Fibroblast-specific expression of a kinase-deficient type II transforming growth factor beta (TGFbeta) receptor leads to paradoxical activation of TGFbeta signaling pathways with fibrosis in transgenic mice

Elevated CCN2 expression in scleroderma: a putative role for the TGFβ accessory receptors TGFβRIII and endoglin

The ability of TGFβ1 to act as a potent pro-fibrotic mediator is well established, potently inducing the expression of fibrogenic genes including type I collagen (COL1A2) and CCN2. Previously we have shown elevated expression of the TGFβ accessory receptor, endoglin on Systemic Sclerosis (SSc) dermal fibroblasts. Here we sought to assess the cell surface expression of the TGFβ receptor complex on SSc dermal fibroblasts (SDF), and investigate their role in maintaining the elevated expression of CCN2. SDF exhibited elevated expression of the TGFβ accessory receptors betaglycan/TGFβRIII and endoglin, but not type I or type II receptors. To determine the effect of altered receptor repertoire on TGFβ responses, we investigated the effect of exogenous TGFβ on expression of two pro-fibrotic genes. SDF exhibited higher basal expression of COL1A2 and CCN2 compared to healthy controls. TGFβ induced a marked increase in the expression of these genes in normal dermal fibroblasts, whereas SDF exhibited only a modest increase. We next sought to determine if higher basal expression in SDF was a result of autocrine expression of TGFβ. Surprisingly basal expression was not affected by a pan-neutralizing TGFβ antibody. To explore if altered accessory receptor expression alone could account for these changes, we determined their effects on CCN2 promoter activity. Endoglin inhibited CCN2 promoter activity in response to TGFβ. TGFβRIII alone or in combination with endoglin was sufficient to enhance basal CCN2 promoter activity. Thus TGFβ accessory receptors may play a significant role in the altered expression of fibrogenic genes in SDF.

Mouse and human lung fibroblasts regulate dendritic cell trafficking, airway inflammation, and fibrosis through integrin αvβ8-mediated activation of TGF-β

The airway is a primary portal of entry for noxious environmental stimuli that can trigger airway remodeling, which contributes significantly to airway obstruction in chronic obstructive pulmonary disease (COPD) and chronic asthma. Important pathologic components of airway remodeling include fibrosis and abnormal innate and adaptive immune responses. The positioning of fibroblasts in interstitial spaces suggests that they could participate in both fibrosis and chemokine regulation of the trafficking of immune cells such as dendritic cells, which are crucial antigen-presenting cells. However, physiological evidence for this dual role for fibroblasts is lacking. Here, in two physiologically relevant models - conditional deletion in mouse fibroblasts of the TGF-β-activating integrin αvβ8 and neutralization of αvβ8 in human COPD fibroblasts - we have elucidated a mechanism whereby lung fibroblast chemokine secretion directs dendritic cell trafficking, in a manner that is critically dependent on αvβ8-mediated activation of TGF-β by fibroblasts. Our data therefore indicate that fibroblasts have a crucial role in regulating both fibrotic and immune responses in the lung.

A novel glycosylation signal regulates transforming growth factor beta receptors as evidenced by endo-beta-galactosidase C expression in rodent cells

The αGal (Galα1-3Gal) epitope is a xenoantigen that is responsible for hyperacute rejection in xenotransplantation. This epitope is expressed on the cell surface in the cells of all mammals except humans and Old World monkeys. It can be digested by the enzyme endo-β-galactosidase C (EndoGalC), which is derived from Clostridium perfringens. Previously, we produced EndoGalC transgenic mice to identify the phenotypes that would be induced following EndoGalC overexpression. The mice lacked the αGal epitope in all tissues and exhibited abnormal phenotypes such as postnatal death, growth retardation, skin lesion and abnormal behavior. Interestingly, skin lesions caused by increased proliferation of keratinocytes suggest the role of a glycan structure [in which the αGal epitope has been removed or the N-acetylglucosamine (GlcNAc) residue is newly exposed] as a regulator of signal transduction. To verify this hypothesis, we introduced an EndoGalC expression vector into cultured mouse NIH3T3 cells and obtained several EndoGalC-expressing transfectants. These cells lacked αGal epitope expression and exhibited 1.8-fold higher proliferation than untransfected parental cells. We then used several cytokine receptor inhibitors to assess the signal transduction cascades that were affected. Only SB431542 and LY364947, both of which are transforming growth factor β (TGFβ) receptor type-I (TβR-I) inhibitors, were found to successfully reverse the enhanced cell proliferation rate of EndoGalC transfectants, indicating that the glycan structure is a regulator of TβRs. Biochemical analysis demonstrated that the glycan altered association between TβR-I and TβR-II in the absence of ligands.

Molecular pathogenesis of skin fibrosis: insight from animal models

Skin fibrosis occurs in a variety of human diseases, most notably systemic sclerosis (SSc). The end stage of scleroderma in human skin consists of excess collagen deposition in the dermis with loss of adnexal structures and associated adipose tissue. The initiating factors for this process and the early stages are believed to occur through vascular injury and immune dysfunction with a dysregulated inflammatory response. However, because of the insidious onset of the disease, this stage is rarely observed in humans and remains poorly understood. Animal models have provided a means to examine these early stages and to isolate and understand the effect of perturbations in signaling pathways, chemokines, and cytokines. This article summarizes recent progress in the understanding of the molecular pathogenesis of skin fibrosis in SSc from different animal models, both its initiation and its maintenance phases.

Vascular alterations upon activation of TGFbeta signaling in fibroblasts--implications for systemic sclerosis

Tissue fibrosis and vascular disease are hallmarks of systemic sclerosis (SSc). Transforming growth factor β (TGFβ) is a key-player in fibroblast activation and tissue fibrosis in SSc. In contrast to fibrosis, evidence for a role of TGFβ in vascular disease of SSc is scarce. Using a transgenic mouse model with fibroblast-specific expression of a kinase-deficient TGFβ receptor type II, Derrett-Smith and colleagues demonstrate that aberrant TGFβ signaling in fibroblasts might result in activation of vascular smooth muscle cells and architectural changes of the vessel wall of the aorta.

Selective expression of connective tissue growth factor in fibroblasts in vivo promotes systemic tissue fibrosis

OBJECTIVE

Connective tissue growth factor (CTGF) is a cysteine-rich secreted matricellular protein involved in wound healing and tissue repair. Enhanced and prolonged expression of CTGF has been associated with tissue fibrosis in humans. However, questions remain as to whether CTGF expression alone is sufficient to drive fibrosis. This study was undertaken to investigate whether CTGF alone is sufficient to cause fibrosis in intact animals and whether its effects are mediated through activation of transforming growth factor beta (TGFbeta) signaling or through distinct signal transduction pathways.

METHODS

We generated mice overexpressing CTGF in fibroblasts under the control of the fibroblast-specific collagen alpha2(I) promoter enhancer. Tissues such as skin, lung, and kidney were harvested for histologic analysis. Mouse embryonic fibroblasts were prepared from embryos (14.5 days postcoitum) for biochemical analysis.

RESULTS

Mice overexpressing CTGF in fibroblasts were susceptible to accelerated tissue fibrosis affecting the skin, lung, kidney, and vasculature, most notably the small arteries. We identified a marked expansion of the myofibroblast cell population in the dermis. RNA analysis of transgenic dermal fibroblasts revealed elevated expression of key matrix genes, consistent with a fibrogenic response. CTGF induced phosphorylation of p38, ERK-1/2, JNK, and Akt, but not Smad3, in transgenic mouse fibroblasts compared with wild-type mouse fibroblasts. Transfection experiments showed significantly increased basal activity of the CTGF and serum response element promoters, and enhanced induction of the CTGF promoter in the presence of TGFbeta.

