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, Mller 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 hypothesize that the Hippo signaling pathway actively blocks mammalian MG-mediated retinal regeneration by preventing sustained MG proliferation and reprogramming to a retinal progenitor-like state.
Our specific aims will precisely define the requirement of Hippo signaling in negative regulation of persistent cell cycle re-entry of MGs responding to retinal damage. We will also determine whether genetic bypass of Hippo signaling results in MG reprogramming to a progenitor-like state. Finally, we will assess the neurogenic potential of reprogrammed MGs. This project will employ a multi-disciplinary approach using genetic loss- and gain-of-function experiments, fate mapping, epigenomics, and single cell transcriptomics. By completion of the described aims, we expect to have identified the Hippo pathway as the endogenous molecular mechanism normally restraining MG proliferation and reprogramming to regenerative, progenitor cells. These data will provide an essential molecular entry point from which to further investigate novel methods to promote Mller glial cell-mediated retinal regeneration and likely have significant influence 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.
The Mller glial cells within the retinae of non-mammalian species have the ability to regenerate retinal neurons and reverse blindness, while mammalian retinae cannot. This proposal aims to establish the Hippo signaling pathway as the biological mechanism that normally prevents Mller glial cell-mediated retinal regeneration in mammals. By uncovering such a role for Hippo signaling, we will establish a new therapeutic target that will have significant influence on the field of retinal regenerative medicine.