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,,
,,1
* Program in Developmental Biology, The Hospital for Sick Children, Toronto, Ontario, Canada;
The Institute for Medical Science, University of Toronto, Toronto, Ontario Canada;
Program in Cancer Research, Arthur and Sonia Labatts Brain Tumor Center, The Hospital for Sick Children, Toronto, Ontario, Canada; and
The Department of Surgery, University of Toronto, Toronto, Ontario, Canada
1Correspondence: 555 University Ave., Toronto, Ontario M5G1X8, Canada. E-mail: benjamin.alman{at}sickkids.ca
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Key Words: ß-catenin • wound healing • transgenic mice
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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2
3)
.
ß-Catenin plays a crucial role as a mediator in the canonical Wnt signaling pathway. In the presence of an appropriate Wnt ligand, a multiprotein complex including axin and GSK3ß inhibits the phosphorylation of amino terminal Ser/Thr residues of ß-catenin. When these residues are phosphorylated, ß-catenin is targeted for ubiquitin-mediated proteosomal degradation. When ß-catenin is not phosphorylated, it accumulates in the cell, translocates to the nucleus, binds to transcription factors of the tcf-lef family, and actives transcription (4
5
6)
.
ß-Catenin protein levels are elevated during the proliferative phase of wound healing, being expressed primarily in dermal mesenchymal cells, where it is transcriptionally active. ß-Catenin stabilization increases the proliferation rate, motility, and invasiveness of fibroblasts (7)
. Unlike its role in mesenchymal cells, ß-catenin is not transcriptionally active in epithelial cells during wound healing. Keratinocytes expressing null alleles of ß-catenin exhibit normal cell differentiation and proliferation (8)
; in wounds in human skin grown as organ culture, ß-catenin inhibits epithelial cell migration (9)
. These disparate roles for ß-catenin in the epithelial and mesenchymal components of wound healing make it difficult to determine its ultimate role in the healing process. This is of clinical importance, as pharmacologic agents such as lithium (10)
can be used to modulate ß-catenin-mediated signaling, and such agents could be used to treat disorders of wound healing if the role of ß-catenin in the process was better defined.
How ß-catenin interacts with other factors important in the wound healing process is poorly understood. Factors expressed during the earlier phases of wound healing were investigated for effects on ß-catenin protein and TCF-dependent transcription. Among the variety of growth factors expressed during the initial stage of healing, transforming growth factor ß (TGF-ß) was found to substantially activate ß-catenin-mediated, TCF-dependent signaling in primary fibroblast cultures (11)
. TGF-ß is secreted early in wound healing (12)
. Active TGF-ß exerts its biological functions by binding to a heteromeric receptor complex consisting of a type I and type II receptor, both of which have intrinsic serine-threonine kinase activity (13)
. In addition to active forms, latent TGF-ßs are also produced and sequestered within the wound matrix, allowing sustained release by proteolytic enzymes. The three TGF-ß isoforms have both distinct and overlapping functions in wound healing, where they are mitogenic for fibroblasts (1
, 2)
.
The canonical TGF-ß signaling pathway activates Smad transcription factors (14
15
16
17
18)
. There are five receptor-activated Smads, a common mediator Smad4, and two inhibitory Smads. The receptor-activated Smads are phosphorylated by the type I TGF-ß receptor. Phosphorylated Smads 2 and 3 bind to Smad4, translocate to the nucleus, and activate their downstream targets. Some effects of TGF-ß on wound repair require Smad3 (19)
. After full-thickness incisional wounding, Smad3 null mice exhibit an enhanced rate of epithelialization associated with a reduction in the number of fibroblasts, leading to an overall decrease in wound size (19
20
21
22
23)
.