CONCLUSION

These results demonstrate that selective expression of CTGF in fibroblasts alone causes tissue fibrosis in vivo through specific signaling pathways, integrating cues from the extracellular matrix into signal transduction pathways to orchestrate pivotal biologic responses relevant to tissue repair and fibrosis.

Systemic vasculopathy with altered vasoreactivity in a transgenic mouse model of scleroderma

Introduction

Vasculopathy, including altered vasoreactivity and abnormal large vessel biomechanics, is a hallmark of systemic sclerosis (SSc). However, the pathogenic link with other aspects of the disease is less clear. To assess the potential role of transforming growth factor beta (TGF-β) overactivity in driving these cardiovascular abnormalities, we studied a novel transgenic mouse model characterized by ligand-dependent activation of TGF-β signaling in fibroblasts.

Methods

The transgenic mouse strain Tβ RIIΔk-fib is characterized by balanced ligand-dependent upregulation of TGF-β signaling. Aortic and cardiac tissues were examined with histologic, biochemical, and isolated organ bath studies. Vascular and perivascular architecture was examined by hematoxylin and eosin (H&E) and special stains including immunostaining for TGF-β1 and phospho-Smad2/3 (pSmad2/3). Confirmatory aortic smooth muscle cell proliferation, phenotype, and functional assays, including signaling responses to exogenous TGF-β and endothelin-1, were performed. Aortic ring contractile responses to direct and receptor-mediated stimulation were assessed.

Results

Aortic ring contractility and relaxation were diminished compared with wild-type controls, and this was associated with aortic adventitial fibrosis confirmed histologically and with Sircol assay. TGF-β1 and pSmad 2/3 expression was increased in the adventitia and smooth muscle layer of the aorta. Aortic smooth muscle cells from transgenic animals showed significant upregulation of TGF-β- responsive genes important for cytoskeletal function, such as transgelin and smoothelin, which were then resistant to further stimulation with exogenous TGF-β1. These cells promoted significantly more contraction of free floating type I collagen lattices when compared with the wild-type, but were again resistant to exogenous TGF-β1 stimulation. Aortic ring responses to receptor-mediated contraction were reduced in the transgenic animals. Specifically, bosentan reduced endothelin-mediated contraction in wild-type animals, but had no effect in transgenic animals, and endothelin axis gene expression was altered in transgenic animals. Transgenic mice developed cardiac fibrosis.

Conclusions

The histologic, biochemical, and functional phenotype of this transgenic mouse model of scleroderma offers insight into the altered biomechanical properties previously reported for large elastic arteries in human SSc and suggests a role for perturbed TGF-β and endothelin activity in this process.

Relative roles of the epithelial and stromal tissue compartment(s) in mediating the actions of relaxin and estrogen on cell proliferation and apoptosis in the mouse lower reproductive tract

Relaxin and estrogen are secreted by the ovary during the second half of pregnancy in rats and mice. Relaxin promotes marked growth of the lower reproductive tract in both species. Relaxin promotes accumulation of epithelial and stromal cells in the cervix and vagina by both stimulating cell proliferation and inhibiting apoptosis. Estrogen acting through estrogen receptor alpha (ERalpha) plays an essential permissive role in relaxin's actions. A fundamental step toward understanding the actions of relaxin and estrogen is to identify the tissue compartments that initiate their effects. Limited studies using either antibodies to human relaxin receptor (LGR7, RXFP1) or an IRES-LacZ reporter cassette in the LGR7 gene revealed relaxin receptors in subepithelial stroma cells and smooth muscle cells but not in epithelial cells in rodent vaginal and/or cervical tissues. ERalpha has been reported in both stromal and epithelial compartments in the rodent reproductive tract. This chapter describes ongoing studies that use relaxin bioactivity as a means of identifying the tissue compartment(s) that initiates the actions of relaxin and estrogen on the lower reproductive tract. Specifically, a tissue separation-recombination methodology in combination with LGR7 knockout mice was initially used to obtain functional evidence that stromal LGR7 is both necessary and sufficient to promote proliferation and inhibit apoptosis in both stromal and epithelial cells in mouse cervix and vagina. The tissue separation-recombination method is currently being used in conjunction with ERalpha knockout mice to determine if the obligatory permissive effect of estrogen on relaxin-induced cell proliferation occurs through stromal and/or epithelial ERalpha.

New perspectives in the treatment of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most frequent idiopathic interstitial pneumonia with a prevalence ranging from 5 to 15 per 100,000 persons, and above 175 per 100,000 in the older population. IPF is a relentlessly progressive fibrotic lung disorder leading to death within a median duration of 3 years. It was hypothesized in the 1970s that pulmonary fibrosis initiates as an "alveolitis" progressing to interstitial fibrosis with connective tissue deposition, derangement of the lung architecture and functional impairment. However, in vitro studies indicated that alveolar/bronchiolar injured epithelial cells can drive the fibrotic process in the absence of macrophages and with minimal inflammation. This, together with the inability of classic immunosuppressive therapy to cure IPF, generated new pathogenesis paradigms and intense research into the role of the lack or the excessive production of anti-fibrotic or profibrotic mediators, oxidant injury, exaggerated coagulation, thus leading to investigate new treatment strategies. Preliminary results of some of such trials have shown significant reductions in lung function decline, disease exacerbation and mortality.

Adenoviral overexpression and small interfering RNA suppression demonstrate that plasminogen activator inhibitor-1 produces elevated collagen accumulation in normal and keloid fibroblasts

Keloids are tumor-like skin scars that grow as a result of the aberrant healing of skin injuries, with no effective treatment. We provide new evidence that both overexpression of plasminogen activator inhibitor-1 (PAI-1) and elevated collagen accumulation are intrinsic features of keloid fibroblasts and that these characteristics are causally linked. Using seven strains each of early passage normal and keloid fibroblasts, the keloid strains exhibited inherently elevated collagen accumulation and PAI-1 expression in serum-free, 0.1% ITS+ culture; larger increases in these parameters occurred when cells were cultured in 3% serum. To demonstrate a causal relationship between PAI-1 overexpression and collagen accumulation, normal fibroblasts were infected with PAI-1-expressing adenovirus. Such cells exhibited a two- to fourfold increase in the accumulation of newly synthesized collagen in a viral dose-dependent fashion in both monolayers and fibrin gel, provisional matrix-like cultures. Three different PAI-1-targeted small interfering RNAs, alone or in combination, produced greater than an 80% PAI-1 knockdown and reduced collagen accumulation in PAI-1-overexpressing normal or keloid fibroblasts. A vitronectin-binding mutant of PAI-1 was equipotent with wild-type PAI-1 in inducing collagen accumulation, whereas a complete protease inhibitor mutant retained approximately 50% activity. Thus, PAI-1 may use more than its protease inhibitory activity to control keloid collagen accumulation. PAI-1-targeted interventions, such as small interfering RNA and lentiviral short hairpin RNA-containing microRNA sequence suppression reported here, may have therapeutic utility in the prevention of keloid scarring.

