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 ß-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.

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.

Mutations in TGM6 induce the unfolded protein response in SCA35.

Spinocerebellar ataxia type 35 (SCA35) is a rare autosomal-dominant neurodegenerative disease caused by mutations in the TGM6 gene, which codes for transglutaminase 6 (TG6). Mutations in TG6 induce cerebellar degeneration by an unknown mechanism. We identified seven patients bearing new mutations in TGM6. To gain insights into the molecular basis of mutant TG6-induced neurotoxicity, we analyzed all the seven new TG6 mutants and the five TG6 mutants previously linked to SCA35. We found that the wild-type (TG6-WT) protein mainly localized to the nucleus and perinuclear area, whereas five TG6 mutations showed nuclear depletion, increased accumulation in the perinuclear area, insolubility and loss of enzymatic function. Aberrant accumulation of these TG6 mutants in the perinuclear area led to activation of the unfolded protein response (UPR), suggesting that specific TG6 mutants elicit an endoplasmic reticulum stress response. Mutations associated with activation of the UPR caused death of primary neurons and reduced the survival of novel Drosophila melanogaster models of SCA35. These results indicate that mutations differently impacting on TG6 function cause neuronal dysfunction and death through diverse mechanisms and highlight the UPR as a potential therapeutic target for patient treatment.

Neurologic Deficits in Patients With Newly Diagnosed Celiac Disease Are Frequent and Linked With Autoimmunity to Transglutaminase 6.

BACKGROUND & AIMS: Celiac disease is an autoimmune disorder induced by ingestion of gluten that affects 1% of the population and is characterized by gastrointestinal symptoms, weight loss, and anemia. We evaluated the presence of neurologic deficits and investigated whether the presence of antibodies to Transglutaminase 6 (TG6) increases the risk of neurologic defects in patients with a new diagnosis of celiac disease. METHODS: We performed a prospective cohort study at a secondary-care gastroenterology center of 100 consecutive patients who received a new diagnosis of celiac disease based on gastroscopy and duodenal biopsy. We collected data on neurologic history, and patients were evaluated in a clinical examination along with magnetic resonance imaging of the brain, magnetic resonance (MR) spectroscopy of the cerebellum, and measurements of antibodies against TG6 in serum samples. The first 52 patients recruited underwent repeat MR spectroscopy at 1 year after a gluten-free diet (GFD). The primary aim was to establish if detection of antibodies against TG6 can be used to identify patients with celiac disease and neurologic dysfunction. RESULTS: Gait instability was reported in 24% of the patients, persisting sensory symptoms in 12%, and frequent headaches in 42%. Gait ataxia was found in 29% of patients, nystagmus in 11%, and distal sensory loss in 10%. Sixty percent of patients had abnormal results from magnetic resonance imaging, 47% had abnormal results from MR spectroscopy of the cerebellum, and 25% had brain white matter lesions beyond that expected for their age group. Antibodies against TG6 were detected in serum samples from 40% of patients-these patients had significant atrophy of subcortical brain regions compared with patients without TG6 autoantibodies. In patients with abnormal results from MR spectroscopy of the cerebellum, those on the GFD had improvements detected in the repeat MR spectroscopy 1 year later. CONCLUSIONS: In a prospective cohort study of patients with a new diagnosis of celiac disease at a gastroenterology clinic, neurologic deficits were common and 40% had circulating antibodies against TG6. We observed a significant reduction in volume of specific brain regions in patients with TG6 autoantibodies, providing evidence for a link between autoimmunity to TG6 and brain atrophy in patients with celiac disease. There is a need for early diagnosis, increased awareness of the neurologic manifestations among clinicians, and reinforcement of adherence to a strict GFD by patients to avoid permanent neurologic disability.

Anti-transglutaminase 6 Antibody Development in Children With Celiac Disease Correlates With Duration of Gluten Exposure.

