Transcriptional Profiling Identifies Upregulation of Neuroprotective Pathways in Retinitis Pigmentosa

Abstract

Hereditary retinal degenerations like retinitis pigmentosa (RP) are among the leading causes of blindness in younger patients. To enable in vivo investigation of cellular and molecular mechanisms responsible for photoreceptor cell death and to allow testing of therapeutic strategies that could prevent retinal degeneration, animal models have been created. In this study, we deeply characterized the transcriptional profile of mice carrying the transgene rhodopsin V20G/P23H/P27L (VPP), which is a model for autosomal dominant RP. We examined the degree of photoreceptor degeneration and studied the impact of the VPP transgene-induced retinal degeneration on the transcriptome level of the retina using next generation RNA sequencing (RNASeq) analyses followed by weighted correlation network analysis (WGCNA). We furthermore identified cellular subpopulations responsible for some of the observed dysregulations using in situ hybridizations, immunofluorescence staining, and 3D reconstruction. Using RNASeq analysis, we identified 9256 dysregulated genes and six significantly associated gene modules in the subsequently performed WGCNA. Gene ontology enrichment showed, among others, dysregulation of genes involved in TGF-β regulated extracellular matrix organization, the (ocular) immune system/response, and cellular homeostasis. Moreover, heatmaps confirmed clustering of significantly dysregulated genes coding for components of the TGF-β, G-protein activated, and VEGF signaling pathway. 3D reconstructions of immunostained/in situ hybridized sections revealed retinal neurons and Müller cells as the major cellular population expressing representative components of these signaling pathways. The predominant effect of VPP-induced photoreceptor degeneration pointed towards induction of neuroinflammation and the upregulation of neuroprotective pathways like TGF-β, G-protein activated, and VEGF signaling. Thus, modulation of these processes and signaling pathways might represent new therapeutic options to delay the degeneration of photoreceptors in diseases like RP.

TGFβ-Neurotrophin Interactions in Heart, Retina, and Brain

“…In the RPE, as in the aqueous humor and vitreous, TGFβ2 is the predominant isoform and its expression in the RPE is several-fold higher compared to the neurosensory retina [164][165][166]. In the retina, TGFβR1 and -2 are expressed in neurons and Müller cells, vascular cells, and the retinal pigment epithelium [167,168] (www.proteinatlas.org, accessed 7 February 2021). Canonical TGFβ signaling plays essential roles in cell growth, migration, proliferation and cell death, both during ocular development as well as in tissue homeostasis during adulthood [34,37,42,[169][170][171][172][173][174][175][176].…”

The Communication between Ocular Surface and Nasal Epithelia in 3D Cell Culture Technology for Translational Research: A Narrative Review

“…Of note, the retina and vitreous body are not directly addressed in this review. However, the retina represents a particular layer of the eye and their corresponding retinal pathologies including retinitis pigmentosa punctata albescens (RPA) which may lead to vision loss and blindness (reviewed in [ 11 , 12 ]) [ 13 ]. Exemplarily, the work of Donato and colleagues examines variants in four known genes that trigger RPA and provides important clues to the etiopathogenesis of the disease [ 14 ].…”

Deficiency in Retinal TGFβ Signaling Aggravates Neurodegeneration by Modulating Pro-Apoptotic and MAP Kinase Pathways

“…Photoreceptor cells are the light-sensitive cells of the retina and as such are responsible for visual perception [ 8 ]. Morphologically, these cells exhibit an outer segment that is connected through a cilium with the inner segment, a perikaryon which is located in the outer nuclear layer (ONL) and a synaptic ending located in the outer plexiform layer (OPL) of the retina [ 8 , 9 ]. Photoreceptor degeneration typically results in a thinning of the ONL concomitant with the loss of the inner and outer segments, resulting in a loss of visual function up to complete blindness [ 2 , 6 ].…”

“…Due to the multiple pathomechanisms of photoreceptor degeneration, it is still challenging to understand and intervene in the molecular mechanisms leading to their degeneration, with the overall goal of mitigating it. We recently analyzed the retinal transcriptome of the VPP mouse model, a genetic mouse model carrying a transgenic rhodopsin V20G/P23H/P27L (VPP), which results in photoreceptor degeneration as observed in autosomal dominant retinitis pigmentosa [ 9 , 10 ]. In the course of that study we aimed to identify molecular key factors and signaling pathways that predominantly influence the course of photoreceptor degeneration [ 9 ].…”

“…We recently analyzed the retinal transcriptome of the VPP mouse model, a genetic mouse model carrying a transgenic rhodopsin V20G/P23H/P27L (VPP), which results in photoreceptor degeneration as observed in autosomal dominant retinitis pigmentosa [ 9 , 10 ]. In the course of that study we aimed to identify molecular key factors and signaling pathways that predominantly influence the course of photoreceptor degeneration [ 9 ]. Amongst other findings, our data indicated a clustering of significantly dysregulated genes coding for components of potentially neuroprotective pathways such as the transforming growth factor β (TGFβ) signaling pathway [ 9 ].…”