Growth factors in wound healing

Aging fibroblasts present reduced epidermal growth factor (EGF) responsiveness due to preferential loss of EGF receptors

Wound healing is compromised in aging adults in part due to decreased responsiveness of fibroblasts to extracellular signals. However, the cellular mechanisms underlying this phenomenon are not known. Aged dermal fibroblasts with reduced remaining replicative capacities demonstrated decreased epidermal growth factor (EGF)-induced cell migrative and cell proliferative capacities, as reported previously. Thus, as cells approach senescence, programmed in vivo or in vitro, EGF responsiveness is preferentially lost. To define the rate-limiting signaling event, we found that the activity of two different EGF receptor (EGFR)-signaling pathways to cell migration (phospholipase-C gamma) and/or mitogenesis (extracellular signal/regulated-mitogen-activated kinases) were decreased in near senescent cells despite unchanged levels of effector molecules. Aged cells presented decreased levels of EGFR, although insulin receptor and transferrin receptor levels were relatively unchanged. EGFR mRNA levels and production of new transcripts decreased during aging, suggesting that this preferential loss of EGFR was due to diminished production, which more than counteracts the reduced ligand-induced receptor loss. Since these data suggested that the decrement in EGF was rate-limiting, higher levels of EGFR were established in near senescent cells by electroporation of EGFR cDNA. These cells presented higher levels of EGFR and recovered their EGF-induced migration and proliferation responsiveness. Thus, the defect in EGF responsiveness of aged dermal fibroblasts is secondary to reduced EGFR message transcription. Our experimental model suggests that EGFR gene delivery might be an effective future therapy for compromised wound healing.

The angiogenesis inhibitor, endostatin, does not affect murine cutaneous wound healing

BACKGROUND

Endostatin is a potent angiogenesis inhibitor, which is currently being used in Phase I trials as an antitumor agent. The purpose of this study was to determine whether endostatin has an effect on wound healing in a murine model.

MATERIALS AND METHODS

The function of endostatin was confirmed using a human microvascular endothelial cell (HMVEC) proliferation assay in which cells are treated for 4 days with growth media plus or minus endostatin. Full-thickness incisions were made on the dorsum of athymic nude mice and closed primarily with skin staples. PVA sponges were implanted in some wounds to determine vascular ingrowth. Subsequently, mice were treated with recombinant human endostatin at 20 mg/kg/day or 50 mg/kg/dose BID versus control for a total of 14 days. On Days 2, 4, 8, 12, and 16, three mice per group had serum samples drawn and were sacrificed. Perpendicular breaking strength (N) was determined using an Instron 5540 tensometer. Wound strength was determined by dividing breaking strength by wound area (N/cm(2)). Vascular density in sponges was determined using CD31 immunohistochemistry. Serum endostatin concentrations were determined using a commercially available ELISA kit.

RESULTS

Endostatin caused a significant reduction of endothelial cell proliferation after 4 days compared to media alone (72%, P = 0.031). At all time points tested, there was no statistical difference in the wound-breaking strength between endostatin and control-treated mice at either the low or high dose. Serum endostatin levels were consistently 10-fold higher in endostatin-treated mice than in controls. No differences in vascular density were seen in endostatin versus control-treated mice as determined by CD31 immunohistochemistry of PVA sponges.

CONCLUSION

Therapy with human endostatin does not induce a significant decrease in breaking strength of cutaneous wounds in mice.

