Activation of in situ tissue transglutaminase by intracellular reactive oxygen species

Exploring Extracellular Matrix Crosslinking as a Therapeutic Approach to Fibrosis

The extracellular matrix (ECM) provides structural support for tissues and regulatory signals for resident cells. ECM requires a careful balance between protein accumulation and degradation for homeostasis. Disruption of this balance can lead to pathological processes such as fibrosis in organs across the body. Post-translational crosslinking modifications to ECM proteins such as collagens alter ECM structure and function. Dysregulation of crosslinking enzymes as well as changes in crosslinking composition are prevalent in fibrosis. Because of the crucial roles these ECM crosslinking pathways play in disease, the enzymes that govern crosslinking events are being explored as therapeutic targets for fibrosis. Here, we review in depth the molecular mechanisms underlying ECM crosslinking, how ECM crosslinking contributes to fibrosis, and the therapeutic strategies being explored to target ECM crosslinking in fibrosis to restore normal tissue structure and function.

Pathogenetic Contributions and Therapeutic Implications of Transglutaminase 2 in Neurodegenerative Diseases

Neurodegenerative diseases encompass a heterogeneous group of disorders that afflict millions of people worldwide. Characteristic protein aggregates are histopathological hallmark features of these disorders, including Amyloid β (Aβ)-containing plaques and tau-containing neurofibrillary tangles in Alzheimer's disease, α-Synuclein (α-Syn)-containing Lewy bodies and Lewy neurites in Parkinson's disease and dementia with Lewy bodies, and mutant huntingtin (mHTT) in nuclear inclusions in Huntington's disease. These various aggregates are found in specific brain regions that are impacted by neurodegeneration and associated with clinical manifestations. Transglutaminase (TG2) (also known as tissue transglutaminase) is the most ubiquitously expressed member of the transglutaminase family with protein crosslinking activity. To date, Aβ, tau, α-Syn, and mHTT have been determined to be substrates of TG2, leading to their aggregation and implicating the involvement of TG2 in several pathophysiological events in neurodegenerative disorders. In this review, we summarize the biochemistry and physiologic functions of TG2 and describe recent advances in the pathogenetic role of TG2 in these diseases. We also review TG2 inhibitors tested in clinical trials and discuss recent TG2-targeting approaches, which offer new perspectives for the design of future highly potent and selective drugs with improved brain delivery as a disease-modifying treatment for neurodegenerative disorders.

A Putative NADPH Oxidase Gene in Unicellular Pathogenic Candida glabrata Is Required for Fungal ROS Production and Oxidative Stress Response

Most previous studies on fungal NADPH oxidases (Nox) focused on multicellular fungi and highlighted the important roles of Nox-derived reactive oxygen species (ROS) in cellular differentiation and signaling communication. However, there are few reports about Nox in unicellular fungi. A novel NOX ortholog, CAGL0K05863g (named CgNOX1), in Candida glabrata was investigated in this study. Deletion of CgNOX1 led to a decrease in both intracellular and extracellular ROS production. In addition, the Cgnox1∆ mutant exhibited hypersensitivity to hydrogen peroxide and menadione. Also, the wild-type strain showed higher levels of both CgNOX1 mRNA expression and ROS production under oxidative stress. Moreover, the absence of CgNOX1 resulted in impaired ferric reductase activity. Although there was no effect on in vitro biofilm formation, the CgNOX1 mutant did not produce hepatic apoptosis, which might be mediated by fungal Nox-derived ROS during co-incubation. Together, these results indicated that the novel NOX gene plays important roles in unicellular pathogenic C. glabrata and its interaction with host cells.

Respiratory syncytial virus infection induces the release of transglutaminase 2 from human airway epithelial cells

Respiratory syncytial virus (RSV) is an important human pathogen that causes severe lower respiratory tract infections in young children, the elderly, and the immunocompromised, yet no effective treatments or vaccines are available. The precise mechanism underlying RSV-induced acute airway disease and associated sequelae are not fully understood; however, early lung inflammatory and immune events are thought to play a major role in the outcome of the disease. Moreover, oxidative stress responses in the airways play a key role in the pathogenesis of RSV. Oxidative stress has been shown to elevate cytosolic calcium (Ca²⁺) levels, which in turn activate Ca²⁺-dependent enzymes, including transglutaminase 2 (TG2). Transglutaminase 2 is a multifunctional cross-linking enzyme implicated in various physiological and pathological conditions; however, its involvement in respiratory virus-induced airway inflammation is largely unknown. In this study, we demonstrated that RSV-induced oxidative stress promotes enhanced activation and release of TG2 from human lung epithelial cells as a result of its translocation from the cytoplasm and subsequent release into the extracellular space, which was mediated by Toll-like receptor (TLR)-4 and NF-κB pathways. Antioxidant treatment significantly inhibited RSV-induced TG2 extracellular release and activation via blocking viral replication. Also, treatment of RSV-infected lung epithelial cells with TG2 inhibitor significantly reduced RSV-induced matrix metalloprotease activities. These results suggested that RSV-induced oxidative stress activates innate immune receptors in the airways, such as TLRs, that can activate TG2 via the NF-κB pathway to promote cross-linking of extracellular matrix proteins, resulting in enhanced inflammation.

Collagen crosslinking: effect on structure, mechanics and fibrosis progression

Biophysical properties of extracellular matrix (ECM), such as matrix stiffness, viscoelasticity and matrix fibrous structure, are emerging as important factors that regulate progression of fibrosis and other chronic diseases. The biophysical properties of the ECM can be rapidly and profoundly regulated by crosslinking reactions in enzymatic or non-enzymatic manners, which further alter the cellular responses and drive disease progression. In-depth understandings of crosslinking reactions will be helpful to reveal the underlying mechanisms of fibrosis progression and put forward new therapeutic targets, whereas related reviews are still devoid. Here, we focus on the main crosslinking mechanisms that commonly exist in a plethora of chronic diseases (e.g. fibrosis, cancer, osteoarthritis) and summarize current understandings including the biochemical reaction, the effect on ECM properties, the influence on cellular behaviors, and related studies in disease model establishment. Potential pharmaceutical interventions targeting the crosslinking process and relevant clinical studies are also introduced. Limitations of pharmaceutical development may be due to the lack of systemic investigations related to the influence on crosslinking mechanism from micro to macro level, which are discussed in the last section. We also propose the unclarified questions regarding crosslinking mechanisms and potential challenges in crosslinking-targeted therapeutics development.

Assessment of Protective Effects of Methanolic Extract of Salvia verbenaca Roots Against Oxidative Damage Induced by Hydrogen Peroxide

Objectives

Salvia verbenaca is a medicinal plant that has been traditionally used in Algeria for the treatment of wounds and emptied abscesses. The present study aimed to evaluate the cytotoxicity of methanolic extract of S. verbenaca roots and explore its ability to bestow protection against oxidative damage induced by H₂O₂ (200 μM).

Materials and Methods

The cytotoxic effects and protective properties of S. verbenaca on human monocytic leukemia cells (THP-1) was studied using thiazolyl blue tetrazolium bromide assay. The protective effects of the extract against H₂O₂-induced oxidative damage was evaluated using single cell gel electrophoresis (comet) assay and 2,7-dichlorodihydrofluorescien diacetate (H2DCFDA) assay.

