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

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.

TGFβ signaling and cardiovascular diseases

Transforming growth factor β (TGFβ) family members are involved in a wide range of diverse functions and play key roles in embryogenesis, development and tissue homeostasis. Perturbation of TGFβ signaling may lead to vascular and other diseases. In vitro studies have provided evidence that TGFβ family members have a wide range of diverse effects on vascular cells, which are highly dependent on cellular context. Consistent with these observations genetic studies in mice and humans showed that TGFβ family members have ambiguous effects on the function of the cardiovascular system. In this review we discuss the recent advances on TGFβ signaling in (cardio)vascular diseases, and describe the value of TGFβ signaling as both a disease marker and therapeutic target for (cardio)vascular diseases.

Alterations in the Smad pathway in human cancers

Members of the TGF-beta superfamily exhibit various biological activities, and perturbations of their signaling are linked to certain clinical disorders including cancer. The role of TGF-beta signaling as a tumor suppressor pathway is best illustrated by the presence of inactivating mutations in genes encoding TGF-beta receptors and Smads in human carcinomas. This perspective is further supported by studies of tumor development in mouse models after modulation of receptors and Smads. TGF-beta also controls processes such as cell invasion, immune regulation, and microenvironment alterations that cancer cells may exploit to their advantage for their progression. Consequently, the output of a TGF-beta response is highly situation dependent, across different tissues, and also in cancer in general. Understanding the mechanisms of TGF-beta superfamily signaling is thus important for the development of new ways to treat various types of cancer. This review focuses on recent advances in understanding the Smad dependent TGF-beta pathway as it relates to human carcinogenesis.

Cytokines, chemokines and growth factors in wound healing

In wound healing, a variety of mediators have been identified throughout the years. The mediators discussed here comprise growth factors, cytokines and chemokines. These mediators act via multiple (specific) receptors to facilitate wound closure. As research in the last years has led to many new findings, there is a need to give an overview on what is known, and on what might possibly play a role as a molecular target for future wound therapy. This review aims to keep the reader up to date with selected important and novel findings regarding growth factors, cytokines and chemokines in wound healing.

Erythropoietin improves skin wound healing and activates the TGF-β signaling pathway

We could recently report that erythropoietin (EPO) accelerates skin wound healing in mice. Now, we provide insight into the molecular mechanisms of this non-hematopoietic property of EPO analyzing the transforming growth factor (TGF)-β signaling pathway. EPO receptor was found expressed in both non-wounded and wounded skin tissue as well as in fibroblasts and keratinocytes. In saline-treated control animals, wounds exhibited a significant upregulation of TGF-β1 and of α-smooth muscle actin (α-SMA) compared with non-wounded skin. EPO treatment accelerated wound epithelialization and induced mRNA expression of TGF-β1 and α-SMA. In addition, EPO significantly enhanced phosphorylation of Smad2 and Smad3 in fibroblasts and also elevated phosphorylation of Smad3 in wound tissue. Blockade of TGF-β using a neutralizing anti-TGF-β antibody attenuated EPO-induced acceleration of wound epithelialization in vivo and markedly reversed EPO effects on mRNA expression of TGF-β1 and α-SMA. In conclusion, EPO caused activation of the Smad-dependent TGF-β signaling pathway, enhanced differentiation of myofibroblasts, and accelerated skin wound closure.

Connexins in wound healing; perspectives in diabetic patients

Skin lesions are common events and we have evolved to rapidly heal them in order to maintain homeostasis and prevent infection and sepsis. Most acute wounds heal without issue, but as we get older our bodies become compromised by poor blood circulation and conditions such as diabetes, leading to slower healing. This can result in stalled or hard-to-heal chronic wounds. Currently about 2% of the Western population develop a chronic wound and this figure will rise as the population ages and diabetes becomes more prevalent [1]. Patient morbidity and quality of life are profoundly altered by chronic wounds [2]. Unfortunately a significant proportion of these chronic wounds fail to respond to conventional treatment and can result in amputation of the lower limb. Life quality and expectancy following amputation is severely reduced. These hard to heal wounds also represent a growing economic burden on Western society with published estimates of costs to healthcare services in the region of $25B annually [3]. There exists a growing need for specific and effective therapeutic agents to improve healing in these wounds. In recent years the gap junction protein Cx43 has been shown to play a pivotal role early on in the acute wound healing process at a number of different levels [4-7]. Conversely, abnormal expression of Cx43 in wound edge keratinocytes was shown to underlie the poor rate of healing in diabetic rats, and targeting its expression with an antisense gel restored normal healing rates [8]. The presence of Cx43 in the wound edge keratinocytes of human chronic wounds has also been reported [9]. Abnormal Cx43 biology may underlie the poor healing of human chronic wounds and be amenable therapeutic intervention [7]. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Integrin β6-deficient mice show enhanced keratinocyte proliferation and retarded hair follicle regression after depilation

Integrin αvβ6 is an epithelial-specific receptor that binds and activates latent transforming growth factor-β1 (TGF-β1). TGF-β1 has been implicated as an endogenous inducer of hair follicle (HF) regression during hair cycling. We hypothesized that αvβ6 integrin-mediated TGF-β1 signaling regulates hair regeneration and HF involution. In wild-type (WT) mice, the expression of integrin αvβ6 was strongly upregulated in the outer root sheath (ORS) during early hair regeneration, and was specifically enhanced in the HF bulge region. Expression gradually decreased in late anagen and remained restricted to the bulge region in the catagen and telogen stage HFs. The first spontaneous hair cycle was not altered in β6 integrin knockout (β6(-/-)) mice. However, after depilation, β6(-/-) mice exhibited retarded HF regression compared with WT controls. β6(-/-) follicles contained significantly higher numbers of proliferating Ki67-positive keratinocytes than WT follicles at an identical cycle stage. The β6(-/-) follicles also demonstrated significantly reduced levels of TGF-β1 expression and Smad2 phosphorylation during early anagen and anagen-catagen transition. Our study indicates that αvβ6 integrin has an important inhibitory role in keratinocyte proliferation in both HFs and interfollicular epidermis. Thus, downregulated TGF-β1 signaling in β6(-/-) mice may affect bulge niche stem cell behavior.

