Requirement for transglutaminase in the activation of latent transforming growth factor-beta in bovine endothelial cells

The function of tissue transglutaminase in celiac disease

Celiac disease is a chronic small bowel disorder caused by an abnormal immune response to an array of epitopes of wheat gluten and related proteins of rye and barley in genetically susceptible individuals who express the HLA-DQ2/-DQ8 haplotype. Gluten peptides are efficiently presented by celiac disease-specific HLA-DQ2- and HLA-DQ8-positive antigen presenting cells to CD4(+) T-cells that, once activated, drive a T helper cell type 1 response leading to the development of the typical celiac lesion-villous atrophy, crypt hyperplasia and intraepithelial and lamina propria infiltration of inflammatory cells. Tissue transglutaminase (tTG) is a calcium dependent ubiquitous enzyme which catalyses posttranslational modification of proteins and is released from cells during inflammation. tTG is suggested to exert at least two crucial roles in celiac disease: as a deamidating enzyme, that can enhance the immunostimulatory effect of gluten, and as a target autoantigen in the immune response. Since glutamine-rich gliadin peptides are excellent substrates for tTG, and the resulting deamidated and thus negatively charged peptides have much higher affinity for the HLA-DQ2 and HLA-DQ8 molecules, the action of tTG is believed to be a key step in the pathogenesis of celiac disease. This review is focused on the function of tTG in celiac disease, although it also deals with novel advances in tTG-based therapies.

Cellular functions of tissue transglutaminase

Transglutaminase 2 (TG2 or tissue transglutaminase) is a highly complex multifunctional protein that acts as transglutaminase, GTPase/ATPase, protein disulfide isomerase, and protein kinase. Moreover, TG2 has many well-documented nonenzymatic functions that are based on its noncovalent interactions with multiple cellular proteins. A vast array of biochemical activities of TG2 accounts for its involvement in a variety of cellular processes, including adhesion, migration, growth, survival, apoptosis, differentiation, and extracellular matrix organization. In turn, the impact of TG2 on these processes implicates this protein in various physiological responses and pathological states, contributing to wound healing, inflammation, autoimmunity, neurodegeneration, vascular remodeling, tumor growth and metastasis, and tissue fibrosis. TG2 is ubiquitously expressed and is particularly abundant in endothelial cells, fibroblasts, osteoblasts, monocytes/macrophages, and smooth muscle cells. The protein is localized in multiple cellular compartments, including the nucleus, cytosol, mitochondria, endolysosomes, plasma membrane, and cell surface and extracellular matrix, where Ca(2+), nucleotides, nitric oxide, reactive oxygen species, membrane lipids, and distinct protein-protein interactions in the local microenvironment jointly regulate its activities. In this review, we discuss the complex biochemical activities and molecular interactions of TG2 in the context of diverse subcellular compartments and evaluate its wide ranging and cell type-specific biological functions and their regulation.

Transforming growth factor-β and atherosclerosis: interwoven atherogenic and atheroprotective aspects

Age-related progression of cardiovascular disease is by far the largest health problem in the US and involves vascular damage, progressive vascular fibrosis and the accumulation of lipid-rich atherosclerotic lesions. Advanced lesions can restrict flow to key organs and can trigger occlusive thrombosis resulting in a stroke or myocardial infarction. Transforming growth factor-beta (TGF-β) is a major orchestrator of the fibroproliferative response to tissue damage. In the early stages of repair, TGF-β is released from platelets and activated from matrix reservoirs; it then stimulates the chemotaxis of repair cells, modulates immunity and inflammation and induces matrix production. At later stages, it negatively regulates fibrosis through its strong antiproliferative and apoptotic effects on fibrotic cells. In advanced lesions, TGF-β might be important in arterial calcification, commonly referred to as "hardening of the arteries". Because TGF-β can signal through multiple pathways, namely the SMADs, a MAPK pathway and the Rho/ROCK pathways, selective defects in TGF-β signaling can disrupt otherwise coordinated pathways of tissue regeneration. TGF-β is known to control cell proliferation, cell migration, matrix synthesis, wound contraction, calcification and the immune response, all being major components of the atherosclerotic process. However, many of the effects of TGF-β are essential to normal tissue repair and thus, TGF-β is often thought to be "atheroprotective". The present review attempts to parse systematically the known effects of TGF-β on both the major risk factors for atherosclerosis and to isolate the role of TGF-β in the many component pathways involved in atherogenesis.

Transglutaminase 2: a molecular Swiss army knife

Transglutaminase 2 (TG2) is the most widely distributed member of the transglutaminase family with almost all cell types in the body expressing TG2 to varying extents. In addition to being widely expressed, TG2 is an extremely versatile protein exhibiting transamidating, protein disulphide isomerase and guanine and adenine nucleotide binding and hydrolyzing activities. TG2 can also act as a protein scaffold or linker. This unique protein also undergoes extreme conformational changes and exhibits localization diversity. Being mainly a cytosolic protein; it is also found in the nucleus, associated with the cell membrane (inner and outer side) and with the mitochondria, and also in the extracellular matrix. These different activities, conformations and localization need to be carefully considered while assessing the role of TG2 in physiological and pathological processes. For example, it is becoming evident that the role of TG2 in cell death processes is dependent upon the cell type, stimuli, subcellular localization and conformational state of the protein. In this review we discuss in depth the conformational and functional diversity of TG2 in the context of its role in numerous cellular processes. In particular, we have highlighted how differential localization, conformation and activities of TG2 may distinctly mediate cell death processes.

Transglutaminase 2 facilitates the distant hematogenous metastasis of breast cancer by modulating interleukin-6 in cancer cells

Introduction

Inflammation has been implicated in cancer aggressiveness. As transglutaminase 2 (TG2), which has been associated with inflammatory signaling, has been suggested to play a role in tumor behavior, we propose that TG2 may be an important linker inducing interleukin (IL)-6-mediated cancer-cell aggressiveness, including distant hematogenous metastasis.

Methods

To investigate the role for TG2 and IL-6, TG2-knocked-down and IL-6-knocked-down cancer cells were generated by using shRNA. Human breast cancer cell xenograft model in highly immunocompromised mice and human advanced breast cancer primary tumor tissue microarrays were used in this study.

Results

IL-6 production in human breast cancer cells was dependent on their TG2 expression level. In vitro tumor-sphere formation was dependent on TG2 and downstream IL-6 production from cancer cells. Primary tumor growth in the mammary fat pads and distant hematogenous metastasis into the lung was also dependent on TG2 and downstream IL-6 expression levels. The effect of TG2 expression on human breast cancer distant metastasis was investigated by analyzing a tissue microarray of primary tumors from 412 patients with their clinical data after 7 years. TG2 expression in primary tumor tissue was inversely correlated with recurrence-free survival (P = 0.019) and distant metastasis-free survival (DMFS) (P = 0.006) in patients with advanced breast cancer. Furthermore, by using public datasets that included a total of 684 breast cancer patients, we found that the combined high expression of TG2 and IL-6 was associated with shorter DMFS, compared with the high expression of IL-6 only (P = 0.013).

Conclusions

We provide evidence that TG2 is an important link in IL-6-mediated tumor aggressiveness, and that TG2 could be an important mediator of distant metastasis, both in a xenograft animal model and in patients with advanced breast cancer.

