Mice lacking Smad3 show accelerated wound healing and an impaired local inflammatory response

Asymmetric migration of human keratinocytes under mechanical stretch and cocultured fibroblasts in a wound repair model

Keratinocyte migration during re-epithelization is crucial in wound healing under biochemical and biomechanical microenvironment. However, little is known about the underlying mechanisms whereby mechanical tension and cocultured fibroblasts or keratinocytes modulate the migration of keratinocytes or fibroblasts. Here we applied a tensile device together with a modified transwell assay to determine the lateral and transmembrane migration dynamics of human HaCaT keratinocytes or HF fibroblasts. A novel pattern of asymmetric migration was observed for keratinocytes when they were cocultured with non-contact fibroblasts, i.e., the accumulative distance of HaCaT cells was significantly higher when moving away from HF cells or migrating from down to up cross the membrane than that when moving close to HF cells or when migrating from up to down, whereas HF migration was symmetric. This asymmetric migration was mainly regulated by EGF derived from fibroblasts, but not transforming growth factor α or β1 production. Mechanical stretch subjected to fibroblasts fostered keratinocyte asymmetric migration by increasing EGF secretion, while no role of mechanical stretch was found for EGF secretion by keratinocytes. These results provided a new insight into understanding the regulating mechanisms of two- or three-dimensional migration of keratinocytes or fibroblasts along or across dermis and epidermis under biomechanical microenvironment.

An electrospun scaffold loaded with anti-androgen receptor compound for accelerating wound healing

Current dermal regenerative scafolds provide wound coverage, and structural support and guidance for tissue repair, but usually lack enough bio-signals needed for speeding up skin cell growth, migration, wound closure, and skin regeneration. In this study, an androgen receptor (AR) inhibitor called ASC-J9 is used to demonstrate the concept and feasibility of fabricating drug-loaded scafolds via electrospinning. Inhibition of androgen is known to promote skin wound healing. The novel ASC-J9 - loaded porous scafold was fabricated for skin wound repair using electrospun fibers of collagen and polycaprolactone (PCL) blend. Our preliminary results indicated that ASC-J9 - loaded scafolds facilitated more efficient attachment and ingrowth of dermal fbroblasts, compared to the control collagen-PCL scafold. A signifcant increase of cell proliferation was observed with the drug-loaded scafold over a 28-day period. The drug-loaded scafold also accelerated keratinocyte migration and wound closure in a contraction-inhibited mouse wound model over 21 days. The data indicated a sustained release of ASC-J9 from the scafold and its potential to accelerate wound healing by promoting cell proliferation and migration over an extended period of time. More importantly, our results proved the concept and feasibility of fabricating drug-releasing or bioactive dermal scaffolds for more efective wound healing.

Differential topical susceptibility to TGFβ in intact and injured regions of the epithelium: key role in myofibroblast transition

Intact and cell contact–deprived regions of an epithelial monolayer are differentially sensitive to the transforming effect of TGFβ. This topical susceptibility is mediated by the interplay between TGFβ- and cell contact–dependent transcription factors and might play a key role in the cell biology of wound healing and fibrosis.

Induction of epithelial–myofibroblast transition (EMyT), a robust fibrogenic phenotype change hallmarked by α-smooth muscle actin (SMA) expression, requires transforming growth factor-β1 (TGFβ) and the absence/uncoupling of intracellular contacts. This suggests that an “injured” epithelium may be topically susceptible to TGFβ. To explore this concept, we use an epithelial wound model in which intact and contact-deprived regions of the same monolayer can be analyzed simultaneously. We show that TGFβ elicits dramatically different responses at these two loci. SMA expression and initially enhanced nuclear Smad3 accumulation followed by Smad3 mRNA and protein down-regulation occur exclusively at the wound. Mechanistically, three transcriptional coactivators whose localization is regulated by cell contact integrity are critical for these local effects. These are myocardin-related transcription factor (MRTF), the driver of the SMA promoter; β-catenin, which counteracts the known inhibitory effect of Smad3 on MRTF and maintains MRTF protein stability and mRNA expression in the wound; and TAZ, a Hippo effector and Smad3 retention factor. Remarkably, active TAZ stimulates the SMA and suppresses the Smad3 promoter, whereas TAZ silencing prevents wound-restricted expression of SMA and loss of Smad3. Such locus-specific reprogramming might play key roles in wound healing and the susceptibility of the injured epithelium to fibrogenesis.

Cell cycle regulation and regeneration

Regeneration of ear punch holes in the MRL mouse and amputated limbs of the axolotl show a number of similarities. A large proportion of the fibroblasts of the uninjured MRL mouse ear are arrested in G2 of the cell cycle, and enter nerve-dependent mitosis after injury to form a ring-shaped blastema that regenerates the ear tissue. Multiple cell types contribute to the establishment of the regeneration blastema of the urodele limb by dedifferentiation, and there is substantial reason to believe that the cells of this early blastema are also arrested in G2, and enter mitosis under the influence of nerve-dependent factors supplied by the apical epidermal cap. Molecular analysis reveals other parallels, such as; (1) the upregulation of Evi5, a centrosomal protein that prevents mitosis by stabilizing Emi1, a protein that inhibits the degradation of cyclins by the anaphase promoting complex and (2) the expression of sodium channels by the epidermis. A central feature in the entry into the cell cycle by MRL ear fibroblasts is a natural downregulation of p21, and knockout of p21 in wild-type mice confers regenerative capacity on non-regenerating ear tissue. Whether the same is true for entry into the cell cycle in regenerating urodele limbs is presently unknown.

Smad phospho-isoforms direct context-dependent TGF-β signaling

Better understanding of TGF-β signaling has deepened our appreciation of normal epithelial cell homeostasis and its dysfunction in such human disorders as cancer and fibrosis. Smad proteins, which convey signals from TGF-β receptors to the nucleus, possess intermediate linker regions connecting Mad homology domains. Membrane-bound, cytoplasmic, and nuclear protein kinases differentially phosphorylate Smad2 and Smad3 to create C-tail (C), the linker (L), or dually (L/C) phosphorylated (p, phospho-) isoforms. According to domain-specific phosphorylation, distinct transcriptional responses, and selective metabolism, Smad phospho-isoform pathways can be grouped into 4 types: cytostatic pSmad3C signaling, mitogenic pSmad3L (Ser-213) signaling, invasive/fibrogenic pSmad2L (Ser-245/250/255)/C or pSmad3L (Ser-204)/C signaling, and mitogenic/migratory pSmad2/3L (Thr-220/179)/C signaling. We outline how responses to TGF-β change through the multiple Smad phospho-isoforms as normal epithelial cells mature from stem cells through progenitors to differentiated cells, and further reflect upon how constitutive Ras-activating mutants favor the Smad phospho-isoform pathway promoting tumor progression. Finally, clinical analyses of reversible Smad phospho-isoform signaling during human carcinogenesis could assess effectiveness of interventions aimed at reducing human cancer risk. Spatiotemporally separate, functionally different Smad phospho-isoforms have been identified in specific cells and tissues, answering long-standing questions about context-dependent TGF-β signaling.