In perspective: murine models of scleroderma

An understanding of the complex pathogenesis of systemic sclerosis (SSc) has been slow to emerge, due in large part to the lack of an animal model recapitulating the three cardinal attributes of SSc: autoimmunity, vasculopathy, and fibrosis. Experimental manipulations in inbred murine strains can lead to conditions that mimic SSc fibrosis. Furthermore, genetic engineering has enabled the creation of novel murine strains that spontaneously develop fibrosis or are protected from fibrosis development. Studies of these mice shed light on the cell types, cell interactions, molecules, and pathways that contribute to SSc manifestations. High-throughput discovery technologies such as DNA microarrays in animal models can identify novel genes and regulatory networks that are important for disease manifestations and that may be targets for therapy. In this brief review, we highlight recent progress in the field and attempt to place the strengths and limitations of popular SSc murine models in perspective.

Transforming growth factor-beta signaling in thoracic aortic aneurysm development: a paradox in pathogenesis

Thoracic aortic aneurysms (TAAs) are potentially devastating, and due to their asymptomatic behavior, pose a serious health risk characterized by the lack of medical treatment options and high rates of surgical morbidity and mortality. Independent of the inciting stimuli (biochemical/mechanical), TAA development proceeds by a multifactorial process influenced by both cellular and extracellular mechanisms, resulting in alterations of the structure and composition of the vascular extracellular matrix (ECM). While the role of enhanced ECM proteolysis in TAA formation remains undisputed, little attention has been focused on the upstream signaling events that drive the remodeling process. Recent evidence highlighting the dysregulation of transforming growth factor-beta (TGF-beta) signaling in ascending TAAs from Marfan syndrome patients has stimulated an interest in this intracellular signaling pathway. However, paradoxical discoveries have implicated both enhanced TGF-beta signaling and loss of function TGF-beta receptor mutations, in aneurysm formation; obfuscating a clear functional role for TGF-beta in aneurysm development. In an effort to elucidate this subject, TGF-beta signaling and its role in vascular remodeling and pathology will be reviewed, with the aim of identifying potential mechanisms of how TGF-beta signaling may contribute to the formation and progression of TAA.

Inhibition of the tumor necrosis factor-alpha pathway is radioprotective for the lung

PURPOSE

Radiation-induced lung toxicity limits the delivery of high-dose radiation to thoracic tumors. Here, we investigated the potential of inhibiting the tumor necrosis factor-alpha (TNF-alpha) pathway as a novel radioprotection strategy.

EXPERIMENTAL DESIGN

Mouse lungs were irradiated with various doses and assessed at varying times for TNF-alpha production. Lung toxicity was measured by apoptosis and pulmonary function testing. TNF receptor 1 (TNFR1) inhibition, achieved by genetic knockout or antisense oligonucleotide (ASO) silencing, was tested for selective lung protection in a mouse lung metastasis model of colon cancer.

RESULTS

Lung radiation induced local production of TNF-alpha by macrophages in BALB/c mice 3 to 24 hours after radiation (15 Gy). A similar maximal induction was found 1 week after the start of radiation when 15 Gy was divided into five daily fractions. Cell apoptosis in the lung, measured by terminal deoxyribonucleotide transferase-mediated nick-end labeling staining (mostly epithelial cells) and Western blot for caspase-3, was induced by radiation in a dose- and time-dependent manner. Specific ASO inhibited lung TNFR1 expression and reduced radiation-induced apoptosis. Radiation decreased lung function in BALB/c and C57BL mice 4 to 8 weeks after completion of fractionated radiation (40 Gy). Inhibition of TNFR1 by genetic deficiency (C57BL mice) or therapeutic silencing with ASO (BALB/c mice) tended to preserve lung function without compromising lung tumor sensitivity to radiation.

CONCLUSION

Radiation-induced lung TNF-alpha production correlates with early cell apoptosis and latent lung function damage. Inhibition of lung TNFR1 is selectively radioprotective for the lung without compromising tumor response. These findings support the development of a novel radioprotection strategy using inhibition of the TNF-alpha pathway.

Comparative proteomic analysis of radiation-induced changes in mouse lung: fibrosis-sensitive and -resistant strains

To determine whether comparative proteomics could detect differential protein expression after lung irradiation in two mouse strains with different radiation responses, lung proteins were subjected to two-dimensional orthogonal liquid-phase separations, with chromatofocusing in the first dimension and nonporous silica reverse-phase high-performance liquid chromatography (NPS-RP-HPLC) in the second. Five weeks after 12 Gy whole-lung irradiation, 15 and 31 proteins had significantly altered expression levels in C3H/HeJ (less likely to develop lung fibrosis) and C57BL/6J mice (more likely to develop lung fibrosis), respectively. These proteins were analyzed by HPLC-electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) and identified by matching sequences in a peptide database. The proteins are associated with redox, energy consumption, glycolysis, or chromatin/ RNA structure formation. Five of the six redox-related proteins, including superoxide dismutase 1 (SOD1), cytochrome c oxidase, glutamate dehydrogenase, biliverdin reductase, peroxiredoxin and carbonyl reductase, were down-regulated in the irradiated C57BL/6J mice, whereas SOD1, sulfurtransferase and carbonyl reductase increased in the irradiated C3H/ HeJ mice. Thus decreased antioxidant proteins in the irradiated C57BL/6J mice may be correlated with increased early lung toxicity. Changes in SOD1 and 8-hydroxydeoxy-guanosine (8-OHdG, an oxidative stress marker) were further confirmed by immunohistochemistry and/or Western blot analysis. These data suggest that a proteomics approach has the potential to detect protein changes relevant to early lung toxicity after irradiation.

Relaxin acts on stromal cells to promote epithelial and stromal proliferation and inhibit apoptosis in the mouse cervix and vagina

The objective of this study was to determine whether stromal and/or epithelial relaxin receptor (LGR7) is required for relaxin to promote proliferation and inhibit apoptosis of stromal and epithelial cells in the mouse cervix and vagina. Tissue recombinants were prepared with stroma (St) and epithelium (Ep) from wild-type (wt) and LGR7 knockout (ko) mice: wt-St+wt-Ep, wt-St+ko-Ep, ko-St+wt-Ep, and ko-St+ko-Ep. Tissue recombinants were grafted under the renal capsule of intact syngeneic female mice. After 3 wk of transplant growth, hosts were ovariectomized and fitted with silicon implants containing progesterone and estradiol-17beta (designated d 1 of treatment). Animals were injected sc with relaxin or relaxin vehicle PBS at 6-h intervals from 0600 h on d 8 through 0600 h on d 10 of treatment. To evaluate cell proliferation, 5-bromo-2'-deoxyuridine was injected sc 10 h before cervices and vaginas were collected at 1000 h on d 10. Terminal deoxynucleotidyl transferase-mediated deoxyuridine 5'-triphosphate nick end labeling was used to quantify apoptosis. Relaxin markedly increased proliferation and decreased apoptosis of epithelial and stromal cells in tissue recombinants containing wt stroma (P < 0.01) but had no effect on tissue recombinants prepared with ko stroma, regardless of whether epithelium was derived from wt or ko mice. In conclusion, this study shows that LGR7-expressing cells in the stroma are both necessary and sufficient for relaxin to promote proliferation and inhibit apoptosis in both stromal and epithelial cells of cervix and vagina, whereas epithelial LGR7 does not affect these processes.

