Interference with transforming growth factor-beta/ Smad3 signaling results in accelerated healing of wounds in previously irradiated skin

TGFβ1 inhibition increases the radiosensitivity of breast cancer cells in vitro and promotes tumor control by radiation in vivo

PURPOSE

To determine whether inhibition of TGFβ signaling prior to irradiation sensitizes human and murine cancer cells in vitro and in vivo.

EXPERIMENTAL DESIGN

TGFβ-mediated growth and Smad phosphorylation of MCF7, Hs578T, MDA-MB-231, and T47D human breast cancer cell lines were examined and correlated with clonogenic survival following graded radiation doses with and without pretreatment with LY364947, a small molecule inhibitor of the TGFβ type I receptor kinase. The DNA damage response was assessed in irradiated MDA-MB-231 cells pretreated with LY364947 in vitro and LY2109761, a pharmacokinetically stable inhibitor of TGFβ signaling, in vivo. The in vitro response of a syngeneic murine tumor, 4T1, was tested using a TGFβ neutralizing antibody, 1D11, with single or fractionated radiation doses in vivo.

RESULTS

Human breast cancer cell lines pretreated with TGFβ small molecule inhibitor were radiosensitized, irrespective of sensitivity to TGFβ growth inhibition. Consistent with increased clonogenic cell death, radiation-induced phosphorylation of H2AX and p53 was significantly reduced in MDA-MB-231 triple-negative breast cancer cells when pretreated in vitro or in vivo with a TGFβ type I receptor kinase inhibitor. Moreover, TGFβ neutralizing antibodies increased radiation sensitivity, blocked γH2AX foci formation, and significantly increased tumor growth delay in 4T1 murine mammary tumors in response to single and fractionated radiation exposures.

CONCLUSION

These results show that TGFβ inhibition prior to radiation attenuated DNA damage responses, increased clonogenic cell death, and promoted tumor growth delay, and thus may be an effective adjunct in cancer radiotherapy.

Human fat grafting alleviates radiation skin damage in a murine model

BACKGROUND

Autogenous fat grafting has been observed to alleviate the sequelae of chronic radiodermatitis. To date, no study has replicated this finding in an animal model.

METHODS

The dorsa of adult wild-type FVB mice were shaved and depilated. The dorsal skin was then distracted away from the body and irradiated (45 Gy). Four weeks after irradiation, 1.5-cc fat or sham grafts were placed in the dorsal subcutaneous space. Gross results were analyzed photometrically. The animals were euthanized at 4 and 8 weeks after fat or sham grafting and their dorsal skin was processed for histologic analysis.

RESULTS

Hyperpigmentation and ulceration were grossly improved in fat-grafted mice compared with sham-grafted controls. This improvement manifested histologically in a number of ways. For example, epidermal thickness measurements demonstrated decreased thickness in fat-grafted animals at both time points (20.6 ± 1.5 μm versus 55.2 ± 5.6 μm, p = 0.004; 17.6 ± 1.1 μm versus 36.3 ± 6.1 μm, p = 0.039). Picrosirius red staining demonstrated a diminished scar index in fat-treated animals at both time points as well (0.54 ± 0.05 versus 0.74 ± 0.07, p = 0.034; and 0.55 ± 0.06 versus 0.93 ± 0.07, p = 0.001).

CONCLUSION

Fat grafting attenuates inflammation in acute radiodermatitis and slows the progression of fibrosis in chronic radiodermatitis.

Fat grafting accelerates revascularisation and decreases fibrosis following thermal injury

BACKGROUND

Fat grafting has been shown clinically to improve the quality of burn scars. To date, no study has explored the mechanism of this effect. We aimed to do so by combining our murine model of fat grafting with a previously described murine model of thermal injury.

METHODS

Wild-type FVB mice (n=20) were anaesthetised, shaved and depilitated. Brass rods were heated to 100°C in a hot water bath before being applied to the dorsum of the mice for 10s, yielding a full-thickness injury. Following a 2-week recovery period, the mice underwent Doppler scanning before being fat/sham grafted with 1.5cc of human fat/saline. Half were sacrificed 4 weeks following grafting, and half were sacrificed 8 weeks following grafting. Both groups underwent repeat Doppler scanning immediately prior to sacrifice. Burn scar samples were taken following sacrifice at both time points for protein quantification, CD31 staining and Picrosirius red staining.

RESULTS

Doppler scanning demonstrated significantly greater flux in fat-grafted animals than saline-grafted animals at 4 weeks (fat=305±15.77mV, saline=242±15.83mV; p=0.026). Enzyme-linked immunosorbent assay (ELISA) analysis in fat-grafted animals demonstrated significant increase in vasculogenic proteins at 4 weeks (vascular endothelial growth factor (VEGF): fat=74.3±4.39ngml(-1), saline=34.3±5.23ngml(-1); p=0.004) (stromal cell-derived factor-1 (SDF-1): fat=51.8±1.23ngml(-1), saline grafted=10.2±3.22ngml(-1); p<0.001) and significant decreases in fibrotic markers at 8 weeks (transforming growth factor-ß1(TGF-ß): saline=9.30±0.93, fat=4.63±0.38ngml(-1); p=0.002) (matrix metallopeptidase 9 (MMP9): saline=13.05±1.21ngml(-1), fat=6.83±1.39ngml(-1); p=0.010). CD31 staining demonstrated significantly up-regulated vascularity at 4 weeks in fat-grafted animals (fat=30.8±3.39 vessels per high power field (hpf), saline=20.0±0.91 vessels per high power field (hpf); p=0.029). Sirius red staining demonstrated significantly reduced scar index in fat-grafted animals at 8 weeks (fat=0.69±0.10, saline=2.03±0.53; p=0.046).

CONCLUSIONS

Fat grafting resulted in more rapid revascularisation at the burn site as measured by laser Doppler flow, CD31 staining and chemical markers of angiogenesis. In turn, this resulted in decreased fibrosis as measured by Sirius red staining and chemical markers.

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.

The lens as a model for fibrotic disease

Fibrosis affects multiple organs and is associated with hyperproliferation, cell transdifferentiation, matrix modification and contraction. It is therefore essential to discover the key drivers of fibrotic events, which in turn will facilitate the development of appropriate therapeutic strategies. The lens is an elegant experimental model to study the processes that give rise to fibrosis. The molecular and cellular organization of the lens is well defined and consequently modifications associated with fibrosis can be clearly assessed. Moreover, the avascular and non-innervated properties of the lens allow effective in vitro studies to be employed that complement in vivo systems and relate to clinical data. Using the lens as a model for fibrosis has direct relevance to millions affected by lens disorders, but also serves as a valuable experimental tool to understand fibrosis per se.

A novel mouse model of cutaneous radiation injury

BACKGROUND

Radiation therapy is a cornerstone of oncologic treatment. Skin tolerance is often the limiting factor in radiotherapy. To study these issues and create modalities for intervention, the authors developed a novel murine model of cutaneous radiation injury.

METHODS

The dorsal skin was isolated using a low-pressure clamp and irradiated. Mice were followed for 8 weeks with serial photography and laser Doppler analysis. Sequential skin biopsy specimens were taken and examined histologically. Tensiometry was performed and Young's modulus calculated.

RESULTS

High-dose radiation isolated to dorsal skin causes progressive changes in skin perfusion, resulting in dermal thickening, fibrosis, persistent alopecia, and sometimes ulceration. There is increased dermal Smad3 expression, and decreased elasticity and bursting strength.