Cytokine mediated tissue fibrosis

Acute inflammation is a recognised part of normal wound healing. However, when inflammation fails to resolve and a chronic inflammatory response is established this process can become dysregulated resulting in pathological wound repair, accumulation of permanent fibrotic scar tissue at the site of injury and the failure to return the tissue to normal function. Fibrosis can affect any organ including the lung, skin, heart, kidney and liver and it is estimated that 45% of deaths in the western world can now be attributed to diseases where fibrosis plays a major aetiological role. In this review we examine the evidence that cytokines play a vital role in the acute and chronic inflammatory responses that drive fibrosis in injured tissues. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Smad2 and myocardin-related transcription factor B cooperatively regulate vascular smooth muscle differentiation from neural crest cells

RATIONALE

Vascular smooth muscle cell (VSMC) differentiation from neural crest cells (NCCs) is critical for cardiovascular development, but the mechanisms remain largely unknown.

OBJECTIVE

Transforming growth factor-β (TGF-β) function in VSMC differentiation from NCCs is controversial. Therefore, we determined the role and mechanism of a TGF-β downstream signaling intermediate Smad2 in NCC differentiation to VSMCs.

METHODS AND RESULTS

By using Cre/loxP system, we generated a NCC tissue-specific Smad2 knockout mouse model and found that Smad2 deletion resulted in defective NCC differentiation to VSMCs in aortic arch arteries during embryonic development and caused vessel wall abnormality in adult carotid arteries where the VSMCs are derived from NCCs. The abnormalities included 1 layer of VSMCs missing in the media of the arteries with distorted and thinner elastic lamina, leading to a thinner vessel wall compared with wild-type vessel. Mechanistically, Smad2 interacted with myocardin-related transcription factor B (MRTFB) to regulate VSMC marker gene expression. Smad2 was required for TGF-β-induced MRTFB nuclear translocation, whereas MRTFB enhanced Smad2 binding to VSMC marker promoter. Furthermore, we found that Smad2, but not Smad3, was a progenitor-specific transcription factor mediating TGF-β-induced VSMC differentiation from NCCs. Smad2 also seemed to be involved in determining the physiological differences between NCC-derived and mesoderm-derived VSMCs.

CONCLUSIONS

Smad2 is an important factor in regulating progenitor-specific VSMC development and physiological differences between NCC-derived and mesoderm-derived VSMCs.

Loss of epithelial hypoxia-inducible factor prolyl hydroxylase 2 accelerates skin wound healing in mice

Skin wound healing in mammals is a complex, multicellular process that depends on the precise supply of oxygen. Hypoxia-inducible factor (HIF) prolyl hydroxylase 2 (PHD2) serves as a crucial oxygen sensor and may therefore play an important role during reepithelialization. Hence, this study was aimed at understanding the role of PHD2 in cutaneous wound healing using different lines of conditionally deficient mice specifically lacking PHD2 in inflammatory, vascular, or epidermal cells. Interestingly, PHD2 deficiency only in keratinocytes and not in myeloid or endothelial cells was found to lead to faster wound closure, which involved enhanced migration of the hyperproliferating epithelium. We demonstrate that this effect relies on the unique expression of β3-integrin in the keratinocytes around the tip of the migrating tongue in an HIF1α-dependent manner. Furthermore, we show enhanced proliferation of these cells in the stratum basale, which is directly related to their attenuated transforming growth factor β signaling. Thus, loss of the central oxygen sensor PHD2 in keratinocytes stimulates wound closure by prompting skin epithelial cells to migrate and proliferate. Inhibition of PHD2 could therefore offer novel therapeutic opportunities for the local treatment of cutaneous wounds.

Pharmacogenomics in colorectal cancer: a genome-wide association study to predict toxicity after 5-fluorouracil or FOLFOX administration

The development of genotyping technologies has allowed for wider screening for inherited causes of variable outcomes following drug administration. We have performed a genome-wide association study (GWAS) on 221 colorectal cancer (CRC) patients that had been treated with 5-fluorouracil (5-FU), either alone or in combination with oxaliplatin (FOLFOX). A validation set of 791 patients was also studied. Seven SNPs (rs16857540, rs2465403, rs10876844, rs10784749, rs17626122, rs7325568 and rs4243761) showed evidence of association (pooled P-values 0.020, 9.426E-03, 0.010, 0.017, 0.042, 2.302E-04, 2.803E-03) with adverse drug reactions (ADRs). This is the first study to explore the genetic basis of inter-individual variation in toxicity responses to the administration of 5-FU or FOLFOX in CRC patients on a genome-wide scale.

Critical Role of Transforming Growth Factor Beta in Different Phases of Wound Healing

SIGNIFICANCE

This review highlights the critical role of transforming growth factor beta (TGF-β)1-3 within different phases of wound healing, in particular, late-stage wound healing. It is also very important to identify the TGF-β1-controlling factors involved in slowing down the healing process upon wound epithelialization.

RECENT ADVANCES

TGF-β1, as a growth factor, is a known proponent of dermal fibrosis. Several strategies to modulate or regulate TGF's actions have been thoroughly investigated in an effort to create successful therapies. This study reviews current discourse regarding the many roles of TGF-β1 in wound healing by modulating infiltrated immune cells and the extracellular matrix.

CRITICAL ISSUES

It is well established that TGF-β1 functions as a wound-healing promoting factor, and thereby if in excess it may lead to overhealing outcomes, such as hypertrophic scarring and keloid. Thus, the regulation of TGF-β1 in the later stages of the healing process remains as critical issue of which to better understand.

FUTURE DIRECTIONS

One hypothesis is that cell communication is the key to regulate later stages of wound healing. To elucidate the role of keratinocyte/fibroblast cross talk in controlling the later stages of wound healing we need to: (1) identify those keratinocyte-released factors which would function as wound-healing stop signals, (2) evaluate the functionality of these factors in controlling the outcome of the healing process, and (3) formulate topical vehicles for these antifibrogenic factors to improve or even prevent the development of hypertrophic scarring and keloids as a result of deep trauma, burn injuries, and any type of surgical incision.

Transforming Growth Factor Beta Signaling in Cutaneous Wound Healing: Lessons Learned from Animal Studies

SIGNIFICANCE

Wound healing is a complex physiological process involving a multitude of growth factors, among which transforming growth factor beta (TGF-β) has the broadest spectrum of effects. Animal studies have provided key information on the mechanisms of TGF-β action in wound healing and have guided the development of therapeutic strategies targeting the TGF-β pathway to improve wound healing and scarring outcome.

