Regeneration of Functional Retinal Ganglion Cells by Neuronal Identity Reprogramming

Abstract

Degeneration of retinal ganglion cells (RGCs) and their axons underlies vision loss in glaucoma and various optic neuropathies. There are currently no treatments available to restore lost vision in patients affected by these diseases. Regenerating RGCs and reconnecting the retina to the brain represent an ideal therapeutic strategy; however, mammals do not have a reservoir of retinal stem/progenitor cells poised to produce new neurons in adulthood. Here, we regenerated RGCs in adult mice by direct lineage reprogramming of retinal interneurons. We successfully converted amacrine and displaced amacrine interneurons into RGCs, and observed that regenerated RGCs projected axons into brain retinorecipient areas. They convey visual information to the brain in response to visual stimulation, and are able to transmit electrical signals to postsynaptic neurons, in both normal animals and in a diseased model. The generation of functional RGCs in adult mammals points to a therapeutic strategy for vision restoration in patients.

Turning lead into gold: reprogramming retinal cells to cure blindness

“…Second, the newly generated neurons were reported to be morphologically, functionally, and molecularly indistinguishable from wild-type neurons in some studies (6-10) but abnormal and immature in others (3)(4)(5). Third, three studies reported that newly generated RGCs rapidly extended axons through the optic nerve to synapse on central targets and mediate visually evoked behaviors (7,8,10), despite the fact that regeneration of axotomized RGCs is highly inefficient in adult mammalian retina and the very limited number of regenerating axons seldom reach central targets (11).…”

“…Put simply, the ability to generate photoreceptors or RGCs from endogenous MG would be far more useful than the ability to generate amacrine and bipolar cells. Cre-expressing transgenic lines used to restrict expression in other studies (3)(4)(5)10) are subject to similar caveats regarding specificity of expression. In these cases, however, the cell-type specificity of the transgenes had been rigorously established in previous studies, and scRNA-Seq analysis was used to demonstrate the presence of bipolar and amacrine-like precursors.…”

“…Over the past few years, a flurry of studies has built on these findings, manipulating key regulators of gene expression to reprogram adult rodent MG (3-9), as well as amacrine cells (10), resulting in generation of functional retinal neurons. The experimental paradigm is similar in all cases: researchers use adeno-associated viruses (AAVs) as vectors with cell type-specific promoters (7)(8)(9) or Cre-expressing transgenic lines (3)(4)(5)10) to selectively target the cells to be reprogrammed. They then exploit this genetic access to introduce fluorescent reporters that track the cells and their progeny, along with interventions (overexpressed cDNAs, shRNAs, gRNAs, or conditional knockouts) to induce reprogramming (Figure 1).…”

“…Despite this methodological similarity, however, the results differ greatly. Three groups report generation of RGCs from MG (7,8) or interneurons (10) by depletion of Ptbp1 (7) or ectopic expression of Pou4f2 (Brn3b) plus Atoh7 (Math5) (8) or Pou4f2 plus Sox4 (8,10). Two groups generated bipolar and amacrine-like cells by overexpression of Ascl1 (3,4) or conditional deletion of three nuclear factor I (NFI) class transcription factors (5).…”

Regenerative Effect of Adipose Derived Mesenchymal Stem Cells on Ganglion Cells in the Hypoxic Organotypic Retina Culture

“…This finding could possibly explained by Müller cells conversion to RGCs converted, as a response to ischemic insult, and also expressed Brn3a. Wei et al ( 18 ) previously showed that retinal neuronal identity switching, triggered migration of amacrine interneurons from the inner nuclear layer to the RGCs layer which may imply that neurons exhibit surprisingly unexpected plasticity, which could result in regenerative manifestations.…”