Molecular mechanism of transglutaminase-2 in corneal epithelial migration and adhesion

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

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

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.

Mesenchymal Stem Cell Exosomes as Immunomodulatory Therapy for Corneal Scarring

Corneal scarring is a leading cause of worldwide blindness. Human mesenchymal stem cells (MSC) have been reported to promote corneal wound healing through secreted exosomes. This study investigated the wound healing and immunomodulatory effects of MSC-derived exosomes (MSC-exo) in corneal injury through an established rat model of corneal scarring. After induction of corneal scarring by irregular phototherapeutic keratectomy (irrPTK), MSC exosome preparations (MSC-exo) or PBS vehicle as controls were applied to the injured rat corneas for five days. The animals were assessed for corneal clarity using a validated slit-lamp haze grading score. Stromal haze intensity was quantified using in-vivo confocal microscopy imaging. Corneal vascularization, fibrosis, variations in macrophage phenotypes, and inflammatory cytokines were evaluated using immunohistochemistry techniques and enzyme-linked immunosorbent assays (ELISA) of the excised corneas. Compared to the PBS control group, MSC-exo treatment group had faster epithelial wound closure (0.041), lower corneal haze score (p = 0.002), and reduced haze intensity (p = 0.004) throughout the follow-up period. Attenuation of corneal vascularisation based on CD31 and LYVE-1 staining and reduced fibrosis as measured by fibronectin and collagen 3A1 staining was also observed in the MSC-exo group. MSC-exo treated corneas also displayed a regenerative immune phenotype characterized by a higher infiltration of CD163+, CD206+ M2 macrophages over CD80+, CD86+ M1 macrophages (p = 0.023), reduced levels of pro-inflammatory IL-1β, IL-8, and TNF-α, and increased levels of anti-inflammatory IL-10. In conclusion, topical MSC-exo could alleviate corneal insults by promoting wound closure and reducing scar development, possibly through anti-angiogenesis and immunomodulation towards a regenerative and anti-inflammatory phenotype.

Transglutaminase-2 is critical for corneal epithelial barrier function via positive regulation of Claudin-1

PURPOSE

Transglutaminase (TG)-2 is a ubiquitous multi-functional protein expressed in all living cells. The purpose of the current study was to investigate the role of TG-2 in corneal barrier function and its potential regulation of epithelial junctional proteins and transcription factors.

METHODS

Corneal barrier function to ions in TG-2-/- and TG-2+/+ mice was assessed by Ussing chamber assay. Hypo-osmolar water or FITC-dextran was applied on top of mouse eyes to evaluate the corneal barrier function to water and macromolecules. Western blots, qPCR and immunofluorescent staining were used to investigate the expression of tight junction proteins in TG-2-/- and TG-2+/+ mouse corneas, and also in TG-2 knockdown human corneal epithelial cells.

RESULTS

Corneal explants from TG-2-/- mice had a lower trans-epithelial electrical resistance compared to TG-2+/+ mice. When challenged by hypo-osmolar water, the central corneal thickness of TG-2-/- mice increased faster, and these mice had a faster rise of fluorescence in the anterior chamber after ocular exposure to FITC-dextran, compared to TG-2+/+. Claudin-1 protein and transcript levels were reduced in the cornea of TG-2-/- mice and in TG-2 knockdown human corneal epithelial cells. Slug which previously reported suppressing Claudin-1 transcription, was increased at both protein and transcript level in TG-2 knockdown cells. TG-2 and Claudin-1 protein levels were unchanged in shRNA and shTG cells after MG132 treatment, while Slug accumulated in treated cells.

CONCLUSION

TG-2 may positively regulate Claudin-1 through repressing Slug at transcript level, and thus it is critical for normal corneal barrier function.

The TGM2 inhibitor cysteamine hydrochloride does not impact corneal epithelial and stromal wound healing in vitro and in vivo

