Transglutaminase 2 Activity Research Articles

Lung-specific interleukin 6 mediated transglutaminase 2 activation and cardiopulmonary fibrogenesis.

Pulmonary hypertension (PH) pathogenesis is driven by inflammatory and metabolic derangements as well as glycolytic reprogramming. Induction of both interleukin 6 (IL6) and transglutaminase 2 (TG2) expression participates in human and experimental cardiovascular diseases. However, little is known about the role of TG2 in these pathologic processes. The current study aimed to investigate the molecular interactions between TG2 and IL6 in mediation of tissue remodeling in PH. A lung-specific IL6 over-expressing transgenic mouse strain showed elevated right ventricular (RV) systolic pressure as well as increased wet and dry tissue weights and tissue fibrosis in both lungs and RVs compared to age-matched wild-type littermates. In addition, IL6 over-expression induced the glycolytic and fibrogenic markers, hypoxia-inducible factor 1α, pyruvate kinase M2 (PKM2), and TG2. Consistent with these findings, IL6 induced the expression of both glycolytic and pro-fibrogenic markers in cultured lung fibroblasts. IL6 also induced TG2 activation and the accumulation of TG2 in the extracellular matrix. Pharmacologic inhibition of the glycolytic enzyme, PKM2 significantly attenuated IL6-induced TG2 activity and fibrogenesis. Thus, we conclude that IL6-induced TG2 activity and cardiopulmonary remodeling associated with tissue fibrosis are under regulatory control of the glycolytic enzyme, PKM2.

Abstract LB444: Identification of a novel and selective Transglutaminase 2 (TGM2) inhibitors modulate tumor microenvironment in Glioblastoma

Abstract Background: TGM (Transglutaminase) family enzymes are Ca2+ dependent and engaged in specific posttranslational modifications by cross-linking extracellular matrix (ECM) proteins. ECM protein complex is more stable and resistant to enzymatic degradation. These enzymes modify proteins by cross-linking epsilon-(gamma-glutamyl), lysine, or (gamma-glutamyl) polyamine bonds. TGM2 (Transglutaminase 2) is a ubiquitous enzyme, and its expression is identified in the cytoplasm, plasma membrane, and the nucleus of various cells. The membrane-bound form of TGM2 binds GTP and functions as a G protein. TGM2 regulates cell survival, proliferation, migration, and modulation through ECM organization. We explored the role of TGM2 in Glioblastoma cells and its role in modulating the tumor microenvironment, cell proliferation, and survival. In addition to TGM2's role in GBM tumors, its expression has been linked to resistance to certain therapies in glioblastoma was investigated. Targeted modulation of macrophages with TGM2 inhibitors impacts the immune response against GBM, potentially enhancing the efficacy. Understanding the intricate interplay between TGM2, and GBM-associated macrophages is a key component of the tumor microenvironment (TME) and crucial for the development of targeted TGM2 inhibitors. Materials and Methods: Human Transglutaminase 2 (hTGM2) activity of inhibitors was assayed using the fluorescent transamination assay incorporating dansylcadaverine into glutamine-donor substrate N, N-dimethyl casein, and DCC. Cellular efficacies of selected TGM2 inhibitors evaluated in U138 and U87 glioblastoma cells in CellTiter-Glo Luminescent cell viability assay. Results: We have identified a series of novel small molecule TGM2 inhibitors based on our initial lead fragment hits with an IC50s 6-29 uM from our in-house MolecuLern fragment library. Fragments2Lead (F2L) optimizations strategies, synthesis, and SAR studies provided a lead SLX-9029 and SLX-9031 inhibitors with IC50s of 1.2, 1.5 uM in inhibiting TGM2 activity in our established cell-free fluorescent transamination assay. The initial TMG2 inhibitor leads further screening for TGM2-expressed U138 and U87 glioblastoma cells demonstrating promising cellular efficacies as singles agents. Additional GBM cell profiling, combination studies along with safety secondary pharmacology, cellular toxicities, and PK results will be discussed. Conclusion: In summary, we identified promising lead TGM2 inhibitors that show activity in both cell-free and cell-based TGM2-expressed GMB cells. The TGM family members, selectivity, additional GBM cellular profiling, ADME, cellular toxicity, and in vivo PK studies are underway, and these results will be presented. Citation Format: Hariprasad Vankayalapati, Chenyu Lin, Zhaoang li, Kyle Medley, David J. Bearss. Identification of a novel and selective Transglutaminase 2 (TGM2) inhibitors modulate tumor microenvironment in Glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB444.

The effect of TG2-inhibitory monoclonal antibody zampilimab on tissue fibrosis in human in vitro and primate in vivo models of chronic kidney disease.