Incisional wound healing in transforming growth factor-beta1 null mice

Expression of endogenous transforming growth factor-beta1 is reduced in many animal models of impaired wound healing, and addition of exogenous transforming growth factor-beta has been shown to improve healing. To test the hypothesis that endogenous transforming growth factor-beta1 is essential for normal wound repair, we have studied wound healing in mice in which the transforming growth factor-beta1 gene has been deleted by homologous recombination. No perceptible differences were observed in wounds made in 3-10-day-old neonatal transforming growth factor-beta1 null mice compared to wild-type littermates. To preclude interference from maternally transferred transforming growth factor-beta1, cutaneous wounds were also made on the backs of 30-day-old transforming growth factor-beta1 null and littermate control mice treated with rapamycin, which extends their lifetime and suppresses the inflammatory response characteristic of the transforming growth factor-beta1 null mice. Again, no impairment in healing was seen in transforming growth factor-beta1 null mice. Instead these wounds showed an overall reduction in the amount of granulation tissue and an increased rate of epithelialization compared to littermate controls. Our data suggest that release of transforming growth factor-beta1 from degranulating platelets or secretion by infiltrating macrophages and fibroblasts is not critical to initiation or progression of tissue repair and that endogenous transforming growth factor-beta1 may actually function to increase inflammation and retard wound closure.

Development of an in vitro wound healing model for periodontal cells

BACKGROUND

Periodontal wound healing and regeneration are influenced by a multitude of factors. While many in vitro investigations have compared the proliferation of periodontal ligament (PDL) cells and gingival fibroblasts (GF), there are no reports directly comparing the abilities of these 2 cell types to fill a wound site. As such, the goals of this research were: 1) to develop an in vitro model of wound healing which would allow for the investigation of the biologic basis of periodontal wound healing and regeneration and 2) to compare the rates of PDL cells and GF to fill an in vitro wound site.

METHODS

Using both human PDL cells and GF confluent cultures, in vitro wounds were mechanically created, removing a 3 mm wide band of the cell layer. Wounded cultures were then incubated for time periods up to 12 days in media containing fetal bovine serum (FBS) concentrations (0, 0.1, 1, 5, 10, and 20%) as appropriate for each experiment. Slides were fixed, stained, and cells quantified within the wound boundaries by computer-assisted histomorphometry. The effect of wounding a cell layer was determined by comparing wounded cells as described above with a cell layer margin created without physically disrupting the cell layer.

RESULTS

The in vitro model for periodontal wound healing established in this study showed that GF fill in the wound site at a significantly (P <0.0025) faster rate than PDL cells over 12 days of healing. In addition, PDL cells and GF were found to have unique concentration-dependent responses to FBS (P<0.0025). It was also shown that wounding resulted in a significant delay (P <0.01) in the initial healing response of an in vitro wound.

CONCLUSION

This in vitro model demonstrated that the characteristics of wound healing are dependent on cell type, disruption (wounding) of the cell layer, and serum concentration. In addition, this model has incorporated both proliferation and migration to provide the first direct evidence demonstrating GF has a significantly greater ability to fill a wound site than PDL cells. This in vitro model may be utilized in future investigations of the biologic basis of periodontal wound healing.

Differences between fibroblasts cultured from oral mucosa and normal skin: implication to wound healing

It is generally agreed that oral mucosa heals faster with less scar than skin does, and hypertrophic scar or keloid is very rare in the oral cavity. Fibroblasts are thought to play an important role in wound healing and scar formation, whose control is mediated by growth factors. We have studied whether there are any differences in the cellular behavior of fibroblasts between oral mucosa and skin, and in their response to growth factors. Oral mucosal fibroblasts proliferated slightly more than dermal fibroblasts on average. Dermal fibroblasts in collagen gel possessed greater contraction potency than oral mucosa fibroblasts, irrespective of the presence of growth factors; however, oral mucosa fibroblasts showed an earlier collagen gel contraction with or without TGF-beta1. There were no differences in basal collagen synthetic rate between dermal and oral mucosal fibroblasts, while the latter synthesized more collagen than dermal fibroblasts when they were stimulated with TGF-beta1. Our study showed that oral mucosal fibroblasts and dermal fibroblasts had selective differences in cellular behavior and in their responses to growth factors, which seems to contribute to the differences in wound healing.

Bone- and non-bone-derived growth factors and effects on bone healing

In the future, it may be possible to manipulate the fracture site with exogenous growth factors to allow successful union of the bone ends without additional surgery. The complex interaction of growth factors, the timing of their appearance and disappearance at the wound site, and the concentrations necessary to achieve specific effects must be studied more thoroughly. For growth factors to find widespread clinical use, there must be evidence that healing is enhanced. It may be difficult to enhance the healing of fresh fractures in normal animals, and it may also be difficult to demonstrate the healing of nonunion fractures. Because of the great variability in fractures of clinical patients, studies designed to determine the effect of growth factors on bone healing must be carefully designed with appropriate attention given to randomizing patients based on the risk of delayed healing and other patient characteristics.