Results

S. verbenaca extract was found to be non-cytotoxic at concentrations <500 μg/mL. However, the use of 500 and 1000 μg/mL of the extract decreasedcell viability. H2DCFDA assay provided evidence for anti-oxidative properties of S. verbenaca. Addition of S. verbenaca (1 and 10 μg/mL) resulted in significant reductionin H₂O₂-induced reactive oxygen species (ROS) production. Further, comet assay showed that addition of the extract resulted in a significant reductionin the length and % DNA content of comet tail. Additionally,nuclei in the cells also appeared to be devoid ofdegradation.

Conclusion

The use of S. verbenaca root extract conferred protection against H₂O₂-induced ROS production and DNA breakage in vitro.

Neuronal and Endothelial Transglutaminase-2 Expression during Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

Transglutiminase-2 (TG2) is a multifunctional enzyme that has been implicated in the pathogenesis of experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis (MS) using global knockout mice and TG2 selective inhibitors. Previous studies have identified the expression of TG2 in subsets of macrophages-microglia and astrocytes after EAE. The aims of the current investigation were to examine neuronal expression of TG2 in rodent models of chronic-relapsing and non-relapsing EAE and through co-staining with intracellular and cell death markers, provide insight into the putative role of TG2 in neuronal pathology during disease progression. Here we report that under normal physiological conditions there is a low basal expression of TG2 in the nucleus of neurons, however following EAE or MS, robust induction of cytoplasmic TG2 occurs in most neurons surrounding perivascular lesion sites. Importantly, TG2-positive neurons also labeled for phosphorylated Extracellular signal-regulated kinase 1/2 (ERK1/2) and the apoptotic marker cleaved caspase-3. In white and gray matter lesions, high levels of TG2 were also found within the vasculature and endothelial cells as well as in tissue migrating pericytes or fibroblasts, though rarely did TG2 colocalize with cells identified with glial cell markers (astrocytes, oligodendrocytes and microglia). TG2 induction occurred concurrently with the upregulation of the blood vessel permeability factor and angiogenic molecule Vascular Endothelial Growth Factor (VEGF). Extracellular TG2 was found to juxtapose with fibronectin, within and surrounding blood vessels. Though molecular and pharmacological studies have implicated TG2 in the induction and severity of EAE, the cell autonomous functions of this multifunctional enzyme during disease progression remains to be elucidated.

Anti-oxidative effect of the tyrosine kinase inhibitor nintedanib: a potential therapy for chronic lung allograft dysfunction?

Background: The long-term survival after lung transplantation (LTx) is often limited by the development of chronic lung allograft dysfunction (CLAD). Increased oxidative stress has been found to occur in chronic lung allograft dysfunction because of several risk factors, e.g. immunological factors or drug related factors. The aim of this study was to investigate the anti-oxidative effect of the receptor tyrosine kinase (RTK) inhibitor nintedanib on immunologically induced oxidative stress and on drug induced oxidative stress.Methods: In-vivo studies were used for investigation of immunologically induced oxidative stress: Immunohistochemistry of transglutaminase-2 (TGM-2) was used to figure out a potential anti-oxidative effect of receptor tyrosine kinase inhibitor nintedanib in a rat model of allogeneic left LTx. In-vitro studies were used for investigation of drug induced oxidative stress: Cell viability assay, 2'7'-dichlorodihydrofluorescein diacetate (DCFDA) and immunofluorescence of transglutaminase-2 were disposed to examine the potential impact of nintedanib on cyclosporin A (CsA) treated lung fibroblasts of the rat.Results: In-vivo studies: Allogeneic transplanted animals without drug interaction showed severe chronic rejection and an excessive expression of TGM-2, whereas the application of nintedanib significantly decreased the number of TGM-2 positive cells. In-vitro studies: Concentrations of CsA ranging from 250 ng/ml to 500 ng/ml demonstrated oxidative stress caused by an increased production of reactive oxygen species (ROS) and an overexpression of TGM-2 without inducing apoptosis in cells. Concentrations of more than 1000 ng/ml led to a considerable decrease of cellularity. 30 min-pre-incubation with nintedanib at a concentration between 25 and 100 nM reduced generation of intracellular ROS and expression of TGM-2.Conclusion: These results demonstrate a downregulation of ROS and TGM-2 by pretreatment with the receptor tyrosine kinase inhibitor nintedanib and present its potential anti-oxidative and immunomodulatory effect in the treatment of chronic lung allograft dysfunction.

Glycolysis regulated transglutaminase 2 activation in cardiopulmonary fibrogenic remodeling

The pathophysiology of pulmonary hypertension (PH) and heart failure (HF) includes fibrogenic remodeling associated with the loss of pulmonary arterial (PA) and cardiac compliance. We and others have previously identified transglutaminase 2 (TG2) as a participant in adverse fibrogenic remodeling. However, little is known about the biologic mechanisms that regulate TG2 function. We examined physiological mouse models of experimental PH, HF, and type 1 diabetes that are associated with altered glucose metabolism/glycolysis and report here that TG2 expression and activity are elevated in pulmonary and cardiac tissues under all these conditions. We additionally used PA adventitial fibroblasts to test the hypothesis that TG2 is an intermediary between enhanced tissue glycolysis and fibrogenesis. Our in vitro results show that glycolytic enzymes and TG2 are upregulated in fibroblasts exposed to high glucose, which stimulates cellular glycolysis as measured by Seahorse analysis. We examined the relationship of TG2 to a terminal glycolytic enzyme, pyruvate kinase M2 (PKM2), and found that PKM2 regulates glucose-induced TG2 expression and activity as well as fibrogenesis. Our studies further show that TG2 inhibition blocks glucose-induced fibrogenesis and cell proliferation. Our findings support a novel role for glycolysis-mediated TG2 induction and tissue fibrosis associated with experimental PH, HF, and hyperglycemia.

Aldosterone nongenomically induces angiotensin II receptor dimerization in rat kidney: role of mineralocorticoid receptor and NADPH oxidase

INTRODUCTION

Previous in vitro studies demonstrated that aldosterone nongenomically induces transglutaminase (TG) and reactive oxygen species (ROS), which enhanced angiotensin II receptor (ATR) dimerization. There are no in vivo data in the kidney.

MATERIAL AND METHODS

Male Wistar rats were intraperitoneally injected with normal saline solution, or aldosterone (Aldo: 150 μg/kg BW); or received pretreatment with eplerenone (mineralocorticoid receptor (MR) blocker, Ep. + Aldo), or with apocynin (nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, Apo. + Aldo) 30 min before aldosterone. Thirty minutes after aldosterone injection, protein abundances of dimeric and monomeric forms of AT₁R and AT₂R, and protein abundances and localizations of TG2 and p47phox, a cytosolic subunit of NADPH oxidase, were determined by Western blot analysis and immunohistochemistry, respectively.

RESULTS

Protein abundances of dimeric forms of AT₁R and AT₂R were enhanced by 170% and 70%, respectively. Apocynin could block dimeric forms of both receptors while eplerenone inhibited only AT₂R. Monomeric protein levels of both receptors were maintained. Aldosterone significantly enhanced TG2 and p47phox protein abundances, which were blunted by eplerenone or apocynin. Aldosterone stimulated p47phox protein expression in both the cortex and the medulla while TG2 was induced mostly in the medulla. Eplerenone or apocynin normalized the immunoreactivity of both TG2 and p47phox.

