Scarless Healing

A fetal wound healing program after intrauterine bile duct injury may contribute to biliary atresia

BACKGROUND & AIMS

Biliary atresia (BA) is an obstructive cholangiopathy that initially affects the extrahepatic bile ducts (EHBDs) of neonates. The etiology is uncertain, but evidence points to a prenatal cause. Fetal tissues have increased levels of hyaluronic acid (HA), which plays an integral role in fetal wound healing. The objective of this study was to determine whether a program of fetal wound healing is part of the response to fetal EHBD injury.

METHODS

Mouse, rat, sheep, and human EHBD samples were studied at different developmental time points. Models included a fetal sheep model of prenatal hypoxia, human BA EHBD remnants and liver samples taken at the time of the Kasai procedure, EHBDs isolated from neonatal rats and mice, and spheroids and other models generated from primary neonatal mouse cholangiocytes.

RESULTS

A wide layer of high molecular weight HA encircling the lumen was characteristic of the normal perinatal but not adult EHBD. This layer, which was surrounded by collagen, expanded in injured ducts in parallel with extensive peribiliary gland hyperplasia, increased mucus production and elevated serum bilirubin levels. BA EHBD remnants similarly showed increased HA centered around ductular structures compared with age-appropriate controls. High molecular weight HA typical of the fetal/neonatal ducts caused increased cholangiocyte spheroid growth, whereas low molecular weight HA induced abnormal epithelial morphology; low molecular weight HA caused matrix swelling in a bile duct-on-a-chip device.

CONCLUSION

The fetal/neonatal EHBD, including in human EHBD remnants from Kasai surgeries, demonstrated an injury response with prolonged high levels of HA typical of fetal wound healing. The expanded peri-luminal HA layer may swell and lead to elevated bilirubin levels and obstruction of the EHBD.

IMPACT AND IMPLICATIONS

Biliary atresia is a pediatric cholangiopathy associated with high morbidity and mortality rates; although multiple etiologies have been proposed, the fetal response to bile duct damage is largely unknown. This study explores the fetal pathogenesis after extrahepatic bile duct damage, thereby opening a completely new avenue to study therapeutic targets in the context of biliary atresia.

Nano drug delivery systems: a promising approach to scar prevention and treatment

Scar formation is a common physiological process that occurs after injury, but in some cases, pathological scars can develop, leading to serious physiological and psychological effects. Unfortunately, there are currently no effective means to intervene in scar formation, and the structural features of scars and their unclear mechanisms make prevention and treatment even more challenging. However, the emergence of nanotechnology in drug delivery systems offers a promising avenue for the prevention and treatment of scars. Nanomaterials possess unique properties that make them well suited for addressing issues related to transdermal drug delivery, drug solubility, and controlled release. Herein, we summarize the recent progress made in the use of nanotechnology for the prevention and treatment of scars. We examine the mechanisms involved and the advantages offered by various types of nanomaterials. We also highlight the outstanding challenges and questions that need to be addressed to maximize the potential of nanotechnology in scar intervention. Overall, with further development, nanotechnology could significantly improve the prevention and treatment of pathological scars, providing a brighter outlook for those affected by this condition.

Incorporation of Bioglass Improved the Mechanical Stability and Bioactivity of Alginate/Carboxymethyl Chitosan Hydrogel Wound Dressing

Recently, hydrogel wound dressings were popular in wound healing because of their advantages over traditional gauze dressings. The alginate/carboxymethyl chitosan (SA/CMCS) hydrogel wound dressing has been widely studied because of its biocompatibility and antibacterial ability. However, the poor mechanical stability and lack of bioactivity limit their applications. Bioglass (BG) has been well acknowledged as a bioactive material, and SA/BG hydrogels have been reported to be able to promote wound healing. Calcium ions released from BG can further cross-link SA, which may enhance the mechanical stability of the SA/CMCS hydrogels. Therefore, in this study, BG was incorporated into SA/CMCS hydrogel in order to obtain a bioactive alginate/CMCS/BG (SA/CMCS/BG) hydrogel wound dressing with improved mechanical stability. Results showed that the Young's modulus of SA/CMCS/BG hydrogel was three times higher than that of SA/CMCS hydrogel. In addition to better antibacterial and coagulation properties, SA/CMCS/BG hydrogels possess stronger bioactivity than SA/CMCS hydrogels as they could accelerate skin wound closure by regulating the host inflammation responses, stimulating angiogenesis, and enhancing collagen deposition in wound sites, which suggests that SA/CMCS/BG hydrogels are good candidates for clinic wound dressings.

Electrospun Biomaterials in the Treatment and Prevention of Scars in Skin Wound Healing

Electrospinning is a promising method for the rapid and cost-effective production of nanofibers from a wide variety of polymers given the high surface area morphology of these nanofibers, they make excellent wound dressings, and so have significant potential in the prevention and treatment of scars. Wound healing and the resulting scar formation are exceptionally well-characterized on a molecular and cellular level. Despite this, novel effective anti-scarring treatments which exploit this knowledge are still clinically absent. As the process of electrospinning can produce fibers from a variety of polymers, the treatment avenues for scars are vast, with therapeutic potential in choice of polymers, drug incorporation, and cell-seeded scaffolds. It is essential to show the new advances in this field; thus, this review will investigate the molecular processes of wound healing and scar tissue formation, the process of electrospinning, and examine how electrospun biomaterials can be utilized and adapted to wound repair in the hope of reducing scar tissue formation and conferring an enhanced tensile strength of the skin. Future directions of the research will explore potential novel electrospun treatments, such as gene therapies, as targets for enhanced tissue repair applications. With this class of biomaterial gaining such momentum and having such promise, it is necessary to refine our understanding of its process to be able to combine this technology with cutting-edge therapies to relieve the burden scars place on world healthcare systems.

Enhanced proliferation of pancreatic acinar cells in MRL/MpJ mice is driven by severe acinar injury but independent of inflammation

Adult pancreatic acinar cells have the ability to re-enter the cell cycle and proliferate upon injury or tissue loss. Despite this mitotic ability, the extent of acinar proliferation is often limited and unable to completely regenerate the injured tissue or restore the initial volume of the organ, thus leading to pancreatic dysfunction. Identifying molecular determinants of enhanced proliferation is critical to overcome this issue. In this study, we discovered that Murphy Roths Large (MRL/MpJ) mice can be exploited to identify molecular effectors promoting acinar proliferation upon injury, with the ultimate goal to develop therapeutic regimens to boost pancreatic regeneration. Our results show that, upon cerulein-induced acinar injury, cell proliferation was enhanced and cell cycle components up-regulated in the pancreas of MRL/MpJ mice compared to the control strain C57BL/6. Initial damage of acinar cells was exacerbated in these mice, manifested by increased serum levels of pancreatic enzymes, intra-pancreatic trypsinogen activation and acinar cell apoptosis. In addition, MRL/MpJ pancreata presented enhanced inflammation, de-differentiation of acinar cells and acinar-to-ductal metaplasia. Manipulation of inflammatory levels and mitogenic stimulation with the thyroid hormone 5,3-L-tri-iodothyronine revealed that factors derived from initial acinar injury rather than inflammatory injury promote the replicative advantage in MRL/MpJ mice.