Many previous studies of ß-catenin in wound healing use in vitro techniques (8
, 9
, 11)
. Since wound repair is a complex process involving the interplay of several cell types, signaling pathways, extracellular matrix components, and soluble factors, the role of various factors and their interactions is best evaluated using an in vivo approach. However, since ß-catenin plays a crucial role during development, mice expressing null or stabilized alleles of ß-catenin in the germ line are not viable. Using conditional alleles is an advantageous technique to study the role of ß-catenin in wound healing, but driving expression of these conditional alleles in specific cell types has the disadvantage of allowing investigation only in a particular cell type. Since a variety of cells are involved in the wound healing process, we investigated the role of ß-catenin and its interaction with TGFß signaling using regulation of conditional alleles by an adenovirus expressing cre-recombinase.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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, which when subjected to cre-recombinase results in a null allele. The Catnblox(ex3) strain contains loxP sequences flanking exon three (25)
. When subjected to cre-recombinase, this results in the expression of a fully functional but stabilized protein. As reported (7)
, TCF reporter mice (TCF-ß-gal) contain a lacZ gene downstream of a c-fos minimal promoter and three consensus TCF binding motifs. Binding of a ß-catenin-TCF complex activates the expression of lacZ (7)
. Mice homozygous for a smad3 targeted null mutation (26)
were used to assess the role of TGFß signaling on healing and were crossed with TCF-ß-gal or Catnblox(ex3) mice. All of the mouse crosses were performed using the same strategy as in our earlier studies (27)
, so that the phenotype would always be compared between littermate controls.
Adenovirus generation
Ad-Cre (Ad:CMV-Cre-IRES-EGFP) was constructed using the Transpose-AdTM Adenoviral Vector System (Q. Biogene, Montreal, Quebec, Canada). An EGFP tag was added to Cre-recombinase (from Dr. Nagy, Toronto) and subcloned into pCR259, a transfer vector containing the human CMV promoter/enhancer (Q. Biogene). The adenovirus (E1, E3 deletion) was generated by homologous recombination of pCR259-Cre-IRES-EGFP with the Transpose-AdTM 294 plasmid. Recombinant virus was grown and titrated in human embryonic kidney (HEK293) cells. Expression of Cre in purified virus was confirmed using Western analysis (antibody from Novagen, Darmstadt, Germany). An identical virus, lacking expression of the transgene but expressing EGFP, was used as a control.
Adenovirus administration, detection of transgene expression, and detection of cre-mediated recombination
Diluted aliquots (1x108 pfu in 50 µL) of the Ad-cre were injected both in an IP and subcutaneous location into the various mice 4 days prior to wounding. A reduction in ß-catenin protein in wounds from mice infected with the virus was verified using Western analysis. Infection rate was determined by detection of GFP using immunoflorescence in the skin samples removed in generation of the full thickness wounds. Cre-mediated deletion of ß-catenin gene exon 3 deletion of floxed allele in Catnbtm2Kem was confirmed by PCR as described previously (24)
. To verify the effectiveness of cre to cause recombination in cells in the wound, tissues from a mouse expressing the Gt(ROSA)26Sortm1Sor allele (Jackson Labs, Bar Harbor, ME, USA) were examined in which cells expresses LacZ when exposed to Cre (28)
.
Cell culture and treatments
Primary dermal fibroblast cultures and keratinocyte cultures were derived from the various mice as reported (7
, 8)
. Cells from the Catnbtm2Kem mice were treated with Ad-cre or the control virus. Cell sorting was used to select a population of cells infected with either Ad-Cre or the control virus. To study whether Smad3 deficiency alters the effect of TGF-ß1 on ß-catenin-mediated signaling, cells from Smad3–/–;TCF-ß-gal mice and controls were used. For TGF-ß1 stimulation studies, cells were kept in 0.5% serum medium 24 h before treatment and media was replaced with serum-free medium containing carrier or recombinant TGF-ß1 (10 ng/mL, Sigma). The dose was selected from studies showing this to be the most effective dose for fibroblast proliferation. Proliferation was measured using bromodeoxyuridine (Brdu, 10 µM) incorporation over 12 h. Cells were stained for Brdu and percent incorporation was determined by counting cells > 10 high-powered fields. There was no difference in proliferation rates between cells infected with the control virus and uninfected cells. Each cell culture experiment was performed nine times.
Protein analysis
Western analysis was performed using antibodies against ß-catenin (Transduction Laboratories, Lexington, KY, USA), Ser9 phospho-GSK3ß (Upstate Biotechnology, Lake Placid, NY, USA), total GSK-3ß (Transduction Laboratories), or actin (Sigma). Beta-galactosidase activity was quantified by measuring ONPG incorporation. Values were normalized by protein concentration and expressed as the percentage change in OD level relative to control.