Epithelial transglutaminase 2 is needed for T cell interleukin-17 production and subsequent pulmonary inflammation and fibrosis in bleomycin-treated mice

Pulmonary fibrosis is a potentially life-threatening disease that may be caused by overt or asymptomatic inflammatory responses. However, the precise mechanisms by which tissue injury is translated into inflammation and consequent fibrosis remain to be established. Here, we show that in a lung injury model, bleomycin induced the secretion of IL-6 by epithelial cells in a transglutaminase 2 (TG2)-dependent manner. This response represents a key step in the differentiation of IL-17-producing T cells and subsequent inflammatory amplification in the lung. The essential role of epithelial cells, but not inflammatory cells, TG2 was confirmed in bone marrow chimeras; chimeras made in TG2-deficient recipients showed reduced inflammation and fibrosis, compared with those in wild-type mice, regardless of the bone marrow cell phenotype. Epithelial TG2 thus appears to be a critical inducer of inflammation after noninfectious pulmonary injury. We further demonstrated that fibroblast-derived TG2, acting downstream of transforming growth factor-β, is also important in the effector phase of fibrogenesis. Therefore, TG2 represents an interesting potential target for therapeutic intervention.

Evidence for early fibrosis and increased airway resistance in bone marrow transplant recipient mice deficient in MMP12

Idiopathic pneumonia syndrome (IPS) is a significant cause of morbidity and mortality post-bone marrow transplantation (BMT) in humans. In our established murine IPS model in which lethally conditioned recipients are given allogeneic bone marrow and splenocytes, recruitment of host monocytes occurs early post-BMT, followed by donor T cells concomitant with development of severe lung dysfunction. Because matrix metalloproteinase 12 (MMP12) is important for macrophage infiltration and injury in other mouse models of lung disease such as emphysema, lethally conditioned MMP12(-/-) mice were used as allogeneic recipients to determine whether MMP12 plays a similar role in potentiating lung injury in IPS. Surprisingly, MMP12(-/-) mice developed IPS and exhibited an accelerated allogeneic T cell-dependent decrease in compliance compared with wild-type (WT) recipients. MMP12(-/-), but not WT, mice also had allogeneic T cell-dependent elevated lung resistance post-BMT. Recruitment of monocytes and T cells into the lungs was not altered on day 7 post-BMT, but the lungs of MMP12(-/-) recipients had increased collagen deposition, a feature normally not seen in our IPS model. MMP12(-/-) mice had a compensatory increase in MMP2 in the lungs post-BMT, as well as increased β6-integrin compared with WT recipients, and only in the presence of allogeneic T cells. Levels of total transforming growth factor (TGF)-β1 protein in the lungs were elevated compared with WT recipients, consistent with the profibrotic function of β6-integrin as an activator of TGF-β. These data indicate that host-derived MMP12 may be important in limiting development of IPS by allowing proper remodeling of extracellular matrix and effective repair of BMT-related injury.

Transforming growth factor-beta2 utilizes the canonical Smad-signaling pathway to regulate tissue transglutaminase expression in human trabecular meshwork cells

Transforming growth factor-beta2 (TGF-β2) is elevated in the aqueous humor of patients with glaucoma. This growth factor is known to increase extracellular matrix (ECM) deposition in the trabecular meshwork (TM) as well as increase intraocular pressure (IOP) in perfused human cultured anterior eye segments. In addition overexpression of TGF-β2 in the mouse TM leads to elevated IOP. Exogenous TGF-β2 also increases tissue transglutaminase (TGM2) protein levels and enzyme activity in TM cells. TGM2 is a calcium-dependent enzyme that mediates cross-linking of ECM proteins, thus making ECM proteins resistant to enzymatic degradation and physical breakdown. We have investigated the signaling pathway by which TGF-β2 induces TGM2 in human TM cells. Primary cultures of human TM cells (N = 6) were treated for 48 h with TGF-β2 (0-10 ng/ml) in serum-free medium. TGM2 enzyme activity differences between non-treated and TGF-β2 treated TM cells were studied using a biotin cadaverine assay. Endogenous TGF-β2 protein levels were examined in normal trabecular meshwork (NTM) and glaucomatous trabecular meshwork (GTM) cell strains. Immunohistochemistry was used to evaluate the expression and co-localization of TGF-β2 and TGM2 in NTM and GTM tissues. Activation of Smad3 signaling pathway was evaluated by western immunoblot analysis using phospho-specific antibodies following exogenous TGF-β2 treatment. Pharmacological specific inhibitor of Smad3 (SIS3) and short interfering (si)RNAs were used to suppress Smad3 activity and CTGF gene expression respectively. Endogenous TGF-β2 levels were significantly elevated in cultured GTM cells (p < 0.05) when compared to NTM cells. Immunohistochemistry studies also demonstrated elevated expression and co-localization of both TGF-β2 and TGM2 in glaucoma human TM tissues. Exogenous TGF-β2 increased both TGM2 protein levels and enzyme activity in TM cells. Phosphorylation of Smad3 was stimulated in TM cell strains by exogenous TGF-β2. TGF-β2 induction of TGM2 was not inhibited with selective siRNA knockdown of CTGF. In contrast, a specific inhibitor of Smad3 (SIS3) and siRNA knockdown of Smad3 (p < 0.05) suppressed TGF-β2 induction of TGM2. This study demonstrated that TGF-β2 induction of TGM2 can be mediated via the canonical Smad-signaling pathway but does not appear to involve CTGF as a downstream mediator. Regulation of the Smad-signaling pathway in the TM may be useful in the therapy for glaucoma associated with aberrant TGF-β2 signaling.

MTA1 coregulation of transglutaminase 2 expression and function during inflammatory response

Although both metastatic tumor antigen 1 (MTA1), a master chromatin modifier, and transglutaminase 2 (TG2), a multifunctional enzyme, are known to be activated during inflammation, it remains unknown whether these molecules regulate inflammatory response in a coordinated manner. Here we investigated the role of MTA1 in the regulation of TG2 expression in bacterial lipopolysaccharide (LPS)-stimulated mammalian cells. While studying the impact of MTA1 status on global gene expression, we unexpectedly discovered that MTA1 depletion impairs the basal as well as the LPS-induced expression of TG2 in multiple experimental systems. We found that TG2 is a chromatin target of MTA1 and of NF-κB signaling in LPS-stimulated cells. In addition, LPS-mediated stimulation of TG2 expression is accompanied by the enhanced recruitment of MTA1, p65RelA, and RNA polymerase II to the NF-κB consensus sites in the TG2 promoter. Interestingly, both the recruitment of p65 and TG2 expression are effectively blocked by a pharmacological inhibitor of the NF-κB pathway. These findings reveal an obligatory coregulatory role of MTA1 in the regulation of TG2 expression and of the MTA1-TG2 pathway, at least in part, in LPS modulation of the NF-κB signaling in stimulated macrophages.

Tissue Transglutaminase (TG2)-Induced Inflammation in Initiation, Progression, and Pathogenesis of Pancreatic Cancer

Pancreatic cancer (PC) is among the deadliest cancers, with a median survival of six months. It is generally believed that infiltrating PC arises through the progression of early grade pancreatic intraepithelial lesions (PanINs). In one model of the disease, the K-ras mutation is an early molecular event during progression of pancreatic cancer; it is followed by the accumulation of additional genetic abnormalities. This model has been supported by animal studies in which activated K-ras and p53 mutations produced metastatic pancreatic ductal adenocarcinoma in mice. According to this model, oncogenic K-ras induces PanIN formation but fails to promote the invasive stage. However, when these mice are subjected to caerulein treatment, which induces a chronic pancreatitis-like state and inflammatory response, PanINs rapidly progress to invasive carcinoma. These results are consistent with epidemiologic studies showing that patients with chronic pancreatitis have a much higher risk of developing PC. In line with these observations, recent studies have revealed elevated expression of the pro-inflammatory protein tissue transglutaminase (TG2) in early PanINs, and its expression increases even more as the disease progresses. In this review we discuss the implications of increased TG2 expression in initiation, progression, and pathogenesis of pancreatic cancer.