CONCLUSIONS

This model of cutaneous radiation injury delivers reproducible localized effects, mimicking the injury pattern seen in human subjects. This technique can be used to study radiation-induced injury to evaluate preventative and therapeutic strategies for these clinical issues.

Postinfarction healing dynamics in the mechanically unloaded rat left ventricle

The healing process is a key determinant for postinfarction left ventricular (LV) remodeling and the development of heart failure, which could be influenced by mechanical (pressure and/or volume) load. So far, limited information exists regarding an indepth characterization of the postinfarct healing process in the mechanically unloaded state. In the present work, we performed isogenic Lewis-to-Lewis rat abdominal heterotopic heart transplantation, which is characterized by hemodynamic unloading in the left ventricle, and simultaneously ligated the left anterior descending coronary artery (T-infarct group). Pathological evolution was dynamically compared with that of in situ infarcted Lewis hearts (I-infarct group) on days 3, 7, 14, and 35. There was a remarkable myocardial salvage in the unloaded heart, as shown by the improvement in infarct size (T-infarct group: 25.47% ± 4.31% vs. I-infarct group: 38.46% ± 4.82%, P < 0.01) and the smaller fraction of fibrosis in infarct segments (T-infarct group: 42.12% ± 8.40% vs. I-infarct group: 75.65% ± 10.51%, P < 0.01). In addition, there was a progressive disorganization of the two-dimensional collagen fiber alignment as well as retarded collagen fiber maturation in the T-infarct group. We also observed enhanced angiogenesis, lymphangiogenesis, and inflammatory cell retention in the infarct region during mechanical unloading. Moreover, capillary density and collagen deposition were significantly increased in the noninfarcted area of the unloaded heart compared with the same region in the in situ infarcted heart. In conclusion, ischemic insult in the mechanically unloaded heart elicits an altered inflammatory and healing response, which is characterized by myocardial salvage, delayed resolution of inflammation, and disorganization of the collagen orientation in the infarcted region. These findings could provide novel insights into the contribution of hemodynamic load in the postinfarction healing process. Further studies are warranted to elucidate its potential mechanism.

Modifying radiation damage

Radiation leaves a fairly characteristic footprint in biological materials, but this is rapidly all but obliterated by the canonical biological responses to the radiation damage. The innate immune recognition systems that sense "danger" through direct radiation damage and through associated collateral damage set in motion a chain of events that, in a tissue compromised by radiation, often unwittingly result in oscillating waves of molecular and cellular responses as tissues attempt to heal. Understanding "nature's whispers" that inform on these processes will lead to novel forms of intervention targeted more precisely towards modifying them in an appropriate and timely fashion so as to improve the healing process and prevent or mitigate the development of acute and late effects of normal tissue radiation damage, whether it be accidental, as a result of a terrorist incident, or of therapeutic treatment of cancer. Here we attempt to discuss some of the non-free radical scavenging mechanisms that modify radiation responses and comment on where we see them within a conceptual framework of an evolving radiation-induced lesion.

Regulators and mediators of radiation-induced fibrosis: Gene expression profiles and a rationale for Smad3 inhibition

OBJECTIVE: Radiotherapy, an essential modality in cancer treatment, frequently induces fibrotic processes in the skin, including accumulation of extracellular matrix. Transforming growth factor-β is essential in regulating extracellular matrix gene expression and is dependent on Smad3, an intracellular mediator/transcription factor. Our study characterized the genetic expression involved in extracellular matrix accumulation during radiationinduced fibrosis. We performed Smad3 gene silencing in an attempt to abrogate the effects of radiation.

STUDY DESIGN: Laboratory research.

SETTING: University laboratory.

SUBJECTS AND METHODS: C57 murine dermal fibroblasts were irradiated with 20 Gy RNA isolated (0, 6, 12, 24, 48, 72 hours postirradiation) and mRNA analyzed (reverse transcriptase polymerase chain reaction) for known regulators (Smad3, interleu-kin-13 [IL-13]), tumor necrosis factor-α [TNF-α]) and mediators of fibrosis (collagen 1A1 [Col1A1]), TGF-β, matrix metalloprotease-1 and −2 (MMP-1, MMP-2), and tissue inhibitor of metallo-protease-1 (TIMP-1). Smad3 gene expression was silenced using siRNA in an effort to restore an unirradiated gene profile.

RESULTS: Following irradiation, there was a steady increase in mRNA expression of Smad3, IL-13, TGF-β, Col1A1, MMP-2, TIMP-1, with peak at 12 to 24 hours and subsequent decline by 72 hours. TNF-α expression remained elevated throughout. MMP-1 showed minimal expression initially, which decreased to negligible by 72 hours. Inhibition of Smad3 significantly decreased expression of Col1A1, TGF-β, MMP-2, and TIMP-1. IL-13 and TNF-α expression was not affected by Smad3 silencing.

CONCLUSION: We have characterized the early-phase mRNA expression profiles of the major mediators of radiation-induced fibrosis. Smad3 siRNA effectively abrogated the elevation of Col1A1, TGF-β, TIMP-1, and MMP-2. IL-13 and TNF-α were unaffected by Smad3 silencing and appear to be minor regulators in fibrosis. These findings suggest a therapeutic rationale for Smad3 silencing in vivo.

Ultrafast mid-IR laser scalpel: protein signals of the fundamental limits to minimally invasive surgery

Lasers have in principle the capability to cut at the level of a single cell, the fundamental limit to minimally invasive procedures and restructuring biological tissues. To date, this limit has not been achieved due to collateral damage on the macroscale that arises from thermal and shock wave induced collateral damage of surrounding tissue. Here, we report on a novel concept using a specifically designed Picosecond IR Laser (PIRL) that selectively energizes water molecules in the tissue to drive ablation or cutting process faster than thermal exchange of energy and shock wave propagation, without plasma formation or ionizing radiation effects. The targeted laser process imparts the least amount of energy in the remaining tissue without any of the deleterious photochemical or photothermal effects that accompanies other laser wavelengths and pulse parameters. Full thickness incisional and excisional wounds were generated in CD1 mice using the Picosecond IR Laser, a conventional surgical laser (DELight Er:YAG) or mechanical surgical tools. Transmission and scanning electron microscopy showed that the PIRL laser produced minimal tissue ablation with less damage of surrounding tissues than wounds formed using the other modalities. The width of scars formed by wounds made by the PIRL laser were half that of the scars produced using either a conventional surgical laser or a scalpel. Aniline blue staining showed higher levels of collagen in the early stage of the wounds produced using the PIRL laser, suggesting that these wounds mature faster. There were more viable cells extracted from skin using the PIRL laser, suggesting less cellular damage. β-catenin and TGF-β signalling, which are activated during the proliferative phase of wound healing, and whose level of activation correlates with the size of wounds was lower in wounds generated by the PIRL system. Wounds created with the PIRL systsem also showed a lower rate of cell proliferation. Direct comparison of wound healing responses to a conventional surgical laser, and standard mechanical instruments shows far less damage and near absence of scar formation by using PIRL laser. This new laser source appears to have achieved the long held promise of lasers in minimally invasive surgery.

p21cip/WAF is a key regulator of long-term radiation damage in mesenchyme-derived tissues

This study aimed to determine the mechanisms responsible for long-term tissue damage following radiation injury. We irradiated p21-knockout (p21(-/-)) and wild-type (WT) mice and determined the long-term deleterious effects of this intervention on mesenchyme-derived tissues. In addition, we explored the mechanisms of radiation-induced mesenchymal stem cell (MSC) dysfunction in isolated bone marrow-derived cells. p21 expression was chronically elevated >200-fold in irradiated tissues. Loss of p21 function resulted in a >4-fold increase in the number of skin MSCs remaining after radiation. p21(-/-) mice had significantly less radiation damage, including 6-fold less scarring, 40% increased growth potential, and 4-fold more hypertrophic chondrocytes in the epiphyseal plate (P<0.01). Irradiated p21(-/-) MSCs had 4-fold increased potential for bone or fat differentiation, 4-fold greater proliferation rate, and nearly 7-fold lower senescence as compared to WT MSCs (P<0.01). Ectopic expression of p21 in knockout cells decreased proliferation and differentiation potential and recapitulated the WT phenotype. Loss of p21 function markedly decreases the deleterious effects of radiation injury in mesenchyme-derived tissues and preserves tissue-derived MSCs. In addition, p21 is a critical regulator of MSC proliferation, differentiation, and senescence both at baseline and in response to radiation.

