Cross-linking of the dermo-epidermal junction of skin regenerating from keratinocyte autografts. Anchoring fibrils are a target for tissue transglutaminase

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.

Dystrophic Epidermolysis Bullosa: Secondary Disease Mechanisms and Disease Modifiers

The phenotypic presentation of monogenetic diseases is determined not only by the nature of the causative mutations but also is influenced by manifold cellular, microenvironmental, and external factors. Here, heritable extracellular matrix diseases, including dystrophic epidermolysis bullosa (DEB), are no exceptions. Dystrophic epidermolysis bullosa is caused by mutations in the COL7A1 gene encoding collagen VII. Deficiency of collagen VII leads to skin and mucosal fragility, which progresses from skin blistering to severe fibrosis and cancer. Clinical and pre-clinical studies suggest that targeting of secondary disease mechanisms or employment of natural disease modifiers can alleviate DEB severity and progression. However, since many of these mechanisms are needed for tissue homeostasis, informed, selective targeting is essential for safe and efficacious treatment. Here, we discuss a selection of key disease modifiers and modifying processes active in DEB, summarize the still scattered knowledge of them, and reflect on ways forward toward their utilization for symptom-relief or enhancement of curative therapies.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

Characterization of TG2 and TG1-TG2 double knock-out mouse epidermis

Transglutaminases (TGs) are a family of enzymes that catalyse the formation of isopeptide bonds between the γ-carboxamide groups of glutamine residues and the ε-amino groups of lysine residues leading to cross-linking reactions among proteins. Four members, TG1, TG2, TG3, and TG5, of the nine mammalian enzymes are expressed in the skin. TG1, TG3 and TG5 crosslinking properties are fundamental for cornified envelope assembly. In contrast, the role of TG2 in keratinization has never been studied at biochemical level in vivo. In this study, taking advantage of the TG2 knock-out (KO) and TG1 heterozygous mice, we generated and characterized the epidermis of TG1-TG2 double knock-out (DKO) mice. We performed morphological analysis of the epidermis and evaluation of the expression of differentiation markers. In addition, we performed analysis of the amino acid composition from isolated corneocytes. We found a significant change in amino acid composition in TG1KO cornified cell envelopes (CEs) while TG2KO amino acid composition was similar to wild-type CEs. Our results confirm a key role of TG1 in skin differentiation and CE assembly and demonstrate that TG2 is not essential for CE assembly and skin formation.

Collagen VII Half-Life at the Dermal-Epidermal Junction Zone: Implications for Mechanisms and Therapy of Genodermatoses

The tissue half-life of proteins largely determines treatment frequency of non-gene-editing-based therapies targeting the cause of genodermatoses. Surprisingly, such knowledge is missing for a vast number of proteins involved in pathologies. The dermal-epidermal junction zone is believed to be a rather static structure, but to our knowledge no detailed analysis of the stability of proteins within this zone has been performed. Here, we addressed the in vivo half-life of collagen type VII using genetic ablation of its expression and therapeutic introduction of exogenous collagen VII in a preclinical model. A similar in vivo stability of collagen VII was observed in the skin, tongue, and esophagus, with a half-life of about 1 month. Collagen VII expressed by intradermally injected mesenchymal stromal cells also exhibited a similar half-life. Our study provides key information needed for the development of protein replacement or cell-based therapies for dystrophic epidermolysis bullosa caused by genetic deficiency of collagen VII. Moreover, by showing what we define as an intermediate half-life of collagen VII, our study challenges the view of the dermal-epidermal junction zone as a static structure with very slow turnover.

Epidermal Basement Membrane in Health and Disease

Skin, as the organ protecting the individual from environmental aggressions, constantly meets external insults and is dependent on mechanical toughness for its preserved function. Accordingly, the epidermal basement membrane (BM) zone has adapted to enforce tissue integrity. It harbors anchoring structures created through unique organization of common BM components and expression of proteins exclusive to the epidermal BM zone. Evidence for the importance of its correct assembly and the nonredundancy of its components for skin integrity is apparent from the multiple skin blistering disorders caused by mutations in genes coding for proteins associated with the epidermal BM and from autoimmune disorders in which autoantibodies target these molecules. However, it has become clear that these proteins not only provide mechanical support but are also critically involved in tissue homeostasis, repair, and regeneration. In this chapter, we provide an overview of the unique organization and components of the epidermal BM. A special focus will be given to its function during regeneration, and in inherited and acquired diseases.

Making more matrix: enhancing the deposition of dermal-epidermal junction components in vitro and accelerating organotypic skin culture development, using macromolecular crowding

Skin is one of the most accessible tissues for experimental biomedical sciences, and cultured skin cells represent one of the longest-running clinical applications of stem cell therapy. However, culture-generated skin mimetic multicellular structures are still limited in their application by the time taken to develop these constructs in vitro and by their incomplete differentiation. The development of a functional dermal-epidermal junction (DEJ) is one of the most sought after aspects of cultured skin, and one of the hardest to recreate in vitro. At the DEJ, dermal fibroblasts and epidermal keratinocytes interact to form an interlinked basement membrane of extracellular matrix (ECM), which forms as a concerted action of both keratinocytes and fibroblasts. Successful formation of this basement membrane is essential for take and stability of cultured skin autografts. We studied interactive matrix production by monocultures and cocultures of primary human keratinocytes and fibroblasts in an attempt to improve the efficiency of basement membrane production in culture using mixed macromolecular crowding (mMMC); resulting ECM were enriched with the deposition of collagens I, IV, fibronectin, and laminin 332 (laminin 5) and also in collagen VII, the anchoring fibril component. Our in vitro data point to fibroblasts, rather than keratinocytes, as the major cellular contributors of the DEJ. Not only did we find more collagen VII production and deposition by fibroblasts in comparison to keratinocytes, but also observed that decellularized fibroblast ECM stimulated the production and deposition of collagen VII by keratinocytes, over and above that of keratinocyte monocultures. In confrontation cultures, keratinocytes and fibroblasts showed spontaneous segregation and demarcation of cell boundaries by DEJ protein deposition. Finally, mMMC was used in a classical organotypic coculture protocol with keratinocytes seeded over fibroblast-containing collagen gels. Applied during the submerged phase, mMMC was sufficient to accelerate the emergence of collagen VII along the de novo DEJ, together with stronger transglutaminase activity in the neoepidermis. Our findings corroborate the role of fibroblasts as important players in producing collagen VII and inducing collagen VII deposition in the DEJ, and that macromolecular crowding leads to organotypic epidermal differentiation in tissue culture in a significantly condensed time frame.

Loss of collagen VII is associated with reduced transglutaminase 2 abundance and activity

Absence of collagen VII leads to widespread cellular and tissue phenotypes. However, the underlying molecular mechanisms are not well understood. To gain insights into cellular responses to loss of collagen VII, we undertook a quantitative disease proteomics approach. By using recessive dystrophic epidermolysis bullosa (RDEB), a skin blistering disease caused by collagen VII deficiency, as a genetic model, collagen VII-dependent differences in cellular protein abundances and protein-protein interactions were analyzed. Absence of collagen VII led to alterations of intracellular protein compositions and to perturbations in cell adhesion, protein trafficking, and the turnover pathway autophagy. A potential linker of the different cellular phenotypes is transglutaminase 2 (TGM2), a multifunctional enzyme important for protein cross-linking. TGM2 was identified as a stable interaction partner of collagen VII. In RDEB, both abundance and activity of TGM2 were reduced, accounting not only for diminished adhesion and perturbed autophagy but also for reduced cross-linking of the extracellular matrix and for decreased epidermal-dermal integrity in RDEB.

