Mechanism of human dermal fibroblast migration driven by type I collagen and platelet-derived growth factor-BB

The use of bioactive wound dressing, stimulating epithelial regeneration of IIIa-degree burn wounds

Clinical and morphological comparison of wound healing after transplantation of living cultured allofibroblast on days 1-2 after the injury, collagen-1-based dressing with PDGF-BB, and traditional dressing with levomecol ointment showed that bioactive dressing accelerated wound epithelialization (5-7 days vs. 20-22 days with gauze dressing); the incidence of suppurative complications decreased, no crust formed, and epithelialization was not associated with the formation of a hypertrophic cicatrix. Biological dressing based on living cultured allofibroblasts and collagen-1 with PDGF-BB exhibited equal stimulatory effects on burn wound healing.

Effect of Prolyl-hydroxyproline (Pro-Hyp), a food-derived collagen peptide in human blood, on growth of fibroblasts from mouse skin

We examined the effect of prolyl-hydroxyproline (Pro-Hyp), which occurs in human peripheral blood after ingestion of collagen peptide, on the migration and growth of mouse skin fibroblasts. Mouse skin discs were cultured on a 24-well plastic plate in a fetal bovine serum (FBS)-free medium. Addition of Pro-Hyp (200 nmol/mL) significantly increased the number of fibroblasts migrating from the skin to the plate after incubation for 72 h. This effect of Pro-Hyp was abolished by the addition of mitomycin C. The fibroblasts that had migrated from the mouse skin were collected and cultured on collagen gel. The growth of fibroblasts on the collagen gel was suppressed even in the presence of FBS, while rapid fibroblast growth was observed on the plastic plate. Addition of Pro-Hyp (0-1000 nmol/mL) to the medium containing 10% FBS enhanced the growth of fibroblasts on the collagen gel in a dose-dependent manner. These results suggest that Pro-Hyp might stimulate the growth of fibroblasts in the skin and consequently increase the number of fibroblasts migrating from the skin.

Fetal ACL fibroblasts exhibit enhanced cellular properties compared with adults

Fetal tendons and skin heal regeneratively without scar formation. Cells isolated from these fetal tissues exhibit enhanced cellular migration and collagen production in comparison to cells from adult tissue. We determined whether fetal and adult fibroblasts isolated from the anterior cruciate ligament (ACL), a tissue that does not heal regeneratively, exhibit differences in cell migration rates and collagen elaboration. An in vitro migration assay showed fetal ACL fibroblasts migrated twice as fast as adult ACL fibroblasts at a rate of 38.90 +/- 7.69 microm per hour compared with 18.88 +/- 4.18 microm per hour, respectively. Quantification of Type I collagen elaboration by enzyme-linked immunosorbent assay showed fetal ACL fibroblasts produced four times the amount of Type I collagen compared with adult ACL fibroblasts after 7 days in culture. We observed no differences in Type III collagen with time for adult or fetal ACL fibroblasts. Our findings indicate fetal ACL fibroblasts are intrinsically different from adult ACL fibroblasts, suggesting the healing potential of the ACL may be age-dependent.

Determination of hierarchical relationship of Src and Rac at subcellular locations with FRET biosensors

Genetically encoded biosensors based on FRET have enabled the visualization of signaling events in live cells with high spatiotemporal resolution. However, the limited sensitivity of these biosensors has hindered their broad application in biological studies. We have paired enhanced CFP (ECFP) with YPet, a variant of YFP. This ECFP/YPet FRET pair markedly enhanced the sensitivity of biosensors (several folds enhancement without the need of tailored optimization for each individual biosensor) for a variety of signaling molecules, including tyrosine kinase Src, small GTPase Rac, calcium, and a membrane-bound matrix metalloproteinase MT1-MMP. The application of these improved biosensors revealed that the activations of Src and Rac by PDGF displayed distinct subcellular patterns during directional cell migration on micropatterned surface. The activity of Rac is highly polarized and concentrated at the leading edge, whereas Src activity is relatively uniform. These FRET biosensors also led to the discovery that Src and Rac mutually regulate each other. Our findings indicate that molecules within the same signaling feedback loop can be differentially regulated at different subcellular locations. In summary, ECFP/YPet may serve as a general FRET pair for the development of highly sensitive biosensors to allow the determination of molecular hierarchies at subcellular locations in live cells.

Berberine inhibits platelet-derived growth factor-induced growth and migration partly through an AMPK-dependent pathway in vascular smooth muscle cells

Platelet-derived growth factor (PDGF) is released from vascular smooth muscle cells (VSMCs), endothelial cells, or macrophages after percutaneous coronary intervention and is related with neointimal proliferation and restenosis. Berberine is a well-known component of the Chinese herb medicine Huanglian (Coptis chinensis), and is capable of inhibiting growth and endogenous PDGF synthesis in VSMCs after in vitro mechanical injury. We analyzed the effects of berberine on VSMC growth, migration, and signaling events after exogenous PDGF stimulation in vitro in order to mimic a post-angioplasty PDGF shedding condition. Pretreatment of VSMCs with berberine inhibited PDGF-induced proliferation. Berberine significantly suppressed PDGF-stimulated Cyclin D1/D3 and Cyclin-dependent kinase (Cdk) gene expression. Moreover, berberine increased the activity of AMP-activated protein kinase (AMPK), which led to phosphorylation activation of p53 and increased protein levels of the Cdk inhibitor p21(Cip1). Compound C, an AMPK inhibitor, partly but significantly attenuated berberine-elicited growth inhibition. In addition, stimulation of VSMCs with PDGF led to a transient increase in GTP-bound, active form of Ras, Cdc42 and Rac1, as well as VSMC migration. However, pretreatment with berberine significantly inhibited PDGF-induced Ras, Cdc42 and Rac1 activation and cell migration. Co-treatment with farnesyl pyrophosphate and geranylgeranyl pyrophosphate drastically reversed berberine-mediated anti-proliferative and migratory effects in VSMCs. Based on these findings, we conclude that berberine inhibited PDGF-induced VSMC growth via activation of AMPK/p53/p21(Cip1) signaling while inactivating Ras/Rac1/Cyclin D/Cdks and suppressing PDGF-stimulated migration via inhibition of Rac1 and Cdc42. These observations offer a molecular explanation for the anti-proliferative and anti-migratory properties of berberine.