RECENT ADVANCES

Development of tissue-specific expression systems for overexpression or knockout of TGF-β signaling pathway components has led to novel insight into the role of TGF-β signaling in wound healing. This work has also identified molecules that might serve as molecular targets for the treatment of pathological skin conditions such as chronic wounds and excessive scarring (fibrosis).

CRITICAL ISSUES

Many of the mouse models with genetic alterations in the TGF-β signaling pathway develop an underlying skin abnormality, which may pose some limitations on the interpretation of wound-healing results obtained in these animals. Also, TGF-β's pleiotropic effects on many cell types throughout all phases of wound healing present a challenge in designing specific strategies for targeting the TGF-β signaling pathway to promote wound healing or reduce scarring.

FUTURE DIRECTIONS

Further characterization of TGF-β signaling pathway components using inducible tissue-specific overexpression or knockout technology will be needed to corroborate results obtained in mouse models that display a skin phenotype, and to better understand the role of TGF-β signaling during distinct phases of the wound-healing process. Such studies will also provide a better understanding of how TGF-β mediates its autocrine, paracrine, and double paracrine effects on cellular responses in vivo during wound healing.

Down-regulation of Smad3 Accelerates Palatal Wound Repair

Smad3-deficient mice exhibit accelerated re-epithelialization and tissue remodeling during palatal wound repair. In addition, transforming growth factor beta 1 (TGF-β1) and other inflammatory factors are down-regulated compared with those in wild-type mice. The aim of this study was to examine whether targeting of Smad3 with small interfering RNA (siRNA) accelerates wound-healing and inhibits wound contraction in palatal mucoperiosteal wounds. An initial histological examination of wound closure in mouse palates treated with Smad3-targeted siRNA vs. a scrambled siRNA found that wound-healing was accelerated when levels of Smad3 were decreased. Furthermore, with real-time PCR, mRNA levels of Smad3, TGF-β1, monocyte chemotactic protein-1 ( MCP-1), and macrophage inflammatory protein-1α ( MIP-1α) were found to be significantly down-regulated in palatal tissue treated with Smad3–targeted siRNA vs. a control siRNA. Protein and mRNA levels of α-smooth-muscle actin (α-SMA), type I collagen, and fibronectin were also lower in palates treated with Smad3-targeted siRNA vs. control siRNA. Taken together, these results indicate that down-regulation of Smad3 expression by siRNA can accelerate wound-healing and may inhibit wound contraction. Therefore, siRNA-targeted inhibition of Smad3 may represent a valuable therapeutic tool for palatal mucoperiosteal wound-healing.

Crosstalk between breast cancer stem cells and metastatic niche: emerging molecular metastasis pathway?

Metastatic colonization represents the final step of metastasis, and is the major cause of cancer mortality. Metastasis as an "inefficient" process requires the right population of tumor cells in a suitable microenvironment to form secondary tumors. Cancer stem cells are the only capable population of tumor cells to progress to overt metastasis. On the other hand, the occurrence of appropriate microenvironmental conditions within the target tissue would be critical for metastasis formation. Metastatic niche seems to be the specialized microenvironment to support tumor initiating cells at the distant organ. Master regulators not only determine cancer stem cell state, but also may have regulatory roles in metastatic niche elements. Meanwhile, both cancer stem cell and metastatic niche may function like two sides of the metastatic coin. Hypoxia inducible factors have multiple roles in regulation of both sides of this coin. TGF-β superfamily, also, have been considered as master regulators of epithelial to mesenchymal transition and metastasis and may play crucial roles in regulation of metastatic niche as well. In this regard, we hypothesize the presence of a possible emerging molecular pathway in the biological process of breast cancer metastasis. In this process, non-Smad TGF-β-induced metastasis connects cancer stem cell and metastatic niche formation through a central path, "Metastasis Pathway".

Anti-melanin-concentrating hormone treatment attenuates chronic experimental colitis and fibrosis

Fibrosis represents a major complication of several chronic diseases, including inflammatory bowel disease (IBD). Treatment of IBD remains a clinical challenge despite several recent therapeutic advances. Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide shown to regulate appetite and energy balance. However, accumulating evidence suggests that MCH has additional biological effects, including modulation of inflammation. In the present study, we examined the efficacy of an MCH-blocking antibody in treating established, dextran sodium sulfate-induced experimental colitis. Histological and molecular analysis of mouse tissues revealed that mice receiving anti-MCH had accelerated mucosal restitution and lower colonic expression of several proinflammatory cytokines, as well as fibrogenic genes, including COL1A1. In parallel, they spared collagen deposits seen in the untreated mice, suggesting attenuated fibrosis. These findings raised the possibility of perhaps direct effects of MCH on myofibroblasts. Indeed, in biopsies from patients with IBD, we demonstrate expression of the MCH receptor MCHR1 in α-smooth muscle actin(+) subepithelial cells. CCD-18Co cells, a primary human colonic myofibroblast cell line, were also positive for MCHR1. In these cells, MCH acted as a profibrotic modulator by potentiating the effects of IGF-1 and TGF-β on proliferation and collagen production. Thus, by virtue of combined anti-inflammatory and anti-fibrotic effects, blocking MCH might represent a compelling approach for treating IBD.

The molecular mechanism of hypertrophic scar

Hypertrophic scar (HTS) is a dermal form of fibroproliferative disorder which often develops after thermal or traumatic injury to the deep regions of the skin and is characterized by excessive deposition and alterations in morphology of collagen and other extracellular matrix (ECM) proteins. HTS are cosmetically disfiguring and can cause functional problems that often recur despite surgical attempts to remove or improve the scars. In this review, the roles of various fibrotic and anti-fibrotic molecules are discussed in order to improve our understanding of the molecular mechanism of the pathogenesis of HTS. These molecules include growth factors, cytokines, ECM molecules, and proteolytic enzymes. By exploring the mechanisms of this form of dermal fibrosis, we seek to provide some insight into this form of dermal fibrosis that may allow clinicians to improve treatment and prevention in the future.

Chondrocyte-intrinsic Smad3 represses Runx2-inducible matrix metalloproteinase 13 expression to maintain articular cartilage and prevent osteoarthritis

OBJECTIVE

To identify mechanisms by which Smad3 maintains articular cartilage and prevents osteoarthritis.

METHODS

A combination of in vivo and in vitro approaches was used to test the hypothesis that Smad3 represses Runx2-inducible gene expression to prevent articular cartilage degeneration. Col2-Cre;Smad3(fl/fl) mice allowed study of the chondrocyte-intrinsic role of Smad3 independently of its role in the perichondrium or other tissues. Primary articular cartilage chondrocytes from Smad3(fl/fl) mice and ATDC5 chondroprogenitor cells were used to evaluate Smad3 and Runx2 regulation of matrix metalloproteinase 13 (MMP-13) messenger RNA (mRNA) and protein expression.