Extracellular control of TGFbeta signalling in vascular development and disease

The intracellular mechanism of transforming growth factor-beta (TGFbeta) signalling via kinase receptors and SMAD effectors is firmly established, but recent studies of human cardiovascular syndromes such as Marfan syndrome and pre-eclampsia have refocused attention on the importance of regulating the availability of active extracellular TGFbeta. It seems that elastic extracellular matrix (ECM) components have a crucial role in controlling TGFbeta signalling, while soluble and membrane bound forms of TGFbeta co-receptors add further layers of regulation. Together, these extracellular interactions determine the final bioavailability of TGFbeta to vascular cells, and dysregulation is associated with an increasing number of vascular pathologies.

Microsatellite unstable colorectal cancer cell lines with truncating TGFβRII mutations remain sensitive to endogenous TGFβ

Disruptions to the TGFbeta signalling pathway have been implicated in most human adenocarcinomas. As cancers progress, many acquire resistance to the growth-suppressing properties of TGFbeta while retaining sensitivity to its tumour-promoting effects. Microsatellite unstable colorectal cancers (MSI-H CRCs) possess truncating mutations in the type II TGFbeta receptor (TGFbetaRII) gene that have been assumed to render these tumours insensitive to TGFbeta. However, numerous reports of TGFbetaRII bypass exist and this study was thus undertaken in order to clarify the true extent of TGFbeta sensitivity in MSI-H CRCs. Using stimulation with exogenous TGFbeta, we demonstrated that, while MSI-H CRCs are capable of binding soluble TGFbeta, two out of three cell lines examined remain refractory to its signalling effects. In contrast, use of a specific inhibitor of the type I TGFbeta receptor (TGFbetaRI) revealed that all remain sensitive to signalling by endogenously produced TGFbeta. Specifically, autocrine signalling via TGFbetaRI mediates constitutive activation of Smad2 as well as repression of Erk signalling. Real-time PCR confirmed that these effects are sufficient to affect the expression level of various TGFbeta-modulated genes. An invasion assay revealed that autocrine TGFbetaRI signalling also promotes the invasion capacity of MSI-H CRCs to an extent similar to that seen in their non-MSI-H counterparts. Independent TGFbetaRI signalling, however, has no effect on the rate of proliferation of MSI-H CRC cells. Together, these results demonstrate that MSI-H CRC cell lines are not completely refractory to TGFbeta, despite lacking functional TGFbetaRII. In addition to clarifying the true consequences of natural TGFbetaRII loss and the independent function of TGFbetaRI, our results highlight the selective nature of TGFbeta resistance developed by cancers.

Therapeutic targets in systemic sclerosis

The precise aetiology of systemic sclerosis (SSc) remains elusive, but significant advances over the past few years have improved our understanding of the underlying pathogenic processes and identified key pathways and mediators that are potential therapeutic targets. The situation is complicated by the clinical heterogeneity of SSc and the differential pathogenesis that underlies the two commonest subsets, namely diffuse and limited cutaneous disease. However, there are common mediators that could be targeted to provide clinical benefit in both types of disease. To date, clinical success with therapies directed against logical profibrotic mediators, such as connective tissue growth factor and transforming growth factor-β, is yet to be reported, although studies are ongoing. More promising clinical results have been obtained with the dual endothelin receptor antagonist bosentan, which has been shown to manage two vascular complications of SSc effectively: pulmonary arterial hypertension and digital ulceration. It remains to be determined whether the identification of additional mediators merely furthers our knowledge of the natural history of SSc or presents targets that can be manipulated to manage SSc patients effectively.

Postnatal induction of transforming growth factor beta signaling in fibroblasts of mice recapitulates clinical, histologic, and biochemical features of scleroderma

OBJECTIVE

Increased signaling by transforming growth factor beta (TGFbeta) has been implicated in systemic sclerosis (SSc; scleroderma), a complex disorder of connective tissues characterized by excessive accumulation of collagen and other extracellular matrix components in systemic organs. To directly assess the effect of sustained TGFbeta signaling in SSc, we established a novel mouse model in which the TGFbeta signaling pathway is activated in fibroblasts postnatally.

METHODS

The mice we used (termed TBR1(CA); Cre-ER mice) harbor both the DNA for an inducible constitutively active TGFbeta receptor I (TGFbetaRI) mutation, which has been targeted to the ROSA locus, and a Cre-ER transgene that is driven by a fibroblast-specific promoter. Administration of 4-hydroxytamoxifen 2 weeks after birth activates the expression of constitutively active TGFbetaRI.

RESULTS

These mice recapitulated clinical, histologic, and biochemical features of human SSc, showing pronounced and generalized fibrosis of the dermis, thinner epidermis, loss of hair follicles, and fibrotic thickening of small blood vessel walls in the lung and kidney. Primary skin fibroblasts from these mice showed elevated expression of downstream TGFbeta targets, reproducing the hallmark biochemical phenotype of explanted SSc dermal fibroblasts. The mouse fibroblasts also showed elevated basal expression of the TGFbeta-regulated promoters plasminogen activator inhibitor 1 and 3TP, increased Smad2/3 phosphorylation, and enhanced myofibroblast differentiation.

CONCLUSION

Constitutive activation of TGFbeta signaling in fibroblastic cells of mice after birth caused a marked fibrotic phenotype characteristic of SSc. These mice should be excellent models with which to test therapies aimed at correcting excessive TGFbeta signaling in human scleroderma.

Evolving concepts of apoptosis in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, relentlessly progressive fibrosing disease of the lung of unknown etiology. Significant progress has been made in recent years in elucidating key aspects of the pathobiology of IPF. Insights into disease pathogenesis have come from studies of cell biology, growth factor/cytokine signaling, animal models of pulmonary fibrosis, and human IPF cells and tissue. A consistent finding in the ultrastructural pathology of IPF is alveolar epithelial cell injury and apoptosis. Another consistent finding in the histopathology of human IPF, described as usual interstitial pneumonia, is the accumulation of aggregates of myofibroblasts in fibroblastic foci. The extent or profusion of fibroblastic foci in lung biopsies is strongly correlated with increased mortality in patients with IPF. There is emerging evidence that myofibroblasts in IPF/usual interstitial pneumonia, both in the in vivo microenvironment and during the process of differentiation in vitro, acquire resistance to apoptosis. Here, we review the current evidence and mechanisms for this apparent "apoptosis paradox" in the pathogenesis of IPF.

Genetic Basis of Thoracic Aortic Aneurysms and Dissections: Potential Relevance to Abdominal Aortic Aneurysms

Ascending thoracic aortic aneurysms leading to type A dissections (TAAD) have long been known to occur in association with a genetic syndrome such as Marfan syndrome (MFS). More recently, TAAD has also been demonstrated to occur as an autosomal dominant disorder in the absence of syndromic features, termed familial TAAD. Familial TAAD demonstrates genetic heterogeneity, and linkage studies have identified TAAD loci at 5q13-14 (TAAD1), 11q23 (FAA1), 3p24-25 (TAAD2), and 16p12.2-13.13. The genetic heterogeneity of TAAD is reflected by variation in disease in terms of the age of onset, progression, penetrance, and association with additional cardiac and vascular features. The underlying genetic heterogeneity of TAAD is reflected in the phenotypic variation associated with familial TAAD with respect to age of onset, progression, penetrance, and association with additional cardiac and vascular features. Mutations in the TGFBR2 gene have been identified as the cause of disease linked to the 3p24-25 locus, implicating dysregulation of TGF-beta signaling in TAAD. Mutations in myosin heavy chain (MYH11), a smooth muscle cell-specific contractile protein, have been identified in familial TAAD associated with patent ductus arteriosus (PDA) linked to 16p12.2-12.13. The identification of these novel disease pathways has led to new directions for future research addressing the pathology and treatment of TAAD.