Fibrotic remodeling is the primary driver of functional loss in chronic kidney disease, with no specific anti-fibrotic agent available for clinical use. Transglutaminase 2 (TG2), a wound response enzyme that irreversibly crosslinks extracellular matrix proteins causing dysregulation of extracellular matrix turnover, is a well-characterized anti-fibrotic target in the kidney. We describe the humanization and characterization of two anti-TG2 monoclonal antibodies (zampilimab [hDC1/UCB7858] and BB7) that inhibit crosslinking by TG2 in human in vitro and rabbit/cynomolgus monkey in vivo models of chronic kidney disease. Determination of zampilimab half-maximal inhibitory concentration (IC50) against recombinant human TG2 was undertaken using the KxD assay and determination of dissociation constant (Kd) by surface plasmon resonance. Efficacy in vitro was established using a primary human renal epithelial cell model of tubulointerstitial fibrosis, to assess mature deposited extracellular matrix proteins. Proof of concept in vivo used a cynomolgus monkey unilateral ureteral obstruction model of chronic kidney disease. Zampilimab inhibited TG2 crosslinking transamidation activity with an IC50 of 0.25 nM and Kd of <50 pM. In cell culture, zampilimab inhibited extracellular TG2 activity (IC50 119 nM) and dramatically reduced transforming growth factor-β1-driven accumulation of multiple extracellular matrix proteins including collagens I, III, IV, V, and fibronectin. Intravenous administration of BB7 in rabbits resulted in a 68% reduction in fibrotic index at Day 25 post-unilateral ureteral obstruction. Weekly intravenous administration of zampilimab in cynomolgus monkeys with unilateral ureteral obstruction reduced fibrosis at 4 weeks by >50%, with no safety signals. Our data support the clinical investigation of zampilimab for the treatment of kidney fibrosis.

The role of transglutaminase 2 in regulation of the balance between autophagy and apoptosis in tumor cells

In normal tissue, cellular homeostasis is largely driven by two catabolic pathways: apoptosis and autophagy. Apoptosis, or programmed cell death, is regulated by pro-apoptotic factors, and promotes the removal of problematic cells. Autophagy, which in turn includes three forms: macro-, micro-, and chaperone-mediated autophagy, can promote both cell survival by selectively removing potentially apoptosis-inducing factors and raising the threshold of stress required for the induction of cell death. Recently, evidence has been accumulating suggesting the existence of common molecular pathways between autophagy and apoptosis, as well as the influence of the extracellular matrix on these processes. One of the important enzymes involved in the coordination and regulation of these processes is transglutaminase 2 (TG2). Different types of TG2 activities are involved in maintaining the dynamic balance between extracellular matrix and intracellular autophagy/apoptosis processes, while dysregulation of these processes may contribute to the pathogenesis of various human diseases, including oncogenesis. For example, TG2 can promote the degradation of pro-apoptotic proteins and the survival of renal cell carcinoma cells under nutrient-deficient conditions by modulating the autophagy process. In cells of various tissues deprived of TG2, aggregates of ubiquitinated proteins and damaged mitochondria are observed, which in turn induces proteotoxic stress and cell death. conversely, the transamidase activity of TG2 was observed to inhibit anti-apoptotic signaling in a human leukemic monocytic lymphoma model. In the present review, a number of important functions of TG2 in oncogenesis are described, along with the dual role of TG2 in modulating such opposite processes as cell survival and cell death.

Transglutaminase 2 Prevents Premature Senescence and Promotes Osteoblastic Differentiation of Mesenchymal Stem Cells through NRF2 Activation.

Transglutaminase 2 (TG2) is a multifunctional enzyme that exhibits transamidase, GTPase, kinase, and protein disulfide isomerase (PDI) activities. Of these, transamidase-mediated modification of proteins regulates apoptosis, differentiation, inflammation, and fibrosis. TG2 is highly expressed in mesenchymal stem cells (MSCs) compared with differentiated cells, suggesting a role of TG2 specific for MSC characteristics. In this study, we report a new function of TG2 in the regulation of MSC redox homeostasis. During in vitro MSC expansion, TG2 is required for cell proliferation and self-renewal by preventing premature senescence but has no effect on the expression of surface antigens and oxidative stress-induced cell death. Moreover, induction of differentiation upregulates TG2 that promotes osteoblastic differentiation. Molecular analyses revealed that TG2 mediates tert-butylhydroquinone, but not sulforaphane, -induced nuclear factor erythroid 2-related factor 2 (NRF2) activation in a transamidase activity-independent manner. Differences in the mechanism of action between two NRF2 activators suggest that PDI activity of TG2 may be implicated in the stabilization of NRF2. The role of TG2 in the regulation of antioxidant response was further supported by transcriptomic analysis of MSC. These results indicate that TG2 is a critical enzyme in eliciting antioxidant response in MSC through NRF2 activation, providing a target for optimizing MSC manufacturing processes to prevent premature senescence.

High-Affinity Fluorogenic Substrate for Tissue Transglutaminase Reveals Enzymatic Hysteresis.