Collagen fibril flow and tissue translocation coupled to fibroblast migration in 3D collagen matrices

In nested collagen matrices, human fibroblasts migrate from cell-containing dermal equivalents into surrounding cell-free outer matrices. Time-lapse microscopy showed that in addition to cell migration, collagen fibril flow occurred in the outer matrix toward the interface with the dermal equivalent. Features of this flow suggested that it depends on the same cell motile machinery that normally results in cell migration. Collagen fibril flow was capable of producing large-scale tissue translocation as shown by closure of a approximately 1-mm gap between paired dermal equivalents in floating, nested collagen matrices. Our findings demonstrate that when fibroblasts interact with collagen matrices, tractional force exerted by the cells can couple to matrix translocation as well as to cell migration.

Profiling motility signal-specific genes in primary human keratinocytes

Regulation of human keratinocyte (HK) migration is critical for skin wound healing. Profiling HK migration-specific genes could help us gain a comprehensive understanding of the process. The main challenge is to separate genes that are unrelated to migration, but simultaneously induced by the same growth factor. In this study, we took advantage of a unique response of HKs to transforming growth factor-beta (TGF-beta), which inhibits proliferation but not migration of HKs, to suppress selectively the proliferation-related genes. Furthermore we stimulated HKs independently with TGF-alpha or insulin and identified the common genes and eliminated TGF-alpha- or insulin-specific genes. Under these conditions, we obtained profiles of the immediate-early genes (IEGs, at 30 minutes), early genes (EGs, at 60 minutes), and delayed-early genes (DEGs, at 120 minutes) by microarray analyses, followed by quantitative real-time reverse transcription-PCR (QRT-PCR) validation and functional characterization by RNA interference (RNAi). Our results revealed the following: (1) 25 upregulated and 1 downregulated IEGs; (2) 58 upregulated and 15 downregulated EGs, and (3) 13 upregulated and 3 downregulated DEGs in both TGF-alpha- and insulin-stimulated HKs. Three genes, all encoding secreted molecules, were investigated in HK migration. These cell motility-specific gene profiles may prove useful to skin wound healing.

Distinguishing fibroblast promigratory and procontractile growth factor environments in 3-D collagen matrices

Understanding growth factor function during wound repair is necessary for the development of therapeutic interventions to improve healing outcomes. In the current study, we compare the effects of serum and purified growth factors on human fibroblast function in three different collagen matrix models: cell migration in nested matrices, floating matrix contraction, and stressed-released matrix contraction. The results of these studies indicate that platelet-derived growth factor (PDGF) is unique in its capacity to promote cell migration. Serum, lysophosphatidic acid, sphingosine-1-phophate (S1P), and endothelin-1 promote stressed-released matrix contraction but not cell migration. In addition, we found that S1P inhibits fibroblast migration and treatment of serum to remove lipid growth factors or treatment of cells to interfere with S1P(2) receptor function increases serum promigratory activity. Our findings suggest that different sets of growth factors generate promigratory and procontractile tissue environments for fibroblasts and that the balance between PDGF and S1P is a key determinant of fibroblast promigratory activity.

The effect of imatinib (Glivec) on scleroderma and normal dermal fibroblasts: a preclinical study

BACKGROUND

Scleroderma skin overexpresses the platelet-derived growth factor receptor beta-subunit (PDGFR-beta) in dermal vessels and PDGFR-beta messenger RNA in cultured fibroblasts. Moreover, increased levels of PDGF and stimulatory autoantibodies to PDGFR have been identified in the serum of scleroderma patients.

OBJECTIVE

Imatinib being an inhibitor of tyrosine kinase receptors such as PDGFR, its effect on scleroderma fibroblasts was evaluated in vitro as a preclinical therapeutic step.

METHODS

The effect of imatinib on fibroblasts grown from normal or involved/uninvolved scleroderma skin was studied by Western blot and the methyltetrazolium test. The pattern of distribution of PDGFR-beta in scleroderma versus normal skin was studied by immunohistochemistry.

RESULTS

In vitro, imatinib inhibited the proliferation of normal dermal and scleroderma fibroblasts at least partly via the inhibition of the phosphorylation of PDGFR. PDGFR-beta was expressed in the epidermis and adnexae in 5 lesional scleroderma biopsies and not in controls.

CONCLUSION

This study suggests that imatinib can serve as therapy to limit dermal fibroblast proliferation in scleroderma.

