Differential collagen–glycosaminoglycan matrix remodeling by superficial and deep dermal fibroblasts: Potential therapeutic targets for hypertrophic scar

Microneedle Patch for Transdermal Sequential Delivery of KGF-2 and aFGF to Enhance Burn Wound Therapy

Severe burn wounds usually destroy key cells' functions of the skin resulting in delayed re-epithelization and wound regeneration. Promoting key cells' activities is crucial for burn wound repair. It is well known that keratinocyte growth factor-2 (KGF-2) participates in the proliferation and morphogenesis of epithelial cells while acidic fibroblast growth factor (aFGF) is a key mediator for fibroblast and endothelial cell growth and differentiation. However, thick eschar and the harsh environment of a burn wound often decrease the delivery efficiency of fibroblast growth factor (FGF) to the wound site. Therefore, herein a novel microneedle patch for sequential transdermal delivery of KGF-2 and aFGF is fabricated to enhance burn wound therapy. aFGF is first loaded in the nanoparticle (NPaFGF) and then encapsulated NPaFGF with KGF-2 in the microneedle patch (KGF-2/NPaFGF@MN). The result shows that KGF-2/NPaFGF@MN can successfully get across the eschar and sequentially release KGF-2 and aFGF. Additional data demonstrated that KGF-2/NPaFGF@MN achieved a quicker wound closure rate with reduced necrotic tissues, faster re-epithelialization, enhanced collagen deposition, and increased neo-vascularization. Further evidence suggests that improved wound healing is regulated by significantly elevated expressions of hypoxia-inducible factor-1 alpha (HIF-1ɑ) and heat shock protein 90 (Hsp90) in burn wounds. All these data proved that KGF-2/NPaFGF@MN is an effective treatment for wound healing of burns.

Polymer-Based Wound Dressings Loaded with Ginsenoside Rg3

The skin, the largest organ in the human body, mainly plays a protective role. Once damaged, it can lead to acute or chronic wounds. Wound healing involves a series of complex physiological processes that require ideal wound dressings to promote it. The current wound dressings have characteristics such as high porosity and moderate water vapor permeability, but they are limited in antibacterial properties and cannot protect wounds from microbial infections, which can delay wound healing. In addition, several dressings contain antibiotics, which may have bad impacts on patients. Natural active substances have good biocompatibility; for example, ginsenoside Rg3 has anti-inflammatory, antibacterial, antioxidant, and other biological activities, which can effectively promote wound healing. Some researchers have developed various polymer wound dressings loaded with ginsenoside Rg3 that have good biocompatibility and can effectively promote wound healing and reduce scar formation. This article will focus on the application and mechanism of ginsenoside Rg3-loaded dressings in wounds.

Human In Vitro Skin Models for Wound Healing and Wound Healing Disorders

Skin wound healing is essential to health and survival. Consequently, high amounts of research effort have been put into investigating the cellular and molecular components involved in the wound healing process. The use of animal experiments has contributed greatly to the knowledge of wound healing, skin diseases, and the exploration of treatment options. However, in addition to ethical concerns, anatomical and physiological inter-species differences often influence the translatability of animal-based studies. Human in vitro skin models, which include essential cellular and structural components for wound healing analyses, would improve the translatability of results and reduce animal experiments during the preclinical evaluation of novel therapy approaches. In this review, we summarize in vitro approaches, which are used to study wound healing as well as wound healing-pathologies such as chronic wounds, keloids, and hypertrophic scars in a human setting.

An Updated Review of Hypertrophic Scarring

Hypertrophic scarring (HTS) is an aberrant form of wound healing that is associated with excessive deposition of extracellular matrix and connective tissue at the site of injury. In this review article, we provide an overview of normal (acute) wound healing phases (hemostasis, inflammation, proliferation, and remodeling). We next discuss the dysregulated and/or impaired mechanisms in wound healing phases that are associated with HTS development. We next discuss the animal models of HTS and their limitations, and review the current and emerging treatments of HTS.

Differential effects of acetylsalicylic acid and mitomycin C on cytokine-induced Tenon's capsule myofibroblast transdifferentiation and activity: Implications for glaucoma surgery

Inflammation-driven scarring is a major contributor to surgical failure after subconjunctival bleb forming glaucoma surgery. The current gold standard anti-scarring adjuvant mitomycin C (MMC) has variable effectiveness and is associated with significant risks. Acetylsalicylic acid (ASA), when delivered locally, repurposes the typically pro-inflammatory cyclooxygenase (COX-2) signaling for the resolution of inflammation and mitigating inflammation-mediated fibrosis. The aim of this study is to compare the effects of ASA and MMC in an in vitro model of subconjunctival scarring. Glaucoma patient-derived Tenon's capsule fibroblasts (HTCFs) were treated with TGFβ1 (2 ng/mL) plus or minus ASA (1600 μg/ml), or MMC (0.05, 0.1, 0.2 mg/mL). In vitro collagen contraction, MTT, LDH, immunofluorescence, and Western blot assays were performed. To elucidate the mechanistic effects of ASA in TGFβ1-induced HTCFs, liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to identify and measure pro-inflammatory and pro-resolving lipid mediator secretion. ASA was at least as effective as MMC in reducing TGFβ1-induced HTCF-mediated collagen contraction, metabolic activity, and pro-fibrotic protein expression, with less cytotoxicity. Within cytokine-activated HTCFs, ASA significantly impaired secretion of pro-inflammatory lipid mediators prostaglandin E2 and 6-keto-prostaglandin F1α and significantly increased secretion of the pro-resolving mediators 5-hydroxyeicosatetraenoic acid (HETE), 15-HETE and 18-hydroxyeicosapentaenoic acid (HEPE). ASA reduces cytokine-induced myofibroblast transdifferentiation in HTCFs, being non-inferior to MMC in vitro. ASA's effects are associated with a unique lipid mediator expression profile, suggesting that the ASA-induced resolution of inflammation may be a promising strategy to mitigate inflammation-mediated scarring and could offer a novel alternative as a surgical adjuvant.

