Transglutaminase facilitates the formation of polymers of the beta-amyloid peptide

The association between genetic variations and morphology-based brain networks changes in Alzheimer's disease

Alzheimer's disease (AD) is a highly heritable disease. The morphological changes of cortical cortex (such as, cortical thickness and surface area) in AD always accompany by the change of the functional connectivity to other brain regions and influence the short- and long-range brain network connections, causing functional deficits of AD. In this study, the first hypothesis is that genetic variations might affect morphology-based brain networks, leading to functional deficits; the second hypothesis is that protein-protein interaction (PPI) between the candidate proteins and known interacting proteins to AD might exist and influence AD. 600 470 variants and structural magnetic resonance imaging scans from 175 AD patients and 214 healthy controls were obtained from the Alzheimer's Disease Neuroimaging Initiative-1 database. A co-sparse reduced-rank regression model was fit to study the relationship between non-synonymous mutations and morphology-based brain networks. After that, PPIs between selected genes and BACE1, an enzyme that was known to be related to AD, are explored by using molecular dynamics (MD) simulation and co-immunoprecipitation (Co-IP) experiments. Eight genes affecting morphology-based brain networks were identified. The results of MD simulation showed that the PPI between TGM4 and BACE1 was the strongest among them and its interaction was verified by Co-IP. Hence, gene variations influence morphology-based brain networks in AD, leading to functional deficits. This finding, validated by MD simulation and Co-IP, suggests that the effect is robust.

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.

The Transglutaminase-2 Interactome in the APP23 Mouse Model of Alzheimer's Disease

Amyloid-beta (Aβ) deposition in the brain is closely linked with the development of Alzheimer’s disease (AD). Unfortunately, therapies specifically targeting Aβ deposition have failed to reach their primary clinical endpoints, emphasizing the need to broaden the search strategy for alternative targets/mechanisms. Transglutaminase-2 (TG2) catalyzes post-translational modifications, is present in AD lesions and interacts with AD-associated proteins. However, an unbiased overview of TG2 interactors is lacking in both control and AD brain. Here we aimed to identify these interactors using a crossbreed of the AD-mimicking APP23 mouse model with wild type and TG2 knock-out (TG2^−/−) mice. We found that absence of TG2 had no (statistically) significant effect on Aβ pathology, soluble brain levels of Aβ_1–40 and Aβ_1–42, and mRNA levels of TG family members compared to APP23 mice at 18 months of age. Quantitative proteomics and network analysis revealed a large cluster of TG2 interactors involved in synaptic transmission/assembly and cell adhesion in the APP23 brain typical of AD. Comparative proteomics of wild type and TG2^−/− brains revealed a TG2-linked pathological proteome consistent with alterations in both pathways. Our data show that TG2 deletion leads to considerable network alterations consistent with a TG2 role in (dys)regulation of synaptic transmission and cell adhesion in APP23 brains.

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.

Ablation of polyamine catabolic enzymes provokes Purkinje cell damage, neuroinflammation, and severe ataxia

BACKGROUND

Polyamine catabolism plays a key role in maintaining intracellular polyamine pools, yet its physiological significance is largely unexplored. Here, we report that the disruption of polyamine catabolism leads to severe cerebellar damage and ataxia, demonstrating the fundamental role of polyamine catabolism in the maintenance of cerebellar function and integrity.

METHODS

Mice with simultaneous deletion of the two principal polyamine catabolic enzymes, spermine oxidase and spermidine/spermine N1-acetyltransferase (Smox/Sat1-dKO), were generated by the crossbreeding of Smox-KO (Smox-/-) and Sat1-KO (Sat1-/-) animals. Development and progression of tissue injury was monitored using imaging, behavioral, and molecular analyses.

RESULTS

Smox/Sat1-dKO mice are normal at birth, but develop progressive cerebellar damage and ataxia. The cerebellar injury in Smox/Sat1-dKO mice is associated with Purkinje cell loss and gliosis, leading to neuroinflammation and white matter demyelination during the latter stages of the injury. The onset of tissue damage in Smox/Sat1-dKO mice is not solely dependent on changes in polyamine levels as cerebellar injury was highly selective. RNA-seq analysis and confirmatory studies revealed clear decreases in the expression of Purkinje cell-associated proteins and significant increases in the expression of transglutaminases and markers of neurodegenerative microgliosis and astrocytosis. Further, the α-Synuclein expression, aggregation, and polyamination levels were significantly increased in the cerebellum of Smox/Sat1-dKO mice. Finally, there were clear roles of transglutaminase-2 (TGM2) in the cerebellar pathologies manifest in Smox/Sat1-dKO mice, as pharmacological inhibition of transglutaminases reduced the severity of ataxia and cerebellar injury in Smox/Sat1-dKO mice.

CONCLUSIONS

These results indicate that the disruption of polyamine catabolism, via coordinated alterations in tissue polyamine levels, elevated transglutaminase activity and increased expression, polyamination, and aggregation of α-Synuclein, leads to severe cerebellar damage and ataxia. These studies indicate that polyamine catabolism is necessary to Purkinje cell survival, and for sustaining the functional integrity of the cerebellum.

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.

Structures of Human Transglutaminase 2: Finding Clues for Interference in Cross-linking Mediated Activity

Human transglutaminase 2 (TGase2) has various functions, including roles in various cellular processes such as apoptosis, development, differentiation, wound healing, and angiogenesis, and is linked to many diseases such as cancer. Although TGase2 has been considered an optimized drug target for the treatment of cancer, fibrosis, and neurodegenerative disorders, it has been difficult to generate TGase2-targeted drugs for clinical use because of the relatively flat and broad active site on TGase2. To design more specific and powerful inhibitors, detailed structural information about TGase2 complexed with various effector and inhibitor molecules is required. In this review, we summarized the current structural studies on TGase2, which will aid in designing drugs that can overcome the aforementioned limitations.