Corneal wound healing is integral for resolution of corneal disease or for post-operative healing. However, corneal scarring that may occur secondary to this process can significantly impair vision. Tissue transglutaminase 2 (TGM2) inhibition has shown promising antifibrotic effects and thus holds promise to prevent or treat corneal scarring. The commercially available ocular solution for treatment of ocular manifestations of Cystinosis, Cystaran®, contains the TGM2 inhibitor cysteamine hydrochloride (CH). The purpose of this study is to assess the safety of CH on corneal epithelial and stromal wounds, its effects on corneal wound healing, and its efficacy against corneal scarring following wounding. Quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC) were first used to quantify and localize TGM2 expression in the cornea. Subsequently, (i) the in vitro effects of CH at 0.163, 1.63, and 16.3 mM on corneal epithelial cell migration was assessed with an epithelial cell migration assay, and (ii) the in vivo effects of application of 1.63 mM CH on epithelial and stromal wounds was assessed in a rabbit model with ophthalmic examinations, inflammation scoring, color and fluorescein imaging, optical coherence tomography (OCT), and confocal biomicroscopy. Post-mortem assessment of corneal tissue post-stromal wounding included biomechanical characterization (atomic force microscopy (AFM)), histology (H&E staining), and determining incidence of myofibroblasts (immunostaining against α-SMA) in wounded corneal tissue. TGM2 expression was highest in corneal epithelial cells. Application of the TGM2 inhibitor CH did not affect in vitro epithelial cell migration at the two lower concentrations tested. At 16.3 mM, decreased cell migration was observed. In vivo application of CH at 57 mM was well tolerated and did not adversely affect wound healing. No difference in corneal scarring was found between CH treated and vehicle control eyes. This study shows that the TGM2 inhibitor CH, at the FDA-approved dose, is well tolerated in a rabbit model of corneal wound healing and does not adversely affect epithelial or stromal wound healing. This supports the safe use of this medication in Cystinosis patients with open corneal wounds. CH did not have an effect on corneal scarring in this study, suggesting that Cystaran® administration to patients with corneal wounds is unlikely to decrease corneal fibrosis.

Topical retinoic acid induces corneal strengthening by upregulating transglutaminase 2 in murine cornea

Transglutaminase 2 (TG2) is the most abundant crosslinking enzyme in murine and human cornea, while retinoids are well-known inducers of TG2 expression. This study aims to determine if the retinoic acid supplementation can increase corneal stiffness by crosslinking through upregulating the corneal TG2 expression. The right eyes of C57BL/6 mice were treated with 2 × 10^-2M retinol palmitate (VApal) eyedrops or control eyedrops and hold for 30 min, once a day for 28 consecutive days. The WB and qPCR results showed increased expression of TG2 in murine cornea with the prolongation of VApal eyedrop application. After 28 days of VApal eyedrop treatment, the increased TG2 were found catalytically active and distributed in corneal epithelium and stroma as detected by 5-(biotinamido) pentylamine (5-BP) incorporation method and immunofluorescence staining. The transmission electron microscope image revealed that VApal treated cornea manifested with increased collagen density in anterior and middle layer of stroma. The higher elastic module was found among VApal treated cornea by nano-indentation test. In cultured corneal epithelial cells and keratocytes, all-trans retinoid acid (ATRA) treatment increased the content of TG2 in cell lysis and in culture medium. These results indicate that retinoic acid induce the reinforcement of the cornea by TG2 mediated crosslinking via increasing the TG2 expression in corneal epithelium and keratocyte. As TG2 was found to be less in the cornea of keratoconus patients in several RNA-sequencing studies, retinoic acid could serve as a non-invasive prevention method for keratoconus progression.

Peucedanum japonicum Thunberg and Its Active Components Mitigate Oxidative Stress, Inflammation and Apoptosis after Urban Particulate Matter-Induced Ocular Surface Damage

We previously demonstrated that urban particulate matter (UPM) exposure decreases the migration activity and survival of human corneal epithelial cells (HCECs). Herein, we investigated the potential to improve the corneal wound-healing ability of Peucedanum japonicum Thunb. leaf extract (PJE) and its active components on UPM-induced ocular surface damage in vitro and in vivo. PJE effectively assisted wound healing without altering HCEC survival and enhanced catalase (CAT), heme oxygenase 1 (HO1) and glutathione peroxidase 1 (GPX1) antioxidant gene expression. A corneal wound was uniformly induced on the right eye in all experimental animals and divided into eight groups such as two control groups (wounded right eye group-NR and non-wounded left eye group-NL), UPM treated group and PJEs (25, 50, 100, 200, 400 mg/kg) treated groups. Corneal abrasion model rats exposed to UPM showed delayed wound healing compared to unexposed rats, but wound healing was dose-dependently enhanced by PJE oral administration. Seventy-two hours after wound generation, inflammatory cells, apoptotic cells and interleukin-6 (IL-6) expression were increased substantially after UPM exposure, but PJE treatment significantly reduced the wound to an almost normal level while enhancing re-epithelialization without changing corneal thickness. Next, we tried to identify the key molecules for enhancing wound healing through fractionation. The major compounds in the fraction, confirmed by high-performance liquid chromatography (HPLC), were chlorogenic acid (CA), neochlorogenic acid (NCA) and cryptochlorogenic acid (CCA). Each type of CA isomers showed slightly different half maximal effective (EC50) and maximal effective (ECmax) concentrations, and their mixtures synergistically enhanced HCEC migration. Thus, corneal abrasion wound recovery after UPM exposure improved after PJE treatment, and the active PJE components were identified, providing an important basis to develop therapeutics for ocular surface damage using PJE.