Cutting into wound repair

The skin is home to an assortment of fibroblastic lineages that shape the wound repair response toward scars or regeneration. In this review, we discuss the distinct embryonic origins, anatomic locations, and functions of fibroblastic lineages, and how these distinct lineages of fibroblasts dictate the skin's wound response across injury depths, anatomic locations, and embryonic development to promote either scarring or regeneration. We highlight the supportive role of the fascia in dictating scarring outcomes; we then discuss recent findings that indicate fascia mobilization by its resident fibroblasts supersede the classical de novo deposition program of wound matrix formation. These recent findings reconfigure our traditional view of wound repair and present exciting new therapeutic avenues to treat scarring and fibrosis across a range of medical settings.

Engineered Skin Substitute Regenerates the Skin with Hair Follicle Formation

Currently, engineered skin substitutes (ESS) are unable to regenerate cutaneous appendages. Recent studies have shown that skin-derived precursors (SKPs), which are extensively available, have the potential to induce hair follicle neogenesis. Here, we demonstrate that ESS consisting of culture-expanded SKPs and epidermal stem cells (Epi-SCs) reconstitute the skin with hair follicle regeneration after grafting into nude mice. SKPs seeded in a C-GAG matrix proliferated and expressed higher levels of hair induction signature genes—such as Akp2, Sox2, CD133 and Bmp6—compared to dermal fibroblasts. Moreover, when ESS prepared by seeding a mixture of culture-expanded murine SKPs and human adult Epi-SCs into a C-GAG matrix was grafted into full-thickness skin wounds in nude mice, black hairs were generated within 3 weeks. Immunofluorescence analysis showed that the SKPs were localized to the dermal papillae of the newly-formed hair follicle. Our results indicate that SKPs can serve as the hair-inductive cells in ESS to furnish it with hair genesis potential

MiR-133a-3p inhibits scar formation in scalded mice and suppresses the proliferation and migration of scar derived-fibroblasts by targeting connective tissue growth factor

Excessive scar formation post burn injury can cause great pain to the patients. MiR-133a-3p has been demonstrated to be anti-fibrotic in some fibrosis-related diseases. However, its possible role in scar formation has not been elucidated yet. In present study, the effect of miR-133a-3p on scar formation was investigated in a scalded model of mice. Moreover, the function of miR-133a-3p on proliferation and migration of scar-derived fibroblasts (SFs) was studied in vitro. It was found that miR-133a-3p was dramatically downregulated in scar tissue of scalded mice. Upregulation of miR-133a-3p by miR-133a-3p agomir obviously inhibited the scar formation in scalded mice. Histological staining showed that upregulation of miR-133a-3p attenuated the excessive deposition of collagen in scar tissue of scalded mice. In vitro study showed that upregulation of miR-133a-3p effectively suppressed the proliferation and migration of SFs. Besides, upregulation of miR-133a-3p attenuated the protein levels of α-smooth muscle actin (α-SMA) and collagen I, indicating that miR-133a-3p could suppress the activation of SFs. The expression of connective tissue growth factor (CTGF), a critical mediator in cell proliferation, migration and extracellular matrix (ECM) synthesis, was also downregulated by the upregulation of miR-133a-3p. Luciferase reporter assay validated that CTGF was directly targeted by miR-133a-3p. In addition, overexpression of CTGF abolished the effect of miR-133a-3p on inhibiting the proliferation, migration and activation of SFs, indicating that miR-133a-3p functioned by targeting CTGF. Therefore, miR-133a-3p might be a promising target for treating pathological scars.

Blood perfusion in hypertrophic scars and keloids studied by laser speckle contrast imaging

BACKGROUND

This study used laser speckle contrast imaging (LSCI) to evaluate the difference in blood perfusion between hypertrophic scars and keloids.

MATERIALS AND METHODS

A total of 30 keloids, 21 early hypertrophic scars, 20 proliferative hypertrophic scars, 20 regressive hypertrophic scars, and 20 mature hypertrophic scars were enrolled into this study. Vancouver Scar Scale (VSS) was assessed by a plastic surgeon. LSCI was used to evaluate perfusion of the whole (W), marginal (M), central (C) regions, and surrounding normal skin of the scars, and ratios (M/N, C/N) were calculated.

RESULTS

The perfusion of the marginal region in the keloid was significantly higher than that of the central region. Nevertheless, there was no significant difference in perfusion between the central and marginal regions in the early, proliferative, regressive, and mature hypertrophic scars. The degree of perfusion and perfusion ratio in the marginal region of keloid was similar to that of proliferative hypertrophic scars, and the degree of perfusion and perfusion ratio in central region of keloid group was similar to that of early and regressive hypertrophic scars.

CONCLUSIONS

The difference in perfusion distribution in keloids and hypertrophic scars may provide ideas for their identification. LSCI may be a useful method for differentiating between keloids and hypertrophic scars.

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.

Modulating cationicity of chitosan hydrogel to prevent hypertrophic scar formation during wound healing

It is of great clinical significance to design wound dressing materials with combined excellent wound healing properties and superior capability to suppress hypertrophic scar formation. This study aimed to examine if and how the cationicity of chitosan would affect the hypertrophic scar-related outcomes, through preparing carboxymethyl chitosan hydrogels with different genipin concentrations (2.5%, 5%, 10% and 15%, respectively). An optimum window of chitosan cationicity (5% in our case) demonstrated potential to mitigate hypertrophic scar in wound healing by suppressing the expression of a-smooth muscle actin (a-SMA) and promoting secretion of type I matrix metalloproteinases (MMP-1). In vivo, the CMCS-5% hydrogel again showed smaller, thinner and smoother wound appearance. Moreover, the CMCS-5% sample with additional incorporation of 2% (V/V) Aloe vera gel exhibited further improved performance in scar inhibition. Overall, such findings might have important implications in chitosan-based wound dressing design for high-quality wound repair and effective scar inhibition.

Topical application of silk fibroin-based hydrogel in preventing hypertrophic scars

Current medications for the treatment of hypertrophic scars suffer from bottlenecks of limited therapeutic efficacy and a slow recovery rate. Silk fibroin (SF) has gained attention for its ability to promote wound healing in burns and cutaneous wounds, but its therapeutic effects against hypertrophic scar have not been thoroughly investigated. We prepared SF-based hydrogels (SFHs) with various SF concentrations (1.5 %, 3 %, and 6 %) and characterized their physicochemical properties. Cell experiments showed that these SFHs had favorable biocompatibility in vitro. Further animal experiments in rabbits revealed that the SFH (3 %)-treated group achieved scars on their ears that were thinner and significantly lighter in color compared with the negative control group. Moreover, treatment with SFHs reduced the density and led to the orderly arrangement of collagen fibers. It was found that the therapeutic effects of SFHs were attributed to the reduced expression levels of α-smooth muscle actin. These results are the first to demonstrate that SFH can be exploited as an effective therapeutic agent for the treatment of hypertrophic scars.

