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

Berberine alleviates neuroinflammation by downregulating NFκB/LCN2 pathway in sepsis-associated encephalopathy: network pharmacology, bioinformatics, and experimental validation

BACKGROUND

Sepsis refers to a systemic inflammatory response caused by infection, involving multiple organs. Sepsis-associated encephalopathy (SAE), as one of the most common complications in patients with severe sepsis, refers to the diffuse brain dysfunction caused by sepsis without central nervous system infection. However, there is no clear diagnostic criteria and lack of specific diagnostic markers.

METHODS

The main active ingredients of coptidis rhizoma(CR) were identified from TCMSP and SwissADME databases. SwissTargetPrediction and PharmMapper databases were used to obtain targets of CR. OMIM, DisGeNET and Genecards databases were used to explore targets of SAE. Limma differential analysis was used to identify the differential expressed genes(DEGs) in GSE167610 and GSE198861 datasets. WGCNA was used to identify feature module. GO and KEGG enrichment analysis were performed using Metascape, DAVID and STRING databases. The PPI network was constructed by STRING database and analyzed by Cytoscape software. AutoDock and PyMOL software were used for molecular docking and visualization. Cecal ligation and puncture(CLP) was used to construct a mouse model of SAE, and the core targets were verified in vivo experiments.

RESULTS

277 common targets were identified by taking the intersection of 4730 targets related to SAE and 509 targets of 9 main active ingredients of CR. 52 common DEGs were mined from GSE167610 and GSE198861 datasets. Among the 25,864 DEGs in GSE198861, LCN2 showed the most significant difference (logFC = 6.9). GO and KEGG enrichment analysis showed that these 52 DEGs were closely related to "inflammatory response" and "innate immunity". A network containing 38 genes was obtained by PPI analysis, among which LCN2 ranked the first in Degree value. Molecular docking results showed that berberine had a well binding affinity with LCN2. Animal experiments results showed that berberine could inhibit the high expression of LCN2,S100A9 and TGM2 induced by CLP in the hippocampus of mice, as well as the high expression of inflammatory factors (TNFα, IL-6 and IL-1β). In addition, berberine might reduce inflammation and neuronal cell death by partially inhibiting NFκB/LCN2 pathway in the hippocampus of CLP models, thereby alleviating SAE.

CONCLUSION

Overall, Berberine may exert anti-inflammatory effects through multi-ingredients, multi-targets and multi-pathways to partially rescue neuronal death and alleviate SAE.

Identification of Transcripts with Shared Roles in the Pathogenesis of Postmenopausal Osteoporosis and Cardiovascular Disease

Epidemiological evidence suggests existing comorbidity between postmenopausal osteoporosis (OP) and cardiovascular disease (CVD), but identification of possible shared genes is lacking. The skeletal global transcriptomes were analyzed in trans-iliac bone biopsies (n = 84) from clinically well-characterized postmenopausal women (50 to 86 years) without clinical CVD using microchips and RNA sequencing. One thousand transcripts highly correlated with areal bone mineral density (aBMD) were further analyzed using bioinformatics, and common genes overlapping with CVD and associated biological mechanisms, pathways and functions were identified. Fifty genes (45 mRNAs, 5 miRNAs) were discovered with established roles in oxidative stress, inflammatory response, endothelial function, fibrosis, dyslipidemia and osteoblastogenesis/calcification. These pleiotropic genes with possible CVD comorbidity functions were also present in transcriptomes of microvascular endothelial cells and cardiomyocytes and were differentially expressed between healthy and osteoporotic women with fragility fractures. The results were supported by a genetic pleiotropy-informed conditional False Discovery Rate approach identifying any overlap in single nucleotide polymorphisms (SNPs) within several genes encoding aBMD- and CVD-associated transcripts. The study provides transcriptional and genomic evidence for genes of importance for both BMD regulation and CVD risk in a large collection of postmenopausal bone biopsies. Most of the transcripts identified in the CVD risk categories have no previously recognized roles in OP pathogenesis and provide novel avenues for exploring the mechanistic basis for the biological association between CVD and OP.

Novel putative causal mutations associated with fat traits in Nellore cattle uncovered by eQTLs located in open chromatin regions

Intramuscular fat (IMF) and backfat thickness (BFT) are critical economic traits impacting meat quality. However, the genetic variants controlling these traits need to be better understood. To advance knowledge in this area, we integrated RNA-seq and single nucleotide polymorphisms (SNPs) identified in genomic and transcriptomic data to generate a linkage disequilibrium filtered panel of 553,581 variants. Expression quantitative trait loci (eQTL) analysis revealed 36,916 cis-eQTLs and 14,408 trans-eQTLs. Association analysis resulted in three eQTLs associated with BFT and 24 with IMF. Functional enrichment analysis of genes regulated by these 27 eQTLs revealed noteworthy pathways that can play a fundamental role in lipid metabolism and fat deposition, such as immune response, cytoskeleton remodeling, iron transport, and phospholipid metabolism. We next used ATAC-Seq assay to identify and overlap eQTL and open chromatin regions. Six eQTLs were in regulatory regions, four in predicted insulators and possible CCCTC-binding factor DNA binding sites, one in an active enhancer region, and the last in a low signal region. Our results provided novel insights into the transcriptional regulation of IMF and BFT, unraveling putative regulatory variants.

S-nitrosoglutathione reductase-dependent p65 denitrosation promotes osteoclastogenesis by facilitating recruitment of p65 to NFATc1 promoter

Osteoclasts, the exclusive bone resorptive cells, are indispensable for bone remodeling. Hence, understanding novel signaling modulators regulating osteoclastogenesis is clinically important. Nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) is a master transcription factor in osteoclastogenesis, and binding of NF-κB p65 subunit to NFATc1 promoter is required for its expression. It is well-established that DNA binding activity of p65 can be regulated by various post-translational modifications, including S-nitrosation. Recent studies have demonstrated that S-nitrosoglutathione reductase (GSNOR)-mediated protein denitrosation participated in cell fate commitment by regulating gene transcription. However, the role of GSNOR in osteoclastogenesis remains unexplored and enigmatic. Here, we investigated the effect of GSNOR-mediated denitrosation of p65 on osteoclastogenesis. Our results revealed that GSNOR was up-regulated during osteoclastogenesis in vitro. Moreover, GSNOR inhibition with a chemical inhibitor impaired osteoclast differentiation, podosome belt formation, and bone resorption activity. Furthermore, GSNOR inhibition enhanced the S-nitrosation level of p65, precluded the binding of p65 to NFATc1 promoter, and suppressed NFATc1 expression. In addition, mouse model of lipopolysaccharides (LPS)-induced calvarial osteolysis was employed to evaluate the therapeutic effect of GSNOR inhibitor in vivo. Our results indicated that GSNOR inhibitor treatment alleviated the inflammatory bone loss by impairing osteoclast formation in mice. Taken together, these data have shown that GSNOR activity is required for osteoclastogenesis by facilitating binding of p65 to NFATc1 promoter via promoting p65 denitrosation, suggesting that GSNOR may be a potential therapeutic target in the treatment of osteolytic diseases.

Mesenchymal Transglutaminase 2 Activates Epithelial ADAM17: Link to G-Protein-Coupled Receptor 56 (ADGRG1) Signalling

A wound healing model was developed to elucidate the role of mesenchymal-matrix-associated transglutaminase 2 (TG2) in keratinocyte re-epithelialisation. TG2 drives keratinocyte migratory responses by activation of disintegrin and metalloproteinase 17 (ADAM17). We demonstrate that epidermal growth factor (EGF) receptor ligand shedding leads to EGFR-transactivation and subsequent rapid keratinocyte migration on TG2-positive ECM. In contrast, keratinocyte migration was impaired in TG2 null conditions. We show that keratinocytes express the adhesion G-protein-coupled receptor, ADGRG1 (GPR56), which has been proposed as a TG2 receptor. Using ADAM17 activation as a readout and luciferase reporter assays, we demonstrate that TG2 activates GPR56. GPR56 activation by TG2 reached the same level as observed with an agonistic N-GPR56 antibody. The N-terminal GPR56 domain is required for TG2-regulated signalling response, as the constitutively active C-GPR56 receptor was not activated by TG2. Signalling required the C-terminal TG2 β-barrel domains and involved RhoA-associated protein kinase (ROCK) and ADAM17 activation, which was blocked by specific inhibitors. Cell surface binding of TG2 to the N-terminal GPR56 domain is rapid and is associated with TG2 and GPR56 endocytosis. TG2 and GPR56 represent a ligand receptor pair causing RhoA and EGFR transactivation. Furthermore, we determined a binding constant for the interaction of human TG2 with N-GPR56 and show for the first time that only the calcium-enabled "open" TG2 conformation associates with N-GPR56.