The vWFA2 domain of type VII collagen is responsible for collagen binding

Type VII collagen (Col7) is the major component of anchoring fibrils and very important for skin integrity. This is emphasized by the Col7 related skin blistering diseases dystrophic epidermolysis bullosa and epidermolysis bullosa acquisita. Structural data that provides insights into the interaction network of Col7 and thus providing a basis for a better understanding of the pathogenesis of the diseases is missing. We proved that the von-Willebrand-factor A like domain 2 (vWFA2) of Col7 is responsible for type I collagen binding. The interaction has a K(D) value of 90 μM as determined by SPR and is enthalpy driven as derived from the van't Hoff equation. Furthermore, a hitherto unknown interaction of this domain with type IV collagen was identified. The interaction of vWFA2 with type I collagen is sensitive to the presence of magnesium ions, however, vWFA2 does not contain a magnesium binding site thus magnesium must bind to type I collagen. A lysine residue has been identified to be crucial for type I collagen binding. This allowed localization of the binding site. Mutational analysis suggests different interaction mechanisms in different species and that these interactions might be of covalent nature.

Transglutaminase 2 and NF-κB: an odd couple that shapes breast cancer phenotype

Owing to numerous pro-survival target genes, aberrant activation of the NF-κB transcription factor is associated with a drug-resistant phenotype and aggressive breast tumor behavior. Transglutaminase 2 (TG2), a ubiquitously expressed protein cross-linking enzyme, activates NF-κB through a non-conventional mechanism that disables the IκBα inhibitor. Our group has recently documented that the TG2 gene (termed TGM2) is a direct transcriptional target of NF-κB. These developments uncover a novel self-reinforcing molecular feedback loop where TG2 activates NF-κB and, in turn, NF-κB directly upregulates the transcription of TGM2. This manuscript reviews the literature that supports the existence of the TG2/NF-κB signaling loop, the nature of the signal transduction that activates this loop, and the phenotypic consequences stemming from the aberrant activation of this novel signaling mechanism in breast cancer.

Epidermal transglutaminase (TGase 3) is required for proper hair development, but not the formation of the epidermal barrier

Transglutaminases (TGase), a family of cross-linking enzymes present in most cell types, are important in events as diverse as cell-signaling and matrix stabilization. Transglutaminase 1 is crucial in developing the epidermal barrier, however the skin also contains other family members, in particular TGase 3. This isoform is highly expressed in the cornified layer, where it is believed to stabilize the epidermis and its reduction is implicated in psoriasis. To understand the importance of TGase 3 in vivo we have generated and analyzed mice lacking this protein. Surprisingly, these animals display no obvious defect in skin development, no overt changes in barrier function or ability to heal wounds. In contrast, hair lacking TGase 3 is thinner, has major alterations in the cuticle cells and hair protein cross-linking is markedly decreased. Apparently, while TGase 3 is of unique functional importance in hair, in the epidermis loss of TGase 3 can be compensated for by other family members.

Tissue transglutaminase inhibits the TRPV5-dependent calcium transport in an N-glycosylation-dependent manner

Tissue transglutaminase (tTG) is a multifunctional Ca(2+)-dependent enzyme, catalyzing protein crosslinking. The transient receptor potential vanilloid (TRPV) family of cation channels was recently shown to contribute to the regulation of TG activities in keratinocytes and hence skin barrier formation. In kidney, where active transcellular Ca(2+) transport via TRPV5 predominates, the potential effect of tTG remains unknown. A multitude of factors regulate TRPV5, many secreted into the pro-urine and acting from the extracellular side. We detected tTG in mouse urine and in the apical medium of polarized cultures of rabbit connecting tubule and cortical collecting duct (CNT/CCD) cells. Extracellular application of tTG significantly reduced TRPV5 activity in human embryonic kidney cells transiently expressing the channel. Similarly, a strong inhibition of transepithelial Ca(2+) transport was observed after apical application of purified tTG to polarized rabbit CNT/CCD cells. Furthermore, tTG promoted the aggregation of the plasma membrane-associated fraction of TRPV5. Using patch clamp analysis, we observed a reduction in the pore diameter after tTG treatment, suggesting distinct structural changes in TRPV5 upon crosslinking by tTG. As N-linked glycosylation of TRPV5 is a key step in regulating channel function, we determined the effect of tTG in the N-glycosylation-deficient TRPV5 mutant. In the absence of N-linked glycosylation, TRPV5 was insensitive to tTG. Taken together, these observations imply that tTG is a novel extracellular enzyme inhibiting the activity of TRPV5. The inhibition of TRPV5 occurs in an N-glycosylation-dependent manner, signifying a common final pathway by which distinct extracellular factors regulate channel activity.

Applying macromolecular crowding to enhance extracellular matrix deposition and its remodeling in vitro for tissue engineering and cell-based therapies

With the advent of multicellular organisms, the exterior of the cells evolved dramatically from highly aqueous surroundings into an extracellular matrix and space crowded with macromolecules. Cell-based therapies require removal of cells from their crowded physiological context and propagating them in dilute culture medium to attain therapeutically relevant numbers whilst preserving their phenotype. However, bereft of their microenvironment, cells under perform and lose functionality. Major efforts currently aim to modify cell culture surfaces and build three dimensional scaffolds to improve this situation. We discuss here alternative strategies that enable cells to re-create their own microenvironment in vitro, using carbohydrate-based macromolecules as culture media additives that create an excluded volume effect at defined fraction volume occupancies. This biophysical approach dramatically enhances extracellular matrix deposition by differentiated cells and stem cells, and boosts progenitor cell differentiation and proliferation. We begin to understand how well cells really can perform ex vivo if given the chance.

Transglutaminases (TGs) in ocular and periocular tissues: effect of muscarinic agents on TGs in scleral fibroblasts

Objective

To investigate the expression of transglutaminases (TGs) in the ocular surface, the eyelid margin and associated glands and to determine effect of muscarinic agents on TGs in scleral fibroblasts (SF).

Materials and Methods

Primary SFs cultured from mouse and human sclera were treated with atropine and carbachol for 5 days. Lysed cell RNA was used for real-time PCR, protein was used for Western blot analysis and TG-2 transamidase activity was measured by ELISA. Immunohistochemistry was done to determine the expression of TGases.

Results

Immunohistochemistry and western blot confirmed the expression of TGs-1, 2, 3 and 5 proteins in cultured SFs and eye tissues. Real time PCR showed TG-1, 2, 5 transcript levels to be down regulated 3 fold (p<0.05) in cultured human and mouse SFs after incubation with atropine and this was reversed by carbachol. However, TG-3 expression was increased with atropine and decreased with carbachol at all concentrations. Atropine abrogated the carbachol-induced activation of SF in a dose-dependent manner. TGs-1, 3, 5 were localized in the entire mouse corneal epithelium, stroma and endothelium but TG-2 was present only in the corneal subepithelium and stroma. All TGs were localized in mouse Meibomian glands however TG-2 had a weak expression.