RESULTS

Chondrocyte-specific reduction of Smad3 caused progressive articular cartilage degeneration due to imbalanced cartilage matrix synthesis and degradation. In addition to reduced type II collagen mRNA expression, articular cartilage from Col2-Cre;Smad3(fl/fl) mice was severely deficient in type II collagen and aggrecan protein due to excessive MMP-13-mediated proteolysis of these key cartilage matrix constituents. Normally, transforming growth factor β (TGFβ) signals through Smad3 to confer a rapid and dynamic repression of Runx2-inducible MMP-13 expression. However, we found that in the absence of Smad3, TGFβ signals through p38 and Runx2 to induce MMP-13 expression.

CONCLUSION

Our findings elucidate a mechanism by which Smad3 mutations in humans and mice cause cartilage degeneration and osteoarthritis. Specifically, Smad3 maintains the balance between cartilage matrix synthesis and degradation by inducing type II collagen expression and repressing Runx2-inducible MMP-13 expression. Selective activation of TGFβ signaling through Smad3, rather than p38, may help to restore the balance between matrix synthesis and proteolysis that is lost in osteoarthritis.

Ligand-dependent actions of the vitamin D receptor are required for activation of TGF-β signaling during the inflammatory response to cutaneous injury

The vitamin D receptor (VDR) has both 1,25-dihydroxyvitamin D-dependent and -independent actions in the epidermis. Ligand-dependent actions of the VDR have been shown to promote keratinocyte differentiation and to regulate formation of the epidermal barrier. In contrast, the actions of the VDR that regulate postmorphogenic hair cycling do not require 1,25-dihydroxyvitamin D. The VDR also has immunomodulatory actions that are dependent on its ligand, 1,25-dihydroxyvitamin D. To determine whether the ligand-dependent or -independent actions of the VDR regulate the inflammatory response to cutaneous injury, studies were performed in control, VDR knockout, and vitamin D-deficient mice. These investigations demonstrate that absence of receptor or ligand impairs the dermal response to cutaneous injury. Although neutrophil recruitment is not affected, the absence of VDR signaling leads to defects in macrophage recruitment and granulation tissue formation. Studies performed to identify the molecular basis for this phenotype demonstrate that absence of the VDR, or its ligand, impairs TGF-β signaling in the dermis, characterized by decreased expression of monocyte chemotactic protein-1 and reduced phosphorylation of phosphorylated Smad-3 as well as attenuated phosphorylated Smad-3 phosphorylation in response to TGF-β in primary dermal fibroblasts lacking the VDR. Thus, these data demonstrate that the liganded VDR interacts with the TGF-β signaling pathway to promote the normal inflammatory response to cutaneous injury.

The use of native chemical functional groups presented by wound beds for the covalent attachment of polymeric microcarriers of bioactive factors

The development of versatile methods that provide spatial and temporal control over the presentation of physical and biochemical cues on wound beds can lead to new therapeutic approaches that expedite wound healing by favorably influencing cellular behaviors. Toward that goal, we report that native chemical functional groups presented by wound beds can be utilized for direct covalent attachment of polymeric microbeads. Specifically, we demonstrated the covalent attachment of maleimide-functionalized and catechol-functionalized microbeads, made of either polystyrene (non-degradable) or poly(lactic-co-glycolic acid) ((PLGA), degradable), to sulfhydryl and amine groups present on porcine dermis used here as an ex vivo model wound bed. A pronounced increase (10-70 fold) in the density and persistence of the covalently reactive microbeads was observed relative to microbeads that adsorb via non-covalent interactions. Complementary characterization of the surface chemistry of the ex vivo wound beds using Raman microspectroscopy provides support for our conclusion that the increased adherence of the maleimide-functionalized beads results from their covalent bond formation with sulfhydryl groups on the wound bed. The attachment of maleimide-functionalized microbeads to wounds created in live wild-type and diabetic mice led to observations of differential immobilization of microbeads on them and were consistent with anticipated differences in the presentation of sulfhydryl groups on the two different wound types. Finally, the incorporation of maleimide-functionalized microbeads in wounds created in wild-type mice did not impair the rate of wound closure relative to an untreated wound. Overall, the results presented in this paper enable a general and facile approach to the engineering of wound beds in which microbeads are covalently immobilized to wound beds. Such immobilized microbeads could be used in future studies to release bioactive factors (e.g., antimicrobial agents or growth factors) and/or introduce topographical cues that promote cell behaviors underlying healing and wound closure.

Selectively reducing cytokine/chemokine expressing macrophages in injured nerves impairs the development of neuropathic pain

It has been well documented that Wallerian degeneration following nerve injury is associated with inflammatory reaction. Such local inflammation contributes to the development of chronic neuropathic pain. Macrophages are one of the major players in the process of either or both degeneration/regeneration and hypersensitivity. To elucidate whether cellular and molecular changes involved in Wallerian degeneration are simultaneously involved in the induction and maintenance of neuropathic pain, and to identify which subpopulation of macrophages can be responsible for the chronic pain following nerve injury, we investigated the peripheral effects of an anti-inflammatory cytokine TGF-β1 in neuropathic pain. Rat sciatic nerves were partially ligated. Macrophages accumulated in injured sciatic nerves displayed heterogeneity with two distinctive functional phenotypes. While MAC1(+) macrophages were able to express IL-6 and MIP-1α, ED1(+) macrophages were always devoid of signals of inflammatory mediators. Intraneural injection of TGF-β1 resulted in delayed and attenuated neuropathic pain behaviour. In parallel, we observed that exposure of the nerve to TGF-β1 dramatically reduced the number of MAC1(+) macrophages. Consequently, the expression of IL-6 and MIP-1α decreased in the injured nerve. Very interestingly, local TGF-β1 treatment had no effect on the population of ED1(+) phagocytic macrophages. In addition to its effect on selective subsets of macrophages, TGF-β1 also reduced T-lymphocyte infiltration. Our results revealed the critical roles of cytokine/chemokine secreting MAC1(+) macrophages in the development of neuropathic pain, and highlighted the needs and benefits of targeting specific populations of macrophages in alleviating neuropathic pain without delaying nerve regeneration.

Common threads in cardiac fibrosis, infarct scar formation, and wound healing

Wound healing, cardiac fibrosis, and infarct scar development, while possessing distinct features, share a number of key functional similarities, including extracellular matrix synthesis and remodeling by fibroblasts and myofibroblasts. Understanding the underlying mechanisms that are common to these processes may suggest novel therapeutic approaches for pathologic situations such as fibrosis, or defective wound healing such as hypertrophic scarring or keloid formation. This manuscript will briefly review the major steps of wound healing, and will contrast this process with how cardiac infarct scar formation or interstitial fibrosis occurs. The feasibility of targeting common pro-fibrotic growth factor signaling pathways will be discussed. Finally, the potential exploitation of novel regulators of wound healing and fibrosis (ski and scleraxis), will be examined.

