Summary

Dérivation efficace des cellules d'épithélium pigmentaire de la rétine à partir de cellules souches

Published: March 08, 2015
doi:

Summary

Stem cell-derived retinal pigment epithelium (RPE) cells may be used for multiple applications including cell-based therapies for retinal degeneration, disease modeling, and drug studies. Here we present a simple protocol for reproducibly deriving RPE from stem cells.

Abstract

No cure has been discovered for age-related macular degeneration (AMD), the leading cause of vision loss in people over the age of 55. AMD is complex multifactorial disease with an unknown etiology, although it is largely thought to occur due to death or dysfunction of the retinal pigment epithelium (RPE), a monolayer of cells that underlies the retina and provides critical support for photoreceptors. RPE cell replacement strategies may hold great promise for providing therapeutic relief for a large subset of AMD patients, and RPE cells that strongly resemble primary human cells (hRPE) have been generated in multiple independent labs, including our own. In addition, the uses for iPS-RPE are not limited to cell-based therapies, but also have been used to model RPE diseases. These types of studies may not only elucidate the molecular bases of the diseases, but also serve as invaluable tools for developing and testing novel drugs. We present here an optimized protocol for directed differentiation of RPE from stem cells. Adding nicotinamide and either Activin A or IDE-1, a small molecule that mimics its effects, at specific time points, greatly enhances the yield of RPE cells. Using this technique we can derive large numbers of low passage RPE in as early as three months.

Introduction

The various cell types that occupy the retina are organized in a functional architecture. The photoreceptors in the back of the retina are responsible for converting light into electrical impulses through phototransduction. However, phototransduction cannot occur without the coordinated efforts of other neighboring cell types including Mueller glia and retinal pigment epithelium (RPE) cells. A monolayer of RPE cells partitions the sensory retina from the choriocapillaris, the primary blood supply for photoreceptors, and are ideally situated to control multiple functions important for photoreceptor homeostasis. In fact, the RPE and photoreceptors are so co-dependent they are widely considered to be one single functional unit. (For a review of all the diverse functions of the RPE see Strauss, 20051.) Death or dysfunction of retinal pigment epithelium cells can induce age-related macular degeneration (AMD), the leading cause of permanent vision loss in industrialized countries2-4.

AMD is a multifactorial disease of RPE, photoreceptors, and the choroidal vasculature; risk factors are diverse and include combinations of environmental and genetic influences5,6. Treatments for AMD are very limited, but one promising potential therapy is RPE cell replacement7,8. While the outcomes have been mixed, the transplantation of RPE cells in AMD patients (and in other patients with retinal degeneration) and also in rodent models of retinal degeneration, has the potential to transiently prevent significant photoreceptor atrophy9-23. (The animal model commonly used for these studies are Royal College of Surgeons (RCS) rats, which harbor a mutation in the MerTK gene. This mutation renders RPE cells incapable of phagocytosing photoreceptor outer segments and promotes retinal degeneration24.) While the reported survival rates of implanted RPE in the subretinal space of RCS rats and mice vary greatly, there is potential for them to survive for several months or years9,10,12,20.

RPE cells can be obtained in sufficient numbers for transplantation by deriving them from pluripotent stem cells9-14,25-28. Several independent groups have demonstrated that these cells function in similar ways to their somatic counterparts, and long term studies suggest that they are safe upon implantation in rat and mouse disease models9,10,12,14,19,20,25,29-32. The use of induced pluripotent stem cells instead of embryonic stem cells may be advantageous since ethical issues and immunological challenges associated with allogeneic RPE may be obviated33,34. Another exciting application for iPS technology is disease modeling35. The ability to interrogate large numbers of RPE cells derived from patients with RPE diseases could be invaluable for understanding their molecular bases. This type of study has been performed recently with Best disease patient RPE and could pave the way for similar studies of inherited maculopathies36.

The derivation of RPE from stem cells is a relatively simple process and can be done entirely in xeno-free conditions. The simplest strategy is to derive monolayers of RPE cells spontaneously, however, the yield can be significantly improved using directed differentiation techniques. But these techniques involve the use of exogenous protein factors that can be expensive and often generated in bacteria or other non-human sources10,12,37. In our studies we followed an established protocol10 that utilizes nicotinamide and Activin A, a signaling factor that has been shown to be sufficient for RPE specification38. Here we will demonstrate that the small molecule IDE-1 can adequately replace Activin A, thus reducing costs and alleviating concerns associated with the use of recombinant proteins39. Additionally, we utilize xeno-free serum replacement, and we culture the differentiating RPE cells on a synthetic xeno-free substrate. RPE cells have been shown previously to differentiate very effectively using this approach40.