Transglutaminases (TGases) are a family of calcium-dependent enzymes primarily known for their ability to cross-link proteins. Transglutaminase 2 (TG2) is one isozyme in this family whose role is multifaceted. TG2 can act not only as a typical transamidase through its catalytic core but also as a G-protein via its GTP binding site. These two discrete activities are tightly regulated by both environmental stimuli and redox reactions. Ubiquitously expressed in humans, TG2 has been implicated in numerous disease pathologies that require extensive investigation. The catalytic activity of TG2 can be monitored through various mechanisms, including hydrolysis, transamidation, or cleavage of isopeptide bonds. Activity assays are required to monitor the activity of this isozyme not only for studying its transamidation reaction but also for validation of therapeutics designed to abolish this activity. Herein, we present the design, synthesis, and evaluation of a new TG2 activity substrate based on a previously optimized inhibitor scaffold. The substrate APH7 exhibits excellent affinity, selectivity, and reactivity with TG2 (KM = 3.0 μM). Furthermore, its application also allowed the discovery of unique hysteresis at play within the catalytic activity and inhibition reactivity of TG2.

FRI131 Abrogation Of Transglutaminase 2 In Myeloid Cells Ameliorates Angiotensin II Induced Vascular Stiffness In Female Mice

Abstract Disclosure: H. Naz: None. A.R. Aroor: None. A.T. Whaley-Connell: None. J. Guanghong: None. J.L. Hulse: None. C.M. Manrique Acevedo: None. G. Lastra: None. Introduction: Chronic low-grade inflammation and vascular stiffening contribute to cardiovascular disease (CVD) in obese and insulin-resistant women. Under these conditions, inappropriate activation of the renin angiotensin aldosterone system (RAAS) stimulates Transglutaminase 2 (TG2), a ubiquitously expressed enzyme that promotes vascular stiffening and remodeling. Additionally, Th17 cells contribute to CVD development in the setting of RAAS activation. However, it is unclear how TG2 activation mediates maladaptive immune responses associated with vascular stiffening in women. In this study, we hypothesize that TG2 abrogation inhibits Ang II-induced vascular stiffness in females by modulating Th17 immunity. Methods: 12-week-old female mice lacking TG2 expression (MyTG2KO) in myeloid cells, and control littermates (LM) were infused with Ang-II (1.4 mg/kg/day) for 2 weeks (n=4-8 per group). Prior to sacrifice, systolic blood pressure (SBP) was measured by tail-cuff method. Aortic stiffness was assessed by atomic force microscopy of thoracic aorta explants, and TG2 activity was examined by Alexa FluorTM 488 cadaverine. Analysis of Th17 cells in blood, spleen and epididymal fat (epi-fat) was done by flow cytometry. Cytokine bead array was used to measure cytokine levels in serum, RT-PCR was used to analyze cytokines in aortic tissue and TG2 knockdown efficiency in myeloid cells. Immunohistochemistry was used to examine fibrosis in aorta. Results: SBP was decreased in MyTG2KO-Ang-II as compared to LM-Ang-II cohort (129.6±5.6 vs 152.5 ±2 mmHg; p=0.04). TG2 mRNA expression in macrophages was lower in MyTG2KO mice as compared to LM (p=0.002). TG2 activity in aortic tissue increased in LM-Ang-II as compared to LM-saline (p=0.004) but was significantly lower in MyTG2KO-Ang-II mice (p=0.02). Aortic stiffness was lower in MyTG2KO-Ang-II mice relative to LM-Ang-II (4.0±0.6 vs 10.3±2.4 kPa; p=0.02). Compared to LM-Ang-II, MyTG2KO-Ang-II mice also had decreased Th17 lymphocytes (CD4+IL-17A+) in blood (3.5±0.2 vs 5.8 ±0.4 %; p=&amp;lt;0.0001), spleen (4.7±0.4 vs 7.1 ±0.5 %; p=0.004) and epi-fat (4.7±0.6 vs 6.8 ±0.5 %; p=0.02). MyTG2KO-Ang II mice also had significant lower levels of proinflammatory cytokines (TNF-a, IL6, IL17A, INF-g) in serum and mRNA expression of proinflammatory cytokines compared to LM-Ang-II mice and decreased total macrophage infiltration (CD68+) in the aorta. Ang-II treated MyTG2KO mice group also exhibited reduced fibrosis in the aorta relative to LM-Ang-II (p=0.003). Conclusion: The results demonstrate that abrogating TG2 in myeloid cells in female mice substantially reduces blood pressure, proinflammatory cytokines, and Th17 immune responses induced by Ang-II. Our findings have potential clinical implications for the prevention and management of CVD in women. Presentation: Friday, June 16, 2023

Metabolic characterisation of transglutaminase 2 inhibitor effects in breast cancer cell lines.

