Research conducted at the National Rehabilitation Center for Persons with Disabilities, and the Center for Regenerative Medicine, National Institute for Child Health and Development, Tokyo, have shown that human dermal fibroblasts may be differentiated to photoreceptor cells by a combination of transcription factors including CRX, RAX and NEUROD. The transcription factors are understood to up-regulate expression of the photoreceptor-specific genes, recoverin, blue opsin and PDE6C. In addition, supplementation with OTX2 gene transduction appeared to up-regulate the photoreceptor-specific genes blue opsin, recoverin, S-antigen, CNGB3 and PDE6C. Re-programming of cells from one lineage to another has been a long-sought goal for generations of researchers, not least of all in the field of retinal degeneration. The prospect of been able to derive fully-differentiated photoreceptor cells from other cell sources has the potential to revolutionise not just the understanding of disease, but potentially to create a replenishable supply of retinal tissues enabling the treatment of currently untreatable diseases.
The combination of CRX, RAX and NEUROD followed previous success in differentiating iris cells to photoreceptor cells however, in the current research, human dermal fibroblasts were transfected with the transcription factor genes and were then assessed for inducible expression of genes specific to photoreceptor cells. The results showed that the combination of transcription factors led to the up regulation of recoverin, blue opsin and PDE6C in all strains of fibroblasts tested. In addition, the researchers showed that the addition of OTX2 appeared to amplify the expression of retina specific genes. Finally, the team employed patch clamp testing of differentiated cells to confirm light sensitivity of the newly derived photoreceptor cells. The potential of using dermal fibrobalsts as a source for differentiating photoreceptor cells is attractive, especially given the ease and convenience of accessing such dermal cells.
To specifically clarify the gene expression profile in cells that had been transfected to induce photoreceptor cell differentiation, the researchers compared the expression profiles of 50,599 probes in both differentiated photoreceptors and parental fibroblasts. Phototransduction-related genes accounted for up to 0.2% of the total analyzed and showed that signals of 16 probes were increased among 30 phototransduction-related oligos. The researchers highlight that their current findings represent the first demonstration that the same transcription factor cocktail that induces photoreceptor differentiation from iris cells, has similar effects when used on fibroblast cells. As dermal cells can be harvested with relative ease, iris cells need to be obtained surgically and therefore dermal cells may provide a far more convenient and readily accessible source from a treatment regimen perspective.