Hippo and Wnt pathway regulation of mammalian Muller glial cell reprogramming and proliferation

Retinal diseases such as glaucoma, macular degeneration, and diabetic retinopathy, as well as traumatic injury, result in loss of retinal neurons and thus sight, depriving many worldwide of one of our most valued senses. Thus, there is a critical need to devise strategies to restore lost retinal neurons, leading to vision recovery. Current efforts in retinal regenerative medicine are heavily invested in cell replacement approaches. However, it may also be possible to induce the mammalian retinae to undergo an intrinsic self-repair mechanism to regenerate neurons. The retinae of non-mammalian vertebrates, such as zebrafish, are known to exhibit the remarkable ability of retinal regeneration. Here, Müller glial cells (MGs) reprogram to proliferative, retinal progenitor-like cells that, in turn, differentiate into new photoreceptors, leading to restoration of vision. Unfortunately, for unknown reasons, mammalian MGs have lost this ability, or it is dormant. Our long-term goal is to identify the cellular and molecular mechanisms blocking mammalian MG-mediated retinal regeneration. By doing so, we may be able to devise strategies to bypass this system and thereby reawaken the regenerative potential of the mammalian retina. In this proposal, we will test the overarching hypothesis that transient modulation of the Hippo signaling pathway drives MGs into a progenitor-like state capable of generating new retinal neurons and MGs. To test this hypothesis, we will employ a multi-disciplinary approach using genetic loss- and gain-of-function experiments, fate mapping, and single-cell transcriptomics. Our specific aims will precisely determine the fate of proliferative MGs, which are non-responsive to Hippo pathway regulation, as being neurons and/or MGs. We will also determine how retinal damage triggers MG cell cycle entry prior to repression by Hippo. These data will provide an essential molecular entry point for further investigating novel methods to promote Müller glial cell-mediated retinal regeneration, and are likely to have a significant impact on the field of retinal regenerative medicine. We anticipate subsequent investigation into more translational, therapeutic methods to modulate Hippo pathway activity to promote retinal regeneration.