Transglutaminase activation in neurodegenerative diseases

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

Transglutaminases and neurodegeneration

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

Increased tissue transglutaminase expression in human atherosclerotic coronary arteries

BACKGROUND AND OBJECTIVE

Transglutaminase 2 (TGase 2) is a calcium-dependent cross-linking enzyme that catalyzes a covalent iso-peptide bond between two proteins. Interestingly, this catalysis can activate the nuclear factor-kappaB (NF-kappaB) through the polymerization of the inhibitory protein of NF-kappaB (I-kappaB). The objective of the present study was to investigate the expression of TGase 2 in the human atherosclerotic human coronary artery, and the possible roles of TGase 2 in NF-kappaB activation.

METHODS AND RESULTS

We explored whether expressions of TGase 2 and NF-kappaB are associated in atherosclerosis. Using human samples, we found that TGase 2 was markedly higher than normal in the neointimal tissue of atherosclerotic coronary arteries with atherosclerosis progression. TGase 2 activity was also increased approximately two-fold in the atherosclerotic vascular wall. In immunofluorescence analysis, NF-kappaB, COX-2, and TNF-alpha were co-localized at TGase 2-positive neointimal smooth muscle cells. A promoter assay test showed that NF-kappaB activity increased in both the human monocyte and human breast carcinoma cell by TGase 2, and that TGase 2-mediated NF-kappaB activation was reversed by TGase 2 siRNA.

CONCLUSION

According to these results, we suggest that TGase 2 may function as an activator in the NF-kappaB pathway; this effect may occur in the atherosclerotic vessel wall.

A new regulatory mechanism of NF-kappaB activation by I-kappaBbeta in cancer cells

Transglutaminase 2 (TGase 2) catalyzes covalent isopeptide bond formation between glutamine and lysine residues. Recently, we reported that TGase 2 activates nuclear factor-kappa B (NF-kappaB) by depleting inhibitor of NF-kappaBalpha (I-kappaBalpha) levels via polymer formation. Furthermore, TGase 2 expression synergistically increases NF-kappaB activity with canonical pathway. The major I-kappaB proteins such as I-kappaBalpha and I-kappaBbeta resemble each other in both primary sequence and tertiary structure. However, I-kappaBbeta does not degrade fully, while I-kappaBalpha degrades immediately in response to most stimuli. We found that I-kappaBbeta does not contain any of the previously identified TGase 2 target sites. In this study, both an in vitro cross-linking assay and a TGase 2 transfection assay revealed that I-kappaBbeta is independent from TGase 2-mediated polymerization. Furthermore, increased I-kappaBbeta expression reversed NF-kappaB activation in cancer cells, compensating for the loss of I-kappaBalpha via TGase 2 polymerization.

Glucosamine is an effective chemo-sensitizer via transglutaminase 2 inhibition

Aberrant increases of transglutaminase 2 (TGase 2) in tumors contribute to drug resistance. The role of TGase 2 in cancer pathogenesis was unknown until we showed that TGase 2 activates NF-kappaB in the absence of kinase-dependent phosphorylation. It appears that increased expression of TGase 2 is responsible for the constitutive activation of NF-kappaB in cancer cells. We have demonstrated that TGase 2 inhibition using siRNA, cystamine or R2 peptide promotes cell death in drug-resistant cancer cells through NF-kappaB inactivation. Therefore, a safe and effective small molecule for TGase 2 inhibition is being sought in the development of therapeutics for malignant cancers. By screening for TGase inhibitors in a natural compound library, we found that glucosamine has a TGase 2 inhibitory effect in vitro. Glucosamine also recovered the depletion of I-kappaBalpha via TGase 2 inhibition, which resulted in a decrease of NF-kappaB activity in EcR293/TG cells. Furthermore, glucosamine efficiently promoted cell death via inhibiting TGase 2-mediated NF-kappaB activation in drug-resistant breast cancer cells. These results suggest that glucosamine, as a TGase 2 inhibitor, might be an attractive novel target for treatment of malignant cancers.

Transglutaminase type II is involved in the pathogenesis of endotoxic shock

The pathogenesis of sepsis is characterized by the inability of the host to regulate the inflammatory response, and as a consequence, dysregulated inflammatory processes induce organ dysfunctions and death. Altered transglutaminase type II (TG2) expression is associated with the development of many inflammatory diseases. Therefore, in this study, we questioned whether TG2 could also contribute to the pathological inflammatory dysregulation occurring in septic shock in vivo. To this aim, we used as an experimental model the TG2 knockout mice, in which the process of septic shock was elicited by treatment with LPS. Interestingly, our results demonstrated that TG2 ablation leads to partial resistance to experimental sepsis. The increased survival of TG2(-/-) mice was reflected in a drastic reduction of organ injury, highlighted by a limited infiltration of neutrophils in kidney and peritoneum and by a better homeostasis of the proinflammatory mediators as well as mitochondrial function. We also showed that in wild-type mice, the TG2 expression is increased during endotoxemia and, being directly involved in the mechanisms of NF-kappaB activation, it may cause a continuous activation cycle in the inflammatory process, thus contributing to development of sepsis pathogenesis. We propose that the inhibition of TG2 could represent a novel approach in the treatment of inflammatory processes associated with sepsis.