Conclusions

Our results confirm that TGs-1, 2, 3 and 5 are expressed in human SF and murine ocular tissues, eyelid and associated Meibomian glands. Real-time PCR and Western blot results showed that muscarinic antagonist down-regulates TGs-1, 2 and 5 in both cultured human and mouse SFs and upregulates TG-3. Atropine abrogated the carbachol-induced activation of SF in a dose-dependent manner. These results suggest that manipulation of TGs by way of muscarinic receptor acting drugs may be a plausible method of intervention in wound healing and scleral remodeling.

Skingineering I: engineering porcine dermo-epidermal skin analogues for autologous transplantation in a large animal model

BACKGROUND

Extended full thickness skin defects still represent a considerable therapeutic challenge as ideal strategies for definitive autologous coverage are still not available. Tissue engineering of whole skin represents an equally attractive and ambitious novel approach. We have recently shown that laboratory-grown human skin analogues with near normal skin anatomy can be successfully transplanted on immuno-incompetent rats. The goal of the present study was to engineer autologous porcine skin grafts for transplantation in a large animal model (pig study = intended preclinical study).

MATERIALS AND METHODS

Skin biopsies were taken from the pig's abdomen. Epidermal keratinocytes and dermal fibroblasts were isolated and then expanded on culture dishes. Subsequently, highly concentrated collagen hydrogels and collagen/fibrin hydrogels respectively, both containing dermal fibroblasts, were prepared. Fibroblast survival, proliferation, and morphology were monitored using fluorescent labelling and laser scanning confocal microscopy. Finally, keratinocytes were seeded onto this dermal construct and allowed to proliferate. The resulting in vitro generated porcine skin substitutes were analysed by H&E staining and immunofluorescence.

RESULTS

Dermal fibroblast proliferation and survival in pure collagen hydrogels was poor. Also, the cells were mainly round-shaped and they did not develop 3D-networks. In collagen/fibrin hydrogels, dermal fibroblast survival was significantly higher. The cells proliferated well, were spindle-shaped, and formed 3D-networks. When these latter dermal constructs were seeded with keratinocytes, a multilayered and partly stratified epidermis readily developed.

CONCLUSION

This study provides compelling evidence that pig cell-derived skin analogues with near normal skin anatomy can be engineered in vitro. These tissue-engineered skin substitutes are needed to develop a large animal model to establish standardized autologous transplantation procedures for those studies that must be conducted before "skingineering" can eventually be clinically applied.

Modular enzymatically crosslinked protein polymer hydrogels for in situ gelation

Biomaterials that mimic the extracellular matrix in both modularity and crosslinking chemistry have the potential to recapitulate the instructive signals that ultimately control cell fate. Toward this goal, modular protein polymer-based hydrogels were created through genetic engineering and enzymatic crosslinking. Animal derived tissue transglutaminase (tTG) and recombinant human transglutaminase (hTG) enzymes were used for coupling two classes of protein polymers containing either lysine or glutamine, which have the recognition substrates for enzymatic crosslinking evenly spaced along the protein backbone. Utilizing tTG under physiological conditions, complete crosslinking occurred within 2 min, as determined by particle tracking microrheology. Hydrogel composition impacted the elastic storage modulus of the gel over 4-fold and also influenced microstructure and degree of swelling, but did not appreciably effect degradation by plasmin. Mouse 3T3 and primary human fibroblasts were cultured in both 2- and 3-dimensions without a decrease in cell viability and displayed spreading in 2D. The properties, which are controlled through the specific nature of the protein polymer precursors, render these gels valuable for in situ therapies. Furthermore, the modular hydrogel composition allows tailoring of mechanical and physical properties for specific tissue engineering applications.

Dystrophic epidermolysis bullosa: pathogenesis and clinical features

Dystrophic epidermolysis bullosa (DEB) is relatively well understood. Potential therapies are in development. This article describes the pathogenesis and clinical features of DEB. It also describes therapeutic options and the future of molecular therapies.

Transglutaminases, involucrin, and loricrin as markers of epidermal differentiation in skin substitutes derived from human sweat gland cells

BACKGROUND/PURPOSE

In a multi-project research line, we are currently testing whether a morphologically and functionally near normal epidermis can be cultured from human sweat gland (SG) cells and be used as a skin substitute. The present study focuses on the stratum corneum of the epidermis that assumes a vital barrier function for the skin. The main process in the formation of the cornified cell envelope in human epidermis, i.e. crosslinking of proteins and lipids, is catalyzed by several transglutaminases (TG). Therefore, we compared the expression patterns of various TG and their substrates in SG-derived versus keratinocyte-derived epidermal substitutes.

METHODS

Sweat gland cells, keratinocytes, and fibroblasts were isolated from human skin samples and cultivated separately to generate epidermal substitutes. These were transplanted onto the back of athymic rats. After 2 weeks, the transplants were excised and analyzed histologically as well as by indirect immunofluorescence. We looked at the expression of TG1, 3, 5, and their substrates involucrin and loricrin (=markers of epidermal differentiation) in SG-derived and keratinocyte-derived skin substitutes as well as in normal skin.

RESULTS

The SG cell-derived epidermis was near normal anatomically, formed a cornified cell envelope and demonstrated TG1, 3, and 5 as well as involucrin and loricrin expression patterns similar to those found in keratinocyte-derived epidermis and normal control skin.

CONCLUSION

These findings support the thesis that SG cells have the potential to form a near normal stratified epidermal analog that might be used as a skin substitute. The expression of TG1 and 3, not normally expressed in human SG, suggests the presence of re-programmed SG cells and/or stem cells capable of both de novo generating and maintaining an epidermis.

Increased TG2 expression can result in induction of transforming growth factor beta1, causing increased synthesis and deposition of matrix proteins, which can be regulated by nitric oxide

In fibrotic conditions increases in TG2 activity has been linked to an increase in the deposition of extracellular matrix proteins. Using TG2 transfected Swiss 3T3 fibroblasts expressing TG2 under the control of the tetracycline-regulated inducible promoter, we demonstrate that induction of TG2 not only stimulates an increase in collagen and fibronectin deposition but also an increase in the expression of these proteins. Increased TG2 expression in these fibroblasts led to NF-kappaB activation, resulting in the increased expression of transforming growth factor (TGF) beta(1). In addition, cells overexpressing TG2 demonstrated an increase in biologically active TGFbeta(1) in the extracellular environment. A specific site-directed inhibitor of TG abolished the NF-kappaB and TGFbeta1 activation and the subsequent elevation in the synthesis and deposition of extracellular matrix proteins, confirming that this process depends on the induction of transglutaminase activity. Treatment of TG2-induced fibroblasts with nontoxic doses of nitric oxide donor S-nitroso-N-acetylpenicillamine resulted in decreased TG2 activity and apprehension of the inactive enzyme on the cell surface. This was paralleled by a reduction in activation of NF-kappaB and TGFbeta(1) production with a subsequent decrease in collagen expression and deposition. These findings support a role for NO in the regulation of TG2 function in the extracellular environment.