Transforming growth factor Beta 3 is required for excisional wound repair in vivo

Wound healing is a complex process that relies on proper levels of cytokines and growth factors to successfully repair the tissue. Of particular interest are the members of the transforming growth factor family. There are three TGF-ß isoforms-TGF- ß 1, 2, and 3, each isoform showing a unique expression pattern, suggesting that they each play a distinct function during development and repair. Previous studies reported an exclusive role for TGF-ß 3 in orofacial development and a potent anti-scarring effect. However, the role of TGF- ß 3 in excisional wound healing and keratinocyte migration remains poorly understood. We tested the effect of TGF-ß 3 levels on excisional cutaneous wounds in the adult mouse by directly injecting recombinant TGF-ß 3 or neutralizing antibody against TGF-ß 3 (NAB) in the wounds. Our results demonstrate that TGF-ß 3 does not promote epithelialization. However, TGF-ß 3 is necessary for wound closure as wounds injected with neutralizing antibody against TGF-ß 3 showed increased epidermal volume and proliferation in conjunction with a delay in keratinocyte migration. Wild type keratinocytes treated with NAB and Tgfb3-deficient keratinocytes closed an in vitro scratch wound with no delay, suggesting that our in vivo observations likely result from a paracrine effect.

Regeneration: the ultimate example of wound healing

The outcome of wound repair in mammals is often characterized by fibrotic scaring. Vertebrates such as zebrafish, frogs, and salamanders not only heal scarlessly, but also can regenerate lost appendages. Decades of study on the process of animal regeneration has produced key insights into the mechanisms of how complex tissue is restored. By examining our current knowledge of regeneration, we can draw parallels with mammalian wound healing to identify the molecular determinants that produce such differing outcomes.

Cutaneous wound healing: recruiting developmental pathways for regeneration

Following a skin injury, the damaged tissue is repaired through the coordinated biological actions that constitute the cutaneous healing response. In mammals, repaired skin is not identical to intact uninjured skin, however, and this disparity may be caused by differences in the mechanisms that regulate postnatal cutaneous wound repair compared to embryonic skin development. Improving our understanding of the molecular pathways that are involved in these processes is essential to generate new therapies for wound healing complications. Here we focus on the roles of several key developmental signaling pathways (Wnt/β-catenin, TGF-β, Hedgehog, Notch) in mammalian cutaneous wound repair, and compare this to their function in skin development. We discuss the varying responses to cutaneous injury across the taxa, ranging from complete regeneration to scar tissue formation. Finally, we outline how research into the role of developmental pathways during skin repair has contributed to current wound therapies, and holds potential for the development of more effective treatments.

Wound healing in development

Wound healing is the inherent ability of an organism to protect itself against injuries. Cumulative evidence indicates that the healing process patterns in part embryonic morphogenesis and may result in either organ regeneration or scarring, phenomena that are developmental stage- or age-dependent. Skin is the largest organ. Its morphogenesis and repair mechanisms have been studied extensively due not only to its anatomical location, which allows easy access and observation, but also to its captivating structure and vital function. Thus, this review will focus on using skin as a model organ to illustrate new insights into the mechanisms of wound healing that are developmentally regulated in mammals, with special emphasis on the role of the Wnt signaling pathway and its crosstalk with TGF-β signaling. Relevant information from studies of other organs is discussed where it applies, and the clinical impact from such knowledge and emerging concepts on regenerative medicine are discussed in perspective.

The role of androgen and androgen receptor in skin-related disorders

Androgen and androgen receptor (AR) may play important roles in several skin-related diseases, such as androgenetic alopecia and acne vulgaris. Current treatments for these androgen/AR-involved diseases, which target the synthesis of androgens or prevent its binding to AR, can cause significant adverse side effects. Based on the recent studies using AR knockout mice, it has been suggested that AR and androgens play distinct roles in the skin pathogenesis, and AR seems to be a better target than androgens for the treatment of these skin diseases. Here, we review recent studies of androgen/AR roles in several skin-related disorders, including acne vulgaris, androgenetic alopecia and hirsutism, as well as cutaneous wound healing.

Wound repair and regeneration

The skin is the biggest organ of the human being and has many functions. Therefore, the healing of a skin wound displays an extraordinary mechanism of cascading cellular functions which is unique in nature. As healing and regeneration processes take place in all parts of the human body, this review focuses on the healing processes of the skin and highlights the classical wound healing phases. While regeneration describes the specific substitution of the tissue, i.e. the superficial epidermis, mucosa or fetal skin, skin repair displays an unspecific form of healing in which the wound heals by fibrosis and scar formation. The first stage of acute wound healing is dedicated to hemostasis and the formation of a provisional wound matrix, which occurs immediately after injury and is completed after some hours. Furthermore, this phase initiates the inflammatory process. The inflammatory phase of the wound healing cascade gets activated during the coagulation phase and can roughly be divided into an early phase with neutrophil recruitment and a late phase with the appearance and transformation of monocytes. In the phase of proliferation the main focus of the healing process lies in the recovering of the wound surface, the formation of granulation tissue and the restoration of the vascular network. Therefore, next to the immigration of local fibroblasts along the fibrin network and the beginning of reepithelialization from the wound edges, neovascularization and angiogenesis get activated by capillary sprouting. The formation of granulation tissue stops through apoptosis of the cells, characterizing a mature wound as avascular as well as acellular. During the maturation of the wound the components of the extracellular matrix undergo certain changes. The physiological endpoint of mammalian wound repair displays the formation of a scar, which is directly linked to the extent of the inflammatory process throughout wound healing.

Transforming growth factor β inhibits bone morphogenetic protein-induced transcription through novel phosphorylated Smad1/5-Smad3 complexes

In vivo cells receive simultaneous signals from multiple extracellular ligands and must integrate and interpret them to respond appropriately. Here we investigate the interplay between pathways downstream of two transforming growth factor β (TGF-β) superfamily members, bone morphogenetic protein (BMP) and TGF-β. We show that in multiple cell lines, TGF-β potently inhibits BMP-induced transcription at the level of both BMP-responsive reporter genes and endogenous BMP target genes. This inhibitory effect requires the TGF-β type I receptor ALK5 and is independent of new protein synthesis. Strikingly, we show that Smad3 is required for TGF-β's inhibitory effects, whereas Smad2 is not. We go on to demonstrate that TGF-β induces the formation of complexes comprising phosphorylated Smad1/5 and Smad3, which bind to BMP-responsive elements in vitro and in vivo and mediate TGF-β-induced transcriptional repression. Furthermore, loss of Smad3 confers on TGF-β the ability to induce transcription via BMP-responsive elements. Our results therefore suggest that not only is Smad3 important for mediating TGF-β's inhibitory effects on BMP signaling but it also plays a critical role in restricting the transcriptional output in response to TGF-β.