WOUND-HEALING PROPERTIES OF TRANSFORMING GROWTH FACTOR β (TGF-β) INDUCIBLE EARLY GENE 1 (TIEG1) KNOCKOUT MICE

Transforming growth factor beta (TGF-β) has a broad effect on wound healing, but many questions remain about the regulation of TGF-β during the healing process. TGF-β inducible early gene 1 (TIEG1) is a primary response gene for TGF-β that controls the activities of the TGF-β/Smad pathway, the primary TGF-β signaling pathway. The purpose of this study was to investigate the role of TIEG1 in cutaneous wound healing using TIEG1 knockout mice. The wound healing in TIEG1 knockout mice and wild-type controls was evaluated by wound breaking strength, Western blot, and histology at postoperative days 3, 7, and 14. Although re-epithelialization of both groups was similarly complete at day 7, the TIEG1 knockout mice had a significantly lower wound breaking strength than the controls at postoperative day 14. These results suggest that TIEG1 expression may be an important factor involved in the initiation and support of normal cutaneous wound healing.

MicroRNA epigenetics: a new avenue for wound healing research

A group of small non-coding RNA molecules, termed microRNAs (miRNAs), have generated considerable interest in recent years due to their central role in a growing number of biologic processes. Serving as post-transcriptional regulators of gene expression, miRNAs have also emerged as critical factors in the pathogenesis of many diseases. As a result, they show great potential as accurate diagnostic and prognostic markers, as well as viable therapeutic targets for treating disease. It has been proposed that miRNAs play a significant role in cutaneous wound repair and that aberrant miRNA expression may result in disorganized or poor healing. Specific patterns of miRNA expression have been identified in wound healing models. miRNAs are important regulators of leucocyte function and the cytokine network, and are necessary for endothelial cell migration and capillary formation. These molecules also control proliferation and differentiation of wound-specific cells and can determine extracellular matrix composition. This article reviews the evidence for miRNA regulation of inflammation, angiogenesis, fibroblast function, keratinocyte function, and apoptosis, which are essential components for effective wound repair. The future potential for improving wound healing outcomes using miRNA-based therapies is also discussed.

Disruption of Smad4 impairs TGF-β/Smad3 and Smad7 transcriptional regulation during renal inflammation and fibrosis in vivo and in vitro

The mechanism by which TGF-β regulates renal inflammation and fibrosis is largely unclear; however, it is well accepted that its biological effects are mediated through Smad2 and Smad3 phosphorylation. Following activation, these Smads form heteromeric complex with Smad4 and translocate into the nucleus to bind and regulate the expression of target genes. Here we studied the roles of Smad4 to regulate TGF-β signaling in a mouse model of unilateral ureteral obstruction using conditional Smad4 knockout mice and in isolated Smad4 mutant macrophages and fibroblasts. Disruption of Smad4 significantly enhanced renal inflammation as evidenced by a greater CD45(+) leukocyte and F4/80(+) macrophage infiltration and upregulation of IL-1β, TNF-α, MCP-1, and ICAM-1 in the obstructed kidney and in IL-1β-stimulated macrophages. In contrast, deletion of Smad4 inhibited renal fibrosis and TGF-β1-induced collagen I expression by fibroblasts. Further studies showed that the loss of Smad4 repressed Smad7 transcription, leading to a loss of functional protein. This, in turn, inhibited IκBα expression but enhanced NF-κB activation, thereby promoting renal inflammation. Interestingly, deletion of Smad4 influenced Smad3-mediated promoter activities and the binding of Smad3 to the COL1A2 promoter, but not Smad3 phosphorylation and nuclear translocation, thereby inhibiting the fibrotic response. Thus, Smad4 may be a key regulator for the diverse roles of TGF-β1 in inflammation and fibrogenesis by interacting with Smad7 and Smad3 to influence their transcriptional activities in renal inflammation and fibrosis.

Development and preclinical efficacy of novel transforming growth factor-β1 short interfering RNAs for pulmonary fibrosis

Idiopathic pulmonary fibrosis is a chronic devastating disease of unknown etiology. No therapy is currently available. A growing body of evidence supports the role of transforming growth factor (TGF)-β1 as the major player in the pathogenesis of the disease. However, attempts to control its expression and to improve the outcome of pulmonary fibrosis have been disappointing. We tested the hypothesis that TGF-β1 is the dominant factor in the acute and chronic phases of pulmonary fibrosis and developed short interfering (si)RNAs directed toward molecules implicated in the disease. This study developed novel sequences of siRNAs targeting the TGF-β1 gene and evaluated their therapeutic efficacy in two models of pulmonary fibrosis: a model induced by bleomycin and a novel model of the disease developed spontaneously in mice overexpressing the full length of human TGF-β1 in the lungs. Intrapulmonary delivery of aerosolized siRNAs of TGF-β1 with sequences common to humans and rodents significantly inhibited bleomycin-induced pulmonary fibrosis in the acute and chronic phases of the disease and in a dose-dependent manner. Aerosolized human-specific siRNA also efficiently inhibited pulmonary fibrosis, improved lung function, and prolonged survival in human TGF-β1 transgenic mice. Mice showed no off-target effects after intratracheal administration of siRNA. These results suggest the applicability of these novel siRNAs as tools for treating pulmonary fibrosis in humans.