Uteroglobin: a steroid-inducible immunomodulatory protein that founded the Secretoglobin superfamily

Blastokinin or uteroglobin (UG) is a steroid-inducible, evolutionarily conserved, secreted protein that has been extensively studied from the standpoint of its structure and molecular biology. However, the physiological function(s) of UG still remains elusive. Isolated from the uterus of rabbits during early pregnancy, UG is the founding member of a growing superfamily of proteins called Secretoglobin (Scgb). Numerous studies demonstrated that UG is a multifunctional protein with antiinflammatory/ immunomodulatory properties. It inhibits soluble phospholipase A(2) activity and binds and perhaps sequesters hydrophobic ligands such as progesterone, retinols, polychlorinated biphenyls, phospholipids, and prostaglandins. In addition to its antiinflammatory activities, UG manifests antichemotactic, antiallergic, antitumorigenic, and embryonic growth-stimulatory activities. The tissue-specific expression of the UG gene is regulated by several steroid hormones, although a nonsteroid hormone, prolactin, further augments its expression in the uterus. The mucosal epithelia of virtually all organs that communicate with the external environment express UG, and it is present in the blood, urine, and other body fluids. Although the physiological functions of this protein are still under investigation, a single nucleotide polymorphism in the UG gene appears to be associated with several inflammatory/autoimmune diseases. Investigations with UG-knockout mice revealed that the absence of this protein leads to phenotypes that suggest its critical homeostatic role(s) against oxidative damage, inflammation, autoimmunity, and cancer. Recent studies on UG-binding proteins (receptors) provide further insight into the multifunctional nature of this protein. Based on its antiinflammatory and antiallergic properties, UG is a potential drug target.

Clara cell 16-kd protein downregulates T(H)2 differentiation of human naive neonatal T cells

BACKGROUND

Levels of the Clara cell 16-kd protein (CC16) are lower in plasma and bronchoalveolar lavage fluid from adults with asthma relative to those seen in healthy control subjects, and CC16 inhibits the T(H)2 cytokine production from murine T cells.

OBJECTIVE

We sought to determine the plasma levels of CC16 in infants and to investigate whether CC16 might inhibit the T(H)2 cytokine production from neonatal T cells.

METHODS

Cord blood and blood samples at 4, 18, and 36 months of age were taken from 64 children prospectively, and CC16 levels were analyzed in plasma. Cord monocyte-derived dendritic cells (DCs) were pulsed with birch allergen extract alone or together with CC16 or prostaglandin D(2) receptor inhibitors, after which autologous naive CD4(+) T cells were added to the DCs. The production of IL-5, IL-13, and IFN-gamma was measured by means of ELISA and flow cytometry.

RESULTS

The plasma levels of CC16 in children peaked at 4 months. CC16 did not directly affect the cytokine production from human T(H)2 cells. However, CC16 inhibited birch pollen extract-stimulated T(H)2 differentiation of naive T cells through the DC. Inhibition of the prostaglandin D(2) receptors did not consistently result in suppressed T(H)2 differentiation.

CONCLUSION

The production of CC16 seems to peak early in life, and CC16 has an inhibitory effect on T(H)2 cell differentiation from human infants by affecting DCs.

CLINICAL IMPLICATIONS

CC16 is an immunoregulatory protein, and its inhibitory effect on T(H)2 cell differentiation might be of importance in the pathogenesis of allergy in infants.

Inverse relation between nasal fluid Clara Cell Protein 16 levels and symptoms and signs of rhinitis in allergen-challenged patients with intermittent allergic rhinitis

BACKGROUND

Decreased levels of the anti-inflammatory Clara Cell Protein 16 (CC16) are found in intermittent allergic rhinitis (IAR) and asthma. In asthma this decrease has been associated with hyperreactivity and the A38G single nucleotide polymorphism (SNP). The aim of this study was to examine if IAR is associated with signs and symptoms of rhinitis and the A38G SNP.

METHODS

Nasal fluid CC16 was analyzed in 20 patients with IAR before allergen challenge and 1 and 6 h after challenge, and from 28 healthy controls. The A38G SNP was analyzed in 80 patients with IAR and 106 controls. Nasal biopsies were obtained from three subjects in each group for immunohistochemical analysis of CC16.

RESULTS

In the allergen-challenged patients symptoms and rhinoscopic signs of rhinitis increased after 1 h and normalized after 6 h. In contrast, nasal fluid CC16 decreased 1 h after allergen challenge and returned to baseline after 6 h. Nasal fluid CC16 levels did not differ from controls before and 6 h after challenge. Immunohistochemical investigation showed intense CC16 staining in the nasal epithelium of both patients before season and healthy controls, but weak staining in symptomatic patients during season. No significant association between the A38G SNP and IAR was found.

