Photoreceptor cells (green) injected into the eye can wire up correctly… (UCL )
Scientists have all kinds of stem cell cures in mind: replacing dopamine-producing nerves in the brains of Parkinson’s patients, fixing damaged spinal cords, curing Type 1 diabetes, etc. The therapies are slow-coming, though researchers are learning lots about how cells and body parts form.
Here’s a study just published in the journal Nature that shows injecting rod precursor cells (cells destined to become rod photoreceptors) into the eye gives mice born without rods the ability to detect dim light.
Rods, recall, are the most numerous photoreceptors in the eye and are responsible for the lion’s share of vision under dim-light conditions. (These mutant mice still had cones, the less-sensitive photoreceptors that sense color.)
It’s the first time that real function has been shown in photoreceptor-implanting experiments of this type, scientists say. And that’s a big distinction: It’s one thing to get cells to integrate into tissues and look like the cells you desire. That’s certainly not the same as showing they wire up the right way and generally function the way they’re supposed to, in a way that would be medically meaningful.
The study, conducted by Robin Ali at University College London and colleagues, assessed in a variety of ways whether the mice could sense light under dim-light conditions requiring rods. The most medically significant test was one in which mice had to sense a light source in order to select the right path out of a water maze. Four out of nine injected mice could complete this task more than 70% of the time compared with those that were untreated or were given sham injections: These performed no better than chance.
Take a look at the video:
Credit: University College London
Normal mice traverse the maze in an average of about seven seconds, ones that received injections with an average time of 15 seconds -- not as speedily as the normal mice, but they get there.
The scientists say they think their attempt worked while others had not because they enriched the cells injected for rod precursor cells, and also because they transplanted so many: an average of 200,000 per eye. Therapy of this type might ultimately be used to treat people with retinal degenerative diseases, but “many additional steps are required before these findings can be translated to the clinic,” the authors write.