Researchers at the Memorial Sloan Kettering Cancer Center, New York, under the leadership of Prof. Lorenz Studer developed embryo stem cells into dopamine neurons in a recently published study and simultaneously built into them a genetic “switch” through which these cells can then be deactivated with a certain light signal.
This process of temporary “switching off” of appropriately equipped cells using light is called optogenetics.
The researchers first disrupted the majority of mice’s natural dopamine neurones with a targeted intervention. The mice develop typical Parkinson’s symptoms such as trembling and slowing down of movement from this. Then they implanted the dopamine neurons grown from embryo stem cells and optogenetically altered. It then took about 4-5 months before the mice lost the Parkinson’s symptoms and could move normally again.
The exciting question in this is what function the transplanted dopamine neurons fulfil: do they stimulate the remaining natural dopamine cells to produce more dopamine? Do they carry out a kind of signal function? Or do they accrete, link actively with their surroundings and so become a new, fully functional part of the brain?
To clarify this, the researchers switched the transplanted dopamine neurons off using light signals. Within a few minutes, the mice again showed the typical Parkinson’s symptoms. Once light signals no longer affected the cells, they became active again and the Parkinson’s symptoms disappeared completely. Thus the researchers were able to show that the transplanted cells play a central role in the preparation of dopamine in the brains of the mice. Together with further investigations, they could also show that more dopamine is released in the brain by the transplanted cells and reaches the right places. This proves that the transplanted dopamine cells really do integrate into the brains of the mice studied.
This had only been assumed up to now but no firm evidence had been found. This evidence is now present, representing an important step in the application of this cell replacement therapy in humans.
Here is the researchers’ report in English.