OBJECTIVES: Antibodies against transglutaminase 6 (anti-TG6) have been implicated in neurological manifestations in adult patients with genetic gluten intolerance, and it is unclear whether autoimmunity to TG6 develops following prolonged gluten exposure. We measured the anti-TG6 in children with celiac disease (CD) at the diagnosis time to establish a correlation between these autoantibodies and the duration of gluten exposure. We investigated a correlation between anti-TG6 and the presence of neurological disorders. METHODS: Anti-TG6 (IgA/IgG) were measured by ELISA in sera of children with biopsy-proven CD and of children experiencing gastrointestinal disorders. CD patients positive for anti-TG6 were retested after 2 years of gluten-free diet (GFD). RESULTS: We analyzed the sera of 274 CD children and of 121 controls. Anti-TG6 were detected in 68/274 (25%) CD patients and in 19/121 (16%) controls, with significant difference between the 2 groups (P = 0.04). None of the CD patients and of the controls testing positive for anti-TG6 were experiencing neurological disorders. Eleven of 18 (61%) CD patients with other autoimmune diseases were positive for anti-TG6. In CD patients, a significant correlation between the gluten exposure before the CD diagnosis and anti-TG6 concentration was found (P = 0.006 for IgA; P < 0.0001 for IgG). After GFD anti-TG6 concentrations were significantly reduced (P < 0.001). No significant correlation was observed between anti-TG6 and anti-TG2 serum concentrations. CONCLUSIONS: Anti-TG6 are more prevalent in children with untreated CD in the absence of overt neurological disorders. The synthesis of the anti-TG6 is related to a longer exposure to gluten before the CD diagnosis, and the autoimmunity against TG6 is gluten dependent and disappeared during GFD.

P2X7 receptor activation regulates rapid unconventional export of transglutaminase-2.

Transglutaminases (denoted TG or TGM) are externalized from cells via an unknown unconventional secretory pathway. Here, we show for the first time that purinergic signaling regulates active secretion of TG2 (also known as TGM2), an enzyme with a pivotal role in stabilizing extracellular matrices and modulating cell-matrix interactions in tissue repair. Extracellular ATP promotes TG2 secretion by macrophages, and this can be blocked by a selective antagonist against the purinergic receptor P2X7 (P2X7R, also known as P2RX7). Introduction of functional P2X7R into HEK293 cells is sufficient to confer rapid, regulated TG2 export. By employing pharmacological agents, TG2 release could be separated from P2X7R-mediated microvesicle shedding. Neither Ca(2+) signaling alone nor membrane depolarization triggered TG2 secretion, which occurred only upon receptor membrane pore formation and without pannexin channel involvement. A gain-of-function mutation in P2X7R associated with autoimmune disease caused enhanced TG2 externalization from cells, and this correlated with increased pore activity. These results provide a mechanistic explanation for a link between active TG2 secretion and inflammatory responses, and aberrant enhanced TG2 activity in certain autoimmune conditions.

P2X7 receptor-mediated TG2 externalization: a link to inflammatory arthritis?

Transglutaminases have important roles in stabilizing extracellular protein assemblies in tissue repair processes but some reaction products can stimulate immune activation, leading to chronic inflammatory conditions or autoimmunity. Exacerbated disease in models of inflammatory arthritis has been ascribed to sustained extracellular enzyme activity alongside formation of select protein modifications. Here, we review the evidence, with a focus on the link between P2X7R signaling and TG2 export, a pathway that we have recently discovered which ties extracellular protein modifications into the danger signal-mediated innate immune response. These recent insights offer new opportunities for therapeutic intervention.

Neurological Dysfunction in Coeliac Disease and Non-Coeliac Gluten Sensitivity.

OBJECTIVES: Non-coeliac gluten sensitivity (NCGS) refers to patients with primarily gastrointestinal symptoms without enteropathy that symptomatically benefit from gluten-free diet (GFD). Little is known about its pathophysiology, propensity to neurological manifestations, and if these differ from patients with coeliac disease (CD). We investigated the clinical and immunological characteristics of patients presenting with neurological manifestations with CD and those with NCGS. METHODS: We compared clinical, neurophysiological, and imaging data of patients with CD and NCGS presenting with neurological dysfunction assessed and followed up regularly over a period of 20 years. RESULTS: Out of 700 patients, 562 were included. Exclusion criteria included no bowel biopsy to confirm CD, no HLA type available, and failure to adhere to GFD. All patients presented with neurological dysfunction and had circulating anti-gliadin antibodies. Out of 562 patients, 228 (41%) had evidence of enteropathy (Group 1, CD) and 334 (59%) did not (Group 2, NCGS). The most common neurological manifestations were cerebellar ataxia, peripheral neuropathy, and encephalopathy. There was a greater proportion of patients with encephalopathy in Group 1 and with a greater proportion of neuropathy in Group 2. The severity of ataxia did not differ between the two groups. Patients in Group 1 had more severe neuropathy. All patients from both groups responded to gluten-free diet. Anti-tissue transglutaminase (TG2) antibodies were found in 91% of patients in Group 1 and in 29% of patients in Group 2. Comparison between those patients in Group 2 with HLA-DQ2/DQ8 and those without as well as those with positive TG2 compared with those with negative TG2 antibodies identified no differences within these subgroups. Serological positivity for TG6 antibodies was similar in the two groups (67 and 60%). CONCLUSIONS: The neurological manifestations of CD and NCGS are similar and equally responsive to a GFD suggestive of common pathophysiological mechanisms.