Interaction between tissue transglutaminase and amyloid-beta: Protein-protein binding versus enzymatic crosslinking

Self-interaction, chaperone binding and posttranslational modification of amyloid-beta (Aβ) is essential in the initiation and propagation of Aβ aggregation. Aggregation results in insoluble Aβ deposits characteristic of Alzheimer's disease (AD) brain lesions, i.e. senile plaques and cerebral amyloid angiopathy. Tissue transglutaminase (tTG) is a calcium-dependent enzyme that catalyzes posttranslational modifications including the formation of covalent ε-(γ-glutamyl)lysine isopeptide bonds (molecular crosslinks), and colocalizes with Aβ deposits in AD. Two independent groups recently found that apart from the induction of Aβ oligomerization, the blood-derived transglutaminase member FXIIIa forms stable protein-protein complexes with Aβ independent of the transamidation reaction. Here, we investigated whether also tTG forms rigid protein complexes with Aβ in the absence of catalytic activation. We found that both Aβ_1-40 and Aβ_1-42 are substrates for tTG-catalyzed crosslinking. In addition, in the absence of calcium or the presence of a peptidergic inhibitor of tTG, stable tTG-Aβ_1-40 complexes were found. Interestingly, the stable complexes between tTG and Aβ_1-40, were only found at 'physiological' concentrations of Aβ_1-40. Together, our data suggest that depending on the Aβ species at hand, and on the concentration of Aβ, rigid protein-complexes are formed between tTG and Aβ_1-40 without the involvement of the crosslinking reaction.

Opening up about Tissue Transglutaminase: When Conformation Matters More than Enzymatic Activity

Tissue transglutaminase (tTG), also referred to as type 2 transglutaminase or Gα_h, can bind and hydrolyze GTP, as well as function as a protein crosslinking enzyme. tTG is widely expressed and can be detected both inside cells and in the extracellular space. In contrast to many enzymes, the active and inactive conformations of tTG are markedly different. The catalytically inactive form of tTG adopts a compact “closed-state” conformation, while the catalytically active form of the protein adopts an elongated “open-state” conformation. tTG has long been appreciated as an important player in numerous diseases, including celiac disease, neuronal degenerative diseases, and cancer, and its roles in these diseases often depend as much upon its conformation as its catalytic activity. While its ability to promote these diseases has been traditionally thought to be dependent on its protein crosslinking activity, more recent findings suggest that the conformational state tTG adopts is also important for mediating its effects. In particular, we and others have shown that the closed-state of tTG is important for promoting cell growth and survival, while maintaining tTG in the open-state is cytotoxic. In this review, we examine the two unique conformations of tTG and how they contribute to distinct biological processes. We will also describe how this information can be used to generate novel therapies to treat diseases, with a special focus on cancer.

Structural aspects of transglutaminase 2: functional, structural, and regulatory diversity

Transglutaminase 2 (TG2) is a multi-functional protein that has both protein cross-linking and guanosine 5'-triphosphate (GTP) hydrolysis activities. The activities of this protein are controlled by many cellular factors, including calcium (Ca²⁺) and GTP, and have been implicated in several physiological activities, including apoptosis, angiogenesis, wound healing, cellular differentiation, neuronal regeneration, and bone development. TG2 is linked to many human diseases such as inflammatory disease, celiac disease, neurodegenerative disease, diabetes, tissue fibrosis, and various cancers and is one of the most dynamic enzymes in terms of its functions, structures, and regulatory mechanisms. The aim of this review was to summarize the functional, structural, and regulatory diversity of TG2, with a particular focus on the structure of TG2.

Hydroxy-substituted trans-cinnamoyl derivatives as multifunctional tools in the context of Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial pathology that requires multifaceted agents able to address its peculiar nature. In recent years, a plethora of proteins and biochemical pathways has been proposed as possible targets to counteract neurotoxicity. Although the complex scenario is not completely elucidated, close relationships are emerging among some of these actors. In particular, increasing evidence has shown that aggregation of amyloid beta (Aβ), glycogen synthase kinase 3β (GSK-3β) and oxidative stress are strictly interconnected and their concomitant modulation may have a positive and synergic effect in contrasting AD-related impairments. We designed compound 3 which demonstrated the ability to inhibit both GSK-3β (IC₅₀ = 24.36 ± 0.01 μM) and Aβ₄₂ self-aggregation (IC₅₀ = 9.0 ± 1.4 μM), to chelate copper (II) and to act as exceptionally strong radical scavenger (k_inh = 6.8 ± 0.5 · 10⁵ M^-1s^-1) even in phosphate buffer at pH 7.4 (k_inh = 3.2 ± 0.5 · 10⁵ M^-1s^-1). Importantly, compound 3 showed high-predicted blood-brain barrier permeability, did not exert any significant cytotoxic effects in immature cortical neurons up to 50 μM and showed neuroprotective properties at micromolar concentration against toxic insult induced by glutamate.

Calcium-dependent activation of transglutaminase 2 by nanosecond pulsed electric fields

Exposure of cultured human cells to nanosecond pulsed electric fields (nsPEFs) elicits various cellular events, including Ca²⁺ influx and cell death. Recently, nsPEFs have been regarded as a novel physical treatment useful for biology and medicine, but the underlying mechanism of action remains to be fully elucidated. In this study, we investigated the effect of nsPEFs on transglutaminases (TGs), enzymes that catalyze covalent protein modifications such as protein-protein crosslinking. Cellular TG activity was monitored by conjugation of cellular proteins with biotin-cadaverine, a cell-permeable pseudosubstrate for TGs. We applied nsPEFs to HeLa S3 cells and found that overall catalytic activity of cellular TGs was greatly increased in a Ca²⁺-dependent manner. The Ca²⁺ ionophore ionomycin significantly augmented nsPEF-induced TG activation, further supporting the importance of Ca²⁺. Among human TG family members, TG2 is known to be the most ubiquitously expressed, and its catalytic activity requires elevated intracellular Ca²⁺. Given the requirement of Ca²⁺ for TG activation by nsPEFs, we performed depletion of TG2 by RNA interference (RNAi). We observed that TG2 RNAi suppressed the nsPEF-induced TG activation and partially alleviated the cytotoxic effects of nsPEFs. These findings demonstrate that TG2 activation is a Ca²⁺-dependent event in nsPEF-exposed cells and exerts negative effects on cell physiology.