Lack of Smad3 signaling leads to impaired skeletal muscle regeneration

Smad3 is a key intracellular signaling mediator for both transforming growth factor-β and myostatin, two major regulators of skeletal muscle growth. Previous published work has revealed pronounced muscle atrophy together with impaired satellite cell functionality in Smad3-null muscles. In the present study, we have further validated a role for Smad3 signaling in skeletal muscle regeneration. Here, we show that Smad3-null mice had incomplete recovery of muscle weight and myofiber size after muscle injury. Histological/immunohistochemical analysis suggested impaired inflammatory response and reduced number of activated myoblasts during the early stages of muscle regeneration in the tibialis anterior muscle of Smad3-null mice. Nascent myofibers formed after muscle injury were also reduced in number. Moreover, Smad3-null regenerated muscle had decreased oxidative enzyme activity and impaired mitochondrial biogenesis, evident by the downregulation of the gene encoding mitochondrial transcription factor A, a master regulator of mitochondrial biogenesis. Consistent with known Smad3 function, reduced fibrotic tissue formation was also seen in regenerated Smad3-null muscle. In conclusion, Smad3 deficiency leads to impaired muscle regeneration, which underscores an essential role of Smad3 in postnatal myogenesis. Given the negative role of myostatin during muscle regeneration, the increased expression of myostatin observed in Smad3-null muscle may contribute to the regeneration defects.

Impaired cutaneous wound healing in transforming growth factor-β inducible early gene1 knockout mice

Transforming growth factor-β inducible early gene (TIEG) is induced by transforming growth factor-β (TGF-β) and acts as the primary response gene in the TGF-β/Smad pathway. TGF-β is a multifunctional growth factor that affects dermal wound healing; however, the mechanism of how TGF-β affects wound healing is still not well understood because of the complexity of its function and signaling pathways. We hypothesize that TIEG may play a role in dermal wound healing, with involvement in wound closure, contraction, and reepithelialization. In this study, we have shown that TIEG1 knockout (TIEG1-/-) mice have a delay in wound closure related to an impairment in wound contraction, granulation tissue formation, collagen synthesis, and reepithelialization. We also found that Smad7 was increased in the wounds and appeared to play a role in this wound healing model in TIEG1-/- mice.

Reduction of burn scar formation by halofuginone-eluting silicone gel sheets: a controlled study on nude mice

Burn scar formations can cause disfiguration and loss of dermal function. The purpose of this study was to examine whether application of modified silicone gel sheets with an antifibrotic drug halofuginone-eluting hybrid surface produce an effect on scar development. There were a total of 2 animal groups. The athymic nude mice (nu/nu) of both groups underwent transplantation of full-thickness human skin grafts onto their backs and setting of partial thickness burn injury. The status of local scar development was observed over a period of 3 months after the application of silicone gel sheets and also after application of surface-modified halofuginone-eluting silicone gel sheets. Subsequently, via real-time polymerase chain reaction, the cDNA levels from key mediators of scar formation (transforming growth factor beta, COL1A1, connective tissue growth factor, fibroblast growth factor 2, matrix metalloproteinase 2, matrix metalloproteinase 9) were established and statistically evaluated. In comparison with uncoated silicone gel sheets, the application of halofuginone-eluting silicone gel sheets lead to a significant difference in gene expression activity in scar tissue. Halofuginone-eluting hybrid surface silicone gel sheets significantly increase the antiscarring effect of adhesive silicone gel sheets by deceleration and downregulation of scar development by normalization of the expression activity.

Smad2 decelerates re-epithelialization during gingival wound healing

During periodontal regeneration, inhibition of gingival downgrowth is necessary to promote migration of mesenchymal cells into the defects. Transforming growth factor (TGF)-β is a pleiotropic cytokine that has numerous cell functions, including regulation of epithelial growth. Recent studies have shown that Smad2, a downstream transcription factor of TGF-β, plays crucial roles in wound healing in the epithelia. Therefore, we investigated the effects of Smad2 overexpression on re-epithelialization of gingival wounds. Transgenic mice overexpressing smad2 driven by the keratin 14 promoter (k14-smad2) were confirmed to have significant Smad2 phosphorylation in gingival basal epithelia. Punch wounds were made in the palatal gingiva, and wound healing was assessed histologically for 7 days. Re-epithelialization was significantly retarded on day 2, while collagen deposition was enhanced on day 7 in k14-smad2 compared with wild-type mice. Moreover, expression of keratin 16 (K16), an indicator of keratinocyte migration, was significantly inhibited in wound-edge keratinocytes in k14-smad2. The inhibition of K16 coincided with the induction of Smad2 in the corresponding epithelia, while BrdU incorporation was unaffected. These results indicated that Smad2 has inhibitory effects in regulating keratinocyte migration during gingival wound healing. TGF-β/Smad2 signaling mediating alteration of K16 expression must be tightly regulated during periodontal regeneration.

Mesenchymal stem cell therapy for attenuation of scar formation during wound healing

Scars are a consequence of cutaneous wound healing that can be both unsightly and detrimental to the function of the tissue. Scar tissue is generated by excessive deposition of extracellular matrix tissue by wound healing fibroblasts and myofibroblasts, and although it is inferior to the uninjured skin, it is able to restore integrity to the boundary between the body and its environment. Scarring is not a necessary process to repair the dermal tissues. Rather, scar tissue forms due to specific mechanisms that occur during the adult wound healing process and are modulated primarily by the inflammatory response at the site of injury. Adult tissue-derived mesenchymal stem cells, which participate in normal wound healing, are trophic mediators of tissue repair. These cells participate in attenuating inflammation in the wound and reprogramming the resident immune and wound healing cells to favor tissue regeneration and inhibit fibrotic tissue formation. As a result, these cells have been considered and tested as a likely candidate for a cellular therapy to promote scar-less wound healing. This review identifies specific mechanisms by which mesenchymal stem cells can limit tissue fibrosis and summarizes recent in vivo studies where these cells have been used successfully to limit scar formation.