Transglutaminase 2 (TG2), which mediates post-translational modifications of multiple intracellular enzymes, is involved in the pathogenesis and progression of cancer. We used 1 H-NMR metabolomics to study the effects of AA9, a novel TG2 inhibitor, on two breast cancer cell lines with distinct phenotypes, MCF-7 and MDA-MB-231. AA9 can promote apoptosis in both cell lines, but it is particularly effective in MD-MB-231, inhibiting transamidation reactions and decreasing cell migration and invasiveness. This metabolomics study provides evidence of a major effect of AA9 on MDA-MB-231 cells, impacting glutamate and aspartate metabolism, rather than on MCF-7 cells, characterised by choline and O-phosphocholine decrease. Interestingly, AA9 treatment induces myo-inositol alteration in both cell lines, indicating action on phosphatidylinositol metabolism, likely modulated by the G protein activity of TG2 on phospholipase C. Considering the metabolic deregulations that characterise various breast cancer subtypes, the existence of a metabolic pathway affected by AA9 further points to TG2 as a promising hot spot. The metabolomics approach provides a powerful tool to monitor the effectiveness of inhibitors and better understand the role of TG2 in cancer.

Cell-Impermeable Inhibitors Confirm That Intracellular Human Transglutaminase 2 Is Responsible for the Transglutaminase-Associated Cancer Phenotype.

Transglutaminase 2 (TG2) is a multifunctional enzyme primarily responsible for crosslinking proteins. Ubiquitously expressed in humans, TG2 can act either as a transamidase by crosslinking two substrates through formation of an Nε(ɣ-glutaminyl)lysine bond or as an intracellular G-protein. These discrete roles are tightly regulated by both allosteric and environmental stimuli and are associated with dramatic changes in the conformation of the enzyme. The pleiotropic nature of TG2 and multi-faceted activities have resulted in TG2 being implicated in numerous disease pathologies including celiac disease, fibrosis, and cancer. Targeted TG2 therapies have not been selective for subcellular localization, such that currently no tools exist to selectively target extracellular over intracellular TG2. Herein, we have designed novel TG2-selective inhibitors that are not only highly potent and irreversible, but also cell impermeable, targeting only extracellular TG2. We have also further derivatized the scaffold to develop probes that are intrinsically fluorescent or bear an alkyne handle, which target both intra- and extracellular TG2, in order to facilitate cellular labelling and pull-down assays. The fluorescent probes were internalized and imaged in cellulo, and provide the first implicit experimental evidence that by comparison with their cell-impermeable analogues, it is specifically intracellular TG2, and presumably its G-protein activity, that contributes to transglutaminase-associated cancer progression.

Transglutaminase 2 Facilitates Murine Wound Healing in a Strain-Dependent Manner.

Transglutaminase 2 (TG2) plays a role in cellular processes that are relevant to wound healing, but to date no studies of wound healing in TG2 knockout mice have been reported. Here, using 129T2/SvEmsJ (129)- or C57BL/6 (B6)-backcrossed TG2 knockout mice, we show that TG2 facilitates murine wound healing in a strain-dependent manner. Early healing of in vivo cutaneous wounds and closure of in vitro scratch wounds in murine embryonic fibroblast (MEF) monolayers were delayed in 129, but not B6, TG2 knockouts, relative to their wild-type counterparts, with wound closure in 129 being faster than in B6 wild-types. A single dose of exogenous recombinant wild-type TG2 to 129 TG2-/- mice or MEFs immediately post-wounding accelerated wound closure. Neutrophil and monocyte recruitment to 129 cutaneous wounds was not affected by Tgm2 deletion up to 5 days post-wounding. Tgm2 mRNA and TG2 protein abundance were higher in 129 than in B6 wild-types and increased in abundance following cutaneous and scratch wounding. Tgm1 and factor XIIA (F13A) mRNA abundance increased post-wounding, but there was no compensation by TG family members in TG2-/- relative to TG2+/+ mice in either strain before or after wounding. 129 TG2+/+ MEF adhesion was greater and spreading was faster than that of B6 TG2+/+ MEFs, and was dependent on syndecan binding in the presence, but not absence, of RGD inhibition of integrin binding. Adhesion and spreading of 129, but not B6, TG2-/- MEFs was impaired relative to their wild-type counterparts and was accelerated by exogenous addition or transfection of TG2 protein or cDNA, respectively, and was independent of the transamidase or GTP-binding activity of TG2. Rho-family GTPase activation, central to cytoskeletal organization, was altered in 129 TG2-/- MEFs, with delayed RhoA and earlier Rac1 activation than in TG2+/+ MEFs. These findings indicate that the rate of wound healing is different between 129 and B6 mouse strains, correlating with TG2 abundance, and although not essential for wound healing, TG2 facilitates integrin- and syndecan-mediated RhoA- and Rac1-activation in fibroblasts to promote efficient wound contraction.

Amelioration of Fibrotic Remodeling of Human 3-Dimensional Full-Thickness Skin by Transglutamase 2 Inhibition.