The Role of Macrophages in Acute and Chronic Wound Healing and Interventions to Promote Pro-wound Healing Phenotypes

Macrophages play key roles in all phases of adult wound healing, which are inflammation, proliferation, and remodeling. As wounds heal, the local macrophage population transitions from predominantly pro-inflammatory (M1-like phenotypes) to anti-inflammatory (M2-like phenotypes). Non-healing chronic wounds, such as pressure, arterial, venous, and diabetic ulcers indefinitely remain in inflammation—the first stage of wound healing. Thus, local macrophages retain pro-inflammatory characteristics. This review discusses the physiology of monocytes and macrophages in acute wound healing and the different phenotypes described in the literature for both in vitro and in vivo models. We also discuss aberrations that occur in macrophage populations in chronic wounds, and attempts to restore macrophage function by therapeutic approaches. These include endogenous M1 attenuation, exogenous M2 supplementation and endogenous macrophage modulation/M2 promotion via mesenchymal stem cells, growth factors, biomaterials, heme oxygenase-1 (HO-1) expression, and oxygen therapy. We recognize the challenges and controversies that exist in this field, such as standardization of macrophage phenotype nomenclature, definition of their distinct roles and understanding which phenotype is optimal in order to promote healing in chronic wounds.

Local Delivery of CTGF siRNA with Poly(sorbitol-co-PEI) Reduces Scar Contraction in Cutaneous Wound Healing

Healing process in scarring inevitably produces a considerable amount of non-organized dense collagen-rich matrix called scar thus impairing the native structure of skin. Connective tissue growth factor (CTGF) overexpression within healing tissues is known to play an imperative role in collagen production stimulated by transforming growth factor-beta in cutaneous wound healing. Undoubtedly, the knockdown of CTGF expression through siRNA-mediated gene silencing could simply impede the scarring process. However, the less stability and low transfection of siRNAs themselves urge a safe carrier to protect and transfect them into cells at a high rate avoiding toxicities. Here, we developed a degradable poly(sorbitol-co-PEI) (PSPEI), prepared by polymerization of sorbitol diacrylate with low molecular weight polyethylenimine, which has high transfection efficiency but low cytotoxicity, and utilized it in siCTGF delivery to silence the expression of CTGF in an animal model of cutaneous wound healing. Unlike contracted scar in normal healing, there was no or less contraction in the healed skin of mice treated with siCTGF using PSPEI. Histologically, the healed tissues also had distinct papillary structures and dense irregular connective tissues that were lacking in the control scar tissues. This study exemplifies a successful treatment of cutaneous wound healing using a polymer system coupled with RNA interference. Hence, the approach holds a great promise for developing new treatments with novel targets in regenerative medicines.

Clinical Evaluation of Hyaluronic Acid Sponge with Zinc versus Placebo for Scar Reduction after Breast Surgery

BACKGROUND

Scar formation is a major source of dissatisfaction among patients and surgeons. Individually, hyaluronan, or hyaluronic acid (HA), and zinc have been shown to reduce scarring. The authors evaluated the safety and efficacy of an HA sponge with zinc compared with placebo when applied to bilateral breast surgery scars; specifically, they evaluated whether the use of this product modulates inflammation and immediate scarring in treated patients after bilateral breast surgery.

METHODS

This double-blind, randomized, prospective study was approved by the local institutional review board. Bilateral breast surgery patients with right and left incision lines were randomly assigned to receive HA sponge with zinc or placebo within 2 to 4 days after their procedure. Participants were followed up at 6 weeks, 12 weeks, and 1 year and evaluated at 12 weeks. Three blinded evaluators reviewed photographs of the incision lines and assessed the scars using a visual analog scale, new scale, and a patient satisfaction survey.

RESULTS

Nineteen bilateral breast surgery patients were enrolled in the study. Statistical analysis was performed on 14 patients who completed the follow-up. The mean visual analog scale score was lower for the side receiving the HA sponge with zinc (2.6) than for the side receiving placebo (3.0), indicating a better outcome (t test; P = 0.08). The HA sponge with zinc was found to have significant positive findings on a patient satisfaction survey (P = 0.01).

CONCLUSIONS

This is a preliminary study that shows zinc hyaluronan was associated with high patient satisfaction in achieving a better scar after bilateral breast surgery, irrespective of skin color. It seems to be safe and effective for early scars.

Defining the identity of mouse embryonic dermal fibroblasts

Embryonic dermal fibroblasts in the skin have the exceptional ability to initiate hair follicle morphogenesis and contribute to scarless wound healing. Activation of the Wnt signaling pathway is critical for dermal fibroblast fate selection and hair follicle induction. In humans, mutations in Wnt pathway components and target genes lead to congenital focal dermal hypoplasias with diminished hair. The gene expression signature of embryonic dermal fibroblasts during differentiation and its dependence on Wnt signaling is unknown. Here we applied Shannon entropy analysis to identify the gene expression signature of mouse embryonic dermal fibroblasts. We used available human DNase-seq and histone modification ChiP-seq data on various cell-types to demonstrate that genes in the fibroblast cell identity signature can be epigenetically repressed in other cell-types. We found a subset of the signature genes whose expression is dependent on Wnt/β-catenin activity in vivo. With our approach, we have defined and validated a statistically derived gene expression signature that may mediate dermal fibroblast identity and function in development and disease. genesis 54:415-430, 2016. © 2016 Wiley Periodicals, Inc.