The Aggregation Paths and Products of Aβ42 Dimers Are Distinct from Those of the Aβ42 Monomer

Extracts of Alzheimer's disease (AD) brain that contain what appear to be sodium dodecyl sulfate-stable amyloid β-protein (Aβ) dimers potently block LTP and impair memory consolidation. Brain-derived dimers can be physically separated the Aβ monomer, consist primarily of Aβ42, and resist denaturation by chaotropic agents. In nature, covalently cross-linked Aβ dimers could be generated in two ways: by the formation of a dityrosine (DiY) or an isopeptide ε-(γ-glutamyl)-lysine (Q-K) bond. We enzymatically cross-linked recombinant Aβ42 monomer to produce DiY and Q-K dimers and then used a range of biophysical methods to study their aggregation. Both Q-K and DiY dimers aggregate to form soluble assemblies distinct from the fibrillar aggregates formed by the Aβ monomer. The results suggest that the cross-links disfavor fibril formation from Aβ dimers, thereby enhancing the concentration of soluble aggregates akin to those in aqueous extracts of AD brain. Thus, it seems that Aβ dimers may play an important role in determining the formation of soluble rather than insoluble aggregates.

Transglutaminase 2 has opposing roles in the regulation of cellular functions as well as cell growth and death

Transglutaminase 2 (TG2) is primarily known as the most ubiquitously expressed member of the transglutaminase family with Ca²⁺-dependent protein crosslinking activity; however, this enzyme exhibits multiple additional functions through GTPase, cell adhesion, protein disulfide isomerase, kinase, and scaffold activities and is associated with cell growth, differentiation, and apoptosis. TG2 is found in the extracellular matrix, plasma membrane, cytosol, mitochondria, recycling endosomes, and nucleus, and its subcellular localization is an important determinant of its function. Depending upon the cell type and stimuli, TG2 changes its subcellular localization and biological activities, playing both anti- and pro-apoptotic roles. Increasing evidence indicates that the GTP-bound form of the enzyme (in its closed form) protects cells from apoptosis but that the transamidation activity of TG2 (in its open form) participates in both facilitating and inhibiting apoptosis. A difficulty in the study and understanding of this enigmatic protein is that opposing effects have been reported regarding its roles in the same physiological and/or pathological systems. These include neuroprotective or neurodegenerative effects, hepatic cell growth-promoting or hepatic cell death-inducing effects, exacerbating or having no effect on liver fibrosis, and anti- and pro-apoptotic effects on cancer cells. The reasons for these discrepancies have been ascribed to TG2's multifunctional activities, genetic variants, conformational changes induced by the immediate environment, and differences in the genetic background of the mice used in each of the experiments. In this article, we first report that TG2 has opposing roles like the protagonist in the novel Dr. Jekyll and Mr. Hyde, followed by a summary of the controversies reported, and finally discuss the possible reasons for these discrepancies.

Catalytically active tissue transglutaminase colocalises with Aβ pathology in Alzheimer's disease mouse models

Alzheimer's disease (AD) is characterised by amyloid-beta (Aβ) protein deposition in the brain. Posttranslational modifications in Aβ play an important role in Aβ deposition. Tissue transglutaminase (tTG) is an enzyme involved in posttranslational cross-linking of proteins. tTG levels and activity are increased in AD brains, and tTG is associated with Aβ deposits and lesion-associated astrocytes in AD cases. Furthermore, Aβ is a substrate of tTG-catalysed cross-linking. To study the role of tTG in Aβ pathology, we compared tTG distribution and activity in both the APPSWE/PS1ΔE9 and APP23 mice models with human AD. Using immunohistochemistry, we found association of both tTG and in situ active tTG with Aβ plaques and vascular Aβ, in early and late stages of Aβ deposition. In addition, tTG staining colocalised with Aβ-associated reactive astrocytes. Thus, alike human AD cases, tTG was associated with Aβ depositions in these AD models. Although, distribution pattern and spatial overlay of both tTG and its activity with Aβ pathology was substantially different from human AD cases, our findings provide evidence for an early role of tTG in Aβ pathology. Yet, species differences should be taken into account when using these models to study the role of tTG in Aβ pathology.

The blood clotting Factor XIIIa forms unique complexes with amyloid-beta (Aβ) and colocalizes with deposited Aβ in cerebral amyloid angiopathy

AIMS

Cerebral amyloid angiopathy (CAA) is a key pathological hallmark of Alzheimer's disease (AD) characterized by accumulation of amyloid-beta (Aβ) protein in blood vessel walls. CAA impairs vessel functioning, affects blood brain barrier integrity and accelerates cognitive decline of AD patients. Unfortunately, mechanisms underlying Aβ deposition in the vessel wall remain largely unknown. Factor XIIIa (FXIIIa) is a blood-derived transglutaminase crucial in blood coagulation by cross-linking fibrin molecules. Evidence is mounting that blood-derived factors are present in CAA and may play a role in protein deposition in the vessel wall. We therefore investigated whether FXIIIa is present in CAA and if FXIIIa cross-link activity affects Aβ aggregation.