Fibrotic tissues are characterized by excessive crosslinking between extracellular matrix (ECM) proteins, rendering them more resistant to degradation. Although increased crosslinking of ECM is thought to play an important role for progression of tissue fibrosis, enhanced ECM crosslinking has not yet been targeted therapeutically in systemic sclerosis (SSc). Here, we investigated the role of transglutaminase 2 (TG2), a central crosslinking enzyme, in the activation of SSc fibroblasts. We assessed TG2 expression and activity using TG2 staining, Western blotting, and TG2 activity assays. We inhibited TG2 in fibroblasts cultured under standard 2-dimensional conditions and in a 3-dimensional full-thickness equivalent skin model using monoclonal inhibitory anti-TG2 antibodies. TG2 expression was increased in the skin of patients with SSc compared with healthy controls, with levels particularly high in patients with SSc-associated interstitial lung disease. TG2 expression and TG2 activity were also increased in SSc dermal fibroblasts. Moreover, the levels of circulating TG2 in the plasma samples from SSc patients were increased versus samples from healthy controls. Anti-TG2 antibodies did not show consistent antifibrotic effects across different fibroblast cell lines under 2-dimensional culture conditions; however, anti-TG2 antibodies effectively reduced transforming growth factor β-induced dermal thickening, myofibroblast differentiation, and collagen accumulation in the 3-dimensional full-thickness model of human skin. We provide the first evidence, to our knowledge, that inhibition of TG2 might be a potential antifibrotic approach in SSc. Our findings have translational potential as anti-TG2 antibodies are currently evaluated in a phase II clinical trial in chronic allograft injury and would thus be available for clinical studies in SSc (ClinicalTrials.gov identifier: NCT04335578).

The Oral Transglutaminase 2 Inhibitor ZED1227 Accumulates in the Villous Enterocytes in Celiac Disease Patients during Gluten Challenge and Drug Treatment.

The enzyme transglutaminase 2 (TG2) plays a key role in celiac disease (CeD) pathogenesis. Active TG2 is located mainly extracellularly in the lamina propria but also in the villous enterocytes of the duodenum. The TG2 inhibitor ZED1227 is a promising drug candidate for treating CeD and is designed to block the TG2-catalyzed deamidation and crosslinking of gliadin peptides. Our aim was to study the accumulation of ZED1227 after oral administration of the drug. We studied duodenal biopsies derived from a phase 2a clinical drug trial using an antibody that detects ZED1227 when bound to the catalytic center of TG2. Human epithelial organoids were studied in vitro for the effect of ZED1227 on the activity of TG2 using the 5-biotin-pentylamine assay. The ZED1227-TG2 complex was found mainly in the villous enterocytes in post-treatment biopsies. The signal of ZED1227-TG2 was strongest in the luminal epithelial brush border, while the intensity of the signal in the lamina propria was only ~20% of that in the villous enterocytes. No signal specific to ZED1227 could be detected in pretreatment biopsies or in biopsies from patients randomized to the placebo treatment arm. ZED1227-TG2 staining co-localized with total TG2 and native and deamidated gliadin peptides on the enterocyte luminal surface. Inhibition of TG2 activity by ZED1227 was demonstrated in epithelial organoids. Our findings suggest that active TG2 is present at the luminal side of the villous epithelium and that inhibition of TG2 activity by ZED1227 occurs already there before gliadin peptides enter the lamina propria.

Targeting transglutaminase 2 mediated exostosin glycosyltransferase 1 signaling in liver cancer stem cells with acyclic retinoid

Transglutaminase 2 (TG2) is a multifunctional protein that promotes or suppresses tumorigenesis, depending on intracellular location and conformational structure. Acyclic retinoid (ACR) is an orally administered vitamin A derivative that prevents hepatocellular carcinoma (HCC) recurrence by targeting liver cancer stem cells (CSCs). In this study, we examined the subcellular location-dependent effects of ACR on TG2 activity at a structural level and characterized the functional role of TG2 and its downstream molecular mechanism in the selective depletion of liver CSCs. A binding assay with high-performance magnetic nanobeads and structural dynamic analysis with native gel electrophoresis and size-exclusion chromatography-coupled multi-angle light scattering or small-angle X-ray scattering showed that ACR binds directly to TG2, induces oligomer formation of TG2, and inhibits the transamidase activity of cytoplasmic TG2 in HCC cells. The loss-of-function of TG2 suppressed the expression of stemness-related genes, spheroid proliferation and selectively induced cell death in an EpCAM+ liver CSC subpopulation in HCC cells. Proteome analysis revealed that TG2 inhibition suppressed the gene and protein expression of exostosin glycosyltransferase 1 (EXT1) and heparan sulfate biosynthesis in HCC cells. In contrast, high levels of ACR increased intracellular Ca2+ concentrations along with an increase in apoptotic cells, which probably contributed to the enhanced transamidase activity of nuclear TG2. This study demonstrates that ACR could act as a novel TG2 inhibitor; TG2-mediated EXT1 signaling is a promising therapeutic target in the prevention of HCC by disrupting liver CSCs.