CONCLUSIONS

This is the first in vivo study demonstrating that aldosterone nongenomically increases renal TG2 and p47phox protein expression and then activates AT₁R and AT₂R dimerizations. Aldosterone-stimulated AT₁R and AT₂R dimerizations are mediated through activation of NADPH oxidase. Aldosterone-induced AT₁R dimer formation is an MR-independent pathway, whereas the formation of AT₂R dimer is modulated in an MR-dependent manner.

Cystamine and cysteamine as inhibitors of transglutaminase activity in vivo

Cystamine is commonly used as a transglutaminase inhibitor. This disulphide undergoes reduction in vivo to the aminothiol compound, cysteamine. Thus, the mechanism by which cystamine inhibits transglutaminase activity in vivo could be due to either cystamine or cysteamine, which depends on the local redox environment. Cystamine inactivates transglutaminases by promoting the oxidation of two vicinal cysteine residues on the enzyme to an allosteric disulphide, whereas cysteamine acts as a competitive inhibitor for transamidation reactions catalyzed by this enzyme. The latter mechanism is likely to result in the formation of a unique biomarker, N-(γ-glutamyl)cysteamine that could serve to indicate how cyst(e)amine acts to inhibit transglutaminases inside cells and the body.

Tissue transglutaminase 2 expression is epigenetically regulated in human lung cancer cells and prevents reactive oxygen species-induced apoptosis

Purpose

Tissue transglutaminase 2 (TG2) is a stress-regulated protein and associated with cancer cell survival. However, the effects of TG2 expression in human non-small-cell lung cancer (NSCLC) cells on reactive oxygen species (ROS) production and redox homeostasis have not been fully elucidated.

Materials and methods

We investigated the TG2 expression and activity in A549, H1299, H1355, and H460 lung cancer cells by Western blots and quantitative polymerase chain reaction assay. The enzyme-linked immunosorbent assay was used for transglutaminase activity. The epigenetic expression was characterized with histone deacetylase inhibitor trichostatin A and DNA methyltransferase inhibitor 5-Aza treatment. TG2 expression was inhibited by siRNA transfection and the intracellular calcium was measured by Flow-3AM assay, apoptosis was analyzed by Annexin V/propidium iodide assay, and intracellular ROS was detected by fluorescence-activated cell sorting analysis. The ROS scavenger N-acetyl-L-cysteine (NAC) was applied to reduce TG2-knockdown-induced oxidative stress.

Results

Only A549 cells expressing high levels of TG2 correlated with high TG2 activity. The expression of TG2 can be regulated by epigenetic regulation in A549, H1299, and H1355 cells. The data also show that TG2 reduction induces apoptosis in A549 and H1299 cells. Furthermore, increased intracellular ROS and calcium levels were both detected in TG2-reduced cells. Moreover, endoplasmic reticulum stress inhibitor (salubrinal) and antioxidant NAC were able to reduce ROS and calcium levels to recover cell viability. Interestingly, the extrinsic and intrinsic apoptosis pathways were activated with a p53 independence upon TG2 reduction. TG2 reduction not only attenuated AKT activation but also reduced superoxide dismutase 2 (SOD2) expression. Exogenous NAC partially recovered SOD2 expression, indicating that mitochondrial-mediated apoptosis accounts for a part of but not all of the TG2-reduction-related death.

Conclusion

TG2 plays a protection role in NSCLC cell lines. Regardless of the endogenous level of TG2 and p53 status, reduction of TG2 may result in oxidative stress that induces apop-tosis. Therefore, target TG2 expression represents a logical strategy for NSCLC management.

The good and the bad collagens of fibrosis - Their role in signaling and organ function

Usually the dense extracellular structure in fibrotic tissues is described as extracellular matrix (ECM) or simply as collagen. However, fibrosis is not just fibrosis, which is already exemplified by the variant morphological characteristics of fibrosis due to viral versus cholestatic, autoimmune or toxic liver injury, with reticular, chicken wire and bridging fibrosis. Importantly, the overall composition of the ECM, especially the relative amounts of the many types of collagens, which represent the most abundant ECM molecules and which centrally modulate cellular functions and physiological processes, changes dramatically during fibrosis progression. We hypothesize that there are good and bad collagens in fibrosis and that a change of location alone may change the function from good to bad. Whereas basement membrane collagen type IV anchors epithelial and other cells in a polarized manner, the interstitial fibroblast collagens type I and III do not provide directional information. In addition, feedback loops from biologically active degradation products of some collagens are examples of the importance of having the right collagen at the right place and at the right time controlling cell function, proliferation, matrix production and fate. Examples are the interstitial collagen type VI and basement membrane collagen type XVIII. Their carboxyterminal propeptides serve as an adipose tissue hormone, endotrophin, and as a regulator of angiogenesis, endostatin, respectively. We provide an overview of the 28 known collagen types and propose that the molecular composition of the ECM in fibrosis needs careful attention to assess its impact on organ function and its potential to progress or reverse. Consequently, to adequately assess fibrosis and to design optimal antifibrotic therapies, we need to dissect the molecular entity of fibrosis for the molecular composition and spatial distribution of collagens and the associated ECM.

Fungus-derived hydroxyl radicals kill hepatic cells by enhancing nuclear transglutaminase

We previously reported the importance of induced nuclear transglutaminase (TG) 2 activity, which results in hepatic cell death, in ethanol-induced liver injury. Here, we show that co-incubation of either human hepatic cells or mouse primary hepatocytes derived from wild-type but not TG2-/- mice with pathogenic fungi Candida albicans and C. glabrata, but not baker's yeast Saccharomyces cerevisiae, induced cell death in host cells by enhancing cellular, particularly nuclear, TG activity. Further pharmacological and genetic approaches demonstrated that this phenomenon was mediated partly by the production of reactive oxygen species (ROS) such as hydroxyl radicals, as detected by a fluorescent probe and electron spin resonance. A ROS scavenger, N-acetyl cysteine, blocked enhanced TG activity primarily in the nuclei and inhibited cell death. In contrast, deletion of C. glabrata nox-1, which encodes a ROS-generating enzyme, resulted in a strain that failed to induce the same phenomena. A similar induction of hepatic ROS and TG activities was observed in C. albicans-infected mice. An antioxidant corn peptide fraction inhibited these phenomena in hepatic cells. These results address the impact of ROS-generating pathogens in inducing nuclear TG2-related liver injuries, which provides novel therapeutic targets for preventing and curing alcoholic liver disease.

Gingival crevicular fluid and plasma oxidative stress markers and TGM-2 levels in chronic periodontitis

OBJECTIVE

This study was aimed to evaluate the gingival crevicular fluid (GCF) and plasma transglutaminase-2 (TGM-2), total antioxidant capacity (TAC), total oxidant status (TOS), ferric reducing antioxidant power (FRAP) and thiobarbituric acid reactive substances (TBARS) in patients with chronic periodontal disease.

