Human retinal ganglion cell neurons generated by synchronous BMP inhibition and transcription factor mediated reprogramming.

In optic neuropathies, including glaucoma, retinal ganglion cells (RGCs) die. Cell transplantation and endogenous regeneration offer strategies for retinal repair, however, developmental programs required for this to succeed are incompletely understood. To address this, we explored cellular reprogramming with transcription factor (TF) regulators of RGC development which were integrated into human pluripotent stem cells (PSCs) as inducible gene cassettes. When the pioneer factor NEUROG2 was combined with RGC-expressed TFs (ATOH7, ISL1, and POU4F2) some conversion was observed and when pre-patterned by BMP inhibition, RGC-like induced neurons (RGC-iNs) were generated with high efficiency in just under a week. These exhibited transcriptional profiles that were reminiscent of RGCs and exhibited electrophysiological properties, including AMPA-mediated synaptic transmission. Additionally, we demonstrated that small molecule inhibitors of DLK/LZK and GCK-IV can block neuronal death in two pharmacological axon injury models. Combining developmental patterning with RGC-specific TFs thus provided valuable insight into strategies for cell replacement and neuroprotection.

Restoring vision and rebuilding the retina by Müller glial cell reprogramming.

Müller glia are non-neuronal support cells that play a vital role in the homeostasis of the eye. Their radial-oriented processes span the width of the retina and respond to injury through a cellular response that can be detrimental or protective depending on the context. In some species, protective responses include the expression of stem cell-like genes which help to fuel new neuron formation and even restoration of vision. In many lower vertebrates including fish and amphibians, this response is well documented, however, in mammals it is severely limited. The remarkable plasticity of cellular reprogramming in lower vertebrates has inspired studies in mammals for repairing the retina and restoring sight, and recent studies suggest that mammals are also capable of regeneration, albeit to a lesser degree. Endogenous regeneration, whereby new retinal neurons are created from existing support cells, offers an exciting alternative approach to existing tissue transplant, gene therapy, and neural prosthetic approaches being explored in parallel. This review will highlight the role of Müller glia during retinal injury and repair. In the end, prospects for advancing retinal regeneration research will be considered.