CONCLUSION

There was an inverse relation between nasal fluid CC16 levels and symptoms and signs of rhinitis in allergen-challenged patients with IAR. However, there was no association between IAR and the A38G SNP.

Reversal of drug resistance in breast cancer cells by transglutaminase 2 inhibition and nuclear factor-kappaB inactivation

Induction of transglutaminase 2 (TGase 2) by epidermal growth factor (EGF) in human breast cancer cells increases their oncogenic potential and chemoresistance. The role of TGase 2 in the development of these tumor-related phenotypes remains to be elucidated, but it has been shown that expression of a dominant-negative form of TGase 2 reverses EGF-mediated chemoresistance in breast cancer cells. We examined several different breast cancer cell lines, representing both EGF receptor (EGFR)-positive and EGFR-negative breast cancers, and found that doxorubicin-resistant cells had a higher level of TGase 2 compared with doxorubicin-sensitive cells independent of the EGFR expression level. TGase 2 inhibition increased the chemosensitivity of drug-resistant cells, concomitant with a decrease in nuclear factor-kappaB (NF-kappaB) activity. Increasing the level of TGase 2 in drug-sensitive cells by transient transfection reduced the level of inhibitory subunit alpha of NF-kappaB (IkappaBalpha) and increased NF-kappaB activity in these cells. Inhibition of TGase 2 in drug-resistant cells by RNA interference increased the levels of IkappaBalpha, and this correlated with a shift in the accumulation of NF-kappaB from the nucleus to the cytosol. We recently showed that TGase 2 activated NF-kappaB through polymerization and depletion of free IkappaBalpha during inflammation. Therefore, increased expression of TGase 2 and subsequent activation of NF-kappaB may contribute to drug resistance in breast cancer cells independently of EGF signaling.

Transglutaminase 2 Mediates Polymer Formation of I-κBα through C-terminal Glutamine Cluster

Recently we reported that transglutaminase 2 (TGase 2) activates nuclear factor-kappaB (NF-kappaB) independently of I-kappaB kinase (IKK) activation, by inducing cross-linking and protein polymer formation of inhibitor of nuclear factor-kappaBalpha (I-kappaBalpha). TGase 2 catalyzes covalent isopeptide bond formation between the peptide bound-glutamine and the lysine residues. Using matrix-assisted laser desorption ionization time-of-flight mass spectra analysis of I-kappaBalpha polymers cross-linked by TGase 2, as well as synthetic peptides in an in vitro competition assay, we identified a glutamine cluster at the C terminus of I-kappaBalpha (amino acids 266-268) that appeared to play a key role in the formation of I-kappaBalpha polymers. Although there appeared to be no requirement for specific lysine residues, we found a considerably higher preference for the use of lysine residues at positions 21, 22, and 177 in TGase 2-mediated cross-linking of I-kappaBalpha. We demonstrated that synthetic peptides encompassing the glutamine cluster at amino acid positions 266-268 reversed I-kappaBalpha polymerization in vitro. Furthermore, the depletion of free I-kappaBalpha in EcR/TG cells was completely rescued in vivo by transfection of mutant I-kappaBalphas in glutamine sites (Q266G, Q267G, and Q313G) as well as in a lysine site (K177G). These findings provide additional clues into the mechanism by which TGase 2 contributes to the inflammatory process via activation of NF-kappaB.

Control of phospholipase A2 activities for the treatment of inflammatory conditions

Phospholipase-A2 (PLA2) enzymes hydrolyze cell membrane phospholipids to produce arachidonic acid (AA) and lyso-phospholipids (LysoPL), playing a key role in the production of inflammatory lipid mediators, mainly eicosanoids. They are therefore considered pro-inflammatory enzymes and their inhibition has long been recognized as a desirable therapeutic target. However, attempts to develop suitable PLA2 inhibitors for the treatment of inflammatory diseases have yet to succeed. This is due to their functional and structural diversity, and their homeostatic and even anti-inflammatory roles in certain circumstances. In the present review we outline the diversity and functions of PLA2 isoforms, and their interplay in the induction and inhibition of inflammatory processes, with emphasis on discussing approaches for therapeutic manipulation of PLA2 activities.

A Peptide with anti-transglutaminase activity decreases lipopolysaccharide-induced lung inflammation in mice

Octapeptide R2 (KVLDGQDP), which has anti-transglutaminas (TGase) activity, decreases inflammation in allergic conjunctivitis model in guinea pigs. The authors examined the effect of R2 on lipopolysaccharide (LPS)-induced lung injury in BALB/c mice. R2 inhalation significantly decreased neutrophil count and cytokine mRNA expression in the lungs of LPS (25 mg/kg)-treated mice (P < .05). It also showed a tendency for decreased tumor necrosis factor (TNF)-alpha-immunoreactive protein in lung homogenates and significantly decreased TNF-alpha-immunoreactive protein in the serum of LPS-injected mice (P < .05). These results indicate that TGase may be a new therapeutic target in LPS-induced lung inflammation.