Lycopene inhibits PDGF-BB-induced signaling and migration in human dermal fibroblasts through interaction with PDGF-BB

In melanoma development and progression, platelet-derived growth factor (PDGF) has been suggested to modulate the microenvironment, especially stromal fibroblasts, to the benefit of melanoma growth, invasion, and metastasis. Lycopene, a natural carotenoid that is abundant in tomato, has been shown to inhibit proliferation of several types of cancer cells. However, little attention has been paid to skin fibroblasts and melanoma cells. In the present study, we determined the effects of lycopene on stromal fibroblasts and their interactions with melanoma cells. We found that lycopene inhibited PDGF-BB-induced human Hs68 skin fibroblast migration on gelatin and collagen. Further analysis showed that lycopene inhibited PDGF-BB-induced signaling in human Hs68 and primary cultured skin fibroblasts. PDGF-BB-induced phosphorylation of PDGF receptor beta (PDGFR-beta), extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and c-Jun N-terminal kinase (JNK) was attenuated by lycopene in a concentration-dependent manner, whereas the total expression of each protein was not affected. Interestingly, dot binding assay revealed that lycopene could directly bind to human PDGF-BB in PBS and human plasma, indicating that lycopene can bind to PDGF-BB in both in vitro and in vivo conditions. In functional studies, lycopene inhibited melanoma-induced fibroblast migration in a noncontact coculture system and attenuated signaling in fibroblasts simulated by melanoma-derived conditioned medium. Our results provide the first evidence showing that lycopene is an effective inhibitor of migration of stromal fibroblasts and this effect may contribute to its antitumor activity.

The extracellular matrix in wound healing: a closer look at therapeutics for chronic wounds

Disappointing results with the use of exogenous recombinant growth factors in chronic wounds have redirected the focus to the extracellular matrix (ECM). Newer research has clearly changed our view on the role of the ECM in tissue repair and dismissed the dogma that the sole function of ECM is a passive physical support for cells. It is now clear that intact or fragmented ECM molecules are capable of transducing signals pivotal for cell processes in wound healing primarily via integrin interactions in concert with growth factor activation. In addition, our knowledge about ECM molecules in minute concentrations with biological activity, but devoid of significant structural influence, is increasing. This article reviews the multifaceted molecular roles of ECM in the normal wound-healing process and some molecular abnormalities in chronic wounds, and touches on potential therapies based on the developments of tissue biology.

Nckbeta adapter controls neuritogenesis by maintaining the cellular paxillin level

The SH2/SH3 adapter Nck has an evolutionarily conserved role in neurons, linking the cell surface signals to actin cytoskeleton-mediated responses. The mechanism, however, remains poorly understood. We have investigated the role of Nck/Nckalpha/Nck1 versus Grb4/Nckbeta/Nck2 side-by-side in the process of mammalian neuritogenesis. Here we show that permanent genetic silencing of Nckbeta, but not Nckalpha, completely blocked nerve growth factor-induced neurite outgrowth in PC12 cells and dramatically disrupted the axon and dendrite tree in primary rat cortical neurons. By screening for changes among the components reportedly present in complex with Nck, we found that the steady-state level of paxillin was significantly reduced in Nckbeta knockdown, but not Nckalpha knockdown, neurons. Interestingly, Nckbeta knockdown did not affect the paxillin level in glial cells and several other cell types of various tissue origins. Genetic silencing of paxillin blocked neuritogenesis, just like Nckbeta knockdown. Reintroducing a nondegradable Nckbeta into Nckbeta short interfering RNA-expressing PC12 cells rescued paxillin from down-regulation and allowed the resumption of neuritogenesis. Forced expression of paxillin in Nckbeta knockdown PC12 also rescued its capacity for neuritogenesis. Finally, Nckbeta, but not Nckalpha, binds strongly to paxillin and treatment of the neurons with proteosome inhibitors prevented paxillin down-regulation in Nckbeta knockdown neurons. Thus, Nckbeta maintains paxillin stability during neuritogenesis.

Involvement of vessels and PDGFB in muscle splitting during chick limb development

Muscle formation and vascular assembly during embryonic development are usually considered separately. In this paper, we investigate the relationship between the vasculature and muscles during limb bud development. We show that endothelial cells are detected in limb regions before muscle cells and can organize themselves in space in the absence of muscles. In chick limbs, endothelial cells are detected in the future zones of muscle cleavage, delineating the cleavage pattern of muscle masses. We therefore perturbed vascular assembly in chick limbs by overexpressing VEGFA and demonstrated that ectopic blood vessels inhibit muscle formation, while promoting connective tissue. Conversely, local inhibition of vessel formation using a soluble form of VEGFR1 leads to muscle fusion. The endogenous location of endothelial cells in the future muscle cleavage zones and the inverse correlation between blood vessels and muscle suggests that vessels are involved in the muscle splitting process. We also identify the secreted factor PDGFB (expressed in endothelial cells) as a putative molecular candidate mediating the muscle-inhibiting and connective tissue-promoting functions of blood vessels. Finally, we propose that PDGFB promotes the production of extracellular matrix and attracts connective tissue cells to the future splitting site, allowing separation of the muscle masses during the splitting process.

Extracellular heat shock protein-90alpha: linking hypoxia to skin cell motility and wound healing

Hypoxia is a microenvironmental stress in wounded skin, where it supports wound healing by promoting cell motility. The mechanism of the hypoxia action remained speculative. Here, we provide evidence that hypoxia promotes human dermal fibroblast (HDF) migration by inducing secretion of heat shock protein-90alpha (hsp90alpha) into the extracellular environment through hypoxia-inducible factor-1alpha (HIF-1alpha). The secreted hsp90alpha in turn executes hypoxia's pro-motility effect. Expression of an activated HIF-1alpha mimicked, whereas expression of an inactive HIF-1alpha or suppression of endogenous HIF-1alpha blocked, hypoxia-induced hsp90alpha secretion and HDF migration. Interestingly, the hypoxia-HIF-1 pathway-induced hsp90alpha secretion required neither changes in the steady-state mRNA level nor in the promoter activity of hsp90alpha. Recombinant hsp90alpha fully duplicated the hypoxia effect on HDFs. Inhibition of extracellular hsp90alpha function completely blocked the hypoxia-HIF-1 pathway-stimulated HDF migration. More intriguingly, topical application of hsp90alpha accelerated wound healing in mice. This study has demonstrated a novel mechanism of hypoxia>HIF-1>hsp90alpha secretion>skin cell migration>wound healing, and identified extracellular hsp90alpha as a potential therapeutic agent for skin wounds.