Fibrogenic fibroblast-selective near-infrared phototherapy to control scarring

Rationale: Fibroblasts, the predominant cell type responsible for tissue fibrosis, are heterogeneous, and the targeting of unique fibrogenic population of fibroblasts is highly expected. Very recently, elevated glycolysis is demonstrated to play a pivotal role in the determination of fibrogenic phenotype of fibroblasts. However, it is lack of specific strategies for targeting and elimination of such fibrogenic populations. In this study, a novel strategy to use the a near-infrared (NIR) dye IR-780 for the targeting and elimination of a fibrogenic population of glycolytic fibroblasts to control the cutaneous scarring is developed. Methods: The identification and cell properties test of fibrogenic fibroblasts with IR-780 were conducted by using fluorescence activated cell sorting, transplantation experiments, in vivo imaging, RNA sequencing in human cell experiments and mouse and rat wound models. The uptake of IR-780 in fibroblasts mediated by HIF-1α/SLCO2A1 and the metabolic properties of IR-780H fibroblasts were investigated using RNA interference or signaling inhibitors. The fibrogenic fibroblast-selective near-infrared phototherapy of IR-780 were evaluated in human cell experiments and mouse wound models. Results: IR-780 is demonstrated to recognize a unique glycolytic fibroblast lineage, which is responsible for the bulk of connective tissue deposition during cutaneous wound healing and cancer stroma formation. Further results identified that SLCO2A1 is involved in the preferential uptake of IR-780 in fibrogenic fibroblasts, which is regulated by HIF-1α. Moreover, with intrinsic dual phototherapeutic activities, IR-780 significantly diminishes cutaneous scarring through the targeted ablation of the fibrogenic population by photothermal and photodynamic effects. Conclusion: This work provides a unique strategy for the targeted control of tissue scarring by fibrogenic fibroblast-selective near-infrared phototherapy. It is proposed that IR-780 based theranostic methodology holds promise for translational medicine aimed at regulation of fibrogenic behavior.

Utilizing Human Dermal Fibroblast Heterogeneity in Autologous Dermal Fibroblast Therapy: An Overcomplicated Strategy or a Promising Approach?

Although human dermal fibroblast heterogeneity has been acknowledged for several decades and a large body of in vitro studies has been performed with zonal dermal fibroblast, current autologous dermal fibroblast therapies do not reflect human dermal fibroblast heterogeneity. To determine if the utilization of human dermal fibroblast heterogeneity in autologous dermal fibroblast therapy is more of a translational perspective that may thus be more likely to make it to the clinic, this article critically reviews the previous studies on dermal fibroblast heterogeneity performed to date. We found that in vitro studies of human dermal fibroblast heterogeneity have run nearly parallel to the in vivo study of autologous dermal fibroblast therapy. Although several human to nude mice xenotransplantation experiments have been performed in different layers of human dermal fibroblast, their clinical significance remains to be considered. We conclude that there is still a great gap between basic experiments and the clinical employment of human dermal fibroblast heterogeneity. To overcome this, it is necessary to conduct clinical trials, which might be restricted by ethical issues. Alternatively, it might be easier to conduct in vivo studies in animal models. Based on our previous study of dermal fibroblast heterogeneity in pigs, we propose the use of pigs as a good animal model for dermal fibroblast heterogeneity. Time will show whether the utilization of human dermal fibroblast heterogeneity in autologous dermal fibroblast therapy is an overcomplicated strategy or a promising approach. Anat Rec, 302:2126-2131, 2019. © 2019 American Association for Anatomy.

Differential effects of dexamethasone and indomethacin on Tenon's capsule fibroblasts: Implications for glaucoma surgery

Dysregulated wound healing and subsequent fibrosis represents the most common cause of failure in glaucoma filtration surgery. Primary means to prevent this outcome are the anti-metabolite surgical adjuvants, however, topical corticosteroids are commonly used postoperatively to permit further control of wound healing and development of the filtration bleb. Unfortunately, they carry important side effects such as raised intraocular pressure, cataract and increased infection risk. Non-steroidal anti-inflammatory drugs (NSAIDs) show promising results in clinical trials as an alternative wound modulatory drug. NSAIDs exhibit non-inferiority to steroids in terms of post-operative intraocular pressure control and secondary IOP lowering interventions, however there is little known about the differing effects these drugs exert on human Tenon's capsule fibroblast (HTCF) mediated wound healing. The purpose of this study was to assess the individual effects of dexamethasone and indomethacin on the extracellular matrix modifying actions of HTCFs in vitro. To this end, HTCFs were cultured in 3D collagen matrices as well as in 2D monolayers and exposed to clinically relevant concentrations of dexamethasone or indomethacin for up to seven days. HTCF-mediated wound healing functions were assayed through collagen matrix contraction, extracellular matrix morphology, estimation of HCTF proliferation and differentiation into myofibroblasts within the collagen matrices, as well as western blot. Both drugs significantly reduced HTCF-mediated collagen contraction relative to control however there was a significant trend towards greater inhibition with indomethacin exposure compared to dexamethasone. Indomethacin exposure significantly reduced HTCF-mediated collagen remodelling activity compared vehicle control, whereas dexamethasone was unable to reduce remodelling activity at any of the studied exposures. Both drugs reduced myofibroblast differentiation, however indomethacin alone demonstrated an inhibitory effect on final cell number relative to control whereas dexamethasone had no significant effect at any studied exposure. These findings demonstrate that both steroidal and NSAID treatment can mitigate HTCF-mediated collagen contraction and αSMA expression. However, NSAIDs may function to better impede HTCF proliferation and remodelling activity. Taken in the context of previous glaucoma surgical trials, NSAIDs appear to be a viable alternative to steroids for post-operative wound modulation.