Wound healing experiments
Each wounding experiment was performed six times on 6-wk-old male mice. In each experiment, littermate mice were used for controls. Two 4 mm diameter full-thickness skin wounds were generated using a dermal biopsy punch (Miltex Instrument Company, York, PA, USA). Mice were killed 3, 8, or 14 days after wounding, and wounds were harvested and processed for histology, protein extraction, or RNA analysis. For mice injected with an adenovirus, the wounding site overlapped the site of injection. The punch biopsy sample was used to verify infection with the adenovirus by detection of GFP, and changes in ß-catenin protein levels were verified using Western analysis. 1 mg TGFß1 was injected subcutaneously along with 50 mL vehicle in select mice. For mice treated with lithium, 600 mg/L of lithium or sodium control (along with sucrose) was added to the drinking water starting 2 wk prior to wounding, a dose reported to be effective (29)
.
Histology
Serial histology sections were cut at a right angle to the skin surface across the wound and the section at the center of the wound with the largest wound diameter was chosen for comparison between samples. Samples were stained using trichrome to more easily measure the size of the collagen-rich dermal component of the wound and H&E for analysis of cell numbers and types in the wound. Wound sizes and cell numbers were measured by an observer blinding to the experimental details.
Analysis of inflammatory cell types
To determine the numbers of lymphocytes present, sections from the earliest time period wounds were stained using a mouse CD3 antibody (Biocarta, San Diego, CA, USA), as previously reported to detect lymphocytes (30)
. The Mac-3 antibody (BD PharMingen, San Diego, CA, USA) was used to detect macrophage cells (31)
. Giemsa staining was performed, as reported (32)
, to detect granular cells. At least 10 high-powered fields were examined from each wound, and the mean number of lymphocytes, macrophages, and granular cells per high-powered was field were averaged for each sample. The means, standard deviations, and 95% confidence intervals were then calculated from wounds from mice expressing the various ß-catenin conditional alleles and from mice expressing wild-type alleles.
RNA preparation and quantitative RT-PCR
RNA analysis was performed in wounds from mice 14 days after wounding. Wounds and unwounded skin from Catnbtm2Kem mice treated with Ad-Cre or Ad-GFP and with TGF-ß1 or carrier were harvested for analysis. Quantitative RT-PCR for Mmp-3, Mmp-14, and Gapdh was carried out using the ABI 7900 (Applied Biosystems, Foster City, CA, USA) with sybergreen master mix. Relative concentrations for wound samples were calculated using the comparative CT method.
Statistical Analysis
Data are presented as the mean ± 95% confidence intervals. The Student’s t test was used to compare results between treatment groups.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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, Catnblox(ex3) (conditional stabilized ß-catenin) (25)
, or Gt(ROSA)26Sortm1Sor (Cre reporter) (26)
homozygous mice. Cre was expressed at high levels in wounded tissues from mice treated with Ad-cre but was absent in mice treated with Ad-GFP (Fig. 1
A). PCR confirmed genomic recombination in wound samples (data not shown). ß-Catenin levels were examined in wound tissues 8 days after injury, as this is when these levels are highest in normal wound repair (7)
. ß-Catenin level in mice expressing the Catnbtm2Kem allele was 33% of wild-type levels, while ß-catenin level in mice expressing the Catnblox(ex3) allele was twice that of wild-type mice. (Fig. 1B
). GFP and Cre protein were identified in 
two-thirds of cells in the wound tissues (Fig. 1C, D
). Using Gt(ROSA)26Sortm1Sor mice, we verified that two-thirds of cells showed effective cre-recombinase activity, as detected by ß-galactosidase (Fig. 1E
). To study the effect of the virus itself on wound healing, we investigated wild-type mice and found no difference in the wound phenotype after infection with either the Ad-cre or the control virus.
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We previously reported that a transgenic mouse expressing ß-catenin driven by a CMV regulated promoter developed larger sized wounds (7)
. To determine whether using the Ad-cre driven recombination results in a similar wound phenotype, we investigated Catnblox(ex3) mice. These mice developed larger wounds than wild-type mice infected with the virus, primarily due to an increase in the size of the mesenchymal, dermal component (Fig. 1F, G, I
). There was no change in the height of the epithelial component compared with wild-type mice, and there was a substantial increase in the number of dermal, mesenchymal cells (Fig. 1J
). Histological analysis did not reveal a major change in the proportion of the cell types present within the healing wound.