Therapeutic improvement of scarring: mechanisms of scarless and scar-forming healing and approaches to the discovery of new treatments

Scarring in the skin after trauma, surgery, burn or sports injury is a major medical problem, often resulting in loss of function, restriction of tissue movement and adverse psychological effects. Whilst various studies have utilised a range of model systems that have increased our understanding of the pathways and processes underlying scar formation, they have typically not translated to the development of effective therapeutic approaches for scar management. Existing treatments are unreliable and unpredictable and there are no prescription drugs for the prevention or treatment of dermal scarring. As a consequence, scar improvement still remains an area of clear medical need. Here we describe the basic science of scar-free and scar-forming healing, the utility of pre-clinical model systems, their translation to humans, and our pioneering approach to the discovery and development of therapeutic approaches for the prophylactic improvement of scarring in man

Radioprotection in normal tissue and delayed tumor growth by blockade of CD47 signaling

Radiation-induced damage of normal tissues restricts the therapeutic doses of ionizing radiation that can be delivered to tumors and thereby limits the effectiveness of radiotherapy. Thrombospondin-1 signaling through its cell surface receptor CD47 limits recovery from several types of stress, and mice lacking either gene are profoundly resistant to radiation injury. We describe strategies to protect normal tissues from radiation damage using CD47 or thrombospondin-1 antibodies, a CD47-binding peptide, or antisense suppression of CD47. A morpholino oligonucleotide targeting CD47 confers radioresistance to human endothelial cells in vitro and protects soft tissue, bone marrow, and tumor-associated leukocytes in irradiated mice. In contrast, CD47 suppression in mice bearing melanoma or squamous lung tumors prior to irradiation result in 89% and 71% smaller tumors, respectively. Thus, inhibiting CD47 signaling maintains the viability of normal tissues following irradiation while increasing the radiosensitivity of tumors.

Radiation therapy causes loss of dermal lymphatic vessels and interferes with lymphatic function by TGF-beta1-mediated tissue fibrosis

Although radiation therapy is a major risk factor for the development of lymphedema following lymphadenectomy, the mechanisms responsible for this effect remain unknown. The purpose of this study was therefore to determine the effects of radiation on lymphatic endothelial cells (LECs) and lymphatic function. The tails of wild-type or acid sphingomyelinase (ASM)-deficient mice were treated with 0, 15, or 30 Gy of radiation and then analyzed for LEC apoptosis and lymphatic function at various time points. To analyze the effects of radiation fibrosis on lymphatic function, we determined the effects of transforming growth factor (TGF)-beta1 blockade after radiation in vivo. Finally, we determined the effects of radiation and exogenous TGF-beta1 on LECs in vitro. Radiation caused mild edema that resolved after 12-24 wk. Interestingly, despite resolution of tail edema, irradiated animals displayed persistent lymphatic dysfunction. Radiation caused loss of capillary lymphatics and was associated with a dose-dependent increase in LEC apoptosis. ASM-/- mice had significantly less LEC apoptosis; however, this finding did not translate to improved lymphatic function at later time points. Short-term blockade of TGF-beta1 function after radiation markedly decreased tissue fibrosis and significantly improved lymphatic function but did not alter LEC apoptosis. Radiation therapy decreases lymphatic reserve by causing depletion of lymphatic vessels and LECs as well as promoting soft tissue fibrosis. Short-term inhibition of TGF-beta1 activity following radiation improves lymphatic function and is associated with decreased soft tissue fibrosis. ASM deficiency confers LEC protection from radiation-induced apoptosis but does not prevent lymphatic dysfunction.

Pathogenesis of radiation-induced capsular contracture in tissue expander and implant breast reconstruction

BACKGROUND

Capsular contracture is the main complication in postmastectomy tissue expander and implant breast reconstruction in patients requiring radiotherapy. There is evidence that the wingless signaling pathway plays a central role in the pathogenesis of fibroproliferation in fibromatosis and hyperplastic skin wounds, involving multiple linked events leading to up-regulation of target genes and fibroproliferation. Here, the authors tested their hypothesis that the wingless signaling pathway may also regulate radiotherapy-induced fibroproliferation in capsular tissue around expanders/implants in breast reconstruction.

METHODS

Biopsies of the periprosthetic capsule were obtained from patients undergoing bilateral expander breast reconstruction in which one side was radiated and the other side was not radiated. Capsular biopsies were snap-frozen and stored at -80 degrees C for Western blot assays to determine protein content of phospho-glycogen-synthase-kinase-3beta (phospho-GSK-3beta), total GSK-3beta, beta-catenin, cyclooxygenase-2 (COX-2), and collagen types I and III (n = three to five patients), normalized to beta-actin. Immunostaining for beta-catenin in radiated and nonradiated capsular tissue was also performed. Slides were scanned and analyzed using Zeiss Mirax Scan.

RESULTS

The following protein content levels were significantly (p < 0.01) increased in radiated capsule compared with nonradiated capsule: phospho-GSK-3beta (6.7-fold), total GSK-3beta (3.0-fold), beta-catenin (2.3-fold), COX-2 (2.8-fold), and collagen type I (1.6-fold) and type III (1.8-fold). Immunohistochemical staining demonstrated increased fibroblast cytosolic beta-catenin staining and evidence of beta-catenin nuclear translocation in radiated compared with nonradiated capsular tissue.

CONCLUSION

Results from this study highlight the importance of the wingless signaling pathway in the pathogenesis of radiation-induced fibroproliferation associated with capsular contracture in expander/implant breast reconstruction.

Fate-determining mechanisms in epithelial-myofibroblast transition: major inhibitory role for Smad3

Smad3 inhibits activation of the smooth muscle actin promoter and functions as a timer for myogenic programming in the epithelium.

Epithelial–myofibroblast (MF) transition (EMyT) is a critical process in organ fibrosis, leading to α–smooth muscle actin (SMA) expression in the epithelium. The mechanism underlying the activation of this myogenic program is unknown. We have shown previously that both injury to intercellular contacts and transforming growth factor β (TGF-β) are indispensable for SMA expression (two-hit model) and that contact disruption induces nuclear translocation of myocardin-related transcription factor (MRTF). Because the SMA promoter harbors both MRTF-responsive CC(A/T)-rich GG element (CArG) boxes and TGF-β–responsive Smad-binding elements, we hypothesized that the myogenic program is mobilized by a synergy between MRTF and Smad3. In this study, we show that the synergy between injury and TGF-β exclusively requires CArG elements. Surprisingly, Smad3 inhibits MRTF-driven activation of the SMA promoter, and Smad3 silencing renders injury sufficient to induce SMA expression. Furthermore, Smad3 is degraded under two-hit conditions, thereby liberating the myogenic program. Thus, Smad3 is a critical timer/delayer of MF commitment in the epithelium, and EMyT can be dissected into Smad3-promoted (mesenchymal) and Smad3-inhibited (myogenic) phases.

