Loss of Otx2 in the Adult Retina Disrupts Retinal Pigment Epithelium Function, Causing Photoreceptor Degeneration

Abstract

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.

Transcription Factor SOX9 Plays a Key Role in the Regulation of Visual Cycle Gene Expression in the Retinal Pigment Epithelium

“…From the literature, we added additional possible connections into the network. The direct relations reported in the RPE are regulation of Mitf and Otx2 by ␤-catenin (14) and regulation of Rdh5 by OTX2 (16). The direct relations reported in non-RPE cells are regulation of MITF by SOX9 in human skin melanocytes (67) and regulation of Sox9 by LHX2 in mouse skin keratinocytes (26) (Fig.…”

“…The critical role of OTX2 in RPE development is well documented (12,15). Its importance in maintaining adult RPE functions has also been reported recently (16). In our previous studies, we identified sex-determining region Y box 9 (SOX9) as a key regulator that activates the human BEST1 promoter in the RPE through interaction with MITF and OTX2 (17).…”

“…The finding that some transcription factors that are critical in RPE development are continuously expressed into mature stages raises the question as to what roles they play in adult RPE. It has been reported recently that tissue-specific inactivation of Otx2 in the mature retina and RPE led to abnormalities in the RPE, such as reduction of the number and size of melanosomes and a loss of RPE contacts with photoreceptor outer segments followed by retinal degeneration, revealing the essential role of OTX2 in maintaining the integrity of the adult RPE (16,55). OTX2 coordinates RPE-specific functions, such as retinoid metabolism and melanogenesis, and directly regulates several visual cycle-related genes, including Rdh5 (16).…”

“…It has been reported recently that tissue-specific inactivation of Otx2 in the mature retina and RPE led to abnormalities in the RPE, such as reduction of the number and size of melanosomes and a loss of RPE contacts with photoreceptor outer segments followed by retinal degeneration, revealing the essential role of OTX2 in maintaining the integrity of the adult RPE (16,55). OTX2 coordinates RPE-specific functions, such as retinoid metabolism and melanogenesis, and directly regulates several visual cycle-related genes, including Rdh5 (16). Although the authors did not report Rpe65 and Rlbp1 as direct targets of OTX2, we found that RPE65 and RLBP1 are also direct targets of OTX2 in this study.…”

Characterization of Three-Dimensional Retinal Tissue Derived from Human Embryonic Stem Cells in Adherent Monolayer Cultures

“…OTX2, a paired-type homeodomain protein, is important for specification and postmitotic function of PRs [73], bipolar neurons, and RPE [74][75][76][77]. OTX2 [+] cells first appear in the developing PRs, and then in the bipolar and RPE cells during mammalian retinogenesis [78].…”