Nanolayered siRNA delivery platforms for local silencing of CTGF reduce cutaneous scar contraction in third-degree burns

Wound healing is an incredibly complex biological process that often results in thickened collagen-enriched healed tissue called scar. Cutaneous scars lack many functional structures of the skin such as hair follicles, sweat glands, and papillae. The absence of these structures contributes to a number of the long-term morbidities of wound healing, including loss of function for tissues, increased risk of re-injury, and aesthetic complications. Scar formation is a pervasive factor in our daily lives; however, in the case of serious traumatic injury, scars can create long-lasting complications due to contraction and poor tissue remodeling. Within this report we target the expression of connective tissue growth factor (CTGF), a key mediator of TGFβ pro-fibrotic response in cutaneous wound healing, with controlled local delivery of RNA interference. Through this work we describe both a thorough in vitro analysis of nanolayer coated sutures for the controlled delivery of siRNA and its application to improve scar outcomes in a third-degree burn induced scar model in rats. We demonstrate that the knockdown of CTGF significantly altered the local expression of αSMA, TIMP1, and Col1a1, which are known to play roles in scar formation. The knockdown of CTGF within the healing burn wounds resulted in improved tissue remodeling, reduced scar contraction, and the regeneration of papillary structures within the healing tissue. This work adds support to a number of previous reports that indicate CTGF as a potential therapeutic target for fibrosis. Additionally, we believe that the controlled local delivery of siRNA from ultrathin polymer coatings described within this work is a promising approach in RNA interference that could be applied in developing improved cancer therapies, regenerative medicine, and fundamental scientific research.

More than just a filler - the role of hyaluronan for skin homeostasis

In recent years, hyaluronan (HA) has become an increasingly attractive substance as a non-immunogenic filler and scaffolding material in cosmetic dermatology. Despite its wide use for skin augmentation and rejuvenation, relatively little is known about the molecular structures and interacting proteins of HA in normal and diseased skin. However, a comprehensive understanding of cutaneous HA homeostasis is required for future the development of HA-based applications for skin regeneration. This review provides an update on HA-based structures, expression, metabolism and its regulation, function and pharmacological targeting of HA in skin.

Innate regeneration in the aging heart: healing from within

The concept of the heart as a terminally differentiated organ incapable of replacing damaged myocytes has been at the center of cardiovascular research and therapeutic development for the past 50 years. The progressive decline in myocyte number as a function of age and the formation of scarred tissue after myocardial infarction have been interpreted as irrefutable proofs of the postmitotic characteristic of the heart. However, emerging evidence supports a more dynamic view of the heart in which cell death and renewal are vital components of the remodeling process that governs cardiac homeostasis, aging, and disease. The identification of dividing myocytes in the adult and senescent heart raises the important question concerning the origin of these newly formed cells. In vitro and in vivo findings strongly suggest that replicating myocytes derive from lineage determination of resident primitive cells, supporting the notion that cardiomyogenesis is controlled by activation and differentiation of a stem cell compartment. It is the current view that the myocardium is an organ permissive of tissue regeneration mediated by exogenous and endogenous progenitor cells.

Stem cell therapy for cardiac repair: benefits and barriers

Cardiovascular disease remains the leading cause of death worldwide. Acute ischaemic injury and chronic cardiomyopathies lead to permanent loss of cardiac tissue and ultimately heart failure. Current therapies aim largely to attenuate the pathological remodelling that occurs after injury and to reduce risk factors for cardiovascular disease. Studies in animal models indicate that transplantation of mesenchymal stem cells, bone-marrow-derived haematopoietic stem cells, skeletal myoblasts, or embryonic stem cells has the potential to improve the function of ventricular muscle after ischaemic injury. Clinical trials using primarily bone-marrow-derived cells and skeletal myoblasts have also produced some encouraging results. However, the current experimental evidence suggests that the benefits of cell therapy are modest, the generation of new cardiac tissue is low, and the predominant mechanisms of action of transplanted stem cells involve favourable paracrine effects on injured myocardium. Recent studies show that the adult heart possesses various pools of putative resident stem cells, raising the hope that these cells can be isolated for therapy or manipulated in vivo to improve the healing of cardiac muscle after injury. This article reviews the properties and potential of the various stem cell populations for cardiac repair and regeneration as well as the barriers that might lie ahead.

Adult urethral stricture disease after childhood hypospadias repair

Background. Adult patients with urethral stricture after childhood hypospadias surgeries are infrequently discussed in the literature. We report our experience in treating such patients. Materials and Methods. A retrospective chart review was performed. From 2002 through 2007, nine consecutive adult patients who had current urethral stricture and had undergone childhood hypospadias surgeries were included. All adult urethral strictures were managed by a single surgeon. Results. Mean patient age was 38.9 years old. The lag time of urethral stricture presentation ranged from 25 to 57 years after primary hypospadias surgery, with an average of 36 years. Stricture length ranged from 1 to 17 cm (mean: 10.3 cm). Open graft-based urethroplasties were performed in 4/9 cases. Salvage perineal urethrostomy was performed in 2/9 cases. Another 3 cases chose to undergo repeat urethrotomy or dilatations-none of these patients was cured by such treatment. Complications included one urethrostomy stenosis and one urinary tract infection. Conclusion. Urethral stricture may occur decades after initial hypospadias surgery. It can be the most severe form of anterior urethral stricture, and may eventually require salvage treatment such as a perineal urethrostomy. Patients undergoing hypospadias surgery should receive lifelong follow-up protocol to detect latent urethral strictures.

Fetal wound healing using a genetically modified murine model: the contribution of P-selectin

PURPOSE

During early gestation, fetal wounds heal with paucity of inflammation and absent scar formation. P-selectin is an adhesion molecule that is important for leukocyte recruitment to injury sites. We used a murine fetal wound healing model to study the specific contribution of P-selectin to scarless wound repair.

METHODS

Linear excisional wounds were created on the dorsa of E15.5 and E17.5 gestation fetuses in wild-type and P-selectin (-/-) mice (term = 19 days). Wounds were harvested at various time-points after wounding and analyzed using histology and immunohistochemistry.

RESULTS

The E15.5 wounds in both wild-type and P-selectin (-/-) fetuses healed scarlessly and with minimal inflammation, whereas E17.5 wounds healed with fibrosis and inflammation. However, the scars of the P-selectin (-/-) wounds appeared slightly different than wild-type. There were significantly more inflammatory cells in E17.5 wild-type wounds 6 hours after injury (P < .001), but the difference was no longer significant by 24 hours. Finally, reepithelialization was slower in the E15.5 knockout wounds compared to their wild-type counterparts.

CONCLUSIONS

Absence of P-selectin delays inflammatory cell recruitment and reepithelialization of fetal wounds; however, scar formation still occurs in late gestation wounds. The contribution of specific molecules to fetal wound healing can be elucidated using murine knockout or transgenic models.