Improved Dermal Regeneration Using a Combination of Dermal Substitutes and Dermal Fibroblast Optimization: A Hypothesis

In human adults, the repair of cutaneous wounds usually leads to scar formation rather than regeneration. Dermal substitutes have been used as a regenerative template for reducing scar formation and improving the extent of dermal regeneration. However, achievement of complete regeneration is still a long way off. Dermal substitutes are characterized by unusual regenerative activity, appearing to function by acting as temporary configurational guides for cell infiltration and synthesis of new stroma. Fibroblasts are important cells with many vital functions in wound-healing processes. They are heterogeneous with distinct characteristics according to their source location, such as subcutaneous tissue, superficial-layer dermis, and deep-layer dermis. Many studies have shown that superficial dermal fibroblasts possess the potential to form dermis-like tissue. Fibroblasts in deep-layer dermis and subcutaneous tissue may play a critical role in the formation of hypertrophic scars. Fibroblast phenotype affects the newly formed dermal architecture and influences the dermal regeneration effect induced by dermal substitutes. It is hypothesized that better regeneration of the dermis can be achieved using dermal substitutes along with dermal fibroblast optimization.

Effects of transplanted adipose derived stem cells on the expressions of α-SMA and DCN in fibroblasts of hypertrophic scar tissues in rabbit ears

To study the effects of transplanted adipose derived stem cells (ADSCs) on the expressions of α-smooth muscle actin (α-SMA) and decorin (DCN) in fibroblasts of hypertrophic scar tissues in rabbit ears. Twelve New Zealand white rabbits were selected; the normal subcutaneous adipose tissues in inguinal region were removed, ADSCs were extracted via enzyme digestion, cultured in Dulbecco's modified Eagle's medium (DMEM) and inoculated into the culture dish (3–5×10⁴ cells/ml). After the rabbit ear hypertrophic scar model was established successfully, the fibroblasts of hypertrophic scar tissues in rabbit ears were separated and cultured using the mechanical method combined with enzyme digestion, and the ADSCs and scar fibroblasts were cultured in non-contact Transwell co-culture system for 21 days (experimental group); the corresponding scar fibroblasts were cultured in an ordinary 6-well plate without any treatment for 21 days (control group). The content of collagen I in fibroblasts was detected using the enzyme-linked immunosorbent assay (ELISA) kit, the mRNA expressions of α-SMA and DCN were detected via reverse transcription-polymerase chain reaction (RT-PCR), the protein expressions of α-SMA and DCN were detected via western blot analysis, and the expressions and distribution of α-SMA and DCN were detected via immunofluorescence assay. The results of ELISA showed that the content of collagen I in experimental group was decreased significantly (p<0.01). The results of RT-PCR and western blot analysis revealed that the mRNA and protein expression levels of α-SMA were significantly decreased (P<0.01, but those of DCN were significantly increased (p<0.01). Moreover, the results of immunofluorescence assay showed that the expression of α-SMA in experimental group was significantly decreased, while the expression of DCN was significantly increased. ADSCs can inhibit the mRNA and protein expressions of α-SMA and promote the mRNA and protein expressions of DCN in in vitro culture system, and they are expected to be used in the prevention and treatment of pathological scars.

Longitudinal Study of Scar Hyperplasia Formation Following Cleft Lip Wound Healing

The purpose of this study was to observe the hyperplasia trend of scar after the cleft lip surgery in a rabbit animal model, and determine the time-point of the highest hypertrophic degree of scar after cleft lip repair. Forty New Zealand white rabbits from the same offspring were used to establish a cleft lip wound healing model using Millard surgery procedure. The scar volumes were measured and granulation tissues were observed visually in the 2, 3, 4, and 5 weeks after operation. The scar tissues were harvested at the indicated time-points. Immunohistochemical (IHC) and Western Blot analyses were performed to detect the expression level of α-smooth muscle actin (α-SMA) in the scar tissue. The scars shrunk and the volumes reduced at 3 to 4 weeks after surgery; however, at 5 weeks postsurgery, the volumes increased. IHC and Western blot analyses indicated the expression of α-SMA was significantly enhanced 3 to 4 weeks, but reduced in the 5 weeks after surgery. Overall, the degree of scar hyperplasia after cleft lip surgery in rabbits was normally distributed and the scarring was most severe in the 3 to 4 weeks after cleft lip surgery. The study confirms a novel animal model for the assessment of therapies for the treatment of scar hyperplasia of human cleft lip in future.

Fibroblast heterogeneity: implications for human disease

Fibroblasts synthesize the extracellular matrix of connective tissue and play an essential role in maintaining the structural integrity of most tissues. Researchers have long suspected that fibroblasts exhibit functional specialization according to their organ of origin, body site, and spatial location. In recent years, a number of approaches have revealed the existence of fibroblast subtypes in mice. Here, we discuss fibroblast heterogeneity with a focus on the mammalian dermis, which has proven an accessible and tractable system for the dissection of these relationships. We begin by considering differences in fibroblast identity according to anatomical site of origin. Subsequently, we discuss new results relating to the existence of multiple fibroblast subtypes within the mouse dermis. We consider the developmental origin of fibroblasts and how this influences heterogeneity and lineage restriction. We discuss the mechanisms by which fibroblast heterogeneity arises, including intrinsic specification by transcriptional regulatory networks and epigenetic factors in combination with extrinsic effects of the spatial context within tissue. Finally, we discuss how fibroblast heterogeneity may provide insights into pathological states including wound healing, fibrotic diseases, and aging. Our evolving understanding suggests that ex vivo expansion or in vivo inhibition of specific fibroblast subtypes may have important therapeutic applications.

Recapitulation of Native Dermal Tissue in a Full-Thickness Human Skin Model Using Human Collagens

OBJECTIVE

Full-thickness skin models comprise a three-dimensional dermal equivalent based on an animal-derived collagen matrix that harbors fibroblasts and an epidermal equivalent formed by keratinocytes. The functionality of both equivalents is influenced by many factors, including extracellular matrix composition and resident cell type. Animal-derived collagens differ in amino acid composition and physicochemical properties from human collagens. This composition could alter the functionality of the dermal equivalent and epidermal morphogenesis with the barrier formation in full-thickness models (FTMs). By replacement of animal-derived collagen for human collagen, we generated and characterized the animal material-free human collagen full-thickness models (hC-FTMs) that better mimic native dermal tissue.