HCE-T cell line lacks cornea-specific differentiation markers compared to primary limbal epithelial cells and differentiated corneal epithelium

PURPOSE

Human corneal epithelial cell-transformed (HCE-T) cell line is used as a widely accepted barrier model for pharmacological investigations in the context of eye application. The differentiation of (limbal) corneal epithelial into mature corneal epithelium coincides with the expression of established differentiation markers. If these differentiation mechanisms are disturbed, it will lead to ocular surface disease. In this study, we want to compare the expression of differentiation markers in the HCE-T cell line to differentiated primary epithelial cells (pCECs) and primary limbal epithelial cell (LEC) culture. This is necessary in order to decide whether HCE-T cells could be a tool to study the differentiation process and its regulatory networks in corneal epithelium.

METHODS

Primary limbal epithelial cells (LECs) for cell culture and primary corneal epithelial cells (pCECs) as differentiated tissue samples were obtained from the limbus or central cornea region of corneal donors. HCE-T cell line was purchased from RIKEN Institute RCB-2280.Expression levels of conjunctival- and corneal-specific keratin and adhesion markers (KRT3, KRT12, KRT13, KRT19, DSG1), stem cell and differentiation markers (PAX6, ABCG2, ADH7, TP63, ALDH1A1), and additional (unvalidated) putative differentiation and stem cell markers (CTSV, SPINK7, DKK1) were analyzed with qPCR. Additionally, KRT3, KRT12, DSG1, and PAX6 protein levels were analyzed with Western blot.

RESULTS

KRT3, KRT12, DSG1, PAX6, ADH7, and ALDH1A1 mRNA expressions were higher in LECs and magnitudes higher in pCECs compared to HCE-T cells. KRT3, KRT12, PAX6, ALDH1A1, ADH7, TP63, and CTSV mRNAs have shown increasing mRNA expression from HCE-T < HCE-T cultured in keratinocyte serum-free medium (KSFM) < LEC < to pCEC.KRT3 and KRT12 protein expressions were only slightly increased in LEC compared to HCE-T samples, and the strongest signals were seen in pCEC samples. DSG1 protein expression was only detected in pCECs. PAX6 protein expression was hardly detected in HCE-T cells, and no difference could be seen between LECs and pCECs.

CONCLUSIONS

The HCE-T cell line is even less differentiated than LECs regarding the investigated markers and therefore might also lack the ability to express differentiation markers at protein level. Hence, this cell line is not suitable to study corneal differentiation processes. Primary LECs in the way cultured here are not an ideal system compared to differentiated epithelium in organ culture but should be preferred to HCE-T cells if corneal differentiation markers are investigated. Other cell models or differentiation protocols should be developed in the future to gain new tools for research on ocular surface diseases.

Cellular therapy of corneal epithelial defect by adipose mesenchymal stem cell-derived epithelial progenitors

Background

Persistent epithelial defects (PED), associated with limbal stem cell deficiency (LSCD), require ocular surface reconstruction with a stable corneal epithelium (CE). This study investigated CE reformation using human adipose mesenchymal stem cells (ADSC), which derived epithelial progenitors via mesenchymal-epithelial transition (MET).

Methods

STEMPRO human ADSC were cultured with specific inhibitors antagonizing glycogen synthase kinase-3 and transforming growth factor-β signaling, followed by culture under a defined progenitor cell targeted-epithelial differentiation condition to generate epithelial-like cells (MET-Epi), which were characterized for cell viability, mesenchymal, and epithelial phenotypes using immunofluorescence and flow cytometry. Tissue-engineered (TE) MET-Epi cells on fibrin gel were transplanted to corneal surface of the rat LSCD model caused by alkali injury. Epithelial healing, corneal edema, and haze grading, CE formation were assessed by fluorescein staining, slit lamp bio-microscopy, anterior segment optical coherence tomography, and immunohistochemistry.