When differentiated as a monolayer, we visualize pigmented colonies containing RPE cells after as early as five weeks12. Once they reach sufficient size, they can be manually excised and transferred to another dish for expansion. RPE cells are notorious for dedifferentiating with each passage, and the use of anything older than five passages should be avoided (we find that sufficient numbers of cells for characterization and transplantation in animal models can easily be generated after two or three passages). Once fully differentiated, we employ multiple techniques to characterize the cells anatomically and functionally to ensure that they will serve as adequate replacements for diseased RPE. The description of these techniques, and protocol for implanting the iPS-RPE in the subretinal space of rodents, are beyond the scope of this methods paper and have been previously published12,32,41.

While developing standardized protocols for effective derivation of iPS-RPE is clearly important for the clinics, there is also significant preclinical work to still be done in animal models. There are concerns regarding immunogenicity of iPS-derived cells, and multiple different implantation techniques, including implanting cells on artificial substrates, are being explored42,43. For these reasons, we feel that the publication of standardized protocols is beneficial to facilitate both clinical and preclinical studies. Especially if direct comparisons will be done of iPS-RPE cells derived in different labs by different research groups.

Protocol

1. différenciation dirigée des cellules souches dérivées RPE Remarque: Toutes les étapes d'incubation sont effectuées à 37 ° C dans 5% de CO 2 Maintenir les lignes ou les hanches (hES nourrir quotidienne) dans les médias de maintenance (MM; Tableau 1). Une fois que les lignes ont atteint les normes suffisantes de contrôle de la qualité, les maintenir sur une couche de cellules nourricières de souris embryonnair…

Representative Results

Les étapes décrites dans ce manuscrit, comme représenté sur la figure 1, peuvent être utilisés pour générer facilement RPE partir de cellules souches tel que présenté antérieurement 10,12. Après avoir maintenu les lignes iPS pour plusieurs semaines, des colonies pigmentées commencent à apparaître dans les colonies après 5-7 semaines (7 semaines vieilles cultures sont présentées à la figure 2A-C). Ces colonies peuvent continuer à croître pendant des semain…

Discussion

Dans ce manuscrit, nous décrivons les étapes pour générer efficacement un grand nombre de cultures iPS-RPE pures. Nous avons montré précédemment en utilisant ce protocole de différenciation dirigée avec activine A que nous pouvons générer iPS-RPE qui ressemblent fortement hRPE basée sur la transcriptomique, protéomique, métabolomique et fonctionnalité, et qu'ils retarder la dégénérescence rétinienne lorsqu'ils sont implantés chez des rats RCS 12,31,32 . Le processus de génération…

Disclosures

The authors have nothing to disclose.

Acknowledgements

We wish to thank the following individuals: Drs. Tim Krohne and Eyal Banin (along with Dr. Mandy Lehmann and David Friedlander) for generous help developing the differentiation protocols. Dr. Felicitas Bucher provided assistance differentiating the RPE cells used in this study. We also acknowledge the National Eye Institute (NEI grants EY11254 and EY021416), California Institute for Regenerative Medicine (CIRM grant TR1-01219), and the Lowy Medical Research Institute (LMRI) for very generous funding for this project.

Materials

Name of Material/ Equipment (A-Z) Company Catalog Number Comments/Description
Corneal knife  Surgipro SPOI-070 knife x 1
DMEM/F-12, HEPES Life Technologies 11330-032 500 mL x 4 
Dulbecco's Phosphate-Buffered Saline, 1X w/out Ca or Mg VWR 45000-434 500 mL x 6
Fetal Bovine Serum, Regular (Heat Inactivated) VWR 45000-736 500 mL x 1
FGF-Basic (AA 10-155) Recombinant Human Protein Life Technologies PHG0021 100 ug x 1
IDE-1 Stemgent 04-0026 2 mg x 1
Knockout DMEM Life Technologies 10829-018 500 mL x 1 
KnockOut Serum Replacement Life Technologies 10828-028 500 mL x 1
L-Glutamine 200 mM  Life Technologies 25030-081 100 mL x 1
MEM Non-Essential Amino Acids Solution 100X  Life Technologies 11140-050 100 mL x 1
Nicotinamide Sigma-Aldrich N0636-100G 100 g x 1
Penicillin-Streptomycin (10,000 U/mL) Life Technologies 15140-148 20 mL x 1
Recombinant Human/Murine/Rat Activin A  PeproTech 120-14E 10 ug x 2
Synthemax-T Surface 6 Well Plates Corning 3877 Case(12) x 1
TrypLE-Express Enzyme (1X), no phenol red  Life Technologies 12604-021 500 mL x 1 
Vacuum Filter/Storage Bottle System, 0.1µm pore, 500mL  Corning 431475 Case(12) x 1 

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Cite This Article
Westenskow, P., Sedillo, Z., Barnett, A., Friedlander, M. Efficient Derivation of Retinal Pigment Epithelium Cells from Stem Cells. J. Vis. Exp. (97), e52214, doi:10.3791/52214 (2015).

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