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Orthodenticle homeobox 2 ( OTX2) controls essential, homeostatic retinal pigment epithelial ( RPE) genes in the adult. Using cocultures of human CD14+ blood monocytes (Mos) and primary porcine RPE cells and a fully humanized system using human-induced pluripotent stem cell-derived RPE cells, we show that activated Mos markedly inhibit RPE OTX2 expression and resist elimination in contact with the immunosuppressive RPE. Mechanistically, we demonstrate that TNF-α, secreted from activated Mos, mediates the downregulation of OTX2 and essential RPE genes of the visual cycle among others. Our data show how subretinal, chronic inflammation and in particular TNF-α can affect RPE function, which might contribute to the visual dysfunctions in diseases such as age-related macular degeneration ( AMD) where subretinal macrophages are observed. Our findings provide important mechanistic insights into the regulation of OTX2 under inflammatory conditions. Therapeutic restoration of OTX2 expression might help revive RPE and visual function in retinal diseases such as AMD. [ABSTRACT FROM AUTHOR]

Photoreceptor degeneration in age-related macular degeneration (AMD) is associated with an infiltration and chronic accumulation of mononuclear phagocytes (MPs). We have previously shown that Cx3cr1-deficient mice develop age- and stress- related subretinal accumulation of MPs, which is associated with photoreceptor degeneration. Cx3cr1-deficient MPs have been shown to increase neuronal apoptosis through IL-1β in neuroinflammation of the brain. The reason for increased IL-1β secretion from Cx3cr1-deficient MPs, and whether IL-1β is responsible for increased photoreceptor apoptosis in Cx3cr1-deficient mice, has not been elucidated. Here we show that Cx3cr1-deficient MPs express increased surface P2X7 receptor (P2RX7), which stimulates IL-1β maturation and secretion. P2RX7 and IL-1β inhibition efficiently blunted Cx3cr1-MP-dependent photoreceptor apoptosis in a monocyte/retina coculture system and in lightinduced subretinal inflammation of Cx3cr1-deficient mice in vivo. Our results provide an explanation for increased CX3CR1-dependent IL-1β secretion and suggest that IL-1β or P2RX7 inhibition can help inhibit the inflammation-associated photoreceptor cell loss in late AMD, including geographic atrophy, for which no efficient treatment currently exists. [ABSTRACT FROM AUTHOR]

Background: Many developmental genes are still active in specific tissues after development is completed. This is the case for the homeobox gene Otx2, an essential actor of forebrain and head development. In adult mouse, Otx2 is strongly expressed in the retina. Mutations of this gene in humans have been linked to severe ocular malformation and retinal diseases. It is, therefore, important to explore its post-developmental functions. In the mature retina, Otx2 is expressed in three cell types: bipolar and photoreceptor cells that belong to the neural retina and retinal pigment epithelium (RPE), a neighbour structure that forms a tightly interdependent functional unit together with photoreceptor cells. Methodology/Principal Findings: Conditional self-knockout was used to address the late functions of Otx2 gene in adult mice. This strategy is based on the combination of a knock-in CreERT2 allele and a floxed allele at the Otx2 locus. Timecontrolled injection of tamoxifen activates the recombinase only in Otx2 expressing cells, resulting in selective ablation of the gene in its entire domain of expression. In the adult retina, loss of Otx2 protein causes slow degeneration of photoreceptor cells. By contrast, dramatic changes of RPE activity rapidly occur, which may represent a primary cause of photoreceptor disease. Conclusions: Our novel mouse model uncovers new Otx2 functions in adult retina. We show that this transcription factor is necessary for long-term maintenance of photoreceptors, likely through the control of specific activities of the RPE. [ABSTRACT FROM AUTHOR]

The coordinated spatial arrangement of organelles within a tissue plane, known as planar cell polarity (PCP), is critical for organ development and function. Gradients of morphogens and their receptors typically set-up PCP, but whether non-molecular cues, akin to phototropism in plants, also play a part remains unknown. Here, we report that basal bodies of newborn photoreceptor cells in the mouse retina are positioned centrally on the apical surface but then move laterally during the first postnatal week, generating cell-intrinsic asymmetry in the retinal plane. After 1 week, when the eyes open, basal bodies of cone cilia, but not rods, become coordinated across the plane to face the center of the retina. We further show that light is essential for cone PCP, triggering a cascade in which cone transducin interacts with the G-protein-signaling modulator protein 2 (GPSM2) to establish PCP. This work identifies a non-canonical PCP pathway initiated by light., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Photoreceptors are specialized neurons of the retina that receive nursing from the adjacent retinal pigment epithelium (RPE). Frequent in the elderly, photoreceptor loss can originate from primary dysfunction of either cell type. Despite intense interest in the etiology of these diseases, early molecular actors of late-onset photoreceptor degeneration remain elusive, mostly because of the lack of dedicated models. Conditional Otx2 ablation in the adult mouse retina elicits photoreceptor degeneration, providing a new model of late-onset neuronal disease. Here, we use this model to identify the earliest events after Otx2 ablation. Electroretinography and gene expression analyses suggest a nonautonomous, RPE-dependent origin for photoreceptor degeneration. This is confirmed by RPE-specific ablation of Otx2, which results in similar photoreceptor degeneration. In contrast, constitutive Otx2 expression in RPE cells prevents degeneration of photoreceptors in Otx2-ablated retinas. We use chromatin immunoprecipitation followed by massive sequencing (ChIP-seq) analysis to identify the molecular network controlled in vivo by Otx2 in RPE cells. We uncover four RPE-specific functions coordinated by Otx2 that underpin the cognate photoreceptor degeneration. Many direct Otx2 target genes are associated with human retinopathies, emphasizing the significance of the model. Importantly, we report a secondary genetic response after Otx2 ablation, which largely precedes apoptosis of photoreceptors, involving inflammation and stress genes. These findings thus provide novel general markers for clinical detection and prevention of neuronal cell death.