METHODS

Using immunohistochemistry, we investigated the distribution of FXIIIa, its activator thrombin and in situ FXIIIa activity in CAA in post-mortem AD tissue. We used surface plasmon resonance and Western blot analysis to study binding of FXIIIa to Aβ and the formation of FXIIIa-Aβ complexes, respectively. In addition, we studied cytotoxicity of FXIIIa-Aβ complexes to cerebrovascular cells.

RESULTS

FXIIIa, thrombin and in situ FXIIIa activity colocalize with the Aβ deposition in CAA. Furthermore, FXIIIa binds to Aβ with a higher binding affinity for Aβ1-42 compared with Aβ1-40 . Moreover, highly stable FXIIIa-Aβ complexes are formed independently of FXIIIa cross-linking activity that protected cerebrovascular cells from Aβ-induced toxicity in vitro.

CONCLUSIONS

Our data showed that FXIIIa colocalizes with Aβ in CAA and that FXIIIa forms unique protein complexes with Aβ that might play an important role in Aβ deposition and persistence in the vessel wall.

Crystal structure of transglutaminase 2 with GTP complex and amino acid sequence evidence of evolution of GTP binding site

Transglutaminase2 (TG2) is a multi-functional protein involved in various cellular processes, including apoptosis, differentiation, wound healing, and angiogenesis. The malfunction of TG2 causes many human disease including inflammatory disease, celiac disease, neurodegenerative diseases, tissue fibrosis, and cancers. Protein cross-linking activity, which is representative of TG2, is activated by calcium ions and suppressed by GTP. Here, we elucidated the structure of TG2 in complex with its endogenous inhibitor, GTP. Our structure showed why GTP is the optimal nucleotide for interacting with and inhibiting TG2. In addition, sequence comparison provided information describing the evolutionary scenario of GTP usage for controlling the activity of TG2.

Di-tyrosine cross-link decreases the collisional cross-section of aβ peptide dimers and trimers in the gas phase: an ion mobility study

Oligomeric forms of Aβ peptide are most likely the main synaptotoxic and neurotoxic agent in Alzheimer’s disease. Toxicity of various Aβ oligomeric forms has been confirmed in vivo and also in vitro. However, in vitro preparations were found to be orders of magnitude less toxic than oligomers obtained from in vivo sources. This difference can be explained by the presence of a covalent cross-link, which would stabilize the oligomer. In the present work, we have characterized the structural properties of Aβ dimers and trimers stabilized by di- and tri-tyrosine cross-links. Using ion mobility mass spectrometry we have compared the collisional cross-section of non-cross-linked and cross-linked species. We have found that the presence of cross-links does not generate new unique forms but rather shifts the equilibrium towards more compact oligomer types that can also be detected for non-cross-linked peptide. In consequence, more extended forms, probable precursors of off-pathway oligomeric species, become relatively destabilized in cross-linked oligomers and the pathway of oligomer evolution becomes redirected towards fibrillar structures.

Tissue transglutaminase colocalizes with extracellular matrix proteins in cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a key histopathological hallmark of Alzheimer's disease (AD) and hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D). CAA is characterized by amyloid-beta (Aβ) depositions and remodeling of the extracellular matrix (ECM) in brain vessels and plays an important role in the development and progression of both AD and HCHWA-D. Tissue transglutaminase (tTG) modulates the ECM by molecular cross-linking of ECM proteins. Here, we investigated the distribution pattern, cellular source, and activity of tTG in CAA in control, AD, and HCHWA-D cases. We observed increased tTG immunoreactivity and colocalization with Aβ in the vessel wall in early stage CAA, whereas in later CAA stages, tTG and its cross-links were present in halos enclosing the Aβ deposition. In CAA, tTG and its cross-links at the abluminal side of the vessel were demonstrated to be either of astrocytic origin in parenchymal vessels, of fibroblastic origin in leptomeningeal vessels, and of endothelial origin at the luminal side of the deposited Aβ. Furthermore, the ECM proteins fibronectin and laminin colocalized with the tTG-positive halos surrounding the deposited Aβ in CAA. However, we observed that in situ tTG activity was present throughout the vessel wall in late stage CAA. Together, our data suggest that tTG and its activity might play a differential role in the development and progression of CAA, possibly evolving from direct modulation of Aβ aggregation to cross-linking of ECM proteins resulting in ECM restructuring.

[Cross-linking in an artificial human cornea via induction of tissue transglutaminases]

PURPOSE

In recent years many three-dimensional cornea models have been developed. However, they show poor collagen stability in the stroma. Transglutaminases (Tgases) are calcium-dependent proteins which play an important role in cross-linking of the corneal stroma. The purpose of this study was to find out whether it is possible to induce in vitro cross-linking of the stroma in an artificial hemicornea model with the help of Tgases.

MATERIALS AND METHODS

For the construction of the hemicornea, human SV40 adenovector corneal epithelial cells (HCE) and human SV40 adenovector corneal keratocytes (HCK) were cultivated. Confluent HCK cells were treated for 24 h with transforming growth factor beta (TGFb) 1, 2 and 3 at different concentrations as well as with other growth factors and the treated cells were compared to untreated cultivated cells. The quantification of the expression of the Tgases by HCKs was examined with the use of real time PCR, Western blot imaging and immunochemistry.

RESULTS

All concentrations of TGFbs used resulted in a significant increase of Tgase-mRNA, Tgase protein level and Tgase activity. The Tgases remained unaffected after treatment with other growth factors in comparison to untreated control cells. Treatment of the hemicornea with TGFb2 showed a very strong contraction and haze in comparison to the untreated hemicornea.

CONCLUSION

It has been shown for the first time that TGFb induces a strong expression of Tgases in HCK cells. This effect caused an undesired contraction and haze of the human hemicornea model. Further research is necessary in order to find out whether the induction of Tgases in the HCK cells can be regulated without losing stability of the constructed hemicornea.