MATERIALS AND METHODS

Twenty patients with chronic periodontitis (CP), 20 patients with gingivitis and 20 healthy subjects were enrolled in the study. Clinical periodontal parameters including probing depth, clinical attachment level, plaque index and papillary bleeding index were recorded. GCF and plasma levels of TGM-2, TAC, TOS, TBARS and FRAP were analyzed.

RESULTS

GCF TGM-2 was significantly lower in CP group than in gingivitis patients (P=0.006). GCF FRAP in CP and gingivitis groups was significantly lower than in healthy subjects (P<0.001). Plasma FRAP level was lower in gingivitis group when compared to healthy subjects (P=0.003). There was no significant difference in GCF and plasma TAC, TOS, TBARS and plasma TGM-2 levels among the study groups (P>0.05). GCF TGM-2 level was positively correlated with GCF TAC and negatively correlated with CAL.

CONCLUSIONS

Decreased FRAP in GCF and plasma indicating lower antioxidant status of CP patients might suggest the role of oxidative stress in periodontitis. GCF TGM-2 data might suggest that TGM2 is associated with stabilization of the extracellular matrix and wound healing in periodontium rather than gingival inflammation.

Protein degradation fragments as diagnostic and prognostic biomarkers of connective tissue diseases: understanding the extracellular matrix message and implication for current and future serological biomarkers

The aim of this review is to discuss the potential usefulness of novel biochemical markers of connective tissues: neo-epitopes of extracellular matrix proteins generated by post-translational modifications by tissue proteinases. As each modification results from a specific local physiological or pathobiological process, the identification of specific proteinase-mediated cleavage products of tissue-specific proteins may produce a unique disease-specific biochemical marker. The authors present a novel interpretation of the process of tissue degradation described by neo-epitope fragments of the interstitial and basement membrane matrix in fibrotic disease, and the diagnostic and prognostic potential of such markers. Moreover, the authors highlight the importance of matrix protein fragments not only as markers of tissue remodeling, but also as players in tissue remodeling, due to their signaling properties.

Essential Role of Transglutaminase 2 in Vascular Endothelial Growth Factor-Induced Vascular Leakage in the Retina of Diabetic Mice

Diabetic retinopathy is predominantly caused by vascular endothelial growth factor (VEGF)-induced vascular leakage; however, the underlying mechanism is unclear. Here we designed an in vivo transglutaminase (TGase) activity assay in mouse retina and demonstrated that hyperglycemia induced vascular leakage by activating TGase2 in diabetic retina. VEGF elevated TGase2 activity through sequential elevation of intracellular Ca(2+) and reactive oxygen species (ROS) concentrations in endothelial cells. The TGase inhibitors cystamine and monodansylcadaverin or TGase2 small interfering RNA (siRNA) prevented VEGF-induced stress fiber formation and vascular endothelial (VE)-cadherin disruption, which play a critical role in modulating endothelial permeability. Intravitreal injection of two TGase inhibitors or TGase2 siRNA successfully inhibited hyperglycemia-induced TGase activation and microvascular leakage in the retinas of diabetic mice. C-peptide or ROS scavengers also inhibited TGase activation in diabetic mouse retinas. The role of TGase2 in VEGF-induced vascular leakage was further supported using diabetic TGase2(-/-) mice. Thus, our findings suggest that ROS-mediated activation of TGase2 plays a key role in VEGF-induced vascular leakage by stimulating stress fiber formation and VE-cadherin disruption.

Gingival Crevicular Fluid and Plasma Levels of Transglutaminase-2 and Oxidative Stress Markers in Cyclosporin A-Induced Gingival Overgrowth

BACKGROUND

Transglutaminase (TGM)-2 has been shown to contribute to fibrosis by extracellular matrix accumulation in some organs and is activated by intracellular reactive oxygen species. The aim of this study is to investigate levels of gingival crevicular fluid (GCF) and plasma TGM-2 and oxidative stress markers (OSMs) in cyclosporin A (CsA)-induced gingival overgrowth (GO).

METHODS

The study enrolled 20 healthy (H) individuals; 20 patients with gingivitis (G); 20 CsA-medicated patients with GO (CsA GO+); and 20 CsA-medicated patients without GO (CsA GO-). GCF and plasma levels of TGM-2 were analyzed by enzyme-linked immunosorbent assay. Spectrofluorometry was used to analyze thiobarbituric acid reactive substance (TBARS); ferric-reducing antioxidant power (FRAP); total oxidant status (TOS); and total antioxidant capacity (TAC).

RESULTS

GCF TGM-2 level was elevated in CsA GO+ compared with G (P = 0.048) and H (P = 0.001) groups. GCF TBARS level was elevated in CsA GO+ compared with other groups (CsA GO- group: P = 0.003; G group: P <0.001; and H group: P <0.001) and was higher in CsA GO- than in H (P = 0.048). GCF FRAP level was lower in CsA GO- than in H (P = 0.04). Both CsA GO+ and CsA GO- groups had lower GCF TOS levels than H (P <0.001 and P = 0.002) and G (P = 0.003 and P = 0.04). GCF TAC was higher in CsA GO+ than in H (P = 0.02). Plasma TGM-2 level was elevated in CsA GO+ compared with G (P = 0.048) and H (P = 0.002). Plasma FRAP level was higher in H and CsA GO- than in CsA GO+ (P = 0.008 and P = 0.02).

CONCLUSIONS

CsA use significantly alters GCF and plasma levels of TGM-2 and OSMs. TGM-2 may contribute to CsA-induced GO in CsA-treated patients by changing GCF and plasma levels of OSMs. Further studies are needed to prove causality and its direction.

Regulation of allergic lung inflammation by endothelial cell transglutaminase 2

Tissue transglutaminase 2 (TG2) is an enzyme with multiple functions, including catalysis of serotonin conjugation to proteins (serotonylation). Previous research indicates that TG2 expression is upregulated in human asthma and in the lung endothelium of ovalbumin (OVA)-challenged mice. It is not known whether endothelial cell TG2 is required for allergic inflammation. Therefore, to determine whether endothelial cell TG2 regulates allergic inflammation, mice with an endothelial cell-specific deletion of TG2 were generated, and these mice were sensitized and challenged in the airways with OVA. Deletion of TG2 in endothelial cells blocked OVA-induced serotonylation in lung endothelial cells, but not lung epithelial cells. Interestingly, deletion of endothelial TG2 reduced allergen-induced increases in respiratory system resistance, number of eosinophils in the bronchoalveolar lavage, and number of eosinophils in the lung tissue. Endothelial cell deletion of TG2 did not alter expression of adhesion molecules, cytokines, or chemokines that regulate leukocyte recruitment, consistent with other studies, demonstrating that deletion of endothelial cell signals does not alter lung cytokines and chemokines during allergic inflammation. Taken together, the data indicate that endothelial cell TG2 is required for allergic inflammation by regulating the recruitment of eosinophils into OVA-challenged lungs. In summary, TG2 functions as a critical signal for allergic lung responses. These data identify potential novel targets for intervention in allergy/asthma.

