Wound healing: an overview of acute, fibrotic and delayed healing

In vitro binding of matrix metalloproteinase-2 (MMP-2), MMP-9, and bacterial collagenase on collagenous wound dressings

Chronic wounds are characterized by failure in wound-healing response and a delay in healing or nonclosure of the wounds. This results in a high effort in clinical treatment and/or home care. A major difference between acute wounds and chronic wounds is the imbalance of proteinase inhibitors and proteinase activity that regulates the degradation and regeneration of the extracellular matrix proteins. Collagen and collagen/oxidized regenerated cellulose dressings act as a competitive substrate for matrix metalloproteinase-2, matrix metalloproteinase-9, and bacterial collagenase and influence this imbalance positively. Both wound dressings, approved for chronic wound treatment, the bovine collagen type I sponge and the oxidized regenerated cellulose collagen sponge, did not differ significantly in their sorption profiles for all enzymes. In general, binding was enhanced with a longer incubation time. The density of the device and the accessible surface, which can be controlled by the manufacturing process, are the crucial factors for the efficiency of the wound dressing.

Activation of human platelet-rich plasmas: effect on growth factors release, cell division and in vivo bone formation

OBJECTIVES

Aims of this controlled study were to determine the effects of activated human platelet-rich plasmas (PRPs) on early and mature bone formation in vivo, and to characterize the effect of PRP activation on growth factors release and endothelial cell division in vitro.

MATERIAL AND METHODS

PRPs were prepared from four volunteers with the platelet concentrate collector system (PCCS) system and activated with three concentrations of calcium and thrombin. Platelet-derived growth factor (PDGF)-BB, vascular endothelial growth factor (VEGF), transforming growth factor beta (TGF-beta) and interleukin-1beta (IL-1beta) levels released in supernatants were measured by ELISA, at time 0, 1h, 24h and 6 days following PRP activation. Mitogenic potential of PRP supernatants were tested on endothelial cells in vitro, and the effects of activated human PRPs on bone formation in vivo were measured in athymic rats by micro-CT analyses.

RESULTS

Activation of PRPs with calcium and thrombin triggered an immediate release of VEGF, PDGF-BB and TGF-beta and a delayed release of IL-1beta in PRP supernatants. Higher endothelial cell division was observed with supernatants from activated PRPs than from non-activated PRPs. Positive correlations were observed between VEGF levels and endothelial cell division and bone formation. A negative correlation was also found between PDGF-BB concentration and bone formation. However, early and mature bone formations with activated PRPs did not significantly differ from the ones obtained in the control group.

CONCLUSIONS

Activation of PRPs with calcium and thrombin regulates growth factors release and endothelial cell division in vitro. However, activated PRPs does not improve the early or mature bone formations in vivo in this athymic rat model.

Impaired cutaneous wound healing in granulocyte/macrophage colony-stimulating factor knockout mice

BACKGROUND

Wound healing involves various cells and cytokines, resulting in the regular progression of remodelling events. Granulocyte/macrophage colony-stimulating factor (GM-CSF) is a multifunctional pleiotropic cytokine and is known to facilitate wound healing, although the precise molecular and cellular mechanisms remain to be explored.

OBJECTIVES

To use GM-CSF gene knockout (GM-CSF KO) mice to investigate the role of GM-CSF in cutaneous wound healing following full-thickness skin injury.

METHODS

Full-thickness skin wounds were made in GM-CSF KO and wild-type mice. The wound closure, leucocyte infiltration, vascularization and extent of cytokine production were determined.

RESULTS

Wound healing was significantly delayed in GM-CSF KO mice, accompanied by reduced cytokine production (interleukin-6, monocyte chemoattractant protein-1 and macrophage inflammatory protein-2), and platelet-endothelial cell adhesion molecule-1 expression. Consequently there was reduced recruitment of neutrophils and macrophages and reduced vascularization in the wounds of GM-CSF KO mice. Although collagen deposition was delayed, it was significantly increased in the wounds of the GM-CSF KO mice in the later stages of wound healing.

CONCLUSIONS

We conclude that GM-CSF plays an important role in the complex network of effector molecules that regulate keratinocyte proliferation and the inflammatory response. These data have important implications for further development of the therapeutic manipulation of wound healing using GM-CSF.

Fibrocytes from burn patients regulate the activities of fibroblasts

Wound healing requires an elaborate interplay between numerous cell types that orchestrate a series of regulated and overlapping events. Fibrocytes are a unique leukocyte subpopulation implicated in this process. One role proposed for these cells in wound healing is to synthesize extracellular matrix. Interestingly, using mass spectrometry to quantify hydroxyproline, we discovered that the capacity of fibrocytes from normal subjects or from burn patients to produce collagen is much less than that of dermal fibroblasts. Therefore, we investigated whether fibrocytes could play an indirect, regulatory, role in the healing of burn wounds by affecting the functions of dermal fibroblasts. Dermal fibroblasts treated with medium conditioned by burn patient fibrocytes, but not by those derived from normal subjects, showed an increase in cell proliferation and migration. Using confocal microscopy, flow cytometry, and immunoblotting, we found the level of alpha-smooth muscle actin (alpha-SMA) expression to be increased in these treated dermal fibroblasts, which also showed an enhanced ability to contract collagen lattices. To determine whether these effects could be attributed to transforming growth factor beta (TGF-beta1) or to connective tissue growth factor (CTGF), we measured total TGF-beta1 levels in the conditioned medium by an enzyme-linked immunosorbtion assay and assessed levels of CTGF mRNA and protein in fibroblasts and fibrocytes by reverse transcription-polymerase chain reaction and Western blotting. The results showed significantly higher levels of TGF-beta1 and CTGF produced by burn patient fibrocytes. In addition, the application of a TGF-beta1 neutralizing antibody significantly reduced the effect of burn patient fibrocyte medium on dermal fibroblast proliferation, migration, and collagen lattice contraction. Our results suggest that in healing burn wounds, fibrocytes could regulate the activities of local fibroblasts.

Differential Effect of Burn Injury on Fibroblasts from Wounds and Normal Skin

BACKGROUND

Although there are well-recognized fluctuations in the systemic concentration of cytokines and growth factors after burn injuries, the effect on wound-healing potential in patients is not well understood. The objective of this study was to characterize the proliferation rate and response of wound and dermal fibroblasts to cytokines in burn patients compared with normal subjects.

