Molecular dissection of abnormal wound healing processes resulting in keloid disease

Organ fibrosis inhibited by blocking transforming growth factor-β signaling via peroxisome proliferator-activated receptor γ agonists

BACKGROUND

Organ fibrosis has been viewed as one of the major medical problems, which can lead to progressive dysfunction of the liver, lung, kidney, skin, heart, and eventually death of patients. Fibrosis is initiated by a variety of pathological, physiological, biochemical, and physical factors. Regardless of their different etiologies, they all share a common pathogenetic process: excessive activation of the key profibrotic cytokine, transforming growth factor-beta (TGF-beta). Peroxisome proliferator-activated receptor gamma (PPARgamma), a ligand-activated transcription factor of the nuclear receptor superfamily, has received particular attention in recent years, because the activation of PPARgamma by both natural and synthetic agonists could effectively inhibit TGF-beta-induced profibrotic effects in many organs.

DATA SOURCES

The English-language medical databases, PubMed, Elsevier and SpringerLink were searched for articles on PPARgamma, TGF-beta, and fibrosis, and related topics.

RESULTS

TGF-beta is recognized as a key profibrotic cytokine. Excessive activation of TGF-beta increases synthesis of extracellular matrix proteins and decreases their degradation, associated with a gradual destruction of normal tissue architecture and function, whereas PPARgamma agonists inhibit TGF-beta signal transduction and are effective antifibrogenic agents in many organs including the liver, lung, kidney, skin and heart.

CONCLUSIONS

The main antifibrotic activity of PPARgamma agonists is to suppress the TGF-beta signaling pathway by so-called PPARgamma-dependent effect. In addition, PPARgamma agonists, especially 15d-PGJ2, also exert potentially antifibrotic activity independent of PPARgamma activation. TGF-beta1/Smads signaling not only plays many essential roles in multiple developmental processes, but also forms cross-talk networks with other signal pathways, and their inhibition by PPARgamma agonists certainly affects the cytokine networks and causes non-suspected side-effects. Anti-TGF-beta therapies with PPARgamma agonists may have to be carefully tailored to be tissue- and target gene-specific to minimize side-effects, indicating a great challenge to the medical research at present.

Keloid disease can be inhibited by antagonizing excessive mTOR signaling with a novel dual TORC1/2 inhibitor

Keloid disease (KD) is a fibroproliferative lesion of unknown etiopathogenesis that possibly targets the PI3K/Akt/mTOR pathway. We investigated whether PI3K/Akt/mTOR inhibitor, Palomid 529 (P529), which targets both mammalian target of rapamycin complex 1 (mTORC-1) and mTORC-2 signaling, could exert anti-KD effects in a novel KD organ culture assay and in keloid fibroblasts (KF). Treatment of KF with P529 significantly (P < 0.05) inhibited cell spreading, attachment, proliferation, migration, and invasive properties at a low concentration (5 ng/mL) and induced substantial KF apoptosis when compared with normal dermal fibroblasts. P529 also inhibited hypoxia-inducible factor-1α expression and completely suppressed Akt, GSK3β, mTOR, eukaryotic initiation factor 4E-binding protein 1, and S6 phosphorylation. P529 significantly (P < 0.05) inhibited proliferating cell nuclear antigen and cyclin D and caused considerable apoptosis. Compared with rapamycin and wortmannin, P529 also significantly (P < 0.05) reduced keloid-associated phenotypic markers in KF. P529 caused tissue shrinkage, growth arrest, and apoptosis in keloid organ cultures and substantially inhibited angiogenesis. pS6, pAkt-Ser473, and mTOR phosphorylation were also suppressed in situ. P529 reduced cellularity and expression of collagen, fibronectin, and α-smooth muscle actin (substantially more than rapamycin). These pre-clinical in vitro and ex vivo observations are evidence that the mTOR pathway is a promising target for future KD therapy and that the dual PI3K/Akt/mTOR inhibitor P529 deserves systematic exploration as a candidate agent for the future treatment of KD.

