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Inhibiting the activation of MAPK (ERK1/2) in stressed Müller cells prevents photoreceptor degeneration

ABSTRACT: MAPK (ERK1/2) signalling was exclusively activated in Müller cells under stress, both ex vivo and in vivo. PD98059, a specific pERK1/2 inhibitor, inhibited the phosphorylation of ERK1/2 in Müller cells, reduced the gliotic marker glial fibrillary acidic protein (GFAP) and increased neuroprotective factor interphotoreceptor retinoid-binding protein (IRBP). Inhibition of pERK1/2 reduced retinal injury in photo-oxidative damaged mice assessed by optical coherence tomography (OCT). However, exactly how Müller cells and photoreceptors communicate under stress, as well as the signalling pathways involved, remains unclear. We explored the RNA and signalling pathway changes after MAPK deactivation in human retina explants by RNA sequence.

ORGANISM(S): Homo sapiens

PROVIDER: GSE205370 | GEO | 2022/10/05

REPOSITORIES: GEO

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Project description:As any other radial glia in the central nervous system, Müller glia derive from the same neuroepithelial precursors, perform similar functions and exhibit neurogenic properties as radial glia in the brain. Müller glial cells retain progenitor-like characteristics in the adult human eye, and can partially restore visual function upon intravitreal transplantation into animal models of glaucoma. Recently, it has been demonstrated that intracellular communication is possible via the secretion of nano-sized membrane-bound extracellular vesicles (EV), which contain bioactive molecules like microRNA (miRNA) and proteins that induce phenotypic changes when internalised by recipient cells. We conducted high-throughput sequencing to profile the microRNA signature of EV populations secreted by Müller glia in culture, and used bioinformatic tools to evaluate their potential role in the neuroprotective signalling attributed to these cells. Sequencing of miRNA within Müller EV suggested enrichment with species associated with stem cells such as miR-21 and miR-16, as well as with miRNA previously found to play a role in diverse Müller cell functions in the retina: miR-9, miR-125b and the let-7 family. A total of 51 miRNA were found to be differentially enriched in EV compared to whole cells from which EV originated. Bioinformatic analyses also indicated preferential enrichment of species demonstrated to regulate genes involved in cell proliferation and survival, including PTEN the master inhibitor of the PI3K/AKT pathway. The results suggest that the release by Müller cells of miRNA-enriched EV abundant in species that regulate anti-apoptotic signalling networks, is likely to represent a significant proportion of the neuroprotective effect observed after transplantation of these cells into animal models of retinal ganglion cell (RGC)-depletion. Future work will seek to evaluate the modulation of putative genes, as well as the activation of these pathways in in vitro and in vivo models following the internalisation of Müller-EV by target retinal neurons.

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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Inhibiting the activation of MAPK (ERK1/2) in stressed Müller cells prevents photoreceptor degeneration

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