MATERIALS AND METHODS

An isolation procedure to obtain soluble collagen from human abdominal dermis was developed. Both FTMs and hC-FTMs were generated with primary human fibroblasts and keratinocytes. Immunohistochemical analyses with biomarkers for the dermal matrix composition, basement membrane (BM) formation, epidermal proliferation, differentiation, and activation were performed. The stratum corneum (SC) lipid composition was studied with liquid chromatography-mass spectrometry. Lipid lamellar organization was determined by small-angle X-ray diffraction.

RESULTS

The FTMs and hC-FTMs exhibit many similarities, including the dermal matrix structure, BM formation, epidermal basal layer proliferation, and execution of differentiation programs. The SC contains a similar number of corneocyte layers and the same level of lipids. The ceramide chain length distribution and ceramide subclass profile showed only minor differences. Subsequently, this led to an unaltered lamellar organization.

CONCLUSION

The animal material-free hC-FTM is generated successfully using collagens isolated from human abdominal dermis. Utilization of human collagens revealed that (epi-)dermal morphogenesis and lipid barrier formation resembled that of original FTMs. The hC-FTMs contain a dermal equivalent that mimics the native stromal tissue to a higher extent. Therefore these in vitro skin models can be used as promising tool for research purposes that contribute to animal-free experimentation.

Theoretical and practical aspects of using fetal fibroblasts for skin regeneration

Cutaneous wounding in late-gestational fetal or postnatal humans results in scar formation without any skin appendages. Early or mid- gestational skin healing in humans is characterized by the absence of scaring in a process resembling regeneration. Tremendous cellular and molecular mechanisms contribute to this distinction, and fibroblasts play critical roles in scar or scarless wound healing. This review discussed the different repair mechanisms involved in wound healing of fibroblasts at different developmental stages and further confirmed that fetal fibroblast transplantation resulted in reduced scar healing in vivo. We also discussed the possible problem in fetal fibroblast transplantation for wound repair. We proposed the use of small molecules to improve the regenerative potential of repairing cells in the wound given that remodeling of the wound microenvironment into a regenerative microenvironment in adults might improve skin regeneration.

Fibroblast heterogeneity and its implications for engineering organotypic skin models in vitro

Advances in cell culture methods, multidisciplinary research, clinical need to replace lost skin tissues and regulatory need to replace animal models with alternative test methods has led to development of three dimensional models of human skin. In general, these in vitro models of skin consist of keratinocytes cultured over fibroblast-populated dermal matrices. Accumulating evidences indicate that mesenchyme-derived signals are essential for epidermal morphogenesis, homeostasis and differentiation. Various studies show that fibroblasts isolated from different tissues in the body are dynamic in nature and are morphologically and functionally heterogeneous subpopulations. Further, these differences seem to be dictated by the local biological and physical microenvironment the fibroblasts reside resulting in "positional identity or memory". Furthermore, the heterogeneity among the fibroblasts play a critical role in scarless wound healing and complete restoration of native tissue architecture in fetus and oral mucosa; and excessive scar formation in diseased states like keloids and hypertrophic scars. In this review, we summarize current concepts about the heterogeneity among fibroblasts and their role in various wound healing environments. Further, we contemplate how the insights on fibroblast heterogeneity could be applied for the development of next generation organotypic skin models.

Advances in Skin Substitutes-Potential of Tissue Engineered Skin for Facilitating Anti-Fibrotic Healing

Skin protects the body from exogenous substances and functions as a barrier to fluid loss and trauma. The skin comprises of epidermal, dermal and hypodermal layers, which mainly contain keratinocytes, fibroblasts and adipocytes, respectively, typically embedded on extracellular matrix made up of glycosaminoglycans and fibrous proteins. When the integrity of skin is compromised due to injury as in burns the coverage of skin has to be restored to facilitate repair and regeneration. Skin substitutes are preferred for wound coverage when the loss of skin is extensive especially in the case of second or third degree burns. Different kinds of skin substitutes with different features are commercially available; they can be classified into acellular skin substitutes, those with cultured epidermal cells and no dermal components, those with only dermal components, and tissue engineered substitutes that contain both epidermal and dermal components. Typically, adult wounds heal by fibrosis. Most organs are affected by fibrosis, with chronic fibrotic diseases estimated to be a leading cause of morbidity and mortality. In the skin, fibroproliferative disorders such as hypertrophic scars and keloid formation cause cosmetic and functional problems. Dermal fibroblasts are understood to be heterogeneous; this may have implications on post-burn wound healing since studies have shown that superficial and deep dermal fibroblasts are anti-fibrotic and pro-fibrotic, respectively. Selective use of superficial dermal fibroblasts rather than the conventional heterogeneous dermal fibroblasts may prove beneficial for post-burn wound healing.

Medical cell technologies for treatment of patients suffering from recessive dystrophic epidermolysis bullosa. Method of intracutaneous administration of fibroblasts

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe inherited disease developing due to genetic abnormalities in the synthesis of Type VII collagen by fibroblasts. A low production rate of Type VII collagen and abnormalities related to the formation of anchoring fibrils weaken the epidermis and derma adhesion strength, which results in the formation of blisters or erosions in case of any mechanical injury. Fibroblasts and keratinocytes belong to the key sources of Type VII collagen in the skin. Application of allogeneic fibroblasts is a promising cell technique for treating RDEB patients. The therapeutic effect of fibroblasts intradermal administration is stipulated by high stability of newly synthesized Type VII collagen and its ability to form anchoring fibrils in the area of the dermoepidermal junction. According to experimental and clinical studies, it is possible to boost the content of Type VII collagen in the dermoepidermal junction area and heal long-term skin defects in RDEB patients by means of intradermal administration of allogeneic fibroblasts.

Where we stand with human hypertrophic and keloid scar models

We have yet to create a human scar model that demonstrates the complex nature of hypertrophic scar and keloid formation as well as ways to prevent them despite emerging advances in our understanding of the immune system, the inflammatory response, and proteomic and genomic changes after injury. Despite more complex in vitro models, we fail to explain the fundamental principles to scar formation, and the timeline of their development. The solution to developing the ideal in vitro scar model is one that mimics the heterogeneous cellular and molecular interactions, as well as the evolving structure and function of human skin.