Novel insights into the function and dynamics of extracellular matrix in liver fibrosis

Emerging evidence suggests that altered components and posttranslational modifications of proteins in the extracellular matrix (ECM) may both initiate and drive disease progression. The ECM is a complex grid consisting of multiple proteins, most of which play a vital role in containing the essential information needed for maintenance of a sophisticated structure anchoring the cells and sustaining normal function of tissues. Therefore, the matrix itself may be considered as a paracrine/endocrine entity, with more complex functions than previously appreciated. The aims of this review are to 1) explore key structural and functional components of the ECM as exemplified by monogenetic disorders leading to severe pathologies, 2) discuss selected pathological posttranslational modifications of ECM proteins resulting in altered functional (signaling) properties from the original structural proteins, and 3) discuss how these findings support the novel concept that an increasing number of components of the ECM harbor signaling functions that can modulate fibrotic liver disease. The ECM entails functions in addition to anchoring cells and modulating their migratory behavior. Key ECM components and their posttranslational modifications often harbor multiple domains with different signaling potential, in particular when modified during inflammation or wound healing. This signaling by the ECM should be considered a paracrine/endocrine function, as it affects cell phenotype, function, fate, and finally tissue homeostasis. These properties should be exploited to establish novel biochemical markers and antifibrotic treatment strategies for liver fibrosis as well as other fibrotic diseases.

Feline Chronic Kidney Disease Is Associated With Upregulation of Transglutaminase 2

Chronic kidney disease is a major cause of morbidity and mortality in cats. Transglutaminase 2 (TG2) is a calcium-dependent enzyme proposed to mediate tubulointerstitial fibrosis in the kidney by cross-linking collagen fibrils. Postmortem kidney tissue was obtained from primary renal azotemic ( n = 10) and nonazotemic ( n = 5) cats (14 domestic short hair, 1 Burmese; aged 9–23.7 years). Extracellular matrix protein deposition was determined by Masson’s trichrome staining and collagen immunofluorescence. Total kidney transglutaminase (TG) enzyme activity and TG2 protein were measured in tissue homogenates by putrescine incorporation and Western blotting. Extracellular TG enzyme activity and TG2 protein were determined in situ by immunofluorescence, quantified by multiphase image analysis. Results were compared using the unpaired Student’s t-test with Welch’s correction. Elevated plasma creatinine, urea, and phosphate concentrations were associated with tubulointerstitial fibrosis but not glomerular fibrosis. Kidney homogenates from azotemic cats showed a 3-fold higher total TG enzyme activity and TG2 protein compared with kidneys from nonazotemic cats. Immunofluorescent studies performed in situ confirmed a 3-fold higher extracellular TG enzyme activity and TG2 protein in cats with azotemia. Tubulointerstitial TG2 showed a positive linear correlation with both renal function and tubulointerstitial fibrosis. In conclusion, for cats with azotemia, both filtration failure and tubulointerstitial fibrosis were associated with the upregulation of TG2, a collagen cross-linking enzyme and the major isoform of transglutaminase in the kidney. TG2 may provide a new therapeutic target for drugs designed to slow the progression of feline chronic kidney disease.

Methylglyoxal in cells elicits a negative feedback loop entailing transglutaminase 2 and glyoxalase 1

Glyoxalase 1 (GlxI) is the key enzyme that converts the highly reactive α-oxo-aldehydes into the corresponding α-hydroxy acids using l-glutathione as a cofactor. In our preliminary data, GlxI was identified as a substrate of transglutaminase 2 (TG2), a ubiquitous enzyme with multiple functions. According to the catalytic properties of TG2, protein cross-linking, polyamine conjugation, and/or deamidation are potential post-translational modifications. In this article, we have demonstrated that TG2 catalyzes either polyamine conjugation or deamidation to GlxI depending on the presence of polyamines or not. Deamidation leads to activation of GlxI while polyamine conjugation results in activation of GlxI as well as stabilization of GlxI against denaturation treatment. In cultured HeLa cells, methylglyoxal challenge causes increase in intracellular levels of reactive oxygen species (ROS) and calcium leading to TG2 activation and subsequent transamidation and activation of GlxI. The inhibition of TG2 significantly weakens the cell resistance to the methylglyoxal challenge. Thus, GlxI is a novel substrate of TG2 and is activated by TG2 in vitro and in cellulo. Exposure to methylglyoxal elicits a negative feedback loop entailing ROS, calcium, TG2 and GlxI, thus leading to attenuation of the increase in the methylglyoxal level. The results imply that cancer cells highly express TG2 or GlxI can endure the oxidative stress derived from higher glycolytic flux and may gain extra growth advantage from the aerobic glycolysis.

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We have demonstrated novel modifications of glyoxalase I by transglutaminase 2.

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The modifications mediated by transglutaminse 2 modulate the glyoxalase I activities.

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Methylglyoxal treatment in cells induces increases in the levels of endogenous reactive oxygen species and activation transglutaminase 2 and glyoxalase I.

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Cells dispose the accumulated intracellular methylglyoxal by a negative feedback loop consisting of reactive oxygen species, calcium, transglutaminase 2 and glyoxalase I.

Transglutaminase 2-mediated serotonylation in pulmonary hypertension

The monoamine serotonin (5-HT) has been previously implicated in pulmonary arterial remodeling and is considered a potential therapeutic target for the disease pulmonary arterial hypertension (PAH). More recently, it has been recognized that the enzyme tissue transglutaminase (TG2) mediates cross-linking of proteins with 5-HT, a posttranslational process of monoaminylation known as "serotonylation." TG2 activity and serotonylation of protein participate in both smooth muscle proliferation and contraction produced by 5-HT. Indeed, markedly increased TG2 activity has now been identified in lung tissue of an experimental rodent model of pulmonary hypertension, and elevated serotonylation of fibronectin and the signaling molecule Rho, downstream products of transglutamidation, have been found in blood of patients with PAH. The basic mechanism by which TG2 is activated and the potential role(s) of serotonylated proteins in pulmonary hypertension remain a mystery. In the present review we have tried to address the current understanding of 5-HT metabolism in pulmonary hypertension and relate it to what is currently known about the evolving cellular process of serotonylation.

Transglutaminse 2 and EGGL, the protein cross-link formed by transglutaminse 2, as therapeutic targets for disabilities of old age

Aging of the extracellular matrix (ECM), the protein matrix that surrounds and penetrates the tissues and binds the body together, contributes significantly to functional aging of tissues. ECM proteins become increasingly cross-linked with age, and this cross-linking is probably important in the decline of the ECM's function. This article reviews the role of ε-(γ-glutamyl)-lysine (EGGL), a cross-link formed by transglutaminase enzymes, and particularly the widely expressed isozyme transglutaminase 2 (TG2), in the aging ECM. There is little direct data on EGGL accumulation with age, and no direct evidence of a role of EGGL in the aging of the ECM with pathology. However, several lines of circumstantial evidence suggest that EGGL accumulates with age, and its association with pathology suggests that this might reflect degradation of ECM function. TG activity increases with age in many circumstances. ECM protein turnover is such that some EGGL made by TG is likely to remain in place for years, if not decades, in healthy tissue, and both EGGL and TG levels are enhanced by age-related diseases. If further research shows EGGL does accumulate with age, removing it could be of therapeutic benefit. Also reviewed is the blockade of TG and active removal of EGGL as therapeutic strategies, with the conclusion that both have promise. EGGL removal may have benefit for acute fibrotic diseases, such as tendinopathy, and for treating generalized decline in ECM function with old age. Extracellular TG2 and EGGL are therefore therapeutic targets both for specific and more generalized diseases of aging.