Consensus Paper: Neuroimmune Mechanisms of Cerebellar Ataxias.

In the last few years, a lot of publications suggested that disabling cerebellar ataxias may develop through immune-mediated mechanisms. In this consensus paper, we discuss the clinical features of the main described immune-mediated cerebellar ataxias and address their presumed pathogenesis. Immune-mediated cerebellar ataxias include cerebellar ataxia associated with anti-GAD antibodies, the cerebellar type of Hashimoto's encephalopathy, primary autoimmune cerebellar ataxia, gluten ataxia, Miller Fisher syndrome, ataxia associated with systemic lupus erythematosus, and paraneoplastic cerebellar degeneration. Humoral mechanisms, cell-mediated immunity, inflammation, and vascular injuries contribute to the cerebellar deficits in immune-mediated cerebellar ataxias.

Gluten-related disorders: gluten ataxia.

The term gluten-related disorders (GRD) refers to a spectrum of diverse clinical manifestations triggered by the ingestion of gluten in genetically susceptible individuals. They include both intestinal and extraintestinal manifestations. Gluten ataxia (GA) is one of the commonest neurological manifestations of GRD. It was originally defined as otherwise idiopathic sporadic ataxia in the presence of circulating antigliadin antibodies of IgA and/or IgG type. Newer more specific serological markers have been identified but are not as yet readily available. GA has a prevalence of 15% amongst all ataxias and 40% of all idiopathic sporadic ataxias. It usually presents with gait and lower limb ataxia. It is of insidious onset with a mean age at onset of 53 years. Up to 40% of patients have evidence of enteropathy on duodenal biopsy. Gastrointestinal symptoms are seldom prominent and are not a reliable indicator for the presence of enteropathy. Furthermore, the presence of enteropathy does not influence the response to a gluten-free diet. Most patients will stabilise or improve with strict adherence to gluten-free diet depending on the duration of the ataxia prior to the treatment. Up to 60% of patients with GA have evidence of cerebellar atrophy on MR imaging, but all patients have spectroscopic abnormalities primarily affecting the vermis. Recent evidence suggests that patients with newly diagnosed coeliac disease presenting to the gastroenterologists have abnormal MR spectroscopy at presentation associated with clinical evidence of subtle cerebellar dysfunction. The advantage of early diagnosis and treatment (mean age 42 years in patients presenting with gastrointestinal symptoms vs. 53 years in patients presenting with ataxia) may protect the first group from the development and/or progression of neurological dysfunction.

Cerebellar degeneration in gluten ataxia is linked to microglial activation.

Gluten sensitivity has long been recognized exclusively for its gastrointestinal involvement; however, more recent research provides evidence for the existence of neurological manifestations that can appear in combination with or independent of the small bowel manifestations. Amongst all neurological manifestations of gluten sensitivity, gluten ataxia is the most commonly occurring one, accounting for up to 40% of cases of idiopathic sporadic ataxia. However, despite its prevalence, its neuropathological basis is still poorly defined. Here, we provide a neuropathological characterization of gluten ataxia and compare the presence of neuroinflammatory markers glial fibrillary acidic protein, ionized calcium-binding adaptor molecule 1, major histocompatibility complex II and cluster of differentiation 68 in the central nervous system of four gluten ataxia cases to five ataxia controls and seven neurologically healthy controls. Our results demonstrate that severe cerebellar atrophy, cluster of differentiation 20+ and cluster of differentiation 8+ lymphocytic infiltration in the cerebellar grey and white matter and a significant upregulation of microglial immune activation in the cerebellar granular layer, molecular layer and cerebellar white matter are features of gluten ataxia, providing evidence for the involvement of both cellular and humoral immune-mediated processes in gluten ataxia pathogenesis.

Transglutaminase 6: a protein associated with central nervous system development and motor function.