Transglutaminase 2 cross-linking of matrix proteins: biological significance and medical applications

This review summarises the functions of the enzyme tissue transglutaminase (TG2) in the extracellular matrix (ECM) both as a matrix stabiliser through its protein cross-linking activity and as an important cell adhesion protein involved in cell survival. The contribution of extracellular TG2 to the pathology of important diseases such as cancer and fibrosis are discussed with a view to the potential importance of TG2 as a therapeutic target. The medical applications of TG2 are further expanded by detailing the use of transglutaminase cross-linking in the development of novel biocompatible biomaterials for use in soft and hard tissue repair.

Supramolecular interactions in the dermo-epidermal junction zone: anchoring fibril-collagen VII tightly binds to banded collagen fibrils

The dermis and the epidermis of normal human skin are functionally separated by a basement membrane but, together, form a stable structural continuum. Anchoring fibrils reinforce this connection by insertion into the basement membrane and by intercalation with banded collagen fibrils of the papillary dermis. Structural abnormalities in collagen VII, the major molecular constituent of anchoring fibrils, lead to a congenital skin fragility condition, dystrophic epidermolysis bullosa, associated with skin blistering. Here, we characterized the molecular basis of the interactions between anchoring fibrils and banded collagen fibrils. Suprastructural fragments of the dermo-epidermal junction zone were generated by mechanical disruption and by separation with magnetic Immunobeads. Anchoring fibrils were tightly attached to banded collagen fibrils. In vitro binding studies demonstrated that a von Willebrand factor A-like motif in collagen VII was essential for binding of anchoring fibrils to reconstituted collagen I fibrils. Since collagen I and VII molecules reportedly undergo only weak interactions, the attachment of anchoring fibrils to collagen fibrils depends on supramolecular organization of their constituents. This complex is stabilized in situ and resists dissociation by strong denaturants.

Three-dimensional culture of keratinocytes and the formation of basement membrane for canine footpad substitute

A pad equivalent for a dog was prepared as a substitute for the loss of footpad. In addition to the time course of formation on epidermal morphogenesis, we investigated expressions of alpha(6) integrin subunit as adhesive molecule, and laminin and type IV and VII collagens as extracellular matrices of basement membrane components. Epithelium of the pad equivalent was thick enough to be easily confirmed at 5 days at the air-liquid interface, but many creases appeared on it at 7 days, and it shrank at 10 and 14 days. Keratinocytes were increased in 4 to 5 cell layers at 1 day at the air-liquid interface, differentiating into basal cell layer. Granular and corneal cell layers were confirmed until 5 days, and maintained their shape at least until 14 days. Alpha 6 integrin was expressed at almost the same fluorescent intensity as native pad tissue at 1 day at the dermal-epidermal junction. Laminin and type IV collagen were intermittently expressed at 5 and 10 days, respectively, at the dermal-epidermal junction, and at 14 days the fluorescence showed almost the same intensity as native pad tissue. The expression of type VII collagen was discontinuous at 2 days at the dermal-epidermal junction, but remained as it was at 14 days. The present findings suggested that although the formation of anchoring fibrils in basement membrane was incomplete, the pad equivalent in the dog was reconstructed similar to a native pad by epidermal morphogenesis.

Transglutaminase inhibitors induce hyperproliferation and parakeratosis in tissue-engineered skin

BACKGROUND

The transglutaminase (TG) family consists of eight distinct isoforms. TG types 1, 3 and 5 play a major role in normal skin development, with TG2 also being elevated during dermal wounding. TG1, 3 and 5 are responsible for the cross-linking of keratin precursors and formation of the cornified envelope during keratinocyte differentiation. TG2 may play a role in keratinocyte basement membrane cross-linking. Abnormal TG expression has been demonstrated in Darier disease, Netherton syndrome, psoriasis and lamellar ichthyosis. During a recent investigation of skin contraction in tissue-engineered skin, transglutaminase inhibitors were found to produce hyperproliferation and parakeratosis.

OBJECTIVES

Accordingly, this study was designed to study the effect of pan-transglutaminase inhibition on morphology of tissue-engineered skin and expression of keratinocyte differentiation and proliferation-associated antigens.

METHODS

We used a tissue-engineered model of human skin, based on de-epidermized acellular human dermis, seeded with normal keratinocytes and dermal fibroblasts and cultured at an air-liquid interface. The pan-transglutaminase inhibitors putrescine, NTU283 (1-dimethyl,2-[(oxopropyl)thio]imidazolium) and NTU285 (N-benzyloxycarbonyl-l-glutaminyl-6-dimethylsulfonium-5-oxo-l-norleucine) were added to the culture medium. After 28 days, histology and immunohistochemistry for collagen IV, involucrin and cytokeratins 6, 10 and 16 were performed.

RESULTS

Keratinocyte hyperproliferation and parakeratosis were seen in response to transglutaminase inhibition. Inhibition of transglutaminase also resulted in loss of basement membrane collagen IV. Involucrin and cytokeratins 6 and 16 were confined to the basal layers in control composites but expressed throughout the epidermis in response to transglutaminase inhibition. A distinct band of expression of cytokeratin 10 was seen in the upper stratum granulosum of control composites but only patchy expression was seen after transglutaminase expression.

CONCLUSIONS

Pan-transglutaminase inhibition inhibits terminal differentiation of keratinocytes, leading to a hyperproliferative epidermis with parakeratosis and enhanced expression of involucrin and cytokeratins 6 and 16. Expression of the differentiation-associated cytokeratin, cytokeratin 10, is reduced. Basement membrane integrity is also lost as a result of transglutaminase inhibition.

Synthesis and in vitro evaluation of enzymatically cross-linked elastin-like polypeptide gels for cartilaginous tissue repair

Genetically engineered elastin-like polypeptide (ELP) hydrogels offer unique promise as scaffolds for cartilage tissue engineering because of the potential to promote chondrogenesis and to control mechanical properties. In this study, we designed and synthesized ELPs capable of undergoing enzyme-initiated gelation via tissue transglutaminase, with the ultimate goal of creating an injectable, in situ cross-linking scaffold to promote functional cartilage repair. Addition of the enzyme promoted ELP gel formation and chondrocyte encapsulation in a biocompatible process, which resulted in cartilage matrix synthesis in vitro and the potential to contribute to cartilage mechanical function in vivo. A significant increase in the accumulation of sulfated glycosaminoglycans was observed, and histological sections revealed the accumulation of a cartilaginous matrix rich in type II collagen and lacking in type I collagen, indicative of hyaline cartilage formation. These results provide evidence of chondrocytic phenotype maintenance for cells in the ELP hydrogels in vitro. In addition, the dynamic shear moduli of ELP hydrogels seeded with chondrocytes increased from 0.28 to 1.7 kPa during a 4-week culture period. This increase in the mechanical integrity of cross-linked ELP hydrogels suggests restructuring of the ELP matrix by deposition of functional cartilage extracellular matrix components.