A mass spectrometric approach for characterization of amyloid-β aggregates and identification of their post-translational modifications

Endogenous amyloid-β (Aβ) oligomeric aggregates have been proposed as toxic agents in Alzheimer's disease (AD). Knowledge of their structures not only may provide insight into the basis of their neurotoxicities but also may reveal new targets for therapeutic drugs and diagnostic tools. However, the low levels of these Aβ oligomers have impeded structural characterization. Evidence suggests that the endogenous oligomers are covalently modified in vivo. In this report, we demonstrate an established mass spectrometry (MS) methodology called precursor ion mapping (PIM) that potentially may be applied to endogenous oligomer characterization. First, we illustrate the use of this PIM technique with a synthetic Aβ(1-40) monomer sample that had been cross-linked with transglutaminase (TGase) and digested with pepsin. From PIM analysis of an Aβ(4-13) MS/MS fragment, precursor ions were identified that corresponded to peptic fragments of three TGase cross-linked species: Aβ(4-19)--(4-19), Aβ(4-19)--(20-34), and Aβ(1-19)--(20-34). Next, we demonstrate the applicability of the PIM technique to an endogenous Aβ sample that had been purified and concentrated by immunoaffinity chromatography. Without pepsin digestion, we successfully identified the full length and C-terminally truncated monomeric Aβ species 1-35 to 1-42, along with select methionine-oxidized counterparts. Because PIM focuses only on a subpopulation of ions, namely the related precursor ions, the resulting spectra are of increased specificity and sensitivity. Therefore, this methodology shows great promise for structural analysis and identification of post-translational modification(s) in endogenous Aβ oligomers.

New insights into the functions and localization of nuclear transglutaminase 2

Transglutaminase 2 (TG2; EC 2.3.2.13) is the most abundantly expressed member of the transglutaminase family and exerts opposing effects on cell growth, differentiation and apoptosis via multiple activities, including transamidase, GTPase, cell adhesion, protein disulfide isomerase, kinase and scaffold activities. It is distributed in and around various parts of a cell, including the extracellular matrix, plasma membrane, cytosol, mitochondria and nucleus. Generally, nuclear TG2 represents only 5-7% of the total TG2 in a cell, and various stimuli will increase nuclear TG2 via cellular stress and/or an increased intracellular Ca(2+) concentration. There is increasing evidence indicating the importance of nuclear TG2 in regulating gene expression via post-translational modification of (or interaction with) transcriptional factors and related proteins. These include E2F1, hypoxia inducible factor 1, Sp1 and histones. Through this mechanism, TG2 controls cell growth or survival, differentiation and apoptosis, and is involved in the pathogenesis and/or treatment of neurodegenerative diseases, liver diseases and cancers. The balance between import from the cytoplasm to the nucleus, and export from the nucleus to the cytoplasm, determines the level of TG2 in the nucleus. Selective regulation of the expression, activity or localization of nuclear TG2 will be important for basic research, as well as clinical applications, suggesting a new era for this long-studied enzyme.

Transglutaminase 1 and its regulator tazarotene-induced gene 3 localize to neuronal tau inclusions in tauopathies

Alzheimer's disease (AD), progressive supranuclear palsy (PSP), frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), and Pick's disease (PiD) are commonly known as tauopathies. Neurodegeneration observed in these diseases is linked to neuronal fibrillary hyperphosphorylated tau protein inclusions. Transglutaminases (TGs) are inducible enzymes, capable of modifying conformational and/or structural properties of proteins by inducing molecular cross-links. Both transglutaminase 1 (TG1) and transglutaminase 2 (TG2) are abundantly expressed in the brain and are associated with fibrillary hyperphosphorylated tau protein inclusions in neurons of AD, so-called neurofibrillary tangles (NFTs). However, other data obtained by our group suggested that tau pathology in the brain may be primarily related to TG1 and not to TG2 activity. To obtain more information on this issue, we set out to investigate the association of TG1, TG2, and TG-catalysed cross-links with fibrillary hyperphosphorylated tau inclusions in tauopathies other than AD, using immunohistochemistry. We found strong TG1 and TG-catalysed cross-link staining in neuronal tau inclusions characteristic of PSP, FTDP-17 with mutations in the tau gene (FTDP-17T), and PiD brain, whereas, in contrast to AD, TG2 was only rarely observed in these inclusions. Furthermore, using a biochemical approach, we demonstrated that tau is a substrate for TG1-mediated cross-linking. Interestingly, we found co-localization of the TG1 activator, tazarotene-induced gene 3 (TIG3), in the neuronal tau inclusions of PSP, FTDP-17T, and PiD, but not in NFTs of AD cases, indicating that these tau-containing protein aggregates are not identical. We conclude that TG1-catalysed cross-linking, regulated by TIG3, might play an important role in the formation of neuronal tau inclusions in PSP, FTDP-17T, and PiD brain.

Iron enhances the neurotoxicity of amyloid β

Brain microbleeds often occur in Alzheimer's disease patients. Our previous studies have demonstrated that iron contributes to brain injury following intracerebral hemorrhage. This study investigated the effect of iron on amyloid β (Aβ)-mediated brain injury. There were two parts to this study. In first part, rats received an intracaudate injection of saline, iron, Aβ 25-35 or iron+Aβ 25-35. In the second part, rats received intracaudate injection of iron+Aβ and were treated with saline or cystamine, an inhibitor of transglutaminase. Rats were killed after 24 hours for brain edema measurement. DNA damage, neuronal death and tissue-type transglutaminase (tTG) expression were also examined. We found that brain water content in the ipsilateral caudate was higher (p<0.05) in rats injected with iron+Aβ than with iron, Aβ or saline. Combined iron+Aβ injection also resulted in more severe DNA damage (both single- and double-strand; p<0.01) and more Fluoro-Jade C staining (p<0.05). Expression of tTG increased markedly in the iron+Aβ group (p<0.05) and treatment with a tTG inhibitor reduced brain edema (p<0.05) and reduced degenerating neurons (124±25 vs. 249±50/mm(2) in vehicle-treated group, p<0.05). These results suggest that increased brain iron from microbleeds may exaggerate brain Aβ toxicity and that tTG is involved in the enhanced toxicity.