Transglutaminases (TG) form a family of enzymes that catalyse various post-translational modifications of glutamine residues in proteins and peptides including intra- and intermolecular isopeptide bond formation, esterification and deamidation. We have characterized a novel member of the mammalian TG family, TG6, which is expressed in a human carcinoma cell line with neuronal characteristics and in mouse brain. Besides full-length protein, alternative splicing results in a short variant lacking the second ß-barrel domain in man and a variant with truncated ß-sandwich domain in mouse. Biochemical data show that TG6 is allosterically regulated by Ca(2+) and guanine nucleotides. Molecular modelling indicates that TG6 could have Ca(2+) and GDP-binding sites related to those of TG3 and TG2, respectively. Localization of mRNA and protein in the mouse identified abundant expression of TG6 in the central nervous system. Analysis of its temporal and spatial pattern of induction in mouse development indicates an association with neurogenesis. Neuronal expression of TG6 was confirmed by double-labelling of mouse forebrain cells with cell type-specific markers. Induction of differentiation in mouse Neuro 2a cells with NGF or dibutyryl cAMP is associated with an upregulation of TG6 expression. Familial ataxia has recently been linked to mutations in the TGM6 gene. Autoantibodies to TG6 were identified in immune-mediated ataxia in patients with gluten sensitivity. These findings suggest a critical role for TG6 in cortical and cerebellar neurons.

Coeliac disease, epilepsy, and cerebral calcifications: association with TG6 autoantibodies.

A 4-year-old boy presented with occipital seizures but normal initial neuroimaging and proved refractory to antiepileptic medications. On repeat neuroimaging after 1 year, he had developed bi-occipital calcification and was then found to have positive coeliac serology. He was diagnosed with coeliac disease, epilepsy, and cerebral calcifications (CEC) and became seizure free after starting the gluten-free diet. Positive antibody binding to neurons and glia was demonstrated on indirect immunofluorescence. High levels of immunoglobulin-A directed against transglutaminase isoenzyme 6 (TG6) were found in the patient's serum. The positive response to the diet, TG6 antibodies, and neuronal antibody binding suggest that CEC might be autoimmune in nature, as in other extra-intestinal manifestations of gluten-related diseases, such as gluten ataxia.

Decorin GAG synthesis and TGF-ß signaling mediate Ox-LDL-induced mineralization of human vascular smooth muscle cells.

OBJECTIVE: Decorin and oxidized low-density lipoprotein (Ox-LDL) independently induce osteogenic differentiation of vascular smooth muscle cells (VSMCs). We aimed to determine whether decorin glycosaminoglycan (GAG) chain synthesis contributes to Ox-LDL-induced differentiation and calcification of human VSMCs in vitro. METHODS AND RESULTS: Human VSMCs treated with Ox-LDL to induce oxidative stress showed increased alkaline phosphatase (ALP) activity, accelerated mineralization, and a difference in both decorin GAG chain biosynthesis and CS/DS structure compared with untreated controls. Ox-LDL increased mRNA abundance of both xylosyltransferase (XT)-I, the key enzyme responsible for GAG chain biosynthesis and Msx2, a marker of osteogenic differentiation. Furthermore, downregulation of XT-I expression using small interfering RNA blocked Ox-LDL-induced VSMC mineralization. Adenoviral-mediated overexpression of decorin, but not a mutated unglycanated form, accelerated mineralization of VSMCs, suggesting GAG chain addition on decorin is crucial for the process of differentiation. The decorin-induced VSMC osteogenic differentiation involved activation of the transforming growth factor (TGF)-ß pathway, because it was attenuated by blocking of TGF-ß receptor signaling and because decorin overexpression potentiated phosphorylation of the downstream signaling molecule smad2. CONCLUSIONS: These studies provide direct evidence that oxidative stress-mediated decorin GAG chain synthesis triggers TGF-ß signaling and mineralization of VSMCs in vitro.

Features of ZED1227: The First-In-Class Tissue Transglutaminase Inhibitor Undergoing Clinical Evaluation for the Treatment of Celiac Disease.

