Future proofing stem cells for transplantation by removing a-synuclein gene
Original article: Engineering synucleinopathy-resistant human dopaminergic neurons by CRISPR-mediated deletion of the SNCA gene, European Journal of Neuroscience: Nov 28, 2018.
One of the potential reasons for the decline in clinical benefit seen after transplantation of stem cell derived neurons is that they eventually start to show Parkinson’s pathology in the form of abnormal alpha-synuclein clumps. In experiments using stem cell derived neurons performed in culture, researchers showed that removing one or both copies of the SNCA gene rendered them much less or completely resistant to this alpha-synuclein pathology.
Why is it important?
It sets out a strategy for developing Parkinson’s resistant neurons, which may have direct implications for the kinds of cells that are transplanted into patients.
- Novelty 80% 80%
- Proximity 75% 75%
- Deliverability 70% 70%
“It has been demonstrated that individuals with Parkinson’s who received cell transplants back in the 1990s, have alpha synuclein pathology in some of the transplanted cells. This appearance of lewy bodies in these transplanted cells is very slow (occuring gradually over decades), but it still raises questions about injecting defenseless cells into the Parkinsonian brain. What Dr Kunath and his team have demonstrated is that it is possible to provide cells with a mechanism of slowing/blocking one of the cardinal hallmarks of this condition, and hopefully this will allow for better outcomes in cell transplantation studies.”
Clinical trials addressing the safety and efficacy of transplanting mature dopamine producing neurons, derived from stem cells, to replace those lost to Parkinson’s have begun. The world’s first induced pleuripotent stem cell trial, using cells derived from skin rather than embryonic cells, began recently, in October 2018 in Japan. While we know that reinnervation can be achieved, one of the difficulties that occurs is that the transplanted cells begin to show the same pathology, and eventually dyskinesias and motor symptoms reappear. This pathology refers to misfolded, abnormal alpha-synuclein, which is the main hallmark of Parkinson’s. It is therefore essential to develop cells that are resistant to this form of pathology, to ensure that grafts last as long as possible.
The researchers used a gene editing method called CRISPR to remove one or both copies of the alpha-synuclein gene, known as SNCA, from clinical grade human embryonic stem cells (hESC). These were then grown into midbrain dopamine neurons. They then investigated whether exposing these two lines of neurons, and a third with the regular SNCA gene, to preformed fibrils of alpha-synuclein, which is known to trigger this synuclein-related pathology. After 5 weeks in this culture medium, the researchers looked for markers of alpha-synuclein pathology in all three neuron lines. They found that while the dopamine neurons derived from regular stem cells had indeed succumbed to this pathology, those with just one copy of the SNCA gene left showed much reduced pathology, and those that had no SNCA gene copies at all were completely intact.
An important next step before this work can translate into clinical practice is to demonstrate resistance to alpha-synuclein pathology for these genetically edited midbrain dopamine neurons in animal models of Parkinson’s. More also needs to be understood about the full effects of deleting SNCA altogether from cells, as some studies have shown they may not be as effective at producing dopamine.
Podcast summary recording
Original article: Chen Y, Dolt KS, Kriek M, Baker T, Downey P, Drummond NJ, Canham MA, Natalwala A, Rosser S, Kunath T: Nov 28, 2018, Engineering synucleinopathy-resistant human dopaminergic neurons by CRISPR-mediated deletion of the SNCA gene, European Journal of Neuroscience.