IP-10 inhibits epidermal growth factor-induced motility by decreasing epidermal growth factor receptor-mediated calpain activity

During wound healing, fibroblasts are recruited from the surrounding tissue to accomplish repair. The requisite migration and proliferation of the fibroblasts is promoted by growth factors including those that activate the epidermal growth factor receptor (EGFR). Counterstimulatory factors in wound fluid are postulated to limit this response; among these factors is the ELR-negative CXC chemokine, interferon inducible protein-10 (IP-10). We report here that IP-10 inhibited EGF- and heparin-binding EGF-like growth factor-induced Hs68 human dermal fibroblast motility in a dose-dependent manner (to 52% and 44%, respectively, at 50 ng/ml IP-10), whereas IP-10 had no effect on either basal or EGFR-mediated mitogenesis (96 +/- 15% at 50 ng/ml). These data demonstrate for the first time a counterstimulatory effect of IP-10 on a specific induced fibroblast response, EGFR-mediated motility. To define the molecular basis of this negative transmodulation of EGFR signaling, we found that IP-10 did not adversely impact receptor or immediate postreceptor signaling as determined by tyrosyl phosphorylation of EGFR and two major downstream effectors phospholipase C-gamma and erk mitogen-activated protein kinases. Morphological studies suggested which biophysical steps may be affected by demonstrating that IP-10 treatment resulted in an elongated cell morphology reminiscent of failure to detach the uropod; in support of this, IP-10 pretreatment inhibited EGF-induced cell detachment. These data suggested that calpain activity may be involved. The cell permeant agent, calpain inhibitor I, limited EGF-induced motility and de-adhesion similarly to IP-10. IP-10 also prevented EGF- induced calpain activation (reduced by 71 +/- 7%). That this inhibition of EGF-induced calpain activity was secondary to IP-10 initiating a cAMP-protein kinase A-calpain cascade is supported by the following evidence: (a) the cell permeant analogue 8-(4-chlorophenylthio)-cAMP (CPT-cAMP) prevented EGF-induced calpain activity and motility; (b) other ELR-negative CXC chemokines, monokine induced by IFN-gamma and platelet factor 4 that also generate cAMP, inhibited EGF-induced cell migration and calpain activation; and (c) the protein kinase A inhibitor Rp-8-Br-cAMPS abrogated IP-10 inhibition of cell migration, cell detachment, and calpain activation. Our findings provide a model by which IP-10 suppresses EGF-induced cell motility by inhibiting EGF-induced detachment of the trailing edges of motile cells.

Left and right ventricular collagen type I/III ratios and remodeling post-myocardial infarction

BACKGROUND

Types I and III collagen have different physical properties, and an increase of type I/III ratio can have a deleterious impact on myocardial compliance and left and right ventricular diastolic function. Post-myocardial infarction, these changes in collagen types may be relevant to the remodeling process and the development of heart failure.

METHODS AND RESULTS

In the rat coronary ligation heart failure model, we studied the time course of changes in types I and III and total collagen levels over 10 weeks postinfarction. Collagen types were separately quantified in the left (LV) and right ventricles (RV) by computerized morphometry and standard immunohistochemistry techniques, and also by hydroxyproline analysis, and these were correlated with hemodynamic changes. Compared with sham-operated rats, total collagen level increased 2.5- to 2.9-fold and 1.7- to 2.9-fold in the noninfarcted areas (NIAs) of the LV and RV, respectively, over the 10-week period and showed a good relation with changes in hydroxyproline content (r2 = 0.62; P < .0001). In the NIAs of both the LV and RV, type III collagen level showed a transient twofold increase at 2 weeks, which declined to normal at 4 weeks. Type I collagen level increased twofold at 4 weeks in the NIA of the LV and remained elevated at 10 weeks. In the RV, type I collagen level increased 2.7-fold to a peak at 4 weeks and declined gradually to 1.7 times baseline at 10 weeks. The patterns of change in type I collagen level in the RV correlated with the changes in LV end-diastolic pressure (r = 0.73; P < .0001) and RV weight to body weight ratio (r = 0.73; P < .0001).