ZED1227 is a small molecule tissue transglutaminase (TG2) inhibitor. The compound selectively binds to the active state of TG2, forming a stable covalent bond with the cysteine in its catalytic center. The molecule was designed for the treatment of celiac disease. Celiac disease is an autoimmune-mediated chronic inflammatory condition of the small intestine affecting about 1-2% of people in Caucasian populations. The autoimmune disease is triggered by dietary gluten. Consumption of staple foods containing wheat, barley, or rye leads to destruction of the small intestinal mucosa in genetically susceptible individuals, and this is accompanied by the generation of characteristic TG2 autoantibodies. TG2 plays a causative role in the pathogenesis of celiac disease. Upon activation by Ca2+, it catalyzes the deamidation of gliadin peptides as well as the crosslinking of gliadin peptides to TG2 itself. These modified biological structures trigger breaking of oral tolerance to gluten, self-tolerance to TG2, and the activation of cytotoxic immune cells in the gut mucosa. Recently, in an exploratory proof-of-concept study, ZED1227 administration clinically validated TG2 as a "druggable" target in celiac disease. Here, we describe the specific features and profiling data of the drug candidate ZED1227. Further, we give an outlook on TG2 inhibition as a therapeutic approach in indications beyond celiac disease.

Multi-Omics Analysis of Glioblastoma and Glioblastoma Cell Line: Molecular Insights Into the Functional Role of GPR56 and TG2 in Mesenchymal Transition.

G protein-coupled receptor 56 (GPR56/ADGRG1) is an adhesion GPCR with an essential role in brain development and cancer. Elevated expression of GPR56 was observed in the clinical specimens of Glioblastoma (GBM), a highly invasive primary brain tumor. However, we found the expression to be variable across the specimens, presumably due to the intratumor heterogeneity of GBM. Therefore, we re-examined GPR56 expression in public domain spatial gene expression data and single-cell expression data for GBM, which revealed that GPR56 expression was high in cellular tumors, infiltrating tumor cells, and proliferating cells, low in microvascular proliferation and peri-necrotic areas of the tumor, especially in hypoxic mesenchymal-like cells. To gain a better understanding of the consequences of GPR56 downregulation in tumor cells and other molecular changes associated with it, we generated a sh-RNA-mediated GPR56 knockdown in the GBM cell line U373 and performed transcriptomics, proteomics, and phospho-proteomics analysis. Our analysis revealed enrichment of gene signatures, pathways, and phosphorylation of proteins potentially associated with mesenchymal (MES) transition in the tumor and concurrent increase in cell invasion and migration behavior of the GPR56 knockdown GBM cells. Interestingly, our analysis also showed elevated expression of Transglutaminase 2 (TG2) - a known interactor of GPR56, in the knockdown cells. The inverse expression of GPR56 and TG2 was also observed in intratumoral, spatial gene expression data for GBM and in GBM cell lines cultured in vitro under hypoxic conditions. Integrating all these observations, we propose a putative functional link between the inverse expression of the two proteins, the hypoxic niche and the mesenchymal status in the tumor. Hypoxia-induced downregulation of GPR56 and activation of TG2 may result in a network of molecular events that contribute to the mesenchymal transition of GBM cells, and we propose a putative model to explain this functional and regulatory relationship of the two proteins.

Transglutaminase 2 is needed for the formation of an efficient phagocyte portal in macrophages engulfing apoptotic cells.

Transglutaminase 2 (TG2), a protein cross-linking enzyme with many additional biological functions, acts as coreceptor for integrin beta(3). We have previously shown that TG2(-/-) mice develop an age-dependent autoimmunity due to defective in vivo clearance of apoptotic cells. Here we report that TG2 on the cell surface and in guanine nucleotide-bound form promotes phagocytosis. Besides being a binding partner for integrin beta(3), a receptor known to mediate the uptake of apoptotic cells via activating Rac1, we also show that TG2 binds MFG-E8 (milk fat globulin EGF factor 8), a protein known to bridge integrin beta(3) to apoptotic cells. Finally, we report that in wild-type macrophages one or two engulfing portals are formed during phagocytosis of apoptotic cells that are characterized by accumulation of integrin beta(3) and Rac1. In the absence of TG2, integrin beta(3) cannot properly recognize the apoptotic cells, is not accumulated in the phagocytic cup, and its signaling is impaired. As a result, the formation of the engulfing portals, as well as the portals formed, is much less efficient. We propose that TG2 has a novel function to stabilize efficient phagocytic portals.

New serology assays can detect gluten sensitivity among enteropathy patients seronegative for anti-tissue transglutaminase.

