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MFRP in the retina is a molecular hub that organizes the apical membrane of RPE cells by engaging in interactions with specific protein and lipid molecules

ABSTRACT: Membrane frizzled-related protein (MFRP) is an integral membrane protein present in the retinal pigment epithelium (RPE) and is essential for ocular development and the physiology of the retina. Mutations in MFRP are associated with autosomal recessive non-syndromic nanophthalmos, leading to severe hyperopia and early-onset retinitis pigmentosa. While several preclinical gene augmentation and gene editing trials hold promise for future therapies aimed at stopping degeneration and restoring retinal function, the molecular mechanisms underlying MFRP biology remain largely undefined. Here, we studied the biochemical properties of MFRP and the molecular consequences of its loss in a mouse model. Using transcriptomic and lipidomic approaches, we observed that DHA accumulation constitutes a primary defect in the MFRP-deficient RPE. In biochemical assays, we showed that MFRP undergoes extensive glycosylation and preferentially binds several classes of lipids, including phosphatidylserine and phosphatidylinositol 4-phosphate, as well as several other transmembrane proteins, notably adiponectin receptor 1 (ADIPOR1) and inward rectifier potassium channel 13 (KCNJ13). Moreover, MFRP determines ADIPOR1 and KCNJ13 subcellular localization in the RPE in vivo. This feature is affected upon MFRP deficiency and can be restored by gene therapy approaches. Overall, our observations suggest that MFRP constitutes an important interaction hub within the apical membrane of RPE cells, essential for protein trafficking and subcellular localization within the RPE and lipid homeostasis within the entire retina.

ORGANISM(S): Mus musculus

PROVIDER: GSE283089 | GEO | 2025/01/31

REPOSITORIES: GEO

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Project description:Mutations in the membrane frizzled-related gene (Mfrp) are linked to posterior microphthalmia, retinitis pigmentosa and nanophthalmia in humans. In homozygous Mfrprd6 mice, a splice site mutation causes a slow photoreceptor degeneration characterized by shortening and disorganization of outer segments with eventual photoreceptor loss. To better understand the function of MFRP in the retina, microarray analysis was carried out in mutant and control mice at postnatal day14 (P14), prior to the loss of photoreceptors. Analysis of the data revealed differentially expressed RPE and neuroretina transcripts. Although the analysis of the microarray data from Mfrprd6 mutant mice compared to age-matched wild-type controls identified some transcripts with relative fold change > 5.0, most of the differentially expressed genes showed a relative fold change between1.5 - 2.0. Global gene expression analysis using Ingenuity Pathway Analysis software identified decreased levels of transcripts in phototransduction and visual pathways in Mfrprd6 mutants. Select candidate transcripts were validated by quantitative real-time PCR analyses. The expression of RPE-specific visual transduction protein, RPE65, was significantly decreased in Mfrprd6 mutants. As an indirect consequence of the primary RPE cell defect due to the Mfrprd6 mutation, retinal specific transcripts Rgr, Pde6a, GuCa1b, and Rgs9 were also significantly decreased. We also confirmed the significantly elevated levels of Prss56, a gene previously associated with myopia and open angle glaucoma. In the Mfrprd6 mutant, a progressive increase in Prss56 mRNA levels from 14- to 70-fold was observed from P7 to P21, respectively. In situ hybridization and glutamine synthetase staining of mutant eyes indirectly identified MM-CM-<ller glia in the inner nuclear layer of retina as the cell type expressing the Prss56 transcript. This experiment had one model term, a combination of strain and time, which consisted of four levels (B6_P0, B6_P14, Rd6_P0 and Rd6_P14). Three biological replicates were used per term level. A total of 12 Affymetrix Mouse 430v2 Arrays were used in gene expression analysis.