Primary chicken embryo fibroblasts seeded acellular dermal matrix (3-D ADM) improve regeneration of full thickness skin wounds in rats

Rat skins were deepithelialized and decellularized by hypertonic saline and sodium deoxycholate (SDC), respectively. Primary chicken embryo fibroblasts (P-CEF) were cultured and seeded on prepared acellular dermal matrix (ADM). A full thickness skin defect (20×20 mm(2)) was created in thirty-six rats and randomly divided into three equal groups. Defect was left open, repaired with ADM and ADM seeded with P-CEF (3-D ADM) in groups 1, 2 and 3, respectively. By day 28, the treated wounds healed completely without scar. By day 7 hydroxyproline contents was higher in group 3 as compared to groups 1 and 2. There was slightly more B cell response in animals implanted with ADM and 3-D ADM. At day 21, stimulation index was lower with acellular dermis antigen as compared to 3-D ADM antigen. In group 1 on day 3, the granulation tissue showed more inflammatory reaction, fibroplasia and neovascularization as compared to group 2 and 3. By day 28, there was complete epithelization was observed in all groups over. However, a large scar was observed in group 1. The graft was completely absorbed and replaced with densely thick and best arranged collagen fibers. On day 7, malonyldialdehyde and superoxide dismutase levels were significantly (P<0.05) increased in group 1. Reduced glutathione values increased and reached to near normal in groups 2 and 3. Catalase values were significantly (P<0.05) higher in group 1 at different time intervals. SEM samples of group 2 showed ingrowth of fibroblasts into acellular matrix at host graft junction. However, in group 3 fibroblasts were infiltrated within the pores of graft. It was concluded that P-CEF cells seeded ADM facilitated early and better healing.

MiR-138/peroxisome proliferator-activated receptor β signaling regulates human hypertrophic scar fibroblast proliferation and movement in vitro

Excessive scars affect a patient's quality of life, both physically and psychologically, by causing pruritus, pain and contractures. Because there is a poor understanding of the complex mechanisms underlying the processes of hypertrophic scar formation, most therapeutic approaches remain clinically unsatisfactory. In this study, we found that miR-138 was downregulated and peroxisome proliferator-activated receptor (PPARβ) was inversely upregulated in hypertrophic scar tissues compared to in paired normal skin tissues. Using a dual-luciferase assay, we validated that miR138 directly targets PPARβ and regulates its expression at the transcriptional and translational levels. In gain-and-loss experiments, we found that miR-138/PPARβ signaling regulated human hypertrophic scar fibroblast proliferation and movement, and affected scarring-related protein expression, which suggests that miR-138/PPARβ signaling is important for hypertrophic scarring. Thus, our study provides evidence to help determine whether miR-138/PPARβ signaling may be a potential target for hypertrophic scarring management.

Angiotensin II stimulates canonical TGF-β signaling pathway through angiotensin type 1 receptor to induce granulation tissue contraction

Hypertrophic scar contraction (HSc) is caused by granulation tissue contraction propagated by myofibroblast and fibroblast migration and contractility. Identifying the stimulants that promote migration and contractility is key to mitigating HSc. Angiotensin II (AngII) promotes migration and contractility of heart, liver, and lung fibroblasts; thus, we investigated the mechanisms of AngII in HSc. Human scar and unwounded dermis were immunostained for AngII receptors angiotensin type 1 receptor (AT1 receptor) and angiotensin type 2 receptor (AT2 receptor) and analyzed for AT1 receptor expression using Western blot. In vitro assays of fibroblast contraction and migration under AngII stimulation were conducted with AT1 receptor, AT2 receptor, p38, Jun N-terminal kinase (JNK), MEK, and activin receptor-like kinase 5 (ALK5) antagonism. Excisional wounds were created on AT1 receptor KO and wild-type (WT) mice treated with AngII ± losartan and ALK5 and JNK inhibitors SB-431542 and SP-600125, respectively. Granulation tissue contraction was quantified, and wounds were analyzed by immunohistochemistry. AT1 receptor expression was increased in scar, but not unwounded tissue. AngII induced fibroblast contraction and migration through AT1 receptor. Cell migration was inhibited by ALK5 and JNK, but not p38 or MEK blockade. In vivo experiments determined that absence of AT1 receptor and chemical AT1 receptor antagonism diminished granulation tissue contraction while AngII stimulated wound contraction. AngII granulation tissue contraction was diminished by ALK5 inhibition, but not JNK. AngII promotes granulation tissue contraction through AT1 receptor and downstream canonical transforming growth factor (TGF)-β signaling pathway, ALK5. Further understanding the pathogenesis of HSc as an integrated signaling mechanism could improve our approach to establishing effective therapeutic interventions.

KEY MESSAGE

AT1 receptor expression is increased in scar tissue compared to unwounded tissue. AngII stimulates expression of proteins that confer cell migration and contraction. AngII stimulates fibroblast migration and contraction through AT1 receptor, ALK5, and JNK. AngII-stimulated in vivo granulation tissue contraction is AT1 receptor and ALK5 dependent.

The effect of keratinocytes on the biomechanical characteristics and pore microstructure of tissue engineered skin using deep dermal fibroblasts

Fibrosis affects most organs, it results in replacement of normal parenchymal tissue with collagen-rich extracellular matrix, which compromises tissue architecture and ultimately causes loss of function of the affected organ. Biochemical pathways that contribute to fibrosis have been extensively studied, but the role of biomechanical signaling in fibrosis is not clearly understood. In this study, we assessed the effect keratinocytes have on the biomechanical characteristics and pore microstructure of tissue engineered skin made with superficial or deep dermal fibroblasts in order to determine any biomaterial-mediated anti-fibrotic influences on tissue engineered skin. Tissue engineered skin with deep dermal fibroblasts and keratinocytes were found to be less stiff and contracted and had reduced number of myofibroblasts and lower expression of matrix crosslinking factors compared to matrices with deep fibroblasts alone. However, there were no such differences between tissue engineered skin with superficial fibroblasts and keratinocytes and matrices with superficial fibroblasts alone. Also, tissue engineered skin with deep fibroblasts and keratinocytes had smaller pores compared to those with superficial fibroblasts and keratinocytes; pore size of tissue engineered skin with deep fibroblasts and keratinocytes were not different from those matrices with deep fibroblasts alone. A better understanding of biomechanical characteristics and pore microstructure of tissue engineered skin may prove beneficial in promoting normal wound healing over pathologic healing.