Delayed re-epithelialization in Ppm1a gene-deficient mice is mediated by enhanced activation of Smad2

Protein phosphatase magnesium-dependent 1A (PPM1A), a protein serine/threonine phosphatase, controls several signal pathways through cleavage of phosphate from its substrates. However, the in vivo function of Ppm1a in mammals remains unknown. Here we reported that mice lacking Ppm1a developed normally but were impaired in re-epithelialization process during cutaneous wound healing. Specifically, complete or keratinocyte-specific deletion of Ppm1a led to delayed re-epithelialization with reduced keratinocyte migration upon wounding. We showed that this effect was the result of an increase in Smad2/3 phosphorylation in keratinocytes. Keratinocyte-specific Smad2 deficient mice displayed accelerated re-epithelialization with enhanced keratinocyte migration. Importantly, Smad2 and Ppm1a double mutant mice also exhibited accelerated re-epithelialization, demonstrating that the effect of Ppm1a on promoting re-epithelialization is mediated by Smad2 signaling. Furthermore, the decreased expression of specific integrins and matrix metalloproteinases (MMPs) may contribute to the retarded re-epithelialization in Ppm1a mutant mice. These data indicate that Ppm1a, through suppressing Smad2 signaling, plays a critical role in re-epithelialization during wound healing.

The impact of Smad3 loss of function on TGF-β signaling and radiation-induced capsular contracture

BACKGROUND

Capsular contracture remains a major problem following prosthetic breast implantation, especially in patients undergoing irradiation. Recent studies suggest that such radiation injuries are a cascading process of cytokine activation, with transforming growth factor (TGF)-β acting as the "master switch." Because TGF-β signals through phosphorylation of Smad3, a plausible approach to abate TGF-β-induced capsular contracture would be to interrupt Smad3 signaling. To test this hypothesis, capsular contracture formation in wild-type and Smad3 knockout mice was compared using micro-computed tomographic and histologic examination.

METHODS

On day 0, 48 mice were implanted with bilateral silicone gel implants. Postoperatively, animals were imaged using live-scan micro-computed tomographic scanning. Animals in the radiation arm then received a 10-Gy directed radiation dose. On postoperative days 21, 28, 35, and 42, animals were imaged again. Histologic evaluation was performed at necropsy.

RESULTS

Irradiated implants in the wild-type mice demonstrated shape and contour deformation on micro-computed tomographic scanning beginning on postoperative day 21 and progressing through day 42. Conversely, micro-computed tomographic scanning of irradiated implants in knockout mice demonstrated few changes from day 0 through day 42. Corresponding histologic specimens from wild-type mice demonstrated irregular capsules composed of disorganized collagen that became thicker from day 21 to day 42. Irradiated knockout specimen maintained thin capsules from day 21 through day 42.

CONCLUSIONS

In this work, inhibiting TGF-β signaling led to a reduction in radiation-induced capsular contracture as measured by micro-computed tomographic and histologic evaluation. The results of this study suggest a promising target for the prevention of capsular contracture through the development of anti-Smad3/TGF-β-based therapies.

Smad phosphoisoform signaling specificity: the right place at the right time

Transforming growth factor (TGF)-β antagonizes mitogenic Ras signaling during epithelial regeneration, but TGF-β and Ras act synergistically in driving tumor progression. Insights into these apparently contradictory effects have come from recent detailed analyses of the TGF-β signaling process. Here, we summarize the different modes of TGF-β/Ras signaling in normal epithelium and neoplasms and show how perturbation of TGF-β signaling by Ras may contribute to a shift from tumor-suppressive to protumorigenic TGF-β activity during tumor progression. Smad proteins, which convey signals from TGF-β receptors to the nucleus, have intermediate linker regions between conserved Mad homology (MH) 1 and MH2 domains. TGF-β Type I receptor and Ras-associated kinases differentially phosphorylate Smad2 and Smad3 to create C-terminally (C), linker (L) or dually (L/C) phosphorylated (p) isoforms. In epithelial homeostasis, TGF-β-mediated pSmad3C signaling opposes proliferative responses induced by mitogenic signals. During carcinogenesis, activation of cytoplasmic Ras-associated kinases including mitogen-activated protein kinase confers a selective advantage on benign tumors by shifting Smad3 signaling from a tumor-suppressive pSmad3C to an oncogenic pSmad3L pathway, leading to carcinoma in situ. Finally, at the edges of advanced carcinomas invading adjacent tissues, nuclear Ras-associated kinases such as cyclin-dependent kinases, together with cytoplasmic kinases, alter TGF-β signals to more invasive and proliferative pSmad2L/C and pSmad3L/C signaling. Taken together, TGF-β signaling specificity arises from spatiotemporal dynamics of Smad phosphoisoforms. Based on these findings, we have reason to hope that pharmacologic inhibition of linker phosphorylation might suppress progression to human advanced carcinomas by switching from protumorigenic to tumor-suppressive TGF-β signaling.

Wound-induced TGF-β1 and TGF-β2 enhance airway epithelial repair via HB-EGF and TGF-α

The abundance of transforming growth factor-beta (TGF-β) in normal airway epithelium suggests its participation in physiological processes to maintain airway homeostasis. The current study was designed to address the hypothesis that TGF-β1 and TGF-β2 might contribute to normal reparative response of airway epithelial cells (AECs). Treatments with exogenous TGF-β1 or TGF-β2 significantly enhanced wound repair of confluent AEC monolayers. Mechanical injury of AEC monolayers induced production of both TGF-β1 and TGF-β2. Wound repair of AECs was significantly reduced by a specific inhibitor of TGF-β type I receptor kinase activity. We investigated whether the TGF-β-enhanced repair required epidermal growth factor receptor (EGFR) transactivation and secretion of EGFR ligands. Both TGF-β1 and TGF-β2 enhanced EGFR phosphorylation and induced production of heparin-binding EGF-like growth factor (HB-EGF) and transforming growth factor-alpha (TGF-α) in AECs. Moreover, treatment with a broad-spectrum metalloproteinase inhibitor or anti-HB-EGF and anti-TGF-α antibodies inhibited the wound repair and the EGFR phosphorylation by TGF-β1 and TGF-β2, indicating that the TGF-β1 and TGF-β2 effects on wound repair required the release of HB-EGF and TGF-α. Our data, for the first time, have shown that both TGF-β1 and TGF-β2 play a stimulatory role in airway epithelial repair through EGFR phosphorylation following autocrine production of HB-EGF and TGF-α. These findings highlight an important collaborative mechanism between TGF-β and EGFR in maintaining airway epithelial homeostasis.