Differential cutaneous wound healing in thermally injured MRL/MPJ mice

Adult wound repair occurs with an initial inflammatory response, reepithelialization, and the formation of a permanent scar. MRL/MpJ mice following ear-hole punch biopsies display accelerated healing and tissue regeneration. In this study, we characterized the healing responses in both MRL/MpJ and BALB/c mice following a 15% total body surface area full-thickness cutaneous burn injury. Macroscopic and histological observations show that delayed wound closure in MRL/MpJ mice is accompanied by an increase in edema, reduced neutrophil infiltration, and more prominent eschar. In vivo bromodeoxyuridine labeling showed no defect in keratinocyte proliferation and migration (reepithelialization). In comparison with BALB/c mice, MRL/MpJ wounds had greater collagen deposition, less granulation tissue formation, and contained fewer alpha-smooth muscle actin-positive myofibroblasts. An observed reduction in dermal neutrophil infiltration and myofibroblast development correlated with enhanced angiogenesis. Overall, BALB/c wounds contracted sooner and to a larger degree, resulting in a significant decrease in scar formation. Interestingly, MRL/MpJ mice showed overt abnormalities in hair follicle proliferation, morphogenesis, and subsequent hair regrowth postburn injury. No substantial evidence of tissue regeneration was observed in either BALB/c or MRL/MpJ wounds. Our results convincingly demonstrate that MRL/MpJ skin burn wounds heal with scar formation with delays in two critical wound healing events: wound closure, and myofibroblast development.

Differential regulation of hyaluronan metabolism in the epidermal and dermal compartments of human skin by UVB irradiation

Hyaluronan (HA), a major component of the cutaneous extracellular-matrix, is involved in tissue repair. Human skin is exposed to and damaged by UVB-irradiation. Here, we investigate the regulation of HA metabolism in human skin during acute UVB-induced inflammation. Expression of HA synthesizing (HAS) and degrading enzymes hyaluronidase (HYAL) as evaluated by quantitative reverse transcribed PCR in response to UVB differed when fibroblasts and HaCaT-keratinocytes, representative cell types in dermis and epidermis, respectively, were compared. Both demonstrated temporally different expression patterns of these genes 3- and 24-hours post-irradiation. This resulted 24-hours post-irradiation in an increase in HAS gene expression in both fibroblasts and HaCaT-keratinocytes, and an increase in HYAL expression only in fibroblasts. HA-production as analyzed by the HA content of conditioned medium was reduced in HaCaT and fibroblast cultures 3-hours post-irradiation, whereas HA increased in HaCaT-cultures 24-hours post-irradiation but remained suppressed in fibroblasts-cultures. Consistently, immunohistochemical staining for HA in human skin 24-hours post-irradiation demonstrated an increased epidermal HA, but a decrease in the dermal compartment. Moreover, analysis of the HA content of dermal microdialysis-fluid revealed increased accumulation of HA degradation products 24-hours post-irradiation. These data demonstrate that there is a complex temporal and spatial regulation of HA-metabolism in skin in response to UVB irradiation.

Hyaluronan-mediated angiogenesis in vascular disease: uncovering RHAMM and CD44 receptor signaling pathways

The correct formation of new blood vessels from existing vasculature (angiogenesis) is essential for embryogenesis and the effective repair of damaged or wounded tissues. However, excessive and detrimental vascularization also occurs in neoplasia, promoting tumour growth and metastasis, as well as in proliferative diabetic retinopathy and atherosclerosis. Greater understanding of the mechanisms controlling the angiogenic process will allow optimization of wound healing, and provide mechanisms to inhibit vascularization in tumours and other diseases. Evidence supports a cascade of events in which the perturbation of one of the steps is sufficient to significantly inhibit neovascularization. The extracellular macromolecules, notably glycosaminoglycans (GAGs), are important mediators of angiogenesis. Hyaluronan (HA), a large, non-sulphated GAG, was first discovered in the vitreous of the eye [.], and is ubiquitously expressed in the extracellular matrix (ECM) of tissues. Native high molecular weight HA (n-HA) is anti-angiogenic, whereas HA degradation products (o-HA; 3-10 disaccharides) stimulate endothelial cell (EC) proliferation, migration and tube formation following activation of specific HA receptors in particular, CD44 and Receptor for HA-Mediated Motility (RHAMM, CD168). The involvement of HA in the regulation of angiogenesis makes it an attractive therapeutic target. We review the role of o-HA in modulation of angiogenesis during tissue injury, and vascular disease, focusing on receptor-mediated signal transduction pathways that have been evaluated.

Foetal surgery and cleft lip and palate: current status and new perspectives

Now-a-days, high-resolution ultrasound allows an accurate and relatively early diagnosis of congenital malformations. In a limited number of such conditions foetal surgery may be lifesaving. However, premature labour has been the major drawback for open foetal surgery. Recently, improvement of video-endoscopic technology has boosted the development of operative techniques for feto-endoscopic surgery, which has been demonstrated to be less invasive than the open approach. Main clinical application of fetoscopic procedures today is the treatment of feto-foetal transfusion syndrome. Although still in development, feto-endoscopic surgery seems to offer new hope for surgical foetal therapy not only in cases of life threatening conditions. Experimental intrauterine correction of cleft lip and palate (CLP) has been lately performed using the feto-endoscopic approach. This procedure offers two major advantages: first, scarless foetal wound healing and bone healing without callus formation, which would also allow a better/normal maxillary growth, and second, significant decrease of foetal and maternal morbidity. Herein, we report the current status of experimental and clinical foetal surgery and propose possible directions for continuing research to make intrauterine procedures safer. Furthermore, we discuss current knowledge and new perspectives of experimental foetal cleft lip and palate repair, which in the future may lead to such excellent results in the operative treatment of clefts, that less or no secondary corrections and therapies, such as orthodontic, dental, logopedic, etc. would be needed. Only if these conditions can be fulfilled, will we be able to improve substantially our therapy for the human foetus with a cleft lip and palate. In spite of all efforts, however, it must be considered that it may not ever be possible to find the optimal treatment method for this or other craniofacial malformations.

Prior injury accelerates subsequent wound closure in a mouse model of regeneration

Tissue regeneration and scarless healing involves the complete replacement and functional restoration of damaged organs and tissues. In this study of the "scarless healing" MRL mouse model, we demonstrate that 2-mm diameter through-and-through holes made in the cartilaginous part of previously injured MRL mouse ears are closed more efficiently, and that the regenerative repair response is significantly accelerated compared with unprimed MRL and control "nonhealer" strains of mice. Accelerated healing was detected both locally and distally from the original site of injury indicating the involvement of systemic components such as circulating cell types or soluble factors. Histologically, we observed early differences during the wound repair process (before Day 4 post injury) with accelerated formation of blastema-like structures, epidermal downgrowths, and enhanced epithelium thickening in wound border zones in primed MRL mice versus unprimed MRL mice. Although the mechanism of tissue regeneration remains unclear, the results from this study justify the use of the MRL model for further experimentation directed toward the identification of proteins and cell types capable of stimulating scarless tissue regeneration.