Pathophysiology of articular chondrocalcinosis--role of ANKH

Calcium pyrophosphate (CPP) crystal deposition (CPPD) is associated with ageing and osteoarthritis, and with uncommon disorders such as hyperparathyroidism, hypomagnesemia, hemochromatosis and hypophosphatasia. Elevated levels of synovial fluid pyrophosphate promote CPP crystal formation. This extracellular pyrophosphate originates either from the breakdown of nucleotide triphosphates by plasma-cell membrane glycoprotein 1 (PC-1) or from pyrophosphate transport by the transmembrane protein progressive ankylosis protein homolog (ANK). Although the etiology of apparent sporadic CPPD is not well-established, mutations in the ANK human gene (ANKH) have been shown to cause familial CPPD. In this Review, the key regulators of pyrophosphate metabolism and factors that lead to high extracellular pyrophosphate levels are described. Particular emphasis is placed on the mechanisms by which mutations in ANKH cause CPPD and the clinical phenotype of these mutations is discussed. Cartilage factors predisposing to CPPD and CPP-crystal-induced inflammation and current treatment options for the management of CPPD are also described.

Role of transglutaminases in cuff-induced atherosclerotic lesion formation in femoral arteries of ApoE3 Leiden mice

Transglutaminases play an important role in vascular remodeling, calcification, cell adhesion and endothelial barrier function. In this study we investigate the influence of combined inhibition of both tissue-type transglutaminase (TG2) and the plasma transglutaminase FXIIIA on early lesion development.

METHODS

A cuff was placed around the femoral arteries of ApoE3 Leiden mice while fed a Western type diet to induce atherosclerotic lesion development. An osmotic minipump was placed in the intraperitoneal cavity containing an irreversible inhibitor of TG2 and FXIIIA activity ((1,3,4,5-tetramethyl-2-[(2-oxopropyl)thio]imidazolium chloride, Zedira). Atherosclerotic lesion composition was analyzed using immunohistochemistry and RT-PCR.

RESULTS

Inhibition of transglutaminases did not influence lesion size or geometric remodeling of the vessels. However, systemic transglutaminase inhibition resulted in 41% less macrophage infiltrate in the media of the vessels. Additional in vitro experiments on HL60 cells confirmed a decreased migratory response during transglutaminase inhibition.

CONCLUSION

Inhibition of TG2 and FXIIIA during early development of lesions reduced the macrophage content in the media of atherosclerotic vessels, while not affecting lesion size or geometric remodeling.

Garlic extract prevents CCl(4)-induced liver fibrosis in rats: The role of tissue transglutaminase

BACKGROUND AND AIM

Tissue transglutaminase contributes to liver damage in the development of hepatic fibrosis. In a model of neurodegeneration, the therapeutic benefit of cystamine has been partly attributed to its inhibition of transglutaminase activity. Garlic extract contains many compounds structurally related to cystamine. We investigated the anti-fibrotic effect of garlic extract and cystamine as specific tissue transglutaminase inhibitors.

METHODS

Rat liver fibrosis was induced by intraperitoneal injection of carbon tetrachloride (CCl(4)) for 7 weeks. Cystamine or garlic extract was administrated by daily intraperitoneal injection, starting from the day after the first administration of CCl(4). Hepatic function, histology, tissue transglutaminase immunostaining and image analysis to quantify Red Sirius stained collagen deposition were examined. Reverse transcription-polymerase chain reaction to detect alpha-SMA, IL-1beta and tissue transglutaminase expression and Western blot for tissue transglutaminase protein amount were performed. Transglutaminase activity was assayed on liver homogenates by a radio-enzymatic method.

RESULTS

Transglutaminase activity was increased in CCl(4) group and reduced by cystamine and garlic extract (p<0.05). Treatment with cystamine and garlic extract reduced the liver fibrosis and collagen deposition, particularly in the garlic extract group (p<0.01). Moreover, the liver damage improved and serum alanine aminotransferase was decreased (p<0.05). Tissue transglutaminase immunolocalised with collagen fibres and is mainly found in the ECM of damaged liver. Alpha-SMA, IL-1beta, tissue transglutaminase mRNA and tissue transglutaminase protein were down-regulated in the cystamine and garlic extract groups compared to controls.

CONCLUSION

These findings concurrently suggest that transglutaminase may play a pivotal role in the pathogenesis of liver fibrosis and may identify garlic cystamine-like molecules as a potential therapeutic strategy in the treatment of liver injury.

Wound healing monitoring using near infrared fluorescent fibrinogen

We demonstrate a method for imaging the wound healing process with near infrared fluorescent fibrinogen. Wound healing studies were performed on a rat punch biopsy model. Fibrinogen was conjugated with a near infrared fluorescent dye and injected into the tail vein. Fibrinogen is a useful protein for tracking wound healing because it is involved in fibrin clot formation and formation of new provisional matrix through transglutaminase's crosslinking activity. Strong fluorescence specific to the wound was observed and persisted for several days, indicating that the fibrinogen is converted to crosslinked fibrin. Administration of contrast agent simultaneously with wound creation led to primary labeling of the fibrin clot, indicating that the wound was in its early phase of healing. Administration on the following day showed labeling on the wound periphery, indicating location of formation of a new provisional matrix. This method may prove to be useful as a diagnostic for basic studies of the wound healing process, in drug development, or in clinical assessment of chronic wounds.

Do changes in transglutaminase activity alter latent transforming growth factor beta activation in experimental diabetic nephropathy?

BACKGROUND

Diabetic nephropathy is the leading cause of end-stage kidney failure worldwide. It is characterized by excessive extracellular matrix accumulation. Transforming growth factor beta 1 (TGF-β1) is a fibrogenic cytokine playing a major role in the healing process and scarring by regulating extracellular matrix turnover, cell proliferation and epithelial mesanchymal transdifferentiation. Newly synthesized TGF-β is released as a latent, biologically inactive complex. The cross-linking of the large latent TGF-β to the extracellular matrix by transglutaminase 2 (TG2) is one of the key mechanisms of recruitment and activation of this cytokine. TG2 is an enzyme catalyzing an acyl transfer reaction leading to the formation of a stable ε(γ-glutamyl)-lysine cross-link between peptides.

METHODS

To investigate if changes in TG activity can modulate TGF-β1 activation, we used the mink lung cell bioassay to assess TGF-β activity in the streptozotocin model of diabetic nephropathy treated with TG inhibitor NTU281 and in TG2 overexpressing opossum kidney (OK) proximal tubular epithelial cells.

RESULTS

Application of the site-directed TG inhibitor NTU281 caused a 25% reduction in kidney levels of active TGF-β1. Specific upregulation of TG2 in OK proximal tubular epithelial cells increased latent TGF-β recruitment and activation by 20.7% and 19.7%, respectively, in co-cultures with latent TGF-β binding protein producing fibroblasts.

CONCLUSIONS

Regulation of TG2 directly influences the level of active TGF-β1, and thus, TG inhibition may exert a renoprotective effect by targeting not only a direct extracellular matrix deposition but also TGF-β1 activation and recruitment.

GPR56 interacts with extracellular matrix and regulates cancer progression

GPR56 is a relatively recent addition to the adhesion-GPCR family. Genetic and biochemical studies uncovered its roles in cancer and development and established its function as an adhesion receptor to mediate the interactions between cells and extracellular matrix. Despite of much progress on understanding its biological implications, the mechanism of its function remains elusive. It has not been firmly established whether GPR56 signals directly through G proteins and what its upstream stimuli and downstream effectors are to execute its various biological effects. This chapter will give an overview of the primary structures of the Gpr56 gene and its encoded protein and attempt to point out open questions in this research area, with an emphasis on its roles in cancer and signal transduction.