The upregulation of transglutaminase-2 by cyclosporin a in human gingival fibroblasts is augmented by oxidative stress

BACKGROUND

Transglutaminase-2 (TGM-2) has been implicated in several fibrotic disorders and can be induced by reactive oxygen species (ROS). Hence, the authors hypothesize that cyclosporin A (CsA) may regulate TGM-2 via ROS, and this regulation may have a role in the pathogenesis of CsA-induced gingival overgrowth.

METHODS

Cytotoxicity, 2',7'-dichlorodihydrofluorescein diacetate assay, and Western blot were used to investigate the effects of CsA in human gingival fibroblasts (HGFs). In addition, extracellular signal-regulated kinase (ERK) inhibitor PD98059, phosphatidylinositol 3-kinase inhibitor LY294002, glutathione precursor N-acetyl-L-cysteine (NAC), curcumin, epigallocatechin-3 gallate (EGCG), and p38 inhibitor SB203580 were added to find the possible regulatory mechanisms.

RESULTS

Concentrations of CsA >500 ng/mL demonstrated cytotoxicity to HGFs (P < 0.05). CsA enhanced the generation of intracellular ROS at concentrations >200 ng/mL (P <0.05). TGM-2 protein induced by CsA was found in HGFs in a dose- and time-dependent manner (P <0.05). The addition of PD98059, LY294002, NAC, curcumin, EGCG, and SB203580 markedly inhibited TGM-2 expression induced by CsA (P <0.05).

CONCLUSIONS

These results demonstrate that CsA significantly upregulates intracellular ROS generation and elevates TGM-2 expression in HGFs. In addition, TGM-2 induced by CsA is downregulated by PD98059, LY294002, NAC, curcumin, EGCG, and SB203580.

Transglutaminase 2 promotes both caspase-dependent and caspase-independent apoptotic cell death via the calpain/Bax protein signaling pathway

Transglutaminase 2 (TG2) is a versatile protein that is implicated in significant biological processes, including cell death and degenerative diseases. A possible role of TG2 in the apoptotic death of cancer cells induced by photodynamic therapy (PDT) was suggested recently; however, the mechanism by which TG2 regulates apoptotic responses to PDT remains to be elucidated. In this study, we investigated the key signaling pathways stimulated during apoptotic cell death following PDT and whether inhibition of TG2 activation using pharmacological approaches and siRNAs affects the signaling pathways. PDT caused the release of both cytochrome c and apoptosis-inducing factor (AIF) by damaging mitochondria, which resulted in caspase-dependent and caspase-independent apoptotic cell death, respectively. Released AIF translocated to the nucleus and, synergistically with the caspase-dependent pathway, led to apoptotic cell death. Both the caspase cascade and the activation of AIF following PDT were mediated by TG2 activation. In addition, PDT-activated calpain was responsible for the sequential events of Bax translocation, the collapse of ΔΨ(m), caspase-3 activation, and AIF translocation, all of which were provoked by TG2 activation. Together, these results demonstrate that PDT with a chlorin-based photosensitizer targets TG2 by activating calpain-induced Bax translocation, which induces apoptotic cell death through both caspase-dependent and AIF-mediated pathways. Moreover, these results indicate that TG2 may be a possible therapeutic target for PDT treatment of cancer.

Protein transamidation by transglutaminase 2 in cells: a disputed Ca2+-dependent action of a multifunctional protein

Transglutaminase 2 (TG2) is the first described cellular member of an enzyme family catalyzing Ca(2+)-dependent transamidation of proteins. During the last two decades its additional enzymatic (GTP binding and hydrolysis, protein disulfide isomerase, protein kinase) and non-enzymatic (multiple interactions in protein scaffolds) activities, which do not require Ca(2+) , have been recognized. It became a prevailing view that TG2 is silent as a transamidase, except in extreme stress conditions, in the intracellular environment characterized by low Ca(2+) and high GTP concentrations. To counter this presumption a critical review of the experimental evidence supporting the role of this enzymatic activity in cellular processes is provided. It includes the structural basis of TG2 regulation through non-canonical Ca(2+) binding sites, mechanisms making it sensitive to low Ca(2+) concentrations, techniques developed for the detection of protein transamidation in cells and examples of basic cellular phenomena as well as pathological conditions influenced by this irreversible post-translational protein modification.

Monitoring of transglutaminase 2 under different oxidative stress conditions

Transglutaminase 2 (TG2) is a multifunctional calcium-dependent enzyme which catalyzes the post-translational protein crosslinking with formation of intra- or inter-molecular epsilon(gamma-glutamyl)lysine bonds or polyamine incorporation. The up-regulation and activation of TG2 have been reported in a variety of physiological events, including cell differentiation, signal transduction, apoptosis, and wound healing, as well as in cell response to stress evoked by different internal and external stimuli. Here we review TG2 role in cell response to redox state imbalance both under physiological and pathological conditions, such as neurodegenerative disorders, inflammation, autoimmune diseases and cataractogenesis, in which oxidative stress plays a pathogenetic role and also accelerates disease progression. The increase in TG activity together with mitochondrial impairment and collapse of antioxidant enzymatic cell defences have been reported to be the prominent biochemical alterations becoming evident prior to neurodegeneration. Moreover, oxidative stress-induced TG2 pathway is involved in autophagy inhibition and aggresome formation, and TG2 has been suggested to function as a link between oxidative stress and inflammation by driving the decision as to whether a protein should undergo SUMO-mediated regulation or proteasomal degradation. Literature data suggest a strong association between oxidative stress and TG2 up-regulation, which in turn may result in cell survival or apoptosis, depending on cell type, kind of stressor, duration of insult, as well as TG2 intracellular localization and activity state. In particular, it may be suggested that TG2 plays a pro-survival role when the alteration of cell redox state homeostasis is not associated with intracellular calcium increase triggering TG2 transamidation activity.

Transglutaminase 2 and its role in pulmonary fibrosis

RATIONALE

Idiopathic pulmonary fibrosis (IPF) is a deadly progressive disease with few treatment options. Transglutaminase 2 (TG2) is a multifunctional protein, but its function in pulmonary fibrosis is unknown.

OBJECTIVES

To determine the role of TG2 in pulmonary fibrosis.

METHODS

The fibrotic response to bleomycin was compared between wild-type and TG2 knockout mice. Transglutaminase and transglutaminase-catalyzed isopeptide bond expression was examined in formalin-fixed human lung biopsy sections by immunohistochemistry from patients with IPF. In addition, primary human lung fibroblasts were used to study TG2 function in vitro.

MEASUREMENTS AND MAIN RESULTS

TG2 knockout mice developed significantly reduced fibrosis compared with wild-type mice as determined by hydroxyproline content and histologic fibrosis score (P < 0.05). TG2 expression and activity are increased in lung biopsy sections in humans with IPF compared with normal control subjects. In vitro overexpression of TG2 led to increased fibronectin deposition, whereas transglutaminase knockdown led to defects in contraction and adhesion. The profibrotic cytokine transforming growth factor-β causes an increase in membrane-localized TG2, increasing its enzymatic activity.