Effects of antiflammins on transglutaminase and phospholipase A2 activation by transglutaminase

Two anti-inflammatory peptides, named antiflammins (AFs), corresponding to a region with high amino acid similarity between lipocortin-1 and uteroglobin were tested for their ability to inhibit transglutaminase (TG) and low-molecular-mass phospholipase A2 (PLA2). Porcine pancreatic PLA2 activity and guinea pig hepatic TG activity were determined by arachidonyl release from arachidonyl-phosphatidylcholine and by the incorporation of putrescine into succinylated casein, respectively. AFs inhibited TG activity but did not affect PLA2 activity. Moreover, porcine pancreatic PLA2 was activated by TG and AFs decreased porcine pancreatic PLA2 activation induced by TG. Taken together, our results support the hypothesis that the anti-inflammatory effects of AFs are, at least in part, due to the action of AFs on TG activity.

Tissue transglutaminase inhibition

Khosla and coworkers report the synthesis of peptidic dihydroisoxazole derivatives, the in vitro evaluation of these novel compounds as inhibitors of recombinant human tissue transglutaminase (TG2), and their oral bioavailability and efficacy for the synergistic treatment of glioblastoma tumors.

Tissue transglutaminase during mouse central nervous system development: lack of alternative RNA processing and implications for its role(s) in murine models of neurotrauma and neurodegeneration

Tissue transglutaminase (tTG) is a member of a multigene family principally involved in catalyzing the formation of protein cross-links. Unlike other members of the transglutaminase family, tTG is multifunctional since it also serves as a guanosine triphosphate (GTP) binding protein (Galpha(h)) and participates in cell adhesion. Different isoforms of tTG can be produced by proteolysis or alternative splicing. We find that tTG mRNA is expressed at low levels in the mouse CNS relative to other tissues, and at lower levels in the CNS of mouse in comparison to that of human or rat. tTG mRNA levels are higher in the heart compared to the CNS, for example, and much higher in the liver. Within the CNS, tTG message is lowest in the adult cerebellum and thalamus and highest in the frontal cortex and striatum. In the hippocampus, tTG expression is highest during embryonic development and falls off dramatically after 1 week of life. We did not find alternative splicing of the mouse tTG. At the protein level, the predominant isoform is approximately 62 kDa. In summary, tTG, an important factor in neuronal survival, is expressed at low levels in the mouse CNS and, unlike rat and human tTG, does not appear to be regulated by alternative splicing. These findings have implications for analyses of rodent tTG expression in human neurodegenerative and neurotrauma models where alternative processing may be an attractive pathogenetic mechanism. They further impact on drug discovery paradigms, where modulation of activity may have therapeutic value.

Pathophysiological effects of glucocorticoids on nasal polyps: an update

PURPOSE OF REVIEW

The exact mechanisms by which glucocorticoids exert their beneficial effects on nasal polyps are not clearly defined. Nasal polyps, asthma and allergic rhinitis share common features such as mucosal infiltration with eosinophils and mast cells as well as local IgE production. The present review is an update on the pathophysiological mechanisms of glucocorticoids on nasal polyps described during the last 2 years.

RECENT FINDINGS

The reduction of leukocyte numbers in nasal polyps following glucocorticoid treatment depends on several mechanisms, for example altered balance between the two isoforms of the human glucocorticoid receptors, GRalpha and GRbeta. Another explanation may be inhibition of CD4+ T by CD8+ T cells. Increased expression of the antiinflammatory cytokine transforming growth factor beta may contribute to this. A DNA microarray study which examined the expression of some 22 000 genes showed increased expression of several antiinflammatory genes in nasal polyps after treatment with glucocorticoids. The antiinflammatory gene that increased most was uteroglobin (also known as Clara cell protein 16) which is abundantly expressed in airway secretions and thought to have an important role in regulating inflammation.

SUMMARY

Glucocorticoids affect both pro and antiinflammatory pathways in nasal polyps. Upregulation of antiinflammatory genes such as transforming growth factor beta and uteroglobin may play an important role. Elucidation of these mechanisms may help us to understand not only the effects of glucocorticoids on nasal polyps, but also on related disorders such as allergic rhinitis and asthma.

Low levels of CC16 in nasal fluid of children with birch pollen-induced rhinitis

BACKGROUND

Clara cell protein 16 (CC16; secretoglobin 1A1) is an anti-inflammatory protein mainly expressed in the epithelial cells in the airways.

OBJECTIVE

To compare the levels of CC16 in nasal lavage (NAL) from children with intermittent allergic rhinitis and healthy controls and to study the effect of a local steroid.

METHODS

Thirty schoolchildren with birch pollen allergy and 30 healthy controls from the same schools were included in the study. The NAL fluid was collected before the season, during the birch pollen season and, for the patients, after 1 week of treatment with a local steroid. Symptom scores were obtained on every occasion. CC16 and eosinophil cationic protein (ECP) were analyzed with enzyme-linked immunosorbent assay.