Intrauterine autogenous foetal bone transplantation for the repair of cleft-like defects in the mid-gestational sheep model

AIM

The success of intrauterine surgery in treating non-life-threatening malformations such as myelomeningocoele, has also renewed strong interest in using this technique for treating craniofacial malformations. Nevertheless, the only experimental cleft-like defect models known, are those concerning wound healing of soft tissues.

MATERIAL AND METHODS

Attempts were made to repair artificial cleft-like defects including transplantation of 11 autogenous foetal bone grafts from the iliac crest or ulna, and were randomly assigned to three study groups, using the mid-gestational sheep model. In a 4th study group, lyophilized collagen, a bone-regenerating bioresorbable implant material, was used to fill the alveolar defect.

RESULTS

In all groups, there was a slight degree of asymmetry and thinning of the lip. Radiological studies demonstrated a variable degree of abnormality of the maxilla, ranging from none to a mild deviation. Three-dimensional computer tomography, two-dimensional maximal intensity projection findings, and histological analysis confirmed bony healing of the alveolar cleft-like defect.

DISCUSSION/CONCLUSION

Intrauterine autogenous foetal bone transplantation for the repair of cleft-like defects in the sheep is feasible. This is a reliable and valuable model toward a possible clinical application for intrauterine treatment of clefts.

Transplantation of the urinary bladder and other organs in the subcutaneous tissue induces cyst formation and epithelialization: its potential usefulness in regenerative medicine

Certain hollow organs are known to form cysts when heterologously transplanted. In order to examine the usefulness of the phenomenon for regenerative medicine, rat urinary bladders and other organs were allo-transplanted under the subcutaneous tissue of the back. These transplanted tissues very often formed cysts covered with epithelia. The epithelia covered an area about twice the original size. In the case of the urinary bladder, the epithelium started moving from the edge of the transplants around day 3 after the operation, and as time proceeded, the tela submucosa and tunica muscularis also moved to encircle the epithelium, and formed the wall of the cyst. The basal laminae were formed under the newly expanded epithelium slightly behind the leading tip. All of the organs tested had the capability of cyst formation and epithelialization, although their rate differed between organs. The results are discussed with reference to the potential use of cyst formation for regenerating damaged organs.

The Effect of Silicone Gel on Basic Fibroblast Growth Factor Levels in Fibroblast Cell Culture

BACKGROUND

Topical silicone gel has shown promise in the treatment of hypertrophic and keloid scars. However, its mechanism of action remains undetermined.

OBJECTIVE

To investigate whether the presence of silicone alters the secretion of basic fibroblast growth factor (bFGF), a key cytokine involved in the scar formation process.

DESIGN

Serum-free fibroblast cell cultures were established from normal, keloid, and fetal skin, which heals without scarring, and exposed to silicone gel. Serial cell counts were performed, and supernatants were collected for bFGF quantification by enzyme-linked immunosorbent assay at 4, 24, 72, and 120 hours.

RESULTS

Growth curves were similar and no statistically significant differences in population doubling times were observed between treated and untreated specimens. Statistically significant differences in bFGF levels between treated and untreated normal fibroblasts were observed at 24, 72, and 120 hours after cell culture initiation. Differences in bFGF levels between treated and untreated fetal fibroblasts that approached statistical significance were observed at 72 and 120 hours.

CONCLUSIONS

These results suggest that silicone gel is responsible for increased bFGF levels in normal and fetal dermal fibroblasts. We postulate that silicone gel treats and prevents hypertrophic scar tissue, which contains histologically normal fibroblasts, by modulating expression of growth factors such as bFGF. Our data support the hypothesis that substances that favorably influence wound healing do so by correcting a deficiency or overabundance of the growth factors that orchestrate the tissue repair process.

Plasminogen activator/plasmin system: a major player in wound healing?

The role of the plasminogen activator/plasmin system in fibrinolysis has been well established. Indeed, clinicians worldwide have successfully utilized recombinant tissue-type plasminogen activator as first-line treatment of acute myocardial infarction for almost 2 decades. Outside the field of cardiology, there has been increasing excitement regarding the possible contribution of this system in many other important biological processes, including cell adhesion, cell migration, cell-cell signaling, tumor invasion and metastasis, ovulation, and wound healing. In this review, we present evidence in the current literature that the plasminogen activator/plasmin system does have a role in wound healing, looking at both normal and abnormal healing. Furthermore, the invaluable insights provided by numerous transgenic animal experiments are summarized.

Regulation of wound healing by growth factors and cytokines

Cutaneous wound healing is a complex process involving blood clotting, inflammation, new tissue formation, and finally tissue remodeling. It is well described at the histological level, but the genes that regulate skin repair have only partially been identified. Many experimental and clinical studies have demonstrated varied, but in most cases beneficial, effects of exogenous growth factors on the healing process. However, the roles played by endogenous growth factors have remained largely unclear. Initial approaches at addressing this question focused on the expression analysis of various growth factors, cytokines, and their receptors in different wound models, with first functional data being obtained by applying neutralizing antibodies to wounds. During the past few years, the availability of genetically modified mice has allowed elucidation of the function of various genes in the healing process, and these studies have shed light onto the role of growth factors, cytokines, and their downstream effectors in wound repair. This review summarizes the results of expression studies that have been performed in rodents, pigs, and humans to localize growth factors and their receptors in skin wounds. Most importantly, we also report on genetic studies addressing the functions of endogenous growth factors in the wound repair process.

Hyaluronic acid prevents peripheral nerve adhesion

The purpose of this study was to clarify the effectiveness of hyaluronic acid (HA) in the prevention of scar formation after neurolysis using a rabbit model. In the first stage, the left sciatic nerve was exposed and elevated along a 3 cm section. Then, the surface of the neural bed was coagulated using a bipolar coagulator. Finally, the sciatic nerve was replaced and fixed to the neural bed with 8/0 nylon sutures, and the wound was closed. In the second stage, the adherent sciatic nerve was re-exposed after 6 weeks. In the neurolysis group, a simple neurolysis was performed. In the HA group, the neurolysis was performed in a surgical field coated with HA from the beginning to the end of the operation. In the steroid group, methyl prednisolone acetate was infiltrated at the end of the neurolysis. In the third stage, electrophysiological, histological and biomechanical measurements were taken 6 weeks after the second stage. While there was no significant difference between the HA and the steroid groups, the electrophysiological functions of the HA and steroid groups were significantly better than that of the neurolysis group. Histology showed that the formation of intraneural and extraneural scar tissue was lowest in the HA group, followed by the steroid and neurolysis groups. The tensile strength required to strip the sciatic nerve from the neural bed of the HA group was significantly less than that of the neurolysis group. However, there was no significant difference between the steroid and neurolysis groups. In conclusion, HA effectively reduced scar formation after neurolysis.

