Retinal stem cells and repair Flashcards
what is the retina?
extension of the brain. It is a layered structure that has 6 major neuronal types and 1 glial cells. There are rods, cones, bipolar cells, horizontal cells and amercing cells, retinal ganglion cells and muller glia
what are the rod photoreceptor cells?
- responsible for dim light, black and white vision. Found mainly in the periphery of the retina
what are the cone cells?
responsible for daytime vision, details and colour/ Concentrated in the region called the macula at the centre of the retina
- what are the retinal epithelium
it is located between the light sensitive outer segments of the photoreceptors and good supply of the choroid. It is responsible for the maintenance and homeostasis of the neuroretina
what is the main cause of irreversible blindness?
loss of photoreceptors - the cones- macular degeneration
what is retinitis pigmentosa?
loss of rods
do photoreceptors regenerate?
no
what are the two main approached to repairing a diseased retina ?
- endogenous repair approach: to reverse the cellular loss by encouraging the retina to repair itself
- transplantation of retinal cells (retinal progenitors, RPE and photoreceptors) generated from stem cells. Cell based therapies, replacing retinal cells by transplantation
why in theory is the replacement of retinal cells like cones and rods seemingly quite straightforward?
- only one type of cell needs to be replaced and only on synapse needs to be formed
wat are the pre-requisites of successful transplantation?
Identification of appropriate donor cells- need to find cell that will have the capacity to migrate and differentiate and also not form cancers
• Successful incorporation of transplanted cells into host retina:
• The transplanted cells need to migrate to the correct layer
• Transplanted cells need to mature
• The newly transplanted neurons need to integrate into the existing neural circuits
• Rescue vision
where can you find stem cells to be used in transplantation?
adult stem cells: a pool of multipoint stem cells persists in several adult tissues able to generate the types of cells present in the tissue where they resides. e.g. retinal progenitor cells, CE and iris cells, Muller glia in the retina
- can also use iPSC or embryonic stem cells.
what is the role of adult stem cells?
they help to replenish some of the boy’s cells when needed
- the are found in several tissues that need a constant supply of new cells such as the blood, skin, lining of the gut and brain
what is the ciliary marginal zone?
- region in the eye which contains stem cells which will give rise to differentiated cells
- in the fish this happens throughout life
- mice have the ciliary epithelium bt doesn’t have this constant capacity to replenish that we see in the fish
what are the 4 sources of stem cells in the mammal eye and what are their characteristics?
- ciliary epithelium-derived stem cells
- RPE-derived stem cells
- Iris-derived stem cells
(all of these cells have the same embrylogical origin and are capable of limited de-differenitation into proliferative retinal progneitors in response to disease and activation of signalling pathway s - the muller glia-derived stem cells can also be induced to proliferate in vivo in response to injury
what is the profile of retinal stem cells in the mammal?
Retinal stem cells in ciliary body (CB), more specifically the pigmented ciliary epithelium (CE) of the CB and the pigmented iris.
• Mammalian CE cells maintain a phenotype analogous to undifferentiated retinal stem/progenitor cells in vitro.
• When induced to differentiate, these cells express markers of both neurons and glia, and some markers of mature retinal cells.
what happens when you transplant of CE which contains retinal progenitor cells, into the sub retinal space?
- these cells survive well but didn’t migrate
- they differentiated into glial cells and remained in the sub retinal
due to the fact transplantation of retinal progenitor cells doesn’t seem to work very well, what is the alternative?
- induce endogenous repair ro find a new source of cels
why are muller cells a good alternative to Retinal progenitor cells?
In contrast to the CE, these cells also demonstrate greater potential for differentiation into mature retinal neurons in vivo, as well as migrating within the neural retina to occupy the correct laminar region appropriate for the newly generated cell type. after injury?
how did they test whether photoreceptor persecutors could be used in the lab?
- they used cells from different points in development- nil GFP mice to label rod cells.
- when you transplant retinal progenitors cells, they do migrate into the outer nuclear layer and stay in the sub retinal space and form their own niche
- but when you take these cells at p4-p8 one of these cells will migrate to the outer nuclear layer
- the did it with mature differentiated neurons- some were able to integrate but not as ll et committed post mitotic precursors (those used before
how do they carry out a transplant?
- they use a label and then use a syringe to take up the cells and then they inject them into the back of the eye and transpant inbeween the RPE ad the neural retina (rod specific marker) and you can see their migration ebecause they are labelled with GFP
- 3 weeks post translation they could see hey had integrated and formed synapses and extended processes
how did they test the response of the integrated receptors?
- they used a mouse with rods that dont function properly
-they looked at the functional connections by following synapse formation - they looked at the appropriate responses to light (patch clamping)
- they visually evoked activity in visual cortex (intrinsic cortical imaging)
they also performed behaviour tests: - they saw improved visual responses in the mouse which the can watch from the mouse tracking the stripes
- they did water maze- the mouse escapes to the platform
even though photoreceptor precursors seem to migrate and integrate really well, what is the problem with using these ofr human clinical trials?
the would need to be harvested from a foetus during the third trimester of pregnancy which ant be done and there is a need for a renewable source of cells for therapy. Therefore we need a better source - iPSC or ESC