Inhibition of Transglutaminase 2 as a Therapeutic Strategy in Celiac Disease-In Vitro Studies in Intestinal Cells and Duodenal Biopsies.

Enzymatic modification of gliadin peptides by human transglutaminase 2 (TG2) is a key mechanism in the pathogenesis of celiac disease (CD) and represents a potential therapeutic target. Recently, we have identified the small oxidative molecule PX-12 as an effective inhibitor of TG2 in vitro. In this study, we further investigated the effect of PX-12 and the established active-site directed inhibitor ERW1041 on TG2 activity and epithelial transport of gliadin peptides. We analyzed TG2 activity using immobilized TG2, Caco-2 cell lysates, confluent Caco-2 cell monolayers and duodenal biopsies from CD patients. TG2-mediated cross-linking of pepsin-/trypsin-digested gliadin (PTG) and 5BP (5-biotinamidopentylamine) was quantified by colorimetry, fluorometry and confocal microscopy. Cell viability was tested with a resazurin-based fluorometric assay. Epithelial transport of promofluor-conjugated gliadin peptides P31-43 and P56-88 was analyzed by fluorometry and confocal microscopy. PX-12 reduced TG2-mediated cross-linking of PTG and was significantly more effective than ERW1041 (10 µM, 15 ± 3 vs. 48 ± 8%, p < 0.001). In addition, PX-12 inhibited TG2 in cell lysates obtained from Caco-2 cells more than ERW1041 (10 µM; 12 ± 7% vs. 45 ± 19%, p < 0.05). Both substances inhibited TG2 comparably in the intestinal lamina propria of duodenal biopsies (100 µM, 25 ± 13% vs. 22 ± 11%). However, PX-12 did not inhibit TG2 in confluent Caco-2 cells, whereas ERW1041 showed a dose-dependent effect. Similarly, epithelial transport of P56-88 was inhibited by ERW1041, but not by PX-12. Cell viability was not negatively affected by either substance at concentrations up to 100 µM. PX-12 did not reduce TG2 activity or gliadin peptide transport in confluent Caco-2 cells. This could be caused by rapid inactivation or degradation of the substance in the Caco-2 cell culture. Still, our in vitro data underline the potential of the oxidative inhibition of TG2. The fact that the TG2-specific inhibitor ERW1041 reduced the epithelial uptake of P56-88 in Caco-2 cells further strengthens the therapeutic potential of TG2 inhibitors in CD.

Factor XIII activation and substrate crosslinking can be influenced by amino acid substitutions from transglutaminase-2.

Factor XIII (FXIII) catalyzes formation of covalent crosslinks between reactive glutamines and lysines in plasma and cellular substrates. Related enzyme Transglutaminase 2 (TG2) also catalyzes crosslinking of cellular substrates, some common with FXIII. FXIII-A2 can be activated proteolytically to FXIII-A∗ by thrombin cleavage of the FXIII activation peptide (AP) and low mM CaCl2. FXIII-A2 can also be activated non-proteolytically by elevated Ca2+ levels (FXIII-A°) with up to three calcium binding sites Ca1, 2, and 3 filled. TG2 is allosterically regulated by Ca2+ and GTP. Kanchan et al (2013) reported that TG2 activity could be increased with a G224V substitution that improves Ca2+ binding. For the current project, two TG2 residues (V224 and N231) located near Ca3 were introduced into comparable positions of FXIII-A2. FXIII WT, G262V, K269N, and (G262V, K269N) were screened for their abilities to catalyze crosslinking of monodansylcadaverine (MDC, lysine mimic) into Fbg αC (233-425, glutamine substrate). For FXIII-A° generated with 100 mM CaCl2, MDC crosslinking ranked as FXIII G262V < FXIII WT ≪ FXIII K269N ≈ FXIII (G262V, K269N). FXIII V262 is proposed to impair a helical segment near Ca3 thus hindering the benefits of effective Ca2+ binding. FXIII K269N with its neutral N269 is hypothesized to enhance the lysine substrate binding surface near Ca3. Comparable crosslinkings occurred for FXIII-A∗ WT and FXIII-A∗ G262V likely due to presence of low mM Ca2+ that would primarily target Ca1 binding. The extent of MDC crosslinking ranked as FXIII-A∗ (WT ≈ G262V) ≪ (G262V, K269N) < K269N. For both FXIII-A∗ and A°, the K269N position in the vicinity of Ca3 and the lysine binding surface generated the greatest improvements in transglutaminase activity. Overall, TG2 substitutions were successfully used to tune properties of FXIII.