BACKGROUND: Some patients with celiac disease (CD) may be seronegative with the commonly used test for IgA anti-tissue transglutaminase (anti-tTG) antibodies. Our aim was to explore whether newer assays incorporating synthetic deamidated gliadin-related peptides (DGPs) or other TG isoenzymes as antigen are useful for detecting gluten sensitivity in IgA anti-tTG-seronegative patients. METHODS: We assayed serum samples obtained at diagnosis from (a) anti-tTG-seronegative patients with a CD-like enteropathy (n = 12), (b) skin biopsy-proven dermatitis herpetiformis (DH) patients (n = 26), and (c) IgA anti-tTG-positive CD patients (n = 26). All patients had typical total IgA concentrations. All patients underwent intestinal biopsy and serum testing for (a) detection of IgA and IgG isotypes of both anti-DGP and anti-tTG in a single assay (tTG/DGP Screen; INOVA Diagnostics), (b) simultaneous detection of both IgA and IgG anti-DGP antibody isotypes (DGP Dual; INOVA Diagnostics), and (c) detection of antibodies to transglutaminase 3 (TG3) or transglutaminase 6 (TG6). RESULTS: All anti-tTG-seropositive patients also tested positive in anti-DGP assays. Overall, tTG/DGP Screen detected 6 (31.6%) of the 19 anti-tTG seronegatives, and anti-DGP Dual produced positive results in 5 (26.3%) of these cases. Whereas both assays detected 2 anti-tTG-negative DH patients with partial villous atrophy, they were positive in only 2 of the 5 cases with no histologically discernible mucosal damage. Testing for antibodies to TG3 and TG6 identified 7 (36.8%) of the 19 anti-tTG-negative patients, 5 of which were also positive for anti-DGP. CONCLUSIONS: Detection of anti-DGP with tTG/DGP Screen or anti-DGP Dual, or detection of antibodies to other TG isoenzymes, enhances the sensitivity for detecting gluten sensitivity among non-IgA- deficient, anti-tTG-seronegative patients with CD-like enteropathy.

TNFalpha and TGF-beta1 influence IL-18-induced IFNgamma production through regulation of IL-18 receptor and T-bet expression.

Bacterial infections can lead to a state of uncontrolled inflammation and also trigger autoimmune disease. At the centre of this are CD4(+) T cell responses in inflammatory tissues or local lymph nodes which are orchestrated by dendritic cells. IL-18 is a pro-inflammatory cytokine that drives dendritic cell maturation and mediates IFNgamma production. In this study, we demonstrate that in the dendritic precursor-like cell line KG-1, IFNgamma production induced by IL-18 is potentiated (>5-fold) by TNFalpha and completely suppressed by TGF-beta1. IL-18 stimulation rapidly activates different MAPK signalling pathways but only blocking of p38 activation alleviates IFNgamma production. The mechanism through which TNFalpha enhances IL-18 induced IFNgamma production is by promoting IL-18 receptor alpha-chain expression which results in higher levels of p38 activation and induces expression of T-bet, a transcriptional regulator of the IFNG gene. In contrast, TGF-beta1 rapidly suppresses IFNgamma production by limiting IL-18 receptor numbers at the cell surface and preventing induction of T-bet expression. TGF-beta1 experience by cells leads to sustained long-term inactivation of TNFalpha/IL-18-mediated cell activation but not IL-18 induced p38 activation suggesting transcriptional silencing of the T-BET and/or IFNG promoter independent of MAPK signalling. These results demonstrate how IL-18 activity is regulated by pro and anti-inflammatory cytokines and thereby provide insight into the mechanism that controls dendritic cell activity and ultimately leads to resolution of an inflammatory response.

Gluten T cell epitope targeting by TG3 and TG6; implications for dermatitis herpetiformis and gluten ataxia.

Transglutaminase 2 (TG2) is well characterized as the main autoantigen of celiac disease. The ability of TG2 to deamidate and crosslink gluten peptides is essential for the gluten-dependent production of TG2 specific autoantibodies. In patients with primarily extraintestinal manifestation of gluten sensitivity the repertoire of autoantibodies may be different. In dermatitis herpetiformis (DH), TG3 appears to be the target autoantigen whereas in gluten ataxia (GA) autoantibodies reactive with TG6 are present. A functional role for TG3 and TG6 in these diseases has yet to be described. It is also not known whether these enzymes can use gluten peptides implicated in the pathology as substrates. We here report that similar to TG2, TG3 and TG6 can specifically deamidate gluten T cell epitopes. However, the fine specificities of the enzymes were found to differ. TG2 can form covalent complexes with gluten by iso-peptide and thioester bonds. We found that both TG3 and TG6 were able to complex with gluten peptides through thioester linkage although less efficiently than TG2, whereas TG6 but not TG3 was able to form iso-peptide linked complexes. Our findings lend credence to the notion that TG3 and TG6 are involved in the gluten-induced autoimmune responses of DH and GA.