TGF-β/Smad3 signaling promotes renal fibrosis by inhibiting miR-29

TGF-β/Smad3 signaling promotes fibrosis, but the development of therapeutic interventions involving this pathway will require the identification and ultimate targeting of downstream fibrosis-specific genes. In this study, using a microRNA microarray and real-time PCR, wild-type mice had reduced expression of miR-29 along with the development of progressive renal fibrosis in obstructive nephropathy. In contrast, Smad3 knockout mice had increased expression of miR-29 along with the absence of renal fibrosis in the same model of obstruction. In cultured fibroblasts and tubular epithelial cells, Smad3 mediated TGF-β(1)-induced downregulation of miR-29 by binding to the promoter of miR-29. Furthermore, miR-29 acted as a downstream inhibitor and therapeutic microRNA for TGF-β/Smad3-mediated fibrosis. In vitro, overexpression of miR-29b inhibited, but knockdown of miR-29 enhanced, TGF-β(1)-induced expression of collagens I and III by renal tubular cells. Ultrasound-mediated gene delivery of miR-29b either before or after established obstructive nephropathy blocked progressive renal fibrosis. In conclusion, miR-29 is a downstream inhibitor of TGF-β/Smad3-mediated fibrosis and may have therapeutic potential for diseases involving fibrosis.

A novel role of peripheral corticotropin-releasing hormone (CRH) on dermal fibroblasts

Corticotropin-releasing hormone, or factor, (CRH or CRF) exerts important biological effects in multiple peripheral tissues via paracrine/autocrine actions. The aim of our study was to assess the effects of endogenous CRH in the biology of mouse and human skin fibroblasts, the primary cell type involved in wound healing. We show expression of CRH and its receptors in primary fibroblasts, and we demonstrate the functionality of fibroblast CRH receptors by induction of cAMP. Fibroblasts genetically deficient in Crh (Crh-/-) had higher proliferation and migration rates and compromised production of IL-6 and TGF-β1 compared to the wildtype (Crh+/+) cells. Human primary cultures of foreskin fibroblasts exposed to the CRF(1) antagonist antalarmin recapitulated the findings in the Crh-/- cells, exhibiting altered proliferative and migratory behavior and suppressed production of IL-6. In conclusion, our findings show an important role of fibroblast-expressed CRH in the proliferation, migration, and cytokine production of these cells, processes associated with the skin response to injury. Our data suggest that the immunomodulatory effects of CRH may include an important, albeit not explored yet, role in epidermal tissue remodeling and regeneration and maintenance of tissue homeostasis.

Inflammation and wound healing: the role of the macrophage

The macrophage is a prominent inflammatory cell in wounds, but its role in healing remains incompletely understood. Macrophages have many functions in wounds, including host defence, the promotion and resolution of inflammation, the removal of apoptotic cells, and the support of cell proliferation and tissue restoration following injury. Recent studies suggest that macrophages exist in several different phenotypic states within the healing wound and that the influence of these cells on each stage of repair varies with the specific phenotype. Although the macrophage is beneficial to the repair of normally healing wounds, this pleotropic cell type may promote excessive inflammation or fibrosis under certain circumstances. Emerging evidence suggests that macrophage dysfunction is a component of the pathogenesis of nonhealing and poorly healing wounds. As a result of advances in the understanding of this multifunctional cell, the macrophage continues to be an attractive therapeutic target, both to reduce fibrosis and scarring, and to improve healing of chronic wounds.

Cytochrome P450 epoxygenase CYP2J2 attenuates nephropathy in streptozotocin-induced diabetic mice

Cytochrome P450 (CYP) epoxygenases metabolize arachidonic acid into epoxyeicosatrienoic acids (EETs), which play important and diverse roles in the cardiovascular system. The anti-inflammatory, anti-apoptotic, pro-angiogenic, and anti-hypertensive properties of EETs in the cardiovascular system suggest a beneficial role for EETs in diabetic nephropathy. This study investigated the effects of endothelial specific overexpression of CYP2J2 epoxygenase on diabetic nephropathy in streptozotocin-induced diabetic mice. Endothelial CYP2J2 overexpression attenuated renal damage as measured by urinary microalbumin and glomerulosclerosis. These effects were associated with inhibition of TGF-β/Smad signaling in the kidney. Indeed, overexpression of CYP2J2 prevented TGF-β1-induced renal tubular epithelial-mesenchymal transition in vitro. These findings highlight the beneficial roles of the CYP epoxygenase-EET system in the pathogenesis of diabetic nephropathy.

The role of p21 in regulating mammalian regeneration

The MRL (Murphy Roths Large) mouse has provided a unique model of adult mammalian regeneration as multiple tissues show this important phenotype. Furthermore, the healing employs a blastema-like structure similar to that seen in amphibian regenerating tissue. Cells from the MRL mouse display DNA damage, cell cycle G2/M arrest, and a reduced level of p21^CIP1/WAF. A functional role for p21 was confirmed when tissue injury in an adult p21^-/- mouse showed a healing phenotype that matched the MRL mouse, with the replacement of tissues, including cartilage, and with hair follicle formation and a lack of scarring. Since the major canonical function of p21 is part of the p53/p21 axis, we explored the consequences of p53 deletion. A regenerative response was not seen in a p53^-/- mouse and the elimination of p53 from the MRL background had no negative effect on the regeneration of the MRL.p53^-/- mouse. An exploration of other knockout mice to identify p21-dependent, p53-independent regulatory pathways involved in the regenerative response revealed another significant finding showing that elimination of transforming growth factor-β1 displayed a healing response as well. These results are discussed in terms of their effect on senescence and differentiation.