Serum-dependent effects on adult and fetal tendon fibroblast migration and collagen expression

Cell migration and extracellular matrix synthesis play an important role in the wound-healing response to injury. Several studies have described differences in migratory behavior and collagen biosynthetic activity in adult vs. fetal skin fibroblasts. The objective of this study was to examine the serum- and age-dependent effects on cell migration and collagen expression in tendon fibroblasts. Medial tendon fibroblasts were isolated from pregnant ewes and their fetuses, and cultured with and without serum for up to 7 days. Cell migration was determined by quantitative image analysis, and collagen expression was assessed by reverse transcription-polymerase chain reaction and immunohistochemical staining. In serum-containing medium, tendon fibroblasts migrated significantly faster than cells in serum-free medium. Additionally, fetal tendon fibroblasts migrated significantly faster than adult tendon fibroblasts under both culture conditions. The expression of types I and III collagen mRNA was significantly up-regulated in tendon cell populations in serum-free medium compared with those in serum-containing medium. Quantitative assessment of collagen staining indicated that fetal tenocytes produced more type I collagen than adult tenocytes under both culture conditions. These findings suggest that there is an inherent difference between adult and fetal tendon fibroblasts, which may have implications in the wound-healing response in tendons.

Influence of serum on adult and fetal dermal fibroblast migration, adhesion, and collagen expression

The wound healing response to injury can be affected by many factors such as cell migration and extracellular matrix elaboration. The objective of this study was to examine the serum- and age-dependent effects on cell migration, adhesion, and collagen expression by skin fibroblasts. Dermal fibroblasts were isolated and plated with and without serum for up to 7 d. Cell migration was determined by quantitative image analysis, adhesion was quantified using a centrifugation assay, and collagen expression was assessed by PCR and immunohistochemical staining. Both adult and fetal fibroblasts migrated significantly faster in serum-containing medium compared to serum-free medium. There was no significant difference in migration between the two cell types in either serum-containing or serum-free medium. There was no significant difference in adhesion in the presence of serum, although there was a greater fraction of adherent fetal skin fibroblasts than adult fibroblasts in serum-free medium. Moreover, the adherent fraction of fetal fibroblasts in serum-free medium was not significantly different from that in serum-containing medium, suggesting that fetal skin fibroblasts possess serum-independent adhesion properties. Collagen mRNA expression was significantly up-regulated in serum-free compared to serum-containing medium for both cell types. With respect to collagen immunohistochemistry, both dermal fibroblast populations exhibited greater type I collagen compared to type III collagen staining. Quantitative assessment of collagen staining indicated significantly enhanced type I collagen secretion in the presence of serum by fetal skin fibroblasts. These findings suggest that intrinsic cellular characteristics may govern the observed differences in adult and fetal wound healing.

Accelerated Healing of Excisional Skin Wounds by PL 14736 in Alloxan-Hyperglycemic Rats1

PL 14736 is a synthetic peptide, originally isolated from human gastric juice, that has anti-inflammatory and tissue-protective actions in experimental models of gastrointestinal inflammation. To investigate its possible benefit in poorly healing skin wounds, the effects of the topical application of PL 14736 in a gel formulation have been studied on full-thickness excisional wounds in rats, either healthy or made hyperglycemic by alloxan (175 mg/kg s.c.) 5 days previously. The effects of becaplermin gel (platelet-derived growth factor, PDGF-BB, Regranex, a standard therapy for diabetic foot ulcers, were investigated for comparison. Healing was evaluated for up to 7 days after wounding, using digital planimetry analysis, macroscopic scoring and histology. While healing was too rapid in healthy rats to observe enhancement by either treatment, in the hyperglycemic rats which exhibited delayed healing, PL 14736 (10-1,000 microg/wound) produced a dose-dependent acceleration of wound healing (determined by macroscopic scoring) equivalent at the highest doses to that observed with becaplermin. The beneficial effect on healing was associated with increased deposition of organized granulation tissue by day 7 for both PL 14736 and becaplermin, as determined histologically. PL 14736 tended to have a greater effect than becaplermin on the formation of granulation tissue containing mature collagen. Wound contraction, as measured by planimetry, was not significantly affected. In conclusion, topical PL 14736 produces a dose-dependent acceleration of deficient skin wound healing in hyperglycemic rats by facilitating granulation tissue formation, similar to the response seen with topical becaplermin, the standard therapy for diabetic skin wounds. PL 14736 may represent an alternative therapy for delayed wound healing, such as that seen with diabetic foot ulcers, without the proliferative concerns or immunogenicity associated with growth factors.