Dermal transforming growth factor-beta responsiveness mediates wound contraction and epithelial closure

Stromal-epithelial interactions are important during wound healing. Transforming growth factor-beta (TGF-beta) signaling at the wound site has been implicated in re-epithelization, inflammatory infiltration, wound contraction, and extracellular matrix deposition and remodeling. Ultimately, TGF-beta is central to dermal scarring. Because scarless embryonic wounds are associated with the lack of dermal TGF-beta signaling, we studied the role of TGF-beta signaling specifically in dermal fibroblasts through the development of a novel, inducible, conditional, and fibroblastic TGF-beta type II receptor knockout (Tgfbr2(dermalKO)) mouse model. Full thickness excisional wounds were studied in control and Tgfbr2(dermalKO) back skin. The Tgfbr2(dermalKO) wounds had accelerated re-epithelization and closure compared with controls, resurfacing within 4 days of healing. The loss of TGF-beta signaling in the dermis resulted in reduced collagen deposition and remodeling associated with a reduced extent of wound contraction and elevated macrophage infiltration. Tgfbr2(dermalKO) and control skin had similar numbers of myofibroblastic cells, suggesting that myofibroblastic differentiation was not responsible for reduced wound contraction. However, several mediators of cell-matrix interaction were reduced in the Tgfbr2(dermalKO) fibroblasts, including alpha1, alpha2, and beta1 integrins, and collagen gel contraction was diminished. There were associated deficiencies in actin cytoskeletal organization of vasodilator-stimulated phosphoprotein-containing lamellipodia. This study indicated that paracrine and autocrine TGF-beta dermal signaling mechanisms mediate macrophage recruitment, re-epithelization, and wound contraction.

Essential roles for early growth response transcription factor Egr-1 in tissue fibrosis and wound healing

The early growth response gene (Egr-1) codes for a zinc finger transcription factor that has important roles in the regulation of cell growth, differentiation, and survival. Aberrant Egr-1 expression is implicated in carcinogenesis, inflammation, atherosclerosis, and ischemic injury. We reported previously that normal fibroblasts stimulated by transforming growth factor-ss showed rapid and transient induction of Egr-1. Moreover, we observed that tissue expression of Egr-1 was elevated in patients with scleroderma, which suggests that Egr-1 may be involved in tissue repair and fibrosis. Here, we investigated matrix remodeling and wound healing in mice harboring gain of function or loss of function mutations of Egr-1. Using the model of bleomycin-induced scleroderma, we found that the early influx of inflammatory cells into the skin and lungs, and the subsequent development of fibrosis in these organs, were markedly attenuated in Egr-1 null mice. Furthermore, full-thickness incisional skin wound healing was impaired, and skin fibroblasts lacking Egr-1 showed reduced migration and myofibroblast transdifferentiation in vitro. In contrast, transgenic mice with fibroblast-specific Egr-1 overexpression showed exuberant tissue repair, with enhanced collagen accumulation and increased tensile strength of incisional wounds. Together, these results point to the fundamental role that Egr-1 plays in the regulation of transforming growth factor-ss-dependent physiological and pathological matrix remodeling.

Therapeutic targets in malignant glioblastoma microenvironment

There is considerable evidence that the tissue microenvironment can suppress cancer and that microenvironment disruption is required for cancer growth and progression. Distortion of the microenvironment by tumor cells can promote growth, recruit nonmalignant cells that provide physiological resources, and facilitate invasion. Compared with the variable routes taken by cells to become cancers, the response of normal tissue to cancer is relatively consistent such that controlling cancer may be more readily achieved indirectly via the microenvironment. Here, we discuss 3 ideas about how the microenvironment, consisting of a vasculature, inflammatory cells, immune cells, growth factors, and extracellular matrix, might provide therapeutic targets in glioblastoma (GBM) in the context of radiotherapy (RT): (1) viable therapeutic targets exist in the GBM microenvironment, (2) RT alters the microenvironment of tissues and tumors; and (3) a potential benefit may be achieved by targeting the microenvironments induced by RT.

Mitochondrial targeting of a catalase transgene product by plasmid liposomes increases radioresistance in vitro and in vivo

To determine whether increased mitochondrially localized catalase was radioprotective, a human catalase transgene was cloned into a small pSVZeo plasmid and localized to the mitochondria of 32D cl 3 cells by adding the mitochondrial localization sequence of MnSOD (mt-catalase). The cell lines 32D-Cat and 32D-mt-Cat had increased catalase biochemical activity as confirmed by Western blot analysis compared to the 32D cl 3 parent cells. The MnSOD-overexpressing 32D cl 3 cell line, 2C6, had decreased baseline catalase activity that was increased in 2C6-Cat and 2C6-mt-Cat subclonal cell lines. 32D-mt-Cat cells were more radioresistant than 32D-Cat cells, but both were radioresistant relative to 32D cl 3 cells. 2C6-mt-Cat cells but not 2C6-Cat cells were radioresistant compared to 2C6 cells. Intratracheal injection of the mt-catalase-plasmid liposome complex (mt-Cat-PL) but not the catalase-plasmid liposome complex (Cat-PL) increased the resistance of C57BL/6NHsd female mice to 20 Gy thoracic irradiation compared to MnSOD-plasmid liposomes. Thus mitochondrially targeted overexpression of the catalase transgene is radioprotective in vitro and in vivo.

A novel TGF-beta antagonist speeds reepithelialization and reduces scarring of partial thickness porcine burns

Scar formation after thermal injury is common and results in significant aesthetic and functional impairment. Transforming growth factor beta (TGF-beta) plays a significant role in scar formation. We tested the hypothesis that a novel TGF-beta peptantagonist would reduce scar formation and wound contraction in partial thickness burns by using a randomized controlled experiment. The subjects include two domestic pigs (20-25 kg). Forty burns were created on the animal's dorsum using an aluminum bar preheated to 80 degrees C and applied for 20 seconds resulting in a partial thickness thermal burn extending half way down the dermis. Burns were treated every other day for 1 week, then twice weekly for 3 weeks with a topical TGF-beta antagonist or its vehicle. Full thickness biopsies were obtained from all burns at 7, 10, and 14 days after injury. The wounds were completely excised after 28 days for histological assessment. Wound sections were stained with H&&E and evaluated by a dermatopathologist masked to treatment assignment for reepithelialization and depth of scar formation. We also determined the number of wounds at 28 days that healed with contracted, hour-glass shaped scars. Data were compared with chi and t-tests. Twenty burns were treated with TGF-beta antagonist and 20 with control vehicle. TGF-beta antagonist increased the percentage of completely reepithelialized wounds at 14 days (90 vs 45%, P = .002) and reduced the percentage of contracted wounds (35 vs 65%, P = .02) and full thickness scars (10 vs 60%, P = .002) at 28 days. Treatment of partial thickness porcine burns with the TGF-beta antagonist speeds reepithelialization and reduces scar formation and wound contraction in partial thickness porcine burns.