TAK1-TAB2 signaling contributes to bone destruction by breast carcinoma cells

Advanced-stage breast cancers frequently metastasize to the bones and cause bone destruction, but the underlying mechanism is not fully understood. This study presents evidence that TGF-β-activated protein kinase 1 (TAK1) signaling in tumor cells promotes bone destruction by metastatic breast carcinoma cells, controlling expression of prometastatic factors including matrix metalloproteinase (MMP) 9 and COX2. Suppression of TAK1 signaling by dominant-negative TAK1 (dn-TAK1) in breast carcinoma MDA-MB-231 cells impairs bone colonization by carcinoma cells and bone osteolysis in the intracardiac injection model. Mechanistic studies showed that inhibition of TAK1 by dn-TAK1 or siRNA blocked expression of factors implicated in bone metastasis, such as MMP-9, COX2/PTGS2, parathyroid hormone-related protein (PTHrP) and interleukin 8 (IL-8), but did not affect activation of p38MAPK by TGF-β. TAK1 signaling is mediated by TAK1-binding partners TAB1, TAB2, and TAB3. Carcinoma cells express elevated mRNA levels of TAB2 and TAB3, whereas the TAB1 expression is noticeably low. Accordingly, depletion of TAB2 by siRNA reduced expression of MMP-9 and COX2. Together, these studies show that the TAK1-TAB2-TAB3 signaling axis is critical for carcinoma-induced bone lesions, mediating expression of proinvasive and osteolytic factors. These findings identify the TAK1-TAB2 axis as a potential therapeutic target in bone metastasis.

Wound repair: toward understanding and integration of single-cell and multicellular wound responses

The importance of wound healing to medicine and biology has long been evident, and consequently, wound healing has been the subject of intense investigation for many years. However, several relatively recent developments have added new impetus to wound repair research: the increasing application of model systems; the growing recognition that single cells have a robust, complex, and medically relevant wound healing response; and the emerging recognition that different modes of wound repair bear an uncanny resemblance to other basic biological processes such as morphogenesis and cytokinesis. In this review, each of these developments is described, and their significance for wound healing research is considered. In addition, overlapping mechanisms of single-cell and multicellular wound healing are highlighted, and it is argued that they are more similar than is often recognized. Based on this and other information, a simple model to explain the evolutionary relationships of cytokinesis, single-cell wound repair, multicellular wound repair, and developmental morphogenesis is proposed. Finally, a series of important, but as yet unanswered, questions is posed.

The regulation and functions of activin and follistatin in inflammation and immunity

The activins are members of the transforming growth factor β superfamily with broad and complex effects on cell growth and differentiation. Activin A has long been known to be a critical regulator of inflammation and immunity, and similar roles are now emerging for activin B, with which it shares 65% sequence homology. These molecules and their binding protein, follistatin, are widely expressed, and their production is increased in many acute and chronic inflammatory conditions. Synthesis and release of the activins are stimulated by inflammatory cytokines, Toll-like receptor ligands, and oxidative stress. The activins interact with heterodimeric serine/threonine kinase receptor complexes to activate SMAD transcription factors and the MAP kinase signaling pathways, which mediate inflammation, stress, and immunity. Follistatin binds to the activins with high affinity, thereby obstructing the activin receptor binding site, and targets them to cell surface proteoglycans and lysosomal degradation. Studies on transgenic mice and those with gene knockouts, together with blocking studies using exogenous follistatin, have established that activin A plays critical roles in the onset of cachexia, acute and chronic inflammatory responses such as septicemia, colitis and asthma, and fibrosis. However, activin A also directs the development of monocyte/macrophages, myeloid dendritic cells, and T cell subsets to promote type 2 and regulatory immune responses. The ability of both endogenous and exogenous follistatin to block the proinflammatory and profibrotic actions of activin A has led to interest in this binding protein as a potential therapeutic for limiting the severity of disease and to improve subsequent damage associated with inflammation and fibrosis. However, the ability of activin A to sculpt the subsequent immune response as well means that the full range of effects that might arise from blocking activin bioactivity will need to be considered in any therapeutic applications.

Smad phosphoisoform signals in acute and chronic liver injury: similarities and differences between epithelial and mesenchymal cells

Hepatocellular carcinoma (HCC) usually arises from hepatic fibrosis caused by chronic inflammation. In chronic liver damage, hepatic stellate cells undergo progressive activation to myofibroblasts (MFB), which are important extracellular-matrix-producing mesenchymal cells. Concomitantly, perturbation of transforming growth factor (TGF)-β signaling by pro-inflammatory cytokines in the epithelial cells of the liver (hepatocytes) promotes both fibrogenesis and carcinogenesis (fibro-carcinogenesis). Insights into fibro-carcinogenic effects on chronically damaged hepatocytes have come from recent detailed analyses of the TGF-β signaling process. Smad proteins, which convey signals from TGF-β receptors to the nucleus, have intermediate linker regions between conserved Mad homology (MH) 1 and MH2 domains. TGF-β type I receptor and pro-inflammatory cytokine-activated kinases differentially phosphorylate Smad2 and Smad3 to create phosphoisoforms phosphorylated at the COOH-terminal, linker, or both (L/C) regions. After acute liver injury, TGF-β-mediated pSmad3C signaling terminates hepatocytic proliferation induced by the pro-inflammatory cytokine-mediated mitogenic pSmad3L pathway; TGF-β and pro-inflammatory cytokines synergistically enhance collagen synthesis by activated hepatic stellate cells via pSmad2L/C and pSmad3L/C pathways. During chronic liver disease progression, pre-neoplastic hepatocytes persistently affected by TGF-β together with pro-inflammatory cytokines come to exhibit the same carcinogenic (mitogenic) pSmad3L and fibrogenic pSmad2L/C signaling as do MFB, thereby accelerating liver fibrosis while increasing risk of HCC. This review of Smad phosphoisoform-mediated signals examines similarities and differences between epithelial and mesenchymal cells in acute and chronic liver injuries and considers Smad linker phosphorylation as a potential target for the chemoprevention of fibro-carcinogenesis.

