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Analysis of the glutathione-deficient lens transcriptome

ABSTRACT: Purpose: To better understand the effects of glutathione (GSH)-deficiency on lens homeostasis and cataractogenesis. Methods: The transcriptome of lens epithelia and fiber cells was obtained from C57BL/6 LEGSKO (lens GSH synthesis knockout) and buthionine sulfoximine (BSO)-treated LEGSKO mice and compared to C57BL/6 wild-type mice using RNA-Seq. Results: RNA-Seq results were in excellent agreement with qPCR (correlation coefficients between 0.87-0.94 and p<5E-6 for a subset of 36 mRNAs). Of the 24,415 transcripts mapped to the mouse genome, 441 genes showed significantly modulated expression. Pathway analysis indicated major changes in EMT signaling, visual cycle, small molecule biochemistry, and lipid metabolism. GSH-deficient lenses showed upregulation of genes relating to detoxification, including Aldh1a1, Aldh3a1 (aldehyde dehydrogenases), Mt1, Mt2 (metallothioneins), Ces1g (carboxylesterase), and Slc14a1 (urea transporter UT-B). These proteins share substrate specificity with GSH or glutathione-S-transferase and may protect GSH-deficient lenses. Genes associated with canonical EMT pathways, including Wnt10a, Egf, and Syk, showed upregulation in lens epithelia samples. Severely GSH-deficient lens epithelia showed a broad downregulation of vision-related genes (including Cryge, Crygf, and Rho). The BSO-treated LEGSKO lens epithelia transcriptome has significant correlation (r=0.63,P<0.005) to that of lens epithelia undergoing EMT. Conclusions: These results show that GSH depletion of the lens leads to expression of detoxifying genes and activation of EMT signaling, in addition to changes in transport systems and lipid homeostasis. These data give new insight into the adaptation and consequences of GSH-deficiency in the lens and suggest that supplementation of GSH or a precursor after cataract surgery could potentially reduce the incidence of EMT-mediated posterior subcapsular opacification.

ORGANISM(S): Mus musculus

PROVIDER: GSE95688 | GEO | 2017/05/18

SECONDARY ACCESSION(S): PRJNA377921

REPOSITORIES: GEO

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Project description:Glutathione (GSH) is a critical endogenous antioxidant that protects against intracellular oxidative stress. As such, pathological alterations in GSH levels are linked to a myriad of diseases including cancer, neurodegeneration and cataract. The rate limiting step in GSH biosynthesis is catalyzed by the glutamate cysteine ligase catalytic subunit (GCLC). The high expression of GCLC in the lens supports the synthesis of millimolar concentrations of GSH in this tissue. Herein, we describe the morphological consequences of deleting (knocking out) Gclc from surface ectoderm-derived ocular tissues (using the Le-Cre transgene; Gclc KO) which includes an overt microphthalmia phenotype and severely disrupted formation of multiple ocular structures (i.e., cornea, iris, lens, retina). Controlling for the Le-Cre transgene revealed that the deletion of Gclc significantly exacerbated the microphthalmia phenotype in Le-Cre hemizygous mice and resulted in dysregulated gene expression that was unique to only the lenses of KO mice. We further characterized the impaired lens development by conducting an RNA-seq experiment on KO and Gclc control (CON) mouse lens at the day of birth. RNA-sequencing revealed significant differences between Gclc knockout (KO) and Gclc control (CON) lenses, including down-regulation of crystallins and lens fiber cell identity genes, and up-regulation of lens epithelial cell identity genes. In addition, genes related to the immune system (e.g., immune system process, inflammatory response, neutrophil chemotaxis) were upregulated, and genes related to eye/lens development were downregulated. TRANSFAC analysis of differentially expressed genes (DEGs) in the lens of Gclc KO mice implicated PAX6 as a key upstream regulator of Gclc KO sensitive genes. This was further supported by a strong positive correlation between the transcriptomes of the lenses of Gclc KO and Pax6 KO mice. Strikingly, the dysregulation of PAX6-regulated genes in Gclc KO mice was observed despite no change in the ocular localization of PAX6 or decrease in the expression of PAX6 in the lens. In vitro experiments demonstrated that suppression of intracellular GSH concentrations resulted in impairment of PAX6 transactivation activity. Taken together, the present results elucidate a novel mechanism wherein intracellular GSH concentrations may modulate PAX6 activity.

Project description:In the current study, we used a mass spectrometry-based redox proteomics approach to test responses of the cysteine (Cys) proteome to selective disruption of the Trx- and GSH-dependent systems. Auranofin (ARF) was used to inhibit Trx reductase without detectable oxidation of the GSH/GSSG couple, and buthionine sulfoximine (BSO) was used to deplete GSH without detectable oxidation of Trx1. Results for 606 Cys-containing peptides (peptidyl Cys) showed that 36% were oxidized over 1.3-fold by ARF, while BSO-induced oxidation of peptidyl Cys was only 10%. Mean fold oxidation of these peptides was also higher by ARF than BSO treatment. Analysis of potential functional pathways showed that ARF oxidized peptides associated with glycolysis, cytoskeleton remodeling, translation and cell adhesion. Of 60 peptidyl Cys oxidized due to depletion of GSH, 41 were also oxidized by ARF and included proteins of translation and cell adhesion but not glycolysis or cytoskeletal remodeling. Studies to test functional correlates showed that pyruvate kinase activity and lactate levels were decreased with ARF but not BSO, confirming the effects on glycolysis-associated proteins are sensitive to oxidation by ARF. These data show that the Trx system regulates a broader range of proteins than GSH system, support distinct function of Trx and GSH in cellular redox control, and show for the first time in mammalian cells selective targeting peptidyl Cys and biological pathways due to deficient function of the Trx system. ICAT-labeled Cys peptides were analyzed by reverse-phase liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Peptide eluents were monitored in an MS survey scan followed by ten data-dependent MS/MS scans on an LTQ-Orbitrap ion trap mass spectrometer (Thermo Finnigan, San Jose, CA). The LTQ was used to acquire MS/MS spectra (2 m/z isolation width, 35% collision energy, 5,000 AGC target, 200 ms maximum ion time). The Orbitrap was used to collect MS scans (300-1600 m/z, 1,000,000 AGC target, 500 ms maximum ion time, resolution 30,000). All data were converted from .raw files to the .dta format using ExtractMS version 2.0 (Thermo Finnigan, San Jose, CA). The acquired MS/MS spectra were searched against a concatenated target-decoy human RefSeq (release 37 - September 2009 - 38108 target proteins) database of the National Center for Biotechnology Information using the SEQUEST Sorcerer algorithm (version 3.11, SAGE-N) searching parameters included partially tryptic restriction, parent ion mass tolerance (+/- 20 ppm), dynamic modifications of oxidized Met (+15.9949 Da), differential ICAT-modified Cys (+9.0302 Da) and static ICAT modification of Cys (+227.1270 Da). The peptides were classified by charge state and tryptic state (fully and partial) and first filtered by mass accuracy (10 ppm for high-resolution MS), and then dynamically by increasing XCorr and deltaCn values to reduce protein false discovery rate to less than 1%, according to the target-decoy strategy.

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Analysis of the glutathione-deficient lens transcriptome

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