Autocrine growth factor production by fetal, keloid, and normal dermal fibroblasts

OBJECTIVE

To evaluate differences in fibroblast autocrine growth factor production by human fetal, keloid, and normal adult dermal fibroblasts.

DESIGN

Serum-free cell lines of fetal, keloid, and normal adult dermal fibroblasts were established. Cell counts were performed and supernatants collected at 4, 24, and 72 hours. Cell-free supernatants were quantitatively assayed for transforming growth factor beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF).

RESULTS

Population doubling times for fetal, keloid, and normal adult fibroblasts were 120.0, 88.1, and 128.4 hours, respectively. Differences in population doubling times did not reach statistical significance. Statistically significant differences between TGF-beta1 levels from fetal and normal adult fibroblasts were seen at 24 and 72 hours. Significant differences between TGF-beta1 levels from keloid and normal adult fibroblasts were also seen at 24 and 72 hours. Fetal fibroblasts demonstrated higher levels of bFGF than normal adult fibroblasts at each time point, but these differences were not statistically significant. No significant differences were observed between keloid and normal adult bFGF levels.

CONCLUSIONS

Both fetal and keloid fibroblasts produce significantly more TGF-beta1 than normal adult fibroblasts. Our data and the data of others suggest that fetal fibroblasts produce more bFGF than adult fibroblasts. The serum-free model we describe can be used to quantitatively measure autocrine growth factor production by cells that underlie clinically different types of wound healing. This model provides information that may allow us to better treat and prevent undesirable scarring.

Thermal preconditioning prevents peritendinous adhesions and inflammation

Adhesion formation is one of the foremost obstacles to a reliably good outcome in tendon and joint surgery. Thermal preconditioning has been found to reduce the inflammatory response through the induction of molecular chaperone expression, a recently described family of cytoprotective intracellular proteins. The authors analyzed the effect of thermal preconditioning on the inflammatory response to surgery, on tendon healing, and on the formation of peritendinous adhesions in 16 New Zealand White rabbits. Very significant decreases in adhesion formation and in the gliding and dimensions of tendons in animals that had thermal preconditioning were found. Tendons from these animals also showed a decreased level of adhesion formation and a significantly diminished inflammatory response on histologic examination with no biomechanically significant deleterious effect on the strength of tendon healing on testing load to failure. These findings are consistent with induction of heat shock proteins by hyperthermic pretreatment. Such prevention of peritendinous adhesions and the inflammatory response to injury and surgery without compromising healing are findings that have significant implications for tendon surgery and all surgery involving joints and soft tissues.

Histologic and rheologic characterization of vocal fold scarring

Scarring of the vocal fold causes considerable dysphonia and presents significant treatment challenges. A rabbit model was developed to investigate the histologic ultrastructure and rheologic properties of the scarred vocal fold lamina propria. Eleven rabbit larynges were scarred by means of forcep biopsy. Sixty days postoperatively, the rabbits were sacrificed and their vocal folds were harvested. Histological analysis of the scarred and normal lamina propria was completed for collagen, procollagen, elastin, and hyaluronic acid. Linear viscoelastic shear properties of the tissues were also measured, including elastic shear modulus and dynamic viscosity. Compared to normal vocal fold lamina propria, scarred tissues demonstrated significantly less collagen, an increase in procollagen, and a decrease in elastin. Rheologically, both elastic shear modulus and dynamic viscosity were significantly higher for the scarred tissues. Increased stiffness and viscosity do not appear to result from an increase in collagen, but rather appear to be related to the presence of new, disorganized collagen scaffolding. Results are interpreted in terms of the possible role of interstitial proteins in the etiology of increased stiffness and viscosity, which requires further investigation. This animal model should allow for systematic future investigations of vocal fold scarring and its treatment.

Hyaluronan and its catabolic products in tissue injury and repair

Hyaluronan is an unbiquitous glycosaminoglycan present in most tissues. Under homeostatic conditions hyaluronan exists as a high molecular mass polymer that has important roles in tissue structural integrity. Under conditions of stress such as following tissue injury, hyaluronan becomes depolymerized and lower molecular mass polymers are generated. The biological properties of these hyaluronan fragments appear to be distinct from the larger precursor molecules. This review examines the biological role of hyaluronan fragments in tissue injury and repair.

Differences in mesenchymal tissue repair

Variations in certain mesenchymal tissue healing processes are not widely recognized. The current review summarizes key differences in healing mechanisms and healing potential after injury to soft tissues having different healing outcomes.

Fetal rat amniotic fluid: transforming growth factor beta and fibroblast collagen lattice contraction

BACKGROUND

In several mammalian animal models, early-gestational-age fetal wounds heal without scar, but wounds of late gestational age heal with scar. This change in wound healing phenotype can be a result of both intrinsic (i.e., cellular characteristics) and extrinsic (i.e., environmental) factors. Our question was: Does amniotic fluid (AF) influence the change from scarless to scar-forming repair in the rat?

METHODS

Rat AF was investigated for its modulation of fibroblast-populated collagen lattice (FPCL) contraction and morphological changes of adult fibroblasts. AF was also assayed for transforming growth factor beta (TGF-beta) levels. Adult rat dermal fibroblasts in monolayer and incorporated into FPCLs were incubated with AF additions from gestational age 14, 16, 18, and 21 days at 10% (v/v).

RESULTS

Day 14 AF significantly stimulated FPCL contraction, but AF of 16, 18, and 21 days inhibited FPCL contraction. Fluorescence histology identified microtubules and microfilaments in AF treated adult rat dermal fibroblasts. The staining pattern of microtubules in Day 14 AF-treated fibroblasts showed denser structures at the cell center. Cells incubated with Day 16 or 18 AF showed fine peripheral microtubules. A mink lung epithelial cell bioassay was used to analyze concentrations of TGF-beta in AF. TGF-beta levels were greatly elevated in Day 14 AF, but were relatively low in Day 16, 18 and 21 AF. The inhibitor of FPCL contraction from AF of Days 16, 18, and 21 was not identified.