METHODS

Polyvinyl alcohol sponges were implanted subcutaneously in normal subjects and burn patients soon after admission. Sponges were removed for wound fibroblast explantation after 12 days. At the same time, a small piece of skin was excised for dermal fibroblast explantation. Fibroblast proliferation was then quantified after exposure to 10% fetal bovine serum, 1% fetal bovine serum, interleukin-1, transforming growth factor-beta1, or interferon-alpha2b.

RESULTS

Normal subjects' dermal fibroblasts (n = 7) exposed to 10% fetal bovine serum showed significantly increased proliferation relative to normal subjects' wound fibroblasts (n = 3) (p < 0.0005), burn patients' dermal fibroblasts (n = 5) (p < 0.05), and burn patients' wound fibroblasts (n = 5) (p < 0.0001). Burn patients' dermal fibroblast proliferation was also significantly augmented relative to burn patients' wound fibroblasts (p < 0.005); however, there was no significant difference between the two wound fibroblast types. Proliferation of burn subjects' fibroblasts was significantly enhanced with the addition of interleukin-1 and significantly decreased for dermal fibroblasts with interferon-alpha2b. A significant elevation of proliferation with transforming growth factor-beta1 was seen only with burn patients' dermal fibroblasts.

CONCLUSIONS

The data suggest that systemic mediators markedly alter the proliferation potential of dermal fibroblasts but not of wound fibroblasts. However, the wound environment substantially alters both the proliferation rate and the responsiveness of fibroblasts to cytokines. Thus, the data support the value of using wound fibroblasts during preliminary in vitro experiments to investigate wound-healing modification by cytokine manipulation.

Soft tissue wounds and principles of healing

Wound healing is a complex interchange, orchestrated between cellular components that play their respective parts signaled by and mediated by different cellular instruments of healing. When healing is performed well, the final product is a thing of beauty. When healing is delayed, interrupted, or excessive, then unsightly scars of chronic painful wounds that are frustrating to the patient and physician occur.

Nucleic acids potentiate Factor VII-activating protease (FSAP)-mediated cleavage of platelet-derived growth factor-BB and inhibition of vascular smooth muscle cell proliferation

FSAP (Factor VII-activating protease) can cleave and inactivate PDGF-BB (platelet-derived growth factor-BB) and thereby inhibits VSMC (vascular smooth-muscle cell) proliferation. The auto-activation of FSAP is facilitated by negatively charged polyanions such as heparin, dextransulfate or extracellular ribonucleic acids. Since auto-activation is essential for the anti-proliferative function of FSAP, the influence of nucleic acids as cofactors for the FSAP-mediated inhibition of PDGF-BB was investigated. Natural or artificial RNA was an effective cofactor for FSAP mediated PDGF-BB degradation, whereas the effect of DNA was weak. RNA-induced cleavage of PDGF-BB was inhibited by serine protease inhibitors. The pattern of PDGF-BB cleavage was identical with either heparin or RNA as a cofactor. One of the cleavage sites in PDGF-BB was at the positions 160-162 (R160KK162), which is an important region for receptor binding and activation. In VSMCs, PDGF-BB-stimulated DNA synthesis was inhibited by FSAP in the presence of RNA. RNA was more effective than DNA and the cofactor activity of RNA was neutralized after pretreatment with RNase. FSAP binding to RNA protected the nucleic acid from degradation by RNase. These data are relevant to situations where extracellular nucleic acids released from necrotic or apoptotic cells could activate local FSAP, leading to inhibition of PDGF-BB.

Wound complications following kidney and liver transplantation

Advances in surgical techniques and immunosuppression (IS) have led to an appreciable reduction in postoperative complications following transplantation. However, wound complications as probably the most common type of post-transplantation surgical complication can still limit these improved outcomes and result in prolonged hospitalization, hospital readmission, and reoperation, consequently increasing overall transplant cost. Our aim was to review the literature to delineate the evidence-based risk factors for wound complications following kidney and liver transplantation (KTx, LTx), and to present the preventive and therapeutic modalities for this bothersome morbidity. Generally, wound complications are categorized as superficial and deep wound dehiscences, perigraft fluid collections and seroma, superficial and deep wound infections, cellulitis, lymphocele and wound drainage. The results of several studies showed that the most important risk factors for wound complications are IS and obesity. Additionally, there are surgical and/or technical factors, including type of incision, reoperation, and surgeon's expertise, as well as comorbidities such as advanced age, diabetes mellitus, malnutrition, and uremia. Preventive management of wound complications necessitates defining their etiological factors so that their detrimental effects on healing processes can be addressed and reduced. IS modalities and agents, especially sirolimus (SRL), and steroids (ST) should be adjusted according to the patient's co-existing risk factors. SRL should be administered three months after transplantation and ST should be tapered as soon as possible. A body mass index (BMI) lower than 30 kg/m2 is advisable for inclusion in a transplantation program, but higher BMIs do not exclude recipients. Surgical risk factors can be prevented by applying precise surgical techniques. Therapeutic modalities must focus on the most efficient and cost-effective medications and/or interventions to facilitate and improve wound healing.

Skin gammadelta T-cell functions in homeostasis and wound healing

There is a resident population of T cells found in murine skin that expresses an invariant Vgamma3Vdelta1 T-cell receptor (TCR), and these cells are significantly different from lymphoid gammadelta T cells and alphabeta T cells in terms of ontogeny, tissue tropism, and antigen receptor diversity. These dendritic epidermal T cells are derived from fetal thymic precursor cells, are in constant contact with neighboring epidermal cells, and express a monoclonal gammadeltaTCR only found in the skin. Skin gammadelta T cells have been shown to play unique roles in tissue homeostasis and during tissue repair through local secretion of distinct growth factors including keratinocyte growth factors and insulin-like growth factor-1. In this review, we discuss evidence supporting a role for cross talk between skin gammadelta T cells and keratinocytes that contributes to the maintenance of normal skin and wound healing.