RESULTS

The nasal fluid levels of CC16 were significantly lower in patients than in controls, before and during pollen season. Before the season, the median CC16 concentrations were 9.1 (range 1.1-117) microg/l in patients and 25.7 (6.1-110.2) microg/l in controls. During the season, the median CC16 concentrations in nasal fluid were 12.9 (2.3-89.7) microg/l in the allergic children and 22.0 (9.5-90.1) microg/l in the healthy controls (P = 0.0005). Symptom scores, nasal fluid eosinophils and ECP were higher in patients during the season. Treatment with a local steroid did not change the CC16 levels.

CONCLUSIONS

Nasal fluid CC16 levels were lower in children with birch pollen-induced allergic rhinitis than in healthy controls both before and during the pollen season. We speculate that reduction in anti-inflammatory activity by CC16 may contribute to the pathogenesis of allergic rhinitis.

Gene profiling reveals decreased expression of uteroglobin and other anti-inflammatory genes in nasal fluid cells from patients with intermittent allergic rhinitis

BACKGROUND

Intermittent allergic rhinitis (IAR) results from interactions between a large number of pro- and anti-inflammatory mediators. Little is known about anti-inflammatory mediators in IAR. DNA microarrays allow simultaneous analysis of the whole transcriptome in a sample.

OBJECTIVE

To identify anti-inflammatory transcripts in nasal fluid cells from patients with IAR during season and from healthy controls.

METHODS

Nasal lavage fluids were obtained from 15 patients with symptomatic birch/and or grass pollen-induced IAR and 28 healthy controls. RNA was extracted from the nasal fluid cells and pooled into one patient- and one control pool. These were analysed with DNA microarrays containing more than 44,927 genes and variants.

RESULTS

Seventeen thousand three hundred and fifty three genes were expressed in the controls and 17 928 in the patients. One thousand five hundred and seventy nine of the genes had higher expression in patients than in controls, and 1570 had lower expression in patients. Out of 189 up-regulated inflammatory genes, 187 were pro-inflammatory and two were anti-inflammatory. These genes regulated key steps of inflammation, ranging from influx of leukocytes to immunoglobulin production. By comparison, out of 49 down-regulated inflammatory genes, 36 were pro-inflammatory and 13 were anti-inflammatory. The anti-inflammatory gene that decreased most in expression in the patients was uteroglobin (also known as Clara Cell protein 16, CC16). The nasal fluid concentrations of uteroglobin protein were significantly lower in patients than in controls, 5.43+/-1.53 and 12.93+/-2.53 ng/mL, respectively (P<0.05).

CONCLUSION

IAR is associated with decreased expression of uteroglobin and other anti-inflammatory genes.

Intestinal involvement is not sufficient to explain hypertransaminasemia in celiac disease?

Chronic unexplained hypertransaminasemia is an isolated clinical manifestation of celiac disease (CD) and lacks of a clear physiopathological explanation. Since CD and tropical sprue (TS) have similar intestinal functional and histological pattern of injury and that an increased inflammatory response has been reported to occur in patients with irritable bowel syndrome (IBS), liver involvement might be expected to occur either in TS or IBS. However, according to author's prior observations, the frequency of hypertransaminasemia is significantly higher in CD than in TS and IBS-diarrhea predominant patients (IBS-D). Thus, based on current knowledge, intestinal mucosal damage, increased intestinal permeability and/or an active intestinal inflammatory response do not completely explain liver damage in CD. We hypothesize that other factors, unique to CD not present in TS or IBS-D, like gluten toxicity and the presence of tissular transglutaminase (tTG) an auto-antigen with pro-inflammatory and remodeling properties, act in addition to intestinal mucosal injury and account to hypertransaminasemia in CD. Further research focusing on the mechanisms of gluten and tTG hepatic toxicity, and/or the characterization of the expression, secretion and enteral-hepatic transport of certain pro-inflammatory cytokines is needed, to understand the possible links between intestinal and liver disorders seen in CD.

Transglutaminase 2 induces nitric oxide synthesis in BV-2 microglia

A hallmark of brain inflammation is the activation of microglia. Excessive production of nitric oxide (NO), as a consequence of increased inducible nitric oxide synthase (iNOS) in glia, contributes to neurodegeneration. Transglutaminase 2 (TGase 2) is a cross-linking enzyme, which is increased in neurodegeneration. TGase 2 is also considered to be a useful and reliable marker for activation levels in resident and inflammatory macrophages. Therefore, an increase of TGase 2 expression may contribute to activation of microglia. To test this hypothesis, we analyzed the expression of TGase 2 in BV-2 microglia activated with lipopolysaccharide (LPS). Total TGase activity was increased about 5-fold after 24h exposure to LPS. The increase of NO synthesis is correlated with increase of TGase 2 expression. Secretion of NO was reduced between 40 and 80% by TGase inhibition in a dose-dependent manner. This suggests that TGase 2 appears to control iNOS transcription.