Inhibition of Transglutaminase 2 Reduces Peritoneal Injury in a Chlorhexidine-Induced Peritoneal Fibrosis Model

Long-term peritoneal dialysis (PD) is often associated with peritoneal dysfunction leading to withdrawal from PD. The characteristic pathologic features of peritoneal dysfunction are widely attributed to peritoneal fibrosis and angiogenesis. The detailed mechanisms remain unclear, and treatment targets in clinical settings have yet to be identified. We investigated transglutaminase 2 (TG2) as a possible novel therapeutic target for peritoneal injury. TG2 and fibrosis, inflammation, and angiogenesis were investigated in a chlorhexidine gluconate (CG)-induced model of peritoneal inflammation and fibrosis, representing a noninfectious model of PD-related peritonitis. Transforming growth factor (TGF)-β type I receptor (TGFβR-I) inhibitor and TG2-knockout mice were used for TGF-β and TG2 inhibition studies, respectively. Double immunostaining was performed to identify cells expressing TG2 and endothelial-mesenchymal transition (EndMT). In the rat CG model of peritoneal fibrosis, in situ TG2 activity and protein expression increased during the development of peritoneal fibrosis, as well as increases in peritoneal thickness and numbers of blood vessels and macrophages. TGFβR-I inhibitor suppressed TG2 activity and protein expression, as well as peritoneal fibrosis and angiogenesis. TGF-β1 expression, peritoneal fibrosis, and angiogenesis were suppressed in TG2-knockout mice. TG2 activity was detected by α-smooth muscle actin-positive myofibroblasts, CD31-positive endothelial cells, and ED-1-positive macrophages. CD31-positive endothelial cells in the CG model were α-smooth muscle actin-positive, vimentin-positive, and vascular endothelial-cadherin-negative, suggesting EndMT. In the CG model, EndMT was suppressed in TG2-knockout mice. TG2 was involved in the interactive regulation of TGF-β. As inhibition of TG2 reduced peritoneal fibrosis, angiogenesis, and inflammation associated with TGF-β and vascular endothelial growth factor-A suppression, TG2 may provide a new therapeutic target for ameliorating peritoneal injuries in PD.

Cytosolic TGM2 promotes malignant progression in gastric cancer by suppressing the TRIM21-mediated ubiquitination/degradation of STAT1 in a GTP binding-dependent modality.

Previous studies have revealed the critical role of transglutaminase 2 (TGM2) as a potential therapeutic target in cancers, but the oncogenic roles and underlying mechanisms of TGM2 in gastric cancer (GC) are not fully understood. In this study, we examined the role and potential mechanism of TGM2 in GC. Western blotting, immunohistochemistry, CCK8, colony formation and transwell assays were used to measure TGM2 expression in the GC cells and tissues and to examine the in vitro role of TGM2 in GC. Xenograft and in vivo metastasis experiments were performed to examine the in vivo role of TGM2 in GC. Gene set enrichment analysis, quantitative PCR and western blotting were conducted to screen for potential TGM2 targets involved in GC. Gain/loss-of-function and rescue experiments were conducted to detect the biological roles of STAT1 in GC cells in the context of TGM2. Co-immunoprecipitation, mass spectrometry, quantitative PCR and western blotting were conducted to identify STAT1-interacting proteins and elucidate their regulatory mechanisms. Mutations in TGM2 and two molecules (ZM39923 and A23187) were used to identify the enzymatic activity of TGM2 involved in the malignant progression of GC and elucidate the underlying mechanism. In this study, we demonstrated elevated TGM2 expression in the GC tissues, which closely related to pathological grade, and predicted poor survival in patients with GC. TGM2 overexpression or knockdown promoted (and inhibited) cell proliferation, migration, and invasion, which were reversed by STAT1 knockdown or overexpression. Further studies showed that TGM2 promoted GC progression by inhibiting STAT1 ubiquitination/degradation. Then, tripartite motif-containing protein 21 (TRIM21) was identified as a ubiquitin E3 ligase of STAT1 in GC. TGM2 maintained STAT1 stability by facilitating the dissociation of TRIM21 and STAT1 with GTP-binding enzymatic activity. A23187 abolished the role of TGM2 in STAT1 and reversed the pro-tumor role of TGM2 in vitro and in vivo. This study revealed a critical role and regulatory mechanism of TGM2 on STAT1 in GC and highlighted the potential of TGM2 as a therapeutic target, which elucidates the development of medicine or strategies by regulating the GTP-binding activity of TGM2 in GC.

Metformin prevents hypoxia-induced podocyte injury by regulating the ZEB2/TG2 axis.