Possible role of the transglutaminases in the pathogenesis of Alzheimer's disease and other neurodegenerative diseases

Transglutaminases are ubiquitous enzymes which catalyze posttranslational modifications of proteins. Recently, transglutaminase-catalyzed post-translational modification of proteins has been shown to be involved in the molecular mechanisms responsible for human diseases. Transglutaminase activity has been hypothesized to be involved also in the pathogenetic mechanisms responsible for several human neurodegenerative diseases. Alzheimer's disease and other neurodegenerative diseases, such as Parkinson's disease, supranuclear palsy, Huntington's disease, and other polyglutamine diseases, are characterized in part by aberrant cerebral transglutaminase activity and by increased cross-linked proteins in affected brains. This paper focuses on the possible molecular mechanisms by which transglutaminase activity could be involved in the pathogenesis of Alzheimer's disease and other neurodegenerative diseases, and on the possible therapeutic effects of selective transglutaminase inhibitors for the cure of patients with diseases characterized by aberrant transglutaminase activity.

Tissue transglutaminase-mediated glutamine deamidation of beta-amyloid peptide increases peptide solubility, whereas enzymatic cross-linking and peptide fragmentation may serve as molecular triggers for rapid peptide aggregation

Tissue transglutaminase (TGase) has been implicated in a number of cellular processes and disease states, where the enzymatic actions of TGase may serve in both, cell survival and apoptosis. To date, the precise functional properties of TGase in cell survival or cell death mechanisms still remain elusive. TGase-mediated cross-linking has been reported to account for the formation of insoluble lesions in conformational diseases. We report here that TGase induces intramolecular cross-linking of β-amyloid peptide (Aβ), resulting in structural changes of monomeric Aβ. Using high resolution mass spectrometry (MS) of cross-linked Aβ peptides, we observed a shift in mass, which is, presumably associated with the loss of NH3 due to enzymatic transamidation activity and hence intramolecular peptide cross-linking. We have observed that a large population of Aβ monomers contained an 0.984 Da increase in mass at a glutamine residue, indicating that glutamine 15 serves as an indispensable substrate in TGase-mediated deamidation to glutamate 15. We provide strong analytical evidence on TGase-mediated Aβ peptide dimerization, through covalent intermolecular cross-linking and hence the formation of Aβ1-40 dimers. Our in depth analyses indicate that TGase-induced post-translational modifications of Aβ peptide may serve as an important seed for aggregation.

The role of genetic variants in human longevity

Human longevity is a complex phenotype with a strong genetic predisposition. Increasing evidence has revealed the genetic antecedents of human longevity. This article aims to review the data of various case/control association studies that examine the difference in genetic polymorphisms between long-lived people and younger subjects across different human populations. There are more than 100 candidate genes potentially involved in human longevity; this article particularly focuses on genes of the insulin/IGF-1 pathway, FOXO3A, FOXO1A, lipoprotein metabolism (e.g., APOE and PON1), and cell-cycle regulators (e.g., TP53 and P21). Since the confirmed genetic components for human longevity are few to date, further precise assessment of the genetic contributions is required. Gaining a better understanding of the contribution of genetics to human longevity may assist in the design of improved treatment methods for age-related diseases, delay the aging process, and, ultimately, prolong the human lifespan.

Biophysical analyses of synthetic amyloid-beta(1-42) aggregates before and after covalent cross-linking. Implications for deducing the structure of endogenous amyloid-beta oligomers

A neuropathological hallmark of Alzheimer's disease (AD) is the presence of large numbers of senile plaques in the brain. These deposits are rich in fibrils that are composed of 40- and 42-residue amyloid-beta (Abeta) peptides. Several lines of evidence indicate that soluble Abeta aggregates as well as fibrils are important in the etiology of AD. Low levels of endogenous soluble Abeta aggregates make them difficult to characterize, but several species in extracts of AD brains have been detected by gel electrophoresis in sodium dodecyl sulfate (SDS) and immunoblotting. Individual Abeta oligomers ranging in size from dimers through dodecamers of 4 kDa monomeric Abeta have been resolved in other laboratories as discrete species by size exclusion chromatography (SEC). In an effort to reconstitute soluble Abeta aggregates in vitro that resemble the endogenous soluble Abeta aggregates, we previously found that monomeric Abeta(1-42) rapidly forms soluble oligomers in the presence of dilute SDS micelles. Here we extend this work in two directions. First, we contrast the size and secondary structure of these oligomers with those of synthetic Abeta(1-42) fibrils. SEC and multiangle light scattering were used to obtain a molecular mass of 150 kDa for the isolated oligomers. The oligomers partially dissociated to monomers through nonamers when incubated with SDS, but in contrast to endogenous oligomers, we saw no evidence of these discrete species prior to SDS treatment. One hypothesis to explain this difference is that endogenous oligomers are stabilized by covalent cross-linking induced by unknown cellular agents. To explore this hypothesis, optimal mass spectrometry (MS) analysis procedures need to be developed for Abeta cross-linked in vitro. In our second series of studies, we began this process by treating monomeric and aggregated Abeta(1-42) with three cross-linking agents: transglutaminase, glutaraldehyde, and Cu(II) with peroxide. We compared the efficiency of covalent cross-linking with these agents, the effect of cross-linking on peptide secondary structure, the stability of the cross-linked structures to thermal unfolding, and the sites of peptide cross-linking obtained from proteolysis and MS.

