Restoration of vision by chemically reprogrammed photoreceptors
Thomas Mock, Thomas
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Purpose: Many retinopathies such as Retinitis Pigmentosa, Stargardt disease, Cone-rod dystrophy, Achromatopsia, Chroideremia and Labor congenital Amaurosis (LCA) comprise a wide range of genetically and phenotypically heterogeneous conditions that share common progressive loss of photoreceptor function accompanied by irreversible vision loss. Majority of the patients affected by these diseases present with uncorrectable decreased visual acuity during their childhood years, which most often progress to legal blindness. Strategy to restore vision with photoreceptor like replacement cell has the advantage of being applied to these patients, regardless of their genetic dysfunction or stage of disease. Currently no FDA approved treatments are available to treat these disorders. We have discovered a chemical engineering method that can convert fibroblasts to chemically induced photoreceptors (CiPCs) with their ability to restore vision in retinal degeneration mouse model. Methods: A combination of small molecule (5C) was used to convert fibroblasts to CiPCs. Gene expression of CiPCs was analyzed by RNA sequencing, RT-PCR and immunofluorescence. Light responsiveness of CiPCs was tested by single cell patch clamp recording upon stimulation with light. In vivo CiPC function was examined by pupil analysis, light aversion test, visual acuity and contrast sensitivity measurement after injecting them into retinal degeneration mouse model. Results: We have identified a set of five small molecules (5C) that induces mouse embryonic fibroblasts (MEFs) and human adult dermal fibroblasts (HADF) into CiPCs both rods and cones, without the use of pluripotent cells or viral transcription factors in less than two weeks time. Detailed analyses have been performed in mouse cells, but in brief, these cells express transcript and proteins consistent with youthful photoreceptors (postnatal day 5). In vitro functional analysis indicated that CiPCs are light responsive. Moreover, when mouse ciPCs are injected into the subretinal space of retinal degeneration mutant mice (rd1), in some mice (approximately 50%) we observed cell survival for several months (more than 120 days), restored light-dark preference/discrimination, improved scotopic-Optomotry testing, fleeting but partial ERG recovery, and restoration of pupillary reflexes. Conclusions: Based upon these observations we demonstrate restoration of visual functions by CiPCs that carry extraordinary translational potential for millions of visually impaired patients worldwide.