AAV-Mediated, Optogenetic Ablation of Muller Glia Leads to Structural and Functional Changes in the Mouse Retina

Muller glia, the primary glial cell in the retina, provide structural and metabolic support for neurons and are essential for retinal integrity. Muller cells are closely involved in many retinal degenerative diseases, including macular telangiectasia type 2, in which impairment of central vision may be linked to a primary defect in Muller glia. Here, we used an engineered, Muller-specific variant of AAV, called ShH10, to deliver a photo-inducibly toxic protein, KillerRed, to Muller cells in the mouse retina. We characterized the results of specific ablation of these cells on visual function and retinal structure. ShH10-KillerRed expression was obtained following intravitreal injection and eyes were then irradiated with green light to induce toxicity. Induction of KillerRed led to loss of Muller cells and a concomitant decrease of Muller cell markers glutamine synthetase and cellular retinaldehyde-binding protein, reduction of rhodopsin and cone opsin, and upregulation of glial fibrillary acidic protein. Loss of Muller cells also resulted in retinal disorganization, including thinning of the outer nuclear layer and the photoreceptor inner and outer segments. High resolution imaging of thin sections revealed displacement of photoreceptors from the ONL, formation of rosette-like structures and the presence of phagocytic cells. Furthermore, Muller cell ablation resulted in increased area and volume of retinal blood vessels, as well as the formation of tortuous blood vessels and vascular leakage. Electrophysiologic measures demonstrated reduced retinal function, evident in decreased photopic and scotopic electroretinogram amplitudes. These results show that loss of Muller cells can cause progressive retinal degenerative disease, and suggest that AAV delivery of an inducibly toxic protein in Muller cells may be useful to create large animal models of retinal dystrophies.