Analysis of the glutathione-deficient lens transcriptome

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. Overall design: Lens epithelia and cortical fiber cells were isolated and only compared to samples of the same tissue type. Wild-type (control) mouse lens tissue was compared to LEGSKO (mildly glutathione deficient) lens tissue and buthionine sulfoxime (BSO)-treated LEGSKO (severely glutathione deficient) lens tissue.