Increased in vitro differentiation of fibrocytes from keloid patients is inhibited by serum amyloid P

Keloid scarring is a form of fibroproliferative dermal wound healing characterized by growth beyond the confines of the original wound. Fibrocytes, derived from peripheral blood mononuclear cells and inhibited by serum amyloid P (SAP), have been linked to other fibroproliferative diseases. We hypothesized that peripheral blood mononuclear cells of keloid formers have a higher propensity to differentiate into fibrocytes and are more resistant to the effects of SAP. To test this hypothesis, plasma was isolated from peripheral blood samples of keloid (n = 10) and age/sex/race-matched control (n = 10) subjects, and SAP levels were measured by enzyme-linked immunosorbent assay. Equal numbers of peripheral blood mononuclear cells were also isolated from these samples and fibrocytes cultured in serum-free media with increasing concentrations of SAP. No difference in plasma SAP levels was found between keloid and control subjects. In the absence of SAP, keloid patients (n = 7) had almost 20 times more fibrocytes than controls (n = 7) in culture (median: 1,087 cells vs. 60 cells; p < 0.01). SAP inhibited the differentiation of keloid fibrocytes in vitro, although a higher concentration of SAP was needed when compared with controls (20 μg/mL keloid vs. 5 μg/mL control). Fibrocytes may contribute to the pathogenesis of keloids, and SAP has potential as a therapeutic agent in the prevention of these lesions.

A RHAMM mimetic peptide blocks hyaluronan signaling and reduces inflammation and fibrogenesis in excisional skin wounds

Hyaluronan is activated by fragmentation and controls inflammation and fibroplasia during wound repair and diseases (eg, cancer). Hyaluronan-binding peptides were identified that modify fibrogenesis during skin wound repair. Peptides were selected from 7- to 15mer phage display libraries by panning with hyaluronan-Sepharose beads and assayed for their ability to block fibroblast migration in response to hyaluronan oligosaccharides (10 kDa). A 15mer peptide (P15-1), with homology to receptor for hyaluronan mediated motility (RHAMM) hyaluronan binding sequences, was the most effective inhibitor. P15-1 bound to 10-kDa hyaluronan with an affinity of K(d) = 10(-7) and appeared to specifically mimic RHAMM since it significantly reduced binding of hyaluronan oligosaccharides to recombinant RHAMM but not to recombinant CD44 or TLR2,4, and altered wound repair in wild-type but not RHAMM(-/-) mice. One topical application of P15-1 to full-thickness excisional rat wounds significantly reduced wound macrophage number, fibroblast number, and blood vessel density compared to scrambled, negative control peptides. Wound collagen 1, transforming growth factor β-1, and α-smooth muscle actin were reduced, whereas tenascin C was increased, suggesting that P15-1 promoted a form of scarless healing. Signaling/microarray analyses showed that P15-1 blocks RHAMM-regulated focal adhesion kinase pathways in fibroblasts. These results identify a new class of reagents that attenuate proinflammatory, fibrotic repair by blocking hyaluronan oligosaccharide signaling.

Microvessel networks [corrected] pre-formed in artificial clinical grade dermal substitutes in vitro using cells from haematopoietic tissues

Forming a microcirculation is critical for vascularisation of artificial skin substitutes. One strategy to improve speed of grafting is to pre-form microvascular networks in the substitute before applying to a wound. For clinical application, this requires sufficient functional endothelial cell numbers. In vitro endothelial colony forming cells (ECFCs) derived cells were expanded from cord and adult blood donations and co-cultured with human dermal fibroblasts or bone marrow mesenchymal stem/stromal cells to form microvascular networks in the presence or absence of dermal substitutes which are in clinical use. The number of endothelial cells generated ranged from 1.03×10(9) to 2.18×10(11) from 10 adult blood donations and 1×10(12) to 1.76×10(13) from 6 cord blood units after 50 days in culture. Two adult donations failed to generate ECFCs. Both cord and adult blood cells formed 2D microvascular networks in vitro, although there was a significant difference in the functional capacity of adult and cord blood ECFCs. While co-culture of the latter within dermal substitutes Matriderm or Integra demonstrated the formation of 3D microvascular networks penetrating 100μm, enhanced expansion, while maintaining functional capacity, of adult blood cells is required for fully pre-vascularising the clinical grade acellular dermal substitutes used here prior to applying these to burns.

Altered angiogenic balance in keloids: a key to therapeutic intervention

Keloids are manifestations of abnormal wound repair with unresolved clinical complications. An effective therapeutic regimen has not been established for keloids, and current strategies are plagued by problems such as recurrence and side effects. Keloids, being a human-specific dermal fibroproliferative disorder are characterized by an excessive accumulation of extracellular matrix (ECM), thickened basement membrane, unregulated expression of matrix metalloproteases, growth factors, and cytokines. The internal milieu in a keloid bears a strong resemblance to a tumor with both exhibiting striking similarities with respect to tissue environment and unregulated vasculature. Abnormal angiogenesis manifested by an imbalance between proangiogenic and antiangiogenic factors has been recognized as a "common denominator" underlying many pathological conditions. However, such an imbalance has not been investigated in keloids. In this study, the angiogenic imbalance in keloids was explored with reference to circulating and tissue level expression of vascular endothelial growth factor (VEGF) and endostatin/collagen XVIII. It was observed that VEGF levels were upregulated and endostatin levels were downregulated in keloid patients in comparison to normal controls in both sera and tissue. Hence, antiangiogenic therapeutics based on endostatin in combination with current curative strategies as in tumors would present a scope for the effective management of keloids.

