Glutamate, Excitatory Amino Acid Transporters, Xc<sup>−</sup>Antiporter, Glutamine Synthetase, and γ-Glutamyltranspeptidase in Human Corneal Epithelium

Langford, Marlyn P.; Redmond, Patrick; Chanis, R.; Misra, Raghunath; Redens, Thomas B.

doi:10.3109/02713680903461489

Cited by 23 publications

(22 citation statements)

References 44 publications

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“…In the case of the 3 enzymes in family T2, ISCW001950, ISCW000866 and ISCW001928, they have been provisionally identified as glycosylasparaginase precursor, threonine type isoaspartyl dipeptidase and taspase-1, enzymes that play important role(s) in the metabolism of β-aspartyl peptides, cell proliferation (Noronkoski et al, 1998; Cantor et al, 2009). Of the 8 enzymes in family T3, 5 sequences ISCW000530, ICSW003582, ISCW009859, ISCW010660 and ISCW012371 have been provisionally identified as gamma-glutamyltransferase homologs, an enzyme that is present in cell membranes and is involved in cross cell membrane trafficking of amino acids and peptides as well as glutathione metabolism (Langford et al, 2010; Leggatt and Iwama, 2009). There are no reports on the role threonine-like enzymes in tick physiology.…”

Section: Threonine Proteasesmentioning

confidence: 99%

A snapshot of the Ixodes scapularis degradome

Mulenga

Erikson

2011

Gene

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Parasitic encoded proteases are essential to regulating interactions between parasites and their hosts and thus they represent attractive anti-parasitic druggable and/or vaccine target. We have utilized annotations of Ixodes scapularis proteases in gene bank and version 9.3 MEROPS database to compile an index of at least 233 putatively active and 150 putatively inactive protease enzymes that are encoded by the Ixodes scapularis genome. The 233 putatively active protease homologs hereafter referred to as the degradome (the full repertoire of proteases encoded by the I. scapularis genome) represents ~1.14% of the 20485 putative I. scapularis protein content. Consistent with observations in other animals, the content of the I. scapularis degradome is ~6.0% (14/233) aspartic, ~19% (44/233) cysteine, ~40% (93/233) Metallo, ~28.3% (66/233) serine and ~6.4% (15/233) threonine proteases. When scanned against other tick sequences, ~11% (25/233) of I. scapularis putatively active proteases are conserved in other tick species with ≥60% amino acid identity levels. The I. scapularis genome does not apparently encode for putatively inactive aspartic proteases. Of the 150 putative inactive protease homologs none are from the aspartic protease class, ~8% (12/150) are cysteine, ~58.7% (88/150) metallo, 30% (45/150) serine and ~3.3% (5/150) are threonine proteases. The I. scapularis tick genome appears to have evolutionarily lost proteolytic activity of at least 6 protease families, C56 and C64 (cysteine), M20 and M23 (metallo), S24 and S28 (serine) as revealed by a lack of the putatively active proteases in these families. The overall protease content is comparable to other organisms. However, the paucity of the S1 chymotrypsin/trypsin-like serine protease family in the I. scapularis genome where it is ~12.7% (28/233) of the degradome as opposed to ~22–48% content in other blood feeding arthropods, Pediculus humanus humanus, Anopheles gambiae, Aedes Aegypti and Culex pipiens quinquenfasciatus is notable. The data is presented as a one-stop index of proteases encoded by the I. scapularis genome.

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Section: Threonine Proteasesmentioning

confidence: 99%

A snapshot of the Ixodes scapularis degradome

Mulenga

Erikson

2011

Gene

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“…In the cornea, GSH maintains the normal hydration level and protects cellular membrane integrity (68). In the only published investigation of system x c -in cornea to date, Langford and colleagues localized xCT immunoreactivity in the superficial epithelial layer and the columnar cells of human corneal epithelium from nondiabetic, nonglaucomatous donor eyes (132). The authors speculated that this localization facilitates the transport of cystine from stroma and tears.…”

Section: Studies Of System X Cmentioning

confidence: 99%

The Cystine/Glutamate Antiporter System x_c⁻in Health and Disease: From Molecular Mechanisms to Novel Therapeutic Opportunities

Lewerenz

Hewett

Huang

et al. 2013

Antioxidants & Redox Signaling

758

655

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The antiporter system x c -imports the amino acid cystine, the oxidized form of cysteine, into cells with a 1:1 counter-transport of glutamate. It is composed of a light chain, xCT, and a heavy chain, 4F2 heavy chain (4F2hc), and, thus, belongs to the family of heterodimeric amino acid transporters. Cysteine is the rate-limiting substrate for the important antioxidant glutathione (GSH) and, along with cystine, it also forms a key redox couple on its own. Glutamate is a major neurotransmitter in the central nervous system (CNS). By phylogenetic analysis, we show that system x c -is a rather evolutionarily new amino acid transport system. In addition, we summarize the current knowledge regarding the molecular mechanisms that regulate system x c -, including the transcriptional regulation of the xCT light chain, posttranscriptional mechanisms, and pharmacological inhibitors of system x c -. Moreover, the roles of system x c -in regulating GSH levels, the redox state of the extracellular cystine/cysteine redox couple, and extracellular glutamate levels are discussed. In vitro, glutamate-mediated system x c -inhibition leads to neuronal cell death, a paradigm called oxidative glutamate toxicity, which has successfully been used to identify neuroprotective compounds. In vivo, xCT has a rather restricted expression pattern with the highest levels in the CNS and parts of the immune system. System x c -is also present in the eye. Moreover, an elevated expression of xCT has been reported in cancer. We highlight the diverse roles of system x c -in the regulation of the immune response, in various aspects of cancer and in the eye and the CNS. Antioxid. Redox Signal. 18, 522-555.

