Abstract
Inherited maculopathies, age related macular degeneration and some forms of retinitis pigmentosa are associated with impaired function or loss of the retinal pigment epithelium (RPE). Among potential treatments, transplantation approaches are particularly promising. The arrangement of RPE cells in a well-defined tissue layer makes the RPE amenable to cell or tissue sheet transplantation. Different cell sources have been suggested for RPE transplantation but the development of a clinical protocol faces several obstacles. The source should provide a sufficient number of cells to at least recover the macula area. Secondly, cells should be plastic enough to be able to integrate in the host tissue. Tissue sheets should be considered as well, but the substrate on which RPE cells are cultured needs to be carefully evaluated. Immunogenicity can also be an obstacle for effective transplantation as well as tumorigenicity of not fully differentiated cells. Finally, ethical concerns may represent drawbacks when embryo-derived cells are proposed for RPE transplantation. Here we discuss different cell sources that became available in recent years and their different properties. We also present data on a new source of human RPE. We provide a protocol for RPE differentiation of retinal stem cells derived from adult ciliary bodies of post-mortem donors. We show molecular characterization of the invitro differentiated RPE tissue and demonstrate its functionality based on a phagocytosis assay. This new source may provide tissue for allogenic transplantation based on best matches through histocompatibility testing.
Highlights
The retinal pigment epithelium (RPE) is a highly specialized epithelium with a neuroectodermal embryonic origin like the retina
We provide a protocol for RPE differentiation of retinal stem cells derived from adult ciliary bodies of post-mortem donors
While the retina was first described by Galen in the second century A.D., discovery of the RPE required the use of the first rudimentary microscopes in the 18th century and was described by Carlo Mondini of Bologna in his “Commentationes Bononienses” (1790) as “a real membrane formed by innumerable globules which makes an excessively delicate network” (Marmor and Wolfensberger, 1998)
Summary
The retinal pigment epithelium (RPE) is a highly specialized epithelium with a neuroectodermal embryonic origin like the retina. The outer stratum is a monolayer of cells that differentiate during embryonic/fetal development and is characterized by pigmentation, which appears during the 5th week of human embryogenesis. RPE differentiation is induced by several factors including the signaling molecule Activin, a member of the TGF family, which is secreted by adjacent mesenchymal cells. These signals induce expression of transcription factors, such as microphthalmia-associated transcription factor (MITF), orthodenticle homolog 2 (OTX2) and paired box 6 (PAX6), that are essential for RPE specification and to drive expression of proteins necessary for the distinguishing functions of the RPE (Bharti et al, 2012; Fuhrmann et al, 2000; Housset et al, 2013). We present a new protocol for the differentiation of adult human retinal stem cells into RPE sheets
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