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New way to watch what stem cells transplanted into the brain do once they get there

binocularsStem cell replacement therapy is a promising but problem-plagued medical intervention.

In a recent news release detailing a possible way forward, I wrote:

Many brain disorders, such as Parkinson's disease, are characterized by defective nerve cells in specific brain regions. This makes disorders such as Parkinson's excellent candidates for stem cell therapies, in which the defective nerve cells are replaced. But the experiments in which such procedures have been attempted have met with mixed results, and those conducting the experiments are hard put to explain them.

That's because there's been no good way to evaluate what those transplanted stems cells are doing once you've put them inside a living individual. I mean, you're not gonna break into someone's brain every couple of days to take a peek, right? Instead, you have to look for behavioral changes. Is the patient or experimental animal walking better (if you're trying to treat Parkinson's), or (if it's Alzheimer's) remembering better ? Then, even when you see those changes, you still don't know whether new nerve cells derived from the newly transplanted cells integrated into the proper brain circuits and are now functioning correctly there, or whether the originally transplanted cells are just sitting around secreting some kind of feel-good factor to pep up ailing cells in the vicinity, juicing their  performance. Or maybe it was a placebo effect.

It's hard to improve on a procedure when you don't really know what went wrong - or even what went right - on the last attempt. Optimizing the regimen becomes a matter of guesswork and luck.

But in a new study in NeuroImage, neuroscientist/bioengineer Jin Hyung Lee, PhD, and her colleagues came up with a way to peer deep into the living brain and view the results of a stem-cell transplant procedure. They combined an established brain-imaging technique with a newer but increasingly widespread one, called optogenetics, that lets researchers stimulate specific cells.

The first step in optogenetics is to genetically modify the cells you want to stimulate, so that their surfaces become coated by a photosensitive protein that generates electric current in response to laser light. Lee's team performed this operation on the stem cells before transplanting them into rats' brains. This way, they could selectively stimulate nerve cells derived from those stem cells and,  using the brain-imaging technique, see if doing so triggered nerve-cell activity at the site of the transplant as well as other places in the brain with which the new cells had established connections.

In these experiments, the stem-cell-derived nerve cells survived, matured into nerve cells, integrated into targeted brain circuits and, most important, fired on cue and ignited activity in downstream nerve circuits. But had all that not happened, at least the researchers would have been able to pinpoint the weak link in the chain.

In principle, the new approach should be possible to use for all kinds of stem-cell therapies, and in humans as well as animals. As Lee told me when I interviewed her for my release on her new study, “If we can watch the new cells’ behaviors for weeks and months after we’ve transplanted them, we can learn - much more quickly and in a guided way rather than a trial-and-error fashion - what kind of cells to put in, exactly where to put them, and how.”

If this light-driven stem-cell-monitoring technique or some others I've reported on hold up, brave explorers may no longer have to poke around in the dark.

Previously: Alchemy: From liposuction fluid to new liver cells, Iron-supplement-slurping stem cells can be transplanted, then tracked to make sure they're making new knees, You've got a lot of nerve! Industrial-scale procedure for generating plenty of personalized nerve cells and Nano-hitchhikers ride stem cells into heart, let researchers watch in real time and weeks later
Photo by Nicki Dugan Pogue

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