CONCLUSION

It is proposed that the robust expression of TGF-beta or cytoskeletal changes induced by Day 14 AF contributes to enhanced FPCL contraction.

The ontogeny of scarless healing II: EGF and PDGF-B gene expression in fetal rat skin and fibroblasts as a function of gestational age

Twenty years ago, surgeons noted the ability of early-gestation fetal skin to heal in a scarless manner. Since that time, numerous investigators have attempted to elucidate the mechanisms behind this phenomenon. As a result of this effort, it is now well established that many animals undergo a transition late in development from scarless cutaneous healing to a scar-forming, adultlike phenotype. The authors have been interested in the role played by cytokines known to be involved in the adult wound-healing process and how they relate to scarless repair. They therefore asked the following question: Are genes for epidermal growth factor (EGF) and platelet-derived growth factor-B (PDGF-B) expressed differentially as a function of gestational age in fetal rat skin and dermal fibroblasts? To answer this question, skin from fetal Sprague-Dawley rats (N = 56) at time points that represented both the scarless and scar-forming periods of rat gestation was harvested. In addition, fibroblasts derived from fetal rat skin were cultured in vitro at similar times. These cells were expanded in culture and, when confluent, total ribonucleic acid from both fibroblasts and whole skin was extracted and subjected to Northern blot analysis with probes for EGF and PDGF-B. Results demonstrated that neither EGF nor PDGF-B gene expression changed markedly as a function of gestational age in fetal fibroblasts alone. In whole skin, however, both EGF and PDGF-B demonstrated a marked decrease in gene expression with increasing gestational age. Furthermore, the most striking decrease in gene expression for both cytokines came between 16 and 18 days of gestation-the transition point between scarless and scar-forming repair in the fetal rat. These data suggest that EGF and PDGF may play a role in the mechanism of scarless cutaneous repair. Moreover, it appears that fetal fibroblasts are not the cell type responsible for this differential gene expression. These results raise questions about the unique cytokine milieu likely to be present during the time of scarless healing and the cells that ultimately guide the mechanisms leading to skin regeneration.

Ontogeny of expression of transforming growth factor-beta 1 (TGF-beta 1), TGF-beta 3, and TGF-beta receptors I and II in fetal rat fibroblasts and skin

Fetal cutaneous wounds that occur in early gestation heal without scar formation. Although much work has been done to characterize the role of transforming growth factor-beta (TGF-beta) isoforms in the adult wound repair process, their function in fetal scarless wound repair is not well understood. The authors hypothesized that the pattern of expression for TGF-beta isoforms and their receptors may influence the phenotypic transition from scarless to scar-forming repair observed during fetal gestation. Using time-dated fetal Sprague-Dawley rat fibroblasts and unwounded skin at gestational ages 14, 16, 18, and 21 days postcoitum of the scarless (< or =16 days) and scar-forming (>16 days) periods of gestation (term = 21.5 days), the authors analyzed the endogenous messenger RNA (mRNA) levels of TGF-beta 1 and TGF-beta 3 and their signaling receptors TGF-beta-RI and TGF-beta-RII. Northern blot analyses in both fibroblasts and unwounded skin revealed that levels of TGF-beta 1 were not differentially expressed, whereas more TGF-beta 3 mRNA transcript was found in early than in late gestation. Fibroblast expression of TGF-beta-RI showed no substantial differences, whereas expression of TGF-beta-RII increased during gestation. In contrast, expression of both TGF-beta-RI and TGF-beta-RII in unwounded skin showed decreasing levels as a function of gestational age. The differential levels of TGF-beta 1 and TGF-beta 3 suggest that the ratio of these cytokines may provide a predominantly antiscarring or profibrotic signal upon wounding during the scar-free or scar-forming periods of gestation, respectively. Furthermore, lower amounts of the ligand-binding TGF-beta-RII seen in early gestation fibroblasts suggest a decreased ability to perceive ligand during the period of scarless repair.

Effect of Tamoxifen on Transforming Growth Factor β1Production by Keloid and Fetal Fibroblasts

BACKGROUND

Evidence suggests that keloid scar formation may be mediated, in part, by deranged growth factor activity, including that of transforming growth factor (TGF) beta1. Tamoxifen citrate has shown promise in the treatment of keloids.

OBJECTIVE

To evaluate the effect of tamoxifen on autocrine growth factor expression in keloid and fetal dermal fibroblasts, which exhibit scar-free healing.

DESIGN

Serum-free cell lines of keloid and fetal dermal fibroblasts were established. Cell cultures were exposed to different concentrations of tamoxifen solution (8 and 12 or 16 micromol/L). Cell counts were performed and supernatants collected at 24, 48, and 96 hours. Cell-free supernatants were quantitatively assayed for TGF-beta1 expression.

RESULTS

Keloid fibroblasts show increased per-cell TGF-beta1 production compared with fetal fibroblasts. Tamoxifen appeared to decrease per-cell TGF-beta1 production at each of the time points evaluated.

CONCLUSIONS

Keloids likely arise due to locally insufficient or excessive concentrations of specific growth factors. The higher level of TGF-beta1 produced by keloid cells compared with fetal fibroblasts could be related to the aberrant wound healing seen with keloids. The addition of tamoxifen may lead to improved wound healing in keloids by decreasing the expression of TGF-beta1.

Unravelling the secrets of foetal wound healing: an insight into fracture repair in the mouse foetus and perspectives for clinical application

This study was designed to investigate the nature of mammalian foetal fracture healing in utero. A compound 'pinch' fracture was created in the foetal mouse ulna at the end of the second trimester, prior to mineralisation, and healing observed in whole mount limbs and in histological section. Cartilaginous ends gained initial contact within a perichondrial sleeve by 24 h. Bony union was achieved within 48 h by cartilage remodelling during the phase of primary endochondral ossification in the limb, a process to which adult fracture healing aspires. The molecular response to wounding was investigated using a whole mount in situ hybridisation technique and antisense mRNA probes to three target genes (BMP-2, BMP-4 and GDF-5). These experiments failed to identify altered expression in wounded limbs compared with controls.

RNA differential display of scarless wound healing in fetal rabbit indicates downregulation of a CCT chaperonin subunit and upregulation of a glycophorin-like gene transcript

BACKGROUND/PURPOSE

Scars form as wounds heal in adult organisms. In addition to disrupting cosmetic appearance, scar tissue can cause significant morbidity, and even death if it blocks vital organ function. Previous work has established that fetal wounds, especially in early to midgestation, can heal without scarring. Because such inherent physiological mechanisms ultimately are under genetic control, a study was initiated to elucidate the differences in gene expression that produce scarless wound healing in the mammalian fetus but scarring in postnatal wounds. Reverse transcription polymerase chain reaction (RT-PCR) differential display (DD) was used to detect differentially expressed mRNA transcripts in a rabbit model of wound healing.