Immunoglobulin, complement and epidermal transglutaminase deposition in the cutaneous vessels in dermatitis herpetiformis

BACKGROUND

Recently, epidermal transglutaminase (TG) has been identified within the papillary IgA granules in dermatitis herpetiformis (DH). Although IgA type autoantibodies to tissue and epidermal TGs are characteristic serological markers for DH, these antibodies do not bind to normal papillary skin structures.

AIMS

To test the possibility of IgA immune complex precipitation within the vessel walls as a first step in the pathogenesis of skin symptoms, we analysed immunoglobulin, complement, and epidermal TG deposition along the vascular system of DH skin.

METHODS

Punch biopsy specimen were taken from 116 DH patients' skin, and evaluated for the presence of vascular immune precipitates by direct immunofluorescence. Skin samples from 16 DH patients were also studied for tissue and epidermal TGs.

RESULTS

In 74 (64%) of the 116 DH skin studied, significant vascular staining accompanied the DH-specific granular IgA fluorescence (IgA and C3 in 39 patients; IgA alone in 18; IgA, C3 and IgM together in five; IgM alone in 12). In most cases (92%), the precipitates were detected in the small vessels of the papillary dermis; however, a subpapillary vascular fluorescence was also observed in a few patients (8%). Skin IgA colocalized with epidermal TG in the vessel walls and within the scattered papillary peri- and intervascular DH bodies. Tissue TG did not colocalize either with the immunoglobulins or with the complement precipitates of the dermis. Furthermore, we could not detect keratinocyte TG in the DH bodies nor in the vessel walls.

CONCLUSIONS

These findings support possible immune complex precipitation in the vessel walls of DH skin and further confirm the significance of epidermal but not tissue TG in the pathomechanism of skin symptoms.

Crosslinking and G-protein functions of transglutaminase 2 contribute differentially to fibroblast wound healing responses

Tissue transglutaminase (TG2) affects cell-matrix interactions in cell spreading, migration and extracellular matrix (ECM) reorganisation. Using fibroblasts deficient in TG2 or overexpressing normal or crosslinking-deficient enzyme, we show that the extracellular crosslinking activity and intracellular G-protein function in signal transduction contribute differentially to regulation of cell-matrix interactions. TG2-deficient cells displayed normal attachment but delayed spreading on ECM substrata and defects in motility unrelated to crosslinking. Blocking antibodies to TG2 failed to induce similar defects in normal fibroblasts. TG2-deficient fibroblasts had defects in focal adhesion turnover and stress fibre formation, showed changes in focal adhesion kinase (FAK) phosphorylation and failed to activate protein kinase C alpha (PKCalpha). Phospholipase C (PLC) and PKCalpha inhibitors blocked spreading of normal fibroblasts whilst PKC activators induced spreading in TG2-deficient cells. In contrast, ECM remodelling was not only compromised by TG2 deficiency but also by overexpression of dominant negative enzyme and TG inhibitors. TG2 activity increased matrix tension and was required for membrane type 1-MMP (MT1-MMP)-dependent activation of MMP-2. Our results demonstrate that TG2 is involved in the control of dynamic adhesion formation in cell spreading and migration via regulation of phospholipase C activity. By virtue of its crosslinking activity, the enzyme plays a central role in regulating ECM remodelling.

Molecular basis of elastic fiber formation. Critical interactions and a tropoelastin-fibrillin-1 cross-link

We have investigated the molecular basis of elastic fiber formation on fibrillin microfibrils. Binding assays revealed high affinity calcium-independent binding of two overlapping fibrillin-1 fragments (encoded by central exons 18-25 and 24-30) to tropoelastin, which, in microfibrils, map to an exposed "arms" feature adjacent to the beads. A further binding site within an adjacent fragment (encoded by exons 9-17) was within an eight-cysteine motif designated TB2 (encoded by exons 16 and 17). Binding to TB2 was ablated by the presence of N-terminal domains (encoded by exons 1-8) and reduced after deleting the proline-rich region. A novel transglutaminase cross-link between tropoelastin and fibrillin-1 fragment (encoded by exons 9-17) was localized by mass spectrometry to a sequence encoded by exon 17. The high affinity binding and cross-linking of tropoelastin to a central fibrillin-1 sequence confirm that this association is fundamental to elastic fiber formation. Microfibril-associated glycoprotein-1 showed calcium-dependent binding of moderate affinity to fibrillin-1 N-terminal fragment (encoded by exons 1-8), which localize to the beads. Microfibril-associated glycoprotein-1 thus contributes to microfibril organization but may also form secondary interactions with adjacent microfibril-bound tropoelastin.

Importance of tissue transglutaminase in repair of extracellular matrices and cell death of dermal fibroblasts after exposure to a solarium ultraviolet A source

Investigations were undertaken to study the role of the protein cross-linking enzyme tissue transglutaminase in changes associated with the extracellular matrix and in the cell death of human dermal fibroblasts following exposure to a solarium ultraviolet A source consisting of 98.8% ultraviolet A and 1.2% ultraviolet B. Exposure to nonlethal ultraviolet doses of 60 to 120 kJ per m2 resulted in increased tissue transglutaminase activity when measured either in cell homogenates, "in situ" by incorporation of fluorescein-cadaverine into the extracellular matrix or by changes in the epsilon(gamma-glutamyl) lysine cross-link. This increase in enzyme activity did not require de novo protein synthesis. Incorporation of fluorescein-cadaverine into matrix proteins was accompanied by the cross-linking of fibronectin and tissue transglutaminase into nonreducible high molecular weight polymers. Addition of exogenous tissue transglutaminase to cultured cells mimicking extensive cell leakage of the enzyme resulted in increased extracellular matrix deposition and a decreased rate of matrix turnover. Exposure of cells to 180 kJ per m2 resulted in 40% to 50% cell death with dying cells showing extensive tissue transglutaminase cross-linking of intracellular proteins and increased cross-linking of the surrounding extracellular matrix, the latter probably occurring as a result of cell leakage of tissue transglutaminase. These cells demonstrated negligible caspase activation and DNA fragmentation but maintained their cell morphology. In contrast, exposure of cells to 240 kJ per m2 resulted in increased cell death with caspase activation and some DNA fragmentation. These cells could be partially rescued from death by addition of caspase inhibitors. These data suggest that changes in cross-linking both in the intracellular and extracellular compartments elicited by tissue transglutaminase following exposure to ultraviolet provides a rapid tissue stabilization process following damage, but as such may be a contributory factor to the scarring process that results.