PKCdelta clustering at the leading edge and mediating growth factor-enhanced, but not ecm-initiated, dermal fibroblast migration

We have previously shown that the immobilized extracellular matrices (ECMs) initiate cell migration and soluble growth factors (GFs) further enhance ECM-initiated cell migration. GFs alone cannot initiate cell migration. To further investigate the specificity of the two signaling mechanisms, we focused on the protein kinase C (PKC) family genes in primary human dermal fibroblasts (DFs). We here show that platelet-derived growth factor-BB (PDGF-BB) strongly stimulates membrane translocation and leading edge clustering of protein kinase Cdelta (PKCdelta). In contrast, attachment to collagen matrix alone does not cause the translocation. Although the kinase function of PKCdelta is dispensable for initial membrane translocation, it is critical for its sustained presence at the cells's leading edge. Blockade of endogenous PKCdelta signaling with dominant-negative kinase-defective PKC (PKCdelta-KD) or PKCdelta-small interfering RNA (siRNA) completely inhibited PDGF-BB-stimulated DF migration. In contrast, neither PKCdelta-KD nor PKCdelta-siRNA affected collagen-induced initiation of DF migration. Overexpression of a constitutively activated PKCdelta (PKCdelta-R144/145A) partially mimics the effect of PDGF-BB. However, PKCdelta-KD, PKCdelta-siRNA, or PKCdelta-R144/145A does not affect PDGF-BB-stimulated activation of p38 mitogen-activated protein kinase, extracellular signal-regulated kinase1/2, or c-Jun N-terminal kinase. Instead, inhibition of PKCdelta blocks PDGF-BB-stimulated activation of signal transducer and activator of transcription 3 (Stat3). This study unveiled the specificity of PKCdelta in the control of DF migration.

The effect of the amelogenin fraction of enamel matrix proteins on fibroblast-mediated collagen matrix reorganization

Enamel matrix proteins (EMP), extracted from developing porcine teeth, promote not only periodontal regeneration but also cutaneous wound healing presumably via the amelogenin fraction. Because it is unclear whether the effect of EMP can be ascribed to amelogenins, we compared EMP with recombinant amelogenin in the relaxed dermal equivalent (DE) in vitro model for early wound contraction. EMP and recombinant porcine amelogenin (rP172) at 1 mg/ml were incorporated into DEs composed of human dermal fibroblasts and a type I collagen matrix. The area reduction, as a measure of contraction, as well as fibroblast numbers and TGF-beta1 levels, were quantified over 7 days in culture in the presence of 10% foetal bovine serum. Both EMP and recombinant amelogenin increased contraction (p < 0.005) and fibroblast numbers (p < 0.005) compared with controls (acetic acid vehicle and 1mg/ml porcine serum albumin) and the positive control TGF-beta1 added at 10 ng/ml. Increased contraction with EMP and recombinant amelogenin was most pronounced after the first day of incubation and was associated with elevated (p < 0.005) TGF-beta1 levels in conditioned medium. In conclusion, the amelogenin component of EMP augmented fibroblast-driven collagen matrix remodelling, at least partially, by increasing the endogenous production of TGF-beta1. These effects of EMP/amelogenin may be beneficial for cutaneous wound healing.

A "traffic control" role for TGFbeta3: orchestrating dermal and epidermal cell motility during wound healing

Cell migration is a rate-limiting event in skin wound healing. In unwounded skin, cells are nourished by plasma. When skin is wounded, resident cells encounter serum for the first time. As the wound heals, the cells experience a transition of serum back to plasma. In this study, we report that human serum selectively promotes epidermal cell migration and halts dermal cell migration. In contrast, human plasma promotes dermal but not epidermal cell migration. The on-and-off switch is operated by transforming growth factor (TGF) beta3 levels, which are undetectable in plasma and high in serum, and by TGFbeta receptor (TbetaR) type II levels, which are low in epidermal cells and high in dermal cells. Depletion of TGFbeta3 from serum converts serum to a plasmalike reagent. The addition of TGFbeta3 to plasma converts it to a serumlike reagent. Down-regulation of TbetaRII in dermal cells or up-regulation of TbetaRII in epidermal cells reverses their migratory responses to serum and plasma, respectively. Therefore, the naturally occurring plasma-->serum-->plasma transition during wound healing orchestrates the orderly migration of dermal and epidermal cells.

Vascular endothelial growth factor-regulated ovarian cancer invasion and migration involves expression and activation of matrix metalloproteinases

Vascular endothelial growth factor (VEGF) expression is elevated in primary ovarian tumors and metastases. We examined the effect of VEGF on epithelial ovarian cancer (EOC) in vitro invasion and migration and underlying mechanisms. Using the Matrigel invasion assay and colloidal gold phagokinetic track assay, we found that VEGF induced EOC DOV13 invasion and migration in a matrix metalloproteinase (MMP)-dependent manner. Using Western blotting, we show that VEGF, at 20-80 ng/ml, induced secretion of pro-MMP-7 and pro-MMP-9 and activation of pro-MMP-2 in DOV13 conditioned medium in a concentration-dependent manner. However, gelatinolytic activity and total MMP-7 protein in DOV13 conditioned medium reached the maximum upon VEGF treatment at 20-40 ng/ml and decreased at higher-concentration VEGF treatment (80 ng/ml), as shown by DQ-gelatin degradation assay and ELISA. In addition to the effect on MMP secretion/activation, VEGF stimulated secretion of TIMP-2; and blocking TIMP-2 activity by an anti-TIMP-2 MAb significantly increased VEGF (80 ng/ml)-induced DOV13 invasion (p < 0.05), suggesting that VEGF may regulate MMP-2 activity in DOV13 conditioned medium through TIMP-2. Using real-time PCR, we found that VEGF, at 20 ng/ml, significantly increased the expression of VEGFR-1 and VEGFR-2 by approximately 4-fold and 31-fold, respectively, compared to untreated control (p < 0.05). However, the inducing effect of VEGF on VEGFR-2 expression and the internal expression of VEGF121 in DOV13 cells decreased with increasing of VEGF concentration, suggesting the existence of a negative feedback regulatory mechanism. In summary, our results indicate that VEGF may regulate EOC invasion and migration through VEGFR-mediated secretion and activation of MMPs.