Podocytes, a vital component of the glomerular filtration barrier, are vulnerable to various noxious stimuli, including Hypoxic. HIF1α that transduces hypoxic adaptations induces Transglutaminase 2 (TG2), which catalyses cross-linking of extracellular matrix proteins. In this study, we investigated the mechanism of regulation of TG2 by HIF1α. HIF1α was induced in podocytes by treating with FG4592 (Roxadustat) or hypoxia (1% oxygen) and in mice by treating with FG4592. Gene expression and protein analysis of ZEB2, TRPC6 and TG2 were performed in both experimental models. Histological and kidney function analyses were performed in mice. Data mining revealed co-expression of HIF1α, ZEB2, TRPC6 and TG2 in the chronic kidney diseases (CKD)-validated dataset. We observed elevated expression of ZEB2, TRPC6 and TG2 in FG4592-treated podocytes. Ectopic expression of ZEB2 resulted in high TRPC6 expression, elevated intracellular calcium levels and increased TG2 activity. Blocking the TRPC6 channel or inhibiting its expression partially attenuated FG4592-induced TG2 activity, whereas suppression of ZEB2 expression significantly abolished TG2 activity. Furthermore, we noticed the induction of the ZEB2/TRPC6/TG2 axis in podocytes in mice administered with FG-4592. Metformin ameliorated the HIF1α-induced podocyte injury and proteinuria in mice administered with FG-4592. This study demonstrates that HIF1α stimulates both TG2 expression and activity via ZEB2/TRPC6 axis, whereas abrogation of HIF1α by metformin prevented hypoxia-induced glomerular injury. Metformin could be explored to treat proteinuric diseases such as CKD, sleep apnea and renal Ischemia-reperfusion-injury, where hypoxia is considered a risk factor.

Identification of Novel GTP Analogs as Potent and Specific Reversible Inhibitors for Transglutaminase 2

ABSTRACT Transglutaminase 2 (TG2) is a calcium-dependent enzyme that catalyzes the N-ϵ-(γ-glutamyl) lysine bonds between side chains of glutamine and lysine residues resulting in proteolytically resistant cross-links. Increased TG2 activity and levels are involved in the pathophysiology of various diseases, including liver injury, cystic fibrosis, celiac sprue, metastatic cancers, and several neurodegenerative conditions. Inhibiting TG2 activity is considered a potential strategy to combat these diseases. Although guanine nucleotide (GTP) could inhibit TG2, its inhibitory activity decreased with increased calcium concentration. Search for GTP analogs that could strongly bind and inhibit TG2 activity is intense. This study screened the PubChem database for about two thousand GTP-like compounds for TG2. Using docking and molecular dynamics simulations we identified three compounds (C4959, C4215, and C9560) that could selectively interact with TG2. These three compounds have less affinity for several other intracellular and extracellular GTP-binding proteins suggesting selectivity for TG2. Interestingly, C9560 showed stronger interactions and better binding energy with TG2 than C4959 and C4215, suggesting that C9560 can form a more stable complex with TG2. Our study indicates that C9560, a GTP analog, could be exploited as a promising candidate to inhibit TG2-mediated fibrotic conditions.

Abstract 049: Abrogation Of Transglutaminase 2 In Vascular Smooth Muscle Cells Attenuates Doca/salt Induced Hypertension In Male Mice

Background: Transglutaminase 2 (TG2) is an enzyme involved in the pathogenesis of vascular remodeling in conditions of chronic over-nutrition and activation of the renin angiotensin aldosterone system (RAAS). Furthermore, it has been shown that pharmacologic inhibition of TG2 significantly reduces blood pressure in male rodents. However, the cell-specific role of TG2 activation in vascular smooth muscle cells (VSMC) in mediating the hypertensive response to RAAS overactivation has not been explored. Methods: We generated a novel inducible model (tamoxifen dose: 50 mg/kg/d oral for 6 weeks) of TG2 deletion in VSMC (VSMCTG2KO) by sequentially crossing Tgm2t/t floxed mice (loxP sites flanking exons 6-8 of the TG2, C polypeptide [Tgm2] gene) with male Myh11-CreERT2 positive mice. Effectiveness of the TG2 deletion was evaluated by immunohistochemistry and TG2 activity was determined by incorporation of Alexa Fluor488 Cadaverine.A cohort of fifteen-month-old wild-type and VSMC TG2KO male mice were implanted with deoxycorticosterone (DOCA; 50 mg, 21-day releasing pellets) and 1 % salt added to the drinking water. Systolic blood pressure was assessed by tail-cuff method prior to sacrifice. Ex vivo aortic stiffness was determined by atomic force microscopy. Student t-test or two-way ANOVA were used for statistical analysis as appropriate. The results were considered significant when p&lt;0.05. Three to six mice were included per treatment group. Results: administration of DOCA/salt induced increases in systolic blood pressure, augmented expression of TG2 in aorta, as well as increased aortic stiffness in wild-type mice (10.47±1.27kPA DOCA/salt vs. 3.91 + 1.01 kPa placebo). The VSMCTG2KO model exhibited 77% downregulation of TG2 expression in VSMC. VSMC TG2 KO suppressed DOCA/salt induced TG2 activity (29.13 + 2.22 arbitrary units (AU) in DOCA/salt vs 14.10 + 2.90 AU in KO cohort). This was accompanied by a significant improvement in DOCA/ salt-induced hypertension (SBP 142 ± 5.4 mmHg in DOCA/salt treated mice vs. 111.8 ± 6.2 mmHg in VSMCTG2KO). Conclusions: Our data demonstrate for the first-time the key role of TG2 activation in VSMC, in the regulation of hypertensive responses in in a male rodent model of RAAS activation.