Evaluation of Human Retinal Ganglion Cell Regenerative Potential

Johns Hopkins University, Baltimore MD

Investigators

Abstract

PROJECT SUMMARY Retinal ganglion cells (RGCs) are solely responsible for transmitting signals from the eye to the brain. They do so via their axons, which make up the optic nerve (ON). As such, loss of RGCs results in diseases like glaucoma, a leading cause of irreversible blindness worldwide. Loss of RGCs is considered irreversible, as the human eye normally fails to regenerate lost RGCs or degenerated RGC axons. Nevertheless, restoring vision to patients via regrowth of the ON represents a major therapeutic goal for the field. Endogenous ON regeneration and RGC transplantation are the two main areas of research being pursued to reach this therapeutic goal. Advances in neuroprotection, stem cell biology, and regenerative medicine are bringing these goals closer to reality. One promising approach for replacing lost RGCs is to inject human stem cell derived RGCs into the eye. Progress has been made in replacing other lost retinal cell types, such as retinal pigment epithelium, with stem cell derived cells. Despite recent studies identifying factors that promote RC survival and neurite outgrowth, promoting transplanted RGC axons to regenerate an ON all the way to the brain to restore visual function remains a major therapeutic challenge. The capacity of human RGCs to achieve this essential goal is unknown. Specifically, it is unclear if modulating intrinsic RGC-expressed factors can promote human RGC axonal regeneration, regrowth of the ON, and restoration of visual function. Preliminary data suggest that even in a highly permissive environment, hRGC neurite outgrowth is limited. This and other recent studies in mice suggest that intrinsic, i.e. RGC expressed, factors are a key barrier to ON regeneration and functional recovery in the clinic. This has yet to be systematically investigated in a regenerative species. Accordingly, I hypothesize that intrinsic factors regulating RGC survival, neurite outgrowth and targeting, and functional recovery can be revealed through a systematic interrogation of gene function in the context of a naturally regenerative environment, the zebrafish. To test my hypothesis, I will explore 1) how intrinsic factors regulate ON regeneration in zebrafish; and 2) test how modulation of intrinsic factors can stimulate ON formation in human RGCs transplanted into zebrafish. I will take advantage of zebrafish amenability to large-scale screening to test ~100 genes for the ability to promote endogenous RGC survival, axonal and dendritic outgrowth, and functional recovery in zebrafish. I will further examine the ability of gene modulation to enhance transplanted human RGC survival, ON growth, and functional recovery in zebrafish. These studies will increase our understanding of the genetic networks governing ON regenerative potential. Characterizing zebrafish and human RGC and ON regenerative potential will bring us closer to understanding how to develop regenerative therapies and successful transplantation strategies for patients.