iPSC-derived retinal pigment epithelial cells | Ref. PCI-RPE
 
In the human retina we find two types of photoreceptors :
- The cones (about 5 million) which are found in three different forms and are each excited a range of specific wavelengths, they are often simplified to blue, green and red cones.
- The rods (about 120 million) capture all photons and produce an electro-chemical signal that is transmitted by the optic nerves to the brain to evaluate luminosity.
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In the human retina, the photoreceptors are directly in contact with a monolayer of pigmented cells : the Retinal Pigment Epithelium (RPE). They are located on the external surface of the retina, between the photoreceptors and the choroid (where there are the blood vessels carriying nutrients). The RPE plays an essential role in the maintenance and survival of photoreceptors by ensuring, among other things :
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- The transfer of nutrients (glucose, vitamine A, ions),
- Secretion of growth factors,
- Recycling of molecules (isomerized by light photons),
- Phagocytosis of cellular debris produced daily by photoreceptors,
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This phagocytotic activity results in the accumulation of a molecule in the RPE : A2E. The photo-excitation of this molecule leads to the production of reactive oxygen derivatives which induce stress and cellular damage. This damage can lead to the death of the RPE cells and therefore of the photoreceptors that depend on them. This chain of reactions is a pathology called AMD.