Radioprotection

Over 40% of cancer patients will require radiation therapy during management of their disease. Although radiation therapy improves the survival of a significant number of cancer patients, both acute radiation toxicity (which manifests during a course of clinical radiotherapy or shortly thereafter), and late toxicity (developing months to years after completion of radiotherapy) compromise overall outcomes for successfully treated cancer patients.

Hyaluronan orchestrates transforming growth factor-beta1-dependent maintenance of myofibroblast phenotype

The differentiation of resident fibroblasts to myofibroblasts is central to wound healing. In the context of organ fibrosis, however, persistence of these myofibroblasts is associated with progressive disease. This study examines mechanisms controlling the maintenance of the myofibroblast phenotype. Myofibroblasts were induced by adding transforming growth factor-beta1 (TGF-beta1) (10 ng/ml) to fibroblasts for 72 h. The phenotype was maintained for up to 120 h following removal of TGF-beta1. Western blot for pSmad2 and -3 demonstrated persistent phosphorylation despite removal of exogenous TGF-beta1. This persistence was because of autocrine synthesis of TGF-beta1, which was inhibited by both anti-TGF-beta1 antibody and the ALK5 inhibitor SB431542. Persistence of phenotype was also associated with increased hyaluronan (HA) generation, synthesis of the hyaladherin TSG6, and HA pericellular coat formation. These were all inhibited by TGF-beta receptor blockade. To further investigate the importance of HA synthesis, 4-methylumbelliferone was used to deplete the cytoplasmic pool of UDP-glucuronic acid, essential for HA chain elongation. This prevented formation of the pericellular HA matrix and decreased expression of alpha-SMA. 4-Methylumbelliferone had no effect, however, on Smad2 and -3 phosphorylation. Similarly inhibition of HAS2 by short interfering RNA prevented phenotypic activation without altering TGF-beta1-dependent Smad phosphorylation, thus suggesting that HA-dependent regulation of cell phenotype was independent of Smad activation. These data suggest that myofibroblasts in areas of fibrosis maintain their own phenotype through autocrine TGF-beta1 action and that extracellular HA matrices are an essential mediator of this. We propose a model in which the formation of the pericellular HA matrix regulates the outcome of Smad-dependent autocrine TGF-beta1-activated signaling, and therefore persistence of the myofibroblast phenotype.

TGF-β1 is a negative regulator of lymphatic regeneration during wound repair

Although clinical studies have identified scarring/fibrosis as significant risk factors for lymphedema, the mechanisms by which lymphatic repair is impaired remain unknown. Transforming growth factor -β1 (TGF-β1) is a critical regulator of tissue fibrosis/scarring and may therefore also play a role in the regulation of lymphatic regeneration. The purpose of this study was therefore to assess the role of TGF-β1 on scarring/fibrosis and lymphatic regeneration in a mouse tail model. Acute lymphedema was induced in mouse tails by full-thickness skin excision and lymphatic ligation. TGF-β1 expression and scarring were modulated by repairing the wounds with or without a topical collagen gel. Lymphatic function and histological analyses were performed at various time points. Finally, the effects of TGF-β1 on lymphatic endothelial cells (LECs) in vitro were evaluated. As a result, the wound repair with collagen gel significantly reduced the expression of TGF-β1, decreased scarring/fibrosis, and significantly accelerated lymphatic regeneration. The addition of recombinant TGF-β1 to the collagen gel negated these effects. The improved lymphatic regeneration secondary to TGF-β1 inhibition was associated with increased infiltration and proliferation of LECs and macrophages. TGF-β1 caused a dose-dependent significant decrease in cellular proliferation and tubule formation of isolated LECs without changes in the expression of VEGF-C/D. Finally, the increased expression of TGF-β1 during wound repair resulted in lymphatic fibrosis and the coexpression of α-smooth muscle actin and lymphatic vessel endothelial receptor-1 in regenerated lymphatics. In conclusion, the inhibition of TGF-β1 expression significantly accelerates lymphatic regeneration during wound healing. An increased TGF-β1 expression inhibits LEC proliferation and function and promotes lymphatic fibrosis. These findings imply that the clinical interventions that diminish TGF-β1 expression may be useful in promoting more rapid lymphatic regeneration.

Accelerated wound healing by smad3 antisense oligonucleotides-impregnated chitosan/alginate polyelectrolyte complex

Smad3 mediates the intracellular signaling of TGF-beta1 superfamily and plays a critical role in the cellular proliferation, differentiation and elaboration of matrix pivotal to cutaneous wound healing. Smad3 antisense oligonucleotides (ASOs) impregnated polyelectrolyte complex (PEC) containing chitosan and sodium alginate was prepared for accelerated wound healing. Physicochemical properties of PEC were characterized by zeta potential, scanning electron microscopy and bioadhesive test. Full-thickness, excisional wounds were made on the dorsum of C57BL6 mice. Then, smad3 ASOs-PEC, PEC alone, smad3 ASOs and gauze dressing were applied to determine concentration of TGF-beta1 and collagen in tissues and observe the wound contraction and histology of tissues. Zeta potentials and bioadhesive strengths of ASOs-PEC were increased as the chitosan ratio in PEC. In smad3 ASOs-PEC, the healing process suggested by wound closure and histological observation was faster than other groups because collagen contents increased and level of TGF-beta1 decreased. These results demonstrate that the smad3 ASOs-PEC composed of chitosan and sodium alginate could be applied for accelerated wound healing.

Thrombospondin-1 and CD47 limit cell and tissue survival of radiation injury

Radiation, a primary mode of cancer therapy, acutely damages cellular macromolecules and DNA and elicits stress responses that lead to cell death. The known cytoprotective activity of nitric oxide (NO) is blocked by thrombospondin-1, a potent antagonist of NO/cGMP signaling in ischemic soft tissues, suggesting that thrombospondin-1 signaling via its receptor CD47 could correspondingly increase radiosensitivity. We show here that soft tissues in thrombospondin-1-null mice are remarkably resistant to radiation injury. Twelve hours after 25-Gy hindlimb irradiation, thrombospondin-1-null mice showed significantly less cell death in both muscle and bone marrow. Two months after irradiation, skin and muscle units in null mice showed minimal histological evidence of radiation injury and near full retention of mitochondrial function. Additionally, both tissue perfusion and acute vascular responses to NO were preserved in irradiated thrombospondin-1-null hindlimbs. The role of thrombospondin-1 in radiosensitization is specific because thrombospondin-2-null mice were not protected. However, mice lacking CD47 showed radioresistance similar to thrombospondin-1-null mice. Both thrombospondin-1- and CD47-dependent radiosensitization is cell autonomous because vascular cells isolated from the respective null mice showed dramatically increased survival and improved proliferative capacity after irradiation in vitro. Therefore, thrombospondin-1/CD47 antagonists may have selective radioprotective activity for normal tissues.

Absence of Smad3 induces neutrophil migration after cutaneous irradiation: possible contribution to subsequent radioprotection

Our previous work showed that 6 weeks after cutaneous irradiation, mice null (knockout, KO) for Smad3, a cytoplasmic downstream mediator of transforming growth factor-beta, demonstrate less epidermal acanthosis and dermal inflammation than wild-type (WT) Smad3 mice. Analysis of the kinetics of inflammation showed that 6 to 8 hours after skin irradiation, there was a transient sevenfold increase in neutrophil influx in Smad3 KO mice compared with WT. Herein we describe bone marrow transplantation and skin grafting between WT and KO mice to assess the contribution of the neutrophil genotype compared with that of irradiated skin to the induction of neutrophil migration after irradiation. Results from bone marrow transplantation showed that WT marrow transplanted into KO mice enhanced neutrophil migration 6 to 8 hours after irradiation by 3.2-fold compared with KO marrow in WT mice. KO skin grafted onto either WT or KO animals showed a sixfold elevation of neutrophils after irradiation compared with grafted WT skin. These results suggest that the genotype of the irradiated skin, rather than the inflammatory cell, controls neutrophil influx. Circulating neutrophils, increased in WT mice after injection of granulocyte colony-stimulating factor, resulted in increased neutrophil migration to the skin 6 to 8 hours after irradiation and less skin damage 6 weeks after irradiation compared with untreated WT mice. Thus, early responses, including enhanced neutrophil influx, appear to contribute to subsequent cutaneous radioprotection.

