Project description:Methods: Profiles of individual human retinal organoids (HRO) at 150, 200 and 250 days of development days were treated for 10 days with HBEGF and TNF, and compared to solvent controls (CTRL). N=6 HROs per timepoint and variable. Single-end sequencing with 30 Mio reads per sample was performed at a length of 75 bases on HiSeq2500 (Illumina). The sequence reads that passed quality filters were analyzed at the transcripts level. Results: Our data independently confirms that this protocol provides HROs with macular-like characteristics and shows low baseline variabilities for rods, cones and Müller glia. These features might be key for disease modeling, since most animal models lack a macula, and most other organoid protocols have low cone cell numbers. We found a significant reduction in the number of rod and cone photoreceptor cells after 10 days after HBEGF-TNF (HT) treatment. Specifically, some photoreceptors show pathologic changes, and some are apically displaced, with their nuclei protruding into or passing out of the retina. Histopathologic changes indicate photoreceptor extrusion of viable or dying cones and rods as a pathomechanism. Notably, photoreceptor displacement through the apical retinal border, and thus ectopy in the region of photoreceptor inner and outer segments, has been described in patients and animal models. In controls, photoreceptors were highly ordered, interspersed and interconnected with each other and with Müller glia processes, and these cell connections make up the outer limiting membrane. Upon HT, glial processes expanded in size, extended laterally along the retinal circumference, and replaced or covered photoreceptors over large areas – forming a seal-like glial scar. Taken together, HT induces photoreceptor degeneration via cell extrusion in conjunction with reactive gliosis, glial proliferation, retinal thickening/dyslamination, and glial seal-like scar formation, which reproduces a complex outer retinal atrophy. Interestingly, our transcriptome data revealed distinct gene expression patterns supporting our histological phenotype, specifically, cone and rod degeneration, reactive gliosis, glial proliferation, and photoreceptor cell extrusion. Conclusions: We show that combined application of HBEGF and TNF, two neuropathology associated factors, is sufficient to induce a complex human retinal pathology. We discovered cone and rod cell extrusion as a pathomechanism for photoreceptor degeneration and a potential interrelationship with glial pathologies. Pharmacological inhibitor experiments support this, and PIEZO1 and MAPK signaling as untapped therapeutic targets, even for complex pathologies. Thus, our model provides mechanistic access to several pathologic processes as well as pathogenic functions of inflammation and biomechanics.

Project description:Epigenetic regulation of the genome through DNA modifications, mainly methylcytosine (mC) and hydroxymethylcytosine (hmC), alters DNA accessibility, genomic organization and gene expression and is thought to be altered during neurodegenerative diseases, such as age-related macular degeneration (AMD). Analysis of retina epigenetic and transcriptomic signatures at the cell-type specific level is crucial to understanding the pathophysiology of retinal degeneration. We have discovered that Aldh1l1 is specifically expressed in the major macroglia of the retina, the Müller glia, and, unlike the brain, is not expressed in retinal astrocytes. This allows a novel model to study paired epigenetic and transcriptomic signatures in Müller glia using Nuclear Tagging and Translating Ribosome Affinity Purification (NuTRAP) for temporally controlled labeling and isolation of Müller glial DNA and RNA. As validated through a variety of approaches, the Aldh1l1cre/ERT2-NuTRAP model provides Müller glia specific translatome and epigenome profiles. Application of this approach to models of acute injury (optic nerve crush) and chronic stress (aging) uncovered common Müller glia-specific transcriptome changes in inflammatory pathways, as well as differential signatures for each stimulus. The expression of components of the IL1b signalling axis, complement system, and markers of gliosis was enhanced in Müller glia in response to optic nerve crush but not in response to aging. The expression of components of the purinergic receptor and focal adhesion signalling pathways changed uniquely in response to aging but not with optic nerve crush. The Aldh1l1cre/ERT2-NuTRAP model allows focusing molecular analyses to a single, minority cell type within the retina, providing more substantial effect sizes than whole tissue analyses. The NuTRAP model, nucleic acid isolation, and validation approaches presented here can be applied to any retina cell type for which a cell type-specific cre is available.

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The Rax homeoprotein in Müller glial cells is required for homeostasis maintenance of the postnatal mouse retina

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