Tissue transglutaminase: a multifunctional and multisite regulator in health and disease

Tissue transglutaminase (TG2) is a widely distributed multifunctional protein involved in a broad range of cellular and metabolic functions carried out in a variety of cellular compartments. In addition to transamidation, TG2 also functions as a Gα signaling protein, a protein disulfide isomerase (PDI), a protein kinase, and a scaffolding protein. In the nucleus, TG2 modifies histones and transcription factors. The PDI function catalyzes the trimerization and activation of heat shock factor-1 in the nucleus and regulates the oxidation state of several mitochondrial complexes. Cytosolic TG2 modifies proteins by the addition of serotonin or other primary amines and in this way affects cell signaling. Modification of protein-bound glutamines reduces ubiquitin-dependent proteasomal degradation. At the cell membrane, TG2 is associated with G protein-coupled receptors (GPCRs), where it functions in transmembrane signaling. TG2 is also found in the extracellular space, where it functions in protein cross-linking and extracellular matrix stabilization. Of particular importance in transglutaminase research are recent findings concerning the role of TG2 in gene expression, protein homeostasis, cell signaling, autoimmunity, inflammation, and hypoxia. Thus, TG2 performs a multitude of functions in multiple cellular compartments, making it one of the most versatile cellular proteins. Additional evidence links TG2 with multiple human diseases including preeclampsia, hypertension, cardiovascular disease, organ fibrosis, cancer, neurodegenerative diseases, and celiac disease. In conclusion, TG2 provides a multifunctional and multisite response to physiological stress.

4,4'-Methylene diphenyl diisocyanate exposure induces expression of alternatively activated macrophage-associated markers and chemokines partially through Krüppel-like factor 4 mediated signaling in macrophages

Occupational exposure to the most widely used monomeric diisocyanate (dNCO), 4,4'-methylene diphenyl diisocyanate (MDI), may lead to the development of occupational asthma (OA). Alveolar macrophages with alternatively activated (M2) phenotype have been implicated in allergic airway responses and the pathogenesis of asthma. Recent in vivo studies demonstrate that M2 macrophage-associated markers and chemokines are induced by MDI-exposure, however, the underlying molecular mechanism(s) by which this proceeds is unclear.Following MDI exposure (in vivo and in vitro) M2 macrophage-associated transcription factors (TFs), markers, and chemokines were determined by RT-qPCR, western blots, and ELISA.Expression of M2 macrophage-associated TFs and markers including Klf4/KLF4, Cd206/CD206, Tgm2/TGM2, Ccl17/CCL17, Ccl22/CCL22, and CCL24 were induced by MDI/MDI-GSH exposure in bronchoalveolar lavage cells (BALCs)/THP-1 macrophages. The expression of CD206, TGM2, CCL17, CCL22, and CCL24 are upregulated by 3.83-, 7.69-, 6.22-, 6.08-, and 1.90-fold in KLF4-overexpressed macrophages, respectively. Endogenous CD206 and TGM2 were downregulated by 1.65-5.17-fold, and 1.15-1.78-fold, whereas CCL17, CCL22, and CCL24 remain unchanged in KLF4-knockdown macrophages. Finally, MDI-glutathione (GSH) conjugate-treated macrophages show increased chemotactic ability to T-cells and eosinophils, which may be attenuated by KLF4 knockdown.Our data suggest that MDI exposure may induce M2 macrophage-associated markers partially through induction of KLF4.

Transglutaminases are oncogenic biomarkers in human cancers and therapeutic targeting of TGM2 blocks chemoresistance and macrophage infiltration in pancreatic cancer

PURPOSE

Transglutaminases (TGs) are multifunctional enzymes exhibiting transglutaminase crosslinking, as well as atypical GTPase/ATPase and kinase activities. Here, we used an integrated comprehensive analysis to assess the genomic, transcriptomic and immunological landscapes of TGs across cancers.

METHODS

Gene expression and immune cell infiltration patterns across cancers were obtained from The Cancer Genome Atlas (TCGA) database and Gene Set Enrichment Analysis (GSEA) datasets. Western blotting, immunofluorescence staining, enzyme-linked immunosorbent assays, and orthotopic xenograft models were used to validate our database-derived results.

RESULTS

We found that the overall expression of TGs (designated as the TG score) is significantly upregulated in multiple cancers and related to a worse patient survival. The expression of TG family members can be regulated through multiple mechanisms at the genetic, epigenetic and transcriptional levels. The expression of transcription factors crucial for epithelial-to-mesenchymal transition (EMT) is commonly correlated with the TG score in many cancer types. Importantly, TGM2 expression displays a close connection with chemoresistance to a wide range of chemotherapeutic drugs. We found that TGM2 expression, F13A1 expression and the overall TG score were positively correlated with the infiltration of immune cells in all cancer types tested. Functional and clinical verification revealed that a higher TGM2 expression is linked with a worse patient survival, an increased IC50 value of gemcitabine, and a higher abundance of tumor-infiltrating macrophages in pancreatic cancer. Mechanistically, we found that increased C-C motif chemokine ligand 2 (CCL2) release mediated by TGM2 contributes to macrophage infiltration into the tumor microenvironment.

CONCLUSIONS

Our results reveal the relevance and molecular networks of TG genes in human cancers and highlight the importance of TGM2 in pancreatic cancer, which may provide promising directions for immunotherapy and for addressing chemoresistance.

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.

Development of peptide-based biosensors for detecting cross-linking and deamidation activities of transglutaminases

Transglutaminases (TGs) are a protein family that catalyzes isopeptide bond formation between glutamine and lysine residues of various proteins. There are eight TG isozymes in humans, and each is involved in diverse biological phenomena due to their characteristic distribution. Abnormal activity of TG1 and TG2, which are major TG isozymes, is believed to cause various diseases, such as ichthyosis and celiac disease. To elucidate TGs' mechanisms of action and develop new therapeutic strategies, it is essential to develop bioprobes that can specifically examine the activity of each TG isozyme, which has not been sufficiently studied. We previously have identified several substrate peptide sequences containing Gln residues for each isozyme and developed a method to detect isozyme-specific activities by incorporating a labeled substrate peptide into lysine residues of proteins. We prepared the fluorescein isothiocyanate (FITC)-labeled Gln substrate peptide (FITC-K5 and FITC-T26) and Rhodamine B-labeled Lys substrate peptide (RhoB-Kpep). Each TG reaction specifically cross-linked these probe pairs, and the proximity of FITC and Rhodamine B significantly decreased the fluorescence intensity of FITC depending on the concentration and reaction time of each TG. In this study, we developed a peptide-based biosensor that quickly and easily measures TG isozyme-specific activity. This probe is expected to be helpful in elucidating TG's physiological and pathological functions and in developing compounds that modulate TG activity.

Tissue transglutaminase exacerbates renal fibrosis via alternative activation of monocyte-derived macrophages

Macrophages are important components in modulating homeostatic and inflammatory responses and are generally categorized into two broad but distinct subsets: classical activated (M1) and alternatively activated (M2) depending on the microenvironment. Fibrosis is a chronic inflammatory disease exacerbated by M2 macrophages, although the detailed mechanism by which M2 macrophage polarization is regulated remains unclear. These polarization mechanisms have little in common between mice and humans, making it difficult to adapt research results obtained in mice to human diseases. Tissue transglutaminase (TG2) is a known marker common to mouse and human M2 macrophages and is a multifunctional enzyme responsible for crosslinking reactions. Here we sought to identify the role of TG2 in macrophage polarization and fibrosis. In IL-4-treated macrophages derived from mouse bone marrow and human monocyte cells, the expression of TG2 was increased with enhancement of M2 macrophage markers, whereas knockout or inhibitor treatment of TG2 markedly suppressed M2 macrophage polarization. In the renal fibrosis model, accumulation of M2 macrophages in fibrotic kidney was significantly reduced in TG2 knockout or inhibitor-administrated mice, along with the resolution of fibrosis. Bone marrow transplantation using TG2-knockout mice revealed that TG2 is involved in M2 polarization of infiltrating macrophages derived from circulating monocytes and exacerbates renal fibrosis. Furthermore, the suppression of renal fibrosis in TG2-knockout mice was abolished by transplantation of wild-type bone marrow or by renal subcapsular injection of IL4-treated macrophages derived from bone marrow of wild-type, but not TG2 knockout. Transcriptome analysis of downstream targets involved in M2 macrophages polarization revealed that ALOX15 expression was enhanced by TG2 activation and promoted M2 macrophage polarization. Furthermore, the increase in the abundance of ALOX15-expressing macrophages in fibrotic kidney was dramatically suppressed in TG2-knockout mice. These findings demonstrated that TG2 activity exacerbates renal fibrosis by polarization of M2 macrophages from monocytes via ALOX15.