Mechanisms of microvascular wound repair II. Injury induces transformation of endothelial cells into myofibroblasts and the synthesis of matrix proteins

Under normal growth conditions, in vitro dermal microvascular endothelial cells (HDMEC) retain an epithelioid morphology and do not synthesize matrix proteins found increased in scar tissue. When injured by a standard scratch, cells at the wound edge and within the culture transform into spindle-shaped, myofibroblast-like cells. To determine if the transformed cells synthesize matrix proteins, expression of type I collagen and alpha smooth muscle actin (alpha-SMA) was investigated by immunohistochemistry and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Twelve hours following injury, a major upregulation in expression of alpha-SMA and type I collagen was observed both in cells proximal and distal to the wound edge. Cells with the typical morphology of myofibroblasts and displaying intracellular alpha-SMA positive fibrils were observed in HDMEC throughout the culture. In contrast, type IV collagen, a basement membrane protein, was not detected in migrating cells. Following completion of wound repair (24-36 h), type I collagen was no longer expressed and type IV collagen synthesis increased to prewound levels. Quantitative RT-PCR confirmed the changes in gene expression for both type I collagen and alpha-SMA at each time point during repair. These results demonstrate that normal skin microvascular endothelial cells retain an ability to transform into myofibroblast-like cells when injured and to synthesize matrix proteins not expressed in noninjured cells. The synthesis of matrix proteins by injured endothelial cells suggests a direct role for the endothelium in the pathology of scar formation.

Phagocytosis and remodeling of collagen matrices

The biodegradation of collagen and the deposition of new collagen-based extracellular matrices are of central importance in tissue remodeling and function. Similarly, for collagen-based biomaterials used in tissue engineering, the degradation of collagen scaffolds with accompanying cellular infiltration and generation of new extracellular matrix is critical for the integration of in vitro grown tissues in vivo. In earlier studies we observed significant impact of collagen structure on primary lung fibroblast behavior in vitro in terms of collagen uptake and matrix remodeling. Therefore, in the present work, the response of human fibroblasts (IMR-90) to the structural state of collagen was studied with respect to phagocytosis in the presence and absence of inhibitors. Protein content and transcript levels for collagen I (Col-1), matrix metalloproteinase 1 (MMP-1), matrix metalloproteinase 2 (MMP-2), tissue inhibitor of matrix metalloproteinase 1 (TIMP-1), tissue inhibitor of matrix metalloproteinase 2 (TIMP-2), and heat shock protein 70 (HSP-70) were characterized as a function of collagen matrix concentration, structure and cell culture time to assess effects on cellular collagen matrix remodeling processes. Phagocytosis of collagen was assessed quantitatively by the uptake of collagen-coated fluorescent beads incorporated into the collagen matrices. Significantly higher levels of collagen phagocytosis were observed for the cells grown on the denatured collagen versus native collagen matrices. Significant reduction in collagen phagocytosis was observed by blocking several phagocytosis pathways when the cells were grown on denatured collagen versus non-denatured collagen. Collagen phagocytosis inhibition effects were significantly greater for PDL57 IMR-90 cells versus PDL48 cells, reflecting a reduced number of collagen processing pathways available to the older cells. Transcript levels related to the deposition of new extracellular matrix proteins varied as a function of the structure of the collagen matrix presented to the cells. A four-fold increase in transcript level of Col-1 and a higher level of collagen matrix incorporation were observed for cells grown on denatured collagen versus cells grown on non-denatured collagen. The data suggest that biomaterial matrices incorporating denatured collagen may promote more active remodeling toward new extracellular matrices in comparison to cells grown on non-denatured collagen. A similar effect of cellular action toward denatured (wound-related) collagen in the remodeling of tissues in vivo may have significant impact on tissue regeneration as well as the progression of collagen-related diseases.

Delayed healing of chronic leg ulcers can result from impaired trafficking of bone marrow-derived precursors of keratinocytes to the skin

In this paper, it is hypothesized that in chronic wounds the process of homing of bone marrow-derived precursors of keratinocytes is disturbed, and that the interaction between cutaneous T-cell attracting chemokine (CTACK/CCL27) and soluble P-selectin glycoprotein ligand-1 (PSGL-1) can be the cause of this impairment. Several studies have revealed that bone marrow-derived cells (BMDC) trans-differentiate into various cellular lineages, and probably they participate also in healing of wounded skin. Recent studies have demonstrated that BMDC can engraft into the epidermis, and probably they do not engraft into epidermis as keratinocyte stem cells, but rather as transient amplifying cells. So, bone marrow-derived keratinocytes build provisional epidermal layer, and later they are replaced by keratinocytes migrating from surrounding skin. Probably after injury BMDC are recruited by pro-inflammatory cytokines, like granulocyte-macrophage colony stimulating factor. Further homing to the skin is mediated by CTACK/CCL27. This chemokine is exclusively secreted by keratinocytes. In chronic wounds the recruitment of BMDC seems to be impaired. Inhibition of CTACK/CCL27 by as yet not determined factor could be the cause of delayed healing. PSGL-1 appears to be a good candidate for such inhibiting factor. PSGL-1 is expressed by several populations of leukocytes, and can be released from surface of activated neutrophils. It was demonstrated that soluble PSGL-1 binds CTACK/CCL27, and inhibits chemotaxis mediated by this chemokine. Because there are many activated neutrophils in the wound, it should be expected that wound exudate contains large amount of soluble PSGL-1. Thus, CTACK/CCL27 in the wound would be inhibited, and homing of bone marrow-derived precursors of keratinocytes would be disturbed. If this interaction were found to be the main cause of wound chronicity, above-mentioned molecules could be the potential targets for pharmaceutical agents.

Mice lacking neutrophil elastase are resistant to bleomycin-induced pulmonary fibrosis

Neutrophil elastase is a serine protease stored in the azurophilic granules of leukocytes. It has been implicated in the pathology of several lung diseases and is generally presumed to contribute to the tissue destruction and extracellular matrix damage associated with these conditions. To delineate the role of neutrophil elastase in pulmonary inflammation and fibrosis, neutrophil elastase-null mice were intratracheally instilled with bleomycin. In neutrophil elastase-null mice, biochemical and morphological characteristics of pulmonary fibrosis were attenuated for at least 60 days after bleomycin administration despite a typical response to bleomycin as evidenced by assessment of indices of DNA and cell damage. Neutrophil burden of bleomycin-treated wild-type and neutrophil elastase-null mice was comparable, and marked neutrophilic alveolitis was manifest in bleomycin-treated neutrophil elastase-null mice. An absence of immunostaining for active transforming growth factor (TGF)-beta in lung tissue from bleomycin-treated neutrophil elastase-null mice suggested a defect in TGF-beta activation, which was confirmed by biochemical assessment of TGF-beta levels in bronchoalveolar lavage fluid and lung tissue. These data point to novel and unexpected fibrogenic consequences of neutrophil elastase activity in the inflamed lung.