Recognition and management of the cutaneous manifestations of celiac disease: a guide for dermatologists

In celiac disease, the ingestion of gluten-containing cereals, such as wheat, rye, and barley, results in small-bowel mucosal inflammation and villous atrophy with crypt hyperplasia. The prevalence of the condition may be as high as 1% in the adult population. The disease can also embrace various extraintestinal manifestations, of which dermatitis herpetiformis is the best known. Earlier, dermatitis herpetiformis was considered a skin disease occurring often concomitantly with celiac disease. At present, a body of evidence shows that dermatitis herpetiformis is a cutaneous manifestation of celiac disease, and affects approximately 25% of patients with celiac disease. Both conditions can appear in the same family and are closely linked to HLA class II locus in chromosome 6; 90% of patients have HLA DQ2 and, almost all the remainder, HLA DQ8. All patients with dermatitis herpetiformis have at least some-degree of mucosal inflammation or lesion consistent with celiac disease. The etiology of celiac disease in not fully understood, but tissue transglutaminase seems to be the predominant autoantigen both in the intestine and the skin. Serum antibodies against tissue transglutaminase can be used in the serologic screening and follow-up of dietary compliance of patients with celiac disease. Gluten-free diet is essential in the treatment of both conditions, and oral dapsone is usually needed in newly detected dermatitis herpetiformis in order to alleviate symptoms. Oral mucosal lesions, alopecia areata, and vitiligo probably occur more frequently in patients with dermatitis herpetiformis than in the general population. By contrast, the reported association of celiac disease with psoriasis seems to be coincidental.

Transglutaminases: crosslinking enzymes with pleiotropic functions

Blood coagulation, skin-barrier formation, hardening of the fertilization envelope, extracellular-matrix assembly and other important biological processes are dependent on the rapid generation of covalent crosslinks between proteins. These reactions--which are catalysed by transglutaminases--endow the resulting supramolecular structure with extra rigidity and resistance against proteolytic degradation. Some transglutaminases function as molecular switches in cytoskeletal scaffolding and modulate protein-protein interactions. Having knowledge of these enzymes is essential for understanding the aetiologies of diverse hereditary diseases of the blood and skin, and various autoimmune, inflammatory and degenerative conditions.

In patients with dermatitis herpetiformis distribution of transglutaminase in cutaneous tissue does not differ from controls

BACKGROUND

Dermatitis herpetiformis may be regarded as the cutaneous counterpart of coeliac disease. These conditions are related to the ingestion of gluten and both are characterised by circulating antibodies against tissue transglutaminase.

AIMS

To study the distribution of tissue transglutaminase in the skin of dermatitis herpetiformis patients and controls, and to investigate whether the dermal IgA deposits, diagnostic for dermatitis herpetiformis, are related to tissue transglutaminase expression in the skin.

METHODS

A series of 11 patients with dermatitis herpetiformis had a 4 mm punch biopsy taken from the uninvolved perilesional skin. A group of 16 controls, undergoing surgical removal of benign nevi, gave perilesional skin. Biopsies were covered with OCT and frozen at -80 degrees C. After washing, skin biopsy sections were incubated with an IgG anti-tissue transglutaminase mouse monoclonal antibody. After washing, sections were incubated with anti-mouse IgG.

RESULTS

The anti-tissue transglutaminase monoclonal antibody specifically recognised the basal epidermal cells. This staining was no different between patients and controls.

CONCLUSION

Our results suggest that tissue transglutaminase can be recognised in the basal epidermal layer both of patients with dermatitis herpetiformis and controls. Since this distribution does not correspond to the distribution of dermal IgA deposits, it is concluded that dermatitis herpetiformis dermal IgA deposits are not due to antibodies directed against cutaneous tissue transglutaminase.

Enhanced expression of transglutaminase 2 in anterior polar cataracts and its induction by TGF-beta in vitro

BACKGROUND/AIMS

Transglutaminase activity has long been implicated in the cataract formation. However, the precise mechanism of how it is produced and involved in this process remains unclear. Here the authors sought to examine whether transglutaminase 2 (TGase 2) is expressed in lens epithelial cells from patients with anterior polar cataracts, to determine whether TGase 2 expression is induced by transforming growth factor (TGF-beta) in cultured lens epithelial cells, and to determine whether TGase 2 participates in the crosslinking of fibronectin in lens epithelial cells in vitro.

METHODS

Lens epithelial cells from anterior polar cataracts, nuclear cataracts, and non-cataractous clear lenses were examined for the expression of TGase 2 using reverse transcription-polymerase chain reaction, western blot analysis, and immunohistochemical analysis. The modulation of extracellular TGase 2 activity by TGF-beta was measured by the formation of fibronectin polymers and the incorporation of fluorescein cadaverine into extracellular matrix proteins. The effect of TGase 2 overexpression was analysed by immunofluorescence staining and western blot analysis of human lens epithelial (HLE) B-3 cells transiently transfected with TGase 2 gene.

RESULTS

The expression of TGase 2 mRNA and its protein was markedly enhanced in lens epithelial cells from patients with anterior polar cataracts. Treatment of HLE B-3 cells with TGF-beta caused an increase in TGase 2 protein, its extracellular activity, and the crosslinking of fibronectin. Transient transfection of HLE B-3 cells with the TGase 2 gene led to the increased production of fibronectin monomers and polymers.

CONCLUSIONS

This study shows that TGase 2 is overexpressed in lens epithelial cells from anterior polar cataracts and that TGF-beta may be a causative factor in the induction of TGase 2. The enhanced expression of TGase 2 might cause the accumulation and crosslinking of the extracellular matrix proteins and might play a part in anterior polar cataract development.

Injury-induced "switch" from GTP-regulated to novel GTP-independent isoform of tissue transglutaminase in the rat spinal cord

We recently found that alternative transcripts of tissue transglutaminase (tTG or TG2) were present in hippocampal brain regions of Alzheimer's disease (AD), but not in control, non-demented, age-matched brains. Since antecedent non-severe trauma has been implicated in AD and other neurodegenerative diseases, such as Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), we were interested in whether alternative transcripts might be detected in a model of neurotrauma, controlled-contusion spinal cord injury (SCI) in the rat. Implicated in diverse roles from growth and differentiation to apoptotic cell death, only bifunctional tTG, of the nine member TG family, has dual catalytic activities: guanine trinucleotide (GTP) hydrolyzing activity (GTPase), as well as protein cross-linking. These functions imply two physiological functions: programmed cell life and death. These may have profound roles in the nervous system since studies in cultured astrocytes found tTG short (S) mRNA transcripts induced by treatment with injury-related cytokines. In the developing rat spinal cord, tTG activity is concentrated in ventral horn alpha motoneurons, but neither studies of spinal cord tTG gene expression, nor evaluation of the GTP-regulated isoforms in tissues, have been reported. We now report increased tTG protein and gene expression occurring rapidly after SCI. In parallel, novel appearance of a second, short form transcript, in addition to the normal long (L) isoform, occurs by 8 h of injury. Up-regulation of tTG message and activity following neural injury. with appearance of a truncated GTP-unregulated S form, may represent new approaches to drug targets in neurotrauma.

Transglutaminases in disease

Transglutaminases (TGases) are enzymes that are widely used in many biological systems for generic tissue stabilization purposes. Mutations resulting in lost activity underlie several serious disorders. In addition, new evidence documents that they may also be aberrantly activated in tissues and cells and contribute to a variety of diseases, including neurodegenerative diseases such as Alzheimer's and Huntington's diseases. In these cases, the TGases appear to be a factor in the formation of inappropriate proteinaceous aggregates that may be cytotoxic. In other cases such as celiac disease, however, TGases are involved in the generation of autoantibodies. Further, in diseases such as progressive supranuclear palsy, Huntington's, Alzheimer's and Parkinson's diseases, the aberrant activation of TGases may be caused by oxidative stress and inflammation. This review will examine the role and activation of TGases in a variety of diseases.

