MicroRNA-processing Enzymes Are Essential for Survival and Function of Mature Retinal Pigmented Epithelial Cells in Mice

Abstract

Edited by Paul E. FraserAge-related macular degeneration (AMD) is a major cause of irreversible vision loss. The neovascular or "wet" form of AMD can be treated to varying degrees with anti-angiogenic drugs, but geographic atrophy (GA) is an advanced stage of the more prevalent "dry" form of AMD for which there is no effective treatment. Development of GA has been linked to loss of the microRNA (miRNA)-processing enzyme DICER1 in the mature retinal pigmented epithelium (RPE). This loss results in the accumulation of toxic transcripts of Alu transposable elements, which activate the NLRP3 inflammasome and additional downstream pathways that compromise the integrity and function of the RPE. However, it remains unclear whether the loss of miRNA processing and subsequent gene regulation in the RPE due to DICER1 deficiency also contributes to RPE cell death. To clarify the role of miRNAs in RPE cells, we used two different mature RPE cell-specific Cre recombinase drivers to inactivate either Dicer1 or DiGeorge syndrome critical region 8 (Dgcr8), thus removing RPE miRNA regulatory activity in mice by disrupting two independent and essential steps of miRNA biogenesis. In contrast with prior studies, we found that the loss of each factor independently led to strikingly similar defects in the survival and function of the RPE and retina. These results suggest that the loss of miRNAs also contributes to RPE cell death and loss of visual function and could affect the pathology of dry AMD. Age-related macular degeneration (AMD)3 is a progressive retinal degenerative disorder that preferentially impacts the macula, the central region of the retina primarily responsible for both color vision and visual acuity. AMD is the leading cause of irreversible vision loss in modern Western societies among adults over 50 and is projected to impact the lives of nearly 200 million people worldwide by the year 2020 (1-4). It presents in two distinct forms, based on the types of lesions that occur in the late stages. The neovascular or "wet" form of AMD is associated with abnormal growth of blood vessels in the choriocapillaris, which extend through Bruch's membrane and cause acute vision loss that can be reversed relatively rapidly through intravitreal injection of vascular endothelial growth factor (VEGF) inhibitors (5-8). In contrast, the dry form of AMD is characterized by a large number of drusen and occasionally by geographic atrophy (GA), the regional loss of macular photoreceptors, retinal pigmented epithelium (RPE), and choriocapillaris. These changes cause deficits in dark adaptation, along with dense visual field scotomas and a gradual decline in visual acuity (9 -11). Currently, there is no effective treatment for the dry form of AMD.Discovered over 2 decades ago in Caenorhabditis elegans, miRNAs regulate gene expression at the post-transcriptional level (12, 13). miRNA biogenesis involves two sequential cleavage steps. The first is accomplished in the nucleus by the microprocessor complex and involves a member of the ribonucleas...

Mouse Models of Inherited Retinal Degeneration with Photoreceptor Cell Loss

“…Further, Category 03 gene Nmnat1 encodes an enzyme that synthesizes nicotinamide adenine dinucleotide in the nucleus, which may regulate the large-scale polyADP-ribosylation of protein targets at sites of DNA damage [402]. Mutations in the genes encoding these proteins all result in PR cell loss [230,384,385,400,401,[403][404][405][406][407][408][409][410][411]. Mutations in five of these genes as included in Figure 6 (Cwc27, Ercc1, Ercc6, Sirt6, and Ubb) caused moderate to slow progression of PR cell loss (D 50 ≥ 2 months), consistent with a steady accumulation of unresolved DNA damage with age.…”

Chronic Dicer1 deficiency promotes atrophic and neovascular outer retinal pathologies in mice

“…Global ablation of Dicer1 results in early embryonic lethality in mice (22,23). Developmental or postnatal cell type-specific deletion of Dicer1 in the RPE results in rapid and profound RPE and retinal atrophy (9,24). In contrast, the Dicer1 Gt(β-geo)Han mouse line, hereafter referred to as Dicer1 d/d , harbors a gene trap insertion in intron 24 of the Dicer1 locus, which results in a functional reduction in Dicer1 expression by ∼80% (25).…”

c-Jun-mediated microRNA-302d-3p induces RPE dedifferentiation by targeting p21Waf1/Cip1

“…In mature organs and tissues, miRNAs have more essential roles in monitoring cellular stress than primary cellular functions 40 . Essential roles of miRNAs and their processing factors in keeping the survival of RPE cells have been revealed 16 , 20 , 41 , 42 . Thus, investigating the influence of miRNAs on retinal degenerative diseases and seeking for potential treatment are promising and expanding.…”