Matrix metalloproteinases: what do they not do? New substrates and biological roles identified by murine models and proteomics

The biological roles of the matrix metalloproteinases (MMPs) have been traditionally associated with the degradation and turnover of most of the components of the extracellular matrix (ECM). This functional misconception has been used for years to explain the involvement of the MMP family in developmental processes, cell homeostasis and disease, and led to clinical trials of MMP inhibitors for the treatment of cancer that failed to meet their endpoints and cast a shadow on MMPs as druggable targets. Accumulated evidence from a great variety of post-trial MMP degradomics studies, ranging from transgenic models to recent state-of-the-art proteomics screens, is changing the dogma about MMP functions. MMPs regulate cell behavior through finely tuned and tightly controlled proteolytic processing of a large variety of signaling molecules that can also have beneficial effects in disease resolution. Moreover, net proteolytic activity relies upon direct interactions between the different protease and protease inhibitor families, interconnected in a complex protease web, with MMPs acting as key nodal components. Such complexity renders simple interpretation of Mmp knockout mice very difficult. Indeed, the phenotype of these models reveals the response of a complex system to the loss of one protease rather than necessarily a direct effect of the lack of functional activity of a protease. Such a shift in the MMP functional paradigm, together with the difficulties associated with current methods of studying proteases this highlights the need for new high content degradomics approaches to uncover and annotate MMP activities in vivo and identify novel interactions within the protease web. Integration of these techniques with specifically designed animal models for final validation should lay the foundations for the development of new inhibitors that specifically target disease-related MMPs and/or their upstream effectors that cause deleterious effects in disease, while sparing MMP functions that are protective.

Bioactive TGF-beta levels can be preserved in plasma samples collected into heparin but not EDTA

Quantifying TGF-beta is important for many research areas since its effects often are dose-dependently bidirectional. The post-transcriptional control of TGF-beta bioavailability points out the need to determine TGF-beta at the protein level. Studies measuring TGF-beta in peripheral blood have to avoid contamination with platelet-derived TGF-beta. Techniques to obtain platelet-poor plasma have been suggested, however, the impact of different anti-coagulants on artificial TGF-beta contamination has not been studied in detail. Here, we compare TGF-beta levels in blood samples collected into heparin and EDTA tubes, stored for 0.5-18 h at various temperatures. We show that contamination with latent TGF-beta can only be prevented by collecting the sample on ice. Importantly, levels of bioactive TGF-beta in blood collected into heparin but not EDTA tubes remained stable up to 18 h, even when kept at RT. Further in vitro experiments indicate that heparin prevents the activation of latent TGF-beta into its bioactive form probably by virtue of accelerating the complex-formation between AT-III and thrombin. Where precise measurement of latent TGF-beta in blood samples is required, samples need to be collected on ice; bioactive TGF-beta can be detected reliably in samples collected into heparin tubes even when stored at RT.

Transglutaminases and disease: lessons from genetically engineered mouse models and inherited disorders

The human transglutaminase (TG) family consists of a structural protein, protein 4.2, that lacks catalytic activity, and eight zymogens/enzymes, designated factor XIII-A (FXIII-A) and TG1-7, that catalyze three types of posttranslational modification reactions: transamidation, esterification, and hydrolysis. These reactions are essential for biological processes such as blood coagulation, skin barrier formation, and extracellular matrix assembly but can also contribute to the pathophysiology of various inflammatory, autoimmune, and degenerative conditions. Some members of the TG family, for example, TG2, can participate in biological processes through actions unrelated to transamidase catalytic activity. We present here a comprehensive review of recent insights into the physiology and pathophysiology of TG family members that have come from studies of genetically engineered mouse models and/or inherited disorders. The review focuses on FXIII-A, TG1, TG2, TG5, and protein 4.2, as mice deficient in TG3, TG4, TG6, or TG7 have not yet been reported, nor have mutations in these proteins been linked to human disease.

Tissue transglutaminase inhibition as treatment for diabetic glomerular scarring: it's good to be glueless

Diabetic nephropathy is characterized by enhanced glomerular and tubulointerstitial deposition of extracellular matrix proteins, which are bound together by tissue transglutaminase (TG2). Huang et al. demonstrate that infusion of a novel TG2 inhibitor in diabetic rats prevented renal scarring and albuminuria and preserved glomerular filtration rate. These studies confirm the role of TG2 in the pathogenesis of diabetic nephropathy and add to an emerging literature that demonstrates that TG2 is an attractive therapeutic target for sclerosing kidney diseases.

Transglutaminase inhibition ameliorates experimental diabetic nephropathy

Diabetic nephropathy is characterized by excessive extracellular matrix accumulation resulting in renal scarring and end-stage renal disease. Previous studies have suggested that transglutaminase type 2, by formation of its protein crosslink product epsilon-(gamma-glutamyl)lysine, alters extracellular matrix homeostasis, causing basement membrane thickening and expansion of the mesangium and interstitium. To determine whether transglutaminase inhibition can slow the progression of chronic experimental diabetic nephropathy over an extended treatment period, the inhibitor NTU281 was given to uninephrectomized streptozotocin-induced diabetic rats for up to 8 months. Effective transglutaminase inhibition significantly reversed the increased serum creatinine and albuminuria in the diabetic rats. These improvements were accompanied by a fivefold decrease in glomerulosclerosis and a sixfold reduction in tubulointerstitial scarring. This was associated with reductions in collagen IV accumulation by 4 months, along with reductions in collagens I and III by 8 months. This inhibition also decreased the number of myofibroblasts, suggesting that tissue transglutaminase may play a role in myofibroblast transformation. Our study suggests that transglutaminase inhibition ameliorates the progression of experimental diabetic nephropathy and can be considered for clinical application.

Keloid scarring: bench and bedside

Wound healing is a fundamental complex-tissue reaction leading to skin reconstitution and thereby ensuring survival. While, fetal wounds heal without scarring, a normal "fine line" scar is the clinical outcome of an undisturbed wound healing in adults. Alterations in the orchestrated wound healing process result in hypertrophic or keloid scarring. Research in the past decades attempted to identify genetic, cellular, and molecular factors responsible for these alterations. These attempts lead to several new developments in treatments for keloids, such as, imiquimod, inhibition of transforming growth factor beta, and recombinant interleukin-10. The urgent need for better therapeutics is underlined by recent data substantiating an impaired quality of life in keloid and hypertrophic scar patients. Despite the increasing knowledge about the molecular regulation of scar formation no unifying theory explaining keloid development has been put forward until today. This review aims to give an overview about the genetic and molecular background of keloids and focus of the current research on keloid scarring with special emphasis on new forthcoming treatments. Clinical aspects and the spectrum of scarring are summarized.

Mice that lack activity of alphavbeta6- and alphavbeta8-integrins reproduce the abnormalities of Tgfb1- and Tgfb3-null mice

The arginine-glycine-aspartate (RGD)-binding integrins alphavbeta6 and alphavbeta8 activate latent TGFbeta1 and TGFbeta3 in vivo, but it is uncertain whether other RGD-binding integrins such as integrins alphavbeta5 and alphavbeta3 activate these TGFbeta isoforms. To define the combined role of alphavbeta6- and alphavbeta8-integrin in TGFbeta activation, we analyzed mice lacking function of both integrins by means of gene deletion and/or pharmacologic inhibition. Most Itgb6-/-;Itgb8-/- embryos die at mid-gestation; those that survive develop cleft palate-as observed in Tgfb3-/- mice. Itgb8-/- mice treated with an anti-alphavbeta6-integrin antibody develop severe autoimmunity and lack Langerhans cells-similar to Tgfb1-null mice. These results support a model in which TGFbeta3-mediated palate fusion and TGFbeta1-mediated suppression of autoimmunity and generation of Langerhans cells require integrins alphavbeta6 and alphavbeta8 but not other RGD-binding integrins as TGFbeta activators.