Alteration of skin properties with autologous dermal fibroblasts

Dermal fibroblasts are mesenchymal cells found between the skin epidermis and subcutaneous tissue. They are primarily responsible for synthesizing collagen and glycosaminoglycans; components of extracellular matrix supporting the structural integrity of the skin. Dermal fibroblasts play a pivotal role in cutaneous wound healing and skin repair. Preclinical studies suggest wider applications of dermal fibroblasts ranging from skin based indications to non-skin tissue regeneration in tendon repair. One clinical application for autologous dermal fibroblasts has been approved by the Food and Drug Administration (FDA) while others are in preclinical development or various stages of regulatory approval. In this context, we outline the role of fibroblasts in wound healing and discuss recent advances and the current development pipeline for cellular therapies using autologous dermal fibroblasts. The microanatomic and phenotypic differences of fibroblasts occupying particular locations within the skin are reviewed, emphasizing the therapeutic relevance of attributes exhibited by subpopulations of fibroblasts. Special focus is provided to fibroblast characteristics that define regional differences in skin, including the thick and hairless skin of the palms and soles as compared to hair-bearing skin. This regional specificity and functional identity of fibroblasts provides another platform for developing regional skin applications such as the induction of hair follicles in bald scalp or alteration of the phenotype of stump skin in amputees to better support their prosthetic devices.

New molecular medicine-based scar management strategies

Keloids and hypertrophic scars are prevalent disabling conditions with still suboptimal treatments. Basic science and molecular-based medicine research have contributed to unravel new bench-to-bedside scar therapies and to dissect the complex signalling pathways involved. Peptides such as the transforming growth factor beta (TGF-β) superfamily, with Smads, Ski, SnoN, Fussels, endoglin, DS-Sily, Cav-1p, AZX100, thymosin-β4 and other related molecules may emerge as targets to prevent and treat keloids and hypertrophic scars. The aim of this review is to describe the basic complexity of these new molecular scar management strategies and point out new fibrosis research lines.

Fibrotic remodeling of tissue-engineered skin with deep dermal fibroblasts is reduced by keratinocytes

Two-thirds of burn patients with deep dermal injuries are affected by hypertrophic scars, and currently, there are no clinically effective therapies. Tissue-engineered skin is a very promising model for the elucidation of the role of matrix microenvironment and biomechanical characteristics and could help in the identification of new therapeutic targets for hypertrophic scars. Conventionally, tissue-engineered skin is made of heterogeneous dermal fibroblasts and keratinocytes; however, recent work has shown that superficial and deep dermal fibroblasts are antifibrotic and profibrotic, respectively. Furthermore, keratinocytes are believed to regulate the development and remodeling of fibrosis in skin. This study aimed to assess the influence of keratinocytes and layered fibroblasts on the characteristics of tissue-engineered skin. Layered fibroblasts and keratinocytes isolated from superficial and deep dermis and epidermis, respectively, of the lower abdominal tissue were independently co-cultured on collagen-glycosaminoglycan scaffolds, and the resulting tissue-engineered skin was assessed for differences in tissue remodeling based on the underlying specific dermal fibroblast subpopulation. Collagen production by deep fibroblasts but not by superficial fibroblasts was significantly reduced upon co-culture with keratinocytes. Also, keratinocytes in the tissue-engineered skin resulted in significantly reduced expression of profibrotic connective tissue growth factor and fibronectin, and increased expression of the antifibrotic matrix metalloproteinase-1 by deep fibroblasts but not by superficial fibroblasts. Tissue-engineered skin made of deep fibroblasts and keratinocytes had lower levels of small proteoglycans, decorin, and fibromodulin, and higher levels of large proteoglycan, versican, compared to tissue-engineered skin made of superficial fibroblasts and keratinocytes. Tissue-engineered skin made of deep fibroblasts and keratinocytes had lower expression of transforming growth factor (TGF)-α, interleukin (IL)-1, and keratinocyte growth factor but higher expression of platelet-derived growth factor and IL-6, compared to tissue-engineered skin made of superficial fibroblasts and keratinocytes. Furthermore, co-culture with keratinocytes reduced TGF-β1 production of deep but not superficial fibroblasts. Additionally, keratinocytes reduced the differentiation of deep fibroblasts to myofibroblasts in tissue-engineered skin constructs, but not that of superficial fibroblasts. Taken together, keratinocytes reduce fibrotic remodeling of the scaffolds by deep dermal fibroblasts. Our results therefore demonstrate that tissue-engineered skin made specifically with a homogeneous population of superficial fibroblasts and keratinocytes is less fibrotic than that with a heterogeneous population of fibroblasts and keratinocytes.

Superficial dermal fibroblasts enhance basement membrane and epidermal barrier formation in tissue-engineered skin: implications for treatment of skin basement membrane disorders

Basement membrane is a highly specialized structure that binds the dermis and the epidermis of the skin, and is mainly composed of laminins, nidogen, collagen types IV and VII, and the proteoglycans, collagen type XVIII and perlecan, all of which play critical roles in the function and resilience of skin. Both dermal fibroblasts and epidermal keratinocytes contribute to the development of the basement membrane, and in turn the basement membrane and underlying dermis influence the development and function of the epidermal barrier. Disruption of the basement membrane results in skin fragility, extensive painful blistering, and severe recurring wounds as seen in skin basement membrane disorders such as epidermolysis bullosa, a family of life-threatening congenital skin disorders. Currently, there are no successful strategies for treatment of these disorders; we propose the use of tissue-engineered skin as a promising approach for effective wound coverage and to enhance healing. Fibroblasts and keratinocytes isolated from superficial and deep dermis and epidermis, respectively, of tissue from abdominoplasty patients were independently cocultured on collagen-glycosaminoglycan matrices, and the resulting tissue-engineered skin was assessed for functional differences based on the underlying specific dermal fibroblast subpopulation. Tissue-engineered skin with superficial fibroblasts and keratinocytes formed a continuous epidermis with increased epidermal barrier function and expressed higher levels of epidermal proteins, keratin-5, and E-cadherin, compared to that with deep fibroblasts and keratinocytes, which had an intermittent epidermis. Further, tissue-engineered skin with superficial fibroblasts and keratinocytes formed better basement membrane, and produced more laminin-5, nidogen, collagen type VII, compared to that with deep fibroblasts and keratinocytes. Overall, our results demonstrate that tissue-engineered skin with superficial fibroblasts and keratinocytes forms significantly better basement membrane with higher expression of dermo-epidermal adhesive and anchoring proteins, and superior epidermis with enhanced barrier function compared to that with deep fibroblasts and keratinocytes, or with superficial fibroblasts, deep fibroblasts, and keratinocytes. The specific use of superficial fibroblasts in tissue-engineered skin may thus be more beneficial to promote adhesion of newly formed skin and wound healing, and is therefore promising for the treatment of patients with basement membrane disorders and other skin blistering diseases.

