Transcriptional Profiling Identifies Upregulation of Neuroprotective Pathways in Retinitis Pigmentosa.

Christina B Bielmeier,Barbara M Braunger,Stefaniya K Boneva,Mario Vallon,Süleyman Ergün,Anja Schlecht,Sabrina I Schmitt,Saskia Roth,Andreas Neueder,Ernst R Tamm

doi:10.3390/ijms22126307

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.

Highlights

This article is an open access articleRetinitis pigmentosa (RP) is a hereditary form of retinal degeneration that results from mutations in any one of more than 70 known susceptibility genes [1,2]
Of factors like leukemia inhibitory factor (Lif ), fibroblast growth factor 2 (Fgf2), and endothelin 2 (Edn2) that are well-known to be upregulated in the context of retinal degeneration [10,11,12]
We found upregulation of quite a considerable number of genes associated with inflammatory or immune response functions such as C-X-C motif chemokine ligand 13 (Cxcl13), glial fibrillary acidic protein (Gfap), T-cell receptor T3 gamma chain (Cd3g), chemokine (C-C motif) ligand 5 (Ccl5), and C-C motif chemokine ligand 2 (Ccl2), as well as factors associated with the complement cascade like complement component factor i (Cfi), complement factor C4B, and the Serping1 gene

Summary

Introduction

Retinitis pigmentosa (RP) is a hereditary form of retinal degeneration that results from mutations in any one of more than 70 known susceptibility genes [1,2]. Photoreceptors are the light sensitive neurons of the retina that are responsible for visual perception [5] These cells consist of the outer and inner segments, which are connected through a cilium with the cell’s perikaryal, located in the outer nuclear layer (ONL). They form a synaptic layer in the outer plexiform layer (OPL) of the retina to signal to the inner retinal neurons [4,5]. VPP mice carry a rhodopsin transgene with three amino acid substitutions: Val-20 → Gly (V20G), Pro-23 → His (P23H), and Pro-27 →

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