lecture 20: stem cells and the eye Flashcards
1
Q
What is Jane’s problem ?
A
- 44 year old female
- tripping over children’s toys (night vision was not a problem at the time)
- a lot of car accidents
- vision seems good
- can’t see at night
2
Q
What is retinitis pigmentosa?
A
- optic nerve
- blood vessels that come from optic nerve
- macula is part of eye that allows us to see centrally
- black stuff and white stuff
- gradual loss of photoreceptors
- tunnel receptors
- can still see centrally because that area is not affected
- unless central vision is affected most people don’t complain
- retinitis pigmentosa is an inherited condition that leads to complete loss of photoreceptors
3
Q
What are the basics of the retina?
A
- contains neurons and glia
- 6 types of neurons
- laminated structure
- complex synapses
- sits on a layer of support cells called the Retinal Pigment Epithelium (RPE) (keep photoreceptors alive)
- immune privileged (the way foreign material is recognised is completely different)
- originates from neural stem cells very early in development
- retinitis pigmentosa is a condition that affects a particular protein found in rods → they die → peripheral loss of vision → loss of cones → complete blindness
- no treatment
- people are really interested in working out how vision can be restored
4
Q
What are retinal degenerations?
A
- photoreceptor death
- genetic mutations affecting proteins important for photoreceptor function
- loss of RPE cells
- barrier to nutrient flow from underlying vasculature
- also seen in age related loss of vision → very applicable treatments
- age-related macular degeneration = the commonest cause of blindness in the western world
5
Q
What are types of “stem cell” technology?
A
- regenerative medicine
- stem cells to replace lost cells (e.g. photoreceptors or RPE)
- ESCs or iPSCs
- trophic support of neurons
- provide growth factors or other environmental support to reduce loss
6
Q
What is the potential of embryonic stem cells in the eye?
A
- can ESCs replace lost photoreceptors?
- MacLaren et al (2006) Nature
- P1 cells incorporated into P1 littermate retinas
- age of donor plays a role in whether cells incorporated into the adult retina
- embryonic stem cells didn’t really do anything → basically formed balls, no connections
- want the progenitor cells as opposed to the ESCs
- translated P1 Nrl-gfp +/+ cells into three mouse models of retinal degeneration → were able to form photoreceptors
- still kind of blind
- tested pupils - showed a response
- ganglion cells → demonstrated a response, not the same as normal but not the same as the blind mice
7
Q
What is the effectiveness of transplanting precursors?
A
- restores vision
- have to inject heaps of precursors into the retina
- you have 120 million photorecpetors in any eye - potentially need to replace all of these
- progenitors formed terminals
- one of the biggest problems is getting connections to second order neurons
- increase the number of these cells → increase the amount this animal can see
8
Q
Do progenitor cells provide useful vision?
A
- these animals have normal retina but the photoreceptors don’t work
- make mouse choose between a side with lines and a side with no lines
- can test how thin/wide lines are etc
- more progenitor cells you put into the retina the more likely you are to restore vision
- very different when trying to restore vision in animal that has lost vision because of a disease process → have had some success in these kinds of mice
9
Q
How do we produce retinal progenitors en masse?
A
- originally got progenitor cells from embryonic stem cells
- can produce a whole retina in a dish
- do over and over again
- harvest progenitor cells from the dish
- take a range of ESCs → put in a suspension of matrigel → wait → embryoid body → eye field → optic vesicle → optic cup → harvest
- more ethically acceptable and feasible way of harvesting the type and number of cells required to perform such treatments
10
Q
What has been done with stem cells to restore vision?
A
- ESCs and RPE cells
- RPE cells are much easier to transplant because they are only a monolayer
- have been shown to restore some vision in clinical trials
- sits right under photoreceptors
- crucial for supplying photoreceptors with nutrients and vitamins (particularly vitamin A) to allow them to detect light
- w/o them photoreceptors die
- recently clinical trials testing whether stem cell replacement of RPE cells can restore vision
- Schwatz et al, The Lancet 2012
- two patients: stargardt’s disease; Dry AMD
- blind in both eyes
- implanted 50,000 cells (low number)
- vision: Patient 1: 0 to 5 letters; 6/240; patient 2: 21 to 28 letters
- proved that it was at least safe to try and use ESCs to create RPEs to try and restore vision
- larger clinical trial now underway
- perhaps more possible than
11
Q
How can iPSCs be used?
A
- harvested skin cells
- reprogramming
- iPSCs
- ex-vivo genetic repair
- directed differentiation
- photoreceptors
- RPE
- photoreceptors and RPE can be derived from iPSCs
- positives
- overcomes ethical issues
- no issues with graft rejection
- shown to be functional
- drawback
- for genetic diseases, the photoreceptors derived from iPSCs carry the same mutation as the host
12
Q
What is regeneration of the adult retina?
A
- in fish, amphibians and some reptiles, if you completely ablate the retina, within a month it will grow back
- why can lower vertebrates do this while we can’t?
- what are the cellular and biochemical mechanisms?
13
Q
What cells have been implicated in repair following intense light treatment?
A
- glial cells
- they are the support cells for neurons
- after light induced damage, glial cells proliferate
- 49% of MCs re-enter cell cycle
- when proliferation of glial cells is prevented, regeneration does not occur
14
Q
How do glia form photoreceptors?
A
- Wnt and Notch signalling pathways instrumental in instigating this proliferation and then sending down stem cell route
- what separates us from fish?
- maybe there are inhibitory factors in humans
15
Q
Do mammalian glia de-differentiate?
A
- answer: yes
- karl et al (PNAS 2008)
- toxic treatment: intraviteal NMDA and/or GFs into mouse vitreous
- caused many cells to proliferate
- these are glial cells
- not many of the cells do this however → don’t have enough cells dividing, less than 5%
- don’t go down the full route of dedifferentiation
- glial cells respond to loss of photoreceptors
- proliferate (~30% proliferate)
- express early markers of stem cell route
- pax6, Hes5
- can we trick them to keep going?