Critical role of transglutaminase and other stress proteins during neurodegenerative processes

Proteolytic stress, resulting from the intracellular accumulation of misfolded or aggregated proteins, which exceed the capacity of the ubiquitin-proteasome system to degrade them, plays a relevant role in neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, and Huntington's chorea. Most of toxic protein aggregates are characterised by the presence of isopeptide bonds (cross-links) catalysed by transglutaminase activity; further, several disease-specific proteins-tau, amyloid-beta, alpha-synuclein, huntingtin-are in vitro and/or in vivo substrates of transglutaminase 2. These findings suggest an important role for transglutaminase 2-mediated cross-linking reactions in neurodegeneration. Therefore, the use of transglutaminase activity inhibitors could ameliorate neuronal cell death. New therapeutic perspectives also arise from the possibility to prevent or reduce protein aggregation by enhancing the activation of heat shock proteins, which have been shown to be potent suppressors of neurodegeneration in cell cultures/animal models. Interestingly, some heat shock proteins have been shown to be in vitro or in vivo cross-linked by transglutaminase 2. These observations seem to suggest that transglutaminase activity could be involved in the stabilization of intracellular protein aggregates by interfering with proteasomal degradation of misfolded proteins. Further studies are needed to validate leading hypotheses and to open new prospects for developing therapeutic tools.

Transglutaminase activation in neurodegenerative diseases

The following review examines the role of calcium in promoting the in vitro and in vivo activation of transglutaminases in neurodegenerative disorders. Diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease exhibit increased transglutaminase activity and rises in intracellular calcium concentrations, which may be related. The aberrant activation of transglutaminase by calcium is thought to give rise to a variety of pathological moieties in these diseases, and the inhibition has been shown to have therapeutic benefit in animal and cellular models of neurodegeneration. Given the potential clinical relevance of transglutaminase inhibitors, we have also reviewed the recent development of such compounds.

Novel role of transglutaminase 1 in corpora amylacea formation?

Corpora amylacea (CA) are both age and neurodegeneration-related spherical bodies, consisting of polymerized proteins, often thought to be involved in sequestration of hazardous products of cellular metabolism in brain. Although CA formation is associated with cellular stress, the process underlying their formation remains obscure. Transglutaminases (TGs) are stress associated enzymes that induce molecular cross-links, leading to polymerization of substrate proteins. TG expression and activity are elevated in Alzheimer's disease (AD) and Parkinson's disease (PD), and TG-catalyzed cross-links are present in their lesions. Considering the nature of CA, the aim of this study was to investigate the presence of TGs and TG cross-links in CA of healthy aging brain, AD and PD brain, using immunohistochemistry. We observed TG1 and TG cross-links in CA, together with typical cytoskeletal proteins. Furthermore, the presence of proteins associated with AD or PD pathogenesis was not altered in CA of disease brain compared to controls. We propose that TG1-catalyzed cross-linking and consequent polymerization of cytoskeletal and cytoskeleton-associated proteins may underlie CA formation.

Transglutaminases and neurodegeneration

Transglutaminases (TGs) are Ca2+-dependent enzymes that catalyze a variety of modifications of glutaminyl (Q) residues. In the brain, these modifications include the covalent attachment of a number of amine-bearing compounds, including lysyl (K) residues and polyamines, which serve to either regulate enzyme activity or attach the TG substrates to biological matrices. Aberrant TG activity is thought to contribute to Alzheimer disease, Parkinson disease, Huntington disease, and supranuclear palsy. Strategies designed to interfere with TG activity have some benefit in animal models of Huntington and Parkinson diseases. The following review summarizes the involvement of TGs in neurodegenerative diseases and discusses the possible use of selective inhibitors as therapeutic agents in these diseases.

Transglutaminases and transglutaminase-catalyzed cross-links colocalize with the pathological lesions in Alzheimer's disease brain

Alzheimer's disease (AD) is characterized by pathological lesions, in particular senile plaques (SPs), cerebral amyloid angiopathy (CAA) and neurofibrillary tangles (NFTs), predominantly consisting of self-aggregated proteins amyloid beta (Abeta) and tau, respectively. Transglutaminases (TGs) are inducible enzymes, capable of modifying conformational and/or structural properties of proteins by inducing molecular covalent cross-links. Both Abeta and tau are substrates for TG cross-linking activity, which links TGs to the aggregation process of both proteins in AD brain. The aim of this study was to investigate the association of transglutaminase 1 (TG1), transglutaminase 2 (TG2) and TG-catalyzed cross-links with the pathological lesions of AD using immunohistochemistry. We observed immunoreactivity for TG1, TG2 and TG-catalyzed cross-links in NFTs. In addition, both TG2 and TG-catalyzed cross-links colocalized with Abeta in SPs. Furthermore, both TG2 and TG-catalyzed cross-links were associated with CAA. We conclude that these TGs demonstrate cross-linking activity in AD lesions, which suggests that both TG1 and TG2 are likely involved in the protein aggregation processes underlying the formation of SPs, CAA and/or NFTs in AD brain.

Transglutaminase induces protofibril-like amyloid beta-protein assemblies that are protease-resistant and inhibit long-term potentiation

An increasing body of evidence suggests that soluble assemblies of amyloid beta-protein (Abeta) play an important role in the initiation of Alzheimer disease (AD). In vitro studies have found that synthetic Abeta can form soluble aggregates through self-assembly, but this process requires Abeta concentrations 100- to 1000-fold greater than physiological levels. Tissue transglutaminase (TGase) has been implicated in neurodegeneration and can cross-link Abeta. Here we show that TGase induces rapid aggregation of Abeta within 0.5-30 min, which was not observed with chemical cross-linkers. Both Abeta40 and Abeta42 are good substrates for TGase but show different aggregation patterns. Guinea pig and human TGase induced similar Abeta aggregation patterns, and oligomerization was observed with Abeta40 concentrations as low as 50 nm. The formed Abeta40 species range from 5 to 6 nm spheres to curvilinear structures of the same width, but up to 100 nm in length, that resemble the previously described self-assembled Abeta protofibrils. TGase-induced Abeta40 assemblies are resistant to a 1-h incubation with either neprilysin or insulin degrading enzyme, whereas the monomer is rapidly degraded by both proteases. In support of these species being pathological, TGase-induced Abeta40 assemblies (100 nm) inhibited long term potentiation recorded in the CA1 region of mouse hippocampus slices. Our data suggest that TGase can contribute to AD by initiating Abeta oligomerization and aggregation at physiological levels, by reducing the clearance of Abeta due to the generation of protease-resistant Abeta species, and by forming Abeta assemblies that inhibit processes involved in memory and learning. Our data suggest that TGase might constitute a specific therapeutic target for slowing or blocking the progression of AD.