ß-Catenin regulates wound size
We then used mice homozygous for the Catnbtm2Kem (knockout) allele to study the effect of ß-catenin deficiency on wound healing. Mice were examined for wound size after Ad-cre or Ad-GFP infection. Wounds in mice expressing the Catnbtm2Kem allele were of a smaller diameter than control wounds (Fig. 1F, H, J
). The small size was related to a substantial decrease in the size of the dermal component and was associated with a smaller number of cells present. There was no difference in the height of the epithelial component of the wound, nor was there a major change in the proportion of cell types present. These concordant results show that ß-catenin regulates the size of wounds and the accumulation of dermal fibroblasts during healing.
ß-Catenin did not regulate the rate of wound closure or the number of inflammatory cells present
Wounds from various mice were examined 3 days after injury, a time when mice deficient in Smad3 show early epithelial closure (19)
. We did not observe epithelial closure in the wounds from mice expressing any of the ß-catenin conditional alleles or in mice expressing wild-type ß-catenin alleles, suggesting that ß-catenin did not alter the rate of wound healing. The number of inflammatory cells per high-powered field was also compared between the wounds from various mice. No significant difference in the numbers of inflammatory cells identified in the early wounds was noted (Fig. 2
).
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The wound phenotype in smad3–/– mice is regulated by ß-catenin
Since Smad3–/– mice are known to have a wound phenotype characterized by a smaller wound size (19
20
21
22
23)
, we examined whether this phenotype is mediated through ß-catenin. We first crossed Smad3–/– mice (26)
with the tcf reporter mice to determine whether Smad3 deficiency alters the activation of ß-catenin-mediated signaling during healing. Changes in ß-catenin and Ser-9 phosphorylated GSK-3ß protein were assessed using Western analysis and tcf-dependent transcriptional activity was measured by ß-galactosidase activity. Ser-9 phosphorylated GSK-3ß levels correlate with activation of the canonical Wnt signaling pathway (5)
. We observed the expected increase in the protein level of ß-catenin in wounds in Smad3+/+ mice, whereas wounds in Smad3–/– mice showed only a very small change in ß-catenin protein level compared with unwounded skin (Fig. 3
A). Ser-9 phosphorylated GSK-3ß protein correlated with ß-catenin protein levels, suggesting that the effect is mediated by GSK-3ß (Fig. 3A
). There was an expected increase in ß-galactosidase activity in wounds from wild-type mice, indicative of an increase in tcf-dependent transcription, but there was little change in activity in fibroblasts from Smad3–/– mice (Fig. 3B
).
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Since Smad3–/– mice exhibit small wounds and lower levels of ß-catenin, we used mice expressing the Catnblox(ex3) allele to determine whether ß-catenin stabilization could revert the smaller size of wounds in Smad3-deficient mice to the size of a wound in a wild-type mice. Smad3–/– mice homozygous for the Catnblox(ex3) allele were treated with Ad-cre or the control virus. Smad3–/– mice, which expressed the stabilized form of ß-catenin developed cutaneous wounds close in size as those in Smad3+/+ mice, with a larger number of fibroblast cells present (Fig. 3C-E
). Thus, the effect of Smad3 deficiency on its wound healing phenotype can be bypassed by the expression of a stabilized form of ß-catenin.
ß-Catenin is required for the TGF-ß1 induced hypertrophic wound phenotype
Injection of TGFß1 subdermally before wounding results in the development of a hypertrophic wound with a substantially larger dermal component (12)
. To determine whether the hypertrophic wound phenotype is due to higher levels of ß-catenin protein, we investigated the size of wounds formed after TGFß1 injection in mice expressing the Catnbtm2Kem allele There was a substantially smaller size to wounds formed in the Catnbtm2Kem mice treated with TGFß1 and Ad-cre compared with those treated with TGFß1 and the control virus (Fig. 4
).
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ß-Catenin is required for the regulation of MMP3 and MMP14 by TGFß during wound healing
TGFß stimulation prior to wounding is associated with an increase in expression of a variety of genes, including matrix metalloproteinases (MMPs) (33)
. To determine whether ß-catenin is also required for TGFß to regulate gene expression, we examined the expression of two MMPs known to be up-regulated in fibrous proliferations (34
, 35)
. Expression of Mmp-3 and Mmp-14 was assayed in wounds and normal unwounded tissue using quantitative PCR. Mmp-3 and Mmp-14 mRNA expression was substantially increased in wounds compared with unwounded tissues 2 wk after injury. In wounds treated with TFG-ß, there was a further increase by 40% and 55%, respectively. However, in mice expressing ß-catenin null alleles, Mmp levels were lower and TGFß was not able to induce a higher level of Mmp expression (Fig. 5
).