Recent progress in genetics of Marfan syndrome and Marfan-associated disorders

Marfan syndrome (MFS, OMIM #154700) is a hereditary connective tissue disorder, clinically presenting with cardinal features of skeletal, ocular, and cardiovascular systems. In classical MFS, changes in connective tissue integrity can be explained by defects in fibrillin-1, a major component of extracellular microfibrils. However, some of the clinical manifestations of MFS cannot be explained by mechanical properties alone. Recent studies manipulating mouse Fbn1 have provided new insights into the molecular pathogenesis of MFS. Dysregulation of transforming growth factor beta (TGFbeta) signaling in lung, mitral valve and aortic tissues has been implicated in mouse models of MFS. TGFBR2 and TGFBR1 mutations were identified in a subset of patients with MFS (MFS2, OMIM #154705) and other MFS-related disorders, including Loeys-Dietz syndrome (LDS, #OMIM 609192) and familial thoracic aortic aneurysms and dissections (TAAD2, #OMIM 608987). These data indicate that genetic heterogeneity exists in MFS and its related conditions and that regulation of TGFbeta signaling plays a significant role in these disorders.

Transcriptional regulation of the human alpha2(I) collagen gene (COL1A2), an informative model system to study fibrotic diseases

During the past two decades, the human pro-alpha2(I) collagen gene (COL1A2) has emerged as an informative model in which to study the general principles that govern the transcriptional control of extracellular matrix deposition in normal and fibrotic conditions. Multiple studies have in fact delineated the genomic regions, cis-acting elements and trans-acting factors implicated in constitutive, cytokine-modulated and tissue-specific expression of COL1A2. These functional components are integrated into a regulatory network that consists of the proximal promoter, far-upstream enhancer and downstream repressor, and which operates according to two mechanisms. The first mechanism is one in which combinatorial interactions among promoter-bound proteins determine transcriptional outcome in different cellular and experimental contexts. The other mechanism is one whereby cooperative assembly of protein complexes at distantly located DNA elements directs spatiotemporal specificity. These transcriptional studies have also an additional value in translational research, in that they are providing the conceptual means to develop new animal models of and therapeutic strategies for fibrotic diseases.

Involvement of alphavbeta5 integrin in the establishment of autocrine TGF-beta signaling in dermal fibroblasts derived from localized scleroderma

Localized scleroderma (LSc) is a connective tissue disorder limited to skin and subcutaneous tissue, which may share pathogenic processes with systemic sclerosis (SSc). We previously demonstrated that upregulated expression of integrin alphavbeta5 might contribute to autocrine TGF-beta signaling in SSc fibroblasts. Based on these data, we presently focused on alphavbeta5 and assessed its involvement in pathogenesis of LSc. We initially demonstrated that LSc fibroblasts might be activated by the stimulation of autocrine TGF-beta. Consistent with SSc fibroblasts, expression levels of alphavbeta5 were elevated in LSc fibroblasts in vitro and in vivo. Anti-alphavbeta5 antibody partially reversed expression levels of type I procollagen and MMP-1 and constitutive DNA-Smad3 binding in LSc fibroblasts. In LSc fibroblasts pretreated with antisense TGF-beta1, exogenous latent TGF-beta1 stimulation increased expression of type I procollagen in an alphavbeta5-dependent manner. The luciferase activities of TMLC cells, Mv1Lu cells stably expressing a portion of the plasminogen activator inhibitor 1 promoter, co-cultured with LSc fibroblasts were significantly elevated compared with those co-cultured with normal fibroblasts and were significantly reduced in the presence of anti-alphavbeta5 antibody. Anti-alphavbeta5 antibody reversed the myofibroblastic features of LSc fibroblasts. These results indicate that upregulated expression of alphavbeta5 contributes to autocrine TGF-beta signaling in LSc fibroblasts.

TGFbeta pathobiology in the eye

Transforming growth factor beta (TGFbeta), a multifunctional growth factor, is one of the most important ligands involved in the regulation of cell behavior in ocular tissues in physiological or pathological processes of development or tissue repair, although various other growth factors are also involved. Increased activity of this ligand may induce unfavorable inflammatory responses and tissue fibrosis. In mammals, three isoforms of TGFbeta, that is, beta1, beta2, and beta3, are known. Although all three TGFbeta isoforms and their receptors are present in ocular tissues, lack of TGFbeta2, but not TGFbeta1 or TGFbeta3, perturbs embryonic morphogenesis of the eyes in mice. Smads2/3 are key signaling molecules downstream of cell surface receptors for TGFbeta or activin. Upon TGF binding to the respective TGF receptor, Smads2/3 are phosphorylated by the receptor kinase at the C-terminus, form a complex with Smad4 and translocate to the nucleus for activation of TGFbeta gene targets. Moreover, mitogen-activated protein kinase, c-Jun N-terminal kinase, and p38 modulate Smad signals directly via Smad linker phosphorylation or indirectly via pathway crosstalk. Smad signals may therefore be a critical threrapeutic target in the treatment of ocular disorders related to fibrosis as in other systemic fibrotic diseases. The present paper reviews recent progress concerning the roles of TGFbeta signaling in the pathology of the eye.

EM703 improves bleomycin-induced pulmonary fibrosis in mice by the inhibition of TGF-beta signaling in lung fibroblasts

BACKGROUND

Fourteen-membered ring macrolides have been effective in reducing chronic airway inflammation and also preventing lung injury and fibrosis in bleomycin-challenged mice via anti-inflammatory effects. EM703 is a new derivative of erythromycin (EM) without the bactericidal effects. We investigated the anti-inflammatory and antifibrotic effects of EM703 in an experimental model of bleomycin-induced lung injury and subsequent fibrosis in mice.

METHODS

Seven-week-old male ICR mice were used. All experiments used eight mice/group, unless otherwise noted in the figure legends. Bleomycin was administered intravenously to the mice on day 0. EM703 was orally administered daily to mice. All groups were examined for cell populations in the bronchoalveolar lavage (BAL) fluid and for induction of messenger RNA (mRNA) of Smad3 and Smad4 in the lung tissues by reverse transcriptase (RT)-polymerase chainreaction (PCR) on day 7. Fibroblastic foci were assessed histologically, and the hydroxyproline content was chemically determined in the lung tissues on day 28. We performed assay of proliferation and soluble collagen production, and examined the induction of mRNA of Smad3 and Smad4 by RT-PCR in murine lung fibroblast cell line MLg2908. We also examined Smad3, Smad4 and phosphorylated Smad2/3 (p-Smad2/3) protein assay by western blotting in MLg2908.

RESULTS

Bleomycin-induced lung fibrosis, and the infiltration of macrophages and neutrophils into the airspace were inhibited by EM703. The expression of Smad3 and Smad4 mRNA was clearly attenuated by bleomycin, but was recovered by EM703. EM703 also inhibited fibroblast proliferation and the collagen production in lung fibroblasts induced by Transforming growth factor-beta (TGF-beta). The expression of Smad3 and Smad4 mRNA in murine lung fibroblasts disappeared due to TGF-beta, but was recovered by EM703. EM703 inhibited the expression of p-Smad2/3 and Smad4 protein in murine lung fibroblasts induced by TGF-beta.