The war on hTG2: warhead optimization in small molecule human tissue transglutaminase inhibitors

Human tissue transglutaminase (hTG2) is a multifunctional enzyme with protein cross-linking and G-protein activity, both of which have been implicated in the progression of diseases such as fibrosis and cancer stem cell propagation when dysregulated, prompting the development of small molecule targeted covalent inhibitors (TCIs) possessing a crucial electrophilic 'warhead'. In recent years there have been significant advances in the library of warheads available for the design of TCIs; however, the exploration of warhead functionality in hTG2 inhibitors has remained relatively stagnant. Herein, we describe a structure-activity relationship study entailing rational design and synthesis for systematic variation of the warhead on a previously reported small molecule inhibitor scaffold, and rigorous kinetic evaluation of inhibitory efficiency, selectivity, and pharmacokinetic stability. This study reveals a strong influence on the kinetic parameters k inact and K I with even subtle variation in warhead structure, suggesting that the warhead plays a significant role in not only reactivity, but also binding affinity, which consequently extends to isozyme selectivity. Warhead structure also influences in vivo stability, which we model by measuring intrinsic reactivity with glutathione, as well as stability in hepatocytes and in whole blood, giving insight into degradation pathways and relative therapeutic potential of different functional groups. This work provides fundamental structural and reactivity information highlighting the importance of strategic warhead design for the development of potent hTG2 inhibitors.

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.

The STING/TBK1/IRF3/IFN type I pathway is defective in cystic fibrosis

Cystic fibrosis (CF) is a rare autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The most common mutation is F508del-CFTR (ΔF) which leads the encoded ion channel towards misfolding and premature degradation. The disease is characterized by chronic bronchopulmonary obstruction, inflammation and airways colonization by bacteria, which are the major cause of morbidity and mortality. The STING pathway is the main signaling route activated in the presence of both self and pathogen DNA, leading to Type I Interferon (IFN I) production and the innate immune response. In this study, we show for the first time the relationship existing in CF between resistant and recurrent opportunistic infections by Pseudomonas aeruginosa and the innate immunity impairment. We demonstrate through ex vivo and in vivo experiments that the pathway is inadequately activated in ΔF condition and the use of direct STING agonists, as 2',3'-cyclic GMP-AMP (2', 3' cGAMP), is able to restore the immune response against bacterial colonization. Indeed, upon treatment with the STING pathway agonists, we found a reduction of colony forming units (CFUs) consequent to IFN-β enhanced production in Pseudomonas aeruginosa infected bone marrow derived macrophages and lung tissues from mice affected by Cystic Fibrosis. Importantly, we also verified that the impairment detected in the primary PBMCs obtained from ΔF patients can be corrected by 2', 3' cGAMP. Our work indicates that the cGAS/STING pathway integrity is crucial in the Cystic Fibrosis response against pathogens and that the restoration of the pathway by 2', 3' cGAMP could be exploited as a possible new target for the symptomatic treatment of the disease.

Effect and mechanism of peanut skin proanthocyanidins on gliadin-induced Caco-2 celiac disease model cells

Proanthocyanidins have been shown to inhibit the signaling pathways related to oxidative stress and inflammation, also improved cell membrane integrity. The effect of peanut skin proanthocyanidins (PSPc) on CD remains unknown. In this paper, the effect and mechanism of PSPc on glial protein-induced Caco-2 cytotoxicity were studied. The results showed that PSPc may inhibit oxidative stress in DPG-induced CD model in vitro by regulating SIRT1/NRF2 pathway. By regulating SIRT1 and IκB signaling pathways, inhibit the phosphorylation of NF-κB and the deacetylation of NF-κB, inhibit inflammatory response, reduce release of inflammatory cytokines (IL-1β, IL-6, TNF-α), the cell survival rate was and the expression of TGM2 were improved, avoiding the damage of cell monolayer model. This experiment proved the prominent effect of PSPc on CD intervention. Studying the mechanism of PSPc in the treatment of CD injury will contribute to explore new therapies for CD which will be of great significance to supplement or replace gluten-free diets.

The Outside-In Journey of Tissue Transglutaminase in Cancer

Tissue transglutaminase (TG2) is a member of the transglutaminase family that catalyzes Ca²⁺-dependent protein crosslinks and hydrolyzes guanosine 5′-triphosphate (GTP). The conformation and functions of TG2 are regulated by Ca²⁺ and GTP levels; the TG2 enzymatically active open conformation is modulated by high Ca²⁺ concentrations, while high intracellular GTP promotes the closed conformation, with inhibition of the TG-ase activity. TG2’s unique characteristics and its ubiquitous distribution in the intracellular compartment, coupled with its secretion in the extracellular matrix, contribute to modulate the functions of the protein. Its aberrant expression has been observed in several cancer types where it was linked to metastatic progression, resistance to chemotherapy, stemness, and worse clinical outcomes. The N-terminal domain of TG2 binds to the 42 kDa gelatin-binding domain of fibronectin with high affinity, facilitating the formation of a complex with β-integrins, essential for cellular adhesion to the matrix. This mechanism allows TG2 to interact with key matrix proteins and to regulate epithelial to mesenchymal transition and stemness. Here, we highlight the current knowledge on TG2 involvement in cancer, focusing on its roles translating extracellular cues into activation of oncogenic programs. Improved understanding of these mechanisms could lead to new therapeutic strategies targeting this multi-functional protein.

Implications of enigmatic transglutaminase 2 (TG2) in cardiac diseases and therapeutic developments

Cardiac diseases are the leading cause of mortality and morbidity worldwide. Mounting evidence suggests that transglutaminases (TGs), tissue TG (TG2) in particular, are involved in numerous molecular responses underlying the pathogenesis of cardiac diseases. The TG family has several intra- and extracellular functions in the human body, including collagen cross-linking, angiogenesis, cell growth, differentiation, migration, adhesion as well as survival. TGs are thiol- and calcium-dependent acyl transferases that catalyze the formation of a covalent bond between the γ-carboxamide group of a glutamine residue and an amine group, thus increasing the stability, rigidity, and stiffness of the myocardial extracellular matrix (ECM). Excessive accumulation of cross-linked collagen leads to increase myocardial stiffness and fibrosis. Beyond TG2 extracellular protein cross-linking action, mounting evidence suggests that this pleiotropic TG isozyme may also promote fibrotic diseases through cell survival and profibrotic pathway activation at the signaling, transcriptional and translational levels. Due to its multiple functions and localizations, TG2 fulfils critical yet incompletely understood roles in myocardial fibrosis and associated heart diseases, such as cardiac hypertrophy, heart failure, and age-related myocardial stiffness under several conditions. This review summarizes current knowledge and existing gaps regarding the ECM-dependent and ECM-independent roles of TG2 and highlights the therapeutic prospects of targeting TG2 to treat cardiac diseases.

Tissue Transglutaminase Knock-Out Preadipocytes and Beige Cells of Epididymal Fat Origin Possess Decreased Mitochondrial Functions Required for Thermogenesis

Beige adipocytes with thermogenic function are activated during cold exposure in white adipose tissue through the process of browning. These cells, similar to brown adipocytes, dissipate stored chemical energy in the form of heat with the help of uncoupling protein 1 (UCP1). Recently, we have shown that tissue transglutaminase (TG2) knock-out mice have decreased cold tolerance in parallel with lower utilization of their epididymal adipose tissue and reduced browning. To learn more about the thermogenic function of this fat depot, we isolated preadipocytes from the epididymal adipose tissue of wild-type and TG2 knock-out mice and differentiated them in the beige direction. Although differentiation of TG2 knock-out preadipocytes is phenotypically similar to the wild-type cells, the mitochondria of the knock-out beige cells have multiple impairments including an altered electron transport system generating lower electrochemical potential difference, reduced oxygen consumption, lower UCP1 protein content, and a higher portion of fragmented mitochondria. Most of these differences are present in preadipocytes as well, and the differentiation process cannot overcome the functional disadvantages completely. TG2 knock-out beige adipocytes produce more iodothyronine deiodinase 3 (DIO3) which may inactivate thyroid hormones required for the establishment of optimal mitochondrial function. The TG2 knock-out preadipocytes and beige cells are both hypometabolic as compared with the wild-type controls which may also be explained by the lower expression of solute carrier proteins SLC25A45, SLC25A47, and SLC25A42 which transport acylcarnitine, Co-A, and amino acids into the mitochondrial matrix. As a consequence, the mitochondria in TG2 knock-out beige adipocytes probably cannot reach the energy-producing threshold required for normal thermogenic functions, which may contribute to the decreased cold tolerance of TG2 knock-out mice.