Smad4 disruption accelerates keratinocyte reepithelialization in murine cutaneous wound repair

Keratinocyte reepithelialization is a rate-limiting event in cutaneous wound repair, which involves the migration and proliferation of keratinocytes to cover the denuded dermal surface. Transforming growth factor-β1 (TGF-β1) has the ability to induce epithelial cell migration while inhibiting proliferation, and controversial results have been generated regarding the effect of TGF-β signaling on reepithelialization. In this study, full-thickness skin wounds were made in keratinocyte-specific Smad4 knockout and the control mice. The wound closure, reepithelialization, keratinocyte proliferation, myofibroblast numbers and collagen deposition of were assessed. The results showed that the proliferation of keratinocytes increased, which accelerated the reepithelialization, and led to faster wound repair in the epidermis of Smad4 mutant mice. Upregulation of keratin 17, 14-3-3 sigma and phosphorylated AKT in the hyperproliferative epidermis may be correlated with the accelerated reepithelialization. We conclude that Smad4 plays an inhibitory role in the keratinocyte-mediated reepithelialization of wound healing.

Using mice to unveil the genetics of cancer resistance

In the UK, four in ten people will develop some form of cancer during their lifetime, with an individual's relative risk depending on many factors, including age, lifestyle and genetic make-up. Much research has gone into identifying the genes that are mutated in tumorigenesis with the overwhelming majority of genetically-modified (GM) mice in cancer research showing accelerated tumorigenesis or recapitulating key aspects of the tumorigenic process. Yet if six out of ten people will not develop some form of cancer during their lifetime, together with the fact that some cancer patients experience spontaneous regression/remission, it suggests there are ways of 'resisting' cancer. Indeed, there are wildtype, spontaneously-arising mutants and GM mice that show some form of 'resistance' to cancer. Identification of mice with increased resistance to cancer is a novel aspect of cancer research that is important in terms of providing both chemopreventative and therapeutic options. In this review we describe the different mouse lines that display a 'cancer resistance' phenotype and discuss the molecular basis of their resistance.

Heme oxygenase, inflammation, and fibrosis: the good, the bad, and the ugly?

Upon injury, prolonged inflammation and oxidative stress may cause pathological wound healing and fibrosis, leading to formation of excessive scar tissue. Fibrogenesis can occur in most organs and tissues and may ultimately lead to organ dysfunction and failure. The underlying mechanisms of pathological wound healing still remain unclear, and are considered to be multifactorial, but so far, no efficient anti-fibrotic therapies exist. Extra- and intracellular levels of free heme may be increased in a variety of pathological conditions due to release from hemoproteins. Free heme possesses pro-inflammatory and oxidative properties, and may act as a danger signal. Effects of free heme may be counteracted by heme-binding proteins or by heme degradation. Heme is degraded by heme oxygenase (HO) that exists as two isoforms: inducible HO-1 and constitutively expressed HO-2. HO generates the effector molecules biliverdin/bilirubin, carbon monoxide, and free iron/ferritin. HO deficiency in mouse and man leads to exaggerated inflammation following mild insults, and accumulating epidemiological and preclinical studies support the widely recognized notion of the cytoprotective, anti-oxidative, and anti-inflammatory effects of the activity of the HO system and its effector molecules. In this review, we address the potential effects of targeted HO-1 induction or administration of HO-effector molecules as therapeutic targets in fibrotic conditions to counteract inflammatory and oxidative insults. This is exemplified by various clinically relevant conditions, such as hypertrophic scarring, chronic inflammatory liver disease, chronic pancreatitis, and chronic graft rejection in transplantation.

The super super-healing MRL mouse strain

The Murphy Roths Large (MRL/MpJ) mice provide unique insights into wound repair and regeneration. These mice and the closely related MRL/MpJ-Fas^lpr /J and Large strains heal wounds made in multiple tissues without production of a fibrotic scar. The precise mechanism of this remarkable ability still eludes researchers, but some data has been generated and insights are being revealed. For example, MRL cells reepithelialize over dermal wound sites faster than cells of other mouse strains. This allows a blastema to develop beneath the protective layer. The MRL mice also have an altered basal immune system and an altered immune response to injury. In addition, MRL mice have differences in their tissue resident progenitor cells and certain cell cycle regulatory proteins. The difficulty often lies in separating the causative differences from the corollary differences. Remarkably, not every tissue in these mice heals scarlessly, and the specific type of wound and priming affect regeneration ability as well. The MRL/MpJ, MRL/MpJ-Fas^lpr /J, and Large mouse strains are also being investigated for their autoimmune characteristic. Whether the two phenotypes of regeneration and autoimmunity are related remains an enigma.

miR-29 inhibits bleomycin-induced pulmonary fibrosis in mice

Loss of microRNA-29 (miR-29) is known to be a mechanism of transforming growth factor-β (TGF-β)-mediated pulmonary fibrosis, but the therapeutic implication of miR-29 for pulmonary fibrosis remains unexplored. The present study investigated whether miR-29 had therapeutic potential for lung disease induced by bleomycin in mice. In addition, the signaling mechanisms that regulated miR-29 expression were investigated in vivo and in vitro. We found that miR-29 was a downstream target gene of Smad3 and negatively regulated by TGF-β/Smad signaling in fibrosis. This was evidenced by the findings that mice or pulmonary fibroblasts null for Smad3 were protected against bleomycin or TGF-β1-induced loss of miR-29 along with fibrosis in vivo and in vitro. Interestingly, overexpression of miR-29 could in turn negatively regulated TGF-β and connective tissue growth factor (CTGF) expression and Smad3 signaling. Therefore, Sleeping Beauty (SB)-mediated miR-29 gene transfer into normal and diseased lung tissues was capable of preventing and treating pulmonary fibrosis including inflammatory macrophage infiltration induced by bleomycin in mice. In conclusion, miR-29 is negatively regulated by TGF-β/Smad3 and has a therapeutic potential for pulmonary fibrosis. SB-mediated miR-29 gene therapy is a non-invasive therapeutic strategy for lung disease associated with fibrosis.

Genetic deficiency of Smad3 protects the kidneys from atrophy and interstitial fibrosis in 2K1C hypertension

Although the two-kidney, one-clip (2K1C) model is widely used as a model of human renovascular hypertension, mechanisms leading to the development of fibrosis and atrophy in the cuffed kidney and compensatory hyperplasia in the contralateral kidney have not been defined. Based on the well-established role of the transforming growth factor (TGF)-β signaling pathway in renal fibrosis, we tested the hypothesis that abrogation of TGF-β/Smad3 signaling would prevent fibrosis in the cuffed kidney. Renal artery stenosis (RAS) was established in mice with a targeted disruption of exon 2 of the Smad3 gene (Smad3 KO) and wild-type (WT) controls by placement of a polytetrafluoroethylene cuff on the right renal artery. Serial pulse-wave Doppler ultrasound assessments verified that blood flow through the cuffed renal artery was decreased to a similar extent in Smad3 KO and WT mice. Two weeks after surgery, systolic blood pressure and plasma renin activity were significantly elevated in both the Smad3 KO and WT mice. The cuffed kidney of WT mice developed renal atrophy (50% reduction in weight after 6 wk, P < 0.0001), which was associated with the development of interstitial fibrosis, tubular atrophy, and interstitial inflammation. Remarkably, despite a similar reduction of renal blood flow, the cuffed kidney of the Smad3 KO mice showed minimal atrophy (9% reduction in weight, P = not significant), with no significant histopathological alterations (interstitial fibrosis, tubular atrophy, and interstitial inflammation). We conclude that abrogation of TGF-β/Smad3 signaling confers protection against the development of fibrosis and atrophy in RAS.