The Kruppel-like factor KLF15 inhibits connective tissue growth factor (CTGF) expression in cardiac fibroblasts

Cardiac fibrosis is a hallmark feature of pathologic remodeling of the heart in response to hemodynamic or neurohormonal stress. Accumulating evidence implicates connective tissue growth factor (CTGF) as a key mediator of this process. Our group has previously identified Kruppel-Like Factor 15 (KLF15) as an important regulator of cardiac remodeling in response to stress; however, the role of this transcription factor in cardiac fibrosis has not been reported. Here we provide evidence that treatment of neonatal rat ventricular fibroblasts (NRVFs) with the potent pro-fibrotic agent Transforming Growth Factor-beta1 (TGFbeta1) strongly reduces KLF15 expression while inducing the pro-fibrotic factor CTGF. Adenoviral overexpression of KLF15 inhibits basal and TGFbeta1-induced CTGF expression in NRVFs. Furthermore, hearts from KLF15-/- mice subjected to aortic banding exhibited increased CTGF levels and fibrosis. From a mechanistic standpoint, KLF15 inhibits basal and TGFbeta1-mediated induction of the CTGF promoter. Chromatin Immunoprecipitation (ChIP) and electrophoretic mobility shift assays demonstrate that KLF15 inhibits recruitment of the co-activator P/CAF to the CTGF promoter with no significant effect on Smad3-DNA binding. Consistent with this observation, KLF15 mediated repression of the CTGF promoter is rescued by P/CAF overexpression. Our result implicates KLF15 as a novel negative regulator of CTGF expression and cardiac fibrosis.

Improvement of the breaking strength of wound by combined treatment with recombinant human G-CSF, recombinant human M-CSF, and a TGF-beta1 receptor kinase inhibitor in rat skin

Effective doses of ionizing radiation during preoperative radiotherapy occasionally cause wound complications after subsequent surgery. The authors attempted to accelerate radiation-impaired wound healing in animal models. Recombinant human granulocyte colony-stimulating factor (rhG-CSF), recombinant human macrophage colony-stimulating factor (rhM-CSF), and an inhibitor of transforming growth factor (TGF)-beta1 receptor kinase, SB431542, were injected s.c. into a full-thickness incisional wound site in the dorsal skin of rats after local irradiation of X-ray (30 Gy). Wound healing of irradiated skin was assessed using the breaking strength of the wound and histological analyses. The impaired wound healing in irradiated skin was found to be associated with impaired mobilization of bone marrow-derived cells and enhanced expression of TGF-beta1 mRNA. The breaking strength of the wound in the irradiated skin was approximately one-eighth of that in the non-irradiated skin; however, following combined treatment with the above three compounds the breaking strength increased to approximately one-half of that in the non-irradiated skin. Histological analysis of the wounded skin revealed an increase in formation of collagen fibers and the panniculus carnosus following the combined treatment. Moreover, the increased breaking strength was associated with an increase in a subpopulation of fibrocytes (collagen I/ED1 double positive cells). These findings suggested that a combined treatment with rhG-CSF, rhM-CSF, and SB431542 is promising as a means of improving radiation-impaired wound healing.

New rationales for using TGFbeta inhibitors in radiotherapy

PURPOSE

The first reports that ionizing radiation (IR) induces rapid and persistent activation of transforming growth factor beta1 (TGFbeta) were nearly two decades ago. Subsequent studies have shown that TGFbeta is a major mediator of cellular and tissue responses to IR and have revealed novel facets of its complex biology.

RESULTS

We and others have recently shown that inhibition of production or signaling of TGFbeta in epithelial cells modulates radiosensitivity and impedes activation of the DNA damage response program. The primary transducer of cellular response to DNA damage caused by ionizing radiation is the nuclear protein kinase ataxia telangiectasia mutated, whose activity is severely compromised when TGFbeta is inhibited. Thus, in conjunction, with its well-recognized contribution to normal tissue fibrosis, the role of TGFbeta in the genotoxic stress program provides a previously unsuspected avenue to modulate radiotherapy.

CONCLUSIONS

We hypothesize that identification of the circumstances and tumors in which TGFbeta manipulation enhances tumor cell radiosensitivity, while protecting normal tissues, could significantly increase therapeutic index.

Transcriptional control of wound repair

Injury to the skin initiates a complex process of events involving inflammation as well as the formation and remodeling of new tissue. These processes result in at least partial reconstitution of the injured skin. However, wounds in adult mammals heal with a scar, which is accompanied by functional and aesthetic impairments. In addition to this problem, a large number of patients, in particular in the aged population, suffer from chronic, nonhealing ulcers. Therefore, there is a strong need to improve the wound healing process. This requires a thorough understanding of the underlying molecular and cellular mechanisms. During the past several years, important regulators of the wound healing process have been identified. In particular, the growth factors and matrix proteins, which orchestrate skin repair, have been characterized in detail. By contrast, much less is known about the transcription factors, which regulate gene expression at the wound site. This review summarizes recent data on the expression of transcription factors in skin wounds and their functions in the repair process.

Rho/ROCK pathway as a molecular target for modulation of intestinal radiation-induced toxicity

More than half of cancer patients are treated with radiation therapy. Despite its high therapeutic index, radiation therapy can cause disabling injuries to normal tissues, especially in long-term survivors. Thus, one of the great challenges of modern radiation therapy is to increase tolerance of normal tissue to ionizing radiation in order to improve the quality of life of cancer survivors and/or enhance local control using dose escalation. The physiopathological aspects of normal tissue toxicity have been widely explored; however, none of these descriptive findings has led to the development of effective therapeutic strategies. Several empirical treatments have also been used in clinical trials (superoxide dismutase, pentoxifylline-tocopherol); however, the results are still controversial, and their mechanisms of action have not been clearly defined. The recent development of high-throughput biological approaches will contribute greatly to the characterization of the molecular pathways associated with normal tissue toxicity and the identification of specific and effective molecular targets for therapeutic interventions using already known or new pharmacological compounds. In this paper, we will discuss recent advances made in the characterization of one of the most serious complications of radiation therapy, late intestinal toxicity, using molecular profiling. We will focus on the involvement of the Rho/ROCK pathway in the development and maintenance of late radiation enteropathy. The role of the Rho/ROCK pathway in tissue response to radiation injury will be reviewed, as well as therapeutic perspectives.

Absence of Smad3 confers radioprotection through modulation of ERK-MAPK in primary dermal fibroblasts

BACKGROUND

Transforming growth factor-beta1 (TGF-beta1), a key biological mediator following ionizing radiation, plays a role in a complex tissue reaction involved in local radiation-induced pathological damage. Knocking out Smad3 (S3KO), a downstream signaling intermediate in the TGF-beta pathway, in mice protects their skin from radiation damage as demonstrated by decreased epithelial acanthosis and dermal fibrosis as compared to Smad3 wild-type (S3WT) mice.