Origins of injection-site sarcomas in cats: the possible role of chronic inflammation-a review

The etiology of feline injection-site sarcomas remains obscure. Sarcomas and other tumors are known to be associated with viral infections in humans and other animals, including cats. However, the available evidence suggests that this is not the case with feline injection-site sarcomas. These tumors have more in common with sarcomas noted in experimental studies with laboratory animals where foreign materials such as glass, plastics, and metal are the causal agent. Tumors arising with these agents are associated with chronic inflammation at the injection or implantation sites. Similar tumors have been observed, albeit infrequently, at microchip implantation sites, and these also are associated with chronic inflammation. It is suggested that injection-site sarcomas in cats may arise at the administration site as a result of chronic inflammation, possibly provoked by adjuvant materials, with subsequent DNA damage, cellular transformation, and clonal expansion. However, more fundamental research is required to elucidate the mechanisms involved.

Smad3-dependent signaling underlies the TGF-β1-mediated enhancement in astrocytic iNOS expression

We previously demonstrated that transforming growth factor-beta1 (TGF-beta1), while having no effect alone, enhances nitric oxide (NO) production in primary, purified mouse astrocytes induced by lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma), by recruiting a latent population of astrocytes to respond, thereby enhancing the total number of cells that express Nos2. In this investigation, we evaluated the molecular signaling pathway by which this occurs. We found that purified murine primary astrocytes express mRNA for TGFbetaRII as well as the TGFbetaRI subunit activin-like kinase 5 (ALK5), but not ALK1. Immunofluorescence microscopy confirmed the expression of TGFbetaRII and ALK5 protein in astrocytes. Consistent with ALK5 signaling, Smad3 accumulated in the nucleus of astrocytes as early as 30 min after TGF-beta1 (3 ng/mL) treatment and persisted upto 32 hr after TGF-beta1 administration. Addition of ALK5 inhibitors prevented TGF-beta1-mediated Smad3 nuclear accumulation and NO production when given prior to the Nos2 induction stimuli, but not after. Finally, astrocyte cultures derived from Smad3 null mutant mice did not exhibit a TGF-beta1-mediated increase in iNOS expression. Overall, this data suggests that ALK5 signaling and Smad3 nuclear accumulation is required for optimal enhancement of LPS plus IFNgamma-induced NO production in astrocytes by TGF-beta1.

Comparative effects of TGF-β2/Smad2 and TGF-β2/Smad3 signaling pathways on proliferation, migration, and extracellular matrix production in a human lens cell line

The signaling pathway of transforming growth factor β2 (TGF-β2)/Smad plays an important role in the pathological process in posterior capsule opacification (PCO) after cataract surgery. Smad2 and Smad3 are both receptor-regulated Smads (R-Smads) of the TGF-β2 signaling pathway. We aim to find which among Smad2, Smad3, and Smad2&3 plays a key role in PCO pathology. The signal characteristics of TGF-β2 and Smad proteins in the human lens cell line HLE-B3 were investigated. Smad2, Smad3, or Smad2&3 were silenced using small interfering RNA. We then tested cell proliferation by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and cell growth curve assays, migration by transwell and wound-healing assays, and extracellular matrix production including α-smooth muscle actin (αSMA), fibronectin, and type I collagen by real-time PCR assay, with and without TGF-β2 exposure. Silencing Smad3 blocked the effect of TGF-β2 on cell proliferation and production of fibronectin and type I collagen. Silencing Smad2 blocked the effect of TGF-β2 on cell migration and production of αSMA. Smad2 depletion enhanced Smad3 activity in cell proliferation and ECM production, whereas Smad3 depletion enhanced Smad2 activity in migration and αSMA expression. Silencing Smad2 and Smad3 efficiently blocked the effect of TGF-β2on cell proliferation, migration, and extracellular matrix production. Smad2 and Smad3 are both key in the TGF-β2 signaling pathway. We can prevent the development of PCO following cataract surgery by blocking the TGF-β2/Smad2&3 signaling pathway.

Smad3 contributes to positioning of proliferating cells in colonic crypts by inducing EphB receptor protein expression

Deficiency of Smad3, an intracellular mediator of TGF-β, was shown to significantly accelerate re-epithelialization of the colonic mucosa. This study was performed to investigate the molecular mechanisms by which Smad3 controls colonic epithelial cell proliferation and crypt formation. Smad3(ex8/ex8) C57BL/6 mice were used in this study and wild-type littermates served as controls. The number of proliferating cells in the isolated colonic epithelium of Smad3(-/-) mice was significantly increased compared to that in wild-type littermates. Protein levels of the cell cycle inhibitors p21 and p27 were significantly decreased, while that of c-Myc was increased in the isolated colonic epithelium from Smad3(-/-) mice. In the colonic tissue of wild-type mice, cell proliferation was restricted to the bottom of the crypts in accordance with nuclear β-catenin staining, whereas proliferating cells were located throughout the crypts in Smad3(-/-) mice in accordance with nuclear β-catenin staining, suggesting that Smad3 is essential for locating proliferating cells at the bottom of the colonic crypts. Notably, in Smad3(-/-) mice, there was loss of EphB2 and EphB3 receptor protein expression, critical regulators of proliferating cell positioning, while EphB receptor protein expression was confirmed at the bottom of the colonic crypts in wild-type mice. These observations indicated that disturbance of the EphB/ephrin B system brings about mispositioning of proliferating cells in the colonic crypts of Smad3(-/-) mice. In conclusion, Smad3 is essential for controlling number and positioning of proliferating cells in the colonic crypts and contributes to formation of a "proliferative zone" at the bottom of colonic crypts in the normal colon.