METHODS

Adult and 21-day fetal full-thickness rabbit skin specimens from wounded and unwounded sites were harvested 12 hours postwounding. RNA extracted from the tissue was used as a template in DD reactions using anchoring and random primers to generate tissue-specific gene expression fingerprints. The over 2,000 resulting amplimers (gene transcripts) were screened for differential expression among the 4 types of specimens: fetal control (unwounded), fetal wound, adult control, and adult wound. Selected bands distinctly upregulated or downregulated in fetal wound lanes on the DD gels were excised, and the cDNA was extracted, reamplified, cloned into vectors, and sequenced. DD results were confirmed by limiting-dilution RT-PCR using sequence-specific primers.

RESULTS

Differential display (DD) showed 22 amplimers that were significantly upregulated in all fetal wound samples as compared with little or no expression in fetal control, adult control, or adult wound tissues. Conversely, 5 transcripts were downregulated in the fetal wound specimens but highly expressed in the 3 comparison tissues. Reamplification of selected transcripts by PCR, followed by cloning and DNA sequencing, yielded 7 distinct sequences, each representing a gene expressed differently in fetal wound than in the other 3 tissues. A transcript that was downregulated in fetal wound showed very high sequence homology to part of the human gene for the eta subunit of the hetero-oligomeric particle CCT (the chaperonin containing T-complex polypeptide 1 or TCP-1). An upregulated amplimer showed significant DNA sequence homology to glycophorins A and B. One sequence was identified as 28S rRNA. The remaining 4 candidate sequences showed no significant homology to known genes, but 1 had high homology to expressed sequence tags of unknown function.

CONCLUSIONS

With careful experimental design and proper controls and verifications, differential display of RNA expression is a potentially powerful method of finding genes that specifically regulate a particular physiological process such as fetal wound healing. No a priori knowledge of what genes might be involved, or why, is necessary. This study indicates that downregulation of a gene that codes for a chaperonin subunit and upregulation of several other genes may be involved in the striking scarless character of wound healing in the mammalian fetus. Results suggest the hypothesis that downregulation of the CCT chaperonin in fetal wound may inhibit the formation of myofibroblasts, a cell type that correlates highly with scarring in postnatal wound healing, by preventing the folding of sufficient alpha-smooth muscle actin to form the stress fibers characteristic of these cells.

Developmental differences in the expression and modulation of extracellular matrix proteases and inhibitors in mouse skin fibroblasts

To investigate developmental differences in the wound repair process between fetal and adult skin fibroblasts, we studied the expression of plasminogen activator, plasminogen activator inhibitor, matrix metalloproteinase, and tissue inhibitor of metalloproteinase in E-15, E-17, newborn and adult mouse skin fibroblasts cultured within three dimensional matrices of either collagen or fibrin. Fibrin overlay and reverse overlay analyses revealed that mouse skin fibroblasts secreted tissue plasminogen activator and type1 plasminogen activator inhibitor. However, only E-15 and E-17 fibroblasts secreted the active form of tissue plasminogen activator, while in newborn and adult fibroblasts tissue plasminogen activator was conjugated to type1 plasminogen activator inhibitor. Only adult fibroblasts expressed a high level of active type1 plasminogen activator inhibitor. Gelatin zymography revealed that the predominant matrix metalloproteinase secreted by all the mouse fibroblasts was gelatinase A (matrix metalloproteinase -2). Matrix metalloproteinase -2 was partially activated in the adult fibroblasts cultured within a collagen matrix. The tissue inhibitor of metalloproteinase-2 was expressed by all fibroblasts, but levels were highest in the newborn and adult fibroblasts. When E-15 fibroblasts were cultured within a fibrin matrix, tissue plasminogen activator was downregulated. Transforming growth factor-betadownregulated tissue plasminogen activator while upregulating type1 plasminogen activator inhibitor, and platelet-derived growth factor enhanced tissue plasminogen activator expression in E-15 fibroblasts. Therefore, plasminogen activator and its inhibitor, and matrix metalloproteinase and its associated tissue inhibitor are differentially expressed in fetal and adult fibroblasts, and their expression is controlled by extracellular matrix components and growth factors present in wounds.

Optimisation of the biology of soft tissue repair

As identified in this review, over the past twenty years there have been a number of very exciting new developments in the quest to optimise soft tissue repair. Comparing fetal soft tissue injuries, which heal by regeneration, to the adult processes of healing by inflammation-induced scar formation has led to a number of insights into how the latter may be improved. Seeding wounds with embryonic stem cells, bridging gaps with cell-derived "engineered tissues", addition of exogenous hyaluronic acid and modification of wounds to either enhance the growth factors which have been implicated in regeneration (e.g. TGF-B3) or block those implicated in scar formation (eg. TGF-B1) have all shown promise. Our group has quantified numerous cellular, molecular, biomechanical and matrix abnormalities of scar in a rabbit model of ligament healing. Based on these studies which we review here, three matrix deficiencies have been identified which appear to have specific implications to scar weakness: organisational "flaws", abnormal hydroxypyridinoline collagen cross-link densities and abnormally small, slow-maturing collagen fibrils. In tests aimed at finding therapeutic solutions in this model, the addition of a 7ug bolus of TGF-B1 at day 21 or 2.5ng/day of TGF-B1 being pumped into a wound x 21 days increased the size of ligament scars but did not improve their material strength. It also did not alter any of the above-noted matrix deficiencies. A liposome-mediated anti-sense gene therapy approach aimed at decreasing the expression of the proteoglycan decorin in 21-day scars, however, has significantly increased the size of scar collagen fibrils as well as improved these scars mechanically. Based on these positive results from a single dose of only one targeted molecule, we believe that this gene therapy approach has great potential for further scar improvement. If combined with some of the other biological strategies reviewed above, a repair which is closer to true regenerative healing of ligaments, and all soft tissues, may eventually be achieved.

Role of metalloproteinases in liver fibrosis

Collagen deposition in the cirrhotic liver is the result of an imbalance between the amount of collagen produced and that, which is degraded. Although several groups have actively investigated the mechanisms that regulate collagen gene expression in the liver, little is known regarding those involved in the regulation of interstitial collagenases. In this study, we shall express our personal ideas regarding the role of metalloproteinases in collagen degradation in the cirrhotic liver, with special emphasis on the interstitial collagenases and some factors that may limit collagen degradation in vivo.