Gene expression profiling of cutaneous wound healing

BACKGROUND

Although the sequence of events leading to wound repair has been described at the cellular and, to a limited extent, at the protein level this process has yet to be fully elucidated. Genome wide transcriptional analysis tools promise to further define the global picture of this complex progression of events.

STUDY DESIGN

This study was part of a placebo-controlled double-blind clinical trial in which basal cell carcinomas were treated topically with an immunomodifier--toll-like receptor 7 agonist: imiquimod. The fourteen patients with basal cell carcinoma in the placebo arm of the trial received placebo treatment consisting solely of vehicle cream. A skin punch biopsy was obtained immediately before treatment and at the end of the placebo treatment (after 2, 4 or 8 days). 17.5K cDNA microarrays were utilized to profile the biopsy material.

RESULTS

Four gene signatures whose expression changed relative to baseline (before wound induction by the pre-treatment biopsy) were identified. The largest group was comprised predominantly of inflammatory genes whose expression was increased throughout the study. Two additional signatures were observed which included preferentially pro-inflammatory genes in the early post-treatment biopsies (2 days after pre-treatment biopsies) and repair and angiogenesis genes in the later (4 to 8 days) biopsies. The fourth and smallest set of genes was down-regulated throughout the study. Early in wound healing the expression of markers of both M1 and M2 macrophages were increased, but later M2 markers predominated.

CONCLUSION

The initial response to a cutaneous wound induces powerful transcriptional activation of pro-inflammatory stimuli which may alert the host defense. Subsequently and in the absence of infection, inflammation subsides and it is replaced by angiogenesis and remodeling. Understanding this transition which may be driven by a change from a mixed macrophage population to predominantly M2 macrophages, may help the interpretation of the cellular and molecular events occurring in the microenvironment of serially biopsied tissues.

Decorin-mediated Transforming Growth Factor-β Inhibition Ameliorates Adverse Cardiac Remodeling

BACKGROUND

Implantation of a left ventricular assist device (LVAD) has been shown to induce regression of fibrosis in patients with congestive heart failure (CHF) and improve myocardial function. The mechanism of reverse remodeling after mechanical circulatory support (MCS), however, has not been fully characterized. In this study we examined the anti-fibrotic effects of decorin, an extracellular matrix (ECM) proteoglycan, on the transforming growth factor-beta (TGF-beta) pathway.

METHODS

Human myocardial tissue samples were obtained from patients undergoing LVAD implantation and again following subsequent transplantation after a sustained period of MCS. The specimens were examined by utilizing different molecular and histologic techniques, including human cardiac fibroblast in vitro studies. We assessed gene expression, mRNA and protein levels.

RESULTS

We found a significant decrease in interstitial fibrosis after MCS, with a decrease in collagen mRNA transcription rates, serving as an indirect measurement of collagen synthesis. Both the mRNA and protein levels of decorin were significantly increased after a period of MCS. Decorin mRNA was up-regulated by 44% after MCS (p < 0.01), which paralleled the increase in interstitial decorin deposition (p < 0.001). In addition, p-SMAD2, a molecular marker downstream of the TGF-beta pathway, was found to be inactivated after MCS (p < 0.02). Moreover, cultured human cardiac fibroblasts exposed to TGF-beta demonstrated decreased collagen production when exogenous decorin was added (p < 0.03).

CONCLUSIONS

The decorin molecule is potentially involved in reverse cardiac remodeling, by directly inhibiting the TGF-beta pathway and its pro-fibrotic effects on the failing human heart.

Lessons learned from psoriatic plaques concerning mechanisms of tissue repair, remodeling, and inflammation

Following injury, skin establishes a balance between too little inflammation increasing risk of infection, and excessive inflammation contributing to delayed wound healing and scarring. Mounting evidence indicates both initiation and termination of inflammation involve active mechanisms. Not only does inflammation itself seem to be a paradox because inflammatory responses are both essential and potentially detrimental, but one chronic inflammatory skin disease (e.g. psoriasis) presents additional paradoxes. While plaques share several factors with wound healing, two understudied and puzzling aspects include why do not inflamed plaques more frequently transform?; and why do not plaques result in scarring? To get at these questions, we review responses involved in wound repair. Oral mucosa was probed because, like fetal skin, wound repair is characterized by its rapidity, low inflammation, and scarless resolution. Active roles for macrophages as both initiators and terminators of inflammation are highlighted. Therapeutic implications are discussed regarding psoriasis and pyoderma gangrenosum. Based on biochemical and immunohistochemical considerations linking psoriatic plaques to hard palate, a novel metaplastic model is presented. We hypothesize saliva and chronic trauma contribute to a constitutive epithelial program where keratinocyte proliferation is more intense prior to differentiation, accompanied by keratin 16 expression in hard palate, thereby resembling plaques. Rather than viewing psoriasis as a nonspecific response to inflammation, we postulate a metaplastic switch by which prepsoriatic skin is converted to a distinct adult tissue type resembling hard palate. In summary, many lessons can be learned by focusing on complex processes involved in regulation of inflammation, tissue repair, and remodeling.

Gene expression profiles of hepatic cell-type specific marker genes in progression of liver fibrosis

AIM: To determine the gene expression profile data for the whole liver during development of dimethylni-trosamine (DMN)-induced hepatic fibrosis.

METHODS: Marker genes were identified for different types of hepatic cells, including hepatic stellate cells (HSCs), Kupffer cells (including other inflammatory cells), and hepatocytes, using independent temporal DNA microarray data obtained from isolated hepatic cells.