CONCLUSION

These findings suggest that EM703 improves bleomycin-induced pulmonary fibrosis in mice by actions of anti-inflammation and regulation of TGF-beta signaling in lung fibroblasts.

Genetic basis of thoracic aortic aneurysms and aortic dissections

Ascending thoracic aortic aneurysms leading to type A dissections (TAAD) can occur in association with a genetic syndrome, such as Marfan syndrome (MFS), or as an autosomal dominant disorder in the absence of syndromic features, termed familial TAAD. Familial TAAD demonstrates genetic heterogeneity, and linkage studies have identified three TAAD loci at 5q13-14 (TAAD1), 11q23 (FAA1), and 3p24-25 (TAAD2). The underlying genetic heterogeneity of TAAD is reflected in the phenotypic variation associated with familial TAAD with respect to age of onset, progression, penetrance, and association with additional cardiac and vascular features. Recently, mutations in the TGFBR2 gene have been identified as the cause of disease linked to the TAAD2 locus, supporting the hypothesis that dysregulation of TGFbeta signaling is a mechanism leading to aneurysms and dissections. The recent identification of the TGFbeta pathway as a key target in the molecular pathogenesis of TAAD has opened new avenues for future genetic and therapeutic research.

Recent progress towards a molecular understanding of Marfan syndrome

Marfan syndrome (MFS) is a systemic disorder of the connective tissue that is inherited as an autosomal dominant trait and which displays variable manifestations in the ocular, skeletal, and cardiovascular systems. These pleiotropic manifestations are accounted for by mutations in fibrillin-1, the building block of extracellular microfibrils. During the past 10 years, we have witnessed significant progress in delineating the pathological events responsible for the manifestations of MFS. Much of this progress has been based on the creation and analysis of fibrillin-1 mutant mouse lines that faithfully recapitulate the spectrum of clinical severity of MFS. These studies have established the critical contribution of fibrillin-1 deficiency to disease progression through altered cell-matrix interactions and dysregulated TGF-beta signaling. As a result, our definition of MFS as the prototypical structural disorder of the connective tissue has changed to that of a developmental abnormality with broad and complex effects on the morphogenesis and function of multiple organ systems. Importantly, new biological targets have emerged that may yield exciting new opportunities for the development of productive treatment strategies in MFS.

Involvement of alphavbeta5 integrin-mediated activation of latent transforming growth factor beta1 in autocrine transforming growth factor beta signaling in systemic sclerosis fibroblasts

OBJECTIVE

To confirm the involvement of alphavbeta5 in the self-activation system in systemic sclerosis (SSc) fibroblasts.

METHODS

Levels of alphavbeta5 expression were analyzed by immunoprecipitation. The promoter activity of the human alpha2(I) collagen gene was determined by transient transfection assay. Phosphorylation levels and DNA binding ability of Smad3 were investigated by immunoprecipitation and DNA affinity precipitation, respectively. The localization of active transforming growth factor beta (TGFbeta) was determined by coculture assay using TMLC cells (mink lung epithelial reporter cells that stably express a portion of the plasminogen activator inhibitor 1 promoter). The morphologic features of cells were determined by immunofluorescence analysis.

RESULTS

Levels of alphavbeta5 expression were significantly elevated in SSc fibroblasts compared with normal fibroblasts. Treatment with anti-alphavbeta5 antibody or beta5 antisense oligonucleotide significantly reduced human alpha2(I) collagen gene promoter activity in SSc fibroblasts. In SSc fibroblasts pretreated with TGFbeta1 antisense oligonucleotide, the exogenous latent TGFbeta1 stimulation significantly increased human alpha2(I) collagen gene promoter activity; this effect was significantly reduced in the presence of anti-alphavbeta5 antibody. Phosphorylation levels and DNA binding ability of Smad3 in SSc fibroblasts were significantly reduced by treatment with beta5 antisense oligonucleotide. The luciferase activity of TMLC cells cocultured with SSc fibroblasts was significantly elevated compared with that of TMLC cells cocultured with normal fibroblasts and was significantly reduced in the presence of anti-alphavbeta5 antibody. Anti-alphavbeta5 antibody reversed the myofibroblastic features of SSc fibroblasts.

CONCLUSION

Up-regulated expression of alphavbeta5 contributes to the establishment of autocrine TGFbeta signaling in SSc fibroblasts through activation of endogenous latent TGFbeta1.

Targeted therapy comes of age in scleroderma

Systemic sclerosis (SSc, also known as scleroderma) has the highest case-specific mortality among the rheumatic diseases; however, advances in understanding of pathogenesis and an appreciation of the clinical heterogeneity of this disease, together with therapeutic advances in other areas, have raised the possibility of substantial improvements in its management. Key areas of advance include the development of clinical and laboratory methods for early detection of complications and the integration of vascular, immunomodulatory and antifibrotic therapies. Disease models have facilitated the identification of key mediators or processes that could be targeted therapeutically and have provided a platform for preclinical testing of novel candidate therapies. This review will consider current clinical aspects of SSc and the emergence of targeted therapy that is linked to key pathogenic processes or that targets pivotal mediators.

Mutations in Transforming Growth Factor-β Receptor Type II Cause Familial Thoracic Aortic Aneurysms and Dissections

Background— A genetic predisposition for progressive enlargement of thoracic aortic aneurysms leading to type A dissection (TAAD) is inherited in an autosomal-dominant manner in up to 19% of patients, and a number of chromosomal loci have been identified for the condition. Having mapped a TAAD locus to 3p24–25, we sequenced the gene for transforming growth factor-β receptor type II ( TGFBR2 ) to determine whether mutations in this gene resulted in familial TAAD.

Methods and Results— We sequenced all 8 coding exons of TGFBR2 by using genomic DNA from 80 unrelated familial TAAD cases. We found TGFBR2 mutations in 4 unrelated families with familial TAAD who did not have Marfan syndrome. Affected family members also had descending aortic disease and aneurysms of other arteries. Strikingly, all 4 mutations affected an arginine residue at position 460 in the intracellular domain, suggesting a mutation “hot spot” for familial TAAD. Despite identical mutations in the families, assessment of linked polymorphisms suggested that these families were not distantly related. Structural analysis of the TGFBR2 serine/threonine kinase domain revealed that R460 is strategically located within a highly conserved region of this domain and that the amino acid substitutions resulting from these mutations will interfere with the receptor’s ability to transduce signals.

Conclusion— Germline TGFBR2 mutations are responsible for the inherited predisposition to familial TAAD in 5% of these cases. Our results have broad implications for understanding the role of TGF-β signaling in the pathophysiology of TAAD.