Double-Stranded RNA Enhances Matrix Metalloproteinase-1 and -13 Expressions through TLR3-Dependent Activation of Transglutaminase 2 in Dermal Fibroblasts

UV-irradiation induces the secretion of double-stranded RNA (dsRNA) derived from damaged noncoding RNAs in keratinocytes, which enhance the expression of matrix metalloproteinases (MMP) in non-irradiated dermal fibroblasts, leading to dysregulation of extracellular matrix homeostasis. However, the signaling pathway responsible for dsRNA-induced MMP expression has not been fully understood. Transglutaminase 2 (TG2) is an enzyme that modifies substrate proteins by incorporating polyamine or crosslinking of proteins, thereby regulating their functions. In this study, we showed that TG2 mediates dsRNA-induced MMP-1 expression through NF-κB activation. Treatment of poly(I:C), a synthetic dsRNA analogue binding to toll-like receptor 3 (TLR3), generates ROS, which in turn activates TG2 in dermal fibroblast. Subsequently, TG2 activity enhances translocation of p65 into the nucleus, where it augments transcription of MMP. We confirmed these results by assessing the level of MMP expression in Tlr3^−/−, TG2-knockdowned and Tgm2^−/− dermal fibroblasts after poly(I:C)-treatment. Moreover, treatment with quercetin showed dose-dependent suppression of poly(I:C)-induced MMP expression. Furthermore, ex vivo cultured skin from Tgm2^−/− mice exhibited a significantly reduced level of MMP mRNA compared with those from wild-type mice. Our results indicate that TG2 is a critical regulator in dsRNA-induced MMP expression, providing a new target and molecular basis for antioxidant therapy in preventing collagen degradation.

Erythrocyte transglutaminase-2 combats hypoxia and chronic kidney disease by promoting oxygen delivery and carnitine homeostasis

Due to lack of nuclei and de novo protein synthesis, post-translational modification (PTM) is imperative for erythrocytes to regulate oxygen (O₂) delivery and combat tissue hypoxia. Here, we report that erythrocyte transglutminase-2 (eTG2)-mediated PTM is essential to trigger O₂ delivery by promoting bisphosphoglycerate mutase proteostasis and the Rapoport-Luebering glycolytic shunt for adaptation to hypoxia, in healthy humans ascending to high altitude and in two distinct murine models of hypoxia. In a pathological hypoxia model with chronic kidney disease (CKD), eTG2 is critical to combat renal hypoxia-induced reduction of Slc22a5 transcription and OCNT2 protein levels via HIF-1α-PPARα signaling to maintain carnitine homeostasis. Carnitine supplementation is an effective and safe therapeutic approach to counteract hypertension and progression of CKD by enhancing erythrocyte O₂ delivery. Altogether, we reveal eTG2 as an erythrocyte protein stabilizer orchestrating O₂ delivery and tissue adaptive metabolic reprogramming and identify carnitine-based therapy to mitigate hypoxia and CKD progression.

Pathophysiology and immunogenetics of celiac disease

Celiac disease (CD) is a chronic inflammatory enteropathy caused by gluten (protein from wheat, rye and, barley) in genetically predisposed individuals carrying the HLA-DQ2/HLA-DQ8 genotype. This pathology has a multifactorial etiology in which HLA genes, the microbiome, gluten and, other environmental factors are involved in the development of the disease. Its pathogenesis involves both innate and adaptive immunity as well as upregulation of IL-15. The objective of this review is to examine the results of current studies on genetic and environmental variables to better understand the pathogenesis of this enteropathy. The complex etiology of celiac disease makes our understanding of the pathogenesis of the disease incomplete, and a better knowledge of the many genetic and environmental components would help us better understand the pathophysiology of celiac disease.

Cystamine reduces vascular stiffness in Western diet-fed female mice

Consumption of diets high in fat, sugar, and salt (Western diet, WD) is associated with accelerated arterial stiffening, a major independent risk factor for cardiovascular disease (CVD). Women with obesity are more prone to develop arterial stiffening leading to more frequent and severe CVD compared with men. As tissue transglutaminase (TG2) has been implicated in vascular stiffening, our goal herein was to determine the efficacy of cystamine, a nonspecific TG2 inhibitor, at reducing vascular stiffness in female mice chronically fed a WD. Three experimental groups of female mice were created. One was fed regular chow diet (CD) for 43 wk starting at 4 wk of age. The second was fed a WD for the same 43 wk, whereas a third cohort was fed WD, but also received cystamine (216 mg/kg/day) in the drinking water during the last 8 wk on the diet (WD + C). All vascular stiffness parameters assessed, including aortic pulse wave velocity and the incremental modulus of elasticity of isolated femoral and mesenteric arteries, were significantly increased in WD- versus CD-fed mice, and reduced in WD + C versus WD-fed mice. These changes coincided with respectively augmented and diminished vascular wall collagen and F-actin content, with no associated effect in blood pressure. In cultured human vascular smooth muscle cells, cystamine reduced TG2 activity, F-actin:G-actin ratio, collagen compaction capacity, and cellular stiffness. We conclude that cystamine treatment represents an effective approach to reduce vascular stiffness in female mice in the setting of WD consumption, likely because of its TG2 inhibitory capacity.NEW & NOTEWORTHY This study evaluates the novel role of transglutaminase 2 (TG2) inhibition to directly treat vascular stiffness. Our data demonstrate that cystamine, a nonspecific TG2 inhibitor, improves vascular stiffness induced by a diet rich in fat, fructose, and salt. This research suggests that TG2 inhibition might bear therapeutic potential to reduce the disproportionate burden of cardiovascular disease in females in conditions of chronic overnutrition.

Midazolam Ameliorates Hyperglycemia-Induced Glomerular Endothelial Dysfunction by Inhibiting Transglutaminase 2 in Diabetes

Midazolam is an anesthetic widely used for anxiolysis and sedation; however, to date, a possible role for midazolam in diabetic kidney disease remains unknown. Here, we investigated the effect of midazolam on hyperglycemia-induced glomerular endothelial dysfunction and elucidated its mechanism of action in kidneys of diabetic mice and human glomerular microvascular endothelial cells (HGECs). We found that, in diabetic mice, subcutaneous midazolam treatment for 6 weeks attenuated hyperglycemia-induced elevation in urine albumin/creatinine ratios. It also ameliorated hyperglycemia-induced adherens junction disruption and subsequent microvascular leakage in glomeruli of diabetic mice. In HGECs, midazolam suppressed high glucose-induced vascular endothelial-cadherin disruption and endothelial cell permeability via inhibition of intracellular Ca²⁺ elevation and subsequent generation of reactive oxygen species (ROS) and transglutaminase 2 (TGase2) activation. Notably, midazolam also suppressed hyperglycemia-induced ROS generation and TGase2 activation in glomeruli of diabetic mice and markedly improved pathological alterations in glomerular ultrastructure in these animals. Analysis of kidneys from diabetic Tgm2^−/− mice further revealed that TGase2 played a critical role in microvascular leakage. Overall, our findings indicate that midazolam ameliorates hyperglycemia-induced glomerular endothelial dysfunction by inhibiting ROS-mediated activation of TGase2.

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.

