Gene Profiling of Postnatal Mfrprd6 Mutant Eyes Reveals Differential Accumulation of Prss56, Visual Cycle and Phototransduction mRNAs

Abstract

Mutations in the membrane frizzled-related protein (MFRP/Mfrp) gene, specifically expressed in the retinal pigment epithelium (RPE) and ciliary body, cause nanophthalmia or posterior microphthalmia with retinitis pigmentosa in humans, and photoreceptor degeneration in mice. To better understand MFRP function, microarray analysis was performed on eyes of homozygous Mfrprd6 and C57BL/6J mice at postnatal days (P) 0 and P14, prior to photoreceptor loss. Data analysis revealed no changes at P0 but significant differences in RPE and retina-specific transcripts at P14, suggesting a postnatal influence of the Mfrprd6 allele. A subset of these transcripts was validated by quantitative real-time PCR (qRT-PCR). In Mfrprd6 eyes, a significant 1.5- to 2.0-fold decrease was observed among transcripts of genes linked to retinal degeneration, including those involved in visual cycle (Rpe65, Lrat, Rgr), phototransduction (Pde6a, Guca1b, Rgs9), and photoreceptor disc morphogenesis (Rpgrip1 and Fscn2). Levels of RPE65 were significantly decreased by 2.0-fold. Transcripts of Prss56, a gene associated with angle-closure glaucoma, posterior microphthalmia and myopia, were increased in Mfrprd6 eyes by 17-fold. Validation by qRT-PCR indicated a 3.5-, 14- and 70-fold accumulation of Prss56 transcripts relative to controls at P7, P14 and P21, respectively. This trend was not observed in other RPE or photoreceptor mutant mouse models with similar disease progression, suggesting that Prss56 upregulation is a specific attribute of the disruption of Mfrp. Prss56 and Glul in situ hybridization directly identified Müller glia in the inner nuclear layer as the cell type expressing Prss56. In summary, the Mfrprd6 allele causes significant postnatal changes in transcript and protein levels in the retina and RPE. The link between Mfrp deficiency and Prss56 up-regulation, together with the genetic association of human MFRP or PRSS56 variants and ocular size, raises the possibility that these genes are part of a regulatory network influencing postnatal posterior eye development.

Functional microRNA targetome undergoes degeneration-induced shift in the retina

“…identified in this study have previously been identified to be located to retinal Müller glial cells (Arnold et al, 2012, Mohammad et al, 2018, Rutar et al, 2011, Sarthy et al, 2005, Soundararajan et al, 2014, Ueki et al, 2015. In addition to this, the expression of these targets seem to be increased after PD suggesting a potential movement of miRNA activity to Müller cells upon stressed conditions, consistent with the finding of miR-124 and Ccl2 previously published by our group (Chu-Tan et al, 2018).…”

“…Approximately 29% of AGO2-bound miR-124-3p targets in PD have been described to localise to the INL of the retina with a further 23% localised to the GCL ( Figure 6A). Amongst those genes reported to be expressed in the INL, 80% were located specifically within the Müller glial cells (Arnold et al, 2012, Mohammad et al, 2018, Rutar et al, 2011, Sarthy et al, 2005, Soundararajan et al, 2014, Ueki et al, 2015. The expression level of these 8 Müller glial genes increased in PD retinas, as determined here by AGO2 HITS-CLIP of DR and PD retinas, with the exception of Rock1 (P<0.05, Figure 6B).…”

“…Multiple miRNAs have been postulated to play a role in the pathogenesis of AMD (Askou et al, 2018, Berber et al, 2017, Bhattacharjee et al, 2016, Ertekin et al, 2014, Grassmann et al, 2014, Lukiw et al, 2012, Menard et al, 2016, Murad et al, 2014, Szemraj et al, 2015, Chu-Tan et al, 2018. One example is miR-124 which has been heavily studied in the central nervous system (CNS) and is the most highly abundant miRNA in the brain (Conaco et al, 2006, Lagos-Quintana et al, 2002, Lim et al, 2005, Makeyev et al, 2007.…”

Loss of Zebrafish Mfrp Causes Nanophthalmia, Hyperopia, and Accumulation of Subretinal Macrophages

“…Interestingly, Mfrp mutations have been associated with altered levels of Prss56, a serine protease associated with angle-closure glaucoma, posterior microphthalmia, and myopia in humans. 41–44 …”

Missense Mutations in the Human Nanophthalmos GeneTMEM98Cause Retinal Defects in the Mouse

“…Crb1 is expressed in photoreceptors and Prss56 , a secreted serine protease, is expressed in the Müller cells. It is possible that these genes interact and affect a common pathway, indeed upregulation of Prss56 has been observed in Mfrp mutants 56 .…”