RESULTS: The cell-type analysis of gene expression gave several key results and led to formation of three hypotheses: (1) changes in the expression of HSC-specific marker genes during fibrosis were similar to gene expression data in in vitro cultured HSCs, suggesting a major role of the self-activating characteristics of HSCs in formation of fibrosis; (2) expression of mast cell-specific marker genes reached a peak during liver fibrosis, suggesting a possible role of mast cells in formation of fibrosis; and (3) abnormal expression of hepatocyte-specific marker genes was found across several metabolic pathways during fibrosis, including sulfur-containing amino acid metabolism, fatty acid metabolism, and drug metabolism, suggesting a mechanistic relationship between these abnormalities and symptoms of liver fibrosis.

CONCLUSION: Analysis of marker genes for specific hepatic cell types can identify the key aspects of fibrogenesis. Sequential activation of inflammatory cells and the self-supporting properties of HSCs play an important role in development of fibrosis.

Thrombin‐activated platelets induce proliferation of human skin fibroblasts by stimulating autocrine production of insulin‐like growth factor‐1

Platelet components have found successful clinical utilization to initiate or to accelerate tissue-repair mechanisms. However, the molecular pathways by which platelet factors contribute to tissue regeneration have not been fully elucidated. We have studied the effect of thrombin-activated platelets (TAPs) on cell growth in vivo and in cultured cell systems. Application of TAPs to ulcerative skin lesions of diabetic patients induced local activation of ERK1/2 and Akt/PKB. Moreover, when applied to cultured human skin fibroblasts, TAPs promoted cell growth and DNA synthesis and activated platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF)-1 receptor tyrosine kinases. PDGF was released by TAPs and rapidly achieved a plateau. At variance, the release of IGF-1 was mainly provided by the TAPs-stimulated fibroblasts and progressively increased up to 48 h. The PDGF-R blocker Ag1296 reduced the activation of Akt/PKB and, at a lesser extent, of ERK1/2. Conversely, inhibition of IGF-1 signaling by Ag1024 and expression of a dominant-negative IGF-1R mutant selectively reduced the stimulation of ERK1/2 by TAPs and fibroblast-released factors, with minor changes of Akt/PKB activity. Thus, platelet factors promote fibroblast growth by acutely activating Akt/PKB and ERK1/2. Sustained activation of ERK1/2, however, requires autocrine production of IGF-1 by TAPs-stimulated fibroblasts.

Collagen and major histocompatibility class II expression in mesenchymal cells from CIITA hypomorphic mice

Major histocompatibility class II (MHC II) transactivator (CIITA) is critical for interferon-gamma (IFN-gamma)-induced repression of collagen [Xu, Y., Wang, L., Buttice, G., Sengupta, P.K., Smith, B.D., 2004. Major histocompatibility class II transactivator (CIITA) mediates repression of collagen (COL1A2) transcription by interferon gamma (IFN-gamma). J. Biol. Chem. 279, 41319-41332] and activation of MHC II transcription. To better understand the role of CIITA and IFN-gamma induced repression of collagen, mesenchymal cells (lung fibroblasts, adventitial fibroblasts, and smooth muscle cells) were isolated from a CIITA deficient mouse (C2ta(tm1Ccum)). IFN-gamma induced MHC II expression and repressed collagen type I expression in all three cell types isolated from the wild type background. As expected, IFN-gamma treatment of cells isolated from CIITA deficient mice did not induce MHC II production or activate the MHC II promoter. Interestingly, collagen gene expression and promoter activity was similar to that of wild type. Moreover, IFN-gamma induced CIITA mRNA and a truncated form of CIITA protein in all cells isolated from CIITA deficient mice. Most importantly, truncated CIITA occupied the collagen alpha 2(I) gene (col1a2) transcription start site during IFN-gamma treatment, but it did not occupy the MHC II promoter as judged by chromatin immunoprecipitation assays. Exogenous expression of a similar truncated form of CIITA maintained its ability to repress col1a2 transcription, but lost its ability to activate MHC II gene transcription suggesting a role for the CIITA C-terminal domain in activation, but not repression. IFN-gamma induced primarily types I and IV CIITA isoforms in the mouse cells. All three isoforms of CIITA were capable of repressing col1a2 and activating MHC II gene transcription. These data suggest that the previously described CIITA knockout mouse carries a hypomorphic mutation, rather than a null mutation. The removal of the leucine rich region in CIITA blocks activation of MHC II without altering repression of collagen transcription.

Natural compounds from danshen suppress the activity of hepatic stellate cells

Danshen is an herbal medication frequently used in oriental medicine to treat liver or kidney malfunction. In the course of our studies, we observed that compounds purified from Danshen exhibit an inhibitory activity against Discoidin Domain Receptor 2 (DDR2) tyrosine kinase. Through this inhibition, these compounds also inhibited the growth of HSC T6 cells and suppressed the expression of alpha-smooth muscle actin and MMP2, as well as collagen synthesis, all of which are increased in activated liver stellate cells. Given that activation of liver stellate cells is the hallmark of liver fibrosis and that DDR2 plays a critical role in this activation, these results suggest that one of the pharmacological activities of Danshen extract that protects the liver is the inhibition of key cell-signaling kinases, such as DDR2, in liver stellate cells.

Angiogenesis, vasculogenesis, and induction of healing in chronic wounds

A key central stage of wound healing requires neovascularization of the wound base granulation tissue. In the adult, neovascularization is now known to occur by both angiogenesis and vasculogenesis. Understanding the biology of these 2 processes offers promising new therapeutic options for patients who suffer from chronic, nonhealing ischemic wounds. The authors review the current literature on the processes of angiogenesis and vasculogenesis and how it relates to wound healing.

Macrophages inhibit neovascularization in a murine model of age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is the leading cause of blindness in people over 50 y of age in at least three continents. Choroidal neovascularization (CNV) is the process by which abnormal blood vessels develop underneath the retina. CNV develops in 10% of patients with AMD but accounts for up to 90% of the blindness from AMD. Although the precise etiology of CNV in AMD remains unknown, the macrophage component of the inflammatory response, which has been shown to promote tumor growth and support atherosclerotic plaque formation, is thought to stimulate aberrant angiogenesis in blinding eye diseases. The current theory is that macrophage infiltration promotes the development of neovascularization in CNV.