Transglutaminase 2 mediates UVB-induced matrix metalloproteinase-1 expression by inhibiting nuclear p65 degradation in dermal fibroblasts

Matrix metalloproteinases (MMPs) play a key role in tissue remodelling by cleaving extracellular matrix (ECM) components. In the skin, UV irradiation increases expression of MMPs that causes dysregulation of ECM homeostasis in dermis, leading to acceleration of skin aging. However, the mediator(s) that links UV irradiation to the upregulation of MMPs have not been fully defined. Previously, we showed that UVB irradiation activated transglutaminase 2 (TG2) in keratinocytes, eliciting an inflammatory response by activating NF-κB signalling. In this study, we reported the role of TG2 in mediating the UVB-induced expression of MMP-1. In human dermal fibroblasts, UVB irradiation enhanced the expression and activity of TG2, which in turn promotes the expression of MMP-1. Analyses of MMP-1 promoter showed that activation of the NF-κB signalling pathway, rather than AP-1, was responsible for the TG2-mediated upregulation of MMP-1. Moreover, Western blot analysis revealed that TG2 increased the activity of NF-κB by inhibiting degradation of p65 in the nucleus. Furthermore, ex vivo skin from TG2-knockout mice exhibited significantly reduced levels of MMP-1 compared to that from wild-type mice. These results indicate that TG2 functions as a mediator for the UVB-induced expression of MMP-1 in dermal fibroblasts, providing a new target for preventing skin photodamage.

Transglutaminase 2 moderates the expansion of mouse abdominal aortic aneurysms

Objective

Previously published work has indicated that transcripts encoding transglutaminase 2 (TG2) increase markedly in a rat model of abdominal aortic aneurysm. This study determines whether TG2 and the related TG, factor XIII-A (FXIII-A), protect against aortic aneurysm development in mice.

Methods

C57BL/6J wild-type, Tgm2 ^-/- knockout, F13a1 ^-/- knockout, and Tgm2 ^-/- /F13a1 ^-/- double knockout mice were subjected to laparotomy and periaortic application of CaCl₂.

Results

Tgm2 ^-/- mice showed slightly greater aortic dilatation at 6 weeks after treatment when compared with wild type. However, vessels from Tgm2 ^-/- mice, but not wild-type mice, continued to dilate up to 6 months after injury and by 24 weeks, a greater number of Tgm2 ^-/- mice had developed aneurysms (16/17 vs 10/19; P = .008). Laparotomy resulted in a high death rate in F13a1 ^-/- knockout mice, more frequently from cardiac complications than from hemorrhage, but among F13a1 ^-/- mice that survived for 6 weeks after CaCl₂ treatment, abdominal aortic aneurysm diameter was unaltered relative to wild-type mice. Laparotomy resulted in a higher death rate among Tgm2 ^-/- /F13a1 ^-/- double knockout mice, owing to an increased frequency of delayed bleeding. Surprisingly, Tgm2 ^-/- /F13a1 ^-/- double knockout mice showed a trend toward decreased dilatation of the aorta 6 weeks after injury, and this finding was replicated in Tgm2 ^-/- /F13a1 ^-/- mice subjected to carotid artery injury. Levels of transcripts encoding TG2 were not increased in the aortas of injured wild-type or F13a1 ^-/- knockout mice relative to uninjured mice, although changes in the levels of other transcripts accorded with previous descriptions of the CaCl₂ aneurysm model in mice.

Conclusions

Knockout of Tgm2, but not F13a1 exacerbates aortic dilatation, suggesting that TG2 confers protection. However, levels of TG2 messenger RNA are not acutely elevated after injury. FXIII-A plays a role in preventing postoperative damage after laparotomy, confirming previous reports that it prevents distal organ damage after trauma. TG2 promotes wound healing after surgery and, in its absence, the bleeding diathesis associated with FXIII-A deficiency is further exposed.

Transglutaminase 6 Is Colocalized and Interacts with Mutant Huntingtin in Huntington Disease Rodent Animal Models

Mammalian transglutaminases (TGs) catalyze calcium-dependent irreversible posttranslational modifications of proteins and their enzymatic activities contribute to the pathogenesis of several human neurodegenerative diseases. Although different transglutaminases are found in many different tissues, the TG6 isoform is mostly expressed in the CNS. The present study was embarked on/undertaken to investigate expression, distribution and activity of transglutaminases in Huntington disease transgenic rodent models, with a focus on analyzing the involvement of TG6 in the age- and genotype-specific pathological features relating to disease progression in HD transgenic mice and a tgHD transgenic rat model using biochemical, histological and functional assays. Our results demonstrate the physical interaction between TG6 and (mutant) huntingtin by co-immunoprecipitation analysis and the contribution of its enzymatic activity for the total aggregate load in SH-SY5Y cells. In addition, we identify that TG6 expression and activity are especially abundant in the olfactory tubercle and piriform cortex, the regions displaying the highest amount of mHTT aggregates in transgenic rodent models of HD. Furthermore, mHTT aggregates were colocalized within TG6-positive cells. These findings point towards a role of TG6 in disease pathogenesis via mHTT aggregate formation.

Co-assembly of Peptides and Carbon Nanodots: Sensitive Analysis of Transglutaminase 2

The structures assembled by peptides have attracted great attention due to their unique physicochemical properties. Moreover, the co-assembly of peptides with additional components can endow the structures with extended functions. In this work, we have explored the co-assembly of peptides and carbon nanodots (CNDs) by taking advantage of their non-covalent binding; thus, the obtained structure may show both the recognition capability of peptides and the catalytic activity of CNDs. Therefore, we have further used the assembled structure for the sensitive analysis of transglutaminase 2 with a low detection limit of 0.25 pg/mL. By simply replacing the peptide sequences or the nanomaterials, the strategy proposed in this work can be developed as a universal model to build the co-assemblies of peptides and nanomaterials, thus leading to their broader applications in biological and biomedical research.

Role of Transglutaminase 2 in Cell Death, Survival, and Fibrosis

Transglutaminase 2 (TG2) is a ubiquitously expressed enzyme catalyzing the crosslinking between Gln and Lys residues and involved in various pathophysiological events. Besides this crosslinking activity, TG2 functions as a deamidase, GTPase, isopeptidase, adapter/scaffold, protein disulfide isomerase, and kinase. It also plays a role in the regulation of hypusination and serotonylation. Through these activities, TG2 is involved in cell growth, differentiation, cell death, inflammation, tissue repair, and fibrosis. Depending on the cell type and stimulus, TG2 changes its subcellular localization and biological activity, leading to cell death or survival. In normal unstressed cells, intracellular TG2 exhibits a GTP-bound closed conformation, exerting prosurvival functions. However, upon cell stimulation with Ca²⁺ or other factors, TG2 adopts a Ca²⁺-bound open conformation, demonstrating a transamidase activity involved in cell death or survival. These functional discrepancies of TG2 open form might be caused by its multifunctional nature, the existence of splicing variants, the cell type and stimulus, and the genetic backgrounds and variations of the mouse models used. TG2 is also involved in the phagocytosis of dead cells by macrophages and in fibrosis during tissue repair. Here, we summarize and discuss the multifunctional and controversial roles of TG2, focusing on cell death/survival and fibrosis.

Spatially Resolved Identification of Transglutaminase Substrates by Proteomics in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by the invariably progressive deposition of fibrotic tissue in the lungs and overall poor prognosis. Transglutaminase 2 (TG2) is an enzyme that crosslinks glutamine and lysine residues and is involved in IPF pathogenesis. Despite the accumulating evidence implicating TG2 as a critical enzyme, the causative function and direct target of TG2 relating to this pathogenesis remain unelucidated. Here, we clarified the distributions of TG2 protein/activity and conducted quantitative proteomics analyses of possible substrates crosslinked by TG2 on unfixed lung sections in a mouse pulmonary fibrosis model. We identified 126 possible substrates as markedly increased TG2-dependently in fibrotic lung. Gene ontology analysis revealed that these identified proteins were mostly enriched in the lipid metabolic process, immune system process, and protein transport. In addition, these proteins enriched in the 21 pathways including phagosome, lipid metabolism, several immune responses, and protein processing in endoplasmic reticulum. Furthermore, the network analyses screened out the 6 clusters and top 20 hub proteins with higher scores, which are related to ER stress and peroxisome proliferator-activated receptor signals. Several enriched pathways and categories were identified, and some of which were the same terms based on transcription analysis in IPF. Our results provide novel pathological molecular networks driven by protein crosslinking via TG2, which can lead to the development of new therapeutic targets for IPF.