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ß-Catenin is required for TGF-ß1 to increase cell proliferation in dermal fibroblasts
ß-Catenin is reported to have disparate effects on keratinocytes and fibroblasts, but its ability to mediate cell processes regulated by TGFß is unknown. We generated primary dermal fibroblast and keratinocyte cultures from the mice, and examined their proliferation rate and the ability of TGFß1 to regulate proliferation in cells expressing ß-catenin null alleles. Cultures were derived from mice containing the Catnbtm2Kem allele, treated with Ad-Cre, or the control Ad-GFP, and sorted to select a population of infected cells. Cells were treated overnight with TGF-ß1 or vehicle. TGF-ß1 treatment increased the percentage of cells exhibiting BrdU incorporation in cells expressing wild-type ß-catenin. In cells expressing null ß-catenin alleles, there was a lower baseline proliferation rate, and TGF-ß1 was not able to induce a higher proliferation rate (Fig. 6
). In contrast, kerationocytes exhibited the same rate of cell proliferation in cells expressing wild-type or null ß-catenin alleles. TGFß1 treatment resulted in a slight decrease in cell proliferation, and this changed also occurred in cells expressing ß-catenin null alleles. ß-Catenin has a substantial effect regulating fibroblast cell proliferation and the response to TGFß1, while it has little effect on keratinocyte proliferation.
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Lithium treatment increases ß-catenin protein level and wound size
To determine whether a pharmacologic agent would have a similar effect as we found using the mice expressing conditional alleles, we examined mice treated with lithium, an agent known to activate ß-catenin-mediated transcription. Mice treated with lithium exhibited an increase in ß-catenin protein level, and healed with larger sized wounds, reminiscent of those found in mice expressing the stabilized ß-catenin allele (Fig. 7
).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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We used an adenoviral approach to regulate expression of conditional alleles, as this would infect a variety of cell types implicated in the healing process and would avoid issues of ß-catenin dysregulation during fetal development. Although the virus we used did not infect all cells, a substantial percentage of cells in the wounds were infected. The mosaic inactivation of ß-catenin allowed us to investigate the role of ß-catenin in wound healing as complete inhibition of ß-catenin signaling may be incompatible with survival. Since we and others (36)
found that infection with adenovirus itself has no effect on wound healing, use of Ad-cre is an effective technique to activate conditional alleles to study their effect on cutaneous wound healing.
Despite the profound effect of ß-catenin deficiency on proliferation in dermal fibroblasts, there is little effect on keratinocytes. A recent study using explant cultures from human skin found that ß-catenin activation inhibited keratinocyte migration across the wound (9)
. Thus, it seems that although ß-catenin may have an inhibitory effect of kerationocytes, on balance it has a positive effect, enhancing wound healing. The difference in the role of ß-catenin between mesenchymal cells and epithelial cells in healing provides further evidence that the molecular mechanisms controlling mesenchymal cell responses to healing differ from the mechanisms controlling epithelial cells. TGFß is also thought to have opposing effects in regulating proliferation in epithelial and mesenchymal dermal cells during healing (12)
. The data that ß-catenin is required for TGFß to induce cell proliferation in fibroblasts, cells in which ß-catenin-mediated, tcf-dependent transcription is activated in wound healing, but not in keratinocytes, cells in which ß-catenin-mediated transcription is not active during wound healing, raise the intriguing possibility that the ability of TGFß to induce cell proliferation is dependent on the ability to activate ß-catenin-mediated tcf-dependent signaling in a particular cell type.
There are a number of ways in which TGF-ß signaling and ß-catenin signaling may interact. For instance, Smad, ß-catenin, and TCF can synergistically regulate transcription (5
, 37)
. TGF-ß signaling may regulate ß-catenin-mediated, TCF-dependent transcription in a more direct manner, such as through TAK1, a kinase activated by TGF-ß, which regulates the NLK-MAPK related signaling pathway (38
, 39)
. TGF-ß may also interact with the canonical Wnt pathway through direct phosphorylation of members of the multiprotein complex regulating ß-catenin degradation (40)
. Our earlier data show that TGF-ß regulates ß-catenin-mediated signaling independent of transcriptional regulation of ß-catenin in dermal fibroblasts, most likely through a GSK3ß-mediated mechanism (11)
. The finding that Smad3–/– cells are incapable of up-regulating ß-catenin and tcf-dependent activation suggests that this regulation requires Smad–dependent transcription. Thus, our data are most consistent with a role for TGFß regulating ß-catenin through a Wnt ligand. However, the specific mechanism is not fully elucidated.