OBJECTIVE

The present study was designed to investigate the molecular mechanisms contributing to increased radioprotection in the absence of Smad3.

METHODS

Primary dermal fibroblasts derived from S3WT and KO mice were exposed to 5Gy ionizing radiation in vitro. Western blot analyses, immunocytochemistry, and reporter transfections were used to dissect the radiation-induced events.

RESULTS

There was increased phosphorylation of ERK-MAPK, p53 and H2A.X in S3KO compared to the S3WT fibroblasts, implicating them in a key signaling cascade in response of these cells to radiation. Pro-fibrotic gene expression was decreased in S3KO fibroblasts post-irradiation.

CONCLUSION

The absence of Smad3 may decrease radio-responsiveness by increasing activation of DNA damage sensing mechanisms and decreasing induction of pro-fibrotic genes.

Molecular mechanisms of late normal tissue injury

Irradiation perturbs the homeostatic network linking parenchymal, mesenchymal, and vascular cells within tissues. Normal communication between cells through soluble, matrix, and cell-associated ligands and receptors is altered so as to set in motion a seemingly inexorable series of events aimed at tissue regeneration and healing. In late responding normal tissues where cell death is not compensated for by rapid regeneration, this process unfortunately often culminates in symptomatic complications of radiation exposure. Cytokines and their receptors are prominent in driving the cascade of molecular responses using the balance between seemingly mutually antagonistic molecules to control and direct the healing processes. There is strong evidence from preclinical models for the importance of cytokine-driven pathways in late radiation damage and growing evidence in humans for their relevance to radiation-induced disease. This review aims to show some general aspects of the molecular torrents that drive responses in irradiated tissues before and during the development of late effects. It attempts to collate some of the findings from preclinical models of late lung, central nervous system, skin, and intestinal damage and from clinical studies in the belief that understanding how irradiation perturbs the cellular communication networks will allow rationale intervention for mitigating late radiation tissue damage and carcinogenesis.

TNF-alpha suppresses alpha-smooth muscle actin expression in human dermal fibroblasts: an implication for abnormal wound healing

Abnormal wound healing encompasses a wide spectrum, from chronic wounds to hypertrophic scars. Both conditions are associated with an abnormal cytokine profile in the wound bed. In this study, we sought to understand the dynamic relationships between myofibroblast differentiation and mechanical performance of the collagen matrix under tissue growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha) stimulation. We found TGF-beta increased alpha-smooth muscle actin (alpha-SMA) and TNF-alpha alone decreased the basal alpha-SMA expression. When TGF-beta1 and TNF-alpha were both added, the alpha-SMA expression was suppressed below the baseline. Real-time PCR showed that TNF-alpha suppresses TGF-beta1-induced myofibroblast (fibroproliferative) phenotypic genes, for example, alpha-SMA, collagen type 1A, and fibronectin at the mRNA level. TNF-alpha suppresses TGF-beta1-induced gene expression by affecting its mRNA stability. Our results further showed that TNF-alpha inhibits TGF-beta1-induced Smad-3 phosphorylation via Jun N-terminal kinase signaling. Mechanical testing showed that TNF-alpha decreases the stiffness and contraction of the lattices after 5 days in culture. We proposed that changes in alpha-SMA, collagen, and fibronectin expression result in decreased contraction and stiffness of collagen matrices. Therefore, the balance of cytokines in a wound defines the mechanical properties of the extracellular matrix and optimal wound healing.

Radiation-induced alterations in cytokine production by skin cells

Ionizing radiation exposure of skin results in a cutaneous radiation reaction comprising all pathophysiological reactions and clinical symptoms in irradiated skin. Biological responses of skin occur in a characteristic temporal pattern and mainly depend on radiation quality, dose rate, total dose, and cellular conditions. Immediately after irradiation, production of cytokines by skin cells is initiated and continues as a cascade during all stages of the cutaneous radiation syndrome leading to progressive late symptoms, the predominant of which is fibrosis. Cytokines are important signaling molecules mediating communicative interactions both locally between different cell types within dermal tissues and distantly between organs. Although during recent years much progress has been made in dissecting the complex cytokine network, the role of cytokines in the pathophysiology of the cutaneous radiation reaction is only beginning to be elucidated. Previous studies indicate that the major cytokines in the response of skin cells to ionizing radiation include IL (interleukin)-1, IL-6, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta, and the chemokines IL-8 and eotaxin. In this paper, existing data on the radiation-induced modulation of cytokine expression by skin cells are reviewed.

Matrix proteolytic activity during wound healing: modulation by acute ethanol exposure

BACKGROUND

Clinical studies demonstrate that intoxicated patients exhibit an increased incidence of wound healing complications. Previous studies in a murine excisional wound model revealed that acute ethanol exposure impairs the wound healing response, causing decreased angiogenesis and a significant reduction in wound collagen content.

METHODS

Using the same murine model of excisional wounding, we examined the effect of a single dose of ethanol on the overall collagen content and collagen type I and type III mRNA expression, transforming growth factor-beta (TGF-beta) production, and levels of several components of the extracellular matrix proteolytic cascade.

RESULTS

Wounds from ethanol-treated mice exhibited a significant decrease in collagen and in the production of collagen type I mRNA compared with saline controls. Exposure to ethanol also caused significant increase in wound TGF-beta by day 2 after injury (1.69 +/- 0.29 vs 12.34 +/- 3.97 pg/microg protein, p<0.01). In addition, wounds from mice exposed to ethanol had significantly increased levels of active urokinase plasminogen activator at day 7, (205.10 +/- 48.79 vs 642.70 +/- 159.80 pg/microg protein, p<0.001). The level of matrix metalloproteinase-8, a collagen type I proteinase, was 2.2-fold higher in wounds of ethanol-treated mice compared with control at day 7 (p<0.05).

CONCLUSIONS

These studies demonstrate that a single dose of ethanol decreases collagen production, increases the production of TGF-beta and increases levels of matrix degrading enzymes. This alteration in protease balance may partially explain the impaired wound healing that follows acute alcohol intoxication.

Increased bleomycin-induced skin fibrosis in mice lacking the Th1-specific transcription factor T-bet

Fibrosis, the pathological hallmark of scleroderma and related conditions, is due to sustained activation of tissue fibroblasts. Accumulating evidence implicates cytokine networks in initiating, and propagating or terminating fibroblast activation, and the specific cytokine phenotype dictates evolution of the fibrotic response toward either resolution or scarring. In particular, cytokines that promote fibroblast proliferation and myofibroblast differentiation and extracellular matrix (ECM) accumulation functionally define a type 2 (Th2) immune response, whereas interferon-gamma, which suppresses diverse fibroblast activities, defines a type 1 (Th1) immune response. It remains unclear what role the balance between Th1 and Th2 cytokines plays in the pathogenesis of fibrosis. Here we used bleomycin-induced skin fibrosis as a murine model for human scleroderma in order to study the fibrotic response in mice lacking T-bet, a transcription factor that is essential for initiating Th1 lineage development of CD4+ T lymphocytes. Spleen cells from T-bet null (T-bet(-/-)) mice exhibited a typical Th2 cytokine profile ex vivo, with elevated production of interleukin-4 (IL-4), IL-5 and IL-13, and diminished production of interferon-gamma. Bleomycin-induced early mast cells and eosinophil accumulation, and eosinophil degranulation, in the lesional tissue were greater in T-bet(-/-) mice than in wild-type control mice. At a later time point, T-bet(-/-) mice developed significantly more extensive dermal and especially hypodermal fibrosis. Elevated TGF-beta expression and intracellular Smad activation were prominent in lesional skin. Infiltrating eosinophils appeared to be an important cellular source of TGF-beta. These results demonstrate that in mice lacking T-bet bleomycin induced exaggerated skin fibrosis, suggesting that T-bet has an important physiologic role in regulation of tissue repair by promoting Th1 immune responses that prevent excessive ECM accumulation.