Results

CD73^high/CD90^high/CD105^high/CD166^high/CD14^negative/CD31^negative human ADSC underwent MET, giving viable epithelial-like progenitors expressing δNp63, CDH1 (E-cadherin), epidermal growth factor receptor, integrin-β4, and cytokeratin (CK)-5, 9. Under defined epithelial differentiation culture, these progenitors generated MET-Epi cells expressing cell junction proteins ZO1 and occludin. When transplanted onto rat corneal surface with LSCD-induced PED, TE-MET-Epi achieved more efficient epithelial healing, suppressed corneal edema, and opacities, when compared to corneas without treatment or transplanted with TE-ADSC. CE markers (CK3, 12, and CDH1) were expressed on TE-MET-Epi-transplanted corneas but not in other control groups.

Conclusion

Human ADSC-derived epithelial-like cells, via MET, recovered the CE from PED associated with LSCD. ADSC can be a viable adult stem cell source for potential autologous epithelial cell-based therapy for corneal surface disorders.

Biomaterials and controlled release strategy for epithelial wound healing

The skin and cornea are tissues that provide protective functions. Trauma and other environmental threats often cause injuries, infections and damage to these tissues, where the degree of injury is directly correlated to the recovery time. For example, a superficial skin or corneal wound may recover within days; however, more severe injuries can last up to several months and may leave scarring. Thus, therapeutic strategies have been introduced to enhance the wound healing efficiency and quality. Although the skin and cornea share similar anatomic structures and wound healing process, therapeutic agents and formulations for skin and cornea wound healing differ in accordance with the tissue and wound type. In this review, we describe the anatomy and epithelial wound healing processes of the skin and cornea, and summarize the therapeutic molecules that are beneficial to the respective regeneration process. In addition, biomaterial scaffolds that inherently possess bioactive properties or modified with therapeutic molecules for topical controlled release and enhanced wound healing efficiency are also discussed.

Mechanistic role of transglutaminase-2 in focal adhesions

Transglutaminase (TG)-2 interacts with matrix proteins and integrins, forming focal adhesions (FA) to initiate cell migration, thus playing a vital role in wound healing. Previously we showed that TG-2 influenced phosphorylation of paxillin and other FA proteins. Here, we aimed to investigate the molecular mechanism of TG-2 regulation of paxillin. Human corneal epithelial cells expressing shRNA against TG-2 (shTG) and scrambled sequence control (shRNA) were cultured. TG-2 was pulled down by anti-paxillin antibody, but not MAP3K12. Cell-free interaction assay with immobilized paxillin shows that TG-2 bind to paxillin directly. JNK was the strongest kinase for paxillin phosphorylation in the in-vitro kinase screen, but TG-2 could not phosphorylate paxillin directly. Increasing TG-2 concentrations did not increase the amount of JNK in the TG-2/paxillin complex. Immunofluoresent staining shows that TG-2 colocalises with vinculin and paxillin in FA of migrating cells. TG-2 binds to paxillin and JNK-containing FA but does not recruit JNK directly. Taken together with previous findings, TG-2 binds paxillin non-covalently, and JNK can phosphorylate paxillin, these processes critically regulate corneal epithelial adhesion and migration.

Transglutaminase 2 Promotes Migration and Invasion of Lung Cancer Cells

Lung cancer is the leading cause of cancer deaths worldwide. Given that the major threat of cancer is metastasis, delineation of the molecular mechanism underlying it would help devise therapeutic strategies. Transglutaminase 2 (TG2), belonging to the transglutaminase superfamily, is a versatile protein with enzymatic and nonenzymatic functions. It mainly localizes inside the cell, but also appears extracellularly. Recent findings have demonstrated the involvement of TG2 in cancer development. Here we examine the role of TG2 in metastasis of lung cancer using a lung cancer cell line CL1-0, which exhibits low invasiveness, and its invasive subline CL1-5. Our results show that CL1-5 cells express a higher amount of TG2 than CL1-0 cells. Overexpression of TG2 in CL1-0 enhances cell migration and invasion, and lowering TG2 expression in CL1-5 cells reduces their ability to do so. The transamidase activity of TG2 is not required since cells expressing the inactive TG2 mutant or treated with a TG2 inhibitor are still able to migrate and invade. TG2-stimulated migration and invasion are, at least in part, mediated by Rac, as inhibition of Rac activity suppresses cell migration and invasion. Lastly, exogenous application of recombinant TG2 protein to CL1-0 cells substantially augments cell migration and invasion, suggesting the significance of extracellular TG2 in promoting these events. Collectively, our results show that TG2 plays a positive role in cell migration and invasion, and this might help metastasis of lung cancer cells.