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“…In addition, age and diabetes-associated losses of lens and retinal GGT and GSH precede lens intumescences and opacification and retinal dysfunction, respectively 6–10. GGT expression by quiescent endothelial cells lining the posterior corneal surface, metabolically active columnar epithelial cells along the anterior stromal surface, and senescent surface epithelial cells at the tear/corneal interface11 supports cell-specific protective effects of corneal GGT against metabolic and environmental oxidative stress factors. Notably, the physiological importance of intra-ocular GGT is supported by the report that inhibition of the corneal endothelial cell GGT activity increases corneal thickness (hydration) and decreases transparency 12…”

Section: Introductionmentioning

confidence: 78%

“…Corneal and Schirmer tear GGT activity was determined using standard assay methods as described previously 11,32. Briefly, whole cornea, endothelial, and epithelial sections were placed in GGT assay medium and incubated at room temperature for 3 hours.…”

Section: Methodsmentioning

confidence: 99%

“…Immunoreactive GGT was detected in epithelial cells of cryo-sectioned conjunctival tissue from a non-diabetic human cadaver eye following reaction with a 1:100 dilution of rabbit antibody to GGT (anti-γ-glutamyl transferase, #53506; AnaSpec Inc, Freemont, CA) and DAPI nuclear stain using previously reported methods 11,28. Digitalized images were captured with a CoolSNAP fx monochrome CCD camera (Photometrics, Tucson, AZ) and color images produced with Scanalytics IPLab software (Spectra Services Inc, Ontario, NY).…”

Section: Methodsmentioning

confidence: 99%

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Diabetic and non-diabetic human cornea and tear γ-glutamyl transpeptidase activity

Burnham¹,

Sakhalkar²,

Langford³

et al. 2013

OPTH

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BackgroundDiabetes-related eye disease is due in part to oxidative stress. Gamma-glutamyl transpeptidase (GGT) is a γ-glutamyl cycle enzyme that protects against oxidative stress via glutathione recapture. This study investigates corneal and Schirmer tears GGT activity in diabetic and non-diabetic adults aged 50 to 83 years old.MethodsGGT activity was determined by colorimetric assay on 50 corneas from 14 diabetic (without keratopathy) and 20 non-diabetic donors and on Schirmer type 1 test strips (no anesthesia) of 14 diabetic and 14 non-diabetic subjects.ResultsType 1 (T1) diabetic cornea GGT activity was 40% lower than Type 2 (T2) diabetic cornea GGT activity (P = 0.04), but GGT activity was similar for corneas (without keratopathy) from diabetic and non-diabetic donors (P ≥ 0.44 for all). The number of endothelial cells/unit of GGT activity in diabetic corneas was 22% higher (P = 0.1) than in non-diabetic corneas. GGT activity per Schirmer strip and GGT activity per mm of tears were 36% and 50% higher (P ≤ 0.008 for all) for non-diabetic (tear volume dependent) than diabetic donors (tear volume independent), respectively. GGT activity per mm was 50% lower in T1 than T2 diabetics (P = 0.02). Higher tear GGT activity in non-diabetic than diabetic females (P ≤ 0.05) was due to higher GGT activity in the African American females.ConclusionGGT activity was less in T1 than T2 diabetics, but comparable to non-diabetic corneas. Schirmer tear GGT activity in diabetic eyes was tear volume independent, less in T1 than T2, lower than in tear volume dependent, non-diabetic female eyes. Low cornea and tear GGT activity suggests loss of antioxidant potential and supports ocular antioxidant therapy for diabetic patients.

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Glutamate, Excitatory Amino Acid Transporters, Xc⁻Antiporter, Glutamine Synthetase, and γ-Glutamyltranspeptidase in Human Corneal Epithelium

Cited by 23 publications

References 44 publications

A snapshot of the Ixodes scapularis degradome

A snapshot of the Ixodes scapularis degradome

The Cystine/Glutamate Antiporter System x_c⁻in Health and Disease: From Molecular Mechanisms to Novel Therapeutic Opportunities

Diabetic and non-diabetic human cornea and tear γ-glutamyl transpeptidase activity

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Glutamate, Excitatory Amino Acid Transporters, Xc−Antiporter, Glutamine Synthetase, and γ-Glutamyltranspeptidase in Human Corneal Epithelium

Cited by 23 publications

References 44 publications

A snapshot of the Ixodes scapularis degradome

A snapshot of the Ixodes scapularis degradome

The Cystine/Glutamate Antiporter System xc−in Health and Disease: From Molecular Mechanisms to Novel Therapeutic Opportunities

Diabetic and non-diabetic human cornea and tear &gamma;-glutamyl transpeptidase activity

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Product

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About

Glutamate, Excitatory Amino Acid Transporters, Xc⁻Antiporter, Glutamine Synthetase, and γ-Glutamyltranspeptidase in Human Corneal Epithelium

The Cystine/Glutamate Antiporter System x_c⁻in Health and Disease: From Molecular Mechanisms to Novel Therapeutic Opportunities

Diabetic and non-diabetic human cornea and tear γ-glutamyl transpeptidase activity