin 6-sulfate (C6-S) and DS; addition of IL-1 resulted in a shift from DS to heparan sulfate (HS), and the emergence of a pericellular GAG profile similar to that of normal dermal fibroblasts.

The effect of platelet-derived growth factor on cell division and glycosaminoglycan synthesis by human skin and scar fibroblasts

The effect of platelet-derived growth factor (PDGF) on cell division and glycosaminoglycan (GAG) synthesis by fibroblasts isolated from skin and scar was measured. We found that PDGF stimulates cell division more efficiently in normal skin fibroblasts than in scar fibroblasts and decreases GAG synthesis in skin and scar fibroblasts. Using a 4-h pulse label with [3H]thymidine ([3H]Thd) following a 20-h incubation of confluent monolayer cultures with 0-5 units PDGF/ml Dulbecco's modified Eagle's medium, we found a concentration-dependent increase in [3H]Thd incorporation. After incubation of fibroblasts with [3H]glucosamine and 35SO4 in the presence or absence of PDGF, labeled constituents were isolated from the extracellular, pericellular, and cellular fractions by pronase digestion and column chromatography on Sepharose CL4B or DEAE-cellulose and analyzed by cellulose acetate electrophoresis. The presence of PDGF decreased the total amount of 35S incorporated into macromolecules by skin and scar fibroblasts and resulted in an altered distribution of labeled GAGs. Dermal fibroblasts exposed to PDGF for 24 h incorporated a greater percentage of radiolabeled 35S into dermatan sulfate prime (DS') and less into dermatan sulfate (DS) in the extracellular fractions and a greater percentage of 35S into heparan sulfate (HS) in the pericellular fractions than did parallel cultures grown in the absence of PDGF. It is thought than PDGF may have an effect on scar formation by increasing the fibroblast population in the wound tissue and by affecting the total amount and types of matrix components synthesized.

Separation and properties of rabbit buccal mucosal wound hyaluronidase

This study establishes the existence of a mammalian buccal mucosal wound hyaluronidase (hyaluronate 4-glycohydrolase; EC 3.2.1.35) having properties distinct from those of the endogenous lysosomal hyaluronidase of normal (uninjured) buccal mucosa. A time-dependent change in hyaluronidase activity was measured, with the highest specific activity occurring on post-wound day 4 (7.7 +/- 1.3 units/mg protein), followed by consecutive decreases until activity was no longer discernible by day 21. Mucosal wound hyaluronidase closely resembled a previously described integumentary wound endoglycosidase in terms of a high pH optimum (5.0-6.0), distinct (but non-exclusive) substrate preference for hyaluronic acid, and ability to generate saturated depolymerization products by an endoglycosidic hydrolysis.