Multiple signaling pathways are involved in endothelin-1-induced brain endothelial cell migration

We have observed that the vasoactive peptide endothelin-1 is a potent inducer of migration of primary human brain-derived microvascular endothelial cells. By blocking signal transduction pathways with specific inhibitors, and using dominant negative mutant infections, we have demonstrated that multiple pathways are involved in endothelin-1-induced migration. Absolutely required for migration are protein tyrosine kinase Src, Ras, protein kinase C (PKC), phosphatidylinositol 3-kinase, ERK, and JNK; partial requirements were exhibited by cAMP-activated protein kinase and p38 kinase. Partial elucidation of the signal transduction sequences showed that the MAPKs ERK, JNK, and p38 are positioned downstream of both PKC and cAMP-activated protein kinase in the signal transduction scheme. The results show that human brain endothelial cell migration has distinct characteristics, different from cells derived from other vascular beds, or from other species, often used as model systems. Furthermore, the results indicate that endothelin-1, secreted by many tumors, is an important contributor to tumor-produced proangiogenic microenvironment. This growth factor has been associated with increased microvessel density in tumors and is responsible for endothelial cell proliferation, migration, invasion, and tubule formation. Because many signal transduction pathways investigated in this study are potential or current targets for anti-angiogenesis therapy, these results are of critical importance for designing physiological antiangiogenic protocols.

LPA-induced epithelial ovarian cancer (EOC) in vitro invasion and migration are mediated by VEGF receptor-2 (VEGF-R2)

OBJECTIVE

Lysophosphatidic acid (LPA) stimulates ovarian tumor growth partially via induction of VEGF expression through transcriptional activation. Previous studies have shown that LPA induces epithelial ovarian cancer (EOC) in vitro metastasis. In this study, we examined the role of VEGF in LPA-induced EOC invasion and migration and underlying mechanisms.

METHODS

The invasiveness of DOV13 cells was determined by in vitro basement membrane Matrigel invasion assay. Ovarian carcinoma cellular migration was quantified by the colloidal gold migration assay. Matrix metalloproteinase (MMP)-2 secretion and activation were detected by gelatin zymography. Urokinase type plasminogen activator (uPA) activity was determined by a coupled colorimetric assay measuring the activity of generated plasmin. Student's t test and one-way ANOVA were used for statistical analysis.

RESULTS

Using a VEGF neutralizing monoclonal antibody (mAb), we show that LPA-induced EOC invasion is dependent upon VEGF. Using the selective VEGF receptor (VEGFR)-2 inhibitor, SU1498, LPA-induced EOC invasion and migration were significantly inhibited in a concentration-dependent manner. In addition, SU1498 inhibits MMP-2 secretion and uPA activity in ovarian cancer DOV13 cells. At 5 and 20 microM, SU1498 almost completely inhibited the activity of MMP-2 and uPA. SU1498 also decreases the LPA-induced increase of uPA activity in DOV13 cells.

CONCLUSIONS

Our results show that LPA-induced EOC invasion is at least partially mediated by VEGF. Further, the VEGFR-2-mediated signaling transduction pathway may be involved in LPA-induced EOC invasion and migration by regulating the secretion and activation of MMP-2 and uPA.

Motogenic substrata and chemokinetic growth factors for human skin cells

Extracellular matrix remodelling and accurate spatio-temporal coordination of growth factor expression are two factors that are believed to regulate mitoses and cell migration in developing and regenerating tissues. The present quantitative videomicroscopical study examined the influence of some of the principal components of extracellular matrix and several growth factors that are known to be expressed in dermal wounds on three important facets of human skin cell behaviour in culture. Keratinocytes, melanocytes and dermal fibroblasts (and myofibroblast controls) exhibited varying degrees of substrate adhesion, division and migration depending on the composition of the culture substrate. Substrates that are recognized components of transitional matrices generally accentuated cell adhesion and proliferation, and were motogenic, when compared with serum-treated control surfaces, whereas components of more stable structures such as basement membrane had less influence. Platelet-derived growth factor (PDGF), epidermal growth factor (EGF) and alpha fibroblastic growth factor (alphaFGF) all promoted cell proliferation and were chemokinetic to dermal fibroblasts, but not keratinocyte growth factor (KGF) or transforming growth factor beta (TGFbeta). PDGF, EGF and KGF, but not TGFbeta or alphaFGF, all enhanced proliferation of dermal keratinocytes. The same growth factors, and in addition KGF, all stimulated motility in keratinocytes, but TGFbeta and alphaFGF again had no effect. Developing a better understanding of the interdependency of factors that control crucial cell behaviour may assist those who are interested in the regulation of histogenesis and also inform the development of rational therapeutic strategies for the management of chronic and poorly healed wounds.

Pathogenesis of pleural fibrosis

Pleural fibrosis resembles fibrosis in other tissues and can be defined as an excessive deposition of matrix components that results in the destruction of normal pleural tissue architecture and compromised function. Pleural fibrosis may be the consequence of an organised haemorrhagic effusion, tuberculous effusion, empyema or asbestos-related pleurisy and can manifest itself as discrete localised lesions (pleural plaques) or diffuse pleural thickening and fibrosis. Although the pathogenesis is unknown, it is likely that the complex interactions between resident and inflammatory cells, profibrotic mediators and coagulation, and fibrinolytic pathways are integral to pleural remodelling and fibrosis. It is generally considered that the primary target cell for pleural fibrosis is the subpleural fibroblast. However, increasing evidence suggests that mesothelial cells may also play a significant role in the pathogenesis of this condition, both by initiating inflammatory responses and producing matrix components. A greater understanding of the interactions between pleural and inflammatory cells, cytokines and growth factors, and blood derived proteins is required before adequate therapies can be developed to prevent pleural fibrosis from occurring.