CONCLUSIONS

TG2 is involved in pulmonary fibrosis in a mouse model and in human disease and is important in normal fibroblast function. With continued research on TG2, it may offer a new therapeutic target.

The combination of selenium and vitamin E inhibits type I collagen formation in cultured hepatic stellate cells

This study investigated the effects of sodium selenite (Se) and of vitamin E (D-α-tochopherol) on the deposition of type I collagen by human LX-2 stellate cells. The cultured cells were treated with or without Se or vitamin E and with or without transforming growth factor β1 (TGFβ1). The combination of Se and vitamin E, but not either alone, protected against hepatic fibrosis by decreasing TGFβ1-mediated collagen secretion and accumulation by the stellate cells. This protective effect is due to a combination of decreased formation, decreased stability and increased degradation of the collagen. Effects of Se and vitamin E in decreasing α(1)(I) collagen mRNA and increasing apoptosis of stellate cells indicate decreased formation of collagen, while decreases in transglutaminase 2, which catalyze cross-linking of collagen, lead to decreased stability of the secreted collagen. Effects of Se and vitamin E on reducing tissue inhibitor metalloproteinase 1 (TIMP-1) are associated with increased degradation. The combination of Se and vitamin E decreased lipid peroxidation, while Se alone increased the activity of the antioxidant enzyme thioredoxin reductase. In conclusion, the combination of Se and vitamin E protected against TGFβ1-mediated hepatic fibrosis by decreasing TGFβ1-mediated type I collagen accumulation by stellate cells. This effect is due to a combination of decreased formation, decreased stability and increased degradation of the collagen.

Matrix metalloproteinases and small artery remodeling

Inward eutrophic remodeling is a common structural change found in small resistance arteries that has been associated with an increased risk for life threatening cardiovascular events, the number one cause of death in industrialized societies. Because inward eutrophic remodeling is the most prevalent small artery structural change found in hypertension, hypertensive animals are the most common in vivo models used to study this particular remodeling process. In vitro, the isolated artery, pressure myograph has also been used as a model to study the mechanisms responsible for the development of small artery remodeling. Compelling recent evidence indicates that the matrix metalloproteinases (MMPs), a family of endopeptidases whose primary function is the cleavage and degradation of extracellular matrix components, are involved in vasoconstriction and the pathogenesis of hypertension. In this review we provide an overview of the known and potential roles that MMPs have on vascular remodeling, paying particular attention to their role on the inward eutrophic remodeling process of small resistance arteries that occurs in hypertension.

An in situ and in vitro investigation for the transglutaminase potential in tissue engineering

Transglutaminases (TGases) constitute a family of enzymes that stabilize protein assemblies by gamma-glutamyl-epsilon-lysine crosslinks. The role of tissue transglutaminase (TGase 2) in several pathophysiologies, wound healing applications, biomaterials functionalization, and drug delivery systems provides grounds for its use in tissue engineering. Herein, we initially studied the endogenous TGase activity and expression under normal (skin, duodenum, colon, and small bowel) and pathophysiological (keloid scar) conditions on cadaveric human tissues. Successful inhibition was achieved using low concentrations of BOC-DON-QIV-OMe (0.1 mM and 1 mM for normal skin and keloid scar, respectively), iodoacetamide (0.1 mM and 1 mM for normal skin and keloid scar, respectively), and cystamine dihydrochloride (1 mM and 10 mM for normal skin and keloid scar, respectively), whilst di-BOC-cystamine was found ineffective even at 100 mM concentration. Secondly, the addition of exogenous guinea pig liver transglutaminase (gpTGase) onto the inhibited tissues and collagen scaffolds was studied, and results presented advocate its use as potential tissue adhesive and drug delivery tool. However, the investigation of its crosslinking extent using second harmonic generation microscopy and differentially scanning calorimetry revealed rather poor stabilization function. Overall, our study indicates that TGase 2 has a role as a biological glue to consolidate various micro-structural components of tissues and biomaterials.

Transglutaminase 2: a multi-functional protein in multiple subcellular compartments

Transglutaminase 2 (TG2) is a multifunctional protein that can function as a transglutaminase, G protein, kinase, protein disulfide isomerase, and as an adaptor protein. These multiple biochemical activities of TG2 account for, at least in part, its involvement in a wide variety of cellular processes encompassing differentiation, cell death, inflammation, cell migration, and wound healing. The individual biochemical activities of TG2 are regulated by several cellular factors, including calcium, nucleotides, and redox potential, which vary depending on its subcellular location. Thus, the microenvironments of the subcellular compartments to which TG2 localizes, such as the cytosol, plasma membrane, nucleus, mitochondria, or extracellular space, are important determinants to switch on or off various TG2 biochemical activities. Furthermore, TG2 interacts with a distinct subset of proteins and/or substrates depending on its subcellular location. In this review, the biological functions and molecular interactions of TG2 will be discussed in the context of the unique environments of the subcellular compartments to which TG2 localizes.

Shear stress, reactive oxygen species, and arterial structure and function

Shear stress is well known to be a key factor in the regulation of small-artery tone and structure. Although nitric oxide is a major endothelium-derived factor involved in short- and long-term regulation of vascular caliber, it is clear that other mechanisms also can be involved. This review discusses the evidence for endothelium-derived reactive oxygen species (ROS) as mediators for shear-dependent arterial tone and remodeling. The work focuses on resistance vessels, because their caliber determines local perfusion. However, work on large vessels is included where needed. Attention is given to the shear-stress levels and profiles that exist in the arterial system and the differential effects of steady and oscillating shear on NO and ROS production. We furthermore address the relation between microvascular tone and remodeling and the effect of ROS and inflammation on the activity of remodeling enzymes such as matrix metalloproteinases and transglutaminases. We conclude that future work should address the role of H(2)O(2) as an endothelium-derived factor mediating tone and influencing structure of small arteries over the long term.

NF-kappaB activation is associated with homocysteine-induced injury in Neuro2a cells

Background

Perinatal exposure to hyperhomocysteinemia might disturb neurogenesis during brain development and growth. Also, high levels of homocysteine trigger neurodegeneration in several experimental models. However, the putative mechanisms of homocysteine-induced toxicity in the developing nervous system have poorly been elucidated. This study was aimed to investigate homocysteine effects in undifferentiated neuroblastoma cells, Neuro2a.

Results

A 4 h exposure to homocysteine in a concentration range of 10–100 μM did not affect cell viability and ROS production in Neuro2a cell cultures. Instead, ROS levels were increased by two-three folds in cells treated with 250 μM and 500 μM homocysteine, respectively, in comparison with control cells. Also, the highest homocysteine dose significantly reduced the viable cell number by 40%. Notably, the treatment with homocysteine (250 μM–500 μM) in the presence of antioxidants, such as N-acetylcysteine and IRFI 016, a synthetic α-tocopherol analogue, recovered cell viability and significantly reduced homocysteine-evoked increases in ROS production. Moreover, antioxidants, particularly IRFI 016, were able to counteract NF-κB activation induced by 250 μM homocysteine.