METHODS AND FINDINGS

We examined the role of macrophages in a mouse model of CNV. IL-10(-/-) mice, which have increased inflammation in response to diverse stimuli, have significantly reduced CNV with increased macrophage infiltrates compared to wild type. Prevention of macrophage entry into the eye promoted neovascularization while direct injection of macrophages significantly inhibited CNV. Inhibition by macrophages was mediated by the TNF family death molecule Fas ligand (CD95-ligand).

CONCLUSIONS

Immune vascular interactions can be highly complex. Normal macrophage function is critical in controlling pathologic neovascularization in the eye. IL-10 regulates macrophage activity in the eye and is an attractive therapeutic target in order to suppress or inhibit CNV in AMD that can otherwise lead to blindness.

Treating a pressure ulcer with bio-electric stimulation therapy

Mr Jones lived independently until he developed necrotic pressure ulcers over his heels and could no longer mobilize to care for himself. He was transferred to a nursing home where he lived for 18 months and where the nurses could care for his wounds. The wound had been on his right heel without changing over the 18 months and, although attempts to hydrate the eschar had been somewhat successful, the necrotic tissue proved stubborn creating large quantity of fibrous slough. Mr Jones was initially assessed by the tissue viability consultant on 14 March 2005 and agreed to the application of bio-electric stimulation therapy (POSiFEC). The wound change was immediate and was fully healed by 16 June 2005, 12 weeks after his initial assessment. This article outlines his care and the background to bio-electrical stimulation in wounds.

Autologous platelet-rich plasma for wound and osseous healing: a review of the literature and commercially available products

The application of autologous platelets that have been sequestered, concentrated, and mixed with thrombin to create growth factor-concentrated, autologous platelet-rich plasma for application to soft tissue wounds and for osseous healing has been a subject of great interest for much of the past 2 decades. Autologous platelet-rich plasma, which consists of both quantitative and qualitative components, has the greatest potency or ability to produce the desired effect. Manufacturers prepare autologous platelet-rich plasma with the ultimate goal of maximizing its benefits while minimizing potential risks. Unfortunately, the manufacturing processes for autologous platelet-rich plasma are highly variable, and the types of proprietary systems available on the market for soft tissue and osseous applications are numerous. The authors provide here an in-depth review of commercially available systems for delivery of autologous platelet-rich plasma that emphasizes the subtle yet important differences among systems. In addition, a detailed review of the literature regarding the use of autologous platelet-rich plasma in soft tissue and osseous healing is provided. Although findings are not yet conclusive, autologous platelet-rich plasma has been shown to be safe, reproducible, and effective in mimicking the natural processes of soft tissue wound and osseous healing.

An in vitro Model System to Study the Damaging Effects of Prolonged Mechanical Loading of the Epidermis

Pressure ulcers are areas of soft tissue breakdown that result from sustained mechanical loading of the skin and underlying tissues. Today, little is known with respect to the aetiology of these ulcers. This study introduces an in vitro model system to study the effects of clinically relevant loading regimes on damage progression in the epidermis, the uppermost skin layer. Engineered epidermal equivalents (EpiDerm) were subjected to 6.7 and 13.3 kPa for either 2 or 20 h using a custom-built loading device. Tissue damage was assessed by (1) histological examination, (2) tissue viability evaluation, and (3) by the release of a pro-inflammatory mediator, interleukin-1alpha (IL-1alpha). Loading the EpiDerm samples for 2 h increased the IL-1alpha release, although no visible tissue damage was observed. However, in the 20 h loading experiments visible tissue damage and a small decrease in tissue viability were observed. Furthermore, in these experiments the IL-1alpha release increased with magnitude of loading. It is concluded that this in vitro model system can be applied to improve insight in the epidermal damage process due to prolonged mechanical loading and can serve as a sound basis for effective clinical identification and prevention of pressure ulcers.

Targeting matrix metalloproteases to improve cutaneous wound healing

Wound repair is a physiological event in which tissue injury initiates a repair process leading to restoration of structure and function of the tissue. Cutaneous wound repair can be divided into a series of overlapping phases including formation of fibrin clot, inflammatory response, granulation tissue formation incorporating re-epithelialisation and angiogenesis and finally, matrix formation and remodelling. Matrix metalloproteases (MMPs) are a family of neutral proteases that play a vital role throughout the entire wound healing process. They regulate inflammation, degrade the extracellular matrix (ECM) to facilitate the migration of cells and remodel the new ECM. However, excessive MMP activity contributes to the development of chronic wounds. Selective control of MMP activity may prove to be a valuable therapeutic approach to promote healing of chronic ulcers. Recent evidence indicates that the anticoagulant, activated protein C may be useful in the treatment of non-healing wounds by preventing excessive protease activity through inhibition of inflammation and selectively increasing MMP-2 activity to enhance angiogenesis and re-epithelialisation.

MCP-1 and MIP-2 expression and production in BB diabetic rat: effect of chronic hypoxia

Type 1 (insulin-dependent) diabetes mellitus is an autoimmune disease characterized by the failure to synthesize or secrete insulin, and diabetics are likely to suffer complications that include kidney and heart disease, as well as loss of sight, angiopathy, tissue hypoxia, reduction in organ blood flow, impaired wound healing, respiratory infections, arteriosclerosis, etc., thus diabetes very closely resembles a state of chronic hypoxia. It is now well recognized that hypoxia is an important environmental stimulus capable of modulating the expression of many genes involved in energy metabolism. The diabetic metabolic stress resulting from impaired energy metabolism, which produce altered production of inflammatory mediators, may increase the risk of oxidative injury. The aim was to investigate whether production of MIP-2 and MCP-1 are implicated in the pathogenesis of diabetes, and if the regulatory effects of these chemokines are affected by hypoxia. Two groups of rats, diabetic and non-diabetic, were kept in normoxic room air conditions or subjected to chronic hypoxia. Expression and production of chemokines were measured by RT-PCR and ELISA assay. In diabetic rats, we found a marked increase of MCP-1 when compared with non-diabetic rats (783.5+/- 49 versus 461.9 +/- 27), while no significant differences were detected for MIP-2 levels. Hypoxia selectively modulated chemokines production, since MCP-1 expression and production was up-regulated in the diabetic groups (783.5+/- 49 versus 461.9+/- 27), but down-regulated MIP-2 expression and production (87.8+/- 23 versus 522.1+/- 72). Our data point to MCP-1 and MIP-2 as important components in the pathophysiology of diabetes, and hypoxia is an important and potent environmental stimulus capable of modulating the expression and production of these chemokines.