Toll-like receptor 2-mediated NF-kappa B pathway activation in ocular surface epithelial cells

BACKGROUND

Gram-positive bacteria stimulate Toll-like receptor (TLR) 2 and then activate the pro-inflammatory nuclear factor-kappa B (NF-κB) pathway. As the human ocular surface is heavily colonised by gram-positive cocci bacteria, a balance of activation/repression of NF-κB target genes is essential to avoid uncontrolled infection or autoimmune-related inflammation. It is advantageous to test NF-κB targeting molecules in an ocular surface culture system that allows assessment of temporal NF-κB activation in a longitudinal fashion without destruction of cells. Such initial testing under standardised conditions should reduce the number of molecules that progress to further evaluation in animal models. This study aims to establish an in-vitro cell culture system to assess NF-κB activation in the context of ocular surface cells.

METHODS

NF-κB activity was evaluated through a secretory alkaline phosphatase reporter assay (SEAP). Immunoblots and immunofluorescence were used to examine IκBα phosphorylation and p65/p50 nuclear localization. Monocyte chemoattractant protein-1 (MCP-1) transcripts were evaluated by real time PCR and protein levels were measured by ELISA.

RESULTS

NF-κB activity in HCE-T cells treated with TLR2 activator Pam3CSK4 was higher than control cells at both 6 and 24 h. Pam3CSK4-stimulated NF-κB activation was inhibited by IκK inhibitors, Wedelolactone and BMS-345541. In Pam3CSK4 treated cells, active NF-κB subunits p50 and p65 increased in cell nuclear fractions as early as 1.5 h. Although the level of total IκB-α remained constant, phospho-IκB-α increased with treatment over time. In the culture media of Pam3CSK4-stimulated cells, MCP-1 protein level was increased, which was suppressed in the presence of IκK inhibitors.

CONCLUSION

NF-κB pathway can be activated by the TLR2 ligand and inhibited by IκK inhibitors in the ocular surface cell culture system. This cell culture system may be used to evaluate TLR-related innate defences in ocular surface diseases.

The proteomic profile of a mouse model of proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) develops as a complication of retinal detachment surgery and represents a devastating condition leading to serious vision loss. A good animal model that permits extensive functional studies and drug testing is crucial in finding better therapeutic modalities for PVR. A previously established mouse model, using dispase injection, was analyzed from the proteomic point of view, examining global protein profile changes by 2D electrophoresis, image analysis and HPLC–tandem mass spectrometry‐based protein identification. The easy applicability of the mouse model was used to study the role of transglutaminase 2 (TG2) in PVR formation by proteomic examination of dispase‐induced TG2 knockout vitreous samples. Our data demonstrate that, despite the altered appearance of crystallin proteins, the lack of TG2 did not prevent the development of PVR.

Lipopolysaccharide and Curcumin Co-Stimulation Potentiates Olfactory Ensheathing Cell Phagocytosis Via Enhancing Their Activation

The gradual deterioration following central nervous system (CNS) injuries or neurodegenerative disorders is usually accompanied by infiltration of degenerated and apoptotic neural tissue debris. A rapid and efficient clearance of these deteriorated cell products is of pivotal importance in creating a permissive environment for regeneration of those damaged neurons. Our recent report revealed that the phagocytic activity of olfactory ensheathing cells (OECs) can make a substantial contribution to neuronal growth in such a hostile environment. However, little is known about how to further increase the ability of OECs in phagocytosing deleterious products. Here, we used an in vitro model of primary cells to investigate the effects of lipopolysaccharide (LPS) and curcumin (CCM) co-stimulation on phagocytic activity of OECs and the possible underlying mechanisms. Our results showed that co-stimulation using LPS and CCM can significantly enhance the activation of OECs, displaying a remarkable up-regulation in chemokine (C-X-C motif) ligand 1, chemokine (C-X-C motif) ligand 2, tumor necrosis factor-α, and Toll-like receptor 4, increased OEC proliferative activity, and improved phagocytic capacity compared with normal and LPS- or CCM-treated OECs. More importantly, this potentiated phagocytosis activity greatly facilitated neuronal growth under hostile culture conditions. Moreover, the up-regulation of transglutaminase-2 and phosphatidylserine receptor in OECs activated by LPS and CCM co-stimulation are likely responsible for mechanisms underlying the observed cellular events, because cystamine (a specific inhibitor of transglutaminase-2) and neutrophil elastase (a cleavage enzyme of phosphatidylserine receptor) can effectively abrogate all the positive effects of OECs, including phagocytic capacity and promotive effects on neuronal growth. This study provides an alternative strategy for the repair of traumatic nerve injury and neurologic diseases with the application of OECs in combination with LPS and CCM.