miRNA expression profiles in keloid tissue and corresponding normal skin tissue

BACKGROUND

Because the molecular mechanism behind keloid pathogenesis is still largely unknown, the clinical management of keloids remains problematic. miRNA (microRNA) is a novel class of small regulatory RNA that has emerged as post-transcriptional gene repressors and participants in diverse pathophysiological processes of skin disease. In the present study we aimed to investigate expression profiles of miRNA in keloid tissue and to develop a further understanding of the molecular mechanism involved in the pathogenesis of keloids.

METHODS

miRNA expression profiles in 12 pairs of keloid tissue and corresponding normal skin tissue were analyzed through a mammalian miRNA microarray containing established whole human mature and precursor miRNA sequences. Real-Time quantitative PCR was performed to confirm the array results. The putative targets of differentially expressed miRNA were functionally annotated by bioinformatics approaches.

RESULTS

miRNA microarray analysis identified 32 differentially expressed miRNAs, and a total of 23 miRNAs exhibited higher expression, while 9 miRNAs demonstrated lower expression in keloid tissue than in normal skin tissue. Functional annotations of differentially expressed miRNA targets revealed that they were enriched in several signaling pathways important for scar wound healing.

CONCLUSION

This study showed that the expressions of many miRNAs were altered in keloid tissue, and their expression profiling may provide a useful clue for exploring the pathogenesis of keloids. miRNAs might partly contribute to the etiology of keloids by affecting several signaling pathways relevant to scar wound healing.

Mast Cells and Wound Healing

BACKGROUND

Mast cells (MC) are ubiquitous resident cells, traditionally viewed as effector cells of allergic reactions that can store and synthesize de novo many mediators upon activation by a variety of stimuli. Exciting new insights are unveiling MC involvement in the pathogenesis of connective tissue disorders including wound healing and fibrosis.

THE PROBLEM

Abnormal wound repair is associated with an increased number of MC strategically located around blood vessels. Therapeutic local manipulation of MC population and reactivity may help improve and even prevent impaired repair processes for which there is no cure.

BASIC/CLINICAL SCIENCE ADVANCES

Chymase, a MC-restricted protease, is pre-stored in MC cytoplasmic granules with other mediators. The development of a highly specific inhibitor targeting chymase established its pivotal effect on fibrosis pathogenesis in a mouse model of silica-induced fibrosis. This novel finding evokes the potential therapeutic relevance of chymase inhibition to prevent aberrant wound healing.

CLINICAL CARE RELEVANCE

MC are increased in number in a variety of fibrotic diseases, compared to normal scars. Chymase has become a rising target prompting the development of chymase-specific inhibitors to be used as prophylactic or therapeutic agents. Another emerging strategy may consist in evaluating the efficacy of mast cell stabilizing drugs such as cromolyn in abnormal wound healing-drugs which are already approved for human use in other MC-driven disorders.

CONCLUSION

Limited treatment success of dysregulated wound healing underscores the need for novel targets be considered such as MC and/or MC-derived mediators and the necessity to design new therapeutic strategies for wounds that remain difficult to treat.

The Amazing Power of Cancer Cells to Recapitulate Extraembryonic Functions: The Cuckoo's Tricks

Inflammation is implicated in tumor development, invasion, and metastasis. Hence, it has been suggested that common cellular and molecular mechanisms are activated in wound repair and in cancer development. In addition, it has been previously proposed that the inflammatory response, which is associated with the wound healing process, could recapitulate ontogeny through the reexpression of the extraembryonic, that is, amniotic and vitelline, functions in the interstitial space of the injured tissue. If so, the use of inflammation by the cancer-initiating cell can also be supported in the ability to reacquire extraembryonic functional axes for tumor development, invasion, and metastasis. Thus, the diverse components of the tumor microenvironment could represent the overlapping reexpression of amniotic and vitelline functions. These functions would favor a gastrulation-like process, that is, the creation of a reactive stroma in which fibrogenesis and angiogenesis stand out.

In vitro effect of 470 nm LED (Light Emitting Diode) in keloid fibroblasts

PURPOSE

To quantify keloid fibroblasts after irradiation with 470nm blue LED, in vitro.

