RESUMO
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.
Assuntos
Regulação da Expressão Gênica/genética , Fatores de Transcrição Otx/deficiência , Células Fotorreceptoras/patologia , Retina/patologia , Epitélio Pigmentado da Retina/fisiopatologia , Fatores Etários , Animais , Astrócitos/fisiologia , Imunoprecipitação da Cromatina , Modelos Animais de Doenças , Eletrorretinografia , Feminino , Perfilação da Expressão Gênica , Regulação da Expressão Gênica/efeitos dos fármacos , Vetores Genéticos/fisiologia , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Humanos , Lentivirus/genética , Masculino , Camundongos , Camundongos Transgênicos , Modelos Biológicos , Análise de Sequência com Séries de Oligonucleotídeos , Fatores de Transcrição Otx/genética , Células Fotorreceptoras/metabolismo , Ligação Proteica/efeitos dos fármacos , Ligação Proteica/genética , RNA Mensageiro , Degeneração Retiniana/genética , Degeneração Retiniana/patologia , Epitélio Pigmentado da Retina/patologiaRESUMO
pH variations in the retina are thought to be involved in the fine-tuning of visual perception. We show that both photoreceptors and neurons of the mouse retina express the H+-gated cation channel subunits acid-sensing ion channel 2a (ASIC2a) and ASIC2b. Inactivation of the ASIC2 gene in mice leads to an increase in the rod electroretinogram a- and b-waves and thus to an enhanced gain of visual transduction. ASIC2 knock-out mice are also more sensitive to light-induced retinal degeneration. We suggest that ASIC2 is a negative modulator of rod phototransduction, and that functional ASIC2 channels are beneficial for the maintenance of retinal integrity.