Project description:Purpose: The purpose of this study was to develop a framework for analyzing RPE expression profiles from zebrafish eye mutants. Methods: The fish model we used was smarca4 (SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily a, member 4), a retinal dystrophic mutant that the retinal phenotype and expression profiles were previously characterized. Histological and Affymetrix GeneChip analyses were conducted to define the RPE defects and underlying differential expression respectively. Results: Histological analysis indicates that smarca4 RPE was formed but its differentiation was abnormal. In particular, ultra-structural analysis of smarca4 RPE by transmission electron microscopy showed a number of defects in melanogenesis, suggesting that the cytoskeletal dynamics was impaired. To compare the expression profile of normal wild-type (WT) and smarca4 RPE, their retinas and RPE-attached retinas were microdissected and the gene expression values of these tissues measured by Affymetrix GeneChip analysis. The RPE expression values were then estimated from these samples using an approach previously established by us. A factorial analysis was conducted using the expression values of RPE, retinal as well as the whole-embryo samples. Specific rules (contrasts) were built using the coefficients of the resulting fitted model to select for three groups of genes: 1) Smarca4-regulated RPE genes, 2) Smarca4-regulated retinal genes, and 3) Smarca4-regulated RPE genes that are not differentially expressed in the retina. The latter group consists of 39 genes that are highly related to cytoskeletal dynamics, melanogenesis, paracrine and intracellular signal transduction. Conclusions: Our analytical framework can potentially identify genes in zebrafish mutants that both retina and RPE are affected by the underlying mutation. The gene expression levels of three independent replicates of WT whole embryos (WA52), WT retinas (WR52), WT RPE-attached retinas (WRR52), smarca4/yng retinas (YR52), smarca4 RPE-attached retinas (YRR52) and smarca4 whole embryos (YA52) were measured by Affymetrix Zebrafish Whole Genome Arrays. All samples were collected at 52 hpf. The probe-level data of these sample groups were background adjusted, normalized and summarized by a robust multiarray average (RMA) algorithm. RPE expression values were estimated from the comparison between the retinal and RPE-attached retinal samples of the same genotype based on a method we previously developed (Leung et al., Invest Ophthalmol Vis Sci. 2007; 48:881). Then, a 3x2 factorial design was used to analyze the expression values of three kinds of tissue (T): whole embryo, retina and RPE in two kinds of mutation (M) background: WT and smarca4. Using the coefficients from the fitted models, contrasts were built to identify candidate genes that fulfilled specific criteria. The false discovery rate (FDR) q-value cutoff for a contrast was 0.001. Several contrasts were ultimately combined to allow for selection of genes that were regulated by Smarca4 in the retina and RPE. These include 1) Smarca4-regulated RPE genes, 2) Smarca4-regulated retinal genes, and 3) Smarca4-regulated RPE genes that are not differentially expressed in the retina.

Project description:Proper spatial differentiation of retinal cell types is necessary for normal human vision. Many retinal diseases, such as Best disease and male germ cell associated kinase (MAK)-associated retinitis pigmentosa, preferentially affect distinct topographic regions of the retina. While much is known about the distribution of cell types in the retina, the distribution of molecular components across the posterior pole of the eye has not been well-studied. To investigate regional difference in molecular composition of ocular tissues, we assessed differential gene expression across the temporal, macular, and nasal retina and retinal pigment epithelium (RPE)/choroid of human eyes using RNA-Seq. RNA from temporal, macular, and nasal retina and RPE/choroid from four human donor eyes was extracted, poly-A selected, fragmented, and sequenced as 100 bp read pairs. Digital read files were mapped to the human genome and analyzed for differential expression using the Tuxedo software suite. Retina and RPE/choroid samples were clearly distinguishable at the transcriptome level. Numerous transcription factors were differentially expressed between regions of the retina and RPE/choroid. Photoreceptor-specific genes were enriched in the peripheral samples, while ganglion cell and amacrine cell genes were enriched in the macula. Within the RPE/choroid, RPE-specific genes were upregulated at the periphery while endothelium associated genes were upregulated in the macula. Consistent with previous studies, BEST1 expression was lower in macular than extramacular regions. The MAK gene was expressed at lower levels in macula than in extramacular regions, but did not exhibit a significant difference between nasal and temporal retina. The regional molecular distinction is greatest between macula and periphery and decreases between different peripheral regions within a tissue. Datasets such as these can be used to prioritize candidate genes for possible involvement in retinal diseases with regional phenotypes. Reprinted from <a href="https://www.ncbi.nlm.nih.gov/pubmed/?term=25446321">Whitmore, S.S., Wagner, A.H., DeLuca, A.P., Drack, A.V., Stone, E.M., Tucker, B.A., Zeng, S., Braun, T.A., Mullins, R.F., Scheetz, T.E., 2014. Transcriptomic analysis across nasal, temporal, and macular regions of human neural retina and RPE/choroid by RNA-Seq. Experimental Eye Research</a>. Used under <a href="http://creativecommons.org/licenses/by-nc-sa/3.0/">Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported </a>license. Additional RNA sequencing was performed on temporal, macular, nasal, inferior, and superior retina from a fifth subject and is included in this dataset. See original publication for details.

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MFRP in the retina is a molecular hub that organizes the apical membrane of RPE cells by engaging in interactions with specific protein and lipid molecules

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