Transglutaminase 2 Induces Nuclear Factor-κB Activation via a Novel Pathway in BV-2 Microglia

Transglutaminase 2 (TGase 2) expression is increased in inflammatory diseases. We demonstrated previously that inhibitors of TGase 2 reduce nitric oxide (NO) generation in a lipopolysaccharide (LPS)-treated microglial cell line. However, the precise mechanism by which TGase 2 promotes inflammation remains unclear. We found that TGase 2 activates the transcriptional activator nuclear factor (NF)-kappaB and thereby enhances LPS-induced expression of inducible nitric-oxide synthase. TGase 2 activates NF-kappaB via a novel pathway. Rather than stimulating phosphorylation and degradation of the inhibitory subunit alpha of NF-kappaB (I-kappaBalpha), TGase2 induces its polymerization. This polymerization results in dissociation of NF-kappaB and its translocation to the nucleus, where it is capable of up-regulating a host of inflammatory genes, including inducible nitric-oxide synthase and tumor necrosis factor alpha (TNF-alpha). Indeed, TGase inhibitors prevent depletion of monomeric I-kappaBalpha in the cytosol of cells overexpressing TGase 2. In an LPS-induced rat brain injury model, TGase inhibitors significantly reduced TNF-alpha synthesis. The findings are consistent with a model in which LPS-induced NF-kappaB activation is the result of phosphorylation of I-kappaBalpha by I-kappaB kinase as well as I-kappaBalpha polymerization by TGase 2. Safe and stable TGase2 inhibitors may be effective agents in diseases associated with inflammation.

Developments in ocular allergy

PURPOSE OF REVIEW

The goal of this article is to evaluate developments in the knowledge of inflammatory mechanisms and treatments of ocular allergy.

RECENT FINDINGS

Research developments in ocular allergy summarized in this article include the following findings: (1) ocular epithelial cells play a role in inflammation; (2) respiratory syncytial virus is a pathogen in allergic conjunctivitis; (3) transglutaminase inhibitors reverse allergic related inflammation; (4) eosinophils and neutrophils both play a role in ocular allergy; (5) eotaxin-1 and eotaxin-2 play a role in eosinophilic recruitment; and (6) loteprednol etabonate, desonide phosphate, and cyclosporine have been shown to be effective and safe in the treatment of ocular allergy.

SUMMARY

This article summarizes the research conducted for each of the above recent findings and outlines their clinical applications.

Trappin ovine molecule (TOM), the ovine ortholog of elafin, is an acute phase reactant in the lung

As large animal models continue to play an important role in translating lung-directed therapeutic strategies from laboratory animals to humans, there is an increasing interest in the analysis of endogenous regulators of inflammation at both a genomic and a therapeutic level. To this end, we have sought to characterize the ovine ortholog of elafin, an important regulator of inflammation in humans. We have isolated both the elafin cDNA and gene, which have a similar structure to other species' orthologs. Interestingly, we have isolated two alleles for ovine elafin, which contain a very high number of transglutamination repeats, thought to be important in binding elafin to the interstitium. The mainly mucosal mRNA distribution for ovine elafin suggests that ovine elafin may, like its human ortholog, have functions in innate immunity. This is supported by analysis of elafin and the related protein secretory leukocyte protease inhibitor (SLPI) in ovine bronchoalveolar fluid in response to locally administered lipopolysaccharide and confirmation of them acting as "alarm" antiproteases. We have also cloned the ovine elafin cDNA into an adenoviral vector and have demonstrated correct processing of the secreted protein as well as biological activity. Overexpression of ovine elafin in a lung-derived epithelial cell line has a protective effect against the enzymes human neutrophil and porcine pancreatic elastase. The identification of the ovine elafin gene and its translated protein are important in developing practical strategies aimed at regulating inflammation in the large mammalian lung.

Alpha1B-adrenoceptor signaling and cell motility: GTPase function of Gh/transglutaminase 2 inhibits cell migration through interaction with cytoplasmic tail of integrin alpha subunits

A multifunctional enzyme, G(h), is a GTP-binding protein that couples to the alpha(1B)-adrenoreceptor and stimulates phospholipase C-delta1 but also displays transglutaminase 2 (TG2) activity. G(h)/TG2 has been implicated to play a role in cell motility. In this study we have examined which function of G(h)/TG2 is involved in this cellular response and the molecular basis. Treatment of human aortic smooth muscle cell with epinephrine inhibits migration to fibronectin and vitronectin, and the inhibition is blocked by the alpha(1)-adrenoreceptor antagonist prazosin or chloroethylclonidine. Up-regulation or overexpression of G(h)/TG2 in human aortic smooth muscle cells, DDT1-MF2, or human embryonic kidney cells, HEK 293 cells, results in inhibition of the migratory activity, and stimulation of the alpha(1B)-adrenoreceptor with the alpha(1) agonist further augments the inhibition of migration of human aortic smooth muscle cells and DDT1-MF2. G(h)/TG2 is coimmunoprecipitated by an integrin alpha(5) antibody and binds to the cytoplasmic tail peptide of integrins alpha(5), alpha(v), and alpha(IIb) subunits in the presence of guanosine 5'-3-O-(thio)triphosphate (GTPgammaS). Mutation of Lys-Arg residues in the GFFKR motif, present in the alpha(5)-tail, significantly reduces the binding of GTPgammaS-G(h)/TG2. Moreover, the motif-containing integrin alpha(5)-tail peptides block G(h)/TG2 coimmunoprecipitation and reverse the inhibition of the migratory activity of HEK 293 cells caused by overexpression G(h)/TG2. These results provide evidence that G(h) function initiates the modulation of cell motility via association of GTP-bound G(h)/TG2 with the GFFKR motif located in integrin alpha subunits.