CONCLUSION

There is a relative greater increase of type I collagen level in the NIA and RV postinfarction, and this may lead to left and right ventricular dysfunction. Separate mechanisms might be involved in the induction of the different types of collagen deposition, with type I collagen levels apparently closely correlating with hemodynamic stress.

Expression of c-erbB receptors and ligands in human bronchial mucosa

The epidermal growth factor receptor (EGFR, c-erbB1) plays a pivotal role in maintenance and repair of epithelial tissues; however, little is known about coexpression of c-erbB receptors and their ligands in human bronchial epithelium. We therefore analyzed the expression of these molecules in cultured bronchial epithelial cells and normal bronchial mucosa, using reverse transcription-polymerase chain reaction (RT- PCR), flow cytometry, and immunohistochemistry. Messenger RNA (mRNA) encoding EGFR, c-erbB2, and c-erbB3, but not c-erbB4, was detected in primary cultures of human bronchial epithelial cells, as well as in the human bronchial epithelial-derived cell lines H292 and 16HBE 14o-. Transcripts encoding epidermal growth factor (EGF), heparin binding epidermal growth factor (HB-EGF), transforming growth factor-alpha (TGF-alpha), and amphiregulin (AR) were also detected, and expression of the three receptors and four ligands was confirmed by immunocytochemical staining of the cultured cells. Immunohistochemical analysis of resin- or paraffin-embedded sections from surgical specimens of bronchial mucosa revealed strong membrane staining for EGFR within the bronchial epithelium; this was particularly evident between basal cells and the basal aspect of columnar cells. The patterns of staining for c-erbB2 and c-erbB3 in the bronchial epithelium were similar to those for EGFR. Immunostaining for EGF, TGF-alpha, AR, HB- EGF, and betacellulin (BTC) was intense in the submucosal glands; with the exception of BTC, EGFR ligand immunoreactivity was also observed in the bronchial epithelium, where it paralleled EGFR staining. Colocalization of c-erbB receptors and ligands demonstrates the potential for productive c-erbB receptor interactions in bronchial epithelium. Further study of these interactions may help to define their role in maintenance and repair of the bronchial epithelium.

Recombinant human granulocyte-macrophage colony-stimulating factor applied locally in low doses enhances healing and prevents recurrence of chronic venous ulcers

BACKGROUND

Chronic venous leg ulcers have a major medical and economic impact on the elderly worldwide. Healing of the large ulcers (>10 cm2) occurs only in two-thirds of the patients and reulceration of healed ulcers recurs in one-third within 1 year. Because both healing and relapse rate influence greatly a patient's quality of life and the overall cost of treatment, every effort should be made to improve these two parameters.

OBJECTIVE

To determine the safety and efficacy of topical low-dose recombinant human granulocyte-macrophage colony-stimulating factor (rhu GM-CSF) for the treatment of venous ulcers, and to document any improvement in healing rates.

METHODS

Thirty-eight patients (29 women, 9 men; median age, 74 years) with chronic venous insufficiency were treated with topical rhu GM-CSF (5 microg/mL 0.9% sodium chloride solution), followed by application of a compression dressing. All subjects were treated as outpatients.

RESULTS

Complete healing was observed in 47 of the 52 ulcers (90.4%). The average healing time was 19 weeks. No systemic or local side-effects from the therapy were observed. Nine chronic ulcers, previously refractory to conventional treatment (pretreatment for more than 46 weeks), showed the same response rate (9/8, or 88.9%) and healing time (mean, 19 weeks). After 40 months, no reulceration of the healed ulcers was observed, but two patients developed new ulcers on the same leg. Healing remained stable, with excellent cosmetic results.