Tissue transglutaminase localization and activity regulation in the extracellular matrix of articular cartilage

Tissue transglutaminase (tTG) catalyzes a Ca2+-dependent transglutaminase (TGase) activity which cross-links proteins and stabilizes many tissues [C.S. Greenberg et al. FASEB J. 5 (1991) 3071]. Because cartilage is subjected to great stress in vivo, an enzyme that strengthens and stabilizes tissue could play an integral role in maintaining cartilage integrity. The purpose of this study was to determine if active tTG is present in the extracellular matrix (ECM) of adult human osteoarthritic articular cartilage. Using a TGase activity assay along with immunolabeling for tTG of cartilage sections, TGase activity and tTG immunoreactivity were localized in the ECM in cartilage sections, predominantly in the superficial layer. Previous in vitro studies have demonstrated that the Mg-GTP complex inhibits the TGase activity of tTG [T.S. Lai et al. J. Biol. Chem. 273 (1998) 1776]. To investigate the in situ regulation of the TGase activity of tTG, a TGase activity assay was done with a dose response of GTP, measuring incorporation of fluorescein cadaverine. TGase activity was inhibited by GTP in a similar manner as in vitro. These results not only confirm tTG presence in the ECM. but also indicate tTG as the major TGase activity of the ECM. Secondly, the study provides a possible mechanism by which extracellular tTG is regulated in vivo.

Transglutaminase-mediated cross-linking is involved in the stabilization of extracellular matrix in human liver fibrosis

BACKGROUND/AIMS

Lysyl oxidase-mediated cross-linking contributes to the stabilization of collagen in liver fibrosis. We have investigated transglutaminase-mediated cross-linking, to determine if it participates in the stabilization of extracellular matrix in human liver fibrosis.

METHODS

Transglutaminase activity was assessed in vitro by incorporation of biotinylated amine into liver proteins. The product of the transglutaminase-catalyzed cross-linking reaction, Nepsilon(gamma-glutamyl)lysine, and the extracellular proteins cross-linked by it, were localized by immunohistochemistry in fibrotic livers. The cross-linked complexes were extracted from liver tissue, immunopurified and characterized by Western blot.

RESULTS

Transglutaminase, detected by immunohistochemistry, Western blot and by enzymatic activity, was found in higher amounts in fibrotic than in normal liver. The Nepsilon(gamma-glutamyl)lysine cross-link, undetectable in normal liver, was present extracellularly in fibrotic liver, where it was co-distributed with osteonectin, mostly in inflammatory areas submitted to an intense remodeling. Cross-linking of osteonectin by transglutaminase was confirmed by Western blot. In parasitic fibrosis transglutaminase also originates from the parasite.

CONCLUSIONS

Transglutaminase-mediated cross-linking occurs in liver extracellular matrix during the early, inflammatory, stage of liver fibrosis, whereas cross-linking by pyridinoline occurs mostly later in the fibrotic process. This could lead to the development of new anti-fibrotic treatments targeted to a specific stage of fibrosis.

Increases in renal epsilon-(gamma-glutamyl)-lysine crosslinks result from compartment-specific changes in tissue transglutaminase in early experimental diabetic nephropathy: pathologic implications

Diabetic nephropathy (DN) is characterized by an early, progressive expansion and sclerosis of the glomerular mesangium leading to glomerulosclerosis. This is associated with parallel fibrosis of the renal interstitium. In experimental renal scarring, the protein cross-linking enzyme, tissue transglutaminase (tTg), is up-regulated and externalized causing an increase in its crosslink product, epsilon-(gamma-glutamyl)-lysine, in the extracellular space. This potentially contributes to the extracellular matrix (ECM) accumulation central to tissue fibrosis by increasing deposition and inhibiting breakdown. We investigated if a similar mechanism may contribute to the ECM expansion characteristic of DN using the rat streptozotocin model over 120 days. Whole kidney epsilon-(gamma-glutamyl)-lysine (HPLC analysis) was significantly increased from Day 90 (+337%) and peaked at Day 120 (+650%) (p < 0.05). Immunofluorescence showed this increase to be predominantly extracellular in the peritubular interstitial space, but also in individual glomeruli. Total kidney transglutaminase (Tg) was not elevated. However, using a Tg in situ activity assay, increased Tg was detected in both the extracellular interstitial space and glomeruli by Day 60, with a maximal 53% increase at Day 120 (p < 0.05). Using a specific anti-tTg antibody, immunohistochemistry showed a similar increase in extracellular enzyme in the interstitium and glomeruli. To biochemically characterize glomerular changes, glomeruli were isolated by selective sieving. In line with whole kidney measurement, there was an increase in glomerular epsilon-(gamma-glutamyl) lysine (+361%); however, in the glomeruli this was associated with increases in Tg activity (+228%) and tTg antigen by Western blotting (+215%). Importantly, the ratio of glomerular epsilon-(gamma-glutamyl) lysine to hydroxyproline increased by 2.2-fold. In DN, changes in the kidney result in increased translocation of tTg to the extracellular environment where high Ca(2+) and low GTP levels allow its activation. In the tubulointerstitium this is independent of increased tTg production, but dependent in the glomerulus. This leads to excessive ECM cross-linking, contributing to the renal fibrosis characteristic of progressive DN.

Assays for transglutaminases in cell death

Several in vivo and in vitro experimental model systems demonstrate a direct relationship between the expression and activity of tissue transglutaminase [tTG; also called transglutaminase type 2 (TGase 2)] and programmed cell death or apoptosis. This is based on mRNA and protein studies, sense and antisense transfection, identification of N epsilon-(gamma-glutamyl)-lysine cross-links in extracted apoptotic bodies, and in blue mouse experiments. In the epidermis, apoptosis occurs under particular conditions in the proliferative basal layer with the involvement of the tTG enzyme. However, in epidermal keratinocytes other TGases (TGase 1, TGase 3, and perhaps TGase X) are normally activated in a terminal differentiation program, called cornification, that leads to cell death. These cells perform their functions after death, providing an elastic physical and permeability barrier to the skin. In fact, TGase 1 mutations cause the skin disease lamellar ichthyosis. Because all TGases share strong similarities in structure and function, being involved in mechanisms of cell death, this chapter describes the current assays for TGases at the mRNA, protein, and enzymatic levels. We also describe procedures to produce, purify, and characterize recombinant TGases, to identify mutation in disease, to isolate cross-linked bodies, and to analyze the N epsilon-(gamma-glutamyl)-lysine isopeptide cross-links. Finally, we discuss general rules for the interpretation and comparison of these events in cell death.