Cytokine gene expression in a murine wound healing model

Inflammatory mediators have been shown to play a major role in the complex series of co-ordinated events that occur in wound healing responses following injury. However, to date most of the studies carried out have addressed the expression, interactions and role of only one or two cytokines that are thought to be involved in wound repair. This study has evaluated, in murine skin samples taken at 0, 3, 12, 18, 24, 48, 72, 120 and 168 h post-wounding, the expression of a wide range of cytokines with potential for a role in wound repair. Various techniques (reverse transcription polymerase chain reaction (RT-PCR), bioassays and ELISA) were used to evaluate cytokine expression in these samples at both the mRNA and protein expressions level. Semi-quantitative analysis using RT-PCR revealed that IL-1beta, IP10, bFGF, and TGFbeta3 up-regulated in wounded samples, compared to non-injured control samples. Expression of mRNA for other cytokines and inflammatory mediators, IL-1alpha, IL-6, TGFbeta1, TNFalpha, MIP-1alpha, MIP-2, JE, KC, PDGFalpha and PDGFbeta, were found to be down-regulated in injured adult murine samples compared to normal control samples. Interestingly we failed to find evidence of mRNA expression for the cytokines IL-2, IL-4, IL-12, GM-CSF, IFNgamma and RANTES, in both non-injured and injured samples. These observations were also generally supported by the results obtained using bioassays for IL-1 and IL-6 and ELISA for IL-1alpha, IL-1beta, IL-6, TNFalpha, and IFNgamma.

Influence of selected wound dressings on PMN elastase in chronic wound fluid and their antioxidative potential in vitro

Exudates from non-healing wounds contain elevated levels of proteolytic enzymes, like elastase from polymorphonuclear granulocytes (PMN elastase), reactive oxygen species (ROS) and reactive nitrogen species (RNS). The overproduction of proteolytic enzymes leads to reduced concentrations of growth factors and proteinase inhibitors, resulting in an imbalance between degradation and remodelling processes. Thus, the reduction of protein-degrading enzymes and scavenging of ROS and RNS seem to be suitable ways to support the healing process of chronic stagnating wounds. The aim of this study was to test selected wound dressings from different biomaterials (collagen, oxidized regenerated cellulose (ORC) and ORC/collagen mixture), regarding their antioxidative potential in vitro and their influence on the concentration and activity of PMN elastase in chronic wound fluid. Antioxidant capacity of the investigated wound dressing was determined by a pholasin-based chemiluminescent assay. PMN elastase concentration was determined by means of ELISA. Enzyme activities could be measured by a fluorescence assay. As the presented data demonstrates, all tested materials showed antioxidant capacity. In addition, the investigated materials were able to reduce the concentration and activity of PMN elastase. Beside other aspects, such as biocompatibility, biodegradability, fluid absorption and clinical effects (e.g. angiogenesis and microcirculation), the understanding of these properties may help to support the further refinement of wound dressings for improved wound healing.

Macrophages sequentially change their functional phenotype in response to changes in microenvironmental influences

Recent studies have described the development of distinct functional subsets of macrophages in association with cancer, autoimmune disease, and chronic infections. Based on the ability of Th1 vs Th2 cytokines to promote opposing activities in macrophages, it has been proposed that macrophages develop into either type 1 inflammatory or type 2 anti-inflammatory subsets. As an alternative to the concept of subset development, we propose that macrophages, in response to changes in their tissue environment, can reversibly and progressively change the pattern of functions that they express. As demonstrated herein, macrophages can reversibly shift their functional phenotype through a multitude of patterns in response to changes in cytokine environment. Macrophages display distinct functional patterns after treatment with IFN-gamma, IL-12, IL-4, or IL-10 and additional functional patterns are displayed depending on whether the cytokine is present alone or with other cytokines and whether the cytokines are added before or concomitantly with the activating stimulus (LPS). Sequential treatment of macrophages with multiple cytokines results in a progression through multiple functional phenotypes. This ability to adapt to changing cytokine environments has significant in vivo relevance, as evidenced by the demonstration that macrophage functional phenotypes established in vivo in aged or tumor-bearing mice can be altered by changing their microenvironment. A concept of functional adaptivity is proposed that has important implications for therapeutic targeting of macrophages in chronic diseases that result in the dominance of particular functional phenotypes of macrophages that play a significant role in disease pathology.

Overview: acute and chronic wounds

Knowledge of normal wound healing and the changes associated with chronic wounds have advanced significantly. Distinct characteristics identified through basic and clinical studies are found in nonhealing wounds, including bacterial and growth factor imbalances, increased inflammatory responses, and proteolytic forces that tip the balance toward tissue degradation rather than repair. This article describes the alterations that reduce healing and that also have important implications for the management of chronic wounds and presents a focus for future developments in wound therapy.

Platelet-rich plasmas: growth factor content and roles in wound healing

Platelet-rich plasmas (PRPs) are used in a variety of clinical applications, based on the premise that higher growth factor content should promote better healing. In this study, we have determined the effects of calcium and thrombin on the release of EGF, TGF-alpha, IGF-1, Ang-2 and IL-1beta from PRPs, and assessed the mitogenic potential of PRP supernatants on osteoblast and endothelial cell division. ELISA assays indicate that (i) mean growth factor concentrations vary from traces (TGF-alpha) to 5.5 ng/mL (IGF-1), (ii) there are significant variations in growth factor concentrations between individuals, and (iii) calcium and thrombin regulate growth factor release, synthesis, and/or degradation in stereotyped patterns that are specific to each growth factor. PRP supernatants promote strong osteoblast and endothelial cell divisions, supporting the concept that PRPs may be beneficial in wound healing.