Tissue Transglutaminase Impairs HTR-8/SVneo Trophoblast Cell Invasion via the PI3K/AKT Signaling Pathway

OBJECTIVES

The pathogenesis of preeclampsia (PE) is associated with impaired trophoblast invasion, which results in placental insufficiency. Our earlier studies demonstrated that tissue transglutaminase (tTG) is highly expressed in human PE serum. However, whether tTG participates in trophoblast invasion remains unclear. The aim of the present study was to determine the role and mechanism of tTG in regulating matrix metalloproteinase (MMP)-2/MMP-9 expression to reduce trophoblast invasiveness in PE.

METHODS

HTR-8/SVneo cells were transfected with a lentivirus vector and small interfering RNA targeting tTG. The protein level was detected by Western blotting. Cell proliferation and apoptosis were assessed by MTS and flow cytometry assays, respectively. Cell invasion was investigated by Transwell assay. In addition, the influence of tTG on PI3K and AKT mRNA levels in HTR-8/SVneo cells was evaluated using reverse transcription-quantitative PCR.

RESULTS

tTG-overexpression inhibited HTR-8/SVneo cell proliferation and invasion and promoted apoptosis. In addition, upregulation of tTG induced an increase of PI3K and phosphorylated AKT and a decrease of MMP-2 and MMP-9 expression. tTG-knockdown significantly promoted the proliferation and invasion of HTR-8/SVneo cells and inhibited the apoptosis. Furthermore, the PI3K expression level was reduced, and the MMP-2/MMP-9 protein levels were increased.

CONCLUSION

Taken together, the present study demonstrated that tTG-overexpression inhibited HTR-8/SVneo cell invasion via reducing the expression of MMP-2 and MMP-9 by activating PI3K/AKT signaling pathway, which may lead to the occurrence or development of PE. The present data provide new insights into modulation of tTG expression as a potential therapeutic target for PE.

Tranglutaminase 2 contributes to the asthmatic inflammation by modulating activation of alveolar macrophages

BACKGROUND

Transglutaminase 2 (TG2), a multifunctional calcium-dependent acyltransferase, is upregulated in asthmatic airways and reported to play a role in the pathogenesis of allergic asthma. However, the underlying mechanism is not fully understood.

OBJECTIVE

To investigate the role of TG2 in alternative activation of alveolar macrophages by using murine asthma model.

METHODS

TG2 expression was assessed in induced sputum of 21 asthma patients and 19 healthy controls, and lung tissue of ovalbumin (OVA)-induced murine asthma model. To evaluate the role of TG2 in asthma, we developed an OVA asthma model in both TG2 null and wild-type mice. The expression of M2 macrophage markers was measured by fluorescence-activated cell sorting (FACS) after OVA sensitization and challenge. To evaluate the effect of TG2 inhibition in vitro, interleukin 4 (IL-4) or IL-13-stimulated expression of M2 macrophage markers was measured in CRL-2456 cells in the presence and absence of a TG2 inhibitor.

RESULTS

The expression of both TG2 and M2 markers was increased in the sputum of asthmatics compared with that of healthy controls. The expression of TG2 was increased in macrophages of OVA mice. Airway hyperresponsiveness, and the number of inflammatory cells, including eosinophils, was significantly reduced in TG2 null mice compared with wild-type mice. Enhanced expression of M2 markers in OVA mice was normalized by TG2 knockout. IL-4 or IL-13-stimulated expression of M2 markers in alveolar macrophages was also attenuated by TG2 inhibitor treatment in vitro.

CONCLUSION

Our results suggest that TG2-mediated modulation of alveolar macrophage polarization plays important roles in the pathogenesis of asthma.

Transglutaminase 2 as a Marker for Inflammation and Therapeutic Target in Sepsis

Sepsis results in lethal organ malfunction due to dysregulated host response to infection, which is a condition with increasing prevalence worldwide. Transglutaminase 2 (TG2) is a crosslinking enzyme that forms a covalent bond between lysine and glutamine. TG2 plays important roles in diverse cellular processes, including extracellular matrix stabilization, cytoskeletal function, cell motility, adhesion, signal transduction, apoptosis, and cell survival. We have shown that the co-culture of Candida albicans and hepatocytes activates and induces the translocation of TG2 into the nucleus. In addition, the expression and activation of TG2 in liver macrophages was dramatically induced in the lipopolysaccharide-injected and cecal ligation puncture-operated mouse models of sepsis. Based on these findings and recently published research, we have reviewed the current understanding of the relationship between TG2 and sepsis. Following the genetic and pharmacological inhibition of TG2, we also assessed the evidence regarding the use of TG2 as a potential marker and therapeutic target in inflammation and sepsis.

The impact of ICAM-1, CCL2 and TGM2 gene polymorphisms on differentiation syndrome in acute promyelocytic leukemia

Background

Although arsenic trioxide (ATO) and all-trans retinoic acid (ATRA) are well-tolerated and effective treatments for Acute Promyelocytic Leukemia (APL), Differentiation Syndrome (DS) is a lethal side effect in some patients. The pathogenesis of DS is complex and not well understood; however, it is considered as an inflammatory response due to cytokines release of differentiated cells. Moreover, adhesion molecules that are widely expressed on the surface of differentiated cells and gene expression changes of transglutaminase2 (TGM2) are mechanisms involved in the development of DS. The purpose of this study was to assess the association of single nucleotide polymorphisms (SNP) of Intercellular Adhesion Molecule-1 (ICAM-1), chemokine (C-C motif) ligand 2 (CCL2) and TGM2 as inflammatory factors with differentiation syndrome susceptibility.

Methods

DNA was extracted from 133 APL patients and 100 normal controls. Assessment according to the PETHEMA criteria revealed that 13.5% of these patients experienced differentiation syndrome. Tetra-ARMS PCR and PCR-RFLP were done to amplify DNA fragments in APL patients with and without DS. Then DNA sequencing was done to validate the results. SNPStats, SPSS and Finch TV were used to analyze the results.

Results

A significant correlation was found between rs4811528 in the TGM2 gene and differentiation syndrome susceptibility (P = 0.002, 95% CI = 1.74–18.81, OR = 5.72) while rs5498 in ICAM-1, rs1024611 in CCL2, and rs7270785 in TGM2 genes showed no correlation with differentiation syndrome. The G allele of rs7270785 and rs4811528 showed a haplotypic association with differentiation syndrome (P = 0.03, 95% CI = 1.13–13.86, OR = 3.96).

Conclusions

AA genotype of the TGM2 SNP (rs4811528) may be a risk factor for development of DS in patients with APL following the use of ATRA/ATO.

Transglutaminase 2 as a novel target in chronic kidney disease - Methods, mechanisms and pharmacological inhibition

Chronic kidney disease (CKD) is a global health problem with a prevalence of 10-15%. Progressive fibrosis of the renal tissue is a main feature of CKD, but current treatment strategies are relatively unspecific and delay, but do not prevent, CKD. Exploration of novel pharmacological targets to inhibit fibrosis development are therefore important. Transglutaminase 2 (TG2) is known to be central for extracellular collagenous matrix formation, but TG2 is a multifunctional enzyme and novel research has broadened our view on its extra- and intracellular actions. TG2 exists in two conformational states with different catalytic properties as determined by substrate availability and local calcium concentrations. The open conformation of TG2 depends on calcium and has transamidase activity, central for protein modification and cross-linking of extracellular protein components, while the closed conformation is a GTPase involved in transmembrane signaling processes. We first describe different methodologies to assess TG2 activity in renal tissue and cell cultures such as biotin cadaverine incorporation. Then we systematically review animal CKD models and preliminary studies in humans (with diabetic, IgA- and chronic allograft nephropathy) to reveal the role of TG2 in renal fibrosis. Mechanisms behind TG2 activation, TG2 externalization dependent on Syndecan-4 and interactions between TG and profibrotic molecules including transforming growth factor β and the angiotensin II receptor are discussed. Pharmacological TG2 inhibition shows antifibrotic effects in CKD. However, the translation of TG2 inhibition to treat CKD in patients is a challenge as clinical information is limited, and further studies on pharmacokinetics and efficacy of the individual compounds are required.