Activation of Key Profibrotic Mechanisms in Transgenic Fibroblasts Expressing Kinase-deficient Type II Transforming Growth Factor-β Receptor (TβRIIΔk)

We have generated transgenic mice expressing a kinase-deficient type II transforming growth factor-beta (TGFbeta) receptor selectively on fibroblasts (TbetaRIIDeltak-fib). These mice develop dermal and pulmonary fibrosis. In the present study we explore activation of TGFbeta signaling pathways in this strain and examine the profibrotic properties of explanted transgenic fibroblasts including myofibroblast differentiation and abnormal metalloproteinase production. Gene expression profiles of littermate wild type or transgenic fibroblasts were compared using high-density gene arrays and validated by Taqman reverse transcriptase-PCR, Northern and Western blotting. Using a specific inhibitor (SD-208) we demonstrate that the abnormal phenotype of these cells is dependent upon TbetaRI kinase (ALK5) activity, and that transgenic fibroblasts show enhanced expression and activation of TGFbeta together with increased levels of wild type TbetaRII. Moreover, we confirm that transgene expression is itself regulated by TGFbeta and that expression at low levels facilitates signaling, whereas high level expression is inhibitory. For a subset of TGFbeta responsive genes basal up-regulation is normalized or suppressed by exogenous recombinant TGFbeta1 at time points coincident with increased transgene expression. These findings explain the profound refractoriness of TbetaRIIDeltak-fib fibroblasts to exogenous TGFbeta1, despite their activated phenotype. Thus, transgenic fibroblasts recapitulate many hallmark biochemical properties of fibrotic cells, including high level CTGF (CCN2) expression and type I collagen overproduction, altered MMP production, and myofibroblast differentiation. These cells also show an enhanced ability to contract collagen gel matrices. Our study demonstrates that altered high affinity TGFbeta receptor function may lead to ligand-dependent activation of downstream signaling, and provides further evidence of a pivotal role for sustained TGFbeta overactivity in fibrosis.

TGF-beta-induced SMAD signaling and gene regulation: consequences for extracellular matrix remodeling and wound healing

Members of the transforming growth factor-beta (TGF-beta) superfamily are pleiotropic cytokines that have the ability to regulate numerous cell functions, including proliferation, differentiation, apoptosis, epithelial-mesenchymal transition, and production of extracellular matrix, allowing them to play an important role during embryonic development and for maintenance of tissue homeostasis. Three TGF-beta isoforms have been identified in mammals. They propagate their signal via a signal transduction network involving receptor serine/threonine kinases at the cell surface and their substrates, the SMAD proteins. Upon phosphorylation and oligomerization, the latter move into the nucleus to regulate transcription of target genes. This review will summarize recent advances in the understanding of the mechanisms underlying SMAD modulation of extracellular matrix gene expression in the context of wound healing and tissue fibrosis.

A syndrome of altered cardiovascular, craniofacial, neurocognitive and skeletal development caused by mutations in TGFBR1 or TGFBR2

We report heterozygous mutations in the genes encoding either type I or type II transforming growth factor beta receptor in ten families with a newly described human phenotype that includes widespread perturbations in cardiovascular, craniofacial, neurocognitive and skeletal development. Despite evidence that receptors derived from selected mutated alleles cannot support TGFbeta signal propagation, cells derived from individuals heterozygous with respect to these mutations did not show altered kinetics of the acute phase response to administered ligand. Furthermore, tissues derived from affected individuals showed increased expression of both collagen and connective tissue growth factor, as well as nuclear enrichment of phosphorylated Smad2, indicative of increased TGFbeta signaling. These data definitively implicate perturbation of TGFbeta signaling in many common human phenotypes, including craniosynostosis, cleft palate, arterial aneurysms, congenital heart disease and mental retardation, and suggest that comprehensive mechanistic insight will require consideration of both primary and compensatory events.

Transgenic analysis of scleroderma: understanding key pathogenic events in vivo

Modern molecular genetic methods have allowed better understanding of established mouse models of scleroderma and also facilitated the development of new and better defined mouse strains for investigating the pathogenesis of the disease. The best characterized scleroderma animal model is the type 1 tight skin mouse (Tsk1). Backcrossing these animals with other mutant strains has been informative. These experiments implicate the IL-4 ligand-receptor axis in the development of skin fibrosis. Parallel expression analysis of genes using microarrays has provided insight into novel mediators of fibrosis including the C-C chemokine MCP-3. Other experiments suggest that embryonically defined fibroblast-specific regulatory elements may be targets for activation in this model. The same lineage-specific elements have been used to selectively activate TGF beta signaling pathways in fibrosis to generate a novel model for scleroderma and also have been used to develop systems for ligand-dependent fibroblast-specific genetic recombination that will allow further analysis key candidate genes implicated in scleroderma pathogenesis. Better mouse models will improve understanding of this intractable rheumatic disease and can be expected to ultimately lead to improved treatments and outcome.

Alterations in the TGFbeta signaling pathway in myogenic progenitors with age

Myogenic progenitors in adult muscle are necessary for the repair, maintenance and hypertrophy of post-mitotic muscle fibers. With age, fat deposition and fibrosis contribute to the decline in the integrity and functional capacity of muscles. In a previous study we reported increased accumulation of lipid in myogenic progenitors obtained from aged mice, accompanied by an up-regulation of genes involved in adipogenic differentiation. The present study was designed to extend our understanding of how aging affects the fate and gene expression profile of myogenic progenitors. Affymetrix murine U74 Genechip analysis was performed using RNA extracted from myogenic progenitors isolated from adult (8-month-old) and aged (24-month-old) DBA/2JNIA mice. The cells from the aged animals exhibited major alterations in the expression level of many genes directly or indirectly involved with the TGFbeta signaling pathway. Our data indicate that with age, myogenic progenitors acquire the paradoxical phenotype of being both TGFbeta activated based on overexpression of TGFbeta-inducible genes, but resistant to the differentiation-inhibiting effects of exogenous TGFbeta. The overexpression of TGFbeta-regulated genes, such as connective tissue growth factor, may play a role in increasing fibrosis in aging muscle.

Animal models of systemic sclerosis: insights into systemic sclerosis pathogenesis and potential therapeutic approaches

PURPOSE OF REVIEW

Animal models have been extremely valuable in contributing to a better understanding of the pathogenesis of systemic sclerosis. Discussed here are recent studies that have examined the molecular pathways and potential therapeutic approaches for systemic sclerosis using animal models.

RECENT FINDINGS

Reported evidence further indicates that the immune system plays a role in modulating the fibrosis observed in the tight skin-1/+ mouse model for systemic sclerosis. CD19, interleukin-6, and interleukin-4 are involved. The injection of spleen cells into immune-compromised mice resulted in fibrotic, vascular, and immunologic alterations quite similar to those of systemic sclerosis. Transforming growth factor-beta and its signaling pathway (JAK kinase and STAT-6, Smad2/3, and Smad7) appear to play a central role in the development of fibrosis as well as monocyte chemoattractant protein-1, CCR-2, platelet-derived growth factor C, and excessive apoptosis. Viruses were shown to be possible cofactors. The therapeutic agents hepatocyte growth factor and halofuginone were shown to prevent fibrosis in animal models of systemic sclerosis.

SUMMARY

The transforming growth factor-beta signaling pathway is a common mechanism of tissue fibrosis in animal models of systemic sclerosis, although numerous additional molecules modulate this pathway or have a direct effect on fibrosis.

Recent advances in fibroblast signaling and biology in scleroderma

PURPOSE OF REVIEW

Systemic sclerosis is a complex disease manifesting itself by fibrosis of skin and other internal organs. Fibroblasts isolated from scleroderma lesions and cultured in vitro are characterized by increased synthesis of collagen and other extracellular matrix proteins, consistent with the disease phenotype. Cultured systemic sclerosis fibroblasts therefore serve as a principal experimental model for studying the molecular and cellular mechanisms involved in collagen overproduction in this disease. This review will discuss recent findings related to intracellular signal transduction pathways implicated in deregulated extracellular matrix deposition by systemic sclerosis fibroblasts.