Cell treatment with 250 μM homocysteine also triggered the onset of apoptosis, as demonstrated by the increased expression of early apoptotic markers such as Bax, caspase-3 and p53. In contrast, Bcl2 expression was not affected by homocysteine exposure. Interestingly, the specific inhibition of NF-κB nuclear translocation by the synthetic peptide SN50 was able to almost completely suppress the homocysteine-evoked rises in pro-apoptotic protein expression as well as in caspase-3 activity. Further, also IRFI 016 and N-acetylcysteine were able to significantly reduce caspase-3 activation induced by homocysteine treatment.

Conclusion

These observations suggest an involvement of redox state alterations and activated NF-κB in apoptosis onset triggered by homocysteine in neuroblastoma cells Neuro2a. However, further investigations are needed to characterize molecular events involved in the NF-κB activation induced by homocysteine.

Tissue transglutaminase and the stress response

The expression of the protein crosslinking enzyme tissue transglutaminase (TG2, tTG), the ubiquitous member of transglutaminase family, can be regulated by multiple factors. Although it has been suggested that TG2 can be involved in apoptotic cell death, high levels of enzyme have also been associated with cell survival in response to different stimuli. Furthermore, evidence indicates that increases in TG2 production cause enzyme translocation to cell membrane. Cell stress can also lead to TG2 accumulation on the cell surface and in the extracellular matrix resulting in changes in cell-matrix interactions.Here, we discuss the underlying mechanisms of TG2 up-regulation induced by various stimuli including glutamate exposure, calcium influx, oxidative stress, UV, and inflammatory cytokines. These findings agree with a postulated role for transglutaminases in molecular mechanisms involved in several diseases suggesting that cross-linking reactions could be a relevant part of the biochemical changes observed in pathological conditions.

Differentiation-specific factors modulate epidermal CYP1-4 gene expression in human skin in response to retinoic acid and classic aryl hydrocarbon receptor ligands

Human epidermal keratinocytes express subsets of cytochromes P450 (P450) (CYP gene products) that are strongly up-regulated, not regulated, or down-regulated by differentiation-specific factors. We investigated how drug exposure affects epidermal expression of CYP1-4 genes, which encode many drug-metabolizing P450s. Real-time polymerase chain reaction (PCR) assays measured CYP1-4 mRNA levels in epidermal keratinocytes differentiated in vitro in the presence of drug or vehicle for 6 days. We confirmed the spinous phenotype at day 6 by changes in cellular morphology and upregulation of cytokeratin 10 and transglutaminase (TGM)1 mRNA in the differentiating keratinocytes. Effects of drug exposure depended on the influence of differentiation-specific factors in controlling epidermal CYP1-4 expression. CYP2C18, 2C19, 2C9, 2W1, 3A4, and 4B1 are up-regulated by cellular differentiation; mRNA levels for these CYP genes were inhibited in differentiating keratinocytes exposed to retinoic acid and aryl hydrocarbon receptor (AhR) ligands. These same drugs effected <or=2-fold change or even augmented mRNA levels for CYP genes that are not regulated by differentiation (CYP2S1, 2J2, 1B1, 1A1, 1A2, 2E1, and 2D6) and for CYP2U1, which is expressed at highest levels in undifferentiated keratinocytes. The clinically relevant drugs miconazole, dexamethasone, rifampicin, and dapsone had little effect on CYP1-4 mRNA levels under assay conditions. The AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin also up-regulated keratinocyte TGM1 mRNA in a concentration- and time-dependent manner. This effect was blocked by the AhR antagonist resveratrol. These findings implicate AhR-dependent up-regulation of TGM1 mRNA in differentiating keratinocytes as one mechanism contributing toward chloracne in humans exposed to toxic levels of dioxin.

Down-regulation of transglutaminase II leads to impaired motility of cancer cells by inactivation of the protein kinase, Akt, and decrease of reactive oxygen species

We employed RNA interference to determine the role of tissue transglutaminase II (TGase II) in motility of cancer cells. Down-regulation of TGase II by small interfering RNA against TGase II impaired adhesion and motility of HeLa cells by decreasing phosphorylation of the protein kinase, Akt, and reactive oxygen species (ROS). Over-expression of TGase II showed opposite effects. These results suggest potential utility of TGase II for development of therapeutic anti cancer vaccine.

Heterologous leaky production of transglutaminase in Lactococcus lactis significantly enhances the growth performance of the host

This study describes a novel strategy to improve the growth performance of Lactococcus lactis by heterologous production of food-grade transglutaminase. The mtg gene from Streptoverticillium mobaraense that encodes the transglutaminase mature protein was cloned into a nisin-inducible expression vector and transformed into L. lactis subsp. cremoris NZ9000. The leaky expression of the mtg gene from the nisA promoter resulted in ammonia formation and carbon flux redistribution at the pyruvate branch. As a consequence, medium acidification was lessened and energy utilization was improved. This led to significantly higher biomass production under aerobic conditions and particularly under non-pH-controlled conditions (up to a 12-fold increase). The results presented here provide a novel way to enhance the growth yield of L. lactis, which is an important step for the purposes of producing proteins of commercial interest using L. lactis as a host.

Regulation of tissue transglutaminase by prolonged increase of intracellular Ca2+, but not by initial peak of transient Ca2+ increase

Tissue transglutaminase (tTGase) is a member of calcium-dependent transamidation enzyme family, but a detailed regulation mechanism of tTGase by intracellular Ca(2+) is not clearly understood. Arachidonic acid (AA) and maitotoxin (MTX) activated tTGase in a dose- and time-dependent manner. Transfection of tTGase siRNA largely inhibited tTGase expression and tTGase activation by MTX. AA induced an initial increase of intracellular Ca(2+) followed by a prolonged increase. Removal of extracellular Ca(2+) with EGTA blocked the prolonged Ca(2+) increase in response to AA, although the initial Ca(2+) increase remained. In contrast, EGTA completely blocked the increase of intracellular Ca(2+) by MTX. The activation of tTGase by AA or MTX was significantly inhibited by EGTA. Moreover, EGTA prevented the prolonged increase of intracellular Ca(2+) and tTGase activation by lysophosphatidic acid, but had no effect on the initial Ca(2+) increase. These results suggested that tTGase is regulated by the prolonged increase of intracellular Ca(2+) originated from Ca(2+) influx, rather than by the initial peak of transient Ca(2+) increase.

Arachidonic acid activates tissue transglutaminase and stress fiber formation via intracellular reactive oxygen species

We have investigated whether arachidonic acid could regulate tissue transglutaminase (tTGase) via intracellular reactive oxygen species (ROS) in NIH3T3 cells. tTGase was identified in NIH3T3 cells by Western blot and confocal microscopy. Arachidonic acid elevated in situ tTGase activity in dose- and time-dependent manners with a maximal level at 1h, and ROS scavengers, N-(2-mercaptopropionyl)glycine and catalase, blocked the tTGase activation by arachidonic acid. The activation of tTGase by arachidonic acid was largely inhibited by transfection of tTGase siRNA. The role of intracellular ROS in the activation of in situ tTGase was supported by the activation of in situ tTGase by exogenous H(2)O(2). Arachidonic acid stimulated the formation of stress fibers in a dose- and time-dependent manner, and the ROS scavengers suppressed the arachidonic acid-induced formation of stress fibers. These results suggested that the activation of in situ tTGase and stress fiber formation by arachidonic acid was mediated by intracellular ROS in NIH3T3 cells.