Transglutaminase binding fusion protein linked to SLPI reduced corneal inflammation and neovascularization

BACKGROUND

To study the effect of topical administration of a fusion protein (PF-MC) made up of N-terminal portion of the protease inhibitor Trappin-2 (which is a substrate of transglutaminasa-2) and SLPI (protein with anti-inflammatory, anti-bacterial and anti-viral ability), in an animal model of corneal inflammation and angiogenesis.

METHODS

An alkali injury was produced with a filter paper of 3 mm with 1 N NaOH during 40 seconds on the right cornea of 36 male Sprague Dawley rats, under general anesthesia. Animals were divided into three groups according to treatment. Group 1 was treated with 10 ul of PF-MC (200 ug/ml; n = 12), Group 2, with 10 ul of SLPI (200 ug/ml; n = 12) and Group 3 was treated with buffer (10 ul; n = 12) topically administered four times a day for up to 7 days. Half of the animals were sacrificed at day 3 before making a re-epithelialization time analysis with fluorescein staining at 18 and 24 hours. In the remaining animals corneal opacity was studied and digital photographs were taken at day 7 before doing euthanasia. Eyes were processed for histology and immunofluorescence.

RESULTS

Corneal ulcerated area was significantly lower in PF-MC treated animals compared to SLPI and buffer-treated animals at 18 hours and 24 hours postinjury. A clear cornea and fundus red reflex was only found among PF-MC treated animals. Histological analysis revealed a stratified corneal epithelium with at least three layers in all PF-MC animals at day 7. In this group there was a reduced number of PMNs in the corneal stroma at 3 and 7 days of follow-up. Besides, corneal neovascularization was much more extended in SLPI and Buffer animals than in animals treated with PF-MC.

CONCLUSIONS

The binding of SLPI with Cementoin to transglutaminase seems to be an effective strategy to treat corneal inflammation and angiogenesis.

Transglutaminase regulation of cell function

Transglutaminases (TGs) are multifunctional proteins having enzymatic and scaffolding functions that participate in regulation of cell fate in a wide range of cellular systems and are implicated to have roles in development of disease. This review highlights the mechanism of action of these proteins with respect to their structure, impact on cell differentiation and survival, role in cancer development and progression, and function in signal transduction. We also discuss the mechanisms whereby TG level is controlled and how TGs control downstream targets. The studies described herein begin to clarify the physiological roles of TGs in both normal biology and disease states.

Transglutaminase-2 in cell adhesion: all roads lead to paxillin?

Cell-matrix adhesion is a fundamental biological process that governs survival, migration, and proliferation of living eukaryotic cells. Paxillin is an important central player in a network of adhesome proteins that form focal adhesion complexes. Phosphorylation of tyrosine and serine residues in paxillin is critical for the coordinated sequential recruitment of other adaptor and kinase proteins to adhesion complexes. Recently, the phosphorylation of serine178 in paxillin has been shown to be vital for epithelial cell adhesion and migration. In vivo and in vitro evidence have shown that transglutaminase (TG)-2 positively regulates this phosphorylation. Here, we propose three possible mechanisms that may explain these observations. First, TG-2 itself may be an adhesome member directly interacting with paxillin in a non-covalent way. Second, TG-2 may cross link a mitogen-activated protein kinase kinase kinase (MAP3K), which eventually activates c-Jun N-terminal kinase (JNK), and the latter phosphorylates paxillin. Lastly, TG-2 may have intrinsic kinase activity that phosphorylates paxillin. Future studies investigating these hypotheses on TG-2-paxillin relationships are necessary in order to address this fundamental process in cell matrix adhesion signaling.