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Transketolase in human Müller cells is critical to resist light stress through the pentose phosphate and NRF2 pathways

ABSTRACT: The Pentose Phosphate Pathway (PPP), a metabolic offshoot of the glycolytic pathway, provides protective metabolites and molecules essential for cell redox balance and survival. Transketolase (TKT) is the critical enzyme that controls the extent of “traffic flow” through the PPP. Here, we explored the role of TKT in maintaining the health of the human retina. We found that Müller cells were the primary retinal cell type expressing TKT in the human retina. We further explored the role of TKT in human Müller cells by knocking down its expression in primary cultured Müller cells (huPMCs), isolated from the human retina (11 human donors in total), under lightinduced oxidative stress. TKT knockdown and light stress reduced TKT enzymatic activities and the overall metabolic activities of huPMCs with no detectable cell death. TKT knockdown restrained the PPP traffic flow, reduced the expression of NAD(P)H Quinone Dehydrogenase 1 (NQO1) and impaired the antioxidative response of NRF2 to light stress. TKT knockdown also inhibited overall glucose intake, reduced expression of Dihydrolipoamide dehydrogenase (DLD) and impaired the energy supply of huPMCs. In summary, Müller cell-mediated TKT activity plays a critical protective role in the stressed retina. Knockdown of TKT disrupted the PPP and impaired overall glucose utilisation by huPMCs and rendered huPMCs more vulnerable to light stress by impairing energy supply and antioxidative NRF2 responses.

ORGANISM(S): Homo sapiens

PROVIDER: GSE198554 | GEO | 2022/06/26

REPOSITORIES: GEO

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Project description:Diabetic retinopathy (DR), the leading cause of blindness in working-age adults, is thought to be primarily a microvascular complication of diabetes. As a central element of the retinal neurovascular unit, Müller cells, the major macroglia of the retina, are important for maintaining a healthy and functional retina and play a critical role in several pathological events during DR disease progression. Here, we aim to improve our understanding of Müller cell-specific signalling pathways that are altered during DR disease progression in order to develop novel gene therapy strategies that target Müller cells. We used a multi-omics approach on purified Müller cells from 6-month-old control and diabetic db/db mice, including (i) RNA-seq followed by oPOSSUM-3 transcription factor (TF) binding site cluster analysis, (ii) glial chromatin landscape analysis by ATAC-seq, and (iii) Müller cell proteomics by MS/MS mass spectrometry. This led to the identification of the glucocorticoid receptor (GR, gene ID: Nr3c1) most highly expressed in Müller cells. In cells from diabetic mice, GR mRNA and protein expression is significantly reduced and its target gene cluster downregulated in Müller cells. Importantly, GR was identified as a potential master regulator not only by oPOSSUM analysis based on differentially expressed mRNA in Müller cells, but also validated by the ATAC-seq approach. In an in vitro cortisol-stimulated retinal explant model cortisol not only increased GR phosphorylation, but also induced changes in the expression of known downstream GR target genes. Finally, we evaluated whether AAV-mediated GR overexpression in Müller cells improves retinal functionality and we found moderate improvements indicated by electroretinography. While synthetic and topical glucocorticoids are widely used in ophthalmology with undeniable beneficial effects, our study provides valuable new insight into the role of GR signalling and glial alterations in the diabetic retina. This supports the therapeutic concept of locally enhancing the GR signaling axis. Our findings of reduced GR levels in Müller cells of the diabetic retina suggests that therapeutic approaches should aim at increasing the expression of the receptor rather than adding more ligand.

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Transketolase in human Müller cells is critical to resist light stress through the pentose phosphate and NRF2 pathways

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