CONCLUSIONS

In this first study, topically applied low-dose rhu GM-CSF was a safe treatment for chronic venous leg ulcers. Healing rates were significantly increased and relapse rates were minimal.

Angiogenesis inhibitor TNP-470 inhibits murine cutaneous wound healing

BACKGROUND

TNP-470 (AGM-1470) is a potent inhibitor of angiogenesis with potential therapeutic applications in neoplastic and angio-proliferative diseases. This study evaluated its effect on cutaneous wound healing in a murine dorsal excisional wound model.

MATERIALS AND METHODS

Full-thickness wounds (1.60 cm2) were created on the dorsum of homozygous/hairless mice (7 to 9 weeks). Wound areas were measured on alternate days for 16 days. Experimental groups consisted of (1) TNP-470 administered in doses of 0.05, 0.5, and 5.0 mg/kg on Days 0, 2, and 4 or Days 0 through 6; (2) TNP-470 (5.0 mg/kg) coadministered with minocycline (4.0 and 10 mg/kg) on Days 0, 2, and 4; and (3) TNP-470 (5.0 mg/kg on Days 0, 2, and 4) coadministered with topical basic fibroblast growth factor (bFGF) 1. 0 microg/wound on Days 0, 1, and 2. Hematoxylin and eosin staining was used to compare experimental and control wounds.

RESULTS

TNP-470 administration significantly decreased wound healing in a dose-dependent manner versus controls (P <.05). The 5.0 mg/kg concentration yielded the greatest effect by maintaining an average wound area 20.4% greater than controls and a marked delay in wound healing on H&E staining. Alternate-day dosing was as effective as consecutive day administration. Minocycline did not augment the wound healing inhibition of TNP-470. Coadministration of TNP-470 and bFGF eliminated any rate-altering effect of TNP-470 upon wound healing and resulted in wound areas similar to controls.

CONCLUSION

Therapy with TNP-470 induces a significant delay in murine cutaneous wound healing. This effect may be exploited for use in situations where wound healing is excessive and debilitating. Topical application of bFGF can overcome TNP-470-induced wound healing inhibition.

Particle-mediated gene transfer of PDGF isoforms promotes wound repair

Several techniques for cutaneous gene transfer have been investigated for either in vitro or in vivo applications. In the present study, we investigated whether the direct delivery of platelet-derived growth factor cDNA into skin results in improvement in tissue repair. Cutaneous transfections were carried out in rats using a particle-bombardment device (Accell). As revealed by reverse transcriptase-polymerase chain reaction, transgene expression in vivo was transient, with low level expression by day 5. When compared with wounds transfected with a control cytomegalovirus-luciferase plasmid, wounds transfected with platelet-derived growth factor A or B in the MFG vector showed a significant increase in wound tensile strength 7 and 14 d after transfection. At both time points platelet-derived growth factor A transfected wounds exhibited the highest increase in tensile strength over controls, resulting in a 3.5-fold increase at day 7 and a 1.5-fold increase at day 14. The degree of stimulation was not remarkably different between wounds transfected with platelet-derived growth factor B, which is predominantly cell associated, or a truncation mutant, platelet-derived growth factor B211, which is predominantly secreted. These findings demonstrate that in vivo gene transfer by particle bombardment can be used to improve the tissue repair response. This approach provides a robust tool to assess the biologic activity of various proteins and will aid in the development of therapeutic cutaneous gene delivery.

Influence of Aloe vera on collagen characteristics in healing dermal wounds in rats

Wound healing is a fundamental response to tissue injury that results in restoration of tissue integrity. This end is achieved mainly by the synthesis of the connective tissue matrix. Collagen is the major protein of the extracellular matrix, and is the component which ultimately contributes to wound strength. In this work, we report the influence of Aloe vera on the collagen content and its characteristics in a healing wound. It was observed that Aloe vera increased the collagen content of the granulation tissue as well as its degree of crosslinking as seen by increased aldehyde content and decreased acid solubility. The type I/type III collagen ratio of treated groups were lower than that of the untreated controls, indicating enhanced levels of type III collagen. Wounds were treated either by topical application or oral administration of Aloe vera to rats and both treatments were found to result in similar effects.