Transglutaminases and Obesity in Humans: Association of F13A1 to Adipocyte Hypertrophy and Adipose Tissue Immune Response

Transglutaminases TG2 and FXIII-A have recently been linked to adipose tissue biology and obesity, however, human studies for TG family members in adipocytes have not been conducted. In this study, we investigated the association of TGM family members to acquired weight gain in a rare set of monozygotic (MZ) twins discordant for body weight, i.e., heavy-lean twin pairs. We report that F13A1 is the only TGM family member showing significantly altered, higher expression in adipose tissue of the heavier twin. Our previous work linked adipocyte F13A1 to increased weight, body fat mass, adipocyte size, and pro-inflammatory pathways. Here, we explored further the link of F13A1 to adipocyte size in the MZ twins via a previously conducted TWA study that was further mined for genes that specifically associate to hypertrophic adipocytes. We report that differential expression of F13A1 (ΔHeavy-Lean) associated with 47 genes which were linked via gene enrichment analysis to immune response, leucocyte and neutrophil activation, as well as cytokine response and signaling. Our work brings further support to the role of F13A1 in the human adipose tissue pathology, suggesting a role in the cascade that links hypertrophic adipocytes with inflammation.

Sodium oleate, arachidonate, and linoleate enhance fibrinogenolysis by Russell's viper venom proteinases and inhibit FXIIIa; a role for phospholipase A2 in venom induced consumption coagulopathy

Life-threatening symptoms produced by Russell's viper (RV, Daboia russelii) envenomation result largely from venom induced consumption coagulopathy (VICC). VICC is thought to be mediated to a large degree by venom serine and metalloproteinases, as well as by snake venom phospholipase A2 (svPLA2), the most abundant constituent of RV venom (RVV). The observation that the phenolic lipid anacardic acid markedly enhances proteolytic degradation of fibrinogen by RVV proteinases led us to characterize the chemical basis of this phenomenon with results indicating that svPLA2 products may be major contributors to VICC. RESULTS: Of the chemical analogs tested, the anionic detergents sodium dodecyl sulfate, sodium deoxycholate, N-lauryl sodium sarcosine, and the sodium salts of the fatty acids arachidonic, oleic and to a lesser extend linoleic acid were able to enhance fibrinogenolysis by RVV proteinases. Enhanced Fibrinogenolysis (EF) was observed with various venom size exclusion fractions containing different proteinases, and also with trypsin, indicating that conformational changes of the substrate and increased accessibility of otherwise cryptic cleavage sites are likely to be responsible for EF. In addition to enhancing fibrinogenolysis, sodium arachidonate and oleate were found to partially inhibit thrombin induced, factor XIIIa (FXIIIa) mediated ligation of fibrin chains. In clotting experiments with fresh blood RVV was found to disrupt normal coagulation, leading to small, partial clot formation, whereas RVV pretreated with the PLA2 inhibitor Varespladib induced rapid and complete clot formation (after 5 min) compared to blood alone. CONCLUSION: The observations that fatty acid anions and anionic detergents induce conformational changes that render fibrin(ogen) more susceptible to proteolysis by RVV proteinases and that RVV-PLA2 activity (which produces FFA) is required to render blood incoagulable in clotting experiments with RVV indicate a mechanism by which the activity of highly abundant RVV-PLA2 promotes degradation and depletion of fibrin(ogen) resulting in incoagulable blood seen following RVV envenomation (VICC).

Gene disruption of medaka (Oryzias latipes) orthologue for mammalian tissue-type transglutaminase (TG2) causes movement retardation

Transglutaminases are an enzyme family that catalyses protein cross-linking essential for several biological functions. In the previous studies, we characterized the orthologues of the mammalian transglutaminase family in medaka (Oryzias latipes), an established fish model. Among the human isozymes, tissue-type transglutaminase (TG2) has multiple functions that are involved in several biological phenomena. In this study, we established medaka mutants deficient for the orthologue of human TG2 using the CRISPR/Cas9 and transcription activator-like effector nucleases systems. Although apparent morphological changes in the phenotype were not observed, movement retardation was found in the mutant fish when evaluated by a tank-diving test. Furthermore, comparative immunohistochemistry analysis using in this fish model revealed that orthologue of human TG2 was expressed at the periventricular layer of the optic tectum. Our findings provide novel insight for the relationship between tissue-type transglutaminase and the nervous system and the associated behaviour.

Transglutaminase 3: The Involvement in Epithelial Differentiation and Cancer

Transglutaminases (TGMs) contribute to the formation of rigid, insoluble macromolecular complexes, which are essential for the epidermis and hair follicles to perform protective and barrier functions against the environment. During differentiation, epidermal keratinocytes undergo structural alterations being transformed into cornified cells, which constitute a highly tough outermost layer of the epidermis, the stratum corneum. Similar processes occur during the hardening of the hair follicle and the hair shaft, which is provided by the enzymatic cross-linking of the structural proteins and keratin intermediate filaments. TGM3, also known as epidermal TGM, is one of the pivotal enzymes responsible for the formation of protein polymers in the epidermis and the hair follicle. Numerous studies have shown that TGM3 is extensively involved in epidermal and hair follicle physiology and pathology. However, the roles of TGM3, its substrates, and its importance for the integument system are not fully understood. Here, we summarize the main advances that have recently been achieved in TGM3 analyses in skin and hair follicle biology and also in understanding the functional role of TGM3 in human tumor pathology as well as the reliability of its prognostic clinical usage as a cancer diagnosis biomarker. This review also focuses on human and murine hair follicle abnormalities connected with TGM3 mutations.

Substrate-independent polymer coating with stimuli-responsive dexamethasone release for on-demand fibrosis inhibition

Tissue fibrosis caused by implantation of tissue engineering scaffolds is an urgent problem in clinical research. In this work, a substrate-independent coating with on-demand release of an antifibrotic drug has been fabricated to effectively address this issue. This coating was formed through a substrate-independent layer-by-layer (LBL) technique via a cationic polyelectrolyte (poly-diallyldimethylammonium, PDDA) and an anionic polyelectrolyte (poly-styrenesulfonate, PSS), where parts of PSS and PDDA were physically replaced by carboxyl functionalized polyethylene glycol grafted onto antifibrotic drug dexamethasone (DEX-PEG-COOH). Considering the easy generation of local inflammation after implantation, an ester bond was designed between PEG-COOH and DEX. Therefore, the overexpressed esterase under inflammatory conditions hydrolyzes the ester bond and thereby releases DEX from the film to inhibit fibrosis occurring in the tissue repair process. The in vivo capacity of this coating to restrain tissue fibrosis was investigated by a skin defect model using porous polycaprolactone (PCL) scaffolds as substrates. The experimental results showed that the fibrosis-related proteins (Col-I, TGF-β and fibronectin) and the infiltration of myofibroblasts (α-SMA) of skin tissues in the coated PCL scaffold group were significantly lower than those in the blank control group and pure PCL scaffold group. Moreover, the histological evaluations showed that the coating group could significantly decrease the deposition of collagen and meanwhile promote the partial regeneration of skin appendages. These results successfully demonstrate that the universal coating prepared with a simple protocol would be an effective strategy to address the fibrosis issues during tissue engineering.

Oláh A, Fésüs L, Mádi A. Transglutaminase 2 Has Metabolic and Vascular Regulatory Functions Revealed by In Vivo Activation of Alpha1-Adrenergic Receptor

The multifunctional tissue transglutaminase has been demonstrated to act as α1-adrenergic receptor-coupled G protein with GTPase activity in several cell types. To explore further the pathophysiological significance of this function we investigated the in vivo effects of the α1-adrenergic receptor agonist phenylephrine comparing responses in wild type and TG2-/- mice. Injection of phenylephrine, but not a beta3-adrenergic agonist (CL-316,243), resulted in the long-term decline of the respiratory exchange ratio and lower lactate concentration in TG2-/- mice indicating they preferred to utilize fatty acids instead of glucose as fuels. Measurement of tail blood pressure revealed that the vasoconstrictive effect of phenylephrine was milder in TG2-/- mice leading to lower levels of lactate dehydrogenase (LDH) isoenzymes in blood. LDH isoenzyme patterns indicated more damage in lung, liver, kidney, skeletal, and cardiac muscle of wild type mice; the latter was confirmed by a higher level of heart-specific CK-MB. Our data suggest that TG2 as an α1-adrenergic receptor-coupled G protein has important regulatory functions in alpha1-adrenergic receptor-mediated metabolic processes and vascular functions.