Fitting a xenobiotic receptor into cell homeostasis: how the dioxin receptor interacts with TGFbeta signaling

As our knowledge on the mechanisms that control cell function increases, more complex signaling pathways and quite intricate cross-talks among regulatory proteins are discovered. Establishing accurate interactions between cellular networks is essential for a healthy cell and different alterations in signaling are known to underline human disease. Transforming growth factor beta (TGFbeta) is an extracellular cytokine that regulates such critical cellular responses as proliferation, apoptosis, differentiation, angiogenesis and migration, and it is assumed that the latency-associated protein LTBP-1 plays a relevant role in TGFbeta targeting and activation in the extracellular matrix (ECM). The dioxin receptor (AhR) is a unique intracellular protein long studied because of its critical role in xenobiotic-induced toxicity and carcinogenesis. Yet, a large set of studies performed in cellular systems and in vivo animal models have suggested important xenobiotic-independent functions for AhR in cell proliferation, differentiation and migration and in tissue homeostasis. Remarkably, AhR activity converges with TGFbeta-dependent signaling through LTBP-1 since cells lacking AhR expression have phenotypic alterations that can be explained, at least in part, by the coordinated regulation of both proteins. Here, we will discuss the existence of functional interactions between AhR and TGFbeta signaling. We will focus on regulatory and functional aspects by analyzing how AhR status determines TGFbeta activity and by proposing a mechanism through which LTBP-1, a novel AhR target gene, mediates such effects. We will integrate ECM proteases in the AhR-LTBP-1-TGFbeta axis and suggest a model that could help explain some in vivo phenotypes associated to AhR deficiency.

Tissue transglutaminase contributes to interstitial renal fibrosis by favoring accumulation of fibrillar collagen through TGF-beta activation and cell infiltration

Renal fibrosis is defined by the exaggerated accumulation of extracellular matrix proteins. Tissue transglutaminase (TG2) modifies the stability of extracellular matrix proteins and renders the extracellular matrix resistant to degradation. In addition, TG2 also activates transforming growth factor-beta (TGF-beta). We investigated the involvement of TG2 in the development of renal fibrosis using mice with a knockout of the TG2 gene (KO). These mice were studied at baseline and 12 days after unilateral ureteral obstruction, which induced a significant increase in interstitial TG2 expression in wild-type mice (P < 0.001). Interstitial fibrosis was evident in both groups, but total and fibrillar collagen was considerably lower in KO mice as compared with wild-type (P < 0.001). Similarly, mRNA and protein expression of collagen I were significantly lower in KO animals (P < 0.05). A statistically significant reduction in renal inflammation and fewer myofibroblasts were observed in KO mice (P < 0.01). Free active TGF-beta was decreased in KO mice (P < 0.05), although total (active + latent) TFG-beta concentration did not differ between groups. These results show that mice deficient in TG2 are protected against the development of fibrotic lesions in obstructive nephropathy. This protection results from reduced macrophage and myofibroblast infiltration, as well as from a decreased rate of collagen I synthesis because of decreased TGF-beta activation. Our results suggest that inhibition of TG2 may provide a new and important therapeutic target against the progression of renal fibrosis.

Inhibition of integrin alphavbeta6 on cholangiocytes blocks transforming growth factor-beta activation and retards biliary fibrosis progression

BACKGROUND & AIMS

Integrin alphavbeta6 is highly expressed on certain activated epithelia, where it mediates attachment to fibronectin and serves as coreceptor for the activation of latent transforming growth factor (TGF)-beta1. Because its role in liver fibrosis is unknown, we studied alphavbeta6 function in vitro and explored the antifibrotic potential of the specific alphavbeta6 antagonist EMD527040.

METHODS

Experimental liver fibrosis was studied in rats after bile duct ligation (BDL) and in Mdr2(abcb4)(-/-) mice. Different doses of EMD527040 were given to rats from week 2 to 6 after BDL and to Mdr2(-/-) mice from week 4 to 8. Liver collagen was quantified, and expression of alphavbeta6 and fibrosis-related transcripts was determined by quantitative reverse-transcription polymerase chain reaction. alphavbeta6-expressing cells, bile duct proliferation, and apoptosis were assessed histologically. The effect of EMD527040 on cholangiocyte adhesion, proliferation, apoptosis, and TGF-beta1 activation was studied in vitro.

RESULTS

alphavbeta6 was highly expressed on proliferating bile duct epithelia in fibrosis, with 100-fold increased transcript levels in advanced fibrosis. EMD527040 attenuated bile ductular proliferation and peribiliary collagen deposition by 40%-50%, induced down-regulation of fibrogenic and up-regulation of fibrolytic genes, and improved liver architecture and function. In vitro alphavbeta6 inhibition reduced activated cholangiocyte proliferation, their adhesion to fibronectin, and endogenous activation of TGF-beta1 by 50% but did not affect bile duct apoptosis.

CONCLUSIONS

Integrin alphavbeta6 is strongly up-regulated in proliferating bile duct epithelia and drives fibrogenesis via adhesion to fibronectin and auto/paracrine TGF-beta1 activation. Pharmacologic inhibition of alphavbeta6 potently inhibits the progression of primary and secondary biliary fibrosis.

Some lessons from the tissue transglutaminase knockout mouse

Transglutaminase 2 (TG2) is an inducible transamidating acyltransferase that catalyzes Ca(2+)-dependent protein modifications. It acts as a G protein in transmembrane signaling and as a cell surface adhesion mediator, this distinguishes it from other members of the transglutaminase family. The sequence motifs and domains revealed in the TG2 structure, can each be assigned distinct cellular functions, including the regulation of cytoskeleton, cell adhesion, and cell death. Though many biological functions of the enzyme have already been described or proposed previously, studies of TG2 null mice by our laboratory during the past years revealed several novel in vivo roles of the protein. In this review we will discuss these novel roles in their biological context.

Tissue transglutaminase expression and activity in normal and glaucomatous human trabecular meshwork cells and tissues

PURPOSE

Glaucoma is a leading cause of irreversible visual impairment and blindness in the world. A major risk factor for glaucoma is elevated intraocular pressure due to increased resistance of aqueous humor outflow through the trabecular meshwork (TM). In the glaucomatous TM, there is increased accumulation of extracellular matrix (ECM) material due to a disruption of the normal balance between ECM deposition and degradation. Tissue transglutaminase (TGM2) belongs to a family of calcium-dependent enzymes that catalyze the posttranslational modification of the ECM by cross-linking proteins, thus making these proteins resistant to enzymatic and physical degradation. It is possible that the increase in ECM proteins in the glaucomatous TM is due to increased cross-linking activity of TGM2. The purpose of this study was to determine whether there are differences in expression and activity of TGM2 between normal and glaucoma TM cells and tissues.

METHODS

Normal (n = 3 NTM) and glaucomatous (n = 3 GTM) human TM cell lines were grown until confluent. Western immunoblot analysis of cell lysates was used to compare TGM2 protein levels in NTM and GTM cells. TGM2 enzyme activity between NTM and GTM cells was studied by using a biotin cadaverine assay. In addition, immunohistochemistry of three normal and three glaucomatous TM tissues was used to evaluate the in vivo expression of TGM2, fibronectin (FN) and epsilon-(gamma-glutamyl) lysine (GGEL) proteins.