Restraint stress slows cutaneous wound healing in mice

The impact of stress on cutaneous wound healing was assessed in a murine model. Female, hairless SKH-1 mice, 6-8 weeks of age were subjected to restraint stress (RST) 3 days before and for 5 days following dorsal application of a 3.5-mm sterile punch wound. Control mice were wounded, but not restrained. Using photography and image analysis, the rate of wound healing was compared between the two groups. Wounds on control mice healed on average 3.10 days sooner than RST-treated mice. In addition, cross-sectional, morphometric analysis of the dermal and epidermal layers revealed reduced inflammation surrounding wounds from RST mice at 1, 3, and 5 days after wounding. In the RST group, serum corticosterone levels averaged 162.5 ng/ml compared to 35.7 ng/ml in the controls. Treatment of RST-stressed animals with the glucocorticoid receptor antagonist RU40555 resulted in healing rates comparable to those of control animals. Thus, the reduction in inflammation and delayed healing correlated with serum corticosterone levels and suggest that disruption of neuroendocrine homeostasis modulates wound healing.

Gene therapy for tissue repair: approaches and prospects

Recent advances in molecular biology have resulted in the development of new technologies for the introduction and expression of genes in human somatic cells. This emerging field, known as gene therapy, is broadly defined as the transfer of genetic material to cells/tissues in order to achieve a therapeutic effect for inherited as well as acquired diseases. We and others are exploring the potential application of this technology to tissue repair. One primary focus has been to transfer genes encoding wound healing growth factors, a broad class of proteins which control local events in tissues such as cell proliferation, cell migration and the formation of extracellular matrix. Using several different strategies for gene transfer, wound healing growth factor genes have been introduced and expressed in cells and tissues in vitro as well as in vivo. Various experimental models of wound healing and tissue repair have been used to evaluate the efficacy of this new and exciting approach to tissue repair.

Tethered epidermal growth factor as a paradigm for growth factor-induced stimulation from the solid phase

We have tethered epidermal growth factor (EGF) to a solid substrate in a manner permitting the factor to retain its biological activity as assessed by both mitogenic and morphological assays. Mouse EGF was covalently coupled to aminosilane-modified glass via star poly(ethylene oxide) (PEO), which allows the ligand to retain significant mobility and active conformation. Tethered EGF was as effective as soluble EGF in eliciting DNA synthesis and cell rounding responses of primary rat hepatocytes under different surface conditions. In contrast, physically adsorbed EGF at comparable surface concentrations showed no activity. Presentation of growth factors in this manner may help to expedite their clinical use by permitting greater control of temporal and spatial availability in the extracellular environment.

Triple helix-forming oligonucleotide corresponding to the polypyrimidine sequence in the rat alpha 1(I) collagen promoter specifically inhibits factor binding and transcription

Type I and III fibrillar collagens are the major structural proteins of the extracellular matrix found in various organs including the myocardium. Abnormal and progressive accumulation of fibrillar type I collagen in the interstitial spaces compromises organ function and therefore, the study of transcriptional regulation of this gene and specific targeting of its expression is of major interest. Transient transfection of adult cardiac fibroblasts indicate that the polypurine-polypyrimidine sequence of alpha 1(I) collagen promoter between nucleotides - 200 and -140 represents an overall positive regulatory element. DNase I footprinting and electrophoretic mobility shift assays suggest that multiple factors bind to different elements of this promoter region. We further demonstrate that the unique polypyrimidine sequence between -172 and -138 of the promoter represents a suitable target for a single-stranded polypurine oligonucleotide (TFO) to form a triple helix DNA structure. Modified electrophoretic mobility shift assays show that this TFO specifically inhibits the protein-DNA interaction within the target region. In vitro transcription assays and transient transfection experiments demonstrate that the transcriptional activity of the promoter is inhibited by this oligonucleotide. We propose that TFOs represent a therapeutic potential to specifically influence the expression of alpha 1(I) collagen gene in various disease states where abnormal type I collagen accumulation is known to occur.