Amplification of transglutaminase 2 enhances tumor-promoting inflammation in gastric cancers

Tumor-promoting inflammation is a hallmark of cancer and is highly associated with tumor progression, angiogenesis, and metastasis. Tumor-associated macrophages (TAMs) are major drivers of tumor-promoting inflammation, but due to the complexity of the tumor microenvironment, the detailed regulatory mechanisms are still under investigation. Here, we investigated a novel role for transglutaminase 2 (TGM2) in the development of tumor-promoting inflammation and recruitment of TAMs to gastric cancer (GC) tissues. When estimated by array comparative genomic hybridization and droplet digital PCR, the copy numbers of the TGM2 gene were amplified in 13.6% (14/103) of GC patients and positively associated with TGM2 expression. Gene set enrichment analysis of expression microarray data for GC samples with high or low TGM2 expression showed that increased TGM2 expression was associated with tumor-promoting inflammation in GC. In addition, the expression of TGM2 was correlated with the expression of markers for macrophages, neutrophils, blood vessels, and lymphatic vessels. Overexpression of TGM2 in GC cells augmented the IL-1β-induced secretion of macrophage-recruiting chemokines and NF-κB activation. TGM2 protein levels were associated with the expression levels of the macrophage marker CD163 in human GC tissue samples. Moreover, GC patients with high expression of TGM2 had a worse prognosis than those with low expression of TGM2. These results suggest TGM2 as a novel regulator of the tumor microenvironment of GC and provide a promising target for constraining tumor-promoting inflammation.

An enzyme linked to harmful inflammation that promotes tumor growth could be a target for stomach cancer treatment. The expression of the enzyme transglutaminase 2 (TGM2) has been shown to increase in several types of cancer, but its precise role has been unclear. Sung-Yup Cho at Seoul National University College of Medicine, Korea and co-workers measured copy numbers and expression levels of TGM2 in gastric cancer cell lines and in tissue samples from patients undergoing gastrectomy. They found that higher levels of TGM2 were closely associated with increases in various genes that promote the recruitment and activity of tumor-associated macrophages, malfunctioning white blood cells that drive tumor-promoting inflammation. In addition, stomach cancer patients with higher expression of TGM2 had poorer prognoses, indicating the potential therapeutic value of targeting this enzyme.

AFF1 inhibits adipogenic differentiation via targeting TGM2 transcription

OBJECTIVES

AF4/FMR2 family member 1 (AFF1), known as a central scaffolding protein of super elongation complex (SEC), regulates gene transcription. We previously reported that AFF1 inhibited osteogenic differentiation of human mesenchymal stromal/stem cells (hMSCs). However, its role in adipogenic differentiation has not been elucidated.

MATERIALS AND METHODS

hMSCs and 3T3-L1 pre-adipocytes were cultured and induced for adipogenic differentiation. Small interfering RNAs (siRNAs) were applied to deplete AFF1 while lentiviruses expressing HA-Aff1 were used for overexpression. Oil Red O staining, triglyceride (TAG) quantification, quantitative real-time PCR (qPCR), Western blot analysis, immunofluorescence staining, RNA sequencing (RNA-seq) analysis and ChIP-qPCR were performed. To evaluate the adipogenesis in vivo, BALB/c nude mice were subcutaneously injected with Aff1-overexpressed 3T3-L1 pre-adipocytes.

RESULTS

AFF1 depletion leads to an enhanced adipogenesis in both hMSCs and 3T3-L1 pre-adipocytes. Overexpression of Aff1 in 3T3-L1 cells results in the reduction of adipogenic differentiation and less adipose tissue formation in vivo. Mechanistically, AFF1 binds to the promoter region of Tgm2 gene and regulates its transcription. Overexpression of Tgm2 largely rescues adipogenic differentiation of Aff1-deficient cells.

CONCLUSIONS

Our data indicate that AFF1 inhibits adipogenic differentiation by regulating the transcription of TGM2.

Keratinocyte transglutaminase 2 promotes CCR6+ γδT-cell recruitment by upregulating CCL20 in psoriatic inflammation

Keratinocyte-derived cytokines and chemokines amplify psoriatic inflammation by recruiting IL-17-producing CCR6⁺ γδT-cells and neutrophils. The expression of these cytokines and chemokines mainly depends on NF-κB activity; however, the pathway that activates NF-κB in response to triggering factors is poorly defined. Here, we show that transglutaminase 2 (TG2), previously reported to elicit a T_H17 response by increasing IL-6 expression in a mouse model of lung fibrosis, mediates the upregulation of cytokines and chemokines by activating NF-κB in imiquimod (IMQ)-treated keratinocytes. TG2-deficient mice exhibited reduced psoriatic inflammation in skin treated with IMQ but showed systemic immune responses similar to wild-type mice. Experiments in bone marrow (BM) chimeric mice revealed that TG2 is responsible for promoting psoriatic inflammation in non-BM-derived cells. In keratinocytes, IMQ treatment activated TG2, which in turn activated NF-κB signaling, leading to the upregulation of IL-6, CCL20, and CXCL8 and increased leukocyte migration, in vitro. Consequently, TG2-deficient mice showed markedly decreased CCR6⁺ γδT-cell and neutrophil infiltration in IMQ-treated skin. Moreover, TG2 levels were higher in psoriatic skin than in normal skin and correlated with IL-6, CXCL8, and CCL20 levels. Therefore, these results indicate that keratinocyte TG2 acts as a critical mediator in the amplification of psoriatic inflammation.

Infection-driven activation of transglutaminase 2 boosts glucose uptake and hexosamine biosynthesis in epithelial cells

Transglutaminase 2 (TG2) is a ubiquitously expressed enzyme with transamidating activity. We report here that both expression and activity of TG2 are enhanced in mammalian epithelial cells infected with the obligate intracellular bacteria Chlamydia trachomatis. Genetic or pharmacological inhibition of TG2 impairs bacterial development. We show that TG2 increases glucose import by up-regulating the transcription of the glucose transporter genes GLUT-1 and GLUT-3. Furthermore, TG2 activation drives one specific glucose-dependent pathway in the host, i.e., hexosamine biosynthesis. Mechanistically, we identify the glucosamine:fructose-6-phosphate amidotransferase (GFPT) among the substrates of TG2. GFPT modification by TG2 increases its enzymatic activity, resulting in higher levels of UDP-N-acetylglucosamine biosynthesis and protein O-GlcNAcylation. The correlation between TG2 transamidating activity and O-GlcNAcylation is disrupted in infected cells because host hexosamine biosynthesis is being exploited by the bacteria, in particular to assist their division. In conclusion, our work establishes TG2 as a key player in controlling glucose-derived metabolic pathways in mammalian cells, themselves hijacked by C. trachomatis to sustain their own metabolic needs.

Transglutaminase 3 Reduces the Severity of Psoriasis in Imiquimod-Treated Mouse Skin

Four transglutaminase (TG) isoforms have been detected in epidermal keratinocytes: TG1, TG2, TG3, and TG5. Except for TG1 and TG3, their contribution to keratinocyte development and structure remains undefined. In this paper, we focused on the roles of TG2 and TG3 in imiquimod-induced psoriasis in mouse skin. We evaluated the severity of psoriasis markers in the skin of imiquimod-treated TG3 null and TG2 null mice. Our results showed that compromised TG3KO mouse skin was more responsive than WT or TG2KO mouse skin to the action of the pro-inflammatory drug imiquimod.

Constitutive Differential Features of Type 2 Transglutaminase in Cells Derived from Celiac Patients and from Healthy Subjects

Type 2 transglutaminase (TG2) is a ubiquitous enzyme able to modify gliadin peptides introduced into the organism through the diet. By means of its catalytic activity, TG2 seems to have an important pathogenetic role in celiac disease (CD), an inflammatory intestinal disease caused by the ingestion of gluten-containing cereals. A strong autoimmune response to TG2 characterizes CD development. Anti-TG2 antibodies specifically derange the uptake of the α-gliadin peptide 31–43 by control, but not by celiac dermal fibroblasts, underlying some different constitutive features regarding TG2 in healthy and celiac subjects. Our aim was to investigate whether these differences depended on a different TG2 subcellular distribution and whether peptide 31–43 differentially regulated TG2 expression and activity in cells of the two groups of subjects. We found that TG2 was more abundantly associated with membranes of celiac fibroblasts than of control cells, in particular with the early endosomal and autophagic compartments. We also found that peptide 31–43 differentially affected TG2 expression and activity in the two groups of cells, activating TG2 more in control than in celiac cells and inducing TG2 expression in celiac cells, but not in control ones. The different TG2 subcellular localization and the different way the peptide 31–43 modulates TG2 activity and availability into control and CD cells suggested that TG2 is involved in the definition of a constitutive CD cellular phenotype, thus having an important and still undefined role in CD pathogenesis.