IL-8/CXCL8 and growth-related oncogene alpha/CXCL1 induce chondrocyte hypertrophic differentiation

Foci of chondrocyte hypertrophy that commonly develop in osteoarthritic (OA) cartilage can promote dysregulated matrix repair and pathologic calcification in OA. The closely related chemokines IL-8/CXCL8 and growth-related oncogene alpha (GROalpha)/CXCL1 and their receptors are up-regulated in OA cartilage chondrocytes. Because these chemokines regulate leukocyte activation through p38 mitogen-activated protein kinase signaling, a pathway implicated in chondrocyte hypertrophic differentiation, we tested whether IL-8 and GROalpha promote chondrocyte hypertrophy. We observed that normal human and bovine primary articular chondrocytes expressed both IL-8Rs (CXCR1, CXCR2). IL-8 and the selective CXCR2 ligand GROalpha (10 ng/ml) induced tissue inhibitor of metalloproteinase-3 expression, markers of hypertrophy (type X collagen and MMP-13 expression, alkaline phosphatase activity), as well as matrix calcification. IL-8 and the selective CXCR2 ligand GROalpha also induced increased transamidation activity of chondrocyte transglutaminases (TGs), enzymes up-regulated in chondrocyte hypertrophy that have the potential to modulate differentiation and calcification. Under these conditions, p38 mitogen-activated protein kinase pathway signaling mediated induction of both type X collagen and TG activity. Studies using mouse knee chondrocytes lacking one of the two known articular chondrocyte-expressed TG isoenzymes (TG2) demonstrated that TG2 was essential for murine GROalpha homologue KC-induced TG activity and critically mediated induction by KC of type X collagen, matrix metalloproteinase-13, alkaline phosphatase, and calcification. In conclusion, IL-8 and GROalpha induce articular chondrocyte hypertrophy and calcification through p38 and TG2. Our results suggest a novel linkage between inflammation and altered differentiation of articular chondrocytes. Furthermore, CXCR2 and TG2 may be sites for intervention in the pathogenesis of OA.

Inhibition of platelet phospholipase A2 activity by catuaba extract suggests antiin?ammatory properties

In the inflammation process, phospholipase A2 (PLA2) catalyses the cleavage of the sn-2 ester-linked fatty acids from phospholipids, being the enzyme responsible for arachidonic acid (AA) release by cells for the biosynthesis of the prostaglandins and thromboxanes via the cyclooxygenase system, and the leukotrienes and eicosatetraenoids via the lipoxygenase pathway. AA mobilization by PLA2 and subsequent prostaglandins synthesis is considered to be a pivotal event in inflammation. Therefore, drugs that inhibit PLA2, thus blocking the COX and LOX pathways in the AA cascade, may be effective in the treatment of inflammatory processes. New strategies for the treatment of inflammatory processes could be detected by a search for active principles of vegetal origin that control the lipid mediator production by inhibition of PLA2. The present data are part of a wide explorative investigation on the effects of Trichilia catigua (catuaba), which found that PLA2 activity was totally inhibited by catuaba at a concentration of 120 microg/mL, suggesting that this natural substance may have antiinflammatory properties.

Prospects for the pharmacotherapy of amyotrophic lateral sclerosis : old strategies and new paradigms for the third millennium

Biomedical researchers interested in amyotrophic lateral sclerosis (ALS) must invoke newly developing technologies if we are to discover pharmaceutical treatments that will help a significant population of patients with the disease. The focus of ALS research over the last 10 years has been on reactive oxygen species (ROS) and glutamate excitotoxicity, resulting in several clinical trials and the launch of the only drug currently available for the treatment of ALS, riluzole. Unfortunately, the therapeutic benefits have been minimal, at best, and the prognosis for patients with ALS has not improved beyond very modest retardation of the disease course. By emphasising ROS and glutamate excitotoxicity, current ALS research has only partially been able to attenuate the rate of motor decline and neuronal loss associated with this illness. Clues to additional therapeutic potentialities will come from an increased understanding of the mode of cell death (apoptotic or other) and the pathways leading to neuronal demise. If death is apoptotic, inhibiting caspases may be useful. The regulatory modifications for cell death at the molecular level remain to be determined and exploited to prevent neuronal loss, although novel pathways have been recently elucidated that impact on protein aggregation and processing. Oxidative stress, seen in both familial and sporadic forms of ALS, may be only one post-translational mechanism likely to affect specific proteins essential for the health and stability of motor neurons. Protein cross-linking by transglutaminase paralleling that may lead to defects in proteasome function may also be a significant mechanism. The latest capabilities to screen protein changes in specific cells represent the kinds of advances needed to combat ALS in the third millennium.

