Scientists have turned fibroblasts from mouse skin into stem cells and injected them into the brains of adult mice. They then went back six months later and checked what happened to these neural stem cells. They could do this because the injected cells were tagged with GFP (green fluorescent protein) so they would glow green under a microscope. The stem cells survived and became three different sorts of brain cells: neurons; astrocytes; and oligodendrocytes. Neurons are what we generally call ‘brain cells’ and are responsible for storing and transmitting information. Astrocytes are the most abundant cells in the brain and are like a support team for the neurons. Astrocytes provide nutrients to neurons, help maintain the blood brain barrier, and transmit messages throughout the brain. Oligodendrocytes insulate axons, the long arms which extend away from neurons to carry messages to other neurons.
More importantly the cells that formed from the stem cells integrated into existing brain tissue and started to function. So man made cells can become a working part of the mouse brain.
Stem cells have been injected into mouse brains before, so we already knew that was possible, but no one has looked at how long the stem cells survive in the brain, or what sorts of cells they become. The beauty of stem cells is that they are able to become many types of cell – they haven’t yet decided what they want to be when they grow up. They haven’t yet differentiated, they are still pluripotent. The flip side of that is that we don’t really understand yet how to make stem cells become the types of cells that we want.
One of the most important results from this study is that the neural stem cells didn’t cause cancer. Stem cells are primed to divide and reproduce, giving birth to many new daughter cells. Cancer cells use many of the same mechanisms to grow and divide. So a major concern with stem cell treatment has been causing cancer. The injected stem cells in this study lost their ‘stemness’. They differentiated into mature cells that could no longer divide, so were not a potential cause of cancer.
This study is a big step forward in showing that stem cell therapy might actually work in the clinic to treat diseases like Alzheimer’s and stroke. I’m looking forward to the next round of research on this topic.
The Scientific Paper (finally one that’s open access for anyone to read):
Hemmer et al. Induced neural stem cells achieve long-term survival and functional integration in the adult mouse brain. Stem Cell Reports. 2014