Transforming growth factor-beta in cancer and metastasis

Transforming growth factor-beta (TGF-beta) is a multifunctional regulatory polypeptide that is the prototypical member of a large family of cytokines that controls many aspects of cellular function, including cellular proliferation, differentiation, migration, apoptosis, adhesion, angiogenesis, immune surveillance, and survival. The actions of TGF-beta are dependent on several factors including cell type, growth conditions, and the presence of other polypeptide growth factors. One of the biological effects of TGF-beta is the inhibition of proliferation of most normal epithelial cells using an autocrine mechanism of action, and this suggests a tumor suppressor role for TGF-beta. Loss of autocrine TGF-beta activity and/or responsiveness to exogenous TGF-beta appears to provide some epithelial cells with a growth advantage leading to malignant progression. This suggests a pro-oncogenic role for TGF-beta in addition to its tumor suppressor role. During the early phase of epithelial tumorigenesis, TGF-beta inhibits primary tumor development and growth by inducing cell cycle arrest and apoptosis. In late stages of tumor progression when tumor cells become resistant to growth inhibition by TGF-beta due to inactivation of the TGF-beta signaling pathway or aberrant regulation of the cell cycle, the role of TGF-beta becomes one of tumor promotion. Resistance to TGF-beta-mediated inhibition of proliferation is frequently observed in multiple human cancers, as are various alterations in the complex TGF-beta signaling and cell cycle pathways. TGF-beta can exert effects on tumor and stromal cells as well as alter the responsiveness of tumor cells to TGF-beta to stimulate invasion, angiogenesis, and metastasis, and to inhibit immune surveillance. Because of the dual role of TGF-beta as a tumor suppressor and pro-oncogenic factor, members of the TGF-beta signaling pathway are being considered as predictive biomarkers for progressive tumorigenesis, as well as molecular targets for prevention and treatment of cancer and metastasis.

Superoxide dismutase mimetic reduces hypoxia-induced O2*-, TGF-beta, and VEGF production by macrophages

Normal tissue injury poses a major limitation to the success of radiation therapy (RT) in the treatment of solid tumors. We propose that radiation-induced lung injury is a result of chronic oxidative stress propagated by hypoxia-induced macrophage activation and cytokine production. Therefore, the objective of our study was two-fold. First, in vivo studies were conducted to support our hypothesis suggesting radiation injury is characterized by chronic hypoxia associated with increased macrophage infiltration/activation and pro-fibrogenic/angiogenic cytokine production. Second, we investigated the proposed mechanism of radiation injury in vitro. We demonstrate that hypoxia (0.5% O2) elicits macrophages to produce higher levels of O2*-, TGF-beta, and VEGF than normoxia. Our hypothesis that O2*- is contributing to increased macrophage cytokine production was supported by a significant reduction in TGF-beta and VEGF when redox signaling was minimized using a small molecular weight metalloporphyrin antioxidant, MnTE-2-PyP5+ .

Effect of low-dose electron radiation on rat skin wound healing

The aim of this study was to assess the effect of low-dose electron irradiation on morphological features of the wound healing process in rat skin. Surgical wounds were inflicted with a 2.3 x 1.4 cm template on 84 male rats that were assigned to 4 groups: IG1, immediately irradiated; IG2, irradiated 3 days after inflicting the wound; CG1 and CG2, control groups. Rats in IG1 and IG2 groups had their wounds exposed to 1 Gy of 6 MeV electron beam radiation, immediately after surgery and on the third postoperative day, respectively. Qualitative and histophotometric evaluations of tissue repair structures were carried out. Data were analyzed by ANOVA and Tukey's test (alpha = 0.05) and regression analysis. The repair process was delayed since the first sacrifice time in both irradiated groups, but in IG1, wound healing was closer to that of CG1; whereas in IG2, the delay was more pronounced. Based on the histological findings, it is possible to conclude that a low-dose of electron radiation delayed tissue repair in rat skin. The delay was longer in the skin irradiated 3 days after the beginning of tissue repair. However, the low-energy electron irradiation did not prevent wound healing.

Fibroblast differentiation in wound healing and fibrosis

The contraction of granulation tissue from skin wounds was first described in the 1960s. Later it was discovered that during tissue repair, fibroblasts undergo a change in phenotype from their normal relatively quiescent state in which they are involved in slow turnover of the extracellular matrix, to a proliferative and contractile phenotype termed myofibroblasts. These cells show some of the phenotypic characteristics of smooth muscle cells and have been shown to contract in vitro. In the 1990s, a number of researchers in different fields showed that myofibroblasts are present during tissue repair or response to injury in a variety of other tissues, including the liver, kidney, and lung. During normal repair processes, the myofibroblastic cells are lost as repair resolves to form a scar. This cell loss is via apoptosis. In pathological fibroses, myofibroblasts persist in the tissue and are responsible for fibrosis via increased matrix synthesis and for contraction of the tissue. In many cases this expansion of the extracellular matrix impedes normal function of the organ. For this reason much interest has centered on the derivation of myofibroblasts and the factors that influence their differentiation, proliferation, extracellular matrix synthesis, and survival. Further understanding of how fibroblast differentiation and myofibroblast phenotype is controlled may provide valuable insights into future therapies that can control fibrosis and scarring.

Radiotherapy and wound healing

Radiotherapy is an invaluable weapon when treating cancer. However, the deleterious effects of radiation, both immediate and long-term, may have a significant effect on local tissues. Problematic wound healing in radiation-damaged tissue constitutes a major problem that is frequently overlooked during the management of patients who require radiotherapy, or have had radiotherapy in the past. Poor wound healing may lead to chronic ulceration, pain, secondary infection and psychological distress and compromise the outcome of general or reconstructive surgery. We discuss the pathophysiology of poor wound healing following radiotherapy, specific problems for radiation-damaged tissue and potential treatments to improve wound healing of irradiated tissues.

Smad3 deficiency alters key structural elements of the extracellular matrix and mechanotransduction of wound closure

The loss of TGFbeta or its downstream mediator, Smad3, key players in tissue repair, accelerates closure of incisional wounds in mice. In contrast, we now report that excisional ear wounds in mice lacking Smad3 enlarge compared with wild-type controls resulting from changes in extracellular matrix molecules, which alter the mechanotransduction properties of these wounds. Specifically, levels of elastin and glycosoaminoglycans are increased, collagen fibers are more compactly organized, and matrix modulators like integrins, TGFbeta1, and matrix metalloproteinases (MMPs) are altered both basally and after wounding in Smad3 knockout mice. Mechanical testing of dorsal skin correlates these changes in matrix composition with functional parameters, specifically an increased elastic modulus, suggesting an imbalance of tissue forces. We propose that the altered mechanical elastic properties translate into a persistent retractile force that is opposed by decreased wound contractile forces contributing to the enlarging ear wound in Smad3 knockout mice. These studies highlight a previously undescribed role for Smad3 in the mechanotransduction of matrix unsupported ear wound closure.