TGFß injection prior to wound healing results in a hyperplastic wound and alters expression of a variety of genes, such as MMPs. MMPs are also up-regulated in aggressive fibromatosis, a fibroproliferative lesion driven by ß-catenin-mediated transcription (34
, 35)
, suggesting that they are ß-catenin target genes in mesenchymal cells. During wound healing, we found elevated levels of Mmp-3 and Mmp-14 in the late proliferative phase of wound healing, and that there was substantially further increases in expression after TGFß stimulation. However, in ß-catenin-deficient TGFß was unable to cause this increased expression of Mmp-3 and Mmp-14. Thus ß-catenin not only regulates the increased wound size caused by TGFß stimulation, but also regulates the expression of TGFß regulated genes during wound healing.
During wound healing, the mesenchymal cells that accumulate in the wound have their source from a variety of locations, including cells in the bone marrow (41
, 42)
. Wnt signaling and ß-catenin can act to maintain adult stem cells in a less differentiated state, and they play such a role in mesenchymal progenitor cells, inhibiting their differentiation (43
44
45
46
47)
. Since the mesenchymal cells populating the wound initially act like less differentiated precursor cells, it is possible that maintaining cells in a less differentiated state is important in the accumulation of fibroblasts in the healing tissues. ß-Catenin may play a role inhibiting terminal differentiation in wound healing. Perhaps TGFß signaling and ß-catenin signaling act together to specify cell fate in the healing fibroblast.
In contrast to the changes observed in mice deficient in Smad3 (19
20
21
22
23)
, wounds from our mice expressing ß-catenin conditional alleles did not show evidence of an accelerated rate of healing, or changes in the numbers of inflammatory cells present. Although ß-catenin may play an important role in regulating inflammatory cell function, the local effect of the Ad-cre, likely is partially responsible for the lack of an observed alteration in the nature of the inflammatory cell infiltrate. The potential negative regulation by ß-catenin on keratinocyte migration (9)
could in part explain the lack of a change in the rate of healing in the mice expressing the conditional ß-catenin alleles.
Successful cutaneous wound healing requires the coordination of a variety of cell types. We found that ß-catenin plays a crucial role regulating the mesenchymal cells during cutaneous healing. In contrast, ß-catenin is not transcriptionally active in epithelial cells, does not regulate cell keratinocyte proliferation, and there is no wound phenotype described in mice expressing conditional ß-catenin null alleles in keratinocytes (48)
. The finding that a signaling pathway primarily active in the dermal compartment regulates wound size, a process in which epithelial cells also play an important role, suggests a close interaction between the various cell types in wound healing. Changing the properties of the dermal compartment will also change the behavior of the epithelial cells. This finding has important implications in the development of therapies for deficient or hyperplastic wounds, as it raises the possibility that targeting one cell type can regulate wound size. In conditions of insufficient wound healing associated with decreased numbers of fibroblasts, such as wounds in patients undergoing radiation therapy, a treatment such as lithium may help to improve outcome. Our data using lithium treatment in mice suggest that such a therapeutic approach is possible.
We show a crucial role for ß-catenin regulating wound size. The wound phenotypes caused by TGF-ß signaling hyperactivity or inhibition can be overcome by deficiency or stabilization of ß-catenin respectively. ß-Catenin protein level regulates the size of murine wounds, and our earlier work in human wounds shows that hyperplastic wounds express a prolonged duration of an elevated ß-catenin protein level. ß-Catenin may act as a mediator, linking the expression of factors important in early wound healing (e.g., TGFß) with factors important in the later remodeling phase (MMPs). Although there are differences in wound healing between mice and humans, we recently found that ß-catenin protein levels are regulated in human wound healing in a similar way as in mice and that hyperplastic human wounds demonstrate prolonged expression of elevated ß-catenin levels (49)
. These data suggest a similar role for ß-catenin in human and murine wound healing. Given its role as a potential mediator regulating wound size, ß-catenin is an enticing target for the treatment of disorders of wound healing.
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ACKNOWLEDGMENTS |
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Received for publication July 29, 2005. Accepted for publication December 8, 2005.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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