ABBREVIATIONS

PRPs, platelet-rich plasmas; GFs, growth factors; EGF, epidermal growth factor; TGF-alpha, transforming growth factor-alpha; IGF-1, insulin-like growth factor-1; Ang-2, angiopoietin-2; IL-1beta, interleukin-1 beta; HUVECs, human umbilical vein endothelial cells; hFOB 1.19, human fetal osteoblasts; and FBS, fetal bovine serum.

Immunosenescence and macrophage functional plasticity: dysregulation of macrophage function by age-associated microenvironmental changes

The macrophage lineage displays extreme functional and phenotypic heterogeneity, which appears to be because, in large part, of the ability of macrophages to functionally adapt to changes in their tissue microenvironment. This functional plasticity of macrophages plays a critical role in their ability to respond to tissue damage and/or infection and to contribute to clearance of damaged tissue and invading microorganisms, to recruitment of the adaptive immune system, and to resolution of the wound and of the immune response. Evidence has accumulated that environmental influences, such as stromal function and imbalances in hormones and cytokines, contribute significantly to the dysfunction of the adaptive immune system. The innate immune system also appears to be dysfunctional in aged animals and humans. In this review, the hypothesis is presented and discussed that the observed age-associated 'dysfunction' of macrophages is the result of their functional adaptation to the age-associated changes in tissue environments. The resultant loss of orchestration of the manifold functional capabilities of macrophages would undermine the efficacy of both the innate and adaptive immune systems. The macrophages appear to maintain functional plasticity during this dysregulation, making them a prime target of cytokine therapy that could enhance both innate and adaptive immune systems.

An ex vivo model for functional studies of myofibroblasts

Migration, proliferation and invasive growth of myofibroblasts are key cellular events during formation of granulation tissue in situations of wound healing, arteriosclerosis and tumor growth. To study the invasive phenotype of myofibroblasts, we established an assay where arterial tissue from chicken embryos was embedded in fibrin gels and stimulated with growth factors. Addition of serum, PDGF-BB and FGF-2, but not VEGF-A, resulted in an outgrowth of cellular sprouts with a pattern that was similar to the organization of cells invading a provisional matrix in an in vivo model of wound healing using the chicken chorioallantoic membrane. Sprouting cells were defined as myofibroblasts based on being alpha-smooth muscle actin-positive but desmin-negative. There was no contribution of endothelial cells in outgrowing sprouts. The acquired myofibroblastic phenotype was stable since sprout-derived cells resumed sprouting in a growth factor-independent manner when re-embedded as spheroids in a fibrin matrix. Invasive growth and sprouting of vascular smooth muscle cells was not limited to chicken cells since a similar response was seen when spheroids composed of purified primary human aortic smooth muscle cells were embedded in fibrin. Finally, a technique for flat visualization of the three-dimensional sprouting and a quantification method is described. This ex vivo model allows quantitative analysis of invasive growth and differentiation of vascular smooth muscle cells and fibroblasts into myofibroblasts.

Growth factors and their relationship to neoplastic and paraneoplastic disease

Growth factors are extracellular signaling molecules that act in an autocrine and paracrine fashion to regulate growth, proliferation, differentiation, and survival of cells. Dysregulation of the growth factor networks is intimately related to the molecular pathogenesis of neoplastic and paraneoplastic disease. Increasing knowledge of the molecular mechanisms underlying growth factors and their actions on cell cycling, cell division, and cell death is shedding light on new therapeutic avenues for molecular targeting of tumors. Epidermal growth factor and vascular endothelial growth factor both offer examples of how growth factor biology and its relationship to cancer can be harnessed to create effective clinical therapeutic tools such as monoclonal antibodies. This approach heralds a future in which rational molecular oncological therapy may increasingly become the norm.

Prolonged beta-catenin stabilization and tcf-dependent transcriptional activation in hyperplastic cutaneous wounds

Mesenchymal cells that accumulate during the proliferative phase of wound healing and that are present in hyperplastic wounds share cytologic similarities with the cells from fibroproliferative lesions in which there is activation of beta-catenin-mediated transcription. Re-excision wounds from a previous biopsy and samples from hyperplastic cutaneous wounds were studied along with normal tissues. During normal wound healing, there was an increase in beta-catenin protein level, peaking 4 weeks following the insult and returning towards baseline level by 12 weeks. Hyperplastic wounds exhibited a prolonged duration of elevated beta-catenin, lasting more than 2 years following the initial injury. The level of expression of genes known to be upregulated in the proliferative phase of wound healing (alpha-smooth muscle actin and type three collagen), correlated with beta-catenin protein level. The phosphorylation level of glycogen synthase kinase-3-beta, a kinase important for beta-catenin protein destabilization, correlated with beta-catenin protein level. Beta-catenin was transcriptionally active in these wounds as demonstrated by the expression of the beta-catenin target genes (MMP-7 and FN) and by activation of a tcf-reporter in primary cell cultures. Beta-catenin stabilization increases cell proliferation and motility in fibroblasts in vitro, and likely has a similar function during its transient elevation in the proliferative phase of normal wound healing. In hyperplastic wounds, there is dysregulation of beta-catenin, maintaining the mesenchymal cells in a prolonged proliferative state. As such, beta-catenin likely plays a central role in mesenchymal cells during the healing process, and is an appealing therapeutic target for disorders of wound healing.

A 3D numerical study of the effect of channel height on leukocyte deformation and adhesion in parallel-plate flow chambers

The effect of channel height on leukocyte adhesion to a lower plate in a parallel-plate flow chamber is studied by direct numerical simulations in three dimensions. The numerical model takes into account deformability and viscoelasticity of the leukocyte, membrane ruffles (microvilli), and the presence of mechanically different regions inside the cell (nucleus and cytoplasm). Leukocyte adhesion is assumed to be mediated by interactions of adhesion molecules on the tips of microvilli with their counterparts on the lower plate. Results of this study indicate that an adherent leukocyte experiences much less drag than a rigid sphere due to its deformation and transient stress growth. While overall leukocyte deformation is modest at shear stresses encountered in the microcirculation, deformation in the contact region is significant. At fixed wall shear stress, the contact area of the cell membrane with the substrate increases with increasing the ratio of cell diameter to channel height, leading to greater adhesion. This suggests that in vitro flow chamber studies typically underestimate leukocyte adhesion that occurs in the microcirculation.