RESULTS

Western blot analysis and immunohistochemistry demonstrated the presence of TGM2 protein in both NTM and GTM cells. There was an increase in TGM2 protein in GTM cells compared with NTM cells, and GTM cells also had increased in TGM2 enzyme activity compared with NTM cells. Immunohistochemical results demonstrated increased expression of TGM2 and FN in GTM tissues. FN and GGEL proteins were colocalized in GTM tissues, indicating significant cross-linking of FN by TGM2.

CONCLUSIONS

This study demonstrated that both NTM and GTM cells express TGM2. In addition, TGM2 protein levels and enzyme activities were elevated in GTM cells. There was also an increase in colocalization of FN and GGEL protein in GTM tissues. These results indicate that TGM2 may play an important role in the pathogenesis of glaucoma by cross-linking ECM proteins such as FN and thus making the ECM more resistant to degradation.

Inhibition of integrin alpha(v)beta6, an activator of latent transforming growth factor-beta, prevents radiation-induced lung fibrosis

RATIONALE

In experimental models, lung fibrosis is dependent on transforming growth factor (TGF)-beta signaling. TGF-beta is secreted in a latent complex with its propeptide, and TGF-beta activators release TGF-beta from this complex. Because the integrin alpha(v)beta6 is a major TGF-beta activator in the lung, inhibition of alpha(v)beta6-mediated TGF-beta activation is a logical strategy to treat lung fibrosis.

OBJECTIVES

To determine, by genetic and pharmacologic approaches, whether murine radiation-induced lung fibrosis is dependent on alpha(v)beta6.

METHODS

Wild-type mice, alpha(v)beta6-deficient (Itgb6-/-) mice, and mice heterozygous for a Tgfb1 mutation that eliminates integrin-mediated activation (Tgfb1(+/RGE)) were exposed to 14 Gy thoracic radiation. Some mice were treated with an anti-alpha(v)beta6 monoclonal antibody or a soluble TGF-beta receptor fusion protein. Alpha(v)beta6 expression was determined by immunohistochemistry. Fibrosis, inflammation, and gene expression patterns were assessed 20-32 weeks postirradiation.

MEASUREMENTS AND MAIN RESULTS

Beta6 integrin expression increased within the alveolar epithelium 18 weeks postirradiation, just before onset of fibrosis. Itgb6-/- mice were completely protected from fibrosis, but not from late radiation-induced mortality. Anti-alpha(v)beta6 therapy (1-10 mg/kg/wk) prevented fibrosis, but only higher doses (6-10 mg/kg/wk) caused lung inflammation similar to that in Itgb6-/- mice. Tgfb1-haploinsufficient mice were also protected from fibrosis.

CONCLUSIONS

Alpha(v)beta6-mediated TGF-beta activation is required for radiation-induced lung fibrosis. Together with previous data, our results demonstrate a robust requirement for alpha(v)beta6 in distinct fibrosis models. Inhibition of alphavbeta6-mediated TGF-beta activation is a promising new approach for antifibrosis therapy.

Inhibitory effect of tissue transglutaminase (tTG) antisense oligodeoxynucleotides on tTG expression in cultured bovine trabecular meshwork cells

To study the effect of tTG fully phosphorothioated antisense oligodeoxynucleotides (tTG-ASDON) on tTG expression in cultured bovine trabecular meshwork cells (BTMCs) in vitro and explore a new treatment alternative for primary open angle glaucoma (POAG), the ASDON1 and ASDON2 complementary to the protein codogram region of tTG were designed, synthesized and phosphorothioated according to the secondary structure of tTG. The ASDON1 and ASDON2 were embedded in Lipofectamine and transfected into BTMCs. The untreated group served as negative controls. The expression of tTG in the mRNA and protein level were measured by semi-quantitative RT-PCR and immunohistochemical technique-Supervision method respectively. Our results showed that both the mRNA and the protein of tTG with tTG-ASDON and tTG-ASDON2 were significantly decreased as compared with that of the controls (P < 0.05). On the other hand, no significant difference was found between the ASDON1 group and the ASDON2 group. It is concluded that the expression of tTG mRNA and protein in cultured BTMC are down-regulated by tTG- ASDON. As a result, tTG-ASDON may be used for the treatment of POAG through the inhibitory effect on the expression of tTG.

Involvement of Transglutaminase-2 in Pathological Changes in Renal Disease

BACKGROUND

Transglutaminase (Tg)-2 is shown to be related to renal fibrosis. However, its roles in human kidney disease have not been fully studied.

METHODS

Using immunohistochemistry, we examined Tg-2 expression in renal biopsy specimens from 22 patients with IgA nephropathy (IgAN) and correlated the intensity of Tg-2 staining with clinical and histopathological parameters. We compared the distribution and intensity of Tg-2 staining with those of transforming growth factor (TGF)-beta staining.

RESULTS

In normal human kidneys, Tg-2 staining was not significant. In IgAN kidneys, glomerular Tg-2 staining correlated with serum creatinine (S-Cr), creatinine clearance (Ccr), urinary protein excretion, glomerular sclerosis, and mesangial cell proliferation. Tubulointerstitial Tg-2 correlated with S-Cr, Ccr, N-acetyl-beta-glucosaminidase, urinary beta(2)-microglobulin, and tubulointerstitial injuries. Tg-2 staining in the vicinity of vascular poles of glomeruli preceded the development of mesangial lesions, and was more remarkable in cases with renal impairment. The distribution and intensity of Tg-2 staining were not consistent with those of TGF-beta staining. In glomerular crescents, Tg-2 staining was remarkable.

CONCLUSION

The present study showed a correlation between Tg-2 expression and renal function and pathological changes. Tg-2 expression in the vicinity of vascular poles was notable because that may be an initial marker of glomerular injury.

Involvement of retinoic acid-induced transglutaminase activity in zonal differences of hepatocyte proliferation after partial hepatectomy

BACKGROUND

The authors have recently demonstrated that there is inverse correlation between transglutaminase (TGase) activity and DNA synthesis in periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) at 1 day after partial hepatectomy in rats. In order to ensure the involvement of TGase in the differential growth capacities between periportal and perivenous regions of regenerating liver, the aim of this study was to investigate the effect of retinoic acid, an inducer of TGase expression, on zonal differences of hepatocyte proliferation between PPH and PVH isolated from regenerating rat liver.

METHODS

Regenerating liver was prepared by 70% partial hepatectomy. PPH and PVH subpopulations were isolated by the digitonin/collagenase perfusion technique. Cell cycle was evaluated for incorporation of BrdU into hepatocytes and detected by flow cytometric analysis. TGase activity was determined by incorporation of 14C-putrescine into dimethylcasein.

RESULTS

When retinoic acid was injected immediately after partial hepatectomy, TGase activity greatly increased in both PPH and PVH at 1 day after partial hepatectomy, and activity was higher in PPH than in PVH. DNA synthesis in both subpopulations did not increase 1 day after partial hepatectomy, with peaks of DNA synthesis shifting to 2 days, and synthesis was higher in PVH than in PPH.

CONCLUSION

These results suggest that TGase might be involved in differential growth capacities between periportal and perivenous regions of regenerating rat liver after partial hepatectomy.

Differential protein expression profiling by iTRAQ-2DLC-MS/MS of lung cancer cells undergoing epithelial-mesenchymal transition reveals a migratory/invasive phenotype

Transforming growth factor-beta (TGF-beta) induces epithelial-mesenchymal transition (EMT) of epithelial cells in both normal embryonic development and certain pathological contexts. Here, we show that TGF-beta induced-EMT in human lung cancer cells (A549; adenocarcinoma cells) mediates tumor cell migration and invasion phenotypes. To gain insights into molecular events during EMT, we employed a global stable isotope labeled profiling strategy using iTRAQ reagents, followed by 2DLC-MS/MS, which identified a total of 51 differentially expressed proteins during EMT; 29 proteins were up-regulated and 22 proteins were down-regulated. Down-regulated proteins were predominantly enzymes involved in regulating nutrient or drug metabolism. The majority of the TGF-beta-induced proteins (such as tropomyosins, filamin A, B, & C, integrin-beta1, heat shock protein27, transglutaminase2, cofilin, 14-3-3 zeta, ezrin-radixin-moesin) are involved in the regulation of cell migration, adhesion and invasion, suggesting the acquisition of a invasive phenotype.