The effect of p38MAPK on cyclic stretch in human facial hypertrophic scar fibroblast differentiation

Hypertrophic scars (HTS), the excessive deposition of scar tissue by fibroblasts, is one of the most common skin disorders. Fibroblasts derived from surgical scar tissue produce high levels of α-smooth muscle actin (α-SMA) and transforming growth factor-β1 (TGF-β1). However, the molecular mechanisms for this phenomenon is poorly understood. Thus, the purpose of this study was to evaluate the molecular mechanisms of HTS and their potential therapeutic implications. Fibroblasts derived from skin HTS were cultured and characterized in vitro. The fibroblasts were synchronized and randomly assigned to two groups: cyclic stretch and cyclic stretch pre-treated with SB203580 (a p38MAPK inhibitor). Cyclic stretch at 10% strain was applied at a loading frequency of 10 cycles per minute (i.e. 5 seconds of tension and 5 seconds of relaxation) for 0 h, 6 h and 12 h. Cyclic stretch on HTS fibroblasts led to an increase in the expression of α-SMA and TGF-β1 mRNA and protein and the phosphorylation of p38MAPK. SB203580 reversed these effects and caused a decrease in matrix contraction. Furthermore, HTS fibroblast growth was partially blocked by p38MAPK inhibition. Therefore, the mechanism of cyclic stretch involves p38 MAPK, and its inhibition is suggested as a novel therapeutic strategy for HTS.

Electrospun poly(L-lactide) fiber with ginsenoside rg3 for inhibiting scar hyperplasia of skin

Hypertrophic scarring (HS) has been considered as a great concern for patients and a challenging problem for clinicians as it can be cosmetically disfiguring and functionally debilitating. In this study, Ginsenoside Rg3/Poly(l-lactide) (G-Rg3/PLLA) electrospun fibrous scaffolds covering on the full-thickness skin excisions location was designed to suppress the hypertrophic scar formation in vivo. SEM and XRD results indicated that the crystal G-Rg3 carried in PLLA electrospun fibers was in amorphous state, which facilitates the solubility of G-Rg3 in the PLLA electrospun fibrous scaffolds, and solubility of G-Rg3 in PBS is increased from 3.2 µg/ml for pure G-Rg3 powders to 19.4 µg/ml for incorporated in PLLA-10% fibers. The released G-Rg3 content in the physiological medium could be further altered from 324 to 3445 µg in a 40-day release period by adjusting the G-Rg3 incorporation amount in PLLA electrospun fibers. In vitro results demonstrated that electrospun G-Rg3/PLLA fibrous scaffold could significantly inhibit fibroblast cell growth and proliferation. In vivo results confirmed that the G-Rg3/PLLA electrospun fibrous scaffold showed significant improvements in terms of dermis layer thickness, fibroblast proliferation, collagen fibers and microvessels, revealing that the incorporation of the G-Rg3 in the fibers prevented the HS formation. The above results demonstrate the potential use of G-Rg3/PLLA electrospun fibrous scaffolds to rapidly minimize fibroblast growth and restore the structural and functional properties of wounded skin for patients with deep trauma, severe burn injury, and surgical incision.

Short-term in vivo biological and mechanical remodeling of porcine acellular dermal matrices

The purpose of this study was to assess the biological revitalization and mechanical integrity of Strattice^™ Reconstructive Tissue Matrix, a porcine-derived acellular dermal matrix, in vivo over time. We expanded the traditional subcutaneous model to incorporate biologic matrix scaffolds large enough to allow evaluation of mechanical properties in addition to the assessment of histological changes. Hematoxylin and eosin histology staining was used to evaluate cellular and tissue changes, and a mechanical testing frame was used to measure the ultimate tensile stress and Young’s modulus of the implanted material over time. Cell infiltration and blood vessel formation into the porcine-derived acellular dermal matrix were evident at 2 weeks and increased with implantation time. Mechanical remodeling resulted in an initial decrease in ultimate tensile stress, not associated with cell infiltration, followed by a significant increase in material strength, concurrent with histological evidence of new collagen synthesis. Young’s modulus followed a similar trend.

Deep dermal fibroblast profibrotic characteristics are enhanced by bone marrow-derived mesenchymal stem cells

Hypertrophic scars are a significant fibroproliferative disorder complicating deep injuries to the skin. We hypothesize that activated deep dermal fibroblasts are subject to regulation by bone marrow-derived mesenchymal stem cells (BM-MSCs), which leads to the development of excessive fibrosis following deep dermal injury. We found that the expression of fibrotic factors was higher in deep burn wounds compared with superficial burn wounds collected from burn patients with varying depth of skin injury. We characterized deep and superficial dermal fibroblasts, which were cultured from the deep and superficial dermal layers of normal uninjured skin obtained from abdominoplasty patients, and examined the paracrine effects of BM-MSCs on the fibrotic activities of the cells. In vitro, deep dermal fibroblasts were found higher in the messenger RNA (mRNA) levels of type 1 collagen, alpha smooth muscle actin, transforming growth factor beta, stromal cell-derived factor 1, and tissue inhibitor of metalloproteinase 1, an inhibitor of collagenase (matrix metalloproteinase 1). As well, deep dermal fibroblasts had low matrix metalloproteinase 1 mRNA, produced more collagen, and contracted collagen lattices significantly greater than superficial fibroblasts. By co-culturing layered fibroblasts with BM-MSCs in a transwell insert system, BM-MSCs enhanced the fibrotic behavior of deep dermal fibroblasts, which suggests a possible involvement of BM-MSCs in the pathogenesis of hypertrophic scarring.