Macrophages in skin injury and repair

After recruitment to the wound bed, monocytes differentiate into macrophages. Macrophages play a central role in all stages of wound healing and orchestrate the wound healing process. Their functional phenotype is dependent on the wound microenvironment, which changes during healing, hereby altering macrophage phenotype. During the early and short inflammatory phase macrophages exert pro-inflammatory functions like antigen-presenting, phagocytosis and the production of inflammatory cytokines and growth factors that facilitate the wound healing process. As such, the phenotype of wound macrophages in this phase is probably the classically activated or the so-called M1 phenotype. During the proliferative phase, macrophages stimulate proliferation of connective, endothelial and epithelial tissue directly and indirectly. Especially fibroblasts, keratinocytes and endothelial cells are stimulated by macrophages during this phase to induce and complete ECM formation, reepithelialization and neovascularization. Subsequently, macrophages can change the composition of the ECM both during angiogenesis and in the remodelling phase by release of degrading enzymes and by synthesizing ECM molecules. This suggests an important role for alternatively activated macrophages in this phase of wound healing. Pathological functioning of macrophages in the wound healing process can result in derailed wound healing, like the formation of ulcers, chronic wounds, hypertrophic scars and keloids. However, the exact role of macrophages in these processes is still incompletely understood. For treating wound repair disorders more should be elucidated on the role of macrophages in these conditions, especially their functional phenotype, to find more therapeutic opportunities. This review summarizes macrophage function in skin injury repair, thereby providing more insight in macrophage function in wound healing and possible interventions in this process.

Adaptive immunity in the host-microbiota dialog

The intestinal tract represents the largest mucosal surface and is a major site of multifaceted interactions between the host mucosal immune system and components of the intestinal microbiota. Host immune responses to the commensal microbiota are tightly controlled and, meanwhile, the microbiota actively shapes intestinal immune responses to itself. Appreciation of these interactions during health and disease may direct therapeutic approaches to a broad range of autoimmune and inflammatory disorders in humans. In this review, we will discuss findings on how the intestinal immune system, especially adaptive immune cells, helps accommodate the large number of resident bacteria, and in turn how the microbiota shapes intestinal immune responses to achieve mutualism.

Small molecule inhibitor of type I transforming growth factor-β receptor kinase ameliorates the inhibitory milieu in injured brain and promotes regeneration of nigrostriatal dopaminergic axons

Transforming growth factor-β (TGF-β), a multifunctional cytokine, plays a crucial role in wound healing in the damaged central nervous system. To examine effects of the TGF-β signaling inhibition on formation of scar tissue and axonal regeneration, the small molecule inhibitor of type I TGF-β receptor kinase LY-364947 was continuously infused in the lesion site of mouse brain after a unilateral transection of the nigrostriatal dopaminergic pathway. At 2 weeks after injury, the fibrotic scar comprising extracellular matrix molecules including fibronectin, type IV collagen, and chondroitin sulfate proteoglycans was formed in the lesion center, and reactive astrocytes were increased around the fibrotic scar. In the brain injured and infused with LY-364947, fibrotic scar formation was suppressed and decreased numbers of reactive astrocytes occupied the lesion site. Although leukocytes and serum IgG were observed within the fibrotic scar in the injured brain, they were almost absent in the injured and LY-364947-treated brain. At 2 weeks after injury, tyrosine hydroxylase (TH)-immunoreactive fibers barely extended beyond the fibrotic scar in the injured brain, but numerous TH-immunoreactive fibers regenerated over the lesion site in the LY-364947-treated brain. These results indicate that inhibition of TGF-β signaling suppresses formation of the fibrotic scar and creates a permissive environment for axonal regeneration.

Radiation-induced liver fibrosis is mitigated by gene therapy inhibiting transforming growth factor-β signaling in the rat

PURPOSE

We determined whether anti-transforming growth factor-β (TGF-β) intervention could halt the progression of established radiation-induced liver fibrosis (RILF).

METHODS AND MATERIALS

A replication-defective adenoviral vector expressing the extracellular portion of human TβRII and the Fc portion of immunoglobulin G fusion protein (AdTβRIIFc) was produced. The entire rat liver was exposed to 30 Gy irradiation to generate a RILF model (RILFM). Then, RILFM animals were treated with AdTβRIIFc (1 × 10(11) plaque-forming units [PFU] of TβRII), control virus (1 × 10(11) PFU of AdGFP), or saline. Delayed radiation liver injury was assessed by histology and immunohistochemistry. Chronic oxidative stress damage, hepatic stellate cell activation, and hepatocyte regeneration were also analyzed.

RESULTS

In rats infected with AdTβRIIFc, fibrosis was significantly improved compared with rats treated with AdGFP or saline, as assessed by histology, hydroxyproline content, and serum level of hyaluronic acid. Compared with AdGFP rats, AdTβRIIFc-treated rats exhibited decreased oxidative stress damage and hepatic stellate cell activation and preserved liver function.

CONCLUSIONS

Our results demonstrate that TGF-β plays a critical role in the progression of liver fibrosis and suggest that anti-TGF-β intervention is feasible and ameliorates established liver fibrosis. In addition, chronic oxidative stress may be involved in the progression of RILF.

Target-seeking antifibrotic compound enhances wound healing and suppresses scar formation in mice

Permanent scars form upon healing of tissue injuries such as those caused by ischemia (myocardial infarction, stroke), trauma, surgery, and inflammation. Current options in reducing scar formation are limited to local intervention. We have designed a systemically administered, target-seeking biotherapeutic for scar prevention. It consists of a vascular targeting peptide that specifically recognizes angiogenic blood vessels and extravasates into sites of injury, fused with a therapeutic molecule, decorin. Decorin prevents tissue fibrosis and promotes tissue regeneration by inhibiting TGF-β activity and by other regulatory activities. The decorin-targeting peptide fusion protein had substantially increased neutralizing activity against TGF-β1 in vitro compared with untargeted decorin. In vivo, the fusion protein selectively accumulated in wounds, and promoted wound healing and suppressed scar formation at doses where nontargeted decorin was inactive. These results show that selective targeting yields a tissue-healing and scar-reducing compound with enhanced specificity and potency. This approach may help make reducing scar formation by systemic drug delivery a feasible option for surgery and for the treatment of pathological processes in which scar formation is a problem.