Facilitated wound healing by activation of the Transglutaminase 1 gene

Transglutaminase 1 (TGase 1) is a Ca(2+)-dependent enzyme which catalyzes epsilon-(gamma-glutamyl)lysine cross-linking of substrate proteins such as involucrin and loricrin to generate the cornified envelope at the cell periphery of the stratum corneum. We have shown that disruption of the TGase 1 gene in mice results in neonatal lethality, absence of the cornified envelope, and impaired skin barrier function. Based on the importance of TGase 1 in epidermal morphogenesis, we have now assessed its role in wound healing. In neonatal mouse skin, TGase 1 mRNA as well as keratin 6alpha was induced in the epidermis at the wound edges as early as 2 hours after injury and that expression continued in the migrating epidermis until completion of re-epithelialization. The TGase 1 enzyme co-localized on the plasma membrane of migrating keratinocytes with involucrin, but not with loricrin, which suggests the premature assembly of the cornified envelope. Similar injuries to TGase 1 knockout mouse skins grafted on athymic nude mice showed substantial delays in wound healing concomitant with sustained K6alpha mRNA induction. From these results, we suggest that activation of the TGase 1gene is essential for facilitated repair of skin injury.

Chicken coagulation factor XIIIA is produced by the theca externa and stabilizes the ovarian follicular wall

Development of the follicle in egg-laying species such as the chicken is regulated by systemic factors as well as by the highly orchestrated interplay of differentially expressed genes within this organ. Differential mRNA display analysis of defined phases of follicle development resulted in the characterization of coagulation factor XIIIA. It is expressed and produced by cells of the theca externa in a highly regulated manner during distinct growth phases of the follicle. Transcripts for factor XIIIA are already detectable at the beginning of follicle development and peak at the end of phase 2. Protein levels, however, still increase during phase 3, peak shortly after ovulation, and persist until the postovulatory tissue is completely resorbed. Factor XIIIA is secreted as a monomer into the extracellular matrix of the theca externa and is not associated with factor XIIIB as is the case in plasma. Our data suggest that, due to its transglutaminase activity, factor XIIIA stabilizes the follicular wall by cross-linking matrix components. Thus, coagulation factor XIIIA might play a key role in coping with the massive mechanical stress exerted by the large amount of yolk accumulating during the rapid growth phase of the oocyte.

Transient expression of transglutaminase C during prenatal development of human muscles

Tissue transglutaminase (TGase C, TGase II) is known to participate in cellular processes during morphogenesis, differentiation, and development of various prenatal tissues and organs. The expression of TGase C during myoblast proliferation and attachment to external laminae was examined by immunohistochemical (IH) localization at 5-12 weeks of developmental stages of prenatal human muscle in 23 embryos. IH detection using a monospecific antibody to TGase C showed a prominent expression of TGase C in muscle cells as stage- and spatial-specific patterns during an early embryonal period. The myoblasts of intervertebral, tongue, and limb muscles, attached to adjacent cartilaginous skeletons or fibrous fascia, showed a pronounced expression of TGase C at 5-6, 6-7, and 7-8 weeks after fertilization, respectively. The most intense activity of TGase C was observed in some cardiac myoblasts infiltrating into endocardial mesenchyme at 6-7 weeks after fertilization. Although weak staining was detected until 14 weeks after fertilization, the level of TGase C expression in all muscles was significantly decreased after 6-7 weeks, with the exception that the smooth muscle cells of blood vessels and gastrointestinal tract showed diffusely intense staining of TGase C between 5 and 12 weeks after fertilization. Western blotting analysis of the cellular extracts of pooled samples showed a single strong band at 80 kD at 6 weeks after fertilization. This band became weaker after 8-10 weeks of prenatal development. These findings of transient expression of TGase C, which coincides with the development of myoblast anchoring and differentiation, suggest that TGase C plays a role in myoblast attachment to the extracellular laminae during the early embryonal period.

Tissue-specific expression and long-term deposition of human collagen VII in the skin of transgenic mice: implications for gene therapy

We report the isolation of a cosmid clone containing the entire human COL7A1 gene in one piece. The ability of the genomic sequences within this clone to direct tissue-specific expression of human collagen VII in transgenic mice was tested. The data show that the gene construct is capable of directing expression of collagen VII in the skin of fetal and neonatal transgenic mice. Expression of COL7A1 in these mice was widespread, in a pattern consistent with that found in human tissues and was in parallel with that of the endogenous mouse gene. Immunostaining, using human-specific antibodies, showed that human collagen VII protein was present at the skin basement membrane zone of the transgenic mice. Dermal extracts from 19-month-old transgenic mice contained mature human collagen VII protein, and fibroblasts derived from skin biopsies of these mice actively synthesized human collagen VII. The demonstration of successful and stable expression of human collagen VII in in vivo gene transfer is the first step towards the future development of therapeutic protocols for the rescue of keratinocyte function in severe blistering diseases such as dystrophic epidermolysis bullosa.

Protein crosslinking in assembly and remodelling of extracellular matrices: the role of transglutaminases

Transglutaminases form a family of proteins that have evolved for specialized functions such as protein crosslinking in haemostasis, semen coagulation, or keratinocyte cornified envelope formation. In contrast to the other members of this protein family, tissue transglutaminase is a multifunctional enzyme apparently involved in very disparate biological processes. By virtue of its reciprocal Ca2+-dependent crosslinking activity or GTP-dependent signal transducing activity, tissue transglutaminase exhibits true multifunctionality at the molecular level. The crosslinking activity can subserve disparate biological phenomena depending on the location of the target proteins. Intracellular activation of tissue transglutaminase can give rise to crosslinked protein envelopes in apoptotic cells, whereas extracellular activation contributes to stabilization of the extracellular matrix and promotes cell-substrate interaction. While tissue transglutaminase synthesis and activation is normally part of a protective cellular response contributing to tissue homeostasis, the enzyme has also been implicated in a number of pathological conditions including fibrosis, atherosclerosis, neurodegenerative diseases, celiac disease, and cancer metastasis. This review discusses the role of transglutaminases in extracellular matrix crosslinking with a focus on the multifunctional enzyme tissue transglutaminase.

Sporadic inclusion body myositis correlates with increased expression and cross-linking by transglutaminases 1 and 2

Sporadic inclusion body myositis (SIBM) is characterized by vacuolar degeneration of muscle fibers and intrafiber clusters of paired helical filaments with abnormal amyloid deposition. Because of their potential involvement in other degenerative disorders, we have examined the expression of transglutaminases (TGases) in normal and SIBM tissues. We report that at least two different enzymes, the ubiquitous TGase 2 as well as the TGase 1 enzyme, are present in muscle tissues. However, in comparison with normal tissue, the expression of TGases 1 and 2 was increased 2.5- and 4-fold in SIBM, accompanied by about a 20-fold higher total TGase activity. By immunohistochemical staining, in normal muscle, TGase 2 expression was restricted to some endomysial connective tissue elements, whereas TGase 1 and beta-amyloid proteins were not detectable. In SIBM muscle, both TGases 1 and 2 as well as amyloid proteins were brightly expressed and co-localized in the vacuolated muscle fibers, but none of these proteins colocalized with inflammatory cell markers. Next, we isolated high molecular weight insoluble proteins from SIBM muscle tissue and showed that they were cross-linked by about 6 residues/1000 residues of the isopeptide bond. Furthermore, by amino acid sequencing of solubilized tryptic peptides, they contain amyloid and skeletal muscle proteins. Together, these findings suggest that elevated expression of TGases 1 and 2 participate in the formation of insoluble amyloid deposits in SIBM tissue and in this way may contribute to progressive and debilitating muscle disease.