RECENT FINDINGS

Recent findings suggest that constitutively elevated synthesis of extracellular matrix by cultured systemic sclerosis fibroblasts is, at least in part, due to the aberrant activation of the autocrine transforming growth factor-beta signaling. Enhanced constitutive transforming growth factor-beta signaling may result from the elevated levels of transforming growth factor-beta receptor type I and/or inappropriate activation of Smad3. These alterations of the transforming growth factor-beta signaling in systemic sclerosis fibroblasts may facilitate increased collagen production in vivo even under conditions of low ligand availability. However, there exist many inconsistencies among published reports regarding the detailed mechanisms of this pathway in systemic sclerosis fibroblasts, and additional studies in this area are needed. Other signaling molecules implicated in fibrotic phenotype include several members of the protein kinase C family, mammalian target of rapamycin, mitogen-activated protein kinase, necdin, reactive oxygen species, and sphingolipids. These signaling pathways may work in conjunction with transforming growth factor-beta signaling to regulate the behavior of systemic sclerosis fibroblasts.

SUMMARY

Alterations in multiple signaling pathways contribute to elevated extracellular matrix synthesis by systemic sclerosis fibroblasts. Improved understanding of the key signaling molecules may provide a novel avenue for therapeutic interventions.

Genetic targeting of relaxin and insulin-like factor 3 receptors in mice

Relaxin (RLN) is a small peptide hormone that affects a variety of biological processes. Rln1 knockout mice exhibit abnormal nipple development, prolonged parturition, agerelated pulmonary fibrosis, and abnormalities in the testes and prostate. We describe here RLN receptor Lgr7-deficient mice. Mutant females have grossly underdeveloped nipples and are unable to feed their progeny. Some Lgr7-/- females were unable to deliver their pups. Histological analysis of Lgr7 mutant lung tissues demonstrates increased collagen accumulation and fibrosis surrounding the bronchioles and the vascular bundles, absent in wild-type animals. However, Lgr7-deficient males do not exhibit abnormalities in the testes or prostate as seen in Rln1 knockout mice. Lgr7-deficient females with additional deletion of Lgr8 (Great), another putative receptor for RLN, are fertile and have normal-sized litters. Double mutant males have normal-sized prostate and testes, suggesting that Lgr8 does not account for differences in Rln1-/- and Lgr7-/- phenotypes. Transgenic overexpression of Insl3, the cognate ligand for Lgr8, does not rescue the mutant phenotype of Lgr7-deficient female mice indicating nonoverlapping functions of the two receptors. Our data indicate that neither Insl3 nor Lgr8 contribute to the RLN signaling pathway. We conclude that the Insl3/Lgr8 and Rln1/Lgr7 actions do not overlap in vivo.

An increased transforming growth factor beta receptor type I:type II ratio contributes to elevated collagen protein synthesis that is resistant to inhibition via a kinase-deficient transforming growth factor beta receptor type II in scleroderma

OBJECTIVE

Aberrant transforming growth factor beta (TGFbeta) signaling has been implicated in the pathogenesis of scleroderma (systemic sclerosis [SSc]), but the contribution of specific components in this pathway to SSc fibroblast phenotype remains unclear. This study was undertaken to delineate the role of TGFbeta receptor type I (TGFbetaRI) and TGFbetaRII in collagen overexpression by SSc fibroblasts.

METHODS

Primary dermal fibroblasts from SSc patients and healthy adults were studied (n = 10 matched pairs). Adenoviral vectors were generated for TGFbetaRI (AdTGFbetaRI), TGFbetaRII (AdTGFbetaRII), and kinase-deficient TGFbetaRII (AdDeltakRII). TGFbetaRI basal protein levels were analyzed by (35)S-methionine labeling/immunoprecipitation and immunohistochemistry. Type I collagen and TGFbetaRII basal protein levels were analyzed by Western blot and newly secreted collagen by (3)H-proline incorporation assay.

RESULTS

Analysis of endogenous TGFbetaRI and TGFbetaRII protein levels revealed that SSc TGFbetaRI levels were increased 1.7-fold (P = 0.008; n = 7) compared with levels in healthy controls, while TGFbetaRII levels were decreased by 30% (P = 0.03; n = 7). This increased TGFbetaRI:TGFbetaRII ratio correlated with SSc collagen overexpression. To determine the consequences of altered TGFbetaRI:TGFbetaRII ratio on collagen expression, healthy fibroblasts were transduced with AdTGFbetaRI or AdTGFbetaRII. Forced expression of TGFbetaRI in the range corresponding to elevated SSc TGFbetaRI levels increased basal collagen expression in a dose-dependent manner, while similar TGFbetaRII overexpression had no effect, although transduction of fibroblasts at higher multiplicities of infection led to a marked reduction of basal collagen levels. Blockade of TGFbeta signaling via AdDeltakRII resulted in approximately 50% inhibition of basal collagen levels in healthy fibroblasts and in 5 of 9 SSc cell lines. A subset of SSc fibroblasts (4 of 9 cell lines) was resistant to this treatment. SSc fibroblasts with the highest levels of TGFbetaRI were the least responsive to collagen inhibition via DeltakRII.

CONCLUSION

This study indicates that an increased TGFbetaRI:TGFbetaRII ratio may underlie aberrant TGFbeta signaling in SSc and contribute to elevated basal collagen production, which is insensitive to TGFbeta signaling blockade via DeltakRII.

Relationship between posterior capsule opacification and intraocular lens biocompatibility

The type of healing process that occurs in response to cataract surgery and intraocular lens (IOL) implantation is dependent on a complex set of variables. Their interactions determine whether or not optical clarity is restored as a result of this procedure. In this process, wound healing entails cells undergoing either epithelial-mesenchymal transition, resulting in the generation of fibroblastic cells and accumulation of extracellular matrix, or lenticular structure formation. Such desperate cellular behaviors are regulated by the localized release of different cytokines, including transforming growth factor beta and fibroblast growth factors, which can result in post-operative capsular opacification. Other factors affecting the biological and mechanical outcome of IOL implantation are its composition, surface properties and shape.

Vascular Smooth Muscle Polyploidization as a Biomarker for Aging and Its Impact on Differential Gene Expression

Polyploidy is characterized by a greater than diploid content of DNA in a cell. Previous measurements of ploidy level in different organs of humans and rodents, including the aorta, indicated an increase in old versus young. We hypothesized that aortic vascular smooth muscle polyploidy is a biomarker for aging and that the augmented DNA dosage affects selective gene-specific transcript expression. Our results demonstrate that tetraploidy increases exponentially over the life span of the animal, serving as an indicator of age. Approximately 60% of the vascular smooth muscle cells in the thoracic aorta of 36-month-old Brown Norway rats are tetraploid compared with 8% in their 3-month-old counterparts. Microarray analysis and reverse transcriptase-PCR was performed with mRNA isolated from sorted diploid (2N) and tetraploid (4N) vascular smooth muscle cells from old rats to identify differentially expressed transcripts. For the majority of detectable transcripts, an increase in DNA content led to a proportional increase in mRNA. A select group of transcripts, however, were reduced in tetraploid compared with diploid cells. These mRNAs correspond to guanine deaminase, to the matrix proteins rat glypican 3 (OCI-5) and decorin, as well as to the inflammation-associated transcripts, insulin-like growth factor-binding protein 6, macrophage inflammatory protein 2 precursor, macrophage galactose N-acetylgalactoseamine-specific lectin, and complement component C4. Our study is the first to describe aortic ploidy level as a biomarker for aging and to indicate that changes associated with increased DNA content per cell may selectively suppress the expression of specific genes.