METHODS

Fibroblasts from keloid and adjacent skin have been obtained from 6 patients. Cells have been cultivated and maintained in DMEM culture medium. In Petri dishes, they were irradiated with energy doses of 6J, 12J and 18J. After 24 h, counting was done by the average of the triplicates for each sample.

RESULTS

There were no significant differences in the number of irradiated keloid fibroblasts at the studied doses (p=0.261). In adjacent skin fibroblasts, differences were observed (p=0.025) concerning the doses of 18 J and 6 J (p=0.03).

CONCLUSIONS

There was a reduction in the number of adjacent skin fibroblasts irradiated with 470nm blue LED at the energy dose of 18 J compared to the ones irradiated at the energy dose of 6 J. There were no changes in keloid fibroblasts counting at any of the doses applied, 24 h after irradiation.

Topical treatment with the opioid antagonist naltrexone facilitates closure of full-thickness wounds in diabetic rats

A major problem associated with diabetes is the complication of chronic non-healing wounds that can lead to the formation of debilitating ulcers, and can progress to more serious problems including amputation. There is no fully effective prevention of these complications, constituting an unmet medical need to understand the pathophysiology and treatment of wound healing in diabetes. This study determined whether blockade of opioid receptors from opioid peptides, known to inhibit cell proliferation and be overexpressed in diabetes, by topical application of the opioid antagonist naltrexone (NTX) reverses delays in wound closure. Rats with streptozotocin-induced type 1 diabetes (T1D) received topical applications of NTX (10(-4)-10(-6) mol/L) or vehicle in a variety of carriers; DNA synthesis was evaluated 12 h later. DNA synthesis in the epithelium of T1D rats was significantly reduced from normal animals. Both systemic and topical application of NTX increased DNA synthesis (up to 2-fold higher) within 12 h of administration. In a second study, diabetic and normal rats received full-thickness cutaneous wounds and were treated three times daily with either 10(-5) mol/L NTX or vehicle in topical carriers. Wound sizes were analyzed, and BrdU (5-bromo-2'-deoxyuridine) labeling in the skin was evaluated to determine DNA synthesis. Application of NTX in a variety of carriers to rats with full-thickness wounds resulted in significantly smaller wound areas relative to T1D animals receiving vehicle, and comparable to that of normal rats. Wound contraction in T1D animals was 50% of that in normal rats, with NTX-treated wounds restoring wound contraction to that of normal cohorts. DNA synthesis was also enhanced in NTX-treated T1D animals compared with T1D vehicle controls. These data suggest that topical application of NTX is a non-toxic and efficacious facilitator for healing full thickness wounds in T1D, with wound contraction serving as a particular target of NTX action.

Identification and characterization of cartilage oligomeric matrix protein as a novel pathogenic factor in keloids

To elucidate pathogenic molecules in keloids, microarray analysis was performed using RNAs extracted from keloid-derived fibroblasts and normal skin-derived fibroblasts from the same patient with a typical keloid. Among 11 up-regulated extracellular matrix genes, cartilage oligomeric matrix protein (COMP) was most prominently increased. Up-regulation of COMP mRNA and protein was confirmed in the keloid tissue by quantitative RT-PCR and Western blot. Using immunohistochemistry, we compared 15 keloids and 6 control normal tissues using a COMP-specific antibody and found that COMP stained positively in 10 keloids (66.7%), whereas no staining was observed in normal tissues, demonstrating the ectopic expression of COMP in keloids. Comparing keloids smaller or larger than 10 cm(2), the larger keloids were significantly more intensely stained with the COMP-specific antibody. Because COMP reportedly accelerates collagen type I fibril assembly, we examined whether extracellular type I collagen deposition is altered by silencing COMP mRNA by small interfering RNA (siRNA). Immunocytochemistry showed at 96 hours after transfection with COMP siRNA that the extracellular deposition of type I collagen was decreased compared to that observed with control siRNA. Further, COMP knockdown decreased amount collagens type I to V in the medium and on the cell surfaces. Our data suggest that COMP facilitates keloid formation by accelerating collagen deposition, thus providing a new therapeutic target.