Tissue transglutaminase: a novel pharmacological target in preventing toxic protein aggregation in neurodegenerative diseases

Alzheimer's disease, Parkinson's disease and Huntington's disease are neurodegenerative diseases, characterized by the accumulation and deposition of neurotoxic protein aggregates. The capacity of specific proteins to self-interact and form neurotoxic aggregates seems to be a common underlying mechanism leading to pathology in these neurodegenerative diseases. This process might be initiated and/or accelerated by proteins that interact with these aggregating proteins. The transglutaminase (TG) family of proteins are calcium-dependent enzymes that catalyze the formation of covalent epsilon-(gamma-glutamyl)lysine isopeptide bonds, which can result in both intra- and intermolecular cross-links. Intramolecular cross-links might modify self-interacting proteins, and make them more prone to aggregate. In addition, intermolecular cross-links could link self-aggregating proteins and thereby initiate and/or stimulate the aggregation process. So far, increased levels and activity of tissue transglutaminase (tTG), the best characterized member of the TG family, have been observed in many neurodegenerative diseases, and the self-interacting proteins, characteristic of Alzheimer's disease, Parkinson's disease and Huntington's disease, are known substrates of tTG. Here, we focus on the role of tTG in the initiation of the aggregation process of self-interacting proteins in these diseases, and promote the notion that tTG might be an attractive novel target for treatment of neurodegenerative diseases.

Oligomerization and transglutaminase cross-linking of the cystatin CRES in the mouse epididymal lumen: potential mechanism of extracellular quality control

CRES (cystatin-related epididymal spermatogenic), a member of the cystatin superfamily of cysteine protease inhibitors, is expressed in the epididymis and spermatozoa, suggesting specialized roles in reproduction. Several cystatin family members oligomerize, including cystatin C that forms amyloid deposits associated with cerebral amyloid angiopathy. Our studies demonstrate that CRES also forms oligomers. Size exclusion chromatography revealed the presence of multiple forms of CRES in the epididymal luminal fluid, including SDS-sensitive and SDS-resistant high molecular mass complexes. In vitro experiments demonstrated that CRES is a substrate for transglutaminase and that an endogenous transglutaminase activity in the epididymal lumen catalyzed the formation of SDS-resistant CRES complexes. The use of a conformation-dependent antibody that recognizes only the oligomeric precursors to amyloid, negative stain electron microscopy, and Congo Red staining showed that CRES adopted similar oligomeric and fibrillar structures during its aggregation as other amyloidogenic proteins, suggesting that CRES has the potential to form amyloid in the epididymal lumen. The addition of transglutaminase, however, prevented the formation of CRES oligomers recognized by the conformation antibody by cross-linking CRES into an amorphous structure. We propose that transglutaminase activity in the epididymal lumen may function as a mechanism of extracellular quality control by diverting proteins such as CRES from the amyloidogenic pathway.

Proteomic analysis of high-molecular-weight protein polymers in a doxorubicin-resistant breast-cancer cell line

We recently reported that increased transglutaminase 2 (TGase 2) expression correlates with increased resistance to the cancer drug doxorubicin in breast-cancer cell lines. Interestingly, high-molecular-weight (HMW) proteins also increased with increased TGase 2 expression in the drug-resistant cell lines. TGase 2 is likely to be responsible for the formation of HMW proteins, because TGase 2 catalyzes cross-linking between proteins. Although the role of the HMW proteins is unclear, we demonstrated that TGase 2 inhibition increases drug sensitivity in breast-cancer cells. Herein we find that TGase 2 inhibition by cystamine dramatically reduces the level of HMW proteins. Identification of the HMW proteins may suggest the mechanism of cancer drug resistance associated with aberrant TGase 2 function. To explore the identities of HMW proteins, we performed in-gel tryptic digestions of unresolved HMW proteins and analyzed the resulting peptides using LC-MALDI-MS/MS. Most of the identified proteins were associated with gene regulation, such as polyadenylate-binding proteins, translation initiation factors, and ribonucleoproteins. This finding suggests that TGase 2 may participate in gene regulation, in addition to its role in cell adhesion.

Coagulation factor XIII Val34Leu gene polymorphism and Alzheimer's disease

Blood coagulation factor XIII (FXIII) plays a role in inflammatory processes and a pathogenetic role of inflammation in neurodegenerative disorders has been proposed. FXIIIa subunit was immunohistochemically detected in a subpopulation of reactive microglia in Alzheimer's disease (AD). Aim of the present study is to evaluate whether a common polymorphism of the FXIII gene is associated with sporadic AD. We examined 90 patients affected by sporadic AD and 139 age- and sex-matched controls to assess the distribution of V/L alleles and genotypes of the FXIIIa-subunit gene. The LL genotype showed a significantly higher frequency in AD patients (p<0.05) with a significantly increased risk of AD in the presence of LL genotype at the logistic regression analysis [odds ratio: 3.6 (1.36-9.44), p<0.01]. This study shows for the first time an association between FXIII Val34Leu polymorphism and AD.