Lowe syndrome protein Ocrl1 is translocated to membrane ruffles upon Rac GTPase activation: a new perspective on Lowe syndrome pathophysiology

Oculocerebrorenal Lowe syndrome is a rare X-linked disorder characterized by bilateral cataract, mental retardation and renal Fanconi syndrome. The Lowe syndrome protein Ocrl1 is a PIP2 5-phosphatase, primarily localized to the trans-Golgi network (TGN), which 'loss of function' mutations result in PIP2 accumulation in patient's cells. Although PIP2 is involved in many cell functions including signalling, vesicle trafficking and actin polymerization, it has been difficult so far to decipher molecular/cellular mechanisms responsible for Lowe syndrome phenotype. We have recently shown that, through its C-terminal RhoGAP domain, Ocrl1 forms a stable complex with Rac GTPase within the cell. In line with this finding, we report here that upon epidermal growth factor induced Rac activation in COS-7 cells, a fraction of Ocrl1 translocates from TGN to plasma membrane and concentrates in membrane ruffles. In order to investigate the functionality of Ocrl1 in plasma membrane, we have analysed PIP2 distribution in human dermal fibroblasts (HDFs) from Lowe patients versus control HDFs. As revealed by both immunodetection and green fluorescent protein-PH binding, PIP2 was found strikingly to accumulate in PDGF induced ruffles in Lowe HDFs when compared with control. This suggests that Ocrl1 is active as a PIP2 5-phosphatase in Rac induced membrane ruffles. Cellular properties such as cell migration and establishment of cell-cell contacts, which depend on ruffling and lamellipodia formation, should be further investigated to understand the pathophysiology of Lowe syndrome.

Wound-Healing Perspectives

Wound-healing in the skin is a complex orchestration of cellular processes, which has been perfected throughout the eons of phylogeny. It has so many coordinated biologic processes invoked both simultaneously and in a regulated orderly fashion that it has been likened to a recapitulation of gestation. Part of the problem with studying wound healing is in analyzing the processes independently and then seeing how they fit together and influence each other. This article discusses selected and recent scientific observations that have given insight into the biology of human skin wound healing. The article then discusses selected clinical advances that are based less on evidence-based observation and more on what works in practice and promotes wound healing.

CXCL11 Attenuates Bleomycin-induced Pulmonary Fibrosis via Inhibition of Vascular Remodeling

Aberrant vascular remodeling is a central hallmark for the development and progression of idiopathic pulmonary fibrosis. The mechanisms underlying the pathophysiologic alterations, however, are poorly understood. A recent phase II trial of interferon gamma-1b has demonstrated a trend toward a decrease in profibrotic and proangiogenic biologic markers, and upregulation of lung CXCL11 mRNA and bronchoalveolar lavage fluid and plasma protein levels of CXCL11. We hypothesized that net aberrant vascular remodeling seen during the pathogenesis of fibroplasia and deposition of extracellular matrix during bleomycin-induced pulmonary fibrosis can be attenuated by treatment with the angiostatic ELR(-) CXC chemokine, CXCL11. In a preclinical model, systemic administration of CXCL11 reduced pulmonary collagen deposition, procollagen gene expression, and histopathologic fibroplasia and extracellular matrix deposition in the lung of bleomycin-treated mice. CXCL11 treatment significantly reduced bleomycin-induced pulmonary fibrosis without altering specific lung leukocyte populations. CXCR3 is not expressed on fibroblasts and CXCL11 had no direct functional effect on pulmonary fibroblasts. The angiogenic activity in the lung was significantly decreased, however, and CXCL11 treatment reduced the total number of endothelial cells in the lung following bleomycin exposure. The results suggest that CXCL11 inhibits pulmonary fibrosis by altering aberrant vascular remodeling.

Deletion of the PDGFR-beta gene affects key fibroblast functions important for wound healing

This study provides new perspectives of the unique aspects of platelet-derived growth factor beta-receptor (PDGFR-beta) signaling and biological responses through the establishment of a mutant mouse strain in which two loxP sequences were inserted into the introns of PDGFR-beta genome sequences. Isolation of skin fibroblasts from the mutant mice and Cre recombinase transfection in vitro induced PDGFR-beta gene deletion (PDGFR-betaDelta/Delta). The resultant depletion of the PDGFR-beta protein significantly attenuated platelet-derived growth factor (PDGF)-BB-induced cell migration, proliferation, and protection from H2O2-induced apoptosis of the cultured PDGFR-betaDelta/Delta dermal fibroblasts. PDGF-AA and fetal bovine serum were mitogenic and anti-apoptotic but were unable to induce the migration in PDGFR-beta Delta/Delta fibroblasts. Concerning the PDGF signaling, PDGF-BB-induced phosphorylation of Akt, ERK1/2, and JNK, but not p38, decreased in PDGFR-betaDelta/Delta fibroblasts, but PDGF-AA-induced signaling was not altered. Overexpression of the phospholipid phosphatases, SHIP2 and/or PTEN, inhibited PDGF-BB-induced phosphorylation of Akt and ERK1/2 in PDGFR-betaDelta/Delta fibroblasts but did not affect that of JNK and p38. These results indicate that disruption of distinct PDGFR-beta signaling pathways in PDGFR-betaDelta/Delta dermal fibroblasts impaired their proliferation and survival, but completely inhibits migratory response, and that PDGF-BB-induced phosphorylation of Akt and ERK1/2 possibly mediated by PDGFR-alpha is regulated, at least in part, by the lipid phosphatases SHIP2 and/or PTEN. Thus, the PDGFR-beta function on dermal fibroblasts appears to be critical in PDGF-BB action for skin wound healing and is clearly distinctive from that of PDGFR-alpha in the ligand-induced biological responses and the underlying properties of cellular signaling.