Extracellular matrix molecules implicated in hypertrophic and keloid scarring

Tissue regeneration repairs the fabric of the skin to maintain homeostasis after injury. The expression and proliferation of extracellular matrix (ECM) molecules in the dermis, mediated by a range of growth factors and cytokines, is a fundamental element of wound repair. Previous work focused on how these complex molecular mechanisms relate to the formation of raised dermal scars, including keloid and hypertrophic scars, characterized by excessive deposition of ECM molecules. However, the mechanisms in the wound repair pathway which lead to the differential expression and organization of ECM molecules observed in different types of scar tissue are not fully understood. To summarize what is known about the expression and composition of ECM molecules in abnormal scarring, an extensive search of the literature was conducted, focusing on keywords connected to skin scarring, hypertrophic scars and keloid disease. The transcription and translation of collagen I and III, fibronectin, laminin, periostin and tenascin are all increased in raised dermal scar tissue. However, hyaluronic acid, dermatopontin and decorin are decreased, and the expression and localisation of fibrillin and elastin fibres in the dermis are altered compared with normal skin and scars. Recent whole genome profiling and proteomic studies have led to the identification of regulatory elements with different expression profiles in hypertrophic and keloid tissue. If the mechanisms of raised dermal scar formation are to be elucidated and effective therapeutic treatments developed, an integrated approach to research is required, focussing on the interactions between ECM molecules, regulatory elements and pathways.

Structural changes in the skin of hairless mice following exposure to sulfur mustard correlate with inflammation and DNA damage

Sulfur mustard (SM, bis(2-chloroethyl)sulfide) is a bifunctional alkylating agent that causes dermal inflammation, edema and blistering. To investigate the pathogenesis of SM-induced injury, we used a vapor cup model which provides an occlusive environment in which SM is in constant contact with the skin. The dorsal skin of SKH-1 hairless mice was exposed to saturated SM vapor or air control. Histopathological changes, inflammatory markers and DNA damage were analyzed 1-14 days later. After 1 day, SM caused epidermal thinning, stratum corneum shedding, basal cell karyolysis, hemorrhage and macrophage and neutrophil accumulation in the dermis. Cleaved caspase-3 and phosphorylated histone 2A.X (phospho-H2A.X), markers of apoptosis and DNA damage, respectively, were increased whereas proliferating cell nuclear antigen (PCNA) was down-regulated after SM exposure. By 3 days, epithelial cell hypertrophy, edema, parakeratosis and loss of epidermal structures were noted. Enzymes generating pro-inflammatory mediators including myeloperoxidase and cyclooxygenase-2 were upregulated. After 7 days, keratin-10, a differentiation marker, was evident in the stratum corneum. This was associated with an underlying eschar, as neoepidermis began to migrate at the wound edges. Trichrome staining revealed increased collagen deposition in the dermis. PCNA expression in the epidermis was correlated with hyperplasia, hyperkeratosis, and parakeratosis. By 14 days, there was epidermal regeneration with extensive hyperplasia, and reduced expression of cleaved caspase-3, cyclooxygenase-2 and phospho-H2A.X. These findings are consistent with the pathophysiology of SM-induced skin injury in humans suggesting that the hairless mouse can be used to investigate the dermatoxicity of vesicants and the potential efficacy of countermeasures.

Lapachol suppresses cell proliferation and secretion of interleukin-6 and plasminogen activator inhibitor-1 of fibroblasts derived from hypertrophic scars

Objectives

The pathogenesis and therapy of hypertrophic scar have not yet been established. Our aim was to investigate the antiproliferative and antisecretory effects of lapachol, isolated from the stem bark of Avicennia rumphiana Hall. f., on hypertrophic scar fibroblasts.

Methods

The effects of lapachol on hypertrophic scar fibroblast proliferation were measured using the MTT assay, cell-cycle analyses and lactate dehydrogenase assays. The type I collagen α-chain (COL1A1), interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1) mRNA and/or protein levels of hypertrophic scar-fibroblasts were quantitated by real-time PCR and ELISA.

Key findings

Lapachol at 25 and 50 µm significantly inhibited the in vitro proliferation of hypertrophic scar fibroblasts, but not fibroblasts from non-lesional skin sites. In addition, lapachol had no apparent effect on cell cycle and lactate dehydrogenase activity in conditioned medium from lapachol-treated hypertrophic scar fibroblasts was nearly equal to that in medium from vehicle-treated cells. Lapachol treatment also inhibited COL1A1 and PAI-1 mRNA levels in hypertrophic scar fibroblasts, but did not affect IL-6 mRNA levels. The protein levels of IL-6 and PAI-1 in conditioned medium from hypertrophic scar fibroblasts treated with 50 µm lapachol were lower than those from vehicle-treated hypertrophic scar fibroblasts.

Conclusions

Lapachol decreased the proliferation rate of hypertrophic scar fibroblasts. As IL-6 and PAI-1 secretion was also lowered in lapachol-treated hypertrophic scar fibroblasts, our findings suggested that lapachol may have suppressed extracellular matrix hyperplasia in wound healing and possibly alleviated the formation of hypertrophic scar.