Scarless fetal wound healing: a basic science review

SUMMARY

Scar formation is a major medical problem that can have devastating consequences for patients. The adverse physiological and psychological effects of scars are broad, and there are currently no reliable treatments to prevent scarring. In contrast to adult wounds, early gestation fetal skin wounds repair rapidly and in the absence of scar formation. Despite extensive investigation, the exact mechanisms of scarless fetal wound healing remain largely unknown. For some time, it has been known that significant differences exist among the extracellular matrix, inflammatory response, cellular mediators, and gene expression profiles of fetal and postnatal wounds. These differences may have important implications in scarless wound repair.

Epimorphic regeneration in mice is p53-independent

The process of regeneration is most readily studied in species of sponge, hydra, planarian and salamander (i.e., newt and axolotl). The closure of MRL mouse ear pinna through-and-through holes provides a mammalian model of unusual wound healing/regeneration in which a blastema-like structure closes the ear hole and cartilage and hair follicles are replaced. Recent studies, based on a broad level of DNA damage and a cell cycle pattern of G₂/M "arrest," showed that p21(Cip1/Waf1) was missing from the MRL mouse ear and that a p21-null mouse could close its ear holes. Given the p53/p21 axis of control of DNA damage, cell cycle arrest, apoptosis and senescence, we tested the role of p53 in the ear hole regenerative response. Using backcross mice, we found that loss of p53 in MRL mice did not show reduced healing. Furthermore, cross sections of MRL. p53(-/-) mouse ears at 6 weeks post-injury showed an increased level of adipocytes and chondrocytes in the region of healing whereas MRL or p21(-/-) mice showed chondrogenesis alone in this same region, though at later time points. In addition, we also investigated other cell cycle-related mutant mice to determine how p21 was being regulated. We demonstrate that p16 and Gadd45 null mice show little healing capacity. Interestingly, a partial healing phenotype in mice with a dual Tgfβ/Rag2 knockout mutation was seen. These data demonstrate an independence of p53 signaling for mouse appendage regeneration and suggest that the role of p21 in this process is possibly through the abrogation of the Tgfβ/Smad pathway.

Overexpression of transforming growth factor (TGF)-beta1 and TGF-beta3 genes in lung of toxic-inhaled patients

Iraq frequently used toxic inhalants during the war with Iran, exposing over 100,000 people to chemical reagents. Bronchiolitis obliterans (BO) is a major pulmonary disease caused by exposure to harmful gases. Recently defect in clearance of apoptotic cells (efferocytosis) has been suggested as a mechanism that leads to several lung diseases. Transforming growth factor (TGF)-beta, a cytokine produced by efferocytotic macrophages, suppresses the inflammation and enhances the regeneration of tissue. In this study, the authors compared the expression of these 3 isoforms of TGF-beta at mRNA level in lung biopsies of Iranian victims of chemical gases with lung biopsies of control healthy volunteers. Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) technique was used to examine the expression level of TGF-beta isoforms using glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene as an internal control. The results indicated that that levels of TGF-beta1 and TGF-beta3 mRNAs were significantly higher in chemical gas-injured patients than noninjured group (P < .05). Therefore, the authors speculate that TGF-beta1 and TGFbeta3, but not TGF-beta2, secretion is a result of efficient efferocytosis in chemically injured patients, playing a protective role by improving airway remodeling and lung homeostasis in this group. These properties of TGF-beta are consistent with long-time survival of chemical-injured people suffering from BO.

Notch1 deficiency results in decreased inflammation during wound healing and regulates vascular endothelial growth factor receptor-1 and inflammatory cytokine expression in macrophages

We investigated whether Notch signaling plays a role in regulating macrophage responses to inflammation. In a wound healing assay, macrophage recruitment was decreased in Notch1(+/-) mice, and the wounds were characterized by decreased TNF-α expression. As wound healing progressed, Notch1(+/-) wounds had increased vascularization and collagen deposition compared with wild-type wounds. In mice with myeloid-specific Notch1 deletion, wounds had decreased macrophage recruitment as well as decreased TNF-α expression, indicating the specific role of Notch1 in the inflammatory response in these cells. In vitro, we found that vascular endothelial growth factor receptor-1 (VEGFR-1) was upregulated in macrophages in response to LPS/IFN-γ and that this upregulation depended on Notch signaling. Furthermore, macrophages from Notch1(+/-) mice had decreased expression of VEGFR-1 compared with macrophages from wild-type mice, whereas VEGFR-1 expression in Notch4(-/-) macrophages was normal. Inhibition of Notch signaling decreased induction of the inflammatory cytokines IL-6, IL-12, CXCL10, MCP-1, monokine induced by IFN-γ, and TNF-α in macrophages in response to LPS/IFN-γ. Additionally, macrophages from Notch1(+/-) mice demonstrated decreased induction of IL-6, IL-12, and TNF-α in response to stimulation compared with wild-type mice. Thus, both pharmacological inhibition of Notch and genetic analysis demonstrate that Notch1 regulates VEGFR-1 and cytokine expression in macrophages. We have also established that Notch1 is important for the inflammatory response during wound healing in mice.

Gene delivery of a mutant TGFβ3 reduces markers of scar tissue formation after cutaneous wounding

The transforming growth factor-β (TGFβ) family plays a critical regulatory role in repair and coordination of remodeling after cutaneous wounding. TGFβ1-mediated chemotaxis promotes the recruitment of fibroblasts to the wound site and their resultant myofibroblastic transdifferentiation that is responsible for elastic fiber deposition and wound closure. TGFβ3 has been implicated in an antagonistic role regulating overt wound closure and promoting ordered dermal remodeling. We generated a mutant form of TGFβ3 (mutTGFβ3) by ablating its binding site for the latency-associated TGFβ binding protein (LTBP-1) in order to improve bioavailability and activity. The mutated cytokine is secreted as the stable latency-associated peptide (LAP)-associated form and is activated by normal intracellular and extracellular mechanisms including integrin-mediated activation but is not sequestered. We show localized intradermal transduction using a lentiviral vector expressing the mutTGFβ3 in a mouse skin wounding model reduced re-epithelialization density and fibroblast/myofibroblast transdifferentiation within the wound area, both indicative of reduced scar tissue formation.