Synthetic Biocompatible Cyclodextrin-Based Constructs for Local Gene Delivery to Improve Cutaneous Wound Healing

The localized, sustained delivery of growth factors for wound healing therapy is actively being explored by gene transfer to the wound site. Biocompatible matrices such as bovine collagen have demonstrated usefulness in sustaining gene therapy vectors that express growth factors in local sites for tissue repair. Here, new synthetic biocompatible materials are prepared and shown to deliver a protein to cultured cells via the use of an adenoviral delivery vector. The synthetic construct consists of a linear, beta-cyclodextrin-containing polymer and an adamantane-based cross-linking polymer. When the two polymers are combined, they create an extended network by the formation of inclusion complexes between the cyclodextrins and adamantanes. The properties of the network are altered by controlling the polymer molecular weights and the number of adamantanes on the cross-linking polymer, and these modifications and others such as replacement of the beta-cyclodextrin (host) and adamantane (guest) with other cyclodextrins (hosts such as alpha, gamma, and substituted members) and inclusion complex forming molecules (guests) provide the ability to rationally design network characteristics. Fibroblasts exposed to these synthetic constructs show proliferation rates and migration patterns similar to those obtained with collagen. Gene delivery (green fluorescent protein) to fibroblasts via the inclusion of adenoviral vectors in the synthetic construct is equivalent to levels observed with collagen. These in vitro results suggest that the synthetic constructs are suitable for in vivo tissue repair applications.

Signals that Initiate, Augment, and Provide Directionality for Human Keratinocyte Motility

Human keratinocytes (HK) migration plays a critical role in the re-epithelialization of acute skin wounds. Although extracellular matrices (ECM) and growth factors (GF) are the two major pro-motility signals, their functional relationship remains unclear. We investigated how ECM and GF regulate HK motility under defined conditions: (1) in the absence of GF and ECM and (2) with or without GF with cells apposed to a known pro-motility ECM. Our results show that HK migrate on selected ECM even in the total absence of GF. This suggests that certain ECM alone are able to "initiate" HK migration. Unlike ECM, however, GF alone cannot initiate HK migration. HK cannot properly migrate when plated in the presence of GF, regardless of the concentration, without an ECM substratum. The role of GF, instead, is to augment ECM-initiated motility and provide directionality. To gain insights into the mechanism of action by ECM and GF, we compared, side-by-side, the roles of three major mitogen-activated protein kinase cascades, extracellular-signal-regulated kinase (ERK)1/2, p38, and c-Jun N-terminal kinase (JNK). Our data show that ERK1/2 is involved in mediating collagen's initiation signal and GF's augmentation signal. p38 is specific for GF's augmentation signal. JNK is uninvolved in HK motility. Constitutively activated p38 and ERK1/2 alone could not initiate HK migration. Co-expression of both constitutively activated p38 and ERK1/2, however, could partially mimic the pro-motility effects of collagen and GF. This study reveals for the first time the specific functions of ECM and GF in cell motility.

The mesenchymal alpha11beta1 integrin attenuates PDGF-BB-stimulated chemotaxis of embryonic fibroblasts on collagens

alpha11beta1 constitutes the most recent addition to the integrin family and has been shown to display a binding preference for interstitial collagens found in mesenchymal tissues. We have previously observed that when alpha11beta1 integrin is expressed in cells lacking endogenous collagen receptors, it can mediate PDGF-BB-dependent chemotaxis on collagen I in vitro. To determine in which cells PDGF and alpha11beta1 might cooperate in regulating cell migration in vivo, we studied in detail the expression and distribution of alpha11 integrin chain in mouse embryos and tested the ability of PDGF isoforms to stimulate the alpha11beta1-mediated cell migration of embryonic fibroblasts. Full-length mouse alpha11 cDNA was sequenced and antibodies were raised to deduced alpha11 integrin amino acid sequence. In the embryonic mouse head, alpha11 protein and RNA were localized to ectomesenchymally derived cells. In the periodontal ligament, alpha11beta1 was expressed as the only detectable collagen-binding integrin, and alpha11beta1 is thus a major receptor for cell migration and matrix organization in this cell population. In the remainder of the embryo, the alpha11 chain was expressed in a subset of mesenchymal cells including tendon/ligament fibroblasts, perichondrial cells, and intestinal villi fibroblasts. Most of the alpha11-expressing cells also expressed the alpha2 integrin chain, but no detectable overlap was found with the alpha1 integrin chain. In cells expressing multiple collagen receptors, these might function to promote a more stable cell adhesion and render the cells more resistant to chemotactic stimuli. Wild-type embryonic fibroblasts activated mainly the PDGF beta receptor in response to PDGF-BB and migrated on collagens I, II, III, IV, V, and XI in response to PDGF-BB in vitro, whereas mutant fibroblasts that lacked alpha11beta1 in their collagen receptor repertoire showed a stronger chemotactic response on collagens when stimulated with PDGF-BB. In the cellular context of embryonic fibroblasts, alpha11beta1 is thus anti-migratory. We speculate that the PDGF BB-dependent cell migration of mesenchymal cells is tightly regulated by the collagen receptor repertoire, and disturbances of this repertoire might lead to unregulated cell migration that could affect normal embryonic development and tissue structure.