Animal models of ocular allergy

PURPOSE OF REVIEW

This review focuses on reports on animal models of ocular allergy published within the past year. A number of animal models are currently being used to clarify the pathophysiology of ocular allergy and to improve the therapeutic interventions for this disease.

RECENT FINDINGS

Published literature examined the role of cytokines and other effector molecules which drive the immunopathology of ocular allergies in several animal models. Animal models were also used to compare the safety and efficacy of currently available drugs, and were utilized in initial trials of novel therapeutic agents. Novel therapeutic options being studied include DNA immunizations and recombinant peptides that block enzymes involved in the inflammatory processes.

SUMMARY

Several animal models are currently being used in the study of ocular allergy. These include different strains within the mouse, rat, guinea pig, rabbit and dog species. Continuing investigations are needed to elucidate the complex molecular and cellular processes involved in the pathogenesis of ocular allergies. A better understanding of the interplay of effector cells, cytokines, adhesion molecules and a number of other inflammatory mediators will broaden our knowledge of the pathophysiology of ocular allergy and allow improved therapeutic options for this disease.

Clara cell secretory protein modulates lung inflammatory and immune responses to respiratory syncytial virus infection

Clara cell secretory protein (CCSP) has been shown to have anti-inflammatory and immunomodulatory functions in the lung. Respiratory syncytial virus (RSV) is the most common cause of respiratory infection in infants and young children. RSV usually infects small airways and likely interacts with the Clara cells of bronchioles. To determine a possible role for CCSP during acute RSV infection, CCSP-deficient (CCSP(-/-)) and wild-type (WT) mice were intratracheally infected with RSV and the lung inflammatory and immune responses to RSV infection were assessed. RSV-F gene expression was increased in the lungs of CCSP(-/-) mice as compared with WT mice following RSV infection, consistent with increased viral persistence. Lung inflammation was significantly increased in CCSP(-/-) mice as compared with WT mice after infection. Moreover, although the levels of Th1 cytokines were similar, the levels of Th2 cytokines and neutrophil chemokines were increased in the lungs of CCSP(-/-) mice following infection. Physiologic endpoints of exacerbated lung disease, specifically airway reactivity and mucus production, were increased in CCSP(-/-) mice after RSV infection. Importantly, restoration of CCSP in the airways of CCSP(-/-) mice abrogated the increased viral persistence, lung inflammation, and airway reactivity. These findings suggest a role for CCSP and Clara cells in regulating lung inflammatory and immune responses to RSV infection.

Distinct transglutaminase 2-independent and transglutaminase 2-dependent pathways mediate articular chondrocyte hypertrophy

Altered chondrocyte differentiation, including development of chondrocyte hypertrophy, mediates osteoarthritis and pathologic articular cartilage matrix calcification. Similar changes in endochondral chondrocyte differentiation are essential for physiologic growth plate mineralization. In both articular and growth plate cartilages, chondrocyte hypertrophy is associated with up-regulated expression of certain protein-crosslinking enzymes (transglutaminases (TGs)) including the unique dual-functioning TG and GTPase TG2. Here, we tested if TG2 directly mediates the development of chondrocyte hypertrophic differentiation. To do so, we employed normal bovine chondrocytes and mouse knee chondrocytes from recently described TG2 knockout mice, which are phenotypically normal. We treated chondrocytes with the osteoarthritis mediator IL-1 beta, with the all-trans form of retinoic acid (ATRA), which promotes endochondral chondrocyte hypertrophy and pathologic calcification, and with C-type natriuretic peptide, an essential factor in endochondral development. IL-1 beta and ATRA induced TG transamidation activity and calcification in wild-type but not in TG2 (-/-) mouse knee chondrocytes. In addition, ATRA induced multiple features of hypertrophic differentiation (including type X collagen, alkaline phosphatase, and MMP-13), and these effects required TG2. Significantly, TG2 (-/-) chondrocytes lost the capacity for ATRA-induced expression of Cbfa1, a transcription factor necessary for ATRA-induced chondrocyte hypertrophy. Finally, C-type natriuretic peptide, which did not modulate TG activity, comparably promoted Cbfa1 expression and hypertrophy (without associated calcification) in TG2 (+/+) and TG2 (-/-) chondrocytes. Thus, distinct TG2-independent and TG2-dependent mechanisms promote Cbfa1 expression, articular chondrocyte hypertrophy, and calcification. TG2 is a potential site for intervention in pathologic calcification promoted by IL-1 beta and ATRA.