Genetic and genomic approaches to asthma: new insights for the origins

PURPOSE OF REVIEW

The aim is to update current understanding of the genes identified by the recent genome-wide association studies (GWASs) of asthma and its associated traits. The review also discusses how to dissect the functional roles of novel genes in future research.

RECENT FINDINGS

More than 10 GWAS aimed at identifying the genes underlying asthma and relevant traits have been published in the past 3 years. The largest of these was from the GABRIEL consortium, which discovered that the IL18R1, IL33, SMAD3, ORMDL3, HLA-DQ and IL2RB loci were all significantly associated with asthma. Many novel asthma genes, including those previously identified by positional cloning, are expressed within the respiratory epithelium, emphasizing the importance of epithelial barriers in causing asthma . The genes controlling IgE levels have surprisingly little overlap with the genes mediating asthma susceptibility, suggesting that atopy is secondary to asthma rather than a primary driver of the disease. The next challenge will be the systematic analysis of the precise functions of these genes in the pathogenesis of asthma.

SUMMARY

GWAS have uncovered many novel genes underlying asthma and detailed functional dissection of their roles in asthma will point the way to new therapies for the disease.

Two sides of the story? Smad4 loss in pancreatic cancer versus head-and-neck cancer

TGFβ signaling Smads (Smad2, 3, and 4) were suspected tumor suppressors soon after their discovery. Nearly two decades of research confirmed this role and revealed other divergent and cancer-specific functions including paradoxical tumor promotion effects. Although Smad4 is the most potent tumor suppressor, its functions are highly context-specific as exemplified by pancreatic cancer and head-and-neck cancer: in pancreatic cancer, Smad4 loss cannot initiate tumor formation but promotes metastases while in head-and-neck cancer Smad4 loss promotes cancer progression but also initiates tumor formation, likely through effects on genomic instability. The differing consequences of impaired Smad signaling in human cancers and the molecular mechanisms that underpin these differences will have important implications for the design and application of novel targeted therapies.

Myostatin-null mice exhibit delayed skin wound healing through the blockade of transforming growth factor-β signaling by decorin

Myostatin (Mstn) is a secreted growth and differentiation factor that belongs to the transforming growth factor-β (TGF-β) superfamily. Mstn has been well characterized as a regulator of myogenesis and has been shown to play a critical role in postnatal muscle regeneration. Herein, we report for the first time that Mstn is expressed in both epidermis and dermis of murine and human skin and that Mstn-null mice exhibited delayed skin wound healing attributable to a combination of effects resulting from delayed epidermal reepithelialization and dermal contraction. In epidermis, reduced keratinocyte migration and protracted keratinocyte proliferation were observed, which subsequently led to delayed recovery of epidermal thickness and slower reepithelialization. Furthermore, primary keratinocytes derived from Mstn-null mice displayed reduced migration capacity and increased proliferation rate as assessed through in vitro migration and adhesion assays, as well as bromodeoxyuridine incorporation and Western blot analysis. Moreover, in dermis, both fibroblast-to-myofibroblast transformation and collagen deposition were concomitantly reduced, resulting in a delayed dermal wound contraction. These decreases are due to the inhibition of TGF-β signaling. In agreement, the expression of decorin, a naturally occurring TGF-β suppressor, was elevated in Mstn-null mice; moreover, topical treatment with TGF-β1 protein rescued the impaired skin wound healing observed in Mstn-null mice. These observations highlight the interplay between TGF-β and Mstn signaling pathways, specifically through Mstn regulation of decorin levels during the skin wound healing process. Thus we propose that Mstn agonists might be beneficial for skin wound repair.

Temporal smad7 transgene induction in mouse epidermis accelerates skin wound healing

The expression of Smad7, a tumor growth factor-β (TGFβ) antagonist, is increased during cutaneous wound healing. To assess this significance, we temporally induced Smad7 transgene expression in wounded skin in gene-switch-Smad7 transgenic (Smad7 tg) mice. Smad7 induction in epidermal keratinocytes caused an increase in keratinocyte proliferation with reduced Smad2 activation, indicating that Smad7 abrogated TGFβ-mediated growth inhibition. Additionally, wounded skin from Smad7 tg mice exhibited accelerated re-epithelialization, with increased activation of extracellular signal-regulated kinase (Erk), and an in vitro migration assay revealed that Erk activation contributed to Smad7-mediated keratinocyte migration. Notably, epidermis-specific Smad7 transgene expression also has a profound effect on the wound stroma, resulting in reduced inflammation, angiogenesis, and production of type I collagen. Reduced Smad2 activation was observed in wounded stroma from Smad7 transgenic (Smad7 tg) mice, possibly owing to fewer infiltrated TGFβ-producing leukocytes compared to those in wounds from control mice. Because Smad7 is not secreted, these effects could reflect functional changes in Smad7 tg keratinocytes. Supporting this notion, the activation of NF-κB, a nonsecreted protein complex that transcriptionally activates inflammatory cytokines, was reduced in wounded epidermis from Smad7 tg mice compared to that in wounded wild-type epidermis. In sum, epidermal Smad7 overexpression accelerated wound healing through its direct effects on keratinocyte proliferation and migration, and through indirect effects on wound stroma.

Ionizing radiation: the good, the bad, and the ugly

Skin changes caused by ionizing radiation have been scientifically documented since 1902. Ionizing radiation is a widely accepted form of treatment for various types of cancer. Despite the technological advances, radiation skin injury remains a significant problem. This injury, often referred to as radiation dermatitis, occurs in about 95% of patients receiving radiation therapy for cancer, and ranges in severity from mild erythema to moist desquamation and ulceration. Ionizing radiation is not only a concern for cancer patients, but also a public health concern because of the potential for and reality of a nuclear and/or radiological event. Recently, the United States has increased efforts to develop medical countermeasures to protect against radiation toxicities from acts of bioterrorism, as well as cancer treatment. Management of radiation dermatitis would improve the therapeutic benefit of radiation therapy for cancer and potentially the mortality expected in any "dirty bomb" attack. Currently, there is no effective treatment to prevent or mitigate radiation skin injury. This review summarizes "the good, the bad, and the ugly" of current and evolving knowledge regarding mechanisms of and treatments for radiation skin injury.