Synthesis and in vitro evaluation of enzymatically cross-linked elastin-like polypeptide gels for cartilaginous tissue repair

Genetically engineered elastin-like polypeptide (ELP) hydrogels offer unique promise as scaffolds for cartilage tissue engineering because of the potential to promote chondrogenesis and to control mechanical properties. In this study, we designed and synthesized ELPs capable of undergoing enzyme-initiated gelation via tissue transglutaminase, with the ultimate goal of creating an injectable, in situ cross-linking scaffold to promote functional cartilage repair. Addition of the enzyme promoted ELP gel formation and chondrocyte encapsulation in a biocompatible process, which resulted in cartilage matrix synthesis in vitro and the potential to contribute to cartilage mechanical function in vivo. A significant increase in the accumulation of sulfated glycosaminoglycans was observed, and histological sections revealed the accumulation of a cartilaginous matrix rich in type II collagen and lacking in type I collagen, indicative of hyaline cartilage formation. These results provide evidence of chondrocytic phenotype maintenance for cells in the ELP hydrogels in vitro. In addition, the dynamic shear moduli of ELP hydrogels seeded with chondrocytes increased from 0.28 to 1.7 kPa during a 4-week culture period. This increase in the mechanical integrity of cross-linked ELP hydrogels suggests restructuring of the ELP matrix by deposition of functional cartilage extracellular matrix components.

Tissue Transglutaminase Expression and Activity in Placenta

Tissue transglutaminase (tTG) expression, distribution and activity were examined in human placenta and derived cells. Immunochemical techniques and RT-PCR were used to demonstrate tTG protein and mRNA in stromal cells and trophoblast in first trimester and at term, with higher levels later in pregnancy. Decidual cells also produce tTG. The data were confirmed using primary cultures of trophoblast, fibroblasts and decidual stromal cells. Substrate incorporation studies indicated tTG activity in association with fibroblast extracellular matrix and the syncytial microvillous membrane (MVM), where several target polypeptides could be observed. tTG is a major autoantigen in Coeliac disease (CoD) which is associated with poor pregnancy outcome. tTG at the placental MVM is a plausible target of maternal autoantibody action.

Effect of retinoic acid-induced transglutaminase on cell growth in regenerating liver

Transglutaminase 2 (TG2) is implicated in the inhibitory regulation of the hepatocyte growth in vitro. In vivo, however, the role of TG2 in liver regeneration after partial hepatectomy (PH) is almost unknown. A dramatic increase of TG2 expression and activation is induced by retinoic acid (RA). Here we show the effect of the RA-induced overexpression of TG2 on liver regeneration after PH. Regenerating rat liver was prepared by 70% PH. RA was intraperitoneally injected immediately after PH. TG2 activity was determined by incorporation of 14C-putrescine into dimethylcasein. Cell cycle was evaluated for incorporation of BrdU into hepatocytes and detected by a flow cytometric analysis. The treatment of RA greatly increased TG2 activity at 1 day after PH. At that time, DNA synthesis was significantly reduced by the treatment of RA. The recovery of liver weight after PH was significantly delayed by the treatment of RA. These results suggested that TG2 was involved in growth capacity in regenerating rat liver after PH.

TGF-beta1 up-regulates transglutaminase two and fibronectin in dermal fibroblasts: a possible mechanism for the stabilization of tissue inflammation

Transglutaminase (TGase) has been reported to stabilize tissue inflammation via the mediation of the polymerization of extracellular matrix proteins. A set of cytokines has been implicated in wound healing processes in the dermis. This study was undertaken in order to evaluate the effects of these cytokines on the expression of TGase 2 in human dermal fibroblasts (hDFs), in that TGase 2 is known to be the principal TGase in the dermis. In Western blot analysis, TGF-beta1 (1 ng/ml) treatment was found to steadily up-regulate TGase 2 expression for up to 7 days. However, such increases were not observed when the cells were treated with IL-1beta, IL-2, and TNF-alpha. In the enzyme assay, total TGase activities were closely related to the levels of TGase 2 expression. TGase 2 mRNA expression was up-regulated as the result of TGF-beta treatment in competitive RT-PCR. In the denatured SDS-PAGE, TGF-beta1 treatment resulted in marked induction of an approximately 220 kDa protein, which was revealed to be a fibronectin (FN) via western immunoblotting with an anti-FN antibody. Next, when the hDFs were treated with TGF-beta1 (1 ng/ml), FN expression was induced beginning at the third day after treatment. The immunoprecipitants generated by anti-FN antibody were positive for the anti-TGase 2 antibody, and the immune complexes were identified at molecular weights of 92 kDa. Collectively, TGF-beta1 stimulates the polymerization of FN via the action of TGase 2, which is supposed to to be an important mechanism in the stabilization of the inflammatory dermis.

Tissue transglutaminase (TG2) acting as G protein protects hepatocytes against Fas-mediated cell death in mice

Tissue transglutaminase (TG2) is a protein cross-linking enzyme known to be expressed by hepatocytes and to be induced during the in vivo hepatic apoptosis program. TG2 is also a G protein that mediates intracellular signaling by the alpha-1b-adrenergic receptor (AR) in liver cells. Fas/Fas ligand interaction plays a crucial role in various liver diseases, and administration of agonistic anti-Fas antibodies to mice causes both disseminated endothelial cell apoptosis and fulminant hepatic failure. Here we report that an intraperitoneal dose of anti-Fas antibodies, which is sublethal for wild-type mice, kills all the TG2 knock-out mice within 20 hours. Although TG2-/- thymocytes exposed to anti-Fas antibodies die at the same rate as wild-type mice, TG2-/- hepatocytes show increased sensitivity toward anti-Fas treatment both in vivo and in vitro, with no change in their cell surface expression of Fas, levels of FLIP(L) (FLICE-inhibitory protein), or the rate of I-kappaBalpha degradation, but a decrease in the Bcl-xL expression. We provide evidence that this is the consequence of the impaired AR signaling that normally regulates the levels of Bcl-xL in the liver. In conclusion, our data suggest the involvement of adrenergic signaling pathways in the hepatic regeneration program, in which Fas ligand-induced hepatocyte proliferation with a simultaneous inhibition of the Fas-death pathway plays a determinant role.

Changes in aqueous humor dynamics with age and glaucoma

Changes in aqueous humor dynamics with age and in glaucoma have been studied for several decades. More recently, techniques have been developed which confirm earlier studies showing that outflow facility decreases with age and in glaucoma and add the newer finding that uveoscleral outflow also decreases. Morphologic studies in aging and glaucoma eyes have shown an increase in accumulation of extracellular material in both the trabecular meshwork and ciliary muscle and a loss of trabecular meshwork cells, which contribute to this reduction in outflow and result in an increase in intraocular pressure. A reduction in hyaluronic acid and increases in fibronectin and thrombospondin contribute to the change in the extracellular environment. Imbalances in responses to age-related stresses such as oxidative damage to long-lived molecules, protein cross-linking and loss of elasticity could trigger excess production of factors such as transforming growth factor beta, interleukin-1 and CD44S that could stimulate pathways leading to increases in fibronectin, transformation of trabecular meshwork cells to a myoepithelial state and decrease the breakdown in extracellular matrix material, allowing excess to accumulate. Ultimately trabecular outflow and uveoscleral outflow are reduced and intraocular pressure becomes elevated, adding more stress and perpetuating the pathological condition. Future research to identify additional factors and clarify their roles in these processes could lead to alternative therapies for age and glaucoma related changes in the eye.

Thrombospondin 1 acts as a strong promoter of transforming growth factor beta effects via two distinct mechanisms in hepatic stellate cells

BACKGROUND AND AIMS

Thrombospondin 1 (TSP-1) is an important activator of latent transforming growth factor beta (TGF-beta) but little is known of the expression patterns and functions of TSP-1 in liver cells. We therefore analysed if and how TSP-1 acts on TGF-beta during fibrogenesis.

METHODS AND RESULTS

Using reverse transcription-polymerase chain reaction, we demonstrated that hepatocytes from normal liver expressed no TSP-1 mRNA whereas Kupffer cells and sinusoidal endothelial cells did. TSP-1 mRNA and protein were detected in quiescent and activated cultured hepatic stellate cells (HSC) and TSP-1 expression was highly inducible by platelet derived growth factor BB (PDGF-BB) and, to a lesser extent, by tumour necrosis factor alpha in activated HSC. Furthermore, addition of PDGF-BB directly led to enhanced TGF-beta mRNA expression and a TSP-1 dependent increase in TGF-beta/Smad signalling. Using either a peptide specifically blocking the interaction of TSP-1 with latent TGF-beta or antibodies against TSP-1 not only abrogated activation of latent TGF-beta but also reduced the effects of the active dimer itself.

CONCLUSIONS

Our data suggest that TSP-1 expression is important for TGF-beta effects and that it is regulated by the profibrogenic mediator PDGF-BB in HSC. Furthermore, the presence of TSP-1 seems to be a prerequisite for effective signal transduction by active TGF-beta not only in rat HSC but also in other cell types such as human dermal fibroblasts.

Transglutaminase 2 in the balance of cell death and survival

Transglutaminase 2 (TG2), a multifunctional enzyme with Ca(2+)-dependent protein crosslinking activity and GTP-dependent G protein functions, is often upregulated in cells undergoing apoptosis. In cultured cells TG2 may exert both pro- and anti-apoptotic effects depending upon the type of cell, the kind of death stimuli, the intracellular localization of the enzyme and the type of its activities switched on. The majority of data support the notion that transamidation by TG2 can both facilitate and inhibit apoptosis, while the GTP-bound form of the enzyme generally protects cells against death. In vivo studies confirm the Janus face of TG2 in the initiation of the apoptotic program. In addition, they reveal a further role: the prevention of inflammation, tissue injury and autoimmunity once the apoptosis has already been initiated. This function of TG2 is partially achieved by being expressed and activated also in macrophages digesting apoptotic cells and mediating a crosstalk between dying and phagocytic cells.

The Involvement of Polyamines as Substrates of Transglutaminase in Zonal Different Hepatocyte Proliferation after Partial Hepatectomy

We have recently demonstrated the inverse correlation between transglutaminase (TGase) activity and DNA synthesis in periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) at 1 d after partial hepatectomy. In order to elucidate a role of polyamines as substrates of TGase in the differential growth capacities between PPH and PVH from regenerating liver, we investigated the zonal differences in alteration of ornithine decarboxylase (ODC) activity and polyamines. In two subpopulations, the inverse correlation between DNA synthesis and epsilon-(gamma-glutamyl) lysine (Gln-Lys) cross-linking catalyzed by TGase was demonstrated at 1 d after partial hepatectomy. ODC activity in PPH significantly increased with a peak at 1 d after partial hepatectomy, whereas did not in PVH. Protein-binding SPD in PPH also transiently increased with a peak at 1 d after partial hepatectomy, but did not in PVH. These results suggest that at 1 d after partial hepatectomy, in PPH, the inhibition of Gln-Lys cross-linking by the formation of N-gamma-glutamyl SPD leads to the increase of DNA synthesis, whereas in PVH, enhanced formation of Gln-Lys cross-linking leads to the lower DNA synthesis.

Vascular endothelial cell growth factor attenuates actions of transforming growth factor-beta in human endothelial cells

Because vascular endothelial cell growth factor (VEGF) and transforming growth factor-beta (TGF-beta) are both involved in cellular growth and differentiation, we examined whether VEGF modifies TGF-beta signaling cascade in human umbilical cord vein endothelial cells (HUVEC). Production of plasminogen activator inhibitor-1 (PAI-1), which is under the specific control of TGF-beta, was strongly enhanced (3.5-fold) by TGF-beta treatment. Remarkably, physiological concentration of VEGF (30 nm) profoundly (by 60%) attenuated the TGF-beta stimulation of PAI-1 production without an effect on the basal PAI-1 production. In HUVECs transiently transfected with an expression construct containing a PAI-1 promoter fused to luciferase reporter gene, TGF-beta-stimulation of transcription of PAI-1 was clearly (by 60%) inhibited by VEGF. TGF-beta phosphorylation of Smad2/3, an obligatory step of intracellular TGF-beta signaling, was also suppressed by VEGF. VEGF attenuation of TGF-beta action was also demonstrated in two other endothelial cell lines. In conclusion, VEGF attenuates TGF-beta action in the human endothelial cell, specifically at the level of transcription of PAI-1 gene and Smad2/3 phosphorylation.

Loss of metal transcription factor-1 suppresses tumor growth through enhanced matrix deposition

Metal transcription factor-1 (MTF-1) is a ubiquitous transcriptional regulator and chromatin insulator with roles in cellular stress responses and embryonic development. The studies described herein establish for the first time the involvement of MTF-1 in tumor development. Genetically manipulated ras-transformed mouse embryonic fibroblasts (MEFs), wild-type (MTF-1+/+), or nullizygous for MTF-1 (MTF-1-/-) were used to develop fibrosarcoma tumors. Loss of MTF-1 resulted in delayed tumor growth associated with increased matrix collagen deposition and reductions in vasculature density. Molecular consequences of MTF-1 loss include increased expression and activation of the transforming growth factor-beta1 (TGF-beta1) and tissue transglutaminase (tTG), two proteins with documented roles in the production and stabilization of extracellular matrix (ECM). Our findings support the hypothesis that MTF-1 enhances the ability of the developing tumor mass to evade fibrosis and scarring of the tumor, a critical step in tumor cell proliferation.

The role of the immune response against tissue transglutaminase in the pathogenesis of coeliac disease

The development of autoimmunity to tissue transglutaminase (TGase 2) is a striking feature of coeliac disease, an enteropathy that develops in genetically susceptible individuals upon exposure to dietary gluten. IgA anti-TGase 2 autoantibodies are present in at least 98% of coeliac patients on a gluten-containing diet and provide a valuable tool for the diagnosis of the disorder. During disease development, the formation of TGase 2-gliadin complexes through TGase 2 activity appears to be central for B-cell epitope spreading from gliadin to TGase 2. However, the potential role of an immune response against TGase 2 in the pathogenesis of coeliac disease and for the development of the intestinal lesion remains unclear. Recently, an inhibitory effect of anti-TGase 2 autoantibodies from coeliac patients on TGase 2 activity in vitro has been described. Here, we report that a cellular and humoral response against TGase 2 can be induced in TGase 2 (-/-) and wildtype mice on a C57BL/6 background by s.c. immunization with human recombinant or guinea pig TGase 2 in complete Freund's adjuvant. Immunized wildtype, but not TGase 2 (-/-) mice develop periductal lymphocytic infiltrates in lacrimal glands. Although no intestinal lesions were found, this observation lends support to the concept that the development of autoimmunity against TGase 2 is a pathological event that might ultimately lead to organ damage.